DE69318095T2 - Shock fluid - Google Patents

Description

This invention relates to hydraulic oil compositions for use in shock absorbers in general and, in particular, to such oil compositions suitable for motor vehicle suspension devices such as shock absorbers.

As conventional hydraulic oils that have been used in automotive buffer devices such as shock absorbers, active suspensions, support dampers and machine dampers, there are known those that contain a phosphoric acid ester and/or a phosphorous acid ester to provide them with friction-reducing and anti-wear properties. In addition, the use of hydraulic oils in which a fatty acid, an aliphatic alcohol, a fatty acid ester, an aliphatic amine or other oily agents are used to further improve the friction-reducing properties of the oils is widely used.

Hydraulic oils are required to reduce friction on the friction surfaces and at the same time prevent wear on the friction surfaces. In the past, sleeve parts impregnated with a Teflon resin have been used experimentally to reduce friction on the friction surfaces with respect to the material or substance used. In addition, buffers of the gas-sealed type and the damping force variable type in particular have been used more frequently, thus increasing the load acting on the friction surfaces of the buffers and making the conditions under which the buffers are used more difficult.

With a change in the conditions or circumstances under which the hydraulic oils are used, conventional oils containing only a phosphoric acid ester and/or an ester of a phosphorous acid, or oils in which a fatty acid, an aliphatic alcohol, a fatty acid ester and other oily agents are used, have problems such that the friction surfaces are considerably worn because their friction-reducing effects are small and poor. In addition, it has been found that the conventional oils in which a phosphoric acid ester and/or an Esters of a phosphorous acid and an aliphatic amine which is an oily agent initially exhibit excellent anti-wear and anti-friction effects on the friction surface of a suspension device when the oils are used therein, but problems arise such that they cannot permanently maintain these effects and the friction coefficient is considerably increased during their use, whereby spherical particles generated by the wear of the friction surfaces adhere to the friction surfaces which are the surfaces of a Teflon resin-impregnated sleeve member.

EP-A-351 964 and EP-A-348 236 each disclose a lubricating oil composition containing a lubricating oil and additives including a hydroxylamine compound and an organic phosphite ester. These power transmission fluids can regulate frictional properties but do not necessarily reduce them.

US-A-4 634 543 discloses a fluid composition for use in a shock absorber which contains as essential components a phosphoric acid ester and a boron-containing detergent in a base lubricating oil.

The development of new hydraulic oils for buffers, which meet the new requirements such as excellent applicability to Teflon resin-impregnated sleeve parts and excellent durability (less deterioration during use) of the friction-reducing and wear-preventing effects, together with the conventional requirements, is urgently required.

The primary objective of this invention is to provide a shock absorber fluid that can be excellently applied to Teflon resin coated sleeve parts, as well as excellent durability (less deterioration in course of use) of the friction-reducing and wear-preventing effects.

After intensive studies to achieve the object of the invention, it was found that the combined use of (A) a phosphoric acid ester and/or an ester of a phosphorous acid and (B) an alkylene oxide of an aliphatic amine in a lubricating oil as a base oil exerts a synergistic effect and thereby a new hydraulic oil can be obtained which has excellent performances in use.

The primary object of this invention is achieved by providing a shock absorber fluid prepared by adding the following ingredients as essential components to a lubricating oil as a base oil:

(A) a phosphoric acid ester and/or an ester of a phosphorous acid and

(B) an alkylene oxide adduct of an aliphatic amine.

The invention is described in detail below.

The lubricating oils used as the base oil in this invention are not particularly limited; both mineral oils and synthetic oils which are usually used as the base oil for lubricating oils can be used as the base oil in this invention.

The mineral oil type lubricating oils which can be used as the base oil include paraffinic and naphthenic oils obtained by refining, for example, lubricating oil fractions obtained by atmospheric and reduced pressure distillation of a crude oil by means of a suitable combination of solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfate washing and alumina treatment.

Synthetic oil type lubricating oils that can be used as base oil include poly-α-olefins (polybutene, 1-octene oligomers, 1-decene oligomers, etc.), alkylbenzenes, Alkylnaphthalenes, diesters (ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.), polyol esters (trimethylolpropane caprylate, trimethylolpropane peralgonate, pentaerithritol 2-ethylhexanoate, pentaerithritol peralgonate, etc.), polyoxyalkylene glycol, polyphenyl ether, silicone oil and perfluoroalkyl ether.

For the sake of simplicity, the lubricating oils used as base oils are occasionally referred to as "base lubricating oils" hereinafter.

