EP1559773A1 - Lubricating grease composition for deceleration gear and electric power steering - Google Patents

Lubricating grease composition for deceleration gear and electric power steering Download PDF

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Publication number
EP1559773A1
EP1559773A1 EP03754089A EP03754089A EP1559773A1 EP 1559773 A1 EP1559773 A1 EP 1559773A1 EP 03754089 A EP03754089 A EP 03754089A EP 03754089 A EP03754089 A EP 03754089A EP 1559773 A1 EP1559773 A1 EP 1559773A1
Authority
EP
European Patent Office
Prior art keywords
grease composition
lubricating grease
reduction gear
electric power
power steering
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03754089A
Other languages
German (de)
French (fr)
Other versions
EP1559773A4 (en
Inventor
Toshiyuki; c/o NSK LTD. IWANO
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NSK Ltd
Original Assignee
NSK Ltd
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Filing date
Publication date
Application filed by NSK Ltd filed Critical NSK Ltd
Publication of EP1559773A1 publication Critical patent/EP1559773A1/en
Publication of EP1559773A4 publication Critical patent/EP1559773A4/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M159/00—Lubricating compositions characterised by the additive being of unknown or incompletely defined constitution
    • C10M159/12—Reaction products
    • C10M159/20—Reaction mixtures having an excess of neutralising base, e.g. so-called overbasic or highly basic products
    • C10M159/24—Reaction mixtures having an excess of neutralising base, e.g. so-called overbasic or highly basic products containing sulfonic radicals
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M135/00—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing sulfur, selenium or tellurium
    • C10M135/08—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing sulfur, selenium or tellurium containing a sulfur-to-oxygen bond
    • C10M135/10—Sulfonic acids or derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M169/00—Lubricating compositions characterised by containing as components a mixture of at least two types of ingredient selected from base-materials, thickeners or additives, covered by the preceding groups, each of these compounds being essential
    • C10M169/06—Mixtures of thickeners and additives
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
    • C10M2205/02—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers
    • C10M2205/0206—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
    • C10M2205/02—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers
    • C10M2205/022—Ethene
    • C10M2205/0225—Ethene used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
    • C10M2205/02—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers
    • C10M2205/024—Propene
    • C10M2205/0245—Propene used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
    • C10M2205/02—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers
    • C10M2205/026—Butene
    • C10M2205/0265—Butene used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
    • C10M2205/02—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers
    • C10M2205/028—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers containing aliphatic monomers having more than four carbon atoms
    • C10M2205/0285—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers containing aliphatic monomers having more than four carbon atoms used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
    • C10M2205/14—Synthetic waxes, e.g. polythene waxes
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
    • C10M2205/16—Paraffin waxes; Petrolatum, e.g. slack wax
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
    • C10M2205/18—Natural waxes, e.g. ceresin, ozocerite, bees wax, carnauba; Degras
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2215/00—Organic non-macromolecular compounds containing nitrogen as ingredients in lubricant Compositions
    • C10M2215/10—Amides of carbonic or haloformic acids
    • C10M2215/102—Ureas; Semicarbazides; Allophanates
    • C10M2215/1026—Ureas; Semicarbazides; Allophanates used as thickening material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2219/00—Organic non-macromolecular compounds containing sulfur, selenium or tellurium as ingredients in lubricant compositions
    • C10M2219/04—Organic non-macromolecular compounds containing sulfur, selenium or tellurium as ingredients in lubricant compositions containing sulfur-to-oxygen bonds, i.e. sulfones, sulfoxides
    • C10M2219/044—Sulfonic acids, Derivatives thereof, e.g. neutral salts
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2219/00—Organic non-macromolecular compounds containing sulfur, selenium or tellurium as ingredients in lubricant compositions
    • C10M2219/04—Organic non-macromolecular compounds containing sulfur, selenium or tellurium as ingredients in lubricant compositions containing sulfur-to-oxygen bonds, i.e. sulfones, sulfoxides
    • C10M2219/046—Overbased sulfonic acid salts
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2219/00—Organic non-macromolecular compounds containing sulfur, selenium or tellurium as ingredients in lubricant compositions
    • C10M2219/04—Organic non-macromolecular compounds containing sulfur, selenium or tellurium as ingredients in lubricant compositions containing sulfur-to-oxygen bonds, i.e. sulfones, sulfoxides
    • C10M2219/046—Overbased sulfonic acid salts
    • C10M2219/0466—Overbased sulfonic acid salts used as thickening agents
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2010/00—Metal present as such or in compounds
    • C10N2010/04—Groups 2 or 12
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
    • C10N2030/06—Oiliness; Film-strength; Anti-wear; Resistance to extreme pressure
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2040/00—Specified use or application for which the lubricating composition is intended
    • C10N2040/04—Oil-bath; Gear-boxes; Automatic transmissions; Traction drives
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2040/00—Specified use or application for which the lubricating composition is intended
    • C10N2040/14—Electric or magnetic purposes
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2050/00—Form in which the lubricant is applied to the material being lubricated
    • C10N2050/10—Form in which the lubricant is applied to the material being lubricated semi-solid; greasy

