Method for producing tribofilm and engine

Abstract

To provide a method of producing a tribo-film capable of obtaining excellent friction reduction effect, and an engine.SOLUTION: A method of producing a tribo-film forms a tribo-film on the surface of a metal oxide film, using a first slide member whose slide surface is coated with a hydrogen-containing DLC thin film containing not less than 30 at% and not more than 50 at% of hydrogen, a second slide member whose slide surface is coated with a metal oxide film containing either or both of ZrO2 and Al2O3, and lubricant oil including ester oil, sliding the first slide member and the second slide member while keeping the lubricant oil between the hydrogen-containing DLC thin film and the metal oxide film, and maintaining the temperature of the lubricant oil in a range of not lower than 50°C and not higher than 200°C.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a tribofilm and an engine. [Background technology]

[0002] In an engine, the mechanical loss of the piston ring and cylinder liner that slide against each other accounts for a large proportion of the mechanical loss of the entire engine. Therefore, the sliding parts of the piston ring and cylinder liner are subjected to a low-friction treatment to improve performance such as fuel efficiency.

[0003] As a method for realizing low friction in engine oil (lubricating oil), a method of using engine oil containing molybdenum disulfide or polytetrafluoroethylene (PTFE) as a solid lubricant is known. However, because the sliding conditions of the piston ring and cylinder liner in the engine are severe, the above method does not provide sufficient wear resistance and makes it difficult to maintain low friction.

[0004] As a surface treatment technology that combines low friction and wear resistance, the application of a hard carbon coating called diamond-like carbon (DLC) is expected. Patent Document 1 discloses the formation of a hydrogen-free DLC film on the surface of a piston ring. Patent Document 2 discloses laminating DLC ​​films of different hardness on the surface of a piston ring. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6181905 [Patent Document 2] Patent No. 6343266 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the friction coefficient of the piston rings described in Patent Documents 1 and 2 in lubricating oil is not sufficient, being approximately the same as that of a piston ring having a hard coating such as chromium nitride formed thereon, and further reduction in friction is required.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a method for producing a tribofilm that can achieve an excellent friction reduction effect, and an engine. [Means for solving the problem]

[0008] The method for producing a tribofilm according to the present disclosure includes using a first sliding member, the sliding part of which is coated with a hydrogen-containing DLC ​​thin film having a hydrogen content of 30 at % or more and 50 at % or less, a second sliding member, the sliding part of which is coated with a metal oxide film containing either one or both of ZrO2 and Al2O3, and a lubricating oil containing an ester oil, sliding the first sliding member and the second sliding member with the lubricating oil present between the hydrogen-containing DLC ​​thin film and the metal oxide film, setting the temperature of the lubricating oil to a range of 50° C. or more and 200° C. or less, and forming a tribofilm on the surface of the metal oxide film.

[0009] The engine of the present disclosure comprises a piston ring, a cylinder liner, and a lubricating oil, the surface of the piston ring that slides against the cylinder liner is coated with a hydrogen-containing DLC ​​thin film having a hydrogen content of 30 at% or more and 50 at% or less, the surface of the cylinder liner that slides against the piston ring is coated with a metal oxide film containing either or both of ZrO2 and Al2O3, the lubricating oil contains ester oil, and the lubricating oil is present between the hydrogen-containing DLC ​​thin film and the metal oxide film. Effect of the Invention

[0010] The method for producing a tribofilm and the engine disclosed herein provide an excellent friction reduction effect. [Brief description of the drawings]

[0011] [Figure 1]FIG. 2 is a partial cross-sectional view showing the configuration of a piston ring and a cylinder liner of the engine according to the embodiment of the present disclosure. [Diagram 2] 2 is an enlarged cross-sectional view of a sliding portion of a piston ring and a cylinder liner of the engine of FIG. 1. [Diagram 3] FIG. 3 is a cross-sectional view showing how a tribofilm is formed on a sliding portion of the piston ring and the cylinder liner in FIG. 2. [Figure 4] FIG. 1 illustrates a reaction mechanism for the formation of a tribofilm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First Embodiment Hereinafter, an engine and a method for producing a tribofilm according to an embodiment of the present disclosure will be described with reference to FIGS. 1 and 2.

