JP2006125254A - Engine valve system component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an engine valve system component capable of realizing a low friction coefficient without depending on adsorption and reaction of an additive included in lubricating oil when used in a wet condition using the lubricating oil. <P>SOLUTION: The engine valve system component used in the wet condition using the lubricating oil comprises a valve system component main body and an amorphous hard carbon film formed on at least part of a sliding face of the other material relative to the valve system component main body. In the formed amorphous hard carbon film, Si content is 1 at% to 20 at%, and surface roughness is below Rzjis 0.5 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an engine valve system component used under a wet condition using a lubricating oil, and more particularly to an engine valve system component having a small friction coefficient during sliding.

  From the viewpoint of resource protection and environmental problems, it is desirable to improve the fuel efficiency of automobiles. For this reason, it is necessary to reduce the energy loss due to the friction of the automobile engine as much as possible. Examples of main sliding parts of an automobile engine include a valve system, a piston system, and a bearing system. The ratio of the valve system to the friction loss is not small, and there is a strong demand for reducing the friction of the valve system parts.

Conventionally, surface treatments such as formation of a coating on a sliding surface and nitriding treatment are known as methods for reducing the friction coefficient of a sliding member and improving wear resistance. For example, an amorphous hard carbon film called a DLC (diamond-like carbon) film is expected as a film that improves the slidability of the sliding surface (see, for example, Patent Documents 1 and 2).
JP-A-3-240957 JP 2001-192864 A

  For example, Patent Document 1 discloses an amorphous hard carbon film containing silicon (Si). This amorphous hard carbon film exhibits a low coefficient of friction under dry conditions where no lubricating oil is used. However, it is difficult to reduce the friction coefficient under wet conditions using lubricating oil. For example, when a drive system oil that assumes high friction for power transmission is used as the lubricating oil, the friction coefficient increases. As this factor, the influence of various additives contained in the lubricating oil can be considered. The additive in the lubricating oil is adsorbed and reacted on the surface of the amorphous hard carbon film to form a boundary film. The friction coefficient is considered to be determined by this boundary film.

  On the other hand, Patent Document 2 discloses an attempt to use a lubricating oil containing an aromatic compound. Since the aromatic compound has a high adsorption power to the amorphous hard carbon film, it forms a strong boundary film on the surface of the amorphous hard carbon film. That is, by forming a strong boundary film on the surface of the amorphous hard carbon film, the solid contact ratio is reduced and the friction coefficient is reduced. However, in this method, when the additive is changed, the reduction of the friction coefficient may be hindered by the adsorption and reaction of substances other than the aromatic compound. In addition, from the viewpoint of environmental problems and the like, it is conceivable that the types of additives will be reviewed and the amount thereof will be optimized in the future. In this case, it is expected that it is difficult to reduce the coefficient of friction by the above-described method depending on the adsorption and reaction of the additive.

  The present invention has been made in view of such a situation, and when used under wet conditions using a lubricating oil, a low friction coefficient is obtained without depending on the adsorption and reaction of additives contained in the lubricating oil. It is an object to provide an engine valve system component that can be realized.

  The engine valve system component of the present invention is an engine valve system component used in a wet condition using a lubricating oil, and slides between the valve system component body and a counterpart material of the valve system component body. An amorphous hard carbon film formed on at least a part of the surface, the Si content of the amorphous hard carbon film is 1 at% or more and 20 at% or less, and the surface roughness is Rzjis 0.5 μm or less. It is characterized by that.

  The engine valve system component of the present invention includes an amorphous hard carbon film having a Si content of 1 at% to 20 at% and a surface roughness of Rzjis 0.5 μm or less. The surface roughness of the amorphous hard carbon film is very small. For this reason, when the amorphous hard carbon film is used as a sliding surface, the ratio of boundary friction due to solid-solid contact is reduced, and the ratio of lubrication with lubricating oil is increased. This reduces the friction coefficient. In addition, the amorphous hard carbon film is harder than the steel material and hardly wears. For this reason, the initial surface roughness can be maintained even in sliding contact with the counterpart material. Further, the amorphous hard carbon film contains a predetermined amount of Si. According to the analysis of the present inventor, by containing Si, silanol (SiOH) is generated on the surface of the amorphous hard carbon film at the time of sliding contact. The generation of silanol is considered to significantly reduce boundary friction even when solids contact each other. As described above, the engine valve system component of the present invention exhibits a low coefficient of friction due to both the increase of the lubrication ratio by the lubricating oil and the reduction of the boundary friction.

  The engine valve system component of the present invention includes an amorphous hard carbon film having a Si content of 1 at% to 20 at% and a surface roughness of Rzjis 0.5 μm or less. Since the amorphous hard carbon film has a small surface roughness, the ratio of lubrication with the lubricating oil increases. Further, since the amorphous hard carbon film contains Si, boundary friction is also reduced. Therefore, if the engine valve system component of the present invention is used, a low friction coefficient can be realized without depending on the adsorption and reaction of the additive in the lubricating oil. Moreover, the friction coefficient can be further reduced by using the engine valve system parts of the present invention in combination.

