JP4433827B2 - Resin gear - Google Patents

Description

  The present invention relates to a resin gear suitable for power transmission.

  In an electric power steering apparatus for a vehicle, a gear reduction mechanism is incorporated between the electric motor and the steering shaft since an electric motor having a relatively high rotation and low torque is used. As a gear reduction mechanism, a gear using a gear such as a spur gear is also known, but it is a drive-side gear connected to the rotating shaft of an electric motor for the reason that a large reduction ratio can be obtained by one set. A worm gear speed reduction mechanism (hereinafter sometimes referred to as a speed reduction gear) composed of a worm and a worm wheel meshing with the worm is generally used.

  In such a reduction gear, if both the worm wheel and the worm are made of metal, there has been a problem that unpleasant noise such as rattling noise and vibration noise is generated when the handle is operated. Therefore, when the worm is made of metal, the generation of unpleasant noise is suppressed by using a worm wheel having resin teeth. In this worm wheel, a resin blank disc is integrally formed on the outer periphery of a metal hub (that is, a metal core), and teeth are formed on the circumferential portion of the blank disc by means such as cutting. .

  As a resin constituting the teeth, for example, as disclosed in Patent Document 1, glass fibers, carbon fibers, and the like are added to base resins such as polyamide 6, polyamide 66, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), and the like. Monomer cast nylon (MC nylon), polyamide 6, polyamide 66, etc. that do not contain a fiber reinforcement are used in addition to materials containing the above fiber reinforcement.

Among these resin materials, in consideration of dimensional stability and cost, MC nylon not containing a fiber reinforcing material, polyamide 6, polyamide 66, polyamide 46 containing glass fiber, etc. are mainly used.
Japanese Patent Publication No. 6-60674

  However, resin gears using monomer cast nylon resin, which is most often used in column-type electric power steering devices, have a resin part where teeth are formed and the outer periphery of a metal hub fused (adhered). Therefore, although the dimensional change due to water absorption is suppressed, the resin itself does not contain a heat stabilizer or the like that remarkably improves heat resistance. Etc. may occur.

If such a decrease in strength occurs, there is a risk of damage to the resin teeth when a large load such as an impact at low temperatures is applied. In the worst case, the electric power steering device will not function. There was a risk of it.
Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a highly reliable resin gear that has excellent heat resistance and is unlikely to cause problems such as tooth breakage.

In order to solve the above-described problems, the present invention has the following configuration. In other words, the resin gear according to claim 1 of the present invention is a resin gear including a hub and a resin portion integrally provided on the outer periphery of the hub and having teeth formed thereon. It is characterized by being composed of a monomer cast nylon resin that has a decrease in tensile strength of less than 10% when left at 120 ° C. for 2000 hours.
A resin gear according to a second aspect of the present invention is the resin gear according to the first aspect, wherein the resin gear is a worm wheel, a helical gear, a spur gear, a bevel gear, or a hypoid gear.
Furthermore, the resin gear according to claim 3 according to the present invention is the resin gear according to claim 1 or 2, wherein the crystallinity of the monomer cast nylon resin is set to 50 to 60% by annealing treatment. and said that you are.
Furthermore, the resin-made gear of Claim 4 which concerns on this invention is a resin-made gear as described in any one of Claims 1-3. WHEREIN: The said monomer cast nylon resin is a copper-type heat stabilizer, a phenol-type heat stability. It contains at least one of an agent, a phosphorus heat stabilizer, a sulfur heat stabilizer, and an amine heat stabilizer.
Furthermore, the resin gear of Claim 5 which concerns on this invention is used for an electric power steering apparatus in the resin gear as described in any one of Claims 1-4.

  Since the resin gear of the present invention has excellent heat resistance, problems such as tooth breakage are less likely to occur and the reliability is high.

