US2651261A - Hydraulic speed-sensitive control system for prime movers - Google Patents

Description

sept, s,- 1953 2,651,261

4 sheets-sheet 1 D. O. DAVIES HYDRAULIC. SPEED-SENSITIVE CONTROL SYSTEM FOR PRIME MOVERS Fiied nec. 2, 195o Sept. 8, -1953 D. o. DAvlEs 2,651,251

HYDRAULIC. SPEED-SENSITIVE CONTROL v SYSTEM FOR PRIME MOVERS Filed Dec. 2, 1950 4 Sheets-Sheet 2 Ill( /NYEIVIM @wma-m Sept. 8, 1953 D. o. DAvlEs 2,651,261

HYDRAULIC. SPEED-SENSITIVE CONTROL' Y l SYSTEM FOR PRIME MOVERS Filed DeG. 2, 1950 f .V Idro? .aar/o p. 4anw-'s Sept. 8, A1.953

. D. o. nAvlEs 2,651,261 HYDRAULIC. SPEED SENSITIVE CONTROL SYSTEM FOR PRIME MOVERS 4 Sh'eets-Sheet 4 Filed Dec. 2, 1950 .wvawroe C. DAY/f5 M@ mY/0 USM Patented Sept. 8, 1953 HYDRAULIC SPEED- SYSTEM FOR David Omri Davies, Edgwar'e,

SENSITIVE CONTROL PRIMEv MOVERS England, ass'ig'ndr to Rolls-Royce Limited, Derby, England, a

British company Application December 2, 1950, Serial No.

In Great Britain December 7, 1949 17 Claims.

'Ihis invention relates t`o` hydraulic', speedsensitive systems ofY the type (hereinafter reerred to as the type specified) comprising a positive-displacement fixed-capacity hydraulic pump driven by a prime mover at a rotational speed proportional' to that of the prime mover, flow restricting meansv through Which passed the delivery flow from the pump, thereby to cause across the flow restricting means a pressure drop which is a function of the rotational speed of the prime mover, and pressure-sensitive means subjected to the pressure dropV and arranged to effect acontrollingactionl associated with the operation ofthe prime. mover.

For example, a hydraulic speed-sensitive system of the type specified may be used to control the fuel supply to the prime moverin a manner such as to maintain. a preselected rotational speed, or to avoid a predetermined maximum rotational speedV being exceeded.V As a further example, a hydraulic system off the type specified may be used to actuate,in pre-determined manner related to the rotational speed of the prime mover, control means aiecting. an aii' flow in the prime mover; such an arrangement suitable for controlling gas-turbineA engines, for instance by adjustment of swirl-or stator vanes in a compressor, adjustment of nozzle-guide vanes in a turbine, or variationof theeective area of a propelling nozzle receiving exhaust-'gases from a turbine.

In such arrangements, the hydraulic system is usually designedltor be'operative ata relatively high rotational speed of the prime mover, and therefore, the capacity of the pump and thespeed at which it is driven, are so-choseninrelation to the restriction aifordeclloy-y the flow-restricting pressure drop across the means that an excessive flow-restricting means isavoided. Sucharrangements, consequently, do not have a high sensitivity at loW rotational speedof` the prime mover.

According to the present invention; a hydraulicc the type specified is oW-restricting-means speed-sensitive system ofcharacterised in thatsaid comprises a rst'iioW-'restricting device to create a rst pressure diiierence to which said pres-V sure-sensitive Adevice responds in a range of high rotational speedsr ofthe prime moyen-andv an additional flow-restricting device- *having a greaterrestriction to iiowthan said-firstflowrestricting device to create a `second pressureudifference to which theT pressure 4sensitive means `re-V sponds in a range-of lowrotationalspeeds-` ofthe prime mover, and in that there is provided by- The by-pass meansV conveniently comprises a y l i to the pressure voliierence across the additional flow-restricting device, and arranged to open when a predetermined pressure In certain cases, either or both the additional flow-restricting device andthe first flow-restricting device may comprise a movable valveelement sensitive to the pressure drop across the flowrestricting deviceso as tol reduce the restriction afforded by the now-restricting device with inn and not; asin the case-of a'xed-area--restrictiom proportional to the square ofthe rotational-speed;

ditionalfiioW-restrictingdevice may differ from that effected by therstflow-restricting device. According toP alfea-ture of the invention,"there An important application second being sensitive to the pressure drop across the second flow-restricting means. In one preferred embodiment of such an arrangement described hereafter actuator members of said pressure-responsive devices are connected Vthrough common linkage mechanism to means controlling adjustable guide vanes of an axial flow compressor.

