JP5101879B2 - Sliding structure - Google Patents

Description

  The present invention relates to a sliding structure used in lubricating oil, and more particularly to a sliding structure in which a friction coefficient between a sliding member and a sliding member is reduced.

  2. Description of the Related Art Conventionally, a sliding member is used in which a curing process is performed on a sliding surface of a sliding member and a curing layer is formed on the sliding surface. Then, a mixed coating of metallic chromium and chromium nitride is formed as a hardened layer on the sliding surface, or a hardened layer is formed by carburizing and quenching the sliding surface.

  By forming a hardened layer on the sliding surface, the wear resistance and seizure resistance on the sliding surface are improved. In this way, the wear resistance of the sliding surface of the sliding member subjected to the curing treatment can be increased, but conversely the sliding surface subjected to the curing treatment slides on the sliding surface of the sliding member. By contacting, the sliding surface of the sliding member was worn.

Moreover, as the sliding member wears the sliding surface of the sliding member, the sliding resistance of the sliding member increases, and the operation of the sliding structure cannot be performed smoothly.
For this reason, not only the lifetime of the sliding structure using the sliding member is limited, but also the performance of the equipment using the sliding structure is lowered.

  Recently, even in mechanical parts such as internal combustion engines and hydraulic equipment that slide in lubricating oil, the energy consumed by the sliding structure is reduced and the sliding surface of the sliding member is prevented from being worn. That is required. In addition, in order not to adversely affect the environmental problems, there is an increasing demand for reducing energy consumption by reducing wear debris caused by wear on the sliding surface or reducing mechanical loss. ing. In particular, in a region where friction loss is large and the sliding conditions are severe, it is desired to reduce the sliding resistance to reduce the generation of wear debris and mechanical loss due to wear.

  In order to improve the slidability of the sliding surface of the sliding member, it has been proposed that the sliding surface is coated with a DLC (diamond-like carbon) film, and the surface of the cured layer formed on the sliding surface is DLC. A bushing fitted with a cylinder, which has a piston with a membrane (see Patent Document 1) and a piston with a DLC membrane coated on its surface, and which is a mating member with which the piston slides, is made of a copper alloy. A fluid machine (see Patent Document 2) has been proposed.

  There has also been proposed a sliding member (see Patent Document 3) in which the hydrogen content on the surface of the amorphous carbon film is limited to 10 at% (the atomic ratio is expressed as at%) or less. As the conventional examples in the present invention, those described in Patent Documents 1 to 3 as Conventional Examples 1 to 3, respectively, the outline of each configuration will be described below.

  The piston described in Patent Document 1 shown as Conventional Example 1 is a piston used in an axial piston pump, and FIG. 7 shows a cross-sectional view thereof. As shown in FIG. 7, the tip of the piston 40 is provided with a spherical portion 41, and a piston shoe (not shown) is rotatably mounted on the spherical portion 41. Further, the outer surface of the piston 40 is subjected to a surface treatment, and a hardening treatment layer 42 and a DLC film 43 are formed.

  That is, a soft nitriding process is performed on the surface of the iron piston 40 to form the hardened layer 42. A compound layer and a diffusion layer below the compound layer are formed in the hardened layer that has been subjected to the soft nitriding treatment. Therefore, by polishing the surface on which the cured layer is formed, the compound layer is removed and the surface is smoothed. In this way, a layer excluding the compound layer is formed as the cured layer 42.

  Then, the DLC film 43 is coated on the outer surface of the piston 40 on which the cured layer 42 is formed. By forming the DLC film 43, the friction coefficient on the outer surface of the piston 40 can be reduced, and the slipperiness can be improved.

  The piston described in Patent Document 2 shown as Conventional Example 2 is also a piston 53 used in an axial piston pump, and FIG. 8 shows a sectional view thereof. As shown in FIG. 8, a cylinder block 50 that is rotationally driven in synchronization with a pump shaft (not shown) is formed with a plurality of bush holes 51 that are formed at equal intervals in the circumferential direction.

