The ABS system increases the active safety of the car and prevents the wheels from locking during sudden braking. At the same time, the car remains controllable until it comes to a complete stop, without skidding.
The ABS consists of a standard braking system, wheel speed sensors, a hydraulic unit, an electronic control unit (ECU-ABS) and an electrical wiring harness.
The ABS wheel speed sensors transmit information in the form of alternating current about the wheel speed to the ABS ECU. The front wheel speed sensors are located on the steering knuckles, and the rear wheel speed sensors are located on the journals.
The ABS control unit measures the acceleration, deceleration or slip of each wheel using signals from all four wheel speed sensors. By comparing the rotational speed of each wheel with the average speed of all wheels, the ABS control unit determines the degree of slip of the individual wheels and can thus determine the moment when one of them is about to lock, and on the basis of this information, it issues control pulses to the electromagnetic valves of the hydraulic unit. As soon as one of the wheels is about to lock, the brake fluid pressure in its caliper becomes too high in relation to the grip of the tire on the road. The hydraulic system, under the influence of the control signals, keeps the brake fluid pressure stable. This means that the pressure in the caliper does not increase even when the brake pedal is further pressed. If the risk of locking remains, the pressure is reduced by opening the release valve, but only to a level where the wheel begins to accelerate slightly again, after which the pressure is again maintained constant.
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If the wheel starts to rotate faster, the ABS ECU issues a signal to increase the pressure, but not higher than the overall pressure in the brake system. The driver feels the ABS action by the pulsation of the brake pedal and the characteristic sound of the hydraulic unit in the engine compartment, which signals him about driving in boundary conditions.
The hydraulic unit is installed on the brake line after the main brake cylinder. Each of the four pipelines approaching the hydraulic unit has an electromagnetic valve that diverts the brake fluid to an electric pump that provides brake pressure in the line of a specific wheel.
If the ABS system fails, the ABS ECU stops generating control pulses, and the ABS indicator lamp in the instrument cluster is constantly lit. Failure of the ABS system allows the vehicle to move, but requires greater attention to the speed and traffic conditions, since control efficiency is sharply reduced.
Attention! All work on the ABS system is carried out with the ignition off and the "-" terminal of the battery removed. Before work using electric welding equipment, disconnect the ECU-ABS connector block.
Attention! Check ABS, repair valve block, ECU-ABS or pipelines at a service station.
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