Fluid actuator with feedback mechanism

This invention relates to a fluid actuator with a feedback mechanism for indicating the position of the actuator and particularly whether the actuator is in the fully extended or retracted position.

In certain actuator installations it is important to be able to translate the actuator position into a remote location. For example, when the actuators are being used to actuate the thrust reversers for a jet engine on an aircraft, the pilot must know when the actuators are in the fully deployed or stowed position in that the engine throttle must be held at idle during either the deploy or stow cycle as the actuator is extending or retracting.

The use of an electrical signal generating device to generate a signal responsive to the positioning of a piston of an actuator for control purposes is generally known from US-A-3 403 365.

According to the present invention there is provided a fluid actuator comprising a cylinder, a piston axially movable within said cylinder, a rotatable member operatively connected to said piston for rotational movement during axial movement of said piston, and a feedback screw operatively connected to said rotatable member for axial movement of said feedback screw in response to such rotational movement of said rotatable member, such axial movements of said feedback screw being proportional to the rate of movement and position of said piston, said feedback screw having a screw-threaded connection with said rotatable member, and means for restraining said feedback screw against rotation, whereby rotation of said rotatable member in opposite directions causes axial inward and outward movement of said feedback screw relative to said rotatable member, characterized in that said means for restraining said feedback screw against rotation comprises a first lever transversely arranged with respect to the longitudinal axis of said feedback screw and pivotally connected to said feedback screw, and a second lever pivotally connected to said first lever and to said actuator thereby preventing rotation of said first lever aboutthe longitudinal axis of said feedback screw.

Preferably an actuator housing is attached to one end of said cylinder, and that said feedback screw is connected to said first lever intermediate the ends thereof, and said second lever having one end connected to one end of said first lever and its other end connected to said actuator housing, the other end of said first lever providing the output for said feedback screw.

Preferably the connections between said first lever and feedback screw and between said second lever and first lever and actuator housing include sleeve bearings and bushings providing for anti-rotation of said feedback screw relative to said levers.

In accordance with a feature of the present invention the first lever provides a mechanical feedback output which is laterally spaced both from the longitudinal axis of said feedback screw and from the axis of said second lever.

Further in accordance with a feature of the invention, a stroke limiting mechanism is preferably provided to prevent the actuator from overstroking the feedback mechanism in the event that they are not properly synchronized. The stroke limiting mechanism preferably includes one or more stop brackets connected to one end of the actuator housing. Preferably two stop brackets are used which overlie opposite sides of the feedback mechanism and have aligned slots therein coinciding with the longitudinal axis of the feedback screw. An elongated stop bolt extends from the feedback screw through the aligned slots. By making the ends of the slots correspond to the extreme end positions of the feedback mechanism, the ends of the slots will act as a mechanical stop for both the feedback mechanism and actuator screw shaft connected thereto thus preventing the feedback mechanism from being overstroked by the actuator regardless of whether the actuator and feedback mechanism are in synchronism with each other.

Some embodiments of the invention will now be described, by way of examples, with reference to the accompanying drawings, in which:

• Figure 1 is a fragmentary side elevation view of a preferred form of fluid actuator with feedback mechanism in accordance with the present invention;
• Figure 2 is a fragmentary bottom view of the actuator of Figure 1 as seen from the plane of the line 2-2 thereof, with portions of the actuator broken away to show how the feedback mechanism is connected thereto;
• Figure 3 is an end elevation view of the fluid actuator of Figure 1 as seen from the plane of the line 3-3 thereof;
• Figure 4 is a fragmentary longitudinal section through the fluid actuator and feedback mechanism of Figure 3, taken along the plane of the line 4-4 thereof;
• Figure 5 is an enlarged transverse section through the bearing mount between one of the feedback mechanism levers and actuator housing, taken on the plane of the line 5-5 of Figure 2;
• Figure 6 is a fragmentary longitudinal section through the sequence-power valve mechanism associated with the fluid actuator, taken along the plane of the line 6-6 of Figure 4;
• Figure 7 is a fragmentary bottom plan view of a modified form of actuator and feedback mechanism which may be substantially identical to the actuator and feedback mechanism of the
• Figures 1-5 embodiment but which additionally includes a stroke limiting mechanism for preventing the actuator from overstroking the feedback mechanism in the event that they are not properly synchronized;
• Figure 8 is a fragmentary longitudinal section through the feedback mechanism and actuator of Figure 7, taken along the plane of the line 8-8 thereof;
• Figure 9 is a fragmentary sectional view through the output end of the feedback mechanism and one of the bearing mounts for the stroke limiting mechanism, taken along the plane of the line 9-9 of Figure 7; and
• Figure 10 is an enlarged transverse section through the bearing mount between one of the levers of the feedback mechanism and actuator housing.

