Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
1999-07-13
2001-08-28
Turner, Archene (Department: 1775)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S440000, C277S434000, C428S323000, C428S325000, C428S408000, C428S446000, C428S457000
Reexamination Certificate
active
06279913
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a sliding member such as a piston ring utilized in reciprocating internal combustion engines and, more particularly, to a piston ring assembled into the ring groove of an aluminum alloy piston.
2. Description of the Related Art
In recent years, engines have been required to meet increased demands for higher outputs, high revolutions per minute and longer product service life and must also comply with ever stricter exhaust gas emission regulations. The piston ring must therefore function in a yet harsher operating environment. Many of such piston rings are formed typically with a chromium plating film, nitrided layer or physical vapor deposition film on the upper and lower surfaces.
However, when the upper and lower surfaces of a piston ring having a nitrided layer or a physical vapor deposition film are subjected to repeated impacts at high temperatures with the ring groove surfaces of the aluminum alloy piston, aluminum adhesion then occurs on the upper and lower surfaces of the piston ring, causing a large increase in ring groove wear.
A method is known however, for suppressing aluminum adhesion in the initial stages of engine operation by coating the upper and lower surfaces of the piston ring with a synthetic resin film containing solid lubricant. However, this synthetic resin film has poor wear resistance, so this method has the drawback that suppression of the aluminum adhesion does not last long.
Methods were also proposed for applying a thin film of artificial diamond material to the top surface and outer circumferential surface and ring groove of the piston and to the piston ring in order to improve durability as described in Japanese Patent Laid-open No. 3-260362. However, no detailed description of this thin film of artificial diamond material is listed in Japanese Patent Laid-open No. 3-260362.
Another method (Japanese Patent Laid-open No. 5- 179451) as described next, involved use of a diamond-like carbon film. In this method, in order to restrict the adhesion of ferrite structures, a film having amorphous carbon as the main constituent in which tungsten and/or silicon was dispersed was formed on the sliding surface which mates with a sliding surface formed of iron-type material containing ferrite. This technology is utilized for instance, in the hydraulic valve in power steering mechanisms. However, this Japanese Patent Laid-open No. 5-179451 listed absolutely no information regarding aluminum adhesion on the upper and lower surfaces of the piston rings mating with aluminum alloy pistons.
SUMMARY OF INVENTION
It is an object of the present invention to provide a sliding member with improved resistance to aluminum adhesion suitable for use at high temperatures and high loads with aluminum alloy as the mating material.
The present invention is a sliding member having a diamond-like carbon film on a sliding surface of the sliding member, wherein the diamond-like carbon film has a surface structure in which diamond-like carbon has been deposited in nodular shapes in sizes of 0.5 to 5 micrometers.
The diamond-like carbon forming a film of the present invention is configured from any one of the following structures.
1. Amorphous carbon structure
2. Amorphous carbon structure having partly a diamond structure.
3. Amorphous carbon structure having partly a graphite structure.
In the process of investigating the property of films comprising diamond-like carbon deposited under various conditions, the inventors discovered that diamond-like carbon films having a surface structure in which diamond-like carbon has been deposited in nodular shapes has two advantages compared to films having a surface structure in which diamond-like carbon has been deposited in a layer shape. The first advantage is that the film has extremely high adhesive strength. The second advantage is that aluminum adhesion is not prone to occur to the film. Aluminum adhesion is easily prone to occur in defect portions where pits or film collapse are present, so the fact that the diamond-like carbon film of the present invention is resistant to aluminum adhesion is probably due to the high adhesive strength of the film.
The precise mechanism by which the deposition structure of the diamond-like carbon film influences adhesive strength is not clear. However, it is thought that in film having a surface structure in which diamond-like carbon has been deposited in nodular shapes, the boundary between respective nodules has a buffer effect so that strain occurring in a localized section is not prone to be conveyed to a remote section. Also thought is that in film having a surface structure in which diamond-like carbon has been deposited in nodular shapes, deposition tends to occur with the internal strain at a low level.
The nodules observed on the surface have preferably a size within a range of 0.5 to 5 micrometers. When the size of the nodules is less than 0.5 micrometers, the diamond-like carbon film has a surface structure with a smooth layer shape. When the size of the nodules is greater than 5 micrometers, pits or film collapse tends to easily occur.
In order to obtain the film having a surface structure in which diamond-like carbon has been deposited in nodular shapes, non-uniform fine irregularities (concavities and protrusions) are first formed on the surface to be covered with the film, and this surface then covered with the diamond-like carbon film. The non-uniform fine irregularities can be formed by means of lapping or blasting. The surface roughness of the irregular surface to be covered is preferably within a range of 0.05 to 1 micrometer Ra.
When the irregularities on the surface to be covered are too fine, the diamond-like carbon film has a surface structure with a smooth layer shape and peeling or cracks are prone to occur. Further, when the irregularities on the surface to be covered are too large, the surface roughness of the diamond-like carbon film becomes large so that the sliding characteristics degrade and peeling or film collapse is prone to occur. A surface formed by a grindstone is not preferred, even if the same surface roughness is achieved, because regular grinding marks are formed. The film comprising diamond-like carbon deposited on such a ground surface has a surface structure with a smooth layer shape and peeling is prone to occur in the groove-shaped mark portions left by the grinding.
The surface roughness of the diamond-like carbon film of the present invention is preferably within a range of 0.07 to 1.5 micrometers Ra and when the film is utilized in a piston ring, a film thickness is preferably within a range of 0.5 to 30 micrometers. When the film thickness is below 0.5 micrometers, the service life of the piston ring decreases, and when above 30 micrometers, the adhesive strength deteriorates and consequently the resistance to aluminum adhesion declines.
The diamond-like carbon film may be directly formed on the sliding surface or may be formed on a hard chromium plating film, a gas nitrided layer, or an ion plating film.
The scuffing resistance of the diamond-like carbon film is inherently high, however a film having improved scuffing resistance, improved wear resistance and improved resistance to aluminum adhesion can be obtained by including one or more elements in an atomic content of 5 to 40 percent selected from the group consisting of silicon, titanium, tungsten, chromium, molybdenum, niobium, and vanadium. The one or more elements are present as metal or carbides or both.
REFERENCES:
patent: 4974498 (1990-12-01), Lemelson
patent: 5237967 (1993-08-01), Willermet et al.
patent: 5478650 (1995-12-01), Davanloo et al.
patent: 5771873 (1998-06-01), Potter et al.
patent: 5989511 (1999-11-01), Gruen et al.
patent: 3-2603362 (1991-11-01), None
patent: 5179451 (1993-07-01), None
Iwashita Takatsugu
Yamashita Nobuyuki
Armstrong Westerman Hattori McLeland & Naughton LLP
Teikoku Piston Ring Co. Ltd.
Turner Archene
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