JP5473344B2 - Lubricating oil composition for continuously variable transmission - Google Patents

Description

  The present invention relates to a continuously variable transmission lubricating oil composition.

  For the purpose of improving the fuel efficiency of automobiles, continuously variable transmissions (hereinafter referred to as “CVT” where appropriate) have been widely used instead of stepped automatic transmissions, and in particular, metal belts and pulleys are used for power transmission. A metal belt type CVT is generally used. The metal belt type CVT includes a metal belt-pulley part that transmits power via a frictional force between a metal belt and a pulley, a torque converter that is a starting element, and a forward / reverse switching mechanism for switching forward / reverse. In general, the same lubricating oil is used for each of these continuously variable transmissions.

  In this continuously variable transmission, loss reduction in hydraulic pumps and bearings is required from the viewpoint of fuel efficiency, so the lubricating oil used in continuously variable transmissions contributes to loss reduction by suppressing viscous resistance. Thus, it has been required to have a lower viscosity than in the past over a wide temperature range. However, when the viscosity of the lubricating oil is lowered, a slight decrease in the viscosity tends to be below the allowable viscosity necessary for preventing wear and seizure of the component, and the durability of the component tends to be affected. Therefore, when reducing the viscosity, it is necessary to pay attention so that the initial viscosity can be maintained over a long period of time.

  Consideration of fuel saving by such low viscosity has already been made for lubricating oil for automatic transmissions. For example, Patent Document 1 proposes a lubricating oil composition that maintains viscosity characteristics over a long period of time by using a viscosity index improver having a weight average molecular weight (Mw) of 40,000 or less. In addition, although it is not a study by lowering the viscosity, Patent Document 2 simultaneously improves the low-temperature viscosity characteristics that affect low-temperature operability and the high-temperature viscosity that affects wear by selecting a viscosity modifier in a specific molecular weight range. Consideration of fuel saving is being made.

Further, the continuously variable transmission lubricating oil preferably has a high coefficient of friction between metals in addition to the above-described reduction in viscosity from the viewpoint of further improving fuel economy. The transmission torque capacity at the metal belt-pulley part is proportional to the product of the pressing pressure between the metal belt and pulley and the friction coefficient, so the higher the friction coefficient of the lubricating oil, the lower the pressing pressure between the metal belt and pulley. This is because the fuel consumption of the metal belt type CVT can be improved as a result.
As a technique for improving the coefficient of friction between metals of a continuously variable transmission lubricating oil, a technique in which an alkaline earth metal detergent such as sulfonate or phenate is blended with the lubricating oil is known (for example, Patent Documents 3 and 4). etc).

  On the other hand, in the torque converter and the forward / reverse switching mechanism of the continuously variable transmission, a shock is generated when the wet friction material is coupled in the lock-up clutch of the torque converter and the clutch when the forward / reverse switching mechanism is operated. Therefore, a friction modifier having a shock suppressing effect is often blended with the continuously variable transmission lubricating oil (for example, Patent Documents 5 and 6).

JP 2004-155873 A Special table 2002-509182 gazette JP-A-9-263788 Japanese Patent Application Laid-Open No. 9-1000048 JP-A-2-175794 JP 2000-355695 A

  Since the continuously variable transmission transmits power by friction between metal parts such as a metal belt and pulley, the metal parts contact and slide under high pressure conditions. There is a need for higher wear resistance and seizure resistance and improved component durability as a result than lubricants for automatic transmissions. For continuously variable transmissions, which combine fuel economy with low viscosity and these performances. Lubricating oil is needed.

  In addition, the blending of friction modifiers is effective in suppressing shocks in torque converters and forward / reverse switching mechanisms, but it causes a reduction in the coefficient of friction between the metal belt and the pulley, and transmission at the metal belt and pulley. The torque capacity is likely to decrease, and as a result, there is a concern that fuel efficiency will be reduced. In addition, the friction modifier is blended with a lower coefficient of dynamic friction with the wet friction material when the clutch is engaged with a torque converter or a forward / reverse switching mechanism, and with static friction with the wet friction material when the clutch slides at an extremely low speed. The coefficient tends to decrease, and there is a concern about power transmission failure with a metal belt, clutch connection delay in a torque converter or a forward / reverse switching mechanism, and clutch slippage. Conversely, if the friction modifier is reduced in order to improve the intermetal friction coefficient, or if the amount of alkaline earth metal is excessively mixed, there is a concern that the shock during clutch engagement will increase.

