Grease composition for constant velocity universal joints and constant velocity universal joint

Abstract

The present invention provides a grease composition for constant velocity universal joints and a constant velocity universal joint that improves boundary lubrication performance, further enhances wear resistance and peel resistance, and achieves high durability. [Solution] The grease comprises a base oil, a thickener, and an extreme pressure additive, and a traction oil, wherein the weight percentage of the traction oil is 1% or more and 50% or less.

Description

Technical Field

[0001] The present invention relates to a grease composition for a constant velocity universal joint and a constant velocity universal joint.

Background Art

[0002] A constant velocity universal joint attached to an automobile is required to transmit power in a state where a joint angle is applied and to transmit rotation at a constant speed, and to have durability corresponding to the life of the automobile. To satisfy these required functions, as shown in Patent Document 1 and Patent Document 2, a lubricant is enclosed inside the constant velocity universal joint to ensure lubricity.

[0003] As the grease for a constant velocity universal joint, as shown in Patent Document 1, a base grease composed of a base oil and a lithium soap or an urea-based thickener, to which an additive such as molybdenum disulfide is blended, is used. Also, by various combinations of various extreme pressure agents and the like, the abrasion resistance and the like can be improved, and an example thereof is shown in Patent Document 2. Patent Document 2 describes that a grease composition containing a diurea-based thickener, a base oil, zinc dialkyldithiophosphate, molybdenum dialkyldithiocarbamate, melamine cyanurate, calcium carbonate, zinc dialkyldithiocarbamate, and a sulfur-nitrogen-based extreme pressure additive is excellent in abrasion resistance under high surface pressure conditions.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent vehicles, miniaturization and increased efficiency of constant velocity universal joints are required for weight reduction and improved fuel efficiency. When higher torque is applied, conventional greases, such as those described in Patent Documents 1 and 2, may cause heat generation due to friction between internal components, as well as premature wear and peeling.

[0006] The present invention aims to provide a grease composition for constant velocity universal joints and a constant velocity universal joint that improves boundary lubrication performance, further enhances wear resistance and peel resistance, and achieves high durability. [Means for solving the problem]

[0007] The present invention relates to a grease composition for constant velocity universal joints, comprising a base oil, a thickener, an extreme pressure additive, a grease, and a traction oil, characterized in that the weight percentage of the traction oil is 1% or more and 50% or less.

[0008] In the grease composition for constant velocity universal joints of the present invention, a grease containing a base oil, a thickener, and an extreme pressure additive is mixed with 1% to 50% by weight of traction oil. As a result, in addition to the lubrication performance normally possessed by grease, an EHL film is formed between each component under high surface pressure conditions, for example, exceeding 1 GPa, during high torque loads in accelerating driving. This reduces metal-to-metal contact, improving boundary lubrication performance and exhibiting wear resistance and peel resistance. In other words, it is possible to combine the lubrication performance of grease with the EHL film formation function of traction oil under high surface pressure conditions, thereby achieving high durability.

[0009] If the traction oil content falls below 1% by weight, the traction oil's effectiveness is diminished. If it exceeds 50% by weight, the lubricating function of the grease is diminished, and the resulting system becomes costly and impractical. To effectively obtain the functions of both grease and traction oil, it is preferable to set the traction oil content in the range of 5% by weight to 20% by weight.

[0010] In the above configuration, it is preferable that the traction oil be a synthetic oil with a relatively large traction coefficient and that an EHL film is easily formed.

[0011] In the above configuration, the traction oil is more preferably one having multiple cyclohexyl groups. Having multiple cyclohexyl groups results in a higher traction coefficient, making it more effective.

