Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Heterocyclic ring compound; a heterocyclic ring is one...
Reexamination Certificate
2003-01-31
2004-10-19
McAvoy, Eileen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Heterocyclic ring compound; a heterocyclic ring is one...
C508S371000, C508S486000, C508S487000, C508S545000, C123S00100A
Reexamination Certificate
active
06806242
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sliding mechanism having excellent low-friction characteristics, particularly of the kind for use in an internal combustion engine.
Global environmental problems, such as global warming and ozone layer destruction, have been coming to the fore. It is said that the global warming is significantly effected by CO
2
emission. The reduction of CO
2
emission, notably the setting of CO
2
emission standards, has therefore become a big concern to each country.
One of challenges to reduce CO
2
emission is to improve vehicle fuel efficiency, and the sliding mechanism of a vehicle engine is largely involved in the improvements in vehicle fuel efficiency. There are the following approaches to improving the vehicle efficiency in terms of the sliding mechanism: (1) to provide a higher abrasion resistance and a lower friction coefficient for sliding members of the sliding mechanism, which are generally made of steel materials in the earlier technology, even under extreme conditions of abrasion and friction; (2) to decrease the viscosity of a lubricant in the sliding mechanism, thereby reducing viscous resistance in hydrodynamic lubrication regions and agitation resistance in the engine; and (3) to mix a suitable friction modifier and other additives into the lubricant so as to reduce friction losses under the conditions of mixed lubrication and boundary lubrication. Heretofore, researches have been made on an organomolybdenum compound, such as molybdenum dithiocarbamate (MoDTC) or molybdenum dithiophosphate (MoDTP), for use as the friction modifier and show that the lubricant containing such an organomolybdenum compound is effective in reducing friction when used for the steel sliding members.
SUMMARY OF THE INVENTION
Various hard coating materials have been recently applied to the sliding member of the sliding mechanism in order to attain high abrasion resistance and a low friction coefficient. In particular, a diamond-like carbon (DLC) material is expected to be useful as a coating material for the sliding member, because the DLC material provides a lower friction coefficient in the air than that of another abrasion-resistant hard coating material (such as TiN or CrN).
However, the DLC material does not provide such a low friction coefficient in the sliding mechanism in the presence of lubricant (as disclosed in Japan Tribology Congress 1999. 5, Tokyo, Proceeding Page 11-12, KANO et.al.). The friction coefficient of the DLC material cannot be lowered to a sufficient degree even when used in combination with the lubricant containing the above organomolybdenum compound (as disclosed in World Tribology Congress 2001. 9, Vienna, Proceeding Page 342, KANO et.al.).
It is therefore an object of the present invention to provide a sliding mechanism that can attain excellent low-friction characteristics and high abrasion resistance by the combined use of a diamond-like carbon material and a lubricant, so that the sliding mechanism, when used in a vehicle engine, shows more improvements in vehicle fuel efficiency than that of the earlier technology.
According to an aspect of the present invention, there is provided a low-friction sliding mechanism, comprising: first and second sliding members slidable relative to each other at sliding surfaces thereof, the first sliding member being made of a diamond-like carbon material, the second sliding member being made of an iron-based material; and a lubricant applied to the sliding surfaces of the first and second sliding members and comprising at least one of an ashless fatty-ester friction modifier and an ashless aliphatic-amine friction modifier.
DESCRIPTION OF THE EMBODIMENTS
The present invention will be described below in detail. In the following description, all percentages (%) are by mass unless otherwise specified.
A sliding mechanism according to the present invention comprises first and second sliding members slidable relative to each other at sliding surfaces thereof and a lubricant applied to the sliding surfaces of the first and second sliding members.
The first sliding member is made of a diamond-like carbon (DLC) material. The DLC material is an amorphous form of carbon in which carbon exists in both sp
2
and sp
3
hybridizations so as to form a composite structure of graphite and diamond. Specific examples of the DLC material usable in the present invention include hydrogen-free amorphous carbon (a-C) consisting of carbon, hydrogen-containing amorphous carbon (a-C:H) and metal carbide (MeC) containing a metal element of titanium (Ti) or Molybdenum (Mo). In the present invention, especially preferred is hydrogen-free amorphous carbon (a-C) for significant reduction in friction.
The second sliding member is made of an iron-based material. Specific examples of the iron-based material usable in the present invention include: low-alloy chilled cast iron; carburized steel based on e.g. SCM420 (according to JIS G4105) and SCr420 (according to JIS G4104); heat-treated carbon steel based on e.g. S40C (according to JIS G 4051); and mixtures of two or more thereof.
Each of the first and second sliding members preferably has at the sliding surface thereof an arithmetic mean surface roughness Ra of 0.1 &mgr;m or less for stable sliding contact. When the surface roughness Ra exceeds 0.1 &mgr;m, there arises a possibility of localized scuffing in the sliding surface so that the friction coefficient between the sliding surfaces becomes largely increased.
Further, the first sliding member preferably has a micro Vickers hardness Hv of 1,000 to 3,500 (with a 1 kg load applied) at the sliding surface thereof and a thickness t of 0.3 to 2.0 &mgr;m, and the second sliding member preferably has a Rockwell hardness HRC of 45 to 60 on C scale at the sliding surface thereof. This makes it possible to maintain the durability of the first and second sliding members even under the sliding condition of a high surface pressure of about 700 MPa (that corresponds to the pressure condition of an engine cam mechanism). When the micro Vickers hardness Hv and the thickness t are less than 1,000 and 0.3 &mgr;m, respectively, the first sliding member tends to wear out. On the other hand, when the micro Vickers hardness Hv and the thickness t exceed 3,500 and 2.0 &mgr;m, respectively, the first sliding member tends to flake off. When the Rockwell hardness HRC is less than 45, the second sliding member tends to buckle under a high surface pressure.
The lubricant comprises a base oil and at least one of an ashless fatty-ester friction modifier and an ashless aliphatic-amine friction modifier.
The base oil is not particularly limited, and can be any oil compounds commonly used for a lubricant, such as mineral oil or synthetic oil.
Specific examples of the mineral oil include oil compounds prepared by extracting a lubricant fraction from petroleum by atmospheric or reduced-pressure distillation and then purifying the obtained lubricant fraction by at least one of the following treatments: solvent deasphalting, solvent extraction, hydrogenolysis, solvent dewaxing, hydrotreating and wax isomerization. In the present invention, the mineral oil prepared through hydrogenolysis, hydrotreating and/or wax isomerization is preferably used.
Specific examples of the synthetic oil include: alkylbenzenes, alkylnaphthalenes, polybutenes and hydrides thereof; poly-&agr;-olefins, such as 1-octene oligomer and 1-decene oligomer, and hydrides thereof; diesters, such as ditridecyl glutarate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate and dioctyl sebacate; polyol esters, such as trimethylolpropane caprylate, trimetylolpropane pelargonate, pentaerythritol-2-ethyl hexanoate and pentaerythritol pelargonate; and mixtures thereof. Among these synthetic oil compounds, preferred are poly-&agr;-olefins, such as 1-octene oligomer and 1-decene oligomer and hydrides thereof.
The above-mentioned mineral and synthetic oil compounds may be used alone, or in the form of a mixture of any two or more thereof with no limitation on its mixture
Kano Makoto
Konishi Shozaburo
Sakane Tokio
Shirahama Shinichi
Yasuda Yoshiteru
Foley & Lardner LLP
McAvoy Eileen M.
Nissan Motor Co,. Ltd.
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