Abstract:
The invention relates to a wheel-and-brake assembly for an aircraft, the assembly comprising:
       a wheel having a rim for mounting on an aircraft axle; and   a brake comprising a stack of disks with alternating stator disks that are stationary in rotation and rotor disks mounted to rotate with the wheel.       
 
     According to the invention, the assembly comprises a drum extending around the disks to be interposed between the disks and the rim, the drum including drive means for driving the rotor disks in rotation and fastener means for fastening the drum to the rim of the wheel.

Description:
[0001]    The invention relates to a wheel-and-brake assembly for aircraft. 
       BACKGROUND OF THE INVENTION 
       [0002]    Brakes are known that comprise a stack of disks made up of rotor disks and stator disks that generally extend inside the rim within the associated wheel. The rotor disks are usually constrained to rotate with the rim by means of keys or splines. 
         [0003]    Presently-envisaged aircraft require brakes to be provided having disks either of increasing thickness or of increasing number so that the disks can no longer be received entirely within the wheel rim. A problem then arises with driving those rotor disks that lie outside the rim in rotation with the wheel. To do this, an immediate solution consists in lengthening the keys so that they project outside the rim in an axial direction. With such an arrangement, the keys are then cantilevered out from the rim and are thus subjected to bending forces which run the risk of breaking the keys. To remedy that problem, it is possible to reinforce the keys by enlarging them, thereby entraining the drawback of increasing the weight and the complexity of the brake assembly. In particular, it becomes difficult to envisage keys that are made integrally with the rim, and it becomes necessary to fit on keys so that they are secured at at least two points along their length, with an inevitable cantilevered-out end portion projecting from the rim. 
       OBJECT OF THE INVENTION 
       [0004]    An object of the invention is to provide a wheel-and-brake assembly that enables rotor disks lying outside the rim to be driven in rotation while avoiding the above-mentioned drawbacks. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    The invention provides more particularly a wheel-and-brake assembly for aircraft comprising a wheel comprising a rim for mounting to rotate on an aircraft axle, and a brake comprising a stack of disks, including stator disks that are stationary in rotation and rotor disks that are driven to rotation together with the wheel. 
         [0006]    According to the invention, the assembly comprises a drum extending around the disks to be interposed between the disks and the rim and that includes firstly drive means for driving the rotor disks in rotation, and secondly fastener means for fastening the drum to the wheel rim. 
         [0007]    The drum thus forms an intermediate element between the rotor disks and the rim, enabling the braking torque generated by friction between the disks to be transmitted to the rim. 
         [0008]    The drum presents a large amount of twisting stiffness so that even if it extends to drive disks that are situated well outside the rim, the braking toque generated by those disks and transmitted to the drum is taken up by the drum and transmitted thereby to the rim without the drum suffering large amounts of deformation, unlike keys fastened to the rim and cantilevered out therefrom. This large amount of twisting stiffness makes it possible to envisage connecting the drum to the rim in such a manner that the drum is connected by bolts extending along diameters of the drum, and distributed around a single circumferential line. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention can be better understood in the light of the following description with reference to the figures of the accompanying drawings, in which: 
           [0010]      FIG. 1  is a section view showing a wheel-and-brake assembly of the invention with a drum; and 
           [0011]      FIG. 2  is a diagrammatic perspective view showing an assembly comprising the rim and the drum of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0012]    With reference to  FIG. 1 , the wheel-and-brake assembly of the invention is shown mounted on an undercarriage axle  34 . The assembly includes a wheel  36 , comprising a rim, here made up of two half-rims  36   a,    36   b,  and rotatably mounted on the axle  34  by means of conical roller bearings  37 . The rim is for receiving a tire (represented symbolically by dashed lines). 
         [0013]    The assembly also includes a brake  40  comprising a torsion tube  50  that is engaged around the axle  34 . The torsion tube  50  is secured to a ring  60  that includes a torque-takeup fitting  90  that co-operates with a torque-takeup catch or bar (not shown) to prevent the torsion tube  50  from turning about the axle  34 . The ring  60  carries brake actuators  80 , in this example hydraulic pistons. 
         [0014]    Disks are engaged on the torsion tube  50 , the disks comprising in alternation stator disks  41  that are fixed in rotation relative to the torsion tube  50 , and rotor disks  42  that are free to rotate relative to the torsion tube  50 , and that rotate with the wheel  36  (only one disk of each category is referenced). The stator disks  41  are prevented from rotating relative to the torsion tube  50  by keys or splines  85  (one of which is visible in section in  FIG. 1 ), which in this example are made integrally with the torsion tube. 
         [0015]    At its end remote from the ring  60 , the torsion tube  50  includes a braking force takeup member  61 , in this example integrally formed with the torsion tube  50 . When the actuators  80  are operated, the stack of disks comes to bear against the force takeup member  61 , thereby enabling the actuators to exert pressure on the stack of disks. 