  Thus, in general, it is difficult to achieve both improvement in the friction coefficient between metals between the metal belt and pulley, improvement in the static friction coefficient and dynamic friction coefficient in the wet friction material of the clutch, and suppression of shock during clutch engagement. It is required to improve both. Furthermore, these performances are required to be maintained not only in the initial stage but also for a long period of time (that is, the stability is good).

  The present invention achieves both fuel economy and component durability by lowering the viscosity in the normal temperature range, and preferably further suppresses shock when the wet friction material is combined, and has a high static friction coefficient in the wet friction material and between the belt and the pulley. An object of the present invention is to provide a continuously variable transmission lubricating oil composition that further improves fuel economy by achieving a high intermetallic friction coefficient.

  As a result of diligent research in view of the above situation, the present inventors have made the viscosity index of the composition higher than that of a normal continuously variable transmission lubricating oil using a specific viscosity index improver, and basic calcium. By blending a specific amount of one or more selected from sulfonate and basic calcium phenate, continuously variable transmission satisfying both low fuel consumption due to low viscosity in normal temperature range and component durability due to securing high temperature range viscosity It has been found that a machine lubricating oil composition can be obtained.

  In addition, a belt that has been difficult with conventional lubricating oil compositions for continuously variable transmissions by selecting a non-dispersed viscosity index improver as a viscosity index improver and blending a specific amount of a specific sulfolane derivative. -High inter-metal friction coefficient between pulleys, high static friction coefficient of clutch wet friction material, and suppression of shock when clutch is engaged, and stability of dynamic friction coefficient of clutch wet friction material is also good It has been found that a lubricating oil composition for a continuously variable transmission can be obtained.

（式（１）中、Ｒ^１は炭素数１〜２０のアルキル基を表す。） That is, the present invention provides the following lubricating oil composition for continuously variable transmissions.
<1> A lubricating oil composition,
Lubricating base oil,
(A-1) A polymethacrylate viscosity index improver having a weight average molecular weight (in terms of polystyrene) of 20,000 to 100,000 and a weight average molecular weight / number average molecular weight of 1.5 to 2.2. A-2) It is selected from polymethacrylate viscosity index improvers having a weight average molecular weight (polystyrene conversion) of 300,000 to 900,000 and a weight average molecular weight / number average molecular weight of 1.0 to 1.5. 1 type or more and 5 mass% or more and 20 mass% or less with respect to this lubricating oil composition whole quantity,
(B) one or more selected from basic calcium sulfonate and basic calcium phenate, 450 mass ppm or more and 700 mass ppm or less in terms of calcium amount with respect to the total amount of the lubricating oil composition,
A lubricating oil composition for a continuously variable transmission, wherein the lubricating oil composition has a kinematic viscosity at 100 ° C of 6.5 to 7.4 mm ² / s and a viscosity index of 205 or more.
<2> The lubricating base oil is
(X) a base oil component having a kinematic viscosity at 100 ° C. of 1.5 to 3.5 mm ² / s, a pour point of −30 ° C. or less, a viscosity index of 100 or more, and a sulfur content of 0.01% by mass or less;
(Y) a base oil component having a kinematic viscosity at 100 ° C. of 4.0 to 8.0 mm ² / s, a viscosity index of 120 or more, and a sulfur content of 0.01% by mass or less;
The lubricating oil composition for continuously variable transmission according to <1>, wherein the content ratio of (X) with respect to the total amount of the base oil is 20 to 80% by mass.
<3> The polymethacrylate viscosity index improver of (A-1) or (A-2) is a non-dispersed viscosity index improver,
(C) The compound represented by the following general formula (1) is further contained in an amount of 0.1% by mass or more and 5.0% by mass or less based on the total amount of the lubricating oil composition <1> or <2> The lubricating oil composition for continuously variable transmissions.

(In formula (1), R ¹ represents an alkyl group having 1 to 20 carbon atoms.)

  According to the present invention, it is possible to achieve both fuel saving and component durability by lowering the viscosity in the normal temperature range, preferably further suppressing the shock when the wet friction material is combined, and the high static friction coefficient and belt in the wet friction material. There is provided a continuously variable transmission lubricating oil composition that further improves fuel economy by achieving a high coefficient of friction between metals between pulleys.