The lubricating base oils may be used individually or together; however, the mineral oil type lubricating base oils are preferably used in this invention in view of their adaptability or compatibility with rubber sealants.

The viscosity of the base lubricating oils used in this invention is optional, but those having a viscosity of 8 to 60 cSt, preferably 10 to 40 cSt at 40°C, are usually used because they must be applicable to the damping force required in conventional buffers.

The component (A), which is added according to the invention as an essential additive to the base lubricating oil, is a phosphoric acid ester and/or an ester of a phosphorous acid.

The phosphoric acid ester is a compound according to the following formula (1),

and the ester of a phosphorous acid is is a compound according to the following formula (2).

In formula (1), R¹ and R² are each a straight-chain or branched-chain alkyl or alkenyl group having 8 to 20 carbon atoms and R³ is hydrogen; in formula (2), R⁴ and R⁵ are each a straight-chain or branched-chain alkyl or alkenyl group having 8 to 20 carbon atoms and R⁶ is hydrogen.

R¹, R², R⁴ and R⁵ each include an alkyl group, such as butyl groups (including all isomeric groups), pentyl groups (including all isomeric groups), hexyl groups (including all isomeric groups), heptyl groups (including all isomeric groups), octyl groups (including all isomeric groups), nonyl groups (including all isomeric groups), decyl groups (including all isomeric groups), undecyl groups (including all isomeric groups), dodecyl groups (including all isomeric groups), tridecyl groups (including all isomeric groups), tetradecyl groups (including all isomeric groups), pentadecyl groups (including all isomeric groups), hexadecyl groups (including all isomeric groups), heptadecyl groups (including all isomeric groups), octadecyl groups (including all isomeric groups), nonadecyl groups (including all isomeric groups), eicosyl groups (including all isomeric groups), heneicosyl groups (including all isomeric groups), and docosyl groups (including all isomeric groups); or an alkenyl group, such as butenyl groups (including all isomeric groups), pantenyl groups (including all isomeric groups), hexenyl groups (including all isomeric groups), heptenyl groups (including all isomeric groups), octenyl groups (including all isomeric groups), nonenyl groups (including all isomeric groups), decenyl groups (including all isomeric groups), undecenyl groups (including all isomeric groups), dodecenyl groups (including all isomeric groups), tridecenyl groups (including all isomeric groups), tetradecenyl groups (including all isomeric groups), pentadecenyl groups (including all isomeric groups), hexadecenyl groups (including all isomeric groups), heptadecenyl groups (including all isomeric groups), octadecenyl groups (including all isomeric groups), nonadecenyl groups (including all isomeric groups), eicosenyl groups (including all isomeric groups), heneicosenyl groups (including all isomeric groups) and docosenyl groups (including all isomeric groups).

In view of the excellent anti-wear and anti-friction effects, the phosphoric acid ester of the component (A) used in this invention is preferably a compound of the formula (1) wherein R¹ and R² are each a straight-chain alkyl group and/or alkenyl group and R³ is hydrogen.

In view of the excellent anti-wear and anti-friction effects in the same manner as the phosphoric acid ester of the formula (1), the phosphorous acid ester of the component (A) used in this invention is preferably a compound of the formula (2) wherein R⁴ and R⁵ are each a straight-chain alkyl or alkenyl group and R⁴ is hydrogen.

The phosphoric acid ester which is one of the components (A) used in this invention includes dioctyl acid phosphate (dicaprylic acid phosphate), didecylic acid phosphate, didodecylic acid phosphate (dilauryl acid phosphate), ditetradecyl acid phosphate (dimyristyl acid phosphate), dihexadecyl acid phosphate (dipalmityl acid phosphate), dioctadecyl acid phosphate (distearyl acid phosphate) and di-9-octadecenyl acid phosphate (dioleyl phosphate). The ester of a phosphorous acid which is included in the components (1) includes dioctyl hydrogen phosphite (dicapryl hydrogen phosphite), didecyl hydrogen phosphite, didodecyl hydrogen phosphite (dilauryl hydrogen phosphite), ditetradecyl hydrogen phosphite (dimyristyl hydrogen phosphite), dihexadecyl hydrogen phosphite (dipalmityl hydrogen phosphite), dioctadecyl hydrogen phosphite (distearyl hydrogen phosphite), di-9-octadecenyl hydrogen phosphite (dioleyl hydrogen phosphite) and mixtures thereof.