  A bush 52 is press-fitted into the bush hole 51. The bush 52 is formed in a hollow shape and is made of a copper alloy suitable as a bearing material such as phosphor bronze, aluminum bronze, manganese bronze, and various brasses. A piston 53 is slidably mounted on the inner peripheral surface of the hollow portion of the bush 52.

  A piston shoe 54 is rotatably attached to the root portion of the piston 53 via a spherical joint 55. A thrust plate 56 provided on the piston shoe 54 is in contact with a swash plate 57 whose swash plate angle can be adjusted variably. As the cylinder block 50 rotates, the piston shoe 54 slides on the swash plate surface. To do. The piston 53 can reciprocate in the bush 52 by sliding the piston shoe 54 on the swash plate surface.

  The piston 53 is made of a ferrous material such as special steel as a base material, and the entire outer surface thereof is covered with a DLC film 58. The cylinder-side bush 52 is made of a copper alloy. With this configuration, the sliding friction coefficient can be reduced by the DLC film 58 formed on the outer surface of the piston 53, and the slidability with the bush 52 can be improved.

  Further, the wear resistance of the piston 53 can be improved, and furthermore, the cylinder-side bush 52 is made of a copper alloy, so that the sliding compatibility with the piston 53 on which the DLC film 58 is formed is compatible. It is possible to maintain good properties.

  The sliding member described in Patent Document 3 shown as Conventional Example 3 can be used for mechanical parts such as an internal combustion engine that slides in lubricating oil. By the way, the conventional hard carbon film-treated sliding member has a solid lubricity, but has a surface roughness equivalent to that in lubricating oil and does not have a solid lubricity, or a superfinished sliding member. There was a problem that it showed only the same degree of friction performance as the processed steel member. As a solution to this problem, a sliding member described in Patent Document 3 has been proposed.

  And the sliding member which has the amorphous carbon film whose surface hydrogen content is 10 at% or less is comprised. In addition, in the case of a sliding member having a DLC film, the surface of the DLC film is subjected to plasma nitrogen treatment or plasma oxygen treatment, and the nitrogen content and oxygen content in the DLC film are 0.5 at% or more and 30 at% or less. It is said.

By setting the nitrogen content and oxygen content on the surface of the DLC film to 0.5 at% or more and 30 at% or less, it is possible to provide a hard carbon film sliding member having a high hardness and a smooth surface and excellent wear resistance. Yes.
JP 2000-320670 A JP 2003-343450 A JP 2000-297373 A

  Incidentally, the DLC film is configured as an amorphous hard carbon film, and is generally composed of carbon and hydrogen. As its characteristics, it has characteristics intermediate between graphite and diamond. In addition, the mechanical properties of the DLC film containing hydrogen vary greatly depending on the film forming method and film forming conditions, and among them, the sliding characteristics and the wear resistance are generally said to have a trade-off relationship. In general, the greater the amount of hydrogen in the DLC film, the lower the hardness and the lower the coefficient of friction.

  In addition, among amorphous hard carbon films, DLC films containing almost no hydrogen produced by physical vapor deposition (PVD method) or the like, DLC films containing hydrogen produced by chemical vapor deposition (CVD method) are used. It is known that low friction is expressed in lubricating oil. On the other hand, it is known that a general DLC film excellent in low friction property in air, that is, a DLC film containing hydrogen has a small friction reducing effect in the presence of lubricating oil. Yes.

  The DLC film produced by the PVD method containing almost no hydrogen has the advantage that low friction is expressed in the lubricating oil, but the DLC film produced by the PVD method is generally free of hydrogen. The film has a high film hardness and hard fused and re-solidified carbon particles are attached, so that protrusions are formed on the surface.

