Swash plate type hydraulic rotary machine

Abstract

To reduce frictional force between a shoe and a swash plate.SOLUTION: The swash plate type hydraulic motor 1 includes a rotary shaft 6, a rotor 7 which is provided in the casing 2 so as to rotate integrally with the rotary shaft 6 and in which a plurality of cylinders 8 are formed, a plurality of pistons 9 which are reciprocatably inserted into the plurality of cylinders 8 of the rotor 7, a plurality of shoes 15 which are respectively provided at tip ends of the plurality of pistons 9, and a swash plate 11 having a sliding surface 11A on which the plurality of shoes 15 slide. The shoe 15 is provided with an annular seal surface 11A that abuts against the sliding surface 16B of the swash plate 11, and an annular groove 17 that is formed on the seal surface 16B concentrically with the seal surface 16B and is annularly recessed with respect to the seal surface 16B, and an inclined surface that intersects the seal surface 16B in a state of being inclined with respect to the seal surface 16B is formed on each of an inner peripheral side and an outer peripheral side of the annular groove 17.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a swash plate type hydraulic rotary machine that is suitably used as a hydraulic motor or a hydraulic pump. [Background technology]

[0002] Construction machinery such as hydraulic excavators are equipped with a hydraulic pump as a hydraulic pressure source, a hydraulic motor (swing motor) that rotates the upper rotating body, a hydraulic motor (travel motor) that drives the lower traveling body, etc. These hydraulic pumps and hydraulic motors are variable displacement or fixed displacement swash plate hydraulic rotary machines.

[0003] A swash plate type hydraulic rotating machine comprises a rotating shaft rotatably mounted within a casing, a rotor formed with a plurality of cylinders mounted within the casing so as to rotate integrally with the rotating shaft, a plurality of pistons reciprocally inserted into the cylinders of the rotor, a plurality of shoes respectively mounted at the tips of the pistons, and a swash plate along which the plurality of shoes slide.

[0004] The sealing surface of the shoe, which slidably contacts the swash plate, is provided with a recess (hydrostatic pocket). When a swash plate-type hydraulic rotary machine is in operation, hydraulic oil is supplied between the recess of the shoe and the swash plate, and as the shoe rotates on the swash plate, hydraulic oil in the casing is drawn into the sliding surface between the shoe and the swash plate. This forms an oil film between the shoe and the swash plate, ensuring lubrication between the shoe and the swash plate.

[0005] A conventional swash plate type hydraulic rotary machine has been proposed that includes a shoe with a funnel-shaped (concave) pressure-receiving surface formed on the sealing surface (Patent Document 1). According to this conventional technology, by providing a funnel-shaped pressure-receiving surface on the sealing surface of the shoe, the pressure-receiving area of ​​the hydraulic pressure acting on the swash plate is increased, ensuring a gap between the shoe and the swash plate and ensuring lubrication between them. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Utility Model Application Publication No. 5-30473 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the shoe described in Patent Document 1 slides on the swash plate, the funnel-shaped pressure-receiving surface creates a reverse wedge effect on the oil film between the shoe and the swash plate at the front of the shoe's travel, resulting in a decrease in oil film pressure. Meanwhile, the funnel-shaped pressure-receiving surface creates a wedge effect on the oil film between the shoe and the swash plate at the rear of the shoe's travel, resulting in an increase in oil film pressure. This narrows the gap between the shoe and the swash plate at the front and widens it at the rear. This makes it difficult for hydraulic oil from the casing to be supplied between the shoe and the swash plate at the front of the shoe's travel, while at the rear of the shoe's travel, hydraulic oil is easily expelled from the sliding surface between the shoe and the swash plate. This results in a thin oil film between the shoe and the swash plate, increasing the friction between them.

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide a swash plate type hydraulic rotary machine that is capable of reducing the frictional force between the shoes and the swash plate. [Means for solving the problem]

[0009] The present invention provides a swash plate type hydraulic rotating machine comprising: a rotating shaft rotatably mounted within a casing; a rotor formed with a plurality of cylinders and mounted within the casing so as to rotate integrally with the rotating shaft; a plurality of pistons reciprocally inserted into the cylinders of the rotor; a plurality of shoes respectively provided at the tips of the pistons; and a swash plate having a sliding surface along which the plurality of shoes slide. The shoe is provided with an annular sealing surface that abuts against the sliding surface of the swash plate, and an annular groove formed in the sealing surface concentrically with the sealing surface and annularly recessed into the sealing surface, and the inner and outer circumferential sides of the annular groove are formed with inclined surfaces that intersect with the sealing surface while being inclined relative to the sealing surface. [Effects of the Invention]

[0010] According to the present invention, the frictional force between the sliding surface of the shoe and the swash plate can be reduced. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a swash plate type hydraulic motor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view showing the shoe according to the first embodiment alone. [Figure 3] 3 is a front view of the shoe as seen from the direction of arrows III-III in FIG. 2. [Figure 4] 4 is a cross-sectional view of the shoe as seen from the direction of arrows IV-IV in FIG. 3. [Figure 5] FIG. 3 is an enlarged cross-sectional view showing the outer peripheral edge of the shoe. [Figure 6] FIG. 3 is a cross-sectional view showing the sliding surface between the shoe and the swash plate. [Figure 7] FIG. 4 is a cross-sectional view showing a state in which the shoe is inclined relative to the swash plate. [Figure 8] 4 is a characteristic diagram showing the relationship between the shape of the sliding surface of the shoe and the oil film pressure between the shoe and the swash plate according to the first embodiment. FIG. [Figure 9]FIG. 10 is a characteristic diagram showing the relationship between the shape of the sliding surface of the shoe and the oil film pressure between the shoe and the swash plate according to a first comparative example. [Figure 10] FIG. 10 is a characteristic diagram showing the relationship between the shape of the sliding surface of the shoe and the oil film pressure between the shoe and the swash plate according to a second comparative example. [Figure 11] FIG. 11 is a characteristic diagram showing the relationship between the shape of the sliding surface of the shoe and the oil film pressure between the shoe and the swash plate according to a third comparative example. [Figure 12] FIG. 11 is a characteristic diagram showing the relationship between the shape of the sliding surface of the shoe and the oil film pressure between the shoe and the swash plate according to a fourth comparative example. [Figure 13] FIG. 4 is an enlarged cross-sectional view showing the cross-sectional shape of an annular groove. [Figure 14] 10 is a characteristic diagram showing the relationship between the shape of the sliding surface of the shoe and the oil film pressure between the shoe and the swash plate when the angle formed between the inclined surface of the annular groove and the seal surface is changed. [Figure 15] FIG. 10 is a characteristic diagram showing the relationship between the shape of the sliding surface of the other shoe and the oil film pressure between the shoe and the swash plate when the angle between the inclined surface of the annular groove and the seal surface is changed. [Figure 16] FIG. 2 is an enlarged cross-sectional view showing the oil film pressure generated between a shoe having two annular grooves formed in its sealing surface and a swash plate. [Figure 17] FIG. 5 is a cross-sectional view of a shoe according to a second embodiment taken in the same position as in FIG. 4. [Figure 18] FIG. 4 is an enlarged cross-sectional view showing an annular groove of the shoe. [Figure 19] FIG. 10 is a perspective view showing a shoe according to a third embodiment. [Figure 20] 20 is a front view of the shoe as seen from the direction of arrows XX-XX in FIG. 19. [Figure 21] 21 is a cross-sectional view of the shoe as seen from the direction of arrows XXI-XXI in FIG. 20. [Figure 22] FIG. 3 is an enlarged cross-sectional view showing the outer peripheral edge of the shoe. [Figure 23] FIG. 10 is a cross-sectional view showing an annular groove according to a first modified example. [Figure 24] FIG. 10 is a cross-sectional view showing an annular groove according to a second modified example. [Figure 25] FIG. 10 is a cross-sectional view showing an annular groove according to a third modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a swash plate type hydraulic rotary machine according to the present invention will be described in detail below with reference to the accompanying drawings, taking a swash plate type hydraulic motor as an example.

[0013] 1 to 8 show a first embodiment of the present invention. In Fig. 1, a variable displacement swash plate hydraulic motor 1 serving as a swash plate hydraulic rotary machine is supplied with pressure oil from a hydraulic source (not shown) such as a hydraulic pump to rotate a rotary shaft 6 (described later).

