US20230174882A1 - Lubricating oil composition and sliding mechanism - Google Patents
Lubricating oil composition and sliding mechanism Download PDFInfo
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- US20230174882A1 US20230174882A1 US17/996,660 US202117996660A US2023174882A1 US 20230174882 A1 US20230174882 A1 US 20230174882A1 US 202117996660 A US202117996660 A US 202117996660A US 2023174882 A1 US2023174882 A1 US 2023174882A1
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- lubricating oil
- oil composition
- pentaerythritol
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- friction coefficient
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- 239000010687 lubricating oil Substances 0.000 title claims abstract description 82
- 239000000203 mixture Substances 0.000 title claims abstract description 82
- 230000007246 mechanism Effects 0.000 title claims description 21
- WXZMFSXDPGVJKK-UHFFFAOYSA-N pentaerythritol Chemical compound OCC(CO)(CO)CO WXZMFSXDPGVJKK-UHFFFAOYSA-N 0.000 claims abstract description 51
- -1 fatty acid ester Chemical class 0.000 claims abstract description 41
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 38
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 38
- 239000001257 hydrogen Substances 0.000 claims abstract description 38
- 235000014113 dietary fatty acids Nutrition 0.000 claims abstract description 32
- 239000000194 fatty acid Substances 0.000 claims abstract description 32
- 229930195729 fatty acid Natural products 0.000 claims abstract description 32
- 239000003607 modifier Substances 0.000 claims abstract description 32
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 14
- 239000002199 base oil Substances 0.000 claims abstract description 11
- 125000002887 hydroxy group Chemical group [H]O* 0.000 claims description 16
- 150000002148 esters Chemical class 0.000 claims description 10
- 238000012360 testing method Methods 0.000 description 32
- 239000000463 material Substances 0.000 description 30
- 239000003921 oil Substances 0.000 description 26
- 125000000217 alkyl group Chemical group 0.000 description 21
- 239000011248 coating agent Substances 0.000 description 19
- 238000000576 coating method Methods 0.000 description 19
- WMYJOZQKDZZHAC-UHFFFAOYSA-H trizinc;dioxido-sulfanylidene-sulfido-$l^{5}-phosphane Chemical compound [Zn+2].[Zn+2].[Zn+2].[O-]P([O-])([S-])=S.[O-]P([O-])([S-])=S WMYJOZQKDZZHAC-UHFFFAOYSA-H 0.000 description 18
- 230000000694 effects Effects 0.000 description 14
- 239000002480 mineral oil Substances 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 11
- 238000013016 damping Methods 0.000 description 11
- 150000004665 fatty acids Chemical group 0.000 description 11
- 235000010446 mineral oil Nutrition 0.000 description 10
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 9
- 229910052698 phosphorus Inorganic materials 0.000 description 9
- 239000011574 phosphorus Substances 0.000 description 9
- 150000001875 compounds Chemical class 0.000 description 8
- 238000005259 measurement Methods 0.000 description 8
- 230000001629 suppression Effects 0.000 description 7
- 125000004432 carbon atom Chemical group C* 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- 229920000459 Nitrile rubber Polymers 0.000 description 5
- 239000003638 chemical reducing agent Substances 0.000 description 5
- 230000001419 dependent effect Effects 0.000 description 5
- 238000011156 evaluation Methods 0.000 description 5
- 238000013461 design Methods 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
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- 239000006096 absorbing agent Substances 0.000 description 3
- 239000010409 thin film Substances 0.000 description 3
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 2
- QQVGEJLUEOSDBB-KTKRTIGZSA-N [3-hydroxy-2,2-bis(hydroxymethyl)propyl] (z)-octadec-9-enoate Chemical compound CCCCCCCC\C=C/CCCCCCCC(=O)OCC(CO)(CO)CO QQVGEJLUEOSDBB-KTKRTIGZSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
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- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 125000001424 substituent group Chemical group 0.000 description 2
- 229920000089 Cyclic olefin copolymer Polymers 0.000 description 1
- AFCARXCZXQIEQB-UHFFFAOYSA-N N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CCNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 AFCARXCZXQIEQB-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 125000001931 aliphatic group Chemical group 0.000 description 1
- 150000004996 alkyl benzenes Chemical class 0.000 description 1
- 150000001412 amines Chemical class 0.000 description 1
- 239000002518 antifoaming agent Substances 0.000 description 1
- 239000003963 antioxidant agent Substances 0.000 description 1
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- 125000003118 aryl group Chemical group 0.000 description 1
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- 125000001183 hydrocarbyl group Chemical group 0.000 description 1
- 238000005984 hydrogenation reaction Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 239000006078 metal deactivator Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 229940049964 oleate Drugs 0.000 description 1
- ZQPPMHVWECSIRJ-KTKRTIGZSA-N oleic acid Chemical compound CCCCCCCC\C=C/CCCCCCCC(O)=O ZQPPMHVWECSIRJ-KTKRTIGZSA-N 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 229920001083 polybutene Polymers 0.000 description 1
- 229920005862 polyol Polymers 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 229920013636 polyphenyl ether polymer Polymers 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
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- 150000005846 sugar alcohols Chemical class 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 239000004711 α-olefin Substances 0.000 description 1
Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
- C10M129/00—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing oxygen
- C10M129/02—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing oxygen having a carbon chain of less than 30 atoms
- C10M129/68—Esters
- C10M129/74—Esters of polyhydroxy compounds
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
- C10M129/00—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing oxygen
- C10M129/02—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing oxygen having a carbon chain of less than 30 atoms
- C10M129/68—Esters
- C10M129/76—Esters containing free hydroxy or carboxyl groups
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
- C10M169/00—Lubricating compositions characterised by containing as components a mixture of at least two types of ingredient selected from base-materials, thickeners or additives, covered by the preceding groups, each of these compounds being essential
- C10M169/04—Mixtures of base-materials and additives
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/02—Parts of sliding-contact bearings
- F16C33/04—Brasses; Bushes; Linings
- F16C33/043—Sliding surface consisting mainly of ceramics, cermets or hard carbon, e.g. diamond like carbon [DLC]
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/02—Parts of sliding-contact bearings
- F16C33/04—Brasses; Bushes; Linings
- F16C33/06—Sliding surface mainly made of metal
- F16C33/10—Construction relative to lubrication
- F16C33/1025—Construction relative to lubrication with liquid, e.g. oil, as lubricant
- F16C33/109—Lubricant compositions or properties, e.g. viscosity
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
- F16F7/00—Vibration-dampers; Shock-absorbers
- F16F7/08—Vibration-dampers; Shock-absorbers with friction surfaces rectilinearly movable along each other
- F16F7/09—Vibration-dampers; Shock-absorbers with friction surfaces rectilinearly movable along each other in dampers of the cylinder-and-piston type
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
- C10M2207/00—Organic non-macromolecular hydrocarbon compounds containing hydrogen, carbon and oxygen as ingredients in lubricant compositions
- C10M2207/28—Esters
- C10M2207/283—Esters of polyhydroxy compounds
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
- C10M2223/00—Organic non-macromolecular compounds containing phosphorus as ingredients in lubricant compositions
- C10M2223/02—Organic non-macromolecular compounds containing phosphorus as ingredients in lubricant compositions having no phosphorus-to-carbon bonds
- C10M2223/04—Phosphate esters
- C10M2223/045—Metal containing thio derivatives
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
- C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
- C10N2030/06—Oiliness; Film-strength; Anti-wear; Resistance to extreme pressure
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
- C10N2040/00—Specified use or application for which the lubricating composition is intended
- C10N2040/08—Hydraulic fluids, e.g. brake-fluids
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2361/00—Apparatus or articles in engineering in general
Definitions
- the present invention relates to a lubricating oil composition and a sliding mechanism.
