Grease composition for constant velocity joint, and constant velocity joint in which same is sealed

Abstract

A grease composition for constant velocity joints, which contains (a) a base oil, (b) a diurea-based thickener, (c) molybdenum dialkyldithiocarbamate that is solid at 25 DEG C, (d) molybdenum dialkyldithiocarbamate that is liquid at 25 DEG C, (e) overbased calcium sulfonate, and (f) zinc dialkyldithiocarbamate. And the content of the component (f) is 0.3-3.5 mass% based on the total mass of the composition.

Description

Technical Field

[0001] This invention relates to a grease composition for constant velocity joints and a constant velocity joint incorporating the grease composition. Background Technology

[0002] In the automotive industry, front-engine, front-wheel-drive (FF) vehicles are widely used due to the need for lightweighting and ensuring living space, with the aim of reducing vehicle environmental impact (CO2 reduction). Constant velocity joints (CVJs) are essential for power transmission in FF vehicles.

[0003] A universal joint (CVJ) is a device that transmits rotation between two shafts rotating at an angle. Therefore, within the universal joint, components undergo complex rolling and sliding movements. Telescopic CVJs also have an axial sliding mechanism, resulting in axial sliding resistance due to friction between internal components. If this sliding resistance is high, it can sometimes cause vibration and noise. It should be noted that vehicle characteristics related to these vibrations and sounds are generally referred to as NV characteristics (N for noise and V for vibration).

[0004] In recent years, the automotive industry has been advancing the electrification of power sources with the aim of achieving carbon neutrality and low fuel consumption, resulting in a significant improvement in vehicle quietness. As mentioned above, compared to vehicles equipped with traditional internal combustion engines, the performance requirements for noise and vibration have become higher, and the requirements related to NV characteristics for telescopic constant velocity joints have also become more stringent.

[0005] Furthermore, with the widespread availability of HEVs, PHEVs, and BEVs in the general market, an environment has emerged where low-torque driving conditions resulting from the popularization of fuel-efficient driving coexist with high-torque driving conditions during acceleration due to electric motors. Based on the above, compared to vehicles equipped with internal combustion engines, telescopic constant velocity joints operate within a wider range of surface pressure environments, ranging from low surface pressure conditions due to fuel-efficient driving inputs to high surface pressure conditions due to electric motor acceleration inputs. Due to the increased internal friction accompanying changes in the lubrication environment of the sliding parts, a decrease in NVH (noise, vibration, and ductility) characteristics can sometimes become a problem. The increased sliding resistance, a major cause of reduced NVH characteristics, is caused by increased internal friction; therefore, reducing friction under a wide range of surface pressure conditions is a necessary countermeasure.

[0006] To address these issues, although structural improvements were made to the CVJ itself, cost became a significant concern, leading to a demand for a lubricant with excellent low friction under a wide range of surface pressure conditions.

[0007] As a grease with excellent vibration suppression for CVJs, the following have also been proposed: a constant velocity joint grease made by mixing molybdenum dithiocarbamate and molybdenum dithiophosphate as additives in base oil and urea grease, or by mixing zinc dithiophosphate in these organic molybdenum compounds (see Patent Document 1); and a constant velocity joint composition containing base oil, diurea thickener, dialkyl dithiocarbamate, zinc sulfonate, sulfur-phosphorus extreme pressure agent and vegetable oil (see Patent Document 2).

[0008] In addition, as a grease that takes into account not only vibration damping performance but also wear of the lubricated parts, a constant velocity universal joint grease composition containing base oil, thickener, lignite wax, zinc sulfonate, and molybdenum dialkyl dithiocarbamate sulfide without trinuclear molybdenum compounds has been proposed (see Patent Document 3).

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Publication No. 5-79280

[0012] Patent Document 2: Japanese Patent Application Publication No. 2011-37650

[0013] Patent Document 3: Japanese Patent No. 6248939 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] Thus, while NV characteristics of grease compositions for CVJs have been studied to date, it cannot be said that sufficient research has been conducted on NV characteristics under a wide range of surface pressure conditions that take into account vehicle electrification.

[0016] Therefore, the objective of this invention is to provide a grease composition for a constant velocity universal joint that exhibits low friction under both low and high surface pressure conditions, and a constant velocity universal joint incorporating the composition.

