What is Differential?
Types of Differentials, Function & How They Work

A differential system can be regarded as a system whose primary function is to transmit an engine’s torque to the wheels. The differential works with the help of the power it takes from the engine and then splits it, which in turn gives the wheels the freedom to turn in different speeds. When on a turn, the outside wheel is observed to travel farther and faster than the wheel which is inside. The differential thus plays an important role as it is a set of gears that is behind the transmission of engine power to the wheels, hence leveraging them to turn at varying speeds approaching a turn.

When considering front-wheel-drive (FWD), the differential placement is such that it is in same direction as of the transmission present inside the housing, and this whole unit is widely regarded as a transaxle. Whereas incase of rear-wheel-drive (RWD), the differential is situated in between the pair of rear wheels, in direct connection with the transmission with the help of a driveshaft. In the case of All-wheel-drive (AWD) and four-wheel-drive (4WD) vehicles, there is an additional setup of Centre differential or transfer case which helps in distribution of power in front and rear.

Battery Electric Vehicle

OPEN DIFFERENTIAL

This complete unit system then further gets an addition of a ring gear to the differential case, the main function of which is to hold the basic core gears in correct position and this ring gear arrangement thus results in the wheels which are to be driven by the drive shaft using the pinion. These are referred to as a type of gearing arrangement which is found in open differential system and is thus considered as the most common type of automotive differential system. This is responsible to form the base for various diverse and complicated set of systems.

The advantage of such type of unit is found to be quite similar to any other differential which is described previously. Keeping a focus on aiding the axle to corner more efficiently by allowing the wheel on the outer side of the turn in order to run it at a speed which is observed to be faster as compared to the inside wheel as it has to cover more ground. One additional benefit of this unit system is that it is found to be comparatively cheaper to the manufacture.

At the same time the system has certain demerits which is that because of an even split of torque within both the wheels, the quantity of power which can be carried forward by the help of the wheels is found to be limited only to the wheel which has the lowest amount of grip on offer.

Full Hybrid Electric Vehicle

LOCKED DIFFERENTIAL

The locked or locking differential is referred to as a type of differential system which is found to be more popular on those vehicles that go off road more frequently primarily. These differentials are considered as an open differential but along with an additional advantage of having it locked in place, if need be, to make it function as a fixed axle rather than an independent one. This is found being happening to either manually or even electronically subject to the technology on the vehicle.

The main advantage of a locked differential is found to be that it is highly prone to develop in order to gain a considerably higher amount of traction which is compared simultaneously with an open differential. As the distribution of the torque in this type of system is not found to be equally 50/50, which can possibly transfer more torque to the wheel that experiences a slight better traction out of the two which are available which is not handicapped by the lower traction that is present on the other wheel at any given point of time.

As it is highly rare for the user who is found travelling at a greater velocity wherein the user is usually found travelling over those surfaces which are found to be rough as well as uneven. There are various problems like wear around the corners on a fixed axle wherein the tyre is found being dragged and thus are less of an issue.

Plug-in Hybrid Electric Vehicle

LIMITED SLIP DIFFERENTIAL

LSD’s is found working in such a way that they are found to add up the advantages of both open as well as locked differentials through a system which is to be simply put, rather cannot be that complicated. These are referred to as the type of LSD functions which work on the same principle of core gearing that is found being seen in the open diff which usually comes accompanied with a pair of pressure rings. The main function of this LSD is to exert the force on both sets of the clutch plates which is found to be positioned in a way that is parallel to the gears. Mechanical Clutch LSDs are the ones which are found to be split further into subtypes that function in a bit different way and is subjected to change when there is observed a pressure change on the clutch plates:

Considering the case of a one-way LSD, the pressure is found to be exerted only at that particular moment when it is found undergoing acceleration. This leads to a conclusion that while performing any operation of cornering and getting off the power, the diff functions as an open type differential, which is responsible for allowing those wheels to independently turn – whereas whenever the force of acceleration is being experienced, the forced rotation of the differential results in friction amongst the clutch plates which leads to locking them in their place in order to gather more traction.

