Auto. Tech.mec.227 Theory 03

7/23/2019 Auto. Tech.mec.227 Theory 03

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UNESCO-NIGERIA TECHNICAL &

VOCATIONAL EDUCATION

REVITALISATION PROJECT-PHASE II

YEAR 2- SEMESTER 2

THEORY

Version 1: December 2008

NATIONAL DIPLOMA IN

MECHANICAL ENGINEERING TECHNOLOGY

AUTOMOTIVE TECHNOLOGY AND PRACTICE

COURSE CODE: MEC227


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AUTOMOBILE TECHNOLOGY AND PRACTICEMEC.227

CONTENT PAGE

WEEK 1

1.1.Introduction

Prime movers.

1.2.The steam engine

1.3.The electric engine

1.4.Internal combustion engine.

1.5 Advantages and disadvantages of internal combustion engine as compared to the steam

and electric powered vehicles.

1.6. Workshop staff and safety

WEEK 2

2.0. THE FUNDAMENTAL CYCLES OF OPERATION OF PETROL, DIESEL INTERNAL

COMBUSTION ENGINES

2.1. Features of the 4-stroke spark ignition engine,

2.2. Futures of the 4 stroke diesel engine

2.3. The advantages and disadvantages of Spark Ignition over Compression Ignition

Engines and vise- visa

2.4 () () ()

() () () .


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2.5. Compare the advantages and disadvantages of the 2- stroke spark ignition to the 2-

stroke compression ignition.

WEEK 3

3,0 THE COMPONENT PART OF AN ATOMOBILE ENGINE

3.1 Definition of terms.

3.1.1.The component parts of an internal combustion engine

3.2 The main functions of the petrol fuel system components

3.3 The main functions of the diesel fuel system components.

WEEK4.0. ENGINE COOLING SYSTEM

4.0.1. Introduction

4.1 Air cooling system

4.2. Water cooling system.

WEEK 5

5.0 LUBRICATION SYSTEM

5.1 Engine Lubricating components and their functions.

5. 2. Engine oil Filtration Methods (Bypass or partial flow and Full flow)

5.3. Engine Lubrication methods

5.4. Common lubricants and their uses


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WEEK 6

6.0 ELECTRICAL SYSTEM

6.1 Introduction

6.2.Major automobile electrical components.

6.3 The purpose of the battery.

6.4 Constructional details of the alkaline and lead acid batteries.

6.5. Charging and discharging processes of the two types of battery.

6.6. Functions of the alternator/ alternator.

6.7. Simple starting system.

6.8. Coil Ignition System

6.9. The Main Components of the Ignition System and their functions

WEEK 7

7.0 Internal combustion engine fuels and combustion

7.1 Introduction to Operating principles of simple carburetor.

7.2. Fuel injection system

7.3. Petrol engine Fuel line

7.4 Exhaust system.

WEEK 8

8.0.THE TRANSMISSION SYSTEM

8.1. Diagram showing component parts of transmission system.

8.2. The automobile clutches.8.2.1 Types of clutches (Single plate multi spring clutch)


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8.2.2. Construction

8.5.3 Operation of Clutch8.3. THE GEARBOX

8.3.1. Speed and load

8.3.2 The Sliding Mesh Four Speed Gearbox

8.3.3 Construction,8.3.4 Operation,

WEEK 9

9.0 THE DRIVE LINE (PROPELLER SHAFT)

9.1 Function

9.2 The universal joints

9.3 The final drive.9.4. Axle shaft arrangement.

WEEK 10

10.0. THE BODY AND CHASSIS10.1. Chassis and Vehicle Body

(General Objectives)

10.2. Separate chassis-body types.

10.3. Integral type

10.4. Motor vehicle body structure: sub -frame assemblies.

WEEK 11

11.1. Steering System functions.

11.2. The steering System components11.3. Types of steering gears

1.4. Steering Geometry

11.5. Illustrations camber and castor angles


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WEEK 12

12.0. Tires and Wheels12.1 Functions of Tires .

12.2, Types of Tires12.3. Tyre valve.

12.4. Tire pressure.

12.5 Tire and rim sizes

WEEK 13

13.0. THE BRAKING SYSTEM

13.1 Braking system and their operating principles.

13.2 The main parts and Function of hydraulic braking system.

13.3 The operation of drum and disc brakes

13.4 The Master Cylinder and the servo.

WEEK 1414.0. SUSPENSION SYSTEMS

14.1. Purpose

14.2. Components parts of suspension system

14.3. Types of springs


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14.4. Torsion bar

14.5. Air spring

14.6. Shock absorbers

WEEK 15

15.0. Features of the modern automobile electronic fuel ignition (EFI) system

Introduction

15.1 Explain the Electronic fuel injector (EFI) system as it replaces the carburetor15.2. Description: features of the electronic spark ignition as it replaces the contact-breaker unit.

15.3. Fuel injection and air "flow control

15.4. System identification of fuel injection engine.

WEEK 11.0 DESCRIBE THE CONSTRUCTION AND OPARATION OF PRIME MOVERS.

1.1. Introduction

The Prime Movers.

The Microsoft Encarta Dictionary of 2008 describes prime mover as follows:-

(i)Most important cause of something, or something that initiates a process or activity

which is usually an important factor in its continuation.

(ii)A natural or physical energy source, such as wind, solar or electricity that can be

harnessed to power a machine.

(iii) An energy converter: a machine that converts energy from a natural or physical source in

order to power equipment such as a windmill or turbine.

(iv) Power vehicles, such as steam engine, electric engine and internal combustion engines

1.2. The steam engine

The development (1629) of the steam turbine is credited to the Italian engineer Giovanni Branca,

who directed a steam jet against a turbine wheel, which in turn powered a stamp mill. The firstrecorded patent for a gas turbine was obtained in 1791 by the British inventor John Barber.


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Fig. 1.1.Early

locomotive

engine.

1.3.

Locomotive

steamengine

valves.Engine No. 44, a Baldwin 2-8-0 steam locomotive engine built in 1921, has two wheels on the

leading truck, eight driving wheels, and no trailing truck. The engine works on the GeorgetownLoop Railroad and formerly ran in Central America. Diesel-electric locomotives began to replace

steam locomotives in the 1930s and 1940s.

Fig. 1.2 Locomotive steam engine valves

(1.3) Electric Engine


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Fig. 1.3 Electrically driven motor vehicle

Electric Car, automobile propelled by one or more electric motors, drawing power from an

onboard source of electricity. Electric cars are mechanically simpler and more durable thangasoline-powered cars. They produce less pollution than do gasoline-powered cars.

(1.4) Internal combustion Engine

The internal combustion engine is a prime mover that uses liquid fuel as its source of energy

to cause continuous rotation of a crankshaft. Other types of prime movers are electric

powered and steam engines.

Fig.1.4. Internal combustion engine: indicating engine parts.


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1.5. Advantages and disadvantages of internal combustion engine as compared to the steam

and electric powered vehicles.

When these three prime movers are compared to each other the following advantages and

disadvantages are derived.

Table 1.1

S/N Steam engine Electric powered Internal combustion

1 Cheaper source of energy No harmful combustion

product

Fuel burn at control level

2 Do not require special sealing Less initial cost. Easier control of engine speeds

3 Good for stationary energy supply Quitter in operation Allow for portable engine

design

4 Easier adoptability to chassis

and drive arrangements

5 Higher thermal efficiency

ADVANTEGES DERIVED FROM THE THREE PRIME MOVERS AS COMPARED TO EACH OTHER.

Table 1.2

S/N Steam engine Electric power Internal combustion

1 Bulkiness Source of energy not quite

reliable

Emits carbon monoxide (CO)

when engine becomes weak.

2 Engine rev/min. not easily Constant check on battery Effective cooling required.


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controlled

3 Noisier in operation Not suitable for commercial

transport e.g. long distant travels

to country sides

Leakage of gas , water or

engine oil can lead to engine

failure

4 Higher cost of maintenance re

5 Requires good precession

DISADVANTAGES DERIVED FROM THE THREE PRIME MOVERS AS COMPARED TO EACH

OTHER.

1.6. Workshop staff and safety

Workshop engineer.

An engineer is a planner, initiator, or supervisor of something, especiallysomething that is achieved with ingenuity or secretiveness. The automobileworkshop engineer conduct planning and initiate activities in the shop. The

technologist and mechanics carry s out the engineers initiative

A number of accidents occur in workshops on daily basis. These accidents can be

avoided, by following safety rules and regulations in work locations. The workshop

engineer could avert accidents by being alert and conscious of what is happening in theworkshop environment. Below are some points to be considered and be observed by staff

and other users of the automatable engineering workshop:

A tidy workshop can help in reducing a number of accidents.

