Sliding member

Abstract

To provide a slide member whose hardness is optimized in accordance with each part to reduce uneven wear and improve wear resistance more than before.SOLUTION: A slide member 30 in the embodiment includes a support layer 32 and a slide layer 31. The slide layer 31 is provided on a side of one end face of the support layer 32 that slides with a mating member. The slide layer 31 has a hardness inclination from the center in an axial direction to an outer peripheral side, where the hardness is set larger on the outer side than at the center.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present embodiment relates to a sliding member, and more particularly to a sliding member used for a piston of a piston pump. [Background technology]

[0002] Conventionally, swash plate type piston pumps have been widely used as hydraulic pumps and hydraulic motors. The swash plate type piston pump includes a swash plate and pistons, and the pistons are reciprocated in the axial direction by the rotating swash plate (Patent Document 1). In this case, the piston slides on the swash plate at the end on the swash plate side. That is, the piston slides on the swash plate by contacting the rotating swash plate at the end on the swash plate side. For this reason, the piston is provided with a sliding member at the end on the swash plate side. This sliding member slides on the rotating swash plate as described above, and receives a force in the axial direction of the piston from the swash plate and the fluid pressurized by the piston. For this reason, the sliding member has a problem in that it is prone to uneven wear in the radial direction around the axis of the piston. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-16150 A Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, an object of the present invention is to provide a sliding member in which the hardness is set to an appropriate level depending on the portion, thereby reducing uneven wear and further improving wear resistance. [Means for solving the problem]

[0005] In order to solve the above problems, the sliding member of this embodiment is Move back and forth a support layer; and a mating member provided on one end surface side of the support layer that slides against the mating member, When the moving direction of the support layer is defined as the axial direction, the diameter perpendicular to this axial direction direction In and a sliding layer having a hardness set to be greater at the outside than at the center.

[0006] The sliding layer is set so that the hardness of the outer side is greater than that of the center side, with the axis as the center. That is, the sliding layer has a gradient of hardness in the radial direction, and the outer side is harder than the center side. Therefore, for example, when sliding with a swash plate, even if a force is applied from the center side to the outside by the rotation of the swash plate, the wear resistance of the sliding layer is improved on the hard outer peripheral side. Also, for example, even if a large force is applied from the fluid to be compressed on the center side, the force is received by the soft part in the center and transmitted to the outside, and the shape is maintained by the hard part on the outside. That is, the structure of the sliding layer in this embodiment is similar to a structure in which a hard blade metal is sandwiched between relatively soft soft iron, such as a Japanese sword, to increase the strength as a whole. As a result, even under severe conditions such as further high pressure, the uneven wear is reduced by the appropriate hardness according to the part. Therefore, the wear resistance as a whole can be further improved.

