JP5991956B2 - Internal combustion engine and automobile - Google Patents

Description

  The present invention relates to an internal combustion engine and an automobile equipped with the same.

  Conventionally, it has been known that a steel material subjected to nitriding as a material for sliding parts such as piston rings used in automobile engines exhibits excellent wear resistance. Further, the steel material subjected to nitriding treatment is used as a sliding component that is slid in the presence of engine oil (see, for example, Patent Documents 1 and 2).

  These sliding parts are manufactured on the assumption that they are used in the engine oil of a gasoline engine vehicle using gasoline as a fuel, that is, in the engine oil containing almost no moisture.

  A technique for improving the wear resistance of stainless steel and the corrosion resistance against salt water by nitriding has also been proposed (see, for example, Patent Document 3). However, this technology is not intended for use in engine oil. Further, a chromium oxide layer is an indispensable component for realizing corrosion resistance. That is, the steel material to be treated has a composition containing a specific element called chromium.

  On the other hand, ethanol fuel has come to be used in carbon neutral automobile fuel in Brazil and the United States, and the use of ethanol fuel is expected to expand in the future. This ethanol fuel is highly hygroscopic and contains moisture in the fuel itself, or produces more moisture than gasoline, so there is an opportunity for a large amount of moisture to be mixed into engine oil by expanding the use of ethanol fuel. Has increased. However, a system in which the engine is stopped relatively frequently (hereinafter, also referred to as an “environmental adaptation system”) such as an automobile that has been popular so far, that is, a hybrid system or a stop operation system (idle stop system) when stopped. In a conventional vehicle (hereinafter also referred to as “conventional vehicle”) in which the engine is continuously operated regardless of whether the vehicle is running or stopped after the engine is started, The steady engine oil temperature at the time reaches 80 ° C. to 90 ° C., and therefore, it is in an environment where moisture easily evaporates. For this reason, even when ethanol fuel is used, the mixed water hardly accumulates in the engine oil.

JP 2012-149743 A JP 2006-2814 A JP 2011-42862 A

  However, in an automobile equipped with an engine using ethanol fuel, an environment adaptation system (such as a hybrid system or an idle stop system) that stops the engine relatively frequently is installed. When the engine oil temperature is in a relatively low temperature range of about 50 ° C., the water mixed in the engine oil may not be evaporated and accumulated in the engine in a large amount.

  Thus, when there is a lot of moisture in the engine, the amount of moisture present in the engine oil present on the sliding surface also increases, and the time during which the sliding member slides in the engine oil containing a large amount of moisture also increases. Thus, if there is a lot of moisture in the engine oil on which the sliding member slides, the amount of wear of the sliding member tends to increase, and there is a concern about a decrease in wear resistance.

  The present invention has been made in view of the above, and when the engine is slid in a lubricating oil containing more water than a lubricating oil of a conventional vehicle not equipped with an environment adaptive system in which the engine stops frequently. An object of the present invention is to provide an internal combustion engine excellent in wear resistance of the sliding member and an automobile equipped with the internal combustion engine, and to achieve the object.

The present invention has been achieved based on the following findings. That is,
If the sliding member is slid in a lubricating oil such as engine oil that contains a relatively large amount of water, the wear resistance of the sliding surface will be reduced compared to sliding in a lubricating oil that contains little water. The knowledge that it is easy, and the nitriding surface of the steel material that constitutes the sliding member easily interacts with the zinc dialkyldithiophosphate, an antiwear agent, and greatly affects the wear resistance of the sliding surface in lubricating oil It is knowledge that it affects. That is, in lubricating oil such as engine oil containing moisture, a sliding member generally used conventionally, specifically, a sliding member using a steel material that has been carburized or quenched (hereinafter referred to as “conventional”). Of the sliding member ”) tends to increase wear on the sliding surface during sliding. As one of the causes of the increased wear in the lubricating oil containing moisture, the knowledge that the amount of the anti-wear coating formed by the anti-wear agent in the lubricating oil is small on the sliding surface was obtained. .

In this invention, based on said knowledge, the interaction which develops between the nitride layer of steel materials and the antiwear agent in lubricating oil is utilized. Specific means for achieving the above-described problems are as follows. That is, in order to achieve the above object, the first invention
Lubricating oil containing moisture and zinc dialkyldithiophosphate, steel material, nitride layer containing a nitride compound in which at least a metal component in the steel material is nitrided, and zinc (Zn), sulfur (S), and phosphorus (P) It is an internal combustion engine for automobiles having a coating film in this order and a sliding component that slides with the coating film as a sliding surface in the presence of lubricating oil. The internal combustion engine according to the first aspect of the present invention is a lubricant sampled after operating for 15 minutes or more while maintaining either the temperature of the lubricating oil (oil temperature) or the temperature of the cooling water inside the internal combustion engine at a temperature condition of 30 ° C. or lower. The content ratio of water contained in the oil is set to 0.2 mass% to 10 mass%.

  In the first invention, the lubricating oil containing moisture further contains zinc dialkyldithiophosphate as an antiwear agent, has a nitride layer on the steel material constituting the sliding member, and this nitride layer is A film containing Zn, S, and P is further formed on the nitride layer by interacting with the zinc dialkyldithiophosphate. Thereby, even when it slides in the lubricating oil containing a water | moisture content, abrasion is reduced more effectively compared with the conventional sliding member. That is, in the internal combustion engine of the present invention, the wear resistance of the sliding member that slides in the lubricating oil containing a relatively large amount of water of 0.2% by mass or more with respect to the entire lubricating oil is water-free ( The water content is less than 0.05% by mass with respect to the whole lubricating oil) and is maintained at the same level or higher when sliding in the lubricating oil.

For sliding members used in internal combustion engines that are installed together with environmental adaptation systems (such as hybrid systems and stationary stop systems (idle stop systems)) that frequently stop operation of the internal combustion engine after startup Compared to sliding members used in internal combustion engines for conventional standard automobiles (conventional vehicles) that are not equipped with a system, the wear resistance of the sliding surfaces in lubricating oil containing more water than conventional vehicles is reduced. It tends to be easy to do. However, as described above, the first invention is configured by providing a specific film on the nitride layer on the sliding member, so that it can be used in a lubricating oil containing more moisture than the conventional vehicle. Good wear resistance can be maintained. That is,
In the internal combustion engine of the present invention, it is important that a coating is formed on the sliding surface by the interaction between the antiwear agent (zinc dialkyldithiophosphate) and the nitriding surface. As a result, even when moisture in the order of% is present in the lubricating oil (for example, in the case of a drive system combining an ethanol fuel engine and a hybrid system), the lubricating oil contains almost no moisture and the moisture content is on the order of ppm. In this case (for example, in the case of a conventional vehicle that does not include an environmental adaptation system), it is possible to achieve the same amount of wear.
It is also significant in that it does not require that the steel material contains a specific metal element.

