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Bike Trader

BMW patents new chain drive

01 March 2007
BMW patents new chain drive BMW has filed a patent for a completely new motorcycle concept that would allow extreme suspension travel while minimising the amount of slack needed in a drive chain, belt or shaft.

A conventional motorcycle needs free play in the drive chain to allow for movement in the rear suspension. On an off-road motorcycle this becomes even more important, and with suspension travel of 300mm the chain needs about 70mm free play at the tightest point. Such a slack chain results in power losses and high wear rates through friction, and would need a chain guide to stop the chain jumping off the sprockets.

The clutch is usually mounted on the gearbox output shaft on a motorcycle, but inventor Markis Theobald, in Patent Number EP1743832 filed on behalf of Bayerische Motoren Werke AG (DE) on 17 January 2007 proposes mounting it on the engine crankshaft. The gearbox output shaft can then be co-axial with the swingarm pivot, so that chain tension is always maintained without unwanted slack.

An added advantage of the BMW design is that because the clutch turns at engine speed instead of the usual half engine speed of a conventionally mounted clutch, a smaller, lighter unit can be used.

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