[0007] In the slide member of this embodiment, the slide layer is porous having a plurality of pores, and the porosity of the slide layer is 0.1% or more and 3.2% or less. When the porosity increases in this way, the amount of lubricating oil held inside the sliding layer increases. That is, the lubricating oil is held in the pores formed in the sliding layer. Therefore, by increasing the porosity, the friction between the sliding layer and the mating member is reduced. Therefore, the wear resistance can be further improved. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a piston pump to which a sliding member according to an embodiment is applied; [Diagram 2] FIG. 1 is a schematic front view showing a piston shoe of a piston pump to which a sliding member according to an embodiment is applied; [Diagram 3] FIG. 1 is a schematic plan view showing a jig used in manufacturing a slide member according to an embodiment; [Figure 4] FIG. 1 is a schematic front view illustrating a method for manufacturing a slide member according to an embodiment; [Diagram 5] FIG. 3 is a schematic diagram illustrating the sliding member as viewed from the direction of arrow V in FIG. 2, for explaining the measurement position of the sliding member; [Figure 6] FIG. 1 is a schematic diagram showing a relationship between measurement positions and hardness of a sliding member according to an embodiment of the present invention; [Figure 7] FIG. 13 is a schematic diagram showing the relationship between the measurement position and the hardness of a sliding member according to a comparative example. [Figure 8] Schematic diagram showing the relationship between the sliding direction and the static and dynamic friction coefficients in Examples and Comparative Examples. [Figure 9] FIG. 1 is a schematic diagram showing the relationship between the sliding position and the number of sliding movements and the static and dynamic friction coefficients in Examples and Comparative Examples. [Figure 10] Schematic diagram for explaining the sliding direction [Figure 11] Schematic diagram showing the relationship between lubricating oils and oil retention in Examples and Comparative Examples [Figure 12] FIG. 1 is a schematic diagram showing the relationship between the sliding position, the number of slidings, and the presence or absence of lubricant and the static and dynamic friction coefficients in an embodiment. [Figure 13] FIG. 1 is a schematic diagram showing the relationship between the sliding position, the number of slidings, and the presence or absence of lubricant and the static and dynamic friction coefficients in a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiment will be described in detail with reference to the drawings. FIG. 1 shows a piston pump 10 to which a sliding member according to an embodiment is applied. The piston pump 10 includes a rotating shaft member 11, a cylinder block 12, a piston 13, and a swash plate 14. Although the present embodiment describes the piston pump 10, the present invention can also be applied to a piston motor by reversing the hydraulic circuit. The rotating shaft member 11 is attached with a swash plate 14. The rotating shaft member 11 is supported by a bearing member (not shown) and rotates together with the swash plate 14. The cylinder block 12 forms a plurality of cylinders 15. Specifically, the cylinder block 12 has a plurality of cylinders 15 in the circumferential direction centered on the rotating shaft member 11. The pistons 13 are provided in the cylinders 15 formed by the cylinder block 12. The outer diameter of the pistons 13 is formed slightly smaller than the inner diameter of the cylinders 15. As a result, the pistons 13 reciprocate in the axial direction inside the cylinders 15 while sliding against the inner wall of the cylinder block 12 that forms the cylinders 15. The cylinder block 12 and the pistons 13 define a fluid chamber 16 at the end opposite to the swash plate 14 in the axial direction.

[0010] The piston 13 has a piston body 21 and a piston shoe 22. The piston body 21 and the piston shoe 22 can move together in the axial direction. The piston shoe 22 has a head 23 and a base 24 as shown in FIG. 2. The head 23 is formed in a spherical shape. The piston body 21 has a spherical inner wall 25 at the end on the piston shoe 22 side as shown in FIG. 1. The head 23 of the piston shoe 22 is fitted into the end of the piston body 21. The outer diameter of the head 23 is formed slightly smaller than the inner diameter of the inner wall 25. Therefore, the head 23 and the inner wall 25 of the piston body 21 are allowed to move in three-dimensional directions. As a result, the piston body 21 and the piston shoe 22 are connected in an articulated manner and can take a posture at any angle within a predetermined range.

[0011] The swash plate 14 is inclined with respect to the central axis C of the rotating shaft member 11. That is, the central axis C of the rotating shaft member 11 and the swash plate 14 form a predetermined angle without intersecting at a right angle. The pistons 13 are in contact with the swash plate 14 at their axial ends, i.e., the ends opposite the fluid chamber 16. As the swash plate 14, which is inclined with respect to the central axis C, rotates together with the rotating shaft member 11, the pistons 13 in contact with the swash plate 14 are driven in the axial direction of the rotating shaft member 11 while sliding against the swash plate 14 in the circumferential direction of the rotating shaft member 11. As a result, the pistons 13 reciprocate in the axial direction inside the cylinder 15 due to the force received from the fluid in the fluid chamber 16 and the force received in the axial direction of the central axis C by the rotation of the swash plate 14. The pistons 13 move back and forth in the axial direction inside the cylinder 15 due to the force received from the fluid in the fluid chamber 16 and the force received in the axial direction of the central axis C by the rotation of the swash plate 14. Since the piston body 21 and the piston shoe 22 are connected in an articulated manner, the pistons 13 move in a stable position inside the cylinder 15.

