Patent Publication Number: US-2022219780-A1

Title: Electric gearmotor assembly for bicycles

Description:
The present invention generally regards a gearmotor assembly for a bicycle and, in particular, an electric gearmotor assembly for a so-called pedal-assisted bicycle or “e-bike”. It is specified that, in this context, the expression pedal-assisted bicycle is used to indicate any vehicle with one (unicycle), two, three (tricycle) or more wheels (quadricycle, rickshaw, etc.) which is both driven by human muscle force and provided with at least one auxiliary electric motor. 
     As known, a pedal-assisted bicycle or “e-bike” is a conventional bicycle to which at least one electric motor, one or more batteries and several sensors which detect, instant by instant, the speed of rotation of the pedal crank/pedal assembly, are applied. This speed of rotation is coded by an electronic control unit which, based on predefined parameters, calibrates the additional support provided by the electric motor to the action of the cyclist. 
     To date, pedal-assisted bicycles use brushless electric motors coupled to various types of reduction gears, which drive the shaft on which the pedal crank/pedal assembly rotates. Problems related to this type of gearmotors generally arise from dimensions, weight and operating temperatures. The transmissions often have multiple reduction stages and they are sometimes coupled to electromagnetic clutches which, operating within the same crankcases in which the reduction gear is arranged, entail an overheating of the entire gearmotor assembly and therefore loss of efficiency. Furthermore, the considerable dimensions of the transmission require the mounting, and therefore the positioning, of the electric motor on the bicycle frame. Lastly, since the general efficiency of these electric motors does not exceed 0.7, there generally arises the need to over-dimension the electric motor in order to achieve the required power. As a matter of fact, when under intense use, the electric motor tends to overheat and, since it cannot cool, it requires an intervention of the electronic control unit which consists in a reduction of the current supplied and, consequently, a reduction of the general performance of the electric motor. 
     Another problem of the current gearmotor assemblies for pedal-assisted bicycles lies in the fact that, in the event of non-use, the electric motor still remains connected to the shaft on which the pedal crank/pedal assembly rotates. Thus, during normal or non-assisted pedaling, the cyclist is forced to also drive the electric motor with the relative transmission. 
     A gearmotor assembly for bicycles according to the prior art is described, for example, in document CN 2234906 Y. 
     Thus, the object of the present invention is to provide a gearmotor assembly for a bicycle, in particular an electric gearmotor assembly for a so-called pedal-assisted bicycle or “e-bike”, which is capable of overcoming the aforementioned drawbacks of the prior art in an extremely simple, cost-effective and particularly functional manner. 
     In detail, an object of the present invention is to provide a gearmotor assembly for a pedal-assisted bicycle which, should the electric motor fail to intervene and therefore of normal or non-assisted pedaling, allows the cyclist not to have to drive such electric motor, with the relative transmission. 
     Another object of the present invention is to provide a gearmotor assembly for a pedal-assisted bicycle which allows to increase both the efficiency of the electric motor and the duration of the battery pack. 
     These and other objects according to the present invention are attained by providing a gearmotor assembly for a pedal-assisted bicycle as outlined in claim  1 . 
     Further features of the invention are highlighted by the dependent claims, which are an integral part of the present description. 
    
    
     
       The features and advantages of a gearmotor assembly for a pedal-assisted bicycle according to the present invention will become more apparent from the following description, provided by way of non-limiting example, with reference to the attached schematic drawings, wherein: 
         FIG. 1  is a perspective view of a preferred embodiment of the gearmotor assembly for a pedal-assisted bicycle according to the present invention; 
         FIG. 2  is a top plan view of the gearmotor assembly of  FIG. 1 ; 
         FIG. 3  is a side elevational view of the gearmotor assembly of  FIG. 1 ; 
         FIG. 4  is a sectional view, obtained along the line IV-IV of  FIG. 3 , of the gearmotor assembly of  FIG. 1 ; 
         FIG. 5  is a partly exploded view of a part of the components of the gearmotor assembly of  FIG. 1 ; and 
         FIG. 6  is a transparency view of another part of the components of the gearmotor assembly of  FIG. 1 . 
