JP2015150984A - electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device having high reliability and excellent in quietness, even when it is applied for a rack assist type which is used under a more severe condition, in addition to a column assist type.SOLUTION: The electric power steering device comprises a deceleration gear having a worm wheel, the worm wheel being formed by providing a resin part formed of a resin composition obtained by blending 10-40 mass% of an organic fiber with respect to the whole amount of the resin composition, and 2 mass% or less of a crystal nucleus agent or crystallization accelerator to a polyamide resin, to an outer periphery of a metal core pipe in an integrated state, and forming gear teeth on an outer peripheral surface of the resin part.

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, and in particular, a metal core bar is made of a resin composition and gear teeth are formed on an outer peripheral surface thereof. The present invention relates to an electric power steering device that includes a driven gear formed integrally with a formed resin portion and is lubricated with grease.

  As a reduction mechanism used in an electric power steering apparatus incorporated in an automobile, a large reduction ratio can be obtained with one set, and the like, for example, is connected to a rotating shaft of an electric motor (not shown) as shown in FIG. Generally, a reduction gear 50 including a worm 52 and a worm wheel 51 that meshes with the worm 52 is used.

  In such a reduction gear 50, if both the worm wheel 51 and the worm 52 are made of metal, there is a problem that an unpleasant sound such as a rattling sound or a vibration sound is generated when the handle is operated. Therefore, a worm wheel 51 is used in which a resin core 63 made of resin and formed with gear teeth 64 on the outer peripheral surface is integrated with the outer periphery of a metal core tube 62, and a metal worm wheel is used. Measures against noise (in the sense that it is adopted).

  In the resin part 63, as shown in Patent Document 1, for example, a base resin such as polyamide 6, polyamide 66, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), glass fiber, carbon fiber, or the like is used. MC nylon (registered trademark of Quadrant Polypenco Japan Co., Ltd.), polyamide 6, polyamide 66, etc. not containing glass fiber or carbon fiber are used in addition to a material containing a reinforcing material. Among these, MC nylon containing no reinforcing material, polyamide 6 containing glass fiber, polyamide 66, polyamide 46, and the like are mainly used from the balance between performance and cost.

  However, when the resin composition reinforced with glass fiber or carbon fiber is applied as a worm wheel material for the reduction gear 50, the strength, rigidity, and dimensional stability are remarkably improved. The aggressiveness to the worm 52 is strong, and it seems that there is still room for improvement in the quietness. Furthermore, the glass fiber or carbon fiber that has fallen from the resin gear teeth due to the progress of normal wear accompanying normal use is interposed between the gear teeth 64 and the worm 52, thereby promoting the abrasive wear of the gear tooth surfaces. As a result, a change in steering feeling of the steering is assumed. In addition, when injection molding a resin reinforced with glass fiber or carbon fiber, the screw of the injection molding machine is also damaged, and the life of the screw tends to be shortened.

  For example, in Patent Documents 2 to 4, in order to improve the problems related to the damage characteristics of the mating member and the screw as described above, in the patent documents 2 to 4, the damage performance to the mating material is reduced by modifying the polymer, or the aramid fiber is added to the thermosetting resin. The sheet is filled. However, there are concerns that the polymer modification takes time for the polymerization, or the crystallization is slowed and the molding cycle becomes long. Further, when reinforced with aramid fibers, the improvement of the crystallization rate cannot be expected unlike inorganic fibers, and the molding cycle becomes long.

  In addition, the electric power steering device includes a column assist type mounted in a vehicle compartment and a rack assist type mounted in an engine room, and the current mainstream material is particularly a column assist type electric power steering device. In many cases. However, in the rack assist type installed in the engine room, the requirements for its performance include compatibility with a higher temperature environment (up to 120 ° C) and higher output compared to the column assist type. In addition, as with the column assist type, there is a strong demand for noise reduction.

Japanese Patent Publication No. 6-60674 JP-A-5-306371 JP-A-10-141477 JP 2002-39329 A

  The present invention has been made by paying attention to such a situation. In particular, the rack-assist type electric power is excellent in quietness and wear resistance, achieves improved cycle time, and has excellent dimensional stability. The present invention provides a resin composition for a worm wheel that can also be applied to steering, and as a matter of course, the column assist type, as well as the reduction gear for electric power steering having high reliability even when applied to a rack assist type, and An object is to provide an electric power steering apparatus using the same.

