Patent Publication Number: US-9410540-B2

Title: Variable displacement hydraulic motor/pump

Description:
FIELD 
     The present invention relates to a variable displacement hydraulic pump/motor in which a displacement is changed by changing a tilt angle of a swash plate and specifically to a lubricating structure of supports for supporting the swash plate in a casing so that the swash plate can tilt. 
     BACKGROUND 
     In a variable displacement hydraulic pump/motor in which a displacement is changed by changing a tilt angle of a swash plate, a swash plate is supported in a casing by a pair of supports so as to be able to tilt, in general. Each of the supports is a circular columnar shaft portion having a tip end provided with a spherical sliding protruding portion. The two supports are mounted at the shaft portions thereof into mounting holes so that a line connecting centers of the spheres of the sliding protruding portions extends along a direction perpendicular to an axial center of a rotating shaft supporting a cylinder block. On the other hand, sliding recessed portions in which the sliding protruding portions are to be fitted are formed in the swash plate and the sliding protruding portions of the supports are respectively fitted for sliding in the respective sliding recessed portions. 
     In the hydraulic pump/motor, if the tilt angle of the swash plate is changed with respect to the axial center of the rotating shaft, stroke movement amounts of pistons disposed in cylinders in the cylinder block change according to the tilt angle of the swash plate and the displacement of the hydraulic pump/motor changes. 
     In this type of hydraulic pump/motor, oil is supplied between the sliding protruding portions of the supports and the sliding recessed portions in the swash plate from a port on a high-pressure side, i.e., a port for discharging the oil in a case of the hydraulic pump and a port to which the oil is supplied in a case of the hydraulic motor to carry out lubrication to thereby prevent problems such as seizing and galling from occurring (see Patent Literature 1, for example). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-open No. 2003-139045 
     SUMMARY 
     Technical Problem 
     The two supports for supporting the swash plate and on the high-pressure side and the low-pressure side receive different reaction forces from the pistons and therefore contact pressures between their sliding protruding portions and the sliding recessed portions are different as well. Here, there is no problem if the oil is supplied from the port on the high-pressure side to the support for supporting a high-pressure side of the swash plate. However, if the oil is supplied between the sliding protruding portion of the support, for supporting a low-pressure side of the swash plate, and the sliding recessed portion from the port on the high-pressure side, a force acting on the swash plate due to pressure of the oil becomes greater than a force received from the piston and the swash plate may move with respect to the casing in such a direction as to approach the cylinder block. 
     With the above-described circumstances in view, it is an object of the present invention to provide a variable displacement hydraulic pump/motor in which reliable lubrication can be carried out between sliding protruding portions of supports and sliding recessed portions in a swash plate without causing a problem such as movement of the swash plate with respect to a casing. 
     Solution to Problem 
     To overcome achieve the object, according to the present invention, a variable displacement hydraulic pump/motor comprises: a rotating shaft rotatably supported in a casing; a cylinder block rotating with the rotating shaft, the cylinder block including a plurality of cylinders on a circumference, a center of which is at an axial center of the rotating shaft; a plurality of pistons respectively disposed to be movable in the cylinders in the cylinder block; and a swash plate disposed to be able to tilt in the casing with a pair of supports interposed between the swash plate and the casing at a position facing openings of the cylinders provided in the cylinder block, the swash plate slidably engaged, at a sliding face of the swash plate facing the cylinder block, with base end portions of the respective pistons, the pistons moving in strokes according to a tilt angle of the swash plate when the cylinder block rotates with respect to the swash plate, wherein the casing includes a bearing rotatably supporting the rotating shaft near the supports, each of the supports has a sliding protruding portion formed in a spherical shape at a tip end of a shaft portion of the each of the supports, and a through oil path formed to extend from an outer surface of the shaft portion to an outer peripheral face of the sliding protruding portion, each of the supports being fitted, at the shaft portion of the each of the supports, in a mounting hole in the casing and being fitted slidably, at the sliding protruding portion of the each of the supports, in a sliding recessed portion in the swash plate so as to cover an opening of the through oil path, a communicating oil path is formed between a housing space for housing the bearing in the casing and the mounting hole and communicates with the through oil path in the shaft portion, and a lubrication groove constantly connecting the opening of the through oil path in the sliding protruding portion to an outside of a sliding contact area between the sliding protruding portion and the sliding recessed portion is formed between the sliding protruding portion of the support and the sliding recessed portion in the swash plate. 
