JP2019137806A - Grease composition for constant velocity joint - Google Patents

Abstract

To provide the grease composition for the constant velocity joint that has both durability and abnormal noise resistance characteristics.SOLUTION: The grease composition for the constant velocity joint having outer race surface roughness Ra less than 0.80 μm comprises a diurea compound represented by R-NHCONH-CH-p-CH-CH-p-NHCONH-R(formula 1), poly-α-olefin with a kinematic viscosity at 40°C of 1000 mm/s or more to less than 1500 mm/s, a mixed base oil including other base oils, copper dithiocarbamate, and molybdenum dithiocarbamate, wherein the mixed base oil has a kinematic viscosity at 40°C of 180 mm/s or more to less than 400 mm/s, and the mixed base oil contains 15 mass% or more to less than 40 mass% of poly-α-olefin based on a total mass of the mixed base oil.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a grease composition for a constant velocity joint.

  A constant velocity joint that has the function of smoothly transmitting the rotational force of the engine to the tire at a constant speed while following the change in the tire turning angle according to the steering wheel operation of the automobile and the vertical movement of the tire according to the road surface condition. This is an indispensable important component especially for front-wheel drive vehicles.

  Although there are several types of constant velocity joints, a Barfield type constant velocity joint having a large allowable operating angle and excellent sealing performance is well known. Such a Barfield type constant velocity joint is disposed between the drive shaft and the tire, and the rotational force of the drive shaft is transmitted to the tire through the constant velocity joint. The constant velocity joint includes an outer race having a ball rolling groove on the inner surface, an inner race having a ball rolling groove on the outer surface, a ball rolling on these ball rolling grooves, and a ball rolling groove on the ball. And a cage for preventing deviation from the above. In the constant velocity joint configured as described above, a contact portion between the ball rolling groove of the outer race and the inner race and the ball is a sliding portion.

  The outer race and the drive shaft are covered with a single boot over the entire circumference, and within the constant velocity joint covered with the boot (that is, between the outer race and the inner race), the sliding portion of the constant velocity joint is It is filled with a grease composition necessary for lubrication. Here, particularly in the fixed constant velocity joint on the tire side, durability and anti-noise characteristics are required as important performances. Abnormal noise is generated when the regenerative (negative) torque is input, because the ball push-out force due to the pinch angle between the joints is smaller than the static frictional force between the ball and the ball rolling groove. Caused by a collision between parts inside the joint when released. Thus, the grease composition for constant velocity joints is required to have an excellent effect for suppressing abnormal noise and improving durability.

  As a grease composition that suppresses the occurrence of abnormal noise in a constant velocity joint, for example, Patent Document 1 discloses the following components (a) to (g): (a) a predetermined diurea thickener and (b) an ester. Synthetic oil, (c) mineral oil and / or synthetic hydrocarbon oil, (d) molybdenum dialkyldithiocarbamate, (e) molybdenum disulfide, (f) polytetrafluoroethylene, and (g) zinc dithiophosphate compound, etc. A grease composition for fast joints is disclosed.

  Patent Document 2 discloses a grease composition for a constant velocity joint containing a thickener, a base oil, an organic copper-based compound, and an organic molybdenum-based compound, and contains 0.6% by mass or more of the organic copper-based compound. In addition, a grease composition having an organic copper compound: organic molybdenum compound = 1: 4.6 to 1: 11.5 (molar ratio) is disclosed.

  On the other hand, regarding the durability of the constant velocity joint, in Patent Document 3, an outer race having a ball rolling groove on the inner surface, an inner race having a ball rolling groove on the outer surface, and rolling the ball rolling groove. A constant velocity joint comprising: a ball to prevent the ball from deviating from the ball rolling groove; and grease filled between the outer race and the inner race. A constant velocity joint that suppresses fretting wear is disclosed in which a coating film treated with manganese phosphate is formed on at least a part of the outer side surface and the inner side surface of the cage.

  However, in Patent Documents 1 and 2, although a certain effect is recognized for suppressing abnormal noise, no complete countermeasure has been reached. For example, in Patent Document 1, an aliphatic diurea compound is used as a thickener, but there is room for improvement in suppressing abnormal noise during long-term operation.

  In Patent Document 2, copper dithiocarbamate and molybdenum dithiocarbamate are used together in a predetermined ratio, but a reaction film is formed under local high surface pressure and high temperature conditions, contributing to noise suppression and durability. Molybdenum dithiocarbamate may not fully exert its effect on the rolling groove surface smoothed by the action of copper dithiocarbamate after long-term operation.

  Also in Patent Document 3, there is room for improvement in terms of achieving both durability and anti-noise characteristics important as the performance of the constant velocity joint.

