2. Gear box is to maintain engine speed on all conditions of load
and vehicle speed, the gear box uses a system of leverage of
keeping the speed of engine up while scarifying some road
speed.
Types of Gear boxes
1) Sliding mesh gear box
2) Constant mesh gear box
3) Synchromesh gear box
a) Three speed gear box
b) Four speed gear box
4) Preselective gear box
5) Epicyclical gear box
6) Auxiliary gear box
7)The freewheel drive
8)Five speed gear box
4. Sliding mesh…
It is the oldest and simplest form of
gear box.
In order to mesh gears on the splined
main shaft with appropriate gears on
the lay shaft for obtaining different
speeds, they are moved to the right or to
the left.
Splines are provided on the main
5. Sliding mesh….
For meshing the pinions with the
mating gears on the lay shaft, the pinions
are slided along the spine.
When the main shaft is driven from the
lay shaft the gear reduction is provided
by the first pair of gears which are always
in mesh.
They are usually known as constant
mesh gears.
6. 2) Constant mesh gear box 1)I speed gear
2)II speed gear
3)main shaft
4)III speed gear
5)top and III speed
engaging dogs
6)top gear
7)primary shaft or
main drive gear
8)counter
shaft/cluster gear
7. Constant mesh…
All the gears whether of the counter
shaft or the main shaft are in constant
mesh with each other.
It also known as a silent or quite gear
box.
It gives a quiteter operation and makes
gear changing easier by employing
helical gears for the constant mesh.
8. Constant mesh….
In constant mesh gear box generally
four or more pairs of gears and two or
more sliding coupling members are
there.
The coupling member is mounted as
well as slided on the splined teeth
machined gear box main shaft.
A selector fork fitting in to a groove in
the coupling member moves the sliding
10. Synchromesh…
To bring the speeds of both the engine
driven and the gear box out put shaft
driven gears which are to engaged to the
rotational speeds for moving their dog
clutches or their equivalent meshing units
in to engagement readily and quietly.
The gear wheel s which are to be
positively connected are first brought in to
frictional contact and when the friction has
equalized their speeds, the positive
connections are made.
11. Synchromesh….
The basic requirements are
A braking device such as cone clutch.
To permit easy meshing means of
releasing pressure on the clutch before
engagement of gears.
12. a) Three speed gear box 1)Main shaft
2)Planetary gear shafts
3,4,7)Internal gears
(5) poking spring
(6) gear regulating ring
(8) Gears
(9) planetary gear shafts
(10) main shaft
(11) planetary gears
(12) fixed internal gear
(13) intermediate gear
disk
(14), (15), (17)
planetary gears
13. Three speed….
It is simple form of gear box in which
engaging of gears is done by means of dog
clutch.
All the three forward speeds are
synchromesh.
In this case the teeth of the sliding member
engage with corresponding teeth on the fixed
position rotating member.
To engage the dog clutch with the
corresponding dog member on the engine
driven shaft it is slide along the splined gear
shaft.
A special hub provides the first(low) gear.
15. Four speed…
For better performance in comparison to
the three speed type gear boxes, many of the
lower powered cars are necessarily using a
four speed gear box.
With comparison three speed gear box in
the driving car, it fails to climb a hill on top
gear while on a slightly lower gear ratio
would climb easily.
18. Preselective…
•It is developed type of gear box used in
Daimler and armstrong siddelely cars.
•It employs wilson pre selective gear
principle.
•In this gear box the gear lever is dispensed
with and is replaced by a small lever mounted
on the steering wheel.
19. Preselective….
•The gear control lever provided moves in an
arc to marked position relating to reverse ,
neutral, first, second, third and fourth or top
speeds.
•The control lever is moved to the required gear
position marked on the steering wheel selector
by hand for changing from one forward gear to
another gear above or below it.
21. Epicyclical…
•Epicyclic gear box is known as planet gear box.
•These were initially fitted to Lanchester and the ford
cars.
Advantages of Epicyclic gear box
In these gear boxes, no dog clutches or sliding
gears are used because the planetary gears are in
constant mesh.
External contracting had brakes or multiple
clutches of relatively small dimensions are used for
making gear changes.
22. Epicyclical….
In stead of having the load only on a pair of gears,
it is distributed over several gear wheels.
To distribution of loads, a greater area of gear
tooth contact can be used by this gear box.
In comparison three speed or four speed gear box,
gears and gear housings of this gear box can be
made smaller in overall dimensions.
It provides a more compact unit operating about a
common central axis because the epicyclic gears
operate within an annuals or ring gear with its
external surface of cylindrical form.
25. Auxiliary….
An auxiliary gear box in order to form single
construction is either made as an entirely
separate unit or is built on or attached to the
main gear box.
It is generally used by providing two gear
ratios.
On e ratio is used in vehicles for “off the
road “ while the other is used for cross
country use.
27. Freewheel..
The free wheel drive is based on the
principle similar to that used on a bicycle.
It transmits a driven in one direction only,
it is known as a unidirectional or one way
clutch.
It is designed as a separate main unit.
It consist of no of rollers.
29. . Five speed…
It is mixed type of gear box having first and
second speeds provided by sliding mesh gears
and others provided by constant mesh gears.
It has a shaft coupled to the driven shaft of
the clutch with a pinion integrally attached to it.
The lay shaft having four gears splined to it is
driven by the pinion.
The main is supported differently at the
centre and the left as well as at the right.
