US3680578A

US3680578A - Fluidic control systems

Info

Publication number: US3680578A
Application number: US78336A
Authority: US
Inventors: Guy Edward Davies
Original assignee: Plessey Co Ltd
Current assignee: Plessey Overseas Ltd
Priority date: 1969-09-10
Filing date: 1970-09-02
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01
Also published as: SU440002A3; FR2061636B1; GB1304010A; JPS5023116B1; DE2044912B2; FR2061636A1; DE2044912A1; DE2044912C3; SE364128B

Abstract

A fluidic pressure bias which is superimposed on a control pressure and becomes effective whenever the control pressure varies, its sign being independent of the sign of the control pressure variation, is derived from the restricted portion of a Venturi tube interposed between the control-pressure source and a reservoir.

Description

United States Patent Davies [45] Aug. 1, 1972 [54] FLUIDIC CONTROL SYSTEMS 3,552,415 1/1971 Small ..l37/8l.5

3,572,357 3/1971 Philbrick ..137/8l.5 [72] Invent Davies Fmham' 3,590,840 7/1971 l-lyer ..l37/81.5 g 3,400,729 9/1968 Boothe ..l37/8l.5 [73] Assignee: The Plessey Company Limited, ll- 3,474,959 10/1969 Katz ..l37 /8l.5 X ford, England 3,542,048 11/1970 Bowles ..137/8l.5

22 Filed: Sept. 2,1970

Primary Examiner-William R. Cline 1 1 pp 73,336 Attorney-Blum, Moscovitz, Friedman & Kaplan [30] Foreign Application Priority Data 57 I ABS CT Sept. 10,1969 Great Britain ..44,708/69 1 A fluidic pressure bias which is superimposed on a U.S. control pressure and becomes efl'ective whenever the [51] Int. Cl ..F 15c l/l4, F156 3/04 control pressure varies, its sign being independent of [58] Field of Search ..l37/8l.5 the sign of the control pressure variation, is derived from the restricted portion of a Venturi tube inter- [56] References Cited posed between the control-pressure source and a reservoir. UNITED STATES PATENTS 3,528,443 9/1970 Swartz ..l37/81.5 7 Claim 5 Drawing Figures SIGNAL INPUT PATENTED 1 1 I97? 3 6 8 0.5 T 8 SHEEI 1 BF 4 SIGNAL INPUT SIGNAL INPUT PAIENIEUAU: 1 I972 SHEET 2 BF 4 SIGNAL INPUT PAIENIEDAus I 1972 SHEU t [1F 4 FLUIDIC CONTROL SYSTEMS This invention relates to fluidic control systems and has for an object to provide, for a control system having 7 an input represented by a pressure difierence, an input bias variable in accordance with the absolute value of the time differential of this pressure difference, the direction of the bias being independent of whether the time differential is positive or negative. The provision of such bias is, for example, desirable when effecting fluidic control of the variable guide vanes at the inlet to a gas-turbine compressor where, while the required setting of the guide vanes is mainly controlled by the pressure ratio generated across the compressor, it is desirable, in order to avoid surge and to improve the engine control, to bias the guide vanes to the low-speed side of the thus determined position both during rapid acceleration and during rapid deceleration of the engme.

While a bias variable according to a time differential of the value of the input may be produced by applying the input signal to the system via a restrictor and connecting a reservoir to the passage leading from the restrictor to the control system, it will be readily appreciated that the sign of this bias will be dependent on the sign of the time differential of the input signal.

According to the present invention a bias which becomes effective whenever the pressure at the control input varies, but has the same direction irrespective of the sign of the variation, is produced by deriving the control pressure from the restricted portion of a Venturi nozzle interposed between the signal-pressure input and a reservoir. In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which FIG. 1 is a circuit diagram of a control system and means for introducing a time lag in the application of an input signal to a fluidic amplifier,

FIG. 2 is a similar circuit diagram modified to produce a time lead instead of a time lag in the application of the input signal,

FIG. 3 is a circuit diagram illustrating an embodiment of the present invention applied to one of the control inputs to a conventional proportional fluidic amplifier of the momentum-interaction type,

FIG. 4 similarly illustrates a modified circuit, and

FIG. 5 diagrammatically illustrates the combination of the system of FIG. 4 with the combustion-air compressor of a gas-turbine engine.

