ABS serves to regulate the pressure in the brake mechanisms of all wheels when braking in difficult road conditions and thereby prevents the wheels from locking.
The ABS system provides the following benefits:
- avoiding obstacles with a higher degree of safety, including during emergency braking;
- reduction of the braking distance during emergency braking while maintaining roadholding and controllability of the car, including when cornering.
In the event of a system failure, functions for diagnosing and maintaining operation in case of system failures are provided.
The hydroelectronic control module receives information about vehicle speed, direction of travel and road conditions from wheel speed sensors, throttle position sensor. After the ignition is switched on, the control unit supplies voltage to the wheel speed sensors, which use the Hall effect. The sensors generate an output signal in the form of rectangular pulses. The signal changes in proportion to the rotational speed of the encoder driving ring.
Based on this information, the control unit determines the optimal wheel braking mode.
There are the following modes of operation of the anti-lock braking system:
- normal braking mode. During normal braking, the intake valve is open and the exhaust valve is closed. When the brake pedal is pressed, brake fluid is supplied under pressure to the working cylinder and actuates the brake mechanisms of the wheels. When the brake pedal is released, the brake fluid returns to the brake master cylinder through the intake and check valves;
- emergency braking mode. If a wheel lock occurs during emergency braking, the module issues a command to the pump motor to reduce the supply of brake fluid, then voltage is applied to each solenoid valve. The intake valve closes and the brake fluid supply from the master cylinder and pump is shut off; the release valve opens, and the brake fluid flows from the working cylinder to the master cylinder, and then to the reservoir, which causes a decrease in pressure;
- pressure maintenance mode. When the pressure in the working cylinder is reduced to the maximum, the module issues a command to maintain the brake fluid pressure, voltage is applied to the intake valve and not applied to the exhaust valve. At the same time, the inlet and outlet valves are closed and the brake fluid does not leave the working cylinder;
- pressure boost mode. If the module determines that the wheel is not blocked, then the voltage is not applied to the solenoid valves, the brake fluid through the inlet valve enters the working cylinder, the pressure in which increases.
To diagnose the anti-lock braking system, special equipment and equipment are required, so if it fails, contact a specialized service center.
This subsection describes only the removal and installation of wheel speed sensors. When removing and installing the hydro-electronic unit, air can get into the valve system of the unit, which requires special equipment to remove. Therefore, we recommend that if you need to remove and install the unit, contact a specialized service center.