Hydraulic rotary machine

Abstract

To provide a hydraulic rotary machine that allows for easy determination of the piston's operating limit. [Solution] A wear indicator 24 is provided on the outer circumferential surface 21 of the piston 7, specifically on the portion that slides against the opening-side peripheral edge 22, which is the edge of the inner circumferential surface of the cylinder bore 6, while the piston 7 is reciprocating between its top dead center and bottom dead center. A wear indicator 24 is also provided on the outer circumferential surface 21 of the piston 7, specifically on the portion that slides against the inner-side peripheral edge 23, which is the edge of the inner circumferential surface of the cylinder bore 6, while the piston 7 is reciprocating between its top dead center and bottom dead center. The wear indicator 24 is a wear determination unit that changes according to the degree of wear on the outer circumferential surface 21 of the piston 7.

Description

Technical Field

[0001] The present disclosure relates to a hydraulic rotary machine mounted on construction machines such as hydraulic excavators, hydraulic cranes, wheel loaders, etc., and used as a hydraulic pump or a hydraulic motor.

Background Art

[0002] From the perspective of circular economy, it is desirable to reuse machine parts to effectively utilize resources, reduce newly manufactured parts, and reduce the CO2 emissions when manufacturing materials and parts. However, for machine parts used in sliding parts, it is difficult to determine whether the parts can be reused or not visually for parts that allow a certain degree of wear, and it is necessary to measure the wear amount using equipment such as a shape measuring instrument and then make a judgment. In this case, after measuring the wear amount, it is necessary to check the wear amount at the usage limit of the part and compare them to make a judgment, which is a laborious task.

[0003] Here, as a general machine part that allows a certain degree of wear, for example, there is a tire used in an automobile. Tires have been conventionally used allowing a certain degree of wear, and their usage limit has been confirmed by a slip sign. As such a technique, for example, Patent Document 1 is known.

[0004] On the other hand, as a technique for monitoring the wear of a reciprocating piston, for example, Patent Document 2 is known. The monitoring monitor of Patent Document 2 installs a sensor in a cylinder and measures the movement and surface state of the piston to perform life prognosis diagnosis and the like. The technique of Patent Document 2 is considered effective when the number of pistons is small, the sensor arrangement is easy, and the size of the machine is very large and part replacement is difficult.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The pistons of hydraulic rotating machinery such as hydraulic pumps and hydraulic motors are components that tolerate a certain degree of wear. However, although wear progresses in the pistons of hydraulic rotating machinery, the amount of wear is minute, making it difficult to determine the service limit by visual inspection of the surface. Therefore, it is necessary to check the amount of wear using a shape measuring machine. In addition, it is also necessary to evaluate the performance of the hydraulic rotating machinery in its assembled state to determine whether the performance is maintained.

[0007] In contrast, for parts with pre-existing grooves, such as automobile tires, an indicator can be placed within the groove to visually confirm the wear limit. However, while pistons in hydraulic rotary machines may have grooves for lubrication purposes, these grooves are located in areas that are less prone to wear (within the range where they do not come out of the cylinder block). Therefore, since wear does not progress in the grooved areas, even if an indicator were to be placed in such grooves, it would not be possible to determine the wear limit. On the other hand, if grooves are placed in areas where wear progresses, there is a possibility of snagging with the corners (edges) of the cylinder block, and there is also a possibility that hydraulic pressure may leak from the sliding surface due to the grooves, which could degrade the performance of the hydraulic rotary machine.

[0008] Furthermore, in configurations where sensors are placed on the cylinder, such as in Patent Document 2, it is easy to place sensors if the cylinder is fixed and the cylinder itself does not move. However, in hydraulic rotary machines, the cylinder block corresponding to the cylinder rotates, making it difficult to install sensors. Moreover, even if a configuration is adopted in which sensors are placed and measurement data can be output externally via slip rings, etc., it is necessary to process and analyze the data measured by the sensors separately when continuously monitoring the behavior and surface condition of the piston. For this reason, a very complex and large-scale system configuration is required, making it difficult to determine the piston's usage limit. In addition, since hydraulic rotary machines have multiple pistons, it is necessary to monitor each piston, which also makes it difficult to determine the piston's usage limit.

[0009] The object of the present invention is to provide a hydraulic rotary machine that can easily determine the operating limit of a piston. [Means for solving the problem]

[0010] The present invention preferably provides a hydraulic rotary machine comprising: a rotating shaft rotatably provided within a casing; a cylinder block having a plurality of cylinder bores and provided within the casing so as to rotate integrally with the rotating shaft; and a plurality of pistons inserted into each cylinder bore of the cylinder block so as to be reciprocable between a top dead center and a bottom dead center, wherein a wear determination part is provided on the outer circumferential surface of the piston at a portion that slides against the edge of the inner circumferential surface of the cylinder bore while the piston is reciprocating between the top dead center and the bottom dead center, and the wear determination part changes according to the degree of wear on the outer circumferential surface of the piston. [Effects of the Invention]

[0011] According to the present invention, the operating limit of the piston can be easily determined. [Brief explanation of the drawing]

[0012] [Figure 1] This is a longitudinal cross-sectional view showing a hydraulic rotary machine according to an embodiment. [Figure 2] This is a cross-sectional view that exaggerates the cylinder bore of the cylinder block and the piston at top dead center. [Figure 3] This is a cross-sectional view that exaggerates the cylinder bore of the cylinder block and the piston at bottom dead center. [Figure 4] This is a cross-sectional view showing the piston and shoe. [Figure 5] This is a side view showing the piston and shoe. [Figure 6] This is a cross-sectional view of the piston wear detection section (bottomed hole) as seen from the direction of arrow VI-VI in Figure 5. [Figure 7] This is a characteristic diagram showing an example of the condition of the outer surface (surface) of a piston (relationship between the axial position of the piston and wear). [Figure 8] This is an explanatory diagram illustrating the flow in the annular gap between the cylinder bore and the piston. [Modes for carrying out the invention]

[0013] The following will describe in detail, with reference to the attached drawings, the hydraulic rotary machine according to the embodiment, for example, when used as a hydraulic pump (variable displacement swashplate hydraulic pump).

