JP2006336814A - Worm wheel structure and power steering device using worm wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a worm wheel is poorly extracted from a mold after injection molding because a synthetic resin tooth portion is conventionally shaped to be fitted along the inclined outer faces of tooth core portions. <P>SOLUTION: This worm wheel structure comprises the plurality of tooth core portions 22 integrally provided on the outer peripheral face of a disc core body 21 of a core 19 at circumferentially equal space positions, and the synthetic resin wheel tooth portion 20 provided on the outer periphery of the core body to cover the tooth core portions for meshing with a worm shaft. The tooth core portions are formed almost linearly extending along a rotation axial direction P of the work wheel, while the wheel tooth portion 20 is formed into a helical shape inclined to the axial direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention particularly relates to a worm wheel structure in which a synthetic resin material is coated on the outer periphery of a core metal to form a plurality of teeth, and to an electric power steering device for a vehicle using the worm wheel, for example.

  As this type of conventional worm wheel structure, a structure described in Patent Document 1 below is known.

  This worm wheel is applied to the deceleration mechanism of an electric power steering device for a vehicle, and is synthesized on the outer periphery of a gear-shaped core bar in order to reduce rattle noise due to backlash and improve wear resistance and transmission efficiency. It is formed in a double structure in which a plurality of wheel teeth are formed by a resin material.

  In the core metal, a tooth core portion constituting a base portion of the plurality of wheel tooth portions is integrally formed on an outer peripheral surface of a thick disc-shaped core metal body, and the tooth core portion is formed of a worm wheel. A helical tooth shape which is inclined with respect to the axial direction is formed, and the wheel tooth portion of the synthetic resin material is formed in a covering state along the outer surface shape.

The plurality of teeth are formed by injection molding, and the gear-shaped cored bar previously molded from a powder alloy or the like is placed in an injection mold, and a synthetic resin material is injected into the mold. Thus, an inclined helical tooth profile is formed along the outer periphery of the inclined tooth core.
Japanese Patent Laid-Open No. 2002-21980 (see FIGS. 1 and 2)

  However, in the conventional worm wheel structure, as described above, the tooth core portion of the metal core is formed to be inclined with respect to the axial direction of the worm wheel, and the synthetic resin wheel. Since the tooth portion is formed in a fitted state along the inclined outer surface shape of the tooth core portion, the moldability of the worm wheel from the injection mold is deteriorated after such forming.

  That is, since the tooth core portion is formed in an inclined shape in accordance with the shape of the wheel tooth portion, when the injection mold is of a type divided in the axial direction, When the worm wheel is pulled out from the mold in the axial direction and the mold is removed, the tooth bottom side portion of the end portions in the axial direction of the tooth base of each wheel tooth portion is caught by the mold and the worm wheel is moved. It becomes difficult to take out from the mold easily. As a result, the molding work efficiency of the worm wheel is reduced.

  The present invention has been devised in view of the actual state of the conventional worm wheel structure, and the invention according to claim 1, in particular, includes the tooth core portion of the metal core along the rotational axis direction of the worm wheel. The wheel teeth are formed in a helical shape inclined with respect to the axial direction.

  According to this invention, since the forming direction of the tooth core portion is substantially linear along the axial direction of the worm wheel, the core metal is molded from, for example, a powder alloy, and then the core metal is removed from the axial direction. When pulling out and punching out, it is possible to easily pull out due to the linearity of the tooth core.

  In addition, when molding the worm wheel, after forming the wheel teeth of the synthetic resin material on the outer surface of the core metal body and the plurality of tooth cores, and cooling the mold, the molded body is moved from the mold in the axial direction. When pulling out, since the forming direction of each tooth core is the same as the pulling direction, when the pulling force acts on each inclined wheel tooth, the wheel tooth moves toward the tooth core. Since it is elastically deformed, that is, elastically deformed so as to be parallel to the tooth core portion, the die cutting operation is facilitated.

  The invention according to claim 2 is a steering shaft connected to the steering wheel, a worm wheel coupled to the steering shaft and having a plurality of teeth formed on the outer periphery, a worm shaft meshing with the worm wheel, An electric motor provided on the worm shaft for applying a steering assist force to the steering shaft via the worm shaft and the worm wheel, and the electric motor based on an output signal of a steering state detecting means provided on the steering shaft. An electric power steering device comprising an electric motor control means for controlling, wherein the worm wheel is integrally provided on a metal core body formed of a metal material and an outer peripheral surface of the metal core body, and is arranged in a circumferential direction. A plurality of tooth core portions provided at equal intervals, and a wheel formed by a synthetic resin material provided on the outer periphery of the core metal body so as to cover the tooth core portions. The tooth core portion is formed to extend along the rotational axis direction of the worm wheel, while the wheel tooth portion is formed into a helical tooth shape inclined with respect to the axial direction. It is characterized by that.

