Sliding member

Abstract

To provide a sliding member with no diamond-like carbon film provided on a sliding surface, capable of achieving excellent friction reducing effects under the conditions that a sliding speed is relatively low.SOLUTION: A sliding member according to the present invention is used in the presence of a lubricant and comprises: a sliding surface formed of a base material; and a recessed part provided in the sliding surface. The sliding surface satisfies conditions represented by the following expression: 2≤α / Ra≤100, where α represents a ratio of the total volume of the recessed part in the sliding surface to the area of a portion of the sliding surface in which the recessed part is not formed, and Ra represents a center line average surface roughness of the portion of the sliding surface in which the recessed part is not formed.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a sliding member used in the presence of a lubricant. [Background technology]

[0002] Sliding members such as valve lifters are used in valve drive mechanisms equipped in internal combustion engines. The valve lifters are in sliding contact with the outer peripheral surface of the cam of a camshaft, and the rotation of the camshaft acts to open and close the valves. Various efforts have been made in the past to reduce the sliding resistance of sliding members. For example, Patent Document 1 discloses a sliding member in which a diamond-like carbon treatment is applied to the sliding surface and a plurality of minute recesses are formed. Patent Document 2 discloses a sliding member having a hard carbon film that serves as the sliding surface, and recesses whose depth distribution changes from the center to the end in a direction perpendicular to the sliding direction on the sliding surface according to the oil film thickness distribution. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-9080 A [Patent Document 2] JP 2004-278705 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional sliding components have a hard coating such as diamond-like carbon, which provides excellent wear resistance and a good friction reduction effect in the fluid lubrication region. However, at low sliding speeds (under high loads) such as in the boundary lubrication region, the friction coefficient is higher than in the fluid lubrication region, leaving room for improvement.

[0005] The present disclosure provides a sliding member that does not have a diamond-like carbon coating on its sliding surface and that can achieve an excellent friction reduction effect under conditions where the sliding speed is relatively low. [Means for solving the problem]

[0006] The slide member according to the present disclosure is a slide member used in the presence of a lubricant, and includes a slide surface made of a base material and a recess provided on the slide surface, and the slide surface satisfies a condition represented by the following formula: 2≦α / Ra≦100 In the formula, α represents the ratio of the total volume of recesses on the sliding surface to the area of ​​the portion of the sliding surface where recesses are not formed (total volume of recesses / area of ​​the portion of the sliding surface where recesses are not formed), and Ra represents the center line average roughness of the portion of the sliding surface where recesses are not formed.

[0007] As described above, the sliding surface being made of the base material means that no hard film is formed on the sliding surface. The hard film is, for example, a diamond-like carbon film, an ion plating film, or a hard plating. When such a sliding surface satisfies the above conditions, an excellent friction reduction effect can be achieved under conditions where the sliding speed is relatively low. That is, the amount of oil film supplied in the sliding direction of the pressure generating area is increased by the pump effect in which the peripheral part of the recess of the base material on which the hard film is not formed on the sliding surface elastically deforms to push out the lubricant in the recessed groove, and the wedge effect in which the lubricant is drawn between the sliding surface and the mating member, so that the lubricating state between the sliding members approaches a fluid lubrication state, and the friction reduction effect is realized.

[0008] The shape of the recess in the sliding surface is, for example, a groove (a long and narrow depression). In a plan view, when the length of the groove is L and the average width of the groove is W, the ratio L / W of the length L to the average width W is preferably 2 or more. The groove may extend linearly or may be spiral. The recess may be a plurality of grooves extending radially or a plurality of concentric grooves. When the recess is a spiral groove or a plurality of concentric grooves, the counter member is evenly affected by the recess in the sliding surface during sliding, so that the friction reduction effect can be more effectively achieved. The average width W of the groove means the average value of the widths measured at a plurality of locations (for example, 5 locations) equally spaced in the extension direction of the groove, depending on the length of the groove.

