Swashplate type hydraulic rotary machine

Abstract

The present invention provides a swashplate type hydraulic rotary machine that allows for easy piston manufacturing while reducing the contact pressure on the piston due to contact with the cylinder. [Solution] The swash plate type hydraulic rotary machine comprises a casing 1, a shaft 2 rotatably supported by the casing 1 via bearings 10A and 10B, a cylinder block 3 having a plurality of cylinders 11 and rotating integrally with the shaft 2, a plurality of pistons 4 inserted into the plurality of cylinders 11, a plurality of shoes 5 pivotably connected to the outer ends 4a of the plurality of pistons 4, a swash plate 6 on which the plurality of shoes 5 slide, and a valve plate 7 having low-pressure ports 16 and high-pressure ports 17 that alternately communicate with the plurality of cylinders 11 as the cylinder block 3 rotates. The radial thickness t between the inner circumference of the hollow part of the piston 4 and the cylindrical outer circumference 23 located on the outer circumference side of the hollow part is, when the outer diameter D of the outer circumference 23, 0

Description

Technical Field

[0001] The present invention relates to a swash plate type hydraulic rotary machine.

Background Art

[0002] A swash plate type hydraulic rotary machine includes a casing, a shaft rotatably supported by the casing via a bearing, a cylinder block having a plurality of cylinders and rotating integrally with the shaft, a plurality of pistons inserted into the plurality of cylinders, a plurality of shoes swingably connected to outer end portions of the plurality of pistons, a swash plate on which the plurality of shoes slide, and a valve plate having a low pressure port and a high pressure port that alternately communicate with the plurality of cylinders as the cylinder block rotates. This swash plate type hydraulic rotary machine is used, for example, as a hydraulic pump or a hydraulic motor mounted on construction machinery such as a shovel.

[0003] When the swash plate type hydraulic rotary machine is used as a hydraulic pump, the shaft is rotated by an engine or a motor, and accordingly, the cylinder block and the pistons rotate. Then, the rotational force (revolution force) of the pistons is converted into a moving force by the swash plate, so that the pistons move inside the cylinders. When the piston in the cylinder moves to the swash plate side (in other words, the side opposite to the valve plate), oil (working fluid) is sucked into the cylinder through the low pressure port. After that, when the piston in the cylinder moves to the valve plate side, pressure oil is discharged from the cylinder through the high pressure port.

[0004] When the swash plate type hydraulic rotary machine is used as a hydraulic motor, pressure oil from a pump is supplied to the cylinder through the high pressure port, and the piston in the cylinder moves to the swash plate side. Then, the moving force of the piston is converted into a rotational force by the swash plate, so that the cylinder block and the shaft rotate. Note that as the cylinder block rotates, when the piston in the cylinder moves to the valve plate side, oil is discharged from the cylinder through the low pressure port.

[0005] Due to the relative positions of the piston, shoe, and swash plate, the piston is inclined relative to the cylinder. As a result, a portion of the central part of the piston contacts the opening of the cylinder, and a portion of the inner end of the piston contacts the cylinder. To suppress piston wear, it is preferable to reduce the contact pressure on the piston caused by contact with the cylinder. Patent Document 1 describes a method to increase the contact area with the cylinder and reduce the contact pressure on the piston by forming the outer circumferential surface of the piston in a convex crown shape or with a raised center. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-032767 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the piston described in Patent Document 1 is difficult to manufacture because its crown size (in other words, the difference between the diameters of the piston's ends and the diameter of its center) is very small, ranging from 0.6 to 3.0 μm.

[0008] The object of the present invention is to provide a swashplate type hydraulic rotary machine that allows for easy manufacturing of the piston while reducing the contact pressure on the piston due to contact with the cylinder. [Means for solving the problem]

[0009] To achieve the above object, the present invention provides a swash plate type hydraulic rotary machine comprising: a casing; a shaft rotatably supported by the casing via a bearing; a cylinder block having a plurality of cylinders and rotating integrally with the shaft; a plurality of pistons inserted into the plurality of cylinders; a plurality of shoes swingably connected to outer end portions of the plurality of pistons; a swash plate on which the plurality of shoes slide; and a valve plate having a low-pressure port and a high-pressure port that alternately communicate with the plurality of cylinders as the cylinder block rotates, wherein a radial thickness t between an inner peripheral portion of a hollow portion of the piston and a cylindrical outer peripheral portion located on an outer peripheral side of the hollow portion is formed to satisfy 0<t<D / 8, where D is an outer diameter of the outer peripheral portion. Effects of the Invention

