United States Patent Williams Feb. 5, 1974 [54] MULTIPLE HYDRAULIC ACTUATOR 2,866,476 12/1958 Orloff r. 9lf4l7 R Inventor: J l ams 2,962,002 ll/l960 Hayner 1. 91/417 R Wolverhampton, England Primary Examiner-Martin P. Schwadron [73] Asslgneez Dowty Boulton Paul Limited, A i mm E i A M Z i Wolverhampton gland Attorney, Agent, or Firm-lrvin S, Thompson ct al. [22] Filed: Dec. 13, 1971 2! Appl. No.: 207,302 {57] ABSTRACT An electro-hydraulic control system in which two similarly signalled electro-hydraulic servo-valves are pro- [301 Foreign Apphcauoq prmmy Data vided to control a hydraulic actuator. In order to de- 1 1970 Urea 58885/70 tect failure or inaccuracy of operation of either servovalve the present invention provides an actuator hav- [52] Cl 91/3 91/166 ing a working space, connections from the working 51 I 91/417 R space to a port of one servo-valve and the correspond- 58 F Flsb 13/02 Flsb 15/17 ing port of the other servo-valve whereby the actuator 1 mid of Search 91/165 is under the simultaneous control of both servo-valves,

91/1 biassing means urging the actuator in a direction opposite to the hydraulic force generated in the working {56] References cued space and an error means connected between the UNlTED STATES PATENTS other two ports of the servo-valves to generate an 3,472,125 10/1969 Noble 91/417 R error signal when there is a substantial pressure differ- 2,916,015 12/1959 Jeffery t t 91/417 R ence between the said ports. The error signal may be ,667,344 6/1972 Westburym. 91/3 used to take any safety action appropriate to the use 3,452,645 Barttrop A of [he actuaton 3,426,650 2/1969 Jenney 9l/363 A 2,894,743 7/1959 Dubinsky U 9l/l65 10 Claims, 2 Drawing Figures PATENTEU FEB 5 1974 Nw aw mm Q mm m @m MULTIPLE HYDRAULIC ACTUATOR This invention relates to an electro-hydraulic control system, in which from the view point of safety two or more similarly signalled electro-hydraulic servo-valves are provided to control a hydraulic actuator, and means are provided to compare the operation of the servo-valves to provide an error signal from which safety action may be taken if the operations of the servo-valves at any instant become substantially dissimilar.

For the purpose of this specification an electrohydraulic servo-valve is defined as an electric motor adapted to receive an electric signal and valve means controlled by the motor to adjust or tend to adjust differentially the liquid pressures at two ports. Depending on the characteristics of the circuit or circuits fed by the two ports, the flow of liquid at the ports may alter the differential pressures. Thus the action of the electric motor could be to adjust differentially the liquid flows at the ports, or to adjust differentially the pres sures and the liquid flows at the ports.

This invention is particularly although not exclusively applicable to electro-hydraulic control systems having a plurality of hydraulic actuators mechanically connected to provide one actuator function and in which each actuator is controlled by two or more similarly signalled electro-hydraulic servo-valves. On occurrence of an error signal the safety action could be the bypassing of one actuator.

In accordance with the present invention, an electrohydraulic control system includes an actuator having a working space, a pair of electro-hydraulic servo-valves, each arranged to receive an electric signal, connections from the working space of the actuator to a port of one servo-valve and the corresponding port of the other servo-valve, whereby the actuator is under the simultaneous control of the two servo-valves, means acting on the actuator for biassing it in a direction opposite to the hydraulic force generated in the working space, and an error means connected between the said other two ports of the servo-valves and arranged to respond when a substantial pressure difference exists between the said other two ports to provide an error signal.

Latching means may be provided to maintain the error signal if the pressure difference between the said two ports falls from said substantial pressure difference to a lower pressure difference.

The actuator may have two opposed working spaces, the one of which is connected to said one ports and the other of which is connected to constant hydraulic pressure to provide the biassing force.

The said other working space may be of smaller effective section than the one working space and the constant hydraulic pressure may be higher than the average pressure at the said one ports. The pressures at the said ports may be variable reductions of the high pressure supply.

A by-pass valve may be operated by the error signal to render the actuator incapable of exerting any hydraulic force.

The error signal may comprise an increase in hydraulic pressure in the passage extending from the error means.

One embodiment of the invention will now be described with reference to the accompanying diagrammatic drawings in which,

FIG. 1 illustrates the electro-hydraulic control system diagrammatically in its normal operating condition, and

FIG. 2 illustrates the error valve device of FIG. I after action has been taken in response to a difference in operation of the servo-valves.

