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TRAINING REPORT
SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING
OF
LUDHIANA COLLEGE OF ENGINEERING AND TECHNOLOGY,
KATANI KALAN, LUDHIANA
AS PART OF COURSE WORK OF
B.TECH. (MECHANICAL ENGINEERING)
PUNJAB TECHNICAL UNIVERSITY
KAPURTHALA
SUBMITTED BY
Harminder Singh
B- Tech., Mech. Engg.
Univ. Roll No. – L-90491175389.
CONTENTS
PREFACE
The globe is shrinking. The world is taken over by the technicians. A day after day
a new technology arises. A technician without practical knowledge is zero, don’t matter
how many books you have studied. Practical know how is must to be successful.
Industrial training is the bridge for a student that takes him from the world of
theoretical knowledge to that of practical one.
Training in a good industry is highly conducive for:
1. Development of solid foundation of knowledge and personality.
2. Confidence building.
3. Pursuit of excellence and discipline.
4. Enhancement of creativity through motivation and drive which helps to
produce professional and well trained for the rigorous of the job/society.
The present report has been done as an industrial training of six weeks for the
completion of 4th semester of B–Tech Mechanical Engineering.
During the training I got the exposure to various equipment and machines their
maintenance and technology concerning the repairing the Diesel Locomotive and hence
was assisted in developing self-confidence. The training helped me in implementing my
theoretical knowledge to the actual industrial environment.
This training at the “NORTHERN RAILWAY DIESEL SHED LUDHIANA”
is definitely going to play an important role in developing an aptitude for acquiring
knowledge hard work and self confidence necessary for successful future.
ACKNOLEDGEMENT
In these six weeks of industrial training, I wish to my attribute my profound
sense of gratitude without whose generous co-operation and co-ordination it would have
been highly difficult for me to have such a successful training experience in the
organization, in every game of life these are multitude of players whose are the real
heroes and this experience there are many loyal and phenomenally selfless friends, co-
workers and my bosses in industry, I am overwhelmed.
Few tasks are more enjoyable and fulfilling than acknowledging my gratitude to
all those, who have helped in this effort in so many ways. I take this opportunity to
express my sincere thanks to the management of “NORTHERN RAILWAY DIESEL
SHED LUDHIANA” of permitting me to observe and study the whole setup of factory.
I owe more than a debt of gratitude to Mr. R.P.Ram (Principal), Senior Section
Engineer Mr. Kuldeep Rai, and specially Thanks to Mr. Sarbjeet Singh (Mechanic) &
all the staff for their corporation & guidance made it possible to complete the work. I am
equally thankful to my faculty teacher for providing me this opportunity to work with
such a big company.
Certificate
OVERVIEW
Early internal combustion engine-powered locomotives used gasoline as their
fuel. Soon after Dr. Rudolf Diesel patented his first compression ignition engine in 1892,
its application for railway propulsion was considered. Progress was slow, however, due
to the poor power-to-weight ratio of the early engines, as well as the difficulty inherent in
mechanically applying power to multiple driving wheels on swivelling trucks (bogies).
Steady improvements in the Diesel engine's design (many developed by Sulzer
Ltd. of Switzerland, with whom Dr. Diesel was associated for a time) gradually reduced
its physical size and improved its power-to-weight ratio to a point where one could be
mounted in a locomotive. Once the concept of Diesel-electric drive was accepted the pace
of development quickened. By the mid 20th century the Diesel locomotive had become
the dominant type of locomotive in much of the world, offering greater flexibility and
performance than the steam locomotive, as well as substantially lower operating and
maintenance costs. Currently, almost all Diesel locomotives are Diesel-electric.
NORTHERN RAILWAY, DIESEL SHED, LUDHIANA
Chapter-1 INTRODUCTION
_____________________________________________________________
Diesel Shed Ludhiana came into existence on 29.09.1977. Initially, the shed was
designed to home 60 WDM2 locos. Later, it was expanded to home 100 WDM2 locos in
the year 1987-88. Further the total holding of shed was increased to 150 locos in the year
1993-94. Present loco holding of Diesel Shed, Ludhiana is 170 having different types of
locos i.e. WDM2, WDM3A & WDG3A.
Diesel Shed, Ludhiana is presently the biggest shed on the Northern Railway and
the 3rd largest on Indian Railways. The total kilometers earning is approximately 22 lakh
kilometers per month and the shed is running a mail link of 96 locos consisting of various
prestigious Mail/Express trains.
Diesel Shed, Ludhiana is also having a Diesel Training School and Hostel attached
to it. The Training School consists of 5 classrooms and various working models of
mechanical and electrical sub assemblies of WDM2 locos. The staying capacity in the
hostel is 72 and is having 38 double-bedded rooms. This training School is being mainly
utilized for training of running staff for Diesel conversion and refresher courses of FZR
& UMB division. In addition to this, this is also being utilized for imparting training to
the maintenance staff of the shed. It is also equipped with the recreation facilities &
gymnasium with high-tech exercise machines, indoor games etc.
Presently, Diesel Shed, LDH is ISO0-14001 Certified Shed, which is headed by
under the dynamic control of Sr.Divl. Mech.Engineer (Diesel), under whom the officers
DME-I, DME-II, ADME/H, ADME/R/Mech., ADME/R/Elect, ACMT & SMM/Stores
are working.
1.1 Various Sections In Diesel Shed:-
Turbo Section
Expressor Section
Compressor Section
Power Assembly Section
Cylinder Head Section
Machine Shop
Cross Head Section
Water Pump & Lube Oil Section
Radiator Section
Traction M/C
Governor Section
Gauge & Valve Section
Air Brake Section
Electrical Complaint Room
Auxillary M/C Section
Electrical Test Room
Magnaflux Section
Bogie Section
Valve Grinding Section
Contactor & Relay Room
Zyglo Testing Room
Fip Section
Tsc Balancing Section
Draftsman Room
Battery Section
Metallurgical Lab.
Spectro Section
Scrap Yard
Various Sections In Diesel Shed
To maintain various parts of locomotives, Diesel Shed, Ludhiana has different
sections for electrical and mechanical repairs & maintenance. Brief details are as under:-
1. 1.1 Turbo Supercharger Section
Turbo Supercharge is a machine, which uses exhaust of the diesel engine to
compress the intake air to improve the engine efficiency to about 1.5 times. At present, 4
types of TSCs are being overhauled in this section.
(i) ALCO Turbo Supercharger
(ii) ABB Turbo Supercharger
(iii) Napier Turbo Supercharger
(iv) Hispano Suiza Turbo Supercharger
All these TSCs are fully dismantled and overhauled in this section. The strength
of staff of this section is 7.
1.1.2 Fip & Injector Section
This section is responsible for maintaining the fuel injection pump and the
injector of diesel locomotives. The fuel injection pump is responsible for maintaining
desired pressure to inject the fuel, whereas the injector has the duty to spray the fuel in
the cylinder after atomization. Two types of FIPs are being used at present.
(i) 15mm FIP
(ii) 17mm FIP
All these subassemblies are being dismantled, overhauled and tested in this
section.
1.1.3 Expresser & Compressor Section
The expresser is used to maintain air pressure and vacuum pressure for breaking
system in the locomotive. This section is responsible for maintaining this subassembly.
Complete expressor or compressor is dismantled and overhauled in this section as per
Work Instructions issued to the section. The staff strength of the section is about 30.
1.1.4 Power Assembly Section
The piston and connecting rod assembly is called as power assembly. 16 power
assemblies are being used in one locomotive. Two types of pistons are being used in the
locomotive. Steel cap pistons are being used in fuel efficient locomotives, whereas
aluminium pistons are being used in conventional locomotives. The shed has switched
over to barrel shape piston rings to provide better fuel efficiency. The pistons and
connecting rods are dismantled, cleaned, zyglo tested and again are made ready for
service in this section. The staff strength of section is about 10.
1.1.5. Cylinder Head Section
This section is responsible for maintenance and overhauling of cylinder heads
of diesel locomotives. 16 Nos. cylinder heads are there in one locomotive. Each cylinder
head has four valves, two exhaust and two inlet valves. In fuel-efficient locomotives, the
valve angle is 300, whereas in conventional locomotives it is 450. The head is completely
dismantled and after cleaning and mating the valve & valve seat and overhauling the
complete components, the head is made ready for service in this section after various
tests. The staff strength of this section is about 7.
1.1.6. Cross Head Section
Crosshead is a subassembly, which is operated by camshaft to operate the valve
lever mechanism of the cylinder heads. There are 16 cross heads in one locomotive. The
cross heads operate the valve levers through two bush rods, one for exhaust and other for
air inlet. Cross heads are completely dismantled and overhauled and also the valve lever
mechanism is completely dismantled and overhauled in this section. The staff strength of
this section is about 4.
1.1.7. Pump Section
The pump section is responsible for overhauling water pump and lube oil pump
of the locomotive. Both the pumps are gear driven through crankshaft split gear train.
Every loco is having one water pump and one no. lubricating oil pump. Both the pumps
are cleaned, overhauled and made ready for service in this section. The staff strength of
this section is 4.
1.1.8. Miscelleneous Sub-assembly & Heat Exchanger Section This section is responsible for maintaining rear truck traction motor blower
which is belt driven, front truck traction motor blower which is gear driven, universal
shaft, which is used to drive radiator fan, eddy current clutch gear box used to provide
drive to radiator fan, over speed trip assembly is responsible for preventing the engine
from over-speeding. In addition to above, various heat exchangers, such as radiator, turbo
aftercooler, compressor after cooler and engine lube oil cooler are cleaned, tested &
overhauled in this section. The self-centrifuging unit of locomotive is also overhauled in
this section.
1.1.9.Bogie Section
This section is responsible for complete overhauling of undergear of the
locomotive. A locomotive is driven on line through 06 No. traction motors, which are
supplied from a generator driven by the diesel engine. These motors are fitted on 6 Nos.
axles and connected to axles through a bull gear pinion arrangement. The motors are
suspended through suspension bearing which is plain bearing in some locomotives,
whereas these are roller bearings in about 50% of locomotives. Two bogie frames are
used to house six axles and wheels and called as front bogie and rear bogie. The braking
arrangement for the locomotives is given through 8 brake cylinders, 4 on each bogie and
various brake riggings, brake shoes and brake blocks. The load of locomotive is shared
by each bogie. Each bogie has two nos. side bearers and one no. central pivot. The load
sharing between the central pivot and the side bearer is in the ratio of 60:40. The chassis
of the locomotive is having 2 Nos. central buffer couplers on each side for connection to
the train. The chassis is also having mounted 4 Nos. buffers, 2 on each side to bear
various pumps during operation. Staff strength in this section is about 70.
1.1.10. Yearly Section
Yearly section is used for complete overhauling of locomotive, engine block
and removal of various mechanical subassemblies. The yearly section carries out 24
monthly and 48 monthly schedules of the locomotives in which engine and various
subassemblies are overhauled completely. Staff strength of this section is about 90.
1.1.11. Air Brake Section
Air brake section is responsible for overhauling of brake valves of air brake
system and other safety items such as wipers, sanders, horns etc. In addition to it, various
gauges are also being maintained by this section. Staff strength of this section is about 50.
1.1.12. Valve Section
This section is responsible for maintaining fuel regulating valve, fuel relief valve,
lube oil regulating valve, lube oil relief valve, lube oil bypass valve of the locomotive.
The valves are overhauled and are set at a required pressure as per Maintenance
Instructions. Staff strength of this section is 2.
1.1.13. Speedometer Section
The speedometer section is responsible for maintaining speedometers of the
locomotive, which are responsible for recording and indicating the speed of the
locomotive. Staff strength of this section is about 16.
1.1.14. Governor Section
Governor section is responsible for maintenance of governor of the locomotive.
The governor of the locomotive is responsible for maintaining constant speed of the
engine as per requirement at every notch. At present, the shed has 3 types of governors.
(i) Woodward governor
(ii) GE or electro hydraulic governor
(iii) Microprocessor based governor
1.2 Minor Repairs Sections
1.2.1 Mail Section
Mail Section is having 2 sections i.e. Mail/Mech. and Mail Elect. section. Mail
section is responsible for maintenance of diesel engine, various mechanical
subassemblies, undergears etc. for trip schedule, monthly schedule and quarterly schedule
for mail and passenger locomotives.
1.2.2 Goods Section
Goods section is also having goods mech. and goods electrical. Goods section is
responsible for maintenance of diesel engine, various mechanical subassemblies,
undergears etc. for trip schedule, monthly schedule and quarterly schedule for goods
locomotives.
1.2.3 Quarterly & Half Yearly Section
Quarterly and half yearly section is responsible for 8 monthly, 12 monthly and 16
monthly schedules of diesel locomotives.
1.2.4 Out-Of-Course Section
OOC section is responsible for attending various major repairs of the locomotives,
which cannot be covered during minor schedule.
1.2.5 M & P Of The Shed
The shed, in its bogie section, is having two 40tonne cranes and one 10 tonne
crane. These cranes are used to lift bogies, engine blocks and various major
subassemblies. Heavy Repair Bay subassembly sections are having two cranes, 0ne
10tonne and the other is 3tonne crane. These are used for handling various
subassemblies. Every minor repair bay i.e. goods, mail, quarterly half yearly sections are
also having 3 tonne self operated cranes which are used to lift various subassemblies of
the locomotive. The shed is also having 3 Nos. fork lifters for material handling.
1.2.6 SCHEMATIC DIAGRAM OF DIESEL – ELECTRIC LOCOMOTIVE
Fig. 1 schematic diagram of diesel electric locomotive
1.2.7BLOCK DIAGRAM OF DIESEL LOCOMOTIVE
Fig. 2 Block diagram of diesel locomotive
A Diesel locomotive is a type of railroad locomotive in which the prime mover is a
Diesel engine
RADIATOR AFTER FRAME
BO
GG
IE
EXPRESSOR OR
COMPRESSOR ROOM
ENGINE ROOM
GENERATOR ROOM
DRIVER CABIN
NOTCH COMPART
MENT
BO
GG
IE
1.2.8 SALIENT FEATURES
Sanctioned staff strength = 1331
Staff on roll = 1206
Total covered area = 12,577 sq. meters.
Berthing capacity = 32 locos.
%age of staff housed = 21%.
Fuel storage capacity = 730 kiloliters.
Average off take of diesel oil per day = 0.3 lakh liters (approx).
Lube oil storage capacity = 350 kiloliters.
Average off-take of lube oil per day = 2700 liters (approx).
Annual budget of shed = Rs.___________ (approx).
Average kms earned/month = 21.61 lakh kilometers.
Stock items in the stores depot. = 1969
Present mail link = 96
Present loco holding = 170
(a) WDM2 = 62(b) WDG3A = 44(c) WDM3A = 64
Total = 170Direct maintenance staff per loco = 4.30
SFC Mail (Lts/1000GTKM) (2008-09) = 3.72
SFC Goods (Lts/1000GTKM) (2008-09) = 2.03
ACTIVITIES IN SHED SCHEDULES GIVEN BY SHOPSSchedules Periodicity Schedules Periodicity
Trip 15/20 days. IOH/M48 (By CB Shop) 4 yearsT2 30 days. POH/M96(By CB Shop) 8 years. M2 60 days. RB (By DMW/PTA) 16-22 years M4 120 days.M12 12 months. NO.OF SCHEDULES UNDERTAKEN IN
A MONTHM24 24 months. Type of Sch No. of Sch.M48 48 months. Trip 280M72 72 months T2 82
M2 40M4/8/16/20 27M12 08M24/48 04
1.2.9 Engine Description
Diesel Engine
Main Alternator
Auxiliary Alternator
Motor Blower
Air Intakes
Rectifiers / inverters
Electric Controls
Control Stands
Batteries
Cab
Traction Motor
Pinion Gear
Fuel Tank
Air compressor
Drive Shaft
Gear Box
Radiator and Radiator Fan
Turbo charging
Sand Box
Truck Frame
Wheel
Brakes
Mechanical Transmission
Fluid Coupling
Final Drive
Hydraulic Transmission
Wheel Slip
Chapter-2 Diesel Engine
_____________________________________________________________
The diesel engine was first patented by Dr Rudolf Diesel (1858-1913) in
Germany in 1892 and he actually got a successful engine working by 1897. By 1913,
when he died, his engine was in use on locomotives and he had set up a facility with
Sulzer in Switzerland to manufacture them. His death was mysterious in that he simply
disappeared from a ship taking him to London.
