JP7478700B2 - Swash plate type hydraulic rotary machine - Google Patents

Description

This disclosure relates to a swash plate type hydraulic rotating machine mounted on construction machinery such as hydraulic excavators and wheel loaders.

A swash plate type hydraulic rotating machine mounted on construction machinery such as hydraulic excavators is used, for example, as a hydraulic pump that constitutes a hydraulic source, or as a hydraulic motor for traveling or turning. A swash plate type hydraulic rotating machine includes a casing, a rotating shaft rotatably arranged within the casing, a cylinder block having multiple cylinders and rotating integrally with the rotating shaft, multiple pistons inserted reciprocally into the cylinders of the cylinder block, multiple shoes respectively provided at the tips of the multiple pistons, a swash plate on which the multiple shoes slide, and a retainer that holds the multiple shoes against the swash plate.

When the rotating shaft rotates during operation of a swash plate type hydraulic rotary machine, the cylinder block rotates together with the rotating shaft, and multiple pistons reciprocate within the cylinders provided in the cylinder block. The multiple pistons slide and displace within the cylinders from top dead center to bottom dead center while the cylinder block rotates once, repeating a suction stroke in which hydraulic oil is sucked into the cylinders, and a discharge stroke in which the hydraulic oil sucked into the cylinders is discharged as high-pressure oil. When a swash plate type hydraulic rotary machine is in operation, the shoes connected to the tips of the pistons are pressed against the swash plate by the thrust of the pistons and slide on the swash plate in a circular trajectory centered on the rotating shaft.

In this way, the shoes connected to the pistons are pressed strongly against the swash plate by the thrust of the pistons, which can cause seizure and galling between the shoes and the swash plate. For this reason, oil passages are provided in the pistons and shoes, and lubricating oil is supplied to the sliding surface between the shoes and the swash plate through these oil passages. The lubricating oil supplied to the sliding surface between the shoes and the swash plate performs the function of a hydrostatic bearing, and the shoes slide on the swash plate while maintaining a good lubricated state against the swash plate.

A conventional swash plate type hydraulic rotary machine has been proposed in which a tapered recess is provided in the center of the end face of the shoe and a tapered portion is provided on the outer periphery of the shoe to form a thin film of oil between the swash plate and the shoe, enhancing lubrication (Patent Document 1). Another proposal has been made to prevent leakage of lubricating oil supplied between the shoe and the swash plate by providing an elastic body between the shoe and a retainer and pressing the shoe against the swash plate using the elastic force of this elastic body (Patent Document 2). Thus, in the conventional technology, a configuration is known in which the wear between the shoe and the swash plate is reduced by enhancing the lubricity of the sliding surfaces between them.

Meanwhile, a swash plate type hydraulic rotating machine has been proposed in which the end face of the shoe is provided with an annular seal portion surrounding a supply hole for supplying lubricant, and a pad portion with a smaller protruding length than the seal portion. In this swash plate type hydraulic rotating machine, when the shoe is pressed against the swash plate and the seal portion is deformed, the pad portion receives surface pressure, thereby preventing excessive friction from occurring on the sliding surface between the shoe and the swash plate and reducing wear between them (Patent Document 3).

Japanese Patent Publication No. 49-37206 JP 2020-16150 A JP 2015-151897 A

However, when the shoes slide on the swash plate in a circular path during operation of the swash plate hydraulic rotary machine, centrifugal force acts on the shoes. This causes the swash plate sliding surface of the shoe sliding on the swash plate to tilt relative to the swash plate, and a part of the outer periphery of the swash plate sliding surface comes into point contact with the swash plate. As a result, the contact surface pressure of the shoe's swash plate sliding surface against the swash plate becomes locally excessive, causing the problem of wear on the sliding surface between the swash plate and the shoe. Furthermore, when the shoe's swash plate sliding surface is tilted relative to the swash plate, a part of the retainer contact surface of the swash plate that contacts the retainer comes into point contact with the retainer. As a result, the contact surface pressure of the shoe's retainer contact surface against the retainer becomes locally excessive, causing the problem of wear on the contact surface between the retainer and the shoe.

The object of the present invention is to provide a swash plate type hydraulic rotating machine that can reduce wear on the sliding surfaces between the shoe and swash plate, and on the contact surfaces between the swash plate and retainer, and that can increase the durability of the shoe.

The present invention is a swash plate type hydraulic rotating machine comprising a casing, a rotating shaft rotatably arranged within the casing, a cylinder block having a plurality of cylinders and rotating integrally with the rotating shaft, a plurality of pistons reciprocably inserted into the cylinders of the cylinder block, a plurality of shoes respectively provided at the tips of the pistons, a swash plate on which the plurality of shoes slide, and a retainer that holds the plurality of shoes so as to press them against the swash plate, the shoes having piston connection parts swingably connected to the tips of the pistons, and a disk part provided with a swash plate sliding surface that slidably abuts against the swash plate and a retainer abutment surface that abuts against the retainer, the outer peripheral surface of the disk part is provided with an outer peripheral groove that is recessed from the outer peripheral surface of the disk part toward the center, the outer peripheral groove has an opening end that opens on the outer peripheral surface of the disk part and a groove bottom portion that is arranged from the opening end toward the center of the disk part, and the groove width of the outer peripheral groove becomes smaller from the opening end toward the groove bottom portion.

The present invention is a swash plate type hydraulic rotating machine comprising a casing, a rotating shaft rotatably arranged within the casing, a cylinder block having a plurality of cylinders and rotating integrally with the rotating shaft, a plurality of pistons inserted into the cylinders of the cylinder block so as to be capable of reciprocating, a plurality of shoes respectively provided at the tips of the pistons, a swash plate on which the plurality of shoes slide, and a retainer that holds the plurality of shoes so as to press them against the swash plate, the shoes having piston connection parts swingably connected to the tips of the pistons, and a disk part provided with a swash plate sliding surface that slidably abuts against the swash plate and a retainer abutment surface that abuts against the retainer, the disk part has an outer peripheral groove that is recessed from the outer peripheral surface of the disk part toward the center, the outer peripheral groove has an opening end that opens on the outer peripheral surface of the disk part and a groove bottom portion that is arranged from the opening end toward the center of the disk part, and the groove bottom portion has a curved shape.