  As described above, for the column assist type, a polyamide resin reinforced with glass fiber or carbon fiber is used as the resin composition for forming the resin portion 63. However, such fiber reinforced resin has a high aggressiveness to the worm 52 of glass fiber or carbon fiber, and there is a potential demand for improvement in terms of quietness. Further, the glass fiber or carbon fiber dropped from the gear teeth 64 due to the progress of normal wear accompanying normal use enters between the gear teeth 64 and the worm 52, and the abrasive wear of the gear tooth surfaces is promoted by interposition. As a result, changes in the steering feeling of the steering were assumed, and there seemed to be room for improvement in this respect as well.

  On the other hand, in addition to the fiber reinforced resin, MC nylon not containing glass fiber or carbon fiber is widely used as a worm wheel material for the column assist type. According to the worm wheel 51 made of MC nylon, of course, it seems possible to overcome the problem of quietness, which has been considered a concern of the fiber reinforced resin worm wheel, but is expected to be used in more severe environments. Assuming application to a rack-assisted type, MC nylon has insufficient heat resistance and durability, and experiments have shown that it does not reach the product level required for rack-assisted electric power steering . In addition, since MC nylon does not contain any reinforcing fiber that contributes to dimensional stability, MC nylon has been regarded as having room for further improvement in terms of dimensional stability due to water absorption. Furthermore, MC nylon has a limited production method, that is, it is difficult to perform high cycle injection molding, and it is extremely difficult to reduce costs from the production side.

  Therefore, the present inventors have established a condition (high temperature: high temperature: a worm wheel made of a resin material (fiber reinforced resin material, fiber non-reinforced resin material) that is currently used in a column assist method. In addition to detailed analysis of the gear durability test finished product under 80 ° C condition, high output: 1.5 times the column assist ratio), repeated earnest research such as repeated tests with worm wheels made of other developed prototype materials As a result, if the thermoplastic resin composition reinforced with aramid fibers that can suppress the wear of the mating metal and the screw of the injection molding machine is applied to the resin tooth as the material for the worm wheel, the above problem can be overcome. I found. However, when an aramid fiber reinforcing material is injection molded, it has been found that the molding cycle is longer than that of a glass fiber reinforcing material, and a crystal nucleating agent or crystallization accelerator can be further added. It was found that it was effective, and the present invention was completed.

That is, in order to solve the above problems, the present invention provides the following electric power steering device.
(1) In an electric power steering device that transmits auxiliary output from an electric motor to a vehicle steering mechanism via a reduction gear mechanism,
The speed reduction gear mechanism is a resin comprising a resin composition in which organic fiber is blended with polyamide resin in an amount of 10 to 40% by mass of the total resin composition, and a crystal nucleating agent or crystallization accelerator is blended in an amount of 2% by mass or less of the total resin composition. An electric power steering apparatus comprising: a reduction gear having a worm wheel that is integrally provided on an outer periphery of a metal core tube and gear teeth are formed on the outer peripheral surface of the resin portion.
(2) The above (1), wherein the crystal nucleating agent or crystallization accelerator contained in the resin composition is at least one selected from inorganic minerals, metal oxides, phosphorus compounds and organic substances. Electric power steering device.
(3) The organic fiber contained in the resin composition is subjected to surface treatment with at least one sizing agent selected from polyurethane resin, polyester resin, polyether resin, vinyl ester resin, epoxy resin, acrylic resin, and bismaleimide resin. The electric power steering device according to the above (1) or (2), wherein

  According to the present invention, by forming the resin part constituting the worm wheel with a polyamide resin composition containing an appropriate amount of a crystal nucleating agent or a crystallization accelerator together with organic fibers, the column assist type is naturally more It becomes possible to efficiently produce an electric power steering device that has high reliability applicable to a rack assist type used in a harsh environment and is excellent in quietness.

It is a schematic structure figure showing an example of a column assist type electric power steering device. It is a schematic block diagram which shows an example of a rack assist type electric power steering device. It is a perspective view which shows an example of the reduction gear of this invention. It is a graph which shows the relationship between a talc compounding quantity and gate seal time. It is a perspective view which shows the conventional reduction gear.

