OIL COMPOSITION FOR POWER STEERING WITH EXCELLENT LOAD CARRYING CAPACITY AND WEAR RESISTANCE

Abstract

An oil composition for power steering, includes: a) 75 to 85 weight percent (wt %) of a paraffinic base oil; b) 5 to 15 wt % of a dioctyl adipate plasticizer; c) 1 to 5 wt % of a polymethacrylate viscosity modifier; d) 0.01 to 1 wt % of an overbased calcium sulfonate detergent/dispersant; and e) 1 to 5 wt % of a load-carrying and wear resistant additive package.

Claims

1. An oil composition for power steering, the oil composition comprising: a) 75 to 85 weight percent (wt %) of a paraffinic base oil; b) 5 to 15 wt % of a dioctyl adipate plasticizer; c) 1 to 5 wt % of a polymethacrylate viscosity modifier; d) 0.01 to 1 wt % of an overbased calcium sulfonate detergent/dispersant; and e) 1 to 5 wt % of a load-carrying and wear resistant additive package.

2. The oil composition of claim 1, wherein the load-carrying and wear resistant additive package comprises at least one additive selected from the group consisting of e1) thiophene, tetrahydro 1,1-dioxide, and 3-(C9-11-isoalkyloxy) derivatives, e2) 1-(tert-dodecylthio)propan-2-ol, and e3) 1,3,4-thiadiazolidine-2,5-dithione.

3. The oil composition of claim 1, wherein the paraffinic base oil comprises a hydrotreated heavy paraffinic distillate.

4. The oil composition of claim 1, wherein the paraffinic base oil comprises a mixture of a first base oil and a second base oil in a mixing ratio of 6:4 to 8:2, wherein the first base oil has: a specific gravity of 0.83 to 0.84; a kinematic viscosity of 4 cSt to 5 cSt, at a temperature of 100 C.; a viscosity index of 120 or higher; and a flash point of 210 C. or higher, and wherein the second base oil has: a specific gravity of 0.84 to 0.85; a kinematic viscosity of 8 cSt to 9 cSt, at a temperature of 100 C.; a viscosity index of 130 C. or higher, and a flash point of 230 C. or higher.

5. The oil composition of claim 1, wherein the plasticizer has: a specific gravity of 0.92 to 0.93; a kinematic viscosity of 7.5 cSt to 8.5 cSt, at a temperature of 40 C.; and a saponification value of 299 to 305.

6. The oil composition of claim 1, wherein the viscosity modifier has: a specific gravity of 0.875 to 0.905; and a kinematic viscosity of 650 cSt to 750 cSt, at a temperature of 100 C.

7. The oil composition of claim 1, wherein the overbased calcium sulfonate detergent/dispersant has: a kinematic viscosity of 50 cSt to 100 cSt at a temperature of 100 C.; and a total base number (TBN) of 290 or more.

8. The oil composition of claim 1, wherein the oil composition has a load-carrying capacity of 200 kgf or more, corresponding to a measurement of the load-carrying capacity in accordance with an ASTM D 2783 Standard test method.

9. The oil composition of claim 8, wherein the ASTM D 2783 Standard test method comprises a four-ball load carrying capacity test.

10. The oil composition of claim 1, wherein the oil composition has a wear resistance of 0.4 mm or less, corresponding to a measurement of the wear resistance in accordance with an ASTM D 4172 Standard test.

11. The oil composition of claim 1, wherein the oil composition has a corrosion resistance rating of Grade 1a, corresponding to a measurement of corrosion resistance in accordance with an ASTM D 130 Standard test.

12. The oil composition of claim 1, wherein the oil composition lubricates a power steering gearbox of a vehicle.

13. The oil composition of claim 1, wherein the oil composition has an aniline point of 90 C. or higher, corresponding to a measurement of the aniline point in accordance with an ASTM D 61 Standard test method.

Description

DETAILED DESCRIPTION

[0025] Hereinafter, the present invention will be described in more detail with reference to embodiments and drawings. However, the following embodiments are provided as examples to aid understanding of the present invention, and the scope of the present invention is not limited thereto. The present invention may be subject to various changes and may be implemented in various forms, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

[0026] The terms used in this application are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the term include or have is intended to designate the presence of features, numbers, steps, operations, elements, parts, or combinations thereof described herein, and it should be understood that it does not exclude in advance the possibility of the presence or addition of other features, numbers, steps, operations, elements, parts, or combinations thereof.

