JP6552022B2 - Valve lifter - Google Patents

Description

  The present invention relates to a valve lifter used in a direct-acting valve operating mechanism, and more particularly to a surface structure of a valve lifter crown surface.

  In order to improve fuel efficiency in response to energy and environmental problems, reduction of friction loss in internal combustion engines has become an important issue. The main sliding parts of the internal combustion engine include a valve operating system, a piston system, and a crankshaft system. The friction loss accounts for 75 to 90% in these main sliding parts, and the proportion of piston rings, pistons and connecting rods is high in the middle high speed rotation range, and the proportion of friction of the valve system is high in the low speed rotation range. These techniques for reducing friction loss are basically variously based on reducing the surface roughness of the sliding surface to lower the frictional resistance, and on the surface structure with improved oil retention from the viewpoint of lubrication. Improvements have been made.

  A valve lifter is one of the typical valve systems of internal combustion engines. The valve lifter is a member which is disposed between the cam and the valve and converts the rotational movement of the cam into the opening and closing movement of the valve (Patent Documents 1, 2 and the like). Since the valve lifter has a valve lifter body including a crown portion and a skirt portion, and the cam slides on the crown surface, it is desirable to reduce the frictional resistance on the valve lifter crown surface. For example, in Patent Document 3, a plateau-like convex portion is formed on the sliding surface of the valve lifter, and the grooved recess has a surface structure which is deepest at the sliding center and shallows toward the stroke end. Prevents oil draining and reduces the friction loss at the center. Further, in Patent Document 4, a large number of rectangular depressions are concentrically formed in the central portion of the crown surface of the valve lifter, and a large number of circular depressions are formed in the annular body portion separated from the center to reduce frictional resistance. .

JP 2008-240601 A JP 2008-215172 A JP 2002-235852 JP 2007-46660 A

  1 (A) is a schematic cross-sectional view of the valve lifter valve system, FIG. 1 (B) is a cross-sectional view when the valve lifter rises and the valve is closed, and FIG. 1 (C) is a valve lifter descended and the valve It is sectional drawing when it opens. A valve lifter 14 is disposed in a bore 12 formed in the cylinder head 10 so as to be movable up and down with an appropriate clearance. A cam 16 that slides on the crown of the valve lifter 14 is attached to a camshaft 18, and the camshaft 18 is rotated by a drive system 20 such as a chain. The lubricating oil supplied to the space 18A in the camshaft 18 is supplied to the cam journal portion 24 and the cam journal cap 26 through the holes 22, and the lubricating oil that has further lubricated the cam journal portion 24 is indirectly outer periphery thereof. The part is sprayed and a part is used to lubricate the valve lifter 14. Although not shown here, a weir for storing lubricating oil is formed on the outer periphery of the bore 12 of the cylinder head 10 so that the lubricating oil is quickly supplied to the valve lifter at the time of startup.

  Thus, the lubricating oil is supplied to the valve lifter 14 as the cam shaft 18 rotates, and the cam 16 slides on the crown surface of the valve lifter in a certain direction. Further, since the center of the cam width is somewhat offset from the center of the valve lifter 14, a rotational moment is given to the valve lifter 14 when the cam 16 slides on the crown surface, and the valve lifter 14 rotates. The sliding condition of the valve lifter crown surface that is slid by such rotational reciprocation of the cam varies depending on the region. In particular, there is a large difference between the sliding conditions of the central area and the outer peripheral area of the crown surface. The top view of a valve lifter crown surface is shown in FIG. 2, and the center area | region 40 and the outer periphery area | region 50 are illustrated by hatching for convenience.

(Surface pressure)
Since the central region 40 is a region that directly transmits the rotational motion of the cam 16 to the valve stem 28 disposed on the back side thereof, the surface pressure Pc of the central region 40 is larger than the surface pressure Pp of the outer peripheral region 50. (Pc> Pp).
(Number of contacts)
Since the valve lifter 14 is always rotated, the contact frequency or the contact frequency Np between the outer peripheral region 50 and the cam 16 is smaller than the contact frequency Nc between the central region 40 and the cam 16 (Nc> Np). That is, since the outer peripheral area 50 in contact with the cam 16 is rotated, there is less chance of contact as compared with the central area 40.