An embodiment of a resin gear according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of a column-type electric power steering device 10 for an automobile using the resin gear of the present embodiment as a speed reduction mechanism. The steering wheel shaft 11 is composed of an upper steering wheel shaft 11a and a lower steering wheel shaft 11b, and is supported inside the steering wheel shaft housing 12 so as to be rotatable about an axis. The steered wheel shaft housing 12 is fixed at a predetermined position in the vehicle interior with the lower portion inclined toward the front of the vehicle. Furthermore, a steering wheel (not shown) is fixed to the upper end of the upper steering wheel shaft 11a.
Further, the upper rudder wheel shaft 11a and the lower rudder wheel shaft 11b are connected by a torsion bar (not shown). The steering torque transmitted from the steering wheel to the lower steering wheel shaft 11b through the upper steering wheel shaft 11a is detected by the torsion bar, and the output of the electric motor 13 is controlled based on the detected steering torque.

The rack-and-pinion type motion converting mechanism 20 includes a pinion having a rack shaft 21 that can move in the axial direction and a pinion that is supported obliquely with respect to the axis of the rack shaft 21 and meshes with the teeth of the rack shaft 21. The shaft 22 and a cylindrical rack shaft case 23 that supports the rack shaft 21 and the pinion shaft 22 are configured. The rack and pinion motion conversion mechanism 20 is disposed substantially horizontally in the engine room at the front of the vehicle so that the longitudinal direction thereof is along the left-right direction of the vehicle.
The pinion shaft 22 and the lower portion of the lower rudder wheel shaft 11b are connected by two universal joints 25 and 26. Further, a worm gear speed reduction mechanism 30 described later is disposed at an intermediate portion of the lower rudder wheel shaft 11b, and a steering assist force is supplied from the electric motor 13 to the lower rudder wheel shaft 11b.

Next, the configuration of the worm gear reduction mechanism 30 will be described with reference to the partial cross-sectional view of FIG. Worm shafts 32 a and 32 b are integrally formed at both ends of the worm 32 that meshes with the worm wheel 31, and these worm shafts 32 a and 32 b are rotatable by ball bearings 34 a and 34 b mounted on the gear case 33, respectively. It is supported. The worm shaft 32 b is splined or serrated to the drive shaft 13 a of the electric motor 13.
Since the core metal 42 of the worm wheel 31 (corresponding to the hub which is a constituent element of the present invention) is connected to the lower steering wheel shaft 11b, the rotation of the electric motor 13 passes through the worm 32 and the worm wheel 31 to lower the lower steering wheel. It is transmitted to the shaft 11b.

Next, the configuration of the worm wheel 31 will be described with reference to the perspective view of FIG. The worm wheel 31 includes a core metal 42 and a resin portion 43 provided integrally on the outer periphery of the core metal 42. Further, teeth 44 that mesh with the metal worm 32 are formed on the outer diameter surface of the resin portion 43.
The resin portion 43 is made of monomer cast nylon resin and has a cylindrical shape, and the worm wheel 31 is obtained by heat-pressing the cored bar 42. At this time, it is preferable to appropriately process the outer peripheral surface of the core metal 42, such as cross knurling, and the processed surface may be heat-pressed into the cylindrical resin portion 43. Then, if the core metal 42 having a coupling agent such as a silane coupling agent applied to the outer peripheral surface is heated and press-fitted, and then high-frequency fusion is performed, the core metal 42 and the resin portion 43 are integrally bonded (adhered). ) Further, the teeth 44 on the outer diameter surface of the resin portion 43 are formed by cutting or the like after the metal core 42 and the resin portion 43 are integrated by fusion or the like. Examples of the method of applying the coupling agent to the core metal 42 include a method of applying a solution diluted with a solvent such as methanol.

The silane coupling agent has a chemical structure having an alkoxy group which is a hydrolyzable group at one end. This alkoxy group is hydrolyzed to change to a hydroxyl group, and the hydroxyl group causes a dehydration condensation reaction with a hydroxyl group on the metal surface, thereby forming a covalent bond having a high binding force with the metal.
Further, the silane coupling agent has an organic functional group at the other end, and this organic functional group remains about 1% by mass in the process of obtaining a monomer cast nylon resin by polymerization of ε-caprolactam. -Bonds with caprolactam and amide bond of monomer cast nylon resin. And the metal core 42 and the resin part 43 are firmly joined by these joints. As the organic functional group, those having an amino group are preferable in consideration of reactivity. Specific examples of such a silane coupling agent having an organic functional group include γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, and the like. can give.

