JP6703849B2 - Propeller shaft spline grease composition and propeller shaft spline - Google Patents

Description

The present invention relates to a grease composition used for lubricating a propeller shaft spline portion.

A power transmission unit and a steering mechanism unit of an automobile or the like usually have a telescopic shaft in order to absorb axial displacement. The telescopic shaft usually has a spline portion in which a male spline shaft and a female spline shaft are fitted together. The male spline shaft and the female spline shaft are produced by forming a spline groove by, for example, hobbing.
Grease is applied to the fitting portions of the male spline shaft and the female spline shaft in order to reduce the sliding resistance of the telescopic shaft in the axial direction. The grease used for a sliding member such as a spline portion usually contains a base oil and a thickener. Examples of the thickener contained in the grease include soap-based materials and non-soap-based materials. As the soap material, for example, lithium soap or the like is used. As the non-soap-based material, for example, in addition to an organic material such as a diurea compound, an inorganic material such as silica powder or carbon fiber is used.
For example, in Patent Document 1, a telescopic shaft for vehicle steering, which is incorporated in a steering shaft of a vehicle and has a male spline shaft and a female spline shaft fitted in a non-rotatable and slidable manner, wherein either the male spline shaft or the female spline shaft is included. A nylon resin film is formed on the surface of the spline fitting portion of one or both shafts, and grease containing at least a base oil and a thickener is interposed between the male spline shaft and the female spline shaft, and The oil contains at least one hydrocarbon oil selected from the group consisting of synthetic hydrocarbon oil and mineral oil, has a kinematic viscosity of 20 mm ² /s or more at 40° C., and the thickener is a metal soap or a metal composite. A telescopic shaft for vehicle steering, characterized in that it contains soap, is described. The document describes that a nylon resin film is formed on the surface of the fitting portion of the spline shaft, and that grease is applied to the sliding portion to reduce sliding resistance and improve wear resistance. ing.
The grease used for the sliding member may contain an additive such as an extreme pressure agent or an antiwear agent as a means for maintaining or improving the sliding characteristics in addition to the base oil and the thickener. Examples of the additive include an S-based additive, a P-based additive, and a Mo-based additive.
In Patent Document 2, in a grease composition containing a base oil, a thickener and an additive, the kinematic viscosity of the base oil at 40° C. is 50 to 200 mm ² /s, and the thickener has a general formula (I). R1-NHCONH-R2-NHCONH-R3 [wherein, R2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R1 and R3 are the same or different groups, cyclohexyl group, and 8 to 22 carbon atoms] Of a linear or branched alkyl group of], the additive is a naphthenic acid metal salt, a salt of a fatty acid having 6 to 10 carbon atoms and an aliphatic amine having 6 to 10 carbon atoms, and A grease composition is described, which is at least one selected from the group consisting of organic sulfonic acid metal salts. The document describes that the grease composition is used for bearings of machine parts such as rolling bearings.

Japanese Patent Laid-Open No. 2006-123820 JP 2011-37975 JP

In the expandable shaft described in Patent Document 1, it is necessary to form a film on the surface of the fitting portion of the spline shaft. For this reason, the manufacturing process of the telescopic shaft becomes complicated, and as a result, the cost of manufacturing the telescopic shaft may increase. Further, when the expandable shaft is used for a long period of time, the coating on the surface of the fitting portion may be worn. When the coating wears, the spline shaft cannot slide smoothly due to the variation of the friction coefficient due to the wear, and a hooking phenomenon occurs especially during the contraction, and when the hooking is released, the occupant receives the impact. There is a possibility that a so-called crank shock phenomenon will occur, which will cause performance deterioration.
Therefore, an object of the present invention is to provide a grease composition capable of maintaining a friction coefficient in a low range in a fitting portion of a propeller shaft spline portion.
Another object of the present invention is to provide a propeller shaft spline encapsulating the grease composition of the present invention.

As a result of various studies on means for solving the above problems, the present inventors have improved friction characteristics of the grease by optimizing the materials of the base oil, the thickener and the additive contained in the grease. The inventors have found what can be done and have completed the present invention. That is, according to the present invention, the following grease composition and a propeller shaft spline encapsulating the grease composition are provided:
1. A grease composition for use in a fitting portion of a propeller shaft spline portion, comprising a base oil, a thickener and an additive, comprising polybutene as the base oil, wax as the additive, and A grease composition in which the kinematic viscosity of the oil at 40° C. is in the range of 5,000 to 40,000 mm ² /s.
2. The grease composition according to Item 1, wherein the polybutene is contained in a range of 40 to 70 mass% with respect to the total mass of the grease composition.
3. 3. The grease composition according to 1 or 2 above, wherein the polybutene has a kinematic viscosity at 40° C. of 140,000 to 180,000 mm ² /s.
4. 4. The grease composition according to any one of 1 to 3 above, wherein the wax is at least one selected from the group consisting of montan wax, polyethylene wax, polypropylene wax, and amide wax.
5. 5. The grease composition according to any one of 1 to 4 above, wherein the wax is contained in the range of 1 to 15 mass% with respect to the total mass of the grease composition.
6. The grease composition according to any one of 1 to 5 above, wherein the thickener is Li soap or a urea thickener.
7. A propeller shaft spline enclosing the grease composition according to any one of 1 to 6 above.