  As the surface pressure Pc of the central region 40 increases, the oil retention of the lubricating oil decreases and the frictional resistance of the central region 40 increases.

  The outer circumferential area 50 may include an area where the drawing speed of the lubricating oil is extremely low or a point where the drawing speed is zero. In such areas or points, the oil retention of the lubricating oil is further degraded. As described above, since the cam 16 slides in a fixed direction on the crown surface, while the valve lifter 14 rotates in a fixed direction, the relative speed between the sliding speed of the cam 16 and the rotational speed of the valve lifter 14 is There is a point where it becomes zero, that is, a point where the drawing speed of the lubricating oil becomes zero. The point at which the pull-in speed becomes 0 may occur in the outer peripheral region 50 where the circumferential speed on the crown surface generally increases, although it depends on the sliding speed of the cam. In addition, the decrease in oil retention of the outer peripheral region 50 adversely affects the lubrication between the skirt portion and the bore of the valve lifter 14. That is, since the valve lifter given the rotational moment moves up and down in the bore while receiving an axially inclined force, when the lubricating oil becomes insufficient, the wear of the upper end or the lower end of the bore 12 increases and the optimum there Clearance is lost, which causes noise.

  As described above, since the sliding conditions are different between the central region 40 and the outer peripheral region 50 of the crown surface of the valve lifter 14, the friction loss is increased and the fuel consumption is improved unless the lubrication of the central region 40 and the outer peripheral region 50 is optimized. Not only that, but there is also a problem that the product life is reduced due to wear.

  An object of the present invention is to solve such a problem of the prior art and to provide a valve lifter having a surface structure adapted to sliding conditions which is excellent in lubricating performance and capable of reducing friction loss.

  The valve lifter according to the present invention is disposed between the valve and the cam, and converts the rotational motion of the cam to the lift motion of the valve, and the first distance in the radial direction from the center of the circular valve lifter crown surface A first textured groove for retaining lubricating oil is circumferentially formed in the central region defined by the and is defined at a second distance in the radial direction across an intermediate region adjacent to the central region. In the outer peripheral region, a second textured groove for holding the lubricating oil is formed in the circumferential direction.

  Preferably, an amorphous hard carbon film is formed on the crown surface of the valve lifter, and first and second texture grooves are formed on the amorphous hard carbon film. Preferably, the outer peripheral area includes an area where the drawing speed of the lubricating oil is zero. Preferably the first and second textured grooves are herringbone patterns. Preferably, at least one of the first and second textured grooves is a circumferentially continuous groove. Preferably, at least one of the first and second texture grooves is a groove discontinuous in the circumferential direction. Preferably, no texture groove is formed in the intermediate region. Preferably, a third textured groove is formed in the intermediate region, the groove being shallower than the first and second textured grooves and having a larger groove pitch. Preferably, the third textured groove is a radially extending straight groove. Preferably, the textured grooves are formed by laser processing. Preferably the lubricating oil is a molybdenum based oil.

  The valve lifter according to the present invention is disposed between the valve and the cam, and converts the rotational movement of the cam into a lift movement of the valve, and an amorphous hard carbon film is formed on the circular valve lifter crown surface. Then, herringbone texture grooves that are continuous in the circumferential direction are formed on the amorphous hard carbon coating.

  ADVANTAGE OF THE INVENTION According to this invention, the valve lifter which was excellent in lubrication performance and reduced the friction loss can be provided.

1 (A) is a cross-sectional view schematically showing the valve lifter valve system, FIG. 1 (B) is a cross-sectional view when the valve lifter is raised and the valve is closed, and FIG. 1 (C) is a valve lifter lowered. It is sectional drawing when a valve opens. It is a top view of the conventional valve lifter crown surface. FIG. 3A is a plan view of the surface structure of the crown surface of the valve lifter of this embodiment, and FIG. 3B is a cross-sectional view taken along the line AA. It is a figure which shows an example of the herringbone-like texture groove | channel formed in the valve lifter crown surface which concerns on the Example of this invention. It is a figure which shows the example of the other texture pattern formed in the valve lifter crown surface which concerns on the Example of this invention. It is a figure which shows the experimental result which compares the friction torque of the valve lifter by a present Example and the valve lifter in which the texture groove | channel is not formed. It is a top view of the surface structure of the valve lifter crown surface concerning a 2nd example of the present invention. It is a figure which shows an example of the texture groove | channel formed in the valve lifter crown surface which concerns on the 2nd Example of this invention.

