Abstract:
The invention relates to a method for manufacturing an arm ( 16 ) in composite material, this arm comprising a main body incorporating a bearing ( 22 ) designed to receive a shaft passing through it transversely, this method comprising the steps of:
       manufacturing a hub ( 11 ) by winding reinforcing fibres around a generally tubular support ( 12 );   manufacturing at least one sleeve ( 14 );   attaching the hub ( 11 ) to one end of the sleeve ( 14 ) and transversely to the sleeve ( 14 ) in order to form a mandrel;   applying one or more layers of braided reinforcing fibres ( 21 ) around this mandrel with a machine for braiding reinforcing fibres ( 19 );   injecting and polymerizing resin into the layer or layers of braided fibres ( 21 ).       
 
     The invention applies notably to an arm forming an undercarriage rocker arm of an aircraft.

Description:
[0001]    The invention relates to an arm forming a structural element of an aircraft undercarriage, such as a rocker arm, that is to say comprising a main body incorporating a bearing designed to receive a rotating shaft, or a fixed shaft forming an axle, oriented transversely relative to the main direction of this main body. 
       BACKGROUND OF THE INVENTION 
       [0002]    A known undercarriage rocker arm that is shown schematically in  FIG. 1  indicated by reference numeral  1  takes the form of a tubular part or an arm extending in a main direction indicated by AP. 
         [0003]    This arm comprises a main portion  2  extending between two ends  3  and  4  and having a circular section that is approximately constant in its central region. 
         [0004]    As can be seen in  FIG. 1 , the front end  3  of this arm is designed to receive a shaft oriented transversely in the direction AT that is in this instance perpendicular to the direction AP. This end therefore forms a portion forming an interface or bearing formed in two bosses protruding transversely from the outer face of the main body  2 . 
         [0005]    Each boss is pierced and bored in the direction AT, so as to form the two bearing surfaces of the bearing in order to engage a mechanical shaft passing transversely through the main body of the arm. 
         [0006]    Similarly, the rear end also comprises an interface forming a generally similar bearing which is designed to receive another transverse shaft not shown. In addition, this rocker arm also comprises an intermediate crevice  8  situated between its two ends and protruding radially from the outer face of the main body. 
         [0007]    Because of the complex shape of the bearings of such a rocker arm that can be seen in  FIG. 1  and because of the considerable mechanical strength that is expected of it, the whole rocker arm is usually manufactured of high strength steel by machining. 
         [0008]    The bosses  6  and  7  in which the bearings are made are determinant in that they constitute local extra thicknesses of material, which is indispensible for ensuring that the forces applied by the mechanical shaft on the rocker arm body do not give rise to concentrations of stresses that are too great in the rocker arm. 
         [0009]    Therefore, in general, the structural elements of the rocker arm or a similar type require the production of extra thicknesses of material at their interfaces with other parts in order to limit the phenomenon of stress concentration that is likely to cause incipient cracks. 
         [0010]    In the case of an undercarriage rocker arm like that of  FIG. 1 , each bearing receives a shaft that is in fact attached relative to the rocker arm and that forms an axle carrying for example two wheels situated on either side of this rocker arm. 
         [0011]    The problem that arises is similar in the case of an arm comprising a bearing receiving a rotary shaft, because the question of concentration of stresses at the bearing remains determinant with respect to the dimensioning of such an arm. 
       OBJECT OF THE INVENTION 
       [0012]    The object of the invention is to propose a solution for manufacturing in composite material an arm comprising a bearing designed to receive a mechanical shaft passing through this arm transversely. 
       SUMMARY OF THE INVENTION 
       [0013]    Accordingly, the subject of the invention is a method for manufacturing an arm in composite material comprising at least one bearing designed to receive a fixed or rotating shaft passing through the arm transversely, this method comprising the steps of:
       manufacturing at least one hub by winding reinforcing fibres around a generally tubular support;   manufacturing at least one sleeve;   manufacturing a mandrel by attaching each hub to at least one sleeve end so that each hub extends transversely to each sleeve;   applying one or more layers of braided reinforcing fibres around this mandrel and over its whole length with a machine for braiding reinforcing fibres;   injecting and polymerizing resin into the layer or layers of braided fibres and optionally into the wound fibre or fibres of the hub in order to establish a cohesion rigidly binding at least the layers of braided fibres with the hub that they surround;   machining the layers of braided reinforcing fibres at each end of the generally tubular support in order to clear each end of this support.       
 
         [0020]    With this solution, the wound hub makes it possible to produce an extra thickness of material that is sufficient to limit the concentrations of stresses in the zones of absorbing forces, and to obtain an optimal cohesion between the body of the arm formed by these layers and the hub. 
         [0021]    The invention also relates to a method as defined above in which each sleeve is manufactured with pieces of fabric of reinforcing fibres preimpregnated with resin, in which the reinforcing fibres wound around the generally tubular support are also preimpregnated with resin, and in which the mandrel is prepolymerized before application of the layers of braided reinforcing fibres. 
