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DESCRIPTION

Technical field

The present invention is relative to a hypocycloidal drive mechanism.

Technological background

The use of drive mechanisms is widely known, in general to transfer motion between an input shaft and an output shaft through a gear in different applications, in particular to vary (namely to multiply or to reduce) the rotation speed and the torque between in input shaft and the output shaft, which are able to rotate around a same rotation axis.

More in detail, the gears are wheels comprising toothed or lobed organs, which can rotate around respective rotation axes and cooperate with one another so as to allow a rotation motion to be transferred. The above-mentioned gears define:

- an ordinary gearing, when they comprise a plurality of toothed or lobed organs, in which the rotation axes are operatively fixed, or

- a planetary gearing, when they comprise at least one toothed or lobed sun organ, whose rotation axis is operatively fixed, and at least another toothed or lobed planet organ, whose rotation axis is operatively movable.

Among the drive mechanisms provided with a gear making up a planetary gearing, epicyclic drive mechanisms and hypocycloidal drive mechanisms are known.

Epicyclic drive mechanisms comprise a gear that makes up a planetary gearing, in which a point, which belongs to the pitch circumference defined by a toothed or lobed planet organ suited to externally roll on - thus engaging - the pitch circumference defined by a toothed or lobed sun organ, operatively describes an epicycloidal trajectory.

Generally, epicyclic drive mechanisms comprise a plurality of toothed or lobed planet wheels, which are mounted with freedom of rotation on a support element called planet carrier, which also supports - thus allowing it to rotate - a toothed or lobed sun wheel, which externally cooperates with the toothed or lobed planet wheels; this is all arranged inside a cam, also called ring, which has an internal toothing or lobing, with which the toothed or lobed planet wheels externally cooperate. Typically, these epicyclic drive mechanisms are built with traditional gears, in particular gears with involute gear profile.

These epicyclic drive mechanisms feature motion reversibility, high precision, reduced mechanical clearance, and need for numerous subsequent stages to reach a suitable gear ratio. For these reasons, they have high manufacturing and assembling costs.

On the other hand, hypocycloidal drive mechanisms comprise a gear that makes up a planetary gearing, in which a point, which belongs to the pitch circumference defined by a toothed or lobed planet organ suited to internally roll on - thus engaging - the pitch circumference defined by a toothed or lobed sun organ, operatively describes a hypocycloidal trajectory.

More specifically, hypocycloidal drive mechanisms are known, which comprise an input shaft and an output shaft, which are able to rotate around a same rotation axis , and a gear defining a hypocycloidal gear train, which is interposed in a kinematic manner between said input shaft and said output shaft; said gear comprising a (primary) drive stage comprising:

- a (primary) cam defining a (primary) internal sun toothing or lobing , which is centered around said rotation axis ; and

- a primary hypocycloidal element, which eccentrically rotates, with an orbital motion, relative to said rotation axis and is provided with a (primary) external planet toothing or lobing, which peripherally meshes with said (primary) internal planet toothing or lobing.

The hypocycloidal drive mechanisms described above generally have a compact structure, in which the sun and planet toothing or lobing have large and sturdy teeth or lobes and the reduction ratio is equal to l:n (with 1 being one rotation of the eccentric and n being the number of teeth or lobes of the rotating part) .

Hence, in the light of what described above, hypocycloidal drive mechanisms are generally appreciated in the technical field for their high reliability, sturdiness and long operating life.

Though, hypocycloidal drive mechanisms of the known type have many drawbacks.

One drawback is due to the fact that these hypocycloidal drive mechanisms are subject to vibrations, in particular caused by the hypocycloidal element, which moves orbiting around the rotation axis, in particular dragged by an eccentric portion carried by the input shaft. In this way, the above-mentioned vibrations are propagated in a kinematic manner along the entire mechanism and negatively affect its operation in terms of performance, effectiveness, and wear of the parts mechanically cooperating with one another. Another drawback, which is at least partially linked to the drawback discussed above, occurs when high reduction ratios need to be generated. To this regard, in order to avoid the vibrations that would be generated by numerous drive stages inside the gear, it is necessary to increase as much as possible the number of teeth and lobes available in every single drive stage, to be distributed in a circular manner on progressively increasing diameters. As a consequence, the number of parts, the external dimensions, the relative tolerances and, last but not least, the manufacturing costs increase as the reduction ratio requested increases.

Another type of drawback derives from the nature of the known hypocycloidal drive mechanisms, in which the rotary movement of the output shaft needs to be separated from the oscillation of the eccentric parts, in particular of the hypocycloidal elements provided with planet toothing or lobing, whose orbital rotation causes the motion of the output shaft. This "separation" requires the eccentric shaft to operate in a projecting manner relative to the cam, thus making it necessary for bearings and bushings to be provided, which are subject to a significant flexing stress and, therefore, need to have appropriate dimensions.

Another drawback is due to the fact that, when different hypocycloidal drive stages are provided in the planetary gearing defined by the gear, they are generally made up of further external planet toothings or lobings, which are integrally supported by the hypocycloidal element itself (besides the external toothing or lobing of the primary stage) , so as to rotate therewith, and cooperate with further cams having corresponding further internal sun toothings or lobings peripherally meshing with them. This configuration makes it necessary for all the external planet toothings or lobings to have the same eccentricity, thus substantially varying only their mutual angular stagger relative to a same rotation axis. Clearly, this restriction deeply limits the choice of gear ratios as a function of the structure of the primary stage.

In the light of the drawbacks mentioned above, in the hypocycloidal drive mechanisms of the known type it is necessary to use bushings that:

- must bear the torque and the radial load of the secondary (outputs haft),

- rotate at the speed of the primary (input shaft), and

- work in a projecting manner.

Therefore, this leads to an increase in the frictions and in the heat developed, unless one adopts expensive roller bearings and accepts the consequent size increase.