The actuator itself comprises a piston 1 slidable within a cylinder 2 and a piston rod 3 of substantial section extending from the piston in a sealed manner through one end of the cylinder. A pair of working spaces 4 and 5 are thus defined, the space 4 being that opposite to the piston rod so that hydraulic pressure may act over the whole area of the piston and space 5 being that adjacent to the piston rod so that hydraulic pressure may act over the area of the piston less the area of the piston rod. The working space 4 is the actuator working space whilst the working space 5 and the hydraulic pressure acting therein on the piston 1 form the means for biassing the actuator.

The forces acting on the piston by virtue of pressure in the two working spaces are opposite to one another. The piston rod 3 includes a connecting eye 6 by which it is connected to a common output member. The actuator shown forms part of a multiple actuator unit in which a plurality of actuators as shown in FIG. 1 are connected for operation of one common output member.

A pair of electro-hydraulic servo-valves 7 and 8 are provided of exactly similar construction. The servovalve 7 comprises a moving hydraulic jet 9 located within a chamber 11 and movable transversely of the jet direction under the operation of an electric force motor 12 of which the electric winding only is shown. The jet 9 receives hydraulic liquid at high pressure from a pipe 13 and directs this jet towards a pair of delivery ports 14 and 15, the pressures developed by the two delivery ports 14 and 15 being dependent on the position of the jet 9 and thereby on the electric signal fed to the force motor 12. Transverse adjustment of the jet will alter the port pressures differentially. The chamber 1 l is connected to drain through a return pipe 16.

The servo-valve 8 similarly includes a moving jet which receives liquid at pressure from the pipe 13 and delivers liquid through a pair of delivery ports 17 and 18. The chamber within servo-valve 8 is similarly connected to the return pipe 16. The two delivery ports 14 and 17 are the first delivery ports of the two servovalves and these are connected together by means of a pipe 19 to the first working space 4 of the actuator. By this arrangement the pressures developed at the two first delivery ports are maintained at the same value to act jointly in the first working space 4.

An error means formed by error valve 21 receives the pressures of the two second delivery ports 15 and 18 through pipes 22 and 23. Within the error valve 21, these pressures act in the two end portions of a cylinder 24 to exert opposing forces on a piston valve member 25. The piston valve 25 includes a waisted portion 26 in constant connection with a high pressure connection 27 supplied from any suitable source. Springs 28 within the two ends of the cylinder 24 act on the piston 25 to hold it in the postion illustrated in FIG. 1.

The error valve 21 controls the operation of a by-pass valve 29 which comprises a cylinder 31 within which a three-landed piston valve member 32 is slidably mounted. The two ends of the cylinder 31 form working chambers 33 and 34. The chamber 33 is connected by pipe 35 to a pair of ports 36 and 37 opening into the logic valve cylinder 24. The ports 36 and 37 are normally closed by the lands of the piston 25, but a predetermined movement of the piston 25 in either direction will connect one or other of the ports 36 or 37 to the waisted portion 26 for connection to the high pressure supply 27. The pipe 35 connects through a restrictor 38 to a port 39 opening into the woring space 34.

The piston 32 comprises three lands 4!, 42 and 43 separated by waisted portions 44 and 45. A port 46 opens into the waisted portion 45 from the pressure pipe 27. Another port 47 connects from the waisted portion 45 to the pipe 13 to carry high pressure to the servo-valves 7 and 8 and to the working space 5 of the actuator. The pipe 19 connects at port 48 into the working space 44. A port 49 connects from the working space 44 to the working space 4 of the actuator. The working space 34 of the by-pass valve is directly connected to reservoir through a pipe 51 which is also connected to a port 52 in cylinder 31 normally closed by the land 42. A spring 53 in the working space 34 acts on the piston 32 to urge it fully to the right as shown in FIG. I in its normal operational position.

For normal operation, a pair of separate electric control circuits carry similar electrical controlling signals to the force motors of the servo-valves 7 and 8 causing similar deflections of the moving jets, thus generating similar pressures in the ports and 18 on the one hand and the ports 14 and 17 on the other hand. Also the pressure differences between ports 14 and 15 will be similar to the pressure differences between ports 17 and 18. The ports 14 and 17 of the two servo-valves are connected together through a common pipe 19, port 48 of the by-pass valve. working space 44 and port 49 into the working space 4 of the actuator when the by-pas piston 32 is in its normal position. High pressure fed through pipe 27 passes through the working space 26 of the error valve, and ports 46 and 47 of the by-pass valve for connection to pipe 13. From pipe 13 high pressure liquid enters both of the servo-valves 7 and 8 and also the working space 5 of the actuator.