[0027] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and unless explicitly defined herein, they are not to be interpreted in an idealistic or overly formal sense.

[0028] The oil composition for power steering according to an embodiment includes a base oil, a plasticizer, a viscosity modifier, a detergent/dispersant, and a load-carrying and wear resistant additive package. The oil composition for power steering may further include a dye if necessary.

[0029] More specifically, the oil composition for power steering, in weight percent (wt %), may include: a) 75 to 85 wt % of a paraffinic base oil; b) 5 to 15 wt % of a dioctyl adipate plasticizer; c) 1 to 5 wt % of a polymethacrylate viscosity modifier; d) 0.01 to 1 wt % of an overbased calcium sulfonate detergent/dispersant; and e) 1 to 5 wt % of a load-carrying and wear resistant additive package.

<Paraffinic Base Oil>

[0030] The base oil accounts for 75 wt % to 85 wt % of the oil composition for power steering. Distillates (petroleum) hydrotreated heavy paraffinic may be used as the base oil.

[0031] According to an embodiment, the paraffinic base oil may be used by mixing two types of base oils with different physical properties. For example, a first base oil may be a paraffinic distillate with a specific gravity of 0.83 to 0.84, a 100 C. kinematic viscosity, in centistokes (cSt), of 4 cSt to 5 cSt, a viscosity index of 120 or higher and a flash point of 210 C. or higher, and a second base oil may be a paraffinic distillate with a specific gravity of 0.84 to 0.85, a 100 C. kinematic viscosity of 8 cSt to 9 cSt, a viscosity index of 130 C. or higher, and a flash point of 230 C. or higher.

[0032] The first base oil and the second base oil may be mixed and used at a mixing ratio of 6:4 to 8:2, and the mixing ratio of 7:3 is preferred because appropriate viscosity and lubricity may be maintained.

<Plasticizer>

[0033] The oil composition for power steering may include dioctyl adipate as a plasticizer that can improve oiliness. The plasticizer may have a specific gravity of 0.92 to 0.93 and a 40 C. kinematic viscosity of 7.5 cSt to 8.5 cSt. The plasticizer preferably has a saponification value in the range of 299 to 305.

<Viscosity Modifier>

[0034] In the oil composition for power steering, polymethacrylate, that is, a methacrylate copolymer, may be used as a viscosity modifier. The viscosity modifier preferably has a specific gravity of 0.875 to 0.905 and a 100 C. kinematic viscosity of 650 cSt to 750 cSt.

<Detergent/Dispersant>

[0035] In the oil composition for power steering, an overbased calcium sulfonate may be used as a detergent/dispersant. The detergent/dispersant preferably has a 100 C. kinematic viscosity of 50 cSt to 100 cSt and a total base number (TBN) of 290 or more.

<Additive Package>

[0036] The oil composition for power steering may include an additive package to improve corrosion resistance, load-carrying capacity, and wear resistance. The additive package includes one or more additives selected from thiophene, tetrahydro 1,1-dioxide, and 3-(C9-11-isoalkyloxy) derivatives (C10-rich), 1-(tert-dodecylthio)propan-2-ol), and 1,3,4-thiadiazolidine-2,5-dithione (reaction products with hydrogen peroxide and tert-nonanethiol).

[0037] In a specific example, based on the total weight of the additive package, e1) 10 to 20 wt % of thiophene, tetrahydro 1,1-dioxide, and 3-(C9-11-isoalkyloxy) derivatives, e2) 1 to 10 wt % of 1-(tert-dodecylthio)propan-2-ol, and e3) 1 to 5 wt % of 1,3,4-thiadiazolidin-2,5-dithione may be included. Within this additive mixing ratio range, the corrosion resistance, load-carrying capacity, and wear resistance of the oil composition may be significantly improved, which may be confirmed through the following experimental examples.

[0038] The additive package may further include alcohols such as dicocoalkylamine, substituted or unsubstituted alkanediols having 1 to 4 carbon atoms, and substituted or unsubstituted alkanols having 2 to 5 carbon atoms, and it may be a mixture of a mineral oil and a paraffinic base oil.

