US3411411A - Redundant actuator valving using parallel and serial connected valves - Google Patents

Description

Nov. 13, 1968 J, J. FLECK ET AL 3,411,411

REDUNDANT ACTUATOR VALVING USING PARALLEL AND SERIAL CONNECTED VALVES 2 Sheets-Sheet 1 Filed Nov. 2, 1965 FIG.|

4o 20 i L g 4. F1 '2 28 n I Q A A E i g 1] 55 G c C l g 0 0 F F O L a ,u 212 i f .8 r 30 Nov. 19, 1968 J.IJ.FLECK ETAL 3,411,411

REDUNUANT ACTUATOR VALVING USING PARALLEL AND SERIAL CONNECTED VALVES Filed Nov. 2, 1965 2 Sheets-Sheet 2 VARIABLE HYDRAULIC RESISTANCE SCHEMATIC United States Patent 3,411,411 REDUNDANT ACTUATOR VALVING USING PARALLEL AND SERIAL CONNECTED VALVES Joel J. Fleck, New York, and David Hogan, Binghamton,

N.Y., assignors to General Electric Company, a corporation of New York Filed Nov. 2, 1965, Ser. No. 506,058 6 Claims. (CI. 91-30) ABSTRACT OF THE DISCLOSURE Redundant actuator valving for a ram type reversible hydraulic motor in which redundancy to protect the system against failure to turn on is part of the reversing apparatus and is accomplished by use of separately controlled parallel hydraulic channels and protection against failure to close is accomplished by use of separately controlled series connected valves in each of the parallel hydraulic channels. The specific arrangement includes control of both high and low pressure conduits of one of the parallel channels simultaneously by crossing both conduits through the same pair of valving devices to actuate pairs of series connected valves simultaneously.

This invention is concerned with redundant hydraulic control apparatus. The invention utilizes redundancy to insure proper control system operation after a control valve element fails by means of passive failure correcting operation. The apparatus controls a two-port hydraulic actuator component such as a piston mounted in a cylinder, or an equivalent component, which is revers ibly driven at variable rates.

Like redundant analog devices generally, redundant hydraulic actuator apparatus faces the problem of having continuous signals to be compared so as to determine a failure. A very different situation exists as compared with triply redundant electronic digital apparatus, for example, where the single value held in common on a majority of independent parallel lines can be treated as a reference value. Digital signals generally require a signal level to be within one of two bands of signal levels to have the correct value. On the other hand, all analog signals can be considered to depart from the correct signal value to some degree, with the problem being neutralized the effects of an element producing a signal outside of accept able limits. This allows the apparatus to operate over a band of values which is continuous, as is inherent in analog devices. For most standard hydraulic actuator controls, this means that the hydraulic supply must be metered or varied continuously, as opposed to merely making ON-OFF connections.

Also, actuators have specific connection requirements. In selecting the proper direction of actuator operation, it is necessary to both connect the hydraulic supply line to the proper port and isolate the hydraulic return line from that port. The reverse operations must be performed for the other load port. Therefore, valve devices must control actuator drive direction by being able to reverse the connections from the supply and return lines to the input ports. This directional function aspect is analogous to the electrical function performed by a double-pole, double-throw switch which is wired to reverse the electrical connections between two pairs of terminals. As an example of the difficulties involved with implementing redundancy in this area, any arrangement of valve devices where a single device can determine the direction of actuator operation is unsatisfactory. The conventional spool valve having two output ports connected to an See actuator load can not, in general, be used in a redundant component if a failure by operation in the wrong direction must be guarded against.

In general, adoption of redundancy more than doubles the complexity of the apparatus involved. For every device for which failure is permitted, another device must be provided and apparatus employed to insure that a failed device does not prevail. For example, apparatus can be triplicated and the highest and lowest value output automatically discarded. Redundancy inherently increases equipment cost, weight, complexity, etc., by a very substantial amount. With the additional possibilities for device failures because of the extra devices, it is apparent that the total number of failures can be increased. One important contribution to this is that completely new functions like voting are usually required which are not required at all in non-redundant systems. This results in the use of additional kinds of devices and a certain amount of additional design costs, etc. Because of these kinds of considerations, simplicity is a critical characteristic in redundant systems, particularly mechanical apparatus which can not normally me microminiaturized.

Accordingly, it is an object of the invention to provide passive redundant control valves for a high performance actuator which perform line reversing and metering with a small number of valve devices.

It is another object of the invention to provide redundant actuator valve apparatus which requires neither failure detecting devices for failure free operation nor switching devices for altering connections in accordance with a failed device.

It is a further object of the invention to provide redundant actuator valve apparatus which requires only conventional valve elements and hydraulic line interconnections.