  Hereinafter, the engine valve system parts of the present invention will be described in detail. The engine valve system component of the present invention is used under wet conditions using a lubricating oil. As the lubricating oil, a commonly used engine oil may be used.

  The engine valve system component according to the present invention includes a valve system component body and an amorphous hard carbon film formed on at least a part of a sliding surface between the valve system component body and a counterpart material of the valve system component body. Examples of the valve operating system component main body include various components constituting a valve operating mechanism that opens and closes a valve by rotation of a camshaft. Examples include camshafts, cams, shims, valve lifters, push rods, rocker arms, rollers, pivots, lash adjusters, valves, stem caps, and the like. The material of the valve system component main body is appropriately selected according to the type of the component. For example, cast iron is mainly used for camshafts and cams. Carbon steel, aluminum alloy, or the like is used for the valve lifter, push rod, shim, pivot, lash adjuster, stem cap, rocker arm, roller, and cam bearing. For the valve, heat resistant steel obtained by adding chromium or the like to carbon steel, or a titanium alloy is used.

  In order to reduce the coefficient of friction, the amorphous hard carbon film needs to be formed at least on the sliding surface with the counterpart material. Here, the amorphous hard carbon film may be formed on the entire sliding surface, or may be formed only on a part of the sliding surface.

When a pair of members slides and slips and rolls on the sliding surface, an amorphous hard carbon film is formed on the sliding surface having a large slip ratio (slip rate), thereby providing a friction coefficient. Can be fully exerted. For example, it is effective to form an amorphous hard carbon film on a sliding surface with a slip ratio of 1% or more, and further on a sliding surface with a slip ratio of 5% or more. In the present specification, the “slip rate” is defined as “a ratio of a difference in rolling speed of both members with respect to an average rolling speed of both members in a pair of sliding members”. Therefore, the “slip rate” is calculated by the following equation (1). In the formula (1), U1 represents the rolling speed of one member, and U2 represents the rolling speed of the other member (U1> U2).
Slip rate (%) = [(U1-U2) / {(U1 + U2) / 2}] × 100 (1)
Sliding surfaces with a slip rate of 1% or more include, for example, the sliding surface between the pivot shaft and the pivot bearing in the roller rocker type valve system, the sliding surface between the valve pressing portion of the rocker arm and the stem cap, Examples include a sliding surface between a cam and a shim in a striking valve system.

  The amorphous hard carbon film included in the engine valve system component of the present invention contains carbon (C), hydrogen (H), and Si. The Si content is 1 at% or more and 20 at% or less. When the Si content is less than 1 at%, the effect of reducing boundary friction is small. In order to further reduce the boundary friction, it is desirable that the Si content is 5 at% or more, further 6 at% or more. Further, from the viewpoint of obtaining a practical film formation rate, it is desirable that the Si content be greater than 5 at%. On the other hand, when the Si content exceeds 20 at%, the amount of wear of the amorphous hard carbon film increases. In consideration of wear resistance and seizure resistance, the Si content is preferably 9.8 at% or less. It is more preferable to set it to 9.5 at% or less.

  The H content is preferably 20 at% or more and 40 at% or less. When the H content is less than 20 at%, the hardness of the amorphous hard carbon film is increased, but the adhesion and toughness are reduced. The H content is preferably 25 at% or more. On the other hand, when the H content exceeds 40 at%, the hardness of the amorphous hard carbon film is reduced, and the wear resistance is lowered. It is preferable that the H content is 35 at% or less.

  The surface roughness of the amorphous hard carbon film is Rzjis 0.5 μm or less. If the surface roughness exceeds Rzjis 0.5 μm, an increase in the lubrication ratio due to the lubricating oil cannot be expected, and the friction coefficient cannot be reduced. Preferably, the surface roughness is Rzjis 0.45 μm or less. Further, Rzjis is preferably 0.3 μm or less. The method for calculating the surface roughness follows the method defined in JIS B 0601 (1994).

  The hardness of the amorphous hard carbon film is not particularly limited. For example, in consideration of wear resistance and the like, the pressure is preferably 15 GPa or more. In the present specification, as the hardness of the amorphous hard carbon film, a value measured by a nanoindenter tester (MTS manufactured by Toyo Corporation) is adopted.

  In general, the life of an automobile engine is said to be 300,000 km or more, and high durability is required for engine valve operating system parts. For this reason, it is desirable that the film thickness of the amorphous hard carbon film be 2 μm or more in consideration of wear and the like. More preferably, it is 5 μm or more.

  In a sliding environment where the sliding surface pressure is as high as 100 MPa or more, the amorphous hard carbon film is easily peeled off from the valve system component body. Therefore, even in such a sliding environment, it is desirable to increase the adhesion between the valve operating system component body and the amorphous hard carbon film in order to suppress the peeling of the amorphous hard carbon film. For example, when the valve system component body is made of steel, it is desirable that the adhesion between the valve system component body and the amorphous hard carbon film be 20 N or more. Further, when used in a sliding environment where the sliding surface pressure is 1000 MPa or more, it is desirable that the adhesion force be 30 N or more. Here, as the adhesive force between the valve system component body and the amorphous hard carbon film, a film peeling load by a normal scratch test is employed. That is, a load is applied to a diamond cone having an apex angle of 120 degrees and a tip radius of 0.2 mm to scratch the film, and the load when the film is peeled is defined as adhesion.

