JPH10205607A - Resin molding gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure high accuracy in the case where the number of gear is few with comparatively small size and a module is comparatively large by arranging a resin filling part formed by a molding die gate of an end surface part of a gear main body having the teeth on an outer periphery, between the roots of two teeth which are adjacent to each other. SOLUTION: A resin filling part 3 is arranged on the intermediate part of the roots of two teeth 4 and 4 which are adjacent to each other, a gear main body 1 is provided with a shaft installing hole 5 penetrating between end surfaces 1a and 1b on its center part, a short projection part 6 is arranged on its end surface part 1a side which is formed in a nearly D-shape. The resin filling part 3 is arranged on a surface of the end surface 1a side of the short projection part 6. Since the resin filling part 3 formed by a gate 2 is arranged between the roots of two teeth 4, 4 which are adjacent to each other and is arranged far from the teeth 4, an influence on the tooth surface of the teeth 4 is suppressed to a minimum by resin flow from the resin filling part 3 at the time of resin molding, and dispersion of a size is prevented from generating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin molded gear having teeth on the outer periphery, and more particularly to a gear structure suitable for a relatively small resin molded gear requiring high precision.

[0002]

2. Description of the Related Art A resin molded gear having a relatively small size, especially a relatively small number of teeth and a relatively large module, generally has
It is difficult to ensure high accuracy. For example, in the case of a small (eg, 1 to several centimeter) resin molded gear with a number of teeth of 20 or less and a module of 0.7 or more, JGMA (Japan Gear Manufacturers Association Standards) double-tooth meshing error can be improved to a molding accuracy of class 3 or higher. It is difficult to secure.

[0003]

SUMMARY OF THE INVENTION The inventor of the present invention has found that one of the main causes of the reduction in molding accuracy of this type of resin molded gear is that the gate position during injection molding is greatly involved. Was found. That is, in general, the resin injection portion from the gate must be close to the teeth in a relatively small resin molded gear, but in the conventional resin molded gear, the resin injection portion from the gate is located radially inward of the tooth root. It has been found that this is the main cause of the decrease in the precision of the resin molded gear, and in particular, causes the peak variation when measuring the meshing error of both tooth surfaces. .

In view of the above problems, an object of the present invention is to provide a resin-molded gear structure which is relatively small in size and has high precision even when the number of teeth is relatively small and the module is relatively large. Is to provide.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a resin molded gear having a resin injection portion formed by a molding die gate on an end surface of a gear body and having teeth on an outer periphery. Wherein the resin injection portion is disposed between the roots of two adjacent teeth.

According to the above configuration, the resin injection portion from the gate is arranged between the roots of two adjacent teeth and is kept away from the tooth, so that the resin flow from the resin injection portion during resin molding is reduced. The influence on the surface is minimized, and the accuracy of the tooth surface is improved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferably, the gear body has a shaft mounting hole penetrating between end faces at the center thereof, and at least a part of the shaft mounting hole in the axial direction has a substantially D-shaped cross section. The resin injection portion is located radially outward of a flat surface portion in the substantially D-shaped cross section of the shaft mounting hole. In this case, since the resin injection portion is located at the intermediate portion between the roots of two adjacent teeth and is located radially outward of the flat surface portion in the substantially D-shaped cross section of the shaft mounting hole and is further away from the teeth, The resin flow from the resin injection section during resin molding minimizes the effect on the tooth surface,
Tooth surface accuracy is improved.

[0008] Preferably, the gear body has a shaft mounting hole at the center thereof penetrating between the end faces, at least a part of the shaft mounting hole in the axial direction has a substantially oval cross section, and The portion is located radially outward of the flat surface portion of the shaft mounting hole in the substantially oval cross section. Also in this case, the resin injection portion is located at the intermediate portion between the roots of two adjacent teeth and is located radially outward of the flat surface portion in the substantially oval cross section of the shaft mounting hole and is further away from the teeth. Therefore, the influence of the resin flow from the resin injection portion on the tooth surface during resin molding is minimized, and the accuracy of the tooth surface is improved.

