JP2014111435A - Electric power steering device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a worm wheel that comprises a resin part having strength and high temperature durability, capable of being applied even to a rack assist-type electric power steering device.SOLUTION: In a reduction gear mechanism 30 of an electric power steering device, a resin part 43, which contains a thermoplastic resin and a fibrous filler and which is made of a resin composition having a loss tangent at 60°C and 100 Hz set to be in the range of 0.01-0.05, is integrally provided on the outer periphery of a metal cored bar 42, and a worm wheel 31 having a gear tooth 44 formed on the outer peripheral surface of the resin part 43 is used.

Description

  The present invention relates to an electric power steering device that transmits auxiliary output from an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism, and more specifically, the reduction gear mechanism has gear teeth on the outer periphery of a metal cored bar. The present invention relates to an electric power steering apparatus that includes a worm wheel having a structure in which a resin portion is integrally provided and is grease lubricated. The present invention also relates to a method for manufacturing the electric power steering device.

  As a reduction mechanism used in an electric power steering device incorporated in an automobile, it is connected to a rotating shaft of an electric motor (not shown) as shown in FIG. In general, a reduction gear mechanism 30 including a worm 32 and a worm wheel 31 meshing with the worm 32 is used.

  In such a reduction gear mechanism 30, if both the worm wheel 31 and the worm 32 are made of metal, unpleasant sounds such as rattling noise and vibration noise are generated during steering of the steering wheel. Noise countermeasures are taken using a worm wheel 31 made of a resin composition and integrated with a resin portion 43 having gear teeth 44 on the outer peripheral surface (see, for example, Patent Document 1). Further, by using the worm wheel 31 including such a resin portion 43, it is possible to reduce the weight of the electric power steering device.

  Examples of the resin composition that forms the resin portion 43 include polyamide 6, polyamide 66, polyamide 46, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), and other base resins, and fibers such as glass fibers and carbon fibers. A material containing a reinforcing material is widely used. Further, MC (monomer cast) nylon (registered trademark), polyamide 6, polyamide 66 and the like which do not contain a reinforcing material are also used. Among them, MC nylon containing no reinforcing material, polyamide 6, glass 66 containing polyamide, polyamide 46, etc. are mainly used.

JP 2007-168482 A

  The electric power steering device includes a column assist type mounted in the vehicle compartment and a rack assist type mounted in the engine room, and the above resin composition is suitably used for the column assist type electric power steering device. ing. However, since the rack assist type electric power steering apparatus has a higher temperature (over 80 ° C.) than the column assist type electric power steering apparatus, high temperature durability is required. Moreover, since high output is also requested | required, intensity | strength is also requested | required.

  However, it is extremely difficult to satisfy all the requirements of the rack assist type electric power steering device in a well-balanced manner with the above-described resin compositions that have been mainstream. Specifically, durability at high temperatures exceeding 80 ° C (tooth surface wear durability, root bending fatigue strength) is insufficient, deterioration of steering feeling due to abnormal wear progress, Due to breakage, it is assumed that the entire apparatus does not function in the worst case.

  Further, in the resin composition containing the reinforcing fiber material, the glass fiber improves the strength, rigidity, and dimensional stability, but has a strong attack on the worm 32, and there is room for improvement in terms of quietness. Furthermore, the abrasive wear of the gear teeth 44 is promoted by the glass fiber that has fallen from the gear teeth 44 of the resin portion 43 due to the progress of normal wear accompanying normal use being interposed between the worm wheel 31 and the worm 32. As a result, it is also assumed that the steering feeling of the steering is significantly impaired.

  The present invention has been made in view of such a situation, and is applied to a rack assist type electric power steering apparatus in an electric power steering apparatus including a reduction gear mechanism including a worm wheel having gear teeth formed on a resin portion. An object is to provide a worm wheel having possible strength and high temperature durability.