[0014] The casing 2 forms the outer shell of the swash plate type hydraulic motor 1. The casing 2 includes a cylindrical casing main body 3 with a bottom and a rear casing 4 fixed to the casing main body 3. One axial side (left side in FIG. 1) of the casing main body 3 forms a front bottom portion 3A. The other axial side (right side in FIG. 1) of the casing main body 3 is closed by the rear casing 4. A swash plate support member 10 that supports a swash plate 11 (described later) so that the swash plate 11 can tilt is provided on the front bottom portion 3A side of the casing main body 3.

[0015] The valve plate 5 is disposed within the casing 2 and fixed to the rear casing 4. The valve plate 5 is configured as a switching valve plate that switches the supply / discharge direction of pressure oil to / from a cylinder 8 (described later), and has a pair of supply / discharge ports 5A, 5B that extend in an eyebrow shape around the rotary shaft 6. The supply / discharge ports 5A, 5B are connected to a hydraulic pump and a tank (neither of which are shown), which serve as a hydraulic source, via supply / discharge passages, hydraulic piping, etc., formed in the rear casing 4.

[0016] The rotating shaft 6 is rotatably disposed within the casing 2. One axial side of the rotating shaft 6 is rotatably attached to the front bottom 3A of the casing main body 3 via a bearing or the like. The other axial side of the rotating shaft 6 is rotatably attached to the rear casing 4 via a bearing. One side of the rotating shaft 6 forms a protruding end 6A that protrudes outward from the front bottom 3A of the casing main body 3. The rotating shaft 6 constitutes the output shaft of the swash plate hydraulic motor 1, and the protruding end 6A side of the rotating shaft 6 can be connected to, for example, a travel reducer or a swing reducer (neither of which are shown) of a hydraulic excavator.

[0017] The rotor (cylinder block) 7 is provided in the casing 2 so as to rotate integrally with the rotary shaft 6. The rotor 7 is formed as a thick-walled cylinder surrounding the rotary shaft 6. The rotor 7 has a plurality of cylinders 8 (only two are shown in FIG. 1 ) that extend axially and are equally spaced circumferentially. One axial side of the rotor 7 is an end face 7A that faces the swash plate 11. A cylindrical protrusion 7B that protrudes toward the swash plate 11 is integrally formed at the center of the end face 7A of the rotor 7. A spherical guide 13, which will be described later, is fitted onto the outer periphery of the cylindrical protrusion 7B so as to be relatively displaceable in the axial direction.

[0018] A stepped shaft hole 7C is formed on the inner periphery of the rotor 7, passing through the inner periphery of the cylindrical protrusion 7B in the axial direction. The shaft hole 7C is splined to the outer periphery of the rotary shaft 6. The rotor 7 is connected to the rotary shaft 6 via the shaft hole 7C so as to rotate integrally with the rotary shaft 6, and is also connected to the spherical guide 13 so as to rotate integrally with the rotary shaft 6. Furthermore, the other axial side of the rotor 7 forms a concave spherical sliding surface 7D that slidably abuts against the valve plate 5.

[0019] A plurality of cylinders 8 are provided at equal intervals around the rotor 7. Each of the cylinders 8 is formed as a bottomed hole with a uniform inner diameter over its entire length. One side of each of the cylinders 8 forms an open end 8A that opens to one end surface 7A of the rotor 7. Meanwhile, the other side of each of the cylinders 8 intermittently communicates with the supply and discharge ports 5A, 5B of the valve plate 5 via a cylinder port 8B.

[0020] The pistons 9 are respectively inserted and fitted into the multiple cylinders 8 of the rotor 7 so as to be able to reciprocate. The pistons 9 are formed as cylindrical rods inserted into the cylinders 8 with a small gap between them. The pistons 9 are driven in the axial direction so as to repeatedly reciprocate within the cylinders 8 by pressure oil supplied to the cylinders 8 from one of the supply and discharge ports 5A, 5B of the valve plate 5. The base ends of the pistons 9 are slidably inserted and fitted into the cylinders 8, and the tip ends of the pistons 9 protrude from the open end 8A of the cylinders 8 to the outside of the rotor 7.

[0021] A concave spherical portion 9A is formed at the tip (protruding end) of the piston 9, and a convex spherical portion 15C of a shoe 15 (described later) is attached to the concave spherical portion 9A so that it can swing. An oil hole 9B is formed in the center of the piston 9, passing through the piston 9 in the axial direction. When the swash plate type hydraulic motor 1 is in operation, some of the hydraulic oil (pressurized oil) supplied into the cylinder 8 is supplied to the shoe 15 as lubricating oil through the oil hole 9B of the piston 9.

[0022] The swash plate support member 10 is disposed inside the casing 2 and fixed to the front bottom portion 3A of the casing body 3. The swash plate support member 10 is provided with a pair of tilt support portions 10A that face each other across the rotary shaft 6. Each of the pair of tilt support portions 10A has a concave curved surface that supports the swash plate 11 so that it can tilt.

[0023] The swash plate 11 is tiltably mounted within the casing 2 and constitutes the variable displacement unit of the swash plate-type hydraulic motor 1. A smooth (flat) sliding surface 11A is formed on the front surface (rotor 7 side) of the swash plate 11, and shoes 15 attached to the tips of the pistons 9 slide on the sliding surface 11A of the swash plate 11. A shaft insertion hole 11B is formed in the center of the swash plate 11, and a rotating shaft 6 is inserted through the shaft insertion hole 11B. Both sides of the rotating shaft 6 sandwiching the swash plate 11 are rotatably engaged with tilt support portions 10A of the swash plate support member 10. The swash plate 11 is tilted while supported by the swash plate support member 10 (tilt support portions 10A) by being pushed by a tilt actuator (not shown) attached to the casing 2, changing the angle between the sliding surface 11A of the swash plate 11 and the rotating shaft 6.

[0024] The retainer 12 is disposed between a shoe 15 attached to the tip of the piston 9 and a spherical guide 13, and holds the shoe 15 slidably against the sliding surface 11A of the swash plate 11. The retainer 12 is formed as an annular plate surrounding the rotary shaft 6, and the spherical guide 13 is slidably fitted to the inner periphery of the retainer 12. The retainer 12 is formed with shoe insertion holes 12A, the same number as the number of shoes 15, spaced equally apart in the circumferential direction. Step portions 15B of the shoes 15 are inserted into these shoe insertion holes 12A. The retainer 12 is biased toward the sliding surface 11A of the swash plate 11 by the spherical guide 13 and a spring member 14. The retainer 12 holds the shoes 15 inserted into the shoe insertion holes 12A in a state pressed against the sliding surface 11A.

[0025] The spherical guide 13 is provided between the cylindrical protrusion 7B of the rotor 7 and the inner periphery of the retainer 12. The spherical guide 13 is formed as a cylindrical body with a spherical outer periphery, and is attached to the cylindrical protrusion 7B so as to be displaceable in the axial direction. The spherical outer periphery of the spherical guide 13 is fitted to the inner periphery of the retainer 12 so as to be able to swing (slide). The inner periphery of the spherical guide 13 is spline-connected to the rotating shaft 6, and the spherical guide 13 rotates integrally with the rotating shaft 6.

[0026] The spring member 14 is located on the outer periphery of the rotary shaft 6 and is provided between the cylindrical protrusion 7B of the rotor 7 and the spherical guide 13. The spring member 14 is formed, for example, by stacking a plurality of disc springs in the axial direction, and biases the rotor 7 and the spherical guide 13 in opposite directions. The spring member 14 presses the sliding surface 7D of the rotor 7 against the valve plate 5, and also presses each shoe 15 against the sliding surface 11A of the swash plate 11 via the spherical guide 13 and the retainer 12.

[0027] Next, the shoe 15 according to this embodiment will be described with reference to FIGS.

[0028] The shoes 15 are attached to the tips of the pistons 9 so as to be able to swing. Each shoe 15 is integrally formed with a disk-shaped portion 15A, a disk-shaped stepped portion 15B having a smaller diameter than the disk portion 15A, and a convex spherical portion 15C protruding from the stepped portion 15B. The disk portion 15A is formed in a disk shape with a larger diameter than the shoe insertion hole 12A of the retainer 12, and has a sliding surface 16 that faces the sliding surface 11A of the swash plate 11. The stepped portion 15B and the convex spherical portion 15C are inserted into the shoe insertion hole 12A of the retainer 12, and the convex spherical portion 15C is attached to the concave spherical portion 9A of the piston 9 so as to be able to swing.

[0029] A linear oil hole 15D is formed in the center of shoe 15, penetrating axially from disc portion 15A to convex spherical portion 15C. A portion of the hydraulic oil (pressurized oil) supplied into cylinder 8 is guided through oil hole 9B of piston 9 through oil hole 15D, and this hydraulic oil is supplied as lubricant between sliding surface 16 of shoe 15 and sliding surface 11A of swash plate 11. Shoe 15 rotates together with rotating shaft 6, rotor 7, and piston 9, and slides smoothly on sliding surface 11A of swash plate 11, tracing a ring-shaped path centered on rotating shaft 6.