According to the present invention, even if the cylinder block rotates and centrifugal force acts on the multiple shoes, causing the swash plate sliding surface of the disc portion to tilt relative to the swash plate, the outer circumferential groove deforms, so that the outer circumferential side of the swash plate sliding surface can come into surface contact with the swash plate. Also, the outer circumferential side of the retainer abutment surface can come into surface contact with the retainer. As a result, wear between the swash plate sliding surface of the shoe and the swash plate, and between the retainer abutment surface of the shoe and the retainer can be reduced. Also, the durability of the shoe can be increased by allowing relatively large deformation on the open end side of the outer circumferential groove and suppressing deformation on the groove bottom side.

1 is a cross-sectional view showing a swash plate type hydraulic pump as a swash plate type hydraulic rotary machine according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a piston and a shoe in FIG. 3 is a left side view of the disk portion of the shoe as viewed from the direction of arrows III-III in FIG. 2. FIG. 4 is a cross-sectional view showing the shoe alone. FIG. 4 is an enlarged cross-sectional view showing an outer peripheral groove of the shoe. 4 is a cross-sectional view showing a state in which a shoe according to the first embodiment slides on a swash plate. FIG. FIG. 2 is a cross-sectional view showing a shoe according to a first comparative example. FIG. 4 is a cross-sectional view showing a state in which a shoe according to a first comparative example slides on a swash plate. FIG. 11 is a cross-sectional view showing a shoe according to a second embodiment. FIG. 11 is a cross-sectional view showing a state in which a shoe according to a second embodiment slides on a swash plate. FIG. 11 is a cross-sectional view showing a shoe according to a second comparative example. FIG. 11 is a cross-sectional view showing a state in which a shoe according to a second comparative example slides on a swash plate. FIG. 11 is a cross-sectional view showing a shoe according to a third embodiment. FIG. 4 is an enlarged cross-sectional view showing an outer peripheral groove of the shoe. FIG. 4 is an enlarged cross-sectional view showing an outer peripheral groove of a shoe according to a first modified example. FIG. 11 is a cross-sectional view showing a second modified example of the shoe. 17 is a left side view of the disk portion of the shoe according to the second modified example, as viewed in the direction of the arrows XVII-XVII in FIG. 16. FIG. 11 is a cross-sectional view showing a third modified example of the shoe. FIG. 11 is a cross-sectional view showing a fourth modified example of the shoe together with the piston.

The following is a detailed explanation of an embodiment of the swash plate type hydraulic rotary machine of the present invention, using an example in which it is applied to a variable displacement swash plate type hydraulic pump, with reference to the attached drawings.

Figures 1 to 6 show a first embodiment of the present invention. A variable displacement swash plate type hydraulic pump 1 (hereinafter referred to as hydraulic pump 1) is driven by a prime mover to suck in hydraulic oil stored in a tank (not shown), pressurize it, and supply this hydraulic oil as pressurized oil to a hydraulic actuator (not shown). The hydraulic pump 1 is composed of a casing 2, a rotating shaft 5, a cylinder block 8, a piston 10, a swash plate 12, a valve plate 16, a shoe 21, etc., which will be described later.

The casing 2 forms the outer shell of the hydraulic pump 1. The casing 2 is composed of a stepped cylindrical casing body 3 with one end formed as a front bottom 3A, and a rear casing 4 that closes the other end of the casing body 3. A pair of supply and exhaust passages 4A, 4B are formed in the rear casing 4. One of the pair of supply and exhaust passages 4A, 4B is connected to the tank, and the other is connected to the hydraulic actuator.

The rotating shaft 5 is rotatably mounted within the casing 2. One axial side of the rotating shaft 5 is rotatably supported via a bearing 6 on the front bottom 3A of the casing body 3, and one axial end 5A of the rotating shaft 5 protrudes to the outside from the front bottom 3A of the casing body 3. The other axial end 5B of the rotating shaft 5 is rotatably supported via a bearing 7 on the rear casing 4. One end 5A of the rotating shaft 5 is connected to a prime mover or the like (not shown), and the rotating shaft 5 is rotationally driven by this prime mover. A male spline portion 5C is provided in the middle of the axial direction of the rotating shaft 5.

The cylinder block 8 is located on the outer periphery of the rotary shaft 5 and is rotatably mounted within the casing 2. A plurality of cylinders 9 are drilled into the cylinder block 8. A cylindrical protrusion 8A that protrudes axially toward the swash plate 12 is integrally formed on one axial side of the cylinder block 8 (the front bottom 3A side). A spherical guide 14 (described later) is inserted on the outer periphery of this cylindrical protrusion 8A so as to be relatively displaceable in the axial direction. The other axial side of the cylinder block 8 (the rear casing 4 side) forms a concavely curved sliding surface 8B, which slidably abuts against the valve plate 16.

The shaft insertion hole 8C is provided axially through the center of the cylinder block 8. The rotating shaft 5 is inserted into the shaft insertion hole 8C. The shaft insertion hole 8C is formed as a stepped hole with a larger diameter on the sliding surface 8B side than on the cylindrical protrusion 8A side. A female spline portion (hole spline) 8D is formed on the inner circumferential surface of the shaft insertion hole 8C on the cylindrical protrusion 8A side, and this female spline portion 8D is splined to the male spline portion 5C of the rotating shaft 5. This allows the cylinder block 8 to rotate integrally with the rotating shaft 5.

The cylinders 9 are formed in the cylinder block 8. The cylinders 9 are arranged at regular intervals around the rotary shaft 5 and extend in the axial direction of the cylinder block 8. One end of each of the cylinders 9 that faces the swash plate 12 opens to one axial end face of the cylinder block 8 (the cylindrical protrusion 8A side). On the other hand, a cylinder port 9A is formed in each of the other ends of the cylinders 9. The cylinder port 9A is intermittently connected to and disconnected from the supply and exhaust passages 4A and 4B of the rear casing 4 via the suction port 17 and discharge port 18 of the valve plate 16 described later.