Tools, components, equipment, and materials must be kept in the appropriatelocations by the technologist in the shop.

Always keep the workshop floor clean and free of grease or oil, and as temporarymeasure cover the slippery floor with sawdust.

Basic PointsThe basic points of safety in the work shop are easy to understand

a) Learn the safe way of doing each task.

b) If you do not understand - ask for explanation

c) If you are not taught - ask for instruction

d) Use the safe method against careless actions by yourself or others

e) Practice good housekeeping at all times.


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f) Co-operate promptly in the event of an accident or fire.

g) Report all accidents to an instructor.

h) Draw your instructor's attention to any potential hazard

WEEK 2

2.0. THE FUNDAMENTAL CYCLES OF OPERATION OF PETROL, DIESEL INTERNAL

COMBUSTION ENGINES

Upon completion of this study the students should be able to:-i. Know the features of the 4 stroke petrol engine and describe its cycles of operation.

ii. Know the features of the 4 stroke diesel engine and describe its cycle of operation

iii. Compare the advantages and disadvantages of the spark ignition and the compression

ignition engines.

iv. Know the features of the 2-stroke petrol engine and describe its cycle of operation.

v. Know the features of the 2-stroke diesel engine and describe its cycle of operation.

vi. Compare the advantages and disadvantages of the 2-stroke spark ignition to compression

ignition engines.

2.1. Features of the 4-stroke spark ignition engine,Main Components of 4 stroke Internal Combustion Engine (Petrol Engine).

.


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Figure (2.1) shows-an outline of the engine main components

. 2.2,

2.2. Futures of the 4 stroke diesel engine


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Fig. 2.3. Compression Ignition Engine circle of operation (Otto cycle)

2.3. The advantages and disadvantages of Spark Ignition over Compression Ignition

Engines and vise- visa

Disadvantages SIE over CIE Disadvantages CIE over SIE


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1

2

3

4

Higher risk of fire accident

Higher cost of maintenance as engine service

interval is more frequent.Complications in ignition systems

In- ability to start the engine without battery

1

2

3

Requires starting aids e.g. heater plugs.

Produces large volume of smoke with

foul odors in some cases prevents clearvisibility of other road udders.

Increased weight of parts due to high-

pressure requirements.Table 1

Advantages of SIE over CIE Advantages of CIE over SIE

1

2

3

4

Easier to start in cold conditions

Quieter in operation.

Lighter in weight and less initial

cost.

Reduced volume in exhaust

product emission

1

2

3

4

5

6

7

8

9

Reduced risk of fire accident due to low volatility

of diesel fuel.

Long intervals between overhauling and services.

Reduced cost of maintenance

Less harmful effect of exhaust products.

Engine could run without battery.

More economical as compared to a similar size

due to high compression ratio.

Higher thermal efficiency.

Greater volumetric efficiency

Injection equipments are more reliable and stable

than the electrical ignition system.

Table 2. 2 showing advantages and disadvantages.


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2.4 () () ()

() () () .

Fig. 2.4. The two stroke cycle: principles of operation

The two stroke engine has no valves but has three ports. The ports are inlet, transfer and the

exhaust. The flow of gas through these ports is controlled by the position. When the piston is atbdc its skirt closes the inlet port. The piston travels up the bore (see diagram) as it reaches tdc. It

opens the inlet port but closes the transfer and exhaust ports, at the same time compresses the gasin the combustion chamber. At top dead centre (tdc) the spark plug ignites the mixture of petrol


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and air, burning takes place and expansion occurs, piston moves down the bore on power stroke

Fig. 2.5. The two stroke diesel fueled engine.

2.5. Compare the advantages and disadvantages of the 2- stroke spark ignition to the 2-

stroke compression ignition.

(i) Advantages of two stroke compression ignition engine over the two stroke sparkignition engine:

The two stroke CIE do not have to compress the charge in the crank case and

discharge through the transfer port to the combustion chamber as occurs with

the petrol engine, instead, a blower is used to force air into the culinders, toscavenge the spent gasses and replace them with a fresh charge through the

induction poppet valve. Fresh charge can not escape along with the burnt

gasses.


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Unlike the two-stroke petrol engine, the fuel is mot assed to the air until both

inlet and exhaust ports are close, therefore one of the drawbacks of two

strokes engines, of fuel waste is overcome.

Forced induction promotes smoother slow running and a reduction in the

combustion delay period.

Volumetric efficiency is improved which gives a higher power to weight ratio.

(ii)Advantages and disadvantages of two-strokes cycle over the 4 strokes engine.

Advantage:

An important advantage of the two-stroke cycle engine is that it needs approximately

only half the cylinder capacity of the four stroke engine to produce equivalent power

for the same number of revolutions of the crankshaft. This result in a smaller lighter

power unit, capable of developing smooth torque with low bearing loads

Disadvantage

A serious disadvantage of the two-stroke, sparkignition engine is that it has a low

thermal efficiency. This is due to (a) incomplete scavenging of the exhaust gases and

(b) Un-burnt mixture passing out of the combustion chamber with the exhaust gases

WEEK 3

Objectives:

Upon completion of this lesson the students should be able to:-

List, describe and explain the function of automobile engine component parts

Define some automotive engineering terms.

3,0 THE COMPONENT PART OF AN ATOMOBILE ENGINE.

3.1 Definition of terms.

Top or bottom dead centre: the maximum a piston travels to the top or bottom of the

cylinder

Piston stroke : this is the measure of distance moved by the piston from top of the

cylinder to the bottom or from the bottom to top.

Piston displacement: this is the movement of piston from one point to the other

Cylinder bore. The hole that accommodate the piston in the engine


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Swept volume: this is the space created by the movement of the piston as it moves from

tdc to bdc.

Mean effective pressure: the average net pressure which, acting on the piston over the

full length of its stoke, does the same amount of work as is actually obtained during a

complete engine cycle.

Engine torque: this is the turning moment on the crankshaft. When the piston moves

down in power stroke, it transmits torque to the engine crankshaft. The harder the push

on the piston the greater the torque applied. Thus the higher the combustion pressure, the

greater amount of torque.

Fig. 3.1. explaining the compression ratio of an engine.

Engine compression ratio: engine compression ratio is the measure of the amount of the

mixture as compared to the volume of the cylinder bore when the piston is at b.d.c. and

when it has risen to t.d.c.

Indicated brake power: this is known as the actual power developed in the cylinder of an

engine

Brake power: this is the useful power available at the crankshaft of the engine . it is

measured by running the engine against some form of absorption brake (dynamometer)


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3.1.1.The component parts of an internal combustion engine


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Fig.3.2 showing exploded view of an internal combustion engine

3.2 The main functions of the petrol fuel system components.


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Fig.3.3. this showing petrol fuel supply system parts.


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Fig 3.4a shows Engine- driven mechanical fuel pump fuel system.

Fig. 3.4b shows Electric pump-feed fuel system

3.3 The main functions of the diesel fuel system components.

The component parts of the diesel fuel system shown below are:-

i. Tank, which is used for containing diesel fuel for the vehicle use.

ii. Fuel pipe and lift pump for lifting fuel from the tank .

iii. Fuel filter: for removing particles from the diesel oil.

iv. Injection pump: this increases fuel pressure to the injector nozzles.

v. Injector nozzles: they allow for the introduction of fuel at high pressure to the

combustion chamber.

Fig.3.5. Distributor type fuel injection system

Fig. 3.6. In-line type of fuel injection system, showing list of component parts


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WEEK 4

4.0. ENGINE COOLING SYSTEM

OBJECTIVES:

Upon completion of this study the students should be able to:-

i. Describe the operation and identify the component parts of air cooling system

ii. Describe the operation and identify the component parts of pressurized cooling system

iii. Draw the flow diagram of pressurized air cooling systems.

IntroductionIn any moving equipment, power machine or running engines heat is generated because

of:

Friction,

Power load,

Burning of fuel.

Therefore some form of cooling must be provided to take the heat away, this is necessary

to forestall excessive heat accumulation that leads to over heating, in which to following

could occur.

i. Seizure of working parts due to heat expansion,

ii. Excessive wear - the lubricant oil would be burnt

iv. Pre-ignition in combustion chamber.

4.1 Air cooling system


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Most motor - cycle engines compressors, are air cooled. The principle is to increase the

area of the hot surface exposed to the flow of cool air. This method of cooling is cheap,

lightweight and is not subject to troubles such as leakage and freezing problems.