[0030] The sliding surface 16 of the shoe 15 is formed on the surface of the disk portion 15A that faces the sliding surface 11A of the swash plate 11. As shown in Figures 2 to 4, the sliding surface 16 includes a hydrostatic pocket 16A, a seal surface 16B, and an annular groove 17 (described later). A chamfered portion (C-chamfered portion) 16C having an inclination angle of 45° is formed around the entire circumference on the outer circumferential side of the seal surface 16B.

[0031] The hydrostatic pocket 16A is located at the center of the sliding surface 16. The hydrostatic pocket 16A is circular, with its center at the axial center A of the shoe 15, and is surrounded from the outer periphery by the seal surface 16B. As a result, the hydrostatic pocket 16A is located on the inner periphery of the seal surface 16B and is formed as a circular recess that is recessed into the seal surface 16B. An oil hole 15D of the shoe 15 opens into the hydrostatic pocket 16A, and hydraulic oil discharged through the oil hole 15D to the swash plate 11 side is supplied to the hydrostatic pocket 16A.

[0032] The seal surface 16B is located radially outward of the hydrostatic pocket 16A and is formed as an annular flat surface that radially surrounds the hydrostatic pocket 16A. An inner peripheral edge 16B1 of the seal surface 16B is circular with a radius R1 centered on the axial center A of the shoe 15 and forms the boundary with the hydrostatic pocket 16A. An outer peripheral edge 16B2 of the seal surface 16B is circular with a radius R2 centered on the axial center A of the shoe 15 and intersects with the chamfered portion 16C. When the axial center A of the shoe 15 is perpendicular to the sliding surface 11A of the swash plate 11, the seal surface 16B abuts (makes surface contact) with the sliding surface 11A of the swash plate 11 as a hydrostatic bearing. The sealing surface 16B surrounds the hydrostatic pocket 16A from the outer periphery, thereby sealing the hydraulic oil supplied to the hydrostatic pocket 16A and preventing the hydraulic oil supplied between the sliding surface 11A of the swash plate 11 and the sliding surface 16 of the shoe 15 from leaking to the outside.

[0033] The hydraulic oil supplied to the hydrostatic pocket 16A generates a hydraulic reaction force on the shoe 15 in a direction that moves it away from the sliding surface 11A of the swash plate 11. This hydraulic reaction force causes the shoe 15 to float slightly (for example, several μm to several tens of μm) above the sliding surface 11A of the swash plate 11, and an oil film is formed between the sliding surface 11A of the swash plate 11 and the sealing surface 16B of the shoe 15 (sliding surface 16). As a result, the sliding surface 11A of the swash plate 11 and the sealing surface 16B of the shoe 15 (sliding surface 16) are appropriately lubricated, allowing the shoe 15 to slide smoothly on the sliding surface 11A of the swash plate 11. At this time, the thrust of the piston 9 that presses the shoe 15 against the swash plate 11 is set to be slightly (for example, several percent) larger than the hydraulic reaction force acting on the shoe 15 by the hydraulic oil supplied to the hydrostatic pocket 16A.

[0034] The annular groove 17 is formed in the seal surface 16B. The annular groove 17 is arranged concentrically with the seal surface 16B and is formed as a circumferential groove recessed into the seal surface 16B. Preferably, one annular groove 17 is provided for the seal surface 16B. As shown in FIG. 5 , the annular groove 17 has a triangular cross-sectional shape where an inner linear inclined surface 17A and an outer linear inclined surface 17B intersect at a linear groove bottom 17C, and the cross-sectional shape is symmetrical at the groove bottom 17C. The distance from the seal surface 16B to the groove bottom 17C is the groove depth D of the annular groove 17. The inner linear inclined surface 17A is arranged on the inner side of the annular groove 17 and is linearly inclined relative to the seal surface 16B. The outer linear inclined surface 17B is arranged on the outer side of the annular groove 17 and is linearly inclined relative to the seal surface 16B. The angle (gradient) θ formed by the inner peripheral linear inclined surface 17A and the outer peripheral linear inclined surface 17B with respect to the seal surface 16B is set to 5° or less (θ≦5°).

[0035] An inner peripheral edge 17A1 of the annular groove 17 (the intersection of the inner peripheral linear inclined surface 17A and the seal surface 16B) is circular and has a radius R3 centered on the axial center A of the shoe 15. An outer peripheral edge 17B1 of the annular groove 17 (the intersection of the outer peripheral linear inclined surface 17B and the seal surface 16B) is circular and has a radius R4 centered on the axial center A of the shoe 15. That is, the inner radius of the annular groove 17 is R3, and the outer radius of the annular groove 17 is R4.

[0036] When the shoe 15 slides on the sliding surface 11A of the swash plate 11 around the rotary shaft 6 during operation of the swash plate-type hydraulic motor 1, hydraulic oil is supplied to the hydrostatic pocket 16A of the shoe 15, and hydraulic oil filled in the casing 2 is drawn between the sliding surface 11A of the swash plate 11 and the sliding surface 16 of the shoe 15. This generates pressure due to an oil film between the sliding surface 11A of the swash plate 11 and the sliding surface 16 of the shoe 15. As shown in FIG. 6, the shoe 15 slides on the sliding surface 11A of the swash plate 11 while floating slightly (several μm to several tens of μm) above the sliding surface 11A of the swash plate 11. Note that in FIG. 6, the distance between the shoe 15 and the sliding surface 11A is shown enlarged to clearly show the state in which the shoe 15 floats above the sliding surface 11A of the swash plate 11; however, the distance between the shoe 15 and the sliding surface 11A is actually so small that it cannot be shown in the figure.

[0037] When the shoe 15 slides on the sliding surface 11A of the swash plate 11 in the direction of arrow B, the annular groove 17 creates a wedge effect and a reverse wedge effect on the oil film formed between the sealing surface 16B of the shoe 15 and the sliding surface 11A of the swash plate 11. Specifically, at the front end of the shoe 15's movement, hydraulic oil flows from the inner periphery of the annular groove 17 toward the inner periphery of the sealing surface 16B, as indicated by arrow F1 in FIG. 6. This wedge effect generates high pressure on the inner periphery of the annular groove 17 (particularly near the inner periphery 17A1), maintaining a high oil film pressure between the sealing surface 16B and the sliding surface 11A of the swash plate 11. Meanwhile, at the rear end of the shoe 15's movement, hydraulic oil is discharged from the sealing surface 16B toward the inner periphery of the annular groove 17, as indicated by arrow F2 in FIG. 6. Due to this reverse wedge effect, the pressure on the inner peripheral side of the annular groove 17 becomes low, and the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11 decreases.

[0038] As a result, the oil film pressure formed between the sliding surface 11A of the swash plate 11 and the sealing surface 16B of the shoe 15 is high at the front of the shoe 15 in the direction of travel and low at the rear of the shoe 15. Therefore, as shown in Figure 7, the gap between the sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11 is wide at the front and narrow at the rear. This creates a wedge effect between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11, increasing the oil film pressure and reducing the frictional force caused by contact between the sliding surface 11A of the swash plate 11 and the sliding surface 16 of the shoe 15.

[0039] In this case, the rear side of the shoe 15 approaches the sliding surface 11A of the swash plate 11, and hydraulic oil flows from the outer periphery of the annular groove 17 toward the outer periphery of the seal surface 16C, as shown by arrow F3 in Figure 7. This wedge effect generates high pressure on the outer periphery of the annular groove 17, increasing the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11, thereby reducing the friction between them. In addition, the annular groove 17 also functions as an oil reservoir for storing hydraulic oil, thereby preventing the oil film from running out between the sliding surface 11A of the swash plate 11 and the seal surface 16B.

[0040] Here, the radius R1 of the inner peripheral edge 16B1 of the seal surface 16B (the inner peripheral radius of the seal surface 16B), the radius R2 of the outer peripheral edge 16B2 of the seal surface 16B (the outer peripheral radius of the seal surface 16B), and the radius R3 of the inner peripheral edge 17A1 of the annular groove 17 (the inner peripheral radius of the annular groove 17) are set to satisfy the relationship given by the following equation 1. That is, the annular groove 17 is positioned closer to the outer periphery (closer to the chamfered portion 16C) than the radial middle position of the seal surface 16B.