[0012] When the piston 13 moves toward the fluid chamber 16 due to the rotation of the inclined swash plate 14, the fluid in the fluid chamber 16 is pressurized. The pressurized fluid is discharged from a discharge passage (not shown) formed in the cylinder block 12. On the other hand, when the piston 13 moves toward the swash plate 14, the fluid is sucked into the fluid chamber 16 via a suction passage (not shown). The rotation of the swash plate 14 causes the piston 13 to reciprocate inside the cylinder 15, so that the suction and pressurization of the fluid into the fluid chamber 16 is repeated.

[0013] Although the present embodiment has been described with reference to the piston pump 10, the piston pump 10 having this configuration can also be applied as a piston motor by reversing the hydraulic circuit. That is, the rotational force of the rotating shaft member 11 is generated by sequentially introducing pressurized fluid into the fluid chamber 16 in the opposite manner to the above-described embodiment. As a result, the present embodiment can also be applied as a piston motor that generates a rotational force by using the pressure of the fluid. Any fluid can be used, for example, a liquid such as water or oil, a gas, or a supercritical fluid.

[0014] The sliding member 30 of this embodiment is provided at the end of the piston 13. Specifically, the sliding member 30 is provided at the end of the piston shoe 22 on the swash plate 14 side as shown in FIG. 2. The sliding member 30 includes a sliding layer 31 and a support layer 32. In this embodiment, the support layer 32 corresponds to the piston shoe 22. The sliding layer 31 is provided on the end face side of the piston shoe 22, which is the support layer, that is, on the end of the base portion 24 located opposite to the head portion 23. The sliding layer 31 is formed of a Cu-based alloy mainly composed of Cu. The sliding layer 31 may contain Sn, Zn, Ni, Pb, Bi, Fe, etc. as an additive element with Cu as the main component. The sliding member 30 slides on the swash plate 14 as the swash plate 14 rotates.

[0015] In this embodiment, the cross section of the sliding layer 31 perpendicular to the axis is circular to match the shape of the tip of the base portion 24 of the piston shoe 22. The cross section of the sliding layer 31 perpendicular to the axis can be arbitrarily set to match the shape of the base portion 24. The sliding layer 31 is Diameter The hardness of the sliding layer 31 is different between the center and the outside in the direction. Diameter The hardness of the sliding layer 31 is set to be greater on the outer side, i.e., on the outer periphery side, than on the center in the direction. Diameter The center of the direction is relatively softer and the outer periphery is relatively harder.

[0016] The sliding layer 31 is porous and has a plurality of pores therein. That is, the sliding layer 31 is not entirely made of a uniform alloy, but has a large number of pores formed therein. In this embodiment, the porosity of the sliding layer 31 is set to 0.1% or more and 3.2% or less by volume. The porosity of the sliding layer 31 is preferably 0.6% or more and 2.6% or less, and more preferably 1.2% or more and 2.0% or less.

[0017] (Method of manufacturing slide member) Next, a method for manufacturing the slide member 30 according to one embodiment will be described. The sliding member 30 is manufactured by using sintering. The material constituting the sliding member 30 is put in a powder form into a recess 42 of a jig 41 shown in FIG. 3 and molded by sintering. The powder put into the recess 42 is an alloy powder corresponding to the composition of the sliding layer 31 to be formed. When molding by sintering in this way, the alloy powder put into the recess 42 is pressed by placing a support member 43 as shown in FIG. 4. In the case of this embodiment, the support member 43 may be, for example, the piston shoe 22 that serves as the support layer. As a result, the powder 44 put into the recess 42 is sintered in a state where it is pressed by the weight of the support member 43. In this sintering process, the powder 44 filled in the recess 42 is heated to about 750°C to 950°C together with the jig 41.