- a damper which is an example of a sliding mechanism, exerts a vibration suppression force through a reciprocating motion.
- the vibration suppression force is a sum of an oil hydraulic damping force generated at a valve and a frictional force generated at a sliding portion between a piston rod and an oil seal or between a piston and a cylinder.
- the vibration suppression force of the damper is large, steering stability increases, but ride comfort is degraded, and conversely, when the vibration suppression force of the damper is small, the steering stability is degraded, but the ride comfort is improved.
- a research has been conducted on the damper to adjust the frictional force of the sliding portion by selecting a friction modifier to be added to a lubricating oil applicable to the sliding portion, thereby improving the ride comfort and the steering stability.
- examples of the friction modifier in the related art include a friction modifier mentioned in “Shock Absorber Technical Trends and Tribology (Hiroshi Nakanishi, Tribologist 2009 (Vol. 54) No. 9, p598)”.
- DLC Diamond-like carbon
- a lubricating oil composition containing a friction modifier in the related art does not sufficiently exhibit a friction adjustment effect on a DLC coating material.
- a hydrogen-containing DLC coating material it is more difficult to set an effective friction modifier and lubricating oil composition, and it is difficult to improve the friction property.
- the present invention has been made in view of the above problem, and an object of the present invention is to improve the friction property of a sliding mechanism that includes a sliding member coated with hydrogen-containing diamond-like carbon.
- FIG. 1 is a schematic diagram illustrating a device for measuring a normal dynamic friction coefficient and a minute low speed friction coefficient.
- the base oil is a mineral oil and/or a synthetic oil.
- the type of the mineral oil or the synthetic oil is not particularly limited, and examples of the mineral oil include a paraffinic mineral oil, an intermediate base mineral oil, and a naphthenic mineral oil which are obtained by an ordinary refinement method such as solvent refinement and hydrogenation refinement.
- the synthetic oil include polybutene, a polyolefin ( ⁇ -olefin (co)polymer), various esters (such as a polyol ester, a dibasic acid ester, and a phosphate ester), various ethers (such as polyphenyl ether), alkylbenzene, and alkylnaphthalene.
- one type of the mineral oil may be used, or two or more types of the mineral oils may be used in combination.
- one type of the synthetic oil may be used, or two or more types of the synthetic oils may be used in combination.
- one or more types of mineral oils and one or more types of synthetic oils may be used in combination.
- the lubricating oil composition according to the present embodiment contains the fatty acid ester of pentaerythritol as the friction modifier.
- the fatty acid ester of pentaerythritol one having a fatty acid residue having 10 or more and 20 or less carbon atoms can be used.
- the fatty acid residue is a decarboxylated residue of a fatty acid, and may be a branched or linear fatty acid.
- the fatty acid residue may be an unsaturated or saturated aliphatic hydrocarbon group.
- a plurality of esters selected from the pentaerythritol monoester, the pentaerythritol diester, the pentaerythritol triester, and the pentaerythritol tetraester described above may be mixed and used.
- a content of the fatty acid ester of pentaerythritol as the (B) friction modifier can be 0.2% by mass or more and 10.0% by mass or less with respect to a total amount of the lubricating oil composition.
- a content of the (B) friction modifier is less than 0.2% by mass, a friction adjustment effect on the hydrogen-containing DLC coating material cannot be achieved, and when the content exceeds 10.0% by mass, the friction adjustment effect reaches a peak, leading to a loss in material costs.
- a total hydroxyl value of the fatty acid ester of pentaerythritol in the friction modifier is 2.20 mgKOH/g or more, it is possible to achieve the friction adjustment effect on the sliding member coated with hydrogen-containing DLC.
- the friction modifier according to the present embodiment may contain a pentaerythritol tetraester whose ester value is 4.
- the friction modifier is used in combination with the pentaerythritol monoester or the like whose hydroxyl value is high to adjust the total hydroxyl value of the fatty acid ester of pentaerythritol to the above specific value.
- the friction modifier applicable in the present embodiment may contain various friction reducing agents such as a phosphorus-based friction reducing agent, an amine-based friction reducing agent, or an ester-based friction reducing agent, in addition to those described above.
- a friction coefficient of the sliding member in a sliding mechanism to which the lubricating oil composition is applied can be adjusted by adjusting an addition amount of these friction reducing agents.
- a phosphorus-containing compound whose chemical structure represented by the following General Formula (1) may be contained.
- Each R in General Formula (1) represents an individual hydrocarbon group, and examples thereof include a linear primary alkyl group, a branched secondary alkyl group, or an aryl group.
- R is not particularly limited, and preferably has one or more secondary alkyl groups having at least a short chain (3 to 5 carbon atoms).
- ZnDTPs having different numbers of alkyl groups can be mixed and used as the ZnDTP.
- an average number of the alkyl groups in the ZnDTP is preferably 1 to 3, and more preferably 1 to 2.
- a method for measuring the average number of the alkyl groups in the ZnDTP is not particularly limited, and the average number can be determined by measuring the hydroxyl value by using an FT-IR, for example.
- the ZnDTP according to the present embodiment preferably has at least a secondary alkyl group, and more preferably has the secondary alkyl group in an amount larger than a primary alkyl group.
- different types of ZnDTPs can be mixed.
- An alkyl group having a short chain is more preferable than an alkyl group having a long chain. Therefore, the ZnDTP according to the present embodiment has a secondary alkyl group having at least a short chain (3 to 5 carbon atoms).
- a method for measuring the alkyl group in the ZnDTP is not particularly limited, and measurement regarding whether the alkyl group is a primary alkyl group or a secondary alkyl group, or whether the alkyl group has a short chain or a long chain can be made based on characteristics of an absorption band of P—O—C and an absorption band of P ⁇ SP—S using a fingerprint region in the FT-IR, for example.
- a constant time is required from rise of an oil hydraulic damping force for providing a vibration suppression force to start of a vibration suppression function.
- the frictional force has high responsiveness. Therefore, during a period until the oil hydraulic damping force rises, that is, a period during which the sliding member shifts from a stationary state to a slipping state, or in a slight amplitude time during which the oil hydraulic damping force hardly acts, the frictional force becomes an important factor of the vibration suppression force of the damper.
- the inventor of the present invention has focused on a matter that, in the sliding member, a friction coefficient during the period until the oil hydraulic damping force rises or in slight vibration during which the oil hydraulic damping force hardly acts (referred to as a “minute low speed friction coefficient”), and a friction coefficient in normal vibration during which the oil hydraulic damping force acts (referred to as a “normal dynamic friction coefficient”) are different from each other, and has found that the difference in the friction property influences performance of the damper. It is also found that it is possible to achieve both steering stability and ride comfort by setting a ratio of the normal dynamic friction coefficient to the minute low speed friction coefficient within a specific numerical range.
- the normal dynamic friction coefficient is a friction coefficient when the damper as the sliding member is vibrated at a predetermined amplitude and a sliding speed of more than 4.0 mm/s.
