Grease composition, machine component, and starter overrunning clutch

Abstract

A silicone grease composition is disclosed. The grease composition contains a silicone oil and zinc dialkyldithiocarbamate as an extreme-pressure additive. The grease composition contains substantially no zinc dialkyldithiophosphate. The grease composition achieves high friction characteristics and wear characteristics. A method for transmitting torque of a clutch or a torque limiter mechanism is also disclosed. Moreover, a method for producing a clutch or a torque limiter mechanism is disclosed. The methods utilize the aforementioned grease composition.

Claims

1. A method for transmitting torque of a clutch or a torque limiter mechanism, the method comprising: enclosing a grease composition in a lubricating part of the clutch or the torque limiter mechanism; wherein the enclosed grease composition consists of: (A) a silicone oil having the general formula (I): R.sup.1.sub.aSiO.sub.(4-a)/2 in which each R.sup.1 is independently selected from the group consisting of monovalent hydrocarbon groups, and a is from 1.8 to 2.2; (B) zinc dialkyldithiocarbamate having the general formula (II): [R.sup.5.sub.2N—C(═S)—S].sub.2—Zn in which each R.sup.5 is a methyl group; and (C) an organic thickener selected from the group consisting of lithium soap and lithium complex soap; wherein a content of the silicone oil (A) is from 60 mass % to 90 mass %, a content of the zinc dialkyldithiocarbamate (B) is from 7.5 mass % to 20 mass %, and a content of the organic thickener (C) is from 2.5 mass % to 20 mass %, each relative to the total amount of the enclosed grease composition, provided the total of components (A), (B), and (C) is 100 mass % of the enclosed grease composition.

2. The method according to claim 1, wherein the silicone oil (A) has an aromatic hydrocarbon group per molecule.

3. The method according to claim 1, wherein the clutch is an overrunning clutch and wherein the enclosed grease composition is enclosed in a clutch cam chamber formed by an outer clutch and an inner clutch.

4. The method according to claim 1, wherein the organic thickener (C) is lithium stearate.

5. The method according to claim 4, wherein the silicone oil (A) is of the general formula
Me.sub.3SiO(Me.sub.2SiO).sub.I(R.sup.2R.sup.3SiO).sub.mSiMe.sub.3 where Me is a methyl group, R.sup.2 is a methyl group or a phenyl group, R.sup.3 is a phenyl group, I is 0 or a positive integer, and m is a positive integer.

6. The method according to claim 1, wherein the silicone oil (A) is of the general formula
Me.sub.3SiO(Me.sub.2SiO).sub.I(R.sup.2R.sup.3SiO).sub.mSiMe.sub.3 where Me is a methyl group, R.sup.2 is a methyl group or a phenyl group, R.sup.3 is a phenyl group, I is 0 or a positive integer, and m is a positive integer.

7. The method according to claim 1, wherein the organic thickener (C) is a lithium soap.

8. The method according to claim 1, wherein: (i) the content of the silicone oil (A) is from 73.74 mass % to 77.14 mass %; (ii) the content of the zinc dialkyldithiocarbamate (B) is from 9.25 mass % to 13.25 mass %; (iii) the content of the organic thickener (C) is from 13.01 mass % to 13.61 mass %; or (iv) each one of (i) to (iii); and wherein each mass % is relative to 100 mass % of the enclosed grease composition.

9. The method according to claim 1, further comprising: providing the grease composition prior to the enclosing step, wherein the grease composition consists of components (A), (B), and (C).

10. The method according to claim 1, further comprising: providing an automobile starter, the automobile starter having the clutch or torque limiter mechanism.

11. The method according to claim 10, wherein the clutch is an overrunning clutch and wherein the enclosed grease composition is enclosed in a clutch cam chamber formed by an outer clutch and an inner clutch.

12. The method according to claim 10, further comprising: powering the automobile starter, thereby transmitting torque of the clutch or torque limiter mechanism via the enclosed grease composition.