  On the other hand, the hardness of the aluminum alloy is around HV100, which is smaller than the hardness of the steel material. For this reason, when the valve system component body is made of an aluminum alloy, it is difficult to evaluate the adhesion by the scratch test method. Cast iron is a structure containing graphite. For this reason, even when the valve system component body is made of cast iron, it is difficult to evaluate the adhesion by the scratch test method. Similarly, even when the valve system component body is made of a titanium alloy, it is difficult to evaluate the adhesion by the scratch test method. Therefore, for example, when the valve system component body is made of aluminum alloy, cast iron, or titanium alloy, the adhesion is evaluated by the Rockwell indentation test method described below.

  The Rockwell indentation test method is a method in which a load of 100 to 1500 N is applied to a conical diamond indenter (Rockwell C scale indenter), and the adhesion is evaluated from the peeled state of the film around the indentation. The Rockwell indentation test method is about to be DIN standardized in Germany. For example, as described in W. Heinke et al, "Eval-uation of PVD nitride coatings, using impact, scratch and Rockwell-C adhesion tests", Thin Solid Films, 270 (1995) p.431-438, When the film is not peeled around the indentation (HF1 to 4), the adhesion is evaluated as good. On the other hand, when peeling of the film is observed (HF5, 6), the adhesion is evaluated as poor. Accordingly, when the valve system component body is made of aluminum alloy, cast iron, or titanium alloy, the contact state between the valve system component body and the amorphous hard carbon film is a lock loaded with a load of 1500 N. It is desirable to be in the state of HF1 to 4 in the evaluation by the well indentation test.

  The amorphous hard carbon film can be formed by a known CVD method or PVD method such as a plasma CVD method, an ion plating method, or a sputtering method. However, as represented by the sputtering method, the PVD method has directivity for the film forming material. Therefore, in order to form a film uniformly, it is necessary to arrange a plurality of targets in the apparatus or to rotate a valve system component body to be formed. As a result, the structure of the film forming apparatus becomes complicated and expensive. Further, it may be difficult to form a film depending on the shape of the valve system component. On the other hand, in the plasma CVD method, a film is formed using a reactive gas, and therefore, the film can be uniformly formed regardless of the shape of the valve operating system parts. Further, the structure of the film forming apparatus is simple and inexpensive. Examples of the plasma CVD method include a high frequency plasma CVD method using high frequency discharge and a direct current plasma CVD method using direct current discharge. In particular, the direct-current plasma CVD method is suitable because the film forming apparatus may be constituted by a vacuum furnace and a direct-current power source, and can be easily formed on valve-operated parts having various shapes.

For example, when an amorphous hard carbon film is formed by a direct-current plasma CVD method, first, a valve system component body is placed in a vacuum vessel, and a reaction gas and a carrier gas are introduced. And what is necessary is just to produce plasma by electric discharge and to make it adhere to a valve operating system component main body. Examples of the reaction gas include hydrocarbon gases such as methane (CH ₄ ) and acetylene (C ₂ H ₂ ), silicon compound gases such as Si (CH ₃ ) ₄ [TMS], SiH ₄ , SiCl ₄ , and SiH ₂ F ₄ . And hydrogen gas, and argon gas may be used as the carrier gas.

  When the engine valve system component of the present invention is in sliding contact with the mating member with the amorphous hard carbon film as a sliding surface, silanol is generated on the surface of the amorphous hard carbon film by the contained Si. The production of silanol can be detected by, for example, XPS analysis using a derivatization method. Derivatized XPS analysis is performed by the following procedure. First, the amorphous hard carbon film after sliding is immersed for 1 hour in sulfuric acid containing the reaction reagent tridecafluoro-1,1,2,2-tetrahydrooctyl-dimethylchlorosilane. At this time, if silanol is generated, OH groups on the film surface react with Cl in the reaction reagent to dehydrochlorinate. Next, the amorphous hard carbon film is taken out and thoroughly washed with chloroform. Thereafter, the amount of silanol can be quantified by determining the amount of F by XPS analysis.

  From the viewpoint of improving the adhesion between the valve-system component body and the amorphous hard carbon film, the surface of the valve-system component body on which the amorphous hard carbon film is formed is preliminarily formed by ion bombardment. It is desirable that processing has been performed. By the unevenness forming process, the surface of the valve-operated component main body becomes an uneven surface having protrusions having an average height of 10 nm to 100 nm and an average width of 300 nm or less. By forming an amorphous hard carbon film on the uneven surface, the adhesion is improved. The convex part of the formed uneven surface is hemispherical. The distance from the bottom to the apex of the hemispherical convex portion is defined as the height of the convex portion. In addition, the horizontal distance corresponding to the maximum diameter of the bottom of the hemispherical convex portion (the diameter when the bottom shape of the convex portion is a perfect circle and the major axis diameter when the bottom shape of the convex portion is an ellipse) is The width of the part.