  Since the structure of the worm wheel itself is the same as that of the first aspect of the present invention, the same effect as that of the first aspect of the invention can be obtained.

  Hereinafter, an embodiment in which a worm wheel structure according to the present invention is applied to an electric power steering device for a vehicle will be described with reference to the drawings.

  As shown in FIGS. 13 and 14, the electric power steering device includes a steering shaft 2 having one end connected to the steering wheel 1 and a part of the pinion housing 3 connected to the other end of the steering shaft 2. A pinion shaft 4 housed therein, a worm wheel 5 coupled to the outer periphery of the pinion shaft 4, a worm shaft 6 meshing with the worm wheel 5, and a motor housing coupled to a side portion of the pinion housing 3. 7 is provided in the motor housing 7 and detects the rotation angle of the steering shaft 2. The motor 8 is accommodated and held in the motor 7 and applies a steering assist torque to the steering shaft 2 via the worm shaft 6 and the worm wheel 5. And a control circuit 9 for controlling the electric motor 8 based on an output signal of the sensor. A rack bar 11 is accommodated in a rack housing 10 provided in the lower part of the pinion housing 2 along the vehicle width direction.

  Left and right front wheels FL and FR are connected to both ends of the rack bar 11 via knuckle arms 12, respectively, and the rack bar 11 is like a pinion shaft 4 and a helical gear in the rack housing 10. Engage and move in the axial direction when the steering shaft 2 rotates.

  As shown in FIG. 14, the electric motor 8 includes a cylindrical rotor 13 fixed to the outer periphery of the worm shaft 6, an annular stator 14 that rotates by exciting the rotor 13, and the worm shaft. A rotation angle sensor 15 that detects the amount of rotation 6 and a coil portion 16 wound around the inner periphery of the stator 14.

  The worm shaft 6 is driven by the electric motor 7, and both end portions thereof are rotatably supported by bearings 17 and 18, and worm tooth portions 6 a that mesh with the worm wheel 5 on one end side are formed.

  As shown in FIGS. 1 and 2, the worm wheel 5 includes a gear-shaped metal core 19 integrally formed by molding a metal material, and a synthetic resin integrally coupled to the outer peripheral side of the metal core 19. It is mainly composed of a plurality of wheel tooth portions 20 made of a material.

  More specifically, the core metal 19 is formed by, for example, molding and sintering a powder alloy material. As shown in FIGS. 3 to 6, as shown in FIGS. The cored bar body 21 is integrally formed on the outer peripheral surface of the cored bar 21, and a plurality of toothed core parts 22 are provided at equal intervals in the circumferential direction.

  The cored bar body 21 is formed to have a predetermined thickness, and a fixing hole 21a through which the pinion shaft 4 is inserted and fixed is formed in the center.

  As shown in FIGS. 5 and 6, the tooth core portion 22 is formed in a substantially rhombic trapezoidal cone shape, and is provided at a substantially central position in the width direction of the core metal body 21, and the worm wheel 5. Are extended substantially linearly along the rotational axis direction, that is, the width direction P of the core metal body 21. Accordingly, both end portions 22c and 22c in the longitudinal direction (axial direction) of the tooth core portion 22 are formed in a tapered shape from the central portion in the axial direction toward the end edge. Further, the tooth core portion 22 has a length L in the longitudinal direction set to about half of the width length of the core metal main body 21, and the center width length is the thickness of the wheel tooth portion 20. The predetermined thickness is set in relation to Further, the height H from the base portion 22a to the flat upper surface 22b is higher than the top portion 6b of the tooth portion 6a when the tooth portion 6a of the worm shaft 6 is engaged with the wheel tooth portion 20, as shown in FIG. And is set slightly lower than the contact position S of the tooth side surfaces of the two tooth portions 6a and 20. Thereby, the strength of the wheel tooth portion 20 is ensured and the durability is improved.

  Further, by forming the tooth core portion 22 in a trapezoidal shape, the rigidity of the base portion 22a is increased, and the durability of the tooth core portion 22 is also improved.

