How does a car rear differential work ?

Educational

Mar 21st, 2019

How does a car rear differential work ?

Have you ever looked at that thing which is located on your car’s rear axle? Yes, we are referring to those ball of gears which give you the ability to round the corner? Has it ever come up in your mind to try to figure out how it works? Well, this article is here to explain everything to you about how a rear differential works.

The truth is that there are many experts out there who are great art mechanics and have been involved in many car projects that believe that a differential is a more alien technology than of human invention. It works almost like magic, and many people cannot fathom how human minds could have come up with such an intriguing invention. Well, of course, we know that referring to the differential as an alien invention is kind of an exaggeration but if you really think about it, do you really understand how the differential works? 

We engage in learning every day, and this time around, it is time to get into another learning session as we will be going into the intricacies of the differential of a vehicle and how it functions. We will be taking the basics of the differential in order to make you understand the mechanics behind this great invention. 


Why the differential was invented

The reason for designing the automatic differential is quite obvious. The purpose is to be able to transfer power to a car’s wheels while giving the wheels the ability to spin at varying speeds. This happens to be a very important addition to any vehicle since the four tires of any car rotate at varying speeds each time a turn is negotiated. For you to be able to arrive at your intended destination, the wheels of the vehicle will have to travel at different distances as you make your way through the bend. Your vehicle’s inside wheels spin slower than the wheels which are on the outside since they have to complete only a short distance while making a turn. This means that they have to rotate more slowly than the outside wheels.

What the differential mechanism does is to give the individual wheels the ability to spin on their own while giving them the needed power. Assuming the wheels on the left hand, as well as, the wheels on the right hand of your car are joined together with the use of a solid axle, your car’s wheels would end up skidding when you try to take make a turn. In virtually all cars manufactured in recent times, as well as, trucks you will find a differential. Then again, a lot of full-time 4WD cars come with a differential. The reason that these AWD cars require a differential between the drive wheel sets, as well as, between the wheels in front and in the back is down to one fact which is that the wheels at the front happen to travel at a distance that is different from the rear wheels as you negotiate a bend.

However, in a part-time four-wheel drive vehicle, you will not find a differential placed between the wheels in front and the wheels at the back. Rather, they happen to be locked together causing the wheels in front and the wheels at the rear to have a similar average speed while turning. This is the reason that part-time four-wheel drive cars happen to be more difficult to navigate at a bend when you activate the 4 wheel drive system.

Basically, we refer to the differential as that component which equalizes the travel distance that exists between the inside wheels and the outside wheels whenever you take your car around a bend. You will find the differential lodged in its own separate case in a rear wheel drive vehicle. Today, many vehicles, as well as, trucks have a differential.


What the differential does

If cars were only driven in straight pathways, then, it will be totally useless to have a differential for your vehicle. Well, you know that it is quite impossible to only drive your car in a single direction. There are times when you must navigate a bend, go around corners, and negotiate a turn and this is where the importance of a differential is made very obvious. Your vehicle's wheels have different rotational speeds when you try to make a turn. We have mentioned earlier that the inside wheels of your car travel at a distance that is much shorter when compared to the outside wheels of your car as you negotiate a bend. What this implies is that your car’s inside wheels will have to travel slower than the outside wheels and without a differential to balance the differences in speed, it will be incredibly difficult to complete a turn.

For cars that have non-driven wheels, this problem does not exist since the wheels all spin independently and are not in any way connected to each other. However, when it comes to driven wheels, a differential has a very essential role to play. The wheels are linked to one another and are controlled by just one engine, as well as, transmission. If a differential is absent, it means that these wheels will have to be linked together to travel at exactly similar speeds and exactly similar distances and this will make it a very difficult task for you to turn your car. 

So, basically, a differential works by performing three key functions which are –

  • It is responsible for sending the power that is generated from the engine to the car’s wheels
  • Performs the task of slowing the transmissions rotation speed just before the wheels receive it.
  • It divides the power that is sent to the car’s wheels from the engine while still allowing them to spin individually.

A differential mechanism simply involves dividing the power which the wheels receive while enabling them to rotate at their individual speeds. Therefore, in the event that a particular set of wheels roll slowly and cover only a short distance, the other set of wheels will continue to rotate and not skid with the aid of the differential. This helps to prevent tire shredding, as well as, loss of torque. 


