Patent Publication Number: US-2021162801-A1

Title: Abutment interface between the head of a nipple and the bridge of a wheel rim and spoked bicycle wheel

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Italian Application No. 102019000022500, filed on Nov. 29, 2019 which is incorporated herein by reference as if fully set forth. 
     FIELD OF INVENTION 
     The present invention relates generally to spoked bicycle wheels, and in particular it relates to fixing the spokes to the wheel rim through nipples. 
     BACKGROUND 
     In the entire present description and in the claims, the spatial indications, such as in particular those of radial, axial or circumferential direction, will be given with reference to the rotation axis of the wheel of the bicycle, unless indicated otherwise. 
     It is well known that in spoked bicycle wheels each single spoke is fixed to the rim of the wheel through a respective nipple, which is a component with a stem provided with a threading (normally internal) and an enlarged head. The rim is provided with a plurality of holes in the bridge thereof (or in the lower bridge thereof, in the case of a rim with two or more bridges). The stem of a nipple is inserted in each hole in the bridge from a radially outer direction, while the head remains outside the bridge hole. The stem of the nipple is thus screwed to the end of a spoke. In this way, the nipple provides the hooking of the spoke to the rim and allows the tensioning thereof: by rotating the nipple, indeed, it is possible to screw in or unscrew the spoke with respect to the stem. Often an abutment washer is arranged between the nipple head and the bridge to improve the contact, particularly when the material of the rim is delicate (for example aluminium or composite materials) and it could be damaged by an excessively high pressure exerted by the nipple on a limited area. 
     During tensioning, the nipple should ideally be arranged aligned with the spoke, as a substantial extension thereof. This is normally true, because normally the spoke is arranged in the wheel in a substantially radial direction. 
     The Applicant has, however, observed that if the spoke is not arranged in the radial direction, for example because it is fastened tangentially to a flange of the hub of the wheel, the tensioning of the spoke-nipple set results in a misalignment between the two, due to the unbalanced abutment of the nipple on the bridge. Indeed, the natural abutment of the nipple (with or without washer) is with the stem in the radial direction, perpendicular to the bridge (or rather to the tangent thereof); if, however, the spoke is not in the radial direction, the nipple fastened to it is also not in the radial direction, before tensioning begins; in this position, the stem of the nipple forms two different angles with the direction tangential to the bridge (observing in the axial direction), one less than 90° and one greater than 90°. Proceeding with tensioning, the head of the nipple will tend to press on the bridge more on one side than on the other, in particular more on the side of the angle greater than 90°, thereby tending to take the tensioned nipple back towards a radial position. 
     This deviation of the nipple with respect to the direction of the spoke increases as the tensioning proceeds and results in an anomalous distribution of stresses on the spoke, on the nipple and on the bridge of the rim. In particular, the nipple is subjected to stresses not only in the radial direction but also in the tangential direction; the spoke is also subject not only to traction forces, but also to flexing forces. The consequence of this anomalous distribution of stresses is that the designer is forced to somehow oversize these components, in order to avoid yielding. This, however, results is an increase in weight, particularly undesirable in high-performance bicycles, in particular racing bicycles. 
     It has been proposed to address this drawback by shaping both the head of the nipple and the face of the washer on which it abuts according to spherical surfaces. However, even with this provision the misalignment between spoke and nipple is not avoided. 
     Indeed, it has been observed that in order to obtain the desired result of the alignment between spoke and nipple in the finished wheel, even when the spoke is in a non-radial direction in the wheel, it is important for the coupling between nipple and rim to have two features, apparently contrasting: firstly, to be such as to allow the nipple to be arranged in the direction of the spoke at the start of the tensioning operation; and then, to be such as to prevent movements of the nipple with respect to the rim during tensioning, so that in the finished wheel the nipple is aligned with the spoke. 
     The problem at the basis of the present invention is to allow a coupling between spoke, nipple and bridge in which the alignment between spoke and nipple is maintained during tensioning and thus in the finished wheel, even when the spoke is not arranged in the radial direction. 
