U.S. patent application number 10/914506 was filed with the patent office on 2005-05-12 for valve lifter for internal combustion engine.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Hamada, Takahiro, Nishimura, Kimio.
Application Number | 20050098134 10/914506 |
Document ID | / |
Family ID | 34067367 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050098134 |
Kind Code |
A1 |
Nishimura, Kimio ; et
al. |
May 12, 2005 |
Valve lifter for internal combustion engine
Abstract
A valve lifter for an automotive internal combustion engine. The
valve lifter includes a main body formed of one of an aluminum
alloy and an iron-based alloy as a base material and having a top
surface and a side surface which are respectively in slidable
contact with opposite members in presence of at least one of a
lubricating oil and a lubricant. Additionally, a hard carbon thin
film is formed on the main body to cover the top surface and the
side surface, the hard carbon thin film containing hydrogen atom in
an amount of not more than 1 atomic %.
Inventors: |
Nishimura, Kimio; (Yokohama,
JP) ; Hamada, Takahiro; (Yokohama, JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
34067367 |
Appl. No.: |
10/914506 |
Filed: |
August 10, 2004 |
Current U.S.
Class: |
123/90.51 ;
123/90.48 |
Current CPC
Class: |
F01L 1/143 20130101;
C23C 14/0605 20130101; F01L 2301/00 20200501; F01M 9/104 20130101;
F01L 1/16 20130101 |
Class at
Publication: |
123/090.51 ;
123/090.48 |
International
Class: |
F01L 001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 11, 2003 |
JP |
2003-207037 |
Jun 29, 2004 |
JP |
2004-190969 |
Claims
What is claimed is:
1. A valve lifter for an internal combustion engine, comprising a
main body formed of a metal as a base material and having a top
surface and a side surface which are respectively in slidable
contact with opposite members in presence of a lubricant; and a
hard carbon thin film formed on the main body to cover the top
surface and the side surface, the hard carbon thin film containing
hydrogen atom in an amount of not more than 20 atomic %.
2. A valve lifter as claimed in claim 1, wherein the lubricant
contains at least one friction modifier selected from the group
consisting of ashless fatty acid ester friction modifier and
ashless aliphatic amine friction modifier.
3. A valve lifter as claimed in claim 2, wherein the at least one
friction modifier has a C.sub.6-C.sub.30 hydrocarbon chain and is
contained in an amount of 0.05 to 3.0% by mass based on a total
mass of the at least one of a lubricating oil and a lubricant.
4. A valve lifter as claimed in claim 2, wherein the lubricant
contains at least one compound selected from the group consisting
of polybutenyl succinimide and a derivative of polybutenyl
succinimide.
5. A valve lifter as claimed in claim 4, wherein the at least one
compound selected from the group consisting of polybutenyl
succinimide and a derivative of polybutenyl succinimide is
contained in an amount of 0.1 to 15% by mass based on a total mass
of the one of the lubricating oil and lubricant.
6. A valve lifter as claimed in claim 2, wherein the lubricating
oil contains zinc dithiophosphate in an amount of 0.1% or less by
mass in terms of a phosphorus element based on a total mass of the
at least one of a lubricating oil and a lubricant. oil and a
lubricant.
7. A valve lifter as claimed in claim 1, wherein the lubricant has
a main component which is a compound containing hydroxyl group.
8. A valve lifter as claimed in claim 7, wherein the compound is at
least one of alcohols.
9. A valve lifter as claimed in claim 8, wherein the at least of
alcohols is at least one of glycerol and ethylene glycol.
10. A valve lifter as claimed in claim 1, wherein the main body
includes a top wall section and a side wall section which are
integral with each other, the top wall section having the top
surface, the side wall section having the side surface.
11. A valve lifter as claimed in claim 1, wherein the metal is at
least one of aluminum alloy and an iron-based alloy.
12. A valve lifter as claimed in claim 1, wherein the lubricant
includes a lubricating oil.
13. A valve lifter as claimed in claim 1, wherein the hard carbon
thin film contains hydrogen atom in an amount of not more than 10
atomic %.
14. A valve lifter as claimed in claim 1, wherein the hard carbon
thin film contains hydrogen atom in an amount of not more than 0.5
atomic %.
15. A valve lifter as claimed in claim 1, wherein the hard carbon
thin film contains hydrogen atom in an amount of not more than 1
atomic %.
16. A method of making a valve lifter for an internal combustion
engine, comprising: preparing a main body of the valve lifter,
formed of one of an aluminum alloy and an iron-based alloy as a
base material and having a top surface and a side surface; forming
a hard carbon thin film on the main body to cover the top surface
and the side surface by a PVD process, the hard carbon thin film
containing hydrogen atom in an amount of not more than 20 atomic %;
and providing a lubricant between the main body of the valve lifter
and the hard carbon thin film.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application has the following related applications:
U.S. application Ser. No. 09/545,181 based on Japanese Patent
Application Hei-11-102205 filed Apr. 9, 1999; Ser. No. 10/468,713
which is the designated state (United States) application number of
PCT Application JP02/10057 based on Japanese Patent Application
2001-117680 filed Apr. 17, 2001; Ser. No. 10/355,099 based on
Japanese Patent Application 2002-45576 filed Feb. 22, 2002; Ser.
No. 10/682,559 based on Japanese Patent Application 2002-302205
filed Oct. 16, 2002; and Ser. No. 10/692,853 based on Japanese
Patent Application 2002-322322 filed Oct. 16, 2002.
BACKGROUND OF THE INVENTION
[0002] This invention relates to improvements in a valve lifter
interposed between a cam lobe of a camshaft and a valve stem so as
to convert rotation of the camshaft to opening and closing actions
of an intake or exhaust valve, for example, in an automotive
internal combustion engine, more particularly to the improvements
in the valve lifter for the internal combustion engine, formed of
an aluminum alloy so as to be light in weight and low in
friction.
[0003] In such a directly driven valve operating system in an
automotive internal combustion engine that intake and exhaust
valves are directly driven by a camshaft, a valve lifter formed of
an iron-based material has been conventionally employed taking
account of reliability. Additionally, the valve lifter in direct
contact with the camshaft is produced upon being subjected to a
treatment of nitriding made at the top surface thereof and a
treatment for obtaining a mirror finished surface in order to
ensure a wear resistance and to lower a friction.
[0004] In recent years, in order to improve a fuel economy, a
weight-lightening is being accomplished by employing a valve lifter
having no shim so as to reduce the load applied to a valve spring.