[0009] When the average width of the groove is W and the average depth of the groove is D, it is preferable that the ratio W / D of the average width W to the average depth D is greater than 1. By satisfying this condition, a sufficient amount of lubricant can be stored, and the lubricant stored during sliding is swept out of the recesses, so that a sufficient amount of lubricant can be supplied to the parts where no recesses are formed. The average depth D of the groove means the average value of the depth measured at multiple points (e.g., five points) equally spaced apart in the extension direction of the groove, depending on the length of the groove.

[0010] The sliding member of the present disclosure may be used in an environment where the relative sliding speed with respect to the counter member is 1.4 m / s or less. When the sliding member of the present disclosure is used in the above environment, the friction reduction effect can be achieved more effectively than when the sliding member is used in an environment where the relative sliding speed with respect to the counter member is more than 1.4 m / s. Effect of the Invention

[0011] According to the present disclosure, there is provided a sliding member that does not have a diamond-like carbon coating on its sliding surface and that can achieve an excellent friction reducing effect under conditions where the sliding speed is relatively low. [Brief description of the drawings]

[0012] [Figure 1]1(A) and 1(B) are cross-sectional views showing a part of a valve train of an internal combustion engine to which a slide member according to an embodiment of the present disclosure is applied. [Diagram 2] FIG. 2 is a cross-sectional view showing the valve lifter shown in FIG. [Diagram 3] FIG. 3 is a top view showing a schematic diagram of one embodiment of a groove formed on the sliding surface of a valve lifter. [Figure 4] FIG. 4 is a top view of a valve lifter, showing a schematic diagram of another embodiment of the groove. [Diagram 5] FIG. 5 is a top view of a valve lifter, showing a schematic diagram of another embodiment of the groove. [Figure 6] FIG. 6 is a graph showing the results of the examples and comparative examples when used in an environment where the relative sliding speed with respect to the counter member is 1.4 m / s. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals and duplicated description will be omitted.

[0014] <Valve train> Fig. 1 shows a part of a valve train of an internal combustion engine to which a slide member according to an embodiment of the present disclosure is applied, Fig. 1(A) is a cross-sectional view showing a state in which a valve lifter is raised and a valve is closed, and Fig. 1(B) is a cross-sectional view showing a state in which the valve lifter is lowered and a valve is open.

[0015] The valve lifter 10 shown in FIG. 1A corresponds to the sliding member according to this embodiment and is provided in a bore 22 of a cylinder head 20. A cam 24 is a mating member for the sliding surface 11 of the valve lifter 10. The cam 24 is attached to a camshaft and rotates with the rotation of the camshaft by a drive system or the like. The cam 24 has a cam profile in which the distance from the center of rotation to the outer circumferential sliding surface is not constant, so that the force pressing the sliding surface 11 of the valve lifter 10 changes with the rotation of the cam 24. As shown in FIG. 1A and FIG. 1B, with the rotation of the cam 24, the valve lifter 10 moves in the bore 22 to open and close a valve 26 connected to the valve lifter 10. The valve 26 is constantly biased upward (toward the cam) by a valve spring 28 arranged on the outer periphery. The opening operation of the valve 26 (see FIG. 1B) is performed when the protruding portion of the cam 24 presses the sliding surface 11. Lubricating oil is supplied from a lubricating oil supply means (not shown) provided on the camshaft side to lubricate the cam 24 and the valve lifter 10. The force with which the cam 24 presses the valve lifter 10 becomes maximum when the protruding tip end (cam nose) of the cam 24 reaches the vicinity of the central region of the sliding surface 11. Note that as the rotation speed of the camshaft increases, the sliding speed with the valve lifter 10 also increases.

[0016] <Valve lifter> Fig. 2 is a cross-sectional view of the valve lifter 10, and Fig. 3 is a top view of the valve lifter 10. As shown in these figures, the valve lifter 10 has a cylindrical shape with one open end, and specifically has a cylindrical skirt portion 12 and a crown portion 13 formed integrally with the skirt portion 12 at an upper end portion that is one end side of the skirt portion 12 in the direction of the central axis X. A circular boss portion 14 is provided near the center of the lower surface of the crown portion 13 (the main surface on the skirt portion 12 side). The boss portion 14 abuts against the upper end (valve stem) of the valve 26. A tapered chamfer is formed at the boundary between the skirt portion 12 and the sliding surface 11.

