Abstract:
A thrust reverser system that includes one or more power drive units operable to supply a drive force. The power drive unit includes a motor and at least two output sections, each operably coupled to transmit the drive force to the thrust reverser movable components. Each of the output sections is operable to decouple the motor from associated thrust reverser movable components upon a torque magnitude being reached in the output section. A deadband coupler is provided to couple the first and second output sections together a time period after the torque magnitude is reached in one of the output sections.

Description:
FIELD OF THE INVENTION 
     The present invention relates to aircraft engine thrust reverser actuation systems and, more particularly, to a decoupler that is used to limit the torque in an aircraft thrust reverser drive train that is driven by a dual output power drive unit. 
     BACKGROUND OF THE INVENTION 
     When a jet-powered aircraft lands, the landing gear brakes and aerodynamic drag (e.g., flaps, spoilers, etc.) of the aircraft may not, in certain situations, be sufficient to slow the aircraft down in the required amount of runway distance. Thus, jet engines on most aircraft include thrust reversers to enhance the braking of the aircraft. When deployed, a thrust reverser redirects the rearward thrust of the jet engine to a generally or partially forward direction to decelerate the aircraft. Because at least some of the jet thrust is directed forward, the jet thrust also slows down the aircraft upon landing. 
     Various thrust reverser designs are commonly known, and the particular design utilized depends, at least in part, on the engine manufacturer, the engine configuration, and the propulsion technology being used. Thrust reverser designs used most prominently with jet engines fall into three general categories: (1) cascade-type thrust reversers; (2) target-type thrust reversers; and (3) pivot door thrust reversers. Each of these designs employs a different type of moveable thrust reverser component to change the direction of the jet thrust. 
     Cascade-type thrust reversers are normally used on high-bypass ratio jet engines. This type of thrust reverser is located on the circumference of the engine&#39;s midsection and, when deployed, exposes and redirects air flow through a plurality of cascade vanes. The moveable thrust reverser components in the cascade design includes several translating sleeves or cowls (“transcowls”) that are deployed to expose the cascade vanes. 
     Target-type reversers, also referred to as clamshell reversers, are typically used with low-bypass ratio jet engines. Target-type thrust reversers use two doors as the moveable thrust reverser components to block the entire jet thrust coming from the rear of the engine. These doors are mounted on the aft portion of the engine and may form the rear part of the engine nacelle. 
     Pivot door thrust reversers may utilize four doors on the engine nacelle as the moveable thrust reverser components. In the deployed position, these doors extend outwardly from the nacelle to redirect the jet thrust. 
     The primary use of thrust reversers is, as noted above, to enhance the braking of the aircraft, thereby shortening the stopping distance during landing. Hence, thrust reversers are usually deployed during the landing process to slow the aircraft. Thereafter, when the thrust reversers are no longer needed, they are returned to their original, or stowed, position. In the stowed position, the thrust reversers do not redirect the jet engine&#39;s thrust. 
     The moveable thrust reverser components in each of the above-described designs are moved between the stowed and deployed positions by actuators. Power to drive the actuators may come from a dual output power drive unit (PDU), which may be electrically, hydraulically, or pneumatically operated, depending on the system design. A drive train that includes one or more drive mechanisms, such as flexible rotating shafts, may interconnect the actuators and the PDU to transmit the PDU&#39;s drive force to the moveable thrust reverser components. 
     Each of the above-described thrust reverser system configurations is robustly designed and is safe and reliable. Nonetheless, analysis has shown that secondary damage to various portions of the thrust reverser system may result under certain postulated conditions. For example, if one of the actuators coupled to one of the PDU outputs becomes jammed, it is postulated that all of the drive force supplied from the PDU would be concentrated, via the synchronization mechanisms, on the jammed actuator. This postulated condition may result in damage to the actuator system components, including the PDU, actuators, drive mechanisms, or the moveable thrust reversers components. Repairing such damage can be costly and result in aircraft down time. One solution is to use stronger components, but this increases the cost and/or weight of the thrust reverser system. Another solution is to include numerous, independently operated torque limiters or decouplers in each drive train coupled to the PDU outputs. However, this solution may also increase system cost and/or weight. 
