Abstract:
An electric brake comprises an actuator module including a module housing, a reciprocating ram, and an electric motor operatively connected to the reciprocating ram for selectively extending and retracting the reciprocating ram with respect to the module housing. The ram has an inner portion of non-circular cross-section and an outer portion of circular cross-sectional, and the housing has a guideway for the ram, which guideway has an inner portion of non-circular cross-section for interacting with the inner portion of the ram to prevent rotation of the inner portion of the ram, and an outer portion of circular cross-sectional. The actuator module can be equipped with a bi-stable holding brake having a first state permitting at least retraction of the ram and a second state preventing at least retraction of the ram.

Description:
This application is a national phase of International Application No. PCT/US2004/013213 filed Apr. 30, 2004 and published in the English language. 
   FIELD OF THE INVENTION 
   The invention herein described relates generally to an electric brake particularly useful in aircraft, and more particularly to an electric brake actuator assembly, components thereof, and associated methods of assembly and operation. 
   BACKGROUND OF THE INVENTION 
   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 stack 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. 
   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. 
   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. 
   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. 
   The repair or maintenance of these previously known brakes including torque motor driven rams heretofore has required significant disassembly of the brake. The complex integrated nature of prior art designs normally requires substantial teardown of the assembly for maintenance, repair and/or overhaul of the assembly even if minor repair or only replacement of a single faulty component is required. Associated with extensive teardown is a lengthy reassembly and retest procedure to verify flight worthiness. Also, a highly integrated design and assembly with complex machining and assembly procedures is costly to process and manufacture. Distribution and parts stocking of individual components of such an assembly is similarly complex and inefficient as can be appreciated by those knowledgeable in this area. Consequently, an aircraft, for example a commercial passenger aircraft, would most likely have to be taken out of scheduled service until a faulty actuator could be serviced. This results in lost revenue for the airline, scheduling adjustments, considerable inconvenience for customers, etc. 
   U.S. Pat. No. 6,095,293 discloses an electric brake and method characterized by the use actuator modules each of which can be easily and quickly replaced as a unit. This enables quick and easy replacement of the actuator modules without requiring disassembly of the overall brake and wheel assembly. Also, it is conceivable that a malfunctioning actuator module could be replaced on an aircraft and tested with a minimum of equipment preferably quickly enough to allow the aircraft to remain in scheduled service and/or with a minimum of downtime. In addition, periodic maintenance of the brake can be done quicker and more efficiently by replacing the actuator modules with reconditioned and/or new actuator modules. 
   The electric brake described in U.S. Pat. No. 6,095,293 comprises a brake disk stack, a brake head, and at least one actuator module mounted to the brake head. The actuator module includes a module housing, a reciprocating ram and a motive device, i.e, an electric motor, operatively connected to the reciprocating ram for selectively moving the reciprocating ram into and out of forceful engagement with the brake disk stack for applying and releasing braking force. The actuator module is removable as a unit from one side of the brake head and most preferably from the side of the brake head opposite the brake disk stack. The ram includes a ram nut, and the electric motor is drivingly connected to a lead screw, e.g. a ball screw, in threaded engagement with the ram nut whereupon rotation of the lead screw effects linear movement of the nut toward and away from the brake disk stack. The module housing includes a guideway for guiding the ram nut, and the guideway and ram nut respectively have polygonal cross-sections defined by plural outer side surfaces which rotationally interfere with one another to restrain rotation of the ram nut relative to the housing. 
   SUMMARY OF THE INVENTION 
   The present invention provides a number of improvements over known electric brakes. The several aspects of the invention are below summarized. 
   According to one aspect of the invention, an electric brake actuator module comprises a module housing; a reciprocating ram; and an electric motor operatively connected to the reciprocating ram for selectively extending and retracting the reciprocating ram with respect to the module housing. The ram has an inner portion of non-circular cross-section and an outer portion of circular cross-section, and the housing has a guideway for the ram, which guideway has an inner portion of non-circular cross-section for interacting with the inner portion of the ram to prevent rotation of the inner portion of the ram, and an outer portion of circular cross-sectional. 
   In a preferred embodiment, an annular seal is provided between the outer portion of the ram and the outer portion of the guideway; the electric motor is operatively connected to the ram by a screw and a nut linearly driven by the screw, with the inner portion of the ram including the nut; the screw and nut are a ball screw and a ball nut; the guideway is formed by a bore in the housing; and/or the drive motor is operatively connected to the screw by reducing gears carried on shafts mounted in the housing for rotation about axes parallel to the rotational axes of the drive motor and screw. 
