Variable displacement piston device

Abstract

The objective is to provide a variable displacement piston device that can ensure sufficient wear resistance and load-bearing capacity even when steel is used for the support ball, and that can be made less expensive. [Solution] The variable displacement piston device according to the present invention comprises a cylinder barrel 110 supported in a housing 102 so as to be rotatable together with a shaft 104, a plurality of pistons 112 inserted into the cylinder barrel 110 so as to be axially slidable, a swash plate 120 that changes the stroke of the pistons 112, and two support balls 130 that rotatably support the swash plate 120, wherein the support balls 130 are made of steel with a tempering temperature of 500°C or higher and have been subjected to soft nitriding treatment on their surface.

Description

Technical Field

[0001] The present invention relates to a variable displacement piston device used in construction machinery, industrial machinery, and the like.

Background Art

[0002] Variable displacement piston devices may be used in construction machinery and industrial machinery. Specifically, variable displacement piston pumps and variable displacement piston motors can be mentioned. One of them, the swash plate type variable displacement piston pump, can change the pump capacity by tilting a swash plate (also referred to as a swashplate).

[0003] For example, Patent Document 1 discloses a variable displacement pump having "a cylinder barrel supported rotatably together with a shaft in a housing, and a swash plate slidably contacting the heads of a plurality of pistons inserted axially slidably into the cylinder barrel and supported in the housing so as not to rotate relative to the rotation of the shaft." In the variable displacement pump of Patent Document 1, the swash plate is pressed by a drive device provided in the housing and is tilted around two balls or cylindrical bodies forming an axis perpendicular to the rotation axis of the shaft to change the tilt angle of the swash plate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the variable displacement pump described in Patent Document 1, the two balls are formed from a ceramic material that "contains 92-99.5% by weight of aluminum oxide (Al2O3), with the remainder being unavoidable impurities such as SiO2, CaO2, MgO, and trace amounts of Na2O, K2O, and Fe." While the hardness of typical bearing copper SUJ2 is around HV840, the hardness of typical ceramics is much higher, around HV1600.

[0006] To process (lap) high-hardness ceramics to a level of precision (sphere diameter, sphericity, surface roughness, etc.) suitable for use as balls supporting a swash plate, it is necessary to use special abrasive grains with a hardness higher than HV1600 and process them for a long time. Therefore, although the ceramic balls used in Patent Document 1 are excellent in terms of wear resistance, they have the problem of being difficult to mass-produce and resulting in high costs.

[0007] In view of these problems, the present invention aims to provide a variable displacement piston device that can ensure sufficient wear resistance and load-bearing capacity even when steel is used for the support ball, and that can be manufactured at a lower cost. [Means for solving the problem]

[0008] To solve the above problems, a typical configuration of the variable displacement piston device according to the present invention comprises a cylinder barrel supported in a housing so as to be rotatable together with a shaft, a plurality of pistons inserted into the cylinder barrel so as to be axially slidable, a swash plate that changes the stroke of the pistons, and two support balls that rotatably support the swash plate, wherein the support balls are made of steel with a tempering temperature of 500°C or higher and have been subjected to soft nitriding treatment on their surface.

[0009] The support spheres described above may have micro-dimples formed on them by micro-shot peening.

[0010] The steel material of the support ball may be one of the following: high-speed tool steel, hot-rolled alloy tool steel, martensitic stainless steel, or molybdenum-based high-speed steel.

[0011] The variable displacement piston device further comprises two cylindrical holes formed in the swash plate opposite to two support balls, and two ball guides housed in the cylindrical holes and supporting the support balls, wherein the ball guides have a cylindrical outer surface and a concave spherical surface that supports the support balls, and both or one of the ball guides are eccentric with respect to the outer surface and rotatable within the cylindrical holes of the swash plate. [Effects of the Invention]

[0012] According to the present invention, even when steel is used for the support ball, sufficient wear resistance and load-bearing capacity can be ensured, and a variable displacement piston device that can be manufactured at a lower cost can be provided. [Brief explanation of the drawing]

[0013] [Figure 1] This figure illustrates a variable displacement piston pump as a variable displacement piston device according to this embodiment. [Figure 2] This diagram illustrates the details of the swash plate and support ball. [Figure 3] This figure illustrates the details of the swash plate and support sphere according to a modified embodiment. [Figure 4] This diagram illustrates the pitch of a pair of cylindrical holes. [Modes for carrying out the invention]

[0014] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. The dimensions, materials, and other specific numerical values ​​shown in these embodiments are merely illustrative to facilitate understanding of the invention and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same function or configuration are denoted by the same reference numerals to avoid redundant explanations, and elements not directly related to the present invention are not shown or described.