     SUMMARY 
     The Applicant has found that providing an abutment interface between a spoke attachment nipple and a bridge of a rim can properly align the tensioned spoke with the rim. A preferred abutment interface includes a first washer with a radially inner face that abuts the bridge and a radially outer face that abuts with a radially inner face of as second washer that has a radially outer face that abuts an enlarged head on the nipple. The faces of two washers are complementarily shaped to allow them to adjust both with respect to each other and with respect to the nipple head. The adjustment takes place during an initial step of the fixing operation of the spoke to the rim and to prevent the washers from making any adjustment movement during a subsequent fixing step of the spoke to the rim during which the nipple will have a tension applied to it through the spoke. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will become clearer from the following description of some preferred embodiments thereof, made with reference to the attached drawings. In such drawings: 
         FIG. 1  is a partial perspective view of a bicycle wheel according to the invention; 
         FIG. 2  is an enlarged section view of a detail of the wheel of  FIG. 1  with an abutment interface according to a first embodiment of the invention, taken according to a plane perpendicular to the axis of the wheel; 
         FIG. 3  is an enlarged section view of the detail of  FIG. 2 , taken along a plane containing the axis of the wheel; 
         FIG. 4  is an exploded view of the wheel of  FIG. 1 , highlighting the abutment interface of  FIGS. 2 and 3 ; 
         FIG. 5  is a further enlarged section view of the abutment interface shown in  FIG. 2 ; 
         FIG. 6  is an enlarged section view of a wheel with an abutment interface according to a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to an abutment interface for controlling the attachment angle between a spoke and a spoke nipple in rim of a bicycle wheel. 
     In general, the invention controls the abutment interface between a nipple head and a bridge of a rim of a bicycle wheel has complementary washers. A first washer has a radially inner first face for abutting on the bridge and a radially outer second face. A second washer has a radially inner first face abutting on the second face of the first washer and a radially outer second face for abutting on the nipple head. The faces of the washers are shaped to allow the washers to make adjustment movements both with respect to each other and with respect to the nipple, during an initial step of the fixing operation of the spoke to the rim, and vice-versa to prevent the washers from making any adjustment movement both with respect to one another and with respect to the nipple during a subsequent fixing step of the spoke to the rim. 
     In a preferred embodiment of the invention, the aforementioned adjustment features are obtained by providing that the abutment between the second face of the first washer and the first face of the second washer takes place along a first abutment track and the abutment between the second face of the second washer and the head of the nipple takes place along a second abutment track, wherein the first and/or the second abutment track have an extension of less than 15%, and preferably less than 10%, of the area of the first face and of the area of the second face of the second washer, respectively. The measurement of the extension of the abutment tracks is meant to be carried out before the tensioning of the spoke, since tensioning naturally implies an increase in the extension of the abutment tracks, due to the deformability of the materials. With the aforementioned values, at least one among the contact between the two washers and the contact between the second washer and the nipple takes place over a limited area, much less than the area of the faces of the second washer; this allows both great initial freedom of movement, when tension is not yet applied, and subsequent substantial locking, when the tension applied on these small areas results in high contact pressures and thus high friction. 
     Preferably, both the first and the second abutment tracks have limited extension, so that the two aforementioned features (initial freedom of movement and prevention of movement under tension) occur singularly both between the two washers themselves, and between the second washer and the nipple. 
     Thanks to this abutment, in the initial step of mounting when the tensioning is zero or minimal, the nipple and the two washers are free to take a position also in a non-radial direction of the wheel, guided by the coupling of the nipple with the spoke. However, as soon as the tension becomes substantial, the abutment tracks having limited extension ensure that the high pressure that is immediately established both between the washers and between the second washer and the nipple prevents any further mutual movement, despite the natural tendency to be oriented in the radial direction due to the tension applied. As the tension progressively increases (and therefore the tendency of the nipple to move towards the radial direction increases), the pressure at the abutment tracks becomes so high as to prevent any movement. 
     Preferably, the first and/or the second abutment tracks are lines, i.e. they have substantially zero width, which maximizes the contact pressure. Of course, this geometric condition refers to the initial conditions, before tensioning, and is lost as the tension applied increases, due to the deformation of the materials. 
     Preferably, the first face of the second washer is delimited by a first inner circumference and a first outer circumference and the second face of the second washer is delimited by a second inner circumference and a second outer circumference, whereby the first abutment track coincides with the first outer circumference and the second abutment track coincides with the second inner circumference. In this way, the feature of the abutment tracks of minimal width is obtained in a constructively simple manner. 
