JP2013126830A - Electric power steering device - Google Patents

Abstract

An electric motor that has a resin portion that is less swelled by water absorption and that has excellent lubricity when using grease based on poly α-α olefin oil, and that has improved dimensional stability, durability, and reliability. A power steering device is provided.
A driven gear of a reduction gear mechanism is formed by integrally providing a resin portion made of a resin composition and having gear teeth formed on an outer peripheral surface thereof on the outer periphery of a metal core tube, and the resin composition includes: In a polycondensate of a diamine component composed of a mixture of 1,9-nonanediamine and 2-methyl-1,8-octanediamine and an oxalic acid diester, the ratio of the resin composition is 10 to 40% by mass of the total amount. An electric power steering device comprising a reinforcing fiber material and a melting point of 230 to 240 ° C.
[Selection] Figure 1

Description

  The present invention relates to an electric power steering apparatus that transmits auxiliary output from an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism.

  In an electric power steering apparatus incorporated in an automobile, an electric motor having a relatively high rotation and low torque is used. Therefore, a speed reduction mechanism is incorporated between the electric motor and the steering shaft. As a speed reduction mechanism, a reduction gear for an electric power steering apparatus including a worm 12 and a worm wheel 11 meshing with the worm 12 as shown in FIG. 20 (hereinafter also simply referred to as “reduction gear”) is generally used. Here, the worm 12 is connected to the rotating shaft of the electric motor 100 shown in FIG. 2 and corresponds to a drive gear, while the worm wheel 11 corresponds to a driven gear.

  In such a reduction gear 20, when both the worm wheel 11 and the worm 12 are made of metal, there is a problem that unpleasant sounds such as rattling noises and vibration sounds are generated when the steering wheel is operated. Therefore, the worm wheel 11 is obtained by integrating the resin portion 3 made of resin and having the gear teeth 10 formed on the outer peripheral surface thereof on the outer periphery of the metal core tube 1 by using an adhesive 8 or the like. Uses noise countermeasures.

  In the resin part 3, for example, as described in Patent Document 1, a base resin such as polyamide 6, polyamide 66, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), glass fiber, MC (monomer cast) nylon, polyamide 6, polyamide 66, etc. that do not contain a reinforcing material are used in addition to a material containing a reinforcing material such as carbon fiber. Among these, in view of dimensional stability and cost, polyamide resins such as MC nylon not containing a reinforcing material, polyamide 6, glass 66, polyamide 46 and the like containing glass fibers are mainly used.

  Further, as shown in FIG. 2, the worm 12 of the reduction gear 20 is supported by a rolling bearing 110 such as a pair of ball bearings and connected to the electric motor 100, and between the pair of rolling bearings 110 of the housing 120. The space is usually filled with grease for lubrication between the gear teeth of the worm 12 and the worm wheel 11. As the base oil for grease, mineral oil and poly α-olefin oil having excellent heat resistance are generally used.

  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 the above information, it is also known that a rubber damper 130 is attached to the worm side of the rolling bearing 110 as shown in the figure. As the rubber used, ethylene acrylic rubber having a small compression set is used. Acrylic rubber represented by is generally used.

Japanese Patent Publication No. 6-60674

  However, among the above resin compositions that form the resin portion 3, the aliphatic polyamide resin is excellent in fatigue resistance, but has high water absorption and absorbs moisture, causing the gear teeth 10 of the worm wheel 11 to swell. When the gap between the worm 12 and the initially set worm disappears and further swells, the worm 12 is compressed. As a result, it is assumed that the resistance of the gear becomes large and the handle becomes heavy, or the gear is worn or damaged, so that the entire apparatus cannot function.

  Low-absorbing polyamide resins are also known, but their melting points are 187 ° C for polyamide 11, 176 ° C for polyamide 12, and 216 ° C for polyamide 612. Polyamide 610 is 220 ° C.), which is lower than that of polyamide 66 (melting point 265 ° C.). Although the reduction gear 20 is required to withstand higher temperatures, a low water-absorbing polyamide resin is not sufficient.

  Further, although mineral oil and poly α-olefin oil have good wettability to metal, they have poor wettability to polyamide resin having a large polarity. Therefore, the gear teeth of the metal worm 12 and the worm wheel 11 are used. The state of lubrication with the gear teeth 10 is not necessarily sufficient.