[0014] In Figure 1, the variable displacement swashplate hydraulic pump 1 (hereinafter referred to as hydraulic pump 1) comprises a casing 2, a rotating shaft 4, a cylinder block 5 also called a cylinder, a plurality of pistons 7, a valve plate 8, a plurality of shoes 9, a swashplate 10, a cradle 11, a retainer 12, a retainer guide 13, a spring 14, and a tilt actuator 15. The hydraulic pump 1 is driven by the rotation of the rotating shaft 4, which is connected to the prime mover (engine or electric motor that serves as the driving source) of a hydraulic excavator, for example, and discharges the hydraulic fluid drawn from the tank into the plurality of cylinder holes 6 as high-pressure pressurized oil.

[0015] The casing 2 is formed in a cylindrical (hollow) shape and constitutes the outer shell of the hydraulic pump 1. The casing 2 includes a bottomed cylindrical casing body 2A and a front casing 2B that closes the opening of the casing body 2A. A cradle 11 is provided on the front casing 2B located on one side (the right side in FIG. 1) of the casing 2 so as to face the back surface side of the inclined plate 10.

[0016] On the other hand, on the other side (the left side in FIG. 1) of the casing body 2A, as shown by the dashed line in FIG. 1, a pair of supply and discharge passages, that is, an inflow passage 3A serving as a supply passage and an outflow passage 3B serving as a discharge passage are provided. One of the pair of supply and discharge passages, that is, the inflow passage 3A serves as a suction passage on the low-pressure side and is connected to a tank (not shown). The other of the pair of supply and discharge passages, that is, the outflow passage 3B serves as a discharge passage and is connected to a discharge pipe (not shown) on the high-pressure side.

[0017] The rotating shaft 4 is rotatably provided in the casing 2. That is, the rotating shaft 4 extends axially within the casing 2 and is rotatably supported by the casing body 2A and the front casing 2B via bearings 19, 19, respectively. Also, an oil seal 20 serving as a seal member is provided between the rotating shaft 4 and the front casing 2B.

[0018] One end side (the right end side in FIG. 1) of the rotating shaft 4 is a protruding end 4A that protrudes axially from the front casing 2B. A prime mover such as an engine is connected to the protruding end 4A of the rotating shaft 4 via a power transmission mechanism (all not shown). Also, a male spline 4B is formed at a portion of the outer peripheral surface of the rotating shaft 4 that faces the cylinder block 5 in the radial direction. The male spline 4B is spline-coupled to the female spline 5A of the cylinder block 5.

[0019] The cylinder block 5 is housed within the casing 2 so as to rotate integrally with the rotating shaft 4. For this purpose, a female spline 5A is formed on the inner circumferential surface of the cylinder block 5, which is spline-coupled to the male spline 4B of the rotating shaft 4. In addition, a small-diameter end 5B, which is smaller in diameter than the other parts, is provided on one end of the cylinder block 5, i.e., the right end facing the swash plate 10. A retainer guide 13 is inserted into the small-diameter end 5B.

[0020] The cylinder block 5 has a plurality of cylinder holes 6 that are spaced apart in the circumferential direction and extend axially. Each cylinder hole 6 of the cylinder block 5 has a cylinder port 6A formed therein that intermittently communicates with the intake port 8A and discharge port 8B of the valve plate 8.

[0021] Multiple pistons 7 are reciprocally (slidably) inserted into each cylinder bore 6 of the cylinder block 5. As the cylinder block 5 rotates, the pistons 7 reciprocate between the top dead center and the bottom dead center within the cylinder bore 6, repeating the intake stroke and the discharge stroke. Therefore, the pressure in each cylinder bore 6, which is in communication with the high-pressure discharge port 8B, acts on the swash plate 10 via the pistons 7.

[0022] The piston 7 is formed as a cylindrical (or columnar) rod. The tip end of the piston 7 (the left end in Figure 1) is a flat surface 7A. On the other hand, the base end of the piston 7 (the right end in Figure 1) is a spherical recess 7B into which the spherical portion 9A of the shoe 9 is attached. The piston 7 is provided with an oil supply hole 7C that extends axially, passing through the space between the flat surface 7A and the spherical recess 7B. The engagement portion between the spherical portion 9A of the shoe 9 and the spherical recess 7B of the piston 7, and the sliding portion between the shoe 9 and the swash plate 10, are lubricated by the hydraulic fluid supplied through the oil supply hole 7C.

[0023] The valve plate 8 is located inside the casing 2 and fixed to the other side of the casing body 2A. That is, the valve plate 8 is provided between the casing body 2A and the cylinder block 5. The valve plate 8 rotatably supports the cylinder block 5, which rotates integrally with the rotating shaft 4, together with the casing body 2A. In this state, the valve plate 8 is in sliding contact with the end face of the cylinder block 5.