13. A method for transmitting torque of a clutch or a torque limiter mechanism, the method comprising: providing an automobile starter, the automobile starter having the clutch or torque limiter mechanism; providing a grease composition; enclosing the grease composition in a lubricating part of the clutch or the torque limiter mechanism of the automobile starter; and powering the automobile starter, thereby transmitting torque of the clutch or torque limiter mechanism via the enclosed grease composition; wherein the enclosed grease composition consists of: (A) a silicone oil having the general formula (I): R.sup.1.sub.aSiO.sub.(4-a)/2 in which each R.sup.1 is independently selected from the group consisting of monovalent hydrocarbon groups, and a is from 1.8 to 2.2; (B) zinc dialkyldithiocarbamate having the general formula (II): [R.sup.5.sub.2N—C(═S)—S].sub.2—Zn in which each R.sup.5 is a methyl group; and (C) an organic thickener selected from the group consisting of lithium soap and lithium complex soap; wherein a content of the silicone oil (A) is from 60 mass % to 90 mass %, a content of the zinc dialkyldithiocarbamate (B) is from 7.5 mass % to 20 mass %, and a content of the organic thickener (C) is from 2.5 mass % to 20 mass %, each relative to the total amount of the enclosed grease composition, provided the total of components (A), (B), and (C) is 100 mass % of the enclosed grease composition.

14. The method according to claim 13, wherein the clutch is an overrunning clutch and wherein the enclosed grease composition is enclosed in a clutch cam chamber formed by an outer clutch and an inner clutch.

15. The method according to claim 13, wherein the organic thickener (C) is lithium stearate.

16. The method according to claim 15, wherein the silicone oil (A) is of the general formula
Me.sub.3SiO(Me.sub.2SiO).sub.I(R.sup.2R.sup.3SiO).sub.mSiMe.sub.3 where Me is a methyl group, R.sup.2 is a methyl group or a phenyl group, R.sup.3 is a phenyl group, I is 0 or a positive integer, and m is a positive integer.

17. The method according to claim 13, wherein: (i) the content of the silicone oil (A) is from 73.74 mass % to 77.14 mass %; (ii) the content of the zinc dialkyldithiocarbamate (B) is from 9.25 mass % to 13.25 mass %; and (iii) the content of the organic thickener (C) is from 13.01 mass % to 13.61 mass %; wherein each mass % is relative to 100 mass % of the enclosed grease composition.

18. The method according to claim 13, consisting of the providing, enclosing, and powering steps.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) A first aspect of the present invention is a grease composition containing a silicone oil (A) and zinc dialkyldithiocarbamate (B) but containing substantially no zinc dialkyldithiophosphate (BX).

(2) The silicone oil which is the component (A) of an embodiment of the present invention needs to be liquid at room temperature (25° C.) and may have a straight-chain or branched structure. The chemical structure thereof is not particularly limited, and examples thereof include a polyorganosiloxane (silicone oil) represented by the general formula (I) below and that is liquid at room temperature.
R.sup.1.sub.aSiO.sub.(4-a)/2  (I)

(3) In the formula, R.sup.1 represents a group selected from the group consisting of monovalent hydrocarbon groups, and the R.sup.1 moieties may be the same or different. a is preferably from 1.8 to 2.2, and more preferably from 1.9 to 2.1, from the perspective of ease in synthesizing a liquid silicone.

(4) The R.sup.1 moieties in Formula (1) above may be each independently an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Preferably, the silicone oil used in the grease composition of an embodiment of the present invention has an aromatic hydrocarbon group as a part of the R.sup.1 moieties.

(5) The number of carbons of the hydrocarbon group of R.sup.1 may be from 1 to 8. Examples of R.sup.1 include alkyl groups, such as a methyl group, an ethyl group, a propyl group, and a hexyl group; cyclohexyl groups, such as a cyclopentyl group and a cyclohexyl group; alkenyl groups, such as a vinyl group and an allyl group; aryl groups, such as a phenyl group and a tolyl group; aralkyl groups, such as a 2-phenylethyl group and a 2-methyl-2-phenylethyl group; and halogenated hydrocarbon groups, such as a 3,3,3-trifluoropropyl group, a 2-(perfluorobutyl)ethyl group, a 2-(perfluorooctyl)ethyl group, and a p-chlorophenyl group. A methyl group, a vinyl group, and a phenyl group are preferable. Particularly preferably, the silicone oil contains a methyl group and a phenyl group.

(6) Specific examples of the silicone oil include the silicones (1) to (3) described below from the perspective of general-purpose properties as a grease. In particular, (1) methyl phenyl silicone and (2) dimethyl silicone, which have high coefficients of friction, are preferably used.

(7) (1) Methyl phenyl silicone:
Me.sub.3SiO(Me.sub.2SiO).sub.1(R.sup.2R.sup.3SiO).sub.mSiMe.sub.3

(8) In the formula, Me is a methyl group, R.sup.2 is a methyl group or a phenyl group, R.sup.3 is a phenyl group, 1 is 0 or a positive integer, and m is a positive integer.