  Hereinafter, a valve lifter according to the present invention will be described with reference to the drawings. It should be noted that the scale of the drawings is emphasized for easy understanding of the features of the invention, and is not necessarily the same as the scale of actual devices and parts.

  The valve lifter according to the present embodiment is disposed between the valve stem and the cam in the direct stroke type valve operating mechanism of the internal combustion engine and has a function of transmitting the lift operation of the cam to the valve. Further, the valve lifter may be provided with a pausing mechanism for pausing or operating the lift operation of the valve stem by controlling the hydraulic ON / OFF. For example, when the internal combustion engine is operated at low speed, the lift operation of the cam is stopped so as not to be transmitted to the valve, and when the internal combustion engine is operated at high speed, the lift operation of the cam is transmitted to the valve.

  FIG. 3A is a schematic plan view of the valve lifter according to the present embodiment, and FIG. 3B is a cross-sectional view taken along the line A-A. As shown in FIG. 3B, the valve lifter 100 according to the present embodiment has a valve lifter main body that is generally inverted cup-shaped, and the valve lifter main body extends in the vertical direction from the circular crown 110 and the crown 110 And a circumferential skirt portion 120. Although not shown in detail here, a valve pausing mechanism can be arranged in the space in the skirt portion 120.

  As the material of the valve lifter main body, one obtained by carburizing SCM material according to JIS standard can be used, and other steel materials, castings, iron alloys, titanium alloys, aluminum alloys, high strength resins, etc. can be used. Preferably, in order to improve the wear resistance, a hard film is formed on the surface of the crown portion 110 by nitriding treatment, such as a nitride layer, a Cr plating film, titanium nitride, or chromium nitride. As a more preferred embodiment, an amorphous hard carbon coating (hereinafter referred to as a DLC (Diamond like carbon) coating) 112 having high hardness and excellent friction characteristics is formed on the surface of the crown 110. The DLC film 112 may be formed directly on the surface of the substrate, but may be formed via an intermediate layer of a metal such as Cr or a metal nitride thereof in order to improve adhesion. The base material for forming the DLC film 112 is a steel material such as SCM 415 material or an iron-based alloy or the above-mentioned steel material or iron-based alloy subjected to hardening heat treatment such as carburizing treatment or quenching treatment to have surface hardness HRC 53 or more It is preferable to use it. In addition, the DLC film 112 can be formed by a PVD method, a CVD method, a PACVD method, or the like. For example, when the DLC film 112 is formed by the arc ion plating method, a hydrogen content of 0.5 atomic% or less is preferable from the viewpoints of hardness and wear resistance. The film thickness of the DLC film 112 can be, for example, about 0.3 to 1.5 μm for the PVD method and about 20 μm for the CVD method. Ra0.01-0.03 is suitable for the surface roughness of the DLC film 112 from a viewpoint of the aggressiveness to a cam. A thick boss 122 is formed on the back surface side of the crown portion 110, and the boss 112 is brought into contact with a valve stem or a shim interposed therebetween. In the following description, a valve lifter in which the DLC film 112 is formed on the crown part 110 is illustrated, but the present invention does not require the DLC film 112 and the valve lifter in which the surface of the crown part 110 is nitrided. It should be noted that it also applies to

  The DLC coating 112 formed on the top layer of the crown 110 provides a crown surface 114 on which the cam slides. A textured groove 132 is formed in the central region 130 of the crown surface 114. The texture groove 132 is a groove of fine irregularities having regularity or periodicity. Such a texture groove 132 has a function of holding lubricating oil as described later. The central region 130 is defined by a distance of radius r1 from the center of the valve lifter 100. Preferably, the radius r1 defines a region where the surface pressure Pc is relatively high due to sliding with the cam or a region where the contact frequency Nc is relatively high. For example, the radius r1 can be set to a value at which the surface pressure Pc is equal to or greater than a predetermined threshold based on engine design specifications or the like, or a value at which the contact frequency Nc is equal to or greater than the threshold. In another example, the radius r1 can be a value equal to or larger than the radius of the boss 122 formed on the back surface of the crown 110 by a certain value.

