Abstract: By using an existing ball nut and ball nut screw of a ball nut screw assembly as master models, imprint molds can be molded from a silicone rubber material which positively profiles the threading of the ball nut and ball nut screw with the crossover channel in the master model of the ball nut. A thermoset resin is added to the imprint molds and cured to form unitized all plastic ball nuts and ball nut screws with the helical grooving for accommodating the train of balls including the crossover channel in the ball nut molded therein to thereby provide an easily reproducable ball nut and screw assembly.

Abstract: This power steering gear comprises a piston nut movably mounted in a housing for turning a gear sector and the steerable wheels of a vehicle operatively connected thereto. The piston nut is mechanically moved by a rotatable screw, threadedly engaged with the piston nut and operatively connected to an input stub shaft. Hydraulic power assist is provided with the piston nut forming separate expansible and contractible chambers filled with hydraulic fluid and controlled by integral valve means in the gear. The threads of the piston nut and screw are profiled to contact at their minor diameters to increase thread efficiency by reducing the friction radius. The threads of the piston nut are made with optimized thickness to reduce flank clearance to further restrict the hydraulic flow path through the thread to effectively seal the chambers from each other.