Such contamination and accumulation of moisture on the order of% in the lubricating oil is frequently caused by the use of fuel that contains moisture and easily releases moisture during combustion, etc. (eg ethanol) and the shutdown of the internal combustion engine after startup This is more likely to occur when constructing a power source that combines the generated environment adaptation system.
Here, the reason why moisture easily mixes and accumulates is shown below.
(1) When a fuel such as ethanol is used, the fuel such as ethanol contains water, so that the water mixes with the engine oil in the vicinity of the combustion chamber during fuel injection (fuel dilution) Moisture is mixed. Moreover, since it is easy to produce | generate a water | moisture content by combustion, the combustion exhaust gas containing water vapor | steam aggregates in the engine oil path | route inside an internal combustion engine, and a water | moisture content mixes in oil.
(2) In the environment adaptation system where the internal combustion engine stops frequently, the oil temperature rises less due to combustion and frictional heat than the conventional car, and the low oil water temperature is maintained, so the water is easy to accumulate without evaporating. .

In the first invention, the nitride compound contained in the nitride layer is preferably at least one selected from Fe _2-3 N and Fe ₄ N. When Fe _2-3 N or Fe ₄ N is contained, it is advantageous in that it is excellent in wear resistance.

  In the first invention, the content of the nitride compound contained in the nitride layer is 3 atomic% (at% (atomic percent); the same applies hereinafter) to 30 with respect to the total mass of the nitride layer. The amount can be atomic% (at%). When the degree of nitriding is in the above range in terms of nitrogen element, the steel material surface has good curability.

  As the automobile in the first invention, an ethanol fuel automobile is suitable. In general, gasoline engine vehicles that use gasoline as fuel produce a relatively small amount of moisture, whereas ethanol-fueled vehicles produce a relatively large amount of moisture, and the lubricating oil in an internal combustion engine such as an engine has a lot of moisture. Easy to mix. Therefore, when the internal combustion engine of the ethanol fuel automobile is the automobile internal combustion engine according to the first aspect of the invention, the effect of improving the wear resistance in the lubricating oil containing water is excellent.

  Moreover, it is preferable that the motor vehicle is equipped with a hybrid system or a stop operation stop system (idle reduction system). Since these systems are systems that stop the internal combustion engine relatively frequently, the engine changes at a relatively low temperature. Therefore, moisture mixed inside the internal combustion engine is difficult to escape to the outside, and the amount of moisture in the lubricating oil. Tends to increase. Therefore, the effect of the present invention is more effectively exhibited in an automobile equipped with an environment adaptation system such as a hybrid system or an idle stop system.

  The influence of moisture in the lubricating oil on wear is great under boundary lubrication (under severe lubrication where the contact pressure is large and the sliding speed is low). Therefore, as a sliding member, the valve lifter and adjusting are advantageous in that they have a greater effect of improving the wear resistance when slid under such lubrication and when slid in a lubricating oil containing a relatively large amount of moisture. More effective from the group consisting of shims, cams, camshafts, rocker arms, roller pins, tappets, piston rings, piston pins, timing gears, timing chains, and oil pump drive gears, driven gears, and rotors It is.

  The nitride layer constituting the sliding member is preferably a layer formed by nitriding a steel material by a plasma nitriding method. By performing the plasma nitriding treatment, a dense layer can be obtained and a nitride layer having excellent wear resistance can be obtained.

  The coating on the sliding member preferably has an order of the X-ray intensity ratio of elements analyzed by an electron beam microanalyzer (EPMA) such that sulfur (S)> zinc (Zn)> phosphorus (P). By increasing in the order of S> Zn> P, the wear resistance when sliding in a lubricating oil containing moisture is further improved.

  As the steel material constituting the sliding member, a known steel material can be selected regardless of the presence or absence of an additive element, but chromium molybdenum steel or carbon steel can be used more suitably.

Next, the second invention is an automobile provided with the internal combustion engine of the first invention described above.
By providing the internal combustion engine of the first invention, the long-term durability is excellent, and the service life of the automobile is dramatically increased.

  According to the present invention, the wear resistance of the sliding member when sliding in a lubricating oil containing more water than the lubricating oil of a conventional vehicle not equipped with an environment adaptive system in which the engine stops frequently. An internal combustion engine excellent in performance and an automobile equipped with the same are provided.

It is a perspective view which shows the piston with which the piston ring which is a sliding member which concerns on embodiment of this invention was attached. It is a schematic sectional drawing which shows the multilayer structure which comprises a piston ring. It is a SEM reflected electron image of the nitriding surface of the steel material after a plasma nitriding process. It is a graph which shows the result of the XRD analysis performed with respect to the sample sliding material using chromium molybdenum steel (SCM420). It is a graph which shows the result of the XRD analysis performed with respect to the sample sliding material using carbon steel (S50C). It is the schematic which shows the block-on-ring type abrasion tester used for an abrasion test. It is a graph which shows the influence which the water | moisture content in an engine oil has on wear. It is a graph which shows the wear increase by the water | moisture content in engine oil. It is a figure which shows the result of having analyzed the wear trace after a friction test by EPMA.

  Hereinafter, an embodiment of an internal combustion engine of the present invention and an automobile including the same will be described in detail with reference to FIGS. However, the present invention is not limited to the embodiments shown below.

In the present embodiment, in an engine that is an internal combustion engine of a hybrid system vehicle including an internal combustion engine and a motor as power sources, a piston ring is attached as one of sliding members to a groove on the outer periphery of the piston. It slides with the cylinder bore inner wall in engine oil.
The engine may be any of a gasoline engine using gasoline as a fuel, an ethanol fuel engine using ethanol as a fuel, and the like. An ethanol fuel engine is desirable from the viewpoint that the amount of water contained in the lubricating oil used in the engine tends to increase and an effect of improving the wear resistance during sliding can be expected more.

  The engine (internal combustion engine) of the present embodiment includes a piston ring 11 which is an annular part fitted in the groove of the piston 10 as shown in FIG. In this embodiment, the piston reciprocates while the piston ring 11 slides against the inner wall of the cylinder bore in the engine oil containing more water than the engine oil of the engine of a conventional vehicle that does not stop the engine that is started frequently. It is the composition to do.