In order to solve the above-described problems, the present invention provides an electric power steering apparatus and a manufacturing method thereof as described below.
(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 worm wheel of the speed reduction gear mechanism is made of a resin part made of a resin composition containing a thermoplastic resin and a fibrous filler and having a loss tangent of 0.01 to 0.05 at 60 ° C. and 100 Hz. An electric power steering apparatus, wherein the electric power steering apparatus is provided integrally on an outer periphery of a core tube and gear teeth are formed on an outer peripheral surface of the resin portion.
(2) The thermoplastic resin is at least one selected from polyamide resins, polyphenylene sulfide resins and polyether ether ketone resins, and the fibrous filler is surface-treated with a sizing agent, aramid fiber, polyarylate The electric power steering device according to (1) above, wherein the electric power steering device is at least one selected from a fiber and a polyparaphenylene benzbisoxal resin.
(3) The electric power steering device according to (1) or (2), wherein the thermoplastic resin contains a nanofiller.
(4) In the reduction gear mechanism, the worm wheel and the worm are lubricated with a grease composition containing a base compound mainly composed of poly α-olefin oil and a urea compound as a thickener. The electric power steering device according to any one of (1) to (3) above.
(6) In a method for manufacturing an electric power steering apparatus that transmits auxiliary output from an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism,
In manufacturing the worm wheel of the reduction gear mechanism,
A step of preparing a molding material of the resin composition according to any one of the above (1) to (3);
A step of injection-molding the molding material into a molding die containing a metal core tube, and integrally providing a resin portion on the outer periphery of the metal core tube;
And a step of cutting the outer peripheral surface of the resin portion to form gear teeth.
(7) In the manufacturing method of 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,
In manufacturing the worm wheel of the reduction gear mechanism,
A step of preparing a molding material of the resin composition according to any one of the above (1) to (3);
And a step of injection compression molding the molding material using a molding die in which a metal core tube is housed and gear teeth are formed.

  According to the present invention, a resin composition having a loss tangent of 0.01 to 0.05 at 100 Hz is used for the resin portion of the worm wheel of the reduction gear mechanism, so that the invention can also be applied to a rack assist type electric power steering device. High temperature durability and strength. Further, it can be naturally applied to a column assist type electric power steering apparatus.

It is a perspective view which shows the reduction gear mechanism of an electric power steering apparatus. It is a schematic diagram showing an example of a column assist type electric power steering device. It is the schematic which shows an example of a rack assist type electric power steering device.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

  FIG. 2 is a schematic view showing an example of a column assist type electric power steering device. In the illustrated column assist type electric power steering device 10, the steering wheel shaft 11 is composed of an upper steering wheel shaft 11a and a lower steering wheel shaft 11b. The rudder wheel shaft 11 is supported in a rudder wheel shaft housing 12 so as to be rotatable about its axis, and the rudder wheel shaft housing 12 is fixed at a predetermined position in the vehicle interior with the lower portion inclined forward. Has been. 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), and the snake steering torque transmitted from the rudder wheel to the lower rudder wheel shaft 11b through the upper rudder wheel shaft 11a is detected by the torsion bar. Then, the output of the motor 13 is controlled based on the detected snake steering torque. A reduction gear mechanism 30 is connected to the motor 13, and the rotation of the motor 13 is transmitted to the lower steering wheel shaft 11b through 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. 3 is a schematic view showing an example of a rack assist type electric power steering apparatus. The illustrated rack assist type electric power steering apparatus 100 includes a rack shaft 101, a first pinion 105 coupled to a steering shaft (not shown), a second pinion 106 on the motor 110 side, and a reduction gear mechanism 130. And. The reduction gear mechanism 130 includes 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.

  In the present invention, in the reduction gear mechanisms 30 and 130 described above, as shown in FIG. 1, a resin made of a resin composition described later on the outer periphery of a metal core 42 and gear teeth 44 formed on the outer peripheral end surface thereof. The worm wheel 31 in which the portion 43 is integrated is used. Moreover, there is no restriction | limiting in the worm | warm 32, It can be made from metal like the past.

  Currently, the resin compositions that are practically used for the worm wheel of the column assist type electric power steering apparatus are glass fiber compounded material and non-glass fiber compounded material. In addition to detailed analysis of the gear durability test finished products under conditions (high temperature: 80 ° C, high output: 1.5 times the column assist ratio) that are assumed to be applied to worm wheels, and with worm wheels made of other developed prototype materials As a result of intensive studies such as repeated tests, it was found that if the loss tangent of the material is below a certain level, it can also be applied to the worm wheel of a rack assist type electric power steering device.

  The loss tangent is an index representing viscoelastic properties, but a large loss tangent value means that internal friction due to molecular motion is large. And the worm wheel provided with the resin part made of a material having a large internal friction has a remarkable internal heat generation due to the use, and the physical property deterioration due to it is remarkable, and it is considered that the functional loss is caused earlier than expected. On the other hand, if the loss tangent is below a certain level, the effect of heat storage due to internal friction is not fatal, and it can be assumed that satisfactory performance can be maintained as the worm wheel of the rack assist type electric power steering device.

  Based on the above, it has been found that the upper limit value of the loss tangent at 60 ° C. and 100 Hz may be 0.05. Furthermore, the present inventors have found that a method of combining with a fibrous filler is extremely important as a means for reducing loss tangent. Further, the fibrous filler needs to be a material that does not damage the metal worm.

