JP2009013370A - Sliding structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sliding structure which can reduce a friction coefficient and improve a wear resistance, even under a severe sliding environment such as high surface pressure. <P>SOLUTION: The present invention relates to a sliding structure comprising: a pair of sliding members on at least one sliding surfaces of which among mutually sliding surfaces a hard carbon coating film is formed; and a lubricant existing between a pair of the sliding members, wherein the lubricant is a vegetable lubricant containing at least one of oleic acid, linoleic acid and linolenic acid. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention includes a pair of sliding members in which a hard carbon film is formed on at least one of the sliding surfaces that slide relative to each other, a lubricating oil present between the pair of sliding members, In particular, the present invention relates to a sliding structure capable of reducing the friction coefficient and improving the wear resistance of a pair of sliding members.

  In recent years, there has been an interest in energy issues and environmental issues surrounding machinery. In today's society, where energy sources depend on oil and nuclear power, the depletion of energy resources is a matter of concern. The 20th century was an era of mass production and mass consumption, but in the 21st century it is important to use limited energy efficiently.

  One energy loss in machines is friction loss. A machine always has a sliding surface and generates friction, and reducing the friction leads to a reduction in energy consumption. Friction reduction is achieved by preventing direct contact between the two surfaces by the lubricant and reducing shear resistance. Many machines still use lubricating oil, and research on the lubricating oil is actively conducted.

  On the other hand, hard carbon coatings such as amorphous carbon coatings, carbon nitride coatings, and diamond coatings are attracting attention as materials for reducing friction, and the friction of sliding members can be reduced by applying these coatings to sliding surfaces.・ Improved wear resistance.

  However, as engine parts, for example, automobile engine parts have recently been remarkably improved in performance due to high output and high rotation. Along with this, in a sliding member used in an engine, the performance improvement is limited only by applying the hard carbon coating on the sliding surface. Therefore, it is necessary to propose a sliding structure with more excellent sliding characteristics in consideration of the optimum combination of the sliding member and the lubricating oil.

  For example, a sliding member whose surface is coated with DLC, and a lubricating oil in which an organic molybdenum compound is added to a base oil such as vegetable oil, animal oil, or synthetic oil supplied to the surface of the sliding member. A sliding structure has been proposed (see, for example, Patent Document 1). According to the present invention, since the organic molybdenum compound as an additive acts as a solid lubricant during sliding, the friction of the sliding member can be reduced and the wear resistance can be improved.

Japanese Patent Laid-Open No. 2004-339486

  In the past research, when only the base oil shown in Patent Document 1 is used as the lubricating oil supplied to the sliding member on which the hard carbon film is formed, the low friction characteristic of the hard carbon film is sufficiently obtained. In general, the sliding characteristic is improved by adding an additive to the lubricating oil as in the sliding structure described in Patent Document 1.

  However, even when the lubricating oil added with the additive is used, the friction coefficient can only be expected to be about 0.1 at most, and the sliding surface is high in the severe sliding environment such as the engine described above. Because of the contact pressure, it may be difficult to say that the sliding characteristics are sufficient. In addition, the lubricant must be adjusted by adding an appropriate amount of additive capable of exhibiting the effect to the lubricant, and the cost of the lubricating oil increases as the type and amount of the additive increase. Furthermore, most of the metal elements added to the lubricating oil are heavy metals. In view of the current trend of development based on environmental conservation, the additives containing the metal elements and the like are not added to the lubricating oil. It can be said that it is more preferable.

  The present invention has been made in view of the above-mentioned problems, and its object is to reduce costs while considering environmental resistance, and even under severe sliding environments such as high surface pressure. Even if it exists, it is providing the sliding structure which can reduce a friction coefficient and can improve abrasion resistance.

  In view of the above problems, the inventors have intensively studied and have considered that it is preferable to use vegetable oil (vegetable lubricating oil) when considering environmental resistance and cost reduction. And as a result of conducting experiments using various vegetable oils as lubricating oils, the specific components contained in the specific vegetable oils contained in the lubricating oils, and, without adding metal additives etc. A new finding has been obtained that the coefficient can be reduced and the wear resistance can be improved.

  The present invention is based on the above-mentioned new knowledge, and the sliding structure according to the present invention includes a pair of slides in which a hard carbon coating is formed on at least one of the sliding surfaces sliding relative to each other. A sliding structure comprising a moving member and a lubricating oil present between the pair of sliding members, wherein the lubricating oil includes at least one of oleic acid, linoleic acid, and linolenic acid. It is a vegetable lubricating oil.