[0024] The valve plate 8 has a pair of eyebrow-shaped supply and discharge ports, namely an intake port 8A and a discharge port 8B. The intake port 8A communicates with the inlet passage 3A of the casing body 2A. The discharge port 8B communicates with the outlet passage 3B of the casing body 2A. The intake port 8A and discharge port 8B of the valve plate 8 intermittently communicate with the cylinder port 6A of each cylinder hole 6 when the cylinder block 5 rotates. At this time, the piston 7, which reciprocates within each cylinder hole 6, draws hydraulic fluid into each cylinder hole 6 from the inlet passage 3A side via the intake port 8A during the intake stroke, and during the discharge stroke, discharges the pressurized oil, which has become high pressure within each cylinder hole 6, to the outlet passage 3B via the discharge port 8B.

[0025] Multiple shoes 9 are pivotably mounted on the protruding end of each piston 7 that protrudes from each cylinder hole 6. In this case, each shoe 9 has a spherical portion 9A that constitutes a spherical bearing, and the spherical portion 9A of each shoe 9 is attached to a spherical recess 7B of the piston 7. The shoes 9 are pressed against the smooth surface 10A of the swash plate 10 by a pressing force (hydraulic pressure) from the piston 7 and are held in this state via a retainer 12 or the like. In this state, each shoe 9 rotates together with the rotating shaft 4, cylinder block 5 and piston 7, sliding and displacing on the smooth surface 10A of the swash plate 10 in a ring-shaped circular trajectory.

[0026] The swash plate 10 is provided within the casing 2 so as to be rotatable via the cradle 11. The front surface of the swash plate 10 is a smooth surface 10A that slidably guides each shoe 9. In contrast, the back surface of the swash plate 10 is rotatably supported by the cradle 11 on the casing 2 side. For this purpose, the back surface of the swash plate 10 is provided with a pair of legs 10C on the left and right sides that protrude in a convex curve towards the cradle sliding surface (not shown) of the cradle 11.

[0027] The legs 10C of the swash plate 10 are spaced apart on either side of the rotating shaft 4 and are slidably fitted onto the cradle sliding surface of the cradle 11. The swash plate 10 is provided with a through hole 10B that extends through in the direction of its plate thickness. The through hole 10B is located between the pair of legs 10C, and the rotating shaft 4 is inserted through it with a gap. The swash plate 10 is tilted using a tilt actuator 15 (control piston 18) in the directions indicated by arrows A and B in Figure 1. The discharge capacity (discharge flow rate of pressurized oil) of the hydraulic pump 1 is variably controlled according to the tilt angle of the swash plate 10.

[0028] The cradle 11 is positioned around the rotating shaft 4 and fixed to the casing 2 (more specifically, the front casing 2B). The cradle 11 serves as the swash plate support portion (swash plate support) of the casing 2. The cradle 11 supports the swash plate 10 so that it can tilt (slide) in the directions indicated by arrows A and B in Figure 1. In this case, the cradle 11 has a shaft insertion hole 11A through which the rotating shaft 4 is inserted with a gap. The cradle 11 has a pair of cradle sliding surfaces integrally formed on the left and right sides of the shaft insertion hole 11A (i.e., the rotating shaft 4). The cradle sliding surfaces of the cradle 11 support the swash plate 10 (leg portion 10C) so that it can tilt.

[0029] The retainer 12 is positioned between the protruding ends of each piston 7 and each shoe 9, with the rotating shaft 4 inserted through it. The retainer 12 brings each shoe 9 into contact with the smooth surface 10A of the swash plate 10. The retainer 12 is made up of an annular plate body as a whole, with a through hole 12A formed in the center. The inner circumferential surface 12B of the through hole 12A is formed, for example, in the shape of a concave sphere or a tapered surface. The outer circumferential surface 13A of the retainer guide 13, which is inserted onto the rotating shaft 4, contacts the inner circumferential surface 12B of the retainer 12.

[0030] The retainer 12 holds each shoe 9 against the swash plate 10. For this purpose, the retainer 12 is provided with a plurality of retaining holes 12C spaced apart in the circumferential direction for holding each shoe 9. The retainer 12 presses and holds each shoe 9 toward the smooth surface 10A of the swash plate 10, compensating for the sliding displacement of each shoe 9 on the smooth surface 10A of the swash plate 10, which would otherwise trace an annular trajectory. In this case, the retainer 12 is biased toward the swash plate 10 (smooth surface 10A) via the retainer guide 13 by a spring 14.

[0031] The retainer guide 13 is provided between the retainer 12 and the cylinder block 5. That is, the retainer guide 13 is positioned between the cylinder block 5 and the retainer 12 and is inserted into the rotating shaft 4. The outer circumferential surface 13A of the retainer guide 13 is formed in a convex spherical shape. The inner circumferential surface 12B of the retainer 12 abuts against this outer circumferential surface 13A of the retainer guide 13. The retainer guide 13 presses the retainer 12 toward the swash plate 10 with its outer circumferential surface 13A.

[0032] The spring 14 is provided between the retainer guide 13 and the cylinder block 5 (small diameter end 5B). The retainer guide 13 constantly presses the retainer 12 toward the swash plate 10 due to the spring force of the spring 14. In other words, the spring 14 applies an elastic force between the cylinder block 5 (small diameter end 5B) and the retainer guide 13 in a direction that moves them apart from each other.

[0033] The tilt actuator 15 drives the swash plate 10 to tilt. The tilt actuator 15 is provided in the casing 2. The tilt actuator 15 consists of a control cylinder 16 formed in the casing body 2A and located radially outward from the cylinder block 5, and a control piston 18, also called a tilt piston (servo piston), which is slidably inserted into the control cylinder 16 and forms a hydraulic chamber 17 between itself and the control cylinder 16.

