Patent Publication Number: US-2019176973-A1

Title: Differential emergency/park electric brake system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and is a divisional application of U.S. patent application Ser. No. 15/427,262 entitled “Differential Emergency/Park Electric Brake System” and filed Feb. 8, 2017, the contents of which are hereby incorporated by reference in its entirety. The &#39;262 Application claims priority to and is a divisional application of U.S. patent application Ser. No. 14/939,663 entitled “Differential Emergency/Park Electric Brake System” and filed Nov. 12, 2015, the contents of which are hereby incorporated by reference in its entirety. The &#39;663 Application claims priority to and is a divisional application of U.S. patent application Ser. No. 12/433,050 entitled “Differential Emergency/Park Electric Brake System” and filed Apr. 30, 2009, the contents of which are hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present invention relates generally to brakes and, more particularly, to brake controls for providing parking and emergency braking functions in an aircraft. 
     BACKGROUND 
     Aircraft, much like other vehicles, incorporate an emergency braking system that activates the brakes for long term parking, and for emergency stopping when the principal brake system fails. Such emergency brake systems may be electrically or hydraulically operated, and are well known to those having ordinary skill in the art. 
     In electrically operated emergency brake systems, an emergency brake command signal (in the form of an analog or digital signal) is generated by an emergency brake lever or handle, and this signal is provided to a brake system control unit (BSCU). The BSCU, based on the signal, commands an electromechanical actuator controller (EMAC) to power an actuator. The EMAC, in response to the command from the BSCU, provides electrical power to an actuator of a brake assembly so as to effect a braking force. 
     Additionally, electrically operated brake systems also include a separate emergency brake control box. The emergency brake control box is configured to control the brake actuators during failure of the primary brake system (e.g., during failure of the BSCU). Typically, such systems are designed to activate all brakes the same amount so as to bring the aircraft to a stop. 
     SUMMARY 
     A brake input device for an emergency brake system is provided that not only allows for emergency and parking brake functions, but also allows differential braking to effect braked steering of an aircraft. This allows the pilot to not only stop the plane in an emergency, but also to steer the plane with the brakes during an emergency stop. More specifically, the brake input device (e.g., a parking and/or emergency brake lever, pedal, handle, etc.) can be used in a brake system including a brake system control unit (BSCU), one or more electro-mechanical actuator controllers (EMACs) and a brake assembly including one or more electrical actuators. Each EMAC is electrically coupled to one or more of the actuators so as to provide electrical power for driving the actuators. Each EMAC is also communicatively coupled to the BSCU so as to receive braking data therefrom. 
     Each EMAC may include a switch or the like for selecting a signal to be provided to the EMAC&#39;s servo compensation network and driver circuits. The switch is controlled via a braking mode signal (normal or park/emergency) generated based on the brake input device. The output of the switch is coupled to an input of the EMAC&#39;s servo compensation network and actuator driver circuits so as to select the signal used by the servo compensation network and driver circuits for controlling the actuators. 
     For normal brake operation, the BSCU generates a brake force signal corresponding to a desired brake force, and provides the brake force signal to each EMAC. Each EMAC&#39;s processor, based on the brake force signal from the BSCU, generates a brake control signal for the servo compensation network and actuator driver. During normal brake mode, the switch selects the signal generated by the EMAC&#39;s processor and provides this signal to the servo compensation network and driver circuits. Thus, overall brake control during normal braking is provided via the BSCU and the EMAC&#39;s processors. 
     For parking and/or emergency braking/steering operation, the brake mode signal provided to each EMAC is indicative of park/emergency/steering mode. Based on this mode, the switch routes the brake command signal(s) as generated by the brake input device directly to the EMAC&#39;s servo compensation network and actuator drivers. The servo compensation network and drivers then control the actuators so as to effect a braking force. Thus, during parking and emergency braking/steering, both the BSCU and the EMAC&#39;s processor are bypassed, and brake control is directly provided by the brake input device (e.g., from the brake handle). Such architecture is advantageous as it eliminates the need for a separate (or isolated) emergency control box to command the EMACs in the event of failure of the primary braking system. 
     According to one aspect of the invention, an emergency brake input device for providing emergency braking signals to at least two brake actuators associated with respective left hand and right hand brake assemblies of a vehicle comprises an input member movable in a first direction corresponding to a braking magnitude and movable in a second direction corresponding to a relative distribution of the braking magnitude between first and second brake signals for the control of the at least two brake actuators. The first and second brake signals can be modulated by a pilot during emergency braking so as to apply differential braking to separate wheels of an aircraft. 