     According to the present invention, each of the lubrication grooves is formed in the sliding protruding portion in such a manner as to draw a spiral about the shaft portion of the support. 
     According to the present invention, the bearing interposed between the casing and the rotating shaft is a tapered roller bearing including a tapered roller having a diameter which is larger at an end portion close to the swash plate. 
     According to the present invention, each of the supports has the sliding protruding portion at a tip end of the shaft portion formed in a circular columnar shape and the through oil path is formed on an axial center of the shaft portion. 
     Advantageous Effects of Invention 
     According to the invention, the housing space for housing the bearing and a space for housing the swash plate communicate each other through the communicating oil paths, the mounting holes, the through oil paths, and the lubrication grooves, and therefore, if the bearing rotates as a result of rotation of the rotating shaft, oil stored in the housing space flows due to a centrifugal force and passes through the lubrication grooves formed between the sliding protruding portions of the supports and the sliding recessed portions in the swash plate. Therefore, with the oil filling the lubrication grooves, it is possible to carry out lubrication between the sliding protruding portions and the sliding recessed portions. Furthermore, pressure of the oil passing through the lubrication grooves due to a centrifugal force is sufficiently lower than pressure of oil on a high-pressure side and therefore a problem such as movement of the swash plate toward the casing is not caused. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view taken along a plane passing through axial centers of a pair of supports in a variable displacement hydraulic pump/motor which is an embodiment of the present invention. 
         FIG. 2  is a sectional view along line A-A in  FIG. 1 . 
         FIG. 3  is an enlarged sectional view of an essential portion of the support which is applied to the variable displacement hydraulic pump/motor illustrated in  FIG. 1 . 
         FIG. 4  is a view taken in a direction of arrow B in  FIG. 3 . 
         FIG. 5  is an enlarged sectional view of an essential portion of the variable displacement hydraulic pump/motor illustrated in  FIG. 1 . 
         FIG. 6  is a sectional view illustrating a variation of the variable displacement hydraulic pump/motor according to the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     A preferred embodiment of a variable displacement hydraulic pump/motor according to the present invention will be described below in detail with reference to the accompanying drawings. 
       FIGS. 1 and 2  illustrate the variable displacement hydraulic pump/motor which is the embodiment of the invention. The hydraulic pump/motor illustrated here as an example operates as a hydraulic pump when power is applied from outside and includes a rotating shaft  20  inside a casing  10 . 
     The casing  10  includes a case main body portion  11  and an end cap portion  12  and an operation space  13  is formed between the case main body portion  11  and the end cap portion  12 . The rotating shaft  20  is a columnar member disposed to extend across the operation space  13  in the casing  10 . The rotating shaft  20  has one end portion rotatably supported in a base end wall  11 A of the case main body portion  11  with a main body-side bearing  21  interposed therebetween and the other end portion rotatably supported in the end cap portion  12  with a cap-side bearing  22  interposed therebetween and the rotating shaft  20  can rotate about its rotation axial center  20 C with respect to the casing  10 . Both of the main body-side bearing  21  for supporting the one end portion of the rotating shaft  20  in the base end wall  11 A of the case main body portion  11  and the cap-side bearing  22  for supporting the other end portion in the end cap portion  12  are what are called tapered roller bearings having tapered rollers and are disposed in such orientations that large-diameter end portions of tapered rollers  21   a  and  22   a  are close to a swash plate  30  which will be described later. The one end portion of the rotating shaft  20  functions as an input end portion  20   a  for receiving the power from an external power source such as an engine and protrudes outside from the base end wall  11 A of the case main body portion  11 . The other end portion of the rotating shaft  20  ends in the end cap portion  12 . The rotating shaft  20  is provided, at a position on its outer periphery corresponding to the operation space  13 , with the swash plate  30  and a cylinder block  40 . 
