JP2018189101A - Sliding structure - Google Patents

Abstract

Provided is a sliding structure capable of generating a good levitation force between a pair of sliding surfaces and reducing sliding resistance between the two. A sliding structure includes a first member having a first sliding surface and a second sliding surface facing the first sliding surface. And a second member 2 that relatively moves in the sliding direction H1. Lubricating fluid is interposed in the gap G between the first sliding surface 1S and the second sliding surface 2S. The second sliding surface 2S includes a microtexture structure portion 30 including a plurality of grooves 3 extending in a direction orthogonal to the sliding direction H1. Each of the grooves 3 of the microtextured structure portion 30 includes a first portion LA that traps turbulent flow of the lubricating fluid flowing through the gap G, a second portion LB that secures laminar flow of the flowing lubricating fluid, and And a third portion LC for confining the laminar flow of the lubricating fluid in a gradually narrowing space. [Selection] Figure 2

Description

  The present invention relates to a sliding structure in which one member slides relative to the other member.

  In a sliding structure in which one member slides relative to the other member, it is required to reduce the sliding resistance between both members. For example, in a reciprocating piston engine, the inner peripheral wall of the cylinder and the outer peripheral wall of the piston skirt, the large end of the connecting rod and the pin portion of the crankshaft can be cited as the sliding structure, and the fuel consumption performance of the engine and In order to improve the output performance, it is required to reduce the sliding resistance between these two members. Patent Document 1 discloses a technique for levitating one member of a sliding structure relative to the other member in order to reduce sliding resistance.

Japanese Patent Laid-Open No. 2006-121597

  However, in the conventional levitation structure, the levitation force that levitates one member of the sliding structure relative to the other member may not be sufficiently secured. That is, even if an attempt is made to realize the levitation by interposing a lubricating fluid such as air, water or oil between the sliding surfaces of a pair of members, for example, a large force in the direction in which one member approaches the other member In such a case, the sliding surfaces may come into contact with each other. In this case, the sliding resistance cannot be reduced sufficiently.

  An object of the present invention is to provide a sliding structure capable of generating a good levitation force between a pair of sliding surfaces and reducing a sliding resistance between them.

  A sliding structure according to one aspect of the present invention includes a first member having a first sliding surface, and a second sliding surface facing the first sliding surface, with respect to the first member. A second member that relatively moves in a predetermined sliding direction, a lubricating fluid is interposed between the first sliding surface and the second sliding surface, and the second sliding surface is Including a microtexture structure portion composed of a plurality of grooves extending in a direction orthogonal to the sliding direction, each of the grooves of the microtexture structure portion is sequentially arranged from the downstream side to the upstream side of the sliding direction, A region including a first portion, a second portion, and a third portion, wherein the first portion traps a turbulent flow of the lubricating fluid flowing between the first sliding surface and the second sliding surface. The second part is a region for securing a laminar flow of the flowing lubricating fluid, and the third part is the lubricating fluid. Characterized in that it is a region for confining gradually narrower space the laminar flow.

  According to this sliding structure, when the first member and the second member slide, the second sliding surface is moved to the first sliding surface by the action of the microtexture structure portion formed on the second sliding surface. Float against the moving surface. That is, at the time of the sliding, the lubricating fluid relatively flows between the first and second sliding surfaces from the downstream side to the upstream side in the sliding direction. And each of the micro size groove | channel with which the said micro texture structure part is provided contains the 1st-3rd part arranged in order toward the said upstream from the said downstream. As a result, turbulent flow of the lubricating fluid that does not substantially contribute to levitation is trapped in the first portion, and only the laminar flow is circulated in the second portion, and finally, the laminar flow is circulated in the third portion. Can be confined in a gradually narrowing space. Therefore, a large levitation force can be generated in the second sliding surface with respect to the first sliding surface, and a sliding resistance between the first member and the second member can be reduced. .

  In the above sliding structure, the groove has a tendency that the downstream side in the sliding direction is deep and the upstream side is shallow, and the groove has an intermediate region between the downstream side and the upstream side. A protrusion that protrudes in the direction of the first sliding surface is formed from a line connecting a top portion that is the portion closest to the first sliding surface and a bottom portion that is the farthest portion, and the protruding portion is the second portion. It is desirable that the portion, the portion on the downstream side of the protruding portion of the groove constitute the first portion, and the portion on the upstream side of the protruding portion of the groove constitute the third portion.

  According to this sliding structure, since the groove has a tendency that the downstream side is deep and the upstream side is shallow, the lubricating fluid is confined from a relatively wide space to a relatively narrow space during the sliding. Flow while repeating. By such a confinement action, a large levitation force can be generated on the second sliding surface with respect to the first sliding surface. And the said 1st part thru | or 3rd part can be easily constructed | assembled in the said groove | channel by arrange | positioning the said projection part in the said groove | channel. That is, the deep region of the groove including the bottom can be used as the first portion to easily enclose the turbulent flow, and the shallow region of the groove including the top can be used as the third portion to easily confine the laminar flow. can do. And the 2nd part which ensures the said laminar flow can be formed by the said projection part. Therefore, the functions required for the first to third parts described above can be realized with a simple structure of protrusions.

  In this case, the protrusion has a vertical wall extending in the direction orthogonal to the sliding direction on the downstream side, and a lateral wall extending in the sliding direction on the upstream side, and the first portion includes the vertical portion. A region defined by a wall, a bottom wall including the bottom, and the downstream groove wall, the second portion is a region where the lateral wall exists, and the third portion is a region of the lateral wall. It is desirable that the region is formed of an inclined surface extending toward the upstream side so as to approach the first sliding surface from the upstream end in the sliding direction.

  According to this sliding structure, since the first portion has a U-shaped configuration defined by the vertical wall, the bottom wall, and the downstream groove wall, the turbulent flow can be more easily enclosed. be able to. Moreover, since the said horizontal wall is arrange | positioned at the said 2nd part, the said laminar flow can be smoothly flowed along the said horizontal wall. Furthermore, since the inclined surface is arranged in the third portion, the laminar flow can be confined in a gradually narrowing space along the inclined surface.

  In the above sliding structure, the groove is an opening edge of the groove and is a downstream edge and an upstream edge in the sliding direction, and a deepest bottom located between the edges, A first surface between the downstream edge and the bottom, and a second surface between the upstream edge and the bottom, wherein the first sliding surface is parallel to the sliding direction. The first surface is a surface having an inclination angle with respect to the first sliding surface in a range of 70 ° to 90 °, and the second surface has a gentler inclination than the first surface. It is desirable to have an inclined surface as a base tone and the protrusion.

  According to this sliding structure, the groove has the first surface and the second surface. When the laminar flow flows between the first and second sliding surfaces from the downstream side to the upstream side, the width of the laminar flow suddenly in the region of the first surface having an inclination in the range of 70 ° to 90 °. And the laminar flow is gradually confined by the second surface (the inclined surface) based on a gentler inclination than the first surface. At this time, the protrusion allows only laminar flow without a turbulent component. A good levitation force is generated by the operation of the laminar flow. Further, by setting an inclination angle of the first surface with respect to the first sliding surface in a range of 70 ° to 90 °, most of the width in the sliding direction of the groove functions as the inclined surface. The second surface can be configured. Therefore, the laminar flow confinement effect can be enhanced.

In the above sliding structure, when the distance between the top and the bottom in the direction perpendicular to the sliding direction is D, and the distance between the top and the top of the protrusion is Y, The following formula: 0.1D ≦ Y ≦ 0.6
It is desirable to be set within the range.

  According to this sliding structure, the relationship between the distance D corresponding to the depth of the groove and the distance Y corresponding to the depth of the apex of the protrusion is optimized, and as a result, a large levitation force is generated. Can be made.

In the above sliding structure, the protrusion has a vertical wall on the downstream side of the apex, and the pitch of the plurality of grooves arranged in the sliding direction is L1, each of the sliding direction in the sliding direction The distance between the downstream edge of the groove and the upstream edge is L2, and the distance between the first surface of the groove and the vertical wall of the protrusion in the sliding direction is X. When L1 = 1μm ~ 1mm
1μm ≦ L2 ≦ L1
0.2L2 ≦ X ≦ 0.6L2
It is desirable to be set within the range.

