JP2008195780A - Lubricating oil composition for manual transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricating oil composition for a manual transmission having excellent oxidation stability and shear stability and capable of improving fatigue characteristics, seizure resistance, low-temperature operability and fuel consumption of the manual transmission. <P>SOLUTION: The lubricating oil composition for the manual transmission comprises a base oil of a mineral oil and/or a synthetic oil having 4-7 mm<SP>2</SP>/s kinematic viscosity at 100°C and 110-130 viscosity index, a polymethacrylate having 10,000-20,000 weight-average molecular weight and containing hydroxy groups and a polymethacrylate having 60,000-80,000 weight-average molecular weight and free of hydroxy group. Furthermore, the lubricating oil composition for the manual transmission contains a zinc dialkyldithiophosphate having a 3-6C secondary alkyl group and has ≤500 mm<SP>2</SP>/s kinematic viscosity at -10°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lubricating oil composition for a manual transmission, and more specifically, has excellent oxidation stability and shear stability while improving low-temperature operability and fuel consumption, The present invention relates to a lubricating oil composition for a manual transmission that can improve seizure resistance.

Since a manual transmission of an automobile is used under conditions of high speed and high load, it is required that transmission oil used for this is excellent in seizure resistance and wear resistance. At the same time, improvement in fuel efficiency is also required.
As a method for improving fuel efficiency, methods of lowering friction by reducing viscosity or adding a friction modifier are common, but in manual transmissions, lowering friction by adding a friction modifier can cause problems with the synchro synchronization mechanism. In order to generate this, a technique for reducing the friction by reducing the viscosity and improving the fuel efficiency has been mainly employed.

  On the other hand, reducing the viscosity of the lubricating oil may cause a problem that the seizure resistance is reduced and the equipment may be damaged. Therefore, in transmission oils for automobiles, sulfurization is required to improve seizure resistance. Sulfur-based additives such as olefins and sulfurized esters, and additives with an increased amount of extreme pressure agents such as phosphoric acid esters or phosphoric acid additives such as amine salts of phosphoric acid esters have been used ( (See Patent Documents 1 to 3.)

In recent years, due to the rapid increase in demand for high-speed transportation using highways, the specific gravity of high-speed driving of automobiles has increased, and from the viewpoint of measures such as higher engine output and improved aerodynamic characteristics, transmission gear units As a result of downsizing and the like, the temperature of transmission oil used in manual transmissions and reduction gears has risen remarkably in the machine.
JP 2004-262980 A Japanese Patent Laid-Open No. 10-259393 JP-A-10-316987

Therefore, in order to cope with this, it is necessary to add an extreme amount of an extreme pressure agent such as the above-mentioned sulfurized olefin or phosphate ester having high seizure resistance, and thereby oxidation at a high temperature (usually 150 ° C. or higher). There is a strong tendency to promote poor stability and corrosive wear, causing problems such as corrosion and sludge formation on metals, particularly copper, and as a result, a phenomenon of promoting gear tooth surface wear and seizure may occur.
In addition, in manual transmissions, the synchronizer ring and gear cone part of the synchromesh mechanism cause friction coefficient reduction and abnormal wear, resulting in problems such as poor synchronization, increased shift force, and inability to shift. Sometimes.

  The present invention has been made in view of such problems of the prior art, and its object is to have excellent oxidation stability and shear stability, and fatigue characteristics and seizure resistance of a manual transmission. It is in providing the lubricating oil composition for manual transmissions which can improve a property, low temperature operativity, and a fuel consumption.

The inventors of the present invention have made extensive studies in order to achieve the above object. As a result, a mineral oil and / or synthetic oil base oil having a kinematic viscosity at 100 ° C. of 4 to 7 mm ² / s and a viscosity index of 110 to 130 is obtained. A polymethacrylate containing a hydroxyl group with a weight average molecular weight of 10,000 to 20,000, a polymethacrylate containing no hydroxyl group with a weight average molecular weight of 60,000 to 80,000, and 3 to 6 carbon atoms The above object can be achieved, for example, by mixing with a zinc dialkyldithiophosphate having a secondary alkyl group to obtain a lubricating oil composition for a manual transmission having a kinematic viscosity at -10 ° C. of 500 mm ² / s or less. As a result, the present invention has been completed.

