JPH0585780B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a toothed belt, and more particularly to a toothed belt used under severe conditions. [Prior Art] As a synchronous transmission device, a toothed belt is known in which teeth are formed at a constant pitch on the inner surface of the belt and are wound around a pulley having teeth that mesh with the teeth. This toothed belt has various advantages over other synchronous transmission devices, such as chain transmissions or gear transmissions, such as being lightweight, quiet, and easy to maintain and inspect, so its uses have been expanded.
It is also increasingly being used as a cam drive element in internal combustion engines. However, since the toothed belts used in internal combustion engines such as those described above are subjected to considerably high load and high temperature conditions and are sometimes used for multi-axis transmission, their durability becomes a problem. As one of the means to improve the durability, it is effective to improve the tensile strength of the tensile body embedded in the toothed belt body, and from this point of view, the tensile strength of the tensile body embedded in the toothed belt is Glass fiber cords are often used because they are large and have little temperature variation. These glass fiber cords are usually ECG-150-
As is known from 3/13, collect 20 pieces of 9μ glass filament, make a strand, collect 3 of these filaments and give them 4.0 times/25mm of first twist, then collect 13 of these and make 2.1 times/ A structure with a 25mm ply twist is used. However, the commonly used glass fiber cords mentioned above still have problems with bending fatigue, and various studies have been conducted regarding the twisting of cords (for example, Japanese Patent Publication No. 55-30757, Japanese Patent Application Laid-Open No. 57-771).
No. 56-105135, No. 59-19744, or No. 59
−83234, etc.) [Problems with the prior art] However, all of the above-mentioned prior arts aim to improve the tension by changing the twist coefficient or twist direction combination of the glass fiber cord or carbon fiber cord, and basically It can be said that the structure is the same as that of conventional glass fiber cords, and as long as such measures are taken, it is impossible to expect a dramatic improvement in tensile strength, and in particular, there is a problem that there is a limit to the improvement of bending resistance. [Problems to be Solved by the Invention] In view of the above-mentioned problems, the present invention solves the problem of not only the ply-twisting and the twisting relationship of the ply-twisted yarns constituting the tensile body, but also the entire structure including these constituent yarns. The aim of this study was to reconsider the structure of tensile bodies, and to dramatically improve the bending resistance of tensile bodies by combining these structures. [Technology for solving the problem] That is, the toothed belt of the present invention has teeth with a constant pitch on the inner surface, the surface of the teeth is covered with canvas, and a tensile material is embedded along the bottom of the teeth. In the toothed belt, the tensile body is formed by ply-twisting a plurality of plied threads, and the pulling ratio per unit length of the ply-twisted threads constituting the tensile member is 1 to 3%, and if the uneven lengths of the plied yarns are arranged in order of length and shortness, and a distribution curve is obtained, the rising inflection point of the curve will be 20% from the short side.
It is characterized by being located at a position of ~50%. [Function] As mentioned above, a normal glass fiber cord is made by twisting together multiple strands (usually 3 strands) of glass filaments to form a first strand, which is then collected into a second strand, usually 13 strands, for final twisting. However, when such a glass fiber cord is cut to a certain length L, untwisted, and separated into pre-twisted yarns, the variation in length of each pre-twisted yarn is within a certain range. Normally, when the maximum length of these ply-twisted yarns is lmax and the minimum length is lmin, the pulling rate (%) = [(lmax - lmin)/L] x 100, the pulling rate is 0.6 It is said to be about %. The inventors of the present invention focused on this pulling ratio, changed the pulling ratio to 0.5% to 5%, and used these glass fiber cords as tensile bodies for toothed belts, and found a peculiar phenomenon. I found out. That is, as shown in Figure 1, the residual tension (Kg/strand) of the cords in the belt was tested by changing the pulling ratio of the first twisted yarn from the current 0.6% to 4%.
