Piston and hydraulic pump or motor

Abstract

Piston (3) for a hydraulic pump or motor, comprising: a piston body (30) containing an interior space (32); a front end member (20) including an insertion portion (22) disposed in the interior space (32) and a projection (21) projecting from a front end surface (31) of the piston body (30); wherein the front end surface (31) is arranged around an opening (34) of the piston body (30) which is connected to the interior (32), and the front end element (20) has an opposite surface (27) facing the front end surface (31); an oil passage (29) arranged between the front end surface (31) and at least a part of the opposing surface (27) and between an inner surface of the inner space (32) and at least a part of an outer surface of the insertion portion (22); and a connecting element (10) placed in the interior (32) and connected to the insertion section (22), wherein the insertion portion (22) includes a deformable portion (24) arranged around the connecting element (10) and configured to deform outwardly in a radiation direction of a central axis (CX) of the piston body (30) upon contact with the connecting element (10).

Description

Area

[0001] The present invention relates to a piston and a hydraulic pump or a hydraulic motor. background

[0002] A variable displacement hydraulic pump or motor is provided with a cylinder block containing a plurality of cylinders, a plurality of pistons each positioned within the plurality of cylinders, and a swash plate that supports the pistons via piston shoes. The rotation of the cylinder block causes the pistons and piston shoes to oscillate, with the piston shoes sliding on the swash plate. As the piston shoes slide on the swash plate, the oscillation of the pistons and piston shoes causes the pistons to reciprocate within the cylinders. The reciprocation of the pistons changes the displacements defined between the pistons and the cylinders. Citation listPatent literature

[0003] JP 2014-152690 A discloses a piston for an axial piston motor or pump, in which an oil passage is provided between an inner surface of a hollow portion of the piston body and an outer surface of the insert. This piston serves to reduce compressibility loss by reducing dead volume and to improve the cooling performance of a hydraulic oil and the adhesive strength.

[0004] Other pistons with a cavity are known from DE 43 01 140 A1, DE 196 20 167 C1, US 2002 / 0 096 047 A1 and DE 15 28 408 A. SummaryTechnical problem

[0005] Reducing the weight of a piston allows the piston to oscillate and reciprocate at high speed. On the other hand, if the inside of the piston is hollowed out to reduce the weight of the piston, the dead volume of a hydraulic pump or motor increases. In addition, for a cylinder, tapering the side closer to top dead center facilitates machinability when machining the cylinder. On the other hand, tapering the side of the cylinder closer to top dead center increases the dead volume. Dead volume is a space defined between the cylinder and the piston when the piston is placed at top dead center, which indicates a position where the piston maximally enters the cylinder. Dead volume is a space that does not contribute to changes in swept volume. A large dead volume requires additional work to compress the dead volume.Therefore, a large dead volume reduces the efficiency of the hydraulic pump or hydraulic motor.

[0006] The object of the present invention was to reduce a dead volume of a hydraulic pump or a hydraulic motor. Solution to the problem

[0007] According to one aspect of the present invention, a piston comprises: a piston body containing an internal space; a front end member including an insertion portion disposed in the internal space and a projection protruding from a front end surface of the piston body, an oil passage, and a connecting member. The piston is configured for a hydraulic pump or motor. Further, the front end surface is disposed around an opening of the piston body that communicates with the internal space. The front end member has an opposing surface facing the front end surface. The oil passage is disposed between the front end surface and at least a part of the opposing surface, and between an inner surface of the internal space and at least a part of an outer surface of the insertion portion. The connecting member is disposed in the internal space and connected to the insertion portion.The insertion portion includes a deformable portion disposed around the connecting member and configured to deform outwardly in a radiation direction of a central axis of the piston body upon contact with the connecting member. Brief description of the drawings Fig. 1 is a view illustrating an example of a hydraulic pump or a hydraulic motor according to a first embodiment. Fig. 2 is a cross-sectional view showing an example of a piston according to the first embodiment. Fig. 3 is a perspective view illustrating a front end member according to the first embodiment. Fig. 4 is a perspective view illustrating a connecting member according to the first embodiment. Fig. 5 is a cross-sectional view showing an example of a piston according to a second embodiment. Fig. 6 is a cross-sectional view illustrating a part of a front end member according to a third embodiment. Description of the embodiments

[0008] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto. Components of the following embodiments can be freely combined. Furthermore, some components may not be used. [First embodiment]<Hydraulikpumpe oder Hydraulikmotor>

[0009] A first embodiment will now be described. Fig. 1 is a view illustrating an example of a hydraulic pump or hydraulic motor 1 according to this embodiment. In this embodiment, the hydraulic pump or hydraulic motor 1 functions as a hydraulic pump. In the following description, the hydraulic pump or hydraulic motor 1 is conveniently referred to as "hydraulic pump 1."

