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SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015
ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 33
Design and Study of Four Speed Sliding Mesh Gear Box
Atthuru Manikanta Reddy1, Aakash.k2
12
Department of Mechanical Engineering, R.M.K. Engineering college, Anna University, Chennai, India
ABSTRACT: This Paper deals with understanding
of the gear transmission system principles with its
design and working. Different types of gears are
used in automobiles. Gears have teeth which mesh
with each other to transmit the drive. A detailed
CAD(Computer-aided design) model has also been
developed according to the theoretical calculations
to validate the design and an brief study of the four
speed sliding mesh gear box.
Keywords -Gear Transmission, Meshing, CAD,
Drive and Automobiles
I.INTRODUCTION Gearbox is enclosed system of assembled gears that
transmits mechanical energy from a prime mover to
an output device. A gearbox can also change the
speed, direction, or torque of mechanical energy.
Gear box is a device placed between the clutch and
propeller shaft. It allows the engine to run at
different speeds relative to road vehicles, so as to
maintain its power and regulates the torque. The
vehicle requires high torque when climbing hills
and when starting, even though they are performed
at low speeds .On the other hand, when the vehicles
are running at high speeds on the road level, high
torque is not required because of momentum.
PURPOSE OF GEAR BOX An automobile is able to provide varying speed
and torque through its gear box. Various functions
of a gear box are listed below To provide high
torque at the time of starting, vehicle acceleration,
climbing.To provide more forward speeds by
providing more than one gear ratios. In modern
cars, four to five forward gears and reverse gear is
provided. For given engine speed, higher speed can
be obtained by running in higher (4th and 5th)
gears.To provide a reverse gear for driving the
vehicle in reverse direction and To give different
speeds and torques. To get high acceleration from
rest .To drive vehicle at low speeds. In the engine
running conditions the vehicle can be stopped by
changing the gear to neutral condition without
applying brake.
II. WORKING PRINCIPLE OF SLIDING
MESH GEARBOX
It is simplest type of gear box out of the available
gear boxes. In this type of gear box, gears are
changed by sliding one gear on the other. This gear
box consists of three shafts; main shaft, clutch shaft
and a counter shaft. In a four speed gear box
(which includes one reverse gear), the counter shaft
has four gears which are rigidly connected to it.
Clutch shaft has one gear and main shaft has two
gears. The two gears on the main shaft can slide in
the horizontal direction along the splines of the
main shaft. However, the gears on the counter shaft
cannot slide. The clutch gear is rigidly fixed to the
clutch shaft. It is always connected to the counter
shaft drive gear.
The two gears on the main shaft can be slide
by the shifter yoke by operating the shift lever (not
shown in Figures). These two gears are second gear
and low/reverse gear respectively. These gears can
be meshed with corresponding gears on the counter
shaft with the help of shifter yoke and shift lever.
Shift lever is operated by hand in four wheelers for
changing the gears. A reverse idler gear is mounted
on another (third) shaft and is always in mesh with
reverse gear on counter shaft.
Neutral position:
The above figure shows sliding mesh gear box
in neutral position. In this position, the engine is in
running condition, clutch remains engaged and
clutch gear drives the counter shaft drive gear. The
direction of rotation of countershaft is opposite to
that of clutch shaft. In this position Ist, IInd and
IIIrd and reverse gears are free. Thus, main
(transmission) shaft does not rotate and automobile
wheels do not rotate. So vehicle remains stationary
First Gear:
When first gear position is selected by the
shift lever, first gear (large gear) on the main shaft
slides and is connected to first gear on the
countershaft. The direction of rotation of main
SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015
ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 34
shaft is same as that of clutch shaft. In first gear,
small gear of counter shaft meshes with larger gear
on main shaft, speed reduction in the ratio 3: 1
(approximate) is obtained.
Second Gear:
When second gear is selected by the shift
lever, second gear on counter shaft meshes with
second gear (small gear on main shaft) on the main
shaft. The direction of main shaft is same as that of
clutch shaft. Speed reduction of the order of 2: 1 is
obtained in second gear.
Third Gear
In third gear, the main shaft is slides axially
towards the clutch shaft so that main shaft is
directly connected to the clutch shaft. In this
position, the main shaft rotates at the speed of
clutch shaft. Thus, a speed ratio of 1: 1 is obtained.
It can be noted that the clutch gear is directly
connected to engine crankshaft and main shaft is
connected to the wheels through propeller shaft.
Reverse Gear
When the shift lever is operated to engage the
reverse gear, the larger (reverse) gear of the main
shaft meshes with the reverse idler gear. Reverse
idler gear is always connected to reverse gear on
counter shaft. The reverse idler gear between
counter shaft reverse gear and main shaft larger
gear changes the direction of rotation of main shaft.
Thus, the direction of main shaft becomes opposite
to that of clutch shaft. Therefore, wheels of the
automobile start moving in backward direction.
(Note: Countershaft is also known as lay shaft.)
III . COMPONENTS USED IN GEAR BOX
Some of the components used in gear box are:
- Shaft
- Bearing
- Selector Forks
Shafts:
Fig 2.1 Drive Shaft
A drive shaft is a mechanical component for
transmitting torque and rotation, usually used to
connect other components of a drive train that
cannot be connected directly because of distance or
the need to allow for relative movement between
them. Drive shafts are carriers of torque: they are
subject to torsion and shear stress, equivalent to the
difference between the input torque and the load.
They must therefore be strong enough to bear the
stress, whilst avoiding too much additional Weight
as that would in turn increase their inertia.
