Anti-Lock Brake System: Operation
Each time a sensor rotor tooth passes by the wheel speed sensor, a magnetic field is distorted, causing an electric signal to be generated. These signals, which are proportional to wheel speed, are transmitted to the Electronic Control Unit (ECU). ECU processes these signals and computes a value defined as reference speed. See Fig 1 .
When a wheel is about to lock, the speed signal from that wheel will be different from reference speed. ECU detects this difference and modulates the solenoid valves. Solenoid valves regulate hydraulic brake pressure to the brake circuits.
ABS operation will continue until ECU detects that wheel speed is decreasing at the same rate for all wheels (all wheel speeds are the same as reference speed). Up to 12 brake pressure modulation cycles per second are possible.