  Hereinafter, an embodiment of the present invention will be described in detail.

  The present invention can be applied to both a column assist type electric power steering device and a rack assist type electric power steering device.

  FIG. 1 is a schematic view showing an example of a column assist type electric power steering apparatus 10. A steering wheel shaft 11 is composed of an upper steering wheel shaft 11 a and a lower steering wheel shaft 11 b. The rudder wheel shaft housing 12 is fixed to a predetermined position in the vehicle interior so as to be inclined with its lower portion directed forward. A steering wheel (not shown) is fixed to the upper end of the upper steering wheel shaft 11a. Further, the upper steering wheel shaft 11a and the lower steering wheel shaft 11b are coupled by a torsion bar (not shown), and the steering torque transmitted from the steering wheel to the lower steering wheel shaft 11b via the upper steering wheel shaft 11a is detected by the torsion bar. The output of the motor 13 is controlled based on the detected steering torque. A reduction gear 30 is connected to the motor 13, and the rotation of the motor 13 is transmitted to the lower steering wheel shaft 11b via the worm and the worm wheel.

  The rack-and-pinion motion conversion mechanism 20 is disposed substantially horizontally in the engine room at the front portion of the vehicle with the longitudinal direction being the left-right direction of the vehicle, and the rack shaft 21 is movable in the axial direction. A pinion shaft 22 including a pinion provided with a tooth portion that is supported obliquely with respect to the core and meshes with a tooth portion of the rack shaft 21, and a rack shaft 21 and a cylindrical rack shaft case 23 that supports the pinion shaft 22. Composed.

  FIG. 2 shows an example of the rack assist type electric power steering apparatus 100. The rack shaft 101, the first pinion 105 connected to the steering shaft (not shown), and the second pinion 106 on the motor 110 side are illustrated. And a reduction gear 30. The reduction gear 30 is composed of a worm and a worm wheel connected to a shaft of the motor 110, and a second pinion 106 is fixed to the worm wheel. The second pinion 106 is engaged with the rack shaft 101.

  The reduction gear 30 is a worm in which a resin portion 43 made of a resin composition and having gear teeth 44 formed on the outer peripheral end face thereof is integrated with the outer periphery of a metal core tube 42 as shown in FIG. A wheel 31 and a worm 32 are provided. The worm 32 may be made of metal.

  The base material of the resin composition forming the resin portion 43 of the worm wheel 31 is a polyamide resin. Specifically, in addition to the polyamide 6, the polyamide 66, and the polyamide 46, a polyamide 6T / 6-6 that is a semi-aromatic polyamide is used. Polyamide 6T / 6I, polyamide 6T / 6I / 6-6, polyamide 6T / M-5T, polyamide 9T, and the like can be suitably used.

  An organic fiber is blended in the resin composition as a reinforcing material. The organic fiber only needs to have a high strength without excessively damaging the metal worm 32. Specific examples include an aramid fiber, a polyarylate fiber, and a polyparaphenylene benzbisoxazal fiber. .

  The organic fiber is selected from a polyurethane resin, a polyester resin, a polyether resin, a vinyl ester resin, an epoxy resin, an acrylic resin, and a bismaleimide resin in order to enhance the adhesion with the polyamide resin and improve the reinforcing effect. It is preferable to use a material that has been surface-treated with at least one sizing agent.

  Moreover, the filling amount of an organic fiber is mix | blended within the range of 10-40 mass% of the resin composition whole quantity as a result of inventors having repeated examination. As the reason, when it is less than 10% by mass, a sufficient reinforcing effect is not exhibited, which is not preferable. Moreover, when it mixes exceeding 40 mass%, it is because the fluidity | liquidity of a resin composition falls and a moldability becomes low and cannot respond to injection molding. A preferable filling amount is 10 to 25% by mass.

  In order to shorten the molding cycle, a crystal nucleating agent or a crystallization accelerator is added to the resin composition. Specifically, inorganic minerals such as talc, kaolin, and clay, metal oxides, phosphorus compounds, and organic substances such as high-melting polyamides are used alone or in combination. The addition amount of these crystal nucleating agents or crystallization accelerators is 2% by mass or less based on the total amount of the resin composition. The reason for this is that when it exceeds 2% by mass, not only a further effect on crystallization can be obtained, but also a decrease in physical properties is a concern. Preferably 0.1-1 mass% is added.

