Linear Actuator

Abstract

a sleeve having an inner sleeve surface, an outer sleeve surface, a second thread on a portion of the inner sleeve surface that engages with the first thread, and a third thread on a portion of the outer sleeve surface; a lead nut that engages with the third thread; and at least one motor that drives the lead nut, wherein, in use, the at least one motor transmits torque to the sleeve, such that when an applied torque is below a threshold value, the sleeve is restricted from rotating about the stroke axis, and rotation of the lead nut causes linear displacement of the sleeve and the actuator rod along the stroke axis; and when an applied torque is equal to or greater than the threshold value, the sleeve is allowed to rotate about the stroke axis, and rotation of the lead nut causes rotation of the sleeve and linear displacement of the actuator rod.

Description

[Technical Field]

[0001] The present invention relates to linear actuators, such as electromechanical linear actuators used in aerospace and other applications, and more particularly to linear actuators that are resistant to jam failure modes. [Background technology]

[0002] Traditional flight control systems use hydraulic actuators. Flight control actuators are typically required to be fail-operational, meaning they must continue to operate even in the event of a single failure. This is typically achieved by placing two actuators on a flight control surface or by using dual redundant actuators. In either case, if one actuator / channel fails, it can be switched into a bypass or damping mode, minimizing resistance from the failed channel while maintaining control from the remaining, functioning actuator. Such hydraulic actuators are also highly tolerant to jamming failure modes.

[0003] There is a growing demand for electrification, particularly electric actuation, in modern aircraft systems. Outside of the aerospace sector, there is also a growing demand for electric actuators. Electric actuators typically use an electric motor driving some sort of rotary or linear mechanical gear. These mechanical mechanisms often have a lower tolerance for jamming failure modes compared to hydraulic actuators. Furthermore, switching a failed actuator / channel to a bypass or damping mode requires complex designs, often resulting in increased manufacturing difficulty, part count, and weight.

[0004] The patent document 1 relates to an actuator that moves between a retracted position and an extended position. The actuator includes an inner ball screw drive unit and an outer ball screw drive unit configured to operate during normal stroke. This configuration limits movement if one of the drive units becomes jammed and allows operation from either end of the actuator.

[0005] Therefore, there is a need to provide a linear actuator that is more tolerant to blockage failure modes, does not limit stroke when a blockage occurs, and can detect and signal blockage failures. Furthermore, when operating the actuator in active-standby mode, it is desirable to be able to verify that the standby lane is not in a potential fault condition. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 5,092,539 Summary of the Invention

[0007] To alleviate at least some of the above problems, a linear actuator is provided, comprising a stroke axis and an actuator rod extending along the stroke axis. The actuator rod comprises an outer surface of the actuator rod, a first thread on a portion of the outer surface of the actuator rod, and a sleeve disposed around the actuator rod and coaxially with the actuator rod. The sleeve comprises an inner surface of the sleeve, an outer surface of the sleeve, a second thread on a portion of the inner surface of the sleeve configured to engage with the first thread, and a third thread on a portion of the outer surface of the sleeve. A lead nut is provided, configured to engage with the third thread. At least one motor is configured to drive the lead nut. In use, the at least one motor transmits torque to the sleeve via the lead nut. When an applied torque is below a threshold, the sleeve is restricted from rotating about the stroke axis, and rotation of the lead nut linearly displaces both the sleeve and the actuator rod along the stroke axis. When an applied torque is equal to or greater than a threshold, the sleeve is allowed to rotate about the stroke axis, and rotation of the lead nut rotates the sleeve, which in turn linearly displaces the actuator rod.

[0008] The advantage of this configuration is that it provides a linear actuator (which can be driven by one or more electric motors) with both a primary operating mode / channel under normal conditions and a secondary operating mode / channel that is automatically activated if a jam occurs in the primary operating mode, for example, if a jam occurs between the screw nut and the third thread, causing the applied torque to exceed a threshold value.

[0009] Optionally, the linear actuator further comprises a tube coaxially disposed with the sleeve, the tube being rotatable about the stroke axis, the tube being one of the following: -Fixed to or part of the sleeve. a tube inner surface, the tube inner surface including at least one axially extending groove; a sleeve including at least one axially extending spline configured to engage the at least one axially extending groove, the sleeve being free to move axially relative to the tube such that rotation of the sleeve causes rotation of the tube. An advantage of this configuration is that it provides a space-efficient basis for efficiently locating means for detecting a blockage fault and / or means for limiting sleeve rotation.