     Preferably, the first and the second face of the second washer are conical or spherical. These surfaces are relatively simple to obtain and ensure the desired results in terms of abutment. 
     Preferably, the first face of the second washer is conical. Preferably, the second face of the second washer is conical. Preferably, the second face of the first washer is spherical. These features of shape, singularly or preferably all together, facilitate the onset of the conditions of initial freedom of movement and prevention of movement under tension. 
     Preferably, the second washer is conical, with vertex facing towards the first washer and angle at the vertex comprised between 70° and 120°, preferably between 85° and 105°, more preferably equal to about 95°. This shape promotes the aforementioned abutment conditions. 
     In another aspect, the invention relates to a bicycle wheel comprising a rim connected to a hub by a plurality of spokes having an abutment interface between the nipple head and the bridge of the rim. The abutment interface has a first washer with a radially inner first face abutting on the bridge and a radially outer second face for abutment with a second washer, with a radially inner first face abutting on the second face of the first washer and a radially outer second face abutting on the head of the nipple. The faces of the washers are shaped to allow the washers to make adjustment movements both with respect to each other and with respect to the nipple, during an initial step of the fixing operation of the spoke to the rim, and vice-versa to prevent the washers from making any adjustment movement both with respect to one another and with respect to the nipple, during a subsequent fixing step of the spoke to the rim. 
     Preferably, the first washer has an opening of a width that would allow the head of the nipple to pass, in the absence of the second washer. This large width of the opening of the first washer facilitates the freedom of movement between the two washers and thus facilitates the alignment, at the start of tensioning of the spoke with the nipple. 
     Preferably, the head of the nipple has a spherical surface facing towards the second face of the second washer. The spherical surface of the head of the nipple promotes the abutment conditions described above, making it easier to limit the extension of the second abutment track. Preferably, the spherical surface of the head of the nipple has a radius comprised between 2 and 4 mm, more preferably equal to about 3 mm. 
     Preferably, the stem of the nipple is joined to the head of the nipple according to a joining angle comprised between 25° and 60°, more preferably between 30° and 50°. This angle is intended as the angle formed by the axis of the stem of the nipple with a plane tangent to the head of the nipple in the point in which the head of the nipple is joined to the stem of the nipple. The aforementioned values make it possible to obtain the desired abutment conditions, particularly in the case in which the second washer has the features of conicity indicated above. 
     Preferably, at least one of the spokes has orientation according to a non-radial direction with respect to the rotation axis of the wheel. It is, indeed, precisely the spokes with such a non-radial inclination that get the maximum benefit from the invention. 
     Preferably, the bridge of the rim is flat in the axial direction of the wheel. In this way, the construction of the rim is particularly simple; in particular, it does not require special processing to form shaped seats for the heads of the nipples. Moreover, thanks to the invention, a precise and balanced hooking of the head of the nipple is equally ensured, without there being misalignments between spoke and stem of the nipple during tensioning. 
     With reference to the figures, there is shown a bicycle wheel  10 , comprising a rim  11  connected to a hub  12  by means of spokes  13  under tension; X is used to indicate the rotation axis of the wheel  10 . As illustrated in  FIG. 1 , The spokes  13  have a head  14  with which they are fastened to the hub  12  and a threaded end  15  opposite to the head  14 , with which they are hooked to a bridge  16  of the rim  11  through a nipple  20 . The bridge  16  is flat in the axial direction, i.e. it extends on a cylindrical surface coaxial to the axis X. 
     Each nipple  20  comprises a stem  21  extending along an axis Y and a head  22  projecting outwardly with respect to the stem  21 . The stem  21  of the nipple  20  is inserted in a hole  17  formed in the bridge  16  and projects from it in the radial direction towards the axis X of the wheel  10 , whereas the head  22  remains in radially outer position with respect to the bridge  16 . A threaded axial hole  23 , engaged with the threaded end  15  of one of the spokes  13 , is formed in the stem  21 ; the spoke  13  coupled with the nipple  20  is thus aligned along the axis Y. The nipple  20  also comprises a first handling portion  24  with non-round section (for example, hexagonal), formed externally on the stem  21 , and a second handling portion  25  with non-round section (for example, square), formed externally on the head  22 ; the two handling portions  24  and  25  make it possible to rotate the nipple  20  with suitable keys (not shown) so as to screw in or unscrew the nipple  20  with respect to the spoke  13 , thus obtaining a change in the length of the spoke  13 —nipple  20  set and thus a change in the tension of such a set in the rim  11 . The handling portion  24  or the handling portion  25  is used depending on the accessibility, i.e. depending on the shape of the rim  11 . The head  22  of the nipple  20  has a convex spherical shape towards the stem  21 . 