[0010] According to the present invention, it is possible to reduce the contact surface pressure of the piston caused by contact with the cylinder while facilitating the manufacture of the piston. Brief Description of the Drawings

[0011] [Figure 1] It is a cross-sectional view showing the structure of a swash plate type hydraulic pump in one embodiment of the present invention. [Figure 2] It is a cross-sectional view showing the structure of a piston and a shoe in one embodiment of the present invention. [Figure 3] It is a cross-sectional view showing the state of the piston in the cylinder in one embodiment of the present invention. [Figure 4] It is a diagram showing the relationship between the radial thickness of the outer peripheral portion of the piston and the contact surface pressure in one embodiment of the present invention and a comparative example. [Figure 5] It is a cross-sectional view showing the structure of a piston and a shoe in a modified example of the present invention. Modes for Carrying Out the Invention

[0012] One embodiment of the present invention will be described by taking a swash plate type hydraulic pump as an application target of the present invention as an example.

[0013] First, the structure of the swashplate hydraulic pump in this embodiment will be explained using Figure 1. Figure 1 is a cross-sectional view showing the structure of the swashplate hydraulic pump in this embodiment.

[0014] A swashplate hydraulic pump comprises a casing 1, a shaft 2, a cylinder block 3, multiple pistons 4, multiple shoes 5, a swashplate 6, and a valve plate 7. The casing 1 consists of a main casing 8 and a rear casing 9.

[0015] The shaft 2 is rotatably supported by bearings 10A and 10B located in the main casing 8 and rear casing 9. One end of the shaft 2 (the right side in Figure 1) protrudes from the main casing 8 and is connected, for example, to the output shaft of an engine or motor. The shaft 2 rotates when driven by the engine or motor.

[0016] The cylinder block 3 is spline-coupled to the outer circumference of the shaft 2 and rotates integrally with the shaft 2.

[0017] The cylinder block 3 has a plurality of cylinders 11. The plurality of cylinders 11 are spaced apart from each other in the circumferential direction of the cylinder block 3 and extend in the axial direction. A plurality of pistons 4 are inserted into the plurality of cylinders 11.

[0018] Multiple shoes 5 are pivotably connected to the outer ends 4a of multiple pistons 4 (in other words, one end protruding from the cylinder 11; see Figure 2 below). The multiple shoes 5 are also held by retainers 13 that are pivotably supported by retainer guides (bushings) 12. The retainer guides 12 are spline-coupled to the outer circumference of the shaft 2 and have a spring (not shown) between them and the cylinder block 3. The biasing force of the aforementioned spring is transmitted through the retainer guides 12 and retainers 13, pressing the multiple shoes 5 against the swash plate 6. When the multiple shoes 5 rotate together with the cylinder block 3 and pistons 4, they slide on the surface of the swash plate 6.

[0019] A low-pressure flow passage 14 and a high-pressure flow passage 15 are formed in the rear casing 9. The valve plate 7 is attached to the rear casing 9, and has a low-pressure port 16 communicating with the low-pressure flow passage 14 and a high-pressure port 17 communicating with the high-pressure flow passage 15. The low-pressure port 16 and the high-pressure port 17 alternately communicate with the plurality of cylinders 11 as the cylinder block 3 rotates.

[0020] The swash plate 6 is supported on the main casing 8 side, and converts the rotational force (revolution force) of the piston 4 into a moving force. When the piston 4 in the cylinder 11 moves toward the swash plate 6 side (in other words, the side opposite to the valve plate 7), oil (hydraulic fluid) is drawn into the cylinder 11 via the low-pressure flow passage 14 and the low-pressure port 16. Thereafter, when the piston 4 in the cylinder 11 moves toward the valve plate 7 side, pressure oil is discharged from the cylinder 11 via the high-pressure flow passage 15 and the high-pressure port 17.

[0021] Next, the structures of the piston 4 and the shoe 5 in the present embodiment will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view showing the structures of the piston 4 and the shoe 5 in the present embodiment.

[0022] The iron piston 4 has a ball joint portion 19 (specifically, a spherical groove) into which a ball joint portion 18 (specifically, a spherical portion) of the shoe 5 is fitted, and an outer end portion 4a of the piston 4 is crimped. The piston 4 further has an oil flow passage 20 (liquid flow passage) and a communication hole 21A that supply part of the oil in the cylinder 11 described above to the ball joint portion 19. The shoe 5 has a flat surface 22 that slides on the swash plate 6 described above, and a communication hole 21B that supplies the oil supplied to the ball joint portion 19 of the piston 4 to the flat surface 22. The cross-sectional areas of the communication hole 21B, the communication hole 21A, and the oil flow passage 20 increase in that order, and the oil flow passage 20 opens at an inner end portion 4b of the piston 4 (in other words, the other end portion located inside the cylinder 11).