     The swash plate  30  is a plate-shaped member having a shaft insertion hole  31  in a central portion. The swash plate  30  is supported on the base end wall  11 A of the case main body portion  11  with a pair of ball retainers (supports)  50  interposed therebetween and with the rotating shaft  20  inserted through the shaft insertion hole  31 . In the case main body portion  11 , the base end wall  11 A provided with the pair of ball retainers  50  is provided in a position close to the main body-side bearing  21  which supports the rotating shaft  20 . 
     Each of the ball retainers  50  is formed by integrally molding a circular columnar shaft portion  51  and a sliding protruding portion  52  formed in a hemispherical shape having a larger diameter than the shaft portion  51 . Each of the ball retainers  50  is mounted to the casing  10  by fitting the shaft portion  51  into a mounting hole  11   b  formed in the base end wall  11 A of the case main body portion  11  and the sliding protruding portion  52  is fitted for sliding in a sliding recessed portion  32  formed in the swash plate  30 . The swash plate  30  supported by these ball retainers  50  can tilt with respect to the casing  10  about a straight line connecting center points of the sliding protruding portions  52  as a tilt center line  50 C (see  FIG. 2 ). In the present embodiment, the tilt center line  50 C of the swash plate  30  by the ball retainers  50  is set in a plane orthogonal to the rotation axial center  20 C of the rotating shaft  20  and in a position displaced upward from the rotation axial center  20 C in  FIG. 2 . The rotation axial center  20 C of the rotating shaft  20  is at equal distances from the center points of the respective sliding protruding portions  52  and is in a vertical plane (hereafter referred to as “division plane H”) which bisects the tilt center line  50 C as illustrated in  FIG. 1 . 
     The swash plate  30  is substantially bilaterally symmetric (not illustrated in the drawings) with respect to the division plane H and has a first sliding face  33  on a side facing the end cap portion  12  and a second sliding face  34  on a side facing an inner surface  11   a  of the base end wall  11 A of the case main body portion  11  as illustrated in  FIGS. 1 and 2 . The first sliding face  33  is formed as an annular flat face, on which a piston shoe  81  (described later) slides, at a portion around the shaft insertion hole  31 . The second sliding face  34  is a flat face formed only at a lower peripheral edge in  FIG. 2  and is inclined so that a plate thickness increases toward the tilt center line  50 C. 
     A servo piston  60  is provided between the second sliding face  34  of the swash plate  30  and the base end wall  11 A of the case main body portion  11 . The servo piston  60  is movably disposed in a servo sleeve  61  fixed to the case main body portion  11  and is in contact with the second sliding face  34  of the swash plate  30  with a servo piston shoe  62  interposed therebetween. The servo piston shoe  62  is supported, at its servo spherical portion  62   a  formed in a shape of a sphere, on a tip end portion of the servo piston  60  so as to be able to tilt and is in contact, at its columnar servo pedestal portion  62   b , with the second sliding face  34  so as to be able to slide. The servo piston  60  is constantly in contact with the second sliding face  34  of the swash plate  30  due to a pressing force of a servo piston spring  63  provided between the case main body portion  11  and the servo piston  60  and tilts the swash plate  30  about the tilt center line  50 C to thereby change a tilt angle of the swash plate  30  with respect to the rotating shaft  20  when hydraulic pressure of a servo hydraulic pressure chamber  64  is changed. 
     The cylinder block  40  is a circular columnar member having a central hole  41  and disposed between the end cap portion  12  and the swash plate  30  with the rotating shaft  20  inserted through the central hole  41 . The central hole  41  of the cylinder block  40  and an outer peripheral face of the rotating shaft  20  are coupled by splines so that the cylinder block  40  rotates with the rotating shaft  20 . An end portion of the cylinder block  40  facing the end cap portion  12  is in contact with an inner wall face of the end cap portion  12  with a valve plate  70  interposed therebetween. On the other hand, an end portion of the cylinder block  40  facing the swash plate  30  is exposed into the operation space  13 . 
