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Sept. 17, 1968 D.wood 3,401,600
CONTROL SYSTEM HAVING A PLURALITY OP CONTROL CHAINS EACH OF WHICH MAY BE DISABLED IN EVENT OF FAILURE THEREOF Filed Dec. 23, 1965 2 Sheets-Sheet 1
Sept. 17, 1968 D.wood 3,401,600
CONTROL SYSTEM HAVING A PLURALITY OF CONTROL CHAINS EACH
OF WHICH MAY BE DISABLED IN EVENT OF FAILURE THEREOF
2 Sheets-Sheet 2
United States Patent Office ^JfSS
CONTROL SYSTEM HAVING A PLURALITY OF CONTROL CHAINS EACH OF WHICH MAY BE DISABLED IN EVENT OF FAILURE _ THEREOF 5 Derek Wood, Sun Valley, Calif., assignor to Bell Aerospace Corporation, a corporation of Delaware Filed Dec. 23, 1965, Ser. No. 515,822 10 Claims. (CI. 91—44)
ABSTRACT OF THE DISCLOSURE
Disclosed is a redundant control system having a plurality of control chains each connected to position a movable member pursuant to input control signals. Each of 15 the chains includes a first transducer receiving input signals such as from a manual input (pilot's control stick) and other inputs (stability augmentation and/or autopilot). The first transducer responsive to the input signals provides an out hydraeric pressure control signal. The pressure signal is connected to a remotely positioned control valve which controls the flow of hydraeric fluid to an actuator which is coupled to the movable member (aircraft control surface). A second transducer is connected to the control valve and produces a hydjaeric pressure monitor signal, respresentative of the position of the control valve. The monitor signals from the plurality of control chains are compared in a comparator apparatus which generates a disabling signal in the event of nonconformity between monitor signals. The disabling signal activates disabling apparatus which disables that control chain not conforming to the remainder of the system control chains.
The present invention relates to control systems and more particularly to a hydraeric-mechanical control sysstem that may be provided in a plurality to accomplish a highly reliable redundant system. 40
The technique of employing power to position the control surfaces of an aircraft in accordance with control movements by the pilot (as well as other input signals) has come into widespread use as a result of the weight and size of control surfaces embodied in present day aircraft. 45 Of course, various techniques have been employed whereby manual control motoins are translated to drive the control surfaces. For example, indirect control has been accomplished by various combinations of mechanical, electrical and hydraulic elements. However, as such sys- 50 terns have been rather complex, reliability has sometimes dropped. Yet, aircraft embodying power control normally demand a high level of reliability. As a result, redundant systems have been developed in which several separate, duplicate control chains are provided to increase 55 reliability. Various techniques have also been proposed for rendering a control chain ineffective in the event of its failure. Usually, because the pilot is not capable of detecting a failure in sufficient time to provide effective correction, the operation of disabling a particular con- 60 trol chain is performed automatically.
Various forms of these control systems have normally included electrical circuits and mechanical linkages. In general, electrical and electornic apparatus is rather complex and sensitive, while -extended mechanical linkages 65 are somewhat subject to failure. As a result, a need exists for an effective nonelectrical control system of limited mechanical structure, and which may be incorporated in a redundant system with the facility to selectively disable an inoperative portion of the system. 70
Accordingly, it is an object of the present invention to provide an improved form of such a control system utiliz
ing hydraeric (pneumatic or hydraulic) pressure control signals to accomplish control of an aircraft control surface for example, or other movable member.
It is another object of the present invention to provide a redundant control system for selectively positioning movable members which system effectively disables a portion thereof upon occurrence of a failure in a portion, which portion then remains disabled until repaired and reset.
Another object of the present invention is to provide a hydraeric control system which include only limited mechanical linkages.
It is a further object of the present invention to provide a nonelectrical control system which is highly reliable in operation yet which is relatively simple to manufacture and maintain.
Still a further object of the present invention is to provide a control system utilizing hydraeric pressure control signals, in which the failure of a component is very rapidly detected and may therefore be substantially immediately disabled.