COMPONENTS OF A DIFFERENTIAL

In this section, we will be considering the different parts which make up a differential. In a standard differential, here are the components that you will find –


  • Differential Case

The differential case is the unit’s main body. Inside the case, you will find the spider gears. In fact, the differential of your car is housed in this casing.

  • Differential Gears

The differential gears are, also, referred to as spider gears. It is the responsibility of the spider gears to transmit power to your vehicle’s axle shafts. The principal reason that differential gears are included is to prevent wheel slips. Wheel slips usually occur at the point where you try to make a turn. For example, if you decide to attempt to turn your vehicle left, the inside wheels of your vehicle will experience slips. The difference in the rotational speeds of the inside wheels, as well as, the outside wheels is the reason that the slip occurs. That is to say that the inside wheel will have a slower rotation than the outside wheel.


So, you probably got it all figured out. It is the job of the differential to enable the wheels to have different rotational speeds via its gear arrangements. The differential gears split the power that is produced from one shaft evenly between both shafts while giving them the ability to rotate at their own individual speeds. So, when one shaft slows, the other immediately picks up speed. 


  • Differential Pin

It is the role of a differential pin to ensure that the spider gears are very much aligned. Also, provides two spider gears with an axis point. This helps for a more effective splitting of power between the wheels on the left and wheels on the right.


There are, also, other components that you can find right inside the axle housing. The axle housing is commonly referred to as Pumpkin Housing and here are the components that you can find –

  • Pinion Gear

These are the point where the drive line power from the axle house starts its internal transfer. Basically, when pairs of gears begin to mesh, the gear that is the smallest is referred to as a pinion gear. This gear, also, is that cylindrical gear in the rack and pinion mechanism which meshes with the rack. This mechanism is responsible for the transformation of rotational motion into the needed linear motion.


  • Ring Gear

On the differential case, you will find a gear that is bolted to it. This gear is the ring gear. It serves as the second point where the transfer of internally generated power takes place. The ring gear in a differential system is carved on a rim that has the shape of a ring. The ring gear is that large gear that is located in a vehicle’s differential which is powered by the pinion and is responsible for the live axle receiving power.


Ring and pinion gears share the responsibility of giving your vehicle's wheels the ability to roll forward or backward. This gear set comprises a ring that has grooves, and these grooves are linked to the rear wheel's axles. It is, also, made of a pinion that has grooves which are linked to your vehicle's front wheels.


  • Miscellaneous Hardware

Inside the housing, you will, also, find things like bearings, shims, as well as, bearing caps. It is the work of the bearing caps to ensure that the differential case stays in place. Then, the bearings ensure that every component has the freedom of movement. As for the shims, they are very much needed in order to set the ring-and-pinion backlash. 

Now, let us discuss the different kinds of differentials and how they operate.


HOW REAR WHEEL DIFFERENTIALS WORK

Just like every other component that you’ll find on a modern car, the differential has continued to undergo innovations and refinements. This has resulted in the development of a wide range of differentials with each of them having their specific benefits and downsides. 

Basically, the differential has a very simple concept which is to give wheels that are fixed on one axle the ability to rotate at their own pace independently. According to history, the differential is not a new invention and was used in the first Millennium BC. Even if the differential was invented a long time ago even before automobiles came into existence, other means of movement such as wagons and chariots, also, experienced the similar difficulty of having one of the wheels slipping while trying to make a turn. This caused an increase in depreciation and lead to a rise in damaged roads.

With the invention of wheels that were powered by engines, this problem only multiplied. It was a dilemma figuring out the best way to power the two wheels while allowing them to rotate independently. This problem could not be fixed in the very first automobiles as issues with traction on an off-road proved to be an issue.

With time, the open differential was developed to tackle this problem. Let us talk about the open differential and how it works –


OPEN DIFFERENTIAL

The most standard and basic form of a differential is comprised of an axle that has two halves which both have a gear on their ends. These gears are linked by another gear, and there is usually a fourth gear that is used to supplement this makeup in order to provide extra strength. Then again, the ring gear is used to augment this unit by adding it to the casing that houses the core gears. Through a pinion, the ring gear connects to a drive shaft, and this enables your wheels to receive power. It is this arrangement that comprises the open differential. The is the most popular differential type for vehicles, and it is from it, but the other complicated differential systems are inspired.