[0010] Optionally, the linear actuator may further include a detector configured to detect rotation of the sleeve about the stroke axis. The detector is configured to output a signal indicating a jam or fault condition when rotation of the sleeve about the stroke axis is detected, thereby effectively indicating a jam fault between the nut and the sleeve. Optionally, the detector is configured to detect rotation of the tube (e.g., by detecting a change in the position of a feature on the tube). Optionally, the tube includes one or more windows, and the detector includes a proximity sensor positioned such that the one or more windows pass the sensor as the tube rotates. Alternatively, or additionally, the detector includes a rotational position sensor that engages with the tube (e.g., via a gear that engages with axial teeth or splines on the surface of the tube).

[0011] Optionally, the linear actuator further comprises a biasing means and an engagement member, and the tube further comprises a detent, wherein the biasing means is configured to bias the engagement member to a first position within the detent and resist rotation of the tube when an applied torque is below a threshold value. When the applied torque is equal to or greater than the threshold value, rotation of the tube displaces the engagement member from the detent to a second position. Advantageously, this configuration functions to limit rotation of the sleeve such that the sleeve only rotates when the applied torque exceeds the threshold value, e.g., when there is a jamming fault condition between the nut and sleeve.

[0012] Optionally, the linear actuator further comprises a latch means configured to retain the engagement member in the second position when the engagement member disengages from the detent, thereby allowing the sleeve tube, and therefore the sleeve, to rotate freely in the event of a jamming fault.

[0013] Optionally, the first thread has an axial length approximately twice the axial length of the third thread, such that in the event of a jamming failure, the linear actuator can extend or retract in the secondary mode a total stroke range equivalent to that of the primary mode (without jamming), regardless of the position of the sleeve relative to the nut.

[0014] Optionally, the torque required to move the third thread relative to the lead nut is less than the torque required to move the second thread relative to the first thread, such that the sleeve does not rotate about the stroke axis when the applied torque is below a threshold value, thus preventing rotation of the sleeve relative to the actuator rod during normal (e.g., unjammed) operation.

[0015] Optionally, the screw nut is a ball screw nut, and the first thread interacts directly with the second thread.

[0016] In another aspect of the present invention, there is provided an aircraft comprising a fixed structure, a flight control surface, and a linear actuator as described above, wherein the linear actuator is connected to the fixed structure and the flight control surface.

[0017] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which like reference numerals refer to like features throughout: [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of a linear actuator according to the present invention in the middle of a normal stroke. FIG. [Figure 2] 2 shows a cross section of the linear actuator of FIG. 1, showing the linear actuator at the normal extension end of its stroke. [Figure 3] 2 shows a cross section of the linear actuator of FIG. 1, illustrating the linear actuator at the retracted end of its normal stroke. [Figure 4] FIG. 2 shows a cross section of the linear actuator of FIG. 1, illustrating the linear actuator at the retracted end of its stroke under a jammed condition. [Figure 5] FIG. 2 shows a cross section of the linear actuator of FIG. 1, illustrating the linear actuator at the extended end of its stroke under a jam condition. [Figure 6] 1A-C are partial cross-sectional views of a linear actuator according to claim 1 employing alternative jam detection means; [Figure 7] 1A-D are partial cross-sectional views illustrating various mechanisms for limiting sleeve rotation, according to embodiments of the present invention. [Figure 8] FIG. 2 is a schematic partial plan view of an aircraft employing the linear actuator of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following embodiments provide linear actuators with improved resistance to jamming failure modes and improved jamming failure detection. It will be appreciated that the described actuators can be utilized in aerospace flight control surface drives and other applications where linear drive is desired.

[0020] 1-5 are cross-sectional views of a linear actuator 100 having a stroke axis 102 (e.g., the central axis shown in FIG. 1) and an actuator rod 104 according to one embodiment of the present invention under various conditions. Components shown in FIGS. 2-5 correspond to those shown in FIG. 1. For clarity, some reference numbers have been omitted from FIGS. 2-5.

[0021] The actuator rod 104 is disposed along the stroke axis 102 and includes a first thread 108 extending along an outer surface 106 of the actuator rod 104. As shown, the first thread 108 extends along a portion 110 of the outer surface 110 of the actuator rod 104, although in other embodiments, the first thread 108 may extend along substantially the entire length of the outer surface 110.

[0022] The actuator rod 104 preferably further includes a first stop 112 and a second stop 114. Each stop 112, 114 is optionally configured as an axial stop formed with an annular flange having an outer diameter larger than the outer diameter of the first thread 114. Alternatively, a torsional stop may be used instead of an axial stop.

[0023] As shown, the actuator rod 104 includes a movable eye assembly 116, although it will be appreciated that any suitable mounting assembly may be provided depending on the end use of the actuator 100.