     Accordingly, there is a need for a thrust reverser system that improves upon one or more of the drawbacks identified above. Namely, a system that reduces the likelihood of component damage if thrust reverser system fails, for example, by a jammed actuator, without significantly increasing the cost and/or the weight of the thrust reverser system components. The present invention addresses one or more of these needs. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and method that sequentially decouples a dual output thrust reverser system PDU assembly from its load in the event a torque magnitude is reached between the assembly and load. Thus, the present invention reduces the likelihood of component damage without significantly increasing the cost and/or weight of the system. 
     In one embodiment, and by way of example only, a thrust reverser control system includes a power drive unit operable to supply a drive force, at least two drive mechanisms, and at least two actuator assemblies. The drive mechanisms are each coupled to receive the drive force, and each actuator assembly is coupled to at least one of the drive mechanisms and operable to move, upon receipt of the drive force, between a stowed position and a deployed position. The power drive unit includes a motor, first and second output sections, and a deadband coupler. The motor has a shaft with at least a first output and a second output and is operable to supply rotational power to a first and a second load, respectively. The first output section is coupled to the first motor output and is operable to decouple the motor from the first load upon a torque magnitude being reached in the first output section. The second output section is coupled to the second motor output and is operable to decouple the motor from the second load upon a torque magnitude being reached in the second output section. The deadband coupler is coupled to the first and second output sections and is operable to selectively couple the first and second output sections together a time period after the first and second output sections have unequal rotational speeds. 
     In another exemplary embodiment, a power drive unit includes a motor, first and second output sections, and a deadband coupler. The motor has at least a first output and a second output and is operable to supply rotational power to a first and a second load, respectively. The first output section is coupled to the first motor output and is operable to decouple the motor from the first load upon a torque magnitude being reached in the first output section. The second output section is coupled to the second motor output and is operable to decouple the motor from the second load upon a torque magnitude being reached in the second output section. The deadband coupler is coupled to the first and second output sections and is operable to selectively couple the first and second output sections together a time period after the first and second output sections have unequal rotational speeds. 
     In still another exemplary embodiment, in a thrust reverser control system including a power drive unit having at least a first and a second output section each coupled to at least one thrust reverser movable component, respectively, a method of operating the system includes rotating the power drive unit first and second output sections to move the thrust reverser movable components between a stow and a deploy position. One of the power drive unit output sections is decoupled from its associated thrust reverser movable component upon a torque magnitude being reached therebetween. The other power drive unit output section is then decoupled from its associated thrust reverser movable component a time period after the power drive unit output sections have unequal rotational speeds. 
     In yet another exemplary embodiment, in a power drive unit including a motor having at least a first and a second output coupled to at least a first and a second power drive unit output section, respectively, a method of operating the power drive unit includes rotating the first and second motor outputs to thereby rotate the power drive unit first and second output sections. One of the power drive unit output sections is decoupled from its respective motor output upon a torque magnitude being reached therebetween. The other power drive unit output section is then decoupled from its respective motor output a time period after the power drive unit output sections have unequal rotational speeds. 
     In yet another exemplary embodiment, a thrust reverser system includes first and a second actuator assemblies, first and second drive mechanisms, and a deadband coupler. The first and second drive mechanisms are operably coupled to the first and second actuators, respectively, and are adapted to rotate upon receipt of a rotational drive force. The deadband coupler is operably coupled between the first and second drive mechanisms and is operable to selectively couple the first and second drive mechanisms together a time period after the first and second drive mechanisms have unequal rotational speeds. 
     Other independent features and advantages of the preferred system and method will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of portions of an aircraft jet engine fan case; 
     FIG. 2 is a simplified end view of a thrust reverser actuation system according to an exemplary embodiment of the present invention; 
     FIG. 3 is a simplified functional schematic diagram of a power drive unit assembly according to an exemplary embodiment of the present invention that may be used in the system of FIG. 2; 
     FIG. 4 is detailed cross section view of an exemplary embodiment of the power drive unit of FIG. 3; 
     FIG. 5 is a partial cross section view of the power drive unit of FIG. 4 showing an alternate configuration thereof; 
     FIG. 6 is a cross section view of the power drive unit of FIG. 4 taken along line  6 — 6  in FIG. 4; 
     FIG. 7 is a simplified depiction of an alternate configuration of the power drive unit of FIG. 3; 
     FIG. 8 is a cross section view of a portion of the power drive unit of FIG. 6 taken along line  8 — 8  in FIG. 7; and 
     FIGS. 9 and 10 are exemplary embodiments of output sections that may be used to implement the power drive units illustrated in FIGS.  3 - 8 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Before proceeding with the detailed description, it is to be appreciated that the described embodiment is not limited to use in conjunction with a specific thrust reverser system design. Thus, although the description is explicitly directed toward an embodiment that is implemented in a cascade-type thrust reverser system, in which transcowls are used as the moveable thrust reverser component, it should be appreciated that it can be implemented in other thrust reverser actuation system designs, including those described above and those known now or hereafter in the art. 
