BACKGROUND OF THE INVENTION

The present invention relates to a speed-changing device for a two-wheeled vehicle, in particular for a cycle or even a motorcycle.

STATE OF THE ART

It is known to use speed gears on bicycles such as racing or urban bikes or mountain bikes.

The aforementioned speed gears comprises a group of toothed wheels of different di ameters, mutually coaxially stacked, and mounted on the hub of the rear wheel, on which a transmission chain engages.

A derailleur organ is provided which, operated by means of a special lever by the us er, moves, at the rear region, the transmission chain from one wheel to the other of the aforesaid group of toothed wheels.

A drawback of these speed gears is that during a change of position of the chain from one toothed wheel to another, the same chain, due to the variation of position along the axis of rotation of the hub, is subjected to an action of bending that is fatiguing and in the long run can damage it. Furthermore, this limit requires avoiding as much as possible to operate the speed gear in conditions of use "under stress", that is when the cyclist is applying a considerable traction force on the bicycle pedals, for example during an acceleration phase or while he travels along a uphill road. Moreover, these speed changes are affected by a non-negligible noise level.

Other types of speed gear for bicycles are also known, which however are particularly complex from the structural and functional point of view, due for example to the high number of components from which they are composed (epicycloid mechanisms with numerous satellites, planetary elements, etc..). In view of the drawbacks above illustrated, it would therefore be desirable to have a speed-changing device which is structurally and functionally simplified, light and si lent in operation, highly reliable and effective in any condition of use, even under stress.

OBJECTS OF THE INVENTION

An object of the invention is to provide a speed-changing device for a bicycle or even a motorcycle which is simple and economical to make, structurally simplified and capable of operating effectively in any operating condition without fatiguing the chain or belt transmission element.

BRIEF DESCRIPTION OF THE INVENTION

These and further objects and advantages can be achieved by means of a speed vary ing device as defined in claim 1.

Owing to the speed-changing device according to the invention all the drawbacks of the state of art are overcome.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the speed-changing device according to the in vention will become more apparent from the following description, with reference to the drawings, in which:

Figure 1 shows the speed-changing device according to the invention connected to the rear wheel of a two-wheeled vehicle, in particular a bicycle;

Figure 2 is an enlarged view of the speed-changing device according to the in vention;

Figure 3 shows a part of a bicycle on which the speed-changing device according to the invention is mounted;

Figure 4 is an enlarged detail of Figure 3; Figure 5 is an interrupted and perspective schematic view of the speed-changing device coupled to a chain or belt transmission element;

Figure 6 is another schematic view of the speed-changing device according to the invention;

Figures 7 to 9 show the speed-changing device object of the invention in differ ent operative configurations corresponding to different kinematic transmission ratios;

Figures 10 and 11 show the speed-changing device in two different operating configurations corresponding respectively to a minimum radius and to a maximum radius of winding of the transmission element, corresponding to two extreme trans mission ratios.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the attached figures, a speed-changing device 1 is described for a two-wheeled vehicle 2, in particular, but not in a limiting way, for a bicycle, or even for a motorcycle.

The speed-changing device 1 comprises circular support means 3 A, 3B, able to be mounted, by means of a connection body 20, on a hub 4 of a rear wheel 5 of the bicy cle 2 or motorcycle, and supporting a plurality of meshing lamellar elements 6 suita ble for engaging with a transmission element T.

The transmission element T is of the flexible type, for example of the chain type or of the belt type, in particular toothed belt.

The circular support means 3A, 3B precisely comprise a pair of distinct support ele ments 3 A, 3B, each of a disc-shaped shape, and rotating about a same rotational axis

A.

The lamellar meshing elements 6 are arranged radially around the aforementioned ro tation axis A.

In particular, as better detailed below, each lamellar element 6 is provided with a shaped meshing edge S which comprises a succession of zones Zl, Z2, Zn placed at different distances from the aforementioned rotation axis A.