[0024] The linear actuator 100 further includes a sleeve 118 concentrically disposed around at least a portion of the actuator rod 104 and aligned along the stroke axis 102. The actuator sleeve includes a second thread (or nut) 120 on a portion of an inner surface 122 of the sleeve 118, the second thread 120 configured to engage the first thread 108 of the actuator rod 104. Rotation of the sleeve 118 relative to the actuator rod 104 results in axial displacement of the sleeve 118 relative to the actuator rod 104. In some embodiments, the second thread 120 is a thread having a pitch corresponding to the pitch of the first thread; however, the pitch may be different. In other configurations, the second thread may be a nut, such as a ball screw nut.

[0025] The sleeve 118 further includes a third stop 124 and a fourth stop 126 disposed on the inner surface 122. As shown in FIG. 1 , the third stop 124 and the fourth stop 126 are formed by a step change in the inner diameter of the sleeve 118, such that the inner diameter of the sleeve 118 at the second thread 120 is smaller than the remainder of the axial length of the sleeve 118. As the sleeve 118 rotates about the stroke axis 102 relative to the actuator rod 104, the maximum downward axial displacement of the actuator rod 104 relative to the sleeve 118 (as shown in FIG. 1 ) is limited by contact of the first stop 112 with the third stop 124. Similarly, the maximum upward axial displacement of the actuator rod 104 relative to the sleeve 118 is limited by contact of the second stop 114 with the fourth stop 126.

[0026] The sleeve 118 has a third thread 128 extending along at least a portion (e.g., a majority, as shown) of its outer surface 130. The sleeve preferably further includes a fifth stop 132 and a sixth stop 134 on its outer surface 130. The fifth and sixth stops 132, 134 are each optionally formed from annular flanges having an outer diameter larger than the outer diameter of the third thread 128.

[0027] The linear actuator 100 further includes a nut 136 concentrically disposed about the sleeve 118 and configured to engage the third thread 128. Rotation of the nut 136 relative to the sleeve 118 about the stroke axis 102 causes the sleeve 118 to move axially relative to the nut. In a preferred embodiment, the nut is a ball screw nut. In alternative configurations, the nut 136 may be a simple screw nut, a roller screw nut, an ACME nut, or the like.

[0028] The nut 136 preferably includes a seventh stop 138 and an eighth stop 140. Optionally, the seventh and eighth stops 138, 140 are formed from the ends of the nut 136, as shown in FIG. 1. As the nut 136 rotates about the stroke axis 102 relative to the sleeve 118, the maximum axial downward displacement of the sleeve 118 relative to the nut 136 (as shown in FIG. 1) is limited by contact of the fifth stop 132 with the seventh stop 138. Similarly, the maximum axial upward displacement of the sleeve 118 relative to the nut 136 is limited by contact of the sixth stop 134 with the eighth stop 140.

[0029] The nut 136 is driven by two motors 142a, 142b via gears 144a, 144b, respectively, to rotate about the stroke axis 102. It will be appreciated that in alternative embodiments, a single motor or two or more motors may be provided depending on the drive torque requirements, packaging constraints, and / or redundancy requirements of a particular application of the actuator 100. For example, multiple motors may be provided in a torque summing or speed summing configuration depending on the end use of the actuator. In a preferred embodiment, the motors 142a, 142b are electric motors. In alternative embodiments, the motors 142a, 142b are hydraulic motors or a combination of electric and hydraulic motors. The gears 144a, 144b may be simple, as shown, or may be complex, with multiple stages, to achieve higher reduction ratios or to accommodate the placement of various components.

[0030] The linear actuator 100 includes a system of nested thread assemblies, in which the nut 136 and the third thread 128 of the sleeve 118 cooperate to form an outer thread assembly, and the second thread 120 of the sleeve 118 and the first thread 108 of the actuator rod 104 cooperate to form an inner thread assembly. Advantageously, the inner threads do not need to be sized to meet the full life requirements of the actuator because they operate under jamming failure of the outer threads. Therefore, the inner threads can be manufactured to a smaller size than would be required for full life requirements.

[0031] The linear actuator 100 preferably further includes a housing 146 having an opening 148 formed therein through which the actuator rod 104 extends. The motors 142a and 142b are fixed within the housing 146. The gears 144a and 144b and the nut 136 are axially and radially constrained by bearings 147a, 147b, and 147c connected to the housing 146. As shown, the nut 136 is radially constrained by bearing 147a and axially constrained by thrust bearing 147b. In the illustrated embodiment, the housing 146 further includes a ground end bearing 150.

[0032] The linear actuator preferably further includes a jam detection assembly 200a, which is described in more detail below.

[0033] During operation, motors 142a, 142b drive respective gears 144a, 144b to rotate nut 136. Under normal operating conditions, friction between nut 136 and sleeve 118 is relatively low, resulting in a relatively low torque being applied to sleeve 118 by the rotating nut 136. In contrast, if a jamming fault occurs, in which nut 136 jams against sleeve 118, friction between nut 136 and sleeve 118 increases, resulting in a higher torque being applied to sleeve 118 by nut 136 driven by motors 142a, 142b.