JP 2007-138110 A Japanese Patent Laid-Open No. 2006-88998 JP 2014-114918 A

  As described above, in the conventional grease composition for constant velocity joints, it was difficult to achieve both durability and anti-noise characteristics. Accordingly, an object of the present invention is to provide a grease composition for a constant velocity joint that has both durability and anti-noise characteristics.

  As a result of studying various means for solving the above problems, the present inventors have extended the durability life by optimizing the surface roughness of the outer race of the constant velocity joint and the characteristics and components of the grease composition. And it discovered that the tolerance with respect to the abnormal noise at the time of regeneration could be improved from the initial stage over the long term, and completed this invention.

That is, the gist of the present invention is as follows.
(1) A grease composition used for a constant velocity joint in which the outer race has a surface roughness Ra of less than 0.80 μm, and contains the following components (a) to (d).
(A) Diurea compound represented by the following formula (1) R ₁ —NHCONH—C ₆ H ₄ —p—CH ₂ —C ₆ H ₄ —p-NHCONH—R ₂ (1)
(Wherein R ₁ and R ₂ are the same or different aryl groups or cyclohexyl groups having 6 or 7 carbon atoms)
(B) A mixed base oil containing a polyalphaolefin having a kinematic viscosity at 40 ° C. of 1000 mm ² / s or more and less than 1500 mm ² / s and another base oil, wherein the mixed base oil has a kinematic viscosity at 40 ° C. 180 mm ² / s or more and less than 400 mm ² / s, and the mixed base oil contains 15% by mass or more and less than 40% by mass of the polyalphaolefin based on the total mass of the mixed base oil ( c) 0.6% by mass or more of copper dithiocarbamate (d) molybdenum dithiocarbamate based on the total mass of the grease composition

  According to the present invention, it is possible to provide a grease composition for a constant velocity joint that has both durability and anti-noise characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing explaining the barfield type constant velocity joint of one Embodiment which can use the grease composition of this invention, (a) is a longitudinal cross-sectional view in the rotating shaft direction of a constant velocity joint, (b) is Sectional drawing cut | disconnected by the AA in (a) is shown.

Hereinafter, preferred embodiments of the present invention will be described in detail.
The present invention relates to a grease composition used for a constant velocity joint. The grease composition of the present invention extends the durability life by optimizing the surface roughness Ra of the outer race of the constant velocity joint and the characteristics and components of the grease composition used in the constant velocity joint, Therefore, it is possible to suppress abnormal noise during regeneration for a long period of time, and achieve both excellent durability and anti-noise characteristics.

  In the present invention, the main mechanism for improving durability and anti-noise characteristics is presumed as follows. Specifically, in the initial stage of operation, the surface of the outer race ball rolling groove of the outer race having a large surface roughness (d): Molybdenum dithiocarbamate, which forms a reaction film under local high surface pressure and high temperature conditions ( Hereinafter, by forming the reaction film on the roughness convex part of the outer race surface), the static frictional force is reduced, and the stick of the ball can be suppressed to suppress abnormal noise. And after a long term operation, joint life can be extended by smoothing the outer race surface with (c): copper dithiocarbamate to form a stable film. Here, after a long period of operation, on the smoothed outer race surface, the component (d): the reaction film formation by molybdenum dithiocarbamate is insufficient, but the component (a) that plays the role of a thickener: the diurea compound and the component (B): The mixed base oil containing the high-viscosity polyalphaolefin enables the oil film to be kept thick for a long period of time, and reduces the static frictional force by suppressing contact between the two surfaces of the ball and the ball rolling groove. In addition, the noise can be suppressed by suppressing the stick of the ball.

  The constant velocity joint includes an outer race having a ball rolling groove on the inner surface, an inner race having a ball rolling groove on the outer surface, a ball rolling on the ball rolling groove, and a ball rolling groove of the ball. A cage for preventing deviation, and a grease composition is filled between the outer race and the inner race.

  In one embodiment, the constant velocity joint is a Barfield type constant velocity joint. A bar field type constant velocity joint is shown in FIG. 1A is a longitudinal sectional view of the constant velocity joint in the rotation axis direction, and FIG. 1B is a sectional view taken along line AA in FIG. 1A.

  The barfield type constant velocity joint J of the present embodiment is disposed between the drive shaft 6 and the tire, and the rotational force of the drive shaft 6 is transmitted to the tire via the constant velocity joint J.

  The bar field type constant velocity joint J of this embodiment includes an outer race 1 having a ball rolling groove 1a on an inner surface, an inner race 2 having a ball rolling groove 2a on an outer surface, and these ball rolling grooves 1a. , 2a, and a cage 4 that prevents the ball 3 from escaping from the ball rolling grooves 1a, 2a. The contact point between the ball rolling grooves 1a, 2a and the ball 3 is It is a sliding part.

