Hybrid Braking System: Brake-By-Wire

Because much of the necessary brake torque required to stop the vehicle can be accomplished through regenerative braking, it is not always necessary to apply the conventional friction brakes. Under most normal brake applications, the ABS module applies the friction brakes as needed.

During a normal brake application, the brake pedal feel simulator allows the pressure applied to the brake pedal by the driver's 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 Modulated (PWM) voltage to a 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. This in turn pushes the piston in the master cylinder creating hydraulic brake pressure. If the brake pedal is applied quickly and forcefully enough, 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.