Definitions

  • the present invention relates to improvement in a lubricating grease composition for a reduction gear (aiming at a lower coefficient of friction), which is optimum for a reduction gear structure of a power steering apparatus or the like of a vehicle and, further, to an electric power steering apparatus in which the lubricating grease composition is used for a reduction gear.
  • a speed reducing mechanism of an electric power steering apparatus of a vehicle uses a worm wheel gear made of a resin (polyamide) and a worm gear made of steel.
  • a grease composition used for lubrication between resin members and between a resin member and a metal member for example, Japanese Patent Laid-open No. H8-209167 discloses a resin grease composition for lubrication containing a fatty acid including a hydroxyl group or a fatty ester of polyhydric alcohol.
  • the grease composition is excellent with respect to the point that, when it is used for a speed reducing mechanism of an electric power steering apparatus of a vehicle, even after use for long time, fluctuations in the torque are suppressed and the user feels that operation on the steering wheel is normal after long time of driving.
  • Japanese Patent Laid-Open No. 2002-371290 filed by the inventors herein discloses a grease composition solving such problems.
  • the composition in the publication is made by an urea compound as a thickener, a synthetic hydrocarbon oil as a base oil, and montan wax as an additive.
  • the outline of the composition is as follows.
  • the montan wax is a generic name for wax whose material is brown coal and whose base is a montanic acid obtained by refining and oxidizing the brown coal.
  • Wax manufactured by Clariant International Ltd. is famous.
  • Typified acid wax includes "Licowax U” and “Licowax S” as acid wax, “Licowax E” and “Licowax KPS” as ester wax, “Licowax OP" and “Licowax O” as partial saponifiable ester wax, and the like.
  • wax is used as a lubricant for a resin
  • use of wax as a lubricant for a resin is known.
  • the wax is classified from the viewpoint of actions into an internal lubricant and an external lubricant in accordance with solubility to a polymer (resin). Both of them are used by being added into a resin.
  • Japanese Patent Publication No. S63-26799 discloses a technique as an example of use of montan wax into a grease.
  • an evaluating method is the Timken text whose object is lubrication between steel and steel, not between resins.
  • the amount of addition of the montan wax is 0.5 to 20%. When the amount of addition is too small, an adding effect is insufficient. When the amount of addition is too large, grease becomes too hard and cannot be used as grease.
  • Any of thickeners can be used but preferable one is an urea-based thickener for the reason that the thickener is low in price and can withstand heat generation caused by lubrication under heavy load.
  • base oils can be used, particularly, a synthetic hydrocarbon oil is preferable since it matches various resins excellently.
  • a lubricant grease composition of Japanese Patent Laid-Open No. 2002-371290 produces an effect that it improves abrasion resistance of a reduction gear constructed by a metal worm and a worm wheel made of polyamide synthetic resin. From the viewpoint of improvement in vehicle response and durability, further improvement in a coefficient of friction of a lubricating grease composition is strongly demanded.
  • an object of the invention is to provide a lubricating grease composition for a reduction gear optimum for an electric power steering apparatus of a vehicle by improving a coefficient of friction and an electric power steering apparatus in which the composition is applied to a reduction gear.
  • the present invention relates to a lubricating grease composition for a reduction gear and the object of the invention is achieved by adding, for lubrication of a reduction gear, at least a Ca sulfonate additive to a lubricating grease made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil and is more effectively achieved by also adding montan wax.
  • the invention also relates to an electric power steering apparatus having a reduction gear structure comprising a steel worm and a worm wheel made of a polyamide synthetic resin, and the object of the invention is achieved by using, for lubrication of the reduction gear structure, a lubricating grease composition made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil, to which at least a Ca sulfonate additive is added, and is more effectively achieved by also adding montan wax to the lubricating grease.
  • At least Ca sulfonate additive is added to a lubricating grease made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil.
  • the coefficient of friction is improved.
  • montan wax By also adding montan wax, the coefficient of friction is further improved.