The diesel engine is a compression-ignition engine, as opposed to the petrol (or
gasoline) engine, which is a spark-ignition engine. The spark ignition engine uses an
electrical spark from a "spark plug" to ignite the fuel in the engine's cylinders, whereas
the fuel in the diesel engine's cylinders is ignited by the heat caused by air being suddenly
compressed in the cylinder. At this stage, the air gets compressed into an area 1/25th of
its original volume. This would be expressed as a compression ratio of 25 to 1. A
compression ratio of 16 to 1 will give an air pressure of 500 lbs/in² (35.5 bar) and will
increase the air temperature to over 800° F (427° C).
The advantage of the diesel engine over the petrol engine is that it has a higher thermal
capacity (it gets more work out of the fuel), the fuel is cheaper because it is less refined
than petrol and it can do heavy work under extended periods of overload. It can however,
in a high speed form, be sensitive to maintenance and noisy, which is why it is still not
popular for passenger automobiles.
2.1 Diesel engine: Mode of Operation
1. Suction stroke: Pure air gets sucked in by the piston sliding downward.
2.Compression stroke: The piston compresses the air above and uses thereby work,
performed by the crankshaft.
3.Power stroke: In the upper dead-center, the air is max. Compressed: Pressure and
Temperature are very high. Now the black injection pump injects heavy fuel in the hot
air. By the high temperature the fuel gets ignited immediately (auto ignition). The piston
gets pressed downward and performs work to the crankshaft.
4.Expulsion stroke: The burned exhaust gases are ejected out of the cylinder through a
second valve by the piston sliding upward again.
Fig. 3 4 stroke compression ignition (diesel) engine cycle
2.2 Diesel-electric control
A Diesel-electric locomotive's power output is independent to road speed, as long as
the units generator current and voltage limits are not exceeded. Therefore, the unit's
ability to develop tractive effort (also referred to as drawbar pull or tractive force, which
is what actually propels the train) will tend to inversely vary with speed within these
limits.
The diesel engine ideally should operate with maximum fuel economy as long as
maximum power is not required. Maintaining acceptable operating parameters was one of
the principal design considerations that had to be solved in early Diesel-electric
locomotive development, and ultimately led to the complex control systems in place on
modern units where all these parameters are solved and regulated by computer modules.
The prime mover's power output is primarily determined by its rotational speed
(RPM) and fuel rate, which are regulated by a governor or similar mechanism. The
governor is designed to react to both the throttle setting, as determined by the engineer
(driver), and the speed at which the prime mover is running.
Locomotive power output, and thus speed, is typically controlled by the engineer (driver)
using a stepped or "notched" throttle that produces binary-like electrical signals
corresponding to throttle position. This basic design lends itself well to multiple unit
(MU) operation by producing discrete conditions that assure that all units in a consist
respond in the same way to throttle position. Binary encoding also helps to minimize the
number of train lines (electrical connections) that are required to pass signals from unit to
unit. For example, only four train lines are required to encode all throttle positions.
In older locomotives, the throttle mechanism was ratcheted so that it was not
possible to advance more than one power position at a time. The engineer could not, for
example, pull the throttle from notch 2 to notch 4 without stopping at notch 3. This
feature was intended to prevent rough train handling due to abrupt power increases
caused by rapid throttle motion ("throttle stripping," an operating rules violation on many
railroads). Modern locomotives no longer have this restriction, as their control systems
are able to smoothly modulate power and avoid sudden changes in train loading
regardless of how the engineer (driver) operates the controls.
2.3 WORKING OF DIESEL LOCOMOTIVE
When the throttle is in the idle position, the prime mover will be receiving minimal
fuel, causing it to idle at low RPM. Also, the traction motors will not be connected to the
main generator and the generator's field windings will not be excited (energized)—the
generator will not produce electricity with no excitation. Therefore, the locomotive will
be in "neutral." Conceptually, this is the same as placing an automobile's transmission
into neutral while the engine is running.
To set the locomotive in motion, the reverser control handle is placed into the correct
position (forward or reverse), the brake is released and the throttle is moved to the run 1
position (the first power notch). An experienced engineer (driver) can accomplish these
steps in a coordinated fashion that will result in a nearly imperceptible start. The
positioning of the reverser and movement of the throttle together is conceptually like
shifting an automobile's automatic transmission into gear while the engine is idling
Placing the throttle into the first power position will cause the traction motors to be
connected to the main generator and the latter's field coils to be excited. It will not,
however, increase prime mover RPM. With excitation applied, the main generator will
deliver electricity to the traction motors, resulting in motion. If the locomotive is running
"light" (that is, not coupled to a train) and is not on an ascending grade it will easily
accelerate. On the other hand, if a long train is being started, the locomotive may stall as
soon as some of the slack has been taken up, as the drag imposed by the train will exceed
the tractive force being developed. An experienced engineer (driver) will be able to
recognize an incipient stall and will gradually advance the throttle as required to maintain
the pace of acceleration.
As the throttle is moved to higher power notches, the fuel rate to the prime mover will
increase, resulting in a corresponding increase in RPM and horsepower output. At the
same time, main generator field excitation will be proportionally increased to absorb the
higher power. This will translate into increased electrical output to the traction motors,
with a corresponding increase in tractive force. Eventually, depending on the
requirements of the train's schedule, the engineer (driver) will have moved the throttle to
the position of maximum power and will maintain it there until the train has accelerated
to the desired speed.
As will be seen in the following discussion, the propulsion system is designed to produce
maximum traction motor torque at start-up, which explains why modern locomotives are
capable of starting trains weighing in excess of 15,000 tons, even on ascending grades.
Current technology allows a locomotive to develop as much as 30 percent of its loaded
driver weight in tractive force, amounting to some 120,000 pounds of drawbar pull for a
large, six-axle freight (goods) unit. In fact, a consist of such units can produce more than
enough drawbar pull at start-up to damage or derail cars (if on a curve), or break couplers
(the latter being referred to in North American railroad slang as "jerking a lung").
Therefore, it is incumbent upon the engineer (driver) to carefully monitor the amount of
power being applied at start-up to avoid damage. In particular, "jerking a lung" could be a
calamitous matter if it were to occur on an ascending grade.
As previously explained, the locomotive's control system is designed so that the
main generator electrical power output is matched to any given engine speed. Due to the
innate characteristics of traction motors, as well as the way in which the motors are
connected to the main generator, the generator will produce high current and low voltage
at low locomotive speeds, gradually changing to low current and high voltage as the
locomotive accelerates. Therefore the net power produced by the locomotive will remain
constant for any given throttle setting.
In older designs, the prime mover's governor and a companion device, the load
regulator, play a central role in the control system. The governor has two external inputs:
requested engine speed, determined by the engineer's throttle setting, and actual engine
speed (feedback). The governor has two external control outputs: fuel injector setting,
which determines the engine fuel rate, and load regulator position, which affects main
generator excitation. The governor also incorporates a separate over speed protective
mechanism that will immediately cut off the fuel supply to the injectors and sound an
alarm in the cab in the event the prime mover exceeds a defined RPM. It should be noted
that not all of these inputs and outputs are necessarily electrical.
The load regulator is essentially a large potentiometer that controls the main
generator power output by varying its field excitation and hence the degree of loading
applied to the engine. The load regulator's job is relatively complex, because although the
prime mover's power output is proportional to RPM and fuel rate, the main generator's
output is not (which characteristic was not correctly handled by the Ward Leonard
elevator drive system that was initially tried in early locomotives).
As the load on the engine changes, its rotational speed will also change. This is detected
by the governor via a change in the engine speed feedback signal. The net effect is to
adjust both the fuel rate and the load regulator position. Therefore, engine RPM and
torque will remain constant for any given throttle setting, regardless of actual road speed.
In newer designs controlled by a “traction computer,” each engine speed step is
allotted an appropriate power output, or “kW reference”, in software. The computer
compares this value with actual main generator power output, or “kW feedback”,
calculated from traction motor current and main generator voltage feedback values. The
computer adjusts the feedback value to match the reference value by controlling the
excitation of the main generator, as described above. The governor still has control of
engine speed, but the load regulator no longer plays a central role in this type of control
system. However, the load regulator is retained as a “back-up” in case of engine
overload. Modern locomotives fitted with electronic fuel injection (EFI) may have no
mechanical governor, however a “virtual” load regulator and governor are retained with
computer modules.
Fig.4 3200Hp Diesel Locomotive Engine
Traction motor performance is controlled either by varying the DC voltage output of
the main generator, for DC motors, or by varying the frequency and voltage output of the
VVVF for AC motors. With DC motors, various connection combinations are utilized to
adapt the drive to varying operating conditions.
Fig. 5 Top View of Diesel Locomotive Engine
Here are some of the specifications of this engine:
Number of cylinders: 12
Compression ratio: 16:1
Displacement per cylinder: 11.6 L (710 in3)
Cylinder bore: 230 mm (9.2 inches)
Cylinder stroke: 279 mm (11.1 inches)
Full speed: 904 rpm
Normal idle speed: 269 rpm
At standstill, main generator output is initially low voltage/high current, often in
excess of 1000 amperes per motor at full power. When the locomotive is at or near
standstill, current flow will be limited only by the DC resistance of the motor windings
and interconnecting circuitry, as well as the capacity of the main generator itself. Torque
in a series-wound motor is approximately proportional to the square of the current.
Hence, the traction motors will produce their highest torque, causing the locomotive to
develop maximum tractive effort, enabling it to overcome the inertia of the train. This
effect is analogous to what happens in an automobile automatic transmission at start-up,
where it is in first gear and thus producing maximum torque multiplication.
As the locomotive accelerates, the now-rotating motor armatures will start to
generate a counter-electromotive force (back EMF, meaning the motors are also trying to
act as generators), which will oppose the output of the main generator and cause traction
motor current to decrease. Main generator voltage will correspondingly increase in an
attempt to maintain motor power, but will eventually reach a plateau. At this point, the
locomotive will essentially cease to accelerate, unless on a downgrade. Since this plateau
will usually be reached at a speed substantially less than the maximum that may be
desired, something must be done to change the drive characteristics to allow continued
acceleration. This change is referred to as "transition," a process that is analogous to
shifting gears in an automobile.
2.4 Starting:
A diesel engine is started (like an automobile) by turning over the crankshaft
until the cylinders "fire" or begin combustion. The starting can be done electrically or
pneumatically. Pneumatic starting was used for some engines. Compressed air was
pumped into the cylinders of the engine until it gained sufficient speed to allow ignition,
then fuel was applied to fire the engine. The compressed air was supplied by a small
auxiliary engine or by high pressure air cylinders carried by the locomotive.
Electric starting is now standard. It works the same way as for an automobile,
with batteries providing the power to turn a starter motor which turns over the main
engine. In older locomotives fitted with DC generators instead of AC alternators, the
generator was used as a starter motor by applying battery power to it.
2.5 Transition methods include:
Series / Parallel or "motor transition."
o Initially, pairs of motors are connected in series across the main generator. At
higher speed, motors are re-connected in parallel across the main generator.
Field shunting," "field diverting" or "weak fielding."
o Resistance is connected in parallel with the motor field. This has the effect of
increasing the armature current, producing a corresponding increase in motor
torque and speed.
Note: Both methods may also be combined, to increase the operating speed range.
Generator transition
o Reconnecting the two separate internal main generator stator windings from
parallel to series to increase the output voltage.
In older locomotives, it was necessary for the engineer to manually execute
transition by use of a separate control. As an aid to performing transition at the right time,
the load meter (an indicator that informs the engineer on how much current is being
drawn by the traction motors) was calibrated to indicate at which points forward or
backward transition should take place. Automatic transition was subsequently developed
to produce better operating efficiency, and to protect the main generator and traction
motors from overloading due to improper transition.
The hybrid diesel locomotive is an incredible display of power and ingenuity. It
combines some great mechanical technology, including a huge, 12-cylinder, two-stroke
diesel engine, with some heavy duty electric motors and generators, throwing in a little
bit of computer technology for good measure.
This combination of diesel engine and electric generators and motors makes the
locomotive a hybrid vehicle. In this article, we'll start by learning why locomotives are
built this way and why they have steel wheels. Then we'll take a look at the layout and
key components.
2.6 Size Does Count
Basically, the more power you need, the bigger the engine has to be. Early
diesel engines were less than 100 horse power (hp) but today the US is building 6000 hp
locomotives. For a UK locomotive of 3,300 hp (Class 58), each cylinder will produce
about 200 hp, and a modern engine can double this if the engine is turbocharged.
The maximum rotational speed of the engine when producing full power will be
about 1000 rpm (revolutions per minute) and the engine will idle at about 400 rpm.
These relatively low speeds mean that the engine design is heavy, as opposed to a high
speed, lightweight engine. However, the UK HST (High Speed Train, developed in the
1970s) engine has a speed of 1,500 rpm and this is regarded as high speed in the railway
diesel engine category. The slow, heavy engine used in railway locomotives will give
low maintenance requirements and an extended life.
There is a limit to the size of the engine which can be accommodated within the
railway loading gauge, so the power of a single locomotive is limited. Where additional
power is required, it has become usual to add locomotives. In the US, where freight
trains run into tens of thousands of tons weight, four locomotives at the head of a train are
common and several additional ones in the middle or at the end are not unusual.
2.7 Important Maintenance Instruction For Cylinder Head.
Study the condition of cylinder head combustion chamber face, cooling jackets
and its valves thoroughly before its dismantling.
Clean cylinder head thoroughly especially cooling jackets.
Do RDF of cylinder head combustion face, defect any cracks.
Check cylinder head hydraulically at 5kg/sq. cm and 8. Temp of water up to a min
of 15 minutes.
Check the diameter of valve guide after removing its carbon deposits.
Check the clean nozzle, cooling sleeves seat of cylinder head.
Use liquid nitrogen for valve seat insert fitting.
Check valve seat inserts for cracks by RDF (After grinding).
Before final assembly check all valve seat inserts as well as of nozzle cooling
sleeve.
Compare seat should be lapped thoroughly and it should be 1/16” thick all over.
2.8 Cylinder Head
Fig. 6 Cylinder Head
2.9 To V or not to V
Diesel engines can be designed with the cylinders "in-line", "double banked" or in
a "V". The double banked engine has two rows of cylinders in line. Most diesel
locomotives now have V form engines. This means that the cylinders are split into two
sets, with half forming one side of the V. A V8 engine has 4 cylinders set at an angle
forming one side of the V with the other set of four forming the other side. The
crankshaft, providing the drive, is at the base of the V. The V12 was a popular design
used in the UK. In the US, V16 is usual for freight locomotives and there are some
designs with V20 engines.
2.10 Tractive Effort, Pull and Power
Before going too much further, we need to understand the definitions of tractive
effort, drawbar pull and power. The definition of tractive effort (TE) is simply the force
exerted at the wheel rim of the locomotive and is usually expressed in pounds (lbs) or
kilo Newtons (KN). By the time the tractive effort is transmitted to the coupling between
the locomotive and the train, the drawbar pull, as it is called will have reduced because of
the friction of the mechanical parts of the drive and some wind resistance.
Power is expressed as horsepower (hp) or kilo Watts (kW) and is actually a rate of
doing work. A unit of horsepower is defined as the work involved by a horse lifting
33,000 lbs one foot in one minute. In the metric system it is calculated as the power
(Watts) needed when one Newton of force is moved one metre in one second. The
formula is P = (F*d)/t where P is power, F is force, d is distance and t is time. One
horsepower equals 746 Watts.
The relationship between power and drawbar pull is that a low speed and a high
drawbar pull can produce the same power as high speed and low drawbar pull. If you
need to increase higher tractive effort and high speed, you need to increase the power. To
get the variations needed by a locomotive to operate on the railway, you need to have a
suitable means of transmission between the diesel engine and the wheels.
One thing worth remembering is that the power produced by the diesel engine is
not all available for traction. In a 2,580 hp diesel electric locomotive, some 450 hp is lost
to on-board equipment like blowers, radiator fans, air compressors and "hotel power" for
the train.
Chapter-3 WDM-2 Diesel Locomotive
_____________________________________________________________
The first few prototype WDM-2s were imported. After Diesel Locomotive Works
(DLW) completed construction of its factory in Varanasi, production of the locomotives
began in India. The first 12 locos were built using kits imported from ALCO in the
United States. After that DLW started manufacturing the WDM-2 locomotives from their
own components. Since then over 2,800 locomotives have been manufactured and the
WDM-2 has become the most popular locomotive in India.