  For this reason, when a sliding member formed with a DLC film containing almost no hydrogen is slid against a sliding member made of, for example, an aluminum alloy, the aggression against the aluminum alloy becomes high, and wear There was a problem that burn-in occurred.

  In the pistons and fluid machines shown in Patent Documents 1 and 2, there is no mention of the hydrogen content contained in the DLC film, and in particular, in order to develop low friction in the lubricating oil, the hydrogen content is reduced. There is no disclosure or suggestion about a configuration using a DLC film of 10 at% or less. Patent Document 3 describes that a sliding member coated with a DLC film having a hydrogen content of 10 at% or less is used in a lubricating oil. It was not taken.

  A countermeasure against the presence of hard molten re-solidified carbon particles called droplet particles is not disclosed or suggested in Patent Documents 1 and 2. Further, the DLC films disclosed in Patent Documents 1 and 2 are not particularly specified in the respective documents, but from the overall description, the DLC films containing hydrogen prepared by the CVD method are described. Can be thought of as using.

  Patent Document 3 describes that the surface roughness of the coated DLC film is preferably 0.1 μm or less in terms of the center line average roughness Ra. No measures are disclosed or suggested about the relationship that exists between the size of the let particles. In particular, the centerline average roughness Ra is a value obtained by folding the roughness curve at the centerline and dividing the area obtained by the folded roughness curve and the centerline by the length measured to obtain the roughness curve. Is expressed as μm.

  Assuming that the surface roughness of the DLC film, which represents the state at this time as the center line average roughness Ra, is 0 μm in the state where the presence of droplet particles is ignored, Considering the case where spherical droplet particles having a diameter of 0.15 μm are present, the following is obtained.

  In other words, if the number of droplet particles present in the measured length for obtaining the roughness curve at this time is small, there is a spherical droplet particle having a diameter of 0.15 μm. However, the surface roughness of the DLC film at this time is 0.1 μm or less in terms of the center line average roughness Ra. In particular, if the number of droplet particles present in the measured length for obtaining the roughness curve is extremely small, even if droplet particles having a diameter larger than 0.15 μm are present, the DLC film The surface roughness is 0.1 μm or less in terms of the center line average roughness Ra.

  Due to the presence of the droplet particles, the droplet particles act as sand in sandpaper. For this reason, the larger the size of the droplet particles, the larger the amount of scraping the sliding surface of the sliding member and the depth of the scratch formed by scratching the sliding surface of the sliding member. .

  In this way, when the sliding member side is worn by the droplet particles, a gap or the like formed by a cut is formed between the sliding member and the sliding member. Become. When the sliding member is a piston, the cylinder side is worn. In this manner, when a gap or a streak is formed between the cylinder and the piston, the hydraulic oil leaks from the gap or the streak. In such a state, the operating performance of the hydraulic equipment is greatly reduced.

  The present invention has been made in view of the above-described problems of the prior art, and achieves both wear resistance and seizure resistance while reducing the friction coefficient of the sliding surface sliding in the lubricating oil. Another object of the present invention is to provide a sliding structure capable of causing low friction sliding. Further, focusing on the droplet particles attached when the DLC film having a hydrogen content of 10 at% or less is coated, the influence of the droplet particles is reduced.

The object of the present invention can be achieved by the inventions described in claims 1 to 4.
That is, according to the present invention, in the sliding structure including the sliding member and the sliding member that repeatedly perform relative sliding in the lubricating oil, one sliding of the sliding member or the sliding member is performed. The surface is coated with a DLC (diamond-like carbon) film having a hydrogen content of 10 at% or less, and the other sliding surface of the sliding member or the sliding member is made of a copper alloy, The height to the top of the droplet particles attached when the DLC film is coated is 0.05 to 0.4 μm from the center line or the average line of the roughness curve on the sliding surface coated with the DLC film. The surface roughness of the coated DLC film is suppressed to be 0.015 to 0.053 μm at the center line average roughness Ra, and 0.176 to 0.497 μm at the maximum height Rmax. The most important features and none There.