As shown in FIG. 2, the piston ring 11 has a multilayered cross-sectional structure. FIG. 2 shows a cross-sectional structure of the piston ring.
The piston ring 11 is provided with an anti-wear coating 15 having a predetermined thickness on the surface that slides with the inner wall of the cylinder bore (the side away from the piston body). By providing the anti-wear coating 15, the surface of the anti-wear coating is slid with the mating member as the sliding surface. Thereby, the sliding surface exhibits excellent wear resistance.

The piston ring 11 is formed using a steel material. The steel material 21 is not nitrided in order from the inside of the steel material to the outermost layer, and the nitrogen diffusion hardened layer 23 is formed by diffusing and hardening nitrogen atoms in the steel material. And a nitride layer 25 in which a nitride compound is formed by nitriding treatment. At the beginning of operation, the piston ring 11 reciprocates in the cylinder bore with the surface of the nitride layer 25 as a sliding surface, but interacts with components in the engine oil simultaneously with sliding, as shown in FIG. The anti-wear coating 15 is formed on the surface of the nitride layer 25, and the anti-wear coating 15 is slid as a sliding surface.
When sliding in engine oil, in particular, a decrease in wear resistance is suppressed, and high durability can be maintained.

The anti-wear coating 15 contains at least zinc (Zn), sulfur (S), and phosphorus (P) as elements forming the film. These elements are elements derived from components in engine oil. Since the anti-wear coating is formed by the interaction between the anti-wear agent (zinc dialkyldithiophosphate) in engine oil and the nitriding surface (nitride layer surface) of the steel material, these elements are included.
In this case, the content ratio of Zn, S, and P contained in the anti-wear coating 15 can be confirmed by the X-ray intensity ratio of elements analyzed by an electron beam microanalyzer (EPMA). Specifically, this content ratio is a value obtained using JXA-8200 (manufactured by JEOL Ltd.).
Especially, it is preferable that the X-ray intensity ratio in the anti-wear coating of Zn, S, and P is in the order of S>Zn> P. Since the X-ray intensity ratio is in this order, it is considered that the wear resistance is excellent because the formation of iron sulfide that is particularly effective for adhesive wear is promoted.

  The thickness of the anti-wear coating is a thin film having a thickness of about several tens to several hundreds of nanometers, preferably 50 nm to 200 nm when evaluated with the maximum thickness in consideration of the thickness distribution.

The nitride layer 25 is a layer hardened by nitriding the surface of the steel material, and is a layer mainly made of an iron-based nitride compound such as Fe _2-3 N and Fe ₄ N. Moreover, you may comprise in the layer which dissolved nitrogen. Since the piston ring 11 has a nitride layer, the piston ring 11 interacts with the anti-wear agent of the engine oil to form an anti-wear coating on the nitride layer and exhibits excellent wear resistance. .

The content of the nitride compound in the nitride layer is preferably 3 atom% to 30 atom% in terms of nitrogen element. That is, the nitrogen concentration of the nitride layer is preferably within the above range. Nitride compound content in the nitride layer, that is, the nitrogen content is 3 atomic% or more, so that the necessary hardness as a sliding material can be obtained and the anti-wear coating formed by interaction with engine oil The formability of becomes better. Further, when the nitrogen content in the nitride layer is 30 atomic% or less, the nitride layer is prevented from being hardened excessively and becomes brittle, and the suitability as a sliding material for the sliding component supporting the load is maintained. Can do.
Especially, as nitrogen content in a nitride layer, it is more preferable that it is the range of 10 atomic%-28 atomic%.

  The presence of the nitrogen compound in the nitride layer 25 can be confirmed by X-ray diffraction (XRD) analysis (for example, analysis using D8 ADVANCE (manufactured by Bruker AXS)). The content of the nitride compound in the nitride layer can be converted from the measured value of the nitrogen content in the nitride layer, and the nitrogen content in the nitride layer can be calculated using an electron beam microanalyzer (EPMA). ; It is calculated | required by measuring the amount of nitrogen using JXA-1500F (made by JEOL Ltd.).

  When the nitride layer 25 includes an additive element (for example, aluminum, chromium, molybdenum, or the like) that forms a compound with nitrogen in the steel material, the nitride layer may include a nitride of these elements.

  The thickness of the nitride layer 25 can be in the range of 0.2 μm to 50 μm, preferably 5 μm to 20 μm. If the thickness is 0.2 μm or more, it is possible to avoid the possibility that the nitride layer is worn out before the service life (about 10 years) of the automobile engine elapses. Conversely, when the thickness is 50 mm or less, the occurrence of cracks in the nitride layer due to internal stress can be suppressed.

  Further, the nitrogen diffusion hardened layer 23 located in the lower layer of the nitride layer 25 is a layer hardened from the steel material due to the diffusion of nitrogen into the layer due to the formation of the nitride layer. Specifically, It is formed as a composite layer in which iron-based nitrides and nitrides of additive elements are dispersed and deposited in a layer in which nitrogen is dissolved or in a layer in which nitrogen is dissolved.

  The thickness of the nitrogen diffusion hardened layer 23 is generally about several tens to several hundreds μm, and preferably 5 μm to 200 μm.

Next, the steel material 21 used for the nitriding process will be described.
As the steel material, a general steel material that is conventionally used for manufacturing sliding parts for automobile engines can be used, and examples thereof include chromium molybdenum steel, carbon steel, and ductile cast iron.
The types of steel materials can be broadly classified into two types depending on the presence or absence of the above-described additive elements, and any of steel materials containing additive elements and steel materials not containing additive elements may be used.

  The nitride layer can be formed by nitriding treatment such as plasma nitriding, gas nitriding, salt bath soft nitriding, gas soft nitriding, plasma soft nitriding or the like. The nitride layer is generally formed as a porous layer. Among these, a nitride layer formed by a plasma nitriding method is preferable because it is advantageous that the outermost layer is more densely formed in terms of wear resistance. The nitride layer formed by the plasma nitriding method is easier to obtain a denser layer than the layer formed by other processing methods other than the plasma nitriding method, and can exhibit more excellent wear resistance. .

In the nitriding method, a fluid such as a gas or an aqueous solution is used as a nitrogen source, and the nitrogen source can easily reach the surface even in a complicated shape. Therefore, the surface can be nitrided regardless of the shape of the steel material. That is, a nitride layer can be formed on any sliding surface.
In addition, these nitriding methods have a great advantage of improving wear resistance by using nitriding because the cost required for nitriding is almost the same as that of general carburizing or quenching.

  The engine oil used for the engine of this embodiment is a lubricating oil containing at least a base oil and zinc dialkyldithiophosphate as components. In particular, by containing zinc dialkyldithiophosphate as an additive, it interacts with the nitriding surface of the steel (nitride layer surface), and wear resistance in oil with relatively high moisture content. An anti-wear coating suitable for improvement is formed.

