Abstract: Vehicle wheel slip is controlled by an add-on brake pressure modulator that may function in addition to limit the brake pressure applied to the vehicle wheels during anti-lock braking. A piston is moved in a cylinder to regulate the braking pressure. During non-operating conditions of the modulator the piston is moved to provide minimum cylinder volume to be in condition to be moved to withdraw fluid from the brake system to limit brake pressure. When a potential for excessive slip of a driven wheel is detected, the piston is moved to increase the volume of the cylinder to draw in braking fluid from a reservoir. The modulator is then in condition to apply regulated brake pressure to limit excessive slip. When the potential for excessive slip no longer exists, the piston is controlled to provide minimum volume while returning the brake fluid to the reservoir. The modulator is then again in condition for limiting brake pressure.

Abstract: A wheel lock control system is described which utilizes both independent and select low modes of wheel lock controlled braking. When braking on a surface in which the coefficients of friction between the two sides of the vehicle are substantially different or when the vehicle is undergoing severe steering maneuvers while braking, the wheel lock control system utilizes a select low mode of braking for the vehicle rear wheels so as to maintain vehicle stability. However, when the four wheels are being braked on a substantially uniform coefficient of friction surface, the wheel lock control system utilizes an independent mode of braking for each of the wheels of the vehicle so as to minimize the vehicle braking distance.

Abstract: An excessive slipping condition of one of the driven wheels of a vehicle that is indicative of a loss of traction of that wheel is sensed based on the difference in the driven wheel speeds. An increasing braking force is applied to the wheel with excessive slip to transfer driving torque through the differential to the non-slipping wheel so as to equalize the driven wheel speeds. In order to provide for compensation of the difference in wheel speeds that is not due to slip that occurs as the vehicle is turning, the speeds of the driven wheels are compensated based on the difference in speeds of the undriven wheels.