   According to another aspect of the invention, an electric brake actuator module, comprises a module housing; a reciprocating ram; an electric motor operatively connected to the reciprocating ram for selectively extending and retracting the reciprocating ram with respect to the module housing; and a bi-stable holding brake having a first state permitting at least retraction of the ram and a second state preventing at least retraction of the ram. 
   In a preferred embodiment, the motor is operatively connected to the reciprocating ram by at least one gear on a shaft, and the bi-stable holding brake is coupled to the shaft for permitting rotation of the shaft when in its first state and preventing rotation of the shaft when in its off state. 
   According to a further aspect of the invention, an electric brake actuator module, comprises a module housing; a reciprocating ram having a movement direction; an electric motor operatively connected to the reciprocating ram for selectively extending and retracting the reciprocating ram with respect to the module housing; and an electrical connector on the housing, the electrical connector having an insertion direction for connecting to a mating connector, and the insertion direction is parallel to the movement direction of the ram. 
   According to a still further aspect of the invention, an electric brake actuator module, comprises a module housing; a reciprocating ram having a movement direction; an electric motor operatively connected to the reciprocating ram for selectively extending and retracting the reciprocating ram with respect to the module housing; and an electrical connector on the housing, the electrical connector having an insertion direction for connecting to a mating connector, and the insertion direction is perpendicular (or alternatively parallel) to the movement direction of the ram. 
   According to yet another aspect of the invention, a cable conduit for an electric brake, comprises a generally arcuate-shaped channel; a plurality of module connectors disposed along the length of the channel for connecting to respective actuator modules of an electric brake; a common connector disposed along the length of the channel for connecting to an external cable; and electrical wiring in the channel for connecting the common connector to each of the module connectors. 
   In a preferred embodiment, each module connector has an insertion direction for connecting to a mating connector that is parallel to the insertion direction of each other module connector. 
   According to still another aspect of the invention, a brake comprises a brake head, and at least one actuator module mounted to the brake head, the actuator module including a reciprocating ram, a motive device operatively connected to the reciprocating ram for selectively moving the reciprocating ram into and out of forceful engagement with a brake disk stack for applying and releasing braking force, and a module housing in which the ram and motive device are carried for removal from the brake head as a unit. The brake head has at least one radially outwardly opening slot at a radially outer side thereof for receiving said one actuator module. 
   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 
       FIG. 1  is perspective rendering of an electric brake according to the invention. 
       FIG. 2  is an end elevational view of the electric brake. 
       FIG. 3  is a radial side elevational view of the electric brake. 
       FIG. 4  is a perspective view of an actuator module used in the electric brake. 
       FIG. 5  is a side elevational view of the actuator module. 
       FIG. 6  is plan view of the actuator module. 
       FIG. 7  is a perspective view of the actuator module with a bottom cover removed. 
       FIG. 8  is another perspective view of the actuator module with a top cover removed. 
       FIG. 9  is a cross-sectional view of the actuator module. 
       FIG. 10  is a perspective view of the actuator module with parts of the housing broken away to reveal internal components. 
       FIG. 11  is a perspective fragmentary rendering showing another mode of connectivity of an actuator module with a cable conduit according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   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. 
   Referring now in detail to the drawings and initially to  FIGS. 1-3 , an electric brake according to the present invention is generally indicated at  10 . The brake  10  generally comprises a brake actuator assembly  11  and a heat sink in the form of a brake disk stack  12 . The brake disk stack  12  can be of a conventional design including stationary brake elements and rotary brake elements that are interleaved and surround a torque tube or equivalent (not shown). The stationary and rotary brake elements usually are in the form of stator disks  15  and rotor disks  16 . The stator disks  15  typically are splined to the torque tube and the rotor disks  16  are splined to a wheel (not shown) 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. 
   The wheel (not shown) typically is supported for rotation on an axle (not shown) by axially spaced apart bearings (not shown). The axle thus forms a wheel mount and typically is attached to an aircraft landing gear strut or truck (not shown). 
   The brake actuator assembly  11  includes a brake head  18  (also commonly referred to as a brake housing) having a central opening  19  for mounting of the brake head on the landing gear axle or other wheel support. For some applications the brake head can be formed integrally with or fixedly secured (as by splines, bolts, etc.) to the axle or other wheel support for direct transfer of braking torque to the axle or other wheel support. In the illustrated embodiment, the brake head is supported on the axle for limited rotational movement, and the brake head is provided with a torque take-out arm  20 . The torque take-out arm  20  extends radially and functions as a torque transfer interface between the brake actuator assembly and the landing gear axle/strut/truck structure. More particularly, the torque take-out arm  20  has an eye  23  the provides for connection to a brake rod that in turn is connected to the landing gear axle/strut/truck structure, as in a conventional manner, to provide for transfer of torque from the torque take-out arm to the landing gear axle/struttruck structure when braking force is being applied to the disk brake stack  12  by the brake actuator assembly  11 . 