[0013] (Engine configuration) As shown in FIGS. 1 and 2, the engine 100 includes at least a cylinder block 110, a cylinder liner 112 as a second sliding member, a piston 114, a piston ring 116 as a first sliding member, and lubricating oil 10.

[0014] In the engine 100, a cylindrical cylinder liner 112 is disposed inside a cylindrical cylinder block 110. A cylinder head (not shown) is provided on the upper side of the cylinder block 110.

[0015] A piston 114 is housed inside the cylinder liner 112. The piston 114 is guided by the cylinder liner 112 and is capable of linearly reciprocating along a central axis C of the cylinder liner 112. The piston 114 is connected via a connecting rod 118 to a crankshaft 120 housed in a crankcase (not shown). The space inside the cylinder liner 112 between the cylinder head and the piston 114 serves as a combustion chamber.

[0016] The piston ring 116 is provided so as to go around the outer circumferential surface of the upper part of the piston 114. In the engine 100, the piston 114 reciprocates within the cylinder liner 112, causing the piston ring 116 and the cylinder liner 112 to slide against each other.

[0017] A surface 116a of the piston ring 116 at a sliding portion with the cylinder liner 112 is coated with a hydrogen-containing DLC ​​thin film 122 having a hydrogen content of 30 at % or more and 50 at % or less. The hydrogen-containing DLC ​​thin film 122 is a DLC thin film that contains hydrogen atoms. The hydrogen-containing DLC ​​thin film 122 may contain fluorine atoms, silicon atoms, nitrogen atoms, boron atoms, tungsten atoms, and titanium atoms in addition to carbon atoms and hydrogen atoms.

[0018] The hydrogen content of the hydrogen-containing DLC ​​thin film 122, i.e., the ratio of hydrogen atoms to all atoms constituting the hydrogen-containing DLC ​​thin film, is 30 at% to 50 at%, and preferably 30 at% to 40 at%. If the hydrogen content is equal to or greater than the lower limit of the range, friction is steadily reduced. If the hydrogen content is equal to or less than the upper limit of the range, durability of the film can be ensured.

[0019] The surface roughness Ra of the hydrogen-containing DLC ​​thin film 122, that is, the surface roughness Ra of the sliding surface of the piston ring 116, is preferably 0.1 μm or less. If the surface roughness Ra is 0.1 μm or less, problems such as peeling of the film can be avoided. The surface roughness Ra is a value measured in accordance with ISO 13565-1.

[0020] The thickness of the hydrogen-containing DLC ​​thin film 122 can be set to, for example, 0.1 μm or more and 5 μm or less. Examples of methods for forming the hydrogen-containing DLC ​​thin film 122 include an ion plating method, a CVD method, and an ionization deposition method.

[0021] A surface 112a of the cylinder liner 112 at a sliding portion with the piston ring 116 is coated with a metal oxide film 124 containing either or both of ZrO2 and Al2O3. Examples of the metal oxide film 124 include a ZrO2 film, an Al2O3 film, and a film made of ZrO2 and Al2O3. Among them, a ZrO2 film is preferable as the metal oxide film 124 because a tribofilm is easily formed thereon.

[0022] The thickness of the metal oxide film 124 can be set to, for example, 1 μm or more and 300 μm or less. The metal oxide film 124 can be formed by, for example, thermal spraying or thermal CVD.

[0023] The lubricant 10 is present between the hydrogen-containing DLC ​​thin film 122 and the metal oxide film 124 . The lubricating oil 10 includes an ester oil.

[0024] Examples of the ester oil include polyol ester (POE) and phosphoric acid ester. As the ester oil, POE is preferred because it is easy to form a tribofilm.

[0025] POE is an ester of a polyol and a fatty acid. The number of carbon atoms in the polyol constituting the POE is preferably 5 to 10, and more preferably 5 to 6, since a tribofilm is easily formed. The number of hydroxyl groups in the polyol constituting the POE is preferably 2 to 7, and more preferably 2 to 3, in terms of facilitating the formation of a tribofilm.

