US3640185A

US3640185A - Servocontrol for dual hydraulic systems

Info

Publication number: US3640185A
Application number: US1151A
Authority: US
Inventors: Kazimierz Korsak
Original assignee: Piasecki Aircraft Corp
Current assignee: Piasecki Aircraft Corp
Priority date: 1970-01-07
Filing date: 1970-01-07
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08

Abstract

An improved servocontrol for redundant hydraulic fluid systems employing dual pressure sources each operating a separate actuator simultaneously to perform a common function. Two servo valve devices are employed, with each including valve elements connected in both hydraulic systems, thereby providing parallel control circuits from each pressure source to its associated actuator. The two servo valve devices are operated in synchronism by an input assembly permitting independent operation of one servo valve device in the event of jamming of the other. The parallel circuits, controlled through separate, independently operably valves, eliminate the possibility of a hydraulic lock in one actuator preventing operation of the other.

Description

0 llmted States Patent [151 3,640,185

Korsak 1 Feb. 8, 1972 [54] SERVOCONTROL FOR DUAL 3,527,143 9/1970 Hayter ..9l/4l 1 HYDRAULIC SYSTEMS Primary Examiner-Edgar W. Geoghegan [72] Inventor: Kazunierz Korsak, Newtovvn, Pa. A"0mey Beveridge & De Grandi 73 A ne Piasecki Aircraft Cor oration Phil d l- 1 mg 8 phi, Pa p a e [57 ABSTRACT [22] Filed: Jan. 7, 1970 An improved servocontrol for redundant hydraulic fluid systems employing dual pressure sources each operating a [2]] Appl. No.1 1,151 separate actuator simultaneously to perform a common function.'Two servo valve devices are employed, with each includ- [52] U S Cl 91/411 R 91,411 A 91/413 ing valve elements connected in both hydraulic systems, [5 Flsb 11/16 thereby providing parallel control circuits from each piessure [58] Fie'ld 41 l A 413 source to its associated actuator. The two servo valve devices are operated in synchronism by an input assembly permitting independent operation of one servo valve device in the event [56] References cued of jamming of the other, The parallel circuits, controlled UNITED STATES PATENTS throughseparate, independently operably valves, eliminate 2 597 418 5,1952 w tb t 1 91/216 A X 7 the possibility of a hydraulic lock in one actuator preventing GS ury e a o ti f h (hen 2,597,419 5/1952 Westbury et al. ...9l/2l 6 A X p 3,272,062 9/1966 Flippo et al. ..9l/4l 1 A X 12 Claims, 5 Drawing Figures SlERVOCONTROL FOR DUAL IIYDRAULIC SYSTEMS This invention relates to redundant hydraulic control systems, and more particularly to an improved fail-safe mechanically actuated control valve mechanism for parallel, redundant hydraulic actuator control systems especially useful in aircraft.

In hydraulic actuator systems where a high degree of operational reliability is essential, such as in servocontrol systems for aircraft, it is the conventional practice to provide redundant hydraulic systems which operate simultaneously to act upon a common output element to produce the desired aircraft control surface movement. The redundant systems are provided solely for the purpose of improving reliability in that, in the event of failure of one hydraulic system, the actuator may still be operated, without interruption, by the other system. The likelihood of simultaneous failure of both systems is, of course, much more remote.

Even in such critical applications as in the control of operation of the primary flight control surfaces of an aircraft, the prior art dual hydraulic control systems have, until recently, been generally considered satisfactory if the output element is connected to and operated by two separate pistons each driven by fluid directed from its respective fluid system by separate servocontrol valves. The pistons, or spools, of'the two servo valves of these prior art systems were conventionally rigidly connected to each other to assure synchronization of operation of the two actuator pistons. However, this arrangement created the possibility that jamming of the spool in one servo valve would render the entire system inoperative due to the two valve spools being rigidly connected. In an effort to avoid this contingency, systems have been provided which employ separate, independent servo valves, one for each of the respective actuator pistons, with electrical controls and/or mechanical linkage mechanisms being employed to synchronize movement of the servo valves. Such systems have not, however, been entirely satisfactory due primarily to the unreliability of known valve linkages and control mechanisms.

