JP2006194296A - Composite gear and its manufacturing method and electric-powered power steering including composite gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite gear that is formed of metal and resin and excellent in durability. <P>SOLUTION: A worm wheel 19 is equipped with an annular and metallic core 40 and a rim 50 fitted into the outer circumference of the core 40. The rim 50 comprises a part molded by the extrusion of a material whose basic resin is a polyphenylene sulfide. In the inner circumference 52 of the rim 50, a protrusion 53 is formed and fitted into a depression 43a of a knurling 43 in the outer circumference 42 of the core 40. After the core 40 is press-fitted into the inner circumference of an manufacturing intermediate for the rim 50, the core 40 is heated to melt a part of the inner circumference of the manufacturing intermediate, thus forming the protrusion 53 that has entered the depression 43a of the core 40. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a composite gear including a metal core portion and a resin rim portion and a method for manufacturing the same, and to an electric power steering apparatus including the composite gear.

A reduction gear is used in an electric power steering device for an automobile. For example, in the column type EPS, the rotational force of the motor is transmitted to a driving gear such as a worm, and further transmitted to a driven gear such as a worm wheel, thereby decelerating the rotation of the motor and amplifying the output of the motor to assist the steering operation with torque. I am doing so.
By the way, an appropriate backlash is required for meshing of the drive gear and the driven gear, but for example, when driving on a rough road such as a stone pavement, the rattling noise caused by the backlash is generated by the reaction force from the tire. Or parts having bearings or other clearances may generate rattle noise. If these sounds are transmitted as noise in the passenger compartment, the driver is uncomfortable.

Therefore, as a driven gear, generally, an annular metal core portion and a polyamide resin rim portion that is injection-molded by inserting the core portion into a mold are provided, and a tooth portion is provided on the outer periphery of the rim portion. A composite gear to be formed is used (see, for example, Patent Document 1).
On the other hand, a worm wheel is provided in which a metal core part is press-fitted into the inner periphery of a centrifugally molded polyamide resin (MC nylon) rim part, and the both are fixedly integrated by high-frequency heating (for example, a patent) Reference 2).

On the other hand, after press-fitting a metal core portion into a press-fit hole of a resin rim portion, a gear is provided in which a part of the core portion is caulked to the rim portion to increase the coupling strength between the two (for example, Patent Documents). 3).
JP-A-11-301501 JP 2004-204902 A Utility Model Registration No. 2606328

However, Patent Documents 1 and 2 have a problem that the dimensional change due to water absorption of the polyamide resin is large.
In recent years, there has been a demand for higher output of the electric power steering apparatus, and as a result, an improvement in the connection strength between the core portion and the rim portion in a high-temperature environment is demanded as a driven gear. On the other hand, the bonding strength between the core portion and the rim portion is not sufficient only by heat fusion as in Patent Document 2 or simply caulking as in Patent Document 3.

  Therefore, an object of the present invention is to provide a composite gear excellent in durability, a method for manufacturing the composite gear, and an electric power steering apparatus including the composite gear.

  The inventor of the present application considered the use of a material having a base resin made of polyphenylene sulfide having excellent heat resistance and small dimensional change due to water absorption. In a material containing polyphenylene sulfide, in order to ensure required toughness, it is necessary to increase the number average molecular weight of the polyphenylene sulfide so as to be, for example, 10,000 or more. However, when the molecular weight is increased in this way, the viscosity at the time of melting of the above material is increased and the fluidity is deteriorated. For this reason, when performing injection molding using the above-described materials, there is a risk of forming defects.

  Therefore, the present invention includes an annular metal core portion and an annular rim portion fitted on the outer periphery of the core portion and having teeth on the outer periphery. The rim portion is made of a material having polyphenylene sulfide as a base resin. A composite gear comprising an extruded product, wherein the outer periphery of the core portion includes a recess for joining the rim portion, and the inner periphery of the rim portion includes a protrusion heat-sealed to the recess. Is to provide.

  According to the present invention, since the rim portion is an extrusion-molded product, a high molecular weight polyphenylene sulfide that is difficult to be injection-molded can be used as a base resin, and as a result, the toughness necessary for the rim portion is ensured. Can improve fatigue strength. In addition, polyphenylene sulfide is excellent in heat resistance as described above, and has little dimensional change due to water absorption.