  The present invention has been made in view of such a situation, and includes a resin portion that is less swelled by water absorption and that has excellent lubricity when using grease based on poly α-olefin oil. An object is to provide an electric power steering device with improved stability, durability, and reliability.

In order to solve the above problems, the present invention provides the following electric power steering apparatus.
(1) An electric power steering device for transmitting auxiliary output from an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism, wherein the driven gear of the reduction gear mechanism has a resin composition on the outer periphery of the metal core tube A resin part made of a material and having gear teeth formed on the outer peripheral surface is integrally provided, and
When the resin composition is a polycondensate of a diamine component composed of a mixture of 1,9-nonanediamine and 2-methyl-1,8-octanediamine and an oxalic acid diester, the total amount of the resin composition is 10 to 40. An electric power steering apparatus comprising a reinforcing fiber material in a proportion of mass% and having a melting point of 230 to 240 ° C.
(2) The above-mentioned (1), characterized in that a grease composition mainly composed of poly α-olefin oil as a base oil is interposed between a driven gear and a drive gear constituting the reduction gear mechanism. The electric power steering apparatus as described.
(3) The electric power steering apparatus according to (1) or (2), wherein the driven gear and the driving gear are a cylindrical worm gear, a helical gear, a spur gear, a bevel gear, or a hypoid gear.

  According to the present invention, since the resin part of the worm wheel of the reduction gear is formed by blending the reinforcing fiber material with the polycondensate of the specific diamine component and Shujiester, the dimensional change due to water absorption is suppressed, and the poly α-olefin Since the lubricity when using grease based on oil is also excellent, an electric power steering device having excellent dimensional stability, durability, and reliability can be obtained.

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. It is a perspective view which shows an example (cylindrical worm gear) of a reduction gear. It is a perspective view which shows the other example (spur gear) of a reduction gear. It is a perspective view which shows the further another example (helical gear) of the reduction gear. It is a perspective view which shows the further another example (bevel gear) of a reduction gear. It is a perspective view which shows the further another example (high void gear) of a reduction gear.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  In the present invention, the configuration of the electric power steering apparatus itself is not limited, and an electric power steering apparatus shown in FIG. 1 can be exemplified. In the illustrated electric power steering apparatus, on the output shaft 60 side of the steering column 50, a gear box configured by housing the reduction gear 20 as shown in FIGS. Yes.

  Further, the steering column 50 is hollow, the steering shaft 70 is inserted, and is rotatably supported by rolling bearings 90 and 91 housed in the housing 120. The steering shaft 70 is a hollow shaft and accommodates a torsion bar 80. A worm wheel 11 is provided on the outer peripheral surface of the steering shaft 70, and a worm 12 is engaged with the worm wheel 11. Further, as shown in FIG. 2, an electric motor 100 is connected to the reduction gear 20 including the worm wheel 11 and the worm 12.

  As shown in FIG. 3, the reduction gear 20 includes a worm wheel 11 in which a resin portion 3 having gear teeth 10 formed on the outer peripheral end surface is integrated with an outer periphery of a metal core tube 1, a metal worm 12, Consists of In the worm wheel 11, the metal core tube 1 and the resin portion 3 may be bonded together with an adhesive 8. As the adhesive 8, for example, a silane coupling agent, a titanate coupling agent, or a triazine thiol compound is used. be able to.

  In the present invention, the resin part 3 is obtained by a polycondensate (hereinafter referred to as “specific polycondensate”) of a diamine component composed of a mixture of 1,9-nonanediamine and 2-methyl-1,8-octanediamine and an oxalic acid diester. ]) And a resin composition containing a reinforcing fiber material.

  The melting point of the specific polycondensate is 230 to 240 ° C. so that the resin part 3 can withstand higher temperatures, and the (1,9-nonanediamine: 2-methyl-1,8-octanediamine) ratio in the diamine component is By adjusting, the melting point can be obtained. Specifically, the (1,9-nonanediamine: 2-methyl-1,8-octanediamine) ratio may be 5:95 to 10:90 mol%, preferably 70:30 to 90:10 mol%. In this range, the melting point is adjusted to be the above-mentioned melting point.

