Radial piston type pumps or motors

Claim 1

A radial piston type pump or motor comprising a body, an inlet and an outlet in the body, a rotor mounted within the body, two axially spaced rows of pistons movable in radial bores in the rotor, the bores communicating in turn with the inlet and with the outlet in the body, a pair of rings defining respective annular inner surfaces with which the rows of pistons engage respectively, to cause the same to be reciprocated as the rotor rotates, the rings being capable of being disposed in positions in which said surfaces are eccentric to one another with respect to an axis of rotation of the rotor, the eccentricity of the respective surfaces of the rings being of equal magnitude with respect to said axis and at opposite sides of the axis, a pair of side by side control pistons arranged at the same side of said rings to act against the outsides of the rings respectively, passage means for entry of fluid under pressure to these pistons to control the eccentricity of the rings respectively, said passage means being capable of communicating with the outlet, the passage means including a bore containing a spool valve for controlling the supply of fluid to the two pistons respectively and said control pistons being of different sizes, with the piston of smaller size being open to high pressure fluid at all times and the piston of larger size being open to high pressure fluid under the control of the spool valve, a valve housing having a longitudinal chamber and a pair of ports, each port communicating with a cylinder in which the control pistons are mounted, a third port supplying fluid at the outlet pressure to the chamber via the cylinder of smaller diameter and the port communicating with the chamber, and subjecting the piston in the smaller cylinder to such outlet pressure, said spool valve having axially spaced lands and being movable in the chamber which constitutes the bore of the passage means, spring means within the valve housing cooperable with the spool valve to move the valve to a position in which one of the lands closes the port providing communication between the chamber and the cylinder of larger diameter and the other land opens the port providing communication between the chamber and the cylinder of smaller diameter, a fourth port providing communication between the cylinder of smaller diameter and the chamber between the spaced lands of the valve, so that upon an increase in the outlet pressure, the valve is moved against the action of the spring means to move the land to open the port between the chamber and the cylinder of larger diameter, whereby the cylinder of larger diameter communicates with the cylinder of smaller diameter via the chamber and fourth port to cause a reduction in eccentricity of both rings to reduce the output volume, while upon a reduction in outlet pressure, the spring means moves the spool valve in the opposite direction to allow fluid in the cylinder of larger diameter to escape through the portion of the valve casing containing the spring means to the body interior at the inlet pressure whereby the piston and the cylinder of larger diameter moves to increase the eccentricity of the ring associated therewith and in turn effect a similar change in the eccentricity of the ring associated with the piston in the cylinder of smaller diameter.