Hereinafter, the present invention will be described in detail.
[1] Base oil The base oil used in the present invention is not particularly limited as long as it is used as a base oil for continuously variable transmission lubricating oils such as mineral base oils, synthetic base oils, and mixed base oils thereof. it is no limitation, but is preferably a kinematic viscosity at 100 ° C. from the viewpoint of easily obtained appropriate lubricating properties as the continuously variable transmission lubricating oil is 5.0 mm ² / s from 3.5 mm ² / s. Moreover, it is preferable that a viscosity index is 110 or more from a viewpoint of ensuring viscosity temperature characteristics, and a sulfur content is 0.01 mass% or less from a viewpoint of ensuring oxidation stability.

In addition, from the viewpoint of easily obtaining an appropriate low temperature viscosity and an appropriate lubricating property as a continuously variable transmission lubricating oil, in the present invention, (X) a kinematic viscosity at 100 ° C. is 1.5 to 3.5 mm ² / s. A base oil component having a pour point of −30 ° C. or less, a viscosity index of 100 or more, and a sulfur content of 0.01% by mass or less, and (Y) a kinematic viscosity at 100 ° C. of 4.0 to 8.0 mm ² / s. , A base oil mixed with a base oil component having a viscosity index of 120 or more and a sulfur content of 0.01% by mass or less, wherein the content ratio of the base oil component (X) with respect to the total amount of the base oil is 20% by mass It is preferable to use a base oil that is ˜80 mass%.

  Any mineral base oil can be used as the mineral oil base oil, but it is highly refined by subjecting hydrorefined oil, catalyst isomerized oil, etc. to treatment such as solvent dewaxing or hydrodewaxing. Paraffinic mineral oil (high viscosity index mineral oil base oil) is preferably used. Examples of mineral base oils other than those described above include, for example, raffinates obtained by solvent refining using lube oil as an aromatic extraction solvent such as phenol and furfural, hydrogen such as cobalt and molybdenum using silica-alumina as a carrier. Examples thereof include hydrotreated oils obtained by hydrotreating using a hydrotreating catalyst, such as 100 neutral oil, 150 neutral oil, and 500 neutral oil.

Examples of the synthetic lubricant base oil include isoparaffin, poly-α-olefin oligomer, polybutene, alkylbenzene, polyol ester, polyglycol ester, dibasic acid ester, phosphoric acid synthesized from natural gas such as methane. Examples include esters and silicone oils.
These base oils may be used individually by 1 type chosen from mineral oil and synthetic oil, and may mix and use 2 or more types in arbitrary ratios.

[2] Viscosity index improver (component (A-1) or (A-2))
In the present invention, as the viscosity index improver, (A-1) the weight average molecular weight (polystyrene conversion) is 20,000 or more and 100,000 or less, and the weight average molecular weight / number average molecular weight is 1.5 or more and 2.2 or less. A certain polymethacrylate viscosity index improver and (A-2) weight average molecular weight (polystyrene conversion) are 300,000 or more and 900,000 or less, and a weight average molecular weight / number average molecular weight is 1.0 or more and 1.5 or less. One or more selected from polymethacrylate viscosity index improvers are used. In addition, the weight average molecular weight (Mw) and the number average molecular weight (Mn) in this invention are standard polystyrene conversion for molecular weight calculation measured by the gel permeation chromatography (GPC).

  The viscosity index improver (A-1) has an Mw of 20,000 or more and 100,000 or less, preferably 25,000 or more and 100,000 or less, more preferably 30,000 or more and 100,000 or less. Mw / Mn is 1.5 or more and 2.2 or less, preferably 1.6 or more and 2.2 or less. If the Mw is less than 20,000, a sufficient viscosity index improvement effect cannot be obtained, and if it exceeds 100,000, sufficient shear stability cannot be obtained, and shear resistance is lowered by long-term use, resulting in wear resistance. -Seizure is reduced and sufficient component durability cannot be ensured. Even if the above Mw range is satisfied, if Mw / Mn is out of the above range, it is difficult to obtain the viscosity index and kinematic viscosity of the lubricating oil composition defined in the present invention. Even if it can be adjusted to the viscosity index and kinematic viscosity of the composition, the blending amount of (A-1) becomes too much, and as a result, it undergoes shearing in a long-term use and lowers its viscosity, thereby reducing wear and seizure. Performance will deteriorate, making it difficult to ensure sufficient component durability.

