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Anti-lock braking system (ABS)

As a special equipment VW T4 has the anti-lock system BOSCH (ABS). Additional installation of ABS is not possible.

ABS prevents the wheels from locking under heavy braking. Consequently, at full braking the vehicle remains controllable.

ABS is as soon as the ignition is on and speed of 5-7 km / h. It governs all the inhibitory processes in the lock as soon as the speed exceeds 12 km / h.

Due RPM sensor, two on the front and rear wheels measured wheel speed. By analyzing the signals of the individual sensors of revolutions, the electronic control unit calculates the average speed, which corresponds approximately to the average speed of the machine. Thanks compared individual wheel speed and the average speed of the wheels, the control unit detects the status of the individual wheel slippage and can thus capture the state of the wheel shortly before its freezing.

Ability to lock the wheel means that the brake fluid pressure in the corresponding brake mechanism is too big in relation to traction, in this case hydraulic, receiving signals from the control unit maintains a constant fluid pressure. Namely, the pressure in the brake mechanism does not rise, even if pressing the brake pedal more strongly. If the possibility of locking is maintained, the fluid pressure decreases as the opening of the exhaust valve, but so that the wheel is slightly accelerated, then the pressure was again kept constant.

If the wheel is accelerated more certain value, the pressure of the hydraulic system increases again, but not more than the total braking pressure.

This operation is repeated when braking for each wheel individually, as long as the brake pedal is returned to its original position or shortly before the machine stops.

The safety device in the electronic control unit ensures that the ABS, in the event of a malfunction (eg open circuit) or too low voltage onboard power supply (battery voltage is less than 10.5) itself is turned off. In this case, the control light ABS on the instrument panel while driving. Normal braking system keeps working. Vehicle braking behaves as if the ABS and is not installed.

If during movement control lamp ABS lights up, this is a signal that the ABS system is disabled. In this case:

- Briefly stop the car, stop the engine and restart;
- Check the battery voltage;
- If the voltage is below 10.5 volts, recharge the battery.

If the control bulb ABS lights up with the beginning of the movement and after a while goes out again, this indicates that the battery voltage at the beginning was too little, but then rose as a result of charging from the generator.