JP2016064751A - Reduction gear for electric power steering device and electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reduction gear for an electric power steering device which is excellent in quietness, abrasion resistance, dimension stability, and heat resistance, and to provide an electric power steering device.SOLUTION: A gear reducer 30 of an electric power steering device includes: a worm 32 to which a steering assisting force output from an electric motor 13 is transmitted; and a worm wheel 31 which meshes with the worm 32 to transmit the steering assisting force to a steering shaft 11. The worm wheel 31 comprises: a core tube 41; and an annular resin part 42 integrally provided with an outer periphery part of the core tube 41 and in which gear teeth 43 are formed on an outer peripheral surface. The resin part 42 is formed by a resin material containing aromatic polyamide 11.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a reduction gear for an electric power steering apparatus and an electric power steering apparatus.

As a gear reducer used in an electric power steering apparatus incorporated in an automobile or the like, a worm and a worm connected to a rotating shaft of an electric motor are generally used because a large reduction ratio can be obtained with a set of gears. A reduction gear for an electric power steering device is used which is composed of a worm wheel meshing with the worm wheel.
In such a reduction gear for an electric power steering device, if both the worm and the worm wheel are made of metal, there is a problem that a noise such as a rattling sound or a vibration sound is generated when the tearing wheel is operated. Therefore, noise countermeasures are taken by using a worm wheel in which an annular resin part having gear teeth formed on the outer peripheral surface is integrally provided on the outer peripheral part of a metal core tube.

  As a resin material constituting the resin portion, for example, as shown in Patent Document 1, a base resin such as polyamide 6, polyamide 66, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide (PPS) is used as glass fiber, Examples thereof include a resin composition reinforced with a reinforcing material such as carbon fiber. Further, MC nylon (registered trademark of Quadrant Polypenco Japan Co., Ltd.), polyamide 6, polyamide 66 and the like which do not contain reinforcing materials such as glass fiber and carbon fiber are also included. Among these, from the balance between performance and cost, MC nylon not containing a reinforcing material, polyamide 6, reinforced with glass fiber, polyamide 66, polyamide 46, etc. are currently mainstream.

There are two types of electric power steering devices: a column assist type mounted in a vehicle compartment and a rack assist type mounted in an engine room. The above-mentioned mainstream resin materials are, in particular, column assist type electric power steering devices. In many cases.
However, when a resin composition reinforced with a reinforcing material is applied as a worm wheel material for a reduction gear for an electric power steering device, although strength, rigidity, and dimensional stability are remarkably excellent, glass fiber, carbon Reinforcing materials such as fibers are highly aggressive to worms and may cause noise. Therefore, there was room for improvement in terms of quietness.

In addition, the reinforcement that has fallen off the gear teeth of the worm wheel due to the progress of normal wear during normal use is interposed between the gear teeth of the worm wheel and the worm, thereby promoting the abrasive wear of the gear teeth. There was a risk of being. As a result, the steering feel may change over time.
On the other hand, for example, when MC nylon that does not contain a reinforcing material is applied as a material for a worm wheel, the above-mentioned problem of quietness and abrasive wear does not occur, but it is mounted in the engine room from the viewpoint of heat resistance. It was difficult to apply to the rack assist type. Furthermore, since the resin material does not contain a reinforcing material that contributes to dimensional stability, there is room for improvement in dimensional stability due to water absorption.

  As techniques for improving dimensional stability due to water absorption, for example, techniques disclosed in Patent Documents 2 and 3 are known. The technique disclosed in Patent Document 2 is to suppress a dimensional change due to water absorption of a polymer by an inorganic filler added in the polymerization process of polyamide. Moreover, the technique disclosed in Patent Document 3 is to coat the teeth of the worm wheel with a film to suppress water absorption itself.

