Abstract:
A brake comprising a brake disk stack including stators alternating with rotors that are rotatable relative to the stators about an axis of the disk stack, an annular torque plate at one axial end of the brake disk stack, and a circumferential arrangement of actuators at the other axial end of the brake disk stack for urging the brake disk stack against the torque plate thereby to effect a braking force on the rotors. A back leg ( 33 ) of the annular torque plate includes a plurality of apertures ( 110   a - 110   f ) arranged asymmetrically around the axis of the brake disk stack.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority of U.S. Provisional Application No. 60/939,192 filed on May 21, 2007, which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to brakes and, more particularly, to an aircraft brake that includes an asymmetrical brake torque plate. 
       BACKGROUND OF THE INVENTION 
       [0003]    Aircraft wheel and brakes heretofore have included a non-rotatable wheel support, a wheel rotatably mounted to the wheel support, and a brake disk stack having 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 brake torque plate is located at the rear end of the disk pack and is comprises a torque tube and a back leg, while a brake head is located at the front end. 
         [0004]    The brake head may house a plurality of actuator rams that extend to compress the brake disk stack against the brake torque plate. The brake torque plate provides the structure onto which the stator disks are splined for torque reaction, provides the reacting surface (back leg) for disk stack actuation loads, and provides the transfer of torque into adjoining structures, such as the brake piston housing or aircraft axle (e.g., via a torque tube). The back leg design of the brake torque plate can be varied to provide proper stiffness and minimum weight. 
         [0005]    A function of aircraft brakes is to provide a stopping force or torque so as to quickly and efficiently convert kinetic energy into heat energy. In providing the stopping force, brakes may subject the aircraft (or parts thereof) to vibration. Such vibration is undesirable, as it can cause fatigue, cracking and/or failure of the aircraft&#39;s components, particularly in the area of the brakes and wheels. 
       SUMMARY OF THE INVENTION 
       [0006]    Conical shape brake torque plate back legs are desirable in aircraft braking systems for a number of reasons. For example, conical shape brake torque plate back legs can be formed to have minimal weight, and yet still be capable of providing the proper stiffness for the braking system. However, it has been discovered that conical shape brake torque plate back legs can contribute to or amplify vibration created by or introduced to the braking system. These vibrations, as noted above, are undesirable. 
         [0007]    An apparatus in accordance with the present invention reduces vibration in brakes, such as aircraft brakes, that utilize conical brake torque plates. As used herein, a brake torque plate refers to the combination of a torque tube and a back leg. A brake torque plate in accordance with the invention is formed so as to reduce symmetry of the brake torque plate (e.g., by including apertures placed asymmetrically around a circumference of the brake torque plate back leg). The brake torque plate with asymmetrically placed apertures significantly reduces vibration in the braking system. 
         [0008]    Moreover, the reduced vibration can provide more consistent brake friction from cycle to cycle for each braking condition (e.g., landing, taxi stop). Brakes equipped with reduced symmetry brake torque plates in accordance with the invention also have been found to provide less variation between hot and cold taxi friction, which provides a more consistent pedal feel for the pilot and may promote improved wear rates. 
         [0009]    According to one aspect of the invention, there is provided a brake system comprising a brake disk stack including stators alternating with rotors that are rotatable relative to the stators about an axis of the disk stack, an annular torque plate including a back leg at one axial end of the brake disk stack, and a circumferential arrangement of actuators at the other axial end of the brake disk stack. The actuators are operative to urge the brake disk stack against the torque plate, thereby effecting a braking force on the rotors. Further, the back leg of the annular torque plate includes a plurality of apertures arranged asymmetrically around the axis of the brake disk stack. 
         [0010]    According to another aspect of the invention, a brake comprising a brake disk stack including stators alternating with rotors that are rotatable relative to the stators about an axis of the disk stack, an annular torque plate including a back leg at one axial end of the brake disk stack, and a circumferential arrangement of actuators at the other axial end of the brake disk stack for urging the brake disk stack against the torque plate thereby to effect a braking force on the rotors. Further, the back leg includes a plurality of circumferentially arranged segments of varying torsional and axial strength. 
         [0011]    To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The forgoing and other embodiments of the invention are hereinafter discussed with reference to the drawings. 