In the shock absorber fluid according to the invention, the amount of phosphoric acid ester and/or phosphorous acid ester added may be arbitrary, but it is preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total weight of the composition.

The component (B), which is another essential component in this invention, is an adduct of an aliphatic amine with an alkylene oxide. The alkylene oxide adduct of an aliphatic amine according to this invention is a compound represented by the following general formula (3)

wherein R⁷ represents a straight chain or branched chain alkyl or alkenyl group having 8 to 22 carbon atoms, R⁸ and R⁹ may be the same or different from each other and each is a straight-chain or branched-chain alkylene group having 2 to 4 carbon atoms, and m and n may be the same or different from each other and each is an integer of 0 to 10, provided that m plus n is 1 to 10, preferably 1 to 5.

R&sup7; is, for example, an alkyl group, such as octyl groups (including all isomeric groups), nonyl groups (including all isomeric groups), decyl groups (including all isomeric groups), undecyl groups (including all isomeric groups), dodecyl groups (including all isomeric groups), tridecyl groups (including all isomeric groups), tetradecyl groups (including all isomeric groups), pentadecyl groups (including all isomeric groups), hexadecyl groups (including all isomeric groups), heptadecyl groups (including all isomeric groups), octadecyl groups (including all isomeric groups), nonadecyl groups (including all isomeric groups), eicosyl groups (including all isomeric groups), heneicosyl groups (including all isomeric groups) and docosyl groups (including all isomeric groups), or an alkenyl group, such as octenyl groups (including all isomeric groups), nonenyl groups (including all isomeric groups), decenyl groups (including all isomeric groups), undecenyl groups (including all isomeric groups), docenyl groups (including all isomeric groups), tridecenyl groups (including all isomeric groups), tetradecenyl groups (including all isomeric groups), pentadecenyl groups (including all isomeric groups), hexadecenyl groups (including all isomeric groups), peptadecenyl groups (including all isomeric groups), octadecenyl groups (including all isomeric groups), nonadecenyl groups (including all isomeric groups), eicosenyl groups (including all isomeric groups), heneicosenyl groups (a including all isomeric groups), and docosenyl groups (including all isomeric groups). R⁸ and R⁹ include ethylene group, trimethylene group, 1-methylethylene group, 2-methylethylene group, tetramethylene group, 1-methyltrimethylene group, 2-methyltrimethylene group, 3-methyltrimethylene group, 1-ethylethylene group, 2-ethylethylene group, 1,1-dimethylethylene group, 1,2-dimethylethylene group and 2,2-dimethylethylene group.

The alkylene oxide adduct of an aliphatic amine represented by formula (3) which is the component (B) used in this invention is preferably a compound represented by formula (3) in which R⁷ is a straight-chain alkyl or alkenyl group having 12 to 18 carbon atoms and R⁸ and R⁹ are each an ethylene group, in view of the excellent anti-wear properties.

The particularly preferred alkylene oxide adducts of an aliphatic amine which are the components (B) used in this invention include ethylene oxide adducts of an aliphatic amine and a mixture of the adducts and, in particular, alkylene oxide adducts of an aliphatic amine such as octylamine (caprylamine), decylamine, dodecylamine (laurylamine), tetradecylamine (mylystylamine), hexadecylamine (palmitylamine), octadecylamine (stearylamine) or 9-octadecenylamine (oleylamine).

In the shock absorber fluid of the present invention, the amount of the alkylene oxide adduct of an aliphatic amine, which is the component (B), added is arbitrary; however, it is desirable to add the adduct in an amount of preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total weight of the composition.

Although the shock absorber fluid of the present invention has excellent properties as mentioned above, it can be obtained by adding only to the base lubricating oil the phosphoric acid ester and/or the ester of a phosphorous acid which is the component (A) and the alkylene oxide adduct of an aliphatic amine which is the component (B) is added to the base lubricating oil. In order to further enhance the properties of the hydraulic oil composition thus obtained, generally known additives for lubricating oils can be used individually or together.

These additives include friction reducing agents, other than the components of the oil composition of the invention, such as an aliphatic alcohol, an aliphatic acid, an aliphatic amine and aliphatic amide; antioxidants, such as phenol-, amine-, sulfur-, zinc dithiophosphate and phenothiazine-based compounds; extreme pressure agents, such as sulfurized fats and oils, sulfides and zinc dithiophosphate; rust inhibitors, such as petroleum sulfonates and dinonylnaphthalenesulfonate; metal deactivators, such as benzotriazole and thiadiazole; metallic detergents, such as alkaline earth metal sulfonates, alkaline earth metal phenates, alkaline earth metal salicylates and alkaline earth metal phosphonates; ashless dispersants, such as succinimide, succinic esters and benzylamine; antifoaming agents, such as methylsilicone and fluorosilicone; Viscosity index improvers such as polymethacrylate, polyisobutylene and polystyrene and pour point improvers.