[0015] Figure 1 is a diagram illustrating a variable displacement piston pump (hereinafter referred to as piston pump 100) as a variable displacement piston device according to this embodiment. Figure 1(a) is a diagram illustrating the internal structure of piston pump 100. Figure 1(b) is a cross-sectional view AA of Figure 1(a). In this embodiment, a variable displacement piston is exemplified as a variable displacement piston device, but the present invention can also be applied to a variable displacement piston motor.

[0016] The piston pump 100 of this embodiment is a device that supplies fluids such as hydraulic oil to construction machinery or industrial machinery (not shown) through a discharge port (not shown). As shown in Figure 1(a), the piston pump 100 of this embodiment has a housing 102. Inside the housing 102 is a cylinder barrel 110 that is rotatably supported together with a shaft 104 (axis).

[0017] Multiple pistons 112 are inserted into the cylinder barrel 110, which are slidable in the axial direction D1 of the shaft 104. The multiple pistons 112 are arranged in a line in the circumferential direction of the cylinder barrel 110, and when the cylinder barrel 110 is rotated, they reciprocate, and hydraulic fluid is discharged from the discharge port. The heads 112a of the pistons are attached to piston shoes 114 that abut and slide against the swash plate 120.

[0018] The swash plate 120 is supported within the housing 102 so as not to rotate relative to the rotation of the shaft 104, and changes the stroke of the piston 112 by tilting. As shown in Fig. 1(b), the swash plate 120 has an insertion hole 120a through which the shaft 104 is inserted.

[0019] Also, as shown in Fig. 1(b), the swash plate 120 is rotatably supported by two support balls 130. Further, as shown in Fig. 1(a), the piston pump 100 is provided with a spring unit 190 that presses the swash plate 120. The spring unit 190 has a spring 192 and a spring holder 194.

[0020] The spring unit 190 is provided to generate a moment in the counterclockwise direction with respect to the clockwise moment generated on the swash plate 120 with the support ball 130 as a fulcrum by the hydraulic pressure from a plurality of pistons 112. With such a structure, due to the clockwise moment caused by the hydraulic pressure and the counterclockwise moment caused by the load of the spring unit 190, the swash plate 120 tilts around the support ball 130.

[0021] Fig. 2 is a diagram for explaining the details of the swash plate 120 and the support ball 130. Fig. 2(a) is a diagram showing the state where the swash plate 120 is supported by the support ball 130. Fig. 2(b) is a front view and a cross-sectional view of the ball guide 140.

[0022] As shown in Fig. 1(b) and Fig. 2(a), hemispherical holes 102a are formed in the housing 102 at positions corresponding to each of the two support balls 130, and the support balls 130 are held therein. Note that the "hemispherical hole" does not only refer to a hole in the shape of bisecting a sphere, but includes several shapes that rotatably support a part of the support ball 130 so that it does not fall off from the support structure.

[0023] Furthermore, in the swash plate 120, two cylindrical holes 122 are formed at positions opposite each of the two support spheres 130. Two ball guides 140 that support the support spheres 130 are housed in the two cylindrical holes 122. In this way, the swash plate 120 is supported by the housing 102 via the support spheres 130. As shown in Figure 2(b), the two ball guides 140 have a cylindrical outer surface 142 and a concave spherical surface 144 that supports the support spheres 130.

[0024] In this embodiment, the support ball 130 is made of steel with a tempering temperature of 500°C or higher. The steel materials include high-speed tool steel (JIS G4403…SKH2 / SKH3 / SKH4 / SKH10 / SKH40 / SKH50 / SKH51 / SKH52 / SKH53 / SKH54 / SKH55 / SKH56 / SKH57 / SKH58 / SKH59), hot-rolled alloy tool steel (JIS G4404…SKD4 / SKD5 / SKD6 / SKD61 / SKD62), and martensitic stainless steel (JIS Examples include G4303 (SUS4303 / SUS410 / SUS410J1 / SUS410F2 / SUS416 / SUS420J1 / SUS420J2 / SUS420F / SUS420F2 / SUS431 / SUS440A / SUS440B / SUS440C / SUS440F) and molybdenum-based high-speed steel (AISI...M1 / M2 / M10 / M50).

[0025] Furthermore, a feature of this embodiment is that the support ball 130 made of the steel material described above has been subjected to soft nitriding treatment on its surface, and micro-dimples have been formed by micro-shot peening treatment.