Furthermore, it has been studied to form the valve lifter of an
aluminum alloy in order to lighten the weight of the valve lifter
itself, as disclosed in Japanese Patent Provisional Publication No.
11-22423.
SUMMARY OF THE INVENTION
[0005] With the above conventional valve lifters, a major part of
friction in the valve operating system is occupied by a friction
between the top surface of the valve lifter and the cam lobe of the
camshaft and another friction between the side surface of the valve
lifter and the lifter bore of the cylinder head. On these days
requiring improved fuel economy, it is very important to reduce
such frictions; however, it will be understood that there is a
limit to reduce the frictions with the above-discussed valve
lifters having conventional structures.
[0006] It is, therefore, an object of the present invention to
provide an improved valve lifter for an internal combustion engine,
which can overcome drawbacks encountered in conventional valve
lifters for internal combustion engines.
[0007] Another object of the present invention is to provide an
improved valve lifter for an internal combustion engine, which can
greatly reduce frictions between the valve lifter and opposite
members, such as a friction between the top surface of the valve
lifter and the cam lobe of a camshaft and another friction between
the side surface of the valve lifter and the surface of a lifter
bore, thereby improving performance and durability reliability of
the engine while improving fuel economy of the engine.
[0008] An aspect of the present invention resides in a valve lifter
for an internal combustion engine. The valve lifter comprises a
main body formed of a metal as a base material and having a top
surface and a side surface which are respectively in slidable
contact with opposite members in presence of a lubricant.
Additionally, a hard carbon thin film is formed on the main body to
cover the top surface and the side surface, the hard carbon thin
film containing hydrogen atom in an amount of not more than 20
atomic %.
[0009] Another aspect of the present invention resides in a method
of producing a valve lifter for an internal combustion engine. The
producing method comprises (a) preparing a main body of the valve
lifter, formed of a metal as a base material and having a top
surface and a side surface; and (b) forming a hard carbon thin film
on the main body to cover the top surface and the side surface by a
PVD process, the hard carbon thin film containing hydrogen atom in
an amount of not more than 20 atomic %.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a vertical sectional view of an embodiment of a
valve lifter for an internal combustion engine, according to the
present invention; and
[0011] FIG. 2 is a vertical sectional view of a valve operating
mechanism using the valve lifter of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present invention will be discussed below in detail. In
the following description, all percentages (%) are by mass unless
otherwise specified.
[0013] Referring now to FIG. 1, an embodiment of valve lifter 1 is
shown including reversed cup-shaped main body or base material 1b
formed of an aluminum alloy. The main body 1b may be formed of an
iron-based alloy. Base material 1b has a cylindrical side wall
section and an annular top wall section which are integral with
each other. Hard carbon thin film 1a is formed or coated at the
outer peripheral surface of cylindrical side wall section and at
the top or outer surface of top wall section. Hard carbon thin film
1a is contiguous to cover the whole outer peripheral surface of
reversed cup-shaped base material 1b. Hard carbon thin film 1a has
a hydrogen (atom) content of not more than 1 atomic %.
[0014] As shown in FIG. 2, valve lifter 1 forms part of a valve
operating mechanism. Valve lifter 1 provided with hard carbon thin
film 1a is movably disposed within a lifter bore 3a of a cylinder
head 3 and installed at the upper end of valve stem 2 forming part
of an engine (intake or exhaust) valve. Valve stem 2 is biased
upward together with valve lifter 1 by a compression coil spring 4
so as to maintain a valve closing condition of the engine valve.
When camshaft 5 rotates, cam lobe 5a of camshaft 5 pushes downward
valve lifter 1 together with valve stem 2 against the biasing force
of coil spring 4, so that the valve opening and closing actions of
the engine valve is carried out at a cycle in accordance with an
engine speed of the engine.
[0015] In this embodiment, hard carbon thin film 1a containing
hydrogen (atom) in an amount of not more than 1 atomic % is formed
at the top surface and the cylindrical side surface of valve lifter
1. The top surface of valve lifter 1 is in slidable contact with
cam lobe 5a of camshaft 5 as an opposite member. The cylindrical
side surface of valve lifter 1 is in slidable contact with the
cylindrical surface of lifter bore 3a of the cylinder head 3 as
another opposite member. By virtue of this hard carbon thin film
1a, the above slidably contactable top and cylindrical side
surfaces of valve lifter 1 is lowered in friction coefficient in
presence of a lubricating oil and/or lubricant. Additionally, hard
carbon thin film 1a is sufficiently high in hardness and therefore
greatly improves a scuffing resistance and a wear resistance of the
valve lifter, thereby contributing to improving performance and
durability-reliability of the internal combustion engine.
[0016] Hard carbon thin film 1a is formed of, for example, DLC
(diamond-like carbon) material which is mainly constituted of
carbon atom. The DLC material takes a diamond structure (SP.sup.3
bonding) and/or a graphite structure (SP.sup.2 bonding) in bonding
mode among carbons. More specifically, the hard carbon (DLC) thin
film 1a is formed of hydrogen-free amorphous carbon (a-C) that
consists of carbon, hydrogen-containing amorphous carbon (a-C:H),
or metal carbide or metal carbon (MeC) that contains as a part a
metal element of titanium (Ti) or Molybdenum (Mo). For a
significant reduction in friction, it is preferable that the DLC
material is as low as possible in hydrogen (atom) content and
therefore has a hydrogen content of not more than 1 atomic %. As
the hydrogen content in the hard carbon thin film increases, the
friction coefficient increases. If the hydrogen content exceeds 1
atomic %, it is difficult to sufficiently lower the friction
coefficient during slidable contact of the valve lifter to opposite
members such as the cam lobe and the cylindrical surface of the
lifter bore 3a.
[0017] The hard carbon thin film having such a low hydrogen content
is obtained by a PVD process that substantially does not use
hydrogen and/or hydrogen-containing compound, such as a sputtering
process or an ion plating process. In this case, it is preferable
to carrying out a film-forming operation for the hard carbon thin
film upon baking of a reactor and tools for supporting the base
material and upon sufficiently cleaning the surface of the base
material in order to reduce the hydrogen content in the hard carbon
thin film, in addition to using gas containing no hydrogen during
the film-forming operation. The hard carbon thin film may be
obtained by a CVD process.
[0018] Next, the lubricating oil and/or lubricant (composition)
used for the vale lifter according to the present invention will be
discussed.
