A clutch is a machine element for rigid, elastic, movable or releasable connection of two shafts. A non-rigid coupling can also be a force-fit connection in addition to a positive locking. Through the connection, it becomes possible to be transferred between the two shafts so that torque and rotation and ultimately mechanical work.

The couplings known from everyday life, used in motor vehicles, it is non-positive, detachable couplings in operation. These are used to interrupt the drive between the engine and transmission when the gear are changed or if the vehicle is to stand with the engine running. The non-positive or frictional connection is required when starting from the state: starting with a slipping clutch.


In contrast to a gearbox with different input and output speed or input and output torque couplings torques and speeds can only be transferred, but not convert. This means that the speed and torque values ​​are greater than or equal to the output shaft to the clutch input shaft.

Colloquially, a releasable coupling is usually referred to as a coupling (for example in the motor vehicle ). In general, any connection of two shafts to transmit torque and speed is a clutch. The counterpart for releasably is the rigid connection, in extreme cases, the production of a long wave of shorter sections.

Besides rigidity and solubility can be a clutch have other functions:

  • With it may be offset within limits, that the two shafts are not aligned, that is, to each other are offset and / or do not have the same direction.
  • One can make a torsionally elastic coupling, which torque and speed bumps are transmitted damped.
  • The material used in a coupling (for example, rubber ), the propagation of structure-borne sound dampening.
  • A clutch may be a overload protection, for example by the use of defined refractive or sliding elements.

Clutches in motor vehicles

Releasable coupling

The foot in the car, the motorcycle hand operated releasable coupling between the engine and gearbox in motor vehicles is the most famous coupling at all due to the high distribution. Is a frictional clutch, which allows the start-up and changing of the gear stages.

The non-positive or frictional connection is when starting from a stop, the motor rotates at a minimum speed required: starting with a slipping clutch.

To change the gear stages ( courses), the torque transmission must be interrupted, so that the corresponding two gears can be brought into engagement with the gear ( corresponding speed matching between the two gears with the help of a so-called Sychronisiereinrichtung ). Restoring the connection between the engine and transmission which any speed difference is bridged by momentary slippage in the clutch.

Usually provided on both sides with a ring-shaped clutch disk friction linings (3) between two of the engine crankshaft (1) is clamped fixed discs. The one disc is rigidly connected to the crankshaft flywheel ( 2), the other is the so-called co-rotating Topf-/Druckscheibe ( 4), which is pressed with a diaphragm spring ( 5) against the flywheel. The clutch disc is rotationally rigidly connected by means of a gear coupling to the transmission shaft (6).

To release the diaphragm, which presses by its outer edge over the well plate to the clutch plate will be " lifted " by being clamped axially at its inner edge. The release ring (7 ) is pressed with pedal force from the clutch pedal against the diaphragm spring, which inverts itself ( rotation about the support bearing ( 10 ) / ( 11) ). The cup wheel away some of the clutch and flywheel.

Torsionally elastic coupling in a clutch plate ( not removable )

The outer portion of the clutch plate with the friction rings is rotationally elastically connected to the hub with the gear teeth for connection to the transmission input shaft. The built-in pressure springs intercept torque and speed bumps.

Other non-releasable clutches in motor vehicles

To transfer the power from the front engine to rear wheel drive is usually a propeller shaft. This is connected to the output shaft of the transmission with a universal joint. This angularly movable coupling allows the sprung vertical movement of the rear axle relative to the built- in principle gear. That or another universal joint can be found also in a divided propshaft.

If the driven rear wheels are not connected to a rigid axle, but move individually resiliently against the vehicle, the two half- axes are often connected by universal joints at the rear axle and the wheels.

With front-wheel drive, the wheels are sprung vertically and included in the guides. Because the rotation transmission varies too much in angled position over one revolution evenly over bearing constant velocity joints are used.

The flexible disk is related to the universal joint. It contains a rubber disc, which is elastically deformed at angular deflections between the two shafts and the rotary joints.

Special detachable couplings

  • Couplings with traction as overload protection: slipping ( slipping clutch when the engine the required torque can not afford, for example, in vehicles, construction machinery and machine tools)
  • Couplings with predetermined breaking point for overload protection: for example, pin coupling with shear pin
  • Automatic disengagement of the clutch when it reaches an upper or below a lower speed: for example centrifugal clutch
  • Automatic disengagement of the clutch when the direction is reversed: for example freewheel for bicycle

Non- detachable flexible couplings

Not releasable couplings can be variously yielding:

  • Torsionally rigid, axially movable: gear coupling, claw coupling, clutch spring web
  • Torsionally rigid, low axial, radial and angular move: Phillips clutch
  • Rotatable and transverse elastic: rubber coupling
  • For spins ( with slip): magnetic powder clutch
  • " bendable ": universal joint ( U-joint )

Distinction by force or form closure

Frictional clutches ( friction clutches ) are particularly as detachable couplings and self-releasing clutches ( friction clutches ) at overload ( including start-up and start-up are ) appropriate. You can have more than one or two non-positive surface contacts have (for example, when fitted with several blades ). The contact surfaces are flat or conically.

Positive clutches are built easier. They include slippage in the transmission, but do not provide protection for overload (except for additional breaking point, for example, with shear pin ). Embodiments are, for example, jaw couplings and gear couplings. Positional errors and collisions yielding positive clutches are correspondingly more complex, such as the flexible disk, the metal bellows, the universal joint, the constant velocity joint, the parallel crank coupling, and the Oldham's coupling.

One difference in comparison to the generally mechanical couplings are the viscous coupling and the fluid coupling. They are not rigid, so rather be counted among the frictional mechanical couplings, but have permament slippage in the order of 10 %.

Similarly, the eddy current coupling ( principle as eddy current brake) is to be classified. This coupling is also not rigid.