  Although the monomer cast nylon resin is a polymer of ε-caprolactam, since the monomer cast nylon resin used in the present invention has at least one of improvement in crystallinity and uniform dispersion of the heat stabilizer, The heat resistance of the resin itself is superior to that of the monomer cast nylon resin. Furthermore, it is excellent in mechanical strength and dimensional stability. The heat resistance of such a monomer cast nylon resin is as follows. That is, the monomer cast nylon resin has a tendency to deteriorate when exposed to high temperature, and the physical properties such as tensile strength decrease. However, the monomer cast nylon resin as described above is left in the air at 120 ° C. for 2000 hours. However, the rate of decrease in tensile strength is less than 10%.

Since the resin portion 43 of the worm wheel 31 is composed of such a monomer cast nylon resin having excellent heat resistance, problems such as tooth breakage hardly occur even when a large load or the like is applied. Therefore, the worm gear speed reduction mechanism 30 has high reliability and a long life, and contributes to high performance of the electric power steering apparatus 10.
Here, the improvement of the crystallinity will be described. When a monomer cast nylon resin (polymer obtained by a normal method) obtained by polymerizing ε-caprolactam by a monomer cast method is annealed, the crystallinity is increased from about 40 to 45% to 50 to 60%. improves. Thereby, mechanical strength such as tensile strength is improved, and fatigue resistance and heat resistance are improved. When the degree of crystallinity is less than 50%, the above improvement effect is insufficient. On the other hand, if it exceeds 60%, the mechanical strength is improved, but the elastic modulus is too high, so that the surface pressure of the gear tooth surface is improved. Moreover, since it is necessary to raise the processing temperature of annealing processing or to lengthen processing time, its practicality is low.

  The conditions for the annealing treatment are not particularly limited, but examples include the following. That is, the temperature is raised from room temperature to 160 to 200 ° C. over 2 to 15 hours, held at the temperature for about 1 to 15 hours, and then gradually cooled to room temperature over 3 to 30 hours. By such annealing treatment, the crystallinity of the monomer cast nylon resin can be improved from about 40 to 45% to 50 to 60%.

Next, the uniform dispersion of the heat stabilizer will be described. In order to uniformly disperse the heat stabilizer in the monomer cast nylon resin, it is necessary to devise a method for mixing the heat stabilizer. A polymer of ε-caprolactam (monomer cast nylon resin) obtained by the monomer casting method and ε-caprolactam (monomer) are mixed while heating to obtain a highly viscous uniform solution. The heating temperature at this time needs to be 69 ° C. or higher, which is the melting point of ε-caprolactam, more preferably about 160 to 210 ° C. In a state where the heat stabilizer is dispersed in this solution and precipitation of the heat stabilizer and uneven concentration are prevented, the polymerization is further advanced by a monomer cast method. Thereby, the heat stabilizer can be uniformly dispersed in the monomer cast nylon resin.
The number average molecular weight of the monomer cast nylon resin is preferably 60000 to 300000, more preferably 100000 to 200000.

The type of heat stabilizer is not particularly limited, and copper heat stabilizers, phenol heat stabilizers, phosphorus heat stabilizers, sulfur heat stabilizers, amine heat stabilizers, and the like can be used. .
Copper compounds that can be used as copper-based heat stabilizers include inorganic acid salts such as copper chloride, copper bromide, copper iodide, copper sulfate, copper nitrate, copper phosphate, copper acetate, copper stearate, Examples thereof include salts of organic acids such as copper myristylate, copper naphthenate, and copper palmitate. These copper heat stabilizers may be used alone or in combination of two or more. In addition, the solubility at the time of superposition | polymerization can be improved by adding the same kind of salt as a copper compound used as a copper-type heat stabilizer (for example, potassium iodide in the case of copper iodide).