In an alternative arrangement infwhich the control operation effected by the additional idowrestricting device is the same as that effected by the first flow-restricting device a single pressure responsive means is used, and a device sensitive to the rotational speed of the prime mover is provided for transferring the control from the additional flow-restricting device to the first flow-restricting device. In a preferred arrangement increased sensitivity of control in the lower speed range may be obtained by providing that the additional flow-restricting device is of the kind in which the pressure drop is directly proportional to the flow therethrough, whilst the first now-restricting device is of the kind in which the pressure drop is proportional to the square of the flow therethrough. To obtain progressive control over the whole speed range it is arranged that the transfer of the control from the additional flow-restricting device to the rst nowrestricting device takes place when the pressure drop across the first flow-restricting device, i. e. the square law device is equal to that across the additional flow-restricting device.

The transfer of the control from one flow-restricting device to the other may be effected by any known or convenient means responsive to the rotational speed of the prime mover; conveniently, the response to speed is obtained from the pressure drop within the hydraulic governing circuit itself. Said pressure drop may, for example, be used for the purpose of controlling an electric circu't including solenoid means effecting the transfer.

Three embodiments of the invention are described with reference to the accompanying diagrammatic drawings in which:

Figure l illustrates a gas turbine engine of the simple jet propulsion type suitable for aircraft propulsion.

Figure 2 illustrates a control system incorporating a control according to this invention applied to introducing extra fuel to the engine combustion equipment during starting, and

Figures 3 and 4 illustrate embodiments in which the two flow-restricting devices effect a single control in adjusting stator blades of an axial-flow compressor.

Referring to Figure l, the engine comprises a compressor illustrated as an axial-flow compressor whereof the entry ring of stator blades I4 are adjustable as to their angle of incidence, combustion equipment II to receive compressed air from the compressor and to have fuel burned in the air to heat it, the fuel being supplied through an injection manifold I5 and injectors I5a, a turbine |2 receiving hot gases from the combustion equipment and having its rotor driving the compressor rotor shaft through a shaft Afby a hydraulic ram device I6, and an exhaust assembly I3 through which exhaust gases from the turbine pass to atmosphere.

Fuel is supplied to the injection manifold l5 from a tank I1 through a suction pipe IB of a fuel pump I9 the delivery of which is connected by pipe 20 to the manifold, there being a throttle 2| and a shut-off cock 22 in the pipe 20. During operation of the engine the shut-olf cock is fullyopen and the fuel supply to the engine is controlled by the throttle device 2|. The pump I9 is driven' from the engine through take-off shaft 23.

The adjustable stator blades |4 may be interlinked to simultaneous operation in any convenient manner andare arranged for adjustment 30 the stem 32a of the ram piston 32 being connected to a radius arm 24 o n one of the adjustable blades |4 by a link 25 and universal joint 26. The ram device 33 comprises (Figure 2) a cylinder 3| in which the piston 32 reciprocates, and a control mechanism 33 whereby the position of piston 32 in cylinder 3| is determined in accordance with the engine rotational speed in the higher range of rotational speeds of the engine. The stem 32a is hollow and works in guides 34, 35 which also act as limit stops for the piston 32. The interior of stem 32a communicates through bore 36 with the space 31 to one side of piston 32 so that the effective area of the piston exposed to the space 31 is greater than that exposed to cylinder space 38. Pressure fluid is conveyed from pipe 20 to cylinder 3| through a pipe 39 and bores 40. 4I. the bore 4| having in it a restrictor 42.

