JP2003080564A - Injection-molded plastic worm - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a injection-molded plastic worm which can secure enough strength and reduce the weight and cost of a product. SOLUTION: The plastic worm 1 constituting together with a worm wheel 2 a worm gear is composed of a half-sprit hand-drum-shaped worm part 3 and a cylindrical worm part which is formed in succession to the small diameter side of the worm part 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a worm used in a power transmission device for various automobile parts, industrial machines, precision machines, etc., and more particularly to an injection-molded plastic worm formed by injection-molding plastic. It is a thing.

[0002]

2. Description of the Related Art For example, a worm gear that can obtain a large reduction ratio with a small volume has been used for a long time in automobile parts that operate by receiving a driving force from a driving source such as a motor. By the way, such a worm gear is generally formed by cutting metal, but in recent years,
In order to reduce the weight and significantly reduce the product cost, it has been considered to use plastic as the material and to form the material by injection molding with high production efficiency.

[0003]

However, if a conventional worm gear consisting of a cylindrical worm and a worm wheel is simply made of plastic, the strength of one tooth against a load is insufficient as compared with a metal worm gear. In order to solve such a problem, the worm is made to be a drum-shaped worm, and the number of teeth meshing at the same time is increased and the tooth contact surface is made larger than that using a cylindrical worm to act on one tooth. It is effective to reduce the load. However,
In order to form a drum-shaped worm with plastic, it has to be cut out from a round bar-shaped material. Because the drum-shaped worm has large diameter at both ends,
This is because it is difficult to take it out of the injection mold and injection molding cannot be performed. As a result, by using a plastic drum-shaped worm formed by cutting, it is possible to achieve higher strength and lighter weight, but to increase production efficiency and significantly reduce product cost. I can't achieve it.

[0004] Therefore, an object of the present invention is to provide an injection-molded plastic worm which can secure a sufficient strength, can be reduced in weight, and can be significantly reduced in product cost.

[0005]

According to the invention of claim 1, there is provided an injection-molded plastic worm which constitutes a worm gear together with a worm wheel, which is continuous with a semi-hour shaped worm portion and a small diameter side of the semi-humid shaped worm portion. And a cylindrical worm portion formed by

The invention of claim 2 is characterized in that, in the injection-molded plastic worm of claim 1, a substance having a higher thermal conductivity than the plastic as a base material is mixed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

[First Embodiment] FIG. 1 is a vertical sectional view of an injection-molded plastic worm 1 according to an embodiment of the present invention. As shown in FIG. 1, the injection-molded plastic worm 1 of the present embodiment includes a worm wheel 2
Is formed on the left side of the center line Y of the worm wheel 2, and on the right side of the center line Y of the worm wheel 2 is formed of a cylindrical worm portion 4. The worm portion 4 is formed so as to be continuous. That is, the cylindrical worm portion 4 is formed continuously on the smaller diameter side of the semi-drum shaped worm portion 3. The center line X is a line parallel to the axis CL of the injection-molded plastic worm 1. And the center lines X, Y and the axis line CL
Are located on the same cross section (central cross section).

Further, the injection-molded plastic worm 1 has a shaft hole 7 formed along the axis CL from one side surface 5 to the other side surface 6, and a metal worm shaft 8 is fitted into the shaft hole 7. It is supposed to meet. The injection-molded plastic worm 1 and the worm shaft 8 are prevented from rotating by a spline, a key, or the like, and are integrally rotated as the worm wheel 2 rotates.

The semi-drum shaped wheel portion 3 of the injection-molded plastic worm 1 having such a shape is composed of the worm wheel 2
The number of meshing teeth with is approximately half that of the hourglass worm. In addition, the cylindrical worm portion 4 of such an injection-molded plastic worm 1 has approximately half the number of meshing teeth as in the case of a cylindrical worm. Therefore, the injection-molded plastic worm 1 of the present embodiment, which is composed of the half drum-shaped worm portion 3 and the cylindrical worm portion 4, has a larger number of meshing teeth with the worm wheel 2 than in the case where the whole is a cylindrical worm, Further, the number of teeth meshing with the worm wheel 2 is larger than that in the case where the whole is a semi-hulled worm. In this way, for example, Japanese Patent Laid-Open No. 9-13215
The number of meshing teeth can be made larger than that of the cone-shaped worm disclosed in FIG. 3 of Japanese Patent No. 4 publication, and the load acting on one tooth can be reduced.

FIG. 2 shows an injection-molded plastic worm 1.
FIG. 3 is a cross-sectional view showing a schematic configuration of the injection molding die 10 of FIG.
As shown in FIG. 2, the injection molding die 10 includes at least a first die 11 for forming the outer shapes of the semi-cylindrical worm portion 3 and the cylindrical worm portion 4 of the injection molding plastic worm 1. The second mold 1 for forming the large-diameter side surface 6 of the semi-drum shaped worm portion 3 of the injection-molded plastic worm 1.
2 and a third mold 13 for forming the shaft hole 7 and the small diameter side surface 5 of the injection-molded plastic worm 1. Of these, the first mold 11 can slide in the direction of arrow A while rotating as shown by arrow R. The second mold 12 can slide in the arrow B direction.