  • Ca sulfonate an effect of decreasing the sliding performance (coefficient of friction) of a reduction gear constructed by a metal worm and a worm wheel made of a polyamide synthetic resin at a room temperature or higher can be obtained.
  • the base oil used for a grease composition of the invention is not particularly limited but all of base oils can be used.
  • Examples are an ester synthetic oil typified by mineral oil, diester, and polyol ester, a synthetic hydrocarbon typified by poly ⁇ olefine, and polybutene, an ether synthetic oil typified by alkyl diphenyl ether and polypropylene glycol, silicone oil, fluorine oil, and the like.
  • the synthetic hydrocarbon oil is particularly preferable.
  • the dynamic viscosity is preferably 6 to 15 mm 2 /s (100°C).
  • the thickener used for a grease composition of the invention is not particularly limited and all of thickeners can be used.
  • the thickener are a soap-based thickener typified by Li soap and composite Li soap, an urea-based thickener typified by diurea, an inorganic thickener typified by organic clay or silica, and an organic thickener typified by PTFE, and the like.
  • a particularly preferable thickener is the urea-based thickener.
  • the urea-based thickener has high resistance to heat generated by lubrication under heavy load and is cheaper than the other thickeners.
  • the content of the thickener in the grease composition of the invention varies according to the kind of the thickener.
  • a preferred consistency is 200 to 400 and the content of the thickener is an amount necessary to obtain the preferred consistency.
  • the normal content of the thickener is 3 to 30% by mass.
  • Ca sulfonate for example, a calcium metal salt of a sulfonated alkyl-substituted aromatic compound and a material obtained by further overbasing the calcium metal salt with a calcium hydroxide or an oxide and carbon dioxide are preferable.
  • Such sulfonate can have, as a substituent group, an alkyl group having the number of carbons of 1 to 20.
  • overbased Ca sulfonate is preferably used since it improves the operation efficiency of an electric power steering gear.
  • the base number of the Ca sulfonate is not limited, preferably, it lies from 10 to 500 mgKOH/g, more preferably, 20 to 300 mgKOH/g.
  • 0.1 to 10% by weight of the Ca sulfonate is contained in the composition of the invention. More preferably, 0.2 to 3% by weight of the Ca sulfonate is contained.
  • the montan wax As the montan wax, the above-described acid wax, ester wax, partial saponifiable ester wax, and the like can be used.
  • the content of the montan wax is 0.5 to 20% by mass and, more preferably, 1 to 10% by mass.
  • the coefficient of friction of the lubricant grease composition can be lowered at a room temperature or higher as compared with that in a conventional one. Consequently, even if the interval between the cores decreases due to self heat generation of the reduction gear, the working torque does not become low. Thus, predetermined vehicle response which is not influenced by the assist state can be obtained.
  • the grease composition of the invention can be easily produced by mixing a base oil, a thickener, a montan wax, and at least a Ca sulfonate additive at desired mix proportion.
  • the kind of the resin to be lubricated by the grease composition of the invention is not particularly limited to the polyamide resin (nylon).
  • a polyamide-imide resin, a polyacetal resin, a polybutylene terephthalate resin, a polyether ether ketone resin, a polyphenylene sulfide resin, and the like are also effective.
  • a synthetic resin obtained by reinforcing any of the above resins by an additive such as glass fibers, carbon fibers, or the like is also effective.
  • a lubricating grease composition is obtained by adding at least a Ca sulfonate additive to a lubricating grease made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil.
  • the result of the Bowden test in the case where the Ca sulfonate additive is added and that in the case where the Ca sulfonate additive is not added are obvious from the tables 1 to 3.
  • the coefficient of friction at room temperature or higher in the case where the Ca sulfonate additive is added is largely improved.
  • the coefficient of friction can be decreased at room temperature or higher by the lubricating grease composition of the invention, in the case of applying the lubricating grease composition of the invention to a reduction gear structure of an electric power steering apparatus of a vehicle, even if the interval between cores is narrowed due to self heat generation of the reduction gear, the working torque does not become low.
  • predetermined vehicle response which is not influenced by the assist state can be obtained.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Organic Chemistry (AREA)
  • Lubricants (AREA)
  • Power Steering Mechanism (AREA)

