JP4269589B2 - Reduction gear for electric power steering device - Google Patents

Description

【００２６】
注１）ＰＡ６６：宇部興産（株）製「ＵＢＥナイロン２０２０Ｕ」（Ｃｕ系熱安定化材含有）
注２）ＰＡ４６：ＤＪＥＰ製「ＳｔａｎｙｌＴＷ３００」（Ｃｕ系熱安定化材含有）
注３）不飽和カルボン酸変性ポリオレフィン樹脂Ｉ：無水マレイン酸変性エチレン−α−オレフィン共重合体、三井化学（株）製「タフマーＭＰ０６０１０」
注４）不飽和カルボン酸変性ポリオレフィン樹脂II：アクリル酸変性ポリプロピレン、三井化学（株）製「アドマーＱＦ５００」
注５）高密度ポリエチレン樹脂：三井化学（株）製「ハイゼックス２２００Ｊ」注６）ＧＦ：シランカップリング剤で処理されたガラス繊維、旭ファイバーグラス（株）製「チョップドストランドＣＳ０３ＤＥＦＴ２Ａ」
注７）トリアリルイソシアヌレート：化薬アクゾ（株）製「パーカリンク３０１」
【００２７】
そして、各ウォームホイール試験体について、下記に示す寸法安定性の評価及び耐久性の評価を行った。
【００２８】
［寸法安定性の評価］
各試験体を、下記条件Ｉまたは条件IIの下に放置し、所定時間経過後にギア外径寸法の変化量を測定した。何れの条件においても、変化量が４０μｍ以下を合格「○」、４０μｍを超えるものを不合格「×」として表２に示す。
・条件Ｉ：６０℃、９０％ＲＨ、７０時間
・条件II：８０℃、９０％ＲＨ、３００時間
【００２９】
［耐久性の評価］
各試験体を実際の自動車減速ギアに組み込み、下記条件Ｉまたは条件IIにて操舵操作を繰り返し行った。何れの条件においても、１０万回の操舵に耐えることができた減速ギアを合格「○」、１０万回の操舵に耐えることができなかった減速ギアを不合格「×」として表２に示す。
・条件Ｉ：３０℃、５０％ＲＨ
・条件II：５０℃、９０％ＲＨ
【００３０】
【表２】

【００３１】
表２に示すように、ポリアミド樹脂のみをベース樹脂とした比較例１の試験体は、温度、湿度が過酷になると寸法安定性が悪くなり、それに伴って耐久性も低下している。また、不飽和カルボン酸変性ポリオレフィン樹脂では無く、高密度ポリエチレン樹脂とポリアミド樹脂とをベース樹脂とする比較例２の試験体は、吸水性には問題がなく寸法安定性が良好であるのの、変性されていないことに起因して相互作用が無いことから、機械的強度が十分ではなく、耐久性が不足している。これに対して本発明に従う実施例１〜６の各試験体は、過酷な条件下でも寸法安定性が高く、耐久性も優れている。
【００３２】
【発明の効果】
以上説明したように、本発明によれば、ウォームホイールの樹脂部をポリアミド樹脂と不飽和カルボン酸変性ポリオレフィン樹脂との混合物をベース樹脂とした樹脂組成物で形成したことにより、樹脂部の耐摩耗性、寸法安定性及び耐熱性が改善され、耐久性に優れる電動パワーステアリング用減速ギアが得られる。
【図面の簡単な説明】
【図１】本発明並びに従来の減速ギアの一例を示す斜視図である。
【図２】ウォームホイールの製造方法を説明するための図であり、芯管の断面図である。
【図３】ウォームホイールの製造方法を説明するための図であり、成形金型の断面図である。
【図４】ウォームホイールの製造方法を説明するための図であり、得られたウォームホイールブランク材の斜視図である。
【図５】ウォームホイールの製造方法を説明するための図であり、得られたウォームホイールの斜視図である。
【図６】本発明の減速ギアの他の例（平歯車）を示す斜視図である。
【図７】本発明の減速ギアの更に他の例（はすば歯車）を示す斜視図である。
【図８】本発明の減速ギアの更に他の例（かさ歯車）を示す斜視図である。
【図９】本発明の減速ギアの更に他の例（ハイボイドギア）を示す斜視図である。
【符号の説明】
１ 芯管
３ 樹脂部
４ スプルー
５ ディスクゲート
１０ ギア歯
１１ ウォームホイール
１２ ウォーム
２０ 減速ギア[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reduction gear for an electric power steering apparatus for transmitting an output of an electric motor for generating a steering assist output to a steering shaft.