[0026] Examples of polyols constituting POE include dipentaerythritol, pentaerythritol, trimethylolpropane, and neopentyl glycol. In terms of easiness of forming a tribofilm, neopentyl glycol and trimethylolpropane are preferred as polyols constituting POE.

[0027] The fatty acids constituting POE include, for example, C6 to C 10 (C6-10) linear or branched saturated fatty acids, C6-C 10Examples of the fatty acid include linear or branched unsaturated fatty acids such as those listed above. Specific examples include octanoic acid, decanoic acid, trimellitic acid, and isononanoic acid. As the fatty acid, branched fatty acids are preferred, and isononanoic acid is preferred.

[0028] As the POE, an ester of neopentyl glycol and isononanoic acid, and an ester of trimethylolpropane and isononanoic acid are preferred because they are easy to form a tribofilm. The POE contained in lubricating oil 10 may be one type or two or more types.

[0029] The content of the ester oil in the lubricating oil 10 is preferably 50% by mass or more and 100% by mass or less, and more preferably 75% by mass or more and 100% by mass or less, based on the total mass of the lubricating oil 10. When the content of the ester oil is equal to or more than the lower limit of the above range, a stable tribofilm can be expected to be formed.

[0030] From the viewpoint of promoting the formation of a tribofilm, the lubricating oil 10 preferably further contains, in addition to the ester oil, either one or both of a polyol and a fatty acid, and more preferably further contains both a polyol and a fatty acid.

[0031] Examples of the polyol include the same polyols as those exemplified as the polyols constituting POE. Among them, dipentaerythritol is preferred as the polyol because of its high effect of promoting the formation of a tribofilm. Lubricating oil 10 may contain one type of polyol, or two or more types of polyol.

[0032] The content of polyol in the lubricating oil 10 is preferably 0% by mass or more and 20% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less, based on the total mass of the lubricating oil 10. If the content of polyol is equal to or more than the lower limit of the above range, the formation of a tribofilm is promoted, and friction reduction is facilitated. If the content of polyol is equal to or less than the upper limit of the above range, the basic lubricating properties of the base oil are not significantly changed.

[0033] The fatty acid may be any of C6 to C6 fatty acids represented by the following formula 1: 72 Examples include fatty acids having 6 to 72 carbon atoms.

[0034] [ka]

[0035] In the above formula 1, R 1 is C5~C 71 R is a linear or branched hydrocarbon group having 5 to 71 carbon atoms. 1 The hydrocarbon group may be a saturated or unsaturated hydrocarbon group. The hydrocarbon group may or may not have a substituent. R 1 The hydrocarbon group preferably has 6 to 50 carbon atoms, and more preferably has 8 to 30 carbon atoms.

[0036] Representative examples of saturated fatty acids are isononanoic acid (C9) and lauric acid (C 12 ), myristic acid (C 14 ), palmitic acid (C 16 ), stearic acid (C 18 A typical example of an unsaturated fatty acid is oleic acid (C 18 ), linoleic acid (C 18 ) can be given as examples. The fatty acid contained in the lubricating oil 10 may be one type or two or more types.

[0037] The content of fatty acid in the lubricating oil 10 is preferably 0% by mass or more and 20% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less, based on the total mass of the lubricating oil 10. If the content of fatty acid is equal to or more than the lower limit of the above range, the formation of tribofilm is promoted, and friction reduction is facilitated. If the content of fatty acid is equal to or less than the upper limit of the above range, excellent heat resistance is easily obtained.

[0038] The lubricating oil 10 may contain other components in addition to the ester oil, polyol, and fatty acid, as required. Examples of other components include additives such as antioxidants, oiliness agents, friction modifiers, antiwear agents, extreme pressure agents, metal detergents, viscosity index improvers, pour point depressants, metal deactivators, metal corrosion inhibitors, rust inhibitors, and antifoaming agents. The other components contained in the lubricating oil 10 may be one type or two or more types.

[0039] The antioxidant is preferably a diphenylamine derivative having an arylalkyl group and a molecular weight of from 400 to 800. The diphenylamine derivative has the effect of suppressing evaporation loss of the lubricating oil. An example of the diphenylamine derivative is a compound represented by the following formula 2.