However, the technique disclosed in Patent Document 2 has a problem that the strength may decrease due to the addition of an inorganic filler. Further, the technique disclosed in Patent Document 3 has a problem that the coating of the tooth portion may be peeled off due to the meshing of the gears.
Furthermore, since MC nylon is produced by a monomer casting method in which polymerization and high molecular weight are achieved during centrifugal molding, high cycle molding is difficult. Therefore, it has been very difficult to take cost reduction measures from the manufacturing aspect.

Japanese Patent Publication No. 6-60674 Japanese Patent Laid-Open No. 10-38053 JP 2002-327830 A

  Accordingly, the present invention provides a reduction gear for an electric power steering device and an electric power steering device that solve the above-described problems of the prior art and are excellent in silence, wear resistance, dimensional stability, and heat resistance. This is the issue.

In order to solve the above-described problem, a reduction gear for an electric power steering apparatus according to an aspect of the present invention includes a drive gear to which a steering assist force output from an electric motor is transmitted, and meshes with the drive gear to transmit the steering assist force. A driven gear that transmits to a steering shaft, and the driven gear includes a core tube and an annular resin portion that is provided integrally with the outer peripheral portion of the core tube and has gear teeth formed on the outer peripheral surface thereof. The resin portion is made of a resin material containing the semi-aromatic polyamide 11.
An electric power steering apparatus according to another aspect of the present invention includes an electric motor that outputs a steering assist force that assists the steering force in accordance with a steering force input to a steering shaft, and a deceleration of the steering assist force. And a gear reduction device that transmits to the steering shaft, and the reduction gear for the electric power steering device is provided as the gear reduction device.

  The reduction gear for an electric power steering device and the electric power steering device of the present invention are excellent in silence, wear resistance, dimensional stability, and heat resistance.

It is a figure explaining the composition of the column assist type electric power steering device which is one embodiment of the electric power steering device concerning the present invention. It is a fragmentary sectional view which shows the structure of the reduction gear for electric power steering apparatuses with which the column assist type electric power steering apparatus of FIG. 1 was equipped. FIG. 3 is a perspective view of a reduction gear for the electric power steering apparatus of FIG. 2. It is a figure explaining the structure of the rack assist type electric power steering apparatus which is other embodiment of the electric power steering apparatus which concerns on this invention.

  Embodiments of the present invention will be described in detail with reference to the drawings. A steering wheel 10 to which a steering force is input by a driver such as an automobile is fixed to the upper end of the steering shaft 11. The steering shaft 11 is composed of an upper shaft 11a and a lower shaft 11b connected by a torsion bar (not shown), and is supported inside the steering shaft housing 12 so as to be rotatable around an axis. The steering shaft housing 12 is fixed at a predetermined position in the vehicle interior in a posture in which the lower portion is inclined toward the front of the vehicle. The steering wheel 10 is fixed to the upper end of the upper shaft 11 a protruding from the steering shaft housing 12.

  A rack and pinion mechanism 20 that converts the rotation of the steering shaft 11 into the motion of left and right steered wheels (not shown) is a rack 21 that is movable in the axial direction and a rack that is supported obliquely with respect to the axis of the rack 21. A pinion 22 having teeth that mesh with the teeth of 21 and a cylindrical rack housing 23 that supports the rack 21 and the pinion 22. The rack and pinion mechanism 20 is arranged substantially horizontally in the engine room at the front of the vehicle so that the longitudinal direction thereof is along the width direction of the vehicle.

Since the upper end portion of the pinion 22 and the lower end portion of the lower shaft 11 b of the steering shaft 11 are connected via two universal joints 25 and 26, the rotation of the steering shaft 11 is rack 21 by the rack and pinion mechanism 20. The left and right sliding motions are converted and steered wheels (not shown) connected to both ends of the rack 21 are steered.
An electric power steering device that outputs a steering assist force that assists the steering force input to the steering shaft 11 is connected to the lower shaft 11 b of the steering shaft 11. The electric power steering device includes an electric motor 13 that outputs a steering assist force that assists the steering force in accordance with the steering force input to the steering shaft 11, and a lower portion of the steering shaft 11 that decelerates the steering assist force. And a gear reducer 30 that transmits to the shaft 11b. As the gear reducer 30, a reduction gear for an electric power steering device constituted by a worm gear is used.

