Abstract:
A bicycle bottom bracket assembly has a shaft having a longitudinal axis X-X, a pair of bearings configured to support the shaft in rotation with respect to a housing box of the bottom bracket assembly provided in a bicycle frame, and a pair of adapter devices configured to be cantilevered with opposite free ends of the box to support the bearings outside of said box. At least one of the adapter devices has at least one first stop element and at least one second stop element arranged on opposite sides with respect to at least one bearing, wherein the first and second stop elements cooperate with the at least one bearing to keep the at least one bearing inside a space having a predetermined axial extension. The bearing&#39;s movement is thus limited in the axial direction, providing a fixed reference to determine the chain line of the bottom bracket assembly.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates to a bicycle bottom bracket assembly. The invention also relates to an adapter device for such an assembly and to a method for mounting a bearing of such an assembly with respect to a housing box of the assembly provided in a bicycle frame.  
       BACKGROUND  
       [0002]     As known, a bicycle bottom bracket assembly comprises a shaft rotatably supported in a housing box provided in the bicycle frame and two crank arms associated with the opposite ends of the shaft. The shaft can be made in a distinct piece from the crank arms or can be made in a single piece with one of the two crank arms.  
         [0003]     The rotation of the shaft with respect to the box is achieved through the use of a pair of rolling bearings mounted on the shaft. Specifically, each bearing is positioned on the shaft at a respective body portion of the shaft adjacent to the crank arm.  
         [0004]     Typically, the bearings are supported inside or outside the box provided in the bicycle frame by suitable adapters mounted at the opposite free ends of such a box.  
         [0005]     It is known that the precision of gearshifting is greatly influenced by the distance between the middle plane of the frame and the middle plane of the crankset, also known as the chain line.  
         [0006]     In the known assembly great attention is put on the chain line at the design stage and assembly stage.  
         [0007]     However, the Applicant has found that often, in currently known assemblies, the shifting of the gear engaged with the chain is not very precise.  
       SUMMARY  
       [0008]     The present invention relates, in a first aspect thereof, to a bicycle bottom bracket assembly, comprising:  
         [0009]     a shaft having a longitudinal axis X-X extending along a predetermined direction;  
         [0010]     a pair of bearings configured to rotatably support said shaft with respect to a housing box of the bottom bracket assembly provided in a bicycle frame;  
         [0011]     a pair of adapter devices coupled with said bearings and configured to be associated with opposite free ends of said box to support said bearings with respect to said box;  
         [0012]     wherein at least one adapter device of said pair of adapter devices comprises at least one first stop element and at least one second stop element arranged on opposite sides with respect to at least one bearing, wherein said at least one first stop element and at least one second stop element cooperate with said at least one bearing to keep said at least one bearing inside a space having a predetermined axial extension. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Further characteristics and advantages shall become clearer from the following detailed description of some preferred embodiments thereof, made with reference to the attached drawings. In such drawings:  
         [0014]      FIG. 1  is a schematic longitudinal sectional view of a first embodiment of a bicycle bottom bracket assembly in accordance with the present invention;  
         [0015]      FIG. 2  is a schematic side view partially in section of a main body of the right adapter device of the assembly of  FIG. 1 ;  
         [0016]      FIG. 3  is a plan view of a stop element used in the assembly of  FIG. 1 ;  
         [0017]      FIG. 4  is a front view partially in section of the right adapter device of  FIG. 1 ;  
         [0018]      FIGS. 5   a  and  5   b  are respectively a front view and a side view of an elastic element used in the left adapter device of the assembly of  FIG. 1 ;  
         [0019]      FIG. 6  is a perspective view of an alternative embodiment of an adapter device that can be used in the assembly of  FIG. 1  in place of the adapter device of  FIG. 4 ;  
         [0020]      FIG. 7  is a perspective view of a further alternative embodiment of an adapter device that can be used in the assembly of  FIG. 1  in place of the adapter device of  FIG. 4 ;  
         [0021]      FIGS. 8   a  and  8   b  are respectively front sectional views of the adapter device of  FIG. 7  in two different operative configurations;  
         [0022]      FIG. 9  is an exploded perspective view of the adapter device of  FIG. 7 ;  
         [0023]      FIG. 10  is a schematic longitudinal sectional view of an alternative embodiment of a bicycle bottom bracket assembly in accordance with the present invention;  
         [0024]      FIG. 11  is a schematic longitudinal sectional view of a further alternative embodiment of a bicycle bottom bracket assembly in accordance with the present invention;  
         [0025]      FIG. 12  is a schematic longitudinal sectional view of a further alternative embodiment of a bicycle bottom bracket assembly in accordance with the present invention;  
         [0026]      FIG. 13  is a schematic longitudinal sectional view of a further alternative embodiment of a bicycle bottom bracket assembly in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS INTRODUCTION  
       [0027]     Advantageously, in the bottom bracket assembly, the aforementioned stop elements ensure that at least one of the two bearings of the assembly (in particular, the right bearing) is kept inside a space having an axial extension which is predetermined so that the chain line remains substantially unvaried during pedaling even in the case of sizing errors of the box of the frame or of other components of the bottom bracket assembly. In this way the chain line is thus prevented from being modified during pedaling by means of the thrust exerted by the chain on the wheels of the crankset, thus ensuring the desired precision of the gearshifting.  
