Abstract:
A bicycle crank arm assembly is provided having at least one axle portion, a crank arm mounted on the at least one axle portion, the crank arm having a coupling seat and the axle portion a coupling portion coupled to the coupling seat, the coupling seat and the coupling portion being shaped so as to make a shape coupling to ensure that the crank arm can transmit a torque to the axle portion. Between the crank arm and the axle portion adhesive material is applied. The shape coupling ensures that the crank arm and the axle portion are integral in rotation, whereas the gluing ensures the sealing of the coupling area against corrosion phenomena. The gluing also ensures a predetermined minimum force limit necessary to disassemble the crank arm assembly. The crank arm assembly has a low overall weight, a simple assembly process, and a suitable resistance to disassembling.

Description:
FIELD OF INVENTION 
     The invention concerns a bicycle crank arm assembly, i.e., an assembly of components of a bottom bracket assembly of a bicycle transmission that comprises a crank arm and at least one central axle portion on which the crank arm is mounted. The invention also concerns a method for assembling such an assembly. 
     BACKGROUND 
     The coupling between the ends of the central axle and a crank arm of the bicycle is typically, according to the prior art, a shape coupling, normally carried out through a grooved or polygonal profile, formed both on the aforementioned ends, and in suitable housing seats made at the ends of the elongated body of which each of the two crank arms of the bicycle consists. A fastening screw or other analogous element also ensures the attachment between the axle and the crank arm, avoiding the crank arm being able to slip off from the axle. 
     By their nature, shape coupling and attachment through screws have a degree of imprecision that allows small relative displacements between the crank arm and the axle. 
     SUMMARY 
     According to a first aspect of the invention, the bicycle crank arm assembly comprises at least one axle portion, a crank arm mounted on the at least one axle portion, the crank arm having a coupling seat and the axle portion having a coupling portion coupled to the coupling seat, the coupling seat and the coupling portion being shaped so as to make a shape coupling to ensure that the crank arm can transmit a torque to the axle portion, wherein between the crank arm and the axle portion adhesive material is applied. 
     According to a second aspect of the invention, more specifically, the method for assembling a crank arm to an axle portion of a bottom bracket assembly of a bicycle transmission comprises the shape coupling between the crank arm and the axle portion, to ensure that the crank arm can transmit a torque to the axle portion, wherein between the crank arm and the axle portion adhesive material is applied. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
       Further characteristics and advantages of the present invention shall become clearer from the following detailed description of some preferred embodiments thereof, made with reference to the enclosed drawings. In such drawings, 
         FIG. 1  is a section view in the axial sense of a bottom bracket assembly of a bicycle transmission that incorporates crank arm assemblies according to the invention; 
         FIG. 2  is a section view in the axial sense of the left crank arm assembly of  FIG. 1 ; 
         FIG. 3  and  FIG. 4  are, respectively, an axonometric view and a section view in the axial sense of the assembly of  FIG. 2 , represented with separated parts; 
         FIG. 5  is an enlarged section view in the axial sense of a detail of the crank arm assembly of  FIG. 2 ; 
         FIGS. 6 ,  7 , and  10  are section views similar to that of  FIG. 5 , referring to different embodiments; 
         FIG. 8  is a transversal section view along the line VIII-VIII of a detail of the assembly of  FIG. 1 ; and 
         FIG. 9  is a section view similar to that of  FIG. 8 , referring to a different embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Introduction 
     The invention concerns a bicycle crank arm assembly, i.e., an assembly of components of a bottom bracket assembly of a bicycle transmission that comprises a crank arm and at least one central axle portion on which the crank arm is mounted. The invention also concerns a method for assembling such an assembly. 
     In relation to a central axle and to a crank arm of a bicycle transmission, by “coupling” the mutual mechanical interaction is meant between axle and crank arm that makes the two elements integral in rotation about the axis of the bottom bracket assembly, allowing the transmission of torque, i.e., power, between the crank arm and the axle. In the same context, on the other hand, by “attachment” the mutual mechanical interaction is meant that makes the two elements integral in translation in the sense of the axis of the bottom bracket assembly, preventing the crank arm from slipping off, thus ending the coupling. 
     Hereafter, reference shall be made to an “axle portion,” meaning both the entire axle and possibly just the portion thereof with which the crank arm is coupled and fixed; such a portion shall then be associated with another axle portion, with techniques and modes not covered by the present invention, so as to restore the structural integrity of the axle as a whole. 
