JP2006143925A - Hydraulic fluid composition for shock absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic fluid composition for shock absorbers further improved in initial damping characteristics and improving comfortable ride feeling in automobiles. <P>SOLUTION: The hydraulic fluid composition for shock absorbers comprises a lubricant base oil containing a silicone oil having ≤10,000 mm<SP>2</SP>/s dynamic viscosity at 25°C and a viscosity index improver. In the composition, the silicone oil is a fluorine-modified silicone oil. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydraulic fluid composition for a shock absorber.

There are various types of shock absorbers, but it basically consists of a piston with a valve and an outer cylinder. The piston is fixed to the rod, the piston slides on the inner surface of the outer cylinder, and the rod slides on the seal of the rod guide portion. The shock absorber encloses hydraulic oil and gas if necessary, and performs a buffering action by the resistance of the hydraulic oil passing through the valve.
Since the hydraulic fluid for the shock absorber is always in a vibrating state and mixed with air or gas, it is in a state where bubbles are easily generated. Further, since the pressure is reduced when the operating speed of the piston is high, bubbles are also generated. Moreover, since the hydraulic fluid for shock absorbers is exposed to the outside air temperature, it changes from a low temperature to a high temperature. For this reason, a viscosity changes and, thereby, a damping force also changes. In order to suppress this viscosity change as much as possible, a viscosity index improver is used. However, it is known that when a viscosity index improver is added, bubbles are easily generated. In this way, the hydraulic fluid for shock absorbers is constantly exposed to the situation where bubbles are generated, but if bubbles are generated, no damping force is generated when the bubbles pass through the valve, so vibrations can be sufficiently absorbed. As a result, the ride comfort of the car deteriorates.

Conventionally, as hydraulic fluids for shock absorbers, friction characteristics, wear prevention properties, durability, and the like of the shock absorbers have been improved by optimizing friction modifiers and antiwear agents (for example, Patent Documents 1 to 6). reference.). Recently, there has been reported a technique for improving the riding comfort of an automobile by increasing the frictional force of a shock absorber (Patent Document 7). In these compositions, a polymethacrylate viscosity index improver is generally used, and an ethylene-propylene copolymer or a styrene-maleic acid ester copolymer is used as one having excellent anti-cavitation performance and durability of damping force. A buffer oil composition for automobiles containing 1 to 15% by mass of a polymer as a resin amount has been reported (Patent Document 8).
However, in order to improve vehicle riding comfort by suppressing vehicle body vibrations when overcoming obstacles such as road surface irregularities, improving characteristics that absorb vehicle body vibrations instantaneously (hereinafter referred to as initial damping characteristics) It has been found that the selection of friction modifiers, antiwear agents or viscosity index improvers alone is insufficient.
JP 7-224293 A JP-A-7-258678 JP-A-6-128581 JP 2000-192067 A JP 2002-194376 A JP-A-5-255683 JP 2004-035624 A JP 2002-053886 A

  An object of the present invention is to provide a hydraulic fluid composition for a shock absorber that has excellent initial damping characteristics and can improve the riding comfort of a vehicle equipped with the shock absorber.

As a result of intensive studies to solve the above problems, the present inventors have improved the initial damping characteristics when dimethylpolysiloxane having a kinematic viscosity at 25 ° C. of less than 10,000 mm ² / s is used. I found that there was a limit. And even if kinematic viscosity in 25 degreeC is less than 10,000 mm < ² > / s, when the fluorine modified silicone oil was contained, it discovered that an initial damping characteristic could be improved remarkably. It has also been found that when such a fluorine-modified silicone oil and a specific viscosity index improver are combined, the initial damping characteristics are further improved and the ride comfort is improved.

That is, the present invention is a hydraulic fluid composition for a shock absorber containing a lubricating base oil containing a silicone oil having a kinematic viscosity at 25 ° C. of less than 10,000 mm ² / s and a viscosity index improver, the silicone oil Is a hydraulic fluid composition for shock absorbers, characterized in that is a fluorine-modified silicone oil.
In the present invention, the viscosity index improver is preferably an olefin (co) polymer based viscosity index improver and / or a polymethacrylate viscosity index improver.
The olefin (co) polymer viscosity index improver is preferably an ethylene-propylene copolymer viscosity index improver.
The olefin (co) polymer viscosity index improver is preferably a polybutene viscosity index improver.
Moreover, it is preferable that content of the said olefin (co) polymer system viscosity index improver is 0.01 to less than 1 mass% as a polymer amount on the basis of the total amount of the composition.

