Abstract:
A landing gear system that includes a landing gear strut rotatable between stowed and deployed positions. An actuator is connected to the landing gear strut, and includes main and emergency drives housed within a common body and operable independently from one another. A controller in communication with the actuator is configured to command the actuator between the stowed and deployed positions in response to an input. The controller commands the main drive during a normal operating condition and commands the emergency drive in a failure condition of the main drive. The actuator includes a body supporting emergency and main leadscrews arranged coaxially with one another. Main and emergency motors respectively are coupled to the main and emergency leadscrews. An output rod is supported by and extends from the body. The output rod is threadingly coupled to and is coaxial with the main leadscrew and configured to move axially in response to rotation of the main leadscrew. A brake selectively enables and disables the emergency drive.

Description:
BACKGROUND 
     This disclosure relates to an aircraft landing gear actuator. More particularly, this disclosure relates to an actuator that when mechanically jammed will not prevent the landing gear from fully deploying. 
     Aircraft employ landing gear arrangements that must be reliably deployed from a stowed position during landing. In one type of arrangement, the landing gear is rotated about a pivot by an extend/retract actuator. A lock-stay is biased over-center to lock the landing gear in a deployed position. To retract the landing gear, an unlock actuator pulls the lock-stay from over-center, which enables the extend/retract actuator to retract the landing gear to the stowed position. Both the extend/retract and unlock actuators are typically hydraulically powered. It is desirable to use electromechanical actuators to benefit from the increasing use of electrically powered aircraft systems. 
     Landing gear actuators must reliably deploy in the event of a mechanical jam within the actuator. If electromechanical actuators are employed, they also must deploy in the event of a main power failure. What is needed is a jam tolerant extend/retract actuator that enables the landing gear to be fully deployed regardless of a mechanical jam or loss of main power. 
     SUMMARY 
     This disclosure relates to a landing gear system that includes a landing gear strut rotatable between stowed and deployed positions. An actuator is connected to the landing gear strut, and includes main and emergency drives housed within a common body and operable independently from one another. A controller in communication with the actuator is configured to command the actuator between the stowed and deployed positions in response to an input. The controller commands the main drive during a normal operating condition and commands the emergency drive in a failure condition of the main drive. 
     The actuator includes a body supporting emergency and main leadscrews arranged coaxially with one another, for example. Main and emergency motors respectively are coupled to the main and emergency leadscrews in one example. An output rod is supported by and extends from the body. The output rod is threadingly coupled to and is coaxial with the main leadscrew and configured to move axially in response to rotation of the main leadscrew. A brake selectively enables and disables the emergency drive in one example embodiment. 
     These and other features of the application can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1D  schematically illustrate the landing gear in deployed and locked, deployed and unlocked, retracting and stowed positions, respectively. 
         FIGS. 2 ,  2 A and  2 B are schematic views of a control system for the extend/retract and unlock actuators. 
         FIG. 3  is a cross-sectional view through main and emergency leadscrews of the extend/retract actuator. 
         FIG. 4  is a cross-sectional view of the extend/retract actuator shown in  FIG. 3  through main and emergency motors and gearboxes. 
         FIG. 5  is another cross-sectional view of the extend/retract actuator shown in  FIG. 3  through the main and emergency motors and gearboxes as well as through a layshaft. 
         FIG. 6  is a highly schematic view of a brake for the extend/retract actuator. 
         FIGS. 7A and 7B  are schematic flow charts for stow and deploy cycles, respectively. 
         FIGS. 8-13  schematically illustrate the extend/retract actuator throughout the retract and deploy cycles with a mechanical jam. 
     
    
    
     DETAILED DESCRIPTION 
     A retracting cycle of a landing gear  10  is illustrated in  FIGS. 1   a - 1   d.    FIG. 1   a  depicts the landing gear  10  in a fully deployed and locked position.  FIG. 1   b  depicts the landing gear  10  in a fully deployed and unlocked position.  FIG. 1   c  depicts the landing gear  10  while it is being retracted.  FIG. 1   d  depicts the landing gear  10  in a stowed position. 
     The landing gear  10  includes a strut  14  supporting wheels  16 . The strut  14  is rotatable about a pivot, which is provided by an airframe  12 , in response to an extend/retract actuator applying a force to an arm  19 . A linkage  20  connects a lower portion of the strut  14  to the airframe  12 , for example. A lock-stay  22  is interconnected between the linkage  20  and the strut  14  to lock the landing gear  10  in the fully deployed position until the pilot retracts the landing gear. 
