Abstract:
A system to reduce or eliminate brake actuator contamination by providing a clean air source for the actuator such that a volume of a void in the actuator can vary without introducing moisture and/or contaminants into the actuator. A movable wall moves in response to changes in the volume of the void of the actuator to compensate for the changes without drawing moisture or contaminants into the actuator housing. By reducing or eliminating actuator contamination the service life of the actuator can be extended.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to actuators and, more specifically, to actuators for brake systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
         [0005]    U.S. Pat. No. 6,095,293 discloses an electric brake and method characterized by the use of 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. 
         [0006]    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. 
         [0007]    International Publication No. WO 01/20188 also discloses another electro-mechanical actuator module including 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. This arrangement provides for greater stroke than prior art actuators without sacrificing durability and performance. To prevent foreign material from entering the housing at the screw, a bellows is used to provide a seal with respect to the housing and screw. 
         [0008]    While such modular actuators represent an improvement insofar as ease of replacement, the actuators are still susceptible to contamination due to the infiltration of moisture and/or contaminants. For example, as an actuator ram moves during operation and/or over time from wear of the brake friction material, the actuator breathes as the void volume of the actuator changes. Breathing can introduce moisture and/or contaminants into the actuator that can lead to premature actuator wear and/or failure (e.g., seizure). Filters may provide a suitable solution in some instances, but generally are not effective at removing water vapor. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a system to reduce or eliminate actuator contamination by providing a clean air source for the actuator. Thus, the void volume of the actuator can vary without introducing moisture and/or contaminants into the actuator thereby potentially extending the actuator service life and avoiding reliability issues that can result in aircraft downtime. 
         [0010]    Accordingly, an actuator for a brake comprises a housing, a linearly movable member extending from the housing for compressively engaging a braking element to effect a braking action, and a movable wall that defines an enclosed chamber with the actuator housing. The enclosed chamber changes volume in response to movement of the linearly movable member and the wall moves to compensate for the changes in a volume of void of the actuator housing. 
         [0011]    More particularly, the movable wall can be a diaphragm that forms a chamber together with the housing and linearly movable member. The actuator housing can generally be sealed except for an inlet for makeup flow from a makeup flow device that includes the movable wall. The makeup flow device can be a piston/cylinder arrangement having a first chamber connected to the actuator housing and a second chamber open to the atmosphere. The piston/cylinder arrangement can be mounted remotely from the actuator, and the first chamber can be connected to the actuator housing by a hose. The piston/cylinder arrangement can have a rod extending from the cylinder, with a degree of extension of the rod from the cylinder corresponding to a degree of brake wear. The actuator can be an electric actuator including an electric motor for driving the linearly movable member. 
         [0012]    According to another aspect, a brake assembly comprises a brake disk stack and an actuator assembly for applying braking force to the brake disk stack, the actuator assembly including at least one actuator module having a housing and a linearly movable member extending from the housing for compressively engaging the brake disk stack. A movable wall defines an enclosed chamber with the actuator housing that changes volume in response to movement of the linearly movable member. The movable wall moves to compensate for changes in a volume of void of the actuator housing. 
         [0013]    The actuator housing can be generally sealed except for an inlet for makeup flow from a makeup flow device that includes the movable wall. The makeup flow device can be a piston/cylinder arrangement having a first chamber connected to the actuator housing and a second chamber open to the atmosphere. The piston/cylinder arrangement can have a rod extending from the cylinder with a degree of extension of the rod from the cylinder corresponding to a degree of brake wear. The piston/cylinder arrangement can be mounted remotely from the actuator, and the first chamber can be connected to the actuator housing by a hose. The actuator can include a plurality of actuator modules and the makeup flow device can provide makeup flow to more than one actuator module. The at least one actuator can be an electric actuator including an electric motor for driving the ram. 
         [0014]    Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of a prior art electric brake. 
           [0016]      FIG. 2  is a perspective view of an actuator module of the prior art brake of  FIG. 1 . 
           [0017]      FIG. 3  is a cross-sectional view of the actuator module of  FIG. 2  in a first position. 
           [0018]      FIG. 4  is a cross-sectional view of the actuator module of  FIG. 2  in a second position. 
           [0019]      FIG. 5  is a schematic diagram of an exemplary actuator module in accordance with the invention in a first position. 
           [0020]      FIG. 6  is a schematic diagram of the exemplary actuator module of  FIG. 5  in a second position. 
           [0021]      FIG. 7  is a schematic diagram of two exemplary actuator modules sharing a common piston/cylinder arrangement in accordance with the invention. 
           [0022]      FIG. 8  is a schematic diagram of another exemplary actuator module in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    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. 
         [0024]    Referring now in detail to the drawings and initially to  FIG. 1 , an exemplary electric brake 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 or other 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 a torque tube  17  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. 
         [0025]    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). For further details, reference may be had to U.S. Pat. No. 6,662,907, which is hereby incorporated herein by reference in its entirety. 
