Swash plate type axial piston pump / motor

Abstract

To provide a swash plate type axial piston pump / motor capable of reducing abrasion of a sliding contact part between a piston and a piston hole of a cylinder block and obtaining a sufficient product life.SOLUTION: A plurality of pistons 19 are brought into slidable contact with a plurality of piston holes 18 formed in a cylinder block 17 in the axial direction so as to be freely reciprocated. Both the cylinder block 17 and the piston 19 are made of stainless steel. Nitriding treatment is applied to a sliding contact part A between the piston 19 and the piston hole 18. The nitrided sliding contact part A has surface hardness of Vickers hardness 1100HV or more, and has a hardened layer depth of 20 μm or more. The DLC coating is applied to the outer peripheral surface of the piston 19 to which the nitriding treatment is applied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a swash plate type axial piston pump / motor in which multiple pistons are arranged in a cylinder block so that they can reciprocate axially using hydraulic fluid, and the amount of reciprocation of the pistons is set by a swash plate. [Background technology]

[0002] This type of swash plate-type axial piston pump / motor has a rotating shaft rotatably supported on a main body, the rotating shaft fixed to a cylinder block, multiple pistons in sliding contact with the cylinder block for axial reciprocation, and a swash plate fixed to the main body, which controls the amount of reciprocation of the pistons. In pump operation, the rotating shaft rotates the cylinder block, causing the pistons to reciprocate, drawing in and discharging hydraulic fluid. In motor operation, the pistons reciprocate due to the hydraulic fluid pressure, causing the rotating shaft to rotate with the cylinder block. Furthermore, as shown in Patent Document 1, the pistons are made of stainless steel and coated with diamond-like carbon (DLC) on the outer surface that slides against the piston bores in the cylinder block. As shown in Patent Document 2, the piston bores in the cylinder block are nitrided to reduce wear at the sliding contact points between the pistons and the piston bores in the cylinder block. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-31040 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-185520 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it has not yet been possible to satisfactorily reduce the wear at the sliding contact points between the piston and the piston hole in the cylinder block, and there has been a problem in that a satisfactory product life cannot be achieved.

[0005] The object of the present invention is to provide a swash plate type axial piston pump / motor that reduces wear at the sliding contact points between the piston and the piston hole in the cylinder block and ensures a sufficient product life. [Means for solving the problem]

[0006] In order to achieve this object, the present invention takes the following measures: the cylinder block is engaged with the rotating shaft in the rotational direction and rotatably supported by the body; a plurality of pistons that are in sliding contact with a plurality of piston holes formed in the axial direction of the cylinder block and are capable of reciprocating freely; a plurality of working chambers that are partitioned by the pistons and the cylinder block and through which working water is drawn in and discharged; a swash plate that is arranged in the body and comes into contact with the tips of the pistons protruding from the cylinder block to set the amount of reciprocating movement of each piston; and a pair of intake and discharge flow paths formed in the body through which working water flows; the cylinder block and pistons are both made of stainless steel, and the sliding areas between the pistons and the piston holes are surface hardened, and the surface hardened sliding areas have a surface hardness of at least 1100 HV on a Vickers hardness basis and a hardened layer depth of at least 20 micrometers from the surface. Here, the stainless steel may be any of ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, austenitic-ferritic stainless steel, and precipitation hardening stainless steel.

[0007] In this case, the surface hardening treatment may be a nitriding treatment or a sulfur-nitriding treatment. The outer peripheral surface of the piston at the sliding contact portion may be nitrided and then coated with DLC. [Effects of the Invention]

[0008] As described above in detail, in the invention described in claim 1, both the cylinder block and the piston are made of stainless steel, the sliding contact points between the piston and the piston bore are surface hardened, and the surface hardened sliding contact points have a surface hardness of 1100 HV or more on a Vickers hardness basis and a hardened layer depth of 20 micrometers or more from the surface. Therefore, since the hardness of the sliding contact points is increased by having a surface hardness of 1100 HV or more on a Vickers hardness basis and the hardened layer depth is increased by having a hardened layer depth of 20 micrometers or more from the surface, strength is improved, wear at the sliding contact points can be reduced over a long period of time, and a sufficient product life can be obtained.