[0039] The additive package preferably includes, based on the total weight of the additive package, 0.1 to 1 wt % of dicocoalkylamine, 1 to 5 wt % of substituted or unsubstituted alkanediol having 1 to 4 carbon atoms, and 0.1 to 1 wt % of substituted or unsubstituted alkanol having 2 to 5 carbon atoms, and it may further include 10 to 20 wt % of mineral oil and 10 to 20 wt % of paraffinic base oil (distillates (petroleum), hydrotreated light paraffinic).

[0040] The oil composition for power steering according to an embodiment has a four-ball load-carrying capacity evaluation result of 200 kilogram-force (kgf) or more according to the ASTM D 2783 standard, and from this result, it can be confirmed that the oil composition has a very high (i.e., excellent) load-carrying capacity, that is, extreme pressure resistance.

[0041] The oil composition for power steering according to an embodiment has a four-ball wear resistance evaluation result of 0.4 mm or less according to the ASTM D 4172 standard, and from this result, it can be confirmed that the oil composition has very high (i.e., excellent) wear resistance.

[0042] In addition, the oil composition for power steering according to an embodiment has a corrosion resistance evaluation result of Grade 1a according to the ASTM D 130 standard, and it can be confirmed that the effect of preventing corrosion is also superior (i.e., excellent).

Example

[0043] Base oils and additives were mixed according to the compositions in Table 1 and Table 2 below.

(1) Base Oil

[0044] Distillates (petroleum), hydrotreated heavy paraffinic, was used as the base oil for the oil composition for power steering, and first and second base oils with the physical properties shown in Table 1 below were mixed at a weight ratio of 7:3.

TABLE-US-00001 TABLE 1 First base oil Second base oil Specific gravity 0.83 to 0.84 0.84 to 0.85 Kinematic 4 cSt GRADE (@ 100 C.) 8 cSt GRADE (@ 100 C.) viscosity Viscosity index 120 or higher 130 or higher Flash point 210 C. or higher 230 C. or higher

(2) Additive Package

[0045] An additive package was prepared to prevent oxidation and improve the wear resistance and extreme pressure properties of the oil composition for power steering.

[0046] Specifically, the additive package includes e1) thiophene, tetrahydro 1,1-dioxide, and 3-(C9-11-isoalkyloxy) derivatives, e2) 1-(tert-dodecylthio)propan-2-ol, e3) 1,3,4-thiadiazolidine-2,5-dithione, e4) a Cr to 04 alkanediol, e5) a 02 to 05 alkanol, e6) dicocoalkylamine, e7) 1H-imidazole-1-ethanol and 2-(8-heptadecenyl)-4,5-dihydro, e8) a mineral oil, and e9) a paraffinic base oil, and the content is as shown in Table 2 below.

TABLE-US-00002 TABLE 2 Content Additive package components (wt %) 1 Distillates (Petroleum), hydrotreated light paraffinic 10 to 20 2 Mineral oil 10 to 20 3 Thiophene, tetrahydro 1,1-dioxide, 3-(C9-11-isoalkyloxy) 10 to 20 derives., C10-rich 4 1-(tert-dodecylthio)propan-2-ol 1 to 10 5 1,3,4-thiadiazolidine-2,5-dithione, reaction products with 1 to 5 hydrogen peroxide and tert-nonanethiol 6 Alkanediol (C = 1-4), substituted, 1 to 5 7 Alkanol (C = 2-5), substituted bis-, N-tallow alkyl 0.1 to 1 derives. 8 Dicoco alkylamine 0.1 to 1 9 1H-limidazole-1-ethanol, 2-(8-heptadecenyl)-4,5-dihydro <0.1

(3) Oil Composition for Power Steering

[0047] After preparing the base oil and the additive, an oil composition for power steering was prepared by heating and mixing components as shown in Table 3 below.

TABLE-US-00003 TABLE 3 Content Additive components (wt %) 1 Base oil Distillates (petroleum), hydrotreated heavy 75 to 85 paraffinic 2 Plasticizer Dioctyl adipate 5 to 15 3 Additive Additive package (e) 1 to 5 4 Viscosity Methacrylate copolymer 1 to 5 modifier 5 Detergent/ Overbased calcium sulfonate <1 dispersant 6 Dye Red powder 0.01

Comparative Example

[0048] The physical properties and performance of the conventionally used oil composition and the oil composition according to the present invention were compared. The specific composition of the oil composition according to Comparative Example is shown in Table 4 below.

