JP5098167B2 - Reduction gear for electric power steering device - Google Patents

Description

  The present invention relates to a reduction gear for an electric power steering apparatus for transmitting the output of an electric motor for generating a steering assist auxiliary output to a steering shaft.

  For example, in an electric power steering apparatus incorporated in an automobile, a gear speed reduction mechanism is incorporated between the electric motor and the steering shaft because an electric motor having a relatively high speed rotation and low torque is used. As a gear reduction mechanism, a mechanism using a spur gear or other gears is also known, but for reasons such as obtaining a large reduction ratio with one set, a worm 32 and a worm 32 as shown in FIG. It is common to use a worm gear speed reduction mechanism 30 (hereinafter also simply referred to as a “speed reduction gear”) composed of a meshing worm wheel 31. Here, the worm 32 is a drive gear connected to the rotating shaft of the electric motor, and the worm wheel 31 is a driven gear.

  In such a reduction gear 30, if both the worm wheel 31 and the worm 32 are made of metal, there is a problem that unpleasant sounds such as rattling noises and vibration sounds are generated when the handle is operated. As a countermeasure, conventionally, when the worm 32 is made of metal, as the worm wheel 31, a resin part made of a resin composition and formed with gear teeth 44 on the outer peripheral surface of the metal core tube 42. Noise countermeasures are taken using 43 integrated. 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, polyacetal, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), and other fiber base materials such as glass fiber and carbon fiber. The one that is blended 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.

  However, in consideration of fatigue resistance, dimensional stability and cost, MC nylon that does not contain fiber reinforcement, and polyamide 6, polyamide 66, and polyamide 46 that contain glass fiber as fiber reinforcement are used today. (For example, see Patent Document 1).

Japanese Patent Publication No. 6-60674

  However, although the above-mentioned aliphatic polyamide-based material is excellent in fatigue resistance, it has high water absorption, absorbs moisture, swells the resin portion 43, and initially exists between the gear teeth 44 and the worm 32. There is a possibility that the gap disappears or further swells and presses the worm 32. As a result, the resistance of the gear increases, and as a result, it is assumed that the handle becomes heavier or that the gear portion is worn or damaged due to compression, and the device as a whole does not function.

  In recent years, electric steering devices have been applied to large vehicles, and accordingly, the output of the electric motor increases, and as a result, the transmission torque transmitted to the reduction gear 30 tends to increase. However, the gear diameter cannot be increased so much due to space saving, and a high surface pressure is applied to the gear teeth 44 of the resin portion 43.

  The conventional glass fiber has a circular cross-sectional shape, and the gear teeth 44 made of polyamide 6, polyamide 66, and polyamide 46 containing this glass fiber are becoming insufficient in wear resistance and mechanical strength. As the surface pressure is expected to increase, improvement is required.

  The present invention has been made in view of such a situation, and improves mechanical strength, water absorption dimensional change, fatigue resistance, etc. in a resin gear made of a resin composition containing glass fiber, and has a particularly high surface pressure. An object of the present invention is to provide a reduction gear for an electric power steering device that can prevent wear and breakage of gear teeth even when added, and has high performance and reliability.

In order to achieve the above object, the present invention provides the following reduction gear for an electric power steering apparatus.
(1) In a reduction gear for an electric power steering device for transmitting the output of an electric motor for generating a steering assist output to a steering shaft,
The outer periphery of the metal core tube is made of a resin composition containing polyamide 66 as a base resin, an oval cross section , and glass fibers surface-treated with a urethane sizing agent in a proportion of 10 to 50% by mass. A reduction gear for an electric power steering apparatus, comprising a gear formed by integrating a resin portion having gear teeth formed on an outer peripheral surface.
(2) In a reduction gear for an electric power steering device for transmitting the output of an electric motor for generating a steering assist output to a steering shaft,
It is made of a resin composition containing polyamide 66 as a base resin and having a cross section of an oval cross section and a glass fiber surface-treated with a urethane sizing agent in a proportion of 10 to 50% by mass, and gear teeth are formed on the outer peripheral surface thereof. A reduction gear for an electric power steering apparatus, comprising:
(3) The reduction gear for an electric power steering apparatus according to the above (1) or (2), wherein the reduction gear is a worm wheel, a helical gear, a spur gear, a bevel gear or a hypoid gear.
(4) The reduction for the electric power steering apparatus according to any one of (1) to (3) above, wherein the ratio of the long diameter portion to the short diameter portion of the glass fiber is 1.5 to 5. gear.

  In the reduction gear for an electric power steering apparatus of the present invention, since the resin portion contains glass fibers having an irregular cross section, the water absorption dimension change is small, and the wear resistance compared to a conventional resin gear containing glass fibers having a circular cross section. It has high mechanical strength and sufficient resistance to higher surface pressure.