First mold 11 and second mold 1 as described above
By combining the second and third molds 13 as shown in FIG. 2, a cavity 14 having the same shape as that of the injection-molded plastic worm 1 is formed, and a plastic melted from a gate (not shown) inside the cavity 14 (for example, , Polyacetal, polyamide, polyphenylene sulfide, polybutylene terephthalate, etc.) are injected. When the plastic in the cavity 14 is solidified, the first mold 11 is moved in the arrow A direction while rotating in the arrow R direction. As a result, the half drum shaped worm portion 3 of the first mold 11 is formed.
And the uneven portion 15 forming the teeth of the cylindrical worm portion 4,
It moves along the teeth of the injection-molded plastic worm 1 without interfering with the teeth of the injection-molded plastic worm 1. As a result, the injection-molded plastic worm 1 is released from the first mold 11. Also, the second mold 1
2 is moved in the direction of arrow B by more than the total length L of the injection-molded plastic worm 1. As a result, the solidified injection-molded plastic worm 1 can be removed (released) from the third mold 13.

As described above, the injection-molded plastic worm 1 according to the present embodiment has a tooth portion which is composed of the semi-hump shaped worm portion 3 and the cylindrical worm portion 4 which is continuous with the tooth portion. Compared to the case of using a worm, the number of meshing teeth is large, the load on one tooth can be reduced, and the strength is such that it can be used in place of a metal cylindrical worm. Therefore, the injection-molded plastic worm 1 of this embodiment can be used in place of the metal cylindrical worm, and the weight of the worm gear can be reduced.

Further, the injection-molded plastic worm 1 of the present embodiment has a tooth portion which is composed of a semi-trum-shaped worm portion 3 and a cylindrical worm portion 4 which is continuous with the tooth portion. It is possible to achieve efficient production, and to significantly reduce the product price.

[Second Embodiment] A worm gear is liable to increase in temperature due to frictional heat, because meshing involves slippage. Therefore, when the worm is made of plastic, it may be necessary to prevent the deterioration of the wear durability due to the temperature rise, depending on the usage state of the worm.

Therefore, the injection-molded plastic worm 1 according to this embodiment has a plastic base material,
A substance that has better thermal conductivity than the plastic (eg,
Iron powder, copper powder, etc.) are mixed in, and a plastic in which this substance having a high thermal conductivity is mixed is injected into the cavity 14 of the injection molding die 10 in FIG. 2 for molding.

In the injection-molded plastic worm 1 thus formed, heat is easily released and heat is less likely to be stored, so that it is difficult for the temperature to rise and it is possible to prevent the deterioration of wear durability due to the temperature rise. it can.

[Other Embodiments] The above-described first embodiment has a structure in which the worm shaft 8 is fitted in the shaft hole 7, but the present invention is not limited to this, and the injection-molded plastic worm 1 is worm-formed. The shaft may be integrally molded. Here, the metal worm shaft may be integrated with the injection-molded plastic worm 1 by insert molding. Alternatively, the injection-molded plastic worm 1 and the worm shaft may be integrally molded from the same plastic.

[0019]

As described above, since the injection-molded plastic worm of the present invention comprises the semi-drum shaped worm portion and the cylindrical worm portion continuous with the semi-drum shaped worm portion, compared to the case where the whole is a cylindrical worm. The number of meshing teeth is large, the load on one tooth can be reduced, and the strength is such that it can be used in place of the metal cylindrical worm.
Therefore, the injection-molded plastic worm of the present invention can be used instead of the metal cylindrical worm, and the weight of the worm gear can be reduced.

Further, since the injection-molded plastic worm of the present invention is composed of the half drum-shaped worm portion and the cylindrical worm portion continuous with the worm-shaped worm portion, injection molding is possible and efficient production by mass production is possible. Therefore, it is possible to significantly reduce the product cost.

[Brief description of drawings]

FIG. 1 is a sectional view of an injection-molded plastic worm according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a schematic configuration of an injection molding die.

[Explanation of symbols]

1 ... Injection-molded plastic worm, 2 ... Worm wheel, 3 ... Semi-cylindrical worm part, 4 ... Cylindrical worm part

Claims (2)

[Claims] 1. An injection-molded plastic worm that constitutes a worm gear together with a worm wheel, comprising: a semi-drum shaped worm portion, and a cylindrical worm portion continuously formed on the small diameter side of the semi-drum shaped worm portion. An injection-molded plastic worm characterized in that 2. The injection-molded plastic worm according to claim 1, wherein a substance having a thermal conductivity higher than that of plastic as a base material is mixed.