Closed cavity hydraulic piston and method of making the same

Abstract

A hydraulic piston for a cylinder block of a hydrostatic power unit has an elongated cylindrical body with first and second ends. An elongated cavity is formed in the body. A cap is adhered to the body to close the cavity. The cap has an external shape to facilitate the operative engagement thereof with a slipper, which is in subsequent engagement with a swashplate mounted adjacent the cylinder block. The piston has an elongated first conduit formed in the body which is separate from the cavity and extends between the opposite ends thereof. The conduit terminates in registering communication with a second conduit in the cap thereof to permit transmission of oil through the conduit without invading the volume of the cavity. The cap preferably has a tapered surface on the inner end thereof engaging a compatible shaped surface on an adjacent end of the body to center and align the cap with the body. The tapered surfaces of the cap and body terminate in parallel wall surfaces to create a continuous arcuate interface therebetween which is filled with an adhesive material such as a brazing medium. The body member and the cap are of metallic construction with the material of the cap member being more malleable than the material of the body so as to permit subsequent crimping of the cap as may be required. The body and the cap are preferably formed by a metal injecting molding process utilizing a molding material comprised at the time of molding of a mixture of metallic grains and a binder. The body member and the cap are subjected to a debinding process whereupon the binder material is removed from the molding material and the components are sintered whereupon controlled shrinking occurs. The cap is adapted to terminate either in a spherical ball for attachment to a slipper element, or is comprised of a spherical socket adapted to receive a ball element attached to a slipper element.