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Title:
CLUTCH ASSEMBLY, IN PARTICULAR FOR MOTORCYCLES, AND TRANSMISSION SYSTEM EQUIPPED WITH SAID CLUTCH ASSEMBLY
Document Type and Number:
WIPO Patent Application WO/2018/234381
Kind Code:
A1
Abstract:
A clutch, in particular for motorcycles, said clutch comprising a bell (102) adapted to be alternatively engaged and disengaged by a rotating transmission component (107), wherein the mutual engagement of said bell (102) and said rotating transmission component (107) by means of a first engagement means results in said bell (102) dragged in rotation by said transmission component (107) in a first rotation direction (A), wherein said bell (102) defines an engagement profile formed so as to be alternatively engaged and disengaged by second engagement means (120) dragged in rotation by said transmission component (107), and wherein the mutual engagement of said second engagement means (120) and said engagement profile arises as a result of both the rotation of said transmission component (107) in a second rotation direction, opposite to said first rotation direction (A), and the rotation of said bell (102) in said first rotation direction (A), whereas the mutual disengagement of said engagement means (120) and said engagement profile arises as a result of both the rotation of said transmission component (107) in said first rotation direction (A) opposite to said second rotation direction, and the rotation of said bell (102) in said second rotation direction.

Inventors:
MORONI, Marco (Via Ticino 165, MARNATE, 21050, IT)
MARABESE, Riccardo (Viale Milano 32, GALLARATE, 21013, IT)
Application Number:
EP2018/066425
Publication Date:
December 27, 2018
Filing Date:
June 20, 2018
Export Citation:
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Assignee:
QUADRO VEHICLES S.A. (Via dei Lauri 4, 6833 VACALLO, 6833, CH)
International Classes:
F16D43/06
Domestic Patent References:
WO2016168069A12016-10-20
Foreign References:
US8297425B12012-10-30
Other References:
None
Attorney, Agent or Firm:
TORTI, Carlo Maria Emilio et al. (NOTARBARTOLO & GERVASI S.P.A, Corso di Porta Vittoria 9, Milano, 20122, IT)
Download PDF:
Claims:
CLAIMS

1. A clutch, in particular for motorcycles, said clutch comprising a bell (102) adapted to be engaged and disengaged alternatively by a rotating transmission component (107), wherein the mutual engagement of said bell (102) and said rotating transmission component (107) by means of a first engagement means results in said bell (102) by dragged in rotation by said transmission component (107) in a first rotation direction (A), characterised in that said bell (102) defines an engagement profile formed so as to be engaged and disengaged alternatively by second engagement means (120) dragged in rotation by said transmission component (107), and in that the mutual engagement of said second engagement means (120) and said engagement profile arises as a result of both the rotation of said transmission component (107) in a second rotation direction, opposite to said first rotation direction (A), and the rotation of said bell (102) in said first rotation direction (A), whereas the mutual disengagement of said engagement means (120) and said engagement profile arises as a result of both the rotation of said transmission component (107) in said first rotation direction (A) opposite to said second rotation direction, and the rotation of said bell (102) in said second rotation direction.

2. The clutch according to claim 1 , characterised in that said bell (102) comprises a substantially cylindrical portion (103), and in that said engagement profile is defined by at least one portion of the outer surface (1 1 1 ) of said substantially cylindrical portion (103).

3. The clutch according to claim 2, characterised in that said at least one substantially cylindrical portion (103) of said bell (102) comprises at least one depression (1 12) with respect to a substantially cylindrical reference surface (1 10), said depression (1 12) being subtended by a predefined angular sector (a) centred on the longitudinal axis (X) of said substantially cylindrical portion (103).

4. The clutch according to claim 3, characterised in that the outer surface (1 1 1 ) of said at least one depression (1 12) is the locus of the generatrix half-lines substantially parallel to the longitudinal axis (X) of said substantially cylindrical portion (103).

