Technical Field

The present invention relates to a cogset of the gears of bicycles or the like. Background Art

With reference to bicycles, from ordinary bicycles to racing bicycles and so- called mountain bikes, the use has been known for some time of gears suitable for allowing the selection of different transmission ratios, so as to facilitate pedalling and adapt it to the different characteristics of the route.

In particular, the most common type of bicycle gears are the so-called derailleur gears.

Derailleur gears comprise a series of gearwheels of different and predefined dimensions, positioned alongside one another, and a mechanism controlled by the rider, known as derailleur, suitable for moving the chain from one gearwheel to another and keeping the chain under tension.

Generally speaking, ordinary bicycles have one series of gearwheels, so-called cogs, fitted on the rear wheel hub and just one rear derailleur, while racing bicycles or mountain bikes can have several crown gears positioned side by side in correspondence to the pedals and a second front derailleur.

In particular, mountain bikes generally have a maximum of ten cogs on the rear wheel and a maximum of three crown gears in correspondence to the pedals, for a total of thirty possible ratios, while racing bicycles generally have a maximum of eleven cogs on the rear wheel and at most two crown gears in correspondence to the pedals, for a maximum of twenty possible ratios.

Gear control is by means of one or more specific levers, by means of which the chain can be moved from one cog to another and/or from one crown gear to another.

One of the most widely adopted solutions, for instance, uses a control having a pair of levers fitted on the handlebars, wherein a first lever of larger size, once operated, tensions the gear cable and moves the derailleur, thereby shifting the chain onto larger cogs.

The operation of a second lever, on the other hand, causes the release of the cable and moves the derailleur, thereby shifting the chain onto smaller cogs. The gears of known type, however, have a number of drawbacks.

In particular, a first drawback is due to the fact that the continual movements of the chain on the cogs and on the crown gears, together with the fact that the chain in many cases has to operate in an out-of-axis, and therefore inclined position, with respect to the teeth of the cogs and of the crown gears, results in considerable wear on the chain itself.

Consequently, the chain becomes gradually less functional over time and can even break, with obvious risks for the rider, and therefore requires continual maintenance and inspection and periodical replacement.

Furthermore, another drawback is caused by the fact that, because it operates in an inclined position with respect to the teeth of the cogs and of the crown gears, the risk increases considerably of the chain coming off, with all the ensuing inconvenience and risks.

Another drawback is caused by the fact that the largest number of possible gear ratios is limited, on the one hand, by the maximum sizes of the cogset in correspondence to the rear wheel hub and, on the other, by the stroke and maximum inclination of the chain with respect to the teeth, which cannot be excessive.

Not the least drawback is caused by the fact that, to overcome all the above problems, the chain itself and the teeth and the structure of the cogs and of the crown gears must be worked, shaped and sized so as to favour the engagement of the chain on the teeth with any possible inclination, as well as to reduce the total weight of the cogset.

Suitably shaped chains and cogs must therefore be made of increasingly smaller thickness, with considerable increase in the total cost of making the gears.

The fact is also pointed out that the cogs of increasingly smaller thickness also imply chains of increasing smaller thickness which, therefore, are more fragile and more subject to breakage.

Description of the Invention

The main aim of the present invention is to conceive a cogset for the gears of bicycles or the like which allows considerably reducing the wear on the chain. Another object of the present invention is to conceive a cogset for the gears of bicycles or the like which allows considerably reducing the risk of the chain coming off.

Another object of the present invention is to conceive a cogset for bicycle gears or the like which allows the largest number of possible gear ratios while at the same time keeping overall dimensions as small as possible.

Another object of the present invention is to conceive a cogset for the gears of bicycles or the like which allows considerably reducing the risk of the chain breaking.

Another object of the present invention is to provide a cogset for the gears of bicycles or the like which allows overcoming the mentioned drawbacks of the state of the art within the ambit of a simple, rational, easy, effective to use and low cost solution.

The above objects are achieved by the present cogset for the gears of bicycles or the like, according to claim 1.

