The gear box allows engines to operate efficiently under different vehicle speeds by providing multiple gear ratios. It converts engine speed and torque for optimal performance and facilitates reversing. Common gear boxes include sliding mesh, constant mesh, synchromesh, planetary, and torque converter types. They increase or decrease torque and speed outputs to suit driving conditions and protect the engine from over-revving.
2. WHAT IS GEAR BOX
● The gear box is necessary in the transmission system to maintain engine
speed (or torque) at the most economical value under all conditions of vehicle
movement.
● An ideal gearbox would provide an infinite range of gear ratios, so that the
engine speed should be kept at or near that the maximum power is developed
whatever the speed of the vehicle.
3. PURPOSE OF GEAR BOX
● Provides speed and torque conversions because of the limitations of
internal combustion engines.
● Also facilitates change of direction of output shaft for reversing.
● Automotive gearboxes are used to reduce load on the engine by
manipulating torque and speed.
● They have the option to select one of several different gear ratios.
● Once the engine has reached number of revolutions per minute, it is
advisable to increase the gear to reduce the engine rpm to reduce wear on
the engine, allow more control, and greater speeds, better acceleration,
and better fuel economy.
● Most gearboxes are used to increase torque & reduce the speed of a
output shaft. This produces a mechanical advantage
● Automotive gearbox also have the provision to do the opposite Le. prov
increase in output shaft speed with a reduction of torque (overdrive)..
4. TYPES OF GEAR BOX
Types of Gear Box
➤ Sliding Mesh type gearbox
➤Constant Mesh type gear box
➤SynchroMesh type gearbox
➤Planetary type gear box
5. SLIDING MESH GEAR BOX
● The power comes from the engine to the clutch shaft and then to the clutch
gear which is always in mesh with gear on the layshaft.
● All the gears on the layshaft are fixed to it and as such they are all the time
rotating when the engine is running and the clutch is engaged.
● Three direct and one reverse speeds are attained on suitably moving the gear
on the main shaft by means of selector mechanism
7. CONSTANT MESH GEAR BOX
Constant Mesh type Gear Box
● In this type of gear box, all the gears are in constant mesh with the corresponding
gears on the layshaft. The gears on the main shaft which is splined are free.
● The dog clutch are provided which are free to slide on the main shaft. The gears
on the lay shaft are, however, fixed.
● When the left dog clutch is slide to the left by means of the selector mechanism,
its teeth are engaged with those on the clutch gear and we get the direct gear.
● The same dog clutch, however, when the slide to right makes contact with the
second gear.
● Similarly movement of the right dog clutch to the left result in low gear and
towards right in reverse gear.
9. SYNCHROMESH TYPE GEARBOX
● His type of gearbox is similar to the constant mesh type in that all the gears on the
main shaft are in constant mesh with the corresponding gears on the layshaft.
● The gears on the layshaft are fixed to it while those on the main shaft are free to
rotate on the same.
● Its working is also similar to the constant mesh type, but in the former there is one
definite improvement over the latter.
● This is the provision of synchromesh device which avoids the necessity of double
declutching. The parts which ultimately are to be engaged are first brought into
frictional contact which equalizes their speed, after which these may be engaged
smoothly.
12. EPICYCLIC/PLANETARY
Epicyclic/Planetary Gear Box
● It consists of two, three or even four epicyclic or planetary gear sets. A simple
gear set has a sun gear, about which planets turn around. These planet gear
are carried by a carrier and a shaft and are also in mesh internally with a ring
gear, which is also called annulus or internal gear sometimes.
● Different torque ratios i.e. speed ratios are obtained by making of the part
stationary. Similarly by locking two parts with each other, a solid drive i.e.
direct gear obtain.