The above-mentioned disadvantages of the prior art are overcome, and a much higher degree of reliability is provided, by the present invention in which means are provided for assuring synchronized movement of separate servo valve spools and, at the same time, assuring freedom of movement of one servo valve spool in the event of jamming or freezing of the other. Further, the present invention provides means for avoiding the possibility of hydraulic lockin the main actuator powerjunit in the event of one of the servo valve spools becoming jammed in the neutral position of the valve. This is accomplished by employing the essential elements of two conventional servocontrol valves, with the two servo valve spools being independently connected to an input element so that movement in the mechanical control input to operate the two servo valves normally will not result in any relative motion between the valve spools. However, should one valve spool become jammed, the independent connection of the valve spools permits the second spool to be moved by the input element independently of the jammed spool.

The two servo valves are constructed to simultaneously serve two independent hydraulic systems, and are each con nected in the two systems to provide parallel control circuits for each actuator piston. Thus, pressure and return lines branch off from each of the two separate hydraulic systems to each of the two servo valves, and lines from each side of each of the actuator pistons run to both of the servo valves so that, in the event that one valve spool becomes jammed in a neutral position, a hydraulic lock is avoided by the lines from the other valve running to both of the actuator pistons.

A primary object of the present invention is to provide an improved hydraulic actuator control means.

Another object of the present invention is to provide an improved means for synchronizing movement of parallel connected servo valves.

Another object of the present invention is to provide a failsafe means for controlling a hydraulic actuator employing a plurality of parallel connected servo valves.

Other objects and advantages of the present invention will become apparent from the following detailed description, taken with reference to the accompanying drawings, in which:

FIG. I is'a schematic view, in section, of a hydraulic actuatorcontrol according to the present invention;

FIG. 2 is an elevation view, partially in section, of the servo valve mechanism schematically illustrated in FIG. 1;

FIG. 3 is a fragmentary sectional view of the input element of the servomechanism shown in FIG. 2;

FIG. 4' is a schematicview of an alternate embodiment of the invention; and

FIG. 5 is an elevation view, partially in section, of the embodiment of the invention schematically illustrated in FIG. 4.

Referring now to the drawings in detail, a servocontrol actuator system according to the present inventionis indicated generally by the reference numeral 10 and includes a main cylinder body 12 having a pair of axially aligned, spaced cylinders l4, 16 formed. therein. A first piston 18 is mounted in cylinder 14 for axial, reciprocating movement therein, and a second piston 20 is mounted in cylinder 16 for axial, reciprocating movement therein. A common piston rod 22 extends through cylinder body 12 and is rigidly attached to pistons 18 and 20 for movement therewith and to prohibit relative axial movement between the two pistons. Piston rod 22 projects axially from one end of the cylinder body I2 to form an output element 23 which may be attached, as by pin 24 and bracket 26 to a rigid member such as the frame structure of an aircraft, indicated generally by the reference numeral 28. The opposite end of the cylinder body 12 is provided with a rigid, outwardly projecting connector element 30 having an opening 32 formed therein for pivotal connection, through suitable linkage not shown, to a movable control sur face of an aircraft. Alternatively, connector 30 may be connected to the rigid structure 28 and the outputmember 23 connected to the movable control surface.

A servocontrol valve mechanism, indicated generally by the reference numeral 34, is provided to direct hydraulic fluid under pressure (pressure fluid) from a source 8-1 to cylinder 16, at either side of piston 20, selectively. Similarly, servo valve 34 directs pressurized fluid from a'second source 5-2 to cylinder 14, at either side of piston 18, selectively. As best seen in FIG. 1, servo valve mechanism 34 includes a valve body 36 having slidably mounted therein a first valve spool 38 and a second valve spool 40.

Spools

38 and 40 are mounted coaxially within a common bore 42 in valve body 36.