     In the illustrated wheel  10  of  FIG. 1 , some of the spokes  13  have substantially radial orientation, others have markedly non-radial orientation; when seen from the axial direction of the wheel  10 , the spokes  13  with substantially radial orientation form substantially right angles with the bridge  16  (i.e. with the tangent T to the bridge  16 ), whereas the spokes  13  with markedly non-radial orientation form an acute angle α and an obtuse angle ß with the bridge  16  (see  FIG. 2 ). 
     Between the head  22  of the nipple  20  and the bridge  16  an abutment interface  30  is arranged, which comprises a first annular washer  31  and a second annular washer  41 . The first washer  31  is in contact with the bridge  16 , whereas the second washer  41  is in contact with the nipple  20 . 
     With reference to  FIGS. 2-5 , the first washer  31  has a radially inner first face  32 , which rests on the bridge  16 , and a radially outer second face  33 , which rests against the second washer  41 . The first face  32  is substantially flat, whereas the second face  33  is concave, with spherical shape. Centrally, the first washer  31  has a very wide opening  39 : the head  22  of the nipple  20  could easily pass through it, if not held by the second washer  41 , as will be seen hereinafter. 
     The second washer  41  has a radially inner first face  42 , which rests on the first washer  31 , and a radially outer second face  43 , which rests against the spherical head  22  of the nipple  20 . The faces  42  and  43  are both conical, with vertex facing towards the first washer  31 , i.e. towards the axis X of the wheel  10 . The angle at the vertex of the cone of the two faces  42  and  43  is comprised between 70° and 120°, preferably between 85° and 105°; in particular and more preferably, such an angle is about 95°. It should be noted that this angle at the vertex is not represented graphically in the figures, so as not to complicate the figures with further lines. 
     The first face  42  of the second washer  41  is delimited by a first inner circumference  44  and by a first outer circumference  45 ; the second face  43  of the second washer  41  is delimited by a second inner circumference  46  and by a second outer circumference  47 . The inner circumferences  44  and  46  are wide enough to allow the stem  21  of the nipple  20  to pass, but not the head  22  of the nipple  20 . 
     Between the second face  33  of the first washer  31  and the first face  42  of the second washer  41  a first abutment track is defined, which ideally coincides with the first outer circumference  45  of the first face  42  of the second washer  41 . Between the second face  43  of the second washer  41  and the head  22  of the nipple  20  a second abutment track is defined, which ideally coincides with the second inner circumference  46  of the second face  43  of the second washer  41 . In reality, the aforementioned abutment tracks can comprise a narrow band around the respective circumferences  45  and  46 , provided that they are indeed narrow, in particular so that the area of the abutment tracks does not exceed 15% (and preferably 10%) of the area of the respective faces  42  and  43  of the second washer  41 . Of course, what has just been stated refers to the initial mounting conditions of the wheel  10 , i.e. before a substantial tension is applied between the spoke  13  and the nipple  20 ; under the traction stress due to tensioning, the abutment tracks tend clearly to widen due to the deformability of the materials. 
     In the construction of the wheel  10 , the mounting of every spoke  13  (whatever the inclination thereof with respect to the radial direction) takes place by firstly fastening the spoke  13  with its head  14  to the hub  12 . Thereafter, a nipple  20  is inserted with its stem  21  in the hole  17  of the bridge  16 , interposing the abutment interface  30 , i.e. the two washers  31  and  32 ; the first washer  31  is placed with its first face  32  against the bridge  16 , the second washer  32  with its first face  42  against the second face  33  of the first washer  31 . It should be noted that the width of the opening  39  of the first washer  31  would not be such as to hold the head  21  of the nipple  20 , which would easily pass through it if the second washer  41  was not present. 
