Wheel Sensors

The wheel sensors are the magnetic contactless type. As the gear pulsar teeth rotate past the wheel sensor's magnetic coil, AC current is generated. The AC frequency changes in accordance with the wheel speed. The ABS control unit detects the wheel sensor signal frequency and thereby detects the wheel speed.

Wheel Speed and Modulator Control

When the wheel speed drops sharply below the vehicle speed, the outlet valve opens momentarily to reduce the calliper fluid pressure. The pump motor starts at this time. As the wheel speed is restored, the inlet valve opens momentarily to increase the calliper fluid pressure.