Finally, no one has ever managed to obtain particularly reduced dimensions in hypocycloidal drive mechanisms. This is due to the fact that the teeth and lobes distributed on the external planet toothing or lobing get smaller and smaller, with working tolerances that become more and more pressing. Therefore, the minimum eccentricities and the reduced height of the teeth or lobes cause a disengagement and a slipping of the parts as soon as the tolerances and the mechanical clearances permit it.

In order to remedy these drawbacks, in the hypocycloidal drive mechanisms of the known type, a compensation of the vibrations has been suggested, which is performed by means of opposite eccentric masses, which causes, in a disadvantageous manner, a duplication of the external planet toothings or lobings rotating, in an orbital manner, around the rotation axis of the input shaft and of the output organ, with a consequent cost increase. Summary of the invention

The object of the present invention is to provide a hypocycloidal drive mechanism, which is able to solve these and other drawbacks of the prior art and which, at the same time, can be produced in a simple and economic fashion.

According to the present invention, this and other objects are reached by means of a mechanism having the features set forth in the appended independent claims.

The appended claims are an integral part of the technical teaches provided in the following detailed description concerning the present invention. In particular, the appended claims define some advantageous embodiments of the present invention and describe optional and detailed technical features.

One of the advantages reached by means of the embodiment described, by mere way of example, in the detailed description is that of obtaining a significant reduction of the vibrations, also by using a plurality of drive stages (in particular, reduction drive stages), which are arranged one after the other in a train-like manner. Preferably, these drive stages conveniently have small and fast eccentric masses in a preceding primary drive stage, and larger and slower eccentric masses in a following secondary drive stage. In other words, the teeth or lobes of the primary drive stage are available in a larger number and smaller (in terms of transverse extension and of axial extension) than the teeth or lobes of the secondary drive stage. As a consequence, one obtains:

a) a uniform distribution of the specific pressure on the single teeth, both in the primary stage and the in secondary stage, with load and wear being uniformly distributed, as well; and

b) a reduction of the amplitude and of the frequency (the so-called "sound timbre") of the vibration itself.

A further advantage reached by means of the embodiment described, by mere way of example, in the detailed description is the possibility to obtain flexible reduction ratios, which are not limited by a common eccentricity of the hypocycloidal planet elements available in the different drive stages of the gear. This benefit, for example, can be obtained due to the fact that between at least one preceding drive stage and one following drive stage there is interposed an intermediate shaft (secondary shaft), which transfers the motion while rotating and, at the same time, is not rigidly connected to the primary stage and to the secondary stage. With reference, in particular to the embodiment shown, in which the gear is made up only of one preceding primary drive stage and of one following secondary drive stage, this specific configuration can be defined, in technical terms, as a "twin shaft independent" hypocycloidal drive mechanism. Therefore, in this way, the toothings or lobings of the drive stages involved can be designed with eccentricities and dimensions that are proportionate to the torques to be delivered in the different drive stages, without having to comply with the structural limitations that are typically applied in the hypocycloidal drive mechanisms according to the prior art .

A further advantage reached by means of the embodiment described, by mere way of example, in the detailed description is due to the fact that the intermediate shaft features with a stable operating mode, which is substantially free from binding and from bending and torsion stresses, which allows the mechanism to work with a reduced friction and a high efficiency and to be produced in a simple and economic fashion. This advantage, for example, can be obtained by means of rotation supports (or so-called main bearings) of the intermediate shaft close to at least one of the axial regions - and preferably both of them - arranged before and after its intermediate eccentric portion, thus preventing it from working in a projecting manner. The rotation supports are preferably obtained by using turning couplings and/or bushings, instead of using roller bearings, which would imply high costs.

A further advantage obtained with the embodiment described, by mere way of example, in the detailed description is due to the fact that the components making up the hypocycloidal drive mechanism are available in a particularly reduced number, thus combining numerous functions in each one of these components and, in particular, permitting an easy and simple cartridge-like assembly, which can be easily performed at a minimum cost.

Another advantage obtained with the embodiment described, by mere way of example, in the detailed description is due to the fact that the hypocycloidal drive mechanism is able to bear high radial and torsional stresses. This advantage, for example, can be especially obtained in those cases in which the drive stage immediately preceding the output shaft is dimensioned so as to have wide meshing surfaces (where a sliding and a rotation between the toothings or lobings take place), which extend in an axial and transverse direction relative to the rotation axis of the hypocycloidal drive mechanism. As a consequence, it is possible to obtain particularly remarkable and significant performances, in which the power or torque delivered per volume unit reaches higher levels than those of the hypocycloidal drive mechanisms currently making up the state of the art.

Another advantage obtained with the embodiment described, by mere way of example, in the detailed description is due to the fact that the above-mentioned hypocycloidal drive mechanism is particularly insensitive to processing tolerances, which translates into the ability to operate even in degraded conditions of wear of the teeth or lobes, without particular degradation of the output performances (only residual clearances slightly more marked) . This advantage makes it particularly easy for the components of the hypocycloidal drive mechanism to be manufactured with a plastic material, in particular by means of injection molding, thus remarkably reducing the mechanical processing costs that are typically requested for objects with more restricted tolerance classes.

Brief description of the drawings

Further features and advantages of the present invention will be best understood upon perusal of the following detailed description, which is provided by way of example and is not limiting, with reference to the accompanying drawings, which specifically show what follows :

- figure 1 is a partial longitudinal section view of a hypocycloidal drive mechanism according to an exemplary embodiment of the present invention;

figure 2 is an exploded prospective view of the mechanism shown in figure 1 ;

- figure 3 is a lateral view of some components of the mechanism shown in the previous figures;

- figures 4 to 7 are section views of the mechanism shown in the previous figures, which are obtained according to the lines IV-IV to VII-VII shown in figure 1; and

- figures 8 and 9 are prospective views of components of the mechanism shown in the previous figures.

