JP2002053886A - Oil composition for shock absorber of automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oil composition for shock of automobiles absorber, improved in a cavitation preventing performance, hardly causing decrease in damping force for a long period, and therefore excellent in sustaining the damping force, in compared with those of conventional ones. SOLUTION: This oil composition for automotive shock absorber is obtained by adding an ethylene-propylene copolymer or a styrene-maleate ester copolymer having a weight average molecular weight (Mw) of 60,000-350,000 as a viscosity index improver in an amount of 1-15 wt.% based on the total weight of the composition to an base oil having a kinematic viscosity of 1-45 mm2/s at 40 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automobile shock absorber oil composition, and more particularly to an automobile shock absorber oil composition used particularly for automobile suspensions.

[0002]

2. Description of the Related Art As a shock absorber used for effectively absorbing vibrations, for example, in the case of automobiles, a hydraulic shock absorber is used for a vehicle body suspension device, an engine support device, a bumper support device, and the like. Oil-filled shock absorbers are widely used. Its structure is based on a cylindrical structure utilizing the flow resistance of oil. A bush, which also serves as a guide, for preventing wear between the cylinder and the piston rod is inserted into the sliding portion, and is sealed to prevent oil leakage. Various types of shock absorbers, such as a double tube type and a gas filled type, are known.

[0003] The function of a shock absorber is to suppress vibration of an automobile quickly. This damping action is to control the resistance (hereinafter referred to as damping force) generated when the oil filled in the shock absorber flows through the valves provided at the piston portion and the bottom portion to an optimum magnitude. But,
This damping force has the disadvantage of being reduced by bubbles generated inside. The phenomenon that this bubble is generated is called cavitation. Cavitation occurs when gas (nitrogen gas, air) originally dissolved in oil flows through the pores from the high pressure side to the low pressure side, which is separated by a valve. Preventing this cavitation is important for exhibiting sufficient damping force.

Japanese Patent Application Laid-Open No. 4-41594 and Japanese Patent Application Laid-Open No.
No. 655491, JP-A-5-70788, JP-A-2000-109876 and JP-A-2000-10
No. 9877 discloses a buffer oil obtained by adding polymethacrylate to a base oil. Although the above-mentioned shock absorber oil can prevent cavitation and prevent a decrease in damping force, it has a problem of poor durability.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above point of view, and has a cavitation preventing performance more than conventional products, is less likely to cause a decrease in damping force for a longer time, and has excellent durability. It is intended to provide a vessel oil composition.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by using a specific polymer as a viscosity index improver, the effects of the above-mentioned objects of the present invention can be improved. It has been found that the present invention has been achieved in an objective manner, and the present invention has been completed.

That is, according to the present invention, a base oil having a kinematic viscosity at 40 ° C. of 1 to 45 mm ² / s has a weight average molecular weight (Mw) of 6 as a viscosity index improver based on the total amount of the composition.
An object of the present invention is to provide an automotive shock absorber oil composition containing 1 to 15% by mass of 10,000 to 350,000 ethylene-propylene copolymer or styrene-maleic acid ester copolymer.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. Mineral oil and / or synthetic oil is used as the base oil constituting the automotive shock absorber oil composition of the present invention. This mineral oil or synthetic oil has a kinematic viscosity of 1 to 45 mm ^{2 at} 40 ° C. because of the need to match the damping force required for the shock absorber.
/ S range. Preferably 3 to 15 mm
² / s. The pour point, which is an index of the low-temperature fluidity of the base oil, is not particularly limited.
It is preferred that:

There are various types of such mineral oils and synthetic oils, and they may be appropriately selected according to the use and the like. As the mineral oil, for example, a distillate obtained by distilling a paraffinic-base crude oil, an intermediate-base crude oil or a naphthenic-base crude oil under normal pressure, or a residual oil obtained by normal-pressure distillation under reduced pressure, or a distillate obtained by a conventional method Accordingly, refined oils obtained by refining, for example, solvent refined oils, hydrogenated refined oils, dewaxed oils, and clay treated oils can be exemplified.

On the other hand, synthetic oils include, for example, poly-α-olefin (PAO), α-olefin copolymer, polybutene, alkylbenzene, polyol ester, dibasic acid ester, polyoxyalkylene glycol, polyoxyalkylene glycol ester, polyoxyalkylene. Glycol ether, silicone oil and the like can be mentioned. PAO is preferred among synthetic oils.

These base oils can be used alone or in combination of two or more, and mineral oil and synthetic oil may be used in combination. In the automotive shock absorber oil composition of the present invention, an ethylene-propylene copolymer or a styrene-maleic acid ester copolymer is blended with the above base oil as a viscosity index improver.

The ethylene-propylene copolymer or the styrene-maleic ester copolymer can be used in either a random form or a block form, and can be used alone or in combination of two or more. Further, the above-mentioned ethylene-propylene copolymer and ethylene-maleic acid ester copolymer can be used in combination. In addition, as said maleic acid ester, maleic acid methyl ester, maleic acid ethyl ester, and maleic acid propyl ester can be mentioned.

It is essential that the weight average molecular weight (Mw) of the above-mentioned ethylene-propylene copolymer or styrene-maleic acid ester copolymer is 60,000 to 350,000. 6
If it is less than 10,000, the cavitation prevention performance is small,
If it exceeds 10,000, the shear stability of the shock absorber oil for automobiles deteriorates, causing a decrease in viscosity and an optimal damping force cannot be obtained.