[0002]
[Prior art]
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 reduction mechanism, a worm 12 that is connected to a rotating shaft of an electric motor (not shown) and a worm wheel that meshes with the worm 12 as shown in FIG. In general, a reduction gear 20 for an electric power steering apparatus (hereinafter also simply referred to as a “reduction gear”) is used.
[0003]
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, noise countermeasures are performed by using a worm wheel 11 in which a resin portion 3 made of resin and formed with gear teeth 10 on the outer peripheral surface is integrated with the outer periphery of a metal core tube 1. .
[0004]
In the resin part 3, for example, as described in Japanese Patent Publication No. 6-60674, a base resin such as polyamide 6, polyamide 66, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), In addition to materials containing reinforcing materials such as glass fibers and carbon fibers, materials such as MC (monomer cast) nylon, polyamide 6 and polyamide 66 that do not contain reinforcing materials have been proposed. However, in view of fatigue resistance, dimensional stability, cost, etc., MC nylon that does not contain a reinforcing material, polyamide 6, glass 66, polyamide 46, and the like that contain glass fibers are currently mainstream.
[0005]
[Problems to be solved by the invention]
In the reduction gear, both the gear teeth of the worm wheel 11 and the worm 12 are cut with high precision for smooth transmission of power, and the shape must be maintained after mounting. However, although the above-mentioned polyamide-based material is excellent in fatigue resistance, it has high water absorption, absorbs moisture, swells the gear teeth 10 of the worm wheel 11, and the gap that exists between the worm 12 in the initial stage. There is a possibility that the worm 12 may be pressed when the swell disappears or further swells. As a result, the resistance of the gear becomes heavy, and as a result, the handle becomes heavy, and it is also assumed that the gear part is worn or damaged due to the compression, and the entire device does not function.
[0006]
The present invention has been made in view of such a situation, and in particular, provides a reduction gear for an electric power steering that improves heat resistance, mechanical strength, and dimensional stability of a resin portion of a worm wheel and has excellent durability. For the purpose.
[0007]
[Means for Solving the Problems]
An object of the present invention is to provide a reduction gear for an electric power steering apparatus for transmitting an output of an electric motor for generating a steering assist output to a steering shaft according to the present invention. A resin composition containing a mixture of 3 to 25% by weight of an unsaturated carboxylic acid-modified polyolefin resin as a base resin and containing a fibrous reinforcing material in a proportion of 10 to 30% by weight of the total amount of the resin composition. This is achieved by a reduction gear for an electric power steering device comprising a gear formed by integrating a resin portion in which gear teeth are formed.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail.
[0009]
The reduction gear of the present invention includes a worm wheel in which a resin portion made of resin and having gear teeth formed on an outer peripheral end face thereof is integrated on the outer periphery of a metal core tube. Such a configuration itself is the same as the conventional worm wheel 11 in which the core tube 1 and the resin portion 3 are integrated as shown in FIG. Moreover, there is no restriction | limiting in the worm | warm 12, It can be made from metal like the past.
[0010]
However, the base resin forming the resin part 3 is a mixed resin of a polyamide resin and an unsaturated carboxylic acid-modified polyolefin resin. The polyamide resin is appropriately selected from polyamide 6, polyamide 66, polyamide 46, and the like as in the conventional case.
[0011]
On the other hand, the unsaturated carboxylic acid-modified polyolefin resin includes a copolymer of ethylene or propylene as a main constituent and a copolymer of an unsaturated carboxylic acid or a derivative thereof, and an olefin containing ethylene or propylene as a main constituent. A graft polymer of the above polymer and an unsaturated carboxylic acid or derivative thereof is preferred.