[0034] In the present invention, the linear actuator is configured such that rotation of the sleeve 118 about the stroke axis 102 is restricted under normal operating conditions, but rotation is permitted in the event of a jamming fault.

[0035] When the torque applied by motors 142a, 142 to sleeve 118 via gears 144a, 144b and nut 136 is below a threshold (e.g., not in a jam fault condition), sleeve 118 is restricted from rotating about stroke axis 102. In this state, rotating nut 136 about the stroke axis moves sleeve 118 (up or down in the orientation of FIG. 1 ). In this state, sleeve 118 and actuator rod 104 do not rotate relative to each other, so the actuator rod also moves along the stroke axis with sleeve 118. Therefore, rotating nut 136 about the stroke axis can extend or retract actuator rod 104.

[0036] This is illustrated in Figures 2 and 3. Figure 2 shows the actuator rod 104 near the fully extended end of its stroke during normal operation when the torque applied to the sleeve 118 by the motors 142a, 142b is below a threshold. The maximum possible extension is limited by the sixth stop 134 contacting the eighth stop 140. Figure 3 shows the actuator rod 104 near the fully retracted end of its stroke during normal operation. The maximum possible retraction is limited by the fifth stop 132 contacting the seventh stop 138. This defines the normal range of stroke for the actuator rod 104 (i.e., the range the actuator rod can extend when the applied torque is below a threshold, i.e., there is no jamming condition). During normal operation, there is no misalignment between the sleeve 118 and the actuator rod 104; rather, as the nut 136 rotates, the sleeve 118 and the actuator rod 104 translate together.

[0037] When the torque applied to the sleeve 118 by the motors 142a, 142 via the gears 144a, 144b and the nut 146 is equal to or greater than a threshold value (e.g., when a jamming fault occurs between the nut 136 and the sleeve 118), the sleeve 118 is able to rotate about the stroke axis 102. In this state, when the nut 136 rotates about the stroke axis, the sleeve 118 also rotates about the stroke axis (e.g., they rotate together). In this state, the rotation of the nut 136 rotates the sleeve 118 relative to the actuator rod 104, and the actuator rod 104 moves along the stroke axis direction (up and down in the orientation of FIG. 1) relative to the sleeve 118.

[0038] Advantageously, even if the nut 136 becomes jammed in the sleeve 118, the actuator rod 104 can still be extended or retracted by rotating the nut 136 about the stroke axis. In this manner, the linear actuator 100 effectively provides a second mode / channel in case of a jamming failure.

[0039] As shown in Figures 4 and 5, when a jam occurs between the nut 136 and the sleeve 118, the sleeve 118 is prevented from moving along the stroke axis but instead rotates with the nut 136. Figure 4 shows the actuator rod 104 near the fully retracted end of its stroke in this jammed fault condition. The maximum possible retraction in this condition is limited by the first stop 112 contacting the third stop 124. Figure 5 shows the actuator rod 104 near the fully extended end of its stroke in this jammed fault condition. The maximum possible extension in this condition is limited by the second stop 114 contacting the fourth stop 126.

[0040] Preferably, the maximum axial displacement of the actuator rod 104 relative to the sleeve (determined by the length of the first thread 108 and the relative positions of the first, second, third, and fourth stops 112, 114, 124, and 126) is twice the maximum axial displacement of the sleeve 118 relative to the nut (determined by the length of the third thread 128 and the relative positions of the fifth, sixth, seventh, and eighth stops 132, 134, 138, and 140). This configuration allows the actuator rod 104 to move to any position corresponding to its normal stroke in the event of a jam, regardless of the position of the sleeve 118 relative to the nut 136. This is also shown in FIGS. 4 and 5. That is, in FIG. 4, the sleeve 118 and nut 136 are jammed and the sixth stop 134 is close to the eighth stop 140, but the actuator rod 104 can be positioned in a position corresponding to the maximum contraction of the normal stroke range; in FIG. 5, the sleeve 118 and nut 136 are jammed and the fifth stop 132 is close to the seventh stop 138, but the actuator rod 104 can be positioned in a position corresponding to the maximum extension of the normal stroke range.

[0041] Various means can be employed to prevent rotation of sleeve 118 about stroke axis 102 when torque applied to the sleeve via nut 136 is below a threshold, and to allow rotation of sleeve 118 when the applied torque is equal to or greater than the threshold. In some embodiments, this is achieved by, for example, selecting an appropriate thread pitch, diameter, and dimensions to make the combination of nut 136 and third thread 128 more efficient than the combination of first thread 106 and second thread 120. Alternatively, or additionally, nut 138 is a highly efficient mechanism, such as a ball screw nut or roller screw nut, configured to provide less friction between nut 138 and third thread 128 than between second thread 120 and first thread 106. In alternative embodiments, a detent mechanism can be used alone or in combination with the above approaches, as described in more detail below.

