Grease composition and rack-and-pinion-type steering device filled with said grease composition

Abstract

The present invention provides a grease composition for use in lubrication between a metal member and a metal member, and in lubrication between a metal member and a resin member. The grease composition contains: a urea thickener; as a base oil, a synthetic hydrocarbon oil and / or mineral oil having a kinetic viscosity of 4-40 mm2 / s at 100°C of the base oil; and as additives, 1-10 mass% of montan wax, 1-5 mass% of a molybdenum-based extreme pressure agent, and 1-5 mass% of a sulfonate-based compound. The grease composition has a consistency of 310-430.

Description

Grease composition and rack-and-pinion steering device filled with said grease composition

[0001] The present invention relates to a grease composition that can be used for both lubrication between metal members and lubrication between a metal member and a resin member.

[0002] A rack and pinion gear is a type of actuator that converts rotational motion into linear motion by meshing a pinion gear, a circular metal gear, with a rack bar, a rod-shaped gear with teeth cut on a metal rod. In automobiles, the pinion gear is attached to the end of the shaft extending from the steering wheel. Operating the steering wheel rotates the pinion gear, causing the rack bar to move horizontally in the direction of travel, thereby changing the direction of the wheels. Rack and pinion gears experience wear due to the sliding lubrication of the gear meshing surfaces. Wear can cause abnormal noise. Meanwhile, the support yoke, which is equipped with a spring that presses against the rack bar and is attached to the back of the rack bar, slidably supports the rack bar to improve the steering performance and quietness of the rack and pinion gear. The support yoke has an eccentric center of curvature that allows it to contact the rack bar within a certain band-width area. The sliding surface that contacts the rack bar is a yoke pad, a resin material formed into a concave arc. The yoke pad slides against the rack bar and provides lubrication, resulting in friction and wear. Friction impairs the support yoke's ability to improve steering performance, while wear impairs its ability to improve quietness. Previously, grease compositions that can be used with resin components have been reported, such as a resin lubrication grease composition containing a base oil, a thickener, and montan wax, which reduces the static friction coefficient and extends durability (Patent Document 1). Previously, grease compositions that can be used with metal components have been reported, such as a grease composition containing a thickener, synthetic oil, mineral oil, MoDTC, and Ca sulfonate, which has extreme pressure properties that can withstand harsh conditions and excellent low-temperature operability (Patent Document 2).

[0003] JP 2002-371290 A JP 2004-269722 A

[0004] The inventors' experiments revealed that grease compositions usable for lubricating metal and resin components reduce the sliding force and wear of the support yoke, but lack the boundary lubricity required for rack and pinion gears, resulting in gear wear and noise from the rack bar. On the other hand, grease compositions usable between metal components do not reduce the sliding force and wear of the support yoke, and lack the boundary lubricity required for rack and pinion gears, resulting in wear of the support yoke and rack and pinion gears, reduced steering performance, and noise from the rack bar. Thus, a grease composition for lubricating between metal and resin components was ineffective when used to lubricate the metal components, and a grease composition for lubricating between metal components was ineffective when used to lubricate the metal and resin components. Therefore, an object of the present invention is to provide a grease composition that can be used both for lubricating between metal and resin components and for lubricating between metal components.

[0005] Surprisingly, it has been found that by selecting the type of thickener, the type and kinematic viscosity of the base oil, the type and amount of additive, and the consistency, it is possible to obtain a grease composition that can lubricate both between metal members and between metal members and resin members. That is, the present invention provides the following grease composition and a rack-and-pinion steering device filled with the grease composition. 1. A urea-based thickener, a base oil having a kinematic viscosity of 4 to 40 mm at 100°C, 2 1. A grease composition for use in lubricating between metal members and between metal members and between metal members and resin members, the grease composition having a consistency of 310 to 430, the grease composition comprising a synthetic hydrocarbon oil and / or mineral oil having a kinematic viscosity of 100°C / s, and 1 to 10 mass% of montan wax, 1 to 5 mass% of a molybdenum-based extreme pressure agent, and 1 to 5 mass% of a sulfonate-based compound as additives. 2. The grease composition according to 1 above, wherein the thickener is an aliphatic diurea compound. 3. The grease composition according to 1 or 2 above, wherein the base oil is a synthetic hydrocarbon oil. 4. The base oil has a kinematic viscosity at 100°C of 4 to 10 mm 2 / s. 5. The grease composition according to any one of 1 to 3 above, wherein the content of montan wax is 2 to 5 mass %. 6. The grease composition according to any one of 1 to 5 above, wherein the molybdenum-based extreme pressure agent is organic molybdenum and the content thereof is 1 to 3 mass %. 7. The grease composition according to any one of 1 to 6 above, wherein the sulfonate-based compound is neutral Ca sulfonate and the content thereof is 0.5 to 2 mass %. 8. The grease composition according to any one of 1 to 7 above, wherein the consistency is 355 to 385. 9. A rack-and-pinion steering device filled with the grease composition according to any one of 1 to 8 above. 10. The rack-and-pinion steering device according to 9 above, wherein a yoke pad of a support yoke constituting the steering device is made of polyamide or PTFE.

