Hydraulic Brake Actuation (G2163191): Operation

As the brake pedal is pressed, the front push rod in the brake booster pushes the master cylinder primary piston along the bore of the housing. This produces pressure in the primary pressure chamber and in conjunction with the primary spring, overcomes the secondary spring and simultaneously moves the secondary piston along the bore.

The initial movement of the pistons away from the piston stops closes the primary and secondary center valves located inside the brake master cylinder. Further movement of the pistons then pressurizes the fluid in the primary and secondary chambers and the brake circuits. The fluid in the chambers behind the pistons is unaffected by the movement of the pistons and will flow unrestricted through the inlet ports, between the chambers and the reservoir.

Pressurized fluid enters the Hydraulic Control Unit (HCU). The HCU then modulates the supply of pressurized fluid to the brakes under control of the Anti-lock Brake System (ABS) control module. For additional information, refer to: Anti-Lock Control - Traction Control .