CA1097087A - Fuel control system - Google Patents
Fuel control systemInfo
- Publication number
- CA1097087A CA1097087A CA289,089A CA289089A CA1097087A CA 1097087 A CA1097087 A CA 1097087A CA 289089 A CA289089 A CA 289089A CA 1097087 A CA1097087 A CA 1097087A
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- Canada
- Prior art keywords
- engine
- fuel
- piston
- set forth
- control system
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02C—GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS
- F02C7/00—Features, components parts, details or accessories, not provided for in, or of interest apart form groups F02C1/00 - F02C6/00; Air intakes for jet-propulsion plants
- F02C7/26—Starting; Ignition
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Output Control And Ontrol Of Special Type Engine (AREA)
- Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
- Engine Equipment That Uses Special Cycles (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A gas turbine fuel control system for controlling the acceleration of an engine during start-up which permits the engine to accelerate substantially along its required-to-run line. Fuel flow to the engine is controlled by a speed governor, and means are included to gradually increase the speed set point of the governor in relation to elapsed time of the start-up period.
A gas turbine fuel control system for controlling the acceleration of an engine during start-up which permits the engine to accelerate substantially along its required-to-run line. Fuel flow to the engine is controlled by a speed governor, and means are included to gradually increase the speed set point of the governor in relation to elapsed time of the start-up period.
Description
- 1097()~7 BACKGROUND OF THE I~VENTION
~ ~ , This invention relates to fuel control systems for delivering fuel flow to gas turbine engines, and relates more particularly to an improved method and apparatus for controlling change in speed of the engine.
Perfon~ance of a gas turbine engine, including its acceleration characteristics, are limited by the onset of compresqor instability or stallO Accordingly, fuel control systemæ for a gas turbine engine are devised to, in one way or another, control fuel flow to avoid the region of compressor instability. For fastest engine acceleration during starting, on the other hand, it has generally been proposed to control fuel flow to the engine such that engine performance clo~ely apprsaches but does not ~counter the region of instability or stallO In this manner, it has been theorized that power i8 developed most rapidly by the engine and maximum acceleration thUC results. To accomplish this result, the majority of prior art fuel control systems are primarily concerned with sensing the proper engine performance parameters which indicate the ; engine is operating at its near maxL~um performance before encounter-i~g stall~ and accordingly scheduling fuel flow in response to these sensed parametersO Thus~ sensing tQmperature and pressure at various lo~t~n !~in the gas flow path through the engine, then scheduling fuel flow in relation to these various sensed tempera-tures~ pre~sures and other factoro~ has been a conventional approach to scheduling fuel flow to the erlgine during its accelerationO By attemp~ing to accelerate the engine closely to its region of in-stability~ such prior art fuel control 3ystems also were well suited to avoid engine operation near its required-to-run line during acceleration to minimize the possibility of "hung" starts~
~09~ 7 Conversely to the instability or stall characteristics of a parti-cular engine, the required-to-run line of the engine dictates the minimum amount of fuel flow required to the engine in order to over-co~ the inertia thereof, load imposed thereon, and the like in order to maintain a given speed. Fuel flow less than ~hat dictated by the required-to-run line causes deceleration of the engine to a slower spsed, and to accelerate the engine, obviously, the fuel flow to the engine must be above the required-to-run line.
A serious drawback for fuel control systems operating to accelerate a gas turbine engine xelates to the inability to obtain ~u~ficiently accurate measuremants of the various parameters of pressure, temperatur~, etc. utilized in controlling fuol flow, Such sensing devices have proved to be somewhat unreliable due to slow response time and ultimate deterioration from the extreme environ-mental conditions to which they may be exposed. Beyond this, it is also recognized that the sensing of such various engine parameters only gives a general NestimateH of how close the engine may be running to its instability region for a given set of external con-ditions~ Onset of compressor instability or engine stall varies greatly dependent upon external ambient conditions such as tempera-ture and pressure of the ambient airflow being received by the engine, as well as even the temperature o~ the fuel flow being delivered to the engine. Such changes in environmental conditions which markedly affect engine performance characteristics are highly pronounced in aircra~t applications of gas turbine engines where the ambient conditions can vary drastically. Accordingly, fuel control sys~ems have become more and more sopbisticated to compensate for various changes in external conditions such that conditions of instability are avoided, yet while assuring the engine can still be .
109'7(~7 maintained above its required-to-run lin~. For instance, the fuel control system must take into account sufficient variations in engine performa~ce characteristics so as to avoid "hot starts" which are more likely to occur at high altitude restarts of an aircraft mo~lted engine~ "Hot starts" are a result of the engine running near its stall line by delivering a high volume fuel flow to the engine combustion chamber such that a relatively high temperature at the discharge of the engine turbine and downstream of the combustion chamber, as well as high temperature exhaust from the engine re~ults~ Excessive temperature on the turbine and exhaust components created by such "hot start" can cause engine failure due to overheating of these downstream components. Exemplary disclosures of prior art systems may be found in U.SO Patents ~umbers 3,011,310 issued December 5, 1961 to The Bendix Corporation; 3,043,367 issued July 10, 1962 to Boeing Airplane Company; 3,085,619 issued April 6, 1963 to Rover Company Limited; 3,13~,892 issued July 7, 1964 to The Bendix Corporation and 3,399,527 issued September 3, 1968 to Joseph Lucaæ ~Industries) Limited.
SUMMARY OF TB I~VENTIO~
It is a primary ob~ect of the present invention to provide an improved fuel control ~y~tem and method wherein the engine accelerates ~ubstantially along or a~ closely adjacent its required-to-run line regardless oL ambient external conditions.
nother important object of the present invention is to provide a fuel control system which accelerate~ a gas turbine engine without reIiance upon ~ensing of various engine temperature and pressure parameters for its operation.
Another important object of the invention is to provide a novel fuel control and method ~or a gas turbine engine which accelerates the engine as a function of the elapsqd time of the ~09~7()~37 engine start-up period.
Anoth~r important object of the invention is to provide fuel controls and methods which control engine speed throughout accelera-tion to a pre-selected speed set point, along with method and means for changing the pre-selected set point speed to produce a desired acceleration.
More particularly, the invention contemplates a fuel control system having a speed governor responsive to engine speed to variably meter fu~l flow delivered to the engine in a feedback loop arrange-ment in order to maintain engine speed at the set point of thegovernor~ In conjunction with this, the invention contemplates method and means for adjusting the set point o the governor along a pre-selected schedule to produce the desired change of speed of the engine at a controlled rate. Specifically, to accelerate the ehgine along its required-to-run line, the speed set point of the governor i5 changed gradually at a rate which is somewhat slower than the corresponding acceleration of the engine when accelerating along its required-to-run line. In a preferred embodiment, such schedule change iD the governor speed set point i8 accomplished by a timing mechanism which is responsive to the elapsed time o the engine start-up period.
These and other more particular objects and advantages of the present invention are specifically set forth or will become apparent from the following detailed description of a preerred embodiment of tho invention, when read in conjunction with the accompanying drawing.