  According to this sliding structure, the relationship between the distance L2 corresponding to the length of the groove in the sliding direction and the distance X corresponding to the length of the first portion in the sliding direction is optimized. As a result, a large levitation force can be generated.

In the above sliding structure, the protrusion has a vertical wall on the downstream side of the apex and a horizontal wall on the upstream side, and the vertical wall is perpendicular to the sliding direction. When the angle formed by α and the angle formed by the lateral wall with respect to the sliding direction is β,
0 ° ≦ α ≦ 20 °
−15 ° ≦ β ≦ 15 °
It is desirable to be set within the range.

  According to this sliding structure, the shape of the protruding portion is optimized, and as a result, a large levitation force can be generated.

  In the above sliding structure, it is desirable that a pitch in which the plurality of grooves are arranged in the sliding direction is set in a range of 1 μm to 1 mm.

  According to this sliding structure, the pitch of the plurality of grooves is optimized, and a larger levitation force can be generated.

In the above sliding structure, when the gap between the top and the first sliding surface is the minimum gap h1, and the gap between the bottom and the first sliding surface is the maximum gap h2,
h1 = 0.5 μm to 2.0 μm,
h2 / h1 = 1.5-5.0,
It is desirable to be set within the range.

  According to this sliding structure, the minimum gap h1 at the top of the groove is set to the above numerical range, and the gap ratio h2 / h1 between the minimum gap h1 and the maximum gap h2 is within the above numerical range. Is set. For this reason, the second sliding surface is further improved from the first sliding surface by the lubricating fluid flowing between the first sliding surface and the second sliding surface during the relative movement of the second member. The sliding resistance can be remarkably reduced.

  In this case, the minimum gap h1 is the surface roughness of the first sliding surface, or when the second sliding surface has a plateau portion between the plurality of grooves, the first sliding surface and the It is desirable that the surface roughness of the plateau portion is set to a value larger than the total surface roughness.

  According to this sliding structure, by setting the minimum gap h1 to the value as described above, the second sliding surface on which the first sliding surface and the microtexture structure portion are formed at the time of sliding levitation. It is possible to prevent contact with the moving surface.

  ADVANTAGE OF THE INVENTION According to this invention, the favorable floating force can be generated between a pair of sliding surfaces, and the sliding structure which can reduce the sliding resistance between both can be provided.

FIG. 1 is a partially broken perspective view schematically showing a sliding structure according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing the configuration of the microtexture structure in the sliding structure of FIG. FIG. 3 is a cross-sectional view schematically showing the flow of the lubricating fluid in the microtexture structure. FIG. 4 is a cross-sectional view schematically showing the flow of the lubricating fluid in the microtexture structure portion of the comparative example. FIG. 5 is a schematic diagram for explaining a profile of the microtexture structure portion. FIG. 6 is a graph showing the relationship between the load capacity coefficient and the gap ratio, which is the ratio between the minimum gap and the maximum gap between the first sliding surface and the second sliding surface. FIG. 7 is a view for explaining a preferred aspect of the protrusion provided in the groove of the microtexture structure portion. FIG. 8 is a graph showing a preferred arrangement position of the vertices of the protrusions. FIG. 9 is a cross-sectional view of a sliding structure including a microtexture structure according to Modification 1 of the first embodiment. FIG. 10 is a cross-sectional view of a sliding structure including a microtexture structure according to Modification 2 of the first embodiment. FIG. 11 is a cross-sectional view of a sliding structure including a microtexture structure according to Modification 3 of the first embodiment. FIG. 12A is a cross-sectional view of the sliding structure according to the second embodiment, and FIG. 12B is an enlarged view of the microtexture structure portion of the second embodiment. FIG. 13 is a schematic cross-sectional view of a reciprocating piston engine in a direction along the cylinder axis and perpendicular to the crankshaft. FIG. 14 is an enlarged view of a main part of FIG. 13, and is a cross-sectional view of a cylinder block and a piston constituting the sliding structure according to the third embodiment. FIG. 15 is an enlarged view of the main part of FIG. 13, and is a cross-sectional view of the large end portion of the connecting rod and the piston pin constituting the sliding structure according to the fourth embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. A sliding structure according to the present invention has a first member having a first sliding surface and a second sliding surface facing the first sliding surface, and a predetermined sliding surface with respect to the first member. It is a sliding structure containing the 2nd member which moves relatively in a moving direction. There is no restriction | limiting in particular in the aspect of a said 1st member and a said 2nd member. For example, as a first aspect, the first member is a plate-like member such as a flat plate, a disk, a curved plate, etc., and has the first sliding surface on one side of the plate-like member, and the second member Is another plate-like member having the second sliding surface on one side, and moves in a straight line with respect to the first member, moves around, or rotates around a predetermined axis. It can be illustrated. In addition, even if it is an aspect in which only the second member moves, an aspect in which both the first member and the second member move may be used.

  As a second aspect, the first member is a cylindrical body such as a cylinder or a square tube, the inner peripheral surface thereof is the first sliding surface, and the second member is accommodated inside the cylindrical body. A column body such as a cylinder or a prism can be exemplified in which the outer peripheral surface thereof is the second sliding surface and the second member moves in the axial direction of the cylindrical body. Conversely, the first member may be the column body, the second member may be the cylinder body, and the cylinder body may move along the column body.

  As a third aspect, the first member is a cylindrical body, an inner peripheral surface thereof is the first sliding surface, and the second member is a columnar body accommodated inside the cylindrical body. An example in which the outer peripheral surface is the second sliding surface and the second member rotates about its own axis can be exemplified. On the contrary, the first member may be the cylindrical body, the second member may be the cylindrical body, and the cylindrical body may rotate around the axis of the cylindrical body.

  When an example is given as a constituent member of an automobile, a disk brake can be exemplified as the first aspect. In this case, the first member is a brake pad, the second member is a disc rotor, the first sliding surface is the surface of the brake pad, and the second sliding surface is the brake pad in the disc rotor. This is the opposite surface. As said 2nd aspect, the engine main-body part of a reciprocating piston engine, a suspension damper, etc. can be illustrated. In the case of the engine main body, the first member is a cylinder and its inner peripheral wall is the first sliding surface, and the second member is a piston skirt and its outer peripheral wall is the second sliding surface. (This aspect is illustrated in FIG. 14 as the third embodiment). In the case of the suspension damper, the first member is a shell (cylinder), and the second member is a piston that reciprocates within the shell.

  As said 3rd aspect, the various rotating shafts with which a motor vehicle is provided, and its bearing part can be mentioned, A crankshaft of a reciprocating piston engine can be illustrated typically. Specifically, the connection part of the big end part of a connecting rod and a crankpin can be illustrated. In this case, the first member is a crank pin, the outer peripheral surface thereof is the first sliding surface, the second member is the connecting rod large end portion, and the inner peripheral surface thereof is the second sliding surface. (This aspect is illustrated in FIG. 15 as the fourth embodiment). In addition, the bearing part of a crank journal can also be mentioned. Other than the crankshaft, for example, a bearing portion of a power steering pump can be cited.

[First Embodiment]
FIG. 1 is a partially broken perspective view schematically showing a sliding structure according to a first embodiment of the present invention. The sliding structure exemplified here corresponds to the second aspect described above. The sliding structure includes a first member 1 and a second member 2 that moves relative to the first member 1. The second member 2 is a cylindrical body. The first member 1 includes a cylindrical space that accommodates the second member 2, and an inner peripheral wall that defines the space is the first sliding surface 1 </ b> S. The outer peripheral wall of the second member 2 is the second sliding surface 2S, and this second sliding surface 2S is spaced apart from the first sliding surface 1S in the Y direction (the radial direction of the second member 2). Confronted.

