The present invention relates to a mechanical transmission, particularly of the chain type.

The invention presented here is aimed at the field of industrial automation or in any case at all fields in which the need to provide mechanical power transmissions arises.

In particular, reference is made to the field of mechanical transmissions between rotating elements arranged at a distance from each other.

Currently, four types of mechanical transmission are fundamentally known for transmitting power between two rotating elements arranged at a distance from each other.

The first type of mechanical transmission consists simply in providing a train of gears by means of which the power is transmitted in each instance among multiple sprockets which are arranged in mutual sequence and mesh with each other.

This type of mechanical transmission has the advantage of flexibility during design, since it allows to reduce or multiply the transmitted torque and speed, also allowing reversal of the rotation speed between the driving sprocket and the driven sprocket. However, once provided, it becomes a rigid system, incapable of adapting the working center distance in an easy manner due to the wear of the individual sprockets of which it is constituted. Moreover, it is a heavy and expensive system.

The second type is called Cardan shaft transmission and consists in using a transfer shaft, indeed known as Cardan shaft, which is interposed transversely between a driving sprocket and a driven sprocket, so that they mesh respectively with two sprockets which are arranged at the ends and integral in rotation with the transfer shaft. In this manner, the motion of the driving sprocket is transmitted directly to the driven sprocket. However, this type of mechanical transmission, which is used in various fields of technology, requires intermediate supports adapted to support rotatably the transfer shaft, in particular in the case of long spans and/or high rotation rates. In fact, the occurrence of excessive flexing of the transfer shaft under the action of static inertial forces, due to the weight of the shaft itself, and dynamic inertial forces, due to any eccentricities of the center of gravity, which under the effect of rotation cause the transfer shaft to flex increasingly, is not rare. In any case, this system, too, is heavy and expensive.

A third type of mechanical transmission uses a belt having a closed profile, which is smooth or provided with teeth on its internal profile and is partially wound around a driving pulley and a driven pulley, which also is provided with teeth or is smooth and/or provided with a peripheral race.

This type of mechanical transmission is very light and simpler and cheaper to provide than the preceding described transmissions, allowing to adapt the tension of the belt at any time, for example by using belt tensioners, in order to compensate for example pulley wear.

The greatest drawback of this type of mechanical transmission resides in that the belt is subject to aging and can be subject to deformations, with consequent offset between the driving pulley and the driven pulley, for example due to plastic deformations and/or slippages of the belt. Accordingly, a response delay can thus occur between the driving pulley and the driven pulley, for example due to elastic deformations. Another significant drawback is constituted by the tension or preloading that must be imparted and maintained on the connecting element of the pulleys, which these transmissions must have in order to transmit power correctly, which is determined essentially by the friction that must be generated between these connecting elements and the corresponding pulleys. This force affects not only the need for a certain elasticity of the connecting element but also the assured calibration of the connecting element and the consequent need to achieve and maintain this calibration in a precise manner. Furthermore, this force worsens the loads on the elements for supporting the rotary motion of the pulley supporting shafts.

The last type of mechanical transmission, similar to the preceding one, uses a transmission chain, constituted by metallic links which are mutually articulated so as to form a closed profile of the chain, instead of the belt, and partially wrapped around a driving sprocket and a driven sprocket.

This type of mechanical transmission is heavier than the preceding one, but maintains its advantages of flexibility in use and economy in manufacture with respect to the first two while obviating the drawbacks dictated by the deformability of the material of which the transmission belts are made and the need for less tension or preloading, since power transmission occurs essentially by "mechanical engagement" between its links and the set of teeth of the pulleys.

Although this last type of mechanical transmission would appear to be the best compromise in the background art, it has however a series of drawbacks, which include the fact of having rather significant inertias, which can thus lower the promptness of the transmission in case of speed changes and/or starting from a standstill and/or sudden interruptions, of not having assurances regarding pretensioning as a consequence of these inertias, of requiring constant lubrication in order to limit the wear of said chain and of the sprockets with which said chain engages, and of being subject to high corrosion in case of use in work environments that are particularly aggressive for example from the chemical standpoint.