         [0026]    The brake actuator assembly  11  includes a brake head  18  that can also be referred to as a brake housing or, in the present case, more particularly as a brake mounting plate. The brake mounting plate has a central opening  19  for mounting of the brake mounting plate on the landing gear axle or other wheel support. For some applications the brake mounting plate 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 mounting plate is supported on the axle for limited rotational movement, and the brake mounting plate is provided with an 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  that 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/strut/truck structure when braking force is being applied to the disk brake stack  12  by the brake actuator assembly  11 . 
         [0027]    The disk stack  12  typically is located between a back pressure member (not shown) and the brake mounting plate  18 . The back pressure member can be formed by a radial flange at the end of the torque tube opposite the brake mounting plate, 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. For further details, reference may be had to U.S. Pat. No. 6,662,907. 
         [0028]    Pressure is applied to the other or inboard end of the disk stack  12  by the ram  26  ( FIG. 2 ) of one or more actuator modules  27  that are mounted to the brake mounting plate  18 . The actuator modules  27  preferably are mounted in a circular arrangement around the center axis of the brake mounting plate  18 , preferably with the actuator rams  26  generally circumferentially equally spaced apart and/or with the rams arranged in diametrically opposed pairs. The actuator modules  27  can be connected by any suitable means such as cables to 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. The brake mounting plate serves as the platform for mounting the actuator modules and for reacting actuation and torque loads from the brake to an aircraft brake rod or other landing gear structure. 
         [0029]    As shown in  FIG. 2 , the housing  34  of each actuator module  27  can be formed from several parts, and these parts can be associated with respective parts or sections of the actuator module. Generally, the actuator module has a ram drive section  55 , a motor section  56  and a transmission section  57  connecting the ram drive section to the motor section. These sections can be removable with respect to one another, as might be desired to facilitate assembly and/or refurbishing the actuator module. 
         [0030]    Referring now to  FIGS. 3 and 4 , the illustrated representative actuator module  27  includes an electric motor  80 , a multi-stage reduction gear train  81 , and a ball screw assembly  82 . The motor  80 , gearing  81  and ball screw assembly  82  are all carried in the module housing  34 . Suitable bearings are provided for the various rotating components. An electrical connector can be provided on the housing for interfacing the motor with control circuitry. 
         [0031]    The ball screw assembly  82  includes a ball nut  90  having a gear  92  in mesh with the output end of gearing  81 . The ball screw assembly further includes a ball screw  94  that moves linearly upon rotation of the ball nut, an anti-rotation guide member  96  extending into the hollow interior of the ball screw, and a ram sleeve  98  that is telescoped over an axially outer portion of the ball nut. The ball screw and ball nut have respective spiral grooves/threads and associated balls for converting rotary motion to linear motion. 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 at its outboard end as the actuator ram. In the illustrated ball screw assembly, the interior bore of the screw and the anti-rotation guide have corresponding non-circular, e.g. polygonal, cross-sections which rotationally interfere with one another to restrain rotation of the screw relative to the housing. 
         [0032]    The ball screw assembly translates the rotary motion from the gear train to the linear motion at the actuator output. Mechanical stops can be provided to limit the stroke of the translating screw, and a stop can be used as an absolute position indicator for calibrating the actuator stroke position. 
         [0033]    The translating ball screw functions as the actuator ram and contacts the carbon brake disc stack through an insulator. For example, the ball screw assembly  82  is shown in an extended position in  FIG. 4  with the ball screw  94  shifted axially from its position shown in  FIG. 3 . The screw can be made of Inconel for thermal considerations. By simply changing the ball screw assembly the stroke length can easily be modified to allow the actuator to operate on many different aircraft brake assemblies with different stroke lengths. 
         [0034]    The ram sleeve  98 , which can be attached to the end of the ball screw, provides a sealing enclosure and can also function as an insulating interface with the brake disk stack. A dynamic seal/scraper  100  is used to seal the ram sleeve to the housing to prevent fluid from entering the actuator. The sleeve telescopically slides on a cylindrical end portion of the ram nut with a sliding fit in the housing. The sleeve has a length sufficient to cover the length of the screw that will project from the housing at full extension, while still remaining coextensive with the ram nut. 
         [0035]    As will be appreciated, rotation of the motor  80  in one direction will effect extension of the screw/ram for engaging and squeezing the brake disk stack, 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 if the gearing or motor is so-equipped. This is desirable, for example, to retain the ram 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. 
         [0036]    Even though the actuator module  27  may be generally sealed, extension of the screw/ram from the actuator housing during braking activities leaves a void within the housing  34  that results in air being drawn into the actuator module  27 . Such air may contain water vapor and/or contaminants that can lead to premature wear and/or require more frequent replacement/repair of the actuator module  27 . 
         [0037]    Turning to  FIGS. 5 and 6 , and in accordance with the invention, an actuator module  27 , such as described above, is schematically illustrated with a movable wall that compensated for changes in a volume of void V of the actuator housing  34  so as to reduce or eliminate contamination of the actuator housing with dirt, moisture, etc. 