In accordance with certain aspects of the invention, redundant hydraulic actuator valve apparatus is provided which uses only metering valves to provide a hammock net type of system. (Note Reliable Circuits Using Less Reliable Relays, by Shannon and Moore, Jour. Franklin Inst., 1952, vol. 262, pp. 281-297.) At least four valve devices (having respective torque motors) are used, each device having a plurality of conventional fluid metering valve elements. Four sets of metering valve elements are provided and each set is comprised of four metering valve elements in a hammock net configuration These sets form two series pairs in two .parallel branches between a hydraulic supply line and a return line. A twoport load actuator such' as a conventional piston actuator is connected between the midpoints of the series parallel sets. It has been discovered that by metering in two of the four sets at any one time, both proper proportional response and the proper direction of the output motion is assured.

The invention, together with further objects and advantages thereof, may best be understood by referring to the following description taken in conjunction with the appended drawings in which like numerals indicate like parts and in which:

FIGURE 1 is a schematic diagram illustrating a preferred embodiment of the invention.

FIGURE 2 is a plan view, partially in cross-section, of a FIGURE 1 redundant actuator.

FIGURE 3 is a bridge diagram illustrating the principle of operation of the FIGURE 1 actuator.

FIGURE 4 is a schematic drawing of a second embodiment of the invention shown in FIGURE 2 and diagramed in FIGURE 1.

'Ilhe preferred form of the invention utilizes four identical valve devices 10, 20, 30 and 40 for controlling a load consisting of actuator component 50 having a piston rod 55. Each valve device is a multi-element spool valve taving four lands and seven ports. A solenoid motor 11 for device drives the spool 12 by means of rod 18 ;0 that the upper center land 14 selectively meters fluid hrough either port A or B in valve sleeve 17, in ac- :ordance with the spool displacement. Similarly, the lower :enter land selectively meters fluid to ports C or D. The ports E and F between the lands 13 and 14 and 15 and 16, respectively, are coupled to the hydraulic supply line 51 and the hydraulic return line 52. In the identical valve devices 20, and 40, the respective components 21-28, 31-38, and 41-48, operate in the same manner as the corresponding components 1118 in valve device 10. For valves 10 and 30 the respective outlet ports G are connected together, and valve devices 20 and similarly have connected. outlet ports G. Accordingly, each port G is selectively coupled to either the hydraulic supply line 51 or hydraulic return line 52 by passing through a pair of valve elements in each of the pair of parent valve devices. Therefore, from each port of hydraulic actuator component there is a network of four valve elements in going to the hydraulic supply line 52 and a similar network in going to the hydraulic return line 52. As diagrammed in FIGURE 3, there are four networks altogether, forming four sets of metering valve elements between the four junctions. The junction points are formed by the pair of supply terminals 51 and 52 and the load terminals formed by the ports 53 and 54- of actuator 50.

Shown in FIGURE 1 is a differential pressure gauge 60, connected between two corresponding lines which connect valve 10 with valve 20 and valve 30 with valve 40. This gauge is used to sense the presence of a fault in any valve. As shown, it is connected between corresponding lines which fill the left side of the actuator 50, al-

though it could be connected between any two corre- 5 sponding lines. Whenever the left side is filling, there will be an appreciable pressure drop across the gauge if any one of the four valves is malfunctioning, unless the valve is stuck in the fill left position. Whenever the right side is filling, an appreciable pressure ditference will develop across the gauge if one of the valves is stuck in fill left. Should the ram be stationary, the gauge will show a large pressure difference unless the fault happens to be a valve stuck in the center position. Therefore, the gauge 60 will indicate an appreciable pressure for an appreciable fraction of the time in the presence of any single valve fault whatsoever. Note that the presence of gauge 60 is not essential for operation; it is used for monitoring purposes only.

In order to drive piston rod 55 to the right, the left side of the cylinder of actuator component 50 is filled through inlet 53. The spools 12 and 32 of valves 10 and 30 are moved up by their motors 11 and 31, while the spools 22 and 42 of valves 20 and 40 are driven down. This results in a parallel connection from hydraulic supply line 51 through ports E and A of valves 20 and 40, which are in series with parallel ports B and G of valves 10 and 30. The hydraulic return line 52 is connected in parallel through ports F and D of actuators 10 and 30, which are in series with parallel ports C and G of valves 20 and 40 that connect to the inlet port 54 on the right side of actuator component 50. In order to drive piston rod 55 to the left, the spools 12, 22, 32, and 42 are moved in the reverse direction; piston rod 55 is then driven in the reverse direction as the right side of the cylinder of actuator component 50 is filled.