[0034] The tilt actuator 15 is positioned opposite the cylinder block 5 in the radial direction relative to the casing body 2A. The tilt actuator 15 drives the swash plate 10 to tilt in the directions indicated by arrows A and B by the control piston 18. That is, tilt control pressure is supplied to and discharged from the outside into the hydraulic chamber 17 of the tilt actuator 15.

[0035] This tilt control pressure causes, for example, when the control piston 18 of one tilt actuator 15 (for example, the lower part of Figure 1) extends out of the control cylinder 16 and the control piston 18 of the other tilt actuator 15 (for example, the upper part of Figure 1) retracts into the control cylinder 16, the swash plate 10 is driven to tilt in the direction of arrow A (i.e., the positive direction in which the tilt angle increases).

[0036] In contrast, when the control piston 18 of the other tilt actuator 15 (for example, the upper part of Figure 1) extends from within the control cylinder 16, and the control piston 18 of the other tilt actuator 15 (for example, the lower part of Figure 1) retracts into the control cylinder 16, the swash plate 10 is driven to tilt in the direction of arrow B (i.e., the opposite direction in which the tilt angle decreases).

[0037] By the way, in hydraulic rotating machines such as hydraulic pumps (hydraulic piston pumps) and hydraulic motors (hydraulic piston motors), determining whether or not a piston can be reused requires time and sophisticated measurement. In other words, according to conventional technology, it is difficult to determine the limit of piston use. Therefore, in this embodiment, a wear indicator with a height (depth) set as the limit of use is attached to the piston in advance. As a result, by observing the presence or absence of this wear indicator, it is possible to easily determine whether or not the piston has reached its limit of use.

[0038] In other words, in this embodiment, a wear indicator, which serves as a piston wear determination unit (wear confirmation means), is provided on the sliding surface of the piston. Therefore, by checking for the presence or absence of this wear indicator, it is easy to determine whether or not the piston is reusable. These points will be explained in detail below.

[0039] As shown in Figure 1, the hydraulic pump 1, as a hydraulic rotary machine, comprises a rotating shaft 4, a cylinder block 5, and a plurality of pistons 7. The rotating shaft 4 is rotatably mounted within the casing 2. The cylinder block 5 is mounted within the casing 2 so as to rotate integrally with the rotating shaft 4. The cylinder block 5 has a plurality of cylinder holes 6. For example, the cylinder block 5 has a plurality of cylinder holes 6 that are spaced apart in the circumferential direction and extend axially. The plurality of pistons 7 are inserted into each cylinder hole 6 of the cylinder block 5 so as to be able to reciprocate between top dead center and bottom dead center.

[0040] When the hydraulic pump 1 is operating, the piston 7 reciprocates within the cylinder bore 6 of the cylinder block 5. Figure 2 exaggerates the state of the piston 7 at top dead center. Figure 3 exaggerates the state of the piston 7 at bottom dead center. As shown in Figures 2 and 3, when the piston 7 reciprocates within the cylinder bore 6, a load of Ft acts on the piston 7 from the swashplate 10, also called the swashplate. In response to this load, the piston 7 tilts within the cylinder bore 6, and as a reaction force, a force of Fc is applied at the opening side of the cylinder bore 6 and a force of Fb is applied at the back side of the cylinder bore 6.

[0041] As the piston 7 moves back and forth, the outer circumferential surface 21 of the piston 7 comes into contact with the opening-side periphery 22, which is the corner (edge) on the opening side of the cylinder bore 6, and the rear-side periphery 23, which is the corner (edge) on the rear side of the cylinder bore 6. Over time, the outer circumferential surface 21 of the piston 7, more specifically the sliding surface 21A of the outer circumferential surface 21 of the piston 7 that slides against the cylinder bore 6, wears down.

[0042] Figure 4 is a cross-sectional view of the piston 7 and shoe 9. The areas labeled "R1" and "R2" in Figure 4 correspond to the parts of the outer circumferential surface 21 of the piston 7 that come into contact with the peripheral edges 22 and 23, which form the corners of the cylinder bore 6. Specifically, "R1" in Figure 4 is the area where the opening-side peripheral edge 22 of the cylinder bore 6 comes into contact with the piston 7 as it reciprocates. "R2" in Figure 4 is the area where the inner-side peripheral edge 23 of the cylinder bore 6 comes into contact with the piston 7 as it reciprocates.

[0043] Figure 5 is a side view of the piston 7 and shoe 9. The areas marked with a "dot pattern" in Figure 5 correspond to the "R1" and "R2" areas in Figure 4. Figure 7 shows an example of the surface shape of the sliding surface 21A of the piston 7 (an example of a worn sliding surface 21A), exaggerated (the radial dimension is greatly stretched relative to the axial dimension). As shown in Figure 7, wear progresses on the sliding surface 21A of the piston 7 in the areas marked with a "dot pattern" in Figure 5, i.e., the "R1" and "R2" areas in Figure 4.

[0044] Therefore, in this embodiment, as shown in Figures 5 and 6, a wear indicator 24 is provided on the outer circumferential surface 21 of the piston 7, in the area where wear is progressing, to determine whether or not the piston 7 has reached its service limit. In addition, a marking 25 is provided on the non-sliding surface 21B of the outer circumferential surface 21 of the piston 7, which is the area away from the sliding surface 21A, to serve as a determination position marker. The marking 25 is provided at a position that coincides with the wear indicator 24 in the axial direction SS of the piston 7.

