Abstract:
An aircraft brake piston housing ( 10 ) has a composite body ( 14 ) including a plurality of fibers embedded in a matrix, the body ( 14 ) including a central bore ( 18 ) and a plurality of circumferentially disposed openings ( 23 ) surrounding the bore ( 18 ), at least some of the circumferentially disposed openings ( 23 ) being configured to receive a brake piston ( 26 ), and a frame ( 12 ) embedded in the composite body ( 14 ) and formed from a material different than the matrix. Also a method of forming such a brake piston housing.

Description:
FIELD OF THE INVENTION 
   The present invention is directed toward a composite housing for aircraft brake pistons and toward a method of forming same, and, more specifically, toward a composite housing having an embedded frame, the housing defining openings for receiving brake pistons, and toward a method of forming same. 
   BACKGROUND OF THE INVENTION 
     FIG. 8  illustrates a portion of a typical aircraft brake system  200  that includes a plurality of spaced, disk shaped stators  202  mounted on a torque tube  204  and a plurality of disk shaped rotors  206  that rotate with an aircraft wheel  207  and extend into the spaces between the stators  202 . Pistons  208  are mounted on a piston housing  210  which is connected to the torque tube  204  by bolts  205 . The pistons  208  apply pressure against a pressure plate  212  (the first stator in the stack of rotors and stators) to compress the stack, and the friction generated as the rotors are pressed into contact with the stators slows the aircraft wheel. 
   Each of the pistons  208  is mounted in a piston chamber  214  and biased into a retracted position relative to pressure plate  212  with springs  216 . Hydraulic fluid flows into piston housing  210  through fitting  218  and into internal channels  220  formed in the aluminum piston housing  210  between the piston chambers  214 . Thus, when pressure is applied to the fluid by an external source, (not shown) the pistons  208  are driven against the pressure plate  212 ; when the hydraulic pressure drops, the pistons  208  are retracted by springs  216 . 
   It is known to replace various metal aircraft components with lightweight composite materials to reduce aircraft weight. Such weight reductions are generally desirable as they either save fuel or increase the carrying capacity of the aircraft. However, brake assemblies are subject to high temperatures and stresses. The rotors and stators can reach 1500° F. during a landing, and the hydraulic fluid pressure in the piston chambers and connecting hydraulic fluid lines can reach thousands of psi. Moreover, it is desirable to provide a suitably rigid piston housing because deformations of the piston housing can misalign the pistons  208  and piston chambers  214  and cause the pistons to bind, hydraulic fluid to leak, and/or the brake system to operate improperly. Aircraft brake assemblies, therefore, have not heretofore appeared to present good opportunities for weight reduction through the use of lightweight composite materials which generally cannot satisfy all the above requirements. It would, however, be desirable to reduce the weight of aircraft brake assemblies using composite materials if the aforementioned problems could be addressed. 
   SUMMARY OF THE INVENTION 
   These and other problems are addressed by the present invention, a first aspect of which comprises an aircraft brake piston housing that includes a composite body having a plurality of fibers embedded in a matrix. The body includes a central bore and a plurality of circumferentially disposed openings surrounding the bore, at least some of the circumferentially disposed openings being configured to receive a brake piston. A frame formed from a material different than the matrix is embedded in the composite body. 
   Another aspect of the invention comprises a method of forming a brake piston housing that includes steps of providing a frame defining at least a central opening and a plurality of additional openings circumferentially disposed around the central opening and placing the frame in a mold. Reinforcing fibers are also placed in the mold and the mold is filled with a composite matrix material to embed the frame and reinforcing fibers in the composite matrix material. 
   Yet another aspect of the invention is an aircraft brake piston housing that includes a composite body having a plurality of fibers embedded in a matrix, the body including a central bore and a plurality of circumferentially disposed openings surrounding the bore. A first brake piston is mounted in a first one of the circumferentially disposed openings and a second brake piston is mounted in a second one of the plurality of circumferentially disposed openings, and a frame formed from a material different than the matrix is embedded in the composite body. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and features of embodiments of the present invention will be better understood after a reading of the following detailed description in connection with the attached drawings wherein: 
       FIG. 1  is an elevational view of an aircraft brake piston housing including a frame embedded in a composite body according to an embodiment of the present invention; 
       FIG. 2  is an elevational view of the frame, piston cups and hydraulic lines of the piston housing of  FIG. 1 ; 
       FIG. 3  is a sectional elevational view taken along line III-III of  FIG. 2 ; 
       FIG. 4  is a sectional elevational view taken along line IV-IV of  FIG. 1 ; 
       FIG. 5  is a side elevational view of an alternate embodiment of the invention wherein a fiber is wrapped around a portion of the frame; 
       FIG. 6  schematically illustrates the frame of  FIG. 2  positioned in a mold and covered with reinforcing fibers and resin during a molding process; 
       FIG. 7  is a flow chart illustrating a method according to an embodiment of the present invention; and 
       FIG. 8  is a perspective view of a portion of an aircraft brake having a conventional brake piston housing. 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings, wherein the showings are for purposes of illustrating preferred embodiments of the invention only and not for the purpose of limiting same,  FIG. 1  illustrates a brake piston housing  10  comprising a frame  12  embedded in a body  14  formed of a composite material which may comprise reinforcing fibers in a resin. The resin may comprise, for example, an epoxy or phenolic resin, and the fibers may comprise carbon, titanium or nylon-66 (Kevlar®). Frame  12  is illustrated in  FIG. 2  without the surrounding composite material and may be formed, for example, from aluminum or other rigid material. Frame  12  includes a central body portion  16  defining a central opening  18 , a plurality of bolt holes  19 , and a plurality of arms  20  extending from the central body portion  16  which arms terminate in rings or ring members  22 . The rings  22  define openings  23  adapted to receive cylindrical inserts  24  which in turn contain a brake piston  26  (illustrated in  FIGS. 3 and 4 ) and a tension spring  28  that holds piston  26  in a retracted position within cylindrical insert  24  under normal circumstances. Each of the cylindrical inserts  24  includes at least one opening  29  in a wall thereof to which a hydraulic fluid line  28  is connected; many of the cylindrical inserts  24  will include a pair of openings  29 , a first for receiving hydraulic fluid and a second for conveying hydraulic fluid and/or pressure to adjoining cylindrical inserts  24  for operating the brake pistons  26  mounted therein. Hydraulic fluid is supplied to the hydraulic fluid lines  28  and brake pistons  26  via fitting  34 . 
