The brake system includes an electrically driven hydraulic pump to generate the servo pressures for ABS/ASR control. The control system also monitors the time taken for the pump to run down after switching off. This provides a measure of the viscosity of the brake fluid and hence its temperature. The temperature values are used for correcting the brake control. The actual time taken for the pump to run down from its operating speed to a threshold speed provides the control signal. The pump speed can be determined directly by monitoring the voltage across the electric motor driving the hydraulic pump. The control system has reference values of run down times versus temperature. Correction is made for the progressive change in run down time with ageing of the pump and motor.
