JP2010139041A - Synthetic resin gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly accurate synthetic resin gear exhibiting enhanced accuracy in molding a tooth, especially accuracy in a tooth width direction center part in a synthetic resin gear wherein an insert member having a recessed groove on an outer peripheral surface is integrated with a tooth part by insert injection molding. <P>SOLUTION: In the synthetic resin gear 1 wherein the tooth part 2 having a plurality of teeth 21 in a shape of a spur gear or a helical gear and the insert member 4 are integrated by injection molding, the recessed groove 41 extended to a direction connecting both end surfaces of the gears is formed on an outer peripheral surface of the insert member 4, a tooth trace direction of the tooth and a direction of the recessed groove of the insert member mutually cross with a prescribed angle in a view from a radial direction, and in a cross section in the tooth width direction center part of the gear, the recessed groove 41 of the insert member is almost coincident with a tooth bottom 21a of the tooth part in a circumferential position. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a synthetic resin gear used for office automation equipment. In particular, the present invention relates to a synthetic resin gear that is insert injection molded so that an insert member is integrated with a central shaft portion of the synthetic resin gear.

In recent years, disk-shaped synthetic resin molded products such as plastic gears and pulleys, which are injection-molded by engineering plastics that are widely used as metal substitutes, are used in copying machines and printing machines. Strict accuracy is required for roundness and runout.
Especially in the case of synthetic resin gears, if the gear accuracy is poor, the positioning accuracy at the time of printing will decrease and the image quality of the printed image will deteriorate, and it will cause abnormal noise when driving the gear. Is required.

In addition, in synthetic resin gears, a metal insert member made of sintered metal or a resin insert member made of high-strength synthetic fiber-containing synthetic resin is used for the gear shaft portion so that it can withstand a strong driving force from the gear shaft portion. However, it is also possible to obtain a synthetic resin gear by integrally molding the insert member and the resin gear portion by insert injection molding. In this case, the outer periphery of the insert member is knurled so as to withstand transmission of the driving force. In many cases, the insert member is firmly integrated in the rotation direction by providing a groove or a ridge.

As a synthetic resin gear in which such an insert member is integrated, Patent Document 1 discloses a resin member in which a tooth portion is formed on the outer periphery of a metal insert member having an uneven cutout (joint portion) on the outer periphery. Is formed by insert injection molding, and the shaft member is press-fitted into the insert member, and the insert member and the resin member are firmly integrated, so that a large driving force can be reliably transmitted. ing.

Further, Patent Document 2 relates to a resin worm wheel in which a metal insert is integrated, and gear teeth are formed on the outer side of a metal insert having a knurled outer periphery by synthetic resin mixed with reinforcing fibers, and further the gear tooth surface. An embodiment is disclosed in which a surface layer is provided that is covered with a synthetic resin that does not contain reinforcing fibers.
Japanese Patent Registration 401 JP-A-2005-214338

However, as described in Patent Document 1, when an insert member having an uneven notch or groove on the outer periphery is integrally formed with a synthetic resin gear, it is synthesized close to the outer peripheral surface of the insert member. In the case where the tooth portion of the resin gear is formed, the accuracy of the gear is sometimes lowered as described below. That is, as shown in FIG. 4, when the tooth portion 90 made of a synthetic resin is insert injection molded on the outer periphery of the insert member 80 having a notch, the tooth 91 of the tooth portion and the notch portion of the insert member (concave groove) ) 81 coincides with the position in the circumferential direction, the amount of molten resin injected in the coincident portion is larger than that in other portions, and the accuracy of the teeth in that portion is likely to deteriorate.

As shown in FIG. 4, in a series of teeth 91, 91..., When teeth that match the notch (concave groove) 81 of the insert member and the circumferential direction are mixed with teeth that are not, teeth 91. , 91... Cause variations in accuracy.

Further, in general, in the gear having the tooth portion 90 formed on the outer periphery of the insert member 80, in the injection process of the insert injection molding, as shown in FIG. Since it is easier to cool than the central portion of the tooth width direction of the portion 90, as shown by the two-dot chain line in the figure, the contraction amount of the central portion of the tooth width direction becomes relatively large, and the tooth width direction of the tooth portion There was a tendency that the accuracy of the central part was likely to decrease.

