JP5248022B2 - Lubricating oil composition for automatic transmission - Google Patents

Description

The present invention relates to a lubricating oil composition for an automatic transmission that can achieve both fuel economy and component durability while maintaining an initial viscosity that affects the wear at the beginning of traveling.

In recent years, vehicle lubricating oils are in the direction of lower viscosity than conventional viscosities in order to reduce stirring resistance in consideration of fuel saving. Even in lubricating oil for automatic transmissions, it is said that by reducing the viscosity, stirring resistance of a torque converter, an oil pump or the like is reduced, and this is effective in improving fuel efficiency (see, for example, Patent Document 1).
However, lowering the viscosity of an automatic transmission fluid may affect wear resistance and component durability, and therefore, a viscosity index improver having a low molecular weight often plays a role in maintaining its performance. For example, by using a viscosity index improver having a weight average molecular weight (Mw) of 40,000 or less, the viscosity characteristics can be maintained over a long period of time (see Patent Document 2), or a viscosity modifier having a specific molecular weight range can be used. By selecting, the low temperature viscosity characteristic affecting low temperature operability and the high temperature viscosity affecting wear are simultaneously improved (see Patent Document 3).

Currently, automatic transmission oils on the market generally have kinematic viscosities at 7.0 ° C. between 7.0 mm ² /9.0 mm ² / s, and many automatic transmissions have this general viscosity. It is designed to use automatic transmission fluid. This is because it is known that ensuring the high temperature viscosity of automatic transmission fluids will prevent wear and ensure the durability of parts, so in many automatic transmissions, the viscosity is significantly lower than the general viscosity. The use of automatic transmission oil is thought to be due to concerns about the deterioration of wear resistance. In particular, since there is a concern about deterioration of initial wear that occurs at a relatively early fitting stage in the sliding portion, it is considered that a higher viscosity is desirable in the initial fitting stage.

On the other hand, since a high initial viscosity reduces fuel efficiency at the initial familiarization stage, an appropriate initial viscosity is required for automatic transmission fluid. Furthermore, it is desirable that the viscosity of the automatic transmission fluid rapidly decreases within a range in which the durability of the parts is ensured in order to quickly exhibit better fuel economy after initial familiarity. And it is necessary to maintain the viscosity for a long time.
As described above, as an automatic transmission oil that imparts fuel saving performance to many automatic transmissions, it is necessary to maintain an initial viscosity that responds to initial running-in and exhibits fuel saving performance, and to exhibit high fuel saving after initial running-in. It is required to maintain viscosity in order to ensure quick and appropriate viscosity reduction and long-term component durability. However, an automatic transmission oil having both of these has not been obtained.

JP 2004-169025 A JP 2004-155873 A Special table 2002-509182 gazette

The present invention provides an automatic transmission oil composition that quickly decreases in viscosity while maintaining an appropriate initial viscosity and maintains the viscosity for a long period of time, thereby obtaining fuel saving performance in many automatic transmissions on the market. The purpose is to provide.

As a result of diligent research in view of the above situation, the present inventor has formulated a conventional lubricating oil composition for automatic transmissions by combining two specific viscosity index improvers in combination with a base oil having specific properties. It has been found that it is possible to obtain a lubricating oil for an automatic transmission capable of achieving both fuel saving and long-term component durability at the time of long-term use by maintaining the initial viscosity and rapidly decreasing the viscosity, which is difficult with conventional products.

That is, the present invention comprises (A) a mineral oil base oil of 70% by mass or more, a base oil having a kinematic viscosity at 40 ° C. of 9 to ²⁰ mm ² / s, and (B) a weight average molecular weight (polystyrene conversion) of 15 0.5 to 20 % by mass of a polymethacrylate viscosity index improver that is 1,000 to 70,000, and (C) a polymethacrylate viscosity index improver that has a weight average molecular weight of 100,000 to 500,000. 5 to 15 % by mass, the content ratio of the component (B) to the component (D) (C) is 3 to 10 by mass ratio, and (E) the kinematic viscosity at 100 ° C. of the composition is 5.2 to 6 A lubricating oil composition for an automatic transmission, characterized in that it is 0.5 mm ² / s, (F) has a viscosity index of 180 or more, and has a BF viscosity at −40 ° C. of 5,000 to 8,900 mPa · s. Is to provide.

