Abstract:
An integrated torque limiter/no-back device for use in an actuator with an input shaft, an output, and a gear reduction. The device includes an input ramp, an output ramp coupled to the gear reduction, a combined ramp disposed between the input ramp and the output ramp, a first plurality of balls arranged between the input ramp and the combined ramp, a second plurality of balls arranged between the combined ramp and the output ramp, a pin, and a brake. The pin extends from the input ramp to the combined ramp and coupled to the input shaft. The combined ramp, the output ramp, and the second plurality of balls therebetween are configured to operate as a torque limiter by causing the combined ramp and the output ramp to separate and the output ramp to engage the brake when the torque from the input shaft exceeds a torque threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This divisional application claims priority from application Ser. No. 13/478,172, filed May 23, 2012 entitled INTEGRATED TORQUE LIMITER/NO-BACK DEVICE, which is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The subject matter disclosed herein relates to actuators in a fixed-wing aircraft. More specifically, the subject matter disclosed herein relates to an integrated torque limiter for use in an actuator for such aircraft. 
         [0003]    The term actuator refers to a member of a class of mechanisms whose primary function is to provide a controllable force for moving an actuated element to a desired position. An actuator system typically includes an actuator, an actuated element, connecting linkage and a power source. Some actuator systems must also perform a force limiting function to prevent damage should the system become jammed. This is sometimes done through torque limiting devices on the actuator input shaft. 
         [0004]    An aircraft actuation system is an example of a system which may use a torque limiter as a force limiter for an actuator. In an aircraft actuation system, a high lift actuator can be used to lift and hold a flight surface in a particular position under a variety of conditions. A torque limiter on this can limit the torque applied to this flight surface. 
       SUMMARY 
       [0005]    An integrated torque limiter/no-back device for use in an actuator with an input shaft, an output, and a gear reduction. The device includes an input ramp, an output ramp coupled to the gear reduction, a combined ramp disposed between the input ramp and the output ramp, a first plurality of balls arranged between the input ramp and the combined ramp, a second plurality of balls arranged between the combined ramp and the output ramp, a pin, and a brake. The first plurality of balls is configured to transfer torque between the input ramp and the combined ramp, and the second plurality of balls is configured to transfer torque between the combined ramp and the output ramp. The pin extends from the input ramp to the combined ramp and coupled to the input shaft. The combined ramp, the output ramp, and the second plurality of balls therebetween are configured to operate as a torque limiter by causing the combined ramp and the output ramp to separate and the output ramp to engage the brake when the torque from the input shaft exceeds a torque threshold. 
         [0006]    A method of limiting torque and backdriving through an actuator includes receiving input torque at an input shaft; transmitting the input torque through an integrated torque limiter/no-back device; sensing torque transferred through the integrated torque limiter/no-back device; engaging the brake when the torque transferred between the combined ramp and the output ramp exceeds a threshold torque such that the output ramp and the combined ramp separate and the output ramp engages the brake. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a typical slat actuation system on an aircraft. 
           [0008]      FIG. 2A  shows a first embodiment of an actuator with an integrated torque limiter/no-back device. 
           [0009]      FIG. 2B  shows views of two adjacent ball ramps of the integrated torque limiter/no-back device with no input torque. 
           [0010]      FIG. 2C  show views of two adjacent ball ramps of the integrated torque limiter/no-back device with input torque. 
           [0011]      FIG. 3  shows a second embodiment of an actuator with an integrated torque limiter/no-back device. 
           [0012]      FIG. 4  shows a third embodiment of an actuator with an integrated torque limiter/no-back device. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  illustrates a typical slat actuation system  10  on an aircraft  11 . The system is located on left wing  12   a  and right wing  12   b  of aircraft  11 , and includes a position indicating device  14 , power drive unit  16 , slat panels  18 , slat actuators  20 , slat panel linkage  22  and torque shafting  30 . Each slat panel  18  is connected to either wing  12   a  or  12   b  by two slat panel linkage mechanisms  22 , with each linkage mechanism connected to slat actuation system  10  through a slat actuator  20 . The power drive unit  16  connects to each slat actuator  20  through the torque shafting  30 . 
