Abstract:
An aircraft braking system includes a brake disk stack ( 22 ) that has at least one brake rotor ( 26 ) rotatable with an aircraft wheel ( 16 ) and at least one brake stator ( 24 ), at least one actuator ( 36 ) movable in response to a braking command to compress the brake disk stack ( 22 ) and slow the wheel ( 16 ), at least one actuator motor ( 32 ) operably connected to the at least one actuator ( 36 ) for moving the at least one actuator ( 36 ), a generator ( 40, 82, 100 ) having a generator rotor ( 42 ) and a generator stator ( 44 ), the generator ( 40, 82, 100 ) being operably connectable to the aircraft wheel ( 16 ) such that said generator rotor ( 42 ) rotates when the wheel ( 16 ) rotates, and a controller ( 50 ) electrically connected to the generator ( 40, 82, 100 ) and the at least one actuator motor ( 32 ). Also a method of generating electrical power from an aircraft wheel ( 16 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to an aircraft electric brake and a generator for powering the electric brake, and to a method of using same, and, more specifically, toward an aircraft electric brake powered by a generator having a generator rotor operably connectable to an aircraft wheel whereby rotation of the wheel rotates the generator rotor and produces power for the electric brake, and to a method of using the generator. 
       BACKGROUND OF THE INVENTION 
       [0002]    Aircraft brakes often include one or more rotors that rotate with an aircraft wheel and stators fixed with respect to aircraft landing gear which extend between the rotors. The rotors and stators are arranged in an alternating manner to form a brake disk stack and are normally spaced so that the aircraft wheel can rotate freely. When the disk stack is compressed, the rotors and stators are forced into contact which produces friction to slow and stop the wheel. 
         [0003]    Various actuators are known for applying a pressure against a disk stack to compress the disk stack. While hydraulic actuators have been used, these are increasingly being replaced by electric actuators that receive power from an aircraft power system and that are controlled by electrical signals from an aircraft control system. Certain known electric actuators include an electric motor, a ram or piston that is moved by the motor toward and away from a disk stack, and a mechanical connection between the motor and the piston to convert the rotary motion of the motor into linear motion of the ram. A ballnut/ballscrew arrangement may be used for this mechanical connection, and the assembly of motor, mechanical connection and piston may be referred to as an electromechanical actuator or “EMA.” 
         [0004]    A motor controller receives braking commands from a higher level controller, such as the aircraft&#39;s main computer or a braking controller, and controls the current supplied to the motor to control the position of the piston and thus the amount of force applied by the piston against the brake stack. The design and control of electric brakes is discussed, for example, in U.S. Pat. No. 6,471,015 to Ralea, and the entire contents of this reference is hereby incorporated by reference. 
         [0005]    Under some circumstances, it may be desirable to operate electric brakes with a high-voltage power supply. However, for safety reasons, which may be the subject of government regulations, for example, it is not always possible or practical to run high-voltage power along a landing gear strut to the brakes. It would therefore be desirable to provide a brake arrangement and method of using same that allows for the provision of high voltage to an aircraft electric brake without running high-voltage cables along an aircraft landing gear strut. 
       SUMMARY OF THE INVENTION 
       [0006]    This problem and others are addressed by the present invention, a first aspect of which is an aircraft braking system that includes a brake disk stack having at least one brake rotor rotatable with an aircraft wheel, at least one brake stator, at least one actuator movable in response to a braking command to compress the brake disk stack and slow the wheel, and at least one actuator motor operably connected to the at least one actuator for moving the at least one actuator. A generator is also provided that has a generator rotor and a generator stator, and the generator is operably connectable to the aircraft wheel so that the generator rotor rotates when the wheel rotates. A controller is electrically connected to the generator and the at least one actuator motor. 
         [0007]    Another aspect of the invention is an aircraft braking system that includes a brake disk stack having a plurality of brake rotors rotatable with an aircraft wheel and a plurality of brake stators projecting between pairs of adjacent rotors, an actuator for compressing the brake disk stack to slow the wheel, and an actuator motor operably connected to the actuator for powering the actuator. A dual mode device is also included which has a device rotor and a device stator, the dual mode device being operable in a first mode as a generator and in a second mode as a motor, the device rotor being operably connectable to an aircraft wheel such that said device rotor rotates when said wheel rotates. A controller is also provided that is electrically connected to the dual mode device and which directs current away from the dual mode device when the dual mode device operates in the first mode. The actuator motor is operably connected to the dual mode device such that the actuator motor is powered by the dual mode device. 