A Two-way LSD is a method which seems to be similar to a one-way LSD and it goes one up and characteristically exerts more pressure on the clutch plates even when they are undergoing deceleration. The main aim of this LSD is to improve the stability under the situation of braking on variable surfaces of road.

Mild Hybrid Electric Vehicle

ACTIVE DIFFERENTIAL

Being more or less similar to a limited slip differential, the active differential ends to work on certain mechanisms so as to provide the system with the required resistance for the further transfer of torque from side to side, but instead of relying on forces which are purely mechanical, these clutches can also be activated electronically.

This active differential is highly capable of making the use of electronics to artificially change the mechanical forces the system is undergoing by changing the conditions of driving. This makes them programmable and henceforth controllable, and with the help of a range of sensors present across the vehicle, a computer can on itself detect which drive wheels and when it requires power.

This improves performance drastically, especially overroad surfaces which are not good, and is particularly used in rally cars which have to endure rapidly changing conditions of driving and require a system that can maintain itself with continuous adjustments the vehicle undergoes.

Fuel Cell Electric Vehicle

TORSEN DIFFERENTIAL

The Torsen (Torque – Sensing) differential makes the use of some particularly clever gearing to function properly and reciprocate the similar effect which is found in a limited Slip Differential without in return making any sort of use of clutches or fluid resistance.

It successfully attains this by addition of a worm gearing layer to an open differential’s traditional set up of gear. These sets of worm gears which are acting on both of the axle provide the required resistance to open up the torque transfer, which then is successfully achieved by the worm gears in mesh (constant) with each other with the help of spur gears which are connected.

Also, an open differential characteristically always has a tendency to split its torque 50/50 between each of its wheel, due to its high capability of directing a considerable higher percentage of torque through one wheel varying on the ratios of the gears, torsion differential is very useful.

Extended Range Electric Vehicle

TORQUE VECTORING DIFFERENTIAL

The Torque Vectoring Differential is considered to be an even more advanced electronically enhanced system which can further even alter and manipulate the angle/dynamics/vector of the vehicle in and out of the turns by permitting only certain specific wheels to achieve more torque at key moments –thus leading to an improved cornering performance.

When approaching a corner, what a multi-way Limited Slip Differential does is that it applies resistance on both the wheels so that it locks the axle partially and stabilizes it while the operation of braking – which soon after that is released as the speed of the wheel slowly drops and the vehicle turns in, permitting the wheels to rotate at different velocities.

However, rather than releasing the resistance on both the wheels, what a TVD does is that it continues to apply the clutch on the wheel present outside– thus increasing the resistance being faced by that particular wheel and making the channel transfer more torque through the same. This resultant power imbalance is the reason behind the vehicle sharp turning into the corner and in return reducing the phenomenon of understeer.

Why You Need a Differential

Car wheels spin at different speeds, especially when turning. You can see from the animation that each wheel travels a different distance through the turn, and that the inside wheels travel a shorter distance than the outside wheels. Since speed is equal to the distance traveled divided by the time it takes to go that distance, the wheels that travel a shorter distance travel at a lower speed. Also note that the front wheels travel a different distance than the rear wheels.

For the non-driven wheels on your car - the front wheels on a rear-wheel drive car, the back wheels on a front-wheel drive car - this is not an issue. There is no connection between them, so they spin independently. But the driven wheels are linked together so that a single engine and transmission can turn both wheels. If your car did not have a differential, the wheels would have to be locked together, forced to spin at the same speed. This would make turning difficult and hard on your car: For the car to be able to turn, one tire would have to slip. With modern tires and concrete roads, a great deal of force is required to make a tire slip. That force would have to be transmitted through the axle from one wheel to another, putting a heavy strain on the axle components.

Courtesy of Engineering Learn.com

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