JP2009041595A - Resinous worm wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable molding, and to keep high rotation accuracy and strength as a worm wheel. <P>SOLUTION: When assuming a half of a difference thickness of the maximum wall thickness and the minimum wall thickness of a tooth thickness of a single tooth in an ordinary worm wheel as T, and a difference height between the maximum height and the minimum height of a tooth bottom surface as H, an under cut portion wherein a half (t) of the difference thickness between the maximum wall thickness and the minimum wall thickness of the tooth thickness of the tooth bottom surface and the difference height (h) between the maximum height and the minimum height of the tooth bottom surface is in a range of t≤0.2T and h≤0.2H at least at the end on a remote side from a mold parting surface is provided. Forced extraction from a mold is enabled, and the strength of the single tooth can be kept. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a resin worm wheel used for a speed reduction mechanism of an electric power steering apparatus.

  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

  This invention is made | formed in view of the said situation, and makes it a subject which should be solved while making mold shaping possible and maintaining high rotation precision and intensity | strength as a worm wheel.

  The resin worm wheel of the present invention that solves the above problems is characterized in that at least the outer peripheral part is made of resin and is molded by a mold, has a curved tooth side surface and a curved tooth bottom surface, and teeth from both ends toward the center part. A worm wheel made of resin having a substantially single-tooth shape with a gradually decreasing thickness, wherein T is half of the difference between the maximum thickness and the minimum thickness of the single tooth thickness in a general worm wheel, When the difference between the maximum height and the minimum height of the root surface is H, at least at the end far from the split surface, half the difference between the maximum thickness and the minimum thickness of the single tooth thickness ( t) and the difference height (h) between the maximum height and the minimum height of the root surface is that there is an undercut portion in the range of t ≦ 0.2T and h ≦ 0.2H.

  More preferably, the undercut portion is in a range of 0.1T ≦ t ≦ 0.2T and 0.1H ≦ h ≦ 0.2H.

  According to the resin worm wheel of the present invention, by having the undercut portion according to claim 1, it is possible to forcibly remove from the mold, mold forming is possible, and conventional machining is unnecessary. It becomes. Since the tooth surfaces other than the undercut portion are in line contact with the worm gear, the rotation accuracy of the worm gear device can be maintained high. By the way, if t and h are zero, the undercut is eliminated.

  Moreover, if the dimensions of the undercut portion are in the range of 0.1T ≦ t ≦ 0.2T and 0.1H ≦ h ≦ 0.2H, the strength of the single tooth can be made sufficient and the life can be extended. .

  In the present invention, the tooth thickness refers to the thickness of a single tooth in the circumferential direction of the worm wheel (thickness in the direction orthogonal to the axial direction), and the tooth bottom refers to the bottom surface of the tooth gap between the single teeth. .

  The worm wheel of the present invention meshes with the worm and changes the rotation axis in a direction intersecting 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 worm wheel is defined as a tooth line inclined with respect to the axial direction of the worm wheel, and a tooth side surface and a tooth bottom surface are curved along the worm. That is, it has a substantially tooth-shaped single tooth having a curved tooth side surface and a curved tooth bottom surface, and the tooth thickness gradually decreases from both ends toward the center.

  In the worm wheel of the present invention, half of the difference between the maximum thickness and the minimum thickness of the single tooth thickness in the conventional worm wheel is T, and the difference height between the maximum height and the minimum height of the root surface is H. When this is done, at least half of the difference between the maximum thickness and the minimum thickness of the tooth thickness of the single tooth at the end in the die-cutting direction (t), and the difference height between the maximum height and the minimum height of the tooth bottom (h) Have undercut portions in the range of t ≦ 0.2T and h ≦ 0.2H.

  That is, in the conventional worm wheel, the end portion of the single tooth protrudes toward the tooth gap by the dimension T, and the end portion of the tooth bottom also rises from the center portion by the dimension H. Therefore, the part becomes undercut, and die cutting cannot be performed, so that single teeth have to be formed by machining.

  However, according to the worm wheel of the present invention, although the undercut portion exists, the projecting dimension (t) toward the tooth gap is 0.2 T or less, and the raised dimension (h) of the tooth bottom is 0.2 H or less. Therefore, it is possible to forcibly remove from the mold and mold forming becomes possible.

  If the dimensions of t and h are zero, the undercut is eliminated and there is no hindrance to mold forming. However, it is conceivable that the root surface becomes too low and the height of the single tooth becomes high, and the stress acting on the root of the single tooth becomes large, causing a problem in strength. Therefore, it is desirable to set the ranges of 0.1T ≦ t ≦ 0.2T and 0.1H ≦ h ≦ 0.2H. By doing in this way, the intensity | strength of a single tooth improves.

