A Limited Slip Differential or LSD is an improvement to the open differential in
that it allows a driven wheel to have a limited amount of slip before the differential
attepmts to correct the slippage of the wheel.
This slip is usually a very limited amount. Your tires don't have to spend five to ten seconds or more skidding
before the limited slip differntial attempts to correct it.
The LSD just needs to establish that there is a loss of traction in that wheel and many
limited slip differential can notice slippage in under two seconds, sometimes in several milliseconds. So the slipping of
the wheels is necessary but sometimes it is corrected before you can notice it.
Limited slip differentials has solved a problem with open differentials. All differentials from the most basic to
the most advanced allow the outside wheel to have more rotations whenever the vehicle is cornering while both wheels are
receiving around the same power.
The problem with open differentials is that the design needed to have the wheels rotated differently causes the
wheel offering less resistance to recieve the torque from the drivetrain.
If a wheel is slipping it will spin freely and naturally offer less resistance than the wheel that is firmly on
the ground. This means that once a wheel starts to slip both wheels becomes useless.
There are basically three types of limited slip differential:
All of the above methods can tolerate slight differences in wheel speed to facilitate the vehicle cornering before the
differential sends power to the other wheel.
- Mechanical - a mechanical LSD has two clutches inside the differential. Whenever a wheel starts to slip it activates
the clutch to the shaft leading to that wheel to cut the power to that wheel thereby sending the power to the other wheel.
- Viscous Coupling - this means that there is a thick liquid inside of the LSD. The liquid spins in the direction of the
wheels and if one wheel starts to spin considerably faster than the other the viscosity of the spinning liquid forces the other
wheel to spin as well. This action is similar to a locking differential as power is not actually
removed from the slipping wheel.
- Electronic - an electronic LSD may also have two clutches inside it and uses an
ECU to determine when one of clutches should restrict the power to a wheel thereby sending the power to the other wheel.
An electronic LSD may operate by itself with its own ECU or may use the systems that operate the
traction control to also operate the LSD.
The average limited slip differential works better at improving on road performance than pulling a stuck vehicle out of
the mud in off roading situations. There are limited slip differentials that work on recognised off road vehicles such as the Jeep
Gran Cherokee but many LSDs work to improve vehicle traction and performance on snow, leaves or even tight corners on road.
Since traction is required for accelerating and turning, an open differential may not be useful here even if the vehicle
is all wheel or four wheel drive. The limited slip differential will continue sending power to the
wheel or wheels with traction in these conditions.