Swash plate type hydraulic rotary machine

Abstract

To reduce a machine loss caused by the shearing of oil without increasing a leakage flow rate from slide faces of cylinder holes with respect to pistons.SOLUTION: Notches 23 are formed at slide faces between a plurality of cylinder holes 6 and a plurality of pistons 8, and since cross sections of the notches 23 in thickness directions are formed so as to face an oil film portion which is formed into a reverse wedge form in progress directions of the pistons 8 in a discharge stroke out of an oil film between the slide faces of the cylinder holes 6 and the pistons 8, tips of the notches are formed in a region of the slide faces of the cylinder holes 6 which is the nearest a rotation center of a cylinder block 5 in a radial direction of the cylinder block 5. Also, it is preferable that the notches 23 are formed in regions from zero-degree angle up to 180-degree angle of the cylinder holes 6, and from 270-degree angle up to 360-degree angle, more preferably, from zero-degree angle up to 170-degree angle, and from 310-degree angle up to 360-degree angle.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] The present invention relates to a swash plate type hydraulic rotary machine used as a pump or a motor in construction machinery such as a hydraulic excavator, a hydraulic crane, and a wheel loader. [Background technology]

[0002] This type of swash plate type hydraulic rotary machine generally comprises a casing, a rotating shaft rotatably supported within the casing, a cylinder block connected within the casing so as to rotate integrally with the rotating shaft and having a plurality of cylinder holes formed therein that are spaced apart circumferentially and extend in the axial direction, a plurality of pistons inserted reciprocally into each of the cylinder holes in the cylinder block, with one axial end side protruding from the cylinder hole, a plurality of shoes attached to the protruding end portions of each of the plurality of pistons, a swash plate provided within the casing opposite the cylinder block and having a sliding surface opposite the cylinder block against which the plurality of shoes slide, and a retainer positioned between the plurality of shoes and the protruding ends of the plurality of pistons to abut the plurality of shoes against the sliding surface of the swash plate.

[0003] When a swash plate type hydraulic rotary machine functions as a pump, as the cylinder block rotates, the shoes move up on the swash plate, pushing the pistons up inside the cylinder bores and discharging high-pressure oil, and as the shoes move down on the swash plate, they draw oil from the tank. Each piston reciprocates within the cylinder bore in response to the rotation of the cylinder block, allowing for a stable discharge of high-pressure oil. The flow rate of the discharged oil is determined by the rotation speed of the cylinder block and the angle of the swash plate. The greater the angle of the swash plate, the longer the piston's reciprocating distance within the cylinder bore, which allows for an increase in the flow rate.

[0004] The piston may rotate within the cylinder bore, so the piston has a cylindrical shape and the cylinder bore has a cylindrical bore shape.

[0005] In such swash plate type hydraulic rotary machines, Patent Documents 1 and 2 describe a machine in which grooves (notches) are formed on the sliding surface of the cylinder bore to prevent seizure between the cylinder bore and the piston and improve durability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-209919 [Patent Document 2] Japanese Patent Application Publication No. 3-189375 Summary of the Invention [Problem to be solved by the invention]

[0007] The sliding surfaces of the cylinder bore and the piston act as a seal to prevent high-pressure oil from leaking from the shoe-side end of the cylinder bore. Oil is present between the cylinder bore and the piston, and this oil acts as a lubricant, allowing the piston to reciprocate within the cylinder bore.

[0008] When a piston is pushed into a cylinder bore, mechanical loss occurs due to shearing of the oil between the cylinder bore and the piston. Enlarging the gap between the cylinder bore and the piston to reduce the shear area of ​​the oil film is an effective way to reduce this loss. One possible method for enlarging the gap is to form a groove (notch) on the sliding surface of the cylinder bore that slides against the piston, as described in Patent Documents 1 and 2.

[0009] However, in both the technologies of Patent Documents 1 and 2, grooves are formed in the locations where high pressure is generated in the oil on the sliding surface in order to prevent seizure between the cylinder bore and the piston. When grooves are formed in this manner, high-pressure oil flows out through the grooves, increasing the leakage flow rate and causing a problem of reduced efficiency as a swash plate type hydraulic rotary machine.

[0010] The present invention has been made in consideration of these problems, and its purpose is to provide a highly efficient swash plate type rolling machine that reduces mechanical loss due to oil shear without increasing the leakage flow rate from the sliding surface of the cylinder bore against the piston. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention provides a swash plate type hydraulic rotary machine comprising: a casing; a shaft rotatably accommodated within the casing; a cylindrical cylinder block provided within the casing to rotate in conjunction with rotation of the shaft, the cylinder block having a plurality of cylinder bores that are cylindrical bores arranged spaced apart from one another along the circumferential direction of the shaft and each extending in the axial direction of the shaft; a plurality of pistons that are reciprocally inserted into the cylinder bores of the cylinder block, with one axial end side protruding from the cylinder bore; a plurality of shoes attached to the protruding end portions of the plurality of pistons; and a swash plate provided within the casing opposite the cylinder block in the axial direction of the shaft, the swash plate having a sliding surface facing the cylinder block on which the plurality of shoes slide, the sliding surface against which the plurality of shoes slide, wherein a notch is formed on the sliding surface with the piston in each of the plurality of cylinder bores, the notch extending axially from a position on the shoe side of the sliding surface toward the axial direction of the cylinder bore and having a width in the circumferential direction of the sliding surface, When the circumferential position of the sliding surface of the cylinder bore is defined as 0 degree and 360 degrees on the innermost circumferential side of the cylinder block, and as 180 degrees on the outermost circumferential side, Each of the notches is The sliding surface of the cylinder bore is within the range of 0 to 180 degrees and 270 to 360 degrees. The cylinder bore is configured to be formed in a region that opens at an end surface of the cylinder block in the axial direction of the cylinder bore. Furthermore, in order to achieve the above object, the present invention provides a cylinder block including a casing, a shaft rotatably accommodated within the casing, a cylindrical cylinder block provided within the casing to rotate in conjunction with the rotation of the shaft, the cylinder block having a plurality of cylinder holes that are cylindrical holes and are arranged spaced apart from one another along the circumferential direction of the shaft and each extending in the axial direction of the shaft, a plurality of pistons that are reciprocally inserted into the cylinder holes of the cylinder block, one axial end side of which protrudes from the cylinder holes, a plurality of shoes attached to the protruding end portions of the plurality of pistons, and a plurality of pistons that are arranged to extend in the axial direction of the shaft. a swash plate provided in the casing opposite the piston block, the swash plate having a sliding surface opposite the cylinder block on which the plurality of shoes slide, wherein the sliding surface with the piston in each of the plurality of cylinder bores has a notch extending from a position on the shoe side of the sliding surface toward the axial direction of the cylinder bore and having a width in the circumferential direction of the sliding surface, the notch being formed in such a manner that it opens at an end face of the cylinder block in the axial direction of the cylinder bore in an area including an area of ​​the sliding surface of the cylinder bore nearest to the center of rotation of the cylinder block in the radial direction of the cylinder block, The notches each have a width in the circumferential direction of the cylinder bore and a depth in the radial direction of the cylinder bore that is constant in the axial direction of the cylinder bore, and the bottom surface of the notch is formed in a shape that forms a part of a cylindrical surface. The configuration is do.