According to the present invention, in the lubrication of the fitting portion of the propeller shaft spline portion, polybutene having a large kinematic viscosity at 40° C. is used to increase the kinematic viscosity of the base oil, and wax is used to form the sliding portion and the stationary portion in the lubricated portion. By maintaining a thick oil film and suppressing direct contact between metal members, it is possible to provide a grease composition in which fluctuations in the friction coefficient are suppressed.
By applying the grease composition of the present invention to the propeller shaft spline portion, it is possible to substantially prevent or reduce the fluctuation of the friction coefficient even during long-term use.

Optical interferometry ultra thin film measuring device SRV test schematic

<Definition>
As used herein, the "propeller shaft spline portion" usually means a spline portion having a groove depth of 2 to 10 µm and a width of 0.5 to 5 mm. The groove can be formed by a conventional means such as hobbing.
As used herein, “polybutene” means poly(n-butene) and poly(isobutene), but unless otherwise specified, it refers to poly(isobutene).

<About base oil>
The base oil used in the grease composition of the present invention contains polybutene.
The kinematic viscosity of 40 ° C. polybutene is not particularly limited, for example, be selected from the range of 140,000~180,000mm ² / s, preferably ^{150,000~170,000mm 2 / s, 155,000~165,000mm 2 /} s is more preferable. When the kinematic viscosity of polybutene at 40° C. is within the above range, it is possible to suppress the fluctuation of the friction coefficient. In this specification, the kinematic viscosity at 40° C. is measured by a method according to JIS K 2283.
The content of polybutene with respect to the total amount of the grease composition is not particularly limited, but is preferably 40% by mass or more (for example, 40 to 70% by mass), and more preferably 45% by mass or more (for example, 45 to 70% by mass).

The base oil may include polymers other than polybutene. The polymer other than polybutene is not particularly limited, ethylene-α-olefin copolymers and ethylene-propylene copolymers, olefin copolymers represented by polymethacrylate, styrene-based polymers represented by styrene-isoprene copolymer, polyisobutylene, poly Examples include isoprene.
The kinematic viscosity of a polymer other than polybutene at 40° C. is, for example, 10,000 to 40,000 mm ² /s.
When a polymer other than polybutene is combined with polybutene, the polymer other than polybutene is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, and 0 parts by mass, with polybutene as 100 parts by mass. Is most preferred.

The base oil other than the polymer is preferably selected from the group consisting of mineral oil and synthetic hydrocarbon oil. The base oil other than the polymer may be composed of either mineral oil or synthetic hydrocarbon oil, or may be composed of a mixture of both materials. When the base oil other than the polymer is constituted as a mixture of mineral oil and synthetic hydrocarbon oil, it is preferable that the mineral oil is 50 parts by mass or more in the mixture of mineral oil and synthetic hydrocarbon oil. It is particularly preferred that the base oil other than the polymer consists only of mineral oil. If the base oil other than the polymer consists only of mineral oil, the cost can be reduced.
The kinematic viscosity of 40 ° C. of the base oil other than the polymer is not particularly limited, for example, it is selected from the range of 10 to 500 mm ² / s, preferably from 50 to 400 mm ² / s, more preferably 80~300mm ² / s ..
When the base oil other than the polymer is combined with polybutene, the base oil other than the polymer is preferably 20 parts by mass to 200 parts by mass, more preferably 25 parts by mass to 150 parts by mass, with polybutene as 100 parts by mass. It is most preferably 25 parts by mass to 100 parts by mass.

As the base oil of the present invention, a mixture of polybutene and mineral oil is particularly preferable. It is especially preferred that the polybutene and mineral oil are mixed oils in the above proportions.
From the viewpoint of keeping the friction coefficient low, it is necessary to secure an oil film thickness, and it is desirable that the kinematic viscosity of the entire base oil is high. The kinematic viscosity of 40 ° C. of the base oil, it is necessary to 5,000~40,000mm ² / s, preferably 7,000~40,000mm ² / s, more preferably 10,000~40,000mm ² / s, 20,000~36,000mm ² / s is particularly preferred. If the kinematic viscosity is lower than the specified range, the oil film thickness is not sufficient and the friction coefficient is high, and if the kinematic viscosity is higher than the specified range, the oil film thickness is thicker, but the sliding lubricates the grease. Since it is removed from the part, the friction coefficient becomes high, which is not preferable.
The content of the base oil with respect to the total amount of the grease composition is not particularly limited, but is preferably 50 to 98% by mass, more preferably 60 to 98% by mass, and further preferably 70 to 98% by mass.

