TRANSMISSION OF MOTION BETWEEN BELT AND PULLEYS

Abstract: Transmission (1) of motion between a belt (2) of flexible polymeric material, in particular elastomeric material, provided with holes (6) and at least two pulleys, one of which (3) comprises radial protuberances (5) or the like having a distance between them equal to the pitch between the holes of the belt. The other pulley (4) having a greater diameter and comprising protuberances (5) having a distance between them equal to an integral multiple of the pitch between the belt holes up to a null value of said protuberances.

Description: TRANSMISSION OF MOTION BETWEEN BELT AND PULLEYS The present invention is directed to a transmission of motion between a belt and at least two pulleys and more particular¬ ly to a transmission of motion in which the belt is formed by a flexible polymeric material, in particular elastomeric material, provided with suitably reinforced holes into which corresponding radial projecting parts disposed on the pulleys penetrate. As known, in some fields of application there are requested high flexibility belts able to operate during the trans¬ mission with high tangential speed, 50 meters in a second and more, and great ratii of transmission from 1 up to 40. It is possible to use transmissions that comprise a belt formed by a flat body provided with ribs in the form of "V in the lower part for the transmission of torques on at least two pulleys provided with corresponding V-shaped grooves placed side by side; the transmission of torque takes place through the friction occuring between the groove of the belt and that of the corresponding pulleys. Transmissions of this type can be used for instance in household electrical apparatus and appliances, in particular washing-machines. Unfortunately in the cited fields of applications it has been noted the arising of wearing phenomena and the consequent short lifetime of the transmission. Mostly, said drawback is found in consequence of the variations of the speed due for instance to slowings down or to the starting of the machine that makes use of the transmission; in other words, in the variations of motion there can occur excessive slidings between parts of the belt and the pulleys with consequent wearing phenomena. A further drawback of the cited applications resides in the particular and complicated construction of the pulleys necessary for the transmission of motion with the corre¬ sponding belt. A further drawback of transmissions according to the state of the art related to the cited fields of application resides in the necessity of providing an initial step for tensioning the belt and of further retensioning between a working cycle and the other. There are also transmissions of other types which are known as synchronous transmissions and comprise belt teeth engaging with grooves of toothed pulleys. Itcould be thought to apply these transmissions to the cited field of applications where the transmission ratio is very high. In these transmissions a first pulley should have a smaller diameter and few teeth and a second pulley should have a number of teeth proportionally higher. Consequently the whole charge acting on the few teeth of th first pulley should be transferred to the higher number of teeth on the second pulley. In other words, each tooth of the second pulley would resul less stressed making thus the second pulley vainly over¬ sized. Therefore the aim of the present invention is a transmissio of motion devoid of the above cited drawbacks. The object of the present invention is a transmission of motion between a belt provided with holes and at least two pulleys, a first one and a second one, characterized by the fact that the first pulley comprises radial protuberances uniformly distributed with a distance between them equal to the pitch between the belt holes and the second pulley having greater diameter comprises protuberances whose distance is equal to an integral multiple of the pitch between the holes of the belt up to a null value of said protuberances. The present invention will be better understood by the following detailed description made by way of non limiting example with reference to the figures of the attached shee of drawing in which: - figure 1 shows a transmission according to the present invention; - figure 2 shows a partial view of a portion of the belt used in the transmission of figure 1 ; - figure 3 shows a further embodiment of a pulley of a transmission of the present invention; - figure 4 shows a further alternative embodiment of the invention. Reference numeral 1 of figure 1 indicates a transmission of motion between a belt 2 of polymeric material, in particular elastomeric material, and at least two pulleys 3, 4 pro¬ vided with radial projecting parts or protuberances 5. The belt is of the type comprising holes along its entire development according to some particular realizations de- sribed by the Applicant in the previous Italian patent applications No. 20 656 A/83, 20 657 A/83, 20 924 A/83. Hereinafter for sake of simplicity, a portion of one of said possible belts is schematized in figure 2, for other details reference is made to what is already described in the cited patent applications. As it is noted in a possible solution shown in figure 2, the belt 2 comprises a flat-shaped body of elastomeric material provided with circular holes 6 at whose sides there are disposed inextensible cords 7 of Kevlar. The hole 6 is suitably reinforced with loop structures 8 or with structures corresponding to the loop, formed by continuous cords or discontinuous inextensible fibers, for instance textile fibers, apt to unload the stresses transmitted by the