Referring now first to FIG. 1, a fluidic proportional amplifier A has a power-supply input P, a pair of mutually opposed control-input connections C and C and two output connections and 0 so arranged that the value of the difference in flow and/or pressure between the output connections 0 and 0 is determined by the difference in control pressures between the control-input connections C and C A control signal appearing at a signal input I is applied to controlinput connection C via a restrictor B, and a reservoir chamber D is connected as a branch to the line connecting the restrictor B with the control-input connection C It will be readily appreciated that in this case the pressure at input connection C always lags behind variations of signal pressure at I, so that when the signal pressure at I increases, the control pressure at C is temporary lower, and when the signal pressure at I decreases, the control pressure at C, is temporary higher than the signal pressure at I, so that when the pressure at the second control-input connection C is kept constant, the pressure at output 0 will be correspondingly modified.

The reversal of the bias according to the sign of the pressure gradient also applies to the circuit of FIG. 2, which causes in a fluidic proportional amplifier A a modulation of the output pressure at 0 to provide a time lead, instead of the time lag obtained by the circuit of FIG. 1, in relation to the control-signal input at I due to the fact that the control signal appearing at input I, in addition to being applied to control-input connection C similarly as described with reference to FIG. 1, is additionally applied via a second restrictor B to a second oppositely acting control-input connection C the inlet of the second restrictor B is also connected to signal-pressure input I, and the outlet of the second restrictor B is directly connected to control-inlet connection C without the provision of a reservoir.

It will be readily appreciated that the circuit of FIG. 2 will produce no output from amplifier A so long as the signal-input pressure at I remains constant, that rising signal-input pressure at I will cause an increase in the output pressure at 0, since, due to the time lag in the pressure rise at control-input connection C the pressure at the other control-input connection C will exceed that at C and that conversely the output pressure at 0 will be decreased when, and as long as, the input-signal pressure at I decreases, since during such decrease of the input pressure at I the control pressure at C will be somewhat higher, due to additional supply from the reservoir D, than the pressure at the other control-pressure connection C which cannot draw on such an auxiliary supply. As in the circuit of FIG. 1, however, the bias will reverse its direction when the sign of the time differential of the pressure signal at input I changes.

Referring now to FIG. 3, the illustrated amplifier has a power-supply input 1 leading to a power nozzle 2, and two control-input ports 7 and 8. The power nozzle 2 generates a jet which, in the absence of a control input at ports 7 and 8, is symmetrical to a splitter member 15, by which the jet is divided between two

output ports

3 and 4, and two vents 5 and 6 are provided to allow the escape of the excess of the fluid supplied by the jet formed in the nozzle 2 over the amount entering the

output ports

3 and 4, more particularly when the latter are closed to obtain a pressure output. Of the two control ports 7 and 8 of the amplifier, the former is shown connected to the throat of a Venturi nozzle 21 which is interposed between a signal-pressure inlet I and a reservoir D, which forms a pressure-energy storage capacitor. At the other control port 8 may be connected to the signal pressure inlet I, when the control is intended to produce only a transient control, or to vent or other reference pressure or control pressure when the control is intended to be also influenced by the steady value of the signal pressure I.

It will be readily appreciated that when the signal pressure I increases, flow through the Venturi nozzle 21 will take place from the inlet I to the reservoir D and that when the signal pressure at inlet I decreases, flow through the Venturi nozzle 21 will take place from the reservoir D to the inlet I. In each case the pressure at the throat of the Venturi nozzle will drop below the pressure at I so that a control is achieved while produces a bias that is effective in a predetermined direction when the pressure at I increases and is efiective in the same direction when the pressure at I decreases.