     In its most general terms, the present invention concerns, in a first aspect thereof, a bicycle crank arm assembly according to the invention and, in a second aspect thereof, an assembly method according to the invention. Preferred characteristics are further described. 
     More specifically, according to the first aspect of the invention, the bicycle crank arm assembly comprises at least one axle portion, a crank arm mounted on the at least one axle portion, the crank arm having a coupling seat and the axle portion having a coupling portion coupled to the coupling seat, the coupling seat and the coupling portion being shaped so as to make a shape coupling to ensure that the crank arm can transmit a torque to the axle portion, wherein between the crank arm and the axle portion adhesive material is applied. 
     The adhesive material preferably has the dual effect of sealing the coupling area and of preventing the relative displacements between the crank arm and the axle portion. Both of these effects contribute to reducing, if not cancelling out, the possibility that corrosion phenomena begin, irrespective of the degree of precision of the shape coupling or the type of attachment system adopted. 
     Preferably, the coupling seat comprises a shoulder for supporting the axle portion in the axial sense, and possibly the shoulder completely closes the coupling seat in the axial direction. Such a shoulder ensures the correct positioning in the axial sense of the axle portion with respect to the crank arm. 
     Preferably, the adhesive material is provided between the coupling seat and the coupling portion, and more preferably it completely seals the coupling portion to the coupling seat. It is thus ensured that there is complete protection of the coupling means from external agents such as dirt and humidity, and therefore the creation of corrosion phenomena is countered in the contact areas between the material of the crank arm and the material of the axle portion. 
     Preferably, the crank arm assembly comprises a gluing chamber formed in at least one of the coupling seat and the coupling portion, the adhesive material being provided in the chamber. The presence of a specific gluing chamber where it is possible to insert a predetermined amount of adhesive material allows a certain barrier against the penetration of external atmospheric agents into the most inner coupling areas to be arranged in a preferred position. Moreover, it allows the gluing conditions, and in particular the adhesion force obtained, to be best controlled in the embodiments in which this is important to prevent the crank arm from slipping off. 
     Even more preferably, the adhesive material is present both in the gluing chamber, and at least in part of the remaining space between the coupling seat and the coupling portion. In this way polluting agents or humidity are prevented from remaining trapped in the inner-most coupling areas. 
     The gluing chamber can take up different shapes, just as it may be just one or else there can be many, concentrated in one or more areas or else distributed between the crank arm and the axle portion. The gluing chamber can comprise an annular channel in the crank arm, formed in the coupling seat, and/or an annular channel in the axle portion, formed in the coupling portion. The gluing chamber can also comprise a free space, left free between the coupling seat and the coupling portion by a tapered front area of the coupling portion itself. Such a tapered front area preferably has an axial extension less than or equal to ⅓ the coupling portion; preferably, the tapered front area has an axial extension equal to 2-5 mm. 
     Preferably, the annular channel is localized in the axial sense in a remote position with respect to the center of the bottom bracket assembly. The effective adhesion is indeed greater in this area, which during use of the bicycle is stressed more and, thus, is more subject to localized deformations that could—if not countered—lead to the attachment being lost. 
     The adhesive material can be of different types. Preferably, the adhesive material is a setting resin, more preferably a thermosetting resin, such as an epoxy or phenolic resin. In this way it is possible to more easily control both the distribution of the adhesive material when its adhesive properties have not yet been activated, and the final adhesion force. 
     In a preferred embodiment, the crank arm assembly comprises fastening means to ensure that the coupling means remain engaged with the crank arm and the axle portion, the fastening means comprising the adhesive material. 
     In this way the shape coupling ensures that the crank arm and the axle portion are integral in rotation, whereas the gluing ensures a predetermined minimum force limit necessary to disassemble the crank arm assembly. The crank arm assembly at the same time has a lower overall weight, a simple assembling process, and a suitable resistance to disassembling. Moreover, the axle portion and the crank arm do not require special processing and the assembling process is simple and cost-effective. 
     The fastening means also preferably comprise a mechanical forcing of the coupling portion of the axle portion in the coupling seat of the crank arm. The combination of mechanical forcing and adhesive material allows the best attachment conditions to be achieved, i.e., it allows the force necessary to disassemble the crank arm from the axle portion to be determined in the most certain way. 
     According to the second aspect of the invention, more specifically, the method for assembling a crank arm to an axle portion of a bottom bracket assembly of a bicycle transmission comprises the shape coupling between the crank arm and the axle portion, to ensure that the crank arm can transmit a torque to the axle portion, wherein between the crank arm and the axle portion adhesive material is applied. 