   The disk stack  12  typically is located between a back pressure member (not shown) and the brake head  18 . The back pressure member can be formed by a radial flange at the end of the torque tube opposite the brake head, which radial flange engages the last brake disk at the outboard end of the disk stack typically through the use of a plurality of circumferentially spaced apart pucks. 
   Pressure is applied to the other or inboard end of the disk stack  12  by the ram  26  of one or more actuator modules  27  that are mounted to the brake head  18 . The actuator modules  27  preferably are mounted in a circular arrangement around the center axis of the brake head  18 , preferably with the actuator rams  26  generally circumferentially equally spaced apart or with the rams arranged in diametrically opposed pairs. In the illustrated preferred embodiment, the actuator modules  27  are each electrically connected to an electrical cable conduit  29  that has a single interface connector  30  to which a mating connector of a control cable (not shown) can be detachably connected for connecting the brake  10  to a brake controller (not shown) located elsewhere. 
   Preferably, the actuator modules  27  are identical and interchangeable, and a representative one of the actuator modules is shown in  FIGS. 4-10 . As best seen in  FIGS. 9 and 10 , each actuator module  27  preferably includes an electric motor  31 , a gear train  32 , a ball screw and nut assembly  33 , and a bi-stable holding brake  34 . The motor  31 , gearing  32 , ball screw and nut assembly  33 , and holding brake  34  are all carried in a module housing  36 . In the illustrated embodiment, the module housing  36  includes a case  39  having a top opening closed by a top cover  40  and a bottom opening closed by a bottom cover  41 . The openings provide for assembly of the various internal components of the actuator module in the module housing. 
   The motor  31  can be of any suitable type, such as a brushless DC servo motor that may have integrated or otherwise associated therewith a resolver  42  for motor rotor commutation, angular velocity sensing and/or position sensing. The resolver can provide motor position feedback and velocity information. In particular, the resolver can provide an electrical signal that is proportional to motor shaft position under normal operating conditions. Power and control and/or output signals to or from the motor, resolver and holding brake  34  can be provided via an electrical connector  43  ( FIGS. 4-6 ), which in the illustrated embodiment is located on an inner side of the actuator module housing for connecting to a mating connector provided in the cable conduit  29 . 
   The gear train  32  provides for multiple stages of reduction. A first stage gear  44  meshes with a gear  45  integral with the drive shaft  46  of the motor  31 . The gear  44  meshes with a gear  94  on a shaft  47  that has a further gear  48  that meshes with a gear  49  provided on a shaft  50 . The gear  49  also meshes with a gear  51  provided on a shaft  52 . The shaft  52  has a further gear  53  that meshes with a screw drive gear  54  that preferably is formed integrally with the ball screw  55  of the ball screw and nut assembly  33 . The axes of the several shafts preferably are parallel with the axis of the ball screw and also the shaft  46  of the motor. Also, the shafts and ball screw are suitably journalled in the housing by suitable bearings for rotation about their respective axes, as is illustrated in  FIGS. 9 and 10 . 
   In addition to the ball screw  55 , the ball screw and nut assembly  33  includes ball nut  56  that moves linearly in response to rotation of the ball screw. It perhaps should be mentioned here that while a ball screw and nut are shown, other types of screw and nut assembly can be alternatively used, as can other types of rotary to linear motion conversion devices. The ball nut  56  is attached to or, as illustrated, formed as part of the actuator ram  26 . The ball nut and thus also the ram are free to translate along the axis of the ball screw  55  upon rotation of the ball screw, while, rotation of the ball nut is constrained. In the illustrated embodiment, rotation is constrained by interaction of the ball nut with a guideway  58  for the ram in the module housing  36 . 
   In the illustrated embodiment, the guideway  58  is formed by a bore in the casing  39  of the housing  18 . The bore has an inner longitudinal portion  62  of  20  non-circular cross-section for interacting with a non-circular cross-section of the ram nut  56  to prevent rotation of the ram nut relative to the housing. By way of a preferred example, the cross-sections of the ball nut and inner portion of the guideway  58  can have corresponding hexagonal or other polygonal shapes. 
   As is preferred, the ram nut  56  extends only partway along the linear extent of the ram  26 , whereas the outer or forward portion  64  of the ram is circular in cross-section. Similarly, the outer or forward portion  65  of the guideway  58  is circular in cross-section for guided movement of the cylindrical outer portion of the ram. The corresponding circular cross-sections are easier to seal than non-circular cross-sections. As shown, the guideway has at its outer end an annular groove for receiving a wiper or other suitable seal  67  for preventing foreign matter from entering the module housing and/or for retaining lubricant with the module housing. As will be appreciated, the length of the non-circular inner portion of the guideway will be greater than the length of the ball nut to allow for linear movement of the ball nut. The length of the non-circular inner portion of the guideway will also determine the stroke of the ram. In the illustrated embodiment, the length of the circular outer portion of the guideway is about equal the length of the ram nut. The particular dimensions can be varied as desired for a given application. 