As shown in FIG. 3, the thus biased output pressure may be applied to a spring-biased servomotor cylinder 22, whose piston 23 acts through a link rod 24 upon a crank 25 provided on the compressor housing 26 of a turbo-compressor to operate variable-angle guide vanes in the compressor portion of the turbo-compressor T.

In some cases it is desired to superimpose a bias in accordance with the rate of variation of the input pressure upon a control in accordance with some other function of the input pressure, and FIG. 4 shows an arrangement in which the invention is used in this manner in conjunction with a proportional amplified 18 which, in order to facilitate this, has a modulated input which is described in more detail in co-pending application Ser. No. 68,965, filed Sept. 2, 1970 corresponding to British patent application No. 44707/69. The output of that amplifier 18 is employed as the normal control input of a further amplifier stage 18A. As described in more detail in said co-pending application, the powersupply jet nozzle 2 of FIG. 3 has, in the case of the firstmentioned proportional amplifier 18, been replaced by two power-

supply branch nozzles

2A and 2B, which are inclined in opposite directions relative to the plane of symmetry of the divider and in substantial respective alignment with the

output ports

4 and 3 of the amplifier l8, and the jets of which are combined to produce the power jet of this amplifier. The inlet to one branch nozzle 2A is directly connected to the signalpressure input I which is utilized as the power supply, and the inlet to the other branch nozzle 2B is connected to the restricted portion of a Venturi nozzle 21 which leads from the signal-pressure input I to a reservoir D. Thus the mass flow of the power jet becomes a function of the signal pressure, and the bias action of the Venturi nozzle is effective to modify the output of the amplifier 18 by altering, in response to variations of the signal pressure at inlet I, the distribution between the two branch nozzles 2A and 28 while the two main control nozzles 7 and 8 of the amplifier 18 are left free for other control actions.

In the illustrated embodiment a pressure input, which may be the same source as that connected to I, is applied to one main control nozzle 7 from a point 17 via a planar jet collector 16. The housing of this collector may be vented, for example to the environmental atmosphere, or connected to some other reference pressure, so that the pressure effective at control port 7 forms a function of that reference pressure as well as of the pressure applied at 17; the other main control nozzle 8 may be connected to a reference-signal or pressure at a connection point 10.

It will be readily appreciated that the arrangement of FIG. 4 may, similarly to that of FIG. 3, be used to control an actuator cylinder for the operation of, for example, variable-angle guide vanes in the compressor portion of a turbo-compressor, the servomotor cylinder being, for this purpose, connected to the two outputs of the second-stage amplifier 18A in the same way in which the

outputs

3 and 4 of the amplifier 18 are connected in FIG. 3.

Such an arrangement is illustrated in FIG. 5, in which the same references as in the preceding Figures have been used for corresponding parts.

Referring now to FIG. 5, the compressor portion 26 of a gas turbine engine, which is fed with ambient air at a pressure P,, and its delivery pressure P, is supplied to the input 1 of the fluidic amplifier 18. This air under pressure P, is also fed to the power input of the secondstage amplifier 18A and to two other branch lines, of which one leads to the input of the planar jet collector 16, whose body has an atmospheric vent at ambient pressure P, and whose output is connected to one main control nozzle 7 of the first-stage amplifier l8,-while the other branch leads, via two series-connected restrictors X and X of which the former has a fixedarea aperture while the latter is adjustable by a lever 31, to an opening exposed to ambient pressure P, and has, between the restrictors X, and X2, 8 tapping 27 connected at 10 to the other main-control nozzle of the first-stage amplifier l8.

It will be readily appreciated that the pressures respectively acting at the inlets to control nozzles 7 and 8 will both lie between the values of P and P, but will, for a given setting of the adjustable restrictor X correspond to different functions of P, and P, (or for a given P, to different functions of P They can, at least when the apparatus is suitably dimensioned, be made equal, at any given values of P, and P,,by suitable adjustment of the orifice X subject to the effect of the Venturi-controlled twin-

jet arrangement

2A, 2B. The latter arrangement introduces the time difierential of the compressor-delivery pressure and is employed, as will be seen further below, to counteract an excessive rate of rise of the compressor-delivery pressure and the inherent risk of compressor stall.

