Abstract:
An electro-mechanical brake assembly comprising a brake disk stack having a center axis; and a plurality electro-mechanical actuators for applying braking pressure to the brake disk stack. The actuators are circumferentially arranged around the center axis, and each actuator includes a housing, a linearly movable ram, a screw for linearly moving the ram, a nut mounted for rotation in the housing and operatively engaged with the screw such that rotation of the nut effects linear movement of the screw for urging the ram into forceful engagement with the brake disk stack, an electric motor for rotating the nut, and an anti-rotation device for preventing rotation of the screw relative to the housing when the nut is rotated to effect linear movement of the screw. The foregoing arrangement provides for greater stroke than prior art actuators without sacrificing durability and performance.

Description:
[0001]     This application is a continuation of U.S. patent application Ser. No. 10/878,290 filed on Jun. 28, 2004, which is a continuation of U.S. patent application Ser. No. 09/660,063 filed on Sep. 12, 2000, which claims benefit of U.S. Provisional Application No. 60/153,731 filed Sep. 13, 1999, all of which are hereby incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention herein described relates generally to an electric brake actuator module particularly useful in aircraft.  
       BACKGROUND OF THE INVENTION  
       [0003]     Known in the prior art are aircraft wheel and brake assemblies including a non-rotatable wheel support, a wheel mounted to the wheel support for rotation, and a brake disk stack having front and rear axial ends and alternating rotor and stator disks mounted with respect to the wheel support and wheel for relative axial movement. Each rotor disk is coupled to the wheel for rotation therewith and each stator disk is coupled to the wheel support against rotation. A back plate is located at the rear end of the disk pack and a brake head is located at the front end. The brake head houses a plurality of actuator rams that extend to compress the brake disk stack against the back plate. Torque is taken out by the stator disks through a static torque tube or the like.  
         [0004]     Electrically actuated aircraft brakes of various configurations are known, as exemplified by U.S. Pat. Nos. 4,381,049, 4,432,440, 4,542,809 and 4,567,967. The brake assemblies shown in these patents include electric motors which respond to an electrical control signal to effect rotation of a ring gear member which interacts through a plurality of balls to drive a linearly movable ram member into contacting engagement with a brake disk stack to effect compression thereof and braking of a wheel.  
         [0005]     In U.S. Pat. No. 4,596,316, another configuration of an electrically actuated brake uses a roller screw drive wherein a ring gear member interacts through a plurality of roller screws to drive a ram member into engagement with the brake pressure plate to effect compression of the brake disk stack for braking action. A plurality of electric motors and their associated pinions drive a ring gear into rotation and the plurality of roller screws effect linear axial movement of the ram member.  
         [0006]     In U.S. Pat. No. 4,865,162, a further electrically actuated aircraft brake employs a roller screw drive mechanism driven by an electric torque motor through a gear drive associated with either the screw or the nut of the roller screw drive mechanism. Rotation of the gear drive by the torque motor moves the other one of the screw or nut into axial engagement with a brake disk stack to compress the stack for braking. A plurality of the roller screw drive mechanisms and respective gear drives and torque motors are mounted in a balanced arrangement about the axis of the wheel to apply and release a brake pressure force on the brake disk stack in response to an electrical control signal to the torque motors.  
         [0007]     In U.S. Pat. No. 4,995,483, there is described a motor position feedback control system for an electrically actuated aircraft brake. The system controller provides brake clamping and declamping in response to a position feedback controlled brake actuator in which an electric torque motor drives a rotating member of a reciprocating drive mechanism to axially move another member into and out of engagement with a brake pressure plate of a multi-disk brake assembly. The position feedback is obtained using a rotor position resolver which provides relative position information to the controller. Such a system requires a re-calibration of the position sensor after a power interruption which may result in loss of braking capability, long recovery time and possible uncommanded brake clamp force application.  