Abstract

For lubrication of a reduction gear, at least a Ca sulfonate additive is added to a lubricating grease made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil.

Description

Technical Field
The present invention relates to improvement in a lubricating grease composition for a reduction gear (aiming at a lower coefficient of friction), which is optimum for a reduction gear structure of a power steering apparatus or the like of a vehicle and, further, to an electric power steering apparatus in which the lubricating grease composition is used for a reduction gear.
Background Art
In recent years, resin members are used more frequently in place of various metal members for the sake of reducing the weight of a vehicle or the like. For example, a speed reducing mechanism of an electric power steering apparatus of a vehicle uses a worm wheel gear made of a resin (polyamide) and a worm gear made of steel. As a grease composition used for lubrication between resin members and between a resin member and a metal member, for example, Japanese Patent Laid-open No. H8-209167 discloses a resin grease composition for lubrication containing a fatty acid including a hydroxyl group or a fatty ester of polyhydric alcohol. The grease composition is excellent with respect to the point that, when it is used for a speed reducing mechanism of an electric power steering apparatus of a vehicle, even after use for long time, fluctuations in the torque are suppressed and the user feels that operation on the steering wheel is normal after long time of driving.
However, when the resin grease composition for lubrication is applied to an electric power steering apparatus of a large car, the load on the lubricating part becomes heavy and use conditions become severe. It causes problems such that the user feels unsmoothness when he/she turns the steering wheel slowly due to increase in static friction, durability deteriorates, and the life becomes shorter.
Japanese Patent Laid-Open No. 2002-371290 filed by the inventors herein discloses a grease composition solving such problems. The composition in the publication is made by an urea compound as a thickener, a synthetic hydrocarbon oil as a base oil, and montan wax as an additive. The outline of the composition is as follows.
The montan wax is a generic name for wax whose material is brown coal and whose base is a montanic acid obtained by refining and oxidizing the brown coal. Wax manufactured by Clariant International Ltd. is famous. Typified acid wax includes "Licowax U" and "Licowax S" as acid wax, "Licowax E" and "Licowax KPS" as ester wax, "Licowax OP" and "Licowax O" as partial saponifiable ester wax, and the like. Although wax is used as a lubricant for a resin, use of wax as a lubricant for a resin is known. The wax is classified from the viewpoint of actions into an internal lubricant and an external lubricant in accordance with solubility to a polymer (resin). Both of them are used by being added into a resin.
Japanese Patent Publication No. S63-26799 discloses a technique as an example of use of montan wax into a grease. Although the purpose of use is also improvement in lubricating properties, an evaluating method is the Timken text whose object is lubrication between steel and steel, not between resins. The amount of addition of the montan wax is 0.5 to 20%. When the amount of addition is too small, an adding effect is insufficient. When the amount of addition is too large, grease becomes too hard and cannot be used as grease. Any of thickeners can be used but preferable one is an urea-based thickener for the reason that the thickener is low in price and can withstand heat generation caused by lubrication under heavy load.
Further, although all of base oils can be used, particularly, a synthetic hydrocarbon oil is preferable since it matches various resins excellently.
A lubricant grease composition of Japanese Patent Laid-Open No. 2002-371290 produces an effect that it improves abrasion resistance of a reduction gear constructed by a metal worm and a worm wheel made of polyamide synthetic resin. From the viewpoint of improvement in vehicle response and durability, further improvement in a coefficient of friction of a lubricating grease composition is strongly demanded.
The invention has been achieved under such circumstances and an object of the invention is to provide a lubricating grease composition for a reduction gear optimum for an electric power steering apparatus of a vehicle by improving a coefficient of friction and an electric power steering apparatus in which the composition is applied to a reduction gear.
Disclosure of the Invention