As in the arrangement of FIG. 4, the

output lines

3 and 4 of the first-stage amplifier 18 are connected respectively to the control nozzles 8A and 7A of the secondstage amplifier 18A, while

theoutput lines

3A and 4A of the latter amplifier are respectively connected to the two ends of an. actuator cylinder 22,. whose piston 23 acts through its piston rod 24 and a linkage 28, 29 upon a crank member 25 to vary the setting of the inlet guide vanes 25 (which, as shown near the top of the Figure, form part of the compressor 26) about their fulcra 25A as required by, varying pressure conditions, while a feedback mechanism 30 acts upon the lever 31 of the adjustable restrictor X so as to restore pressure balance between the control nozzles 7 and 8 of the first-stage amplifier 18 after appropriate movement of the guide vanes.

While we have so far assumed that the Venturi nozzle 12 is of symmetrical construction, which results in equal bias for equal and opposite rates of input-pressure variation, a Venturi nozzle of asymmetrical construction may alternatively be employed, thus causing the amount of bias to depend on the sign of the pressure variation. If, for example, the fluid-expansion ratio between the throat and the reservoir is increased, the response to a rising pressure will be greater than to a falling pressure. When signal pressure changes likely to occur at inlet I are sufiicient to produce sonic flow in the throat of the Venturi nozzle 21, the pressure in the throat will not fall below a predetermined percentage of the absolute pressure upstream, but according to a supplementary feature of the invention, asymmetry of the bias may be achieved even under such so-called choking conditions if the pressure tapping is arranged slightly to one side, i.e., upstream or downstream, of the throat. When the tapping is on the upstream side of the throat, less suction is obtained at the tapping than at the throat because the speed of the fluid at the same tapping point is below the throat speed. When the flow is reversed, the tapping is downstream of the throat relative to the reversed flow, so that under sonic conditions of flow in the throat the suction produced at the tapping by the reversed flow is increased beyond the suction at the throat, because at the location of the tapping the flow speed in the downstream part of the Venturi nozzle is supersonic. It should, however, be appreciated that when the pressure ratio across the nozzle, and thus the flow rate, is lower than that corresponding to sonic flow in the throat, the asymmetric effect of the offsetting of the tapping disappears, and if asymmetric operation of the bias device is then required, other means of producing such asymmetry must be employed.

It will be readily recognized that in the embodiment of FIG. 5 the present invention is employed, together with that of our co-pending application Ser. No. 68,965, filed Sept. 2, 1970, corresponding to British patent application No. 44707/69, in a system for the control of accessories and subsystems in gas-turbine engines, and more specifically it has been employed, by way of a modification, in the fluidic control system described in co-pending application Ser. No. 22,453, filed Mar. 25, 1970, corresponding to British patent application No. 15475/69, for variable guide vanes at the inlet of the compressor an aircraft turbojet engine, in which the reference pressure is produced between two series-connected orifices interconnecting the input pressure source with the pressure of the ambient atmosphere. Such combination of the bias device of the present invention and of the said patent application Ser. No. 68,965 with the position control system of said patent application Ser. No. 22,453 also constitutes an aspect of the present invention.

Although the apparatus mentioned has been hereinabove described for operation on compressible gases, it can be readily modified to work satisfactorily on liquid subject to certain differences which will be readily apparent to those skilled in the art, and which include inter alia the fact that in practice choking, which may be utilized with a gaseous fluid to keep the total flow through the fixed-area throttle X, constant, will not occur in a system operating with hydraulic liquid at any practically occurring pressure ratio. To achieve this modification, the reservoir completely filled with operating fluid may be replaced by a hydraulic accumulator, which may comprise a free piston acted-upon by the pressure of the hydraulic liquid and acting against a spring, or alternatively the accumulator may include a pressurizing chamber containing gas under pressure which may for example, as indicated in broken lines in FIG. 3, be isolated by a diaphragm 27 from the operating liquid against whose pressure it acts.