  The oxalic acid diester is not particularly limited as long as it has reactivity with an amino group. Dimethyl oxalate, diethyl oxalate, di-n- (or i-) propyl oxalate, di-n- (or i-) oxalate Or oxalic acid diesters of aliphatic monohydric alcohols such as t-) butyl, oxalic acid diesters of alicyclic alcohols such as dicyclohexyl oxalate, and oxalic acid diesters of aromatic alcohols such as diphenyl oxalate. Of these, oxalic acid diesters of aliphatic monohydric alcohols having 3 or more carbon atoms, oxalic acid diesters of alicyclic alcohols, and oxalic acid diesters of aromatic alcohols are preferred, and dibutyl oxalate and diphenyl oxalate are particularly preferred.

  The ratio of the diamine component to the oxalic acid diester is preferably 0.99 to 1.01 in terms of the (oxalic acid diester / diamine component) ratio.

  The molecular weight of the specific polycondensate is preferably in the range that can be injection-molded in the state containing the reinforcing fiber material, that is, the number average molecular weight is preferably 13,000 to 30000, and the number average molecular weight is 18000 to 26000 in consideration of fatigue resistance and moldability. Is more preferable. When the number average molecular weight is less than 13,000, the molecular weight is too low, the fatigue resistance is poor, and the practicality is low. On the other hand, when the number average molecular weight exceeds 30000, the melt viscosity in a state containing the specified amount of the reinforcing fiber material is too high, and it becomes difficult to perform injection molding with high accuracy.

  The saturated water absorption of such a specific polycondensate is 0.9 to 1.3%, and polyamide 66 (saturated water absorption 5.6%) and polyamide 6 ( Compared to 10.7% of saturated water absorption, the dimensional change due to water absorption is very small, and the dimensional stability is excellent.

The polymerization method is preferably performed in the order of (1) pre-polycondensation step and (2) post-polycondensation step as shown below, for example.
(1) Pre-polycondensation step After the inside of the reactor is purged with nitrogen, the diamine component and the oxalic acid diester are mixed in the above ratio. In mixing, a solvent in which both the diamine component and the oxalic acid diester are soluble can be used. For example, toluene, xylene, trichlorobenzene, phenol, trifluoroethanol, or the like can be used. And for example, after heating the toluene solution which melt | dissolved the diamine component to 50 degreeC, oxalic-acid diester is added. Subsequently, it heats up under a normal pressure, stirring and / or nitrogen bubbling in the inside of a reactor. The reaction temperature is controlled so that the final temperature reaches 80 to 150 ° C, preferably 100 to 140 ° C. The reaction time at the final temperature is 3 to 6 hours.
(2) Post-polycondensation step In order to increase the molecular weight, the polymer produced in the pre-polycondensation step is gradually heated in the reactor under normal pressure. From the final temperature reached in the pre-polycondensation step (80 to 150 ° C.) in the temperature raising process, the temperature is finally 220 ° C. or higher and 300 ° C. or lower, preferably 230 ° C. or higher and 280 ° C. or lower, more preferably 240 ° C. or higher and 270 ° C. or lower. Let reach the range. It is preferable to carry out the reaction for 1 to 8 hours including the temperature raising time, preferably 2 to 6 hours. Furthermore, in the post-polymerization step, polymerization can be performed under reduced pressure as necessary. The preferable final ultimate pressure in the case of performing the vacuum polymerization is less than 0.1 MPa to 13.3 Pa.

  The specific polycondensate itself exhibits a certain level of durability, works favorably against wear of the worm 12 that is the counterpart of the worm wheel 11, and functions sufficiently as the reduction gear 20, but is more severe. Since it is assumed that the gear teeth 10 are damaged or worn when used under the use conditions, a reinforcing fiber material is blended in order to improve reliability.

  As the reinforcing fiber material, glass fiber, carbon fiber, potassium titanate whisker, aluminum borate whisker and the like are preferable, and those treated with a silane coupling agent in consideration of adhesiveness with a specific polycondensate are more preferable. . Moreover, these reinforcing fiber 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. Further, the glass fiber having an average fiber diameter of 5 to 7 μm or a modified cross-section that can increase the strength and improve the wear resistance with a small blending amount is more preferable.