[0010] As in Fig. 1, the hydraulic pump 1 includes a housing 1H, a drive shaft 2, a cylinder block 6 placed around the drive shaft 2 and having a plurality of cylinders 6S, a plurality of pistons 3 respectively placed in the plurality of cylinders 6S, piston shoes 4 respectively disposed at the base ends of the pistons 3, a swash plate 5 supporting the piston shoes 4, and a valve plate 7 opposed to the cylinder block 6.

[0011] The drive shaft 2 rotates about a rotation axis RX. The drive shaft 2 is rotatably supported by a bearing 16. The drive shaft 2 is rotated by power generated by a power source, e.g., a hydraulic motor.

[0012] The cylinder block 6 is arranged around the drive shaft 2. The cylinder block 6 is arranged inside the housing 1H. The cylinder block 6 is a cylindrical member. At least a portion of the drive shaft 2 is arranged in a center hole 6H of the cylinder block 6. The cylinder block 6 is fixed to the drive shaft 2. The cylinder block 6 and the drive shaft 2 are connected, for example, by a spline coupling. The rotation of the drive shaft 2 causes the cylinder block 6 to rotate together with the drive shaft 2 about the rotation axis RX.

[0013] The cylinders 6S are spaces in which the pistons 3 are respectively placed. The plurality of cylinders 6S are arranged around the rotation axis RX. The plurality of cylinders 6S are placed at regular intervals around the rotation axis RX. The cylinders 6S have a circular shape in a cross section perpendicular to the rotation axis RX. A front end of each cylinder 6S is connected to an opening 61H arranged on a front end surface of the cylinder block 6 via a connecting port 61. Each connecting port 61 has a smaller inner diameter than each cylinder 6S. Each cylinder 6S has an opposing surface 62 opposing at least a part of a front end of each piston 3.

[0014] The pistons 3 move back and forth within the cylinders 6S in a direction parallel to the rotation axis RX. The reciprocating movement of the pistons 3 changes the displacements defined between the pistons 3 and the cylinders 6S.

[0015] Each piston shoe 4 is arranged at the lower end of each piston 3. Each piston shoe 4 includes a spherical portion 4A connected to each piston 3 and a leg portion 4B that comes into contact with the swash plate 5. A plurality of piston shoes 4 are held by a bracket 9.

[0016] Each spherical portion 4A is disposed in a spherical space 3H located at the base end of each piston 3. Each spherical portion 4A is placed in each space 3H by compressing at least a portion of each piston 3. The spherical portions 4A are rotatable within the spaces 3H. The spherical portions 4A and the pistons 3 can move relative to each other.

[0017] The swash plate 5 is arranged around the drive shaft 2. The swash plate 5 supports the plurality of piston shoes 4. The swash plate 5 includes a sliding surface 5A that contacts the leg portion 4B of each piston shoe 4. The swash plate 5 can be inclined with respect to the rotation axis RX. An actuator for driving the swash plate 5 generates power to adjust an inclination angle of the swash plate 5 with respect to the rotation axis RX.

[0018] The valve plate 7 faces the front end surface of the cylinder block 6. The valve plate 7 includes an inlet port 71 and an outlet port 72. The inlet port 71 is connected to an inlet passage 71H arranged in the housing 1H. The inlet port 71 is connected to a hydraulic oil tank via the inlet passage 71H. The outlet port 72 is connected to an outlet passage 72H arranged in the housing 1H. The outlet port 72 is connected to a hydraulic oil supply destination via the outlet passage 72H. An example of the hydraulic oil supply destination is a hydraulic cylinder that drives working tools of a construction machine. <kolben>

[0019] Fig. 2 is a cross-sectional view showing an example of a piston 3 according to this embodiment.

[0020] As in Fig. 2, the piston 3 is provided with a piston body 30 having an inner space 32 and a front end member 20 having an insertion portion 22 placed in the inner space 32 and a projection 21 protruding from a front end surface 31 of the piston body 30.

[0021] The piston 3 is further provided with a connecting element 10 which is arranged in the interior space 32 of the piston body 30 and is connected to the insertion section 22, and with a bolt 8 which connects the front end element 20 and the connecting element 10.