- the minute low speed friction coefficient is a friction coefficient when the damper is vibrated at a predetermined amplitude and a sliding speed of 0.20 mm/s or less.
- the ratio of the normal dynamic friction coefficient to the minute low speed friction coefficient can be set to a specific numerical range by applying the lubricating oil composition according to the present embodiment to the sliding member coated with the hydrogen-containing DLC coating material.
- a value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to 1.
- the vibration can be suppressed by the frictional force at an initial stage of movement of a piston, which is a stage before an oil hydraulic force for suppressing the vibration is generated. Therefore, with the lubricating oil composition according to the present embodiment, it is possible to easily set the oil hydraulic damping force of the damper using a shock absorbing member coated with hydrogen-containing DLC.
- the fatty acid ester of pentaerythritol one having a fatty acid residue having 10 or more and 20 or less carbon atoms can be used.
- pentaerythritol monooleate can be used as an example of the partial ester of pentaerythritol.
- the lubricating oil composition according to the present embodiment contains 0.2% by mass or more of the fatty acid ester of pentaerythritol, it is possible to achieve the friction adjustment effect on the hydrogen-containing DLC coating material.
- the total hydroxyl value of the fatty acid ester of pentaerythritol in the friction modifier is 2.20 mgKOH/g or more, it is possible to achieve the friction adjustment effect on the sliding member coated with hydrogen-containing DLC.
- the lubricating oil composition according to the present embodiment may further contain a phosphorus-containing compound.
- the lubricating oil composition according to the present embodiment can reduce the difference between the minute low speed friction coefficient and the normal dynamic friction coefficient by containing the phosphorus-containing compound. Accordingly, it is possible to easily adjust the friction coefficient to a friction coefficient suitable for the ride comfort and the steering stability.
- the phosphorus-containing compound particularly a ZnDTP is suppressed from being deteriorated (decomposed) by pentaerythritol, and thus the adjusted frictional force can be maintained over a long period of time.
- the lubricating oil composition according to the present embodiment enables the friction adjustment for the sliding mechanism that includes the sliding portion coated with the hydrogen-containing DLC coating material.
- the lubricating oil composition according to the present embodiment is suitable as a lubricating oil used for, in addition to the damper, an internal combustion engine, a driving system transmission machine, industrial equipment, metal processing, and the like to which a low-friction sliding member coated with the hydrogen-containing DLC coating material as a hard thin film material is applied.
- a sliding mechanism according to the present embodiment is a sliding mechanism using the lubricating oil composition according to the present embodiment described above, and includes at least a sliding portion coated with hydrogen-containing DLC.
- Examples of the sliding mechanism according to the present embodiment include a piston rod, a cylinder, a gear, a bearing, a transmission, and a damper to which the low-friction sliding member coated with the hydrogen-containing DLC coating material as the hard thin film material is applied.
- the sliding mechanism according to the present embodiment By applying the lubricating oil composition described above to the sliding mechanism according to the present embodiment, it is possible to perform the friction adjustment which is difficult in the sliding mechanism coated with the hydrogen-containing DLC coating material.
- the sliding mechanism according to the present embodiment is a damper, it is possible to improve durability to friction and wear by coating the sliding portion with the hydrogen-containing DLC coating material, and it is possible to achieve both the ride comfort and the steering stability at a high level.
- the lubricating oil composition according to the present embodiment when applied to a damper, the value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) among components constituting the oil hydraulic damping force of the damper can be brought close to 1 regardless of the speed. Accordingly, it is possible to easily set the oil hydraulic damping force of the damper. Therefore, it is possible to design a damper capable of achieving both the steering stability and the ride comfort.
- FIG. 1 is a schematic view illustrating a device that measures the normal dynamic friction coefficient and the minute low speed friction coefficient.
- the normal dynamic friction coefficient and the minute low speed friction coefficient of a test specimen are measured using a friction testing device 10 shown in FIG. 1 .
- the friction testing device 10 shown in FIG. 1 is a pin-on-disk type friction testing device.
- the friction testing device 10 a frictional force generated by reciprocating, by an electromagnetic oscillator 3 , a disk-shaped test piece 2 fixed on a slide bearing 1 , and pressing and sliding a pin-shaped test piece 4 on the disk-shaped test piece 2 is measured using a strain gauge 6 attached to a fixed shaft 5 of the pin-shaped test piece 4 .
- acrylonitrile-butadiene rubber (NBR) used as an oil seal in a damper is used as the pin-shaped test piece 4 .
- a tip of the pin-shaped test piece 4 is cut so as to have an angle of 140° imitating an oil lip shape.
- the disk-shaped test piece 2 is coated with hydrogen-containing diamond-like carbon used for a surface of a piston rod and is polished to a surface roughness Ra of 0.01 ⁇ m or less.
- the frictional force (friction coefficient) between the pin-shaped test piece 4 of NBR and the disk-shaped test piece 2 coated with hydrogen-containing diamond-like carbon is measured using this device.
- Measurement of the normal dynamic friction coefficient and measurement of the minute low speed friction coefficient are performed.
- the measurement of the normal dynamic friction coefficient the measurement is performed under conditions of an amplitude of 5.0 mm, a frequency of 5.0 Hz, and a sliding speed of 4.0 mm/s in a friction test using the friction testing device 10 shown in FIG. 1 .
- the measurement is performed under conditions of an amplitude of 5.0 mm, a frequency of 5.0 Hz, and a sliding speed of 0.20 mm/s.
- an amplitude dependent index is an index adopted for evaluating the lubricating oil composition according to the present embodiment, and can be treated as one of evaluation indices for the ride comfort of the damper.
- the amplitude dependent index is expressed by (normal dynamic friction coefficient)/(minute low speed friction coefficient). As the amplitude dependent index is closer to 1, the difference between the friction coefficient at the time of the slight amplitude and the friction coefficient at the time of the normal amplitude is small, and it is possible to evaluate that the ride comfort is excellent.
- stick-slip In the measurement of the normal dynamic friction coefficient or the minute low speed friction coefficient, stick-slip is evaluated as “Yes” when the stick-slip occurred, and oil bleeding and deterioration in lip durability occurred.
- the amplitude dependent index and the stick-slip evaluation are integrated to determine whether the lubricating oil composition is passed or failed.
- a lubricating oil composition with a pass level is indicated by “G” and a lubricating oil composition with a failure level is indicated by “F”.
- Test specimens of lubricating oil compositions of examples, comparative examples and reference examples are prepared according to compositions shown in Table 1.
- lubricating oil compositions whose total hydroxyl values are different by changing a mixing ratio of fatty acid esters of pentaerythritol whose ester values are different or using a fatty acid ester of pentaerythritol alone, as a composition of the friction modifier in the lubricating oil composition.
- An oleate having a fatty acid residue having a carbon number of C18 was used as the fatty acid ester of pentaerythritol.
- a mineral oil was used as the base oil. If necessary, zinc dithiophosphate (ZnDTP) was used as the friction modifier.
- a friction test using acrylonitrile-butadiene rubber (NBR) as the pin-shaped test piece 4 , and a material coated with hydrogen-containing diamond-like carbon (DLC) as the disk-shaped test piece 2 was performed in the friction testing device 10 shown in FIG. 1 using these lubricating oil compositions.