  The material of the first member 1 and the second member 2 is not particularly limited as long as it is a member having a predetermined rigidity, but is preferably a metal. For example, the 1st member 1 and the 2nd member 2 which were comprised with aluminum, SUS, etc. can be illustrated preferably. The first member 1 is a member that is fixedly arranged, and the second member 2 is a member that moves linearly in the X direction (the axial direction of the second member 2) perpendicular to the Y direction. In the first embodiment, the moving direction of the second member 2, that is, the sliding direction of the second sliding surface 2S with respect to the first sliding surface 1S is the + X direction. That is, + X is the downstream side in the sliding direction, and -X is the upstream side in the sliding direction.

In the present embodiment, when the second member 2 moves, a gap is formed between the first sliding surface 1S and the second sliding surface 2S, and the lubricating fluid F is planned to be interposed between the two. ing. That is, the second sliding surface 2S floats from the first sliding surface 1S via the lubricating fluid F. Thereby, the sliding resistance of the second member 2 can be minimized. The lubricating fluid F may be either liquid or gas, for example, air (viscosity = 1.8 × 10 ⁻⁵ [Pa · s]), water (8.9 × 10 ⁻⁴ [Pa · s]). ) Or low viscosity oil of the 0W-20 class (6.8 × 10 ⁻³ [Pa · s]), particularly preferably air.

  In order to realize the above levitation, the micro-texture structure portion 30 is provided on the second sliding surface 2S. That is, the microtextured structure portion 30 is formed to float the second sliding surface 2S from the first sliding surface 1S when the second member 2 slides relative to the first member 1. Yes. The microtextured structure portion 30 includes a plurality of grooves 3 extending in the circumferential direction of the second member 2 made of a cylindrical body, that is, in a direction orthogonal to the sliding direction of the second member 2. Each groove 3 is a minute groove having a groove width on the order of microns, and is arranged at a predetermined pitch in the sliding direction.

  The direction in which the groove 3 extends may not be completely orthogonal to the sliding direction, and may be inclined from the orthogonal direction as long as the effect of levitation described later is obtained. For example, the groove 3 may extend in a direction inclined by about 10 ° to 20 ° with respect to the orthogonal direction. Further, the formation region of the groove 3 (microtextured structure portion 30) may be either the entire region or a partial region of the second sliding surface 2S.

  When the microtexture structure portion 30 is formed in a partial region, the region where the second slide surface 2S is supposed to contact the first slide surface 1S is selected as the formation region of the microtexture structure portion 30. It is desirable to do. In the example of FIG. 1, the second member 2 is a member that moves in the + X direction, but it is planned that a load in the Y direction is applied to the second member 2 during this movement. For this reason, there is a concern that the second sliding surface 2S may contact the first sliding surface 1S in the Y direction and increase the sliding resistance. Accordingly, the microtextured structure portion 30 is disposed only in the region of the second sliding surface 2S that is oriented in the Y direction. Thereby, when the 2nd sliding surface 2S approaches the 1st sliding surface 1S, a levitation | floating force can be generated and the said contact can be suppressed.

<Groove structure and action>
FIG. 2 is a cross-sectional view along the X direction showing the configuration of the microtexture structure 30 in the sliding structure according to the first embodiment. The plurality of grooves 3 provided in the microtextured structure portion 30 illustrated here substantially have a sawtooth shape in the cross section in the X direction. Each of the grooves 3 is formed in a top portion 31 that is the portion closest to the first sliding surface 1S, a bottom portion 32 that is the farthest portion, an inclined surface 33 between the top portion 31 and the bottom portion 32, and an inclined surface 33. Projecting portion 34. The inclined surface 33 is an inclined surface having a tendency that the downstream side (+ X side) in the sliding direction H1 (+ X direction) is deep and the upstream side (−X side) is shallow.

  The opening edges of one groove 3 are an upstream edge 3U and a downstream edge 3D in the sliding direction H1. These edge parts 3U and 3D are also a pair of top parts 31 adjacent to the sliding direction H1. In other words, the top portion 31 of one groove 3 also serves as the downstream edge 3D of the groove 3 adjacent to the upstream side of the one groove 3. That is, there is no flat portion such as a plateau portion between adjacent grooves 3, and a plurality of grooves 3 are continuously provided in the sliding direction H1. Therefore, the groove pitch L1 is the same as the length (groove width) in the X direction between the upstream edge 3U and the downstream edge 3D.

  The groove 3 includes a first surface 3A (downstream groove wall) between the downstream edge 3D and the bottom 32 (the deepest portion between the edges 3U and 3D), the upstream edge 3U and the bottom 32. And the second surface 3B. In the X-direction cross section, the first sliding surface 1S is a surface parallel to the sliding direction H1, but the first surface 3A is a plane extending in a direction orthogonal to the first sliding surface 1S. The second surface 3B is a flat surface having an inclination with respect to the first sliding surface 1S, but is not an orthogonal surface like the first surface 3A, but an inclined surface based on a relatively gentle inclination, and upstream of the inclined surface. A protrusion 34 is provided in an intermediate region between the side and the downstream side. In the present embodiment, the second surface 3B is the inclined surface 33 described above. In the example of FIG. 2, since the first surface 3A is a surface orthogonal to the sliding direction H1, the width of the second surface 3B (inclined surface 33) in the sliding direction H1 matches the groove width (groove pitch L1). ing.

  In the cross section along the sliding direction H1, the protruding portion 34 has a shape protruding in the direction of the first sliding surface 1S from a line connecting the top portion 31 and the bottom portion 32 (inclined surface 33). In this embodiment, the cross-sectional shape along the sliding direction H1 of the protrusion 34 is a right triangle. That is, the protrusion 34 includes a vertex 341 that is the most protruding portion with respect to the inclined surface 33, a vertical wall 342 extending from the vertex 341 in the Y direction, and a horizontal wall 343 extending from the vertex 341 in the X direction. And the horizontal wall 343 have an angle of 90 °. That is, the horizontal wall 343 extends in a direction parallel to the sliding direction H1, and the vertical wall 342 extends in a direction orthogonal to the sliding direction H1. The inclined surface 33 is divided into two parts by the protrusions 34, and the inclined surface 33 is formed between the first inclined surface 33 </ b> A (the bottom wall including the bottom portion) between the bottom portion 32 and the lower end of the vertical wall 342, and the horizontal wall 343. -X side edge and the 2nd inclined surface 33B between the top parts 31 are included.

  The plurality of grooves 3 can be formed by various cutting processes using a minute cutting blade. In the case where the grooves 3 are provided on the entire circumferential surface of the cylindrical second sliding surface 2S, it is necessary to bring the cutting blade into contact with the second sliding surface 2S while rotating the second member 2 with a lathe. The groove 3 can be formed. As shown in FIG. 1, when the groove 3 is provided in a partial region of the second sliding surface 2S, a minute cutting blade is brought into contact with the second sliding surface 2S while drawing an elliptical or circular locus. Necessary grooves 3 can be formed by elliptical vibration cutting.

  Each of the grooves 3 has a first portion LA and a second portion LB that are sequentially arranged from the downstream side (+ X side) to the upstream side (−X side) in the sliding direction H1 from the viewpoint of the function performed by the groove 3. And a third portion LC. In general, the protrusion 34 constitutes the second portion LB, the portion downstream of the protrusion 34 constitutes the first portion LA, and the portion upstream of the protrusion 34 constitutes the third portion LC. Yes.

  Specifically, the first portion LA is a region defined by the vertical wall 342 of the protrusion 34, the first inclined surface 33A, and the first surface 3A. The first portion LA is a U-shaped region having a space extending in a direction orthogonal to the first sliding surface 1S, and serves as a trap space T for confining a turbulent flow FB described later. The second portion LB is a region where the horizontal wall 343 exists, and is a wall surface region parallel to the first sliding surface 1S. The third portion LC is a region composed of an inclined surface extending upstream from the upstream end of the lateral wall 343 in the sliding direction H1 so as to gradually approach the first sliding surface 1S, that is, a region composed of the second inclined surface 33B. is there.