The present invention relates to a lubricating grease composition for a reduction gear and the object of the invention is achieved by adding, for lubrication of a reduction gear, at least a Ca sulfonate additive to a lubricating grease made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil and is more effectively achieved by also adding montan wax.
The invention also relates to an electric power steering apparatus having a reduction gear structure comprising a steel worm and a worm wheel made of a polyamide synthetic resin, and the object of the invention is achieved by using, for lubrication of the reduction gear structure, a lubricating grease composition made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil, to which at least a Ca sulfonate additive is added, and is more effectively achieved by also adding montan wax to the lubricating grease.
Best Mode for carrying out the Invention
In the present invention, for lubrication of a reduction gear, at least Ca sulfonate additive is added to a lubricating grease made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil. By the addition, the coefficient of friction is improved. By also adding montan wax, the coefficient of friction is further improved. By adding Ca sulfonate, an effect of decreasing the sliding performance (coefficient of friction) of a reduction gear constructed by a metal worm and a worm wheel made of a polyamide synthetic resin at a room temperature or higher can be obtained.
The base oil used for a grease composition of the invention is not particularly limited but all of base oils can be used. Examples are an ester synthetic oil typified by mineral oil, diester, and polyol ester, a synthetic hydrocarbon typified by poly α olefine, and polybutene, an ether synthetic oil typified by alkyl diphenyl ether and polypropylene glycol, silicone oil, fluorine oil, and the like. Among them, the synthetic hydrocarbon oil is particularly preferable. The dynamic viscosity is preferably 6 to 15 mm2/s (100°C).
The thickener used for a grease composition of the invention is not particularly limited and all of thickeners can be used. Examples of the thickener are a soap-based thickener typified by Li soap and composite Li soap, an urea-based thickener typified by diurea, an inorganic thickener typified by organic clay or silica, and an organic thickener typified by PTFE, and the like. A particularly preferable thickener is the urea-based thickener. The urea-based thickener has high resistance to heat generated by lubrication under heavy load and is cheaper than the other thickeners.
The content of the thickener in the grease composition of the invention varies according to the kind of the thickener. A preferred consistency is 200 to 400 and the content of the thickener is an amount necessary to obtain the preferred consistency. The normal content of the thickener is 3 to 30% by mass.
As Ca sulfonate, for example, a calcium metal salt of a sulfonated alkyl-substituted aromatic compound and a material obtained by further overbasing the calcium metal salt with a calcium hydroxide or an oxide and carbon dioxide are preferable. Such sulfonate can have, as a substituent group, an alkyl group having the number of carbons of 1 to 20. As the Ca sulfonate, overbased Ca sulfonate is preferably used since it improves the operation efficiency of an electric power steering gear. Although the base number of the Ca sulfonate is not limited, preferably, it lies from 10 to 500 mgKOH/g, more preferably, 20 to 300 mgKOH/g. Preferably, 0.1 to 10% by weight of the Ca sulfonate is contained in the composition of the invention. More preferably, 0.2 to 3% by weight of the Ca sulfonate is contained.
As the montan wax, the above-described acid wax, ester wax, partial saponifiable ester wax, and the like can be used. The content of the montan wax is 0.5 to 20% by mass and, more preferably, 1 to 10% by mass.
In the electric power steering apparatus of a vehicle, when a motor is driven to generate an assist torque and a reduction gear operates, self heat generation occurs due to engagement between a steel worm and a worm wheel made of polyamide synthetic resin as components of a reduction gear. When the polyamide synthetic resin is PA6GF30, tooth surface temperature becomes about 60 °C at an outside air temperature of 25 °C. The reduction gear is set so that the interval of gears do not change at an atmospheric temperature as disclosed in, for example, Japanese Patent Laid-Open No. H7-215227. However, in engagement of the gears, the temperature of the polyamide synthetic resin having a high coefficient of linear thermal expansion concentrative rises, so that the interval between the cores in the reduction gear is narrowed and the working torque of the gear decreases. In an uncontrolled range (a small steering angle at the time of straight travel) in the electric power steering apparatus, the low working torque brings about friction at the time of steering the steering wheel. Consequently, when an assist control is continued, the vehicle does not respond to a slight steering angle.
