Patent Application
20140186196
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.
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).
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.
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.
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.
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.
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 11A 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 20C 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 11A 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 21a and 22a 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 20a for receiving the power from an external power source such as an engine and protrudes outside from the base end wall 11A 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 11A 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 11A 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 11b formed in the base end wall 11A 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 50C (see
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 11a of the base end wall 11A of the case main body portion 11 as illustrated in
A servo piston 60 is provided between the second sliding face 34 of the swash plate 30 and the base end wall 11A 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 62a 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 62b, 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 50C 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
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 20C of the rotating shaft 20. The cylinders 42 are holes formed parallel to the rotation axial center 20C 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 20C.
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 81a formed in a shape of a sphere and a main pedestal portion 81b in a shape of a column. Each piston shoe 81 is supported, at its main spherical portion 81a, 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 81b, with the first sliding face 33 of the swash plate 30.
As illustrated in
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 20C 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 81b 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
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 12b. To put it concretely, if the servo piston 60 moves in a protruding direction (rightward in
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
As illustrated in
As illustrated in
As illustrated in
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 11b 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 21A of the main body-side bearing 21 through the mounting hole 11b 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 21A flows due to a centrifugal force. Especially, in the embodiment, because the tapered rollers 21a 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 21A moves into the mounting hole 11b through the communicating oil path 56 and then reaches the operation space 13 in the casing 10 from the mounting hole lib through the through oil path 53 in the ball retainers 50 and the lubrication groove 54, as illustrated in
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
In this variation, for the ball retainer 50 supporting the low-pressure side, the oil in the housing space 21A of the main body-side bearing 21 moves into the mounting hole 11b through the communicating oil path 56 and then reaches the operation space 13 in the casing 10 from the mounting hole 11b through the through oil path 53 in the ball retainer and the lubrication groove 54. 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. 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 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-037707 | Feb 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/076556 | 11/17/2011 | WO | 00 | 11/8/2012 |
