JPH0754965A - Adjusting shim and is manufacture - Google Patents

Abstract

PURPOSE:To reduce the friction coefficient simply and certainly and improve the sliding characteristics by forming an adjusting shim to slide in mating with a cam from a ceramic material having a Vickers hardness which exceeds a certain specific value, and furnishing a specific denatured layer over the sliding surface with cam. CONSTITUTION:A linear motion type dynamic valve device of an internal combustion engine has a valve lifter 4 which moves in the axial direction through the interaction of a valve spring 5 and a cam 1 rotating round a cam shaft 2, and thereby the suction/exhaust valve 6 at the cylinder head 7 is opened and closed. An adjusting shin 3 to slide in mating with the cam 1 is installed on the oversurface of the valve lifter 4. The shins 3 is made of a ceramic material having a Vickers hardness exceeding 1000. A denatured layer as formed by embrittling or removing partially the grain boundary phase of the ceramic is provided at least over the sliding surface with the cam 1. The depth of this denatured layer should be 0.2-1.0mum. The sliding surface of the cam 1 is polished by a run-in operation for improvement of the surface roughness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cam follower adjusting shim which constitutes a valve train of an internal combustion engine such as an automobile engine, and a method for manufacturing the adjusting shim.

[0002]

2. Description of the Related Art In recent years, exhaust gas from automobiles has become a problem from the viewpoint of protecting the global environment, and as one of countermeasures against this, there is an increasing demand for fuel saving by improving engine efficiency. It is effective to reduce the friction loss of the internal combustion engine as a method of reducing automobile fuel consumption, and the friction loss ratio of the valve train is large especially in the low rotation speed region where lubrication is severe. It is rare.

By the way, generally, in the presence of a lubricant such as lubricating oil, the minimum oil film thickness formed between the sliding surfaces of the opposing sliding parts and the properties of the sliding surfaces of both sliding parts are related to the sliding characteristics. It is said to have a great influence. For example, "Hydraulic pressure and air pressure", Vol. 18, No. 4, 1987, 247-25.
8 pages, or “Technical Lecture Preprints 92” edited by the Society of Automotive Engineers of Japan
4 ”, 1992, pp. 85-88, the oil film parameter Λ defined by the following formula 1 is often used as a value indicating the lubrication state.

[0004]

[Formula 1] Λ = h _min / σ = h _min / (R _rms1 ² + R _rms2 ² ) ^1/2 where h _{min is} the minimum oil film thickness between the sliding surfaces of the facing sliding parts σ is the facing sliding Composite surface roughness of sliding surfaces of moving parts R _rms1 : _Root mean square roughness of sliding surfaces of one sliding part R _rms2 : _Root mean square roughness of sliding surfaces of the other sliding part

When the value of the oil film parameter Λ is 3 or more, it is in a fluid lubrication state, when it is 1 or less, it is in a boundary lubrication state, and when it is 1
In the case of 3 to 3, it is considered to be a mixed lubrication state in which fluid lubrication and boundary lubrication are mixed, and it is said that as the value of Λ is larger, the contact between the sliding surfaces is alleviated and the sliding characteristics are improved. Therefore, since the minimum oil film thickness h _min is constant under the same sliding condition, it can be understood that reducing the surface roughness of the sliding surfaces of the two sliding parts is effective in reducing the friction coefficient. .

Therefore, it is generally practiced to subject the sliding surface of the sliding component to highly precise ultra-precision finishing to reduce the surface roughness as much as possible. However, since the cam, which is one of the valve train components, has a surface with a complicated shape such as a curved surface, it is difficult to perform high-precision, ultra-precision finishing, and machining costs a lot of time and labor, which results in processing costs. Since it also becomes extremely high, only the surface finish by ordinary grinding is performed, and the desired reduction of the friction coefficient has not been realized yet.

[0007]

SUMMARY OF THE INVENTION In view of such conventional circumstances, the present invention is to improve the surface roughness by polishing the sliding surface of the cam constituting the valve train mechanism of the internal combustion engine during the running-in operation. Therefore, it is possible to provide an adjusting shim for a cam follower that can reduce the friction coefficient and obtain good sliding characteristics without performing special ultra-precision finishing on the cam, which is difficult and expensive. With the goal.

[0008]

In order to achieve the above object, the adjusting shim used in combination with the cam provided by the present invention is made of ceramics having a Vickers hardness of 1000 or more, and at least the sliding surface with the cam has ceramics. The grain boundary phase has a deteriorated layer that is embrittled or partially removed.

The adjusting shim manufacturing method of the present invention is characterized in that at least the sliding surface of the base material made of ceramics having a Vickers hardness of 1000 or more with respect to the cam is etched with molten alkali. Here, the molten alkali means a liquid obtained by melting alkali such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) by heating.