  The undercut part said to this invention is formed in the edge part at the side far from a mold parting surface at least. For example, if one end surface in the axial direction of the worm wheel is a parting surface, the undercut portion is formed at least at the other end portion in the axial direction. In this case, you may form an undercut part in both ends. Further, when the parting surface is the central part in the axial direction of the worm wheel, the undercut parts need to be formed at both ends in the axial direction. Furthermore, when the mold parting surface is between the central part in the axial direction and one end face, the end part on one end face side close to the parting face may be 0.2T <t or 0.2H <h. It is necessary to form an undercut portion in the range of t ≦ 0.2T and h ≦ 0.2H at the end portion on the other end surface side far from the mold parting surface.

  Hereinafter, the present invention will be specifically described with reference to conventional examples and examples.

(Conventional example)
FIG. 1 shows a conventional worm wheel 100. The worm wheel 100 includes a plurality of single teeth 101 as worm teeth. As shown in FIG. 2, the single teeth 101 are inclined with respect to the axial direction, and a tooth gap 102 is formed between the single teeth 101.

  The single tooth 101 has a substantially drum shape in which the tooth side surface has a curved surface shape and the tooth thickness gradually decreases from both ends toward the center. At both ends in the axial direction, the tooth side surfaces protrude toward the tooth gap 102 by half (T) of the difference between the maximum thickness and the minimum thickness of the single teeth 101.

  Further, the bottom surface (tooth bottom surface 103) of the tooth gap 102 has a circular arc shape as shown in FIG. 3, and both end portions in the axial direction of the worm wheel 100 are higher than the center portion by a height (H). . Therefore, when trying to mold this worm wheel 100 with the mold split surface (PL) set to one end face, the hatched area shown in FIGS. It is difficult to do.

Example 1
The worm wheel 1 of the present embodiment whose cross section is shown in FIG. 4 is made of a metal fitting member 10 having a perforated disk shape and a fiber reinforced resin integrally formed on the outer peripheral edge of the fitting member 10. And a tooth portion 11. The worm wheel 1 is manufactured by insert molding in which the tooth portion 11 is molded in a state where the fitting member 10 is disposed in the mold.

  As shown in FIG. 5, the tooth portion 11 of the worm wheel 1 includes a plurality of single teeth 12 that are inclined with respect to the axial direction and arranged at equal intervals in the circumferential direction, and teeth between adjacent single teeth 12. Grooves 13 are formed. The single tooth 12 has a curved surface having a circular arc cross section, and the tooth bottom surface of the tooth gap 13 is formed as a concentric curved surface having a slightly larger diameter than the circle corresponding to the outer diameter of the worm.

  In FIG. 6, the front view which looked at the tooth | gear part 11 from the outer peripheral side is shown. The tooth portion 11 is formed by setting the mold dividing surface (P.L.) to the one end surface 14 in the axial direction. The single tooth 12 has a substantially drum shape when viewed from the front, has a large tooth thickness portion 21 with the largest tooth thickness on the one end face 20 side, and a small tooth thickness portion 22 with the smallest tooth thickness in the central portion in the axial direction. The tooth thickness gradually decreases from the large tooth thickness portion 21 toward the small tooth thickness portion 22, and the tooth side surface is a concave curved surface having an arcuate cross section. From the small tooth thickness portion 22, the tooth thickness gradually increases toward the other end surface 23, and a curved surface portion 24 is formed in which the tooth side surface is a concave curved surface having an arcuate cross section. A flat portion 25 that is straight and extends in the inclination direction of the single tooth 12 is continuous with the other end surface 23.

  Half the difference T between the maximum thickness and the minimum thickness of the single tooth 12 (T = 1.2 mm) is drawn from the small tooth thickness portion 22 in the inclined direction of the single tooth 12, and the tangent Expressed by the distance from the intersection with the one end face 20 to the intersection between the tooth side face and the one end face 20, or the distance from the intersection between the tangent line and the other end face 23 to the intersection between the extension line of the tooth side face and the other end face 23 .

  Half (t) of the difference between the maximum thickness and the minimum thickness of the single tooth 12 on the other end face 23, that is, half the difference between the thickness of the flat portion 25 and the thickness of the small tooth thickness portion 22. (T) has a relationship of t = 0.2T. Therefore, when the die is cut from the other end surface 23 side, the tooth side surface of the single tooth 12 becomes an undercut portion having a thickness t = 0.2 T on one side, but this is an undercut that can be forcibly removed.