Air flow is to be natural or be forced by a fan through ducted passages and over thefinned surfaces (fig. 4.1).

Fig. 4.1) Air cooling system

4.2. Water cooling system.

(i) Thermosyphon


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Fig. 4. 2 Thermosyphon cooling system

(ii) Impeller assisted pressurized cooling method.


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Fig. 4. 3 Pressurized impeller cooling diagram with thermostat and direction of flow.

Fig. 4.4. Radiator pressure cap

(ii) Water pump:This is a small centrifugal pump driven by a belt at the front of the

crankshaft.

(Fig. 4.8).


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Fig (4.8) Impeller type water pump


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Fig. 4.9 Water cooled engine thermostat positions in the engine

(iii)Pressurized sealed system.

Toping up of water in pressurized sealed cooling system is only occasionally necessary as

water get exhausted. Rugged pipes and expansion tanks are provided, such that excess water


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as a result of increased in its temperature is contained in the reservoir an later used for

replenishment when system cools down.

Fig. 4.10 Pressurized sealed cooling system arrangement

WEEK 5

5.0 LUBRICATION SYSTEM

Objectives

Upon completion of this study the students should be able to:-

i. Identify and state functions of lubricating components

ii. Use line diagram to explain the operation of the full flow and bypass oil filtration.iii. State common lubricants and their uses.

5.1 Engine Lubricating components and their functions.

Introduction


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Examination of two metallic components in a machine that has rubbed together for a period of

time, shows that.(i). Heat is generated - this indicates that a part of energy has been used in overcoming friction.

(ii). Wear or scoring has occurred due to the high spots on the two surfaces.

The extent of these effects is governed by the friction so if energy losses are to be kept to aminimum, friction should be reduced. Friction may exist in dry or wet. One way to reduce

friction is to lubricate the surfaces.

(iii) Components of the Lubrication System

A good example ofa pressurized lubrication system is the lubrication ofinternal combustionengine; see diagram for pressurized lubricating system in (fig. 5.1 )

Fig. 5.1. shows oil lubricating parts and oil circulation format.

1) Oil in sump2) Oil pump3) Gear sprocket the drive the oil pump.4) Dip stick


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1- Oil pump:

Internal combustion engine oil pumps are usually driven by the camshaft; the pump forces oilfromthe sump to the main oil gallery.

a) Rotor Type:It is a pump ofdisplacement type fig. (6.8a) with an internal and

external toothed rotors. The inner rotor, has one tooth fewer thanthe outer rotor, as the rotor revolves the cavities on the section side

becomes larger. So that the pump draws in oil. On the dischargeside, the cavities become smaller, so that oil forces into the

discharge line, and to oil gallery.

Fig. (5.2a) rotor type oil pump

b) Gear-Type:

It conveys the oil from one half of the pump to the other in the gaps

between the individual gear teeth and the inner wall of the pump.The gears mesh together to prevent the oil from flowing back. Fig

(5.2b)

Fig. (5.2b) Gear type oil pump

2- Relief Valve

To prevent excessive pressure in the lubricating system, a relief valve opens to release part of the

oil when pressure goes too high (Fig 5.3)

Fig. (5.3) Relief valve operation

3- Oil Filter


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The filter removes solid particles generated due to parts wear deposited in the oil. There is a

bypass relief valve that opens, to allow unfiltered oil to go directly to the engine when the filter

becomes clogged. However the filter is not likely to become clogged if it is replaced regularly

(Fig.5.4)

Fig. (5.4) Oil filter type

4- Oil Galleries

These are oil holes drilled in the cylinder block to carry

oil from the pump to the main bearings fig. (5.5).

Fig. (5.5)


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Fig. 5.6 Internal combustion Engine lubricating block diagram.

Network of drillings called oil galleries is used to transport oil from the sump to the bearings an

the rocker shaft for lubrication.

5- Oil Coolers

Some engine lubricating systems include an oilcooler to take the excessive heat of the oil. One

type is a small radiator mounted on the side of the

engine block; Fig. (4.14).

Fig. (5.7) oil cooler

6- Oil-level Indicator


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Fig. (5.8) Dipstick

A dipstick is used to measure the level of the oil in the oil pan fig. (5.8).Some engines now' havea low - oil level indicator light.

5. 2. Engine oil Filtration Methods (Bypass or partial flow and Full flow)

With the partial-flow system (fig. 5.9a) approximately 10% of the total oil delivery passesthrough the filter and returns to the sump, while the remainder circulates through the engine

bearings and before it reaches the moving parts . The rate of oil flow through the filter is

comparatively slow, and a very fine filtering medium can be employed so that its efficiency ishigh. If a by-pass filter becomes choked, the lubricating oil will no longer be filtered.

Full flow system as shown in (figure 5.9b) is more efficient, it ensures complete and immediateprotection from any foreign matter in the oil. The filter is located in the main oil-supply and

takes the full delivery of oil from the pump before it reaches the moving parts of the engine.

The full-flow filter is fitted with a relief valve to ensure that oil is supplied to the engine when

the filters become chocked.

Fig. 5.9a. Partial flow. Fig.5.9b. Full flow.

5.3. Engine Lubrication methods1. Boundary Lubrication:this is only a thin film of lubricant, a few molecules in thickness,

which prevents metal to metal contact, with certain parts, the film breaks down, and the surfaces

make occasional contact. Parts such as piston rings and valve trains are subjected to occasional

failure of the oil film, and the properties of oiliness, film strength or load-carrying ability.


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2. Full fluid film (pressurized) lubrication: full

fluid film lubrication builds up quickly to protectrotating parts, such as crankshaft and bearing. This is

most frequently used. The system has a pump that

draws the oil from the sump usually through a mesh

strainer, and forces it at high pressure through the oillines after passing through a filter in most cases. As

Fig. (5.9) shows.

Fig. 5.10

3. Splash lubrication:When crankshaft and its masses hits the engine during rotation, oil issplashed to the interior of the engine. This method is used to lubricate parts which do not

require pressure lubrication but just small quantity. Parts such as piston rings and bore requires

just small amount of oil for its lubrication.

In this type some machines components are providedwith small scoops or discs (Fig. 5.11). Which dip

into the oil sump, and scatter the oil throughout the

casing.

Fig.(5.11) Oil

scoop arrangement in

big-end assembly

4. Mix lubrication:this type of lubrication is commonly applied on motor bike and two stroke

engines, where engine oil is mixed with the petrol in the tank.

5.4. Common lubricants and their uses

The common lubricants used on motor vehicle are:-

i. Engine oil: used for engine lubrication

ii. Gear oil: this is also known as extreme pressure oil, and it is used for lubricating gears in

the gearbox or final drive arrangements.


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iii. Grease: grease is for the lubrication of bearings and gears.

WEEK 66.0. Know the minor and major electrical components of a vehicle and describe

their functions.Objectives :-

Upon completion of this lesson the students should be able to:-

List the major electrical components of a vehicle

Explain purpose of the battery.

Explain the constructional details of the lead-acid battery

Explain the constructional details of the alkaline battery

Describe the charging and discharging processes of the two types of battery

State the functions of the alternator

Describe a simple starting system.

Draw the component parts of the coil ignition system.

Identify the main components of the coil ignition system.

6.1 Introduction

Electricity and electronics play a vital role in the safe and reliable operation of modern

automotive vehicles. Demand range from a simple door switch and courtesy lamp to an engineelectrical system so complex that a. it logically follows that anyone who expects to successfully

maintain, troubleshoot, and repair todays vehicles must have a through knowledge of the

fundamentals of electricity and electronic.

6.2.Major automobile electrical components.The simple diagram ( fig. 6.1) shows how the main items of the electrical

equipment are connected. It can be seen that the electrical system can be broadly

divided into three parts.

(i)Generator.

(ii)Storage battery


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(iii) Distribution.

Fig. 6.1. Layout of main electrical components.6.3 The purpose of the battery.The lead acid batteryused on motor vehicle stores electrical energy in the form of chemical

energy to start the engine and for other purposes. When the ignition switch is turned on, the

battery sends current to the starter motor that turns the engines crankshaft. Turning the

crankshaft moves pistons inside the cylinders, compressing fuel vapor for combustion. While theengine is running, an alternator (electric generator) recharges the battery and supplies power to

other electrical components

6.4. The constructional details of alkaline and the Lead acid batteries.The lead acid battery is made up of a number of positive and negative plates, sandwiched

together and separated by a corrosion resistant papers, called separators. The unit is refered to

as cell and are immersed in a solution of hydrolyte contained in a re-enforce corrosion resistantcontainer. The cells are then connected in series and a negative and positive terminals are

produce each, at the upper part of the battery casing.


