JP2009008201A - Worm gear device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable die forming by eliminating undercut and maintain rotating accuracy as a worm gear device at a high level. <P>SOLUTION: A tooth part of a worm wheel 2 includes a helical tooth part 23 comprising a helical tooth formed on one half side of the cog width and a worm tooth part 24 comprising a worm tooth formed on the other half side of the cog width and having a tooth flank of a curved surface. The worm tooth part 24 has an extension part 25 at least of which tooth flank is extended along a rotation trajectory of a worm 1. Due to the helical tooth part 23, undercut is prevented so as to enable die forming, and due to the extension part 25, a range of linear contact with the worm 1 can be widely secured. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a worm gear structure used for a speed reduction mechanism of an electric power steering device.

  An electric power steering device for an automobile includes a torque sensor that detects a steering torque of a steering wheel by a driver, an electric motor for assisting steering, and a speed reduction mechanism that decelerates the rotation of the electric motor and transmits it to a steering shaft. The steering is assisted by controlling the driving of the electric motor based on the detection signal of the torque sensor.

  As the speed reduction mechanism, a mechanism composed of a worm as a driving gear connected to a rotating shaft of an electric motor and a worm wheel as a driven gear fitted to a steering shaft is widely used. The rotation of the electric motor is decelerated by meshing with the worm wheel and transmitted to the steering shaft.

  By the way, from the viewpoint of reducing the weight of the vehicle body, various gears used tend to be changed from metal to resin. The above-described reduction mechanism is no exception, and the worm and worm wheel are being made of resin. However, the worm wheel has an arc shape along the outer periphery of the worm and the tooth surface is a curved surface having an arc shape, so that it is undercut and difficult to release from the mold. For this reason, teeth are formed by machining after molding, but there is a problem in that the number of man-hours is large.

  Therefore, it is conceivable to use a helical gear instead of the worm wheel. The helical gear has a flat surface parallel to the axial direction of the helical gear, and the tooth surface is also a flat surface. Therefore, the helical gear can be easily manufactured by molding without undercutting, thereby reducing the number of man-hours. It becomes possible.

  However, when a helical gear is used as a substitute for the worm wheel, the contact between each single tooth of the helical gear and the worm is all point contact, and there is a problem that the rotational accuracy of the worm gear device is lowered. .

  Japanese Utility Model Laid-Open No. 04-049254 proposes a worm wheel in which the tooth bottom of one half of the tooth width of the tooth portion is formed parallel to the axial direction. By adopting such a shape, undercut is eliminated, and it becomes possible to manufacture by molding, so that productivity is greatly improved. Moreover, since the opposite half of the tooth width is a worm tooth, it is in line contact with the worm. Therefore, since the range of line contact is larger than when the whole is a helical tooth, it is possible to satisfy the rotation accuracy as a gear to some extent.

  However, in the case of a worm wheel used for a speed reduction mechanism of an electric power steering device, even the worm wheel manufactured by the technique described in the above publication lacks the rotation accuracy as a worm gear device, and further rotation accuracy. Improvement is demanded.

  Moreover, in the worm wheel manufactured by the technique described in the above publication, since the tooth bottom of one half of the tooth width is formed in parallel with the axial direction, the rigidity of each single tooth is lowered. Furthermore, since one side half of the tooth width makes point contact with the worm, the load concentrates on the contact point. Accordingly, there is a possibility that the single teeth are deformed during the rotation, and the rotation accuracy is further reduced.

  In JP-A-2006-290019, helical gears are used in place of the worm wheel, and single teeth adjacent in the circumferential direction are connected via a connecting portion that protrudes to the outer diameter side on one axial side. Proposed. According to the helical gear, since the single teeth are reinforced by the connecting portion, it is possible to withstand the load concentrated on the contact point with the worm.

However, when the helical gear is used, the contact between each single tooth of the helical gear and the worm is all point contact as described above, so that the problem that the rotational accuracy of the worm gear device is lowered is solved. It is difficult.
Japanese Utility Model Publication No. 04-049254 JP 2006-290019 A

  The present invention has been made in view of the above circumstances, and it is an object to be solved to solve the problem of undercut being eliminated and enabling mold forming and maintaining high rotation accuracy as a worm gear device.

A feature of the worm gear device of the present invention that solves the above-mentioned problem is a worm gear device that includes a worm and a resin worm wheel that has at least an outer peripheral portion made of resin and meshes with the worm,
The tooth portion of the worm wheel has a helical tooth portion made of a helical tooth formed on one half of the tooth width, and a worm tooth portion made of a worm tooth having a curved tooth surface formed on the other half of the tooth width. The worm tooth portion has an extension portion in which at least the tooth surface is extended along the rotation trajectory of the worm.