The identical valve devices 10, 20, etc. may, for the purposes ofdescription, be regarded as five port valve units by considering the A and B and also the C and D double ports as a single port. In this way each set of three consecutive ports may be regarded as a three-way valve, as for example, ports G, A and C can be considered a three-way valve with G being the common port, or A-E-G can be considered a three-way valve with A the common port. In another way, by considering cooperating pairs of valve devices, as for example 10 and 20, the system can be described in terms of three-way valves with each valve device 10 and 20 constituting two threeway valves. The set of two valve devices would, therefore, amount to four three-way valves in which one pair have their common ports A interconnected and another pair have their common ports C connected, and in which the two three-way valves located in each valve device are further joined by having their adjoining branch ports constitute a single port G. The same set of two valve devices can also be regarded as a pair of three-way valves for supplying and exhausting the motor chamber wherein in each case G would be the common port and A and C the branch ports, and in which ducting between the branch port and the hydraulic line is interdicted by a two-way valve which is physically attached to the opposite three-way valve. In this sense, the three-way valve at G of device 10 is supplying and exhausting the motor chamber at 53 and when open through branch port B to high pressure conduit 51 has its supply line interdicted or interrupted by two-way valve A-23-E operation of which is controlled by valve device 20. By regarding the valve devices of this invention in any of these several ways, it is possible to describe them in terminology commonly used in the art.

A second embodiment of the invention is shown in FIGURE 4 in schematic form. As compared with the FIGURE 1 embodiment, this valve system appears to be simpler. However, this appearance is only because of the topology of the connections. Actually, the second embodiment has the disadvantage of requiring two different types of valves. Valves and are 2-land 7- port spool valves and valves 120 and are 3-land 6- port spool valves. These valves form a bridge network of valve elements which is functionally identical with the bridge of FIGURE 1.

It will be evident to those skilled in the art that the invention may take a large number of forms. In its basic form, the invention requires the bridge illustrated in FIG- URE 3. That is, a hammock net of servo valve metering elements is connected between each adjacent pair of the four terminals formed by two hydraulic source lines and two load ports. Where the pressures at the source lines can not be reversed, directional control of an actuator must be achieved by connecting each load port to a selected one, and only one, of the two source lines. It has been found that this switching function and metering can be performed with passive redundancy with four valve devices. With the hammock net connections, the metering valve elements perform the switching operations in addition to metering. It is a sufficient condition for failure correction to have, between each load port and each supply line, a pair of parallel connected valve elements with a valve element in series with each of the parallel valve elements.

A diiferential pressure gauge 60' is shown in FIG- URE 4. It serves the same purpose of error sensing as does the gauge in FIGURE 1. Note that another configuration can be obtained from both FIGURES 1 and 4 by connecting lines across where the gauge is inserted and across the other three possible places where it might be inserted. In this case, error sensing can be accomplished by placing a flow meter in one of the lines thus added. The only functional difference (other than a different error sensor) between the configurations thus derived and the configurations shown in FIGURES 1 and 4 is that they tolerate different combinations of two valve faults. There are 54 possible combinations of four valves taken two at a time, each of which can fault into three principal modes (stuck left, stuck center, and stuck right):

Of these 54 possibilities, FIGURE 1, as it stands, can

tolerate 22, and FIGURE 1 modified by the four extra connections can tolerate 32. Thus, it would appear that addition of the four extra connections will improve the reliability. However, inspection shows that the extra combinations of two faults all involve at least one valve stuck center, which is probably not as likely as sticking into fill left or into dump left. Consequently, the reliability advantage of adding the four extra connections is probably marginal.

It is evident from inspection of the FIGURE 3 diagram that a valve failure will cause a reduction by half of the rate at which piston 50 is driven, if the servo loop of which the actuator forms a part does not compensate therefor such as by an electrical gain change. However, the actuator has excellent hardover failure characteristics so that transient effects which accompany failures are not serious. With a single failure of a metering valve element, there are always valve" elements both in series and in parallel with the failed element. While the invention is particularly useful in high performance control systems using hydraulic oil-s, it can be employed with any fluid devices including gas operated valves.

While particular embodiments of the invention have been shown and described herein, it is not intended that the invention be limited to such disclosure, but that changes and modifications can be made and incorporated within the scope of the claims.

What is claimed is:

1. Redundant hydraulic actuator valving comprising:

(a) a double acting hydraulic motor;

(b) a first three-way valve for supplying and exhausting one chamber of said motor;

(c) a second three-way valve for supplying and exhausting the other chamber of said motor;

(d) both three-way valve being connected to high and low pressure hydraulic supplies;

(e) additional valve meansnconnected for operation with each three-Way valve and interdicting flow of hydraulic fluid between the other said three-way valve and said supplies;

(f) a second identical set of first and second threeway valves and additional valve means connected between said motor and said supplies in parallel to the first set of three-way valves and additional valve means.

