JPH1018023A - Production of sliding member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a sliding member capable of securely obtaining a sliding member grinding the sliding face of the mating member into a mirror face and causing no contamination of the environment owing to the good working environment. SOLUTION: The surface roughness of the contact face of a sliding member to be slid and contacted with the mating member 15 regulated to <=0.3mRz, and the thickness of oxidized coating in the contact face is regulated to <=8nm. By an arc type ion plating method, from the contact face finished so as to regulate the surface roughness to <=0.3mRz, the oxidized coating is removed by ion bombarding to form a coating layer having the fine ruggedness of the material having >=1000Hv hardness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sliding member such as a shim which comes into contact with a mating member such as a cam.

[0002]

2. Description of the Related Art An intake valve or an exhaust valve of an internal combustion engine is driven by a shim that is displaced according to the shape of a cam provided on a cam shaft driven by the internal combustion engine. Therefore, since the contact resistance between the cam and the shim causes a loss in the internal combustion engine, the surface roughness of the contact surface between the cam and the shim is reduced by the thickness of the oil film formed by the lubricating oil supplied to the contact portion between the cam and the shim. It is necessary to reduce to the same extent.

However, while the thickness of the oil film is about 0.09 μm, the surface roughness of the contact surface of the cam is at most 1.6 to 3.2 μm Rz according to the well-known processing technology, and the contact resistance is sufficiently high. Could not be reduced. Therefore, the present applicant provides a coating layer made of, for example, titanium nitride so as to have an appropriate surface roughness on the contact surface of the previously mirrored shim, and mirrors the contact surface of the cam with the shim during the initial rubbing operation. A cam contact portion structure has already been proposed (see Japanese Patent Application Laid-Open No. 5-163909). In order to make the initial rubbing more efficient, the present applicant has set the surface roughness of the contact surface of the sliding member that slides on the cam to 0.3 μmR.
z and a sliding member provided with a coating layer having fine irregularities of a material having an Hv hardness of 1,000 or more on the contact surface thereof and a method of manufacturing the sliding member have been proposed (see Japanese Patent Application Laid-Open No. 7-118832).

[0004]

The rubbing action of the cam is weakened if the fine irregularities on the contact surface of the shim are too small, and the contact surface of the cam is roughened if the fine irregularities on the contact surface of the shim are too large. Increase sliding resistance. Therefore, formation of a highly reliable coating layer having fine irregularities is a problem.
Further, in manufacturing the sliding member, there is a demand for a method that has a good working environment and does not deteriorate the environment.

[0005] The present invention solves these problems.

[0006]

A method of manufacturing a sliding member according to the present invention comprises a pretreatment step of finishing the surface roughness of a contact surface of a sliding member which slides and contacts a mating member to 0.3 μmRz or less. Forming a coating layer having fine irregularities of a material having an Hv hardness of 1,000 or more on its contact surface finished to a surface roughness of 0.3 μm Rz or less by an arc ion plating method. The method of manufacturing a member, wherein the pretreatment step is a step of setting a surface roughness of a contact surface of the sliding member to 0.3 μmRz or less and an oxide film thickness of the contact surface to 8 nm or less. The step is a step including an oxide film removing process for removing the oxide film by ion bombardment by the arc ion plating method.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for manufacturing a sliding member according to the present invention comprises a pretreatment step and a coating step. The pretreatment step is a step for ensuring that a coating layer having predetermined characteristics is obtained by a later coating step. In the pretreatment step, at least the surface serving as the sliding surface of the substrate forming the sliding member has a surface roughness of 0.3 μmRz or less and an oxide film forming the surface has a thickness of 8 nm or less.

A rough surface having a surface roughness exceeding 0.3 μm Rz is not preferable because the sliding resistance (coefficient of friction) increases. The oxide film should be removed to secure the adhesion strength of the coating layer. However, an oxide film is inevitably formed in the step of performing mirror finishing with a small surface roughness on the substrate or performing degreasing. The inventor has found that, as shown in FIG. 1, when the thickness of the oxide film is 8 nm or less, the adhesion strength of a coating layer formed in a subsequent coating step is not greatly reduced. Even if the oxide film is thicker than 8 nm, it can be removed by ion bombardment performed in a later coating step. However, in this case, a large amount of droplets forming minute unevenness are generated, and the desired characteristics of the sliding member cannot be obtained. Therefore, in the present invention, it is limited to 8 nm or less. This will be described in detail later.