[0017] The sliding surface 11 may be circular, for example, as shown in FIG. 3. When the sliding surface is circular, the cam 24 slides in a part of the area (sliding range Sa shown by a dashed line in FIG. 3) of the circular sliding surface in the direction of the arrow S shown in FIG. 3. That is, the arrow S indicates the sliding direction of the cam 24, and the contact point between the cam 24 rotating in one direction and the sliding surface 11 reciprocates in the direction along the arrow S. The sliding range Sa shown by the dashed line indicates the movement range of the cam 24 sliding along the arrow S. In order to rotate the valve lifter 10 about its central axis in the bore 22 when sliding with the cam 24, the center position of the cam width may be slightly offset from the central axis of the valve lifter crown surface toward the outer periphery, and the sliding range Sa of the cam may be slightly larger than the cam width in consideration of the offset. The sliding surface 11 refers to the area with which the cam 24 can come into contact.

[0018] The main body (sliding surface 11, skirt portion 12, crown portion 13, and boss portion 14) of the valve lifter 10 is made of a base material. The material of the base material is not particularly limited, but for example, a heat-treated steel material can be used, or a steel material that has been carburized, nitrided, sulfurized, or the like can also be used.

[0019] The valve lifter 10 is used in the presence of a lubricant. For example, engine oil can be used as the lubricant. When the valve lifter 10 is applied to a part other than an internal combustion engine, for example, a lubricating oil such as machine oil, grease, etc. can be used as the lubricant.

[0020] The lubricant may contain an additive. The additive is not particularly limited, but it is preferable to use one containing at least one element selected from molybdenum, phosphorus, sulfur, zinc, and calcium. When the additive contains at least one element selected from molybdenum, phosphorus, sulfur, zinc, and calcium, a tribofilm is easily generated between the sliding surface and the counter member during sliding, and the friction reduction effect is easily achieved. The tribofilm is generated when the additive contained in the lubricant is adsorbed to the base material on the sliding surface, and the temperature and pressure generated by sliding act as driving forces to react between the components of the base material and the components of the additive. It is more preferable that the additive contains one or more elements selected from molybdenum, phosphorus, sulfur, and calcium.

[0021] As shown in FIG. 3, a groove 16 (recess) is provided on the sliding surface 11. The groove 16 is spiral-shaped about the central axis X of the sliding surface 11 (hereinafter simply referred to as the "axis X"), and is continuously formed from the end of the sliding surface 11 on the outer periphery side to the end of the central portion (near the axis X). The groove 16 can be formed by a method of irradiating the sliding surface 11 with a laser. For example, a valve lifter before the groove 16 is formed is rotated about the axis X, and a laser is irradiated radially from the outer periphery side of the sliding surface 11 toward the center. At this time, the groove 16 shown in FIG. 3 can be formed by controlling the rotation speed of the valve lifter, the moving speed of the laser, the irradiation intensity of the laser, and the like. Examples of lasers that can be used include an ultrashort pulse laser and a linearly polarized laser. Of these, it is preferable to adopt an ultrashort pulse laser with a pulse interval of picoseconds to femtoseconds as the laser for forming the groove 16.

[0022] The sliding surface 11 satisfies the condition expressed by the following formula. 2≦α / Ra≦100 α indicates the ratio of the total volume of grooves 16 on the sliding surface 11 to the area of ​​the portion of the sliding surface 11 where grooves 16 are not formed (total volume of recesses / area of ​​the portion of the sliding surface 11 where grooves 16 are not formed), and Ra indicates the center line average roughness of the portion of the sliding surface 11 where grooves 16 are not formed.