[0042] In a preferred embodiment, the linear actuator 100 includes a means for detecting a jam between the nut 136 and the sleeve 118. FIGS. 1-5 show an example jam detection assembly 200a including a tube 202 centered about the stroke axis 102 and concentric with the sleeve 118. The tube 202 is rotatable about the stroke axis 102 and is limited in radial and axial movement by one or more suitable bearings. In this example, the tube 202 includes at least one, and preferably multiple, axially extending slots 203 located on the inner surface of the tube 202. The sleeve 118 includes one or more dogs or splines 204 located on the outer surface of the sleeve 118 (e.g., near the sixth stop 134 shown in FIGS. 1-5), which slidably fit within the corresponding slots 203. The tube 202 further includes one or more openings 206a extending radially therethrough and one or more proximity sensors 208a, 208b. As the tube 202 rotates about the stroke axis 102, the one or more openings 206a follow a circular path. The proximity sensors are held in a fixed position relative to the housing 146 and are configured to detect changes in the position of the one or more openings 206a as the tube 202 rotates. For example, each proximity sensor 208a, 208b is preferably oriented along the circular path followed by the one or more openings 206a as the tube 202 rotates, thereby causing the one or more openings 206a to pass in front of the proximity sensor 208a, 208b during rotation. It should be understood that alternative means for detecting rotation of the tube 202 may be employed, such as using an appropriate sensor to detect other surface characteristics or marks on the tube 202.

[0043] During normal actuator operation (i.e., when nut 136 and third thread 128 are not jammed and the torque applied to sleeve 118 is below the threshold), rotation of nut 136 causes sleeve 118 to move axially, causing spline 204 to slide axially within slot 203. As nut 136 rotates, neither sleeve 118 nor tube 202 rotate. Therefore, opening 206a remains fixed and the proximity sensor detects no change.

[0044] When the nut 136 and third thread 128 become jammed (and the torque applied to the sleeve 118 is equal to or exceeds a threshold), rotation of the nut 136 causes rotation of the sleeve 118 about the stroke axis 102. In this case, the splines 204 press against the corresponding slots 203, causing the tube 202 to rotate with the sleeve 118. As a result, the position of the opening 206a changes, which is detected by the proximity sensors 208a and 208b. The proximity sensors 208a and 208b preferably generate a signal indicating that a jam fault has been detected, while the linear actuator 100 can continue to operate in the secondary mode as described above. This allows a user (e.g., a crew member of an aircraft on which the actuator 100 is installed or an operator of a machine on which the actuator is installed) to know that the actuator 100 has experienced a jam fault and is operating in the secondary mode.

[0045] Alternative clog detection assemblies 200b, 200c, and 200d are shown in Figures 6A-6C. These devices may be used in addition to or instead of the clog detection assembly 200a shown in Figures 1-5.

[0046] The clog detection assembly 200b shown in FIG. 6A is similar to the clog detection assembly 200a shown in FIGS. 1-5 and employs one or more apertures 206b and proximity sensors 208a, 208b. However, in this example, the tube 202 is fixed to or is an integral part of the sleeve 118, and the tube 202 and sleeve 118 move together both in rotation about and translation along the stroke axis 102. The axial length of the aperture 206b corresponds to at least the full stroke length of the actuator when the actuator is operating in its normal primary (unclogged) mode. During normal operation, the sleeve 118, tube 202, and aperture 206b move axially in unison relative to the position sensors 208a, 208b. However, due to the length of the aperture 206a, the position sensor detects the presence (or absence) of the aperture 206a throughout the normal stroke. If the nut 136 and third thread 128 become jammed, both the sleeve 118 and the tube 202 will rotate about the stroke axis, and the proximity detectors 208a, 208b will detect a change in the annular movement of the opening 206b relative to the proximity sensors. Similar to the example jam detection assembly 200a described in Figures 1-5, the proximity sensors 208a, 208b will generate a signal indicating that a jam fault has been detected, while the linear actuator 100 can continue to operate in the secondary mode as described above.