In the present invention, the lubricating oil base oil contains a silicone oil having a kinematic viscosity of less than 10,000 mm ² / s at 25 ° C. and a hydraulic fluid for a shock absorber containing a viscosity index improver. A method is provided for improving the initial damping characteristics and / or ride comfort of a vehicle equipped with a shock absorber, characterized in that it contains silicone oil.
In the present invention, the lubricating oil base oil contains a silicone oil having a kinematic viscosity of less than 10,000 mm ² / s at 25 ° C. and a hydraulic fluid for a shock absorber containing a viscosity index improver. An initial damping characteristic of a vehicle equipped with a shock absorber, characterized in that the silicone oil contains an olefin (co) polymer based viscosity index improver and / or a polymethacrylate viscosity index improver as a viscosity index improver, and / or Alternatively, a method for improving riding comfort is provided.

Hereinafter, the present invention will be described in detail.
The lubricating base oil in the hydraulic fluid composition for shock absorbers of the present invention is not particularly limited, and mineral base oils and synthetic base oils used for ordinary lubricating oils can be used.
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 include those refined by performing one or more treatments such as solvent dewaxing, hydrorefining, etc., or base oils produced by a method of isomerizing wax isomerized mineral oil, GTL WAX (Gas Liquid Wax).

  Specific examples of synthetic base oils include polybutene or hydrides thereof; poly-α-olefins such as 1-octene oligomers and 1-decene oligomers or hydrides thereof; ditridecyl glutarate, di-2-ethylhexyl adipate , Diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc .; neopentyl glycol ester, trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol pelargonate Examples thereof include polyol esters such as alkyl naphthalene, alkylbenzene, aromatic synthetic oils such as aromatic esters, and mixtures thereof.

  As the lubricating base oil in the present invention, the above mineral base oil, the above synthetic base oil, or an arbitrary mixture of two or more selected from these can be used. Examples thereof include one or more mineral base oils, one or more synthetic base oils, a mixed oil of one or more mineral base oils and one or more synthetic base oils, and the like.

The kinematic viscosity of the lubricating base oil used in the present invention is not particularly limited, but the lower limit of the kinematic viscosity at 40 ° C. is preferably 3 mm ² / s from the viewpoint of adapting to the damping force required for a general shock absorber. More preferably 6 mm ² / s, while the upper limit is preferably 60 mm ² / s, more preferably 40 mm ² / s, even more preferably 20 mm ² / s, and a lower friction composition. From the viewpoint that it can be obtained, it is more preferably 10 mm ² / s or less, and particularly preferably 9 mm ² / s or less.

  Also, the viscosity index of the lubricating base oil used in the present invention is not particularly limited and is arbitrary. However, the damping action, which is a basic performance required for the shock absorber, depends on the viscosity of the hydraulic fluid, and is attenuated by temperature. From the viewpoint of minimizing the change in force, the viscosity index is preferably 80 or more, more preferably 95 or more.

Next, the fluorine-modified silicone oil will be described.
The fluorine-modified silicone oil used in the hydraulic fluid composition for a shock absorber according to the present invention has a kinematic viscosity at 25 ° C. of less than 10,000 mm ² / s, preferably 10 to 5,000 mm ² / s. , more preferably 50~2,000mm ² / s, particularly preferably from 100 to 500 mm ² / s. When a silicone oil having a kinematic viscosity at 25 ° C. of less than 10,000 mm ² / s and not fluorine-modified is used, the effect of improving the initial damping characteristics is small. In addition, by setting the kinematic viscosity at 25 ° C. of the fluorine-modified silicone oil to a particularly preferable value of 100 mm ² / s or more, it is possible to obtain a composition that is more excellent in the initial damping property improvement effect.

Examples of the fluorine-modified silicone oil of the present invention include known fluorine-modified silicone oils having the above kinematic viscosity, and the structure thereof is not particularly limited. For example, the organopolysiloxane represented by the following general formula (1) Examples include those in which part or all of the substituents are substituted with a fluoroalkyl group having 1 to 10 carbon atoms.

  In formula (1), R shows a C1-C10 hydrocarbon group or hydrogen, and may be the same or different. Examples of the hydrocarbon group having 1 to 10 carbon atoms include an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an aryl group, an alkylaryl group, an arylalkyl group, and the like, and an alkyl group having 1 to 4 carbon atoms is A methyl group is preferable and a methyl group is particularly preferable.

