A buffer

Abstract

The lubricating oil composition of the present embodiment is a lubricating oil composition for a sliding member coated with hydrogen-containing diamond-like carbon, and contains a base oil and a friction modifier, wherein the friction modifier contains a pentaerythritol fatty acid ester.

Description

Technical Field

[0001] The present invention relates to a lubricating oil composition and a sliding mechanism. Background Art

[0002] The shock absorber, which is an example of a sliding mechanism, exerts a damping force by reciprocating motion. As is well known, the damping force is the resultant force of the hydraulic damping force generated by the valve and the friction force generated in the sliding portion between the piston rod and the oil seal or between the piston and the cylinder. In addition, it is known that when the damping force of the shock absorber is large, the handling stability increases but the ride comfort deteriorates, and conversely, when the damping force of the shock absorber is small, the handling stability deteriorates but the ride comfort is good.

[0003] Therefore, research has been conducted to improve ride comfort and handling stability by adjusting the friction force of the sliding part by selecting a friction modifier added to the lubricating oil of the sliding part in the shock absorber. For example, as an existing friction modifier, there is a friction modifier mentioned in "Technical Trends and Tribology of Shock Absorbers" (Hiroshi Nakanishi, Journal of Japanese Society of Tribologists, 2009 (Vol. 54) No. 9, p. 598). Summary of the invention

[0004] In recent years, the application of hard film coating technology has been gaining momentum as a surface treatment technology for parts with severe friction and wear environments. Diamond-like carbon (hereinafter referred to as "DLC"), an example of such a coating material, has excellent low friction properties and is widely used as a low-friction sliding component.

[0005] However, it is known that lubricating oil compositions containing conventional friction modifiers do not fully exert friction modifier effects on DLC coating materials. In particular, it is more difficult to set effective friction modifiers and lubricating oil compositions for hydrogen-containing DLC ​​coating materials, thereby making it difficult to improve friction characteristics.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to improve the friction characteristics of a sliding mechanism having a sliding member coated with hydrogen-containing diamond-like carbon.

[0007] The main technical content of one embodiment of the present invention is the following lubricating oil composition.

[0008] A lubricating oil composition is a lubricating oil composition for a sliding member coated with hydrogen-containing diamond carbon, the lubricating oil composition comprising a base oil and a friction modifier, wherein the friction modifier comprises a pentaerythritol fatty acid ester. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram for explaining an apparatus for measuring the normal dynamic friction coefficient and the micro-low-speed friction coefficient. DETAILED DESCRIPTION

[0010] [Lubricating oil composition]

[0011] Hereinafter, the lubricating oil composition according to the embodiment of the present invention will be described.

[0012] The lubricating oil composition of the present embodiment is a lubricating oil composition for sliding members 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, wherein the friction modifier (B) contains a pentaerythritol fatty acid ester.

[0013] (A) Base oil

[0014] In the lubricating oil composition of the present embodiment, the base oil is a mineral oil and / or a synthetic oil. The type of the mineral oil or synthetic oil is not particularly limited, and examples of the mineral oil include paraffin-based mineral oils, intermediate-based mineral oils, naphthenic mineral oils, etc. obtained by conventional purification methods such as solvent purification and hydrogenation purification. In addition, examples of the synthetic oil include polybutene, polyolefins [α-olefin (co)polymers], various esters (such as polyol esters, dibasic acid esters, phosphate esters, etc.), various ethers (such as polyphenylene ethers, etc.), alkylbenzenes, alkylnaphthalenes, etc.

[0015] In the present embodiment, as the base oil, one of the above-mentioned mineral oils may be used, or two or more of them may be used in combination. In addition, one of the above-mentioned synthetic oils may be used, or two or more of them may be used in combination. In addition, one or more mineral oils and one or more synthetic oils may be used in combination.