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6.2. The constructional details of the lead-acid battery

Constructional details of the alkaline batteryBatteries convert chemical energy into electrical energy. In storage batteries, two metal rods,

called electrodes, are connected by a circuit and immersed in a liquid, called an electrolyte. The

rods chemically react with the electrolyte to produce a flow of electrons through the circuit. Thestorage batteries of the time were called lead-acid batteries because they had electrodes made of

lead and lead dioxide and an electrolyte made of acid. They were heavy, bulky, difficult to

recharge, and susceptible to rapid corrosion. To reduce corrosion, Edison decided to use an

alkaline solution instead of acid for the electrolyte in his battery. Finding a suitable electrode,however, proved difficult. Edison finally decided on a combination of nickel flake and nickel

hydrate for the positive electrode and pure iron for the negative electrode. He used an electrolyte

of potassium hydroxide with a small amount of lithium hydroxide

Fig.6.3. Chloralkali Electrolysis

Chloralkali electrolysis is a technique for the industrial production of chlorine and the alkali

known as caustic soda (sodium hydroxide) from brine, a solution of common table salt (sodiumchloride) in water. Three processes are in use: the diaphragm-cell process, the membrane-cell

process, and the mercury-cell process. In the diaphragm-cell process, a porous diaphragm divides

the electrolytic cell, which contains brine, into an anode compartment and a cathodecompartment. When an electric current passes through the brine, the salts chlorine ions andsodium ions move to the electrodes. Chlorine gas is produced at the anode, and sodium ions at

the cathode react with the water, forming caustic soda. Some salt remains in the solution with the

caustic soda and can be removed at a later stage. In the membrane-cell process, thecompartments are separated by a membrane rather than a diaphragm. Brine is pumped into the

anode compartment, and only sodium ions pass into the cathode compartment, which contains

pure water. Thus, the caustic soda produced has very little salt contamination. In the mercury-


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cell process, mercury, which flows along the bottom of the electrolytic cell, serves as the

cathode. When an electric current passes through the brine, chlorine is produced at the anode andsodium dissolves in the mercury, forming an amalgam of sodium and mercury. The amalgam is

then poured into a separate vessel, where it decomposes into sodium and mercury. The sodium

reacts with water in the vessel, producing the purest caustic soda, while the mercury returns to

the electrolytic cell.

6.5. Charging and discharging processes of the two types of battery.Battery charging methods vary, based on several considerations

(i) Electrical capacity of battery being serviced

(ii)Temperature of the electrolyte.

(iii)Battery state of charge.

(iv)Batter age and condition.

Battery charging methods include high or fast and slow or trickling charging. Fast rate chargingprovides high charging rate for a short time and should be limited to 60 amperes for

12v batteries. Battery may be discharged when charging system becomes faulty or constantoperation of the starter for too long a time, probably because of engine fault.

6.6. Functions of the alternator.The automotive generator or alternator is an electromagnetic device that converts

the mechanical energy supplied by the engine into electrical energy. In operation,

the generator or alternator maintains the storage battery in fully charged condition

and supplies electrical power for the ignition system and accessory equipment.

Fig. 6.4 Alternator charging system circuit

6.7. Simple starting system.


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The automotive starting motor (fig. 7.5 ) Is an electromagnetic device that comverts electrical

energy into mechanical energy. It is designed specifically for cranking internal combustionengines at speeds which will permit starting.

Fig. 6.5.

6.8. Coil Ignition System

(i) Ignition System is the arrangement put together to provides the high quality spark needed toignite fuel in a gasoline internal-combustion engine. The ignition system produces, distributes,

and regulates electric sparking that ignites fuel vapor in the combustion chambers.

Fig. 6.6 Spark ignition circuit.


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(ii)Types of Ignition Systems

Electric sparking is the most popular ignition system used in modern gasoline engines, but the

manner of producing and regulating the spark has changed with new technology. Computers

control the ignition systems in modern automobiles, although many older vehicles still rely on

mechanically operated and controlled ignition systems. Two broad categories of ignition systems

are defined by whether or not a battery is used to store electricity for starting the engine. Most

automobile engines have battery-powered ignition systems. Ignition systems without batteries

rely on a generator called a magneto.

The purpose of the ignition system is to ignite the mixture of air and petrol at the correcttiming

Fig. (6.7) ignition system of petrol engine

6.9. The Main Components of the Ignition System and their functions

1- Battery: Battery is used on motor vehicle stores electrical energy in the form of chemical

energy to start the engine and for other purposes. When the ignition switch is turned on, the

battery sends current to the starter motor that turns the engines crankshaft. Turning the

crankshaft moves pistons inside the cylinders, compressing fuel vapor for combustion. While the

engine is running, an alternator (electric generator) recharges the battery and supplies power to

other electrical components.


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2- Ignition Switch: It allows current to flow from the battery to the coil, it also operates

the starter motor.

3- Distributor:The distributor routes high-voltage pulses to individual cylinders in the correct

sequence and with precise timing. It also houses a mechanical switching system involving

breaker points, that open to interrupt the flow of electric current. A rotating shaft in the

distributor moves the pivot arm, causing the two metal points to contact each other and then

move apart. When the points touch each other, low-voltage current flows through them to a

transformer called the coil. When the points separate, they break the low-voltage circuit to the

coil. In an eight-cylinder engine running at 3000 revolutions per minute (rpm), the breaker points

open and close about 200 times per second. Inside the coil interruptions in the low-voltage circuit

(12 volts, normally) create pulses of 20,000 volts or more.

4- Contact breaker point ( CB ):A mechanically operated device, which breaks the low

tension circuit when the spark is required

5- Condenser or Capacitor:is a device that temporarily stores electric charge. In the ignition

system a capacitor helps produce a sharply defined cutoff of current when the breaker points

open. The capacitor also absorbs the surge of high-voltage electricity as it moves from the coil to

the points. In so doing the capacitor minimizes arcing across the breaker points when they open,

greatly increasing their service life.

6- Spark plug: is made of a material that conducts electricity encased in a ceramic body. Its

threaded base screws into the top of an engine cylinder. Two electrodes on the base of the spark

plug project into the combustion chamber. High-voltage current passes from the top of the spark

plug to electrodes on its base. The current then arcs, or jumps the gap, between the electrodes,

igniting fuel vapor in the combustion chamber.

7- High tension wires:these special wires, connects the distributor to spark with Plug

8. Ignition Coil.When the breaker points opens, the low-voltage current stops and the magnetic

field collapses, inducing a high-voltage surge in the secondary winding.

A wire conductor carries the pulses from the coil to the distributor, which routes them through

other wires to individual spark plugs. .


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WEEK 7

AUTOMOTIVE TECHNOLOGY AND PRACTICE MEC. 227

7.0 Internal combustion engine fuels and combustion

Objectives:Upon completion of this lesson the students should be able to:-

i. . Describe operating principles of a simple carburetor

ii. List main parts of the fuel injection systemiii. Describe the operating principles of fuel injection engine

iv. Draw the lay out of petrol fuel line

v. Identify exhaust system and state its functions

7.1 Introduction:

Operating principles of simple carburetor

Carburetor, is a device that mixes fuel and air for burning in an internal-combustion engine. Acarburetor atomizes (converts into a vapor of tiny droplets) liquid gasoline. An airflow carriesthe atomized gasoline to the engines cylinders, where the gas is ignited.


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Fig. 7.1 Simple carburetor showing its parts

Fig. 7.2 Simple carburetor showing exaggerated venturi.

The basic carburetor is built around a hollow tube called a throat, or barrel. Downward motion of

the engines pistons creates a partial vacuum inside the cylinders that draws air into the

carburetors throat and past a nozzle that sprays fuel. The mixture of air and fuel produced inside

the carburetor is delivered to the cylinders for combustion.

7.2. Fuel injection system

(i) Electronic Ignition

Electronic ignition systems use semiconductors and other solid-state electronic components to

switch current flows on and off in the coil, eliminating the need for breaker points. Automobile

manufacturers began installing electronic ignition systems in the 1970s and 1980s in an effort to

produce cleaner, more efficient engines.