  Here, the gear reducer 30 (the reduction gear for the electric power steering device) will be described in detail. The gear reducer 30 is accommodated in a gear box 33 provided continuously to the steering shaft housing 12. The gear reducer 30 includes a worm wheel 31 (corresponding to a “driven gear” which is a constituent element of the present invention) fitted to the outer periphery of the lower shaft 11b, and a metal worm 32 (engaged with the worm wheel 31). Corresponding to a “driving gear” that is a constituent element of the present invention.

Worm shafts 32 a and 32 b are integrally formed at both ends of the worm 32, and these worm shafts 32 a and 32 b are rotatably supported by rolling bearings 34 a and 34 b that are press-fitted and fixed to the gear box 33, respectively. . In addition, the electric motor 13 is attached to the gear box 33 by means such as bolt fastening, for example, and the drive shaft 13a and the worm shaft 32b of the electric motor 13 are spline-coupled or serrated-coupled, for example.
Since the worm wheel 31 is connected to the lower shaft 11 b, the steering assist force output from the electric motor 13 is transmitted to the lower shaft 11 b while being decelerated via the worm 32 and the worm wheel 31.

  When a steering force (rotational force) is input to the steering wheel 10 by the driver, the steering shaft 11 rotates. This steering force is detected by a torsion bar. Then, the output (steering assist force) of the electric motor 13 is controlled according to the detected steering force. The steering assist force output from the electric motor 13 is transmitted to the worm 32, supplied to the lower shaft 11b of the steering shaft 11 from the worm wheel 31 while being decelerated by the gear reducer 30, and combined with the steering force. As the steering shaft 11 rotates, the pinion 22 rotates, and the rotation of the pinion 22 is converted into a sliding motion in the horizontal direction of the rack 21 by the rack and pinion mechanism 20, and the steered wheels are driven to steer the automobile. Is done.

The worm wheel 31 includes, for example, a metal core tube 41 and an annular resin portion 42 provided integrally with the outer peripheral portion of the core tube 41 and having a plurality of gear teeth 43 formed on the outer peripheral surface thereof. . The worm 32 can be made of resin.
The resin part 42 of the worm wheel 31 is made of a resin material containing the semi-aromatic polyamide 11. The semi-aromatic polyamide 11 is a copolymerized polyamide resin composed of hexamethylene terephthalamide units and undecanamide units.

  The hexamethylene terephthalamide unit corresponds to, for example, polyamide 6T obtained by polycondensation of hexamethylene diamine and terephthalic acid in equimolar amounts, and the hexamethylene terephthalamide unit is, for example, 11-aminoundecanoic acid or undecane lactam. Is equivalent to polyamide 11 obtained by polycondensation. An example of the semi-aromatic polyamide 11 is Vylamide (registered trademark) manufactured by Toyobo Co., Ltd. This resin material may contain only the semi-aromatic polyamide 11 without containing a reinforcing material, or may contain an organic reinforcing material.

In such an electric power steering device and gear reducer 30 (reduction gear for electric power steering device) of this embodiment, the resin portion 42 of the worm wheel 31 is made of a resin material containing the semi-aromatic polyamide 11. Therefore, it is excellent in silence, wear resistance, dimensional stability, and heat resistance.
More specifically, the electric power steering device and the gear reducer 30 (reduction gear for the electric power steering device) of the present embodiment are excellent in silence because the gear teeth 43 of the worm wheel 31 are made of a resin material. Yes. Moreover, since the semi-aromatic polyamide 11 has better wear resistance than the polyamide 6, polyamide 66, polyamide 46, etc., the tooth surfaces of the gear teeth 43 are less likely to wear. Therefore, it is difficult for the steering feeling of the steering wheel 10 to change over time.