     Turning now to the description, and with reference first to FIG. 1, a perspective view of portions of an aircraft jet engine fan case  100  that incorporates a cascade-type thrust reverser is depicted. The engine fan case  100  includes a pair of semi-circular transcowls  102  and  104  that are positioned circumferentially on the outside of the fan case  100 . The transcowls  102  and  104  cover a plurality of non-illustrated cascade vanes. A mechanical link  202  (see FIG.  2 ), such as a pin or latch, may couple the transcowls  102  and  104  together to maintain the transcowls  102  and  104  in correct alignment on non-illustrated guides on which the transcowls  102  and  104  translate. When the thrust reversers are commanded to deploy, the transcowls  102  and  104  are translated aft. This, among other things, exposes the cascade vanes, and causes at least a portion of the air flowing through the engine fan case  100  to be redirected in a forward direction. This re-direction of air flow in a forward direction creates a reverse thrust and, thus, works to slow the airplane. 
     As shown more clearly in FIG. 2, a plurality of actuators  210  are individually coupled to the transcowls  102  and  104 . In the depicted embodiment, half of the actuators  210  are coupled to one of the transcowls  102 , and the other half are coupled to another transcowl  104 . While not critical to understand or enable the present invention, it is noted that some or all of the actuators  210  may include locks, some or all of which may include position sensors. In addition, the transcowls  102  and  104  may also, or alternatively, each include locks. It is noted that the actuators  210  may be any one of numerous actuator designs presently known in the art or hereafter designed. However, in this embodiment the actuators  210  are ballscrew actuators. It is additionally noted that the number and arrangement of actuators  210  is not limited to what is depicted in FIG. 2, but could include other numbers of actuators  210  as well. The number and arrangement of actuators is selected to meet the specific design requirements of the system. 
     The actuators  210  are interconnected via a plurality of drive mechanisms  212 , each of which, in the particular depicted embodiment, is a flexible shaft. Using flexible shafts  212  in this configuration ensures that the actuators  210  and the transcowls  102  and  104  move in a substantially synchronized manner. For example, when one transcowl  102  is moved, the other transcowl  104  is moved a like distance at substantially the same time. Other synchronization mechanisms that may be used include electrical synchronization or open loop synchronization, or any other mechanism or design that transfers power between the actuators  210 . 
     A power drive unit (PDU) assembly  220  having at least two output sections, a first output section  216   a  and a second output section  216   b , is coupled to the actuators  210  via one or more flexible shafts  212 . In the depicted embodiment, the PDU assembly  220  includes a dual output motor  214  that is coupled to the two output sections  216   a ,  216   b . The motor  214  may be any one of numerous types of motors such as, for example, an electric (including any one of the various DC or AC motor designs known in the art), a hydraulic, or a pneumatic motor. The first  216   a  and second  216   b  output sections are each coupled between an output of the motor  214  and one of the flexible shafts  212 . Moreover, though not explicitly depicted, the PDU assembly  220  may include a lock mechanism. In any case, with the depicted arrangement, the rotation of the PDU assembly  220  results in the synchronous operation of the actuators  210 , via the flexible shafts  212 , thereby causing the transcowls  102  and  104  to move at substantially the same rate. 
     The PDU assembly  220  is controlled by a control circuit  218 . The control circuit  218  receives commands from a non-illustrated engine control system such as, for example, a FADEC (full authority digital engine control) system, and provides appropriate activation signals to the PDU assembly  220  in response to the received commands. In turn, the PDU assembly  220  supplies a drive force to the actuators  210  via the flexible shafts  212 . As a result, the actuators  210  cause the transcowls  102  and  104  to translate between the stowed and deployed positions. 