[0012] The constant velocity universal joint of the present invention is one in which the constant velocity universal joint grease composition of the present invention is sealed. In this case, the constant velocity universal joint to be sealed may be a fixed constant velocity universal joint on the outboard side or a sliding constant velocity universal joint on the inboard side. As a result, the constant velocity universal joint of the present invention can have both the lubrication performance of grease and the EHL film formation function of traction oil under high surface pressure conditions, thereby achieving high durability. In particular, in the case of a constant velocity universal joint with rough surface roughness of each component, partial metal-to-metal contact occurs in the initial state, but as the initial settling progresses through the break-in period of the vehicle, the surface roughness of the constant velocity universal joint improves, and the EHL film is more easily formed due to the effect of the traction oil, resulting in high durability. [Effects of the Invention]

[0013] According to the grease composition for constant velocity universal joints and the constant velocity universal joint of the present invention, boundary lubrication performance is improved, and further wear resistance and peel resistance are improved, resulting in high durability. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view of a drive shaft equipped with a constant velocity universal joint containing the constant velocity universal joint grease composition of this embodiment. [Modes for carrying out the invention]

[0015] The grease composition for constant velocity universal joints of the present invention will be described in detail below. The grease composition of the present invention contains the following components (a), (b), (c), and (d). (a) Base oil (b) Thickener (c) Extreme pressure additives (d) Traction oil

[0016] Examples of the base oil for component (a) above include commonly used lubricating oils such as mineral oil, ester-based synthetic oil, ether-based synthetic oil, and hydrocarbon-based synthetic oil, or mixtures thereof. These may be used individually or as a mixture of two or more. Alternatively, a base oil consisting mainly of mineral oil mixed with synthetic oil may be used. Considering the cost and the impact on the boots required for constant velocity universal joints, it is also possible to use only mineral oil. The base oil content is, for example, 70 to 90% by mass or more of the total amount of the grease composition for constant velocity universal joints.

[0017] Examples of thickeners in (b) above include metallic soaps such as lithium soap, lithium complex soap, calcium soap, calcium complex soap, aluminum soap, and aluminum complex soap, as well as urea compounds such as diurea compounds and polyurea compounds. The thickener content is, for example, 5 to 20% by weight.

[0018] Unlike soap-based thickeners, urea-based thickeners do not contain metal components that promote oxidative degradation of the base oil, and therefore exhibit excellent high-temperature stability. While the thickener is not particularly limited, considering the durability of the constant velocity universal joint, a diurea compound represented by general formula (1) is preferred. A-NH-(C=O)-NH-R1-NH-(C=O)-NH-B (1) In general formula (1), R1 represents a divalent organic group, preferably a divalent hydrocarbon group. Specific examples of such divalent hydrocarbon groups include linear or branched alkylene groups, linear or branched alkenylene groups, cycloalkylene groups, arylene groups, alkylarylene groups, arylalkylene groups, and the like. Further, A and B represent monovalent organic groups, preferably monovalent hydrocarbon groups. Specific examples of such monovalent hydrocarbon groups include linear or branched alkyl groups, linear or branched alkenyl groups, cycloalkyl groups, aryl groups, alkylaryl groups, arylalkyl groups, and the like.

[0019] When the temperature rises due to frictional heat, the extreme pressure additive in (c) above easily reacts with the metal surface, forms a solid film, and has the effect of enhancing lubricity. A molybdenum-based extreme pressure additive or other extreme pressure additives, such as sulfur-based extreme pressure additives, chlorine-based extreme pressure additives, phosphorus-based extreme pressure additives, etc. can be used. These extreme pressure additives may be used alone or in combination of two or more. The content of the extreme pressure additive is, for example, 10% by weight or less based on the total amount of the grease composition for constant velocity joints.

[0020] The traction oil in (d) above is an oil for forming an oil film between two rolling elements in a traction drive device (a device that transmits power between two rolling elements pressed against each other through a lubricating oil film and rolling). It has a high traction coefficient μ and is distinguished from other lubricating oils. Here, the traction coefficient μ is expressed as Ft / Fn, where Fn is the pressing load (normal force) of the rolling element and Ft is the traction force (tangential force). Since a larger value of μ results in a larger traction force with the same normal force, the traction coefficient μ is an important value.

