Swash plate type variable displacement piston pump

Abstract

To provide a swash plate type variable displacement piston pump which can reduce the leakage of a working fluid into a body while suppressing friction between a cradle and a cradle guide.SOLUTION: A constitution of a swash plate type variable displacement piston pump (piston pump 100) of the present invention comprises a body 102, a cylinder barrel 110 rotatably supported in the body together with a shaft 104, a plurality of pistons 112 slidably inserted into the cylinder barrel in an axial direction, a swash plate 120 for changing strokes of the pistons, a cradle formed at the swash plate, and having a cylinder face, a pressure oil groove 128 formed at the cylinder face of the cradle, a cradle guide 102a formed at the body, and being the cylinder face for receiving the cradle, and an oil supply port 102b which is opened at the cylinder face of the cradle guide. The pressure oil groove is formed in a position in which pressure is high in a pressure distribution of the cylinder face of the cradle.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a swash plate type variable displacement piston pump for use in construction machinery, industrial machinery, etc. [Background technology]

[0002] Variable displacement pumps are sometimes used in construction and industrial machinery. A swash plate type variable displacement piston pump, which is one type of variable displacement pump, can change the pump capacity by tilting the swash plate (also called a swash plate). The swash plate has a cylindrical surface called a cradle, and it tilts smoothly by sliding against the cradle guide of the body.

[0003] For example, Patent Document 1 discloses a swash plate type piston pump / motor in which "multiple pistons are arranged circumferentially in a cylinder block that rotates with a rotating shaft, and the pistons are caused to reciprocate by the tip of each piston being guided along the sliding surface of a swash plate, and the swash plate is slidably supported on a swash plate support base so that it can tilt relative to the rotating shaft."

[0004] In the swash plate type piston pump and motor of Patent Document 1, "the surface of the swash plate opposite the sliding surface is provided with a circular arc-shaped smooth convex surface facing the swash plate support base, and a groove portion for retaining an oil film is formed in the convex surface extending in the sliding direction." Also, "the sliding surface of the swash plate support base that supports the convex surface of the swash plate is a circular arc-shaped concave surface, and the concave surface is provided with a pressure oil supply port that opens toward the groove portion," and "the concave surface of the swash plate support base has a hardened portion that is partially hardened by laser light." According to Patent Document 1, "the hardened portion becomes convex due to thermal expansion, and unevenness is formed between the hardened portion and the non-hardened portion, improving compatibility and sliding characteristics and enhancing seizure resistance." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4754313 Summary of the Invention [Problem to be solved by the invention]

[0006] A cradle having a cylindrical surface is formed on the swash plate, and a cradle guide having a cylindrical surface that receives the cradle is formed on the bearing. The cylindrical surfaces of the cradle and the cradle guide are parts of a cylinder. When hydraulic oil is supplied between the cradle and the cradle guide and hydraulic pressure acts on the pressure oil groove provided in the cradle, a buoyant load is generated in a direction that separates them due to the hydraulic oil pressure. Therefore, the pressure (piston reaction force) applied to the cradle is reduced, and the surface (sliding surface) where the cradle and the cradle guide slide is lubricated, thereby suppressing wear of the cradle guide.

[0007] Here, the pressure on the cradle is higher the closer it is to the shaft, and lower the further it is from the shaft. If the pressure oil groove is too long in the axial direction of the cylindrical surface (the direction of the rotation axis of the swash plate) and pressure oil is guided to high and low pressure positions in the same way, pressure oil will leak at the low pressure positions, making it easier for the hydraulic oil (pressurized oil) supplied between the cradle and the cradle guide to leak out. This will increase the amount of hydraulic oil leaking into the pump body, resulting in a decrease in the volumetric efficiency of the pump.

[0008] In addition, because the cylindrical surfaces of the cradle and cradle guide are curved, even a slight difference in the diameter (radius of curvature) of the curved surface will cause a bias in pressure. For example, if the diameter (radius of curvature) of the cylindrical surface of the cradle of the swash plate is smaller than the diameter of the cylindrical surface of the cradle guide of the bearing, the pressure on the outside in the circumferential direction of the cylindrical surface of the cradle will be lower. If the pressure oil groove is too long in the circumferential direction of the cylindrical surface, pressure oil leakage will be more likely to occur.