Moreover, as regards mechanical transmissions of the known type, the subject matter of the following patent publications is part of the background art: US 5,215,616 A, WO 2009/115249 Al, DE 10.45.744 B and JP H03.204423 A.

In greater detail, patent application US 5,215,616 A describes a classic configuration of a transmission chain, the individual link of which is formed by two rings arranged parallel to each other and mutually associated by two pins.

The individual rings are made of polymeric fibers and are shaped so as to have a transverse thickening, so as to form a receptacle for accommodating with abutment the individual pin that has the purpose of meshing between the teeth of a sprocket. The rings made of polymeric material have the task of connecting the pins and operate only by traction.

As regards international application WO 2009/115249 Al, with particular reference to Figure 5, a transmission chain is described the links of which are made of a polymeric material and are shaped, in a mutually alternating manner, like a strap and like a rope in order to allow correct shape mating between them at the respective surrounding portions. With this shape mating, the strap-like link partially wraps around the rope-like link around the contact portion in a mutually complementary manner.

Differently, German patent DE 10.45.744 B and Japanese patent application TP H03.204423 A both describe transmission chains in which the individual links are constituted by a rigid external body which is provided internally with strong filaments made of polymeric material. In this manner, the meshing and tensile strength of the chain are ascribed separately, respectively, to the shell and to the internal filaments.

The aim of the present invention is to devise a mechanical transmission that is capable of obviating the drawbacks observed above, overcoming therefore the limitations of the background art.

Within this aim, an object of the present invention is to provide a transmission of the mechanical type that has modest costs, is easy to provide, easy to install and maintain, and capable of withstanding high work loads and chemically aggressive work environments.

This aim, and these and other objects which will become better apparent hereinafter, are achieved by a mechanical transmission, particularly of the chain type, comprising a transmission chain constituted by a plurality of mutually articulated links and partially wound around at least two sprockets, characterized in that said links are made of multilayer closed-loop fabric fibers concatenated with each other in such a manner as to give rise to a transmission chain of the type that is flexible in all directions, and in that the end portion of each one of said links passes through the corresponding end portion of the adjacent link, partially wrapping around it and having a transverse tapered region so as to give the articulation defined between said two links the shape of a so-called spherical toggle.

The intended aim and objects are also achieved by a forming method for providing a transmission chain usable in the mechanical transmission, comprising the steps of provision of said transmission chain, engagement of the chain between two forming sprockets, impregnation of the chain with a water-based mixture for the softening, compaction and shaping of the fibers that compose the fabrics of which its links are made; rotation of the impregnated transmission chain around the at least two forming sprockets for a preset number of cycles, preferably in both directions of rotation; drying of the transmission chain.

Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of a mechanical transmission, particularly of the chain type, according to the invention, illustrated by way of nonlimiting example with the aid of the accompanying drawings, wherein:

Figure 1 is a front elevation view of the mechanical transmission according to the present invention;

Figure 2 is an enlarged- scale view of a first detail of the mechanical transmission shown in Figure 1 ;

Figure 3 is an enlarged- scale view of a second detail of the mechanical transmission shown in Figure 1 ;

Figures 4 and 5 are two schematic views of the transmission chain used in the mechanical transmission shown in the preceding figures before and after the forming process.

With particular reference to Figure 1, the mechanical transmission, particularly of the chain type, designated generally by the reference numeral 1, comprises a transmission chain 2 which is constituted by a plurality of mutually articulated links 3, so as to form a transmission chain 2 having a closed profile, i.e., closed onto itself, and partially wrapped at least around two sprockets 4.

According to the invention, the individual links 3 of the transmission chain 2 are made of multilayer closed-loop fabric fibers and are mutually concatenated so as to give rise to a transmission chain of the type that is flexible in all directions.

More specifically, said links 3 are made of ultra high molecular weight polyethylene (UHMWPE).

They can be provided by means of commercially available materials which are currently known for example by the trademark Dyneema®, by the trademark Spectra®, or by the trademark Tekmilon®.

For particular uses, where the use of UHMWPE can be considered redundant or inadequate, these links 3 can be made of fabrics composed of different fibers, such as polyamide, Kevlar®, glass fibers and in general of all materials from which fibers that give rise to fabrics are made.