  Further, a nano-size filler may be added to the resin composition to further improve durability reliability. Specifically, smectites such as montmorillonite, hectorite, and saponite having a layered crystal structure in which crystals having a thickness of about 1 nm are stacked are particularly suitable. By uniformly dispersing the smectite layered crystal in the resin, it is possible to improve mechanical properties such as strength, elastic modulus, heat distortion temperature, and dimensional stability of the resin composition.

  The nanofiller may be a nanomaterial called POSS (polyhydrate oligosesquioxane) other than the layered crystal of smectite. Here, POSS is one of organic-inorganic hybrid materials, and its molecular structure is a cage structure having a cubic skeleton composed of Si and O at the center and an organic substituent bonded to the apex thereof.

  In addition, the addition amount of a nanosize filler is 0.1-30 mass% with respect to the resin composition whole quantity, Preferably it is 0.5-15 mass%. When the addition amount is less than 0.1% by mass, the addition amount of the nano-size filler as an active ingredient is too small, and a sufficient effect cannot be obtained, which is not preferable. In addition, when the nano-size filler exceeds 30% by mass, the nano-size filler aggregates in the resin, making it difficult to achieve uniform dispersion, and the effect of increasing the nano-size filler is manifested. It is not preferable.

  Furthermore, as additives, in order to prevent deterioration due to heat during molding and use, iodide-based heat stabilizers and phenol-based or amine-based antioxidants are added either alone or in combination. May be.

  Further, grease is used for the reduction gear 30 in order to keep the lubrication state between the tooth portion of the resin worm wheel and the tooth portion of the metal worm good.

  The grease used in the present invention is mainly composed of a thickener and a base oil, the base oil is based on a poly α-olefin oil, and the thickener is a urea compound composed of an amine and an isocyanate. , Li soap, Li complex soap, Ba soap, Ba complex soap and the like. The base oil may be a mixture of diester oil or aromatic ester oil in order to improve the lubricity of the poly α-olefin oil. The mixing amount is 30% by mass or less based on the entire base oil.

  In addition, other additives can be added to the grease. For example, amine-based and phenol-based antioxidants, rust preventives such as Ca sulfonate, extreme pressure additives such as MoDTC, montanic acid ester wax, montanic acid ester partly saponified wax, polyethylene wax, oleic acid and other oily improvers Etc.

The grease preferably has a consistency of 200 to 300, and the kinematic viscosity of the base oil is preferably ²⁰ to 90 mm ² / s (40 ° C.) in consideration of fluidity from a low temperature to a high temperature. If the penetration level is less than 200, not only is it too hard and light steering feeling is lost, but also the transmission efficiency particularly at low temperatures is lowered to a level that cannot be overlooked, which is not preferable. On the other hand, when the consistency exceeds 300, an oil film breakage is likely to occur, and the oil film breakage is not preferable, so that it is not possible to expect a gear noise suppression effect due to grease. A preferred consistency is 265-295.

  In the present invention, spur gears, helical gears, bevel gears, hypoid gears and the like can be used as the types of the reduction gear 30 in addition to those shown in FIG. The resin part in which the gear teeth are formed is integrated.

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

[Preparation of Resin Composition for Worm Wheel of Examples and Comparative Examples]
As shown in Table 1, in Example 1, 20% by mass of para-aramid fiber (Teijin “Technola”) and 20% by mass of talc were added to polyamide 6 (“UBE nylon” series of Ube Industries, Ltd .: 1015B). 1% by mass was mixed and kneaded to obtain a resin composition.

  In Comparative Examples 1 and 2, glass fiber reinforced polyamide resin (glass fiber reinforced polyamide 6: Toray Amilan “CM1011G-30”), polyamide 6 (Ube), both of which are conventional worm wheel materials, is used. The material which mix | blended the para-aramid fiber (Teijin "Technola") with the solid material of "UBE nylon" series: 1015B) of Kosan Co., Ltd. was used.

[Preparation of worm wheel specimen and evaluation of formability]
Each of the resin compositions of the example and the comparative example is prepared by placing an S45C core tube having an outer diameter of 45 mm and a width of 13 mm that has been subjected to cross knurling and placed in a mold equipped with a sprue and a disk gate, and using an injection molding machine. The product was filled into a worm wheel blank 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.

