FR2578219A1 - CRANKSET FOR A BICYCLE WITH A CAVITY IN ITS MIDDLE PART - Google Patents

Abstract

A BICYCLE CRANKSHAFT SHAPES, IN ITS INTERMEDIATE PART, A CAVITY WITH A AREA OF SECTION GREATER THAN THOSE OF THREADED THREADS AT ITS ENDS TO RECEIVE THE SCREWS LOCKING THE PEDAL CRANKS. THIS SHAFT 11 IS MADE IN STEEL BY SUBSEQUENT COLD WIPING AND FORGING.

Description

The present invention relates to a bottom bracket axle for

  sport and competition bicycles, with

  weight, mechanical strength and improved rigidity

  and that we can get much cheaper than the known type of crankset pins in use today.

  The bottom bracket is the body of a bicycle which

  links the two pedal cranks and on which the cyclist's weight and muscular effort bear. This member therefore undergoes cyclically bending, shearing and

  considerable torsion, which currently requires to have re-

  course, for the manufacture of this axis, to very robust materials such as case hardening or quenching steel or tempering or special steels (even titanium alloys) - and to

  different types of processing, such as turning

  shot from a drawn bar, forging or cold forging, standard

  followed by a finishing operation.

  Considering that, as we know, we get more out of the material - in terms of the advantages

  weight, mechanical strength and rigidity - in displacement

  cutting the material even while moving away from the neutral axis and that, in the axes of current cranksets, one obtains only this result by drilling on a diameter at most equal to that

  screws blocking the pedal cranks, we thought of exceeding

  ser this limit by realizing the axis by the technique of impact spinning, known per se but never yet applied

  to the manufacture of these kinds of products.

  This technique makes it possible to obtain, according to the present invention, a crankset axle for a bicycle that is lighter and, simultaneously, more rigid and more robust than those according to the

prior art.

  Said bottom bracket axle is essentially characterized in that it has, in its middle part, a cavity with a cross-sectional area larger than that of the internal threads

  at its ends to receive the crank locking screws

  those of the pedal, and therefore a larger cross-sectional area than that of the current lightening holes of the known bottom bracket axles. Said axis is made of steel by spinning and subsequent cold forging and, more particularly, by cold spinning

  a steel billet, pushed until a blank is obtained

  rod-shaped che, and by subsequent forging making

  sorting said blank in a moving matrix.

  We can realize said axis in monolithic form or obtain by the above process two elements that are welded

  then to each other, or to a tubular element

  common manufacturing intermediary.

  The axis according to the invention is furthermore preferably

  rence so that its ends are prismatic, pre-

  feeling an octagonal and not square section, which increases

  advantageously the resistant section of the ends.

  The invention will now be described in more detail, simply by way of example, with reference to the accompanying drawings, in which: - Figure 1 illustrates the spinning of a monolithic bottom bracket axle according to the invention;

  - Figure 2 illustrates the forging of the axis according to fig-

  gure 1; - Figures 2A and 2B are enlarged sectional and side views of one of the octagonal prismatic ends of the axis according to Figures 1 and 2; - Figure 3 is a partial sectional view of the axis obtained by the technique according to Figures 1 and 2; and - Figures 4 and 5 are similar views of bottom bracket axles according to two variants of the invention, respectively produced in two parts and in three parts, by techniques similar to those used for the monolithic axis according

Figure 3.

  The pedal axis of FIG. 3, according to the invention,

  is obtained by executing the two successive operations pre-

  seen in Figures 1 and 2: the starting material 1 - which

  comes roughly in the form of a steel billet -

  is first deformed by pushing back through a die

  2, under the effect of a punch 3 and a counter-punch 4 pre-

  feeling an interior cavity or imprint 5. It is sensitive to

  of a spinning treatment which begins as shown on the left in Figure 1 and ends as shown on the right

  of this same figure. The draft obtained at the end of this pre-

  first operation is presented as a cylindrical rod 6,

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  having a profiled end 7 corresponding in part to the profile of the axis to be manufactured, and the other end of which constitutes a thickened crown 8, from which will be taken

  the material deformed during the second stage of the process.

  During this second stage, the blank obtained in the first stage is introduced (as indicated on the left of the

  Figure 2) in an appropriate matrix 9. The crown 8 sail-

  lant at one of its ends is then deformed (on the right of figure 2) through a moving matrix 10 in sight

  obtaining the axis 11, shown finished in FIG. 3.

  When the matrix 10 recedes, the axis 11 is expelled by a

ejector 12.

  Then, we execute on the outline of axis 11 the operations

  necessary to obtain the finished product.

  We see immediately, from Figure 3, that the cavity

  mean of the axis thus obtained has a positive cross-sectional area-

  Tment greater than that of the tapped holes at the ends to receive the screws blocking the pedal cranks (and therefore greater than the section of current lightening holes of known bottom bracket axles). We also see, from the same figure, how the particular geometry of the axis It allows to optimize the distribution in the material of the stresses undergone in operation, in order to reach

  the objectives of lightness and rigidity.