     More particularly, the input member can be movable linearly between first and second positions corresponding to minimum and maximum braking magnitudes, with the position of the handle being indicative of a desired magnitude of braking. The input member can be rotatable about its central axis with an angular position of the input member being indicative of a desired distribution of the braking magnitude between the first and second signals. For example, the input member can include a handle that is both slideable linearly and rotatable. At least one sensor can be provided for sensing a position of the input member and generating the brake signals in response thereto. The input device can also include a parking brake lock for locking the input member in a parking brake position, which may correspond to a maximum magnitude of braking. A parking brake sensor for sensing when the input device is in a parking brake mode and for generating a signal in response thereto can also be provided. 
     In accordance with another aspect, an aircraft braking system comprises at least one brake assembly for braking a wheel of an aircraft, the braking assembly including at least one actuator for effecting a braking action in response to a braking signal provided thereto, and a brake input device as set forth above for providing the braking signal to the actuator. 
     In accordance with another aspect, an emergency brake system comprises at least two brake assemblies having actuators for braking respective wheels of an aircraft, and an emergency brake input device for providing emergency braking signals to each actuator. The input device has first and second input members for generating first and second brake signals for the control of the at least two brake assemblies, the input members each being movable between a first position corresponding to a minimum magnitude of braking and a second position corresponding to a maximum magnitude of braking. The first and second brake signals can be modulated by a pilot during emergency braking so as to apply differential braking to separate wheels of an aircraft. 
     More particularly, the first and second input members can be pedals. At least one sensor can be provided for sensing a position of an input member and generating a brake signal in response thereto. A parking brake lock can be provided for locking the input members of the input device in a parking brake position, which position may correspond to a maximum magnitude of braking. The parking brake lock can include a latch that maintains the first and second input members in the parking brake position. A parking brake sensor for sensing when the input device is in a parking brake mode and for generating a signal in response thereto can also be provided. 
     According to another aspect, a method of applying differential braking of wheels of an aircraft during emergency braking comprises generating a first brake signal indicative of a braking force to be applied to a first wheel by a first brake assembly, generating a second brake signal indicative of a braking force to be applied to a second wheel by a second brake assembly, and feeding the first and second signals to the first and second brake assemblies to effect braking of respective wheels in response to the respective first and second signals. 
     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 
         FIG. 1  is a simple schematic diagram illustrating an exemplary architecture for controlling an aircraft braking system in accordance with the present invention. 
         FIG. 2  is a diagrammatic illustration of an exemplary multi-actuator computer controlled brake actuation system. 
         FIG. 3  is a diagrammatic illustration of a brake actuator and associated servo amplifier employed in the system of  FIG. 2 . 
         FIGS. 4A and 4B  are schematic diagrams illustrating an exemplary brake input device in accordance with the invention. 
         FIGS. 5A-5D  are schematic diagrams illustrating another exemplary brake input device in accordance with the invention in various modes of operation. 
         FIG. 6  is a schematic diagram illustrating a side view of the exemplary brake input device of  FIGS. 5A-5D . 
         FIG. 7  is a schematic diagram illustrating a top view of the exemplary brake input device of  FIGS. 5A-5D  with a sensor arrangement for detecting activation of the device. 
         FIGS. 8A-8C  are schematic diagrams illustrating another exemplary brake input device in accordance with the invention in various modes of operation. 
         FIG. 9  is another schematic drawing of the brake input device of  FIGS. 8A-8C . 
         FIG. 10  is a schematic side view of another exemplary brake input device. 
         FIG. 11  is a schematic top view of the brake input device of  FIG. 10 . 
         FIG. 12  is a perspective view of another exemplary brake input device in accordance with the invention. 
         FIG. 13  is a schematic top view of the brake input device of  FIG. 12 . 
         FIG. 14  is a schematic side view another exemplary brake input device. 
         FIG. 15  is a schematic plan view of the exemplary brake input device of  FIG. 14  in various positions. 
         FIG. 16  is a graph illustrating the brake command level generated by the brake input device of  FIGS. 14-15  in various positions. 
         FIG. 17  is a functional diagram of the brake input device of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     The principles of the invention will now be described with reference to the drawings. 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 braking systems in other types of vehicles. Moreover, the following discussion of an exemplary multi-actuator computer controlled brake actuation system is given for the sake of illustration and not by way of limitation, except as defined in the claims included at the end of this specification. Accordingly, only general operational details and features of such system will be described so as not to obscure the teachings of the present invention with details that may vary from one particular application to another. 