Further , the main feature of the present invention is that the thickness of the DLC film is specified.
Furthermore , the main feature of the present invention is that the member constituting the sliding surface covered with the DLC film is specified.
Furthermore , the main feature of the present invention is that the application using the sliding member and the sliding member is specified.

  In the present invention, in order to reduce the sliding resistance in the lubricating oil, a DLC film having a hydrogen content of 10 at% or less is coated on one sliding surface of the sliding member or the sliding member. The other sliding surface on which the sliding member or the sliding member covered with is slid is made of a copper alloy. Thereby, it becomes possible to maintain good slidability between the sliding surface of the member coated with the DLC film in the lubricating oil and the mating sliding surface made of copper alloy, Moreover, the occurrence of seizure on the sliding surface and the friction coefficient of the sliding surface on the copper alloy side can be reduced.

  As described above, the DLC film having a hydrogen content of 10 at% or less and the copper alloy reduce the sliding resistance in the lubricating oil, improve the sliding conformability, and wear resistance on the copper alloy side. Can be improved at the same time. Therefore, the reliability of the sliding structure can be greatly enhanced.

  In particular, if the present invention is applied to the relationship between a piston and a cylinder bore in a hydraulic piston pump or the like, the sliding resistance of the piston is reduced, and the efficiency as a pump can be greatly improved.

In the present invention, the droplet particles present in the DLC film can be formed so as to be within 0.05 to 0.4 μm from the center line or average line of the roughness curve in the DLC film. By comprising in this way, the sliding surface of the member which coat | covered the DLC film can be made into a smooth state, and the slidability in lubricating oil can be kept further favorable. And generation | occurrence | production of the baking on a sliding surface and abrasion of the sliding surface by the side of a copper alloy can be prevented significantly.
And since the protrusion amount of the droplet particle | grains which exist in a DLC film can be suppressed, it can reduce significantly that an other party member is worn by a droplet.

Further, the surface roughness of the DLC film is formed so as to be within 0.015 to 0.053 μm at the center line average roughness Ra, and so as to be within 0.176 to 0.497 μm at the maximum height Rmax. By forming, the smoothness on the sliding surface of the member coated with the DLC film can be further improved.
Note that when measuring the surface roughness of the DLC film, it is necessary to measure such that an unusually deep valley portion that is recognized as a scratch is not included in the reference length.

  If the thickness of the DLC film is formed to be thicker than 1.0 μm, a long time is required for the work time required to form the DLC film. Moreover, as the thickness of the DLC film increases, the DLC film is more easily peeled off, and the durability of the DLC film is reduced. And the ratio which droplet particle adheres will also increase.

  For this reason, in order to improve the workability at the time of manufacture, to increase the durability, and not to increase the adhesion amount of the droplet particles, it is desirable that the thickness of the DLC film is 1.0 μm or less. Become.

  In general, it is said that the hardness of the base material covering the DLC film is preferably hard. However, in the present invention, the sliding surface of the steel material can be treated by, for example, nitriding or soft nitriding. It is desirable to form a hardened layer by performing carburization, induction hardening, or the like.

  When coating the DLC film having a hydrogen content of 10 at% or less on the sliding surface of the steel material subjected to surface hardening treatment, the center line average roughness Ra on the sliding surface of the steel material subjected to nitriding treatment is set to 0. It is desirable to form it below 1 μm. By forming the center line average roughness Ra on the sliding surface to be 0.1 μm or less, the size of the unevenness existing on the base surface can be reduced. Therefore, even when the DLC film is coated, the underlying irregularities do not appear on the surface of the DLC film, and a uniform DLC film can be formed.

