Abstract:
An apparatus ( 10 ) that houses functional components of a mechanical assembly includes a frame component ( 12 ) formed of a first material, the frame component ( 12 ) bearing primary load, torque or pressure applied to the apparatus ( 10 ) during operation of said mechanical assembly. The housing apparatus ( 10 ) further includes a composite reinforcement component ( 130 ) for resisting forces applied to the apparatus during operation of the mechanical assembly and an enclosure component ( 80 ) formed of a second material of lower density than the first material of the frame component ( 12 ), the enclosure component ( 80 ) covering and sealing at least the functional components of the mechanical assembly from external conditions during operation of the mechanical assembly.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed toward a composite structural housing of a mechanical assembly with a portion serving an enclosure function to separate internal and external operating environments and a second portion serving a structural function to support or transmit local loads or resist pressure. In one implementation, the present invention is directed toward a composite housing for aircraft brake pistons. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many housings for mechanical equipment are required to serve two generally different functions: (1) to enclose the internal components of the assembly to prevent any undesired exchange to or from the external environment; and (2) to handle large forces, torques or pressures generated internally among equipment components or transmitted to or from an external source through the housing wall. 
         [0003]    With a conventional metal housing, both the enclosure and load bearing functions are handled by locally changing the metal from thick (load bearing) to thin (separation) by shaping the housing as a whole during manufacture. Manufacture may be by casting, forging, machining, or some other method. Generally a metal housing has a uniform composition with mechanical properties being uniform in all directions (isotropic). 
         [0004]    Composite materials offer a much greater range of materials and properties including properties that are highly directional (anisotropic). Properties and cost are highly dependent on material variables and method of manufacture. Manufacture of composite structures by placement of plies of material leads to very strong, stiff, and light weight structures which may be very expensive, especially for hand layup. Structures made of metals can also be very strong and stiff, but tend to be heavy and in some cases prone to corrosion. Conversely lower cost composite manufacturing processes, such as molding or stamping, generally employ short fibers and do not control fiber orientation. These processes give structures with lower mechanical properties. Generally composite materials are less prone to corrosion than metals. 
         [0005]    In the past, attempts to reduce weight and to meet structural requirements by fabricating an enclosure by a single high performance manufacturing process, for example hand layup, have resulted in high manufacturing costs and the decision not to convert to composites. 
       SUMMARY OF THE INVENTION 
       [0006]    These and other problems are addressed by the present invention, a first aspect of which comprises an apparatus that houses functional components of a mechanical assembly comprising: a frame component formed of a first material, the frame component bearing primary load, torque or pressure applied to the apparatus during operation of the mechanical assembly; a composite reinforcement component for resisting forces applied to the apparatus during operation of the mechanical assembly; and an enclosure component formed of a second material of lower density than the first material of the frame component, the enclosure component covering and sealing the functional components of the mechanical assembly from external conditions during operation of the mechanical assembly. 
         [0007]    Another aspect of the present invention comprises a method of manufacturing an apparatus that houses functional components of an mechanical assembly comprising: providing a frame component formed of a first material, the frame component being configured for bearing primary load, torque or pressure to be applied to the apparatus during operation of the mechanical assembly; providing a composite reinforcement component for resisting force applied to the apparatus during operation of the mechanical assembly; and forming an enclosure component of a second material of lower density than the first material of the frame component, the enclosure component being formed to cover and seal the functional components of the mechanical assembly from external conditions that occur during operation of the mechanical assembly. 
