B20.40-0025-81
1 Cap
2 Ball bearing
3 Flange
4 Magnetic ring with permanent magnets
5 Winged ring
6 Rotor
7 Coil
8 Ball bearing
9 Bearing assembly, coil and electric wire
10 Spacer bushing
11 Ball bearing
12 Shaft
13 Anchor disc
14 Wire with electric connector
The electromagnetic fan coupling operates in two stages
Operation of the 1st stage
With the coil (7) not energized, the vehicle's fan spins at low speed due to the drag force generated by the attraction between the permanent magnets installed in the magnetic ring (4) and the winged ring (5), free of mechanical friction. The drag force makes the flange assembly (3) and the fan to spin at a fraction of the pulley speed. This 1st stage guarantees a minimum cooling of the system. The winglets of the ring (5) are to dissipate heat of the electromagnetic coupling.
The permanent magnets can loose their efficiency along the time due to heating. In this case the drag speed diminishes. In general there is no need to replace the magnets before 1000000 km are covered.
Operation of the 2nd stage
The 2nd stage is activated when the cooling provided by the 1st stage is insufficient. Energizing the coil (7) with 24 V creates an electromagnetic attraction between the rotor (6) installed on the shaft (12) and the anchor disc (13), installed on the flange (3) by means of a spring. The spring will give and the anchor disc will come in contact with the rotor, transmitting the rotor torque to the flange and, consequently, to the fan. The coupling is carried out in a fraction of a second, after the coupling there is no more relative movement between rotor and anchor disc.
The surfaces of the rotor and of the anchor disc wear only at the moment of coupling. The higher the frequency of couplings, greater will be the wear. Wear increases the distance between the anchor disc and the rotor, consequently, increases the force to flex the spring. There will be a moment when the electromagnetic force will not be enough to ensure the coupling without slippage between the anchor disc and the rotor. The disc, rotor and bearing assembly has to be replaced.