  In addition, when producing the worm wheel blank material, the gate seal time was measured to evaluate the moldability. The results are shown in Table 1, with the gate seal time of Comparative Example 1 as a reference, “◯” when the time is equal or greater, and “X” when the time is longer. In Example 1, by adding talc, which is a crystal nucleating agent, a gate seal time equivalent to that of a material containing a glass fiber reinforcing material that could not be realized in Comparative Example 2 was realized.

  Furthermore, based on the formulation of Example 1, the resin composition was prepared by changing the amount of talc, and the gate seal time in the production of the worm wheel blank material was measured. The results are shown in FIG. 4, and it can be seen that when the blending amount of talc exceeds 2% by mass, the contribution to shortening the gate seal time is reduced.

[Evaluation of attack on worms]
For the purpose of grasping the worm wheel's aggressiveness to the worm, a plate-shaped test piece was prepared from the resin compositions of the examples and comparative examples, and a ball-on-disk test was performed. Damage status was evaluated. That is, in this test, grease was interposed between the plate-shaped test piece and the metal ball, the metal ball was rotated at an ambient temperature of 23 ° C., and the surface state of the metal ball was observed after a predetermined time.

  As a result, in Comparative Example 1 which is a glass fiber reinforcing material, damage marks due to glass fibers were clearly recognized in the metal balls after the test was completed, whereas in Example 1 and Comparative Example 2 which were aramid fiber reinforcing materials, The surface condition of the metal balls was extremely good. From this, unlike conventional products using glass fiber reinforcement, the use of aramid fibers can suppress the generation of unpleasant noise caused by glass fibers sliding while attacking the worm during steering operation. I understand that I can do it.

[Evaluation of durability]
The manufactured worm wheel specimens of Examples and Comparative Examples were incorporated in an actual electric power steering apparatus of an automobile and durability was evaluated. In the test, the atmosphere temperature was controlled at 80 ° C., steering was performed 100,000 times, and no breakage (tooth cracks, etc.) was observed, and the wear was determined to be a predetermined amount or less was determined to be acceptable.

  As a result, the worm wheel specimen of Example 1 was judged to be acceptable because it did not show any cracks even after being steered 100,000 times, and had little wear and operated without problems. On the other hand, the worm wheel specimen of Comparative Example 1 made of glass fiber reinforced polyamide 6 was unacceptable due to excessive wear.

[Evaluation of dimensional stability]
The worm wheel specimens of Examples and Comparative Examples were left in an environment of 80 ° C. and 90% RH, and the amount of change in the outer diameter of the gear after 500 hours was measured. The results are shown in Table 1, and after leaving under the above conditions, the change amount of 40 μm or less was indicated as “◯” as acceptable, and those exceeding 40 μm were indicated as “x” as unacceptable. As is apparent from the results in Table 1, by adding talc as a crystal nucleating agent, dimensional stability equivalent to that of polyamide 6 containing 30% by mass of glass fiber is realized.

30 Reduction gear 31 Worm wheel 32 Worm 42 Core tube 43 Resin part 44 Gear teeth

Claims (3)

In the electric power steering device that transmits the auxiliary output by the electric motor to the steering mechanism of the vehicle via the reduction gear mechanism,
The speed reduction gear mechanism is a resin comprising a resin composition in which organic fiber is blended with polyamide resin in an amount of 10 to 40% by mass of the total resin composition, and a crystal nucleating agent or crystallization accelerator is blended in an amount of 2% by mass or less of the total resin composition. An electric power steering apparatus comprising: a reduction gear having a worm wheel that is integrally provided on an outer periphery of a metal core tube and gear teeth are formed on the outer peripheral surface of the resin portion.   2. The electric power steering according to claim 1, wherein the crystal nucleating agent or crystallization accelerator contained in the resin composition is at least one selected from inorganic minerals, metal oxides, phosphorus compounds and organic substances. apparatus.   The organic fiber contained in the resin composition is surface-treated with at least one sizing agent selected from polyurethane resin, polyester resin, polyether resin, vinyl ester resin, epoxy resin, acrylic resin, and bismaleimide resin. The electric power steering apparatus according to claim 1 or 2, characterized by the above.

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