           [0013]      FIG. 1  is a schematic cross-sectional view of an exemplary aircraft brake assembly showing a piston housing with an actuating cylinder, pressure plate, torque plate and brake stack. 
           [0014]      FIG. 2  is perspective view of a brake torque plate in accordance with the invention. 
           [0015]      FIGS. 3A and 3B  are a cross sectional view and an end view of the torque plate of  FIG. 2 . 
           [0016]      FIGS. 4 and 5  are plots showing average friction coefficient relative to the number of stops for a brake employing a conventional torque plate and the torque plate according to  FIGS. 2 and 3 . 
           [0017]      FIG. 6  illustrates two vibration plots for a brake using a torque plate having a conventional back leg. 
           [0018]      FIG. 7  illustrates two vibration plots for a brake using a torque plate having a back leg in accordance with the present invention. 
           [0019]      FIGS. 8A-8D  show transient vibration plots during a landing snub for brakes using a torque plate having a conventional back leg and a back leg in accordance with the present invention. 
           [0020]      FIGS. 9A-9D  show transient vibration plots during a hot taxi stop for brakes using a torque plate having a conventional back leg and a back leg in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Referring to the drawings, wherein like reference numerals designate like or corresponding parts throughout the several views, there is schematically depicted in  FIG. 1  a friction brake mechanism  10  mounted on axle  11  for use with a wheel (not illustrated) rotatable about axial centerline  12  in a manner fully described in U.S. Pat. No. 4,018,082 to Rastogi et al., U.S. Pat. No. 4,878,563 to Baden et al., and U.S. Pat. No. 5,248,013 to Hogue et al. The friction brake mechanism  10  includes a pressure plate  38  adjacent the hydraulic piston motor  25 , an end plate  36  distal from the piston motor, and a plurality of interleaved rotor disks  44  and stator disks  39  which together form the brake heat sink or brake stack. The friction brake mechanism  10  also includes a torque plate  32 ,  33  on which the pressure plate  38 , end plate  36  and stator disks  39  are slidably mounted against rotation relative to the wheel and rotor disks  44 . 
         [0022]    Torque plate  32 ,  33  includes an annular brake torque plate back leg  33  at its end distal the piston motor  25 . The brake torque plate back leg  33  may be made integral with the torque tube  32  as shown in  FIG. 1  or may be made as a separate annular piece and suitably connected to the stationary torque tube  32 . Torque tube  32  may include a support structure  32   a  formed in an inner surface of the torque tube  32 . Torque tube  32  has a plurality of circumferentially spaced splines  35  that are axially extending. Splines  35  on torque tube  32  support the axially moveable nonrotatable pressure plate  38  and axially moveable nonrotatable stator disks  39 . All of such stator disks  39  and pressure plate  38  have notches  40  in the form of slotted openings at circumferentially spaced locations on their inner periphery for captive engagement by the spline members  35  as is known in the art. The respective annular stator disks  39  each have friction linings  42  secured to opposite faces thereof as shown in  FIG. 1 . Pressure plate  38  also has a friction lining  42  on one surface thereof to act in concert with the other friction linings  42  when a braking action occurs. The end plate  36  carries an annular friction lining  42  and is suitably connected to the brake torque plate back leg  33  of the torque plate  32 ,  33  and acts in concert with the stator disks  39  and the pressure plate  38 . The friction linings  42  and the disks they are attached to may be an integral piece such as in carbon composite brakes. 
         [0023]    The plurality of axially spaced rotor disks  44  interleaved between the pressure plate  38  and the stator disks  39  have a plurality of circumferentially spaced notches  40  along their outer periphery for engagement by corresponding ribs secured to or integral with the inner periphery of the wheel. Such stator disks  39  with their friction linings  42  and rotor disks  44  with their friction linings  52  acting together during a braking action provide a heat sink. The number and size of the disks may be varied as is necessary for the application involved. 
         [0024]    The actuating mechanism for the brake includes a plurality of hydraulic piston assemblies  25  circumferentially spaced around the annular piston housing  26  in known manner. Only one piston assembly is shown in  FIG. 1 . Upon actuation by fluid pressure, the piston motors  25  effect a braking action by moving the pressure plate  38  and the stator disks  39  into frictional engagement with the rotor disks  44  and against the brake torque plate  33 . Alternatively, an electrically driven actuator may be used in place of the hydraulic assembly. 