[0019] The lubricating oil and/or lubricant (composition)
preferably includes a base oil and at least one of an ashless fatty
acid ester (ester of fatty acid) friction modifier and an ashless
aliphatic amine friction modifier. In other words, the ashless
fatty acid ester friction modifier and/or aliphatic amine friction
modifier are/is contained in the base oil. Such a lubricating oil
and/or lubricant is presence at a slidably contacting surface
formed between the top surface of valve lifter 1 and another
slidably contacting surface formed between the cylindrical side
surface of valve lifter 1 and the cylindrical surface of lifter
bore 3a, thereby achieving an extremely low friction coefficient at
the slidably contacting surfaces.
[0020] Here, the base oil is not particularly limited and can be
any base oil (compound or compounds) commonly used for a
lubricating oil and/or lubricant, such as a mineral oil, a
synthetic oil, an oil and fat (compound), or any combination of the
mineral oil, the synthetic oil and the oil and fat.
[0021] Specific examples of the mineral oil include paraffin-based
or naphthene-based oil, and n-paraffin, prepared by extracting a
lubricating oil and/or lubricant fraction from petroleum by
atmospheric or reduced-pressure distillation, and then, purifying
the obtained lubricating oil and/or lubricant fraction by using at
least one of the following treatments: solvent deasphalting,
solvent extraction, hydrogenolysis, solvent dewaxing, hydrogenation
purification, sulfuric acid treatment, clay treatment and the like
which may be used in suitable combination. It is general to purify
the obtained lubricating oil and/or lubricant fraction by using
hydrogenation purification or solvent purification. Additionally,
it is preferable to use the mineral oil which is obtained by
purifying the lubricating oil and/or lubricant fraction using
high-hydrogenolysis process which is capable of largely decreasing
aromatic components, or the mineral oil produced by a process for
isomerizing GTL (gas to liquid) Wax.
[0022] Specific examples of the synthetic oil include:
poly-.alpha.-olefins (such as 1-octene oligomer, 1-decene oligomer
and ethylene-propylene oligomer), hydrides of poly-.alpha.-olefins,
isobutene oligomers, hydrides of isobutene oligomers, isoparaffins,
alkylbenzenes, alkylnaphthalenes, diesters (such as ditridecyl
glutarate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate
and dioctyl sebacate), polyol esters (such as trimethylolpropane
caprylate; trimetylolpropane pelargonate; trimethylolpropane ester
such as trimethylolpropane isostearinate; pentaerythritol ester
such as pentaerythritol-2-ethyl hexanoate and pentaerythritol
pelargonate), polyoxyalkylene glycol, dialkyldiphenyl ether, and
polyphenyl ether. Among these synthetic oil compounds, preferred
are poly-.alpha.-olefins, such as 1-octene oligomer and 1-decene
oligomer and hydrides thereof.
[0023] 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 the mixture ratio.
[0024] The sulfur content of the base oil is not particularly
restricted. The sulfur content is preferably not more than 0.2%,
more preferably not more than 0.1%, much more preferably not more
than 0.05%. Additionally, it is preferable to use, as the base oil,
mineral oil which is purified by hydrogenation or synthetic oil
because such oil has a sulfur content of not more than 0.005% or
substantially no sulfur content (not more than 5 ppm).
[0025] The aromatic content of the base oil is also not
particularly restricted. The aromatic content of the base oil is
preferably 15% or less, more preferably 10% or less, and most
preferably 5% or less in order that the lubricating oil and/or
lubricant for internal combustion engines maintain its low friction
characteristics for a long time. When the aromatic content exceeds
15%, the base oil undesirably deteriorates in oxidation stability.
Herein, the aromatic content is defined as the amount of aromatics
fractions determined according to ASTM D2549 "Standard Test Method
for Separation of Representative Aromatics and Nonaromatics
Fractions of High-Boiling Oils by Elution Chromatography".
[0026] The kinematic viscosity of the base oil is not particularly
restricted. When the lubricating oil and/or lubricant is used for
an internal combustion engine, the kinematic viscosity of the base
oil is preferably 2 mm.sup.2/s or higher, more preferably 3
mm.sup.2/s and, at the same time, is preferably 20 mm.sup.2/s or
lower, more preferably 10 mm.sup.2/s or lower, most preferably 8
mm.sup.2/s or lower, as measured at 100.degree. C. When the
kinematic viscosity is lower than 2 mm.sup.2/s at 100.degree. C.,
the lubricating oil and/or lubricant can provide a sufficient wear
resistance and be inferior in vaporization characteristics. When
the kinematic viscosity exceeds 20 mm.sup.2/s, the lubricating oil
and/or lubricant is difficult to exhibit a low frictional
characteristics and may be degraded in vaporization
characteristics, which are not preferable. In connection with the
present invention, at least two base oils may be freely selected to
be mixed to form a mixture, in which the kenematic viscosity of the
single base oil may be out of the above-mentioned range as far as
the kinematic viscosity of the mixture at 100.degree. C. falls
within the above-mentioned preferable range.
[0027] The viscosity index of the base oil is not particularly
restricted, and is preferably 80 or higher, more preferably 100 or
higher, most preferably 120 or higher, when the lubricating oil
and/or lubricant is used for an internal combustion engine.
Increasing the viscosity index of the base oil can provide the
lubricating oil and/or lubricant for the internal combustion
engine, excellent in low temperature viscosity characteristics and
fuel economy performance.
[0028] Examples of the fatty acid ester friction modifier and the
aliphatic amine friction modifier are an fatty acid ester and an
aliphatic amine each having C.sub.6-C.sub.30 straight or branched
hydrocarbon chains or groups, preferably C.sub.8-C.sub.24 straight
or branched hydrocarbon chains, more preferably C.sub.10-C.sub.20
straight or branched hydrocarbon chains. When the carbon number of
the hydrocarbon chain is not within the range of 6 to 30, there
arises a possibility that the lubricating oil and/or lubricant may
not produce a sufficient friction reducing effect as expected. It
will be understood that a suitable mixture of fatty acid ester and
the aliphatic amine may be used.
[0029] Specific examples of the C.sub.6-C.sub.30 straight or
branched hydrocarbon chain include: alkyl groups, such as hexyl,
heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl,
tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl,
nonadecyl, icosyl, heneicosyl, docosyl, tricosyl, tetracosyl,
pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl and
triacontyl; and alkenyl groups, such as hexenyl, heptenyl, octenyl,
nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl,
pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, nonadecenyl,
icosenyl, heneicosenyl, docosenyl, tricosenyl, tetracosenyl,
pentacosenyl, hexacosenyl, heptacosenyl, octacosenyl, nonacosenyl
and triacontenyl. The above alkyl and alkenyl groups include all
possible isomers. Additionally, the position of alkenyl groups is
free.
