Gear Box Design

1. Created by Davis Hans S J for Jansons Institute of Technology
Design of Gear Box
Presented By
A.Mohan M.E.,
Assistant Professor
Department of Mechanical Engg
Vel Tech-Avadi
Chennai-62

2. Created by Davis Hans S J for Jansons Institute of Technology
Gear Box - Need
Vehicle or in a machine requires high
torque when starting (to overcome
the inertia forces and load).
High torque is achieved only in low
speed.
The same vehicle or machine
requires (or may require) high speed
in later operations, to perform the
desired purpose of the machine.
If high speed is achieved only in low
torque is transmitted.

3. Created by Davis Hans S J for Jansons Institute of Technology
So a same machine has to operate slowly (with
high torque at starting stage) and with high
speed (with out high torque) later in operation.
A gearbox is introduced to provide the demand
of variable torque or variable speeds for the
machines or vehicles.
The gear box is also called as the transmission
box, torque converter, speed reducer unit or
sometimes as transmission.

4. Created by Davis Hans S J for Jansons Institute of Technology
Gear Box
Gear box is a device which provides
controlled power that uses gears and
gear trains to provide variable speed
and torque from a rotating power source
to another device.

5. Created by Davis Hans S J for Jansons Institute of Technology
Functions of Gearbox
1. Provide the torque needed to move the vehicle or machine under a variety of
load conditions. It does this by changing the gear ratio.
2. Be shifted into reverse so the vehicle or machine can move backward or
reverse rotation.
3. Be shifted into neutral for starting the engine or motor .

6. Created by Davis Hans S J for Jansons Institute of Technology
Components in gear box
1. Gears
2. Counter shaft or lay shaft
3. Main shaft
4. Input or primary or clutch shaft
5. Dog clutch
6. Selector fork

7. Created by Davis Hans S J for Jansons Institute of Technology
Types of gearbox
1. Sliding Mesh gearbox
2. Constant mesh gearbox
3. Synchromesh gearbox (constant mesh)

8. Created by Davis Hans S J for Jansons Institute of Technology
Sliding Mesh gearbox
• Uses spur gear
• Clutch gear is rigidly fixed
• Gears in lay shaft is
rigidly fixed
• Gears in main shaft can
only be moved on spline.
• A idler gear provided for
reversing
• Selector fork

9. Created by Davis Hans S J for Jansons Institute of Technology
Working of a sliding mesh gear box
• The selector fork is moved by the
gear leaver.
• The selector fork moves the gear
over the spline and encages with
the gear in lay shaft.
• Thus the power form the clutch
shaft is transmitted to the main
shaft through the lay shaft.

10. Created by Davis Hans S J for Jansons Institute of Technology
Working of a sliding mesh gear box – 1st
gear
In the first gear, the gearbox provides
maximum torque at low speed.
The smallest gear on the lay shaft
engages with the biggest gear in
main shaft, thus transmitting high
torque.

11. Created by Davis Hans S J for Jansons Institute of Technology
Working of a sliding mesh gear box – 2nd
gear
In the second gear, the gearbox
provides low torque and high speed
when compared to 1st
gear .

12. Created by Davis Hans S J for Jansons Institute of Technology
Working of a sliding mesh gear box – 3rd
gear
In the third gear, the gearbox
provides low torque and high speed
when compared to 2nd
gear .

13. Created by Davis Hans S J for Jansons Institute of Technology
Working of a sliding mesh gear box – 4th
gear
For fourth gear the clutch shaft and
the main shaft is engaged by a dog
clutch, there by the main shaft rotates
at maximum speed as that of clutch
shaft.

14. Created by Davis Hans S J for Jansons Institute of Technology
Reverse Gear
When selecting reverse, the direction
of rotation of the output shaft is
changed This is achieved by using an
idler gear.
The idler gear is meshed between a
counter shaft gear (layshaft or 2nd
motion shaft) and an output shaft
gear(mainshaft or 3rd
motion shaft.
Reverse
idler gear

15. Created by Davis Hans S J for Jansons Institute of Technology
Constant Mesh Gearbox
• Uses Helical gears
• Gears in lay shaft is rigidly fixed
• Gears in lay shaft and output shaft
is meshed together
• The gears in output shaft rotates
freely and do not transmit power as
they are not engaged in shaft.
• Dog clutch is used to engage gears
• A idler gear provided for reversing
• Selector fork is used
Input shaft Output
shaft
Reverse
idler gear
Counter
shaft
Reverse
shaft (fixed)

16. Created by Davis Hans S J for Jansons Institute of Technology
Working of a constant mesh gearbox
When the gear lever is pushed, the
gear selector fork pushes the dog
clutch.
The dog clutch engages the gear and
the output shaft, thus power from lay
shaft now transmitted to output shaft.