TABLE-US-00004 TABLE 4 Content Additive components (wt %) 1 Base oil Mineral oil 91 2 Plasticizer x 3 Lubricating additive Sulfur-based wear resistant 3 and extreme pressure agent 4 Viscosity modifier Olefin copolymer (OCP) 5 5 Detergent/dispersant Sodium-based dispersant 1 6 Dye x

Experimental Example 1

[0049] The physical properties of oil compositions for power steering prepared according to the above example and comparative example were measured using the following test methods.

(1) Appearance

[0050] Red dye was used to prevent mixing with other oils, and the oil used in Comparative Example was light yellow.

(2) Specific Gravity

[0051] Specific gravity (=oil density/water density) was measured according to the ASTM D 1298 standard in order to check whether it is a specified lubricant or whether foreign substances are mixed, and it is possible to predict the type of base oil and the molecular composition of hydrocarbons and calculate the amount of heat.

(3) Kinematic Viscosity

[0052] Kinematic viscosity was measured using a Stabinger Viscometer (Anton Paar/SVM3000) according to the ASTM D 7042 standard. Kinematic viscosity is the time it takes for the oil to fall by gravity over a certain distance, and it needs to have sufficient viscosity at high temperatures to prevent gear wear.

(4) Viscosity Index

[0053] The viscosity index was measured using a Stabinger Viscometer (Anton Paar/SVM3000) according to ASTM D 7042 standard. The higher the viscosity index (VI), the lower the viscosity change due to temperature changes. The test method calculates the viscosity index using the kinematic viscosity measured at a certain temperature (40 C., 100 C.) and the correlation known in the ASTM D 2270 standard.

(5) Flash Point

[0054] The flash point was measured using a Flash Point Tester (Duck woo scientific) according to the ASTM D 92 standard. The flash point refers to the lowest temperature at which oil vapor generated by continuous heating can be ignited. It is an indicator of the risk of ignition during handling and use, and it is possible to determine whether impurities are added. After filling the specified cup with an oil to the specified level, a test flame is passed over the cup. The temperature at which the test flame ignites the vapor above the oil is called the flash point.

(6) Pour Point

[0055] The pour point was measured in a low-temperature chamber according to the ASTM D 97 standard. The pour point is defined as the temperature at which an oil initially flows at low temperatures. After cooling 45 ml of an oil to 60 C. or lower without stirring in a test tube with a thermometer inserted, the temperature of the sample is raised at 3 C. intervals, and the temperature when the sample moves within 5 seconds is called the pour point.

[0056] It is appropriate to have a low pour point in order to easily shift gears in cold weather. When the temperature of the lubricant is continuously lowered, the wax begins to precipitate and solidify, and the pour point refers to the temperature just before this point. The pour point is a value that determines the use, storage, and supply of oil in extremely cold areas.

(7) Low-Temperature Viscosity

[0057] The viscosity index was measured using a Stabinger Viscometer (Anton Paar/SVM3000) according to the ASTM D 7042 standard. The low-temperature viscosity of the oil composition needs to be sufficiently low to easily shift gears. It is suitable for the low-temperature viscosity to be 2,000 Centipose (cP) or less at 20 C., 5,000 cP or less at 30 C., and 20,000 cP or less at 40 C. The low-temperature viscosity is a physical property of the engine oil related to initial engine startability, and the lower the low-temperature viscosity, the shorter the time it takes for the oil to reach the entire engine.

(8) Aniline Point

[0058] The aniline point was measured according to the ASTM D 61 standard. This test method is used to find the point where equal volumes of hydrocarbon and aniline are completely dissolved and become transparent, which determines the usability of an oil. In the case of CA, CN, the more double bonds, the lower the aniline point, and in the case of Cp, the fewer double bonds, that is, the higher the oxidation stability, the higher the aniline point. It is suitable for oil compositions for power steering according to the present invention to have an aniline point of 90 C. or higher.

[0059] The measurement results of the physical properties of oil compositions according to Example and Comparative Example are shown in Table 5 below. Accordingly, it can be confirmed that the oil composition according to Example satisfies all the physical properties required for oil compositions for power steering.

