JP2006335286A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a total durability life by providing wear resistance of a worm wheel and restraining softening and swelling of a rubber damper in an electric power steering device having resin worm wheels and lubricated with grease. <P>SOLUTION: In this electric power steering device, a driven gear of a deceleration gear mechanism has a resin part which is made of a resin composition, and on the outer periphery of which gear teeth are formed. The deceleration gear mechanism is lubricated with a grease composition containing calcium sulfonate-calcium carbonate composite as thickening agent in amount of 5-50 mass% to the total mass of grease, and base oil in amount of 50-95 wt% to the total weight of grease. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering device that transmits auxiliary output from an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism, and in particular, a resin portion made of a resin composition as a driven gear and having gear teeth formed on an outer peripheral surface thereof. And an electric power steering apparatus that is grease lubricated.

  An electric power steering apparatus incorporated in an automobile is configured as shown in FIGS. 1 and 2, for example. As shown in the figure, a steering shaft 70 is inserted into a hollow steering column 50 and is rotatably supported by rolling bearings 90 and 91 housed in a housing 120. The steering shaft 70 is a hollow shaft and accommodates a torsion bar 80. On the output shaft 60 side, the worm wheel 11 is provided on the outer peripheral surface of the steering shaft 70, and the worm 12 is engaged with the worm wheel 11. A reduction gear mechanism composed of the worm wheel 11 and the worm 12 is connected to an electric motor and housed in a housing 120. Here, the worm 12 is connected to the rotating shaft of the electric motor 100 and corresponds to a drive gear, while the worm wheel 11 corresponds to a driven gear.

  FIG. 3 is an enlarged view showing an example of the reduction gear mechanism 20. However, when both the worm wheel 11 and the worm 12 are made of metal, an unpleasant sound such as a rattling sound or a vibration sound is generated when the handle is operated. Therefore, as the worm wheel 11, the resin portion 3 made of resin and having the gear teeth 10 formed on the outer peripheral surface is integrated on the outer periphery of the metal core tube 1 through the adhesive 8. Noise measures are taken using things.

  The resin part 3 is made of, for example, a material in which a reinforcing material such as glass fiber or carbon fiber is mixed with a base resin such as polyamide 6, polyamide 66, polyacetal, polyether ether ketone (PEEK), or polyphenylene sulfide (PPS). In addition, MC (monomer cast) nylon, polyamide 6, polyamide 66, etc. that do not contain a reinforcing material are used. Among these, in consideration of dimensional stability and cost, MC nylon not containing a reinforcing material, polyamide 6, glass 66 containing polyamide, polyamide 46, and the like are mainly used.

  The worm 12 is supported by a rolling bearing 110 such as a pair of ball bearings and connected to the electric motor 100, and the space between the pair of rolling bearings 110 of the housing 120 is usually in the worm 12 and the worm wheel. 11 is filled with grease for lubrication between both gear teeth (see, for example, Patent Documents 1 to 4). Furthermore, preload is applied to the rolling bearing 110, and when a minute kickback input is input from the tire side, the worm 12 is moved in the axial direction to prevent the electric motor 100 from rotating, and only the kickback is applied to the handle side. In order to convey this information, a rubber damper 130 is attached to the worm side of the rolling bearing 110.

JP-A-8-209167 JP-A-9-194867 JP 2002-371290 A JP 2003-3185 A

  The grease composition described in Patent Document 1 includes a fatty acid containing a hydroxyl group or a fatty acid ester of a polyhydric alcohol. Moreover, the grease composition described in Patent Document 2 contains 0.5 to 40% by mass of polyethylene wax having an average molecular weight of 900 to 10,000. In addition, the grease composition described in Patent Document 3 contains synthetic hydrocarbon oil as a base oil, urea compound as a thickener, and montan wax. Further, the grease composition described in Patent Document 4 is a blend of polyethylene oxide wax.

  These grease compositions are for resin lubrication, and have the effect of improving the wear resistance of the gear teeth 10 of the worm wheel 11 made of resin. However, the electric power steering apparatus includes a rubber damper 130, and the above-described grease compositions are not taken into account until the damper 130 is softened or swelled by the grease composition.