  There is no restriction | limiting in particular as said base oil, The oil (oil) conventionally used for the lubricating oil for engines can be selected and used as desired.

The zinc dialkyldithiophosphate is a compound represented by the following chemical formula, and when contained in engine oil, has an effect of improving wear resistance.
^{(R 2 OR 1 O (=} S) P-S) Zn (-SP (= S) OR 3 OR 4)
R ¹ , R ² , R ³ , and R ⁴ each independently represents a hydrocarbon group having 1 to 24 carbon atoms.
Examples of the hydrocarbon group represented by R ^{1 to} R ⁴ include a linear or branched alkyl group having 1 to 24 carbon atoms, a linear or branched alkenyl group having 3 to 24 carbon atoms, and 5 carbon atoms. A cycloalkyl group having 13 to 13 carbon atoms, a linear or branched alkylcycloalkyl group having 5 to 13 carbon atoms, an aryl group having 6 to 18 carbon atoms, or a linear or branched alkylaryl group having 6 to 18 carbon atoms. In addition, it is desirable to be selected from arylalkyl groups having 7 to 19 carbon atoms. Further, the alkyl group or alkenyl group may be any of primary, secondary, and tertiary.

Among the above, examples of the alkyl group having 1 to 24 carbon atoms represented by R ^{1 to} R ⁴ include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, Nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, icosyl group, henocosyl group, docosyl group, tricosyl group, tetracosyl group, etc. It is done.

Examples of the alkenyl group having 3 to 24 carbon atoms represented by R ^{1 to} R ⁴ include a propenyl group, an isopropenyl group, a butenyl group, a butadienyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, and a nonenyl group. Group, decenyl group, undecenyl group, dodecenyl group, tridecenyl group, tetradecenyl group, pentadecenyl group, hexadecenyl group, heptadecenyl group, octadecenyl group (e.g. oleyl group), nonadecenyl group, icocenyl group, heicosenyl group, dococenyl group, tricocenyl group, tricocenyl group, Groups and the like.

Examples of the cycloalkyl group having 5 to 13 carbon atoms represented by R ^{1 to} R ⁴ include a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group.

Examples of the alkylcycloalkyl group having 5 to 13 carbon atoms represented by R ^{1 to} R ⁴ include a methylcyclopentyl group, a dimethylcyclopentyl group, an ethylcyclopentyl group, a propylcyclopentyl group, an ethylmethylcyclopentyl group, a trimethylcyclopentyl group, diethyl Cyclopentyl group, ethyldimethylcyclopentyl group, propylmethylcyclopentyl group, propylethylcyclopentyl group, dipropylcyclopentyl group, propylethylmethylcyclopentyl group, methylcyclohexyl group, dimethylcyclohexyl group, ethylcyclohexyl group, propylcyclohexyl group, ethylmethylcyclohexyl group, Trimethyl cyclohexyl group, diethyl cyclohexyl group, ethyl dimethyl cyclohexyl group, propyl methyl cyclohexyl group Propylethylcyclohexyl group, dipropylcyclohexyl group, propylethylmethylcyclohexyl group, methylcycloheptyl group, dimethylcycloheptyl group, ethylcycloheptyl group, propylcycloheptyl group, ethylmethylcycloheptyl group, trimethylcycloheptyl group, diethylcyclohexane Examples include heptyl group, ethyldimethylcycloheptyl group, propylmethylcycloheptyl group, propylethylcycloheptyl group, dipropylcycloheptyl group, propylethylmethylcycloheptyl group and the like.

Examples of the aryl group having 6 to 18 carbon atoms represented by R ^{1 to} R ⁴ include a phenyl group and a naphthyl group.

Examples of the alkylaryl group having 6 to 18 carbon atoms represented by R ^{1 to} R ⁴ include tolyl group, xylyl group, ethylphenyl group, propylphenyl group, ethylmethylphenyl group, trimethylphenyl group, butylphenyl group, Propylmethylphenyl, diethylphenyl, ethyldimethylphenyl, tetramethylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, decylphenyl, undecylphenyl, dodecylphenyl Groups and the like.

Examples of the arylalkyl group having 7 to 19 carbon atoms represented by R ^{1 to} R ⁴ include benzyl group, methylbenzyl group, dimethylbenzyl group, phenethyl group, methylphenethyl group, and dimethylphenethyl group.

  The above hydrocarbon group includes all possible linear and branched structures, and also includes the position of the double bond of the alkenyl group, the position of bond of the alkyl group to cycloalkyl, and the aryl of the alkyl group. The bonding position to the group and the bonding position of the aryl group to the alkyl group can be arbitrarily selected.

  Preferred examples of zinc dialkyldithiophosphate include zinc diisopropyldithiophosphate, zinc diisobutyldithiophosphate, zinc di-sec-butyldithiophosphate, zinc di-sec-pentyldithiophosphate, zinc di-n-hexyldithiophosphate, di- -Sec-hexyl dithiophosphate zinc, dioctyl dithiophosphate zinc, di-2-ethylhexyl dithiophosphate zinc, di-n-decyl dithiophosphate zinc, di-n-dodecyl dithiophosphate zinc, diisotridecyl dithiophosphate zinc, and these The mixture etc. which combined 1 or 2 or more arbitrarily can be mentioned.

  The content of the zinc dialkyldithiophosphate in the engine oil is preferably 0.02% by mass to 0.20% by mass in terms of phosphorus element with respect to the total mass of the engine oil, and 0.05% by mass to 0.00%. 10 mass% is more preferable. When the content ratio of the zinc dialkyldithiophosphate is 0.02% by mass or more, the wear prevention layer formed on the nitride layer has good formability and an excellent wear prevention effect. Moreover, when the content ratio of the zinc dialkyldithiophosphate is 0.20% by mass or less, it is advantageous in terms of suppressing poisoning of the exhaust catalyst.

  Commercially available products that are commercially available may be used as the zinc dialkyldithiophosphate, and as examples of commercially available products, LZ-1371 manufactured by Lubrizol, Deophos Zn 8 manufactured by DOG, and the like can be used.

The water content in the engine oil in the present embodiment is the content obtained when the temperature of the lubricating oil inside the internal combustion engine and the water temperature are maintained at a temperature condition of 30 ° C. or lower and continuously operated for 15 minutes or longer. As 0.2 mass% to 10 mass% with respect to the total mass of the engine oil. This water content is the maximum amount of water that can be contained in the engine oil when the engine mounted / removed in a system where the engine is stopped relatively frequently, such as a hybrid system or an idle stop system, is repeatedly operated. Is assumed.
That is, the water content of 0.2% by mass or more contains a larger amount of water than the engine oil of an engine of a conventional vehicle not equipped with an environment adaptive system that frequently stops the engine after starting. It is shown that. Moreover, when the water content is 10% by mass or less, for example, when a system combining an internal combustion engine using a fuel such as ethanol, which is expected to increase the water content, and an environment adaptive system such as a hybrid system is considered. Indicates the maximum amount of water contained in the lubricating oil.

