Multi-cylinder barrel hydraulic pumps or motors

Claim 1

A pump or motor of the multi-cylinder barrel type, of which the capacity is adapted to be varied by displacing the barrel in a support adapted to be inclined in the pump body about a pivot axis perpendicular to the axis of rotation of the barrel, the pistons being provided with ball-headed rods positively connecting said pistons to an impeller plate which positively connects the barrel with the pump driving shaft, said barrel comprising a slide face into which open the cylinder ports, said slide face being in rotary contact with a distributing slide face of a distributor plate in which two fluid passages are formed which open each into said distributing slide face through a port having the shape of a sector of an annulus and communicating with suction and delivery ducts of the pump, wherein the impeller plate is balanced axially by a hydrostatic bearing having an alignment with the bearing face of the impeller plate in the pump body at least one port corresponding to the delivery port of said distributing slide face and adapted to be connected to the pump delivery side through a balancing valve which comprises in the barrel support a control piston responsive to the delivery pressure and in the pump body a valve controlling the communication between the aforesaid port of the hydrostatic bearing and the delivery side of the pump, said control piston and said valve coacting in opposition with each other whereby the balancing pressure exerted against the hydrostatic bearing of said impeller plate varies as a function of the inclination of the barrel support during operation, and therefore as a function of the axial stress to be balanced at the impeller plate.