Furthermore, since semi-aromatic polyamide 11 has higher crystallinity and lower water absorption than polyamide 6, polyamide 66, polyamide 46, etc., it contains an additive that suppresses dimensional changes due to water absorption, or a film that suppresses water absorption. Even without coating, the dimensional stability due to water absorption is excellent.
Further, since the semi-aromatic polyamide 11 is superior in heat resistance as compared with polyamide 6, polyamide 66, polyamide 46, etc., the electric power steering device and the gear reducer 30 of this embodiment are provided with a column assist type electric power. It can be applied not only to a steering device but also to a rack assist type electric power steering device that requires higher heat resistance (for example, an operating environment temperature of 80 ° C.) because it is mounted in an engine room.

  Furthermore, if the resin material containing the semi-aromatic polyamide 11 and the reinforcing material is used, the strength and heat resistance of the resin portion 42 of the worm wheel 31 are high. This can also be applied when the steering assist force is large (for example, 1.5 times the steering assist force in the column assist type electric power steering device). Further, the present invention can also be applied to a rack assist type electric power steering device used in a severe environment.

  Here, an example of the configuration of the rack assist type electric power steering apparatus will be described with reference to FIG. 4 includes a rack shaft 101, a first pinion 105 connected to a steering shaft (not shown), a second pinion 106 on the electric motor 110 side, and a gear reducer 130. And. The gear reducer 130 includes a worm (not shown) and a worm wheel (not shown) connected to the drive shaft of the electric motor 110 that outputs a steering assist force, and the second pinion 106 is a worm. It is fixed to the wheel. The second pinion 106 is engaged with the rack shaft 101.

The type and blending ratio of the reinforcing material in the resin material is not particularly limited, but the metal worm 32 is excessive depending on the displacement, weight, usage conditions, etc. of the automobile equipped with the electric power steering device. It is preferable to select a kind and a blending ratio so as not to damage.
In other words, glass fiber or carbon fiber can be used as the reinforcing material, but an organic reinforcing material formed of an organic compound such as a polymer is used so that the metal worm 32 is not excessively damaged. It is preferable. By using an organic reinforcing material, excellent strength and dimensional stability can be obtained without impairing silence and wear resistance. Examples of the organic reinforcing material include polyamide fiber (aramid fiber, nylon fiber), aromatic polyimide fiber, polyester fiber (polyarylate fiber), and poly (paraphenylenebenzobisoxazole) fiber. These organic reinforcing materials may be used alone or in combination of two or more.

Moreover, it is preferable that the reinforcing material has been subjected to a surface treatment with a sizing agent. The type of the sizing agent is not particularly limited, but a sizing agent such as urethane resin, epoxy resin, acrylic resin, bismaleimide resin is preferable.
Furthermore, the compounding ratio of the reinforcing material in the resin material is preferably 35% by mass or less. If it exceeds 35% by mass, the melt fluidity of the resin material is lowered, the moldability is lowered, and injection molding with excellent moldability may not be performed.

Furthermore, a nano-size filler may be added to the resin material to further improve durability reliability. As the nanosize filler, for example, smectite such as montmorillonite, hectorite, saponite and the like having a layered crystal structure in which crystals having a thickness of about 1 nm are laminated is particularly suitable. By uniformly dispersing the smectite layered crystal in the resin material, it is possible to improve mechanical properties such as strength, elastic modulus and dimensional stability of the resin material and thermal properties such as heat distortion temperature.
Moreover, you may use the nanomaterial called POSS (polyhedral oligosilsesquioxane) as a nanosize filler. POSS is one of organic-inorganic hybrid materials, and its molecular structure has a cubic skeleton composed of silicon (Si) and oxygen (O) in the central part, and an organic substituent is bonded to the apex. The type structure.

  The compounding ratio of the nano-sized filler in the resin material is preferably 0.1% by mass or more and 30% by mass or less, and more preferably 0.5% by mass or more and 15% by mass or less. If it is less than 0.1% by mass, the effect of improving mechanical properties and thermal properties may be insufficient, and if it is more than 30% by mass, the nano-sized filler aggregates in the resin material, It may be difficult to achieve uniform dispersion. As a result, there is a possibility that the effect of using a large amount of the nano-size filler does not appear.