  In the sliding structure according to the present invention, a hard carbon coating is formed on at least one sliding surface of a pair of sliding members that slide relative to each other. Furthermore, the lubricating oil exists between the sliding surface of the sliding member on which the hard carbon film is formed and the sliding surface of the sliding member that slides on the sliding surface. In the present invention, “sliding relative to each other” means that at least one sliding member slides relative to the other sliding member, and relative sliding refers to linear motion, Sliding by rotational movement or a combination of these movements.

  As is apparent from the experiments described later by the inventors, a vegetable lubricating oil containing at least one unsaturated fatty acid among the unsaturated fatty acids of oleic acid, linoleic acid, and linolenic acid is used as the lubricating oil. As a result, the friction coefficient of the sliding member on which the hard carbon film is formed can be reduced and the wear resistance can be improved. Oleic acid, linoleic acid, or linolenic acid has an unsaturated molecular structure and a polar molecular structure, and this molecular structure is considered to contribute to a reduction in friction coefficient and an improvement in wear resistance. It is done. Further, by using vegetable lubricating oil, that is, vegetable oil, as the lubricating oil, it is environmentally friendly. Furthermore, these vegetable oils are easily available at low cost and are economical.

  Examples of vegetable lubricating oils include olive oil, cacao oil, sesame oil, soybean oil, corn oil, rapeseed oil, palm oil, sunflower oil, safflower oil, wheat germ oil, palm oil, peanut oil, or linseed oil It may be a mixed oil obtained by mixing these vegetable oils. More preferred are olive oil, safflower oil, linseed oil, etc., which will be described later, containing at least one of these unsaturated fatty acids as a main ingredient.

  The sliding structure according to the present invention has a hard carbon coating as compared with a base material on which the coating is applied, such as a coating obtained by crystallizing carbon such as a diamond coating or a coating containing an amorphous structure such as an amorphous carbon coating. If it is a hard carbon film, it will not be limited to gain. However, a more preferable hard carbon coating is an amorphous carbon coating (a coating made of Diamond Like Carbon: a DLC coating) or a carbon nitride coating (CNx coating). Moreover, an amorphous carbon nitride film is more preferable among the carbon nitride films. Since the surface of the coating is more active than the amorphous carbon coating, it is considered that a stronger boundary lubricating film can be formed during sliding. As a result, a lower friction coefficient can be obtained as compared with the amorphous carbon coating.

  When forming the hard carbon film described above on the surface of the base material of the sliding member, the film is formed by physical vapor deposition (PVD) using vacuum deposition, sputtering, ion plating, ion beam mixing, or the like. Alternatively, the film may be formed by chemical vapor deposition (CVD) utilizing plasma treatment or the like, or may be formed by a combination of these methods. In addition, when forming an amorphous carbon nitride film, which is a kind of DLC film, when forming a carbon nitride film (CNx film), in order to obtain more stable low friction characteristics, film formation and ion It is more preferable to form these films by an ion beam method based on a dynamic mixing method in which the implantation is performed simultaneously. Further, during such film formation, an additive element such as Si, Ti, Cr, Fe, Mo, W, or B may be included in the hard carbon film, and by adding such an element, the film The surface hardness can be adjusted.

  Further, when forming the hard carbon film on the surface of the sliding member, an intermediate layer made of silicon (Si) may be provided in order to increase the adhesion between the base material of the sliding member and this film. Further, chromium (Cr), titanium (Ti), or tungsten (W) may be used instead of silicon.

  Furthermore, if the base material on which the hard carbon film is formed has a material and surface hardness that can ensure adhesion to the hard carbon film during sliding, iron, non-ferrous metal, etc. There is no particular limitation, and the other sliding member that slides with this sliding member is also extremely low in surface hardness with respect to this hard carbon coating and is not easily worn when sliding. The material is not particularly limited.

  Moreover, as for the sliding structure which concerns on this invention, the said lubricating oil contains at least oleic acid, and it is more preferable that this oleic acid contains 70-85 mass% with respect to the said lubricating oil. According to the present invention, by containing oleic acid so as to have a content in the above range, the friction coefficient of the pair of sliding members can be reduced, and the wear resistance can be improved. . If the amount is less than the above range, a more favorable sliding characteristic may not be obtained, for example, the friction coefficient becomes high. Even if the amount is more than the above range, no further effect can be expected. Moreover, it is difficult to obtain more oleic acid than this range from natural vegetable oil, and when manufactured by oil production etc., there exists a possibility that cost may become high. In addition, olive oil is mentioned as a suitable vegetable oil containing the oleic acid of the said range content rate, for example.