     As illustrated in  FIG. 1 , the valve plate  70  is a plate-shaped member having an intake port  71  and a discharge port  72 . The intake port  71  is connected to an intake passage  12   a  formed in the end cap portion  12  and is connected to an oil tank (not illustrated) through the intake passage  12   a . The discharge port  72  is connected to a discharge passage  12   b  formed in the end cap portion  12  and is connected to an object of supply of oil, e.g., a hydraulic operating machine (not illustrated) through the discharge passage  12   b . Though it is not clearly illustrated in the drawings, the intake port  71  and the discharge port  72  in the valve plate  70  are in shapes of arcs formed on the same circumference the center of which is at the rotation axial center  20 C of the rotating shaft  20  and the discharge port  72  and the intake port  71  are formed independently of each other while separated by the division plane H. 
     In the cylinder block  40 , a plurality of cylinders  42  are formed on the circumference the center of which is at the rotation axial center  20 C of the rotating shaft  20 . The cylinders  42  are holes formed parallel to the rotation axial center  20 C of the rotating shaft  20  and having circular cross sections and are disposed at equal intervals along a circumferential direction. Each of the cylinders  42  is open in an end face of the cylinder block  40  facing the swash plate  30  and has an end portion which is close to the valve plate  70 , ends in the cylinder block  40 , and then is open in an end face of the cylinder block  40  through a small-diameter communicating port  43 . An opening of the communicating port  43  is positioned on the same circumference on which the intake port  71  and the discharge port  72  of the valve plate  70  are formed and selectively communicates with the intake port  71  or the discharge port  72  when the cylinder block  40  rotates about the rotation axial center  20 C. 
     A piston  80  is disposed in each of the cylinders  42  in the cylinder block  40 . The piston  80  is in a shape of a column having a circular cross section and is fitted in the cylinder  42  to be movable along an axial center. At a tip end portion of each piston  80  facing the swash plate  30 , the piston shoe  81  is provided. The piston shoe  81  is formed by integrally molding a main spherical portion  81   a  formed in a shape of a sphere and a main pedestal portion  81   b  in a shape of a column. Each piston shoe  81  is supported, at its main spherical portion  81   a , in a tip end portion of the piston  80  so as to be able to tilt and is in contact, at its main pedestal portion  81   b , with the first sliding face  33  of the swash plate  30 . 
     As illustrated in  FIGS. 1 and 2 , a portion of the main pedestal portion  81   b  in contact with the first sliding face  33  of the swash plate  30  is formed to be broad in each of the plurality of piston shoes  81  and the plurality of piston shoes  81  are linked with each other by a pressing plate  90  disposed between the broad portions and the main spherical portions  81   a . The pressing plate  90  is a plate-shaped member having substantially the same outer diameter as the cylinder block  40  and has a pressing hole  91  at a central portion. In the pressing plate  90  and on a circumference a center of which is at the rotation axial center  20 C of the rotating shaft  20 , shoe mounting holes  92  are respectively formed in positions facing the cylinders  42  in the cylinder block  40 . Each of the shoe mounting holes  92  is a through hole having such a dimension that the main spherical portion  81   a  of the piston shoe  81  can be inserted and the broad portion of the main pedestal portion  81   b  cannot be inserted. The pressing plate  90  is disposed between the cylinder block  40  and the swash plate  30  with the rotating shaft  20  inserted through the pressing hole  91  and the main spherical portions  81   a  of the piston shoes  81  inserted through the respective shoe mounting holes  92 . 
     The pressing hole  91  formed in the pressing plate  90  has an inner peripheral face formed in a spherical shape and a retainer guide  100  is supported in the pressing hole  91 . The retainer guide  100  is in a shape of a hemisphere having such an outer diameter as to be fitted in the pressing hole  91  in the pressing plate  90  and is disposed between the pressing plate  90  and the cylinder block  40  with the rotating shaft  20  inserted through a central portion of the retainer guide  100  and with the spherical portion in contact with the pressing hole  91  in the pressing plate  90 . The retainer guide  100  and the outer peripheral face of the rotating shaft  20  are coupled by splines so that the retainer guide  100  can rotate with the rotating shaft  20  and move along the rotation axial center  20 C of the rotating shaft  20 . To the retainer guide  100 , a pressing force of a pressing spring  101  mounted in the cylinder block  40  is constantly given through a transmission rod  102 . The pressing force of the pressing spring  101  and given to the retainer guide  100  is given to the piston shoes  81  through the pressing plate  90  and acts to constantly keep the main pedestal portions  81   b  of the piston shoes  81  in contact with the first sliding face  33  of the swash plate  30 . 
