JP2001214711A - Lightweight cam shaft for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lightweight cam shaft for an internal combustion engine capable of suppressing wear of a cam lobe in sliding and also suppressing attacking to a counterpart when the cam lobe made of aluminum alloy is used. SOLUTION: This light weight cam shaft for the internal combustion engine is formed with the cam lobe made of an aluminum alloy containing 16.0 wt.% or more of Si where an average particle size of Si in a structure of the alloy is 10 μm or less. Roughness of a sliding surface of the cam lobe is Ra 0.1 μm or less, and 0.5 wt.% of SiC hard particle is contained in the cam lobe made of the aluminum alloy. A lifter shim or a valve lifter covered with hard thin film of the roughness of surface of Ra 0.05 μm or less is assembled with the cam lobe made of the aluminum alloy to make the lightweight cam shaft for the internal combustion engine, and the hard thin film covering the lifter shim or the valve lifter is a hard coat selected from TiN, CrN, Cr2N, DLC (diamond like carbon).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight camshaft used for an internal combustion engine of an automobile or the like. More specifically, the present invention relates to a lightweight camshaft for an internal combustion engine, which is capable of suppressing wear of a cam lobe itself made of an aluminum alloy and suppressing aggression of a partner.

[0002]

2. Description of the Related Art As a conventional lightweight camshaft using an aluminum alloy, for example, Japanese Unexamined Patent Publication No. 9-246819 discloses a method of manufacturing an assembled camshaft mainly by fastening an aluminum alloy cam to the shaft. Have been. However, in this prior art, regarding the components of the aluminum alloy cam, in the examples, it is described that alumina or SiC (silicon carbide) particles are dispersed in AC4C to improve wear resistance.

[0003]

However, in the above-mentioned conventional method, the hardness of alumina or silicon carbide added to the base material of AC4C, which is an aluminum alloy, is Hv2200 to 2600 and Hv250, respectively.
It is very hard, ie, 0, and the abrasion resistance of the aluminum alloy itself is improved, but the aggression to the opponent is increased.
Usually, a rocker arm made of carburized steel, an outer shim, or an inner shim type valve lifter is used as a mating material of the cam material, and their hardness is Hv100.
Since it is 0 or less, there is a problem that the mating material is worn out in combination with alumina or an aluminum alloy containing silicon carbide used as a cam lobe.

Therefore, when an aluminum alloy cam lobe is used, the wear of the cam lobe itself during sliding is suppressed,
In addition, it has been an issue to provide a lightweight camshaft for an internal combustion engine that can suppress opponent aggression.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems.
A lightweight camshaft for an internal combustion engine in which a cam lobe made of an aluminum alloy containing 6.0 Wt% or more and having an average grain size of Si of 10 μm or less in an alloy structure is formed. The roughness is Ra0.
A lightweight camshaft for an internal combustion engine having a thickness of 1 μm or less, a lightweight camshaft for an internal combustion engine containing 0.5 to 3 Wt% of SiC hard particles in a cam lobe made of an aluminum alloy, and a surface roughness of Ra0. A lightweight camshaft for an internal combustion engine combining a lifter shim or valve lifter provided with a hard thin film having a thickness of not more than 05 μm and a cam lobe made of an aluminum alloy. _This problem has been solved by using a lightweight camshaft for an internal combustion engine, which is a hard coating selected from 2N and DLC (diamond-like carbon).

Hereinafter, the function and effect of the present invention will be described. According to the invention of claim 1, Si in the aluminum alloy
The wear resistance can be ensured by the particles, and the particle diameter of Si is small and the hardness is about Hv1200, and the difference between the hardness and the mating material is small. Therefore, the abrasion of the cam lobe itself can be suppressed and the mating aggressiveness can be suppressed. .

According to the second aspect of the invention, the sliding surface of the cam lobe is made a smooth surface of Ra 0.1 μm or less, so that the lubrication state at the time of sliding between the cam lobe and the mating material is improved, and solid contact is achieved. Therefore, the opponent aggressiveness can be further suppressed, and the wear of the cam lobe itself can be suppressed. Furthermore, it comes off due to wear,
Since an attack by the generated hard particles (secondary particles) can be suppressed beforehand, wear of both the cam lobe and the partner can be suppressed.

