1. Electromagnetic clutch

2. In heavy trucks the manner in which the clutch is disengaged and re-engaged can adversely affect the clutch wear, produce speed feedbacks to the engine, result in acceleration jolts, and ultimately subject the driver to undesirable physiological stresses.
In the drive mechanism of a heavy truck, the friction disc clutch is generally the weakest member in the torque transmission. Thus improper operation can easily destroy the clutch. Prior art systems have failed to minimize these effects.
object of the invention is to provide a method and an apparatus, which upon command, automatically disengages the clutch of a vehicle and then re-engages the clutch in such a manner as to reduce clutch wear to a minimum, minimize speed feedback to the vehicles' engine and avoid sudden acceleration jolts so as to protect the transmission parts and limit physiological stresses upon the driver to the lowest possible level.
another object is automatically to control the engagement of the clutch members so as to minimize the danger of excessive clutch wear.

3. The electromagnetic clutch is most suitable for remote operation since no linkages are required to control its engagement. It has fast, smooth operation. However, because energy dissipates as heat in the electromagnetic actuator every time the clutch is engaged, there is a risk of overheating. Consequently the maximum operating temperature of the clutch is limited by the temperature rating of the insulation of the electromagnet. This is a major limitation. Another disadvantage is higher initial cost.

4. Automobiles
When the electromagnetic clutch is used in automobiles, there may be a clutch release switch inside the gear lever. The driver operates the switch by holding the gear lever to change the gear, thus cutting off current to the electromagnet and disengaging the clutch. With this mechanism, there is no need to depress the clutch pedal.
Alternatively, the switch may be replaced by a touch sensor or proximity sensor which senses the presence of the hand near the lever and cuts off the current. The advantages of using this type of clutch for automobiles are that complicated linkages are not required to actuate the clutch, and the driver needs to apply a considerably reduced force to operate the clutch. It is a type of semi-automatic transmission.
Electromagnetic clutches are also often found in AWD systems, and are used to vary the amount of power sent to individual wheels or axles.
A smaller electromagnetic clutch connects the air conditioning compressor to a pulley driven by the crankshaft, allowing the compressor to cycle on only when needed.

5. How it works
Engagement
When the clutch is required to actuate, current flows through the electromagnet, which produces a magnetic field. The rotor portion of the clutch becomes magnetized and sets up a magnetic loop that attracts the armature. The armature is pulled against the rotor and a frictional force is generated at contact. Within a relatively short time, the load is accelerated to match the speed of the rotor, thereby engaging the armature and the output hub of the clutch. In most instances, the rotor is constantly rotating with the input all the time.
Disengagement
When current is removed from the clutch, the armature is free to turn with the shaft. In most designs, springs hold the armature away from the rotor surface when power is released, creating a small air gap.