During normal operation, the working spaces 33 and 34 of the by-pass valve are maintained at reservoir pressure whereby the spring 53 will hold the piston 32 in its right-hand position as shown in FIG. 1. For normal operation the pressures at the ports 14 and 17 will vary similarly to one another by virtue of the application of similar electric signals to the servo-valves 7 and 8 and these two pressures are jointly connected by the pipe 19 for feeding to the working space 4 of the actuator to cause movement of the piston 1 in accordance with the variation of the electric signals. Hydraulic liquid at high pressure from pipe 27 acts in working space 5 over the cross-sectional area of piston 1 less the cross-sectional area of piston rod 3 producing a constant biassing force acting on the piston to the left in FIG. 1. The variable pressure from pipe 19 will act in working space 4 over the cross-sectional area of piston 5 producing a variable force on the piston acting to the right in FIG. 1. For a particular pressure in working space 4, lower than the high pressure in working space 5, the hydraulic forces acting on the piston 5 are equal and opposite producing a zero hydraulic force on piston rod 3. For pressures in space 4 above the particular value, piston 1 will exert a force to the right on rod 3 and for pressures in space 4 below the particular value,

piston 1 will exert a force to the left on rod 3. Since the electro-hydraulic-servo-valve structures 7 and 8 provide variable pressures at ports l4, l5, l7, 18, which in practice are variable reductions of the high pressure supplied to both the swinging jets and to the working space 5, it will be seen that movement of the swinging jets by hydraulic signals to the force motors of the servo-valves 7 and 8 can cause application of hydraulic force to the piston rod 3 either to the left or to the right, the actual direction of the force depending on the values of signals. Movement of piston l to the right causes displacement of liquid at high pressure from working space 5 into the high pressure pipe l3, and movement of the piston l to the left causes displacement of liquid from chamber 4 through ports 14 and 17 of the servovalves 7 and 8 and into the return pipe 16. The ports 15 and 18 under the control of the electric signals in the servo-valves will vary differentially having regard to the ports 14 and 17, but at any instant for normal operation, the pressures at the ports 15 and 18 should be the same as one another. These pressures are fed to the two ends of the error valve cylinder 24 and will act similarly and oppositely on the piston 25 which will therefore remain in its central position.

Assume now a fault in operation. Such fault may occur in either servo-valve 7 or 8 or in the electric means for feeding the electric control signals to the servo-valves. Wherever the fault occurs it will almost certainly result in difference of operation of the two servovalves and therefore in a difference in the pressure differences of the ports 14 and 15 on the one hand and ports 17 and 18 on the other hand. Since ports 14 and 17 are connected together by the common pipe 19, the difference of the two pressure differences must show as differing pressures at the ports 15 and 18 which when fed to the two ends of the error valve cylinder 24 will cause movement of piston 24 in one direction or the other. lrrespectively of the direction of movement, when the pressure difference at the ends of the erorr valve cylinder exceeds a predetermined substantial value, one of the ports 36 or 37 will be connected to pressure, feeding pressure from the supply 27 through pipe 35 to the working space 33 of the bypass valve moving the by-pass valve piston 32 to the left to the position shown in FIG. 2. High pressure in pipe 35 thus forms the error signal. During such movement the land 43 will extend the working space 33 so that the port 46 is connected to port 35 thus permanently maintaining the working space 33 at high pressure and preventing the possibility that the by-pass valve will return to its normal position even if the operational fault at one or the other of the servo-valves should correct itself. Thus the relative arrangement of port 46 and land 43 forms a latching means to retain the error signal in working space 33. The waisted space 45 now connects the reservoir port 52 to the two ports 47 and 49 thus connecting both working spaces of the actuator to reservoir pressure so that little or no force can be exerted on the actuator piston rendering it capable of free movement in either direction. Connection of the port 47 to reservoir will also connect the pipe 13 which supplies high pressure to the two servo-valves to reservoir thus rendering the two servo-valves inoperative. The lands 41 and 42 will close respectively the ports 39 and 48 thus disconnecting the pipe 19 from the working space 4 and also cutting off flow through restrictor 38 from ports 35, 36 and 37. After the movement of the by-pass valve to the FIG. 2 position, the cutting off of high pressure to the two servo-valves through the pipe 13 will remove the pressure difference fed from ports 15 and 18 to the two ends of the error valve and therefore the error valve piston 25 will return to its central position in which it closes ports 36 and 37. The function of the restrictor 38 is normally to provide a connection between the working spaces 34 and 33 so that there is no hydraulic force tending to move the by-pass valve piston 32 when ports 36 and 37 are closed by the error piston, but during emergency conditions the restrictor 38 will enable high pressure to be generated in the working space 33 of the by-pass valve with a small leakage back to reservoir through port 39. Immediately the by-pass valve moves over to its operative position as shown in FIG. 2, the leak through the restrictor 38 is cut off from port 39 and the high pressure fed to the working space 33 will permanently hold the piston 32 in its deflected condition.

