Abstract:
A device and method for determining whether a no-back device is functioning properly includes a no-back device coupling an input shaft and an output shaft. A no-back output gear is coupled to the output shaft, and a reaction gear is operably coupled to the no-back output gear. A check device includes a rotatable drive feature having a first end accessible for rotation and a second end engaged with the reaction gear. The functionality of the no-back device is evaluated by applying a rotational torque to the drive feature.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 13/413,858, filed Mar. 7, 2012, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to an actuation system and more particularly to an actuation system having a no-back device. 
     Modern aircrafts are commonly equipped with actuators containing no-back devices. These actuators are subjected to aerodynamic loads resulting from the distribution of loads in the aircraft, from the trajectory of the aircraft, and from the flight conditions. No-back devices are employed in actuators of mechanical drive systems where it is necessary to prevent an aerodynamic load, from back driving the system in the event of a structural failure or disconnect of the input shaft to an actuator. A typical no-back device has a releasable brake associated with an output shaft as well as an input shaft connected to a prime mover. A coupling between the input shaft and output shafts operates in response to the transmission of torque from the output shaft to the input shaft to prevent movement of the output shaft, and assure that the element associated with the output shaft will remain in the position in which it was originally placed by operation of the prime mover. 
     The functionality of the no-back device is critical in instances where it is required. A failure of a no-back device is potentially dangerous since a shaft could be driven by the aerodynamic forces acting on the element to be actuated. The element would then not be held in the desired position, and could flutter rendering the aircraft unstable. It is therefore desirable to develop a system that easily and efficiently allows a mechanic to verify that the no-back device in an actuator is functioning properly. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one embodiment, a method for verifying the functionality of a no-back device is provided including locking an output shaft against rotation and allowing an input shaft to freely rotate. The stop device is then removed from the check device such that the drive feature may freely rotate. The drive feature is rotated to a first position and the rotation of an input shaft is evaluated. The drive feature is then rotated to a second position where the rotation of an input shaft is again evaluated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view of an actuator assembly; 
         FIG. 2A  is a detailed view of an embodiment of the invention as shown in circled area A in  FIG. 1 ; 
         FIG. 2B  is a bottom view of the  FIG. 2A ; 
         FIG. 3A  is an top view of an alternate embodiment of the invention; 
         FIG. 3B  is a top view of  FIG. 3A  with the cover removed; and 
         FIG. 3C  is a cross-sectional side view of  FIG. 3A  taken across line B-B. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to  FIG. 1 , an actuator assembly  100  usable in an aircraft is shown. The actuator assembly  100  includes an actuator housing  110 . An input shaft  120  is coupled to an output shaft  130  in a coaxial relation. Providing a connection between the input shaft  120  and output shaft  130  is a no-back device  140 . The output shaft  130  is locked by the no-back device  140  to prevent external loads from back driving the actuator assembly  100  into a potentially hazardous position in the event of a structural failure or disconnect of the input shaft to the actuator. The input shaft  120  may be driven either clockwise or counterclockwise. When the no-back device  140  is functioning properly and the input shaft  120  is stationary, the output shaft  130  is automatically locked against back driving, in either the clockwise or counterclockwise directions. No-back devices are known and a person having ordinary skill in the art would be able to select a no-back device appropriate for the particular application. 
     Positioned adjacent an external surface of the no-back device  140  is a no-back output gear  142 , such as a sun gear for example. A reaction gear  146  is coupled with the no-back output gear  142 . In one embodiment, the reaction gear  146  is directly coupled to the no-back output gear  142 . In an alternate embodiment, the reaction gear  146  is indirectly coupled to the no-back output gear  142  through a planetary gear assembly  144  having at least one additional gear. A check device  150  engages the reaction gear  146 , such that rotation of the check device  150  while the output shaft  130  is locked determines whether the no-back device  140  is functioning properly. 
     In a first embodiment of the invention, shown in  FIGS. 2A and 2B , the check device  150  includes a drive feature  152 , extending through a hole  114  in the actuator housing  110 , allowing rotation between a first position and a second position. A first end  152   a  of the drive feature  152  is accessible from outside the actuator by a person, such as a mechanic for example. The first end  152   a  is positioned adjacent the outer surface  112  of the actuator housing  110 . In one embodiment, this first end  152   a  of the drive feature  152  includes a head, such as a hex head, that allows a mechanic to easily apply a rotational torque to the drive feature  152 . A stop device  144 , such as a lock washer for example, is disposed between the first end  152   a  of the drive feature  152  and the actuator housing  110  to prevent unwanted rotation of the drive feature  152  when a mechanic is not checking the functionality of the no-back device. The body of the drive feature  152  between the first end  152   a  and the second end  152   b  includes a first groove  156 . An axial retention feature  157 , such as a C-clip for example, connects to drive feature  152  and is positioned within the first groove  156  to prevent the drive feature  152  from sliding vertically relative to the actuator housing  110 . Disposed along the body of the drive feature  152  between the first groove  156  and the first end  152   a  is a circumferential second groove  158 . A seal  159  fits between the second groove  158  and the actuator housing  110  to prevent moisture from entering the actuator assembly  100 . 