  Among the above, the water content in the engine oil is preferably 0.5% by mass to 10% by mass, and more preferably 1.0% by mass to 10% by mass with respect to the total mass of the engine oil.

  When the water content in the engine oil is within the above range, the wear resistance of the sliding surface of the sliding member is likely to decrease. However, as described above, the engine oil contains zinc dialkyldithiophosphate. (Lubricating oil) and a sliding member that slides in the engine oil and has a wear preventing coating containing Zn, S, and P on the nitride layer on the steel material. Especially excellent in wear resistance.

In the above embodiment, the piston ring has been described as an example. However, as the sliding member, in addition to the piston ring, a valve lifter, an adjusting shim, a cam, a camshaft, a rocker arm, a roller pin, a tappet, a piston pin, a timing gear A timing chain, and an oil pump drive gear, driven gear, rotor, and the like are preferable.
In the case of these sliding members as well as in the case of the above-described piston ring, the sliding portion includes a nitride layer containing a nitride compound obtained by nitriding the steel material, and Zn, S, and P on the steel material. By having a coating (a wear-preventing coating) in this order, excellent wear resistance can be exhibited in engine oil containing moisture.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.

<Production of sliding member>
-1. Preparation of steel
As the steel material, chromium molybdenum steel (SCM420) and carbon steel (S50C) were prepared. The chemical composition of these steel materials is shown in Table 1 below. As shown in Table 1, chromium molybdenum steel is a steel material containing chromium (Cr) and molybdenum (Mo) as additive elements, and carbon steel is a steel material not containing such an additive element.

-2. Nitriding treatment
Each of chromium molybdenum steel (SCM420) and carbon steel (S50C) prepared as steel materials was nitrided by plasma nitriding under the nitriding conditions shown in Table 2 below.
By the above, like the multilayer structure shown in FIG. 2, the sliding member (sample sliding material 1-2; Examples 1-2) which has a nitrogen diffusion hardening layer and a nitride layer superimposed on steel materials is carried out. Produced.

-EPMA analysis-
In order to confirm the formation of the desired nitride layer for the produced sample sliding materials 1 and 2, while observing chromium molybdenum steel and carbon steel subjected to plasma nitriding treatment under the conditions shown in Table 2, Analysis by EPMA (Electron Probe MicroAnalyser Analysis) was performed. Specifically, the cross section of chromium molybdenum steel and carbon steel subjected to plasma nitriding treatment is polished, and the polished cross section is imaged with a scanning electron microscope (SEM) and the reflected electron image is observed, Moreover, quantitative analysis of nitrogen (N) and iron (Fe) was performed using an electron beam microanalyzer (JXA-1500F (manufactured by JEOL Ltd.)).
Further, X-ray diffraction (XRD) analysis was performed on the surfaces of chromium molybdenum steel and carbon steel subjected to plasma nitriding treatment, and crystal structure analysis was performed on the nitride layer of chromium molybdenum steel and the nitride layer of carbon steel. Here, analysis was also performed on untreated (before nitriding) chromium molybdenum steel and carbon steel.

First, the results of SEM image (reflection electron image) and EPMA analysis are shown in FIG. Note that the EPMA analysis results vary somewhat depending on the analysis points, so a five-point analysis was performed on one nitride layer, and evaluation was performed using an average value thereof.
As shown in FIG. 3 and Table 3, in both sample sliding materials 1 and 2, a layer containing nitrogen is formed at a high concentration (at least 20 at% in terms of nitrogen element) about 10 μm from the surface. I understand. As is apparent from the XRD analysis described later, it can be seen that nitrogen exists as a nitride compound in the layer containing nitrogen at a high concentration. In addition, a layer containing nitrogen at a low concentration was observed deeper than the layer containing nitrogen at a higher concentration even inside the solid, and it was found that nitrogen diffused to the deep portion.
Therefore, it was confirmed that the desired nitride layer was formed by performing plasma nitriding treatment on chromium molybdenum steel and carbon steel.

Next, X-ray diffraction (XRD) analysis was performed on each sample sliding material using chromium molybdenum steel (SCM420) or carbon steel (S50C) using D8 ADVANCE (Bruker AXS). The results of XRD analysis are shown in FIGS. Here, the result with respect to the untreated surface of each steel material used for the sample sliding materials 1-2 for a comparison is also shown.
As shown in FIGS. 4 and 5, it can be seen that clear peaks of the Fe ₃ N phase and the Fe ₄ N phase are observed in the nitride layer of chromium molybdenum steel and the nitride layer of carbon steel. From this, it can be seen that any nitride layer includes an Fe ₃ N phase and an Fe ₄ N phase. The Fe ₃ N phase and the Fe ₄ N phase are typically found in the nitride layer of plasma nitrided steel.

<Preparation of comparative materials>
The following comparative material 1 (comparative example 1) and comparative material 2 (comparative example 2) were prepared as comparative sliding materials.
Comparative material 1:
Sliding material / comparative material 2 in which gas carburizing treatment and shot blasting treatment are applied to chromium molybdenum steel (SCM420):
Sliding material with quenching and shot blasting applied to carbon steel (S50C)

In addition, as said gas carburizing process, quenching process, and shot blasting process, all performed the general surface treatment at the time of using chromium molybdenum steel or carbon steel as a sliding component for automobile engines.
For example, a carburized layer is a layer formed by carburizing the surface, and carburizing is a process in which low carbon steel or low carbon alloy steel is machined and then hardened by increasing the amount of carbon on the surface. It means a treatment method in which carbon is infiltrated into the surface to be dissolved and hardened. Examples of the carburizing process include solid carburizing, gas carburizing, liquid carburizing, vacuum gas carburizing, and plasma carburizing.

Hereinafter, for the sake of convenience, the gas carburizing process and the shot blasting process are collectively referred to as “carburizing process”, and the quenching process and the shot blasting process are collectively referred to as “quenching process”, respectively.
The carburized chromium molybdenum steel (SCM420) surface hardened layer formed on the surface of the carburized layer and the carburized carbon steel (S50C) surface hardened layer formed on the surface of the hardened steel. Each of these is referred to as a “layer”.