  The present invention has been made under such circumstances, and in an electric power steering apparatus that includes a resin worm wheel and is grease-lubricated, the rubber damper is softened and swollen together with the wear resistance of the worm wheel. The purpose is to improve the overall durability life.

In order to achieve the above object, the present invention provides the following conductive power steering apparatus.
(1) An electric power steering device that transmits auxiliary output from an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism,
The driven gear of the reduction gear mechanism has a resin portion made of a resin composition and formed with gear teeth on the outer peripheral surface, and the reduction gear mechanism is represented by the following general formula (I) as a thickener. Characterized in that it is lubricated by a grease composition containing 5 to 50% by weight of the calcium sulfonate / calcium carbonate composite to be used and a base oil in a proportion of 50 to 95% by weight of the total amount of grease. Electric power steering device.
(R-SO ₃ ) ₂ Ca · nCaCO ₃ (I)
(In the formula, R is a hydrocarbon group having 6 to 28 carbon atoms or an aryl group, and n is an integer of 6 to 50.)
(2) The electric power steering device according to (1), wherein the driven gear includes a metal core tube, and a resin portion is integrally provided on an outer periphery of the metal core tube.
(3) The electric power steering apparatus as described in (1) or (2) above, wherein the lubricating oil is at least one of poly-α-olefin, polyol ester, diester and alkyl diphenyl ether.

  According to the present invention, since the calcium sulfonate / calcium carbonate composite is used as the thickener of the encapsulated grease composition, the softness and swelling of the rubber damper can be suppressed as well as the wear resistance of the resin warm oil. The overall durability is improved, and a long-life electric power steering apparatus is provided.

  Embodiments of the present invention will be described below.

  In the present invention, the electric power steering apparatus is not limited in configuration as long as the gear teeth of the worm wheel are made of resin and have a rubber damper in the reduction gear mechanism. For example, the electric power steering apparatus is shown in FIGS. An electric power steering device can be exemplified.

  The reduction gear mechanism can also be configured as illustrated in FIG. That is, the worm wheel 11 is configured by integrating a resin portion 3 made of a polyamide resin composition on the outer periphery of a metal core tube 1 and having gear teeth 10 formed on the outer peripheral end face thereof. For this integration, an adhesive 8 may be used. As the adhesive 8, for example, a silane coupling agent, a titanate coupling agent, or a triazine thiol compound can be used.

  As the polyamide resin forming the resin portion 3, from the viewpoint of water absorption and fatigue resistance, polyamide 6, polyamide 66, polyamide 46, polyamide 610, polyamide 612, polyamide 12, polyamide 11, polyamide MXD6, polyamide 6I6T, modified polyamide 6T and the like are preferable. Among them, polyamide 6, polyamide 66, and polyamide 46 are preferable because of excellent fatigue resistance. Further, these polyamide resins may be mixed with other resins having compatibility with the polyamide resin. Examples thereof include polyolefins modified with an acid such as maleic anhydride (for example, polyethylene, polypropylene, ethylene-α-olefin copolymer, propylene-α-olefin copolymer, etc.).

  These polyamide resins, or mixed resins of polyamide resins and other resins, exhibit a certain level of durability even with the resin alone, and work favorably against wear of the metal worm 12 that is the counterpart material of the worm wheel 11, Functions sufficiently as a reduction gear. However, since the gear teeth 10 may be damaged or worn when used under more severe use conditions, it is preferable to add a reinforcing material in order to further improve the reliability.

  As the reinforcing material, glass fiber, carbon fiber, potassium titanate whisker, aluminum borate whisker or the like is preferable, and a surface treated with a silane coupling agent is more preferable in consideration of adhesiveness with the polyamide resin mentioned above. . Moreover, these reinforcing materials can be used in combination of multiple types. Considering the impact strength, it is preferable to mix a fibrous material such as glass fiber or carbon fiber, and considering the damage of the worm 12, it is preferable to combine the whisker-like material with the fibrous material. The mixing ratio in the case of using the mixture varies depending on the types of the fibrous material and the whisker-like material, and is appropriately selected in consideration of impact strength, damage to the worm 12, and the like. These reinforcing materials are preferably blended in a proportion of 5 to 40% by weight, particularly 10 to 30% by weight. When the blending amount of the reinforcing material is less than 5% by weight, the mechanical strength is hardly improved, which is not preferable. When the compounding amount of the reinforcing material exceeds 40% by weight, the worm 12 is likely to be damaged, wear of the worm 12 is promoted and durability may be insufficient.