   Preferably, a lubricant, particularly a suitable grease, is used to lubricate the relatively sliding surfaces of the ball nut/ram and the guideway  58 . It has been found that the grease and close clearance between the ball nut  56  and guideway  58  prevent entry of any appreciable amount of dirt or other foreign material at the sliding surfaces interface so as to prevent any significant degradation of performance. However, as above mentioned, a suitable seal  67 , such as a wiper seal or a rolling diaphragm seal, is employed to seal against passage of dirt or other undesirable materials between the sliding surfaces. An exemplary grease for the ball screw and ram nut assembly is MIL-G-81322 and an exemplary grease for the gear train is MIL-G-81827. 
   As shown, the ram  26  may be tubular and have its outer end closed by a cap  70  screwed into the end of the bore in the ram or otherwise secured to the ram. The cap can also be used as a convenient means to attach an insulating pad  71  to the end of the ram as depicted in  FIG. 3 , which pad provides the interface to the brake disk pressure plate and inhibits heat transfer into the actuator module. 
   As will be appreciated, rotation of the motor  31  in one direction will effect extension of the ram  26  for engaging and squeezing the brake disk stack  12 , whereas rotation in the opposite direction will effect retraction of the ram, as for releasing braking force. In any given position of the ram, the gear train can be locked by the bi-stable holding brake  34 . This is desirable, for-example, to retain the rams in an extended position applying braking force to the brake disk stack when the plane is parked, thereby to keep the brake engaged to prevent movement of the aircraft. Although other types of braking devices can be used to maintain the actuators in a brake-engaged condition, preferably the holding brake is a bi-stable device that will latch and hold in either on or off positions, even when no power is being applied to the brake. However, when pulsed the device can be switched between its on and off positions. A suitable bi-stable holding brake can be obtained from Electroid Company of Springfield, N.J., USA. and reference may be had to U.S. Pat. No. 5,185,542, which is hereby incorporated herein by reference in its entirety. As shown in  FIG. 9 , the bi-stable holding brake can be coupled to the shaft  49  to permit or prevent rotation of the shaft  50  when the brake is on or off, respectively. 
   As seen in  FIGS. 4-10 , a mounting flange  73  is provided on the housing for securing the module to the brake head  18 . As seen in  FIGS. 1 and 2 , the brake head  18  has a plurality of radially outwardly opening slots  75  at radially outer sides thereof for receiving respective actuator modules  27 . That is, the actuators can be inserted radially into and radially removed from the slots. Moreover, this can be done without having to remove the brake disk stack  12 . Accordingly, a defective actuator module can be swapped out without having to undergo any major disassembly of the overall brake assembly. 
   The mounting flange  73  of each module  27  preferably engages the surface of the brake head facing the brake stack. This surface can be provided with recesses  77  ( FIG. 3 ) for receiving the flanges of the actuator modules, as may be desired to facilitate proper locating of the actuator modules in the brake head and alignment of holes for bolt or other fastening devices. Also, a heat shield  79  can be attached to the side of the brake head nearest the brake stack, which shield can be provided with opening for passage of the actuator rams. 
   The connector  43  on each actuator module  27  and the mating connector of the cable conduit  29  can be configured to provide for connection of the connectors when the actuator module is inserted radially into its respective slot in the brake head. To that end, the connectors can be oriented for radial insertion of one connector into the other connector. In an alternative configuration shown in  FIG. 11 , each module connector  43 ′ and mating conduit connector  81  can be oriented axially. Accordingly, the actuator modules  27 ′ are first installed, and then the cable conduit is pressed into place to mate the connectors  81  thereof with the respective connectors  43 ′ of the actuator modules. As is preferred, the cable conduit is a single line replacement unit which provides for all electrical connectivity to the actuator modules. The conduit can be formed by a base member having a channel that opens to one side of the base member. The cabling can be placed in the channel and then a cover can be secured to the base member to close the channel. Such securement can be effected by one or more threaded fasteners. The fasteners can be positioned such that when the conduit is installed to the brake head, the fasteners are covered by respective portions of the brake head, thereby to prevent the screws from falling out should they become loose. The conduit can be sealed to prevent entry of foreign material, and the external connectors can be of a type that when mated provide a hermetic seal. 
   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. 
   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.