[0017] Solution for solving the problem

[0018] 1. A grease composition for constant velocity joints, comprising:

[0019] (a) Base oil,

[0020] (b) Diurea-based thickeners,

[0021] (c) Molybdenum dialkyldithiocarbamate, which is a solid at 25°C,

[0022] (d) Molybdenum dialkyldithiocarbamate, which is liquid at 25°C

[0023] (e) Superalkaline calcium sulfonate, and

[0024] (f) Zinc dialkyl dithiocarbamate,

[0025] Based on the total mass of the composition, the content of component (f) is 0.3% to 3.5% by mass.

[0026] 2. The constant velocity universal joint grease composition according to 1 above, wherein, based on the total mass of the composition, the content of component (e) is 0.5% to 8.5% by mass.

[0027] 3. The constant velocity universal joint grease composition according to 1 or 2 above, wherein, based on the total mass of the composition, the content of component (d) is 0.3% to 7.0% by mass.

[0028] 4. The constant velocity universal joint grease composition according to any one of 1 to 3 above, wherein, based on the total mass of the composition, the content of component (c) is 0.2% to 4.0% by mass.

[0029] 5. The constant velocity universal joint grease composition according to any one of 1 to 4 above, further comprising component (g) sulfur-based extreme pressure agent.

[0030] 6. The constant velocity universal joint grease composition according to any one of 1 to 5 above, wherein component (b) is at least one selected from the group consisting of diurea compounds shown in formulas (1-1), (1-2), or (1-3).

[0031] [Chemistry 1]

[0032]

[0033] In the formula, R 1 R is a cycloalkyl group with 6 to 12 carbon atoms. 2 It is an alkyl group with 6 to 30 carbon atoms.

[0034] 7. The constant velocity universal joint grease composition according to any one of technical solutions 1 to 6, wherein component (a) contains a plurality of mineral oil.

[0035] 8. The constant velocity joint grease according to any one of 1 to 7 above, which is used in a sliding constant velocity joint.

[0036] 9. A three-ball pin type sliding constant velocity universal joint, wherein the constant velocity universal joint grease composition described in any one of 1 to 7 above is sealed.

[0037] Invention Effects

[0038] According to the present invention, a grease composition for constant velocity joints that exhibits excellent low-friction characteristics even under a wide range of surface pressure conditions, from low to high surface pressure, can be provided. Furthermore, according to the present invention, a constant velocity joint incorporating a grease composition that exhibits excellent low-friction characteristics even under a wide range of surface pressure conditions, from low to high surface pressure, can be provided. Detailed Implementation

[0039] (a) Base oil

[0040] In this invention, the type of base oil affects the flowability of the grease to the lubricated part or the oil film formation characteristics, but it is considered that the type of base oil has almost no impact on the low-friction characteristics of this invention. Therefore, the type of base oil that can be used in this invention is not particularly limited, and mineral oil, synthetic oil, or mixtures thereof can be used. Examples of mineral oils include alkane-based mineral oils and cycloalkane-based mineral oils. Examples of synthetic oils include hydrocarbon-based synthetic oils such as polyalphaolefins and ether-based synthetic oils represented by alkyl diphenyl ethers. It should be noted that synthetic oils can be so-called biomass oils made from biological resources produced by animals and plants. For example, biomass ester oils synthesized from various fatty acids and alcohols made from vegetable oils can also be used, as well as biomass hydrocarbon oils using vegetable oils such as palm oil, corn oil, and soybean oil. From a cost point of view, mineral oil is preferred as the base oil of this invention. It is preferable that the base oil contains a large proportion of mineral oil, for example, when it is 15% by mass or more based on the total mass of the base oil, it is effective for cost reduction.

[0041] From the viewpoint of oil film formation characteristics, the kinematic viscosity of the base oil of the present invention at 100°C is preferably 6 to 25 mm. 2 / s, more preferably 8~20mm 2 / s, further preferably 10~15mm 2 / s. As a result, an oil film of appropriate thickness can be formed, thus obtaining a grease composition with excellent durability (peel resistance) required for CVJ grease.