[0009] In addition, in the invention described in claim 2, the surface hardening treatment of the sliding contact parts is nitriding or sulfur-nitriding, which further reduces wear of the sliding contact parts and ensures a longer product life.

[0010] In addition, in the invention described in claim 3, the outer peripheral surface of the piston at the sliding contact points is nitrided and then coated with DLC, which further reduces wear at the sliding contact points and ensures a longer product life. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a longitudinal sectional view of a swash plate type axial piston pump motor according to an embodiment of the present invention. FIG. [Figure 2] Graph (A) shows the relationship between the hardness of the sliding contact area and the amount of wear, and graph (B) shows the relationship between the hardened layer depth of the sliding contact area and the amount of wear. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention in which a swash plate type axial piston pump motor is used as a swash plate type axial piston pump will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes a main body composed of a cylindrical housing 2, a front cover member 3, and a rear cover member 4. One end of a mounting hole 5, which penetrates axially through the housing 2, is closed by the front cover member 3, and the other end of the mounting hole 5 is closed by the rear cover member 4. The two cover members 3 and 4, which hold the housing 2 in place, are fastened together by multiple bolts 6. The two cover members 3 and 4 are concentrically fitted with spigots at both ends of the mounting hole 5. Reference numeral 7 denotes a rotating shaft, which passes through the mounting hole 5 and is rotatably supported by a radial ball bearing 8 placed in the front cover member 3 and a radial ball bearing 9 placed in the rear cover member 4. Its tip protrudes from the front cover member 3 and is connected to an electric motor (not shown), while its rear end is exposed to the outside. Each radial ball bearing 8 and 9 contains grease, and its axially outward end is exposed to the outside. Radial ball bearing 9 has a smaller diameter than radial ball bearing 8. 2A and 2B are drain holes formed in the housing, and are connected to pipes (not shown) to discharge the drainage from inside the main body 1.

[0013] A sealing member 10 is disposed on the front cover member 3, axially inward of the radial ball bearing 8. The sealing member 10 is annular and fits around the rotating shaft 7 to seal the inside of the main body 1. 11 is an annular shielding member provided on the front cover member 3, which is disposed between the radial ball bearing 8 and the sealing member 10 and is loosely fitted around the rotating shaft 7. The shielding member 11 shields the side of the radial ball bearing 8 and prevents working water inside the main body 1 that has leaked from the sealing member 10 from getting onto the radial ball bearing 8. 12 is a first drain passage open to the atmosphere, which is composed of a front cover drain passage 12A formed in the front cover member 3 and a shield drain passage 12B formed in the shielding member 11, and discharges working water that has leaked from the sealing member 10.

[0014] A sealing member 13 is disposed on the rear cover member 4 axially inward of the radial ball bearing 9. The sealing member 13 is annular and has a smaller diameter than the sealing member 10, and is fitted around the rotating shaft 7 to seal the inside of the main body 1. 14 is an annular shielding member provided on the rear cover member 4, with a smaller diameter than the shielding member 11, disposed between the radial ball bearing 9 and the sealing member 13, and fitted loosely onto the rotating shaft 7. The shielding member 14 shields the side of the radial ball bearing 9, preventing working water inside the main body 1 that has leaked from the sealing member 13 from getting onto the radial ball bearing 9. 15 is a second drain passage open to the atmosphere, and is composed of a rear cover drain passage 15A formed in the rear cover member 4 and a shield drain passage 15B formed in the shielding member 14, and discharges water that has leaked from the sealing member 13.

[0015] Reference numeral 16 denotes a circular swash plate, fixed to the inclined surface of the front cover member 3 facing the inside of the main body 1. The rotary shaft 7 is loosely fitted around the axis of the swash plate 16. The swash plate 16 is inclined at a certain angle relative to a line perpendicular to the axis of the rotary shaft 7. Reference numeral 17 denotes a cylinder block, which is housed in the housing 5 of the main body 1 and is spline-engaged with the rotary shaft 7 at its axis, thereby being rotationally driven by the rotary shaft 7. The cylinder block 17 has multiple piston holes 18 formed in it, spaced equally circumferentially on the same circumference radially outward from the axis. Each piston hole 18 opens into one end face of the cylinder block 17 opposite the swash plate 16. Reference numeral 19 denotes pistons, which are inserted into the piston holes 18 of the cylinder block 17 so as to be able to reciprocate axially, defining working chambers 20 in the cylinder block 17. Each piston 19 has a through hole 21 penetrating the axial direction at its axis, and has a spherical protrusion at its tip facing the swash plate 16 to which a shoe 22 is pivotally attached.

