Brake Pedal Feel Simulator and Cut-Off Device

When the ignition is turned on, the ABS module runs a series of checks to make sure the system is running properly. Once these checks are complete, the ABS module closes the valve in the simulator cut-off device which puts the brake system into brake-by-wire mode. Brake-by-wire mode is when the pedal feedback to the driver is provided by the pedal feel simulator and not by the pressure in the hydraulic brake system. The simulator uses spring pressure to provide a familiar brake pedal sensation. When the driver presses the brake pedal, the ABS module interprets the pedal movement through the brake pedal angle sensor. Based on the pedal angle and the amount of brake torque that can be provided through regenerative braking, the ABS module determines how much brake torque will be provided by the powertrain and how much will be provided by the hydraulic brakes. The brake pedal is uncoupled from the brake booster push rod allowing the system to hold off hydraulic pressure when regenerative braking is providing the necessary brake torque. When hydraulic braking is required, the ABS module activates the booster solenoid which allows the vacuum booster to push on the master cylinder creating pressure in the hydraulic system. In the event a fault occurs which inhibits the brake-by-wire mode, the ABS module will open the cut-off device valve. This puts the system into conventional mode with vacuum boosted hydraulic brakes and no regenerative braking. In this mode, the pedal feedback to the driver is provided by the booster. When the driver pushes the pedal, the uncoupling between the pedal and the booster push rod is overcome, and the pedal arm will push on the booster push rod as in a conventional brake system.