         [0028]     Even more advantageously, the presence of the stop elements at the opposite sides of the bearing allows such a bearing to absorb lateral knocks in both axial directions, thus ensuring that the correct position of the shaft with respect to the box of the frame is maintained even in the presence of such lateral knocks.  
         [0029]     The adapter devices can be associated cantilevered with the opposite ends of said box to support said bearings outside of said box or they can be housed inside said box to support said bearings inside said box.  
         [0030]     In a first embodiment of the bottom bracket assembly, said space has an axial extension equal to the axial extension of said at least one bearing. In this embodiment, therefore, the bearing is blocked between the aforementioned stop elements and any possible relative movement thereof with respect to the adapter device in both ways of the axial direction is prevented. Preferably, in this embodiment an axial movement between the other bearing and the shaft or the respective adapter device is permitted to allow the recovery of sizing errors of the box of the bicycle frame without varying the positioning of the shaft with respect to the box and, therefore, without altering the determination of the chain line.  
         [0031]     In a preferred embodiment of the bottom bracket assembly, said space has an axial extension greater than the axial extension of said at least one bearing by a value of between 0 and 0.3 mm, preferably between 0.05 and 0.15 mm. In this embodiment, therefore, a limited axial movement is foreseen between bearing and respective adapter device, after which when the bearing goes into abutment against the stop element any possible further axial movement is prevented. Such limited movement is however such as not to cause a significant variation of the chain line and therefore does not negatively influence the precision of the gearshifting.  
         [0032]     Advantageously, the possibility of axial movement between bearing and adapter device allows small sizing errors of the box of the frame to be recovered, either by excess or by defect, without this influencing the position of the shaft and therefore the chain line. Such a provision thus makes the chain line at least partially independent from the sizing errors of the box of the frame.  
         [0033]     Preferably, said at least one first stop element and at least one second stop element act on an outer ring of said at least one bearing. Nevertheless, it is contemplated the possibility that said at least one first stop element and at least one second stop element act on an inner ring of said at least one bearing, for example in cases in which the bearing is housed in a seat formed in the body of the crank arm, as described in U.S. patent application Ser. No. 11/607,688 filed Dec. 1, 2006 to the same Applicant.  
         [0034]     In a specific embodiment of the bottom bracket assembly, said at least one adapter device comprises a main body configured to be associated with one end of said box and said at least one first stop element and at least one second stop element are defined by first shoulders integrally made with said main body. Such an adapter device is advantageously very cost-effective and allows the bearing to be stably incorporated inside it, thus reducing the number of components to be assembled to manufacture the bottom bracket assembly.  
         [0035]     Preferably, such a type of adapter device is obtained by forming in the main body of the adapter device a bearing housing seat comprising a first shoulder, inserting the bearing in such a housing seat and deforming a free end of said main body to obtain a second shoulder.  
         [0036]     In a particularly preferred embodiment of the bottom bracket assembly, said at least one adapter device comprises a main body configured to be associated with one end of said box, said at least one first stop element is defined by a shoulder made in a single piece with said main body and said at least one second stop element is associated with said main body at an axially outer free end portion thereof.  
         [0037]     Preferably, said at least one second stop element is removably associated with said main body. Advantageously, such a type of adapter device allows the bearing to be mounted and dismounted in and from the main body of the adapter device, for example to allow the replacement or the maintenance of the bearing.  
         [0038]     Preferably, said main body comprises, at said axially outer free end portion, an annular body portion comprising at least one through hole extending radially. As described hereinafter, such a through hole allows the passage of a free end portion of the at least one second stop element so that this free end portion can block or limit the relative axial movement between bearing and main body of the adapter device.  
         [0039]     More preferably, said at least one through hole is at an axial distance from said at least one first stop element greater than the axial extension of said at least one bearing by a value of between 0 and 0.3 mm.  
         [0040]     Even more preferably, said at least one through hole is formed in an annular throat made on an outer surface of said annular body portion of said main body.  
