专利汇可以提供Toothed belt专利检索,专利查询,专利分析的服务。并且A toothed elastomeric belt for use in a power transmission system includes teeth having a cross-sectional configuration that includes a cycloidal convex curve (6) that extends from the tooth tip (5) and is smoothly connected to the bottom land (8) between adjacent teeth by an arcuate fillet (7).,下面是Toothed belt专利的具体信息内容。
The present invention relates to a toothed belt having a plurality of elastic teeth formed of elastomeric material for meshing engagement with the teeth of a toothed pulley. More particularly, the invention relates to an improved tooth shape for such a toothed belt.
Trapezoid teeth are well known as a tooth shape for a toothed belt which is adapted to be trained around a plurality of toothed pulleys and constitute therewith a power transmitting device. In order to eliminate drawbacks of such trapezoid teeth, there have been proposed tooth shapes as disclosed in Japanese Patent Publication Nos. 52-20629, 56-37457, and 57-44866, Japanese Laid-Open Patent Publication No. 59-89582, Japanese Patent Publication Nos. 57-1714 and 57-60501.
In order for a toothed belt and a toothed pulley, hereinafter simply referred to as a "pulley", to mesh with each other without interference, the following three conditions must be met:
The present invention is concerned with the problem indicated as (3) above, as it concerns the toothed belts disclosed in the aforesaid publications. As shown in Figure 1, a trapezoid tooth 01 is generally used as a belt tooth. Such tooth shape, when it meshes with a pulley tooth 03, contacts the pulley tooth at a root fillet 02. Therefore, the root fillet is subjected to a concentrated stress in the form of shearing stress, and the belt tooth tends to suffer from localized damage.
To overcome this shortcoming, there has been proposed an arcuate tooth 04 which, as shown in Figure 2, contacts a pulley tooth at a position near the tooth tip when it meshes with the pulley tooth so that the tooth bears the force in its entirety (see Japanese Patent Publication Nos. 52-20629 and 57-44866). The arcuate tooth 04 can distribute the produced stress into the entire root portion of the tooth, and transmit the load uniformly at the tooth root portion to a load carrying member 05 on the belt pitch line. Consequently, the tooth root portion is less liable to break and is more durable.
There is also known an improved arcuate tooth in which the difference between the tooth shape and its envelope is made as small as possible so as to reduce the backlash of the arcuate tooth. Such a tooth shape is described in Japanese Laid-Open Patent Publication No. 59-89852.
When under low loads, the trapezoid tooth and the improved arcuate tooth are less deformable than the arcuate tooth. When subjected to high loads, however, the trapezoid tooth has been known to jump over the pulley tooth and the improved arcuate tooth has been known to slip against the pulley tooth, resulting in a large deformation. The arcuate tooth, on the other hand, is deformed at high loads to an extent which is substantially the same as that under the low loads.
When a high load is transmitted by a toothed belt, it is the general tendency for the belt to become more elongated, and for the belt teeth to be more deformed and to slip more on the pulley teeth. As a result, proper meshing engagement between the belt and pulley teeth is not effected, and the belt teeth tend to ride over the pulley teeth and are largely deformed.
Such behavior of the belt appears to depend on the pressure angle (ϑ) and the ratio (H/W) of the height (H) and the width (W) of the tooth shape.
As shown in Figure 3, it can be assumed that, when a pulley tooth 07 and a belt tooth 06 are in mesh with each other, the force applied from the belt tooth 06 to the pulley tooth 07 at a point A is indicated by P; the coefficient of friction between the teeth by µ; the produced frictional force by F; and the pressure angle by ϑ. Then, the following equations (1), (2) and (3) are established;
P1 = P cos ϑ ...(1)
P2 = P sin ϑ ...(2)
F = µP1 = µP cos ϑ ...(3)
In order to satisfy the condition P2 <F for preventing the meshing teeth from slipping, the following inequality (4) must be met:
P sin ϑ < µP cos ϑ ...(4)
∴ tan ϑ < µ ...(5)
If it is assumed here that the coefficient of friction µ between a steel pulley and a rubber belt having teeth reinforced with woven farbic is 0.25 based on the coefficient of friction µ = 0.21 between a steel pulley and a woven-fabric belt and the coefficient of friction µ = 0.30 between a steel pulley and a rubber belt, then, from inequality (5), ϑ < 14°. Therefore, in the described example the pressure angle ϑ must be smaller than 14 degrees in order to avoid a tooth-to-tooth slippage.
Moreover, as shown in Figure 4, while the belt tooth 06 was restrained on one side, a load (F = 1 kg) was applied to the belt tooth 06 on the assumption that no slippage occurs between the teeth, and the belt tooth 06 was checked for the amount of lift (δ) due to deformation thereof. It was found that the amount of lift (δ) varies from tooth shape to tooth shape, and results as were obtained from these experiments are indicated in Table 1. The differences between the amounts of lift (δ) greatly depend upon the ratio (H/W) (see Table 1).
According to the present invention there is provided a toothed belt for use in a power transmission system, said belt having elastic, longitudinally spaced teeth including a tooth tip with intermediate bottom lands for meshing with cooperating teeth of a toothed pulley, each said belt tooth having a longitudinal sectional shape comprising a cycloidal convex curve extending from the tooth tip and an arc smoothly connecting said cycloidal convex curve and said bottom land.
The tooth shape plus defined is suitable for transmitting high loads since the pressure angle (ϑ) is small and the ratio (H/W) of the tooth height (H) to the tooth width (W) is large.
Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:-
With particular reference to Figures 6 through 8 there is shown a toothed belt 1 according to the present invention. The toothed belt 1 is trained around a plurality of pulleys 12A, 12B, 12C, as shown in Figure 6 and has a tooth shape as shown in Figure 7. The toothed belt 1 is made of an elastomer, such as rubber, and comprises a base layer 2 having a plurality of integral belt teeth 4 and a flexible load carrying member 3 in the form of steel cords, or the like, embedded in the base layer 2. The load carrying member 3 lies on a belt pitch line L. When the belt 1 is trained around a pulley 12, as shown in Figure 8, the load carrying member 3 is aligned with a pitch circle C of the pulley 12 which lies outside of the tips of the pulley teeth.
The tip or top land 5 of the belt tooth 4 is of a straight-line shape parallel to the belt pitch line L and having a length 2D. Assuming that the central point of the tip 5 is used as an origin O, a straight line passing through the origin O parallel to the belt pitch line L serves as an x axis, and a straight line extending perpendicularly to the x axis at the origin O serves as a y axis, the tooth surface 6 in the shape of a cycloidal convex curve can be defined by the following equations (6) and 7:
x = A(1 - cos α) + D ...(6)
y = A (α - sin α) ...(7)
where A and D are positive constants and 0 ≦ α ≦ π .
The curve which defines the tooth surface 6 is smoothly joined to an arcuate root fillet 7 which is smoothly joined to a bottom land 8.
A straight line 10 passed through the point 9 of the intersection between the tooth surface 6 and the tooth fillet 7 is tangent to both the cycloidal curve of the tooth surface 6 and the arc of the tooth fillet 7. The straight line 10 crosses a straight line 11 extending parallel to the y axis at an angle (ϑ) which represents the pressure angle. The tooth has a width (W) as measured between the opposite points 9 of the tooth.
The following Table 2 presents typical dimensions and other relevant comparative data pertaining to toothed belts employing the cycloidal tooth shape of the present invention (column 1), as well as other conventional tooth shapes.
While the top land 5 is shown in Figure 7 as being of a straight-line shape, it may be defined by a curve deflected in a direction to increase the tooth height.
Figure 8 fragmentarily shows a pulley 12 having a plurality of pulley teeth 13 for meshing with the belt teeth 4 of the toothed belt 1. The pulley 12 has a bottom land 14 defined by a straight line having a length 2D. Where a straight line passing through a central point 0 of the straight line of the bottom land 14 and the center of rotation of the pulley 12 is used as the Y axis and a straight line extending perpendicularly to the Y axis at the point 0 serves as an X axis, the straight line of the length 2D defining the bottom land 14 lies on the X axis. A tooth surface 15 joined to the bottom land 14 is defined by a cycloidal convex curve expressed by the following equations (8) and (9):
X = 1.1A (1 - cos α) + D ...(8)
Y = 1.15A (α - sin α) - 0.05 ...(9)
where 0 ≦ α ≦ π, 0 ≦ Y ≦ 0.7H, and A and D are positive constants.
The curve which defines the tooth surface 15 is smoothly joined to an arcuate tooth tip surface 16 at a position indicated by Y = 0 7H (see straight line ℓ), and the tooth tip surface 16 is smoothly joined to a straight tip or top land 17.
The "maximum backlash position (H1/W)" given in Table 2 represents a value that indicates a position, which is spaced a height (H1) from the bottom land and where maximum backlash occurs, as the ratio of the height (H1) to the tooth width (W).
Table 2 shows that the pressure angle (ϑ) of the tooth shape of this toothed belt 1 according the present invention is 3.50° which meets the condition, ϑ < 14°, and that the tooth shape is much smaller than the other tooth shapes, causing much less tooth-to-tooth slippage. The ration (H/W) of the tooth height (H) to the tooth width (W) of the belt tooth 4 is sufficiently greater than that of the trapezoid tooth. According to the test method shown in Figure 4, the amount of lift (δ) of the belt tooth is 0.8 mm which is smaller than those of the other tooth shapes, so that any irregular meshing engagement is less apt to happen.
Belts having teeth bearing the shape of the present invention were evaluated against belts having teeth of conventional shape according to the following procedures:
It follows from Figures 9 through 14 that:
As is apparent from the foregoing description, there is provided a toothed belt having a tooth shape defined by a straight tooth tip line or a tooth tip curve deflected in a direction to increase the tooth height and a cycloidal convex curve joining the straight tooth tip line or tooth tip curve and an arc smoothly connecting the cycloidal convex curve to a bottom land.
The tooth shape of the toothed belt is defined by the cycloidal convex curve and has a small pressure angle, so that tooth-to-tooth slippage is less apt to occur. Since the ratio of the tooth height to the tooth width is large, the tooth is less liable to separate from the pulley even when a high load is applied. When a high load is imposed on the tooth, it is distributed throughout the tooth and uniformly transmitted to a load carrying member in the toothed belt. Therefore, there is provided a configuration in which any tooth deformation is small. The tooth is, moreover, highly durable and it has less tendency to cause irregular meshing engagement with an associated pulley.
It will thus be seen that the present invention, at least in its preferred forms, provides a toothed belt which is less deformable under loads; is subject to sufficiently reduced tooth-to-tooth slippage; and is less apt to cause irregular meshing engagement.
It is to be clearly understood that there are no particular features of the foregoing specification, or of any claims appended hereto, which are at present regarded as being essential to the performance of the present invention, and that any one or more of such features or combinations thereof may therefore be included in, added to, omitted from or deleted from any of such claims if and when amended during the prosecution of this application or in the filing or prosecution of any divisional application based thereon.
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