[0026] Soft nitriding is a type of surface treatment that involves compounding nitrogen (N) with iron (Fe) on the surface of a metal to create a thin, hard layer of Fe3N or similar material (shown by hatching). In this embodiment, the steel material used for the support ball was subjected to soft nitriding (salt bath soft nitriding) at a treatment temperature of approximately 580°C for a treatment time of no more than 3 hours. As a result, a compound layer (nitrided layer) with a hardness of HV900 or higher and a depth of 30 μm or less from the surface was formed on the surface of the treated steel material, and the hardness inside the ball became HV400 (≒HRC40) or higher. By performing soft nitriding in this way, the wear resistance and load-bearing capacity of the support ball can be improved.

[0027] Here, by using steel with a tempering temperature of 500°C or higher as the material for the support ball 130, the reduction in hardness is small even after soft nitriding treatment. Therefore, even if soft nitriding treatment is performed after heat treatment (quenching and tempering), it is possible to prevent a decrease in the hardness of the support ball 130.

[0028] Microshot peening is a surface modification (surface shaping) treatment that uses fine particles with a diameter of several tens to several hundred micrometers to perform shot peening (impact) on the surface of a metal at a high speed of 100 m / sec or more to form microdimples. Examples of fine particles that can be used include steel particles, stainless steel particles, glass particles, ceramic particles, indium lead particles, tin particles, silver particles, molybdenum disulfide particles, tungsten disulfide particles, boron nitride particles, and fluororesin particles.

[0029] According to the piston pump 100 of this embodiment, by subjecting the steel material that forms the support ball 130 to soft nitriding treatment, sufficient wear resistance and load-bearing capacity required for supporting the swash plate 120 can be ensured in the support ball 130. Furthermore, by applying micro-shot peening treatment to the support ball 130 in addition to soft nitriding treatment, further hardness can be improved through work hardening. In addition, by forming micro-dimples on the surface of the support ball 130, the recessed parts of the micro-dimples become oil reservoirs, resulting in smooth operation.

[0030] As explained above, the support ball 130 has a shorter processing time than ceramic balls and can be mass-produced, resulting in higher productivity. Therefore, the support ball 130 of this embodiment is less expensive than ceramic support balls. Furthermore, despite using steel for the support ball 130, sufficient wear resistance, load-bearing capacity, and durability can be ensured, making it possible to reduce the cost of variable displacement piston devices.

[0031] It is possible to obtain similar wear resistance and load-bearing capacity by applying soft nitriding and micro-shot peening treatments to the ball guides 140 instead of the support balls 130. However, the ball guides 140 are larger and have a larger surface area than the support balls 130. Furthermore, if the ball guides 140 are to be treated, it would be necessary to install ball guides 140 on both the housing 102 and the swash plate 120, requiring a total of four ball guides 140 to be treated. This would significantly increase the total cost of soft nitriding and micro-shot peening treatments, making it preferable to treat the support balls 130 instead.

[0032] (modified version) A modified example of this embodiment will now be described. Figure 3 is a diagram illustrating the details of the swash plate 120 and support ball 130 according to a modified example of the embodiment. Figure 3(a) shows the state in which the swash plate 120 is supported by the support ball 130. Figure 3(b) is a front view and a cross-sectional view of the ball guide 140. Figure 3(c) shows the state in which the support ball 130 has been removed from the swash plate 120.

[0033] As shown in Figures 1(b) and 3(a), the housing 102 has hemispherical holes 102a formed at positions corresponding to each of the two support spheres 130, where the support spheres 130 are held. In the swash plate 120, two cylindrical holes 122 are formed at positions opposite each of the two support spheres 130. Two spherical guides 140 that support the support spheres 130 are housed in the two cylindrical holes 122. Thus, the swash plate 120 is supported by the housing 102 via the support spheres 130. Note that the term "hemispherical hole" does not only refer to a hole shaped like a sphere divided in half, but also includes several shapes that allow a portion of the support sphere 130 to rotatably support it so that it does not fall out of the support structure.

[0034] As shown in Figure 3(b), the two ball guides 140 each have a cylindrical outer surface 142 and a concave spherical surface 144 that supports the support ball 130. A feature of the piston pump 100 in this embodiment is that the ball guide 140 has an eccentricity between the center C2 of the concave spherical surface 144 and the center C1 of the outer surface 142. Let this eccentricity be t. The ball guide 140 is rotatable within the cylindrical hole 122 of the swash plate 120.

[0035] Figure 4 illustrates the pitch of a pair of cylindrical holes 122. Figures 4(a) to 4(e) illustrate the state in which the ball guides 140 are not housed in the pair of cylindrical holes 122. Figures 4(f) to 4(j) illustrate the state in which the ball guides 140 supporting the support balls 130 are housed in the pair of cylindrical holes 122.

