Differential Gearbox

 

What is a Differential Gearbox?

A differential is a device, usually but not necessarily employing gears, capable of transmitting torque and rotation through three shafts, almost always used in one of two ways: in one way, it receives one input and provides two outputs—this is found in most automobiles—and in the other way, it combines two inputs to create an output that is the sum, difference, or average, of the inputs.

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In automobiles and other wheeled vehicles, the differential allows each of the driving roadwheels to rotate at different speeds, while for most vehicles supplying equal torque to each of them.

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.

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Functions of Differential Gearbox:

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.

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Parts of Differential Gearbox:

1. Differential Side Gear or Sun Gears-

The differential consists of a small bevel gear called differential side gear or sun gear. It is mounted on the inner ends of each axle. In this, two bevel gears are fixed together to combine both the driving and driven shafts at 90° angles.

2. Differential Case-

A differential case is attached with two-wheel axles and differential side gears. It is consists of bearings that rotate two axle shafts.

3. Pinion Shaft -

These are two pinion gears and their supporting shaft is called the pinion shaft. It is fitted in the differential case.

4. Axle Shafts-

The pinion shaft meshes with two differential side gears connected to the inner ends of the axle shafts.

5. Ring Gear or Crown Wheel-

The ring gear is also known as a crown wheel. It moves to a flange on the differential case. The ring gear rotates the differential case.

6. Bevel Pinion-

The drive pinion is also known as bevel pinion. It is assembled with a differential housing called a differential case or carrier. The driver shaft is connected to the drive pinion by a universal joint and it engages with a ring gear. Therefore, when the driver rotates the shaft the drive pinion rotates, and thus, the ring gear rotates.

7. Differential Pinions -

Planetary gears are used in the differential. Since the axles of the planetary gears rotate around the common axis of the sun and ring gear that coincides and rolls in the middle of the differential system.

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How Differential Gearbox Works?

The power from the engine is transferred to the ring gear through a pinion gear. The ring gear is connected to a spider gear, which is at the heart of the differential system. The spider gear is free to rotate in two different ways, one along with the ring gear and two on its own axis. The spider gear meshes with two side gears, so power from the engine flows from the pinion to the left and right wheels. Let’s consider some cases.

The vehicle moves straight: In this case, spider gear rotates along with the ring gear but it does not rotate on its own axis. Spider gear will push and make the side gears turn, and both will turn at the same speed.

The vehicle is taking a turn: Spider gear plays an important role here. Along with the rotation of the ring gear, it rotates on its own axis. So the spider gear is having a combined rotation.

When properly meshed side gear should have the same peripheral velocity as that of the spider gear. When the spider gear is spinning as well as rotating, peripheral velocity as the left side of spider gear is the sum of spinning and rotational velocities.

But on the right side, it is a difference between the two. Or left side gear will have higher speed compared to the right side gear. This is how the differential manages to turn the left and right wheels at different speeds.

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Types of Differential Gearbox:

1. Conventional Type-

Conventional type differential 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.

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.

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Wrapping It Up:

As far as we discussed, the differential is used to drive a pair of wheels while providing them to rotate at different speeds. This mainly gives proportional RPM between the left and right wheels.

So now, we hope we’ve covered everything about the Differential and Types of Differential Gearbox. If you have any questions or doubts about this blog, you can ask in the comments. If you liked this article, then please share it with your friends.

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Blog By :S. Y. Mech Div. - B Batch 2_Group 3

1. Kashyap Kadam

2. Sahil Kadu

3. Prajwal Kakade

4. Anjali Kale

5. Dhruva Kale

6. Shardul Kandarkar