[0006] The present invention provides a grease composition that can be used between metal members and between metal members and resin members. The present invention improves the load-bearing capacity of rack and pinion gears and also improves durability by reducing friction and wear between the yoke pad and the rack bar.

[0007] [Urea-based thickener] The urea-based thickener of the present invention is preferably a diurea-based thickener represented by the following formula (1): 1 NH-CO-NH-C6H4-p-CH2-C6H4-p-NH-CO-NHR 1 ' (1) (wherein, R 1 and R 1 The diurea thickeners of formula (1) include R 1 and R 1 aliphatic diureas, where both R and R′ are octyl, dodecyl, hexadecyl, or octadecyl groups; 1 and R 1 alicyclic aliphatic diureas including diurea compounds in which one of R ' is an octyl group, a dodecyl group, a hexadecyl group, or an octadecyl group and the other is a cyclohexyl group, and1 and R 1 The urea-based thickener of the present invention is preferably an aliphatic diurea compound, and in formula (1), R 1 and R 1 Diurea compounds in which R ' are each independently an octyl group, a dodecyl group, a hexadecyl group, or an octadecyl group are more preferred, 1 and R 1 An aliphatic diurea compound in which one of the groups is an octyl group and the other is an octadecyl group is more preferred. The content of the urea-based thickener may be any amount that can adjust the consistency of the grease to 310 to 430, and specifically, it is preferably 2 to 15 mass % based on the total mass of the composition, more preferably 3 to 10 mass %, and even more preferably 3 to 7 mass %. In this specification, "mass %" is based on the total mass of the composition.

[0008] [Base oil] The base oil in this specification has a kinematic viscosity at 100°C of 4 to 40 mm 2 The base oil is a synthetic hydrocarbon oil and / or a mineral oil having a kinematic viscosity of 4 to 10 mm / s. By using such a base oil, it is possible to maintain good inflow of grease between the rack bar and the yoke pad, and to form an oil film sufficient for lubricating the support yoke and the rack bar. The kinematic viscosity of the base oil at 100°C is 4 to 10 mm / s. 2 / s. Poly-α-olefin is preferred as the synthetic hydrocarbon oil. The synthetic hydrocarbon oil may be so-called biomass oil, which is produced using biological resources derived from animals and plants as raw materials. For example, biomass hydrocarbon oil using vegetable oil such as palm oil, corn oil, soybean oil, etc. can also be used. As the mineral oil, either naphthenic or paraffinic can be used. The base oil preferably contains a synthetic hydrocarbon oil, more preferably poly-α-olefin, in order to improve the low-temperature fluidity of the grease. The base oil should have a kinematic viscosity at 100°C of 4 to 10 mm 2 Preferably, the oil contains a synthetic hydrocarbon oil having a kinematic viscosity of 6 to 10 mm / s at 100°C. 2From the viewpoint of lubricity, the content of the base oil is preferably 75 to 95 mass %, more preferably 80 to 90 mass %, based on the total mass of the composition.

[0009] [Additives] The grease composition of the present invention contains, as additives, 1 to 10 mass% of montan wax, 1 to 5 mass% of a molybdenum-based extreme pressure agent, and 1 to 5 mass% of a sulfonate-based compound. In the present invention, montan wax refers to a wax based on montanic acid obtained by refining and oxidizing brown coal. It has a dropping point of about 90°C or higher as measured by ASTM D 127 and is insoluble in base oil. Examples of montan waxes that can be used in the present invention include acid waxes with an acid value of 110 to 160 mgKOH / g, ester waxes having both nonpolar and polar moieties, esterified products of montanic acid, partially saponified ester waxes with a saponification value of 100 to 130 mgKOH / g, and sodium or calcium salts thereof. The montan wax used in the present invention is preferably a partially saponified montanic acid ester wax, particularly a partially saponified montanic acid ester wax with an acid value of 5 to 15 mgKOH / g and a saponification value of 100 to 130 mgKOH / g. The acid value is measured in accordance with ASTM D 1386. The saponification value is measured in accordance with ASTM D 1387. In the present invention, montan wax mainly functions as a friction modifier and, when used in combination with a molybdenum-based extreme pressure agent and a sulfonate-based compound, also functions as an extreme pressure agent. In the present invention, by setting the montan wax content to 1 to 10 mass%, it is possible to maintain good low friction and wear resistance of the rack bar and yoke pad, and good wear resistance of the rack and pinion gear portion. The content is preferably 2 to 5 mass%.