The multiple pistons 10 are slidably inserted into the multiple cylinders 9 formed in the cylinder block 8. The multiple pistons 10 reciprocate within each cylinder 9 as the cylinder block 8 rotates, pressurizing the hydraulic oil sucked into the cylinder 9 and then discharging it as high-pressure oil. The multiple pistons 10 reciprocate between the bottom dead center at which they protrude (extend) significantly from the cylinder 9 and the top dead center at which they are inserted into the cylinder 9. During one rotation of the cylinder block 8, the multiple pistons 10 repeat an intake stroke in which they slide from the top dead center to the bottom dead center within the cylinder 9 to suck hydraulic oil into the cylinder 9, and a discharge stroke in which they slide from the bottom dead center to the top dead center to discharge the hydraulic oil in the cylinder 9 as high-pressure oil.

The tip (protruding end) of the piston 10 protruding from the cylinder 9 is provided with a spherical recess 10A, to which a shoe 21 (described later) is connected so as to be able to swing (see FIG. 2). In addition, an oil passage 10B is provided in the center of the piston 10, penetrating it in the axial direction, and a portion of the hydraulic oil sucked into the cylinder 9 is supplied to the shoe 21 side through the oil passage 10B.

The cradle 11 is provided on the front bottom 3A of the casing body 3 and supports the swash plate 12. The cradle 11 is located around the rotating shaft 5, on the back side of the swash plate 12 (the surface opposite to the smooth surface 12A described below), and is fixed to the front bottom 3A of the casing body 3. The cradle 11 is provided with a pair of tilting sliding surfaces 11A that support the swash plate 12 so that it can be tilted. The pair of tilting sliding surfaces 11A are each formed as a concave curved surface, and are arranged opposite each other with the rotating shaft 5 in between.

The swash plate 12 is tiltably mounted in the casing 2 and constitutes the capacity variable part of the hydraulic pump 1. The swash plate 12 is attached to the front bottom 3A side of the casing body 3 via the cradle 11. The front surface side (cylinder block 8 side) of the swash plate 12 is a smooth surface 12A that slidably guides the multiple shoes 21. A shaft insertion hole 12B is formed in the center of the swash plate 12, and a rotating shaft 5 is inserted into this shaft insertion hole 12B. A convex curved surface 12C is formed on the back side (opposite the smooth surface 12A) of the swash plate 12, and this convex curved surface 12C is slidably fitted to the tilt sliding surface 11A of the cradle 11. The swash plate 12 is tilted from a neutral position where the tilt angle is zero by a tilt actuator (not shown), and the capacity of the hydraulic pump 1 (the amount of pressure oil discharged) is variably controlled according to the tilt angle of the swash plate 12.

The retainer 13 is provided between the cylinder block 8 and the smooth surface 12A of the swash plate 12. The retainer 13 is formed as an annular plate, and a spherical guide 14 (described later) is slidably fitted to the inner periphery of the retainer 13. The retainer 13 is formed with a plurality of shoe retaining holes 13A spaced apart in the circumferential direction, and the shoe 21 provided on the protruding end of the piston 10 is held in the shoe retaining hole 13A. The retainer 13 is biased toward the smooth surface 12A of the swash plate 12 via the spherical guide 14 by the spring force of the spring 15 (described later). As a result, the retainer 13 presses the shoe 21 held in the shoe retaining hole 13A against the smooth surface 12A, guiding the plurality of shoes 21 to draw a circular trajectory on the smooth surface 12A.

The spherical guide 14 is provided between the cylindrical protrusion 8A of the cylinder block 8 and the inner circumference of the retainer 13. The spherical guide 14 is made of a cylindrical body having a semispherical outer peripheral surface, and a female spline portion 14A is formed on the inner circumference side of the spherical guide 14. The female spline portion 14A is splined to the male spline portion 5C of the rotating shaft 5. Therefore, the spherical guide 14 rotates integrally with the rotating shaft 5 while being movable in the axial direction of the rotating shaft 5. Meanwhile, the inner circumference side of the retainer 13 is fitted to the semispherical outer peripheral surface of the spherical guide 14 in a swingable (slidable) manner.

The spring 15 is provided between the cylindrical protrusion 8A of the cylinder block 8 and the spherical guide 14. The spring 15 is disposed on the outer periphery of the rotating shaft 5 and biases the cylinder block 8 and the spherical guide 14 in opposite directions. As a result, the multiple shoes 21 are pressed against the smooth surface 12A of the swash plate 12 via the spherical guide 14 and the retainer 13. The sliding surface 8B of the cylinder block 8 is pressed against the valve plate 16.

The valve plate 16 is provided in the casing 2, located between the rear casing 4 and the cylinder block 8. The valve plate 16 is formed in a hollow disk shape, and a shaft insertion hole 16A is formed in its center. The rotating shaft 5 is inserted into the shaft insertion hole 16A of the valve plate 16. The back side of the valve plate 16 is fixed to the rear casing 4, and the front surface of the valve plate 16 is in sliding contact with the sliding surface 8B of the cylinder block 8. In this way, the valve plate 16 supports the cylinder block 8 so that it can rotate together with the rotating shaft 5. The valve plate 16 is provided with an intake port 17 and a discharge port 18.

The suction port 17 and the discharge port 18 are arranged so as to form an eyebrow shape (arc shape) along an imaginary circle centered on the center of the valve plate 16. The suction port 17 is connected to a tank (not shown) through the supply and discharge passage 4A of the rear casing 4, and the discharge port 18 is connected to a hydraulic actuator (not shown) through the supply and discharge passage 4B of the rear casing 4. The suction port 17 and the discharge port 18 of the valve plate 16 are intermittently connected to the cylinder ports 9A of the multiple cylinders 9 when the cylinder block 8 rotates. As a result, hydraulic oil is sucked into the cylinder 9 from the suction port 17, and this hydraulic oil is pressurized by the piston 10 to become high-pressure oil and is discharged from the discharge port 18.

Next, the shoe 21 used in this embodiment will be described with reference to Figures 2 to 5.

The multiple shoes 21 are swingably connected to the tips (protruding ends) of the multiple pistons 10 protruding from the cylinder 9. These multiple shoes 21 are pressed against the smooth surface 12A of the swash plate 12 by the pressing force (hydraulic force) from the pistons 10, and in this state rotate together with the rotating shaft 5, the cylinder block 8, and the multiple pistons 10, sliding on the smooth surface 12A of the swash plate 12 in a circular trajectory centered on the rotating shaft 5. The shoes 21 are configured to include a piston connection part 22 connected to the tip of the piston 10, and a disk part 23 formed integrally with the piston connection part 22 and abutting against the swash plate 12.