The gear body has a shaft mounting hole having a circular cross section penetrating between the end surfaces at the center thereof, and the resin injection portion is located radially outward of the shaft mounting hole. Also in this case, the resin injection portion is located at the intermediate portion between the roots of two adjacent teeth radially outward of the shaft mounting hole having a circular cross section and is kept away from the teeth. The influence of the resin flow on the tooth surface is minimized, and the accuracy of the tooth surface is improved.

Preferably, the two resin injection portions are arranged substantially symmetrically with respect to the center axis of the gear body. Also in this case, since each resin injection portion is located at the intermediate portion between the roots of two adjacent teeth, even if the number of teeth is even or odd, the injection from the resin injection portion at the time of resin molding is performed. The effect of resin flow on the tooth surface is minimized. Further, since the two resin injection portions are arranged substantially symmetrically with respect to the center axis of the gear body, the resin molded gear is formed by the balanced resin flow from the two resin injection portions. Therefore, the accuracy of the tooth surface is further improved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention, wherein (a) is a schematic front view of a resin molded gear, and (b)
FIG. 3A is a cross-sectional view taken along line AA in FIG. 3A, and FIG. 3C is a schematic rear view. Referring to FIG. 1, the resin molded gear has a resin injection portion 3 formed by a gate 2 of a molding die on one end surface 1a of a gear main body 1, and has teeth 4, 4,. ··have. As can be seen from FIG. 1 (a), the resin injection portion 3 is disposed between the roots of two adjacent teeth 4 and 4, preferably at an intermediate portion between the two roots.

In the first embodiment, the gear main body 1 has a shaft mounting hole 5 penetrating between the end surfaces 1a and 1b at the center thereof.
A short convex portion 6 is provided on the end surface 1a side of the shaft mounting hole 5 so as to project from the end surface portion 1a toward the end surface portion 1b on both sides of the short convex portion 6. A long convex portion 7 extending longer than the short convex portion 6 is provided so as to protrude. The opening of the shaft mounting hole 5 has a substantially D shape on the end surface 1a side and a circular shape on the end surface 1b side. I have. The resin injection portion 3 is arranged on the surface of the short convex portion 6 on the side of the end surface 1a.

Therefore, in the resin-molded gear having the above-described structure, the resin injection portion 3 formed by the gate 2 is disposed between the roots of two adjacent teeth 4 and 4 and is kept away from the teeth 4. Resin injection part 3 during resin molding
The influence of the resin flow from the surface of the tooth 4 on the tooth surface is minimized. In particular, the resin injection portion 3 is
Since it is located at the intermediate portion between the roots of the two teeth 4 and 4 and is located on the surface on the end surface 1a side of the short convex portion 6 protruding into the shaft mounting hole 5, it is further away from the tooth. Has become.

FIG. 7 (a) shows a measurement result of a meshing error of both tooth surfaces in the resin molded gear of the first embodiment of the present invention, and FIG. It is each showing the tooth surface meshing error measurement result.
Referring to the figure, in the resin molded gear of the comparative example, a peak-shaped dimensional variation portion E occurs on the tooth surface near the tooth bottom near the resin injection portion. It can be seen that such a peak-shaped dimensional variation portion is prevented from being formed in the formed gear. The resin molded gear of the comparative example had JGMA class 4 accuracy, but the resin molded gear of the first example could secure JGMA class 2 accuracy.

FIG. 2 shows a second embodiment of the present invention, in which (a) is a schematic front view of a resin molded gear, and (b)
(A) is a cross-sectional view along line BB in (a), and (c) is a schematic rear view. Referring to FIG. 1, the resin molded gear has a resin injection portion 3 formed by a molding die gate 2 on one end surface 1a of a gear main body 1, and has teeth 4, 4,. ··have. As can be seen from FIG. 2 (a), the two resin injection portions 3, 3 are arranged between the roots of two adjacent teeth 4, 4 respectively, preferably in the middle of the two roots.

In the second embodiment, the gear main body 1 has a shaft mounting hole 5 penetrating between the end surfaces 1a and 1b at the center thereof.
At least a part of the shaft mounting hole 5 in the axial direction has a substantially oval cross section. And
The two resin injection portions 3 are located on the surfaces of the short protrusions 6, 6 ′ protruding into the shaft mounting hole 5 on the end surface 1 a side.