         [0016]    The rim, the disks, and the torsion tube extend coaxially about the axis of rotation X of the wheel as defined by the axle  34 . 
         [0017]    In the invention, the disks are surrounded by a drum  100  that is generally circularly cylindrical in shape and that includes keys or splines  110  extending inside the drum  100  to drive the rotor disks in rotation. In this example, the keys  110  are made integrally with the drum  100 . One of them can be seen in section in  FIG. 1 . Bolts  128  extend through the drum, in this case through the keys  110  so as to penetrate into lateral projections  130  of the half-rim  36   b  in order to secure the drum  100  to the rim  36 . As can be seen more particularly in  FIG. 2 , the bolts  128  extend along a circumferential line of the drum  100 , thereby forming a single line of bolts that thus extends in a plane perpendicular to the axis X. Such a connection between the drum and the rim is sufficient to transmit braking torque to the rim  36  effectively, given the high degree of twisting stiffness of the drum  100 . 
         [0018]    As can be seen more particularly in  FIG. 2 , protective sheets  160  cover the keys  110  of the drum  100  and are secured to the keys  110  by bolts. 
         [0019]    The assembly of the invention operates as follows: pressure is applied to the disks by means of the actuators  80 . The rotor disks  42  rub against the stator disks  41 . The stator disks  41  are prevented from rotating on the torsion tube and they brake the rotor disks  42  by generating braking torque. This braking torque is transmitted by the rotor disks  42  via the keys  110  to the drum  100 , and then via the bolts  128  to the rim  36 , thereby braking the wheel. 
         [0020]    As can be seen particularly clearly in  FIG. 1 , the stack of disks does not extend entirely within the rim  36  of the wheel, but extends at least in part outside the rim, such that the drum  100  extends at least in part outside the rim. Nevertheless, the drum  100  presents twisting stiffness that enables the torque generated by the rotor disks, including those that lie outside the rim  36 , to be transmitted without the drum suffering a large amount of deformation. 
         [0021]    The use of a drum thus enables very long stacks of disks to be installed that can project outside the rim. If, as in this example, the stack of disks is remote from the central web of the rim, the half-rims  36   a,    36   b  can then be designed to be substantially symmetrical, thereby reducing the cost price of the wheel, and enabling it to work under better conditions, thereby enabling weight to be saved. In addition, the disks are easier to cool because of a space R extending between the stack of disks and the web of the rim. For this purpose, and as can be seen in  FIG. 2 , the drum  100  is advantageously provided with orifices  300  enabling the disks to be ventilated. In this example, the ventilation orifices are oblong and disposed in a circumferential row. 
         [0022]    Finally, the fact that the pile of disks is remote from the rim limits the extent to which the rim is heated when the disks heat up. This disposition thus makes it possible to subject the disks of the brake to higher temperatures, while retaining the same acceptable temperature for the rim and the tire it carries. The possibility of the disks reaching temperatures that are higher than those that would be permissible if the stack of disks extending essentially inside the rim serves to reduce the weight of the brake disks, thereby achieving significant savings. 
         [0023]    During maintenance of the wheel-and-brake assembly of the invention, it should be observed that the rim and the drum are connected together so that they can be handled as though they formed a unitary assembly suitable for dismantling as a single piece, as is shown more particularly in  FIG. 2 . The drum  100  is connected to the rotor disks  42  solely via the keys  110 , thus enabling the drum  100  to move axially relative to the disks, so it is entirely possible to withdraw the wheel and the drum simultaneously. 
         [0024]    Such a drum is preferably made of aluminum, having a coefficient of expansion that is close to the material used for making the rims. The drum  100  works in twisting only, is of large diameter, and is not subjected to the braking forces delivered by the actuators. There is thus, a priori, no need to use a material of higher performance, and thus greater expense, such as titanium. 
         [0025]    The invention is not limited to the above description, but on the contrary covers any variant coming within the ambit of the claims. 
         [0026]    In particular, although the drive means in the example shown for driving the rotor disks  42  by means of the drum  100  are constituted by keys  110  formed integrally with the drum  100 , it is possible to use other drive means. For example, the keys  110  could be fitted to the drum  100 . The keys  110  could also be welded to the drum  100 . 
         [0027]    Similarly, although the means for fastening the drum to the rim are shown as being constituted by bolts extending through the keys and lying on a circumferential line, the invention is not restricted to this particular form of connection, and variants are possible within the ambit of the invention: 
         [0028]    the bolts may extend over a plurality of circumferential rows, e.g. in a zigzag configuration relative to one another; 
         [0029]    the bolts may pass through the drum other than through the keys; and 
         [0030]    the drum may be riveted or welded to the rim.