BACKGROUND OF THE INVENTION The invention relates to an assisted pedalling propulsion device for a two- wheeled vehicle, in particular for a bicycle of the e-bike type, and the two-wheeled vehicle.

PRIOR ART The use of various assisted pedalling systems fitted to bicycles is widely known.

Current bicycles provided with assisted pedalling systems generally comprise, in addition to the traditional bottom bracket mechanism (crank, shaft, crankset with chainring and transmission chain, etc.), an electric motor, fitted to a lower zone of the frame of the bicycle and supplied by a battery, which is also located on the aforesaid frame.

The bicycles are provided with a transmission system, which is necessary for transmitting the muscle power of the cyclist from the shaft of the bottom bracket to the rear wheel and consequently set the vehicle in motion. In the case of bicycles with gears, the system is defined by a transmission chain, a cassette and a crankset. The cassette is fitted to the hub of the rear wheel and consists of one or more sprockets, i.e. circular toothed elements of growing diameter, thus correspondingly with a growing number of respective teeth. The crankset is on the other hand fitted to the shaft of the bottom bracket and consists of one to three toothed chainrings. The gear ratio defined between the bottom bracket mechanism and the rear wheel is determined by the ratio between the diameters of the chainrings and the sprockets.

The chain consists of modular units known as links that couple with the toothing of the sprocket and the chainring: in this manner, the torque generated by the muscle power discharged on the pedal, which rotates the shaft of the bottom bracket mechanism, is transmitted by the transmission chain to the rear wheel to which the cassette is fitted. It is possible to modify the gear ratio of the vehicle manually through the gear shift by acting on the levers present on the handlebar of the bicycle: in this manner, the front or rear derailleur included in the gear shift is moved, which forces the chain to “derail”, moving from one sprocket to another (in the case of the rear derailleur) or from one chainring to another (in the case of the front derailleur).

The use of this transmission system has various drawbacks although it is the most used system.

The chain is subject to wear both from environmental agents and following normal use. The corrosion and wear process is accelerated by contact with mud, water, dust and chemical agents on the asphalt and on the terrain on which the bicycle advances. The deterioration of the aforesaid chain and the connected transmission components compromises the correct transmission function. In fact, the chain, in order to be able to operate properly, has to remain constantly taut. The chain tends to extend because of the chain stretching phenomenon: the traction to which the links of the chain are subjected constantly causes link pitch elongation. For the reasons set out above, prolonged use of a worn chain is disadvantageous and even potentially hazardous for the cyclist, the probability being high that a breakage event will occur. In order to avoid the risk of accidents, the user of the bicycle frequently has to replace and/or maintain the chain, with consequent huge expenditure.

Further, the transmission chain, in order to operate correctly, has to be well lubricated. Unexpectedly, during use, the cyclist may come into contact with the chain, get smeared and dirty.

If the chain comes or falls off the crankset whilst the vehicle is being used the cyclist has to first stop the vehicle and refit the chain manually in the correct seat, the hands of the cyclist inevitably getting dirty and smeared because of the lubricant on the chain.

The gear ratios are on the other hand defined by the possible sprocket-chainring combinations. Each combination corresponds to a given metric development, i.e. the distance travelled at each revolution of the pedals. The total number of gears that are at the disposal of a bicycle is the product of the number of sprockets of the cassette multiplied by the number of chainrings of the crankset. It is important to remember that not all gears can be used, or rather, certain “extreme” gears exist the use of which is inadvisable for fear of damaging the transmission components. For example, the gear ratios that result from selecting a chainring and a sprocket placed at a reciprocal maximum distance according to the direction that is transverse to the direction of normal development of the chain cause a condition in which the transmission chain is very tilted with respect to the direction of longitudinal extent of the frame; these gear ratios cannot be used except for short periods because of the great strain to which the chain is subjected (i.e. a state of bending stress) that promotes premature chain wear. A discrete and limited number of gear ratios and thus possible speeds exists, depending on the number of sprockets and chainrings. Increasing the number of sprockets and chainrings in order to increase the possible choice of gear ratios, and thus refine the gear ratio values, increases total dimensions and the weight respectively of the cassette and of the crankset, making the vehicle more difficult to move. In addition, increasing sprockets and chainrings would lead to an excessively taut transmission chain because of the tilt. The structural complexity and the corresponding cost increase that result must also be mentioned. Further, the presence of the teeth, which have rather pointed or sharp profiles, on the sprockets and on the chainrings constitutes a possible cause of injury if the cyclist accidentally knocks against them.