The lubricating oil composition for an automatic transmission according to the present invention is based on the synergistic effect of the base oil as the component (A), the component (B), and the two polymethacrylate viscosity index improvers as the component (C). It is possible to combine maintenance of the initial viscosity, which has been considered difficult, and influence on wear at the initial stage of travel, fuel saving and component durability.
Further, the lubricating oil composition for an automatic transmission according to the present invention is applied to AT (Automatic Transmission), CVT (Continuously).
VARIABLE TRANSMISSION (continuous transmission), other automatic transmissions for vehicles with wet clutches, power steering, hydraulic actuators for general work, fluid couplings, etc., especially for devices that generate viscosity drop due to shear Thus, the performance is good and the environmental load can be reduced from the initial use to the long-term use.

In the present invention, as component (A), a base oil containing 70% by mass or more of a mineral oil base oil and having a kinematic viscosity at 40 ° C. of 9 to ²⁰ mm ² / s is used. By setting the kinematic viscosity at 40 ° C. to 9 to ²⁰ mm ² / s, it is possible to obtain the desired lubrication characteristics as a lubricating oil for automatic transmissions. The kinematic viscosity at 40 ° C. is more preferably 9 to 14 mm ² / s.
As the base oil, a mineral base oil, a synthetic base oil or a mixture thereof is used.

As the mineral base oil, any refining method or treatment may be used as long as it satisfies the above properties, and the production method is not limited, but hydrorefined mineral oil, catalyst isomerized oil, etc. A highly refined paraffinic mineral oil (high viscosity index mineral oil base oil) obtained by subjecting to a treatment such as solvent dewaxing or hydrodewaxing is preferably used. In addition to the above, mineral base oils obtained by various production methods can be used, for example, raffinate obtained by solvent purification using an aromatic extraction solvent such as phenol and furfural for mineral oil-based lubricating oil raw materials, Examples thereof include hydrotreated oils obtained by hydrotreating using a hydrotreating catalyst such as cobalt or molybdenum using silica-alumina as a carrier, and examples include 100 neutral oil, 150 neutral oil, and 500 neutral oil. be able to. These mineral oil-based base oils may be used alone or in combination of two or more at any ratio as long as the properties defined in the present application are satisfied.

Synthetic lubricating base oils include, for example, isoparaffins, poly-α-olefin oligomers, polybutenes, alkylbenzenes, polyol esters, polyglycol esters, dibasic acid esters, phosphate esters synthesized from natural gas such as methane. And silicon oil.
(A) As long as the base oil of a component satisfy | fills the property prescribed | regulated by this application, you may use 1 type each of mineral base oil and synthetic base oil individually, and mix and mix 2 or more types in arbitrary ratios. It may be used.

The component (A) which is the base oil component of the present invention is a mixture of one or more synthetic lubricant base oils with one or more mineral oil base oils described above. Can be used. From the viewpoint of the solubility of the additive, at least 70% by mass or more of the mineral oil base oil is contained in the component (A) .

In the present invention, a polymethacrylate viscosity index improver (hereinafter sometimes referred to as PMA viscosity index improver) having a weight average molecular weight (Mw) of 15,000 to 70,000 is used as the component (B). The weight average molecular weight (Mw) in the present invention is a standard polystyrene conversion for molecular weight calculation measured by gel permeation chromatography (GPC).

The PMA-based viscosity index improver may be a dispersion type as exemplified in Formula (1) or a non-dispersion type as exemplified in Formula (2) as long as Mw is 15,000 to 70,000. It is well selected without any particular restrictions. Further, it may contain a polar monomer unit such as a nitrogen compound or polyalkylene glycol ester, or may contain an element component other than hydrocarbon. Further, even if a part of the structure is a polymer compound other than polymethacrylate, most of the polymer is polymethacrylate, which is generally used as a PMA viscosity index improver, and the object of the present invention is If it has the specific property to achieve, it can be used, without being restrict | limited to the goods classification. The majority of the polymer is preferably polymethacrylate, and the proportion of methacrylate units is preferably 80 mol% or more of the whole polymer.