  In this case, if the average height is less than 10 nm, the mechanical anchor effect cannot be obtained, and the adhesion improving effect is not sufficient. On the other hand, if it exceeds 100 nm, it becomes difficult to form a smooth amorphous hard carbon film. When the average height is 20 nm or more and 70 nm or less, the adhesion is further improved. On the other hand, if the average width exceeds 300 nm, the anchor effect cannot be obtained, and the adhesion improving effect is not sufficient. What is necessary is just to measure the height and width of a convex part with a scanning electron microscope (SEM), an atomic force microscope (AFM), etc. FIG.

  Moreover, the area ratio of the convex part which occupies for an uneven surface is good in it being 30% or more when the area of an uneven surface is 100%. By making the area ratio of the convex portions 30% or more, the effect of improving the adhesion of the amorphous hard carbon film can be sufficiently exhibited.

  The procedure of the ion bombardment method is as follows. First, the valve system component body is installed in a sealed container, and the gas in the container is exhausted to a predetermined gas pressure. The gas pressure is desirably 0.13 Pa or more and 2666 Pa or less. When the gas pressure is less than 0.13 Pa, the valve system component main body cannot be heated sufficiently. If it exceeds 2666 Pa, fine irregularities cannot be formed. Next, an unevenness forming treatment gas is introduced. As the concavo-convex forming gas, a rare gas consisting of one or more selected from helium, neon, argon, krypton, xenon, and radon may be used. In addition, when hydrogen is added to the rare gas, oxidation of the surface of the valve system component main body can be suppressed. Next, ion bombardment is given. As means for applying ion bombardment, glow discharge or an ion beam may be used. When ion bombardment is performed at a discharge voltage of 200 to 1000 V and a current of 0.5 to 3.0 A for 30 to 60 minutes, uniform and fine irregularities on the order of nanometers can be formed. Further, when the ion bombardment is applied, heating to a temperature (200 ° C. or higher is necessary) at which the hardness of the valve operating system component body does not decrease can form more uniform and fine irregularities.

  Further, in order to form uniform and fine irregularities on the surface of the valve system component main body, it is desirable to perform a nitriding treatment before the irregularity forming process. Examples of the nitriding method include a gas nitriding method, a salt bath nitriding method, and an ion nitriding method. After the nitriding treatment, the surface may be polished so that the surface roughness becomes Rzjis 0.5 μm or less, and the above-described ion bombardment may be applied.

  The engine valve system component of the present invention exhibits a low coefficient of friction in sliding contact with the counterpart material. Here, the sliding surface of the mating material may be an aspect of the material of the mating material such as carbon steel, alloy steel, cast iron, aluminum alloy, etc., or may be an aspect that has already been subjected to a known surface treatment. In particular, when an amorphous hard carbon film having a Si content of 1 at% to 20 at% and a surface roughness Rzjis of 0.5 μm or less is formed on the sliding surface of the counterpart material, the friction coefficient is further reduced. Is preferred. That is, the friction coefficient can be further reduced by using the engine valve system parts of the present invention in combination.

  Hereinafter, an embodiment of an engine valve system component of the present invention will be described. First, the configuration of the valve mechanism in which the engine valve system parts of this embodiment are arranged will be described. FIG. 1 shows a partial cross-sectional view of a valve mechanism in which engine valve system parts of this embodiment are arranged. FIG. 2 shows an enlarged view of a dotted frame II in FIG.

  As shown in FIG. 1, the valve mechanism 3 includes a cam shaft 40, a cam 41, a rocker arm 5, a valve 7, and a pivot 6. The cam 41 is disposed on the camshaft 40. The cam 41 has a protruding portion 410 that protrudes in the diameter increasing direction. The rocker arm 5 includes a roller 50, a support shaft 51, a needle 52, a valve pressing portion 53, a pivot shaft connecting portion 54, and an arm main body 55.

  The arm body 55 has a rectangular shape. The roller 50 has a cylindrical shape. The roller 50 is disposed approximately at the center in the longitudinal direction of the arm body 55. The outer peripheral surface of the roller 50 abuts on the outer peripheral surface of the protruding portion 410 of the cam 41.

  The support shaft 51 is separate from the roller 50. The support shaft 51 is disposed on the inner peripheral side of the roller 50. The needle 52 has a round bar shape. The needle 52 is interposed between the outer peripheral surface of the support shaft 51 and the inner peripheral surface of the roller 50. A plurality of needles 52 are arranged side by side in the circumferential direction. The roller 50 is rotatable with respect to the support shaft 51.

  The valve pressing portion 53 has a rectangular plate shape. The valve pressing portion 53 is disposed at one end in the longitudinal direction of the arm main body 55. The pivot shaft connecting portion 54 has a rectangular plate shape. The pivot shaft connecting portion 54 is disposed at the other longitudinal end of the arm body 55. A connecting hole 540 is formed in the pivot shaft connecting portion 54.