(9) Specific examples thereof include:
Me.sub.3SiO(Me.sub.2SiO).sub.1(MePhSiO).sub.mSiMe.sub.3
and
Me.sub.3SiO(Me.sub.2SiO).sub.1(Ph.sub.2SiO).sub.nSiMe.sub.3

(10) (2) Dimethyl silicone:
Me.sub.3SiO(Me.sub.2SiO).sub.nSiMe.sub.3

(11) In the formula, Me is a methyl group, and n is a positive integer.

(12) (3) Alkyl fluoride-modified silicone:
Me.sub.3SiO(Me.sub.2SiO).sub.r(MeR.sup.4SiO).sub.sSiMe.sub.3

(13) In the formula, Me is a methyl group, R.sup.4 is an alkyl fluoride group, r is 0 or a positive integer, and s is a positive integer.

(14) Specifically,
Me.sub.3SiO(Me(CF.sub.3CH.sub.2CH.sub.2)SiO).sub.sSiMe.sub.3

(15) Note that, in the silicones (1) to (3), the methyl group in the side chain may be a branched methyl group substituted with another siloxane group, and the terminal group may be substituted with a hydroxy group, a vinyl group, or the like.

(16) Particularly preferable silicone oil is a methyl phenyl silicone represented by (1) above. In the methyl phenyl silicone, the content of the phenyl group is preferably in a range of 1 to 50 mol %, more preferably 3 to 25 mol %, and particularly preferably 3 to 10 mol %. This is because, when the content is less than 1 mol % relative to the total amount of the organic groups, heat resistance becomes lower and, when the content is greater than 50 mol %, the viscosity change due to temperature becomes larger, pour point becomes higher, and torque at low temperatures becomes larger.

(17) The kinematic viscosity of the silicone oil used in an embodiment of the present invention is preferably from 20 to 1000 cSt, and more preferably from 50 to 500 cSt, at 25° C. This is because, when the kinematic viscosity is less than 20 cSt, the silicone oil is easily separated from the grease and, when the kinematic viscosity is greater than 10000 cSt, torque at low temperatures becomes larger due to viscous drag, and the grease is deteriorated due to heat build-up during high-speed rotation. The kinematic viscosity is a value measured in accordance with JIS Z 8803.

(18) In the grease composition of an embodiment of the present invention, the content of the silicone oil may be from 10 wt. % to 99 wt. %, preferably from 30 wt. % to 97 wt. %, and more preferably from 50 wt. % to 95 wt. %, relative to the total amount of the composition.

(19) By use of the silicone oil as described above as the base oil, it is possible to realize the grease with high friction that is required for overrunning clutches because the oil agent has a high coefficient of friction, excellent heat resistance properties, and small temperature dependence of viscosity change.

(20) The grease composition of an embodiment of the present invention contains zinc dialkyldithiocarbamate (B) as the extreme-pressure additive. The grease composition of an embodiment of the present invention preferably, contains from 5 mass % to 30 mass % of the zinc dialkyldithiocarbamate (B). Because of the component (B), higher friction characteristics and wear characteristics of the silicone grease composition can be achieved. Only the case where the component (B) is used alone achieves such high friction characteristics and wear characteristics and effective transmission of torque while slipping of a clutch is suppressed. Furthermore, when another typical sulfur-based additive is used, such effects cannot be achieved.

(21) The zinc dialkyldithiocarbamate of the component (B) used in an embodiment of the present invention is preferably zinc dialkyldithiocarbamate represented by the general formula (II) below.
[R.sup.5.sub.2N—C(═S)—S].sub.2—Zn  (II)

(22) In the formula, R.sup.5 is a primary or secondary alkyl group having from 1 to 24 carbons. A primary or secondary alkyl group having from 1 to 8 carbons is particularly preferable. In particular, a methyl group, an ethyl group, and a propyl group are preferable.

(23) In the grease composition of an embodiment of the present invention, the content of the zinc dialkyldithiocarbamate (B) may be from 1 mass % to 50 mass %, preferably from 5 mass % to 40 mass %, more preferably from 5 mass % to 30 mass %, and most preferably from 7.5 mass % to 20 mass %, relative to the total amount of the composition.