  The viscosity index improver (A-2) has an Mw of 300,000 or more and 900,000 or less, preferably 350,000 or more and 900,000 or less, more preferably 400,000 or more and 500,000 or less. Further, Mw / Mn is 1.0 or more and 1.5 or less, preferably 1.0 or more and 1.4 or less. If the Mw is less than 300,000, a sufficient viscosity index improvement effect cannot be obtained, and if it exceeds 900,000, sufficient shear stability cannot be obtained, and shear resistance is lowered by long-term use, resulting in wear resistance. -Seizure is reduced and sufficient component durability cannot be ensured. Further, even if the above Mw range is satisfied, when Mw / Mn deviates from the above range, it is difficult to obtain the viscosity index and kinematic viscosity of the lubricating oil composition defined in the present invention, and the composition defined in the present invention. Even if the viscosity index and kinematic viscosity of the product can be adjusted, the blending amount of (A-2) becomes too large. As a result, it becomes difficult to ensure sufficient component durability.

  The blending amount of the polymethacrylate viscosity index improver (A-1) or (A-2) is 5% by mass to 20% by mass, more preferably 7% by mass to 18% by mass with respect to the total amount of the lubricating oil composition. % Or less, more preferably 6 mass% or more and 17 mass% or less. If the blending amount is less than 5% by mass, it is difficult to obtain the viscosity index and kinematic viscosity of the composition defined in the present invention, and if it exceeds 20% by mass, the effect of shearing from the machine is likely to occur, and the viscosity should be lowered by long-term use. As a result, wear resistance and seizure resistance are reduced, and sufficient component durability cannot be ensured.

  The polymethacrylate viscosity index improver of (A-1) or (A-2) has a structure having a polymer of methacrylic acid ester shown as an example in the following general formula (5), and the monomer is methacrylic acid ester. Even if the monomer is a polymer only, the monomer may be a copolymer of a methacrylic acid ester and another monomer, or may contain a polymer compound other than polymethacrylate in a part of the structure As long as it has a specific property that achieves the object of the present invention, it can be used without being limited to its product category.

In formula (5), R ⁹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and k is an integer of 1 or more.

  The polymethacrylate viscosity index improver used in the present invention is an amino group or a sulfonic acid group in the molecule in order to further improve fuel economy by maintaining the initial high friction coefficient in the wet friction material for a long period of time. It is preferable to use a “non-dispersed type” having no polar group such as

In addition, the above (A-2) is preferably a so-called “star polymer” in which seven or more arm polymers are branched from the central portion of the polymer serving as a nucleus. By using a polymer having seven or more arm polymers, it tends to be easy to obtain a high viscosity index and a suppression of a decrease in viscosity due to permanent shear.
Moreover, the viscosity index improver of (A-1) or (A-2) may be used individually by 1 type, or may use 2 or more types together. (A-1) and (A-2) may be used in combination. In addition, when using 2 or more types together, the total compounding quantity needs to be the said range.

[3] Basic calcium sulfonate and basic calcium phenate (component (B))
In the present invention, one or more selected from basic calcium sulfonate and basic calcium phenate is blended in an amount of 450 mass ppm to 700 mass ppm in terms of calcium amount with respect to the total amount of the lubricating oil composition. Basic calcium sulfonate and basic calcium phenate have an effect of preventing wear of parts, which is likely to be a problem when the viscosity of the composition is lowered for improving fuel efficiency. Further, these increase the coefficient of static friction in the wet friction material of the clutch and the friction between metals between the belt and the pulley, and as a result, have the effect of improving the slip prevention property and fuel efficiency of the clutch. However, when the blending amount of the component (B) is too large, a shock at the time of clutch engagement is likely to occur, and the dynamic friction coefficient of the clutch wet friction material is difficult to maintain for a long period of time. From such a viewpoint, in the present invention, at least one compounding amount selected from basic calcium sulfonate and basic calcium phenate is 450 mass ppm or more and 700 mass ppm in terms of calcium amount with respect to the total amount of the lubricating oil composition. The ratio is as follows. This blending amount is preferably 450 mass ppm or more and 650 mass ppm, more preferably 480 mass ppm or more and 600 mass ppm or less.