  As the fluorine-modified silicone oil of the present invention, for example, a part of the methyl group in the dimethylpolysiloxane in which R in the formula (1) is a methyl group, a fluorine-modified alkyl group having 1 to 10 carbon atoms, preferably A fluorine-modified silicone oil having a structure substituted with a fluorine-modified alkyl group having 1 to 4 carbon atoms is preferable. Specific examples of the fluorine-modified alkyl group having 1 to 10 carbon atoms include mono, di or trifluoromethyl groups, mono, di or trifluoroethyl groups, mono, di or trifluoropropyl groups, and mono groups. , Di- or trifluorobutyl group, and the like. In the present invention, specific examples include trifluoropropylmethyl polysiloxane in which R is a methyl group, a part of which is substituted with a trifluoropropyl group.

  The content of the fluorine-modified silicone oil is not particularly limited, but is preferably 1 to 100 mass ppm, more preferably 2 to 30 mass ppm, and further preferably 3 to 20 mass based on the total amount of the hydraulic fluid composition for shock absorbers. ppm, particularly preferably 3 to 10 ppm by mass, most preferably 3 to 8 ppm by mass. When the content of the fluorine-modified silicone oil is less than 1 mass ppm, the effect of improving the initial damping is small. When the content exceeds 100 mass ppm, not only the effect corresponding to the content cannot be expected but also the generated foam Since it is difficult to disappear, the effect of improving the initial damping characteristic is lowered, which is not preferable.

  Further, as the viscosity index improver used in the hydraulic fluid composition for a shock absorber of the present invention, various known viscosity index improvers, for example, olefin (co) polymer viscosity index improvers, and olefin (co) polymer systems are known. Viscosity index improvers other than viscosity index improvers can be used, and it is preferable to use an olefin (co) polymer based viscosity index improver in terms of improving initial damping characteristics with a small amount of content. It is preferable to contain a viscosity index improver other than the olefin (co) polymer based viscosity index improver, for example, a polymethacrylate viscosity index improver, in terms of further improving the damping characteristics and the viscosity-temperature characteristics of the composition. It is particularly preferable to use it in combination.

  Specific examples of the olefin (co) polymer viscosity index improver include polybutene (polyisobutylene) or a hydride thereof, an ethylene-α-olefin copolymer (α-olefin includes propylene, 1-butene, 1- Pentene or the like) or a hydride thereof. Polyisobutylene is effective in improving the initial damping characteristics, and an ethylene-α-olefin copolymer is more preferable because it is excellent in improving the initial damping characteristics and more easily maintains the initial damping characteristics.

  The weight average molecular weight of the olefin (co) polymer viscosity index improver used in the present invention needs to be large, and the polybutene viscosity index improver is usually 100,000 to 1,000,000, preferably 150,000 to It is preferably 600,000, more preferably 250,000 to 550,000, particularly preferably 250,000 to 350,000 in view of excellent initial damping characteristics and the ability to maintain it for a long period of time. In the case of an ethylene-α-olefin copolymer, it is usually 100,000 to 1,000,000, preferably 150,000 to 600,000, more preferably 250,000 to 550,000, particularly preferably 250,000. Those of ˜350,000 are preferred. When the weight average molecular weight of the olefin (co) polymer viscosity index improver is less than 100,000, the effect of improving the damping force is small. When the weight average molecular weight is greater than 1,000,000, the molecular weight is reduced by shearing during use. This is not preferable because the ride comfort changes.

In the present invention, the content of the olefin (co) polymer-based viscosity index improver as the polymer amount (active ingredient) is preferably 0. In the polybutene viscosity index improver, based on the total amount of the hydraulic fluid composition for the shock absorber. 005 to 5% by mass, more preferably 0.01 to less than 1% by mass, particularly preferably 0.01 to 0.1% by mass. In the ethylene-α-olefin copolymer viscosity index improver, preferably 0 0.005 to 5% by mass, more preferably 0.01 to less than 1% by mass, and particularly preferably 0.05 to 0.5% by mass. In addition to exhibiting an excellent damping force by adding a very small amount of the content of these olefin (co) polymer viscosity index improvers as described above as a polymer amount, it has excellent damping force maintenance, that is, This is particularly preferable because a composition in which the ride comfort is hardly changed can be obtained.
In addition, as an olefin (co) polymer system viscosity index improver, for the purpose of improving the solubility in a lubricating oil and handling, etc., those containing a diluent of about 10 to 95% by mass are usually available. It is preferable to blend so that the polymer as the active ingredient is in the above-described range.

