This type of clutch has been employed on some Renault cars.
The construction and working of this clutch may be understood by means of a simplified figure.
A is the engine flywheel incorporating the winding B.
Clutch plate C is lined with friction surfaces and is free to slide on splines on the clutch shaft.
D is the pressure plate.
The winding B is supplied with current from battery dynamo.
When the winding B is energized, it attracts the pressure plate D, thereby engaging the clutch.
When supply to winding B is cut off, the clutch is disengaged.
There is a clutch release switch in the gear lever.
This which is operated as soon as driver holds the gear lever to change the gear, cutting off current to the winding and thus causing clutch disengagement.
Ordinarily the winding is connected to engine dynamo.
At lower engine speeds, dynamo output is also low which makes the force in winding very small.
Three springs are also provided in the clutch to balance this reduced the electromagnetic force at low speeds, thus disengaging the clutch.
During normal operation, the electromagnetic force of the winding is regulated by means of an electrical resistance, which itself is controlled by means of accelerator pedal.
As the acceleration pedal is pressed the resistance is gradually cut, thus increasing the electromagnetic force.
The electromagnetic type of clutch is best suited where remote operation is desired since no linkages are required to control its engagement.
A major limitation of this type is that of heat capacity since the clutch operating temperature is limited by the temperature rating of the insulation of the magnetic coil.
Another disadvantage is its higher initial cost.
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