However, even before the arrival of WDM-2 another type of diesel locomotive
was imported from ALCO beginning in 1957. This locomotive was classified as WDM-1.
Later a number of modifications were made and a few subclasses were created.
This includes WDM-2A, WDM-2B and WDM-3A (formerly WDM-2C).
The WDM-2 is the diesel workhorse of the Indian Railways, being very reliable
and rugged.
The class WDM-2 is Indian Railways' workhorse diesel locomotive. The first
units were imported fully built from the American Locomotive Company (Alco) in 1962.
Since 1964, it has been manufactured in India by the Diesel Locomotive Works (DLW),
Varanasi. The model name stands for broad gauge (W), diesel (D), mixed traffic (M)
engine. The WDM-2 is the most common diesel locomotive of Indian Railways.
The WDM-2A is a variant of the original WDM-2. These units have been retro-
fitted with air brakes, in addition to the original vacuum brakes. The WDM-2B is a more
recent locomotive, built with air brakes as original equipment. The WDM-2 locos have a
maximum speed of 120 km/h (75 mph), restricted to 100 km/h (62 mph) when run long
hood forward. The gear ratio is 65:18.
Types of Diesel locomotives
WDM2 BG Main Line Locomotive 2600HP
WDM3 BG Main Line Locomotive 3100HP
WDM6 BG Main Line Locomotive 1350HP
WDM7 BG Main Line Locomotive 2150HP
WDG4BG Main Line Goods Locomotive 4000HP
WDP4 BG Main Line Passenger Locomotive 4000HP
WDS6 BG Shunting Locomotive 1350HP
WDP1 BG Inter City Express Locomotive 2300HP
WDP2 BG High HP Passenger Locomotive 3100HP
WDG3A BG High Goods Locomotive 3100HP
WDG3C BG High HP Goods Locomotive 3300HP
YDM4 MG Main Line Locomotive 1350HP
3.1 Technical specifications
Builders Alco, DLW
Engine
Alco 251-B, 16 cylinder, 2,600 hp (2,430 hp site rating) with Alco
710/720/?? Turbo supercharged engine. 1,000 rpm max, 400 rpm idle;
228 mm x 266 mm bore/stroke; compression ratio 12.5:1. Direct fuel
injection, centrifugal pump cooling system (2,457 l/min at 1,000 rpm),
fan driven by eddy current clutch (86 hp at 1,000 rpm).
Governor GE 17MG8 / Woodward’s 8574-650.
TransmissionElectric, with BHEL TG 10931 AZ generator (1,000 rpm, 770 V, 4,520
amps).
Traction motorsGE752 (original Alco models) (405 hp), BHEL 4906 BZ (AZ?) (435 hp)
and (newer) 4907 AZ (with roller bearings)
Axle load 18.8 tones, total weight 112.8 t.
Bogies Alco design cast frame trimount (Co-Co) bogies
Starting TE30.4 t, at adhesion 27%.
Length over
buffer beams15,862 mm.
Distance
between bogies10,516 mm.
The above requirement, in the year 1987, led to the creation of test beds at Engine
Development Directorate of RDSO at Lucknow having state of the art facilities for
developmental testing of all the variants of diesel engines being used by Indian Railways.
It included the computer based test facility for both data logging and control of engines.
The above facilities comparable to the best facilities in the world were created to
meet the following objectives:
Development of technology for improving existing Rail Traction Diesel Engines for
1. Better Fuel Efficiency
2. Higher Reliability
3. Increased Availability
Development of technology for increasing power output of existing Diesel Engines.
Develop capability for designing new Rail Traction Diesel Engines for meeting future needs of Indian Railways.
To provide effective R&D backup to Railways and Production units to
1. Maintain Quality
2. Facilitate Indigenization
3.2 Broad Gauge Main Line Freight Locomotive WDG 3A
3.2.1 Technical Information Diesel Electric main line, heavy duty goods service locomotive, with 16 cylinder ALCO
engine and AC/DC traction with micro processor controls.
Wheel Arrangement Co-Co
Track Gauge 1676 mm
Weight 123 t
Length over Buffers 19132 mm
Wheel Diameter 1092 mm
Gear Ratio 18 : 74
Min radius of Curvature 117 m
Maximum Speed 105 Kmph
Diesel Engine Type : 251 B,16 Cyl.- V
HP 3100
Brake IRAB-1
Loco Air, Dynamic
Train Air
Fuel Tank Capacity 6000 litres
3.3 Broad Gauge Main Line Mixed Service LOCO WDM 3D
3.3.1 Technical Information Diesel Electric Locomotive with micro processor control suitable for main line
mixed Service train operation.
Wheel
Arrangement
Co-Co
Track Gauge 1676 mm
Weight 117 t
Max. Axle
Load
19.5 t
Length over
Buffer
18650 mm
Wheel
Diameter
1092 mm
Gear Ratio 18 : 65
Maximum
Speed
120 Kmph
Diesel Engine Type: 251 B-16 Cyl. ‘V’ type
HP 3300 HP (standard UIC condition)
Transmission Electric AC / DC
Brake IRAB-1 system
Loco Air, Dynamic, Hand
Train Air
Fuel Tank
Capacity
5000 litres
3.4 Broad Gauge Shunting Locomotive WDS 6AD
3.4.1Technical Information
A heavy duty shunting Diesel Electric Locomotive for main line and branch line
train operation. This locomotive is very popular with Steel Plants and Port Trusts.
Wheel Arrangement Co-Co
Track Gauge 1676 mm
Weight 113 t
Length over Buffer 17370 mm
Wheel Diameter 1092 mm
Gear Ratio 74 : 18
Maximum Speed 50 Kmph
Diesel Engine Type : 251 D-6 Cyl. in-line
HP 1350 / 1120 HP (std.)
Transmission Electric AC / DC
Brake IRAB-1
Loco Air
Train Air
Fuel Tank Capacity 5000 litres
3.5 Engine Test Bed Facilities
The test bed facilities in RDSO are equipped with four Test Cells. These Test Cells
house four (16 cylinders GMEMD, 16 cylinders ALCO, 12 cylinders ALCO, 6 cylinders
ALCO) types of DLW manufactured Engines. Each test cell has its own microprocessor
controlled data acquisition and control systems and Video Display Unit (VDU) for
pressure, temperature and other parameters. Various transducers relay the information
from the test engines to the microprocessor based test commander for further processing
with the help of sophisticated software. Each test cell has an instrumentation catering to
60 to 120 pressures / temperature transducers along with sophisticated equipments like
gravimetric fuel balance for measurement of fuel consumption and the equipment for
measurement of air flow.
Fig. 8 Test Bed 3.6 Fuel Consumption on 8th Notch
Since the fuel consumption at 8th notch is highest and also since Locomotives run
at this notch for longer duration as compared to other notches, fuel consumption at this
notch is one of the important fuel efficiency index. This is measured in terms of gm / bhp
- hr.
3.7 Fuel Consumption Over Duty Cycle
An Engine runs in the field at different notch as per requirement of speed / load of
the locomotive. The notch wise percentage running of locomotive over duty cycle for
passenger and freight operations of Indian Railways locomotives is as under:
3.8 Speed at different Notch position
Notch Speed (RPM)1 4002 4503 5504 6505 7506 8507 915
8 1000
3.9 Driving a Locomotive
You don't just hop in the cab, turn the key and drive away in a diesel locomotive.
Starting a train is a little more complicated than starting your car.
The engineer climbs an 8-foot (2.4-m) ladder and enters a corridor behind the cab. He or
she engages a knife switch (like the ones in old Frankenstein movies) that connects the
batteries to the starter circuit. Then the engineer flips about a hundred switches on a
circuit-breaker panel, providing power to everything from the lights to the fuel pump.
Next, the engineer walks down a corridor into the engine room. He turns and holds
a switch there, which primes the fuel system, making sure that all of the air is out of the
system. He then turns the switch the other way and the starter motor engages. The engine
cranks over and starts running.
Next, he goes up to the cab to monitor the gauges and set the brakes once the
compressor has pressurized the brake system. He can then head to the back of the train to
release the hand brake.
Finally he can head back up to the cab and take over control from there. Once he
has permission from the conductor of the train to move, he engages the bell, which rings
continuously, and sounds the air horns twice (indicating forward motion).
The throttle control has eight positions, plus an idle position. Each of the throttle
positions is called a "notch." Notch 1 is the slowest speed, and notch 8 is the highest
speed. To get the train moving, the engineer releases the brakes and puts the throttle into
notch 1.
In this General Motors EMD 710 series engine, putting the throttle into notch 1
engages a set of contactors (giant electrical relays). These contactors hook the main
generator to the traction motors. Each notch engages a different combination of
contactors, producing a different voltage. Some combinations of contactors put certain
parts of the generator winding into a series configuration that results in a higher voltage.
Others put certain parts in parallel, resulting in a lower voltage. The traction motors
produce more power at higher voltages.
As the contactors engage, the computerized engine controls adjust the fuel injectors
to start producing more engine power.
Chapter-4 Main Parts Of An Engine
_____________________________________________________________
4.1 Main Alternator
The diesel engine drives the main alternator which provides the power to move the
train. The alternator generates AC electricity which is used to provide power for the
traction motors mounted on the trucks (bogies). In older locomotives, the alternator was
a DC machine, called a generator. It produced direct current which was used to provide
power for DC traction motors. Many of these machines are still in regular use. The next
development was the replacement of the generator by the alternator but still using DC
traction motors. The AC output is rectified to give the DC required for the motors.
4.2 Auxiliary Alternator
Locomotives used to operate passenger trains are equipped with an auxiliary
alternator. This provides AC power for lighting, heating, air conditioning, dining
facilities etc. on the train. The output is transmitted along the train through an auxiliary
power line. In the US, it is known as "head end power" or "hotel power". In the UK, air
conditioned passenger coaches get what is called electric train supply (ETS) from the
auxiliary alternator.
4.3 Motor Blower
The diesel engine also drives a motor blower. As its name suggests, the motor
blower provides air which is blown over the traction motors to keep them cool during
periods of heavy work. The blower is mounted inside the locomotive body but the
motors are on the trucks, so the blower output is connected to each of the motors through
flexible ducting. The blower output also cools the alternators. Some designs have
separate blowers for the group of motors on each truck and others for the alternators.
Whatever the arrangement, a modern locomotive has a complex air management system
which monitors the temperature of the various rotating machines in the locomotive and
adjusts the flow of air accordingly.
4.4 Air Intakes
The air for cooling the locomotive's motors is drawn in from outside the locomotive. It
has to be filtered to remove dust and other impurities and its flow regulated by
temperature, both inside and outside the locomotive. The air management system has to
take account of the wide range of temperatures from the possible +40° C of summer to
the possible -40° C of winter.
4.5 Rectifiers/Inverters
The output from the main alternator is AC but it can be used in a locomotive with
either DC or AC traction motors. DC motors were the traditional type used for many
years but, in the last 10 years, AC motors have become standard for new locomotives.
They are cheaper to build and cost less to maintain and, with electronic management can
be very finely controlled. To see more on the difference between DC and AC traction
technology try the Electronic Power Page on this site.
To convert the AC output from the main alternator to DC, rectifiers are required. If the
motors are DC, the output from the rectifiers is used directly. If the motors are AC, the
DC output from the rectifiers is converted to 3-phase AC for the traction motors.
In the US, there are some variations in how the inverters are configured. GM
EMD relies on one inverter per truck, while GE uses one inverter per axle - both systems
have their merits. EMD's system links the axles within each truck in parallel, ensuring
wheel slip control is maximized among the axles equally. Parallel control also means
even wheel wear even between axles. However, if one inverter (i.e. one truck) fails then
the unit is only able to produce 50 per cent of its tractive effort. One inverter per axle is
more complicated, but the GE view is that individual axle control can provide the best
tractive effort. If an inverter fails, the tractive effort for that axle is lost, but full tractive
effort is still available through the other five inverters. By controlling each axle
individually, keeping wheel diameters closely matched for optimum performance is no
longer necessary.
4.6 Electronic Controls:
Almost every part of the modern locomotive's equipment has some form of
electronic control. These are usually collected in a control cubicle near the cab for easy
access.
The controls will usually include a maintenance management system of some
sort which can be used to download data to a portable or hand-held computer.
Fig.9 Controls, indicators and the radio
4.7 Control Stand
This is the principal man-machine interface, known as a control desk in the UK
or control stand in the US. The common US type of stand is positioned at an angle on the
left side of the driving position and, it is said, is much preferred by drivers to the modern
desk type of control layout usual in Europe and now being offered on some locomotives
in the US.
4.8 Batteries
Just like an automobile, the diesel engine needs a battery to start it and to provide
electrical power for lights and controls when the engine is switched off and the alternator
is not running.
The locomotive operates on a nominal 64-volt electrical system. The locomotive has
eight 8-volt batteries; each weighing over 300 pounds (136 kg). These batteries provide
the power needed to start the engine (it has a huge starter motor), as well as to run the
electronics in the locomotive. Once the main engine is running, an alternator supplies
power to the electronics and the batteries.
4.9 Cab
Most US diesel locomotives have only one cab but the practice in Europe is two
cabs. US freight locos are also designed with narrow engine compartments and
walkways along either side. This gives a reasonable forward view if the locomotive is
working "hood forwards". US passenger locos, on the other hand have full width bodies
and more streamlined ends but still usually with one cab. In Europe, it is difficult to tell
the difference between a freight and passenger locomotive because the designs are almost
all wide bodied and their use is often mixed. The cab of the locomotive rides on its own
suspension system, which helps isolate the engineer from bumps. The seats have a
suspension system as well.
4.10 Traction Motor
Since the diesel-electric locomotive uses electric transmission, traction motors are
provided on the axles to give the final drive. These motors were traditionally DC but the
development of modern power and control electronics has led to the introduction of 3-
phase AC motors. There are between four and six motors on most diesel-electric
locomotives. A modern AC motor with air blowing can provide up to 1,000 hp.
Propulsion: The traction motors provide propulsion power to the wheels. There is one
on each axle. Each motor drives a small gear, which meshes with a larger gear on the axle
shaft. This provides the gear reduction that allows the motor to drive the train at speeds of
up to 110 mph.
Fig. 10 Traction Motor
Each motor weighs 6,000 pounds (2,722 kg) and can draw up to 1,170 amps of electrical
current.
4.11 Fuel Tank
A diesel locomotive has to carry its own fuel around with it and there has to be
enough for a reasonable length of trip. The fuel tank is normally under the loco frame
and will have a capacity of say 1,000 imperial gallons (UK Class 59, 3,000 hp) or 5,000
US gallons in a General Electric AC4400CW 4,400 hp locomotive. The new AC6000s
have 5,500 gallon tanks. In addition to fuel, the locomotive will carry around, typically
about 300 US gallons of cooling water and 250 gallons of lubricating oil for the diesel
engine. Air reservoirs are also required for the train braking and some other systems on
the locomotive. These are often mounted next to the fuel tank under the floor of the
locomotive.
This huge tank in the underbelly of the locomotive holds 2,200 gallons (8,328 L)
of diesel fuel. The fuel tank is compartmentalized, so if any compartment is damaged or
starts to leak, pumps can remove the fuel from that compartment.
4.12 Governor
Once a diesel engine is running, the engine speed is monitored and controlled through a
governor. The governor ensures that the engine speed stays high enough to idle at the
right speed and that the engine speed will not rise too high when full power is demanded.
The governor is a simple mechanical device which first appeared on steam engines. It
operates on a diesel engine as shown in the diagram below.
The governor consists of a rotating shaft, which is driven by the diesel engine. A pair
of flyweights is linked to the shaft and they rotate as it rotates. The centrifugal force
caused by the rotation causes the weights to be thrown outwards as the speed of the shaft
rises. If the speed falls the weights move inwards. The flyweights are linked to a collar
fitted around the shaft by a pair of arms. As the weights move out, so the collar rises on
the shaft. If the weights move inwards, the collar moves down the shaft. The movement
of the collar is used to operate the fuel rack lever controlling the amount of fuel supplied
to the engine by the injectors.
Fig. 11 Principle of Governor
4.12.1 Function and types of governors
The purpose of a governor is to control the speed of an engine. If an engine is loaded
beyond its rated capacity, it will slow down or may even stop. Governors act through the
fuel injection system to control the amount of fuel delivered to the cylinders. The
quantity of fuel delivered, in turn, governs the power developed.