[0010] In the present invention, the molybdenum-based extreme pressure agent primarily exhibits wear resistance. Examples of molybdenum-based extreme pressure agents that can be used in the present invention include organic molybdenum, such as oil-soluble or oil-insoluble molybdenum dithiocarbamate, preferably molybdenum dialkyldithiophosphate, and particularly preferably molybdenum dibutyldithiocarbamate. In the present invention, by setting the content of the molybdenum-based extreme pressure agent to 1 to 5 mass%, the wear resistance of the rack bar, yoke pad, and rack and pinion gear portion can be maintained at a good level. It is preferably 2 mass%. It is more preferable to include 1 to 3 mass% of organic molybdenum. It is particularly preferable to include 1 to 3 mass% of molybdenum dibutyldithiocarbamate.

[0011] Sulfonate compounds are generally used as metal detergent-dispersants and rust inhibitors in lubricating oils such as engine oils. In the present invention, they serve to improve extreme-pressure properties. Examples of sulfonate compounds that can be used in the present invention include Ca sulfonate, Ba sulfonate, and Na sulfonate. Of these, Ca sulfonate is preferred. While overbased sulfonates (e.g., having a base number of 375 mg KOH / g or more as measured by JIS K 2501) may be included, neutral Ca sulfonate is more preferred. Among neutral Ca sulfonates, calcium dinonylnaphthalene sulfonate is preferred. In the present invention, by adjusting the sulfonate compound content to 1 to 5 mass%, the wear resistance of the rack bar, yoke pad, and rack and pinion gear portion can be maintained at a good level. The content is preferably 0.5 to 2 mass%. It is more preferred to include 0.5 to 2 mass% of neutral Ca sulfonate. It is particularly preferable to contain 0.5 to 2 mass % of calcium dinonylnaphthalenesulfonate.

[0012] The additives of the present invention are particularly preferably 2 to 5 mass %, 2 mass %, and 1 mass % of partially saponified montanic acid ester wax, molybdenum dibutyldithiocarbamate, and calcium dinonylnaphthalenesulfonate. The grease composition of the present invention may contain additives other than the above three components. Examples of such additives include antioxidants, rust inhibitors, metal corrosion inhibitors, oiliness agents, anti-wear agents, and solid lubricants. The content of these other additives is typically 0.1 to 5 mass %, and preferably 0.5 to 3 mass %.

[0013] [Lubricated Members] While grease compositions used for lubricating between metal members and between metal and resin members typically have different formulations, the grease composition of the present invention can be used for both lubricating between metal members and between metal and resin members. Therefore, the grease composition of the present invention can be used in both locations within a single device or apparatus, including both sliding locations between metal members and sliding locations between metal and resin members. Examples of lubrication between metal members include lubrication between steel and steel, such as between a rack and pinion gear (i.e., a rack bar and a pinion). Examples of lubrication between metal and resin members include lubrication between steel and resin, such as between a rack bar and a support yoke. Therefore, an example of a device with both steel-to-steel and steel-to-resin lubrication locations is a rack and pinion steering device. While the resin constituting the yoke pad of the support yoke is not particularly limited, polyamide or PTFE is preferred from the viewpoints of sliding properties, durability, and environmental resistance, with polyamide being more preferred.

[0014] [Consistency] The consistency of the grease composition of the present invention is 310 to 430. Within this range, the flowability of the grease can be maintained to improve the low friction and wear resistance of the rack bar and yoke pad, and the wear resistance of the rack and pinion gear portion. The consistency of the grease composition of the present invention is more preferably 355 to 385. The grease composition of the present invention can be simultaneously applied both between metal members and between metal members and resin members, but can also be used only between metal members or only between metal members and resin members. For example, when used in rack and pinion gears, the consistency is preferably about 310 to 415 to prevent leakage, and when used to lubricate the rack bar and support yoke, the consistency is preferably about 340 to 430 to maintain flowability into the lubrication portion.

[0015] The grease composition of the present invention is a grease composition comprising: 1 and R 1 an aliphatic diurea thickener in which one of the groups is an octyl group and the other is an octadecyl group, and in particular, an aliphatic diurea thickener in which the molar ratio of octyl group to octadecyl group is 1:1; 2 and as additives, 2 to 5 mass% of a partially saponified Montan acid ester wax having an acid value of 5 to 15 mgKOH / g and a saponification value of 100 to 130 mgKOH / g, 1 to 3 mass% of molybdenum dibutyldithiocarbamate, and 0.5 to 2 mass% of calcium dinonylnaphthalenesulfonate, and the grease composition has a consistency of 355 to 385 and is particularly preferred for use in lubricating between metal members and between metal members and resin members.