In injection molding, the thickness of the molded product could not be increased too much in order to avoid voids during molding. It becomes possible to do. Therefore, noise due to rattling noise can be reduced. Further, the durability can be remarkably improved, and it is possible to withstand high-power transmission.
In other words, since toughness and fatigue strength are improved, even if a smaller and lighter gear than the conventional one is used, the same output as the conventional one can be transmitted and the same durability can be achieved.

The polyphenylene sulfide is preferably a linear polyphenylene sulfide having a number average molecular weight of 10,000 to 20,000 g / mol. If the number average molecular weight is 10,000 or more, for example, toughness required when used as a reduction gear can be ensured.
A step of extruding a material having polyphenylene sulfide as a base resin to form an intermediate for manufacturing a rim portion, a step of press-fitting a metal core into the inner periphery of the intermediate for manufacturing, and an intermediate for manufacturing And heating the core portion press-fitted into the inner periphery of the intermediate member to form a convex portion that is heat-sealed with the concave portion on the outer periphery of the core portion on the inner periphery of the intermediate for production. The manufacturing method of this is provided.

According to this manufacturing method, after the metal core portion is press-fitted, the core portion and the rim portion are concavo-convexly fitted using heat fusion, so that the core portion and the rim portion can be firmly bonded.
An electric power steering device that assists steering by transmitting the power of an electric motor to a steering mechanism via a transmission device including a worm and a worm wheel as the above composite gear, is excellent in durability even if the output is increased. . Therefore, it becomes possible to apply this electric power steering apparatus to a vehicle having a displacement of 2 liters or more, for example.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, A pinion shaft 7 connected to the intermediate shaft 5 via a universal joint 6 and a steering shaft extending in the left-right direction of the automobile having rack teeth 8a meshing with pinion teeth 7a provided in the vicinity of the end of the pinion shaft 7 As a rack bar 8. The pinion shaft 7 and the rack bar 8 constitute a steering mechanism A including a rack and pinion mechanism.

The rack bar 8 is supported in a housing 9 fixed to the vehicle body so as to be capable of linear reciprocation through a plurality of bearings (not shown). Both end portions of the rack bar 8 protrude to both sides of the housing 9, and tie rods 10 are coupled to the respective end portions. Each tie rod 10 is connected to a corresponding wheel 11 via a corresponding knuckle arm (not shown).
When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack bar 8 along the left-right direction of the automobile by the pinion teeth 7a and the rack teeth 8a. Thereby, steering of the wheel 11 is achieved.

The pinion shaft 7 is divided into an input-side upper shaft 71 connected to the steering member 2 and an output-side lower shaft 72 provided with a pinion 7 a. These upper and lower shafts 71, 72 are connected via a torsion bar 12. They are connected to each other so as to be relatively rotatable on the same axis.
A torque sensor 13 for detecting a steering torque is provided by a relative rotational displacement amount between the upper shaft 71 and the lower shaft 72 via the torsion bar 12, and the torque detection result of the torque sensor 13 is obtained from an ECU (Electronic Control Unit: electronic). Control unit) 14. The ECU 14 drives and controls the steering assisting electric motor 16 via the drive circuit 15 based on a torque detection result or a vehicle speed detection result given from a vehicle speed sensor (not shown). The output rotation of the electric motor 16 is decelerated via the speed reducer 17 as a transmission device and transmitted to the lower shaft 72 of the pinion shaft 7 and converted into a linear motion of the rack bar 8 to assist steering.

The speed reducer 17 is a composite gear (driven gear) that is engaged with the worm shaft 18 as a drive gear that is rotationally driven by the electric motor 16 and that is meshed with the worm shaft 18 and is integrally connected to the lower shaft 72 of the pinion shaft 7. The worm wheel 19 is provided.
The housing 20 that houses the pinion shaft 7 includes a sensor housing 21 and a gear housing 22 that are fitted together. The lower shaft 72 of the pinion shaft 7 is rotatably supported on both sides of the worm wheel 19 via bearings 23 and 24. The bearing 23 is held by the sensor housing 21, and the bearing 24 is held by the gear housing 22. The bearings 23 and 24 are, for example, ball bearings.

Referring to FIG. 2, worm shaft 18 is arranged coaxially with output shaft 25 of electric motor 16. The worm shaft 18 has first and second end portions 18a and 18b that are separated from each other in the axial length direction, and has a tooth portion 18c at an intermediate portion between the first and second end portions 18a and 18b.
The connecting portion 18d provided at the first end portion 18a of the worm shaft 18 and the opposite end portion of the output shaft 25 of the electric motor 16 can transmit power coaxially through a joint 26 using serration fitting, for example. It is connected to.