  It is desirable that both the tooth surface and the root of the extension are extended along the rotation path of the worm, and the extension of the tooth bottom connects adjacent tooth surfaces of adjacent teeth.

  According to the worm gear structure of the present invention, the tooth portion of the worm wheel has a helical tooth portion formed of a helical tooth formed on one half of the tooth width. Therefore, even if the other half is a worm tooth portion, it is possible to mold without undercut.

  The tooth portion of the worm wheel according to the present invention includes a worm tooth having a curved tooth surface on the other half of the tooth width, and at least the tooth surface is extended along the rotation locus of the worm. ing. Therefore, a wide range of line contact with the worm can be secured, and the rotation accuracy as the worm gear device can be maintained high.

  If both the tooth surface and the tooth base are extended along the rotation path of the worm, and the tooth root extension is connected to the tooth surfaces of the adjacent single teeth, the single tooth adjacent by the tooth bottom extension is used. Since the teeth are connected to each other, the strength of the single tooth is improved and the strength of the tooth portion is improved. Therefore, the meshing abnormality due to single-tooth bending or the like can be prevented, and problems such as the occurrence of abnormal noise can be prevented.

  As the worm used in the present invention, those conventionally used can be used. It may be made of metal, or may be made of resin, fiber reinforced resin, or the like. In the present invention, the tooth width means the length of a single tooth extending in an inclined direction with respect to the axial direction of the worm wheel. Further, the tooth bottom refers to the bottom surface of the tooth gap between the single teeth, and the tooth surface refers to the side surface of the single tooth rising from the tooth bottom.

  The worm wheel used in the present invention meshes with the worm and changes the rotation axis in a direction crossing the axial direction of the rotation of the worm. As a result, the rotation of the worm wheel is decelerated from the rotation of the worm. This worm wheel can be manufactured from resin by molding. It is desirable to use a fiber reinforced resin.

  The tooth part of the worm wheel is composed of a helical tooth part formed of a helical tooth formed on one half of the tooth width and a worm tooth part formed on the remaining half of the tooth width. In the helical tooth portion, the tooth line is inclined with respect to the axial direction of the worm wheel, and the tooth surface and the tooth bottom are planar. By having this helical tooth portion, undercut is avoided and mold forming becomes possible.

  The worm wheel is defined as a tooth line that is inclined with respect to the axial direction of the worm wheel and at least a tooth surface is a curved surface along the teeth of the worm. Since the pitch circle of the worm teeth becomes the line contact portion, the line contact portion with the worm tooth on the tooth surface becomes a substantially perfect circle when viewed from the direction perpendicular to the tooth surface. Therefore, the shape of the tooth bottom may be a flat surface, but is generally an arc-shaped concave curved surface along the pitch circle.

  The worm tooth portion in the present invention is composed of a worm tooth having a curved tooth surface similar to the above. The tooth bottom may be a plane parallel to the axial direction of the worm wheel, but in that case, the height of the worm tooth is increased by the extension of the tooth surface, and the principle of the tooth base increases the load of the tooth root. Become.

  Therefore, both the tooth surface and the root of the extension part are extended along the worm's rotation trajectory, that is, along the pitch circle of the worm, and the extension part of the tooth base connects adjacent tooth surfaces of adjacent teeth. It is desirable. By comprising in this way, since single teeth are connected by the edge part of a worm tooth part, the rigidity of a single tooth improves. Therefore, deformation is suppressed, and the rotational accuracy of the worm gear device is further improved.

  Hereinafter, the present invention will be described specifically by way of examples.

Example 1
FIG. 1 shows a worm gear device according to an embodiment of the present invention. The worm gear device includes a worm 1 and a worm wheel 2 that meshes with the worm 1. FIG. 2 shows only the worm wheel 2. Both the tooth part of the worm 1 and the tooth part 21 of the worm wheel 2 were manufactured by molding from glass fiber reinforced resin.

  The worm wheel 2 having a cross section shown in FIGS. 3 and 4 includes a metal fitting member 20 having a perforated disk shape, and a tooth portion 21 integrally formed on the outer peripheral edge of the fitting member 20. Become. The worm wheel 2 is manufactured by insert molding in which the tooth portion 21 is molded with the fitting member 20 disposed in the mold.

  The tooth portion 21 of the worm wheel 2 is formed with a plurality of single teeth 22 that are inclined with respect to the axial direction and are arranged at equal intervals in the circumferential direction. The tooth portion 21 includes a helical tooth portion 23 formed of a helical tooth formed on one half of the tooth width, and a worm tooth portion 24 formed of a worm tooth having a curved tooth surface formed on the other half of the tooth width. It is configured. The helical tooth portion 23 makes point contact with the worm 1 at one point on the pitch circle 10 of the worm 1.