[0012] In this way, a notch is formed on the sliding surface of each of the plurality of cylinder bores that slides against the piston, extending from a position on the shoe side of the sliding surface toward the axial direction of the cylinder bore and having a width in the circumferential direction of the sliding surface, When the circumferential position of the sliding surface of the cylinder bore is defined as 0 degrees and 360 degrees on the innermost circumferential side of the cylinder block, and as 180 degrees on the outermost circumferential side, The notches are formed in the ranges of 0 to 180 degrees and 270 to 360 degrees of the sliding surface of the cylinder bore so as to open at the end surface of the cylinder block in the axial direction of the cylinder bore. Alternatively, the notch may be formed in a region including the region of the sliding surface of the cylinder bore closest to the center of rotation of the cylinder block in the radial direction of the cylinder block, so as to open at the end surface of the cylinder block in the axial direction of the cylinder bore. This expands the gap between the piston and the cylinder bore at the sliding surface of the cylinder bore where an inverted wedge-shaped oil film is formed, reducing mechanical loss due to oil shear. Also, because the inverted wedge-shaped oil film is at low pressure, it is possible to suppress an increase in the amount of oil leakage from the sliding surface. As a result, mechanical loss due to oil shear can be reduced without increasing the amount of oil leakage from the sliding surface, and the mechanical efficiency of the swash plate rolling machine can be improved. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a highly efficient swash plate type rolling machine that reduces mechanical loss due to oil shearing without increasing the amount of leakage from the sliding surface of the cylinder bore against the piston. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing an embodiment of a swash plate type hydraulic rotary machine of the present invention. [Figure 2A] FIG. 10 is a schematic diagram of a sliding portion via an oil film, showing the state of oil when the cross-sectional shape of the oil film in the thickness direction is wedge-shaped in the direction of travel of the moving flat plate. [Figure 2B] FIG. 10 is a schematic diagram of a sliding portion via an oil film, showing the state of oil when the cross-sectional shape of the oil film in the thickness direction is an inverted wedge shape in the direction of travel of the moving flat plate. [Figure 3] 2 is a cross-sectional view illustrating the operation of a cylinder bore and a piston in the swash plate type hydraulic rotary machine shown in FIG. 1. FIG. [Figure 4] FIG. 1 is a perspective view of a cylinder block of a general swash plate type hydraulic rotary machine. [Figure 5] FIG. 1 is a diagram showing a front view of a cylinder block of a general swash plate type hydraulic rotary machine as seen from the swash plate side, and a cross-sectional view taken along line AA of the front view. [Figure 6] This is a front view and a cross-sectional view of a cylinder block similar to Figure 5, and shows the contact position between the piston and the shoe side of the cylinder bore and the low-pressure oil film portion (thick line) during the pump discharge stroke under Condition 1, which does not take into account the influence of centrifugal force. [Figure 7] 7 is a diagram showing the pressure distribution of the oil film on the sliding surface, and the shoe-side contact position and piston end face-side contact position of the piston and cylinder bore, with the sliding surface of the cylinder bore shown in FIG. 6 expanded. [Figure 8] This is a front view of a cylinder block similar to the front view of the cylinder block on the left side of Figure 5, and shows the contact position between the piston and the shoe side of the cylinder bore, and the oil film portion (thick line) where pressure is low, during the pump discharge stroke under condition 2, in which centrifugal force acts on the piston and the shoe. [Figure 9] 9 is a diagram showing the pressure distribution of the oil film on the sliding surface, and the shoe-side contact position and piston end-face-side contact position of the piston and cylinder bore, with the sliding surface of the cylinder bore shown in FIG. 8 expanded. [Figure 10] This is a front view of a cylinder block similar to the cylinder block on the left side of Figure 5, showing the contact position between the piston and the shoe side of the cylinder bore, and the oil film portion (thick line) where pressure is low, during the pump discharge stroke under Condition 3, where the swash plate angle and discharge pressure are small and centrifugal force is dominant. [Figure 11] 11 is a diagram showing the pressure distribution of the oil film on the sliding surface, and the shoe-side contact position and piston end face-side contact position of the piston and cylinder bore, with the sliding surface of the cylinder bore shown in FIG. 10 expanded. [Figure 12] This figure shows a front view of a cylinder block similar to the cylinder block on the left side of Figure 5, with the contact position between the piston and the shoe side of the cylinder bore added for condition 2 shown in Figure 8, and the oil film portion (thick line) where pressure is always low for conditions 2 and 3 shown in Figures 8 and 10. [Figure 13] 13 is a view similar to FIG. 9 showing the sliding surface of the cylinder bore shown in FIG. 12 developed, illustrating the maximum angle range of notching in the low pressure oil film region and the notch formed as wide as possible. [Figure 14] FIG. 4 is a diagram showing a range in which a notch is formed in the axial direction of a cylinder bore. [Figure 15] 1 is a perspective view of a cylinder block of a swash plate type hydraulic rotary machine according to a first embodiment of the present invention. [Figure 16] 1 is a diagram showing a front view of a cylinder block of a swash plate type hydraulic rotary machine according to a first embodiment of the present invention, as seen from the swash plate side, and a cross-sectional view taken along line AA of the front view. FIG. [Figure 17] 1 is a perspective view of a cylinder block of a swash plate type hydraulic rotary machine according to a first embodiment of the present invention; [Figure 18] 1 is a front view of a cylinder block of a swash plate type hydraulic rotary machine according to a first embodiment of the present invention, seen from the swash plate side, and a cross-sectional view taken along line AA of the front view. FIG. [Figure 19] FIG. 4 is a perspective view of a cylinder block of a swash plate type hydraulic rotary machine according to a second embodiment of the present invention. [Figure 20] FIG. 10 is a diagram showing a front view of a cylinder block of a swash plate type hydraulic rotary machine according to a second embodiment of the present invention, as viewed from the swash plate side, and a cross-sectional view taken along line AA of the front view. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A swash plate type hydraulic rotary machine according to an embodiment of the present invention will now be described with reference to the drawings.