Brief Description of the Drawings

Other characteristics and advantages of the present invention will become more evident from the description of two preferred, but not sole, embodiments of a cogset for the gears of bicycles or the like, illustrated purely as an example but not limited to the annexed drawings in which:

figure 1 is a side view of a first embodiment of the cogset according to the invention fitted on an ordinary bicycle.

figure 2 is an exploded view of the cogset in figure 1 ;

figures 3 and 4 are axonometric and partial exploded views of the first cassette sprocket of the cogset in figure 1 ;

figure 5 is an axonometric broken view which shows the cogset in figure 1 ; ; figure 6 is an axonometric and partial exploded view of the first disc of the cogset in figure 1 ;

figures from 7 to 16 are plan and lateral views which show the operation of the first embodiment of the cogset according to the invention;

figure 17 shows a particular embodiment of the control means of the cogset according to the invention;

figures ^' .18 and 19 are partial axonometric views which show in a simplified way a possible second embodiment of the cogset according to the invention;

figures 20 and 21 are axonometric and partial section views which show the operation of the cogset in figures 18 and 19.

Embodiments of the Invention

With particular reference to a first embodiment, shown in figures from 1 to 17, globally indicated by 1 is a cogset for the gears of bicycles or the like, in particular replacing the traditional cogset commonly used on racing bicycles, mountain bikes, ordinary bicycles or the like.

The cogset 1 comprises a first fixed cog 2 fixed integral and coaxial to the hub A of the wheel B of a bicycle C.

In particular, the first fixed cog 2 is arranged in correspondence to a first work position and is suitable for being engaged by the chain D of the bicycle C.

The cogset 1 also comprises a second fixed cog 3 fixed integral and coaxial to the hub A.

In particular, the second fixed cog 3 is arranged in correspondence to a second work position, defined in the proximity of the first work position, and is suitable for being engaged by the chain D.

The first fixed cog 2 and the second fixed cog 3 are composed of suitable toothed crown gears of different diameter.

For example, with reference to the preferred embodiment of the cogset 1 shown in the illustrations, the first fixed cog 2 is composed of a cog with eleven teeth, while the second fixed cog 3 is composed of a cog with twelve teeth.

Advantageously, the cogset 1 comprises at least a first mobile cog 4, associated sliding and integral in rotation with the hub A and suitable for being moved along a sliding direction E between a first retracted position, defined alongside the first work position, wherein it is substantially moved away with respect to the chain D, and the first work position, wherein it is suitable for being engaged by the chain D.

The cogset 1 also comprises at least a second mobile cog 5 of different diameter with respect to the first mobile cog 4, associated sliding and integral in rotation with the hub A and suitable for being moved along the sliding direction E between a second retracted position, defined alongside the second work position, wherein it is substantially moved away with respect to the chain D, and the second work position, wherein it is suitable for being engaged by the chain D.

Advantageously, the cogset 1 has a first cassette sprocket, indicated altogether in the illustrations by the reference 6, comprising a plurality of first mobile cogs 4, and a second cassette sprocket, indicated altogether in the illustrations by the reference 7, comprising a plurality of second mobile cogs 5.

In particular, the first mobile cogs 4 of the first cassette sprocket 6 are composed of suitable toothed crown gears of different diameter.

Furthermore, the second mobile cogs 5 of the second cassette sprocket 7 are composed of suitable toothed crown gears of different diameter and with a diameter different to that of the first mobile cogs 4.

For example, with reference to the preferred embodiment of the cogset 1 shown in the figures, the first cassette sprocket 6 comprises a cog with fourteen teeth 4a, a cog with seventeen teeth 4b, a cog with twenty-one teeth 4c, a cog with twenty- five teeth 4d and a cog with twenty-eight teeth 4e, for a total of five first mobile cogs 4.

The second cassette sprocket 7, on the other hand, comprises a cog with fifteen teeth 5a, a cog with nineteen teeth 5b, a cog with twenty-three teeth 5c, a cog with twenty-seven teeth 5d and a cog with thirty teeth 5e, for a total of five second mobile cogs 5.

Consequently, always according to the particular embodiment shown in the figures, if added to the first and second fixed cogs 2 and 3 the total number of the cogs of the cogset 1 is twelve.