         [0014]    Prior to flight or upon landing, power drive unit  16  powers slat actuators  20  to extend slat panels  18  away from wings  12   a  and  12   b  and into the airstream. Slat panel linkages  22  are used to extend slat panels  18 , and position indicating device  14  work with power drive unit  16  to hold slat panels  18  in place. Once airborne, power drive unit  16  powers slat actuators  20  to retract slat panels  18  toward wings  12   a  and  12   b  to cut down on drag during flight. 
         [0015]    In some instances, there is a jam in slat panel linkage  22  when slat actuator  20  is driving the linkage  22  to extend or retract slat panel  18 . When a jam occurs, power drive unit  16  could generate enough torque to damage the slat panel or structure of the aircraft. Therefore, a torque limiter is usually included in each slat actuator  20 . The torque limiter senses the torque going through actuator  20  to slat panel  18 . If the torque sensed gets too high, the torque limiter locks up and grounds any additional torque coming from power drive unit  16  to the wing with the lock up. 
         [0016]    During flight, and especially when slat panels  18  are extended by slat actuators  20  into an airstream, slat panels  18  are exposed to many different forces. Some of these forces act on slat panels  18  to push in the direction opposite of the direction slat actuator  20  is extending panels  18 . No-back systems prevent this load from actually driving actuator  20  backwards. 
         [0017]      FIG. 2A  shows a first embodiment of an actuator  20  with an integrated torque limiter/no-back device  36 . Actuator  20  includes input shaft  30 , gear reduction  32 , actuator output  34  and integrated torque limiter/no-back device  36 . Integrated torque limiter/no-back device  36  includes torque limiter ball ramp  38 , combined ball ramp  40 , no-back ball ramp  42 , brake plates  44 , cone brake  45 , balls  46 ,  48  and pin  50 . While only one ball  46 ,  48  is respectively shown, a plurality of balls  46 ,  48  can be used in actuator  20 . 
         [0018]    Actuator input shaft  30  is connected to torque limiter ball ramp  38 . Torque limiter ball ramp  38  is in contact with balls  46 , which are in contact with combined ball ramp  40 . Gear reduction  32  is connected to output  34 . Actuator gear reduction  32  can be any type of gear system including but not limited to a simple gear arrangement, epicyclic gearing, worm gearing, or wheel gearing. When no-back is not engaged, ball ramp  40  pushes pin  50 , which pushes no-back ball ramp  42  and gear reduction  32 . When no-back is engaged, gear reduction  32  pushes no-back ball ramp  42 , causing balls  48  to roll up no-back ball ramp  42  and combined ball ramp  40 , separating them and engaging cone brake  45 . 
         [0019]      FIGS. 2B-2C  show views of adjacent ball ramps  38 ,  40  with ball  46  of the integrated torque limiter/no-back device  36 . While ball ramps  38 ,  40  and ball  46  are shown, this is demonstrative of ball ramps  40  and  42  with ball  48  as well.  FIG. 2B  shows torque limiter ball ramp  38  and combined ball ramp  40  when no torque is acting on actuator  20 .  FIG. 2C  shows torque being transferred from torque limiter ball ramp  38  to combined ball ramp  40  through ball  46 , causing ball  46  to roll up ramp and move ramps  38 ,  40  away from each other. 
         [0020]    Torque is applied to actuator  20  by rotating input shaft  30 . This rotary motion is transferred from input shaft  30  to integrated torque limiter/no-back device  36  to gear reduction  32 , and then from gear reduction  32  to output  34 . Output  34  is connected to a rack and pinion or other type of device to translate rotary motion from gear reduction  32  to linear motion to provide drive to extend or retract slat panels through linkage mechanisms as shown in  FIG. 1 . In alternative embodiments, actuator  20  is connected to the line of rotation of the surface. 
         [0021]    When torque is transferred from torque limiter ball ramp  38  to combined ramp  40  through ball  46 , this causes ball  46  to roll up ramps  38 ,  40 , as shown in  FIG. 2C . As ball  46  rolls up ramps  38 ,  40 , the angle on ramps  38 ,  40  cause the torque to be transferred. As ball  48  rolls up ramps  38 ,  40 , this also causes ramps  38 ,  40  to separate. At a certain point, when ramps  38 ,  40 , separate sufficiently, ramps  38  and  40  encounter brake plates  44  and input torque limiter is engaged. This engagement means that torque has reached a critical point and must be transferred out of the system so as not to damage flight surfaces. Any additional torque going into the system at this point can be grounded into an actuator housing (not shown). 