The two types of governors, each of which serves a distinctly different purpose, are :
over speed governor and regulating governor. The over speed type is used on most
marine engines where the speed of the engine is variable. By necessity, the marine engine
requires flexibility in speed due to the maneuvering of the ship. This type of governor is
installed as a safety measure and comes into action when the engine approaches
dangerous over speed. This condition could occur before the operator had time to bring
the engine under control by other means. The over speed trip functions only if the
regulating governor fails. This governor controls all abnormal speed surges.
Overspeed governors are of the centrifugal type; that is, the action of the governor
depends upon the centrifugal force created as the governor weights revolve. Centrifugal
force is the force that tends to move a body away from the axis about which it is
revolved. This force is transmitted to the fuel injection system by means of levers
connected to the governor collar and a linkage system. In some types of over speed
governors the action merely cuts off the fuel until the engine has slowed to a point of
safety and then allows the resumption of normal operation. The other type trips a fuel
cutout mechanism and affects a complete stopping of the engine. The F-M engines
employ an F-M design over speed governor and the GM engines use Woodward over
speed governors.
For this discussion governors will be classified as either hydraulic or mechanical.
The mechanical type embodies the principle of centrifugal force similar to the over speed
type, while the hydraulic type employs a centrifugally actuated pilot valve to regulate the
flow of a hydraulic medium under pressure. The mechanical governor is more applicable
to the small engine field not requiring extremely close regulation while the hydraulic type
finds favor with the larger installations demanding very close regulation. The regulating
governor is much more sensitive to slight speed fluctuations than is the overspeed
governor. Its duty is to control the speed within very narrow limits when an engine is
operating under varying loads. It takes the place of the operator's manual control of the
throttle. When the load on the engine increases, and before the engine's speed has
appreciably dropped, it permits an increase of fuel to the cylinders, thus maintaining the
engine speed at the set rate. To perform this function, the governor must be sensitive to
the slightest variation in speed. The Woodward hydraulic governor of the regulating type
is widely used in the United States Navy & Railway Engines.
4.12.2 Description and operation
The type of regulating governor used on all submarine main engines is the
Woodward SI hydraulic type governor. On F-M engines, it is driven from the lower
crankshaft, and on GM engines, from one of the camshafts. The purpose of the governor
is to regulate the amount of fuel supplied to the cylinders so that a predetermined engine
speed will be maintained despite variations in load. Figure 10-2 is a schematic diagram of
the governor. The principal parts of the governor are a gear pump and accumulators
which serve to keep a constant oil pressure on the system at all times; a pilot valve
plunger, pilot valve bushing, and flyweights which control the amount of oil going to the
power assembly; a speed adjusting spring whose tension governs the speed setting of the
governor; the power element, consisting of the power spring, power piston, and power
cylinder; and the compensating assembly which consists of the actuating compensating
plunger, the receiving compensating plunger, the compensating spring, and two
compensation needle valves. The pilot valve plunger is constructed with a land which
serves to open or close the port in the pilot valve bushing leading to the power cylinder.
In this governor the flyweights are linked hydraulically to the fuel control
cylinder. The downward pressure of the power spring is balanced by the hydraulic lock
on the lower side of the power piston. The amount of oil below the power piston is
regulated by the pilot valve plunger controlled by the flyweights.
Fig. 12 Woodward regulating governor installed
When the engine is running at the speed set on the governor, the land on the pilot
valve plunger covers the regulating port in the bushing. The plunger is held in this
position by the flyweights. However, if the engine load decreases, the engine speeds up
and the additional centrifugal force moves the flyweights outward, raising the pilot valve
plunger. This opens the regulating port of the bushing, and trapped oil from the power
cylinder is then allowed to flow through the pilot valve cylinder into a drainage passage
to the oil sump. As the trapped oil drains to the oil sump, the power spring forces the
piston down, actuating the linkage to the fuel system controls, and the supply of fuel to
the engine is diminished. As the engine speed returns to the set rate, the flyweights
resume their original position and the, pilot valve plunger again covers the regulating
port.
Fig. 13 Schematic diagram of Woodward regulating governor
If the load increases, the engine slows down, and the flyweights move inward. This
lowers the pilot valve plunger, allowing pressure oil to flow through the pilot valve
chamber to the power cylinder. This oil supplied by a pump is under a pressure sufficient
to overcome the pressure of the power spring. The power piston moves upward, actuating
the linkage to increase the amount of fuel injected into the engine cylinders. Once again,
as the speed returns to the set rate, the flyweights resume their central position. The gear
pump that supplies the high-pressure oil is driven from the governor drive shaft and takes
suction from the governor oil sump. A spring-loaded accumulator maintains a constant
pressure of oil and allows excess oil to return to the sump.
To prevent overcorrection in the regulating governor a compensating mechanism
is used. This acts on the pilot valve bushing so as to anticipate the pilot valve movement
and close the regulating port slightly before the centrifugal flyballs would normally direct
the pilot valve to cover the port. A compensating plunger on the power piston shaft
moves in a cylinder that is also filled with oil. When the engine speed increases and the
power piston moves downward, the actuating compensating plunger is also carried down,
drawing oil into its cylinder. This creates a suction above the receiving compensating
plunger which is part of the pilot valve bushing. The bushing moves upward, closing the
port to the power piston. Thus the power piston is stopped, allowing no time for
overcorrection. As the flyweights and pilot valve return to their central position, oil
flowing through a needle valve allows the compensating spring to return to its central
position. To keep the port closed, the bushing and plunger must return to normal position
at exactly the same speed. Therefore, the needle valve must be adjusted so that the oil
passes through at the required rate for the particular engine.
When the engine speed drops below the set rate, the actuating compensating
plunger moves upward with the power piston. This increases the pressure above the
actuating compensating plunger and consequently above the receiving compensating
piston which therefore moves down, carrying with it the pilot valve bushing. As before,
the lower bushing port is closed. The excess oil in the compensating system is now forced
out through the needle valve as the compensating spring returns the bushing to its central
position.
The governing speed of the engine is set by changing the tension of the speed adjusting
spring. The pressure of this spring determines the engine speed necessary for the
flyweights to maintain their central position. Oil allowed to leak past the various plungers
for lubricating purposes is drained into the governing oil sump.
In actual operation, the events described above occur almost simultaneously.
4.12.3 Regulating governor sub-assemblies:-
The governor consists of five principal subassemblies as follows:
a. Drive adapter: - The drive adapter assembly serves as a mounting base for the
governor. The upper flange of the casting is bored out at the center to form a bearing
surface for the hub of the pump drive gear and for the upper end of the drive shaft.
b. Power case assembly:- This assembly includes the governor oil pump, oil pump
check valves, oil pressure accumulators, and compensating needle valves.
The oil pump drive gear turns the rotating sleeve to which it is attached. The
pump idler gear is carried on a stud and rotates in a bored recess in the power case. These
two gears and their housing constitute the governor oil pump. On opposite sides of the
central bore in the power case, and parallel to it, are two long oil passages leading from
the bottom of the power case to the top of the accumulator bores. Check valve seats are
arranged at the top and bottom of each chamber. Both check valves have openings
leading from the space between the valves to the oil pump. In this way the pump is
arranged for rotation in either direction, pulling oil through the lower check valve on one
side and forcing it through the upper check valve on the opposite side.
There are two oil pressure accumulators. Their function is to regulate the
operating oil pressure and insure a continuous supply of oil in the event that the
requirements of the power cylinder should temporarily exceed the capacity of the oil
pump. There is no adjustment for oil pressure, as this pressure is determined by the size
of the springs in the accumulators. The two compensating needle valves control the size
of the openings in the two small tapered ports in the passage that connects the area above
the actuating compensating plunger in the Servo motor and the space above the receiving
compensating plunger in the pilot valve bushing of the rotating sleeve assembly. These
ports open the compensating oil passage to the oil sump tank. Only one needle valve and
one port are necessary for operation, but two are provided so that adjustment can be made
on the one that is more accessible.
Fig. 14 Governor-sections through adapter, power, case, power cylinder and rotating sleeve assembly.
c. Power cylinder assembly: - The power cylinder assembly consists of the cylinder,
power piston, piston rod, power spring, and the actuating compensating plunger. The
power piston is single acting. Any oil pressure acting on the lower side forces the piston
up against the power spring, thereby increasing the fuel flow. If no oil pressure is present,
the power spring acting on the upper side forces the piston down to decrease the fuel
flow.
The area underneath the power piston is connected to the pilot valve regulating
ports. An oil drain is provided in the space above the power piston to permit any oil that
may leak by the piston to drain into the governor case oil sump. No piston rings are used
in the closely fitting piston. A shallow, helical groove permits equal oil pressure on all
sides of the piston, thus preventing wear and binding.
An adjustable load limit stop screw is provided in the power cylinder. This screw
prevents the power piston from traveling beyond the predetermined load limit. The screw
can be adjusted by removing the cap nut on top of the power cylinder, loosening the lock
nut, and turning the screw up or down with a screwdriver.
d. Speed control column:- The basic speed control column assembly includes the
speeder plug screw, speed adjusting spring, rack shaft, rack shaft gear, and the speed
adjustment knob with gear train. The gear train consists of the dial shaft gear, dial shaft
pinion, and the pinion shaft gear and pinion. Movement of the gear train changes the
compression of the speed adjusting spring. The amount of compression determines the
speed at which the flyballs will be vertical. Hence, the compression determines the
engine speed. The speeder plug screw allows the adjustment of the governor speed setting
to match the actual speed of the engine.
e. Rotating sleeve assembly: - The principal parts of the rotating sleeve assembly
(Figure 10-13) are: the pump drive gear, pilot valve bushing, pilot valve plunger,
ballhead, and flyballs. The central bore in the power case forms a bearing for the entire
rotating sleeve. The port grooves in the sleeve align with the ports in the power case
(Figure 10-10). Since these grooves extend completely around the diameter of the
rotating sleeve, the results are the same as if the sleeve were stationary and the ports were
permanently in line with those in the case. From top to bottom the ports are as follows:
accumulator pressure to pilot valve, regulating pressure to power cylinder, drain from the
lower end of the pilot plunger, compensating pressure from the power piston to the
receiving compensating plunger on the pilot valve bushing, and drain from the lower side
of the receiving compensating plunger.
4.12.4 ADJUSTMENTS
a. Speed adjustment: - The speed setting of the governor is changed by increasing or
decreasing the compression of the speed adjusting spring which opposes the centrifugal
force of the flyballs. Increasing the spring compression will make it more difficult for the
flyballs to move outward; consequently a higher flyball (and engine) speed must be
attained to move the flyballs outward and thereby reduce the fuel supply.
Conversely, decreasing the compression of the speed adjusting spring will permit
the flyballs to move outward when they, and the engine, are running at a lower speed.
Thus, decreasing the spring compression decreases the speed at which the engine will
run.
Speed adjustments may be made manually at the governor, or electrically from the
governor control cabinet in the maneuvering room as follows:
1. Manual adjustment:- The manual adjustment is made by means of the speed
control knob located on the front of the regulating governor. This knob is connected
through a gear train to the rack shaft which in turn is- geared to a rack on the speed
adjusting plug. The knob also actuates a pointer that travels over a dial graduated to
show engine speeds corresponding to deflection of the speed adjusting spring.
2. Electrical adjustment:- For electrical control, a Selsyn receiving motor is also
geared to the rack shaft. This receiving motor operates in parallel with a Selsyn
transmitter generator in the governor control cabinet mounted on the main control
cubicle instrument panel in the maneuvering room. When the speed setting is
changed at the transmitter generator, the receiving motor in the governor moves to
establish the same setting in the governor.
b. Compensating needle valve adjustment:- This adjustment is made with the engine
running from 200 rpm to 300 rpm as set by the speed adjustment knob or by remote
control.
Either of the two needle valves may be used for adjustment. The one not used must be
turned in against its seat. When performing the adjustment, the more accessible valve is
opened a full turn or more and the engine is allowed to surge for approximately 30
seconds to eliminate trapped air. Then the valve is closed until surging is just eliminated.
The needle valve will usually be open about one-fourth of a turn for best performance.
However, the adjustment depends on the characteristics of the engine. The needle valve
should be kept open as far as possible to prevent sluggishness. Once the valve has been
adjusted correctly for the engine, it should not be necessary to change the adjustment
except for a permanent temperature change affecting the viscosity of the oil.
4.12.5 Air Compressor
The air compressor is required to provide a constant supply of compressed air for
the locomotive and train brakes. In the US, it is standard practice to drive the compressor
off the diesel engine drive shaft. In the UK, the compressor is usually electrically driven
and can therefore be mounted anywhere. The Class 60 compressor is under the frame,
whereas the Class 37 has the compressors in the nose.
4.12.6 Gear Box
The radiator and its cooling fan is often located in the roof of the locomotive.
Drive to the fan is therefore through a gearbox to change the direction of the drive
upwards.
4.12.7 Fuel Injection
Ignition is a diesel engine is achieved by compressing air inside a cylinder until it
gets very hot (say 400° C, almost 800° F) and then injecting a fine spray of fuel oil to
cause a miniature explosion. The explosion forces down the piston in the cylinder and
this turns the crankshaft. To get the fine spray needed for successful ignition the fuel has
to be pumped into the cylinder at high pressure. The fuel pump is operated by a cam
driven off the engine. The fuel is pumped into an injector, which gives the fine spray of
fuel required in the cylinder for combustion.
Fig. 15 Fuel injection pump Fig. 16 FIP cut section
The original fuel injection pumps used on ALCO Engines had plunger diameter of
15 mm. The plunger diameter of the fuel injection pump was increased from 15 mm to 17
mm. This modification led to sharper fuel injection i.e. injection at higher-pressure. The
modification resulted in increase of peak fuel line pressure from 750 to 850 bars and,
thus, improvement in the fuel efficiency.
The estimated fuel and lube oil economy with this modification is approx. 1.5%
and 4% respectively.
4.12.8 FIP Testing
Ensure the level of servo calibration. Oil is above the low mark in storage tank of test
stand.
Heat the oil to 100° F to 120° F.
Mount the m/c nozzle according to FIP type to be used on m/c.
Mount the overhauled FIP on cam housing & tighten. The FIP rack should be against
the spring loaded plunger.
Screw the fuel inlet union.
Connect the high pressure tube b/w FIP discharge & calibrating nozzle.
Keep the control rack in full fuel oil position & insert horse shoe space according to
FIP type to be tested b/w the rack positioning tool & FIP face.
Reset the counter to zero.
Operate the calibrating m/c & set the oil pressure 25-30 psi.
Measure the oil delivery in beaker for 300 strokes. Do this process five times & check
the average of last three measurement of oil delivery.
If specified delivery is not achieved adjust the rack by rotating rack position tool in
the required direction to get the specified delivery & when it is found within specified
limit, stop the m/c.
Adjust the pointer of full fuel position to proper mm reading. Remove the horse shoe
space & ensure rack length is at idle fuel length i.e. at 9 mm & record the full fuel
delivery in calibration data nozzle.
4.12.9 Injector Assembly Sequence
1. Nozzle holder body.
2. Compensating washer.
3. Spring.
4. Spindle with guide bush.
5. Intermediate disc.
6. Nozzle.
7. Nozzle cap nut.
4.12.9.1 Maintenance Instruction Of Injector While Re-Conditioning
Nozzle value lift 0.024˝ max.
Testing pressure
Min. 3100 Psi-260 kg/cm
Max. 4100 Psi-290 kg/cm
Spring pattern should be uniform.
Nozzle should give healthy chartering sound.
Seat tightness test, there should be no dribbling.
4.12.9.2Tool, Gauges, Torque Wrenches Used In FIP Section
Torque Wrench – 100 to 400 ft. lbs.
Torque Wrench – 450 to 750 ft. lbs.
Socket – 1 (⅜)˝ & 2((⅜)˝
Box Spanner 36 mm & 70 mm.
Reamer 23/32 HSS.
Centering Sleeve For Injector Nozzle.
True Running Tool For Injection.
Pin Vice Kit.
Dial Gauge.
Temp. Gauge 0 to 110° C.
Pressure Gauge 0 to 100 psi.
Pressure Gauge 0 to 8960 psi.
Nose Plier.
Clean all the components once again using clean HSD oil & assemble them wet.
Place the injector nozzle holder body in the fixture with nozzle & upward.
Position the spring seat & spring in the body.
Keep spindle with guide bush & intermediate disc on spring.