protuberances 5 of the pulleys on the sides of the holes where there are the inextensible cords 7. In the embodiment of figure 1 , the pulley 3 comprises a number of radial projecting parts 5 equal to eight and the pulley 4 having a greater diameter comprises only two projecting parts 5 diametrically opposed to each other with a distance between them equal to an integral multiple of the pitch between the holes 6 of the belt 2. In another embodiment shown in figure 3, the protuber¬ ances 5' on the pulley 4 • can be four and are disposed at a maximum distance from one another equal to an integral multiple of the belt pitch. Figure 4 shows a further embodiment of the invention in which one of the two pulleys of the transmission, i.e. the pulley 4" having a greater diameter in relation to the other pulley of the transmission, has three protuber- ances 5" which are offset the one with respect to the other at 12o°, always with a distance between them equal to an integral multiple of the belt pitch. In practice the solution shown in the figures 3 and 4 provides that at least one protuberance 5 is always acting with one of the holes 6 of the belt 2. In one practical embodiment, a transmission forming the object of the present invention characterizes for the following data: 1° Pulley - Outer diameter of the pulley at the root of the protu¬ berances D=21 mm; - height of the protuberances measured in radial direction h = 3 mm; - number of the protuberances uniformly distributed on the first pulley, z = 6 mm; - pitch, p = 11 mm; 2° Pulley - Outer diameter, d = 298 mm; - number of protuberances, 3 at 120° between them; Belt - peripherical development = 1400 mm; - number of holes 111; - width of the belt = 16 mm; - hardness Shore A of the elastomeric material consti¬ tuting the belt, between 70 and 95. In the cited example as well as in the further embodiment, the protuberances disposed on both the pulleys can be carried into effect and manufactured as described in the Italian patent application No. 21 174 A/83 of the Applicant. In all the cited solution, the essential characteristic of the present invention is constituted by the fact that the smaller pulley of the transmission comprises protu¬ berances which are uniformly districuted and the greater pulley of the transmission comprises protuberances which arranged in greater distances than those of the first one; anyhow the distance of these latter protuberances on the pitch line of the pulley is no more equal to the belt pitch', but to a whole number of times the belt pitch, for instance 2, 3, 4, 8 times and more the pitch between the holes of the belt, depending on the circumstances. Thus it is possible to have transmissions in which sup¬ posing that the number of the protuberances of the smaller pulley is equal to n. and supposing that _____ is the number of the protuberances acting on the same pulley, the greater pulley has a number n~ of protuberances according to the formula n 2 : 1 . In particular when the diameter of the second pulley is considerably greater than that of the first one, with equal value for the indexes n.. and n 2 as already indicated, it is possible to have solutions in which the number of the protuberances n_ of the second pulley is equal or lower than the number of protuberances of the first pulley acting with the holes of the belt, care being taken that the value of n 2 does not become lower than two. In a realization of the present invention the transmission is characterized for having a synchronous movement between the belt and the first pulley having smaller diameter and for an asynchronous movement between the belt itself and the second pulley having greater diameter. The mixed transmission comprises also radial protuberances uniformly distributed on the first pulley and no protuberances on the pulley having greater diameter whose outer surface will consequently be cylindrical and smooth. In particular, this latter realization is used when there are great transmission ratii, i.e. when the second pulley has a diameter considerably greater than that of the first pulley and a very wide arc of winding with the relative bel , for instanc with an angle subtended by the arc equal to 240°. The present invention achieves all the aimed purposes. In fact, the presence of radial protuberances uniformly distributed on the entire periphery of the transmission smaller pulley and of further radial protuberances in a very limited number distributed on the second pulley with greater diameter, permit to avoid any risk of sliding of the belt relative to the two pulleys. In practice, the same condition in opposing to slidings occurs in the realization in which the pulley having greater diameter has a smooth periphery, thanks to the wide surface of contact between the belt and the pulley. Consequently the present invention provides the advantage of eliminating the wearing risk and an extension of the lifetime of the materials with respect to what happened in the trans¬ missions relating to the belts of the state of the art pro- vided in the lower part with projecting parts coupled to pulleys comprising V-shaped grooves placed side by side and/or to V-belts with a multiple arrangement associated to corre¬ sponding pulleys provided with corresponding grooves placed side by side. The obtained result cannot be achieved with the synchronous toothed belts or with the chain drives. In fact, in the toothed belt and pulley transmissions it is possible to have a correct operation only if also the pulley having greater diameter of the .transmission comprises protuberances in the form of teeth or the like uniformly distributed with a distance between two adjacent teeth