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

  In the present invention, the type of the resin gear is not limited, and the reduction gear 30 as shown in FIG. The illustrated reduction gear 30 includes a worm wheel 31 that is made of a resin composition described later on the outer periphery of a metal core tube 42 and is integrated with a resin portion 43 having gear teeth 44 formed on the outer peripheral end face thereof. Moreover, there is no restriction | limiting in the worm | warm 32, It can be made from metal like the past.

The base resin that forms the resin portion 43 of the worm wheel 31 is made of polyamide 66 with priority given to fatigue resistance . In addition , it is possible to reduce water absorption by blending polyolefin modified with acid anhydride, and impact resistance by blending rubbery substances such as ethylene propylene non-conjugated diene rubber (EPDM), acrylic rubber, and nitrile rubber. It is possible to improve the performance.

  Moreover, it is preferable that the said base resin sets it as the molecular weight which can be injection-molded in the state containing glass fiber in consideration of productivity. Specifically, the number average molecular weight is preferably 13,000 to 30000, and more preferably 18000 to 26000 in terms of number average molecular weight in consideration of fatigue resistance, moldability and the like. When the number average molecular weight is less than 13,000, the molecular weight is too low, the fatigue resistance is poor, and the practicality is low. On the other hand, when the number average molecular weight exceeds 30000, the melt viscosity in a state where the glass fiber is contained in a specified amount is too high, and it is difficult to produce by high precision injection molding.

In the base resin, glass fibers are blended as a reinforcing material. In the present invention, glass fibers having an oval cross section are used . Good Mashiku is profiled ratio (ratio of long diameter portion and the minor axis portion) of the glass fiber is 1.5 to 5, more preferably glass fibers is 2-4. If the profile ratio is less than 1.5, the effect of improving the mechanical strength is small, and if the profile ratio exceeds 5, it is too flat and it is difficult to produce stably. Moreover, it is preferable that a short diameter part is 5-12 micrometers. If the short diameter portion is less than 5 μm, it is too thin and breaks or breaks during production. Therefore, it is difficult to maintain a stable quality at a low cost, and the practicality is low. On the other hand, when the minor axis portion exceeds 12 μm, the fiber is too thick considering the profile ratio, and the dispersibility in the resin becomes inferior, which may cause unevenness in the strength of the resin portion 43.

The content of the glass fiber having an oval cross section is 10 to 50% by mass, preferably 15 to 30% by mass, based on the total amount of the resin composition forming the resin part 43. When the content is less than 10% by mass, the reinforcing effect is small. When the content exceeds 50% by mass, not only fluidity suitable for injection molding is obtained, but the worm 12 is easily damaged, and the worm 12 is greatly worn. Therefore, the durability of the reduction gear 30 may be reduced.

The glass fiber having an oval cross section used in the present invention is less likely to break than a glass fiber having a conventional circular cross section, and is kneaded with a base resin and is longer in the resin than the glass fiber having a circular cross section when injection molded. scatter. Therefore, when compared with the same content, the effect of increasing the mechanical strength and dimensional stability of the resin portion 43 is superior to that of glass fibers having a circular cross section. In addition, since the glass fiber having an oval cross section is oriented so as to be parallel to the tooth surface of the gear teeth 44 at the time of molding, the wear resistance of the tooth surface is increased and it can withstand higher surface pressure. Furthermore, since a slight reinforcing effect appears also in the direction of the minor axis portion, the effect of suppressing the dimensional change due to water absorption is enhanced.

In addition, glass fibers with an oval cross-section are sized such as a silane coupling agent having an epoxy group or an amino group at one end, or epoxy, urethane, acrylic, etc. in consideration of adhesiveness with the base resin. It is preferable to use a surface-treated product. Silane coupling agents and sizing agents are selected according to the type of base resin. For example, silane coupling agents having an epoxy group or amino group have an epoxy group or amino group acting on the amide bond of the polyamide resin. Improve the reinforcement effect.

The glass fiber having an oval cross section preferably has a fiber length of 300 to 900 μm, and more preferably has a fiber length of 350 to 600 μm in the obtained resin portion 43. If the fiber length is less than 300 μm, the reinforcing effect and the dimensional stability effect are small, which is not preferable. On the other hand, it is difficult to maintain a long fiber state exceeding 900 μm in the process of kneading with the base resin and injection molding, and the upper limit of the fiber length is a value set from the manufacturing process. In order to obtain such a fiber length, kneading conditions and molding conditions may be adjusted.

A part of the glass fiber having an oval cross section may be replaced with another fibrous reinforcing material such as carbon fiber or a whisker-like reinforcing material such as potassium titanate whisker.

  Furthermore, a colorant such as carbon black or bengara may be added to the base resin. When using a base resin with insufficient heat resistance, in order to prevent deterioration due to heat during molding and use. It is preferable to add an iodide heat stabilizer and an amine antioxidant, either alone or in combination.