Additional objects and advantages of the present invention will be apparent to one skilled in the art from a consideration of the following description taken in conjunction with the accompanying drawings which are presented by way of example only, and are not intended as a limitation upon the scope of the present invention as defined in the appended claims and in which:
FIGURE 1 is a diagrammatic representation of a redundant control system constructed in accordance with the present invention;
FIGURE 2 is a detailed diagrammatic illustartion of a single control chain portion of the system of FIGURE 1; and
FIGURE 3 illustrates one form of pressure montior signal unbalance detecting unit which may be employed in the system of FIGURE 1.
A control system for positioning movable members in accordance with the present invention may be provided in a redundant system embodiment by incorporating several individual control chains, each of which serves to position a movable member. In an illustrative embodiment of this system, the movable members may comprise the control surfaces of an aircraft which generally accomplish the same purpose so that control of the aircraft is not lost upon loss of the ability to control one, or even several of the control surfaces, so long as some control remains.
In the illustrative system, an individual control chain may include a transducer for translating the pilots manual control movements (along with other control signals) into a hydraeric pressure control signal which is communicated through a pressure line to a location near the member to be controlled. At that location, the hydraeric pressure control signal is applied to a control valve (as a hydraeric amplifier) to provide a physical displacement that is representative of the hydraeric signal. The physical displacement of the valve then controls fluid pressure to drive an actuator which is in turn connected to. the movable member. Furthermore, the movement of the valve is translated into a hydraeric feedback signal to stabilize the operation of the valve and is also translated into a hydraeric monitor signal which may be compared with similar signals from other control chains to detect a nonconforming chain. The system may further incorporate structure for disabling a nonconforming control chain and locking the related control surface of such a chain in a neutral or ineffective position.
Referring now to the drawings and more particularly to FIGURE 1, thereof, a system in accordance with the present invention is illustrated. As shown, three movable members, represented by control surfaces 10, 12 and 14
(extreme right) are the objects of control positioning. The control information is provided by physical displacement of manual controls 16 and 18 (extreme left). The controls 16 and 18 are interconnected dual controls (as for pilot and copilot) each including a pivotally mounted lever 20 and 22, respectively incorporating transverse extensions 24 and 26 which are interconnected by a link 28. Therefore, manual movement of either of the levers 20 or 22 produces a similar movement of the other lever.
The lever 22 is connected through a translating linkage 30 to three perpendicularly extending arms Rl, R2 and R3. In a similar manner, a linkage 38 connects the lever 22 to three perpendicular arms R4, R5 and R6. This mechanical arrangement including the manual controls 16 and 18 results in the application of a representative mechanical signal or physical displacement to each of six transducers Tl, T2, T3, T4, T5 and T6 which are individually coupled respectively to the arms Rl, R2, R3, R4, R5 and R6.
In addition to receiving manually-applied control signals, the transducers Tl through T6 also receive electrical input signals through conductors CI through C6 respectively. The signals so applied may comprise damper signals or autopilot signals as somewhat conventionally employed in various aircraft. The mechanical and electrical signals are combined within the transducers Tl through T6 to provide six independent hydraeric pressure signals that are individually transmitted through lines LI through L6 respectively. The transducers Tl through T6 (as described in detail below) also provide six hydraeric pressure signals in lines PI through P6 which are inversely related to the signals appearing in the lines LI through L6. That is, for example, if a control operation is performed which causes the pressure in line LI to rise, the pressure in a related line PI will drop. The lines PI through P6 are thus related, to control opposed surfaces, for example.
The purpose of providing inverse signals arises in several applications, for example, it is frequently desired to provide opposed control signals to the two wings of an aircraft. Therefore, the signals carried in the lines LI through L6 may be employed to control the surfaces 10, 12 and 14 as shown in FIGURE 1 while the pressure signals appearing in the lines PI through P6 may be employed in a similar system to control inverse positioning of related control surfaces.