The first and second end portions 18a and 18b of the worm shaft 18 are rotatably supported by the gear housing 22 via corresponding first and second bearings 27 and 28, respectively. The first and second bearings 27 and 28 are ball bearings, for example.
Inner rings 29, 30 of the first and second bearings 27, 28 are fitted to the first and second end portions 18a, 18b of the worm shaft 18 so as to be integrally rotatable. The inner rings 29 and 30 are in contact with corresponding positioning step portions of the worm shaft 18 which are opposite to each other. The outer rings 31 and 32 of the first and second bearings 27 and 28 are held non-rotatably in the corresponding bearing holding holes 33 and 34 of the gear housing 22.

A screw member 36 is screwed into the screw hole 35 connected to the bearing holding hole 33, and the screw member 36 contacts the end surface of the outer ring 31 of the first bearing 27, so that the first bearing 27 is moved in the axial direction of the worm shaft 18. Is positioned. The screw member 36 is fixed by a lock nut 37.
Referring to FIGS. 1 and 2, the worm wheel 19 as a compound gear (driven gear) is connected to an intermediate portion in the axial direction of the lower shaft 72 of the pinion shaft 7 so as to be integrally rotatable and non-movable in the axial direction. . The worm wheel 19 includes an annular metal core portion 40 that is coupled to the lower shaft 72 so as to be integrally rotatable, and an annular rim portion 50 that is fitted to the outer periphery of the core portion 40.

With reference to FIG. 3, the core portion 40 includes a fitting hole 41 as a central hole for fitting the lower shaft 72 of the pinion shaft 7. A knurl 43 is provided on the outer periphery 42 of the metal core portion 40 to prevent relative rotation of the rim portion 50 and prevent the rim portion 50 from being removed from the core portion 40 in the axial direction. . The knurl 43 includes a recess 43a.
A plurality of tooth portions 51 are formed on the outer periphery of the rim portion 50, and a convex portion 53 is formed on the inner periphery 52 of the rim portion 50. The convex portion 53 enters the concave portion 43 a of the core portion 40 and is heat-sealed. Yes. The relative rotation of the core part 40 and the rim part 50 is restricted by the fitting of the concave part 43a and the convex part 53 of the knurl 43, and the rim part 50 is restricted from being removed from the core part 40 in the axial direction. The

  The rim portion 50 is made of an extruded product of a material having polyphenylene sulfide (PPS) as a base resin. Polyphenylene sulfide includes linear polyphenylene sulfide having a number average molecular weight of 10,000 to 20,000 g / mol. If the number average molecular weight is 10,000 or more, toughness required as a reduction gear for an electric power steering apparatus can be ensured. Further, when the number average molecular weight exceeds 20000 g / mol, the extrudability in extrusion molding is poor, and there are problems such as an increase in molding cost and a decrease in physical properties. Therefore, the number average molecular weight is set in the above range.

Next, a method of manufacturing the worm wheel 19 as the above composite gear (reduction gear) will be described with reference to FIGS.
First, a material having polyphenylene sulfide as a base resin is extruded to form a manufacturing intermediate 60 for the rim portion 50 as shown in FIG. A tooth portion 51 is formed on the outer periphery of the manufacturing intermediate 60, and the inner periphery 62 of the manufacturing intermediate 60 is a cylindrical surface.

  A metal core portion 40 is press-fitted into the inner periphery 62 of the manufacturing intermediate 60 as shown in FIG. A space S <b> 1 is formed between the recess 43 a of the knurled portion 43 and the inner periphery 62 of the manufacturing intermediate 60 in a state where the outer periphery 42 of the core portion 40 is fitted to the inner periphery 62 of the manufacturing intermediate 60. Although not shown, actually, as shown in FIG. 4B, the inner periphery 62 of the manufacturing intermediate 60 slightly bites into the recess 43 a of the knurled 43 when the core portion 40 is press-fitted. .

  Next, the core part 40 press-fitted into the manufacturing intermediate 60 is pressed against the hot plate 80 as shown in FIG. 5 or the core part 40 is heated by high-frequency heating, so that the knurl part of the core part 40 is obtained. The inner periphery 62 of the production intermediate 60 is heat-sealed to the recess 43 a of 43. As a result, as shown in FIG. 6, a convex portion 53 that is heat-sealed to the concave portion 43 a of the knurled portion 43 of the core portion 40 is formed, and the core portion 40 and the rim portion 50 are firmly coupled to each other in FIG. 3. A worm wheel 19 as shown is obtained.