The method for producing the worm wheel 31 using the above base resin, glass fiber having an oval cross section and other compounds is not limited, and 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 core tube 42 is placed in a mold equipped with a sprue and a disk gate, and the resin composition 43 is filled with the resin composition by an injection molding machine to mold the resin portion 43. Thereafter, gear teeth 44 are formed on the outer periphery of the resin portion 43 by cutting.

  The reduction gear 30 is used, for example, in a reduction mechanism of the electric power steering apparatus shown in FIG. In the illustrated electric power steering apparatus 10, the steering wheel shaft 11 is composed of an upper steering wheel shaft 11 a and a lower steering wheel shaft 11 b, and the steering wheel shaft 11 is rotatably supported around the shaft center inside the steering wheel shaft housing 12. The rudder wheel shaft housing 12 is fixed at a predetermined position in the vehicle interior in a state where the lower portion thereof is inclined forward. 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 electric motor 13 is controlled based on the detected snake steering torque.

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

  FIG. 3 is a partial cross-sectional view showing a reduction mechanism of the electric power steering apparatus 10 shown in FIG. 2, and the reduction gear 30 described above is incorporated therein. In the reduction gear 30, a worm wheel 31 having the resin portion 43 and a worm 32 are accommodated in a gear case 33. Also, the worm 32 is integrally formed with worm shafts 32 a and 32 b at both ends thereof, and the worm shafts 32 a and 32 b are splined or serrated to the drive shaft 13 a of the electric motor 13. The core tube 42 of the worm wheel 31 is coupled to the lower rudder wheel shaft 11b, and the rotation of the electric motor 13 is transmitted to the lower rudder wheel shaft 11b via the worm 32 and the worm wheel 31.

  In addition to the configuration shown in FIG. 1, the reduction gear 30 can be a spur gear shown in FIG. 4, a helical gear shown in FIG. 5, a bevel gear shown in FIG. 6, a hypoid gear shown in FIG. In any case, the outer periphery of the metal core tube is made of the polyamide resin composition described above, and the resin portion having the gear teeth formed on the outer peripheral surface thereof is integrated.

  Furthermore, although the reduction gear 30 is not shown, the entire worm wheel may be formed of only the resin portion 43 having the above-described composition without using the core tube 42.

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

<Test-1>
( Comparative Example 3 )
Polyamide 66 (“UBE Nylon 2020U” manufactured by Ube Industries, Ltd., average molecular weight 20000, containing copper iodide-based additive) 75% by mass, cross-sectional eyeglass type glass fiber (“CSH 3PA-870” manufactured by Nitto Boseki Co., Ltd.) , Profile ratio 2, short diameter portion 10 μm, urethane sizing agent treatment) S45C core tube with outer diameter of 65 mm and width of 16 mm obtained by knurling the resin composition of 25% by mass with a groove depth of 0.5 mm As a core, insert molding was performed to obtain a blank material having an inner diameter of 64 mm, an outer diameter of 84 mm, and a width of 15.5 mm. Further, gear teeth were cut on the outer periphery to produce a worm wheel as shown in FIG. The produced worm wheel was subjected to the following (1) dimensional stability evaluation and (2) durability evaluation.

(Example 1 )
Except for the glass fiber having an oval cross section (“CSG 3PA-820” manufactured by Nitto Boseki Co., Ltd., deformed ratio 4, short diameter portion 7 μm, urethane sizing agent treatment) 25 mass%, the same as in Example 1 A worm wheel was produced. The produced worm wheel was subjected to the following (1) dimensional stability evaluation and (2) durability evaluation.

( Reference Example 1 )
As a base resin, linear polyphenylene sulfide (“Fortron Unfilled Grade 0220A9” manufactured by Polyplastics Co., Ltd.) is 70% by mass, and glass fiber having an oblong cross section (“CSG 3PA-820” manufactured by Nitto Boseki Co., Ltd.) A worm wheel was manufactured in the same manner as in Example 2 with an irregularity ratio of 4, a short diameter portion of 7 μm, and a urethane sizing agent treatment) of 25 mass%. The produced worm wheel was subjected to the following (1) dimensional stability evaluation and (2) durability evaluation.

(Comparative Example 1)
Using polyamide 66 ("UBE Nylon 2020GU5" manufactured by Ube Industries, Ltd., average molecular weight 20000, containing copper iodide-based additive) containing 25% by mass of a circular glass fiber having a cross section of 13 μm in diameter, as in Example 1 Thus, a worm wheel was produced. The produced worm wheel was subjected to the following (1) dimensional stability evaluation and (2) durability evaluation.