Bearings:
Fig 2.2 Bearings
Bearings are highly engineered, precision-made
components that enable machinery to move at
extremely high speeds and carry remarkable loads
with ease and efficiency. It must be able to offer
high precision, reliability and durability, as well as
the ability to rotate at high speeds with minimal
noise and vibration. Bearings are found in
applications ranging from automobiles, airplanes,
computers, construction equipment, machine tools,
DVD players, refrigerators and ceiling fans. If
something twists, turns or moves, it probably has a
bearing in it.
Selector fork:
Fig 2.3 Selector Fork
The shifter fork and fork rods have a
mechanism using a plunger with a ball in it and is
supported with a slide able ball bearing. The detent
mechanisms give the driver distinctive detent
SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015
ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 35
feeling and the sliding ball bearings help reduce the
shift lever operating force. All shifter forks are
made of aluminium die casting and the shifter arm
shaft is formed as a hollow type to minimize the
overall weight of the transmission. Gear double
meshing is prevented by a mechanism that uses
interlock blocks. The select return mechanism
(which returns the selector lever to the neutral
position) uses a U shaped leaf spring.
IV . DESIGN CALCULATION OF GEAR BOX
For design calculation of the spur gear,
Power : 3kw
Speed (N) : 750 rpm
Speed ratio : 2
STEP-1
TO FIND THE GEAR RATIO:
i =2 (assumed); Hence, = 2;
= 375 rpm
STEP-2
TO SELECT THE MATERIAL
For gear and pinion, let us select the
same material. i.e., C45 (STEEL)
STEP-3
INITIAL DESIGN TORQUE
[ ] = [ ]. k.
[ ] = = 389.68 kgf.cm
Assume, k. =1.3;
[ ] = 50.6 X N.mm
STEP -4
TO FIND BENDING AND CRUSHING
SRESSES
FROM DESIGN DATA BOOK
Bending stress: 140
Crushing stress: 500
STEP-5
TO FIND MINUIMUM CENTRE DISTANCE
a (i+1) Assume, = 0.3
a 88 mm.
STEP -6
TO FIND THE MODULE
m 1.26
Assume, =10; = 10; = 20 and
y = 0.3890
m 3
STEP – 7
TO FIND THE NUMBER OF TEETH
= 33
= 22
STEP – 8
TO FIND THE PITCH CIRCLE DIAMETER
= 52.5 mm
= 36 mm.
STEP – 9
TO FIND THE ACTUAL CENTER
DISTANCE
a = m. = 83.
Initial centre distance is less than
actual centre distance.
So, the design is feasible.
STEP -10
TO FIND THE FACE WIDTH
=
= 0.3(83)
b= 25 mm
STEP – 11
TO FIND THE ACTUAL DESIGN TORQUE
[ ] = [ ]. k.
SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015
ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 36
=
= 0.6
From design data book for , k=1.06
V =
V= 1.143
From design data book, for velocity 1.143m/s the
corresponding = 1.3
Therefore the actual design torque [Mt] (actual) =
50.6 X N.mm
STEP- 12:
TO CHECK THE INDUCED STRESSES:
Crushing stress =
= 92.5
The Crushing stress is less than the assumed
crushing stress and so the design is safe.
Bending stress =
= 68.8
The Bending stress is less than the assumed
bending stress and so the design is safe
STEP- 13:
TO FIND THE OTHER DIMENSIONS
Take ( ) = 1
BOTTOM CLEARENCE
C =0.25 (m)
= 0.25 (3)
= 0.75 mm
TIP DIAMETER
= ( + 2 ) m
= 72mm
= ( + 2 ) m
= 75 mm
ROOT DIAMETER
= ( - 2 ) m
= 60 mm
= ( - 2 ) m
= 93 mm.
STEP-14:
DESIGN CALCULATION FOR SHAFT, KEY
FOR SHAFT
50.6 X = ; [ = 140
; F.O.S = 2 (assumed)]
D = 14.76 mm
D (Std) = 15 mm diameter.
FOR KEY
For the calculated diameter the size of key chosen
is 6mm X 3mm X 100mm.
CAD MODELLING PHOTOGRAPHY:
Fig 4.1 Model diagram of Four Speed Sliding
Mesh Gear Box
SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015
ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 37
Fig 4.2 Design of Four Speed Sliding Mesh
Gear Box
V. CONCLUSION
The aim of our paper is that we have
undertaken in our engineering course is to improve
our practical knowledge in design and fabrication
of a particular component in a technical manner.
This improves not only our practical skills, but also
our various managing functions such as planning
the project design, fabrication and erection and cost
analysis etc. This paper is planned and completed
as per the schedule and regulations. And In
addition to that, by accomplishing this project of
“FOUR SPEED GEAR BOX” successfully we felt
that we have obtained enough knowledge regarding
this topic, with full of satisfaction and forward the
project to concerned.
REFERENCES
[1] A Text Book of Machine Design(S.I.Unit)2005
Edition By R.S.KHURMI & GHUPTA.
[2] Design of Spur Gears for Improved Efficiency by N.E.Anderson and S.H.Loewenthal
[3] Design of Spur Gear and Its tools by MR.A
.Gopichand
[4] Design of Machine Elements by V. B. Bhandari.
[5] Book of Gear design By William Alfred Tuplin.
[6] Dudleys Handbook of Practical Gear Design and
Manufacturing,Second Edition Hardcopy - 10 May
2012 By Stephan P.Radzevich.
[7] Wear of Spur and Helical Gears by Anders Flodin.
[8] Stress and deformations in involute Gears by Zeping Wei.
[9] Wikipedia (www.wikipedia.org)
[10] what-when-howInDepthTutorialsand
Informationhttp://what-when-
how.com/automobile/sliding-mesh-gearbox-automobile
[11] How Stuff Works(www.howstuffworks.com