[0022] The piston body 30 is a substantially cylindrical member. A central axis CX of the piston body 30 and the rotational axis RX are substantially parallel. In the following description, a direction parallel to the central axis CX of the piston body 30 is conveniently referred to as the "axial direction," a radiation direction of the central axis CX of the piston body 30 is conveniently referred to as the "radiation direction," and a rotational direction about the central axis CX of the piston body 30 is conveniently referred to as the "circumferential direction."

[0023] Further, in the axial direction, a direction toward the valve plate 7 or a position near the valve plate 7 is conveniently referred to as a "front end side," and a direction toward the swash plate 5 or a position near the swash plate 5 is conveniently referred to as a "base end side." The front end side indicates a direction toward the top dead center or a position near the top dead center. The base end side indicates a direction toward the bottom dead center or a position closer to the bottom dead center. The top dead center indicates a position of the piston 3 when the piston 3 maximally enters the corresponding cylinder 6S. The bottom dead center indicates a position of the piston 3 when the piston 3 maximally retracts from the cylinder 6S.

[0024] The piston body 30 contains a metal. For example, the piston body 30 contains a low-alloy steel such as chromium molybdenum steel. In this embodiment, the specific gravity of a material contained in the piston body 30 is 7.8. Note that the specific gravity of a material is the mass [t] of the material per 1 [m 3 ] indicates.

[0025] The piston body 30 includes the inner space 32 and an inner channel 33 which is located closer to the base end side than the inner space 32. The inner space 32 is connected to an opening 34 formed on the front end surface 31.

[0026] The interior space 32 extends in the axial direction. The interior space 32 contains the central axis CX. In a cross-section perpendicular to the central axis CX, the interior space 32 has a circular shape. In a cross-section perpendicular to the central axis CX, the center of the interior space 32 and the central axis CX coincide.

[0027] The inner channel 33 is connected to a base end of the inner space 32. The inner channel 33 connects the inner space 32 and the space 3H.

[0028] The front end surface 31 is arranged around the opening 34 of the piston body 30, which is connected to a front end of the internal space 32. In the cross-section perpendicular to the central axis CX, the front end surface 31 has an annular shape. The front end surface 31 is flat. The front end surface 31 is parallel to the cross-section perpendicular to the central axis CX.

[0029] Fig. 3 is a perspective view illustrating the front end member 20 according to this embodiment. As shown in Fig. 2 and Fig. As shown in Figure 3, the front end member 20 includes the insertion portion 22 disposed in the internal space 32 and the projection 21 projecting from the front end surface 31 toward the front end side. In the cross section perpendicular to the central axis CX, the external shape of the projection 21 is larger than that of the insertion portion 22.

[0030] The front end member 20 has a through hole 25 parallel to the central axis CX of the piston body 30. The through hole 25 connects an end surface of the protrusion 21 on the front end side and an end surface of the insertion portion 22 on the base end side. In a cross section perpendicular to the central axis CX, the through hole 25 has a circular shape. In a cross section perpendicular to the central axis CX, the center of the through hole 25 and the central axis CX coincide with each other.

[0031] The projection 21 is arranged closer to the front end side than the front end surface 31. The projection 21 includes a surface 26 facing the front end side and an opposite surface 27 facing the front end surface 31.

[0032] The surface 26 of the protrusion 21 is inclined to approach the central axis CX while moving away from the front end surface 31 in the axial direction. In this embodiment, the surface 26 is linear in a cross section including the central axis CX. In other words, the surface 26 has a conical shape with an outer diameter that gradually decreases toward the front end side.

[0033] As in Fig. 1, the surface 26 of the front end member 20 and the opposite surface 62 of the cylinder 6S are substantially parallel to each other.

[0034] In the radiation direction, the surface 26 of the projection 21 is arranged within the outer circumference of the piston body 30. In other words, the projection 21 is provided such that it does not protrude beyond the outer circumference of the piston body 30 in the radiation direction.

[0035] The opposing surface 27 faces the front end surface 31. Viewed in the axial direction, the opposing surface 27 has an annular shape. The opposing surface 27 is flat. The front end surface 31 and the opposing surface 27 are parallel. The front end surface 31 and at least a portion of the opposing surface 27 are in contact with each other.

[0036] The insertion portion 22 has a cylindrical shape. The insertion portion 22 is inserted into the interior space 32. The insertion portion 22 has an outer surface 28 facing an inner surface of the interior space 32. The inner surface of the interior space 32 and at least a portion of the outer surface 28 of the insertion portion 22 are in contact with each other.