[0023] Incidentally, due to the positional relationship among the piston 4, the shoe 5, and the swash plate 6, the piston 4 is inclined relative to the cylinder 11 as shown in FIG. 3. As a result, a part of the central portion of the piston 4 comes into contact with the opening of the cylinder 11, generating a load F1 on the piston 4. In addition, a part of the inner end portion 4b of the piston 4 comes into contact with the cylinder 11, generating a load F2 on the piston 4. In order to suppress wear and the like of the piston 4, it is preferable to reduce the contact surface pressure of the piston 4 caused by contact with the cylinder 11.

[0024] Accordingly, as a feature of the present embodiment, when the outer diameter of the outer peripheral portion 23, which is located on the outer peripheral side of the oil flow passage 20 that is the hollow portion of the piston 4, is defined as D, the outer peripheral portion 23 is formed such that the radial thickness t between the inner peripheral portion of the oil flow passage 20 and the outer peripheral portion 23 satisfies 0 < t < D / 8. As a result, the outer peripheral portion 23 of the piston 4 is elastically deformed (in particular, the shape of the radial cross section changes), the contact area with the cylinder 11 increases, and the contact surface pressure of the piston 4 decreases. This effect will be described with reference to FIG. 4.

[0025] FIG. 4 is a diagram showing the relationship between the radial thickness t of the outer peripheral portion 23 of the piston 4 and the contact surface pressure in the present embodiment and the comparative example, and shows, for example, a case where the outer diameter D of the piston 4 is 34 mm.

[0026] In the comparative example, the radial thickness t of the outer peripheral portion 23 of the piston 4 is t ≧ D / 8 (for example, t = D / 7.5), and the outer peripheral portion 23 hardly undergoes elastic deformation. Therefore, the contact surface pressure of the piston 4 is relatively large. In contrast, in the present embodiment, the radial thickness t of the outer peripheral portion 23 of the piston 4 is 0 < t < D / 8 (for example, t = D / 8.5, D / 9.5, D / 11, D / 13.5, or D / 17), and the outer peripheral portion 23 is elastically deformed. Therefore, in the order of the aforementioned radial thickness t, the contact area with the cylinder 11 increases, and the contact surface pressure of the piston 4 is reduced.

[0027] The piston of Patent Document 1 has an outer peripheral surface formed in a convex crown shape or a middle-high shape, and the crown amount is as small as 0.6 to 3.0 μm, which makes manufacturing difficult. On the other hand, the piston 4 of the present embodiment only requires reducing the radial thickness t of the outer peripheral portion 23, so manufacturing is easy. Accordingly, while the piston 4 is easy to manufacture, the contact surface pressure of the piston 4 generated by contact with the cylinder 11 can be reduced.

[0028] Further, in the present embodiment, when the radius of the ball joint portion 19 is r and the axial length from the inner end 4b of the piston 4 to the center of the ball joint portion 19 is H, the outer peripheral portion 23 of the piston 4 is formed such that the axial length L of the outer peripheral portion 23 satisfies 0<L<(H-r-t). That is, the outer peripheral portion 23 of the piston 4 and the oil flow passage 20 do not reach the ball joint portion 19. Therefore, the load strength of the ball joint portion 19 can be increased.

