The ABS system improves the vehicle's active safety and prevents the wheels from locking during heavy braking. At the same time, the car maintains controllability until it comes to a complete stop, without skidding.
The ABS includes a standard braking system, wheel speed sensors, a hydraulic unit, an electronic control unit (ECU-ABS) and wiring harness.
The ABS wheel speed sensors provide wheel speed information in the form of AC voltage to the ABS-ECU. The speed sensors for the front wheels are located on the steering knuckles, and the rear wheels - on the trunnions.
The ABS ECU uses signals from all four wheel speed sensors to measure the acceleration, deceleration or slip of each wheel. By comparing the speed of rotation of each wheel with the average speed of all wheels, the ABS-ECU determines the degree of slippage of individual wheels and thus can determine the moment when one of them comes close to blocking, and on the basis of this information issues control pulses to the solenoid valves of the hydraulic unit. As soon as one of the wheels approaches blocking, the pressure of the brake fluid in its caliper becomes too high in relation to the grip of the tire with the road. The hydraulic system under the influence of control signals maintains the pressure of the brake fluid stable. This means that the pressure in the caliper does not increase even with further pressure on the brake pedal. If the danger of blocking persists, the pressure is reduced by opening the exhaust valve, but only to such a level that the wheel begins to accelerate somewhat again, after which the pressure is again maintained constant.
If the wheel starts to turn faster, the ABS-ECU issues a signal to increase the pressure, but not higher than the total pressure in the brake system. The driver feels the action of the ABS by the pulsation of the brake pedal and the characteristic sound of the valve body in the engine compartment, which signals him to move in boundary conditions.
The valve body is installed on the brake line after the main brake cylinder. A solenoid valve is installed on each of the four pipelines suitable for the valve body, which diverts the brake fluid to an electric pump that provides brake pressure in the line of a particular wheel.
In the event of a malfunction of the ABS system, the ABS ECU stops generating control pulses, and the ABS warning lamp in the instrument cluster is constantly lit. The failure of the ABS system allows the car to move, but requires more attention to speed and road conditions, as the efficiency of control is sharply reduced.
Attention! All work on the ABS system is carried out with the ignition off and the terminal removed «–» AB. Before working with electric welding equipment, disconnect the connector block of the ABS-ECU.
Attention! Check the ABS, repair the valve block, ECU-ABS or pipelines at a workshop.
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