     Referring initially to  FIG. 1 , there is shown an exemplary electrical brake system  10  having architecture in accordance with the present invention. The exemplary electrical brake system includes a brake system control unit (BSCU)  12  configured to carryout braking operations of the aircraft as is conventional. The BSCU  12  is configured to receive various operator inputs, such as left and right pilot brake pedal signals from left and right pilot brake pedals  14   l  and  14   r,  and left and right co-pilot brake pedal signals from left and right co-pilot brake pedals  16   l  and  16   r.  The brake pedal signals can be generated, for example, via LVDTs (linear variable differential transformers—not shown) operatively coupled to the respective pedals. As the pedals are depressed, each LVDT generates a voltage signal corresponding to the degree of pedal deflection, and this voltage signal can be provided to the BSCU  12  as is conventional. As will be appreciated, other known methods for generating the brake pedal signals may also be employed, including encoders, potentiometers, or the like. 
     The BSCU  12  may also receive other operator inputs, such as data from an autobrake switch  18  for configuring autobrake logic. The autobrake switch  18  may include several settings, such as an enable/disable input, an auto braking level input (e.g., low, medium, high) and a rejected take off (RTO) input (e.g., for enabling or disabling RTO functionality). The BSCU  12  may also receive other aircraft data  20 , such as discrete data (e.g., sensor data such as weight-on-wheels, landing gear up/down, etc.), analog data (e.g., force data, temperature data, etc.), serial data, etc. as is conventional. 
     The BSCU  12  is communicatively coupled to one or more electromechanical actuator controllers (EMACs)  24 , wherein the BSCU  12  provides a brake force signal to the respective EMACs during normal braking operations. Preferably, the coupling is via a serial communication link, although data also can be exchanged via discrete and/or analog connections. The BSCU  12  is configured to derive the brake force signal based on brake data generated by the pedals  14   l,    14   r,    16   l,    16   r,  and/or autobrake and antiskid control. 
     A brake input device  22 , preferably a combination parking brake/emergency brake device (e.g., a handle, lever, pedal, or the like), provides a brake command signal to each EMAC  24 . The brake command signal can be generated using known techniques, such as an LVDT as described above with respect to the brake pedals  14   l,    14   r,    16   l,    16   r,  or via an encoder or potentiometer configured to provide data corresponding deflection or rotation of the brake input device  22 . As will be appreciated, other known methods of generating the brake command signal may also be employed. Preferably, the brake input device includes a mode selector to indicate when normal or parking/emergency braking is desired. For example, the brake input device  22  may include contacts that are open when the brake input device is in a first position (e.g., rotated to the left or pushed inward) and closed when the brake input device is in a second position (e.g., rotated to the right or pulled outward). Alternatively, the brake mode selector may be separate from the brake input device  22 . The brake input device  22  can also provide separate braking signals for respective left and right side brakes as will be described in more detail below. Further details regarding various brake input devices are provided below with respect to  FIGS. 4A through 9 . 
     The EMACs  24  are electrically coupled to one or more actuators  26  of a brake assembly  28 , wherein each brake assembly  28  includes the one or more actuators  26 , corresponding rams  30  operatively coupled to each actuator  26 , and a brake-disk stack  30  having a plurality of rotors coupled for rotation with a wheel  34  and stators rotationally fixed with respect to the wheel  34 . Each actuator  26  and ram  30  are configured for forceful engagement with the brake-disk stack  30  so as to provide a brake force to a corresponding wheel  34 . Wheel speed sensors  36  provide wheel speed data to the BSCU  12  for implementing anti-skid and autobrake functions as is conventional. 
     As noted above, each EMAC  24  receives the brake force signal from the BSCU  12 . In addition to the brake force signal, each EMAC  24  is configured to receive the brake command signal from the brake input device  22 , and the brake mode signal indicative of whether normal brake operation or park/emergency brake operation is desired. Based on the brake mode signal, each EMAC  24  selects a signal corresponding to the brake force signal provided by the BSCU  12  or the brake command signal provided by the brake input device  22  and, based on the signal, controls the actuators to effect a braking force. Further details regarding EMAC operation are discussed below with respect to  FIGS. 2 and 3 . 