- NBR acrylonitrile-butadiene rubber
- DLC hydrogen-containing diamond-like carbon
- Comparative Example 1 of a group of comparative examples a pentaerythritol tetraester is used, and a material coated with hydrogen-free DLC is used as the test piece 2 in the friction testing device 10 .
- Comparative Example 2 a pentaerythritol tetraester is used, and the material coated with hydrogen-containing DLC is used as the test piece 2 in the friction testing device 10 .
- a lubricating oil composition containing only a mineral oil and not containing a fatty acid ester of pentaerythritol is applied to the friction testing device 10 using the material coated with hydrogen-free DLC as the test piece 2 .
- the lubricating oil composition containing only a mineral oil and not containing a fatty acid ester of pentaerythritol is applied to the friction testing device 10 using the material coated with hydrogen-containing DLC as the test piece 2 .
- lubricating oil compositions in Examples 1 and 7 are applied to a material coated with hydrogen-free diamond-like carbon (DLC) in the friction testing device 10 shown in FIG. 1 .
- DLC hydrogen-free diamond-like carbon
- the lubricating oil composition containing the fatty acid ester of pentaerythritol can achieve an effect of reducing the friction coefficient of the material coated with hydrogen-containing DLC, whose friction coefficient is difficult to be adjusted up to now, in the same manner as the material coated with hydrogen-free DLC.
- a lubricating oil composition according to the present embodiment is a lubricating oil composition to be used in a sliding member coated with hydrogen-containing diamond-like carbon (DLC), contains a base oil and a friction modifier, and contains a fatty acid ester of pentaerythritol as the friction modifier.
- DLC hydrogen-containing diamond-like carbon
- the lubricating oil composition enables friction adjustment for a sliding mechanism that includes the sliding member coated with the hydrogen-containing DLC coating material and for which friction adjustment is difficult in the related art. Therefore, the lubricating oil composition can improve the friction property of the sliding member coated with the hydrogen-containing DLC coating material.
- a ratio of a normal dynamic friction coefficient to a minute low speed friction coefficient can be set to a specific numerical range. More specifically, when the lubricating oil composition according to the present embodiment is applied to a damper that includes the sliding member coated with the hydrogen-containing DLC coating material, a value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to 1.
- the terminal hydroxy group in pentaerythritol contributes to the sliding member coated with hydrogen-containing DLC. Therefore, in the present embodiment, when the total hydroxyl value of the fatty acid ester of pentaerythritol as the friction modifier is 2.20 mgKOH/g or more, it is possible to achieve the friction adjustment effect on the sliding member coated with hydrogen-containing DLC.
- the lubricating oil composition according to the present embodiment further contains a phosphorus-containing compound.
- the lubricating oil composition according to the present embodiment can reduce a difference between the minute low speed friction coefficient and the normal dynamic friction coefficient by containing the phosphorus-containing compound. Accordingly, it is possible to easily adjust the friction coefficient to a friction coefficient suitable for ride comfort and steering stability.
- the phosphorus-containing compound is zinc dithiophosphate (Zn-DTP), and has at least a secondary alkyl group having 3 to 5 carbon atoms.
- the phosphorus-containing compound particularly a Zn-DTP is suppressed from being deteriorated (decomposed) by pentaerythritol, and thus the adjusted frictional force can be maintained over a long period of time.
- a sliding mechanism according to the present embodiment is a sliding mechanism using the lubricating oil composition described above, and includes at least a sliding portion coated with hydrogen-containing DLC.
- the friction adjustment can be performed by the lubricating oil composition containing the fatty acid ester of pentaerythritol, and (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to 1.
- such a sliding mechanism is, for example, a damper
- a damper capable of achieving the vibration reduction effect in a stage before an oil hydraulic force for suppressing vibration is generated. Accordingly, it is possible to expand a design width of the oil hydraulic damping force of the damper, and it is possible to design a damper capable of achieving both the steering stability and the ride comfort.
- At least one component selected from an ashless detergent dispersant, a metal-based detergent, a lubricity improver, an antioxidant, a rust inhibitor, a metal deactivator, a viscosity index improver, a pour point depressant, and an antifoaming agent can be appropriately blended as an optional component as long as the object of the present invention is not impaired.
- a component that can be used as an additive of the lubricating oil composition for the damper can be appropriately blended.
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Abstract
A lubricating oil composition according to the present embodiment is a lubricating oil composition to be used in a sliding member coated with hydrogen-containing diamond-like carbon, and contains a base oil and a friction modifier. The friction modifier contains a fatty acid ester of pentaerythritol.
Description
- The present invention relates to a lubricating oil composition and a sliding mechanism.
- A damper, which is an example of a sliding mechanism, exerts a vibration suppression force through a reciprocating motion. It is known that the vibration suppression force is a sum of an oil hydraulic damping force generated at a valve and a frictional force generated at a sliding portion between a piston rod and an oil seal or between a piston and a cylinder. It is also known that when the vibration suppression force of the damper is large, steering stability increases, but ride comfort is degraded, and conversely, when the vibration suppression force of the damper is small, the steering stability is degraded, but the ride comfort is improved.
- Therefore, a research has been conducted on the damper to adjust the frictional force of the sliding portion by selecting a friction modifier to be added to a lubricating oil applicable to the sliding portion, thereby improving the ride comfort and the steering stability. For example, examples of the friction modifier in the related art include a friction modifier mentioned in “Shock Absorber Technical Trends and Tribology (Hiroshi Nakanishi, Tribologist 2009 (Vol. 54) No. 9, p598)”.
- In recent years, a technique for coating a portion under a severe friction and wear environment with a hard thin film material has been applied widely as a surface treatment technique for the portion. Diamond-like carbon (hereinafter referred to as “DLC”), which is an example of such a coating material, has an excellent low-friction property and is widely applied as a low-friction sliding member.
- However, it is well known that a lubricating oil composition containing a friction modifier in the related art does not sufficiently exhibit a friction adjustment effect on a DLC coating material. In particular, for a hydrogen-containing DLC coating material, it is more difficult to set an effective friction modifier and lubricating oil composition, and it is difficult to improve the friction property.
- The present invention has been made in view of the above problem, and an object of the present invention is to improve the friction property of a sliding mechanism that includes a sliding member coated with hydrogen-containing diamond-like carbon.
- An aspect of the present invention is summarized as the following lubricating oil composition.
- A lubricating oil composition to be used in a sliding member coated with hydrogen-containing diamond-like carbon contains a base oil and a friction modifier. The friction modifier contains a fatty acid ester of pentaerythritol.
-
FIG. 1 is a schematic diagram illustrating a device for measuring a normal dynamic friction coefficient and a minute low speed friction coefficient. - [Lubricating Oil Composition]
- Hereinafter, a lubricating oil composition according to an embodiment of the present invention will be described.
- The lubricating oil composition according to the present embodiment is a lubricating oil composition to be used in a sliding member coated with hydrogen-containing diamond-like carbon (hereinafter referred to as “hydrogen-containing DLC”), and contains (A) a base oil and (B) a friction modifier. The (B) friction modifier contains a fatty acid ester of pentaerythritol.