<About thickener>
The thickener used in the grease composition of the present invention is not particularly limited. Preferred examples are soap thickeners represented by Li soap and complex Li soap, urea thickeners represented by diurea, inorganic thickeners represented by organic clay and silica, and PTFE. Examples of the organic thickeners include More preferred are Li soap-based thickeners and urea-based thickeners. Among the Li soap-based thickeners, Li stearate and Li 12 hydroxystearate are preferred. It is particularly preferable to use these in combination. Among the urea thickeners, diurea compounds represented by the following formula (1) are preferable.
R1-NHCONH-R2-NHCONH-R3 (1)
(In the formula, R2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R1 and R3 may be the same or different from each other, and may be an alkyl group having 6 to 30 carbon atoms, 6 carbon atoms or 7 is an aryl group or a cyclohexyl group.)
More preferably R2 is tolylene diisocyanate or diphenylmethane diisocyanate, most preferably R2 is diphenylmethane diisocyanate.
More preferably, R1 and R3, which may be the same or different from each other, are linear alkyl groups having 6 to 30 carbon atoms, particularly linear alkyl groups having 6 to 18 carbon atoms, and particularly those having 8 carbon atoms. It is a straight-chain alkyl group.
Most preferably, the urea thickener is a compound of the formula (1) in which R2 is diphenylmethane diisocyanate and R1 and R3 are linear alkyl groups having 8 carbon atoms.
The content of the thickener in the grease composition of the present invention varies depending on the type of the thickener. The grease composition of the present invention preferably has a workability of 200 to 440, and the content of the thickener is the amount necessary to obtain this workability. The content of the thickener in the grease composition of the present invention is usually 2 to 30% by mass, preferably 3 to 25% by mass.

<About additives>
The grease composition of the present invention contains wax as an additive. The wax is preferably at least one selected from the group consisting of montan wax, polyethylene wax, polypropylene wax and amide wax.
As the montan wax, an acid wax having an acid value of 110 to 160 mgKOH/g, an ester wax having both a non-polar part and a polar part, a partially saponified ester which is a mixture of an esterified product of montanic acid and a saponified product of calcium hydroxide. Examples thereof include waxes, saponified waxes of sodium and calcium salts of montanic acid, and montan waxes to which ethylene oxide is added. The acid value is measured according to JIS K 2501.3.
Polypropylene wax and polyethylene wax include those having a weight average molecular weight of 4,000 to 20,000 and having no branch, and those having a branch, and examples thereof include a high density type and a high molecular weight high density type.
The content of the wax in the grease composition is preferably 1 to 15% by mass, more preferably 2 to 10% by mass.
These waxes are preferably dissolved in the grease base oil, cooled, and then added to the base grease to be contained in the grease composition.

Further, the grease composition of the present invention may contain any additive other than wax, if necessary. Examples include amine-based, phenol-based antioxidants, inorganic passivating agents such as sodium nitrite, sulfonate-based, succinic acid-based, amine-based, rust-preventive agents represented by carboxylates, and benzotriazole. Representative metal corrosion inhibitors, oiliness agents such as fatty acids, fatty acid esters, and phosphoric acid esters, antiwear agents and extreme pressure agents such as phosphorus-based, sulfur-based, and organometallic agents, metal oxide salts and disulfides Solid lubricants typified by molybdenum are included. The amount of these components used is usually about 0.1 to 20% by mass, preferably 0.5 to 20% by mass.
Basically, an oil film is not formed at rest, but since the grease composition of the present invention uses polybutene, which is a polymer having a high base oil kinematic viscosity and preferably a high pressure viscosity coefficient (preferably 28- 40, more preferably 30 to 40), and an oil film is formed in the center of the contact portion at rest. In addition, by including the predetermined wax, it is possible to prevent the oil film formed especially at rest from being thinned over time, and the oil film is easily maintained. As a result, direct contact between the metal members can be suppressed as much as possible, and fluctuations in the friction coefficient can be suppressed.

<Mixed penetration>
The penetration of the grease composition of the present invention is adjusted according to the purpose of use, but is preferably 200 to 440. From the viewpoint of fluidity to the lubrication part, it is particularly preferably 250 to 440. The blending consistency in this specification is JIS K 2220 7. The 60-minute work penetration measured by.