The control mechanism 33 comprises two compartments 43, 44 separated by a flexible diaphragm 45, whereof the compartment 43 is connected by pipe to a pipe B0 downstream of a large area flow restrictor orifice 6| and compartment 44 is connected by pipe 41 to upstream of the restrictor 6|. The pipe B0 is connected as a loop to pipe |8 and has located in it a fixedcapacity positive-displacement pump 64 which is driven through take-0E 64a (Figure l) from shaft l5 so that the pressure drop across orifice 5| is a function of the engine rotational speed. The fluid pressure load on diaphragm 45 is therefore also a function of engine rotational speed.

The diaphragm 45 is loaded by a spring 50 through rod 5|, this load being dependent on the position of the piston 32 in cylinder 3|, and by a secondary spring 52 which acts in the same direction as spring and against the fluid pressure load.

The diaphragm movements are communicated to rod 53 carrying a half ball valve element 54 controlling the outflow of fluid from space 31 through a duct 55 leading from space 31 to a chamber 56 from which a pipe 51 leads to the suction side of pump I9.

It will be clear that when acting on diaphragm 45 increases to a sufficient value to overcome spring 52, the half ball valve will lift allowing fiuid to bleed from space 31, the pressure within which therefore falls and the piston 32 moves to the right until the load due to spring 50 overcomes the fluid pressure load on diaphragm 45. Thus for each value of engine rotational speed in the range of speeds the piston 32 will occupy a, corresponding position in cylinder 3| and the blades |4 will have a particular angle of incidence tothe inflowing air.

The effective area of restrictor orifice 6|, the

the fluid pressure 2&5 1,253.1

area oil diaphragm-.45 and .the strength vof spring 52 are so selected inrelation to.i.the output of pump` 64 that this control. of the .blades I4v is effective in. a higher rangeofrotational speeds, springv 52 determining the. lower limit of this higher range of speeds, The flow restrictor orifice 6| is made of relatively large-area, so that at maximumA rotationalspeed ofthe engine the pressure drop across this orifice does not reach an excessive value.

This form of control mechanism 33. for adjusting the stator blades |.4 of axial-ow air compressors Il)` of the engine progressively throughout a speed range within the higher range-of rotational speeds does not form an essential part of` this invention, but is merely exemplary ofa pressure-sensitive means in the type of hydraulic speed-sensitive. control with which this invention is concerned.

The control system illustrated in Figure 2 also includes means to control. the introduction of extra fuel to the combustion equipment, in a limited speed range in thelowerrange of engine speeds, and in thisinstance during starting to increase the rate ofV engine lrun-up to idling speed. v

In the pipe 60 on the delivery side of the positive-displacement pump i641 .and upstream of orifice 6|, there is providedan additional ow restriction device 65l which comprises a movable poppet-type valve 66 which is loaded by-spring 61 towards a seatingA 68-around` an orice. This device 65 is designed tov afford a greater restriction to flow of fluid through .pipe 60 than the rst-mentioned flow-restricting orifice 6| and the valve memberV |56 is arranged to be moved byfuel ilow through the orifice against the-action of spring 61 so that the pressure drop across device 65 is substantially directlyproportional to the engine rotationalspeed throughout a predetermined speed range within the lower speed range of the engine.

A by-pass pipe 69 is provided around the flowrestricting device 65 andA the by-pass 69 includes in it a poppet valve 10whichis loaded bya spring 1| in the sense of closure-onto a seating 12 and isarranged tofopen when a-predetermined pressure drop is reached across the additional ilowrestricting device 65. This relief' valve 10is so designed that once it has-opened, the pressure drop across device 65 does not substantiallyincrease withincreaseofflow through the by-pass pipe 69 resulting from increase. of rotational speed of the engine.

The pressure drop across the additional now restricting device 65r is. applied to a pressuresensitive device 13, which is separate from that formed by diaphragm 45 to .whichthepressure drop across the first flow restrictor orifice 6| is applied,` and which` ink this embodiment comprises a cylinder 14 closed at its endsl and two diaphragms 15, 16 mounteolH-onl a common operating rod 11 and located in the cylindertodivide it into three spaces 18, 19, 80 the two diaphragms 15, 16 are of equal area and the space 19 between the diaphragms is open through port 8l to atmosphere.

Connections are made through pipes 82, 83 from the end spaces 18, 80. respectively to the upstream and downstream sidesof the additional flow restrictiondevice 65 so that the pressure drop across device65 is appliedto the diaphragm assembly.

