Abstract:
A derailleur including an articulated quadrilateral mechanism, having four parallel articulation axes is provided. At a first articulation axis, between a fixed member and a first connecting rod, the fixed member includes a first forked structure embracing the first connecting rod. The first forked structure includes two opposite flanges having respective holes aligned along the first articulation axis, and the first connecting rod includes a hole aligned with the first articulation axis. A pin is inserted through the two holes of the first forked structure and the first connecting rod. The use of the fixed member creates a more favorable distribution of the stresses induced in the first connecting rod and the pin by the traction of the derailleur control cable.

Description:
FIELD OF INVENTION 
       [0001]    The present invention concerns a front derailleur for a bicycle. 
       BACKGROUND 
       [0002]    Front derailleurs are used to move a bicycle chain during travel from one toothed wheel of the bottom bracket to another one having a different diameter. This process functions to carry out gearshifting, varying the transmission ratio. 
         [0003]    Known derailleurs typically comprise a chain guide positioned above the bicycle chain and a chain guide positioning mechanism, normally an articulated parallelogram mechanism, which is fixed to the bicycle frame along the tube that connects the bottom bracket to the saddle (seat-tube). 
         [0004]    The chain guide is formed from an inner plate and an outer plate that face one another and are substantially parallel. The inner plate acts by pushing upon the chain to make it pass from a wheel having a small diameter to one having a larger diameter (upward gearshifting), and the outer plate acts by pushing upon the chain to make it pass from a wheel having a larger diameter to one having a smaller diameter (downward gearshifting). 
       SUMMARY 
       [0005]    The present invention concerns, a front bicycle derailleur having a fixed member and a mobile member provided with a bicycle chain-guide. A connecting rod is hinged to the fixed member about a first articulation axis and to the mobile member about a second articulation axis. An actuation arm for controlling the derailleur is provided with a driving area, and the connecting rod transfers force exerted on the driving area to the mobile member, causing it to move. At the first articulation axis, the fixed member comprises a forked structure that embraces the first connecting rod. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of a derailleur according to a first embodiment of the invention; 
           [0007]      FIG. 2  is a view of the derailleur of  FIG. 1 , taken from direction II; 
           [0008]      FIG. 3  is an enlarged perspective view of the fixed member of the derailleur of  FIG. 1 ; 
           [0009]      FIG. 4  is a view of the fixed or stationary member of  FIG. 3 , taken from direction IV; 
           [0010]      FIG. 5  is a partially exploded top view of a derailleur according to a second embodiment of the invention; 
           [0011]      FIG. 6  is an enlarged view of the fixed member of the derailleur of  FIG. 5 ; 
           [0012]      FIG. 7  is a view of a variant of a fixed member of the derailleur of  FIG. 5 ; 
           [0013]      FIG. 8  is a perspective view of a derailleur according to a third embodiment of the invention; 
           [0014]      FIG. 9  is an enlarged perspective view of the fixed member of the derailleur of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS INTRODUCTION TO THE EMBODIMENTS 
       [0015]    The present invention concerns a front derailleur for a bicycle. The claimed front derailleur includes a mobile member provided with a chain-guide suitable for sliding engagement with a transmission chain of the bicycle. The mobile member is mobile between a first position and at least one second position. Also included is a fixed member, suitable for being fixed to a part of the bicycle frame. A first connecting rod, and a second connecting rod are hinged to the fixed member and to the mobile member, about four substantially parallel articulation axes so as to form an articulated quadrilateral, able to be deformed so as to move the chain-guide between the first and at least one second position. An actuation arm of the first connecting rod is provided with a driving area for controlling the derailleur through application of a thrust to the actuation arm so as to deform the deformable quadrilateral. At a first of the four articulation axes between the fixed member and the first connecting rod the fixed member includes a first forked structure that embraces the first connecting rod. The first forked structure is defined by opposite flanges. 
         [0016]    It has been found that providing the fixed member of a bicycle front derailleur with a forked structure that surrounds the first connecting rod creates a more favorable distribution of the stresses caused by the traction of a derailleur control cable. In the derailleur of the present invention, the stress exerted on the actuation arm of the first connecting rod during the actuation of the control cable is distributed in a central area of the pin, because the ends of the pin are supported by the fixed member. This configuration simplifies the process of sizing the actuation arm, which can be made narrower or longer without jeopardizing its strength. The weight of the arm can also be reduced without this jeopardizing its mechanical strength. Moreover, the improved distribution of stresses also reduces the deformability of the biased parts, allowing for better rotational coupling and a consequent lower wear on the pins. 
