ABS prevents the wheels from locking when braking. This reduces the braking distance, especially when there is poor traction on the road surface (for example, in the rain or snow). Thanks to this, the car does not lose control even under full braking.
The anti-lock braking system works as follows. The speed of rotation of the wheels is measured by speed sensors, one on each wheel. From the signals from the sensors, the computer calculates an average speed, which roughly corresponds to the speed of the car. By comparing the rotation speed of each individual wheel with this calculated value, the computer recognizes the state of slippage of one or more wheels.
As soon as the wheel becomes prone to locking, that is, the brake fluid pressure in the caliper of this wheel is too high in relation to the force of the wheel's adhesion to the road, the brake system, on a signal from the computer, begins to prevent the pressure in the caliper of this wheel from increasing (the pressure remains constant even when the brake pedal is pressed harder). If the tendency to lock remains, the computer reduces the fluid pressure in the caliper of that wheel, but as soon as the wheel speed increases again, the pressure stops decreasing. When a certain wheel speed is reached, the computer increases the pressure, without exceeding the total pressure value in the brake system at that time.
This process is repeated many times for each wheel. The ABS works until the foot is removed from the brake pedal and also shortly before the car comes to a complete stop (at about 4 km/h).
To ensure normal operation of the ABS on all-wheel drive vehicles, the rear wheel brakes are automatically released by a viscous coupling if necessary.
The emergency shutdown system disables the ABS in case of failure (for example, a broken wire) or at low voltage in the on-board network (below 10.5 V). In this case, the ABS indicator light comes on on the instrument panel. The braking system works as if the car does not have ABS.
When the ABS indicator light comes on while driving, it indicates that the system is disabled.
1 - computer
2 - ABS indicator lamp
3 - speed sensor (in all-wheel drive vehicles, the rear sensors are located on the left and right sides of the rear axle gearbox)
4 - hydraulic block
5 - overvoltage protection relay
(Material copied from the portal: OpelBook)
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