         [0008]     Among other things, it would be desirable to have an electrically actuated aircraft brake actuator that has a greater stroke than prior art actuators, thereby to provide longer use between brake disk replacement.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides an electro-mechanical brake assembly comprising a brake disk stack having a center axis; and a plurality electro-mechanical actuators for applying braking pressure to the brake disk stack. The actuators are circumferentially arranged around the center axis, and each actuator includes a housing, a linearly movable ram, a screw for linearly moving the ram, a nut mounted for rotation in the housing and operatively engaged with the screw such that rotation of the nut effects linear movement of the screw for urging the ram into forceful engagement with the brake disk stack, an electric motor for rotating the nut, and an anti-rotation device for preventing rotation of the screw relative to the housing when the nut is rotated to effect linear movement of the screw. The foregoing arrangement provides for greater stroke than prior art actuators without sacrificing durability and performance.  
         [0010]     According to one embodiment of the invention, the screw has a bore opening to an end thereof opposite the ram, and the anti-rotation device includes an anti-rotation guide extending into the bore opening in the screw for rotationally interfering with one another to restrain rotation of screw relative to the housing. Preferably, the anti-rotation guide further functions to support the screw against lateral movement. To this latter end, anti-rotation guide extends to a point overlapping the internally threaded portion of the nut that is operatively engaged with the screw.  
         [0011]     A preferred nut and screw are a ball-screw device. Also, it is preferably that the electric motor be mounted to and carried by the housing. Ideally, each actuator is a self-contained unit mounted to a wheel mount of a wheel and brake assembly for removal independently of one another and the brake disk stack.  
         [0012]     According to another embodiment of the invention, the anti-rotation device includes a bellows connected between the screw and the housing and fixed against rotation relative to the housing, the bellows functioning to restrain rotation of screw relative to the housing. The bellows preferably is sealed with respect to the housing and screw to prevent foreign material from entering the housing at the screw.  
         [0013]     Further in accordance with the invention, a position sensor supplies a position signal representative of the position of the ram. The position sensor is fully enclosed within the housing and is connected directly to the screw or ram, or indirectly to a threaded portion on the nut.  
         [0014]     The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is cross-sectional view of an aircraft wheel and brake assembly  
         [0016]      FIG. 2  is a plan view of an exemplary electro-mechanical actuator that has particular application in the aircraft wheel and brake assembly of  FIG. 1 .  
         [0017]      FIG. 3  is a cross-sectional view of the brake actuator of  FIG. 1  taken along the line  2 - 2  of  FIG. 2 .  
         [0018]      FIG. 4  is an exploded perspective view of the brake actuator of  FIG. 1 .  
         [0019]      FIG. 5  is a diagrammatic illustration of another embodiment of an electro-mechanical actuator according to the invention.  
         [0020]      FIG. 6  is an illustration similar to  FIG. 5 , but showing the ram extended. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Because the invention was conceived and developed for use in an aircraft braking system, it will be herein described chiefly in this context. However, the principles of the invention in their broader aspects can be adapted to other types of braking systems, such as in train brake systems.  
         [0022]     Referring now in detail to the drawings and initially to  FIG. 1 , a wheel and brake assembly according to the present invention is generally indicated at  10 . The assembly  10  generally comprises a brake  11  and an aircraft wheel  12  which is supported for rotation by bearings  13  and  14  on an axle  15 . The axle  15  forms a wheel mount and is attached to the end of an aircraft landing gear strut (not shown) or a truck attached to the end of a landing gear strut. The brake  11  includes a brake disk stack, torque tube and an actuator assembly.  
         [0023]     The brake  11  includes a brake head  20  having an integral torque take-out arm. The torque take-out arm extends radially and functions as an interface between the brake actuator assembly and a landing gear axle structure. The torque reaction arm and torque take-out arm have interengaging devices which provide for transfer of torque from the torque take-out arm to the torque reaction arm when braking force is being applied to the disk brake stack by the brake actuator assembly. In the illustrated embodiment, the take-out arm has on the outboard side thereof an axially opening recess (socket) for receiving a torque reaction lug on the torque reaction arm and a load transducer. The load cell output may be supplied to a brake controller for use in controlling the braking operation.  