What we claim is:

1. A flu'dic control aratus, co ri in l. a jet-interaction fliel zlic proport i h a iphfier having an interaction chamber, a power-jet nozzle for projecting a power jet of fluid into said chamber, a jet splitter facing said nozzle across said chamber, two output passages extending from said chamber along opposite sides respectively of said jet splitter, and a further jet nozzle for projecting into said chamber a further jet impinging upon the power jet in the chamber at an angle to the power jet to deflect the power jet away from one and towards the other of said output passages, and

2. a signal-pressure differentiation line having a signal-input aperture at one end and a pressureenergy storage capacitor connected to its other end and including, between said ends, a Venturi nozzle having a throat and a tapping located at least in the vicinity of said throat, said tapping being connected to said further jet nozzle to provide the supply of fluid for such further jet.

2. Apparatus as claimed in claim 1, wherein said further nozzle is a second power-jet nozzle arranged with its axis intersecting the axis of the first-mentioned power-jet nozzle to produce a second power jet which merges with the power jet produced by said first-mentioned power-jet nozzle to form a composite power jet of a direction intermediate between the respective directions of said power jet and second power jet.

3. Apparatus as claimed'in claim 2, wherein said power-jet nozzle and said second power-jet nozzle are arranged symmetrically to the jet splitter.

4. Apparatus as claimed in claim 2, including a substantially free connection from said signal-input aperture to said second power-jet nozzle.

5. Apparatus as claimed in claim 1, which includes a fluid-pressure operated actuator having an operating chamber the pressure in which is controlled by the pressure in one of said output passages.

6. Apparatus as claimed in claim 1, which includes an actuator having a piston acted-upon in opposite directions by the respective pressures in said output passages.

7. A fluidic control apparatus, comprising 1. a jet-interaction fluidic proportional amplifier having an interaction chamber, a power-jet nozzle for projecting a power jet of fluid into said chamber, a jet splitter facing said nozzle across said chamber, two output passages extending from said chamber along opposite sides respectively of said jet splitter, and a control-jet nozzle for projecting into said chamber a control jet impinging upon the power jet in the chamber transversely to the power jet to deflect the power jet away from one and towards the other of said output passages, and

2. a signal-pressure differentiation line having a signal-input aperture at one end and a pressureenergy storage capacitor connected to its other end and including, between said ends, a Venturi nozzle having a throat and a tapping located at least in the vicinity of said throat, said tapping being connected to said control-jet nozzle to provide the supply of fluid for such control jet.

Claims

1. A fluidic control apparatus, comprising 1. a jet-interaction fluidic proportional amplifier having an interaction chamber, a power-jet nozzle for projecting a power jet of fluid into said chamber, a jet splitter facing said nozzle across said chamber, two output passages extending from said chamber along opposite sides respectively of said jet splitter, and a further jet nozzle for projecting into said chamber a further jet impinging upon the power jet in the chamber at an angle to the power jet to deflect the power jet away from one and towards the other of said output passages, and 2. a signal-pressure differentiation line having a signal-input aperture at one end and a pressure-energy storage capacitor connected to its other end and including, between said ends, a Venturi nozzle having a throat and a tapping located at least in the vicinity of said throat, said tapping being connected to said further jet nozzle to provide the supply of fluid for such further jet.

2. a signal-pressure differentiation line having a signal-input aperture at one end and a pressure-energy storage capacitor connected to its other end and including, between said ends, a Venturi nozzle having a throat and a tapping located at least in the vicinity of said throat, said tapping being connected to said further jet nozzle to provide the supply of fluid for such further jet.

2. a signal-pressure differentiation line having a signal-input aperture at one end and a pressure-energy storage capacitor connected to its other end and including, between said ends, a Venturi nozzle having a throat and a tapping located at least in the vicinity of said throat, said tapping being connected to said control-jet nozzle to provide the supply of fluid for such control jet.

3. Apparatus as claimed in claim 2, wherein said powEr-jet nozzle and said second power-jet nozzle are arranged symmetrically to the jet splitter.

7. A fluidic control apparatus, comprising