  The outer race 1 and the drive shaft 6 are covered with a single boot 7 all around the circumference, and the constant velocity joint J covered with the boot 7 has grease necessary for lubricating the sliding portion of the constant velocity joint J. Composition 5 is sealed. That is, the grease composition 5 is filled between the outer race 1 and the inner race 2.

  The outer race 1 has a spherical inner surface, on which six ball rolling grooves 1a are formed at equal intervals. The inner race 2 has a spherical outer surface, and six ball rolling grooves 2a are formed at positions corresponding to the ball rolling grooves 1a of the outer race 1 thereon. Each of these six ball rolling grooves 1 a and 2 a contains six steel balls 3, and the rotational force of the drive shaft 6 is transmitted at the contact portion of the six balls 3. .

  The cage 4 is a cylindrical body whose outer surface and inner surface are part of a spherical surface, and a ball holding hole having an inner dimension slightly larger than the diameter of the ball 3 is provided at a position corresponding to the six balls 3. Are formed at equal intervals in the circumferential direction. There are gaps between the outer side surface of the cage 4 and the inner side surface of the outer race 1 and between the inner side surface of the cage 4 and the outer side surface of the inner race 2, so that they are not sliding portions.

  The constant velocity joint J may form films 14 a and 14 b as films for holding a hygroscopic film and a grease composition on the outer and inner surfaces of the cage 4. As the hygroscopic film, for example, a film composed of a sodium compound can be used. As a film for holding the grease composition, for example, a manganese phosphate film can be used. In the constant velocity joint using the grease composition of the present invention, the coatings 14a and 14b are not essential, and the grease composition of the present invention can be used for a constant velocity joint that does not include the coatings 14a and 14b.

  In the present invention, the surface roughness Ra of the outer race of the constant velocity joint is less than 0.80 μm. In the present invention, the surface roughness of the outer race refers to the surface roughness of the ball rolling groove formed inside the outer race, that is, the surface roughness of the ball rolling surface of the outer race. In the present invention, it is only necessary that at least the surface roughness Ra of the ball rolling groove of the outer race is less than 0.80 μm, and other portions of the outer race may not satisfy this surface roughness. When the surface roughness Ra of the outer race is less than 0.80 μm, the durability life can be extended in combination with the characteristics and components of the grease composition, and the contact between the ball and the ball rolling groove is between the two surfaces. By suppressing the static friction force, the noise can be suppressed by suppressing the stick of the ball. The surface roughness Ra of the outer race is preferably 0.10 μm or more and less than 0.80 μm, more preferably 0.20 μm or more and less than 0.70 μm. When the surface roughness Ra of the outer race is less than 0.10 μm, the effect reaches a peak, and the processing cost is not preferable.

The grease composition contains the following components (a) to (d).
(A) Diurea compound represented by the following formula (1) R ₁ —NHCONH—C ₆ H ₄ —p—CH ₂ —C ₆ H ₄ —p-NHCONH—R ₂ (1)
(Wherein R ₁ and R ₂ are the same or different aryl groups or cyclohexyl groups having 6 or 7 carbon atoms)
In the formula (1), R ₁ and R ₂ are preferably a combination of an aryl group having 6 carbon atoms and a cyclohexyl group.

The alicyclic aromatic diurea compound of component (a) acts as a thickener. The diurea compound represented by the formula (1) can be obtained, for example, by a reaction between a monoamine such as aniline, p-toluidine, cyclohexylamine and diphenylmethane-4,4′-diisocyanate. In this reaction, a phenyl group, a tolyl group, a cyclohexyl group, and the like are generated as the aryl groups for R ₁ and R ₂ .

  A grease composition using a thickener composed of such an alicyclic aromatic diurea compound has a longer shearing condition than that using an aliphatic diurea compound using an aliphatic amine as a thickener. Even under the thickener, the micelle structure of the thickener is stable, and the adhesion to the metal surface is strong. Therefore, it is considered that the buffering action for preventing the metal contact of the thickener itself is stronger.

  The content of the diurea compound represented by the formula (1) of the component (a) in the grease composition is preferably 10% by mass or more and less than 25% by mass based on the total mass of the grease composition. Preferably they are 10 mass% or more and less than 20 mass%. If it is less than 10% by mass, the grease may leak from the constant velocity joint due to softening during shearing acting on the grease. On the other hand, when it is 25% by mass or more, the viscous resistance tends to increase (the fluidity of grease decreases), and for example, the torque during driving of the vehicle increases.

(B) mixing the base oil mixed base oil is a mixed oil of two or more base oils, and polyalphaolefin kinematic viscosity at 40 ° C. is less than 1000 mm ² / s or more 1500 mm ² / s, other base oils including.

