This invention relates to planetary gear type rotary mechanical actuators and more particular to an actuator which is used in series with at least one other actuator and which disconnects itself from the series and from the load if it jams and allows the transmission of power to the other actuators in the series.

In aircraft flight control, actuators are used on the leading edge flaps, the trailing edge flaps, ailerons, flaperons, and rudders in order to adjust the surfaces to the desired position. Trailing edge surfaces and rudders are referred to as the primary flight control surfaces since their position is critical in aircraft control. It is imperative therefore that control of these flaps or surfaces is not compromised. Until now, because of the possibility of jamming of the rotary mechanical actuators, the primary flight control surfaces have used linear hydraulic actuators since they typically fail "open" and it is easy to override the hydraulic actuator in order to use a back up actuator to lock the control surface in a neutral position. On the other hand, the leading edge of an aircraft wing is referred to as the secondary flight control surface since the loss of its use restricts aircraft performance, but does not cripple the aircraft. Because of this difference, mechanical actuators, either linear or rotary, are used on the leading edge of an aircraft. If an actuator jams, it is permissible that the flap be allowed to lock in the jammed position. However, a jammed actuator can cause damage to the aircraft wing if one continues to drive the jammed actuator. Therefore, there is a need for an actuator which is designed to reduce the possibility of jamming and if it jams, to disconnect itself from the actuation system and to allow the transmission of the driving torque to the other actuators downstream of the jammed actuator.

Furthermore, an actuator which is used in series with several other actuators and which can disconnect itself from the system if it becomes jammed, can be used on the primary flight control surface as well as the secondary flight

control surfaces.

The present invention relates to the problem of providing a mechanical actuator which, if it jams, disconnects itself from the load and a series of actuators, yet allows the driving force to be transmitted therethrough. In accordance with the present invention a non-jamming rotary mechanical actuator comprises a moveable ring gear and a fixed ring gear on each side of said moveable ring gear. Each ring gear includes an internal gear surface about an opening therethrough and an attachment means for securing said ring gear to either the support structure, in the case of the fixed ring gear, or to a load, in the case of the moveable ring gear. The actuator further includes a side plate having a central bore therethrough secured over the openings in said outermost sides of said fixed gear rings; a bearing mounted within said side plate bore; a shaft; and a means for driving said shaft. The shaft includes a cam offset extending generally the length of the shaft between said two side plates. The cam offset comprises an inner or first cam member, having a desired first offset from said axis of said shaft, and an outer or second cam member, having a second offset. Each cam member has an axially extending slot formed therein into which a shear member is press or interference fit. The first and second offset are sized so that when the second cam member is rotated approximately 180° from its principal operating position, it has an axis which coincides with the axis of said shaft. This feature unloads the compound planetary gear from engagement with the fixed and moving ring gears if the shear member fails.

Fig,, 1 is a schematic design of a prior art actuation system.

Fig. 2 is a schematic diagram of the actuation system which is used with the present invention. Fig. 3 is a cross-sectional view of the actuator of the present invention.

Fig. 4 is a cross-sectional end view taken along line

4-4 in Fig. 3, showing the actuator input shaft during normal operation.

Fig. 5 is a cross-sectional end view taken along line 4-4 in Fig. 3 showing the actuator input shaft during its disengaged condition.

Fig. 1 is a schematic depiction of a typical actuation system (10) for a flight control surface. As shown, the flight control surface or flap, or in generic terms the load (12) , is driven by a series of actuators; in this case three actuators (14) , (16) and (18) which are in series. The series of actuators is driven by a prime mover or motor (20) . A fuse (22) is located between the prime mover (20) and the actuators (14) , (16) and (18) . A jammed actuator (14) at Point A will cause the load (12) to lock in the jammed position. As explained above, this is unacceptable if the load (12) represents the primary flight control surface and may or may not be acceptable if load (12) represents the secondary flight control system. If a fuse (22) is not included in the system, the prime mover (20) will continue to operate until a weak link in the system is broken, such as at Point B. The break will disconnect the prime mover (20) from actuator (14) , thereby locking the load (12) at whatever position actuator (14) is n at the time it is disconnected. Prime mover (20) will continue to drive actuators (16) and (18). even though the load is locked at actuator (14) . This causes extensive damage to the actuation system and/or the load and is therefore unacceptable. Unlike the prior art system shown in Fig. 1, an actuator system using an actuator of the present invention is schematically shown in Fig. 2. As shown, the' load (12) is driven by three actuators (24) , (26) and (28) , the details of which are set forth below. The series of actuators are in turn driven by a prime mover (20) via input shaft (30). The fuse (22) is not required with the series of actuators ^' (24) , (26) and _. (28) of the present invention.

In the system of Fig. 2, if a failure or jammed actuator occurs at Point A, the input shaft (30) is disconnected from the actuator (24) and then it disconnects the load (12) from the failed actuator at Point B as is described below. Thus the load (12) is unlocked from (no longer driven by) the failed actuator (24) , which in turn is isolated from the input shaft (30) , allowing the prime mover (20) to continue driving the load (12) through the two good actuators (26) and (28). In this manner, the load (12) will be driven by actuators (26) and (28) and will only be ¹ hinged by actuator (24).