Different embodiments of the cogset 1 cannot however be ruled out wherein the first cassette sprocket 6 and the second cassette sprocket 7 envisage a different number of first and second mobile cogs 4 and 5 and wherein such first and second mobile cogs 4 and 5 have a different diameter and number of teeth.

Advantageously, when the first mobile cogs 4 are in the first retracted position, then they are substantially coplanar and concentric with one another.

This way, when all the first mobile cogs 4 are packaged up in the first retracted position, then the first cassette sprocket 6 is composed of a single disc with a diameter the same as the diameter of the first mobile cog 4e of larger dimensions (cog with twenty-eight teeth) and with thickness the same as the thickness of a single first mobile cog 4.

Consequently, the dimensions of the first cassette sprocket 6 are considerably reduced.

Usefully, the first mobile cog 4a of smaller diameter has a greater diameter than the first fixed cog 2 and, when it is arranged in the first work position, such first mobile cog 4a is arranged substantially coplanar and concentric with respect to the first fixed cog 2.

In such first work position therefore, the outer profile, and therefore the toothing, of the first mobile cog 4a is overlapped to the outer profile, and therefore on the toothing, of the first fixed cog 2 and is suitable for being engaged by the chain D .

Usefully, the first mobile cog 4a of smaller diameter (the cog with fourteen teeth) has a first seat 8a for housing the first fixed cog 2 (cog with eleven teem). In particular, the first seat 8a is obtained in correspondence to the inner profile and along the entire circumference of the first mobile cog 4a and substantially reproduces the outer profile of the first fixed cog 2.

Furthermore, when two or more first mobile cogs 4a, 4b, 4c, 4d and 4e are arranged in correspondence to the first work position, then they are substantially coplanar and concentric and the outer profile, i.e., the toothing, of the first mobile cog 4 of greater diameter, e.g., the mobile cog 4b, is overlapped to the outer profile, i.e., the toothing, of the first mobile cog 4 of smaller diameter, e.g., the mobile cog 4a.

This way, the overall dimensions of the first mobile cogs 4 in the first work position are reduced to the utmost and the toothing of the first mobile cog 4 of greater diameter can be engaged by the chain D.

Usefully, each first mobile cog 4b, 4c, 4d and 4e has a first seat 8b, 8c, 8d, 8e for housing the first mobile cog 4a, 4b, 4c and 4d of smaller diameter.

In particular, each first seat 8b, 8c, 8d, 8e is obtained in correspondence to the inner profile and along the entire circumference of each first mobile cog 4b, 4c, 4d and 4e and substantially reproduces the outer profile of the first mobile cog 4a, 4b, 4c and 4d of smaller diameter.

According to the preferred embodiment, shown in the illustrations, the second cassette sprocket 7 is made in the same way as the first cassette sprocket 6.

In particular, when all the second mobile cogs 5 of the second cassette sprocket 7 are packaged up in the second retracted position, then the second cassette sprocket 7 is composed of a single disc with a diameter equal to the diameter of the second mobile cog 5e of larger dimensions (cog with thirty teeth) and with thickness equal to the thickness of a single second mobile cog 5.

Consequently, the dimensions of the second cassette sprocket 7 are considerably reduced.

Usefully, the second mobile cog 5a of smaller diameter has a greater diameter than the second fixed cog 3 and, when it is arranged in the second work position, such second mobile cog 5a is substantially arranged coplanar and concentric with respect to the second fixed cog 3.

In such second work position, therefore, the outer profile, and therefore the toothing, of the second mobile cog 5a is overlapped to the outer profile, and therefore on the toothing, of the second fixed cog 3 and is suitable for being engaged by the chain D .

Usefully, the second mobile cog 5a of smaller diameter (the cog with fifteen teeth) has a second seat 9a for housing the second fixed cog 3 (cog with twelve teeth).

In particular, the second seat 9a is obtained in correspondence to the inner profile and along the entire circumference of the second mobile cog 5a and substantially reproduces the outer profile of the second fixed cog 3.