Detailed description of the invention

With reference to the figures from 1 to 9, number 10 indicates, as a whole, a hypocycloidal drive mechanism according to an exemplary embodiment of the present invention .

Mechanism 10 comprises an input shaft 12, which, in the embodiment shown, is provided with an eccentric portion 14, and an output shaft 16, which are able to rotate around a same rotation axis X-X, and a gear 18 defining a hypocycloidal gear train, which is interposed in a kinematic manner between input shaft 12 and output shaft 16. Gear 18 comprises, in turn, a primary drive stage comprising :

- a primary cam 20 defining a primary internal sun toothing or lobing 22, which is centered around rotation axis X-X; and

- a primary hypocycloidal element 24, which eccentrically rotates, with an orbital motion, relative to rotation axis X-X, in the embodiment shown driven by eccentric portion 14, and is provided with a primary external planet toothing or lobing 26, which peripherally meshes with the above-mentioned primary internal sun toothing or lobing 22.

The above-mentioned gear 18 comprises, furthermore:

- a secondary drive stage comprising

a secondary hypocycloidal element 32, which eccentrically rotates, with an orbital motion, relative to rotation axis X-X and is provided with a secondary external sun toothing or lobing 34, and

a secondary cam (36), which, in the embodiment shown, is integral to output shaft 16, so as to rotate therewith, and defines a further secondary internal sun toothing or lobing 38, which peripherally meshes with the further secondary external planet toothing or lobing 34; and

- an intermediate shaft 28, which is kinematically interposed between primary hypocycloidal element 24 and secondary hypocycloidal element 32 in a rolling manner so as to be rigidly disengaged from them, can rotate around rotation axis X-X and, in doing so, is controlled by primary hypocycloidal element 24, and is provided with an intermediate eccentric portion 30, which is adapted to cause secondary hypocycloidal element 32 to rotate.

Therefore, the eccentricities relative to rotation axis X-X, the dimensions and the profiles of the primary and secondary internal sun toothings or lobings 22, 38 and of the complementary primary and secondary external planet toothings or lobings 26, 34 can be selected in a mutually independent manner between the primary drive stage and the secondary drive stage of gear 18. Moreover, this also leads to a significant reduction of the vibrations transmitted through the primary drive stage and the secondary drive stage .

In the embodiment shown, mechanism 10 works as a reduction gear, which means that hypocycloidal gear 18 allows the rotation speed transmitted by input shaft 12 to be reduced.

In the embodiment shown and as described more in detail below, input shaft 12 is a shaft that can be connected to a motor (not shown), for example an electric motor, which is able to cause it to rotate around rotation axis X-X. In particular, the above-mentioned shaft has a cylindrical shape and a circular section, eccentric portion 14 preferably being a cylindrical end having a circular transverse section with an axis that is staggered relative to the rest of the above-mentioned shaft. Preferably, the transverse section of the eccentric portion has a radius that is smaller than the one of the rest of the shaft.

In further embodiments, inlet shaft 12 can be the rotor of the electric motor, thus reducing the overall number of pieces.

Preferably, input shaft 12 is made of steel, in particular ground steel.

In the embodiment show, eccentric portion 14 is manufactured as one single piece together with input shaft 12.

In the embodiment shown, mechanism 10 comprises a casing 40 defining a through cavity, which houses gear 18 and in which input shaft 12, output shaft 16 and intermediate shaft 28 are supported during their rotation around the same rotation axis X-X. Preferably, casing 40 is manufactured with a plastic material, for example by means of an injection molding process.

As described more in detail below, the rotation transmitted by input shaft 12, which acts as the "driving element" of mechanism 10, can be indifferently transmitted:

- to output shaft 16 through gear 18, in case casing 40 is operatively kept stationary, or

- to casing 40 through gear 18, in case output shaft 16 is operatively kept stationary.

Therefore, the role of "driven element", through which the rotation motion is delivered to the outside of mechanism 10, can be played by output shaft 16 or by casing 40, according to which one of these two elements is kept stationary during the use of mechanism 10.

In the embodiment shown, input shaft 12 is coupled in a turning manner (i.e. with freedom of axial rotation) relative to casing 40, preferably by means of a bushing 42, which is mounted inside it. In particular, bushing 42 axially rests on an abutment 44 obtained in casing 40. Preferably, bushing 42 has a collar or radial flange 46, which is arranged, for example, in correspondence to an end and rests against abutment 44.

In the embodiment shown, bushing 42 is manufactured with a plastic material, for example by means of an injection molding process. Preferably, bushing 42 is of the self-lubricating type and, in particular, is made of a plastic material known as Iglidur®.

In the embodiment shown, abutment 44 is manufactured as an end narrowing of the cavity defined by casing 40, in particular arranged in correspondence to the axial end into which input shaft 12 is inserted.

In the embodiment shown, primary cam 20 is integral to casing 40, so as to rotate therewith. Preferably, the primary internal sun toothing or lobing 22 is defined by a circumferential succession of protuberances, between which corresponding recesses are interposed. In particular, the protuberances have a substantially semi-circular shape and project from the lateral inner cylindrical walls of the cavity defined by casing 40, whereas the recesses join the protuberances defining circular arcs with the concavity radially facing the inside.

In the embodiment shown, primary internal sun toothing or lobing 22 is arranged on the inner walls of casing 40 and, in particular, is manufactured as one single piece together with said casing 40. In an alternative embodiment (not shown), the above-mentioned primary internal sun toothing or lobing can be made up of a plurality or rollers or pins, which are arranged in a circumferential manner inside the casing, for example on an annular body that can be inserted into the cavity defined by the casing.