BRIEF DESCRIPTIO~ OF THE DRAWING
Fig. 1 is a partially schematic, partially cross sectional view of a gas turbine engine and fuel delivery system constructed in accordance with the principles of the present invention Fig. 2 is an exploded perspective view of the timing mechanism contemplated by the present invention; and F~g. 3 is a graphical representation of the fuel flow rate, W, dalivered to the engine versus engine speed, ~.
DETAI~ED DESCRIPTION OF ~EE PREFERRED_EMBODIME~T
Referring now more particularly to the drawing, a gas turbine engins 10 incorporates a combustian chamber 12 and a fuel delivery system 14 for controlling fuel flow to the combustion chamber. The fuel control system 14 includes a housing 16 having a fuel pump 18 of the type including a pair of intermeshing qears 19 which are driven by a shaft 20 operably coupled to the ro~atin~ drive shaft of the engine by an appropriate drive train schematically illustrated by dashod lines 22. Pressurized fuql flow f~om pump 18 is delivered through its outlet port 24 to a first fuel chamber 26 in housing ~; ~ 16. ~ second fue} chamber 28 in the housing communicates with the combustion chamber 12 through an appropriate conduit 30. The present fuel control 14 can be used in conjunction with various :. ~
~ other cQnventional fuel control devices as schematically illustrated ,~ :
by element 32. Chambers 26 and 28 communicate through a by-pass ` passag- 34 having a minimum uel control element therein, illustrat-~i~ ed a- a ~ixed orifice 36, which dictates the minimu~ rate o~ fuel flow delivered from chamber 26 to chamber 28 throughou~ operation of the engine. Rousing 16 further include an exhaust duct 38 pre-~erably interconn-cted with the inlet (not shown) of the pump 18.
metering valve 40 movably mounted within housing 16 and urged _ 5 -leftwardly by a biasing spring 42 acts to variably meter exhaust fuel flow from chamber 26 through exhaust duct 38. The opposite sides of the piston represented by valve 40 are respectively ex-posed to the pressure of fuel maintained in chambers 26 and 28.
In conventional manner therefore, the valve 40 acts to maintain a substantially constant pressure differential between chambers 26 and 28 by variably metering exhaust flow from chamber 26 through duct 38.
The fuel control system further includes timing mechanism in the form of a timing shaft 44 rigidly secured to rotate with fuel pump 18 and thus be rotatably driven by the engine 10~ Shaft 44 extends between first and second chambers 26 and 28 and includes a first internal flow passageway 46 having opposite ends communicating with the chambers 26, 28 through cross bores 47. The timing shat 44 further includes a second passage in a form of a groove 48 on a portion of the external surface of shaft 44, which groove 48 con-tinually commu~icates with second fuel chamber 280 A non-rotating pi3ton means 50 is disposed in chamber 26 to divide the latter into first and second compartments 52, 54 on oppo~ite side of pi~ton 50.
Compartment 52 directly communicates with.the pump outlet 24, while th- second compartment 54 present~ a substantially trapped fluid : volume. A light biasing spring 56 is mounted in compartment 54 to urge piston 50 lefwardly against the force exerted by pump outlet fIuid pre~sure in chamber 52, and a one-~ay check valve 58 permits oneJway fluid communication from second chamber 28 to second com-partment 54 while prahibiting reversa fluid flow therebetween. Firm-ly affixed to pi~ton 50 i9 a non-rotating sleeve 60 disposed in sub-stantially surrounding relationship to timing sha~t 44. A cross duct 62 in sleeve 60 permits periodic communication of the second compartment 54 with the exhaust path defined by groove 48 once each revolution of shaft 44~
Metering means in the form of a non-rotating element having a leftwardly extending valve portion 64 is cooperabla with rotating shaft 44 to variably meter fluid flow from passage 46 through cross ~ore 47 to second chamber 28. Biasing means in the form of a single helical coil spring 66 urges valve 64 rightwaxdly as viewed in Figs.
1 and 2 to increase the rate of fuel flow into chamber 28. Spring 66 is grounded to an abutment shoulder 68 secured to sleeve 60 and thus operably carried by piston 50. It will be apparent that the rightwardly directed biasing force exerted by spring 66 varies in relationship to the axial movement of piston 50. ~ ~omewhat con-ventionally structured speed governor generally denoted by the numeral 70 operates to exert a leftward force on valve 64 opposing that created by biasing spring 66~ The governor includes a disc 72 secured to rotate with timing shaft 44, and a plurality fly-weight~ 74 are rotatably mounted at the periphery of disc 72 such that the inwardly extending arms of the flyweights 74 are engagable with an inner rotating race 76 as shaft speed increases and the flyweights 74 tend to rotate outwardly under centrifugal forces.
Inner race 76 rotate~ with shaft 44, and through ball bearings 78 transmits the axial force exerted by the flyweight arms 74 to a non-rotating outar race 80 which engages valve 64. Thus, upon incr~a~e in speed of shaft 44 the flywoight arms 74 tend to rotate radially outwardly and exert a corresponding force tending to shift valve 64 laftwardly to restrict fluid flow from passage 46 to chamber 28. If desired, a valvo 82 may be incorporated which is 5hiftable between its closed po~ition illustrated blocking fluid communication batween compartments 52 and 54, to a flow permitting ~ L0~7~3~il7 ~lle~c; r.
position ~ fluid pres~uxe flow from first chamber 52 is directed into second chamber 54.
In operation, the performance characteristics of a conventional gas turbine engine can be most clearly understood by reference to Fig. 3 which provides a plot of the fuel flow rate, "W", versus the engine speed of opsration "N". Characteristically, the gas turbine engine operates below an upper line ~S" which indicates the con-ditions under which stall, surge or compressor instability can be encountered, and thus defines the upper limlt of operation of the gas turbine engin~. The engine thus must operate under the line "S", and yet above the lower curved line "R" which is indicative of the required-to-run line characteri~tic of the engine. The re-quired-to-run line simply means the minimum amount of fuel flow required to maintain the engine at a certain engine speed. Each of the engine operating limit lines "S" and "R" can vary substantial-ly dependent upon various changes in different operating parameters, including the changes in external ambient conditions. Upon con-sideration, it will be appreciated that the required-to-run line "R" is an indication of the overall inertia, load of the engine, etc., which must be overcome in order to maintain a certain ~ngine speed. The required-to~run line specifies the minimum power re-quired, at a given set of ambient conditions and other parameters such as engine load, required to maintain a certain engine ~peed.
It will al90 be apparent that thare exists a corresponding engine acceleration for the engine to accelerate from a lower to a higher speed and yet while operating substantially along or closely adjacent to this required-to-run line "R". Fuel control sy~tem 14 of the present invention is operable to assure that the engine does accelerate substantially along or closely adjacent to the required-7~7 -.o-run line "R" regardless of changes in the required-to-run line i~se]f due to ~arious external operating parameters such as external ambient conditions.