Furthermore, when two or more second mobile cogs 5a, 5b, 5c, 5d and 5e are arranged in correspondence to the second work position, then they are substantially coplanar and concentric with one another and the outer profile, i.e., the toothing, of the second mobile cog 5 of greater diameter, e.g., the second mobile cog 5b, is overlapped to the outer profile, i.e., on the toothing, of the second mobile cog 5 of smaller diameter, e.g., the second mobile cog 5a.

This way, the overall dimensions of the second mobile cogs 5 in the second work position is reduced to the utmost and the toothing of the second mobile cog 5 of greater diameter can be engaged by the chain D.

Usefully, each second mobile cog 5b, 5c, 5d and 5e has a second seat 9b, 9c, 9d and 9e for housing the second mobile cog 5a, 5b, 5c and 5d of smaller diameter. In particular, each second seat 9b, 9c, 9d and 9e is obtained in correspondence to the inner profile and along the entire circumference of each second mobile cog 5b, 5c, 5d and 5e and substantially reproduces the outer profile of a respective second mobile cog 5a, 5b, 5c and 5d of smaller diameter.

The cogset 1 furthermore comprises supporting and guiding means, indicated altogether in the illustrations by the reference 10, suitable for supporting, integral in rotation, the first and the second mobile cogs 4 and 5 with respect to the hub A and suitable for guiding the sliding of the first and second mobile cogs 5 along the sliding direction E, parallel with the longitudinal axis of the hub A.

In particular, the supporting and guiding means 10 comprise a first supporting element 11 associated integral with the hub A.

Preferably, the first supporting element 11 is composed of a first plate substantially disc shaped and of reduced thickness.

For each of the first mobile cogs 4, the supporting and guiding means 10 furthermore comprise three through holes 12, made on the first plate 11 and distanced the one from the other, and respective three pins 13, substantially parallel with one another, which extend protruding from the side of each first mobile cog 4 opposite with respect to the chain D and which are fitted inside the through holes 12 axially sliding along the sliding direction E.

In particular, the through holes 12 are made on the first plate 11 in three rows extending along radial directions and which are arranged substantially at 120° from one another and, similarly, the pins 13 are made on the first mobile cogs 4 of the first cassette sprocket 6 in three rows extending along radial directions and which are arranged substantially at 120° from one another.

In the same way, the supporting and guiding means 10 comprise a second supporting element 14 associated integral with the hub A.

Preferably, the second supporting element 14 is composed of a second plate, substantially disc shaped and of reduced thickness. For each of the second mobile cogs 5, the supporting and guiding means 10 furthermore comprise three through holes 15, made on the second plate 14 and distanced from one another, and respective three pins 16, substantially parallel with one another, which extend protruding from the side of each second mobile cog 5 opposite with respect to the chain D and which are fitted inside the through holes 15 axially sliding along the sliding direction E.

In particular, the through holes 15 are made on the second plate 14 in three rows extending along radial directions and which are arranged substantially at 120° from one another and, similarly, the pins 16 are made on the second mobile cogs 5 of the second cassette sprocket 7 in three rows extending along radial directions and which are arranged substantially at 120° from one another.

The cogset 1 comprises movement means 17, operatively associated with the first and second mobile cogs 5 and suitable for moving the first and the second mobile cogs 4 and 5 in succession, between the first and second retracted positions and the first and second work positions, respectively.

The movement means 17 comprise a first adjustment element 18 associated revolving with the hub A around a rotation axis substantially parallel with the longitudinal axis of the hub itself.

In particular, with reference to the preferred embodiment shown in the illustrations, the first adjustment element 18 is composed of a first disc coupled axially revolving with the hub A and arranged in correspondence to the side of the first plate 11 opposite with respect to the first cassette sprocket 6.

The movement means 17 furthermore comprise first means of transformation of the rotation movement of the first disc 18 into translation movement of the first mobile cogs 4 along the sliding direction E and between the first retracted position and the first work position.

In particular, the movement means 17 comprise a plurality of first circular guides 19 of different diameter, one for each first mobile cog 4, made on the side of the first disc 18 turned towards the first plate 11 and arranged concentrically the one to the other.