  On the other hand, as shown in FIGS. 7 and 8, the wheel teeth portion 20 of the synthetic resin material is molded and fixed integrally with the core metal 19 by an injection molding machine, and the outer peripheral surface of the core metal main body 21 and the tooth core portion 22. The outer surface of the worm shaft 6 is formed in a covered state and is inclined with respect to the longitudinal direction of the tooth core portion 22, that is, the axial direction P of the worm wheel 5. The toothed teeth are in mesh. Therefore, the wall thickness of each wheel tooth portion 20 is formed large as shown in FIG. 8, and in particular, both end portions 20d and 20d in the axial direction where the tooth core portion 22 is not located are the tooth core portions 22. It is formed relatively thick as much as it does not exist.

  Further, the wheel tooth portion 20 has a tooth side surface 20a, 20b that is a meshing portion that has a transverse section formed in a substantially truncated trapezoidal shape and meshes with the tooth side surface of the tooth portion 6a of the worm shaft 6, Each tooth side surface 20a, 20b is formed in a concave arc surface whose shape abuts on the tooth side surface of each tooth portion 6a of the worm shaft 6 in a sufficient surface contact state.

  Further, the wheel tooth portion 20 is formed with four relief portions 23 in the front, rear, left and right positions in the axial direction on the tooth base side of the tooth side surfaces 20a, 20b. Each escape portion 23 avoids interference with the mold when the wheel mold 20 is pulled out from the injection mold in the tooth trace direction, and the outer edge 23a is in the tangential direction of the worm wheel 5, That is, it is formed so as to be substantially perpendicular to the side surface, and is formed so that its width is smaller on the tooth root side than the concave curved surface constituting the tooth side surfaces 20a, 20b. Accordingly, the two escape portions 23 and 23 facing each other in the circumferential direction of the adjacent wheel tooth portions 20 and 20 are formed substantially in parallel.

  The synthetic resin material forming the wheel tooth portion 20 is formed in a fitted state up to substantially the center position in the radial direction of both side portions of the core metal main body 21.

  Further, as shown in FIG. 10, each tooth bottom surface 24 provided between the adjacent wheel tooth portions 20, 20 extends from a substantially central position in the axial direction toward an edge provided on the side of each relief portion 23. The circumferential width W1 is formed so as to be gradually reduced.

  Therefore, according to this embodiment, first, when the core metal 19 is molded by a mold, and then the core metal 19 is pulled out from the mold to perform die cutting, formation of each tooth core portion 22 of the core metal 19 is formed. Since the direction is substantially linear along the axial direction P of the worm wheel 5, it can be easily pulled out of the mold by the linear structure of each tooth core portion 22.

  Next, in order to mold and fix the wheel tooth portion 20 to the preformed metal core 19 as described above, it is accommodated and held in the cavity 30a of the injection mold 30 as shown in FIG. By injecting a molten synthetic resin material into the cavity 30a, the worm wheel 5 as shown in the figure is formed. Subsequently, after the mold 30 is cooled, the molded body of the worm wheel 5 is pulled out from the mold.

  As described above, when the molded body is pulled out from the mold 30 in the axial direction, the forming direction of each tooth core portion 22 is the same as the pulling direction. When acting on the side surfaces of both end portions 20c, 20c of the tooth portion 20, the both end portions 30c, 20c are elastically deformed linearly toward the tooth core portion 22 direction side. That is, since the wheel tooth portion 20 as a whole is elastically deformed so as to be parallel to the tooth core portion 22, the die cutting operation is facilitated.

  In particular, since the thickness on the both end portions 20c, 20c side is relatively thick, the elastic deformation becomes easier, so that the drawing operation becomes easier.

  Further, since the escape portion 23 can be easily pulled out from the mold 30, the mold forming operation is facilitated. In particular, since each of the relief portions 23 is formed substantially perpendicular to the tangential direction of the worm wheel 5, the effects of both ensuring the strength of the wheel tooth portion 20 and easily pulling out from the mold 30 are achieved. Can be obtained.

  Further, since the relief portions 23 are provided on both sides of the wheel tooth portion 20 in the axial direction, and each relief portion 23 is formed at an axially symmetric position of the worm wheel 5, each wheel tooth portion formed in an inclined shape. The drawing operation from the mold 20 is further facilitated, and the worm wheel 5 can obtain uniform characteristics with respect to the forward rotation or the reverse rotation in relation to the worm shaft 6.

  Further, each relief portion 23 is formed so that the width in the circumferential direction of the tooth base portion is smaller than the curved surface obtained by continuously extending the curved surfaces constituting the tooth side surfaces 20a and 20b. When pulling out the wheel tooth portion 20 of the synthetic resin material at the time of molding, as described above, it is possible to pull out using each relief portion 23 while obtaining elastic deformation of each wheel tooth portion 20, so that the pulling out Good.

