JP2819946B2 - Cam contact structure of valve train of internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a cam contact portion for transmitting a displacement of a cam to a counterpart member such as a valve tappet or a rocker arm by contacting and sliding with the cam in a valve mechanism of an internal combustion engine.

[0002]

2. Description of the Related Art In a valve operating mechanism of an internal combustion engine, for example, in a direct drive type valve operating mechanism, a cam is formed of a cold-chilled or Tig-remelted chilled material of an alloy cast iron.
Polished to about 6 to 3.2 μm Rz. On the other hand, the valve adjusting shim that forms the cam contact surface of the tappet, which is the mating side of the cam, is made of a carburized and quenched material of alloy steel and the like, and is polished to a surface roughness of 1.6 to 3.2 μm Rz. A salt film treatment is applied to deal with seizure at the beginning of operation. Most of the friction loss of the direct drive valve mechanism occurs between the cam and the valve adjusting shim, and it is necessary to reduce the shim surface roughness in order to suppress the friction loss. As a technique for reducing the friction loss of a sliding portion of a cam follower such as a valve tappet or a rocker arm, there is a technology for reducing the surface roughness of the sliding portion (for example, Japanese Patent Application Laid-Open No. 61-124581).

In order to reduce friction loss, it is necessary to reduce the surface roughness of the cam and the shim in contact with the cam to the same extent as the thickness of the oil film between the cam and the shim. That is, by making the surface roughness close to the thickness of the oil film, the ratio of the fluid lubrication increases, and the friction can be reduced. However, the thickness of the oil film between the cam and the shim was calculated to be 0.1μ.
m, while the surface roughness of the processed surface of the cam, apart from the shim, is 1.6 to 3.2 μm
It is at most practical technology to make it about
In this case, there is a disadvantage that the friction loss is large because the thickness is coarse with respect to the thickness of the oil film.

In order to solve this drawback, the applicant of the present invention disclosed a thin film having an Hv hardness of 1500 to 7000 on the surface of a base material of a shim which is a mating member in contact with a cam in Japanese Patent Application No. 3-328794. It is proposed to coat. When the internal combustion engine is operated for the first time after the valve train is assembled, the coating made of a hard material rapidly wears the cam and makes its surface mirror-like, while the coating itself contacts the cam and its progresses with the cam. It is relatively slow but worn. When the cam surface is just mirror-finished, the thin coating is worn out, and the base material surface is exposed.After that, keep the low-friction contact between the mirror-finished cam surface and the base material surface. And

[0005]

In the above-mentioned prior application, when a hard thin film having an Hv hardness of 1500 to 7000 becomes a mirror surface of the cam, the thin film disappears, and thereafter, the thin film between the cam and the iron material of the base material of the shim. Be in touch. In this case, there is a problem that the amount of wear of the shim is large. That is, when the shim wears, the clearance between the base circle portion of the cam and the shim increases, which leads to the generation of a tapping sound when the cam and the shim come into contact. Because of the exhaustion, the base material of the shim is exposed, and the abrasion resistance of the shim may not be sufficiently secured.

An object of the present invention is to suppress shim wear.

[0007]

According to the present invention, a mating member in contact with a cam in a valve train of an internal combustion engine is:
The base material has a surface roughness of at least 0.1 μmRz, and the surface of the base material that comes into contact with the cam has a Hv hardness of 1500, which is cut off after the cam is mirror-finished.
And a first thin film having a thickness Hv which is larger than the first thin film and is larger than the hardness of the counterpart member under the first thin film.
A cam contact portion structure for a valve train of an internal combustion engine is provided, which is coated with a multilayer thin film comprising a second thin film having a hardness of less than 1500.

[0008]

At the beginning of assembly, the rough surface of the cam is mirror-finished by contact with the first thin film having an Hv hardness of 1500 to 7000, and when the mirror-finish is completed, the first surface is completed.
Is completely scraped off to expose the second thin film, and thereafter, the cam surface which has been mirrored comes into contact with the second thin film.