As the viscosity index improver other than the olefin (co) polymer viscosity index improver, various known viscosity index improvers such as polymethacrylate viscosity index improver, styrene-diene copolymer viscosity index improver, styrene- A maleic anhydride ester copolymer-based viscosity index improver or a polyalkylstyrene-based viscosity index improver can be used, and among them, a polymethacrylate-based viscosity index improver is preferably contained.
The weight average molecular weight of the viscosity index improver other than the olefin (co) polymer viscosity index improver is not particularly limited, but is usually 10,000 to 1,000,000, preferably 100,000 to 500,000, Preferably those having 150,000 to 300,000, particularly preferably 150,000 to 250,000 are suitable.
The content in the case of containing a viscosity index improver other than the olefin (co) polymer viscosity index improver is not particularly limited, but as a polymer amount (active ingredient amount) based on the total amount of the hydraulic fluid composition for shock absorbers Preferably, it is 0.01-10 mass%, More preferably, it is 0.1-5 mass%, Most preferably, it is 0.5-3 mass%.

  The hydraulic fluid composition for a shock absorber according to the present invention further includes any additive generally used in lubricating oil, if necessary, to further improve its performance or depending on other purposes. Can be added. Examples of such additives include friction modifiers, antiwear agents, ashless dispersants, antioxidants, fluidity improvers, metal deactivators, metal detergents, corrosion inhibitors, rust inhibitors, Various additives, such as a demulsifier, an antifoamer, and a coloring agent, can be mentioned.

  As the friction modifier, any compound usually used as a friction modifier for lubricating oils can be used. For example, molybdenum dithiocarbamate, molybdenum dithiophosphate, molybdenum amine complex, molybdenum-succinimide complex, molybdenum disulfide Molybdenum friction modifiers such as C6-30 alkyl groups or alkenyl groups, especially amine compounds and imide compounds having at least one C6-30 linear alkyl group or linear alkenyl group in the molecule Ashless friction modifiers such as fatty acid esters, fatty acid amides, fatty acids, fatty alcohols, aliphatic ethers, etc., and can be contained in the range of usually 0.01 to 5% by mass based on the total amount of the composition. It is.

  As the antiwear agent, any compound usually used as an antiwear agent for lubricating oils can be used, and examples thereof include phosphorus and / or sulfur-containing antiwear agents. For example, (thio) phosphate esters (Thio) phosphites, derivatives thereof, metal salts, amine salts thereof, and sulfur-containing compounds such as disulfides, sulfurized olefins, sulfurized fats and oils, dithiocarbamate, zinc dithiocarbamate, and the like. . These antiwear agents can be contained in the composition of the present invention usually in the range of 0.01 to 5% by mass based on the total amount of the composition.

  As the ashless dispersant, any compound usually used as an ashless dispersant for lubricating oils can be used. For example, succinimide, benzylamine, polyamine and the like having an alkyl group or alkenyl group having 40 to 400 carbon atoms and the like Examples thereof include derivatives modified with boron compounds, phosphorus compounds, sulfur compounds, oxygen-containing organic compounds, and the like. The ashless dispersant is generally 0.01 to 20% by mass, preferably 0.01 to 5% by mass, more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less, based on the total amount of the composition. It can be contained in the composition of the present invention.

  As the antioxidant, any compound usually used as an antioxidant for lubricating oils can be used. For example, 2,6-di-tert-butyl-p-cresol, 4,4′-methylenebis (2, 6-di-tert-butylphenol), octyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 3-methyl-5-tert-butyl-4-hydroxyphenyl substituted fatty acid esters, etc. And phenolic antioxidants such as phenyl-α-naphthylamine, alkylphenyl-α-naphthylamine, and dialkyldiphenylamine. These antioxidants can be contained in the composition of the present invention usually in the range of 0.01 to 5% by mass based on the total amount of the composition.

As the fluidity improver, any compound usually used as a fluidity improver for lubricating oils can be used, and examples thereof include a polymethacrylate fluidity improver.
Metal deactivators include imidazoline, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles or derivatives thereof, 1,3,4-thiadiazole polysulfides, 1,3,4-thiadiazolyl-2,5-bisdialkyldithio Examples thereof include carbamate, 2- (alkyldithio) benzimidazole, and β- (o-carboxybenzylthio) propiononitrile.