[0016] (B) Friction modifier

[0017] The lubricating oil composition of the present embodiment contains pentaerythritol fatty acid ester as a friction modifier. Here, the pentaerythritol fatty acid ester can be a fatty acid ester having a fatty acid residue with a carbon number of 10 or more and 20 or less. The fatty acid residue refers to a decarboxylation residue of a fatty acid, and may be a branched or straight-chain fatty acid. In addition, the fatty acid residue may be an unsaturated or saturated aliphatic hydrocarbon group.

[0018] Pentaerythritol is a tetravalent sugar alcohol. Pentaerythritol includes: pentaerythritol tetraester obtained by combining all four terminal substituents with fatty acid residue esters, and pentaerythritol monoester, pentaerythritol diester and pentaerythritol triester obtained by combining any terminal substituent with fatty acid residue esters.

[0019] In the present embodiment, as the friction modifier, a plurality of esters selected from the above-mentioned pentaerythritol monoester, pentaerythritol diester, pentaerythritol triester and pentaerythritol tetraester may be used in combination.

[0020] In the present embodiment, as the factor that can realize the friction adjustment of the sliding member that is coated with hydrogenated DLC, it is inferred that the terminal hydroxyl group is more dominant than the fatty acid residue that constitutes pentaerythritol fatty acid ester.Therefore, preferably use the higher pentaerythritol partial ester of hydroxyl value.In the present embodiment, can use pentaerythritol monooleate, but the carbon number of fatty acid residue is not limited to C18.

[0021] In this embodiment, the content of the pentaerythritol fatty acid ester as the friction modifier (B) can be 0.2 mass % or more and 10.0 mass % or less relative to the total amount of the lubricating oil composition. If the content of the friction modifier (B) is less than 0.2 mass %, the friction modifier effect on the hydrogen-containing DLC ​​coating material cannot be obtained, and if it exceeds 10.0 mass %, the friction modifier effect reaches a limit, resulting in material cost loss.

[0022] In the present embodiment, specifically, when the total hydroxyl value of the pentaerythritol fatty acid ester in the friction modifier is 2.20 mgKOH / g or more, a friction modifier effect on the sliding member coated with the hydrogen-containing DLC ​​can be obtained.

[0023] Therefore, the friction modifier of the present embodiment may contain pentaerythritol tetraester having an ester value of 4. In this case, it may be used in combination with pentaerythritol monoester having a high hydroxyl value to adjust the total hydroxyl value of pentaerythritol fatty acid ester to the above-mentioned specific value.

[0024] The friction modifiers applicable to the present embodiment may include various friction reducers such as phosphorus, amines, or esters in addition to the above. By adjusting the amount of these friction reducers added, the friction coefficient of the sliding member in the sliding mechanism to which the lubricating oil composition is applied can be adjusted.

[0025] (C) Zinc dithiophosphate (ZnDTP)

[0026] In this embodiment, in order to assist in adjusting the friction coefficient based on the above-mentioned (B) friction modifier, a phosphorus compound represented by the following general formula (1) may be contained. R in formula (1) represents a single hydrocarbon group, and examples thereof include a straight-chain primary alkyl group, a branched secondary alkyl group, or an aryl group. In this embodiment, R is not particularly limited, but preferably has at least one short-chain (3 to 5 carbon atoms) secondary alkyl group.

[0027] [Chemistry 1]

[0028]

[0029] In this embodiment, ZnDTPs having different numbers of alkyl groups may be mixed and used as ZnDTP. In this case, the average number of alkyl groups in ZnDTP is preferably 1 to 3, more preferably 1 to 2. The method for measuring the average number of alkyl groups in ZnDTP is not particularly limited, and it can be determined, for example, by measuring the hydroxyl value by FT-IR.