[0017] First, the configuration of the swash plate type hydraulic rotary machine common to each embodiment will be described with reference to FIGS. 1, 2 and 3, and then the characteristic configuration of each embodiment will be described in detail for each embodiment.

[0018] ~Configuration of swash plate type hydraulic rotating machine~ FIG. 1 is a cross-sectional view showing an embodiment of a swash plate type hydraulic rotary machine of the present invention.

[0019] The swash plate type hydraulic rotary machine 1 shown in FIG. 1 includes a hollow casing 2 composed of a front casing 3a and a rear casing 3b, a shaft 4 as a rotating shaft rotatably accommodated within the casing 2 via bearings 13a and 13b, and a cylindrical cylinder block 5 connected to the shaft 4 via splines 15 so as to rotate integrally with the rotation of the shaft 4 within the casing 2. A plurality of cylinder bores 6 are formed in the cylinder block 5 and arranged along the circumferential direction of the shaft 4. The cylinder bores 6 are spaced apart from one another in the circumferential direction of the shaft 4 (the rotational direction of the cylinder block 5), and are cylindrical holes formed to extend in the axial direction of the shaft 4. A piston 8 is inserted and arranged in each cylinder bore 6 so as to be able to reciprocate. A shoe 9 is swingably attached to the end of each piston 8 protruding from the cylinder bore 6 by a spherical joint SJ, and the base surface of this shoe 9 (the surface opposite the piston 8) is in slidable contact with the surface of a swash plate 10 that is tiltably held in the front casing 3a. In other words, the swash plate 10 is provided inside the front casing 3a facing the cylinder block 5 in the axial direction of the shaft 4, and the base surface of each shoe 9 slides on the surface (sliding surface) facing the cylinder block 5. The retainer 11 is made of an annular flat plate that is positioned between each shoe 9 and the protruding end of each piston 8 and is inserted onto the shaft 4, and has a plurality of insertion holes 11a formed around its circumferential direction, through which each shoe 9 and each piston 8 is inserted. A shaft 4 is inserted into the end of the central shaft portion of the cylinder block 5 on the swash plate 10 side, and a retainer guide 12 is attached via a spring 14. The retainer 11 is pressed from the cylinder block 5 by the outer surface of the retainer guide 12 via the pressure spring 14, thereby pressing the base surface of the shoe 9 against the sliding surface of the swash plate 10 and preventing the shoe 9 from moving irregularly during operation.

[0020] On the other hand, a valve plate 7, on which the cylinder block 5 slides, is fixed to the rear casing 3b, and this valve plate 7 has high-pressure ports and low-pressure ports (not shown) that alternately communicate with the multiple cylinder holes 6 of the cylinder block 5.

[0021] Therefore, in the swash plate type hydraulic rotary machine 1 of this example, when the shaft 4 is driven to rotate by a prime mover (not shown), the cylinder block 5 rotates integrally with the shaft 4, and in response to this, the shoes 9 rotate while sliding on the swash plate 10, causing the pistons 8 to reciprocate within the cylinder bores 6. When the pistons 8 extend, hydraulic oil supplied from the low-pressure port of the valve plate 7 is sucked into the cylinder bores 6, and when the pistons 8 retract, the hydraulic oil sucked into the cylinder bores 6 is compressed by the pistons 8, and the compressed hydraulic oil is discharged from the high-pressure port of the valve plate 7, thereby functioning as a hydraulic pump.

[0022] In addition, in this swash plate type hydraulic rotary machine 1, hydraulic oil supplied from the high-pressure port of the valve plate 7 flows into the cylinder bore 6, causing the piston 8 to reciprocate within the cylinder bore 6. As the piston 8 reciprocates, each shoe 9 rotates while sliding on the swash plate 10, causing the cylinder block 5 to rotate, and the shaft 4 rotates integrally with the rotation of the cylinder block 5, so that the machine also functions as a hydraulic motor.

[0023] ~Invention Principles~ 2A and 2B are schematic diagrams of the sliding part via an oil film, and FIG. 2A shows the state of oil when the cross-sectional shape of the oil film in the thickness direction is wedge-shaped in the direction of movement of the moving flat plate 17, and FIG. 2B shows the state of oil when the cross-sectional shape of the oil film in the thickness direction is inverted wedge-shaped in the direction of movement of the moving flat plate 17.