[0021] The traction oil to be used preferably has a traction coefficient within the range of 0.04 or more and 0.10 or less, more preferably within the range of 0.06 or more and 0.09 or less. Also, the kinematic viscosity at 40 °C is preferably within the range of, for example, 9.9 to 220 mm 2 / s.

[0022] Traction oils come in two types: mineral oil-based and synthetic oil-based. Mineral oils are refined by distilling crude oil and have the advantage of requiring less labor-intensive processing. Examples of mineral oils include paraffinic mineral oil and naphthenic mineral oil. On the other hand, synthetic oils are produced by chemically decomposing and synthesizing crude oil to adjust its molecular weight. They have advantages such as good cold-start performance, high heat resistance, strong resistance to oxidation, less degradation, and durability for long-term use.

[0023] Examples of synthetic oils include polyolefins (e.g., hydrogenated isobutylene oligomers, 2,4-dicyclohexyl-2-methylpentane, etc.), cycloalkanes (e.g., dicyclohexyl-cyclohexylmethane, etc.), hydrindanes (e.g., 1,1,3-trimethyl-3-cyclohexylhydrindanes, etc.), adamandanes (e.g., diadamantylalkanes, etc.), and ketals (e.g., tricyclic ketals, etc.). Since synthetic oils generally have higher traction coefficients than mineral oils, it is preferable to use synthetic oils in this embodiment.

[0024] Furthermore, compounds having multiple cyclohexyl groups in their molecules (among the above, 2,4-dicyclohexyl-2-methylpentane, dicyclohexyl-cyclohexylmethane, 1,1,3-trimethyl-3-cyclohexylhydrindan, and tricyclic ketal) are particularly preferred because they exhibit high traction coefficients. In addition, they have high viscosity under high pressure, and can be expected to extend the fatigue life of rolling elements.

[0025] The constant velocity universal joint grease composition of this embodiment is formed from a grease containing (a), (b), and (c), and a traction oil of (d). Any type of traction oil may be used, but among them, one of the above-mentioned configurations (synthetic oil, or one having multiple cyclohexyl groups) will have a particularly high traction coefficient.

[0026] The weight percentage of the traction oil is preferably 1% to 50% of the total amount of the grease composition for constant velocity universal joints. If the amount of traction oil is less than 1% of the weight, the effect of the traction oil will not be fully realized, and if it is more than 50% of the weight, the effect of the grease will not be fully realized, and it will be costly and difficult to put into practical use. To effectively obtain the functions of both grease and traction oil, it is more preferable to set the weight percentage of the traction oil in the range of 5% to 20% of the weight.

[0027] The constant velocity universal joint grease composition of this embodiment may further contain additives as needed, in addition to (a) to (d) above. Examples of such additives include detergents, dispersants, anti-wear agents, viscosity index improvers, antioxidants, rust inhibitors, and corrosion inhibitors.

[0028] As described above, the constant velocity universal joint grease composition of this embodiment is a grease containing a base oil, a thickener, and an extreme pressure additive, to which 1% to 50% by weight of traction oil is mixed. As a result, in addition to the lubrication performance normally possessed by grease, an EHL film is formed between each component under high surface pressure conditions, for example, exceeding 1 GPa, during high torque loads in accelerating driving, thereby reducing metal-to-metal contact and improving boundary lubrication performance, resulting in improved wear resistance and peel resistance. In other words, it is possible to combine the lubrication performance of grease with the EHL film formation function of traction oil under high surface pressure conditions, thereby obtaining high durability. Boundary lubrication refers to a lubrication state in which the oil film on the lubricated surface becomes thin (for example, less than the surface roughness), and localized metal-to-metal contact points occur through the oil film.

[0029] The grease composition according to this embodiment is used, for example, by sealing it in a constant velocity universal joint of an automobile drive shaft. The constant velocity universal joint may be a fixed constant velocity universal joint on the outboard side or a sliding constant velocity universal joint on the inboard side. When sealing it in a fixed constant velocity universal joint, a consistency of 0 to 2 is good, and a consistency of 1 is preferable, depending on the method of use.