         [0041]     In a preferred embodiment of the bottom bracket assembly a plurality of through holes are provided, preferably even in number, more preferably 2 or 4 through holes. Advantageously, the arrangement of many holes allows the simultaneous use of a plurality of second stop elements, so as to improve the efficiency of the blocking or limiting action of the relative axial movement between bearing and main body of the adapter device exerted by such second stop elements.  
         [0042]     Preferably, said radial through holes are arranged in radially opposite positions. As shall become clearer throughout the present description, such an arrangement ensures greater efficiency of the blocking or limiting action of the relative axial movement between bearing and main body of the adapter device.  
         [0043]     Preferably, said at least one second stop element is housed in said at least one annular throat and comprises at least one end portion projecting from said at least one through hole. Advantageously, the arrangement of the aforementioned through holes at the aforementioned axial distance that is greater than the axial extension of the bearing makes it possible to avoid the end portion of the second stop element from being able to slide or bang against the ring of the bearing when the second stop element is inserted in the through hole. On the other hand, as already stated, the aforementioned clearance between bearing and the second stop element is such as not to substantially vary the chain line of the bottom bracket assembly, thus ensuring the desired precision of the gearshifting.  
         [0044]     Advantageously, the housing of the second stop element in the annular throat ensures a stable positioning of such a stop element with respect to the main body of the adapter device.  
         [0045]     More preferably, said at least one second stop element is made from an elastic material and comprises a substantially circular central body portion having a bending radius less than or equal to the bending radius of said annular throat. Advantageously, the second stop element elastically deforms when inserted in the annular throat of the main body of the adapter device, thus achieving a greater stability of the housing of the second stop element in the aforementioned throat.  
         [0046]     In an alternative embodiment of the assembly said at least one through hole is a threaded hole and said at least one second stop element comprises at least one screw housed in said at least one threaded hole and having a free end projecting from said at least one threaded hole. In this case, preferably, to improve the efficiency of the blocking or limiting action of the relative axial movement between bearing and main body of the adapter device, a plurality of screws are used, each one screwed into a respective threaded hole.  
         [0047]     In a further alternative embodiment of the assembly said at least one second stop element is permanently associated with said main body and is selectively mobile between a disengagement position in which said at least one second stop element does not project from said main body and an engagement position in which said at least one second stop element projects at least partially from said main body. Also in this case, advantageously, an adapter device is made that allows the mounting and dismounting of the bearing in and from the main body of the adapter device, for example to allow the replacement or maintenance of the bearing.  
         [0048]     In the specific case of this last embodiment, preferably, the bottom bracket assembly comprises a control element selectively mobile between a first operative position in which said at least one second stop element is in said disengagement position and a second operative position in which said at least one second stop element is in said engagement position.  
         [0049]     Preferably, said control element comprises a ring rotatably mounted on said axially outer annular end portion of said main body.  
         [0050]     Preferably, said at least one second stop element comprises at least one pawl having a head rotatably housed in a recess formed on an inner surface of said ring and a body housed in a through opening formed in said annular end portion of said main body, said body having a free end that, when said ring is in said first operative position, projects from said through opening and when said ring is in said second operative position is housed in said through opening.  
         [0051]     Preferably, said through opening comprises a side surface that is inclined with respect to a radial direction and configured to thrust said pawl from said engagement position to said disengagement position when said ring is moved from said second operative position to said first operative position.  
         [0052]     Preferably, in this case the assembly comprises elastic means acting between said ring and said annular end portion of said main body to thrust said at least one second stop element in said engagement position. Advantageously, the second stop element is normally in the operative position configured to block or limit the relative axial movement between bearing and main body of the adapter device and is only brought to the disengagement position when the bearing has to be dismounted from or mounted into the aforementioned main body.  
         [0053]     Preferably, said elastic means comprise at least one compression spring acting between a first thrusting surface defined in a first seat formed in said inner surface of said ring and a second thrusting surface defined in a second seat formed on an outer surface of said annular end portion of said main body.  
         [0054]     Preferably, said control element comprises an outer surface having a grooved profile, configured to allow an easier actuation of the control element through a maneuvering key.  
         [0055]     More preferably, said main body comprises an axially inner body portion adjacent to said axially outer annular end portion and having an outer surface having a grooved profile identical to the grooved profile of said control element. In this way it is possible to use the same maneuvering key both to screw the main body of the adapter device into the box and to actuate the control element. Moreover, the provision of a grooved profile on the main body of the adapter device allows a better grasping of such an element to keep it still during the actuation of the control element.  