         [0025]    The pressure plate  38  can be formed of carbon or ceramic composite material and has an annular friction lining  42  of carbon or ceramic composite material attached as by rivets to the surface of pressure plate  38  opposite to the face of the pressure plate carrier  37  that receives the head of the hydraulic piston motors  25 . The carrier  37  of pressure plate  38  is engaged to the torque tube  32  via slotted opening at circumferentially spaced locations on its inner periphery. The friction lining  42  may be riveted to the pressure plate carrier  37  to locate the lining in position. The friction lining  42  may be an integral part of the pressure plate  38 . 
         [0026]    The end plate  36  can include a friction lining  80  having a plurality of torque transfer recesses  57  for engagement with a plurality of torque transfer buttons  58 . The friction lining  80  may be secured to the torque buttons  58  by a plurality of rivets which pass through the regions of greatest thickness of the friction lining and recessed regions of the torque buttons. 
         [0027]    With further reference to  FIGS. 2 ,  3 A and  3 B, there is shown a perspective, cross sectional and end view of a torque plate that can be used in the brake mechanism  10  of  FIG. 1 , wherein the torque plate includes a torque tube  32  and an exemplary brake torque plate back leg  33  in accordance with the invention. The torque tube  32  may be formed as an elongated shaft having a hollow central portion  100 . An annular mounting surface  102  or the like is formed on a proximal end  103  of the torque tube  32  and includes a plurality of threaded bores  104  formed therein. The torque tube  32  can be attached to the piston housing  26  via the annular mounting surface  102 , wherein bolt fasteners  105  (see  FIG. 1 ) hold the torque tube  32  to the piston housing  26 . 
         [0028]    The torque tube  32  may include a plurality of symmetrically or asymmetrically spaced apertures  101  formed along an inner radial surface of the torque tubes&#39;s proximal end  103 . The apertures  101  can have varying shapes, and can serve as an alignment aid when attaching the torque tube  32  to the piston housing  26 . Bores  102   a  formed through an outer radial surface of the torque tube&#39;s proximal end  103  can be used as an alternate means for attaching the torque tube  32  to the piston housing  26 . 
         [0029]    A distal end  107  of the torque tube  32  includes or is otherwise attached to the back leg  33 . For example, and as noted above, the brake torque plate back leg  33  may be formed integral to the torque tube  32 , or the brake torque plate back leg  33  may be formed as a separate piece and attached to the torque tube  32 , e.g., via bolt fasteners (not shown). The brake torque plate back leg  33  flares outward from the central portion  100  of the torque tube  32  so as to have a conical shape. 
         [0030]    A peripheral ring  106  formed along an outer diameter of the conical portion of the brake torque plate back leg  33  includes circular torque transfer buttons  58 . The torque transfer buttons  58  can react to the brake actuation loads and also serve as torque reaction points (i.e., the back leg) for the end plate  36 . 
         [0031]    Formed on the radially outer areas of the conical portion of the brake torque plate back leg  33  are a plurality of apertures  110   a - 110   f  or slots, wherein the apertures are unevenly spaced around the circumference of the conical portion. For example, the torque transfer buttons  58  are shown evenly (i.e., symmetrically) spaced around the circumference of brake torque plate conical portion. The apertures  110   a - 110   f , however, are not evenly spaced along the circumference (e.g., one torque transfer button  58  is between apertures  110   c  and  110   d , while two torque transfer buttons  58  are between the remaining apertures. Although six apertures are shown, more or fewer apertures may be provided without departing from the scope of the invention. Further, the spacing between apertures also may vary (e.g., some may be separated by 1 button, some by two buttons, some by three buttons, etc.). 
         [0032]    The apertures may be formed anywhere along the area between the outer peripheral ring  106  and the torque tube  32 . Preferably, the apertures  110   a - 110   f  are formed along the peripheral ring  106 , and may be machined into the brake torque plate back leg  33  or formed therein to a depth that does not intrude greatly into the conical portion, which provides most of the stiffness. The apertures or “segments” (also referred to as “fingers”) may be thought of as providing varying torsional and axial strength to the torque plate back leg  33 . 