[0037] Regarding the through hole 25 of the insertion portion 22, an inner diameter on the base end side is larger than an inner diameter on the front end side. The connecting member 10 on the base side is supported in the through hole 25 of the insertion portion 22. In the following description, a part of the through hole 25 on the base end side, which has an inner diameter capable of accommodating the connecting member 10, is conveniently referred to as "storage space 23."

[0038] The insertion section 22 is arranged around the connecting element 10 and contains deformable sections 24 that are elastically deformable in the radiation direction. The storage space 23 is defined by the inside of the deformable sections 24. As shown in Fig. 3, notches 24N are formed at a base end of the insertion portion 22. A plurality of notches 24N are arranged in the circumferential direction. A deformable portion 24 is disposed between adjacent notches 24N. A plurality of deformable portions 24 are arranged in the circumferential direction. Due to the notches 24N, the deformable portions 24 can elastically deform in the radiation direction.

[0039] Furthermore, at least a part of the inner surface of the storage space 23 has a slope 23T inclined with respect to the central axis CX. The slope 23T is inclined from one end of the storage space 23 on the base end side to the front end side so as to approach the central axis CX. In other words, the slope 23T has a conical shape with an inner diameter that gradually decreases toward the guide side.

[0040] An outer diameter of at least a portion of the connecting member 10 is slightly larger than an inner diameter of the storage space 23. When the connecting member 10 is placed in the storage space 23 and an outer surface of the connecting member 10 comes into contact with the inner surface of the storage space 23, the deformable portions 24 deform outward in the radiation direction. The deformable portions 24 deformed outward in the radiation direction come into contact with the inner surface of the interior space 32 of the piston body 30. When the deformable portions 24 come into contact with the inner surface of the interior space 32 of the piston body 30, the front end member 20 and the connecting member 10 are fixed to the piston body 30.

[0041] An oil passage 29 through which hydraulic oil flows is arranged between the front end surface 31 and at least a part of the opposing surface 27 and between the inner surface of the inner space 32 and at least a part of the outer surface 28 of the insertion portion 22. As shown in Fig. 3, a passage groove 29A is formed on a part of the opposing surface 27. A passage groove 29B is formed on a part of the outer surface 28. The passage groove 29A and the passage groove 29B are connected to each other. The oil passage 29 is defined between the passage groove 29A and the front end surface 31 and between the passage groove 29B and the inner surface of the inner space 32. A base end of the oil passage 29 is connected to the inner passage 33. An inlet 35 is arranged between an outer end of the passage groove 29A in the radiation direction and an outer end of the front end surface 31 in the radiation direction. The hydraulic oil flows into the oil passage 29 through the inlet 35. The hydraulic oil flowing through the oil passage 29 is supplied to an inner passage 4C arranged in the piston shoe 4 via the inner passage 33. The inner channel 4C connects a front end of the spherical portion 4A and a base end of the leg portion 4B.An outlet 36 for hydraulic oil is provided at a base end of the inner channel 4C. The hydraulic oil flowing through the inner channel 4C is guided between the piston shoe 4 and the swash plate 5 via the outlet 36.

[0042] The front end member 20 is less dense than the piston body 30. The front end member 20 contains metal. An example material for the front end member 20 is at least one of cast iron (specific gravity 7.2), zinc (specific gravity 7.2), titanium (specific gravity 4.5), and aluminum (specific gravity 2.7). The front end member 20 may contain synthetic resin. An example material for the front end member 20 is at least one of MC nylon (specific gravity 1.2), polyacetal resin (specific gravity 1.4), ultra-high molecular weight polyethylene (specific gravity 1.0), fluororesin (specific gravity 2.2), polyetheretherketone (specific gravity 1.3), and acrylonitrile-butadiene-styrene copolymer resin (specific gravity 1.1). Note that the front end member 20 may have a density equal to that of the piston body 30.

[0043] Fig. 4 is a perspective view showing the connecting element 10 according to this embodiment. As in Fig. 2 and Fig. As shown in Figure 4, the connecting element 10 is a tubular element. The connecting element 10 is arranged in the storage space 23 of the insertion section 22 in the interior space 32. The outer surface of the connecting element 10 and the inner surface of the storage space 23 face each other.

[0044] At least a part of the outer surface of the connecting member 10 is inclined to approach the central axis CX as it approaches the front end surface 31 in the axial direction.

[0045] In this embodiment, the connecting member 10 includes a cylindrical portion 11 and a tapered portion 12 located at the base end side of the cylindrical portion 11. In the cross section perpendicular to the central axis CX, the outer shape of the tapered portion 12 is larger than that of the cylindrical portion 11.