  Moreover, it is preferable to mix | blend a reinforcing fiber material in the ratio of 10 to 40 weight% of the whole, especially 15 to 30 weight%. When the amount of the reinforcing fiber material is less than 10% by weight, the mechanical strength is hardly improved, which is not preferable. When the amount of the reinforcing fiber material exceeds 40% by weight, the worm 12 is liable to be damaged, wear of the worm 12 is promoted, and durability as a reduction gear may be insufficient.

  Furthermore, in order to prevent deterioration due to heat during molding and use, iodide-based heat stabilizers and amine-based antioxidants are added to specific polycondensates, either alone or in combination. Also good.

  In the electric power steering apparatus configured as described above, the grease for lubrication between the gear teeth of 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 prior art. Is filled (see FIG. 2). In the present invention, in consideration of wettability with a specific polycondensate, it is preferable to use a grease containing a base oil mainly composed of poly α-olefin oil. Since the specific polycondensate has a molecular structure that does not contain a long hydrocarbon chain or aromatic ring between amide groups, the specific polycondensate is excellent in wettability with poly α-olefin oil as compared with polyamide 6 and polyamide 66.

  Here, the main component means that the poly α-olefin oil exceeds 50% by mass of the total amount of the base oil, and preferably 70% by mass or more is the poly α-olefin oil. Examples of the lubricating oil that can be mixed with the poly α-olefin oil include diester oil and aromatic ester oil because of the effect of improving the lubricity of the poly α-olefin oil.

In addition, the kinematic viscosity of the base oil is preferably 40 to 220 mm ² / s (40 ° C.).

  The thickener is not limited, and metal soaps and urea compounds can be used, but urea compounds that are similar in structure to a specific polycondensate and excellent in adsorptivity are preferred. Further, the blending amount of the thickener is not limited as long as the grease can be formed with the base oil, but 10 to 20% by weight of the total amount of the grease is appropriate.

  Various additives may be added to the grease as necessary. For example, amine-based and phenol-based antioxidants, rust preventives such as calcium sulfonate, extreme pressure additives such as molybdenum dithiocarbamate, montanic acid ester wax, montanic acid ester partly saponified wax, oleic acid and other oil improvers Etc. can be added.

  In the electric power steering apparatus of the present invention, as the reduction gear 20, in addition to the worm wheel 11 and the worm 12, the spur gear shown in FIG. 4, the helical gear shown in FIG. 5, and the bevel gear shown in FIG. The hypoid gear shown in FIG. 7 can be used. In either case, the worm wheel 11 is formed on the outer periphery of the metal core tube 1 and the resin portion 3 is formed of the resin composition and the gear teeth 10 are formed on the outer peripheral surface thereof. , And the like, using an adhesive 8 or the like.

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

Example 1
Polycondensate A obtained by polymerizing diamine component consisting of 85 mol% of 1,9-nonanediamine and 15 mol% of 2-methyl-1,8-octanediamine and dibutyl oxalate in a ratio of 1: 1. Was prepared. The number average molecular weight of the polycondensate A was 22,000, and the melting point was 235 ° C. In addition, to the polycondensate A, a copper iodide heat stabilizer was added as a heat stabilizer.

  Next, a resin composition was prepared by blending the polycondensate A with glass fibers (average fiber diameter 6.5 μm) treated with a silane coupling agent at a ratio of 25 mass%.

  Then, the S45C core tube having an outer diameter of 45 mm and a width of 13 mm, which has been subjected to cross knurling, is placed in a mold equipped with a sprue and a disk gate, and the above resin composition is injection-molded to have an outer diameter of 60 mm. A product having helical gear teeth on the outer peripheral portion having a width of 13 mm was prepared. Next, gear teeth were finished by cutting using a bob cutter, and a worm wheel specimen was produced.

(Example 2)
A polycondensate B was prepared in the same manner as in Example 1 except that the diamine component was changed to 6 mol% of 1,9-nonanediamine and 94 mol% of 2-methyl-1,8-octanediamine. A worm wheel specimen was prepared. The polycondensate B had a number average molecular weight of 22,000 and a melting point of 232 ° C.