That is, the lubricating oil composition for manual transmission of the present invention comprises a mineral oil and / or synthetic oil base oil having a kinematic viscosity at 100 ° C. of 4 to 7 mm ² / s and a viscosity index of 110 to 130, and a weight average molecular weight. Containing a hydroxyl group having a hydroxyl group of 10,000 to 20,000 and a polymethacrylate having a weight average molecular weight of 60,000 to 80,000 and not containing a hydroxyl group, and further having 3 to 6 carbon atoms A lubricating oil composition for a manual transmission containing a zinc dialkyldithiophosphate having a secondary alkyl group, wherein the kinematic viscosity at −10 ° C. is 500 mm ² / s or less.

According to the present invention, a base oil of mineral oil and / or synthetic oil having a kinematic viscosity at 100 ° C. of 4 to 7 mm ² / s and a viscosity index of 110 to 130, and a weight average molecular weight of 10,000 to 20,000 A polymethacrylate containing a certain hydroxyl group, a polymethacrylate containing no hydroxyl group having a weight average molecular weight of 60,000 to 80,000, and a zinc dialkyldithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms, And a lubricating oil composition for a manual transmission having a kinematic viscosity at −10 ° C. of 500 mm ² / s or less, etc., so that it has excellent oxidation stability and shear stability, A lubricating oil composition for a manual transmission that can improve fatigue characteristics, seizure resistance, low-temperature operability, and fuel consumption can be provided.

Hereinafter, the lubricating oil composition for manual transmission of the present invention will be described. In the present specification and claims, the “weight average molecular weight (M _w )” is obtained by measuring using gel permeation chromatography and converting to polystyrene. The “number average molecular weight (M _n )” was also determined in the same manner.

As described above, the lubricating oil composition for manual transmission of the present invention has a mineral oil and / or synthetic oil base oil having a kinematic viscosity at 100 ° C. of 4 to 7 mm ² / s and a viscosity index of 110 to 130, and a weight. A polymethacrylate containing a hydroxyl group having an average molecular weight of 10,000 to 20,000 and a polymethacrylate not containing a hydroxyl group having a weight average molecular weight of 60,000 to 80,000 are contained. A lubricating oil composition for a manual transmission containing a zinc dialkyldithiophosphate having 6 secondary alkyl groups, wherein the kinematic viscosity at −10 ° C. is 500 mm ² / s or less.
With such a configuration, it has excellent oxidation stability and shear stability, and improves the fatigue characteristics, seizure resistance, low temperature operability and fuel consumption of the manual transmission, and reduces friction torque loss. A manual transmission lubricating oil composition is obtained, and such a manual transmission lubricating oil composition is preferably used even when the manual transmission itself is miniaturized and used under conditions of high speed and high load. Can do.

Here, the base oil is not particularly limited as long as it satisfies the conditions of the kinematic viscosity and the viscosity index at 100 ° C., and is usually a mineral base oil or a synthetic oil base used for lubricating oil. A base oil can be used.
When the base oil has a kinematic viscosity at 100 ° C. of less than 4 mm ² / s, the oil film is not sufficiently formed at the lubrication location, the lubricity is inferior, and the tooth surface is seized and worn. Further, it is not desirable because the evaporation loss of the base oil increases. On the other hand, if it exceeds 7 mm ² / s, the fuel consumption deteriorates.
Further, when the viscosity index at 100 ° C. of the base oil is less than 110, it is necessary to increase the content of polymethacrylate which is a viscosity index improver described in detail later, and by using polymethacrylate having a large molecular weight, Shear stability deteriorates. On the other hand, when it exceeds 130, formation of an oil film is insufficient.

  Specifically, as the mineral base oil, the lubricating oil fraction obtained by subjecting the crude oil to atmospheric distillation obtained under reduced pressure is subjected to solvent removal, solvent extraction, hydrocracking, Examples thereof include those purified by performing one or more treatments such as solvent dewaxing and hydrorefining, and wax isomerized mineral oil.

Specific examples of the synthetic oil base oil include poly-α-olefin, α-olefin copolymer, polybutene, polyol ester, dibasic acid ester, polyhydric alcohol ester, polyoxyalkylene glycol, and polyoxyalkylene glycol ester. , Polyoxyalkylene glycol ethers, cycloalkane compounds, and the like. The mineral oil base oils and synthetic oil base oils described above are suitable mineral oil base oils, synthetic oil base oils, mineral oil bases. A base oil and a synthetic oil base oil can be mixed and used at an arbitrary ratio.
In the case of a mixed system, it is sufficient that the conditions of the kinematic viscosity and the viscosity index at 100 ° C. are satisfied as a whole.

