Device for quickly and easily connecting or disconnecting a pair of rotatable coaxial shafts. Clutches are usually placed between the driving motor and the input shaft to a machine and provide a convenient means for starting and stopping the machine and permitting the driving motor or engine to be started in an unloaded state (as in an automobile). Mechanical clutches provide either a positive (no-slip) or a friction-dependent drive; centrifugal clutches provide automatic engagement. An overrunning clutch transmits torque in one direction only and permits the driven shaft of a machine to freewheel (continue rotating after the driver stops); on bicycles, such clutches permit the rider to coast without moving the pedals.
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A clutch is a mechanism for transmitting rotation, which can be engaged and disengaged. Clutches are useful in devices that have two rotating shafts. In these devices, one shaft is typically driven by a motor or pulley, and the other shaft drives another device. In a drill, for instance, one shaft is driven by a motor, and the other drives a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed (engaged), or be decoupled and spin at different speeds (disengaged).
The clutch plate is lined with a friction material with the output shaft running through the center. This type has the advantage of a lever that allows the operator to manually engage and disengage the drive via the pressure plates. This type of clutch allows for a smooth take away and gear changes.
When engaging the clutch, the engine speed may need to be increased from idle, using the manual throttle, so that the engine does not stall. (Although in some cars, especially diesels, there is enough torque at idling speed that the car can move. This requires fine control of the clutch.) However, raising the engine speed too high while engaging the clutch will cause excessive clutch plate wear. Engaging the clutch abruptly when the engine is turning at high speed causes a harsh, jerky start. This kind of start is necessary and desirable in drag racing and other competitions where speed is more of an issue than comfort.
A manual transmission contains cogs for selecting gears. These cogs have matching teeth, called dog teeth, which means that the rotation speeds of the two parts have a synchronizer, a device that uses frictional contact to bring the two parts to the same speed, and a locking mechanism called a blocker ring to prevent engagement of the teeth (full movement of the shift lever into gear) until the speeds are synchronized.
Clutches: a chain is only as strong as its weakest link, right? So, understanding how a clutch works, and knowing its capabilities and limitations will help you spec a clutch that will be as strong as the other links in your powertrain-chain. (Savvy Spec'ing).
Oct 01, 2002; You WOULDN'T WANT TO BE A clutch. YOU WOULD repeatedly be mashed against a spinning flywheel. You would slip and grab....