(24) Furthermore, the second characteristic of the grease composition of an embodiment of the present invention is that the grease composition contains substantially no zinc dialkyldithiophosphate (BX). The case where the zinc dialkyldithiophosphate is not substantially contained can enhance friction characteristics and wear characteristics and can achieve a high torque transmission efficiency because slipping can be reduced, compared to the case where zinc dialkyldithiophosphate is contained.

(25) Note that “containing substantially no” means no target compound exists at all or almost no target compound exists. That is, it means that the target compound is not intended to be contained. Therefore, it does not exclude aspects where the target compound is contained as an impurity. Specifically, in the composition of an embodiment of the present invention, the content of the zinc dialkyldithiophosphate (BX) needs to be 0.10 mass % or less, preferably 0.05 mass %, and more preferably 0.01 mass % or less, and particularly preferably, the zinc dialkyldithiophosphate (BX) is not contained to two significant figures after the decimal point (0.00 mass %), relative to the total amount of the composition from the perspective of technical effect of the present invention.

(26) Note that, even when a trace amount of zinc dialkyldithiophosphate (BX) is contained, it is conceived that a lubricating film is formed in response to pressure and, in particular, slipping of an overrunning clutch increases and torque cannot be transmitted efficiently.

(27) The grease composition of an embodiment of the present invention may further contain an organic or inorganic thickener. The grease composition of an embodiment of the present invention preferably contains as the component (C), a lithium soap and/or a lithium complex soap, which are organic thickeners. By allowing the lithium soap to be contained, it is possible to impart heat resistance, shear stability, and water resistance to the grease composition. Furthermore, by allowing the lithium complex soap to be contained, it is possible to impart even better shear stability and heat resistance than those imparted by the lithium soap.

(28) The grease composition of an embodiment of the present invention may further contain an organic thickener of a urea compound or the like or an inorganic thickener of silica and bentonite or the like.

(29) In the grease composition of an embodiment of the present invention, the content of the thickener may be from 1 mass % to 30 mass %, preferably from 2 mass % to 25 mass %, and more preferably from 2.5 mass % to 20 mass %, relative to the total amount of the composition.

(30) The grease composition of an embodiment of the present invention preferably contains substantially no partial esters of polyhydric alcohols. The ester is used as an oil agent and is a component that adsorbs a metal at the hydroxy group moiety and prevents contact of another metal by a hydrocarbon group extended from the ester bond. However, in the present invention, slippage may be reduced at low temperatures, which is not preferable.

(31) The grease composition of an embodiment of the present invention may further contain additives that are typically used in a grease composition. Examples of the additives include antioxidants, corrosion inhibitors, metal deactivators, detergent dispersants, extreme-pressure additives except those described above, anti-foaming agents, and demulsifiers, oiliness improvers. One type of these may be used alone, or a combination of two or more types of these may be used. The content thereof may be from 0 wt. % to 5 wt. % relative to the total amount of the composition as long as the effect of the present invention is not impaired.

(32) The grease composition of an embodiment of the present invention is used in a lubricated part of a power transmission device. The power transmission device is a series of mechanism to transmit the output from an engine to a wheel. The power transmission device includes a clutch, a change gear, a propeller shaft, a joint, a final reduction drive, a drive wheel axle, and the like. The grease composition of an embodiment of the present invention is preferably used for a lubricated part of a clutch, and more preferably used for a lubricated part of a starter overrunning clutch.

(33) The second aspect of the present invention is a machine component in which the grease composition of an embodiment of the present invention is enclosed, and preferably a clutch or a torque limiter mechanism. Particularly preferably, the second aspect is a starter overrunning clutch in which the grease composition of an embodiment of the present invention is enclosed. The starter overrunning clutch includes a cylindrical clutch outer and a cylindrical clutch inner arranged concentrically in the inner circumferential side of the clutch outer. A clutch roller is displaced in a circumferential direction in a clutch cam chamber formed by the clutch outer and the clutch inner. The grease composition of an embodiment of the present invention can be enclosed in the clutch cam chamber.

(34) Another aspect of the present invention is a method of increasing the friction of a lubricated part of a power transmission device and/or reducing the wear of the lubricated part wherein the grease composition of an embodiment of the present invention is enclosed in the power transmission device. In addition, there is also a method of increasing the friction of a lubricated part of an overrunning clutch and/or reducing the wear of the lubricated part wherein the grease composition of an embodiment of the present invention is enclosed in a clutch cam chamber formed from an outer clutch and an inner clutch of the overrunning clutch.

