Anti-lock brakes (ABS)

Braking performance is greatest when the grip of the tire with the road surface is greatest. During braking, tire slips on the surface, and the rolling velocity wheel becomes smaller than the vehicle speed.

Anti-lock braking system limits the pressure generated in the hydraulic brake actuator, so that the value of the optimum slip hold about. The effect of this system should be immediate and separate for each wheel. The system should respond immediately to each change of the surface (coefficient of friction), and the load on the car.

Anti-lock braking system prevents the wheels from locking under heavy braking, thereby improving the car's handling during braking, especially in poor grip in the rain and snow. The adhesive force between the wheels and the road in this case is greater when the braking wheel continues to rotate. Even at full braking the vehicle remains controllable. Speed sensors, one for each wheel, the wheel speed is measured. According to the signals from the wheel speed sensor electronic control unit calculates the average speed approximately corresponding to the vehicle speed. Comparing the speed of each individual wheel from the average speed calculation, the electronic unit determines individual wheel slip state, and thus determines which wheel is in a locked state.

When one of the four speed sensors transmit a signal lock on the wheel, the electronic control unit immediately produces a signal corresponding to the closing of the inlet solenoid valve that shuts off the brake fluid through the brake line to the wheel - braking force remains constant. If the slide continues, the exhaust valve opens and the pressure in the hydraulic circuit of the wheel brake is reduced - the wheel is released and the excess brake fluid returned to the reservoir. Once again, the wheel begins to rotate, the inlet valve opens and closes the exhaust valve. Circuit pressure increases, and the wheel is braked again.

Such a braking cycle and free wheel speed is very fast (on the order of 20 times per second).

This procedure is performed when braking for each wheel as long as the brake pedal is released or when the vehicle speed decreases to 2-3 km / h.

Emergency shutdown system will disable ABS for any failure or low voltage in the vehicle electrical system (below 10). The electronic control unit also performs the diagnostic function to alert the driver fire of a control lamp on the registration of malfunctions in electrical circuits, or elements of an anti-lock system. ABS fault does not influence the operation of the brakes, they operate as if the system is not in the car.