[0030] In addition, the ZnDTP of the present embodiment preferably has at least a secondary alkyl group, and preferably the secondary alkyl group is more than the primary alkyl group. In addition, in the present embodiment, different types of ZnDTP can be mixed, but in this case, it is preferred to contain a ZnDTP having at least a secondary alkyl group, and it is preferred that the ZnDTP as a whole has more secondary alkyl groups than primary alkyl groups. In addition, short-chain alkyl groups are superior to long-chain alkyl groups. Therefore, the ZnDTP of the present embodiment has at least a short-chain (3 to 5 carbon atoms) secondary alkyl group. The method for determining the alkyl group of ZnDTP is not particularly limited. For example, the FT-IR fingerprint area can be used and the alkyl group can be determined from the characteristics of the PO-OC absorption band and the P=SP-S absorption band to determine whether the alkyl group is a primary alkyl group or a secondary alkyl group, and whether it is a short-chain alkyl group or a long-chain alkyl group.

[0031] When ZnDTP is added, the friction coefficient can be easily adjusted by the amount of the friction modifier added.

[0032] [Effects]

[0033] The lubricating oil composition of the present embodiment is a lubricating oil composition for sliding members coated with hydrogen-containing diamond-like carbon, and contains a base oil and a friction modifier, wherein the friction modifier contains a pentaerythritol fatty acid ester. Such a lubricating oil composition can achieve friction adjustment for a sliding mechanism having a sliding member coated with a hydrogen-containing DLC ​​coating material, which has been difficult to adjust friction in the past.

[0034] In a shock absorber, it takes a certain amount of time for the damping force generated by the hydraulic pressure for applying the damping force to rise and start the damping action. In contrast, the friction force has a high responsiveness. Therefore, the friction force is an important factor of the damping force of the shock absorber during the period before the hydraulic damping force rises, that is, during the period when the sliding member changes from a stationary state to a sliding state or at a small amplitude when the hydraulic damping force hardly acts.

[0035] The inventors of the present invention have focused on the fact that the friction coefficient in a sliding member during a period before the hydraulic damping force rises or during a small vibration when the hydraulic damping force hardly acts (referred to as a "micro low-speed friction coefficient") is different from the friction coefficient during a normal vibration when the hydraulic damping force acts (referred to as a "normal dynamic friction coefficient"), and have found that this difference in friction characteristics affects the performance of the shock absorber. In addition, they have found that by setting the ratio of the normal dynamic friction coefficient to the micro low-speed friction coefficient within a specific numerical range, both operational stability and ride comfort can be achieved.

[0036] In this embodiment, as an example, the normal dynamic friction coefficient refers to the friction coefficient when the buffer as a sliding member vibrates at a sliding speed exceeding 4.0 mm / s with a predetermined amplitude. In addition, the micro-low-speed friction coefficient refers to the friction coefficient when the shock absorber vibrates at a sliding speed of 0.20 mm / s or less with a predetermined amplitude.

[0037] By applying the lubricating oil composition of the present embodiment to a sliding member coated with a hydrogen-containing DLC ​​coating material, the ratio of the normal dynamic friction coefficient to the slight low-speed friction coefficient can be set within a specific numerical range.

[0038] More specifically, when the lubricating oil composition of the present embodiment is applied to a shock absorber having a sliding member coated with a hydrogen-containing DLC ​​coating material, the value of (normal dynamic friction coefficient) / (slightly low-speed friction coefficient) can be made close to 1.

[0039] The value of (normal dynamic friction coefficient) / (slightly low-speed friction coefficient) is 1, indicating that the friction coefficient is constant regardless of the sliding speed of the sliding member, and less than 1.20 indicates that the fluctuation of the friction coefficient can be reduced relative to the change of the sliding speed of the sliding member. The value of (normal dynamic friction coefficient) / (slightly low-speed friction coefficient) is less than 1, indicating that the friction force is large at slightly low speeds and small at normal times.

[0040] Therefore, when the lubricating oil composition of the present embodiment is applied to a shock absorber as a shock absorber, for example, the vibration can be suppressed by the friction force at a certain initial stage when the piston starts to move, which is a pre-stage for generating hydraulic pressure for suppressing vibration. Therefore, according to the lubricating oil composition of the present embodiment, the hydraulic vibration damping force of the shock absorber using the shock absorber member coated with hydrogen-containing DLC ​​can be easily set.