       FIG. 2  diagrammatically illustrates an exemplary multi-actuator computer controlled electrical brake actuation system  10 ′ to which the principles of the invention may be applied. The major functions of the system  10 ′ are performed by an EMAC controller  40  and a brake actuator assembly  42 . The brake actuator assembly  42  may be mounted in a conventional manner on a wheel and brake assembly  44  to apply and release braking force on a rotatable wheel  34  of such wheel and brake assembly. Wheel speed data is provided to the controller  40  via a wheel speed sensor  36  coupled to each wheel  34 . 
     In the illustrated exemplary system  10 ′, the brake actuator assembly  42  includes at least one and preferably a plurality of actuators  26 , such as electromechanical actuators (EMAs)  26 . The EMAC controller  40  includes a corresponding number of independent servo amplifiers  46 , a micro-processor  48  with associated peripherals, and a data input/output (I/O) circuitry  50 . As depicted, plural (for example, four) independent, linear electro-mechanical servo loops operate in a position mode, i.e., the linear position of each actuator is a function of an analog input voltage (or digital equivalent for a digital signal processor) applied to a position command input. 
     As noted above, the brake input device  22 , via signal generator  22   a,  generates the brake command signal, which is provided to each EMAC (e.g., to each amplifier  46  of the EMAC). Also provided to each amplifier is a brake mode input, which is generated via switch  22   b.  During normal braking operations, switch  22   b  is closed, and brake control is performed via the BSCU  12  and EMAC controller  40 . However, during park/emergency braking operations, switch  22   b  is open, and each amplifier  46  uses the braking command as provided by the brake input device  22 , thereby bypassing the BSCU  12  and EMAC controller  40 . Thus, each amplifier can include a switching means for selecting between the data generated by the BSCU  12  and processor  48 , or the actual data provide by the brake input device  22 . 
     In  FIG. 3 , a representative electro-mechanical brake actuator  26  and associated servo amplifier  46  are illustrated in greater detail. The brake actuator  26  includes an electric servo motor  52 , gear train  54 , and a reciprocating output ram  30 . The brake actuator has associated therewith an output ram position sensor  56  which provides for actuator position feedback as depicted, and a force sensor  58  that provides data indicative of a force applied by the brake actuator on the brake-disk stack. Although not shown, the brake actuator  26  also has associated therewith a motor tachometer to provide for velocity feedback. 
     The servo amplifier  46  includes servo loop compensation network and amplifiers  60 , and a DC motor driver  62  with associated control logic and current control circuitry. More particularly, the servo amplifier  46  may include an inner motor current control servo loop  64 , an intermediate motor velocity servo loop  66 , and a ram position servo loop  68 . Force feedback data  69  may be provided to the BSCU for control of actual applied force. Each loop may be compensated to obtain desired performance in terms of bandwidth, and to provide for uniform dynamic response of all brake actuators  26 . In addition, the servo amplifier  46  includes means for controlling motor current and therefore the output force of the brake actuator in response to a force control input. The force control input may be an analog input signal that controls motor current level while the aforesaid position command input controls actuator displacement. As will be appreciated, the analog input signals may be replaced by digital input signals if a digital signal processor is used in the servo amplifier for actuator control. 
     A switch  65  provides an input to the servo loop compensation network  60 . Preferably, switch  65  is an electronic or software switch. However, a mechanical switch may be employed depending on the configuration of the EMAC  24 . The switch  65  includes a first input I 1  configured to receive the brake control signal from the EMAC controller  40  (which effectively is derived from the pedals  14   l,    14   r,    16   l,    16   r  and/or autobrake/antiskid logic from the BSCU  12 ), and a second input  12  configured to receive the brake command signal from the brake input device  22 . A select input SE of switch  65  is coupled to the mode switch  22   a,  and an output of switch  65  is coupled to the servo loop compensation network as noted above. Based on the particular braking mode as indicated by the mode switch  22   b,  the switch  65  will provide either the brake control signal (from the EMAC controller  40 ) or the brake command signal (from the brake input device  22 ) to the servo loop compensation network  60 . Although not shown, scaling logic may be included in the EMAC to properly scale the brake command signal for use with the EMAC circuitry. Further, while the switch is shown as part of the EMAC, it is possible for the switch to be separate from the EMAC  24 . 
