JP2010014253A - Steering auxiliary gear for electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering auxiliary gear for an electric power steering device, in which the volume of a core bar part is minimized for weight reduction, only a gear part is formed by thermoplastic resin with favorable workability, and the volume of the thermoplastic resin is reduced to eliminate extra weight, and whose entire strength is secured. <P>SOLUTION: In the electric steering device generating steering auxiliary force from a steering auxiliary motor and transmitting it to an output shaft 13, the steering auxiliary gear (worm wheel) 1 has the core bar part 2 fit together with the output shaft 13, an annulus ring part 3 of thermoplastic resin fixed to an outer circumference of the core bar part 2, and a teeth part 4 of thermoplastic resin fixed to an outer circumference of the annulus ring part 3, and the teeth part 4 is meshed with a driving gear (worm) provided on a rotary shaft driven by the steering auxiliary motor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus, and more particularly to a steering auxiliary gear of a reduction gear mechanism in an electric power steering apparatus provided between a rotating shaft of a steering auxiliary motor and an output shaft of a steering shaft.

  A steering assist mechanism of an electric power steering device for a vehicle has a steering shaft that is divided into an input shaft side and an output shaft side, which are connected via a torsion bar, and provided with a torque sensor mechanism in a gear housing. It has a structure in which the rotating shaft of the motor mounted on the housing and the output shaft of the steering shaft are connected by a reduction gear device of the worm and worm wheel, and the output and rotating direction of the motor are controlled by the torque detection signal from the torque sensor mechanism. By controlling, steering assist of the steering wheel is performed.

  In order to reduce the weight of the worm wheel used in the reduction gear device of this electric power steering device to reduce the steering inertia force and to suppress the generation of noise due to the meshing of the gear, a worm wheel made of a synthetic resin is known. (Patent Documents 1 and 2).

Patent Document 1 discloses a worm wheel in which an annular tooth body made of a thermosetting synthetic resin in which a ring-shaped aramid fiber is filled on the outer periphery of a fitting body with a shaft portion is fixed as a steering assist gear in an electric steering apparatus by molding. Is described. Patent Document 2 describes a worm wheel in which a synthetic resin tooth portion is fixed to the outer periphery of a metal fitting portion that is similarly fitted to a shaft body, and the fitting portion and the tooth portion are fixed. In order to make it stronger, one end of the fitting portion is extended to the outer peripheral side in the radial direction, the extended end portion is further bent into a plurality of L shapes, and a synthetic resin material is fixed to the outer peripheral portion of the bent portion. As a part.
Japanese Patent No. 3496119 (Japanese Patent Laid-Open No. 2002-39329) Japanese Patent No. 3698605 (Japanese Patent Laid-Open No. 2001-206230)

  In this type of electric power steering device, the worm wheel fixed to the output shaft needs to be reduced in weight in order to reduce the inertial force during steering as much as possible to improve the steering performance, and at the same time sufficient strength must be ensured. Don't be. For this reason, as described in Patent Documents 1 and 2, only the core metal part is made of metal and the outer periphery thereof is formed of a synthetic resin material up to the tooth part. Because the direct synthetic resin tooth part is formed by injection molding, if you try to mold with good precision with less waste, it is necessary to extend the cored bar part near the bottom of the tooth part. Even if it is omitted, the metal cored bar portion is basically small and does not reduce the weight.

  In Patent Document 2, in order to ensure the strength of the worm wheel, a part of the cored bar is elongated to the outer peripheral side, and a thermosetting resin material is fixed to the tip to form a tooth part. Although satisfactory in terms of heat resistance and strength, the problem is that the processability is poor because the teeth are formed in the thermosetting resin part, accurate tooth parts are difficult to obtain, and the weight reduction is not sufficient. There is.

  In view of such circumstances, the present invention aims to reduce the volume of the cored bar as much as possible to reduce the weight, and to form only the tooth part with a thermoplastic resin having good workability. The present invention provides a steering assist gear of an electric power steering apparatus that has a reduced volume to eliminate waste and that has ensured the overall strength.

  In order to achieve the above object, a steering auxiliary gear of an electric power steering apparatus according to claim 1 of the present invention is the electric power steering apparatus that generates a steering auxiliary force from a steering auxiliary electric motor and transmits the steering auxiliary force to an output shaft. A core metal part fitted to the shaft, an annular part of a thermosetting resin material fixed to the outer periphery of the core metal part, and a tooth part of a thermoplastic resin material fixed to the outer periphery of the annular part; And the tooth portion meshes with a drive gear provided on a rotating shaft driven by the steering auxiliary electric motor.

  Further, in the steering assist gear of the electric power steering apparatus according to claim 2 of the present invention, the core metal part has an overhang part provided with an uneven groove, and the annular part has an outer peripheral edge provided with an uneven groove. The annular portion is fixed to the core metal portion by insert molding so as to embed the overhang portion of the core metal portion, and the tooth portion is injection molded so as to embed the outer peripheral edge of the annular portion. It is fixed to the outer peripheral edge of the annular portion.

