JP2006138329A - Low friction sliding mechanism - Google Patents

Abstract

An object of the present invention is to provide a low-friction sliding mechanism that has both wear resistance and seizure resistance while reducing the friction coefficient of the sliding surface.
An amorphous hard carbon film is disposed on two or more sliding surfaces formed with lubricating oil between a mating material and sliding with different amounts of hydrogen contained in the amorphous hard carbon film. This is a low friction sliding mechanism having two or more surfaces. It is composed of a piston ring and a piston and / or cylinder bore. An amorphous hard carbon film having a hydrogen content of 10% or less is disposed on the upper and lower surfaces of the piston ring and the ring groove of the piston. An amorphous hard carbon film having a hydrogen content of 20% or more is disposed on the side surface of the piston ring. Amorphous hard carbon films disposed on the upper and lower surfaces and side surfaces of the piston ring are formed by the PVD method and the CVD method, respectively.
[Selection] Figure 1

Description

  The present invention relates to a low-friction sliding mechanism, and more particularly to a low-friction sliding mechanism that can be suitably used for a sliding portion formed by a piston ring of an internal combustion engine.

Environmental problems including global warming due to carbon dioxide is largely closeup on a global scale, is one of the automobile fuel efficiency improvement technologies major issues for CO ₂ reduction, the role reduction plays a friction loss is large. For example, if attention is paid to the friction loss at the sliding portion of the engine, it is important to develop a material / surface treatment technology that exhibits excellent wear resistance and a low friction coefficient for the sliding member.

With regard to the piston ring, for the purpose of improving wear resistance and seizure resistance, for example, it has been proposed to combine an amorphous hard carbon coated member and an iron-based member (see, for example, “Patent Document 1”). This Patent Document 1 aims to improve the sliding between the piston ring and the inner surface of the bore by the excellent seizure resistance and wear resistance of the amorphous hard carbon film. is not. Further, attention is focused only on the portion where the piston ring and the bore are in contact with each other, and there is no limitation on the upper and lower surfaces of the piston ring where the piston and the piston ring contact, or the portion relating to the ring groove of the piston.
Japanese Patent Application No. 2002-345628 (P2002-345628)

  From such a background, the present inventors pay attention to the excellent seizure resistance, wear resistance, and low friction property of the amorphous hard carbon film, and when applying it to the piston ring, the excellent effect is obtained. It has been found that it is important to reduce the friction between the upper and lower surfaces of the piston ring in order to maximize the expression. That is, when an amorphous hard carbon film is applied to the piston ring, it is extremely important to reduce the friction not only at the location where the piston ring and the bore contact but also at the location where the piston ring groove and the piston ring contact. I found out.

The piston is connected to the crankshaft by a connecting rod, and is structured to receive thrust and anti-thrust loads at the piston skirt. On the other hand, since a constant tension acts on the piston ring, a force acts uniformly on the inner surface of the bore.
However, it has been found that when the coefficient of friction between the piston ring and the ring groove of the piston is large, the piston ring is also affected by the behavior of the piston in the thrust and anti-thrust directions. For this reason, it has been found that in the contact between the piston ring and the bore, for example, bore wear in the vicinity of the top and bottom dead center is not constant on the circumference but is large on the thrust and anti-thrust sides.

  Conventionally, among amorphous hard carbon films, those containing almost no hydrogen prepared by physical vapor deposition (PVD) have a lower friction in engine oil than chemical vapor deposition (CVD). However, the amorphous hard carbon film produced by PVD has a high presence of unmelted metal atoms called droplets and the film hardness is high. When used, there was a concern about wear and seizure due to its high aggressiveness to the aluminum alloy.

  The present invention has been made in view of such problems of the prior art, and its object is to achieve both wear resistance and seizure resistance while reducing the friction coefficient of the sliding surface. Another object of the present invention is to provide a low friction sliding mechanism.

  As a result of intensive studies to solve the above problems, the present inventors have developed an amorphous hard carbon thin film disposed at a site where the friction coefficient is desired to be reduced and a site where the wear resistance and seizure resistance are desired to be improved. The inventors have found that the above problems can be solved by adjusting the hydrogen content with the amorphous hard carbon thin film to be disposed, and have completed the present invention.

  According to the present invention, the hydrogen content of the amorphous hard carbon thin film disposed in the portion where the friction coefficient is desired to be reduced and the portion where the wear resistance and seizure resistance are desired to be adjusted is low friction characteristics, A low friction sliding mechanism with excellent wear resistance and seizure resistance can be realized.

  Hereinafter, the low friction sliding mechanism of the present invention will be described in detail. In the present specification, “%” indicates a mass percentage unless otherwise specified.

The low-friction sliding mechanism of the present invention has two or more sliding surfaces formed with lubricating oil between the counterpart material. In addition, an amorphous hard carbon film is provided on these sliding surfaces so that there are two or more sliding parts having different amounts of hydrogen contained in the amorphous hard carbon film.
As a result, even when there are multiple sliding surfaces and the conditions such as surface pressure, surface roughness, sliding area and sliding speed of each sliding surface are different, each sliding surface is arranged for each sliding surface. By adjusting the hydrogen content of the amorphous hard carbon film to be provided, a sliding mechanism that achieves both low friction characteristics, wear resistance and seizure resistance can be obtained.