  FIG. 3 is a cross-sectional view schematically showing the flow FA of the lubricating fluid F at the time of sliding in the microtexture structure portion 30. When the second member 2 moves in the sliding direction H1 toward the + X direction, the lubricating fluid F is downstream of the sliding direction H1 in the gap G between the first sliding surface 1S and the second sliding surface 2S. It flows relatively from the side (+ X side) toward the upstream side (−X side). That is, the lubricating fluid F flows into the gap G from the inflow direction H2 that is the direction opposite to the sliding direction H1. The lubricating fluid F forms a flow FA that flows through the gap G from the + X side to the −X side. This flow FA is a laminar flow. This laminar flow contributes to the levitation of the second sliding surface 2S.

  Here, each of the grooves 3 has an inclined surface 33 having a tendency that the + X side is deep and the −X side is shallow. Since the laminar flow of the lubricating fluid F flows along the microtexture structure portion 30 in which a plurality of such inclined surfaces 33 are arranged in the sliding direction H1, a good levitation force can be created. That is, when the laminar flow flows from the + X side to the −X side, the inclined surface 33 of each groove 3 that gradually narrows the interval between the first and second sliding surfaces 1S and 2S is relatively It flows while repeating the action of being confined in a relatively narrow space from a wide space. That is, the flow FA is gradually confined in a narrow space by the inclined surface 33 that narrows the gap G with the first sliding surface 1S toward the −X side, and the density is increased. By such a confinement action, a large levitation force can be generated on the second sliding surface 2S with respect to the first sliding surface 1S. Therefore, the sliding resistance between the first member 1 and the second member 2 can be reduced.

  The first portion LA provided in each of the grooves 3 of the microtextured structure portion 30 includes the trap space T and functions as a region for trapping the turbulent flow FB of the lubricating fluid F flowing through the gap G. That is, when the flow FA passes through the top 31 where the gap G is the narrowest, a turbulent flow FB having no directivity in the flow is likely to occur. This turbulent flow FB is enclosed in the trap space T. The second portion LB functions as a region for securing a laminar flow (flow FA) of the flowing lubricating fluid F. The second portion LB can also be said to be a region for preventing the turbulent flow FB from being generated. The third portion LC functions as a region for confining the laminar flow of the lubricating fluid F in a gradually narrowing space and increasing the density.

  By providing the groove 3 with the first to third portions LA to LC, the turbulent flow FB that does not substantially contribute to the levitation is trapped by the first portion LA, and only the laminar flow is gap G in the second portion LB. The laminar flow can be confined in a gradually narrowing space in the third portion LC. Therefore, a large levitation force can be generated in the second sliding surface 2S with respect to the first sliding surface 1S, and the sliding resistance between the first member 1 and the second member 2 can be reduced. .

  FIG. 4 is a cross-sectional view schematically showing the flow FA of the lubricating fluid F in the microtextured structure portion of the comparative example. The second member 200 of the comparative example has a groove 300 that does not include the protrusion 34 as shown in FIGS. That is, the groove 300 has a groove shape obtained by removing the protrusion 34 from the inclined surface 33 in the groove 3 of the above embodiment. In this case, since there is no space surrounding the turbulent flow FB that does not contribute to levitation, the turbulent flow FB spreads in a relatively wide area in the groove 300. For this reason, in the flow FA, the proportion of the laminar flow contributing to levitation decreases, and the levitation force of the second member 200 is weakened. On the other hand, according to the present embodiment, the turbulent flow FB is taken in the trap space T and thus is reduced, and the proportion of the laminar flow in the flow FA can be increased. Therefore, the levitation force can be increased.

<Sliding surface profile>
In order to effectively express the action of sliding levitation by the microtexture structure portion 30, it is necessary to optimize the profile of the groove 3. What is important in this profile is the minimum gap h1 that is the distance between the top 31 of the groove 3 and the first sliding surface 1S, and the maximum that is the distance between the bottom 32 and the first sliding surface 1S. The gap ratio h2 / h1 is a ratio to the gap h2. It is also important to set the minimum gap h1 within an optimum range. This point will be described with reference to FIG.

  FIG. 5 is a schematic diagram for explaining the profile. FIG. 5 shows a state in which the sliding member B having the sliding surface SB formed of the inclined surface slides in the sliding direction H1 along the sliding surface SA of the sliding member A. The sliding surface SA corresponds to the first sliding surface 1S, and the sliding surface SB corresponds to the inclined surface 33 (second sliding surface 2S) of one groove 3. In addition, since the protrusion part 34 does not affect the setting of h1 and h2, description is abbreviate | omitted here. The sliding surface SB has a top portion P that is the portion closest to the sliding surface SA and a bottom portion Q that is disposed on the downstream side (+ X side) of the sliding direction H1 of the top portion P and is farthest from the sliding surface SA. And has a shape that gradually separates from the sliding surface SA from the upstream side to the downstream side in the sliding direction H1.

When the sliding member B slides in the sliding direction H1 at the speed U, the sliding levitation force W generated between the sliding surface SB and the sliding surface SA is obtained by the following equation (1). be able to.

  In Equation (1), η is the viscosity of the lubricating fluid F interposed between the sliding surface SB and the sliding surface SA, and B is the length of the sliding surface SB in the sliding direction (the top portion P in FIG. 5). C is the length in the direction perpendicular to the sliding direction H1 of the sliding surface SB (the length in the direction perpendicular to the paper surface of FIG. 5), and U is the sliding of the sliding surface SB. Speed. h1 is the minimum gap, which is the distance between the top portion P and the sliding surface SA, that is, the minimum value of the gap G between the sliding surface SB and the sliding surface SA. m is the above-mentioned gap ratio, and is the distance between the bottom Q and the sliding surface SA, that is, the minimum gap h1 and the maximum gap h2 when the maximum value of the gap G is the maximum gap h2. It is a ratio and is represented by m = h2 / h1.

In equation (1), if the second item is the load capacity coefficient Kw (Kw = 6 / (m−1) ² {lnm−2 (m−1) / (m + 1)}), the sliding levitation force W is This is proportional to the load capacity coefficient Kw.

  FIG. 6 is a graph showing the relationship between the load capacity coefficient Kw and the gap ratio m. As shown in this graph, the sliding levitation force W becomes maximum when the gap ratio m is 2.2, and becomes smaller as the gap ratio m is separated from this value. From this finding, a high sliding levitation force W can be obtained if the gap ratio m is set in the vicinity of 2.2. Specifically, by setting the gap ratio m in the range of 1.5 to 5.0, the sliding levitation force W can be made equal to or higher than the line C in FIG. In this case, as the sliding levitation force W, a high value that is 60% or more of the maximum value (value when the gap ratio m is 2.2) can be obtained.

  Based on equation (1), the sliding levitation force W increases as the minimum gap h1 decreases. However, the minimum gap h1 that is too small increases the coefficient of friction generated between the sliding surface SA and the sliding surface SB. That is, there exists an optimum range in which the friction coefficient can be kept small for the minimum gap h1. The magnitude of the friction coefficient corresponds to the magnitude of friction during sliding levitation of the sliding surface SB. The smaller the friction coefficient, the better the sliding levitation can be realized. From this viewpoint, the desirable minimum gap h1 is in the range of 0.5 μm to 2.0 μm. When h1 exceeds 2.0 μm, the tendency of the sliding levitation force W to become smaller becomes significant from the above equation (1). On the other hand, when h1 is less than 0.5 μm, the coefficient of friction increases, and the tendency to inhibit good sliding levitation becomes significant. The desired minimum gap h1 is a gap that is desired when the sliding member B is actually performing a sliding operation. When the sliding member B is a member that thermally expands in a sliding operation, it is desirable to determine the normal temperature design value so that the minimum gap h1 is ensured in the thermally expanded state.

From the above, the profile of the groove 3 shown in FIG.
Minimum gap h1 = 0.5 μm to 2.0 μm
Gap ratio m = h2 / h1 = 1.5-5.0
It is desirable to set it within the range. The groove depth D, which is the maximum gap h2, and the difference h2-h1 between the maximum gap h2 and the minimum gap h1, is naturally determined by setting h1 and m. A preferable groove depth D is in the range of 0.25 μm to 8.0 μm from (h1_min × m_min−h1_min) to (h1_max × m_max−h1_max).