(ii) Computer Electronic Ignition is a devices that detect the position of the crankshaft and

trigger electrical impulses at the correct moments. Some systems integrate ignition coils,

mounted either above each spark plug or to the side of the engine, that produce 40,000 volts or

more. The higher voltage produces a hotter spark with cleaner burning, longer plug life, and

improved fuel economy. Computers monitor and control the entire ignition process, adjustingignition timing and fuel delivery for the specific driving conditions, vehicle speed, and strain on

the engine.


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Fig.7.3. Fuel electronic injection system

1. Ignition key 2. Security control 3.swetch 4.switch body 5. Relay 6. Electroinc ControlUnit

7. Plug 8.Injector nozzle. 9.Pump

This system operates on ectromechanical principles in that injection pump and nozzles are

used in conjuction with the distributor and the plugs. This ignition system in more reliable ascompared to the two known traditional mean of providing fuel and its ignition in the

combustion chambet.


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7.4 Fuel injection system main parts

The fuel-injection system replaces the carburetor in most new vehicles to provide a more

efficient fuel delivery system. Electronic sensors respond to varying engine speeds and

driving conditions by changing the ratio of fuel to air. The sensors send a fine mist of fuel

from the supply through a fuel-injection nozzle into a combustion chamber, where it is mixed

with air. The mixture of fuel and air triggers ignition.

(iii) Fuel injection principles of operation

In fuel injection system, the air is directed into the combustion chamber, through the intake

manifold with uniform volume and velocity. The fuel is injected directly into the combustion

chamber or at intake valve under calibrated pressure. This process ensures precise fuel control

for all conditions of operation, which allow for better handling of leaner mixtures than can be

found in conventional carburetor.

Another feature of fuel injection, is its ability to ram air into the combustion chambers of the

engine.


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1. Injector nozzle 2. Piston 3. Vaporized atomized fuel

Fig 7.5 Fuel injection system, showing two methods of injecting fuel into combustion chamber.

7.3. Petrol engine Fuel line

The main purpose of fuel system is, to supply fuel to the engine cylinders in a vaporized

form, to ease combustion. Fig. (3.4) shows a simple fuel system used in the motor

vehicles.

Fuel system main components and other purpose are briefly described as follows:

1- Fuel tank: to store fuel

2- Fuel pump: to draw fuel from fuel tank to the carburetor.

3- Fuel filter: to filter the fuel from small foreign particles

4- Carburetor: to meter and mix the fuel at correct air-fuel ratio and to atomize the fuel

into fine particles so as to burn it quickly.

5- Fuel lines (pipes and hoses): to connect components together.


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Fig. (7.6) fuel injection system components

7.4 Exhaust system.

Each exhaust stroke emits a sound wave composed of higher and lower frequencies of

compression vibration. These frequencies of combustion vibration can be damped down by

passing the gases through an absorption type of silencer in which a perforated steel tube insurrounded by glass or wire wool. The gases pass through the tube in an unobstructed flow,

while the high frequency sound waves pass through the tube in an unobstructed flow, while the

high frequency sound waves pass through the perforations to be damped down by the wool.

Exhaust system consists of a steel drop pipe connected to the manifold.


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Fig 7. 7 A silencer muffler showing the internal components..

WEEK 8

8.0.THE TRANSMISSION SYSTEM

General Objectives:

1. Know the general arrangements and layout of the various types of transmissionsystem.

2. Understand the constructional details and operations of friction clutches used inroad vehicles.

3. Understand the constructional details and operations of manually-operated gear-boxes.

4. Know the components, and describe the constructional details and operation of thepropeller and drive shafts.

Understand the methods of bearing mountings, adjustment and lubrication requirements

of final drive.

8.1. Diagram showing component parts of Transmission system.

Fig. 8.1. Power transmission path


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5.

8.2 The automobile clutchThe main function of the clutch is to interrupt the transmission of crankshaft torque to the

gearbox. Different trains of gears, providing different combinations of speed and toque,

must be used to suit different driving and load conditions but it is almost impossible to

engage, or release gears when they are transmitted torque. It is also practically impossible

to engage a rotating gear, under torque, with a stationary or slower running gear and it

certainly cannot be done without damage.

The clutch is also designed to absorb the shock of engaging two shafts running at different

speeds, and to absorb small torque irregularities.

Fig.8. 2. Clutch hydraulic system


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8.2.1 Types of clutches

The most widely used form of clutch is the friction type. This may be:(a) The cone clutch, which is now only used in the synchromesh units of gearboxes, and

in overdrives and some epicyclic gearboxes;

(b) The single-plate clutch (multi spring or diaphragm spring) which is used in most

cars and small commercial vehicles.

(c) The multi-plate clutch, which is, used in motorcycles and in some racing cars and

tractor, and also in special types of very heavy commercial and civil engineering

vehicles.

The single and multi-plate friction clutches are usually dry types but some wet types are

still in use. In these cork-insert or phosphor-bronze plates are fitted between steel plates, all

the plates being immersed in oil.

Other forms of clutch are coming into wider use and generally form a part of the pre-

selector, two pedal, or fully automatic transmission systems. These are the centrifugal and

magnetic clutches, the fluid flywheel, and the hydraulic torque converter.

8.2.2 Single plate multi spring clutch

Construction


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Fig. 8.3. Single plate clutch

The single-plate clutch consists of a centre plate which is clamped between two other plates.

These two outer plates are driven by the engine crankshaft, and in turn drive the centre

plate which is mounted upon the splined gearbox input shaft. The rear face of the flywheel

is used as one driving plate and the second, or pressure, plate is mounted inside the clutchbody which is bolted to the flywheel. The pressure plate is forced towards the flywheel by a

set of strong springs which are arranged radially inside the body. Three levers, or fingers,

are carried on pivots suspended from the case of the body, and are so arranged as to be

able to pries the pressure plate away from the flywheel by the inward movement of a

carbon or ball thrust-release bearing. The bearing is mounted upon a forked shaft and is

moved forward by the depression of the clutch pedal. The connection between the pedal

and the shaft may be made by means of rods, cables, chain, or by a hydraulic system.

8.2.3 Operation of the single plate Clutch

Basically, the clutch consists of three parts. These are the engine flywheel, a friction disk,

and a pressure plate. When the engine is running, the flywheel is rotating. The pressureplate is attached to the flywheel so the pressure plate also rotates. The friction disk is

located between the two. When the clutch is released, the driver has pushed down on the

clutch pedal. This action forces the pressure plate to move away from the friction disk.

There are now air gaps between the flywheel and the friction disk, and between the friction

disk and the pressure plate. No power can be transmitted through the clutch.

Bearin

Clutch

Splined

Inputshaft


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When the driver releases the clutch pedal, power can flow through the clutch. Springs in

the clutch force the pressure plate against the friction disk. This action clamps the friction

disk tightly between the flywheel and the pressure plate. Now, the pressure plate and

friction disk rotate with the flywheel. The friction disk is assembled on a splined shaft that

carries the rotary motion to the transmission. This shaft is called the Clutch shaft, or

transmission input shaft

.

Fig.8. 4

It is located between the engine


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THE GEARBOX

8.3.1. Speed and loadThe petrol engine can only operate efficiently within a limited range of engine speeds,

usually between 2000 and 4000 crankshaft revolutions per minute. The power produced by

the engine is available at the crankshaft as a combination of speed and torque. This power

will be capable of propelling the vehicle against a certain maximum load or resistance; any

load in excess of this maximum will result in slowing down the engine. It will, therefore,

produce less and less power until it is brought to a standstill or stalled.

The loads imposed upon the engine will vary with the weight being moved the nature of the

road, i.e. the level, uphill or downhill. The greatest amount of power is required when first

moving the vehicle form rest.

Fig. 8.5 Speed and loading.

As power is the speed multiplied by the torque (p = S x T) it follows that if the speed is

reduced the torque can be increased. By placing a train of gears between the crankshaft

and the driving road wheels the turning power of the wheels can be increased by reducing

their speed. This enables an engine of a given power output to overcome a greater load

Pinion A

Pinion B

F

Pinion A

C = F x r

F x 2r = 2C

Pinion B

r

2r


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but at a lower speed. In practice three or four alternative gear trains are used which give a

choice of speeds and torques to suit all conditions of vehicles speed and engine loading.

A neutral position must be available to allow the running of the engine while the vehicle is

stationary and a reversing gear train must also be available. All the various gear trains and

their selector mechanisms are built into a gearbox which is fitted between the clutch andthe final drive mechanism in the rear axle.

Fig.8. 6. Transmission gearbox

In construction and arrangement this gearbox is generally similar to the three speed type

but there are a few important differences. These are:

(1) The incorporation of an extra gear train makes available an extra series of

intermediate torques, which enables the engine to overcome the loads acting against

it without either being overworked or having to operate at excessive speeds.