     In  FIG. 1   a,  the landing gear  10  is shown locked in the fully deployed position. The example lock-stay  22  includes first and second links  21 ,  23  pivotally secured to one another at a joint D, best shown in  FIG. 1   b.  One end of the first link  21  is connected to the strut  14  at pivot B. A portion of the second link  23  is connected to the linkage  20  at pivot C. A biasing member  26  is arranged between the lock-stay  22  and the linkage  20  to bias the lock-stay  22  to the locked position shown in  FIG. 1   a.  An unlock actuator  24  is interconnected between the linkage  20  and lock-stay  22  to pull the joint D from over-center, as depicted by the arrow in  FIG. 1   b  (from the locked position shown in  FIG. 1   a ), so that the extend/retract actuator  18  can move the landing gear  10  to a stowed position. 
     For the example unlock actuator  24 , once the lock-stay  22  has been moved from over-center, the unlock actuator  24  free-drives. That is, the lock-stay  22  is no longer moved under the power of the unlock actuator  24 , but rather, the extend/retract actuator  18  moves the lock-stay  22  and unlock actuator  24  as the landing gear  10  is stowed. 
     A controller  32  is used to control the operation of the landing gear and sense the location of various components. The controller  32  can be hardware and/or software and constructed as single or multiple units. For example, a lock position sensor  28  communicates with the controller  32  to detect the lock-stay  22  in a locked position, as shown schematically in  FIG. 1   a.  The stowed position sensor  30  communicates with the controller  32  and detects the position of a portion of the landing gear  10  to ensure that the landing gear  10  is fully stowed. 
     Other sensors can be used to detect faults in the operation of the landing gear. For example, position sensors  54  are associated with the extend/retract actuator  18  to determine positions of components within the extend/retract actuator  18 , as shown in  FIG. 2 . The position sensors  54  are in communication with the controller  32  and are used to evaluate whether a fault has occurred. Input and output devices  31 ,  33  are also in communication with the controller  32 . The input device  31  includes one or more pilot initiated controls, for example. The output device  33  includes a fault indicator or a position indicator, for example. 
     Referring to  FIG. 2 , the extend/retract actuator  18  includes a body that houses two independent actuators that are mated back-to-back with leadscrews that are coaxially and telescopically arranged, for example. The locations of the components within the extend/retract actuator  18  are schematic and may be arranged in a different manner, if desired. 
     Referring to  FIGS. 2-5 , the extend/retract actuator  18  includes opposing ends  34  that are connected to the aircraft and landing gear strut  14 . During “normal” operation in which there is no mechanical jam, an output rod  36  is extended and retracted axially to move the strut  14  while an emergency leadscrew  38  is maintained in an axially fixed position. More specifically, a main motor  44  rotationally drives a main leadscrew  40  through a main gearbox  46 . The main motor  44  rotates a main driveshaft  70 , which rotationally drives a main drive gear  58  through a layshaft  64 , best shown in  FIGS. 4 and 5 . In the example, the main driveshaft  70  is parallel to the main leadscrew  40 . The main drive gear  58  is affixed to an end of the main leadscrew  40  opposite the output rod  36 , which includes a nut  56  that receives the main leadscrew  40 . 
     The main motor  44  is selectively energized to rotationally drive the main leadscrew  40  and axially move the output rod  36  in and out relative to the body. A portion of the main leadscrew  40  is received by an inner cavity  42  of the output rod  36 . The main motor  44  includes two separate and independently wound coils  66 ,  68 , schematically shown in  FIG. 4 , that are connected to two separate power sources  43 ,  45 , shown in  FIG. 2 . This provides redundancy in the main drive and enables the pilot to select a different power source when attempting to operate the landing gear  10  after a failed attempt. 
     Referring to  FIG. 3 , the main leadscrew  40  is supported by a bearing  57  arranged at main drive gear  58 . A bearing  59  at an emergency drive gear  60  supports the emergency leadscrew  38 . Roller bearings  61  are arranged between the main and emergency drive gears  58 ,  60  to support the leadscrews  38 ,  40  in the axial direction. 
     When there is a mechanical jam, failure or power loss to the main drive, an emergency motor  48  is used to drive the emergency leadscrew  38  axially in and out relative to the body, as shown in  FIG. 4 . Bellows  62  enclose the emergency leadscrew  38  where it extends from the body to the end  34 . During failure of the main drive, the output rod  36  is maintained in an axially fixed position relative to the body. In one example, the emergency motor  48  is supplied power using a different power supply (schematically shown at  47  in  FIG. 2 ) than at least one of the coils  66 ,  68  in the main motor  44  so that the emergency drive will continue to function in the event of a power loss to the main drive. 
