The principle of the limited-slip differential was patented by engineer, Hermann Knab, in 1925. His follow-up patent (filed in 1930) was bought by transmission specialist, ZF, in 1932. Ferdinand Porsche recognised the potential for the design to benefit the monstrously powerful Auto Union race cars of the mid-1930s and is widely recognised for championing and further refining the technology. The idea has been continually developed since, and though purely mechanical limited-slip differentials (LSD) are still in widespread use today, the onward march of computer-driven sophistication has allowed automotive engineers to design LSDs to work hand-in-hand with electronic driving assistance features, such as traction control, stability control and anti-lock brakes.
Refreshing our basic knowledge of differentials, a pair of driven wheels needs such a device to allow the two wheels the capability to rotate at different speeds, such as when navigating a corner. This type of differential is referred to as ‘open’ and splits torque output equally between the wheels. For this to happen, and for there to be a speed differential, the power output at each wheel is variable. In other words, if