However, in the case of applying the lubricating grease composition of the invention to the reduction gear, the coefficient of friction of the lubricant grease composition can be lowered at a room temperature or higher as compared with that in a conventional one. Consequently, even if the interval between the cores decreases due to self heat generation of the reduction gear, the working torque does not become low. Thus, predetermined vehicle response which is not influenced by the assist state can be obtained.
The grease composition of the invention can be easily produced by mixing a base oil, a thickener, a montan wax, and at least a Ca sulfonate additive at desired mix proportion.
The kind of the resin to be lubricated by the grease composition of the invention is not particularly limited to the polyamide resin (nylon). For example, a polyamide-imide resin, a polyacetal resin, a polybutylene terephthalate resin, a polyether ether ketone resin, a polyphenylene sulfide resin, and the like are also effective. A synthetic resin obtained by reinforcing any of the above resins by an additive such as glass fibers, carbon fibers, or the like is also effective.
Example
The coefficient of friction in the case where an overbased Ca sulfonate is added to a composition as a base obtained by mixing diurea A as a thickener, PAO(8) as a base oil, and montan wax as an additive was evaluated by Bowden test.
Conditions:
  • Material ... a plate of S45C and a rod of MC nylon (made by Nippon Polypenco Limited)
  • Sliding speed ... 1 mm/sec
  • Surface pressure ... 0.5 Mpa
    • (1) The effect of adding the Ca sulfonate at different temperatures is shown in the following table 1. "○" is filled in items in which the coefficient of friction was lower than that of a conventional one (in the case where the Ca sulfonate is not added) and "Δ" is filled in items in which the coefficient of friction is unchanged. In the example, the consistency is fixed at "285" at each of the temperatures and the addition amount of the Ca sulfonate is fixed to 0.5%.
      Temperature -40°C -10°C 23°C 60°C 90°C 120°C
      Δ Δ Δ ○ ○ ○
      Consistency: fixed at 285
      Addition amount: fixed at 0.5%
    • (2) The effect of adding the Ca sulfonate is shown in the following table 2. "○" is filled in items in which the coefficient of friction was lower than that of a conventional one (in the case where the Ca sulfonate is not added) and "Δ" is filled in item in which the coefficient of friction is unchanged. In the example, the consistency is fixed at "285".
      Addition amount 0.5% 1% 2% 3%
      Room temperature 60°C Δ ○ ○ ○
      ○ ○ ○ ○
      Consistency: fixed at 285
    • (3) The effect of consistency when the addition amount of the Ca sulfonate is fixed is shown in the following table 3. "○" is filled in items in which the coefficient of friction was lower than that of a conventional one (in the case where the Ca sulfonate is not added) and "Δ" is filled in items in which the coefficient of friction is unchanged. The addition amount of Ca sulfonate is fixed at 0.5%.
      Consistency 305 295 285 275
      Room ○ Δ Δ ○
      temperature 60°C ○ ○ ○ ○
      Addition amount: fixed at 0.5%
    Industrial Applicability
    In the invention, a lubricating grease composition is obtained by adding at least a Ca sulfonate additive to a lubricating grease made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil. The result of the Bowden test in the case where the Ca sulfonate additive is added and that in the case where the Ca sulfonate additive is not added are obvious from the tables 1 to 3. The coefficient of friction at room temperature or higher in the case where the Ca sulfonate additive is added is largely improved.
    Since the coefficient of friction can be decreased at room temperature or higher by the lubricating grease composition of the invention, in the case of applying the lubricating grease composition of the invention to a reduction gear structure of an electric power steering apparatus of a vehicle, even if the interval between cores is narrowed due to self heat generation of the reduction gear, the working torque does not become low. Thus, there is an advantage that predetermined vehicle response which is not influenced by the assist state can be obtained.