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(2) The reverse idler gear has two sets of teeth, of different diameter, and is engaged by

being moved bodily along its own shaft i.e. it is not permanently engaged with the

lay shaft.

(3) The reverse idler gear has its own selector shaft and fork, and the gear lever

has five different positions. The reverse gear selector mechanical is so arranged thatreverse cannot be selected by accident. This is usually accomplished by having to

use extra force, or an unusual lifting or side movement of the gear lever.

8.3.3 Construction,The input and output shafts lie on the same axis and, although the forward end of the

output shaft is supported in a bush fitted inside the input shaft, there is no direct

connection between them. These shafts are supported and located by ball bearingsmounted in the end walls of the gearbox case.

The lay shaft axis is parallel with the other two shafts and lies under or to one side of them,

the largest lay shaft gear wheel, or pinion, being permanently engaged with the integral

pinion of the input shaft. The lay shaft rotates upon plain bushes or needle-roller bearings

which are supported by a non-rotating shaft. End-float is controlled by phosphor bronze

spacer washers.

The lay shaft has four integral pinions which have spur teeth. The output shaft is splined

and carries splined pinions which provide the third, second and first gear ratios. The

movement of the gear lever, acting through the selector shafts and forks, causes the selectedpinion to slide along the output shaft and be meshed with one of the lay shaft pinion.

8.3.4 Operation, Fig.8.6

First or bottom gear:The selector fork moves the double-output pinion (6 and 8) to therear to engage (8) with the rear lay shaft pinion (7). The torque is transmitted through

input (1) to lay shaft pinion (2), then lay shaft pinion (7) to output pinion (8). This ratio

proves the greatest forward speed reduction and torque increase.

Second gear:The selector fork moves the double-output pinion (6) and (8) forward toengage pinion (6) with the third lay shaft gear (5). The torque is transmitted through input(1) to lay shaft pinion (2), then lay shaft pinion (5) to output pinion (6). This ratio provides

more speed but less torque increase than that of the first gear.


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Fig.8. 6

Third gear:The selector fork of the third and top-gear selector shaft moves the outputpinion to the rear to engage with the second lay shaft pinion. The torque is transmitted

through input to lay shaft and from lay shaft to output. This ratio proves more speed but

less torque increase than the first and second gear ratios.

Top gear:The selector fork moves the output forward to engage with input pinion (1) bymeans of dogs. The input and output shafts now rotate as one shaft and the output speed

and torque are the same as that of the crankshaft.

N.B:Note that bottom gear provides the greatest forward speed reduction and the greatest

torque increase. As the other ratios are engaged the output speed is increased while the

output torque is reduced until, when top gear is engaged, the input and output speeds and

torques are the same as those of the crankshaft.

Reverse gear:The output remain in the neutral position, that is between lay shaft andbetween lay shaft the reverse selector shaft and fork move the double reverse idler pinion

to engage with lay shaft and output at the same time. The torque is now transmitted

through input to lay shaft and from lay shaft (7) to reverse idler . Then from reverse idler


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to output. In many gearboxes the reverse ratio provides the greatest reduction in speed and

the greatest increase in torque

WEEK 9

9.0 THE DRIVE- LINE (PROPELLER AND SHAFT)

9.1 FunctionThe propeller shaft is used to connect the output shaft of the gearbox to the pinion shaft of

the final drive mechanism in the rear axle. As the suspension system operates, the rear axle

rises and falls continuously. It also moves backwards and forwards as it rises and falls in anarc, having as its centre the forward shackle pin of the rear spring. In addition, the pinion

nose itself is forced upward when the engine torque is applied to the pinion, and is forced

down when the brakes are applied. The propeller shaft must be so designed as to transmit

the torque from the gearbox to the final drive smoothly and continuously in spite of all

these different movements.

ArrangementThe propeller shaft is a tubular steel unit with a Hook joint at each end. The joints consists

of two U-shaped steel forgings or yokes which are connected at 90o to each other by a

four-legged cross or spider. Needle roller or rubber bearings may be used to support the

spider legs in the forgings. These U-joints, or universal joints, allow the smoothtransmission of torque even though the gearbox and pinion shafts are never in exact

alignment.


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Fig.9.1The main types of propeller shaft.

9.2. UNIVERSAL JOINT

These are used to connect two shafts when their centre lines intersect.

Fig. 9.2The universal joint (yoke)

Types of universal jointsThe three main types of universal joint used in vehicle construction are:

(1) The cross type such as the Hardy-Spicer

(2) The ring type such as the Lay rub

(3) The constant velocitytypes such as the Tracta and the Rzeppa joints.


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9.3. THE FINAL DRIVEThis is generally referred to as the differential but includes the crown wheel and pinion or

gear assembly having the same functions.

FunctionsThe crown wheel and pinion assembly is used

a) To change the direction of the drive through a right angle, andb) To increase the available torque by reducing the speed [power =torque times speed].

The ratios used in cars are about 4; 1 while those of commercial vehicles may be as high

as 10; 1.

The differential is a second gear assembly which is bolted to the side of the crown

wheel, or inside a worm-wheel and which rotates with it.

This unit allows the half-shafts to rotate at different speeds but under the same torque,

and only comes into operation when the vehicle is cornering. Its function or purpose is

to reduce the tendency for the tires to be dragged sideways instead of rolling around the

curved path. It also reduces the stresses imposed upon the shafts and bearings and

reduces tire wear. Skidding is also much less liable to occur.


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Fig 9.3 The deferential units

Construction

Crown wheel and pinionThese are hardened and tempered steel bevel gears which are arranged with their axes at

right angles. The larger is the crown wheel and this carries the differential assembly. The

pinion is the smaller and is integral with a short shaft to which is bolted the propeller shaft.

The complete final drive gear assembly is mounted in a strong steel casting which is bolted

into the rear axle case. A tubular part of the casting, called the pinion nose, supports the

pinion and its integral shaft either in double thrust ball bearings or in opposed taper- roller

bearings. Some designs may use a plain roller bearing at the inner end of the pinion. The

differential case is formed into two arms which carry the bearings used to support andlocate the crown wheel. These bearings may be both ball or tapper-roller types and their

thrust directions are opposed. Provision is made to adjust the meshing of the gears either

by screwed sleeves, shims, or by pre-loading jigs and shims.


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Figure 9.4. Rear wheel and front wheel drives

9.8. Differential,FigThis consists of a case [which may be in two parts] which bolted or riveted to the side of the

crown wheel and rotates with it. Two or four planet wheels are mounted upon a spider

shaft and are fitted inside the case in such a way that the spider shaft is turned end over

end. Also fitted inside the case, and meshing with the plane wheels, are two sun wheels

which are internally splined, and which support and drive the inner ends of the half-shafts.

The gear teeth and the spider shaft are the most highly stressed part of the assembly and

are those most liable to fracture.


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Fig. 9.5 diagram showing planet and sun gears

Differential principle, Fig. 9.5

This is similar to the simple bar type of brake compensator. In Fig 8.3 the end of the beam

are fitted into slots in the circumference of the discs. If a force is applied to the centre of


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the beam and at a tangent to the discs [at right angles to their radii], and if each disc offers

the same resistance to being turned, then the reaction forces acting on each disc will rotate

at the same speeds, and two torques or turning moments will be the same. In the practical

differential the discs are the sun wheels on the half-shafts and the beam is the spider shaft

and it planet wheels. When one disc does offer more resistance to being turned than the

other, the beam is forced to pivot about its centre. The disc with the greatest resistancewill hold back while the other is push forward by the pivoting of the beam. Under the of a

continuous tangential force at the centre of the beam one is slower and one faster in

rotation than the tangential force; i.e. the revolution per minute lost by the disc with the

greater resistance are gained by the other. The reaction forces on the discs are the same

because the force available is divided equally by the beam. The radii are the same so the

toque acting on each is the (torque= force * radius) although their speeds are now

different.

. OperationVehicle running straight, Fig. 9.6

The driving torque of the propeller shaft and of the pinion is increased by his speed

reduction between the pinion and the crown wheel. The direction of the drive is turned

bodily through a right angle. T he differential spider is rotated end over end, carrying the

planet wheels with it although they do not rotate on the spider. The road wheels, half-

shafts and sun wheels offer the same resistance to being turned and the differential gearing

does not therefore operate.