In addition to the above, the following Comparative Material 3 (Comparative Example 3) and Comparative Material 4 (Comparative Example 4) were prepared as comparative sliding materials for clarifying the superiority of the nitride layer. .
Comparative material 3:
The nitride layer which is the outermost layer of the sample sliding material 1 is polished to remove the nitride layer, the nitrogen diffusion hardened layer is exposed, and the nitrogen diffusion hardened layer on the chromium molybdenum steel is used as a sliding surface. Sliding material / comparative material 4:
The nitride layer which is the outermost layer of the sample sliding material 2 is polished to remove the nitride layer, the nitrogen diffusion hardened layer is exposed, and the nitrogen diffusion hardened layer on the carbon steel is used as a sliding surface. In the above, the polishing depth for removing the nitride layer was determined based on the result of cross-sectional observation performed on the sample sliding materials 1 and 2 as described above. Further, the fact that the nitride layer is removed and the nitrogen diffusion hardened layer is exposed is determined by measuring the Vickers hardness of the polished surface and confirming that the hardness is 90% or less with respect to the nitride layer. did. The Vickers hardness was determined by measuring and averaging the hardness of 2 points of 0.5 mm from the both ends of the test piece and a total of 3 points at the center using MVK-E (manufactured by Akashi Seisakusho).

<Preparation of test engine oil>
As the engine oil to be tested, a commercially available engine oil (hereinafter referred to as “commercial oil”), which is a general lubricating oil for gasoline engines, and an engine oil prepared using a base oil and a plurality of additives (hereinafter referred to as “ "Prototype oil").
・ Commercial oil:
ILSAC GF-4 standard oil manufactured by Toyota Motor Corporation, viscosity grade: 5W-30
・ Prototype oil:
Prototype oil having the composition shown in Table 4 below

The procedure for producing the trial oil is shown below. That is,
The base oil consists only of an overbased calcium sulfonate with a calcium element conversion value of 0.24% by mass and a succinimide-based ashless dispersant containing no boron with respect to the total amount (mass basis) of the prototype oil. A succinimide-based ashless dispersant was blended in an amount such that the nitrogen element equivalent value was 0.06% by mass, and a zinc dialkyldithiophosphate was an amount such that the phosphorus element equivalent value was 0.08% by mass. Then, it stirred at the oil temperature of 60 degreeC for 1 hour. Note that the types and amounts of the base oil and additive used in the prototype oil simulate those of general engine oil.

<Preliminary experiment on maximum amount of water mixed in engine oil>
In preparing an engine oil containing water as a lubricating oil for use in the wear test, the maximum amount of water that can be mixed into the engine oil was examined.
Specifically, in order to quantitatively understand the influence of the engine environment on the amount of water in the engine oil, the difference in the test fuel (100% ethanol fuel or commercially available high-octane gasoline fuel) and the oil temperature (low temperature) (Or high temperature) and the effect of the water content in the engine oil. Here, the high oil temperature condition simulates the engine environment of a conventional vehicle (that is, the environment in which the engine continues to operate while the vehicle is running after the engine is started), and the low oil temperature condition is a hybrid system (environment adaptation system). The engine environment is simulated in a system where the engine after starting is frequently stopped.
The amount of water in the engine oil was measured by periodically collecting the engine oil from the engine while performing a bench driving test using an actual automobile engine. The sampling location was an oil pan, head deck, and head cover. The results are shown in Table 5 below.
In Table 5, the water temperature represents the temperature of the cooling water in the internal combustion engine, and the oil temperature represents the temperature of the lubricating oil in the internal combustion engine.

First, focus on the case where commercial high-octane gasoline fuel is used as the test fuel.
As shown in Table 5, when the engine was operated for 15 minutes at a water temperature of 30 ° C., the water content in the engine oil was 0.16%. On the other hand, when operated for 20 minutes at a water temperature of 100 ° C., the water content in the engine oil was 0.034%. From this, it can be seen that when the oil water temperature is kept at a low temperature, the amount of water in the oil tends to increase. In addition, when an engine using gasoline fuel is installed with an environmental adaptation system such as a hybrid system that frequently stops the engine, the maximum amount of water that can be mixed into the engine oil is about 0.2% by mass. Can do.
Next, attention is paid to the case where 100% ethanol fuel is used as the test fuel.
When operated for 15 minutes at a water temperature of 30 ° C., the maximum water content in the engine oil was 7.8%. On the other hand, when it was operated for 20 minutes at a water temperature of 100 ° C., the water content in the engine oil was 0.032%. As a result, when an engine using 100% ethanol fuel is used in an environment where a conventional vehicle is used (that is, an environment where the engine continues to operate while the vehicle is running after the engine is started), the amount of water that can be mixed into the engine oil Is about 0.05% by mass at the maximum. On the other hand, when an engine using 100% ethanol fuel is mounted together with an environmentally adaptive system such as a hybrid system in which the engine stops frequently, the amount of water that can be mixed into the engine oil is about 10% by mass at maximum. be able to.
From the above results, the relationship between the engine environment and the maximum amount of water that can be mixed in the engine oil is as shown in Table 6 below.

As shown in Table 6 above, in a system in which the engine is frequently stopped after starting, as a result of a low temperature environment, the amount of water in the engine oil is larger than that of the engine oil of a conventional vehicle, and ethanol etc. It can be seen that the amount of water in the engine oil increases significantly when fuel containing water is used.
On the other hand, it has been the case that automobiles that use fuels containing water such as ethanol and that are equipped with environmentally compatible systems such as hybrid systems have not been provided so far. The wear resistance of the sliding member in a moisture environment in which the amount of moisture in the engine oil is in the range of 0.2% by mass to 10% by mass is not taken into consideration.
Under such circumstances, as described above, a lubricating oil containing zinc dialkyldithiophosphate and a sliding component having a coating containing Zn, S, and P on a nitride layer on a steel material were provided. The configuration is suitable for maintaining the wear resistance in the engine oil containing a large amount of moisture as described above.

<Preparation of moisture-containing engine oil>
Based on the above examination, the water content in the engine oil was set to 0 mass%, 0.2 mass%, 0.5 mass%, 1 mass%, and 10 mass%. These water-containing engine oils were prepared by adding water into the oil and then stirring at room temperature (25 ° C.) for 24 hours.