Specific examples of the basic calcium sulfonate include the following general formulas (2) and (3).

In the above formulas (2) and (3), R ⁴ and R ⁵ each represent a hydrogen atom or an alkyl group having 1 to 30 carbon atoms, preferably an alkyl group having 6 to 18 carbon atoms, and there are a plurality of them. When doing so, they may be the same or different. n is an integer of 1 to 4.

Specific examples of the basic calcium phenate include the following general formula (4).

In the above formula (4), R ⁷ and R ⁸ represent a hydrogen atom or an alkyl group having 1 to 30 carbon atoms, preferably an alkyl group having 6 to 18 carbon atoms. They may be the same or different. X of Sx is 1 or 2, and preferably 1. These may be used alone or as a mixture of two or more as necessary.
Further, calcium sulfonate and calcium phenate may be used in combination.

  In addition, if it is a small amount within the range not impairing the performance of the present invention, it contains alkali metals and alkaline earth metals other than calcium, for example, sulfonates and phenates such as magnesium, barium and sodium, and salicylates of alkali metals and alkaline earth metals. You may do it.

  The basic calcium sulfonate and the basic calcium phenate preferably have a base number of 150 mgKOH / g or more measured by the perchloric acid method of JIS K2501. By setting the base number to 150 mgKOH / g or more, it is easy to obtain a high friction coefficient and a high intermetal friction coefficient in the wet friction material of the clutch. The base number is preferably 200 mgKOH / g or more, more preferably 250 mgKOH / g or more. Even if the base number is too high, there is no particular inconvenience, but those which are usually readily available are those up to about 500 mgKOH / g.

[4] Compound represented by general formula (1) (component (C))
The lubricating oil composition of the present invention preferably further contains a compound represented by the following general formula (1) in order to improve shock during clutch engagement.

In the general formula (1), R ¹ is an alkyl group having 1 to 20 carbon atoms, and preferably an alkyl group having 8 to 16 carbon atoms.

  The compound represented by the general formula (1) has an effect of improving the shock at the time of clutch engagement, and has been conventionally formulated for the purpose of improving the shock at the time of clutch engagement of a continuously variable transmission lubricant. It becomes possible to suppress the blending of friction modifiers such as amide compounds, amine compounds and alcohol compounds. The compound represented by the general formula (1) reduces the static friction coefficient in the wet friction material of the clutch and the metal-to-metal friction coefficient in the belt-pulley, as in the conventional friction modifier as described above. In addition, the dynamic friction coefficient of the wet friction material of the clutch can be maintained for a long time, and the shock at the time of clutch engagement can be improved while ensuring the effect of improving the fuel efficiency.

  The compounding quantity of the compound represented by General formula (1) is 0.1 mass% or more and 5.0 mass% or less with respect to lubricating oil composition whole quantity, Preferably it is 0.2 mass% or more and 2.0 mass%. Hereinafter, it is more preferably 0.5% by mass or more and 2.0% by mass or less. In order to obtain a good shock improvement effect at the time of clutch engagement, it is preferably blended in an amount of 0.1% by mass or more, and from the viewpoint of compatibility with organic materials, it is preferably 5.0% by mass or less.

[5] The lubricating oil composition of the properties present invention compositions may kinematic viscosity at 100 ° C. is not more than 6.5 mm ² / s or more 7.4 mm ² / s, and is the viscosity index of 205 or more It is essential.
The range of this kinematic viscosity is not greatly reduced compared to the conventional kinematic viscosity, but at the same time by setting the viscosity index to 205 or more, the room temperature range (about 20 ° C. to about 80 ° C.) or the low temperature range (about The viscosity at 0 ° C. to about −40 ° C. can be kept lower than that of conventional lubricating oils for continuously variable transmissions, and as a result, fuel efficiency can be improved in all temperature ranges. And since it is not greatly reduced in viscosity compared to the conventional kinematic viscosity, and because it uses a specific viscosity index improver, it has good shear stability and can suppress wear resistance and seizure resistance due to viscosity reduction. Long-term component durability can be secured. A higher viscosity index is desirable, but in order to increase the viscosity index, there are many cases where the amount of the viscosity index improver is increased, resulting in poor shear stability and wear resistance due to a decrease in viscosity. The seizure may be deteriorated. Therefore, about 270 or less is a realistic upper limit value.
The Brookfield viscosity (BF viscosity) at −40 ° C. is preferably less than 10,000 mPa · s from the viewpoint of fuel economy.

