Speed Converters (Clutches)
Speed converters (clutches) are used in the drivetrain of vehicles in order to level out speed differences between the input and output. This is valid on the one hand during the starting phase in which the speed difference between standstill and the lowest engine operating speed have to be bridged, while on the other hand during the shift phases of commonly used manual transmissions. Speed converters are almost exclusively based on adherent or frictional coupling methods. The figure shows the power balance of at a speed converter with the corresponding input and output parameters.
A constant torque is characteristic for a speed converter. The power output PO is smaller by the power dissipation Pdiss when compared to the input power PI. From the ratio of power output to the power input, the clutch efficiency ηC can be calculated.

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The slip s, defined as the difference of input and output speeds relative to the input speed, is a standardized dimension used to represent the operating condition of a speed converter.



Based on the definitions of efficiency and slip, during a coupling process a relationship totally dependent on speed can be deduced for the power dissipated in the form of heat.


The clutches used in different fields of application in a motor vehicle, can be classified based on the type of power transmission into:
Mechanical clutches
Hydrodynamic clutches
Visco-hydraulic clutches