  As another aspect, in the sliding structure according to the present invention, the lubricating oil contains at least linoleic acid, and the linoleic acid may contain 60 to 80% by mass with respect to the lubricating oil. preferable. According to the present invention, by including linoleic acid so that the content ratio is in the above range, the friction coefficient of the pair of sliding members can be reduced, and the wear resistance can be improved. it can. In addition, since linoleic acid has a higher degree of unsaturation than the oleic acid, it is lower than the content of the oleic acid. Further, if the amount is less than the above range, a more favorable sliding characteristic may not be obtained, for example, the friction coefficient becomes high. Even if the amount is more than the above range, no further effect can be expected. Furthermore, it is difficult to obtain more linoleic acid than this range from natural vegetable oil, and the cost may increase when it is produced by oil production or the like. In addition, as a suitable vegetable oil containing linole of the said range content rate, a sunflower oil, safflower oil, or a wheat germ oil etc. are mentioned, for example.

  Furthermore, as another aspect, in the sliding structure according to the present invention, the lubricating oil may contain at least linolenic acid, and the linolenic acid may contain 30 to 60% by mass with respect to the lubricating oil. preferable. According to the present invention, by including linolenic acid so as to have a content in the above range, the friction coefficient of the pair of sliding members can be reduced, and the wear resistance can be improved. it can. Since linolenic acid has a higher degree of unsaturation than linoleic acid, it is lower than the content of linoleic acid. Further, if the amount is less than the above range, a more favorable sliding characteristic may not be obtained, for example, the friction coefficient becomes high. Even if the amount is more than the above range, no further effect can be expected. Furthermore, it is difficult to obtain more linolenic acid from this range from natural vegetable oils. An example of a suitable vegetable oil containing linolenic acid in the above range is linseed oil.

  Further, the sliding structure according to the present invention has a circulating lubrication mechanism as a mechanism for arranging (supplying) the lubricating oil on the sliding member in order to allow the lubricating oil to stably exist between the pair of sliding members. In addition, a mist lubrication mechanism or an oil bath lubrication mechanism using an oil bath may be further provided, and the mechanism is particularly limited as long as the lubricating oil is stably supplied between the sliding members during sliding. It is not something. Furthermore, an antioxidant, an antiwear agent, an extreme pressure agent, a friction modifier, a metal deactivator, a detergent, a rust inhibitor, an antifoaming agent, and the like can be added as appropriate to the lubricating oil.

  According to the sliding structure of the present invention, the cost is reduced while considering the environmental resistance, and the friction coefficient is reduced and the wear resistance is reduced even in a severe sliding environment such as a high surface pressure. Can be improved.

  Hereinafter, the present invention will be described by way of examples. In addition, this invention is not limited to the Example shown below.

(Example 1-1)
Of the pair of sliding members of the sliding structure according to the present invention, the following disk test piece is manufactured as one sliding member on which a hard carbon film is formed, and the other sliding member sliding with this sliding member As a member, the following ball test piece was manufactured.

<Disk specimen>
A disk-shaped silicon wafer S having a diameter of 50 mm, a thickness of 0.3 mm, and a circular surface (sliding surface) in a mirror surface state (100 plane orientation) was prepared as a base material on which a hard carbon film was formed. Then, using an ion beam mixing apparatus 10 (1X-30-30, manufactured by Hitachi, Ltd.) as shown in FIG. 1, an amorphous carbon nitride (CNx) film (hard carbon film) is formed on the surface of the circular portion of the silicon wafer S. ) Was formed. In the ion beam mixing method, since the mixing layer is formed between the substrate and the thin film (surface modified layer), there is no conventional substrate / film boundary, adhesion to the film, and composition of the film. This is a film forming method capable of surface treatment with excellent controllability.

  As shown in FIG. 1, the ion beam mixing apparatus 10 includes at least a vacuum chamber 11, a substrate holder 12, an assisting ion source and gas supply source 14, a sputter ion source 15, and a cryopump 16. The ion source is a sputter. Both of the ion source and the assist type are bucket types, the sputter ion source has an acceleration voltage of 1500 eV at the maximum, an ion current of 200 mA at the maximum, and an effective diameter of the ion beam of about 80 mm. The substrate holder 12 is configured to rotate during film formation and to change the angle between the ion beam and the substrate surface within a range of 0 ° to 90 °. Using such an apparatus 10, a film was formed as follows.