[0036] In the swash plate 120 of Figure 4(c), the distance between the pair of cylindrical holes 122 is the specified distance L. That is, there is no deviation in the pitch of the pair of cylindrical holes 122 in the swash plate 120 of Figure 4(c). In contrast, the swash plate 120 of Figure 4(a) has a deviation of "-2t" from the specified distance L, and the swash plate 120 of Figure 4(b) has a deviation of "-t" from the specified distance L.

[0037] Furthermore, the swash plate 120 in Figure 4(d) is offset by "+t" from the specified interval L, and the swash plate 120 in Figure 4(e) is offset by "+2t" from the specified interval L. The spacing of the pair of cylindrical holes 122 in Figures 4(f) to 4(j) corresponds to Figures 4(a) to 4(e), respectively.

[0038] If there is no misalignment in the pitch of the pair of cylindrical holes 122, as shown in the swash plate 120 in Figure 4(c), the center distance of the support balls 130 supported by the ball guide 140 is also L, as shown in Figure 4(h). At this time, the rotation angle of the ball guide 140 within the cylindrical hole 122 is 0°, and the center distance of the concave spherical surface 144 is also L.

[0039] In contrast, if there is a misalignment in the pitch of the pair of cylindrical holes 122, as shown in Figures 4(f), 4(g), 4(i), and 4(j), the ball guides 140 housed in the pair of cylindrical holes 122 are pressed against the support balls 130 via the swash plate 120 by the hydraulic pressure of the multiple pistons 112 and the load of the spring unit 190, and rotate within the cylindrical holes 122 following (being pushed by) the support balls 130.

[0040] As a specific example, in Figures 4(g) and 4(i), the spacing between the cylindrical holes 122 is L±t, but by rotating the ball guide 140 ±30°, the center spacing of the concave spherical surfaces 144 becomes L. Similarly, in Figures 4(f) and 4(j), the spacing between the cylindrical holes 122 is L±2t, but by rotating the ball guide 140 ±90°, the center spacing of the concave spherical surfaces 144 becomes L. In this way, the pitch misalignment of the pair of cylindrical holes 122, i.e., the pitch misalignment of the pair of spherical holes, is absorbed. Therefore, the support balls 130 and the concave spherical surfaces 144 can slide across their entire surfaces, improving the wear resistance of the support balls 130 and the swash plate 120, and preventing abnormal changes in performance (capacity) due to changes in the support angle of the swash plate due to wear, as well as damage due to excessive wear.

[0041] In this modified example, both of the two ball guides 140, which are housed in two cylindrical holes 122 formed in the swash plate 120 and support the support ball 130, have their concave spherical surfaces eccentric with respect to the outer surface. However, the present invention is not limited to this. For example, the present invention can also be applied to a configuration where only one of the two ball guides 140 has its concave spherical surface eccentric with respect to the outer surface, or to two ball guides housed in two cylindrical holes formed in the housing 102 and supporting the support ball.

[0042] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but it goes without saying that the present invention is not limited to such examples. It will be clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. [Industrial applicability]

[0043] This invention can be used as a variable displacement piston device for construction machinery, industrial machinery, and the like. [Explanation of Symbols]

[0044] D1…Axial direction, 100…Piston pump, 102…Housing, 102a…Hemispherical hole, 104…Shaft, 110…Cylinder barrel, 112…Piston, 112a…Head, 114…Piston shoe, 120…Swash plate, 120a…Through hole, 122…Cylindrical hole, 130…Support ball, 140…Ball guide, 142…Outer surface, 144…Concave spherical surface, 190…Spring unit, 192…Spring, 194…Spring holder

Claims

1. A cylinder barrel supported within the housing so as to be rotatable together with the shaft, Multiple pistons are inserted into the cylinder barrel so as to be slidable in the axial direction, A swash plate that changes the stroke of the aforementioned piston, Two support balls that rotatably support the aforementioned swash plate, Equipped with, The aforementioned support ball is Using steel materials whose tempering temperature is 500°C or higher, A variable displacement piston device characterized by having its surface treated with soft nitriding.

2. The variable displacement piston device according to claim 1, characterized in that the support ball has micro-dimples formed by micro-shot peening treatment.

3. The variable displacement piston device according to claim 1, characterized in that the steel material of the support ball is one of high-speed tool steel, hot-rolled alloy tool steel, martensitic stainless steel, or molybdenum-based high-speed steel.

4. Two cylindrical holes are formed in the swash plate at positions opposite to the two support balls, The system further comprises two ball guides housed in the cylindrical hole and supporting the support ball, The aforementioned ball guide is It has a cylindrical outer surface and a concave spherical surface that supports the support ball, Both or one of the aforementioned ball guides are eccentric with respect to the outer circumferential surface, The variable displacement piston device according to any one of claims 1 to 3, characterized in that it is rotatable within the cylindrical hole of the swash plate.

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