The number of zones Zl, Z2, Zn can be chosen in a desired manner according to the specific needs and intended use of the speed-changing device 1. For example, for each meshing shaped edge S a number of the aforesaid Z zones can be provided vary ing from about 12 to about 15, corresponding to as many transmission ratios, and therefore dynamic transmission torques.

The two disc-shaped support elements 3A, 3B, which are mutually parallel and coax ial, can be translated (by means of a distance-adjusting member 10 described later) along the aforesaid rotation axis A to move closer/away from each other so as to vary a ratio, therefore dynamic torque, kinematic transmission for the bicycle 2.

The lamellar meshing elements 6 are grouped in a first series Wl of lamellar meshing elements 6 and a second series W2 of mutually opposite lamellar meshing elements 6 movable to and from one another to change a meshing radius R with the transmission element T with a chain or toothed belt and therefore vary a corresponding kinematic transmission ratio (i.e. a speed ratio for the bicycle 2).

As already specified, the number of zones Zl, Z2, Zn is chosen in such a way as to obtain a desired discrete number of winding radius R, thus corresponding kinematic transmission ratios. The greater the number of the aforementioned zones, i.e. the steps of the shaped profiles S, the greater the number of speed ratios obtainable and therefore the finer the adjustment of the transmission ratio will be.

Also the number of laminar meshing elements 6 can be chosen appropriately accord ing to the specific requirements and intended use of the speed-changing device 1.

For example, a number of lamellar elements 6 ranging from about 8 to about 15 can be provided.

From a comparison of figures 7, 8, 9, it is possible to see three different radii from the increasing meshing radius Rl, R2, R3, corresponding to different kinematic transmission ratios.

Figures 10 and 11 show the speed-changing device in two different operating config urations corresponding respectively to the minimum meshing radius Rl and to a maximum meshing radius of the transmission element T, thus corresponding to two extreme values of transmission ratios.

More precisely, the lamellar meshing elements 6 of the first series Wl are supported by a first disc-shaped support element 3A of the aforesaid pair, and the lamellar meshing elements 6 of the second series W2 are supported by a second disc-shaped support element 3B of the aforesaid couple.

The first disc-shaped support element 3A and the second disc-shaped support ele ment 3B are then mounted on the connection body 20 on which they can axially slide along the rotation axis A.

Two groups are therefore defined - one opposed to the other - of lamellar meshing el ements 6. The two groups, or series Wl, W2, of lamellar elements are therefore op posite to one other so as to define, in correspondence with a median or central area of the connecting body 20, an annular band, or arc portion, on which the transmission element T can wind with a desirable meshing radius from time to time. Owing to this configuration, the transmission element T can always operate in a same plane, with out the need to have to translate on planes that change from time to time with respect to the plane containing the driving crown 21 moved by the cyclist's feet. Owing to the speed-changing 1 according to the invention, therefore, the undesired effect of sub jecting the chain or belt T to bending actions with respect to the plane on which the same chain or belt advances is thus avoided. In this way, the belt or chain element T can operate in a less tired and less noisy manner.

The lamellar elements 6 of the first series Wl protrude from an inner face 7 of the first disc-shaped support element 3A, and the lamellar elements 6 of the second se ries W 1 protrude from a further inner face 8 of the disk-shaped second support ele- ment 3B, wherein the aforesaid further inner face 8 faces the inner face 7 of the first disc-shaped support element 3A.

Each lamellar element 6 of the first series Wl is approached to, and relatively slida bly on a corresponding lamellar element 6 of the second series W2 in such a way that the respective mutually opposite shaped edges S define together, from time to time, a respective meshing tooth seat 9 for the transmission element T.

The first series W 1 and the second series W2 of lamellar elements 6 are sliding paral lel to the axis A of rotation and are movable in directions Dl, D2 mutually opposite to approach to, or move away from, one another.

The shaped meshing edge S of each lamellar element 6 has a stepped profile which extends from the respective disc-shaped support element 3A, 3B in a downward manner towards the axis A of rotation.

The shaped meshing edges S are configured to define a plurality of discrete transmis sion ratios.

