U.S. patent application number 12/295533 was filed with the patent office on 2009-05-07 for low-friction sliding mechanism.
Invention is credited to Makoto Kano, Jean Michel Martin, Takumaru Sagawa, Masahiko Watanabe.
Application Number | 20090118148 12/295533 |
Document ID | / |
Family ID | 38581151 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090118148 |
Kind Code |
A1 |
Martin; Jean Michel ; et
al. |
May 7, 2009 |
LOW-FRICTION SLIDING MECHANISM
Abstract
[Summary] [Object] To provide a low-friction sliding mechanism
capable of exhibiting an extremely excellent ultra-low friction
characteristics at a sliding face existing in a variety of uses.
[Solving means] A low-friction sliding mechanism is constituted by
disposing a lubricant containing glycerol, at a sliding face formed
between sliding members which have respectively hard carbon thin
films. A low-friction sliding mechanism is constituted by disposing
a lubricant containing hydroxyl group, at a sliding face formed
between sliding members which have respectively hard carbon thin
films, wherein a friction coefficient of smaller than 0.02 is
exhibited in a sliding contacting condition under a boundary
lubrication which exhibits a friction coefficient of 0.1 to 0.14 at
a sliding face between a steel and a steel in presence of an engine
oil. Each hard carbon thin film is formed of a-C or ta-C. Each hard
carbon thin film has a hardness of 1500 to 5000 Hv in micro-Vickers
hardness under a load of 10 g. Each hard carbon thin film has a
film thickness of 0.3 to 2.0 .mu.m. The lubricant containing
hydroxyl group is one of alcohols, and is glycerol.
Inventors: |
Martin; Jean Michel; (Chazay
d'Azergues, FR) ; Kano; Makoto; (Kanagawa, JP)
; Sagawa; Takumaru; (Kanagawa, JP) ; Watanabe;
Masahiko; (Saitama, JP) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Family ID: |
38581151 |
Appl. No.: |
12/295533 |
Filed: |
April 2, 2007 |
PCT Filed: |
April 2, 2007 |
PCT NO: |
PCT/JP2007/057409 |
371 Date: |
September 30, 2008 |
Current U.S.
Class: |
508/109 |
Current CPC
Class: |
C10M 105/14 20130101;
C10N 2080/00 20130101; C10N 2040/25 20130101; F16C 33/16 20130101;
C10N 2030/06 20130101 |
Class at
Publication: |
508/109 |
International
Class: |
C10M 129/06 20060101
C10M129/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2006 |
JP |
2006-102831 |
Mar 2, 2007 |
JP |
2007-052227 |
Claims
1. A low-friction sliding mechanism comprising sliding members
which respectively have hard carbon thin films between which a
sliding face is formed, and a lubricant containing glycerol,
existing at the sliding face.
2. A low-friction sliding mechanism comprising sliding members
which respectively have hard carbon thin films between which a
sliding face is formed, and a lubricant containing hydroxyl group,
existing at the sliding face, wherein a friction coefficient of
smaller than 0.02 is exhibited in a sliding contacting condition
under a boundary lubrication which exhibits a friction coefficient
of 0.1 to 0.14 at a sliding face between steels in presence of an
engine oil.
3. A low-friction sliding mechanism as claimed in claim 1, wherein
the hard carbon thin film is a diamond-like carbon thin film formed
of amorphous carbon (a-C) and/or tetrahedral carbon (ta-C).
4. A low-friction sliding mechanism as claimed in claim 1, wherein
the hard carbon thin film has a hardness of 1500 to 5000 Hv in
micro-Vickers hardness under a load of 10 g.
5. A low-friction sliding mechanism as claimed in claim 1, wherein
the hard carbon thin film has a hardness of 2000 to 3500 Hv in
micro-Vickers hardness under a load of 10 g.
6. A low-friction sliding mechanism as claimed in claim 1, wherein
the hard carbon thin film has a film thickness of 0.3 to 2.0
.mu.m.
7. A low-friction sliding mechanism as claimed in claim 1, wherein
the hard carbon thin film has a film thickness of 0.5 to 1.5
.mu.m.
8. A low-friction sliding mechanism as claimed in claim 2, wherein
the lubricant containing hydroxyl group is one of alcohols.
9. A low-friction sliding mechanism as claimed in claim 2, wherein
the lubricant containing hydroxyl group is glycerol.
10. A low-friction sliding mechanism as claimed in claim 1, wherein
hydrogen group and hydrogen group face each other to form a sliding
interface of a tribo-film, at the sliding face.
11. A low-friction sliding mechanism as claimed in claim 10,
wherein the hydrogen group is a part of the lubricant.