The pretreatment step is not limited to a specific pretreatment method as long as the surface roughness of the surface of the substrate is 0.3 μm Rz or less and the thickness of the oxide film forming the surface is 8 nm or less. . The more preferable surface roughness of the substrate surface is 0.1 μmRz or less. However, it is very difficult to make the surface roughness of the substrate less than 0.3 μm Rz and the thickness of the oxide film forming the surface less than 8 nm.

As a method of reducing the surface roughness of the substrate surface to 0.3 μmRz or less, buffing can be considered. However, buff polishing has low productivity. The recommended method is mechanical polishing with a grindstone. As shown in FIG. 2, the mechanical polishing using a grindstone is affected by the surface roughness and oxide film thickness achieved by the grindstone pressure. When the grindstone pressure is reduced, the thickness of the oxide film can be reduced, but the surface roughness is rough. Become. Conversely, increasing the grindstone pressure can lower the surface roughness, but increases the oxide film thickness.

Sufficient care must be taken in the degreasing of the pretreatment step. By heating the substrate during the degreasing step and during the drying of the degreasing agent, an oxide film having a thickness exceeding 8 nm can be easily formed. Degreasing using a fluorine-based solvent enables relatively easy degreasing without increasing the thickness of the oxide film. However, the use of cleaning agents containing ozone depleting substances is not preferred.
The recommended degreasing method is to use a hydrocarbon-based cleaning agent and treat at a relatively low temperature. Decompression for drying the detergent,
It is also preferable to achieve drying of the cleaning agent by reducing the pressure with a high degree of vacuum. In the usual vacuum drying, 100 to 150
Although conditions of about 5 ° C. and 5 ° C. are used, it is difficult to suppress the formation of an oxide film under such conditions, and it is preferable to set the temperature to a lower temperature, a lower pressure, for example, 50 ° C. or less, 0.1 torr or less.

Although a method of chemically etching the oxide film is also conceivable, it is not preferable because the number of pretreatment steps needs to be increased and adverse effects due to the use of corrosive substances need to be considered. In the coating step of the method for manufacturing a sliding member according to the present invention, the contact surface of the substrate finished to have a surface roughness of 0.3 μmRz or less by an arc ion plating method is H.
This is a step of forming a coating layer having fine irregularities of a material having a v hardness of 1,000 or more. In the arc ion plating method, an arc is blown to a target in a vacuum chamber, a hot spot is formed on the surface of the target where the arc flies, and the spot is instantaneously heated to discharge the target material in an ionized atomic state or droplet and statically. The substrate is hit with electric power to remove an oxide film on the substrate surface and form a coating layer containing particulate droplets on the substrate surface. These droplets form fine irregularities.

More specifically, when titanium is used as a coating material, nitrogen gas at a pressure of 20 mTorr is used as an atmosphere gas, and the bias voltage is set to -50 V for 50 minutes, fine irregularities shown in FIG. The coating layer made of titanium nitride has a deviation. The unevenness of the coating layer will be described with reference to a schematic diagram shown in FIG. 4A is a sectional view, and FIG. 4B is a sectional view taken along line XX of FIG. 4A. The droplets 52 are randomly generated on the substrate 50, and the titanium nitride film 51 is formed on the substrate 50 including the droplets 52. It is difficult to control the size, height or position of the droplets 52, but the density can be controlled to some extent by the current.

When the number of droplets per unit area is small, the contact surface of the counterpart member cannot be sufficiently mirror-finished during the rubbing operation. Causes wear. Therefore, in order to complete the mirroring of the contact surface of the mating member and the mirroring of the sliding member itself in a short rubbing operation, the number of droplets per unit area needs to be within an appropriate range. is there.

Further, since the size or height of the droplet cannot be controlled as described above, the contact surface of the mating member is excessively worn even when a sliding member having a small number of large droplets is used. There is a possibility that. Therefore, not the number of droplets per unit area, but the cross-sectional area of the droplet when the droplet is cut at a certain height with respect to the area of the substrate 50 (FIG. 4B)
(The total area of the diagonal lines and the concentric dotted lines) must be within an appropriate range. Since it is difficult to measure the area of only the droplet in practical use, the cross section of the droplet 52 (the hatched portion in FIG. 4B) and the cross section of the titanium nitride film 51 around it (FIG. 4B The cross-sectional area of the droplet including the concentric dotted line portion of ()) is used.

