JPH10246315A - Timing pulley - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the slippage of a timing belt effectively by forming a dent which is curved symmetrically centered on a substantially central part in the direction of width on a top face of a tooth shape in a timing pulley provided with a plurality of tooth shapes which mesh with a toothed belt which transmits power at a fixed interval along the peripheral direction in an outer peripheral part. SOLUTION: A pulley 1 is formed into a shape in which a tooth part 2 of outer periphery which has a predetermined width and is formed into an annular shape and a boss part of inner periphery are integrally connected by a reinforcing rib 4, and a flange part 5 which prevents the leaning to one side is formed in a circumferential part at one end of the tooth part 2. Moreover, a plurality of tooth shapes 6 are uniformly formed in the peripheral direction of the tooth part 2. At this time, by molding the pulley 1 by using dies in which wall thickness of the reinforcing rib 4 is larger than wall thickness of the tooth part 2, a drop occurs on a surface of the tooth part 2. That is, a symmetrical curved part having a depth h is caused on a top face 6a of the tooth shape 6 due to shrinkage caused when resin is cooled at the time of molding. Consequently, a timing belt is not removed from the pulley 1 easily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a timing pulley for preventing a timing belt from shifting.

[0002]

2. Description of the Related Art Conventionally, a timing pulley (hereinafter simply referred to as a pulley) fitted to a drive shaft has been used as a power transmission mechanism for a small precision mechanism, office equipment, a machine tool, an automobile, or the like.
And a power transmission means in which a timing belt made of an elastic body is stretched by tension between pulleys fitted to the driven shaft. As a conventional example of a pulley constituting such a transmission means, there is a pulley disclosed in Japanese Utility Model Publication No. 7-33009. FIG.
FIG. 3 is a partially cutaway perspective view of a tooth shape of a pulley disclosed in the publication. The pulley 51 is provided with a plurality of tooth profiles 52 arranged at regular intervals along the circumferential direction. The tooth profiles 52 have a pulley large-diameter portion 54 at the other end with respect to the outer diameter d1 at the pulley small-diameter portion 53 at one end in the axial direction. The outer diameter d2 on the side is tapered so as to be slightly larger. Tooth profile 52 of this pulley 51
Has a trapezoidal cross-sectional shape, and a corner 57 where the top surface 55 and the side surface 56 of the tooth profile 52 intersect is formed in an arc shape. Then, by setting the arc radius r2 of the large-diameter pulley portion 54 to be larger than the arc radius r1 of the small-diameter portion 53 of the pulley, and by making the two smoothly continuous, the tooth shape 5 of the pulley 51 is improved.
The second corner 57 is formed so as to be smoothly curved from the pulley small diameter portion 53 side to the pulley large diameter portion 54 side. For this reason, in this conventional example, the load on the tooth root portion of the timing belt is alleviated, so that cracking is prevented.

[0003]

However, such a toothed pulley having a taper as shown in the above-mentioned conventional example generally has an effect of eliminating shocking engagement with a timing belt and preventing the engagement noise. While
There is a problem that the timing belt is easily displaced and sometimes comes off. This is a problem not only in a pulley having a taper but also in a horizontal pulley having a tooth profile.

Accordingly, an object of the present invention is to provide a timing pulley in which a timing belt is prevented from shifting.

[0005]

According to the timing pulley of the present invention, a plurality of tooth profiles meshing with a toothed belt for transmitting power are provided at regular intervals on an outer peripheral portion along a circumferential direction, and a top surface of the tooth profile is: It is characterized in that a dent which is symmetrically curved about a substantially central portion in the width direction is formed.
Further, in the timing pulley of the present invention, a reinforcing rib connecting the boss portion and the tooth portion is formed at the center in the width direction of the tooth portion,
It is preferable that the thickness of the reinforcing rib is larger than the thickness of the boss portion and the tooth portion.

The timing pulley of the present invention is formed by heating and plasticizing a thermoplastic resin, injecting the thermoplastic resin into a mold, and cooling and solidifying the thermoplastic resin. The reinforcing rib for connecting the boss portion and the tooth portion is formed. In the width direction center of the tooth portion, the thickness of the reinforcing rib is made larger than the thickness of the boss portion and the tooth portion,
By injecting the thermoplastic resin into a mold in which the draft of the tooth profile top surface is set to 0 °, a recess which is symmetrically curved around the substantially central portion in the width direction on the tooth profile top surface due to sinkage generated during cooling and solidification. Is formed.

[0007]

Next, an embodiment of a timing pulley (hereinafter, simply referred to as a pulley) according to the present invention will be described. The pulley of the present embodiment is formed of a resin, and is formed by utilizing the molding characteristics of the resin. The range of metal gears made by casting has been narrowing due to the remarkable progress in mechanical gear cutting and the demand for precision.However, resin gears have been reduced due to the progress of mold manufacturing methods by electric discharge machining. Gear molding is used for mass production of gears. Therefore, resin-made pulleys and the like are still produced by injection molding, and the above-mentioned conventional products are one of them. By the way, the injection molding of this resin product has a problem of "sink", and eliminating the "sink" is one of the problems in molding. However, in the present embodiment, attention has been paid to this "sink", and the intended problem has been solved by using it in reverse. Less than,
This will be described with reference to the drawings.