[0016] More particularly, the grease composition is preferably for use in a rack-and-pinion steering device. It is more preferable that the yoke pad of the support yoke constituting the steering device is made of polyamide or PTFE.

[0017] <Preparation of Grease Composition> Grease compositions of Examples and Comparative Examples were prepared using the following components. Specifically, 2 One mole of 4',4-diphenylmethane diisocyanate was reacted with two moles of amine (octylamine:octadecylamine = 1:1, molar ratio) in a base oil at 1 / s, heated, cooled, and then kneaded on a three-roll mill to obtain a base grease. The additives shown in Table 1 were then blended thereto, and further base oil was added to obtain the thickener amount shown in Table 2. The mixture was then dispersed on a three-roll mill to obtain the grease compositions of the Examples and Comparative Examples. In addition to the additives shown in Table 1, the antioxidant contained 0.5% by mass of a reaction product of N-phenylbenzenamine and 2,4,4-trimethylpentene, and the rust inhibitors contained 0.05% by mass of 1-[N,N-bis(2-ethylhexyl)aminomethyl]-4-methylbenzotriazole and 0.05% by mass of 1-[N,N-bis(2-ethylhexyl)aminomethyl]-5-methylbenzotriazole. The kinematic viscosity of the base oil was measured in accordance with JIS K 2283. The consistency means the 60-time worked consistency, and was measured in accordance with JIS K2220 7.

[0018]

[0019] The grease compositions prepared above were subjected to the following tests. The results are shown in Table 2. <Evaluation of Metal-Resin Sliding Force and Durability by Reciprocating Motion Test> Test Conditions Load: 3000 N Speed: 62.5 mm / sec Stroke: 150 mm Durability: 20,000 cycles Ambient temperature: Room temperature Evaluation criteria for sliding force (based on the same criteria as Comparative Example 6) ⊚: Lower sliding force than the standard ∘: Lower sliding force than the standard Δ: Equivalent to the standard ×: Higher sliding force than the standard Evaluation criteria for durability (based on the same criteria as Comparative Example 6) ⊚: Lower wear amount than the standard ∘: Lower wear amount than the standard Δ: Equivalent to the standard ×: Higher wear amount than the standard Note that a reciprocating motion test using a PTFE yoke pad was also conducted for the grease composition of Example 6. The results were ⊚ for both sliding force and durability. For the grease compositions of Comparative Examples 7 and 8, a reciprocating motion test was conducted using a PTFE yoke pad instead of a polyamide yoke pad. <Metal-to-metal durability evaluation by high-speed four-ball load-bearing performance test> The welding load (WP) was measured according to ASTM D 2596-97. Test conditions: Rotation speed: 1770 rpm, Test time: 10 seconds

[0020]

[0021] In Examples 1 to 8, all durability tests were rated as ◯ or above, and the high-speed four-ball load-bearing performance was good, whereas in Comparative Examples 1 to 8, the durability tests were rated as △ or ×, or as ◎, but the high-speed four-ball load-bearing performance was poor.

Claims

1. Urea-based thickeners, The base oil has a kinematic viscosity of 4 to 40 mm at 100°C. 2 / s, synthetic hydrocarbon oils and / or mineral oils, Additives include 1 to 10 mass% of montan wax, 1 to 5 mass% of a molybdenum-based extreme pressure agent, and 1 to 5 mass% of a sulfonate-based compound. Contains The consistency is 310 to 430, A grease composition for use in lubricating between metal members and between metal members and resin members.

2. 2. The grease composition according to claim 1, wherein the thickener is an aliphatic diurea compound.

3. 3. The grease composition according to claim 1, wherein the base oil is a synthetic hydrocarbon oil.

4. The kinematic viscosity of the base oil at 100°C is 4 to 10 mm 2 4. The grease composition according to claim 3, wherein the grease composition is:

5. 2. The grease composition according to claim 1, wherein the content of the montan wax is 2 to 5 mass %.

6. 2. The grease composition according to claim 1, wherein the molybdenum-based extreme pressure agent is an organic molybdenum, and the content thereof is 1 to 3 mass %.

7. 2. The grease composition according to claim 1, wherein the sulfonate compound is a neutral Ca sulfonate, and the content thereof is 0.5 to 2 mass %.

8. 2. The grease composition according to claim 1, having a consistency of 355 to 385.

9. A rack and pinion steering device filled with the grease composition according to claim 1 or 2.

10. 10. The rack-and-pinion steering device according to claim 9, wherein a yoke pad of a support yoke constituting the steering device is made of polyamide or PTFE.