In the present invention, 0.5
The cross-sectional area of the droplet with respect to the area of the substrate 50 when cut at μm (hereinafter referred to as droplet ratio)
Defines the number of droplets per unit area. Five types of shims with different droplet ratios (adopted as sliding members) to determine the optimal droplet ratio (droplet ratio = 0.7, 3.0, 5.
2, 7.2, 8.0%), and tests for the time required for mirror finishing and the effect of reducing contact resistance were performed.

Five types with different droplet ratios and a droplet ratio of 0% (a surface roughness of 0.01 to 0.30 μm)
The following tests were carried out for a total of six types of mRz) shims. FIG. 5 is a graph showing the amount of wear on the contact surface of the cam (adopted as a mating member) when three types of shims having droplets are applied. The horizontal axis represents the droplet ratio, and the vertical axis represents the cam wear. Take.

That is, as the droplet ratio increases, the cam abrasion increases. However, if the cam abrasion increases, a predetermined valve displacement cannot be obtained, and the intake and exhaust loss increases. Has an upper limit. Therefore, in order to make the cam wear amount equal to or less than the predetermined upper limit, the droplet ratio needs to be adjusted to 5.2% or less. FIG. 6 is a graph showing the contact resistance reduction rate when six types of shims are applied, in which the horizontal axis represents the droplet ratio and the vertical axis represents the contact resistance reduction rate. As shown in this graph, when the droplet ratio is 0.7% or less, the contact resistance reduction rate increases with an increase in the droplet ratio. Saturates at 30%. Therefore, it is necessary to set the droplet ratio to 0.7% or more in order to obtain a mirror surface with a surface roughness of 0.2 μmRz or less.

That is, the droplet ratio is 0.7 to 5.2%.
It is better to FIG. 7 is a graph showing the time required for making the cam contact surface mirror-finished by the droplet in the rubbing at 1000 rpm. The vertical axis indicates contact resistance (N · m), and the horizontal axis indicates time. The broken line shows the change over time in the contact resistance of a shim with a droplet ratio of 0%, and the solid line shows the change over time with the contact resistance of a shim with a droplet ratio of 0.7%. As shown in this graph, the droplet ratio was 0.1.
According to the shim of 7%, the contact resistance is saturated at the minimum value (about 1.5 N · m) by the rubbing time of about 10 hours, and is improved by about 30% as compared with the shim contact resistance of 0% of the droplet ratio. You.

That is, if the shim has a droplet ratio of 0.7%, the contact resistance can be reduced in a short rubbing time. FIG. 8 is a graph showing the effect of the rubbing. The vertical axis represents the surface roughness of the cam contact surface, and the horizontal axis represents the shim surface roughness. That is, when shims having a droplet ratio of 0% (surface roughness 0.01 to 0.30 μmRz) are used as shown by white circles, the surface roughness of the cam contact surface is reduced from 2.8 μmRz to 0.8 by rubbing. Although it is mirror-finished to 8 μmRz, a rubbing time of 200 hours or more is required.

On the other hand, when a shim having a droplet ratio of 0.7% (surface roughness of about 1.5 μm Rz) is used as shown by a black circle, the surface roughness of the cam contact surface is 2. It is mirror-finished from 8 μmRz to 0.2 μmRz or less with a rubbing time of about 10 hours. At the same time, the surface roughness of the shim is mirror-finished from about 1.5 μm Rz to 0.01 to 0.30 μm Rz, which is the same level as the coating base roughness.

As described above, the droplet ratio has an optimum range for exhibiting characteristics as a sliding member. In addition, there is a required thickness in the thickness of the coating layer.
The film thickness is determined by the film forming conditions in the coating process. When the film forming conditions are determined, the amount of droplets generated during the process is determined. In order to control the amount of droplets in the above optimum range, it is necessary to control the amount of droplets generated in the ion bombardment process. In this case, if the oxide film is thick and ion bombardment must be performed for a long time, a large amount of droplets will be generated and it will not be possible to control the droplets to an optimum range. Therefore, in the present invention, a numerical value of 8 nm is defined from processing conditions for obtaining the characteristics of the sliding member.