Referring now in detail to the drawings, and initially to Figures 1-6 thereof, one form of fluid actuator 1 in accordance with this invention is designated generally by the reference numeral 1. As clearly shown in Figure 4, such fluid actuator 1 includes a cylinder 2 containing a piston 3 axially movable therewithin. Attached to the piston 3 is a hollow rod 4 which extends through the rod end of the cylinder 2 and has a rod end assembly 5 on its outboard end (see Figure 1) to facilitate connection to the movable part of the device to be actuated, such as the thrust reversers for a jet engine on an aircraft. A suitable trunnion mount may also be provided on the cylinder 2 to facilitate connection to the other part of the device to be actuated.

The piston 3 has a nut 8 provided with high lead Acme thread in the centre thereof which is coupled to a mating screw shaft 9 having a similar screw thread. One end of the screw shaft 9 is journaled in suitable bearings 10 within an actuator housing 11 attached to the head end of the cylinder 2, whereas the other end of the screw shaft 9 extends into the hollow piston rod 4 a substantial distance beyond the nut 8. As the piston 3 moves back and forth in the cylinder 2, the screw shaft 9 rotates at a speed proportional to the velocity of the piston 3.

The bearings 10 may be held in place on the screw shaft 9 by a bearing retainer 19 adjacent the outer end of the screw shaft 9. Attached to the screw shaft 9 is a high lead worm gear 12 which mates with a worm shaft 13 mounted for rotation within a transverse bore 14 in the actuator housing 11. Since the speed of the worm shaft 13 is also proportional to the velocity of the piston rod 4, when the worm shafts 13 of two or more actuators 1 are connected together by a synchronous drive shaft or the like, they will be mechanically synchronized in both position and motion, as well known in the art.

When the actuator piston 3 is in the retracted or stowed position shown in Figure 4, such actuator may be locked in such position by a suitable lock mechanism 15. As shown, such lock mechanism 15 includes a movable lock sleeve 16 axially movable toward and away from the adjacent end of the worm gear 12. A splined connection 17 is provided between the movable lock sleeve 16 and a piston stop 18 within the actuator housing 11 to prevent rotation of the lock sleeve 16 within the actuator housing 11 while permitting limited axial movement therewithin.

The adjacent end faces of the worm gear 12 and movable lock sleeve 16 have cooperating lock teeth 20 thereon with ramp angles which when engaged permit ratcheting of the worm gear 12 relative to the movable lock sleeve 16 during retraction of the piston 3 but not during extension thereof. Accordingly, the piston 3 will continue to retract until it engages the piston stop 18. However, if at any time an attempt is made to reverse the piston direction while such lock teeth 20 are in contact with each other, the lock teeth 20 will instantly engage thus locking the screw shaft 9 against rotation and preventing the piston 3 from extending.

When the piston 3 is fully retracted, the movable lock sleeve 16 is normally maintained in engagement with the worm gear 12 by a lock spring 21 interposed between the movable lock sleeve 16 and piston 3. During retraction of the actuator, as the piston 3 approaches the end of its stroke, the piston 3 compresses the lock spring 21, causing the teeth on the movable lock sleeve 16 to move into engagement with the teeth on the worm gear 12.

Before the actuator 1 can be extended, the lock sleeve 16 must be moved away from the worm gear 12 to disengage the lock teeth 20, and then system pressure must be applied to the extend side of the actuator. Preferably, both such functions are accomplished by actuation of a sequence-power valve 22 which may be contained in a separate housing 23 having a generally right angle extension 24 at one end received in a valve port 25 in one side of the actuator housing 11 and releasably retained in place as by bolts 21 or the like. The extension contains a transverse bore 26 in which a toggle-type lock release lever 27 is mounted on a shaft 28 for limited pivotal movement. The inner end of the lock release lever 27 extends into the actuator housing 11 and has a fork 29 thereon surrounding the movable lock sleeve 16. When the lever 27 is pivoted about the shaft 28 in a generally clockwise direction as viewed in Figure 4, the fork 29 will engage a shoulder 30 on the movable lock sleeve 16 thus forcing the movable lock sleeve 16 out of engagement with the worm gear 12.