In the embodiment shown, the primary hypocycloidal element comprises a disc, in particular with a circular cross section, which peripherally supports the primary external planet toothing or lobing 26. Preferably, the primary external planet toothing or lobing 26 is manufactured as one single piece together with the disc.

In the embodiment shown, eccentric portion 14 is coupled in a turning manner (i.e. with freedom of rotation) to primary hypocycloidal element 24. In particular, primary hypocycloidal element 24 comprises a seat 48, which is obtained axially, in particular through the disc, and is adapted to house eccentric portion 14 by means of a turning coupling. Preferably, seat 48 is manufactured as an eccentric hole (which is centered in the spot indicated with reference 0) , advantageously a through hole, which houses eccentric portion 14.

In the embodiment shown, primary hypocycloidal element 24 and intermediate shaft 28 have, respectively, a plurality of projections 50, arranged on a transverse cooperation surface 24a and a series of holes 52, axially obtained on another transverse cooperation surface 28a, which create a rolling driving interface, in particular by means of a tangential contact. Transverse cooperation surface 24a is axially spaced apart from the transverse cooperation surface 28a, thus avoiding friction or sliding. Each one of projections 50 supported by respective transverse cooperation surface 24a is adapted to be eccentrically inserted into a corresponding hole 52 supported by the other transverse cooperation surface 28a, and can be moved, by means of relative rolling, on the cylindrical walls of the above-mentioned hole 52, thus provoking a rotation of intermediate shaft 28 by means of the orbital motion of primary hypocycloidal element 24.

For example, the distance between transverse cooperation surfaces 24a and 28a is created during the assembly, thus permitting the creation of a clearance in the axial direction between the components making up these surfaces, in particular between the primary hypocycloidal element 24 and the intermediate shaft 28.

In other words, the relative radial thrust between projections 50 and holes 52, due to the orbital motion transmitted from inlet shaft 12 to primary hypocycloidal element 24, generates a rotation motion around axis X-X in intermediate shaft 28.

Preferably, projections 50 and corresponding holes 52 are arranged in a circumferential and radial manner on the respective transverse cooperation surfaces 24a and 28a.

In the embodiment shown, all projections 50 axially protrude from transverse cooperation surface 24a offered by primary hypocycloidal element 24, whereas all holes 52 are accordingly obtained on the transverse cooperation surface 28a exhibited by intermediate shaft 28. In an alternative embodiment (not shown), it is also possible to switch the arrangement of the projections and of the holes between the transverse cooperation surfaces of the primary hypocycloidal element and of the intermediate shaft. In a further alternative embodiment (not shown), it is also possible to create an alternate sequence of projections and holes on the transverse cooperation surface of the primary hypocycloidal element and, at the same time, another complementary alternate sequence of projections and holes on the transverse cooperation surface of disc 54 of the intermediate shaft.

In the embodiment shown, projections 50 are manufactured as pins with a circular cross section that is smaller and eccentric relative to the circular cross- section of holes 52. In particular, the axes of projections 50 and of holes 52 are parallel to rotation axis X-X.

In the embodiment shown, holes 52 are manufactured as through openings extending through the respective transverse surface 28a.

In the embodiment shown, primary hypocycloidal element 24 is manufactured as one single piece, wherein, in particular, the above-mentioned disc peripherally has the primary external planet toothing or lobing 26 and axially supports seat 48 and projections 50 and/or holes 52 of transverse cooperation surface 24a.

In the embodiment shown, primary hypocycloidal element

24 is manufactured with a plastic material, for example by means of an injection molding process. Preferably, the plastic material used is of the self-lubricating type, for example of the type marketed under the name of Delrin®.

In the embodiment shown, intermediate shaft 28 comprises :

- a disc 54, and

- a stem 56, which has a smaller diameter relative to disc 54 and supports intermediate eccentric portion 30.

Therefore, disc 54 is coupled and integral - so as to rotate therewith - to intermediate eccentric portion 30.

In the embodiment shown, disc 54 creates a rolling driving interface, in particular by means of a tangential contact, with primary hypocycloidal element 24. In particular, disc 54 supports the transverse surface 28a facing transverse surface 24a of primary hypocycloidal element 24.

In particular, disc 54 and stem 56 are both centered around rotation axis X-X and are integral to one another, so as to rotate together around the latter.

In the embodiment shown, disc 54 and stem 56 are manufactured as two separate pieces and are caused to become integral during the assembly. In particular, stem 56 has an end 60, which is splined to disc 54. Advantageously but not necessarily, end 60 has a cross section with a substantially polygonal shape (in the example shown in figure 5, it has the shape of a regular hexagon), optionally with curved sides. The structure of the coupling between end 60 and disc 54 guarantees an easy and stable assembly .

In the embodiment shown, disc 54 has an outer diameter that is smaller than the inner diameter of the through cavity defined by casing 40. In other words, disc 54 has a radial clearance relative to the above-mentioned cavity, hence without the presence of a contact to the inner walls of casing 40 (or of a turning coupling to casing 40) during the rotation of intermediate shaft 28, thus reducing possible unwanted friction phenomena in this region of hypocycloidal drive mechanism 10.

In the embodiment shown, secondary eccentric portion 30 has a circular cross section having a center 0' that is staggered relative to the one of the rest of stem 56. In particular, the above-mentioned cross section has a diameter that is larger than the one of the rest of stem 56 and, more in detail, has an eccentricity that is different from the one existing between driving shaft 12 and its eccentric part 14.

In the embodiment shown, intermediate shaft 28 is made of a plastic material. Preferably, the plastic material used is of the self-lubricating type, for example of the type marketed under the name of Delrin®. In particular, disc 54 and stem 56 are made of a plastic material, for example each one of them being manufactured by means of an injection molding process.