  According to a third aspect of the present invention, there is provided a steering assist gear of the electric power steering apparatus according to the present invention, wherein the steering assist gear is fitted to the output shaft and provided on the rotating shaft of the steering assist motor. A worm wheel that meshes with each other.

  According to a fourth aspect of the present invention, there is provided an electric power steering apparatus having the steering assist gear.

  According to the present invention, only the tooth part is formed of a thermoplastic resin having a small volume, the volume of the cored bar part is also reduced, and a high-strength thermosetting property is provided between the toothed part and the cored bar part. Since they are connected by a resin material, a steering assist gear excellent in weight reduction, high workability and high strength reliability can be obtained.

  Hereinafter, a steering assist gear of an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a perspective view showing a worm wheel which is a steering assist gear of the electric power steering apparatus according to the first embodiment of the present invention in a partially cut state, and FIG. 2 is a longitudinal sectional view of the worm wheel shown in FIG. It is. The worm wheel 1 is fixed to a core metal part 2 fitted to an output shaft of an electric power steering device to be described later, an annular part 3 fixed to the outer periphery of the core metal part 2, and an outer periphery of the annular part 3. It is comprised with the tooth part 4 which is.

  First, the cored bar portion 2 is made of metal, and has an inner diameter portion 5 formed with a predetermined fitting tolerance with respect to the output shaft, and a radially outward radial direction from the outer peripheral surface of one end portion in the axial direction slightly toward the inner side in the axial direction. A flange-like overhanging portion 6 is formed, and an uneven portion 7 as clearly shown in FIG. 1 is formed on the outer peripheral portion of the overhanging portion 6. In this embodiment, as shown in FIG. 2, the tip portion 6a of the overhang portion 6 is bent in the radial direction and slightly extended outward in the radial direction. In the embodiment shown in FIG. 2, the length from the inner diameter portion of the cored bar portion 2 to the outer peripheral portion (including the overhang portion) is about 30% of the distance from the inner diameter portion to the outer peripheral portion of the entire worm wheel. Further, the radial length of the annular portion 3 is about 60% of the length from the inner diameter portion to the outer peripheral portion of the worm wheel 1, and therefore the volume of the core metal portion 2 is compared with the volume of the entire worm wheel. The volume is very small.

The annular portion 3 is formed of a thermosetting resin material and is fixed to the outer peripheral portion of the cored bar portion 2. The annular portion 3 is formed on the outer periphery of the core metal portion 2 by insert molding so that the entire overhang portion 6 is embedded in the resin of the annular portion 3 from the outer peripheral surface of the core metal portion 2. As the thermosetting resin, a resin having high strength and generating less gas during molding is selected. Examples of the thermosetting resin include phenol resin, melamine resin, cross-linked polyester amide, and epoxy resin. Further, these resins are used in a form reinforced with fibers (for example, reinforced with aramid, carbon, glass, etc.).
In addition, the surface 3a on one side of the annular portion 3 is formed to be a concave surface to some extent due to the mounting space to the output shaft described later, except for the base portion 3b and the outer peripheral edge 3c portion on the center side. ing. A plurality of concave and convex portions 8 are formed on the outer peripheral edge 3 c of the annular portion 3.

  The tooth part 4 of the worm wheel fixed to the outer periphery of the annular part 3 is formed of a thermoplastic resin material. In this case, it is formed so as to be integrated with the annular portion 3 by injection molding so that the concavo-convex portion 8 at the outer peripheral edge portion of the annular portion 3 is embedded in the tooth resin. The volume of the tooth portion 4 may be a volume within a range in which the strength of the tooth portion 4 can be secured and the tooth surface 4a of the gear can be formed on the outer periphery, and the overall size of the worm wheel is mainly the size of the annular portion 3. It is determined by As the thermoplastic resin, one having good cutting workability is selected.

  After the core part 2, the ring part 3 and the tooth part 4 are integrated as described above, a gear tooth surface 4a necessary as the worm wheel 1 is formed on the outer periphery of the tooth part 4 by cutting. The thermosetting resin of the annular portion 3 has a higher strength than the thermoplastic resin of the tooth portion 4 and sufficiently exhibits the function as the core metal structure of the worm wheel 1. Moreover, since it is excellent also in heat resistance, even when the thermoplastic resin of the tooth part 4 is injection-molded, there is no trouble such as the influence of heat.

  As described above, in the present invention, only the portion that fits with the shaft body is made of the metal core 2 and the majority of the volume of the worm wheel 1 is made of synthetic resin, so that the weight can be reduced. Furthermore, unnecessary extra meat can be suppressed by using a thermosetting resin with high strength and less gas generation during molding of the outer peripheral portion of the cored bar portion 2. Good processability can be obtained by making the tooth part 4 made of a thermoplastic resin, and by making only the tooth part 4 a thermoplastic resin, the volume of the thermoplastic resin can be reduced. Generation of voids can be suppressed. By setting it as the above structures, the worm wheel which improved weight reduction, workability, and intensity | strength reliability can be obtained.