[0012]
Preferred examples of the copolymer in the copolymer include an ethylene-vinyl acetate copolymer, an ethylene-acrylic acid copolymer, and an ethylene-ethylacrylic acid copolymer. Moreover, as unsaturated carboxylic acid or its derivative (s), acrylic acid, methacrylic acid, methylmethacrylic acid, vinyl acetate, glycidyl methacrylate, etc. can be mentioned suitably. The unsaturated carboxylic acid or derivative thereof is preferably in a proportion of 40 mol% or less with respect to the total amount of the copolymer, and if it exceeds 40 mol%, the entire unsaturated carboxylic acid-modified polyolefin resin becomes too polar. Therefore, the compatibility with the polyamide resin is lowered, which is not preferable.
[0013]
Examples of the olefin polymer in the graft polymer include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene-1 copolymer, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer. Can be preferably mentioned. Examples of unsaturated carboxylic acids or derivatives thereof include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, fumaric acid, and acid anhydrides or esters thereof, among which maleic anhydride is reactive. It is preferable because it is high. The graft amount of the unsaturated carboxylic acid or derivative thereof is 0.05 to 2% by weight, preferably 0.2 to 1.5% by weight, based on 100% by weight of the olefin polymer. desirable. If the unsaturated carboxylic acid or derivative thereof is less than 0.05% by weight, the unsaturated carboxylic acid-modified polyolefin resin as a whole is too low in polarity and not very compatible with the polyamide resin. The interaction with the amide bond also becomes weak, and there is a possibility that the mechanical strength is lowered particularly when the proportion in the base resin is increased. Further, when the graft amount of the unsaturated carboxylic acid or derivative thereof exceeds 2% by weight, it is difficult to produce even if the reaction efficiency is increased by adding an organic oxide during the polymerization, and the practicality is low.
[0014]
In the unsaturated carboxylic acid-modified polyolefin resin, considering the interaction with the amide bond of the polyamide resin, the functional group of the modified part is a carboxyl group or an acid that reacts easily with two carboxyl groups by the addition of moisture. A group consisting of an anhydride is preferred.
[0015]
In the present invention, the heat resistance, mechanical strength, etc., which are advantages of the polyamide resin, are maintained by mixing a polyamide resin having excellent fatigue resistance and an unsaturated carboxylic acid-modified polyolefin resin that hardly absorbs water to make a base resin. However, the water absorption rate of the entire base resin is lowered by the unsaturated carboxylic acid-modified polyolefin resin, and the dimensional change as a gear is suppressed. Therefore, in order to satisfy the heat resistance, mechanical strength, and low water absorption in a well-balanced manner, when the base resin is 100% by weight, the polyamide resin is 75 to 97% by weight, and the unsaturated carboxylic acid-modified polyolefin resin is 3 to 25%. It mixed at a ratio of weight%. More preferably, when the base resin is 100% by weight, the polyamide resin is mixed at a ratio of 85 to 95% by weight and the unsaturated carboxylic acid-modified polyolefin resin is mixed at a ratio of 5 to 15% by weight. If the polyamide resin is less than 75% by weight, the heat resistance and mechanical strength of the resin part 3 are insufficient, and if the polyamide resin exceeds 97% by weight, that is, if the unsaturated carboxylic acid-modified polyolefin resin is less than 3% by weight, water absorption The rate is large and the dimensional change is large.
[0016]
In addition, in order to mutually connect the polyamide resin and the unsaturated carboxylic acid-modified polyolefin resin, triallyl isocyanurate, triallyl cyanurate, diallyl phthalate, divinylbenzene, diisopropenylbenzene, N, N′-m-phenylene If a polyfunctional monomer having at least two carbon-carbon double bonds is added to a molecule such as bismaleimide or polybutadiene, crosslinking may be partially advanced by heating when the resin part 3 is molded. it can. As a result, the amide bond of the polyamide resin and the interaction with the modified portion such as the carboxyl group of the unsaturated carboxylic acid-modified polyolefin resin are added, and problems such as a decrease in strength due to the mixing of the two resins can be prevented. The polyfunctional monomer is added in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 2 parts by weight, based on 100 parts by weight of the base resin. If the addition amount is less than 0.01 parts by weight, the absolute value is too small and the crosslinking reaction hardly proceeds. Moreover, even if it is added in excess of 5 parts by weight, the degree of crosslinking does not change so much, and unreacted substances and generated radicals may remain, leading to deterioration of physical properties of the resin part 3.
[0017]
These base resins exhibit a certain level of durability even when the resin alone is used, work favorably against the wear of the metal worm 12 which is the counterpart material of the worm wheel 11, and sufficiently function 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.