  The first sliding surface 1S is desirably a surface having high smoothness. In other words, it is desirable that the minimum gap h1 is set to a value larger than the surface roughness of the first sliding surface 1S. This is to prevent the first sliding surface 1S from contacting the second sliding surface 2S on which the microtextured structure portion 30 is formed during sliding levitation. For example, when the surface roughness (arithmetic average roughness Ra) of the first sliding surface 1S is 0.6 μm, when the minimum gap h1 is set to 0.5 μm, the top 31 of the groove 3 becomes the first sliding surface 1S. Can touch. In order to avoid this contact problem, it is desirable that the minimum gap h1 is set to about twice or more the surface roughness of the first sliding surface 1S.

  The groove pitch L1 in which the plurality of grooves 3 are arranged in the sliding direction H1 is desirably set in a range of 1 μm to 1 mm, preferably in a range of 5 μm to 100 μm. None of the microtextured structure portions 30 composed of the grooves 3 having the groove pitch L1 that is too short and the groove pitch L1 that is too long can exhibit the above-described confinement action satisfactorily. By setting the groove pitch L1 in the above range, a large levitation force can be generated.

<About the aspect of the protrusion>
FIG. 7 is a view for explaining a preferable aspect of the protrusion 34 provided in the groove 3 of the microtextured structure portion 30. Here, a preferable range of the height position of the vertex 341 and the position in the sliding direction is shown. First, regarding the height position of the vertex 341, the distance between the top 31 and the bottom 32 in the direction orthogonal to the sliding direction H1 is D (groove depth D described above), and the vertex 341 of the top 31 and the protrusion 34 is 341. When the distance between and is Y, it is desirable that the range of the following equation (2) is set.
0.1D ≦ Y ≦ 0.6 (2)

Next, regarding the position of the vertex 341 in the sliding direction, the pitch of the plurality of grooves 3 arranged in the sliding direction H1 is L1 (groove pitch L1), and the downstream edge 3D and the upstream of each groove 3 in the sliding direction H1. When the distance between the side edge 3U is L2 (groove width L2) and the distance between the first surface 3A of the groove 3 and the vertical wall 342 of the protrusion 34 in the sliding direction H1 is X, the following It is desirable that the value is set in the range of the expression (3).
L1 = 1 μm to 1 mm
1μm ≦ L2 ≦ L1
0.2L2 ≦ X ≦ 0.6L2 (3)

  FIG. 8 is a graph showing a preferable arrangement position of the vertex 341 of the protrusion 34. This graph shows the result of changing the arrangement position of the vertex 341 in the cavity of the groove 3 to various places and measuring the levitation force at each position. The horizontal axis in FIG. 8 indicates the groove width (μm) in the sliding direction H1 of the groove 3, and the vertical axis indicates the groove depth D (μm) of the groove 3, and the first surface of the groove 3 tested. 3A and the size of the inclined surface 33 are added to the graph with a solid line. The tested groove 3 has a groove width of 9.75 μm and a groove depth of 5.4 μm. The circles marked in the graph indicate the position of the apex 341 where the levitation force was measured. That is, the projecting portion 34 having the apex 341 at the coordinates of each circle is projected on the inclined surface 33, and the levitation force generated by such a groove 3 is measured.

  Among the circles marked in the graph, the solid circles indicate the coordinates of the apex 341 where the buoyancy is improved over the grooves 3 that do not have the protrusions 34, and the dotted line o indicates the apex where the levitation force has decreased. The coordinates of 341 are shown. The size of the circles indicates the rate of change in levitation force. In short, the coordinates on the solid line where the large ◯ mark is located are the coordinates of the vertex 341 effective in improving the levitation force.

  From the result of FIG. 8, it can be said that the area K shown in the graph is an area where the coordinates of the vertex 341 effective in improving the levitation force are concentrated. From the size of the region K, the numerical values included in the equations (2) and (3) are derived. That is, when the distance Y corresponding to the height position of the vertex 341 is in the range of about 10% to 60% of the groove depth D, it can be seen that it contributes to the improvement of levitation force. Therefore, Expression (2) is derived. Further, it can be seen that when the distance X corresponding to the position of the vertex 341 in the sliding direction is in the range of about 20% to 60% of the groove width L2, the levitation force is improved. Therefore, Expression (3) is derived. In the test example of FIG. 8, the groove pitch L1 = the groove width L2.

  Therefore, according to the groove 3 having the protrusion 34 that satisfies the above formulas (2) and (3), the relationship between the groove depth D and the distance Y and the relationship between the groove width L2 and the distance X are appropriate. As a result, a large levitation force can be generated. Note that the vertex 341 may not be a corner vertex as shown in FIG. 2, but may be a vertex composed of an inflection point on the R plane.

<Modification 1>
FIG. 9 is a cross-sectional view of a sliding structure including a microtexture structure 30a according to Modification 1 of the first embodiment. In the first embodiment, the example in which the first surface 3A of the groove 3 is a flat surface extending in a direction orthogonal to the first sliding surface 1S has been described. In Modification 1, a groove 3a is shown in which the first surface 3A is a surface inclined from the orthogonal direction.

  The groove 3a of the microtextured structure 30a has a first surface 3A between the top 31 and the bottom 32 which is the downstream edge 3D, and a first surface 3A between the top 31 and the bottom 32 which is the upstream edge 3U. 2 side 3B. Both the first surface 3A and the second surface 3B are flat surfaces that are inclined with respect to the first sliding surface 1S. The first surface 3A has an inclination angle θ1 with respect to the first sliding surface 1S, and the second surface 3B has an inclination angle θ2 with respect to the first sliding surface 1S. Here, the first surface 3A is a surface (θ1> θ2) having a larger inclination than the second surface 3B. A desirable range of the inclination angle θ1 of the first surface 3A with respect to the first sliding surface 1S is 70 ° to 90 °. The inclination angle θ2 of the second surface 3B is desirably sufficiently small with respect to θ1, and can be selected from a range of about 10 ° to 55 °, for example.

  The first surface 3A is desirably a plane orthogonal to the first sliding surface 1S, but may be a plane inclined with respect to the orthogonal direction within the above-mentioned limitation. With such a groove 3a having the first surface 3A, the laminar flow (flow FA) of the lubricating fluid F flows along the inflow direction H2 through the gap G between the first and second sliding surfaces 1S, 2S. At this time, the width of the laminar flow suddenly expands in the region of the first surface 3A having a relatively large inclination angle θ1, and the laminar flow is gradually increased by the second surface 3B (inclined surface 33) having a relatively small inclination angle θ2. The action of being trapped is repeated. A good levitation force is generated by the operation of the laminar flow.

<Modification 2>
FIG. 10 is a cross-sectional view of a sliding structure including a microtexture structure portion 30b according to Modification 2 of the first embodiment. In the first embodiment, the vertical wall 342 of the protrusion 34 extends in a direction orthogonal to the sliding direction H1, and the horizontal wall 343 extends in a direction parallel to the sliding direction H1. The vertical wall 342 may have a slight inclination with respect to the orthogonal direction, and the horizontal wall 343 may also have a slight inclination with respect to the parallel direction.

  The groove 3b shown in FIG. 10 shows an example in which the vertical wall 342 is a surface inclined at an inclination angle α on the upstream side in the sliding direction H1 with respect to the orthogonal direction. Further, an example is shown in which the horizontal wall 343 is a surface inclined at an inclination angle β in a direction away from the first sliding surface 1S with respect to the parallel direction. Although it is practically impossible for the vertical wall 342 to have an inclination angle on the downstream side in the sliding direction H1 due to processing reasons, the horizontal wall 343 has an inclination angle − in a direction approaching the first sliding surface 1S. It may be a surface having β.