  According to the present embodiment, since the rim portion 50 is an extrusion-molded product, a high molecular weight polyphenylene sulfide that is difficult to be injection-molded can be used as the base resin. As a result, the rim portion 50 is necessary. Toughness can be ensured and fatigue strength is improved. In addition, polyphenylene sulfide is excellent in heat resistance as described above, and has little dimensional change due to water absorption.

  In particular, after the metal core portion 40 is press-fitted into the inner periphery of the intermediate body 60 for manufacturing the rim portion 50, the core portion 40 is heated so that a part of the inner periphery of the rim portion 50 is changed to the outer periphery of the core portion 40. In the recess 43a. Thereby, after the metal core portion 40 is press-fitted, the predetermined portions of the core portion 40 and the rim portion 50 are concavo-convexly fitted using heat fusion, so that the core portion 40 and the rim portion 50 are firmly integrated. Became possible.

  In conventional injection molding, the thickness of the injection-molded product could not be increased so much as to avoid voids during injection molding. However, the rim portion 50 made of an extrusion-molded product is subject to such limitations. It becomes possible to make it thick. Therefore, the buffer effect by resin can be improved and the noise by a rattling sound can be reduced. Further, the durability can be remarkably improved, and it is possible to withstand high-power transmission.

  In other words, since the worm wheel 19 can be increased in strength including improved toughness and fatigue strength, the worm wheel 19 can be reduced in size and weight, for example, by reducing the diameter of the worm wheel 19 when transmitting the same torque. It becomes. Further, by reducing the gear module of the worm wheel 19, it is possible to increase the reduction gear ratio. As a result, the output of the electric motor 16 can be reduced, leading to cost reduction.

Further, the electric power steering apparatus 1 that assists the steering by transmitting the power of the electric motor 16 to the steering mechanism A via the speed reducer 17 including the worm wheel 19 as described above makes it durable even if the output is increased. Excellent. Therefore, the electric power steering apparatus 1 can be applied to a high horsepower vehicle with a displacement of 2 liters or more, for example.
FIG. 7 shows another embodiment of the present invention. Referring to FIG. 7, in worm wheel 19A of the present embodiment, an involute spline 44 is formed on outer periphery 42 of core portion 40A. As shown in FIG. 8, the spline 44 has spline teeth 45 extending in the axial direction of the core portion 40 </ b> A arranged at equal intervals in the circumferential direction of the core portion 40 </ b> A, and a recess 46 formed of a spline groove between the adjacent spline teeth 45, 45. Is forming. On the other hand, the inner periphery of the rim portion 50 includes convex portions 54 that are heat-sealed in the concave portions 46 of the core portion 40A. The convex portion 54 functions to restrict relative rotation between the core portion 40A and the rim portion 50A.

  Referring to FIG. 7 again, concave portions 47 are provided by chamfering at both ends of the spline teeth 45 of the core portion 40A by chamfering, and the inner periphery 52 of the rim portion 50A is provided on the concave portion 47. A convex portion 55 that is heat-sealed is formed. These convex portions 55 restrict relative movement of the core portion 40A and the rim portion 50A in the axial direction. That is, the convex portion 55 prevents the rim portion 50 </ b> A from being detached from the core portion 40. Also in the present embodiment, the convex portions 54 and 55 are formed by heat fusion after the core portion 40A is press-fitted into the intermediate for manufacturing the rim portion 50A.

  FIG. 9 shows still another embodiment of the present invention. Referring to FIG. 9, the worm wheel 19 </ b> B of the present embodiment is different from the worm wheel 19 </ b> A of the embodiment of FIG. 7 in that the rim portion 50 </ b> B is replaced with the fitting of the convex portion 55 and the concave portion 47. The pair of convex portions 55B having a trapezoidal cross section are fitted into the concave portions 47B at the pair of end portions of the spline teeth 45B of the core portion 40B, respectively, in a wedge shape. In the present embodiment, the rim portion 50B is also prevented from being pulled out radially outward of the core portion 40B.