Advantageously, with particular reference to Figure 2, the end portion 5a of each link 3 passes through the corresponding end portion 5b of the adjacent link 3, wrapping around it partially and being provided with a transverse tapered region so as to give the articulation formed between said two links 3 a "spherical toggle" configuration.

Conveniently, with particular reference to Figure 3, the two sprockets 4 are provided with an external set of teeth which is complementary with respect to the pitch of the transmission chain 2 so as to mesh thereon in an easy manner. With particular reference to Figures 4 and 5, in order to give the transmission chain 2 the correct degree of flexibility and the correct shape, such as to allow its use as a power transmission element with precise meshings with the sprockets 4, the transmission chain 2 can be subjected to a forming process which comprises the following steps:

- provision of the transmission chain 2,

- engagement of the transmission chain 2 between two forming sprockets,

- impregnation of the transmission chain 2 with a water-based mixture for softening the fibers of which the links 3 are made,

- rotation of the impregnated transmission chain 2 around the two forming sprockets for a preset number of cycles,

- drying of the transmission chain 2.

Advantageously, said water-based mixture can be composed of only water or of water and conventional commercial soaps.

As an alternative, it can also be constituted by the liquid in which the chain is designed to work, once installed, optionally immersed and/or in any case by a low-viscosity liquid.

Furthermore, in order to prevent unwanted elongations of the transmission chain 2 during its use in preset operating conditions, the transmission chain 2 can be provided, during supply, with fibers that are pretensioned to a predefined value.

In this manner, during operation, up to a load equal to the predefined value the fibers with which the individual links 3 of the transmission chain 2 are provided, after the forming process described previously, do not undergo elongations, thus preventing the need to use tension adjustment systems to recover the elongations caused by wear or by elastoplastic states, such as automatic or non-automatic mechanical tensioners or other similar devices.

Another advantage, in the case of use of fabrics based on UHMWPE fibers, is determined by the fact that this material has a very low sliding friction coefficient even with itself as well as a high tenacity, understood as resistance to "unraveling". Not least, these materials constituted by UHMWPE have considerable thermal stabilities comprised in a temperature range between -40/120°C. These factors ensure that the transmission according to the invention requires practically no maintenance.

The low friction coefficient, combined with high tenacity, in addition to ensuring perfect operation of the spherical toggle that forms after the forming process, also facilitate the design of the set of teeth of the pulleys and the choice of the materials of which they can be composed.

In this regard, it has been found that the minimum number of teeth of the pulleys, in order to ensure optimum operation of the transmission, is equal to 3, while there is no limitation as regards their maximum number.

The optimum transmission ratios are, in particular, all the ones constituted by integers. This occurs regardless of the pitch, understood as the distance "B" indicated in Figure 5, of the rings that compose the links.

With reference to Figures 3 and 5, the teeth of the pulley preferably have a maximum length "Al " measured in the midpoint of the groove bottom connection "R", preferably slightly smaller (between 0.1 mm and 1 mm) than the internal length "A", measured on the midpoint of the external radius of the spherical toggle generated after the forming process, of the links that engage thereon.

The free length "L" between one tooth and the next and the seat of the links that are not meshing with the teeth can be advantageously slightly greater (between 0.1 mm and 1 mm) than the measurement indicated by "C" in Figure 5 related to said links and always measured on the midpoint of the external radius of the spherical toggle generated after the forming process. In this manner, by following the indicated parameters it is possible to simply establish the medium radius "Rm", on which the geometry of the pulley and of the set of teeth is to be constructed.

The height "FT of the tooth depends on the height "HI " of the links 3 and in general is greater than said measurement "HI " also in relation to the bending radius "Rk" of the head of the tooth.

The groove bottom radius "R" is instead preferably slightly smaller (0.2 mm to 0.5 mm) than the external radius of the spherical toggle generated after the forming process and designated by the reference "Rl " in Figure 5.

The pitch angle of the tooth "a" can be comprised between 1° and 25° measured, as shown in Figure 3, on a line that is parallel to the radius of the pulley, depending on the torque and speed parameters of the power to be transmitted.

