Principles of Operation: Brake-By-Wire

During a normal brake application, the brake pedal feel simulator allows the pressure applied to the brake pedal by the drivers foot to act against a spring instead of the brake booster push rod. The brake pedal angle sensor is mounted to the brake pedal assembly and provides the ABS module with an analog signal indicating the amount of deceleration the driver is demanding. If it is necessary for the conventional friction brakes to be applied, the ABS module applies a Pulse-Width Modulation (PWM) voltage to a vacuum solenoid inside the active brake booster. The solenoid allows vacuum from either the combustion engine (if the engine is running) or the electric vacuum pump to move the booster push rod in turn pushing the piston in the master cylinder creating hydraulic brake pressure. If the brake pedal is applied quickly and forcefully, the driver can overcome the brake pedal feel simulator spring pressure, allowing a direct connection between the brake pedal, booster push rod and master cylinder.