(Comparative Example 1)
Polyamide 66 (“Nylon 2020GU6” manufactured by Ube Industries, Ltd.) containing a glass fiber (average fiber diameter of 13 μm) treated with a silane coupling agent: Cu-based heat stabilizer contained, number average molecular weight 20000, melting point 265 ° C. ) Was used to produce a similar worm wheel specimen.

(Comparative Example 2)
A polycondensate C was prepared in the same manner as in Example 1 except that the diamine component was changed to 50 mol% of 1,9-nonanediamine and 50 mol% of 2-methyl-1,8-octanediamine. A worm wheel specimen was prepared. The polycondensate C had a number average molecular weight of 22,000 and a melting point of 206 ° C.

(Comparative Example 3)
The same worm using polyamide 9T (Kuraray “Genesta G1300A”: thermal stabilizer containing grade, melting point 304 ° C.) containing glass fiber (average fiber diameter 10 μm) treated with a silane coupling agent in a proportion of 30% by mass A wheel specimen was prepared.

  Table 1 shows the compositions and melting points of the resin compositions of the above Examples and Comparative Examples.

Moreover, about each worm wheel test body of said Example and comparative example, dimensional stability and durability were evaluated as shown below. The results are shown in Table 2.
(1) Dimensional stability The worm wheel specimen was left under the following conditions I or II, the gear outer diameter was measured after being left, and the amount of change from the gear outer diameter before being left was determined. In any condition, the case where the amount of change was 40 μm or less was regarded as acceptable “◯”, and the case where the amount of change exceeded 40 μm was regarded as unacceptable “x”.
・ Condition I: 60 ° C., 90% RH, 70 hours ・ Condition II: 80 ° C., 90% RH, 300 hours (2) Durability A worm wheel specimen is incorporated in the reduction gear of an actual electric power steering device. Steering operation was repeatedly performed in I-III. For the reduction gear, a poly α-olefin oil (kinematic viscosity; 8 mm ² / s @ 40 ° C.) is used as a base oil, an aliphatic diurea compound is used as a thickener (thickener amount: 13% by mass), and a polyethylene wax ( Antiwear agent), 4,4′-dioctyldiphenylamine (antioxidant) and neutral calcium sulfonate (rust inhibitor). The grease adjusted to 2 was filled. In any condition, a case where the vehicle could endure 100,000 times of steering was “good”, and a case where it could not endure 100,000 times of steering was determined as “failed”.
Condition I: 30 ° C., 50% RH
Condition II: 50 ° C., 90% RH
Condition III: 80 ° C., 50% RH

  As shown in Table 2, Examples 1 and 2 according to the present invention are excellent in dimensional stability and durability under any conditions. On the other hand, Comparative Example 1 using polyamide 66, which is a conventional resin material, is inferior in dimensional stability and durability under severe conditions of high temperature and high humidity. Moreover, when the polycondensate C of Comparative Example 2 is used, the melting point is low and the durability at high temperature is lowered. Further, in Comparative Example 3 using polyamide 9T, although there is no problem in dimensional stability, since the wettability with grease based on poly α-olefin oil is poor, the wear of the resin progresses quickly. It is inferior in durability even under conditions.

DESCRIPTION OF SYMBOLS 1 Core pipe 3 Resin part 10 Gear tooth 11 Worm wheel 12 Worm 20 Reduction gear 50 Steering column 70 Steering shaft 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 is integrally provided with a resin portion made of a resin composition and formed with gear teeth on the outer peripheral surface on the outer periphery of the metal core tube, and
When the resin composition is a polycondensate of a diamine component composed of a mixture of 1,9-nonanediamine and 2-methyl-1,8-octanediamine and an oxalic acid diester, the total amount of the resin composition is 10 to 40. An electric power steering apparatus comprising a reinforcing fiber material in a proportion of mass% and having a melting point of 230 to 240 ° C.   2. The electric power according to claim 1, wherein a grease composition mainly composed of poly-α-olefin oil as a base oil is interposed between a driven gear and a drive gear constituting the reduction gear mechanism. Steering device.   3. The electric power steering apparatus according to claim 1, wherein the driven gear and the driving gear are a cylindrical worm gear, a helical gear, a spur gear, a bevel gear, or a hypoid gear.

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