Limited-slip differential
In 1932, Ferdinand Porsche designed a Grand Prix racing car for the Auto Union company.
In 1935, Porsche commissioned the engineering firm ZF to design a limited-slip differential to improve performance.
[citation needed] The ZF "sliding pins and cams" became available,[2] and one example was the Type B-70 used during the Second World War in the military VWs (Kübelwagen and Schwimmwagen), although technically this was not a limited-slip differential, but a system composed of two freewheels, which sent the whole of the engine power to the slower-turning of the two wheels.
In early 1956, Packard introduced a clutch-type limited-slip differential under the Twin Traction trademark, promoting it as an aid for driving in severe winter weather.
[4] In 1957, General Motors (GM) introduced a competing system for Chevrolet branded vehicles under the Positraction name.
[1] Despite the myriad marketing names used by competing brands, the popularity of Chevrolet vehicles resulted in Positraction becoming a generic trademark in the U.S. for limited-slip differentials generally.
[6] The advantages of LSD in high-power, rear-wheel drive automobiles were demonstrated during the United States "Muscle-Car" era from the mid 1960s through the early 1970s.
Cars of this era normally were rear-wheel drive and did not feature independent suspension for the rear tires (but instead used a live axle).
The amount of preload (hence static coupling) on the clutches or cones is affected by the general condition (wear) and by how tightly they are loaded.
The spider gears mount on the pinion cross shaft which rests in angled cutouts forming cammed ramps.
The mating of the vertical ramp (80–85° in practice to avoid chipping) surfaces in a one-way LSD on overrun produces no cam effect or corresponding clutch stack compression.
[11] A 1.5-way differential refers to one where the forward and reverse limiting torques, Trq d_fwd, d_rev , are different but neither is zero as in the case of the 1-way LSD.
This type of differential is common in racing cars where a strong limiting torque can aid stability under engine braking.
The result is a differential that does not bind up like some LSD types and locking ones, but still gives increased power delivery under many road conditions.
The viscous type is generally simpler because it relies on hydrodynamic friction from fluids with high viscosity.
Here, a cylindrical chamber of fluid filled with a stack of perforated discs rotates with the normal motion of the output shafts.
In contrast to the mechanical type, the limiting action is much softer and more proportional to the slip, and so is easier to cope with for the average driver.
New Process Gear used a viscous coupling of the Ferguson style in several of their transfer cases including those used in the AMC Eagle.
In particular, any sustained load which overheats the silicone results in sudden permanent loss of the differential effect.
This style limited-slip differential works by using a gerotor pump to hydraulically compress a clutch to transfer torque to the wheel that is rotating slower.
The newest gerotor pump based system has computer regulated output for more versatility and no oscillation.
[19] The Jeep Quadra-Drive II four-wheel-drive system produced beginning in 2005 utilizes this type of differential.
Another example began on the first year (1992) production of the re-styled, and new 4.6L V-8 overhead cam Ford Crown Victoria model with its optional anti-lock brakes.
In The Beach Boys' song "409", the lyrics mention the presence of a limited-slip differential: "...My four-speed, dual-quad, Positraction 4-0-9 (4-0-9, 4-0-9)."
In the 1992 film My Cousin Vinny, the proof of innocence of two young men falsely accused of murder relies heavily on a photograph of tire marks made by a car which has a limited-slip differential, which (as Marisa Tomei's character famously declares in an Oscar-winning performance) "was not available on the '64 Buick Skylark,"[22] the car driven by the defendants.