[0009]

1 shows a direct drive type valve train in which the present invention is implemented. 10 is a cam shaft, 12 is a cam, 14
Is a cylinder head, 16 is a valve stem, 18 is a valve spring, 20 is a spring seat, and the spring seat 20 is fixed to the valve stem 16 by a cotter 22. The valve lifter 24 is slidably provided in a bore formed in the cylinder head 14. An adjusting shim (hereinafter, shim) 26 is fitted into a circular recess formed on the upper surface of the valve lifter 24. Shim 26 is cam 1
2 are provided so as to be opposed to each other. The shim 26 has a multi-layer coating on its surface in accordance with the present invention.

FIG. 2 shows the structure of the shim 26 according to the present invention. The base metal 28 is a steel material having an Hv hardness of 350 to 1000, the surface of which is finished to a surface roughness of 0.1 μmRz or less, and the upper surface of which has an Hv hardness of not more than 0.1 μmRz. 1500 to 7000
And a second thin film 32 having a Hv hardness of less than 1500 and greater than the hardness of the counterpart member in the lower layer of the first thin film 30.

The surface roughness of the shim base material 28 is 0.1 μmR.
z or less because the oil film thickness in the normal rotation range is 0.1μ
m. Further, the base material 28 having an Hv hardness of 350 or more is required to have a high pitting resistance of 70 kg / mm ² because the contact stress at this portion is as high as 70 kg / mm ² . Two
The durability is said to be 0.3 times, and a suitable lower limit is about 350 Hv hardness. The hardness is preferably about Hv 700 to 1000 rather than too hard in consideration of the surface sagging when the surface is finely processed, the scratch due to the drag of the hard film due to abrasion, and the scratch due to the cementite in the cam. On the other hand, if the hardness is too high, the toughness value is deteriorated.

Although the cam 12 is rough at the beginning of assembly, when the rotating cam 12 comes into contact with the shim 26, the first thin film 30 having an Hv hardness of 1500 to 7000 on the surface of the shim is formed.
Wears the rough surface of the cam 12 and mirrors the surface of the cam 12. The thickness of the first thin film 30 is
When the surface of the base material 28 has a surface roughness of about 0.1 μmRz, the first thin film 30 has a thickness (for example, 0.2 μm) that is just worn out. The thin film 32 is exposed on the surface. This second thin film 32
Has a hardness intermediate between the base material 28 and the first thin film 30 and is harder than the cam 12 so that the second thin film 32 is hardly worn, and as a result, the progress of wear of the shim as a whole is slowed down. on the other hand,
In relation to the cam 12, since the second thin film 32 has an intermediate hardness and the cam itself is mirror-finished to reduce friction, the progress of wear of the cam 12 is also suppressed.

Hv hardness of the upper surface side is 1500 to 7000
The material constituting the first thin film 30 is TiC, Ti
_{N, TiCN, TiAlN, Al 2} O 3, CrN, Cr
₂ N, there is CrC etc., Ni is a second thin film 32 of greater Hv hardness than the hardness of the lower surface of the base material is less than 1500
-P, Cr, chromium compound (CrN, Cr ₂ N), and the like. The second thin film 32 does not have to be thin, and may be formed by a method such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), or by plating depending on the material. . After the formation of the second thin film 32 by PVD, the first thin film 30 is formed on the second thin film 32 by a technique such as physical vapor deposition (PVD) or chemical vapor deposition (CVD).

As an embodiment of the present invention, a second thin film 32 made of CrN and having a thickness of 5 μm is applied by PVD to the surface of a base material 28 made of SKD11 material, and then TiC
A first thin film 30 having a thickness of 0.2 μm was applied by evaporation to obtain a shim 26. The shim 26 thus obtained was mounted as shown in FIG. 1, and a wear test was performed.
The test conditions were a 2.0 liter engine, 5W30 engine oil, and 80 ° C.

