B. BRAKING WITH EBD INTO OPERATION: In case of a braking where the ABS ECU detects a slip difference between the front and rear wheels, EBD comes into operation. If the difference in wheel slip between the front and rear wheels exceeds a predetermined threshold the ABS activates the pressure inlet valves for the rear wheels, closing the valves and preventing further pressure build up at that rear axle. If during the braking event, this slip ratio between the front and rear axle reduces below the threshold level the inlet valves will be de-activated and switch back to their normally open state allowing further pressure increase at the rear axle. In this way the rear axle can follow more closely to the Ideal braking force distribution curve for the rear axle. If the driver releases the brake, the inlet valves will be deactivated and fluid can return to the TMC via the inlet valve and the one-way valve. EBD control only acts upon the rear axle and can only limit pressure being applied to a rear wheel; it cannot perform pressure reductions. Fig: Pressure increase on rear axle following ideal brake force distribution curve. C. BRAKING WITH ABS INTO OPERATION: In the case of braking where the ABS ECU detects a significant difference in the wheel speed information from the individual wheels. The electronic control unit instructs the hydraulic modulator to modulate the brake pressure being applied at the affected wheel(s). There are three stages to this control. 1. Pressure increase Phase: As the ECU detects that the speed of the controlled wheel has increased to the vehicle reference speed and hence the % slip reduced. It will sequentially deactivate the outlet and inlet valves switching them to their normal positions. With the outlet valve closed further pressure reduction is prevented and the inlet valve can be opened to allow brake fluid from the TMC to enter the wheel brake increasing the brake pressure once again. If the driver releases the brake at any time during ABS control the inlet valves will be deactivated and fluid can return to the TMC via the inlet valve and the one-way valve. SOLENO ID VALVE ELECTRI CITY STATUS VALVE OPEN OPEN- CLOSE CHANNE L CLOSE INLET ON CLOSE Master cylinder Wheel cylinder OUTLET OFF CLOSE Wheel cylinder Reservoir SOLENO ID VALVE ELECTRI CITY STATUS VALVE OPEN OPEN- CLOSE CHANNE L CLOSE INLET OFF OPEN Master cylinder Wheel cylinder OUTLET OFF CLOSE Wheel cylinder Reservoir BRAKE_PETROL 13
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