With each of the first circular guides 19, the free extremities of the three pins 13 of each of the first mobile cogs 4 are associated sliding. Usefully, each of the first circular guides 19 comprises three ramps 20 substantially arranged at 120° the one from the other and the rotation of the first disc 18 in one direction or another is suitable for moving the extremities of the pins 13 along the respective ramps 20, for the translation of the first mobile cog 4 along the sliding direction E, between the first retracted position and the first work position.

In particular, the first circular guides 19 can be made up of first circular channels made on one side of the first disc 18, inside which respective heads 13a of the pins 13 are housed sliding and retained.

The movement means 17 furthermore comprise a second adjustment element 21 associated revolving with the hub A around a rotation axis substantially parallel with the longitudinal axis of the hub itself.

In particular, with reference to the preferred embodiment shown in the illustrations, the second adjustment element 21 is made of a second disc coupled axially revolving with the hub A and arranged in correspondence to the side of the second plate 14 opposite with respect to the second cassette sprocket 7. The movement means 17 furthermore comprise second means of transformation of the rotation movement of the second disc 21 into translation movement of the second mobile cogs 5 along the sliding direction E and between the second retracted position and the second work position.

In particular, the movement means 17 comprise a plurality of second circular guides 22 of different diameter, one for each second mobile cog 5, made on the side of the second disc 21 turned towards the second plate 14 and arranged concentrically the one to the other.

With each of the second circular guides 22, the free extremities of the three pins 16 of each of the second mobile cogs 5 are associated sliding.

Usefully, each of the second circular guides 22 comprises three ramps 23 substantially arranged at 120° the one from the other and the rotation of the second disc 21 in one direction or another is suitable for moving the extremities of the pins 16 along the ramps 23 for the translation of the second mobile cog 5 along the sliding direction E, between the second retracted position and the second work position. In particular, the second circular guides 22 can be made up of second circular channels made on one side of the second disc 21, inside which respective heads 16a of the pins 16 are housed sliding and retained.

The cogset 1 furthermore comprises a first external plate 24 and a second external plate 25 associated integral and coaxial with the hub A, in correspondence to the faces of the first and of the second discs 18 and 21 respectively, opposite the first and second plates 11, 14.

Advantageously, the movement means 17 comprise alternated operation means, indicated altogether in the illustrations by the reference 26, operatively connected to the first and second discs 18 and 21 to move each of the first and second mobile cogs 4 and 5 in succession, between the first and second retracted positions and the first and second work positions, respectively.

In particular, with reference to the embodiment shown in the illustrations, the alternated operation means 26 are made up of a gear system operatively associated with the first and the second adjustment element 21 and operatively associated with a command device F of the gears of the bicycle C.

The command device F can be made, e.g., of one or more levers of the type commonly used in gears of conventional type.

Preferably, the command device F comprises a first lever which can be operated to position the chain D on cogs of greater diameter, and therefore to change the gears towards higher ratios, and a second lever which can be operated to position the chain D on cogs of smaller diameter, and therefore to change the gears towards lower ratios.

The gears of the bicycle C furthermore comprise means for the relative shift between the chain D of the bicycle C and the cogset 1, indicated in the illustrations by the reference G, operatively connected to the command device F.

In particular, the shift means G can be made of at least a derailleur device suitable for shifting the chain D in correspondence to the first work position and the second work position.

The gear system 26 comprises four first gear wheels 27 coupled with a first toothing 28 made internally along a through opening made at the centre of the first disc 18.

The gear system 26 furthermore comprises four second gear wheels 29 coupled with a second toothing 30 made internally along a through opening made at the centre of the second disc 21.

Each of the first gear wheels 27 is axially revolving and is associated integral with a respective second gear wheel by means of a rod 31.

Usefully, each first and second gear wheels 27 and 29 has respective partial toothings 32 made along portions of the circumference profile substantially opposite to each other and suitable for engaging alternately on the first toothing 28 and on the second toothing 30 respectively, so as to cause the first disc 18 and the second disc 21 to rotate alternately.