  Furthermore, the resin material may contain additives such as an antioxidant and a lubricant regardless of the presence or absence of the reinforcing material. By adding an antioxidant, deterioration due to heat during molding and use of the resin material can be suppressed. Examples of the antioxidant include iodide-based heat stabilizers, phenol-based antioxidants, and amine-based antioxidants. These antioxidants may be used alone or in combination of two or more.

Further, the worm 32 and the worm wheel 31 may be lubricated with a lubricant such as grease. The type of grease is not particularly limited. For example, the base oil can be composed mainly of poly α-olefin oil, and the thickener can be a urea compound (for example, a reaction of amine and isocyanate). Obtained), Li soap, Li complex soap, Ba soap, Ba complex soap and the like.
In order to improve the lubricity of the poly α-olefin oil, a diester oil or an aromatic ester oil may be mixed with the base oil. The mixing ratio is preferably 30% by mass or less of the entire base oil.

  Furthermore, you may add the additive for lubricants to this grease. Examples of additives for lubricants include amine-based and phenol-based antioxidants, rust preventive agents such as calcium sulfonate, and extreme pressure additives such as molybdenum dialkyldithiocarbamate. Moreover, oiliness improvers such as montanic acid ester wax, montanic acid ester partly saponified wax, polyethylene wax, oleic acid and the like can be mentioned.

  In the present embodiment, the present invention has been described with reference to an example in which the gear reduction gear 30 (the reduction gear for the electric power steering device) is configured by a cylindrical worm gear including a worm and a worm wheel. However, the invention is not limited to this, and it is needless to say that other types of gears may be used. For example, a spur gear, a helical gear, a bevel gear, a hypoid gear, or the like may be used. In any type of gear, the driven gear is obtained by integrally providing an annular resin portion having gear teeth on the outer peripheral surface thereof on the outer peripheral portion of a metal core tube.

  The present invention will be described more specifically with reference to the following examples. Three types of resin materials were prepared as resin materials used for the resin portion of the worm wheel. The resin material of Example 1 is semi-aromatic polyamide 11, and no reinforcing material is blended. The resin material of Example 2 is a resin composition in which an organic reinforcing material is blended with the semi-aromatic polyamide 11. Furthermore, the resin material of Comparative Example 1 is a glass fiber reinforced polyamide resin composition in which glass fibers are blended with polyamide 66.

  In any of the resin materials of Examples 1 and 2, the semi-aromatic polyamide 11 is Toyobo Co., Ltd. Vyloamide MJ-300NZ. The organic reinforcing material in the resin material of Example 2 is para-aramid fiber (Technola (trade name) manufactured by Teijin Limited), and the blending ratio of para-aramid fiber is 15% by mass of the entire resin material. . Furthermore, the resin material of Comparative Example 1 is Amilan (trade name) CM3006G-30, which is a glass fiber reinforced polyamide resin composition manufactured by Toray Industries, Inc., and the blending ratio of the glass fibers is 30% by mass of the entire resin material. .

[Evaluation of worm wheel attack against worm]
In order to evaluate the attack of the worm wheel against the worm, the resin materials of Examples 1 and 2 and Comparative Example 1 were molded to produce a plate-shaped test piece, subjected to a ball-on-disk test, and a metal ball after completion of the test The damage state of was evaluated.
The contents of the ball-on-disk test are as follows. A metal ball is placed on the plate test piece, and grease (base oil: poly α-olefin oil, thickener: urea compound) is interposed between the plate test piece and the metal ball, and the ambient temperature. The metal ball was moved at 23 ° C. while applying a vertical load (constant load 39.2 N) to the metal ball (moving speed 1000 mm / s). Then, after the metal ball was moved for a predetermined time, the surface state of the metal ball was observed. The results are shown in Table 1.