  Phenol-based heat stabilizers include N, N′-hexamethylenebis (3,5-di-t-butyl-4-hydroxyhydrocinnamamide), 1,3,5-tris (4-t-butyl- 3-hydroxy-2,6-dimethylbenzyl) isocyanate, triethylene glycol bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1-oxy-3- Methyl-4-isopropylbenzene, 2,6-di-t-butyl-4-ethylphenol and the like can be used.

  As the phosphorus-based heat stabilizer, a phosphite-based compound is preferable. Specifically, diphenylisodecyl phosphite, diphenylisooctyl phosphite, triphenyl phosphite, triisodecyl phosphite, tris (2 , 4-Di-t-butylphenyl) phosphite, tetraphenyltetra (tridecyl) pentaerythritol tetraphosphite, cyclic neopentanetetraylbis (2,4-di-t-butylphenylphosphite), distearyl pentaerythritol Diphosphite or the like can be used.

Examples of sulfur-based heat stabilizers include dilauryl thiodipropionate, distearyl thiodipropionate, dimyristyl-3,3′-thiodipropionate, ditridecyl-3,3′-thiodipropionate, dilauryl thiodipropionate. Nate etc. can be used.
Examples of the amine heat stabilizer include alkyl-substituted diphenylamine such as 4,4′-dioctyldiphenylamine, and p-phenylenediamine having a substituent such as N, N′-di-2-naphthyl-p-phenylenediamine. Can be used.

  These various heat stabilizers may be used alone or in combination of two or more, but the preferred content varies depending on the type of heat stabilizer. In the case of a copper-based heat stabilizer, the content is preferably 0.0005 to 0.3% by mass with respect to the entire resin composition containing a monomer cast nylon resin as a main component. When the content is less than 0.0005% by mass, the effect of improving heat resistance is poor. On the other hand, even if the content exceeds 0.3% by mass, the effect of improving the heat resistance is not improved any more, and since the content is too large, it becomes difficult to perform sufficiently uniform dispersion, and some of the particles May occur. When aggregation occurs, physical properties such as fatigue resistance may be deteriorated starting from the aggregation point. In order to make such inconvenience less likely to occur, the content of the copper-based heat stabilizer is more preferably 0.001 to 0.1% by mass.

  In the case of the above organic heat stabilizers other than the copper heat stabilizer, it is preferably 0.05 to 4% by mass with respect to the entire resin composition containing the monomer cast nylon resin as a main component. When the content is less than 0.05% by mass, the effect of improving heat resistance is poor. On the other hand, even if the content exceeds 4% by mass, the effect of improving the heat resistance is not further improved, and it becomes difficult to make it compatible with the monomer cast nylon resin. In order to make such inconvenience less likely to occur, the content of the heat stabilizer is more preferably 0.1 to 2% by mass.

  The monomer cast nylon resin may contain various additives such as an ultraviolet absorber, a flame retardant, and an antibacterial agent in addition to the heat stabilizer. Also contains acicular fillers such as wollastonite, potassium titanate whisker, aluminum borate whisker, calcium carbonate (aragonite), basic magnesium sulfate (mosheidi), sepiolite, zonotolite, and colorants such as carbon black. You may let them.

  This embodiment shows an example of the present invention, and the present invention is not limited to this embodiment. For example, in the present embodiment, the present invention has been described by exemplifying a worm wheel. However, it goes without saying that the resin gear of the present invention is not limited to a worm wheel and can be applied to other types of gears. . For example, the present invention can be applied to the spur gear shown in FIG. 4, the helical gear shown in FIG. 5, the bevel gear shown in FIG. 6, the hypoid gear shown in FIG.

〔Example〕
Hereinafter, the present invention will be described more specifically with reference to examples. Two types (Examples and Comparative Examples) of worm wheel specimens were produced by using the resin compositions having the compositions shown in Table 1 by the method described below. As can be seen from Table 1, the worm wheel specimens of the examples are made of a monomer cast nylon resin containing 2.0% by mass of a thermal stabilizer, and the worm wheel specimens of the comparative examples are made of a thermal stabilizer. It consists of a monomer cast nylon resin that does not contain.