- (A) Base Oil
- In the lubricating oil composition according to the present embodiment, the base oil is a mineral oil and/or a synthetic oil. The type of the mineral oil or the synthetic oil is not particularly limited, and examples of the mineral oil include a paraffinic mineral oil, an intermediate base mineral oil, and a naphthenic mineral oil which are obtained by an ordinary refinement method such as solvent refinement and hydrogenation refinement. Examples of the synthetic oil include polybutene, a polyolefin (α-olefin (co)polymer), various esters (such as a polyol ester, a dibasic acid ester, and a phosphate ester), various ethers (such as polyphenyl ether), alkylbenzene, and alkylnaphthalene.
- In the present embodiment, as the base oil, one type of the mineral oil may be used, or two or more types of the mineral oils may be used in combination. In addition, one type of the synthetic oil may be used, or two or more types of the synthetic oils may be used in combination. Further, one or more types of mineral oils and one or more types of synthetic oils may be used in combination.
- (B) Friction Modifier
- The lubricating oil composition according to the present embodiment contains the fatty acid ester of pentaerythritol as the friction modifier. As the fatty acid ester of pentaerythritol, one having a fatty acid residue having 10 or more and 20 or less carbon atoms can be used. The fatty acid residue is a decarboxylated residue of a fatty acid, and may be a branched or linear fatty acid. The fatty acid residue may be an unsaturated or saturated aliphatic hydrocarbon group.
- Pentaerythritol is a tetravalent sugar alcohol. Examples of fatty acid ester of pentaerythritol include a pentaerythritol tetraester in which all of four terminal substituents are ester-bonded to fatty acid residues, and a pentaerythritol monoester, a pentaerythritol diester, and a pentaerythritol triester in which any of the terminal substituents is ester-bonded to the fatty acid residue.
- In the present embodiment, as the friction modifier, a plurality of esters selected from the pentaerythritol monoester, the pentaerythritol diester, the pentaerythritol triester, and the pentaerythritol tetraester described above may be mixed and used.
- In the present embodiment, it is presumed, as a factor that enables the friction adjustment for the sliding member coated with hydrogen-containing DLC, that a terminal hydroxy group is dominant than the fatty acid residues constituting the fatty acid ester of pentaerythritol. Therefore, it is preferable to use a partial ester of pentaerythritol whose hydroxyl value is higher. In the present embodiment, pentaerythritol monooleate can be used, but the number of carbon atoms in the fatty acid residue is not limited to C18.
- In the present embodiment, a content of the fatty acid ester of pentaerythritol as the (B) friction modifier can be 0.2% by mass or more and 10.0% by mass or less with respect to a total amount of the lubricating oil composition. When a content of the (B) friction modifier is less than 0.2% by mass, a friction adjustment effect on the hydrogen-containing DLC coating material cannot be achieved, and when the content exceeds 10.0% by mass, the friction adjustment effect reaches a peak, leading to a loss in material costs.
- Specifically, in the present embodiment, when a total hydroxyl value of the fatty acid ester of pentaerythritol in the friction modifier is 2.20 mgKOH/g or more, it is possible to achieve the friction adjustment effect on the sliding member coated with hydrogen-containing DLC.
- Therefore, the friction modifier according to the present embodiment may contain a pentaerythritol tetraester whose ester value is 4. In this case, the friction modifier is used in combination with the pentaerythritol monoester or the like whose hydroxyl value is high to adjust the total hydroxyl value of the fatty acid ester of pentaerythritol to the above specific value.
- The friction modifier applicable in the present embodiment may contain various friction reducing agents such as a phosphorus-based friction reducing agent, an amine-based friction reducing agent, or an ester-based friction reducing agent, in addition to those described above. A friction coefficient of the sliding member in a sliding mechanism to which the lubricating oil composition is applied can be adjusted by adjusting an addition amount of these friction reducing agents.
- (C) Zinc Dithiophosphate (ZnDTP)
- In the present embodiment, in order to assist in the adjustment of the friction coefficient by the (B) friction modifier described above, a phosphorus-containing compound whose chemical structure represented by the following General Formula (1) may be contained. Each R in General Formula (1) represents an individual hydrocarbon group, and examples thereof include a linear primary alkyl group, a branched secondary alkyl group, or an aryl group. In the present embodiment, R is not particularly limited, and preferably has one or more secondary alkyl groups having at least a short chain (3 to 5 carbon atoms).
- In the present embodiment, ZnDTPs having different numbers of alkyl groups can be mixed and used as the ZnDTP. In this case, an average number of the alkyl groups in the ZnDTP is preferably 1 to 3, and more preferably 1 to 2. A method for measuring the average number of the alkyl groups in the ZnDTP is not particularly limited, and the average number can be determined by measuring the hydroxyl value by using an FT-IR, for example.
- The ZnDTP according to the present embodiment preferably has at least a secondary alkyl group, and more preferably has the secondary alkyl group in an amount larger than a primary alkyl group. In the present embodiment, different types of ZnDTPs can be mixed. In this case, it is preferable to contain the ZnDTP having at least a secondary alkyl group, and it is preferable that the ZnDTP as a whole has the secondary alkyl group in an amount larger than a primary alkyl group. An alkyl group having a short chain is more preferable than an alkyl group having a long chain. Therefore, the ZnDTP according to the present embodiment has a secondary alkyl group having at least a short chain (3 to 5 carbon atoms). A method for measuring the alkyl group in the ZnDTP is not particularly limited, and measurement regarding whether the alkyl group is a primary alkyl group or a secondary alkyl group, or whether the alkyl group has a short chain or a long chain can be made based on characteristics of an absorption band of P—O—C and an absorption band of P═SP—S using a fingerprint region in the FT-IR, for example.
- It is easy to adjust the friction coefficient according to an addition amount of the friction modifier when the ZnDTP is added.
- [Function and Effect]
- The lubricating oil composition according to the present embodiment is a lubricating oil composition to be used in the sliding member coated with hydrogen-containing diamond-like carbon, contains the base oil and the friction modifier, and contains the fatty acid ester of pentaerythritol as the friction modifier. Such a lubricating oil composition enables the friction adjustment for the sliding mechanism that includes the sliding member coated with the hydrogen-containing DLC coating material and for which friction adjustment is difficult in the related art.
- In a damper, a constant time is required from rise of an oil hydraulic damping force for providing a vibration suppression force to start of a vibration suppression function. In response to this, the frictional force has high responsiveness. Therefore, during a period until the oil hydraulic damping force rises, that is, a period during which the sliding member shifts from a stationary state to a slipping state, or in a slight amplitude time during which the oil hydraulic damping force hardly acts, the frictional force becomes an important factor of the vibration suppression force of the damper.
- The inventor of the present invention has focused on a matter that, in the sliding member, a friction coefficient during the period until the oil hydraulic damping force rises or in slight vibration during which the oil hydraulic damping force hardly acts (referred to as a “minute low speed friction coefficient”), and a friction coefficient in normal vibration during which the oil hydraulic damping force acts (referred to as a “normal dynamic friction coefficient”) are different from each other, and has found that the difference in the friction property influences performance of the damper. It is also found that it is possible to achieve both steering stability and ride comfort by setting a ratio of the normal dynamic friction coefficient to the minute low speed friction coefficient within a specific numerical range.
- In the present embodiment, as an example, the normal dynamic friction coefficient is a friction coefficient when the damper as the sliding member is vibrated at a predetermined amplitude and a sliding speed of more than 4.0 mm/s. The minute low speed friction coefficient is a friction coefficient when the damper is vibrated at a predetermined amplitude and a sliding speed of 0.20 mm/s or less.
