The anti-lock braking system limits the pressure generated in the hydraulic brake actuator so that the amount of slip is optimal. The operation of this system must be separate for each wheel. The system must immediately respond to every surface change (adhesion coefficient) and vehicle loads.
The anti-lock braking system prevents the wheels from locking during heavy braking, thereby reducing the braking distance. The grip force between the wheels and the road in this case is greater if the wheels continue to rotate during braking. Even with full braking, the car remains steerable. Speed sensors, one for each wheel, measure wheel speed. Based on the signals from the sensors, the electronic control unit calculates an average speed that approximately corresponds to the speed of the vehicle. By comparing the rotational speed of each individual wheel with the average calculated speed, the ECU determines the slip state of the individual wheel and thereby determines which wheel is in the pre-lock state.
When one of the four wheel speed sensors transmits a lock signal to the corresponding wheel, the ECU immediately sends a close signal to the corresponding inlet solenoid valve, which shuts off the brake fluid supply through the wheel brake line. In this case, the braking force remains constant. If the sliding continues, the release valve opens and the pressure in the hydraulic system of this brake is reduced. The wheel does not brake, excess brake fluid returns to the reservoir. As soon as the wheel starts spinning again, the intake valve opens and the exhaust valve closes. The pressure in the circuit increases and the wheel brakes again.
The change between braking and free spinning cycles is very fast (several times per second) and continues until the vehicle stops or the brake pedal is released.
The process is repeated under hard braking separately for each wheel until the brake pedal is released.
The emergency system ensures that the ABS is turned off in case of any malfunction or low voltage in the car's on-board network (below 10 V). A faulty ABS does not affect the operation of the brakes.
The hydraulic drive consists of a hydraulic block, brake calipers and brake pipes. The hydraulic unit includes an electric pressure pump and solenoid valves.