Purpose and Function
The Anti-lock Brake System - ABS - is an additional active vehicle safety element.
The advantages are:
- Stability while braking
- Steerability while braking, evasive manoeuvres possible while braking
- Optimal braking distance
The electronic ABS 4/4-F, used for the first time in the Corsa-B, is a new system. In contrast to normal ABS systems with two solenoid valves per channel, the so-called intake solenoid valve is replaced here by a hydraulic valve (volume governor).
The use of microcomputers in the electronic control unit has made it possible to equip the ABS with self-diagnosis and thus make diagnosis with TECH 1 possible.
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1 Hydraulic modulator 6 Diagnostic plug
2 Brake master cylinder 7 Electronic control unit
3 Brake servo 8 Wheel speed sensors, front
4 Brake proportioning valve 9 ABS telltale
5 Wheel speed sensors, rear
ABS Regulation
The ABS is intended as an addition to the conventional brake system (add-on system).
As long as there is no danger of wheel lock, the ABS remains passive, i.e. the brake pressure to the wheel cylinders corresponds to the pressure exerted by the driver. The pressure increase during normal braking is not influenced by the ABS hydraulic modulator.
If a wheel tends to lock, the ABS decreases the pressure at the brake on the relevant wheel by draining off part of the brake fluid in the brake cylinder into the hydraulic modulator reservoir chambers and then pumping it back into the brake master cylinder (recirculation principle).
ABS regulation occurs in millisecond pulses during the complete braking process.
This activity is signalled to the driver by:
- Brake pedal pulsing
- Sound of ABS activity
The pulsing in the brake pedal with slight brake pedal travel oscillations is caused by the brake fluid being pumped back from the hydraulic modulator.