Fail-Safe System Operation (Four or Two Wheel Push Through)

With the system active, and working normally, the normally open and normally closed valves become active when the driver steps on the pedal, and friction braking is desired. This opens up the simulator to the fluid input from the MC, and allows the boost valve to build pressure in the boost circuit that will actuate the wheel brakes. If the brake is applied with no power, or if the system detects a critical failure, these valves are not energized, resulting in a fail-safe system operation (push through) that allows the driver to push primary chamber fluid directly into the braking/boost circuits of all four wheels (four wheel push through). If a hydraulic failure occurs in the boost circuit a further pedal input will result in the primary piston of the MC directly contracting the secondary pistons and applying pressure to the front hydraulic circuits (two wheel push through). Slip control function are done by controlling the four isolation valves and the four dump valves in a manner common to how slip control functions are done in standard systems and is not described here.