Therefore, in the resin-molded gear having the above configuration, the resin injection portions 3 and 3 formed by the gate 2 are provided.
Are located between the roots of two adjacent teeth 4 and 4 and are kept away from the teeth 4, so that the influence of the resin flow from the resin injection portion 3 on the tooth surface of the teeth 4 during resin molding is minimized. It has been kept to a minimum. In particular, the resin injection portions 3 and 3 are located at the intermediate portions between the roots of the adjacent two teeth 4 and 4, and on the surface of the short protrusions 6 and 6 ′ protruding into the shaft mounting hole 5 on the end surface 1 a side. Is located further away from the teeth. Therefore, also in the resin molded gear of the second embodiment, the tooth surface accuracy is greatly improved.

In the first and second embodiments, the axial thickness of the shaft mounting hole 5 of the short projections 6 and 6 ′ provided with the resin injection portion 3 is determined by adjusting the axial thickness of the shaft mounting hole 5. Extremely thin compared to the length.

In general, when resin is injection-molded, the amount of shrinkage generated in the resin fixing step in the vicinity of the resin injection portion tends to be larger than that of other portions. As the thickness increases, it becomes more difficult to form with high precision.

For this reason, in the above embodiment, by setting the thickness of the short projections 6 and 6 'to the minimum necessary thickness, the area which is difficult to form with high precision is made as small as possible, and the dimensional accuracy is reduced. The structure is such that it is easy to increase

In these cases, the rotational force from a shaft having a cross section D or an oval shape inserted into the shaft mounting hole 5 is mainly received by the long convex portions 7, 7 '.

If the requirements for the dimensional accuracy of the shaft mounting hole 5 in the radial direction are so high and sufficient for practical use, FIGS. 3 (a) and 3 (b) and FIGS. 4 (a) and 4 (b) If the thickness of the short protrusions 6 and 6 ′ and the thickness of the long protrusions 7 and 7 ′ are substantially equal to the axial length of the shaft mounting hole 5, as shown in FIG. Processing of the mold becomes easy.

FIG. 5 shows a third embodiment of the present invention, in which (a) is a schematic front view of a resin molded gear, and (b)
FIG. 3A is a cross-sectional view along the line EE in FIG. Referring to FIG. 1, a resin molded gear is formed on one end face 1 a of a gear body 1.
Has two resin injection portions 3, 3 formed by the gate 2 of the molding die, and has an even number of teeth 4,
4...

In the fifth embodiment, the gear main body 1 has a shaft mounting hole 5 having a circular cross section at the center thereof and penetrating between the end face portions 1a and 1b. As can be seen from FIG. 5A, the two resin injection portions 3, 3 are located radially outward of the shaft mounting hole 5 between the roots of two adjacent teeth 4, 4.
Preferably, it is arranged at the intermediate portion between the two tooth roots, and is arranged symmetrically with respect to the center axis of the gear body 1.

Therefore, in the resin molded gear having the above structure, the resin injection portions 3 and 3 formed by the gate 2 are provided.
Are located between the roots of two adjacent teeth 4 and 4 and are spaced apart from the teeth 4, so that the resin flow from the resin injection portions 3 and 3 during resin molding affects the tooth surface of the teeth 4. Has been minimized. In addition, since the two resin injection portions 3 and 3 are arranged substantially symmetrically with respect to the center axis of the gear body 1, the resin molded gear can maintain a balanced resin flow from the two resin injection portions 3 and 3. Is formed. Therefore, also in the resin molded gear of the fifth embodiment, the tooth surface accuracy is greatly improved.

FIG. 6 shows a sixth embodiment of the present invention, in which (a) is a schematic front view of a resin molded gear, and (b)
FIG. 3A is a cross-sectional view along the line FF in FIG. Referring to FIG. 1, a resin molded gear is formed on one end face 1 a of a gear body 1.
Has two resin injection portions 3, 3 formed by the gate 2 of the molding die, and has an odd number of teeth 4,
4,...

In the sixth embodiment, the gear body 1 has a shaft mounting hole 5 having a circular cross section at the center thereof and penetrating between the end face portions 1a and 1b. As can be seen from FIG. 6A, the two resin injection portions 3, 3 are located radially outward of the shaft mounting hole 5 between the roots of two adjacent teeth 4, 4.
Preferably, it is arranged at the intermediate portion between the two tooth roots, and is arranged symmetrically with respect to the center axis of the gear body 1.