[0045] Specifically, a wear indicator 24 is provided on the outer circumferential surface 21 of the piston 7, specifically on the portion that slides against the opening-side peripheral edge 22, which becomes the edge of the inner circumferential surface of the cylinder bore 6, while the piston 7 is reciprocating between its top dead center and bottom dead center. A wear indicator 24 is also provided on the outer circumferential surface 21 of the piston 7, specifically on the portion that slides against the inner-side peripheral edge 23, which becomes the edge of the inner circumferential surface of the cylinder bore 6, while the piston 7 is reciprocating between its top dead center and bottom dead center. The wear indicator 24 is a wear determination unit that changes according to the degree of wear on the outer circumferential surface 21 of the piston 7.

[0046] The wear determination unit changes, for example, its appearance, shape, state quantity, state value, properties, etc., depending on the degree of wear on the outer circumferential surface 21 of the piston 7. In this embodiment, the wear indicator 24 is a closed hole with a circular opening. That is, the depth of the closed hole, which is the wear indicator 24, changes according to the degree of wear on the outer circumferential surface 21 of the piston 7. Also, the opening area (size of the opening) of the closed hole, which is the wear indicator 24, changes according to the degree of wear on the outer circumferential surface 21 of the piston 7.

[0047] As shown in Figures 5 and 6, multiple wear indicators 24 are provided spaced apart in the axial direction of the piston 7. Specifically, two wear indicators 24 are provided spaced apart in the axial direction of the piston 7 on the outer circumferential surface 21 of the piston 7 where the opening edge 22 of the cylinder bore 6 makes contact with the piston 7 during its reciprocating motion. Additionally, two wear indicators 24 are provided spaced apart in the axial direction of the piston 7 on the outer circumferential surface 21 of the piston 7 where the inner edge 23 of the cylinder bore 6 makes contact with the piston 7 during its reciprocating motion.

[0048] The depth of the wear indicator 24 changes as the outer surface 21 of the piston 7 wears down. In other words, the depth of the wear indicator 24 decreases as the outer surface 21 of the piston 7 wears down. Furthermore, the depth (deepest part) of the wear indicator 24 corresponds to the wear amount that marks the end of the piston 7's service life. Therefore, when the wear indicator 24 disappears due to wear of the piston 7, it corresponds to the end of the piston 7's service life, i.e., when the piston 7 needs to be replaced (it can no longer be reused).

[0049] Furthermore, as shown in Figure 5, on the outer circumferential surface 21 of the piston 7, the portion that does not come into sliding contact with the inner circumferential surface of the cylinder bore 6 during the reciprocating motion of the piston 7 between top dead center and bottom dead center (non-sliding surface 21B) is provided with a wear indicator 24 and a marking 25 as a determination position marker corresponding to the axial direction of the piston 7. As a result, if there is no wear indicator 24 at the axial position of the marking 25, it can be determined that the piston 7 has reached its service limit, that is, it is time to replace the piston 7 (it is no longer reusable).

[0050] As shown in Figure 5, the wear indicator 24 is circular in shape in the projection plane. Also, as shown in Figure 6, the wear indicator 24 is perforated. Thus, the wear indicator 24 is configured as a circular, bottomed hole. The wear indicator 24 is formed using means such as laser processing, cutting, or etching. The marking 25 can also be formed using means such as laser processing, cutting, or etching. Furthermore, since the marking 25 is provided on a non-sliding surface 21B that does not slide against the cylinder hole 6, it may be a mark made of paint, for example.

[0051] Furthermore, the wear indicator could be, for example, a groove shape extending in the circumferential direction of the piston 7. However, in this case, when the piston 7 reciprocates within the cylinder bore 6, the groove-shaped wear indicator may become lodged in the peripheral edges 22, 23 which form the corners (edges) of the inner circumferential surface of the cylinder bore 6, potentially accelerating wear. On the other hand, the wear indicator could be, for example, a groove shape extending in the axial direction of the piston 7. However, in this case, liquid (oil) may be discharged from the contact area between the sliding surface 21A of the piston 7 and the inner circumferential surface of the cylinder bore 6 via the groove-shaped wear indicator, potentially causing poor lubrication.

[0052] Furthermore, it is conceivable to make the opening of the wear indicator a polygon, such as a triangle or a square. However, in this case, when a sliding load is applied to the sliding surface 21A of the piston 7, stress may concentrate near the vertices of the corners of the opening, potentially becoming the starting point for fracture of the piston 7's surface. For these reasons, it is desirable that the wear indicator 24 have a circular, bottomed opening.

[0053] Furthermore, as shown in Figure 5, the diameter of the piston 7 is Dp. Also, as shown in Figure 6, the depth of the bottomed hole that serves as the wear indicator 24 is H, and its diameter is D. In this case, the depth H of the wear indicator 24 is such that it satisfies the following equation 1.

[0054]

number

[0055] Furthermore, the diameter D of the wear indicator 24 should satisfy the following equation 2.

[0056]

number

[0057] Next, we will explain the reason for restricting the depth H and diameter D of the bottomed hole, which serves as the wear indicator 24, to the ranges given by equations 1 and 2 above.

[0058] As shown in Figure 8, let the radius of the piston 7 be "r", the radius of the cylinder bore 6 be "R", the radial clearance be "δ", the fitting length between the piston 7 and the cylinder bore 6 be "l", the differential pressure be "Δp", the viscosity of the hydraulic fluid be "μ", and the flow rate of the liquid passing between the piston 7 and the cylinder bore 6 be "Q". In this case, the flow rate Q can generally be expressed by the following three equations. Furthermore, if the piston 7 is eccentrically positioned within the cylinder bore 6, the flow rate can be up to 2.5 times higher. These points are described, for example, in "(General Incorporated Association) Japan Fluid Power Industry Association, Practical Hydraulics Pocketbook (2020 Edition), published March 2020".