Under normal operating conditions, the common member operated by theactuator piston 1 could be subject to variable external forces and it is clear that the pressure in the working space 4 and at the ports 14 and 17 could vary without there being a variation in electric signal to the servo-valves. In turn this means that the pressure differences of the two ports for each servo-valve could vary without there being a change in electric signal. Nevertheless, the two ports 15 and 18 which connect to the error valve are substantially isolated from the actuator and the pressures generated at these ports will be dependent substantially solely on the signals fed to the servo-valves. Thus the operation of the error valve detects a difference in operation of the two servo-valves quite independently of the external forces operating from the common member on to the actuator piston. In the illustrated example, the safety action taken on occurrence of an error signal is to operate the by-pass valve 29 to open a by-pass across the actuator to render it free to move without restriction. The safety action also includes the disconnection of high pressure from the servo-valves. Nevertheless, within the broad scope of the present invention. operation of the error valve to produce an error signal may be arranged to bring about any form of safety action suitable to the use of the actuator. The actuator might be a single actuator forming the sole control of movement of an output member and the safety action taken must be determined by the function performed by the actuator. It might be for example reasonable for any of the following operations to form the safety action when the error valve detects a difference in operation between the servo-valves.

A. Completely closing the working spaces 4 and 5 of the actuator to lock the piston in position.

B. Hydraulically energising a control device to move the actuator piston to a predetermined position within its cylinder.

C. Isolation of one servo-valve leaving the actuator under the direct control of the other servo-valve.

D. Operation of a warning device.

E. Isolation of the actuator working space from the servo-valve ports and the connection of this working space to an alternative hydraulic control circuit.

The particular kind of electro-hydraulic servo-valve shown in the illustration is that employing a moving jet ofliquid. Many other types of electro-hydraulic servovalve may be used with the invention, the most com mon of the other types comprising that in which a flapper is moved by the electric motor to vary the escape flows from two opposed orifices in a differential manner and thus to vary the pressures supplying the orifices. The pressures supplying these orifices will be connected to the two ports of the servo-valve.

In the illustrated embodiment no means are shown to ensure proportionality between the electric signals and the resulting movement of the actuator. Any conventional means for ensuring such proportionality may be provided such for example as the provision of a mechanical spring feed back of movement of the actuator on to each of the moving jets of the servo-valves. For each moving jet the spring feed back will apply force thereto in opposition to the force applied by the associated electric motor.

I claim:

1. An electro-hydraulic control system including a pair of electro-hydraulic servo valves each comprising an electric motor adapted to receive an electric signal and a pair of ports and valve means controlled by the motor to adjust the liquid pressures differentially at the two ports, an actuator having a working space, connections from the working space of the actuator to a port of one servo valve and to the corresponding port of the other servo valve whereby the actuator is under the simultaneous control of the two servo valves, means exerting a biassing force on the actuator in a direction opposite to the hydraulic force generated in the working space and an error means connected between the said other two ports of the servo valves and arranged to respond when a substantial pressure difference exists between the said other two ports to provide an error signal.

2. An electro-hydraulic control system as claimed in claim 1 including latching means to maintain the error signal if the pressure difference between the said other two ports falls from said substantial difference to a lower pressure difference.

3. An electro-hydraulic control system as claimed in claim 1 wherein the means acting on the actuator for exerting a biassing force comprises a further working space connected to constant hydraulic pressure.

4. An electro-hydraulic control system as claimed in claim 3, wherein the said further working space is of smaller effective section than the actuator working space and the constant hydraulic pressure is higher than the average pressure at the said one ports.

5. An electro-hydraulic control system as claimed claim 4 wherein a high pressure supply is fed to the two servo-valves.

6. An electro-hydraulic control system as claimed in claim 5, wherein the high pressure fed to the servovalves is also fed to the further working space of the actuator.

7. An electrohydraulic control system as claimed in claim 11 including a by-pass valve operated by the error signal to render the actuator incapable of exerting a hydraulic force.

8. An electro-hydraulic control system as claimed in claim 7, wherein said error signal comprises an increase in hydraulic pressure in a passage extending from the error means.

9. An electro-hydraulic control system as claimed in claim 8, wherein the by-pass valve is arranged for movement into its by-pass position by the hydraulic 8 claim ll, wherein the servo-valves both comprise the kind in which the electric motor is arranged to adjust the position ofa jet fed with high pressure liquid relatively to the servovalve ports.

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