Differential gear Box – Diagram, parts, Types, Working, Advantages

Functions Of Differential gear Box.

When a four-wheeler (car) takes a turn, the outer wheel turns faster than the inner wheel. Thus, there is relative movement between the inner and outer wheel.

The function of the differential is to permit the relative movement between inner and outer wheels when vehicle negotiates (takes) a turn. The torque transmitted to each rear wheel is equal in this case, although their speed is different.

The differential is made up of a system of gears that connect the propeller shaft and rear axles. It is a part of inner axle housing assembly. The assembly consists of differential, rear axles, wheels, and bearings.

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.

principle of differential gear box
principle of the differential gearbox

Differential gearbox Diagram 

differential gear box diagram
differential gear box diagram

Construction of differential:

Major Components of Differential

The following main components are used in the differential assembly.
l. Drive pinion or Bevel pinion
2. Ring gear or Crown wheel
3. Differential case
4. Differential side gear or Sun gears
5. Differential pinions (or) Planet gears
6. Axle shafts or Half shafts
7. Pinion shaft or Cross pin (or) spider.
Figure. shows the basic parts of the type of differential used in rear-wheel-drive cars.
On the inner ends of each axle a smaller bevel gear called differential side gear is mounted. Two bevel gears are put together to mesh both driving and driven shafts at an angle of 90°. The differential case is mounted with two-wheel axles and differential side gears. The differential case has bearings that rotate two axle shafts. Then, the two pinion gears and their supporting shaft, called pinion shafts, are fitted into the differential case. Then, the pinion shaft meshes with the two differential side gears connected to the inner ends of the axle shafts.
The ring gear is bolted to a flange on the differential case. The’ ring gear rotates the differential case. Finally, the drive pinion is mounted. The drive pinion is assembled with the differential housing called differential case or carrier. The driver shaft is connected with the drive pinion by a universal joint and it meshes with the ring gear. So, the drive pinion is rotated when the drive shaft turns. Thus, the ring gear is rotated.
differential gear box working
differential gear box working

Working of differential gearbox :

1. When Running Straight:
When the vehicle moves in a straight line, the power comes from the propeller shaft to the bevel pinion which drives the crown wheel. Then it is carried to the differential cage in which a set of planet pinions and sun gears are located. From the sun gear it is transmitted to the road wheels through-axle half shafts. In this case, the crown wheel, differential cage, planet pinions, and sun gears all turn as a single unit and there is no relative motion between the sun gear and planet pinion. The planet pinions do not rotate about their own axis. The road wheels, half shafts, and sun wheels offer the same resistance to being turned and the differential gearing does not therefore operate. Both the road wheels turn at the same speed.
2. When taking a turn:
When the vehicle takes a turn, the inner wheel experiences resistance and tends to rotate in the opposite direction. Due to this the planet pinions start rotating about their own axis and around the sun gear and transmit more rotary motion to the outer side sun gear. So that outer sun gear rotates faster than the inner sun gear. Therefore the outer road wheel runs faster than the inner road wheel and covers a more distance.


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

1) 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.

2) 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.

3) 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.

Actual Practical Differential Gearbox Working Video : 

Differential Gearbox Animation Video : 

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

Some Questions related to Differential Gearbox 

1. What is the function of differential gears?


The function of differential gears:
1. To transmit the torque at the right angle in equal proportion when the vehicle moves straight ahead.
2. To differentiate the speed of road wheels while taking a turn.
3. Equal distribution of torque in all running situations.

2. What is a differential lock?


Differential lock:
If one of the rear wheels lying on soft mud or loose dirt and sand, while the other is on the solid ground. At that
time, the wheel which is on soft mud are having less resistance. The wheel lying on soft ground spins or rotates around
its own axis due to differential action, while the wheel on the solid ground is not driven and remains stationary. When
the differential locking is applied, the differential action is stopped and the whole torque is then applied to the
wheel which is gripping on the road.

3. State function of differential. 


The function of differential:
1. To transmit the power from the propeller shaft at the right angle to the axle shafts for moving the wheel.
2. To differentiate the speed of two rear wheels when the vehicle makes a turn, i.e. the outer wheel has to travel more distance than the inner wheel or the outer wheel has to run faster than the inner wheel.

More Resources /articles

Automobile Engineering Parts and System Notes , Article

Mechanical Subjectwise Basic Concept Notes ,Articles

Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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