Mixed base oil has a kinematic viscosity at 40 ° C. of less than 180 mm ² / s or more 400 mm ² / s, preferably less than 180 mm ² / s or more 320 mm ² / s, more preferably 180 mm ² / s or more 250 mm ² / is less than s. When the kinematic viscosity at 40 ° C of the mixed base oil is within this range, the oil film is kept thick for a long time, and the static frictional force is reduced by suppressing contact between the two surfaces of the ball and the ball rolling groove. Sound can be suppressed. The kinematic viscosity at 40 ° C. of the mixed base oil or base oil can be measured according to JIS K 2220.23.

Mixed base oil, as a kind of base oil, comprising a polyalphaolefin kinematic viscosity at 40 ° C. is less than 1000 mm ² / s or more 1500 mm ² / s (hereinafter, also referred to as high viscosity polyalphaolefins). The kinematic viscosity at 40 ° C. of the polyalphaolefin is preferably 1100 mm ² / s or more and less than 1500 mm ² / s, more preferably 1200 mm ² / s or more and less than 1500 mm ² / s.

  The mixed base oil contains high-viscosity polyalphaolefin, so that the oil film is kept thick for a long time, and the static frictional force is reduced by suppressing the contact between the two surfaces of the ball and the ball rolling groove. In addition, the aniline point of the mixed base oil can be set to less than 135 ° C. which is a preferable range.

  The content of the high-viscosity polyalphaolefin in the mixed base oil is 15% by mass or more and less than 40% by mass, preferably 15% by mass or more and less than 35% by mass based on the total mass of the mixed base oil. If the content of the high-viscosity polyalphaolefin in the mixed base oil is within this range, the kinematic viscosity at 40 ° C of the mixed base oil will be sufficiently high. By suppressing the contact between the two surfaces of the groove, the static friction force can be reduced and abnormal noise can be suppressed.

  Other base oils other than the high-viscosity polyalphaolefin contained in the mixed base oil are not particularly limited, and for example, mineral oil and synthetic oil can be used. Other base oils may be used alone or in combination of two or more.

  The mineral oil is not particularly limited, and for example, one obtained by appropriately combining, for example, vacuum distillation, oil removal, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, clay purification, hydrorefining, etc. is used. be able to. The mineral oil is preferably a paraffinic mineral oil, more preferably group I and II in the American Petroleum Institute (API) classification.

As the synthetic oil, any synthetic oil other than the high-viscosity polyalphaolefin may be used, and is not particularly limited. For example, a co-oligomer oil of alpha olefin and ethylene, a phenyl ether synthetic oil, an ester synthetic oil, Examples include polyglycol synthetic oil and silicone oil. As synthetic oil, kinematic viscosity at 40 ° C. may be used polyalphaolefin is outside the range of less than 1000 mm ² / s or more 1500 mm ² / s.

  As other base oils, mineral oil is preferable and paraffinic mineral oil is more preferable in consideration of cost and adverse effects of boots.

  The aniline point of the mixed base oil is preferably below 135 ° C. When the aniline point of the mixed base oil is lower than 135 ° C., it is preferable in that the boot swells appropriately and the grease sealing property is maintained.

(C) Copper dithiocarbamate (CuDTC)
In the grease composition of the present invention, copper dithiocarbamate is used as an additive effective in wear resistance.
As copper dithiocarbamate, what is represented by following formula (2) can be used.

（式中、Ｒ₁及びＲ₂は、互いに同一でも異なっていてもよく、それぞれ炭素数１〜１０の直鎖又は分岐アルキル基であり、好ましくは炭素数１〜４の直鎖アルキル基であり、より好ましくは、Ｒ₁及びＲ₂は炭素数１のメチル基である。）

(In the formula, R ₁ and R ₂ may be the same or different from each other, and each is a linear or branched alkyl group having 1 to 10 carbon atoms, preferably a linear alkyl group having 1 to 4 carbon atoms. More preferably, R ₁ and R ₂ are C ₁ methyl groups.)

Incidentally, dithiocarbamates of formula (2) R ₁ and R ₂ are methyl group having one carbon atom is a dimethyl copper dithiocarbamate.

  The content of copper dithiocarbamate in the grease composition is 0.6% by mass or more, preferably 0.8% by mass or more, more preferably 0.8% by mass, based on the total mass of the grease composition. % Or more and less than 1.6% by mass. When the content of copper dithiocarbamate in the grease composition is within this range, the surface of the ball rolling groove can be sufficiently smoothed and good wear characteristics can be maintained.