Examples of metal detergents include alkali metal or alkaline earth metal sulfonates, phenates, salicylates, and phosphonates.
Examples of the corrosion inhibitor include benzotriazole, tolyltriazole, thiadiazole, and imidazole compounds.
Examples of the rust inhibitor include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenyl succinic acid ester, and polyhydric alcohol ester.

Examples of the demulsifier include polyalkylene glycol nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether.
As the defoaming agent, for example, (except for the fluorine-modified silicone oil) 25 kinematic viscosity at ℃ is 0.5~10,000mm ² / s less than the silicone oil, 25 kinematic viscosity at ℃ is 10,000 mm ² / s or more Silicone oil, alkenyl succinic acid derivative, ester of polyhydroxy aliphatic alcohol and long chain fatty acid, methyl salicylate and o-hydroxybenzyl alcohol, aluminum stearate, potassium oleate, N-dialkyl-allylamine nitroaminoalkanol, isoamyl octyl phosphate Aromatic amine salts, alkylalkylene diphosphates, metal derivatives of thioethers, metal derivatives of disulfides, fluorine compounds of aliphatic hydrocarbons, triethylsilane, dichlorosilane, alkylphenyl polyethylene Examples include glycol ether sulfide and fluoroalkyl ether.

  When these additives are contained in the hydraulic fluid composition for a shock absorber of the present invention, the content is based on the total amount of the composition, a fluidity improver, a metallic detergent, a corrosion inhibitor, a rust inhibitor, It is usually selected in the range of 0.005 to 5% by mass for the demulsifier, 0.005 to 1% by mass for the metal deactivator, and 0.0001 to 0.01% by mass for the antifoaming agent.

  As described above, by incorporating a specific fluorine-modified silicone oil and a viscosity index improver into the lubricating base oil, it has excellent initial damping characteristics and can improve the ride comfort of automobiles. An oil composition is obtained.

  Hereinafter, the content of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these.

[Examples 1 to 3 and Comparative Example 1]
An additive having the composition shown in Table 1 is blended in the lubricating base oil, and the hydraulic fluid composition of the present invention (Examples 1 to 3) and comparative examples are used so that the kinematic viscosity at 40 ° C. is 10 mm ² / s. A hydraulic fluid composition (Comparative Example 1) was prepared. The resulting composition was evaluated for initial damping characteristics under the conditions shown below, and the results are also shown in Table 1.

(Initial damping characteristics)
A vertical accelerometer is installed in a passenger car equipped with a shock absorber filled with the hydraulic fluid composition of the present invention, and after traveling for 30 minutes with three passengers on board, an obstacle with a height of 3 cm is moved at a speed of 60 km / h. We measured the acceleration change in the vertical direction when we got over. Table 1 shows the maximum value of the acceleration change (the sum of absolute values in the extension direction and the compression direction). The smaller the change in acceleration, the easier it is to absorb vertical vibration.
In addition, the initial damping characteristics at the same time as the measurement of the acceleration change are based on a rating of 3.0 when the composition of Comparative Example 1 is used as a reference, and a rating of 5.0 as the maximum guideline. went. Table 1 shows the results obtained by rotating the boarding position of each occupant for each test and averaging the scores for 3 times × 3 persons. The higher the initial damping characteristic score, the easier the vibration is to settle and the better the ride quality.

As shown in Table 1, when the hydraulic fluid composition for a shock absorber according to the present invention (Examples 1 to 3) is used, a silicone oil containing no fluorine having a kinematic viscosity at 25 ° C. of less than 10,000 mm ² / s is used. Compared to the case of using (Comparative Example 1), it can be seen that the change in acceleration in the vertical direction is small, the initial damping characteristics are remarkably improved, and the riding comfort is improved. It can also be seen that when the olefin (co) polymer viscosity index improver is used, the vertical acceleration change and the initial damping characteristics are improved as compared with the case where the polymethacrylate viscosity index improver is used.
In addition, from the measurement result of the time-dependent change of the acceleration in the vertical direction, when the compositions of Examples 1 to 3 are used, the disappearance time of the vehicle body vibration is clearly shorter than when the composition of Comparative Example 1 is used. I have confirmed that.

Claims (1)

A hydraulic fluid composition for a shock absorber containing a lubricating base oil containing a silicone oil having a kinematic viscosity at 25 ° C. of less than 10,000 mm ² / s and a viscosity index improver, wherein the silicone oil is a fluorine-modified silicone oil A hydraulic fluid composition for a shock absorber.