         [0056]     Irrespective of the specific embodiment of the assembly, preferably the other bearing of said pair of bearings is left free to move with respect to at least one from the respective adapter device and said shaft in at least one way of said predetermined direction. Advantageously, the possibility of having a relative axial movement between the other bearing and the respective adapter device or the shaft allows sizing errors of the box of the frame to be recovered, without influencing the position of the shaft and therefore the determination of the chain line.  
         [0057]     Preferably, said bearing is left free to move in both ways of said predetermined direction to allow the recovery of sizing errors of the box, either in excess or in defect.  
         [0058]     Preferably, at least one from said adapter device and said shaft comprises at least one second shoulder and a preloaded elastic element arranged between said bearing and said at least one second shoulder. Advantageously, thanks to the presence of the preloaded elastic element it is possible to allow the relative movement between bearing and adapter or shaft to recover the sizing errors of the box at the same time maintaining a preloaded thrust on the bearing that is not cancelled out by the movement of the bearing itself. The preloading indeed allows a thrust to be exerted on the bearing not only in the case of movement of the adapter or of the bearing towards the outside of the box to recover an error due to an excessive axial sizing of the box, but also in the case of movement of the adapter or of the bearing towards the inside of the box to recover errors in defect in the axial sizing of the box. In any case a more stable positioning of the bearing is achieved.  
         [0059]     In a first preferred embodiment of the bottom bracket assembly, said at least one second shoulder is defined in a first adapter device and the other adapter device comprises said at least one first stop element and at least one second stop element.  
         [0060]     In a second preferred embodiment of the bottom bracket assembly, said second shoulder is defined in said shaft and both of the adapter devices comprise said at least one first stop element and at least one second stop element. Advantageously, such an assembly is very strong since possible overloading caused by lateral knocks is shared out over both bearings. Even more advantageously, in such an assembly the bearings are closer to the crank arms; this allows the bending stress to which the shaft is subjected during pedaling to be reduced.  
         [0061]     In a third preferred embodiment of the bottom bracket assembly, both of the adapter devices comprise said at least one first stop element and at least one second stop element and a preloaded elastic element is arranged between said at least one first stop element and at least one second stop element of at least one adapter device.  
         [0062]     Preferably, said elastic element comprises a washer having an undulating lateral profile.  
         [0063]     Preferably, the bottom bracket assembly, irrespective of its specific embodiment, also comprises a third stop element fixedly connected to said shaft on the opposite side to said at least one second stop element with respect to said at least one bearing. Advantageously, such a third stop element allows a relative movement between bearing and shaft to be avoided in the case of a very hard knock that pushes the shaft sideways, which would make the assembly unusable.  
         [0064]     Preferably, said third stop element is a ring inserted in a throat made on said shaft.  
         [0065]     In a second aspect thereof, the present invention relates to an adapter device for supporting a bearing of a bottom bracket assembly with respect to a housing box of such an assembly provided in a bicycle frame, comprising a main body configured to be associated cantilevered with a free end of said box, at least one first stop element and at least one second stop element facing one another and arranged at a predetermined distance from the first stop element, wherein the first and second stop elements define a range of motion of a bearing along a longitudinal axis of the housing box.  
         [0066]     Advantageously, such an adapter device can be used in the bottom bracket assembly and thus allows the advantages mentioned above with reference to the adapter device of the assembly to be achieved.  
         [0067]     Preferably, the aforementioned adapter device comprises, individually or in combination, the structural and advantageous features described above as preferred features of the adapter device of the bottom bracket assembly.  
         [0068]     In a third aspect thereof, the present invention relates to a method for mounting a bearing of a bottom bracket assembly with respect to a housing box of such an assembly provided in a bicycle frame, comprising the steps of:  
         [0069]     providing an adapter device comprising a main body, at least one first stop element and at least one second stop element facing each other and arranged at a predetermined distance;  
         [0070]     associating said main body with a free end of said box.  
         [0071]     Advantageously, the aforementioned method allows assembling the bottom bracket assembly and thus allows the advantages mentioned above with reference to the assembly to be achieved. Preferably, such an assembly comprises, individually or in combination, the structural and advantageous features described above as preferred features of the bottom bracket assembly.  
       DESCRIPTION  
       [0072]     In  FIGS. 1, 10 ,  11 ,  12  and  13 , a bottom bracket assembly in accordance with the present invention is indicated with  1 .  
         [0073]     The assembly  1  comprises a shaft  5  rotatably supported inside a box  10  provided in a bicycle frame (not illustrated) through the interposition of a right bearing  15  and of a left bearing  20 . Preferably the right bearing  26  is press fitted on the shaft  5 . The shaft  5  is coupled, at its respective left and right ends, to a left crank arm  80  and to a right crank arm  84 . The right crank arm  84  has a connecting portion  82  to be connected at least to a toothed gear. In the assembled configuration the shaft  5 , the right crank arm  84  and the toothed gear  86  are rigidly connected to each other. The distance between the middle plane of the frame of the bicycle and the middle plane of the toothed gear  86  is called chain line (CL in  FIG. 1 ).  
