1. Speed sensor for front wheels. 2. Speed sensor for the rear axle. 3. Hydraulic block. 4. Electronic control device. 5. Servo cylinder. 6. Steering column lock. 7. Control lamp of system ABS. 8. High voltage protection device. 9. Relay.
The ABS system prevents the brakes from locking up during hard braking, which leads to a shorter braking distance, as the positive control between the wheels and the road is improved when the wheels turn slightly. In addition, even with heavy braking, the car does not lose control.
The ABS system comes into a state of readiness after turning on the ignition and reaching a speed of 5-7 km / h. It begins to regulate all braking processes that can lead to blocking when the car exceeds a speed of 12 km / h.
Wheel speed is measured by speed sensors (two for the front wheels and one for the rear axle). Based on the signals from the sensors, the electronic control device calculates the average speed of the machine, which more or less coincides with the actual speed. By comparing the speed of rotation of an individual wheel with the average speed of movement, the control device quickly recognizes a possible skid and determines which of the wheels is close to blocking.
As soon as the wheel shows a tendency to lock up and the caliper pressure becomes too high for the wheel to hold the road, the control device sends a signal to the hydraulic system and the caliper pressure is reduced to a certain constant level. This means that the pressure in the caliper will not increase even with further pressure on the brake pedal. If the tendency to block the wheel does not disappear, the exhaust valve will open and the fluid pressure will decrease.
If the wheel speed increases beyond a certain amount, the hydraulic system will increase the pressure in the calipers, which, however, will not be able to exceed the pressure in the brake system as a whole.
During heavy braking, this process will be repeated until the brake pedal is released or until the vehicle speed drops to a very low value (5-7 km/h).
The safety switch of the electronic control unit ensures that the ABS system switches itself off in the event of any defects or if the operating voltage becomes too low (battery discharge to voltages below 10.5 V). At the same time, the control lamp of the system will light up on the dashboard while driving. The normal brake system will continue to work, however, when braking hard, the wheels will no longer be blocked.
The hydraulic block consists of a rear drop pump and three solenoid valves (one for each of the front wheels and one valve for the rear axle).
Pressure set: the inlet valve of the solenoid valve is open. The fluid pressure in the caliper can increase to a value determined by the brake master cylinder.
Maintaining a constant pressure: the inlet and outlet valves of the solenoid valve are closed. The fluid pressure in the caliper does not change even as the pressure between the master cylinder and the solenoid valve increases.
Pressure release: solenoid valve release valve is open. Brake fluid flows through the manifold block into the rear supply pump, which pumps it into the master cylinder.
The pump is necessary so that the brake fluid is not forced out of the master cylinder under pressure. The operation of the pump is felt by the pulsation of the brake pedal. Each of the brake circuits has one muffler, which removes noise from a running pump.
If the ABS warning light comes on while driving, it means that the system has switched itself off.
Shut off the engine and restart it.
Check battery voltage. If it is below 10.5 V, the battery must be recharged.
Note: If the ABS warning light comes on at the very beginning of the journey and then goes out, this indicates that the battery voltage was initially too low, but then increased due to charging from the alternator.
Raise and support the car, remove the front wheels. Check wiring for external damage.
A further check of the anti-lock braking system must be carried out in a specialized workshop.