Considering the control operation in further detail, the lines LI through L6 transmit pressure signals contained therein to the proximity of the control surfaces 10, 12 and 14 which are to be positioned. At this location, the lines LI through L6 are connected to control valves VI through V6 respectively which may take the form of spool valves as disclosed below and incorporate feedback means for stabilized operation. In the operation of the control valves VI through V6, the physical position thereof in turn positions the control surfaces by amplifying received signals through actuators Al through A6. Specifically, the control valves VI through V6 individually position the actuators Al through A6 respectively which in turn act through yoke linkages SO, 52 and 54 to position the control surfaces 10, 12 and 14, respectively. Therefore, the positions of the control valves are in effect signals that are representative of the desired displacement. Those physical positions are translated by mechanical connections Ml through M6 from the control valves VI through V6 respectively to transducers XI through X6 respectively. The transducers XI through X6 then provide hydraeric pressure monitor signals through lines HI through H6 respectively, to a comparator system 56 which senses any non-conformity by one of the control chains as manifest in the monitor signal and then operates to lock the associated actuator in a neutral position. Specifically, the lines Dl through D6 from the comparator system 56 carry hydraeric pressure lock-out signals to control lock-out devices Bl through B6 which lock the actuators Al
through A6 respectively in a neutral position in the event an associated monitor signal indicates a failure.
Considering the detailed sequence of operation in the system of FIGURE 1, assume for example that the lever 5 20 of the manual control 16 is urged in the direction indicated by the arrow 64. As a result of this movement, the extension 24 is urged downwardly (clockwise about a pivot point 66) causing the extension 26 to be moved downwardly (counterclockwise about a pivot point 68) 10 in turn mo\i.ig the lever 22 as indicated by the arrow 70. This movement of each of the levers 20 and 22 causes the linkages 30 and 38 to be moved to the right, as shown in FIGURE 1, thereby moving each of the arms Rl through R6 to the right. This displacement of the arms 15 Rl through R6 may be assumed to be in a direction to cause the hydraeric pressure in each of the lines LI through L6 to rise, which signal is communicated to the valves VI through V6 and may be assumed to urge the actuators Al through A6 to move each of the yoke 20 linkages 50, 52 and 54 to the right thereby accomplishing the deisred control by placing each of the control surfaces 10,12 and 14 in the desired position.
In the event that the transducers XI through X6 sense a nonconformity in any one of the control valves VI 25 through V6, for example, in the valve VI, an appropriate signal will appear in one of the outputs from the comparator system 56. Specifically in the selected example, a hydraeric signal appears in the line Dl from the comparator 56 and is applied to the lock-out device Bl causing 30 the actuator Al to become disabled in a neutral position. Thereafter, the control surface 10 is moved only by the actuator A2 with the result that substantially half displacement operation occurs. However, such operation may be adequately compensated by system design so that the 35 loss of one control chain is of little consequence.
Of course, the comparator system 56 may continue to perform comparisons among the monitor signals from the control chains remaining operative and continue to disable any of such chains upon an indication of noncon40 formity. As a result, the system may tolerate considerable failure and still continue to be sufficiently operative for the desired control function. The structure of the individual control chains may vary somewhat in accordance with various embodiments of the present invention; however, 4_ one rather-detailed illustrative form of a control chain is 0 shown in FIGURE 2 and will now be considered in detail. The transverse arm Rl as shown in FIGURE 1 is connected to a mechanical linkage 102 (FIGURE 2) which is in turn connected through a spring 104 to the upper end -0 106 of a flapper 108 supported at a pivot point 110 and integrally formed with an armature 112 of a torque motor 114. The torque motor 114 is connected to receive electrical signals at terminals 116, which, as previously indicated may comprise damper signals or signals from an autopilot g5 as well known in the field of aircraft control.
The forces applied by the torque motor 114 and the spring 104 are summed on the flapper 108 which operates in cooperation with opposed nozzles 118 and 120. The interior of the nozzle 118 is supplied with fluid through 60 an orifice 122 from a source PS1 of fluid under pressure. In a similar fashion the nozzle 120 is supplied from the same source PS1 through an orifice 124. Therefore, depending upon the position of the flapper 108, the nozzles 118 and 120 are variously restricted to accordingly de65 velop hydraeric pressure control signals within the chambers 126 and 128. The signal in the chamber 126 represents the output signal to the line PI as shown in FIGURE 1 while the pressure developed in the chamber 128 is 7Q applied through the line LI (FIGURE 2) to the control valve VI. As it will be explained in detail, the control valve VI variously positions the actuator Al to in turn control a movable member (not shown) as a control surface. Furthermore, the position of the moving element 75 in the valve VI is sensed by a transducer XI to develop