[6] Other additives In addition to the above-mentioned components, the lubricating oil for continuously variable transmission of the present invention may contain known additives such as an ashless dispersant, an oily agent, an antiwear agent, Extreme pressure agents, rust inhibitors, friction modifiers, antioxidants, corrosion inhibitors, metal deactivators, pour point depressants, antifoaming agents, colorants, package additives for automatic transmission oils, or any of these Various lubricating oil package additives containing at least one kind can be added. However, depending on the type of the friction modifier, there is a case where the friction coefficient is lowered to affect the fuel saving effect. Therefore, it is desirable to select one that does not interfere with the fuel saving effect or to suppress the blending amount as much as possible.

  Examples of the ashless dispersant include alkenyl succinimides, alkenyl succinates, amides of long chain fatty acids and polyamines (aminoamide type), and boride derivatives thereof. Examples of oil agents include oleic acid, stearic acid, higher alcohols, amines, esters, sulfurized fats and oils, acidic phosphate esters, and acidic phosphite esters. Examples of the antiwear agent include dithiophosphate metal salts, thiophosphate metal salts, sulfur compounds, phosphate esters, phosphite esters, acidic phosphate esters and amine salts thereof. Examples of extreme pressure agents include hydrocarbon sulfides, sulfurized fats and oils, zinc dithiophosphate, phosphate esters, phosphite esters, chlorinated paraffins, and chlorinated diphenyls. Examples of the rust inhibitor include carboxylic acid and its amine salt, ester, sulfonate, boron compound and the like. Examples of the friction modifier include organic molybdenum compounds, polyhydric alcohol partial esters, amines, amides, sulfurized esters, phosphate esters, acidic phosphate esters and amine salts thereof. Examples of the antioxidant include amine-based, phenol-based, and sulfur-based antioxidants. Examples of the corrosion inhibitor include benzotriazole and alkenyl succinate. Examples of the pour point depressant include polymethacrylate and polybutene. Examples of the antifoaming agent include silicon compounds, fluorosilicon compounds, ester-based compounds, and the like.

  Next, although an Example and a comparative example demonstrate further in detail, this invention is not specifically limited to these Examples.

  Lubricating oil for continuously variable transmissions, using the following base oils mixed in the ratios shown in Tables 1 and 2 and the following additives in the ratios shown in Tables 1 and 2 (mixing ratios relative to the total amount of the composition). A composition was prepared.

<Base oil>
Base oil A: hydrorefined base oil (pour point: −50 ° C., viscosity index: 105, sulfur content: 0.0001 mass%, 100 ° C. kinematic viscosity: 3 mm ² / s)
Base oil B: hydrorefined base oil (pour point: −12 ° C., viscosity index: 124, sulfur content: 0.0006 mass%, 100 ° C. kinematic viscosity: 6 mm ² / s)
Base oil C: hydrorefined base oil (pour point: −12 ° C., viscosity index: 124, sulfur content: 0.0002 mass%, 100 ° C. kinematic viscosity: 4 mm ² / s)

<Additives>
Package additive 1: Package additive for continuously variable transmission oil (contains 0.5% by mass of calcium content of basic calcium sulfonate having a base number of 300)
Package additive 2: Basic calcium sulfonate excluded from package additive 1Sulfonate: Basic calcium sulfonate (base number 300, calcium content: 11 mass%)
- Formula (1) compound represented by: the formula (1), those ^{wherein R 1} an alkyl group of 12 carbon atoms, PMA1: weight average molecular weight (Mw) in the 35,000 Mw / Mn is 1. 8 non-dispersed polymethacrylate viscosity index improver PMA2: non-dispersed polymethacrylate viscosity index improver with a weight average molecular weight (Mw) of 98,000 and Mw / Mn of 2.1 PMA3: weight Non-dispersed polymethacrylate viscosity index improver with an average molecular weight (Mw) of 93,000 and Mw / Mn of 2.5. PMA4: Weight average molecular weight (Mw) of 440,000 and Mw / Mn of 1.2 A non-dispersible polymethacrylate viscosity index improver that is a star polymer having 7 or more arms. PMA5: A dispersed polymer having a weight average molecular weight (Mw) of 300,000 and Mw / Mn of 1.7. Remethacrylate viscosity index improver / pour point depressant

  Measurement of each property of the composition, evaluation of wear resistance, evaluation of shear stability, evaluation of friction characteristics with a wet friction material, and evaluation of the coefficient of friction between the element and the pulley were performed as follows.