     In the hydraulic pump/motor formed as described above, if the rotating shaft  20  is rotated with respect to the casing  10 , the cylinder block  40  rotates with the rotating shaft  20  and the pistons  80  in contact with the first sliding face  33  of the swash plate  30  with the piston shoes  81  interposed therebetween move in strokes with respect to the cylinders  42 . To put it concretely, in a half area (on a low-pressure side below the division plane H in  FIG. 1 ) which is separated off by the division plane H and in which the intake port  71  is provided, the pistons  80  move in strokes so as to protrude successively (leftward in  FIG. 1 ) from the cylinders  42  and oil in the oil tank is taken into the cylinders  42  through the intake passage  12   a  and the intake port  71 . On the other hand, in a half area (on a high-pressure side above the division plane H in  FIG. 1 ) in which the discharge port  72  is provided, the pistons  80  move in strokes so as to recede into the cylinders  42  in the cylinder block  40  (move rightward in  FIG. 1 ) and the oil in the cylinders  42  is discharged to the hydraulic operating machine (not illustrated) through the discharge port  72  in the valve plate  70  and the discharge passage  12   b.    
     If the hydraulic pressure to be applied to the servo piston  60  is changed according to a load pressure of the hydraulic operating machine (not illustrated), for example, the servo piston  60  properly moves forward or backward with respect to the servo sleeve  61  provided in the case main body portion  11  to change the tilt angle of the swash plate  30  according to the hydraulic pressure. If the tilt angle of the swash plate  30  is changed, stroke movement amounts of the pistons  80  as a result of rotation of the cylinder block  40  change to change a flow rate of the oil to be discharged to the hydraulic operating machine (not illustrated) through the discharge passage  12   b . To put it concretely, if the servo piston  60  moves in a protruding direction (rightward in  FIG. 2 ), the first sliding face  33  of the swash plate  30  approaches a direction orthogonal to the rotation axial center  20 C of the rotating shaft  20  and therefore the stroke movement amounts of the pistons  80  as a result of the rotation of the cylinder block  40  reduce and the flow rate of the oil discharged to the hydraulic operating machine (not illustrated) per unit rotation reduces as well. On the other hand, if the servo piston  60  moves in a receding direction (leftward in  FIG. 2 ), the first sliding face  33  of the swash plate  30  moves away from the direction orthogonal to the rotation axial center  20 C of the rotating shaft  20  and therefore the stroke movement amounts of the pistons  80  as a result of the rotation of the cylinder block  40  increase and the flow rate of the oil discharged to the hydraulic operating machine (not illustrated) per unit rotation increases as well. 
     Because pressing forces are applied on the swash plate  30  as reaction forces from the plurality of pistons  80  during the above-described operation, the sliding recessed portions  32  in the swash plate  30  and the sliding protruding portions  52  of the ball retainers  50  slide on each other while receiving the pressing forces. Therefore, problems such as seizing and galling may be caused between the sliding recessed portions  32  in the swash plate  30  and the sliding protruding portions  52  of the ball retainers  50  unless appropriate lubrication is carried out between them. 
     Therefore, in the above-described hydraulic pump/motor, the oil which leaks into the casing  10  and is stored is positively supplied between the sliding recessed portions  32  in the swash plate  30  and the sliding protruding portions  52  of the ball retainers  50  to carry out lubrication between them. 
     To put it concretely, as illustrated in  FIGS. 3 to 5 , in each retainer of the pair of ball retainers  50 , a through oil path  53  is formed to extend from a base end face of the shaft portion  51  to an outer peripheral face of the sliding protruding portion  52  and a lubrication groove  54  is formed in the outer peripheral face of the sliding protruding portion  52 . An opening of the through oil path  53  on a side of the shaft portion  51  is not necessarily in the base end face but may be in any face, if the opening appears in an outer surface of the shaft portion  51  of the ball retainer  50  and the face is a face facing the mounting hole  11   b.    