For effecting such pivotal movement of the lock release lever 27, a movable lock plunger 31 is provided in a longitudinal bore 32 in the sequence-power valve housing 23 extending in a direction generally parallel to the longitudinal axis of the actuator cylinder 2. The lock plunger 31 has a longitudinal slot 33 therein which receives the outer end of the lock release lever 27. Attached to the lock plunger 31 is a lock piston 34 having a differential area which is acted upon by fluid pressure admitted to a lock-in annulus 35 within the bore through an exterior port 36 (see Figures 1-3 and 6) to cause the lock piston 34 to move to the left as viewed in Figure 4, dragging the lock plunger 31 with it. This causes the lock release lever 27 to pivot about the shaft 28 and move the lock sleeve 16 axially inwardly against the force of the lock spring 21 to disengage the lock sleeve 16 from the worm. gear 12.

Before system pressure is admitted to the lock-in annulus 35 to release the lock, such system pressure is first desirably applied to the retract end 40 of the actuator through a retract port 41 and porting tube 42 (see Figure 1) to remove any axial tension loads on the actuator 1 which might otherwise interfere with release of the lock 15. Then, with system pressure still applied to the retract port, system pressure is also applied to the lock-in annulus 35 to release the lock in the manner previously described.

After the lock piston 34 has moved far enough to release the lock, the system pressure acting on the lock piston 34 is ported to the extend end of the actuator through another annulus 43 in the lock piston bore 32 which is uncovered by the lock piston 34 following such movement. Such annulus 43 communicates with the actuator port 25 through an extend passage 44 in the sequence-power valve housing 23. Since the area of the actuator piston 3 exposed to the extend pressure is greater than that exposed to the retract pressure, the actuator will extend. An extend orifice 45 in the extend passage 44 prevents the external pressure at the lock-in port 35 from dropping below a predetermined level so that the lock piston 34 will not cycle during extension of the actuator.

To retract the actuator, the pressure acting on the extend end of the actuator is reduced, as by connecting the lock-in port 35 to return pressure, while still maintaining system pressure on the retract end of the actuator. With reduced pressure at the lock-in port, a return spring 46 acting on the lock piston 34 will cause the lock piston to return to its original position blocking fluid flow from the extend end of the actuator through the lock piston bore 32. However, as can be seen in Figure 6, return flow from the extend end of the actuator still occurs through a check valve 47 in another passage 48 in the housing 23 providing communication between the extend end of the actuator and the lock-in port.

As the actuator retracts, the lock teeth 20 are prevented from prematurely engaging by a torsion spring 50 acting on the lock release lever 27 to maintain the lock release lever 27 in the unlocking position until the actuator piston 3 engages the lock spring 21 and compresses same sufficiently to overcome the relatively light force of the torsion spring 50 and force the lock teeth 20 into engagement. This normally occurs within the last 0.76 cm (3/10 inch) or so of the retract stroke. However, the actuator 1 will continue to move in the stow direction until the actuator piston 3 engages the internal stop 18 because of the torque developed by the screw shaft 9 and the ramp angles of the lock teeth 20 which cause the lock teeth to ratchet over each other. When the actuator piston 3 engages the retract stop 18, the screw shaft 9 also stops, and since the lock teeth 20 are already in engagement with each other, any motion that tends to extend the actuator 1 will cause the locking faces of the lock teeth 20 to engage thus providing a positive lock against such motion.

Additional actuators of the same or similar construction with or without the lock mechanism 15 and associated sequence-power valve 22 may be mechanically synchronized both in position and motion with the locking actuator 1 by connecting the worm gears 12 of the actuators together by flexible shafts or the like. The extend pressure acting on the extend end of the locking actuator 1 may also be trasmitted to the extend ends of the other actuators through sealed tubes surrounding the flexible shafts, whereby extend pressure will be simultaneously applied to the extend ends of all of the actuators, but not before the lock mechanism of the locking actuator 1 has been released. The retract ends of all of the actuators may similarly be interconnected by hydraulic conduits to ensure that the same hydraulic pressure is also simultaneously applied thereto.