Although the coating process of the manufacturing method of the sliding member of the present invention has been described by using a combination of a cam as a sliding member and a mating member as the sliding member, the sliding member other than the shim may be coated in the same manner as the shim. can do. In particular, a sliding member obtained by the manufacturing method of the present invention is optimal for a partner member whose sliding surface is complicated like a cam and whose sliding surface is difficult to be mirror-finished, such as a cam.

Although titanium nitride has been described as a coating material, TiCN, C
rN, Al ₂ O ₃ , diamond-like carbon and the like can be employed.

[0025]

According to the method for manufacturing a sliding member of the present invention, the surface roughness of the contact surface of the sliding member is reduced to 0.3 μm Rz by the pretreatment step.
And the oxide film thickness of the contact surface is 8 nm or less. Then, the oxide film is removed by ion bombardment by an arc ion plating method in the coating process, and the Hv hardness of 1, is directly applied to the surface of the substrate without the oxide film.
A coating layer having fine irregularities of 000 or more materials is formed. The fine irregularities are formed by fine droplets adhering to the surface of the base material by performing the arc ion plating method.

[0026]

FIG. 9 is a partial cross-sectional view of an internal combustion engine having a direct drive valve train having a shim manufactured according to the present invention. This direct drive type valve train has two camshafts 12 and 14 disposed above a cylinder head 10. One camshaft 12 is connected to a crankshaft (not shown) via a timing pulley and a timing belt (both not shown).
Is slid by The intake cam 16 fixed to the one cam shaft 12 drives an intake valve 21 against an intake valve spring 20 via an intake valve lifter 18.

The gear 2 fixed to the one camshaft 12
2 meshes with a gear 24 fixed to the other camshaft 14,
The other camshaft 14 is driven. An exhaust cam 25 fixed to the other camshaft 14 drives an exhaust valve 30 against an exhaust valve spring 28 via an exhaust valve lifter 26. Adjusting shims (hereinafter referred to as shims) are provided on the contact surface of the intake valve lifter 18 with the intake cam 16 and the contact surface of the exhaust valve lifter 26 with the exhaust cam 25, respectively.
34 and 36 are arranged. These shims 34 and 36 are sliding members made by the manufacturing method of the present invention.

FIG. 10 is a side sectional view of the shims 34 and 35. These shims 34 and 36 are composed of a substrate 50 and a coating layer 51 formed on the surface thereof. The base 50 of the shims 34 and 35 has a diameter of 28 mm and a thickness of 3.
It is a 0 mm disk and is made of chromium molybdenum steel. One surface of the substrate 50 is subjected to first roughing and second roughing by mechanical grinding using a grindstone, and finally, is mechanically ground as a final polishing at a grindstone pressure of 3.6 kg / cm ² , and has a surface roughness of 0.1 μmRz. Mirror surface. Next, the obtained substrate 5
0 was degreased with a hydrocarbon solvent. The solvent was dried at room temperature under a vacuum of 0.1 torr or less. Thus, a base 50 was obtained. The surface roughness of one surface serving as the sliding surface of the substrate was 0.1 μmRz, and the thickness of the oxide film formed on that surface was 4.0 nm.

Next, a coating layer 51 is formed on one surface of the substrate 50 by a well-known arc-type ion plating method.
Was formed. FIG. 11 shows a schematic sectional view of the ion plating apparatus used in this embodiment. In this device, a target made of titanium metal is fixed to an inner wall of a vacuum device, and this target is connected to a cathode side of an arc power supply. Then, arc electrodes are arranged above and below the target, and the arc electrodes are connected to the anode side of the arc power supply. A sample stage is placed at the center of the vacuum device facing the target, and a bias power supply is connected to this. In addition, this vacuum apparatus is provided with a nitrogen gas introduction hole and a nitrogen gas discharge hole.

Using this apparatus, the base 50 was fixed to the sample table, the inside of the vacuum apparatus was set to a high vacuum of 8 × 10 ⁻⁵ Torr, a bias power supply of −600 to −800 volts was connected to the sample table, and an arc power supply was connected. Was connected, and an arc was blown between the arc electrode and the target at a current of 100 A. This arc discharge causes the target titanium to fly out as fine lump called ions and droplets, and collide with the surface of the substrate 50. The oxide film on the surface of the substrate 50 was removed by the collision (bombardment) of titanium ions, and droplets adhered to the surface of the substrate 50 from which the oxide film had been removed. This state was continued for 10 minutes.