Open differentials are designed in a way that they divide the power that is generated by the engine into two equal parts and sends each part to the two wheels linked to it. Where any wheel loses contact with the surface or is on an off-road surface, the torque that is transferred to the other wheel becomes zero. That is to say that despite the fact that a high traction level is present on the other wheel, no torque will be sent to it. Once the combined traction limit for the two wheels is attained, you will notice that the wheel which happens to have the lowest traction level begins to spin. If that limit is reduced, even more, the wheel that already spins will have a much lower resistance.

Basically, this type of differential has a benefit which is limited. It mostly focuses on giving the axle the ability to corner better as it helps the wheel that is on the outside move faster in relation to the wheel that is on the inside. Then again, the open differential happens to be relatively cheaper to manufacture.

The downside that exists with the open differential is that since there is an even division of torque between the two wheels, the level of torque which can be sent through the wheels has a limitation that results from the wheel that has very low traction.

It is the limitations of the open differential that lead to the invention of other types of differentials which will be now highlighted.


Locking Differential

In some vehicles, you will find the locking differential. It is mostly used for cars that usually go off-road. You can liken it to an open differential that is equipped with a locking ability to produce an axle that is fixed rather than an independent axle. Based on the technology involved, this process is usually manual or automated.

A locked differential has its own benefits. It can produce a relatively higher level of traction when compared to an open differential. Since there is no even division of torque, it has the ability to send increased torque to any of the wheels that have more traction. If the other wheel seems to have no traction, it still does not limit this process. Then again, since you likely will not be traveling with so much speed due to uneven terrain, you are less likely to encounter the problems of tire depreciation around the fixed axle corners. 

The locking differential has its own disadvantage which is referred to as binding. If so much torque builds up and needs to be released, then, binding has occurred. To release the excess energy, the wheels need to lose contact with the ground for a position resetting. Also, you could release the locks if you do not need them.

Binding is created due to the different speeds at which the wheels move. It causes the axles to twist and mounts so much pressure on your vehicle's gears. However, since there are load and enhanced traction, it prevents the tires from slipping in order to release pressure. 


Spool Differential

Spool Differentials are similar to a locking differential. The only difference is that it is welded permanently into an axle that is fixed. This is usually carried out in special circumstances that require the desirable features of a locking differential. And instance is in vehicles which are meant for drifting. Experts do not really recommend this since the strength of the components can be compromised due to the heat that comes from welding. This may enhance the possibility of the failure of parts. 


Limited Slip Differential

A slip differential is built to fuse the desirable qualities of open differentials, as well as, locking differentials in a system that is very much complicated. There are two kinds of limited slip differentials –

  • Mechanical Clutch:

The mechanical clutch limited slip differential still surrounds a similar core gearing that you can find in the open differential that comes with some pressure rings. The core gearing exerts pressure on both clutch plate sets which you find alongside the gears. Thus, the independently rotating wheels become resistant, and the effect is transformed from an open differential to that of a locking differential. Also, increased traction is provided unlike in an open differential. This kind of limited-slip differential is subdivided according to how they behave with the exertion of pressure on your vehicle's clutch plates. 


The first one is the one-way limited slip differential where pressure exertion occurs only during acceleration. Therefore, when you turn a corner, the differential acts just like an open differential and lets your wheels rotate independently. However, when you accelerate, the first differential rotation leads to clutch plate friction, thereby, making them have more traction by keeping them locked in place.


For the two-way limited slip differential, it levels up the process by creating clutch plate pressure during deceleration too. This is done for stability enhancement while braking on various types of road surfaces.


The combination of both sub types results in the creation of the one-and-half way limited slip differential. 


Mechanical limited slip differentials have to be maintained very often and can easily depreciate rapidly. Thus, replacing its parts becomes expensive.


  • Viscous limited slip differential

In this limited slip differential, thick liquid performs the role of the clutches in creating resistance that is required for altering the open differential and locked differential behavior. Relatively, it has fewer parts that move when compared to the mechanical limited slip differential. It provides more advantages and disadvantages too.


Basically, its operation produces an effect that is very smooth when compared to mechanical limited-slip differentials. This is because the resistance that is created is unified with the level of wheel speed when compared to its differential case. This causes the increase to be gradual.


Viscous limited slip differentials have the ability to send torque a lot more effectively where there is more traction. Its fluid is speed resistance, and if a wheel happens to lose traction and spin, the speed difference that exists between both wheels in the differential leads to the creation of increased resistance on the wheel which moves slower. This channels more torque to that wheel.