  Furthermore, in order to prevent deterioration due to heat at the time of molding and use, an iodide-based heat stabilizer and an amine-based antioxidant may be added to the polyamide resin composition alone or in combination. Good.

  In order to form the resin portion 3, the above base resin and reinforcing material, and if necessary, an antioxidant, a heat stabilizer, and a filler are kneaded at a temperature equal to or higher than the melting temperature of the base resin. The melted and kneaded product thus obtained may be filled in a mold having the core tube 1 and cured. And the gear tooth 10 is formed in the outer peripheral surface of the resin part 3 by cutting, and the worm wheel 11 is obtained.

  Moreover, although illustration is abbreviate | omitted, the worm wheel 11 may abbreviate | omit the core pipe 1 and may form the whole with a polyamide resin composition.

  The damper 130 is generally made of an acrylic rubber such as ethylene acrylic rubber.

  In the electric power steering apparatus schematically configured as described above, the grease composition for lubrication between the worm 12 and the worm wheel 11 is further provided in the space between the pair of rolling bearings 110 of the housing 120 as in the conventional case. Is filled.

  In the present invention, mineral oil or synthetic lubricating oil can be used as the base oil of the grease composition. As for synthetic hydrocarbon oils, poly α-olefins are conventionally used in consideration of the influence on rubbers, particularly acrylic rubbers. However, in the present invention, as described later, calcium sulfonates are used as thickeners. Since the calcium carbonate composite is used, heat-resistant lubricating oils such as diesters, polyol esters, and alkyl diphenyl ethers can be used. The base oil may be a mixed oil of these.

  The calcium sulfonate / calcium carbonate composite described later forms a protective film made of calcium carbonate on the surface of a resin or rubber, thereby preventing softening or swelling of the resin or rubber. However, since it takes some time to form the protective film made of calcium carbonate, when diester, polyol ester, or alkyl diphenyl ether is used as the base oil, the worm wheel 11 and the damper 130 are softened and swollen at an extremely early stage. There is a possibility to make it. Therefore, among the lubricating oils, it can be said that mineral oil and poly α-olefin are preferable.

The base oil preferably has a kinematic viscosity at 40 ° C. of 15 to 500 mm ² / s in consideration of lubrication performance. If the kinematic viscosity is less than 15 mm ² / s (@ 40 ° C.), the oil film forming ability is inferior, and the friction coefficient may increase and wear may occur. When the kinematic viscosity exceeds 500 mm ² / s (@ 40 ° C.), the flow resistance becomes too large, which may lead to loss of transmission torque. From these viewpoints, the kinematic viscosity of the base oil is more preferably 15~400mm ² / s, the optimal range is 20 to 200 mm ² / s.

In the present invention, a calcium sulfonate / calcium carbonate composite represented by the following general formula (I) is used as a thickener.
(R-SO ₃ ) ₂ Ca · nCaCO ₃ (I)
In the formula, R is a hydrocarbon group or aryl group having 6 to 28 carbon atoms, and n is an integer of 6 to 50. Specific examples of R each include a linear saturated hydrocarbon having 6 to 28 carbon atoms, a branched saturated hydrocarbon, an alkylbenzene having a linear saturated hydrocarbon substituent, and a saturated hydrocarbon group having a branch. Alkylbenzene. In the calcium sulfonate / calcium carbonate composite, calcium carbonate is presumed to exist in an aggregate (micelle) formed by calcium sulfonate.

  In addition, calcium sulfonate, which is a raw material for thickeners, is obtained by treating neutral alkyl or calcium alkylbenzenesulfonate with a high total base number of 400 mgKOH / g (measurement method: JlSK2501). Also called calcium sulfonate. In this treatment, carbon dioxide gas is introduced into the alkyl or calcium alkylbenzenesulfonate synthesized in a solvent.