[0042] Based on the total mass of the composition, the content of base oil in the composition of the present invention is preferably 57-93% by mass, more preferably 63-90% by mass, and even more preferably 68-88% by mass. By containing base oil within such a range, the flowability of the grease composition of the present invention can be obtained, resulting in excellent low friction properties in the lubricated part.

[0043] (b) Thickener

[0044] The thickener of this invention is a diurea-based thickener. Diurea-based thickeners soften easily due to shearing, thus ensuring sufficient lubrication is supplied to the sliding parts within the CVJ.

[0045] Generally, diurea thickeners can be classified into aliphatic diurea thickeners, alicyclic diurea thickeners, alicyclic aliphatic diurea thickeners, aromatic diurea thickeners, etc., depending on the type of monoamine used as the raw material for the diurea compound. In this invention, the type or structure of the diurea thickener may affect the fluidity of the grease, but it is considered to have almost no impact on the low-friction characteristics of this invention. Therefore, there are no particular limitations on the diurea thickeners used in this invention.

[0046] As the diurea-based thickener of the present invention, it is preferably selected from at least one of the groups consisting of diurea compounds represented by formulas (1-1), (1-2), or (1-3).

[0047] [Chemistry 2]

[0048]

[0049] In the formula, R 1 It is a cycloalkyl group with 6 to 12 carbon atoms, preferably 6 to 7 carbon atoms, and more preferably cyclohexyl.

[0050] R 2 It is an alkyl group having 6 to 30 carbon atoms, preferably 8 to 20 carbon atoms, and more preferably 8 to 18 carbon atoms.

[0051] As the thickener of the present invention, a mixture of the diurea compound of formula (1-1), the diurea compound of formula (1-2), and the diurea compound of formula (1-3) is preferred, namely, an alicyclic aliphatic diurea thickener. By using an alicyclic aliphatic diurea thickener as the thickener of the present invention, excellent fluidity can be obtained, and lubricating grease can be easily supplied to the sliding parts within the CVJ.

[0052] R is the preferred choice 1 Cyclohexyl, R 2 It is an alicyclic aliphatic diurea thickener with an alkyl group having 18 carbon atoms.

[0053] The content of the thickener is preferably an amount sufficient to adjust the cone penetration of the grease composition of the present invention to 310-340. Specifically, based on the total mass of the composition, it is preferably 5-13% by mass, more preferably 6-12% by mass, and even more preferably 7-11% by mass. When the cone penetration of the grease composition of the present invention is 310-340, excellent fluidity can be obtained, and grease can be easily supplied to the sliding parts within the CVJ. It should be noted that, in this specification, "cone penetration" refers to the 60 working cone penetration measured by JIS K22207.

[0054] (c) Molybdenum dialkyldithiocarbamate, which is a solid at 25°C

[0055] (d) Molybdenum dialkyldithiocarbamate, which is liquid at 25°C

[0056] Molybdenum dialkyl dithiocarbamate (MoDTC), which can be used as (c) or (d) of this invention, is a general term for materials with molybdenum as the metal-based metal in organometallic load-bearing additives. It is widely used as a friction modifier (it should be noted that MoDTC is sometimes classified as an extreme pressure agent, but in recent years it has been more often classified as a friction modifier). MoDTC contains both non-oil-soluble (i.e., solid at 25°C) and oil-soluble (i.e., liquid at 25°C) substances. By using non-oil-soluble MoDTC and oil-soluble MoDTC together, a stable low-friction coating can be formed, achieving excellent low-friction properties over a wide range from low to high surface pressure.

[0057] As a preferred example of MoDTC, compounds represented by formula (2) can be listed.

[0058] [R 3 R 4 N-CS-S]2-Mo2O m S n (2)

[0059] In equation (2), R 3 and R 4 They can be the same or different from each other, each independently representing a straight-chain or branched alkyl group with 1 to 24 carbon atoms, preferably 3 to 18, m is 0 to 3, n is 4 to 1, and m+n=4.

[0060] MoDTC is necessary to achieve low friction, but as it is an expensive additive, its content needs to be balanced between low friction properties and cost.

[0061] From the viewpoint of low friction characteristics and cost, the content of component (c) is preferably 0.2 to 4.0% by mass, more preferably 0.3 to 3.0% by mass, and even more preferably 0.4 to 2.5% by mass, based on the total mass of the composition.