  However, since a material with a small loss tangent is generally inferior in vibration absorption performance (vibration suppression, quietness), a certain level or more is required, and if the lower limit of loss tangent at 60 ° C. and 100 Hz is 0.01 It has been found that sufficient quietness as an electric power steering device is secured.

  That is, in the present invention, the resin portion 43 of the worm wheel 31 of the reduction gear mechanism 30 or 130 is formed of a resin composition having a loss tangent of 0.01 to 0.05 at 60 ° C. and 100 Hz. The resin composition is mainly composed of a thermoplastic resin and a fibrous filler. The thermoplastic resin and the fibrous filler are not limited as long as the above loss tangent is satisfied, but the following are preferable in view of heat resistance and strength.

  Examples of the thermoplastic resin include polyamide resins such as polyamide 6, polyamide 66, polyamide 46, polyamide 6T / 6-6, polyamide 6T / 6I, polyamide 6T / 6I / 6-6, polyamide 6T / M-5T, and polyamide 9T. Polyphenylene sulfide resin and polyether ether ketone resin are preferable. These thermoplastic resins may be used alone or in combination of two or more.

  As the fibrous filler, organic fibers such as aramid fiber, polyarylate fiber, polyparaphenylene benzbisoxazal resin and the like surface-treated with a sizing agent are preferable. These organic fibers may be used alone or in combination of two or more. Further, these organic fibers do not damage the counterpart material (worm) like glass fibers.

  As the sizing agent, urethane resin, epoxy resin, acrylic resin, bismaleimide resin or the like is appropriately selected in consideration of the affinity with the thermoplastic resin.

  In order to make the loss tangent 0.01-0.05, the content of the organic fiber needs to be 10-40% by mass of the total amount of the resin composition.

  Moreover, it is preferable that a resin composition contains a nano filler with said fibrous filler. Nanofiller is a nano-sized fine filler, and by uniformly dispersing in the resin, the strength and elastic modulus, thermal deformation temperature, dimensional stability, and mechanical properties of the resulting worm wheel are improved. Further improvement can be achieved. By adding the nano filler, the dispersion state of the fibrous filler in the resin composition is improved as compared with the case where the nano filler is not added. The improvement of dispersibility can be evaluated from the appearance of the obtained worm wheel, for example, and the surface property is better when the fibrous filler and nanofiller are used in combination than when only the fibrous filler is added. As a result, the aggression (damage, etc.) against the worm as the counterpart material is reduced. Although the reason why the dispersion state of the fibrous filler is improved is not clear, it is considered that the nanofiller improves the affinity between the fibrous filler and the resin.

  As the nanofiller, 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 suitable. A nanomaterial called POSS (polyhedral oligosilsesquioxane) is also suitable. This POSS is an organic-inorganic hybrid material, and its molecular structure has a cubic skeleton composed of Si and O at the center, as represented by the following general formula, and is represented by R1 to R8 in Si at the apex. This is a cage structure in which organic substituents are bonded. The three-dimensional skeleton in the center is a rigid inorganic skeleton, and an organic substituent at each vertex makes a good dispersion state in the resin. As a result, mechanical properties such as heat resistance and dimensional stability are improved.

  R1 to R8 in the formula are an amine residue, an ester residue, an epoxy residue, an acrylic residue, an olefin residue, a halogen atom, a thiol residue, and the like. Also good.

  However, nanofillers tend to cause secondary aggregation due to their relatively large surface energy, and when they are kneaded with resin using general equipment that does not have very high kneading efficiency, the effects of addition (strength, heat resistance, dimensional stability, etc.) In general, it is difficult to achieve a morphology in which the improvement effect of (a) is optimally exhibited, that is, a uniformly dispersed form of nanofillers. In order to uniformly disperse the nano filler, a high shear type kneader, for example, a fully meshed co-rotating four-axis (or eight-axis) kneading extruder manufactured by Technobell Co., Ltd., or Niigata Machine Techno equipped with a feedback screw This can be realized by using a high shear molding machine manufactured by the company.

  Moreover, content of a nano filler is 0.1-30 mass% with respect to the resin composition whole quantity, Preferably it is 0.5-15 mass%. If the content of the nanofiller is less than 0.1% by mass, the above effect cannot be obtained.

  Furthermore, if necessary, non-fibrous fillers such as zeolite, kaolin, true, talc, alumina, and silica can be added to the resin composition. In addition, solid lubricants such as pigments, dyes, antistatic agents, fluororesins, iodide heat stabilizers to prevent deterioration due to heat during molding and use, phenolic or amine antioxidants, etc. These may be added alone or in combination of two or more.