Although the amount of these additives added is arbitrary, the content of the antifoaming agent, the viscosity index improver, the metal deactivating agent and each of the other additives in the oil composition is usually 0.0005 to 1 wt%, 1 to 30 wt%, 0.005 to 1 wt% and 0.1 to 15 wt%, respectively, based on the total amount of the oil composition, in this order.

The method for preparing the hydraulic oil compositions of the present invention is not particularly limited. However, this method may usually consist of mixing a base lubricating oil and additives including the essential components (A) and (B), heating the resulting mixture to 30 to 100°C and then keeping it at that temperature for 20 minutes to 5 hours with shaking, or all Additives (where the solid additives have previously been dissolved in a small amount of the base lubricating oil) are heated separately to 30 to 100ºC, these additives are mixed in portions or as a whole into the base lubricating oil heated to 20 to 80ºC and then the resulting mixture is left at 30 to 100ºC for 20 minutes to 5 hours with stirring.

This invention will be better understood from the non-limiting Examples and Comparative Examples.

Examples 1 to 3 and Comparative Examples 1 to 4

In each of these examples, the ingredients shown in Table 1 were mixed together and the resulting mixture was heated at 50°C with stirring for 2 hours to prepare the hydraulic oil composition of the present invention (Examples 1 to 3). The thus prepared hydraulic oil compositions of the present invention were subjected to a durability test using a conventional apparatus to evaluate their friction reducing and wear preventing effects.

For comparison, hydraulic oil compositions were prepared according to the procedure of the above examples, with the difference that component (A) alone was used (Comparative Example 1), component (B) alone was used (Comparative Example 2), component (B) was replaced by an aliphatic amine (Comparative Example 3) or component (A) was replaced by a fatty acid (Comparative Example 4). The comparative oil compositions thus obtained were subjected to the same durability test.

Durability test using a conventional device

Using two commercially available strut-type shock absorbers, durability tests were conducted under the following conditions until the end of use of two million oscillations were carried out.

Test oil temperature: 80ºC

Amount of test oil used: 330 ml/shock absorber

Lateral load: 200 kgf

Total amplitude of applied vibration: 50 mm

Speed of applied vibration: 0.5 m/s

(1) Friction-reducing effects

The friction coefficients on the surfaces of the shock absorbers were determined at the time of vibration application frequency of 0 (at the initial stage of the durability test) and at the time of vibration application frequency of 2 million (at the time of completion of the durability test). The friction coefficients thus measured are shown in Table 1.

(2) Anti-wear effects

After the durability test was completed, the shock absorbers were disassembled to visually evaluate the surface condition of their friction surfaces (cylinders, pistons, rods and oil seals of the shock absorbers); the results are shown in Table 1. The degree of anti-wear effects is indicated with values from 0 to 5 (number 5 indicates the best effect).

As can be seen from the results of the examples, the hydraulic oil compositions (Examples 1 to 3) have excellent friction-reducing effects in the initial stage of the durability test and show less decline in their friction-reducing performances with the passage of time. In addition, they also show less wear on the friction surfaces at the end of the durability test, thus also showing excellent wear-preventing effects.

On the other hand, the comparative compositions (Comparative Examples 1 to 4) have excellent friction-reducing effects in the initial stage of the durability test, but show significantly more deterioration in their friction-reducing performances with the passage of time. In addition, they have inferior wear-preventing effects compared with the compositions of the present invention.