  The valve 7 includes a valve main body 70, a stem cap 71, a retainer 72, a cotter 73, a valve spring 74, and an oil seal 75. The valve body 70 has a trumpet shape that expands downward. The valve body 70 is inserted into a valve guide of a cylinder head (not shown). The cotter 73 consists of two cylindrical halves. The cotter 73 is mounted on the upper part of the valve body 70. The retainer 72 has a ring shape. The retainer 72 is disposed on the outer peripheral side of the cotter 73.

  The valve spring 74 is interposed between the lower surface of the retainer 72 and a spring seat (not shown) formed on the cylinder head. The valve spring 74 urges the retainer 72, that is, the valve main body 70 upward. The stem cap 71 has a cup shape opening downward. The stem cap 71 covers the upper end of the valve body 70. The upper bottom wall of the stem cap 71 abuts on the valve pressing portion 53. The oil seal 75 has a ring shape. The oil seal 75 is mounted around the lower portion of the retainer 72 in the valve body 70. The oil seal 75 covers the upper end of a valve guide (not shown).

  The pivot 6 includes a pivot shaft 60, a nut 61, and a pivot bearing 62. The pivot shaft 60 is made of carbon steel and has a cylindrical shape with a spherical bottom surface. The upper part of the pivot shaft 60 is screwed into the connecting hole 540 of the pivot shaft connecting portion 54. The nut 61 is screwed to the outer peripheral surface of the pivot shaft 60. As shown in FIG. 2, a DLC-Si film 600 of an amorphous hard carbon film is formed on the hemispherical surface 64 at the lower end of the pivot shaft 60. The composition of the DLC-Si film 600 is Si: 6 at%, C: 64 at%, H: 30 at%, and the surface roughness is Rzjis 0.2 μm. That is, the pivot shaft 60 is included in the engine valve operating system component of the present invention.

  The pivot bearing 62 is made of carbon steel and has a bolt shape. The pivot bearing 62 is fixed to the cylinder head 66. A hemispherical surface 64 of the pivot shaft 60 and an inverted hemispherical surface 65 that is substantially symmetric with respect to the top surface of the pivot bearing 62 are recessed. On the reverse hemispherical surface 65, an amorphous hard carbon film DLC-Si film 620 is formed as shown in FIG. The composition of the DLC-Si film 620 is the same as that of the DLC-Si film 600. That is, the pivot bearing 62 is also included in the engine valve system parts of the present invention. The DLC-Si film 620 having the inverted hemispherical surface 65 and the DLC-Si film 600 having the hemispherical surface 64 are in sliding contact.

  Next, the movement of the valve mechanism in which the engine valve system parts of this embodiment are arranged will be described. When the camshaft 40 rotates in the clockwise direction, the cam 41 also rotates in the same direction. When the protrusion 410 of the cam 41 comes into contact with the roller 50, the roller 50 is pressed, and the roller 50 rotates counterclockwise about the support shaft 51. When the roller 50 is pressed, the arm body 55 swings downward with the center O of the hemispherical surface 64 of the pivot shaft 60 as a fulcrum. As a result, the valve pressing portion 53 also swings downward. When the valve pressing portion 53 swings downward, the valve body 70 moves downward and opens against the urging force of the valve spring 74. When the protruding portion 410 of the cam 41 passes the roller 50, the valve main body 70 moves upward due to the urging force of the valve spring 74 and closes. Further, the valve pressing portion 53, that is, the arm main body 55 swings upward with the center O as a fulcrum.

  As the arm body 55 swings, the pivot shaft 60 screwed into the connecting hole 540 of the pivot shaft connecting portion 54 swings about the center O of the hemispherical surface 64. On the other hand, the pivot bearing 62 is fixed to the cylinder head 66 and does not move. Due to the difference in the movement, the DLC-Si film 600 formed on the hemispherical surface 64 of the pivot shaft 60 and the DLC-Si film 620 formed on the reverse hemispherical surface 65 of the pivot bearing 62 are relatively pressed together. To slide.

  According to this embodiment, the following effects can be obtained. That is, in this embodiment, the Si content of the DLC-Si films 600 and 620 is 6 at%, and the surface roughness is Rzjis 0.2 μm. Since the surface roughness is small, the ratio of boundary friction due to solid-solid contact is small, and the ratio of lubrication with lubricating oil is increased. Further, since a predetermined amount of Si is contained, silanol is generated on the surfaces of the DLC-Si films 600 and 620 during sliding, and the boundary friction is greatly reduced. As described above, the friction coefficient between the pivot shaft 60 having the DLC-Si film 600 and the pivot bearing 62 having the DLC-Si film 620 is reduced by both the increase of the lubrication ratio by the lubricating oil and the reduction of the boundary friction. To do.

  The embodiment of the engine valve system component of the present invention has been described above. However, the engine valve system parts of the present invention are not limited to the above-described embodiments, and various modifications and improvements can be made by those skilled in the art without departing from the spirit of the present invention. Can be implemented.