According to the present invention, silicon carbide (Si) is contained in the aluminum alloy cam lobe.
C), the wear resistance is improved, but the aggressiveness of the opponent is increased. However, by using a combination in which a hard thin film of TiN, CrN, Cr ₂ N, and DLC having a hardness of about Hv2000 is applied to the mating material, the hardness is balanced and wear of both the cam lobe and the mating material is suppressed. be able to. Since the surface roughness of the hard thin film, which is the mating material of the cam lobe, is also Ra 0.05 μm or less, the mating aggressiveness to the cam lobe is small, and the generation of falling particles, which is one of the factors that increase wear, is also suppressed. Can be.

In the present invention, the surface roughness of the sliding surface of the cam lobe can be controlled to Ra 0.1 μm or less by, for example, machining such as mechanical polishing, electrolytic polishing or chemical polishing.

The present invention is not limited to the type in which the camshaft is made of an integral material. However, when the camshaft is made integral, the dispersion of hard particles is effective for improving the rigidity of the shaft portion, and the diameter of the shaft is reduced. It is possible to expect further weight reduction.

FIG. 1 shows a sectional shape of an assembled camshaft of the lightweight camshaft for an internal combustion engine according to the present invention.
FIG. 2 shows a sectional shape of the integral camshaft.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a lightweight camshaft for an internal combustion engine according to the present invention will be described in more detail with reference to examples and comparative examples.

In order to confirm the effects of the present invention, various combinations were evaluated by a single wear test simulating a direct-acting valve train. The apparatus used for the test is of a type for evaluating a cam lobe and a lifter shim as a mating material. As the aluminum material used in the test, a material obtained by gravity casting and a die casting method and a material obtained by forging a rapidly solidified powder by an atomizing method were used. According to the die casting method and the powder forging using the rapidly solidified powder, a fine structure having an average Si particle size of 10 μm or less could be obtained. Each cam lobe is formed from a rough material into a predetermined shape by grinding with a diamond grindstone, and the surface roughness is Ra.
For the cam lobes of 0.1 μm or less, final finishing was performed by tape wrapping. The cam lobe shape was the same as that of a commercially available product. The material of the shim is the same as the SC
M415 carbon steel was used. For some shims, the surface that slides on the cam lobe was polished with a superfinishing stone to finish the surface roughness to Ra 0.05 μm or less, and then coated with a hard thin film. All coatings were performed by the PVD method.

Table 1 shows details of Examples 1 to 7 and Comparative Examples 1 to 6.

(Evaluation Conditions) Evaluation conditions are as follows. Camshaft rotation speed: 300 rpm Maximum surface pressure: 700 MPa Oil type: 5W30SG Oil temperature: 80 ° C Evaluation time: 100 hours Wear amount measurement: Maximum length change (cam lobe), maximum wear depth (shim)

Table 1 also shows the test results of the examples and comparative examples.

[0017]

[Table 1]

In Examples 1 to 7 of the present invention,
In any case, the wear amount of the cam / shim is extremely small, and the effects of the invention are recognized, and the structure is such that the original function as a lightweight camshaft can be maintained.

In Comparative Example 1, the primary crystal Si had a large crystal grain size due to gravity casting, and the addition amount of silicon carbide (SiC) was as large as 20%. It is thought that the wear on the cam side increased with the generation of abrasion powder and the deterioration of the shim roughness.

Comparative Example 2 is a powder forged product using a rapidly solidified powder and has a crystal grain size within the scope of the claims. However, since silicon carbide is included, the mating aggressiveness is high and abrasion on the shim side is large. It was done. This shows that the addition amount of this level has a large effect on the shim side.