For the above reasons, it is thus deemed that there is currently ample room for improvement of current motion propulsion and transmission devices for bicycles and bicycles of the e-bike type.

OBJECTS OF THE INVENTION An object of the present invention is to improve current transmission and propulsion devices and to provide a propulsion device, in particular an assisted pedalling device for a bicycle, that is able to overcome the aforesaid limits of the prior art. Another object of the present invention is to provide a propulsion device, in particular an assisted pedalling device, which is able to ensure improved and optimized motion transmission. Another object of the present invention is to improve current systems for assisted pedalling, and to provide a technical solution that is advantageous from the economic point of view, also involving a general reduction of weight and overall dimensions. In particular, it is intended to provide a propulsion device that is easily adaptable and fittable to any type of bicycle.

Another object of the present invention is to provide a propulsion device that is such that the use of the vehicle can be more versatile and easier, which provides a wider choice di gear ratios and thus vehicle speed, which is free of the limits in traditional systems.

These objects of the invention are achieved with a propulsion device according to one or more of the attached claims.

SHORT DESCRIPTION OF THE INVENTION

The above is achievable by a propulsion device according to claim 1. Owing to the invention, all the set objects are achieved.

SHORT DESCRIPTION OF THE DRAWINGS

The features and advantages of the propulsion device according to the invention will be clearer from the following description, with reference to the drawings, in which:

Figure 1 is a side view of the propulsion device according to the invention, connected to the rear wheel of a two-wheeled vehicle, in particular a bicycle. Figure 2 is an enlarged side view of the propulsion device according to the invention, in particular it shows an alternative way of connection to the rear wheel. Figure 3 is an enlarged view of figure 1. DETAILED DESCRIPTION OF THE INVENTION

With reference to the attached figures, a propulsion device 1 is disclosed below for a two-wheeled vehicle 2, in particular for an e-bike, i.e. a bicycle provided with an electric motor 10 to assist the pedalling of the user, reducing at least partially the physical effort of the user.

The propulsion device 1 is provided with a mechanism 3 for the bottom bracket, to which the cranks 4 and pedals 5 are connected. Manual advancement of the vehicle 2 is made possible owing to the force of traction of the cyclist applied to the pedals 5, transmitted to the rear wheel 6 by a system that is now disclosed in detail.

The mechanism 3 for the bottom bracket is rotated by the system consisting of cranks 4 and pedals 5. The rotary movement is transmitted to a first epicyclic gear reducer 7, coupled with the mechanism 3 for the bottom bracket. By suitably varying the geometric configuration of the inner components of the first epicyclic gear reducer 7, it is possible to modify the gear ratio of the movement to the rear wheel 6.

The first epicyclic gear reducer 7 is serially connected to a second epicyclic gear reducer 11, in one embodiment, completely similar to the gear reducer 5: in this manner the variability range of the gear ratio is increased. The mechanical connection between the first gear reducer 7 and second gear reducer 11 is installed at outer coupling surfaces of the gear reducers, for example by meshing, if these surfaces are provided with toothing. More precisely, in the embodiment shown in the figures, the toothing 8 of the first gear reducer 7 couples with the toothing 12 of the second gear reducer 11.

The second epicyclic gear reducer 11 couples with an electric motor 10 through the assistance of the pedal revolution.

The second epicyclic gear reducer 11 is in turn directly in contact and coupled with a lateral surface 14 of the rear wheel 6, so as to transmit the movement from the propulsion device 1 thereto. To summarize, the electric motor 10 and the second epicyclic gear reducer 11 coupled therewith are situated between and connected to the rear wheel 6 and the first epicyclic gear reducer 7 coupled with the bottom bracket mechanism 3.

Of the many possible coupling embodiments between the rear wheel 6 and the epicyclic gear reducer 8, two are shown: the first is shown in Fig.2, whereas the second is shown in Fig.3. In the first case, the lateral surface 14 is provided on a side 15 having an annular shape, of a rim 16 of the rear wheel 6: on the lateral surface 14 there is obtained a toothing 17 which is shaped for meshing with and receiving transmission-motion from the toothing 12 provided on the second epicyclic gear reducer 11. In the second case, the lateral surface 14 is provided on a tyre 18 of the rear wheel 6: on the lateral surface 14 a toothing 19 is obtained which is shaped for meshing with and receiving transmission-motion from the toothing 12 provided on the second epicyclic gear reducer 11. The toothing 19 obtained on the lateral surface 14 of the tyre 18 is made of a material having stiffness greater than the remaining part of the tyre 18.