- The ratio of the normal dynamic friction coefficient to the minute low speed friction coefficient can be set to a specific numerical range by applying the lubricating oil composition according to the present embodiment to the sliding member coated with the hydrogen-containing DLC coating material.
- More specifically, when the lubricating oil composition according to the present embodiment is applied to a damper that includes the sliding member coated with the hydrogen-containing DLC coating material, a value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to 1.
- The value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) of 1 means that the friction coefficient is constant regardless of the sliding speed of the sliding member, and the value of less than 1.20 means that a variation in the friction coefficient can be reduced with respect to a change in the sliding speed of the sliding member. The value of normal dynamic friction coefficient)/(minute low speed friction coefficient) of less than 1 means that the frictional force at a minute low speed is large, and the frictional force at a normal time is small.
- Accordingly, when the lubricating oil composition according to the present embodiment is applied to, for example, a shock absorber as a damper, the vibration can be suppressed by the frictional force at an initial stage of movement of a piston, which is a stage before an oil hydraulic force for suppressing the vibration is generated. Therefore, with the lubricating oil composition according to the present embodiment, it is possible to easily set the oil hydraulic damping force of the damper using a shock absorbing member coated with hydrogen-containing DLC.
- In the present embodiment, when the value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) is about 0.4, it is possible to achieve a vibration reduction effect in the stage before the oil hydraulic force for suppressing the vibration is generated.
- In the lubricating oil composition according to the present embodiment, as the fatty acid ester of pentaerythritol, one having a fatty acid residue having 10 or more and 20 or less carbon atoms can be used. In addition, in the lubricating oil composition according to the present embodiment, it is preferable to use a partial ester of pentaerythritol having 1 to 3 hydroxy groups from a viewpoint of setting the total hydroxyl value of the fatty acid ester of pentaerythritol to an appropriate value. Further, in the lubricating oil composition according to the present embodiment, pentaerythritol monooleate can be used as an example of the partial ester of pentaerythritol.
- According to these characteristics, the value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to 1.
- When the lubricating oil composition according to the present embodiment contains 0.2% by mass or more of the fatty acid ester of pentaerythritol, it is possible to achieve the friction adjustment effect on the hydrogen-containing DLC coating material.
- Further, in the present embodiment, when the total hydroxyl value of the fatty acid ester of pentaerythritol in the friction modifier is 2.20 mgKOH/g or more, it is possible to achieve the friction adjustment effect on the sliding member coated with hydrogen-containing DLC.
- The lubricating oil composition according to the present embodiment may further contain a phosphorus-containing compound. The lubricating oil composition according to the present embodiment can reduce the difference between the minute low speed friction coefficient and the normal dynamic friction coefficient by containing the phosphorus-containing compound. Accordingly, it is possible to easily adjust the friction coefficient to a friction coefficient suitable for the ride comfort and the steering stability.
- Among the phosphorus-containing compound, particularly a ZnDTP is suppressed from being deteriorated (decomposed) by pentaerythritol, and thus the adjusted frictional force can be maintained over a long period of time.
- Therefore, the lubricating oil composition according to the present embodiment enables the friction adjustment for the sliding mechanism that includes the sliding portion coated with the hydrogen-containing DLC coating material.
- The lubricating oil composition according to the present embodiment is suitable as a lubricating oil used for, in addition to the damper, an internal combustion engine, a driving system transmission machine, industrial equipment, metal processing, and the like to which a low-friction sliding member coated with the hydrogen-containing DLC coating material as a hard thin film material is applied.
- [Sliding Mechanism]
- A sliding mechanism according to the present embodiment is a sliding mechanism using the lubricating oil composition according to the present embodiment described above, and includes at least a sliding portion coated with hydrogen-containing DLC. Examples of the sliding mechanism according to the present embodiment include a piston rod, a cylinder, a gear, a bearing, a transmission, and a damper to which the low-friction sliding member coated with the hydrogen-containing DLC coating material as the hard thin film material is applied.
- By applying the lubricating oil composition described above to the sliding mechanism according to the present embodiment, it is possible to perform the friction adjustment which is difficult in the sliding mechanism coated with the hydrogen-containing DLC coating material. When the sliding mechanism according to the present embodiment is a damper, it is possible to improve durability to friction and wear by coating the sliding portion with the hydrogen-containing DLC coating material, and it is possible to achieve both the ride comfort and the steering stability at a high level.
- Therefore, when the lubricating oil composition according to the present embodiment is applied to a damper, the value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) among components constituting the oil hydraulic damping force of the damper can be brought close to 1 regardless of the speed. Accordingly, it is possible to easily set the oil hydraulic damping force of the damper. Therefore, it is possible to design a damper capable of achieving both the steering stability and the ride comfort.
- Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.
- [Method for Measuring Normal Dynamic Friction Coefficient and Minute Low Speed Friction Coefficient]
-
FIG. 1 is a schematic view illustrating a device that measures the normal dynamic friction coefficient and the minute low speed friction coefficient. In the present example, the normal dynamic friction coefficient and the minute low speed friction coefficient of a test specimen are measured using afriction testing device 10 shown inFIG. 1 . - <Friction Testing Device>
- The
friction testing device 10 shown inFIG. 1 is a pin-on-disk type friction testing device. Thefriction testing device 10, a frictional force generated by reciprocating, by anelectromagnetic oscillator 3, a disk-shapedtest piece 2 fixed on aslide bearing 1, and pressing and sliding a pin-shapedtest piece 4 on the disk-shapedtest piece 2 is measured using astrain gauge 6 attached to a fixedshaft 5 of the pin-shapedtest piece 4. - In the
friction testing device 10 shown inFIG. 1 , acrylonitrile-butadiene rubber (NBR) used as an oil seal in a damper is used as the pin-shapedtest piece 4. - A tip of the pin-shaped
test piece 4 is cut so as to have an angle of 140° imitating an oil lip shape. The disk-shapedtest piece 2 is coated with hydrogen-containing diamond-like carbon used for a surface of a piston rod and is polished to a surface roughness Ra of 0.01 μm or less. - The frictional force (friction coefficient) between the pin-shaped
test piece 4 of NBR and the disk-shapedtest piece 2 coated with hydrogen-containing diamond-like carbon is measured using this device. - <Measurement of Normal dynamic friction coefficient and Minute Low Speed Friction Coefficient>
- Measurement of the normal dynamic friction coefficient and measurement of the minute low speed friction coefficient are performed. Regarding the measurement of the normal dynamic friction coefficient, the measurement is performed under conditions of an amplitude of 5.0 mm, a frequency of 5.0 Hz, and a sliding speed of 4.0 mm/s in a friction test using the
friction testing device 10 shown inFIG. 1 . Regarding the minute low speed friction coefficient, the measurement is performed under conditions of an amplitude of 5.0 mm, a frequency of 5.0 Hz, and a sliding speed of 0.20 mm/s. - <Calculation of Amplitude Dependent Index>
- In the present embodiment, an amplitude dependent index is an index adopted for evaluating the lubricating oil composition according to the present embodiment, and can be treated as one of evaluation indices for the ride comfort of the damper. The amplitude dependent index is expressed by (normal dynamic friction coefficient)/(minute low speed friction coefficient). As the amplitude dependent index is closer to 1, the difference between the friction coefficient at the time of the slight amplitude and the friction coefficient at the time of the normal amplitude is small, and it is possible to evaluate that the ride comfort is excellent.