[0024] When oil 18 is interposed between a stationary plate 16 and an opposing moving plate 17, if the cross-sectional shape of the oil film in the thickness direction is a wedge shape (a) with a wide gap in the direction of movement of the moving plate 17, as the moving plate 17 moves, the oil 18 from the wide gap is pushed into the narrowing gap, and the oil film pressure distribution 19 rises as the gap narrows. This causes a separation force to act on the stationary plate 16 and the moving plate 17, making it difficult for solid contact to occur.

[0025] On the other hand, if the cross-sectional shape of the oil film in the thickness direction is an inverted wedge shape (b) where the gap in the moving direction of the moving plate 17 is narrow, no separation force is generated by the oil film pressure. Also, the gap may suddenly expand, resulting in low pressure and causing cavitation 20.

[0026] Whether the cross-sectional shape of the oil film in the thickness direction is a wedge shape (a) or an inverted wedge shape (b), mechanical loss occurs due to shearing of the oil present on the sliding surface. Enlarging the gap and reducing the shear area of ​​the oil film is an effective way to reduce this loss. In the wedge-shaped region of the cylinder bore 6 of the swash plate-type hydraulic rotating machine 1, the oil film does not have this effect, preventing solid contact with the piston 8 due to the separation force caused by the oil film pressure. However, in the inverted wedge-shaped region, the oil film does not have this effect, and only mechanical loss occurs due to shearing of the oil, as described above. By forming a notch on the sliding surface in this region, the shear area of ​​the oil film is reduced, thereby reducing mechanical loss due to shearing of the oil film. Furthermore, because the inverted wedge-shaped oil film portion is under low pressure, the increase in leakage flow rate from the sliding surface can also be suppressed.

[0027] Figure 3 is a cross-sectional view illustrating the operation of the cylinder and piston in the swash plate-type hydraulic rotary machine 1 shown in Figure 1. During the discharge stroke, when the cylinder block 5 rotates and the cylinder bore 6 functions as a pump to discharge high-pressure oil, the shoe 9 moves up the sliding surface of the swash plate 10 in the direction indicated by the white arrow, forcing the piston 8 into the cylinder bore 6. At this time, the upper surface of the piston 8 receives a reaction force from the high-pressure oil, and the base surface of the shoe 9 is pressed against the sliding surface of the swash plate 10. Due to sliding friction with the sliding surface of the swash plate 10, the shoe 9 receives a force in the opposite direction to the shoe's forward movement, as indicated by the black arrow. More precisely, the shoe 9 receives a force in the downward direction of the inclination of the sliding surface of the swash plate 10. Here, the inclination direction of the sliding surface of the swash plate 10 is defined as the direction in which the inclination angle of the sliding surface of the swash plate 10 is greatest (the inclination direction of the sliding surface of the swash plate 10 as viewed in Figure 1). 3, the gap between the piston 8 and the sliding surface of the cylinder bore 6 narrows on the shoe 9 side on the downward side of the inclination of the sliding surface of the swash plate 10 (the side indicated by the black arrow), and the gap between the piston 8 and the sliding surface of the cylinder bore 6 narrows on the piston end face side on the upward side of the inclination of the sliding surface of the swash plate 10 (the side indicated by the white arrow). As a result, a high-pressure oil film 21 is formed on the sliding surface of the cylinder bore 6 on the downward side of the inclination of the sliding surface of the swash plate 10 (the side indicated by the black arrow), whose cross section in the thickness direction is wedge-shaped in the direction of movement of the piston 8. A low-pressure oil film 22 is formed on the upward side of the inclination of the sliding surface of the swash plate 10 (the side indicated by the white arrow), whose cross section in the thickness direction is inverted wedge-shaped in the direction of movement of the piston 8. Furthermore, on the downward inclination side (black arrow side) of the sliding surface of the swash plate 10, on the shoe side, the sliding surface of the cylinder bore 6 comes into contact with the piston 8 at a location indicated as "contact position Ca," and on the upward inclination side (white arrow side) of the sliding surface of the swash plate 10, on the piston end face side, the sliding surface of the cylinder bore 6 comes into contact with the piston 8 at a location indicated as "contact position Cb."

[0028] In the above explanation, the wedge-shaped oil film 21 is formed on the inclined upward side of the sliding surface of the swash plate 10, and the inverted wedge-shaped oil film 22 is formed on the inclined downward side of the sliding surface of the swash plate 10. However, in the actual swash plate type hydraulic rotary machine 1, the cylinder block 5 rotates at high speed, so that centrifugal force acts on the pistons 8 and shoes 9, displacing the shoes 9 toward the outer periphery of the cylinder block 5. Therefore, as shown in Figure 8, which will be described later, the area of ​​the wedge-shaped oil film 21 is formed toward the outer periphery of the cylinder block 5, and the area of ​​the inverted wedge-shaped oil film 22 is formed toward the Oil film 22 area is displaced in the inner circumferential direction.

[0029] On the other hand, the swash plate type hydraulic rotary machine 1 is a variable displacement machine in which the swash plate 10 is held so as to be tiltable, so the angle of the sliding surface of the swash plate 10 changes during operation of the machine 1. The discharge pressure of the machine 1 also changes during operation. Therefore, the action of centrifugal force on the pistons 8 and shoes 9 changes depending on the angle of the swash plate 10 and the frictional force between the shoes 9 and the swash plate 10, which is based on the oil pressure (discharge pressure) in the cylinder bores 6. When the angle of the swash plate 10 is small or the discharge pressure is low, the frictional force also becomes small, so the centrifugal force becomes dominant, and the wedge-shaped oil film 21 region moves close to the outermost position of the cylinder block 5, as shown in Figure 10, which will be described later.

[0030] FIG. 4 is a perspective view of a cylinder block of a typical swash plate type hydraulic rotary machine, and FIG. 5 is a front view of the cylinder block as seen from the swash plate side and a cross-sectional view taken along line AA of the front view.