         [0022]    The invention also relates to a method as defined above in which the reinforcing fibres are wound around the generally tubular support so as to form a hub having a generally spherical outer shape. 
         [0023]    The invention also relates to a method as defined above in which the generally tubular support has a larger section in its central portion than at its ends. 
         [0024]    The invention also relates to a method as defined above in which each sleeve end is attached to the hub by bonding. 
         [0025]    The invention also relates to a method as defined above, in which each sleeve has an end having a flared shape in order to closely follow the outer shape of the hub to which this end is attached. 
         [0026]    The invention also relates to a method as defined above, in which the hub is situated at one end of the mandrel. 
         [0027]    The invention also relates to a method as described above in which the mandrel is manufactured by assembling to the hub two sleeves extending on either side of the hub. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0028]      FIG. 1  is an overview in perspective of a known rocker arm manufactured in high-strength steel; 
           [0029]      FIG. 2  is a view showing in perspective a wound hub according to the invention shown on its own; 
           [0030]      FIG. 3  is a view in section of the wound hub according to the invention shown on its own; 
           [0031]      FIG. 4  is a view in perspective showing an end of the mandrel manufactured according to the invention; 
           [0032]      FIG. 5  is a view in perspective illustrating schematically a braiding machine; 
           [0033]      FIG. 6  is a view in perspective showing one end of the rocker arm incorporating a bearing while being manufactured according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    The basic idea of the invention is to manufacture a hub by winding so as to form an extra thickness of composite material at the interfaces of the future part, to assemble each hub to a sleeve in order to form a mandrel about which layers of braided fibres are subsequently applied. The layers of reinforcing fibres are thus rigidly secured to the hub after injection and polymerization of resin in these layers and at the junction of these layers with the hub. 
         [0035]    The hub, which is shown on its own in  FIG. 2 , indicated by reference numeral  11 , is manufactured from a generally tubular support  12 , extending along an axis marked in this instance AT, about which reinforcing fibres are wound. 
         [0036]    The fibres may take the form of strands, the form of a strip of woven fibres, or another form and they may be impregnated with resin or not impregnated. They are wound about the outer face of the support  12  so as to form a hub having a generally spherical outer shape in the middle of the hub. 
         [0037]    This can be obtained with a support  12  formed by a portion of tube of constant section, by winding a greater quantity of fibres around the central region of this tube than around its ends. 
         [0038]    But the generally tubular support  12  may also have a changing section which is greater in its central region than at its ends, as illustrated in  FIG. 3 , in which the support  12  has in its central region an approximately spherical outer shape. 
         [0039]    The winding of the fibres  13  can then be optimized to have a greater thickness at the ends of the tube because they are subjected to the highest stresses in operation, and have a lesser thickness in the central region which is less highly stressed from the mechanical point of view. 
         [0040]    As shown schematically in  FIG. 3 , it is possible to obtain a thickness of fibres that differs from one region to the other along the axis AT of the tube, by modifying the angle of winding of the fibres  13  during the winding operation. Thus, in the example of  FIG. 3 , the angle of winding is small at the ends in order to form a considerable thickness, and it is great in the central region in order to form a lesser fibre thickness. 
         [0041]    This can be obtained both when the fibres take the form of a directly wound strand, and when these fibres take the form of a woven ribbon or a strip that is then wound around the support  12 . 
         [0042]    Thus, as can be seen in  FIG. 2 , the hub  11  formed by the tube and the reinforcing fibres that surround it, indicated here by reference numeral  13 , has a general shape approaching that of a sphere traversed by a hole which is delimited by the inner face of the tube  12 . 
         [0043]    This hub corresponds to the body of the bearing or diffusing element incorporated into the arm, and it forms the extra thickness of material making it possible to limit the effect of stress concentration induced by the forces that are applied to the arm by the mechanical shaft passing through the bearing. 
         [0044]    The tube  12  is for example manufactured with reinforcing fibres taking the form of a fabric preimpregnated with resin, which is applied to a cylindrical part so as to form the tube shape. The tube thus formed is prepolymerized so as to give it a sufficient rigidity to be manipulated and to wind the reinforcing fibres  13 . 
         [0045]    As shown in  FIG. 4 , the hub  11  is then attached to one end of a sleeve  14  so that the tube  12  of the hub extends transversely to this sleeve  14 , this assembly being produced by bonding with resin. 
         [0046]    This operation can be carried out with an autoclave, for example in two portions, delimiting an inner shape corresponding to the outer shape of the mandrel. The operation then consists in applying, in the semicylindrical region of the autoclave, layers of fabric of preimpregnated reinforcing fibres in order to form the sleeve. 
         [0047]    The hub  11  is then installed in the corresponding recess of the autoclave, adhesive then being able to be placed in the zones of junction in order to ensure a bonding of the hub  11  at the end of each half-sleeve. A film is then applied to the inner face of the sleeve before establishing a vacuum in order to flatten the wall of this sleeve  14  against the corresponding faces of the autoclave. 