     During normal braking, the select input SE is true, and the switch  65  connects the first input I 1  to the switch output, thereby coupling the brake control signal from the EMAC controller  40  to the servo loop compensation network  60  (and thus the motor driver  62 ). Accordingly, the displacement of each actuator  26  is controlled by the electronic controller  40  ( FIG. 2 ) and the BSCU  12 . The micro-processor  48  of the controller  40  provides brake control algorithm processing, temporary data storage in RAM, program memory storage, nonvolatile data storage, and control of the servo amplifiers  46  via the input/output circuitry  50 . The input/output circuitry  50  provides for digital-to-analog data conversion, generating the analog position commands and the analog motor current control commands to the four actuators, analog-to-digital data conversion to monitor the actuator position sense and motor current feedback signals, and signal discretes for auxiliary functions such as motor brake control. Although micro-processors are utilized in the illustrated preferred embodiment, processing could be done analog as opposed to digital, or intermixed with digital processing as may be desired. 
     During park/emergency braking operations, both the BSCU  12  and controller  40  are bypassed, and the displacement of each actuator  26  is directly controlled by brake input device  22 . More specifically, when the brake mode corresponds to park/emergency braking, the select input SE is false, and the switch  65  connects the second input  12  to the switch output, thereby directly coupling the brake command signal from the brake input device  22  to the servo loop compensation network  60 . Thus, in the event of primary brake system failure, park/emergency braking can be provided via the each EMAC, without the need for an emergency control unit. As will be appreciated, the brake input device  22  can provide brake signals to respective left and right brake assemblies, for example, for implementing braked steering. Further details of the brake system are set forth in commonly-assigned U.S. patent application Ser. No. 12/429,303 filed on Apr. 24, 2009 titled “ELECTRIC BRAKE ARCHITECTURE WITH DISSIMILAR EMERGENCY BRAKING PATH,” which is hereby incorporated by reference herein in its entirety. 
     Referring now to  FIGS. 4A and 4B , a brake input device  22  is schematically shown from a top view ( FIG. 4A ) and a side view ( FIG. 4B ). The exemplary brake input device  22  includes a handle  70  configured for movement along a channel or guide  72 . Operatively coupled to the handle  70  is a signal generator  22   a,  such as a potentiometer  22   a,  wherein movement of the handle  70  along the channel  72  causes a corresponding deflection of a wiper arm  23   a  of the potentiometer. By applying a voltage across the outer terminals  23   b  and  23   c  of the potentiometer  22   a,  a brake command signal can be generated at the wiper arm terminal  23   d  that corresponds to the position of the handle within the channel (and thus the desired amount of braking). 
     It is noted that reference to a potentiometer is merely exemplary, and other devices, such as an LVDT, encoder, etc. may be used in place of the potentiometer to derive the brake command signal. Although not shown in  FIG. 4A , the terminals of the potentiometer  22   a  are electrically coupled to the EMAC  24  so as to provide the brake command signal thereto. 
     With further reference to  FIG. 4B , a simple side schematic view of the exemplary brake input device  22  is shown. The handle  70 , in addition to being operatively coupled to the signal generator  22   a,  is also operatively coupled to switch  22   b.  Preferably, handle  70  is a maintained push-pull handle such that it can be maintained in an out position (pull) or an in position (push). When in the “out/pull” position, switch  22   b  is in an electrically closed state, and while in the “in/push” position, switch  22   b  is in an electrically open state. The “out/pull” position can correspond to normal braking mode (i.e., brake control via the BSCU  12 ), while the “in/push” position can correspond to park/emergency mode. Switch  22   b  is electrically coupled to switch  65  so as to provide an indication of the current braking mode (normal or park/emergency). 
     In another embodiment, the brake input device can comprise a rotatable handle (as opposed to a push/pull device). In this embodiment, rotation of the handle in one direction (e.g., left) may correspond to normal brake mode, and rotation of the handle in another direction (e.g., right) can correspond to park/emergency brake operation. 
     Accordingly, the brake input device  22  can provide both a park/emergency brake reference, and a mode indicator that can be used to configure the brake system&#39;s mode of operation. This is advantageous, as the pilot need only manipulate a single controller for park/emergency brake operation. 
     Turning to  FIGS. 5A-5D and 6 , and initially to  FIGS. 5A and 6 , a brake input device  82  is shown that provides functionality similar to the brake input device  22  described above, but also facilitates differential braking to effect braked steering during emergency braking. The brake input device  82  is similar to the device  22  in both form and function with the exception of the handle  70 , which is rotatable about its central axis to control an amount of braking applied to separate brake assemblies, for example left and right brake assemblies. 
