In Reply to: Something to read... posted by Beefer on July 27, 2000 at 14:57:05:
Note the availability in UK at the end...
Slip Sliding ....... Away !
The new, third generation BMW M3 will not only pack a more powerful engine but also a revolutionary differential - the Variable M Differential Lock. The ultimate advantage for the driver is that he or she can accelerate more consistently on surfaces with varying coefficients of friction, due to improved traction. The new system improves both handling and driving stability, thereby enhancing safety and driving pleasure at the same time.
The Variable M Differential Lock, developed jointly by BMW M GmbH and GKN Viscodrive GmbH, offers decisive traction advantages in demanding conditions and, in conjunction with the finely-tuned Dynamic Stability Control System (DSCIII) and 50/50 weight distribution, delivers handling in slippery conditions formerly regarded as impossible with a rear wheel drive sporting car.
Every car has a differential to compensate for the different distances covered by the inside and outside wheel when cornering, while performance-oriented cars have used limited slip differentials (LSD) for many years. The LSD limits loss of traction by locking the planet gears when one of the two drive wheels threatens to slip on, for example, a wet patch of road. However in more extreme conditions the benefits of the differential lock are limited.
The Variable M Differential Lock recognises the differential speed building between the driven wheels (for example when one wheel is relieved of load) and generates pressure in an integrated shear pump. This pressure activates a multiple plate clutch via a piston, and conveys drive forces to the wheel with better grip according to the difference in wheel rotation speed. In extreme cases the entire drive forces may be transmitted to the wheel with a better frictional coefficient.
Once the difference in wheel rotation speed reduces, pump pressure is reduced accordingly and the locking action decreases. The pump system is maintenance-free. The new BMW M3 will be available in the United Kingdom in the first quarter of 2001.