  An intermediate region 140 is defined adjacent to the central region 130. The middle area 140 is an area surrounded by the radius r1 and the radius r2 (r1 <r2). In the present embodiment, no texture groove is formed in the intermediate region 140, and the surface of the intermediate region 140 is the DLC film 112.

  Adjacent to the intermediate region 140, an outer peripheral region 150 is defined. The outer circumferential area 150 is an area surrounded by the radius r2 and the radius r3 (r3> r2). Texture grooves 152 are formed in the outer peripheral region 150. Texture groove 152 may have the same configuration as texture groove 132 formed in central region 130, or may have a different configuration. The configuration of the texture groove is specified from, for example, a pattern, depth, pitch, size, area ratio, and cross-sectional shape.

  The outer peripheral region 150 is a region in which the surface pressure Pp is relatively small, the number of contact times Np with the cam is relatively small, and the pull-in of the lubricating oil is small. For example, the radius r3 can be set to a value at which the surface pressure Pp is less than or equal to a predetermined threshold value or a value at which the number of contacts Np is less than or equal to the threshold value. Furthermore, the outer peripheral region 150 includes a point where the lubricating oil pull-in speed is equal to or lower than the threshold value, that is, a point where the relative speed between the cam and the crown surface is equal to or lower than the threshold value. Includes the point where the retraction speed or the relative speed is zero.

  In a preferred embodiment of the present embodiment, the texture grooves 132 and 152 in the central region 130 and the outer peripheral region 150 are formed by laser processing. By scanning the laser beam optically, a fine and complicated texture groove having periodicity or regularity can be formed on the DLC film 112. The depth of the groove can be arbitrarily adjusted by the output of the laser beam. For example, a groove of about 300 nm can be formed. The pitch of the grooves is also arbitrary, but for example, a pitch of 0.1 to 0.2 mm can be formed.

  The texture groove is a periodic structure including fine asperities and has an effect of holding the lubricating oil supplied to the sliding surface in the groove. If the oil retention is increased by holding the lubricating oil, the oil film is prevented from being thinned, and good lubrication with reduced friction loss can be obtained.

  In terms of the amount of oil (film thickness) between the sliding cam and the crown surface 114, in the outer peripheral region 150, theoretically, the timing at which the oil film thickness instantaneously becomes approximately 0 (oil film breakage) is included At this moment, the oil film can not be dynamically configured. On the other hand, in the central region 130, although the oil film is formed somewhat even though the surface pressure is high, it is theoretically possible to obtain a better lubrication condition than the peripheral region 150, but the contact load is high, Also, the lubrication state of the crown surface 114 becomes severe due to abnormal behavior (bounce, spring surging) of the inertia system at high rotation. Furthermore, since the number of repetitions of sliding with the cam is several times larger than that of the outer peripheral region 150, the amount of wear also inevitably increases.

  By forming the texture groove 132 in the central region 130, the supplied lubricating oil is effectively held in the groove, and even when the number of contacts Nc is high and a high surface pressure is applied, a constant oil film of the lubricating oil It is maintained, thus improving the lubrication performance of the central region 130.

  By forming the texture groove 152 in the outer peripheral region 150, a small amount of lubricating oil is held in the groove and a constant oil film is maintained, and therefore the lubricating performance of the outer peripheral region 150 is improved.

  Further, in the present embodiment, no texture groove is formed in the intermediate region 140. The intermediate region 140 has a smaller surface pressure than the central region 130. Therefore, in the intermediate region 140, sufficient lubrication can be obtained by surface treatment with the DLC film 112, and the texture grooves are not essential. By eliminating the need for processing the texture groove in the intermediate region 140, the cycle time for forming the texture groove by laser processing can be increased, productivity can be improved, and cost can be reduced.