As a first comparative example, the prior application (Japanese Patent Application No. 3-328)
No. 794), a thin film of TiC having a thickness of 0.2 μm was applied to the surface of a base material composed of SKD11 by vapor deposition to form a shim, and a wear test was performed. As a second comparative example, a shim was formed by plating a thin film of TiC having a thickness of 3 μm on the surface of a base material made of SKD11 material to form a shim, and a wear test was performed.

FIG. 3A shows the relationship between the operating time and the amount of wear at the center of the shim in the embodiment of the present invention. When the cam rotates, the hard first thin film 30 on the shim scrapes off the rough surface of the cam 12 and mirrors to a surface of about 0.1 μm Rz. At this point in time, the first thin film 30 as thin as 0.2 μm is shaved off, and the second thin film 32 thereunder is exposed. Since this layer is harder than the material of the cam 12, the progress of wear of the shim is suppressed. You. On the other hand, as for the wear of the cam 12, as shown in FIG. 4b, the first thin film 30 is worn rapidly for a while by the hard first thin film 30 on the shim surface. Exhausted, a second thin film 32 of intermediate hardness comes out on the surface and at this point the cam 12
The surface of the cam 12 is mirror-finished and the friction is reduced, so that the wear of the cam 12 does not progress much further.

FIG. 3c shows a thickness of 0.2 μm made of TiC.
5 shows the wear results of the shim of the first comparative example having only the thin film of Example 1. The rotation of the cam causes the hard first thin film 30 on the shim to scrape off the rough surface of the cam 12 and mirror-finish to a surface of about 0.1 μm Rz.
Of the first thin film 30 is scraped off, and the base material is exposed. Since the base material is soft, the shim is scraped off by the cam 12, and the wear of the shim with respect to time progresses significantly.

FIG. 4 shows the wear of the cam by the shim of the second comparative example having a thin film made of TiC and having a thickness of 3 μm. In this case, since the thin film is thick, it will not be completely removed, but the cam 12 will wear significantly due to its hard surface.

[0019]

According to the present invention, the mating member which comes into contact with the cam in the valve train of the internal combustion engine has a base material of at least 0.1 μmR.
The surface of the base material having a surface roughness finer than z and having a Hv hardness of from 1500 to 7000
After the assembly, the first thin film having a thickness of about m and a second thin film having a Hv hardness less than 1500 and a thickness lower than 1500 and being thicker than the first thin film, which is larger than the hardness of the counterpart member in the lower layer, are coated. The surface of the cam is mirror-finished in a short operation, and the thickness of the coating h is completely removed by the mirror-finish of the cam surface. After that, the second thin film having an intermediate hardness is exposed. Since the thin film contacts the cam, the wear of both the shim and the cam can be prevented from progressing, and the cam does not require a high polishing finish at the time of manufacture, so that the manufacturing cost can be reduced and maintained. .

[Brief description of the drawings]

FIG. 1 is a view showing a valve mechanism for a directly driven internal combustion engine.

FIG. 2 is a side view of an adjusting shim according to the embodiment of the present invention.

FIG. 3 is a graph showing the relationship between operating time and progress of shim wear.

FIG. 4 is a graph showing the relationship between operating time and progress of cam wear.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Cam shaft 12 ... Cam 14 ... Cylinder head 16 ... Valve stem 18 ... Valve spring 24 ... Valve lifter 26 ... Shim 28 ... Base material 30 ... First thin film 32 ... Second thin film

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01L 1/14 F01L 1/16 F01L 1/20

Claims (1)

(57) [Claims] A mating member in contact with a cam in a valve train of an internal combustion engine has a base material of at least 0.1 μmR.
z having a surface roughness finer than z and a thickness of the base material that comes into contact with a cam,
Coating a multilayer thin film comprising a first thin film having an Hv hardness of 1500 to 7000 and a second thin film having a thickness greater than that of the first thin film and having an Hv hardness of less than 1500 and lower than the hardness of the counterpart member thereunder. A cam contact portion structure of a valve train of an internal combustion engine.