The amount of the ethylene-propylene copolymer or styrene-maleic acid ester copolymer is in the range of 1 to 15% by mass based on the total amount of the composition. 1 mass%
If it is less than 1, the cavitation prevention performance is not improved, so that the object of the present invention is not sufficiently achieved. If it exceeds 15% by mass, it may exceed the upper limit of 24 mm ² / s (20 ° C.) of the optimum viscosity range of the automotive shock absorber oil. Preferably, it is in the range of 2 to 13% by mass.

Incidentally, the ethylene-propylene copolymer or the styrene-maleic acid ester copolymer is generally used after being diluted with a mineral oil to a resin concentration of 70 to 80% by mass. The blending amount of the ethylene-propylene copolymer or the styrene-maleic ester copolymer is the amount of the undiluted resin.

The above-mentioned automotive shock absorber oil composition has a kinematic viscosity at 20 ° C. of 19 to 24 mm ² / s and a kinematic viscosity at −20 ° C. of 200 mm, based on the basic characteristics (damping characteristics) of the shock absorber oil. It is preferably at most ² / s.

The automobile shock absorber oil composition of the present invention can be obtained by blending a base oil with a polyolefin or polyalkylstyrene as a viscosity index improver, and usually has basic performance as a shock absorber oil. To maintain
Antioxidants, ashless detergents and dispersants, metal deactivators, defoamers, friction modifiers, extreme pressure agents and the like can be appropriately blended within a range not to impair the object of the present invention.

Examples of the antioxidant include phenolic compounds, amine compounds, carbamate compounds, and the like.
2% by mass. Examples of the ashless detergent / dispersant include alkenyl succinimide, benzylamine, polyoxyalkyleneamide, fatty acid amide, and the like, and the amount thereof is usually 0.1 to 7% by mass based on the total amount of the composition.

Examples of the metal deactivator include benzotriazole and thiadiazole, and the amount of the metal deactivator is usually 0.005 to 1% by mass based on the total amount of the composition. Examples of the antifoaming agent include dimethylpolysiloxane and polyacrylate, and the compounding amount is based on the total amount of the composition.
Usually, it is 0.0005 to 1% by mass. Examples of the friction modifier include fatty acids, acidic phosphoric acid esters, phosphoric acid ester amine salts, fats and the like, and the compounding amount is usually 0.1 to 1.0% by mass based on the total amount of the composition. Examples of the extreme pressure agent include dialkyl phosphite, trialkyl phosphate, zinc dithiophosphate, and the like, and the compounding amount is usually 0.1 to 1.0% by mass based on the total amount of the composition.

[0020]

[Evaluation conditions]

Testing machine: damping force evaluation device (see FIG. 1) The shock absorber 4 is fixed to a foundation 6 by a fixture 5. The rod 3 is connected to the load cell 2, and the load cell 2 is connected to the hydraulic cylinder 1. Hydraulic cylinder 1
Is fixed to a gantry (not shown) above the tester. Used shock absorber type: Double wishbone type (oil quantity; 26
0 ml) Filled gas pressure: 0.7 MPa Rod diameter: 12.5 mm Operating condition Stroke length: 70 mm Speed: 2 Hz Bottom temperature: 80 ± 5 ° C. Lateral load: 196 N Evaluation item: 10% of initial damping force is reduced Time (the damping force is the sum of the elongation step and the compression step)

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

(Note) * 1: Kinematic viscosity at 40 ° C. of 40 neutral with paraffinic mineral oil and 60 neutral with paraffinic mineral oil is 1
1.0 mm ² / s. * 2: The kinematic viscosity at 40 ° C of 1-decene dimer hydride and paraffinic mineral oil at 40 neutral was 11.0.
mm ² / s. * 3: Ethylene-propylene random copolymer (Mw2
10,000, resin concentration 90 mass%) * 4: Ethylene-propylene random copolymer (Mw1
* 5: Ethylene-propylene random copolymer (Mw1
* 30: Ethylene-propylene random copolymer (Mw7)
* 7, polymethacrylate (Mw 37,000, resin concentration 4)
* 8: polymethacrylate (Mw: 140,000, resin concentration: 50)
* 9: polymethacrylate (Mw 210,000, resin concentration 50)
* 10: polymethacrylate (Mw 550,000, resin concentration 6)
* 3 to * 10 are the amounts including the mineral oil as a diluent. * 11: Antioxidant, ashless detergent / dispersant, metal deactivator, friction modifier, defoamer * 12: Time until the damping force decreases by 10% (minutes) Buffer oil composition of Example The product has a damping force of 1 compared to the comparative example.
It can be seen that the time until the decrease by 0% is long and the durability is excellent.

[0026]

The automotive shock absorber oil composition of the present invention has cavitation prevention performance, is less likely to cause a decrease in damping force for a long time, and has excellent durability as compared with conventional products.

[Brief description of the drawings]

FIG. 1 A damping force evaluation device

[Explanation of symbols]

 1: hydraulic cylinder 2: load cell 3: rod 4: shock absorber 5: fixture 6: basic

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Claims (1)

[Claims] A kinematic viscosity at 40 ° C. of 1 to 45 mm ^2.
/ S of a base oil having a weight average molecular weight (Mw) of 60,000 to 350,000 as a viscosity index improver, based on the total amount of the composition, and 1 to 1 of an ethylene-propylene copolymer or a styrene-maleic acid ester copolymer. An automobile shock absorber oil composition containing 15% by mass.