Description
TECHNICAL FIELD
[0001] This invention relates to a low-friction sliding mechanism,
and more particularly to a low-friction sliding mechanism capable
of improving a friction characteristics of a variety of sliding
faces, for example, in an internal combustion engine or a
drive-system transmission machine.
BACKGROUND ART
[0002] Global environmental problems such as global warming and
ozone layer destruction of whole the earth are coming to the fore.
As it has been said that the global warming is significantly
affected by CO.sub.2 emission, the reduction of CO.sub.2 emission,
notably the setting of CO.sub.2 emission standards, has become a
big concern to each country.
[0003] One of challenges to reduce CO.sub.2 emission is to lower an
energy loss due to friction loss of machines, facilities and the
like, particularly to improve a fuel economy of motor vehicles, in
which sliding materials and lubricants play important roles.
[0004] The roles of the sliding materials are to demonstrate an
excellent wear resistance and a low friction coefficient in a
section severe in frictional condition, sliding sections of an
engine, an electric motor, a fuel pump and the like, in which
application of a variety of hard thin films are recently
proceeding.
[0005] In general, a DLC (diamond-like carbon) material is low in
friction coefficient in air and in the absence of lubricating oil
as compared with abrasion-resistant hard coating materials such as
titanium nitride (TiN) and chromium nitride (CrN), and therefore it
is expected as a low friction sliding material.
[0006] As fuel economy improving measures or the role played by the
lubricating oil, the following are proposed: (1) lowering the
viscosity of the lubricating oil, thereby reducing viscous
resistance in hydrodynamic lubrication regions and agitation
resistance in the engine; and (2) adding an optimum friction
modifier and various additives into the lubricating oil so as to
reduce friction losses under the conditions of mixed lubrication
and boundary lubrication.
[0007] For example, for the friction modifier, many studies have
been made on and around organic molybdenum compounds such as
molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate
(MoDTP). As a result of the studies, a lubricating oil composition
blended with the organic molybdenum compound demonstrating an
excellent low friction coefficient at an initial period in use is
applied so as to be effective.
[0008] Such a friction characteristics of the DLC material and a
performance of the organic molybdenum compound as the friction
modifier are reported by, for example, non-patent literatures 1 and
2.
Non-patent literature 1: Japan Tribology Congress preliminary
theses, May 1999, Tokyo, Pages 11-12, KANO et al. Non-patent
literature: World Tribology Congress 2001. 9, Vienna, Proceeding
Page 342, KANO et al.
[0009] Additionally, it has been proposed to obtain a large
friction reduction by lubricating a DLC and an iron-based material,
an aluminum alloy, a magnesium alloy or a DLC material with an oil
agent containing an ester-based additive or the like (see, for
example, Patent literatures 1 to 4).
Patent literature 1: Patent Provisional Publication No. 2002-45576
Patent literature 2: Patent Provisional Publication No. 2002-322322
Patent literature 3: Patent Provisional Publication No. 2003-208193
Patent literature 4: Patent Provisional Publication No.
2003-207056
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0010] However, in the non-patent literature 1, it is reported that
general DLC materials excellent in low friction characteristics in
air are not always high in friction reduction effect in the
presence of a lubricating oil.
[0011] Additionally, in the non-patent literature 2, it is
understood that there is such a possibility that a friction
reduction effect cannot be sufficiently demonstrated even if a
lubricating oil composition containing an organic molybdenum
compound is applied to such a sliding material.
[0012] Further, in the above-mentioned patent literatures, it is
not disclosed to demonstrate a super friction characteristics in
which a friction coefficient exceeds a level of 1/1000 (smaller
than 0.01).
[0013] This invention has been made in view of such problems of the
conventional techniques and is intended to provide a low-friction
sliding mechanism in which sliding faces existing under various
applications can exhibit a highly excellent ultra-low friction
characteristics.
Means for Solving the Problems
[0014] As a result of eagerly conducted studies in order to solve
the above-mentioned problems, the present inventors have reached
completion of the present invention upon finding to solve the
above-mentioned problems by combining a lubricant containing
hydroxyl group with sliding members which have respectively hard
carbon thin films thereby forming a very thin and low shearing
stress compound at the surfaces of the members.
[0015] In other words, a low-friction sliding mechanism according
to the present invention is a low-function sliding mechanism
characterized in that a lubricant containing glycerol exists at a
sliding face which is formed between sliding members which
respectively have hard carbon thin films, or characterized in that
a friction coefficient of smaller than 0.02 is exhibited in a
sliding contacting condition under a boundary lubrication which
exhibits a friction coefficient of 0.1 to 0.14 at a sliding face
between steels in the presence of an engine oil, at the sliding
face which is formed between sliding members which respectively
have hard carbon thin films.