         [0024]     The break disk stack stationary brake elements and rotary brake elements that are interleaved and surround the torque tube. The stationary and rotary brake elements are in the form of stator disks  25  and rotor disks  26 . The stator disks  25  are splined to the torque tube and the rotor disks  26  are splined to the wheel  12  interiorly of the wheel&#39;s rim. As is conventional, the splined connection may be effected by a plurality of spline or drive keys that are spaced around the circumference of the rim/torque tube to permit axial movement of the rotor/stator disks while being held to the wheel/torque tube against relative rotation.  
         [0025]     The disk stack  27  is located between a back pressure member  31  and the brake head  20 . The back pressure member  31  is formed by a radial flange at the outer end of the torque tube  22 . The radial flange carries thereon a plurality of circumferentially spaced torque pucks  33  engaged with the last brake disk  34  at the rear end of the disk stack  27 . The torque pucks  33  may be attached in a known manner to the radial flange  31  by several torque pucks which have the stems thereof loosely fitted in holes in the radial flange to permit some swiveling movement thereof. The torque pucks in the illustrated embodiment secure the last brake disk  34  against rotation relative to the torque tube. In a modified arrangement, the radial flange could be configured to engage directly the disk pack, and still other arrangements could be used.  
         [0026]     Pressure is applied to the front end of the disk stack  27  by one or more actuator rams  35 . The actuator rams  35  are included in respective actuator modules  36  mounted to the brake head  20  by removable bolt fasteners  37  or other suitable means enabling quick and easy attachment and detachment of the actuator modules to and from the brake head. The actuator modules  36  preferably are mounted in a circular arrangement around the rotational axis of the wheel, preferably with the actuator rams circumferentially equally spaced apart.  
         [0027]     Preferably, the modules are identical and interchangeable, and a representative one of the actuator modules is shown in  FIG. 3 . Each actuator module  36  preferably includes an electric motor  50 , a gear train  51 , and a ball screw assembly  52 . The motor  50 , gearing  51  and ball screw assembly are all carried in a module housing  53 . A mounting flange (not shown) may be provided on the housing securing the module to the brake head  20 .  
         [0028]     The gearing  51  includes a pinion  59  on the drive shaft of the electric motor  50 , a first-stage transfer gear member  60  in mesh at it input end with the pinion, a second stage transfer gear member in mesh at its input end with the output end of the first stage gear member, and a ball nut gear in mesh with the output end of the second stage gear. The ball nut gear may be formed integrally with the ball nut of the ball screw assembly  52  (although reference herein is made to certain structures as being integral as is preferred, it should be understood such structures alternatively may be composed of discrete components joined together to form a functionally equivalent structure).  
         [0029]     The ball screw assembly  52  is comprised of the ball nut  62  with the integral gear  61 , a ball screw  63  that moves linearly upon rotation of the ball nut, an anti-rotation guide rod extending into the hollow interior of the ball screw, and a ram pad  64  that attaches to the end of the ball screw and provides an insulating interface with the brake disk stack ( FIG. 2 ). The ball screw and ball nut may be of a known configuration and thus the respective spiral grooves thereof and associated balls have not been illustrated as the same would be immediately evident to one skilled in the art. Also, other rotary to linear motion conversion devices may by employed, if desired, with the linear moving member coinciding with the ball screw and functioning as the actuator ram. In the illustrated ball screw assembly, the interior bore of the screw and the anti-rotation guide rod have corresponding polygonal cross-sections defined by plural inner/outer side surfaces which rotationally interfere with one another to restrain rotation of the screw relative to the housing. As is preferred and illustrated, one or more of the side surfaces, most preferably all of the side surfaces, are planar and form regular polyhedrons providing a close sliding fit between the ball screw and the guide rod. It will be appreciated, however, that other configurations may be used although less preferred.  