     Turning now to FIGS. 3-10, a description of various embodiments of the PDU assembly  220  and its operation will be provided. Beginning with FIG. 3, which depicts a functional schematic representation of the PDU assembly  220 , a general description of the PDU assembly  220  and its operation will first be provided. Thereafter, a more detailed description of various embodiments of the PDU assembly  220  will be provided. 
     As shown in FIG. 3, the PDU assembly  220  includes the motor  214 , the output sections  216   a ,  216   b , and a deadband coupler  302 . The motor  214 , as was alluded to above, includes at least two outputs, a first output  304   a  and a second output  304   b . The first output section  216   a  is coupled to the motor first output  304   a , and the second output section  216   b  is coupled to motor second output  304   b . In addition, the first  216   a  and second  216   b  output sections are each adapted to couple to a load such as, for example, the above-mentioned device mechanisms  212  and one or more actuators  210 . The deadband coupler  302  is coupled to the first  216   a  and second  216   b  output sections. 
     As was noted above, the PDU assembly  220 , when installed in a thrust reverser actuation system, supplies a drive force to the actuators  210 . While the PDU assembly  220  is supplying the drive force, if the torque in the first (or second) output section  216   a  (or  216   b ) exceeds a magnitude due, for example, to a jammed actuator  210 , then the first (or second) output section  216   a  (or  216   b ) will decouple the first (or second) motor output  304   a  (or  304   b ) from the drive mechanisms  212  and the jammed actuator  210 . Thereafter, if the motor  214  continues rotating, the output sections  216   a  and  216   b  will rotate at unequal speeds, and relative rotation will exist between the first and second output sections  216   a  and  216   b . After a deadband time period, the deadband coupler  302  couples the first  216   a  and second  216   b  output sections together. When this occurs, the torque in the second (or first) output section  216   b  (or  216   a ) will then exceed the torque magnitude, and decouples the motor second (or first) output  304   b  (or  304   a ) from the drive mechanisms  212 . As a result, the PDU assembly  220  is fully decoupled from the load. 
     Sequentially decoupling both motor outputs  304   a  and  304   b  from the respective drive mechanisms  212  when the torque magnitude in one of the output sections  216   a  or  216   b  reaches the magnitude reduces the likelihood of any additional component damage. If only one of the motor outputs  304   a  or  304   b  were decoupled by, for example, including only a single torque limiter device, the output section  304   a  or  304   b  that was not decoupled would continue supplying the drive force to its respective drive mechanism  212 . If the thrust reverser transcowl halves  102  and  104  are linked by, for example, the mechanical link  202 , the non-decoupled output section  304   a  or  304   b  would continue to drive, or attempt to drive, the transcowl half  102  or  104  to which it is coupled. This could result in additional damage. In addition, if a single torque limiter were used to decouple both output sections  216   a  and  216   b , the torque limiter would have to have a torque limit set point that is significantly higher than with two torque limiters, to prevent nuisance decouplings. Thus, the motor outputs  304   a  and  304   b  and the output sections  216   a  and  216   b  may need to be more robustly designed to withstand higher torque limits, which can increase system size, weight, and/or cost. 
     With reference now to FIG. 4, a detailed description of a particular embodiment of the PDU assembly  220  will be provided. The depicted PDU assembly  220  includes a housing  402 , which may be constructed of one or more pieces. The motor  214  is mounted within the housing  402 , and includes a shaft  404  having a first end  406  and a second end  408 . The shaft  404  is rotationally mounted within the housing  402  by first  412   a  and second  412   b  bearing assemblies. In the depicted embodiment, the first  216   a  and second  216   b  output sections include first  216   a  and second  216   b  torque decouplers, which are also mounted within the housing  402 . The first and second torque decouplers  216   a ,  216   b , each include an input section  416   a ,  416   b  and an output section  418   a ,  418   b . The first torque decoupler input section  416   a  is coupled to the motor shaft first end  406 , and the second torque decoupler input section  416   b  is coupled to the motor shaft second end  408 , via first and second gimbal springs  420   a ,  420   b , respectively. The gimbal springs  420   a ,  420   b  supply a preload that biases the torque decoupler input sections  416   a ,  416   b  toward their respective output sections  418   a ,  418   b . The first and second torque decoupler output sections  418   a ,  418   b  are rotationally mounted within the housing  402  by third  412   c  and fourth  412   d  bearing assemblies, respectively. 
