Editing Clutch (section)

== Usage in automobiles ==
=== Manual transmissions===
Most cars and trucks with a [[manual transmission]] use a dry clutch, which is operated by the driver using the left-most pedal. The motion of the pedal is transferred to the clutch using mechanical linkage, hydraulics (master and slave cylinders) or a cable. The clutch is only disengaged at times when the driver is pressing on the clutch pedal, 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.

The clutch is required for standing starts and in vehicles whose transmissions lack synchronising means to assist in matching the speeds of the engine and transmission during gear changes to avoid gear “crashing,” which can cause serious damage to gear teeth.

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. The friction material used for the clutch disk varies, with a common material being an [[organic compound]] resin with a [[copper]] wire facing or a [[ceramic]] material.<ref>{{Cite journal |last1=Yu |first1=Liang |last2=Ma |first2=Biao |last3=Chen |first3=Man |last4=Li |first4=Heyan |last5=Ma |first5=Chengnan |last6=Liu |first6=Jikai |date=2019-09-15 |title=Comparison of the Friction and Wear Characteristics between Copper and Paper Based Friction Materials |journal=Materials |volume=12 |issue=18 |page=2988 |doi=10.3390/ma12182988 |issn=1996-1944 |pmc=6766303 |pmid=31540186|bibcode=2019Mate...12.2988Y |doi-access=free }}</ref>

=== Automatic transmissions ===
In an [[automatic transmission]], the role of the clutch is performed by a [[torque converter]]. However, the transmission itself often includes internal clutches, such as a ''lock-up clutch'' to prevent slippage of the torque converter, in order to reduce the energy loss through the transmission and therefore improve fuel economy.<ref>{{cite web|url=http://youronlinemechanic.com/what-is-lock-up-clutch-mechanism/ |title=What is Lock-up Clutch Mechanism? |publisher=Your Online Mechanic |access-date=2014-07-17}}</ref>

=== Fans and compressors ===
Older belt-driven engine cooling fans often use a heat-activated clutch, in the form of a [[bimetallic strip]]. When the temperature is low, the spring winds and closes the valve, which lets the fan spin at about 20% to 30% of the [[crankshaft]] speed. As the temperature of the spring rises, it unwinds and opens the valve, allowing fluid past the valve, making the fan spin at about 60% to 90% of crankshaft speed.

A vehicle's air-conditioning [[compressor]] often uses magnetic clutches to engage the compressor as required.