         [0022]    When torque has not reached a critical point to engage torque limiter, and is still being transferred through actuator  20 , torque transfers into no-back portion of integrated torque limiter and no-back device  36 . Pin  50  engages no-back ramp  42 , gear reduction  32  and combined ramp  40  so that ball  48  is not allowed to climb between ramps  40 ,  42 , as shown in  FIG. 2C . When torque through gear reduction  32  has reached a certain level pin  50  becomes disengaged from no-back ball ramp  42  and gear reduction  32 , causing torque to be transferred through ball  48  (instead of pin  50 ). This causes balls  48  to move up ramps  40 ,  42 , separating ramps  40 ,  42 . Sufficient separation of ramps  40 ,  42  causes no-back ramp  42  to encounter cone brake  45 , engaging no-back device to hold slat panels  18  steady and prevent backdriving of actuator  20 . 
         [0023]    Past actuators  20  included separate no-back and torque limiting devices. Past no-back devices typically included an inefficient gear set or two disks, balls and a set of brakes. Past torque limiting devices typically included two disks, balls and a set of brakes. Integrated torque limiter/no-back device  36  provides torque limiting and no-back features capabilities needed for actuator  20  while eliminating various parts of past systems by using combined ball ramp  40  for both torque limiting functions and no-back functions, resulting in an overall smaller envelope for torque limiting and no-back features as well as an overall smaller envelope for actuator  20 . This results in weight and cost savings for actuator  20 . Combining torque limiter/no-back device results in fewer parts, making a simpler and more efficient system as well. 
         [0024]      FIG. 3  shows a second embodiment of actuator  20  with an integrated torque limiter/no-back device  36 . Similar parts have the same numbers as in  FIG. 2A . Actuator  20  includes input shaft  30 , gear reduction  32 , actuator output  34  and integrated torque limiter/no-back device  36 . Integrated torque limiter/no-back device  36  includes torque limiter ball ramp  38 , combined ball ramp  40 , no-back ball ramp  42 , brake plates  44 , cone brake  45 , balls  46 ,  48  and pin  50 . 
         [0025]    Integrated torque limiter/no-back device  36  works in the same manner as in  FIG. 2A , with ramps  38 ,  40  acting as a torque limiter, and ramps  40 ,  42  acting as the no-back device. In this embodiment, cone brake  45  for no-back is located between torque limiter ball ramp  38  and combined ramp  40 . The placement of cone brake  45  between ramps  38 ,  40  can result in faster no-back braking by working to stop the movement of both no-back ramps, to ground torque more quickly. This can result in less backdriving, which enables more precise control of flight surfaces. 
         [0026]      FIG. 4  shows a third embodiment of actuator  20  with an integrated torque limiter/no-back device  36 . Similar parts have the same numbers as in  FIGS. 2A and 3 . Actuator  20  includes input shaft  30 , gear reduction  32 , actuator output  34  and integrated torque limiter/no-back device  36 . Integrated torque limiter/no-back device  36  includes ball ramp  38 , combined ball ramp  40 , ball ramp  42 , brake plates  44 , balls  46 ,  48  and pin  50 . 
         [0027]    Torque is transferred through pin  50  initially to combined ramp  40 , and then is transferred to ball ramp  42  through ball  48 . Ball ramp  42  transfers torque to gear reduction  32 . Brake plates  44  would work to engage no-back and torque limiting portions of integrated device  36 . 
         [0028]    Actuator  20  with integrated torque limiter/no-back device  36  shown in  FIG. 4  can provide additional space and weight savings by eliminating a set of brakes in actuator  20 . This embodiment may result in a slower reaction time of integrated torque limiter/no-back device  36 , and may be best used in systems with lower loads or which are less prone to jamming. 
         [0029]    Integrated torque limiter/no-back device  36  provides actuator with no-back and torque limiting capabilities while reducing weight and space needed for past actuators which had separate torque limiting and no-back systems. Using combined ball ramp  40  to provide no-back and torque limiting system functions eliminates at least one disk, making an overall simpler actuator with fewer parts needed to provide no-back and torque limiting abilities for an aircraft system. 
         [0030]    While the invention has been described with reference to exemplary embodiments, 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 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 embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.