Place assemble nozzle over the intermediate disc & screw the nozzle cap nut & torque
to 105 ft. lbs.
4.13 Fuel Control
In an automobile engine, the power is controlled by the amount of fuel/air mixture
applied to the cylinder. The mixture is mixed outside the cylinder and then applied by a
throttle valve. In a diesel engine the amount of air applied to the cylinder is constant so
power is regulated by varying the fuel input. The fine spray of fuel injected into each
cylinder has to be regulated to achieve the amount of power required. Regulation is
achieved by varying the fuel sent by the fuel pumps to the injectors.
Fig. 17 Fuel System
The amount of fuel being applied to the cylinders is varied by altering the effective
delivery rate of the piston in the injector pumps. Each injector has its own pump,
operated by an engine-driven cam, and the pumps are aligned in a row so that they can all
be adjusted together. The adjustment is done by a toothed rack (called the "fuel rack")
acting on a toothed section of the pump mechanism. As the fuel rack moves, so the
toothed section of the pump rotates and provides a drive to move the pump piston round
inside the pump.The fuel rack can be moved either by the driver operating the power
controller in the cab or by the governor. If the driver asks for more power, the control
rod moves the fuel rack to set the pump pistons to allow more fuel to the injectors. The
engine will increase power and the governor will monitor engine speed to ensure it does
not go above the predetermined limit.The limits are fixed by springs limiting the weight
movement.
Fig.18 Fuel Supply system
4.14 Radiators
They are used for cooling internal combustion engines, chiefly in automobiles but
also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating
plant or any similar use of such an engine.
They operate by passing a liquid coolant through the engine block, where it is heated,
then through the radiator itself where it loses this heat to the atmosphere. This coolant is
usually water-based, but may also be oil. It's usual for the coolant flow to be pumped,
also for a fan to blow air through the radiator.
In railway with a liquid-cooled internal combustion engine a radiator is connected to
channels running through the engine and cylinder head, through which a liquid (coolant)
is pumped. This liquid may be water (in climates where water is unlikely to freeze), but is
more commonly a mixture of water and antifreeze in proportions appropriate to the
climate. Antifreeze itself is usually ethylene glycol or propylene glycol (with a small
amount of corrosion inhibitor).
The radiator transfers the heat from the fluid inside to the air outside, thereby
cooling the engine. Radiators are also often used to cool automatic transmissions, air
conditioners, and sometimes to cool engine oil. Radiators are typically mounted in a
position where they receive airflow from the forward movement of the vehicle, such as
behind a front grill. Where engines are mid- or rear-mounted, it is common to mount the
radiator behind a front grill to achieve sufficient airflow, even though this requires long
coolant pipes. Alternatively, the radiator may draw air from the flow over the top of the
vehicle or from a side-mounted grill. For long vehicles, such as buses, side airflow is
most common for engine and transmission cooling and top airflow most common for air
conditioner cooling.
4.14.1 Radiator Construction
Railway radiators are constructed of a pair of header tanks, linked by a core with
many narrow passageways, thus a high surface area relative to its volume. This core is
usually made of stacked layers of metal sheet, pressed to form channels and soldered or
brazed together. For many years radiators were made from brass or copper cores soldered
to brass headers. Modern radiators save money and weight by using plastic headers and
may use aluminium cores. This construction is less easily repaired than traditional
materials.
An earlier construction method was the honeycomb radiator. Round tubes were
swaged into hexagons at their ends, then stacked together and soldered. As they only
touched at their ends, this formed what became in effect a solid water tank with many air
tubes through it.
Fig.19 Honeycomb Radiator Tubes
Temperature Control
4.14.2 Water Flow Control
The engine temperature is primarily controlled by a wax-pellet type of thermostat, a
valve which opens once the engine has reached its optimum operating temperature.
Fig.20 Radiator Thermostat
When the engine is cold the thermostat is closed, with a small bypass flow so that the
thermostat experiences changes to the coolant temperature as the engine warms up.
Coolant is directed by the thermostat to the inlet of the circulating pump and is returned
directly to the engine, bypassing the radiator. Directing water to circulate only through
the engine allows the temperature to reach optimum operating temperature as quickly as
possible whilst avoiding localized "hot spots". Once the coolant reaches the thermostat's
activation temperature it opens, allowing water to flow through the radiator to prevent the
temperature rising higher.
Once at optimum temperature, the thermostat controls the flow of coolant to the
radiator so that the engine continues to operate at optimum temperature. Under peak load
conditions, such as labouring slowly up a steep hill whilst heavily laden on a hot day, the
thermostat will be approaching fully open because the engine will be producing near to
maximum power while the velocity of air flow across the radiator is low. (The velocity of
air flow across the radiator has a major effect on its ability to dissipate heat.) Conversely,
when cruising fast downhill on a motorway on a cold night on a light throttle, the
thermostat will be nearly closed because the engine is producing little power, and the
radiator is able to dissipate much more heat than then engine is producing. Allowing too
much flow of coolant to the radiator would result in the engine being over cooled and
operating at lower than optimum temperature. A side effect of this would be that the
passenger compartment heater would not be able to put out enough heat to keep the
passengers warm.
The thermostat is therefore constantly moving throughout its range, responding to
changes in vehicle operating load, speed and external temperature, to keep the engine at
its optimum operating temperature.
4.14.3 Airflow Control
Other factors influence the temperature of the engine including radiator size and the type
of radiator fan. The size of the radiator (and thus its cooling capacity) is chosen such that
it can keep the engine at the design temperature under the most extreme conditions a
vehicle is likely to encounter (such as climbing a mountain whilst fully loaded on a hot
day).
Airflow speed through a radiator is a major influence on the heat it loses. Vehicle speed
affects this, in rough proportion to the engine effort, thus giving crude self-regulatory
feedback. Where an additional cooling fan is driven by the engine, this also tracks engine
speed similarly.
4.14.4 Coolant
Before World War II, radiator coolant was usually plain water. Antifreeze was used
solely to control freezing, and this was often only done in cold weather.
Development in high-performance aircraft engines required improved coolants with
higher boiling points, leading to the adoption of glycol or water-glycol mixtures. These
led to the adoption of glycols for their antifreeze properties too.
Since the development of aluminium or mixed-metal engines, corrosion inhibition has
become even more important than antifreeze and in all regions and seasons too.
Because the thermal efficiency of internal combustion engines increases with
internal temperature the coolant is kept at higher-than-atmospheric pressure to increase
its boiling point. A calibrated pressure-relief valve is usually incorporated in the radiator's
fill cap. This pressure varies between models, but is typically 9 psi (0.6 bar) - 15 psi
(1.0 bar).
4.14.5 Boiling Or Overheating
On this type system, if the coolant in the overflow container gets too low, fluid
transfer to overflow will cause an increased loss by vaporizing the engine coolant.
Severe engine damage can be caused by overheating, by overloading or system defect,
when the coolant is evaporated to a level below the water pump. This can happen without
warning because, at that point, the sending units are not exposed to the coolant to indicate
the excessive temperature.
To protect the unwary the cap often contains a mechanism that attempts to relieve the
internal pressure before the cap can be fully opened. Some scalding of one's hands can
easily occur in this event. Opening a hot radiator drops the system pressure immediately
and may cause a sudden ebullition of super-heated coolant which can cause severe burns
(see geyser).
4.14.6 Radiator Thrust
An aircraft radiator comprises a duct wherein heat is added. As a result, this is
effectively a jet engine. High-performance piston aircraft with well-designed low-drag
radiators (notably the P-51 Mustang) derived a significant portion of their thrust from this
effect. At one point, there were even plans to equip the Spitfire with a ramjet, by injecting
fuel into this duct after the radiator and igniting it. Although ramjets normally require a
supersonic airspeed, this light-up speed can be reduced where heat is being added, such
as in a radiator duct.
4.14.7 Steam Cooling
Pressurized cooling systems operate by adding heat to the coolant fluid, causing it
to rise in temperature in inverse proportion to its specific heat capacity. With the need to
keep the final temperature below boiling point, this limits the amount of heat that a given
mass-flow of coolant can dissipate.
Attempts were made with aero-engines of the 1930s, notably the Rolls-Royce
Goshawk, to exceed this limit by allowing the coolant to boil. This absorbs an amount of
heat equivalent to the specific heat of vaporization, which for water is more than five
times the energy required to heat the same quantity of water from 0°C to 100°C.
Obviously this allows the necessary cooling effect with far less coolant requiring to be
circulated.
The practical difficulty was the need to provide condensers rather than radiators.
Cooling was now needed not just for hot dense liquid coolant, but for low-density steam.
This required a condenser far larger and with higher drag than a radiator. For aircraft,
especially high-speed aircraft, these were soon realized to be unworkable and so steam
cooling was abandoned.
Work instruction Radiator Fan Assembly Stripping & Cleaning
Remove the radiator fan assembly from the loco and place on the sand.
Remove the radiator fan from bearing housing.
Clean bearing housing externally with diesel oil and place it on work bench.
Dismantle the components in the following sequence:
o Universal end hub.
o Bearing housing covers.
o Shaft & bearing using hydraulic press.
Open bearing seal plate.
Clean the bearing with HSD oil and water and dry air.
Pack the bearing with servogen 3 grease and seal.
Press bearing to shaft by hydraulic press.
Apply both bearing covers duly ensuring for free rotation of shaft.
Fit hub at universal end.
Fix the bearing housing in the fixture.
Set the fan end key to fan and fan shaft.
Fix the fan to the shaft and tighten the nut and secure the split pin.
Chapter-5 Cooling System
_____________________________________________________________
Like an automobile engine, the diesel engine needs to work at an optimum
temperature for best efficiency. When it starts, it is too cold and, when working, it must
not be allowed to get too hot. To keep the temperature stable, a cooling system is
provided. This consists of a water-based coolant circulating around the engine block, the
coolant being kept cool by passing it through a radiator.
The coolant is pumped round the cylinder block and the radiator by an electrically or belt
driven pump. The temperature is monitored by a thermostat and this regulates the speed
of the (electric or hydraulic) radiator fan motor to adjust the cooling rate. When starting
the coolant isn't circulated at all. After all, you want the temperature to rise as fast as
possible when starting on a cold morning and this will not happen if you a blowing cold
air into your radiator. Some radiators are provided with shutters to help regulate the
temperature in cold conditions.
Fig. 21 Piping System
If the fan is driven by a belt or mechanical link, it is driven through a fluid
coupling to ensure that no damage is caused by sudden changes in engine speed. The fan
works the same way as in an automobile, the air blown by the fan being used to cool the
water in the radiator. Some engines have fans with an electrically or hydrostatically
driven motor. An hydraulic motor uses oil under pressure which has to be contained in a
special reservoir and pumped to the motor. It has the advantage of providing an in-built
fluid coupling.
A problem with engine cooling is cold weather. Water freezes at 0° C or 32° F
and frozen cooling water will quickly split a pipe or engine block due to the expansion of
the water as it freezes. Some systems are "self draining" when the engine is stopped and
most in Europe are designed to use a mixture of anti-freeze, with Gycol and some form of
rust inhibitor. In the US, engines do not normally contain anti-freeze, although the new
GM EMD "H" engines are designed to use it. Problems with leaks and seals and the
expense of putting 100 gallons (378.5 litres) of coolant into a 3,000 hp engine, means that
engine in the US have traditionally operated without it. In cold weather, the engine is left
running or the locomotive is kept warm by putting it into a heated building or by
plugging in a shore supply. Another reason for keeping diesel engines running is that the
constant heating and cooling caused by shutdowns and restarts, causes stresses in the
block and pipes and tends to produce leaks. Water up to 1210lts used.
Shown below are the percentages of useful work and various losses obtained
from the combustion of a fuel oil in a diesel cylinder:
To useful work (brake thermal efficiency) 30-35 percent
To exhaust gases 30-35 percent
To cooling water and friction 30-35 percent
Radiation, lube oil, and so forth 0- 5 percent
There are three practical reasons for cooling an engine:
1. To maintain lubricating oil film on pistons, cylinder walls, and other moving
parts: - This oil film must be maintained to insure adequate lubrication. The
formation of an oil film depends in large degree on the viscosity of the oil. If the
engine cooling system did not keep the engine temperature at a value that would
insure the formation of an oil film, insufficient lubrication and consequent excessive
engine wear would result. If the engine is kept too cool, condensation takes places in
the lube oil and forms acids and sludge.
2. To avoid too great a variation in the dimensions of the engine parts: - Great
differences between operating temperatures at varying loads cause excessive changes
in the dimensions of the moving parts. These excessive changes also occur when
there are large differences between the cold and operating temperatures of the parts.
These changes in dimensions result in a variation of clearances between the moving
parts. Under normal operating conditions these clearances are very small and any
variation in dimension of the moving parts may cause insufficient clearances and
subsequent inadequate lubrication, increased friction, and possible seizure.
3. To retain the strength of the metals used: - High temperatures change the strength
and physical properties of the various ferrous metals used in an engine. For example,
if a cylinder head is subjected to high temperatures without being cooled, the tensile
strength of the metal is reduced, resulting in possible fracture. This high temperature
also causes excessive expansion of the metal which may result in shearing of the
cylinder bolts.
Cylinder heads, cylinder jackets, cylinder liners, exhaust headers, valves, and exhaust
elbows usually are cooled by water. Pistons may be cooled either by water or oil. In
present fleet type submarine installations, the pistons are cooled by lubricating oil which
is in turn cooled by engine cooling water. It is important to keep all parts of the engine at
as nearly the same temperature as possible. This can be accomplished to some extent by
engine design. For instance, the water jacket should cover the entire length of the piston
stroke to avoid possible unequal expansion of various sections of the cylinder and
cylinder liner.
It requires time to conduct heat through any substance, therefore the thicker the metal, the
slower the conduction. This is one of the reasons the size of cylinders in diesel engines is
limited, because the larger the cylinder, the thicker the material necessary for liners and
cylinder heads in order to withstand the pressures of combustion. Thicker metals cause
the inside surfaces to run hotter, because the heat is not conducted so rapidly to the
cooling water.
5.1 Water pump:
Fig.22 Water cooling system
5.1.1 Inspection and maintenance
Examine impeller for wear & score marks.
Examine bearing and see that there are no damage balls or chattered races.
Ensure while pressing, pressure should be applied only against the inner race of
bearing.
Lubricating ball bearing with a light grease before final assembly.
Examine visually the impeller and remove any slight burs or Feathers.
Check seal plate for erosion and cavitation damages.
Check the run out of shaft and don’t permit more than 2 thou.
The torquing of the impeller nut should be done at 125lbs.
Use only stainless steel split pin.
Check the locking properly of the lock nut.
Chapter-6 Lubrication
_____________________________________________________________
Like an automobile engine, a diesel engine needs lubrication. In an arrangement
similar to the engine cooling system, lubricating oil is distributed around the engine to the
cylinders, crankshaft and other moving parts. There is a reservoir of oil, usually carried
in the sump, which has to be kept topped up, and a pump to keep the oil circulating
evenly around the engine. The oil gets heated by its passage around the engine and has to
be kept cool, so it is passed through a radiator during its journey. The radiator is
sometimes designed as a heat exchanger, where the oil passes through pipes encased in a
water tank which is connected to the engine cooling system.
The oil has to be filtered to remove impurities and it has to be monitored for low
pressure. If oil pressure falls to a level which could cause the engine to seize up, a "low
oil pressure switch" will shut down the engine. There is also a high pressure relief valve,
to drain off excess oil back to the sump.
Fig. 23 Lube oil system
6.1 Lubricating Oil: WDM2 – 910lts WDM3 – 1110lts
Chapter-7 Turbocharger
________________________________________________________________________
A turbocharger, or turbo, is a gas compressor used for forced-induction of an
internal combustion engine. Like a supercharger, the purpose of a turbocharger is to
increase the density of air entering the engine to create more power. However, a
turbocharger differs in that the compressor is powered by a turbine driven by the engine's
own exhaust gases.
Fig. 24 Air foil bearing-supported turbocharger
7.1 Nomenclature
Early manufacturers of turbochargers referred to them as "turbosuperchargers". A
supercharger is an air compressor used for forced induction of an engine. Logically then,
adding a turbine to turn the supercharger would yield a "turbosupercharger". However,
the term was soon shortened to "turbocharger". This is now a source of confusion, as the
term "turbosupercharged" is sometimes used to refer to an engine that uses both a
crankshaft-driven supercharger and an exhaust-driven turbocharger.