[0016] Additionally, a preferable embodiment of the low-friction
sliding mechanism according to the present invention is
characterized in that the above-mentioned hard carbon thin film is
a diamond-like carbon thin film formed of amorphous carbon (a-C)
and/or tetrahedral carbon (ta-C).
[0017] Further, another preferable embodiment of the low-friction
sliding mechanism according to the present invention is
characterized in that the hard carbon thin film has a hardness of
1500 to 5000 Hv in micro-Vickers hardness under a load of 10 g, and
the hard carbon thin film has a film thickness of 0.3 to 2.0
.mu.m.
[0018] Furthermore, a further preferable embodiment of the
low-friction sliding mechanism according to the present invention
is characterized in that the above-mentioned lubricant containing
hydroxyl group is one of alcohols, particularly glycerol.
EFFECTS OF THE INVENTION
[0019] The low-friction sliding mechanism according to the present
invention is constituted by combining a lubricant containing
glycerol with sliding members which respectively have hard carbon
thin films thereby forming a very thin and low shearing stress
compound, so as to making is possible to exhibit an extremely
excellent ultra-low friction characteristics at a sliding face
existing in a variety of uses.
THE BEST MODE FOR CARRYING OUT THE INVENTION
[0020] Hereinafter, the low-friction sliding mechanism according to
the present invention will be discussed further in detail. In the
specification and claims, [%] for concentration, content, filled
amount and the like is represented by "mass percent" unless
otherwise specified.
[0021] As discussed above, the low-friction sliding mechanism
according to the present invention is constituted by disposing a
lubricant containing glycerol or a lubricant containing hydroxyl
group to a sliding face formed between sliding members which
respectively have hard carbon thin films.
[0022] Additionally, a friction coefficient of not less than 0.02
is exhibited in a sliding contacting condition at the sliding face
under a boundary lubrication which exhibits a friction coefficient
of 0.1 to 0.14 at a sliding face between steels in the presence of
an engine oil.
[0023] With such a configuration, an organic compound layer having
hydroxyl group and very low in shearing stress is formed at the
surface of the sliding member, thereby exhibiting a ultra-low
friction characteristics.
[0024] A mechanism for forming this organic compound layer is not
apparent at the present time; however, it is assumed that hydrogen
group and hydrogen group face each other thereby to form a sliding
interface of a tribo-film at the sliding face. For example, as
shown in FIG. 2, it is considered that hydrogen groups forming part
of glycerol face each other thereby forming a sliding interface
under hydrogen-bonding, when glycerol is used as a lubricant.
[0025] Here, the above-mentioned sliding member is formed by
coating a base material with a hard carbon thin film.
[0026] Examples of the hard carbon thin film are crystalline or
amorphous thin films containing carbon, particularly a diamond thin
film, a diamond-like carbon (DLC) thin film, and the like.
[0027] This hard carbon thin film is preferably formed at whole the
sliding section of the sliding member and may be formed at a part
of the sliding section.
[0028] The above-mentioned DLC thin film is constituted of a
so-called DLC material. This DLC material is an amorphous material
principally formed of carbon atom and includes two carbon-to-carbon
bonding modes of a diamond structure (sp.sup.3 bonding) and a
graphite structure (sp.sup.2 bonding).
[0029] A specific example of the DLC material is a-C (amorphous
carbon) based material formed substantially of only carbon;
however, a ta-C (Tetrahedral Type amorphous carbon) based material
mainly formed of sp.sup.2 bonding may be suitably used.
[0030] The above-mentioned hard carbon thin film are affected by
kinds and required performances of objective sliding mechanisms,
kinds of materials constituting the sliding member, surface
roughness of the sliding section, and the like. For example, the
hard carbon thin film preferably has a surface hardness of 1500 to
5000 Hv in micro-Vickers hardness under a load of 10 g. The surface
hardness is more preferably 2000 to 4000 Hv, and particularly
preferably 2500 to 3500 Hv.
[0031] Additionally, the above-mentioned hard carbon thin film
preferably has a film thickness of 0.3 to 2.0 .mu.m. The film
thickness is more preferably 0.5 to 1.5 .mu.m and particularly
preferably 0.7 to 1.2 .mu.m.
[0032] If the surface hardness and film thickness are outside the
above-mentioned range so as to be smaller than 1500 Hv in hardness
and 0.3 .mu.m in thickness, abrasion tends to occur. To the
contrary, if they are outside the above-mentioned range so as to
exceed 3500 Hv in hardness and 2.0 .mu.m in thickness, peeling
tends to occur.
[0033] Further, the above-mentioned hard carbon thin film has a
surface roughness in Ra (according to JIS), preferably of not
larger than 1 .mu.m, more preferably of not larger than 0.05 .mu.m,
particularly preferably not larger than 0.03 .mu.m. If Ra exceeds 1
.mu.m, scuffing is locally formed, thereby resulting in the
possibility of largely increasing the friction coefficient.