     Accordingly, brake input device  82  includes handle  70  mounted on guide  72  for both sliding and rotating movement, and a pair of side buttons  84  for permitting emergency braking and also for locking the handle  70  in the park position, as will be described in more detail below. Similar to input device  22  described above, sliding the handle  70  forward produces an increasing brake signal. In this embodiment, however, rotation of the handle  70  produces respective left and right brake signals that can be fed directly to each EMAC to effect differential braking. A directional indicator  86  indicates the direction in which the aircraft will be steered relative to the forward direction (e.g., with respect to the longitudinal axis of the guide  72 ). 
     More specifically, and with further reference to the remaining  FIGS. 5B-5D , the input device  82  is shown in various positions corresponding to various braking actions. In  FIG. 5A  the handle  70  is locked in the aft position corresponding to no braking activity. The side buttons  84  are not depressed and serve to hold or otherwise lock the handle in the illustrated position to avoid inadvertent brake actuation.  FIG. 6  illustrates a schematical side view of the brake input device  82  in the position of  FIG. 5A . 
     In  FIG. 5B , the side buttons  84  have been depressed and the handle  70  has been moved to a position corresponding to moderate emergency braking. The indicator  86  is pointing straight forward thus indicating that the brake input device  82  is providing identical (or nearly identical) first and second signals to the brake actuators for actuating respective left and right brake assemblies such that the aircraft brakes in a relatively straight line. 
     In  FIG. 5C , the handle  70  has been rotated counterclockwise such that it is now pointing to the left of the longitudinal axis of the guide  72 . This position corresponds to differential (steered) braking wherein the aircraft tends to rotate left during emergency braking. As will be appreciated, the brake input device  82  can be configured to generate respective output signals for the left and right brake assemblies in response to rotation of the handle  70 . For example, when rotated to the left, the left hand brake assembly or assemblies would be activated to a greater extent than the right hand brake assembly or assemblies causing the aircraft to rotate towards the left. Conversely, when the handle is rotated to the right (not shown), the right side brake assembly or assemblies would be activated to a greater extent than the left side brake assembly or assemblies causing the aircraft to rotate towards the right. 
     In  FIG. 5D , the handle  70  is in its forward-most position corresponding to full braking and/or parking brake mode. In this instance, the side buttons  84  have returned outward indicating that the handle  70  is locked in the parking brake position. Once in this position and with the side buttons  84  locked, the brake input device  82  generates a signal indicative of the parking brake being applied as described previously. 
     Accordingly, the brake input device  82  of  FIGS. 5A-5D  facilitates both differential emergency braking for steering the aircraft during an emergency stop, as well as a parking brake function. The exemplary device  82  is intuitive since braking action is applied by sliding the handle  70  forward (much like depressing a pedal), while differential braking is achieved by rotating the handle  70  in the direction the pilot desires to steer the plane. Of course, the handle  70  could be configured to be pulled rather than pushed to generate the braking signal. As will be appreciated, the brake input device  82  need not have a particular form or shape. For example, the handle  70  can be made to look like the wheels of an aircrafts, while the side buttons  84  can be made to look like wheel chocks. In the illustrated embodiment, the input device is biased towards the position shown in  FIG. 5A  (e.g., no braking and no differential braking). 
     Further, the side buttons  84  can be configured to work in a variety of ways. For example they may restrict initial movement of the handle  70  from the position of  FIG. 5A  until depressed. The side buttons may then remain in the depressed state as the handle is slid fore and aft by the pilot, only to return to the locked position upon return of the handle  70  to the position of  FIG. 5A , or upon engagement of the parking brake (e.g., by pushing the handle  70  all the way forward). The side buttons  84  may then retain the handle  70  in the parking brake position. 
     Turning to  FIG. 7 , further details of the brake input device  82  are illustrated. The handle  70  is supported for sliding and rotational movement on the guide (not shown in  FIG. 7 ) and is coupled to a pair of cog belts  90   a  and  90   b.  Each cog belt  90   a  and  90   b  passes around a respective idler pulley  92   a  and  92   b  and a respective angular displacement sensor  94   a  and  94   b,  thus coupling the handle  70  to the sensors. Idler wheels  96  are fixed for sliding movement along with the handle  70  for helping guide the cog belts  90   a  and  90   b  around respective sides of the handle  70 . The handle  70  and idler wheels may all be supported by a carriage  98  that is operatively coupled to the guide for sliding movement. 