     
    
    
     With reference to the figures, shown is a preferred embodiment of the gearmotor assembly for a pedal-assisted bicycle according to the present invention. The gearmotor assembly is indicated in its entirety with reference number  10 . The gearmotor assembly  10  is configured to be applied to the pedal crank/pedal assembly  12  of a bicycle (not shown) of the type comprising at least one frame and at least one drive wheel. The drive wheel is connected to the pedal crank/pedal assembly  12  by means of a transmission system which can be of conventional type, such as for example a chain transmission system which comprises one or more toothed chainrings, integrally joined with the pedal crank/pedal assembly  12 , and one or more sprockets, integrally joined with the drive wheel. 
     The bicycle, which is of the per se known type, can therefore be provided with a steering, with at least one front steering wheel, with a braking system, with a saddle and with other possible accessories. The bicycle to which the gearmotor assembly  10  can be applied may also not be of the conventional two-wheel type, but it may consist of a unicycle, a tricycle or a rickshaw, provided that it is provided with a pedal crank/pedal assembly  12  and with a transmission system with at least one drive wheel. 
     The gearmotor assembly  10  comprises at least one pedal crank shaft  14  which can move with rotary motion around a predefined axis A, typically horizontal and perpendicular to the advancement direction of the bicycle. In a per se known manner, the pedal crank shaft  14  is integrally joined with the pedal crank/pedal assembly  12  to receive the torque delivered by the cyclist through said pedal crank/pedal assembly  12  and to transmit the torque to the drive wheel of the bicycle through the transmission system. 
     The gearmotor assembly  10  further comprises at least one electric motor  16  provided with an electronic control unit and with its own reduction gear mechanism  18 ,  20 . In a per se known manner, the electronic control unit can be integrated with various expansion modules, such as for example Wi-Fi modules, Bluetooth, GSM, accelerometers, gyroscopes, load cells, etc. 
     In detail, the reduction gear mechanism  18 ,  20  is of the type comprising a worm screw  18 , integrally joined with the output shaft  42  of the electric motor  16 , and a gear wheel  20 , arranged coaxially around the pedal crank shaft  14 . Still, in a per se known manner, the reduction gear mechanism  18 ,  20  is configured to receive the torque delivered by the electric motor  16  and to transmit such torque to the driving wheel of the bicycle through the pedal crank shaft  14  and the transmission system, for example of conventional chain type with one or more toothed chainrings and one or more sprockets. 
     According to the invention, the gearmotor assembly  10  comprises at least one internal overrunning clutch  22 , mounted coaxially around the pedal crank shaft  14 , and at least one external overrunning clutch  24 , mounted coaxially inside the gear wheel  20  of the reduction gear mechanism  18 ,  20 . Both the internal overrunning clutch  22  and the external overrunning clutch  24  consist of respective free-wheel mechanisms. As known, a freewheel mechanism is a mechanical device which, interposed between two coaxially rotating assemblies, allows to connect or uncouple these two assemblies according to their relative angular velocity. 
     Between the external overrunning clutch  24  and the internal overrunning clutch  22  there is interposed at least one hollow tubular element  26  kinematically connected to the drive wheel of the bicycle to transmit the torque delivered by the cyclist or by the electric motor  16  through the reduction gear mechanism  18 ,  20 . In other words, the hollow tubular element  26  is directly connected to the bicycle transmission system, which can be for example of the conventional chain type with one or more toothed chainrings, one of which is shown in  FIG. 4  with reference number  50  and it is directly mounted on said hollow tubular element  26 , and one or more sprockets. 
