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A slipper clutch (also known as a back-torque limiter) is a specialized clutch developed for performance oriented motorcycles to mitigate the effects of engine braking when riders decelerate as they enter corners.
The slipper clutch consists of two bases, one with dog clutches and ramps with ball bearings, a splined hub, and clutch plates. In normal operation, the dog clutches mate, driving the transmission. When a back torque comes from the transmission, the splined hub slides up the bearing ramps, disconnecting from the clutch plates.
They are designed to partially disengage or "slip" when the rear wheel tries to drive the engine faster than it would run under its own power. The engine braking forces in conventional clutches will normally be transmitted back along the drive chain causing the rear wheel to hop, chatter or lose traction. This is especially noted on larger displacement four-stroke engines, which have greater engine braking than their two-stroke or smaller displacement counterparts. Slipper clutches eliminate this extra loading on the rear suspension giving riders a more predictable ride and minimize the risk of over-revving the engine during downshifts. Slipper clutches can also prevent a catastrophic rear wheel lockup in case of engine seizure. Generally, the amount of force needed to disengage the clutch is adjustable to suit the application.
Slipper clutches have been used in most high displacement four stroke racing motorcycles since the early 1990s having been introduced on the Honda NR500 in the early eighties in 500GP racing. Slipper clutches are now fitted to many current sport bikes.
Slipper clutches have also been used to a lesser extent on automobiles, primarily those powered by motorcycle engines. They can also be found on racing remote control cars. Some experimental aircraft use a slipper clutch to control torsional resonance in the drive train and protect the engine from shock in the event of a propeller strike. A slipper clutch for an automobile was patented with a French priority date of 1953 to J.Maurice ETAL. The principle of this slipper clutch was exactly the same as found in modern motorcycles.
One-way sprag clutches have also been used for the same purpose, but are generally not adjustable for disengagement force. Early Honda Shadow models used a design wherein a sprag clutch is connected to just half of the clutch friction plates, allowing the clutch to slip during heavy backloading sufficiently to prevent rear-wheel lockup, while still allowing moderate engine compression braking with the remaining friction plates.
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