     As will be appreciated, linear (sliding) or rotational movement of the handle  70  results in rotation of the angular sensors  94   a  and  94   b.  For example, sliding the handle  70  to the left in  FIG. 7  results in rotation of both angular sensors  94   a  and  94   b  which rotation can be converted to brake signals and fed to the actuators as described previously. Meanwhile, rotation of the handle  70  either clockwise or counterclockwise also results in rotation of the angular sensors  94   a  and  94   b  such that left and right side brake signals can be generated. Although the linear position of the handle  70  could be determined solely by analyzing the signals produced by the angular sensors  94   a  and  94   b,  a linear sensor could also be provided to measure such movement directly. By comparing the signals from each angular sensor  94   a  and  94   b  to each other (and/or a linear sensor if so equipped), differential emergency brake signals can be generated. As will be appreciated, redundant sensors could be provided in place of or in addition to the various idler wheels and/or pulleys. 
     Turning now to  FIGS. 8A-8C and 9 , another embodiment of a brake input device is illustrated and generally referred to by reference numeral  100 . In this embodiment, the brake input device  100  includes a pair of pedals  104   a  and  104   b.  The pedals  104   a  and  104   b  may be made to look like aircraft rudder pedals or the like. The pedals may be activated by a pilot&#39;s feet as conventional pedals, or may be manual controls intended to be activated by a pilot&#39;s hands. In this regard, the pedals can be ergonomically shaped for grasping by a pilot&#39;s hand or hands, and can be configured to be pushed or pulled to initiate and/or increase braking. 
     Each pedal  104   a  and  104   b  is operatively coupled to sensors  108  ( FIG. 9 ) that sense movement of each pedal  104   a  and  104   b  (e.g., depression). For example, each pedal could be coupled to an angular sensor for measuring rotation about respective pivot points P of each pedal as a pedal is depressed. Alternatively, a linear displacement sensor could be operatively coupled to each pedal so as to measure depression as a function of the movement of the free end of the pedal, for example. The sensors  108  convert movement of the pedal into respective brake signals that are then fed to the actuators as previously described to implement emergency braking/steering. 
     In the position of  FIG. 8A , the brake input device  100  is deactivated, and no signal is being sent to the actuators (e.g. neither pedal  104   a  or  104   b  is depressed). In  FIG. 8B , the left pedal  104   a  is partially depressed while the right pedal  104   b  remains in the position of  FIG. 8A . This corresponds to a differential braking mode wherein the left hand brakes of the aircraft are activated to a greater extent than the right hand brakes resulting in the aircraft rotating towards the left during braking. Of course, the right side pedal could be depressed slightly or even more so than the left pedal, the latter instance resulting in rotation of the aircraft to the right. 
     In  FIG. 8C , both pedals  104   a  and  104   b  are fully depressed, and a parking brake latch  110  is positioned above the pedals  104   a  and  104   b  to maintain both pedals in the parking brake position. As will be appreciated, a switch associated with the parking brake latch  110  (see  FIG. 2 ) can indicate to the BCSU when the parking brake latch  110  is in the parking brake applied position. 
     Turning now to  FIGS. 9 and 10 , another exemplary embodiment is illustrated. In this embodiment, a handle  140  having a grip  144  to be grasped by a pilot&#39;s hand is provided. The handle  140  is supported for pivoting movement in a vertical plane at pivot P 1 . The handle  140  can pivot between a horizontal position and more vertical position, for example, as shown. Movement of the handle  140  between such positions can be detected by a suitable sensor (not shown), such as a rotary motion sensor, and can be used to generate a braking magnitude signal in a manner similar to that set forth above in connection with the other embodiments. As will be appreciated, the greater the angle φ the greater the magnitude of overall braking. A lock/release button  148  can be provided for locking the handle in a brake applied position (e.g., parking brake). 
     Turning to  FIG. 11 , it will be appreciated that the handle  140  also is configured to pivot in a second plane (e.g., the horizontal plane in  FIG. 11 ). To this end, a second pivot point P 2  permits pivoting of the handle  140  to the left and right as shown to generate a signal corresponding to the distribution of the overall braking level between left and right brake assemblies. Moving the handle  140  left corresponds with more left hand braking and less right hand braking resulting in the aircraft steering towards the left. Moving the handle  140  to the right corresponds with more right hand braking and less left hand braking resulting in the aircraft steering towards the right. As will be appreciated, the greater the angle θ the greater the braking bias to a given side. 