Specifically, as shown in FIG. 1, the holder 12 in the vacuum chamber 11 is arranged so that the circular surface of the silicon wafer S faces the carbon target T with a purity of 99.9999% arranged on the support base 13. A silicon wafer S was attached to the substrate. Thereafter, the pressure in the vacuum chamber 11 is adjusted to 2.0 × 10 ⁻⁴ Pa or less with a cryopump 16, and nitrogen ions gn (acceleration voltage 1 keV, ion current density μA / cm ² ) is applied to the silicon wafer for 5 minutes. Irradiation toward S and sputter cleaning was performed. Thereafter, the pressure in the vacuum chamber 11 is adjusted to 1.4 × 10 ⁻² Pa, and the carbon target T is irradiated with argon ions ga from the sputter ion source 15 to convert the carbon target T into carbon sputtered particles sc. The silicon wafer S was rotated at 4 rpm together with the holder 12, and an amorphous carbon nitride film (CNx film) having a thickness of 100 nm was formed on the circular surface of the silicon wafer.

<Ball specimen>
A silicon nitride sphere having a diameter of 8 mm and shown in Table 1 below was prepared, and a carbon nitride film was formed in a thickness of 200 nm on the surface of the sphere in the same manner.

<Lubricating oil>
Acylglycerol, which is a structure obtained by adding linoleic acid and unsaturated fatty acid of oleic acid to glycerin with vegetable lubricating oil, was prepared. This vegetable lubricating oil is a lubricating oil that can be obtained from rapeseed oil and soybean oil.

<Abrasion test>
A pin-on-disk friction tester 30 shown in FIG. 2 was used. The “pair of sliding members” according to the present invention indicates a disk test piece and a ball test piece.

  As a preliminary preparation for the wear test, the ball specimen B was ultrasonically cleaned with acetone and ethanol for 10 minutes each. Thereafter, the ball test piece B is removed from the main body of the testing machine, fixed to the ball holder 31, and after confirming that there is no scratch on the surface using an optical microscope (not shown), these are placed in a desiccator (not shown). The ball test piece B was dried. On the other hand, foreign matters such as dust on the surface (sliding surface) of the CNx film formed on the surface of the disk test piece D were removed by hand blow (not shown).

  Next, the disc test piece D was held by the disc holder 32, and the ball holder 31 to which the ball test piece B was fixed was attached to the main body of the testing machine so as to be integrated with the stage 33. Then, the lubricating oil was supplied to the holder 32 until the height reached 1 mm so that the lubricating oil L was always present on the surface of the disk test piece D during the test. Further, a ball test piece B is added to the surface of the CNx coating of the disk test piece D using a strain gauge 34 (Kyowa Dengyo Co., Ltd., KF-1-120-C1-16) bonded to the parallel leaf spring 34. The stage 33 was adjusted so that the value of the applied load was 1.0 N, and the ball test piece B was pressed against the disk test piece D.

Holding this pressed state, the motor 37 is driven to rotate the disk test piece D of the disk holder 32 through the coupling 38 so that the sliding speed is 1.26 × 10 ⁻² m / s. The frictional force at this time was measured with a strain gauge 34, and data was taken into a computer and recorded via a sensor interface (PCD-300A, manufactured by Kyowa Dengyo). And the friction coefficient was converted. The result is shown in FIG.

(Example 1-2)
As in Example 1-1, a disk test piece D, a ball test piece B, and a lubricating oil L were prepared. The difference from Example 1-1 is that a DLC film (HT-DLC (thick film, highly reliable DLC: manufactured by Japan IT Corporation)) is formed on the surface of the disk specimen D by plasma CVD. The friction coefficient was measured under the same friction test conditions as in Example 1-1, and the results are shown in FIG.

(Comparative Examples 1-1 to 7-1)
As in Example 1-1, a disk test piece D, a ball test piece B, and a lubricating oil L were prepared. The difference from Example 1-1 is a lubricating oil, and Comparative Examples 1-1 to 7-1 are, in place of the lubricating oil, base oil 5W-30, which is a mineral oil, pure water, ethanol (C ₂ H ₅ OH), kerosene (kerosene), silicon oil, formaldehyde (HCONH ₂ : amide of formic acid), and hexane (C ₆ H ₁₄ ). And the friction coefficient was measured on the friction test conditions similar to Example 1-1. The result is shown in FIG.