In view of the above, it is an object of the present invention to increase tooth forming accuracy in a synthetic resin gear in which an insert member having a groove-shaped notch is integrated with a tooth portion by insert injection molding. In particular, an object of the present invention is to provide a highly accurate synthetic resin gear by preventing a decrease in accuracy in the center portion in the tooth width direction.

As a result of intensive studies, the inventor of the present invention has made the groove of the insert member and the tooth stripe direction of the gear intersect at a predetermined angle when viewed from the radial direction, and at the center in the tooth width direction, It has been found that by making the circumferential positions of the bottoms substantially coincide with each other, it is possible to suppress a reduction in the accuracy of the shape of the gear due to the shrinkage of the resin in the groove portion, and to solve the above problems, and the present invention has been completed.

In the present invention, a synthetic resin is injection-molded outside the outer peripheral surface of the insert member to integrally form a tooth portion having a plurality of teeth of a spur gear or a helical gear, and the insert member and the tooth portion are integrated. In the synthetic resin gear, a groove is formed on the outer peripheral surface of the insert member so as to extend in the direction connecting the both end surfaces of the gear, and the tooth streak direction and the direction of the groove of the insert member have a radius. In the cross-section at the center of the gear in the tooth width direction, the groove of the insert member substantially coincides with the tooth bottom of the tooth at the circumferential position. A synthetic resin gear characterized by being configured as described above.

In the synthetic resin gear, it is preferable to further provide the same number of grooves as the number of teeth of the tooth portion (Claim 2), or when the grooves of the insert member are viewed from the radial direction, It is preferable not to exceed the tooth tip adjacent to the intersecting tooth bottom (claim 3).

According to the synthetic resin molded product of the present invention, at the central portion in the tooth width direction, even if the resin injected into the concave groove portion contracts, it is suppressed from causing a decrease in tooth shape accuracy, and the tooth molding accuracy is increased. Can do.

Further, if the same number of grooves as the number of teeth of the tooth portion is provided (Claim 2), the variation in gear shape accuracy between a series of teeth can be suppressed, and the accuracy of the gear can be further increased.
Further, if the specifications of the tooth part and the concave groove are set so as to satisfy the relationship of claim 3, the tendency of the dimensional error occurrence of the conventional synthetic resin gear that the central part tends to shrink in the tooth width direction is compensated. A highly accurate synthetic resin gear having uniform tooth shape accuracy in the tooth width direction can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a synthetic resin gear 1 according to a first embodiment of the present invention, and a section XX shows a section at the center in the tooth width direction.

The synthetic resin gear 1 is a disc-shaped helical gear, and a plurality of teeth 21 and 21 are provided at a predetermined pitch on the outer periphery thereof, and the teeth 21 and 21 are formed of an annular tooth portion 2. It is integrally formed on the outer periphery. An insert member 4 forming a shaft portion of the gear is integrated with the central portion of the synthetic resin gear 1 by insert injection molding so as to be concentric with the tooth portion 2.

The tooth portion 2 of the synthetic resin gear 1 of the present invention is molded by an injection molding method using an engineering plastic such as a polyacetal resin or a thermoplastic resin such as a polyamide resin.

The insert member 4 is a member formed of a metal material such as a sintered metal or a resin material such as a synthetic resin containing a reinforcing fiber, and is a member formed in a predetermined shape prior to the insert injection molding process. In the present embodiment, the insert member 4 is provided with spur gear-like irregular stripes on the outer periphery thereof at equal intervals in the circumferential direction in the direction connecting the both end faces of the gear. It is made to become the same as the number of teeth of the teeth 21 and 21 provided in. In addition, in the figure of the right side of FIG. 1, the uneven | corrugated strip of the insert member 4 is drawn with the broken line.

In the present embodiment, the teeth 21 and 21 of the tooth portion 2 are formed in a helical gear having a helix angle α, and the concave and convex strips of the insert member 4 are provided in a spur gear shape. The direction of the streaks of the teeth 21 and the direction of the recessed grooves of the insert member 41 are not parallel to each other but are provided so as to intersect at an angle α.

Further, in the synthetic resin gear 1, the groove 41 of the insert member 4 substantially coincides with the tooth bottom 21 a of the tooth portion 2 at the circumferential position in the cross section XX in the center portion in the tooth width direction, and the tooth 21. The tooth tips 21b are provided so as to be shifted from each other in the circumferential direction.