The inclination angle α, which is the angle formed by the vertical wall 342 with respect to the direction orthogonal to the sliding direction H1, and the inclination angle β, which is the angle formed by the horizontal wall 343 with respect to the sliding direction H1, respectively.
0 ° ≦ α ≦ 20 °
−15 ° ≦ β ≦ 15 °
It is desirable to be set within the range. By setting the ranges of the inclination angles α and β in this manner, the shape of the protrusion 34 is optimized, and as a result, a large levitation force can be generated by the groove 3b.

<Modification 3>
FIG. 11 is a cross-sectional view of a sliding structure including a microtexture structure 30c according to Modification 3 of the first embodiment. In the first embodiment, the example in which the plurality of grooves 3 are closely connected in the sliding direction H1 has been described. In the third modification, an example in which a plateau is provided between adjacent grooves 3 is shown.

  The microtextured structure portion 30 c includes a plurality of grooves 3 and a plateau portion 35 disposed between the adjacent grooves 3. The plateau part 35 is a plane substantially parallel to the first sliding surface 1S. The plateau part 35 is a flat surface extending between the top part 31 which becomes the upstream edge part 3U of one groove 3 and the downstream edge part 3D of the groove 3 adjacent to the upstream side of the one groove 3. In this case, the groove pitch L1 is obtained by adding the groove width L2 that is the length of the upstream edge 3U to the downstream edge 3D of the groove 3 in the sliding direction H1 and the length of the plateau 35. . Thus, even if the plateau part 35 exists between the grooves, the levitation force can be generated as long as the plateau part 35 is not too long with respect to the groove width L2.

  It is desirable that the plateau part 35 has a high smoothness. This is because the plateau portion 35 is a surface at the same height as the top portion 31 that defines the minimum gap h1, and if the smoothness is low, contact with the first sliding surface 1S becomes a problem. In this case, it is desirable that the minimum gap h1 is set to a value larger than the total surface roughness obtained by adding the surface roughness of the first sliding surface 1S and the surface roughness of the plateau portion 35. For example, when the arithmetic average roughness Ra of the first sliding surface 1S and the plateau part 35 is both 0.5 μm, the minimum gap h1 is a value that exceeds these combined surface roughnesses 1 μm, preferably a value that is twice or more. It is desirable to set to.

[Second Embodiment]
In the first embodiment, an example in which the microtexture structure portion 30 is provided on the second sliding surface 2S that extends linearly in the cross section in the X direction has been described. In the second embodiment, an example in which a macro levitation structure is also applied to the second sliding surface 2S itself is shown. FIG. 12A is a cross-sectional view of a sliding structure including the microtexture structure portion 30A according to the second embodiment, and FIG. 12B is an enlarged view of the microtexture structure portion 30A.

  The sliding structure having the microtextured structure portion 30A includes a first member 1 having a first sliding surface 1S and a second member 21 having a second sliding surface 21S facing the first sliding surface 1S. It consists of. The first sliding surface 1S is a plane parallel to the sliding direction H1 as in the first embodiment. On the other hand, the second sliding surface 21S has an overhanging shape portion M that projects to the first sliding surface 1S side in the cross section in the X direction. Here, an example in which the projecting shape portion M has an arcuate shape is shown. In FIG. 12, the arcuate shape of the second sliding surface 21S is greatly exaggerated for easy understanding, and actually has an arcuate shape having a micron-order overhang that is difficult to visually distinguish.

  The protruding shape portion M has a top portion P that protrudes most to the first sliding surface 1S side at the center portion in the X direction, and is closest to the first sliding surface 1S side at + X side and −X side end portions. Skirts Q1 and Q2 are small. The overhanging shape portion M is used because the second member 21 is scheduled to move in both the + X direction and the −X direction at predetermined speeds U1 and U2. When movement in only one direction is planned, for example, when the second member 21 moves only in the + X direction, a skirt portion Q1 is provided at the end portion on the + X side, and a top portion P is provided at the end portion on the −X side. Be placed. In the present embodiment, when the second member 21 moves in the + X direction, a load in the Y direction is applied to the second member 21, and when the second member 21 moves in the -X direction, the load is not substantially applied. .

  When the speed is given to the second member 21, the lubricating fluid F existing in the periphery is drawn into the gap G between the first and second sliding surfaces 1S, 21S. The lubricating fluid F that has lost its destination generates a drag in a direction in which the space between the first and second sliding surfaces 1S and 21S is enlarged. This drag acts to float the second sliding surface 21S from the first sliding surface 1S. More specifically, when the velocity U1 in the + X direction is given to the second member 21, the lubricating fluid F enters the gap G from the skirt portion Q1 toward the top portion P. Thereby, a sliding levitation force is generated between the first and second sliding surfaces 1S and 21S. On the other hand, when the velocity U2 in the −X direction is given to the second member 21, the lubricating fluid F enters the gap G from the skirt portion Q2 toward the top portion P. Thereby, a sliding levitation force is generated between the first and second sliding surfaces 1S and 21S. The projecting shape portion M is a surface having a macro profile that generates a sliding levitation force by using the entire length of the second sliding surface 21S in the X direction.

  The technical idea shown in FIGS. 5 and 6 and the formula (1) can also be applied to the profile of the second sliding surface 21S. That is, the distance between the top portion P of the projecting shape portion M and the first sliding surface 1S is the minimum clearance h3, and the distance between the skirt portions Q1 and Q2 and the first sliding surface 1S is the maximum clearance h4. When doing so, it is desirable to set the gap ratio m = h4 / h3 in the range of 1.5 to 5.0. The minimum gap h3 is naturally 0.5 μm to 2.0 μm, similar to the minimum gap h1 for the groove 3. Further, the maximum gap h4 and the peak height DA (h4-h3) are naturally determined by setting the minimum gap h1 and the gap ratio m.

  The microtexture structure portion 30A is provided to assist the levitation of the second sliding surface 21S created by the macro profile of the projecting shape portion M. That is, the microtextured structure portion 30A is disposed in order to strengthen the sliding levitation force created by the projecting shape portion M and make the second sliding surface 21S more difficult to contact the first sliding surface 1S. For this reason, in the microtextured structure portion 30A, when a load in the Y direction is applied when the second member 21 moves in the X direction, the second sliding surface 21S may come into contact with the first sliding surface 1S. Arranged in the expected part. That is, the contact is likely to occur around the top portion P, and the microtextured structure portion 30A is arranged in the peripheral region of the top portion P.

  The grooves 3 included in the microtextured structure portion 30A are the same as those described in the first embodiment. As described above, a load in the Y direction is applied to the second member 21 when the second member 21 moves in the + X direction. Therefore, when the second member 21 moves in the + X direction, the profile of the groove 3 having the protrusion 34 is set so that the microtexture structure portion 30A can assist the levitation.

  Specifically, as shown in FIG. 12B, each inclined surface 33 of the groove 3 is inclined such that the downstream side (+ X side) in the sliding direction H1 is deep and the upstream side (−X side) is shallow. It is considered a surface. The minimum gap h1, the maximum gap h2, and the gap ratio m are the same as in the first embodiment. It should be noted that h1, h2, and m of the groove 3 are set so as to be established in a situation where levitation assistance is required for the projecting shape portion M, that is, immediately before the peripheral region of the top portion P contacts the first sliding surface 1S. Is done.

[Third Embodiment]
In 3rd Embodiment (and 4th Embodiment), the sliding structure which concerns on this invention shows the example applied to the sliding part of a reciprocating piston engine. FIG. 13 is a schematic cross-sectional view of the reciprocating piston engine in a direction along the cylinder axis AX and orthogonal to the crankshaft 5. The reciprocating piston engine includes a cylinder 41, a crankshaft 5 and a connecting rod 6.