[0041] In the present embodiment, if the value of (normal dynamic friction coefficient) / (slightly low-speed friction coefficient) is approximately 0.4, a vibration reduction effect can be obtained at a stage before the hydraulic pressure for suppressing vibration is generated.

[0042] In the lubricating oil composition of the present embodiment, as the pentaerythritol fatty acid ester, a fatty acid ester having a fatty acid residue having 10 or more and 20 or less carbon atoms can be used. In addition, from the viewpoint of making the total hydroxyl value of the pentaerythritol fatty acid ester an appropriate value, the lubricating oil composition of the present embodiment preferably uses a pentaerythritol partial ester having 1 to 3 hydroxyl groups. In addition, in the lubricating oil composition of the present embodiment, as an example of the pentaerythritol partial ester, pentaerythritol monooleate can be used.

[0043] These features can make the value of (normal dynamic friction coefficient) / (slightly low-speed friction coefficient) close to 1.

[0044] Furthermore, since the lubricating oil composition of the present embodiment contains 0.2 mass % or more of pentaerythritol fatty acid ester, it is possible to obtain a friction regulating effect on the hydrogen-containing DLC ​​coating material.

[0045] Furthermore, in the present embodiment, when the total hydroxyl value of the pentaerythritol fatty acid ester in the friction modifier is 2.20 mgKOH / g or more, a friction modifier effect on the sliding member coated with the hydrogen-containing DLC ​​can be obtained.

[0046] In addition, the lubricating oil composition of the present embodiment may further contain a phosphorus-containing compound. The lubricating oil composition of the present embodiment can reduce the difference between the micro-low-speed friction coefficient and the normal dynamic friction coefficient by containing a phosphorus compound. Thereby, the friction coefficient can be easily adjusted to a suitable level for ride comfort and handling stability.

[0047] Furthermore, among the phosphorus-containing compounds, ZnDTP in particular is suppressed from degrading (decomposing) by pentaerythritol, so that the adjusted friction force can be maintained for a long period of time.

[0048] Therefore, the lubricating oil composition of the present embodiment can achieve friction adjustment in a sliding mechanism having a sliding portion coated with a hydrogen-containing DLC ​​coating material.

[0049] The lubricating oil composition of this embodiment is suitable as a lubricating oil for internal combustion engines, drive system transmission engines, industrial equipment, metal processing, etc., in addition to shock absorbers, to which low-friction sliding components are applied, wherein the low-friction sliding components are coated with a hydrogen-containing DLC ​​coating material as a hard film material.

[0050] [Sliding mechanism]

[0051] The sliding mechanism of the present embodiment is a sliding mechanism using the lubricating oil composition of the present embodiment, wherein at least the sliding portion is coated with hydrogen-containing DLC. As an example of the sliding mechanism of the present embodiment, there can be cited a piston rod, a cylinder, a gear, a bearing, a transmission, a buffer, etc. to which a low-friction sliding member coated with a hydrogen-containing DLC ​​coating material as a hard film material is applied.

[0052] The sliding mechanism of the present embodiment can achieve friction adjustment which is difficult in the sliding mechanism coated with the hydrogen-containing DLC ​​coating material by applying the above-mentioned lubricating oil composition. In addition, when the sliding mechanism of the present embodiment is a shock absorber, by coating the sliding part with the hydrogen-containing DLC ​​coating material, the durability against friction and wear can be improved, and the ride comfort and handling stability can be achieved at a high level.

[0053] Therefore, when the lubricating oil composition of the present embodiment is applied to a shock absorber, the value of (normal dynamic friction coefficient) / (slightly low-speed friction coefficient) among the components constituting the hydraulic damping force of the shock absorber can be close to 1 regardless of the speed. This makes it easy to set the hydraulic damping force of the shock absorber. Therefore, a shock absorber having both operational stability and ride comfort can be designed.