[0031] As shown in FIGS. 4 and 5, the sliding surface of the cylinder bore 6 with the piston 8 is cylindrical and generally has no notch.

[0032] Figure 6 is a front view and cross-sectional view of a cylinder block similar to Figure 5, and adds to the front view of the cylinder block the contact position Ca between the piston 8 and the cylinder bore 6 on the shoe side, and the oil film portion (thick line) where pressure is low, during the pump discharge stroke under condition 1, where the effect of centrifugal force is not taken into account.

[0033] In the front view on the left side of FIG. 6, a small black oval indicates the contact position Ca between the piston 8 and the cylinder bore 6 on the shoe 9 side during the pump discharge stroke described above.

[0034] As explained in Fig. 3, when the piston 8 is subjected to a force in the inclined direction of the sliding surface of the swash plate 10 due to sliding friction with the sliding surface of the swash plate 10 during the pump discharge stroke, the piston 8 contacts the sliding surface of the cylinder bore 6 at the shoe-side contact position Ca on the downward side of the inclined sliding surface of the swash plate 10. Here, assuming that the inclination direction of the sliding surface of the swash plate 10 is constant and that no centrifugal force acts on the piston 8 and the shoe 9, the shoe-side contact position Ca also becomes constant, and as shown by the black oval in Fig. 6, the contact position Ca faces downward in the drawing (the downward side of the inclined sliding surface of the swash plate 10) throughout the entire range of the pump discharge stroke.

[0035] Here, if the circumferential position of the sliding surface of the cylinder bore 6 is defined as 0 degrees and 360 degrees on the innermost side of the cylinder block 5, and as 180 degrees on the outermost side, when the contact position Ca faces the downward inclination side of the sliding surface of the swash plate 10 throughout the entire range of the pump discharge stroke, the contact position Ca changes within a range from 180 degrees at bottom dead center to 0 degrees (360 degrees) at top dead center.

[0036] In addition, a high-pressure oil film 21 (see Figure 3) is formed on the side of contact position Ca, whose cross-sectional shape in the thickness direction shown in Figure 3 is wedge-shaped in the direction of movement of piston 8, and a low-pressure oil film 22 (see Figure 3) is formed in the portion indicated by thick lines T sandwiching contact position Ca, whose cross-sectional shape in the thickness direction is inverted wedge-shaped in the direction of movement of piston 8.

[0037] Figure 7 shows the oil film pressure distribution on the sliding surface of the cylinder bore 6 at the position indicated by the symbol M in Figure 6, as well as the shoe-side contact position Ca and the piston end face-side contact position Cb between the piston 8 and the cylinder bore 6. Position M is approximately the middle of the discharge stroke.

[0038] Contact position Cb on the piston end face side of the piston 8 and cylinder bore 6 is located approximately 180 degrees away from contact position Ca on the shoe side. Also, as mentioned above, the oil film on the sliding surface forms a high-pressure wedge shape on the side of contact position Ca on the shoe side, whereas the oil film on the sliding surface forms a low-pressure inverted wedge shape on the side of contact position Cb on the end face side of the piston 8. Therefore, as shown without hatching in Figure 7, even if the pressure inside the cylinder bore 6 is high, the oil film pressure drops sharply in the inverted wedge-shaped region.

[0039] Furthermore, during the pump discharge stroke, the contact position Ca on the shoe 9 side varies within a range of 180 degrees to 360 degrees as described above, and the contact position Cb on the piston end face side, which is approximately 180 degrees shifted from the contact position Ca on the shoe side, varies within a range of 0 degrees to 180 degrees.

[0040] Figure 8 is a front view of a cylinder block similar to the cylinder block on the left side of Figure 5, and shows the contact position Ca between the piston 8 and the shoe side of the cylinder bore 6, as well as the oil film portion where pressure is low (thick line), during the pump discharge stroke under condition 2 in which centrifugal force acts on the piston and the shoe. Figure 9 is a diagram showing the pressure distribution of the oil film on the sliding surface, the shoe side contact position Ca and the piston end face side contact position Cb between the piston 8 and the cylinder bore 6, developed on the sliding surface of the cylinder bore 6 at the position indicated by symbol M in Figure 8.

[0041] Figure 6 assumes that there is no centrifugal force, but in reality, contact position Ca moves toward the outer periphery of cylinder block 5 due to the centrifugal force acting on piston 8 and shoe 9. The effect of this centrifugal force also varies depending on the angle of swash plate 10 and the frictional force between shoe 9 and swash plate 10, which is generated based on the oil pressure (discharge pressure) inside cylinder bore 6. Therefore, when the swash plate angle is small or the discharge pressure is low, the frictional force between shoe 9 and swash plate 10 is also small, and the effect of centrifugal force becomes greater. As contact position Ca moves, the region of low oil film pressure (the inverted wedge-shaped oil film portion), indicated by the thick line T in Figure 8, also moves.

[0042] Also, as shown in Figure 9, during the pump discharge stroke, the contact position Ca on the shoe 9 side changes within a range from 180 degrees to less than 360 degrees, and the contact position Cb on the end face side of the piston 8 also changes within a range from 0 degrees to less than 180 degrees.

[0043] More specifically, due to centrifugal force acting on the piston 8 and shoe 9 and friction between the shoe 9 and the swash plate 10, the range of movement of the shoe-side contact position Ca on the high-pressure side is 180 degrees at bottom dead center and approximately 300 degrees at top dead center, and the contact position Ca changes within this range of 180 degrees to approximately 300 degrees.

[0044] As the movement range of the contact position Ca on the shoe 9 side changes, the contact position Cb on the end face side of the piston 8 also changes within an angular range that is approximately 180 degrees off from the contact position Ca on the shoe side, and the region where no solid contact occurs on the shoe side and an inverted wedge-shaped low-pressure oil film is formed is in the ranges of 0 to 180 degrees and 300 to 360 degrees excluding the movement range of the contact position Ca on the shoe side.