[0059]

number

[0060] Here, the radial clearance δ [μm] between the piston 7 and the cylinder bore 6 is a value that varies depending on the manufacturer's design philosophy, and is set at various values ​​by each company. For example, as a guideline, the diameter clearance is sometimes set at 1 / 1000 of the piston diameter Dp [mm]. In this case, the radial clearance δ is "δ = Dp / (2 × 1000)". If the diameter Dp of the piston 7 is 20 [mm], then the radial clearance δ will be 10 [μm]. The depth H [μm] of the wear indicator 24 should be in the range of "3 × {Dp / (1000 × 2)} ≥ H" when the piston diameter is Dp [mm]. That is, H should be 3 times or less the radial clearance δ.

[0061] The depth H at which the wear indicator 24 disappears corresponds to a wear of 30 μm when the diameter Dp of the piston 7 is 20 mm. In this case, the radial gap δ expands to 40 μm, which is four times the initial guideline radial gap δ. In equation 3 above, when the radial gap δ increases fourfold, the flow rate Q expands to 64 times, or 4 to the power of 3. The hydraulic pump 1's work output decreases as fluid leaks out through the gap between the piston 7 and the cylinder hole 6. The same applies to the hydraulic motor.

[0062] For example, consider a square-stroke hydraulic pump 1 in which the piston 7 strokes by a length equal to the diameter of the piston 7. In this case, the volume is (20 / 2) 2 ×π × 20 / 1000 = 6.28 cm 3 This is the result. The rotational speed of the rotating shaft 4, which will be the pump shaft, is 1800 min⁻¹. -1 In this case, the piston 7 has a discharge capacity of "6.28 × 1800 / 1000 = 11.3 L / min". Here, if the radial clearance δ is 10 [μm], the flow rate Q passing between the piston 7 and the cylinder bore 6 is 0.015 L / min. Even if the piston 7 is eccentric, it remains 0.037 L / min. Therefore, the loss is less than 1%, which is very small.

[0063] In contrast, if the piston 7 is worn down until the wear indicator 24 disappears, and the radial clearance δ is 40 [μm], the flow rate Q will be 0.938 L / min. If it is eccentric, it will be 2.346 L / min. In this case, the loss is 20%. This depends on the volume setting and discharge pressure of the hydraulic pump 1, but in the region where the maximum work is performed, there will be approximately a 20% decrease in performance, i.e., a decrease in discharge volume. If it is a hydraulic motor, a 20% decrease in rotational speed will occur. Also, the increased amount of leaking liquid (oil) will increase the pressure inside the hydraulic pump 1, which may lead to seal failure. For this reason, continued use will become difficult. As a product, it is necessary to design it with a safety factor in mind, so it is preferable to set the wear indicator depth H in the range of the above equation 1, i.e., "3 × {Dp / (1000 × 2)} ≥ H", according to the performance and specifications of the parts, etc.

[0064] Furthermore, if the diameter of the wear indicator 24 is D [μm] and the diameter of the piston 7 is Dp [mm], the diameter D of the wear indicator 24 is set within the range of the above equation 2, i.e., "0.01 × Dp ≥ D". When the diameter D of the wear indicator 24 is near "0.01 × Dp", it is easily visible and can be seen with the naked eye. If it is set to a value smaller than "0.01 × Dp", it can be confirmed using a microscope or the like. In that case, the approximate measurement position can be confirmed by the marking 25 placed on the non-sliding surface 21B.

[0065] On the other hand, if the diameter D of the wear indicator 24 is made larger than "0.01 × Dp", the wear indicator 24 will cover an area of ​​1% or more of the projected surface of the sliding surface 21A of the piston 7. This may affect the sliding characteristics when the piston 7 and the cylinder bore 6 perform relative motion. In other words, if the diameter D of the wear indicator 24 is large, the fluid (lubricating fluid) in the parts of the piston 7 that are in sliding contact with the peripheral edges 22, 23 of the cylinder bore 6 at the tip and base ends tends to flow into the wear indicator 24. As a result, the amount of fluid (lubricating fluid) in those parts decreases, which may lead to poor lubrication.

[0066] Furthermore, the gap between the sliding surface 21A of the piston 7 and the inner circumferential surface of the cylinder bore 6 widens in the area where the wear indicator 24 is provided. As a result, hydraulic pressure may leak out through this gap during the reciprocating motion of the piston 7, potentially reducing operational performance. For this reason, it is preferable to set the diameter D [μm] of the wear indicator 24 within the range of Equation 2 above, i.e., "0.01 × Dp ≥ D".

[0067] Thus, in this embodiment, a piston 7 with a wear indicator 24 is used. This allows for the reuse of parts after the hydraulic pump 1 has been operated, by disassembling the hydraulic pump 1, checking for the presence or absence of the wear indicator 24, and determining that the part can be reused if the wear indicator 24 remains, or not reused if it has disappeared.

[0068] The hydraulic pump 1 according to this embodiment has the configuration described above, and its operation will now be explained.