The diaphragm assemblyisloaded by a coil spring il-.aecommodatedinthe end spacegamin which the pressuredownstreamof thev additional flow-restricting device 65. is. applied. In addition a further spring is provided in the rspace 80, the spring 8.5. having a movable abutment 86 which is contacted by one end of thel rod 11 when the diaphragm assembly has moved against the action of the rst spring 84 by a predetermined amount. lWhen the rod 1=1 is free from the movable abutment 86, the latter engages a fixed stop 81.

An electrical contact arrangement is provided within the space 1.9 between the two diaphragms 15, 16, the contact arrangement comprising a pair of xed contacts 90. and a bridge contact 9| on the rod 11 to co-operate with the xed contacts 90. The contacts 99, 9| are so arranged that when the pressure drop applied to. the diaphragm assembly reaches a rst predetermined value and the first spring. 84 has been. compressed to a predetermined` extent, and the contact 9| bridges the fixed contacts 9|) to complete an electrical circuit containing the contacts. At a second and higher predetermined value of the pressure drop resulting from van increase of speed, it is arranged that both the first and second springs 84, 85 are overcome and the resulting movement of thel diaphragm assembly is arranged to carry contact Sllutol a positionin which contacts 90 are not bridged, thereby to open the circuit.

The electrical circuit includes in series with the contacts a solenoid 92. which isarranged-tooperate a valve 93 controlling the flow of extra fuel to the engine, The VVsolenoid 9.2 is Ieriergised to open the valve 93 when the circuit is completed and is de-energised when thecircuit is-broken to permit the valve 93 to close under the influenceof a loading spring-94;

The solenoid-operated valve. 93 is arrangedA in a pipe 93a which is hydraulicallyv in parallel with themain fuel throttle 2| thereby to by-pass the latter when the solenoid92 isenergised.

The operation Vof the. system is as follows: During starting of the engine, the. main fuel throttle 2| in thefuelsupplypipe 20 tothecombustion equipment is normally set for idling f-uel flow and is thusalmost closedand'offers a large resistance to fuel ow therethrough. During the starting of the enginev the pressure drop across the additional flow restricting device65'buildsup such that at a predetermined-.low rotational speed, say, 800 R. P. M. theiirst spring 84 is compressed to such an extent that the contacts 90 are bridged by contact 9| Acausingenergisation of the solenoid zand opening of the valve 93 in the by-pass pipe 93a. Thus the restrictioninthe-fuel delivery line 2l] to the engine is reduced and an increase in the fuel supply to thecombustion equipment occurs.

As the engine speed increases., the pressure drop across device continuesto build up, but the further movement of the diaphragmassembly 15, 16, 11 is restrained. byfengagement Aof the rod 11 against abutment.` 86 yforsthe second spring 85; until the pressure drop reachesasecond predetermined value when the load of the rst and second springs 84, 85 is overcome; thismay bearranged to occur for examplelat an engine speed of, say, 2,000' R. P. M. At this stagathe diaphragm assembly moves to break the-.-circuit and the sole.-v noid 92. is thus de-eriergised, allowing the fuel control valve 93 to-close, so that .the fuelsupply to .the engine is .-nowdeiinedibyithe idling. setting of the main throttle valve 2| and the engine speed- Vstabilises .atiitsidlingspeed say, at; 25,50.0"R.. P; M.

Thereafter, the engine` can "be controlled in the normal manner by opening and closing the throttle valve 2 I.

On further increase of engine rotational speed, the pressure drop across the additional flow-restricting device 65 causes the by-pass relief valve to open, preventing furtherincrease in this pressure drop across device 65 and avoiding excessive loads being applied to the diaphragm assembly 15, 16, 11.

in the higher range of rotational' speed,'e. g. from 4,000 R. P. M. to 8,000 R. P. M. the delivery flow .from the hydraulic governor pump passing through the first flow-restricting orifice 6| effects the progressive adjustment of the compressor stator blades |4. In the arrangement described therefore a single hydraulic pump, the pump 64, .of a hydraulic, speed-sensitive control is utilised to perform the two control functions in the operation of the engine in the two distinct ranges of rotational speed.