Thereafter, nitrogen gas was introduced from a nitrogen gas introduction hole, and a vacuum was applied in a vacuum atmosphere of 20 mTorr in a nitrogen atmosphere, a 50-volt bias was applied, and an arc discharge was performed at a current of 140 A. As a result, the titanium ions jumping out of the target react with nitrogen on the substrate 50 and collide with and adhere to the surface of the substrate 50. At this time, the droplets also adhere at the same time. This state was continued for 50 minutes.

By this treatment, a coating layer 51 was formed on one surface of the substrate 50. Thus, a shim as the sliding member of the present example was manufactured. The measurement results of the surface roughness of the shim coating layer 51 are shown in FIG. The droplet area ratio of the coating layer 51 (cross-sectional area of the droplet with respect to the area of the substrate 50 when cut at 0.5 μm on the surface of the substrate 50) was 3%.

Next, the cam 1 shown in FIG.
4 and a cam 16 were prepared. This cam was made of cast iron and had a cam surface having a surface roughness of 3.2 μmRz. Then, the cam and the shim manufactured in the example were assembled in a direct drive type valve train shown in FIG. 10 and rubbed for 1000 rpm2. As a result, the surface roughness of the shim is 0.1μ.
The surface roughness of the cam surface of the cam is 0.2 μm on the mRz mirror surface.
It became a mirror surface of Rz. The sliding friction coefficient between the shim and the cam in this state was 0.08.

[0034]

According to the manufacturing method of the present invention, it is possible to surely obtain a sliding member which mirrors the sliding surface of the mating member by rubbing. In addition, the method for manufacturing the sliding member has a good working environment and does not deteriorate the environment.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the thickness of a surface oxide film on a substrate and the adhesion strength between a substrate and a coating layer.

FIG. 2 is a diagram showing a relationship between a grinding wheel pressure by mechanical grinding, an obtained surface roughness, and a thickness of a formed oxide film.

FIG. 3 is a diagram showing measurement results of surface roughness after coating of a sliding member obtained in an example.

FIG. 4 is a schematic diagram for explaining a droplet.

FIG. 5 is a diagram showing a relationship between a droplet area ratio indicating a wear amount of a cam contact surface and a cam wear amount when three types of shims having droplets are applied.

FIG. 6 is a diagram showing a relationship between a droplet area ratio and a contact resistance reduction rate when four types of shims are applied.

FIG. 7 is a diagram showing a relationship between a contact time and a contact resistance reduction rate required to mirror a cam contact surface with a droplet.

FIG. 8 is a diagram showing a relationship between a shim surface roughness and a cam surface roughness showing an effect of rubbing.

FIG. 9 is a partial cross-sectional view of an internal combustion engine having a direct drive valve train.

FIG. 10 is a sectional view of a shim obtained by the manufacturing method according to the present embodiment.

FIG. 11 is a schematic sectional view of an ion plating apparatus used in this embodiment.

[Explanation of symbols]

50: Base 51: Titanium nitride 52: Titanium lump

Claims (4)

[Claims] 1. A pretreatment step of finishing the surface roughness of a contact surface of a sliding member which comes into sliding contact with a mating member to 0.3 μmRz or less, and a surface roughness of 0.3 μmRz by an arc ion plating method. A step of forming a coating layer having fine irregularities of a material having an Hv hardness of 1,000 or more on the contact surface, which is finished as follows. The surface roughness of the contact surface of the moving member is not more than 0.3 μmRz and the oxide film thickness of the contact surface is not more than 8 nm; and the coating is performed by ion bombardment by the arc ion plating method. A method for producing a sliding member, comprising: an oxide film removing process for removing a film; and a film forming process. 2. The method for manufacturing a sliding member according to claim 1, wherein said pre-treatment step is a step of mechanically polishing said contact surface of said sliding member, and then washing and drying with a non-halogenated hydrocarbon. 3. The method for manufacturing a sliding member according to claim 1, wherein said coating step comprises ion-bombarding titanium by said arc-type ion plating method and thereafter coating titanium nitride. 4. The method according to claim 1, wherein the mating member is a cam.