AskDefine | Define clutch

Dictionary Definition



1 the act of grasping; "he released his clasp on my arm"; "he has a strong grip for an old man"; "she kept a firm hold on the railing" [syn: clasp, clench, clutches, grasp, grip, hold]
2 a tense critical situation; "he is a good man in the clutch"
3 a number of birds hatched at the same time
4 a collection of things or persons to be handled together [syn: batch]
5 a pedal that operates a clutch [syn: clutch pedal]
6 a coupling that connects or disconnects driving and driven parts of a driving mechanism


1 take hold of; grab; "The salesclerk quickly seized the money on the counter"; "She clutched her purse"; "The mother seized her child by the arm"; "Birds of prey often seize small mammals" [syn: seize, prehend]
2 hold firmly, usually with one's hands; "She clutched my arm when she got scared" [syn: cling to, hold close, hold tight]
3 affect; "Fear seized the prisoners"; "The patient was seized with unberable pains"; "He was seized with a dreadful disease" [syn: seize, get hold of]

User Contributed Dictionary




  1. A device to interrupt power transmission, commonly used between engine and gearbox in a car.
  2. The pedal in a car that disengages power transmission.
  3. A hand or claw, when it is grasping something firmly.
  4. A small handbag or purse with no straps or handle.
  5. A group or bunch, especially of eggs or baby birds.
  6. An important or critical situation.


A device to interrupt power transmission
The pedal in a car that disengages power transmission
A small handbag or purse with no straps or handle
A group or bunch, especially of eggs or baby birds


  1. To grip or grasp tightly.
    She clutched her purse tightly and walked nervously into the building.


  1. Tending to perform well in difficult, high-pressure situations.


Alternative spellings



From clutch


  1. clutch (device between engine and gearbox)



Extensive Definition

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).


There are many different vehicle clutch designs but most are based on one or more friction discs, pressed tightly together or against a flywheel using springs. The friction material varies in composition depending on whether the clutch is dry or wet, and on other considerations. Friction discs once contained asbestos, but this has been largely eliminated. Clutches found in heavy duty applications such as trucks and competition cars use ceramic clutches that have a greatly increased friction coefficient, however these have a "grabby" action and are unsuitable for road cars. The spring pressure is released when the clutch pedal is depressed thus either pushing or pulling the diaphragm of the pressure plate, depending on type, and the friction plate is released and allowed to rotate freely.
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 most 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 desired in drag racing and other competitions, however.

Wet and dry

A 'wet clutch' is immersed in a cooling lubricating fluid, which also keeps the surfaces clean and gives smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. A 'dry clutch', as the name implies, is not bathed in fluid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil), stacking multiple clutch disks can compensate for slippage.

Operation in automobiles

In a car the clutch is operated by the left-most pedal using hydraulics or a cable connection from the pedal to the clutch mechanism. Even though the clutch may physically be located very close to the pedal, such remote means of actuation are necessary to eliminate the effect of slight engine movement, engine mountings being flexible by design. With a rigid mechanical linkage, smooth engagement would be near-impossible, because engine movement inevitably occurs as the drive is "taken up." No pressure on the pedal means that the clutch plates are engaged (driving), while depressing the pedal disengages the clutch plates, allowing the driver to shift gears or coast.
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.

Non-powertrain in automobiles

There are other clutches found in a car. For example, a belt-driven engine cooling fan may have a clutch that is heat-activated. The driving and driven elements are separated by a silicone-based fluid. When the temperature is low, the fluid is thin and so the clutch slips. When the temperature is high, the fluid thickens, causing the fan to spin. There are also electronically engaged clutches (such as for an air conditioning compressor) that use magnetic force to lock the pulley and compressor together.

Operation in motorcycles

On most motorcycles, the clutch is operated by the clutch lever, located on the left handlebar. No pressure on the lever means that the clutch plates are engaged (driving), while pulling the lever back towards the rider will disengage the clutch plates, allowing the rider to shift gears. Motorcycle clutches are usually made up of a stack of alternating plain steel and friction plates. One type of plate has lugs on its inner diameter that key it to the engine crankshaft, while the other type of plate has lugs on its outer diameter that key it to a basket that turns the transmission input shaft. The plates are forced together by a set of coil springs when the clutch is engaged. Racing motorcycles often use slipper clutches to eliminate the effects of engine braking.


Some cars and mopeds have a centrifugal clutch, using centrifugal effects to engage the clutch above certain rpm, see Saxomat.

Other clutches

External links

  • HowStuffWorks has a detailed explanation of the working of a clutch.
clutch in Afrikaans: Koppelaar
clutch in Czech: Spojka (stroj)
clutch in German: Kupplung
clutch in Estonian: Sidur
clutch in Spanish: Embrague
clutch in Esperanto: Kluĉilo
clutch in Persian: کلاچ
clutch in French: Embrayage
clutch in Korean: 클러치
clutch in Italian: Frizione (meccanica)
clutch in Hebrew: מצמד
clutch in Dutch: Koppeling
clutch in Japanese: クラッチ
clutch in Norwegian: Kobling
clutch in Polish: Sprzęgło
clutch in Portuguese: Embraiagem
clutch in Russian: Сцепление (механика)
clutch in Slovenian: Sklopka
clutch in Serbian: Спојница
clutch in Finnish: Kytkin (konetekniikka)
clutch in Swedish: Koppling (bildel)
clutch in Chinese: 離合器

Synonyms, Antonyms and Related Words

abduct, adhere to, amount, array, batch, bear hug, bind, bite, body, brood, budget, bunch, bundle, carry off, catch, cherish, chunk, clamp, clasp, cleave to, clench, climacteric, clinch, cling, clinging, clip, clump, cluster, clutches, complication, cone clutch, control, convergence of events, count, crisis, critical juncture, critical point, crossroads, crucial period, crunch, deal, death grip, disk clutch, dominance, domination, dose, embarrassing position, embarrassment, embrace, emergency, exigency, extremity, farrow, fine how-do-you-do, firm hold, foothold, footing, freeze to, friction clutch, fry, get, gob, grab, grapple, grasp, grip, gripe, group, hang on, hang on to, harbor, hatch, heap, hell to pay, high pressure, hinge, hobble, hold, hold fast, hold on, hold on to, hold tight, hot water, how-do-you-do, hug, hunk, imbroglio, imperativeness, influence, iron grip, jam, keep, keep hold of, kidnap, large amount, lay hold of, litter, lot, measure, mess, mix, morass, multiple-disk clutch, nab, nail, nest, never let go, nip, number, pack, parcel, parlous straits, part, pass, pickle, pinch, plate clutch, plight, portion, possession, power, predicament, press, pressure, pretty pass, pretty pickle, pretty predicament, purchase, push, quagmire, quantity, quicksand, ration, rim clutch, rub, scrape, seize, seizure, set, shanghai, slip friction clutch, slough, small amount, snag, snatch, spat, spawn, spot, squeeze, stew, stick to, sticky wicket, strait, straits, stress, sum, swamp, take, take hold of, tension, tenure, throttle, tight grip, tight spot, tight squeeze, tightrope, toehold, tricky spot, turn, turning point, unholy mess, urgency, young
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