- <Stick-slip Evaluation>
- In the measurement of the normal dynamic friction coefficient or the minute low speed friction coefficient, stick-slip is evaluated as “Yes” when the stick-slip occurred, and oil bleeding and deterioration in lip durability occurred. The amplitude dependent index and the stick-slip evaluation are integrated to determine whether the lubricating oil composition is passed or failed. A lubricating oil composition with a pass level is indicated by “G” and a lubricating oil composition with a failure level is indicated by “F”.
- [Examples, Comparative Examples, and Reference Examples]
- Test specimens of lubricating oil compositions of examples, comparative examples and reference examples are prepared according to compositions shown in Table 1.
- In a group of examples, there are provided lubricating oil compositions whose total hydroxyl values are different by changing a mixing ratio of fatty acid esters of pentaerythritol whose ester values are different or using a fatty acid ester of pentaerythritol alone, as a composition of the friction modifier in the lubricating oil composition. An oleate having a fatty acid residue having a carbon number of C18 was used as the fatty acid ester of pentaerythritol. A mineral oil was used as the base oil. If necessary, zinc dithiophosphate (ZnDTP) was used as the friction modifier.
- A friction test using acrylonitrile-butadiene rubber (NBR) as the pin-shaped
test piece 4, and a material coated with hydrogen-containing diamond-like carbon (DLC) as the disk-shapedtest piece 2 was performed in thefriction testing device 10 shown inFIG. 1 using these lubricating oil compositions. - In Comparative Example 1 of a group of comparative examples, a pentaerythritol tetraester is used, and a material coated with hydrogen-free DLC is used as the
test piece 2 in thefriction testing device 10. In Comparative Example 2, a pentaerythritol tetraester is used, and the material coated with hydrogen-containing DLC is used as thetest piece 2 in thefriction testing device 10. - In Comparative Example 3, a lubricating oil composition containing only a mineral oil and not containing a fatty acid ester of pentaerythritol is applied to the
friction testing device 10 using the material coated with hydrogen-free DLC as thetest piece 2. In Comparative Example 4, the lubricating oil composition containing only a mineral oil and not containing a fatty acid ester of pentaerythritol is applied to thefriction testing device 10 using the material coated with hydrogen-containing DLC as thetest piece 2. - In a group of reference examples, lubricating oil compositions in Examples 1 and 7 are applied to a material coated with hydrogen-free diamond-like carbon (DLC) in the
friction testing device 10 shown inFIG. 1 . - [Evaluation Results]
- Evaluation results are shown in Table 1.
-
TABLE 1 Reference Example Comparative Example Example 1 2 3 4 5 6 7 1 2 3 4 1 2 Compo- Pentaerythritol 1.0 0 0 2.0 6.0 0 10.0 0 0 0 0 1.0 10.0 sition (mono-) (% by Pentaerythritol 0 2.0 6.0 0 0 0 0 0 0 0 0 0 0 mass) (di-) Pentaerythritol 0 0 0 0 0 6.0 0 0 0 0 0 0 0 (tri-) Pentaerythritol 9.0 0 0 4.0 0 0 0 10.0 10.0 0 0 9.0 0 (tetra-) Zn-DTP 0 1.0 0 0 0 0 0 0 0 0 0 0 0 Base oil 90 97 94 94 94 94 90 90 90 100 100 90 90 Total hydroxyl 2.22 2.32 5.10 2.20 4.68 3.78 18.8 1.6 1.6 0 0 2.22 18.8 value (mgKOH/g) Type of Hydrogen- ◯ ◯ ◯ ◯ ◯ ◯ ◯ — ◯ — ◯ — — coating containing film DLC Hydrogen-free — — — — — — — ◯ — ◯ — ◯ ◯ DLC Evalua- Minute low 0.114 0.065 0.062 0.061 0.054 0.062 0.093 0.274 0.250 0.320 0.315 0.099 0.094 tion speed friction result coefficient (A) Normal 0.050 0.060 0.060 0.060 0.060 0.07 0.05 0.120 0.070 0.390 0.380 0.050 0.050 dynamic friction coefficient (B) B/A 0.455 0.997 1.030 1.003 1.076 1.073 0.519 0.434 0.280 1.223 1.218 0.495 0.535 Stick-slip No No No No No No No Yes Yes Yes Yes No No Comprehensive G G G G G G G F F F F G G determination - According to Examples 1 and 10, and Reference Examples 1 and 2, it is clear that the lubricating oil composition containing the fatty acid ester of pentaerythritol can achieve an effect of reducing the friction coefficient of the material coated with hydrogen-containing DLC, whose friction coefficient is difficult to be adjusted up to now, in the same manner as the material coated with hydrogen-free DLC.
- It is clear from comparison between Examples 1 to 7 and Comparative Examples 1 and 2 that when the total hydroxyl value of the lubricating oil composition is about 1.6 mgKOH/g, for both the material coated with hydrogen-containing DLC and the material coated with hydrogen-free DLC, the value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to the extent that the vibration reduction effect is achieved in the stage before the oil hydraulic force for suppressing the vibration is generated, but the stick-slip is likely to occur, and the lubricating oil composition is practically inapplicable when mounted on a predetermined shock absorber.
- According to Examples 1 to 7, it is clear that when the total hydroxyl value of the lubricating oil composition is 2.20 mgKOH/g or more, the value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to 0.4 to 1, and when the lubricating oil composition is applied to a damper, the vibration reduction effect can be achieved without causing the stick-slip in the stage before the oil hydraulic force for suppressing the vibration is generated.
- A configuration, functions, and effects of the embodiment of the present invention configured as described above will be collectively described.
- A lubricating oil composition according to the present embodiment is a lubricating oil composition to be used in a sliding member coated with hydrogen-containing diamond-like carbon (DLC), contains a base oil and a friction modifier, and contains a fatty acid ester of pentaerythritol as the friction modifier.
- The lubricating oil composition enables friction adjustment for a sliding mechanism that includes the sliding member coated with the hydrogen-containing DLC coating material and for which friction adjustment is difficult in the related art. Therefore, the lubricating oil composition can improve the friction property of the sliding member coated with the hydrogen-containing DLC coating material.
- With the lubricating oil composition, a ratio of a normal dynamic friction coefficient to a minute low speed friction coefficient can be set to a specific numerical range. More specifically, when the lubricating oil composition according to the present embodiment is applied to a damper that includes the sliding member coated with the hydrogen-containing DLC coating material, a value of (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to 1.
- It is presumed that in the lubricating oil composition according to the present embodiment, the terminal hydroxy group in pentaerythritol contributes to the sliding member coated with hydrogen-containing DLC. Therefore, in the present embodiment, when the total hydroxyl value of the fatty acid ester of pentaerythritol as the friction modifier is 2.20 mgKOH/g or more, it is possible to achieve the friction adjustment effect on the sliding member coated with hydrogen-containing DLC.
- The lubricating oil composition according to the present embodiment further contains a phosphorus-containing compound.
- The lubricating oil composition according to the present embodiment can reduce a difference between the minute low speed friction coefficient and the normal dynamic friction coefficient by containing the phosphorus-containing compound. Accordingly, it is possible to easily adjust the friction coefficient to a friction coefficient suitable for ride comfort and steering stability.