2. Redundant valving for control of a hydraulic motor comprising:

(a) a first set of two three-way valves each for supplying and exhausting one motor chamber of a double acting hydraulic motor; I

(b) two two-way valves connected to each three-way valve for joint operation therewith;

(c) each said two two-way valve being in series with the opposite three-way valve, one with each alter nately acting port whereby failure of one said threeway valve and its connected two-way valves in the open position will not prevent the other from stopping the motor; and

(d) at least two additional set of two three-way valves and four two-way valves identical to said first set connected in parallel with said first set whereby failure of one three-way valve and connected twoway valves in the closed position will not prevent actuation of the motor.

3. Redundant actuator valving for control of a double acting hydraulic motor comprising:

(a) a set of four three way valves (1) connected in two series pairs by conduits between the common ports of the valves of each pair,

(2) connected in two operational pairs by two valve actuating means each of which means is connected to one valve of each of said series pairs,

(3) each operational pair of valves having one port of each valve other than the common port connected in hydraulic communication with one chamber of said motor and the second ports other than the common port connected one each to low and high pressure hydraulic supply whereby simultaneous operation of said actuating means will activate or stop said motor and operation of only one said means to close its operational pair of valves will stop said motor;

(b) an identical second set of four three-way valves connected in parallel between said motor and said supply.

4. Redundant actuator valving for a double acting hydraulic motor comprising:

(a) a first five port valve wherein:

( 1) each combination of three consecutive ports constitutes a three-way valve,

(2) the center port is in communication with one chamber of said motor,

(3) of the two end ports, one communicates with high, the other low pressure hydraulic conduits,

(b) a second five port valve identical to said first five port valve with its center port in communication with the other chamber of said motor to form a first set of five port valves;

(c) the corresponding remaining intermediate ports of said first and second valves being connected to each other whereby simultaneous actuation of said first and second valves will select and place pairs of said three-way valves in series to actuate said motor and closing of said first or second valve will stop said motor; and

(d) at least one additional identically arranged set of first and second five port valves in parallel with said first set whereby actuation of any one set of five port valves will actuate said motor.

5. Redundant actuator valving for a double acting hydraulic motor comprising:

(a) a first five port valve wherein:

(1) each combination of three consecutive ports constitutes a three-way valve,

(2) the center port constitutes the valve output port supplying and exhausting one chamber of a double acting hydraulic motor,

(3) the two end ports constitute respectively high and low pressure hydraulic supply ports;

(b) a second five port valve identical to said first five port valve with its center port constituting the valve output port for supplying and exhausting the other chamber of said motor "to form a first set of five port valves;

(c) the corresponding remaining intermediate ports of said first valve and said second valve being connected to each other whereby simultaneous reverse actuation of said first and second -valves in either direction will select and place pairsgof said three-way valves in series to open parallel paths within said set of valves between a high pressure supply port of one five port valve and the valve outlet port of the other five port valve and between the outlet port of said other five port valve and the low pressure hydraulic supply port of said one five port valve and closing either said first or second valve will interdict said paths;

(d) at least one additional identically arranged set of first and second five port valves connected in parallel with said first set whereby actuation of any one set of five port valves will open at least one pair of said parallel paths.

6. Redundant actuator valving for a double acting hydraulic motor comprising:

(a) a first valve having at least five ports wherein (1) each combination of middle, end and an intervening intermediate port and of middle and adjacent to middle ports constitutes a three-way valve,

(2) the center port is in communication with one chamber of said motor,

(3) of the two end ports, one communicates with high, the other low pressure hydraulic sources;

(b) a second valve identical to said first valve having at least five ports with its center port in communication with the other chamber of said motor to form a first set of valves;

(c) the remaining intermediate ports of said first and second valves being connected to each other whereby simultaneous actuation of said first and second valves will select and place pairs of said three-way valves in series to actuate said motor and closing of either said first or second valve will stop said motor;

(d) at least one additional identically arranged set of first and second valves in parallel with said first set whereby actuation of any one set of valves will actuate said motor.

References Cited UNITED STATES PATENTS 2,826,896 3/1158 Glaze 91-411 2,921,562 1/1960 Westbury 916 3,222,993 12/ 1965 Rasmussen 91-20 3,065,739 11/1962 Boroson 91-445 3,257,911 6/1966 Garnjost 91411 3,270,623 9/1966 Garnjost 91-411 3,043,331 7/1962 Petus 137-458 MARTIN P. SCHWADRON, Primary Examiner.

B. L. ADAMS, Assistant Examiner.

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