  For example, in the above embodiment, the pivot shaft 60 and the pivot bearing 62 are constituted by the engine valve system parts of the present invention. However, the engine valve system parts of the present invention are not limited to these parts. For example, it can be embodied as various parts such as the camshaft 40, the cam 41, the rocker arm 5, the valve body 70 of the valve 7 and the stem cap 71 of the above embodiment. In this case, the shape, arrangement, and the like of each component are not limited to the above embodiment. Further, the composition and surface roughness of the amorphous hard carbon film are not limited to the above embodiment.

  Based on the above embodiments, amorphous hard carbon films were formed on substrates having different surface roughnesses. Then, a sliding test using a ring-on-block friction tester was performed to measure the friction coefficient of the amorphous hard carbon film. Further, the engine valve system parts of the present invention were embodied in a pivot shaft and a pivot bearing of a pivot, and an operation test was performed using an actual engine, and their friction coefficients were measured. Hereinafter, each test method and the measurement result of the friction coefficient will be described.

(1) Sliding test by ring-on-block type friction tester (a) Formation of Si-containing amorphous hard carbon film (hereinafter referred to as “DLC-Si film” as appropriate) DC plasma CVD shown in FIG. A DLC-Si film was formed on the surface of the substrate using a (PCVD) film forming apparatus. As shown in FIG. 3, the direct-current plasma CVD film forming apparatus 1 includes a stainless steel container 10, a base 11, a gas introduction pipe 12, and a gas outlet pipe 13. The gas introduction pipe 12 is connected to various gas cylinders (not shown) through valves (not shown). The gas outlet pipe 13 is connected to a rotary pump (not shown) and a diffusion pump (not shown) via a valve (not shown).

  First, the base material 15 was disposed on the base 11 installed in the container 10. The base material 15 was a block test piece (6.3 mm × 15.7 mm × 10.1 mm) made of martensitic stainless steel SUS440C (quenched and tempered product HRC58). Next, the container 10 was sealed, and the gas in the container 10 was exhausted by a rotary pump and a diffusion pump connected to the gas outlet pipe 13. Hydrogen gas was introduced at 15 sccm from the gas introduction pipe 12 into the container 10, and the gas pressure was set to about 133 Pa. Thereafter, a DC voltage of 200 V was applied between the stainless steel anode plate 14 provided on the inside of the container 10 and the base 11 to start discharging. And it heated up by ion bombardment until the temperature of the base material 15 was set to 500 degreeC. Next, 500 sccm of nitrogen gas and 40 sccm of hydrogen gas were introduced from the gas introduction tube 12, and plasma nitriding was performed for 1 hour at a pressure of about 800 Pa, a voltage of 400 V (current of 1.5 A), and a temperature of 500 ° C. When the cross-sectional structure of the base material 15 was observed, the nitriding depth was 30 μm.

  After the plasma nitriding treatment, hydrogen gas and argon gas are introduced from the gas introduction tube 12 by 30 sccm at a time, and sputtering is performed at a pressure of about 533 Pa, a voltage of 300 V (current of 1.6 A), and a temperature of 500 ° C. Unevenness was formed (irregularity forming treatment). The width of the convex portion was 60 nm and the height was 30 nm. Next, 1 sccm of TMS gas and 100 sccm of methane gas are introduced from the gas introduction pipe 12 as reaction gases, and 30 sccm of hydrogen gas and argon gas are further introduced, pressure of about 533 Pa, voltage of 320 V (current of 1.8 A), temperature The film was formed at 500 ° C. The film formation time was controlled to set the film thickness to 2.7 μm.

  In this way, three types of DLC-Si films having different surface roughness (Rzjis 0.15 μm, 0.45 μm, 0.80 μm) were formed on the block test piece. The formed DLC-Si films were numbered DLC-Si-1 to 3 respectively. The composition of these DLC-Si films was Si: 6 at%, C: 64 at%, and H: 30 at%. In addition, the adhesion between the DLC-Si film and the base material was 50 N in all cases. The hardness of each DLC-Si film was 17 GPa. In the following sliding test, the DLC-Si film formed on each block test piece serves as a sliding surface with the counterpart material.

  The Si content in the DLC-Si film was quantified by electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Rutherford backscattering method (RBS). Moreover, H content was quantified by the elastic recoil particle detection method (ERDA). ERDA is a method of measuring the hydrogen concentration in the film by irradiating the surface of the film with a 2 MeV helium ion beam, detecting hydrogen ejected from the film with a semiconductor detector.

(B) Sliding test and measurement of friction coefficient The sliding test using a ring-on-block type friction tester (LFW-1, manufactured by FALEX) was performed on each of the prepared block test pieces. FIG. 4 shows a schematic diagram of a ring-on-block friction tester. As shown in FIG. 4, the ring-on-block friction tester 2 includes a block test piece 20 and a ring test piece 21 that is a counterpart material. The block test piece 20 and the ring test piece 21 are installed in a state in which the coating film 200 formed on the block test piece 20 and the ring test piece 21 are in contact with each other. The ring test piece 21 is rotatably installed in the oil bath 22. In this sliding test, as a ring test piece 21, an S-10 ring test piece (material: SAE 4620 steel carburized material, shape: φ35 mm, width 8.8 mm, surface roughness: a standard test piece of this friction tester: Rzjis 0.37 μm, 1.95 μm, two types, manufactured by FALEX) were used. For the oil bath 22, engine oil (castle motor oil SL5W-30) heated and held at 80 ° C. was used.