[0040] [ka]

[0041] In the above formula 2, R 2 and R 3 are each independently an arylalkyl group. R 2 and R 3 An example of the arylalkyl group of R is a dimethylbenzyl group. 2 and R 3 may be the same group or different groups. An example of a diphenylamine derivative is 4,4-bis(dimethylbenzyl)diphenylamine.

[0042] The content of the diphenylamine derivative in the lubricating oil 10 is preferably 0% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, based on the total mass of the lubricating oil 10. If the content of the diphenylamine derivative is equal to or more than the lower limit of the above range, it is easy to reduce evaporation loss. If the content of the diphenylamine derivative is equal to or less than the upper limit of the above range, it is easy to suppress solidification due to supersaturation.

[0043] The method for preparing the lubricating oil 10 is not particularly limited, and an example of the method is mixing the components using a heated mixer.

[0044] (Procedure for manufacturing tribofilms) The method for producing a tribofilm according to an embodiment of the present disclosure uses an engine 100 including a piston ring 116, a cylinder liner 112, and a lubricating oil 10. In this embodiment, the piston ring 116 is used as a first sliding member, and the cylinder liner 112 is used as a second sliding member.

[0045] In the method for producing a tribofilm of this embodiment, the piston ring 116 and the cylinder liner 112 are slid together in a state where the lubricating oil 10 is present between the hydrogen-containing DLC ​​thin film 122 and the metal oxide film 124, and the temperature of the lubricating oil 10 is set to a range of 50° C. or more and 200° C. or less. That is, the engine 100 is driven to reciprocate the piston 114, so that the piston ring 116 and the cylinder liner 112 are slid together in a state where the lubricating oil 10 is present between the hydrogen-containing DLC ​​thin film 122 and the metal oxide film 124, and the temperature of the lubricating oil 10 is set to a range of 50° C. or more and 200° C. or less.

[0046] When the temperature of the lubricating oil 10 is in the range of 50° C. or more and 200° C. or less, a tribofilm 130 is formed on the surface of the metal oxide film 124 in the lubricating oil 10, as shown in Fig. 3. The reaction mechanism by which the tribofilm 130 is formed will be described later.

[0047] The temperature of the lubricating oil 10 when the tribofilm 130 is formed is 50° C. or higher and 200° C. or lower, and preferably 90° C. or higher and 110° C. or lower. If the temperature of the lubricating oil 10 is equal to or higher than the lower limit of the above range, the tribofilm 130 is formed on the surface of the metal oxide film 124, and the friction of the sliding portion between the piston ring 116 and the cylinder liner 112 is reduced. If the temperature of the lubricating oil 10 is equal to or lower than the upper limit of the above range, the evaporation of the lubricating oil 10 can be suppressed, and the friction reduction effect by the tribofilm 130 can be stably obtained.

[0048] To evaluate the formation of tribofilms in the lubricating oil 10 at the sliding portion between the piston ring 116 and the cylinder liner 112 of the engine 100, the test results under conditions satisfying the following (a) and (b) that mimic the conditions when the engine is running can be used as an index. (a) Contact surface pressure between the first sliding member (piston ring 116) and the second sliding member (cylinder liner 112): 0.01 GPa or more and 1.2 GPa or less. (b) Relative sliding speed of the first sliding member (piston ring 116) with respect to the second sliding member (cylinder liner 112): greater than 0 mm / s and less than or equal to 10 mm / s.

[0049] In this manner, when the tribofilm manufacturing method of the present disclosure is applied to a piston ring and a cylinder liner of an engine, the lubricating oil is preferably a lubricating oil that forms a tribofilm under the condition that satisfies the contact surface pressure of (a) and the sliding speed of (b).

[0050] (Action and effect) In the engine 100 and the method for producing a tribofilm having the above configuration, the piston ring 116 and the cylinder liner 112 are slid against each other to set the temperature of the lubricating oil 10 to 50° C. or higher and 200° C. or lower, thereby forming a tribofilm 130 having a low friction coefficient on the surface of the metal oxide film 124 in the lubricating oil 10. Therefore, according to the engine 100 and the method for producing a tribofilm of the embodiment, it is possible to reduce friction in the sliding portion between the piston ring 116 and the cylinder liner 112. In the engine 100 and the method for producing a tribofilm of the embodiment, it is possible to achieve a friction coefficient of less than 0.05.