(35) Furthermore, another aspect of the present invention is use of the grease composition of an embodiment of the present invention to increase the friction of a lubricated part of a power transmission device and/or to reduce the wear of the lubricated part. In addition, there is also use of the grease composition of an embodiment of the present invention to increase the friction of a lubricated part of an overrunning clutch and/or to reduce the wear of the lubricated part.

INDUSTRIAL APPLICABILITY

(36) Because the grease composition of an embodiment of the present invention has a high coefficient of friction and thus exhibits high torque transmission, and also has high wear resistance, the grease composition is suitable for use in a clutch and/or a torque limiter mechanism that are frequently used, a unidirectional clutch mechanism in which idling at high rotation is performed, and, especially, a lubricated part of a unidirectional overrunning clutch for a starter by which driving torque is transmitted to the engine and which idles so that the rotation of the engine is not transmitted to the starter motor after ignition of the engine and racing of the engine.

EXAMPLES

(37) The present invention is specifically described below by using examples and comparative examples; however, the present invention is not limited to the examples described below.

(38) Preparation of Grease Composition

(39) According to the composition shown in Table 1, methyl phenyl silicone (A), either one of zinc dialkyldithiocarbamate (B) or a combination of zinc dialkyldithiocarbamate (B) and zinc dialkyldithiophosphate (BX), and a thickener (C) (Li soap) (added to adjust the consistency to approximately 300) were mixed and agitated as a whole. Thereafter, the mixture was adjusted to Grade No. 1 to Grade No. 2 consistency using three roll mills, and thus a grease composition of each of the Examples 1 to 4 and Comparative Examples 1 and 2 was prepared. Note that the details of each component are as follows.

(40) Methyl phenyl silicone (A): available from Dow Corning Corporation, DC510-100 mm.sup.2/s (25° C.)

(41) Zinc dialkyldithiocarbamate (B): zinc dimethyldithiocarbamate

(42) Zinc dialkyldithiophosphate (BX): zinc bis(2-ethylhexyl)dithiophosphate

(43) Thickener (C):

(44) Li soap: lithium stearate

(45) Overrunning Clutch Torque Transmission Test

(46) A stipulated amount of the grease composition was enclosed in an overrunning clutch member of an automobile starter, and then a ring gear to which the starter motor was fixed was engaged under a stipulated condition (−30° C.). It was determined whether the clutch could transmit the torque generated by the motor of the starter without slipping to the fixed ring gear side. A reduction starter was used for the test. With a fixed interval, the number of times at which electricity was turned on was recorded. Occurrence of slipping was evaluated by setting 3000 time as a reference.

(47) Overrunning Clutch Wear Test

(48) A stipulated amount of the grease composition was enclosed in an overrunning clutch member of an automobile starter. Under a stipulated condition, while the starter motor was rotated without any load, the ring gear engaged with the starter motor was idled in the inner part of the overrunning clutch of the starter by performing high-speed rotation at the rate that is not lower than five times the number of rotation of the starter motor without any load. After completion of a stipulated number of operation, diameter after the wear (=wear diameter, μm) of the roller was determined and used as an wear loss. For the test, a planetary starter was used.

(49) Evaluation of Effect

(50) (1) Overrunning clutch torque transmission test

(51) Passed: Slipping did not occur in 3000 times or greater.

(52) Failed: Slipping occurred in less than 3000 times.

(53) (2) Overrunning clutch wear test

(54) Passed: Wear loss was less than 130 μm.

(55) Failed: Wear loss was 130 μm or greater.

(56) TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 3 4 1 2 Base oil: Methyl phenyl 73.74 77.14 75.44 75.01 73.74 73.74 silicone (A) (mass %) Zinc dialkyldithiocarbamate 13.25 9.25 11.25 11.75 11.25 9.25 (B) (mass %) Zinc dialkyldithiophosphate 0 0 0 0 2.0 4.0 (BX) (mass %) Li soap (C) (mass %) 13.01 13.61 13.31 13.24 13.01 13.01 Overruning clutch torque Passed Passed Passed Passed Failed Failed transmission test >3000 >3000 >3000 >3000 <3000 1700-2400 Overrunning clutch Passed Passed Passed Passed Passed Failed abrasion test 60-100 90-130 80-130 70-110 60-120 110-200

(57) As described above, only the case where the zinc dialkyldithiocarbamate was used alone as the extreme-pressure additive reduced slipping, efficiently transmitted torque, and achieved high friction characteristics and wear characteristics. On the other hand, when the zinc dialkyldithiophosphate was used together, friction characteristics or wear characteristics were deteriorated.