Grease composition for constant velocity joint, and fixed type constant velocity joint

Abstract

To provide: a grease composition that is excellent in terms of seizure resistance, wear resistance, and low friction properties under a high contact pressure condition as compared with a conventional CVJ sliding part environment; and a fixed type constant velocity joint.SOLUTION: There is provided a grease composition for a constant velocity joint, which contains (a) a base oil, (b) a diurea-based thickener represented by a formula (1), (c) a molybdenum dialkyldithio-carbamate that is in a solid state at 25°C, (d) zinc oxide that has an average particle diameter of 0.3 to 4.0 μm, and (e) an oil-based agent. A content of the zinc oxide (d) is 0.40 to 2.50 mass% based on a total mass of the grease composition and a content of the oil-based agent (e) is 0.80 to 4.00 mass% based on a total mass of the grease composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition for a constant velocity joint and a fixed constant velocity joint containing the same. [Background technology]

[0002] In recent years, front-engine, front-wheel drive (FF) vehicles have become more common in order to reduce weight and secure interior space for environmental reasons (CO2 reduction), and constant velocity joints (CVJs), which are essential for power transmission in FF vehicles, are widely used. CVJs are an important component in automobiles, responsible for transmitting the power (torque) from the powertrain unit, such as the engine and motor, to the tires. A CVJ is a device that transmits rotation between two shafts that rotate at an angle, and the parts inside the joint perform a complex rolling and sliding motion. In particular, with outboard constant velocity joints (fixed constant velocity joints), the sliding distance of each sliding part increases when the steering angle is increased through steering operation, increasing the load between the balls and ball grooves. Therefore, the sliding surface pressure is the most severe condition of all the sliding parts of the joint. Furthermore, in recent years, with the promotion of a decarbonized society, the automotive industry has been working to reduce CO2 emissions and improve fuel and electricity costs, and there is a growing demand for CVJs to be smaller, lighter, and with higher capacity. As the trend toward smaller and lighter CVJs progresses, the internal components have become smaller, and the sliding contact area has become smaller, which has resulted in a trend toward higher surface pressure, especially between the balls and ball grooves, and the sliding environment has become more severe. Furthermore, in today's CVJ environment, cost reduction is a major focus, and value analysis (VA) in the processing process is becoming increasingly common. During the forging process of CVJ outer races, grinding is performed to eliminate forged abnormalities in the ball groove and optimize the sliding environment. These processing steps have been costly. As a result of recent VA efforts to reduce costs by reviewing the processing process, the surface roughness of the ball groove (roughness of the groove) has become higher in the processing mark height (maximum height of the roughness peaks) and wider in the pitch interval (the distance between the roughness peaks). This has resulted in an increase in the true contact pressure (the pressure generated between the ball and the groove's processing mark peaks). Furthermore, due to the reduction in load-bearing points, the contact pressure in the groove has become even higher and more severe. Due to the recent shift to such harsh surface pressure environments in CVJs, ball grooves are increasingly experiencing issues such as micro-seizure at the tops of the grooves, abnormal wear, and reduced durability due to high friction (flaking). The most common type of damage to ball grooves in CVJs is surface-originated flaking. Surface-originated flaking begins as micro-seizure or abnormal wear in the sliding area under high surface pressure, and progresses due to the frictional force (tangential force) of the sliding area. Therefore, the key to improving surface-originated flaking in CVJs is improving seizure resistance, wear resistance, and reducing friction under harsh surface pressure environments.