5. The clutch according to any one of the previous claims 3 and 4 characterised in that the distance of said generatrix half-lines from said longitudinal axis (X) of said substantially cylindrical portion (103) varies within said angular sector (a).

6. The clutch according to claim 5, characterised in that the distance of said generatrix half-lines from said longitudinal axis (X) of said substantially cylindrical portion (103) varies continuously within said angular sector (a).

7. The clutch according to claim 5 or 6, characterised in that said angular sector (a) comprises a first subsector (cM ) and a second subsector (a2), and in that in the first subsector (cM ) the curve defined by the intersection between a plane perpendicular to the longitudinal axis (X) of said substantially cylindrical portion (103) and the external surface (1 1 1 ) of said at least one depression (1 12) comprises at least one concavity (C1 ) faced towards said cylindrical reference surface (1 10).

8. The clutch according to claim 7, characterised in that in said second subsector (a2) the curve defined by the intersection between a plane perpendicular to the longitudinal axis (X) of said substantially cylindrical portion (103) and said outer surface (1 1 1 ) of said at least one depression (1 12) comprises at least one convexity (C2) faced towards said cylindrical reference surface (1 10).

9. The clutch according to claim 8, characterised in that said at least one concavity (C1 ) and at least one convexity (C2) are connected in a continuous manner.

10. A transmission system (100), in particular for motorcycles, said system comprises a rotating transmission component (107), first engagement means and second engagement means (120) and a bell (102) adapted to be engaged and disengaged alternatively by said rotating transmission component (107), wherein the mutual engagement of said bell (102) and said rotating transmission component (107) by means of first engagement means, results in said bell (102) being dragged in rotation by said transmission component (107) in a first rotation direction (A), characterised in that said bell (102) is a bell according to one of the claims from 1 to 9, and therefore in that the mutual engagement of said second engagement means (120) and said engagement profile arises as a result of both the rotation of said transmission component (107) in a second rotation direction opposite to the said first rotation direction (A), and the rotation of said bell (102) in said first rotation direction (A), whereas the mutual disengagement of said second engagement means (120) and said engagement profile arises as a result of both the rotation of said transmission component (107) in said first rotation direction (A), opposite to said second rotation direction, and the rotation of the bell (102) in said second rotation direction.

11. The transmission system (100) according to claim 10, characterised in that said transmission component (107) comprises a first pulley positioned outside of said bell (102), and in that said second engagement means (120) comprises at least one pawl (122) fixed to said first pulley and adapted to be switched between a first engagement position wherein it engages said at least one depression (1 12) and a second disengagement position in which it is disengaged from said at least one depression (1 12), and in that the switching of said at least one pawl (122) from said first engagement position to said disengagement position arises as a result of both the rotation of said first pulley in said first rotation direction (A), and the rotation of said bell (102) in said second rotation direction.

12. The transmission system (100) according to claim 1 1 , characterised in that said at least one pawl (122) is constrained to said first pulley so that it can be switched by rotation, and in that both the rotation of said first pulley (102) in said first rotation direction (A), and the rotation of said bell (102) in said second rotation direction, result in said at least one pawl (122) being rotated in a first own rotation direction and therefore in being switched from said first engagement position to said second engagement position.

13. The transmission system (100) according to claim 12, characterised in that said system comprises first elastic means interposed between said pulley and said at least one pawl (122), and in that said at least one pawl (122) is switched by rotation from said engagement position to said second disengagement position against the elastic resistance exerted by said first elastic means, whereas said at least one pawl (122) is switched by rotation from said second engagement position to said first engagement position due to the thrusting action exerted by said first elastic means.