[0051] The reaction mechanism by which the tribofilm 130 is formed on the surface of the metal oxide film 124 in the lubricating oil 10 is believed to be as follows. ZrO2 and Al2O3 contained in the metal oxide film 124 exhibit catalytic activity in hydrolysis reactions. When the temperature of the lubricating oil 10 is between 50°C and 200°C, the ester oil is hydrolyzed by the catalytic action of ZrO2 and Al2O3, and alcohol is generated in the oil. Then, as shown in FIG. 4, the generated alcohol undergoes a dehydration reaction to form unsaturated hydrocarbons having double bonds. It is believed that the double bonds of the unsaturated hydrocarbons are cleaved and bonded to the surface of the metal oxide film 124, and polymerization proceeds to elongate the carbon chains, forming a tribofilm 130.

[0052] When the lubricating oil 10 further contains either or both of a polyol and a fatty acid, the hydroxyl groups contained therein further promote the hydrolysis of the ester oil by the catalytic action of ZrO2 or Al2O3, thereby promoting the formation of a tribofilm 130.

[0053] The tribofilm 130 formed on the surface of the metal oxide film 124 has the property of dissolving in oil. If the temperature of the lubricating oil 10 is 50° C. or higher, the formation of the tribofilm 130 dominates over the dissolution into the oil, so that the tribofilm 130 is stably formed and the friction reducing effect is fully exerted.

[0054] <Other embodiments> Although the embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like that do not depart from the gist of the present disclosure are also included. In the above embodiment, one piston ring is provided as the first sliding member for the cylinder liner as the second sliding member, but this is not limited to this. For example, two or more piston rings may be provided for one cylinder liner.

[0055] In the above embodiment, the first sliding member is a piston ring and the second sliding member is a cylinder liner, but this is not limited to this. For example, the first sliding member may be a cylinder liner and the second sliding member may be a piston ring.

[0056] <Additional Notes> The method for producing a tribofilm and the engine described in each embodiment can be understood, for example, as follows.

[0057] (1) A first embodiment of a method for producing a tribofilm 130 includes a first sliding member having a sliding portion surface 116a coated with a hydrogen-containing DLC ​​thin film 122 having a hydrogen content of 30 at % or more and 50 at % or less, a second sliding member having a sliding portion surface 112a coated with a metal oxide film 124 containing either one or both of ZrO2 and Al2O3, and a lubricating oil 10 containing an ester oil. The first sliding member and the second sliding member are caused to slide with the lubricating oil 10 being present between the hydrogen-containing DLC ​​thin film 122 and the metal oxide film 124, the temperature of the lubricating oil 10 being in the range of 50° C. or more and 200° C. or less, and a tribofilm 130 is formed on the surface of the metal oxide film 124. An example of the first sliding member is the piston ring 116 of the engine 100. An example of the second sliding member is the cylinder liner 112 of the engine 100.

[0058] According to this method for producing the tribofilm 130, the first sliding member and the second sliding member are slid together, and the temperature of the lubricating oil 10 is set in the range of 50°C to 200°C, thereby forming a tribofilm 130 with a low friction coefficient on the surface of the metal oxide film 124. This is believed to be because the ester oil is hydrolyzed in the lubricating oil 10 by the catalytic action of ZrO2 or Al2O3, and the double bond formed by the dehydration reaction of the resulting alcohol is cleaved, and a carbon chain is bonded to the surface of the metal oxide film 124. If the temperature of the lubricating oil 10 is 50°C to 200°C, the formation of the tribofilm 130 is dominant over the dissolution into the oil, so that the tribofilm 130 is stably formed, and an excellent friction reduction effect is fully exhibited.

[0059] (2) A second embodiment of the method for producing the tribofilm 130 is the method for producing the tribofilm 130 of (1), in which the ester oil is POE.