[0069] The hydraulic pump 1 converts the rotational motion of the rotating shaft 4 (cylinder block 5) into the motion of oil. That is, when the rotating shaft 4 is rotated by a prime mover such as an engine, the cylinder block 5 rotates together with the rotating shaft 4 within the casing 2. As a result, multiple shoes 9 slide along the surface (smooth surface 10A) of the swash plate 10 in a ring-shaped trajectory, and in conjunction with this, each piston 7 repeatedly reciprocates within each cylinder bore 6.

[0070] During this time, as the cylinder block 5 rotates once, each piston 7 repeatedly performs an intake stroke, sliding from top dead center to bottom dead center within the cylinder bore 6, and a discharge stroke, sliding from bottom dead center to top dead center. In the intake stroke of the piston 7, for example, hydraulic fluid is drawn into the cylinder bore 6 from the inlet passage 3A side via the intake port 8A and cylinder port 6A of the valve plate 8. In the discharge stroke of the piston 7, the piston 7 converts the fluid in each cylinder bore 6 into high-pressure pressurized oil and discharges it from the outlet passage 3B side via the cylinder port 6A and the discharge port 8B of the valve plate 8.

[0071] In this embodiment, a wear indicator 24 is provided as a wear determination unit on the outer circumferential surface 21 of the piston 7, specifically on the portion that slides against the peripheral edges 22 and 23 of the inner circumferential surface of the cylinder bore 6 while the piston 7 is reciprocating between the top dead center and the bottom dead center. The state of the wear indicator 24 changes according to the degree of wear on the outer circumferential surface 21 of the piston 7. Therefore, the degree of wear on the outer circumferential surface 21 of the piston 7 can be determined based on the change in the wear indicator 24. This makes it easy to determine the service limit of the piston 7.

[0072] According to the embodiment, the non-sliding surface 21B of the outer circumferential surface 21 of the piston 7, which does not slide against the inner circumferential surface of the cylinder bore 6 while the piston 7 is reciprocating between the top dead center and the bottom dead center, is provided with a wear indicator 24 and a marking 25 that serves as a determination position marker corresponding to the axial direction of the piston 7. Therefore, the marking 25 indicates the circumferential position of the wear indicator 24. In other words, it is possible to determine the position where the presence or absence of the wear indicator 24 is to be determined. As a result, the degree of wear on the outer circumferential surface 21 of the piston 7 can be determined according to the state of the wear indicator 24 at the axial position of the marking 25.

[0073] Furthermore, even if the wear indicator 24 disappears due to wear on the outer surface 21 of the piston 7, it is possible to determine where the wear indicator 24 was located. Moreover, if the wear indicator 24 is not present on the outer surface 21 of the piston 7, the presence or absence of the marking 25 indicates whether the wear indicator 24 was never present in the first place or whether it disappeared due to wear. In other words, the presence or absence of the marking 25 indicates whether or not the piston 7 is equipped with a wear indicator 24.

[0074] According to this embodiment, the wear indicator 24 is a closed hole with a circular opening. Therefore, the degree of wear can be determined based on the presence or absence of the closed hole. In this case, by correlating the depth H of the closed hole with the amount of wear (service limit) at which the piston 7 needs to be replaced, it can be determined that the piston 7 needs to be replaced (service limit reached) when the wear indicator 24, which is a closed hole, disappears.

[0075] According to the embodiment, when the depth of the bottomed hole that serves as the wear indicator 24 is H and the diameter of the piston 7 is Dp, then 3 × {Dp / (1000 × 2)} ≥ H. Therefore, the depth H of the bottomed hole and the amount of wear (service limit) at which the piston 7 needs to be replaced can be appropriately matched. If the depth H of the wear indicator 24 exceeds the maximum value of "3 × {Dp / (1000 × 2)}", that is, if it is made larger (deeper) than "3 × {Dp / (1000 × 2)}", the replacement period for the piston 7 can be extended, but the performance degradation when the replacement period approaches will be greater. Also, the minimum value of the depth H of the wear indicator 24 can be set to a small value when shortening the replacement period, for example, and to a large value when lengthening the replacement period.

[0076] According to the embodiment, when the diameter of the bottomed hole that serves as the wear indicator 24 is D and the diameter of the piston 7 is Dp, then 0.01 × Dp ≥ D. Therefore, lubrication failure due to the provision of a bottomed hole that serves as the wear indicator 24 can be suppressed. Note that if the diameter D of the wear indicator 24 exceeds "0.01 × Dp", which corresponds to the maximum value, that is, if it is made larger than "0.01 × Dp", the degree of lubrication failure will increase. In addition, the minimum value of the diameter D of the wear indicator 24 can be set to a size that is not easily overlooked when the wear indicator 24 is still present, for example.

[0077] According to this embodiment, multiple wear indicators 24 are provided spaced apart in the axial direction of the piston 7. Therefore, the degree of wear on the outer surface of the piston 7 can be determined using multiple wear indicators 24. This improves the accuracy of determining the degree of wear, and consequently, whether or not the piston 7 needs to be replaced (whether or not it has reached its service limit). When multiple wear indicators 24 are provided, the depth of each wear indicator 24 may be different.

[0078] In this embodiment, the case in which multiple wear indicators 24 are provided as wear determination units was described as an example. However, the invention is not limited to this, and for example, one wear indicator may be provided.

[0079] In the embodiment, the case in which the wear indicator 24, which serves as the wear determination part, is a closed hole was described as an example. However, the wear determination part is not limited to this, and may be constructed by, for example, embedding sintered metal, soft metal material, synthetic resin, etc., in a closed hole. That is, the wear determination part may be constructed by providing a different member on the outer surface of the piston from the member that constitutes the outer surface of the piston. In this case, the wear determination part can be constructed from a member that wears together with the outer surface of the piston.

