Patent Publication Number: US-2022235835-A1

Title: Bar for a braked aircraft wheel

Description:
The present invention relates to the field of aviation and, more particularly, to braking aircraft wheels. 
     BACKGROUND OF THE INVENTION 
     Aircraft wheels are known that are mounted on undercarriages and that are provided with respective brakes. Such a brake generally comprises stator disks arranged in alternation with rotor disks that are driven in rotation by Inconel® alloy bars secured to the inner periphery of a rim of the wheel. The bars are received in peripheral notches in the rotor disks, and they extend in a direction that is substantially parallel to the axis of rotation of said wheel. Controlled pressure applied to the stack of disks gives rise to friction between the facing disks, and thus to a braking torque that slows down the rotation of the wheel. 
     The bars may be made integrally with the rim of the wheel, or they may be fitted thereto. With reference to  FIG. 1A , certain prior art bars  1  have a cylindrical tail at one end  1   a  for engaging in orifices made in a disk or “web” of the rim, and at an opposite end  1   b  they have an orifice arranged to receive a screw that is screwed into a tapped orifice in the rim. Titanium wedges  2  are interposed between the bars  1  and the rim, firstly in order to position the bars  1  in a direction parallel to the axis of rotation of the wheel, and secondly in order to contribute to limiting the transfer of heat between the brake disks and the rim, which could be harmful for a tire mounted on said rim. 
     As shown in  FIG. 1B , the bars  1  sometimes present an H-shaped cross-section that is broadly constant. Such a cross-section serves to withstand the stresses induced by braking and in particular the shear and bending stresses generated by slowing down the rotor disks. 
     By way of example, such bars are known from Document FR-A-2 937 949. 
     A braked aircraft wheel may have seven to eleven bars  1 , depending on the size of the wheel. For an aircraft having two to six wheels per undercarriage and for a bar  1  weighing 500 grams (g) to 800 g, it can be seen that the bars contribute significantly to the overall weight of the wheel-and-brake assembly. 
     However, lightening aircraft has become an imperative for all aircraft manufacturers, particularly since regulations have been encouraging them to do so. Specifically, environmental standards require reduction in emissions of pollutants, and in particular of carbon dioxide (CO2). 
     OBJECT OF THE INVENTION 
     An object of the invention is thus to propose a bar for a braked aircraft wheel that makes it possible in particular to reduce the weight of the wheel-and-brake assembly of an aircraft without degrading the mechanical strength of said bar. 
     SUMMARY OF THE INVENTION 
     For this purpose, the invention provides a bar for a braked aircraft wheel, the bar being for fitting to a rim of the wheel in order to drive rotor brake disks in rotation. The bar comprises a substantially rectilinear body having at least one segment including two wings connected together by a core and intended to co-operate with the rotor disks. 
     According to the invention, the bar includes at least one brace element connecting a free edge of each of the wings to a central portion of the core. 
     Such brace elements enable the thicknesses of the wings and of the core to be optimally determined, thereby enabling the overall weight of the bar to the reduced without degrading its mechanical strength. 
     In a particular embodiment, the brace element is a wall extending in a longitudinal direction of the bar between said free edge and the central portion of the core. 
     According to a particular characteristic, a portion of the body forms a fastener wedge for fastening the bar to the rim. 
     There is thus no longer any need to provide an operation of adding a wedge while putting the bar into place, thereby limiting the number of operations needed for putting the bar into place on the rim of the wheel. 
     Advantageously, the wedge includes recesses, thereby enabling the overall weight of the bar to be limited and also limiting the transfer of heat to the rim. 
     According to another particular characteristic, a portion of the body includes a trellis structure. 
     The invention also provides a braked aircraft wheel comprising a rim having an inner periphery defining a space for receiving both rotor brake disks and also such bars fastened to the rim in order to constrain the rotor brake disks to rotate with the rim. 
     The invention also provides landing gear including at least one such wheel and an aircraft including such landing gear. 
     The invention also provides a method of fabricating such a bar, the method comprising at least one operation of fabricating the body of the bar by additive fabrication. 