[0030] The fatty acid ester can be exemplified by esters of fatty
acids having the above C.sub.6-C.sub.30 hydrocarbon groups or
chains and monohydric or polyhydric aliphatic alcohols. Specific
examples of such fatty acid esters include glycerol monooleate,
glycerol dioleate, sorbitan monoleate and sorbitan dioleate.
[0031] The aliphatic amine can be exemplified by aliphatic
monoamines and alkylene oxide adducts thereof, aliphatic
polyamines, imidazoline compounds, and derivatives thereof.
Specific examples of such aliphatic amines include: aliphatic amine
compounds, such as laurylamine, lauryldiethylamine,
lauryldiethanolamine, dodecyldipropanolamine, palmitylamine,
stearylamine, stearyltetraethylenepentamine, oleylamine,
oleylpropylenediamine, oleyldiethanolamine and
N-hydroxyethyloleylimidazo- lyne; adducts of the above aliphatic
amines (C.sub.6-C.sub.28 alkyl or alkenyl amines) with alkylene
oxides, such as N,N-dipolyoxyalkylene-N-alk- ylamines; and
acid-modified compounds prepared by reacting the above aliphatic
amines with C.sub.2-C.sub.30 monocarboxylic acids (such as fatty
acids) or C.sub.2-C.sub.30 polycarboxylic acids (such as oxalic
acid, phthalic acid, trimellitic acid and pyromellitic acid) so as
to neutralize or amidate the whole or part of the remaining amino
and/or imino groups. In connection with the present invention,
N,N-dipolyoxyethylene-N-oleylamine is preferably used.
[0032] The amount of the fatty acid ester friction modifier and/or
the aliphatic amine friction modifier added in the lubricating oil
and/or lubricant is not particularly restricted, and is preferably
0.05 to 3.0%, more preferably 0.1 to 2.0%, and most preferably 0.5
to 1.4%, based on the total mass of the lubricating oil and/or
lubricant. When the amount of the fatty acid ester friction
modifier and/or the aliphatic amine friction modifier is less than
0.05%, there arises a possibility that the lubricating oil and/or
lubricant may not produce a sufficient friction reducing effect.
When the amount of the fatty acid ester friction modifier and/or
the aliphatic amine friction modifier exceeds 3.0%, the lubricating
oil and/or lubricant produce a good friction reducing effect but
undesirably deteriorates in storage stability and compatibility to
cause precipitations.
[0033] Further, the lubricating oil and/or lubricant preferably
includes polybutenyl succinimide and/or a derivative thereof as an
ashless dispersant. Specific examples of the polybutenyl
succinimide usable in connection with the present invention include
compounds represented by the following general formulas (1) and
(2). 1
[0034] In each of the formulas (1) and (2), n represents an integer
of 1 to 5, preferably 2 to 4, so as to attain a good detergent
effect. Further, PIB represents a polybutenyl group derived from
polybutene. The polybutene can be prepared by polymerizing
high-purity isobutene or a mixture of 1 butene and isobutene in the
presence of a boron fluoride catalyst or an aluminum chloride
catalyst in such a manner that the polybutene attains a
number-average molecular weight of 900 to 3,500, preferably 1,000
to 2,000. When the number-average molecular weight of the
polybutene is less than 900, there is a possibility of failing to
attain a sufficient detergent effect. When the number-average
molecular weight of the polybutene exceeds 3,500, the polybutene
may undesirably deteriorate in low-temperature fluidity. In the
production of the polybutenyl succinimide, the polybutene may be
used after purified by removing trace amounts of fluorine and
chlorine residues, which result from the above polybutene
production catalyst, by any suitable treatment (such as adsorption
process or washing process). The amount of the fluorine and
chlorine residues is preferably controlled to 50 ppm or less, more
preferably 10 ppm or less, most preferably 1 ppm or less.
[0035] The production method of the polybutenyl succinimide is not
particularly restricted. For example, the polybutenyl succinimide
can be prepared by reacting an chloride of the above-mentioned
polybutene, or the polybutene from which fluorine and chlorine
residues are removed, with maleic anhydride at 100 to 200.degree.
C. to form polybutenyl succinate, and then, reacting the
thus-formed polybutenyl succinate with polyamine (such as
diethylene triamine, triethylene tetramine, tetraethylene pentamine
or pentaethylene hexamine).
[0036] The polybutenyl succinimide derivative can be exemplified by
boron- and acid-modified compounds obtained by reacting the
polybutenyl succinimide of the formulas (1) and (2) with boron
compounds or oxygen-containing organic compounds so as to
neutralize or amidate the whole or part of the remaining amino
and/or imide groups. Among these, boron-containing polybutenyl
succinimide, especially boron-containing
bis(polybutenyl)succinimide, is preferably used.
[0037] The above boron compound can be a boric acid, a borate or a
boric acid ester. Specific examples of the boric acid include
orthoboric acid, metaboric acid and paraboric acid. Specific
examples of the borate include: ammonium salts including ammonium
borates, such as ammonium metaborate, ammonium tetraborate,
ammonium pentaborate and ammonium octaborate. Specific examples of
the boric acid ester include: esters of boric acids and
alkylalcohols (preferably C.sub.1-C.sub.6 alkylalcohols), such as
monomethyl borate, dimethyl borate, trimethyl borate, monoethyl
borate, diethyl borate, triethyl borate, monopropyl borate,
dipropyl borate, tripropyl borate, monobutyl borate, dibutyl borate
and tributyl borate. Herein, the content ratio of nitrogen to boron
(B/N) by mass in the boron-containing polybutenyl succinimide is
usually 0.1 to 3, preferably 0.2 to 1.
[0038] The above oxygen-containing organic compound can be
exemplified by: C.sub.1-C.sub.30 monocarboxylic acids, such as
formic acid, acetic acid, glycolic acid, propionic acid, lactic
acid, butyric acid, valeric acid, caproic acid, enanthic acid,
caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric
acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic
acid, margaric acid, stearic acid, oleic acid, nonadecanoic acid
and eicosanoic acid; C.sub.2-C.sub.30 polycarboxylic acids, such as
oxalic acid, phthalic acid, trimellitic acid and pyromellitic acid,
and anhydrides and esters thereof; C.sub.2-C.sub.6 alkylene oxides;
and hydroxy(poly)oxyalkylene carbonates.
