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
2001-12-04
Browne, Lynne H. (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S443000, C277S444000, C277S938000, C277S943000
Reexamination Certificate
active
06325385
ABSTRACT:
BACKGROUND OF INVENTION
1. Technical Field of Invention
The present invention relates to a piston ring for use in internal combustion engines.
2. Description of Related Art
In recent years, engines must meet increased demands for higher output, 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 hard surface treatment layer such as chromium plating film, nitrided layer or physical vapor deposition film on the upper and lower surfaces and the outer circumferential surface.
However, piston rings having a nitrided layer or physical vapor deposition film are prone to wear the ring grooves of the aluminum alloy pistons. In particular, piston rings having nitrided layers are prone to cause aluminum adhesion on the upper and lower surfaces, increasing the wear on the ring grooves.
In the initial stage of engine operation, break-in between the cylinder and piston ring is not sufficient so that scuffing may occur between the cylinder and piston ring formed with the above mentioned hard surface treatment layer. Accordingly, a method to improve initial break-in characteristics of these hard surface treatment layers or a hard surface treatment layer having both scuffing resistance and wear resistance is needed.
To respond the above problem, the following arts have been proposed.
1. Japanese Patent Laid-open No. 8-184375
A film of either 98.0 to 99.5 percent molybdenum or chromium or both and the remainder of nitrogen was formed by physical vapor deposition on a nitrided layer or physical vapor deposition film in order to improve the initial break-in characteristics.
2. Japanese Patent Publication No. 5-54594
A TiN film was formed over a hard film comprised of CBN, TiC, Ti (C,N), SiC, diamonds or Al
2
O
3
in order to improve the scuffing resistance.
On the other hand, the following art involved coating of artificial diamond material has been proposed.
3. Japanese Patent Laid-open No. 3-260362
A thin film of artificial diamond material was formed on the piston ring and on the top surface, external circumferential surface and ring groove of the piston in order to improve durability.
Further, the following art involved use of a diamond-like carbon film has been proposed.
4. Japanese Patent Laid-open No. 5-179451
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, under harsh engine operating conditions, the technology proposed in the above first method has the drawback that the molybdenum or chromium film wears away quickly. The technology proposed in the above second method has a TiN film with excessive hardness so that resistance to scuffing is inadequate. The technology proposed in the above third method has no detailed description of any kind regarding the thin film of artificial diamond material. The technology proposed in the above fourth method provides no description of aluminum adhesion on the upper and lower surfaces of the piston rings mating with aluminum alloy pistons. Besides the above mentioned technologies, a method is known, 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.
SUMMARY OF INVENTION
It is an object of the present invention to provide a piston ring with superior sliding characteristics such as resistance to aluminum adhesion, resistance to scuffing and initial break-in characteristics.
The present invention is a piston ring covered on a sliding surface of the piston ring with a diamond-like carbon film, wherein an under film is formed beneath the diamond-like carbon film and is comprised of one or more elements selected from the group consisting of silicon, titanium, tungsten, chromium, molybdenum, niobium and vanadium in an atomic content of 70 percent or more and below 100 percent, and the remaining content consisting of carbon, or one or more of said elements in an atomic content of 100 percent.
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.
The sliding surface is the upper, lower or outer circumferential surfaces of the piston ring. The film of the present invention covers at least one surface of the upper, lower and outer circumferential surfaces of the piston ring.
The sliding surface of the piston ring of the present invention comprises a laminated structure of piston ring base material, under film, and diamond-like carbon film; or a laminated structure of piston ring base material, hard surface treatment layer, under film, and diamond-like carbon film. The hard surface treatment layer may be a chromium plating film, a nitrided layer or an ion plating film.
The resistance to aluminum adhesion, wear resistance and scuffing resistance of the diamond-like carbon film are 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.
The under film is firmly bonded to the piston ring base material or the hard surface treatment layer of any one of chromium plating film, nitrided layer and ion plating film, and also bonded to the diamond-like carbon film. The under film simultaneously alleviates strain occurring internally in the diamond-like carbon film.
Accordingly, the diamond-like carbon film of the present invention has high adhesive strength and is not prone to generate defects such as cracks, film collapse or pits during use.
The thickness of the under film is preferably within a range of 1 to 35 percent of the sum of the diamond-like carbon film thickness and the under film thickness. When the thickness is below 1 percent, the effect of alleviating strain occurring internally in the diamond-like carbon film can not be achieved. When the thickness exceeds 35 percent, the protective effect of the hard surface treatment layer that protects the diamond-like carbon film from the rear against deformation or loads from the sliding surface side can not be obtained. Further, the scuffing resistance of the under film exposed after wear of the diamond-like carbon film is poor so that the scuffing resistance becomes low.
The under film of the present invention has a film thickness taking resistance to scuffing into account, and quickly wears away not to deteriorate resistance to scuffing after the diamond-like carbon film has fulfilled its job in the initial break-in period and worn away.
The hard surface treatment layer consisting of any one of a chromium plating film, a nitrided layer or an ion plating film has a high level of hardness and can protect the diamond-like carbon film from the rear against deformation or loads from the sliding surface side and can keep the piston ring resistant to wear after the diamond-like carbon film and under film have worn away.
The piston ring of the present invention as explained above, has a diamond-like carbon film with superior adhesive strength and has superior resistance to aluminum adhesion, resistance to scuffing and initial brea
Iwashita Takatsugu
Yamashita Nobuyuki
Armstrong Westerman Hattori McLeland & Naughton LLP
Browne Lynne H.
Pickard Alison K.
Teikoku Piston Ring Co. Ltd.
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