(Comparative Examples 1-2 to 7-2)
As in Example 1-2, a disk test piece D, a ball test piece B, and a lubricating oil L were prepared. The difference from Example 1-2 is the lubricating oil, and the lubricating oil supplied in Comparative Examples 1-2 to 7-2 corresponds to the lubricating oil in Comparative Examples 1-1 to 7-1 in order. ing. And the friction coefficient was measured on the friction test conditions similar to Example 1-2. The result is shown in FIG.

(Result 1 and Discussion 1)
From this test result, it was confirmed that the friction coefficient obtained using the CNx film tends to be lower than the friction coefficient obtained using the DLC film. This is considered to be because the CNx film has higher activity than the DLC film, and a stronger boundary lubricating film was formed during sliding. When the kerosene of Comparative Example 4 and the hexane of Comparative Example 7 are lubricated, the friction coefficient obtained using the CNx coating is higher than that obtained using the DLC coating. This is because the shear resistance is larger than that.

  Moreover, under the vegetable lubricating oil of Examples 1-1 and 1-2, a low friction coefficient was obtained for both the CNx film and the DLC film. This is because the vegetable lubricating oils of Examples 1-1 and 1-2 have a lot of unsaturated molecules such as linoleic acid and oleic acid, and molecules having polarity compared to others. It is thought that it is from.

(Examples 2 to 4)
As in Example 1-1, a disk test piece D, a ball test piece B, and a lubricating oil L were prepared. The difference from Example 1-1 is a lubricating oil, and the lubricating oil supplied in Examples 2 to 4 is changed to oleic acid, linoleic acid, and linolenic acid. And the friction coefficient was measured on the friction test conditions similar to Example 1-1. The condition different from that of Example 1-1 is that the sliding speed is set to 3.14 × 10 ⁻² m / s. The result is shown in FIG. Further, after the test is completed, each disk specimen D is taken out from the testing machine 30 and the cross-sectional area of the wear mark formed on the CNx film is obtained using an atomic force microscope (AFM), and the specific wear of this film is determined. The amount was calculated. The result is shown in FIG.

(Comparative Example 8)
As in Comparative Example 1-1, a disk specimen D, a ball specimen B, and a lubricating oil (base oil) L were prepared. In the same manner as in Example 2, the friction coefficient and the specific wear amount were measured. The results are shown in FIGS.

(Result 2 and discussion 2)
As shown in FIGS. 4 and 5, the friction coefficients of Examples 2 to 4 are about 1/3 of those of Comparative Example 8, and the specific wear amount of Examples 2 to 4 is 1/20. It became about. The degree of unsaturation (number of double bonds with respect to the number of carbon atoms) increased in the order of oleic acid, linoleic acid, and linolenic acid in Examples 2 to 4, and the friction coefficient averaged 0 for any unsaturated fatty acid. It was about .024 to 0.035. However, as is clear from the results of specific wear amounts of Examples 2 and 3, the fatty acid having a low degree of unsaturation such as oleic acid and linoleic acid had a smaller friction coefficient than that of the other. From this result, it is considered that the lower the degree of unsaturation, the smaller the friction coefficient tends to be. Similarly, from the result of the specific wear amount, it is considered that the lower the degree of unsaturation, the smaller the coefficient of friction.

(Examples 5-7)
As in Example 4, a disk specimen D, a ball specimen B, and a lubricating oil L were prepared. The difference from the fourth embodiment is the lubricating oil.

  Specifically, Example 5 used olive oil as a lubricating oil containing 70 to 85% by mass of oleic acid. Specifically, this olive oil is a lubricating oil containing oleic acid (80% by mass), palmitic acid (10% by mass), and other remaining fatty acids (for example, saturated fatty acids). In Example 6, safflower oil was used as a lubricating oil containing 60-80% by mass of linoleic acid. Specifically, this safflower oil is a lubricating oil containing linoleic acid (60% by weight), oleic acid (20% by weight), palmitic acid (10% by weight), and the remaining other fatty acids (eg, saturated fatty acids). Oil. In Example 7, linseed oil was used as a lubricating oil containing 30 to 60% by mass of linolenic acid. Specifically, this linseed oil contains linolenic acid (50-60% by weight), linoleic acid (15% by weight), oleic acid (10% by weight), and the remaining other fatty acids (eg, saturated fatty acids). Lubricating oil. In addition, the ratio which contains an unsaturated fatty acid is increasing in order of olive oil, safflower oil, and linseed oil mentioned above.

