Abstract: A brake fluid pressure modulator (108) for an anti-lock braking system (ABS) (100) employs a combined isolation valve/displacement cylinder (130) to effect modulation of brake fluid pressure being delivered to a vehicle's wheel brakes (110F, 110R, 111F, 111R). A control valve assembly (140) reduces and reapplies brake fluid pressure by controlling flow of hydraulic fluid to a stepped piston (1315, 1317) in the displacement cylinder to move the piston against a biasing element (1321) such as a coil die spring. Piston movement against the spring closes an isolation check valve (1307, 1309) to prevent further brake fluid from the vehicle's master cylinder from being delivered to the wheel brakes. The cylinder cavity (1312) resulting from piston movement enables brake fluid to drain from the wheel brake back into the displacement cylinder.

Abstract: The device of the invention comprises a ball and socket and shoe assembly ich is pressure balanced with hydraulic fluid. This combination provides for low friction and relatively large travels when used as a linear to rotary motion actuator. In accordance with the contributions of the structural elements of the device, hydraulic pressure is applied to the rear of a piston by modulating the fluid pressure through a servo valve. Four pistons are typically used with two pistons driving the support spider clockwise and the other two driving the support spider counter clockwise. The control pressure produces a force through both the piston and pressure balanced shoes. The force is transmitted to the spider which is pivoted about flexures to produce a torque which results in a rotary motion of the spider (support).