~ uel control system 14 operatas in the following manner. Upon start:-up of engine 10 through an external power source such as an electric motor, pump 18 gradually begins increasing in speed and displacing pressurizad fuel flow through its outlet 24 into com-partment 52, Piston 50 is located at its far leftward position upon start-up, In this position, fluid flow from compartment 52 into internal passage 46 of the timing shaft is substantially less than that allowed through the bypass orifice 36. ~ccordingly, the size of bypass orifice 36 is the controlling parameter during the initial start-up phase o the engine. As illustrated by line "A" in Fig. 3, the bypass orifice 36 is appropriately sized to allow engine start fuel flow into second chamber 28 and thus into combustion chamber 12.
During this initial phase of start-up and throughout engine operat-ion, the pressure diffsrential valve 40 operates to maintain a sub-stantially constant pressure differential between compartment 52 and chamber 28. In this context it i9 noted that pump 18 i~ conventional-ly sized such that its output displacement is somewhat greater thanthat required by the fuel delivery system such that a certain amount of return exhau9t flow continue~ through exhaust duct 38 to the inlet of the pump. In this manner the pump i5 90 sized that the rate of fuel flow delivered therefrom is not a factor in the control function itself.
During the start-up period, the speed of the engine 10 is relatively low and governor 70 does not exert sufficient force on valve 64 to control engine operation. Accordingly, the rate of fuel flow as depicted by line "AN dictate~ that a $uel enriched _ g _ ~)9~0~
nitial start phase has occurred. Once engine speed picks up to a certain mlnimum level, the speed governer 70 comes on control by exerting a leftward force on valve 64 strong enough to overcome the force of spring 66 and urge valve 54 to a po~ition metering fuel flow from passage 46 into chamber 28, In combination with the movement of the sp~ed governor flyweights 74, the initial re-volutions of shaft 44 have allowed enough exhaust of fuel flow from second compartment 54 to duct 62 and groove 48 into chamber 28 to allow slight rightward movement of piston 50 to cleax communication between first compartment 52 and internal passage 46. Accordingly, at a pre-selected engine speed, and at a pre-selected elapsed time of the engine start-up period as determined by pre-selected numher of revolutions of t~ming shaft 44, fuel flow from compartment 52 passes primarily through passage 46 to second chamber 28, and the position of valve 64 becomes the fuel controlling parameter.
By allowing only a single spurt of fuel from compartment 54 through groove 48 once each revolution of timing shaft 44, the r ightward movement of pi~ton 50 is quite slaw, particularly in compar~son to the response time of the feedback speed control pre-~ented by governor 72. In this context, the response time ofgovernor 70 in shifting and moving the valve 64 leftwardly and rightwardly is ~uffi¢iently faster than the relatively slow movement of piston 50, ~uch that the valve 64 is capable of modulating the rate of fuel flow into chamber 28 so as to bring engine ~peed to a pre-selected level in accordance with the speed feedback control ~y~tem provided by governor 70. Thus, once the position of valve 64 becomes the parameter controlling fual flow, the engine operat-ing line A of Fig. 3 immediately is brought down to the required-to-run line R by governor 70. Being a ~imple feedback loop control 7V~7 system, it is apparent that governor 70 operates to reduce fuel flow to the engine so as to maintain engine speed at a certain pre-selected value, and thus dictates that the engine run on its required-to-run line R regardless of parameters such as ambient pressure and temperature which affect the required-to-run line.
As the engine continues to operate, however, it will be apparent that piston 50 continues to shift at a slow speed gradually rightwardly as a small spurt of fluid leaves compartment 54 during each revolution of timing shaft 44. The rightward movement of piston 50 also moves abutment 68 rightwardly increasing the compression of biasing spring 66. This increases the speed set point and thus requires the engine to increase its speed to produce a greater force on governor 70 to counteract the increased biasing force of the more compressed spring 66. In this manner it can be seen that as the piston 50 gradually moves rightwardly, the engine gradually accelerates along the required-to-run line. Once piston 50 is shifted completely rightwardly, the governor 70 continues to maintain a constant engine speed thereafter as the biasing spring 66 exerts the precise force required to maintain engine speed at its maximum desired constant speed value.
It will be apparent that the timing piston 50 gradually increases the compression of spring 66 and thus the speed set point of the governor 70 in relation to the elapsed time of the start-up or acceleration period. Thus, the position of abutment 68 which determines the compression of spring 66, is in essence a signal generator producing a signal that is indicative of a desired engine speed. Accordingly, the value of this desired engine speed signal is automatically varied in relation to the elapsed time as sensed by movement of piston 50. Preferably, the speed of movement of piston 50 is sufficiently slow to assure that the engine runs along its required-to-run line in order to ~ ..
minimize unnecessary heat buildup in the engine as exemplified - 1~
1()97V~7 by an increasing turbine discharge or engine exhaust temperature.
However, if desired, the speed of movement of piston 50 may be otherwise controlled as by the size of . ~
- lla -:
- .-: .
. - , . .
:
~C)9~70~'7 duct 62 and/or groove 48 to allow the engine to accelerate at a faster rate, i.e,, substantially displaced from the required-to-run line R and closer to the stall line S.
To assure that the engine accelerates substantially ~ ong or closely adjacent the required-to-run line R, it is required that the speed of movement of piston 50 be less than the corresponding acceleration of the engine when accelarating along its required-to-run line. For instance, if it is assumed that an engine normally requires 40 seconds to accelerate to 100~ speed if operating com-pletely along its required-to-run line, then the duct 62 and groove 48 are sized such that the time required for piston 50 to move from its completely leftward to its completely rightward position bs slightly more than 40 seconds; i.e., 45 seconds.
Once the engine is decelerated and/or stopped t second com-partment 54 i5 automatically refilled with fuel throuyh oneJway check valve 58 by virtue of the leftward movement of piston 50 created by biasing spring 56 once pressure in compartment 52 is relieved. Thus piston 50 is automatically reset for another engine start. It will be apparent from the foregoing that the selected maximum engine speed may also be varied from that dictated by complete rightward movement o the piston 50, simply by modulat-ing the inf low and outflow of fluid through compartment 54 in order to hold piston 50 at a pOSitiQn other than its ~ar rightward po~ition during constant speed engine opera*ion. For instance, a second engine speed may be select2d simply by actuating a valve 82 to interconnect compartments 52 and 54. By relatively sizing these two compartments and spring 56, the force of spring 56 can overcome the egual pressures maintained in compartments 52 and 54 to shift piston 50 completely leftwardly so that fuel flow to the combustion 1()S~'7(~7 chamber 12 is controlled solely by orifice 36. In response, the engine will be maintained at a constant speed determined by the rate of fuel fl~w permitt~d thr~ugh orifice 360 In the preferred embodiment fluid exhausts from compartment 54 to chamber 28 and on to the combustion chamber 12 This small fuel flow has a ne~ligible effect on the engine, but in any case can be taken into account in controlling engine accelsration. If desired, flow from compartment 54 could be exhausted elsewhere, such as to exhaust duct 38. It will be also apparent that the present invention may be utilized in conjunction with other conventional angine fuel delivery controls as exemplified by controls 32, and that the fu~l control system 14 may be easily adapted to different engines simply by modifying the size, shape, or number of duct 62, groove 48, and voluma of compartmant 54.