[0060] This promotes the formation of the tribofilm 130, and the tribofilm 130 is more stably formed on the surface of the metal oxide film 124 in the oil, thereby achieving an excellent friction reduction effect.

[0061] (3) A third embodiment of the method for producing the tribofilm 130 is the method for producing the tribofilm 130 of (1) or (2), in which the lubricating oil 10 further contains either one or both of a polyol and a fatty acid.

[0062] This further promotes hydrolysis of the ester oil due to the catalytic action of ZrO2 and Al2O3, which in turn promotes the formation of the tribofilm 130, thereby achieving an excellent friction reduction effect.

[0063] (4) A fourth aspect of the method for manufacturing the tribofilm 130 is the method for manufacturing the tribofilm 130 of any one of (1) to (3), in which the first sliding member is the piston ring 116 of the engine 100 and the second sliding member is the cylinder liner 112 of the engine 100.

[0064] As a result, a tribofilm 130 is formed in the sliding portion between the piston ring 116 and the cylinder liner 112 of the engine 100, and an excellent friction reducing effect is obtained.

[0065] (5) A fifth aspect of the method for producing the tribofilm 130 is the method for producing the tribofilm 130 according to any one of (1) to (4), in which the lubricating oil 10 forms the tribofilm 130 under the condition that the contact surface pressure between the first sliding member and the second sliding member is 0.01 GPa or more and 1.2 GPa or less, and the relative sliding speed of the first sliding member with respect to the second sliding member is more than 0 mm / s and 10 mm / s or less.

[0066] This allows the tribofilm 130 to be formed more stably in the sliding portion between the piston ring 116 and the cylinder liner 112 of the engine 100, thereby achieving an excellent friction reduction effect.

[0067] (6) The engine 100 of the sixth aspect comprises a piston ring 116, a cylinder liner 112, and lubricating oil 10, wherein a surface 116a of the sliding portion of the piston ring 116 with the cylinder liner 112 is coated with a hydrogen-containing DLC ​​thin film 122 having a hydrogen content of 30 at% or more and 50 at% or less, a surface 112a of the sliding portion of the cylinder liner 112 with the piston ring 116 is coated with a metal oxide film 124 containing either or both of ZrO2 and Al2O3, the lubricating oil 10 contains ester oil, and the lubricating oil 10 is present between the hydrogen-containing DLC ​​thin film 122 and the metal oxide film 124.

[0068] In the engine 100, when the piston ring 116 and the cylinder liner 112 slide against each other and the temperature of the lubricating oil 10 reaches 50°C or higher and 200°C or lower, a tribofilm 130 with a low friction coefficient is formed on the surface of the metal oxide film 124, thereby providing an excellent friction reduction effect.

[0069] (7) The engine 100 of a seventh embodiment is the engine 100 of (6), in which the ester oil is POE.

[0070] This promotes the formation of the tribofilm 130, and the tribofilm 130 is more stably formed on the surface of the metal oxide film 124 in the oil, thereby achieving an excellent friction reduction effect.

[0071] (8) The engine 100 of an eighth embodiment is the engine 100 of (6) or (7), in which the lubricating oil 10 further contains either one or both of a polyol and a fatty acid.

[0072] This further promotes hydrolysis of the ester oil due to the catalytic action of ZrO2 and Al2O3, which in turn promotes the formation of the tribofilm 130, thereby achieving an excellent friction reduction effect. EXAMPLES

[0073] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to the following description. [material] The materials used in this example are shown below. (oil) POE-1: Polyol ester (product name POE (VG5), manufactured by JXTG Nippon Oil & Energy Corporation). PAO-1: Poly-α-olefin (product name PAO(VG5), manufactured by JXTG Nippon Oil & Energy Corporation). PAG-1: Polyalkylene glycol (manufactured by Japan Sun Oil Co., Ltd.).

[0074] (Additives) Additive A: Isononanoic acid. Additive B: A mixture of isononanoic acid and dipentaerythritol.