[0003] To solve these problems, structural improvements have been made to the constant velocity joint, but due to significant cost issues, greases are now required to have excellent seizure resistance and wear resistance, as well as low friction, to withstand the harsh sliding conditions caused by recent changes in the environment surrounding CVJs. For conventional CVJs, a grease composition containing a base oil, a diurea-based thickener, benzotriazole and / or a derivative thereof, and a phosphate ester and / or an amine salt thereof has been proposed as a grease composition having excellent wear resistance and flaking resistance (Patent Document 1). Furthermore, as grease compositions with excellent flaking resistance for conventional CVJs, there have been proposed a grease composition containing a base oil, a diurea-based thickener, molybdenum disulfide, molybdenum sulfide dialkyldithiocarbamate, a calcium salt of petroleum sulfonic acid, a sulfur extreme pressure agent, vegetable oil, and zinc dialkyldithiocarbamate (Patent Document 2), and a grease composition containing a base oil, a thickener, an organic molybdenum compound, and at least one compound selected from the group consisting of oxides of divalent typical metals having a Mohs hardness lower than that of steel and compounds of divalent typical metals that rapidly change into oxides having a Mohs hardness lower than that of steel under boundary lubrication conditions (Patent Document 3). However, these grease compositions were developed based on their flaking resistance or wear resistance under the conventional sliding environment of CVJs, and therefore there is room for further improvement in grease compositions with respect to flaking resistance under the increasingly severe sliding conditions caused by recent changes in the environment surrounding CVJs, i.e., in terms of achieving both seizure resistance, wear resistance, and low friction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6292569 [Patent Document 2] Patent No. 5344424 [Patent Document 3] International Publication No. 2005 / 083044 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a grease composition that is excellent in seizure resistance, wear resistance, and low friction, and a fixed constant velocity joint that contains the grease composition. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have found that the above problems can be solved by a grease composition containing the following components (a) to (e). That is, the present invention has the following configuration. [1] (a) a base oil; (b) a diurea-based thickener represented by formula (1); R 1 -NHCONH-C6H4-p-CH2-C6H4-p-NHCONH-R 2 (1) (In the formula, R 1 and R 2 may be the same or different and are an aryl group or a cyclohexyl group having 6 to 7 carbon atoms. (c) a molybdenum dialkyldithiocarbamate that is solid at 25°C; (d) zinc oxide having an average particle size of 0.3 to 4.0 μm; (e) an oily agent, (d) the zinc oxide content is 0.40 to 2.50 mass% based on the total mass of the grease composition, (e) The grease composition, wherein the content of the oily agent is 0.80 to 4.00 mass % based on the total mass of the grease composition. [2] (c) The grease composition of [1], wherein the content of the molybdenum dialkyldithiocarbamate is 0.60 to 4.50 mass % based on the total mass of the grease composition. [3] (f) The grease composition of [1], further comprising a sulfur-based extreme pressure agent. [4] [1] A grease composition for fixed constant velocity joints. [5] A fixed constant velocity joint filled with any one of the grease compositions [1] to [4]. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a grease composition and a fixed constant velocity joint filled with the grease composition that have excellent seizure resistance, wear resistance, and low friction not only in conventional CVJs but also in today's CVJ sliding part environments that are subject to higher surface pressure conditions than in conventional CVJ sliding part environments. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 10 is a diagram for explaining a method for calculating a wear scar width in the evaluation of abrasion resistance. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Grease composition] (a) Base oil In the present invention, the type of base oil may affect the inflow of the grease into the lubricated parts or the oil film formation characteristics, but it is thought that it has almost no effect on the seizure resistance, wear resistance, and low friction properties in the present invention. Therefore, the type of base oil that can be used in the present invention is not particularly limited, and mineral oil, synthetic oil, or a mixture thereof can be used. Mineral oils include paraffinic mineral oils, naphthenic mineral oils, and mixtures thereof. Examples of synthetic oils include hydrocarbon synthetic oils such as poly-α-olefins (PAOs) and ether synthetic oils such as alkyl diphenyl ethers. The synthetic oil may be a so-called biomass oil, which is produced using biological resources derived from animals and plants as raw materials. For example, biomass ester oils synthesized from various fatty acids and alcohols derived from vegetable oils, and biomass hydrocarbon oils derived from vegetable oils such as palm oil, corn oil, and soybean oil can also be used. From the viewpoint of cost, it is preferable to use mineral oil as the base oil of the present invention. It is preferable that the base oil contains a high proportion of mineral oil, and the content of mineral oil is, for example, preferably 50 mass% or more, more preferably 55 mass% or more, and even more preferably 60 mass% or more, based on the total mass of the base oil. It is also preferable that the base oil contains 100 mass% of mineral oil based on the total mass of the base oil. The kinematic viscosity of the base oil in the present invention at 100°C is 8 to 24 mmHg from the viewpoint of oil film forming properties. 2 / s is preferable, and 10 to 22 mm 2 / s is more preferable, and 12 to 20 mm 2 / s is more preferable, and 12 to 18 mm 2 / s. A kinematic viscosity in this range makes it possible to form an oil film of appropriate thickness, and to obtain a grease composition with excellent oil film-forming properties required for CVJ greases. In this specification, the kinematic viscosity is a value measured in accordance with JIS K2283. The content of the base oil in the grease composition of the present invention is preferably 52 to 87 mass %, more preferably 56 to 85 mass %, and even more preferably 60 to 84 mass %, based on the total mass of the composition. By having the content of the base oil in this range, the grease composition of the present invention can obtain good flowability and, as a result, can exhibit excellent lubrication properties.