[0041]

number

[0042] Furthermore, a radius R2 (outer radius of sealing surface 16B) of outer peripheral edge 16B2 of sealing surface 16B and a radius R4 (outer radius of annular groove 17) of outer peripheral edge 17B1 of annular groove 17 are set to satisfy the relationship of the following equation 2. That is, the outer diameter of annular groove 17 is set to be smaller than the outer diameter of sealing surface 16B, and an inner peripheral edge 17A1 and outer peripheral edge 17B1 of annular groove 17 are configured to be completely contained within sealing surface 16B.

[0043]

number

[0044] The swash plate type hydraulic motor 1 according to this embodiment has the shoes 15 as described above, and the operation of the swash plate type hydraulic motor 1 will be described below.

[0045] Hydraulic oil (pressurized oil) discharged from a hydraulic pump (not shown) is supplied to a supply / discharge passage (not shown) formed in the rear casing 4. This pressurized oil is supplied to and discharged from a plurality of cylinders 8 formed in the rotor 7 through supply / discharge ports 5A and 5B of the valve plate 5, and a plurality of pistons 9 repeatedly reciprocate within each of the cylinders 8.

[0046] At this time, the piston 9 presses the shoe 15 axially toward the sliding surface 11A of the swash plate 11 by the hydraulic oil supplied to the cylinder 8. Meanwhile, part of the hydraulic oil supplied to the cylinder 8 is supplied to a hydrostatic pocket 16A formed on the sliding surface 16 of the shoe 15 through an oil hole 9B in the piston 9 and an oil hole 15D in the shoe 15. The hydraulic oil supplied to the hydrostatic pocket 16A generates a hydraulic reaction force on the shoe 15 in a direction moving it away from the sliding surface 11A of the swash plate 11. This hydraulic reaction force causes the shoe 15 to float slightly above the sliding surface 11A of the swash plate 11, and an oil film is formed between the sliding surface 11A of the swash plate 11 and the sealing surface 16B of the shoe 15 (sliding surface 16).

[0047] As a result, the sliding surface 11A of the swash plate 11 and the sealing surfaces 16B of the shoes 15 are appropriately lubricated, and the shoes 15 slide on the sliding surface 11A of the swash plate 11, tracing a ring-shaped path centered on the rotary shaft 6. As the shoes 15 slide on the sliding surface 11A of the swash plate 11, the pistons 9 reciprocate within the cylinders 8, applying a rotational force to the rotor 7 about the rotary shaft 6. This rotational force of the rotor 7 rotates the rotary shaft 6, which in turn drives a mechanical element connected to the protruding end 6A of the rotary shaft 6.

[0048] When the swash plate type hydraulic motor 1 is in operation, and the shoe 15 slides on the sliding surface 11A of the swash plate 11 around the rotary shaft 6, hydraulic oil is supplied to the hydrostatic pocket 16A of the shoe 15, and hydraulic oil filled in the casing 2 is drawn between the sliding surface 11A of the swash plate 11 and the sliding surface 16 of the shoe 15. This generates pressure due to an oil film between the sliding surface 11A of the swash plate 11 and the sliding surface 16 of the shoe 15, and the shoe 15 slides on the sliding surface 11A while floating slightly (several μm to several tens of μm) above the sliding surface 11A of the swash plate 11.

[0049] In this embodiment, the sliding surface 16 of the shoe 15 is formed with an annular seal surface 16B that contacts the sliding surface 11A of the swash plate 11 and an annular groove 17 that is recessed into the seal surface 16B. As a result, at the front end of the shoe 15 in the direction of travel, hydraulic oil flows from the inner periphery of the annular groove 17 toward the inner periphery of the seal surface 16B, as indicated by arrow F1 in FIG. 6. This wedge effect generates high pressure on the inner periphery of the annular groove 17, increasing the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11. Meanwhile, at the rear end of the shoe 15 in the direction of travel, hydraulic oil is discharged from the seal surface 16B toward the inner periphery of the annular groove 17, as indicated by arrow F2 in FIG. 6. This reverse wedge effect reduces the pressure on the inner periphery of the annular groove 17, decreasing the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11.

[0050] In this way, the oil film pressure formed between the sliding surface 11A of the swash plate 11 and the sealing surface 16B of the shoe 15 is high at the front of the shoe 15 in the direction of travel and low at the rear of the shoe 15. As a result, the gap between the sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11 becomes wider at the front of the shoe 15 and narrower at the rear of the shoe 15, as shown in Figure 7. This creates a wedge effect between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11, increasing the oil film pressure.

[0051] In this case, the rear side of the shoe 15 approaches the sliding surface 11A of the swash plate 11, and hydraulic oil flows from the outer periphery of the annular groove 17 toward the outer periphery of the seal surface 16C, as shown by arrow F3 in Figure 7. This wedge effect generates high pressure on the outer periphery of the annular groove 17, increasing the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11, thereby reducing the friction between them. As a result, the friction caused by contact between the sliding surface 11A of the swash plate 11 and the sliding surface 16A of the shoe 15 is reduced, extending the life of the shoe 15 and enabling the swash plate-type hydraulic motor 1 to operate stably for a long period of time.

[0052] Next, the results of comparing the oil film pressure generated between the sliding surface 16 of the shoe 15 and the swash plate 11 in this embodiment with the oil film pressure generated between the sliding surface of the shoe and the swash plate in Comparative Examples 1 to 4 will be explained with reference to Figures 8 to 12.

[0053] 8 shows the relationship between the oil film pressure generated between the sliding surface 16 and the swash plate 11 and the shape of the sliding surface 16 when the shoe 15 of this embodiment slides on the swash plate 11 (sliding surface 11A) in the direction of arrow B. In this case, the groove depth D of the annular groove 17 is set to D=4 μm, the groove width (the distance between the inner peripheral edge 17A1 and the outer peripheral edge 17B1) of the annular groove 17 is set to 1 mm, and the angle θ formed by the inner peripheral linear inclined surface 17A and the outer peripheral linear inclined surface 17B of the annular groove 17 with respect to the sealing surface 16B is set to θ=5°.

[0054] 8, in this embodiment, the oil film pressure generated between the sliding surface 16 of the shoe 15 and the swash plate 11 increases from pressure value P1 to pressure value P4 between the outer peripheral edge 16B2 of the sealing surface 16B and the annular groove 17 at the front side of the shoe 15 in the direction of travel (arrow B), decreases from pressure value P4 to pressure value P3 between the annular groove 17 and the inner peripheral edge 16B1 of the sealing surface 16B, and then maintains pressure value P3 within the hydrostatic pocket 16A (between the front inner peripheral edge 16B1 of the sealing surface 16B and the rear inner peripheral edge 16B1 of the sealing surface 16B). On the other hand, at the rear side of the shoe 15 in the direction of travel, the oil film pressure decreases from pressure value P3 to pressure value P1 between the inner peripheral edge 16B1 of the sealing surface 16B and the annular groove 17, and then increases from pressure value P1 to pressure value P2 between the annular groove 17 and the outer peripheral edge 16B2 of the sealing surface 16B.

[0055] As described above, when the shoe 15 of this embodiment slides on the sliding surface 11A of the swash plate 11 in the direction of arrow B, the oil film pressure between the sliding surface 16 of the shoe 15 and the swash plate 11 increases at the front of the shoe 15 and decreases at the rear of the shoe 15. Therefore, the gap between the sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11 increases at the front and decreases at the rear, creating a wedge effect between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11. Furthermore, at the rear of the shoe 15, hydraulic oil flows from the outer periphery of the annular groove 17 toward the outer periphery of the sealing surface 16C, as shown by arrow F3 in Fig. 7, and this wedge effect increases the oil film pressure between the sealing surface 16B and the sliding surface 11A of the swash plate 11. Therefore, at the rear side in the traveling direction of the shoe 15, although the gap between the sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11 becomes narrower, the frictional force therebetween can be reduced.

[0056] 9 shows the relationship between the oil film pressure generated between the sliding surface 102 and the swash plate 11 and the shape of the sliding surface 102 when the shoe 101 of Comparative Example 1 slides on the swash plate 11 in the direction of arrow B. The sliding surface 102 of the shoe 101 of Comparative Example 1 has a hydrostatic pocket 102A and a sealing surface 102B.