It will be noted that the required-to-run line R approximates a second order curve while the varying force ~reated by a single helical coil compression spring 66 is normally approximating a first order function. To compensate for the second order curve R, a pair of helical coil compression springs 66 may be incorporated. By in-corporating such a pair of compression ~prings, the bypass orifice36 may be made quite small such that tha governor 70 and valve 64 begin controlling engine operation at a relatively low speed; iOe., 10% of rat~d maximum speed. On the other hand, it has been found preferable in many instance~ to size orifice 36 and the movement of pi-qton 50, such that the ori~ice 36 controls engine operation up to approximately 45% of rated speed. This provides a fuel enrichment during initial startup as discussed previously, and also then allows a qingle spring 66 to be utilized since the required-to-run line from the 40~ speed point to 100% speed poin~ can be closely approxi-7u~7 uated by a linear function such as that by spring 66.
While it would appear that a somewhat slower engine acceleration would result ~rom the present invention,it has been found in actual practice that since the engine operates substantially at its required-to-run line throughout acceleration and at greater engine efficiency, the acceleration time is only slightly longer than if the engine were operating near curve S. Thus, the better engine efficiency at curve R substantially offsets any time decrease a~ford-ed by operating near curve S. Tests have also shown a substantial 10 reduction in turbine discharge temperature during acceleration, and the automatic compensation for changes in the parameters that affect the required-to-run line.
From the foregoing, it will be apparent that the present invention contemplates an improved apparatus and method for control-ling fuel flow to a gas turbine engine by adjusting fuel flow to the engine during a start-up period in relation to the elapsed time of the start-up period. Further, it will be apparent that the invention contemplates a method of accelerating a gas turbine engine wherain engine speed is sensed, fuel flow to the engine i9 adjusted in re-20 lation to the sensed speed to maintain the engine at a pre~selectedspeed, and then the pre-s~lected speed set point is increased at a selected rate. Preferably this selected rate is slower than the corresponding acceleration of the engine when operating its required-to-run line. In other words, the pre-selected speed as dictated by the position of piston 5Q and the compression of spring 66, is in-creased at a rate slower than the corresponding accelera~on which occurs as the engine develops power along a minimum power requirement schedule defined as that power required to overcome engine inertia and the like to maintain a certain engine speed. Further the invention 10$1~70~7 contemplates such a m~thod wherei.n fuel flow to the engine is ad-justed to the difference between actual and selected engine speeds to minimize the difference therebetween by the action of the qovernor 70 and speed feedback control, and the value of the desirad engine speed signal is automatically changed at a pre-selected rate, pre-ferably the response rate of the speed feedback control being sub-stantially faster than the pre-selected rate at which the value of the desired speed signal is changed. In the illustrated embodiment these methods and apparatus are carried out by increasing the force created by compression spring 66 in order to cause engine acceler-ation. The spring force is increased by movement of the piston 50 which is controlled in relation to the cumulative number of re- -volutions of the timing mechanism represented by timing shaft 44, The foregoing detailed description of a preferred embodiment of the invention should be considered exemplary in nature and not as limiting ~o the scope and spirit of the invention as set forth ~ ppe,r.~e~
in the ~=o~ed claims~
_ 15 -
~ ~ , This invention relates to fuel control systems for delivering fuel flow to gas turbine engines, and relates more particularly to an improved method and apparatus for controlling change in speed of the engine.
Perfon~ance of a gas turbine engine, including its acceleration characteristics, are limited by the onset of compresqor instability or stallO Accordingly, fuel control systemæ for a gas turbine engine are devised to, in one way or another, control fuel flow to avoid the region of compressor instability. For fastest engine acceleration during starting, on the other hand, it has generally been proposed to control fuel flow to the engine such that engine performance clo~ely apprsaches but does not ~counter the region of instability or stallO In this manner, it has been theorized that power i8 developed most rapidly by the engine and maximum acceleration thUC results. To accomplish this result, the majority of prior art fuel control systems are primarily concerned with sensing the proper engine performance parameters which indicate the ; engine is operating at its near maxL~um performance before encounter-i~g stall~ and accordingly scheduling fuel flow in response to these sensed parametersO Thus~ sensing tQmperature and pressure at various lo~t~n !~in the gas flow path through the engine, then scheduling fuel flow in relation to these various sensed tempera-tures~ pre~sures and other factoro~ has been a conventional approach to scheduling fuel flow to the erlgine during its accelerationO By attemp~ing to accelerate the engine closely to its region of in-stability~ such prior art fuel control 3ystems also were well suited to avoid engine operation near its required-to-run line during acceleration to minimize the possibility of "hung" starts~
~09~ 7 Conversely to the instability or stall characteristics of a parti-cular engine, the required-to-run line of the engine dictates the minimum amount of fuel flow required to the engine in order to over-co~ the inertia thereof, load imposed thereon, and the like in order to maintain a given speed. Fuel flow less than ~hat dictated by the required-to-run line causes deceleration of the engine to a slower spsed, and to accelerate the engine, obviously, the fuel flow to the engine must be above the required-to-run line.
A serious drawback for fuel control systems operating to accelerate a gas turbine engine xelates to the inability to obtain ~u~ficiently accurate measuremants of the various parameters of pressure, temperatur~, etc. utilized in controlling fuol flow, Such sensing devices have proved to be somewhat unreliable due to slow response time and ultimate deterioration from the extreme environ-mental conditions to which they may be exposed. Beyond this, it is also recognized that the sensing of such various engine parameters only gives a general NestimateH of how close the engine may be running to its instability region for a given set of external con-ditions~ Onset of compressor instability or engine stall varies greatly dependent upon external ambient conditions such as tempera-ture and pressure of the ambient airflow being received by the engine, as well as even the temperature o~ the fuel flow being delivered to the engine. Such changes in environmental conditions which markedly affect engine performance characteristics are highly pronounced in aircra~t applications of gas turbine engines where the ambient conditions can vary drastically. Accordingly, fuel control sys~ems have become more and more sopbisticated to compensate for various changes in external conditions such that conditions of instability are avoided, yet while assuring the engine can still be .
109'7(~7 maintained above its required-to-run lin~. For instance, the fuel control system must take into account sufficient variations in engine performa~ce characteristics so as to avoid "hot starts" which are more likely to occur at high altitude restarts of an aircraft mo~lted engine~ "Hot starts" are a result of the engine running near its stall line by delivering a high volume fuel flow to the engine combustion chamber such that a relatively high temperature at the discharge of the engine turbine and downstream of the combustion chamber, as well as high temperature exhaust from the engine re~ults~ Excessive temperature on the turbine and exhaust components created by such "hot start" can cause engine failure due to overheating of these downstream components. Exemplary disclosures of prior art systems may be found in U.SO Patents ~umbers 3,011,310 issued December 5, 1961 to The Bendix Corporation; 3,043,367 issued July 10, 1962 to Boeing Airplane Company; 3,085,619 issued April 6, 1963 to Rover Company Limited; 3,13~,892 issued July 7, 1964 to The Bendix Corporation and 3,399,527 issued September 3, 1968 to Joseph Lucaæ ~Industries) Limited.
