Power steering piston and cylinder combination with plastic wear surfaces

Abstract

Plastic wear strips are provided on a power steering piston or cylinder to improve the efficiency of translation movement of the piston in the cylinder during operation. The plastic surface of the strip, which is preferably on the piston, minimizes wear by providing a differential molecular structure at the interface between the cylinder wall and the surface of the piston since the cylinder wall is machined metal. The strips are positioned adjacent the ends of the rack where wear, caused by the load from the pressurized hydraulic fluid on the opposite side of the piston adjacent the inlet slot, is potentially the greatest. Plastic filling is provided in preferred arcuate grooves around the piston to form the wear strips. A single strip, or alternatively a group of independent strips, can be used and both serve to interrupt the surface of the piston so that molecular interaction of the two surfaces, or 'slip-stick' effect, is effectively prevented. The wear strips extend through a 60.degree. arc on both sides of the center line of the piston and the plastic is cured epoxy resin fixed in the grooves. Homogeneously dispersed metal chips stabilize the plastic. In a second embodiment, the plastic strips float within the grooves on a layer of hydraulic fluid provided by longitudinal channels formed on the surface of the piston. The method of preparing or manufacturing the piston and cylinder includes filling the grooves with the plastic and finishing the outer face within the mold and by milling the surface.