If the Mw of the PMA viscosity index improver in the present invention is 15,000 to 70,000, the desired performance can be obtained, but preferably 20,000 to 60,000, more preferably 20,000. ~ 55,000. By setting Mw to 15,000 or more, the viscosity index improvement effect required for the lubricating oil for automatic transmission can be obtained. Moreover, by setting Mw to 70,000 or less, it is stable in the initial stage and in the long term against the shear received from the machine. The content of the component (B) is 0.5 to 20 wt%, more preferably from 3 to 20 mass%. If it is less than 0.5% by mass, it is unstable to shear from the machine in any of the initial, medium and long term, even if the component (C) is added in an amount sufficient to improve the viscosity index. Therefore, if the amount exceeds 30% by mass, it is stable against shear received from the machine, and therefore, sufficient viscosity reduction does not occur after initial conforming.

（式中、Ｒ^１は水素原子又は炭素数１〜２０のアルキル基である。ｋは1以上の整数である。）

(In the formula, R ¹ is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. K is an integer of 1 or more.)

（式中、Ｒ^１は水素原子又は炭素数１〜２０のアルキル基であり、Ｒ^２はＨ又はＣＨ_３であり、Ｘはアミノ基、エステル基又はスルホン酸基である。ｍ及びｎは１以上の整数である。）

(Wherein R ¹ is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, R ² is H or CH ₃ , X is an amino group, an ester group or a sulfonic acid group. M and n are 1) (It is an integer above.)

In the present invention, a polymethacrylate viscosity index improver having a weight average molecular weight (Mw) of 100,000 to 500,000 is used as the component (C). The PMA-based viscosity index improver may be a dispersion type as exemplified in Formula (1) or a non-dispersion type as exemplified in Formula (2) as long as Mw is 100,000 to 500,000. It is well selected without any particular restrictions. Further, it may contain a polar monomer unit such as a nitrogen compound or polyalkylene glycol ester, or may contain an element component other than hydrocarbon. Further, even if a part of the structure is a polymer compound other than polymethacrylate, most of the polymer is polymethacrylate, which is generally used as a PMA viscosity index improver, and the object of the present invention is If it has the specific property to achieve, it can be used, without being restrict | limited to the goods classification.

If the Mw of the PMA viscosity index improver in the present invention is 100,000 to 500,000, the desired performance can be obtained, but preferably 120,000 to 500,000, more preferably 120,000. ~ 450,000. By setting Mw to 100,000 or more, fuel saving performance during long-term use can be imparted. Moreover, the solubility with respect to base oil is favorable because Mw shall be 500,000 or less.
The content of component (C) is 0.5 to 15 wt%, more preferably from 1 to 15 wt%. If it is less than 0.5% by mass, even if blending the component (B) in such an amount that a sufficient effect of improving the viscosity index is obtained, it is not preferable because an appropriate decrease in viscosity cannot be obtained in the medium and long term, If it exceeds 30% by mass, the effect of shearing from the machine tends to occur, and the viscosity retention during long-term use deteriorates.

The PMA viscosity index improver of component (B) and component (C) is a copolymer of various alkyl methacrylates in which R ¹ is an alkyl group having 1 to 20 carbon atoms in formula (1) and formula (2). There may be.
Further, the raw material monomers and chemical structures of the component (B) and the component (C) may be the same or different, but the difference in the weight average molecular weight (Mw) between the component (B) and the component (C) is 30, More than 000 is preferable, more preferably 40,000 or more, and most preferably 50,000 or more. In addition, the PMA viscosity index improvers of the component (B) and the component (C) used in the present invention have the polymethacrylate structure for achieving the object of the present invention. Without limitation, any material that is generally used as a viscosity index improver (polymer) for lubricating oils can be used. As the viscosity index improver, olefin copolymer (OCP) is also used in engine oils and the like, but in the present invention, it cannot be used because the low-temperature viscosity deteriorates.
The (B) component and the (C) component PMA year index improver may be used alone or in combination of two or more.