     As illustrated in  FIG. 5 , the through oil path  53  shown in the embodiment is a through hole formed in a portion which is on an axial center of the shaft portion  51 , opens in the base end face of the shaft portion  51  through a tapered portion  53   a , and opens in the outer peripheral face of the sliding protruding portion  52  through a small-diameter portion  53   b . The ball retainer  50  is provided with a step portion  55  between the sliding protruding portion  52  and the shaft portion  51 . The step portion  55  is for restricting an insertion amount of the shaft portion  51  inserted into the mounting hole  11   b  in the case main body portion  11  to maintain a clearance d between the base end face of the shaft portion  51  and an inner bottom face of the mounting hole  11   b.    
     As illustrated in  FIGS. 3 and 4 , the lubrication groove  54  is the groove formed in the outer peripheral face of the sliding protruding portion  52 . In the embodiment, the lubrication groove  54  is formed in the outer peripheral face of the sliding protruding portion  52  to extend from the opening of the through oil path  53  in such a manner as to draw a spiral about the axial center of the shaft portion  51  and to end at an edge portion between the outer peripheral face of the sliding protruding portion  52  and the step portion  55 . The lubrication groove  54  is open in the edge portion between the outer peripheral face of the sliding protruding portion  52  and the step portion  55 , even when the opening of the through oil path  53  is covered with the sliding recessed portion  32  in the swash plate  30 , to thereby constantly connect the through oil path  53  to the operation space  13  which is outside a sliding contact area between the sliding protruding portion  52  and the sliding recessed portion  32 . In the sliding recessed portion  32  in the swash plate  30 , a storage recessed portion  32   a  is formed in a position facing the opening of the through oil path  53 . 
     As illustrated in  FIG. 5 , in the casing  10 , a communicating oil path  56  is formed in a portion between a housing space  21   b  for housing the main body-side bearing  21  and each of the respective mounting holes  11   b  in which the two ball retainers  50  are mounted. The communicating oil path  56  is for connecting the housing space  21   b  and an inside of the mounting hole  11   b  and is formed in the housing space  21   b  while displaced from the rotation axial center  20 C toward an outer periphery side. 
     The through oil path  53  formed in the ball retainer  50  is formed so that the opening in the sliding protruding portion  52  is constantly covered with an inner wall face of the sliding recessed portion  32  and that the opening in the shaft portion  51  is covered with an inner wall face of the mounting hole  11   b  when the sliding protruding portion  52  is fitted in the sliding recessed portion  32  in the swash plate  30 . However, the opening of the through oil path  53  in the sliding protruding portion  52  is communicating with the operation space  13  in the casing  10  through the spiral lubrication groove  54  formed in the outer peripheral face. Similarly, the opening of the through oil path  53  in the shaft portion  51  is communicating with the housing space  21   b  of the main body-side bearing  21  through the mounting hole  11   b  and the communicating oil path  56 . 
     Therefore, if the rotating shaft  20  rotates, the main body-side bearing  21  rotates and therefore the oil stored in the housing space  21   b  flows due to a centrifugal force. Especially, in the embodiment, because the tapered rollers  21   a  are disposed in such orientations that their large-diameter portions are close to the swash plate  30 , when the main body-side bearing  21  rotates, the oil stored in the housing space  21   b  moves into the mounting hole  11   b  through the communicating oil path  56  and then reaches the operation space  13  in the casing  10  from the mounting hole  11   b  through the through oil path  53  in the ball retainers  50  and the lubrication groove  54 , as illustrated in  FIG. 5 . As a result, the oil passing through the lubrication groove  54  carries out the lubrication between the sliding protruding portion  52  of the ball retainer  50  and the sliding recessed portion  32  in the swash plate  30  to prevent the problems such as galling and seizing. Moreover, the larger the rotation number of the rotating shaft, the more an amount of oil passing through the lubrication groove  54  increases, and therefore it is possible to more reliably prevent the problems such as galling and seizing. Furthermore, pressure of the oil passing through the lubrication groove  54  is sufficiently lower than that of the oil discharged from the discharge port  72  and therefore the problem such as movement of the swash plate  30  toward the cylinder block  40  is not caused even in the ball retainer  50  supporting the low-pressure side. 
     Although the above-described embodiment is described as an example to be used as the hydraulic pump, the embodiment may be similarly used as the hydraulic motor. 