         [0074]     In the examples illustrated in  FIGS. 1, 10 ,  11 ,  12  and  13 , the shaft  5  is made in two separate pieces coupled together at their heads, but this should not be considered a limitation, given that the shaft could be made in a single piece.  
         [0075]     The assemblies  1  of  FIGS. 1, 10 ,  11 ,  12  and  13  represent alternative embodiments of the assembly. In particular,  FIGS. 1, 10 ,  11  and  12  illustrate assemblies in which the bearings are supported cantilevered outside of the box  10 , whereas  FIG. 13  illustrates an assembly in which the bearings are supported inside the box  10 .  
         [0076]     With reference to  FIG. 1 , the shaft has, at the opposite end portions thereof, a right shoulder  22  and a left shoulder  24  that act in abutment against the inner ring  26  of the right bearing  15  and against the inner ring  28  of the left bearing  20  to prevent the bearings slipping towards the outside of the bottom bracket assembly.  
         [0077]     The bearings  15 ,  20  are coupled with the box  10  through a right adapter device  30  and a left adapter device  35 . The adapter devices are preferably made of light material, such as light metal alloy, or of composite material, The composite material can comprise structural fibers incorporated in a polymeric material.  
         [0078]     Typically, the structural fibers are chosen from the group comprising carbon fibers, glass fibers, aramidic fibers, ceramic fibers, boron fibers and combinations thereof. Carbon fibers are particularly preferred.  
         [0079]     The arrangement of the structural fibers in the polymeric material can be a random arrangement of pieces or small sheets of structural fibers, an ordered substantially unidirectional arrangement of fibers, an ordered substantially two-dimensional arrangement of fibers, or a combination of the above.  
         [0080]     Preferably, the polymeric material is thermosetting. However it is possible to use a thermoplastic material.  
         [0081]     More preferably, the polymeric material comprises an epoxy resin.  
         [0082]     The right adapter device  30  comprises a main body  40  in turn defined by a first cylindrical portion  42  having a greater diameter and by a second cylindrical portion  44  having a smaller diameter (see also  FIG. 2 ). The portion  42  having a greater diameter is configured to be supported cantilevered outside of the box  10 , whereas the portion having a smaller diameter  44  has an outer threading  46  configured to screw into a threading  48  inside the box  10 . The bearing  15  is housed in the cylindrical portion  42  having a greater diameter.  
         [0083]     The portion having a greater diameter  42  is defined, on the side where it joins to the portion having a smaller diameter  44 , by an outer annular surface  50 , and has a grooved profile  53  ( FIG. 2 ) on the outer surface  49  of an end portion thereof to allow engagement with a maneuvering key.  
         [0084]     The adapter device  30  is screwed into the box  10  acting with the maneuvering key until the annular surface  50  abuts against the front surface  52  of the front end of the box  10 .  
         [0085]     The portion having a greater diameter  42  has an inner hole  54  ( FIG. 2 ) that defines a seat in which the right bearing  15  is housed. In particular, the diameter of the cylindrical surface  55  of the hole  54  substantially coincides with the outer diameter of the bearing  15 , whereas the bottom surface  56  of the hole  54 , in an assembled condition, defines a shoulder having the function of a first stop element for the outer ring  58  of the bearing  15 , said shoulder being configured to prevent the axial translation of the bearing towards the inside of the assembly  1 .  
         [0086]     The cylindrical surface  55  has an axial extension A greater than the axial extension B of the outer ring  58  of the bearing  15  ( FIG. 2 ), for which reason when the latter is inserted therein a free end portion  60  remains.  
         [0087]     At such a free portion  60  of the cylindrical surface  55  one or more through holes  62  are formed extending radially that open out into an annular throat  64  formed on the outer surface  66  of the portion having a greater diameter  42  of the main body  40  of the adapter device  30 . Preferably, the holes  62  are even in number, and even more preferably there are 2 or 4 holes. In the preferred embodiment illustrated in  FIG. 4  the holes  62  are radial and arranged in diametrically opposite positions.  
         [0088]     Into the holes  62  are inserted the ends  70  of a second stop element (for example, a split pin  72  as illustrated in  FIGS. 3 and 4 ) of the outer ring  58  configured to cooperate with the shoulder  56  to keep the bearing  15  inside a space having a predetermined axial extension.  