(D) Molybdenum dithiocarbamate (MoDTC)
In the grease composition of the present invention, molybdenum dithiocarbamate is used as an additive for forming a reaction film under local high surface pressure and high temperature conditions.

As molybdenum dithiocarbamate, what is represented by following formula (3) or (4) can be used.
_{[R 3 R 4 N-CS} -S] 2 -Mo 2 O m S n (3)
(In the formula, R ₃ and R ₄ may be the same or different from each other, and each is a linear or branched alkyl group having 1 to 24 carbon atoms, preferably a linear alkyl group having 1 to 10 carbon atoms. More preferably, it is a linear alkyl group having 1 to 4 carbon atoms, m is 0 to 3, n is 1 to 4, and m + n = 4.

（式中、Ｒ₅、Ｒ₆、Ｒ₇及びＲ₈は、互いに同一でも異なっていてもよく、それぞれ炭素数１〜２４の直鎖又は分岐アルキル基であり、好ましくは炭素数１〜１０の直鎖アルキル基であり、より好ましくは炭素数１〜４の直鎖アルキル基である。）

(In the formula, R ₅ , R ₆ , R ₇ and R ₈ may be the same or different from each other, and each is a linear or branched alkyl group having 1 to 24 carbon atoms, preferably 1 to 10 carbon atoms. A straight-chain alkyl group, more preferably a straight-chain alkyl group having 1 to 4 carbon atoms.)

  The content of molybdenum dithiocarbamate in the grease composition is preferably 0.8% by mass or more, more preferably 1.0% by mass or more, and particularly preferably based on the total mass of the grease composition. It is 1.4 mass% or more and less than 3.0 mass%, Most preferably, it is 1.6 mass% or more and less than 2.6 mass%. When the content of molybdenum dithiocarbamate in the grease composition is 0.8% by mass or more, a reaction film is sufficiently formed on the roughness convexity of the ball rolling groove surface of the outer race surface having a large initial roughness. Can suppress abnormal noise. Further, when the content of molybdenum dithiocarbamate in the grease composition is less than 3.0% by mass, the effect of competitively adsorbed copper dithiocarbamate is not hindered.

  In addition to the above additives, other additives can be used in the grease composition as necessary. Examples of such additives include antioxidants typified by phenolic, amine-based, sulfur-based and phosphorus-based materials; sulfurized fats and oils, sulfurized olefins, phosphoric acid esters, phosphorous acid esters, acidic phosphoric acid ester amine salts, etc. Load-bearing additives; oily agents such as animal and vegetable oils, triglycerides, diglycerides, monoglycerides, fatty acids, alcohols, amines; rust inhibitors such as metal sulfonates, metal salicylates, metal phenates; molybdenum disulfide, graphite, polytetrafluoro Examples thereof include solid lubricants such as ethylene (PTFE) and zinc oxide; and thickeners such as polybutene and polymethacrylate. The amount of these components used is usually 0.1% by mass or more and 20% by mass or less, preferably 0.5% by mass or more and 10% by mass or less, based on the total mass of the grease composition.

  The penetration of the grease composition is preferably 220 or more and 430 or less, more preferably 265 or more and 385 or less, and particularly preferably 285 or more and 340 or less. When the grease composition has a miscibility of 220 or more, the grease composition can be prevented from leaking from the constant velocity joint due to softening during shearing acting on the grease composition, while the grease composition has a miscibility. When it is 430 or less, the viscous resistance is sufficiently low, and the fluidity of the grease composition can be maintained.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples.

In Examples 1 to 3 and Comparative Examples 1 to 10, Evaluation 1 was performed using a predetermined grease composition, a joint having a surface roughness Ra of a ball rolling groove of a predetermined outer race, and a predetermined grease Evaluation 2 was performed using the combination of compositions.
The grease composition was prepared as follows.

Example 1
The following were used as components of the grease composition.
(A) Alicyclic aromatic diurea represented by the above formula (1) (in the formula (1), R ₁ and R ₂ are a phenyl group and a cyclohexyl group)
(B) Mixed base oil Mixed oil A of two types of paraffinic mineral oils (kinematic viscosity 130 mm ² / s at 40 ° C.) (P mineral oil-A) and polyalphaolefin A (kinematic viscosity 1240 mm ² / s at 40 ° C. ) (PAO-A) mixed base oil additive:
(C) Copper dimethyldithiocarbamate (CuDTC): Nouchira TTCU, manufactured by Ouchi Shinsei Chemical Co., Ltd.
(D) Molybdenum dibutyldithiocarbamate (MoDTC): R.I. T. T. et al. MOLYVAN A, manufactured by Vanderbilt
(E) Additive package: Contains molybdenum disulfide (MoS ₂ ), sulfurized fat, castor oil, calcium sulfonate, zinc oxide, polybutene, and amine antioxidant