[0023] The area of ​​the portion of the sliding surface 11 where the grooves 16 are not formed can be calculated by, for example, measuring using a surface roughness / contour shape measuring instrument (SURFCOM1400D manufactured by Tokyo Seimitsu Co., Ltd.) in accordance with JIS B 0601-2001. The area may also be calculated by image processing. Measurement conditions may include, for example, a cutoff value of 0.25 mm, an evaluation length of 1.25 mm, and a measuring speed of 0.3 mm / s, and a 60-degree cone-shaped stylus with a tip radius of 2 μm may be used as the stylus. The area of ​​the portion of the sliding surface 11 where the grooves 16 are formed can also be calculated by, for example, measuring using a surface roughness / contour shape measuring instrument (SURFCOM1400D manufactured by Tokyo Seimitsu Co., Ltd.) in accordance with JIS B 601-2001. The area may also be calculated by image processing.

[0024] In plan view, when the length of groove 16 is L and the average width of groove 16 is W, the ratio L / W of length L to average width W is preferably 2 or more. The average width W of groove 16 can be measured, for example, by a surface roughness / contour shape measuring instrument (SURFCOM1400D manufactured by Tokyo Seimitsu Co., Ltd.). The average width may also be obtained by image processing.

[0025] When the average width of the grooves 16 is W and the average depth of the grooves 16 is D, the ratio W / D of the average width W to the average depth D is preferably greater than 1, and more preferably equal to or greater than 10. The average depth D of the grooves 16 can be measured, for example, by a surface roughness / contour shape measuring instrument (SURFCOM1400D manufactured by Tokyo Seimitsu Co., Ltd.). When the value of W / D is greater than 1, the lubricant in the grooves 16 is easily supplied to the sliding surface, while when it is 500 or less, the area of ​​the portion of the sliding surface 11 where the grooves 16 are not formed is easily secured. When the grooves 16 are formed by laser processing, the depth of the grooves 16 is, for example, 100 to 400 nm.

[0026] The volume of the groove 16 on the sliding surface 11 can be measured, for example, using a surface roughness / contour shape measuring instrument (SURFCOM1800D manufactured by Tokyo Seimitsu Co., Ltd.) and calculated from the average depth of the groove 16 and the area of ​​the portion of the sliding surface 11 where the groove 16 is formed.

[0027] The center line average roughness of the sliding surface 11 in the portion where the grooves 16 are not formed is expressed as the center line average roughness (Ra) determined by JIS B-0601. Ra is obtained by analyzing a surface profile measured over an evaluation length of 4 μm using an atomic force microscope. The center line average roughness Ra of the sliding surface 11 in the portion where the recesses are not formed may be, for example, 0.5 μm or less.

[0028] The value of α / Ra in the sliding surface 11 is, for example, 2 to 100, and may be 2 to 50 or 2 to 10. When the value of α / Ra is 2 or more, the resistance caused by the surface roughness of the sliding surface 11 is suppressed, or the amount of lubricant supplied to the portion of the sliding surface 11 where the recessed portion is not formed is adjusted by the pump effect and wedge effect that push out the lubricant, thereby achieving an excellent friction reduction effect. In addition, when the value of α / Ra is 100 or less, the amount of lubricant supplied to the portion of the sliding surface 11 where the groove 16 is not formed is prevented from becoming excessive, and an increase in sliding resistance caused by the lubricant can be suppressed.

[0029] The valve lifter 10 may be used in an environment where the relative sliding speed with respect to the mating member is 1.4 m / s or less. When the valve lifter 10 is used in the above environment, the friction reduction effect can be achieved more effectively than when the valve lifter 10 is used in an environment where the relative sliding speed with respect to the mating member is more than 1.4 m / s.

[0030] The cross-sectional shape of the groove 16 is not particularly limited. For example, the side and bottom surfaces may be continuously curved, or the side and bottom surfaces may be clearly distinguished. Furthermore, the groove 16 may have a so-called V-groove shape in which the inside is formed by two surfaces.

[0031] Although the embodiment of the present disclosure has been described in detail above, the present invention is not limited to the above embodiment. For example, in the above embodiment, the spiral groove 16 formed continuously from one end to the other end is exemplified, but the groove 16 may be formed intermittently as long as the value of α / Ra on the sliding surface 11 is within the range of 2 to 100. In addition, the recess does not have to be spiral, and for example, as shown in FIG. 4, a plurality of concentric grooves 17 may be formed on the sliding surface 11. The plurality of annular grooves 17 may also be formed continuously in the circumferential direction, or may be formed intermittently. As shown in FIG. 5, a plurality of linear grooves 18 may be formed on the sliding surface 11. The plurality of linear grooves 18 may also be formed continuously or may be formed intermittently.