  And also about Examples 5-7, similarly to Example 4, the friction coefficient and the specific wear amount were measured. The results are shown in FIGS.

(Result 3 and discussion 3)
As shown in FIGS. 6 and 7, the friction coefficients of Examples 5 to 7 are smaller than those of Comparative Example 8. Particularly, olive oil and linseed oil have friction coefficients of 0.017 and 0.018, and others. It became a small value compared with the one. In addition, as shown in Examples 5 to 7, the specific wear amount increased as the proportion of unsaturated fatty acids increased in the order of olive oil, safflower oil, and linseed oil.

  Thus, since Examples 5-7 have reduced friction coefficients and specific wear amounts, it is considered that the amount of unsaturated fatty acid to be contained may be small as the degree of unsaturation increases. And, in order to collect oleic acid, linoleic acid, and linolenic acid from natural vegetable oil, it is preferable that the ranges are as shown above, respectively, and further, when each is less than the above range for unsaturated fatty acids. May not be able to obtain a more favorable sliding characteristic such as a higher friction coefficient, and it is considered that no further effect can be expected even if the friction coefficient exceeds the above range.

  As mentioned above, although the embodiment of the present invention has been described in detail, the specific configuration is not limited to this embodiment, and even if there is a design change within a scope not departing from the gist of the present invention, they are not limited to the present invention. Is included.

  For example, in this example, a hard carbon film was formed on a silicon wafer as a base material of one sliding member. However, if the hard carbon film does not peel or crack when sliding, iron, etc. The metal material may be coated. Moreover, it is not necessary to form the hard carbon film on both sliding surfaces of the pair of sliding members, and the hard carbon film may be formed only on one of the sliding surfaces.

The figure for demonstrating the ion mixing beam apparatus which concerns on an Example. The figure for demonstrating the pin-on-disk friction testing machine which concerns on an Example. The figure which showed the result of the friction coefficient which concerns on Examples 1-1 and 1-2, Comparative Examples 1-1 to 7-1, and Comparative Examples 1-2 to 7-2. The figure which showed the result of the friction coefficient which concerns on Examples 2-4 and the comparative example 8. FIG. The figure which showed the result of the specific wear amount which concerns on Examples 2-4 and the comparative example 8. FIG. The figure which showed the result of the friction coefficient which concerns on Examples 5-7 and the comparative example 8. FIG. The figure which showed the result of the specific wear amount which concerns on Examples 5-7 and the comparative example 8. FIG.

Explanation of symbols

  10: Ion beam mixing device, 11: Vacuum chamber, 12: Holder, 13: Support base, 14: Assist ion source and gas supply source, 15: Sputter ion source, 16: Cryo pump, 30: Pin-on-disk friction test Machine: 31: Ball holder, 32: Disc holder, 33: Stage, 34: Strain gauge, 35: Parallel leaf spring, 37: Motor, 38: Coupling, B: Ball specimen (sliding member), D: Disc Test piece (sliding member), S: silicon wafer (base material), T: carbon target

Claims (5)

A sliding member comprising a pair of sliding members having a hard carbon film formed on at least one of the sliding surfaces sliding relative to each other, and a lubricating oil present between the pair of sliding members. Dynamic structure,
The sliding structure, wherein the lubricating oil is a vegetable lubricating oil containing at least one of oleic acid, linoleic acid, and linolenic acid.   The sliding structure according to claim 1, wherein the hard carbon film is an amorphous carbon film (DLC film) or a carbon nitride film (CNx film).   The sliding structure according to claim 1 or 2, wherein the lubricating oil includes at least oleic acid, and the oleic acid is included in an amount of 70 to 85 mass% with respect to the lubricating oil.   The sliding structure according to claim 1 or 2, wherein the lubricating oil contains at least linoleic acid, and the linoleic acid is contained in an amount of 60 to 80 mass% with respect to the lubricating oil.   The sliding structure according to claim 1 or 2, wherein the lubricating oil contains at least linolenic acid, and the linolenic acid is contained in an amount of 30 to 60 mass% with respect to the lubricating oil.

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