[0054] [Example]

[0055] The present invention will be further described in detail below by way of examples and comparative examples, but the present invention is not limited to these examples.

[0056] [Method for measuring normal dynamic friction coefficient and micro-low speed friction coefficient]

[0057] Figure 1 Schematic diagram of a device for measuring the normal dynamic friction coefficient and the micro-low-speed friction coefficient. Figure 1 The friction test device 10 shown is used to measure the normal dynamic friction coefficient and the micro-low-speed friction coefficient of the sample.

[0058] <Friction test device>

[0059] Figure 1 The friction test device 10 shown is a pin-disc type friction test device. The friction test device 10 reciprocates a disc test piece 2 fixed to a sliding bearing 1 by means of an electromagnetic exciter 3, presses a pin test piece 4 thereon and causes the pin test piece 4 to slide to generate friction force, and measures the generated friction force using a strain gauge 6 mounted on a fixed shaft 5 of the pin test piece 4.

[0060] exist Figure 1 In the friction test device 10 shown, acrylonitrile-butadiene rubber (NBR) used as an oil seal in a shock absorber is used as the pin test piece 4 .

[0061] The tip of the pin test piece 4 was cut at an angle of 140° following the shape of the oil lip. The disk test piece 2 was coated with hydrogen-containing diamond-like carbon for piston rod surfaces and ground and polished to a surface roughness Ra of 0.01 μm or less.

[0062] Using this apparatus, the friction force (friction coefficient) between the NBR pin test piece 4 and the disk test piece 2 coated with hydrogen-containing diamond-like carbon was measured.

[0063] <Determination of normal dynamic friction coefficient and low-speed friction coefficient>

[0064] The normal dynamic friction coefficient and the low-speed friction coefficient were measured. Figure 1The friction test of the friction test device 10 shown was conducted under the conditions of an amplitude of 5.0 mm, a frequency of 5.0 Hz, and a sliding speed of 0.20 mm / s. In addition, the low-speed friction coefficient was measured under the conditions of an amplitude of 5.0 mm, a frequency of 5.0 Hz, and a sliding speed of 0.20 mm / s.

[0065] <Calculation of amplitude-related indicators>

[0066] In this embodiment, the amplitude-related index is an index used to evaluate the lubricating oil composition of this embodiment, and can be treated as one of the evaluation indexes of the ride comfort of the shock absorber. The amplitude-related index is represented by (normal dynamic friction coefficient) / (micro low-speed friction coefficient). The closer the value of the amplitude-related index is to 1, the smaller the difference between the friction coefficient at micro amplitude and the friction coefficient at normal amplitude is, and the ride comfort can be evaluated as good.

[0067] <Slip-stick evaluation>

[0068] In the measurement of the above-mentioned normal dynamic friction coefficient or the above-mentioned low-speed friction coefficient, if stick-slip occurs and oil bleeding or lip durability decreases, the stick-slip evaluation is "yes". In addition, the amplitude-related index and the stick-slip evaluation are combined to judge whether the lubricating oil composition is qualified, and the qualified one is indicated as "G" and the unqualified one is indicated as "F".

[0069] [Examples, Comparative Examples and Reference Examples]

[0070] According to the formulations shown in Table 1, samples of lubricating oil compositions of Examples, Comparative Examples and Reference Examples were prepared.

[0071] <Example>

[0072] In the group of examples, as the composition of the friction modifier in the lubricating oil composition, the total hydroxyl value of the lubricating oil composition is changed by changing the mixing ratio of pentaerythritol fatty acid esters with different ester values ​​or using them alone. As the pentaerythritol fatty acid ester, an oleic acid ester with a carbon number of C18 in the fatty acid residue is used. In addition, mineral oil is used as the base oil. In addition, zinc dithiophosphate (ZnDTP) is used as a friction modifier as needed.