14. The transmission system (100) according to one of the claims from 10 to 13, characterised in that said rotating transmission component (107) comprises a second pulley or cap equipped with said first engagement means, said first engagement means comprising a plurality of back-pushing and/or engaging shoes at least partially housed inside said bell (102), in that each of said shoes is adapted to be translated along a radial direction, and in that the rotation of said rotating component (107) in said first rotation direction (A) results in said shoes being radially translated, and therefore in the mutual engagement of said second pulley or distributor cap and said bell (102), and therefore in said bell (102) being dragged in rotation by said rotating transmission component (107).

15. The transmission system (100) according to one of the claims from 10 to 14, characterised in that said system comprises a continuously variable transmission (CVT), and in that said rotating transmission component (107) belongs to the driven rotating component of said continuously variable transmission.

Description:
CLUTCH ASSEMBLY, IN PARTICULAR FOR MOTORCYCLES, AND TRANSMISSION SYSTEM EQUIPPED WITH SAID CLUTCH ASSEMBLY

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FIELD OF THE INVENTION

The present invention relates to an innovative clutch, in particular but not exclusively, for motorcycles with two, three and four wheels, scooters, quads and similar vehicles. In particular, the present invention relates to a clutch assembly, particularly but not exclusively adapted to be used in transmission systems for vehicles of the aforesaid type, in particular in transmission systems with automatic variation of the speed, in particular of the transmission ratio. The present invention further relates to a transmission system, in particular but not exclusively with automatic transmission ratio variation, e.g. a CVT (Continuously Variable Transmission).

BACKGROUND ART

The use of transmission systems with automatic transmission ratio variation is widespread in the field of motorcycles (but not only), in particular in the field of motorcycles with two, three and four wheels, of scooters, quads and similar vehicles; in particular, in the field of motorcycles of the aforesaid type, the use of continuously variable transmissions or CVTs is particularly popular (and appreciated by users). With reference to figure 1 , the operation of a continuously variable transmission CVT can be summarized as follows.

The rotation of the drive shaft 1 1 deriving from the action of the engine 10, obviously results in the rotation of the drive pulley 12 (keyed onto the drive shaft 1 1 ) and of the driven pulley 13, the latter put into rotation by the drive belt 14, engaged both on the drive pulley 12 and the driven pulley 13. The situation in figure 1 is also the one in which the gear ratio (i.e. the ratio between the circumference of the drive pulley 12 and that of the driven pulley 13) is minimum and therefore corresponds to the shortest "gear"; the situation in figure 1 occurs with the engine 10 off or idling slowly. The drive pulley 12 also comprises a fixed half-pulley 15 (rigidly fixed to the drive shaft 1 1 ) and a movable half-pulley 16, in particular translatable along the drive shaft 1 1 . A containment cap 17, which is also fixed, defines a space or housing with the movable half-pulley 16, in which "expansion" rollers 18, in variable number according to requirements and/or circumstances, are housed. In particular, said rollers 18 are can translate, in radial direction (perpendicularly to the shaft 1 1 ), where the outward translation (away from the shaft 1 1 ) of rollers 18 occurs by virtue of the action of the centrifugal force which acts on them when a predetermined rotation speed of the shaft 1 1 (and therefore of the pulley 12) is reached, the speed being higher than the one corresponding to the idling speed of the engine 10. The outward translation of the rollers 18 obviously results in a push on the half-pulley 16, which is thus translated along the drive shaft 1 1 (from the right leftwards with respect to Figure 1 ), whereby the rolling circumference of the belt 14 is varied (increased) in this manner on the two opposite half-pulleys 15 and 16 with conical surfaces. In practice, the belt 14 "moves up" towards the outside in the pulley 12.