[0010] (b) Thickener The grease composition of the present invention contains a diurea-based thickener. Diurea-based thickeners are generally classified into aliphatic diurea-based thickeners, alicyclic diurea-based thickeners, alicyclic-aliphatic diurea-based thickeners, aromatic diurea-based thickeners, etc., depending on the type of monoamine that is the raw material for the diurea compound. In the present invention, the type and structure of the diurea-based thickener may affect the grease flowability and shear stability, but are thought to have little effect on the seizure resistance, wear resistance, and low friction properties of the present invention. The diurea thickener of the present invention is a diurea thickener represented by formula (1). R 1 -NHCONH-C6H4-p-CH2-C6H4-p-NHCONH-R 2 (1) In formula (1), R 1 and R 2may be the same or different and are an aryl group having 6 to 7 carbon atoms or a cyclohexyl group. Examples of the aryl group having 6 to 7 carbon atoms include a phenyl group and a tolyl group. The aryl group having 6 to 7 carbon atoms is more preferably a phenyl group. The diurea thickener represented by formula (1) is preferably at least one selected from the group consisting of diurea compounds represented by formulas (1-1), (1-2), and (1-3).

[0011] [ka]

[0012] In formulas (1-1), (1-2), and (1-3), R 1 is a cyclohexyl group, and R 2 is an aryl group having 6 to 7 carbon atoms. Examples of the aryl group having 6 to 7 carbon atoms include a phenyl group and a tolyl group. The aryl group having 6 to 7 carbon atoms is more preferably a phenyl group. The thickener of the present invention is preferably an alicyclic-aromatic diurea thickener, which is a mixture of diurea compounds represented by formula (1-1), formula (1-2), and formula (1-3). In the compound represented by formula (1) or in a mixture of compounds represented by formulas (1-1), (1-2), and (1-3), the molar ratio of cyclohexyl groups is preferably 60 to 80 mol %, more preferably 65 to 75 mol %, based on the total number of moles of cyclohexyl groups and aryl groups having 6 to 7 carbon atoms. When the molar ratio of cyclohexyl groups is in this range, excellent shear stability is achieved. In particular, in outboard constant velocity joints, steering input due to steering operation places a load on the seal between the boot and the outer ring, making them more susceptible to grease leakage than inboard constant velocity joints. When grease leaks from the seal, poor lubrication may occur. By using the above-mentioned alicyclic-aromatic diurea thickener as the thickener in the present invention, a grease composition with excellent shear stability can be obtained, thereby ensuring leakage resistance. The thickener content is preferably an amount that allows the consistency of the grease composition of the present invention to be adjusted to preferably 250 to 355, more preferably 265 to 340, and even more preferably 280 to 325. Specifically, the thickener content in the grease composition of the present invention is preferably 9 to 20 mass%, more preferably 10 to 18 mass%, and even more preferably 11 to 16 mass%, based on the total mass of the composition. By keeping the content in such a range, it is possible to obtain a grease composition that has excellent shear stability, and the flowability that maintains sufficient lubricity makes it easy to supply the grease to the sliding parts of the CVJ. In this specification, the consistency refers to the 60-stroke worked consistency measured according to JIS K 2220 7.