         [0017]    Preferably, the driving area on the actuation arm of the first connecting rod comprises a hook for receiving a derailleur control cable, and more preferably the derailleur comprises an elastic return member, acting on the articulated quadrilateral in a direction to push the chain-guide towards said first position, in which the thrust applied by the cable to the hook acts in the opposite direction to the return of the elastic return member. Alternatively, in a motorized derailleur (also known as an automatic or electric derailleur) the driving area can be a toothed sector engaged with a driving screw. 
         [0018]    Preferably, the flanges of the first forked structure are provided with respective holes aligned along the first articulation axis and the first connecting rod comprises a hole aligned with the first articulation axis. A pin is inserted through the two holes of the first forked structure and further through the hole of the first connecting rod. Alternatively, it is possible for the pin to be formed as one piece with the connecting rod and for the flanges to consequently be in two pieces, so as to permit mounting on the pin. Alternatively, the pin may be formed in two parts and be formed as a single piece with the flanges and the connecting rod may consequently be formed as two pieces, so as to permit mounting on the pin. 
         [0019]    Preferably, the first connecting rod comprises a main arm extending between the first and second of said four articulation axes, between the first connecting rod and the mobile member, and the main arm and the actuation arm substantially extend in the same plane perpendicular to the four articulation axes. The first connecting rod therefore has a very regular and uniform configuration, such as to regularly and uniformly transmit the stresses induced by the control cable to the pin. 
         [0020]    Preferably, at a third of said four articulation axes between the fixed member and the second connecting rod, the fixed member comprises a second forked structure that embraces the second connecting rod, and the second forked structure comprises two opposite flanges. More preferably, the flanges of the second forked structure are provided with respective holes aligned along the third articulation axis, the second connecting rod comprises a hole aligned with the third articulation axis, and a pin is inserted through the two holes of the second forked structure and further through the hole of the second connecting rod. Alternatively, it is possible for the pin to be formed as a single piece with the connecting rod and for the flanges to consequently be formed as separate pieces, so as to permit mounting on the pin. Alternatively, it is possible for the pin to be formed in two parts and be formed as a single piece with the flanges and for the connecting rod to consequently be formed as two pieces, so as to permit mounting on the pin. 
         [0021]    Alternatively, at a third of said four articulation axes between the fixed member and the second connecting rod, the fixed member comprises a cantilevered pin, and the second connecting rod comprises a hole aligned with the third articulation axis, inserted on the cantilevered pin of the fixed member. 
         [0022]    Preferably, at a fourth of said four articulation axes between the second connecting rod and the mobile member, the mobile member comprises two opposite flanges perforated along the fourth articulation axis, in which the second connecting rod comprises a hole aligned with the fourth articulation axis, and in which a pin is inserted into the flanges and into the hole of the second connecting rod. More preferably, the elastic return member is a helical spring, mounted on the pin and provided with two ends, one engaged with an abutment tooth formed on the second connecting rod, the other engaged with an abutment portion formed on the mobile member. 
         [0023]    Preferably, the fixed member comprises a cylindrical portion for a braze-on attachment to the bicycle frame. Alternatively, the fixed member comprises two semi-circular portions articulated together and a locking element for locking such semi-circular portions about the part of bicycle frame. According to this embodiment, the fixed member preferably is formed as a single piece with one of the two articulated semi-circular portions. 
         [0024]    Preferably, the second connecting rod is substantially S-shaped and extends between the third and a fourth of said four articulation axes, between a first plane at the third articulation axis and a second plane at the fourth articulation axis. The first and the second planes are perpendicular to the four articulation axes and spaced apart by a predetermined distance. 
         [0025]    Further characteristics and advantages of a derailleur according to the invention shall become clearer from the following description of some preferred embodiments thereof, made with reference to the attached drawings. 
       DETAILED DESCRIPTION 
       [0026]      FIGS. 1 to 4  show a derailleur  10  suitable for being mounted on a bicycle according to one preferred embodiment of the invention. The derailleur  10  comprises a chain guide  11 , which is suitable for sliding engagement with a transmission chain of the bicycle, to move the chain between a first position and at least one second position, corresponding to distinct transmission ratios. 