The driven pulley 13 also consists of a fixed half-pulley 19 and a movable half-pulley 20 (translatable along the respective rotation shaft 21 , whereby the half-pulley 20 thus moves gradually away from the half-pulley 19 as the rotation speed of the shaft 21 increases, thus decreasing the rolling circumference of the belt 14 on the half- pulleys 19 and 20; in practice, the belt 14 progressively "moves down" into the groove defined by the two mutually opposite half-pulleys 19 and 20 with conical surfaces. In practice, the maximum transmission ratio, corresponding to the longest gear, occurs with the belt positioned on the maximum rolling circumference of the pulley 12 and on minimum rolling circumference of the pulley 13. The translation of the half-pulley 20 away from the half-pulley 19 occurs against the elastic bias of the spring 22, whereby the semi pulley 20 is approached to the half pulley 19 by spring 22 (the half-pulley 21 is translated in the opposite direction, i.e. from the left rightwards with respect to Figure 1 ) as the rotation speed of the shaft 21 decreases (as a result of the reduction of rpm of the motor 1 0 and thus of the rotation speed of the drive shaft 1 1 and of the pulley 12); at the same time, the rollers 18 also retract towards the shaft 1 1 , whereby the half-pulley 16 thus moves away again from half- pulley 15 (i.e. translates on the shaft 1 1 from the left rightwards with respect to Figure 1 ).

The transmissions of the type described above with reference to figure 1 allow a continual, automatic variation of the gear ratio, by modifying the transmission ratio between the drive pulley and the driven pulley indeed automatically and continuously, as explained, whereby the engine thus tends to remain at a given speed of operation. Furthermore, again as shown in figure 1 , a clutch assembly 24, the operation of which can be summarized as follows, is interposed between the driven pulley 13 and the hub 23 (of a wheel, not shown).

A cap 25, which is then dragged into rotation by the shaft 21 , is keyed on the shaft 21 of the driven pulley 13. The cap 25 is further equipped with a plurality of shoes 26 (variable in number according to requirements and/or circumstances), said shoes

26 being radially translatable outwards by virtue of the bias of the centrifugal force generated by the rotation of the cap 25. The progressive translation of the shoes 26 towards the outside of the cap 25 results in the progressive engagement of the bell

27 by the shoes 26 and thus in the mutual coupling of the cap 25 and of the bell 27, which is then dragged into rotation, where the rotation of the bell 27 results in the rotation of the shaft 23, and thus of the wheel.

Obviously, as the rpm of the engine 10, and thus of the pulley 13 and of the cap 25, decreases, the shoes 26 retract and so the decoupling of the bell 27 from the cap 25, and thus ultimately the decoupling of the shaft 23 from the transmission and from the engine 10, occurs.

The described clutch, said centrifuge (present in the driven pulley) thus allows disconnecting the engine automatically from the wheel when the engine is running at a speed close to idling speed and making it integral when such a rotation speed increases and avoids the need for a clutch lever; indeed, as explained, the clutch is of the centrifugal type and adheres to the clutch bell when a given rotation speed of the driven pulley is achieved.

Transmission-clutch systems or even only clutch assemblies of the described type, although appreciable from various points of view (e.g. high reliability and/or simplicity of construction and of use), are not however free from drawbacks and/or disadvantages that the present invention intends to remedy.

A first drawback relates to the fact that it is not possible to put the hub 23 and the respective wheel into rotation in the opposite direction and so to reverse the vehicle with the engine off or idling; indeed, even assuming one were to put the drive shaft

1 1 in reverse rotation, e.g. by using (through a suitable inverter) the motive energy of the current generator, the low speeds in play would not allow to the masses (at the shoes 26) of the clutch normally used, to expand and thus to transmit the motion from the transmission to the wheel, according to the methods described above. If the shoes 26 of the clutch 24 do not reach the rotational speed needed to expand them, and thus to couple them to the clutch bell 25, the rotation of the drive shaft 1 1 does not transmit the motion to the wheel because wheel and transmission are not mutually coupled: as this condition occurs when the drive shaft 1 1 is put into reverse rotation by using the current generator as a motive force by putting the rotor fixed to the drive shaft into rotation, it explains why the vehicle cannot be reversed.

A second drawback relates to the fact that with the engine off, and thus in decoupling condition between transmission and wheel, it is not possible to push-start the engine (e.g. in the case of flat battery), since the wheel rotation generated by the push is not transmitted to the engine.