As viscous limited-slip differentials continue to be used, their effectiveness reduces. With the heating up of the fluid, it loses its viscose property and begins to provide lesser resistance. Then again, it is unable to lock just like a mechanical limited slip differential. 


The downside of the just considered limited slip differential systems is that when cornering at a high speed, they do not transfer torque effectively every time. This is because it has a tendency to see the outside wheel that moves more quickly as a sign of traction loss. Then, more torque is transferred to the inside wheel causing over steer or under steer.



Torsen Differential

This kind of differential uses clever gearing for the production of a similar effect to a limited slip differential system. Torsen differential does not need clutches, as well as, fluid resistance. An extra worm gearing layer is added to the main gear set that is found in open differentials. The added gears act on the individual axles for the provision of resistance which is needed to activate the transfer of torque. This is achieved by constantly meshing the worm gears together through spur gears that are connected.

As both sides of the differential continue to mesh, it enhances the immediate transfer of torque which helps it respond rapidly to changes in road conditions, as well as, driving conditions. Unlike in open differentials where the torque is always shared equally among the wheels, Torsen differentials have the ability to send a greater amount of torque through a particular wheel based on gear ratio. This helps to eliminate the limitations of open differentials since the available levels of torque are not in any way inhibited by the traction of any of the wheels.

Additionally, it is possible to machine the gear in order to impart different resistance ratios as you accelerate and decelerate. All of these are implemented mechanically, and no electronics are needed, as well as, no part being sacrificed. in general, Torsen differential happens to be a mechanical system that is superior as it combines the top advantages of the differentials that we have just discussed above. 



Active Differential

The active differential has so many similarities with the limited slip differential. It makes use of mechanisms for the supply of resistance which is needed for torque transfer between both sides. However, it doesn’t rely just on the mechanical force as it makes use of clutches which may be activated via electronic means. This kind of differential uses electronics that are designed for the alteration of the mechanical forces which are being experienced by the system via varying driving conditions. 

Therefore, it is possible to control and program them. With the aid of certain sensors in your car, a computer can be used to determine the wheels which need power at particular points in time. This helps to enhance power, and rally drivers usually love these kinds of cars since they always have to change their conditions of driving.



Torque Vectoring Differential

The torque vectoring differential steps up the electronic system even more. It uses it for vector manipulation of your car as you make a series of turns. Basically, it helps to improve your cornering effectiveness by helping particular wheels to get higher torque at certain points in time. 

This assists you as you steer the vehicle while, also, creating more power which helps to overcome the downsides of the limited slip differential system. As you enter a corner, a limited slip differential that is multi-way give resistance to the wheels of your car in order to, at least, get the axle locked to an extent and keep it stabilized under braking. Then, it releases it with a drop in the speed of the tires as you turn in, thus, giving your wheels the ability to spin at varying speeds.

This time, rather than getting the resistance of the two wheels released, the torque vectoring differential will keep the outside wheel clutch activated. This helps to increase that wheel's resistance, thereby, causing more torque to be sent through it. Power imbalance created by this process helps to reduce under steer by allowing the car to make a sharper turn.

As more resistance is applied as you go through the corner, your car goes past the apex and will start to accelerate out. During this process, the multi-way limited slip differential will keep being overridden. As such, the outside wheel which moves faster will be interpreted to be experiencing a slip and torque will be diverted to the wheel that is on the inside since it is perceived to have a greater grip.

As the torque vectoring differential exerts more resistance on the clutch of the outside wheels, the system is deceived into torque diversion through it. This enhances the power level which is applied and helps to reduce understeer that occurs when you try to accelerate out from a turn. Torque vectoring differentials have the ability to channel the entire torque to one particular wheel in extreme circumstances.

The disadvantage that comes with the torque vectoring system is related to how expensive and complicated it is. Mostly, it is applied in racing cars due to its potential for cornering at very high speeds. 



CONCLUSION

 All rear wheel differential systems come with their individual benefits and downsides. However, you will notice that the more complicated the system is, the more superior it is, and this affects their cost in relation to simpler systems. When it comes to making a choice, the level of benefit that you can get from any of these systems relates to what you actually need a vehicle for and what you expect the differential of your vehicle to do in any particular situation.

.Did you learn from this article ? try how a four wheel drive works ? or how does a automatic transmission work