[0029] A supplementary explanation is provided for the critical significance that the radial thickness t of the outer peripheral portion 23 of the piston 4 satisfies t<D / 8. The discharged oil of the swash plate type hydraulic pump is accompanied by discharge pressure pulsation caused by the compressibility of the oil, which causes vibration and noise in the casing 1 and the hydraulic piping. More specifically, when the inside of the cylinder 11 switches from low pressure to high pressure, backflow of oil corresponding to the compressed volume occurs from the high-pressure port 17 into the cylinder 11, resulting in a pressure drop in the high-pressure port 17. Eventually, when the internal pressure of the cylinder 11 becomes the same as the pressure of the high-pressure port 17 and the pressure difference disappears, the backflow ceases, and the oil pushed out by the displacement of the piston 4 is discharged. The state in which the pressure in the high-pressure port 17 momentarily drops and immediately recovers repeatedly as described above is referred to as pressure pulsation. A notch or the like is provided in the high-pressure port 17 of the valve plate 7 to moderate the pressure change when the internal pressure of the cylinder 11 switches from the suction pressure to the discharge pressure, thereby reducing the pressure pulsation and suppressing vibration and noise caused by the pressure pulsation. Further, the oil remaining in the cylinder 11 at the top dead center of the stroke of the piston 4 is called a dead volume, which is a factor that increases the volume of oil compressed when the oil in the cylinder 11 is at high pressure, and reducing this dead volume is one of the pressure pulsation reduction methods. Therefore, it is preferable to design the shape of the piston 4 to be solid so as to reduce the dead volume. However, as the pump becomes larger, the mass of the piston 4 increases, and accordingly, the centrifugal force during rotation also increases, and the contact surface pressure between the piston 4 and the cylinder 11 increases. In particular, at the minimum tilt angle during no-load high rotation, the stroke of the piston 4 is very small, which may lead to damage of the piston 4 due to poor lubrication. Therefore, in large-sized pumps, the piston 4 has to be designed to be hollow in order to reduce the mass of the piston 4. Therefore, in order to minimize the increase in pressure pulsation while maintaining the rigidity of the piston 4, in the prior art, the radial thickness t of the outer peripheral portion 23 of the piston 4 is set to satisfy t≧D / 8. In the present invention, the radial thickness t of the outer peripheral portion 23 of the piston 4 is reduced to t<D / 8. Thereby, the contact surface pressure between the piston 4 and the cylinder 11 can be reduced by utilizing the elastic deformation accompanying the reduction in the rigidity of the piston 4. As a result, the risk of seizure of the piston 4 is reduced, and the pump can also cope with higher rotation speeds.

[0030] In the above embodiment, the example described was that the ball joint portion 18 of the shoe 5 is a spherical portion and the ball joint portion 19 of the piston 4 is a spherical groove, but the invention is not limited to this. For example, as shown in the modified example in Figure 5, the ball joint portion 18 of the shoe 5 may be a spherical groove and the ball joint portion 19 of the piston 4 may be a spherical portion. The communication hole 21A of the piston 4 may extend through the ball joint portion 19 to the outer end 4a of the piston 4. In this modified example as well, the above-described effects can be obtained due to the same features as in the above embodiment.

[0031] In the above description, a swashplate hydraulic pump was used as an example of the application of the present invention, but it is not limited to this, and may also be a swashplate hydraulic motor or a swashplate hydraulic rotary machine using a working fluid other than oil. [Explanation of Symbols]

[0032] 1 Casing 2 shafts 3 Cylinder block 4 pistons 4a Outer edge 4b Inner end 5 Multiple shoes 6 Swash plate 7 valve plate 10A, 10B bearings 11 cylinders 16 Low-voltage ports 17 High-voltage ports 18. Ball joint section (first ball joint section) 19. Ball joint section (second ball joint section) 20 Oil flow path (liquid flow path) 23 Outer periphery

Claims

1. A swash plate type hydraulic rotary machine comprising a casing, a shaft rotatably supported in the casing via bearings, a cylinder block having a plurality of cylinders and rotating integrally with the shaft, a plurality of pistons inserted into the plurality of cylinders, a plurality of shoes pivotably connected to the outer ends of the plurality of pistons, a swash plate on which the plurality of shoes slide, and a valve plate having low-pressure ports and high-pressure ports that alternately communicate with the plurality of cylinders as the cylinder block rotates, A swashplate type hydraulic rotary machine characterized in that the radial thickness t between the inner circumference of the hollow portion of the piston and the cylindrical outer circumference located on the outer circumference side of the hollow portion is formed such that 0 < t < D / 8 when the outer diameter D of the outer circumference is equal to the outer diameter D of the outer circumference.

2. In the swashplate type hydraulic rotary machine according to claim 1, The piston has a second ball joint portion into which the first ball joint portion of the shoe engages, and a liquid passage opening at the inner end of the piston to supply a portion of the working fluid in the cylinder to the second ball joint portion. A swashplate type hydraulic rotary machine characterized in that the outer circumference of the piston is located on the outer circumference side of the liquid flow path.

3. In the swashplate type hydraulic rotary machine according to claim 2, A swashplate type hydraulic rotary machine characterized in that the outer circumference of the piston is formed such that, when the radius of the second ball joint is r and the axial length H is the distance from the inner end of the piston to the center of the second ball joint, the axial length L of the outer circumference is 0 < L < (H - r - t).

Images