Pressure fluid from source S-l enters the valve body 36 through inlet 44 and passes through conduit 46 into the chamber 48 defined by the lands 50 and 52 on spool 38, and the inner wall of bore 42. Movement of spool 38 to the left in the direction of arrow 54 in FIG. 1 will permit the pressure fluid to flow from chamber 48 through conduit 56 into chamber 58 of cylinder 16, thereby tending to force piston 20 to the right relative to valve body 12. Actually, since the piston rod 22 and output member 23 are connected to a rigid frame member 28, the application of fluid pressure in chamber 58 will move the actuator cylinder body 12 and the valve body 36 to the left until the input signal, resulting from moving valve spool to the left, is cancelled. This movement will result in fluid in chamber 60 of cylinder 16 being forced out through conduit 62 into the chamber 64 defined by lands 52 and 66, then out through conduit 68 and outlet 70 to return to the source 8-].

Simultaneously, pressure fluid from the source S2 will be directed into valve body 36 through inlet 72 and pass through conduit 74 to the chamber 76 defined by lands 78 and 80. From chamber 76, the pressure fluid will pass through conduits 82, 83 into the chamber 84 of cylinder 14 to urge piston 18 in the same direction that piston 20 is being urged by the pressure fluid from source 8-1. At the same time, any fluid from chamber 86 of cylinder I4 will be urged through conduits 88, 89 into the chamber 90 defined by lands and 92 on valve spool 38. From the chamber 90, the fluid can return through conduit 92 and outlet 94 to be returned to source S-2.

Thus, it is seen that movement of valve spool 38 to the left, in the direction of arrow 54 will direct pressure fluid from source S1 to chamber 58 of cylinder 16, and simultaneously will direct pressure fluid from source S2 to chamber 84 of cylinder 14. Thus, the pressure fluid in

cylinders

14 and 16 simultaneously urge the cylinder body 12 to the left in the direction of movement of valve spool 38.

in the event of movement of the valve spool 38 to the right, in the direction of arrow 96, pressure fluid from source S-l will flow from chamber 48 through conduit 62 into chamber 60 of cylinder 16, and fluid in the chamber 58 will be urged out through conduit 56 into the chamber 98 defined by lands 50 and 100, then out through

conduits

102 and 68 to be returned to source S-l. Similarly, pressure fluid from source -2 will flow from chamber 76 through conduits 89 and 88 into chamber 86, and fluid from chamber 84 will be urged out through conduits 83 and 82 into the chamber 104 defined by lands 78 and 106, then out through conduits 108 and 92 to be returned to source S-2.

Valve spool 40 is coupled to spool 38 for simultaneous movement therewith through a resilient input coupling assembly 110, described more fully herein below. As seen in FlG. 1, valve spool 40 is provided with a series of spaced lands corresponding substantially with the lands on valve spool 38, and forms, in combination with the inner wall of bore 42, a second servo valve connected in parallel with the servo valve defined by spool 38 to provide parallel controlled paths for pressure fluid from source S-l to cylinder 16 and from source S-2 to cylinder 14. Referring specifically to FIG. 1, it is seen that conduit 112 is connected in fluid communication with conduit 46 to direct pressure fluid from source S-1 into the fluid chamber 114 defined by lands 116 and 118. In the event of movement of spool 40 to the left, in the direction of arrow 54, the pressure fluid will be directed through conduit 120 to the conduit 56, thereby providing an alternate, controlled path for the pressure fluid from source S-l to the chamber 58. At the same time, pressure fluid from source S-2 will be directed through conduit 122, connected in fluid communication with conduit 74, into the chamber 124 defined by lands 126 and 128. From the chamber 124, this pressure fluid will flow through conduits 130 and 83 to the chamber 84. The resultant relative movement of piston will urge fluid out of chamber 60 into conduit 132, connected in fluid communication with conduit 62, and into the chamber 134 defined by lands 118 and 136. From chamber 134, this fluid will flow out through conduit 138, connected in fluid communication with conduit 68, and be returned to the source S-l. Similarly, movement of piston 18 relative to cylinder 14 will urge fluid from chamber 86 out through conduit 140, connected in fluid communication with conduit 88, and into the chamber 142 defined by the

lands

128 and 144. From chamber 142, this fluid will flow through conduit 146 into conduit 92 and be returned to source 5-2.