[0046] The cylindrical portion 11 has an end surface 13 on the front end side. In a cross section parallel to the central axis CX, an outer surface of the cylindrical portion 11 is parallel to the central axis CX. The tapered portion 12 has an end surface 14 on the base end side.

[0047] An outer surface of the tapered portion 12 is inclined to approach the center axis CX from the boundary with the end surface 14 toward the front end side. In other words, the tapered portion 12 has a tapered shape with an outer diameter that gradually decreases toward the front end.

[0048] The outer diameter of at least a part of the tapered portion 12 is larger than the inner diameter of the storage space 23. The outer surface of the tapered portion 12 comes into contact with the slope 23T of the storage space 23.

[0049] The connecting element 10 includes a screw hole 15 parallel to the central axis CX. A threaded groove is formed on an inner surface of the screw hole 15. The screw hole 15 connects the end surface 13 and the end surface 14. In a cross-section perpendicular to the central axis CX, the screw hole 15 is substantially circular. In a cross-section perpendicular to the central axis CX, the center of the screw hole 15 and the central axis CX coincide with each other.

[0050] The connecting member 10 is smaller in density than the piston body 30. The connecting member 10 contains a metal. A material for the connecting member 10 may be the same as or different from the material for the front end member 20. A material for the connecting member 10 is exemplified by at least one of cast iron (specific gravity 7.2), zinc (specific gravity 7.2), titanium (specific gravity 4.5), and aluminum (specific gravity 2.7). The connecting member 10 may contain synthetic resin. An exemplary material for the connecting member 10 is at least one of MC nylon (specific gravity 1.2), polyacetal resin (specific gravity 1.4), ultra-high molecular weight polyethylene (specific gravity 1.0), fluororesin (specific gravity 2.2), polyetheretherketone (specific gravity 1.3), and acrylonitrile-butadiene-styrene copolymer resin (specific gravity 1.1).Note that the connecting element 10 may have a density equal to that of the piston body 30.

[0051] The bolt 8 has a shank disposed in the through hole 25, a threaded front end, and a head. The thread at the front end of the bolt 8 is coupled to the thread groove of the screw hole 15. A part of the through hole 25 is provided with a stepped portion 25D for supporting the head of the bolt 8. <montageverfahren>

[0052] A method for assembling the piston 3 according to this embodiment will be described below. Before the connecting member 10 and the front end member 20 are inserted into the internal space 32, the connecting member 10 and the front end member 20 are connected (temporarily assembled) with the respective bolt 8. In other words, while the slope 23T of each deformable portion 24 of the front end member 20 is wrapped around the outer surface of the tapered portion 12 of the connecting member 10, the shank of the bolt 8 is placed into the through hole 25 of the front end member 20, and the front end of the bolt 8 is screwed into the screw hole 15 of the connecting member 10.

[0053] On the outside of the inner space 32, the connecting element 10 and the front end element 20 are connected with the involved bolt 8. Then, the connecting element 10 and the insertion portion 22 of the front end element 20 are inserted into the inner space 32 from the opening 34. The connecting element 10 is inserted into the inner space 32 such that the tapered portion 12 is positioned closer to the base end side than the cylindrical portion 11. The insertion portion 22 is inserted into the inner space 32 such that the deformable portions 24 are positioned between the outer surface of the connecting element 10 and the inner surface of the inner space 32. The insertion portion 22 is inserted into the inner space 32 such that the front end surface 31 and the opposing surface 27 come into contact with each other.

[0054] In this embodiment, the insertion portion 22 is inserted into the internal space 32 with the slope 23T of each deformable portion 24 arranged around the outer surface of the tapered portion 12. When the insertion portion 22 is placed in the internal space 32, the front end surface 31 of the piston body 30 and the opposing surface 27 of the projection 21 face each other.

[0055] After the insertion portion 22 of the connecting member 10 and the front end member 20 are placed in the internal space 32, the bolt 8 is rotated so that the bolt 8 is screwed into the screw hole 15. By rotating the bolt 8, the front end member 20 is tightened to the connecting member 10, so that the opposing surface 27 approaches the front end surface 31 and the end surface 13 moves toward the front end side.

[0056] When the front end member 20 is tightened onto the connecting member 10 so that the opposing surface 27 approaches the front end surface 31 and the end surface 13 moves toward the front end side, the connecting member 10 moves toward the front end side with respect to the inner surface of the storage space 23.