SUMMARY OF TB I~VENTIO~
It is a primary ob~ect of the present invention to provide an improved fuel control ~y~tem and method wherein the engine accelerates ~ubstantially along or a~ closely adjacent its required-to-run line regardless oL ambient external conditions.
nother important object of the present invention is to provide a fuel control system which accelerate~ a gas turbine engine without reIiance upon ~ensing of various engine temperature and pressure parameters for its operation.
Another important object of the invention is to provide a novel fuel control and method ~or a gas turbine engine which accelerates the engine as a function of the elapsqd time of the ~09~7()~37 engine start-up period.
Anoth~r important object of the invention is to provide fuel controls and methods which control engine speed throughout accelera-tion to a pre-selected speed set point, along with method and means for changing the pre-selected set point speed to produce a desired acceleration.
More particularly, the invention contemplates a fuel control system having a speed governor responsive to engine speed to variably meter fu~l flow delivered to the engine in a feedback loop arrange-ment in order to maintain engine speed at the set point of thegovernor~ In conjunction with this, the invention contemplates method and means for adjusting the set point o the governor along a pre-selected schedule to produce the desired change of speed of the engine at a controlled rate. Specifically, to accelerate the ehgine along its required-to-run line, the speed set point of the governor i5 changed gradually at a rate which is somewhat slower than the corresponding acceleration of the engine when accelerating along its required-to-run line. In a preferred embodiment, such schedule change iD the governor speed set point i8 accomplished by a timing mechanism which is responsive to the elapsed time o the engine start-up period.
These and other more particular objects and advantages of the present invention are specifically set forth or will become apparent from the following detailed description of a preerred embodiment of tho invention, when read in conjunction with the accompanying drawing.
BRIEF DESCRIPTIO~ OF THE DRAWING
Fig. 1 is a partially schematic, partially cross sectional view of a gas turbine engine and fuel delivery system constructed in accordance with the principles of the present invention Fig. 2 is an exploded perspective view of the timing mechanism contemplated by the present invention; and F~g. 3 is a graphical representation of the fuel flow rate, W, dalivered to the engine versus engine speed, ~.
DETAI~ED DESCRIPTION OF ~EE PREFERRED_EMBODIME~T
Referring now more particularly to the drawing, a gas turbine engins 10 incorporates a combustian chamber 12 and a fuel delivery system 14 for controlling fuel flow to the combustion chamber. The fuel control system 14 includes a housing 16 having a fuel pump 18 of the type including a pair of intermeshing qears 19 which are driven by a shaft 20 operably coupled to the ro~atin~ drive shaft of the engine by an appropriate drive train schematically illustrated by dashod lines 22. Pressurized fuql flow f~om pump 18 is delivered through its outlet port 24 to a first fuel chamber 26 in housing ~; ~ 16. ~ second fue} chamber 28 in the housing communicates with the combustion chamber 12 through an appropriate conduit 30. The present fuel control 14 can be used in conjunction with various :. ~
~ other cQnventional fuel control devices as schematically illustrated ,~ :
by element 32. Chambers 26 and 28 communicate through a by-pass ` passag- 34 having a minimum uel control element therein, illustrat-~i~ ed a- a ~ixed orifice 36, which dictates the minimu~ rate o~ fuel flow delivered from chamber 26 to chamber 28 throughou~ operation of the engine. Rousing 16 further include an exhaust duct 38 pre-~erably interconn-cted with the inlet (not shown) of the pump 18.
metering valve 40 movably mounted within housing 16 and urged _ 5 -leftwardly by a biasing spring 42 acts to variably meter exhaust fuel flow from chamber 26 through exhaust duct 38. The opposite sides of the piston represented by valve 40 are respectively ex-posed to the pressure of fuel maintained in chambers 26 and 28.
In conventional manner therefore, the valve 40 acts to maintain a substantially constant pressure differential between chambers 26 and 28 by variably metering exhaust flow from chamber 26 through duct 38.
The fuel control system further includes timing mechanism in the form of a timing shaft 44 rigidly secured to rotate with fuel pump 18 and thus be rotatably driven by the engine 10~ Shaft 44 extends between first and second chambers 26 and 28 and includes a first internal flow passageway 46 having opposite ends communicating with the chambers 26, 28 through cross bores 47. The timing shat 44 further includes a second passage in a form of a groove 48 on a portion of the external surface of shaft 44, which groove 48 con-tinually commu~icates with second fuel chamber 280 A non-rotating pi3ton means 50 is disposed in chamber 26 to divide the latter into first and second compartments 52, 54 on oppo~ite side of pi~ton 50.
Compartment 52 directly communicates with.the pump outlet 24, while th- second compartment 54 present~ a substantially trapped fluid : volume. A light biasing spring 56 is mounted in compartment 54 to urge piston 50 lefwardly against the force exerted by pump outlet fIuid pre~sure in chamber 52, and a one-~ay check valve 58 permits oneJway fluid communication from second chamber 28 to second com-partment 54 while prahibiting reversa fluid flow therebetween. Firm-ly affixed to pi~ton 50 i9 a non-rotating sleeve 60 disposed in sub-stantially surrounding relationship to timing sha~t 44. A cross duct 62 in sleeve 60 permits periodic communication of the second compartment 54 with the exhaust path defined by groove 48 once each revolution of shaft 44~
Metering means in the form of a non-rotating element having a leftwardly extending valve portion 64 is cooperabla with rotating shaft 44 to variably meter fluid flow from passage 46 through cross ~ore 47 to second chamber 28. Biasing means in the form of a single helical coil spring 66 urges valve 64 rightwaxdly as viewed in Figs.
1 and 2 to increase the rate of fuel flow into chamber 28. Spring 66 is grounded to an abutment shoulder 68 secured to sleeve 60 and thus operably carried by piston 50. It will be apparent that the rightwardly directed biasing force exerted by spring 66 varies in relationship to the axial movement of piston 50. ~ ~omewhat con-ventionally structured speed governor generally denoted by the numeral 70 operates to exert a leftward force on valve 64 opposing that created by biasing spring 66~ The governor includes a disc 72 secured to rotate with timing shaft 44, and a plurality fly-weight~ 74 are rotatably mounted at the periphery of disc 72 such that the inwardly extending arms of the flyweights 74 are engagable with an inner rotating race 76 as shaft speed increases and the flyweights 74 tend to rotate outwardly under centrifugal forces.
Inner race 76 rotate~ with shaft 44, and through ball bearings 78 transmits the axial force exerted by the flyweight arms 74 to a non-rotating outar race 80 which engages valve 64. Thus, upon incr~a~e in speed of shaft 44 the flywoight arms 74 tend to rotate radially outwardly and exert a corresponding force tending to shift valve 64 laftwardly to restrict fluid flow from passage 46 to chamber 28. If desired, a valvo 82 may be incorporated which is 5hiftable between its closed po~ition illustrated blocking fluid communication batween compartments 52 and 54, to a flow permitting ~ L0~7~3~il7 ~lle~c; r.
position ~ fluid pres~uxe flow from first chamber 52 is directed into second chamber 54.