[0039] The amount of the polybutenyl succinimide and/or the
derivative thereof added in the lubricating oil and/or lubricant is
not particularly restricted, and is preferably 0.1 to 15%, more
preferably 1.0 to 12%, based on the total mass of the lubricating
oil and/or lubricant. When the amount of the polybutenyl
succineimide and/or the derivative thereof is less than 0.1%, there
arises a possibility of failing to attain a sufficient detergent
effect. It becomes uneconomical when the amount of the polybutenyl
succineimide and/or the derivative thereof exceeds 15%. In
addition, such a large amount of the polybutenyl succineimide
and/or the derivative thereof tends to cause a deterioration in
demulsification ability.
[0040] Furthermore, the lubricating oil and/or lubricant preferably
includes zinc dithiophosphate represented by the following general
formula (3) as an antioxidant and as an anti-wear agent. 2
[0041] In the general formula (3), R.sup.4, R.sup.5, R.sup.6 and
R.sup.7 each represent C.sub.1-C.sub.24 hydrocarbon groups. The
C.sub.1-C.sub.24 hydrocarbon group is preferably a C.sub.1-C.sub.24
straight-chain or branched-chain alkyl group, a C.sub.3-C.sub.24
straight-chain or branched-chain alkenyl group, a C.sub.5-C.sub.13
cycloalkyl or straight-chain or branched-chain alkylcycloalkyl
group, a C.sub.6-C.sub.18 aryl or straight-chain or branched-chain
alkylaryl group, or a C.sub.7-C.sub.19 arylalkyl group. The above
alkyl group or alkenyl group can be primary, secondary or tertiary.
Specific examples of R.sup.4, R.sup.5, R.sup.6 and R.sup.7 include:
alkyl groups, such as methyl, ethyl, propyl, butyl, pentyl, hexyl,
heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl,
tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl,
nonadecyl, icosyl, heneicosyl, docosyl, tricosyl and tetracosyl;
alkenyl groups, such as propenyl, isopropenyl, butenyl, butadienyl,
pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl,
dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl,
heptadecenyl, octadecenyl (oleyl), nonadecenyl, icosenyl,
heneicosenyl, docosenyl, tricosenyl and tetracosenyl; cycloalkyl
groups, such as cyclopentyl, cyclohexyl and cycloheptyl;
alkylcycloalkyl groups, such as methylcyclopentyl,
dimethylcyclopentyl, ethylcyclopentyl, propylcyclopentyl,
ethylmethylcyclopentyl, trimethylcyclopentyl, diethylcyclopentyl,
ethyldimethylcyclopentyl, propylmethylcyclopentyl,
propylethylcyclopentyl, di-propylcyclopentyl,
propylethylmethylcyclopenty- l, methylcyclohexyl,
dimethylcyclohexyl, ethylcyclohexyl, propylcyclohexyl,
ethylmethylcyclohexyl, trimethylcyclohexyl, diethylcyclohexyl,
ethyldimethylcyclohexyl, propylmethylcyclohexyl,
propylethylcyclohexyl, di-propylcyclohexyl,
propylethylmethylcyclohexyl, methylcycloheptyl,
dimethylcycloheptyl, ethylcycloheptyl, propylcycloheptyl,
ethylmethylcycloheptyl, trimethylcycloheptyl, diethylcycloheptyl,
ethyldimethylcycloheptyl, propylmethylcycloheptyl,
propylethylcycloheptyl, di-propylcycloheptyl and
propylethylmethylcyclohe- ptyl; aryl groups, such as phenyl and
naphthyl; alkylaryl groups, such as tolyl, xylyl, ethylphenyl,
propylphenyl, ethylmethylphenyl, trimethylphenyl, butylphenyl,
propylmethylphenyl, diethylphenyl, ethyldimethylphenyl,
tetramethylphenyl, pentylphenyl, hexylphenyl, heptylphenyl,
octylphenyl, nonylphenyl, decylphenyl, undecylphenyl and
dodecylphenyl; and arylalkyl groups, such as benzyl, methylbenzyl,
dimethylbenzyl, phenethyl, methylphenethyl and dimethylphenethyl.
The above hydrocarbon groups include all possible isomers.
[0042] The above-mentioned hydrocarbon groups formable with
R.sup.4, R.sup.5, R.sup.6 and R.sup.7 include all considerable
straight or branched chain structures. The position of double bond
of alkenyl group, the bonding position of alkyl group to cycloalkyl
group and the bonding position of alkyl group to aryl group are
free. Among the above-mentioned hydrocarbon groups, especially
preferable ones are straight or branched alkyl groups having a
carbon number ranging from 1 to 18, aryl groups having a carbon
number ranging from 6 to 18, and straight or branched alkylaryl
groups.
[0043] Specific examples of the zinc dithiophosphate usable in
connection with the present invention include zinc
diisopropyldithiophosphate, zinc diisobutyldithiophosphate, zinc
di-sec-butyldithiophosphate, zinc di-sec-pentyldithiophosphate,
zinc di-n-hexyldithiophosphate, zinc di-sec-hexyldithiophosphate,
zinc di-octyldithiophosphate, zinc di-2-ethylhexyldithiophosphate,
zinc di-n-decyldithiophosphate, zinc di-n-dodecyldithiophosphate,
zinc diisotridecyldithiophosphate and mixtures thereof.
[0044] The amount of the zinc dithiophosphate added in the
lubricating oil and/or lubricant is not particularly restricted.
The zinc dithiophosphate is preferably contained in an amount of
0.1% or less, more preferably in an amount of 0.06% or less, most
preferably in a minimum effective amount, in terms of the
phosphorus element based on the total mass of the lubricating oil
and/or lubricant in order to produce a higher friction reducing
effect. When the amount of the zinc dithiophosphate exceeds 0.1%,
there arises a possibility of inhibiting the effect of the ashless
fatty acid ester friction modifier and/or the ashless aliphatic
amine friction modifier, particularly at a sliding surface (plane)
between the DLC thin film and the opposite member formed of
iron-based material.