In the event of movement of spool 40 to the right in the direction of arrow 96, fluid under pressure from source Sl will flow from chamber 114 through

conduits

132 and 62 into the chamber 60, and fluid from chamber 58 will flow out through conduits 56 and 120 into the chamber 148 defined by lands 116 and 150. Fluid from this chamber 148 will then flow out through conduit 152 into conduit 138 and be returned to the source S-l in the manner described above. Similarly, fluid from chamber 124 will be directed through

conduits

140 and 88 into chamber 86, and fluid from chamber 84 will flow through conduits 83 and 130 into the chamber 154 defined by lands 126 and 156. Fluid from chamber 154 will then flow out through conduit 158 into conduit 146 and be returned to source S-2 through conduit 92 in the manner described above.

To avoid the possibility of any mixing of fluids from sources S1 and S-2, by leakage along the valve spools 38 and 40, a suitable drain or vent 160 is provided between lands 66 and 106, and a similar vent 164 is provided between lands 136 and 156. Also, a vent 162 is provided between lands 92 and 150,

and a suitable vent 166 is provided along piston rod 22 between

chambers

60 and 84.

Referring now particularly to FIG. 2 and 3, it is seen that valve spool 38 is provided with an axial bore 168 extending therethrough, and spool 40 has an elongated cylindrical stem 170 integrally formed on its end adjacent spool 38. Stem 170 is disposed in and extends through bore 168. The stem 170 and the end of spool 38 project outwardly from body 36 and extend into an opening 172 in the bottom of a cup-shaped housing 174 of resilient input member 110. The stem 170 is freely slidable within the bore 168, but the respective elements are spring loaded and resiliently retained into fixed relative positions within the cup 174.

Referring to FIG. 3, it is seen that spool 38 terminates in an outwardly directed flange 176, and a rigid annular collar 178 extending around the body of spool 38 is urged into firm engagement with the flange 176 by a coil spring 180 disposed between the end wall 182 of cup 174 and the collar 178. Movement of the collar 178 away from the end wall 182 is limited by an inwardly directed shoulder 184 formed on a sleeve 186 snugly received within the cup 174 and having its end bearing against wall 182. Sleeve 186 is retained in fixed position within the cup 174 by a cylindrical sleeve 188 and a pair of

sleeves

190, 192, having inwardly directed

shoulders

194, 196, respectively, formed thereon. A cap member 198 is threadably attached to the open end of cup member 174 and rigidly clamps the

sleeve members

186, 188, 190 and 192 against the end wall 182.

To prevent any possible fluid leakage through bore 168 along stem 170, an O-ring seal 200 is positioned within a recess 202 in the end of spool 38. The seal is retained in place by a sleeve 204 having an outwardly directed flange 206 overlying flange 176. The combined thicknesses of

flanges

176 and 206 equals the thickness of flange 184.

A second annular collar 208 is disposed around the end of stem 170, within the cylindrical sleeve 188, and is urged into engagement with the flange 184 and the flange 206 by a resilient coil spring 210 disposed between the collar and the flange 194.

Springs

180 and 210 are each compressed against flange 184 to provide a preload, in either axial direction, for the spool 38, which preload must be overcome before any relative movement between the housing 17 4 and spool 38 may be realized.

The stem 170 terminates in a reduced diameter, threaded portion 212 projecting through the bore 168. The juncture of threaded portion 212 with the body stem 170 defines a shoulder 214 for supporting a flat washer 216 which is rigidly retained on the threaded portion 212 by a locknut 218. An annular collar 220 disposed within the sleeve 190 is urged in the direction of washer 216 and shoulder 196 by a coil spring 222 disposed between the collar and flange 194. Another annual collar 224 is disposed within annual sleeve 192 and is resiliently urged in the direction of washer 216 and flange 196 by a resilient coil spring 226 between the flange 196 and the end wall 228 on threaded cap 198. Washer 216 is the same thickness as the flange 196, and springs 222 and 226 are compressed to resiliently urge

collars

220 and 224 toward one another to clamp the flange 196 and washer 216 therebetween. Thus, the preload in the coil springs resiliently retain the end of the stem 170 in fixed relation within the housing 174. A coupling member 230 is rigidly fixed on the end of threaded cap 198, and has an opening 232 formed therein for pivotally connecting the assembly to a suitable input linkage, now shown.