[0009] In view of such problems, the present invention aims to provide a swash plate type variable displacement piston pump that can reduce leakage of hydraulic oil into the body while suppressing friction between the cradle and the cradle guide. [Means for solving the problem]

[0010] In order to solve the above problems, a typical configuration of a swash plate type variable displacement piston pump according to the present invention includes a body, a cylinder barrel rotatably supported together with a shaft in the body, a plurality of pistons slidably inserted into the cylinder barrel in the axial direction, a swash plate that changes the stroke of the pistons, a cradle formed on the swash plate and having a cylindrical surface, an oil pressure groove formed on the cylindrical surface of the cradle, a cradle guide that is a cylindrical surface formed on the body and receives the cradle, and an oil supply port that opens onto the cylindrical surface of the cradle guide, and the oil pressure groove is formed at a position where the pressure is high in the pressure distribution on the cylindrical surface of the cradle.

[0011] In the case where the pressure distribution on the cylindrical surface of the cradle increases toward the shaft, it is preferable that the circumferential width of the pressure oil groove increases toward the shaft. Effect of the Invention

[0012] According to the present invention, it is possible to provide a swash plate type variable displacement piston pump that can reduce leakage of hydraulic oil into the body while suppressing friction between the cradle and the cradle guide. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating a swash plate type variable displacement piston pump according to an embodiment of the present invention. FIG. [Diagram 2] 1 is a diagram illustrating a swash plate type variable displacement piston pump according to an embodiment of the present invention. FIG. [Diagram 3] 3A and 3B are a plan view and a perspective view of a swash plate. [Figure 4] FIG. 13 is a diagram illustrating pressure distribution on a cylindrical surface of a cradle. [Diagram 5] 4A to 4C are diagrams illustrating pressure oil grooves in a discharge-side cradle of the present embodiment and a cradle of a comparative example. [Figure 6] 10A to 10C are diagrams illustrating other shapes of the pressure groove according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific values ​​shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are given the same reference numerals to avoid repeated explanations, and elements not directly related to the present invention are not shown or described.

[0015] 1 and 2 are diagrams illustrating a swash plate type variable displacement piston pump (hereinafter referred to as piston pump 100) according to this embodiment. Fig. 1 is a side view of the piston pump 100 at a dead head when the tilt angle of the swash plate 120 is minimum. Fig. 2 is a side view of the piston pump 100 at a full discharge when the tilt angle of the swash plate 120 is maximum.

[0016] The piston pump 100 of this embodiment is a device that supplies fluid such as hydraulic oil to construction machinery or industrial machinery (not shown) through a discharge port 190. As shown in Figures 1 and 2, a cylinder barrel 110 that is rotatably supported together with a shaft 104 (axis) is disposed within a body 102 of the piston pump 100. A plurality of pistons 112 that are axially slidable are inserted into the cylinder barrel 110.

[0017] Heads 112a of pistons 112 are attached to piston shoes 114 that come into contact with swash plate 120. When swash plate 120 tilts in conjunction with control piston 130, piston shoes 114 also tilt. As a result, when cylinder barrel 110 is rotated, multiple pistons 112 aligned in the circumferential direction of cylinder barrel 110 reciprocate, and hydraulic oil is discharged from discharge port 190. At this time, by adjusting the tilt angle of swash plate 120, the stroke of pistons 112 changes, and the pump capacity can be changed.

[0018] FIG. 3 is a plan view and a perspective view of the swash plate 120. FIG. 3(a) is a plan view and a side view of the swash plate 120, and FIG. 3(b) is a perspective view of the swash plate 120. As shown in FIG. 3(a) and (b), the swash plate 120 has an insertion hole 120a through which the shaft 104 (see FIG. 1 and FIG. 2) is inserted, and a pair of cradles consisting of a suction side cradle 122 and a discharge side cradle 124 are formed on both sides of the insertion hole 120a. As shown in FIG. 1 and FIG. 2, the suction side cradle 122 and the discharge side cradle 124 (the discharge side cradle 124 is shown in this embodiment) each have a cylindrical surface 126. The cylindrical surface 126 is a part of a cylinder whose axis is the center of rotation of the swash plate 120.