     By rotating the nipple  20 , it is thus possible to screw it to the threaded end  15  of the spoke  13 , until the contact is established at the abutment tracks  45  and  46 . In this condition, the freedom of movement ensured by the washers  31  and  41  allows the nipple  20  to be arranged easily as an extension of the spoke  13 , so that the assembly of spoke  13  and nipple  20  is perfectly aligned according to the axis Y, even if it does not coincide with a radial direction of the wheel  10 . 
     By further rotating the nipple  20 , there is thus progressive tensioning of the nipple  20  at the spoke  13 , so that they exert a traction between the rim  11  and the hub  12 . This tensioning, thanks to the very limited extension of the abutment tracks  45  and  46 , quickly causes a high contact pressure between the parts, in particular between the nipple  20  and the second washer  41  and between the latter and the first washer  31 . The friction that is produced due to this high pressure prevents any mutual movement of the washers  31 ,  41  and of the nipple  20 , ensuring that the alignment of the nipple  20  and of the spoke  13  along the axis Y is maintained, even if such an axis Y is not oriented radially in the wheel  10 , see  FIG. 2 . Consequently, the spoke  13  is not subjected to bending stress and the nipple  20  is not subjected to stresses in the tangential direction. 
       FIG. 6  shows a wheel  110  according to a second embodiment of the invention; elements of the wheel  110  the same as those of the wheel  10  are indicated by the same reference numerals and are not described, whereas elements corresponding generally but that are in some way different are indicated with reference numerals increased by 100 and are described by comparison with the elements of the wheel  10 . 
     In the wheel  110 , the nipples  120  differ from the nipples  20  because their head  122  has a conical shape instead of spherical. The abutment interface  130  differs from the interface  30  for the shape of the second face of the first washer. More precisely, the first washer  131  has its first face  132  flat (like the face  32  of the washer  31 ), whereas its second face  133  has a substantially toric shape. The second washer, on the other hand, is substantially the same as the washer  41 . 
     Consequently, as can be seen in  FIG. 6 , the first abutment track is defined roughly in an intermediate annular area in the first face  42  of the second washer  41 , whereas the second abutment track is defined on an inner area of the second face  43  of the second washer  41 . The first abutment track—even if different from that of the interface  30 —still remains narrow (preferably with an area of less than 15% of the area of the first face  42  of the second washer  41 , more preferably less than 10% thereof); the second abutment track, on the other hand, has a wider extension, but still less than 40%. For this reason, the abutment interface  130  is less suitable where the inclination of the spoke with respect to the radial direction is very high. 
     The construction of the wheel  110  takes place in the same way already described for the wheel  10 . 
     The conditions described above, whereby the first abutment track between the first washer and the second washer and/or the second abutment track between the second washer and the nipple have limited extension, can also be obtained with other combinations of shapes of the faces of the washers, as well as of the nipple. 
     An embodiment that is not illustrated could, for example, provide for a nipple with conical head, a conical second washer (with two conical faces) and a first washer with the second face also conical. In this case, the abutment tracks having limited extension are obtained by selecting conical shapes with different angles at the vertex: for example, an angle at the vertex of the conical second washer that is markedly greater than the angle at the vertex of the nipple and of the second face of the first washer. 
     Another embodiment that is not illustrated could, for example, be similar to the wheel  10 , with the sole difference that the second face of the first washer is not spherical but rather conical or toric. 
     Another embodiment could, for example, be similar to the wheel  110 , with the sole difference that the second face of the first washer is not toric, but rather spherical, with concavity facing towards the second washer. 
     Another embodiment could, for example, be similar to the wheel  10  or to the wheel  110 , with the nipple conical instead of spherical; in this case, the second washer (conical) has a different angle at the vertex, in particular greater, with respect to the nipple. 
     Other embodiments could, for example, provide that one or other of the faces of the second washer be spherical or toric. 
     In the choice of the shape of the nipple, of the two faces of the second washer and of the second face of the first washer there is thus a certain freedom, provided that dimensional values (angles at the vertex of the conical surfaces, radii of curvature of the spherical or toric surfaces) are chosen that make it possible to have the first abutment track between the first washer and the second washer and/or the second abutment track between the second washer and the nipple with limited extension; the advantage begins to be visible if the extension is less than 40%, without departing from the indicated optimal values.