     In particular, the internal overrunning clutch  22  is housed by interference in the hollow tubular element  26 , while the external overrunning clutch  24  is housed by interference outside such hollow tubular element  26 . The internal overrunning clutch  22  is configured to transmit torque in a first direction of rotation of the pedal crank shaft  14 , while the external overrunning clutch  24  is configured to transmit torque in a second direction of rotation of the pedal crank shaft  14  which is opposite to the first direction of rotation. 
     In detail, as shown in the sectional view of  FIG. 4 , the pedal crank shaft  14  is provided with two opposite rectified seats  28 , around each of which a respective internal overrunning clutch  22  is mounted by interference. The gearmotor assembly  10  is therefore preferably provided with two distinct internal overrunning clutches  22  placed directly at contact with the pedal crank shaft  14 . 
     The hollow tubular element  26 , which forms the outer housing of the two internal overrunning clutches  22 , preferably consists of a rectified tube around which it centrally houses, i.e. in a median position between the two internal overrunning clutches  22 , the gear wheel  20  within which a single external overrunning clutch  24  is coaxially mounted. In other words, as shown in  FIG. 4 , the external overrunning clutch  24  is interposed between the gear wheel  20 , which surrounds it, and the hollow tubular element  26 . 
     The two internal overrunning clutches  22  are configured to lock in the same direction of rotation, which coincides with the first direction of rotation of the pedal crank shaft  14 . On the other hand, the external overrunning clutch  24  is configured to lock in the opposite direction of rotation, which coincides with the second direction of rotation of the pedal crank shaft  14 . 
     Preferably, as shown in  FIG. 6 , the pedal crank shaft  14  is centrally provided, at the external overrunning clutch  24  and at the gear wheel  20 , with at least one radial groove  30  forming a housing for at least one pin  32 . The pin  32  has a function for centring the pedal crank shaft  14 , i.e. avoiding the displacements thereof in the axial direction, and it allows the freedom of rotation backwards, i.e. in the second direction of rotation, of the pedal crank/pedal assembly  12 . 
     A respective axial bearing  34 , which is engaged around the hollow tubular element  26 , is positioned on both sides of the gear wheel  20 , with reference to the predefined axis A of the pedal crank shaft  14 . Each axial bearing  34  is held in place by a corresponding spacer element  36 . Lastly, positioned on the outer sides of the two spacer elements  36  are two further bearings  38  which, besides holding all the elements of the gearmotor assembly  10  which are coaxial with respect to the pedal crank shaft  14  in position, guarantee the freedom of rotation of said pedal crank shaft  14  in both directions. 
     Thus, the gearmotor assembly  10  according to the present invention operates as follows. The two internal overrunning clutches  22 , which are mounted between the hollow tubular element  26  and the pedal crank shaft  14 , are locked during the normal pedaling. The hollow tubular element  26  is then rotated by the pedal crank/pedal assembly  12  and it transmits the torque to the toothed chainring  50 . 
     Still during normal pedaling, the external overrunning clutch  24 , which is mounted between the gear wheel  20  of the reduction gear mechanism  18 ,  20  and the hollow tubular element  26  and which is locked in the opposite direction with respect to the two internal overrunning clutches  22 , is instead free. Thus, both the electric motor  16  and the reduction gear mechanism  18 ,  20  are freed from the bicycle transmission system and the pedaling is fluid. 
     When the electric motor  16  intervenes, together with the reduction gear mechanism  18 ,  20 , the external overrunning clutch  24  is engaged, driving the hollow tubular element  26 , and therefore the toothed chainring  50  too, in the same direction of rotation as the pedaling. Even if the electric motor  16  and the reduction gear mechanism  18 ,  20  were to rotate faster than their predefined maximum limit (this is a hypothetical situation, since the electronic control unit would intervene to bring the rotation regimen back to the predefined maximum limit), they would still not drive the pedal crank/pedal assembly  12 , given that the two internal overrunning clutches  22  would be unlocked with respect to the pedal crank shaft  14 . On the contrary, should the cyclist pedal at a very fast frequency, the cyclist would block the two internal overrunning clutches  22  arranged around the pedal crank shaft  14 , but releasing the external overrunning clutch  24  arranged in the gear wheel  20  of the reduction gear mechanism  18 ,  20 . In any case, the result is always that of obtaining a pedaling that is free from the electric motor  16  and that is as natural as possible. 