Typically, in an internal combustion engine, it is preferable to employ a sliding part formed by arbitrarily combining a piston ring and one or both of a piston and a cylinder bore.
Here, when the piston reciprocates within the cylinder bore, the upper and lower surfaces of the piston ring slide with the ring groove of the piston in a direction perpendicular to the reciprocating direction of the piston, and the side surface of the piston ring is the inner wall surface of the cylinder bore. And slides in the reciprocating direction of the piston. In such a case where the sliding conditions are different, for example, as shown in FIG. 1, the upper and lower surfaces of the piston ring are coated with an amorphous hard carbon film, or the upper and lower surfaces and side surfaces of the piston ring contain different hydrogen. Amorphous hard carbon film having an amount can be coated. Further, as shown in FIG. 2, the upper and lower surfaces of the ring groove of the piston can be coated with an amorphous hard carbon film.
As a result, the friction coefficient between the piston ring upper and lower surfaces and the piston ring groove is reduced, the movement between the piston ring and the piston ring groove becomes very smooth, and the piston ring side surface that contacts the cylinder bore is seized. And wear resistance can be improved.

Here, the amorphous hard carbon film disposed on the sliding surface of the low friction sliding mechanism of the present invention is a film composed only of carbon except for inevitable impurities. Films can be formed by various PVD methods and CVD methods. Specifically, a DLC thin film (diamond-like carbon thin film) formed by an arc ion plating method can be used. This DLC thin film is a hard carbon thin film in which the bonding form between carbons consists of both a diamond structure (SP ³ bond) and a graphite bond (SP ² bond).

  In order to reduce the coefficient of friction, it is preferable to form an amorphous hard carbon film containing almost no hydrogen on the sliding surface. Specifically, an amorphous hard carbon film having a hydrogen content of 10% or less can be disposed on one or both of the upper and lower surfaces of the piston ring and the ring groove of the piston. Thereby, a very small coefficient of friction is exhibited in the engine oil, and the movement between the piston ring and the ring groove of the piston can be very smooth.

  Further, an amorphous hard carbon film having a hydrogen content of 20% or more is preferably disposed on the side surface of the piston ring that slides with the cylinder bore. Thereby, the outstanding effect that abrasion of a cylinder bore inner wall surface is suppressed is acquired. In particular, when the inner wall surface of the cylinder bore is made of an aluminum die-cast material such as ADC12, the wear resistance remarkably appears.

Furthermore, when the amorphous hard carbon film is disposed on the upper and lower surfaces of the piston ring and the side surface of the piston ring that slides with the cylinder bore, the respective films are formed by PVD (physical vapor deposition) or CVD (chemical vapor deposition). It is preferable to form a film by a phase deposition method. For example, a film can be formed like a piston ring shown in FIG.
At this time, even when the inner wall surface of the cylinder bore is made of an aluminum die-cast material such as ADC12, the friction between the piston and the upper and lower surfaces of the piston ring is reduced and the movement tends to be smooth while suppressing the wear of the inner wall surface of the cylinder bore.

The amorphous hard carbon film disposed on one or both of the upper and lower surfaces of the piston ring and the ring groove of the piston is made of nickel (Ni), manganese (Mg), cobalt (Co), and these. It is preferable to include any combination.
At this time, the friction on the sliding surface is further reduced and the movement becomes smooth, so that wear on the inner wall surface of the cylinder bore is easily suppressed.

On the other hand, it is preferable to form fine concave portions on the inner wall surface of the cylinder bore, in other words, on the surface where the cylinder bore rubs against the side surface of the piston ring. Thereby, while reducing the fluid friction during reciprocating sliding, the friction reduction effect in the return part of a vertical dead center is acquired.
Specifically, the area ratio of the fine recesses is preferably 0.5 to 10% or less of the sliding surface of the cylinder bore, and the depth is preferably 1 to 15 μm. For example, a recess as shown in FIG. 3 can be formed. When the area ratio is smaller than 0.5% or when the depth is smaller than 1 μm, the effect of the recess is not sufficiently obtained, and there is a concern that seizure may occur because the lubricating oil retaining effect is small. On the other hand, when the area ratio is larger than 10% and the depth is larger than 15 μm, the load capacity decreases, the fluid lubrication effect cannot be obtained sufficiently, and the friction increases with the occurrence of metal contact, and wear and seizure occur. Is likely to occur.

Further, when the amorphous hard carbon film is disposed on the side surface of the piston ring or when the recess is formed in the cylinder bore, the cylinder bore can be made of an aluminum alloy. At this time, the excellent seizure resistance of the amorphous hard carbon film and the excellent retention of the lubricating oil can be imparted by the recess formed in the cylinder bore, which makes it possible to make the cylinder bore aluminum alloy, which has been difficult in the past. Become.
Further, the cylinder bore preferably contains silicon (Si) at a ratio of 12% or less. For example, an aluminum alloy such as Al-Si-Cu-based ADC 12 having Si of about 10.8% can be used. In this case, wear resistance and seizure resistance can be achieved without using a material such as ADC14, which is made by adding Cu or Mg to an Al-Si hypereutectoid alloy developed to reduce the weight of the engine block. Can be overcome, and low friction can be achieved.