  Next, a preferred example of the texture groove is shown in FIG. FIG. 4A shows a part of the texture grooves 132 and 152 in the central area 130 and the outer peripheral area 150. The texture grooves 132, 152 are composed of grooves of a so-called herringbone pattern. Each groove is substantially V-shaped, and is circumferentially continuous and radially arranged in plural sets. The herringbone has a groove that intersects the cam sliding direction at a constant angle, and this is continuous in the circumferential direction, so that the lubricating oil is easily held in the groove.

  FIG. 4B is a modification of a part of the herring bone in FIG. 4A. In FIG. 4B, the groove at the tip of the herring bone is eliminated, and the continuity in the circumferential direction is cut off. Such a herringbone pattern particularly improves the retention of oil film pressure in the cam width direction of the outer peripheral region 150. Therefore, the texture groove 132 in the central region 130 may be formed in the pattern shown in FIG. 4A, and the texture groove 152 in the outer peripheral region 150 may be formed in the pattern shown in FIG. 4A and 4B, the size and pitch of the herringbone in the outer peripheral region 150 are made larger than the size and pitch of the herringbone in the central region 130 according to the area. It may be the same or may be appropriately changed according to the sliding conditions.

  The texture grooves 132 and 152 in this embodiment are not limited to herringbone, and may be other patterns (patterns). An example is shown in FIG. In FIG. 5A, diamond-shaped grooves are continuously formed in the circumferential direction, and the same effect as the herringbone groove shown in FIG. 4A can be obtained. FIG. 5 (B) is a block of the continuous continuity in the circumferential direction of the rhombic groove and the outer peripheral side of the crown surface of FIG. 5 (A), and this makes it possible to maintain the oil film pressure.

  In FIG. 5C, diagonal grooves of 45 ° and 135 ° are alternately set in the circumferential direction to form a continuous V-shaped groove in the radial direction. The length of the groove is set relatively long. FIG. 5D is a diagram in which the continuity in the radial direction of each hatched groove in FIG. 5C is cut off. FIG. 5E shows a structure in which a relatively short groove of 45 ° is formed in the circumferential direction, each groove position is offset in the radial direction, and the groove is rectangularized. FIG. 5F shows a hatched groove formed in the 135 ° direction, which is a pattern in the reverse direction to that of FIG. 5E. FIG. 5G shows a configuration in which rectangular grooves are formed in the circumferential direction and upper and lower grooves are offset in the radial direction.

  Next, FIG. 6 shows experimental data for comparing the friction torque between the valve lifter according to this embodiment and the valve lifter (comparative example) in which the texture groove is not formed on the crown surface. In the valve lifter of the present embodiment, a texture groove of herring bone as shown in FIG. 4A is formed on the DLC coating 112, while on the other hand, the valve lifter of the comparative example only has the DLC coating formed on the crown surface. is there. 6A, 6B and 6C show the friction when the friction torque of the comparative example is 1 at a cam rotation speed of 500 rpm, 1000 rpm and 1500 rpm when the oil temperature is 40 ° C., 80 ° C. and 120 ° C. The torque ratio is shown.

  In the valve lifter of this embodiment, when the oil temperature is relatively low, 40 ° C., the friction torque is significantly lower than that of the comparative example when the cam rotation speed is around 500 rpm. When the cam rotation speed is 500 rpm, in the valve lifter of this example, a reduction in friction torque of 8% was confirmed as compared with the comparative example. Furthermore, it can be seen that as the oil temperature increases, the cam rotation speed that causes a reduction in the friction torque also increases. When the cam rotation speed at an oil temperature of 80 ° C. is 500 rpm, a reduction in friction torque of 15% is confirmed in the valve lifter of the present embodiment than in the comparative example, and at a cam rotation speed of an oil temperature of 120 ° C., it is 26% A reduction in friction torque was confirmed.