[0062] From the viewpoint of low friction characteristics and cost, based on the total mass of the composition, the content of component (d) is preferably 0.3 to 7.0% by mass, more preferably 0.8 to 6.0% by mass, and even more preferably 1.0 to 5.0% by mass. By making components (c) and (d) within this range, the low friction characteristics are particularly excellent.

[0063] (e) Superalkaline calcium sulfonate

[0064] The calcium sulfonate used in this invention is over-alkaline due to its association with calcium carbonate; if it were neutral calcium sulfonate, excellent low friction properties would not be achieved. Furthermore, examples of metal components for metal sulfonates include sodium, magnesium, and barium, but to obtain low friction properties across a wide range of surface pressures from low to high, the metal component must be calcium.

[0065] As a superalkaline calcium sulfonate, the preferred alkalinity is 200-500 mg KOH / g, more preferably 300-470 mg KOH / g, and even more preferably 350-450 mg KOH / g. Within this range, satisfactory low friction can be obtained.

[0066] It should be noted that the alkalinity value in this invention is a value measured using ASTM D-2896.

[0067] From the viewpoint of low friction, the content of superalkaline calcium sulfonate is preferably 0.5 to 8.5% by mass, based on the total amount of the composition. If a balance between low friction and cost is taken into account, it is preferably 1.0 to 7.0% by mass, and more preferably 1.5 to 6.0% by mass.

[0068] (f) Zinc dialkyl dithiocarbamate

[0069] Zinc dialkyl dithiocarbamate (ZnDTC) used in this invention is preferably zinc dialkyl dithiocarbamate (ZnDTC) represented by formula (3).

[0070] [R 5 2N-CS-S]2-Zn (3)

[0071] The alkyl structure of ZnDTC has almost no impact on the low friction in this invention, but in formula (3), R 5 Preferably, it is a primary or secondary alkyl group having 1 to 24 carbon atoms, and more preferably an alkyl group having 3 to 8 carbon atoms.

[0072] Excessive ZnDTC content can sometimes lead to increased friction due to corrosion of the lubrication parts (the lubrication parts of CVJ are made of metal). Therefore, in order to ensure low friction (especially low friction under low surface pressure) and prevent increased friction caused by corrosion, the ZnDTC content is 0.3% to 3.5% by mass, preferably 0.5% to 3.0% by mass, and more preferably 0.7% to 2.5% by mass, based on the total mass of the composition.

[0073] In addition to components (a) to (f), the compositions of the present invention may also contain additives commonly used in lubricating greases, as needed.

[0074] (g) Sulfur-based extreme pressure agents

[0075] Examples of sulfur-based extreme pressure agents that can be used in this invention include, for example, sulfurized oils and esters obtained by sulfurizing castor oil, rapeseed oil, tallow and other animal and vegetable oils, sulfurized olefins obtained by sulfurizing olefins, and polysulfides.

[0076] From the viewpoint of low friction in this invention, it is not necessary to contain a sulfur-based extreme pressure agent, but considering extreme pressure performance, it is preferable to contain a sulfurized olefin, and more preferably, a sulfurized olefin with a sulfur content of 35-50% by mass. It should be noted that the sulfur content in this invention is a value determined using JIS K 2541.

[0077] It should be noted that if an excessive amount of sulfur-based extreme pressure agent is present, it can sometimes become a major cause of increased friction due to corrosion of the lubricated parts. Considering the low friction and extreme pressure properties, the content is preferably 0.3 to 1.5% by mass, more preferably 0.3 to 1.2% by mass, and even more preferably 0.3 to 1.0% by mass, based on the total mass of the composition. Low friction and excellent extreme pressure properties can be obtained within this range.

[0078] Any additive other than sulfur extreme pressure additives can be listed as a solid lubricant, antioxidant, rust inhibitor, extreme pressure additive, or oiliness agent.

[0079] Examples of solid lubricants include molybdenum disulfide, soil graphite, scaly graphite, carbon black, boron nitride, potassium borate, and calcium carbonate. Examples of organic compounds include melamine cyanurate, polytetrafluoroethylene, copper and iron salts of dithiocarbamate, stearic acid, and calcium, aluminum, sodium, and lithium salts of sebacic acid.