From the above, it can be seen that the

spools

38 and 40 are spring loaded in fixed relation to one another for simultaneous movement upon any movement of the input member 110. However, in the event of one of the spools becoming jammed, a slight increase in input force will overcome the preload in the spring involved, so that the other spool may be actuated independently of the jammed spool.

By providing two separate servo valve devices, each connected in both conduit systems, parallel control paths are provided from each pressure source to its associated actuator cylinder. Since these parallel paths are controlled by two different servo valve devices which are normally operated simultaneously but operably independently, a very high degree of reliability is achieved. If one valve spool were to become jammed in the closed, or dead center position (the position illustrated in FIGS. 1 and 4), the other spool would still be operable to provide a controlled path for fluid to each of the actuator cylinders, thereby avoiding any possibility of a hydraulic. lock in one system preventing operation of the other. This would be true regardless of which servo valve spool becamejammed.

Referring now to FIGS. 4 and 5 of the drawings, an alternate embodiment of the invention will be described. In this alternate embodiment, the servo valve spools are positioned in separate bores in the valve body, and are coupled together through a mechanical linkage for simultaneous movement. The mechanical linkage, however, provides for independent movement of the respective valve spools in the event of jamming one spool, thereby avoiding the possibility of a hydraulic lock in the same manner as the spring loaded input assembly 110 illustrated in FIGS. 1-3.

The actuator assembly of this alternate embodiment is indicated generally by the reference numeral 300 and includes a cylinder body 312 having a pair of axially aligned

cylinders

314, 316 formed therein. A first piston 318 is mounted in cylinder 314 for axial reciprocating movement therein, and a second piston 320 is similarly mounted in cylinder 316. A common piston rod 322 extends through cylinder body 312 and is rigidly attached to

pistons

318 and 320 for movement therewith and to prohibit relative axial movement between the two pistons. Piston rod 322 extends axially from one end of the cylinder body to form an output element 323 which may be attached, in the manner described above, to a rigid member such as frame structure of an aircraft, now shown. The opposite end of cylinder body 312 is provided with a rigid, outwardly projecting connector element 330 having an opening 332 formed therein for pivotal connection, through suitable linkage, to a moveable control surface of the aircraft.

The servocontrol valve mechanism of this embodiment, indicated generally by the reference number 334, is operable to direct pressure fluid from a source S-l, selectively to either side of the piston 320 in cylinder 316, and simultaneously to direct pressure fluid from source S-2 selectively to either side of piston 318 in cylinder 314. As indicated schematically in FIG. 4, the servo valve mechanism 334 includes a valve body 336 having a first valve spool 338 slidably mounted within a bore 339, and a second valve spool 340 slidably mounted within a second bore 342.

Pressure fluid from source S-1 enters the valve body 336 through an inlet 344 and passes through conduit 346 into chamber 348 defined by the

lands

350 and 352 on valve spool 338. Movement of the valve spool 338 to the left in the direction of arrow 354 in FIG. 4 will permit the pressurefluid to flow from chamber 348 through conduit 356 into the chamber 358 of cylinder 316. Since piston is fixed, the pressure in chamber 358 will tend to force cylinder body 312 to the left in the direction of the movement of valve spool 338. At the same time, fluid in chamber 360 of cylinder 316 will be forced out through conduit 362 into the chamber 364 defined by

lands

352 and 366, then out through

conduits

368, 369, 370 and outlet 371 to be returned to source S-1.

Simultaneously, pressure fluid from the source 8-2 will be directed into the valve body 336 through inlet 372 and pass through the conduit 374 into the chamber 376 defined by the

lands

378 and 380. From the chamber 376, the pressure fluid will pass through conduit 382 into the chamber 384 of cylinder 14 to urge the cylinder body 312 to the left. At the same time, fluid in chamber 386 of cylinder 314 will be urged through conduit 388 into the chamber 390 defined by the

lands

380 and 392 on valve stem 338. From the chamber 390, the fluid may return, through

conduits

392, 393 and outlet 394 to source S-2. Thus, as in the first embodiment, movement of valve spool 338 to the left, in the direction of arrow 354, will direct pressurized fluid from the source S-1 to chamber 358 and simultaneously will direct pressure fluid from source 8-2 to chamber 384 so that

pistons

318 and 320 cooperate to urge the piston rod 322 to the right relative to the cylinder body 312.