- In the lubricating oil composition according to the present embodiment, the phosphorus-containing compound is zinc dithiophosphate (Zn-DTP), and has at least a secondary alkyl group having 3 to 5 carbon atoms.
- Among the phosphorus-containing compound, particularly a Zn-DTP is suppressed from being deteriorated (decomposed) by pentaerythritol, and thus the adjusted frictional force can be maintained over a long period of time.
- A sliding mechanism according to the present embodiment is a sliding mechanism using the lubricating oil composition described above, and includes at least a sliding portion coated with hydrogen-containing DLC.
- In such a sliding mechanism, the friction adjustment can be performed by the lubricating oil composition containing the fatty acid ester of pentaerythritol, and (normal dynamic friction coefficient)/(minute low speed friction coefficient) can be brought close to 1.
- When such a sliding mechanism is, for example, a damper, it is possible to design a damper capable of achieving the vibration reduction effect in a stage before an oil hydraulic force for suppressing vibration is generated. Accordingly, it is possible to expand a design width of the oil hydraulic damping force of the damper, and it is possible to design a damper capable of achieving both the steering stability and the ride comfort.
- Although the embodiment of the present invention has been described above, the above embodiment is merely a part of application examples of the present invention, and is not intended to limit the technical scope of the present invention to the specific configurations of the above embodiment.
- In the lubricating oil composition according to the present embodiment, in addition to the components described above, at least one component selected from an ashless detergent dispersant, a metal-based detergent, a lubricity improver, an antioxidant, a rust inhibitor, a metal deactivator, a viscosity index improver, a pour point depressant, and an antifoaming agent can be appropriately blended as an optional component as long as the object of the present invention is not impaired. In addition to the optional component described above, a component that can be used as an additive of the lubricating oil composition for the damper can be appropriately blended.
- The present application claims priority under Japanese Patent Application No. 2020-77577 filed to the Japan Patent Office on Apr. 24, 2020, and the entire content of this application is incorporated herein by reference.
Claims (16)
1. A lubricating oil composition to be used in a sliding member coated with hydrogen-containing diamond-like carbon, the lubricating oil composition comprising:
a base oil; and
a friction modifier, wherein
the friction modifier contains a fatty acid ester of pentaerythritol.
2. The lubricating oil composition according to claim 1 , wherein
the fatty acid ester of pentaerythritol is contained in an amount of 0.2% by mass or more.
3. The lubricating oil composition according to claim 1 , wherein
a total hydroxyl value of the fatty acid ester of pentaerythritol is 2.20 mgKOH/g or more.
4. (canceled)
5. (canceled)
6. The lubricating oil composition according to claim 1 , wherein
the fatty acid ester of pentaerythritol is a plurality of esters selected from a pentaerythritol monoester, a pentaerythritol diester, a pentaerythritol triester, and a pentaerythritol tetraester.
7. The lubricating oil composition according to claim 2 , wherein
a content of the fatty acid ester of pentaerythritol is 0.2% by mass or more and 10.0% by mass or less with respect to a total amount of the lubricating oil composition.
8. The lubricating oil composition according to claim 2 , wherein
as the fatty acid ester of pentaerythritol, a pentaerythritol monoester or a pentaerythritol diester is contained in an amount of 2.0% by mass or more and 6.0% by mass or less with respect to a total amount of the lubricating oil composition.
9. The lubricating oil composition according to claim 1 , wherein
the sliding member is a damper.
10. The lubricating oil composition according to claim 2 , wherein
the sliding member is a damper.
11. The lubricating oil composition according to claim 3 , wherein
the sliding member is a damper.
12. The lubricating oil composition according to claim 6 , wherein
the sliding member is a damper.
13. The lubricating oil composition according to claim 7 , wherein
the sliding member is a damper.
14. The lubricating oil composition according to claim 8 , wherein
the sliding member is a damper.
15. A sliding mechanism using the lubricating oil composition according to claim 1 , wherein
at least a sliding portion is coated with hydrogen-containing diamond-like carbon.
16. The sliding mechanism according to claim 15 , wherein
a ratio of a normal dynamic friction coefficient to a very low speed friction coefficient, which is (normal dynamic friction coefficient)/(very low speed friction coefficient), is less than 1.20.
Applications Claiming Priority (3)
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JP2020-077577 | 2020-04-24 | ||
JP2020077577 | 2020-04-24 | ||
PCT/JP2021/016296 WO2021215499A1 (en) | 2020-04-24 | 2021-04-22 | Lubricating oil composition and sliding mechanism |
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US20230174882A1 true US20230174882A1 (en) | 2023-06-08 |
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US17/996,660 Pending US20230174882A1 (en) | 2020-04-24 | 2021-04-22 | Lubricating oil composition and sliding mechanism |
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US (1) | US20230174882A1 (en) |
CN (1) | CN115461432A (en) |
DE (1) | DE112021002590T5 (en) |
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US20230159845A1 (en) * | 2020-04-23 | 2023-05-25 | Kyb Corporation | Shock absorber lubricant composition, shock absorber, and method for adjusting friction characteristics of shock absorber lubricant |
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JP2022076932A (en) * | 2020-11-10 | 2022-05-20 | 日本アイ・ティ・エフ株式会社 | Slide member, lubricant and slide mechanism |
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US20080248981A1 (en) * | 2007-03-30 | 2008-10-09 | Nippon Oil Corporation | Lubricating oil composition |
US8575076B2 (en) * | 2003-08-08 | 2013-11-05 | Nissan Motor Co., Ltd. | Sliding member and production process thereof |
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JP2005090738A (en) * | 2003-08-13 | 2005-04-07 | Nissan Motor Co Ltd | Rolling bearing |
JP5226242B2 (en) * | 2007-04-18 | 2013-07-03 | 出光興産株式会社 | Lubricating oil composition for refrigerator |
JP5466502B2 (en) * | 2007-04-18 | 2014-04-09 | 出光興産株式会社 | Lubricating oil composition for refrigerator and compressor using the same |
US9695379B2 (en) * | 2013-08-23 | 2017-07-04 | Idemitsu Kosan Co., Ltd. | Lubricating oil composition for shock absorber and friction reduction method for shock absorber |
-
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- 2021-04-22 CN CN202180030533.2A patent/CN115461432A/en active Pending
- 2021-04-22 WO PCT/JP2021/016296 patent/WO2021215499A1/en active Application Filing
- 2021-04-22 DE DE112021002590.2T patent/DE112021002590T5/en active Pending
- 2021-04-22 US US17/996,660 patent/US20230174882A1/en active Pending
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
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US8575076B2 (en) * | 2003-08-08 | 2013-11-05 | Nissan Motor Co., Ltd. | Sliding member and production process thereof |
US20080248981A1 (en) * | 2007-03-30 | 2008-10-09 | Nippon Oil Corporation | Lubricating oil composition |
Cited By (1)
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US20230159845A1 (en) * | 2020-04-23 | 2023-05-25 | Kyb Corporation | Shock absorber lubricant composition, shock absorber, and method for adjusting friction characteristics of shock absorber lubricant |
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DE112021002590T5 (en) | 2023-02-16 |
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JPWO2021215499A1 (en) | 2021-10-28 |
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