[0057] The outer diameter of at least a portion of the connecting element 10 is slightly larger than the inner diameter of the storage space 23. In this embodiment, the outer diameter of at least a portion of the tapered portion 12 is larger than the inner diameter of the storage space 23.

[0058] While the outer surface of the tapered portion 12 is in contact with the slopes 23T of the storage space 23, the front end member 20 is tightened onto the connecting member 10, so that the connecting member 10 moves toward the front end side with respect to the inner surface of the storage space 23. Accordingly, the deformable portions 24 are deformed outward in the radiating direction along with the movement of the connecting member 10. The deformable portions 24 deformed outward in the radiating direction come into contact with the inner surface of the inner space 32 of the piston body 30. When the deformable portions 24 come into contact with the inner surface of the inner space 32 of the piston body 30, the front end member 20 and the connecting member 10 are fixed to the piston body 30. <betrieb>

[0059] The operation of the hydraulic pump 1 is described below. When the drive shaft 2 rotates, the cylinder block 6 rotates together with the drive shaft 2 about the rotation axis RX. The rotation of the cylinder block 6 causes the piston 3 placed in the cylinder 6S and the piston shoe 4 connected to the piston 3 to oscillate about the rotation axis RX. The piston shoe 4 oscillates while sliding on the sliding surface 5A of the swash plate 5. While the piston shoe 4 slides on the swash plate 5, the oscillation of the piston shoe 4 causes the piston 3 to reciprocate within the cylinder 6S. The piston 3 moves between the top dead center, which indicates a position where the piston 3 maximally enters the cylinder 6S, and the bottom dead center, which indicates a position where the piston 3 maximally exits the cylinder 6S. The reciprocating movement of the piston 3 changes the displacement defined between the piston 3 and the cylinder 6S.When the inclination angle of the swash plate 5 changes, the capacities of the hydraulic pump 1 change.

[0060] With the rotation of the cylinder block 6, the connection port 61 is connected to at least one of the inlet port 71 and the outlet port 72. When the piston 3 moves from the top dead center to the bottom dead center, the connection port 61 and the inlet port 71 are connected to each other. With the movement of the piston 3 from the top dead center to the bottom dead center, the hydraulic oil in the hydraulic oil tank is sucked into the cylinder 6S via the inlet passage 71H and the inlet port 71. When the piston 3 moves from the bottom dead center to the top dead center, the connection port 61 and the outlet port 72 are connected to each other. With the movement of the piston 3 from the bottom dead center to the top dead center, the hydraulic oil of the cylinder 6S is discharged to the hydraulic oil supply destination via the outlet port 72 and the outlet passage 72H.

[0061] When the inclination angle of the swash plate 5 changes, the reciprocating motion of the piston 3 associated with the rotation of the cylinder block 6 varies, causing a change in the flow rate of the hydraulic oil discharged to the hydraulic oil supply destination via the discharge passage 72H.

[0062] At least a portion of the hydraulic oil of the cylinder 6S flows into the oil passage 29. After passing through the oil passage 29, the hydraulic oil flows into the inner passage 33 of the piston body 30. The hydraulic oil supplied from the inner passage 33 of the piston body 30 to the inner passage 4C of the piston shoe 4 flows through the inner passage 4C and then through the outlet 36, so that the hydraulic oil is supplied between the base end of the leg portion 4B of the piston shoe 4 and the sliding surface 5A of the swash plate 5. Accordingly, even when the base end of the leg portion 4B and the sliding surface 5A of the swash plate 5 come into contact with each other, a frictional force between the piston shoe 4 and the swash plate 5 is prevented from increasing excessively. <wirkung>

[0063] As described above, according to this embodiment, the piston body 30 is provided with the internal space 32, and the front end member 20 is configured to close the opening 34 of the internal space 32. The insertion portion 22 of the front end member 20 is placed in a part of the internal space 32. Such a configuration reduces the weight of the piston 3 while preventing hydraulic oil from infiltrating into the internal space 32. Accordingly, it is possible to reduce the dead volume while reducing the weight of the piston 3. Moreover, the front end member 20 includes the protrusion 21 projecting from the front end surface 31 of the piston body 30 toward the front end side. Such a configuration reduces the dead volume when the piston 3 is located at the top dead center. Accordingly, it is possible to prevent deterioration of the volumetric efficiency of the hydraulic pump 1.

[0064] The surface 26 of the projection 21 is inclined to approach the central axis CX while moving away from the front end surface 31 toward the front end side. As shown in Fig. 1, when the cylinder 6S has the opposing surface 62 inclined with respect to the central axis CX, the shape of the surface 26 is determined to be parallel to the opposing surface 62. Accordingly, the dead volume is reduced.