  The worm tooth portion 24 has a curved surface with an arcuate tooth surface, and the bottom of the tooth is formed in a concentric curved surface having a slightly larger diameter than the circle corresponding to the outer diameter of the worm 1. At the end of the worm tooth portion 24, an extension portion 25 in which the tooth surface and the tooth bottom are extended along the rotation locus of the worm 1 is formed. The extension portion 25 extends along a circle concentric with the circle corresponding to the outer diameter of the worm 1, and the worm tooth portion 24 and the extension portion 25 have a length close to ¼ of the circumference of the pitch circle 10 of the worm 1. It is comprised so that it may line-contact with. Further, on the end surface of the extension portion 25 opposite to the helical tooth portion 23, a ring-shaped connecting portion 26 is formed by connecting tooth surfaces of single teeth adjacent to the extension portion of the tooth bottom.

  Therefore, according to the worm gear device of the present embodiment, a sufficient length of line contact with the worm 1 can be secured, so that the rotation accuracy as the worm gear device can be maintained high. Further, due to the connecting portion 26, the strength of the single tooth 22 is improved and the strength of the tooth portion 21 is improved. Therefore, the meshing abnormality due to the bending of the single teeth 22 is prevented, the rotation accuracy as the worm gear device is further improved, and problems such as the generation of abnormal noise can be prevented.

  And since there is no site | part which becomes an undercut, the worm wheel 2 can be easily manufactured by mold shaping, and it can be set as an inexpensive worm gear apparatus.

(Example 2)
FIG. 5 shows a cross-sectional view of the worm wheel 3 used in this embodiment. The worm wheel 3 is the same as the first embodiment except that the tooth bottom is flat in the extension portion 35 of the worm tooth portion 34 and the connecting portion 26 is not formed.

  As in the first embodiment, the tooth portion 31 of the worm wheel 3 is formed with a plurality of single teeth that are inclined with respect to the axial direction and are arranged at equal intervals in the circumferential direction. The tooth portion 31 includes a helical tooth portion 33 formed of a helical tooth formed on one half of the tooth width, and a worm tooth portion 34 formed of a worm tooth having a curved tooth surface formed on the other half of the tooth width. It is configured. The lotus tooth portion 33 makes point contact with the worm 1 at one point on the pitch circle 10 of the worm 1.

  The worm tooth portion 34 has a curved surface with an arcuate tooth surface, and the bottom of the tooth is formed as a concentric curved surface having a slightly larger diameter than the circle corresponding to the outer diameter of the worm 1. At the end of the worm tooth portion 34, an extension portion 35 in which the tooth surface is extended along the rotation locus of the worm 1 is formed. The extension portion 25 extends along a circle concentric with the circle corresponding to the outer diameter of the worm 1, and the worm tooth portion 34 and the extension portion 35 have a length close to ¼ of the circumference of the pitch circle 10 of the worm 1. It is comprised so that it may line-contact with.

  According to the worm gear device of the present embodiment, since the connecting portion 26 is not formed, a single-tooth reinforcing effect cannot be obtained. However, the tooth surface of the worm tooth portion 34 has a curved surface as in the first embodiment, and the extension portion 35 has the same tooth surface as that in the first embodiment. The rotation accuracy of the worm gear device can be maintained high.

  The worm gear device according to the present invention has a remarkably increased rotational accuracy as the worm gear device, and is therefore preferably used for a portion requiring high accuracy such as a speed reduction mechanism in a power steering device of an automobile.

It is a perspective view of the worm gear apparatus of one Example of this invention. It is a perspective view of the worm wheel used for the worm gear apparatus of one Example of this invention. It is sectional drawing of the worm gear apparatus of one Example of this invention. It is a principal part expanded sectional view of FIG. It is a principal part expanded sectional view of the worm gear apparatus of the 2nd Example of this invention.

Explanation of symbols

1: Worm 2: Worm wheel 21: Teeth
22: Single tooth 23: Lotus tooth part 24: Worm tooth part
25: Extension 26: Connection

Claims (2)

A worm gear device comprising a worm and a worm wheel made of resin and having at least an outer periphery made of resin and meshing with the worm,
The tooth portion of the worm wheel includes a helical tooth portion formed of a helical tooth formed on one half of the tooth width, and a worm tooth portion formed of a worm tooth having a curved tooth surface formed on the other half of the tooth width. Mochi,
The worm gear device has a worm gear device having an extension portion in which at least the tooth surface is extended along a rotation locus of the worm.   2. The extension portion according to claim 1, wherein both the tooth surface and the tooth bottom are extended along the rotation trajectory of the worm, and the extension portion of the tooth bottom connects adjacent tooth surfaces. The worm gear device described.

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