(Comparative Example 2)
A worm wheel was produced in the same manner as in Example 1 using polyphenylene sulfide (“Fortron Reinforced Grade 1130A64” manufactured by Polyplastics Co., Ltd.) containing 30% by mass of a circular glass fiber having a cross section of 13 μm in diameter. The produced worm wheel was subjected to the following (1) dimensional stability evaluation and (2) durability evaluation.

(1) Dimensional stability evaluation The produced worm wheel was left in the environment of the following condition A or condition B, and the amount of change in the outer diameter of the gear after 70 hours, 300 hours and 500 hours was measured. The results are shown in Table 1. Under any environmental condition, a change amount of 40 μm or less was indicated as “◯” as a pass, and those exceeding 40 μm were indicated as “x” as a failure.
Condition A: 60 ° C., 90% RH
Condition B: 80 ° C., 90% RH

(2) Durability Evaluation The manufactured worm wheel was incorporated into a reduction gear of an actual automobile, and the snake operation was repeated under the following environmental conditions C to F to evaluate the durability. The results are shown in Table 1, but when it can withstand 100,000 times of snake operation in any environmental condition, it is indicated as “O” as acceptable, and when it cannot withstand 100,000 times of snake operation, it is rejected. And “×”.
Environmental condition C: 30 ° C., 50% RH
Environmental condition D: 50 ° C., 90% RH
Environmental condition E: 80 ° C., 50% RH
Environmental condition F: 80 ° C., 90% RH

As shown in Table 1, by forming the resin part with a resin composition containing a glass fiber having an oval cross section , dimensional change due to water absorption is suppressed, and excellent durability even under severe conditions with higher humidity It can be seen that Polyamide 66 is originally a resin with a large dimensional change due to water absorption, but the amount of change is suppressed by blending glass fibers having an oval cross section .

<Test-2>
A plate-shaped test piece was molded from the resin composition having the same composition as in Comparative Example 3 and Example 1 and Comparative Example 1, and a ball-on-disk test using this plate-shaped test piece and SUJ2 balls was performed. Sex was evaluated. That is, grease (base oil: poly α-olefin oil, thickener: aliphatic urea) is interposed between the plate-shaped test piece and the ball, and three balls are arranged equally at 120 °, and the ambient temperature is 80 ° C. Then, the ball was rotated at a contact portion peripheral speed of 1 m / sec for 8 hours while changing the contact surface pressure, and the wear state of the surface of the plate-shaped test piece after rotation was observed. The results are shown in Table 2.

As shown in Table 2, it can be seen that the wear resistance is enhanced by forming the resin portion with a resin composition containing glass fibers having an oval cross section . The polyamide 66 is originally a resin having poor durability, but the wear resistance is greatly improved by blending glass fibers having an oval cross section .

It is a perspective view which shows an example (cylindrical worm gear) of a reduction gear. It is a schematic block diagram which shows an example of a power steering apparatus. It is a fragmentary sectional view of the deceleration mechanism part. It is a perspective view which shows the other example (spur gear) of a reduction gear. It is a perspective view which shows the further another example (helical gear) of the reduction gear. It is a perspective view which shows the further another example (bevel gear) of a reduction gear. It is a perspective view which shows the further another example (high void gear) of a reduction gear.

Explanation of symbols

11 Steering wheel shaft 12 Steering wheel shaft housing 13 Electric motor 20 Rack / pinion motion conversion mechanism 21 Rack shaft 22 Pinion shaft 30 Reduction gear 31 Worm wheel 32 Worm 42 Core tube 43 Resin portion 44 Gear teeth

Claims (4)

In the reduction gear for the electric power steering device for transmitting the output of the electric motor for generating the snake steering auxiliary output to the steering shaft,
The outer periphery of the metal core tube is made of a resin composition containing polyamide 66 as a base resin, an oval cross section , and glass fibers surface-treated with a urethane sizing agent in a proportion of 10 to 50% by mass. A reduction gear for an electric power steering apparatus, comprising a gear formed by integrating a resin portion having gear teeth formed on an outer peripheral surface. In the reduction gear for the electric power steering device for transmitting the output of the electric motor for generating the snake steering auxiliary output to the steering shaft,
It is made of a resin composition containing polyamide 66 as a base resin and having a cross section of an oval cross section and a glass fiber surface-treated with a urethane sizing agent in a proportion of 10 to 50% by mass, and gear teeth are formed on the outer peripheral surface thereof. A reduction gear for an electric power steering apparatus, comprising:   3. The reduction gear for an electric power steering apparatus according to claim 1, wherein the reduction gear is a worm wheel, a helical gear, a spur gear, a bevel gear, or a hypoid gear.   The reduction gear for an electric power steering apparatus according to any one of claims 1 to 3, wherein the ratio of the long diameter portion to the short diameter portion of the glass fiber is 1.5 to 5.

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