In operation, the performance characteristics of a conventional gas turbine engine can be most clearly understood by reference to Fig. 3 which provides a plot of the fuel flow rate, "W", versus the engine speed of opsration "N". Characteristically, the gas turbine engine operates below an upper line ~S" which indicates the con-ditions under which stall, surge or compressor instability can be encountered, and thus defines the upper limlt of operation of the gas turbine engin~. The engine thus must operate under the line "S", and yet above the lower curved line "R" which is indicative of the required-to-run line characteri~tic of the engine. The re-quired-to-run line simply means the minimum amount of fuel flow required to maintain the engine at a certain engine speed. Each of the engine operating limit lines "S" and "R" can vary substantial-ly dependent upon various changes in different operating parameters, including the changes in external ambient conditions. Upon con-sideration, it will be appreciated that the required-to-run line "R" is an indication of the overall inertia, load of the engine, etc., which must be overcome in order to maintain a certain ~ngine speed. The required-to~run line specifies the minimum power re-quired, at a given set of ambient conditions and other parameters such as engine load, required to maintain a certain engine ~peed.
It will al90 be apparent that thare exists a corresponding engine acceleration for the engine to accelerate from a lower to a higher speed and yet while operating substantially along or closely adjacent to this required-to-run line "R". Fuel control sy~tem 14 of the present invention is operable to assure that the engine does accelerate substantially along or closely adjacent to the required-7~7 -.o-run line "R" regardless of changes in the required-to-run line i~se]f due to ~arious external operating parameters such as external ambient conditions.
~ uel control system 14 operatas in the following manner. Upon start:-up of engine 10 through an external power source such as an electric motor, pump 18 gradually begins increasing in speed and displacing pressurizad fuel flow through its outlet 24 into com-partment 52, Piston 50 is located at its far leftward position upon start-up, In this position, fluid flow from compartment 52 into internal passage 46 of the timing shaft is substantially less than that allowed through the bypass orifice 36. ~ccordingly, the size of bypass orifice 36 is the controlling parameter during the initial start-up phase o the engine. As illustrated by line "A" in Fig. 3, the bypass orifice 36 is appropriately sized to allow engine start fuel flow into second chamber 28 and thus into combustion chamber 12.
During this initial phase of start-up and throughout engine operat-ion, the pressure diffsrential valve 40 operates to maintain a sub-stantially constant pressure differential between compartment 52 and chamber 28. In this context it i9 noted that pump 18 i~ conventional-ly sized such that its output displacement is somewhat greater thanthat required by the fuel delivery system such that a certain amount of return exhau9t flow continue~ through exhaust duct 38 to the inlet of the pump. In this manner the pump i5 90 sized that the rate of fuel flow delivered therefrom is not a factor in the control function itself.
During the start-up period, the speed of the engine 10 is relatively low and governor 70 does not exert sufficient force on valve 64 to control engine operation. Accordingly, the rate of fuel flow as depicted by line "AN dictate~ that a $uel enriched _ g _ ~)9~0~
nitial start phase has occurred. Once engine speed picks up to a certain mlnimum level, the speed governer 70 comes on control by exerting a leftward force on valve 64 strong enough to overcome the force of spring 66 and urge valve 54 to a po~ition metering fuel flow from passage 46 into chamber 28, In combination with the movement of the sp~ed governor flyweights 74, the initial re-volutions of shaft 44 have allowed enough exhaust of fuel flow from second compartment 54 to duct 62 and groove 48 into chamber 28 to allow slight rightward movement of piston 50 to cleax communication between first compartment 52 and internal passage 46. Accordingly, at a pre-selected engine speed, and at a pre-selected elapsed time of the engine start-up period as determined by pre-selected numher of revolutions of t~ming shaft 44, fuel flow from compartment 52 passes primarily through passage 46 to second chamber 28, and the position of valve 64 becomes the fuel controlling parameter.
By allowing only a single spurt of fuel from compartment 54 through groove 48 once each revolution of timing shaft 44, the r ightward movement of pi~ton 50 is quite slaw, particularly in compar~son to the response time of the feedback speed control pre-~ented by governor 72. In this context, the response time ofgovernor 70 in shifting and moving the valve 64 leftwardly and rightwardly is ~uffi¢iently faster than the relatively slow movement of piston 50, ~uch that the valve 64 is capable of modulating the rate of fuel flow into chamber 28 so as to bring engine ~peed to a pre-selected level in accordance with the speed feedback control ~y~tem provided by governor 70. Thus, once the position of valve 64 becomes the parameter controlling fual flow, the engine operat-ing line A of Fig. 3 immediately is brought down to the required-to-run line R by governor 70. Being a ~imple feedback loop control 7V~7 system, it is apparent that governor 70 operates to reduce fuel flow to the engine so as to maintain engine speed at a certain pre-selected value, and thus dictates that the engine run on its required-to-run line R regardless of parameters such as ambient pressure and temperature which affect the required-to-run line.
As the engine continues to operate, however, it will be apparent that piston 50 continues to shift at a slow speed gradually rightwardly as a small spurt of fluid leaves compartment 54 during each revolution of timing shaft 44. The rightward movement of piston 50 also moves abutment 68 rightwardly increasing the compression of biasing spring 66. This increases the speed set point and thus requires the engine to increase its speed to produce a greater force on governor 70 to counteract the increased biasing force of the more compressed spring 66. In this manner it can be seen that as the piston 50 gradually moves rightwardly, the engine gradually accelerates along the required-to-run line. Once piston 50 is shifted completely rightwardly, the governor 70 continues to maintain a constant engine speed thereafter as the biasing spring 66 exerts the precise force required to maintain engine speed at its maximum desired constant speed value.
It will be apparent that the timing piston 50 gradually increases the compression of spring 66 and thus the speed set point of the governor 70 in relation to the elapsed time of the start-up or acceleration period. Thus, the position of abutment 68 which determines the compression of spring 66, is in essence a signal generator producing a signal that is indicative of a desired engine speed. Accordingly, the value of this desired engine speed signal is automatically varied in relation to the elapsed time as sensed by movement of piston 50. Preferably, the speed of movement of piston 50 is sufficiently slow to assure that the engine runs along its required-to-run line in order to ~ ..
minimize unnecessary heat buildup in the engine as exemplified - 1~
1()97V~7 by an increasing turbine discharge or engine exhaust temperature.
However, if desired, the speed of movement of piston 50 may be otherwise controlled as by the size of . ~
- lla -:
- .-: .
. - , . .
:
~C)9~70~'7 duct 62 and/or groove 48 to allow the engine to accelerate at a faster rate, i.e,, substantially displaced from the required-to-run line R and closer to the stall line S.
To assure that the engine accelerates substantially ~ ong or closely adjacent the required-to-run line R, it is required that the speed of movement of piston 50 be less than the corresponding acceleration of the engine when accelarating along its required-to-run line. For instance, if it is assumed that an engine normally requires 40 seconds to accelerate to 100~ speed if operating com-pletely along its required-to-run line, then the duct 62 and groove 48 are sized such that the time required for piston 50 to move from its completely leftward to its completely rightward position bs slightly more than 40 seconds; i.e., 45 seconds.