     When in operation, the emergency motor  48  rotationally drives the emergency drive gear  60  using the emergency driveshaft  72  through the emergency gearbox  50  to axially move the emergency leadscrew  38  in and out relative to the body. In the example, the emergency driveshaft  72  is parallel to the emergency leadscrew  38 . During “normal” operation in which the main drive is used to axially move the output rod  36 , a brake  52  is used to lock the emergency leadscrew  38  and prevent its rotation. Thus, the brake  52  is in a normally engaged condition to prevent operation of the emergency drive. Upon a loss of power to the main motor  44 , the brake  52  automatically releases or disengages which permits rotational drive of the emergency leadscrew  38  using the emergency motor  48 . 
     The brake  52  is shown schematically in  FIG. 6 . The brake  52  is normally engaged by friction discs  80  that are secured relative to an actuator housing  79  and hub  82 . The actuator housing  79  is associated with the extend/retract actuator  18  body, and the hub  82  is associated with the emergency driveshaft  72  ( FIG. 4 ). A spring  86  biases a pressure plate  84  to force the friction discs  80  into engagement with one another, thus fixing the hub  82  relative to the actuator housing  79 . One of three coils  74 ,  76 ,  78  can be used to disengage the brake  52  by retracting the pressure plate  84  along pin  88  thereby overcoming the spring  86 . In one example, the coil  74  is operated by the main power source, and coils  76 ,  78  are independently operated by the emergency power source. 
     The operation of the landing gear  10  is schematically illustrated by the flow charts shown in  FIGS. 7   a  and  7   b.    FIG. 7   a  illustrates a stow cycle  90  starting with the landing gear in the deployed position, as shown at block  92 . The pilot sends a command to raise the landing gear, as indicated at block  94 , thereby moving the lockstay from over-center (block  96 ). The output rod  36  begins extending to retract the landing gear (block  98 ), but becomes jammed (block  100 ) in the example. The sensors  28 ,  30 ,  54  cooperate to with the controller  32  to send a signal (block  102 ) to the pilot that the landing gear has not stowed, as desired. If the landing gear is only jammed in the retract direction, then the landing gear can be fully deployed and locked, as indicated at blocks  104 ,  106 . The pilot is notified that the landing gear is fully deployed (block  108 ) and what has failed (block  110 ). The pilot can try to recycle the landing gear to the stowed position again to determine if the jam can be cleared (block  112 ). 
     A bi-direction jam is depicted at block  114 . After a failed recycle attempt (block  116 ), the pilot can employ the emergency drive (block  118 ) to fully deploy the landing gear (blocks  120  and  122 ). The pilot is then alerted to the failure mode of the extend/retract actuator  18  (block  124 ). The operation of the emergency drive to fully deploy the landing gear will be discussed in greater detail below relative to the deploy cycle  126  schematically illustrated in  FIG. 7   b.    
     Referring to  FIG. 7   b,  the landing gear is shown in a stowed position at block  128 . The pilot commands the landing gear to deploy (block  130 ). Referring to  FIG. 8 , the extend/retract actuator  18  is shown in a stowed position. To retract the landing gear, the main motor  44  is energized (with brake  52  engaged) to rotational drive the main leadscrew  40 , which axially moves the output rod  36  inward, as shown in  FIG. 9 . While the landing gear is deploying (block  132 ), the landing gear may become jammed (block  134 ). In one example, the main drive becomes jammed in the position shown in  FIG. 10  during the deploy cycle, or the power to the main motor  44  is lost when in this position. The pilot is notified of the jam (block  136 ) and the can attempt to recycle the landing gear (block  138 ) to clear the jam. This can be achieved at times by partially retracting the landing gear ( 140 ) and then again deploying the landing gear (blocks  142 ,  144 ,  146 ). 
     If landing gear again jams during the reattempted deploy (block  148 ), the pilot can employ the emergency drive to fully deploy the landing gear (block  118 ). One of the coils  74 ,  76 ,  78  ( FIG. 6 ) is energized to release the brake  52  thereby permitting rotation of the emergency drive gear  60 . The emergency motor  48  is energized to rotationally drive the emergency drive gear  60  through the emergency gearbox  50 , which axially moves the emergency leadscrew  38  outward relative to the body, as shown in  FIGS. 11 and 12 , until the landing gear has been fully deployed (block  122 ). In this manner, the landing gear  10  is permitted to cycle to a fully deployed position when there is a jam or power loss to the main drive. 
     Once the jam has been cleared in the main drive or the power has been restored to it, the main motor  44  is used to reset the position of the components within the extend/retract actuator  18 , as shown in  FIG. 13 . With the brake  52  released using the coil  74 , for example, the main motor  44  rotationally drives the main leadscrew  40  into the output rod  36 . At the same time the main leadscrew  40  back-drives the emergency leadscrew  38  to return in to its “home” or “normal” axial position relative to the body. 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.