  First, the ring test piece 21 was rotated in an unloaded state. Next, a load of 300 N (Hertz surface pressure: 310 MPa) was applied from the top of the block test piece 20, and the block test piece 20 and the ring test piece 21 were slid at a sliding speed of 0.3 m / s for 30 minutes, and then the friction. The coefficient was measured. Here, the Hertz surface pressure is the maximum value of the pressure on the actual contact surface considering the elastic deformation of the contact portion between the block test piece 20 and the ring test piece 21.

  On the other hand, for comparison, a DLC film not containing Si (hereinafter, simply referred to as “DLC film”) is formed on the same block test piece as the DLC-Si film by a magnetron sputtering (SP) method. Filmed. The formed DLC films were three types having different surface roughnesses, and each was numbered as DLC-1 to DLC-3. Similarly, a CrN film was formed on the block test piece by a holo cathode (HCD) method. The formed CrN films were of three types with different surface roughness, and each was numbered CrN-1 to 3. A sliding test using the same ring-on-block friction tester was performed on each of the block test pieces formed with the DLC film, the CrN film, and the block test piece itself without the coating.

  In FIG. 5, the measurement result of the friction coefficient of each block test piece is shown. The horizontal axis in FIG. 5 represents the surface roughness of the sliding surface before sliding of each block test piece. FIG. 5 shows the measurement results for both the case where the surface roughness of the ring specimen is Rzjis 0.37 μm and the case where Rzjis is 1.95 μm. Specifically, in FIG. 5, among the plots of the same surface roughness in each block test piece, the higher friction coefficient is the result of Rzjis 1.95 μm, and the lower is the result of Rzjis 0.37 μm. Table 1 summarizes the thickness, surface roughness, and adhesion of the coating formed on each block test piece. In addition, the block test piece itself (SUS440C) in which the film is not formed is shown as SUS440C-1 and 2 by the difference in surface roughness.

図５に示すように、ＤＬＣ膜、ＣｒＮ膜、ＳＵＳ４４０Ｃでは、表面粗さを小さくしても、摩擦係数はあまり低下しなかった。これに対して、ＤＬＣ−Ｓｉ膜では、表面粗さをＲzjis０．５μｍ以下と小さくすることにより、摩擦係数は大幅に低下した。これは、潤滑油による潤滑割合の増加に加え、境界摩擦の低減効果が発揮されたためと考えられる。特に、相手材の表面粗さがＲzjis０．３７μｍの場合、ＤＬＣ−Ｓｉ膜の表面粗さをＲzjis０．４５μｍから０．１５μｍにすることで、摩擦係数は約５０％低下した。これより、Ｓｉ含有量１ａｔ％以上２０ａｔ％以下、表面粗さＲzjis０．５μｍ以下のＤＬＣ−Ｓｉ膜を摺動面とすることにより、摩擦係数を低減できることがわかる。特に、表面粗さをＲzjis０．３μｍ以下とすると、摩擦係数の低減効果が大きいことがわかる。

As shown in FIG. 5, in the DLC film, CrN film, and SUS440C, the friction coefficient did not decrease so much even if the surface roughness was reduced. On the other hand, in the DLC-Si film, the coefficient of friction was significantly reduced by reducing the surface roughness to Rzjis 0.5 μm or less. This is thought to be due to the effect of reducing the boundary friction in addition to the increase in the lubrication ratio by the lubricating oil. In particular, when the surface roughness of the counterpart material was Rzjis 0.37 μm, the friction coefficient was reduced by about 50% by changing the surface roughness of the DLC-Si film from Rzjis 0.45 μm to 0.15 μm. From this, it can be seen that the friction coefficient can be reduced by using a DLC-Si film having a Si content of 1 at% to 20 at% and a surface roughness Rzjis of 0.5 μm or less as a sliding surface. In particular, when the surface roughness is Rzjis 0.3 μm or less, it can be seen that the effect of reducing the friction coefficient is large.

(2) Engine operation test The engine valve system component of the present invention was embodied in a pivot shaft and a pivot bearing of a pivot, and an engine operation test was conducted. That is, an engine operation test was performed using an actual engine (diesel engine, displacement of 1.4 L) having the valve operating mechanism shown in FIGS. The test conditions are an engine oil temperature of 80 ° C. and a valve spring load of 39 kg (Hertz surface pressure of 500 MPa). The camshaft rotation speed was changed from 500 to 2000 rpm, and the coefficient of friction between the pivot shaft and the pivot bearing was measured at a predetermined rotation speed. And the average value of the measured friction coefficient was employ | adopted as an average friction coefficient.