Whilst in the embodiment described above, the control functions are of a distinct nature, the invention may also be used for effecting a single control function over a wide speed range.

Such an arrangement is shown in Figure 3 in which, two pressure-sensitive devices |30, 230 are provided, the one |30 connected to be sensitive to the pressure drop across restricting orifice |6| and the other 230 connected to be sensitive to the pressure drop across the restricting device |65. Movements of the operating pistons |32, 232, of the pressure-sensitive devices |30, 230, are proportional to the pressure drops to which the pressure-sensitive devices |45, 245 are subjected, and it is arranged that the operating pistons are connected to links |25, 225 pivoted to the ends of a Boating link 21. A rod 28 is pivoted to the iioating link 21 intermediate its ends, and is connected to the operating radius arm 24 of the adjustable stator blades.

It is arranged that the effective area of the restricting device |65 is less than that of the restricting orifice IBI, and consequently the pressure drop across it is higher for a given flow. The by-pass valve 10 is arranged to open at the desired maximum pressure drop across the restricting device |65.

In operation, over the lower part of the engine speed range, up to the engine speed at which the by-pass valve 10 opens, the arm 225 of the pressure-sensitive device 230 moves progressively over its full range of travel in accordance with the pressure drop across restricting device |65, thereby adjusting the angle of the adjustable stator blades, while ar-m |25 of pressure-sensitive device moves simultaneously over a small part of its range of travel, because, as the restricting orice |6| is of greater effective area than the restricting device |65, the pressure drop across diaphragm |45 is less than that across the diaphragm 245. When the by-pass valve opens, the pressure drop across the restricting device |65 remains substantially constant, and therefore the arm 225 remains in substantially the same position. As the engine speed, and therefore the flow through the restricting orifice |6| increase further, the arm |25 of the pressure-sensitive device |30 moves progressively over its full range of travel in accordance with the pressure drop across flow-restricting orifice |6I. This movement is transmitted through the floating link 21 to the radius arm 24 by which the guide vanes are adjusted.

The rod 28 may be pivoted to the floating link ',21 at any suitable'point between its ends to achieverthe desired movement of rod 28 due to the movement of pistons |32, 232. It will thus be seen that the control force available, as represented by the pressure drop applied across diaphragm |45, is greatly increased as compared with systems in which there is only a single diaphragm, sensitive to the pressure drop across a single restricting orifice.

In an alternative arrangement shown in Figure 4 a. control is shown for adjustable stator blades i4 such that in the low speed range the diaphragm 45 of the device'30 is subjected to the pressure drop across restrictor device 65 and in a higher speed range the diaphragm 45 is subjected to the pressure drop across the restrictor orice 6|. To apply these pressure drops alternatively to the diaphragm, the pipe 60 is provided with three branches 95, 96, 91, whereof the branch 95 is connected to pipe 60 downstream of orice 6| and leads to one port 98a of a changeover valve 98, branch 96 is connected to pipe 60 between the orifice 6| and the device 65 and leads to a second port 98h of valve 98 and to a first port 99a of a second changeover valve 99, and whereof branch 91 is connected to pipe 60 between the device 65 and pump 64 and leads t0 a second port 99h of the changeover valve 99. The outlets 98o, 99e from valves 9B and 99 lead respectively to pipes 46, 41 and thus to compartments 43, 44 on each side of diaphragm 45. The valves 98. 99 are coupled together, as indicated at |00, and are arranged so that in one position e, 99e are connected to ports 98a, 99a respectively and in a second position (ports 98o, 99e are connected) to ports 98h, 99h respectively. Thus in the first Valve position .the diaphragm is subjected to the pressure drop across orice 6| and in the second position the diaphragm 45 is subjected to the pressure drop across device 65.

The valvesV 98, 99 are operated by a solenoid device |02 energised under control of a pressureoperated switch device |0| which operates when the pressure drop across the device 65 reaches a preselected value, say a value which is a fixed margin below the pressure drop at which by-pass device 10 is arranged to open, which value of the pressure drop is correlated with the rotational speed of the engine.