[0047] FIG. 6B illustrates another example of a clog detection assembly 200c. This example is similar to the clog detection assembly 200b illustrated in FIG. 6A and includes a tube 202 secured to the sleeve 118. However, instead of using an aperture and a proximity sensor, this example includes a plurality of axially extending male teeth / splines 209 on the outer surface of the tube 202 (e.g., the male splines 209 are evenly spaced around the entire circumference of the tube 202, forming a hollow cylindrical gear). The clog detection assembly 200c further includes a rotational position sensor 210 (e.g., a resolver or encoder) fixed relative to the housing 146 and connected to a gear 212. In this example, the gear 212 engages gear teeth on the outer diameter of a ring 211. The ring 211 has a female spline 213 on its inner diameter sized to engage the male spline 209 on the tube 202. During normal operation, the sleeve 118 and the tube 202 connected to the sleeve 118 move axially, causing the teeth 209 to slide axially relative to the rotational position sensor 210, ring 211, and gear 212. The male spline 209 has an axial length that allows it to remain engaged with the female spline 213 as the sleeve 118 moves through its full normal stroke range. When the nut 136 and third thread 128 become jammed, both the sleeve 118 and the tube 202 rotate about the stroke axis 102, causing the male spline 209 to move the ring 211, which in turn moves the gear 212, actuating the rotational position sensor. The rotational position sensor is configured to provide a signal indicating that rotation has been detected, thereby indicating a jam fault. It will be appreciated that instead of fixing the tube 202 to the sleeve 118, as described above in connection with the exemplary clog detection assembly 200a shown in Figures 1-5, the sleeve 118 can be slidably connected to the tube 202 via cooperating axial splines 204 and slots 203.

[0048] FIG. 6C illustrates yet another superior clog detection assembly 200d. This example is similar to the clog detection assembly 200b illustrated in FIG. 6B and includes a tube 202 secured to a sleeve 118. In this example, the tube 202 includes a detent 216a on its outer surface. As shown, the detent 216a has the shape of a channel formed between adjacent male axial splines, such as spline 209, described above in connection with FIG. 6B. The clog detection assembly 200d further includes an engagement member 216a that is urged against and positioned within the detent 214 by a suitable biasing means 218 (e.g., a spring or other resiliently deformable member) during normal operation. The engagement member 216a is configured to move (e.g., slide or roll) axially relative to the detent 214. The engagement member 216a is configured to disengage from the detent 214 when the tube 202 rotates about the stroke axis 102. A position sensor (not shown) is also provided that is configured to detect the radial position of the engagement member 216a. Any suitable position sensor known in the art can be used for this purpose. In the illustrated example, the engagement member 216a is a ball bearing, although it will be understood that other suitable configurations may be used. During normal operation, the sleeve 118, tube 202, and detent 214 / spline 209 move axially, causing the engagement member 216a to slide or rotate along the detent 214. If the nut 136 and third thread 128 become jammed, the sleeve 118 and tube 202 rotate about the stroke axis 102, causing the engagement means to move (upward relative to the orientation in FIG. 6C ). The position sensor is configured to detect a change in the radial position of the engagement member 216a and output a signal indicative of a jam fault.

[0049] Advantageously, any of the above-described clog detection assemblies can also be used to test for a potentially faulty secondary channel / mode. To do this, motors 142a, 142b rotate nut 136 in a predetermined direction (and axially move sleeve 118) to extend or retract actuator rod 104 to the extreme ends of its normal stroke range, until either fifth stop 132 contacts seventh stop 138 (maximum retraction) or sixth stop 134 contacts eighth stop 140 (maximum extension). Motors 142a, 142b are then instructed to continue rotating in the same direction. If no jamming fault occurs between the actuator rod 104 and the sleeve 118, the sleeve 118 will rotate with the nut 136 (because the sleeve 118 cannot move further relative to the nut 136 as the nut 136 continues to rotate), which in turn will rotate the tube 202 and activate the jam detection assemblies 200a, 200b, 200c, and 200d. If a jamming fault occurs between the actuator rod 104 and the sleeve 118, the nut 136, the sleeve 136, or the tube will not be able to rotate any further, and the jam detection assemblies 200a, 200b, 200c, and 200d will not be activated and will not be able to reach the additional overtravel stroke corresponding to the axial movement of the actuator rod 104 relative to the sleeve 118. Therefore, the lack of a signal from the jam detection assemblies 200a, 200b, 200c, and 200d during this procedure indicates a potential secondary mode / channel fault. This potential fault test can be performed periodically during use.

[0050] Advantageously, the blockage detection means 200a, 200b, 200c, 200d can be used to detect faults in both the primary and secondary channels / modes.

[0051] 7A-7D illustrate various detent mechanisms configured to prevent rotation of sleeve 118 when the applied torque is below a threshold. These mechanisms provide a particularly effective means of ensuring that the bypass channel of linear actuator 100 operates only when necessary.