[0018]
As the reinforcing 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 the base resin mentioned above are more preferable. . 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.
[0019]
The amount of the reinforcing material is the percentage of 1 0 to 30% by weight of the total resin portion. When the compounding amount of the reinforcing material is less than 10 % by weight, the improvement in mechanical strength is small, which is not preferable. If the amount of reinforcing material is greater than 3 0% by weight, liable to damage the worm 12, there is a possibility that durability is insufficient as a speed reduction gear wear is accelerated in the worm 12 is not preferable.
[0020]
Furthermore, in order to prevent deterioration due to heat during molding and use, it is preferable to add an iodide heat stabilizer and an amine antioxidant, either alone or in combination, to the base resin.
[0021]
The method for manufacturing the worm wheel 11 is not limited, and for example, the steps shown in FIGS. Specifically, the outer peripheral surface 1a of the metal core 1 is subjected to a cross knurling process and degreased with a solvent (FIG. 2), and then the core tube 1 is placed in a mold equipped with a sprue 4 and a disk gate 5 and injected. The resin part 3 is filled by filling the resin composition containing the base resin or the reinforcing material with a molding machine (FIG. 3). Next, the sprue 4 and the disk gate 5 are cut away to obtain a worm wheel blank material 7 in which the resin portion 3 is integrated with the outer periphery of the core tube 1 (FIG. 4). And the worm wheel 11 is obtained by forming the gear tooth | gear 10 of a predetermined shape by cutting on the outer peripheral surface 3a of the resin part 3 of the worm wheel blank material 7 (FIG. 5).
[0022]
As mentioned above, although the worm wheel which is a cylindrical worm gear was illustrated and demonstrated regarding this invention, this invention is not limited to this, A various change is possible. For example, the spur gear shown in FIG. 6, the helical gear shown in FIG. 7, the bevel gear shown in FIG. 8, the hypoid gear shown in FIG. The resin portion 3 made of the resin composition and having the gear teeth 10 formed on the outer peripheral surface thereof is integrally formed. Note that an adhesive layer made of a silane coupling agent or the like may be interposed between the outer periphery of the metal core 1 and the inner periphery of the resin portion 3.
[0023]
【Example】
The present invention will be further described below with reference to examples, but the present invention is not limited thereto.
[0024]
[Preparation of worm wheel test material]
A polyamide resin, a polyolefin resin, a reinforcing material and a polyfunctional monomer shown in Table 1 were blended and pre-kneaded with a Henschel mixer (manufactured by Mitsui Miike Seisakusho Co., Ltd.), and then a twin screw extruder ("PCM-" manufactured by Ikekai Co., Ltd.). 30 ") to obtain resin pellets. Using the obtained resin pellets, a worm wheel specimen was produced according to FIGS. That is, an 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 fitted with a sprue and a disk gate, and an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd.) SG75M ") was used to produce a worm wheel blank material having an outer diameter of 60 mm and a width of 13 mm, and then the outer periphery of the resin portion was cut to form gear teeth to produce a worm wheel specimen.
[0025]
[Table 1]

[0026]
Note 1) PA66: “UBE nylon 2020U” manufactured by Ube Industries, Ltd. (including Cu-based heat stabilizer)
Note 2) PA46: DJEP "Stanyl TW300" (Cu-based heat stabilizer included)
Note 3) Unsaturated carboxylic acid-modified polyolefin resin I: maleic anhydride-modified ethylene-α-olefin copolymer, “Tuffmer MP06010” manufactured by Mitsui Chemicals, Inc.
Note 4) Unsaturated carboxylic acid-modified polyolefin resin II: Acrylic acid-modified polypropylene, “Admer QF500” manufactured by Mitsui Chemicals, Inc.
Note 5) High-density polyethylene resin: “Hi-Zex 2200J” manufactured by Mitsui Chemicals, Inc. Note 6) GF: Glass fiber treated with silane coupling agent, “Chopped Strand CS03DEFT2A” manufactured by Asahi Fiber Glass Co., Ltd.
Note 7) Triallyl isocyanurate: “PARKALINK 301” manufactured by Kayaku Akzo Co., Ltd.
[0027]
Each worm wheel specimen was evaluated for dimensional stability and durability as shown below.