Therefore, in the resin-molded gear having the above structure, the resin injection portions 3 and 3 formed by the gate 2 are provided.
Are located between the roots of two adjacent teeth 4 and 4 and are spaced apart from the teeth 4, so that the resin flow from the resin injection portions 3 and 3 during resin molding affects the tooth surface of the teeth 4. Has been minimized. In addition, since the two resin injection portions 3 and 3 are arranged substantially symmetrically with respect to the center axis of the gear body 1, the resin molded gear can maintain a balanced resin flow from the two resin injection portions 3 and 3. Is formed. Therefore, also in the resin molded gear of the fourth embodiment, the tooth surface accuracy is greatly improved.

Although the illustrated embodiment has been described above, the present invention is not limited to the above embodiment. For example, the number of resin injection portions formed by the gate is not limited to one or two, and may be three or more. Further, as shown in FIG. 1, a step may be formed at the end face of the gear body 1 where the resin injection section 3 is formed, but the step may be omitted. The type of tooth is not particularly limited, and may be, for example, a spur tooth or a helical tooth.

[0031]

As is apparent from the above description, according to the present invention, a resin molding which is relatively small and has high precision even when the number of teeth is relatively small and the module is relatively large. A gear structure can be provided.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the present invention, in which (a) is a schematic front view of a resin molded gear, (b) is a sectional view taken along line AA in (a), (C) is a schematic rear view.

FIG. 2 shows a second embodiment of the present invention, in which (a) is a schematic front view of a resin molded gear, (b) is a cross-sectional view taken along line BB in (a), (C) is a schematic rear view.

FIG. 3 shows a third embodiment of the present invention, in which (a) is a schematic front view of a resin molded gear, and (b) is a cross-sectional view taken along line CC in (a). is there.

FIG. 4 shows a fourth embodiment of the present invention, in which (b) is a schematic front view of a resin molded gear, and (b) is a cross-sectional view taken along line DD in (a). is there.

5A and 5B show a fifth embodiment of the present invention, in which FIG. 5A is a schematic front view of a resin molded gear, and FIG. 5B is a sectional view taken along line EE in FIG. is there.

FIG. 6 shows a sixth embodiment of the present invention, in which (a) is a schematic front view of a resin molded gear, and (b) is a cross-sectional view taken along line FF in (a). is there.

FIG. 7 (a) shows a measurement result of a double-tooth flank meshing error in the resin molded gear of the first embodiment of the present invention, and FIG.
7 shows the measurement results of the meshing error of the both tooth surfaces of the comparative example in which the resin injection portion was formed at the root portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gear main body 1a, 1b End surface part 2 Gate 3 Resin injection part 4 Teeth 5 Axis mounting hole 5a, 5b Flat surface part

Claims (5)

[Claims] 1. A resin molded gear having a resin injection portion formed by a gate of a molding die on an end surface portion of a gear body and having teeth on an outer periphery, wherein the resin injection portion is a root of two adjacent teeth. A resin molded gear, which is disposed between the resin molded gears. 2. The gear body has a shaft mounting hole at the center thereof, which penetrates between end faces, at least a part of the shaft mounting hole in the axial direction has a substantially D-shaped cross section, and the resin injection portion 2. The resin-molded gear according to claim 1, wherein the shaft mounting hole is located radially outward of a flat surface portion in the substantially D-shaped cross section of the shaft mounting hole. 3. The gear body has a shaft mounting hole at the center thereof, which penetrates between end faces, at least a part of the shaft mounting hole in the axial direction has a substantially oval cross section, and the resin injection portion The resin-molded gear according to claim 1, wherein the shaft is located radially outward of a flat surface portion of the shaft mounting hole in the substantially oval cross section. 4. The gear body has a shaft mounting hole having a circular cross section penetrating between end surfaces at a center portion thereof, and the resin injection portion is located radially outward of the shaft mounting hole. The resin molded gear according to claim 1, wherein: 5. The resin molding according to claim 1, wherein the two resin injection portions are arranged at positions substantially symmetric with each other with respect to a center axis of the gear body. gear.