  As a method of manufacturing the worm wheel 31 using the above resin composition, for example, the following steps can be followed. First, shot blasting, knurling, spline processing, or the like is performed on the outer peripheral surface of the metal cored bar 42. Among them, knurl processing and spline processing are preferable, and the depth of the V-shaped groove in the knurl processing is preferably 0.2 to 0.8 mm, more preferably 0.3 to 0.7 mm, while press forming in spline processing. Involute spline machining that can be machined at a low cost is most suitable. Next, after degreasing with a solvent, the cored bar 42 is placed in a mold equipped with a sprue and a disk gate, and the resin composition 43 is filled with an injection molding machine to mold the resin part 43. Therefore, it is preferable that the resin composition has fluidity that allows injection molding. Thereafter, gear teeth 44 are formed on the outer periphery of the resin portion 43 by cutting.

  However, when an aramid fiber is used as the fibrous filler, the aramid fiber has a high cutting resistance in the cutting process. Therefore, the cutting used when manufacturing a worm wheel made of a resin composition containing the current glass fiber. It is assumed that the tool life is shortened in the tool. As a result, the replacement frequency of the cutting tool increases and the manufacturing cost increases. Moreover, in the cutting process, the chip of the resin composition is discharged as waste, which is not preferable from an environmental point of view, and the material cost of the chip is wasted.

  Therefore, it is preferable to adopt a manufacturing method that does not cause a cutting loss. For example, it is preferable to manufacture a worm wheel by an injection compression molding method. Injection compression molding is a molding method in which compression is applied to the filled molding material by moving the movable mold to the fixed mold side after filling the molding material into the cavity. For example, the following technique is known. Thus, the present invention can be similarly performed.

  That is, using the mold clamping mechanism of the molding machine, the movable side mold is kept waiting at the position where the cavity is in a shape that matches the obtained worm wheel, and the melt of the resin composition is placed there. After (molding material) is injection-molded and filled, the movable mold is moved to a position where the cavity becomes the same shape as the obtained worm wheel, and compression is applied to solidify the compressed state.

  In addition, a separate mechanism dedicated to compression is prepared, the fixed mold (frame) and the movable mold are completely clamped, the molding material is injection-molded, and the molded product is solidified before it is solidified. It may be transferred to another mechanism for compression and solidified in the compressed state.

  Furthermore, a cavity is formed at a proper position of the cavity having the same shape as the obtained worm wheel, and a molding die provided with a movable pin sliding in the cavity is used. The movable pin is pulled and the tip of the movable pin is inserted into the cavity. After the molding material is injected and the cavity and the void are filled with the void formed between them, the mold pin is pushed up so that the tip of the movable pin coincides with the wall surface of the cavity before the molding material solidifies. May be compressed and solidified in the compressed state.

  The injection compression molding method as described above is not limited to the case where an aramid fiber is used as the fibrous filler, but can also be applied to other organic fibers.

  In the present invention, the reduction gear mechanisms 30 and 130 may be cylindrical worm gears, helical gears, spur gears, bevel gears, hypoid gears, etc. in addition to the configuration shown in FIG.

  In the reduction gear mechanisms 30 and 130, the lubrication between the worm wheel 31 and the worm 32 is preferably grease lubrication. The base oil of the grease composition to be used preferably contains a poly-α-olefin oil as a main component. That is, the base oil may be a poly-α-olefin oil alone, and in order to improve lubricity, a diester oil, an aromatic ester oil or the like may be mixed in an amount of 30% by mass or less of the total amount of the base oil.

  The thickener of the grease composition may be a metal compound such as a urea compound, a lithium soap, a lithium complex soap, a barium soap, or a barium complex soap, which is a reaction product of an amine and an isocyanate, but a urea compound is preferred. .

  In addition, the grease composition may contain an amine or phenolic antioxidant, a rust inhibitor such as calcium sulfonate, an extreme pressure additive such as molybdenum dithiocarbamate, a montanic ester wax or a montanic ester, if necessary. Oily improvers such as partially saponified wax, polyethylene wax and oleic acid may be added.

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

(Examples 1-4, Comparative Examples 1-3)
As shown in Table 1, as a resin composition for forming the resin part of the worm wheel, polyamide 6 (“UBE nylon 6” manufactured by Ube Industries Co., Ltd.) is used in Example 1, and polyamide 66 (Ube) is used in Example 2. "UBE Nylon 66" manufactured by Kosan Co., Ltd.), and in Example 3, polyamide 9T ("Genesta" manufactured by Kuraray Co., Ltd.) and para-aramid fibers ("Clanola" manufactured by Teijin Ltd.) were blended. Using. In Example 4, para-aramid fibers and nanofillers (POSS; manufactured by Toyotsu Chemiplus Co., Ltd.) were used in combination as fillers.