  The highly basic calcium sulfonate in a state dispersed in a solvent is usually 15 to 60% by weight as a content and is a viscous substance, but it is a semi-solid such as grease. It is not in the shape. Therefore, the following processing steps are required to obtain a semi-solid grease using highly basic calcium sulfonate as a raw material.

  First, the base oil and the highly basic calcium sulfonate dispersed in the base oil are mixed, heated and stirred, and water is added at 60 ° C. Next, the mixture is heated to 85 ° C., an aliphatic alcohol having 1 to 4 carbon atoms and a fatty acid having 2 to 4 carbon atoms are added, and water, the aliphatic alcohol and the fatty acid are evaporated while heating and stirring. In this step, the crystal form of calcium carbonate in the highly basic calcium sulfonate changes, and the whole changes to a viscous semi-solid. This process takes about 1 hour.

  Next, water and calcium hydroxide are added to the semi-solid mixture and heating is continued to completely remove volatile components. Thereafter, a higher fatty acid is added and reacted for the main purpose of converting calcium hydroxide or calcium oxide generated with the change in the crystal form of calcium carbonate and calcium hydroxide added later into metal soap. This reaction can be confirmed by a decrease in fatty acid absorption and an increase in metal soap absorption by the infrared absorption spectrum. This process also takes about 1 hour. After this, heating of the semisolid mixture is continued and the temperature is raised to 165 ° C. After the temperature of the mixture reaches 165 ° C., the mixture is cooled to room temperature and processed by a general dispersion processing apparatus for grease such as a homogenizer, three rolls, etc. to obtain a grease composition.

  The blending amount of the base oil and the calcium sulfonate / calcium carbonate composite in the grease composition is 50 to 95% by weight of the base oil for the total grease, and the calcium sulfonate / calcium carbonate composite is 5 to 5% of the total grease. 50% by mass. If the blending amount of calcium sulfonate / calcium carbonate composite is less than 5% by mass, the thickening action is not sufficient, and the ability to form a calcium carbonate protective film becomes poor. As a result, the fluidity is impaired due to excessive hardness, which may limit the supply of grease from the grease composition adhering to the periphery of the friction surface into the friction surface. From such a viewpoint, the blending amount of the calcium sulfonate / calcium carbonate composite is preferably 8 to 40% by mass of the total amount of grease.

  Moreover, you may add various additives to the said grease composition as needed. Any of them may be known ones, for example, antioxidants such as amines, phenols, sulfurs, zinc dithiophosphates, extreme pressure agents such as phosphoruss, zinc dithiophosphates, organic molybdenums, fatty acids, animal and vegetable oils, etc. Oiliness improvers, benzotriazole metal deactivators, viscosity index improvers such as polymethacrylate, polyisobutylene, and polystyrene can be added singly or in combination of two or more. Although there is no restriction | limiting in these addition amounts, 10 mass% or less of grease whole quantity is suitable.

  Hereinafter, the present invention will be further described with reference to examples and comparative examples, but the present invention is not limited thereby.

Example 1
A high basic calcium sulfonate (calcium alkylbenzene sulfonate) containing 50% by mass of mineral oil and mineral oil were charged into a reaction kettle, and when the reaction kettle was heated and the temperature of the contents reached 60 ° C., water was added, Acetic acid and cellosolve were added when the temperature reached 85 ° C. Subsequently, after maintaining the temperature of the contents at 91 ° C. for 1 hour, calcium hydroxide and water were added. Next, after heating to evaporate water from the contents, the mixture was further heated and stearic acid was added at 130 ° C., and heating was continued to raise the temperature to 165 ° C. Then, 1-phenyl-2-naphthylamine, which is an antioxidant, was added to the contents and mixed, and then the contents were allowed to cool to room temperature and treated with a three-roll mill to obtain test grease A.

(Example 2)
Test grease B was obtained in the same manner as in Example 1 except that the mineral oil was replaced with poly α-olefin.

