ABS is used to regulate the pressure in the brake mechanisms of all wheels when braking in difficult road conditions, which prevents the wheels from locking.
The ABS system provides the following benefits:
- avoiding obstacles with a higher degree of safety, including during emergency braking;
- reducing the braking distance during emergency braking while maintaining the vehicle's directional stability and controllability, including when turning.
In case of system failure, diagnostic functions and system failure support are provided.
The hydroelectronic control module receives information about the vehicle speed, direction of travel and road conditions from the wheel speed sensors. After the ignition is turned on, the ABS module supplies voltage to the sensors. The sensors, which use the Hall effect, generate an output signal in the form of rectangular pulses. The signal changes proportionally to the rotational speed of the pulse ring of the sensor, built into the front hub bearing seal and directly into the rear hub.
Based on this information, the module determines the optimal wheel braking mode.
The following operating modes of the anti-lock braking system are distinguished:
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- normal braking mode. During normal braking, the electromagnetic valve is de-energized, the inlet valve is open, and the outlet valve is closed. When the brake pedal is pressed, the brake fluid under pressure is supplied to the working cylinder through the electromagnetic valve and activates the wheel brake mechanisms. When the brake pedal is released, the brake fluid returns to the main brake cylinder through the inlet and check valves;
- emergency braking mode. If the wheel starts to lock during emergency braking, the module sends a command to the electromagnetic valve to reduce the supply of brake fluid, then voltage is supplied to each electromagnetic valve. The inlet valve closes, and the supply of brake fluid from the master brake cylinder is blocked: the outlet valve opens, and the brake fluid flows from the slave cylinder to the master cylinder, and then to the reservoir - the pressure decreases;- pressure maintenance mode. When the pressure in the working cylinder drops to the maximum, the module issues a command to the electromagnetic valve to maintain the brake fluid pressure, voltage is supplied to the input valve and is not supplied to the output valve. In this case, the input and output valves are closed and the brake fluid does not leave the working cylinder;
- pressure increase mode. If the module determines that the wheel is not locked, it de-energizes the electromagnetic valve. Voltage is not supplied to the electromagnetic valves, the brake fluid enters the working cylinder through the inlet valve, where the pressure increases.
The ABS hydro-electronic module and wheel speed sensors are also used in the electronic stability program (ESP), which is installed on vehicles by special order. In this system, the hydro-electronic module analyzes signals from the wheel speed sensors, as well as the angular and linear acceleration sensor of the vehicle and the steering wheel angle sensor of the vehicle. Based on the signals from the sensors, the hydro-electronic module determines whether the front axle is understeered or the rear axle is skidding. In the event of a front axle understeer, the module corrects the vehicle's trajectory by braking both front wheels and the rear wheel on the inside of the turn, and also by sending a signal to the control unit to reduce torque. In the event of a rear axle skid, the trajectory is corrected by braking the front wheel on the outside of the turn, and, if necessary, both rear wheels. The ESP steering wheel angle sensor is installed in the steering column, and the angular and linear acceleration sensor is located under the floor tunnel lining.
If a fault occurs in the ABS system, contact a service station, as special equipment is required for its diagnosis and repair.