The connection to the head of the tooth "Rk" can be sized, with respect to the other described geometric parameters, so as to provide a good guide for entry and separation of the links meshing on the pulley and corresponding set of teeth.

The average width of the tooth identified by the reference "G" in

Figure 3 can preferably be slightly smaller than the internal width "Gl " of the links 3.

The pulley can have along its entire circumference a minimum thickness "F" that is slightly larger than the external width "Fl " of the links 3.

The pulley can also be provided with two external rings 6, for guiding and containing the links during the step for engagement, grip and release from said pulley.

The materials related to the construction of the pulleys can be of various kinds, comprised and chosen within the categories of metals and alloys thereof, of plastic materials or composite materials, and wood.

In practice it has been found that the mechanical transmission, particularly of the chain type, according to the invention achieves fully the intended aim and objects, since it allows to obviate the drawbacks observed for the background art in a simple manner while maintaining negligible production costs and maintenance costs which are quite minimal if not indeed absent, in general and/or if compared with those of the background art.

Furthermore, by virtue of the lightness of its structure it is possible to reduce considerably the inertia of the rotating masses, with all the advantages that arise from this in terms of promptness of response and easy of "disengagement" at the exit of the sprockets. This consequently minimizes one of the main defects of steel link chains, which are affected, due to the their great weight, by the centrifugal forces that seek to "wind them back" onto the sprockets. By way of example, it has been observed that a chain with a length of approximately 5 linear meters has a mass of approximately only 1.3 kilograms with a weight/power ratio that is distinctly lower (up to 15 times) than a traditional chain with carbon steel links.

The chain thus conceived and described in all of its prerogatives

(including the possibility of pretensioning the fibers, the forming process, the low weight, the low friction coefficient, the high tenacity) is therefore a system for transmission of rotary motion that is characterized by ease and economy in production and assembly and which, combined with a practically total lack of maintenance, also overcomes the limitations of steel link chains, such as their high inertia, which causes the above described rewinding effect, the highly uncertain and scarcely determined pretensioning, the need in this regard to check it and restore it manually or automatically, the need for continuous lubrication.

Another advantage of the mechanical transmission according to the present invention resides in that it can be used in power transmissions between two sprockets that do not lie on the same plane, differently from transmissions for example with toothed belts or friction belts. A further advantage of the mechanical transmission according to the present invention resides in that it has an extremely high efficiency, equal to approximately 0.98, understood as the ratio between the energy actually transmitted and the energy to be transmitted.

Another advantage of the mechanical transmission according to the present invention resides in that during the production step the fibers of which the links of the chain are made can be pretensioned up to a certain value and in that during operation, after the forming process, the links no longer undergo any elongation where said value is not exceeded.

In this manner it is no longer necessary to tension in successive steps the transmission chain for its use or to calibrate with excessive precision its tension upon first assembly, since it is sufficient to size correctly the entire mechanical transmission for the loads that it must withstand, all this being in favor of a distinct decrease in the loads on the supporting elements of the driving and driven parts.

All this leads to substantial economic and flexibility advantages with respect to chains made of steel or the like with links of a known type.

A further advantage of the mechanical transmission according to the present invention resides in that since the transmission chain is made of UHMWPE fibers, by virtue of the self-lubricating capabilities of these materials, differently from mechanical transmissions of the known type it is not necessary to use additional external substances to compensate for the increase in internal frictions and the consequent dispersion of energy needed to overcome these frictions.

Another advantage of the mechanical transmission according to the present invention resides in that for uses in environments with temperatures that are compatible with those of the materials of which it is composed, the transmission chain thus conceived has excellent thermal stability, which, together with what has been described previously, makes this type of transmission practically free from any type of maintenance.

The mechanical transmission, particularly of the chain type, thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

All the details may furthermore be replaced with other technically equivalent elements.

In practice, the materials used, as well as the dimensions and the contingent shapes, may be any according to the requirements and the state of the art.

The disclosures in Italian Patent Application no. 102016000106679 (UA2016A007597), from which this application claims priority, are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.