Some companies such as Teledyne Continental Motors still use the term
turbosupercharger in its original sense.
7.2 Working Principle
A turbocharger is a small radial fan pump driven by the energy of the exhaust gases
of an engine. A turbocharger consists of a turbine and a compressor on a shared shaft.
The turbine converts heat to rotational force, which is in turn used to drive the
compressor. The compressor draws in ambient air and pumps it in to the intake manifold
at increased pressure, resulting in a greater mass of air entering the cylinders on each
intake stroke.
The objective of a turbocharger is the same as a supercharger; to improve the
engine's volumetric efficiency by solving one of its cardinal limitations. A naturally
aspirated automobile engine uses only the downward stroke of a piston to create an area
of low pressure in order to draw air into the cylinder through the intake valves. Because
the pressure in the atmosphere is no more than 1 atm (approx 14.7 psi), there ultimately
will be a limit to the pressure difference across the intake valves and thus the amount of
airflow entering the combustion chamber. Because the turbocharger increases the
pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will
be forced in as the inlet manifold pressure increases. The additional oxygen makes it
possible to add more fuel, increasing the power and torque output of the engine.
Because the pressure in the cylinder must not go too high to avoid detonation and
physical damage, the intake pressure must be controlled by controlling the rotational
speed of the turbocharger. The control function is performed by a wastegate, which
routes some of the exhaust flow away from the exhaust turbine. This controls shaft speed
and regulates air pressure in the intake manifold.
Fig. 25 Principle of turbocharger
7.3 History
The turbocharger was invented by Swiss engineer Alfred Büchi. His patent for a
turbocharger was applied for use in 1905. Diesel ships and locomotives with
turbochargers began appearing in the 1920s.
7.4 Aviation
During the First World War French engineer Auguste Rateau fitted turbo chargers to
Renault engines powering various French fighters with some success.
In 1918, General Electric engineer Sanford Moss attached a turbo to a V12 Liberty
aircraft engine. The engine was tested at Pikes Peak in Colorado at 14,000 feet (4,300 m)
to demonstrate that it could eliminate the power losses usually experienced in internal
combustion engines as a result of reduced air pressure and density at high altitude.
Turbochargers were first used in production aircraft engines in the 1930s before World
War II. The primary purpose behind most aircraft-based applications was to increase the
altitude at which the airplane could fly, by compensating for the lower atmospheric
pressure present at high altitude. Aircraft such as the P-38 Lightning, B-17 Flying
Fortress, and P-47 Thunderbolt all used turbochargers to increase high altitude engine
power.
7.5 Design And Installation
7.5.1 Components:
Fig. 26 On the left, the brass oil drain connection. On the right are the braided oil supply line and water
coolant line connections.
Fig.27 Compressor impeller side with the cover removed.
Fig.28 Turbine side housing removed.
Fig.29 A wastegate installed next to the turbocharger:
The turbocharger has four main components. The turbine (almost always a radial
turbine) and impeller/compressor wheels are each contained within their own folded
conical housing on opposite sides of the third component, the center housing/hub rotating
assembly (CHRA).
The housings fitted around the compressor impeller and turbine collect and direct the gas
flow through the wheels as they spin. The size and shape can dictate some performance
characteristics of the overall turbocharger. Often the same basic turbocharger assembly
will be available from the manufacturer with multiple housing choices for the turbine and
sometimes the compressor cover as well. This allows the designer of the engine system to
tailor the compromises between performance, response, and efficiency to application or
preference. Twin-scroll designs have two valve-operated exhaust gas inlets, a smaller
sharper angled one for quick response and a larger less angled one for peak performance.
The turbine and impeller wheel sizes also dictate the amount of air or exhaust that can be
flowed through the system, and the relative efficiency at which they operate. Generally,
the larger the turbine wheel and compressor wheel, the larger the flow capacity.
Measurements and shapes can vary, as well as curvature and number of blades on the
wheels. Variable geometry turbochargers are further developments of these ideas.
The center hub rotating assembly (CHRA) houses the shaft which connects the
compressor impeller and turbine. It also must contain a bearing system to suspend the
shaft, allowing it to rotate at very high speed with minimal friction. For instance, in
automotive applications the CHRA typically uses a thrust bearing or ball bearing
lubricated by a constant supply of pressurized engine oil. The CHRA may also be
considered "water cooled" by having an entry and exit point for engine coolant to be
cycled. Water cooled models allow engine coolant to be used to keep the lubricating oil
cooler, avoiding possible oil coking from the extreme heat found in the turbine. The
development of air-foil bearings has removed this risk.
In the automotive world, boost refers to the increase in pressure that is
generated by the turbocharger in the intake manifold that exceeds normal atmospheric
pressure. Atmospheric pressure is approximately 14.5 psi or 1.0 bar, and anything above
this level is considered to be boost. The level of boost may be shown on a pressure gauge,
usually in bar, psi or possibly kPa. This is representative of the extra air pressure that is
achieved over what would be achieved without the forced induction. Manifold pressure
should not be confused with the volume of air that a turbo can flow.
In contrast, the instruments on aircraft engines measure absolute pressure in
inches of mercury. Absolute pressure is the amount of pressure above a total vacuum.
The ICAO standard atmospheric pressure is 29.92 inches (760 mm) of mercury at sea
level. Most modern aviation turbochargers are not designed to increase manifold
pressures above this level, as aircraft engines are commonly air-cooled and excessive
pressures increase the risk of overheating, pre-ignition, and detonation. Instead, the turbo
is only designed to hold a pressure in the intake manifold equal to sea-level pressure as
the altitude increases and air pressure drops. This is called turbo-normalizing.
Boost pressure is limited to keep the entire engine system, including the turbo, inside its
thermal and mechanical design operating range. The speed and thus the output pressure
of the turbo is controlled by the wastegate, a bypass which shunts the gases from the
cylinders around the turbine directly to the exhaust pipe.
The maximum possible boost depends on the fuel's octane rating and the inherent
tendency of any particular engine towards detonation. Premium gasoline or racing
gasoline can be used to prevent detonation within reasonable limits. Ethanol, methanol,
liquefied petroleum gas (LPG) and diesel fuels allow higher boost than gasoline, because
of these fuels' combustion characteristics.
To obtain more power from higher boost levels and maintain reliability, many engine
components have to be replaced or upgraded such as the fuel pump, fuel injectors,
pistons, valves, head-gasket, and head bolts.
7.5.2 Wastegate
By spinning at a relatively high speed, the compressor turbine draws in a large volume of
air and forces it into the engine. As the turbocharger's output flow volume exceeds the
engine's volumetric flow, air pressure in the intake system begins to build. The speed at
which the assembly spins is proportional to the pressure of the compressed air and total
mass of air flow being moved. Since a turbo can spin to RPMs far beyond what is
needed, or of what it is safely capable of, the speed must be controlled. A wastegate is the
most common mechanical speed control system, and is often further augmented by an
electronic or manual boost controller. The main function of a wastegate is to allow some
of the exhaust to bypass the turbine when the set intake pressure is achieved. Passenger
cars have wastegates that are integral to the turbocharger.
7.5.3 Anti-Surge/Dump/Blow off Valves:
Turbocharged engines operating at wide open throttle and high rpm require a large
volume of air to flow between the turbo and the inlet of the engine. When the throttle is
closed compressed air will flow to the throttle valve without an exit (i.e. the air has
nowhere to go).
This causes a surge which can raise the pressure of the air to a level which can damage
the engine. If the pressure rises high enough, a compressor stall will occur, where the
stored pressurized air decompresses backwards across the impeller and out the inlet. The
reverse flow back across the turbocharger causes the turbine shaft to reduce in speed
quicker than it would naturally, possibly damaging the turbocharger. In order to prevent
this from happening, a valve is fitted between the turbo and inlet which vents off the
excess air pressure. These are known as an anti-surge, bypass, blow-off valve (BOV) or
dump valve. It is basically a pressure relief valve, and is normally operated by the excess
pressure in the intake manifold.
The primary use of this valve is to maintain the turbo spinning at a high speed. The air is
usually recycled back into the turbo inlet but can also be vented to the atmosphere.
Recycling back into the turbocharger inlet is required on an engine that uses a mass-
airflow fuel injection system, because dumping the excessive air overboard downstream
of the mass airflow sensor will cause an excessively rich fuel mixture. A dump valve will
also shorten the time needed to re-spool the turbo after sudden engine deceleration.
7.5.4 Charge cooling:
Compressing air in the turbocharger increases its temperature, which can cause a number
of problems. Excessive charge air temperature can lead to detonation, which is extremely
destructive to engines. When a turbocharger is installed on an engine, it is common
practice to fit the engine with an intercooler, a type of heat exchanger which gives up
heat energy in the charge to the ambient air. In cases where an intercooler is not a
desirable solution, it is common practice to introduce extra fuel into the charge for the
sole purpose of cooling. The extra fuel is not burned. Instead, it absorbs and carries away
heat when it changes phase from liquid to vapor. The evaporated fuel holds this heat until
it is released in the exhaust stream. This thermodynamic property allows manufacturers
to achieve good power output by using extra fuel at the expense of economy and
emissions. Diesels are particularly suitable for turbocharging for several reasons:
Turbocharging can dramatically improve an engine's specific power and power-to-
weight ratio, performance characteristics which are normally poor in non-
turbocharged diesel engines.
Diesel engines are optimized to operate within a relatively narrow rpm range,
reducing problems with turbo lag and compressor stall caused by sudden
accelerations and decelerations.
Diesel engines are not prone to detonation because diesel fuel requires much higher
pressures to detonate than gasoline does. Because of this, diesel engines can use much
higher boost pressures than spark ignition engines, limited only by the engine's ability
to withstand that pressure.
The turbocharger's small size and low weight have production and marketing advantage
to vehicle manufacturers. By providing naturally-aspirated and turbocharged versions of
one engine, the manufacturer can offer two different power outputs with only a fraction
of the development and production costs of designing and installing a different engine.
The compact natures of a turbocharger mean that bodywork and engine compartment
layout changes to accommodate the more powerful engine are not needed or minimal.
Parts commonality between the two versions of the same engine reduces production and
servicing costs.
Today, turbochargers are most commonly used on gasoline engines in high-performance
automobiles and diesel engines in transportation and other industrial equipment. Small
cars in particular benefit from this technology, as there is often little room to fit a large
engine. Volvo, Saab, and Subaru have produced turbocharged cars for many years, the
turbo Porsche 944's acceleration performance was very similar to that of the larger-
engined non-turbo Porsche 928, and Chrysler Corporation built numerous turbocharged
cars in the 1980s and 1990s.
7.5.5 Sand Box:
Locomotives always carry sand to assist adhesion in bad rail conditions. Sand is
not often provided on multiple unit trains because the adhesion requirements are lower
and there are normally more driven axles.
Chapter-7 Truck Frame Or Bogie
________________________________________________________________________
A bogie (pronounced /bogie/) is a wheeled wagon or trolley. In mechanics terms, a
bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in
place, as on a cargo truck, mounted on a swivel, as on a railway carriage or locomotive,
or sprung as in the suspension of a caterpillar tracked vehicle.
Archbar type truck with journal bearings as used on some steam locomotive tenders.
Fig.30 bogie function
Bettendorf-style freight car truck displayed at the Illinois Railway Museum. This
one uses journal bearings.
A bogie in the UK, or a wheel truck, or simply truck in the USA and Canada as
well as Mexico, is a structure underneath a train to which axles (and, hence, wheels) are
attached through bearings.
Bogies serve a number of purposes:
To support the rail vehicle body.
To run stably on both straight and curved track.
To ensure ride comfort by absorbing vibration, and minimizing centrifugal forces
when the train runs on curves at high speed
To minimize generation of track irregularities and rail abrasion
Usually two bogies are fitted to each carriage, wagon or locomotive, one at each end. An
alternate configuration often is used in articulated vehicles, which places the bogies under
the connection between the carriages or wagons.
Most bogies have two axles as it is the simplest design, but some cars designed
for extremely heavy loads have been built with up to five axles per bogie. Heavy-duty
cars may have more than two bogies using span bolsters to equalize the load and connect
the bogies to the cars.
Usually the train floor is at a level above the bogies, but the floor of the car may
be lower between bogies, such as for a double decker train to increase interior space
while staying within height restrictions, or in easy-access, stepless-entry low-floor trains.
Key components of a bogie include:
The bogie frame itself.
Suspension to absorb shocks between the bogie frame and the rail vehicle body.
Common types are coil springs, or rubber airbags.
At least one wheelset composed of an axle with a bearings and wheel at each end.
Axle box suspension to absorb shocks between the axle bearings and the bogie frame.
The axle box suspension usually consists of a spring between the bogie frame and
axle bearings to permit up and down movement, and sliders to prevent lateral
movement. A more modern design uses solid rubber springs.
Brake equipment . Two main types are used: brake shoes that are pressed against the
tread of the wheel, and disc brakes and pads.
In powered vehicles, some form of transmission, usually an electrically powered
traction motors or a hydraulically powered torque converter.
The connection of the bogie with the rail vehicle allows a certain degree of rotational
movement around a vertical axis pivot (bolster), with side bearers preventing excessive
movement. More modern bolster less bogie designs omit these features, instead taking
advantage of the sideways movement of the suspension to permit rotational movement.
7.1 Types of Bogie
7.1.1 BR1 bogie:
The British Railways Mark 1 coach brought into production in 1950 utilized the BR1
bogie, which was rated to run at 90 mph (145 km/h). The wheels were cast as a one-piece
item in a pair with their axle. The simple design involved the bogie resting on four leaf
springs (one spring per wheel) which in turn were connected to the axles. The leaf springs
were designed to absorb any movement or resonance and to have a damping effect to
benefit ride quality.
Each spring was connected to the outermost edge of the axle by means of a roller
bearing contained in oil filled axle box. The oil in these boxes had to be topped up at
regular maintenance times to avoid the bearing running hot and from seizing.
There was also a heavy-duty version designated BR2.
7.1.2 Commonwealth bogie:
Fig. 31 Commonwealth bogie as used on BR Mark 1 and CIE Park Royals.
The SKF or Timken manufactured Commonwealth bogie was introduced in the late
1950s for all BR Mark 1 vehicles. The bogie was a heavy cast steel design weighing 6.75
ton with fitted sealed roller bearings on the axle ends, avoiding the need to maintain axle
box oil levels.
The leaf springs were replaced with coil type springs (one per wheel) running
vertically rather than horizontally. The advanced design gave a superior ride quality to
the BR1, being rated for 100 miles per hour (160 km/h).
The side frame of the bogie was usually of bar construction, with simple horn
guides attached, allowing the axle boxes vertical movements between them. The axle
boxes had a cast steel equaliser beam or bar resting on them. The bar had two steel coil
springs placed on it and the bogie frame rested on the springs. The effect was to allow the
bar to act as a compensating lever between the two axles and to use both springs to soften
shocks from either axle. The bogie had a conventional bolster suspension with swing
links carrying a spring plank.
7.1.3 B4 bogie:
B4 bogie as used on BR Mark 2 and Irish Cravens.
The B4 bogie was introduced in 1963. It was a fabricated steel design as versus cast iron
and was hence 1.55 tons lighter than the Commonwealth, weighing in at 5.2 tons. It also
had a speed rating of 100 miles per hour (160 km/h).
Axle/spring connection was again with fitted roller bearings. However, now two coil
springs rather than one were fitted per wheel.
Only a very small amount of Mark 1 stock was fitted with the B4 bogie from new, it
being used on the Mark 1 only to replace worn out BR1 bogies. The British Rail Mark 2
coach however carried the B4 bogies from new. A heavier duty version, the B5, was
standard on Southern Region Mk1 based EMUs from the 1960s onwards. Some Mark 1
catering cars had mixed bogies—a B5 under the kitchen end, and a B4 under the seating
end. Some of the B4 fitted Mark 2s, as well as many B4 fitted Mark 1 BGs were allowed
to run at 110 miles per hour (180 km/h) with extra maintenance, particularly of the wheel
profile, and more frequent exams.
7.1.4 BT10 Bogie
BT10 High speed bogie as used on MK3.
The BT10 bogie was introduced on the British Rail Mark 3 coach in the 1970s. Each
wheel is separately connected to the bogie by a swing-arm axle.
There is dual suspension
Primary suspension via a coil spring and damper mounted on each axle.
Secondary suspension via two air springs mounted on the pivot plank. This is
connected to the bogie by pendulum links. A constant coach height is maintained by
air valves.