The ceramic used as the base material of the adjusting shim should have a Vickers hardness of 1000 or more, but is a light-weight, high-strength, silicon nitride (Si ₃ N ₄ ) sintered body excellent in thermal shock resistance. Is particularly preferable. Further, a composite material of silicon nitride, for example, a silicon nitride sintered body reinforced with fibers such as silicon carbide or whiskers, or a silicon nitride sintered body reinforced with titanium nitride particles or silicon carbide nanoparticles can be used.

[0011]

In the adjusting shim of the present invention, the ceramic surface exposed on the sliding surface is deteriorated by the etching treatment with molten alkali, and the strength is lower than that of the original material of the base material. That is, an altered layer in which a grain boundary phase such as a Si ₃ N ₄ sintered body is embrittled or partially removed by molten alkali is formed to a certain depth from the surface.

Therefore, during the sliding operation with the cam due to the running-in operation, the fine hard particles are easily removed from the altered layer of the adjusting shim, and the sliding surface of the cam is polished by the removed fine hard particles. It Therefore, the surface roughness of the sliding surface of the cam having a complicated shape is automatically improved by the running-in operation with the adjusting shim of the present invention, without performing highly precise ultra-precision finishing in advance.

On the other hand, on the sliding surface of the adjusting shim, the deteriorated layer on the surface is worn due to sliding with the cam, and when it is almost completely consumed, the raw material portion of the base material appears on the surface. The base material of the adjusting shim is composed of ceramics with a Vickers hardness of 1000 or more, and has higher hardness and better wear resistance than steels that compose the current cam. Almost stops.
Further, the high-hardness adjusting shim is unlikely to be locally deformed due to the contact with the cam, and the uneven wear due to the local deformation does not occur.

As a result, the adjusting shim can continue sliding with the cam in a state where the progress of wear is almost stopped, and at the same time, the surface roughness of the sliding surface of the adjusting shim is in the initial state where the deteriorated layer exists. Better than. At this time, traces of fine recesses from which fine hard particles have fallen are left on the sliding surface of the adjusting shim.These fine recesses serve as oil reservoirs for lubricating oil and act as a lubricating oil supply source. It improves the ability to form an oil film during operation and helps reduce the friction coefficient and prevent seizure.

As described above, according to the adjusting shim of the present invention, the surface roughness of the sliding surface of the cam can be automatically improved by the running-in operation, and at the same time, the sliding surface of the adjusting shim itself can be improved. Since the surface roughness is also improved,
The oil film parameter Λ (the ratio of the minimum oil film thickness h _min between the sliding surface of the cam and the adjusting shim and the combined surface roughness σ of both sliding surfaces) shown in the above formula 1 becomes large, and the conventional cam The friction coefficient is significantly reduced as compared with the case of the combination of the adjusting shim and the adjusting shim.

In order to obtain such an altered layer of ceramics, etching treatment with molten alkali is necessary, and satisfactory effect cannot be obtained by etching treatment with an aqueous solution of acid or alkali. Although the reason is not clear, it is considered that the surface condition suitable for the removal of the fine hard particles can be obtained only by etching with the molten alkali.

The depth of the deteriorated layer of the adjusting shim is preferably 0.2 to 1.0 μm from the surface. If the depth of the altered layer is less than 0.2 μm, the amount of fine hard particles that fall off is insufficient, making it difficult to polish the surface of the cam to a satisfactory surface state, and conversely, it exceeds 1.0 μm. And the surface roughness of the adjusting shim itself deteriorates to reduce the film thickness parameter Λ, and the cam surface is damaged due to the deterioration of the lubrication state and the excessive removal of hard particles.

As a material for such an adjusting shim, a Si ₃ N ₄ sintered body having high strength and excellent thermal shock resistance is particularly preferable, but an altered layer having the above depth is formed on the surface of the Si ₃ N ₄ sintered body. When forming, for example, sodium hydroxide at 80 ℃
Immerse in molten NaOH that has been heated to a certain degree and melted for several minutes.

[0019]

EXAMPLES S having a Vickers hardness of 1400
A plate of a predetermined size made of each i ₃ N ₄ sintered body was immersed in molten NaOH at 80 ° C. for 1 minute to perform an etching treatment. On the surface of the obtained adjusting shim,
An altered layer having a depth of 0.5 μm was formed. A scanning electron micrograph of the surface of this adjusting shim is shown in FIG.

This adjusting shim was used as the adjusting shim 3 of the cam follower in the direct-acting valve operating system for an internal combustion engine shown in FIG. That is, the camshaft 2
By the action of the cam 1 and the valve spring 5 which rotate around, the valve lifter 4 moves in the axial direction to open and close the intake / exhaust valve 6 of the cylinder head 7. The adjusting shim 3 was attached so as to slide relative to 1. A chill-hardened cast iron alloy was used for the cam 1.

Regarding the cylinder head including the valve train of this internal combustion engine, the cam shaft 2 is actually driven directly by an external motor under the conditions of a rotation speed of 1500 rpm and an oil temperature of 80 ° C.
The composite surface roughness σ of the sliding surface where the cam 1 and the adjusting shim 3 contact each other was measured every predetermined operating time, and the results are shown in Table 1. In addition, cam 1 and adjusting shim 3
The composite surface roughness σ of the sliding surface is defined by the following equation 2.