[0013] (c) Molybdenum dialkyldithiocarbamate that is solid at 25°C The grease composition of the present invention contains molybdenum dialkyldithiocarbamate that is solid at 25°C. Molybdenum dialkyldithiocarbamate (MoDTC), which can be used as component (c) of the present invention, is a general term for organometallic load-bearing additives whose metal group is molybdenum, and is generally used widely as a friction modifier. MoDTC is sometimes classified as an extreme-pressure additive, but in recent years it has often been classified as a friction modifier. MoDTC exists in both oil-insoluble (i.e., solid at 25°C) and oil-soluble (i.e., liquid at 25°C) forms. In the present invention, from the viewpoint of providing not only low friction but also extreme-pressure properties (seizure resistance) of a solid lubricant, the use of oil-insoluble MoDTC forms a coating that is stable, low friction, and excellent seizure resistance, thereby achieving excellent low friction and seizure resistance in today's CVJ sliding environment, which is subject to higher surface pressure conditions than conventional CVJ sliding environments. A preferred example of the molybdenum dialkyldithiocarbamate is a compound represented by formula (2). [R 3 R 4 N-CS-S]2-Mo2O m S n (2) In formula (2), R 3 and R 4 may be the same or different and each independently represent a linear or branched alkyl group having 1 to 13 carbon atoms, preferably 2 to 10 carbon atoms, and more preferably 3 to 8 carbon atoms, m is 0 to 3, n is 4 or 1, and m+n=4 is satisfied. In the present invention, MoDTC is used to exhibit low friction, but since it is an expensive additive, its content is preferably determined by taking into consideration both low friction and cost. From the viewpoints of low friction and cost, the content of MoDTC, which is solid at 25°C, in the grease composition of the present invention is preferably 0.60 to 4.50 mass%, more preferably 0.70 to 4.00 mass%, even more preferably 0.80 to 3.50 mass%, and even more preferably 0.80 to 2.50 mass%, based on the total mass of the composition. By keeping it in such a range, a grease composition with even more excellent low friction properties can be obtained.

[0014] (d) zinc oxide Zinc oxide (ZnO) that can be used in the present invention is generally used in various industrial fields, such as a vulcanization accelerator for rubber materials, an ultraviolet absorber (for cosmetics, inks, paints, resins, etc.), and various electronic materials such as ferrite. On the other hand, in the field of lubrication, it is sometimes used as a solid lubricant, for example, as an extreme pressure agent that exhibits wear resistance and seizure resistance by interposing as a solid component on the lubricated surface (between the two surfaces in metal-to-metal contact between the ball and ball groove in a CVJ) and suppressing metal-to-metal contact. As the zinc oxide, it is preferable to use zinc oxide particles having a predetermined average particle size. In the present invention, from the viewpoint of intercalation with lubricated surfaces, the zinc oxide has an average particle size of 0.3 to 4.0 μm, preferably 0.4 to 3.0 μm, more preferably 0.5 to 2.0 μm, even more preferably 0.5 to 1.5 μm, and even more preferably 0.5 to 1.0 μm. Within this range, intercalation between two surfaces in metal contact is achieved, resulting in excellent seizure resistance and wear resistance. However, if the average particle size exceeds 4.0 μm, intercalation with lubricated surfaces becomes difficult, and sufficient effects cannot be expected. In this specification, the average particle size refers to the D50 (median diameter) obtained from the particle distribution integrated on a volume basis, and is a value measured by the laser diffraction scattering method using, for example, the MT3300EXII manufactured by Microtrack Bell. An excessive amount of ZnO can cause abrasive wear on the lubricated surface, resulting in increased friction. On the other hand, a low content can result in insufficient penetration into the lubricated surface, making it difficult to achieve sufficient seizure resistance and wear resistance. Therefore, it is necessary to consider the possibility of powder wear due to excessive content and the reduction in effectiveness due to insufficient content. In the grease composition of the present invention, the content of zinc oxide having an average particle size of 0.3 to 4.0 μm is 0.40 to 2.50 mass%, preferably 0.40 to 2.20 mass%, and more preferably 0.40 to 2.00 mass%, based on the total mass of the composition. The lower limit of each of the above content ranges is also preferably 0.50 mass%. By maintaining the content within these ranges, powder wear does not occur, performance degradation due to insufficient content can be prevented, and excellent seizure resistance and wear resistance can be achieved.