In the event of movement of the valve spool 338m the right, in the direction of arrow 396, pressure fluid from the source S-l will flow through the chamber 348 and conduit 362 into chamber 360 of cylinder 316, and fluid in .the chamber 358 will be urged out through conduit 356 to the chamber 398 defined by

lands

350 and 400, then out through conduit 370 to be returned to source S1. Similarly, pressure fluid from source S-2 will flow from chamber 376 through conduit 388 into chamber 386, and fluid from chamber 384 will be urged out through conduit 382 into the chamber 404 defined by the

lands

378 and 406, then through

conduits

408, 392, and 393 to be returned to source S-2.

Valve spool 340 is coupled to valve spool 338 for simultaneous movement therewith through a whiffeltree type linkage comprising a transverse beam 409 having one end pivotally connected to the projecting end of valve spool 338, as by a pin 410, and having its other end pivotally connected, in a similar manner, to valve spool 340 by a pin 411. An input linkage 412 is pivotally connected, as by pin 413, to the center of beam 409 so that any force applied through the input linkage 412 will be equally distributed between valve spools 338 and 340. The pivotal joints formed by

pins

410 and 411 are provided with sufficient clearance to permit limitedmovement of the valve spools with respect to one another, so that, in the event of one spool becoming jammed, the other may still be actuated by a force applied through the input linkage 412. In FIG. 5, an alternative means of providing for this relative movement is illustrated in which an intermediate link 414 is pivotally connected between the beam 409 and the end of valve 340.

It is believed apparent that, if desired, the input linkage 412 could be rigidly connected to beam 409, and the

spools

338 and 340 in turn connected to the ends of the beam by a preloaded spring coupling in a manner similar to that employed in the embodiment illustrated in FIGS. 1-3.

The valve spool 340 is provided with a series of spaced lands corresponding substantially with the lands on valve spool 338 to form a second servo valve connected in parallel with the servo valve defined by the valve spool 338 to supply pressure fluid from source 8-1 to cylinder 316 and from source 8-2 to the cylinder 314. Referring specifically to the schematic illustration in FIG. 4, it is seen that conduit 346 directs pressure fluid from the source S1 into the fluid chamber 415 defined by

lands

416 and 418. This pressure fluid will then flow through conduit 420 into conduit 356, thereby providing an alternate path for the pressure fluid from the source S-l to the chamber 358. At the same time, pressure fluid from source 8-2 will be directed through the conduit 374 into valve chamber 424 defined by

lands

426 and 428. From the chamber 424, this pressure fluid will flow through

conduits

430 and 382 to the chamber 384.

Relative movement of the piston 320 to the right in cylinder 316 will urge fluid out of chamber 360 into the conduit 432, connected in fluid communication with conduit 362, and into the chamber 434 defined by

lands

418 and 436. From chamber 434, this fluid will then flow out through

conduits

368, 369, and 370 to be returned to the source S1. Simultaneously, relative movement of piston 318 to the right in cylinder 314 will urge fluid out of chamber 386 through conduit 440 connected in fluid communication with conduit 388, into the chamber 442 defined by the

lands

428 and 444. From chamber 442, this fluid will flow through

conduits

392 and 393 to be returned to the source 5-2.

In the event of movement of the input linkage 412 to the right, in the direction of arrow 396, fluid under pressure from source S-l will flo w from the chamber 415 through

conduits

432 and 362 into the chamber 360, and fluid from the chamber 358 will flow out through

conduits

356 and 420 into the chamber 448 defined by

lands

416 and 450. Fluid from this chamber 448 will then flow out through conduits 370 and be returned to source S-l. Similarly, fluid from the chamber 424 will be directed through

conduits

440 and 388 into chamber 386, and the fluid chamber 384 will flow out through conduits 383 and 430 into the chamber 454 defined by

lands

426 and 456. Fluid from chamber 454 will then flow through

conduits

458, 392 and 393 to be returned to the source S-2.