<Preparation of test grease>
Grease compositions of Examples and Comparative Examples were prepared using the thickeners, base oils and additives shown in Tables 1 and 2. Specifically, in the case of Li soap grease, a base oil, lithium stearate and lithium 12-hydroxystearate were mixed in a container and heated and cooled with stirring to obtain a lithium base grease. To the obtained lithium-based grease, wax dissolved in base oil and cooled was added to obtain a predetermined thickening agent amount. The obtained mixture was kneaded with a three-roll mill to prepare a mixture having a predetermined workability (test method JIS K2220 7.). In the case of urea grease, diphenylmethane diisocyanate was reacted with a predetermined amine in base oil, and the temperature was raised and cooled to obtain a urea base grease. To the obtained urea base grease, a wax dissolved in a base oil and cooled was added to obtain a predetermined thickening agent amount. The obtained mixture was kneaded with a three-roll mill to prepare a mixture having a predetermined workability.
The grease composition prepared above was evaluated by the following test methods. The results are shown in the table.

<Test method>
〇EHL film thickness measurement The film thickness of the grease formed on the sliding contact portion was measured using the optical interferometry ultra thin film measuring device shown in FIG. In the measurement, a steel ball having a diameter of 19.05 mm was brought into contact with a glass disk under a load of 20 N and 25° C., the steel ball was fixed, and the glass disk was rotated to make a pure sliding condition. Was measured. Details of the measurement conditions are shown below.
<Measurement conditions>
Load: 20N
Maximum surface pressure: 0.5 GPa
Speed: Gradually reduce the speed from 1 m/s to 0.002 m/s and stop the rotation.
Measures the maximum oil film thickness immediately after rest and 10 minutes after rest.
Temperature: 25°C
Steel ball: Diameter 19.05 mm, material SUJ2
Glass disc: Silica+Chromium coated
Pass/Fail Judgment Maximum oil film thickness at rest 200 nm or more: ○ (Pass)
Less than 200 nm: × (fail)

-Friction coefficient measurement The static friction coefficient was measured using the SRV tester shown in FIG. Details of the measurement conditions are shown below.
<Measurement conditions>
Upper test piece: S35C, 12 mm diameter cylinder, Rz=3.5 μm
Lower test piece: SUJ2, 24 mm diameter plate, Rz=0.5 μm
Upper test piece speed: 0.2 mm/s
Test temperature: 25°C
Surface pressure: 3 MPa
Stroke: 1 mm
Test time: 300 seconds Measurement item: Static friction coefficient of the last stroke for 300 seconds
Pass/fail judgment static friction coefficient less than 0.10: ○ (pass)
0.10 or more: × (fail)
Comprehensive judgment Passes both maximum oil film thickness at rest and coefficient of static friction: ○ (Pass)
Fail any one: × (fail)
Results The grease compositions of Examples 1 to 9 both passed the maximum value of the oil film thickness at rest and the friction coefficient, and their effects were confirmed as compared with Comparative Examples 1 to 5.

*1 Aliphatic diurea: Reaction product of 2 mol of octylamine and 1 mol of diphenylmethane diisocyanate *2 Mineral oil: Mineral oil with a kinematic viscosity of 180 mm ² /s at 40°C Polybutene A: 160000 mm ² of kinematic viscosity at 40°C /s polybutene (pressure viscosity coefficient 33)
Polybutene B: Polybutene having a kinematic viscosity of 9500 mm ² /s at 40°C (pressure viscosity coefficient 37)
Ethylene-α-olefin copolymer: kinematic viscosity at 40°C is 37500 mm ² /s About ethylene-α-olefin copolymer *3 Montan wax: Licowax OP Flakes manufactured by Clariant Japan Co., Ltd. (acid value 11 mgKOH/g)
Polyethylene wax: Licowax PE190 manufactured by Clariant Japan Co., Ltd.
Polypropylene wax: Licocene PP7502 manufactured by Clariant Japan KK
Amide wax: Armoslip HT powder manufactured by Lion Corporation

Claims (5)

A grease composition containing a base oil, a thickening agent and an additive, which is used for a fitting portion of a propeller shaft spline portion, and which contains polybutene as the base oil, wherein the polybutene is the total mass of the grease composition. In the range of 40 to 70% by mass, the polybutene has a kinematic viscosity at 40° C. of 140,000 to 180,000 mm ² /s, a wax as the additive, and 40° C. of the base oil. A grease composition having a kinematic viscosity in the range of 5,000 to 40,000 mm ² /s. The grease composition according to claim 1, wherein the wax is at least one selected from the group consisting of montan wax, polyethylene wax, polypropylene wax, and amide wax. The grease composition according to claim 1 or 2 , wherein the wax is contained in the range of 1 to 15% by mass based on the total mass of the grease composition. Thickener is Li soap or urea thickener, any one grease composition according to claim 1-3. The any one grease composition according to claim 1-4 and sealed, the propeller shaft splines.