  A donut-shaped resin blank was molded with the monomer cast nylon resin having the composition shown in Table 1. About the Example, the resin blank was immersed in silicone oil, the annealing process was performed, and the crystallinity degree was improved. The temperature conditions are as follows. That is, the temperature was raised from room temperature to 170 ° C. over 4 hours, held at 170 ° C. for 3 hours, and then gradually cooled to room temperature over 4 hours.

Moreover, the core metal which gave the cross knurling process was prepared, and it was immersed in the methanol solution (concentration is 5 mass%) of a silane coupling agent. As a silane coupling agent, A-1122 (N-β-aminoethyl-γ-aminopropyltrimethoxysilane) manufactured by Nippon Unicar Co., Ltd. was used.
The resin blank was heated at 140 ° C. for 1 hour to expand, and the above-described core metal was press-fitted therein. Thereafter, high frequency fusion was performed immediately, and the cored bar and the resin blank were completely joined via the silane coupling agent. After joining, the outer periphery of the resin part (resin blank) was cut to form teeth, and a worm wheel specimen was obtained.

  These worm wheel specimens were incorporated into a worm gear reduction mechanism of an electric power steering apparatus as shown in FIG. The durability was evaluated by repeatedly performing steering until the worm wheel specimen was damaged. The temperature condition of this durability test is 120 ° C. As shown in Table 1, in the case of the example, the worm wheel specimen was not damaged even after repeating 100,000 times of steering, whereas in the case of the comparative example, the tooth bottom was cracked by 10,000 times of steering. There has occurred.

  Table 1 also shows the tensile strength, crystallinity, water absorption rate, and heat resistance test results of the two resin compositions. The tensile strength is the result of measurement under both temperature conditions of 23 ° C. and 120 ° C. The water absorption is a numerical value when immersed in water for 24 hours. Furthermore, the heat resistance test is a test in which the rate of decrease in tensile strength due to the heat treatment is measured by leaving in air at 120 ° C. for 2000 hours.

  As can be seen from the results shown in Table 1, the monomer cast nylon resin of the example contains a thermal stabilizer and has improved crystallinity, so that it has excellent mechanical strength such as tensile strength and heat resistance. Excellent water absorption rate. Therefore, the gear dimensional change due to water absorption is suppressed, and the conventional monomer cast nylon resin gear cannot be used due to insufficient heat resistance and insufficient strength at high temperature even at a high temperature of about 120 ° C. Can be used.

  The resin gear of the present invention is suitable, for example, for a gear reduction mechanism that constitutes a power assist portion of an electric power steering device.

It is a figure explaining the structure of an electric power steering device. It is a fragmentary sectional view which shows the structure of a worm gear reduction mechanism. It is a perspective view which shows the structure of a worm wheel. It is a perspective view of a spur gear. It is a perspective view of a helical gear. It is a perspective view of a bevel gear. It is a perspective view of a hypoid gear.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 30 Worm gear reduction mechanism 31 Worm wheel 32 Worm 42 Core metal (hub)
43 Resin part 44 Teeth

Claims (5)

  In a resin gear comprising a hub and a resin portion integrally provided on the outer periphery of the hub and having teeth formed thereon, the tensile strength of the resin portion is reduced by being left in air at 120 ° C. for 2000 hours. A resin gear comprising a monomer cast nylon resin having a rate of less than 10%.   The resin gear according to claim 1, wherein the resin gear is a worm wheel, a helical gear, a spur gear, a bevel gear, or a hypoid gear. The resin gear according to claim 1 or 2, wherein the crystallinity of the monomer cast nylon resin is set to 50 to 60% by annealing treatment .   The monomer cast nylon resin contains at least one of a copper-based heat stabilizer, a phenol-based heat stabilizer, a phosphorus-based heat stabilizer, a sulfur-based heat stabilizer, and an amine-based heat stabilizer. The resin gear according to any one of claims 1 to 3.   The resin gear according to any one of claims 1 to 4, wherein the resin gear is used in an electric power steering device.

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