LS400 – NEW FEATURES 9 Operation When the driver depresses the brake pedal, the Skid Control ECU measures the depressing speed and force of the brake pedal from the master cylinder pressure sensor signals. Based on these measurements and the vehicle speed calculated from the speed sensors, the ECU determines whether the vehicle is in the state of emergency braking. Once the ECU determines a state of emergency braking, the ECU causes the solenoid valves in the brake actuators and the pump motor to operate. The hydraulic pressure that is generated by the pump is then sent to the wheel cylinders.
Accordingly, a higher hydraulic pressure than that generated by the brake pedal ap- plication is applied to the wheel cylinders, thus increasing the braking force. Furthermore, the ECU controls the solenoid valves to provide the proper amount of assist force in accordance with the driver’s brake pedal application. Brake Actuator Master Cylinder Master Cylinder Pressure Sensor a a b a b c c d d d d e e e e Pumps Reservoirs Rear Left Wheel Cylinder Rear Right Wheel Cylinder Front Left Wheel Cylinder Front Right Wheel Cylinder 173LS04 a: Master Cylinder Cut Solenoid Valve d: Pressure Holding Valve b: Reservoir Cut Solenoid Valve e: Pressure Reduction Valve c:
Pressure Regulator Valve Cut Solenoid Valve Fail Safe In the event of a malfunction in the ABS or VSC system, the Skid Control ECU prohibits the Brake Assist system.