As apparent from the foregoing, the hydraulic oil compositions of this invention not only can be excellently applied to Teflon resin-impregnated sleeve members, but also have excellent durability (less deterioration with the passage of time) of the friction reducing effects and wear preventing effects. Table 1

Notes on Table 1:

#1: kinematic viscosity 10 cSt (at 40ºC)

#2: Ra-N-(C2 H4 -OH)2 (Ra: oleyl group)

#3: Rb-NH-(C2 H4 -O)2 -H (Rb: stearyl group)

#4: Average of the two shock absorbers (strut type)

Claims (11)

1. Shock absorber fluid containing a lubricating oil as a base oil and (A) at least one phosphoric acid ester and/or an ester of a phosphorous acid and (B) an adduct of an aliphatic amine with an alkylene oxide as essential components, wherein the phosphoric acid ester, the ester of the phosphorous acid and the adduct of an aliphatic amine with an alkylene oxide each correspond to the following formulas (1), (2) and (3) wherein in formula (1) R¹ and R² are each a straight-chain or branched-chain alkyl or alkenyl group having 8 to 20 carbon atoms and R³ is hydrogen; in formula (2) R⁴ and R⁵ are each a straight-chain or branched-chain alkyl or alkenyl group having 8 to 20 carbon atoms and R⁶ is hydrogen; and in formula (3) R⁴ is a straight-chain or branched-chain alkyl or alkenyl group having 8 to 22 carbon atoms and R⁴ and R⁵9 are the same or different from each other and each is a straight-chain or branched-chain alkylene group having 2 to 4 carbon atoms; m and n may be the same or different from each other and each is an integer from 0 to 10, provided that m plus n is 1-10. 2. Shock absorber fluid according to claim 1, wherein R¹, R², R⁴ and R⁵ are each a straight chain alkyl or alkenyl group. 3. Shock absorber fluid according to claim 1, wherein the phosphoric acid ester is dioctyl acid phosphate (dicaprylic acid phosphate), didecylic acid phosphate, didodecylic acid phosphate (dilaurylic acid phosphate), ditetradecylic acid phosphate (dimyristic acid phosphate), dihexadecylic acid phosphate (dipalmityl acid phosphate), dioctadecylic acid phosphate (distearyl acid phosphate) or di-9-octadecenyl acid phosphate (dioleyl acid phosphate) or a mixture thereof; the ester of phosphorous acid diacyl hydrogen phosphite (dicaprylic hydrogen phosphite), didecyl hydrogen phosphite, didodecyl hydrogen phosphite (dilauryl hydrogen phosphite), ditetradecyl hydrogen phosphite (dimyristyl hydrogen phosphite), dihexadecyl hydrogen phosphite (dipalmityl hydrogen phosphite), dioctadecyl hydrogen phosphite (distearyl hydrogen phosphite), di-9-octadecenyl hydrogen phosphite (dioleyl hydrogen phosphite) or a mixture thereof; and the alkylene oxide adduct of an aliphatic amine is an ethylene oxide adduct of octylamine (caprylamine), decylamine, dodecylamine (laurylamine), tetradecylamine (mylystylamine), hexadecylamine (palmitylamine), octadecylamine (stearylamine) or 9-octadecenylamine (oleylamine). 4. Shock absorber fluid according to at least one of claims 1 to 3, wherein R⁷ is a straight-chain alkyl or Alkenyl group with 12 to 18 carbon atoms. 5. Shock absorber fluid according to at least one of claims 1 to 4, wherein R⁸ and R⁹ are each an ethylene group. 6. Shock absorber fluid according to at least one of claims 1 to 5, wherein m plus n is 1-5. 7. Shock absorber fluid according to at least one of claims 1 to 6, wherein the base oil is a paraffinic or naphthenic oil which has been refined by subjecting lubricating oil fractions produced by atmospheric and pressure-reduced distillation of a crude oil to one or more of the following refining steps: solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfate washing and/or alumina treatment, or one of the synthetic oils polybutene, 1-octene oligomer, 1-decene oligomer, alkylbenzene, alkylnaphthalene, tridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, trimethylolpropane caprylate, Trimethylolpropane peralgonate, pentaerythritol 2-ethylhexanoate, pentaerythritol peralgonate, polyoxyalkylene glycol, polyphenyl ether, silicone oil and/or perfluoroalkyl ether. 8. Shock absorber fluid according to at least one of claims 1 to 7, wherein the base oil has a viscosity of 8 to 60 cSt at 40°C. 9. Shock absorber fluid according to at least one of claims 1 to 8, wherein the phosphoric acid ester and/or the ester of phosphorous acid is added to the base oil in an amount from 0.05 to 10 wt.% of the total amount of the oil composition and the alkylene oxide adduct of an aliphatic amine is added to the base oil in an amount of 0.05 to 10 wt.% of the total amount of the oil composition. 10. Preparation of a shock absorber fluid according to at least one of the preceding claims 1 to 9 by adding component (A) and component (B) to the base oil. 11. Use of the fluid according to at least one of claims 1 to 9, which contains the base oil, component (A) and component (B), as a shock absorber fluid.