         [0008]    Yet another aspect of the present invention comprises an aircraft brake piston housing that includes an internal frame that includes a plurality of circumferentially disposed openings surrounding a central bore. The frame is supported by a series of windings winding circumferentially around the central bore and at least one of the circumferentially disposed openings. A cover encases the supported frame, and is made of material different than the frame. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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: 
           [0010]      FIG. 1A  is a perspective view of a portion of an aircraft brake having a conventional brake piston housing; 
           [0011]      FIG. 1B  illustrates an aircraft brake piston housing including a frame embedded in a composite body according to an embodiment of the present invention; 
           [0012]      FIG. 2  illustrates a top view and partial side view the interior of a brake piston housing showing the use of fiber and composite laminate insert blocks to bear loads in the brake components according to an embodiment of the present invention; 
           [0013]      FIG. 3  illustrates an enclosure or top cover for the brake piston housing according to an embodiment of the present invention; 
           [0014]      FIG. 4  is a flow diagram for a method of manufacturing an aircraft assembly housing according to an embodiment of the present invention; and 
           [0015]      FIG. 5  is a flow diagram illustrating a method of manufacturing a brake piston housing according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Embodiments of the present invention described herein address the issues described above by separating the enclosure and load bearing requirements of an aircraft assembly housing and generally providing two or more sets of materials, structures, and processes that in combination meet the performance requirements in an economic way. Although aspects of the invention are described in detail below with reference to an aircraft brake piston housing, it should be recognized that the present invention is applicable to other mechanical assemblies such as gear boxes, transmission housings, and motor housings. 
         [0017]    Referring now to the drawings, wherein the showings are for purposes of illustrating embodiments of the invention only and not for the purpose of limiting same,  FIG. 1A  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. 
         [0018]    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  containing central bore  211  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 . 
         [0019]    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. 
         [0020]      FIG. 1B  illustrates a brake piston housing  10  comprising a frame  12  embedded in a body  14  formed of a composite material according to an embodiment of the present invention. In one implementation, frame  12  is comprised of high-strength metal, such as stainless steel or titanium. Frame  12  includes a central body portion  16  defining a central opening  18 , a plurality of bolt holes  19 ; at least one torque arm  15  with torque arm attachment  17 , 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 piston chamber inserts  24  which in turn contain a brake piston  26  and a tension spring that holds piston  26  in a retracted position within cylindrical insert  24  under normal circumstances. The structures of rings  22  define the piston cylinders of the brake piston housing. 
         [0021]    In designing a housing which functions as a structural enclosure, the forces and torques are determined between various locations in the housing and pressures are noted. In many cases those forces and torques that represent tensile or compressive forces between two locations within the housing can be resisted by windings of fibers or fiber tapes (tensile) or laminate block inserts (compression) between the locations. The fibers, which may or may not be coated with resin, are particularly capable of resisting tensile loads but are not as able to resist compression. If fibers extend appropriately in various directions around a component, any motion by the component may be resisted by the tension in certain fibers even though other fibers will be in compression. Composite laminates, for example consisting of fabric layup with holes for attachment, are not as effective on a weight basis as fiber windings in resisting tension forces between locations. Conversely, compressive forces can be resisted by relatively thick laminated composite structures where the thick cross-section resists buckling. These laminate structures may include honeycomb or rigid foam layers. Fiber windings in combination with thick laminate blocks are effective between points experiencing both tension and compression. The fibers may be any of the various grades of carbon, glass or ceramic fibers that are well known in the art. The resins may be epoxy, bismaleimide, polyimide or others resins commonly using in composite applications. 
         [0022]    Using the brake piston housing in  FIG. 2  as an example of the reinforcement component, the fibers or fabric  130  are wound around support tubes  111  at bolt locations  112  surrounding the torque tube  110  and around the outside circumference of the piston chamber  122 . The winding around a chamber  122  may process around one or more support tubes  111  to an adjacent chamber or skip any number of chambers before winding the next chamber. The piston chambers  122  are supported at their base by the ring members  22  which are part of the frame  12  in  FIG. 1B . Tension in these wound fibers resists any outward radial motion  144  of the piston chamber  122 . Any radial inward motion  142  by the piston chamber  122  is resisted by the composite laminate block  134  positioned between the piston cup and support tubes. In a second direction  146  normal to the radial direction a resin impregnated fiber or fabric band  132  wound around all the chambers  122  resists any circumferential  146  movement of the cups by putting the fibers in one direction into tension while the fibers or fabric in the opposite direction would be in compression and provide less support. When the piston forces the brake plates together, a reaction force arises in a third direction  148  normal to radial and circumferential directions just described. This force is resisted by tension in the fibers  133  between an appendage  152  on the piston cup and an appendage  154  on the base plate  114 . No corresponding laminate structure is needed because the piston cups do not experience significant compressive forces opposite to the direction  148 . In other embodiments this structure could be a gear case with a structural assembly supporting gears or an assembly in an motor housing which supports the motor in resisting torque generated by the drive shaft. The brakes are actuated by pressurized hydraulic fluid which is transmitted to the piston chambers  122  through hydraulic lines  117  from a central ring  115 . 
