Attention! On models with a speed control system, the ABS unit performs the functions of an anti-lock braking system (ABS) and vehicle speed control systems (ASR).
Models without Vehicle Speed Control
The anti-lock braking system is installed by the manufacturer on most cars, and on the remaining cars it can be installed as an option. The system consists of a hydraulic unit with three hydraulic solenoid valves, one for each front brake and one valve for the rear brakes, an electrically driven pump, three wheel sensors and an electronic control device (ECU). The anti-lock braking system prevents the wheels from locking during heavy braking. Thanks to this, the car remains steerable under full braking. Based on the signals from the wheel sensors, the ECU can determine the speed of the vehicle. By comparing the speed of a single wheel with the average speed of the vehicle, the control unit determines the state of wheel lock. When the wheel approaches blocking, the brake fluid pressure is too high, so the pressure in the caliper is reduced on a signal to the control unit by turning on the corresponding solenoid valve, which isolates the corresponding brake caliper from the brake master cylinder.
If the wheel speed continues to decrease, the ECU turns on the return pump and pumps fluid from the corresponding caliper to the brake master cylinder. After the wheel begins to rotate at normal speed, the pump turns off and the solenoid valve opens, as a result of which the brake fluid is supplied to the caliper in normal mode and the wheel is braked. The operation of the anti-lock braking system during hard braking is repeated on each wheel until force is applied to the pedal or the car stops. The cycle of the anti-lock braking system is repeated up to 10 times per second. When the anti-lock braking system is operating, a pulsation is felt on the brake pedal.
In the event of any malfunction in the anti-lock braking system, it is disabled. In this case, the ABS warning lamp on the instrument panel comes on and the brake system operates normally. Troubleshooting of the anti-lock braking system must be carried out at a service station.
Models with Vehicle Speed Control (ASR)
On models with vehicle speed control, the hydraulic system consists of four solenoid valves, an electrically operated return pump, a valve that switches the hydraulic device from anti-lock to vehicle speed control, and a pressure control system pressure control valve. The vehicle has two electronic control devices (ECU), one of which controls the hydraulic unit, and the second controls the throttle position actuators. An additional pump and pressure accumulator are also installed. In order to create and maintain the pressure in the system necessary to perform the braking functions during the operation of the vehicle speed control system.
The vehicle speed control system eliminates the loss of wheel traction with the road surface. The system adjusts the rear wheel speed by braking the wheel or closing the throttle, depending on the speed of the vehicle. In some cases, both wheel braking and throttle closing can be performed.
Wheel braking is carried out as follows. In case of loss of adhesion of the wheel to the road surface, the wheel begins to rotate at an increased speed, and the hydraulic device from the pressure accumulator supplies brake fluid under pressure to the caliper of the corresponding wheel and brakes the wheel. After the wheel returns to normal speed, the hydraulic device returns fluid to the pressure accumulator.
Throttle control is as follows. Upon loss of wheel traction, the second electronic control device actuates the throttle actuator, which reduces engine speed by closing the throttle. As soon as the wheel begins to rotate at normal speed, the throttle actuator returns it to its original position.
If a fault is found in the vehicle speed control system, contact a service station.