    Claims (4)

    1. A lubricating grease composition for a reduction gear,
         wherein, at least a Ca sulfonate additive is added to a lubricating grease made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil for lubrication of a reduction gear.
    2. The lubricating grease composition for a reduction gear according to claim 1, wherein montan wax is also added.
    3. An electric power steering apparatus having a reduction gear structure comprising a steel worm and a worm wheel made of a polyamide synthetic resin,
         characterized in that, for lubrication of the reduction gear structure, a lubricating grease composition made by an urea compound as a thickener and a synthetic hydrocarbon oil as a base oil, to which at least a Ca sulfonate additive is added is used.
    4. The electric power steering apparatus according to claim 3, wherein montan wax is also added to the lubricating grease composition.
    EP03754089A 2002-10-28 2003-10-10 Lubricating grease composition for deceleration gear and electric power steering Withdrawn EP1559773A4 (en)

    Applications Claiming Priority (3)

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    JP2002312576 2002-10-28
    JP2002312576 2002-10-28
    PCT/JP2003/013081 WO2004037958A1 (en) 2002-10-28 2003-10-10 Lubricating grease composition for deceleration gear and electric power steering

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    EP1559773A1 true EP1559773A1 (en) 2005-08-03
    EP1559773A4 EP1559773A4 (en) 2010-01-20

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    EP (1) EP1559773A4 (en)
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    EP2000524A4 (en) * 2006-03-24 2010-09-15 Japan Energy Corp SEMI-SOLID LUBRICANT COMPOSITION FOR TRANSMISSION ELEMENT AND MECHANICAL SYSTEM HAVING THE SAME

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    EP2000524A4 (en) * 2006-03-24 2010-09-15 Japan Energy Corp SEMI-SOLID LUBRICANT COMPOSITION FOR TRANSMISSION ELEMENT AND MECHANICAL SYSTEM HAVING THE SAME
    US7973000B2 (en) 2006-03-24 2011-07-05 Japan Energy Corporation Semi-solid lubricant composition for transmission element and mechanical system provided with the same

    Also Published As

    Publication number Publication date
    US20060154831A1 (en) 2006-07-13
    WO2004037958A1 (en) 2004-05-06
    AU2003272980A1 (en) 2004-05-13
    JPWO2004037958A1 (en) 2006-02-23
    EP1559773A4 (en) 2010-01-20

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