When the pilot desires to deploy the locking actuator 1, he first connects the pressure side of the aircraft hydraulic system to the retract port 41 to supply pressure to the retract end of the actuator 1 to make certain that the actuator piston 3 is seated firmly on the stow stop 18 within the actuator cylinder, which unloads the lock mechanism. The actuator 1 will remain in the stowed position until the pilot supplies system pressure to the lock-in port 36 of the sequence-power valve 22, first to unlock the locking actuator 1, and then to pressurize the extend end of the actuator in the manner previously described. Although there will then be system pressure on both sides of the actuator piston 3, the actuator will extend because of the unbalanced area of the piston as aforesaid.

During either the deploy or stow cycle, as the actuator is extending or retracting, the engine throttle must be held at idle. Accordingly, it is important to be able to communicate to the pilot when the actuator 1 reaches the fully deployed or stowed position.

In the preferred form of actuator construction disclosed herein, such actuator position is made known as by providing a feedback mechanism 60 operatively connected to the actuator screw shaft 9. Such feedback mechanism 60 comprises a feedback screw 61 which as can be seen in Figures 2 and 4 has a screw-threaded inner end 62 extending into a. central recess 64 in the enlarged outer end portion 65 of the actuator screw shaft 9. The bearing retainer 19 may be screw-threadedly connected to the screw shaft 9 for rotation therewith, and has an internal screw-threaded central bore 66 for screw-threaded engagement by the screw-threaded inner end 62 of the feedback screw 61. Accordingly, rotation of the actuator screw shaft 9 will cause the feedback screw 61 to move at a rate and position proportional to the piston rod 4.

The feedback screw 61 extends through a sealed opening in the actuator housing end wall 67 and outwardly therebeyond a sufficient distance to permit limited axial movement of the feedback screw 61 in opposite directions during extension and retraction of the actuator 1 in a manner to be subsequently described. At the outer end of the feedback screw 61 is a clevis or yoke 68 having a pair of arms 69 between which is journaled a feedback lever 70 intermediate the ends thereof. As best seen in Figures 1 and 4, the feedback lever 70 is connected to the feedback screw 61 by a bolt 72 and nut 73 and is restrained against lateral movement relative to the feedback screw 61 by an elongated kinematic sleeve bearing 74 extending between the clevis arms 69 and a pair of bushings 75, 76 received in the openings in the clevis arms 69 through which the bolt 72 extends. The bushings 75, 76 are pressed against the opposite ends of the bearings 74 upon tightening the nut 73 to provide anti-rotation of the feedback screw 64 laterally relative to the feedback lever 70.

The feedback lever 70 is restrained against lateral movement by a drag lever 78 extending between the actuator housing 11 and one end of the feedback lever 70. As best seen in Figures 2 and 3, the outer end of the drag lever 78 has a clevis 79 thereon for journaling of one end of the feedback lever 70 thereto, much in the same manner as the journal connection between the feedback lever 70 and feedback screw 61, to provide an anti-rotation connection therebetween in a lateral direction.

The inner end of the drag lever 78 is connected to a clevis 80 on one side of the actuator housing 11, but as seen in Figures 1 and 5, the journal mount between the drag lever 78 and clevis 80 is otherwise substantially the same as the journal mount between the feedback lever 70 and feedback screw 61. Accordingly, the same reference numerals are used to designate like parts. Also, another clevis 81 may be provided on the opposite side of the actuator housing 11 to permit a shipping link 82, shown in phantom lines in Figure 2, to be used to connect the output end 83 of the feedback lever 70 to the actuator housing 11 during shipment.

A suitable linkage mechanism, not shown, may be connected to the output end of the feedback lever 70 to provide the feedback signal to the pilot indicating the position of the actuator 1. When the output end 83 is in its outermost position shown in solid lines in Figure 2, it signals that the actuator 1 is in the fully stowed and locked position, whereas when such output end is in its innermost position shown in phantom lines in Figure 2, it signals that the actuator 1 is in the fully extended or deployed position.