         [0008]    An additional aspect of the invention comprises a method of operating an aircraft electric brake having an electric motor that includes steps of providing a generator having a generator rotor, operably connecting the generator rotor to an aircraft wheel such that motion of the wheel turns the generator rotor, electrically connecting an output of the generator to the electric motor, and powering the electric motor with energy produced by the generator. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    These features and aspects of the invention and others will be better understood after a reading of the following detailed description together with the accompanying drawings, wherein, 
           [0010]      FIG. 1  schematically illustrates an aircraft brake system according to a first embodiment of the present invention; 
           [0011]      FIG. 2  is a schematic front elevational view of an aircraft brake system according to a second embodiment of the present invention; 
           [0012]      FIG. 3  is a schematic side elevational view, partly in section, of the aircraft brake system of  FIG. 2 ; and 
           [0013]      FIG. 4  is a schematic side elevational view, partly in section, of an aircraft brake system according to a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring now to the drawings, wherein the showings are for the purpose of illustrating preferred embodiments of the invention only and not for the purpose of limiting same,  FIG. 1  schematically illustrates an aircraft landing gear system  10  that includes a strut  12 , an axle  14  connected to strut  12 , first and second wheels  16  having interiors  18 , mounted for rotation about axle  14 , and first and second tires  20  mounted on wheels  16 . A brake stack  22  is provided in one or each wheel interior  18  and includes a plurality of stators  24  fixed to axle  14  and a plurality of rotors  26  connected to wheel  16  for rotation therewith between pairs of stators  24 . An actuator ring  28  is mounted on axle  14  and supports a plurality of electromechanical actuators  30 , each of which comprises an electric motor  32 , a ballnut/ballscrew assembly  34  and a piston  36 . 
         [0015]    A generator  40  is also mounted in wheel interior  18  and includes a generator rotor  42  connectable to wheel  16  for rotation therewith and a generator stator  44  connected to axle  14 . Thus, as will be appreciated from  FIG. 1 , the generator rotor  42  rotates relative to the generator stator  44  as wheel  16  rotates, and this causes generator  40  to produce a current on output line  46 . While many pancake style axial gap generators could be used, one generator that has useful properties is a segmented electromagnetic array (SEMA) generator such as the one disclosed in U.S. Pat. No. 5,744,896 to Kessinger, the entire contents of which are hereby incorporated by reference. 
         [0016]    Output line  46  is connected to power controller  50 . Power controller  50  may condition and output the AC current produced by generator  40  and/or may provide commutation to produce the direct current used by many aircraft systems. Beneficially, power controller may provide power to actuators  30  on power lines  48  so that the energy of an aircraft landing can be used to generate the power necessary for braking the aircraft. 
         [0017]    Far more energy is produced by a typical landing than is needed to control the aircraft brakes. Therefore, power controller  50  also controls the charging and later discharging of a energy storage device  52 . Energy storage device  52  may include one or more batteries; however, batteries may not charge rapidly enough to allow the capture of a substantial portion of the energy generated by an aircraft landing, which may last, for example, on the order of 30 seconds and produce approximately one megawatt of power per wheel. Therefore, energy storage device  52  alternately may comprise a bank of supercapacitors that charge more quickly than presently known batteries and that can absorb all or a substantial amount of the energy produced. 
         [0018]    Energy stored in storage device  52  can later be used to provide power to aircraft power bus  54  for general use on an aircraft (not shown) or to actuators  30  when wheels  16  are no longer rotating rapidly enough to produce sufficient energy for controlling actuators  30 , when the aircraft has nearly stopped or when the actuators  30  are used to perform a park brake function, for example. A connection to the aircraft power bus  54  provides redundancy and a source of electricity for actuators  30  in addition to the power produced by generator  40 . System controller  60  controls power controller  50  and determines how the energy produced by generator  40  is directed and used. 
         [0019]      FIG. 1  also illustrates a forced air cooling system  70 , which may also be under the control of system controller  60 . Forced air cooling of generator  40  allows more efficient operation of the generator  40  and allows for the use of a smaller generator  40  that might be required if no forced air cooling was provided. 
         [0020]    Beneficially, generator  40  will function as a motor if current is supplied to the generator  40  on line  46 , and generator  40  may therefore sometimes be referred to herein as a dual mode device to emphasize that the device may operate as either a generator or a motor. A generator such as the one disclosed in U.S. Pat. No. 5,744,896, for example, will function as a motor without modification and is an example of such a dual-mode device. Because the generator rotor is coupled to wheel  16 , wheel  16  can be caused to rotate by applying power to the dual mode device  40 . Therefore, wheels  16  can be pre-rotated prior to landing so that the wheel speed will substantially match the aircraft ground speed at landing to reduce wear on tires  20 . Additionally, dual mode device  40  can be used to rotate wheels  16  when the aircraft is on the ground and thus reduce or eliminate the use of aircraft engines for taxiing. Moreover, because system controller  60  can drive the wheels on opposite sides of an aircraft at different speeds, an aircraft can be steered using the main landing gear wheels and reduce or eliminate the need for a separate nose-wheel steering system. 