  Next, FIG. 10 shows still another embodiment of the present invention. Referring to FIG. 10, the worm wheel 19C of the present embodiment is different from the worm wheel 19B of the embodiment of FIG. 9 as follows. That is, in the embodiment of FIG. 9, the concave portions 47B are formed at both ends of the spline teeth 45B of the core portion 40B. Instead of this, in the embodiment of FIG. 10, the spline teeth 45C of the core portion 40C are formed. A concave portion 47C is provided at the central portion in the tooth line direction, and the convex portion 55C of the rim portion 50C is heat-sealed to the concave portion 47C. By fitting the concave portion 47C and the convex portion 55C, the axial removal of the rim portion 50C from the core portion 40C is prevented.

  Next, FIG. 11 shows still another embodiment of the present invention. Referring to FIG. 11, in worm wheel 19 </ b> D of the present embodiment, a plurality of concave grooves 47 </ b> D as concave portions arranged at equal intervals in the circumferential direction are provided on outer periphery 42 of core portion 40 </ b> D. As shown in FIG. 12, these concave grooves 47D extend long in the axial direction of the core portion 40D, and each concave groove 47D has an end in the longitudinal direction. In other words, both ends of each concave groove 47D are closed. On the other hand, the rim portion 50D includes a convex portion 55D that is heat-sealed to each concave groove 47D. Due to the fitting of the concave portion 47D and the convex portion 55D, relative movement in the circumferential direction and the axial direction of the core portion 40D and the rim portion 50D is prevented.

1 is a schematic cross-sectional view of an electric power steering apparatus using a worm wheel according to an embodiment of the present invention. It is sectional drawing which follows the II-II line of FIG. It is sectional drawing of the principal part of a worm wheel. It is a schematic sectional drawing of the intermediate body for manufacture and the core part which shows the press injection process in the manufacturing process of a worm wheel. It is a schematic sectional drawing of the intermediate body for manufacture and the core part which shows the heat-fusion process in the manufacturing process of a worm wheel. It is an expanded sectional view of the principal part of a core part and a rim | limb part, and has shown the recessed part of the core part, and the convex part of the rim | limb part heat-fused by this. It is a schematic sectional drawing of the worm wheel of another embodiment of this invention. It is sectional drawing of the principal part of the worm wheel of FIG. 7, and has shown the recessed part of the core part, and the convex part of the rim | limb part heat-sealed to this. It is a schematic sectional drawing of the worm wheel of another embodiment of this invention. It is a schematic sectional drawing of the worm wheel of another embodiment of this invention. It is a schematic sectional drawing of the worm wheel of another embodiment of this invention. It is a perspective view of the principal part of the outer periphery of the core part of the worm wheel of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering member, 3 ... Steering shaft, 5 ... Intermediate shaft, 7 ... Pinion shaft, 71 ... Upper shaft, 72 ... Lower shaft, 7a ... Pinion tooth, 8 ... Rack bar, 8a ... Rack Tooth, A ... Steering mechanism, 11 ... Wheel, 13 ... Torque sensor, 14 ... ECU, 16 ... Electric motor, 17 ... Reducer, 18 ... Worm shaft, 19 ... Worm wheel, 40, 40A, 40B, 40C, 40D ... Core part, 41 ... fitting hole, 42 ... outer periphery, 43 ... knurled, 43a ... recessed part, 44 ... spline, 45, 45B, 45C ... spline tooth, 46 ... spline groove (recessed part), 47, 47B, 47C ... recessed part, 50, 50A, 50B, 50C, 50D ... rim part, 51 ... tooth part, 52 ... inner periphery, 53 ... convex part, 54 ... convex part, 55, 55B, 55C ... convex part

Claims (4)

An annular metal core portion and an annular rim portion fitted on the outer periphery of the core portion and having teeth on the outer periphery, the rim portion is made of an extruded product of a material having polyphenylene sulfide as a base resin,
The outer periphery of the core part includes a recess for joining the rim part,
An inner periphery of the rim portion includes a convex portion heat-sealed to the concave portion.   The composite gear according to claim 1, wherein the polyphenylene sulfide is a linear polyphenylene sulfide having a number average molecular weight of 10,000 to 20,000 g / mol.   A step of extruding a material having polyphenylene sulfide as a base resin to form an intermediate for manufacturing a rim portion, a step of press-fitting a metal core into the inner periphery of the intermediate for manufacturing, and an intermediate for manufacturing And a step of heating the core portion press-fitted into the inner circumference to form a convex portion heat-sealed in the concave portion on the outer circumference of the core portion on the inner circumference of the production intermediate.   An electric power steering apparatus, wherein the power of an electric motor is transmitted to a steering mechanism via a transmission including a worm and a worm wheel as a composite gear according to claim 1 or 2 to assist steering.

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