[0045] The zinc dithiophosphate can be prepared by any known
method. For example, the zinc dithiophosphate may be prepared by
reacting alcohols or phenols having the above R.sup.4, R.sup.5,
R.sup.6 and R.sup.7 hydrocarbon groups with phosphorous
pentasulfide to form dithiophosphoric acid, and then, neutralizing
the thus-formed dithiophosphoric acid with zinc oxide. Herein, the
molecular structure of zinc dithiophosphate differs according to
the alcohols or phenols used as a raw material for the zinc
dithiophosphate production. It will be understood that at least two
kinds of zinc dithiophosphates represented by the above general
formula (3) may be mixed at suitable ratio so as to be used.
[0046] As discussed above, in connection with the present
invention, the lubricating oil and/or lubricant can exhibit an
extremely excellent low friction characteristics in case that it is
used at the sliding surface between the hard carbon thin film
(formed of DLC) and metal materials. In order to raise performances
required particularly for the lubricating oil and/or lubricant
(composition) of internal combustion engines, the lubricating oil
and/or lubricant may contain other additives, such as a metallic
detergent, an antioxidant, a viscosity index improver, a friction
modifier other than the above-mentioned fatty acid ester friction
modifier and/or the aliphatic amine friction modifier, an ashless
dispersant other than the above-mentioned polybutenyl succinimide
and/or the derivative thereof, an anti-wear agent or
extreme-pressure additive, a rust inhibitor, a nonionic surfactant,
a deemulsifier, a metal deactivator and/or an anti-foaming agent,
when used in an internal combustion engine. These additives may be
used alone or in the form of a mixture of two or more thereof so as
to meet the lubricating oil and/or lubricant performance
required.
[0047] The metallic detergent can be any metallic-detergent
compound commonly used for a lubricating oil and/or lubricant.
Specific examples of the metallic detergent usable in connection
with the present invention include sulfonates, phenates and
salicylates of alkali metals or alkali-earth metals; and mixtures
of two or more thereof. Examples of the alkali metals include
sodium (Na) and potassium (K), and examples of the alkali-earth
metals include calcium (Ca) and magnesium (Mg). In connection with
the present invention, sodium and calcium sulfonates, sodium and
calcium phenates, and sodium and calcium salicylates are suitably
used. The total base number and amount of the metallic detergent
can be selected in accordance with the lubricating oil and/or
lubricant performance required. The total base number of the
metallic detergent is usually 0 to 500 mgKOH/g, preferably 150 to
400 mgKOH/g, as measured by perchloric acid method according to ISO
3771 "Determination of base number--Perchloric acid potentiometric
titration method". The amount of the metallic detergent is usually
0.1 to 10% based on the total mass of the lubricating oil and/or
lubricant.
[0048] The antioxidant can be any antioxidant compound commonly
used for a lubricating oil and/or lubricant. Specific examples of
the antioxidant usable in connection with the present invention
include: phenolic antioxidants, such as
4,4'-methylenebis(2,6-di-tert-butylphenol) and
octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; amino
antioxidants, such as phenyl-.alpha.-naphthylamine,
alkylphenyl-.alpha.-naphthylamine and alkyldiphenylamine; and
mixtures of two or more thereof. The amount of the antioxidant is
usually 0.01 to 5% based on the total mass of the lubricating oil
and/or lubricant.
[0049] The viscosity index improver can be exemplified by:
non-dispersion type viscosity index improvers, such as copolymers
of one or two monomers selected from various methacrylic acids, and
hydrides of the copolymers; and dispersion type viscosity index
improvers, such as copolymers of methacrylates (including nitrogen
compounds). There may be also used, as the viscosity index
improver, copolymers of ethylene and .alpha.-olefins (such as
propylene, 1-butene and 1-pentene) and hydrides thereof,
polyisobutylenes and hydrides thereof, a hydrogenated copolymer of
styrene and diene, a copolymer of styrene and maleic anhydride and
polyalkylstyrenes. The molecular weight of the viscosity index
improver needs to be selected in view of shear stability. For
example, the number-average molecular weight of the viscosity index
improver is desirably in a range of 5,000 to 1,000,000, more
desirably 100,000 to 800,000, for dispersion or non-dispersion type
polymethacrylates; in a range of 800 to 5,000 for polyisobutylenes
and hydrides thereof; and in a range of 800 to 300,000, more
desirably 10,000 to 200,000 for ethylene/.alpha.-olefin copolymers
and hydrides thereof. The above viscosity index improving compounds
can be used alone or in the form of a mixture of two or more
thereof. The amount of the viscosity index improver is preferably
0.1 to 40.0% based on the total mass of the lubricating oil and/or
lubricant.
[0050] The friction modifier other than the above-mentioned fatty
acid ester friction modifier and/or the aliphatic amine friction
modifier can be exemplified by ashless friction modifiers, such as
boric acid esters, higher alcohols and aliphatic ethers, and
metallic friction modifiers, such as molybdenum dithiophosphate,
molybdenum dithiocarbamate and molybdenum disulfide.
[0051] The ashless dispersant other than the above-mentioned
polybutenyl succinimide and/or the derivative thereof can be
exemplified by polybutenylbenzylamines and polybutenylamines each
having polybutenyl groups of number-average molecular weight of 900
to 3,500, polybutenyl succinimides having polybutenyl groups of
number-average molecular weight of less than 900 and derivatives
thereof.
[0052] The anti-friction agent or extreme-pressure additive can be
exemplified by disulfides, sulfurized fats and oils, olefin
sulfides, phosphate esters having one to three C.sub.2-C.sub.20
hydrocarbon groups, thiophosphate esters, phosphite esters,
thiophosphite esters and amine salts of these esters.
[0053] The rust inhibitor can be exemplified by alkylbenzene
sulfonates, dinonylnaphthalene sulfonates, esters of
alkenylsuccinic acids and esters of polyhydric alcohols.
[0054] The nonionic surfactant and the deemulsifier can be
exemplified by noionic polyalkylene glycol surfactants, such as
polyoxyethylene alkylethers, polyoxyethylene alkylphenyleters and
polyoxyethylene alkylnaphthyleters.
[0055] The metal deactivator can be exemplified by imidazoline
compounds, pyrimidine derivatives, thiazole and benzotriazole.
[0056] The anti-foaming agent can be exemplified by silicones,
fluorosilicones and fluoroalkylethers.
[0057] Each of the friction modifier other than the fatty acid
ester friction modifier and/or the aliphatic amine friction
modifier, the ashless dispersant other than the polybutenyl
succinimide and/or the derivative thereof, the anti-wear agent or
extreme-pressure additive, the rust inhibitor and the demulsifier
is usually contained in an amount of 0.01 to 5% based on the total
mass of the lubricating oil and/or lubricant, and the metal
deactivator is contained in an amount of 0.0005 to 1% based on the
total mass of the lubricating oil and/or lubricant.