[0019] 1 and 2, the body 102 is formed with a cradle guide 102a, which is a cylindrical surface that receives a cradle (the discharge side cradle 124 is shown in this embodiment). The body 102 is also formed with an oil supply port 102b and an oil supply path 102c. The oil supply port 102b opens into the cylindrical surface of the cradle guide 102a, and when the hydraulic oil is discharged from the discharge port 190, the hydraulic oil is supplied to the oil supply port 102b through the oil supply path 102c.

[0020] In the piston pump 100 of this embodiment, as shown in Fig. 3, a pressure oil groove 128 is formed in the cylindrical surface 126 of the discharge side cradle 124. Note that, in the present embodiment, a configuration in which the pressure oil groove 128 is formed only in the cylindrical surface 126 of the discharge side cradle 124 out of the pair of the suction side cradle 122 and the discharge side cradle 124 has been exemplified, but this is not limiting. As another configuration, a configuration in which the pressure oil groove 128 is formed in the cylindrical surfaces 126 of both the suction side cradle 122 and the discharge side cradle 124 may be used.

[0021] Fig. 4 is a diagram for explaining pressure distribution on the cylindrical surface 126 of the cradle. For ease of understanding, the shaft 104 is illustrated by a virtual line in Fig. 4. In Fig. 4 and subsequent figures, areas on the cylindrical surface 126 where the pressure (piston reaction force) is high are indicated by hatching, and the pressure level is indicated by a vector quantity (length of the arrow).

[0022] 4, in the cradle, the pressure is higher (longer arrow) and the region of high pressure is wider (wider hatched area) on the cylindrical surface 126 of the discharge side cradle 124 than on the cylindrical surface 126 of the suction side cradle 122. In addition, in both the cylindrical surfaces of the suction side cradle 122 and the discharge side cradle 124, the region of high pressure on the cylindrical surface 126 becomes larger in the circumferential direction as it approaches the shaft 104.

[0023] Therefore, in the piston pump 100 of this embodiment, the pressure oil groove 128 is formed at a position where the pressure is high in the pressure distribution on the cylindrical surface of the cradle. Furthermore, in the case where the pressure increases toward the shaft 104 in the pressure distribution on the cylindrical surface of the cradle, the pressure oil groove 128 is formed so that its circumferential width becomes wider toward the shaft 104. In other words, the pressure oil groove 128 is formed inside a range where the pressure is high. In further other words, the position of the pressure oil groove 128 is determined so that there are positions of high pressure around the pressure oil groove 128 and so that the pressure oil groove 128 is not applied to a position of low pressure.

[0024] Specifically, the pressure oil groove 128 in this embodiment is composed of a first pressure oil groove 128a and a second pressure oil groove 128b arranged adjacent thereto. The first pressure oil groove 128a is a "groove with a wide circumferential width" arranged on the "side closer to shaft 104" where the high-pressure region is wide in the circumferential direction. The second pressure oil groove 128b is a "groove with a narrow circumferential width" arranged on the "side farther from shaft 104" where the high-pressure region is narrower in the circumferential direction.

[0025] Fig. 5 is a diagram illustrating the pressure oil grooves of the discharge side cradle 124 of this embodiment and the cradle 24 of the comparative example. Fig. 5(a) is a diagram showing the discharge side cradle 124 of this embodiment. Fig. 5(b) is a diagram showing the cradle 24 of the comparative example. In Fig. 5, the load applied from the pressure oil to the pressure oil groove is shown by a vector in the opposite direction to the pressure applied to the cradle.

[0026] A rectangular pressure groove 28 is formed in the center of the cylindrical surface 26 of the cradle 24 of the comparative example shown in FIG. 5(b). In the pressure groove 28, the hydraulic load is uniform. Meanwhile, the pressure (piston reaction force) acting on the cylindrical surface 26 of the cradle 24 is higher on the side closer to the shaft 104. Therefore, in the cylindrical surface 26 of the conventional cradle 24, it is not possible to eliminate the pressure difference between the side closer to the shaft 104 and the side farther from the shaft 104.

[0027] In addition, the corners of the pressure grooves 28 in the comparative example (corners on the side farther from the shaft 104) overlap with areas of low pressure, i.e., areas not hatched, on the cylindrical surface 26 of the cradle 24. For this reason, pressure oil leaks from the corners of the pressure grooves 28, making it easy for pressure oil to leak out.