[0034] The base material of the above-mentioned sliding members is
not particularly restricted, so that examples thereof are metal
materials and the like such as a ferrous material, an
aluminum-based material, a magnesium-based material, a
titanium-based material and the like. Examples of the base material
are also resinous materials such as various rubbers, plastics,
non-metal materials such as carbon and the like, and the like.
[0035] Particularly, the ferrous material, the aluminum-based
material and the magnesium-based material are preferable from the
viewpoints of being readily applicable to the sliding sections of
existing machines, apparatuses and the like and of capable of
extensively contributing to energy saving measures in various
fields.
[0036] The above-mentioned ferrous material is not particularly
restricted, and therefore not only iron of high purity but also
various ferrous alloys (containing nickel, copper, zinc, chromium,
cobalt, molybdenum, lead, silicon or titanium, any combination
thereof, or the like) can be used. Specific examples include
carburized steel SCM 420, SCr 420 (according to JIS) and the
like.
[0037] The above-mentioned aluminum-based material is not
particularly restricted, and therefore not only aluminum of high
purity but also various aluminum-based alloys can be sued.
Specifically, a hypo-eutectic or hyper-eutectic aluminum alloy and
the like containing, for example, silicon (Si) by 4 to 20% and
copper (Cu) by 1.0 to 5.0% is preferable. Preferred examples of the
aluminum alloy include AC2A, AC8A, ADC12, ADC14 (according to JIS)
and the like.
[0038] Further, a material formed by applying a thin film coating
of various kinds on these metal materials or non-metal materials
can be used as the base material. Specific examples of the material
are various metal materials such as the ferrous material, the
aluminum-based material, the magnesium-based material or the
titanium-based material mentioned above with a thin film coating of
TiN, CrN or the like.
[0039] As the sliding face formed between the above-mentioned
sliding members, all sliding faces each of which is formed between
the surfaces of two sliding members in such a manner that a
lubricant containing hydroxyl group exists at the sliding face can
be used without restriction. Examples of the sliding face are
sliding faces at sliding sections in an internal combustion engine
of a 4 stroke cycle engine or a 2 stroke cycle engine (for example,
a valve driving system, a piston, a piston ring, a piston skirt, a
cylinder liner, a connecting rod, a crank shaft, a bearing, a
roller bearing, a bearing metal, a gear, a chain, a belt, an oil
pump and the like), also at sliding sections in a drive system
transmission mechanism (for example, gears and the like), sliding
sections in a hard disc drive, and other various sliding faces
which are severe in frictional conditions and requiring low
friction characteristics.
[0040] The above-mentioned lubricant containing hydroxyl group is
not particularly restricted if it is an organic compound whose
molecule contains hydroxyl group.
[0041] The lubricant containing hydroxyl group may be, for example,
an organic compound is constituted of carbon, hydrogen and oxygen,
and may be an organic compound containing elements other than the
carbon, hydrogen and oxygen, such as nitrogen, sulfur, halogen
(fluorine, chlorine and the like), phosphorus, boron, a metal and
the like.
[0042] Particularly from the viewpoint of further reducing the
friction at the sliding face, it is preferable that the lubricant
containing hydroxyl group is one of alcohols. Additionally, the
alcohols have two or more hydroxyl groups in a molecule, so that
glycerol and the like are preferably used. For the same reason, the
lubricant containing hydroxyl group is preferably an organic
compound which is less in sulfur content or contains no sulfur.
[0043] Here, the above-mentioned alcohols are organic compounds
represented by the following general formula (1):
R--(OH).sub.n (1)
[0044] Examples of the organic compounds are compounds having one
or two hydroxyl groups in a molecule.