Usefully, the movement means 17 can comprise control means 33 for controlling the gear system 26 connected to the command device F and suitable for controlling the operation of the gear system 26 in one direction or another so as to change the gears towards higher or lower transmission ratios.

With reference to a particular but not exclusive embodiment shown by way of example in figure 17, the control means 33 can comprise a suitable planetary system.

In particular, the control means 33 comprise at least a first gear 34 associated integral and coaxial with at least one of the first and second gear wheels 27 and 29.

For example, the first gear 34 can be associated integral and coaxial with the extension of the rod 31 bearing at least one of the pairs of first and second gear wheels 27 and 29.

Usefully, the control means 33 comprise four first gears 34 associated integral and coaxial with extensions of the rods 31 of each pair of first and second gear wheels 27 and 29.

In particular the rods 31 extend through respective holes made on the second external plate 25.

The control means 33 comprise a first crown gear 35 which extends around the four first gears 34 and has a rotation axis substantially coaxial with the axis of the hub A. The first crown gear 35 comprises an internal toothing 35a on which the four first gears 34 engage.

The control means 33 furthermore comprise at least a second gear 36 associated integral and axially revolving with the second external plate 25.

For example, the second gear 36 can be associated integral and coaxial with a pin 37 fixed to the second external plate 25.

Usefully, the control means 33 comprise four second gears 36 associated integral and coaxial with the respective pins 37.

The first crown gear 35 comprises an external toothing 35b on which the four second gears 36 engage.

The control means 33 comprise a second crown gear 38 which extends around the four second gears 36 and which has a rotation axis substantially coaxial with the axis of the hub A.

The second crown gear 38 comprises an internal toothing 38a on which the four second gears 36 engage.

The command device F is suitable for blocking the first crown gear 35 or the second crown gear 38 during the rotation of the wheel B, so as to start the rotation of the four first gears 34, and therefore of the four first and second gear wheels 27 and 29, in an anti-clockwise and in a clockwise direction respectively, so as to change the gears towards a higher or lower transmission ratio.

Different embodiments of the movement means 17 cannot however be ruled out.

The movement means 17 can comprise, e.g., one of more electronic drive devices operatively connected to the gear system 26.

The operation of the cogset 1 is described below and is schematically illustrated in the figures from 7 to 16.

In the figures 7 and 8 a possible initial configuration of the cogset 1 is illustrated, wherein all the first mobile cogs 4 are packaged up in the first retracted position, all the second mobile cogs 5 are packaged up in the second retracted position and the chain D is positioned on the first fixed cog 2, in correspondence to the first work position. In this configuration the lowest transmission ratio is selected.

As shown in the figures 9 and 10, the pressure of the specific lever of the command device F causes the shift of the derailleur device, with consequent movement of the chain D from the first fixed cog 2, in the first work position, to the second fixed cog 3, in the second work position.

As shown in the figures 11 and 12, the return movement of the lever of the command device F causes the operation of the gear system 26.

Usefully, if the control means 33 are used shown in figure 17, such rotation is commanded blocking the first crown gear 35 during the normal rotation of the wheel B.

In particular, the first and the second gear wheels 27 and 29 rotate by 180°, causing the rotation of the first disc 18 for a predefined angular distance.

In particular, the partial toothings 32 of the first gear wheels 27 engage on the first toothing 28 of the first disc 18, causing the first disc itself to rotate. During such rotation, the second gear wheels 29 turn empty, being without teeth along the circumference section turned towards the second toothing 30 of the second disc 21 and, consequently, the second disc 21 stays still.

Consequently, the pins 13 of the first mobile cogs 4 slide inside the respective first circular channels 19 and the pins 13 inside the innermost first circular channel 19 cover the respective ramps 20, pushing the smallest of the first mobile cogs 4a (the cog with fourteen teeth) from the first cassette sprocket 6, and therefore from the first retracted position, to the first work position.

In such first work position, therefore, the first mobile cog 4a is arranged around the first fixed cog 2 and is ready to be engaged by the chain D in the event of a higher transmission ratio being selected.

As shown in the figures 13 and 14, a further pressure of the lever of the command device F causes the shift of the derailleur device G, with consequent movement of the chain D from the second fixed cog 3, in the second work position, to the first mobile cog 4a, in the first work position.

