Magnetic Clutch

Courtesy of VOLVO CARS CORPORATION

1. Gear wheel to gear unit
2. Return springs (x3)
3. Flange
4. Friction plate
5. Contact
6. Coil

Clutch 

In order to disengage the compressor from the crankshaft, there is a magnetic clutch. The clutch is very similar in its design to an A/C compressor clutch. In no power state, the clutch is disengaged by the return springs. During the mechanical connection of the compressor, as smooth an engagement as possible is ensured by retarding the ignition while the clutch engagement is controlled to a controlled slippage for approx. half a second. The control signal, a custom PWM signal, initially gives a strong signal to quickly move the magnetic clutch to the engaged position. Thereafter, the signal strength is reduced to allow the clutch to slip easily during the action. Exactly how the PWM signal looks depends on relevant parameters such as speed, temperature and ageing.