Types of gearbox notes PPT/PDF

GEARBOX

Gearbox is a speed and torque changing device.

It changes speed and torque between engine  and driving wheels.

The mechanism through which the driving torque of the engine is transmitted to the driving wheel is the gearbox.

PURPOSES/ FUNCTIONS OF GEAR BOX

It helps the engine to disconnect from driving wheels.

It helps the running engine to be connected to the driving wheel smoothly and without shock.

It provides the leverage between engine and driving wheels to be varied.

It helps the driving wheel to be driven at different speeds.

It gives the relative movement between engine and driving wheels due to flexing of the road springs.

TRACTIVE EFFORT

The torque available on the wheel produces a driving force which is parallel to the road known as “Tractive effort”.

TYPES OF GEARBOX

1.            Manual transmission

                i) sliding mesh gearbox

                ii) Constant mesh gearbox

                iii) Synchromesh gearbox

2.            Automatic transmission

                i) Hydromantic gearbox

                ii) Torque converter gearbox

3.            Epicyclical gearbox

SLIDING MESH GEAR BOX

Simple in construction, Simplest type of gearbox.

In this gearbox, spur gears are used.

It consist of following parts.

                1. output shaft 

                2.Low and reverse sliding gear 

                3. Second sliding gear

                4. clutch

                5. Input shaft

                 6. Clutch gear

                  7. Counter shaft drive gear

                8. Counter shaft

                9.Low speed gear

                10. Second gear

                11. reverse gear

                12. Reverse idler gear

                13. Gear shift fork

There are three gears (1,6 and 5) attached on the main shaft and four gears (2,3,4 and 7) are on the lay shaft.

The two gears on the main shaft (6 and 5) can be slide by a shifting yoke and mesh with the gears (3 and 4) on lay shaft.

Therefore it is called “sliding mesh gearbox”. A separated idler gear (8) is mounted on the idler shaft.

GEARS IN NEUTRAL

When the engine is running and the clutch is engaged, the counter shaft is driven by the clutch gear.

The clutch gear rotates in opposite direction to the counter shaft.

The low speed and high speed gears that are fitted on the transmission main shaft or gearbox shaft do not rotate because they are not engaged with any driving gears.

Therefore there is no motion transmitted from clutch to output shaft.

Hence the vehicle is stationary.

CONSTANT MESH GEARBOX

All gears are constantly mesh and dog clutches are used for engaging and disengaging the gears.

Helical and double helical gear teeth can be used for the gears.

This type gears having less damaging during meshing because the gear diameter are smaller with few numbers of teeth.

So this type has more defects when compared o synchronous type.

ADVANTAGES OF CONSTANT MESH GEARBOX OVER SLIDING MESH GEARBOX

Quicker gearing can be achieved

Only damage occurs on dog clutch teeth not teeth of gear wheels.

Synchronizing devices can be used for smooth engagement of gears.

Once the dog clutches are engaged there is no motion between their teeth but the power is transmitted through the sliding action on teeth on one wheel on those of other when the gear teeth are engaged.

To transmit the motion properly, the teeth are suitably shaped.

SYNCHROMESH GEARBOX

To simplify the operations of changing gears without the occurrence of clashes and their consequent damage, a synchromesh gearbox is used in different type of motor vehicles.

Helical gears are used

It has synchromesh unit instead of dog clutch.

The synchronizer helps to synchronize the speeds of two gears to be engaged.

ADVANTAGES

Gear changing is very much simplified

Less wear in gears

Quiet

DISADVANTAGES:

Design is very much complex

Initial cost is high

Quick change of gears occurs due to noise of crashing

TORQUE CONVERTER

Constructional features are similar to fluid flywheel.

The only difference is that it has an ordinary stationary member called “stator or reaction member”.

All the members have blades or vanes of specified shape.

But the operation is not similar.

In fluid flywheel same torque is transmitted as given by the engine shaft.

But the torque converter increases the torque in the ratio of about 2:1 to 3:1