Views: 0 Author: Site Editor Publish Time: 2023-05-12 Origin: Site
Many differentials cannot limit the amount of engine power sent to the output shaft to which they are connected.Therefore, if a tire loses traction under acceleration, either because of a low traction situation (for example, driving on gravel or ice) or because engine power exceeds available traction, a non-spinning tire receives little or no power from the engine.In very low traction situations, this can stop the vehicle from moving at all.To overcome this, several designs of differentials can limit the amount of slip (these are called "limited slip" differentials) or temporarily lock the two output shafts together to ensure that engine power reaches all drive wheels equally.
A locking differential works by temporarily locking the output shafts of the differential together so that all wheels turn at the same speed, providing torque during slippage.This is usually used in the center differential, which distributes power between the front and rear axles. While a drivetrain that turns all wheels equally can often conflict with the driver and cause handling issues, this isn't an issue when the wheels are slipping.The two most common factory-installed locking differentials use computer-controlled multi-plate clutches or viscous coupling units to connect the shafts, while other differentials more commonly used in off-road vehicles typically use manually-operated locking devices.In a multi-plate clutch, the vehicle's computer senses the slip and locks the axle, causing a slight jerk when activated, which can bother the driver or cause additional loss of traction.In a viscously coupled differential, the shear stress of high shaft speed differences causes the expanding fluid in the differential to become solid, connecting the two shafts.This design exhibits fluid degradation and exponential locking behavior over time.Some designs use gears to create a small rotational difference that speeds up torque transfer.
A third way to limit slip is to employ a Torsen differential, which allows output shafts to receive varying amounts of torque.When one wheel spins freely, this design provides no traction, no torque, but excellent handling in less extreme situations.A typical Torsen II differential can provide up to twice the torque for high traction on the low traction side over the side before traction.A recent innovation in the automotive world is electronic traction control.It usually uses the vehicle's braking system to slow down the spinning wheel.This forced deceleration simulates the function of a limited-slip differential, and by using the brakes more aggressively to ensure the wheels move at the same speed, a locking differential can also be simulated.This technology typically requires wheel sensors to detect when the wheels are slipping and is only activated when wheel slip is detected.Therefore, there is usually no mechanism to actively prevent wheel slip (i.e., it is impossible to lock the differential before the wheels slip); instead, the system is designed to explicitly allow wheel slip to occur, and then try to send torque to the wheels with optimal traction.This is a restrictive design if required to prevent all-wheel skid.