Radial piston hydrostatic machine with a first sweeping-displacement

Abstract

A radial piston hydrostatic machine having a first fluid displacement stage and a second fluid displacement stage, the machine having an outer housing structure for defining an internal chamber, a drive-shaft supported in the housing and operatively connected to a cylinder-barrel located within the internal chamber, the cylinder-barrel having a number of radial cylinders and each cylinder containing a piston operatively connected to a surrounding annular track-ring, the cylinder-barrel and pistons defining a rotating-group and where the rotating-group is positioned in a sub-chamber generally defined axially by the width of the track-ring and radially by the radial distance between the cylinder-barrel and surrounding track-ring. The volume space between adjacent pistons defined as cells and fluid distribution means in the housing comprising two or more ducts lying axially adjacent the rotating-group and generally radially inwards of said track-ring to communicate with the sub-chamber to provide a first stage pumping motion when the track-ring is eccentric in position in relation to the cylinder-barrel in order to 'prime' the second stage piston reciprocating assembly in the cylinder-barrel. The invention further allows more than one hydrostatic machine to be driven by the same drive-shaft whereby the drive-shaft can be extended to pass through the machine without problems arising because the low-pressure fluid passages are restricted in size.