Fig. 9.6.deferential unit showing operations: Vehicle running straight


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Vehicle cornering. Fig. 9. 7

During a turn the outer wheel has to move along an arc of greater radius than the inner

wheel, and to do this in the same time it must be speeded up. The inner wheel is slowed

down as the vehicle turns and this increase the resistance of its sun wheel. The spider shaft

is still being turned end over at crown wheel speed, and as the inner sun wheel slows theplanet wheels are forced to rotate on the spider shaft and about the inner sun wheel. In so

doing the speed of the outer sun, and the outer road wheel, is increased by the same

proportion as the speed of the inner sun is reduced.

The torque is still divided equally between the two half-shafts but their speeds are

different. Note. The differential system only operates when there is a difference between

the resistances to turning of the road wheels. When one wheel loses its grip on a poor

surface its resistance is reduce to zero. The planet gear wheels therefore rotate on their

spider and run around the sun of the opposite wheel. This remains stationary and the

slipping wheel is driven by all available torque. Vehicles which, have to operate over poor

ground (e.g. Tractors, civil engineering and military vehicles) are often fitted with a devisewhich puts the differential gearing out of operation as required. In effect the two half-

shafts joined together so that one wheel can drive when the other slips.

Fig. 9.7.Deferential action: vehicle cornering.

9.4. Axle shaft arrangements


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Three main methods are used to support the half-shafts in the rear axle case. In all of them

the inner ends of the shafts are splined into, and supported by, the sun wheels of the

differential assembly (see Fig.). The differences lie in the arrangement of the hub bearings

in relation to both the case and shaft, and in the forces or loads imposed upon the shaft

itself.

Semi-floating, Fig.The hub and the half-shaft are, in effect, a one-piece unit although they may in be splined

or fitted together by means of a taper, key and lock-nut. The bearing is carried on the

shaft and is located by a nut or a sleeve. The outer track of the bearing is fitted a recess in

the axle case and is located by a retainer plats bolted to the end flange of the axle case.

This retainer usually encloses a spring-loaded oil seal and often in corporate an oil or

grease trap to prevent excess lubricant ruining the brake linings.

Three quarter floating, Fig.9.8The bearing is mounted on the casing and is held against a shoulder by a lock-nut and tabwasher. The hub is made in two parts, the inner part fitting over the bearing and also

enclosing a spring-loaded oil seal. The outer part may be integral with the half-shaft, be a

splined and interference fit upon it, or be secured to the shaft by a taper, key and lock-nut.

The brake drum may be integral with the hub outer half or secured to it by countersunk-

headed set screw. The back-plate mounting flange is nearer to the centre of the axle than

in the semi-floating designs.


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Fig. 9.8. Diagram showing axle supports

Fully floating, Fig 9.8This is a design generally used in commercial vehicles. The hub is a heavy forging or

casting of steel and is carried on the axle case by two heavy-duty opposed taper-roller

bearings. The tracks of these bearings are located by shoulders and a lock-nut, and are

adjustable. The hub drive planet is integral with the shaft and is secured to the hub by

radially arranged set bolts, a gasket being fitted between the two. A spring-loaded oil seal

is fitted into the inner side the hub near the back-plate flange.

WEEK 10

10.0. THE BODY AND CHASSIS

Fig.10. 1 Formation BVM

10.1. Chassis and Vehicle Body Technology

General Objectives:

On completion of this module, the students should be able to:

1. Know the reason for the general layout and distinguish between body constructions.


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2. Appreciate the construction of the vehicle chassis with respect to materials, frame andmethods of reinforcement.

3. Know the essential features of construction and in pressed steel and customized bodywork.

4. Know the various types of body construction and body styling.

5. Appreciate the integral construction of a vehicle body and means of mounting its maincomponents.6. Appreciate the principle of car body construction and finishing.

10.2. Separate chassis-body types (fig.10 A)

In this form of construction, now confined to the larger and heavier vehicles, the chassis and thebody are each made as a separate unit and then bolted together. Although the body adds to the

weight of the complete assembly it adds very little to its strength.

The shape of the chassis is determined by the location of the power unit, the arrangement of the

suspension system and the loads to be carried. The function of the chassis is to act as the frame

or skeleton of the vehicle, providing a mounting for all the other assemblies and keeping them in

their correct relative positions, in spite of all the varying loads to which they are subject. It must

be strong and rigid, and is usually made from steel pressings which are welded and rivetedtogether. Reinforcement is provided, where necessary, to add to its rigidity.

Essentially the chassis consists of two long side-members with shorter cross-members. The

assembled shape varies between the different types of vehicle, those for commercial vehiclebeing simpler but much stronger and heavier. The side members are usually of channel section

in commercial vehicles and of box section in cars, the latter being deeper in section between the

wheels to provide greater resistance to bending load. The forward and rear ends are upswept toallow for the movement of the axles, and (in plan view) are made narrow at the forward end to

allow a greater steering lock and therefore a smaller vehicle turning circle.

The cross-members connect the side members and are of channel, box or tubular section. Theyare welded, riveted or bolted to the side members. Additional cross-members are sometimes

added to provide extra resistance to engine torque.

When independent types of suspension are used the chassis has to be made much more rigid to

resist the twisting of the chassis members. The upsweep at the forward end is reduced and


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engine is arranged lower in the chassis. This improves the road-holding of the vehicle and is

only possible because allowance for axle movement is now no longer required (no beam axle).

Fig. 10.2 Car body skeleton(A separate and B integral types)

10.3. Integral body type (fig. 10.2 B)This the modern form of construction for almost all cars and lighter commercial vehicles. It is

light in weight and, when produce in very large numbers, is relatively cheap. The chassis, floorand body are assembled by welding from a very large number of mild steel pressings, each being

correctly aligned by using jigs. Although particularly light the assembly is very strong becauseall the load acting on it is spread over the whole of it. The chassis becomes a sub-frame in this

form of construction and other sub-frames are usually attached by rubber mountings to reduce

the amount of noise and vibration transmitted to the body shell.These body assemblies must be well protected from corrosion because of the thin steel

employed. Chemical compounds and special paints have to be applied to the underside of the

vehicle at regular intervals, and all boxed sections should be sprayed internally with anti-corrosion solutions. Water drain holes in these sections and in doors must be clear. The

vibration or drumming of the larger panels is a common fault and special compounds are

painted on their inner sides to reduce this. Felt may also be used.


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10.4. Motor vehicle body structure sub frame assemblies

Fig 10.3. Motor vehicle body structures

WEEK 11 differentiate

General objectives:

At the end of the lesson the students should be able to:-

1. identify automobile steering parts by their correct names2. to sketch steering Colum and show major parts

3. differentiate between the rack and pinion steering box from other makes

11.1. The steering System functionsThe steering system of the motor vehicle must:

(a) Enable the driver to control accurately the path taken by the vehicle at all times.

(b) Be light and easy to operate(c) Be self centering

(d) Be as direct as possible in action

(e) Not be affected by the action of the suspension and braking systems.

11.2. STEERING SYSTEM COMPONENTS


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The steering system has four major components:

1. The steering wheel and steering shaft that transmit the drivers movement to the

steering gear.Fig. 11.1. steering ring and colum

2. The steering gear that increases the mechanical advantage while changing therotary motion of the steering wheel to linear motion.

3. The steering Colum4. The steering linkage that carries that carries the linear motion to the steering arms

11.3. TYPES OF STEERING GEARS

Two types of steering gears widely used in automotive

vehicles, are the cam and peg steering gear and the

Rack-and-pinion steering gears are made in manual and

power versions.

Fig 11.2. Rack and pinion steering

Fig.11.3. Cam and peg steering box

CONSTRUCTION:

The complete steering system consists of a steering wheel and gearbox, and a system of

rods, levers, and ball pin joints which transmit the motion of the drop arm of the steering

gearbox to the track arms of the swiveling stub axles. Where a beam axle is used, the drop


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arm is connected to the track arm of the stub axle by the drag link. The track arm of the

opposite stub axle is connected to the first arm by a track rod. This may be arranged

longitudinally or transversely and is adjustable in length. It may be fitted behind or in

front of the axle, its function being to keep the front wheels parallel with each other when

the vehicle is running straight forward. The drag link may or may not be adjustable, and it

is so arranged that its operation is not affected by the movement of the axle and thesprings.

The various rods and links are connected by ball pin joints which permit movement in

more than one plane. These joints may or may not be adjustable, and are spring loaded to

take up wear and free play. They may be pre-packed with lubricant or require lubricating

at regular intervals. They must be protected from the entry of dirt and water.