In the embodiment shown, mechanism 10 comprises, furthermore, an annular stop organ 58, which is inserted into casing 40 so as to integrally rotate therewith. Annular stop organ 58 is run thorough by intermediate shaft 28, in particular by stem 56, thus creating a support for the rotation around rotation axis X-X by means of a turning coupling (i.e. with freedom of axial rotation) .

In the embodiment shown, after mechanism 10 has been assembled, disc 54 is arranged, on one side, with a slight axial clearance relative to primary hypocycloidal element 24 and, on the other side, with a slight axial clearance relative to annular stop organ 58. In this way, it is possible to avoid a friction or sliding of disc 54 between the transverse surfaces exhibited by primary hypocycloidal element 24 and by annular stop organ 58 and facing, on opposite sides, disc 54.

Preferably, intermediate shaft 28 is supported, during its rotation around rotation axis X-X, close to at least one of the axial ends of intermediate eccentric portion 30, in particular in the axial regions of intermediate shaft 28 that are arranged before and after intermediate eccentric portion 30, so as to be adjacent thereto. In the embodiment shown, these axial regions have a circular cross section centered around rotation axis X-X, unlike intermediate eccentric portion 30, which is staggered relative to this axis. As described more in detail below, these axial regions are preferably the ones indicated by numbers 62 and 74. In this way, the entire rotary structure firmly rests on two main bearings at the end, without rotary projecting parts. This further reduces, in a significant manner, the vibrations and the wear of the eccentric masses available in drive mechanism 10.

More preferably, intermediate shaft 28 is coupled in a turning manner around rotation axis X-X close to:

- one of the above-mentioned axial ends, with annular stop organ 58 inserted into casing 40 in a rotatory integral manner; and/or

- the other one of the above-mentioned axial ends, with secondary cam 36.

In the embodiment shown, intermediate shaft 28 is supported, during its rotation, close to both the axial ends of intermediate eccentric portion 30, in particular, on one side, with annular stop organ 58 and, on the other side, with secondary cam 36.

In the embodiment shown, with reference in particular to figures 8 and 9, annular stop organ 58 is mounted by means of interference in the inner walls of casing 40. By way of example, at least one between annular stop organ 58 and casing 40 has, in its periphery, at least one radial bulge or wedge 59a, 59b, adapted to be interlocked on the lateral interface walls supported by the other one between annular stop organ 58 and casing 40. Preferably, both annular stop organ 58 and casing 40 have at least a plurality of radially external bulges or wedges 59a and, respectively, a plurality of radially internal bulges or wedges 59b, which are complementary to one another and, in particular, are adapted to create a shape coupling. For example, bulges 59a and 59b can define a coupling that is substantially of the dovetail type between annular stop organ 58 and casing 40.

In the embodiment shown, intermediate shaft 28 has a segment 62 (e.g. on its stem 56), which has a circular cross section centered around rotation axis X-X and is coupled in a turning manner in a central opening 64, which supported by annular stop organ 58. In particular, segment 62 is axially arranged between end 60 and intermediate eccentric portion 30.

In the embodiment shown, therefore, intermediate shaft 28 is integral to intermediate eccentric portion 30, so as to rotate therewith around rotation axis X-X, by means of a turning coupling on the rotation support (or main bearing) defined by the bushing-like cooperation created between segment 62 and central opening 64.

In the embodiment shown, as illustrated by way of example in figure 5, the cross section of segment 62 is comprised - and especially inscribed - in the cross section of end 60 (and, as a consequence, in the cross section of segment 62) . This makes it easier for mechanism 10 to be assembled, due to the fact that one can introduce into casing 40, in sequence, disc 54, annular stop organ 58 and, subsequently, stem 56, causing it to be coupled to disc 54, in particular allowing end 60 to run through central opening 64, so that it can be interlocked in disc 54, hence allowing segment 62, which is coaxial to end 60, to be supported during its rotation in the above-mentioned central opening. In the embodiment shown, secondary hypocycloidal element 32 is guided, in its orbital motion around rotation axis X-X, by means of a rolling guide interface, in particular by means of a tangential contact with annular stop organ 58.

In the embodiment shown, annular stop organ 58 and secondary hypocycloidal element 32 have a pair of respective transverse cooperation surfaces 58a and 32a, which face one another and create the above-mentioned rolling interface, in particular by means of a tangential contact. Furthermore, in the embodiment shown, surfaces 58a and 32a are axially spaced apart, thus avoiding mutual friction and sliding. Each transverse cooperation surface 58a and 32a has a plurality of projections 66 and/or holes 68, which are obtained in an axial direction, wherein each one of projections 66 supported by respective transverse cooperation surface 32a is adapted to be eccentrically inserted into a corresponding hole 68 arranged on the other transverse cooperation surface 58a and can be moved by rolling on the cylindrical walls of corresponding hole 68, thus guiding the orbital motion of secondary hypocycloidal element 32.

For example, the distance between transverse cooperation surfaces 58a and 32a is created during the assembly, thus permitting the creation of a clearance in the axial direction between the components making up these surfaces, in particular between stop organ 58 and intermediate shaft 28. In other words, the constraint between projections 66 and holes 68 helps guide the orbital motion around rotation axis X-X of secondary hypocycloidal element 32.

Preferably, projections 66 and corresponding holes 68 are arranged in a circumferential and radial manner on respective transverse surface 32a and 58a.

In the embodiment shown, all projections 66 axially protrude from transverse surface 32a offered by secondary hypocycloidal element 32, whereas all holes 68 are accordingly obtained on transverse surface 58a exhibited by annular stop organ 58. In an alternative embodiment (not shown) , it is also possible to switch the arrangement of the projections and of the holes between the transverse cooperation surfaces of the primary hypocycloidal element and of the annular stop organ. In a further alternative embodiment (not shown), it is also possible to create an alternate sequence of projections and holes on the transverse surface of the secondary hypocycloidal element and, at the same time, another complementary alternate sequence of projections and holes on the transverse surface of the annular stop organ.