[0018] In this way, the powder 44 filled in the recess 42 is heated while being pressed by the weight of the support member 43, and the sliding layer 31 formed by sintering is Diameter The outer periphery is harder than the center in the direction. This is because the powder 44 filled in the recesses 42 softens due to heating during sintering, and the softened powder 44 is pressed in the recesses 42 by the weight of the support member 43, which causes it to tend to move toward the outer periphery. The softened and moving powder 44 is restricted from further movement by the inner wall 45 of the jig 41 that forms the recesses 42. Therefore, the sliding layer 31 formed by sintering the powder 44 has a higher density and higher hardness toward the outer periphery near the inner wall 45, whereas the density and hardness decrease toward the center. As a result, the sliding layer 31 formed by sintering the powder 44 has Diameter A hardness gradient occurs between the center and the outer periphery in the radial direction, with the hardness increasing toward the outer periphery. In the sliding layer 31, a hardness gradient is formed in the radial direction by sintering the powder 44 accompanied by pressure applied by the support member 43, and fine voids are formed inside.

[0019] Next, evaluation of the performance of the sliding member 30 according to the above embodiment will be described. The performance of the sliding member 30 is evaluated based on the friction coefficient, the oil retention, and the friction coefficient in a state where the sliding member 30 is impregnated with lubricating oil. (Examples and Comparative Examples) The sliding member 30 in the embodiment of the present invention has a disk shape with a diameter of 28 mm. The sliding member 30 in the embodiment of the present invention uses a Cu-based alloy of Cu-11Sn-0.3P. The powder 44 of the material made of this Cu-based alloy was sintered at 800°C to 900°C to form the sliding member 30. The obtained sample of the embodiment contracted in volume by about 20% due to sintering accompanied by pressure. The sample of the embodiment of the sliding member 30 had a porosity of about 1.5%. The porosity was determined by visually photographing an enlarged image of an arbitrary cross section of the sample, binarizing the photographed image, and identifying the pores. Then, the area ratio in the observation field of the image was measured, and the ratio of the pores in the observation field was calculated as the porosity. In the present embodiment, a plurality of observation fields were observed in the sample, and the porosity was calculated by averaging the porosity in each observation field. The porosity was calculated in the same manner for the following comparative examples.

[0020] A comparative example was prepared for comparison with this embodiment. The comparative example was a sample formed in the same disk shape using the same material as the embodiment. The comparative example was formed by repeatedly sintering and rolling an alloy material to form a uniform plate-shaped member, and then punching it into a disk shape using a press. This comparative example has a configuration that is generally used as a sliding member for the piston shoe 22. The sample of the comparative example shrinks in volume by about 20% due to sintering, and shrinks in volume by 20% or more due to rolling. Therefore, the comparative example has a structure that is uniform overall and does not easily contain voids. As a result, the comparative example had a very dense structure with a porosity of 0.012%. That is, the comparative example had a porosity of 1 / 100 or less compared to the embodiment of this embodiment.

[0021] For the samples of the examples and the comparative examples of the sliding member 30, the measurement positions were set as shown in FIG. 5, and the hardness (Hv) was measured at each of the measurement positions. Specifically, the measurement positions r1 to r12 were set according to the distance from the center O in the radial direction. In the case of this embodiment, the hardness was measured at each of the measurement positions r1 to r12 at positions P1 to P8, which are equally divided into eight parts in the circumferential direction, and the average was used to determine the hardness at each measurement position r1 to r12. In this embodiment, the measurement positions r1 to r12 were set at equal intervals in the radial direction from the center O. As shown in FIG. 6, it can be seen that the measured hardness in the examples increases from the measurement position r1 closer to the center O to the measurement position r12. Thus, in the examples of this embodiment, the measurement position r1 closer to the center O is relatively softer, and the measurement position r12 farther from the center O is harder.

[0022] In contrast, in the case of the comparative example, the entire surface is formed into a uniform plate shape. Therefore, in the comparative example, there is almost no difference in hardness depending on the location. Specifically, as shown in FIG. 7, in the comparative example, the measured hardness is almost the same from measurement position r1 close to the center O to measurement position r12. Thus, in the comparative example, there is only a small difference in hardness from measurement position r1 close to the center O to measurement position r12 far from the center O.