[0058] It will be understood that a further friction lowering
effect can be obtained by supplying the lubricant whose main
component is a compound containing hydroxyl group, to the sliding
surface between the valve lifter of the present invention and the
opposite member formed of an aluminum alloy or an iron-based alloy.
Preferable examples of the lubricant whose main component is the
compound containing hydroxyl group are alcohols, particularly
glycerol and ethylene glycol.
EXPERIMENT 1
[0059] The present invention will be more readily understood with
reference to the following Examples in comparison with Comparative
Examples; however, these Examples are intended to illustrate the
invention and are not to be construed to limit the scope of the
invention.
EXAMPLE 1
[0060] A generally semicylindrical test piece as a base material
having a dimension of 8.times.12.times.40 mm was cut out from a raw
material of an aluminum alloy for a valve lifter. The test piece
had a semicylindical surface which longitudinally extends and had a
radius of curvature of 17 mm. A DLC film was formed at the
semicylindrical surface of this test piece by an arc ion plating
process (PVD), thereby producing a specimen corresponding to the
valve lifter. The DLC thin film had a hydrogen (atom) content of
0.2 atomic %, a Knoop hardness Hk of 2170 kg/mm.sup.2, a maximum
height (surface roughness) Ry of 0.03 .mu.m, and a thickness h of
0.5 .mu.m. The maximum height Ry was explained as R.sub.2 in JIS
(Japanese Industrial Standard) B 0601 (:2001).
[0061] For an opposite specimen, a plate-shaped test piece having a
dimension of 40.times.60.times.7 mm was cut out from a raw material
AC2A (Al--Cu--Si based) according to JIS H5202. The plate-shaped
test piece was finished to have a sliding surface having a surface
roughness Ra of 0.1 .mu.m, and then subjected to a so-called T7
heat treatment, thus producing the opposite specimen corresponding
to an opposite member with which the valve lifter was in slidable
contact. The surface roughness Ra is explained as R.sub.a75 in JIS
(Japanese Industrial Standard) B 0601 (:2001). In the T7 heat
treatment, the test piece underwent a solution treatment, followed
by undergoing an overaging treatment.
[0062] Then, the specimen in combination with the opposite specimen
underwent a frictional wear test in which the specimen made
reciprocating motions relative to the opposite specimen in a state
where the semicylindrical surface of the specimen was in slidable
contact with the surface of the sliding surface of the opposite
specimen. The frictional wear test was conducted in a lubricating
oil (composition) H shown in Table 1 so as to determine a friction
coefficient.
EXAMPLE 2
[0063] Procedure of Example 1 was repeated to produce the specimen
and the opposite specimen. The specimen in combination with the
opposite specimen underwent a frictional wear test in which the
specimen made reciprocating motions relative to the opposite
specimen in a state where the semicylindrical surface of the
specimen was in slidable contact with the surface of the sliding
surface of the opposite specimen. The frictional wear test was
conducted in a lubricating oil (composition) A shown in Table 1 so
as to determine a friction coefficient.
EXAMPLE 3 TO EXAMPLE 8
[0064] Procedure of Example 1 was repeated to produce the specimen
and the opposite specimen. The specimen in combination with the
opposite specimen underwent each of frictional wear tests in which
the specimen made reciprocating motions relative to the opposite
specimen in a state where the semicylindrical surface of the
specimen was in slidable contact with the surface of the sliding
surface of the opposite specimen. The frictional wear tests were
conducted respectively in lubricating oils (compositions) B, C, D,
E, F and G shown in Table 1 so as to determine friction
coefficients.
EXAMPLE 9
[0065] Procedure of Example 1 was repeated to produce the specimen
and the opposite specimen. The specimen in combination with the
opposite specimen underwent a frictional wear test in which the
specimen made reciprocating motions relative to the opposite
specimen in a state where the semicylindrical surface of the
specimen was in slidable contact with the surface of the sliding
surface of the opposite specimen. The frictional wear test was
conducted in a lubricating oil or lubricant (composition) which was
glycerol, so as to determine a friction coefficient.
COMPARATIVE EXAMPLE 1
[0066] A generally semicylindrical test piece as a base material
having a dimension of 8.times.12.times.40 mm was cut out from a raw
material of an aluminum alloy for a valve lifter. The test piece
had a semicylindical surface which longitudinally extends and had a
radius of curvature of 17 mm. A treatment for forming a Ni--P
coating was made at the semicylindrical surface of this test piece,
thereby producing a specimen corresponding to the valve lifter. For
an opposite specimen, a plate-shaped test piece having a dimension
of 40.times.60.times.7 mm was cut out from a raw material AC2A
(Al--Cu--Si based) according to JIS H5202. The plate-shaped test
piece was finished to have a sliding surface having a surface
roughness Ra of 0.1 .mu.m, and then subjected to a so-called T7
heat treatment, thus producing the opposite specimen corresponding
to an opposite member with which the valve lifter was in slidable
contact. The surface roughness Ra is explained as R.sub.a75 in JIS
(Japanese Industrial Standard) B 0601 (:2001). In the T7 heat
treatment, the test piece underwent a solution treatment, followed
by undergoing an overaging treatment.
[0067] Then, the specimen in combination with the opposite specimen
underwent a frictional wear test in which the specimen made
reciprocating motions relative to the opposite specimen in a state
where the semicylindrical surface of the specimen was in slidable
contact with the surface of the sliding surface of the opposite
specimen. The frictional wear test was conducted in a lubricating
oil (composition) H shown in Table 1 so as to determine a friction
coefficient.
COMPARATIVE EXAMPLE 2
[0068] A generally semicylindrical test piece as a base material
having a dimension of 8.times.12.times.40 mm was cut out from a raw
material of an iron-based alloy (stainless steel, SUS 304 according
to JIS) for a valve lifter. The test piece had a semicylindical
surface which longitudinally extends and had a radius of curvature
of 17 mm. The semicylindrical surface of this test piece was
lapped, thereby producing a specimen corresponding to the valve
lifter. For an opposite specimen, a plate-shaped test piece having
a dimension of 40.times.60.times.7 mm was cut out from a raw
material AC2A (Al--Cu--Si based) according to JIS H5202. The
plate-shaped test piece was finished to have a sliding surface
having a surface roughness Ra of 0.1 .mu.m, and then subjected to a
so-called T7 heat treatment, thus producing the opposite specimen
corresponding to an opposite member with which the valve lifter was
in slidable contact. The surface roughness Ra is explained as
R.sub.a75 in JIS (Japanese Industrial Standard) B 0601 (:2001). In
the T7 heat treatment, the test piece underwent a solution
treatment, followed by undergoing an overaging treatment.