         [0023]    An example of transport of force or torque through a housing is given by the torque arm  115  ( 15  in  FIG. 1B ) which is a component of the frame  12  in  FIG. 1B . This arm  115  transmits torque from the torque tube  110  attached to the aircraft brake disks to the torque arm attachment  117  ( 17  in  FIG. 1B ) which connects to the aircraft structure. Because of the high loads, the torque arm is made of metal in this embodiment. 
         [0024]      FIG. 3  illustrates a top and side view of an enclosure  80  for the brake piston housing. The enclosure keeps water, aircraft runway fluids, jet fuel and hydraulic fluid from entering the housing. For the brake piston housing the enclosure can be relatively thin and light and made by a molding process. Sealing gaskets may be molded in or applied in a post-processing step along the sealing surface  81  of the enclosure. In the case of an enclosure supporting a shaft, for example in a motor housing embodiment, structural components, as described elsewhere, would need to be bonded into the enclosure. In other embodiments, this enclosure could be a gear case which primarily retains lubricating fluids or a motor housing which primarily protects electrical components from contamination. In some implementations, one or more of the composite reinforcement elements (“blocks”) or frame may be located outside of the assembly enclosure. 
         [0025]      FIG. 4  illustrates a method of manufacturing an mechanical assembly housing according to an embodiment of the present invention. In step  401 , the housing design is examined to determine which portions perform the enclosure function primarily and which serve as structural members. In step  402  the forces, torques and pressures within or through the walls of the housing are identified and those of sufficient magnitude to require structural reinforcement are called out. Step  403  involves selection of materials and the appropriate light weight composite or metal structure to resist or transmit the loads. Since high performance composite structures can be very expensive, step  404  is to select the most cost effective manufacturing methods. Iteration with step  403  may be required. In step  405  the shapes of the enclosure assembly are determined and the appropriate light weight materials are selected to resist and seal against the environmental substances both inside and external to the enclosure. Step  406  involves selection of low cost fabrication methods, such as molding or stamping, for the enclosure components. Since the enclosure and load bearing functions are designed and optimized separately, step  407  ensures the assembled housing performs to specification. 
         [0026]      FIG. 5  illustrates a method of manufacturing the brake piston housing according to the embodiment shown in  FIG. 2 . In step  500 , a metal frame is fabricated with a central body portion and a plurality of metal frame arms disposed around the central body portion. In step  502  piston chambers are disposed at the ends of the frame arms and composite blocks are inserted. 
         [0027]    In step  504 , a winding comprised of a fabric or unidirectional carbon fiber preimpregnated with epoxy is wound around the piston chambers and then around the metal enclosures which extend from the bolts on the central body portion. In step  506  the windings  132  are made around the circumference of the piston chambers. 
         [0028]    In step  508 , the assembly is cured in an oven. Alternatively open areas of the assembly may be filled with metal inserts and the entire assembly placed in a vacuum bag and cured in an autoclave. After curing, the assembly is inspected, cleaned and machined as needed to meet specification in step  510 . A composite cover is molded in a separate operation and inspected and any attachment hardware is added in step  512 . The composite cover is further described in co-pending U.S. patent application Ser. No. 11/704,239, entitled “Composite Piston Housing For Aircraft Brakes” (the entire contents of which are hereby incorporated by reference). As the final step ( 514 ), the piston housing is assembled and tested according to the appropriate protocols. 
         [0029]    In another alternative embodiment, the plurality of arms extending from the central body portion is comprised of composite material instead of metal. In another alternative embodiment, dry fiber or fabric is used instead of preimpregnated material for the windings and composite block. The assembly is placed in a mold and resin is introduced by resin transfer molding. 
         [0030]    The present invention has been described herein in terms of specific 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.