[0015] (e) Oily agent The oiliness agent used in the present invention is generally widely used as a friction reducer and, by adsorbing to the metal surface, forms an adsorption film, exhibiting a low-friction effect. The type of oiliness agent is not particularly limited, and examples include fats and oils obtained from animals or plants, such as beef tallow, lard, fish oil, castor oil, palm oil, soybean oil, and rapeseed oil; esters such as trimethylolpropane oleate, pentaerythritol stearate, dioctyl sebacate, dioctyl adipate, dioctyl phthalate, and dibutyl phthalate; and higher alcohols such as cetyl alcohol, stearyl alcohol, and oleyl alcohol. In the present invention, these oiliness agents may be used alone or in combination of two or more. The inclusion of these oiliness agents provides excellent low-friction properties. From the viewpoint of adsorption onto the lubricated surface, the oily agent is preferably a fatty acid ester, more preferably a vegetable fatty acid ester, and even more preferably castor oil, a vegetable oil in which the alkyl chain length of the fatty acid moiety has 8 to 18 carbon atoms. By using such an oily agent, better adsorption can be obtained. The content of the oiliness agent in the grease composition of the present invention is 0.80 to 4.00 mass%, preferably 0.90 to 3.50 mass%, and more preferably 1.00 to 3.00 mass%, based on the total mass of the composition. By including the oiliness agent in such a range, the low friction properties are particularly excellent.

[0016] (f) Sulfur-based extreme pressure agents The grease composition of the present invention may further contain a sulfur-based extreme pressure agent. Examples of sulfur-based extreme pressure agents that can be used in the present invention include sulfurized oils and fats and sulfurized esters obtained by sulfurizing animal and vegetable oils such as castor oil, rapeseed oil, and beef tallow, sulfurized olefins obtained by sulfurizing olefins, and polysulfides. From the viewpoints of anti-seizure property, wear resistance, and low friction in the present invention, it is not necessary to contain a sulfur-based extreme pressure agent, but when extreme pressure properties are taken into consideration, it is preferable to contain sulfurized fats and oils, polysulfides, or sulfurized olefins, more preferably to contain sulfurized olefins, and even more preferably to contain sulfurized olefins with a sulfur component of 35 to 50 mass%. Note that the amount of sulfur components in the present invention is a value measured according to JIS K 2541. The content of the sulfur-based extreme pressure agent in the grease composition of the present invention is preferably 0.50 to 3.0 mass %, and more preferably 1.0 to 2.5 mass %, based on the total mass of the composition. By including the sulfur-based extreme pressure agent in such a range, the extreme pressure properties are excellent.

[0017] The grease composition of the present invention may further contain other additives, such as solid lubricants, antioxidants, rust inhibitors, detergents and dispersants, extreme pressure agents, and viscosity index improvers. Examples of solid lubricants include inorganic solid lubricants such as molybdenum disulfide, amorphous graphite, flaky graphite, carbon black, boron nitride, potassium borate, and calcium carbonate, and organic solid lubricants such as melamine cyanurate, polytetrafluoroethylene, copper or iron salts of dithiocarbamic acid, stearic acid, and calcium, aluminum, sodium, or lithium salts of sebacic acid. Examples of the antioxidant include amine-based, phenol-based, quinoline-based, and sulfur-based antioxidants. Examples of the rust inhibitor include zinc-based, carboxylic acid-based, carboxylic acid salts (for example, dibasic acid salts such as sodium sebacate), and amine-based rust inhibitors. Examples of detergent dispersants include calcium salts, magnesium salts, sodium salts, and zinc salts of petroleum sulfonic acids. Examples of extreme pressure agents include phosphate esters such as triphenyl phosphate, triaryl phosphate, and tricresyl phosphate; azole compounds such as benzotriazole and dialkylmercaptothiadiazole; fatty acids obtained by decomposing and modifying fats and oils obtained from animals or plants; monoglycerides or diglycerides; polyhydric alcohols such as glycerin; alkyd resins; hardened oils; chlorinated fats and oils; and thiophosphoric acids. Viscosity index improvers include polystyrene, polybutene, polyisobutylene, polymethacrylate, olefin copolymers, and the like. The content of these additives is, for example, preferably 0.1 to 15.0 mass %, more preferably 0.3 to 14.0 mass %, and even more preferably 0.5 to 13.0 mass %, based on the total mass of the composition.

