JP2590225B2 - Plastic mold gear - Google Patents

Description

The present invention relates to a plastic molded gear, and more particularly, to a plastic molded gear.
The present invention relates to a plastic molded gear having high gear accuracy and large transmission force.

[Conventional technology]

Plastic molded gears have advantages such as low noise and low cost, and are widely used.

[Problems to be solved by the invention]

However, the biggest disadvantages of the conventional plastic molded gear are that the load capacity is small and high accuracy cannot be obtained. Therefore, the conventional use thereof is as shown in, for example, Japanese Utility Model Publication No. 57-31651. In addition, it has been limited to applications that require a very small transmission force and applications that do not require rotational accuracy.

More specifically, a plastic gear is often made of a polyacetal resin in terms of performance such as fatigue strength and wear resistance. In general, engineering plastics have a relatively large molding shrinkage, while polyacetal has a molding shrinkage of about 1.6 to 2.2%,
Further, it has the property that the molding shrinkage changes depending on the cooling rate. For this reason, when the thickness is increased to increase the transmission force of the plastic mold gear, not only the sink is generated and the accuracy is reduced, but also a void is generated in the core and the strength is reduced conversely. For this reason, conventional plastic molded gears have low accuracy and it is difficult to increase the transmission capacity, and the range of use is limited.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a plastic molded gear having high transmission capability and high precision.

[Means for solving the problem]

The object is to form a cylindrical boss, a disk-shaped disk portion integrally formed so as to extend from the outer periphery of the boss in the outer peripheral direction, and to integrally form the disk portion and the outer periphery of the disk portion. A plastic molded gear integrally formed of a plastic having a cylindrical rim portion and gear teeth formed on the outer periphery of the rim portion, wherein a long side is provided on the side surface of the disk portion. A large number of large ribs and a plurality of small ribs having a short length are formed radially, and the inner peripheral end of the large rib is connected to the outer periphery of the boss, and the outer peripheral end of the small rib is connected to the inner periphery of the rim portion. This is achieved by forming such that the outer peripheral end of the large rib is spaced apart from the inner periphery of the rim portion, and the inner peripheral end of the small rib is spaced apart from the outer periphery of the boss.

Further, the above object is also achieved by providing a rib which connects only the disk portion and the rim of the plastic molded gear and does not reach the boss.

Further, the above object is also achieved by providing a rib between the rim of the plastic molded gear and the boss and providing a notch therebetween to make each rib independent.

[Action]

In order to find a way to improve the accuracy and transmission capacity of plastic molded gears, an experimental plastic molded gear with the shape shown in Fig. 4 was manufactured, and the transmission force T when the rim thickness t was changed and the accuracy grade according to JIS Is shown in FIG. Transmission force T from the relationship between the operating frequency to failure torque was measured incorporating the present Morudogiya the reduction gear (not shown), indicating the torque values were destroyed 10 ⁴ times as a relative value.

Next, when examining the broken form of the test article used in the above experiment, it was found that there were two forms shown in FIG. 6 and FIG. Among them, FIG. 6 shows the rim thickness t.
= 3 mm or less, and that of FIG. 7 was observed when the thickness was larger than this. Observation of the fractured surface in FIG. 7 shows that voids were generated, and the dispersion of the measured values was large. on the other hand,
With the rim thickness t = 3 mm or less, a phenomenon was observed in which the diameter of the rim portion became smaller as the operation time elapsed. Note that this is, as shown in FIG. 8, in a direction radial load F _r represented by F _r = F _t sin .alpha by meshing pressure angle α with respect to the transmission force F _t during operation reduce the rim portion inwardly Although it works, in the area where the rim thickness is small, the vicinity of both ends is deformed inward due to this force, and the transmission torque is mainly borne only at the central part, and the transmission torque is small. It turned out to be. On the other hand, when examining the accuracy class, it was found that as the rim thickness increased, sink marks became larger and thus worsened.

Based on such experimental results, in the present invention,
By making the shape of the plastic mold gear the shape shown in the section of the above-mentioned [Means for Solving the Problems],
The rim thickness is suppressed to a thickness that does not deteriorate the accuracy, and a rib having a length that does not affect the accuracy of the rim is provided to reinforce the rim inward.