  By coating the sliding surface of the piston with the DLC film and forming the cylinder bore surface on which the piston slides with a copper alloy, the above-described effects specific to the present invention can be achieved. Further, the sliding resistance of the piston is reduced, and the efficiency as a pump or a motor can be greatly improved. In addition, the durability life of the piston and the cylinder bore can be increased. As a result, it is possible to configure a hydraulic device with low sliding resistance.

  Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. As the sliding structure of the present invention, in addition to the shapes and arrangements described below, those shapes and arrangements can be adopted as long as they can solve the problems of the present invention. Is. For this reason, this invention is not limited to the Example demonstrated below, A various change is possible.

  Further, the description of the sliding structure of the present invention will be made by taking an axial piston pump as an example, but the sliding structure of the present invention is not limited to the axial piston pump. For example, the sliding structure of the present invention is also suitably applied to a hydraulic pump including a radial piston pump, a hydraulic motor, a hydraulic pump / motor, a bearing structure, an engine valve seat, a tappet for controlling an engine fuel valve, and the like. Is something that can be done.

  In addition to this, the sliding structure of the present invention can also be suitably applied to a sliding structure including a sliding member that can be used in lubricating oil and a sliding member. The sliding member may be configured to slide relative to the sliding member, and the sliding member may be fixed or movable.

  FIG. 1 is a schematic sectional view of an axial piston pump according to an embodiment of the present invention. FIG. 2 schematically shows an enlarged sectional view of the piston. FIG. 3 shows an enlarged relationship between the cylinder bore and the piston. In FIG. 2 and FIG. 3, the piston shoe attached to the piston is indicated by a virtual line.

  The axial piston pump 1 includes a rotating shaft 7 and a cylinder block 3 that rotates integrally with the rotating shaft 7 in a casing 8. A plurality of cylinder bores 12 are formed in the cylinder block 3 in the circumferential direction in parallel with the rotating shaft 7.

  The inner peripheral surface 14 of each cylinder bore 12 is made of a copper alloy, and the piston 5 is arranged to reciprocate along the inner peripheral surface 14 of the cylinder bore 12. The head of each piston 5 is formed with a recess 5a (see FIG. 2) for rotatably accommodating the spherical portion 6a of the piston shoe 6. After the spherical portion 6a is stored, the open end side of the concave portion 5a is crimped to attach the piston shoe 6 to the tip portion of the piston 5 in a swingable manner.

  The piston shoe 6 is in sliding contact with the swash plate 2 that can be tilted with respect to the rotating shaft 7 and is held by a retainer 10. The retainer 10 is rotatably guided through a retainer guide 13 urged toward the swash plate 2 by a spring 17 and a pressing rod 16.

  The swash plate 2 that determines the pump capacity of the axial piston pump 1 is controlled to have a desired tilt angle with respect to the rotary shaft 7 by a tilt mechanism (not shown). A port is formed on the bottom side of each cylinder bore 12, and each port selectively communicates with half-moon shaped ports 9a, 9b (not shown) formed on the valve plate 11 as the cylinder block 3 rotates. The ports 9a and 9b are connected to the suction port 18a and the discharge port 18b of the axial piston pump 1, respectively.

  The pressure oil sucked from the suction port 18a can be sucked into the cylinder bore 12 by the expansion process of the piston 5, and the pressure oil in the cylinder bore 2 compressed by the compression process of the piston 5 can be discharged from the discharge port 18b. The configuration of such an axial piston pump is a well-known configuration and does not constitute a feature of the present invention. As the axial piston pump, an axial piston pump having a known configuration can be used.

  As shown in FIG. 2, a hardened layer 23 is formed on the outer surface of the piston 5 by soft nitriding, and a DLC having a hydrogen content of 10 at% or less is formed on the surface of the hardened layer 23 by a PVD method or the like. A film 20 is formed. That is, the sliding surface of the piston 5 is covered with the DLC film 20 that hardly contains hydrogen. 1 and 3, the DLC film 20 is indicated by a thick line. As shown in the enlarged view of FIG. 3, the surface of the cylinder bore 12 that slidably houses the piston 5 is made of a copper alloy.