  FIG. 7 shows a cross-sectional view of the tooth portion 11 cut along a plane perpendicular to the axis at the center of the tooth gap 13. The tooth bottom surface of the tooth gap 13 gradually decreases in height from one end surface 20, and forms a concave curved surface having a circular arc shape in which the height gradually increases again from the central portion corresponding to the small tooth thickness portion 22. A second flat surface portion 26 is formed on the other end surface 17 side as a flat surface.

  Here, the difference height between the maximum height and the minimum height of the tooth bottom surface on the one end face 20 is defined as H. That is, the intersection of the extension line of the root surface from the central portion corresponding to the small tooth thickness portion 22 and the other end surface 23, and the intersection point of the tangent to the tooth bottom surface in the central portion corresponding to the small tooth thickness portion 22 and the other end surface 23 Is H (H = 2.4 mm). Then, the height difference (h) between the height of the tooth bottom surface at the other end surface 23 and the height of the tooth bottom surface at the central portion corresponding to the small tooth thickness portion 22 has a relationship of h = 0.2H. Therefore, when the die is cut from the other end face 23 side, the tooth bottom surface becomes an undercut portion having a height h = 0.2H, but this is an undercut that can be forcibly removed.

  Therefore, the worm wheel of the present embodiment can form the tooth portion 11 including the single tooth 12 and the tooth gap 13 by molding. Then, the tooth thickness on the other end face 23 side becomes thicker than that in the case of t = 0, and the tooth bottom on the other end face 23 side becomes higher than in the case of h = 0. Further, since the tooth portion 11 is basically a worm tooth portion, the range of line contact with the worm is large. Therefore, the strength of the single teeth 12 is improved and the durability during use is improved.

(Example 2)
8 and 9 are enlarged views of the main part of the worm wheel of the present embodiment. In this embodiment, the parting surface (PL) is set at the center in the axial direction. Therefore, similarly to the other end surface 23 side in the first embodiment, an undercut portion having a thickness t = 0.2 T is formed on one side on the one end surface 20 side, and the height h = An undercut portion of 0.2H is formed.

  In the worm wheel of the present embodiment, the molds are punched in both directions from the split surface (P.L.), but can be easily punched by forcible punching.

(Example 3)
A worm wheel similar to that in Example 1 was molded in the same manner as in Example 1 except that the dimension of h was changed at 6 levels from 0 to 0.25 mm. The punching property at that time was investigated, and the results are shown in Table 1. The strength of the single tooth 12 is estimated and shown in Table 1. With respect to the die-cutting property, those that can be punched were evaluated as “good”, and those that could not be punched were evaluated as “x”. In addition, the strength was simulated using a computer and evaluated as ◯ when the strength was sufficient, × when the strength was insufficient, and Δ when the strength was insufficient in some cases.

  From Table 1, it is clear that the range of 0.1H ≦ h ≦ 0.2H is preferable. In addition, when the relationship between t and T was also simulated in the same manner, it was clearly found that the range of 0.1T ≦ t ≦ 0.2T was preferable.

It is sectional drawing of the conventional worm wheel. It is a front view of the tooth surface of the conventional worm wheel. It is an expanded sectional view of the tooth | gear part of the conventional worm wheel. It is sectional drawing of the worm wheel which concerns on one Example of this invention. It is a front view of the tooth surface of the worm wheel which concerns on one Example of this invention. It is an enlarged front view of the tooth surface of the worm wheel which concerns on one Example of this invention. It is an expanded sectional view of the tooth | gear part of the worm wheel which concerns on one Example of this invention. It is a front view of the tooth surface of the worm wheel which concerns on 2nd Example of this invention. It is an expanded sectional view of the tooth surface of the worm wheel concerning the 2nd example of the present invention.

Explanation of symbols

1: Worm wheel 11: Tooth part 12: Single tooth
13: tooth gap 20: one end face 23: other end face
25: Flat part (undercut part)
26: 2nd plane part (undercut part)

Claims (2)

At least the outer peripheral part is made of resin and is molded by a mold, and it has a curved tooth side and a curved tooth bottom, and has a substantially single drum-shaped tooth whose tooth thickness gradually decreases from both ends toward the center. Worm wheel,
When T is half of the difference between the maximum thickness and the minimum thickness of a single tooth in a general worm wheel, and H is the difference between the maximum height and the minimum height of the root surface,
At least at the end far from the parting surface, half the difference between the maximum thickness and the minimum thickness of the tooth thickness of a single tooth (t) and the difference height between the maximum height and the minimum height of the root surface (h ) Has an undercut portion in the range of t ≦ 0.2T and h ≦ 0.2H.   2. The resin worm wheel according to claim 1, wherein the undercut portion is in a range of 0.1T ≦ t ≦ 0.2T and 0.1H ≦ h ≦ 0.2H.

Images