In Comparative Example 3, the primary crystal Si had a large particle size due to gravity casting, and abrasion occurred on the shim side. In addition, abrasion also occurred on the cam side, and the Si dropped from the cam lobe due to abrasion.
It is thought to be the effect of the particles.

Comparative Example 4 has a small grain size due to powder forging, but has a high aggressiveness to shims because it contains as much as 10% of silicon carbide. Could not. In addition, the thickness of the thin film is 1 μm, and abrasion of the base material (SCM415) occurs beyond the film.

In Comparative Example 5, the die casting method was used, but the cooling rate was insufficient and the average grain size of primary crystal Si was 15 μm.
Met.

Further, in Comparative Example 6, since the amount of Si in the aluminum alloy was as small as 14%, the abrasion resistance on the cam side was insufficient and the amount of wear on both the cam and shim was large.

As described above, the results of the test evaluation for each combination have been described. It has been found that in each of the combinations other than the present invention, the amount of wear of both or one of the cams and the shims is significantly inferior.

[0026]

As described above in detail, according to the present invention, the structure is such that Si is contained at 16.0 Wt% or more and the average grain size of Si in the alloy structure is 10 μm or less. A light-weight camshaft for an internal combustion engine having a cam lobe made of an aluminum alloy formed thereon; and a light-weight camshaft for an internal combustion engine having a sliding surface roughness of Ra 0.1 μm or less, and a cam lobe made of an aluminum alloy In addition, 0.5-3 Wt% of SiC hard particles
A lightweight camshaft for internal combustion engines containing
A lightweight camshaft for an internal combustion engine combining a lifter shim or valve lifter with a hard thin film having a surface roughness Ra of 0.05 μm or less and a cam lobe made of an aluminum alloy, and the hard thin film applied to the lifter shim or valve lifter is , TiN, CrN, Cr
_{By using a} lightweight camshaft for an internal combustion engine, which is a hard coating selected from 2N and DLC (diamond-like carbon), the wear of the cam lobe itself made of an aluminum alloy can be suppressed, and the opponent aggressiveness can be suppressed. Thus, a lightweight camshaft for an internal combustion engine can be obtained. When the camshaft is integrated,
The dispersion of hard particles is effective for improving the rigidity of the shaft,
It is possible to obtain an excellent effect that the weight can be further reduced, for example, the shaft diameter can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a cross-sectional shape of an assembled camshaft.

FIG. 2 is a diagram illustrating a cross-sectional shape of an integral camshaft.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cam lobe part 2 Shaft part 3 Cam shaft

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoshio Okada 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. In-house F-term (reference) 3G016 AA08 BA19 BA28 BA34 BB04 BB05 BB06 BB31 BB40 CA32 EA08 EA24 FA21 GA01 GA02 4K044 AA06 AB10 BA18 BC06 CA13

Claims (5)

[Claims] 1. A lightweight camshaft for an internal combustion engine having a cam lobe made of an aluminum alloy, wherein the aluminum alloy contains 16.0 Wt% or more of Si and the average grain size of Si in the alloy structure is 10 μm.
m. A light weight camshaft for an internal combustion engine, wherein a cam lobe of not more than m is formed. 2. The lightweight camshaft for an internal combustion engine according to claim 1, wherein the sliding surface of the cam lobe has a roughness of Ra 0.1 μm or less. 3. The lightweight camshaft for an internal combustion engine according to claim 1, wherein the aluminum alloy cam lobe contains 0.5 to 3 Wt% of SiC hard particles. Camshaft. 4. The lightweight camshaft for an internal combustion engine according to claim 1, wherein a lifter shim or a valve lifter provided with a hard thin film having a surface roughness of Ra 0.05 μm or less, and an aluminum alloy cam lobe. A light weight camshaft for an internal combustion engine, characterized in that: 5. The lightweight camshaft for an internal combustion engine according to claim 4, wherein the hard thin film applied to a lifter shim or a valve lifter combined with the aluminum alloy cam lobe comprises:
TiN, CrN, Cr ₂ N, lightweight camshaft for an internal combustion engine, which is a hard coating selected from DLC (diamond-like carbon).