[0057] As shown by characteristic line 103 in Figure 9, the oil film pressure generated between the sliding surface 102 of the shoe 101 and the swash plate 11 in the comparative example increases from pressure value P1 to P2 within the range of the seal surface 102B at the front side of the shoe 101's travel direction and maintains pressure value P2 within the range of the hydrostatic pocket 102A. Meanwhile, at the rear side of the shoe 101's travel direction, the oil film pressure decreases from pressure value P2 to P1 within the range of the seal surface 102B. Thus, in the shoe 101 of Comparative Example 1, there is little difference in the change in oil film pressure between the front and rear sides of the shoe 101's travel direction. Therefore, if the position of the shoe 101 changes due to centrifugal force acting on the shoe 101, for example, if the gap between the sliding surface 102 and the swash plate 11 narrows at the front side and widens at the rear side, a reverse wedge effect occurs across the entire oil film between the sliding surface 102 and the swash plate 11. As a result, the oil film pressure may decrease, and the friction force between the shoe 101 and the swash plate 11 may increase.

[0058] 10 shows the relationship between the oil film pressure generated between the sliding surface 105 and the swash plate 11 and the shape of the sliding surface 105 when the shoe 104 of Comparative Example 2 slides on the swash plate 11 in the direction of arrow B. The sliding surface 105 of the shoe 104 of Comparative Example 2 has a hydrostatic pocket 105A, a funnel-shaped pressure-receiving surface 105B, and a sealing surface 105C, similar to that described in Patent Document 1.

[0059] As shown by characteristic line 106 in Figure 10, the oil film pressure generated between the sliding surface 105 of the shoe 104 and the swash plate 11 in Comparative Example 2 maintains a pressure value P1 on the outer circumferential side of the pressure-receiving surface 105B at the front side in the direction of movement of the shoe 104. The oil film pressure increases from pressure value P1 to P2 between the middle of the pressure-receiving surface 105B and the hydrostatic pressure pocket 105A, and maintains a pressure value P2 within the range of the hydrostatic pressure pocket 105A. On the other hand, at the rear side in the direction of movement of the shoe 104, the oil film pressure increases from pressure value P2 between the hydrostatic pressure pocket 105A and the pressure-receiving surface 105B.

[0060] In this way, in the shoe 104 of Comparative Example 2, the funnel shape of the pressure-receiving surface 105B creates a reverse wedge effect on the oil film formed between the sliding surface 105 and the swash plate 11 at the front of the traveling direction, reducing the oil film pressure, while creating a wedge effect at the rear of the traveling direction, increasing the oil film pressure. As a result, the position of the shoe 104 narrows the gap between the sliding surface 105 and the swash plate 11 at the front of the traveling direction, making it difficult for hydraulic oil to be supplied between them, while widening the gap at the rear of the traveling direction, making it easier for hydraulic oil to be discharged between them. As a result, the oil film formed between the sliding surface 105 and the swash plate 11 becomes thinner, which may increase the frictional force between the shoe 104 and the swash plate 11.

[0061] 11 shows the relationship between the oil film pressure generated between the sliding surface 108 and the swash plate 11 and the shape of the sliding surface 108 when the shoe 107 of Comparative Example 3 slides on the swash plate 11 in the direction of arrow B. The sliding surface 108 of the shoe 107 of Comparative Example 3 has a hydrostatic pocket 108A, a seal surface 108B, and multiple (two) groove-shaped pressure-receiving surfaces 108C formed on the seal surface 108B, similar to that described in Patent Document 1. The pressure-receiving surface 108C has a semicircular cross section, and the inner and outer circumferential edges of the pressure-receiving surface 108C are perpendicular to the seal surface 108B.

[0062] As shown by characteristic line 109 in Figure 11, the oil film pressure generated between the sliding surface 108 of the shoe 107 of Comparative Example 3 and the swash plate 11 increases stepwise from pressure value P1 to pressure value P2 between the outer and inner circumferential edges of the seal surface 108B at the front end of the shoe 107's travel direction, sandwiching constant values ​​at the two pressure-receiving surfaces 108C, and maintains pressure value P2 within the hydrostatic pocket 108A. Meanwhile, at the rear end of the shoe 107's travel direction, the oil film pressure decreases stepwise from pressure value P2 to pressure value P1 between the inner and outer circumferential edges of the seal surface 108B, sandwiching constant values ​​at the two pressure-receiving surfaces 108C. Thus, the shoe 107 of Comparative Example 3, like the shoe 101 of Comparative Example 1, exhibits little difference in oil film pressure change between the front and rear ends of the shoe 107's travel direction. Therefore, if the attitude of the shoe 107 changes due to centrifugal force acting on the shoe 107, for example, and the gap between the sliding surface 108 and the swash plate 11 narrows at the front side in the direction of travel and widens at the rear side in the direction of travel, a reverse wedge effect occurs in the entire oil film between the sliding surface 108 and the swash plate 11. As a result, the oil film pressure decreases, and the frictional force between the shoe 107 and the swash plate 11 may increase.

[0063] In contrast, the shoe 15 of this embodiment has an annular groove 17 formed on the sealing surface 16B of the sliding surface 16. The annular groove 17 has an inner linear inclined surface 17A and an outer linear inclined surface 17B that are inclined relative to the sealing surface 16B. As a result, when the shoe 15 slides on the swash plate 11, the oil film pressure between the sliding surface 16 of the shoe 15 and the swash plate 11 increases at the front of the sliding direction and decreases at the rear of the sliding direction. As a result, the gap between the sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11 widens at the front of the sliding direction and narrows at the rear of the sliding direction, resulting in a wedge effect that increases the oil film pressure between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11. As a result, the wedge effect increases the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11, thereby reducing the frictional force therebetween.

[0064] In this case, the inner radius R1 of the seal surface 16B, the outer radius R2 of the seal surface 16B, and the inner radius R3 of the annular groove 17 are set to satisfy the relationship of Equation 1, and the annular groove 17 is positioned closer to the outer periphery than the radial center of the seal surface 16B. As a result, at the front side of the moving direction of the shoe 15, as shown by arrow F1 in Fig. 6, a wedge effect occurs in which hydraulic oil flows from the inner periphery of the annular groove 17 toward the inner periphery of the seal surface 16B, increasing the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11. On the other hand, at the rear side of the moving direction of the shoe 15, as shown by arrow F2 in Fig. 6, a reverse wedge effect occurs in which hydraulic oil is discharged from the seal surface 16B toward the inner periphery of the annular groove 17, decreasing the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11. 7, the gap between the sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11 becomes wider at the front side in the direction of travel and narrower at the rear side in the direction of travel. As a result, a wedge effect occurs between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11, increasing the oil film pressure and reducing the frictional force caused by contact between the sliding surface 16 of the shoe 15 and the swash plate 11.

[0065] 12 shows the relationship between the shape of the sliding surface 111 of the shoe 110 according to Comparative Example 4 and the oil film pressure generated between the sliding surface 111 of the shoe 110 and the swash plate 11 when the shoe 110 according to Comparative Example 4 slides on the swash plate 11 in the direction of arrow B. The sliding surface 111 of the shoe 110 according to Comparative Example 4 has a hydrostatic pocket 111A and a seal surface 111B. The seal surface 111B is formed with an annular groove 111C having the same shape as the annular groove 17 of the shoe 15 according to this embodiment, and this annular groove 111C is located in the radial center of the seal surface 111B.

[0066] As shown by characteristic line 112 in Figure 12, the oil film pressure generated between the sliding surface 111 of the shoe 110 and the swash plate 11 in Comparative Example 4 maintains a pressure value P1 on the outer periphery of the seal surface 111B at the front side of the shoe 110's traveling direction and then rises to a pressure value P4 at the annular groove 111C. The oil film pressure also decreases from a pressure value P4 to a pressure value P3 between the annular groove 111C and the inner periphery of the seal surface 111B and maintains a pressure value P3 within the hydrostatic pocket 111A. Meanwhile, at the rear side of the shoe 110's traveling direction, the oil film pressure decreases from a pressure value P3 to a pressure value P2 between the inner periphery of the seal surface 111B and the annular groove 111C, then rises from a pressure value P2 to a pressure value P5 at the annular groove 111C, and then drops from a pressure value P5 at the outer periphery of the seal surface 111B.

[0067] As described above, the shoe 110 of Comparative Example 4 has the annular groove 111C disposed in the radial center of the sealing surface 111B, which means that the oil film pressure generated between the sliding surface 111 of the shoe 110 and the swash plate 11 is greater at the rear side than at the front side in the direction of travel of the shoe 110. Therefore, the position of the shoe 110 narrows the gap between the sliding surface 111 and the swash plate 11 at the front side in the direction of travel, making it difficult for hydraulic oil to be supplied between them, while the gap widens at the rear side in the direction of travel, making it easier for hydraulic oil to be discharged between them. As a result, the oil film formed between the sliding surface 111 and the swash plate 11 becomes thinner, which may increase the frictional force between the shoe 110 and the swash plate 11.