In a prototype container, 4100 g of mixed base oil and 1012 g of diphenylmethane-4,4′-diisocyanate having the specified mixing ratio shown in Table 1 were taken, and the mixture was heated to 70 to 80 ° C. In a separate container, 4100 g of the mixed base oil having the above-mentioned specified mixing ratio, 563 g of cyclohexylamine and 225 g of aniline were taken, heated to 70-80 ° C., and added to the previous container. The mixture was allowed to react with thorough stirring for 30 minutes, heated to 160 ° C. and allowed to cool to obtain a base alicyclic aromatic diurea grease. The alicyclic aromatic diurea in this grease is one in which R ₁ and R ₂ in the formula (1) are a phenyl group or a cyclohexyl group.

  To this base grease, an additive (the components (c) to (e)) shown in Table 1 was added, and a mixture in which a mixed base oil having a predetermined blending ratio was appropriately added was blended with a three-stage roll mill. : Based on JIS K 2220.7, it adjusted to the range of the target penetration degree 285-315.

Example 2
The same procedure as in Example 1 was conducted except that the ratio of the mixed oil A of the paraffinic mineral oil and the polyalphaolefin A in the mixed base oil was changed so that the kinematic viscosity at 40 ° C. of the mixed base oil was 300 mm ² / s. The grease composition of Example 2 was produced.

Example 3
A grease composition of Example 3 was produced in the same manner as Example 1.

Comparative Example 1
The same procedure as in Example 1 was conducted except that the ratio of the mixed oil A of the paraffinic mineral oil and the polyalphaolefin A in the mixed base oil was changed and the kinematic viscosity at 40 ° C. of the mixed base oil was 173 mm ² / s. The grease composition of Comparative Example 1 was produced.

Comparative Example 2
As a mixed base oil, the grease composition of Comparative Example 2 was used in the same manner as in Example 1 except that a mixed oil A of paraffinic mineral oil was used alone and the kinematic viscosity at 40 ° C. of the mixed base oil was 130 mm ² / s. Was made.

Comparative Example 3
Polyalphaolefin B (kinematic viscosity at 40 ° C. 420 mm ² / s) (PAO-B) is used instead of polyalphaolefin A in the mixed base oil, and the kinematic viscosity at 40 ° C. of the mixed base oil is 172 mm ² / s. A grease composition of Comparative Example 3 was produced in the same manner as in Example 1 except that.

Comparative Example 4
A grease composition of Comparative Example 4 was prepared in the same manner as Example 1.

Comparative Example 5
Example 1 except that an aliphatic diurea (in the formula (1), R ₁ and R ₂ are octyl groups) was used in a content shown in Table 1 instead of the alicyclic aromatic diurea as a thickener. Similarly, a grease composition of Comparative Example 5 was produced.

Comparative Example 6
A grease composition of Comparative Example 6 was produced in the same manner as Example 1 except that CuDTC was not used.

Comparative Example 7
A grease composition of Comparative Example 7 was produced in the same manner as in Example 1 except that the CuDTC content was changed to 0.4% by mass.

Comparative Example 8
A grease composition of Comparative Example 8 was produced in the same manner as in Example 1 except that MoDTC was not used.

Comparative Example 9
A grease composition of Comparative Example 9 was produced in the same manner as in Example 1 except that a predetermined amount of polyalphaolefin B (PAO-B) was used instead of polyalphaolefin A in the mixed base oil.

Comparative Example 10
A grease composition of Comparative Example 10 was prepared in the same manner as in Example 1 except that paraffinic mineral oil B (kinematic viscosity at 40 ° C. 200 mm ² / s) (P mineral oil-B) was used as the mixed base oil. .

[Physical property measurement]
About the base oil or mixed base oil used for the grease composition of Examples 1-3 and Comparative Examples 1-10, the kinematic viscosity and aniline point in 40 degreeC were measured.

<Kinematic viscosity at 40 ° C.>
The kinematic viscosity at 40 ° C. of the base oil or mixed base oil was measured according to JIS K 2220.23.

<Aniline point>
The aniline point of the base oil or mixed base oil was measured according to JIS K 2256.

[Evaluation 1]
The grease compositions of Examples 1 to 3 and Comparative Examples 1 to 10 were subjected to friction coefficient measurement, wear evaluation, and low temperature rheometer measurement.

<Friction coefficient measurement>
The friction coefficient was measured with an SRV tester (condition 1). Specifically, the friction coefficient was measured by a ball / plate reciprocating rocking test using an Optimol SRV tester. The coefficient of friction that rises when the reciprocating direction is switched and the friction force is reversed was evaluated as the coefficient of static friction.