In such a synthetic resin gear 1, an insert member 4 formed in advance is placed and fixed in an injection mold so as to have a predetermined rotational posture, and then a molten resin is injected into the mold. Thus, the tooth portion 2 can be formed around the insert member 4 by so-called insert injection molding.

Hereinafter, the operation and effect of the synthetic resin gear of the present invention will be described.
First, in the synthetic resin gear of the present invention, the insert member 4 and the tooth portion 2 are firmly integrated in the gear rotation direction by the function of the concave groove 41 of the insert member 4, and a large driving force can be transmitted.

Further, by the injection molding method, the molten resin is injected into the cavity of the mold, and the synthetic resin gear 1 (especially the tooth portion 2) of the present invention is manufactured by holding and cooling, but in this embodiment, In the cross section XX at the center in the tooth width direction, the groove 41 of the insert member 4 substantially coincides with the tooth bottom 21a in the circumferential direction, and the tooth tip 21b of the tooth 21 deviates from each other in the circumferential direction. Therefore, even if the molten resin injected into the concave groove portion contracts, the influence on accuracy on the teeth 21 and 21 is reduced. Therefore, according to the present invention, it is possible to suppress a decrease in the accuracy of the teeth 21 due to the groove 41 of the insert member 4 in the center portion in the tooth width direction.

Furthermore, according to the present embodiment, the same number of the grooves 41 and 41 of the insert member as the teeth 21 and 21 of the tooth portion 2 are provided, and the groove 41 has the same positional relationship with respect to all the teeth 21. Since the resin is uniformly cooled and contracted between the series of teeth 21, 21, the variation in accuracy between the teeth 21, 21 is reduced, and the synthetic resin has higher accuracy. It is more preferable in obtaining a gear.

Other embodiments are shown below.
FIG. 2 is a view showing a synthetic resin gear 5 according to a second embodiment of the present invention. Similarly, the XX section shows a section at the center in the tooth width direction. In the description of the present embodiment, the description will mainly focus on parts that are different from the first embodiment, and description of the parts that are the same will be omitted.

In the present embodiment, the tooth portion 6 of the synthetic resin gear 5 is formed as a spur gear, and the outer peripheral surface of the insert member 7 is provided with grooves 71 intermittently spaced apart from each other in the circumferential direction. The groove 71 is provided in a helical shape so as to form a twist angle β.

Furthermore, also in the present embodiment, in the cross section XX in the center portion in the tooth width direction of the gear 5, the concave groove 71 substantially coincides with the tooth bottom 61 a of the tooth portion 6 at the circumferential position, and the tooth tip of the tooth 61. 61b is provided so as to be shifted from each other in the circumferential direction. Also in the present embodiment, the insert member concave groove 71 that is likely to affect the forming accuracy of the teeth 61, 61 is provided at the central portion in the tooth width direction so as to avoid the teeth 61, 61. The reduction in molding accuracy of the teeth 61 and 61 due to the shrinkage of the existing resin is suppressed, and the accuracy of the gear can be improved as in the first embodiment.

Although the embodiments of the present invention have been described above, the present invention can be implemented with the following modifications.

In the above-described embodiment, an example in which the gear tooth direction of the gear and the direction of the groove of the insert member are one spur gear and the other is a helical gear is described. However, the present invention is limited to this. The groove of the insert member is provided in the direction connecting the both end faces of the gear (for example, so as to form an angle of about 0 to 30 degrees with respect to the gear rotation axis). The present invention can be applied as long as the direction of the groove of the member is a gear that is oriented at a predetermined angle when viewed from the radial direction. For example, the direction of the tooth stripe of the gear and the direction of the groove of the insert member The direction includes the helical gears having different twist angles.

Furthermore, in the present invention, it is more preferable to determine the tooth stripe direction of the gear and the direction of the concave groove 41 of the insert member so as to satisfy the following relationship. In FIG. 3, which is a schematic diagram viewed from the radial direction for explaining the relationship, the tooth bottom 21 a, the tooth tip 21 b, and the groove 41 are expressed by solid lines or broken lines, respectively.
As shown in FIG. 3, when the tooth tooth direction of the gear and the direction of the groove of the insert member are viewed from the radial direction, the groove 41 intersects with the tooth bottom line 21 a only at the center in the tooth width direction, It is preferable not to intersect with the adjacent tooth bottom line 21a. Such an angular relationship is that the twist angle of the tooth 21 is α, the twist angle of the groove 41 is β, the pitch circle diameter of the tooth 21 is D1, the number of teeth is Z, the tooth width is W, and the outer diameter of the insert member 4 is When it is set to D2, it is implement | achieved by determining the tooth | gear tooth | gear direction (twisting angle (alpha)) of a gearwheel, and the direction (twisting angle (beta)) of the groove of an insert member so that Numerical formula 1 shown below may be satisfied.