         [0038]    In the illustrated embodiment, a piston and cylinder arrangement  102  provides a source of clean make-up fluid, which may be a liquid or a gas, to the actuator module  27 . The piston and cylinder arrangement includes a piston  106  (e.g., movable wall) supported within a cylinder  110  for sliding axial movement. The piston  106  divides the cylinder  110  into first and second chambers  114  and  118  that are generally sealed from each other. In this regard, a seal (not shown), may typically be provided for sealing the piston  106  to the inside diameter of the cylinder  110 . 
         [0039]    The first chamber  114  of the piston/cylinder arrangement  102  is fluidly connected to the interior of the housing  34  of the actuator module  27  by a tube  116  or other suitable conduit. The second chamber  118  is open to the atmosphere, for example, via port  122 . Thus, air is free to move into and out of the second chamber  118  in response to movement of the piston  106  within the cylinder  110 . Although the second chamber  118  is illustrated as open to atmosphere, it could alternatively be connected to a fluid reservoir or other source of fluid, for example. If open to the atmosphere, one or more drain holes could be provided for draining accumulated liquid from the second chamber  118 . 
         [0040]    With reference to  FIG. 6 , during operation of the actuator module  27  the ball screw  94  shifts axially within the housing  34 . This axial shifting results in a change in the void volume V of the interior of the housing  34  causing respective negative and positive pressures within the housing  34 . In the past, such pressure differentials were typically equalized by the influx or outflow of ambient air, moisture, contaminants, etc. into the actuator housing  34 . 
         [0041]    In accordance with the invention, the piston/cylinder arrangement  104  provides closed system makeup flow to the actuator module  27  thereby allowing the actuator module  27  to breathe without inducing moisture and/or contaminants to the interior of the housing  34 . Thus, for example, as the void volume V of the actuator module  27  increases resulting in a negative pressure, fluid is drawn into the actuator housing  34  from chamber  114  of the piston/cylinder arrangement  104 . If the void volume of the actuator module  27  decreases, the resulting positive pressure results in fluid being expelled from the housing  34  to chamber  114 . As will be appreciated, the fluid (e.g., air) in the first chamber  114  is generally isolated from environmental contaminants such as moisture and particulates thus providing a source of clean makeup flow to the actuator module  27 . 
         [0042]    Over time, the friction material of the brake will typically wear down resulting in an overall increase in the void volume V of the actuator housing  34  as the screw  94  extends further and further out of the housing  34 . Accordingly, the volume of chamber  114  will tend to decrease to compensate for the increase in volume of the void V. A piston rod  128  extending from the cylinder  108  can be provided as illustrated to give a visual indication of the state of brake wear based on the length of the piston rod  128  extending from the cylinder  110 , wherein a degree of extension of the rod from the cylinder corresponds to a degree of brake wear. 
         [0043]    For example, the piston rod  128  can include graduations  132  as shown corresponding to varying levels of wear. The illustrated piston rod  128  of  FIG. 5  may be considered to indicate a slight amount of wear. As wear increases and the piston rod  128  shifts leftward such as shown in  FIG. 6  (i.e., into the cylinder  110 ), less of the piston rod  128  will extend from the housing thereby indicating more wear. A sensor (not shown) may be provided for sensing the position of the piston rod  128  in order to sense brake wear. Such a brake wear indicator would typically be provided in addition to standard brake wear indicators and/or sensors, or to provide a simple visual indicator of break wear useful during brake inspection. Such indicators could be placed in a location on an aircraft that is easily viewed by maintenance personnel, for example. 
         [0044]    Turning now to  FIG. 7 , another exemplary embodiment in accordance with the present invention in illustrated. In this embodiment, two actuator modules  27  share a common piston/cylinder arrangement  102 . As will be appreciated, virtually any number of actuator modules  27  could share a common piston/cylinder arrangement  102  provided that the piston/cylinder arrangement is appropriately sized. 
         [0045]    In  FIG. 8  another exemplary actuator module  27  is illustrated. The actuator module  27  is identical to the actuator modules of  FIGS. 5 and 6  with the exception of the closed loop makeup flow device. In  FIG. 8 , a diaphragm  134  is provided instead of the piston/cylinder arrangement. 
         [0046]    The diaphragm  134 , as will be appreciated, is configured to flex in response to changes in pressure within the actuator housing  34  due to a change in void volume V therein to supply makeup flow to the actuator housing  34 . Accordingly, the diaphragm  134  works in much the same way as the piston/cylinder arrangement  102  in  FIGS. 5 and 6  by providing a source of clean makeup flow to the actuator to prevent contamination thereof. As will be appreciated, the diaphragm  134  could be integral with the actuator housing  34  forming a portion thereof, for example, and a brake wear indicator could be provided wherein a degree of flex of the diaphragm corresponds to a degree of brake wear. 
         [0047]    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 elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (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 or more 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.