The lubricating oil composition for an automatic transmission according to the present invention has a kinematic viscosity at 100 ° C. of 5.2 to 6.5 mm ² / s, preferably 5.8 to 6.5 mm ² / s. The index is 180 or more. If the kinematic viscosity is less than 5.2 mm ² / s, there is a concern about deterioration of initial wear due to low viscosity, which is not preferable. On the other hand, if it exceeds 6.5 mm ² / s, the fuel saving performance in the initial stage of travel cannot be obtained, which is not preferable. On the other hand, when the viscosity index is less than 180, the viscosity in the normal temperature region increases, so the fuel saving performance is lowered, which is not preferable. There is no upper limit to the viscosity index, but in practice it is often 230 or less. Moreover, the BF viscosity at -40 ℃ from the response at the time of low temperature, or less 8,900 mPa · s, the lower limit of the BF viscosity at -40 ℃ is 5,000 mPa · s or more.

Moreover, as total amount of (B) and (C) component in this invention , Preferably it is 4-20 mass%, Most preferably, it is 5-15 mass%. By setting it within this range, it is possible to obtain both the effect of further preventing wear and fuel saving.
In the present invention, the content ratio of the component (B) to the component (C), that is, the ratio of the content of the component (B) / the content of the component (C) is 3 to 10 in terms of mass ratio, and is particularly preferable. Is 4-7. By setting it within this range, it is possible to obtain an effect of achieving both further fuel saving and component durability.

In addition to the components (A), (B) and (C), the lubricating oil for automatic transmissions according to the present invention may contain known additives such as ashless dispersants, metal detergents as necessary. , Oiliness agent, antiwear agent, extreme pressure agent, rust inhibitor, friction modifier, antioxidant, corrosion inhibitor, metal deactivator, pour point depressant, antifoaming agent, colorant, for automatic transmission oil A package additive or a package additive for various lubricating oils containing at least one of them can be added.

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 metal detergents include neutral, basic, and overbased sulfonates, phenates, salicinates, phosphonates, and the like. 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.
The lubricating oil composition for an automatic transmission of the present invention can be produced by blending and mixing the above component (A), component (B) and component (C), and if necessary, the above additives. .

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

(Examples 1-3)
The following base oils and additives were mixed in the blending amounts shown in Table 1 to prepare a lubricating oil composition for an automatic transmission. Table 1 shows the performance characteristics of the obtained lubricating oil composition for automatic transmissions. The blending was carried out so that the composition had a 100 ° C. viscosity of 6.0 to 6.4 mm ² / s and a viscosity index of 180 or more.
(Comparative Examples 1-5)
In the same manner as in the examples, the following base oils and additives were mixed in the blending amounts shown in Table 2 to prepare a lubricating oil composition for an automatic transmission. Table 2 shows performance characteristics of the obtained lubricating oil composition for automatic transmissions.

<Base oil>
Base oil A: Hydrogenated refined paraffin base oil with 40 ° C. viscosity of 10 mm ² / s Base oil B: Hydrogenated refined paraffin base oil with 40 ° C. viscosity of 15 mm ² / s Base oil C: Highly refined Base oil D with mineral oil base oil and 40 ° C. viscosity of 11 mm ² / s D: Highly refined mineral oil base oil with 40 ° C. viscosity of 20 mm ² / s Base oil E: Poly-α-olefin with 40 ° C. viscosity 17 mm ² / s

<Additives>
Additive F: Package additive for automatic transmission oil (substantially free of viscosity index improver)
Additive G: Non-dispersed PMA viscosity index improver with a weight average molecular weight (Mw) of 20,000 Additive H: Non-dispersed PMA viscosity index improver with a weight average molecular weight (Mw) of 52,000 Additive I: Dispersed PMA viscosity index improver additive having a weight average molecular weight (Mw) of 150,000 J: Non-dispersed PMA viscosity index improver having a weight average molecular weight (Mw) of 450,000 Agent K: Dispersed PMA viscosity index improver having a weight average molecular weight (Mw) of 400,000 * The molecular weights (Mw) of additives G, H, I, J, and K are converted to standard polystyrene for molecular weight calculation. It is.

Test method:
The test was conducted by the following three test methods with different shear levels as an evaluation of the shear stability assuming a long-term use after an initial familiar phase and an intermediate familiar phase.