DESCRIPTION OF THE PRESENT INVENTION

It is the object of the present invention to overcome or at least minimize the drawbacks found in the solutions according to the prior art, in particular those summarized above with reference to figure 1 .

In particular, it is an object of the present invention to suggest and provide a solution which allows reversing the vehicle with the engine off and/or push-starting the engine, e.g. in case of flat battery and/or of fault in the electrical system.

Furthermore, according to the present invention, the objects above must be achieved by using a small number of component parts of simple construction which can be manufactured and assembled at a low cost.

The present invention is based on the general consideration that the vehicle can be reversed with the engine off and the engine can be push-started by means of a solution which allows:

the mutual automatic constraint between drive shaft and wheel with the engine off or running at very slow speed, either close to or slower than idle speed (idling speed being intended as the minimum turning speed useful to keep the engine running), both in the case of reverse rotation of the drive shaft and in the case of rotation of the wheel in the travel direction, e.g. generated by pushing;

the mutual automatic release, with the engine on and at rpm sufficient to start the vehicle. Given the purposes summarized above, as well as the drawbacks encountered in the prior art and finally the aforesaid considerations, the present invention relates to a clutch assembly, in particular for motorcycles, said clutch comprising a bell adapted to be engaged and disengaged alternatively by a rotating transmission component, where the mutual engagement of said bell and said rotating transmission component by means of a first engagement means results in said bell dragged in rotation by said transmission component in a first rotation direction, where said bell defines an engagement profile formed so as to be engaged and disengaged alternatively by second engagement means dragged in rotation by said transmission component, and where the mutual engagement of said second engagement means and said engagement profile is achieved as a result of both the rotation of said transmission component in a second rotation direction, opposite to said first rotation direction, and the rotation of said bell in said first rotation direction, whereas the mutual disengagement of said engagement means and said engagement profile is achieved as a result of both the rotation of said transmission component in said first rotation direction opposite to said second rotation direction, and the rotation of said bell in said second rotation direction.

According to an embodiment, said bell comprises a substantially cylindrical portion, where the engagement profile is defined by at least one portion of the outer surface of said substantially cylindrical portion.

According to an embodiment, said at least one substantially cylindrical portion of said bell comprises at least one depression with respect to a substantially cylindrical reference surface, said depression being subtended by a predefined angular sector centred on the longitudinal axis of said substantially cylindrical portion.

According to an embodiment, the outer surface of said at least one depression is the locus of the generatrix half-lines substantially parallel to the longitudinal axis of said substantially cylindrical portion.

According to an embodiment, the distance of said generatrix half-lines from said longitudinal axis of said substantially cylindrical portion varies within said angular sector. According to an embodiment, the distance of said generatrix half-lines from said longitudinal axis of said substantially cylindrical portion varies continuously within said angular sector.

According to an embodiment, said angular sector comprises a first subsector and a second subsector, where in the second subsector the curve defined by the intersection between a plane perpendicular to the longitudinal axis of said substantially cylindrical portion and the external surface of said at least one depression comprises at least one concavity faced towards said cylindrical reference surface.

According to an embodiment, in said first subsector the curve defined by the intersection between a plane perpendicular to the longitudinal axis of said substantially cylindrical portion and the external surface of said at least one depression comprises at least one convexity faced towards said cylindrical reference surface.

According to an embodiment, said at least one concavity and at one convexity are connected in a continuous manner.