[0030] Figure 1 shows a drive shaft 1 installed in an automobile. The drive shaft 1 comprises a fixed constant velocity universal joint 2 installed on the outboard side (outside in the vehicle width direction), a sliding constant velocity universal joint 3 installed on the inboard side (center side in the vehicle width direction), and an intermediate shaft 4 connecting both constant velocity universal joints 2 and 3.

[0031] The fixed constant velocity universal joint 2 shown in Figure 1 is a Zeppa type and comprises an outer joint member 21, an inner joint member 22, a plurality of balls 23 as torque transmission members, and a retainer 24. A plurality of ball tracks are formed by a plurality of track grooves 21a formed on the inner spherical surface of the outer joint member 21 and a plurality of track grooves 22a formed on the outer spherical surface of the inner joint member 22, with one ball 23 placed on each ball track. Torque is transmitted at a constant velocity between the outer joint member 21 and the inner joint member 22 via the balls 23 while allowing angular displacement. Note that the fixed constant velocity universal joint 2 is not limited to the above, and may also be an undercut-free type or a cross-groove type, for example.

[0032] The sliding constant velocity universal joint 3 is of the tripod type and comprises an outer joint member 31, an inner joint member (tripod member) 32, and a plurality of rollers 33 as torque transmission members. The rollers 33 are arranged on the outer circumference of three leg shafts 32a provided on the inner joint member 32 via needle rollers. The rollers 33 are arranged in a plurality of track grooves 31a formed on the inner circumferential surface of the outer joint member 31. Torque is transmitted at a constant velocity between the outer joint member 31 and the inner joint member 32 via the rollers 33, while allowing angular and axial displacements. The sliding constant velocity universal joint 3 is not limited to the above, and may also use balls as torque transmission members (e.g., double offset type or cross groove type).

[0033] The fixed constant velocity universal joint 2 is equipped with a boot 40 fitted between the outer joint member 21 and the shaft 4, and the sliding constant velocity universal joint 3 is equipped with a boot 50 fitted between the outer joint member 31 and the shaft 4. The boots 40 and 50 prevent the constant velocity universal joint grease composition of this embodiment, which is sealed inside, from leaking to the outside and prevent foreign matter from entering the inside.

[0034] A constant velocity universal joint containing the grease composition of this embodiment can combine the lubrication performance of grease with the EHL film formation function of traction oil under high surface pressure conditions, thereby achieving high durability. In particular, in the case of a constant velocity universal joint with rough surface roughness of each component, partial metal-to-metal contact occurs in the initial state, but as the initial break-in period of the vehicle progresses, the surface roughness of the constant velocity universal joint improves, and the EHL film is more easily formed due to the effect of the traction oil, resulting in high durability.

[0035] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its gist. The specific types and contents of the base oil, thickener, and extreme pressure additive are not particularly limited, and the types and contents can be appropriately selected considering the cost and the impact on the boots required for constant velocity universal joints. The types of traction oil described above are also examples and are not limiting. The traction oil content can be appropriately set within the range of 1% by weight or more and 50% by weight or less, taking into consideration various factors such as the type and contents of the base oil, thickener, and extreme pressure additive, the traction coefficient of the traction oil used, and cost. [Explanation of symbols]

[0036] 2. Fixed constant velocity universal joint 3. Sliding constant velocity universal joint

Claims

1. A grease containing a base oil, a thickener, and an extreme pressure additive, It has traction oil, A grease composition for constant velocity universal joints, characterized in that the weight percentage of the traction oil is 1% by weight or more and 50% by weight or less.

2. The grease composition for constant velocity universal joints according to claim 1, characterized in that the traction oil is a synthetic oil.

3. The grease composition for constant velocity universal joints according to claim 1, characterized in that the traction oil has a plurality of cyclohexyl groups.

4. A constant velocity universal joint characterized by containing the constant velocity universal joint grease described in any one of claims 1 to 3.

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