The piston connection part 22 is swingably connected to the tip (protruding end) of the piston 10 protruding from the cylinder 9. The piston connection part 22 is formed as a spherical protrusion corresponding to the spherical recess 10A of the piston 10, and is slidably fitted into the spherical recess 10A. The disk part 23 is formed in a stepped disk shape having a large diameter disk part 23A larger in diameter than the shoe retaining hole 13A of the retainer 13, and a small diameter disk part 23B smaller in diameter than the shoe retaining hole 13A of the retainer 13.

The shoe 21 is pressed against the swash plate 12 by the retainer 13 when the small diameter disk portion 23B is inserted into the shoe holding hole 13A of the retainer 13. As a result, the disk portion 23 of the shoe 21 has a swash plate sliding surface 23C that slidably abuts against the smooth surface 12A of the swash plate 12, and a retainer abutment surface 23D that abuts against the retainer 13. An oil hole 21A is provided in the center of the shoe 21, passing through the piston connection portion 22 and the disk portion 23 in the axial direction, and the oil hole 21A is connected to the oil passage 10B of the piston 10. In addition, a circularly recessed pocket 23E is provided in the swash plate sliding surface 23C of the disk portion 23, and the oil hole 21A opens in the center of the pocket 23E. As a result, a portion of the hydraulic oil supplied through the oil passage 10B of the piston 10 and the oil hole 21A of the shoe 21 is held in the pocket 23E, and the hydraulic oil held in this pocket 23E functions as a hydrostatic bearing, so that the area between the swash plate sliding surface 23C of the shoe 21 and the smooth surface 12A of the swash plate 12 is constantly lubricated.

The outer peripheral groove 24 is provided on the outer peripheral surface of the disc portion 23 constituting the shoe 21. Specifically, the outer peripheral groove 24 is formed as a full-circumferential groove that is annularly recessed from the outer peripheral surface of the large diameter disc portion 23A of the disc portion 23 toward the center. The outer peripheral groove 24 has an opening end 24A that opens on the outer peripheral surface of the large diameter disc portion 23A, and a groove bottom portion 24B that is located from the opening end 24A toward the center of the large diameter disc portion 23A. The outer peripheral groove 24 is formed in the center of the large diameter disc portion 23A in the thickness direction, and the thickness dimension of the large diameter disc portion 23A from the outer peripheral groove 24 to the swash plate sliding surface 23C and the thickness dimension from the outer peripheral groove 24 to the retainer abutment surface 23D are set to be approximately equal.

The groove width Hb1 at the opening end 24A is set larger than the groove width Hb2 at the groove bottom 24B (Hb1>Hb2). Thus, the outer peripheral groove 24 has a tapered cross-sectional shape in which the groove width gradually decreases from the opening end 24A toward the groove bottom 24B. This allows relatively large deformation on the opening end 24A side of the outer peripheral groove 24, while suppressing deformation on the groove bottom 24B side.

When the rotating shaft 5 of the hydraulic pump 1 rotates together with the cylinder block 8, the multiple pistons 10 reciprocate within the cylinder 9 due to the rotation of the cylinder block 8. At this time, the shoes 21 provided at the tips of the pistons 10 are pressed against the smooth surface 12A of the swash plate 12 by the thrust of the pistons 10, and slide on the smooth surface 12A of the swash plate 12 in a circular trajectory centered on the rotating shaft 5.

When the multiple shoes 21 slide along a circular path on the smooth surface 12A of the swash plate 12, a large centrifugal force acts on the shoes 21, and as shown in FIG. 6, a moment acts on the swash plate sliding surface 23C of the shoes 21 in the direction of arrow F. As a result, the outer peripheral portion of the swash plate sliding surface 23C, which is far from the rotation shaft 5, rises up from the smooth surface 12A, and the swash plate sliding surface 23C of the shoes 21 is inclined relative to the smooth surface 12A of the swash plate 12.

Therefore, when the shoe 21 slides on the smooth surface 12A of the swash plate 12 to trace a circular path around the rotating shaft 5, the inner circumferential side of the circular path of the swash plate sliding surface 23C of the shoe 21, i.e., the outer peripheral portion 23C1 of the swash plate sliding surface 23C located on the rotating shaft 5 side, abuts against the smooth surface 12A, and the gap between the opening ends 24A of the outer peripheral groove 24 is narrowed. As a result, the outer peripheral portion 23C1 of the swash plate sliding surface 23C located on the rotating shaft 5 side comes into surface contact with the smooth surface 12A of the swash plate 12. Therefore, even if a large centrifugal force acts on the shoe 21 when the hydraulic pump 1 is in operation, the contact surface pressure between the smooth surface 12A of the swash plate 12 and the swash plate sliding surface 23C of the shoe 21 can be reduced.

On the other hand, when the retainer contact surface 23D of the disk portion 23 constituting the shoe 21 is focused on, as shown in FIG. 6, when the swash plate sliding surface 23C of the shoe 21 is inclined with respect to the smooth surface 12A of the swash plate 12, the outer peripheral side of the annular trajectory centered on the rotating shaft 5, that is, the outer peripheral side portion 23D1 located on the side away from the rotating shaft 5, of the retainer contact surface 23D is deformed so that the interval between the opening ends 24A of the outer peripheral groove 24 is narrowed by contacting the retainer 13. As a result, the outer peripheral side portion 23D1 located on the side away from the rotating shaft 5 of the retainer contact surface 23D comes into surface contact with the retainer 13. Therefore, even if a large centrifugal force acts on the shoe 21 when the hydraulic pump 1 is in operation, the contact surface pressure between the retainer contact surface 23D of the shoe 21 and the retainer 13 can be alleviated.

As shown in FIG. 5, the groove depth Lb from the opening end 24A to the groove bottom 24B of the outer circumferential groove 24 is set to be larger than the groove width Hb1 of the opening end 24A (Lb>Hb1). This allows the opening end 24A side of the outer circumferential groove 24 to deform with appropriate elasticity when centrifugal force acts on the shoe 21 and the swash plate sliding surface 23C of the shoe 21 is inclined relative to the smooth surface 12A of the swash plate 12. This allows the outer circumferential side portion 23C1 of the swash plate sliding surface 23C located on the rotating shaft 5 side to come into surface contact with the smooth surface 12A of the swash plate 12 (see FIG. 6).

