There are various types of differential suitable for a specific vehicle as they serve the purpose of transmitting the engine power to the wheels. In my previous post, the differential was explained to be a mechanism that transmits an engine’s torque to the wheels for the purpose of splitting the power, allowing the wheels to move at varying speed.
Today we’ll be looking deep into the various types of differential and their working principle.
Types of differential
The following are the different types of differential that can be found on automobiles:
- Open differential
- Locked differential
- Welded/Spool differential
- Limited slip differential
- Torsen differential
- Active differential
- Torque vectoring differential
Now let’s see their explanations!
The basic form of an open differential contains two halves of an axle with a gear on each end which is connected together by a third gear making up three sides of a square. Completing the square, a fourth gear is added to increase the strength. The strength is increased with the ring gear added to the differential case that holds the basic core gears. This ring gear warrants the wheels to be powered by connecting the drive shaft through a pinion.
The advantage of an open differential is to allow the axle to corner more effectively, which is achieved as the outside wheel of turn moves at a faster speed than the wheel inside as it covers the ground. Another benefit is that it is relatively cheap to produce and common. Disadvantages also occur in this type of differential as the torque is split evenly between both wheels. Because of this, the power transmitted to the wheels is wheel is limited by the wheel with the lowest amount of grip.
The locked type of differential is often found on a vehicle that goes off-road. It is basically an open differential with the effect of locking the axle in place to create a fixed one instead of an independent one. This effect can manually or electronically take place in the vehicle.
The advantage of a locked differential is to obtain an appreciable amount of traction than the open differential. This will be achieved because the torque is not equally split 50/50 to the wheel. More torque can be a channel to the wheel that has better traction.
One of the disadvantages of locked diffs is called binding, it happens when excess rotational energy (torque) is built up within the drive train and needs releasing. This release can be done when the wheels leave the ground the reset the position or by simply unlocking the axle when they are no longer needed.
The welded differential is quite similar to the locked type, only that it has been permanently welded from an open differential into a fixed axle. The welding of the fixed axle is purposely done in order to keep both wheels spinning simultaneously. Vehicles with such differential are meant for drifting.
The differential is not suitable for any other driving condition, as the welding already tampered with the component strength. it also increases the risk of catastrophic part failure which may result in broken differential gears exploding through the differential casing.
Limited Slip Differential:
This type of differential is abbreviated as LSD. It combines the benefits of both open and locked differential through a more complicated system. A different form of resistance is used to achieve the same in this differential. They are categorized into:
- Mechanical clutch LSD
- Viscous LSD
Mechanical clutch LSD
The mechanical clutch SLD contains the same core gearing found in the open differentials with a pair of pressure rings. The pressure rings exert force on two sets of clutch plates positioned beside the gears. This provides resistance to the independent rotation of the wheels, which changes the effect of the differential from open to locked. It also provides increased traction to it.
In this type of mechanical clutch LSD, the pressure rings surround the core gears, which are forced apart by the central gear pins. It pushes against the angled surfaces under rotation and pushes the pressure rings into the clutch park (yellow and blue) on either side. This generates resistance and changes the working of the axle open to a fixed effect.
The mechanical clutch LSD is further split into subtypes that function in different manners. They change when the pressure on the clutch plates and pressure ring is exerted. Below are the various types of mechanical clutch LSD:
- One-way LSD: the pressure is only exerted under deceleration, which means it behaves as an open type when cornering. This makes the wheel turn independently. But under acceleration, the clutch rotation of the differential creates friction in the clutch plates. This locks them in place in order to gain more traction.
- Two-way LSD: the pressure is also exerted on the clutch plates under deceleration. It helps to improve stability under braking on variable road surfaces.
- One and a half way LSD: it tries to combine the benefits of the subtypes, by exerting a good amount of pressure under acceleration and a lesser amount under deceleration.
The viscous is the second type of limited-slip differential that uses a thick liquid in replacement of the clutch to create the resistance needed to change the differentials working between open and locked. This type is simpler because it has fewer moving parts than the mechanical LSD.