(Example 3)
A test grease C was obtained in the same manner as in Example 1 except that the mineral oil was replaced with a polyol ester.

(Comparative Example 1)
The poly α-olefin and diphenylmethane diisocyanate were charged into the reaction kettle, and the temperature of the contents was raised to 70 ° C. while expanding sales. Subsequently, octylamine was poured little by little into the reaction kettle to produce diurea. Stirring was continued and the temperature of the contents was raised to 150 ° C. to complete the reaction. Then, 1-phenyl-2-naphthylamine as an antioxidant, polyethylene wax as a friction reducing agent, and calcium sulfonate anticorrosive are added to the contents, mixed, and then the contents are allowed to cool to room temperature. Test grease D was obtained by treatment with a three-roll mill.

(Comparative Example 2)
A test grease E was obtained in the same manner as in Comparative Example 1, except that the mineral oil was replaced with a polyol ester.

(Test 1)
For the test grease, the coefficient of friction between the resin and metal was measured using a friction tester shown in FIG. 4 as an index of the efficiency of the reduction gear mechanism. The illustrated friction tester is configured to press the end face of a S45C φ5 × 10 mm test roller against a resin test plate and swing it with a cam. The test was performed such that the roughness of the sliding surface was 0.8a in terms of arithmetic average roughness Ra, the maximum contact surface pressure was 10 MPa, the rocking distance was 10 mm, the frequency was 4.3 Hz, and the test temperature was 60 ° C. A horizontal stress caused by friction was detected by a load cell, and a friction coefficient was calculated from the output voltage. If the friction coefficient is 0.05 or less, it can be used practically without any problem. The results are shown in Table 1.

(Test 2)
A disk made of ethylene acrylic rubber (diameter 10 mm, thickness 5 mm) was immersed in each test grease and left in a thermostat bath at 130 ° C. for 3000 hours. The ethylene acrylic rubber disc was taken out every predetermined time and the dimensional change in thickness was measured. The results are shown graphically in FIG.

  From the above test results, according to the present invention, the test grease containing a specified amount of calcium sulfonate / calcium carbonate composite as a thickener has a practical coefficient of friction and can suppress softening and swelling of ethylene acrylic rubber. I understand.

It is a partial section lineblock diagram showing an example of an electric power steering device. It is AA sectional drawing of FIG. 1, and is a schematic block diagram which shows the connection part periphery of an electric motor and a reduction gear mechanism. It is a perspective view which shows an example of a worm wheel and a worm. It is a schematic diagram which shows the structure of the test apparatus used in order to measure a friction coefficient in an Example. It is a graph which shows the relationship between the leaving time and the dimensional change rate of ethylene acrylic rubber which were obtained in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core pipe 3 Resin part 8 Adhesive 10 Gear tooth 11 Worm wheel 12 Worm 13 Tooth part 14 Recessed 15 Lubricant containing polymer 50 Stelling column 70 Steering shaft 80 Torsion bar 90 Bearing 91 Bearing 100 Electric motor 110 Rolling bearing 120 Housing 130 Damper

Claims (3)

An electric power steering device that transmits auxiliary output by an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism,
The driven gear of the reduction gear mechanism has a resin portion made of a resin composition and formed with gear teeth on the outer peripheral surface, and the reduction gear mechanism is represented by the following general formula (I) as a thickener. Characterized in that it is lubricated by a grease composition containing 5 to 50% by weight of the calcium sulfonate / calcium carbonate composite to be used and a base oil in a proportion of 50 to 95% by weight of the total amount of grease. Electric power steering device.
(R-SO ₃ ) ₂ Ca · nCaCO ₃ (I)
(In the formula, R is a hydrocarbon group having 6 to 28 carbon atoms or an aryl group, and n is an integer of 6 to 50.)   2. The electric power steering apparatus according to claim 1, wherein the driven gear includes a metal core tube, and a resin portion is integrally provided on an outer periphery of the metal core tube. The electric power steering apparatus according to claim 1 or 2, wherein the lubricating oil is at least one of a poly α-olefin, a polyol ester, a diester, and an alkyl diphenyl ether.

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