The present invention further relates to a transmission system, in particular for motorcycles, said system comprising a rotating transmission component, first engagement means and second engagement means and a bell adapted to be engaged and disengaged alternatively by said rotating transmission component, where the mutual engagement of said bell and said rotating transmission component by means of first engagement means, results in said bell being dragged in rotation by said transmission component in a first rotation direction, where said bell is a bell according to one of the preceding embodiments, and therefore in that the mutual engagement of said second engagement means and said engagement profile arises as a result of both the rotation of said transmission component in a second rotation direction opposite to the said first rotation direction, and the rotation of said bell in said first rotation direction, whereas the mutual disengagement of said second engagement means and said engagement profile arises as a result of both the rotation of said transmission component in said first rotation direction, opposite to said second rotation direction, and the rotation of the bell in said second rotation direction. According to an embodiment, said transmission system, comprises a first pulley positioned outside said bell, and where said second engagement means comprises at least one pawl fixed to said first pulley and adapted to be switched between a first engagement position where it engages said at least one depression and a second disengagement position in which it is disengaged from said at least one depression, and where the switching of said at least one pawl from said first engagement position to said disengagement position arises as a result of both the rotation of said first pulley in said first rotation direction, and the rotation of said bell in said second rotation direction.

According to an embodiment, said at least one pawl is constrained to said first pulley so that it can be switched by rotation, where both the rotation of said first pulley in said first rotation direction, and the rotation of said bell in said second rotation direction result in said at least one pawl being put into rotation in a first own rotation direction and thus in it being switched from said first engagement position to said second engagement position.

According to an embodiment, said system comprises first elastic means interposed between said pulley and said at least one pawl, and where said at least one pawl is switched by rotation, in particular by centrifugal force of said at least one pawl from said engagement position to said second disengagement position against the elastic resistance applied by said first elastic means, whereas said at least one pawl is switched by rotation from said second engagement position to said first engagement position by virtue of the thrusting action applied by said first elastic means.

According to an embodiment, said rotating transmission component comprises a second pulley or cap equipped with said first engagement means, said first engagement means comprising a plurality of back-pushing and/or engaging shoes at least partially housed inside said bell, where said shoes are adapted to be translated along a radial direction, and in that the rotation of said rotating component in said first rotation direction results in said shoes being radially translated, and thus in the mutual engagement of said second pulley and of said bell, and thus in said bell being dragged in rotation by said rotating transmission component. According to an embodiment, said system comprises a continuously variable transmission (CVT), where said rotating transmission component belongs to the driven rotating component of said continuously variable transmission.

Further possible embodiments of the present invention are defined in the claims. BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, the present invention will be explained by means of the following detailed description of the embodiments shown in the drawings. However, the present invention is not limited to the embodiments described hereinafter and shown in the drawings; on the contrary, all variants of the embodiments described below and shown in the drawings, which will become apparent to those skilled in the art, are within the scope of the invention.

In the drawings:

- figure 1 shows a diagrammatic view of a transmission-clutch system according to the prior art;

- figure 2 shows a perspective view of part of a transmission-clutch system according to an embodiment of the present invention;

- figure 3 shows a side view of a rotating part of a transmission-clutch system according to an embodiment of the present invention;

- figure 4 shows a perspective view of part of a system according to an embodiment of the present invention;

- figure 5 shows a perspective view of a system according to an embodiment of the present invention;