The non-jamming, mechanical actuator (24) , (26) or (28) of the present invention is shown in Figs. 3 to 5. Shown are two fixed ring gears (32) and (36) on either side of a moveable ring gear or output gear (34) .

Fixed ring gears (32) and (36) are attached to a fixed surface, such as the spar of an aircraft wing, and the moveable ring gear (34) is attached to the control surface or flap of the aircraft wing. Each moveable and fixed ring gear comprises a housing member (40) which defines a central bore (41) therethrough and an attachment member (42) integral with the housing member (40) . The internal surface of the ring gear which defines the bore is formed as a gear- toothed surface (33) , (35) and (37) respectively. As shown, the three ring gears (32) , (34) , and (36) are placed in side-by-side relationship so that the axes of the bores are aligned.

A pair of side plates or covers (44) enclose the two outermost sides of the fixed ring gear (32) and (36) . Ball bearings (46) are secured to the side covers (44) to rotatably support the input shaft (30) . Bearings (46) include an outer and an inner race, (47) and (48) respectively. Retainers (50) are threaded onto the shaft (30) in order to secure the ring gears in place. In operation, the retainers (50) and the inner race (48) of bearings (46) rotate with input shaft (30) .

The input shaft (30) includes an offset portion thereon

which extends substantially the length of the shaft between the two fixed ring gears (32) and (36). The offset is generally formed by the use of a first cam member (52) . The first or inner cam member (52) however can be formed

5 integrally with the shaft (30) if desired. As shown, the axis of the first cam member (52) is offset by an amount X along the vertical axis of the shaft (30) . The second cam member (54) is cylindrical in shape and includes a bore therethrough, the axis of which is offset by an amount of 'Y

10 from the axis to the second cam member (54) . A key or shear member (60) is press or interference fit into the opening

(61) formed by the slots (61a) and (61b) formed within the outer surface of the inner cam (52) and in the internal surface of the outer cam (54) . Second cam member (54) is

15. fit over the first cam member (52) and aligned so that the offset in the vertical direction is equal to X plus Y as shown in Fig. 4. Furthermore, offset X and Y are sized to be approximately equal.

The input shaft (30) is formed with threads (31) 0 thereon on both sides of the outer cam member (54) . A shoulder (53) is formed in each end of the inner cam member (52) . The retainers (50) secure the inner race (48) of the bearing (46) between itself and the shoulder (53) . In this manner, the outer race (47) locates the axial position of 5 said side plates (44) which in turn capture in a side-by- side relationship, the fixed and moveable ring gears (32) , (34) and (36). The axis of the input shaft (30) and the axis of the central bore through the adjacent ring gears, are aligned. 0 A cylindrically shaped needle bearing (62) is slid over the second cam member (54) and a compound gear (64) is thereafter, positioned over the needle bearing (62) . The compound gear (64) has three sets of gear teeth (65), (66) and (67) in order to engage the internal gear surfaces (33) , 5 (35) and (37) of the ring gears (32), (34) and (36). In this manner, the gear teeth of the compound gear are engaged with the internal gear surfaces of the ring gear on the top

portion thereof. The gear teeth lose contact with the internal gear surfaces as one travels down around the gear teeth of the compound gear (64) , until at point D, the contact is broken due to the offset of cams (52) and (54) .

During normal operation, the gear teeth of the compound planetary gear (64) rotate into and out of contact with the gear teeth of the internal gear surface of each of the fixed and moving ring gears. As the input shaft (30) rotates, the moveable ring gear (34) rotates with respect to the two fixed ring gears, (32) and (36), thereby raising or lowering the load (12) .

This type of drive mechanism is known as an orbiting compound planetary drive. As the input shaft rotates, the cam forces the gear teeth (65) , (66) and (67) of compound gear (64) into engagement with the gear teeth of the internal gear surfaces (33) , (35) and (37) . Depending on the gear teeth count, the moveable ring gear (34) will rotate with respect to the fixed ring gears (32) and (36) , in the same or opposite direction as that of the input shaft.

Hence, when using this type of drive, the diameter of the central bore (44) can be formed smaller than two inches (5«1 cm) and still transmit a torque necessary to rotate the moving ring gear. Needle bearing (62) improves the efficiency of the torque transmission between the input shaft and the moving ring gear (34) .

If any of the actuators jam, the driving torque transmitted through the input shaft (30) will cause the shear member (60) to shear, which in turn separates the second cam member (54) from the first cam member (52) (i.e. the input shaft (30)). When this occurs, the input shaft (30) continues to rotate. Once it turns approximately 180 ^β the offset between the first and second cam member has been cancelled; i.e. the central axis of the input shaft (30) and the second cam member (54) become aligned; see Fig. 5. When this happens all the gear teeth of the compound gear (64) are withdrawn from the internal gear surface of each ring

gear; thus allowing input shaft to continue to supply torque to the actuator (26) and (28) downstream of the jammed actuator (24) . Just as important, the moveable ring gear

(34) which is attached to the load (12) is free to rotate with movement of the load (12). Hence, actuators (26) and

(28) will continue to drive the load and actuator (24) will act as a hinge.

Various modifications to the depicted and described apparatus will be apparent to those skilled in the art. For example, any number of actuators could be used in series and any number of fixed and moveable ring gears could be used to construct an actuator.