  The cylinder bore 12 is formed hollow, and the inner peripheral surface 14 is made of lead-bronze alloy, aluminum-bronze alloy, manganese-bronze alloy, lead-bronze alloy, copper-lead alloy, It is made of a copper alloy suitable as various bearing materials such as a copper-lead-tin-iron alloy and a copper-tin-iron alloy.

  The outer surface of the piston 5 on which the hardened layer 23 is formed by soft nitriding may be subjected to a treatment such as polishing so that the center line average roughness Ra is 0.1 μm or less. A DLC film 20 having a hydrogen content of 10 at% or less using the PVD method is applied to the outer surface of the piston 5 on which the hardened layer 23 having a center line average roughness Ra of 0.1 μm or less is formed. The coating is performed so that the thickness is 0 μm or less.

  The surface of the DLC film 20 deposited by the PVD method is 0.05 μm or less at the center line average roughness Ra and 0.5 μm or less at the maximum height Rmax. It can be polished by polishing, abrasive grains, buffing or the like. The surface roughness of the DLC film 20 may be configured to satisfy both the above-described centerline average roughness Ra and the maximum height Rmax, or the above-described centerline average roughness Ra or the maximum height. It is also possible to configure so that one of Rmax is satisfied.

  At this time, in the roughness curve obtained with respect to the surface of the DLC film 20, the peak with respect to the surface of the DLC film 20 is not generated so that a peak protruding from 0.4 μm at the height from the center line or average line does not occur. It is necessary to carry out a polishing process sufficiently with a diamond grindstone, abrasive grains, buffing or the like. Thereby, all the heights from the center line or the average line to the top of the later-described droplet can be kept to 0.4 μm or less.

  With this configuration, it is possible to greatly reduce the wear of the inner peripheral surface 14 of the cylinder bore 12 and the formation of scratches due to the droplets. In addition, due to the good compatibility between the DLC film containing almost no hydrogen and the copper alloy constituting the inner peripheral surface 14 of the cylinder bore 12, the sliding resistance in the lubricating oil is reduced, and the sliding compatibility is improved. Improvement of wear resistance on the copper alloy side can be realized at the same time.

When the surface of the spherical portion 6a of the piston shoe 6 is made of a copper alloy, the DLC film 20 containing almost no hydrogen can also be formed in the concave portion 5a of the piston 5 that is in sliding contact with the spherical portion 6a. In the illustrated example, an example in which the DLC film 20 is formed on the inner peripheral surface of the recess 5a of the piston 5 is shown.
Further, when the DLC film 20 containing almost no hydrogen is formed on the spherical portion 6a of the piston shoe 6, the surface of the concave portion 5a of the piston 5 can be made of a copper alloy.

  As a result, even between the piston shoe 6 and the piston 5, it is possible to reduce sliding resistance in the lubricating oil, improve sliding conformability, and improve wear resistance on the copper alloy side.

  The PVD method is a method of forming a film on a substrate by evaporating a metal or a non-metallic material. A reactive gas is introduced at the same time as evaporation, and an evaporated metal or reactive gas is generated using plasma generated by discharge. Is ionized to form a compound film on the substrate.

  As a PVD method for forming a compound film on a substrate, a vacuum deposition method, an ion plating method, a laser ablation method, an arc method, and a sputtering method are generally known. As an ion plating method, an HCD is used. Method, high frequency excitation method, and cluster method. Further, as a sputtering method, a direct current method, a high frequency method, a magnetron method and the like are known.

  A DLC film having a hydrogen content of 10 at% or less can be formed by using a PVD method that does not use hydrocarbon gas plasma at least when the film is formed on the substrate. In the present invention, by using the PVD method as described above, the surface of the sliding member subjected to the hard treatment can be coated with a DLC film having a hydrogen content of 10 at% or less.