         [0033]    Regardless of how the apertures are formed, they reduce symmetry in the back leg area of the brake torque plate  32 ,  33 . This has the effect of reducing general high frequency (e.g., 3-5 kHz) vibration levels in the brake assembly (tests have shown 50 percent or more reduction in high frequency vibration levels), which increases the life expectancy of the braking system components. Further, this reduction in vibration has been found to provide more consistent brake friction from cycle to cycle for each braking condition (e.g., landing, taxi stop), which can promote improved wear rates. 
         [0034]      FIGS. 4 and 5  are graphical charts that demonstrate friction variability effects of the asymmetrically placed apertures on a braking system. More specifically,  FIG. 4  illustrates the dynamics of average friction data for a 5-stop service cycle for two different brake configurations. A service cycle includes a landing stop and hot taxi stops. T-24423 represents test data for a brake employing a conventional, symmetrical torque plate, while T-24481 represents test data for a brake employing a torque plate in accordance with the invention. 
         [0035]    As can be seen in  FIG. 4 , the test data shows that for T-24481 both hot taxi stop coefficient of friction  120  and landing stop coefficient of friction  122  remain relatively constant through a number of stops. For example, the service landing stop coefficient of friction exhibits very little variation after about stop  30  (the coefficient of friction remains about 0.30), and effectively approaches a straight line plot. Similarly, the hot taxi stop coefficient of friction also remains substantially constant throughout the test (e.g., between about 0.39 and 0.40). 
         [0036]    In contrast, the service landing stop friction and the hot taxi stop friction vary significantly in the test data for T-24423. In particular, service landing stop coefficient of friction varies from about 0.26 all the way up to about 0.38. Similarly, the hot taxi stop coefficient of friction varies from about 0.42 to 0.47 
         [0037]    With reference to  FIG. 5 , the coefficient of friction variation between the two different brake types can be seen in testing performed using design landing (normal) energy, high deceleration stops with cold and hot taxi stops. In particular, the coefficient of friction variation for the brake using the torque plate in accordance with the present invention (T-24481) is between about 0.32 and 0.44 (i.e., a variation of about 0.12). In contrast, the coefficient of friction variation for the brake using a conventional, symmetrical torque plate (T-24423) is between about 0.21 and 0.40 (i.e., a variation of about 0.19). 
         [0038]    Thus, the torque plate in accordance with the invention reduces vibration in the brake system. This reduced vibration in turn reduces variation in the coefficient of friction for the braking components, thus providing more consistent braking torque. 
         [0039]    As noted above, the torque plate in accordance with the present invention also reduces vibration during a stop. It is believed that the apertures in the back leg offer decoupling of the torque plate barrel and back leg vibration modes. 
         [0040]      FIGS. 6 and 7  compare the peak vibration levels recorded for all stops over the spectrum of frequencies, wherein peak values for each of the high frequency modes are noted on each graph. The data shown in  FIG. 6  (T-24423) pertain to a conventional back leg design, while the data in  FIG. 7  (T-24540) pertain to a back leg in accordance with the present invention. 
         [0041]    Further,  FIGS. 8A-8D  and  9 A- 9 D show transient vibration plots for individual landing and taxi stops for two qualification test, wherein  FIGS. 8A ,  8 C,  9 A and  9 C pertain to a conventional back leg design, and  FIGS. 8B ,  8 D,  9 B and  9 D pertain to a back leg in accordance with the present invention. The data in these plots includes the full range of frequencies measured during the tests. 
         [0042]    Comparing the results of the tests, it is noted that peak vibration between comparable development and qualification hardware configurations are very consistent in both cases (baseline back leg and slotted back leg). Some differences are present between higher frequencies in test no. 24481 and 24540 due to variations in torque plate section thickness in the back leg. Also, there is a noticeable reduction in peak vibration at frequencies below 5 kHz for the back leg design in accordance with the invention. 
         [0043]    Accordingly, a brake torque plate for use in an aircraft braking system has been disclosed. The brake torque plate reduces high frequency vibration in aircraft braking systems, thereby increasing the life expectancy of the system. Further, the brake torque plate in accordance with the invention provides for consistent coefficients of friction, even after repeated stops. 
         [0044]    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.