  Further, since the wheel tooth portion 20 is formed in a tooth shape corresponding to the tooth side surface of the worm shaft 6, the meshing contact area between the worm wheel 5 and the worm shaft 6 increases, and the tooth side surface of the worm wheel 5. The surface pressure between 20a, 20b and the tooth side surface of the worm shaft 6 decreases. Thereby, the durability of the worm wheel 5 is improved by reducing the surface pressure of each tooth side surface.

  Further, the synthetic resin material constituting the wheel tooth portion 20 is slightly contracted and deformed when cooled in the mold after completion of molding. For this reason, in consideration of this shrinkage deformation, by setting the interval between the escape portions 23, 23 facing each other in the circumferential direction, it is possible to ensure good pullability from the inside of the mold 30, and the escape portion 23, Since the size of 23 can be minimized, the rigidity of the worm wheel 5 can be secured.

  Since the adjacent relief portions 23, 23 are formed substantially in parallel, the formation range of the relief portions can be made as small as possible. As a result, the rigidity of the worm wheel 5 can be increased.

  As described above, both end portions 22c, 22c in the axial direction of the tooth core portion 22 are tapered from the center portion in the axial direction toward the end portion, thereby covering the outer periphery of the tooth core portion 22. Although the thickness of the wheel tooth portion 20 is not uniform, the thickness of the synthetic resin material can be sufficiently increased, so that the amount of elastic deformation can be increased.

  Further, for example, the tooth core portion 22 can be formed into a plane ellipse shape as shown in FIG. 12 by changing to a rhombus shape, and the whole is formed into a truncated frustoconical shape. Both end portions 20 c and 20 c are extended along the axial direction of the worm wheel 5. Furthermore, the height, width, etc. of each tooth core portion 22 are set in substantially the same manner as in the first embodiment. Therefore, this embodiment can obtain the same effects as those of the first embodiment.

  The present invention is not limited to the configuration of the above-described embodiment. For example, the structure of the tooth core portion 20 can be further changed, and the structure of the wheel tooth portion 20 can be changed. It is also possible to apply the worm wheel to devices other than the electric power steering device.

  The technical ideas other than the invention described in the claims, as grasped from the embodiment, will be described below.

  (1) The tooth portion is provided at a meshing portion having a tooth profile corresponding to a tooth side surface of the worm shaft, and at a tooth base portion at least one end portion in the axial direction, and the tooth portion forming gold The worm wheel structure according to claim 1, further comprising an escape portion that avoids interference with the mold when the tooth portion is pulled out from the die in the direction of the tooth trace.

  Since the tooth portion is formed in a tooth profile corresponding to the tooth side surface of the worm shaft, the meshing contact area between the worm wheel and the worm shaft increases, and the surface pressure of the meshing portion decreases. Thereby, the durability of the worm wheel is improved by reducing the surface pressure of the meshing portion.

  Moreover, since it becomes possible to pull out easily from a metal mold | die by an escape part, this metal mold | die shaping | molding operation | work becomes easy.

  (2) The worm wheel structure according to (1), wherein the relief portion is formed substantially perpendicular to the tangential direction of the worm wheel.

  According to the present invention, it is possible to obtain both effects of ensuring the strength of the tooth portion and easily pulling out from the mold by the unique configuration of the relief portion.

  (3) The worm wheel structure according to (1), wherein the relief portions are provided on both sides of the tooth portion in the axial direction.

  Since the relief part of each tooth part is formed at an axially symmetric position of the worm wheel, the operation of pulling out each tooth part formed on a helical tooth (inclined shape) from the mold becomes easier and the worm shaft Therefore, the worm wheel can obtain uniform characteristics with respect to forward rotation or reverse rotation.

  (4) The relief portion is formed so that a width in the circumferential direction of the tooth base portion is smaller than a curved surface obtained by continuously extending the curved surface constituting the meshing portion. The worm wheel structure according to item (1).

  According to this invention, when pulling out the tooth portion of the synthetic resin material at the time of molding, it is possible to pull out using each relief portion while obtaining elastic deformation of each tooth portion. Become good.

  (5) The bottom surface formed between the adjacent tooth portions gradually decreases in width in the circumferential direction from the substantially central position in the axial direction toward the end surface in the axial direction provided on the escape portion side. The worm wheel structure according to claim 1, wherein the worm wheel structure is formed as described above.