  The cylinder 41 is partitioned by a cylinder block 42 (first member). In the cylinder 41, a piston 43 (second member) is accommodated so as to be capable of reciprocating in the cylinder axis AX direction. The piston 43 includes a head portion 44 having a crown surface on the upper surface, a skirt portion 45 extending below the head portion 44, and a piston boss 46. The crankshaft 5 includes a crank journal 51, a crankpin 52, a crank arm 53, and a balance weight 54. The piston 43 is coupled to the crankshaft 5 by a connecting rod 6. The small end portion 61 at the upper end of the connecting rod 6 and the piston 43 are connected via a piston pin 47 held by a piston boss 46. Further, the large end 62 at the lower end of the connecting rod 6 and the crank pin 52 are connected. The crankshaft 5 is assumed to rotate clockwise as indicated by an arrow in FIG.

  In 3rd Embodiment, the example to which the sliding structure which concerns on this invention is applied to the sliding part comprised by the skirt part 45 of the piston 43 and the inner peripheral wall of the cylinder 41 is shown. FIG. 14 is an enlarged view of the main part of FIG. 13, and is a cross-sectional view of the cylinder block 42 and the piston 43 that constitute the sliding structure according to the third embodiment. A cylinder head 421 is disposed on the upper surface of the cylinder block 42. A combustion chamber 48 is defined by the cylinder 41 of the cylinder block 42, the crown of the piston 43, and the cylinder head 421. The cylinder head 421 is provided with an intake port 481 and an exhaust port 482 that communicate with the combustion chamber 48.

  The inner peripheral wall of the cylinder 41 includes a thrust side inner peripheral wall 41A (left side in FIG. 14; first sliding surface) and an anti-thrust side inner peripheral wall 41B facing this with reference to the swinging direction of the piston 43. The skirt portion 45 includes a thrust side skirt portion 45A having a sliding surface 45SA (second sliding surface) facing the thrust side inner peripheral wall 41A and a sliding surface 45SB facing the anti-thrust side inner peripheral wall 41B. It consists of an anti-thrust side skirt portion 45B. These sliding surfaces 45SA and 45SB have projecting shape portions M that project in a direction facing the inner peripheral walls 41A and 41B in a cross section along the cylinder axis AX. The projecting shape portion M has a macro profile similar to that shown in FIG.

  The skirt portion 45 is originally scheduled to slide with the inner peripheral walls 41A and 41B of the cylinder 41 so that the piston 43 does not swing due to the secondary motion during the reciprocating motion of the piston 43. . However, in this embodiment, when the piston 43 is reciprocated, a gap G is planned to be formed between the sliding surfaces 45SA and 45SB of the skirt portions 45A and 45B and the inner peripheral walls 41A and 41B. That is, the sliding surfaces 45SA and 45SB having the projecting shape portion M are levitated from the inner peripheral walls 41A and 41B via the lubricating fluid. This levitation mechanism is as described in the second embodiment. As a result, the sliding resistance of the skirt portion 45 can be minimized. The lubricating fluid is, for example, air, water, or a low viscosity oil of 0W-20 class, and particularly preferably air.

  In addition to the protruding shape portion M, a microtexture structure portion 30B is formed on the thrust side sliding surface 45SA. That is, for the thrust side skirt portion 45A, in order to assist the levitation created by the macro profile of the protruding shape portion M, the microtexture structure portion 30B is arranged in a superimposed manner.

  This microtexture structure portion 30B is the same as the microtexture structure portion 30A shown in FIGS. The groove 3 extends in the circumferential direction of the cylinder 41 and is continuously provided in the direction of the cylinder axis AX. However, in the third embodiment, the profile of the groove 3 is set so that the sliding direction H1 shown in FIG. That is, each inclined surface 33 of the groove 3 is an inclined surface in which the downstream side (lower side) in the descending direction of the piston 43 is deep and the upstream side (upper side) is shallow.

  A large load swinging in the thrust direction is applied to the piston 43 due to an explosion load being applied to the piston 43 at a crank angle slightly exceeding top dead center. That is, in the initial stage of the expansion stroke in which the piston 43 descends, a load in the direction in which the sliding surface 45SA of the thrust side skirt portion 45A approaches the thrust side inner peripheral wall 41A (thrust direction) is applied to the piston 43. In order to prevent the sliding surface 45SA from coming into contact with the thrust side inner peripheral wall 41A due to this load, the microtexture structure portion 30B is provided on the sliding surface 45SA. As a result, the sliding levitation force created by the projecting shape portion M of the sliding surface 45SA is strengthened, and the sliding surface 45S can be made more difficult to contact the thrust side inner peripheral wall 41A.

  The piston 43 moves up and down in the cylinder 41, but the large load in the thrust direction is applied to the piston 43 when the expansion stroke is lowered. In other words, the levitation assist by the microtextured structure portion 30B is required when the piston 43 moves in the downward direction, and as described above, the protruding portion has the inclined surface 33 in which the lower side is deeper and the upper side is shallower. A groove 3 with 34 is formed. The microtextured structure portion 30B is disposed in a portion of the sliding surface 45SA that is supposed to be in contact with the thrust side inner peripheral wall 41A, that is, in a peripheral region of the top portion of the protruding shape portion M. From such a microtexture structure portion 30B, a levitation force can be generated in a superimposed manner on the sliding surface 45SA by the action described above with reference to FIG. A similar microtexture structure portion 30B may be provided on the sliding surface 45SB of the anti-thrust side skirt portion 45B.

[Fourth Embodiment]
FIG. 15 is an enlarged view of a main part of FIG. 13, and is a cross-sectional view of the connecting portion of the large end 62 of the connecting rod 6 and the crank pin 52 constituting the sliding structure according to the fourth embodiment. In the fourth embodiment, an example in which the present invention is applied to the sliding structure according to the third aspect described above, in which the large end 62 rotates and slides around the crankpin 52. Show.

  The large end portion 62 has a circular bearing hole 63, and a bearing metal 64 (second member) is fitted into the bearing hole 63. The bearing metal 64 is a sliding bearing in which a band-shaped metal circle is formed in an annular shape. In this embodiment, the crank pin 52 is the first member, the bearing metal 64 is the second member, the outer peripheral surface 52A of the crank pin 52 is the first sliding surface, and the inner peripheral surface 64A of the bearing metal 64 is the second sliding surface. It is.

  The inner circumferential surface 64A and the outer circumferential surface 52A face each other through the gap G when the large end portion 62 rotates and slides. In the gap G, a lubricating fluid made of air, water, or low viscosity oil of 0W-20 class is interposed. 64 A of inner peripheral surfaces are provided with the overhang | projection shape part M1 which protrudes in the crossing direction orthogonal to the axial direction of the crankpin 52 (cross section of FIG. 15) with 52 A of outer peripheral surfaces. In FIG. 15, the overhanging shape portion M1 is exaggeratedly drawn, but it is actually a shape having an overhang of micron order that is difficult to visually distinguish.

  The overhang shape portion M1 forms one overhang (macro profile) around the circumferential direction of the inner peripheral surface 64A, and has a top portion P and a bottom portion Q. The top portion P is the portion that protrudes most toward the outer peripheral surface 52A. The skirt portion Q is a portion that is located farthest from the outer peripheral surface 52A. The width of the gap G at the top P is the minimum gap h5, and the width of the gap G at the skirt Q is the maximum gap h6. FIG. 15 shows an example in which the apex P is arranged in the vicinity of the point where the line segment 6A connecting the axis of the small end 61 and the axis of the large end 62 of the connecting rod 6 intersects the bearing metal 64. ing. The cross-sectional shape orthogonal to the axial direction of the projecting shape portion M1 has a spiral shape that gradually decreases in diameter toward the center of the bearing hole 63 during one round of the inner peripheral surface 64A. The cross-sectional shape protrudes most at the top portion P, and then retreats rapidly outward in the radial direction, and is connected to the skirt portion Q.

  By providing such a protruding shape portion M1, when the large end portion 62 rotates and slides, the inner peripheral surface 64A floats with respect to the outer peripheral surface 52A. When the large end 62 rotates and slides in the sliding direction H1 (counterclockwise), a flow in the inflow direction H2 opposite to the sliding direction H1 occurs in the lubricating fluid existing in the gap G. That is, the fluid flows from the skirt Q toward the top P. As a result, the inner peripheral surface 64A floats with respect to the outer peripheral surface 52A by the action of the macro profile previously described in the second embodiment, and the sliding resistance therebetween can be significantly reduced.