equal to the pitch of the toothed belt. Here, as previously mentioned in the solution of the in¬ vention the protuberances distributed on the pulley having greater diameter are not spaced according to the pitch, but to an integral multiple-of the belt pitch. Therefore, contrary to what occuring in the synchronous toothed transmissions, in the solution of the present in¬ vention the pulley having greater diameter has a number of protuberances that can even be lower than that of the first pulley or equal to the number of protuberances of the first pulley acting with the belt with the advantage of distri¬ buting more uniformly the load on the protuberances of the second pulley and anyhow in a way substantially equal to the stress that involves the protuberances of the pulley with smaller diameter of the transmission. Moreover, unlike what can be found in a transmission pro¬ vided with two pulleys having pins uniformly distributed with a distance between them equal to the belt pitch, in the present realization the number of the belt holes acting on the pins of the second pulley having greater diameter is very limited and said holes at the end of a complete rotation of the belt could be offset with respect to the second pulley before starting a further rotation so as to make the stresses which are transmitted on the holes uniform in time. Anyhow, it is clear that a lower number of holes stressed in the belt which engages with the second pulley can corre¬ spond to a longer lifetime of the belt, with the cited gradual offset operation of the holes between one cycle and the other. The transmission according to the present invention has also the characteristic of a belt apt to different uses, i.e. with the possibility of engaging indifferently not only with both the faces but also with two pulleys whose pins are distributed in a localized way on one pulley and uniformly on the other one or also with two pulleys whose pins are uniformly distributed on the periphery of both the pulleys.. Transmissions in which the pulley with greater diameter com¬ prises always a very limited and localized number of pro¬ tuberances, derive also from the above cited inventive principle, but now with the centering function, entrusting the gripping condition to a wide surface of contact between the belt and the pulley. Transmissions in which the second pulley has a greater outer diameter with regard to the diameter of the first pulley and in particular pulleys whose transmission ratio between the smaller pulley and the greater pulley is comprised between 4 and 20 proved to be suitable for the purposes of the invention. A further advantage of the present invention resides in the practical elimination of the initial and periodical stretch¬ ing of the belt between the pulleys and this since the engagement of the belt on the protuberances is almost in¬ dependent of the approaching force between belt and pulley, so that the grooves of the belt do not become dis¬ engaged by the teeth of the pulleys. Although some particular preferred embodiment according to the present invention have been described and illustrated, it is understood that the present invention comprises in its scope any other alternative embodiment accessible to a technician of the field. For instance, it is possible to have transmissions in which the pulley having greater diameter comprises protuberances in nonsymmetrical positions to one another. Also for instance, there could be transmissions in which the pulley having greater diameter comprises protuberances or projecting parts or pins arranged according to multiples of the belt pitch and also astride of one or more protuberances, further like and/or auxiliary elements,also different from the main ones spaced of a multiple of the pitch or also of the belt pitch.

Claims: C L A I M S : 1. Transmission (1) of motion between a belt (2) provided with holes (6) and at least two pulleys (3, 4), a first one and a second one, c h a r a c t e r i z e d by the fact that the first pulley (3) comprises radial protuberances (5) uniformly distributed with a distance between them equal to the pitch between the holes (6) of the belt (2), and the second pulley (4) having greater diameter comprises protuberances (5) whose distance is equal to an integral multiple of the pitch between the holes of the belt up to a null value of said protuberances. 2. Transmission as in claim 1, characterized by the fact that the number of protuber¬ ances (5') on.the pulley (4') haying greater diameter is equal or lower than the number of protuberances (5) on the first.pulley (3) having smaller diameter. 3. Transmission as in claim 1, characterized by the fact that said protuberances on the pulley (4") having greater diameter are three (5") at 120° between them. 4. Transmission as in claim 1, characterized by the fact that said protuberances (5) on the pulley (4) having greater diameter are two diametri- cally opposed to each other. 5. Transmission as in claim.2 or 3, characterized by the fact that said protuberances on the pulley having greater diameter are equal to one another. 6. Transmission as in claim 1 , characterized by the fact of comprising on the pulley having greater diameter two equal protuberances diamet¬ rically opposed to each other at whose sides there are auxiliary protuberances. 7. Transmission as in claim 1, characterized by the fact that the ratio between the diameter of the greater pulley and the diameter of the smaller pulley of the transmission is comprised between 4 and 20.

Inventors: TANGORRA GIORGIO, TANGORRA, GIORGIO
Applicants: PIRELLI, INDUSTRIE PIRELLI S.P.A.
Application year: 1985
Main classification: F16H7
IPC codes: F16H7, F16H55