FIG. 1 is a sectional view showing a pulley according to the present embodiment, and FIG. 2 is an enlarged sectional view of a tooth portion. Also,
FIG. 3 is a plan view showing the pulley. The pulley 1 is formed by integrally forming an outer peripheral tooth portion 2 and an inner peripheral boss portion 3 formed in a ring shape having a predetermined width by a reinforcing rib 4, and one end circumferential portion of the tooth portion 2. Is formed with a flange portion 5 for preventing displacement. Further, in the circumferential direction of the tooth portion 2, a plurality of uniform tooth shapes 6, not specifically shown, are formed. In the pulley 1 having such a shape, normally, the tooth portions 2, the boss portions 3, and the reinforcing ribs 4 have the same thickness. This is because, as described above, conventionally, an injection-molded product made of a resin has been aimed at preventing sink marks. That is, the "shrinkage" is because, in a resin product having a large molding shrinkage, the thickness of the molded product is not uniform.

Therefore, in the pulley 1 of the present embodiment, a mold for the pulley 1 in which the thickness of the reinforcing rib 4 is larger than the thickness of the tooth portion 2 as shown in FIG. It was decided to mold by this. Although the mold is not shown,
The feature is that the reinforcing ribs 4 are formed so as to be thicker than those used for forming the conventional pulleys, and the draft of the top surface 6a of the tooth profile 6 is formed as 0 °. Have. The reason why the reinforcing ribs 4 are made thicker than the tooth portions 2 is to cause “sink” on the surface of the tooth portions 2. This is to cause a symmetrical "sink" in 6a.

Then, such a mold is prepared, and a resin (a polyacetal resin is used in the present embodiment) is injected into the mold in the same manner as in general injection molding, and then cooled and solidified to be molded. . At the time of cooling and solidification, in the present embodiment, since the thickness of the reinforcing ribs 4 is larger than the thickness of the tooth portions 2, when the resin is cooled, the central portion in the width direction of the tooth portions 2 including the tooth shape 6 is cooled. Is symmetrically contracted, and the top surface 6a of the tooth profile 6 is
A symmetrical curved portion having a depth h as shown in FIG. In this way, the resin shrinks during cooling and solidification to form a sink mark, so even if a mold with a shape that is simply recessed in the center is made, it will be undercut and the molded product will not come off On the other hand, the molded product can be easily taken out.

Therefore, the pulley 1 thus formed is used, attached to a drive shaft and a driven shaft, and the timing belt 7 is passed over both pulleys 1. Normally, it is necessary to give a proper tension to the timing belt 7,
In this case, it is provided at the center of the curved portion formed on the top surface 6a of the tooth profile 6. Then, as shown in FIG. 4, the timing belt 7 does not shift on both sides even when a force acts toward the center, and the timing belt 7 does not come off the pulley 1 much. Therefore, according to the present embodiment, the timing belt 7 is actively used by utilizing the molding characteristics of the resin in the injection molding, that is, the phenomenon of “sink” caused by the large shrinkage of the resin.
The pulley 1 in which the displacement was effectively prevented could be formed. This has the effect that the displacement of the timing belt 7 can be prevented and the effect that the pulley 1 exhibiting such an effect can be provided at low cost.

It should be noted that the present invention is not limited to the embodiments described above, and various changes can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, POM is used as the material of the pulley 1, but other resins may be used.

[0013]

According to the present invention, a plurality of tooth profiles meshing with a toothed belt for transmitting power are provided on the outer peripheral portion at regular intervals along the circumferential direction, and the top surface of the tooth profile extends substantially in the center in the width direction. Since the dent is formed symmetrically at the center, it is possible to provide a timing pulley in which the displacement of the timing belt is prevented. Further, the present invention is formed by heating and plasticizing a thermoplastic resin, injecting the thermoplastic resin into a mold, and cooling and solidifying the thermoplastic resin. The reinforcing rib for connecting the boss portion and the tooth portion is formed at the center in the width direction of the tooth portion. The thickness of the reinforcing ribs is set to be larger than the thickness of the boss portion and the tooth portion, and the thermoplastic resin is injected into a mold in which the draft of the top surface of the tooth profile is set to 0 °, thereby cooling and solidifying. Since the dent which is curved symmetrically about the substantially central portion in the width direction is formed on the top surface of the tooth profile by the sink generated at the time, it is possible to provide a timing pulley in which the displacement of the timing belt is prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a pulley according to the present invention.

FIG. 2 is an enlarged sectional view showing a tooth portion of a pulley.

FIG. 3 is a plan view showing a pulley.

FIG. 4 is an enlarged cross-sectional view showing a tooth portion of a pulley in a state where a timing belt operates.

FIG. 5 is a partially cutaway perspective view showing teeth of a conventional pulley.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pulley 2 Tooth part 3 Boss part 4 Reinforcement rib 6 Tooth shape 6a Top surface 7 Timing belt

Claims (3)

[Claims] 1. A timing pulley in which a plurality of tooth profiles meshing with a toothed belt for transmitting power are provided at regular intervals on an outer peripheral portion along a circumferential direction, wherein a top surface of the tooth profile extends substantially at a central portion in a width direction. A timing pulley having a dent formed symmetrically at the center. 2. The timing pulley according to claim 1, wherein a reinforcing rib for connecting the boss portion and the tooth portion is formed at the center of the tooth portion in the width direction, and the thickness of the reinforcing rib is equal to the thickness of the boss portion and the tooth portion. A timing pulley characterized by being larger than the thickness of the teeth. 3. A timing pulley formed by heating and plasticizing a thermoplastic resin, injecting it into a mold, and cooling and solidifying the reinforcing resin. A reinforcing rib connecting the boss portion and the tooth portion is centered in the width direction of the tooth portion, By increasing the thickness of the reinforcing ribs in comparison with the thickness of the boss portion and the tooth portion, and injecting the thermoplastic resin into a mold having a draft of the tooth profile top surface of 0 °, during cooling and solidification, A timing pulley, characterized in that a dent which is symmetrically formed around a substantially central portion in the width direction is formed on the top surface of the tooth profile by the sink mark generated.