         [0089]     As illustrated in  FIG. 1 , the second stop element  72  is thus removably associated with the main body  40  of the adapter device  30  at an axially outer annular end portion of said main body  40 .  
         [0090]     In particular, as illustrated in  FIG. 4 , the ends  70  of the second stop element, in assembled condition, project from the main body  40  of the adapter device  30  to block or limit the axial movement of the outer ring  58  of the bearing  15 , so as to prevent it from slipping in the axial direction from the right adapter device  30  towards the outside of the assembly  1 .  
         [0091]     Preferably, the holes  62  are positioned at an axial distance C ( FIGS. 1 and 2 ) from the bottom surface  56  that is greater than or equal to the axial extension of the outer ring  58  of the right bearing  15 . This makes it easier to insert the end  70  of the split pin  72  in the holes  62 , since sliding and banging against the outer ring  58  of the bearing  15  is prevented. Preferably, the difference between such a distance C and the axial extension B of the outer ring  58  is between 0 and 0.3 mm, even more preferably it is between 0.05 and 0.15 mm. Such a clearance allows the recovery of small sizing errors of the box  10 .  
         [0092]     Despite the clearance deriving from the slight difference indicated between C and B, the outer ring  58  of the right bearing  15  is considered substantially blocked in the adapter device  30  between the bottom surface  56  and the ends  70  of the split pin  72 , in the sense that the possible relative axial movement between bearing  15  and main body  40  of the adapter device  30  is in any case limited at most to 0.3 mm, preferably to 0.15 mm.  
         [0093]     The split pin  72  is preferably made with a shaped steel wire for springs and can for example have a circular central portion  74  having a radius R 1  that is smaller than or equal to the radius R 2  of the bottom of the throat  64  of the main body  40  of the adapter  30 . In assembled condition the centre of curvature O 1  of the split pin  72  and the centre of curvature O 2  of the throat  64  ( FIGS. 3 and 4 ) are offset. The ends  70  of the split pin  72  are formed by bending the edges of the circular portion towards the centre of curvature O 1  of the circular central portion  74 . Preferably the orientation of the ends  70  is not perfectly radial. In this way, and also thanks to the distance between O 1  and O 2 , the split pin  72 , when it is inserted into the main body  40  of the adapter device  30 , elastically deforms, as illustrated in  FIG. 4 , and is retained in the throat  64 .  
         [0094]     The section of the split pin  72  can be of whatever type, for example circular or quadrangular.  
         [0095]     In the example illustrated in  FIG. 1  the left adapter device  35  differs from the right one  30  since the main body  40 ′ thereof neither has the annular throat  64  nor the holes  62 , and is not associated with any element to prevent or limit the axial translation of the outer ring  74  of the left bearing  20  towards the outside of the assembly  1 . The shape of the main body  40 ′ of the left adapter device  35 , apart from the annular throat  64  and the holes  62 , is identical to that of the main body  40  of the right adapter device  30 .  
         [0096]     Between the outer ring  74  and the bottom surface  56 ′ of the adapter body  40 ′ an elastic element  76 , for example a spring like the one illustrated in  FIGS. 5   a  and  5   b , is arranged in preloaded condition. Such a spring consists of a washer having an undulating lateral profile. The washer is designed so that, in a mounted configuration, it exerts a force of between 0 and 2,5 N on the bearing  20 , depending upon the sizing error of the box that has been recovered, and preferably between 1 and 2 N.  
         [0097]     The spring  76  has the task of allowing the bearing  20  to move with respect to the left adapter device  35  to recover the sizing errors of the box at the same time remaining preloaded.  
         [0098]     The preloading of the spring  76  indeed allows a thrust to be exerted on the left bearing  20  not only in the case of movement towards the outside to recover excessive sizing of the box, but also in the case of movement towards the inside due to an error in defect of the size of the box  10 .  
         [0099]     The position of the spring  76  can be modified provided that it allows the recovery of the sizing errors of the box  10 , for which reason it can for example be inserted between the shoulder  56  of the right adapter device  30  and the outer ring  58  of the right bearing  15 , or between the ends  70  of the split pin  72  and the outer ring  58 , or between the inner ring  26 ,  28  of any one of the bearings  15 ,  20  and a third stop element against which it abuts.  
         [0100]      FIG. 10  shows an alternative embodiment of the bottom bracket assembly  1 . In this FIG., elements that are the same as or corresponding to those of the assembly of  FIG. 1  are indicated with the same reference numeral.  
         [0101]     In the assembly  1  of  FIG. 10 , the sizing error of the box  10  is recovered allowing the inner ring of at least one of the two bearings to move with respect to the shaft. In particular, in the illustrated assembly  1 , the shaft  5  has two shoulders  6  and  7  arranged on the inner side of the inner rings  26  and  28  of the right and left bearings  15  and  20 . The spring  76  is arranged between the inner ring  28  of the left bearing  20  and the left shoulder  6 .  