In addition, if the thickness dimension of the large diameter disc portion 23A is H2, it is desirable to set the groove width Hb2 of the groove bottom portion 24B of the outer peripheral groove 24 within the range of the following (Equation 1) relative to the thickness dimension H2 of the large diameter disc portion 23A.

Furthermore, if the radial dimension of the retainer abutment surface 23D of the large diameter disc portion 23A is L2, it is desirable to set the groove depth Lb of the outer peripheral groove 24 within the range of the following (Equation 2) relative to the radial dimension L2 of the retainer abutment surface 23D.

In this manner, in this embodiment, the groove width Hb2 of the groove bottom 24B of the peripheral groove 24 is set within the range of the above (Equation 1), and the groove depth Lb of the peripheral groove 24 is set within the range of the above (Equation 2). This allows the deformation of the peripheral groove 24 to bring the swash plate sliding surface 23C into surface contact with the swash plate 12 (smooth surface 12A) with appropriate elasticity, and the retainer abutment surface 23D into surface contact with the retainer 13 with appropriate elasticity, while also improving the durability of the large diameter disc portion 23A that constitutes the shoe 21.

The hydraulic pump 1 according to the first embodiment is equipped with the shoe 21 as described above, and the operation of the hydraulic pump 1 will be described below.

When the rotating shaft 5 of the hydraulic pump 1 rotates, the cylinder block 8 rotates integrally with the rotating shaft 5. As a result, the multiple pistons 10 provided in each of the multiple cylinders 9 of the cylinder block 8 reciprocate within the cylinders 9 with a stroke amount corresponding to the tilt angle of the swash plate 12, pressurizing the hydraulic oil sucked into the cylinders 9 from the supply and discharge passage 4A side, for example, and discharging it as high-pressure oil to the supply and discharge passage 4B side. The multiple pistons 10 slide from top dead center to bottom dead center within the cylinders 9 while the cylinder block 8 rotates once, repeating the intake stroke in which the hydraulic oil is sucked into the cylinders 9 and the discharge stroke in which the pistons slide from bottom dead center to top dead center and discharge the hydraulic oil in the cylinders 9 as high-pressure oil.

When the hydraulic pump 1 is in operation, the shoe 21 attached to the tip of the piston 10 is pressed against the smooth surface 12A of the swash plate 12 by the thrust of the piston 10 and slides on the smooth surface 12A of the swash plate 12 in a circular trajectory centered on the rotating shaft 5. At this time, a large centrifugal force acts on the shoe 21 sliding on the smooth surface 12A, and a moment acts on the swash plate sliding surface 23C of the shoe 21 in the direction of arrow F in Figure 6. As a result, the swash plate sliding surface 23C of the shoe 21 is inclined with respect to the smooth surface 12A of the swash plate 12.

At this time, the outer peripheral portion 23C1 of the swash plate sliding surface 23C located on the rotating shaft 5 side is deformed so that the gap between the opening ends 24A of the outer peripheral groove 24 narrows, and the outer peripheral groove 24 deforms so that the gap between the opening ends 24A narrows, and the outer peripheral groove 24 deforms so that the smooth surface 12A of the swash plate 12 and the swash plate sliding surface 23C of the shoe 21 do not come into point contact with each other, preventing an increase in surface pressure, even if a large centrifugal force acts on the shoe 21 when the hydraulic pump 1 is in operation. As a result, the contact surface pressure between the smooth surface 12A of the swash plate 12 and the swash plate sliding surface 23C of the shoe 21 is alleviated, and localized wear between the smooth surface 12A and the swash plate sliding surface 23C is prevented, thereby reducing wear on both surfaces.

On the other hand, when the retainer abutment surface 23D of the disk portion 23 constituting the shoe 21 is focused on, when the swash plate sliding surface 23C of the shoe 21 is inclined with respect to the smooth surface 12A of the swash plate 12, the outer peripheral portion 23D1 of the retainer abutment surface 23D located on the side away from the rotating shaft 5 is deformed so that the distance between the opening end 24A of the outer peripheral groove 24 is narrowed, and the retainer abutment surface 23D of the shoe 21 and the retainer 13 are in surface contact with each other. Therefore, even if a large centrifugal force acts on the shoe 21 when the hydraulic pump 1 is in operation, the retainer abutment surface 23D of the shoe 21 and the retainer 13 can be prevented from coming into point contact and increasing the surface pressure. As a result, the contact surface pressure between the retainer abutment surface 23D of the shoe 21 and the retainer 13 is alleviated, and local wear between the retainer abutment surface 23D and the retainer 13 is suppressed, thereby reducing wear on both.

Next, we will explain the comparison between the shoe 21 of this embodiment and a shoe of a comparative example.

As shown in Figures 7 and 8, the shoe 101 according to the comparative example includes a spherical piston connection portion 102 that is connected to the tip of the piston 10, and a disk portion 103 that is integrally formed with the piston connection portion 102. The disk portion 103 has a large diameter disk portion 103A and a small diameter disk portion 103B, and the large diameter disk portion 103A is provided with a swash plate sliding surface 103C that slidably contacts the smooth surface 12A of the swash plate 12, and a retainer contact surface 103D that contacts the retainer 13. However, the outer peripheral surface of the large diameter disk portion 103A does not have the outer peripheral groove 24 according to this embodiment.

When the shoe 101 of the comparative example slides on the smooth surface 12A of the swash plate 12 in a circular path, centrifugal force acts on the shoe 101, and as shown in FIG. 8, a moment in the direction of arrow F acts on the swash plate sliding surface 103C of the shoe 101. As a result, the swash plate sliding surface 103C of the shoe 101 is inclined with respect to the smooth surface 12A of the swash plate 12, and the outer peripheral portion 103C1 of the swash plate sliding surface 103C located on the rotating shaft 5 side comes into point contact with the smooth surface 12A of the swash plate 12. As a result, the contact surface pressure of the swash plate sliding surface 103C of the shoe 101 against the smooth surface 12A of the swash plate 12 becomes locally excessive, which causes wear to progress on the smooth surface 12A of the swash plate 12 and the swash plate sliding surface 103C of the shoe 101.