[0045] Figure 10 is a front view of a cylinder block similar to the cylinder block on the left side of Figure 5, and shows the contact position Ca between the piston 8 and the shoe side of the cylinder bore 6, as well as the low-pressure oil film portion (thick line) during the pump discharge stroke under Condition 3, where the swash plate angle and discharge pressure are small and centrifugal force is dominant. Figure 11 is a diagram showing the pressure distribution of the oil film on the sliding surface, as well as the contact position Ca between the piston 8 and the cylinder bore on the shoe side and the contact position Cb on the piston end face side, developed on the sliding surface of the cylinder bore 6 at the position indicated by symbol M in Figure 10.

[0046] When the angle of the swash plate 10 or the discharge pressure is small and centrifugal force is dominant, the contact position Ca between the piston 8 and the shoe 9 side of the cylinder bore 6 moves close to the outermost position of the cylinder block 5, and the contact position Ca is always located near 180 degrees. Furthermore, during the pump discharge stroke, the contact position Ca on the shoe 9 side hardly changes from near 180 degrees, and the contact position Cb on the piston end face side also hardly changes from near 0 degrees (360 degrees).

[0047] Figure 12 is a front view of a cylinder block similar to the cylinder block on the left side of Figure 5, with the contact position Ca between the piston 8 and the cylinder bore 6 on the shoe side under condition 2 shown in Figure 8, and the oil film portion (thick line) where pressure is always low under conditions 2 and 3 shown in Figures 8 and 10. Figure 13 is a view similar to Figure 9, showing the sliding surface of the cylinder bore 6 at the position indicated by the symbol M in Figure 12, developed, and showing the maximum angle range of notch in the low-pressure oil film region, and the notch formed as wide as possible.

[0048] In the case of condition 2 in Figure 8, as mentioned above, the shoe-side contact position Ca on the high-pressure side during the pump discharge stroke varies within a range of approximately 180 to 300 degrees, and the region where no solid contact occurs on the shoe side and an inverted wedge-shaped low-pressure oil film is formed is within the ranges of 0 to 180 degrees and 300 to 360 degrees, excluding the range of movement of the shoe-side contact position Ca. Therefore, if a notch is formed within this range, it is possible to reduce mechanical loss without increasing the leakage flow rate.

[0049] Here, the difference in radius (gap) between the piston 8 and the cylinder bore 6 is small, on the order of microns, and the range of about 10 degrees before and after the contact position Ca is the region where the oil film pressure is high. For this reason, the range of cutout in the region where the inverted wedge-shaped low-pressure oil film is formed, excluding the movement range of the contact position Ca on the shoe side, is preferably between 0 and 170 degrees, or between 310 and 360 degrees, taking that 10 degrees into consideration.

[0050] 10, as described above, the contact position Ca on the shoe 9 side during the pump discharge stroke remains almost constant at around 180 degrees. Therefore, the cutout range excluding the contact position Ca on the shoe side is preferably between 0 and 170 degrees, or between 190 and 360 degrees, taking into account the above 10 degrees.

[0051] Therefore, the ranges where conditions 2 and 3 overlap and where chipping always occurs at low pressure are the ranges of 0 to 170 degrees and 310 to 360 degrees.

[0052] Furthermore, the position of 300 degrees at top dead center within the range of movement of contact position Ca under condition 2 further varies depending on the influence of the frictional force and centrifugal force between the shoe 9 and the swash plate 10. For example, if the frictional force between the shoe 9 and the swash plate 10 is large, the position of contact position Ca near top dead center may be near 270 degrees, which is on the opposite side to the rotational direction of the cylinder block 5 (the direction of movement of the shoe 9).

[0053] On the other hand, even in the range of about 10 degrees before and after the contact position Ca, which is the region where the oil film pressure is high as described above, the range in which the oil film becomes high pressure may be smaller or larger than the above 10 degrees depending on the difference in radius between the piston 8 and the cylinder bore 6 and the hardness of the contact surfaces of the piston 8 and the cylinder bore 6.

[0054] For this reason, depending on the model, the maximum range of cutout is between 0 and 180 degrees and between 270 and 360 degrees.

[0055] The present invention was made based on the above findings, and when forming notches on each of the sliding surfaces between multiple cylinder bores 6 and multiple pistons 8, extending from the shoe side of the sliding surface toward the axial inward direction of the cylinder bore 6, the notches are formed so as to face the oil film portion between the sliding surface of the cylinder bore 6 and the piston 8, whose cross-sectional shape in the thickness direction is an inverted wedge shape in the direction of movement of the piston 8 during the discharge stroke.

[0056] In other words, each of the notches is formed in an area including the area of ​​the sliding surface of the cylinder bore 6 that is closest to the center of rotation of the cylinder block 5 in the radial direction of the cylinder block 5 .

[0057] By forming such a notch, the clearance between the piston 8 and the cylinder bore 6 is enlarged at the sliding surface portion of the cylinder bore 6 where an inverted wedge-shaped oil film is formed, thereby reducing mechanical loss due to oil shear. Also, because the inverted wedge-shaped oil film portion is at low pressure, an increase in the amount of oil leakage from the sliding surface can be suppressed. As a result, mechanical loss due to oil shear can be reduced without increasing the amount of oil leakage from the sliding surface, and the mechanical efficiency of the swash plate rolling machine can be improved.

[0058] Furthermore, in the present invention, the notches are preferably formed in the ranges of 0 to 180 degrees and 270 to 360 degrees, and more preferably in the ranges of 0 to 170 degrees and 310 to 360 degrees.

[0059] As an example, dotted lines in Figure 13 show notches formed in the ranges of 0 to 170 degrees and 310 to 360 degrees so as to face the oil film portion of the inverted wedge region where pressure is low. By forming such wide notches, the effect of reducing mechanical loss is maximized.

