Antilock brake system with controlled pressure augmentation

Abstract

An electrically controlled fluid displacement piston positioned in a bore modulates braking pressure at a wheel brake for antilock controlled braking by modulating the position of the piston in the bore. At a fully extended home position, a check valve is unseated by the piston to hydraulically couple the brake system master cylinder to the wheel brake. To minimize the occurrences of the condition where the check valve is opened during ABS controlled braking, the piston is initialized prior to entry into antilock controlled braking at a position away from the check valve resulting in a greater volume of fluid being trapped upon entry into antilock controlled braking when a hydraulic passage in parallel with the check valve is closed in response to a detected incipient wheel lock condition. This permits the antilock brake system to apply a controlled brake pressure greater than the pressure initially trapped in the closed system. The position of the displacement piston is monitored and when the piston approaches the position at which the check valve will be opened thereby opening the fluid communication between the master cylinder and wheel brake, the antilock brake system control parameters are adjusted to increase the system sensitivity to wheel slip.