- figure 6 shows a diagrammatic view of constructional details of a system to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention is particularly advantageously applied in case of transmission ratio automatic variation and/or continuous transmission systems, in particular in the case of CVTs; for this reason, hereinafter, the present invention will be explained with reference to its applications to continuously variable transmissions (CVTs). It is further worth noting that the possible applications of the present invention are not limited to continuously variable transmissions (CVTs) but include transmission systems of any kind. In figure 2, reference numeral 100 identifies a transmission-clutch system according to an embodiment of the present invention, where, for clarity reasons, only the parts essential for describing the system are shown in the figure. Reference numeral 101 identifies a clutch, said clutch 101 comprising a bell 102, which thus comprises a portion which is substantially cylindrical 103 and which extends from a flange 104 to which a wheel hub can be connected, according to substantially known methods (see the description of figure 1 ), normally by means of a gear final reduction. Moreover, in figure 2, reference numeral 105 identifies a driven pulley, in turn comprising a movable half-pulley 106 (again according to the methods described above) and a fixed half-pulley 107. Again according to substantially known methods, a cap integral in rotation with the half-pulley 107 is housed in the inner space defined by the cylindrical portion 103 of the bell 102 positioned facing the half-pulley 107, said cap (not shown in the figure) being equipped with back-pushing and/or engagement shoes (first engagement means) radially translatable (expandable) as a consequence of the centrifugal force generated by the rotation of the fixed half- pulley 107 and thus of the cap is housed in the substantially cylindrical portion 103 of the bell 102. Thus, assuming for clarity purposes that the half-pulley 107 is put into rotation by the vehicle engine in the rotation direction indicated by the arrow A, and that consequently the rotation direction indicated by the arrow A corresponds to the forward direction of the vehicle, the rotation of the half-pulley 107 in the direction of the arrow A, and therefore of the cap housed in the bell, with sufficient rotation speed, results in the engagement of the bell 102 by the expandable shoes, and thus in the rotation of the bell 102 in the same rotation direction A, and finally in rotation of the wheel hub and of the wheel itself in the same rotation direction A. Furthermore, the bell 102 has innovative features, as described below in detail with reference to figures 2 and 6.

As shown in the figures, with respect to a substantially cylindrical reference surface 1 10, the outer surface 1 1 1 of the cylindrical portion 103 comprises mutually contiguous recesses 1 12 each subtended by an angular sector a centred on the longitudinal symmetry axis X of the substantially cylindrical portion 103. The surface of each depression 1 12 may be defined as the locus of the generatrix half-lines parallel to the X axis, where the distance of said generating lines from the X axis varies as a function of the angular position, in particular from a maximum substantially corresponding to the radius of the reference surface 1 10 at the opposite ends of the angular sector a, to a minimum in intermediate position between the two extremes, where the minimum distance of the directrix of the X axis naturally corresponds to the maximum depth of the depression 1 12. Furthermore, and again as shown, the curvature of the outer surface 1 1 1 of each depression 1 12 is such that the curve defined by the intersection of the surface 1 1 1 with a reference plane perpendicular to the X axis (and therefore parallel to the plane of figure 6) is such as to comprise a concavity C1 facing towards the reference surface 1 10 on a first sub-sector α1 , and a convexity C2 facing towards the reference surface 1 10 in a second sub-sector a2 of the angular sector a, where also the convexity C2 and the concavity C1 are joined continuously.

Further peculiarities of the present invention may be appreciated with reference to figures 3 and 2; indeed, as shown, on the driven half-pulley 107, and in particular on its inner face facing towards the bell 102, second engagement means 120 are applied, two in number in the example shown, where in all cases the number may vary from a minimum of one to a maximum corresponding to the number of depressions 1 12, according to requirements and/or circumstances. The constructional and functional features of engagement means or element 120 will be described below for brevity purposes. Each element 120 comprises a plate 123 substantially parallel to the half-pulley 107 and interposed between the pulley 107 and the bell 102, the plate 123 then being positioned outside the bell 102. The plate 123 is rotatably constrained to the half-pulley 107 by means of a constraint or pin 121 , the plate 123 then being switchable by rotation about the pin 121 in the two opposite rotation directions indicated by the double arrow in figure 3. A pawl extends from the plate 123, which pawl is substantially cylindrical 122 in a direction transversal to the plate 123 and thus substantially parallel to the axis X of the cylindrical portion 103 of the bell 102, where the pawl 122 extends from the plate 123 so as to be positioned above the outer surface 1 1 1 of said cylindrical portion 103. Elastic back-pulling means, e.g. a spring, are interposed between the plate 123 and the half-pulley 107, where the switch by rotation of the element 120 in a first rotation direction towards the outside and thus with the pawl 122 away from the surface 1 1 1 occurs against the elastic bias applied by the spring, while the switch for rotation of the element 120 in a second rotation direction opposite to the first one, in particular towards the inside and thus with the pawl 122 approaching towards the surface 1 1 1 is promoted by the elastic reaction of the spring itself.