[0065] The surface 26 of the projection 21 is arranged within the outer circumference of the piston body 30 in the radiation direction. Since the projection 21 does not protrude from the piston body 30 in the radiation direction, the projection 21 is prevented from coming into contact with the inner surface of the cylinder 6S.

[0066] The front end surface 31 is arranged around the opening 34 of the piston body 30, which is connected to the internal space 32. The projection 21 of the front end member 20 includes the opposing surface 27, which is opposite to the front end surface 31. In other words, in this embodiment, the projection 21 has a flange shape extending outward from the insertion portion 22 in the radiation direction. Accordingly, it is possible to sufficiently reduce the dead volume.

[0067] The oil passage 29 is disposed between the front end surface 31 and the opposing surface 27, and between at least a portion of the outer surface of the insertion portion 22 and the inner surface of the inner space 32. Accordingly, the hydraulic oil can flow around the outer periphery of the piston body 30, preventing an excessive temperature rise on the outer periphery of the piston body 30.

[0068] The front end member 20 is smaller in density than the piston body 30. Accordingly, it is possible to reduce the weight of the piston 3 while maintaining the strength of the piston 3.

[0069] The connecting member 10, which is connected to the insertion portion 22 of the front end member 20, is placed in the internal space 32. The insertion portion 22 includes the deformable portions 24 placed around the connecting member 10. The deformable portions 24 are deformed outward in the radiation direction upon contact with the connecting member 10. Accordingly, by simply inserting the connecting member 10 into the deformable portions 24 (within the storage space 23), it is possible to deform the deformable portions 24 outward in the radiation direction and easily fix the connecting member 10, the front end member 20, and the piston body 30.

[0070] The connecting member 10 includes the tapered portion 12 whose outer surface is inclined to approach the central axis CX as it approaches the front end surface 31 in the axial direction. Accordingly, when the connecting member 10 is to be moved toward the front end side to deform the deformable portions 24, it is possible to smoothly move the connecting member 10 and smoothly deform the deformable portions 24.

[0071] The front end member 20 includes the through hole 25 parallel to the central axis CX. The connecting member 10 includes the screw hole 15 formed with the threaded groove. The bolt 8 includes the shank that is placed in the through hole 25 and the front end formed with the thread that connects with the threaded groove. With such a configuration, the front end member 20 can be easily tightened onto the connecting member 10 by simply turning the bolt 8.

[0072] The connecting element 10 is smaller in density than the piston body 30. Accordingly, it is possible to reduce the weight of the piston 3 while maintaining the strength of the piston 3. [Second embodiment]

[0073] A second embodiment will now be described. In the following description, components identical or similar to those of the previous embodiment are denoted by the same reference numerals, and the description thereof will be simplified or omitted.

[0074] Fig. Fig. 5 is a cross-sectional view illustrating an example of a piston 3 according to this embodiment. In the above embodiment, the piston shoe 4 includes the spherical portion 4A, and the piston body 30 includes the space 3H that accommodates the spherical portion 4A. As shown in Fig. 5, a spherical portion 40 may be disposed on a piston body 30. In this case, a piston shoe includes a space in which the spherical portion 40 is supported. [Third Embodiment]

[0075] A third embodiment will now be described. Fig. Fig. 6 is a cross-sectional view illustrating a portion of a front end member 20 according to this embodiment. In the previous embodiments, the surface 26 is linear in cross-section perpendicular to the central axis CX. As shown in Fig. 6, the surface 26 may be curved in a cross-section including the central axis CX. In the cross-section shown in Fig. 6, the surface 26 has an arc shape which protrudes towards the front end side. [Other embodiments]

[0076] In the above embodiments, the pin 8 can be provided with an oil passage. Hydraulic oil can be supplied between the piston shoes and a swash plate via the oil passage arranged in the pin 8.

[0077] In the above embodiments, the front end member 20 has a lower density than the piston body 30, and the connecting member 10 has a lower density than the piston body 30. The front end member 20 may have a density equal to that of the piston body 30. The connecting member 10 may have a density corresponding to that of the piston body 30. Even in these cases, it is possible to reduce the dead volume.

[0078] In the above embodiments, the front end member 20 is fixed to the piston body 30 via the connecting member 10. The connecting member 10 may be omitted. For example, a thread is provided on an outer surface of the insertion portion 22 of the front end member 20, and a thread groove is provided on an inner surface of the inner space 32. When the thread and the thread groove are combined, the front end member 20 and the piston body 30 are fixed to each other. In this case, an oil passage can be formed inside the front end member 20.