[Second Embodiment]
Next, the main structure of the electric power steering apparatus employing the worm wheel according to the present invention will be described with reference to FIG. In FIG. 3, a sensor yoke 11 of a torque detection device, a sensor coil 12, a sensor substrate, a sleeve, and the like are mounted on the inner peripheral portion of the gear housing 10, and a hollow output shaft 13 is connected to the inner diameter portion via bearings 14 and 15. It is inserted so that it can rotate but cannot move in the axial direction. A torque detection groove 16 is formed on the outer periphery of the output shaft 13 at a position facing the sensor yoke 11. A sensor-side shaft 17 is connected to a vehicle front side end portion of a steering shaft (not shown) connected to the steering wheel. A vehicle front side base portion 17a of the sensor side shaft 17 is housed in the gear housing 10, and an output shaft 13 is joined to an end surface concave portion of the base portion so as to be relatively rotatable, and a vehicle rear side end portion of the torsion bar 18 (steering wheel) Side) is fixed by spline press-fitting.

  The torsion bar 18 is inserted into the hollow portion of the output shaft 13, and the vehicle front side end portion thereof is fixed to the vehicle front side end portion of the output shaft 13 by a fixing pin 19. The tip of the output shaft 13 is connected to a steering device (not shown). One end of a column 20 that covers the sensor side shaft 17 and the steering shaft is fixed to the vehicle rear side end of the gear housing 10. A steering assist motor (not shown) is attached to the gear housing 10, and a worm 22 is fixed to the motor rotation shaft 21 in the gear housing 10. A worm wheel (steering auxiliary gear) 1 according to the present invention shown in FIGS. 1 and 2 is fixed to the output shaft 13 so as to mesh with the worm 22.

The steering operation of the steering wheel of the electric power steering device is transmitted from the sensor side shaft 17 of the steering shaft to the steering device via the torsion bar 18 and the output shaft 13, and the turning operation of the wheel is performed by the operation of this steering device. The
In the steering operation of the vehicle, when an excessive turning load from the wheel side is applied to the output shaft 13, the steering torque is detected by the torque sensor mechanism based on the torsional displacement of the torsion bar 18, and the detection signal from the sensor coil 12 is detected. Based on this, the rotation amount and direction of the electric motor are controlled so as to eliminate the torsional displacement of the torsion bar 18 based on this, and the worm 22 on the motor rotation shaft and the worm on the output shaft side are controlled. An appropriate steering assist force is applied to the output shaft 13 via the wheel 1.

  As described with reference to FIGS. 1 and 2, the worm wheel 1 fixed to the output shaft 13 is formed only of a fitting portion to the output shaft 13 from metal, and most of the entire worm wheel is formed of synthetic resin. Therefore, it is extremely lightweight, and the load on the steering assist motor is reduced accordingly, and the inertial force of the worm wheel 1 during steering is reduced, and a good steering feeling can be obtained. In addition, since most of the volume of the synthetic resin portion other than the fitting portion with the output shaft 13 is formed of a high-strength thermosetting resin, the same strength as a conventional metal worm wheel is ensured, Since the coupling between the cored bar 2 and the annular part 3 and the coupling between the annular part 3 and the tooth part 4 are also performed by embedding the resin material in the concave and convex grooves of the counterpart member, these parts are operated during operation. Therefore, there is no possibility of causing a deviation in the rotation direction, and there is an effect that the steering assist gear becomes highly reliable.

It is the perspective view shown in the state where a worm wheel used as the steering auxiliary gear of the electric power steering device by a 1st embodiment of the present invention was partially cut. It is a longitudinal cross-sectional view of the worm wheel shown in FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing a main part structure of an electric power steering device employing a worm wheel according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Worm wheel 2 Core part 3 Ring part 4 Tooth part 6 Overhang part 7,8 Uneven part 10 Gear housing 13 Output shaft 17 Sensor side shaft 18 Torsion bar 21 Motor rotating shaft 22 Worm

Claims (4)

  In an electric power steering apparatus that generates a steering assist force from a steering assist motor and transmits the generated steering assist force to an output shaft, a core metal portion fitted to the output shaft, and a thermosetting resin material fixed to an outer periphery of the core metal portion And a tooth portion of a thermoplastic resin material fixed to the outer periphery of the annular portion, and the tooth portion meshes with a drive gear provided on a rotating shaft driven by the steering auxiliary motor. A steering assisting gear for an electric power steering apparatus.   The cored bar has an overhanging part with an uneven groove, the annular part has an outer periphery with an uneven groove, and the annular part embeds the overhanging part of the cored bar part 2. The method according to claim 1, wherein the core portion is fixed to the core portion by insert molding, and the tooth portion is fixed to the outer peripheral portion of the annular portion by injection molding so as to embed the outer peripheral portion of the annular portion. A steering auxiliary gear of the electric power steering apparatus according to the description.   3. The electric power according to claim 1, wherein the steering auxiliary gear is a worm wheel that is fitted to the output shaft and meshes with a worm provided on the rotating shaft of the steering auxiliary electric motor. Steering assist gear of the steering device.   An electric power steering apparatus comprising the steering assist gear according to any one of claims 1 to 3.

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