System ABS (Antilock Braking System)

Removal and installation of components of system ABS

On cars Golf III / Vento is installed as an option Antilock Braking System ABS manufactured by ITT Teves.

As a rule, if the vehicle is equipped with ABS, then in his rear wheels installed disc brakes. However, the ABS can be set and drum brakes at the rear wheels. In this case, inside the drums on the axle mounted wheel ring gears 1 (fig. 8.28) to determine the wheel speed.

The effectiveness of the braking of the car is higher, the greater is the friction between the tires and the road surface and the slip ratio is determined. The minimum slip (0%) occurs when the free rotation of the wheel, and the maximum (100%) - if the wheel is locked. When a slip ratio of 15% maximizes the braking effect of the wheels. When this condition is reached the best level of controllability and stability of the car under braking.

The ABS system enhances the active safety of the car and prevents the wheels from locking under heavy braking. Thus the car to a full stop shall be controllable without skidding. This is achieved by automatically releasing the brakes at the relevant wheel, then the braking is resumed.

The structure of ABS include: standard braking system, trailer wheel speed sensor, a hydraulic unit, an electronic control unit (ECU-ABS) and electrical wire harness. The general scheme of the ABS system is shown in Fig. 8.29.

For vehicles manufactured before January 1993, the control system ABS (computer-ABS) is located under the mat on the right front footwell. On models manufactured between January 1993 and February 1995, it is located under the rear right seat, and on models manufactured after February 1995, the control unit is mounted on the base of the hydraulic unit.

Wheel speed sensor ABS system transmit information in the form of an electric current alternating voltage of frequency of rotation of the wheels on the ABS-ECU. Speed sensors mounted on the front axle steering knuckle and the rear wheels - on the axis of the rear wheel paired with a ring gear arranged on the hub. ABS-ECU by signals from the four wheel speed sensors detects the signals, evaluates all deviations in relation to the pre-programmed parameters and measures the acceleration, deceleration or the slip of each wheel. Comparing the speed of each wheel with an average speed of all wheels, determines the degree of slip of the individual wheels and thus can set a time when one of them comes close to blocking. In addition, the sensor 6 (Fig. 8.30), brake pedal position, mounted on servo 1 also reports the computer-ABS as the brake pedal is pressed.

Based on this information, ABS ECU issues control pulses to the solenoid valves of the hydraulic unit 10, which turns off the master cylinder from the brake caliper 2 on the wheel, which can be locked.

If, however, the speed of rotation of the wheel continues to decline, the ABS-ECU activates the electric return pump, which pumps the brake fluid back into the master cylinder, reducing the pressure in the brake caliper so that the deceleration stop. As soon as the wheel speed becomes acceptable, the pump turned off, the solenoid valve opens, restoring in the caliper pressure generated by the master cylinder, resulting in a caliper braking starts again. This cycle can be made up to 10 times per second, much faster than can be achieved with "intermittent" brake pedal in cars. In addition, you can control a brake each wheel individually, not simultaneously, which occurs when you press the brake pedal in cars that do not have the system ABS.

If the wheel starts to spin faster, the ABS-ECU sends a signal to the pressure increase, but not above the total pressure in the brake system.

The driver feels the effects of ABS pulsing of the brake pedal and the characteristic sound of the hydraulic unit in the engine compartment that signals him of movement in border conditions.

ABS system operation depends entirely on the electrical signals. To prevent the system response to any false alarms, a built-in circuit monitoring of all signals received by ABS-ECU. Upon detection of a false signal or when the battery voltage is below 10 V, the system ABS is automatically disabled, and the dashboard warning lamp, notifying the driver that ABS is exhausted.

When the lamp is lit during the movement to stop and turn off the ignition and devices, and then restart the engine. After ignition hydraulic unit 60 for restoring the operating pressure in the system. ABS indicator flashes on 2-20 c depending on the pressure in the system. Then, the HV-ABS check individual components. Should be noticed any deviations from the ABS braking system will work as normal without the ABS braking system and warning lamp will illuminate. Failure of the ABS system allows the car to move, but requires more attention to the speed of traffic and road conditions, as management efficiency drops sharply.

If the warning light goes out, it means that the system voltage is above 10 V. If necessary, recharge the battery.

If the warning light does not glow due to the voltage drop, check the wires and connections associated with limit switches.

More sophisticated testing should be performed at service stations.

Reading the fault information from the ABS system memory self-diagnosis integrated into the ABS-ECU is made using special equipment VAG-1551.

However, you can make an ABS control system in the home with the help of the tester and megohmmeter by measuring voltage or resistance between terminals ABS-ECU connector. Control electrical values, the possible failure of ABS and remedies are presented in the Table. 8.3.