In the embodiment shown, projections 66 are manufactured as pins with a circular cross section that is smaller and eccentric relative to the circular cross- section of holes 68. In particular, the axes of projections 66 and of holes 68 are parallel to rotation axis X-X.

In the embodiment shown, holes 68 are manufactured as through openings extending through respective transverse surface 58a.

In the embodiment shown, holes 68 are peripheral and arranged in a circumferential and radial manner relative to central opening 64 as well as centered around rotation axis X-X.

In the embodiment shown, annular stop organ 58 is manufactured as one single piece, for example with a plastic material (in particular, by means of an injection molding process) . Preferably, the plastic material used is of the self-lubricating type, for example of the type marketed under the name of Delrin®.

In the embodiment shown, secondary hypocycloidal element 32 comprises:

- a ring 67, which cooperates in a rolling manner with annular stop organ 58, and

- a sleeve 69, which has a diameter that is narrowed relative to ring 67 and peripherally supports secondary external toothing or lobing 34.

Preferably, secondary hypocycloidal element 32 is made of a plastic material. Preferably, the plastic material used is of the self-lubricating type, for example of the type marketed under the name of Delrin®.

In the embodiment shown, ring 67 is manufactured as one single piece together with sleeve 69, for example with the above-mentioned plastic material (in particular, by means of an injection molding process) . In the embodiment shown, secondary hypocycloidal element 32 has a through cavity 70, in which intermediate eccentric portion 30 is coupled in a turning manner (i.e. with freedom of axial rotation) . In particular, through cavity 70 extends through ring 67 and sleeve 69, which are both assembled so as to be eccentric relative to rotation axis X-X.

Preferably, through cavity 70 is axially crossed, in particular in a through manner, by the above-mentioned intermediate eccentric portion 30. In particular, through cavity 70 has a cross section with a circular shape, which is centered in the same center 0' arranged in a staggered position relative to rotation axis X-X and belonging to intermediate eccentric portion 30.

In the embodiment shown, secondary cam 36 has a cup- shaped portion 71 defining, on the inside, an axial cavity having the above-mentioned secondary internal sun toothing or lobing 38 and in which secondary hypocycloidal element 32 (especially the above-mentioned sleeve 69) is housed with a peripheral engagement. Preferably, the outer walls of cup-shaped portion 71 have a circular cross section and are coupled in a turning manner to inner walls 40a of casing 40 around rotation axis X-X.

In the embodiment shown, output shaft 16 axially projects from cup-shaped portion 71 and is integral thereto .

In the embodiment shown, after mechanism 10 has been assembled, ring 67 is arranged, on one side, with a slight axial clearance relative to annular stop organ 58 and, on the other side, with a slight axial clearance relative to secondary cam 36, in particular relative to cup-shaped portion 71. In this way, it is possible to avoid a friction or sliding of ring 67 between the transverse surfaces exhibited by annular stop organ 58 and by secondary cam 36, in particular by cup-shaped portion 71.

In the embodiment shown, ring 67 has an outer diameter that is smaller than and arranged eccentrically relative to the inner diameter of through cavity 40a defined by casing 40. In any case, during the rotation of secondary cam 32, ring 67 has a radial distance relative to cavity 40a, hence without the presence of a contact to the inner walls of casing 40 (or of a turning coupling to casing 40 itself), thus reducing possible unwanted friction phenomena in this region of hypocycloidal drive mechanism 10. Preferably, output shaft 16 ends with an appendage 72, which is suited to be mechanically coupled to an external component.

In the embodiment shown, intermediate shaft 28 is coupled in a turning manner to secondary cam 36, preferably in correspondence to a distal shank 74 (for example supported by stem 56), which has a circular cross section centered around rotation axis X-X. Preferably, shank 74 axially projects beyond secondary hypocycloidal element 32, in particular beyond its sleeve 69. Advantageously, shank 74 is coupled to the bottom of cup-shaped portion 71 in a turning manner.

In the embodiment shown, shank 74 extends from eccentric portion 30, in particular from the part that is axially opposite to disc 54.

Preferably, secondary cam 36 is manufactured with a plastic material, for example by means of an injection molding process. Preferably, the plastic material used is of the self-lubricating type, for example of the type marketed under the name of Delrin®. In the embodiment shown, output shaft 16 and secondary cam 36 are manufactured as one single piece, in particular including cup-shaped portion 71, for example with a plastic material, such as the one mentioned above. In alternative embodiments, the output shaft and the secondary cam could be separate components, for example further drive stages could be interposed between them.

In the embodiments shown, the lobes or teeth of primary external toothing or lobing 26 have an axial and transverse extension that are smaller than those of the teeth or lobes of secondary external toothing or lobing 34. Furthermore, the lobes or teeth of primary external toothing or lobing 26 are available in a larger number than those of secondary external toothing or lobing 34.

In the embodiment shown, output shaft 16 is axially constrained in casing 40, thus allowing it to rotate around axis X-X but simultaneously preventing it from moving in an axial direction beyond casing 40 itself. In particular, to this regard, an elastic retaining element 76, for example a so-called elastic ring (also known as "Seeger" o "circlip") is used, which is locked in the inner walls of casing 40 and on which the bottom of cup-shaped portion 71 axially rests. By way of example, elastic retaining element 76 is housed in a groove 78, which is obtained on the inner walls of the cavity defined by casing 40.

In the embodiment shown, the output shaft 16 axially projects with its appendage 72 beyond elastic retaining element 76.