[0023] (Coefficient of friction) The friction coefficients were measured for the example and comparative example of the sliding member 30, both the static friction coefficient μs in a stationary state and the kinetic friction coefficient μk in a sliding state. These friction coefficients were measured by a reciprocating sliding test using a Bowden test. The test conditions were set to a vertical load of 1 kg, a reciprocating movement distance of 12 mm, and a movement speed of 12 mm / sec, respectively, and the static friction coefficient μs and the kinetic friction coefficient μk were measured after 1 reciprocating slide and 100 reciprocating slides, respectively. In the case of the example shown in FIG. 8, the reciprocating sliding direction was set to the radial direction, i.e., between the center O of the sliding member and the outer periphery.

[0024] As shown in FIG. 8, it can be seen that the static friction coefficient μs and the dynamic friction coefficient μk of the embodiment are both lower than those of the comparative example when the number of reciprocating slides is the same. On the other hand, the static friction coefficient μs and the dynamic friction coefficient μk of the embodiment are different when the sliding direction is from the center O to the outside and when it is from the outside to the center O. Specifically, in the case of the embodiment, the static friction coefficient μs is larger when moving from the center O to the outside, and is smaller when moving from the outside to the center O. Also, the dynamic friction coefficient μk is smaller when moving from the center O to the outside, and is larger when moving from the outside to the center O. This is because the embodiment is harder from the center O to the outer periphery. That is, it is considered that the embodiment, whose outer periphery is harder than the center O, is less likely to generate wear powder due to sliding when moving from the center O to the outside, and conversely, when moving from the outside to the center O, wear powder due to sliding is more likely to be generated. In contrast, the comparative example has a uniform hardness overall, so no relationship is observed between the sliding direction and the friction coefficient.

[0025] FIG. 9 shows an example in which the reciprocating sliding direction is set to be parallel in the portion close to the center O and the outer portion. That is, as shown in FIG. 10, the sliding direction between the sample and the testing machine is set to be parallel in the portion close to the center O and the outer portion. As shown in FIG. 9, in the working example, the friction coefficient tends to be larger in the position close to the center O than in the outer portion. This is thought to be because, in the working example, the position close to the center O has a lower hardness than the outer portion, and friction is more likely to occur. In contrast, in the comparative example, the hardness is uniform overall, and therefore no relationship is observed between the sliding position and the friction coefficient.

[0026] (Oil retention) In the examples and comparative examples of the sliding member 30, the ability to retain lubricating oil was confirmed as oil retention. The oil retention was measured based on the change in mass of the sample. Specifically, the samples of the examples and comparative examples were washed and dried, and then the dry mass was measured. At this time, if the dry mass did not change twice consecutively, the measured mass was set as the dry mass of the sample. The sample whose dry mass was measured was immersed in lubricating oil for 24 hours to be impregnated with the lubricating oil. The lubricating oil on the surface of the sample impregnated with the lubricating oil was wiped off, and the wet mass was measured. Then, the ratio of the mass increased by using the sample for the test was taken as the oil retention. That is, the oil retention was calculated as oil retention = (wet mass - dry mass) / (wet mass) x 100. In addition, two types of lubricating oil with different viscosities were used. Specifically, VG-22, which has a low viscosity, and VG-68, which has a high viscosity, were used as the lubricating oil. In the comparative example, the oil retention was measured under the same conditions as in the above examples.

[0027] As shown in FIG. 11, the oil retention of the Examples is improved compared to the Comparative Examples for all lubricating oils of different viscosities. This is thought to be because, as described above, the Examples have a high porosity and therefore are more likely to retain oil than the Comparative Examples, in which almost no pores are formed. Thus, it can be seen that the Examples, which have pores, have improved oil retention compared to the Comparative Examples. The "improvement rate" shown in FIG. 11 indicates the rate at which the oil retention of the Examples is improved relative to the Comparative Examples. In other words, the improvement rate is calculated as follows: oil retention of the Examples / oil retention of the Comparative Examples x 100.

[0028] (Friction coefficient when lubricated with oil) In the examples and comparative examples, the static friction coefficient μs and the dynamic friction coefficient μk were measured in a state in which the lubricant oil was impregnated. These friction coefficients were measured by the reciprocating sliding test according to the Bowden test described above, and the measurement conditions were the same as those of the example shown in Figure 8. However, the number of reciprocating sliding was 1 time and 1000 times.

