Braking is most effective when the tyre has maximum grip on the road surface. When braking, the tire slides on the surface and the peripheral speed of the wheel becomes less than the speed of the car.
Minimal slip is when the wheel rolls freely and maximum slip is when the wheel is locked. The greatest braking efficiency is achieved when the peripheral speed of the wheel is almost equal to the speed of the vehicle.
The anti-lock braking system operates based on information from four sensors transmitted to the ABS unit. The system controls each wheel separately and reduces the fluid pressure in the wheel brake mechanism whose wheel begins to lock.
Under normal conditions, the standard brake system applies the brakes until the wheel locks up, which is detected by the ABS control unit. When the ABS control unit detects a wheel lock up, it controls each valve to increase or decrease the pressure.
The ABS control unit determines the rotation speed and deceleration rate of each wheel based on information from the wheel speed sensors. When braking, the wheel speed decreases and the ABS unit detects the difference between the vehicle speed and the wheel speed. If the deceleration of some wheels exceeds the expected value, the ABS unit detects the onset of locking and opens the corresponding solenoid valves to reduce the brake fluid pressure. At the same time, the wheel rotation speed increases and the electromagnetic pressure relief valve closes, increasing the brake fluid pressure in the working brake cylinder of the corresponding wheel.
Electrohydraulic control unit for anti-lock braking system
Control unit
The ABS control unit performs self-diagnostics and checks of the ABS electrical system every time the ignition is turned on. During the test, the ABS indicator light comes on.
The control unit also performs functional tests of the solenoid valves, pump, and modulator, and a slight pulsation in the brake pedal is felt.
If a fault occurs that affects the operation of the ABS, the control unit switches off the ABS, turns on the ABS indicator lamp and stores the fault code.
The absence of a signal from one front wheel speed sensor does not result in ABS being disabled, as the control unit will continue to control the system using the remaining signal from the second front wheel sensor.
If there is a fault in the ABS, the system switches to conditional braking mode.
Error codes can be read with the TECH 2 device.
The shift control unit sends a signal to the ABS control unit while driving whether the drive is on two or four wheels. Based on this signal, the ABS control logic changes the braking parameters.
Visitor comments