Owing to the above, we list below some advantageous aspects of the embodiment of hypocycloidal drive mechanism 10 shown, which do not limit the scope of protection of the present invention. More in detail, mechanism 10 consists of a very small number of pieces or elements, which are obtained by means of structures conceived based on the principle of combining different functions in one single piece or element; among these pieces or elements we would like to mention, by mere way of non limiting example:

- input shaft 12, which is able to fulfill the function of a primary eccentric;

- outer casing 40, which is able to fulfill at least one among the functions belonging to the assembly consisting of a coupling and centering to the metal sheet of the motor, a support for the bushing of input shaft 12, a roller toothing of primary cam 20, a position reference and an interlock for stop organ 58, a guide bushing of output shaft 16, and a seat for elastic retaining element 76;

- primary cam 20, which is able to fulfill at least one among the functions belonging to the assembly consisting of a bushing of the primary eccentric and a separator between the planet rotary motion and the sun rotary motion (by means of its own transfer pins);

- in intermediate shaft 28, disc 54, which is able to fulfill at least one among the functions belonging to the assembly consisting of an organ supporting and orienting the pins of primary cam 20 and a driving seat of stem 56 (torque transmitting element);

- stop organ 58, which is able to fulfill at least one among the functions belonging to the assembly consisting of a bushing of intermediate shaft 28 (one of the two rotation supports or main bearings) and an organ supporting and orienting the pins of secondary cam 36;

- eccentric portion 30, which is able to fulfill at least one among the functions belonging to the assembly consisting of: a seat for the hubs of the two rotation supports (or main bearings) acting as a section of a crank shaft, and a rotation bushing of the secondary cam;

- secondary cam 36, which is able to fulfill at least one among the functions belonging to the assembly consisting of: a bushing of intermediate shaft 28 and a separator between the planet rotary motion and the sun rotary motion (by means of the reference pins inserted into stop element 58); and

- output shaft 16, which is able to fulfill at least one among the functions belonging to the assembly consisting of: a support bushing for radial and torsional external loads relative to casing 40, and a rotation support (or main bearing) for intermediate shaft 28 arranged on the inside.

Optionally, the level at which the functions are combined can clearly be extended also to a motor, to which mechanism 10 can be connected, so that bushing 42 and input shaft 14 of the reduction gear cannot be distinguished based on their belonging to the motor or to the reduction gear. Hence, we are dealing with a hypocycloidal drive mechanism (in this specific case, a two-stage reduction gear), which can combined with a motor so as to be made up of a small number of elements.

In the embodiment shown, casing 40 is manufactured with a plastic material, preferably as one single piece. Preferably, the plastic material used is of the self- lubricating type, for example of the type marketed under the name of Delrin®.

In the embodiment shown, all the components of drive mechanism 10, except for shaft 12, bushing 42, and elastic retaining element 76, are made of a plastic material, preferably of the self-lubricating type, for example the material marketed under the name of Delrin®.

With reference to the embodiment shown, the assembly of the mechanism will be described below as a mere way of example.

First of all, a casing 40 is prepared, into which one inserts, from the output end (namely, the one where output shaft 16 will be mounted), bushing 42, which settles with its flange 46 against abutment 44 obtained on casing 40.

Now casing 40 is already ready to be fitted on the metal sheet of the motor, preferably receiving from the latter input shaft 12, which will be coupled, in a turning manner, inside the bushing, thus leaving eccentric portion 14 projecting inside casing 40. In less preferred alternative embodiments, it is also possible for input shaft 12 to be separate and distinct from the shaft of the motor to which drive mechanism 10 is adapted to be coupled so as to form a single motor-reduction gear assembly.

Subsequently, primary hypocycloidal element 24 is inserted, always from the output end, so that eccentric portion 14 is inserted into seat 48 in a turning manner and primary external toothing or lobing 26 peripherally engages the primary internal toothing or lobing of casing 40.

Subsequently, always from the output end, disc 54 of the intermediate shaft is inserted from the intermediate shaft 28, , so that the transverse cooperation surface 28a engages, in a rolling manner, the transverse cooperation surface 24a supported by the primary hypocycloidal element 24. Furthermore, the outer periphery of disc 54 is radially spaced apart, since it has a smaller diameter, relative to the inner periphery of the cavity defined by casing 40.

Subsequently, annular stop organ 58 is inserted, always from the output end, so as to be integral, during its rotation, to casing 40, for example by means of the coupling by radial interference created by bulges or wedges 59a, 59b.

Subsequently, stem 56 of intermediate shaft 28 is inserted, its projection 60 being locked in disc 54, thus axially extending beyond central opening 64 of annular stop organ 58. At the same time, segment 62 is inserted with a turning coupling to above-mentioned central opening 64.

Subsequently, secondary hypocycloidal element 32 is inserted, which is run through by intermediate eccentric portion 30 of intermediate shaft 28. During the assembly of secondary hypocycloidal element 32, pins 66 projecting from the surface of its ring 67 are coupled in corresponding holes 68 of annular stop organ 58, preferably until a depth is reached that is such as not to determine any contact or sliding between surface 32a exhibited from secondary hypocycloidal element 32 and surface 58a of annular stop ring 58.

Subsequently, output shaft 16 is inserted, so that cup-shaped portion 71 has its secondary internal sun toothing or lobing 38 in engagement with respective secondary external planet toothing or lobing 34 exhibited by secondary hypocycloidal element 32, in particular in correspondence to its sleeve 69. At the same time, shank 74, which belongs to stem 56 of intermediate shaft 28 and projects beyond sleeve 69 of secondary hypocycloidal element 32, is coupled on the bottom of cup-shaped portion 71 so as to turn around axis X-X. Simultaneously, the outer periphery of cup-shaped portion 71 is coupled, in a turning manner, to the inner periphery of the cavity defined by casing 40.

Subsequently, elastic ring 76 is inserted, which surrounds appendage 72 of output shaft 16 and is peripherally coupled in groove 78 obtained on the inner walls of casing 40.

