A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft (driving shaft) to a driven shaft. [1] In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). In these devices, one shaft is typically attached to an engine and other to power unit (the driving member), while the other shaft (the driven member) provides output power for work. Typically the motions involved are rotary, but linear clutches also exist.

In a motor vehicle, the clutch acts as a mechanical linkage between the engine and transmission, and briefly disconnects, or separates the engine from the transmission system. This disconnects the drive wheels whenever the clutch pedal is depressed, allowing the driver to smoothly change gears.

In a torque-controlled drill, for instance, one shaft is driven by a motor, and the other drives a drill chuck. [2] The clutch connects the two shafts so they may be locked together and spin at the same speed (engaged), locked together but spinning at different speeds (slipping), or unlocked and spinning at different speeds (disengaged).

Materials

A common friction material is an organic compound resin with a copper wire facing or a ceramic material. [3] Ceramic materials can often transmit higher torque loads, but they can cause increased wear rates of the flywheel. Until the mid 1990s asbestos was also used in clutch plates.

Usuage

Manual transmissions

Most cars and trucks with a manual transmission have a clutch consisting of friction disc(s) which is operated using the left-most pedal with the motion transferred to the clutch using hydraulics (master and slave cylinders) or a cable. The clutch is only disengaged at times when the driver is pressing the clutch pedal towards the floor, therefore the default state is for the transmission to be connected to the engine. A "neutral" gear position is provided, so that the clutch pedal can be released with the vehicle remaining stationary.

In addition to standing starts, the clutch is usually required for gear changes. Although the gearbox does not stop rotating during a gear change, there is no torque transmitted through it, thus less friction between gears and their engagement dogs. The output shaft of the gearbox is permanently connected to the final drive, then the wheels, and so both always rotate together, at a fixed speed ratio. With the clutch disengaged, the gearbox input shaft is free to change its speed as the internal ratio is changed. Any resulting difference in speed between the engine and gearbox is evened out as the clutch slips slightly during re-engagement.

The clutch is usually mounted directly to the face of the engine's flywheel, as this already provides a convenient large-diameter steel disk that can act as one driving plate of the clutch. Some racing clutches use small multi-plate disk packs that are not part of the flywheel. Both clutch and flywheel are enclosed in a conical bellhousing for the gearbox. A small number of front-engine, rear-wheel drive cars (such as the Alfa Romeo Alfetta, Porsche 924 and Chevrolet Corvette C5) use a transaxle layout with the transmission located near the rear of the car; in this case the clutch is mounted with the transaxle (therefore the driveshaft rotates continuously with the engine, even when the clutch is disengaged).

Automatic Transmissions

Some automatic transmissions use a lock-up clutch to prevent slippage of the torque converter when cruising at higher speeds. The purpose of the lock-up clutch is to improve fuel economy by minimising energy losses caused by slippage of the torque converter. [17]

http://www.cncpartscustom.com/