         [0102]     The outer rings  58  and  74  of the bearings, on the other hand, are blocked in both axial directions by respective adapter devices  30  that are the same as the right adapter device  30  of the assembly of  FIG. 1 .  
         [0103]     The embodiment of  FIG. 10  allows the crank arms (not illustrated) to be brought closer to the bearings, subjecting the shaft to less bending stress. Moreover, due to the presence of the two adapter devices  30 , the assembly is capable of absorbing axial overloading in both ways, given that it is shared out over both bearings.  
         [0104]     In a further embodiment of the assembly  1  illustrated in  FIG. 11 , the sizing error of the box  10  is recovered allowing a ring of one of the two bearings to translate with respect to an adapter device, and axially blocking a ring of the other bearing with respect to the other adapter device.  
         [0105]     In  FIG. 11 , elements that are the same as or corresponding to those of the assembly of  FIGS. 1 and 10  are indicated with the same reference numeral.  
         [0106]     In particular, the assembly  1  of  FIG. 11  differs from the assembly  1  of  FIG. 10  since the left adapter device  35  has an axial distance C′. between the bottom surface  56  and the ends  70  of the split pin  72  greater than the axial extension B of the outer ring  74  of the left bearing  20 .  
         [0107]     Springs  76  are arranged both between the bottom wall  56  and the outer ring  74  and between the outer ring  74  and the ends  70  of the split pin  72 .  
         [0108]     The right adapter device  30  is identical to the right adapter device  30  of  FIG. 10  and of  FIG. 1 .  
         [0109]      FIG. 12  shows a further alternative embodiment of the bottom bracket assembly  1 . In this FIG., elements that are the same as or corresponding to those of the assembly of  FIG. 1  are indicated with the same reference numeral.  
         [0110]     The assembly  1  of  FIG. 12  differs from the one of  FIG. 1  in that it comprises a stop ring  90  (for example a Seeger ring) fitted onto a suitable annular seat  91  formed on the shaft  5  immediately to the left of the right bearing  15 . Preferably, the ring  90  does not exert any pressure on the ring  26  of the bearing  15 , providing a clearance of 0-0.2 mm. The advantage brought by the presence of the stop ring  90  is that of avoiding the inner ring  26  of the right bearing  15  from being able to slide on the shaft  5 , making the assembly  1  unusable, in the case of very hard lateral knocks that thrust the shaft from left to right. The Seeger ring can thus be considered a third stop element for the right bearing.  
         [0111]      FIG. 13  shows a further alternative embodiment of the bottom bracket assembly  1 . In this FIG., elements that are the same as or corresponding to those of the assembly of  FIG. 1  are indicated with the same reference numeral.  
         [0112]     The assembly of  FIG. 13  differs from that of  FIG. 1  only in that the adapter devices, and consequently the bearings, are housed inside the box  10  through a right adapter device  300  and a left adapter device  350  screwed inside the box  10 .  
         [0113]     The right adapter device  300  comprises a main body  400  inside which a shoulder  560  is defined to prevent the axial translation of the bearing  15  towards the inside of the assembly  1 . At one end portion of the main body  400  configured to remain outside the box  10  a split pin  72  identical to the one described with reference to FIGS.  1  to  4  is associated with the main body  400 . The ends of the split pin  72  are configured to act on the outer ring  58  of the right bearing  15  through holes  62  formed on a free end portion of the main body  400 , in a totally similar way to what has been described above.  
         [0114]     The main body  400  also comprises an end flange  600  configured to abut against the front surface of a right end of the box  10 .  
         [0115]     Also in this case, the left adapter device  350  differs from the right one  300  since the main body  400 ′ thereof does not have the holes  62 , and is not associated with any element for preventing or limiting the axial translation of the outer ring  74  of the left bearing  20  towards the outside of the assembly  1 .  
         [0116]     The shape of the main body  400 ′ of the left adapter device  350 , apart from the holes  62 , is identical to that of the main body  400  of the right adapter device  300 . Also in this case, between the outer ring  74  and the bottom surface  56 ′ of the adapter body  40 ′ an elastic element  76  identical to the one described with reference to  FIGS. 1, 5   a  and  5   b  is arranged in preloaded condition.  
