The Different Types of Differentials
There are four common types of differentials. If you ever heard a mechanic talk about a differential or this is the first time you are hearing about it, we understand it is a part of vehicles not often discussed. We will be covering what a differential is and the different types. Keep reading to learn more about it.
What is a differential? Connecting the wheels together, a differential takes power from the engine and sends it to the wheels. Different types control how much or little power makes it to the wheels. There are four common types of differentials on the market – open, locking, limited-slip and torque-vectoring.
What are the four types?
Open differential – As one of the more common types of differentials which is found in most family sedans and economy cars, the open differential splits the engine torque in two and allows the wheels to rotate at different speeds.
Locking differential – Also known as a welded differential, this connects the wheels, so they go at the same speed. This made turning a little more difficult. Most full-sized trucks have this type of differential. There are three types of locking differentials.
Automatic lockers – Automatic lockers lock and unlock automatically with no direct input from the driver. Some automatic locking differential designs ensure that engine power is always transmitted to both wheels, regardless of traction conditions, and will "unlock" only when one wheel is needed to spin faster than the other during cornering.
Selectable lockers MRT – Selectable lockers allow the driver to lock and unlock the differential at will from the driver's seat.
Spool – A spool is a device that connects the two axles directly to the ring gear. There is no differentiation side to side, so a vehicle equipped with a spool will bark tires in turns and may become unmanageable in wet or snowy weather. Spools are usually reserved for competition vehicles not driven on the street.
Limited-slip differential – Found in sports cars, the limited-slip differential acts like an open differential by default. Once a wheel loses traction, then it shifts to act as a locking differential so there is more traction and control on the road. A limited-slip differential (LSD) is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts. Limited-slip differentials are often known by the generic trademark Posi traction, a brand name owned by General Motors. Several types of LSD are commonly used in passenger cars.
Fixed value – In this differential the maximum torque difference between the two outputs, Trq d , is always a fixed value regardless of torque input to the differential or speed difference between the two outputs. Typically, this differential used spring-loaded clutch assemblies.
Torque sensitive (HLSD) – These limited-slip differentials use helical gears, clutches or cones (an alternative type of clutch) where the engagement force of the gears or clutch is a function of the input torque applied to the differential (as the engine applies more torque the gears or clutches grip harder and Trq d decreases).
Speed sensitive – Speed-sensitive differentials limit the torque difference between the outputs, Trq d , based on the difference in speed between the two output shafts. Thus, for small output speed differences the differential’s behavior may be close to an open differential. As the speed difference increases, the limiting torque increases. This results in different dynamic behavior as compared to a torque sensitive differential.
Electronically controlled – An electronic limited-slip differential will typically have a planetary or bevel gear set like that of an open differential and a clutch pack like that in a torque sensitive or gerotor pump-based differential. In the electronic unit the clamping force on the clutch is controlled externally by a computer or other controller. This allows the control of the differential’s limiting torque, Trq d , to be controlled as part of a total chassis management system. An example of this type of differential is Subaru’s DCCD used in the Subaru WRX STi. Another example is the Porsche PSD system used on the Porsche 928. A third example is the SAAB XWD (Haldex Generation 4) with eLSD, it uses a common (electronically controlled via the vehicle computer network) hydraulic power pack to control both the longitudinal and transversal torque transfer of the XWD system. The same Haldex system is used on several other GM Epsilon based vehicles such as the Cadillac SRX etc.
Torque-vectoring differential – With added gear trains, the torque-vectoring differential can fine-tune the amount of torque delivered to each wheel. Torque vectoring is a technology employed in automobile differentials that can vary the torque to each half-shaft with an electronic system. This method of power transfer has recently become popular in all-wheel drive vehicles. Some newer front-wheel drive vehicles also have a basic torque vectoring differential. As technology in the automotive industry improves, more vehicles are equipped with torque vectoring differentials. This allows for the wheels to grip the road for better launch and handling.
Front/rear wheel drive – Torque vectoring differentials on front or rear wheel drive vehicles are less complex yet share many of the same benefits as all-wheel drive differentials. The differential only varies torque between two wheels. The electronic monitoring system only checks two wheels, making it less complex.
All-wheel drive – Most torque vectoring differentials are on all-wheel drive vehicles. A basic torque vectoring differential varies torque between the front and rear wheels. This means that, under normal driving conditions, the front wheels receive a set percentage of the engine torque, and the rear wheels receive the rest. If needed, the differential can transfer more torque between the front and rear wheels to improve vehicle performance.
Here is a video by Yukon Gear & Axle that helps explain which Traction Device is right for you.
Tate from Yukon Gear and Axle goes over the different types of traction devices and highlights the advantages and applications for the different types of differentials.
Here is a video by Allegroracing that explainshow a Differential works and types of differentials.
How a Differential Works and Types of Differentials
by: Allegroracing
Desert Wranglers is not affiliated with or is sponsored by Yukon Gear & Axle, or Allegroracing. These videos are intended as information sources only.