  Next, a second embodiment of the present invention will be described. FIG. 7 is a view showing the surface structure of the valve lifter crown according to the second embodiment, and the same reference numerals are assigned to the same parts as those in the first embodiment. In the second embodiment, the texture groove 142 is formed in the middle region 140. Since the middle region 140 has a sliding condition different from that of the central region 130 and the peripheral region 150, a texture groove suitable for the sliding condition is formed. The outer peripheral region 150 is less likely to be drawn in with lubricating oil than the central region 130, so the texture grooves 142 of the intermediate region 140 are formed in a pattern that facilitates the flow of lubricating oil from the central region 130 to the outer peripheral region 150. For example, the texture groove 142 can be a radially extending groove that continues the texture groove 132 and the texture groove 152. In this case, it is desirable that the texture groove 142 is shallower and has a larger groove pitch than the texture grooves 132 and 152 in the center region 130 and the outer peripheral region 150. Thereby, the flow resistance of the lubricating oil can be reduced.

  FIG. 8 shows an example of the texture groove of the second embodiment. In FIG. 8A, the texture groove 142 is configured by a substantially vertical groove extending in the radial direction, and the fluid resistance from the central region 130 to the outer peripheral region 150 is reduced. 8A is a combination with the herringbone of FIG. 4A, FIG. 8B is a combination with the pattern shown in FIG. 5A, and FIG. 8C is FIG. 5C. FIG. 8D shows a combination with the pattern shown in FIG. 5G. Although not shown here, it may be a combination with FIGS. 5 (B), (D) and (F).

  In addition to the above combination, the textured groove is formed on the entire valve lifter crown surface, and the depth of the textured groove 142 in the intermediate area 140 is shallower than the depth of the textured grooves 132 and 152 in the central area 130 and the peripheral area 150. The laser output may be controlled. In this case, the texture grooves 132 and 152 and the texture grooves 142 may have the same pattern or different patterns.

  In the above-described embodiment, the texture groove formed on the crown surface of the valve lifter improves the oil retention of the lubricating oil and improves the lubricating performance, but the formation of such a texture groove further results in the following: An effect can be obtained.

  By forming a texture groove optimum for the roughness and hardness of the cam, it is possible to obtain an initial leveling effect with the cam sliding surface. Also, the DLC film 112 may not have good oil retention due to the combination of lubricating oils. For example, molybdenum oil has poor affinity with the DLC film and is easily repelled by the DLC film. By forming textured grooves having periodicity, regularity, and continuity in the DLC film 112 as in this embodiment, molybdenum oil is easily retained on the DLC film.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. Is possible.

100, 100A: valve lifter 110: crown 112: DLC coating 114: crown 120: skirt 122: boss 130: central region 132: texture groove 140: middle region 142: texture groove 150: outer circumference region 152: texture groove

Claims (9)

A valve lifter disposed between a valve and a cam, which converts the rotational movement of the cam into a valve lift movement,
A first texture groove for holding lubricating oil is formed in the circumferential direction in the central region defined by a first distance in the radial direction from the center of the circular valve lifter crown surface, and is adjacent to the central region. In the outer peripheral region defined by a second distance that is larger than the first distance in the radial direction across the intermediate region, a second texture groove for holding the lubricating oil is formed in the circumferential direction,
The first distance is set to a value at which the surface pressure with the cam or the number of contact with the cam is equal to or greater than a predetermined threshold value, and the second distance is the surface pressure with the cam or the cam. The number of contacts is set to a value that is less than or equal to a predetermined threshold,
The valve lifter, wherein a third texture groove that is shallower than the first and second texture grooves is formed in the intermediate region. The valve lifter according to claim 1, wherein the pitch of the third textured groove is wider than the pitch of the first and second textured grooves. The amorphous hard carbon film is formed on the valve lifter crown surface, and the depths of the first, second and third textured grooves are smaller than the film thickness of the amorphous hard carbon film. Or the valve lifter described in 2 The valve lifter according to any one of claims 1 to 3, wherein the third textured groove is a radially extending straight groove. The valve lifter according to claim 1 or 2, wherein the first and second texture grooves have a herringbone pattern. The valve lifter according to claim 1, wherein at least one of the first and second textured grooves is a circumferentially continuous groove. The valve lifter according to claim 1, wherein at least one of the first and second textured grooves is a circumferentially discontinuous groove. The valve lifter according to any one of claims 1 to 7, wherein the first, second and third textured grooves are formed by laser processing. The valve lifter according to any one of claims 1 to 7, wherein the lubricating oil is a molybdenum-based oil.

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