[0052] 7A shows a partial cross-sectional view of tube 202 (which optionally also forms part of one or more of clog detection assemblies 200a, 200b, 200c, and 200d described above). Tube 202 includes one or more detents (e.g., axial slots) 214a, 214b, 214c, 214d, and 214e disposed on its radially outer surface. Similar to clog detection assembly 200d described in connection with FIG. 6C, actuator 100 includes engagement member 216a that, during normal operation, is urged against and disposed within one of detents 214a, 214b, 214c, 214d, and 214e by suitable biasing means 218 (e.g., a spring or other resiliently deformable member). The engagement member 216a and the detents 214a, 214b, 214c, 214d, and 214e are configured to interact to resist rotation of the tube 202, and thus rotation of the tube 202 about the stroke axis. However, when the tube 202 is subjected to sufficient torque, the engagement member 216a is configured to disengage from its corresponding detent 214a, 214b, 214c, 214d, and 214e. Therefore, if the torque applied to the sleeve 118 by the motors 142a and 142b through the nut 136 is below a threshold, insufficient torque is transferred to the tube 202 to move the engagement member 216a. As a result, the tube 202 and the sleeve 118 do not rotate about the stroke axis 102. If the torque applied to sleeve 118 is equal to or exceeds a threshold value (e.g., if nut 136 and sleeve 118 become jammed), sufficient torque is transmitted to tube 202 to disengage engaging members 216a from their corresponding detents 214a, 214b, 214c, 214d, and 214e (upward relative to the orientation in FIG. 7A ). At this point, tube 202 and sleeve 118 can rotate about stroke axis 102.

[0053] 7A, a plurality of detents 214a, 214b, 214c, 214d, and 214e are provided, and the engaging means 216a is capable of engaging with the other detents 214a, 214b, 214d, and 214e after disengaging from the first detent 214c. Alternatively, a single detent 214 may be provided.

[0054] Figure 7B shows a similar arrangement operating on the same principles as Figure 7A. In this example, the tube 202 includes a single detent 214, and a detent mechanism retains the engagement member 216b to allow free rotation of the tube 202 after the engagement member initially disengages from the detent 214. In this example, a latch member 220a is provided, which includes a latch portion 222a (e.g., a ball bearing) and a latch biasing means 224a (e.g., a spring or other resiliently deformable member) that biases the latch portion 222a against the engagement member 216b. The engagement member includes a socket 226 configured to receive the latch portion 222a. In normal operation, engagement member 216a is biased against and disposed within detent portion 214, socket 226 and latch portion 222a are offset from one another, and the latch portion is biased against the side of engagement member 216b. When a threshold torque or greater is applied to sleeve 118 (e.g., in the event of a jamming fault between nut 136 and sleeve 118), sufficient torque is transmitted from sleeve 118 to tube 202 to disengage engagement member 216b from detent portion 214. When engagement member 216b is displaced, socket 226 aligns with latch portion 222a, and latch portion 222a is forced into socket 226 by latch portion biasing means 224a. Thereafter, engagement means 216b is prevented from further movement by latch portion 222a, and tube 202 (and thus sleeve 118) is free to rotate about the stroke axis without engagement member 216b re-engaging detent portion 214. Advantageously, this latching mechanism reduces resistance and wear on tube 202.

[0055] 7C and 7D show a detent mechanism that operates on the same principle as that shown in FIG. 7B, but employs an alternative latching means 220b. In this example, the tube 202 includes a detent portion 214 into which an engaging member 216c is pressed by a biasing means 218 during normal operation. The latching portion 222b includes an opening or notch 230. The opening has a first side 231 and a second side 232 that define a sloped portion 232. The latching portion 222b is biased by a latching biasing means 224b. The arrangement also includes a proximity sensor 234 configured to detect the relative position of the latching portion 222b.

[0056] 7C shows a situation during normal operation, i.e., when the nut 136 is not jammed in the sleeve 118. The engagement member 216c is biased into the anti-rotation portion 214 by the biasing means 218. The engagement member 216c extends through the opening 230, and the latch portion 222b (specifically, the second side surface 232) is biased against the engagement member 216c by the latch portion biasing means 224b. The engagement member 216c holds the latch portion 222b in a first position away from the proximity sensor 234.

[0057] 7D illustrates a situation in which nut 136 becomes jammed in sleeve 118 and the torque applied to sleeve 118 exceeds a threshold, causing tube 202 to rotate and disengage engagement means 216c from detent portion 214. Due to the combination of the sloped shape of second side surface 232 and the shape of engagement means 216c, when tube 202 rotates and engagement means 216c disengages from detent portion 214, the sloped portion of second side surface 232 receives force from latch portion biasing means 224b and pushes engagement means away from tube 202. The body of latch portion 222b then passes between engagement means 216c and tube 202 and moves toward proximity sensor 234, thereby retaining engagement means 216c and allowing tube 202 to rotate freely. Furthermore, proximity sensor 234 detects the change in the position of latch portion 222b. This provides an alternative / additional means for detecting and signaling a jam fault condition between the sleeve 118 and the nut 136.