[0045] Specific examples of alcohols are (A) to (D) set forth
below. [0046] Monoalcohols (A) [0047] Dialcohols (B). [0048] Tri
and higher polyalcohols (C). [0049] Mixtures of one kind or more
kinds selected from the above-mentioned three kinds of alcohols
(D)
[0050] The above-mentioned monoalcohols (A) have one hydroxyl group
in a molecule, and include, for example, monohydric alkyl alcohols
having 1 to 40 carbon atoms (in which the alkyl group may be linear
or branched) such as methanol, ethanol, propanol (1-propanol,
2-propanol), butanol (1-butanol, 2-butanol, 2-methyl-1-propanol,
2-methyl-2-propanol), pentanol (1-pentanol, 2-pentanol, 3-pentanol,
2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol,
2-methyl-2-butanol, 2,2-dimethyl-1-propanol), hexanol (1-hexanol,
2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol,
2-methyl-3-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pentanol,
3-methyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl-2-pentanol,
2,3-dimethyl-1-butanol, 2,3-dimethyl-2-butanol,
3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,
2,2-dimethylbutanoyl), heptanol (1-heptanol, 2-heptanol,
3-heptanol, 2-methyl-1-hexanol, 2-methyl-2-hexanol,
2-methyl-3-hexanol, 5-methyl-2-hexanol, 3-ethyl-3-pentanol,
2,2-dimethyl-3-pentanol, 2,3-dimethyl-3-pentanol,
2,4-dimethyl-3-pentanol, 4,4-dimethyl-2-pentanol,
3-methyl-1-hexanol, 4-methyl-1-hexanol, 5-methyl-1-hexanol,
2-ethylpentanol), octanol (1-octanol, 2-octanol, 3-octanol,
4-methyl-3-heptanol, 6-methyl-2-heptanol, 2-ethyl-1-hexanol,
2-propyl-1-pentanol, 2,4,4-trimethyl-1-pentanol,
3,5-dimethyl-1-hexanol, 2-methyl-1-heptanol,
2,2-dimethyl-1-hexanol), nonanol (1-nonanol, 2-nonanol,
3,5,5-trimethyl-1-hexanol, 2,6-dimethyl-4-heptanol,
3-ethyl-2,2-dimethyl-3-pentanol, 5-methyloctanol, and the like),
decanol (1-decanol, 2-decanol, 4-decanol, 3,7-dimethyl-1-octanol,
2,4,6-trimethylheptanol, etc.), undecanol, dodecanol, tridecanol,
tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol
(stearyl alcohol, and the like), nonadecanol, eicosanol,
heneicosanol, tricosanol, tetracosanol; monohydric alkenyl alcohols
having 2 to 40 carbon atoms (in which the alkenyl group may be
linear or branched, and the double bond may be in any desired
position) such as ethenol, propenol, butenol, hexenol, octenol,
decenol, dodecenol, octadecenol (oleyl alcohol, and the like);
monohydric (alkyl)cycloalkyl alcohols having 3 to 40 carbon atoms
(in which the alkyl group may be linear or branched, and the alkyl
group and the hydroxyl group may be in any desired position) such
as cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol,
methylcyclopentanol, methylcyclohexanol, dimethylcyclohexanol,
ethylcyclohexanol, propylcyclohexanol, butylcyclohexanol,
dimethylcyclohexanol, cyclopentylmethanol, cyclohexylmethanol,
cyclohexylethanol (1-cyclohexylethanol, 2-cyclohexylethanol, and
the like), cyclohexylpropanol (3-cyclohexylpropanol, and the like),
cyclohexylbutanol (4-cyclohexylbutanol, and the like)
butylcyclohexanol, 3,3,5,5-tetramethylcyclohexanol, and the like;
(alkyl)aryl alcohols (in which the alkyl group may be linear or
branched, and the alkyl group and the hydroxyl group may be in any
desired position) such as phenyl alcohol, methylphenyl alcohol
(o-cresol, m-cresol, p-cresol), creosol, ethylphenyl alcohol,
propylphenyl alcohol, butylphenyl alcohol, butylmethylphenyl
alcohol (3-methyl-6-tert-butylphenyl alcohol, and the like),
dimethylphenyl alcohol, diethylphenyl alcohol, dibutylphenyl
alcohol (2,6-di-tert-butylphenyl alcohol, 2,4-di-tert-butylphenyl
alcohol, and the like), dibutylmethylphenyl alcohol
(2,6-di-tert-butyl-4-methylphenyl alcohol, and the like),
dibutylethylphenyl alcohol (2,6-di-tert-butyl-4-ethylphenyl
alcohol, and the like), tributylphenyl alcohol
(2,4,6-tri-tert-butylphenyl alcohol, etc.), naphthol
(.alpha.-naphthol, .beta.-naphthol, and the like), dibutylnaphthol
(2,4-di-tert-butyl-.alpha.-naphthol, and the like), and the like;
6-(4-hydroxy-3,5-di-tert-butylaniline)-2,4-bis(n-octylthio)-1,3-
,5-triazine, and the like; and their mixtures.
[0051] Of these monoalcohols, linear or branched alkyl or alkenyl
alcohols having from 12 to 18 carbon atoms such as oleyl alcohol
and stearyl alcohol are more preferable to be used from the
viewpoints of more effectively reducing the friction at the sliding
face and from the viewpoint of being low in volatility and of
capable of exhibiting a friction reduction effect even at a high
temperature condition, for example, a sliding condition in an
internal combustion engine or the like.