     Preferably, the adhesive material is applied to one of the crank arm and the axle portion before they are engaged, after which the crank arm and the axle portion are forced in the axial sense. In this way a good distribution of the adhesive material between them is obtained in a simple way. 
     DETAILED DESCRIPTION 
     In the figures, a bottom bracket assembly of a bicycle transmission is wholly indicated with  10 ; just the frame box  11  of the bicycle that supports the bottom bracket assembly  10  is illustrated. 
     With reference in particular to  FIG. 1 , the bottom bracket assembly  10  comprises two crank arm assemblies  20  and  40 , left and right, each of which comprises a crank arm  21  and  41  and an axle portion  22  and  42 , respectively. The two axle portions  22  and  42  are substantially the same as each other and are integral in rotation through a coupling with front teeth  13  and a lock nut  14 , only schematically represented since they are per se conventional, so as to form, in use, an axle assembly, globally indicated with  12 . It should be noted that in other embodiments (not shown) two different axle portions could be provided, and one of the two portions could even be left out whereas the other could comprise the entire axle. 
     The right crank arm assembly  40  differs from the left crank arm assembly  20  in that it also comprises—according to widely accepted practice—spokes  47 , intended for engagement with crowns, not illustrated. Hereafter, the left crank arm assembly  20  shall be described being understood that what has been stated is also valid for the right crank arm assembly  40 . 
     The axle  12  is rotatably supported in the frame box  11  about a main axis X of the bottom bracket assembly  10 , for example, through rolling bearings  15  mounted on adapter supports  16 , fixed projecting axially from the frame box  11 . 
     In the left crank arm assembly  20 , the crank arm  21  and the axle portion  22  are engaged with each other through coupling means, to allow the transmission of a torque from the crank arm  21  to the axle portion  22 , and fastening means to prevent the disengagement of the coupling means. 
     The coupling means comprise a coupling seat  23  formed in the crank arm  21  and a coupling portion  24  formed on the axle portion  22  (as represented in  FIG. 3 ); the seat  23  and the portion  24  are shaped so as to make a shape coupling, for example, according to a grooved profile. Such a grooved profile, as shown in detail in  FIG. 8 , is, for example and preferably, of the type described in co-assigned U.S. application Ser. No. 11/442,848, incorporated herewith by reference, in which a profile  25  in the seat  23  and a matching profile  26  on the axle portion  24  follow a succession of matching waves. In a different embodiment, shown in  FIG. 9 , a similar grooved profile is provided, with grooved profiles  25 ′ in the seat  23  and  26 ′ on the axle portion  24  that differ from the profiles  25  and  26  in that the crests of the waves both in the seat  23  and in the portion  24  are levelled, so as to leave empty spaces  33 ′ between the two profiles  25 ′ and  26 ′. 
     The tolerances of the matching profiles  25  and  26  (or  25 ′ and  26 ′) are such as to make a forced coupling between the crank arm  21  and the axle portion  22 . 
     As can be seen in  FIG. 3 , as well as in  FIGS. 5 to 7 , the coupling seat  23  extends in the body of the crank arm  21  axially along the axis X and comprises a shoulder  28  at the end facing in the opposite direction to the center K of the bottom bracket assembly  10 . The shoulder  28  can simply project in the radial sense towards the axis X, or else (in a different embodiment, not illustrated) it can extend up to the same axis X, thus completely closing the seat  23 . The coupling portion  24  comprises a main portion  27  with generatrices substantially parallel to the axis X and a tapered front area  29  both in the peaks and in the channels of the grooved profile. The front area  29  has the function of an insertion guide portion, and it extends for a length L (represented in  FIG. 4 ) in the sense from the axis X, so as to leave a free space  30  between the coupling seat  23  in the crank arm  21  and the coupling portion  24  of the axle portion  22 . The length L is preferably less than or equal to ⅓ the axial extension A of the entire coupling portion  24 , and even more preferably is between ⅙ and ⅓ of A, i.e.—in absolute terms—between 2 and 5 mm. 
     The crank assembly  20  also comprises an annular channel  31 , formed in the coupling seat  23  in a position adjacent to the shoulder  28 , as can be seen in  FIG. 5 . In the embodiments of  FIGS. 6 and 7 , respectively, a channel  31 ′ is formed in the coupling portion  24  opposite the channel  31 , and two further channels  31 ″ are formed in the coupling seat  23 , axially spaced from the shoulder  28  and from the channel  31 . 