     Although the lubrication groove  54  is formed only on the sliding protruding portion  52  of the ball retainer  50 , the lubrication groove  54  may be formed only in the inner peripheral face of the sliding recessed portion  32  in the swash plate  30  or may be formed in each of them. Because the spiral lubrication groove  54  is formed about the axial center of the shaft portion  51  in the above-described embodiment in forming the lubrication groove  54  in the outer peripheral face of the sliding protruding portion  52  of the ball retainer  50 , it can be formed easily by using a rotating tool of a lathe and a manufacturing process is not complicated. However, the lubrication groove  54  does not necessarily have to be in the spiral shape and may be in other shapes such as a plurality of radiated shapes, if the lubrication groove  54  can connect the through oil path  53  to the operation space  13 . 
     Moreover, although both of the ball retainer  50  for supporting the high-pressure side of the swash plate  30  and the ball retainer  50  for supporting the low-pressure side are lubricated with the same lubricating structure for carrying out the lubrication between the sliding protruding portions  52  of the ball retainers  50  and the sliding recessed portions  32  in the swash plate  30  in the above-described embodiment, the invention is not limited to this. For example, in a variation shown in  FIG. 6 , the above-described lubricating structure is applied only to the ball retainer  50  for supporting the low-pressure side which is a portion of the swash plate  30  below the division plane H and, for a ball retainer  150  for supporting the high-pressure side above the division plane H, the oil discharged from the discharge port  72  or the discharge passage  12   b  on the high-pressure side is supplied into the mounting hole  11   b  in the casing  10  through a supply oil path  200 . Although a through oil path  201  similar to that in the embodiment is formed in the ball retainer  150  mounted into the mounting hole  11   b  in the casing  10 , a lubrication groove  202  which ends in a sliding contact area between a sliding protruding portion  152  and the sliding recessed portion  32  in the swash plate  30  is formed on the sliding protruding portion  152 . At the ball retainer  150  on the high-pressure side, the oil discharged from the discharge port  72  is pumped into the sliding contact area between the sliding protruding portion  152  and the sliding recessed portion  32  through the through oil path  201  and the lubrication groove  202  to carry out lubrication between them. In the variation shown in  FIG. 6 , the same structures as those in the embodiment are provided with the same reference signs and are not described in detail. 
     In this variation, for the ball retainer  50  supporting the low-pressure side, the oil in the housing space  21   b  of the main body-side bearing  21  moves into the mounting hole  11   b  through the communicating oil path  56  and then reaches the operation space  13  in the casing  10  from the mounting hole  11   b  through the through oil path  201  in the ball retainer and the lubrication groove  202 . As a result, the oil passing through the lubrication groove  202  carries out the lubrication between the sliding protruding portion  152  of the ball retainer  50  and the sliding recessed portion  32  in the swash plate  30 . Furthermore, pressure of the oil passing through the lubrication groove  202  is sufficiently lower than that of the oil discharged from the discharge port  72  and therefore the problem such as movement of the swash plate  30  toward the cylinder block  40  is not caused even in the ball retainer  50  supporting the low-pressure side. Although the high-pressure oil discharged from the discharge port  72  is pumped into the sliding contact area between the sliding protruding portion  152  and the sliding recessed portion  32  for the ball retainer  150  supporting the high-pressure side, the reaction force from the piston  80  is large and therefore the problem such as movement of the swash plate  30  toward the cylinder block  40  is not caused. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  CASING 
               11   b  MOUNTING HOLE 
               20  ROTATING SHAFT 
               20 C ROTATION AXIAL CENTER 
               21  MAIN BODY-SIDE BEARING 
               21   b  HOUSING SPACE 
               21   a  TAPERED ROLLER 
               30  SWASH PLATE 
               32  SLIDING RECESSED PORTION 
               33  FIRST SLIDING FACE 
               40  CYLINDER BLOCK 
               50  BALL RETAINER (SUPPORT) 
               51  SHAFT PORTION 
               52  SLIDING PROTRUDING PORTION 
               53  THROUGH OIL PATH 
               54  LUBRICATION GROOVE 
               56  COMMUNICATING OIL PATH 
               80  PISTON