[0073] Using these lubricating oil compositions, Figure 1 In the friction test apparatus 10 shown, a friction test was performed using acrylonitrile-butadiene rubber (NBR) as the pin test piece 4 and a material coated with hydrogen-containing diamond-like carbon (DLC) as the disk test piece 2 .

[0074] <Comparative Example>

[0075] In the group of comparative examples, Comparative Example 1 used pentaerythritol tetraester and a material coated with hydrogen-free DLC as the test piece 2 in the friction test device 10. In addition, Comparative Example 2 used pentaerythritol tetraester and a material coated with hydrogen-containing DLC ​​as the test piece 2 in the friction test device 10.

[0076] In addition, in Comparative Example 3, a lubricating oil composition containing only mineral oil and not containing pentaerythritol fatty acid ester was applied to a friction test apparatus 10 using a material coated with hydrogen-free DLC as a test piece 2; in Comparative Example 4, a lubricating oil composition containing only mineral oil and not containing pentaerythritol fatty acid ester was applied to a friction test apparatus 10 using a material coated with hydrogen-containing DLC ​​as a test piece 2.

[0077] <Reference example>

[0078] In the reference group, Figure 1 In the friction test apparatus 10 shown, the lubricating oil compositions of Example 1 and Example 7 were applied to a material coated with hydrogen-free diamond-like carbon (DLC).

[0079] [Evaluation results]

[0080] The evaluation results are shown in Table 1.

[0081] [Table 1]

[0082]

[0083] According to Examples 1 and 10 and Reference Examples 1 and 2, it can be seen that the lubricating oil composition containing pentaerythritol fatty acid ester can achieve the effect of reducing the friction coefficient even for materials coated with hydrogen-containing DLC, which has been difficult to adjust the friction coefficient, as well as materials coated with hydrogen-free DLC.

[0084] Furthermore, as can be seen from the comparison between Examples 1 to 7 and Comparative Examples 1 and 2, when the total hydroxyl value of the lubricating oil composition is about 1.6 mgKOH / g, even for a material coated with hydrogen-containing DLC ​​or a material coated with hydrogen-free DLC, the value of (normal dynamic friction coefficient) / (slightly low-speed friction coefficient) can be made close to a level at which a vibration reduction effect in the front stage of generating a hydraulic pressure for suppressing vibration can be obtained, but stick-slip is likely to occur, and when mounted on a predetermined shock absorber, it is not suitable for actual use.

[0085] Furthermore, according to Examples 1-7, if the total hydroxyl value of the lubricating oil composition is 2.20 mgKOH / g or more, the value of (normal dynamic friction coefficient) / (micro-low-speed friction coefficient) can be close to 0.4 to 1, and when applied to a shock absorber, a vibration reduction effect can be obtained in the early stage of generating a hydraulic pressure for suppressing vibration without stick-slip.

[0086] [Summarize]

[0087] The configuration, operation, and effects of the embodiment of the present invention configured as above will be summarized and described.

[0088] The lubricating oil composition of the present embodiment is a lubricating oil composition for sliding members coated with hydrogen-containing diamond-like carbon (DLC), and contains a base oil and a friction modifier, wherein the friction modifier contains a pentaerythritol fatty acid ester.

[0089] The lubricating oil composition can achieve friction adjustment even for sliding mechanisms having sliding members coated with hydrogen-containing DLC ​​coating materials, which have been difficult to adjust friction in the past. Therefore, the lubricating oil composition can improve the friction characteristics of sliding members coated with hydrogen-containing DLC ​​coating materials.

[0090] In addition, the lubricating oil composition can set the ratio of the normal dynamic friction coefficient to the micro-low-speed friction coefficient within a specific numerical range. More specifically, when the lubricating oil composition of this embodiment is applied to a shock absorber having a sliding member coated with a hydrogen-containing DLC ​​coating material, the value of (normal dynamic friction coefficient) / (micro-low-speed friction coefficient) can be made close to 1.