Most diesel locomotives and electric locomotives are carried on bogies (UK) or trucks
(US). Trucks used in the USA include AAR type A switcher truck, Bloomberg B, HT-C
truck and Flexicoil.
Chapter-8 Suspension
_____________________________________________________________
The trucks also provide the suspension for the locomotive. The weight of the locomotive
rests on a big, round bearing, which allows the trucks to pivot so the train can make a
turn. Below the pivot is a huge leaf spring that rests on a platform. The platform is
suspended by four, giant metal links, which connect to the truck assembly. These links
allow the locomotive to swing from side to side.
Fig.32 Suspension System
The weight of the locomotive rests on the leaf springs, which compress when it passes
over a bump. This isolates the body of the locomotive from the bump. The links allow the
trucks to move from side to side with fluctuations in the track. The track is not perfectly
straight, and at high speeds, the small variations in the track would make for a rough ride
if the trucks could not swing laterally. The system also keeps the amount of weight on
each rail relatively equal, reducing wear on the tracks and wheels
8.1 Wheels
Ever wonder why trains have steel wheels, rather than tires like a car? It's to reduce
rolling friction. When your car is driving on the freeway, something like 25 percent of
the engine's power is being used to push the tires down the road. Tires bend and deform a
lot as they roll, which uses a lot of energy. The amount of energy used by the tires is
proportional to the weight that is on them. Since a car is relatively light, this amount of
energy is acceptable (you can buy low rolling-resistance tires for your car if you want to
save a little gas).
Since a train weighs thousands of times more than a car, the rolling resistance is a
huge factor in determining how much force it takes to pull the train. The steel wheels on
the train ride on a tiny contact patch -- the contact area between each wheel and the track
is about the size of a dime.
By using steel wheels on a steel track, the amount of deformation is minimized,
which reduces the rolling resistance. In fact, a train is about the most efficient way to
move heavy goods. The downside of using steel wheels is that they don't have much
traction. In the next section, we'll discuss the interesting solution to this problem.
8.2 Traction:
Traction when going around turns is not an issue because train wheels have
flanges that keep them on the track. But traction when braking and accelerating is an
issue.
This locomotive can generate 64,000 pounds of thrust. But in order for it to use
this thrust effectively, the eight wheels on the locomotive have to be able to apply this
thrust to the track without slipping. The locomotive uses a neat trick to increase the
traction.
In front of each wheel is a nozzle that uses compressed air to spray sand, which is
stored in two tanks on the locomotive. The sand dramatically increases the traction of the
drive wheels. The train has an electronic traction-control system that automatically starts
the sand sprayers when the wheels slip or when the engineer makes an emergency stop.
The system can also reduce the power of any traction motor whose wheels are slipping.
Chapter-9 Transmission
Like an automobile, a diesel locomotive cannot start itself directly from a stand. It will
not develop maximum power at idling speed, so it needs some form of transmission
system to multiply torque when starting. It will also be necessary to vary the power
applied according to the train weight or the line gradient. There are three methods of
doing this: mechanical, hydraulic or electric. Most diesel locomotives use electric
transmission and are called "diesel-electric" locomotives. Mechanical and hydraulic
transmissions are still used but are more common on multiple unit trains or lighter
locomotives.9.1 Mechanical Transmission
A diesel-mechanical locomotive is the simplest type of diesel locomotive. As the
name suggests, a mechanical transmission on a diesel locomotive consists a direct
mechanical link between the diesel engine and the wheels. In the example below, the
diesel engine is in the 350-500 hp range and the transmission is similar to that of an
automobile with a four speed gearbox. Most of the parts are similar to the diesel-electric
locomotive but there are some variations in design mentioned below.
Fig.33 diesel mechanical locomotive
9.2 Gearbox
This does the same job as that on an automobile. It varies the gear ratio between the
engine and the road wheels so that the appropriate level of power can be applied to the
wheels. Gear change is manual. There is no need for a separate clutch because the
functions of a clutch are already provided in the fluid coupling.
9.3 Final Drive
The diesel-mechanical locomotive uses a final drive similar to that of a steam engine.
The wheels are coupled to each other to provide more adhesion. The output from the 4-
speed gearbox is coupled to a final drive and reversing gearbox which is provided with a
transverse drive shaft and balance weights. This is connected to the driving wheels by
connecting rods.
9.4 Hydraulic Transmission
Hydraulic transmission works on the same principal as the fluid coupling but it allows a
wider range of "slip" between the engine and wheels. It is known as a "torque
converter". When the train speed has increased sufficiently to match the engine speed,
the fluid is drained out of the torque converter so that the engine is virtually coupled
directly to the locomotive wheels. It is virtually direct because the coupling is usually a
fluid coupling, to give some "slip". Higher speed locomotives use two or three torque
converters in a sequence similar to gear changing in a mechanical transmission and some
have used a combination of torque converters and gears.
Some designs of diesel-hydraulic locomotives had two diesel engines and two
transmission systems, one for each bogie. The design was poplar in Germany (the V200
series of locomotives, for example) in the 1950s and was imported into parts of the UK in
the 1960s. However, it did not work well in heavy or express locomotive designs and has
largely been replaced by diesel-electric transmission.
Chapter-10 Dynamic braking________________________________________________________________________ A common option on Diesel-electric locomotives is dynamic (rheostat) braking.
Dynamic braking takes advantage of the fact that the traction motor armatures are always
rotating when the locomotive is in motion and that a motor can be made to act as a
generator by separately exciting the field winding. When dynamic braking is utilized, the
traction control circuits are configured as follows:
The field winding of each traction motor is connected across the main generator.
The armature of each traction motor is connected across a forced-air cooled
resistance grid (the dynamic braking grid) in the roof of the locomotive's hood.
The prime mover RPM is increased and the main generator field is excited,
causing a corresponding excitation of the traction motor fields.
Fig 34 air brake system The aggregate effect of the above is to cause each traction motor to generate
electric power and dissipate it as heat in the dynamic braking grid. Forced air-cooling is
provided by a fan that is connected across the grid. Consequently, the fan is powered by
the output of the traction motors and will tend to run faster and produce more airflow as
more energy is applied to the grid.
Ultimately, the source of the energy dissipated in the dynamic braking grid is the
motion of the locomotive as imparted to the traction motor armatures. Therefore, the
traction motors impose drag and the locomotive acts as a brake. As speed decreases, the
braking effect decays and usually becomes ineffective below approximately 16 km/h (10
mph), depending on the gear ratio between the traction motors and axles.
Dynamic braking is particularly beneficial when operating in mountainous
regions, where there is always the danger of a runaway due to overheated friction brakes
during descent (see also comments in the air brake article regarding loss of braking due to
improper train handling). In such cases, dynamic brakes are usually applied in
conjunction with the air brakes, the combined effect being referred to as blended braking.
The use of blended braking can also assist in keeping the slack in a long train stretched as
it crests a grade, helping to prevent a "run-in," an abrupt bunching of train slack that can
cause a derailment. Blended braking is also commonly used with commuter trains to
reduce wear and tear on the mechanical brakes that is a natural result of the numerous
stops such trains typically make during a run.
Advantages:
Regenerative braking.
No gear shifting.
No backlash and breaking of couplings during shifting.
Constant availability of maximum diesel generator power.
Easy addition of multiple power units.
Less maintenance with modern ac generators and motors without commutators.
Disadvantages:
More weight.
Less efficient in fuel use.
Needs high tech electronics with use of ac generators and motors.
10.1 BRAKE: A traditional clasp brake: the brake shoe (brown) bears on the surface
(tyre) of the wheel (red), and is operated by the levers (grey) on the left
Fig.35 brake
Brakes are used on the vehicles of railway trains to slow them, or to keep them standing
when parked. While the principle is familiar from road vehicle usage, operational features
are more complex because of the need to control trains, i.e. multiple vehicles running
together, and to be effective on vehicles left without a prime mover.
10.2 Early days:
In the earliest days of railways, braking technology was primitive. The first trains had
brakes operative on the locomotive tender and on vehicles in the train, where “porters”
or, in the United States brakemen, traveling for the purpose on those vehicles operated
the brakes. Some railways fitted a special deep-noted brake whistle to locomotives to
indicate to the porters the necessity to apply the brakes. All the brakes at this stage of
development were applied by operation of a screw and linkage to brake blocks applied to
wheel treads, and these brakes could be used when vehicles were parked. In the earliest
times, the porters travelled in crude shelters outside the vehicles, but “assistant guards”
who travelled inside passenger vehicles, and who had access to a brake wheel at their
posts supplanted them.
The braking effort achievable was limited, and an early development was the application
of a steam brake to locomotives, where boiler pressure could be applied to brake blocks
on the locomotive wheels.
As train speeds increased, it became essential to provide some more powerful braking
system capable of instant application and release by the train driver, described as a
continuous brake because it would be effective continuously along the length of the train.
However there was no clear technical solution to the problem, because of the necessity of
achieving a reasonably uniform rate of braking effort throughout a train, and because of
the necessity to add and remove vehicles from the train at frequent points on the journey.
(At these dates, unit trains were a rarity).
The chief types of solution were:
The chain brake, such as the Heberlein brake, in which a chain was connected
continuously along the train.
When pulled tight it activated a friction clutch that used the rotation of the wheels to
tighten a brake system at that point; this system has severe limitations in length of train
capable of being handled, and of achieving good adjustment.
The simple vacuum system. An ejector on the locomotive created a vacuum in a
continuous pipe along the train, and the vacuum operated brake cylinders on every
vehicle. This system was very cheap and effective, but it had the major weakness that
it became inoperative if the train became divided or if the train pipe was ruptured.
The automatic vacuum brake. This system was similar to the simple vacuum system,
except that the creation of vacuum in the train pipe exhausted vacuum reservoirs on
every vehicle and released the brakes. If the driver applied the brake, his driver's
brake valve admitted atmospheric air to the train pipe, and this atmospheric pressure
applied the brakes against the vacuum in the vacuum reservoirs. Being an automatic
brake, this system applies braking effort if the train becomes divided or if the train
pipe is ruptured. Its disadvantage is that the large vacuum reservoirs were required on
every vehicle, and their bulk and the rather complex mechanisms were seen as
objectionable.
Fig.36 Rotair Valve Westinghouse Air brake Company
The Westinghouse air brake system. In this system, air reservoirs are provided on
every vehicle and the locomotive charges the train pipe with a positive air pressure,
which releases the vehicle brakes and charges the air reservoirs on the vehicles. If the
driver applies the brakes, his brake valve releases air from the train pipe, and triple
valves at each vehicle detect the pressure loss and admit air from the air reservoirs to
brake cylinders, applying the brakes. The Westinghouse system uses smaller air
reservoirs and brake cylinders than the corresponding vacuum equipment, because a
moderately high air pressure can be used. However, an air compressor is required to
generate the compressed air and in the earlier days of railways, this required a large
reciprocating steam air compressor, and this was regarded by many engineers as
highly undesirable.
10.3 Later British practice:
In British practice, only passenger trains were fitted with continuous brakes until about
1930, and goods and mineral trains ran at slower speed, and relied on the brake force
from the locomotive and tender, and the brake van – a heavy vehicle provided at the rear
of the train and occupied by a guard.
Goods and mineral vehicles were provided with hand brakes, by which the brakes could
be applied by a hand lever operated by staff on the ground. These hand brakes were used
where necessary when vehicles were parked, but also when these trains needed to
descend a steep gradient; the train then stopped before descending, and the guard walked
forward to pin down the handles of sufficient brakes to give adequate braking effort.
Early goods vehicles had brake handles on one side only, and random alignment of the
vehicles gave the guard sufficient braking, but from about 1930 so-called "either-side"
brake handles were provided. These trains, not fitted with continuous brakes were
described as "unfitted" trains and they survived in British practice until about 1985.
However from about 1930 semi-fitted trains were introduced, in which some goods
vehicles were fitted with continuous brakes, and a proportion of such vehicles marshalled
next to the locomotive gave sufficient brake power to run at somewhat higher speeds than
unfitted trains.
In the early days of diesel locomotives, a purpose-built brake tender was attached to the
locomotive to increase braking effort when hauling unfitted trains. The brake tender was
low, so that the driver could still see the line and signals ahead if the brake tender was
propelled (pushed) ahead of the locomotive, which was often the case.
10.4 Continuous brakes:
As train loads, gradients and speeds increased, braking became a problem. In the late
19th century, significantly better continuous brakes started to appear. The earliest type of
continuous brake was the chain brake which used a chain, running the length of the train,
to operate brakes on all vehicles simultaneously.
The chain brake was soon superseded by air operated or vacuum operated brakes. These
brakes used hoses connecting all the wagons of a train, so the driver could apply or
release the brakes with a single valve in the locomotive.
These continuous brakes can be simple or automatic, the essential difference being what
happens should the train break in two. With simple brakes, pressure is needed to apply
the brakes, and all braking power is lost if the continuous hose is broken for any reason.
Simple non-automatic brakes are thus useless when things really go wrong, as is shown
with the Armagh rail disaster.
Automatic brakes on the other hand use the air or vacuum pressure to hold the brakes off
against a reservoir carried on each vehicle, which applies the brakes if pressure/vacuum is
lost in the train pipe. Automatic brakes are thus largely "fail safe", though faulty closure
of hose taps can lead to accidents such as the Gare de Lyon accident.
The standard Westinghouse Air Brake has the additional enhancement of a triple valve,
and local reservoirs on each wagon that enable the brakes to be applied fully with only a
slight reduction in air pressure, reducing the time that it takes to release the brakes as not
all pressure is voided to the atmosphere.
Non-automatic brakes still have a role on engines and first few wagons, as they can be
used to control the whole train without having to apply the automatic brakes.
10.5 Types Of Brakes
10.5.1 Air versus vacuum brakes:
In the early part of the 20th century, many British railways employed vacuum brakes
rather than the air brakes used in America and much of the rest of the world. The main
advantage of vacuum was that the vacuum can be created by a steam ejector with no
moving parts (and which could be powered by the steam of a steam locomotive), whereas
an air brake system requires a noisy and complicated compressor.
However, air brakes can be made much more effective than vacuum brakes for a given
size of brake cylinder. An air brake compressor is usually capable of generating a
pressure of 90 psi (620 kPa) vs only 15 psi (100 kPa) for vacuum. With a vacuum system,
the maximum pressure differential is atmospheric pressure (14.7 psi or 101 kPa at sea
level, less at altitude). Therefore, an air brake system can use a much smaller brake
cylinder than a vacuum system to generate the same braking force. This advantage of air
brakes increases at high altitude, e.g. Peru and Switzerland where today vacuum brakes
are used by secondary railways. The much higher effectiveness of air brakes and the
demise of the steam locomotive have seen the air brake become ubiquitous; however,
vacuum braking is still in use in India, in Argentina and in South Africa, but this will be
declining in near future.
10.5.2 Air brake enhancements:
One enhancement of the automatic air brake is to have a second air hose (the main
reservoir or main line) along the train to recharge the air reservoirs on each wagon. This
air pressure can also be used to operate loading and unloading doors on wheat wagons
and coal and ballast wagons. On passenger coaches, the main reservoir pipe is also used
to supply air to operate doors and air suspension.
Air Brake System: Most air brake equipped vehicles on the road today are using a dual
air brake system. The system has been developed to accommodate a mechanically
secured parking brake that can be applied in the event of service brake failure. It also
accommodates the need for a modulated braking system should either one of the two
systems fail. It is actually two brake systems in one, with more reservoir capacity
resulting in a much safer system. At first glance, the dual system might seem
complicated, but if you understand the basic air brake system described so far, and if the
dual system is separated into basic functions, it becomes quite simple.
As its name suggests, the dual system is two systems or circuits in one. There are
different ways of separating the two parts of the system. On a two–axle vehicle, one
circuit operates the rear axle and the other circuit operates the front axle. If one circuit
has a failure, the other circuit is isolated and will continue to operate.
Fig.37 Compressor
In the illustration, air is pumped by the compressor (1) to the supply/wet reservoir
(5) (blue), which is protected from over pressurization by a safety valve (4). Pressurized
air moves from the supply/wet reservoir to the primary/dry reservoir (8) (green) and the
secondary/dry reservoir (10) (red) through one–way check valves (7). At this point, the
dual circuits start.