     In a particular implementation, the additive fabrication operation is performed in such a manner as to obtain the bar in a vertical position. 
     Alternatively, the additive fabrication operation is performed in such a manner as to obtain the bar in a horizontal position and it includes a step of making a trellis supporting a wall of the body of the bar. 
     Preferably, the additive fabrication operation makes use of laser beam melting on a bed of powder. 
     In particular manner, the powder is an Inconel® alloy powder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention can be better understood in the light of the following description, which is purely illustrative and nonlimiting, and that should be read with reference to the accompanying drawings, in which: 
         FIG. 1A  is a perspective view of a prior art bar; 
         FIG. 1B  is a cross-section view on a plane A-A of the bar shown in  FIG. 1A ; 
         FIG. 2  is a side view of an aircraft including landing gear provided with braked wheels; 
         FIG. 3  is an axial section view of one of the braked wheels of the aircraft shown in  FIG. 2 , the rim of the wheel being fitted with bars in a particular embodiment of the invention; 
         FIG. 4A  is a perspective view of a bar of the braked wheel shown in  FIG. 3 ; 
         FIG. 4B  is a cross section view on a plane a′-a′ of the bar shown in  FIG. 4A ; 
         FIG. 4C  is a detail face view of a portion of the bar shown in  FIG. 4A ; 
         FIG. 4D  is a detail rear view of a portion of the bar shown in  FIG. 4A ; and 
         FIG. 5  is a cross-section view of a variant of the bar shown in  FIG. 4A  including a portion having a trellis structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 2 and 3 , an aircraft  100  of the invention comprises a structure provided with undercarriages  101 . Each undercarriage  101  comprises a leg having one end hinged to the structure of the aircraft  100  and an opposite end carrying an axle  102  on which a wheel  103  is rotatably mounted. 
     The wheel  103  comprises a rim  104  and a web  105  connecting the rim  104  to a hub that is rotatably received on the axle  102  so that an inside surface of the rim  104  extends facing an outside surface of the hub and co-operates with the hub to define a space for receiving a stack of brake disks. The stack comprises stator disks  106   a  prevented from rotating relative to the leg of the undercarriage and rotor disks  106   b  including peripheral notches that receive bars, given overall reference  10 , which bars are fastened to the inside surface of the rim  104 . 
     With reference to  FIG. 4A , each bar  10  comprises a body  11  extending along a longitudinal axis X. The body  11  has a first end  11   a  in the form of a cylindrical tail that is to be received in an orifice of the rim  104  extending parallel to the axis of rotation of the wheel  103 , and a second end  11   b  including a hole  12  in a radial direction for receiving a fastener screw for fastening the bar  10  to the rim  104 . 
     The body  11  also has two lateral bearing faces  13  extending parallel to the axis X for the purpose of cooperating with clips arranged in the peripheral notches of the rotor brake disks  106   b.  The two bearing faces  13  form a nonzero angle a so that in service they extend radially relative to the rim  104 . High velocity oxy fuel (HVOF) surface treatment is applied to the bearing faces  13  in order to obtain appropriate tribological behavior between the bar  10  and the clips. All this is well-known and it is recalled merely for information purposes. Between the first end and the second end, and as shown in  FIG. 4B , the body  11  includes a segment  14  that presents a cross-section that is broadly constant and symmetrical about a midplane of the body  11 . The cross-section is substantially H-shaped and the segment  14  thus comprises two wings  15  having inside faces that are connected together by a core  16  and outside faces that form the bearing faces  13 . Each wing  15  has a bottom portion  15   a  and a top portion  15   b,  which portions extend on opposite sides of the core  16 . In this example, the top portions  15   b  of the wings  15  present a height that is greater than the height of the bottom portions  15   a.  In this example, the height of the top portions  15   b  of the wings  15  is substantially equal to four times the height of the bottom portions  15   a  of the wings  15 . The distance between the free edges of the top portions  15   b  of the wings  15  is slightly greater than the distance between the free edges of the bottom portions  15   a  of the wings  15 . 