[0028] In contrast, in the cylindrical surface 126 of the discharge-side cradle 124 of this embodiment shown in Fig. 5(a), the first oil groove 128a arranged on the side closer to the shaft 104 has a wide circumferential width, and the second oil groove 128b arranged on the side farther from the shaft 104 has a narrow circumferential width. In other words, the first oil groove 128a has a large area and the second oil groove 128b has a small area, so that the load due to the hydraulic pressure of the working oil is large on the side closer to the shaft 104 and small on the side farther from the shaft 104, similar to the pressure distribution of the cradle. Therefore, in the cylindrical surface 26 of the discharge-side cradle 124, the pressure difference between the side closer to the shaft 104 and the side farther from the shaft 104 can be mitigated (cancelled).

[0029] In the present embodiment, both the first oil groove 128a and the second oil groove 128b are formed in a high pressure region (hatched region). This makes it possible to suitably prevent leakage of hydraulic oil into the pump body 102. Therefore, by suitably retaining the hydraulic oil in the oil groove 128, it is possible to suppress friction between the cradle and the cradle guide, and to prevent a decrease in the volumetric efficiency of the pump due to leakage of hydraulic oil.

[0030] FIG. 6 is a diagram for explaining another shape of the pressure groove of this embodiment. In the discharge side cradle 124a shown in FIG. 6(a), the diameter (radius of curvature) of the cylindrical surface 126a of the discharge side cradle 124a of the swash plate 120 is larger than the diameter (radius of curvature) of the cylindrical surface of the cradle guide 102a of the bearing (see FIG. 1 and FIG. 2). In this case, as shown in FIG. 6(b), the pressure in the cylindrical surface 126a of the discharge side cradle 124a is higher on the outside than on the inside in the circumferential direction. In the axial direction, the pressure is still higher on the side closer to the shaft 104.

[0031] Therefore, a U-shaped pressure oil groove 128c that is open on the side farther from the shaft 104 (see FIG. 4) is formed in the cylindrical surface 126a of the discharge-side cradle 124a shown in FIG. 6(b). As a result, the pressure oil groove 128c is positioned to avoid the region of low pressure on the inside in the circumferential direction, so that leakage of pressure oil from the pressure oil groove 128c can be suitably prevented.

[0032] Although the preferred embodiment of the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such an embodiment. It is clear that a person skilled in the art can think of various modifications or alterations within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Industrial Applicability]

[0033] INDUSTRIAL APPLICABILITY The present invention can be used as a swash plate type variable displacement piston pump for use in construction machinery and industrial machinery. [Explanation of symbols]

[0034] 24...cradle, 26...circular surface, 28...pressure groove, 100...piston pump, 102...body, 102a...cradle guide, 102b...oil supply port, 102c...oil supply path, 104...shaft, 110...cylinder barrel, 112...piston, 112a...piston head, 114...piston shoe, 120...swash plate, 120a...insertion hole, 122...suction side cradle, 122a...suction side cradle, 124...discharge side cradle, 126...circular surface, 126a...circular surface, 128...oil pressure groove, 128a...first oil pressure groove, 128b...second oil pressure groove, 128c...oil pressure groove, 130...control piston, 190...discharge port

Claims

1. Body and a cylinder barrel supported within the body so as to be rotatable together with the shaft; A plurality of pistons slidably inserted in the cylinder barrel in the axial direction; A swash plate that changes the stroke of the piston; A cradle having a cylindrical surface formed on the swash plate; A pressure oil groove formed on a cylindrical surface of the cradle; A cradle guide which is a cylindrical surface formed on the body and receives the cradle; A fuel supply port opening on the cylindrical surface of the cradle guide; Equipped with A swash plate type variable displacement piston pump, characterized in that the pressure oil groove is formed at a position where the pressure is high in the pressure distribution on the cylindrical surface of the cradle.

2. The swash plate type variable displacement piston pump according to claim 1, characterized in that, when the pressure in the pressure distribution on the cylindrical surface of the cradle increases toward the shaft, the circumferential width of the pressure oil groove increases toward the shaft.

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