Clutch for a drive shaft: The clutch disc (center) spins with the flywheel (left). To disengage, the lever is pulled (black arrow), causing a white pressure plate (right) to disengage the green clutch disc from turning the drive shaft, which turns within the thrust-bearing ring of the lever. At rest, all 3 rings connect, with no gaps.An Electromagnetic clutch is a clutch (a mechanism for transmitting rotation) which can be engaged and disengaged by an electromagnet: it operates via an electric actuation, but transmits torque mechanically.
The electromagnetic clutch is best suited where remote operation is desired since no linkages are required to control its engagement. These clutches have fast, smooth operation. A major limitation of this type is heat capacity since the clutch operating temperature is limited by the temperature rating of the insulation of the magnetic coil. Another disadvantage is higher initial cost.
How It Works In RC Cars
Engagement
When the clutch is required to actuate, voltage/current is applied to the clutch coil. The coil becomes an electromagnet and produces magnetic lines of flux. This flux is then transferred through the small air gap between the field and the rotor. 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 applied 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/voltage 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.
Cycling
Cycling is achieved by turning the voltage/current to the coil on and off. Slippage should occur only during acceleration. When the clutch is fully engaged, there is no relative slip (if the clutch is sized properly). Torque transfer is 100% efficient.
Automobiles
When the electromagnetic clutch is used in automobiles, there can be a clutch release lever in the gear lever. The driver operates the switch when he holds the gear lever to change the gear, cutting off current to the winding and thus causing clutch disengagement, thus obviating the 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 automobile 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. This 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.
Posted by:Raja Babu Dwivedy.
ID: 4810750499.
Reference: http://en.wikipedia.org/wiki/Electromagnetic_clutch
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