     Furthermore, brace elements  17  connect the free edges of the top portions  15   b  of the wings  15  to a central portion of the core  16 . Each brace element  17  has a wall with a plane zone  17   a  extending between the central portion of the core  16  and a rounded zone  17   b  that connects the plane zone  17   a  to the free edge of the top portion  15   b  of one of the wings  15 . Relative to the core  16 , the plane zone  17   a  of each brace element  17  forms an angle β that is substantially equal to 45° in this example. The brace elements  17  serve to oppose any tendency of the wings  15  to be deformed or overturned while the bar  10  is in service, thereby enabling the thickness of the wings  15  and of the core  16  to be optimized. 
     A portion of the end  11   b  of the body  11  is shaped to constitute a fastener wedge  18  for fastening the bar  10  to the rim  104 . The wedge  18  is thus made integrally with the bar  10  and the hole  12  passes through its center in order to be able to pass the fastener screw for fastening the bar  10  to the rim  104 . At its top portion, the wedge  18  has two plane bearing faces  18   a  extending in the same plane for the purpose of cooperating with a plane surface of the rim  104 . The two bearing faces  18   a  are arranged symmetrically on either side of the hole  12 . 
     With reference to  FIGS. 4C and 4D , the wedge  18  is hollowed out by making two channels  18   b  that extend on either side of the hole  12  substantially in a longitudinal direction relative to the bar. The channels  18   b  have several functions: they enable air to flow inside the wedge  18 , in particular under the effect of a forced flow of air imparted by a brake cooling fan, and their presence limits the quantity of material of the wedge  18  that enables heat to be transferred by conduction from the rotor brake disks  106   b  to the rim  104 . 
     The channels  18   b  thus reduce considerably the rate of heat conduction by the wedge  18 , thereby contributing to significantly limiting the temperature rise of the rim  104 , in particular where the bearing faces  18   a  of the wedge  18  bear against the rim  104 , while preserving the ability of the wedge  18  to transmit braking torque to the rim  104 . 
     The bar  10  is made by additive fabrication vertically along its axis X, and more particularly fabrication by laser beam melting (LBM) on a bed of metal powder. The bar  10  is then obtained in the vertical position. This method enables the bar  10  to be fabricated in a single operation on the basis of a three-dimensional (3D) digital file for said bar  10 . The bar  10  is constructed by using selective melting of a powder of Inconel® alloy under a controlled atmosphere. The Inconel® alloy powder is spread by a scraper to form a bed of varying thickness in the range 30 micrometers (μm) to 90 μm. An optical fiber laser beam is steered by mirrors to scan the bed so as to melt the powder selectively in zones that are defined upstream by the 3D digital file. By way of example, the laser beam may be an yttrium aluminum garnet (YAG) laser beam. 
     In comparison with the bar  1  and for an identical fastener interface, the bar  10  makes it possible to achieve a weight saving for the bar-and-wedge assembly that lies in the range 15% to 20%. Furthermore, the mechanical strength and in particular the bending strength of the bar is improved. 
     Naturally, the invention is not limited to the implementations described, but covers any variant coming within the ambit of the invention as defined by the claims. 
     The body  11  of the bar  10  need not be integral with the wedge, but could have a bearing face arranged to receive a wedge that is fitted on the bar. 
     In order to increase the stiffness of the bar  10 , and also in order to enable the bar  10  to be additively fabricated from a powder in such a manner as to obtain the bar horizontally, a portion of the body  11  of said bar  10  may include a lattice structure  19 , as shown in  FIG. 5 , in other words a hollowed-out trellis structure with a unit pattern that may for example be a tetrahedron, and that serves to support a wall of the bar. 
     The brace elements  17  may be of a shape other than those shown in  FIG. 4B . 
     Although in this example the bar  10  is made by additive fabrication, it could also be made by other methods, e.g. by lost wax casting. 
     Powders other than Inconel® alloy powder could be used for fabricating the bar  10 , in particular depending on the operating requirements for said bar (e.g. steel powder . . . ).