Air from the primary/dry reservoir is directed to the foot valve (31). Air is also directed
from the secondary/dry reservoir to the foot valve. The foot valve is similar to the one
described earlier in the basic air brake system, but is divided into two sections (two foot
valves in one). One section of this dual foot valve controls the primary circuit and the
other controls the secondary circuit. When a brake application is made, air is drawn from
the primary reservoir through the foot valve and is passed on to the rear brake chambers.
At the same time, air is also drawn from the secondary reservoir, passes through the foot
valve and is passed on to the front brake chambers. If there is air loss in either circuit, the
other will continue to operate independently. Unless air is lost in both circuits, the vehicle
will continue to have braking ability. The primary and secondary circuits are equipped
with low air pressure warning devices, which are triggered by the low air pressure
indicator switch (9) and reservoir air pressure gauges (29) located on the dash of the
vehicle.
10.5.3 Electro pneumatic brakes:
A higher performing EP brake has a train pipe delivering air to all the reservoirs on the
train, with the brakes controlled electrically with a 3-wire control circuit. This can give
seven levels of braking, from mild to severe, and allows the driver greater control over
the level of braking used, which greatly increases passenger comfort. It also allows for
faster brake application, as the electrical control signal is propagated effectively instantly
to all vehicles in the train, whereas the change in air pressure which activates the brakes
in a conventional system can take several seconds or tens of seconds to propagate fully to
the rear of the train. This system is not however used on freight trains due to cost.
The system adopted on the Southern Region of British Railways in 1950 is more fully
described at Electro-pneumatic brake system on British railway trains
10.5.4 Electronically controlled pneumatic brakes:
Electronically controlled pneumatic brakes (ECP) are a development of the late 20th
Century to deal with very long and heavy freight trains, and are a development of the EP
brake with even higher level of control. In addition, information about the operation of
the brakes on each wagon can be returned to the driver's control panel.
With ECP, a power and control line is installed from wagon to wagon from the front of
the train to the rear. Electrical control signals are propagated effectively instantaneously,
as opposed to changes in air pressure which propagate at a rather slow speed limited in
practice by the resistance to air flow of the pipe work, so that the brakes on all wagons
can be applied simultaneously rather than from front to rear. This prevents wagons at the
rear "shoving" wagons at the front, and results in reduced stopping distance and less
equipment wear.
There are two brands of ECP brakes under development, one by New York Air Brake and
the other by Wabtec. A single standard is desirable, and it is intended that the two types
be interchangeable.
10.5.5 Brake Control:
The brake control varies the air pressure in the brake cylinders to apply pressure to the
brake shoes. At the same time, it blends in the dynamic braking, using the motors to slow
the train down as well.
The engineer also has a host of other controls and indicator lights.
Fig. 38 The brake and throttle controls
A computerized readout displays data from sensors all over the locomotive. It can
provide the engineer or mechanics with information that can help diagnose problems. For
instance, if the pressure in the fuel lines is getting too high, this may mean that a fuel
filter is clogged.
Fig. 39 This computerized display can show the status of systems all over the locomotive.
10.5.6 Reversibility:
Brake connections between wagons may be simplified if wagons always point the same
way, such as in Tasmania. An exception would be made for locomotives which are often
turned on turntables or triangles.
On the new Fortescue railway opened in 2008, wagons are operated in sets, although their
direction changes at the balloon loop at the port. The ECP connections are on one side
only and are unidirectional
10.5.7 Vacuum brake:
The vacuum brake is a braking system used on trains. It was first introduced in the mid
1860s and a variant, the automatic vacuum brake system became almost universal in
British train equipment, and in those countries influenced by British practice.
It enjoyed a brief period of adoption in the USA, primarily on narrow gauge railroads.
Its limitations caused it to be progressively superseded by compressed air systems, in the
United Kingdom from the 1970's.
The vacuum brake system is now obsolescent; it is not in large-scale use anywhere in the
world, supplanted in the main by air brakes.
10.5.8 How the automatic vacuum brake works:
Fig40 Vacuum brake cylinder in running position: the vacuum is the same above and below the piston
Fig. 41 Air at atmospheric pressure from the train pipe is admitted below the piston, which is forced up
In its simplest form, the automatic vacuum brake consists of a continuous pipe -- the train
pipe -- running throughout the length of the train. In normal running a partial vacuum is
maintained in the train pipe, and the brakes are released. When air is admitted to the train
pipe, the air pressure acts against pistons in cylinders in each vehicle. A vacuum is
sustained on the other face of the pistons, so that a net force is applied. A mechanical
linkage transmits this force to brake shoes which act by friction on the treads of the
wheels.
The fittings to achieve this are therefore:
A train pipe: a steel pipe running the length of each vehicle, with flexible vacuum
hoses at each end of the vehicles, and coupled between adjacent vehicles; at the end
of the train, the final hose is seated on an air-tight plug;
An ejector on the locomotive, to create vacuum in the train pipe;
controls for the driver to bring the ejector into action, and to admit air to the train
pipe; these may be separate controls or a combined brake valve;
A brake cylinder on each vehicle containing a piston, connected by rigging to the
brake shoes on the vehicle; and
A vacuum (pressure) gauge on the locomotive to indicate to the driver the degree of
vacuum in the train pipe.
The brake cylinder is contained in a larger housing - this gives a reserve of vacuum as the
piston operates. The cylinder rocks slightly in operation to maintain alignment with the
brake rigging cranks, so it is supported in trunnion bearings, and the vacuum pipe
connection to it is flexible. The piston in the brake cylinder has a flexible piston ring that
allows air to pass from the upper part of the cylinder to the lower part if necessary.
When the vehicles have been at rest, so that the brake is not charged, the brake
pistons will have dropped to their lower position in the absence of a pressure differential
(as air will have leaked slowly into the upper part of the cylinder, destroying the
vacuum).
When a locomotive is coupled to the vehicles, the driver moves his brake control
to the "release" position and air is exhausted from the train pipe, creating a partial
vacuum. Air in the upper part of the brake cylinders is also exhausted from the train pipe,
through the ball valve.
If the driver now moves his control to the "brake" position, air is admitted to the
train pipe. According to the driver's manipulation of the control, some or all of the
vacuum will be destroyed in the process. The ball valve closes and there is a higher air
pressure under the brake pistons than above it, and the pressure differential forces the
piston upwards, applying the brakes. The driver can control the severity of the braking
effort by admitting more or less air to the train pipe.
Practical considerations:
The automatic vacuum brake as described represented a very considerable technical
advance in train braking. In practice steam locomotives had two ejectors, a small ejector
for running purposes (to exhaust air that had leaked into the train pipe) and a large ejector
to release brake applications. Later Great Western Railway practice was to use a vacuum
pump instead of the small ejector.
Graduable brake valve (right) and the small (upper) and large ejector cocks from a GWR
locomotive
The driver's brake valve was usually combined with the steam brake control on the
locomotive.
The ejectors on steam locomotives are set to create a certain degree of vacuum in the
train pipe; in British practice a full release is 21 inches of mercury (533.4 Torr). An
absolute vacuum is about 30 inches of mercury (760 Torr), depending on atmospheric
conditions; the Great Western Railway adopted 25 inches of mercury (635 Torr) as its
standard degree of vacuum.
Release valves are provided on the brake cylinders; when operated, usually by manually
pulling a cord near the cylinder, air is admitted to the upper part of the brake cylinder on
that vehicle. This is necessary to release the brake on a vehicle that has been uncoupled
from a train and now requires to be moved without having a brake connection to another
locomotive, for example if it is to be steam ejector shunted.
In the United Kingdom the pre-nationalization railway companies standardized around
systems operating on 21 inches of vacuum, with the exception of the Great Western
Railway, which used 25 inches. This could cause problems on long distance cross-
country services when a GWR locomotive was replaced with another company's engine,
as the new engine's large ejector would sometimes not be able to fully release the brakes
on the train. In this case the release valves on each vehicle in the train would have to be
released by hand. This time consuming process was not infrequently seen at large GWR
stations such as Paddington and Bristol Temple Meads.
The provision of a train pipe running throughout the train enabled the automatic vacuum
brake to be operated in emergency from any position in the train. Every guard's
compartment had a brake valve, and the passenger communication apparatus (usually
called "the communication cord" in lay terminology) also admitted air into the train pipe
at the end of coaches so equipped. This is called pulling the tail.
When a locomotive is first coupled to a train, or if a vehicle is detached or added, a brake
continuity test is carried out, to ensure that the brake pipes are connected throughout the
entire length of the train.
Limitations:
The progress represented by the automatic vacuum brake nonetheless carried some
limitations; chief among these were:
The practical limit on the degree of vacuum attainable means that a very large brake
piston and cylinder are required to generate the force necessary on the brake blocks;
when a proportion of the British ordinary wagon fleet was fitted with vacuum brakes
in the 1950's, the physical dimensions of the brake cylinder prevented the wagons
from operating in some private sidings that had tight clearances;
For the same reason, on a very long train, a considerable volume of air has to be
admitted to the train pipe to make a full brake application, and a considerable volume
has to be exhausted to release the brake (if for example a signal at danger is suddenly
lowered and the driver requires to resume speed); while the air is traveling along the
train pipe, the brake pistons at the head of the train have responded to the brake
application or release, but those at the tail will respond much later, leading to
undesirable longitudinal forces in the train. In extreme cases this has led to breaking
couplings and causing the train to divide.
The existence of vacuum in the train pipe can cause debris to be sucked in. An
accident took place near Ilford in the 1950's, due to inadequate braking effort in the
train. A rolled newspaper was discovered in the train pipe, effectively isolating the
rear part of the train from the driver's control. The blockage should have been
detected if a proper brake continuity test had been carried out before the train started
its journey.
A development introduced in the 1950's was the direct admission valve, fitted to every
brake cylinder. These valves responded to a rise in train pipe pressure as the brake was
applied, and admitted atmospheric air directly to the underside of the brake cylinder.
American and continental European practice had long favoured compressed air brake
systems, the leading pattern being a proprietary Westinghouse system. This has a number
of advantages, including smaller brake cylinders (because a higher air pressure could be
used) and a somewhat more responsive braking effort. However the system requires an
air pump. On steam engines this was usually a reciprocating steam pump, and it was quite
bulky. Its distinctive shape and the characteristic puffing sound when the brake is
released (as the train pipe has to be recharged with air) make steam locomotives fitted
with the Westinghouse brake unmistakable, for example in old films.
In the UK, the Great Eastern Railway, the North Eastern Railway, the London Brighton
and South Coast Railway and the Caledonian Railway adopted the Westinghouse system.
It was also standard on the Isle of Wight rail system. Inevitably this led to compatibility
problems in exchanging traffic with other lines. It was possible to provide through pipes
for the braking system not fitted to any particular vehicle so that it could run in a train
using the "other" system, allowing through control of the fitted vehicles behind it, but of
course with no braking effort of its own.
10.6 Dual brakes:
Vehicles can be fitted with dual brakes, vacuum and air, provided that there is room to fit
the duplicated equipment. It is much easier to fit one kind of brake with a pipe for
continuity of the other. Train crew need to take note that the wrong-fitted wagons do not
contribute to the braking effort and make allowances on down grades to suit. Many of the
earlier classes of diesel locomotive used on British Railways were fitted with dual
systems to enable full usage of BR's rolling stock inherited from the private companies
which had different systems depending on which company the stock originated from.
Fig.42 Dual Brake System
When spring brakes are added to a dual air brake system, the same type of dash control
valve discussed previously is used. Blended air is used to supply the spring parking brake
control valve (27). Blended air is air taken from the primary and secondary circuits
through a two–way check valve (26). With this piping arrangement the vehicle can have a
failure in either circuit without the spring brakes applying automatically. If air is lost in
both circuits, the spring brakes will apply.
Air brakes need a tap to seal the hose at the ends of the train. If these taps are incorrectly
closed, a loss of brake force may occur, leading to a dangerous runaway. With vacuum
brakes, the end of the hose can be plugged into a stopper which seals the hose by suction.
It is much harder to block the hose pipe compared to air brakes.
10.6.1 Twin pipe:
Vacuum brakes can be operated in a twin pipe mode to speed up applications and release.
Braking is provided by a mechanism that is similar to a car drum brake. An air-powered
piston pushes a pad against the outer surface of the train wheel.
Fig.43 The brakes are similar to drum brakes on a car.
In conjunction with the mechanical brakes, the locomotive has dynamic braking. In this
mode, each of the four traction motors acts like a generator, using the wheels of the train
to apply torque to the motors and generate electrical current. The torque that the wheels
apply to turn the motors slows the train down (instead of the motors turning the wheels,
the wheels turn the motors). The current generated (up to 760 amps) is routed into a giant
resistive mesh that turns that current into heat. A cooling fan sucks air through the mesh
and blows it out the top of the locomotive -- effectively the world's most powerful hair
dryer.
On the rear truck there is also a hand brake -- yes, even trains need hand brakes. Since the
brakes are air powered, they can only function while the compressor is running. If the
train has been shut down for a while, there will be no air pressure to keep the brakes
engaged. Without a hand brake and the failsafe of an air pressure reservoir, even a slight
slope would be enough to get the train rolling because of its immense weight and the very
low rolling friction between the wheels and the track.
The hand brake is a crank that pulls a chain. It takes many turns of the crank to tighten
the chain. The chain pulls the piston out to apply the brakes.
10.7 Vacuum brakes in 2007:
Today's largest operators of trains equipped with vacuum brakes are the Railways of
India and Spoornet (South Africa), however there are also trains with air brakes and dual
brakes in use. Other African railways are believed to continue to use the vacuum brake.
Other operators of vacuum brakes are narrow gauge railways in Central Europe, largest
of them is Ferrovia Retica.
Vacuum brakes have been entirely superseded on the National Rail system in the UK,
although they are still in use on most heritage railways. They are also to be found on a
number (though increasingly fewer) main line vintage specials.
C & E has developed the automatic vacuum brake and designed it in its simplest form;
the automatic vacuum brake consists of a continuous pipe -- the train pipe -- running
throughout the length of the train.
Chapter-11 Engine Control
________________________________________________________________________
11.1 Engine Control Development:
So far we have seen a simple example of diesel engine control but the systems used by
most locomotives in service today are more sophisticated. To begin with, the drivers
control was combined with the governor and hydraulic control was introduced. One type
of governor uses oil to control the fuel racks hydraulically and another uses the fuel oil
pumped by a gear pump driven by the engine. Some governors are also linked to the
turbo charging system to ensure that fuel does not increase before enough turbocharged
air is available. In the most modern systems, the governor is electronic and is part of a
complete engine management system.
11.2 Power Control:
The diesel engine in a diesel-electric locomotive provides the drive for the main
alternator which, in turn, provides the power required for the traction motors. We can see
from this therefore, that the power required from the diesel engine is related to the power
required by the motors. So, if we want more power from the motors, we must get more
current from the alternator so the engine needs to run faster to generate it. Therefore, to
get the optimum performance from the locomotive, we must link the control of the diesel
engine to the power demands being made on the alternator.
In the days of generators, a complex electro-mechanical system was developed to achieve
the feedback required to regulate engine speed according to generator demand. The core
of the system was a load regulator, basically a variable resistor which was used to very
the excitation of the generator so that its output matched engine speed. The control
sequence (simplified) was as follows:
1. Driver moves the power controller to the full power position
2. An air operated piston actuated by the controller moves a lever, which closes a
switch to supply a low voltage to the load regulator motor.
3. The load regulator motor moves the variable resistor to increase the main generator
field strength and therefore its output.
4. The load on the engine increases so its speed falls and the governor detects the
reduced speed.
5. The governor weights drop and cause the fuel rack servo system to actuate.
6. The fuel rack moves to increase the fuel supplied to the injectors and therefore the
power from the engine.
7. The lever (mentioned in 2 above) is used to reduce the pressure of the governor
spring.
8. When the engine has responded to the new control and governor settings, it and the
generator will be producing more power.
On locomotives with an alternator, the load regulation is done electronically. Engine
speed is measured like modern speedometers, by counting the frequency of the gear teeth
driven by the engine, in this case, the starter motor gearwheel. Electrical control of the
fuel injection is another improvement now adopted for modern engines. Overheating can
be controlled by electronic monitoring of coolant temperature and regulating the engine
power accordingly. Oil pressure can be monitored and used to regulate the engine power
in a similar way.
My Activities
I joined my training on_____. I used to observe the working of machines, different manufacturing process, use of gauges and measuring instruments and added a lot to our knowledge. It was my first chance to get knowledge about different machines used for the maintenance of engines.