In the arrangement described, the pressure drop across orice 6| varies as the square of the now therethrough and the pressure drop across Aorifice 65 is directly proportional to the flow therethrough. To obtain progressive control of the guide vanes over the whole speed range it is arranged that the transfer of the control from the oriiice 6| to orifice 65 by means of the valves 98 and 99 and pressure operated switch device |0| is effected when the pressure drop across the orice 65 is substantially equal to that across the orice 6|, i. e. at the point of intersectionv of the linear and square law pressure/now curves.

I claim:

l. A hydraulic speed-sensitive system comprising a fixed-capacity pump, means to drive said pump at a rotational speed proportional to the speed to which said device is to be sensitive, flowrestricting means connected to the pump to receive the delivery fiow therefrom including a first flow-restricting device of relatively large effective area and in series therewith an additional now-restricting device of relatively small effective area, pressure-sensitive means subjected to pressure differences across said flow-restricting devices. flow by-pass means connected to the p'stream and "downstream sides of said additional flow-restricting device, and a nvalve in said Icy-'pass means `to control kthe ow therethrough.

i2, j'A hydraulic i speed-sensitive system as claimed in claim 1, comprising a pair of pressuresensitive devices, the first such device being connected to be `subjected to the pressure diierence across said first flow-restricting device and the second such device being connected to be subjected to the pressure diiTerence across said additional flow-restricting device.

'3. lA hydraulic speed-sensitive system, comprising a fixed-capacity pump, means to drive said pump at a rotational speed proportional to the speed to which said device is to be sensitive, now-restricting means connected to the pump to receive the delivery iiow therefrom, including a rst now-restricting device land an additional now-restricting device in series, pressure-'sensitive means,l means to connectsaid pressuresensitive means, in opposition, tolocations upstream and downstream respectively of said first now-restricting device, whereby said pressuresns'itivemeans is responsive to the pressure drop across `said first flow-restricting device, and means to connect said pressure-sensitive means, in oppositionito locations upstream and downstream Y respectively of said additional iiowrestricting device, wherebysaid pressure-sensitive `means is responsive to the pressure drop across said additional flow-restritcing device, said additional now-restricting device having a smaller effective Yarea than said first flow-restricting device, by-pass means connected directly to the upstream and downstream sides of said additional now-restricting device, and a valve in said by-pass means to control the flow therethrough.

4. A hydraulic speed-sensitive system comprising a iiXed capacity pump, means. Vto drive said pump at arotational speed proportional to the speed to which said device is to be sensitive, flowrestricting means connected to the pump to receive the delivery flow therefrom, including a rst dow-restricting device of relativelyvlarge eiective area and in series therewith an additional flow-restricting device of relatively small effective area, a rst pressure-sensitive device, a second pressure-sensitive device, means for subjecting said pressure-sensitive devices to pressure diierences across said now-restricting devices, flowby-pass means connected to the upstream and downstream sides of said i additional iiow-restricting device, and a valve in vsaid by-pass means to control the flow therethrough.

5. In combination, a prime mover, a hydraulic speed-sensitive system asv claimed in lclaim 4, whereof said pump is driven ata speed proportional to that of said prime mover,l means for effecting a rst control action of said prime mover, means for eiecting a .second control action of said prime mover, an operative connection between said first pressure-sensitive device and said means for effecting the first control action, and an operative connection between said second pressure-sensitive,device and said means for ef- Afecting the second control action.

6. In combination, a prime mover, a hydraulic speed-sensitive system as claimed in claim 4, whereof the pump is connected to be driven at a speed proportional to that of the prime mover, further comprising means for effectingA a single control action on said prime mover and operative connections between said iirst and second pressure-responsive devices and rsaid means for effecting the Control actionr 7. A hydraulic speed-sensitive system for effecting control of a prime mover, comprisinga fixed-capacity, pump, means to drive said pump at a vrotationalspeed proportional to that of the prime mover, flow-restricting means connected to the pump to receive the delivery ilow therefrom, including a rst now-restricting device and an additional dow-restricting device, the eifective area of said additional flow-restricting device 'being less than that of said first flow-restricting device, a first pressure-sensitive device, conduit means connecting said rst pressure-sensitive device to the upstream and downstream sides respectively of said rst flow-restricting device, whereby said pressure-sensitive device is subjected to the pressure drop across said rst flowrestricting device, a second pressure-sensitive device, `conduit means connecting said second pressure-sensitive device to the lupstream and. downstream sides respectively of said additional flowrestricting device, whereby said second pressuresensitive device is subjected to the pressure drop across said additional `flow-restricting device, iirst control means for said prime mover connected to said first pressure-sensitive device for operation thereby in a rst rotational speed range of said prime mover, second control means for said prime mover connected to said second pressuresensitive device for operation thereby in a second rotational Aspeed range of said primemover, lower than said first rotational speed range, bypass means Yconnected respectively toI the upstream and downstream sides of said additional flow-restricting device, and a valve in said bypass means to control the flow therethrough.