[0018] It goes without saying that the grease composition of the present invention exhibits its performance most effectively when used as a grease composition for constant velocity joints, but it exhibits its performance even more effectively when used in fixed constant velocity joints, and among fixed constant velocity joints, it exhibits its performance even more effectively when used in ball type fixed constant velocity joints.

[0019] The grease composition of the present invention is, among others, (a) As a base oil, a kinematic viscosity at 100°C of 12 to 20 mm 2 / s mineral oil, (b) a mixture of diurea compounds represented by formulas (1-1), (1-2), and (1-3) as a diurea-based thickener; [ka] (In formulas (1-1), (1-2), and (1-3), R 1 is a cyclohexyl group, and R 2 is a phenyl group. (c) a molybdenum dialkyldithiocarbamate that is solid at 25°C; (d) zinc oxide having an average particle size of 0.5 to 2.0 μm; (e) Castor oil as an oily agent A grease composition for a constant velocity joint comprising: (d) the zinc oxide content is 0.40 to 2.00 mass% based on the total mass of the grease composition, The above grease composition is preferred, wherein the content of the (e) oiliness agent is 1.00 to 3.00 mass % based on the total mass of the grease composition. In particular, in this embodiment, the grease composition is preferably a grease composition for a constant velocity joint (CVJ), more preferably a grease composition for a fixed constant velocity joint, and even more preferably a grease composition for a ball joint type fixed constant velocity joint.

[0020] [Constant velocity joint] The constant velocity joint of the present invention is a fixed constant velocity joint filled with the grease composition of the present invention. The fixed constant velocity joint may be a ball joint type fixed constant velocity joint. Such a fixed constant velocity joint filled with the grease composition of the present invention can more effectively exhibit the effects of the present invention, i.e., it is excellent in seizure resistance, wear resistance, and low friction. [Example]

[0021] (Preparation of Grease Composition) Grease compositions of Examples and Comparative Examples were prepared using the components listed in Tables 1 and 2 below. Specifically, 1 mole of 4',4-diphenylmethane diisocyanate and 2 moles of a specific amine were reacted in a base oil, heated, cooled, and then kneaded on a three-roll mill to obtain a base grease. Additives were blended into the base grease in the amounts shown in Tables 1 or 2, and base oil was added to obtain the thickener amount shown in Tables 1 or 2. The mixture was then dispersed on a three-roll mill to obtain the grease compositions of Examples and Comparative Examples. Each grease composition was adjusted to a consistency of 300 as measured in accordance with JIS K2220 7. The base oils, thickeners, and additives in the table are as follows: Unless otherwise specified, the numbers for the components in the table represent mass % based on the total mass of the composition. <Base oil> Mineral oil (paraffinic mineral oil): kinematic viscosity at 100°C = 14.20 mm 2 / s PAO (poly-α-olefin): kinematic viscosity at 100°C = 8.000 mm 2 A mixture of two types: / s and kinematic viscosity at 100°C = 40.00. The grease composition of Example 10 was prepared by mixing mineral oil and PAO in a mass ratio of 70:30, and the kinematic viscosity of the entire base oil at 100°C was 14.20 mm 2 The voltage was adjusted to be / s. <Thickener> Thickener: Diurea thickener obtained by using cyclohexylamine and aniline (cyclohexylamine:aniline = 7:3 (molar ratio)) as amines. <Additives> MoDTC (solid): Molybdenum dialkyldithiocarbamate (MOLYVAN A, manufactured by Vanderbilt, solid at 25°C) MoDTC (liquid): Molybdenum dialkyldithiocarbamate (MOLYVAN 822, manufactured by Vanderbilt, liquid at 25°C) Ultra-small diameter ZnO: Zinc oxide (fine zinc oxide, manufactured by Honjo Chemical, average particle size 0.1 μm) Small diameter ZnO: Zinc oxide (Zinc oxide type 2, manufactured by Honjo Chemical, average particle size 0.4-0.7 μm) ·Medium-sized ZnO: Zinc oxide (LPZINC-2, manufactured by Sakai Chemical Industry Co., Ltd., average particle size 2.0 μm) Large diameter ZnO: Zinc oxide (LPZINC-11, manufactured by Sakai Chemical Industry Co., Ltd., average particle size 11.0 μm) Oily agent A: Oily agent (Industrial No. 1 castor oil, manufactured by Toyokuni Oil Co., Ltd., mainly consisting of alkyl chains with 16-18 carbon atoms in the fatty acid portion) Oily agent B: Oily agent (SOFTISAN GC8, manufactured by IOI Oleo GmbH, mainly consisting of alkyl chains with 8 carbon atoms in the fatty acid portion) Sulfur-based extreme pressure agent: sulfurized olefin (ANGLAMOL 33, manufactured by Lubrizol, sulfur content (S) 43.0%)