         [0027]    As shown in  FIGS. 3 and 4 , the chain guide  11  forms part of a mobile member  12 , or cage, of an actuation mechanism that also includes a fixed member  13 , a first connecting rod  14  (or outer connecting rod), and a second connecting rod  15  (or inner connecting rod). The terms “inner” and “outer,” just like “lower” and “upper” as used hereafter, refer to the position taken up with respect to the mounting position of the derailleur in the bicycle. 
         [0028]    The fixed or stationary member  13 , the mobile member  12 , and the two connecting rods  14  and  15  are articulated together along four parallel articulation axes A, B, C, D, such that they form an articulated parallelogram. More precisely, the fixed member  13  and the first connecting rod  14  are articulated about the first axis A; the first connecting rod  14  and the mobile member  12  are articulated about the second axis B; the fixed member  13  and the second connecting rod  15  are articulated about the third axis C; and the second connecting rod  15  and the mobile member  12  are articulated about the fourth axis D. 
         [0029]    The mobile member  12  comprises an inner plate  17  facing an outer plate  18 , which form the chain guide  11 . The mobile member  12  is provided with lower flanges  19 ,  20  perforated along the axis D for connection to the second connecting rod  15 , and with upper flanges  21 ,  22  for connection to the first connecting rod  14 . 
         [0030]    The first connecting rod  14  comprises a main arm  24 , extending between the axes A and B, and an actuation arm  25 , at the end of which a driving area is provided, in particular a hook  27  for receiving a derailleur control cable (not shown). The first connecting rod  14  is configured so that the main arm  24  and the actuation arm  25  substantially extend in a plane perpendicular to the four articulation axes A, B, C, D. The main arm  24  and the actuation arm  25  are substantially collinear with each other are substantially the same length. 
         [0031]    At the axis B, a pin  29  rotatably connects the flanges  21  and  22  to a hole  28  made in the connecting rod  14  (see  FIG. 2 ). 
         [0032]    The second connecting rod  15  is substantially S-shaped and has an upper portion  34  articulated to the fixed member  13  about the third articulation axis C, an intermediate portion  35  and a lower portion  36  articulated to the mobile member  12  about the fourth articulation axis D. With respect to the common direction of the axes A, B, C, D, the upper and lower portions  34  and  36  of the connecting rod  15  extend in distinct planes M and N, spaced apart by a distance k. 
         [0033]    At the axis D, a pin  39  rotatably connects the flanges  19  and  20  to a hole made in the lower portion  36  of the connecting rod  15 . About the axis D, an elastic return member, preferably a preloaded helical spring  40 , is arranged. The spring  40  is provided with an end  41  abutting a tooth  42  of the lower portion  36  of the second connecting rod  15  and with an end  43  abutting a portion  44  of the mobile member  12 . The spring  40  keeps the articulated parallelogram mechanism pushing towards a rest position, which is normally the position in which the chain guide  11  is closest to the bicycle, and the axis A is at its farthest possible position from the axis D. 
         [0034]    A pair of screws  50  and  51  are adjustably mounted in respective threaded holes on the fixed member  13  and cooperate with the upper portion  34  of the second connecting rod  15  to define the extreme rotational positions of the connecting rod  15  itself and therefore the extreme deformation positions of the articulated parallelogram and of its parts, including in particular the position of the chain guide  11 . These extreme positions are adjustable through screwing and unscrewing of the screws  50  and  51 . 
         [0035]    The fixed member  13  (which can be seen separate from the rest of the derailleur in  FIGS. 3 and 4 ) comprises a cylindrical surface  61  for attachment to a portion of the seat-tube of the bicycle frame of a shape matching the cylindrical surface  61  (braze-on attachment). The cylindrical surface  61  extends around a central axis Y. 
         [0036]    The fixed member  13  further comprises, at the first axis A, a first forked structure  62  that embraces the first connecting rod  14 . The first forked structure  62  is formed from a first flange  63  facing a second flange  64 , each provided with respective holes  65  and  66  aligned along the axis A. A pin  68  is inserted through the holes  65  and  66  and further through a hole  69  aligned with them formed in the first connecting rod  14 , so as to provide the articulated coupling between the fixed member  13  and the connecting rod  14 . 
         [0037]    The fixed member  13  also comprises, at the third axis C, a second forked structure  72  that embraces the second connecting rod  15 . The second forked structure  72  formed from a first flange  73  facing a second flange  74 . The flanges are provided with respective holes  75  and  76  aligned along the axis C. A pin  78  is inserted through the holes  75  and  76  and further through a hole aligned with them formed in the upper portion  34  of the second connecting rod  15  to provide the articulated coupling between the fixed member  13  and the connecting rod  14 . 