[0058] 7C and 7D, the engagement means 216c is a sphere, and when the sphere is fully engaged with the detent portion 214, a majority of the sphere is located radially closer to the stroke axis 102 than the end of the inclined surface of the second side surface 232. As the tube 202 rotates, the sphere is displaced such that a majority of the sphere is located radially farther from the stroke axis than the end of the inclined surface of the second side surface 232, thereby allowing the ball to climb the inclined surface as the latch portion 222b moves generally toward the proximity detector 234. It will be appreciated that other shapes can be provided for both the inclined second side surface 232 and the engagement means 216c to achieve the same effect.

[0059] 8 shows a schematic diagram of an aircraft 300 comprising a fixed structure 302 (e.g., a fixed portion of a wing) and a flight control surface 304 (e.g., a flap, a slat, an elevon, etc.), employing the linear actuator 100 described above. The linear actuator is connected to both the fixed structure 302 and the flight control surface 304, and is configured such that, in operation, the actuator 100 moves the flight control surface 304 relative to the fixed structure 302.

[0060] The above embodiments are provided by way of example only, not by way of limitation. The scope of the invention is as set forth in the appended claims. Other aspects of the invention will be apparent from the appended claims.

Claims

1. 1. A linear actuator comprising: A stroke axis; an actuator rod extending along the stroke axis, the outer surface of the actuator rod; and an actuator rod having a first thread on a portion of an outer surface of the actuator rod; a sleeve disposed around the actuator rod and coaxial with the actuator rod, inner surface of the sleeve, Outer surface of sleeve, a second thread on a portion of the inner surface of the sleeve, the second thread configured to engage the first thread; and a sleeve having a third thread on a portion of the sleeve outer surface; a lead nut configured to engage the third thread; and at least one motor configured to drive the lead nut; In use, the at least one motor transmits torque to the sleeve via the lead nut; When an applied torque is below a threshold, the sleeve is restricted from rotating about the stroke axis, and rotation of the lead nut causes linear displacement of the sleeve and the actuator rod along the stroke axis; A linear actuator wherein the sleeve is capable of rotating about the stroke axis when an applied torque is equal to or greater than the threshold, wherein rotation of the lead nut rotates the sleeve, and rotation of the sleeve linearly displaces the actuator rod.

2. The linear actuator of claim 1 , wherein the applied torque exceeds the threshold when a jam condition occurs between the lead nut and the third thread.

3. a tube arranged coaxially with the sleeve, the tube being rotatable about the stroke axis; the tube has an inner tube surface, the inner tube surface having at least one axially extending groove; 3. The linear actuator of claim 1, wherein the sleeve includes at least one axially extending spline configured to engage the at least one axially extending groove, the sleeve being free to move axially relative to the tube, and rotation of the sleeve causing rotation of the tube.

4. 4. The linear actuator of claim 1, further comprising a detector configured to detect rotation of the sleeve about the stroke axis, the detector configured to provide a signal indicative of a jam or fault condition when rotation of the sleeve about the stroke axis is detected.

5. The linear actuator of claim 4 , wherein the detector is configured to detect rotation of the tube.

6. the tube comprises one or more windows; 6. The linear actuator of claim 5, wherein the detector comprises a proximity sensor positioned adjacent the tube such that the one or more windows pass by the sensor when the tube rotates.

7. The linear actuator of claim 5 , wherein the detector comprises a rotational position sensor engaging the tube.

8. Further comprising a biasing means and an engagement member; The tube further includes a rotation prevention portion, the biasing means biases the engagement member to a first position within the detent to resist rotation of the tube when an applied torque is less than the threshold; The linear actuator of any one of claims 3 to 7, wherein rotation of the tube displaces the engagement member from the detent to a second position when an applied torque is equal to or greater than the threshold.

9. 9. The linear actuator of claim 8, further comprising latching means configured to retain the engaging member in the second position after the engaging member is displaced from the detent portion.

10. The linear actuator of any one of claims 1 to 9, wherein the first thread has an axial length that is approximately twice the axial length of the third thread.

11. 11. The linear actuator of claim 1, wherein a torque required to move the third thread relative to the lead nut is less than a torque required to move the second thread relative to the first thread, whereby the sleeve does not rotate about the stroke axis when an applied torque is below the threshold.

12. 2. The linear actuator of claim 1, wherein the screw nut is a ball screw nut or a roller screw nut, and the first thread directly interacts with the second thread.

13. An aircraft, fixed structure, flight control surfaces, and A linear actuator according to any one of claims 1 to 12, The linear actuator is connected to the fixed structure and the flight control surface.

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