[0022] (SRV test) The SRV test was conducted on each grease composition of the Examples and Comparative Examples, and the friction coefficient, which is an index of low friction, and the wear scar width, which is an index of wear resistance, were evaluated. The results are shown in Tables 1 and 2. A test in which the evaluation results of both the friction coefficient and the wear scar width were ◯ or △ was deemed to be pass. Furthermore, a test in which the friction coefficient exceeded 0.200 during the test was deemed to have caused seizure. The test conditions simulated the high surface pressure conditions between the balls and ball grooves, which are the most susceptible to flaking in fixed constant velocity joints, and reproduced the increasingly harsh surface properties of today's CVJs by using plates with rough surface properties (high Ra values). SRV test conditions Surface pressure: 2.5GPa Stroke: 1.5mm Frequency: 70Hz Test time: 1800 seconds Test temperature: 80℃ Ball: Diameter 17.5mm Plate: Surface roughness Ra=2.5μm <Low friction> The average value of the friction coefficient for 10 seconds from 1790 seconds to 1800 seconds after the start of the test was measured and evaluated using the following criteria. [Evaluation criteria] Friction coefficient less than 0.125: ○ Friction coefficient between 0.125 and 0.135: △ Friction coefficient is greater than 0.135 and less than 0.200: × Friction coefficient over 0.200: ×× <Wear resistance, seizure resistance> As shown in Figure 1, the wear mark on the ball after 1800 seconds of testing was measured. The length of the wear mark in the x-axis direction (sliding direction) was L X and the length in the y-axis direction L Y Measure L X and L Y The average of these was taken as the wear scar width. [Evaluation criteria] Wear scar width 0.80mm or less: ○ Wear scar width over 0.80mm: × Friction coefficient over 0.200: (seizure)

[0023] [Table 1]

[0024] [Table 2]

Claims

1. (a) a base oil; (b) a diurea-based thickener represented by formula (1); R 1 -NHCONH-C 6 H 4 -p-CH 2 -C 6 H 4 -p-NHCONH-R 2 (1) (In the formula, R 1 and R 2 may be the same or different and are an aryl group having 6 to 7 carbon atoms or a cyclohexyl group. (c) a molybdenum dialkyldithiocarbamate that is solid at 25°C; (d) zinc oxide having an average particle size of 0.3 to 4.0 μm; (e) an oily agent, (d) the zinc oxide content is 0.40 to 2.50 mass % based on the total mass of the grease composition; (e) The grease composition, wherein the content of the oily agent is 0.80 to 4.00 mass % based on the total mass of the grease composition.

2. 2. The grease composition according to claim 1, wherein the content of (c) molybdenum dialkyldithiocarbamate is 0.60 to 4.50 mass % based on the total mass of the grease composition.

3. 10. The grease composition of claim 1, further comprising: (f) a sulfur-based extreme pressure agent.

4. The grease composition according to claim 1, which is for use in a fixed constant velocity joint.

5. A fixed constant velocity joint packed with the grease composition according to any one of claims 1 to 4.

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