45 ABS 5.3 (3-channel system) system description · ABS operation

45 ABS 5.3 (3-channel system) system description ABS operation In addition,whenevera journey is begun and aThe ABS control module receives a signal from speed of 6 km/h is exceeded,a testthe brake~ightswitch and the AC voltage signals from the four speed sensors. These signals are programme is started. The solenoid valves and the pump motor are electricallyactuated andconverted into digital wheel-speedsignals inde- checked. If a fault is detected, the controlpendently of each other by two microproces- module switches the ABS function off, the ABSsors. The wheel slip (approximatelyproportional warning light is switched on and tlIe fault isto the computed vehicle reference speed)is for- stored.med from these wheel-speedsignals. Function of the individualcomponents on Page If vehicle deceleration and excess slip at a 45 -7.wheel are detected, the pressure-holdingphase is initiated, i.e. the inlet valve for the relevant wheel is closed to prevent a further increase in pressure. If in spite of the pressure being held constant the wheel tends to continue to lock up, the pressure in the wheel cylinder is reduced. For this purpose, the outlet valve is opened and the brake fluid is pumped back to the brake master cylinder via the return pump (pressure- reduction phase)until the wheel turns again. Then, depending on the control cycle, further appropriate cycles are initiated. This function and the input signals are con- tinuouslymonitored. If a fault is detected, the control module switches the ABS function off.. switches on the ABS warning light and stores the fault in a non-volatilememory in the control module. 45 -2 45 ABS 5.3 (3-channel system) system description 996451 Printed in Germany, 1997