     In assembling the crank arm assembly  20 , with reference to  FIGS. 3 and 4 , initially the annular channel  31  of the crank arm  20  is filled with an adhesive material, generically indicated with  50  in the figures. The adhesive material  50  is a setting resin, preferably thermosetting, selected, for example, from an epoxy resin and a phenolic resin, where the former is preferred. According to a first preferred embodiment, the amount of adhesive material  50  applied corresponds exactly to the capacity of the channel  31 , so that a single sealing cord is formed inside the latter. 
     According to a second preferred embodiment, the adhesive material  50  is arranged in the channel  31  in an amount in excess of its capacity. 
     The front guide area  29  of the axle portion  22  is then inserted into the coupling seat  23  of the crank arm  21 , and the axle portion  22  is forced to penetrate into the crank arm  21  applying a suitable insertion force in the axial sense. 
     The front guide area  29  of the axle portion  22  is made to advance in the coupling seat  23  of the crank arm  21  until it abuts against the shoulder  28 . In this step, the adhesive material  50 , if placed in excess, is pushed out from the annular channel  31 , and—due to the mechanical forcing—penetrates between the grooved profile  25  and the grooved profile  26 . 
     At this point the crank arm assembly  20  is taken into conditions such as to cause the setting of the adhesive  50 . In particular, if the adhesive  50  is thermosetting, the crank arm assembly  20  is taken to the setting temperature of the adhesive material itself, and is kept at such a temperature until it is completely solidified. Typical temperature values are between 120° and 180°, for a time of between 10 and 60 minutes. 
     In the aforementioned way, the adhesive  50  with the channels  31  (and possibly  31 ′,  31 ″) contributes to constituting the fastening means of the crank arm  21  to the axle portion  22 . 
     Between the crank arm  21  and the axle portion  22  a gluing chamber is thus formed from the annular channel  31  and from the free space  30 ; in the embodiments of  FIGS. 6 and 7 , the channels  31 ′ and  31 ″ are respectively added. By suitably calibrating the size of the annular channel  31  and of the free space  30  (length L) it is possible to obtain a gluing area that allows the desired extraction force values of the crank arm  21  to be obtained, typically between 30 and 40 kN. 
     It should be noted that preferably the fastening means of the crank arm  20  and of the axle portion  22  comprise a forced coupling in addition to the adhesive material  50 . 
     It should also be noted that in some crank arm assemblies  20 , gaps  51  (purposefully represented substantially enlarged in  FIG. 5 ) can be created between the profile  25  and the profile  26 , due to processing defects or embossing due to inaccurate insertion of the axle portion  22 . In these assemblies, the small sizes of the gaps and the fluidity of the adhesive material before it has set promote penetration into the gaps  51  by capillarity, making it possible to wet the entire coupling area even from one extreme to the other and thus maximizing protection against corrosion, and the attachment effect of the crank arm. 
     It should be noted that in the embodiment illustrated in  FIG. 6 , the channel  31 ′ defines a radially projecting edge  32 ′ that remains enclosed in the adhesive material  50  present in the channels  31  and  31 ′ once set; in this way, in addition to the adhesive effect, there is a mechanical holding effect of the crank arm  21 . 
     The additional channels  31 ′ and  31 ″ are preferably annular. 
     It should also be noted that in the embodiment of  FIG. 7 , the channels  31 ″ can be made on both the coupling portion  24  and the coupling seat  23 , as well as on both of the elements. 
     The additional channels  31 ″ can be one or more than one, as illustrated in  FIG. 7 . The embodiment of  FIG. 10  shows a particular additional channel  3 ′″ in the coupling seat  23 , which is deeper than the grooves of the grooved profile  25  of the coupling seat  23 . Preferably, the additional channel  31 ′″ is closer to the shoulder  28  than to the side wall  60  of the crank arm  21  facing the bicycle&#39;s frame box  11 . A preferred range of distance T is between 1 and 15 mm. In  FIG. 10  the channel  31 ′ is optional. 
     The additional channel  31 ′″ advantageously performs as a chip breaker during the machine operation to obtain the grooved profile  25  of the coupling seat  23 . A preferred machine operation consists of broaching the coupling seat  23  by inserting a tool (not shown) from the side of the side wall  60  and by moving the tool until it reaches the channel  31 . Since the coupling seat  23  is closed by the shoulder  28 , the tool has a limited stroke, and the additional channel  31 ′″ avoids the chip to remain attached to the crank arm inside the channel  31 . This is also useful in case of a completely blind coupling seat. 
     It should also be noted that the crank arms  21  and  41  are made from metal material, such as aluminium or titanium alloys, and that the axle portions  22  are made from steel or light metal alloys.