TABLE-US-00005 TABLE 5 Suitability Physical assessment Comparative properties for test Test method Units criteria Example Example Appearance Naked eye Red Light yellow Specific gravity ASTM D 0.84 to 0.88 0.854 0.845 1298 Kinematic 40 C. ASTM D cSt 30 to 35 33.09 33.87 viscosity 100 C. 445 cSt 7.0 or higher 7.312 7.245 Viscosity index ASTM D 190 or 195 192 2270 higher Flash point ASTM D 92 C. 180 or 228 206 higher Pour point ASTM D 97 C. 45 or below 54 57 Low- 20 C. ASTM D cP 2,000 or 967 933 temperature 2983 below viscosity 30 C. cP 5,000 or 2758 2444 below 40 C. cP 20,000 or 9461 9213 below Aniline point ASTM D 61 C. 90 or higher 110 115

Experimental Example 2

[0060] The durability performance of the oil compositions for power steering prepared according to Example and Comparative Example was measured using the following test methods.

(1) Corrosion Resistance

[0061] The copper plate corrosion (100 C.3 hr) grade of the oil compositions was measured according to the ASTM D 130 standard. It is a method to check whether metals are corroded due to organic sulfur and corrosive substances contained in the oil, which is divided into Grades 1a to 4c. For use as oil for power steering, Grade 1 or lower is suitable.

(2) Four-Ball Load-Carrying Capacity

[0062] The four-ball load-carrying capacity, that is, breaking limit load, was measured according to the ASTM D 2783 standard. Gears are small, but since they transmit large forces to a small area, the local load is very large. Thus, the oil composition for power steering needs to undergo a performance test for wear prevention from extreme pressure loads, that is, an oil-film risk assessment. When the test result according to ASTM D 2783 is 80 kfg or more, it is suitable for oil compositions for power steering. [0063] Test conditions: Speed (177060 rpm), Load (80 to 8000 kgf), Duration (10 sec), Temperature (room temperature)

(3) Four-Ball Wear Resistance

[0064] The load-carrying capacity of the oil compositions was measured using a four-ball tester (SETA STANHOPE-SETA/Seta-Shell Four Ball Lubricant Tester) according to the ASTM D 4172 standard. It is a standard for determining the wear resistance of oil, and those of 0.4 mm or less are suitable for oil compositions for power steering.

[0065] The test method is specifically the shell-type four-ball test, and after operating under certain conditions by making point contact with 3 fixed balls and 1 rotating ball, the average wear surface of the 3 fixed balls in mm is confirmed. [0066] Test conditions: Speed (120060 rpm), Load (400.2 kgf), Duration (601 min), Temperature (752 C.)

(4) Seal Compatibility

[0067] The compatibility of the oil composition with a seal made of rubber was evaluated according to the ASTM D 471 standard. After immersing a sample (rubber) in the oil composition, leakage prevention performance was tested by measuring the volume, tensile strength, elongation, and hardness change rates. An oil composition with a volume change rate of 10% or less, a tensile strength change rate of 30% or less, an elongation change rate of 50% or less, and a hardness change in the range of 10 to 10 Hs is suitable as an oil composition for power steering.

[0068] The performance measurement results of the oil compositions according to Example and Comparative Example are shown in Table 6 below. Accordingly, it can be seen that the corrosion resistance, load-carrying capacity, wear resistance, and seal compatibility of the oil composition for power steering according to Example are significantly improved.

TABLE-US-00006 TABLE 6 Com- par- Suitability ative Physical properties Test assessment Ex- Ex- for test method Units criteria ample ample Copper plate corrosion ASTM D Grade 1 or less 1a 1a (100 C. 3 hr) 130 Four-ball load-carrying ASTM D kgf 80 or more 200 160 capacity 2783 (Baking limit load) Four-ball wear resistance ASTM D mm 0.4 or less 0.37 0.52 (40 kg 1200 rpm 4172 100 C. 1 hr) Seal Volume ASTM D % 0 to 10 0.2 1.9 com- change rate 471 patibility Tensile Nitrile- % 30 or less 13.7 13.4 strength based change rate sample: Elongation 120 C. % 50 or less 27.3 19.2 change rate 70 hr Acrylic Hardness sample: Hs 10~10 3 4 change 150 C. 70 hr

[0069] An oil composition for power steering according to the present invention has high (i.e., excellent) wear resistance and load-carrying capacity and effectively prevents corrosion, which can significantly reduce noise and vibrations due to friction when applied to the support yoke in the gearbox of a power steering system, thereby greatly improving the performance of automotive power steering system.