  The fact that these objectives are fully achieved - which results in considerable advantages - is confirmed by torsion tests carried out on crankset axles of

  current type and on axes of the type according to the invention, fa-

  briqued by the applicant, these tests being summarized in the following table: Table next page

BOARD

  TORSION TEST ON CRANKSETS FIXED AT AN END

  AND SUBJECT TO THE OTHER END AT A CONSTANT MOMENT

  (170 mm arm) Type of axis Weight Load Offset from (g) (newtons) point of force application (mm) to) Classic axis with cavity having a cross-sectional area equal to that

ex-holes

extremity 141.44 1450 16.65

B) Axis according to the in-

cavity having an area

upper section

higher than that

ex-holes

  end 138.53 1450 13.27 As can be seen from this table, a load

  equal standard generates, in a crankset axis according to the

  vention, a torsional force about 20% lower than that generated in a current axis, the weight of the second axis being

  addition about 2 grams lower than the first.

  It should also be noted that, by its particular geometry, the axle according to the invention lends itself better to drilling, the latter no longer having to be carried out over its entire length - as in the common bottom bracket axles - but only at both ends, from which come great advantages from the point of view of realization and reduction of the cost. Other advantages arise from the fact that the same blank can be used to obtain axes of various standard sizes, in

  changing only the tooling model.

  The axis according to FIG. 3 is in the defined shaping state.

  tif, its ends 7 being of octagonal section and not square - see details of Figures 2A and 2B - which improves its resistance. The hatched areas in FIG. 2A very clearly indicate how this form of the ends of the axis makes it possible to notably increase the resistant section compared to the current square ends. In addition, the concrete shape of the axle ends also improves contact

with pedal cranks.

  Figures 4 and 5 respectively represent - as we said - an axis 13 according to the invention in two welded parts 1 '

  one to the other and an axis 14 according to the invention in three parts

  these welded together: these two versions build

  tives constitute a variant to the previous version and differ in that it is necessary to provide one or more stages

welding.

  In the case of axis 13 - made of two elements 15 and 16, connected to each other by a weld 17 (Figure 4) - we proceed to the spinning for each of said elements, respecting in exactly the same way that for the monolithic axis 11,

  except that the blank does not have the cost

  protruding column 8. The two elements 15 and 16 are then joined together by the weld 17, so as to obtain the axle 13 ready for

  be trimmed by machine tools.

  The advantages of this achievement lie in the re-

  reduction of the cost price of the material and in the reduction

  handling costs of the parts before their assembly.

  In addition, the parts thus manufactured have, from the outset, better dimensional accuracy and a higher degree of finish than the monolithic axis. In addition, standardization

  of various lengths is easier to operate.

  In the case of axis 14 - formed of three elements 18, 19 and 20, connected to each other by two welds 21 and 22 (Figure 5) - the process is even simpler than in the previous cases. Indeed, the two extreme parts 18, 19, cold forged with great precision and a high degree of finish, are obtained by means of a single matrix (in the sense that, in this case too, we take advantage of the perfect symmetry of these parts), while the middle part 20 is obtained from industrial tube, in a material of the same type as that used to obtain the blanks 18 and 19 and / or, in any case, suitable for the operations of welding which must be carried out at 21 and 22 to connect the three elements of the axis

bottom bracket.

  This solution offers a large number of advantages: in addition to those listed for axis 13 welded in two parts, there appears to be an additional cost reduction resulting from the fact that the

  middle part 20 of the axis consists of industrial tube

  triel. In addition, you can change the section of the tube, depending on the use to be made of the bottom bracket.

  The invention also covers, of course, other variations.

  tes of the bicycle bottom bracket, of which only

  certain exemplary embodiments have been described and illustrated.

  For example, the scope of the invention also covers bottom bracket axles in which the middle part has a cavity and the end parts are free of holes and have

  other means of blocking the pedal cranks.

Claims (6)

  1. Bottom bracket for a bicycle, characterized in that it has, in its middle part, a cavity with an area of   section larger than that of the threads formed at its ex-   hoppers to receive the screws blocking the pedal cranks. 2. Bottom bracket according to claim 1, characterized in that it is made of steel by spinning and forging by subsequent shock.   3. bottom bracket according to claim 1, obtained by   cold spinning of a steel billet, pushed until   tion of a rod-shaped blank (6) and by subsequent forging   laughing making this blank penetrate a soft matrix   vement. 4. Bottom bracket according to claim 1, characterized   in that it is obtained in the form of a monolithic body (11).   5. Bottom bracket according to claim 1, characterized in that it is obtained in the form of a body in two elements (15, 16) or in three elements (18, 19, 20) spun in forges, connected by welding.   6, bottom bracket axle according to claim 1, characterized   in that it has ends (7) of orthogonal section.