     In an alternate embodiment, a portion of which is shown in FIG. 5, the first  420   a  and second  420   b  gimbal springs are not included. Instead, the motor shaft first  406  and second  408  ends are coupled to the first  416   a  and second  416   b  torque decoupler input sections, respectively, and biasing springs  502   a ,  502   b  (only  502   b  shown) are used to bias the torque decoupler input sections  416   a ,  416   b  toward their respective output sections  418   a ,  418   b . However, the use of gimbal springs is preferred, since this reduces the likelihood of frictional forces. 
     Returning now to FIG. 4, the deadband coupler  302  may be constructed in any one of numerous configurations. In the embodiment depicted in FIG. 4, the deadband coupler  302  is a quill shaft assembly  426  that is coupled to the first  418   a  and second  418   b  torque decoupler output sections. The quill shaft assembly  426  includes a first quill shaft  428 , a second quill shaft  430 , and a deadband stop  442 . The first quill shaft  428  has a first end  432  and a second end  434 . The first end  432  is coupled to the first torque decoupler output section  418   a . As shown more clearly in FIG. 6, in this particular depicted embodiment, the first quill shaft second end  434  includes two or more prongs, forks, or gear sections  435   a ,  435   b , and rotates free of contact during normal PDU assembly  220  operations. Similarly, the second quill shaft  430  has a first end  436  and a second end  438 . The second quill shaft first end  436  is coupled to the second torque decoupler output section  418   b . The second quill shaft second end  438  also includes two or more prongs, forks, or gear sections  435   a ,  435   b , and rotates free of contact during normal PDU assembly  220  operations. The deadband stop  442  is coupled to, or is integrally formed with, the shaft  404 , and includes two or more quill shaft contacts  444  that are spaced apart from the first and second quill shaft second ends  434  and  438  during normal PDU assembly  220  operations. 
     During normal operations of the PDU assembly  220  depicted in FIGS. 4-6, the forks, prongs, or gear sections  435   a ,  435   b  on the second ends  434 ,  438  of the first  428  and second  430  quill shafts rotate free of contact with the deadband stop contact surfaces  444 . Thus, rotation of the motor  214  during normal operation causes the first  216   a  and second  216   b  torque decouplers to rotate in unison, which in turn causes the first  428  and second  430  quill shafts to rotate in unison with one another, and in unison with the deadband stop  442 . If, however, the load on the PDU assembly  220  causes the torque in, for example, the first torque decoupler  216   a  to reach or exceed a first magnitude, then the first torque decoupler input section  416   a  will decouple from its output section  418   a . This will cause the first quill shaft  428  to no longer rotate in unison with the second quill shaft  430  and the deadband stop  442 . As a result, after some period of time, the second quill shaft second end  438  contacts and/or meshes with the deadhand stop contact surfaces  444 , which couples the first  418   a  and second  418   b  decoupler output sections together. With the first  418   a  and second  418   b  torque decoupler output sections coupled together, the torque in the second torque decoupler  216   b  will then reach or exceed a second torque magnitude (which may be substantially equal to the first torque magnitude), and decouple its input section  416   b  from its output section  418   b . At this time, the PDU assembly  220  is completely unloaded. It will be appreciated that the time for the first and second quill shaft second ends  434 ,  436  to contact and/or mesh with the deadband stop contact surfaces  444  may be adjusted by, for example, adjusting the amount of angular displacement between the quill shaft second ends  434 ,  436  and the contact surfaces  444 . 
     As was noted above, the deadband coupler  302  is not limited to the quill shaft assembly shown in FIGS. 4 and 6, but could be any one of numerous other devices and/or mechanisms that provide the same functionality. For example, FIGS. 7 and 8 depict a simplified diagram of a PDU assembly  220  that includes one such alternative deadband coupler configuration. In this configuration, the deadband coupler  302  is a quill shaft assembly  702  that is substantially unitary in construction. It will be appreciated that the quill shaft assembly  702  could be unitarily constructed of multiple sections. The quill shaft assembly  702  has a first end  704  that is coupled to the first torque decoupler output section  418   a , and a second end  706  that is rotationally mounted within the second torque decoupler output section  418   b . It will be appreciated that either end of the quill shaft assembly  702  could be rigidly coupled to its output section  418   a ,  418   b , while the opposite end is rotationally mounted. 