[0080] As antioxidants, examples include amine-based, phenolic-based, quinoline-based, and sulfur-based antioxidants.

[0081] Examples of rust inhibitors include zinc-based, carboxylic acid-based, carboxylate salts (such as sodium sebate and other dicarboxylate salts), or amine-based agents.

[0082] Examples of extreme pressure agents include phosphate esters such as triphenyl phosphate, triaryl phosphate, and tricresyl phosphate; azole compounds such as benzotriazole and dialkylthiodiazole; fatty acids obtained by decomposing and modifying oils and fats from animals and plants; monoglycerides, diglycerides, polyols such as glycerol; alkyd resins; hydrogenated oils; chlorinated oils; and thiophosphates.

[0083] As oiling agents, examples include fats and oils such as tallow, lard, fish oil, castor oil, palm oil, soybean oil, and rapeseed oil obtained from animals and plants; esters such as trimethylolpropane oleate, pentaerythritol stearate, dioctyl sebacate, dioctyl adipate, dioctyl phthalate, and dibutyl phthalate; higher alcohols such as cetyl alcohol, stearyl alcohol, and oleyl alcohol; and ester waxes based on lignite acid obtained from lignite through refining and oxidation.

[0084] Based on the total mass of the composition, the content of these arbitrary additives is, for example, 0.1 to 5.0% by mass, preferably 0.3 to 4.0% by mass, more preferably 0.5 to 3.5% by mass.

[0085] When used as a grease composition for constant velocity joints, the grease composition of the present invention can certainly perform most effectively. However, when used in sliding constant velocity joints (i.e., telescopic constant velocity joints), it can perform even more effectively. In sliding constant velocity joints, it can perform even more effectively when used in three-ball-pin type sliding constant velocity joints.

[0086] Example

[0087] The grease compositions of the Examples and Comparative Examples were prepared using the following components. Specifically, 1 mole of 4',4-diphenylmethane diisocyanate was reacted with 2 moles of a predetermined amine in a base oil. After heating and cooling, the mixture was kneaded using a three-roll mill to obtain a base grease. Additives were added to the base oil in the proportions shown in Table 1 or Table 2 (unless otherwise specified, the numbers in the tables represent mass percentages based on the total mass of the composition), and the mixture was further added to the base oil in the manner of thickening dosages shown in Table 1 or Table 2. The mixture was then dispersed using a three-roll mill to obtain the grease compositions of the Examples and Comparative Examples. Furthermore, the cone penetration was measured according to JIS K2220 7 and standardized to 325.

[0088] <Base Oil>

[0089] • Mineral oil (kinematic viscosity at 100°C = 12.44 mm) 2 / s)

[0090] Thickener

[0091] • The thickener used is a diurea-based thickener obtained by using cyclohexylamine and octadecylamine (cyclohexylamine: octadecylamine = 9:1, molar ratio) as amines.

[0092] <Additives>

[0093] • MoDTC (solid): solid molybdenum dialkyl dithiocarbamate (Adeka Sakura-lube 600, manufactured by ADEKA), is the molybdenum dialkyl dithiocarbamate in formula (2) 3 and R 4 A compound consisting of a straight-chain alkyl group with 4 carbon atoms, m = 2, and n = 2.

[0094] • MoDTC (liquid): liquid molybdenum dialkyl dithiocarbamate (Adeka Sakura-lube 525, manufactured by ADEKA), is the molybdenum dialkyl dithiocarbamate in formula (2)3 and R 4 A compound in which R is 2-ethylhexyl, m is 2, and n is 2 and R 3 and R 4 is isotridecyl, m is 2, and n is 2, and a mixture of the compounds.

