LIMITED SLIP DIFFERENTIALS
THE PURPOSE, AS THE NAME SUGGESTS, IS TO LIMIT THE AMOUNT OF WHEEL SLIP. HOWEVER, THERE ARE SEVERAL DIFFERENT VARIATIONS WITH DIFFERENT DEGREES OF EFFECTIVENESS.
This type has a multi-plate clutch pack similar to that in a motorcycle. One side of the clutch assembly is connected to the driveshafts and the other to the differential gear carrier. Various methods such as ramps or the natural force of separation between gear teeth are used to engage the clutch pack when the differential experiences one wheel turning faster than the other, which then transfers some of the power to the slower-turning wheel.
ONE-WAY, ONE AND A HALF, AND TWO-WAY
A one-way LSD will only provide the limited-slip action in one direction – for example, under acceleration but not under braking.
By contrast, a 1.5-way LSD will provide differing amounts of slip limitation under acceleration and braking, which can aid stability under heavy braking.
A two-way LSD will provide the same amount of limited-slip effect under both acceleration and braking.
The torque-sensing differential is a limited slip-type differential that uses the oneway action of worm drive gearing to limit slip. They also have the ability of being manufactured with a TBR (torque bias ratio), where there is an ability to send more torque to the rear wheel in a centre differential application.
When thinking of auto lockers, many think of ‘lunchbox lockers’ that replace the spider gear mechanism in the middle of differential carrier. Probably better referred to as un-lockers, lunchbox lockers are locked when driving under power in a straight line. When they experience different torque loads, such as coasting around a corner, they unlock. This can make for interesting handling characteristics on the road, and if installed in the front they’re much better in combination with a part-time 4WD system.
Viewed as the Holy Grail by many, selectable lockers come in two main flavours: air operated (TJM/ARB) and electromagnetic (Elocker). Both pneumatic lockers use a simple dog clutch-type mechanism that removes the differential action when activated. However, the Elocker uses a pin and ramp mechanism to operate a series of pins that lock the differential. When transitioning from forward to reverse, they unlock then relock due to the forward and reverse activation ramps used.
There are two main types of traction control: one reduces engine power, the other reduces the differential’s ‘power to the path of least resistance’ characteristic. Modern systems monitor individual wheel speeds and if two wheels on the same axle are travelling at differing speed it brakes the spinning wheel – this requires more torque from the engine. As there is always even torque on either side of a conventional diff, the slower wheel receives extra torque. Early systems weren’t great but now traction control is almost a viable alternative to lockers – the latest Landcruisers and Pajeros are particularly good.