`8. A hydraulic speed-sensitive system as claimed in claim 7, characterised in that said prime mover is a gas turbine engine, including a compressor having adjustable compressor stator blading, combustion equipment, and a turbine, and comprising adjusting means to adjust said adjustable compressor stator blading, and means to interconnect said rst control means and said adjusting means,v whereby the adjustment is effected in accordance with the pressure drop sensed by said rst pressure-sensitive device, second adjusting means for permitting the injection of additional fuel into the combustion equipment of said gas turbine engine, and control means connected to said second pressure-sensitive device and to said adjusting means, whereby introduction of said extra fuel is controlled inaccordance with the pressure difference sensed by said I second pressure-sensitive device.

9. A hydraulic speed-sensitive system for effecting control of a gas turbine engine, comprising a first conduit, a fixed-capacity pump delivering solely into said conduit, constant-ratio drive means by which said pump is driven from said engine, a rst Vdow-'restricting device in said conduit, affirst casing, a diaphragm assembly dividing said casing into two chambers, one on each side of the assembly, a second conduit connecting one of saidI chambers with said iirst conduit on the upstream `side of said :How-restricting device, a third conduit connecting the other of said chambers with said first ,conduit on the downstream side of said dow-restricting device, an additional flow-restricting device in said conduit in series with andhaving a lesser effective area than said first flow-restricting device, a second casing, a second diaphragm assembly dividing said second casing into two chambers one on each side of said second connecting one of said last-'mentioned chambers assembly, a fourth conduit with said first conduit on the upstream side of said additional now-restricting device, a fifth conduit connecting the other of said last-mentioned chambers with said rst conduit on the downstream side of said additional flow-restricting device, a by-pass conduit from upstream to downstream of said additional flow-restricting device, a relief valve in said by-pass conduit to control the flow therethrough, a first control system of said gas turbine engine connected to said rst diaphragm assembly, and a second control system oi said gas turbine engine connected to said second diaphragm assembly, whereby a given control force is obtained at a higher speed to actuate said rst control system and at a lower speed to actuate said second control system.

10. A hydraulic speed-sensitive system for effecting control or a prime mover comprising a nrst conduit, a fixed-capacity pump delivering solely into said conduit, constant-ratio drive means by which said pump is driven from said prime mover, a rst flow-restricting device in said conduit, a first casing, a diaphragm assembly dividing said casing into two chambers, one on each side of the assembly, a second conduit connecting one of said chambers with said first conduit on the upstream side of said flow-restricting device, a third conduit connecting the other of said chambers with said first conduit on the downstream side of said flow-restricting device, an additional flow-restricting device in said conduit in series with, and having a lesser effective area than, said rst flow-restricting device, a second casing, a second diaphragm assembly dividing said second casing into two chambers, one on each side of the assembly, a fourth conduit connecting one of said last-mentioned chambers with said rst conduit on the upstream side of said additional flow-restricting device, a ifth conduit connecting the other of said last-mentioned chambers with said first conduit on the downstream side of said additional now-restricting device, a by-pass conduit from upstream to downstream of said additional now-restricting device, a relief valve in said by-pass conduit controlling the flow therethrough, and a control system of said prime mover connected to said rst and second diaphragm assemblies, whereby a given control force is obtained both at a higher speed and at a lower speed to actuate said control system.

ll. A hydraulic speed-sensitive system as claimed in claim 10, wherein the prime mover is a gas turbine engine having adjustable compressor guide vanes, and wherein the control system is operatively connected to said adjustable guide vanes.

