Axial piston pump including ball piston

Claim 1

A piston pump assembly (10,10') comprising: housing means; a cylinder barrel (18,18') having an axis of rotation and being rotatably supported in said housing means about said axis of rotation, said cylinder barrel (18,18') including a plurality of piston cavities (20,20'); cam means (30,30'); and piston means (22,22') reciprocally supported in each of said piston cavities (20,20') for reciprocating movement and reacting with said cam means (30,30') and causing said reciprocating movement of said piston means (22,22'), said piston means (22,22') including a body portion (44,44') having a longitudinally extending central bore (46,46'), one end of said bore (46,46') defining a fluid inlet (48,48') into said bore (46,46') and the other end of said bore (46,46') defining a fluid outlet (51,51'), said assembly (10,10') characterized by said fluid inlet (48,48') including a ball seat (50,50') and a ball member (52,52') seated therein and substantially over said fluid inlet (48,48'), said ball member (52,52') engaging said cam means (30,30'), said seating surface (50,50') including at least one groove (54,54') extending from said fluid inlet (48,48') to the remainder of said bore (46,46') for facilitating fluid flow about said ball member (52,52'), said bore (46,46') including an enlarged main portion (60,60') extending along substantially the length of said piston means (22,22') and a secondary portion (62,62') in fluid communication between said main bore (60,60') and said fluid inlet (48,48') and having a smaller diameter than said main bore (60,60'), said main bore (60,60') including a terminal wall (64,64') having an opening (66,66') therethrough defining said secondary bore (62,62'), a check ball (74,74') disposed adjacent to said secondary bore (62,62') and biasing means for biasing said check ball (74,74') against said secondary bore (62,62') for allowing one way fluid flow through said secondary bore (62,62') to said main bore (60,60'), said biasing means including a support member (70,70') having a hub portion (76,76') and a rim portion (78,78'), an external spring member (80,80') disposed within said main bore (60,60') and engaging said rim portion (78,78') for biasing said support member (70,70') against said terminal wall (64,64') and an internal spring (82,82') disposed between said hub portion (76,76') and said check ball (74,74') for urging said check ball (74,74') into sealing engagement with said secondary bore (62,62').