(1) Property measurement of composition 100 degreeC kinematic viscosity, 0 degreeC kinematic viscosity, and the viscosity index were measured by the JISK2283 kinematic viscosity test method. In the temperature range from 100 ° C. to 0 ° C., the temperature and the viscosity are generally linear on the ASTM diagram. When the viscosity at 100 ° C. is about 7 mm ² / s, the viscosity at 0 ° C. is low. Since the viscosity in the normal temperature range (about 20 ° C. to about 80 ° C.) also decreases, the viscosity at 0 ° C. was used as an index of the normal temperature range viscosity. The lower the viscosity, the lower the room temperature viscosity.
Moreover, the high temperature high shear viscosity (HTHS viscosity) measured the viscosity in 150 degreeC and 1 * 10 < ⁶ > s < ^-1 > using the TBS viscometer based on ASTMD4683. The HTHS viscosity is an index of oil film retention. The larger this value, the better the oil film retention.

(2) Wear resistance evaluation between belt and pulley As wear resistance evaluation, the wear width of the block after sliding for 30 minutes with a load of 1112 N was measured according to the high surface pressure method of JASO M358. The smaller this value, the better the wear resistance and the better the component durability. This made 0.9 mm or less a pass.

(3) Shear stability evaluation It carried out based on JASO M347-05. The criterion for determination was a rate of viscosity reduction at 100 ° C. of 10% or less. When the viscosity reduction rate exceeds 10%, there is a concern about abnormal wear or component damage.

(4) Friction characteristic evaluation with wet friction material SAE No. defined in the automobile standard JASO M348 “Automatic transmission oil friction characteristic test method” of the Japan Society of Automotive Engineers. 2 The friction characteristics of the wet friction material were examined using a test apparatus. That is, 5000 cycles of the test were performed by the JASO method, and the friction characteristics of the wet friction material were determined from the friction coefficients μ0, μd, and μt measured under the following measurement conditions in the cycle specified by JASO M348. Evaluated by criteria.

<Measurement conditions for each coefficient of friction>
・ Μd:
After the friction disk is rotated at a constant speed of 3600 rpm, the drive power of the motor for dynamic friction test is turned off, and at the same time a pressing load is applied to brake the inertia disk with the friction torque generated by the friction disk and the steel plate. This is a dynamic friction coefficient value calculated by the equation (x) with the friction torque Td when the rotation speed reaches 1800 rpm as the friction torque T of the following equation (x).

・ Μ0:
This is a dynamic friction coefficient value calculated by the equation (x) with the maximum torque T0 at 200 rpm or less immediately before the friction plate stops as the friction torque T of the following equation (x).

・ Μt:
After applying the pushing load and sandwiching the friction disk and steel plate, the friction plate is rotated at a constant speed of 0.7 rpm, and the stable torque Tt after 2 seconds from the start of rotation is expressed as the friction torque T of the following formula (x) ( It is a static friction coefficient value calculated in x).

μ: friction coefficient T: friction torque (Nm)
n: number of friction discs re: average friction effective radius P: pressing load A: friction area

<Evaluation criteria for friction characteristics of wet friction materials>
・ Maximum value of μ0 / μd:
Index of shock when wet friction materials are combined. The lower this value, the smaller and better the shock at the time of binding, and 1.07 or less was accepted.
・ Minimum value of μt (Coefficient of static friction):
An indicator of power transmission in wet friction materials. The higher this value, the better the transfer torque capacity with the wet friction material, and 0.125 or more was considered acceptable.
・ Μd change rate:
Index of friction characteristic stability (dynamic friction coefficient stability) in a wet friction material obtained by the following formula (y). The smaller this value, the more stable and good the friction characteristics with the wet friction material were, and 7% or less was acceptable.