As a person skilled in the art can clearly assume from the present description, the above-mentioned mechanism 10 can be adopted - in combination with a motor coupled to input shaft 12 - as an actuator in many application fields.

In particular, in case casing 40 is kept in a stationary position, the rotation motion generated by input shaft 12 is transmitted, through the gear 18, to output shaft 16, which actually acts as a "driven element", thus delivering a rotation motion to a rotary component or element connected thereto.

On the other hand, in case output shaft 16 is kept in a stationary position, the rotation motion generated by input shaft 12 is directly transmitted, through gear 18, to casing 40, which - in this case - acts as a "driven element", thus delivering the rotation motion as an the output. This application can be particularly useful in case mechanism 10 fulfills the function of a winding element and casing 40 fulfills the function of a spool or drum, around which an external element can be wound. In the embodiment shown - in case output shaft 16 is kept stationary - casing 40, in particular, is suited to be controlled so as to be caused to rotate around rotation axis X-X due to the movement that is operatively transmitted, when mechanism 10 is in use, to at least one between primary cam 20 and stop element 58, which are mounted so as to be integral, hence rotating together relative to casing 40. More in particular, primary cam 20 and stop element 58 can be built so as to both contribute - if necessary, in synergy - to the actuation of the rotation of casing 40 around above- mentioned rotation axis X-X.

Owing to the above, when mechanism 10 is combined with a motor that controls the rotation of input shaft 12, this assembly can be used as:

- a winding or stretching device, for example for roller shutters and blinds that can be applied to house windows or to the windows of vehicles, such as cars; and

- an actuator device to actuate the rotation of further driven organs (driven by casing 40 or by output shaft 16), for example to control the inclination of the back of chairs or seats, in particular in vehicles, such as cars.

Furthermore, as already partly mentioned above, thanks to the presence of intermediate shaft 28, primary toothings or lobings 22, 26 can have a geometry, i.e. shape and number of teeth or lobes, that is independent of the geometry of secondary toothings or lobings 34, 38. This leads to the advantage of causing the gear ratios of the primary stage and of the secondary stage to be independent, which permits an improved designing flexibility compared to the mechanisms according to the prior art.

In the embodiment shown, primary internal toothing or lobing 22 has one more primary internal tooth or lobe compared to the primary external teeth or lobes of primary external toothing or lobing 26. In particular the primary internal teeth or lobes are ten, whereas the primary external teeth or lobes are nine.

In the embodiment shown, secondary internal toothing or lobing 38 has one more secondary internal tooth or lobe compared to the secondary external teeth or lobes of secondary external toothing or lobing 34. In particular the secondary internal teeth or lobes are six, whereas the secondary external teeth or lobes are five.

As already mentioned above, the motor with which input shaft 12 is suited to be coupled is preferably of the electric type. In particular, the electric motor is of the AC type, more in detail it is a synchronous electric motor, for example a brushless motor.

The use of an AC electric motor of the brushless synchronous type is extremely preferred due to the fact that, in this type of motor, the rotor does not have:

- induced currents, which is typically the case in asynchronous electric motors, or

- armature currents, which is generally the case in DC electric motors.

As a matter of fact, induced currents and armature currents knowingly determine a localized heating in the rotor. The heat would be immediately transferred to a region where significant mechanical friction phenomena occur, which means close to input shaft 12 and, possibly, to the bushing on which it is supported during its rotation, thus causing the development of further heat. This situation would be disadvantageous due to the fact that the hypocycloidal drive mechanism would suffer a significant reduction of its operating abilities.

In particular, the excessive concentration of the heat in spaces with small dimensions inevitably leads to an increase in the temperature of the hypocycloidal drive mechanism, with remarkable consequences in terms of useful life, operating regularity, and physical possibilities, due to the restrictions to the maximum temperatures that can be reached during the operation and on the outer surface that is in contact with the other parts and components.

Therefore, owing to the above, it is particularly advantageous to couple the hypocycloidal drive mechanism described above to an AC electric motor of the brushless synchronous type, since this combination allows the efficiency of the mechanism to be optimized and, at the same time, guarantees particularly small dimensions and spaces .

Furthermore, when input shaft 12 of the hypocycloidal drive mechanism described above is assembled with an electric motor, it is also advantageous to use a tubular shaped casing 40, which is able to dissipate the residual heat developed by the electric motor on its own case.

Furthermore, one should consider again the case in which an AC electric motor of the brushless synchronous type is combined with the hypocycloidal drive mechanism described above. These two elements require an electronic control or driver, which replaces the function of the electromechanical commutator, thus switching the windings in an appropriate manner, so as to obtain the correct direction of rotation.

In order to obtain the result desired, one normally uses Hall effect sensors (to determined the initial position of the magnetic field) , often combined with angular encoders (to obtain a sufficient angular positioning precision, as requested by specific applications, for example in machine tools) . The adoption of these devices to control the motor is, in this context, less preferred, since it implies high costs and a complication of the overall structure of the assembly consisting of the motor and the hypocycloidal drive mechanism, as described above.

For this reason, it is preferred, but not necessary, to use a sensorless control to control the electric motor. This sensorless control is performed by detecting a signal of a voltage induced on one of the windings of the electric motor, this winding temporarily assuming the role of "sensor" in an alternate manner and in turn with the available windings (which are typically available, overall, in the number of three) . As a consequence, the sensorless control controls the remaining windings with a current that is determined as a function of the voltage signal detected by the winding that has temporarily assumed the role of " sensor " .

Naturally, the principle of the present invention being set forth, the embodiments and the implementation details can be widely changed with respect to what described above and shown in the drawings as a mere way of non-limiting example, without in this way going beyond the scope of protection provided by the accompanying claims.