         [0030]     It also is noted that for some applications the motor may be dimensioned or positioned other than as shown, such that the motor may not pass completely through the brake head or even partially into the brake head. In one arrangement for example, the motor may extend only into a hole in the brake head that only opens to the outboard side of the brake head and thus is closed at its other end. Also, it the brake envelope permits, the motor could be located completely outwardly of the brake head and may be otherwise oriented, such as with its axis extending perpendicular to the movement axis of the actuator ram.  
         [0031]     The actuator includes an output ram position sensor which provides for actuator position feedback. For example, the ball nut  63  (actuator ram  35 ) may be mechanically connected to an LVDT position sensor by a bracket. The LVDT armature may be adjustably attached to the bracket (or the sensor body to the module housing) by suitable means that provides for LVDT setting and position calibration. Other types of position sensors/transducers may be used as desired for a particular application.  
         [0032]     The ram  35  of each actuator is mechanically connected to an LVDT position sensor  74 , such as by bracket  75 . The LVDT armature  76  may be adjustably attached to the bracket (or the sensor body to the brake housing) by suitable means that provides for LVDT setting and position calibration. A cover (not shown), or the like, may be provided to protect for the LVDT mounting mechanism. Although an LVDT sensor is preferred, other types of position sensors/transducers may be used as desired for a particular application.  
         [0033]     As shown in  FIGS. 12-15 , the intermediate cluster gear member  151  provides for two stages of reduction gearing and includes a first stage gear  155  and a second stage gear  156 . The first stage gear, which provides the first stage of gear reduction, is a bevel gear that meshes with a bevel gear  157  integral with the drive shaft  158  of the motor. The second stage gear  156  is a straight spur gear that mates with a ball screw gear  159  formed integrally with a ball screw  162 . The intermediate cluster gear member is supported by ball bearings  160  and  161  at its ends. Although reference herein is made to certain structures as being integral as is preferred, it should be understood such structures alternatively may be composed of discrete components joined together to form a functionally equivalent structure.  
         [0034]     The ball screw assembly  152  is comprised of the ball screw  162  with the integral gear  159 , a hexagonal ball nut  163  that translates rotary motion to linear motion of the ball nut, and a pad  164  that attaches to the end of the ball nut and provides the interface to the brake disk pressure plate. The ball screw and ball nut, which provide a third stage of reduction, may be of a known configuration and thus the respective spiral grooves thereof and associated balls have not been illustrated as the same would be immediately evident to one skilled in the art. The ball nut (also herein referred to as a ram or ram nut) is free to translate along the axis of the ball screw upon rotation of the ball screw, but not to rotate, as the ball nut is guided by a hexagonal bore  165  in the housing  147 .  
         [0035]     Referring now to  FIGS. 5 and 6 , another embodiment of electro-mechanical brake actuator according to the invention is illustrated, respectively in a retracted and extended position. The brake actuator is essentially as above described, except that in place of the anti-rotation guide, a metal bellows is used as an anti-rotation device. The bellows is connected at one end to the housing and at its other end to the screw directly or via the ram. The bellows additionally functions as a seal preventing foreign material from entering the housing at the screw.  
         [0036]     The brake actuator also differs in that an absolute position sensor is provided within the interior of the screw. The sensor may by an LVDT with one end connected to the screw and the other end connected to the housing, as at an actuator component cover forming part of the overall housing.  
         [0037]     Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described integers (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such integers are intended to correspond, unless otherwise indicated, to any integer which performs the specified function of the described integer (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.  
         [0038]     In addition, the invention is considered to reside in all workable combinations of features herein disclosed, whether initially claimed in combination or not and whether or not disclosed in the same embodiment.