[0028]
[Evaluation of dimensional stability]
Each specimen was left under the following condition I or condition II, and the change in the outer diameter of the gear was measured after a predetermined time. Under any condition, the change amount is 40 μm or less as pass “◯”, and the change exceeding 40 μm is shown as fail “×” in Table 2.
Condition I: 60 ° C., 90% RH, 70 hours Condition II: 80 ° C., 90% RH, 300 hours
[Durability evaluation]
Each test body was incorporated into an actual automobile reduction gear, and the steering operation was repeated under the following condition I or condition II. Under any condition, Table 2 shows that the reduction gear that could withstand 100,000 times of steering was “O”, and that the reduction gear that could not endure 100,000 times of steering was rejected “X”. .
Condition I: 30 ° C., 50% RH
Condition II: 50 ° C., 90% RH
[0030]
[Table 2]

[0031]
As shown in Table 2, the test body of Comparative Example 1 using only the polyamide resin as the base resin deteriorates in dimensional stability when the temperature and humidity become severe, and the durability decreases accordingly. Moreover, the test body of Comparative Example 2 which uses not a unsaturated carboxylic acid-modified polyolefin resin but a high-density polyethylene resin and a polyamide resin as a base resin has no problem in water absorption and has good dimensional stability. Since there is no interaction due to not being modified, the mechanical strength is not sufficient and the durability is insufficient. On the other hand, each test body of Examples 1 to 6 according to the present invention has high dimensional stability and excellent durability even under severe conditions.
[0032]
【The invention's effect】
As described above, according to the present invention, the resin part of the worm wheel is formed of a resin composition that uses a mixture of a polyamide resin and an unsaturated carboxylic acid-modified polyolefin resin as a base resin. Thus, a reduction gear for electric power steering with improved durability, dimensional stability and heat resistance is obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of the present invention and a conventional reduction gear.
FIG. 2 is a view for explaining a method of manufacturing a worm wheel, and is a cross-sectional view of a core tube.
FIG. 3 is a view for explaining a manufacturing method of a worm wheel, and a sectional view of a molding die.
FIG. 4 is a view for explaining a method of manufacturing a worm wheel, and is a perspective view of the obtained worm wheel blank material.
FIG. 5 is a view for explaining a manufacturing method of a worm wheel, and is a perspective view of the obtained worm wheel.
FIG. 6 is a perspective view showing another example (spur gear) of the reduction gear of the present invention.
FIG. 7 is a perspective view showing still another example (helical gear) of the reduction gear of the present invention.
FIG. 8 is a perspective view showing still another example (bevel gear) of the reduction gear of the present invention.
FIG. 9 is a perspective view showing still another example (high void gear) of the reduction gear of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Core pipe 3 Resin part 4 Sprue 5 Disc gate 10 Gear tooth 11 Worm wheel 12 Worm 20 Reduction gear

Claims (5)

In a reduction gear for an electric power steering apparatus for transmitting the output of an electric motor for generating a steering assist output to a steering shaft, 75 to 97% by weight of a polyamide resin and an unsaturated carboxylic acid-modified polyolefin resin 3 are provided on the outer periphery of the metal core tube. A resin part comprising a resin composition containing a mixture of up to 25% by weight as a base resin and containing a fibrous reinforcing material in a proportion of 10 to 30% by weight of the total amount of the resin composition, and gear teeth formed on the outer peripheral surface thereof A reduction gear for an electric power steering apparatus, comprising a gear formed by integrating   2. The reduction gear for an electric power steering apparatus according to claim 1, wherein the polyamide resin is polyamide 6, polyamide 66 or polyamide 46.   3. The unsaturated carboxylic acid-modified polyolefin resin is a copolymer of an ethylene or propylene polymer or a copolymer thereof and an unsaturated carboxylic acid or a derivative thereof. Reduction gear for electric power steering device.   The polyfunctional monomer having at least two carbon-carbon double bonds in the molecule is contained in a proportion of 0.01 to 5 parts by weight with respect to 100 parts by weight of the base resin. 4. The reduction gear for an electric power steering apparatus according to any one of 3.   The reduction gear for an electric power steering apparatus according to any one of claims 1 to 4, wherein the gear is a cylindrical worm gear, a helical gear, a spur gear, a bevel gear, or a hypoid gear.

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