[0052] Dialcohols (B) are concretely those having two hydroxyl
groups in the molecule, and include, for example, alkyl or
alkenyldiols having 2 to 40 carbon atoms (in which the alkyl or
alkenyl group may be linear or branched, the double bond of the
alkenyl group may be in any desired position, and the hydroxyl
group may also be in any desired position) such as ethylene glycol,
diethylene glycol, polyethylene glycol, propylene glycol,
dipropylene glycol, polypropylene glycol, neopentyl glycol,
1,3-propanediol, 1,4-butanediol, 1,2-butanediol,
2-methyl-1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol,
2-ethyl-2-methyl-1,3-propanediol, 2-methyl-2,4-pentanediol,
1,7-heptanediol, 2-methyl-2-propyl-1,3-propanediol,
2,2-diethyl-1,3-propanediol, 1,8-octanediol, 1,9-nonanediol,
2-butyl-2-ethyl-1,3-propanediol, 1,10-decanediol,
1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol,
1,14-tetradecanediol, 1,15-heptadecanediol, 1,16-hexadecanediol,
1,17-heptadecanediol, 1,18-octadecanediol, 1,19-nonadecanediol,
1,20-eicosadecanediol, and the like; (alkyl)cycloalkanediols (in
which the alkyl group may be linear or branched, and the alkyl
group and the hydroxyl group may be in any desired position) such
as cyclohexanediol, methylcyclohexanediol, and the like; dihydric
(alkyl)aryl alcohols having from 2 to 40 carbon atoms (in which the
alkyl group may be linear or branched, and the alkyl group and the
hydroxyl group may be in any desired position) and the like such as
benzenediol (catechol, and the like), methylbenzenediol,
ethylbenzenediol, butylbenzenediol (p-tert-butylcatechol, and the
like) dibutylbenzenediol (4,6-di-tert-butylresorcinol, and the
like), 4,4'-thiobis(3-methyl-6-tert-butylphenol),
4,4'-butylidenebis(3-methyl-6-tert-butylphenol),
2,2'-methylenebis(4-methyl-6-tert-butylphenol),
2,2'-thiobis(4,6-di-tert-butylresorcinol),
2,2'-methylenebis(4-ethyl-6-tert-butylphenol),
4,4'-methylenebis(2,6-di-tert-butylphenol),
2,2'-(3,5-di-tert-butylhydroxy)propane,
4,4'-cyclohexylidenebis(2,6-di-tert-butylphenol), and the like;
p-tert-butylphenol/formaldehyde condensate,
p-tert-butylphenol/acetaldehyde condensate, and the like; and their
mixtures.
[0053] Of these dialcols, preferred to be used are ethylene glycol,
propylene glycol, neopentyl glycol, 1,4-butanediol,
1,5-pentanediol, neopentyl glycol, 1,6-hexanediol,
2-methyl-2,4-pentanediol, 2-ethyl-2-methyl-1,3-propanediol,
1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol,
1,11-undecanediol, 1,12-dodecanediol, and the like, from the
viewpoint of capable of more effectively reducing the friction at
the sliding face. In addition, high-molecular-weight hindered
alcohols having a molecular weight of not less than 300, preferably
not less than 400 such as
2,6-di-tert-butyl-4-(3,5-di-tert-butyl-4-hydroxybenzyl)phenyl
alcohol are also preferred from the viewpoint of being hardly
volatile even at high temperature conditions (for example, in a
sliding condition in an internal-combustion engine or the like) and
excellent in heat resistance, being capable of exhibiting a
friction reduction effect and providing an excellent antioxidation
stability.
[0054] Tri- and higher polyalcohols are concretely those having
three or more hydroxyl groups. In general, tri- to deca-alcohols,
preferably tri- to hexa-alcohols are used. Examples of these
components are trimethylolalkanes such as glycerin,
trimethylolethane, trimethylolpropane, trimethylolbutane; as well
as erythritol, pentaerythritol, 1,2,4-butanetriol,
1,3,5-pentanetriol, 1,2,6-hexanetriol, 1,2,3,4-butanetetrol,
sorbitol, adonitol, arabitol, xylitol, mannitol; and their polymers
or condensates (e.g., glycerin dimers to octamers and the like such
as diglycerin, triglycerin, tetraglycerin and the like;
trimethylolpropane dimers to octamers and the like such as
ditrimethylolpropane; pentaerythritol dimers to tetramers and the
like such as dipentaerythritol and the like; sorbitan; condensates
such as sorbitol/glycerin condensate (including intramolecular
condensates, intermolecular condensates, and self-condensates), and
the like.
[0055] Saccharides such as xylose, arabitol, ribose, rhamnose,
glucose, fructose, galactose, mannose, sorbose, cellobiose,
mantose, isomaltose, trehalose, sucrose and the like are also
usable.
