Swash plate type hydraulic pump or motor

Abstract

A swash plate type hydraulic pump or motor has a first swash plate ( 30 ) and a second swash plate ( 40 ) which cause a first piston ( 8 ) and a second piston ( 9 ), respectively, to move reciprocally, opposing each other, so as to expand and contract a volume chamber ( 10 ) according to rotation of a cylinder block ( 4 ). A rod shape valve body ( 60 ) is disposed pushed into a through hole ( 12 ) of a shaft axis of the cylinder block ( 4 ) so as to be free to rotate relative to the cylinder block ( 4 ). A pair of supply and discharge ports ( 61 ) that open and supply high pressure and low pressure, respectively, are formed in an outer circumferential surface of the valve body ( 60 ). A cylinder port ( 11 ) is formed connecting the volume chamber ( 10 ) and an inner circumferential surface of the through hole of the cylinder block. The cylinder port ( 11 ) is arranged in a position opposite to the supply and discharge port ( 61 ).

1 . A swash plate type hydraulic pump or motor comprising: 
 a cylinder block supported so as to be free to rotate within a pump case;    a plurality of cylinder bores formed in the cylinder block from both sides in an axial direction, respectively, the plurality of cylinder bores communicating with each other;    a first piston inserted into the cylinder bore of one side of the cylinder block;    a second piston inserted into the cylinder bore of the other side of the cylinder block;    a volume chamber formed in inner portion of the cylinder bore and defined by the first piston and the second piston;    a first swash plate disposed on one side in an axial direction of the cylinder block, with which the first piston is in sliding contact;    a second swash plate disposed on the other side in an axial direction of the cylinder block, with which the second piston is in sliding contact;    a rod shape valve body that is inserted into a through hole formed in a shaft center of the cylinder block, the rod shape valve body relatively rotating to the cylinder block;    a pair of supply and discharge ports that are disposed in an outer circumferential surface of the valve body and that open in symmetrical positions in a circumferential direction;    a pair of passages that extend in an inner portion of the valve body in an axial direction and that are each connected to one of the pair of supply and discharge ports, guiding high pressure and low pressure hydraulic fluid; and    cylinder ports formed in the cylinder block and disposed in positions opposing the supply and discharge ports, the cylinder ports connecting the volume chamber and the through hole in the shaft center of the cylinder block;    wherein each of the cylinder ports communicates in turn with the high pressure side supply and discharge port of the valve body and the low pressure side supply and discharge port of the valve body according to rotation of the cylinder block.    
   
   
       2 . The hydraulic pump or motor as defined in  claim 1 , further comprising: 
 a support hole formed in the pump case, into which an end portion of the valve body is inserted; and    a seal ring disposed between the valve body and the support hole;    wherein the end portion of the valve body is elastically supported by the support hole through the seal ring.    
   
   
       3 . The hydraulic pump or motor as defined in  claim 2 , further comprising a bushing disposed in the through hole of the cylinder block, the bushing supporting the other end portion of the valve body.  
   
   
       4 . The hydraulic pump or motor as defined in  claim 1 , further comprising at least one pair of groove shape ports formed in an outer circumferential surface of the valve body, aligned in an axial direction with the supply and discharge ports, wherein one of the groove shape ports adjacent to the high pressure side supply and discharge port communicates with the low pressure side, and the other groove shape port adjacent to the low pressure side supply and discharge port communicates with the high pressure side.  
   
   
       5 . The hydraulic pump or motor as defined in  claim 4 , further comprising closed end shape dummy ports formed in an inner circumferential surface of the through hole of the cylinder block, positioned opposing the groove shape ports, wherein the number of the dummy ports formed is equal to the number of the cylinder ports.  
   
   
       6 . The hydraulic pump or motor as defined in  claim 1 , further comprising drive pistons that push the first swash plate and the second swash plate in order to change a tilt angle of the first swash plate and a tilt angle of the second swash plate, respectively.