(1) Shear stability test 1:
It implemented based on JPI-5S-29-88. Ultrasonic irradiation was performed under the following test conditions to determine the rate of decrease in viscosity at 100 ° C. This test has the lowest shear level among the three types of shear tests, and serves as an index of viscosity reduction at the initial familiarization stage. The smaller the 100 ° C. viscosity reduction rate, the better the viscosity retention at the beginning of running.
The ultrasonic output and irradiation time of the test conditions were as follows.
Ultrasonic output: An output that reduces the viscosity at 40 ° C. by 15% by irradiating ASTM standard oil A with ultrasonic waves for 10 minutes.
Irradiation time: 30 minutes

(2) Shear stability test 2:
It carried out according to JASO M347-05. Ultrasonic irradiation was performed under the following test conditions to determine the rate of decrease in viscosity at 100 ° C. This test is an intermediate shear level among the three types of shear tests, and serves as an index of viscosity reduction during the medium term use after familiarization. The criterion for determining the rate of decrease in viscosity at 100 ° C. was 9 to 15%. If the viscosity reduction rate is less than 9%, a rapid viscosity reduction after fitting cannot be expected, and if the viscosity reduction rate exceeds 15%, there is a concern about abnormal wear or component damage.
The ultrasonic output and irradiation time of the test conditions were as follows.
Ultrasonic output: Output that reduces the viscosity at 100 ° C. by 30% by irradiating ASTM standard oil A with ultrasonic waves for 10 minutes,
Irradiation time: 60 minutes

(3) Shear stability test 3:
It implemented based on CEC-L-45-A-99. It implemented on the following test conditions and calculated | required the decreasing rate of 100 degreeC viscosity. This test has the highest shear level among the three types of shear tests, and serves as an index for viscosity reduction during long-term use. The criterion for determining the rate of decrease in viscosity at 100 ° C. was 9 to 15%. When the viscosity reduction rate is less than 9%, sufficient fuel saving performance cannot be expected, and when the viscosity reduction rate exceeds 15%, there is a concern about abnormal wear or component damage.
The motor speed, test load, and test time of the test conditions were as follows.
Motor rotation speed: 1475 rpm,
Test load: 5000N
Test time: 20 hours

The above examples show excellent results in all of the shear stability tests 1, 2, and 3, and satisfy the goal of achieving both fuel economy and component durability while maintaining the initial viscosity. It became clear.
On the other hand, Comparative Examples 1 and 5 that do not contain the component (C) are excellent in shear stability in the staircase stability test 1, but have a small viscosity reduction rate in the shear stability tests 2 and 3 and excellent fuel economy. Is not demonstrated. On the contrary, in Comparative Examples 2 and 3 that do not contain the component (B), the viscosity reduction rate in the shear stability test 1 is large, and the wear resistance at the initial familiarization stage is inferior. Furthermore, the rate of decrease in viscosity in the shear stability tests 2 and 3 is large, and a fuel saving effect is expected, but there is a concern about abnormal wear and component damage during long-term use.
Further, even in Comparative Example 4 in which the content ratio of the component (B) to the component (C) is out of the range of the present invention, the rate of decrease in the viscosity in the shear stability tests 1 to 3 is large, and initial wear and long-term use There is concern about abnormal wear and component damage.

Claims (4)

(A) A mineral oil-based base oil is contained in an amount of 70% by mass or more, and a kinematic viscosity at 40 ° C. is 9 to ²⁰ mm ² / s.
(B) 0.5 to 20 % by mass of a polymethacrylate viscosity index improver having a weight average molecular weight (in terms of polystyrene) of 15,000 to 70,000, and (C) a weight average molecular weight of 100,000 to 500, 000 polymethacrylate viscosity index improver 0.5 to 15 % by mass,
(D) The content ratio of the component (B) to the component (C) is 3 to 10 by mass ratio,
(E) the composition has a kinematic viscosity at 100 ° C. of 5.2 to 6.5 mm ² / s,
(F) A lubricating oil composition for an automatic transmission having a viscosity index of 180 or more and a BF viscosity at -40 ° C of 5,000 to 8,900 mPa · s. The lubricating oil for automatic transmission according to claim 1, wherein the content of the component (B) is 1.5 to 20% by mass, and the content of the component (C) is 0.5 to 20/3% by mass. Composition. The lubricating oil composition for an automatic transmission according to claim 1 or 2 , wherein the viscosity index of (F) is more than 180. The lubricating oil composition for an automatic transmission according to any one of claims 1 to 3, wherein the viscosity index of (F) is 185 to 230.