[0022]

[Equation 2] σ = (R _rms1 ² + R _rms2 ² ) ^1/2 where R _{rms1 is} the root mean square roughness of the surface of the _adjusting shim R _{rms2 is} the root mean square roughness of the surface of the cam

Further, as the adjusting shim of the comparative example, the maximum surface roughness R _max which is made of the same Si ₃ N ₄ sintered body as above but is not subjected to etching treatment by only grinding finish.
Is 0.2 μm and an adjusting shim consisting of a conventional SCM415 carburized and hardened product is used, and the composite surface roughness of the sliding surface of the cam and the adjusting shim obtained in the same manner as above is obtained. The height σ is also shown in Table 1.

[0024]

[Table 1] Composition Surface roughness σ (μm) Operating time Etching untreated SCM415 (hr) Si ₃ N ₄ Sintered body Si ₃ N ₄ Sintered body Carburized and hardened product 0 0.45 0.38 0.3 52 2 0.23 0.27 0.33 5 0.15 0.23 0.28 10 0.10 0.18 0.26 20 0.06 0.12 0.22 50 0.01 0.09 0.0. 20

As is clear from the results shown in Table 1, by using the adjusting shim made of the Si ₃ N ₄ sintered body of the present invention which has been subjected to the etching treatment with the molten alkali, the usual Si ₃ N ₄ sintering is performed. Compared to the case of using a body or steel, the sliding surface of the cam, which is the mating member, is polished to reduce its surface roughness, and at the same time the surface roughness of the adjusting shim itself is also reduced. The roughness is reduced.

Further, in the actual drive test by the above-mentioned device, immediately after the start of the operation and 5 times for each adjusting shim.
The camshaft torque after 0 hours was measured and the conventional material, SCM
The camshaft torque reduction rate based on the camshaft torque immediately after the start of the operation of the adjusting shim made of the 415 carburized and hardened product was calculated and shown in Table 2. The camshaft torque reduction rate was calculated by the following equation 3.

[0027]

[Equation 3] Camshaft torque reduction rate = ((1-Camshaft torque when each adjusting shim is used) / SCM immediately after starting operation
415 Carburized and hardened product Cam shaft torque of adjusting shim} × 100 (%)

[0028]

[Table 2] Cam axis torque Low reduction rate (%) Operating time Unetched SCM415 (hr) Si ₃ N ₄ Sintered body Si ₃ N ₄ Sintered body Carburized and hardened product 0 11.8 12.1 Standard 50 30.2 21.5 5.1

From the results shown in Table 2, when the adjusting shim of the present invention is used, the sliding characteristics are improved by improving the combined surface roughness of the sliding surfaces of the cam and the adjusting shim, and the camshaft torque is improved. Since it can be significantly reduced, it is possible to provide an internal combustion engine with high energy efficiency.

[0030]

According to the adjusting shim of the present invention, it is possible to improve the surface roughness of the cam during the running-in operation with the cam after mounting the cam in combination in the cylinder head. Even if the surface of the shaped cam is not subjected to special ultra-precision finishing, good sliding characteristics with less friction loss can be obtained, and therefore an internal combustion engine with high energy efficiency can be provided.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph (× 2000) showing a surface particle structure of an adjusting shim manufactured in an example.

FIG. 2 is a schematic cross-sectional view showing a direct-acting valve train system for an internal combustion engine used in an embodiment.

[Explanation of symbols]

 1 cam 2 cam shaft 3 adjusting shim 4 valve lifter 5 valve spring 6 intake / exhaust valve 7 cylinder head

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaoru Murabe 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Akira Yamakawa 1-chome, Konyo Kita, Itami City, Hyogo Prefecture No. 1 in Sumitomo Electric Industries Itami Works

Claims (5)

[Claims] 1. An adjusting shim used in combination with a cam, which is made of ceramics having a Vickers hardness of 1000 or more, and a grain boundary phase of the ceramics is embrittled or partially removed at least on a sliding surface with the cam. An adjusting shim having an altered layer. 2. The adjusting shim according to claim 1, wherein the depth of the altered layer is 0.2 to 1.0 μm. 3. The adjusting shim according to claim 1, wherein the sliding surface of the cam, which is a mating member, is ground by the run-in operation to improve its surface roughness. 4. A method of manufacturing an adjusting shim used in combination with a cam, which has a Vickers hardness of 100.
A method for producing an adjusting shim, characterized in that at least a sliding surface of a base material made of 0 or more ceramics with respect to a cam is subjected to an etching treatment with a molten alkali. 5. The method for producing an adjusting shim according to claim 4, wherein the depth of the altered layer of the ceramic obtained by the etching treatment is 0.2 to 1.0 μm.