     The second end  152   b  of the drive feature  152  includes an eccentric feature that extends into a slot  148  in the reaction gear  146 . In one embodiment, the drive feature  152  is an eccentric pin, wherein the central axis Z of the first end  152   a  of the pin is offset from the central axis Y of the second end  152   b  of the pin. When a rotational force or torque is applied to the first end  152   a  of the drive feature  152 , the eccentric feature of the second end  152   b  moves with respect to the slot  148 . This movement of the second end  152   b  creates a rotation of the reaction gear  146  which in turn causes a magnified rotation of the no-back output gear  142 . 
     In an alternate embodiment of the check device  150 , shown in  FIGS. 3A-3C , a threaded insert  160  is threadably engaged with hole  114  of the actuator housing  110 . The threaded insert  160  includes a flange attached to a body having a plurality of threads on an external surface  162  of the threaded insert  160 . The threaded insert  160  extends substantially from the reaction gear  146  to the actuator housing  110  such that when the threaded insert  160  is seated in position, the top surface of the flange is substantially flush with the outer surface  112  of the actuator housing  110 . Disposed within the threaded insert  160  is a drive feature  152  having a first end  152   a  accessible from the actuator housing  110  and a second end  152   b  extending into a slot  148  of reaction gear  146 . Coupled to the drive feature between the first end  152   a  and the second end  152   b  is a bearing  164  to minimize the drag of the drive feature  152  as it rotates within the threaded insert  160 . A seal  158  is located between the threaded insert  160  and the actuator housing  110 . An additional seal exists between the threaded insert  160  and a cover plate  170  of the check device  150  to prevent moisture from entering the actuator assembly  100 . 
     A cover plate  170  having at least one fastener  172  attaches to the outer surface  112  of the actuator housing  110 . Positioned between each fastener  172  and the housing  110  may be a washer  174 . Removal of the cover plate  170  from engagement with the actuator housing  110  exposes the first end  152   a  of the drive feature  152 . A stop device  144  is incorporated into the cover plate  170 . The surface of the cover plate  170  facing the drive feature  152  includes a protrusion  144  having a shape complementary to the first end  152   a  of the drive feature  152 . In one embodiment, the first end  152   a  of the drive feature  152  is square. When the cover plate  170  is attached to the actuator housing  110 , the first end  152   a  of the drive feature  152  aligns with the inner edge of the protrusion  144  such that the first end  152   a  is confined within the protrusion  144  and is thereby prevented from freely rotating. 
     To check the functionality of the no-back device  140 , an aircraft mechanic first adjusts the actuator assembly  100  such that the output shaft  130  is locked and the input shaft  120  is free to rotate. The mechanic then removes the stop device  144  of the check device  150  so that the drive feature  152  can rotate. In the illustrated embodiments, removal of the stop device  144  includes removing either a lock washer or a cover plate from engagement with the drive feature  152 . The first end  152   a  of the drive feature  152  is then rotated clockwise ninety degrees from a normal to a first “Check-Clockwise” position. After the mechanic performs a check of the no-back device  140  with the drive feature  152  in the first position, the first end  152   a  of the drive feature  152  is rotated back to the normal position. The mechanic then rotates the drive feature  152  ninety degrees in counterclockwise to a second “Check-Counterclockwise” position where the mechanic again evaluates the functionality of the no-back device  140 . After the functionality of the no-back device  140  has been verified in both the clockwise and counterclockwise positions, the drive feature  152  is returned to the normal position, and the stop device  144  is re-engaged. The rotation of the drive feature  152  to each of the first and second positions results in a specific amount of rotation of the reaction gear  146 . Dependent on the gear ratio between the reaction gear  146  and the no-back output gear  142 , the generally small amount of rotation of the reaction gear  146  will result in a substantially magnified angular rotation of the no-back output gear  142 . 
     This rotation of the no-back output gear  142  is used to verify the functionality of the no-back device  140 . If the no-back device  140  has no lost motion, braking of the no-back output gear should result if the no-back device  140  is functioning correctly. If the no-back device  140  includes lost motion, the no-back output gear  142  must be sufficiently rotated beyond the lost motion threshold for braking of the no-back output gear  142  to result, thereby demonstrating the proper functioning of the no-back device  140 . If, however, the no-back device  140  is not functioning properly, regardless of whether it includes lost motion, rotation of the no-back output gear  142  will result in visible rotation of input shaft  120 , and service is required. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.