  In addition, the state of the sliding surface of the pivot shaft and the pivot bearing was changed, and an engine operation test similar to the above was performed. Table 2 summarizes the presence / absence of a DLC-Si film on each sliding surface of the pivot shaft and the pivot bearing subjected to the engine operation test and the value of the surface roughness. FIG. 6 shows the measurement results of the friction coefficient.

図６に示すように、ピボット軸およびピボット軸受のいずれの摺動面にもＤＬＣ−Ｓｉ膜が形成されていない場合（＃３〜＃５）には、各摺動面の表面粗さが小さくなるとともに、摩擦係数は低下した。例えば、＃３の摩擦係数を基準とすると、＃３より両摺動面の表面粗さが小さい＃５の摩擦係数は、２０％程度低下した。一方、ピボット軸側の摺動面の表面粗さが大きくても、ピボット軸受側の摺動面がＲzjis０．２μｍのＤＬＣ−Ｓｉ膜である場合（＃２）には、＃５と同程度の低摩擦係数となった。さらに、両摺動面をＲzjis０．２μｍのＤＬＣ−Ｓｉ膜とした場合（＃１）には、＃３と比較して、摩擦係数は５０％程度低下した。これより、Ｓｉ含有量１ａｔ％以上２０ａｔ％以下、表面粗さＲzjis０．５μｍ以下のＤＬＣ−Ｓｉ膜による摩擦低減効果が確認された。また、同ＤＬＣ−Ｓｉ膜どうしを摺動させた場合には、摩擦係数の低減効果が大きいことが確認された。

As shown in FIG. 6, when the DLC-Si film is not formed on any sliding surface of the pivot shaft and the pivot bearing (# 3 to # 5), the surface roughness of each sliding surface is small. As a result, the friction coefficient decreased. For example, when the friction coefficient of # 3 is used as a reference, the friction coefficient of # 5, in which the surface roughness of both sliding surfaces is smaller than # 3, is reduced by about 20%. On the other hand, even if the surface roughness of the sliding surface on the pivot shaft side is large, when the sliding surface on the pivot bearing side is a DLC-Si film of Rzjis 0.2 μm (# 2), it is about the same as # 5. The coefficient of friction was low. Further, when both sliding surfaces were Rzjis 0.2 μm DLC-Si films (# 1), the friction coefficient was reduced by about 50% compared to # 3. From this, the friction reducing effect by the DLC-Si film having a Si content of 1 at% to 20 at% and a surface roughness Rzjis of 0.5 μm or less was confirmed. It was also confirmed that when the DLC-Si films were slid, the effect of reducing the friction coefficient was great.

1 is a partial cross-sectional view of a valve mechanism in which an engine valve system component according to an embodiment of the present invention is disposed. It is an enlarged view of the dotted line frame II in FIG. It is the schematic of a direct-current plasma CVD film-forming apparatus. It is a schematic diagram of a ring on block type friction tester. It is a graph which shows the relationship between the surface roughness of various coating films, and a friction coefficient. It is a graph which shows the measurement result of the friction coefficient in an engine operation test.

Explanation of symbols

1: DC plasma CVD film forming apparatus 10: Container 11: Base 12: Gas introduction pipe 13: Gas outlet pipe 14: Stainless steel anode plate 15: Base material 2: Ring-on-block type friction tester 20: Block test Piece 21: Ring test piece 22: Oil bath 200: Film 3: Valve mechanism 40: Cam shaft 41: Cam 410: Protruding portion 5: Rocker arm 50: Roller 51: Support shaft 52: Needle 53: Valve pressing portion 54: Pivot Shaft coupling portion 540: coupling hole 55: arm body 6: pivot 60: pivot shaft 61: nut 62: pivot bearing 64: hemispherical surface 65: inverted hemispherical surface 66: cylinder head 600, 620: DLC-Si film 7: valve 70 : Valve body 71: Stem cap 72: Retainer 73: Cotter 74: Valve spring 75: Oil seal Le

Claims (6)

Engine valve system parts used under wet conditions using lubricating oil,
A valve system component body, and an amorphous hard carbon film formed on at least a part of the sliding surface of the valve system component body with a mating member,
An engine valve operating system component, wherein the amorphous hard carbon film has a Si content of 1 at% or more and 20 at% or less, and a surface roughness of Rzjis 0.5 μm or less. The amorphous hard carbon film is formed on a sliding surface with a counterpart material,
The engine valve system component according to claim 1, wherein the sliding rate of the sliding surface is 1% or more.   The engine valve operating system component according to claim 1, wherein the amorphous hard carbon film has a thickness of 1 μm or more. The valve system component body is made of steel,
The engine valve system component according to claim 1, wherein an adhesion force between the valve system component body and the amorphous hard carbon film is 20 N or more.   The surface of the valve-operated component body on which the amorphous hard carbon film is formed is an uneven surface having protrusions having an average height of 10 nm to 100 nm and an average width of 300 nm or less by an unevenness forming process by an ion bombardment method. The valve operating part for an engine according to claim 1.   The engine valve system component according to claim 1, wherein the amorphous hard carbon film is formed by a direct-current plasma CVD method.

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