All about Differential Gearbox

 

What is a differential gear box:  Differential gear, in automotive mechanics, gear arrangement that permits power from the engine to be transmitted to a pair of driving wheels, dividing the force equally between them but permitting them to follow paths of different lengths, as when turning a corner or traversing an uneven road. On a straight road the wheels rotate at the same speed; when turning a corner the outside wheel has farther to go and will turn faster than the inner wheel if unrestrained.

 

What is the function of differential:  The differential is a system of gears that allows different drive wheels (the wheels to which power is delivered from the engine) on the same axle to rotate at different speeds, such as when the car is turning. A differential is also the component through which a rotating driveshaft can change direction; for example, in a rear-wheel-drive car whose driveshaft runs the length of the car, it joins and transfers its power to an axle that runs perpendicular to the car to drive the left and right wheels.

 Differentials are low-maintenance, sealed components that are expected to last the life of the vehicle but may have a recommended service interval to check and/or replace the oil. Note that a car with four-wheel drive can have two or more differentials. A failing differential can cause vibration, binding during turns and/or sounds ranging from clunking to howling.

§  How does differential works:  

 

§  When driving straight: The engine drives the differential cage. The planetary gears are stationary at this time. As a result, the cage and the two output shafts all turn at the same speed. This means that the two wheels on the axle also turn at the same speed.

§  https://www.youtube.com/watch?v=nC6fsNXdcMQ.

§  When driving around curves:   Now the outer wheel on an axle has to cover a longer distance, so the two output shafts have to turn at different speeds. To achieve this, the planetary gears in the differential rotate around their own axes at different speeds. This balances out the difference in the speeds of the two wheels.

 

 

The need of differential gearbox:

When a vehicle travels in a straight line, the two rear wheels turn on the road exactly at the same speed and there is no relative movement between two rear wheels.
But when vehicle takes a turn the outer wheel travels on a longer radius than the inner wheel. The outer wheel turns faster than inner wheel i.e. there is relative movement between two rear wheels. If two rear wheels are rigidly fixed to a rear axle, the inner wheel will slip, which will cause rapid tire wear, steering difficulties and poor road holding. Therefore there must be some device, which will divide the input torque of the transmission system between two rear axles. Differential serves this purpose.

Differential gearbox Location:

Location in a different type of vehicle layouts-

1. In Front-engine front-wheel-drive layout – differential is located at the front next to gearbox.
2. In Rear engine rear-wheel-drive layout – differential is located at the rear next to gearbox.
3. Four wheels drive layout – differential is located at the front as well as rear.
4. Front engine rear-wheel-drive layout – it is located at the rear in between two half shafts.

Principle of differential-

If a vehicle travels in a straight line, the two rear wheels turn exactly at the same speed, and there is no relative movement between them. But when the vehicle takes a turn the outer wheel travels a longer radius than the inner wheel i.e. there is relative movement between the two rear wheels. The outer wheel turns faster and covers a larger distance than the inner wheel. The inner wheel makes a larger angle than the outer wheel. thus the vehicle negotiates the turn safely.

TYPES OF DIFFERENTIAL

There are three types of differential:
(a) Conventional type,
(b) Non-slip or self-locking type, and
(c) Double reduction type.

a) Conventional Type

Conventional type differential described in Section 5.6 delivers the same torque to each rear wheel. If any of the wheels slips due to any reason the wheel does not rotate and the vehicle does not move.

b) Non-slip or Self Locking Type

Non-slip or self-locking type differential overcomes this drawback. It construction is similar to that of conventional type differential. But, two sets of clutch plates are provided additionally. Also, the ends of planet shafts are left loose in notches provided on the differential cage.

c) Double Reduction Type

Double reduction type differential provides further speed reduction by additional gear. This type of differential is used in heavy-duty automobiles which require larger gear reduction between engine and wheels.

Advantages of Differential Gearbox: 

1) Both driving wheels can rotate in the same direction at the same speed.
2) Both driving wheels can rotate in the same direction at different speeds.
3) Both driving wheels can rotate in the opposite direction at the same speed.
4) Both driving wheels can rotate in the opposite direction at a different speed