  In Comparative Example 1, 30% glass fiber reinforced polyamide resin (“Amilan CM3006GS-30” manufactured by Toray Industries, Inc.), and in Comparative Example 2, MC nylon (non-fiber reinforced: “MC901” manufactured by Quadrant Polypenco Japan, Inc.), In Comparative Example 3, polyphenylene sulfide (non-fiber reinforced: “PPS Z-200-E5” manufactured by DIC Corporation) was used.

  Then, an S45C cored bar having an outer diameter of 45 mm and a width of 13 mm, which has been subjected to cross knurling, is placed in a mold equipped with a sprue and a disk gate, and each of the above resin compositions is injection-molded to obtain an outer diameter. A worm wheel blank material having a width of 60 mm and a width of 13 mm was formed, and then the outer periphery of the resin portion was cut to form gear teeth to produce a worm wheel as shown in FIG. In addition, a metal worm was prepared and incorporated into a reduction gear mechanism of an actual electric power steering device of an automobile together with the manufactured worm wheel, and durability was evaluated.

  Durability was determined to be acceptable if the atmospheric temperature was maintained at 80 ° C. and no damage (tooth cracks, etc.) was observed even after 100,000 steerings, and the wear was less than a predetermined amount. . The results are also shown in Table 1.

  As shown in Table 1, the worm wheel of the embodiment according to the present invention is not damaged after 100,000 times of steering, wears little, operates without problems, and is of course used for a column assist type electric power steering apparatus. In other words, it can be said that the present invention can also be used for a rack assist type electric power steering apparatus. In particular, in Example 4 in which the nanofiller is used in combination, excessive wear is not confirmed even after steering 200,000 times, and durability is further improved.

  On the other hand, the worm wheel of Comparative Example 1 using glass fiber reinforced polyamide 66 resin was severely worn and used MC nylon or polyethylene sulfide resin which is a non-fiber reinforced material and whose loss tangent is outside the scope of the present invention. In the worm wheels of Comparative Example 2 and Comparative Example 3, tooth root cracks were observed, which were unacceptable.

30, 130 Reduction gear mechanism 31 Worm wheel 32 Worm 42 Core metal 43 Resin part 44 Gear teeth

Claims (7)

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 worm wheel of the speed reduction gear mechanism is made of a resin part made of a resin composition containing a thermoplastic resin and a fibrous filler and having a loss tangent of 0.01 to 0.05 at 60 ° C. and 100 Hz. An electric power steering apparatus, wherein the electric power steering apparatus is provided integrally on an outer periphery of a core tube and gear teeth are formed on an outer peripheral surface of the resin portion.   The thermoplastic resin is at least one selected from polyamide resins, polyphenylene sulfide resins and polyetheretherketone resins, and the fibrous filler is surface-treated with a sizing agent, aramid fibers, polyarylate fibers and poly 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is at least one selected from paraphenylene benzbisoxal resin.   The electric power steering apparatus according to claim 1 or 2, wherein the thermoplastic resin contains a nanofiller.   In the reduction gear mechanism, the worm wheel and the worm are lubricated with a grease composition containing a base oil mainly composed of poly α-olefin oil and a urea compound as a thickener. The electric power steering device according to any one of 1 to 3.   5. The electric power steering apparatus according to claim 1, wherein the worm wheel and the worm are configured by a cylindrical worm gear, a helical gear, a spur gear, a bevel gear, or a hypoid gear. In a method for manufacturing an electric power steering apparatus that transmits auxiliary output by an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism,
In manufacturing the worm wheel of the reduction gear mechanism,
Preparing a molding material of the resin composition according to any one of claims 1 to 3,
A step of injection-molding the molding material into a molding die containing a metal core tube, and integrally providing a resin portion on the outer periphery of the metal core tube;
And a step of cutting the outer peripheral surface of the resin portion to form gear teeth. In a method for manufacturing an electric power steering apparatus that transmits auxiliary output by an electric motor to a steering mechanism of a vehicle via a reduction gear mechanism,
In manufacturing the worm wheel of the reduction gear mechanism,
Preparing a molding material of the resin composition according to any one of claims 1 to 3,
And a step of injection compression molding the molding material using a molding die in which a metal core tube is housed and gear teeth are formed.

Images