<Evaluation of wear resistance>
-Evaluation method-
Using the block-on-ring type wear tester shown in FIG. 6, the container is sequentially charged with the above-mentioned commercially available oil or the prepared prototype oil as the engine oil, and the ring test piece is placed so that a part of the oil is immersed in the engine oil. While arranging, each said sliding material (sample sliding materials 1-2, comparative materials 1-4) was attached to the sliding surface of the block test piece one by one. And the sliding material attached to the block test piece is a commercially available ring test piece (hardness: HV560-770, surface roughness (Ra): 0.35 mm) rotating under a predetermined load under the following sliding wear conditions. Falex S-10 test piece (AISI 4620 carburized and hardened alloy steel)) was subjected to a friction test under continuous sliding conditions in a line contact form, and the wear resistance of each sliding material was evaluated.
Here, in order to make each surface roughness uniform, each nitride layer of the sample sliding materials 1 and 2 and the carburized layer or the quenching layer of the comparative materials 1 to 4 are polished under the same conditions after the plasma nitriding treatment. Using.
<Sliding wear conditions>
・ Load (W): 286N
・ Sliding speed (v): 0.3 m / sec
Oil temperature (T): 40 ° C
Test time (t): 30 min

When sliding under the above-described sliding wear condition and test piece shape, the lubrication state is boundary lubrication. The boundary lubrication is a severe lubrication state in which an oil film is not sufficiently formed and solids contact each other. In automobile engines, sliding parts that slide under boundary lubrication include valve lifters, adjusting shims, cams, camshafts, rocker arms, roller pins, tappets, piston rings, piston pins, timing gears, timing chains, and There are oil pump drive gears, driven gears, and rotors.
The wear resistance was evaluated by measuring the depth of wear on the block test piece after the wear test using a white interference type non-contact surface shape measuring machine. Here, the wear scar depth is a height difference between the non-sliding portion and the deepest portion of the concave wear scar.

-Evaluation results-
(1) Effect of water content in engine oil on wear First, the water content in engine oil is changed to a nitride layer of chromium molybdenum steel and a carburized layer of chromium molybdenum steel (engine slides commonly used at present). FIG. 7 shows the influence of wear on moving parts).
As shown in FIG. 7, in the case where the sliding surface is a carburized layer, the wear increases remarkably at a moisture content of 0.2% by mass, whereas the sample sliding materials 1-2 in which the sliding surface is a nitride layer are used. However, the effect of water content on wear was observed, but there was almost no significant effect on wear. Furthermore, paying attention to the influence of the moisture content on the wear of the carburized layer, the wear scar depth when the moisture content was 1% by mass was about four times that when the moisture content was 0% by mass. Moreover, in the area | region where the moisture content is 1 mass% or more, the wear scar depth remained high, and the influence which the moisture content has on the wear was not observed.
From this result, the nitride layer was able to maintain the same wear resistance as when the engine oil contained almost no water even when a large amount of water was present in the engine oil. On the other hand, when the conventional sliding material is used in the range of the amount of moisture contained in the engine oil of the conventional vehicle (moisture amount ≦ 0.2% by mass), there is no significant problem in wear, but the moisture amount is low. It was found that excessive wear occurred in the range of 0.2% by mass or more and it could not be used.

  Next, based on the result of the friction test performed on each of the sliding materials prepared above (sample sliding materials 1 and 2 and comparative materials 1 to 4), the influence on the increase in wear due to moisture in the engine oil Is shown in FIG. FIG. 8 shows the effect of moisture in the oil on the wear of each sliding material when a friction test is performed using the prototype oil.

First, attention is focused on the case where the steel material is chromium molybdenum steel (SCM420).
When 10% by weight of water is present in the oil, the wear scar depth is increased 2.6 times in the carburized layer, and the wear scar depth is increased 4.7 times in the nitrogen diffusion hardened layer. In the nitride layers of the sample sliding materials 1 and 2 (Examples 1 and 2), the increase in the wear scar depth remained 1.4 times.
Next, attention is focused on the case where the steel material is carbon steel (S50C).
When 10% by mass of water is present in the oil, the wear scar depth increases 4.1 times in the quenched layer and the wear scar depth increases 2.4 times in the nitrogen diffusion hardened layer. On the other hand, in the nitride layers of the sample sliding materials 1 and 2 (Examples 1 and 2), the increase in the wear scar depth remained at 1.4 times.
As described above, in chromium molybdenum steel and carbon steel, the nitride layer maintains wear resistance even in engine oil containing water compared to conventional carburized layers, quenched layers, and nitrogen diffusion hardened layers. It was done.
In this example, the case where the water content was 10% by mass was shown as an example. However, the moisture content (0.2% by mass to 10% by mass) specified in the present invention is good when the water content is the highest. Since wear resistance was obtained, it is presumed that good wear resistance can be ensured in the range of 0.2 mass% to 10 mass% other than 10 mass%.

  Further, in this example, similar results were obtained for both chromium molybdenum steel containing an additive element and carbon steel containing no additive element. It is played.

(2) Actions and effects-Maintaining the formability of the anti-wear coating-
Prior to showing the reason why the nitride layer of the steel material maintains the wear resistance performance in the engine oil containing moisture, first, the conventional phenomenon of increased wear of sliding parts due to the moisture in the engine oil will be described.
When a carburized layer of chromium molybdenum steel is slid in engine oil that does not contain moisture, the zinc dialkyldithiophosphate (antiwear agent) in the engine oil and the steel material undergo a chemical reaction on the sliding surface, and the sliding surface In addition, an anti-wear coating composed of zinc (Zn), sulfur (S), phosphorus (P), iron (Fe) and the like is formed. The wear of the carburized layer is suppressed by this anti-wear coating. This phenomenon also occurs when a general steel material is used as a sliding material.
On the other hand, when the carburized layer of chromium molybdenum steel is slid in engine oil containing moisture, the amount of the anti-wear coating formed on the sliding surface decreases. This is because the zinc dialkyldithiophosphate is altered by a chemical reaction between the zinc dialkyldithiophosphate, moisture, and calcium carbonate on the friction surface. Calcium carbonate is contained in the overbased calcium sulfonate in the oil component, and calcium carbonate has a function of neutralizing an acid generated by combustion.
Based on the above phenomenon of increased wear, the reason why the nitride layer maintains the wear resistance in engine oil containing water is that the dialkyldithiophosphorus on the nitride layer is higher than that on the carburized layer and the quenched layer. It is considered that the amount of the anti-wear coating formed in the presence of zinc acid, moisture, and calcium carbonate is large.

  In order to verify this mechanism, elemental analysis by EPMA was performed on the wear scar (sample sliding material 1) after the friction test, which obtained the results of FIG. In this elemental analysis, attention was focused on zinc (Zn), sulfur (S), and phosphorus (P) derived from the anti-wear coating. The results of this elemental analysis are shown in FIG.