Once the engine is decelerated and/or stopped t second com-partment 54 i5 automatically refilled with fuel throuyh oneJway check valve 58 by virtue of the leftward movement of piston 50 created by biasing spring 56 once pressure in compartment 52 is relieved. Thus piston 50 is automatically reset for another engine start. It will be apparent from the foregoing that the selected maximum engine speed may also be varied from that dictated by complete rightward movement o the piston 50, simply by modulat-ing the inf low and outflow of fluid through compartment 54 in order to hold piston 50 at a pOSitiQn other than its ~ar rightward po~ition during constant speed engine opera*ion. For instance, a second engine speed may be select2d simply by actuating a valve 82 to interconnect compartments 52 and 54. By relatively sizing these two compartments and spring 56, the force of spring 56 can overcome the egual pressures maintained in compartments 52 and 54 to shift piston 50 completely leftwardly so that fuel flow to the combustion 1()S~'7(~7 chamber 12 is controlled solely by orifice 36. In response, the engine will be maintained at a constant speed determined by the rate of fuel fl~w permitt~d thr~ugh orifice 360 In the preferred embodiment fluid exhausts from compartment 54 to chamber 28 and on to the combustion chamber 12 This small fuel flow has a ne~ligible effect on the engine, but in any case can be taken into account in controlling engine accelsration. If desired, flow from compartment 54 could be exhausted elsewhere, such as to exhaust duct 38. It will be also apparent that the present invention may be utilized in conjunction with other conventional angine fuel delivery controls as exemplified by controls 32, and that the fu~l control system 14 may be easily adapted to different engines simply by modifying the size, shape, or number of duct 62, groove 48, and voluma of compartmant 54.
It will be noted that the required-to-run line R approximates a second order curve while the varying force ~reated by a single helical coil compression spring 66 is normally approximating a first order function. To compensate for the second order curve R, a pair of helical coil compression springs 66 may be incorporated. By in-corporating such a pair of compression ~prings, the bypass orifice36 may be made quite small such that tha governor 70 and valve 64 begin controlling engine operation at a relatively low speed; iOe., 10% of rat~d maximum speed. On the other hand, it has been found preferable in many instance~ to size orifice 36 and the movement of pi-qton 50, such that the ori~ice 36 controls engine operation up to approximately 45% of rated speed. This provides a fuel enrichment during initial startup as discussed previously, and also then allows a qingle spring 66 to be utilized since the required-to-run line from the 40~ speed point to 100% speed poin~ can be closely approxi-7u~7 uated by a linear function such as that by spring 66.
While it would appear that a somewhat slower engine acceleration would result ~rom the present invention,it has been found in actual practice that since the engine operates substantially at its required-to-run line throughout acceleration and at greater engine efficiency, the acceleration time is only slightly longer than if the engine were operating near curve S. Thus, the better engine efficiency at curve R substantially offsets any time decrease a~ford-ed by operating near curve S. Tests have also shown a substantial 10 reduction in turbine discharge temperature during acceleration, and the automatic compensation for changes in the parameters that affect the required-to-run line.
From the foregoing, it will be apparent that the present invention contemplates an improved apparatus and method for control-ling fuel flow to a gas turbine engine by adjusting fuel flow to the engine during a start-up period in relation to the elapsed time of the start-up period. Further, it will be apparent that the invention contemplates a method of accelerating a gas turbine engine wherain engine speed is sensed, fuel flow to the engine i9 adjusted in re-20 lation to the sensed speed to maintain the engine at a pre~selectedspeed, and then the pre-s~lected speed set point is increased at a selected rate. Preferably this selected rate is slower than the corresponding acceleration of the engine when operating its required-to-run line. In other words, the pre-selected speed as dictated by the position of piston 5Q and the compression of spring 66, is in-creased at a rate slower than the corresponding accelera~on which occurs as the engine develops power along a minimum power requirement schedule defined as that power required to overcome engine inertia and the like to maintain a certain engine speed. Further the invention 10$1~70~7 contemplates such a m~thod wherei.n fuel flow to the engine is ad-justed to the difference between actual and selected engine speeds to minimize the difference therebetween by the action of the qovernor 70 and speed feedback control, and the value of the desirad engine speed signal is automatically changed at a pre-selected rate, pre-ferably the response rate of the speed feedback control being sub-stantially faster than the pre-selected rate at which the value of the desired speed signal is changed. In the illustrated embodiment these methods and apparatus are carried out by increasing the force created by compression spring 66 in order to cause engine acceler-ation. The spring force is increased by movement of the piston 50 which is controlled in relation to the cumulative number of re- -volutions of the timing mechanism represented by timing shaft 44, The foregoing detailed description of a preferred embodiment of the invention should be considered exemplary in nature and not as limiting ~o the scope and spirit of the invention as set forth ~ ppe,r.~e~
in the ~=o~ed claims~
_ 15 -
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In combination with a gas turbine engine fuel delivery system:
metering means for adjusting the rate of fuel flow delivered to said engine;
governor means responsive to engine speed for exerting a first force on said metering means in relation to engine speed;
biasing means for exerting a second, opposing force on said metering means;
time sensing means for sensing the elapsed time of a preselected portion of engine operation, said time sensing means including mechanism rotatably driven by the engine, and means for sensing the cumulative number of revolutions of said mechanism during said preselected portion of engine operation;
and means responsive to said time sensing means fox increasing said second force as a predetermined function of said elapsed time to accelerate said engine.
metering means for adjusting the rate of fuel flow delivered to said engine;
governor means responsive to engine speed for exerting a first force on said metering means in relation to engine speed;
biasing means for exerting a second, opposing force on said metering means;
time sensing means for sensing the elapsed time of a preselected portion of engine operation, said time sensing means including mechanism rotatably driven by the engine, and means for sensing the cumulative number of revolutions of said mechanism during said preselected portion of engine operation;
and means responsive to said time sensing means fox increasing said second force as a predetermined function of said elapsed time to accelerate said engine.
2. In a gas turbine engine fuel control system having a passage directing fuel flow to the engine:
metering means for adjusting the rate of fuel flow through said passage;
governor means responsive to engine speed and exerting a first force on said metering means in relation to engine speed;
biasing means exerting a second force on said metering means opposing said first force;
mechanism including a timing shaft rotatably driven by the engine; and means operably associated with said mechanism for increasing said second force in relation to the cumulative number of revolutions of said mechanism during start-up of the engine.
metering means for adjusting the rate of fuel flow through said passage;
governor means responsive to engine speed and exerting a first force on said metering means in relation to engine speed;
biasing means exerting a second force on said metering means opposing said first force;
mechanism including a timing shaft rotatably driven by the engine; and means operably associated with said mechanism for increasing said second force in relation to the cumulative number of revolutions of said mechanism during start-up of the engine.
3. A fuel control system as set forth in Claim 2, further including a fuel pump driven by said engine and directing pressurized fuel flow to said passage.
4. A fuel control system as set forth in Claim 3, wherein said means for increasing the second force includes piston means movable to alter the compression of said biasing means to adjust said second force, said piston operably associated with said shaft whereby piston movement is operably controlled by said shaft.