[0016] Both the cylinder block 17 and each piston 19 are made of ferritic stainless steel SUS430, as specified in Japanese Industrial Standard JIS G4303:2012 "Stainless Steel Bar." Note that SUS430 is not required, and other materials such as SUS403 and SUS447J1 may also be used. Surface hardening is performed on the sliding contact points between each piston hole 18 and each piston 19. Specifically, nitriding is performed as a surface hardening treatment on the inner circumferential surface of each piston hole 18 and the outer circumferential surface of each piston 19, which serve as sliding contact points A. The nitriding process involves heating the cylinder block 17 and each piston 19, causing nitrogen atoms to diffuse and penetrate from their surfaces into the interior.

[0017] The nitrided inner surface of each piston bore 18 has a surface hardness of 1130 HV on a Vickers hardness scale and a hardened layer depth of 31 micrometers from the surface. The nitrided outer surface of each piston 19 has a surface hardness of 1130 HV on a Vickers hardness scale and a hardened layer depth of 85 micrometers from the surface. Furthermore, the nitrided outer surface of each piston 19 is coated with a DLC (Diamond-Like Carbon) coating. DLC coatings are thin films composed primarily of carbon and hydrogen, and have hard properties. The DLC-coated outer surface of each piston 19 has a surface hardness of 1546 HV on a Vickers hardness scale.

[0018] Each shoe 22 has a through-hole 23 formed axially at its axis, communicating with the flow holes 21 of the pistons 19. The shoe 22 is provided with a sliding contact member 24 at its tip that slides against the swash plate 16. The sliding contact member 24 is formed from a resin material in an annular shape and press-fitted onto the shoe 22. The swash plate 16 determines the amount of reciprocation of each piston 19 based on its tilt angle. Each shoe 22 is pressed against the swash plate 16 by the spring force of a spring 25 housed in the axial center of the cylinder block 17 via a pin 26, a retainer 27, and a retainer plate 28. The volume of the working chamber 20 increases as each piston 19 moves forward (leftward in FIG. 1) to draw in hydraulic fluid, and decreases as each piston 19 moves backward (rightward in FIG. 1) to discharge hydraulic fluid. Each working chamber 20 is connected to a connecting hole 29, which opens at equal intervals circumferentially on the same circumference on the opposite end face of the cylinder block 17.

[0019] Reference numeral 30 denotes a circular valve plate that slides against the other end face of the cylinder block 17, and has a pair of intake and exhaust ports 31, 32 formed therethrough, through which working water flows to and from each working chamber 20 via each connecting hole 29. Both intake and exhaust ports 31, 32 are semicircular and arranged symmetrically about the axis of the valve plate 30. The outer periphery of the valve plate 30 is spigot-fitted into the mounting hole 5 that spigot-fits the rear cover member 4, and the valve plate 30 is arranged in the main body 1 concentrically with the rotary shaft 7. The spring force of the spring 25 is applied to the valve plate 30 via the cylinder block 17, pressing it against the rear cover member 4. The valve plate 30 is prevented from rotating by engaging a pin member (not shown) with the rear cover member 4.

[0020] One of the intake and exhaust ports 31 communicates with the working chamber 20, the volume of which increases as the piston 19 moves forward, and functions as an intake port through which the working water flows to be drawn into the working chamber 20. The other intake and exhaust port 32 communicates with the working chamber 20, the volume of which decreases as the piston 19 moves backward, and functions as a discharge port through which the working water flows to be discharged from the working chamber 20. Reference numerals 33 and 34 denote a pair of intake and exhaust passages formed in the rear cover member 4 that constitutes the main body 1 and through which the working water flows, with one intake and exhaust passage 33 connected to one intake and exhaust port 31 that functions as an intake port, and the other intake and exhaust passage 34 connected to the other intake and exhaust port 32 that functions as a discharge port.

[0021] Next, the operation of this configuration will be explained. 1, when the rotary shaft 7 is driven to rotate, the cylinder block 17 rotates together with the rotary shaft 7. As the cylinder block 17 rotates, the shoes 22 at the ends of the pistons 19 slide along the swash plate 16, causing each piston 19 to reciprocate by an amount corresponding to the inclination angle of the swash plate 16, thereby increasing or decreasing the volume of each working chamber 20.

[0022] Working water is drawn into the working chamber 20, whose volume increases with the rotation of the cylinder block 17, via the intake / exhaust passage 33 and the intake / exhaust port 31. Meanwhile, working water in the working chamber 20, whose volume decreases with the rotation of the cylinder block 17, flows through the intake / exhaust port 32 and is discharged from the intake / exhaust passage 34. In this way, a pump operates by continuously drawing in and discharging working water as the cylinder block 17 rotates. When the rotation of the rotary shaft 7 is stopped, the pump operation stops.

[0023] In this operation, both the cylinder block 17 and the piston 19 are made of stainless steel, and the sliding contact point A between the piston 19 and the piston bore 18 is surface hardened, with the surface hardened sliding contact point A having a Vickers hardness of 1100 HV or more and a hardened layer depth of 20 micrometers or more from the surface. Therefore, since the hardness of the sliding contact point A is increased with a surface hardness of 1100 HV or more and the hardened layer depth is increased with a hardened layer depth of 20 micrometers or more from the surface, the strength is improved, and wear at the sliding contact point A can be reduced over a long period of time, resulting in a sufficient product life.

[0024] Furthermore, the surface hardening treatment of the sliding contact area A is nitriding or sulfur-nitriding, which further reduces wear at the sliding contact area A and ensures a longer product life.

[0025] In addition, the outer peripheral surface of the piston 19 at the sliding contact point A is nitrided and then coated with DLC, which further reduces wear at the sliding contact point A and ensures a longer product life.

[0026] Now, a swash plate type axial piston pump with a configuration equivalent to that shown in Figure 1 was tested for 10 hours with various changes to the materials and surface hardening treatment of the cylinder block 17 and piston 19, with a discharge pressure of 7 MPa, a discharge volume of 8 cc / rev, and a rotation speed of the rotating shaft 7 of 1500 min-1. The results of the test are shown in Figures 2(A) and 2(B).

[0027] Figure 2(A) shows the test results for the relationship between the hardness of sliding contact point A and the amount of wear. Point a is the outer surface of the piston 19 made of ferritic stainless steel SUS430, which was subjected to sulfur-nitriding treatment to give a surface hardness of 1030 HV Vickers hardness, and the wear amount was 22 micrometers (■). The hardened layer depth was 85 micrometers.

[0028] Point b is the inner surface of the piston hole 18 of the cylinder block 17 made of austenitic stainless steel SUS304, which was subjected to sulfur-nitriding treatment to a surface hardness of 1010 HV Vickers hardness, and the wear amount was 20 micrometers. The hardened layer depth was 32 micrometers.

[0029] Point c corresponds to the embodiment described above, where the inner surface of the piston hole 18 of the cylinder block 17 made of ferritic stainless steel SUS430 was nitrided to a surface hardness of 1130 HV Vickers hardness, and the wear amount was 5 micrometers. The hardened layer depth was 31 micrometers.

[0030] Point d shows the inner surface of the piston hole 18 of the cylinder block 17 made of austenitic stainless steel SUS304, which was subjected to sulfur-nitriding treatment to give a surface hardness of 1200 HV Vickers hardness. The wear amount was 5 micrometers. The hardened layer depth was 35 micrometers.

[0031] Point e indicates the inner surface of the piston hole 18 of the cylinder block 17 made of austenitic stainless steel SUS304 that was subjected to sulfur-nitriding treatment to give a surface hardness of 1150 HV Vickers hardness, with a wear amount of 3 micrometers. The hardened layer depth was 35 micrometers.

[0032] Point f corresponds to the embodiment described above, in which the outer surface of the piston 19 made of ferritic stainless steel SUS430 was nitrided to a surface hardness of 1130 HV Vickers, and the nitrided outer surface of the piston 19 was then coated with DLC (Diamond-Like Carbon) to a surface hardness of 1546 HV Vickers, and the wear amount was 1 micrometer. The depth of the hardened layer from the nitriding was 85 micrometers.

[0033] Line g is an approximation curve based on points a to f. Line g shows that the amount of wear increases sharply when the surface hardness is less than 1100 HV Vickers hardness. Therefore, it is preferable that sliding contact point A has a Vickers hardness of 1100 HV or more.

[0034] Next, Figure 2(B) shows the test results for the relationship between the hardened layer depth at sliding contact point A and the amount of wear. Point h is the inner surface of the piston hole 18 of the cylinder block 17 made of austenitic stainless steel SUS304, which was subjected to sulfur-nitriding treatment to a hardened layer depth of 10 micrometers, and the wear amount was 14 micrometers. The surface hardness was 1130 HV Vickers hardness.

[0035] Point i corresponds to the embodiment described above, in which the inner surface of the piston hole 18 of the cylinder block 17 made of ferritic stainless steel SUS430 was nitrided to a hardened layer depth of 31 micrometers, and the wear amount was 5 micrometers. The surface hardness was 1130 HV Vickers hardness.

[0036] Point j shows the inner surface of the piston hole 18 of the cylinder block 17 made of austenitic stainless steel SUS304, which was subjected to sulfur-nitriding treatment to a hardened layer depth of 35 micrometers, and the wear amount was 5 micrometers. The surface hardness was 1200 HV Vickers hardness.

[0037] At point k, the inner surface of the piston hole 18 of the cylinder block 17 made of austenitic stainless steel SUS304 was subjected to sulfur-nitriding treatment to a hardened layer depth of 35 micrometers, and the wear amount was 3 micrometers. The surface hardness was 1150 HV Vickers hardness.

[0038] Point m corresponds to the embodiment described above in which the outer surface of the piston 19 made of ferritic stainless steel SUS430 was nitrided to a hardened layer depth of 85 micrometers and then further nitrided and coated with a DLC coating, and the wear amount was 1 micrometer. The surface hardness of the nitrided surface was 1130 HV Vickers hardness, and the surface hardness of the DLC coating was 1546 HV Vickers hardness.

[0039] n is an approximation curve based on points h to m. Approximation curve n shows that the amount of wear increases sharply when the hardened layer depth is less than 20 micrometers. Therefore, it is preferable that sliding contact point A has a hardened layer depth of 20 micrometers or more.

[0040] In the above-described embodiment, the inner circumferential surface of each piston bore 18 and the outer circumferential surface of each piston 19 are nitrided. However, sulfur-nitriding or other surface hardening treatments may also be used. While both the cylinder block 17 and the pistons 19 are made of ferritic stainless steel SUS430, either one or both may be made of SUS403, SUS405, SUS434, or SUS447J1, or austenitic stainless steel SUS304, SUS303, or SUS316. While the present invention is a swash plate axial piston pump, it may also be a swash plate axial piston motor. In this case, the cylinder block 17 is rotated by hydraulic fluid supplied from an external source, which in turn rotates the rotary shaft 7. While the present invention is a fixed displacement type in which the inclination angle of the swash plate 16 is fixed, it may, of course, be a variable displacement type in which the inclination angle of the swash plate is variable. [Explanation of symbols]

[0041] 1: Main unit 7: Rotation axis 16: Swash plate 17: Cylinder block 18: Piston hole 19: Piston 20: Working chamber 33, 34: Intake and exhaust flow paths A: Sliding contact point

Claims

1. a plurality of pistons in sliding contact with a plurality of piston holes formed in the axial direction of the cylinder block so as to be able to reciprocate; a plurality of working chambers defined by the pistons and the cylinder block for drawing in and discharging working water; a swash plate disposed in the body and in contact with the tips of the pistons protruding from the cylinder block to set the amount of reciprocation of each piston; and a pair of intake and exhaust flow paths formed in the body for passing working water;

2. 2. The swash plate type axial piston pump / motor according to claim 1, wherein the surface hardening treatment is nitriding or sulfuric nitriding.

3. 3. A swash plate type axial piston pump / motor according to claim 2, wherein the outer peripheral surface of the piston at the sliding contact portion is nitrided and further coated with DLC.

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