[0068] In contrast, in the shoe 15 of this embodiment, the inner radius R1 of the sealing surface 16B, the outer radius R2 of the sealing surface 16B, and the inner radius R3 of the annular groove 17 are set to satisfy the relationship of Equation 1. This allows the annular groove 17 to be positioned closer to the outer periphery than the radially central position of the sealing surface 16B. As a result, when the shoe 15 slides on the swash plate 11, the oil film pressure increases due to the wedge effect of the annular groove 17 at the front side in the direction of movement, widening the gap between the sliding surface 16 of the shoe 15 and the swash plate 11. On the other hand, the oil film pressure decreases due to the reverse wedge effect of the annular groove 17 at the rear side in the direction of movement, narrowing the gap between the sliding surface 16 of the shoe 15 and the swash plate 11. As a result, the wedge effect increases the oil film pressure between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11, reducing the frictional force caused by contact between the sliding surface 16 of the shoe 15 and the swash plate 11.

[0069] In addition, in the shoe 15 according to this embodiment, the outer radius R2 of the seal surface 16B is set larger than the outer radius R4 of the annular groove 17 (R2 > R4), so that the inner circumferential edge 17A1 and the outer circumferential edge 17B1 of the annular groove 17 are completely contained within the seal surface 16B. As a result, even if the gap between the sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11 narrows toward the rear side in the direction of travel (arrow B), as shown in Figure 7, hydraulic oil flows from the outer circumferential side of the annular groove 17 toward the seal surface 16C. This wedge effect increases the oil film pressure between the seal surface 16B and the swash plate 11, thereby reducing the friction between them.

[0070] The oil film pressure generated between the sliding surface 16 of the shoe 15 and the swash plate 11 varies depending on the angle θ that the inner linear inclined surface 17A and the outer linear inclined surface 17B of the annular groove 17 form with respect to the sealing surface 16B. Fig. 13 shows the cross-sectional shape of the annular groove 17. If the groove depth from the sealing surface 16B to the groove bottom 17C of the annular groove 17 is D, the groove width is X, and the radial length of the inner linear inclined surface 17A and the outer linear inclined surface 17B is Y, the angle θ is determined by the radial length Y of the inner linear inclined surface 17A (outer linear inclined surface 17B) and the groove depth X.

[0071] FIG. 14 shows the change in oil film pressure formed between the sliding surface 16 and the swash plate 11 when a shoe 15 having an annular groove 17 with a groove depth D of 4.4 μm, a groove width X of 1 mm, and a radial length Y of the inner linear inclined surface 17A (outer linear inclined surface 17B) of 0.5 mm slides on the swash plate 11 in the direction of arrow B.

[0072] 14, the oil film pressure increases from pressure value P1 to P4 between the outer peripheral edge 16B2 of the sealing surface 16B and the annular groove 17 on the front side in the traveling direction of the shoe 15, decreases from pressure value P4 to P3 between the annular groove 17 and the inner peripheral edge 16B1 of the sealing surface 16B, and then maintains the pressure value P3 within the hydrostatic pocket 16A. On the other hand, on the rear side in the traveling direction of the shoe 15, the oil film pressure decreases from pressure value P3 to P1 between the inner peripheral edge 16B1 of the sealing surface 16B and the annular groove 17, and then increases from pressure value P1 to pressure value P2 between the annular groove 17 and the outer peripheral edge 16B2 of the sealing surface 16B.

[0073] 14, the oil film pressure increases between the outer peripheral edge 16B2 of the sealing surface 16B and the annular groove 17 at the front side in the direction of travel, and decreases between the annular groove 17 and the outer peripheral edge 16B2 of the sealing surface 16B at the rear side in the direction of travel. Therefore, in the shoe 15 shown in FIG. 14, the distance between the sliding surface 16 and the sliding surface 11A of the swash plate 11 increases at the front side in the direction of travel and decreases at the rear side in the direction of travel, so that a wedge effect can be achieved between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11, increasing the oil film pressure.

[0074] Next, Figure 15 shows the change in oil film pressure formed between the sliding surface 16 and the swash plate 11 when a shoe 15 having an annular groove 17 with a groove depth D of 4.4 μm, a groove width X of 1 mm, and a radial length Y of the inner linear inclined surface 17A (outer linear inclined surface 17B) of 0.05 mm slides on the swash plate 11 in the direction of arrow B.

[0075] As shown by characteristic line 114 in Figure 15, the oil film pressure increases from pressure value P1 to P4 between the outer peripheral edge 16B2 of the seal surface 16B and the annular groove 17 on the front side of the shoe 15 in the direction of travel, then decreases from pressure value P4 to P3 between the annular groove 17 and the inner peripheral edge 16B1 of the seal surface 16B, and then maintains pressure value P3 within the hydrostatic pocket 16A. In this case, although the pressure difference between pressure values ​​P3 and P4 is small, the oil film pressure (pressure value P4) between the outer peripheral edge 16B2 of the seal surface 16B and the annular groove 17 is greater than the oil film pressure (pressure value P3) on the seal surface 16B. Meanwhile, on the rear side of the shoe 15 in the direction of travel, the oil film pressure decreases from pressure value P3 to P1 between the inner peripheral edge 16B1 of the seal surface 16B and the annular groove 17, and then increases from pressure value P1 to pressure value P2 between the annular groove 17 and the outer peripheral edge 16B2 of the seal surface 16B.

[0076] 15, the oil film pressure increases slightly between the outer peripheral edge 16B2 of the sealing surface 16B and the annular groove 17 at the front side in the direction of travel, and decreases at the rear side in the direction of travel between the annular groove 17 and the outer peripheral edge 16B2 of the sealing surface 16B. Therefore, in the shoe 15 shown in FIG. 15, the distance between the sliding surface 16 and the sliding surface 11A of the swash plate 11 increases at the front side in the direction of travel and decreases at the rear side in the direction of travel, so that a wedge effect can be achieved between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11, increasing the oil film pressure.

[0077] The shoe 15 shown in FIG. 15 has a groove depth D of 4.4 μm and a radial length Y of the inner linear inclined surface 17A (outer linear inclined surface 17B) of 0.05 mm. Therefore, the angle θ between the inner linear inclined surface 17A (outer linear inclined surface 17B) and the seal surface 16B is θ≈5°. On the other hand, if the radial length Y of the inner linear inclined surface 17A (outer linear inclined surface 17B) is set to less than 0.05 mm, the angle θ becomes excessively large (θ>5°). Therefore, a wedge effect that causes hydraulic oil to flow from the inner side of the annular groove 17 toward the inner side of the seal surface 16B is not generated at the front side of the moving direction of the shoe 15. As a result, the oil film pressure cannot be increased between the outer peripheral edge 16B2 of the seal surface 16B and the annular groove 17. From the above results, it is considered that by setting the angle θ of the annular groove 17 relative to the sealing surface 16B to θ≦5°, a wedge effect is generated in the annular groove 17, and the gap between the sliding surface 16 and the swash plate 11 becomes wider on the front side in the direction of travel and narrower on the rear side in the direction of travel.

[0078] 16, if multiple (e.g., two) annular grooves 17' are formed on the sealing surface 16B' of the shoe 15', when the shoe 15' slides on the swash plate 11 in the direction of arrow B, a pressure-reducing force (arrow Pl) and a pressure-increasing force (arrow Ph) act on the oil film pressure between the multiple annular grooves 17' and the swash plate 11, canceling each other out. Thus, if multiple annular grooves 17' are formed on the sealing surface 16B', the wedge effect will not be sufficient to increase the oil film pressure between the sealing surface 16B' and the swash plate 11. Therefore, it is preferable to provide only one annular groove 17 on the sealing surface 16B', as in the shoe 15 of this embodiment.

[0079] Thus, in the embodiment, in the swash plate type hydraulic motor 1, which comprises a rotating shaft 6 rotatably arranged within the casing 2, a rotor 7 arranged within the casing 2 so as to rotate integrally with the rotating shaft 6 and having a plurality of cylinders 8 formed thereon, a plurality of pistons 9 inserted reciprocally into the plurality of cylinders 8 of the rotor 7, a plurality of shoes 15 respectively provided at the tips of the plurality of pistons 9, and a swash plate 11 having a sliding surface 11A along which the plurality of shoes 15 slide, the shoe 15 is provided with an annular sealing surface 16B that abuts against the sliding surface 11A of the swash plate 11, and an annular groove 17 formed on the sealing surface 16B concentrically with the sealing surface 16B and annularly recessed relative to the sealing surface 16B, and inclined surfaces are formed on the inner and outer peripheral sides of the annular groove 17 that intersect with the sealing surface 16B while being inclined relative to the sealing surface 16B.