[Test conditions]
Ball Material: SUJ-2, Shape: φ17.5mm
Plate Material: SUJ-2, Surface roughness Ra: 0.2 μm, 0.6 μm, 1.2 μm Three level load: 20N
Amplitude: 2 mm
Frequency: 2Hz
Temperature: 25 ° C
Surface pressure: 880 MPa
Speed: 8mm / s
Time: 10 sec

[Judgment criteria]
Coefficient of static friction: (good) ○>△> × (bad)
○: Less than 0.14, Δ: 0.14 or more and less than 0.18, ×: 0.18 or more

<Abrasion evaluation>
Wear evaluation was performed with an SRV tester (condition 2). Specifically, a ball / plate reciprocating rocking test was performed for a specified time using an Optimum SRV testing machine, and then the wear state of the ball sliding surface was observed to evaluate the wear.

[Test conditions]
Ball Material: SUJ-2, Shape: φ10mm
Plate material: SUJ-2, surface roughness Rz: 5 μm
Load: 200N
Amplitude: 3 mm
Frequency: 30Hz
Temperature: 25 ° C
Surface pressure: 2740 MPa
Speed: 180mm / s
Time: 10min

[Judgment criteria]
Of the following wear ratings, Rate 4 or higher was considered acceptable.
Rate 5: Thin and shallow wear marks exist throughout.
Rate 4: The linear wear scars over the entire surface form an uneven surface, and there are slight adhesion traces caused by contact.
Rate3: The linear wear scars over the entire surface together form an uneven surface, and there are adhesion marks. However, the adhesion mark is shallow and the outline is unclear.
Rate 2: The linear wear scars over the entire surface form an uneven surface, and there are adhesion marks. However, the adhesion mark is deep and the outline is clear.
Rate 1: Adhesion traces that are deep and have a clear outline occur throughout, and the adhesion traces together form an uneven surface.

<Low temperature rheometer measurement>
Low temperature shear stress was measured using a rotational viscometer Physica MCR301. Specifically, grease was set between two surfaces, cooled at −30 ° C. and held for 5 minutes, and then measured. The value at which the shear stress was maximum was taken as the maximum shear stress.

[Test conditions]
Geometry: Parallel plate diameter 25mm
Temperature: -30 ° C
Shear rate: 0.1 to 1000 s ^-1

[Judgment criteria]
Pass: Maximum shear stress less than 60 kPa (excellent: less than 50 kPa, good: 50 kPa or more and less than 56 kPa)
Fail: Maximum shear stress 60kPa or more

[Evaluation 2]
For Examples 1 to 3 and Comparative Examples 1 to 10, abnormal noise measurement and durability test for a combination of a fixed constant velocity joint having a surface roughness Ra of a ball rolling groove of a predetermined outer race and a predetermined grease composition Went.

<Constant velocity joint>
An outer race having a ball rolling groove on the inner surface, an inner race having a ball rolling groove on the outer surface, a ball rolling on the ball rolling groove, and a cage that prevents the ball from departing from the ball rolling groove The grease composition was filled between the outer race and the inner race using a Barfield type constant velocity joint (a constant velocity joint shown in FIG. 1 having no coatings 14a and 14b). The surface roughness Ra of the ball rolling groove of the outer race of the constant velocity joint was set to three levels of 0.2 μm, 0.6 μm, and 1.2 μm.

<Abnormal sound characteristics>
The grease compositions of Examples 1 to 3 and Comparative Examples 1 to 10 were sealed between the outer race and the inner race of the evaluation joint, and a table noise test was performed under the following conditions to evaluate the noise characteristics. As for the abnormal noise characteristics, a new joint was used for the initial abnormal noise characteristics for the two conditions after the initial test and the durability test, a post-endurance test joint was used for the abnormal noise characteristics after the durability test, and the joint angle was 0 deg. Based on the above, the presence or absence of sound was evaluated by a sensory test.

[Test conditions]
Load torque: 400Nm
Rotation speed: 200rpm
Joint angle: 6 deg.
New joint: unused evaluation after joint durability test Joint: Use joint after joint durability test under the following conditions

[Judgment criteria]
Pass: No sound generated Fail: Sound generated

<Durability test>
Each grease composition of Examples 1 to 3 and Comparative Examples 1 to 10 is sealed between the outer race and inner race of a new evaluation joint, and the bench durability test is performed under the following conditions, and the joint is disassembled after a specified time. The durability was evaluated by observing the presence or absence of flaking in the ball rolling groove of the outer race after the test.

[Test conditions]
Load torque: 300Nm
Rotation speed: 1900rpm
Joint angle: 6 deg.
Test time: 300 hours

[Judgment criteria]
Pass: No flaking Fail: Flaking

  Table 1 shows the compositions of the grease compositions of Examples 1 to 3 and Comparative Examples 1 to 10, constant velocity joints used for measurement, and evaluation results.