[0075] [Example 1] A Si substrate was prepared as the first sliding member, and SUJ2 having a ZrO2 film on its surface was prepared as the second sliding member. A hydrogen-containing DLC ​​thin film (film thickness: 2 μm, surface roughness Ra: 0.05 μm) with a hydrogen content of 30 at % was formed by CVD on the surface of the sliding portion of the first sliding member against the second sliding member. A lubricating oil prepared by mixing POE-1 and additive B to obtain the composition shown in Table 1 was applied to the surface of the ZrO2 film at a rate of 0.02 g / cm2. 2 After coating so as to give the following results, the first sliding member and the second sliding member were slid together under the conditions of a contact pressure of 0.8 GPa and a sliding speed of 10 mm / s, and the temperature of the lubricant was set to 90 to 110° C. Then, the presence or absence of tribofilm formation on the surface of the ZrO2 film was evaluated, and the friction coefficient was measured.

[0076] [Examples 2 to 7] The presence or absence of tribofilm formation was evaluated and the friction coefficient was measured in the same manner as in Example 1, except that the metal oxide film on the surface of the second sliding member, the composition of the lubricating oil, and the temperature of the lubricating oil during sliding were changed as shown in Table 1. In Example 6, Additive A was used instead of Additive B. However, Examples 4 to 6 are reference examples.

[0077] [Comparative Examples 1 to 15] The presence or absence of tribofilm formation was evaluated and the friction coefficient was measured in the same manner as in Example 1, except that the metal oxide film on the surface of the second sliding member, the composition of the lubricating oil, and the temperature of the lubricating oil during sliding were changed as shown in Table 1. In Comparative Example 11, Additive A was used instead of Additive B.

[0078] [Friction coefficient] The coefficient of friction was measured by a load cell.

[0079] The evaluation results for each example are shown in Table 1.

[0080] [Table 1]

[0081] As shown in Table 1, in Examples 1 to 7 in which the first sliding member and the second sliding member were slid against each other and the temperature of the lubricating oil containing POE present between the hydrogen-containing DLC ​​thin film having a specific hydrogen content and the ZrO2 film or the Al2O3 film was set to a range of 50°C or higher and 200°C or lower, a tribofilm was formed and the friction coefficient was lower than those of Comparative Examples 1 to 15. [Explanation of symbols]

[0082] 10 Lubricating oil 100 Engine 110 Cylinder block 112 Cylinder liner 114 Piston 116 Piston ring 118 Connecting rod 120 Crankshaft 122 Hydrogen-containing DLC ​​thin film 124 Metal oxide film

Claims

1. a first sliding member having a sliding portion having a surface covered with a hydrogen-containing DLC ​​thin film having a hydrogen content of 30 at % or more and 50 at % or less; ZrO ２ and Al ２ O ３ A second sliding member having a sliding portion having a surface coated with a metal oxide film containing either one or both of the above. A lubricating oil containing a polyol ester, a polyol and a fatty acid, a first sliding member and a second sliding member are caused to slide against each other in a state in which the lubricating oil is present between the hydrogen-containing DLC ​​thin film and the metal oxide film, and a temperature of the lubricating oil is set in a range of 50° C. or more and 200° C. or less, and a tribofilm is formed on a surface of the metal oxide film.

2. The method for producing a tribofilm according to claim 1 , wherein the first sliding member is a piston ring of an engine, and the second sliding member is a cylinder liner of the engine.

3. 3. The method for producing a tribofilm according to claim 1, wherein the lubricating oil forms the tribofilm under conditions where a contact surface pressure between the first sliding member and the second sliding member is 0.01 GPa or more and 1.2 GPa or less, and a relative sliding speed of the first sliding member with respect to the second sliding member is more than 0 mm / s and 10 mm / s or less.

4. The piston ring, the cylinder liner, and the lubricating oil are included. The surface of the piston ring that slides against the cylinder liner is coated with a hydrogen-containing DLC ​​thin film having a hydrogen content of 30 at% or more and 50 at% or less, The surface of the cylinder liner that slides against the piston ring is made of ZrO. ２ and Al ２ O ３ and The lubricating oil comprises a polyol ester, a polyol, and a fatty acid, The lubricating oil is present between the hydrogen-containing DLC ​​thin film and the metal oxide film.

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