Figure 11.4 Rack and pinion steering

11.4. STEERING GEOMETRY

True Rolling MotionIn order to provide effective control of the steering of the vehicle, and to reduce tyre and

bearing wear, it is important that the wheels rotate, under all conditions, with a true rolling

motion i.e. free from side drag (tyre scrub).

When the vehicle is running straight, all the wheels should rotate truly automatically.

When the vehicle has to negotiate a curve or a corner, the steering inner road wheel has tobe swiveled through a larger angle than the outer wheel to maintain true rolling motion.

The difference between the two angles has to vary with the sharpness of the turn, and it

must be provided both accurately and automatically. This is to ensure that each wheel is

aligned at 90oto its own radius of turn, i.e. the line between the centre of the wheel and the

centre of the turn. As near as practicable, these differences is swiveling angles are obtained

by using the Ackerman system.


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Ackerman principles.the Ackerman system the end of the track man of each stub axleis secured to the end of a transverse track rod, the rod being of such a length that at each

side one end lies upon the line between the kingpin and a point on, or near, the pinion nose

of the rear axle. The angle formed by these two lines is called the Ackerman angle, and its

size is such that when the track rod is moved it ceases to remain parallel with the axle,taking up instead a position in which it moves

the two track arms and their respective road

wheels through the require different angles.

The size of the Ackerman angle and the angular

differences at the wheels depends upon the ratio

of

fig. 11.5

the vehicle track divided by the wheel base. In

the Ackerman system the correct differences

are, in fact, only obtained in the straight

forward position and in one position in eachlock. Slight inaccuracies in all other wheel

positions are normally absorbed by slight

deflections of the tires.

While the Ackerman system provides reasonably accurate steering geometry for slow-

moving vehicle it has to be modified, by a combination of calculation and experiment, for

faster-moving and lighter vehicles. This is because of the effects upon the steering of low-

pressure tires, differences in tyre tread and construction, the distribution of vehicle weight,

the softer suspensions, and the effects of centrifugal force and cross winds.

11.5 principles of camberFig.11.6. Camber angle Fig. Castor angle

WEEK 12


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12.0. TIRES AND WHEELS

12.1 Functions of tires

Tires have two functions.

First, they are air-filled cushions that absorb most of the shocks caused by road

irregularities. The tires flex as they meet those irregularities. This reduces the effect of

road shocks on the vehicle, passengers, and load.

Second, the tires grip the road to provide good traction. This enables the vehicle to

accelerate, brake, and make turns without skidding.

12.2, TYPES OF TIRES

Fig. 12.1. Tyre thread patterns.

There are two types of tires: tube and tubeless. Tube tires have an inner tubeinside the

tire. This is a round rubber container that holds the air which supports the vehicle. Both

the tube and tire mount on the wheel rim. A tirevalve is part of the tube and protrudes

through the rim. Compressed air is forced through the valve to inflate the tube. The airpressure in the tube then causes the tire to hold its shape.

Tubes are used in some truck and motorcycle tires. Tubes are seldom used in passenger

and light-duty vehicles. Most automotive vehicle use tubeless tires. The tire mounts on an

airtight rim so air is retained between the flange and the tire bead.

12.3. TIRE VALVE


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Air is put into the tire or tube through a spring-loaded tire valve or Schrader valve. On

tube tires, the valve is on the inner tube and sticks out through a hole in the rim. Tubeless

tires use a separate tire valve mounted in a hole in the rim.

12.4 TIRE PRESSURE

The amount of air pressure in the tire depends on the type of tire and how it is used.Passenger-car tires are inflated from about 22 to 36 psi [152 to 248 kPa]. The maximum

inflation pressure is marked on the tire sidewall. A tireplacardor tireinformation

label.

This label is usually located on a door edge or door jamb, or inside the glove box door.

The label also lists maximum load and tire and tire size (including spare).

Figure 22.2. Tyre and rim sizes

Pneumatic tires are made in a variety of sizes. The size is usually indicated by a code such as

195/60 R 15. 88H. The number 195 is the width of the tire measured in millimeters. The number

60 is the tires height-to-width, or aspect, ratio. This tire has sidewalls that are 88 percent as high

as the tires width. The letter R stands for radial, which is a design type, and 15 means that the

tire will fit a rim 15 inches (38 cm) in diameter.

12.5 Motor vehicle tyre rim


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Fig. 12.3. Rims


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13

13.0.

13.1. .

The purpose of the brake system is to allow the driver to slow down or stop the vehicle

as required. A braking system provides the means of retarding a motor vehicle by

converting the Kinetic energy it possessed into heat energy through friction.

In order to provide effective retardation a brake unit is fitted to each road wheel of the

vehicle.

The layout of a single line hydraulic braking system.

Fig. (13.1) Single line Brake system


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13.2 The main part sand functions of hydraulic braking system

The main parts in the brake system and their function are given is Table (2.7.1)

FunctionBrake Component

Enables transferring driver's foot pedal force to each brake unitthrough the hydraulic fluid

Master cylinder

Assists the drivers effort in applying the brakesServo unit

Contains a reserve quantity of hydraulic brake fluidReservoir

Connect the components in the hydraulic circuitSteel pipe line

Allowsforsuspension and steering movement of the wheels.Flexible pipes

Forces the shoes to expand outwards.wheel cylinder

Table (13.2.1) brake system and function


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13.3. Operation of drum and disc brake assemble.

A brake drum rotates together with thewheel. The brake shoes press againstthe drum from the inside. This frictioncontrols the rotation of the wheel. It isnecessary to inspect the brake drum andbrake lining. :The brake shoes press against therotating drum from the inside to getbraking power. When pressed in thesame direction as the drum rotates, theshoes make inroads into the rotationaldirection by the friction with the drum. Asa result, the friction power increases,

which is called self-energizing action.

Wheel cylinder Brake shoe Brake lining

Brake drum Piston Piston cup

Fig. 13.3 Brake expander action

Figure 33.2. A comprehensive hydraulic brake futures


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13.4. The brake servo.

Brake servo unit: thest units are

used to obtain a more powerfulretardation of the vehicle without

the use of increased pwdal force.

They are fitted into the fluid system

after the master cylinder, and use a

pressyre difference between the two

sides of a vacuum piston to increase

the pressure acting in the wheel

cylinders.

This pressure must always be directly proportional to the applied pedal force to enable

the driver to feel his braking. Usually the pressure in the cylinders is between one and

therr times that provided by the master cylinder.

Figure 43.4. Brake servo unit


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WEEK 14

14.0. SUSPENSION SYSTEMS

14.1. PURPOSE

The suspension system is located between the wheel axles and the vehicle body or

frame. Its purpose is to;

1. support the weight of the vehicle

2. Cushion bumps and holes in the road.

3. Maintain traction between the tires and the road.

4. Hold the wheels in alignment.

The suspension system allows the vehicle to travel over rough surfaces with a

minimum of up-and down body movement. It also allows the vehicle to corner

with minimum roll or tendency to lose traction between the tires and the road

surface. This provides a cushioning action so road shocks have a minimal effect on

the occupants and load in the vehicle. Road shocks are the actions resulting from

the tires moving up and down as they meet bumps or holes in the road.

14.2. COMPONENTS OF SUSPENSION SYSTEM

The suspension system components include the springs and related parts that

support the weight fo the vehicle body on the axles and wheels. The springs and the

shock absorbers are the two main parts. The springs support the weight fo the

vehicle and its load, and absorb road shocks. The shock absorbers help control or

dampen spring action. Without this control, spring oscillation occurs. The springs

keep the wheels bouncing up and down after they pass bumps or holes. Shock

absorbers allow the basic spring movement, but quickly dampen out the unwanted

bouncing that follows. These ride control componentssprings and shock

absorbermay be mechanically or electronically controlled. Following sections

describe both types.

14.3. TYPES OF SPRINGSFour types of springs are used in automotive suspension systems. These are coil,leaf, torsion bar, and air.

14.4..COIL SPRING


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The coil spring is made of a length fo round spring-steel rod wound into a coil. Some

coil springs are made from a tapered rod. This gives the spring a variable spring

rate. As the spring is compressed, its resistance to further compression increases.

14.5. LEAF SPRING

Two types of leaf springs are single-leaf and multileaf springs. These have severalflexible steel plates of graduated length, stacked and held together by clips. In

operation, the spring bends to absorb road shocks. The plates bend and slide on

each other permit this action.

14.6. TORSION BARThe torsion bar is a straight rod of spring steel, rigidly fastened at one end to the

vehicle frame or body. The other end attaches to an upper or lower control arm.

Documents

Auto. Tech.mec.227 Theory 03