A suitable O-ring seal 460 is provided between

lands

366 and 406 on valve spool 33S, and a similar O-ring 462 is provided between

lands

436 and 456 on valve spool 340. Alternatively, as illustrated in FIG. 5, a suitable drain, or vent, 466 may be provided between

chambers

364 and 404, and a similar drain 468 may be provided between

chambers

434 and 454. A suitable drain 470 is also provided along piston rod 322 between

chamber

360 and 384, as illustrated in FIG. 4.

From the above, it should be apparent that either illustrated embodiment of the invention will provide a highly reliable, hydraulically redundant actuator control system which clearly avoids the above-described deficiencies of the prior art devices. By providing parallel paths for the pressure fluid from the first source, through the two servo valve devices, to operate one actuator piston and simultaneously providing parallel control paths for the pressure fluid from the second source through the same two servo valve devices, to operate the second actuator piston, both pistons will be operated in their normal manner even if one of the servo valve spools is jammed closed. Yet, by maintaining the two fluid systems entirely separated, failure of one system, as by loss of fluid pressure, will not in any way interfere with operation of the device through the other system.

While the actuator has been described as a linear reciprocating fluid motor, or cylinder and piston device, it should be apparent that the servo control assembly would be equally operable with various devices. For example, the servocontrol could readily be employed with a rotary hydraulic actuator of the general type illustrated in the US. Pat. No. 3,318,20l. Thus, while I have disclosed and described preferred embodiments of my invention, 1 wish it understood that i do not intend to be restricted solely thereto, but I do intend to include all embodiments thereof, which would be apparent to one skilled in the art and which come within the spirit and scope of my invention.

lclaim:

l. A hydraulic actuator system comprising, in combination, first and second fluid chambers, a piston mounted in each of said fluid chambers, means connecting said pistons for equal, simultaneous movement within their respective fluid chambers, a first source of pressure fluid, first conduit means connecting said first source to said first fluid chamber, a second source of pressure fluid, second conduit means connecting said second source to said second fluid chamber, a servo valve assembly operatively connected in said first conduit means and providing controlled parallel fluid circuits between said first source and said first fluid chamber, said servo valve assembly also being operatively connected in said second conduit means and providing controlled parallel fluid circuits between said second source and second fluid chamber, and signal input means operating said servo valve assembly to control the flow of pressurized fluid through each of said fluid circuits simultaneously.

2. The hydraulic actuator system defined in claim 1 wherein said servo valve assembly comprises first and second servo valves each operatively connected in said first conduit means and in said second conduit means, said first and said second servo valves cooperating to provide said parallel circuits between said first source and said first fluid chamber and between said second source and said second fluid chamber.

3. The hydraulic actuator system defined in claim 2 wherein said signal input means comprises an input assembly normally applying equal operating loads to said first and said second servo valves to thereby synchronize operation of the two valves.

4. The hydraulic actuator system defined in claim 3 wherein said signal input means further comprises means for operating one of said servo valves independently of operation of the other of said servo valves in the event said other servo valve becomes inoperable.

5. The hydraulic actuator system as defined in claim 4 wherein said first and said second servo valves are positioned in side-byside relation, and said signal input means comprises a whiffletree operatively connected to each of said servo valves for operation thereof.

6. The hydraulic actuator system as defined in claim 4 wherein said signal input means further comprises a prestressed resilient connector assembly connected to each of said servo valves, said connector assembly being deformable by either of said servo valves only upon said valves encounter ing a substantial increase in resistance to operation.