[0060] FIG. 14 shows the structure of a notch (for example, a notch 23 described later). In the cylinder axial direction 1 is a diagram showing the formation range. If the notch opens into the cylinder chamber on the end face side of the piston 8 at bottom dead center, when the piston 8 is furthest removed from the cylinder bore 6, high-pressure oil in the cylinder chamber may leak through the notch, increasing the leakage flow rate. Therefore, the formation range of the notch in the cylinder axial direction needs to be from the shoe-side end of the cylinder bore 6 to the end face of the piston 8 when the piston 8 is at the position furthest removed from the cylinder bore 6 (i.e., when the piston 8 is at bottom dead center).

[0061] As described above, in the present invention, the notch 23 is formed so that the cross-sectional shape in the thickness direction of the oil film between the sliding surface of the cylinder bore 6 and the piston 8 faces the oil film portion where the cross-sectional shape in the thickness direction of the oil film becomes an inverted wedge shape in the direction of movement of the piston 8. By forming the notch 23 in this manner, the formation range of the notch 23 in the axial direction of the cylinder is the range shown in FIG. 14, and it is possible to reduce mechanical loss without increasing the leakage flow rate of high-pressure oil from the cylinder chamber on the end face side of the piston 8.

[0062] Preferred embodiments of the present invention will be described below with reference to the drawings.

[0063] First Embodiment FIG. 15 is a perspective view of the cylinder block 5 of the swash plate type hydraulic rotary machine according to the first embodiment of the present invention, and FIG. 16 is a diagram showing a front view of the cylinder block 5 as seen from the swash plate side and a cross-sectional view taken along line AA of the front view.

[0064] In this embodiment, the cylinder block 5 is provided with a plurality of (nine) cylinder bores 6 arranged along the rotation direction (circumferential direction of the shaft 4) and each extending in the axial direction. The sliding surfaces between the plurality of cylinder bores 6 and the plurality of pistons 8 are each Axial direction These notches 23 are formed so as to face the oil film portion formed between the sliding surface of the cylinder bore 6 and the piston 8, the cross-sectional shape in the thickness direction of which is an inverted wedge shape in the direction of movement of the piston 8 during the discharge stroke.

[0065] Furthermore, as mentioned above, when the circumferential position of the sliding surface of the cylinder bore 6 is defined by defining the circumferential position of the innermost side of the sliding surface of the cylinder block 5 as 0 degrees and 360 degrees, and the circumferential position of the outermost side as 180 degrees, the notch 23 is formed on the sliding surface of the cylinder bore 6 within the ranges of 0 to 180 degrees and 270 to 360 degrees, preferably within the ranges of 0 to 170 degrees and 310 to 360 degrees.

[0066] In addition, each notch 23 is formed in the axial direction of the cylinder bore 6 over a length range from the shoe-side end of the cylinder bore 6 to the end face of the piston 8 when the piston 8 is at its farthest position from the cylinder bore 6.

[0067] The notches 23 are formed symmetrically in the width direction in a region including the innermost circumferential position of the sliding surface of the cylinder bore 6 in the cylinder block 5, with the center of the circumferential width being located on the innermost circumferential side of the sliding surface of the cylinder bore 6 in the cylinder block 5. In other words, the notches 23 are formed in a region including the region of the sliding surface of the cylinder bore 6 that is closest to the center of rotation of the cylinder block 5 in the radial direction of the cylinder block 5.

[0068] Furthermore, the notches 23 are each open at the end surface of the cylinder block 5 in the axial direction of the cylinder bore 6 and Circumferential Width and Radial direction of cylinder bore 6 Depth In the axial direction of the cylinder bore 6 Constant Yes, cutout 23 The bottom surface is formed in a shape that forms a part of a cylindrical surface.

[0069] According to this embodiment, the following effects can be obtained.

[0070] 1. By forming the notch 23 within the ranges of 0 to 180 degrees and 270 to 360 degrees, preferably 0 to 170 degrees and 310 to 360 degrees, of the sliding surface of the cylinder bore 6 in the region where the oil film has a low oil film pressure and forms an inverted wedge shape, the notch 23 is formed in the region including the innermost circumferential position of the sliding surface of the cylinder bore 6 in the cylinder block 5 (the sliding region closest to the rotation center of the cylinder block 5). This reduces mechanical loss without increasing the leakage flow rate from the sliding surface, making it possible to provide a highly efficient swash plate type hydraulic rotary machine.

[0071] 2. The notch 23 is formed in the area where the oil film pressure is low and the oil film forms an inverted wedge shape, and the formation range of the notch 23 in the axial direction of the cylinder bore 6 is set to the length range from the shoe side end of the cylinder bore 6 to the end face of the piston 8 when the piston 8 is at the position where it is furthest out of the cylinder bore 6. This makes it possible to reduce mechanical loss without increasing the leakage flow rate of high-pressure oil from the cylinder chamber on the end face side of the piston 8.

[0072] 3. The notch 23 is formed in an area including the innermost circumferential position of the sliding surface of the cylinder bore 6 in the cylinder block 5 (the sliding area closest to the center of rotation of the cylinder block 5). This makes it possible to apply the present invention to a bi-tilting swash plate type hydraulic rotary machine in which the swash plate 10 is tilted in both directions around the neutral position to change the discharge direction of pressurized oil.

[0073] 4. The notches 23 are formed symmetrically in the width direction so that the center of the circumferential width is located on the innermost side of the cylinder block 5 on the sliding surface of the cylinder bore 6. This makes it easy to apply the present invention to different models, improving versatility.

[0074] 5. By opening the notch 23 at the end face of the cylinder block 5, the inverted wedge-shaped oil film portion where pressure is low is exposed to the outside, effectively reducing oil shear loss.

[0075] 6. The notch 23 is opened at the end face of the cylinder block 5, and the width of the sliding surface of the cylinder bore 6 in the circumferential direction is constant. Cutout 23 By forming the bottom surface into a shape that forms a part of the cylindrical surface, it becomes easy to cut the inner surface of the cylinder hole 6 using a cylindrical tool and form the notch 23.