[0069] Then, the specimen in combination with the opposite specimen
underwent a frictional wear test in which the specimen made
reciprocating motions relative to the opposite specimen in a state
where the semicylindrical surface of the specimen was in slidable
contact with the surface of the sliding surface of the opposite
specimen. The frictional wear test was conducted in a lubricating
oil (composition) H shown in Table 1 so as to determine a friction
coefficient.
Evaluation of Performance
[0070] Each of the specimens of Examples and Comparative Examples
underwent the frictional wear (reciprocating) test using a test
apparatus, in which a tip section (having the semicylindrical
surface) of the specimen of Examples and Comparative Examples was
pressed on the surface of the plate-shaped opposite specimen with a
load P, upon which the specimen made its reciprocating motion.
During making the reciprocating motion of the specimen, a friction
coefficient was measured at a turning end of a region in which the
reciprocating motion was made. Results of this test are tabulated
in Table 2. The frictional wear (reciprocating) test was carried
out under the following test conditions:
[0071] Specimen: Semicylindrical, having the dimension of
8.times.12.times.40 mm and formed of aluminum alloy or iron-based
alloy;
[0072] Opposite specimen: plate-shaped, having a dimension of
40.times.60.times.7 mm, and formed of material AC2A;
[0073] Test apparatus: Reciprocating motion-type;
[0074] Reciprocating motions of specimen: 600 cycles (reciprocating
motions) per minute;
[0075] Test temperature: 25.degree. C.;
[0076] Pressing load (P): 10 kgf; and
[0077] Measuring time: 60 min. after initiation of the test.
1TABLE 1 Lubricating oil (composition) A B C D E F G H Composition
Base oil Mineral oil.sup.1) 100 100 -- 100 100 100 100 100 (mass %)
Synthetic oil.sup.2) -- -- 100 -- -- -- -- -- Additives Ester
friction modifier.sup.3) 1.0 1.0 1.0 -- 1.0 1.0 0.2 -- Amine
friction modifier.sup.4) -- -- -- 1.0 -- 0.5 -- -- Ashless
dispersant.sup.5) 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Zinc
dithiophosphate (in terms of 0.00 0.047 0.047 0.047 0.094 0.094
0.047 0.094 phosphorous element).sup.6) Metallic detergent (in
terms of 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 metal
element).sup.7) Others.sup.8) 0.50 0.50 0.50 0.50 0.50 0.50 0.50
0.50 Others.sup.9) 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90
Properties Kinematic viscosity at 100.degree. C. mm.sup.2/s 10.3
10.2 10.0 10.2 10.3 10.3 10.3 10.3 Total base number according to
6.2 6.2 6.2 6.2 6.5 6.5 6.5 6.5 perchloric acid method mgKOH/g
Total base number according to 4.5 4.5 4.5 4.5 5.2 5.2 5.2 5.2
hydrochloric acid method mgKOH/g [Note] .sup.1)Hydrocracked mineral
oil (kinematic viscosity at 100.degree. C.: 5.0 mm.sup.2/s,
viscosity index: 120, aromatic content: 5.5 mass %) .sup.2)1-Decene
oligomer hydride (kinematic viscosity at 100.degree. C.: 3.9
mm.sup.2/s, viscosity index: 124, aromatic content: 0.0 mass %)
.sup.3)Glycerol monooleate
.sup.4)N,N-dipolyoxyethylene-N-oleylamine .sup.5)Polybutenyl
succinimide (nitrogen content: 1.2 mass %) .sup.6)Zinc
dialkyldithiophosphate (zinc content: 9.3 mass %, phosphrous
content: 8.5 mass %, alkyl group: secondary butyl or hexyl group)
.sup.7)Calcium sulfonate (total base number: 300 mgKOH/g, calcium
content: 12.0 mass %) .sup.8)Calcium phenate (total base number:
255 mgKOH/g, calcium content: 9.2 mass %) .sup.9)Including
viscosity index improver, antioxidant, rust inhibitor, demulsifier,
nonionic surfactant, metal deactivator and anti-foaming agent
[0078]
2TABLE 2 Lubricating oil Opposite or lubricant Friction Item
Specimen specimen (composition) coefficient Example 1 DLC thin film
AC2A H 0.08 Example 2 DLC thin film AC2A A 0.05 Example 3 DLC thin
film AC2A B 0.08 Example 4 DLC thin film AC2A C 0.09 Example 5 DLC
thin film AC2A D 0.11 Example 6 DLC thin film AC2A E 0.11 Example 7
DLC thin film AC2A F 0.11 Example 8 DLC thin film AC2A G 0.08
Example 9 DLC thin film AC2A Glycerol 0.07 Comparative Ni-P coating
AC2A H 0.13 Example 1 Comparative SUS 304 AC2A H 0.13 Example 2
[0079] The test results in Table 2 reveals that by forming the hard
carbon thin film such as the DLC thin film at the sliding surface
and/or by using the lubricating oil containing the ester additive
and/or the lubricant (glycerol), the friction coefficient can be
sharply lowered while the scuffing resistance and wear resistance
are expected to be improved.
[0080] As appreciated from the above, according to the present
invention, the hard carbon thin film having a hydrogen content of
not more than 1 atomic % is formed at the top and side surfaces of
the valve lifter which surfaces are sliding surfaces to the
opposite members. Accordingly, the friction coefficient and
friction resistance between the valve lifter and the opposite
members can be sharply reduced while sharply reducing wear amounts
of the valve lifter and the opposite members. This largely
contributes to improving fuel economy and durability-reliability of
internal combustion engines.
[0081] The entire contents of Japanese Patent Applications
P2003-207037 (filed Aug. 11, 2003) and P2004-190969 (filed Jun. 29,
2004) are incorporated herein by reference.
[0082] Although the invention has been described above by reference
to certain embodiments and examples of the invention, the invention
is not limited to the embodiments and examples described above.
Modifications and variations of the embodiments and examples
described above will occur to those skilled in the art, in light of
the above teachings. The scope of the invention is defined with
reference to the following claims.
* * * * *