l2. A hydraulic speed-sensitive system, comprising a Xed-capacity pump, means to drive said pump at a rotational speed proportional to the speed to which the system is to be sensitive, flow-restricting means connected to the pump to receive the delivery flow therefrom including a first now-restricting device and an additional now-restricting device, a pressure-sensitive device, means to connect said pressure-sensitive device, in opposition, to the upstream and downstream sides respectively of said first ilow-restricting device, whereby said pressure-sensitive device is responsive to the pressure drop across said rst now-restricting device, and means to connect said pressure-sensitive device in opposition to the upstream and downstream sides respectively of said additional flow-restricting device, whereby said pressure-sensitive device is responsive to the pressure drop across said addtional now-restricting device, said additional now-restricting device having a smaller effective area than said iirst now-restricting device, a change-over mechanism interposed in said connections from the upstream and downstream sides respectively of said first and said additional flow-restricting devices, whereby the pressure-sensitive device is connected alternatively to the upstream and downstream sides respectively of said rst now-restricting device and tol the upstream and downstream sides respectively of said additional now-restricting device, by-pass means connected to the upstream and downstream sides cf said additional :dow-restricting device, and a valve in said by-pass means to control the iiow therethrough.

13. A hydraulic speed-sensitive system as claimed in claim 12, wherein the first now-restricting device is of the orifice type, the ixed area pressure drop varying as the square of the flow therethrough, and wherein the additional flow-restricting device comprises a movable valve element sensitive to the pressure difference across the flow-restricting device and arranged to reduce the restriction aiTorded with increase of said pressure difference, and resilient means loading said movable valve element in the sense of closure, whereby the pressure drop across said additional flow-restricting device is substantially directly proportional to the flow therethrough.

14. A hydraulic speed-sensitive system, comprising a fixed-capacity pump, means to drive said pump at a rotational speed proportional to the speed to which said device is to be sensitive, flow-restricting means connected to the pump to receive the delivery flow therefrom including a nrst flow-restricting device and an additional flow-restricting device, said additional flow-restricting device having a smaller effective area than said iirst flow-restricting device, a pressuresensitive device, a rst valve body part, first conduit means between said first valve body part and the downstream side of said additional flowrestricting device, second conduit means between said rst valve body part and the downstream side of said first flow-restricting device, third conduit means between said first valve body part and said pressure-sensitive device, a second valve body part, fourth conduit means between said second valve body part and the upstream side of said additional flow-restricting device, fth conduit means between said second valve body part and the upstream side of said rst flow-restricting device, sixth conduit means between said second valve body part and said pressuresensitive device, and valve means to connect said third and sixth conduit means alternatively to said second and fth conduit means respectively in one position and to said first and fourth conduit means respectively in another position, operating means for moving said valve means between said one position and said other position, and by-pass means connected to the upstream and downstream sides of said additional flow-restricting device, and a valve in said by-pass means to control the flow therethrough.

l5. A hydraulic speed sensitive system as claimed in claim 14, further comprising a speedresponsive device responsive to the speed of the prime mover and connected to said operating means to actuate it at a predetermined speed. whereby said valve means is shifted from said one position to said other position at said speed.

16. A hydraulic speed-sensitive system as claimed in claim 14, wherein said valve in said by-pass means comprises a relief valve sensitive to the pressure difference across said additional flow-restricting device and arranged to open when a predetermined pressure difference is reached and to prevent any substantial increase in said pressure difference with increase of rotational speed beyond the rotational speed at which said predetermined pressure difference is reached.

17.- A hydraulic speed-sensitive system comprising a fixed-capacity pump adapted to be driven at a rotational speed proportional to the speed to which said system is to be sensitive, iiowrestricting means connected to the pump to receive the delivery iiow therefrom including a rst flow-restricting device of relatively large effective area and in series therewith an additional flow-restricting device of relatively small effective area, pressure-sensitive means subjected to pressure differences across said How-restricting devices, flow b-y-pass means connected to the upstream and downstream sides of said additional now-restricting device and a valve in said bypass means to control the ow therethrough.

DAVID OMRI DAVIES.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,910,202 Crago May 23, 1933 2,408,851 Hillier et al. Oct. 8, 1946

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