     As with the alternate embodiment of FIG. 5, in this particular embodiment, the motor shaft first  406  and second  408  ends are directly coupled to the first  416   a  and second  416   b  torque decoupler input sections, respectively, and first and second springs  502   a ,  502   b  bias the torque decoupler input sections  416   a ,  416   b  toward their respective output sections  418   a ,  418   b . It will be appreciated, however, that gimbal springs could instead be used, as with the embodiment depicted in FIG.  3 . In addition, as shown most clearly in FIG. 8, the second torque decoupler output section  418   b  includes a plurality of deadband stops  802 . It will be appreciated that either or both decoupler output sections  418   a ,  418   b  could include the deadband stops  802 . Moreover, although two diametrically opposed deadband stops  802  are illustrated, it will be appreciated that the number and/or spacing of the deadband stops may be varied to implement the desired deadband time period. 
     During normal operation of the PDU assembly  220  shown in FIG. 8, the quill shaft assembly  702  rotates in synchronism with the motor shaft  402 , and does not contact the deadband stops  802 . If the torque in the first torque decoupler  216   a  reaches or exceeds a first magnitude, then the first torque decoupler input section  416   a  will decouple from its output section  418   a . As a result, the quill shaft assembly  702  will not rotate in synchronism with the motor shaft  402 . After a time period, the quill shaft second end  706  will contact the deadband stops  802  in the second torque decoupler output section  418   b , coupling the first  418   a  and second  418   b  torque decoupler output sections together. With the first  418   a  and second  418   b  torque decoupler output sections coupled together, the torque in the second decoupler  216   b  will then reach or exceed a second torque magnitude (which may be substantially equal to the first torque magnitude), and decouple its input section  416   b  from its output section  418   b . At this time, the PDU assembly  220  is completely unloaded. 
     Similar to the sequence described above, if the torque in the second decoupler  216   b  reaches the second torque magnitude first, then the second torque decoupler input section  416   b  will decouple from its output section  418   b . As a result, the second torque decoupler output section  418   b  will not rotate in synchronism with the motor shaft  402  and, thus, the quill shaft assembly  702 . After the time period, the quill shaft second end  706  will contact the deadband stops  802  in the second torque decoupler output section  418   b , coupling the first  418   a  and second  418   b  torque decoupler output sections together. With the first  418   a  and second  418   b  torque decoupler output sections coupled together, the torque in the first torque decoupler  216   a  will then reach or exceed the first torque magnitude, and decouple its input section  416   a  from its output section  418   a , leaving the PDU assembly  220  completely unloaded. 
     In addition to the various embodiments explicitly illustrated and described, it will be appreciated that various other deadband coupler configurations may also be used to implement the described functionality. For example, the first and second quill shafts could be configures so that, during normal operations, the ends of each at least partially overlap, are angularly displaced from, and do not contact, one another. 
     In addition to various deadband coupler configurations, it will be appreciated that the torque decouplers  216   a ,  216   b  may also be variously configured. Two particular embodiments of a torque decoupler  216  that may be used in the PDU assembly  220  are shown in FIGS. 9 and 10. In the embodiment shown in FIG. 9, the torque decoupler  216  is a toothed-clutch type of decoupler, and in the embodiment shown in FIG. 10, the torque decoupler is a ball-and-ramp type of decoupler. Both of these decoupler configurations are known in the art and will, therefore, not be described in detail. It will be appreciated that the torque decouplers  216   a ,  216   b  are not limited to those illustrated in FIGS. 9 and 10, but that various other configurations may also be used. 
     Furthermore, it will be appreciated that the first  216   a  and second  216   b  output sections are not limited to the implementations explicitly depicted and described above. By way of non-limiting example, the output sections could be either hydraulically operated, electrically operated, or a combination of both. The output sections could include any one of numerous torque sensors and the hydraulically and/or electrically operated output sections could operate in response to the sensors. 
     The PDU assembly  220  described above reduces the likelihood of component damage if a coupled load, such as a thrust reverser actuator, jams, without significantly increasing the cost and/or the weight of the thrust reverser system and/or the system components. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.