[0091] In addition, it is estimated that the terminal hydroxyl group of pentaerythritol in the lubricating oil composition of the present embodiment contributes to the sliding member coated with hydrogen-containing DLC. Therefore, in the present embodiment, if the total hydroxyl value of the pentaerythritol fatty acid ester as a friction modifier is 2.20 mgKOH / g or more, a friction modifier effect on the sliding member coated with hydrogen-containing DLC ​​can be obtained.

[0092] Furthermore, the lubricating oil composition of the present embodiment further contains a phosphorus-containing compound.

[0093] The lubricating oil composition of the present embodiment can reduce the difference between the slight low-speed friction coefficient and the normal dynamic friction coefficient by containing the phosphorus compound, thereby making it easy to adjust the friction coefficient to a value suitable for ride comfort and steering stability.

[0094] Furthermore, in the lubricating oil composition of the present embodiment, the phosphorus-containing compound is zinc dithiophosphate (Zn-DTP) and contains at least a secondary alkyl group having 3 to 5 carbon atoms.

[0095] Among phosphorus-containing compounds, Zn-DTP is particularly inhibited from degrading (decomposing) by pentaerythritol, so that the adjusted friction force can be maintained for a long period of time.

[0096] The sliding mechanism of the present embodiment is a sliding mechanism using the above-mentioned lubricating oil composition, wherein at least the sliding portion is coated with hydrogen-containing DLC.

[0097] In such a sliding mechanism, the lubricating oil composition containing pentaerythritol fatty acid ester can adjust the friction and make (normal dynamic friction coefficient) / (slightly low-speed friction coefficient) close to 1.

[0098] If such a sliding mechanism is a buffer, for example, the buffer can be designed so that a vibration reduction effect can be obtained before the hydraulic pressure for suppressing vibration is generated. This can expand the design range of the hydraulic vibration reduction force of the shock absorber and design a buffer that combines operational stability and ride comfort.

[0099] [Other embodiments]

[0100] Although the embodiments of the present invention have been described above, the above embodiments merely represent a part of application examples of the present invention and are not intended to limit the technical scope of the present invention to the specific structures of the above embodiments.

[0101] The lubricating oil composition of the present embodiment may contain, in addition to the above-mentioned components, at least one component selected from ashless detergent dispersants, metal detergents, lubricity improvers, antioxidants, rust inhibitors, metal deactivators, viscosity index improvers, pour point curing agents, and defoamers as an optional component, as long as the purpose of the present invention is not impaired. In addition to the above-mentioned optional components, components that can be used as additives for the lubricating oil composition for a shock absorber may be appropriately contained.

[0102] This application claims priority based on Japanese Patent Application No. 2020-77577 filed with the Japan Patent Office on April 24, 2020, and all the contents of that application are incorporated into this specification by reference.

Claims

1. A buffer, comprising: Sliding mechanism coated with hydrogen-containing diamond-like carbon, and A lubricating oil composition applied to the sliding mechanism coated with hydrogen-containing diamond-like carbon, The lubricating oil composition contains a base oil and a friction modifier; The friction modifier contains pentaerythritol fatty acid ester, The total hydroxyl value of the pentaerythritol fatty acid ester is 2.20 mgKOH / g or more, The content of the pentaerythritol fatty acid ester is 0.2% by mass or more and 10.0% by mass or less relative to the total amount of the lubricating oil composition.

2. The buffer according to claim 1, wherein: The pentaerythritol fatty acid ester is a plurality of esters selected from pentaerythritol monoester, pentaerythritol diester, pentaerythritol triester and pentaerythritol tetraester.

3. The buffer according to claim 1, wherein: The ratio of the normal dynamic friction coefficient to the micro-low-speed friction coefficient, ie, (normal dynamic friction coefficient) / (micro-low-speed friction coefficient) is less than 1.20.

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