  The synthetic resin material constituting the tooth portion is slightly contracted and deformed when cooled in the mold after completion of molding. For this reason, the distance between the opposing relief portions is set in consideration of the contraction deformation amount, that is, the retractability from the inside of the mold is improved by the contraction deformation amount, thereby minimizing the size of the escape portion. This makes it possible to secure the rigidity of the worm wheel.

  (6) The worm wheel structure according to (1), wherein the opposing relief portions of the adjacent tooth portions are formed substantially in parallel.

  Since the worm wheel after mold forming is pulled out in the axial direction from the inside of the mold, by forming the part that interferes with the mold, that is, the escape part in parallel, the formation range of the escape part can be minimized. As a result, the rigidity of the worm wheel can be increased.

  (7) The width in the circumferential direction of the mold corresponding to the substantially axial center portion of the tooth bottom surface formed between the adjacent tooth portions is set to be larger than the interval between the adjacent relief portions. The worm wheel structure according to claim 1, wherein:

  Since the synthetic resin material that constitutes the tooth portion slightly shrinks when cooled in the mold, considering the amount of shrinkage, by setting the interval between the opposing relief portions, It becomes possible to make the size as small as possible. As a result, the rigidity of the worm wheel can be increased.

  Further, since the synthetic resin material has elasticity, even if the escape portion interferes with the die when the tooth portion is pulled out from the die, the worm wheel is not adversely affected.

  (8) The axial end portions of the tooth core portion are formed such that the circumferential dimension decreases from the axial center portion toward the end portion. Worm wheel structure.

  According to this invention, since the longitudinal direction of the tooth core portion and the forming direction of the tooth portion do not coincide with each other, the thickness of the synthetic resin material covering the outer periphery of the tooth core portion is non-uniform, but both end portions of the tooth core portion are tapered. By forming it into a shape, the synthetic resin material can be prevented from becoming extremely thin.

It is a front view which shows the worm wheel which concerns on this invention. It is a top view of the worm wheel. The right half shows the core metal of the worm wheel, and the left half is a cross-sectional view in which the teeth are formed. It is A arrow directional view of FIG. It is a plane fracture | rupture figure which shows the principal part of the metal core provided to this embodiment. It is a side surface broken view which shows the principal part of a concentric bar. It is a principal part perspective view of the worm wheel of this embodiment. It is a principal part top view of the worm wheel. It is principal part sectional drawing of the worm wheel. It is a principal part top view of the worm wheel. It is a perspective view which shows the state extracted from the metal mold | die after injection-molding the worm wheel provided for this embodiment. It is a principal part perspective view of the metal core which shows 2nd Embodiment. 1 is an overall perspective view of an electric power steering apparatus to which a worm wheel of an embodiment is applied. It is principal part sectional drawing of the same electric power steering device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Steering wheel 3 ... Steering shaft 5 ... Worm wheel 6 ... Worm shaft 8 ... Electric motor 19 ... Core metal 20 ... Wheel tooth part 20a, 20b ... Tooth side surface (meshing part)
21 ... Core metal body 22 ... Tooth core part 22 ... Both ends 23 ... Escape part 24 ... Tooth base 30 ... Injection mold

Claims (2)

A cored bar body formed of a metal material;
Tooth core portion integrally provided on the outer peripheral surface of the core metal body, and provided at a plurality of equally spaced positions in the circumferential direction;
A worm wheel structure provided on the outer periphery of the metal core body so as to cover the tooth core part, and provided with a wheel tooth part of a synthetic resin material meshing with the worm shaft,
While the tooth core portion is formed to extend substantially linearly along the rotational axis direction of the worm wheel,
A worm wheel structure in which the wheel tooth portion is formed in a helical shape inclined with respect to the axial direction. A steering shaft connected to the steering wheel;
A worm wheel coupled to the steering shaft and having a plurality of teeth formed on the outer periphery;
A worm shaft meshing with the worm wheel;
An electric motor provided on the worm shaft for applying a steering assist force to the steering shaft via the worm shaft and the worm wheel;
An electric power steering apparatus comprising: motor control means for controlling the electric motor based on an output signal of a steering state detection means provided on the steering shaft;
The worm wheel,
A cored bar body formed of a metal material;
Tooth core portion integrally provided on the outer peripheral surface of the core metal body, and provided at a plurality of equally spaced positions in the circumferential direction;
It is provided on the outer periphery of the core metal main body so as to cover the tooth core part, and is constituted by a wheel tooth part formed of a synthetic resin material,
While the tooth core portion is formed to extend substantially linearly along the rotational axis direction of the worm wheel,
An electric power steering apparatus characterized in that the wheel tooth portion is formed in a helical tooth shape inclined with respect to the axial direction.

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