7. A hydraulic actuator system comprising, in combination, first and second fluid chambers, a pair of pistons mounted one in each of said fluid chambers, an output member, means connecting said pistons to said output member for simultaneous movement therewith, a first source of pressure fluid, first conduit means connecting said first source to said first fluid chamber, a second source of pressure fluid, second conduit means connecting said second source to said second fluid chamber, first servo valve means connected in said first eonduit means and providing a controlled circuit for pressure fluid between said first source and said first fluid chamber and connected in said second conduit means and providing a controlled circuit for pressure fluid between said second source and said second fluid chamber, second servo valve means connected in said first conduit means in parallel with said first servo valve and providing a second controlled circuit for pressure fluid between said first source and said first fluid chamber and in said conduit means in parallel with said first servo valve means and providing second controlled circuit for pressure fluid between said second source and said second fluid chamber, signal input means operating said first and said second valve means, said signal input means including means synchronizing operation of said first and said second servo valve means to simultaneously direct pressurized fluid through each of said controlled circuits.

8. The hydraulic actuator system defined in claim 7 wherein said first and said second servo valve means each comprise a valve spool moveably mounted within a valve body, a plurality of ports in said valve body including first inlet and outlet ports connected to said first source, second inlet and outlet ports connected to said second source, a first pair of distribution ports connected to said first fluid chamber, and a second pair of distribution ports connected to said second fluid chamber, said valve spool being moveable within said valve body to simultaneously control flow through said first inlet and outlet ports and said first distribution ports between said first source and said first fluid chamber and through said second inlet and outlet ports and said second distribution ports between said second source and said second fluid chamber.

9. The hydraulic actuator system as defined in claim 8 wherein said valve spools in said first and said second servo valves are slidably mounted within axial bores in said valve body to control the flow of pressure fluid through said inlet and outlet ports and said distribution ports.

10. The hydraulic actuator system defined in claim 9 wherein said valve spools are slidably mounted in coaxial relation in a single bore in a common valve body.

11. The hydraulic actuator system defined in claim 9 wherein said input means comprises linkage means independently connected to said valve spools in said first and said second servo valves for simultaneous movement, said linkage means including means moving one of said valve spools independently of movement of the other valve spool in the event of said other valve spool requiring excessive operating force.

12. The hydraulic actuator system defined in claim 11 wherein said means independently connecting said valve spools include prestressed resilient connecting means.

Claims

1. A hydraulic actuator system comprising, in combination, first and second fluid chambers, a piston mounted in each of said fluid chambers, means connecting said pistons for equal, simultaneous movement within their respective fluid chambers, a first source of pressure fluid, first conduit means connecting said first source to said first fluid chamber, a second source of pressure fluid, second conduit means connecting said second source to said second fluid chamber, a servo valve assembly operatively connected in said first conduit means and providing controlled parallel fluid circuits between said first source and said first fluid chamber, said servo valve assembly also being operatively connected in said second conduit means and providing controlled parallel fluid circuits between said second source and second fluid chamber, and signal input means operating said servo valve assembly to control the flow of pressurized fluid through each of said fluid circuits simultaneously.

5. The hydraulic actuator system as defined in claim 4 wherein said first and said second servo valves are positioned in side-by-side relation, and said signal input means comprises a whiffletree operatively connected to each of said servo valves for operation thereof.

6. The hydraulic actuator system as defined in claim 4 wherein said signal input means further comprises a prestressed resilient connector assembly connected to each of said servo valves, said connector assembly being deformable by either of said servo valves only upon said valves encountering a substantial increase in resistance to operation.

7. A hydraulic actuator system comprising, in combination, first and second fLuid chambers, a pair of pistons mounted one in each of said fluid chambers, an output member, means connecting said pistons to said output member for simultaneous movement therewith, a first source of pressure fluid, first conduit means connecting said first source to said first fluid chamber, a second source of pressure fluid, second conduit means connecting said second source to said second fluid chamber, first servo valve means connected in said first conduit means and providing a controlled circuit for pressure fluid between said first source and said first fluid chamber and connected in said second conduit means and providing a controlled circuit for pressure fluid between said second source and said second fluid chamber, second servo valve means connected in said first conduit means in parallel with said first servo valve and providing a second controlled circuit for pressure fluid between said first source and said first fluid chamber and in said conduit means in parallel with said first servo valve means and providing second controlled circuit for pressure fluid between said second source and said second fluid chamber, signal input means operating said first and said second valve means, said signal input means including means synchronizing operation of said first and said second servo valve means to simultaneously direct pressurized fluid through each of said controlled circuits.