Moreover, it is necessary to use what has a weight average molecular weight in said range as polymethacrylate containing a hydroxyl group.
When a weight average molecular weight of less than 10,000 or more than 20,000 is used, a lubricating oil composition for a manual transmission having good shear stability cannot be obtained.
Here, the “polymethacrylate containing a hydroxyl group” is a copolymer comprising an alkyl methacrylate having an alkyl group having 1 to 20 carbon atoms and a hydroxyl group-containing vinyl monomer as essential constituent monomers. The “polymethacrylate not containing a hydroxyl group” described later is a conventional polymethacrylate.

The polymethacrylate containing the hydroxyl group preferably has a dispersity (M _w / M _n ) of 1.2 to 2.0, and preferably 1.5 to 1.7. From the viewpoint of Also, a lubricating oil composition for a manual transmission having better shear stability is obtained when the degree of dispersion is smaller.

Furthermore, the polymethacrylate containing the hydroxyl group preferably has a solubility parameter of 9.2 or more, more preferably 9.3 or more, and preferably 10.5 or less. It is more preferable that it is 9.7 or less. Those having a solubility parameter within the above range are desirable because the solubility in the base oil is better.
The “solubility parameter” is calculated by the Fedors method (Polym. Eng. Sci. 14 (2), 152, (1974)).

On the other hand, as polymethacrylate which does not contain a hydroxyl group, it is necessary to use what has a weight average molecular weight in said range.
When one having a weight average molecular weight of less than 60,000 or more than 80,000 is used, a lubricating oil composition for a manual transmission having good shear stability cannot be obtained.

  The content ratio of the polymethacrylate containing a hydroxyl group and the polymethacrylate not containing a hydroxyl group is, by weight ratio, hydroxyl group-containing polymethacrylate: hydroxyl group-free polymethacrylate = 70: 30 to 40:60. It is desirable from the viewpoint of maintaining the thickness.

Moreover, as said zinc dialkyl dithiophosphate, it is required to use what has a C3-C6 secondary alkyl group.
When the carbon number is within the above-mentioned range and a secondary alkyl group that does not have an alkyl group is used, the wear resistance is inferior.

  Specific examples of the zinc dialkyldithiophosphate include zinc dipropyldithiophosphate, zinc dibutyldithiophosphate, zinc dipentyldithiophosphate, zinc dihexyldithiophosphate, and the like.

Moreover, it is preferable that content of the said zinc dialkyldithiophosphate in the lubricating oil composition for manual transmission is 0.04-0.5% as zinc content, and is 0.08-0.4%. Is more preferable.
Such a lubricating oil composition for a manual transmission is more excellent in fatigue characteristics and seizure resistance.

Furthermore, the lubricating oil composition for a manual transmission needs to have a kinematic viscosity at −10 ° C. of 500 mm ² / s or less.
When the kinematic viscosity at −10 ° C. of the lubricating oil composition for manual transmission exceeds 500 mm ² / s, the low temperature operability and the fuel consumption are deteriorated.

  Furthermore, in the lubricating oil composition for a manual transmission according to the present invention, as necessary, other additives such as a rust inhibitor, a detergent, a dispersant, an antioxidant, an extreme pressure agent, an oil agent, and friction adjustment. An agent, a pour point depressant, an antifoaming agent, and the like can be added as appropriate.

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

First, the following constituent materials (1) to (6) were prepared.
(1) Base oil: Mixed oil of Group 1, Group 2, and Group 3 in API (American Petroleum Institute, American Petroleum Institute) base oil category (characteristic: kinematic viscosity at 40 ° C; 18.7 mm ² / s at 100 ° C) Kinematic viscosity: 4.1 mm ² / s, viscosity index at 100 ° C .; 122)
(2) Polymethacrylate containing hydroxyl groups (weight average molecular weight (M _w ); 16,000)
(3) Conventional polymethacrylate containing no hydroxyl group (weight average molecular weight (M _w ); 75,000)
(4) zinc dialkyldithiophosphate (ZnDTP): zinc dialkyldithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms (zinc dihexyldithiophosphate)
(5) Phenol antioxidant (6) Other additives: detergent + dispersant + antioxidant

(Example 1)
The above constituent materials were blended as shown in Table 1 and mixed to obtain a lubricating oil composition for a manual transmission of this example.

(Comparative Example 1)
A lubricating oil composition for a manual transmission of this example was obtained by repeating the same operation as in Example 1 except that the constituent materials were blended as shown in Table 1.

(Comparative Example 2)
As Comparative Example 2, a commercially available lubricating oil composition for manual transmission (manufactured by Nissan Motor Co., Ltd .: manual transmission oil GL-4 75W-85) was used. Table 1 shows the specifications of the lubricating oil composition for manual transmission in each of the above examples.