         [0048]    A heating cycle is then begun in order to prepolymerize the impregnated resin in the layers  13  forming the hub and in the layers forming the sleeve  14 . This heating cycle is adjusted to ensure a polymerization of the resin that is sufficient to give the mandrel  15  formed by the hub  11  and the sleeve  14  a sufficient mechanical strength to be handled for the purpose notably of applying to the outer face of this mandrel several layers of braided reinforcing fibres. 
         [0049]    As can be seen in  FIG. 4 , the sleeve  14  has a generally tubular shape, but its end is advantageously designed to be flared so as to closely follow the approximately spherical outer shape of the hub  11  in the region in which it is secured to the end of the sleeve  14 . 
         [0050]    Other solutions can be applied to form the mandrel. For example, the sleeve  14  and the hub  11  may be manufactured and prepolymerized separately, before securing the end of the sleeve  14  to the hub  11  simply by bonding. 
         [0051]    When the whole of the mandrel has been manufactured, a sealing test is advantageously carried out so as to ensure that it cannot traversed by resin injected around this mandrel, during a subsequent operation described below. 
         [0052]    Once the whole mandrel  15  is formed and sufficiently rigid, several layers of braided reinforcing fibres are applied successively all around this mandrel and over the whole of its length by means of a braiding machine. 
         [0053]    As shown in  FIG. 5 , the mandrel  15  is then installed in the braiding machine  17  which essentially comprises a ring  18  supporting at its rear face a series of fibre windings such as carbon fibres, supported by movable supports that can rotate relative to the ring. These fibres  19  join together in a region called the braiding point which is situated substantially on the axis AP while being offset along this axis relative to the plane of the supporting ring  18 . 
         [0054]    In the example of  FIG. 5 , the supporting ring  18  is centred on the axis AP, and extends along a plane normal to this axis. When the braiding cycle is begun, the mandrel  15  is moved along the axis AP relative to the supporting ring  18 , which causes the braiding of a boot of fibres on the outer face of the mandrel  14 . 
         [0055]    Several passes are thus made to form several layers of braided fibres surrounding the mandrel  15  over the whole of its length, that is to say around the sleeve and around the hub, each layer having a substantially constant thickness. 
         [0056]    Once the various layers of braided fibres have been applied, the part thus formed, which therefore comprises the mandrel surrounded by the various fibre layers, is placed in a mould such as a mould in two portions that are symmetrical with one another relative to a parting line. Each portion then comprises a semicylindrical portion corresponding to one half of the sleeve, and terminating in a recess in which one half of the hub  11  is housed. 
         [0057]    The resin is then injected so as to completely impregnate the various layers of braided fibres and optionally the wound fibres of the hub, until it reaches the outer faces of the support  12  and of the sleeve  14  so as to ensure the best possible cohesion between the mandrel and these layers, in particular at the hub. This gives an optimal transmission of the forces applied to the hub  11 , to the peripheral layers of braided fibres forming the body of the arm. 
         [0058]    The sealing of the mandrel mentioned above ensures that the injected resin cannot penetrate the inside of the sleeve that is provided to be hollow in order to optimize the weight of the assembly. This seal is provided by the tubular support  12  and by the sleeve  14 , the ends of the sleeve advantageously having been closed off before assembly with the hub  11 . 
         [0059]    After injection of the resin, the mould is controlled to carry out a curing cycle which ensures on the one hand the complete curing of the layers of braided composite material  21  surrounding the mandrel and which terminates moreover in the curing of the elements forming the mandrel, that is to say the sleeve and the hub. 
         [0060]    When the curing is complete, the hub and the layers of braided reinforcing fibres with the resin that binds the assembly form the main structure of the arm or rocker arm. The rough part thus obtained is then machined so as to give the bearing its final shape, as illustrated in  FIG. 6 . 
         [0061]    These machinings consist essentially of two milling operations along the planes normal to the transverse axis AT, at the hub. These milling operations therefore consist in removing layers of reinforcing fibres in the regions situated facing each end of the tube  12  so that these ends are no longer closed off. Additionally, the ends of the connecting rod are also machined. 
         [0062]    The inside of the tube  12  can also be bored in order to give it a precise internal diameter corresponding to a predefined tolerance dimension. Once the boring of the internal diameter of the tube  11  has been carried out, one or more metal rings may be installed inside this tube so as to accommodate the mechanical shaft passing through this bearing. 
         [0063]    It should be noted that, in the example of the figures, the bearing is situated at one end of the arm, but the invention also makes it possible to produce in a similar manner an arm or a structural element having a bearing situated for example in its central region. 
         [0064]    In this case, provision is made for example of two sleeves that are fitted on either side of the hub while being rigidly secured to the latter so as to form the mandrel. The two sleeves may be positioned so as to form an angle relative to one another so that the arm then has a bent shape, the bearing being situated in the bent zone while extending transversely relative to each sleeve. 
         [0065]    If necessary, one or two other hubs may additionally be attached to the free ends of these two sleeves so as to form a structural element that may comprise two or three bearings.