〔Example〕

Hereinafter, the present invention will be described with reference to one embodiment of FIGS. 1 and 2. FIG. 1 is a longitudinal sectional front view of a plastic molded gear according to the present invention, and FIG. 2 is a side view of the same. 1 is a plastic molded gear boss, 2 is a disk portion, 3 is a rim, 4 is a tooth, 6 is a large rib, and the large rib 6 is connected to the disk portion 2 and the boss 1 and extends to the vicinity of the rim 3, The rim 3 is provided evenly without being connected. 7 is a small rib, and the small rib 7 is connected only to the disk portion 2 and the rim 3 and is also connected to the large rib 6.
Like the above, they are provided evenly.

The present invention is as described above, and in the above embodiment, by providing two types of large and small ribs 6, 7 having a length that does not affect the rim accuracy of the plastic molded gear,
The rim thickness can be reduced to a thickness that does not degrade accuracy,
According to the prototype experiment, as shown in FIG. 5, the accuracy class was improved from class 6 to class 4 by two classes, and at the same time, the gear transmission torque was able to be improved by about 25%.

In addition, comparing the precision of the plastic molded gear shown in the above embodiment with the precision of the conventional plastic molded gear employing the rib structure indicated by reference numeral 5 in FIG. Compared to the precision of the conventional gear shown in FIG. 9, the precision of the gear of the present embodiment shown in FIG.
It can be seen that remarkably good results are obtained.

FIG. 11 shows another embodiment of the present invention. In the embodiment of FIG. 11, the disk portion 2 of the plastic mold gear is provided.
The rim 3 is connected to the rim 3 only, and the rib 8 that does not reach the boss 1 is provided. With this configuration, the same effect as in the first embodiment can be obtained.

FIG. 12 shows still another embodiment of the present invention. In the embodiment of FIG. 12, the rim 3 of the plastic mold gear is provided.
Ribs 9 and 10 are provided between
Since the ribs 11 and 11 are provided to make the ribs 9 and 10 independent of each other, this embodiment can also provide the same effects as those of the first and second embodiments.

[Effects of the Invention] As described above, according to the present invention, not only can the transmission force of the plastic molded gear be significantly improved, but also its precision can be greatly improved, and the disadvantages of the conventional plastic molded gear In other words, it is possible to solve the disadvantage that the load capacity is small and the accuracy is low, and the range of use can be greatly expanded.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional front view showing an embodiment of a plastic molded gear according to the present invention, FIG. 2 is a side view thereof, FIG. 3 is a side view of a conventional plastic molded gear, and FIG. FIG. 5 is a vertical sectional front view of the experimentally produced plastic molded gear, FIG. 5 is a performance diagram showing the rim thickness, transmission torque and accuracy class of the plastic molded gear, and FIGS. 6 and 7 are the teeth of the plastic molded gear. FIG. 8 is a perspective view showing a broken form, FIG. 8 is an explanatory view showing a component force of a gear transmission force, and FIGS. 9 and 10 are both teeth of a conventional plastic mold gear and the plastic mold gear of the present invention shown in the above embodiment. FIG. 10 is a diagram showing surface meshing test data,
FIG. 11 and FIG. 12 are side views of a plastic molded gear showing different embodiments of the present invention. 1 ... boss, 2 ... disk part, 3 ... rim, 4 ...
Tooth, 6 ... large rib, 7 ... small rib.

Claims (3)

(57) [Claims] 1. A cylindrical boss, a disk-shaped disk portion integrally formed so as to extend from the outer periphery of the boss in the outer peripheral direction, and an integral part of the disk portion and the outer periphery of the disk portion. In a plastic molded gear integrally molded with a plastic having a cylindrical rim portion formed and gear teeth formed on an outer periphery of the rim portion, a side of the disc portion has a length. A large number of long large ribs and a small number of short ribs each having a short length are radially formed, and the inner peripheral end of the large rib is connected to the outer periphery of the boss, and the outer peripheral end of the small rib is connected to the inner periphery of the rim portion. A plastic rib formed so that an outer peripheral end of the large rib is separated from an inner periphery of the rim portion and an inner peripheral end of the small rib is separated from an outer periphery of the boss. gear . 2. A plastic molded gear having integrally molded teeth, a rim, a boss, and a disk portion, wherein a rib that connects only the disk portion and the rim and does not reach the boss is provided. 3. A plastic molded gear having integrally molded teeth, a rim, a boss, and a disc portion, wherein a rim-side rib extending inward from the rim and a boss-side rib extending outward from the boss are respectively provided. Radially forming a large number, the inner end of the rim side rib is separated from the outer periphery of the boss, the outer end of the boss side rib is separated from the inner periphery of the rim,
A plastic molded gear, wherein the rib on the rim side and the rib on the boss side are arranged so that the side faces are closely opposed to each other.