17. Created by Davis Hans S J for Jansons Institute of Technology
Synchromesh Gearbox
Output
shaft
1st
gearBush
2nd & 1st
synchronizer
2nd gear
blocking ring
2nd gear
Bush
3rd gear
4th and 3rd gear
synchronizer
4th gear
blocking
ring

18. Created by Davis Hans S J for Jansons Institute of Technology
Synchromesh Gearbox
When the dog teeth make contact with
the gear, but the two parts are spinning
at different speeds, the teeth will fail to
engage and a loud grinding sound will
be heard as they clatter together.
For this reason, a modern dog clutch in
an automobile has a synchronizer
mechanism or synchromesh, which
consists of a cone clutch and blocking
ring.

19. Created by Davis Hans S J for Jansons Institute of Technology
Synchromesh Gearbox Working
• Before the teeth can engage, the cone clutch engages first, which
brings the selector and gear to the same speed using friction.
• Until synchronization occurs, the teeth are prevented from making
contact, because further motion of the selector is prevented by a
blocker (or baulk) ring.
• When synchronization occurs, friction on the blocker ring is relieved
and it twists slightly, bringing into alignment certain grooves or notches
that allow further passage of the selector which brings the teeth
together.

20. Created by Davis Hans S J for Jansons Institute of Technology
Types of gears used in gear box
• Spur (in sliding mesh gear box)
• Helical (in constant mesh and synchromesh gearbox)
• Bevel (differential drives)
• Worm

21. Created by Davis Hans S J for Jansons Institute of Technology
Gearbox and gear ratio of some vehicles

22. Created by Davis Hans S J for Jansons Institute of Technology
Gear Box
Design using PSG Data book

23. Created by Davis Hans S J for Jansons Institute of Technology
Geometric Progression
• By using geometric progression the speed is reduced uniformly in
different stages.
• Geometric progression, also known as a geometric sequence, is a sequence of
numbers where each term after the first is found by multiplying the
previous one by a fixed, non-zero number called the common ratio or
preferred ratio.

24. Created by Davis Hans S J for Jansons Institute of Technology
Preferred numbers or Basic series
• The preferred ratio is mentioned
as basic series, named as R5,
R10,R20,R40 and R80.
• Each basic series has a specific
step ratio.
• The R in basic series is added to
honour the Engineer Charles
Renard, who introduced the usage
of preferred numbers.

25. Created by Davis Hans S J for Jansons Institute of Technology
Why use preferred numbers ?
• Preferred numbers are arrived using geometric progression(GP)
• GP provides even range of spindle speeds at each step.
• Speed loss is minimum.
• Gear box layout is very compact comparatively.
• Numbers of gears is minimum.

26. Created by Davis Hans S J for Jansons Institute of Technology
Step ratio
The ratio between the two adjacent
speeds is called as the step ratio or
progression ratio (ɸ).
N1, N2, N3, Nn be the adjacent speeds.
n is the maximum number of steps of
speed.
Then ,ɸ
� 2
�1
=
�3
�2
=
� 4
� 3
=…
��
��−1
=ɸ

27. Created by Davis Hans S J for Jansons Institute of Technology
Preferred structural formula
The structural formula helps to arrive
the number of stages and required
gears to obtain the desired speeds.
The maximum number of speed that
can be obtained from two shafts is
three.
Output Speed Structural Formula Stages
6
3 (1) 2 (3)
2 (1) 3 (2)
2
2
8
1 (1) 2 (2) 2 (4)
4 (1) 2 (4)
3
2
9 3 (1) 3 (3) 2
12
3 (1) 2 (3) 2 (6)
2 (1) 3 (2) 2 (6)
2 (1) 2 (2) 3 (4)
3
3
3
14
3 (1) 3 (3) 2 (5)
4 (1) 2 (4) 2 (6)
3
3
16
4 (1) 2 (4) 2 (8)
2 (1) 4 (2) 2 (8)
2 (1) 2 (2) 4 (4)
3
3
3
18
3 (1) 3 (3) 2 (9)
3 (1) 2 (3) 3 (6)
2 (1) 3 (2) 3 (6)
3
3
3

28. Created by Davis Hans S J for Jansons Institute of Technology
Kinematic Diagram
A kinematic layout is a pictorial
representation of a gearbox,
describing the arrangement of
gears. It provides information
like number of stages, number
of shafts used, number of gear
pairs and its arrangement.

29. Created by Davis Hans S J for Jansons Institute of Technology
Ray diagram
A ray diagram is a representation of
structural formula. It provides
information such as speed in each
stage, the transmission ratio in each
stage, The total number of speeds
and its values.

30. Created by Davis Hans S J for Jansons Institute of Technology