As the actuator piston 3 moves back and forth in the cylinder 2, the actuator screw shaft 9 rotates at a speed proportional to the velocity of the piston 3. Accordingly, by proper selection of the number of threads on the feedback screw 61, the axial movement of the feedback screw 61 may be substantially less than the piston stroke. Likewise, by proper selection of the length of the feedback lever 70 and drag lever 78 and location of the journal mount between the feedback lever and feedback screw, the feedback stroke at the output end 83 of the feedback lever may be made proportionally greater than the stroke of the feedback screw itself. As an example, a 3.81 cm (1-1/2 inch) feedback screw movement may be equivalent to 55.25 cm (21-3/4 inches) of piston stroke and may provide 8.90 cm (3-1/2 inches) of feedback stroke at the output end 83 of the feedback lever 70.

To synchronize the feedback mechanism 60 and actuator 1 movements so that the extreme end positions of the output end of the feedback lever 70 will correspond to the fully retracted and extended positions of the actuator piston 3, before the rod end assembly is connected to the device to be actuated, the piston rod 4 may be manually rotated after release of the lock mechanism 15 to cause the piston 3 and actuator screw shaft 9 to rotate as a unit, thus causing axial movement of the feedback screw 61. When the piston 3 is fully retracted, the piston rod 4 and actuator screw shaft 9 may be rotated until a gauge bar, not shown, will just fit between a predetermined point on the feedback lever 70 and a point on the housing 11. This will place the output end of the feedback mechanism 60 at its extreme retracted position corresponding to the fully retracted position of the actuator.

Alternatively the feedback screw 61 may be disconnected from the feedback lever 70 so that the actuator 1 can be fully retracted without overstroking the feedback mechanism 60. Then the feedback screw 61 may be rotated relative to the actuator 1 until its length is such that when it is reconnected to the feedback lever 70, a gauge bar, not shown, will just fit between a predetermined point on the feedback lever 70 and a point on the housing 11.

To prevent the actuator 1 from overstroking the feedback mechanism 60 in the event that they are not properly synchronized, a stroke limiting mechanism 85 such as shown in Figures 7-10 may be provided on the outer end of the actuator housing 11. Such stroke limiting mechanism 85 desirably consists of a pair of stop brackets 86, 87 disposed on opposite sides of the feedback mechanism 60. One end of each stop bracket 86, 87 may be connected to the same clevis 80, 81 on opposite sides of the actuator housing 11 to which the drag lever 78 and shipping lever 82 are connected by using longer bolts 88 than the bolts 72 of the Figures 1-5 embodiment. The brackets have aligned slots 90, 91 therein coinciding with the longitudinal axis of the feedback screw 61. Extending between the slots 90, 91 is an elongated stop bolt 92 which is also used to connect the feedback screw 61 to the feedback lever 70.

As can be seen in Figures 8 and 9, the head 93 of the bolt 92 will engage the ends of the slot 91 in one of the stop brackets 87 at the extreme end positions of the feedback mechanism, whereas the other end of the bolt desirably has a stop bushing 94 thereon for engaging the ends of the slot 90 in the other bracket 86 at such extreme end positions. Also, as seen in Figure 8, the stop bushing 94 may be an extension of the bushing 76 shown in Figure 4. Otherwise, the construction of the feedback mechanism 60 shown in Figures 7-10 is substantially identical to the feedback mechanism 60 previously described, and the same reference numerals are used to designate like parts.

Preferably the length of the slots 90, 91 in the stop brackets 86, 87 correspond to a slight overstroke condition of the feedback mechanism 60, for example, approximately 0.16 cm (1/16") extra stroke on each end of the actuator stroke so that during normal operation the actuator will stop on the actuator stops at the ends of its stroke and not on the feedback stops provided at the ends of the slots 90, 91. However, the feedback stops will provide a mechanical stop for both the feedback mechanism 60 and actuator screw shaft 9 connected thereto when the actuator 1 and feedback mechanism 60 are not properly synchronized thus preventing the feedback mechanism 60 from being overstroked by the actuator 1 beyond such slight overstroke condition so as to protect the feedback mechanism against damage due to overstroking.

From the foregoing, it will now be apparent that the fluid actuator of the present invention includes a relatively compact and lightweight feedback mechanism that is driven by the actuator screw shaft for accurately indicating the position of the actuator and particularly whether the actuator is fully extended or retracted. Provision is also made for synchronizing the feedback mechanism and actuator movements so that the extreme end positions of the feedback mechanism may be made to correspond to the fully retracted and extended positions of the actuator. Also, a stroke limiting mechanism may be provided for preventing the actuator from overstroking the feedback mechanism in the event that they are not properly synchronized.