Also, as shown in FIG. 4, the surface of the recess 32a of the piston shoe 32 that rotatably receives the spherical portion 31a formed on the piston 31 is made of a copper alloy, and almost no hydrogen is applied to the surface of the spherical portion 31a of the piston 31. An uncontained DLC film can also be formed. Alternatively, the surface of the spherical portion 31a of the piston 31 can be made of a copper alloy, and a DLC film containing almost no hydrogen can be formed on the surface of the recess 32a of the piston shoe 32.
The spherical portion 31a of the piston 31 is housed in the recess 32a and the open end of the recess 32a is crimped so that the piston shoe 32 can be rotatably mounted on the piston 31.

  The surface of the swash plate 6 and 32 that is in contact with the swash plate 2 and the surface of the swash plate 2 that is in contact with the piston shoes 6 and 32 are configured by a combination of a DLC film and a copper alloy in the same manner as described above. With the swash plate 2, it is possible to reduce sliding resistance in the lubricating oil, improve sliding conformability, and improve wear resistance on the copper alloy side.

  The fact that the droplet 30 adheres when the DLC film 20 is coated on the sliding surface will be described with reference to FIGS. In order to reduce the adhesion of the droplet 30 in forming the DLC film, a method of ionizing the amount of the non-metallic material and the reaction gas little by little and covering the substrate 21, or the schematic diagram shown in FIG. In addition, a method of disposing the jammer plate 27 on the front side of the substrate 21 can be used. The droplets 30a and 30b in FIGS. 5 and 6 are shown with exaggerated sizes.

  A method of using the jammer plate 27 shown in FIG. 5 will be described. For example, the jammer plate 27 is disposed between the cathode 25 using a non-metallic material and the substrate 21. The cathode 25, the substrate 21, and the baffle plate 27 are disposed in a sealed processing chamber (not shown), and a reactive gas is introduced into the processing chamber. Since the droplets 30a and 30b generated from the cathode 25 have the property of going straight, they can be blocked by the jammer plate 27.

  In this way, the droplets 30a and 30b can be configured to hardly reach the substrate 21. In particular, since the droplet 30a having a large diameter can be attached to the jammer plate 27, the droplet 30a having a large diameter can be prevented from reaching the substrate 21.

  Even if a part of the droplet 30b reaches the substrate 21 by bypassing the jammer plate 27, the droplet 30b that can reach the substrate 21 has only a small diameter. By using the jammer plate 27 in this way, it is assumed that the droplet 30a having a large diameter as shown by the phantom dotted line in FIG. 6 does not adhere to the sliding surface of the sliding member 21 which is the substrate, but adheres to it. Also, the droplet 30b can have a small diameter.

  Further, by lowering the ionization concentration, it is possible to prevent the ionized droplets from adhering to each other and grow into a droplet having a large diameter. In this manner, the height of the droplet 30b protruding from the center line or average line 35 of the roughness curve in the DLC film 20 coated on the sliding surface can be configured to be 0.4 μm or less.

  If the protruding height of the attached droplet 30b is 0.4 μm or more from the center line or average line 35 shown in FIG. 6, a buffing process or the like is performed on the surface of the DLC film 20. Therefore, the height of the droplet 30b protruding from the center line or the average line 35 can be suppressed to 0.4 μm or less.

  By comprising in this way, in this invention, the low friction in lubricating oil is realizable between a sliding member and a to-be-slidable member. In addition, the DLC film is formed with a thickness of 1 μm or less, the roughness of the DLC film is formed with a center line average roughness Ra of 0.05 μm or less, and a maximum height Rmax of 0.5 μm or less, and the height of the droplets Therefore, good sliding characteristics can be maintained for a long time without wearing the inner peripheral surface 14 of the cylinder bore 12 made of a copper alloy.