     FIG. 3  is a sectional view of one of arms  20  without a covering of composite material and  FIG. 4  is a sectional view of the same arm  20  covered with a body  13  of composite material. As should be apparent from a consideration of  FIGS. 2 and 3  together, cylindrical inserts  24  project into the page as viewed in  FIG. 2 , and hydraulic fluid lines  28  connect the cylindrical inserts  24  in a plane spaced from central body portion  16  and arms  20 . The cylindrical inserts  24  may include threading (not shown) on an outer surface complementary to threading (not shown) on the inside of rings  22  to allow the cylindrical inserts to be securely connected to frame  12  before composite body  14  is formed around the frame. The cylindrical inserts  24  may be mechanically connected to frame  12  using other arrangements without exceeding the scope of this invention. 
     FIG. 6  illustrates a mold  30  into which frame  12  is placed during the process of forming brake piston housing  10 . A method according to an embodiment of the present invention includes a step  100  of providing a frame such as frame  12  and a step  102  of placing the frame  12  into the mold  30 . Reinforcing fibers  32  are added to mold  30  at a step  104 . These fibers may be loosely placed into the spaces surrounding arms  20  and central body portion  10  as illustrated in portions of  FIG. 5  or, as illustrated in  FIGS. 5 and 6 , some or all elements of frame  12  and cylindrical inserts  24  may first be wound with one or more fibers  32  which may improve the mechanical bond between composite body  10  and frame  12 . After the fibers are in place, the mold is closed with a second mold element (not shown) and a suitable resin, such as, without limitation, a polymer resin, is poured or injected into the mold and cured or allowed to cure in a well known manner at a step  106 . Other methods of forming a composite body around frame  12 , such as the method of combustion synthesis described in co-pending U.S. patent application Ser. No. 11/583,922, entitled “Carbon Filament Ignition Of Combustion Synthesis Materials” (the entire contents of which are hereby incorporated by reference) could also be used without exceeding the scope of embodiments of the present invention. Frame  12 , cylindrical inserts  24  and hydraulic fluid lines  28  are illustrated in dashed lines in  FIG. 1  embedded in the composite material that forms body  14 . 
   The completed brake piston housing will be mounted on a torque tube similar to torque tube  204  illustrated in  FIG. 6 , by passing bolts (not shown) through bolt holes  19  in frame  12  and into the torque tube, and an aircraft brake system that includes brake piston housing  10  will be operated in substantially the same manner as a system that includes an aluminum brake piston housing. However, because body  14  is formed from a composite material and is lighter than a conventional brake piston housing, a significant weight savings is realized. The composite material should also provide a brake piston housing substantially stronger and longer lasting than conventional brake piston housings. 
   Moreover, cylindrical inserts  24  and hydraulic fluid lines  28  are formed from metal and can therefore withstand the heat and pressures to which the brakes are subjected. In addition, frame  12  provides structural support and maintains cylindrical inserts  24  in a proper orientation in mold  30  during the molding process. Additionally, the physical connection between cylindrical inserts  24  and rings  22  helps maintain a secure connection between the cylindrical inserts  24  and the composite material that forms body  14  because stresses imparted on the inserts  24  during brake use are partially transmitted to the metal frame  12  instead of entirely to the composite body  14 . Beneficially, substantially all metal parts are encapsulated with the composite material of body  14  which reduces the potential for corrosion. In addition, it is believed that body  14  formed from composite material will be stiffer than aluminum and thus flex less when forces are applied thereto when the brake pistons are extended. In conventional brake piston housings, such flexing can misalign conventional pistons and may lead to hydraulic fluid leakage and/or damage to the brake pistons or undesired excessive compliance of the brake system. 
   The present invention has been described herein in terms of preferred embodiments. Obvious modifications and additions to these embodiments will become apparent to those skilled in the relevant arts upon a reading of the foregoing disclosure. It is intended that all such obvious modifications and additions form a part of this invention to the extent they fall within the scope of the several claims appended hereto.