Since the resin material of Comparative Example 1 was reinforced with glass fiber, damage marks due to the glass fiber were clearly recognized on the surface of the metal ball after the test. On the other hand, since the resin materials of Examples 1 and 2 do not contain glass fiber, they do not attack the counterpart material, no damage marks are observed on the surface of the metal ball after the test, and the surface state is It was very good.
From these results, if the resin part of the worm wheel is manufactured with the resin material of Examples 1 and 2, unlike the case where the resin part of the worm wheel is manufactured with the conventional glass fiber reinforced polyamide resin composition, the glass during steering is used. It can be seen that the noise caused by the fiber sliding while attacking the worm can be suppressed.

[Evaluation of durability of worm wheel]
In order to evaluate the durability of the worm wheel, the worm wheel was manufactured using the resin materials of Examples 1 and 2 and Comparative Example 1. First, a S45C core tube having an outer diameter of 45 mm and a width of 13 mm was subjected to cross knurling and then degreased. This core tube is placed in a mold equipped with a sprue and a disk gate, the resin materials of Examples 1 and 2 and Comparative Example 1 are injection-molded, and an annular resin portion is integrated with the outer periphery of the core tube. A worm wheel blank material having an outer diameter of 60 mm and a width of 13 mm was obtained. The outer peripheral surface of the resin part of this worm wheel blank was cut to form gear teeth, and a worm wheel specimen was obtained.

  The worm wheel specimen obtained in this manner was incorporated into an actual electric power steering apparatus of an automobile, and was steered 100,000 times while controlling the atmospheric temperature at 80 ° C. And durability was evaluated by the damage and abrasion amount which arose to the gear tooth of the resin part of the worm wheel test body after a test. As for durability, a case where no damage such as a root crack was found in the gear teeth and the wear amount was a predetermined amount or less was determined to be acceptable. The results are shown in Table 1.

  The worm wheel specimen manufactured using the resin material of Examples 1 and 2 showed no damage such as tooth root cracks in the gear teeth even after 100,000 times of steering, and the amount of wear was small, causing problems. It was judged to be acceptable because it worked. On the other hand, the worm wheel specimen manufactured using the resin material of Comparative Example 1 was rejected because a large amount of wear was observed on the gear teeth after steering 100,000 times.

[Evaluation of dimensional stability of worm wheel]
The dimensional stability was evaluated using the same worm wheel specimen used for the durability evaluation. The worm wheel specimen was left in an environment at a temperature of 80 ° C. and a humidity of 90% RH, and the amount of change in the outer diameter was measured after 500 hours. The results are shown in Table 1. The case where the amount of change in the outer diameter after being allowed to stand in the environment for 500 hours was 40 μm or less was regarded as acceptable.
As is clear from the results in Table 1, the worm wheel test specimen produced using the resin material of Example 1 was used in spite of using a solid material in which no reinforcing material was blended as the resin material. Due to the low water absorption of the aromatic polyamide 11, it has the same dimensional stability as the polyamide 66 containing 30% by mass of glass fiber.

11 Steering shaft 13 Electric motor 30 Gear reducer (Reduction gear for electric power steering device)
31 Worm wheel (driven gear)
32 Worm (drive gear)
41 Core tube 42 Resin part 43 Gear teeth

Claims (2)

A drive gear that transmits the steering assist force output from the electric motor, and a driven gear that meshes with the drive gear and transmits the steering assist force to the steering shaft,
The driven gear is composed of a core tube and an annular resin portion that is integrally provided on the outer peripheral portion of the core tube and has gear teeth formed on the outer peripheral surface thereof.
The resin portion is a reduction gear for an electric power steering device that is made of a resin material containing a semi-aromatic polyamide 11.   An electric motor that outputs a steering assist force that assists the steering force in accordance with a steering force input to the steering shaft; and a gear reducer that decelerates the steering assist force and transmits the steering assist force to the steering shaft. An electric power steering apparatus comprising the reduction gear for an electric power steering apparatus according to claim 1 as the gear reducer.

Images