  In addition to the protruding shape portion M1, a microtexture structure portion 30C is formed on a part of the inner peripheral surface 64A. That is, in order to assist the levitation created by the macro profile of the projecting shape portion M1, the microtexture structure portion 30C is arranged in a superimposed manner. The region where the microtextured structure portion 30 </ b> C is provided is a region serving as a transmission path for a load accompanying the maximum in-cylinder combustion pressure received by the connecting rod 6 from the piston 43. Specifically, the line segment 6 </ b> A intersects with the bearing metal 64 and is near the intersection on the small end 61 side.

  A high load is transmitted to the bearing structure portion of the crank mechanism through the connecting rod 6 when an explosion load (in-cylinder combustion pressure) in the combustion / expansion stroke is applied to the piston 43. In particular, at the timing when the in-cylinder maximum combustion pressure is generated, a high load is transmitted to the bearing structure. Such a high load may cause the inner peripheral surface 64A to approach or collide with the outer peripheral surface 72A during sliding levitation of the inner peripheral surface 64A based on the projecting shape portion M1, thereby causing a reduction or disappearance of the levitation effect. .

  Therefore, by providing the micro-texture structure portion 30C at a place where a collision with the outer peripheral surface 72A is assumed, the sliding levitation force created by the overhanging shape portion M1 of the inner peripheral surface 64A is strengthened, and the inner peripheral surface 64A It can be made difficult to contact the outer peripheral surface 72A. In the microtextured structure portion 30C, the profile of the groove 3 is set so that the sliding direction H1 shown in FIG. 12B matches the rotational sliding direction H1 of the bearing metal 64. That is, each inclined surface 33 of the groove 3 provided with the protruding portion 34 is an inclined surface in which the downstream side in the rotational sliding direction H1 of the bearing metal 64 is deep and the upstream side is shallow. From such a microtextured structure portion 30C, a levitation force can be generated in a superimposed manner on the inner peripheral surface 64A by the action described above with reference to FIG.

[Description of Other Modified Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to this. For example, although the cross-sectional shape of the groove 3 in the sliding direction H1 is a sawtooth type, the shape is deformed as long as the inclined surface 33 has a tendency that the downstream side in the sliding direction H1 is deep and the upstream side is shallow. Good. For example, the bottom portion 32 may not be an acute angle but may be an R surface. In addition, the inclined surface 33, the vertical wall 342 and the horizontal wall 343 of the protrusion 34 may be gently convex or concave.

DESCRIPTION OF SYMBOLS 1 1st member 1S 1st sliding surface 2, 21 2nd member 2S, 21S 2nd sliding surface 30, 30a, 30b, 30A, 30B, 30C Microtextured structure part 3, 3a, 3b Groove 3A 1st surface ( Downstream groove wall)
3B 2nd surface 3U, 3D Upstream edge part, downstream edge part 31 Top part 32 Bottom part 33 Inclined surface 33A 1st inclined surface (bottom wall including a bottom part)
34 Protruding part 341 Vertex 342 Vertical wall 343 Horizontal wall 35 Plateau part 41 Cylinder 41A Thrust side inner peripheral wall (first sliding surface)
42 Cylinder block (first member)
43 Piston 45 Skirt (second member)
45SA sliding surface (second sliding surface)
5 Crankshaft 52 Crankpin (first member)
52A Outer peripheral surface (first sliding surface)
6 Connecting rod 64 Bearing metal (second member)
64A Inner peripheral surface (second sliding surface)
F Lubricating fluid L1 Groove pitch L2 Groove width LA, LB, LC First part, second part, third part H1 Sliding direction

Claims (10)

A first member having a first sliding surface;
A second member having a second sliding surface facing the first sliding surface and moving relative to the first member in a predetermined sliding direction,
A lubricating fluid is interposed between the first sliding surface and the second sliding surface,
The second sliding surface includes a microtextured structure portion including a plurality of grooves extending in a direction orthogonal to the sliding direction,
Each of the grooves of the microtextured structure portion includes a first portion, a second portion, and a third portion, which are sequentially arranged from the downstream side to the upstream side in the sliding direction,
The first portion traps a turbulent flow of the lubricating fluid flowing between the first sliding surface and the second sliding surface;
The second portion is a region that ensures a laminar flow of the lubricating fluid that circulates; and
The third portion is a sliding structure, which is a region for confining the laminar flow of the lubricating fluid in a gradually narrowing space. The sliding structure according to claim 1,
The groove has a tendency that the downstream side in the sliding direction is deep and the upstream side is shallow,
More than the line connecting the top of the groove closest to the first sliding surface and the bottom of the furthest part in the intermediate region between the downstream side and the upstream side of the groove. A protrusion protruding in the direction of the sliding surface is formed,
The protruding portion constitutes the second portion, the downstream portion of the groove from the protruding portion constitutes the first portion, and the upstream portion of the groove from the protruding portion constitutes the third portion. , Sliding structure. In the sliding structure according to claim 2,
The protrusions each have a vertical wall extending in a direction perpendicular to the sliding direction on the downstream side and a lateral wall extending in the sliding direction on the upstream side,
The first portion is a region defined by the vertical wall, a bottom wall including the bottom, and the downstream groove wall;
The second portion is a region where the lateral wall exists,
The third structure is a sliding structure that is an area including an inclined surface that extends to the upstream side so as to approach the first sliding surface from the upstream end of the lateral wall in the sliding direction. In the sliding structure according to claim 2,
The groove is an opening edge of the groove, the downstream edge and the upstream edge in the sliding direction, the deepest bottom located between these edges, the downstream edge and the bottom A first surface between and a second surface between the upstream edge and the bottom,
The first sliding surface is a surface parallel to the sliding direction;
The first surface is a surface having an inclination angle in a range of 70 ° to 90 ° with respect to the first sliding surface,
The second structure is a sliding structure that is an inclined surface based on a gentler inclination than the first surface, and has the protrusions. In the sliding structure according to claim 4,
When the distance between the top and the bottom in the direction perpendicular to the sliding direction is D, and the distance between the top and the top of the protrusion is Y, the following expression 0.1D ≦ Y ≦ 0.6
A sliding structure set in the range of In the sliding structure according to claim 4 or 5,
The protrusion has a vertical wall on the downstream side of the apex,
The pitch of the plurality of grooves arranged in the sliding direction is L1, the distance between the downstream edge and the upstream edge of each groove in the sliding direction is L2, and the distance in the sliding direction is When the distance between the first surface of the groove and the vertical wall of the protrusion is X, the following formula L1 = 1 μm to 1 mm
1μm ≦ L2 ≦ L1
0.2L2 ≦ X ≦ 0.6L2
A sliding structure set in the range of In the sliding structure according to claim 4 or 5,
The protrusion has a vertical wall on the downstream side of the apex and a horizontal wall on the upstream side,
When the angle formed by the vertical wall with respect to the direction perpendicular to the sliding direction is α, and the angle formed by the horizontal wall with respect to the sliding direction is β,
0 ° ≦ α ≦ 20 °
−15 ° ≦ β ≦ 15 °
A sliding structure set in the range of In the sliding structure according to any one of claims 1 to 5, and 7,
A sliding structure in which a pitch in which the plurality of grooves are arranged in the sliding direction is set in a range of 1 μm to 1 mm. In the sliding structure according to any one of claims 2 to 8,
When the gap between the top and the first sliding surface is the minimum gap h1, and the gap between the bottom and the first sliding surface is the maximum gap h2,
h1 = 0.5 μm to 2.0 μm,
h2 / h1 = 1.5-5.0,
A sliding structure set in the range of In the sliding structure according to claim 9,
The minimum gap h1 is
Surface roughness of the first sliding surface, or
When the second sliding surface has a plateau portion between the plurality of grooves, the sliding surface is set to a value larger than the total surface roughness of the surface roughness of the first sliding surface and the plateau portion. A moving structure.