[0056] Of these tri- and higher polyalcohols, more preferred are
polyalcohols of tri to hexa-alcohols such as glycerin,
trimethylolalkanes (e.g., trimethylolethane, trimethylolpropane,
trimethylolbutane), pentaerythritol, 1,2,4-butanetriol,
1,3,5-pentanetriol, 1,2,6-hexanetriol, 1,2,3,4-butanetetrol,
sorbitol, sorbitan, sorbitol/glycerin condensate, adonitol,
arabitol, xylitol, mannitol, and the like, and their mixtures; and
even more preferred are glycerin, trimethylolethane,
trimethylolpropane, pentaerythritol, sorbitan and their mixtures.
Especially preferred are polyalcohols having a hydroxyl group
content of not less than 20%, preferably not less than 30%, more
preferably not less than 40%. Polyalcohols that are higher than
hexa-alcohols will too much increase the viscosity.
[0057] The above-mentioned lubricant containing hydroxyl group is
further blended with one or combination of plural kinds selected
from an ashless dispersant, an abrasion preventing agent or extreme
pressure agent, a metal-based cleaning agent, an antioxidant, a
viscosity index improving agent, a friction modifier, an
antirusting agent, a nonionic surfactant, a demulsification agent,
a metal deactivator, a defoaming agent, and the like, thereby to be
improved in required performances.
[0058] The low-friction sliding mechanism having the
above-mentioned configuration, according to the present invention
exhibits a friction coefficient of smaller than 0.02, preferably
smaller than 0.01 in a sliding contacting condition under a
boundary lubrication which exhibits a friction coefficient of 0.1
to 0.14 at a sliding face formed between steel and steel in the
presence of an engine oil.
[0059] Here, typical examples of the engine oil is a 5W-30SF engine
oil and the like which do not contain a friction modifier such as
MoDTC and the like.
[0060] Additionally, examples of the above-mentioned steel are
SNC415, SNC815 SNCM220, SNCM415, SNCM420, SNCM616, SNCM815 SCr415,
SCr420, SCM415, SCM418, SCM420, SCM421, SCM822, SMn420, SMnC420
(according to JIS), and the like; however, the above-mentioned
steel is not limited to these.
EXAMPLE
[0061] Hereinafter, the present invention will be discussed with
reference to Examples and Comparative Examples; however, the
present invention is not limited to these Examples.
Examples 1 to 9, and Comparative Examples 1 to 3
[0062] As shown in FIG. 3, as a sliding mechanism of each Example,
a reciprocating sliding friction tester was used in which a
reciprocating pin was pressed on a fixed disc plate wetted with a
lubricating oil. At this time, a load is 400 N, the pin had a
dimension of 22 mm.times.18 mm diameter, and a plate had a
dimension of 8 mm.times.24 mm.
[0063] Additionally, friction sliding specimens of respective
Examples were produced according to the specifications of materials
as shown in Table 1 mentioned below.
[0064] The plate was formed of SCM415 carburized steel and of
cemented carbide in a part of Examples.
[0065] Additionally, 5 ml of a lubricant shown in Table 1 was
dropped on the obtained plate in such a manner that the surface of
the plate was uniformly wetted with the lubricant.
[0066] In Examples 1 to 9 and Comparative Examples 1 and 2,
glycerol 100% was used as the lubricant.
[0067] In Comparative Example 3, a lubricant used was prepared by
adding 1.0% of GMO (glycerol monooleate) to PAO
(poly.alpha.-olefin) as a lubricant base oil.
[0068] In Comparative Examples 4 and 5, a 5W-30 engine oil was used
as the lubricant.
[0069] The pin was formed of a SUJ2 (according to JIS) heat-treated
material and had a finished surface on which a variety of coatings
were formed by PVD treatments.
[0070] In Table 1, "a-C" indicates amorphous carbon, in which a DLC
having a hardness of lower than 2000 Hv was coated by a UBM
(Unbalanced Magnetron Sputtering) process, while a DLC having a
hard DLC having a hardness of not lower than 2000 Hv was coated by
an arc ion plating process.
[0071] Additionally, the surface hardness and the surface roughness
in Table 1 are values which were obtained after the final
finishing, i.e., after the finishing for the specimen with no
coating, and after the coating for the specimen with coating.