         [0038]    A through hole  60  facing into the cylindrical surface  61  is formed in the fixed member  13 , to receive an attachment screw (not shown) for connecting to the seat of the seat-tube. 
         [0039]    As can be seen more clearly in  FIG. 2 , the first forked structure  62  with its flanges  63  and  64  laterally embraces the first connecting rod  14  and supports the articulation pin  68  at the ends thereof. When a traction force is applied to the hook  27  of the actuation arm  25  by the derailleur control cable, the stress is transmitted from the actuation arm  25  into the articulation area at the pin  68 . The stress is distributed through the central area of the pin  68 , located between the two flanges  63  and  64 , instead of being concentrated at one end, as in derailleurs of the prior art. 
         [0040]      FIGS. 5 and 6  show a view from above of an alternative embodiment of a derailleur  110  according to the present invention, which differs from the derailleur  10  described above in that it connects to the seat-tube, through a clamp attachment instead of in a seat with cylindrical surface. 
         [0041]    The derailleur  110  is similar to that which is described above and shall only be described with respect to those features that differ from the first described embodiment. In  FIGS. 5 and 6 , the parts of the derailleur  110  that correspond to the derailleur  10  of  FIG. 1  are indicated with the same reference numerals increased by 100. 
         [0042]    In the derailleur  110 , a clamp adapter element  181  is attached, preferably screwed, to the fixed member  113 , to connect the derailleur  110  to the seat-tube of the bicycle. For this purpose, the clamp adapter element  181  comprises two semi-circular portions  182 ,  183 , articulated together, to allow them to open out, with respective circular surfaces  184 ,  185  that are clamped on the frame by a bolt  186  when the derailleur  110  is in mounted configuration. 
         [0043]      FIG. 7  shows a variant  213  of the fixed member of the derailleur that differs from the fixed member  113  of  FIGS. 5 and 6  in that it comprises two semi-circular portions  282 ,  283 , articulated together, and having respective circular surfaces  284 ,  285  that are clamped on the frame by a bolt  286  when the derailleur is in its mounted configuration. The fixed member  213  is formed as a single piece with the semi-circular portion  283 . 
         [0044]      FIG. 8  shows a perspective view of another embodiment of the derailleur  310 , which comprises a fixed member  313 ′ that differs from the fixed member  13  of the derailleur  10 . The fixed member  313 ′ is shown in greater detail in  FIG. 9 . 
         [0045]    Aside from the fixed member  313 ′, the derailleur  310  is similar to the derailleur  10 . In  FIGS. 8 and 9 , the parts of the derailleur  310  that correspond to the derailleur  10  are indicated with the same reference numerals increased by 300. 
         [0046]    The fixed member  313 ′ shown in  FIGS. 8 and 9  differs from the fixed member  13  of  FIG. 1  only in the area of the articulation axis C. In this area, the fixed member  313 ′ comprises a flange  373 ′ provided with a hole  375 ′ for receiving a pin  378 ′ arranged cantilevered with respect to the flange  373 ′. The fixed member  313 ′ does not have an additional flange facing the flange  373 ′, as in the embodiment of  FIG. 1 . The second connecting rod  315  is connected to the fixed member  313 ′ such that it is cantilevered on the pin  378 ′, as can be seen in  FIG. 8 . 
         [0047]    Other variations are possible, while still remaining covered by the present invention as defined by the following claims. For example, it is possible to make a derailleur similar to the derailleur  310  of  FIG. 8 , but suitable for connection to the bicycle like the derailleur  110  of  FIG. 1 , possibly with a fixed group like the group  213  of  FIG. 7 . 
         [0048]    Furthermore, in the couplings between any of the described forked structures and connecting rods, it is possible for the pin to be formed as a single piece with the connecting rod and for the flanges of the forked structure to consequently be formed as two pieces, to permit mounting on the pin. Alternatively, the pin may be formed in two pieces and as part of a continuous structure with the flanges. The connecting rod is consequently formed in two pieces to permit mounting on the pin. 
         [0049]    Furthermore, in the case of a motorized derailleur (also known as an automatic or electric derailleur) the driving area of the actuation arm of the first connecting rod can consist of a toothed sector engaged with a driving screw.