The working is smoother in the application, as the resistance builds in unison with the wheel’s speed, providing a very gradual increase. The viscous LSD transfers torque more effectively to the wheel that has more traction. This is because the fluid acts as resistance under speed. if a wheel ever loses traction and spins the difference in speed between the two wheels inside the differential. It creates more resistance on the slower-moving wheel by channeling more torque from the driveshaft to it.
The disadvantage of this type that makes its use limited is that the fluid heats and becomes less viscose leading to less resistance. It also cannot lock fully as the mechanical LSD because the fluid is unable to provide absolute resistance within an adequate space.
the Torsen differential uses a bright gearing to produce the same effect as the limited-slip differential. However, it does not work with either clutches or fluid resistance. Instead, a layer of worm gearing is added to a traditional gear setup of an open differential. The sets of worm gears acting on each axle provide the resistance required to enable torque transfer. This is achieved by having the worm gears in constant mesh with each other through a connected spur gear.
The constant mesh between the two sides of the differential helps in transferring the torque immediately. This makes it more sensitive while changing road and driving conditions. The Torsen differential is also capable of directing a high percentage of torque to one wheel depending on the gear’s rate. Unlike the open differential that has to split its torque equally between the wheels.
In the Torsen differential, the gearing can be machined in a way the different ratio of resistance will impact when accelerating and decelerating just like the one-and-half of a limited-slip differential. this is achieved mechanically without the use of electronics or any other evaporative form. The Torsen differential is the best mechanical system that has all the qualities of other differential listed in this post.
The active type of differential is very similar to the limited-slip differential as it still employs mechanisms. The mechanism is used to offer the resistance needed to transfer torque from one side to another. Clutches are electronically activated instead of relying on purely mechanical force.
Active differentials use electronics to artificially change the mechanical forces the system is facing through the changing driving conditions. This is why they are controllable and hence programmable. With sensors on such vehicles, a computer can automatically detect which wheels to transfer power to and when it should be transferred.
These types of differential are good in performance, especially on bad roads, and help to improve cars that endure rapidly changing driving conditions. But this will be a system that can keep up their continuous adjustments to the vehicle.
Torque Vectoring differential:
The torque-vectoring type of differential also uses an electronically enhanced system and even use it to change the angle or vector of the vehicle. It encourages specific wheels to take more torque when needed which improves its cornering performance. When an opposite clutch is activated, that which is purely mechanical driven LSD would normally engage, can be used to assist with steering. While also putting more power down, overcoming the deficiencies in the LSD system.
In the corner of this differential, a multi-way LSD exerts resistance to both wheels till the axle partially locks. And also stabilizes it under braking, which is then released as the wheel speed drops and the vehicle turns in. This allows the wheels to rotate at different speeds. But, instead of releasing the resistance on both wheels, a TVD will continue to apply the clutch on the outside wheel only. This increases the resistance experienced by the wheel and makes the system channel more torque to it. An imbalance of power will cause to the outside, making the vehicle take a sharp corner and reducing understeer.
When the resistance is experienced continually through the corner, as the vehicle passes the apex and begins to accelerate out, it will continue to override a normal multiway-LSD. This would again interpret the faster move outside wheel as slipping and diverting torque during acceleration to the inside wheel as it perceives having more grip.
The TVD exerts more resistance onto the outside wheel clutch, the system is tricked to divert more torque through it. this is achieved by increasing the amount of power that can be applied and reducing the understeer experienced under acceleration out of a corner.
Torque vectoring differentials are capable of transmitting 100% of the available torque through a single wheel. This is only when it needed the torque in the most extreme circumstances.
The limitation of this TVD is that it’s very complicated and very expensive and is typically used for racing/track applications for its high-speed cornering potential.
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All types of differential have their own advantages and disadvantages, I hope you now know the various differential types. If you have any questions kindly ask via the comment box and please share this article with other technical students. Thanks!