         [0117]     A person of ordinary skill in the art will note that the right adapter device  300  inside the box  10  of the assembly of  FIG. 13  has in common with the adapter devices  30  and  35  of the assemblies of  FIGS. 1, 10 ,  11  and  12  a shoulder  560 ,  56  arranged between the bearing  26  and the inside of the assembly, and a stop element  72  arranged between the bearing  26  and the outside of the assembly, the stop element being selectively removable and insertable from/into the holes  62  of the adapter device acting from outside of the assembly. For this reason, adapter devices that are the same as or similar to the adapter device  300  of  FIG. 13  can be applied to the assemblies of  FIGS. 1, 10 ,  11  and  12  to transform them into assemblies with bearings retained inside the box of the frame.  
         [0118]     In each of the above illustrated examples, a fine realization of the box  10  would avoid the use of the spring  76 .  
         [0119]      FIG. 6  illustrates an adapter device  130  alternative to the one described and illustrated with reference to FIGS.  1  to  4 . In such a device, a bearing  120  is substantially blocked in the seat  154  through radial screws  122 . The screws  122  are inserted in radial threaded holes  124  so as to project inside the seat  154  exactly as stated for the ends  70  of the split pin  72  of  FIG. 4 . In an alternative embodiment that is not illustrated, the screws can press radially on the bearing so as to block it under pressure.  
         [0120]      FIGS. 7, 8   a ,  8   b  and  9  illustrate a further alternative adapter device  230  in which a bearing  220  is substantially blocked in the seat  254  through pawls  222  selectively mobile from an engagement position, illustrated in  FIG. 8   b , to a disengagement position, illustrated in  FIG. 8   a , by acting on a control element  224 .  
         [0121]     The control element  224  comprises, in particular, a ring rotatably mounted on the cylindrical edge  266  of the main body  240  ( FIG. 9 ).  
         [0122]     The pawls  222  each comprise an elongated body housed in a respective opening  226  made passing through the cylindrical edge  266  of the main body  240  of the adapter device  230 . Each pawl  222  has the control element  224  arranged on the top thereof. The heads  228  of each pawl  222  project from the openings  226  and are rotatably housed in suitable recesses  232  formed on the inner side of the control element. When the control element  224  is rotated from the position of  FIG. 8   b  to the position of  FIG. 8   a , it brings the pawls  222  along with it until their heads  228  rotate in the recesses  232  through the thrust exerted by an inclined side surface  290  of the openings  226 , and take up the disengagement position of  FIG. 8   a , in which a free end of each pawl does not project from the through opening  226  on the opposite side to the head  228  of the pawl  222 . The thickness of the pawls  222  is such as to be able to completely house them in the openings  226 . Similarly, the length of the pawls  222  is such that, when they take up the disengagement position of  FIG. 8   a , the body of the pawls is completely housed in the openings  226 .  
         [0123]     The inclined surfaces  290  extend along a non-radial direction for which reason they act as cam means with respect to the pawls  222 .  
         [0124]     The control element  224  is normally kept in the engagement position of  FIG. 8   b  by compression springs  291  housed in seats  292 , a first portion  292   a  of which being made in the cylindrical edge  266  and a second portion  292   b  of which being made in the control element  224  ( FIG. 8   a ).  
         [0125]     The first and second portions  292   a  and  292   b  of the seats  292  have thrusting surfaces  293   a  and  293   b  that are mobile towards and away from each other to compress the springs  291  in the passage from the position of  FIG. 8   b  to that of  FIG. 8   a.    
         [0126]     The heads  228  of the pawls  222  form an undercut  229  ( FIG. 9 ) with respect to the cylindrical edge  266  of the main body  240  of the adapter device  230 , so that the pawls cannot slip from the recesses  226  when the control element  224  is inserted.  
         [0127]     The control element  224  is mounted so that it can rotate on the cylindrical edge  266  to which it remains fixedly connected thanks to an annular projection  295  snap-inserted into a corresponding annular throat  296  ( FIG. 9 ).  
         [0128]     The control element  224  can easily be installed since the portions  292   b  of the seats  292  and the recesses  232  are open on the side facing towards the main body  240  of the adapter device  230  ( FIG. 9 ).  
         [0129]     To actuate the control element  224  more easily, it has a grooved profile  251  on the outer surface thereof, this profile being configured to engage with a maneuvering key.  
         [0130]     The main body  240  of the adapter device  230  also has a similar profile  253  ( FIG. 9 ) at an outer surface of a body portion thereof adjacent to the control element  224 . Such a grooved profile  253 , in addition to make easier the screwing of the main body  240  into the box  10  of the frame, also allows a better grasping of such a main body  240  to keep it still during the actuation of the control element  224 .  
         [0131]     Preferably, the engagement profiles  251  and  253  are identical so that it is possible to use the same key both to screw the adapter device  230  into the box  10  and to actuate the control element  224 .