[0079] In the above embodiments, the hydraulic pump or hydraulic motor 1 functions as a hydraulic pump. The hydraulic pump or hydraulic motor 1 may function as a hydraulic motor. List of reference symbols 1 HYDRAULIC PUMP (HYDRAULIC PUMP OR MOTOR) 1H HOUSING 2 DRIVE SHAFT 3 PISTONS 3H ROOM 4 PISTON SHOE 4A SPHERICAL PART 4B THIGH SECTION 4C INNER CHANNEL 5 SWASH PLATE 5A SLIDING SURFACE 6 CYLINDER BLOCK 6H CENTER HOLE 6S CYLINDER 7 VALVE PLATE 8 BOLTS 9 BRACKET 10 CONNECTING ELEMENT 11 CYLINDRICAL SECTION 12 Tapered Section 13 END FACE 14 END FACE 15 SCREW HOLE 16 WAREHOUSES 20 FRONT ELEMENT 21 ADVANTAGE 22 INTRODUCTORY SECTION 23 STORAGE SPACE 23T SLOPE 24 DEFORMABLE PART 24N NOTCH 25 THROUGH HOLE 25D GRADUATED SECTION 26 AREA 27 OPPOSITE AREA 28 EXTERIOR AREA 29 OIL PASSAGE 29A Channel groove 29B Channel groove 30 PISTON BODY 31 FRONT END SURFACE 32 INTERIOR 33 INNER CHANNEL 34 OPENING 35 ENTRY 36 OUTLET 40 SPHERICAL SECTION 61 COMMUNICATIONS PORT 61H OPENING 62 OPPOSITE AREA 71 INLET CONNECTION 71H INLET PASSAGE 72 OUTLET CONNECTION 72H OUTLET PASSAGE CX CENTER AXLE RX ROTATION AXIS< / wirkung> < / betrieb> < / montageverfahren> < / kolben>

Claims

[1] Piston (3) for a hydraulic pump or motor, comprising: a piston body (30) containing an interior space (32); a front end member (20) including an insertion portion (22) disposed in the interior space (32) and a projection (21) projecting from a front end surface (31) of the piston body (30); wherein the front end surface (31) is arranged around an opening (34) of the piston body (30) which is connected to the interior (32), and the front end element (20) has an opposite surface (27) facing the front end surface (31); an oil passage (29) arranged between the front end surface (31) and at least a part of the opposing surface (27) and between an inner surface of the inner space (32) and at least a part of an outer surface of the insertion portion (22); and a connecting element (10) placed in the interior (32) and connected to the insertion section (22), wherein the insertion portion (22) includes a deformable portion (24) arranged around the connecting element (10) and configured to deform outwardly in a radiation direction of a central axis (CX) of the piston body (30) upon contact with the connecting element (10). [2] A piston (3) according to claim 1, wherein the projection (21) has a surface (26) inclined to approach the central axis (CX) while becoming further away from the front end surface (31) in an axial direction parallel to the central axis (CX) of the piston body (30). [3] Piston (3) according to claim 1, wherein the projection (21) has a surface (26) arranged within an outer circumference of the piston body (30) in the radiation direction of the central axis (CX) of the piston body (30). [4] Piston (3) according to one of claims 1 to 3, wherein the front end element (20) has a density which is less than or equal to a density of the piston body (30). [5] Piston (3) according to one of claims 1 to 4, wherein the connecting member (10) has an outer surface, at least a part of which is inclined to approach the central axis (CX) of the piston body (30) while approaching the front end surface (31) in an axial direction parallel to the central axis (CX). [6] Piston (3) according to one of claims 1 to 5, wherein the front end element (20) includes a through hole (25) parallel to the central axis (CX) of the piston body (30), the connecting element (10) contains a screw hole (15) formed with a threaded groove, and the piston (3) comprises a bolt (8) having a shaft placed in the through hole (25) and a front end containing a thread connected to the thread groove. [7] Piston (3) according to one of claims 1 to 6, wherein the connecting element (20) has a density which is less than or equal to a density of the piston body (30). [8] Hydraulic pump or motor (1), comprising: a cylinder block (6) containing a cylinder (6S) in which the piston (3) according to any one of claims 1 to 7 is placed; a piston shoe (4) arranged at a base end of the piston (3); and a swash plate (5) arranged to support the piston shoe (4).

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