     The gearmotor assembly  10  is provided with a crankcase  40  housing the pedal crank shaft  14 , the entire reduction gear mechanism  18 ,  20  and the internal  22  and external  24  overrunning clutches, together with the respective additional components (bearings, spacer elements, etc.). In other words, only the electric motor  16  of the gearmotor assembly  10  is located outside the crankcase  40  to connect to the reduction gear  40 , while the respective output shaft  42  is at least partially inserted into said crankcase  40  to connect to the reduction gear mechanism  18 ,  20 . 
     Since it is separated from the electric motor  16 , the reduction gear mechanism  18 ,  20  is therefore far from the heat source constituted by the electric motor  16 . Furthermore, the fact that the worm screw  18  is positioned tangentially with respect to the gear wheel  20 , as well as orthogonally with respect to the rotation axis A of the pedal crank shaft  14 , makes the electric motor  16  free to be positioned at any angle (up to 360°) with respect to the bicycle frame. 
     The electric motor  16  can be provided with a cooling system which comprises a hydraulic circuit  44 , which at least partially surrounds such electric motor  16 , and at least one pump  46 , arranged to circulate a cooling fluid at a predefined pressure inside the hydraulic circuit  44 . The pump  46  can be driven by the output shaft  42  of the electric motor  16 , or it can be driven autonomously and powered by the battery pack normally provided on the pedal-assisted bicycle. 
     Since the electric motor  16  is preferably of the brushless type and it is contained in a cylindrical casing, the hydraulic circuit  44  is preferably serpentine-shaped for externally winding the largest possible surface of the casing of said electric motor  16 . One or more dissipating elements (not shown) mounted at the casing of the electric motor  16  may also be provided for. Thanks to the forced cooling of the electric motor  16  it is possible to use a much smaller brushless motor, in terms of size and power, and with lesser weight with respect to the conventional electric motors for pedal-assisted bicycles, without reducing the efficiency and performance under load. In addition, considering the same available power, the battery pack will last longer. 
     The pedal crank shaft  14  can be provided with at least one torque sensor  48 , such as for example a torque meter, operatively connected to the electronic control unit and preferably positioned at the toothed chainring  50 . Besides measuring the torque, this torque sensor  48  is particularly advantageous when starting from standstill, especially when pedaling uphill or on muddy ground. As a matter of fact, this torque sensor  48  proportionally detects the torque applied by the cyclist on the pedal crank/pedal assembly  12  and, interfacing with the electronic control unit, it allows the selective activation of the electric motor  16  so as to guarantee a standing start without effort. 
     In general, the current electric motors for pedal-assisted bicycles are not provided with torque sensors, but with simple sensors of the angular velocity of the pedal crank shaft. Thus, in standing starts of the current assisted-pedal bicycles, it is necessary to push a lot on the pedal crank/pedal assembly and then slightly drive the pedal crank shaft in rotation and allow the angular velocity sensor to identify even the least speed and therefore to make the electric motor intervene. 
     It has thus been seen that the gearmotor assembly for a pedal-assisted bicycle according to the present invention attains the objects outlined above. 
     The gearmotor assembly for a pedal-assisted bicycle according to the present invention thus conceived is susceptible in any case to numerous modifications and variations, all of which fall within the scope of the same inventive concept; furthermore, all the details may furthermore be replaced with technically equivalent elements. Basically, the materials used as well as the shapes and dimensions may vary according to the technical needs. 
     The scope of protection of the invention is therefore defined by the attached claims.