The operation of the system according to the embodiment of the present invention described above can be summarized as follows.

Figure 2 shows a first configuration in which each one of the pawls 122, by virtue of the action of the respective spring, is pushed against the surface 1 1 1 and engages a corresponding depression 1 12, being in particular housed in the concavity C1 of the depression itself. In this configuration, a possible rotation of the bell 102 in the rotation direction A shown in figure 2 results into dragging into rotation the driven pulley 105. So, assuming a situation in which the engine is off, and thus a situation in which the pads inside the bell 102 are in the retracted position and so the bell 102 is released from the cap (so that any rotation of the bell 102 would not result in rotation of the driven pulley 105), this is why, on the contrary, by virtue of the engagement of the elements 120 on the surface 1 1 1 of the bell 102, the rotation of the bell 102 results in the rotation respectively of the pulley 105, of the driving pulley, and thus of the drive shaft, whereby allowing starting the engine itself, if, for example, the rotation of the bell 102 is caused by pushing the vehicle. On the other hand, the configuration in figure 2, does not hinder the normal operation of the vehicle, in particular of the transmission of the vehicle itself, in any manner. Indeed, assuming that the pulley 105 is put into rotation in rotation direction A by starting the engine and then through the transmission (drive pulley, belt etc.), the rotation of the half-pulley 107 in the rotation direction A results in putting into rotation the bell 102 in an entirely normal manner, in the moment of the coupling between the bell 102 and the half-pulley 107 deriving from the expansion of the shoes housed inside the bell 102 and thus by virtue of the dragging action applied by the shoes on the inner surface of the cylindrical portion 103 of the bell 102, instead of by the action of the engagement elements 120 on the bell. Indeed, on the contrary, the pawls 122 are switched to the disengagement configuration (Figures 4 and 5) as a result of both the thrust action applied on each pawl 122 of the assembly C2 of the respective depression 122 and of the centrifugal force, where the pawls 122 thus are rotated away from the outer surface 1 1 1 and thus disengaged from the respective depressions 122.

A further possibility of use of the system according to the present invention can finally be summarized as follows.

Assuming the driven pulley 105 is put into rotation in the rotation direction opposite to the rotation direction A shown in figure 2, e.g. when the engine is off or running at a very slow speed, either close to or lower than idling speed (and thus in disengagement condition between bell 102 and pads inside it, being the pads in retracted position), and for example by applying the drive force generated by the alternator to the drive shaft, on the contrary, and again by virtue of the engagement of the pawls 122 in the respective depressions 1 12, the bell 102 is also dragged into rotation in the rotation direction opposite to the rotation direction A, where the hub applied to the bell 102 and the wheel are thus put into rotation in the rotation direction contrary to the forward travel rotation direction, thus allowing to reverse the vehicle, precisely by exploiting the contrary rotation on the drive shaft, for instance. We have thus demonstrated by means of the detailed description of the embodiments of the present invention shown in the drawings given above that the present invention achieves the predetermined objects by overcoming the drawbacks found in the prior art.

In particular, the present invention provides a solution which allows both reversing the vehicle with engine off or running at a very slow rpm, close to idling, and/or push- starting the engine, e.g. in case of flat battery and/or of fault in the electrical system. According to the present invention, moreover, the aforesaid objects are achieved by using a limited number of component parts of simple construction which can be manufactured at a low cost.

Although the present invention is explained above by means of a detailed description of the embodiments shown in the drawings, the present invention is not limited to the embodiments described above and shown in the drawings. On the contrary, all modifications and/or variants of the embodiments described above and shown in the drawings, which will appear obvious and immediate to those skilled in the art, are included in the scope of the present invention.

The scope of the present invention is thus defined by the claims.