(5) Evaluation of friction coefficient between belt and pulley between metals It was carried out according to JASO M358.
The evaluation was performed by the high surface pressure method, and the friction coefficient μ at a sliding speed of 0.25 m / s was measured. The higher this value, the better the transmission torque capacity between the belt and the pulley, and a value of 0.135 or higher was accepted.
Tables 1 and 2 show the results of Examples and Comparative Examples, respectively.

  By said Examples 1-4, in this invention, a specific viscosity index improver and a metal type detergent are mix | blended, and the property of a composition is made into a specific property, A low temperature region viscosity and a high temperature region viscosity It can be seen that good fuel economy and durability of parts can be secured. Moreover, it turns out that Examples 1-3 containing the compound of General formula (1) have improved the friction characteristic of the wet friction material, ensuring favorable fuel-saving property and component durability.

On the other hand, in Comparative Example 1 in which the Mw / Mn of the (A-1) component of the polymethacrylate viscosity index improver is out of the range of the present invention, the viscosity index is low and the low temperature range viscosity is high. In Comparative Example 2 in which Mw / Mn of the component (A-2) of the polymethacrylate viscosity index improver is outside the scope of the present invention, the shear stability is poor. Further, in Comparative Example 2, since the polymethacrylate viscosity index improver is a dispersion type, the friction characteristics in the wet friction material are inferior.
Moreover, in Comparative Example 3 where the composition has a high kinematic viscosity at 100 ° C., the viscosity in the low temperature range is high and the fuel economy is poor. On the other hand, in Comparative Example 4 having a low kinematic viscosity at 100 ° C. and a low viscosity index, the HTHS viscosity is low, the high temperature region viscosity cannot be ensured, and the wear resistance is poor.
Moreover, in Comparative Example 5 containing no basic calcium sulfonate, the wear resistance is inferior. Further, in Comparative Example 5 containing no basic calcium sulfonate, in addition to the above-described reduction in wear resistance, the static friction coefficient and the intermetallic friction coefficient are also inferior.
On the other hand, in Comparative Example 6 containing an excessive amount of basic calcium sulfonate, the wear resistance is good, but the friction characteristics in the wet friction material are inferior.

Claims (3)

A lubricating oil composition comprising:
Lubricating base oil,
(A-1) A polymethacrylate viscosity index improver having a weight average molecular weight (in terms of polystyrene) of 20,000 to 100,000 and a weight average molecular weight / number average molecular weight of 1.5 to 2.2. A-2) It is selected from polymethacrylate viscosity index improvers having a weight average molecular weight (polystyrene conversion) of 300,000 to 900,000 and a weight average molecular weight / number average molecular weight of 1.0 to 1.5. 1 type or more and 5 mass% or more and 20 mass% or less with respect to this lubricating oil composition whole quantity,
(B) one or more selected from basic calcium sulfonate and basic calcium phenate, 450 mass ppm or more and 700 mass ppm or less in terms of calcium amount with respect to the total amount of the lubricating oil composition,
A lubricating oil composition for a continuously variable transmission, wherein the lubricating oil composition has a kinematic viscosity at 100 ° C of 6.5 to 7.4 mm ² / s and a viscosity index of 205 or more. The lubricating base oil is
(X) a base oil component having a kinematic viscosity at 100 ° C. of 1.5 to 3.5 mm ² / s, a pour point of −30 ° C. or less, a viscosity index of 100 or more, and a sulfur content of 0.01% by mass or less;
(Y) a base oil component having a kinematic viscosity at 100 ° C. of 4.0 to 8.0 mm ² / s, a viscosity index of 120 or more, and a sulfur content of 0.01% by mass or less;
2. The lubricating oil composition for continuously variable transmission according to claim 1, wherein the content ratio of the (X) with respect to the total amount of the base oil is 20 to 80% by mass. The (A-1) or (A-2) polymethacrylate viscosity index improver is a non-dispersed viscosity index improver,
(C) The compound represented by the following general formula (1) is further contained in an amount of 0.1% by mass or more and 5.0% by mass or less based on the total amount of the lubricating oil composition. The lubricating oil composition for continuously variable transmission according to claim 2.

(In formula (1), R ¹ represents an alkyl group having 1 to 20 carbon atoms.)