As shown in FIG. 9, when the water content is 0% by mass, X-rays containing zinc (Zn), sulfur (S), and phosphorus (P) of 0.20% or more in any of the four types of sliding surfaces. It was detected by the intensity ratio, and it was shown that a sufficient anti-wear coating was formed.
Next, attention is paid to the case where the water content is 10% by mass.
In the nitride layer of chrome molybdenum steel and the nitride layer of carbon steel, X of zinc (Zn), sulfur (S), and phosphorus (P) is compared with the carburized layer of chrome molybdenum steel and the hardened layer of carbon steel. It can be seen that the line intensity ratio is large. That is, in the nitride layer of chrome molybdenum steel and the nitride layer of carbon steel, an engine containing zinc dialkyldithiophosphate, moisture, and calcium carbonate as compared with a carburized layer of chrome molybdenum steel and a hardened layer of carbon steel. This shows that the anti-wear coating was retained in the oil.
From the above results, the nitride layer of the steel material has a wear-resistant coating film derived from zinc dialkyldithiophosphate in an engine oil containing zinc dialkyldithiophosphate, moisture, and calcium carbonate as compared with the carburized layer and the quenched layer. It was confirmed that the amount formed could be maintained. This is considered to be a reason why the nitride layer of the steel material maintains the wear resistance performance in the engine oil containing moisture.

-Interaction between sliding surface and anti-wear agent-
Compared with carburized and hardened layers, the steel nitride layer maintains the amount of anti-wear coating derived from zinc dialkyldithiophosphate in engine oils containing zinc dialkyldithiophosphate, moisture, and calcium carbonate. Consider the mechanism.
Regarding the interaction between the sliding surface of steel and engine oil additives, for example, “Boundary lubrication from the viewpoint of surface chemistry-Role of new surface for tribochemical reaction of lubricating oil additives-, Masayuki Mori, JTEKT ENGINEERING JOURNAL, No. 1008 (2010) "reports that the metal oxide coating the metal surface has a high chemical affinity with fatty acids and phosphorus-based antiwear agents. This is because of the principle of Pearson's Hard and Soft Acids and Bases (HSAB), that is, a combination of a hard acid and a hard base, and a soft acid and a soft base. This combination is based on the principle of forming a strong bond that is easy to react (see RG Pearson (ed.): Hard and Soft Acids and Bases, Dowden, Huchinson & Ross, Inc. (1973)). Specifically, metal oxides are classified as hard acids because they are ion-bonded and polar, and are strong and easily react with fatty acids and polar antiwear agents that have polar functional groups and are classified as hard bases. It is a mechanism that forms a bond.
Here, since iron nitride (Fe _2-3 N, Fe ₄ N), which is the main component of the nitride layer, is ion-bonded, it is a carburized layer or a quenching layer that dissolves carbon, and nitrogen is dissolved. Compared with a diffusion layer mainly composed of a layer, it can be classified as a hard acid. On the other hand, zinc dialkyldithiophosphate can also be classified as a hard base because it has a higher polarity than other additives in the trial oil. When the above mechanism is applied, it is presumed that the nitride layer and the zinc dialkyldithiophosphate form a strong bond that is more likely to react than the carburized layer or the quenched layer. Further, it is assumed that the anti-wear coating on the nitride layer and the anti-wear coating on the carburized layer and the quenched layer have different structures.
When looking at the results when the moisture content in each layer (sliding surface) in FIG. 9 is 0% by mass, in the carburized layer of chromium molybdenum steel and the hardened layer of carbon steel, the order of the X-ray intensity ratio is zinc (Zn), In contrast to sulfur (S) and phosphorus (P), the order of the X-ray intensity ratio in the nitride layer is sulfur (S), zinc (Zn), and phosphorus (P). This suggests that in the nitride layer, an anti-wear coating having a different structure is formed as compared with the carburized layer and the quenched layer.
It is assumed that the mechanism in which the amount of the anti-wear coating derived from the zinc dialkyldithiophosphate in the nitride layer is large is as described above.

  From the above results, the use of a sliding member having a sliding surface made of a nitride layer of a steel material allows the conventional sliding member to be worn even in engine oil with a relatively high water content that increases wear. It becomes possible to maintain the same wear resistance as when almost no moisture is contained.

  In the above description, the nitride layer of chromium molybdenum steel and the nitride layer of carbon steel have been mainly described. However, the effect of improving wear resistance is not limited to the nitride layer of these steel materials. The reason for this is that even when other steel materials are nitrided, from the viewpoint of wear resistance, when the steel materials contain additive elements, a compound layer similar to the compound layer of chromium molybdenum steel is formed, and the steel material This is because when no additive element is contained, a compound layer similar to the compound of carbon steel is formed.

DESCRIPTION OF SYMBOLS 10 ... Piston 11 ... Piston ring 15 ... Abrasion prevention coating 21 ... Steel material 23 ... Nitrogen diffusion hardening layer 25 ... Nitride layer

Claims (10)

A lubricating oil comprising moisture and zinc dialkyldithiophosphate;
A steel layer, a nitride layer containing a nitride compound in which at least a metal component in the steel material is nitrided, and a coating containing zinc (Zn), sulfur (S), and phosphorus (P) in this order; A sliding member sliding in the presence of the coating as a sliding surface;
The water content ratio contained in the lubricating oil collected after operating for 15 minutes or more while maintaining either the temperature of the lubricating oil or the water temperature in the internal combustion engine at a temperature condition of 30 ° C. or lower is 0. An internal combustion engine for automobiles of 2 mass% to 10 mass%. The internal combustion engine according to claim 1, wherein the nitride compound contained in the nitride layer is at least one selected from Fe _2-3 N and Fe ₄ N.   The content of the nitride compound contained in the nitride layer is an amount such that the nitrogen element conversion value is 3 atomic% to 30 atomic% with respect to the total mass of the nitride layer. Internal combustion engine.   The internal combustion engine according to any one of claims 1 to 3, wherein the automobile is an ethanol fuel automobile.   The internal combustion engine according to any one of claims 1 to 4, wherein the automobile is equipped with a hybrid system or a stop operation stop system.   The sliding members include valve lifters, adjusting shims, cams, camshafts, rocker arms, roller pins, tappets, piston rings, piston pins, timing gears, timing chains, and oil pump drive gears, driven gears, and rotors. The internal combustion engine according to any one of claims 1 to 5, wherein the internal combustion engine is at least one selected from the group consisting of:   The internal combustion engine according to any one of claims 1 to 6, wherein the nitride layer is a layer formed by nitriding a steel material by a plasma nitriding method.   The order of the X-ray intensity ratio of the elements in the film analyzed by an electron beam microanalyzer (EPMA) is Sulfur (S)> Zinc (Zn)> Phosphorus (P). The internal combustion engine according to item 1.   The internal combustion engine according to any one of claims 1 to 8, wherein the steel material is chromium molybdenum steel or carbon steel.   The motor vehicle provided with the internal combustion engine of any one of Claims 1-9.