As shown in the figures 15 and 16, the return movement of the lever of the command device F causes the operation of the gear system 26.

Usefully, if the control means 33 are used illustrated in the figure 17, such rotation is commanded blocking the first crown gear 35 during the normal rotation of the wheel B.

In particular, the first and the second gear wheels 27 and 29 rotate by 180°, causing the rotation of the second disc 21 for a predefined angular section.

In particular, the partial toothings 32 of the second gear wheels 29 engage on the second toothing 30 of the second disc 21, causing the second disc itself to rotate. During such rotation, the first gear wheels 27 rotate idle, being without teeth along the circumference section turned towards the first toothing 28 of the first disc 18 and, therefore, the first disc 18 stays still.

Consequently, the pins 16 of the second mobile cogs 5 slide inside the respective second circular channels 22 and the pins 16 inside the innermost second circular channel 22 cover the respective ramps 23, pushing the smallest of the second mobile cogs 5a (the cog with fifteen teeth) from the second cassette sprocket 7, and therefore from the second retracted position, to the second work position.

In such second work position, therefore, the second mobile cog 5a is arranged around the second fixed cog 3 and is ready to be engaged by the chain D in the event of a higher transmission ratio being selected.

The highest transmission ratios can all be reached in the same way as has been described above, wherein the alternated rotation of the first disc 18 and of the second disc 21 permits moving, in sequence, the first mobile cogs 4 and the second mobile cogs 5 from the respective first and second retracted positions to the respective first and second work positions.

Lower transmission ratios are also obtainable in the same way as described above.

In such case, preferably, the command device F has a second lever and the operation of such lever permits the translation of the derailleur device G and the rotation of the first and of the second disc in the opposite direction to what has been described above and illustrated in the figures from 9 to 16.

Usefully, if the control means 33 illustrated in the figure 17 are used, the alternated rotation of the first and second discs 18 and 21 is commanded blocking the second crown gear 38 during the normal rotation of the wheel B. Described below is a second possible embodiment, illustrated in the figures from 18 to 21, wherein the cogset is indicated altogether by the reference Γ. With reference to such particular embodiment, it is pointed out that in the above illustrations is shown, in way, only a first fixed cog 2', fixable integral and coaxial to the hub A of the wheel B of the bicycle C, and a first cassette sprocket 6' , having a mobile cog 4a' and a mobile cog 4b' .

Such simplified and partial representation of the cogset 1 ' is provided for the sole purpose of permitting a quicker understanding of the operation of the cogset itself.

In the same way as the first embodiment described above, in fact, the cogset 1 ' also has an analogous second fixed cog and a second cassette sprocket. Furthermore each cassette sprocket can have a different number of cogs of different diameter and with a different number of teeth.

Advantageously, when the first mobile cogs 4' are in the first retracted position, then they are substantially coplanar and concentric.

This way, when all the first mobile cogs 4' are packaged up in the first retracted position, then the first cassette sprocket 6' is made up of a single disc with a diameter equal to the diameter of the first mobile cog 4b' of larger dimensions and with a thickness equal to the thickness of a single first mobile cog 4'.

Usefully, the mobile cogs 4a' and 4b' have respective substantially annular portions 39a' and 39b'.

In particular, the annular portion 39a' of the mobile cog 4a' of smaller dimensions is fitted sliding with prismatic type coupling inside the annular portion 39b' of the mobile cog 4b' of larger dimensions. ^"

In the same way as has been described with reference to the first embodiment, in the first work position, the outer profile, and therefore the toothing, of the first mobile cog 4a' is overlapped to the profile, and therefore on the toothing, of the first fixed cog 2' and is suitable for being engaged by the chain D.

Furthermore, the first mobile cog 4a' of smaller diameter has a first seat 8a' for housing the first fixed cog 2'.