     During operation, a pilot will pull upward on the handle  140  pivoting the handle  140  through an angle φ in order to apply the brakes. To apply differential braking, the pilot can then pivot the handle left or right while maintaining the handle at an angle φ. 
     With reference to  FIG. 17 , functional diagram  1700  is shown depicting the embodiment shown in  FIGS. 10 and 11 . Handle  144  is shown with rotary sensors  1702  and  1704 . 
     In  FIG. 12 , another exemplary embodiment of the brake input device is illustrated. In this embodiment, the brake input device is a T-handle  200  that is slideable fore and aft to control overall braking level, and rotatable about a central axis A to control differential braking. The T-handle  200  includes a leg  204  that can be connected to suitable sensors via a carriage such as previously described or via other means. A handle portion  208  is supported by the leg  204  for manipulation by a pilot. A lock button  212  is provided on a side of the handle portion  204  for locking the handle  200  in a parking brake position. 
     With reference to  FIG. 13 , the T-handle  200  is illustrated in a variety of positions corresponding to varying levels of overall braking and/or differential braking. The T-handle  200  is slideable forward to the emergency mode as shown. The T-handle  200  also is rotatable clockwise and counterclockwise (as shown about axis A in  FIG. 12 ) to control differential braking. For example, rotating the handle  204  clockwise can correspond to more right hand braking and less left hand braking thus causing an aircraft to tend to steer towards the right. Conversely, rotation of the handle  204  counterclockwise can correspond to more left hand braking and less right hand braking thus causing an aircraft to tend to steer leftward. As will be appreciated, the lock button  212  can be depressed to lock the handle in a park position corresponding to full overall braking level in the emergency mode, for example. 
     Turning to  FIGS. 14-16 , yet another exemplary brake input device is illustrated. In this embodiment, the brake input device is in the form of a cantilevered handle  220  that is pivotable in a vertical plane about a pivot point P for indicating overall braking level, and also is rotatable about differential pivot point P D  for indicating differential braking offset as shown in  FIG. 15 . For example, in  FIG. 14  the greater the angle φ the greater the overall braking level. In  FIG. 15 , the greater the angle θ, either positive or negative as the case may be, the greater the braking bias to a given side. For example, if the handle  220  is rotated clockwise (e.g., negative θ) more braking may be applied to the right hand brakes and less to the left hand brakes while if the handle  220  is rotated counterclockwise (e.g., positive θ) more braking may be applied to the left hand brakes and less to the right hand brakes. 
     To illustrate this concept,  FIG. 16  shows the overall braking level and differential braking offset generated by the handle  220  in various positions. As will be appreciated, the concept illustrated in  FIG. 16  generally is applicable to other embodiments described above. The four positions of the handle  220  on the left hand side of the graph under “Equal LH/RH Braking” relate to varying degrees of overall braking. The positions range from about zero degrees psi to about 45 degrees psi correspond to zero overall braking and maximum overall braking, respectively. The intermediate positions illustrate overall braking amounts between zero and the maximum. Thus, the handle is shown at varying degrees of the angle φ, with a greater angle corresponding to a greater level of overall braking as described above. 
     On the right side of the graph under “Differential Braking” the handle  220  is shown in five different positions H 1 -H 5 , each position corresponding to a different angle θ. The line L θ  represents the angle θ at the various positions. Positive values of angle θ corresponds to more left hand braking and less right hand braking, while negative values of angle θ corresponds to more right hand braking and less left hand braking. Meanwhile, lines L LH  and L RH  represent the respective left hand and right hand braking values at a give angle θ. 
     Beginning with position H 1 , the handle is rotated counterclockwise towards the left thereby increasing the angle θ to a positive value. Accordingly, L LH  indicates an increased amount of left hand braking while L RH  indicates a decreased amount of right hand braking. 
     At position H 2 , the handle  220  is rotated counterclockwise back towards the right causing angle θ to decrease in value towards zero and eventually go negative. Thus, L LH  trends back towards zero while L RH  increases. At position H 3 , L RH  is positive while L LH  is negative thereby indicating more right hand braking and less left hand braking. 
     At position H 3 , the handle  220  is rotated counterclockwise back towards the left but remains at a negative angle θ until position H 4 . Thus, L RH  increases at lesser rate while L LH  decreases at a lesser rate. At position H 4 , the handle  220  is rotated counterclockwise to a positive angle θ and thus L RH  returns to zero and then goes negative, while L LH  goes positive. 
     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. 
     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.