  From Table 1, the grease compositions of Examples 1 to 3 were good results in any evaluation of Evaluation 2.

On the other hand, in Comparative Examples 1 to 3, the abnormal noise evaluation after the durability test was unacceptable. This is because the kinematic viscosity at 40 ° C. of the mixed base oil decreases due to the low or no content of the polyalphaolefin A in the mixed base oil, and the oil film cannot be kept thick for a long time. This is probably because the static frictional force increased due to the decrease in the oil film thickness. From this result, it is preferable that the mixed base oil contains polyalphaolefin having a high viscosity (kinematic viscosity at 40 ° C. of 1000 mm ² / s or more and less than 1500 mm ² / s) at a content of 15% by mass or more and less than 40% by mass. I can say that.

  In Comparative Example 4, the abnormal noise evaluation and durability were unacceptable. This is because the surface roughness of the outer race of the constant velocity joint increases, so that the metal contact ratio increases, and therefore, the coefficient of static friction increases from the beginning of operation, and the sliding is repeated with the metal contact ratio being large. It is considered that the durability was lowered. From this result, it can be said that the surface roughness Ra of the outer race of the constant velocity joint is preferably less than 0.8 μm.

  In Comparative Example 5, the abnormal noise evaluation and durability after the durability test were unacceptable. This is because the thickener was changed from alicyclic aromatic diurea to aliphatic diurea, and the thickener was severely cut by long-term shearing, and the oil film could not be kept thick over the long term. This is thought to be due to an increase in the contact ratio between metals. From this result, it can be said that alicyclic aromatic diurea is preferable as the thickener.

  In Comparative Example 6, the initial abnormal noise evaluation and durability were unacceptable. This is because CuDTC is not included, so the metal surface of the outer race with a large initial surface roughness cannot be smoothed, abnormal noise is generated, and the convex portion between the two surfaces of the ball and the ball rolling groove This is thought to be because the durability life decreased due to repeated contact. Moreover, in the comparative example 7, durability was unacceptable. This is because the CuDTC content is low, so the metal surface of the outer race with a large initial surface roughness cannot be sufficiently smoothed, and it is durable due to repeated contact of the convex portions between the two surfaces of the ball and the ball rolling groove. This is thought to be due to a decrease in life. From this result, it can be said that it is preferable to use copper dithiocarbamate at a content of 0.6% by mass or more in the grease composition.

  In Comparative Example 8, the initial abnormal noise evaluation and durability were unacceptable. This is probably because MoDTC is not included, and therefore, a reaction film made of MoDTC cannot be formed on the roughness convex portion of the metal surface of the outer race having a large initial surface roughness. From this result, it can be said that it is preferable to use molybdenum dithiocarbamate in the grease composition.

  In Comparative Example 9, when a predetermined amount of polyalphaolefin B (PAO-B) was used instead of polyalphaolefin A in the mixed base oil, the content of polyalphaolefin increased, The aniline point was 135 ° C. or higher, which was not preferable.

In Comparative Example 10, when the kinematic viscosity at 40 ° C. of the mixed base oil was 200 mm ² / s using only the paraffinic mineral oil without using the high-viscosity polyalphaolefin, the maximum shear in the low temperature rheometer measurement was obtained. The stress was not preferable because it was 65 kPa or more.

J: constant velocity joint, 1: outer race, 1a: ball rolling groove, 2: inner race, 2a: ball rolling groove, 3: ball, 4: cage, 5: grease composition, 14a, 14b: coating

Claims (1)

A grease composition for use in a constant velocity joint having a surface roughness Ra of an outer race of less than 0.80 μm, comprising the following components (a) to (d):
(A) Diurea compound represented by the following formula (1) R ₁ —NHCONH—C ₆ H ₄ —p—CH ₂ —C ₆ H ₄ —p-NHCONH—R ₂ (1)
(Wherein R ₁ and R ₂ are the same or different aryl groups or cyclohexyl groups having 6 or 7 carbon atoms)
(B) A mixed base oil containing a polyalphaolefin having a kinematic viscosity at 40 ° C. of 1000 mm ² / s or more and less than 1500 mm ² / s and another base oil, wherein the mixed base oil has a kinematic viscosity at 40 ° C. 180 mm ² / s or more and less than 400 mm ² / s, and the mixed base oil contains 15% by mass or more and less than 40% by mass of the polyalphaolefin based on the total mass of the mixed base oil ( c) 0.6% by mass or more of copper dithiocarbamate (d) molybdenum dithiocarbamate based on the total mass of the grease composition

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