The first epicyclic gear reducer 7 is controlled by a first control means 9 whereas the second gear reducer 11 is controlled by second control means 13. The first control means 9 and the second control means 13 comprise motor means designed to vary the geometric configuration of said first epicyclic gear reducer 7 and/or said second epicyclic gear reducer 11, then vary the gear ratio of the motion to the rear wheel 6.

The first control means 9 and the second control means 13 are controllable by the rider by suitable lever means 20 provided on the handlebar 21 of the vehicle 2.

The epicyclic gear mechanisms, like the first gear reducer 7 and the second gear reducer 11, are cogged wheel systems having different diameters, meshed with one another, that collaborate so that the movement is transmitted from one wheel to another. Depending on which components of the epicyclic gear mechanism are locked or left free to move, by then acting on the geometry of the mechanism, it is possible to adjust continuously the gear ratios, both in cases of increasing and reducing the speed.

The main components of the mechanism are the sun gear 22, the planet gears 23 and the ring gear 24. The sun gear 22 is placed in the centre of the mechanism and meshes with one or more sprockets defined as the planet gears 23, housed on a component known as a planet carrier. Generally, the sun gear radius is greater than that of the planet gears. In turn, the planet gears 23 mesh with the ring gear 24. In Figs 2 and 3, the components of the first epicyclic gear reducer 7 are illustrated better.

Similarly to the first gear reducer 7, the second gear reducer 11 comprises a respective sun gear 32, planet gears 33, and a ring gear 34. The sun gear 32 is placed in the centre of the mechanism and meshes with the planet gears 33, housed on a respective planet carrier.

In the case of the first gear reducer 7, the sun gear 22 is connected and moved by the mechanism 3 for the bottom bracket. On the other hand, in the case of the second gear reducer 11, the sun gear 22 is connected and moved by the electric motor 10.

The vehicle 2 can operate with or without the help of the motor 10. If the electric motor 10 is switched off, the vehicle 2 moves only because of the muscle power of the rider. Movement is transmitted by the bottom bracket mechanism 3 to the first epicyclic gear reducer 7, then to the second epicyclic gear reducer 11, and lastly to the rear wheel 6. On the other hand, in the event of operation of the electric motor 10, this moves at a constant angular speed, whilst the epicyclic gear reducer 8 adjusts the actual traction given to the rear wheel 6, thus the speed at which the vehicle 2 moves. The system is provided with sensors for detecting the movement of the bottom bracket mechanism 3 and consequently activating the motor 10. It is also possible to provide switch means for if necessary disabling the motor 10 totally. In particular, the presence of two epicyclic gear reducers (the first gear reducer 7 and the second gear reducer 11) increases the variability range of the gear ratio. This is a change and an advantage over the traditional method for adjusting speed changes: the latter provide a discrete number of possible speeds, because of the possible chainring and sprocket combinations whereas the claimed solution enables the variability range of the gear ratios to be increased. In other words, the value of the gear ratios is variable in a continuous way and not in a discrete way as in traditional bicycle gear changes. Further, the propulsion device 1 as disclosed is simplified and lightened from the structural point of view: the high number of sprockets and chainrings has been replaced by a direct transmission system based on epicyclic gearing. The absence of chainrings and sprockets results in a system that is less bulky and simpler to move because of the reduction in the weight of the vehicle. The possibility of getting injured by knocking against the toothed wheels is eliminated.

The claimed method of transmission does not involve the use of a transmission chain, resulting in a system that is simpler and more intuitive to use, avoiding the problems linked to the use thereof.

Any element that is part of the propulsion device 1 according to the invention can be replaced by other elements that are equivalent in structural and functional terms, and the materials insofar as they are compatible with the specific use for which they are intended, can be chosen suitably according to the requested requirements and according to the available prior art.

It is possible to configure and size the propulsion device 1 on the basis of specific needs and applications, with possible variations and/or additions to what has been disclosed above and illustrated in the attached drawings without thereby falling outside the claimed area of protection.