On the other hand, when focusing on the retainer abutment surface 103D of the disc portion 103, when the swash plate sliding surface 103C of the shoe 101 is inclined relative to the smooth surface 12A of the swash plate 12, the outer peripheral portion 103D1 of the retainer abutment surface 103D located on the side away from the rotating shaft 5 comes into point contact with the retainer 13. As a result, the contact pressure of the retainer abutment surface 103D of the shoe 101 against the retainer 13 becomes locally excessive, causing wear to progress on the retainer abutment surface 103D of the retainer 13 and the shoe 101.

In contrast, the shoe 21 according to this embodiment has an outer circumferential groove 24 on the outer circumferential surface of the disk portion 23. Even if a large centrifugal force acts on the shoe 21 when the hydraulic pump 1 is in operation and the swash plate sliding surface 23C of the shoe 21 is tilted relative to the smooth surface 12A of the swash plate 12, the outer circumferential groove 24 deforms, allowing the outer circumferential portion 23C1 of the swash plate sliding surface 23C located on the rotating shaft 5 side to come into surface contact with the smooth surface 12A of the swash plate 12. As a result, the contact pressure between the smooth surface 12A of the swash plate 12 and the swash plate sliding surface 23C of the shoe 21 is alleviated, and local wear between the smooth surface 12A and the swash plate sliding surface 23C can be reduced.

Similarly, the outer peripheral portion 23D1 of the retainer contact surface 23D of the shoe 21, which is located on the side away from the rotating shaft 5, can be brought into surface contact with the retainer 13. As a result, the contact pressure between the retainer contact surface 23D of the shoe 21 and the retainer 13 can be alleviated, and local wear between the retainer contact surface 23D and the retainer 13 can be reduced. Furthermore, the shoe 21 has an outer peripheral groove 24 formed on the outer peripheral surface of the large diameter disc portion 23A, which has a tapered cross-sectional shape in which the groove width gradually decreases from the opening end 24A to the groove bottom 24B. This allows relatively large deformation on the opening end 24A side of the outer peripheral groove 24, while deformation is suppressed on the groove bottom 24B side, thereby improving the durability of the shoe 21.

Thus, the hydraulic pump 1 according to this embodiment comprises a casing 2, a rotating shaft 5 rotatably arranged within the casing 2, a cylinder block 8 which rotates integrally with the rotating shaft 5, a plurality of pistons 10 reciprocably inserted within cylinders 9 of the cylinder block 8, a plurality of shoes 21 respectively provided at the tips of the pistons 10, a swash plate 12 against which the shoes 21 slide, and a retainer 13 which holds the shoes 21 against the swash plate 12. The shoe 21 has a piston connection portion 22 which is swingably connected to the tip of the piston 10, and a disc portion 23 which is provided with a swash plate sliding surface 23C which slidably abuts against the swash plate 12 and a retainer abutment surface 23D which abuts against the retainer 13. The outer peripheral surface of the disc portion 23 is provided with an outer peripheral groove 24 that is recessed from the outer peripheral surface of the disc portion 23 toward the center. The outer peripheral groove 24 has an opening end 24A that opens onto the outer peripheral surface of the disc portion 23 and a groove bottom 24B that is located from the opening end 24A toward the center of the disc portion 23, and the groove width of the outer peripheral groove 24 becomes smaller from the opening end 24A toward the groove bottom 24B.

With this configuration, even if centrifugal force acts on the shoe 21 during operation of the hydraulic pump 1 and the swash plate sliding surface 23C of the disc portion 23 is inclined relative to the smooth surface 12A of the swash plate 12, the outer peripheral groove 24 deforms, so that the outer peripheral side of the swash plate sliding surface 23C can be brought into surface contact with the smooth surface 12A of the swash plate 12, and the outer peripheral side of the retainer abutment surface 23D can be brought into surface contact with the retainer 13. As a result, local wear between the swash plate sliding surface 23C and the swash plate 12 (smooth surface 12A), and between the retainer abutment surface 23D and the retainer 13 can be suppressed. Moreover, since a relatively large deformation is permitted on the open end 24A side of the outer peripheral groove 24 and deformation is suppressed on the groove bottom 24B side, the durability of the shoe 21 can be increased.

Next, Figures 9 and 10 show a second embodiment of the present invention. The feature of this embodiment is that a peripheral groove is formed on the outer peripheral surface of a shoe having a disc portion with a small thickness. Note that in this embodiment, the same components as those in the first embodiment are given the same reference numerals and their explanation is omitted.

In the figure, the shoe 31, like the shoe 21 according to the first embodiment, is configured to include a spherical piston connection portion 32 connected to the tip of the piston 10 and a disk portion 33 that abuts against the swash plate 12, and has an oil hole 31A that penetrates the piston connection portion 32 and the disk portion 33. The disk portion 33 is formed in a stepped disk shape having a large diameter disk portion 33A and a small diameter disk portion 33B, and the large diameter disk portion 33A is provided with a swash plate sliding surface 33C, a retainer abutment surface 33D, and a pocket 33E. However, the thickness dimension H3 of the large diameter disk portion 33A is formed smaller than the thickness dimension H2 of the large diameter disk portion 23A of the shoe 21 according to the first embodiment (H3<H2).

The outer peripheral groove 34 is formed as a full circumferential groove that is recessed in an annular shape from the outer peripheral surface of the large diameter disc portion 33A of the disc portion 33 toward the center. The outer peripheral groove 34 has an opening end 34A that opens onto the outer peripheral surface of the large diameter disc portion 33A, and a groove bottom portion 34B that is disposed from the opening end 34A toward the center of the large diameter disc portion 33A. The outer peripheral groove 34 has a tapered cross-sectional shape in which the groove width gradually decreases from the opening end 34A toward the groove bottom portion 34B, similar to the outer peripheral groove 24 of the shoe 21 according to the first embodiment. The groove depth Lc of the outer peripheral groove 34 from the opening end 34A to the groove bottom portion 34B is set to be larger than the groove width Hc of the opening end 24A (Lc>Hc).

The shoe 31 according to the second embodiment has the configuration described above, and the operation of the shoe 31 when the hydraulic pump 1 is in operation will be described below.