[0076] ~ Reference example ~ FIG. 17 shows the Reference example 18 is a perspective view of a cylinder block 5 of a swash plate type hydraulic rotary machine in FIG. 18, and FIG. 18 is a diagram showing a front view of the cylinder block 5 as seen from the swash plate side and a cross-sectional view taken along line AA of the front view.

[0077] In the first embodiment shown in FIGS. 15 and 16, the notch 23 is shaped to open at the shoe side end of the cylinder bore 6. Reference example In this embodiment, the notch 23 is not opened to the shoe side end of the cylinder bore 6, and a sliding surface remains at the end. The other configurations are the same as those of the first embodiment.

[0079] ~No. 2 Embodiments of the present invention FIG. 19 shows the structure of the present invention. 2 20 is a perspective view of a cylinder block of a swash plate type hydraulic rotary machine according to the embodiment, and FIG. 20 is a diagram showing a front view of the cylinder block 5 as seen from the swash plate side and a cross-sectional view taken along line AA of the front view.

[0080] In this embodiment, the notches 23 formed on the sliding surface of the cylinder bore 6 are Circumferential Width and Radial direction of cylinder bore 6 Depth In the axial direction of the cylinder bore 6 It gets smaller as it goes deeper into the cylinder bore 6. Cutout 23 The bottom surface is formed in a shape that forms a part of a cone. The other configurations are the same as those of the first embodiment.

[0081] The inverted wedge-shaped oil film region formed between the sliding surface of the cylinder bore 6 and the piston 8 narrows in width as it goes deeper into the cylinder bore 6, but the notch 23 of this embodiment also narrows in width as it goes deeper into the cylinder bore 6, just like the inverted wedge-shaped oil film. This makes it easier to fit the notch 23 within the inverted wedge-shaped oil film region, more reliably preventing an increase in the leakage flow rate of high-pressure oil from the cylinder chamber on the end face side of the piston 8. Furthermore, the notch 23 can be easily formed in the cylinder block 5 by tilting the cylindrical tool during processing. [Explanation of symbols]

[0082] 1. Swash plate type hydraulic rotary machine 2 Casing 3a Front casing 3b Rear casing 4 Shaft (rotating axis) 5 Cylinder block 6 Cylinder bore 7 Valve plate 8 pistons 9. Shoe 10 Swash plate 11 Retainer 12 Retainer guide 13a, 13b Bearings 14 Compression spring 15 Splines 16 Stationary plate 17 Moving plate 18 Oil 19 Oil film pressure distribution 20 Cavitation 21 Wedge-shaped oil film 22 Inverted wedge-shaped oil film 23 Cutout Ca Shoe side contact position Cb Contact position on the piston end face

Claims

1. a cylindrical cylinder block provided within the casing to rotate with the rotation of the shaft, the cylinder block having a plurality of cylinder holes spaced apart from one another along the circumferential direction of the shaft and each of the cylinder holes being a cylindrical hole extending in the axial direction of the shaft; a plurality of pistons reciprocally inserted within the cylinder holes of the cylinder block, each having one axial end protruding from the cylinder hole; a plurality of shoes attached to the protruding end portions of the plurality of pistons; and a swash plate provided within the casing opposite the cylinder block in the axial direction of the shaft, the swash plate having a sliding surface opposite the cylinder block against which the plurality of shoes slide, a notch extending from a position on the shoe side of the sliding surface in the axial direction of the cylinder bore and having a width in the circumferential direction of the sliding surface is formed on the sliding surface of each of the plurality of cylinder bores with the piston, 1. A swash plate-type hydraulic rotary machine comprising: a cylinder block having a cylinder bore, a cylinder head, a cylinder head shaft ...

2. 2. The swash plate type hydraulic rotary machine according to claim 1, The notches are formed symmetrically in the width direction so that the centers of the circumferential widths are located on the innermost side of the sliding surfaces of the cylinder bores in the cylinder block.

3. 3. The swash plate type hydraulic rotary machine according to claim 1 or 2, a piston that is in a position farthest from the cylinder bore and has a shoe-side end, and ...

4. 2. The swash plate type hydraulic rotary machine according to claim 1, The cylinder bore is provided with a swash plate-type hydraulic rotary machine, characterized in that the width of the notches in the circumferential direction of the cylinder bore and the depth in the radial direction of the cylinder bore become smaller as they go deeper in the axial direction of the cylinder bore, and the bottom surface of the notch is formed into a shape that forms part of a conical surface.

5. A swash plate type hydraulic rotary machine comprising: a casing; a shaft rotatably accommodated within the casing; a cylindrical cylinder block arranged within the casing to rotate with the rotation of the shaft, the cylinder block having a plurality of cylinder holes spaced apart from one another along the circumferential direction of the shaft and each of which is a cylindrical hole extending in the axial direction of the shaft; a plurality of pistons reciprocally inserted into each cylinder hole of the cylinder block, one axial end of which protrudes from the cylinder hole; a plurality of shoes attached to the protruding ends of each of the plurality of pistons; and a swash plate arranged within the casing opposite the cylinder block in the axial direction of the shaft, the surface opposite the cylinder block being formed with a sliding surface along which the plurality of shoes slide, a notch extending from a position on the shoe side of the sliding surface in the axial direction of the cylinder bore and having a width in the circumferential direction of the sliding surface is formed on the sliding surface of each of the plurality of cylinder bores with the piston, Each of the notches is formed in an area including the sliding surface area of ​​the cylinder bore that is closest to the center of rotation of the cylinder block in the radial direction of the cylinder block, so as to open at the end surface of the cylinder block in the axial direction of the cylinder bore, and the circumferential width and radial depth of each of the notches are constant in the axial direction of the cylinder bore, and the bottom surface of each notch is formed in a shape that forms a part of a cylindrical surface.

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