  The lubricating oil used for the sliding surface includes, for example, a lubricant base oil, a fatty acid ester-based ashless friction modifier, an aliphatic amine-based ashless friction modifier, polybutenyl succinimide, Examples thereof include lubricating oil containing a derivative of tenenyl succinimide or zinc dithiolinate and any combination thereof. The lubricating base oil is not particularly limited and may be used regardless of the type as long as it is normally used as a base oil for lubricating oil, such as mineral oil, synthetic oil, fats and oils, and mixtures thereof. Can do. The lubricating oil includes semi-solid grease in addition to liquid lubricating oil.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in full detail, this invention is not limited to these Examples.

(Examples 1 and 2 and Comparative Examples 1 and 2)
A prototype engine was actually manufactured, and the low friction sliding mechanism in which the piston ring is composed of the piston and cylinder bore was evaluated. The engine used was an in-line four-cylinder engine QR25DE. A cast iron liner is cast in a normal engine, but this time, this cast iron liner was cut off by cutting, and instead, a die cast liner made of ALDC12 material was prototyped and evaluated by press fitting.
Further, the inner surface of the pressed aluminum alloy was subjected to mask blasting as necessary to form regular recesses. In the mask blasting process, a concave fine shape is formed on a resin mask using optical lithography technology, and the resin mask is attached to the cylindrical surface, and then alumina abrasive grains having an average particle diameter of 20 μm are applied from the projection nozzle to the workpiece. The distance was set to 100 mm, and projection was performed under the conditions of a projection flow rate of 100 g / min and a projection pressure of 0.4 MPa, thereby obtaining a concave fine shape. Then, the bulge of the edge part formed in the circumference | surroundings of the recessed micro shape was removed with the tape wrap film with a particle size of 9 micrometers, and it used for the test.
The piston ring was formed with an amorphous hard carbon film on all of the top ring, the second ring, and the oil ring. The amorphous hard carbon film was formed using two types of chemical vapor deposition (CVD) and physical vapor deposition (PVD).
In the experiment, the engine was assembled with different specifications from cylinder 1 to cylinder 4 as shown in Table 1. A 30-hour firing test was conducted at 5600 rpm, full load, 5W30 engine oil, and oil temperature of 90 ° C., and the amount of thrust side wear near the top dead center of the bore surface after the test was measured.

  As shown in Table 1, in the low friction sliding mechanism (second and third cylinders) of Examples 1 and 2, which is a preferred embodiment of the present invention, an effect of suppressing the amount of wear was obtained.

It is the schematic which shows an example of the amorphous hard carbon film | membrane formed in a piston ring. It is the schematic which shows an example of the amorphous hard carbon film formed in a piston groove part. It is the schematic which shows an example of the fine recessed part formed in the inner wall of a cylinder bore.

Claims (10)

A low-friction sliding mechanism having two or more sliding surfaces formed with lubricating oil between the counterpart material,
A low-friction sliding mechanism characterized in that an amorphous hard carbon film is disposed on the two or more sliding surfaces, and there are two or more sliding surfaces having different amounts of hydrogen contained in the amorphous hard carbon film. .   2. The low friction sliding mechanism according to claim 1, wherein the internal combustion engine comprises a piston ring and a piston and / or a cylinder bore.   3. The low friction sliding mechanism according to claim 2, wherein an amorphous hard carbon film having a hydrogen content of 10% or less is disposed on the upper and lower surfaces of the piston ring and / or the ring groove of the piston. .   4. The low friction sliding mechanism according to claim 2, wherein an amorphous hard carbon film having a hydrogen content of 20% or more is disposed on a side surface of the piston ring that slides with the cylinder bore.   The said piston ring WHEREIN: The amorphous hard carbon film | membrane arrange | positioned on the upper and lower surfaces of a piston ring and the side surface which slides with a cylinder bore was formed into a film by PVD method and CVD method, respectively. The low friction sliding mechanism according to any one of the items.   The amorphous hard carbon film disposed on the upper and lower surfaces of the piston ring and / or the ring groove of the piston comprises at least one selected from the group consisting of nickel, manganese and cobalt. The low friction sliding mechanism according to any one of claims 2 to 5.   The low friction sliding mechanism according to any one of claims 2 to 6, wherein in the cylinder bore, a fine recess is formed on the rubbing surface.   The low-friction sliding mechanism according to claim 7, wherein an area ratio of the fine recesses is 0.5 to 10% or less and a depth thereof is 1 to 15 µm.   The low friction sliding mechanism according to any one of claims 2 to 8, wherein the cylinder bore is made of an aluminum alloy.   The low friction sliding mechanism according to any one of claims 2 to 9, wherein silicon is contained in the cylinder bore at a ratio of 12% or less.

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