         [0021]    In addition, in the foregoing embodiment, generator  40  is housed in the interior  18  of wheel  16  and power controller  50  may be located on the landing gear assembly as well. With this arrangement, power lines  46  and  48  do not need to run along strut  12  but instead can be kept at the distal end of strut  12  near wheels  16 . Various regulations limit the use of high-voltage wiring on an aircraft strut; because power lines  46  and  48  do not run along strut  12 , they can carry high voltage without violating these safety rules. This provides greater design flexibility in the design of actuators  30  which may now, if it is desirable, be operated with high voltage. 
         [0022]    In operation, when landing gear is deployed prior to landing, power controller  50  sends current to dual mode device  40  to accelerate wheels  16  so that the tires  20  will be rotating at approximately the ground speed of the aircraft when it lands. Shortly before landing, power controller  50  will switch dual mode device  40  into generator mode to convert the forward momentum of the aircraft into usable energy. This energy is then provided to energy storage device  52  and to actuators  30  to compress the brake stack. It will be recognized that the magnetic interaction between the generator rotor and generator stator tends to resist rotation of the aircraft wheel, and therefore the generator itself will provide additional braking for the aircraft. Controller  50  may therefore beneficially take into account the amount of braking force that will be produced by a given generator and thereby reduce the amount of frictional braking force produced by the disk stack  22  so that the total braking force produced by generator action and friction will equal the braking force commanded by a pilot or system controller, with less wear to the consumable (and often expensive) brake rotors and brake stators. A system that uses only a generator for braking is disclosed in U.S. 2005/0224642 to Sullivan, the entire contents of which is hereby incorporated by reference. Various operating methods disclosed in Sullivan may optionally be used in connection with the present invention as well. 
         [0023]    The forgoing embodiment may be useful on wheels and landing gear systems designed to accommodate generator  40  within a wheel interior. However, existing wheels may not be able to accommodate a generator as described above. Therefore, according to a second embodiment of the invention illustrated in  FIGS. 2 and 3 , one or more generators may be mounted outside wheel  16  and electrically connected to a brake actuator inside the wheel. In this embodiment, elements common to the first embodiment are identified with like reference numerals. 
         [0024]    Referring to  FIG. 2 , a tire  20  is illustrated mounted on a wheel  16  which rotates about the axis of axle  14 . A gear  80  is connected to wheel  16  so as to rotate with the wheel, and first and second generators  82  are mounted adjacent wheel  16 . Each generator  82  includes a generator gear  84  connected to a generator rotor (not shown), and the generator gears  84  are connected to wheel gear  80  so that the rotation of wheel  16  drives wheel gear  80  and first and second generators  82  to produce an electrical current. Wires  46  connect first and second generators  82  to power controller  50 , and wires  48  connect power controller  50  to actuators  30  as in the first embodiment. Wheel  16  can be driven by operating generators  82  in a second mode, as motors, as discussed above in connection with the first embodiment. With this embodiment, two generators can be mounted with rotor axes of rotation offset from the axis of rotation of wheel  16  which provides additional design flexibility. A single generator could also be coaxially mounted with the wheel axis and mounted outside wheel  16  without exceeding the scope of this invention. 
         [0025]    As noted above, this arrangement may be useful as a retro-fit for existing aircraft wheels that cannot accommodate a dual-mode device in their interiors. Alternately, this arrangement may be used on smaller aircraft wheels, such as nose wheels. Even if the nose wheels do not include a braking arrangement, the dual-mode device can be useful to generate power for use elsewhere in the aircraft and to operate as a motor and power the nose wheel to reduce or eliminate the need to use aircraft engines for taxiing. 
         [0026]    A third embodiment of the invention is illustrated in  FIG. 4 . In this embodiment, a generator  100  is mounted adjacent to the a wheel, for example on an aircraft strut  12 . A friction wheel  102  engages tire  20  and is connected by rod  104  to a rotor (not shown) of generator  100 . This arrangement avoids the need to connect a generator directly to a wheel and a simple frictional connection with a tire provides similar benefits to those discussed above. The generator  100  is connected to a power controller  50  and other system elements in the same manner discussed above in connection with the first and second embodiments. 
         [0027]    The present invention has been described herein in terms of several preferred embodiments. Obvious additions to and modifications of these embodiments will become apparent to those of ordinary skill in the art upon a reading of the foregoing description, and it is intended that all such obvious additions and modifications form a part of the present invention to the extent that they fall within the scope of the several claims appended hereto.