The above-mentioned zones Zl, Z2, .. Zn of each shaped edge S are positioned one after the other at a distance from the axis A of rotation which progressively decreases from a maximum distance value, in the vicinity of the disc- shaped support elements 3 A, 3B, at a minimum distance value in the region farthest from respective support elements 3 A, 3B.

The mutual approach or removal of the support elements 3A, 3B determines corre spondingly a greater interpenetration or an expansion of the two series Wl and W2 of lamellar elements 6 and consequently there is an increase or a decrease in the mesh ing radius of the transmission element T, which therefore translates into the desired variation of the kinematic transmission ratio.

More precisely, the step profile of each shaped meshing edge S comprises horizontal portions H parallel to the rotation axis A, arranged to receive the chain transmission element T in support, and inclined portions I to define converging surfaces for receiv ing the transmission element T. The inclined portions I of two opposite lamellar ele ments 6 are shaped to guide and facilitate a radial movement of the transmission el ement T, and cooperate together so that, with a reciprocal approach movement, they progressively impose the transmission element T a centrifugal movement to move away from the axis A of rotation.

The aforementioned distance-adjusting organ 10 is now described, which can be ac tuated to move closer to, away from, each other the first series W 1 and the second se ries W2 of lamellar meshing elements 6.

The distance-adjusting member 10 comprises two lever elements 11 A, 11B mutually hinged and having a pad shaped end 12. The pad shaped end 12 are shaped to slida bly engage in respective grooves or gorges 13 which are formed and extend circum ferentially on the disc-shaped support elements 3 A, 3B.

The lever elements 11A, 11B, movable to close or mutually open like a pair of scis sors, can be operated by means of a cable element 14, which can be controlled by means of a suitable lever placed on the handlebar of the bicycle 2.

In a possible version, not shown, the distance-adjusting member 10 can include a mo torized electric/electronic unit capable of automatically varying - by predetermined quantities - the distance between the aforementioned disc- shaped support elements 3A, 3B to achieve the desired transmission ratios. The aforementioned motorized unit can be controlled by a suitable lever located on the handlebar and configured to send the appropriate electrical/electronic control signals. The communication be tween the aforesaid motor-driven unit and the control lever can be achieved by means of an electrical connection cable or by means of a wireless connection.

The speed-changing device 1 according to the invention also includes a tensioning unit 15 provided with wheels 16, 17, at least one of which is pivoted and elastically oscillating, configured to keep the transmission element T in tension as the meshing radius on the lamellar meshing elements 6 varies. From the above description and shown in the attached figures, it is evident that the speed-changing device 1 according to the invention successfully achieves all the pre fixed purposes.

In particular, the speed-changing device 1 according to the invention is remarkably simplified from the structural and functional point of view, and is also very mechani cally reliable. In addition, less "fatiguing" and also quieter functioning is made possi ble for the transmission element T and the other components of the bicycle. Thanks to the configuration described above, the speed-changing device 1 can be operated in any condition of use and effort, and the variation of the discrete type transmission ra tio can be performed at any time, even during a condition operating "under stress", i.e. while the cyclist applies a considerable traction force on the driving crown 21 and therefore on the speed-changing device 1, without this causing any risk of damage to any component. For example, the cyclist can operate the speed-changing device 1 under stress to vary a transmission ratio while traveling along a stretch of road uphill, or during an acceleration phase, without any problem for the components of the speed-changing device 1 itself.

The speed-changing device 1 is cheaper to realize due to its high structural simplicity with respect to the speed gear belonging to the state of the art.

Any element forming part of the speed-changing device 1 according to the invention can be replaced with other equivalents in structural and functional terms, and the ma terials, insofar as they are compatible with the specific use for which they are intend ed, can be suitably chosen depending on the requirements and depending on the state of art available.

It is possible to configure and size the speed-changing device 1 according to the spe cific requirements and applications, with possible variations and/or additions to what has been described above and illustrated in the attached drawings without departing from the claimed protection scope.