When the hydraulic pump 1 is operated and the cylinder block 8 rotates together with the rotary shaft 5, the shoe 31 provided at the tip of the piston 10 is pressed against the smooth surface 12A of the swash plate 12 by the thrust of the piston 10 and slides on the smooth surface 12A of the swash plate 12 in a circular trajectory centered on the rotary shaft 5. At this time, the swash plate sliding surface 33C of the large diameter disc portion 33A abuts against the smooth surface 12A, and the retainer abutment surface 33D abuts against the retainer 13. In this case, since the thickness dimension H3 of the large diameter disc portion 33A of the shoe 31 is small, the central portion of the disc portion 33 is pressed against the smooth surface 12A by the thrust of the piston 10, and the outer periphery of the swash plate sliding surface 33C is deformed so as to be warped in a direction away from the smooth surface 12A.

In this case, an outer peripheral groove 34 is formed around the entire circumference between the swash plate sliding surface 33C of the large diameter disk portion 33A and the retainer abutment surface 33D. Therefore, even if the outer peripheral edge of the swash plate sliding surface 33C is deformed so as to be warped in a direction away from the smooth surface 12A, this deformation does not affect the retainer abutment surface 33D, and the retainer abutment surface 33D can come into surface contact with the retainer 13 with a large contact surface pressure. As a result, localized wear between the retainer abutment surface 33D of the shoe 31 and the retainer 13 during operation of the hydraulic pump 1 can be suppressed.

Next, we will explain the comparison between the shoe 31 of this embodiment and a shoe of a comparative example.

As shown in Figs. 11 and 12, the shoe 111 according to the comparative example includes a spherical piston connection portion 112 connected to the tip of the piston 10 and a disk portion 113 that abuts against the swash plate 12. The disk portion 113 has a large diameter disk portion 113A and a small diameter disk portion 113B, and the thickness dimension of the large diameter disk portion 113A is set to be equal to the thickness dimension H3 of the large diameter disk portion 33A according to this embodiment. The large diameter disk portion 113A is provided with a swash plate sliding surface 113C that slidably abuts against the smooth surface 12A of the swash plate 12 and a retainer abutment surface 113D that abuts against the retainer 13. However, the outer peripheral surface of the large diameter disk portion 113A does not have the outer peripheral groove 34 according to this embodiment.

When the shoe 111 of the comparative example slides on the smooth surface 12A of the swash plate 12 in a circular path, the swash plate sliding surface 113C of the large diameter disc portion 113A abuts against the smooth surface 12A, and the retainer abutment surface 113D abuts against the retainer 13. In this case, since the thickness dimension H3 of the large diameter disc portion 113A of the shoe 111 is small, when the center of the disc portion 113 is pressed against the smooth surface 12A by the thrust of the piston 10, the outer periphery of the large diameter disc portion 113A is deformed so as to be warped in a direction away from the smooth surface 12A. As a result, the outer periphery of the retainer abutment surface 113D comes into point contact or line contact with the retainer 13. As a result, the contact pressure of the retainer abutment surface 113D of the shoe 111 against the retainer 13 becomes locally excessive, causing localized wear between the retainer abutment surface 113D and the retainer 13.

In contrast, the shoe 31 according to this embodiment has an outer circumferential groove 34 on the outer circumferential surface of the large diameter disk portion 33A. Even if the thrust of the piston 10 causes the outer circumferential edge of the swash plate sliding surface 33C to deform so as to warp away from the smooth surface 12A, this deformation does not affect the retainer abutment surface 33D, and the retainer abutment surface 33D can be brought into surface contact with the retainer 13 with a large contact surface pressure. As a result, when the hydraulic pump 1 is in operation, localized wear between the retainer abutment surface 33D of the shoe 31 and the retainer 13 can be suppressed, reducing wear on both surfaces.

Next, Figures 13 and 14 show a third embodiment of the present invention. The feature of this embodiment is that the bottom of the peripheral groove is curved. Note that in this embodiment, the same components as in the first embodiment are given the same reference numerals and their description will be omitted.

The shoe 41 according to this embodiment, like the shoe 21 according to the first embodiment, is configured to include a spherical piston connection portion 42 connected to the tip of the piston 10 and a disk portion 43 that abuts against the swash plate 12, and has an oil hole 41A that penetrates the piston connection portion 42 and the disk portion 43. The disk portion 43 is formed in a stepped disk shape having a large diameter disk portion 43A and a small diameter disk portion 43B. The large diameter disk portion 43A is provided with a swash plate sliding surface 43C, a retainer abutment surface 43D, and a pocket 43E, and an outer peripheral groove 44 is formed on the outer peripheral surface of the large diameter disk portion 43A. However, the shape of the outer peripheral groove 44 is different from that of the outer peripheral groove 24 according to the first embodiment.

The outer peripheral groove 44 of the shoe 41 has an opening end 44A that opens onto the outer peripheral surface of the large diameter disc portion 43A, and a groove bottom portion 44B that is located toward the center of the large diameter disc portion 43A from the opening end 44A. The groove bottom portion 44B has a groove width equal to that of the opening end 44A, and is formed into a semicircular curved shape with the groove width as its diameter.

The shoe 41 according to the third embodiment has the peripheral groove 44 as described above, and its basic effects are not particularly different from those of the shoe 21 according to the first embodiment. However, the peripheral groove 44 according to this embodiment has a curved groove bottom 44B, which can prevent stress from concentrating around the groove bottom 44B when the opening end 44A of the peripheral groove 44 is deformed to narrow the groove width, thereby improving the durability of the shoe 41.

In the first embodiment, the groove bottom 24B of the outer circumferential groove 24 formed in the large diameter disk portion 23A of the shoe 21 is formed in a flat shape. However, the present invention is not limited to this, and for example, as in the first modified example shown in Figure 15, an outer circumferential groove 24' may be provided that is composed of an opening end 24A' and a groove bottom 24B' that has a groove width smaller than that of the opening end 24A' and is formed in a semicircular curved shape.

In the first embodiment, the shoe 21 has a pocket 23E on the swash plate sliding surface 23C of the large diameter disk portion 23A, and the outer circumferential groove 24 is provided on the shoe 21. However, the present invention is not limited to this, and the outer circumferential groove may be provided on the shoe 51 according to the second modified example shown in Figures 16 and 17.