TABLE-US-00001 [Reciprocating sliding friction test] Lubricating
oil supply manner No supply from outside Plate temperature
80.degree. C. Maximum Hertz's pressure 270 MPa Amplitude of
reciprocating movement 3 mm Frequency of reciprocating movement 50
Hz Test time 15 min
TABLE-US-00002 TABLE 1 Pin-on-disc materials Surface Surface
Lubricant Plate Pin Film thickness hardness roughness specification
Base Base .mu.m Plate Pin Ra .mu.m Lubricant Friction Example
material Coating material Coating Plate Pin Hv Hv Plate Pin used
coefficient Example 1 SCM415 a-C SUJ2 heat- a-C 0.7 1.1 1500 1600
0.03 0.03 Glycerol 0.009 carburized treated material Example 2
SCM415 a-C SUJ2 heat- a-C 0.8 1.8 1600 1800 0.03 0.03 Glycerol
0.008 carburized treated material Example 3 SCM415 a-C SUJ2 heat-
a-C 0.8 0.9 1600 1500 0.05 0.05 Glycerol 0.008 carburized treated
material Example 4 SCM415 a-C SUJ2 heat- ta-C 0.9 0.9 1600 2800
0.05 0.05 Glycerol 0.008 carburized treated material Example 5
SCM415 ta-C SUJ2 heat- ta-C 1.1 0.9 2900 2800 0.04 0.05 Glycerol
0.007 carburized treated material Example 6 SCM415 ta-C SUJ2 heat-
ta-C 1.1 0.8 2900 2700 0.05 0.02 Glycerol 0.007 carburized treated
material Example 7 SCM415 ta-C SUJ2 heat- ta-C 0.9 1.1 2800 2900
0.05 0.03 Glycerol 0.007 carburized treated material Example 8
Cemented ta-C SUJ2 heat- ta-C 0.3 0.9 2800 3500 0.05 0.10 Glycerol
0.007 carbide treated WC-Co material Example 9 Cemented ta-C SUJ2
heat- ta-C 0.7 0.3 3200 2900 0.05 0.04 Glycerol 0.007 carbide
treated WC-Co material Comparative SCM415 a-C SUJ2 heat- Nil 0.8
1600 750 0.10 0.03 Glycerol 0.02 example 1 carburized treated
material Comparative SCM415 ta-C SUJ2 heat- Nil 0.8 2700 750 0.04
0.03 Glycerol 0.03 example 2 carburized treated material
Comparative SCM415 ta-C SUJ2 heat- ta-C 0.9 0.8 2800 2700 0.04 0.04
PAO + GMO 1 mass % 0.02 example 3 carburized treated material
Comparative SCM415 ta-C SUJ2 heat- ta-C 0.8 1.1 2700 2900 0.10 0.03
5W-30 engine oil 0.06 example 4 carburized treated material
Comparative SCM415 Nil SUJ2 heat- Nil 710 750 0.05 0.03 5W-30
engine oil 0.14 example 5 carburized treated material Number
indicates mass % *PAO: Poly Alpha-Olefin *GMO: Glycerol
monooleate
[0072] As depicted in Table 1, in the cases that sliding was made
under the combination of the coating film obtained in Examples 1 to
9 and the lubricant, an excellent ultra-low friction called
"Super-low friction" at which the friction coefficient was lower
than 0.01 was exhibited in any case.
[0073] In the cases (Comparative Examples 1 and 2) that sliding was
made under the combination of a steel material and a steel material
(as base materials) either one of which was without coating of DLC,
and in the cases (Comparative Examples 3 and 4) that sliding was
made under the combination of the specimens with the lubricant
containing no hydroxyl group, the friction coefficient could not
lower below 0.01.
[0074] As understood from Comparative Example 5, the sliding
mechanisms of Examples 1 to 9 which were within the preferable
ranges of the present invention lower two digits in friction
coefficient as compared with a case that sliding was made under a
widely used combination of sliding materials of steel-to-steel and
an engine oil.
[0075] Additionally, in Examples 1 to 9, it was confirmed that no
problem arises in shape of the plates and the pins after the test,
and the specimens were very excellent in abrasion resistance.
[0076] It was confirmed that Examples 5 to 9 using the hard DLC
(ta-C based) formed by the ion plating process were further
improved in friction reduction effect as compared with Examples 1
to 4 using the relatively soft DLC material coated by the UBM
process.
[0077] Accordingly, it was confirmed that the thin film formed of
the ta-C based DLC material providing a high friction reduction
effect was more effective as a DLC thin film.
[0078] Thus, a remarkable friction reduction effect can be expected
to all mechanical sliding parts. For example, a remarkable effect
in direct connection with a fuel economy improvement for an
automotive engine can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0079] FIG. 1 is an explanatory view showing the ranges of a a-C
based material and a ta-C based material.
[0080] FIG. 2 is a schematic illustration of an organic compound of
a low shearing stress.
[0081] FIG. 3 is a rough perspective view showing a reciprocating
sliding type friction testing method.
EXPLANATION OF REFERENCE NUMERALS
[0082] 1 pin [0083] 2 plate
* * * * *