[0080] Thus, the wear determination unit can employ various shapes, components, and materials as a part whose appearance, shape, state quantity, state value, properties, etc., change according to the degree of wear on the outer surface of the piston. In this case, the wear determination unit can be a part that shows changes according to the degree of wear on the outer surface of the piston, for example, corresponding to the amount of wear corresponding to the service limit or the amount of wear corresponding to the replacement time (for example, a significant change appears before and after these points). In other words, the wear determination unit corresponds to a part that changes according to the degree of wear on the outer surface of the piston.

[0081] In the embodiment, the case in which the inner circumferential surface of the cylinder bore 6 has an opening-side periphery 22 and a rear-side periphery 23 was described as an example. However, it is not limited to this, and for example, the rear-side periphery may be omitted. In this case, the wear determination part (wear indicator) provided at the part that slides against the rear-side periphery can be omitted. Also, for example, if the cylinder bore has a rear-side periphery, the wear determination part (wear indicator) provided at the part that slides against the opening-side periphery may be omitted, and the wear determination part (wear indicator) may be provided only at the part that slides against the rear-side periphery. That is, the wear determination part can be provided at the part of the outer circumferential surface of the piston that slides against the edge (periphery, corner) of the inner circumferential surface of the cylinder bore while the piston is reciprocating between the top dead center and the bottom dead center.

[0082] In this embodiment, the case where both a wear indicator 24 as a wear determination unit and a marking 25 as a determination position marker are provided was described as an example. However, the invention is not limited to this, and for example, the determination position marker (marking) may not be provided. In other words, the determination position marker (marking) may be omitted.

[0083] In the embodiment, a hydraulic pump 1 with unidirectional tilt, where the swash plate 10 tilts to one side, was used as an example. However, it is not limited to this, and may also be used in a hydraulic pump with bidirectional tilt, where the swash plate tilts to both sides of a tilt angle of 0.

[0084] In this embodiment, a hydraulic pump 1, which converts the rotational motion of the cylinder block 5 into the motion of oil, was used as an example of a hydraulic rotating machine. However, it is not limited to this, and other hydraulic rotating machines such as a hydraulic motor, which converts the motion of oil into the rotation of the cylinder block, may also be used. For example, in the case of a hydraulic motor, hydraulic fluid is introduced into and out of the cylinder block from a hydraulic source such as a hydraulic pump via a valve plate. This causes the piston to reciprocate along the swash plate, converting the motion of the oil into the rotational motion of the cylinder block, thereby converting the motion of the oil into the rotational motion of the rotating shaft.

[0085] In this embodiment, a variable displacement swashplate type hydraulic rotary machine was used as an example. However, the hydraulic rotary machine is not limited to this, and may be, for example, a fixed-displacement swashplate type hydraulic rotary machine. Furthermore, the hydraulic rotary machine is not limited to the swashplate type, but may be, for example, a slanted-shaft type. Moreover, the hydraulic rotary machine is not limited to the axial piston type, but may be a radial piston type. In other words, the hydraulic rotary machine corresponds to various types of hydraulic rotary machines having pistons.

[0086] In the embodiment, the application of the hydraulic pump 1 to a hydraulic excavator was used as an example. However, it is not limited to this, and may be applied to construction machinery other than hydraulic excavators, such as hydraulic cranes and wheel loaders. Furthermore, it is not limited to construction machinery, but can be widely applied as a hydraulic rotating machine used in various machines, such as hydraulic pumps and hydraulic motors incorporated into industrial machinery or general machinery. [Explanation of symbols]

[0087] 1. Hydraulic pump (hydraulic rotary machine) 2 Casing 4 rotation axes 5 Cylinder block 6 Cylinder holes 7 pistons 21 Outer surface 21A Sliding surface 21B Non-sliding surface 22. Peripheral edge (end edge) of the opening side 23. Rear edge (edge) 24. Wear indicator (wear detection section) 25. Marking (marker for judgment position)

Claims

1. A rotating shaft rotatably mounted within the casing, A cylinder block having multiple cylinder bores and provided within the casing so as to rotate integrally with the rotating shaft, Multiple pistons are inserted into each cylinder bore of the cylinder block so as to be able to reciprocate between top dead center and bottom dead center, In a hydraulic rotary machine equipped with, A wear determination section is provided on the outer circumferential surface of the piston, in the portion that slides against the edge of the inner circumferential surface of the cylinder bore while the piston is reciprocating between the top dead center and the bottom dead center, and which changes according to the degree of wear on the outer circumferential surface of the piston. A hydraulic rotary machine characterized by the following features.

2. On the outer circumferential surface of the piston, in the portion that does not come into sliding contact with the inner circumferential surface of the cylinder bore while the piston is reciprocating between the top dead center and the bottom dead center, a wear determination position marker is provided corresponding to the wear determination portion and the axial direction of the piston. The hydraulic rotary machine according to feature 1.

3. The wear determination unit has a circular, bottomed hole opening. The hydraulic rotary machine according to feature 1.

4. When the depth of the bottomed hole that serves as the wear determination section is H, and the diameter of the piston is Dp, then 3 × {Dp / (1000 × 2)} ≥ H. The hydraulic rotary machine according to feature 3.

5. If the diameter of the bottomed hole that serves as the wear determination section is D, and the diameter of the piston is Dp, then 0.01 × Dp ≥ D. The hydraulic rotary machine according to feature 3.

6. Multiple wear determination units are provided spaced apart in the axial direction of the piston. The hydraulic rotary machine according to feature 1.

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