[0080] With this configuration, when the shoe 15 slides on the sliding surface 11A of the swash plate 11, a high pressure is generated on the inner periphery of the annular groove 17 at the front side of the shoe 15 due to a wedge effect, and a low pressure is generated on the inner periphery of the annular groove 17 at the rear side of the shoe 15 due to a reverse wedge effect. As a result, the oil film pressure formed between the sliding surface 16 of the shoe 15 and the swash plate 11 is high at the front side of the shoe 15 and low at the rear side of the shoe 15. Therefore, the gap between the sliding surface 16 of the shoe 15 and the swash plate 11 is wide at the front side and narrow at the rear side of the shoe 15. As a result, the wedge effect increases the oil film pressure between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11, thereby reducing the friction between the sliding surface 16 of the shoe 15 and the swash plate 11.

[0081] In this embodiment, the inclined surfaces are formed by linear inclined surfaces (inner peripheral linear inclined surface 17A and outer peripheral linear inclined surface 17B) that are linearly inclined relative to seal surface 16B. With this configuration, a wedge effect can be generated when the hydraulic oil flows from inner peripheral linear inclined surface 17A or outer peripheral linear inclined surface 17B of annular groove 17 to seal surface 16B.

[0082] In the embodiment, when the inner radius of the seal surface 16B is R1, the outer radius of the seal surface 16B is R2, the inner radius of the annular groove 17 is R3, and the outer radius of the annular groove is R4, R1+(R2-R1) / 2≦R3 and R2>R4 are satisfied.

[0083] With this configuration, the annular groove 17 is positioned closer to the outer periphery than the radial center position of the sealing surface 16B. As a result, when the shoe 15 slides on the swash plate 11, the oil film pressure increases due to the wedge effect of the annular groove 17 at the front side in the direction of movement, widening the gap between the sliding surface 16 of the shoe 15 and the swash plate 11. On the other hand, the oil film pressure decreases due to the reverse wedge effect of the annular groove 17 at the rear side in the direction of movement, narrowing the gap between the sliding surface 16 of the shoe 15 and the swash plate 11. As a result, the wedge effect increases the oil film pressure between the entire sliding surface 16 of the shoe 15 and the sliding surface 11A of the swash plate 11, reducing the frictional force caused by contact between the sliding surface 16 of the shoe 15 and the swash plate 11.

[0084] Furthermore, by setting the outer radius R2 of the seal surface 16B and the outer radius R4 of the annular groove such that R2 > R4, the inner peripheral edge 17A1 and outer peripheral edge 17B1 of the annular groove 17 can be completely contained within the seal surface 16B. As a result, even if the gap between the sliding surface 16 of the shoe 15 and the swash plate 11 narrows at the rear in the direction of travel, the wedge effect of hydraulic oil flowing from the outer periphery of the annular groove 17 toward the seal surface 16C increases the oil film pressure between the seal surface 16B and the sliding surface 11A of the swash plate 11, thereby reducing the friction between them.

[0085] In this embodiment, the angle θ formed by the inner linear inclined surface 17A and the outer linear inclined surface 17B with respect to the seal surface 16B is set to 5° or less (θ≦5°). With this configuration, when the shoe 15 slides on the swash plate 11, hydraulic oil flows from the inner periphery of the annular groove 17 toward the seal surface 16B at the front side in the direction of travel. This wedge effect increases the oil film pressure between the outer periphery of the seal surface 16B and the annular groove 17, widening the gap between the sliding surface 16 of the shoe 15 and the swash plate 11 at the front side in the direction of travel. As a result, the wedge effect increases the oil film pressure between the entire sliding surface 16 of the shoe 15 and the swash plate 11, reducing the frictional force caused by contact between the sliding surface 16 of the shoe 15 and the swash plate 11.

[0086] 17 and 18 show a second embodiment of the present invention. The feature of this embodiment is that the inclined surface of the annular groove is formed as a curved inclined surface that is curved relative to the seal surface. In this embodiment, the same components as those in the first embodiment are given the same reference numerals, and their description will be omitted.

[0087] In the drawings, the shoe 21 of this embodiment, like the shoe 15 of the first embodiment, is integrally formed with a disc portion 21A, a disc-shaped stepped portion 21B, and a convex spherical portion 21C, and an oil hole 21D is formed in the center of the shoe 21. The disc portion 21A has a sliding surface 22 facing the sliding surface 11A of the swash plate 11. The sliding surface 22 includes a hydrostatic pocket 22A, a seal surface 22B, and a chamfered portion 22C. The inner peripheral edge 22B1 of the seal surface 22B is circular with a radius R1 centered on the axial center A of the shoe 21, and the outer peripheral edge 22B2 of the seal surface 22B is circular with a radius R2 centered on the axial center A of the shoe 21. A circular annular groove 23 is formed in the seal surface 22B, centered on the axial center A of the shoe 21, and is concentric with the seal surface 22B.

[0088] The annular groove 23 is formed as a circumferential groove recessed in an annular shape relative to the seal surface 22B. The annular groove 23 has an inner curved inclined surface 23B and an outer curved inclined surface 23C that face each other across a flat groove bottom 23A. The inner curved inclined surface 23B is located on the inner periphery of the annular groove 23 and is inclined in a curved manner relative to the seal surface 22B. The outer curved inclined surface 23C is located on the outer periphery of the annular groove 23 and is inclined in a curved manner relative to the seal surface 22B.

[0089] The boundary between inner curved inclined surface 23B and seal surface 22B forms inner peripheral edge 23B1 of annular groove 23, which is circular and has a radius R3 centered about axial center A of shoe 21. The boundary between outer curved inclined surface 23C and seal surface 22B forms outer peripheral edge 23C1 of annular groove 23, which is circular and has a radius R4 centered about axial center A of shoe 21. Angle θ formed by a tangent L1 of inner curved inclined surface 23B at inner peripheral edge 23B1 of annular groove 23 and seal surface 22B, and angle θ formed by a tangent L2 of outer curved inclined surface 23C at outer peripheral edge 23C1 of annular groove 23 and seal surface 22B are each set to 5° or less (θ≦5°).

[0090] Here, the radius R1 of the inner peripheral edge 22B1 of the seal surface 22B (the inner peripheral radius of the seal surface 22B), the radius R2 of the outer peripheral edge 22B2 of the seal surface 22B (the outer peripheral radius of the seal surface 22B), and the radius R3 of the inner peripheral edge 23B1 of the annular groove 23 (the inner peripheral radius of the annular groove 23) are set to satisfy the relationship given by the above-mentioned mathematical expression 1. Furthermore, the outer peripheral radius R2 of the seal surface 22B and the radius R4 of the outer peripheral edge 23C1 of the annular groove 23 (the outer peripheral radius of the annular groove 23) are set to satisfy the relationship given by the above-mentioned mathematical expression 2.

[0091] The shoe 21 according to the second embodiment, having the above-described configuration, achieves the same effects as those of the first embodiment. Specifically, when the shoe 21 slides on the sliding surface 11A of the swash plate 11, a high pressure is generated on the inner periphery of the annular groove 23 at the front side of the shoe 21 due to a wedge effect, while a low pressure is generated on the inner periphery of the annular groove 23 at the rear side of the shoe 21 due to a reverse wedge effect. This causes the gap between the sliding surface 22 of the shoe 21 and the swash plate 11 to widen at the front side and narrow at the rear side. As a result, the wedge effect increases the oil film pressure between the entire sliding surface 22 of the shoe 21 and the sliding surface 11A of the swash plate 11, thereby reducing the friction between the sliding surface 22 of the shoe 21 and the swash plate 11.

[0092] 19 to 22 show a third embodiment of the present invention. This embodiment is characterized in that first and second inner pads are provided on the inner periphery of the seal surface, and an outer pad is provided on the outer periphery of the seal surface. In this embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and their description will be omitted.

[0093] In the drawings, the shoe 31 according to this embodiment, like the shoe 15 according to the first embodiment, is integrally formed of a disk portion 31A, a disk-shaped stepped portion 31B, and a convex spherical portion 31C, and an oil hole 31D is formed in the center of the shoe 31. The disk portion 31A has a sliding surface 32 facing the sliding surface 11A of the swash plate 11, and the sliding surface 32 is configured to include a hydrostatic pocket 32A, a seal surface 32B, and a chamfered portion 32C.