In the same way, the second mobile cog 4b' has a second seat 8b' for housing the first mobile cog 4a'. The cogset 1 furthermore comprises supporting and guiding means, indicated altogether in the illustrations by the reference 10', associated integral with the frame of the bicycle C and suitable for guiding the sliding of the first mobile cogs 4' (as well as of the second mobile cogs, not shown) along the sliding direction E, parallel with the longitudinal axis of the hub A.

In particular, the supporting and guiding means 10' comprise a first plate 11 ' and a second plate 14' which are substantially disc shaped and of reduced thickness and associated integral with one another.

For each of the first mobile cogs 4', the supporting and guiding means 10' furthermore comprise two through holes 12', made on the first plate 11' and distanced the one from the other, and respective two pins 13', substantially parallel with one another, which extend protruding from the side of each first mobile cog 4' opposite with respect to the chain D and which are fitted inside the through holes 12' axially sliding along the sliding direction E.

A different number and arrangement of the through holes 12' and of the respective pins 13' cannot however be ruled out.

The cogset comprises movement means 17', operatively associated with first mobile cogs 4' and suitable for moving the first mobile cogs 4' (alternately with respect to the second mobile cogs, not shown) between the first retracted position and the first work position.

The movement means 17' comprise a first adjustment element 18' associated revolving with the frame of the bicycle C around a rotation axis substantially parallel with the longitudinal axis of the hub A.

In particular, with reference to the preferred embodiment shown in the illustrations, the first adjustment element 18' is made up of a first disc coupled revolving with the frame of the bicycle C and arranged in correspondence to the side of the first plate 11 ' opposite with respect to the first cassette sprocket 6' . The movement means 17' furthermore comprise first means of transformation of the rotation movement of the first disc 18' into the translation movement of the first mobile cogs 4' along the sliding direction E and between the first retracted position and the first work position.

In particular, the movement means 17' comprise a plurality of first circular guides 19' of different diameter, one for each first mobile cog 4', made on the side of the first disc 18' turned towards the first plate 11 ' and arranged concentrically the one to the other.

In this respect, it is pointed out that, for a better understanding, in the illustrations from 18 to 21 only one first circular guide 19' has been shown, suitable for allowing the movement of the first mobile crown gear 4a'.

With each of the first circular guides 19' is associated sliding the free extremity of the respective pins 13' connected to each of the first mobile cogs 4a' and

4b'.

Usefully, each of the first circular guides 19' comprises two ramps 20' arranged substantially at 180° the one to the other, and the rotation of the first disc 18' in one direction or another is suitable for moving the extremities of the pins 13' along the respective ramps 20', for the translation in sequence of each first mobile cog 4a' and 4b' along the sliding direction E, between the first retracted position and the first work position.

Usefully, each first mobile cog 4a' and 4b' has respective circular channels made along the respective circular portions 39a' and 39b', inside which respective heads 13a' of the pins 13' are housed sliding and retained.

Usefully the heads 13a' of the pins 13' have specific sliding bearings.

Furthermore, the movement means 17' comprise push springs 40' mounted on respective pins 13' and suitable for returning the first cogs 4a' arid 4b' to respective retracted positions.

Usefully, the movement means 17' can comprise, e.g., one or more devices of electronic or mechanical type for causing the rotation of the first disc 18' in stops and starts.

It has in fact been ascertained how the described invention achieves the proposed objects.

In particular, the fact is underlined that the cogset according to the invention permits considerably reducing the wear on the chain.

In fact, the chain is moved only between the first and the second work position and, therefore, for short distances.

Furthermore the chain always works in axis, i.e., with practically zero inclination with respect to the teeth of the cogs and, this way, the wear on the chain caused by rubbing against the teeth of the cogs is considerably limited. Furthermore, another advantage stems from the fact that the position of the chain in axis with the teeth permits considerably reducing the risk of the chain coming off.

Another advantage stems from the fact that the position of the chain in axis with the teeth permits considerably reducing the risk of the chain breaking.

Another advantage stems from the fact that the presence of the first and second mobile cogs, translatable between the respective first and second retracted positions and the respective first and second work positions, together with the fact that such first and second mobile cogs are packaged up in a first and in a second cassette sprocket, permits obtaining a larger number of possible ratios while, at the same time, maintaining reduced overall dimensions.