[0029] As shown in FIG. 12, it can be seen that the number of reciprocating slides in the embodiment is reduced both at 1 and 1000 times by impregnating the lubricating oil. This is due to the reduction in friction by the lubricating oil. In particular, in the embodiment, the friction coefficient is reduced even when the number of reciprocating slides increases at both positions close to and far from the center O by impregnating the lubricating oil. In this way, it can be seen that the embodiment contributes to reducing the friction coefficient by retaining the lubricating oil by the pores. In contrast, as shown in FIG. 13, the comparative example has a uniform hardness overall and has almost no pores, so the retention of the lubricating oil is small. Therefore, it can be seen that the friction coefficient increases with the increase in the number of reciprocating slides in the comparative example, even when a lubricating oil is used.

[0030] As described above, in this embodiment, the hardness of the sliding layer 31 is set to be greater on the outer side than on the center O side. Therefore, when the sliding layer 31 slides on the swash plate 14 of the piston pump 10, even if the sliding layer 31 receives a force due to the rotation of the swash plate 14 and the pressurization of the fluid, the wear resistance of the sliding layer 31 is improved on the hard outer peripheral side. Even if a large force is applied to the sliding layer 31 due to the pressurization of the fluid in the fluid chamber 16, the force is received by the soft part of the sliding layer 31 near the center O and transmitted to the outside, and the shape of the sliding layer 31 is maintained by the harder outer part. As a result, even under severe conditions such as further high pressure, the uneven wear is reduced by the appropriate hardness according to the part. Therefore, the wear resistance as a whole can be further improved.

[0031] In this embodiment, the slide layer 31 is porous and has pores. When the porosity, which is the ratio of pores in the slide layer 31, increases, the amount of lubricating oil held inside the slide layer 31 increases. That is, the lubricating oil is held in the pores formed in the slide layer 31. Therefore, by increasing the porosity, the friction between the slide layer 31 and the counter member can be reduced. Therefore, the wear resistance can be further improved.

[0032] In the manufacturing method of the sliding member 30 according to the present embodiment, the powder 44 of the material forming the sliding layer 31 is filled in the recess 42 of the jig 41, and then the support member 43 is placed thereon and sintered. Therefore, the powder 44 filled in the recess 42 is sintered in a state where it is pressed in the axial direction by the support member 43. As a result, when the powder 44 forming the sliding layer 31 is softened by heating due to sintering, it moves from the center O toward the outer periphery under the force, and the movement is restricted by the inner wall 45 of the jig 41. Therefore, the formed sliding layer 31 has a lower density on the center O side and is relatively soft, whereas the density on the outer periphery side is increased and is relatively hard. As a result, the formed sliding layer 31 has a hardness gradient between the center O and the outer periphery side. Moreover, since the sliding layer 31 is formed by sintering the powder 44, voids are formed inside. Therefore, voids can be formed inside the formed sliding member 30, and a hardness gradient can be formed in the radial direction.

[0033] The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist of the invention. [Explanation of symbols]

[0034] In the drawings, 30 denotes a sliding member, 31 denotes a sliding layer, 32 denotes a support layer, 41 denotes a jig, 42 denotes a recess, 43 denotes a support member, and 44 denotes powder.

Claims

1. A support base that moves back and forth, a sliding layer which is porous and has a plurality of pores, is provided on one end surface side of the support layer which slides against a counter member, and when the moving direction of the support layer is defined as an axial direction, the porosity, which is the ratio of the pores based on the volume, is reduced outside the center in a radial direction perpendicular to the axial direction, thereby increasing the density outside the center and setting the hardness high; A sliding member comprising:

2. 2. The sliding member according to claim 1, wherein the cross section perpendicular to the axis of the sliding layer is circular.

3. A sliding member according to claim 1 or 2, wherein the porosity of the sliding layer is 0.1% or more and 3.2% or less.

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