[Performance evaluation]
(ISOT test)
A new oil of the lubricating oil composition for manual transmission of each example was obtained by performing an oxidation test under the conditions of 135 ± 0.5 ° C. and 96 h in accordance with JIS K2514. Compared to the new oil of the lubricating oil composition for transmission, the amount of kinematic viscosity change at 40 ° C and the amount of kinematic viscosity change at 100 ° C are measured. Viscosity change rate (rise rate) was calculated. The obtained results are shown in Table 2. In addition, the thing with few raise rates is favorable, and the pass value was 7 or less.

(SONIC test)
The oil obtained by irradiating the new oil (30 ml) of the lubricating oil composition for manual transmission in each example with ultrasonic waves for 1 hour under the test conditions defined in JASO M347-95 The kinematic viscosity change amount at 40 ° C. and the kinematic viscosity change amount at 100 ° C. are measured as compared with the new oil of the machine lubricating oil composition. The change rate (decrease rate) was calculated. The obtained results are also shown in Table 2. In addition, the thing with few fall rates is favorable, and the pass value was 7 or less.

(FZG pitching test)
Using the lubricating oil composition for manual transmission of each example, it was performed in accordance with DIN 51354. A TYPE PT-C gear was used and the load was 9 stage, the oil temperature was 120 ° C., and the rotation speed was 1440 / min.
In the fatigue life determination method, the test apparatus was stopped, the tooth surface was regularly observed, and the time (h) when 1 mm ² pitching occurred was measured. The interval of regular observation was set every 8 hours for the first 24 hours and every 2 to 4 hours thereafter. The obtained results are also shown in Table 2.

(FZG extreme pressure test)
The lubricating oil composition for manual transmission of each example was used, and the test equipment specified in ISO 14635 was used. A TYPE A gear was used, a pinion gear having a tooth width of 10 mm, oil temperature: 120 ° C., and rotation speed: 2880 / min.
In the determination method, a load (circulation power torque) is applied for 1 stage, the operation is performed for 7.5 minutes, and the tooth surface state of the gear is confirmed. Until scuff marks generated total 2 cm ² or more onto the tooth surface, repeating the operation of 1stage increments added with 7.5 minutes a load could be operated in a state where scuff marks does not occur total 2 cm ² or more onto the tooth surface The maximum stage was recorded. The obtained results are also shown in Table 2. Note that the higher the stage (numerical value), the better the seizure resistance.

(Friction torque evaluation test)
Using the lubricating oil composition for manual transmissions of each example, a motoring test was performed under the following conditions using an FF 6-speed manual transmission (ND unit) manufactured by Nissan Motor Co., Ltd. At that time, the torque loss was defined as the difference between the input shaft torque during operation and the output shaft torque divided by the reduction ratio.
The friction torque reduction rate of Example 1 was calculated with Comparative Example 2 being a commercially available oil as a reference (= 0). The obtained results are also shown in Table 2.

According to Table 2, Example 1 belonging to the scope of the present invention has 62 hours of time required for the occurrence of pitching in the FZG pitching test compared to Comparative Example 1 outside the present invention, and almost twice the fatigue characteristics (life performance) ).
Moreover, the ISO test and the SONIC test satisfy the passing values, and good results are obtained. From this result, it can be seen that Example 1 is a lubricating oil composition for manual transmission having excellent fatigue characteristics, oxidation stability, and shear stability.
Further, in Example 1, although the viscosity is about half that of the commercially available manual transmission oil of Comparative Example 2, the result of the seizure resistance equivalent to that of Comparative Example 2 was obtained in the FZG seizure test. It was.
Moreover, the pass stage of the FZG image sticking test was 9 for both Example 1 and Comparative Example 2, and both were good.
Furthermore, it can be seen from the friction torque reduction rate of the first embodiment that the torque loss can be reduced as compared with the second comparative example, and the overall efficiency of the manual transmission can be improved.

Claims (1)

A mineral oil and / or synthetic oil base oil having a kinematic viscosity at 100 ° C. of 4 to 7 mm ² / s and a viscosity index of 110 to 130;
A polymethacrylate containing hydroxyl groups having a weight average molecular weight of 10,000 to 20,000,
And a polymethacrylate containing no hydroxyl group having a weight average molecular weight of 60,000 to 80,000, and further containing a zinc dialkyldithiophosphate having a secondary alkyl group having 3 to 6 carbon atoms. A lubricating oil composition for
A lubricating oil composition for a manual transmission, wherein the kinematic viscosity at −10 ° C. is 500 mm ² / s or less.