Experimental example

Cylinder bore after operating for about 1 hour at suction pressure 0 ± 9.8KPa under the conditions that the rotational speed in the axial piston pump is 2000rpm, the pump discharge pressure is 0-380Kg / cm ² , and the oil temperature is 50-80 ° C. The amount of wear was measured in the following two cases. The cylinder bore was made of a copper-based material.

  As an experimental example according to the present invention, the surface roughness of the DLC film coated on the piston is Rmax = 0.176 to 0.497 μm (Ra = 0.015 to 0.053 μm, dropped from the center line of the roughness curve). A lett particle height of 0.05 to 0.4 μm was used. Further, as a comparative example, the surface roughness of the DLC film coated on the piston is Rmax = 0.596 to 0.964 μm (Ra = 0.074 to 0.127 μm, droplet particles from the center line of the roughness curve). The one having a height of 0.4 to 0.6 μm was used.

As a result of this experiment, when the piston of the experimental example according to the present invention was used, the wear amount of the cylinder bore made of a copper-based material was 10 μm or less, whereas the piston of the comparative example was used. In this case, the wear amount of the cylinder bore made of a copper-based material was 57 to 72 μm.
Moreover, in the experimental example, it was confirmed that the torque efficiency was improved by 1 to 3% compared to the case where the DLC film was not coated.

  Thus, by adopting the configuration of the present invention, the amount of wear of the counterpart member made of a copper-based material can be reduced, and the sliding structure has excellent durability and low sliding resistance. Can be obtained.

  The technical idea of the present invention can be applied to a device or the like to which the technical idea of the present invention can be applied.

It is sectional drawing of the axial piston pump concerning embodiment of this invention. (Example) It is sectional drawing of a piston. (Example) It is an enlarged view which shows the arrangement | positioning relationship between a piston and a cylinder bore. (Example) It is sectional drawing which shows the modification of a piston and piston shoe. (Example) It is explanatory drawing which prevents that a large diameter droplet adheres. (Example) It is sectional drawing which shows the adhesion state of a droplet. (Example) It is sectional drawing of a piston. (Conventional example 1) It is sectional drawing which shows the arrangement | positioning relationship between a piston and a cylinder bore. (Conventional example 2)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Axial piston pump 2 ... Swash plate 3 ... Cylinder block 5 ... Piston 6 ... Piston shoe
14 ... Cylinder bore inner peripheral surface 20 ... DLC film 21 ... Substrate 23 ... Hardened layer 25 ... Cathode 27 ... Baffle plates 30a, 30b ... Droplet 31 ... Piston 32 ... Piston shoe 40 ... Piston 42 ... Hardened layer 43 ... DLC film 50 ... Cylinder block 52 ... Bush 53 ... Piston 58 ... DLC film

Claims (4)

In a sliding structure including a sliding member and a sliding member that repeatedly perform relative sliding in lubricating oil,
One sliding surface of the sliding member or the sliding member is coated with a DLC (diamond-like carbon) film having a hydrogen content of 10 at% or less,
The other sliding surface of the sliding member or the sliding member is made of a copper alloy,
The height to the top of the droplet particles attached when the DLC film is coated is 0.05 to 0.4 μm from the center line or the average line of the roughness curve on the sliding surface coated with the DLC film. Be suppressed,
The coated DLC film has a surface roughness of 0.015 to 0.053 μm as a center line average roughness Ra, and 0.176 to 0.497 μm as a maximum height Rmax. A sliding structure.   The sliding structure according to claim 1, wherein the DLC film is formed to have a thickness of 1.0 μm or less. The DLC film is coated on a sliding surface of a steel material subjected to surface hardening treatment,
The sliding structure according to claim 1 or 2, wherein a sliding surface of the steel material covering the DLC film is formed to have a center line average roughness Ra of 0.1 µm or less.   The sliding member having a sliding surface coated with the DLC film is a piston, and the sliding member is a cylinder bore having a sliding surface made of a copper alloy. The sliding structure according to the above.

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