[0094] An inner peripheral edge 32B1 of the sealing surface 32B is circular with a radius R1 centered on the axial center A of the shoe 31, and an outer peripheral edge 32B2 of the sealing surface 32B is circular with a radius R2 centered on the axial center A of the shoe 31. A circular annular groove 33 is formed in the sealing surface 32B, centered on the axial center A of the shoe 31, concentrically with the sealing surface 32B. However, it differs from the shoe 15 of the first embodiment in that first and second inner peripheral pads 34, 35 are arranged on the inner peripheral side of the sealing surface 32B, and an outer peripheral pad 36 is arranged on the outer peripheral side of the sealing surface 32B.

[0095] The annular groove 33 is formed as a circumferential groove recessed in an annular shape relative to the seal surface 32B. The annular groove 33 has a V-shaped inner linear inclined surface 33A and an outer linear inclined surface 33B, each of which has a line-symmetrical cross section. The inner linear inclined surface 33A is disposed on the inner periphery of the annular groove 33 and is inclined linearly relative to the seal surface 32B. The outer linear inclined surface 33B is disposed on the outer periphery of the annular groove 33 and is inclined linearly relative to the seal surface 32B. The angle θ formed by the inner linear inclined surface 33A and the outer linear inclined surface 33B relative to the seal surface 32B is set to 5° or less (θ≦5°).

[0096] The radius of the inner peripheral edge 33A1 of the annular groove 33 centered on the axial center A of the shoe 31, i.e., the inner radius of the annular groove 33, is R3. The radius of the outer peripheral edge 33B1 of the annular groove 33 centered on the axial center A of the shoe 31, i.e., the outer radius of the annular groove 33, is R4. The inner radius R1 of the seal surface 32B, the outer radius R2 of the seal surface 32B, and the inner radius R3 of the annular groove 33 are set to satisfy the relationship expressed by the above mathematical expression 1. Furthermore, the outer radius R2 of the seal surface 32B and the outer radius R4 of the annular groove 33 are set to satisfy the relationship expressed by the above mathematical expression 2.

[0097] The first inner pad 34 is located within the hydrostatic pocket 32A and is provided on the inner circumferential side of the seal surface 32B. The first inner pad 34 is composed of two semicircular pad pieces 34A arranged concentrically with the seal surface 32B, with an oil passage 34B formed between the two pad pieces 34A. The second inner pad 35 is provided on the inner circumferential side of the seal surface 32B and outer circumferential side of the first inner pad 34. The second inner pad 35 is composed of two semicircular pad pieces 35A arranged concentrically with the seal surface 32B, with an oil passage 35B formed between the two pad pieces 35A. The oil passage 34A of the first inner pad 34 and the oil passage 35A of the second inner pad 35 are offset by 90° in the circumferential direction. The first inner peripheral pad 34 and the second inner peripheral pad 35 protect the seal surface 32B against cavitation erosion that occurs when hydraulic oil is supplied to the hydrostatic pocket 32A through the oil hole 31D of the shoe 31.

[0098] The outer pad 36 is provided on the outer periphery of the seal surface 32B. The outer pad 36 is composed of two pad pieces 36A arranged concentrically with the seal surface 32B, and an oil passage 36B is formed between the two pad pieces 36A. When the sliding surface 32 of the shoe 31 is tilted relative to the sliding surface 11A of the swash plate 11, the outer pad 36 comes into contact with the swash plate 11 before the seal surface 32B does, thereby protecting the seal surface 32B.

[0099] The shoe 31 according to the third embodiment has the above-described configuration, and this embodiment also achieves the same effects as those of the first embodiment. Specifically, when the shoe 31 slides on the sliding surface 11A of the swash plate 11, a high pressure is generated on the inner periphery of the annular groove 33 at the front side of the shoe 31 due to a wedge effect, and a low pressure is generated on the inner periphery of the annular groove 33 at the rear side of the shoe 31 due to a reverse wedge effect. This causes the gap between the sliding surface 32 of the shoe 31 and the swash plate 11 to widen at the front side and narrow at the rear side. As a result, the wedge effect increases the oil film pressure between the entire sliding surface 32 of the shoe 31 and the sliding surface 11A of the swash plate 11, thereby reducing the friction between the sliding surface 32 of the shoe 31 and the swash plate 11.

[0100] The annular groove 17 of the shoe 15 according to the first embodiment has a triangular cross-sectional shape in which the inner linear inclined surface 17A and the outer linear inclined surface 17B intersect at a linear groove bottom 17C. However, the present invention is not limited to this. For example, the annular groove 17" of the shoe 15" according to a first modified example shown in Figure 23 may have a trapezoidal cross-sectional shape in which a flat groove bottom 17C" is formed between the inner linear inclined surface 17A" and the outer linear inclined surface 17B".

[0101] Furthermore, the annular groove 23 of the shoe 21 according to the second embodiment has a trapezoidal cross-sectional shape with a flat groove bottom 23A formed between an inner curved inclined surface 23B and an outer curved inclined surface 23C. However, the present invention is not limited to this, and the annular groove 23' of the shoe 21' according to a second modified example shown in Figure 24 may have a triangular cross-sectional shape in which an inner curved inclined surface 23B' and an outer curved inclined surface 23C' intersect at a linear groove bottom 23A'.

[0102] Furthermore, the annular groove 17 of the shoe 15 according to the first embodiment has a cross-sectional shape in which the inner linear inclined surface 17A and the outer linear inclined surface 17B are symmetrical at the position of the groove bottom 17C. However, the present invention is not limited to this, and for example, a shoe 41 according to a third modified example shown in Fig. 25 may have an asymmetric cross-sectional shape in which the inner curved inclined surface 42A and the outer linear inclined surface 42B intersect at the groove bottom 42C.

[0103] Furthermore, while the first embodiment exemplifies shoe 15 having convex spherical portion 15C attached to concave spherical portion 9A of piston 9, the present invention is not limited to this and can be applied to, for example, a shoe having a concave spherical portion attached to a convex spherical portion formed on the tip of a piston. The same applies to shoe 21 according to the second embodiment and shoe 31 according to the third embodiment.

[0104] Furthermore, in the embodiment, the swash plate type hydraulic rotating machine has been described by taking as an example a variable displacement swash plate type hydraulic motor 1. However, the present invention is not limited to this, and may be applied to, for example, a fixed displacement swash plate type hydraulic motor, or a variable displacement or fixed displacement swash plate type hydraulic pump. [Explanation of symbols]

[0105] 2 Casing 6 Rotation Axis 7 rotor 8 cylinders 9 pistons 11 Swash plate 11A Sliding surface 15,15″,21,21′,31,41 shoes 16B, 22B, 32B sealing surface 17, 17″, 23, 23′, 33, 42 Circular groove 17A,17A″,33A Inner circumferential straight inclined surface (slanted surface) 17B,17B″,33B,42B Outer straight inclined surface (slanted surface) 23B, 23B′, 42A Inner curved inclined surface (inclined surface) 23C,23C′ Outer curved inclined surface (inclined surface)

Claims

1. a rotating shaft rotatably provided within the casing; a rotor provided in the casing so as to rotate integrally with the rotary shaft and having a plurality of cylinders; a plurality of pistons reciprocatably inserted into the plurality of cylinders of the rotor; a plurality of shoes respectively provided at the tips of the plurality of pistons; a swash plate having a sliding surface on which the plurality of shoes slide, The shoe is provided with an annular seal surface that contacts the sliding surface of the swash plate, and an annular groove that is formed concentrically with the seal surface and annularly recessed relative to the seal surface, a swash plate type hydraulic rotary machine, characterized in that an inclined surface is formed on the inner peripheral side and the outer peripheral side of the annular groove, the inclined surface intersecting with the seal surface in a state inclined with respect to the seal surface;

2. 2. The swash plate type hydraulic rotary machine according to claim 1, wherein the inclined surface is formed as a linear inclined surface that is inclined linearly with respect to the sealing surface.

3. 2. The swash plate type hydraulic rotary machine according to claim 1, wherein the inclined surface is formed as a curved inclined surface that is curved relative to the seal surface.

4. When the inner radius of the seal surface is R1, the outer radius of the seal surface is R2, the inner radius of the annular groove is R3, and the outer radius of the annular groove is R4, R1+(R2-R1) / 2≦R3, and R2>R4 2. The swash plate type hydraulic rotary machine according to claim 1, wherein the following is satisfied:

5. 3. The swash plate type hydraulic rotary machine according to claim 2, wherein the angle formed by the linear inclined surface with respect to the seal surface is set to 5 degrees or less.

6. 4. The swash plate type hydraulic rotary machine according to claim 3, wherein an angle formed by a tangent of said curved inclined surface and said seal surface is set to 5 degrees or less.

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