The shoe 51 according to the second modification includes a piston connection portion 52, a disk portion 53, and an oil hole 51A that penetrates the piston connection portion 52 and the disk portion 53. The disk portion 53 has a large diameter disk portion 53A and a small diameter disk portion 53B, and the large diameter disk portion 53A is provided with a swash plate sliding surface 53C, a retainer abutment surface 53D, and a pocket 53E. Furthermore, the swash plate sliding surface 53C is formed with, for example, two annular oil grooves 53F and three pads 53G separated by the oil grooves 53F. The large diameter disk portion 53A on which the oil grooves 53F and pads 53G are formed may be configured to have an outer peripheral groove 54 formed around the entire outer peripheral surface.

In the first embodiment, an outer peripheral groove 24 is formed in the center of the thickness direction of the large diameter disc portion 23A of the shoe 21, and the thickness dimension of the large diameter disc portion 23A from the outer peripheral groove 24 to the swash plate sliding surface 23C is set equal to the thickness dimension from the outer peripheral groove 24 to the retainer abutment surface 23D.

However, the present invention is not limited to this, and may be configured as a shoe 61 according to a third modified example shown in FIG. 18. The shoe 61 according to the third modified example is configured to include a piston connection portion 62, a disk portion 63, and an oil hole 61A. The disk portion 63 has a large diameter disk portion 63A and a small diameter disk portion 63B, and the large diameter disk portion 63A is provided with a swash plate sliding surface 63C, a retainer abutment surface 63D, and a pocket 63E. An outer peripheral groove 64 is provided on the outer peripheral surface of the large diameter disk portion 63A, and this outer peripheral groove 64 is formed at a position biased toward the retainer abutment surface 63D side from the center in the thickness direction of the large diameter disk portion 63A. Therefore, the large diameter disk portion 63A of the shoe 61 has a thickness on the swash plate sliding surface 63C side greater than the thickness on the retainer abutment surface 63D side across the outer peripheral groove 64.

As a result, when centrifugal force acts on the shoe 61 during operation of the hydraulic pump 1 and the swash plate sliding surface 63C is inclined relative to the smooth surface 12A of the swash plate 12, deformation of the swash plate sliding surface 63C is suppressed. As a result, hydraulic oil is retained in the pocket 63E, and lubrication between the smooth surface 12A of the swash plate 12 and the swash plate sliding surface 63C is ensured, thereby reducing wear between the swash plate 12 and the shoe 61.

In the first embodiment, the piston 10 has a spherical recess 10A at the tip, the shoe 21 has a piston connection portion 22 consisting of a spherical protrusion that fits into the spherical recess 10A of the piston 10, and a disk portion 23 having a swash plate sliding surface 23C, and an outer peripheral groove 24 is provided on the outer peripheral surface of the disk portion 23 (large diameter disk portion 23A). However, the present invention is not limited to this, and for example, a configuration in which an outer peripheral groove is provided on a shoe 71 according to a fourth modified example shown in FIG. 19 may be used.

The shoe 71 according to the fourth modification includes a concave spherical piston connection portion 72 and a disk portion 73. The piston connection portion 72 is fitted to a spherical protrusion 74A provided at the tip of the piston 74 so as to be able to swing. The disk portion 73 of the shoe 71 thus configured may be configured to have an outer peripheral groove 75 provided around the entire outer peripheral surface.

Furthermore, in the embodiment, a variable displacement hydraulic pump 1 is exemplified as a swash plate type hydraulic rotating machine. However, the present invention is not limited to this, and may be applied to, for example, a fixed displacement swash plate type hydraulic pump or a swash plate type hydraulic motor.

REFERENCE SIGNS LIST 1 Hydraulic pump 2 Casing 5 Rotating shaft 8 Cylinder block 9 Cylinder 10, 74 Piston 12 Swash plate 12A Smooth surface 13 Retainer 21, 31, 41, 51, 61, 71 Shoe 22, 32, 42, 52, 62, 72 Piston connection portion 23, 33, 43, 53, 63, 73 Disk portion 23C, 33C, 43C, 53C, 63C Swash plate sliding surface 23D, 33D, 43D, 53D, 63D Retainer abutment surface 24, 34, 44, 54, 64, 75, 24' Outer circumferential groove 24A, 34A, 44A, 24A' Open end 24B, 34B, 44B, 24B' Groove bottom portion

Claims (3)

the compressor comprises a casing, a rotary shaft rotatably provided within the casing, a cylinder block having a plurality of cylinders and rotating integrally with the rotary shaft, a plurality of pistons reciprocably inserted within the cylinders of the cylinder block, a plurality of shoes respectively provided at the tips of the plurality of pistons, a swash plate on which the plurality of shoes slide, and a retainer for holding the plurality of shoes against the swash plate,
In a swash plate type hydraulic rotary machine, the shoe has a piston connection portion swingably connected to a tip end of the piston, and a disk portion provided with a swash plate sliding surface slidably contacting the swash plate and a retainer contact surface abutting the retainer,
An outer circumferential groove is provided on the outer circumferential surface of the disk portion, the outer circumferential groove being recessed from the outer circumferential surface of the disk portion toward the center,
the outer circumferential groove has an opening end that opens to an outer circumferential surface of the disk portion and a groove bottom portion that is disposed toward the center of the disk portion from the opening end,
A swash plate type hydraulic rotary machine, characterized in that a groove width of the outer peripheral groove decreases from the opening end toward the groove bottom. the compressor comprises a casing, a rotary shaft rotatably provided within the casing, a cylinder block having a plurality of cylinders and rotating integrally with the rotary shaft, a plurality of pistons reciprocably inserted within the cylinders of the cylinder block, a plurality of shoes provided at the tips of the plurality of pistons, a swash plate along which the plurality of shoes slide, and a retainer for holding the plurality of shoes against the swash plate;
In a swash plate type hydraulic rotary machine, the shoe has a piston connection portion swingably connected to a tip end of the piston, and a disk portion provided with a swash plate sliding surface slidably contacting the swash plate and a retainer contact surface abutting the retainer,
An outer circumferential groove is provided on the outer circumferential surface of the disk portion, the outer circumferential groove being recessed from the outer circumferential surface of the disk portion toward the center,
the outer circumferential groove has an opening end that opens to an outer circumferential surface of the disk portion and a groove bottom portion that is disposed toward the center of the disk portion from the opening end,
4. A swash plate type hydraulic rotary machine, comprising: a groove bottom portion having a curved surface shape. The swash plate type hydraulic rotary machine according to claim 2, characterized in that the groove width of the outer peripheral groove becomes smaller from the opening end toward the groove bottom.

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