[0095] • Overbased calcium sulfonate: Overbased calcium sulfonate (Bryton C-400CKY, manufactured by Lanxess, base number = 405 mgKOH / g)

[0096] • Neutral calcium sulfonate: Neutral calcium sulfonate (ALOX 2292B, manufactured by Lubrizol, TBN = 2.5 mgKOH / g)

[0097] • ZnDTC: Zinc dialkyldithiocarbamate (VANLUBE AZ, manufactured by R.T. VANDERBILT)

[0098] • Sulfur-based extreme pressure agent: Sulfurized olefin (ANGLAMOL 33, manufactured by Lubrizol, sulfur content 43.0%)

[0099] • Wax: Montan wax (LICOWAX E, manufactured by Clariant Japan)

[0100] • Zinc sulfonate: Zinc sulfonate (NA-SUL ZS, manufactured by KING INDUSTRIES)

[0101] The respective grease compositions of the examples and comparative examples were tested by the following method. The test results of the examples are shown in Table 1, and the test results of the comparative examples are shown in Table 2. In addition, Comparative Example 8 corresponds to Example 1 of Japanese Patent No. 6248939.

[0102] <Evaluation of SRV test>

[0103] Only when the results under both conditions of (1) high surface pressure condition and (2) low surface pressure condition are Δ or more are regarded as qualified.

[0104] It should be noted that this condition assumes the condition of the entire sliding constant velocity joint.

[0105] <(1) Evaluation of NV characteristics under high surface pressure condition>

[0106] The arithmetic mean of the friction coefficients during the 10-second period from 1790 seconds to 1800 seconds from the start of the test was calculated and compared for evaluation. <0​​​​​​Stroke: 3.6mm

[0110] Frequency: 4.3Hz

[0111] Test duration: 1800 seconds

[0112] Test temperature: 40℃

[0113] Ball: 17.5mm

[0114] Plate: Surface roughness Rz = 5.0 μm

[0115] [evaluate]

[0116] ○(passed): <0.045

[0117] △(Qualified): 0.045~0.055

[0118] × (Unacceptable): >0.055

[0119] <(2) Evaluation of NV characteristics under low surface pressure conditions>

[0120] Calculate the arithmetic mean of the friction coefficients during the 10-second period from 590 to 600 seconds after the start of the experiment, and then compare and evaluate them.

[0121] • Test conditions

[0122] Surface pressure: 0.15 GPa

[0123] Stroke: 1.5mm

[0124] Frequency: 33Hz

[0125] Test duration: 600 seconds

[0126] Test temperature: 50℃

[0127] Roller bearing: φ15mm×22mm

[0128] Plate: Surface roughness Rz = 1.5 μm

[0129] [evaluate]

[0130] ○(passed): <0.088

[0131] △(Qualified): 0.088~0.095

[0132] × (Unacceptable): >0.095.

[0133]

[0134]

Claims

1. A grease composition for constant velocity universal joints, comprising: (a) Base oil, (b) Diurea-based thickeners, (c) Molybdenum dialkyldithiocarbamate, which is a solid at 25°C, (d) Molybdenum dialkyldithiocarbamate, which is liquid at 25°C (e) Superalkaline calcium sulfonate, and (f) Zinc dialkyl dithiocarbamate, Based on the total mass of the composition, the content of component (f) is 0.3% to 3.5% by mass.

2. The constant velocity universal joint grease composition according to claim 1, wherein, Based on the total mass of the composition, the content of component (e) is 0.5% to 8.5% by mass.

3. The constant velocity universal joint grease composition according to claim 1, wherein, Based on the total mass of the composition, the content of component (d) is 0.3% to 7.0% by mass.

4. The constant velocity universal joint grease composition according to claim 1, wherein, Based on the total mass of the composition, the content of component (c) is 0.2% to 4.0% by mass.

5. The constant velocity universal joint grease composition according to claim 1, further comprising component (g) a sulfur-based extreme pressure agent.

6. The constant velocity universal joint grease composition according to claim 1, wherein, Component (b) is at least one of the following groups consisting of diurea compounds represented by formulas (1-1), (1-2), or (1-3). [Chemistry 1] In the formula, R 1 R is a cycloalkyl group with 6 to 12 carbon atoms. 2 It is an alkyl group with 6 to 30 carbon atoms.

7. The constant velocity universal joint grease composition according to claim 1, wherein, Ingredient (a) contains a high proportion of mineral oil.

8. The constant velocity joint grease according to any one of claims 1 to 7, which is used in a sliding constant velocity joint.

9. A three-ball pin type sliding constant velocity universal joint, wherein a constant velocity universal joint grease composition according to any one of claims 1 to 7 is sealed.

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