5. A fuel control system as set forth in Claim 4, wherein said piston includes a shoulder engaging said biasing means, said biasing means including compressible spring means extender between said metering means and said shoulder.
6. A fuel control system as set forth in Claim 5, further including a housing cooperable with said piston to define first and second fluid compartments on opposite sides of said piston, said piston arranged whereby pressurized fuel from said pump is delivered to said first compartment to move said piston in a first axial direction contracting said second compartment and increasing said second force.
7. A fuel control system as set forth in Claim 6, wherein said shaft defines a fluid exhaust path periodically communi-cating with said second compartment to permit fluid escape therefrom and corresponding piston movement in said first direction in relation to the cumulative number of revolutions of said shaft.
8. A fuel control system as set forth in Claim 7, further including a minimum flow bypass passage arranged in parallel relationship to said metering means whereby fuel from said pump is delivered to the engine through said bypass passage in bypassing relationship to said metering means.
9. A fuel control system as set forth in Claim 8, wherein said bypass passage is of a size such that fuel flow there-through is capable of accelerating said engine to approximately 45% of its rated speed.
10. A fuel control system as set forth in Claim 9, wherein said biasing means is a single helical coil compression spring.
11. A fuel control system as set forth in Claim 8, further including an exhaust duct communicating with said fuel delivery passage at a location upstream of said metering means, and valve means for controlling flow of fuel through exhaust duct to maintain a substantially constant pressure differential across said metering means.
12. A fuel control system as set forth in Claim 7, wherein said governor means includes a flyweight rotatably driven by said engine for urging said metering means to move in a second axial direction in relation to speed of rotation of said flyweight.
13. A fuel control system as set forth in Claim 12, wherein said flyweight is operably driven by said timing shaft.
14. In combination with a gas turbine engine having a combustion chamber, a fuel delivery system comprising:
a housing having first and second fuel chambers therein;
means communicating said second fuel chamber with said combustion chamber;
a timing piston movably mounted in and traversing said first fuel chamber to divide the latter into first and second compartments;
a fuel pump having an outlet port communicating with said first compartment;
a shaft operably driven by said engine and mounted in said housing, said shaft defining a first passage communicating said first compartment with said second fuel chamber, and a second passage defining a fluid exhaust;
a sleeve carried by said piston in surrounding relation-ship to said shaft and having a duct therein periodically communicating said second compartment with said second passage once each revolution of said shaft to permit corresponding movement of said piston;
fuel metering means for variably restricting fuel flow from said first passage to said second fuel chamber;
governor means responsive to engine speed for urging said metering means to move in a first direction;
a reaction shoulder carried by said piston; and compressible biasing means extending between said reaction shoulder and said metering means for urging the latter to move in a second, opposite direction.
a housing having first and second fuel chambers therein;
means communicating said second fuel chamber with said combustion chamber;
a timing piston movably mounted in and traversing said first fuel chamber to divide the latter into first and second compartments;
a fuel pump having an outlet port communicating with said first compartment;
a shaft operably driven by said engine and mounted in said housing, said shaft defining a first passage communicating said first compartment with said second fuel chamber, and a second passage defining a fluid exhaust;
a sleeve carried by said piston in surrounding relation-ship to said shaft and having a duct therein periodically communicating said second compartment with said second passage once each revolution of said shaft to permit corresponding movement of said piston;
fuel metering means for variably restricting fuel flow from said first passage to said second fuel chamber;
governor means responsive to engine speed for urging said metering means to move in a first direction;
a reaction shoulder carried by said piston; and compressible biasing means extending between said reaction shoulder and said metering means for urging the latter to move in a second, opposite direction.
15. A combination as set forth in Claim 14 further including valve means for selectively interconnecting said first and second compartments.
16. A combination as set forth in Claim 14, further including a one-way check valve extending between said second chamber and said second compartment for permitting one-way fluid flow from said second chamber to said second compartment.
17. A combination as set forth in Claim 16, further including a biasing spring disposed in said second compartment and engaging said piston to exert a force thereon opposing the hydraulic force developed by fluid in said first compartment.
18. A combination as set forth in Claim 14, wherein said second passage comprises a groove on the exterior of said shaft continuously communicating with said second chamber.
19. In a fuel delivery system as set forth in Claim 1, wherein said preselected portion of engine operation is the start-up period of engine operation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA365,988A CA1128326A (en) | 1976-11-19 | 1980-12-02 | Fuel control system |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US74338776A | 1976-11-19 | 1976-11-19 | |
| US743,387 | 1976-11-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1097087A true CA1097087A (en) | 1981-03-10 |
Family
ID=24988597
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA289,089A Expired CA1097087A (en) | 1976-11-19 | 1977-10-17 | Fuel control system |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5365518A (en) |
| CA (1) | CA1097087A (en) |
| DE (1) | DE2750981C2 (en) |
| FR (1) | FR2371578A1 (en) |
| GB (1) | GB1544565A (en) |
| SE (1) | SE434868B (en) |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3002349A (en) * | 1956-07-26 | 1961-10-03 | Bendix Corp | Fuel control apparatus for an internal combustion engine |
| US3059427A (en) * | 1956-10-15 | 1962-10-23 | Robert J Thorpe | Apparatus for controlling the fuel supply to an internal combustion engine during starting |
| US3075350A (en) * | 1958-12-19 | 1963-01-29 | Bendix Corp | Gas turbine fuel control including timing device for scheduling acceleration |
| US3208218A (en) * | 1963-09-25 | 1965-09-28 | Woodward Governor Co | Gas turbine speed regulator |
| FR1449491A (en) * | 1964-10-12 | 1966-03-18 | Bendix Corp | Fuel supply control for combustion engine |
| DE1751493A1 (en) * | 1968-06-08 | 1971-03-18 | Kloeckner Humboldt Deutz Ag | Control device for the starting process in gas turbines |
| JPS5082417A (en) * | 1973-11-28 | 1975-07-03 | ||
| JPS5246572B2 (en) * | 1973-11-28 | 1977-11-25 | ||
| US3962863A (en) * | 1973-11-28 | 1976-06-15 | Nissan Motor Co., Ltd. | Gas turbine engine fuel supply control |
-
1977
- 1977-10-17 CA CA289,089A patent/CA1097087A/en not_active Expired
- 1977-11-03 FR FR7732995A patent/FR2371578A1/en active Granted
- 1977-11-15 DE DE19772750981 patent/DE2750981C2/en not_active Expired
- 1977-11-17 SE SE7712998A patent/SE434868B/en not_active IP Right Cessation
- 1977-11-18 GB GB4813877A patent/GB1544565A/en not_active Expired
- 1977-11-18 JP JP13800477A patent/JPS5365518A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB1544565A (en) | 1979-04-19 |
| DE2750981A1 (en) | 1978-05-24 |
| FR2371578A1 (en) | 1978-06-16 |
| SE7712998L (en) | 1978-05-20 |
| DE2750981C2 (en) | 1982-12-16 |
| JPS5713726B2 (en) | 1982-03-18 |
| JPS5365518A (en) | 1978-06-12 |
| SE434868B (en) | 1984-08-20 |
| FR2371578B1 (en) | 1982-12-10 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |