GB2086527A

GB2086527A - Drive belt

Info

Publication number: GB2086527A
Application number: GB8132002A
Authority: GB
Original assignee: Industrie Pirelli SpA; Pirelli SpA
Current assignee: Industrie Pirelli SpA; Pirelli and C SpA
Priority date: 1980-10-28
Filing date: 1981-10-23
Publication date: 1982-05-12
Also published as: BE890673A; IT8025608A0; FR2492934B1; FR2492934A1; IT1134066B; GB2086527B; ES517959A0; AR227440A1; ES8505775A1; BR8106995A; DE3141985A1; JPS57103951A

Abstract

A drive transmission belt for use in continuous speed variators comprises an annular body 1 made of a polymeric (e.g. elastomeric) material in which there is embedded a tension- resistant structure constituted by flexible, substantially inextensible cords 6 laid parallel to and co-planar with one another. Additional rigid elements 7 are connected to said body (internally or externally); said elements 7 may be equally spaced but of different dimensions when measured lengthwise of the belt, or may be of identical dimensions but unequally spaced. <IMAGE>

Description

SPECIFICATION Drive belt This invention relates to a transmission or drive belt, particularly for continuous speed variators.

There are already known diverse types of drive belts for continuous speed variators and, in general, they comprise a tape or length of polymeric material (and more specifically of an elastomeric material) whose ends are joined to form a closed ring, and a tension-resistant structure constituted by a plurality of flexible and inextensible cords which are parallel to and coplanar with each other. There are also connected to said tape or length (preferably by being embedded in said polymeric material) a plurality of rigid inserts for imparting transverse rigidity to said tape and for increasing the torque transmission.

These known drive belts for continuous speed variators present at least two drawbacks. The first drawback is the short duration of the service-life of the known belts for continuous speed variators, and this drawback is serious enough to have prevented the development of said variators despite the fact that the use of them can theoretically offer considerable advantages for saving energy in those machines in which they are used or are useable. In order to overcome this drawback, numerous types of drive belts have been proposed which differ one from the other substantially in the form of the rigid inserts, in the form of the polymeric belt itself and in the manner in which the connection of the rigid inserts to or the embedding of the rigid inserts in the polymeric material has been carried out.All of these attempted solutions, however, have not been able to overcome the disadvantage of the short duration of the service-life of the known belts for speed variators.

A second drawback is the high level of noise produced by the known belts in question when operating in said speed variators. In spite of all the improvements made in the various component parts of the variator proper, it has not been possible to reduce the excessive noise level substantially.

The aim of the present invention is to overcome the above-indicated drawbacks of the known belts for speed variators in such a way as to obtain a longer service-life for the belts and a lower noise level during operation.

Accordingly, the present invention consists in a drive transmission belt comprising a belt body which is made of a polymeric material and which is annular, said belt body incorporating a tension-reistant structure formed by a plurality of cords which are parallel to and coplanar with one another; and a plurality of rigid elements which are spaced apart from each other along the development of the belt and which are connected to said belt body in such a manner as to define in the latter two series of tracts having different transverse rigidites, the length of the tracts of one series being variable, whereas the length of the tracts of the other series is constant.

The present invention will now be more particularly described with reference to the accompanying diagrammatic drawing, in which: Figure 1 shows a perspective view of an exemplary drive belt according to the invention, the drawing depicting said belt as though the polymeric material of the belt body were transparent; and Figure 2 shows a lateral view of a different embodiment of a drive belt according to the invention.

In general terms, a drive belt for continuous speed variators according to the present invention comprises an annular body in polymeric (elastomeric) material having in cross-section perpendicular to its development a trapezoid form and having embedded or incorporated in said material a tension-resistant structure comprising a plurality of cords which are parallel to and coplanar with each other, and a plurality of substantially rigid bodies that are spaced apart from each other along the development of the belt. The essential element of the present invention is the idea of the two series of constituent lengths or tracts having a diverse transverse rigidity (which results from the presence of the rigid bodies connected to the belt), the tracts of one series having a variable length whereas the tracts of the other series have a constant length.

The sequence in which the tracts of diverse lengths follow each other along the development of the belt is not necessarily purely random; indeed, it is preferably appropriately predetermined according to calculations which come within the scope of this invention as hereinafter discussed in detail.

In particular, it is a feature of the invention that the tracts of different lengths are obtained by making the distances between the various median planes of the rigid continuous bodies variable along the development of the belt; said distance will be henceforth called the "pitch". The variation of the pitch can be obtained in two ways: (a) utilizing rigid bodies which are of different dimensions measured along the direction of the development of the belt and disposing said rigid bodies inside the belt body in such a way that the distance between adjacent bodies is constant.

(b) utilizing rigid bodies of equal dimensions measured along the direction of the development of the belt and disposing said rigid bodies inside the belt body in such a way that the distance between adjacent bodies is variable. Of the two ways (a) and (b), the preferred way is that given in point (b) above.

In Figure 1,there is shown by way of a non-limiting example a perspective view of a tract of a drive belt for speed variators, said belt comprising a belt body 1 of an elastomeric material and having a trapezoid cross-sectional shape when the section is made perpendicular to the belt development; hence said belt 1 has a greater base 2, a lesser base 3 and two sides 4 and 5, the bases 2 and 3 lying on spaced parallel planes and the sides 4, 5 being non-parallel.

In the material of the belt body 1, there is embedded a tension-resistant structure formed by a plurality of flexible, substantially inextensible cords 6 whose longitudinal axes lie on a single plane which is parallel to those on which the bases 2,3 lie. As far as concerns the material of the cords 6, they may be made of glass fibres or filaments, of steel, of aliphatic or aromatic polyamides, of carbon fibres or any other suitable material having a high resistancetotension.

Moreover, with the body of the bell, there are also embedded identical rigid inserts 7, each of which is constituted by an approximately M-shaped piece of plate. Each piece of plate has two limbs 8 lying on planes parallel to and inwardly of the sides 4 and 5 respectively, and a central portion 9 lying on a plane parallel to the bases 2,3 and disposed inside the belt in such a way as to be adjacent to the cords 6. The two zones 10 of the piece of plate where the connection is made between the respective limbs 8 and the portion 9 are U-shaped with the concavities turned towards the base 3 of the belt.

An important element of this embodiment of belt according to the present invention for achieving the proposed aims is the determination of the number of inserts 7 that must be incorporated in or connected in some way to the body 1. Experimentally, it has been found that, in order to obtain the best results, one must determine the number of the inserts 7 with the following formula: N = Sm (1 + )a where N is the number of inserts 7 to be determined; Sm is the averae development of the belt defined as the length of that circumference measured on the median plane where said plane intersects the central portions 9 of said inserts; a is the width of the inserts measured in the direction of the belt development; is is a coefficient deduced by way of experiment, whose value is to be selected from the range from 0,6 to 1,4.

The choice of the value of coefficient < is effected by a technician of the field on the basis of the characteristics of flexional rigidity and of transverse rigidity which it is desired to impart to the belt. In particular, if a rigid belt is required, the value of coefficient must be near to the lesser value of the above-mentioned range whereas, if a less rigid belt is required, the value of coefficient oc must be near to the greatervalue of said range.

As already stated previously, the fundamental concept underlying the present invention is that of preventing an ordinate succession of the embedded or otherwise connected rigid inserts all having equal dimensions and being disposed at a uniform distance from each other (i.e. eliminating a constant pitch disposition).Nevertheless, among the infinite number of ways to obtain pitch variability, the best results (consistant with constructional simplicity) can be obtained by choosing just two pitch values determined in the way defined herebelow: Of the two pitch values, one will be shorter than the other, and in this text the shorter pitch will be henceforth called "short pitch" and will be indicated with the symbol "p," whereas the greater pitch will be called "long pitch" and will be indicated with the symbol "pre' The total number of pitches - short pitches plus long pitches - is equal to the number N of inserts defined previously hereabove.

The division between long pitches and short pitches must be established in the following manner. The total number of long pitches Ne, is determined by the relation: Ne = pN. As a consequence, the number of short pitches Nc results: Nc = (1 -)N. In both of these formulae, the coefficient ss has a value falling within the range from 0.3 to 0.7, and preferably its value is 0.5.

The length of the single pitches is calculated from the following formula: Pe = Sm (1 +y)N where p, is the short pitch; Sm is the average development of the belt; N is the number of rigid inserts embedded in or otherwise connected to the belt; y is a coefficient ranging rom 0.1 to 0.9, and preferably selected from the sub-range of values from 0.25 to 0.50; (3is the coefficient indicated previously.

The long pitch p, is determined from the following formula: = = (1+ y) pc Once the dimensions of said long pitch p, and short pitch p, have been established, there are very many possible combinations for said pitches, and all of these combinations must be held to fall within the scope of the present invention because since all of them are able to bring about a reduction, at least to some extent, of vibration and noise in a belt used in a continuous speed variator. Among all of the possible combinations, however, there do exist some that are capable of bringing about a reduction of vibration and noise regardless of the speed of and of the power transmitted by the belt, and said some combinations also facilitate simplification of the construction of the belt.The criterion for establishing these advantageous combinations and their definition is as follows: In view of the fact that the zone of the belt which actually makes contact with the pulleys is sensibly less in length than the overall length of the belt development itself, it is possible ideally to subdivide the belt into many tracts or portions which are equal to each other in such a way as to be able to establish for each tract the same pitch sequence. In each tract, the sequence which obtains the desired result mentioned in the preceding paragraph is obtained by symmetrically grouping the pitches; in particular, the most elementary grouping is the one formed by a single short pitch, or by a single long pitch.More complex groupings can be formed by providing a succession of two or more short pitches or two or more long pitches or, byway of another example, a succession of short pitches and long pitches disposed in symmetrical order; an example of the latter is long-pitch - long-pitch - short-pitch - short-pitch.

The groupings described constitute the elements for the formation of the sequence mentioned above that are obtained by disposing the diverse types of groupings one after the other. The essential feature for obtaining a reduction of vibration and noise during variator operation is that each grouping of pitches is followed by a symmetrical grouping. For example, if a grouping is formed by three short pitches, it will be immediately followed by a grouping of three long pitches and successively there can be inserted, for example, the grouping of short-pitch - long-pitch - short-pitch, that will be followed by the grouping long-pitch - short-pitch - long-pitch.In fact, it has been found that the sequence capable of giving the highest grade of uniformity possible in reducing noise and vibration is as follows: PePe-PcPc-PePe-PcPc-PePe-PcPc-PcPc-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe PcPc-PcPc-PePe-PcPc-PePe-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe PcPc-PePe-PcPc-PePe-PcPc-PcPc-PePe-PcPc-PcPc-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe where (as before) p, indicates a long pitch, and p, indicates a short pitch.

All that has been stated above is referred to the particular embodiment represented in Figure 1, where the rigid inserts 7 are embedded in the elastomeric material of the body of the belt.

However, the same things said with regard to the embodiment represented in Figure 1 can also be said with regard to the alternative embodiment represented in Figure 2, where the rigid inserts are outside (in contradistinction to embedded in) the belt body and are connected externally to it. Referring to Figure 2, the belt has a body 11 of elastomeric material in which there is embedded a tension-resistant structure formed by a plurality of flexible and substantially inextensible cords 12 which are parallel to and coplanar with one another. On one face of the body 11 there are present a plurality of reliefs or bosses 13, the number of which, the reciprocal distance and their distribution is established by utilizing the formulae explained in the description of the embodiment illustrated in Figure 1.Elements 14 are placed on and engaged by the reliefs 13, each element 14 having the form of a prismatic block which, in correspondence of the sides of the body 11, present inclined surfaces, and which is provided with a cavity for housing the respective one of said reliefs 13. Moreover, each prismatic block has a pair of fins 15 adapted to contact that face or base of the belt which is opposite to the one from which the reliefs 13 extend or project.

As stated previously, the preferred embodiment of a drive belt according to the present invention is the one indicated in point (b) previously described, namely, the one obtained by connecting to or embedding in the belt body of rigid bodies having identical dimensions and being disposed in such a way that the distances between the rigid bodies are variable. The experimental formulae, given previously, are valid for this situation.

Within the scope of the present invention there is also, however, comprised the arrangement given in point (a) previously described above where the rigid bodies have variable dimensions in the direction of the development of the belt and where the distance between any two adjacent rigid bodies is constant. In such a case, the previously given formulae are formally identical, provided that the meaning to be given to the symbol 'a' therein is changed as follows: a - indicates the width of the free spaces, nameiy, the distance between any one insert and the one adjacent to it.

With this modification of the meaning of the symbol a, the values of ,13 and of y are the same as those previously indicated and all the variations described for the preferred embodiment are valid for the alternative embodiment.

With a drive belt made according to the invention, the aims of the invention are achieved and this can be proved experimentally. The reason why these experimental results are obtained is believed to be as follows: A drive belt is an element of a transmission which comprises at least two pulleys engaged by the belt, transmission of motion from the belt to the pulleys taking place through contact between the sides of the belt and the opposite flanges or sides of the pulleys. In the belts used in continuous speed variators, there are embedded or otherwise connected rigid bodies which, when in contact with the flanges or sides of the pulleys, produce impacts which originate vibrations in the belt and/or in the pulleys. These vibrations, in the first place, cause noise and, in the second place, cause uncontrollable overstresses in the belt itself and, hence, a short service-life of the belt. It is considered that, by reducing and evening out the vibrations in the belt, one succeeds in increasing the service-life of the belt itself and in reducing noise of operation of the speed variators.

Claims

1. A drive transmission belt comprising a belt body which is made of a polymeric material and which is annular, said belt body incorporating a tension-resistant stricture formed by a plurality of cords which are parallel to and coplanar with one another; and a plurality of rigid elements which are spaced apart from each other along the development of the belt and which are connected to said belt body in such a manner as to define in the latter two series of tracts having different transverse rigidities, the length of the tracts of one series being variable whereas the length of the tracts of the other series is constant.

2. A belt as claimed in Claim 1, wherein the series of tracts with a constant length is the one in which there are present the rigid bodies in a number which is derived from the formula N = Sm where (1+α)a Sm is the average development of the belt; a is the dimension of the rigid body in the direction of the belt development; and is is a coefficient chosen from a range of values whose extremities are 0.6 and 1.4.

3. A belt as claimed in Claim 1, wherein the length of the tracts of said one series is due to variability in the pitch of the rigid bodies connected to the belt body.

4. A belt as claimed in Claim 3, wherein said variability in the pitch of the rigid bodies is provided by two constant pitches of which one is of a higher value than the other other and having the ratio (1 +y) between the long pitch and the short pitch, the value y falling within the range of values whose extremities are 0.1 and 0.9.

5. A belt as claimed in Claim 4, wherein said value y falls within the sub-range of values whose extremities are 0.25 and 0.50.

6. A belt as claimed in any one of the preceding Claims, wherein a short pitch Pc is defined by the formula Sm Pc = (1+ ssγ)N where Sm is the average development of the belt; N is the number of rigid bodies connected to the belt; y is the ratio between a long pitch and a short pitch minus 1; and ss is a coefficient whose value falls within the range of values whose extremities are 0.3 and 0.7.

7. A belt as claimed in Claim 6, wherein the value of the coefficient ss is 0.5.

8. A belt as claimed in any one of the preceding Claims, wherein the long pitch pc is defined by the formula p, = (1+y)p0.

9. A belt as claimed in any one of the preceding Claims, wherein, in the belt development, there are distinguishable repeated tracts, whereby in each tract there exist symmetrical sequences of pitches.

10. A belt as claimed in Claim 9, wherein the symmetrical sequence along the belt development is: pepo- p0p0- PePe- p0p0- p8pe - p0p0- p0p0- PePe- p0p0- PePe- p0p0- PePe- p0p0- p0p0- PePe- PePe- PcPc-PcPc-PePe-PcPc-PePe-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe-PcPc-PePe PcPc-PePe-PcPc-PePe-PcPc-PcPc-PePe-PcPc-PcPc-PePe-PcPc-PePe-PcPc-PePe-PcPc-pePe where p, is a long pitch and pc, is a short pitch.

11. A drive transmission belt constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as iilustrated in Figure 1 or Figure 2 of the accompanying diagrammatic drawing.

12. Any features of novelty, taken singly or in combination, of the embodiment of the invention hereinabove described with reference to the accompanying diagrammatic drawing.