(Formula 1)

In this way, when the tooth 21 is viewed in the tooth stripe direction, it does not cross the concave groove many times, and the molding accuracy is prevented from changing in the tooth stripe direction, which is effective in improving the gear accuracy. is there.

More preferably, when the tooth tooth direction of the gear and the direction of the groove of the insert member are viewed from the radial direction, the groove 41 intersects the tooth bottom line 21a at the center in the tooth width direction and the adjacent tooth tip. It is preferable not to cross the line 21b. Such an angular relationship is realized by determining the gear tooth line direction (twist angle α) and the direction of the concave groove of the insert member (twist angle β) so as to satisfy Formula 2 shown below.

(Formula 2)

If it does in this way, in the tooth width direction center part, the circumferential direction position of the ditch | groove 41 will substantially correspond with the tooth bottom 21a, and the circumferential direction position of the ditch | groove 41 will be set to a tooth | gear as it goes to an edge part from a tooth width direction center. From the bottom 21a, it is possible to gradually change in a direction that coincides with the tooth tip 21b in the circumferential direction. The tooth 21 can be greatly affected as it goes. Therefore, by adopting such a configuration, the shrinkage of the resin forming the teeth 21 and 21 is suppressed in the center portion in the tooth width direction, and the shrinkage suppressing action is lost toward the end portion in the tooth width direction. , The contraction tendency of the center portion of the tooth width as shown by a two-dot chain line in FIG. 5 can be compensated, the tooth shape can be made uniform in the tooth width direction, and the tooth shape accuracy can be further improved. Can do.

In the description of the above embodiment, an example in which the synthetic resin gear is disk-shaped has been shown. However, the present invention is limited to a disk-shaped gear having a relatively small axial thickness compared to the diameter of the outer circumferential circle. The present invention also includes a synthetic resin gear having a shape (so-called cylindrical shape) in which the axial thickness is relatively larger than the diameter of the outer circumference circle. In particular, the present invention can be suitably applied to a synthetic resin gear in which the insert member outer peripheral surface and the teeth are closer to each other than the tooth width and the insert member shape easily affects the accuracy of the teeth.

According to the present invention, a synthetic resin gear in which an insert member is integrally molded can be manufactured by injection molding with high dimensional accuracy.

The figure which shows 1st Embodiment of the synthetic resin gear of this invention. The figure which shows 2nd Embodiment of the synthetic resin gear of this invention. The schematic diagram which shows the relationship between the tooth stripe and the ditch | groove in the synthetic resin gear of this invention. The figure explaining the factor of the precision fall of the conventional synthetic resin gear. The figure explaining the tendency of the precision fall in the conventional synthetic resin gear.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Synthetic resin gear 2 Tooth part 21 Tooth 21a Tooth bottom 21b Tooth tip 4 Insert member 41 Groove 5 Synthetic resin gear 6 Tooth part 7 Insert member 80 Insert member 90 Tooth part

Claims (3)

Synthetic resin is injection-molded on the outside of the outer peripheral surface of the insert member to integrally form a tooth portion having a plurality of spur gears or helical gears, and the insert member and the tooth portion are integrated. In gears,
On the outer peripheral surface of the insert member, a concave groove extending in the direction connecting the both end surfaces of the gear is formed,
The tooth stripe direction of the teeth and the direction of the groove of the insert member are set to intersect each other at a predetermined angle when viewed from the radial direction,
Furthermore, in the cross section in the center part in the tooth width direction of the gear, the synthetic resin gear is characterized in that the concave groove of the insert member substantially coincides with the tooth bottom of the tooth part at the circumferential position. The synthetic resin gear according to claim 1, wherein the same number of concave grooves as the number of teeth of the tooth portion is provided. The synthetic resin gear according to claim 1 or 2, wherein the concave groove of the insert member does not exceed a tooth tip adjacent to a tooth bottom where the concave groove intersects when viewed from the radial direction.

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