Contrary to expectations, it was found that a pulling ratio of about 1% to 3% resulted in stronger residual tension. Furthermore, when we measured the distribution rate of uneven lengths of the plied yarns for the residual tension of 2.5%, which is the average pulling rate, we found a pattern as shown in Figure 2 A to E. Obtained. In addition, FIG. 2F shows the length irregularity distribution pattern of the current ply-twisted yarn with a pulling ratio of 0.6%. FIG. 3 shows the curves A to F of FIG. 2 in the form of a curve graph. When we tested the correlation between the distribution pattern of these ply-twisted yarns and the residual tension of the belt after bending fatigue, we found that
It has been found that the pattern shown in FIG. 2D is very excellent. That is, in this pattern, the inflection point P of the rise of the distribution curve of the first twisted yarn is 20 to 20 mm from the short fiber side.
At 50%. The reason why good results can be obtained by setting the pulling ratio of the above-mentioned ply-twisted yarn to 0.5 to 3.5% and the uneven distribution curve pattern as shown in Fig. 2 D is due to the stress generated when the belt is subjected to severe bending. It is inferred that there is some kind of favorable correlation with the flexibility caused by the unevenness of the length of the first strands of the tensile material, but the detailed reasons for this are still unknown to the present invention. It is unknown. [Example] Next, an example of the present invention will be described. Collect 200 glass filaments with a thickness of 9μ and make them into a strand, collect 3 of these strands and apply a first twist of 4.0/25 mm, collect 13 of these strands and apply a final twist using a twisting machine. The pulling rate can be adjusted by using the difference in the supply speed of the first twisted yarn supplied to the ring.
Various types of glass fiber cords containing 0.5-3.5% were obtained. A toothed belt 1 having the structure shown in FIG. 4 was manufactured using these glass fiber cords by a conventional method. This toothed belt 1 consists of a back part 2 made of a rubber elastic material, a tooth part 3, a tensile member 4 embedded along the bottom part of the tooth, and a surface coating canvas layer 5 that covers the surface of the tooth part. In order to satisfy the abrasion resistance and friction coefficient required for a belt-toothed canvas, a canvas whose constituent yarns are aromatic polyester-based material was used. The obtained toothed belt 1 is an endless toothed belt, with a circumference of 40 inches, a belt width of 17 mm, and a tooth pitch of 8.
mm, cord pitch was 1.5mm. This toothed belt 1 was applied to the bending fatigue tester 10 shown in FIG.
¹⁰⁷ , the entire belt was pulled after running and the residual tension was determined, and the results shown by the solid line in FIG. 1 were obtained. In addition, the graph shown by the chain line in FIG. 1 shows the original tension (Kg/cord) before the fatigue test of the tensile strength cord. Next, for the ply yarn pulling rate of 2.5%,
A toothed belt 1 is obtained in the same manner as described above using the irregular patterns shown in FIG. 2 A to D, respectively.
When the tensile strength was tested using the bending fatigue tester 10, the results shown in the table below were obtained.

【table】

〔effect〕

As explained above, contrary to conventional expectations, this invention exhibits extremely excellent bending resistance by regulating the pulling ratio of the first twisted yarns constituting the tensile body and the unevenness of their lengths. This makes it possible to create a toothed belt with sufficient durability even under high heat and high load conditions.

[Brief explanation of the drawing]

1 to 3 are graphs showing test results of an embodiment of the present invention, FIG. 4 is a cross-sectional view of the embodiment, and FIG. 5 is a side view of the test apparatus.

Claims (1)

[Claims] 1. In a toothed belt having teeth at a constant pitch on the inner surface, the surface of the tooth portion is covered with canvas, and a tensile member is embedded along the bottom of the tooth, the tensile member has a plurality of It is made by ply-twisting the ply-twisted threads of the tensile body, and the pulling ratio per unit length of the ply-twisted threads constituting the tensile body is 1 to 3%, and the unevenness of the lengths of the ply-twisted threads is 1 to 3%. A toothed belt arranged in order of length and length, and when a distribution curve is obtained, the rising inflection point of the curve is located 20 to 50% from the short side.