[0032] In the above embodiment, a valve lifter has been exemplified as a sliding member. However, the sliding member according to the present disclosure may be applied to sliding parts of valve train parts such as shims, rocker arms, finger followers, etc., or sliding parts of gears, bearings, etc. EXAMPLES

[0033] The present invention will be described below based on examples, but the present invention is not limited to the following examples.

[0034] <Example 1> A valve lifter was produced whose sliding surface had the same structure as that shown in Fig. 3. The valve lifter according to this embodiment has the following features. Valve lifter material: SCM420 -Sliding surface diameter: 28.5mm Groove shape: Continuous spiral Average groove depth D: 0.254μm Average groove width W: 105μm Area A of the sliding surface where no recesses are formed: 432.34 mm 2 Total volume of recesses on sliding surface V: 0.032 mm 3 The area A of the sliding surface where no recesses are formed (unit: mm 2 ) for the total volume V of the recesses on the sliding surface (unit: mm 3 ) ratio (α=V / A): 0.074μm Center line average roughness (Ra) of the sliding surface where no recesses are formed: 0.024 μm Alpha / Ra: 3.1 Groove processing method: Laser processing

[0035] <Examples 2 to 5, Comparative Examples 1 to 2> Valve lifters of Examples 2 to 5 and Comparative Examples 1 and 2 were produced in the same manner as Example 1, except that the average depth of the grooves on the sliding surface, the average width of the grooves, the area of ​​the parts on the sliding surface where no recesses are formed, and the total volume of the recesses on the sliding surface, Ra, were changed as shown in Table 1 below.

[0036] <Comparative Examples 3 to 5> Except for the fact that a diamond-like carbon coating was provided on the sliding surface, valve lifters of Comparative Examples 3 to 5 were produced in the same manner as in Example 1. The measurement results are shown in Table 1.

[0037] [Table 1]

[0038] <Confirmation of friction reduction effect> For the valve lifters produced in Examples 1 to 5 and Comparative Examples 1 to 5, the outer surface of a mating member was slid against the sliding surface of the valve lifter using a motoring tester, and the torque value was measured when the relative sliding speed with the mating member was changed to 0.6, 0.9, 1.4, or 1.7. The torque value of Comparative Example 4 was set to 1, and the relative torque values ​​for each are shown in Table 2.

[0039] [Table 2]

[0040] FIG. 6 shows the measurement results of Examples 1 to 5 and Comparative Examples 1 to 5 when the relative sliding speed was 1.4 m / s. [Explanation of symbols]

[0041] 11: sliding surface; 16: spiral groove; 17: annular groove; 24: cam

Claims

1. A sliding member used in the presence of a lubricant, A sliding surface made of a base material; A recess provided on the sliding surface; Equipped with The sliding surface of the sliding member satisfies the condition represented by the following formula: 2≦α / Ra≦100 In the formula, α represents the ratio of the total volume of the recesses on the sliding surface to the area of ​​the portion of the sliding surface where the recesses are not formed, and Ra represents the center line average roughness of the portion of the sliding surface where the recesses are not formed.

2. The sliding member according to claim 1 , wherein the recessed portion is a spiral groove or a plurality of concentric grooves.

3. The sliding member according to claim 1 , wherein the recess is a groove extending linearly.

4. The sliding member according to claim 1 , wherein the recessed portion is a plurality of radially extending grooves.

5. The groove has a length L and an average width W; 5. The sliding member according to claim 2, wherein a ratio L / W of the length L to the average width W is 2 or greater.

6. The groove has an average width W and an average depth D; 6. The sliding member according to claim 2, wherein a ratio W / D of the average width W to the average depth D is greater than 1.

7. The sliding member according to any one of claims 1 to 6, which is used in an environment in which the relative sliding speed with respect to a counter member is 1.4 m / s or less.

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