~35~30 BAC'~GROU~D OF T~iE INV~:~LlTIOi~
.
This inven-tion relates to gas turbine engines, and relates more particularly to an improvecl gas turbine engine and method and control therefor particularly useful as the power plant for a ground vehicle.
Recent advances in gas turbine engine technology have irnproved their overall efficiency and economy to such an extent that this type of power plant has become competitive in many instances wîth more conventional in-ternal combustion type power plants such as Otto or ~iesel cycle engines. For instance, gas turbine technoloyy has made sic~nificant inroads as the power plant for aircraft engines. Similar].y, attempts have been made to develop a gas turbine en~ine which would be competitive with the more conventional internal cornbustion engines in high-production ground vehicles 5uch as on-the-road automobiles and heavy trucks.
Th~ gas turbine ofers significant advantages of equivalent or better operational ~fficiency, fuel savings, and less emissions as well as being able to utili~e a variety of different fu~ls on an economic basis. Furthcr, the gas turbine engine in many instances offers cJre~ter overal:L economy over the erlt:ire operational l:ife of a vchicle.
The :inhereflt o~r~t:i.ona]. char~cteristics of a CJ-IS turbine engine pr~sent, however, c~rtairl problerns whcn ut~ .cd in a ground vehicle. Moxe specif.ical]y, a gas turbinc etlgine gen~r~llly includes a gas ~enerator seckion which provides a l~lrc3e pressurized air flow to a combustor wherein the air flow is mixed and iynited with fuel to greatly incre~ase the temperature of the resulting gas flow. Hot pressurized gas flow then drives one or more turbines to produce useful rotary mechanical ou-tput power. Normally one of these turbines is a portion of the gas generator section for driving
- 2 - ~
s~ 3580 the fan which provides the high volume pressurized air inlet flow. Dowllstream power output turbines.then gen2rate the useful mechanical power output. Conventionally, the high speed, high volume gas flow from the gas generator drives the turbines at relatively high speeds. Other inherent characteristics of such gas turbine engines relates to the thermodynamic and aerodynamic processes carried out therewithin which dictate that operational efficiency of the engine increases substantially with increasing maximum temperature of the gas flow.
These operating characteristics of a gas turbine engine present certain disadvantages in comparison to the normal operation of reciprocating or rotary piston type internal . combustion enyines fox ground vehicles. More particularly, the internal combustion engine inherently provides a substantial . 15 amount of deceleration horsepower for the vehicle upon reducing ., fuel flow ~hereto through the drag imposed by the reciprocating portio~ of the engine. In contrast, the hi.gh rotational inertia of the turbines of the gas turbine eng:ine normcllly do not permit such immediate, relatively high horr;epower bra~iny for a grouncl vehicle simply upon reducing ~uel f:Low to the combustor of the gas turbine enyine. 'rO overcome th.is disadvantage, ~n var:iety o;E
proposals have been offercd in the past to increa.C;e th(! hrak:ing characteristi.cs o:~ a gas turh:in~ ~ngirle when utili.zed Eor d.riving a ground vehicle. Pr:im..l.rily, these concep-t~; relatc to completel,y ext.ingu:Lslling the combustion proccss within the com~nCtor to produce maxi.m~n dynamic b.rak.i.rlc3. Ilowe~ver, operat:ional l:i~e o:E a gas turbine engine is suhstan~ially rcduced by cont:inucll thermal cycling of the entire enyine as c.reated upon ex-tin~;ui.shinc,3 the combustion process. Further, such approaches adversely affect emissions. Other concepts relatiny to improving the dynamic braking characteristics of a gas turbine engine revolve around the utilization of a "fixe~d shaf-~" type of gas turhine engine o wherein the gas yenerator section and the power drive section are mechanically interconnected to drive the vehicle. While such an arrang~ment improves the d~narnic bra~ing, it greatly reduces the adaptability of t~.e engine to perform various other processes for driving a ground vehicle, and due to this limited adaptability has met with limited success in use as the power source for a hiyh-production type of ground vehicle. An example of such prior art structure i5 found in U. S. Patent No. ~,237,404. The normal method for dynarnic braking in gas turbine powered aircraft, thrust reversal, is of course not readily applicable to yround vehicles.
Prior arrangements for yas turbine engines for ground vehicles also have suEfered from the disadvanta~e of not providing efficient, yet hiyhly responsive acceleration in comparison to internal combustion enyines. Inheren-tly, a free turbine engine normally requires a substantially longer time in deve]oping the maximum torque required during acceleration of the ground vehicle. Prior attempt~ to solve this problem have centered about method~s such as operatiny the y~s genera~or at a constant, maximum speecl, o~ otber techn~clues which are ~qually inefficient in utilizat:k~n of fu~l Over~ll, prior ~Ja~5 turbine engines for grourld vehicl.es nonnally have sufE~red from a reduced operational eficiency .in attcmptirly to improve the c~ccelerati~n or deceleration characterist.ic~ of the eng:ine, and or resulted in reduced efficiency by subc;tant.ia:ll.y vc-ry~ g the turbine inlet temperature of the yas turblne enyine which is a primary factor in the fuel consumption of the engine. Further, prior art attempts have generally been deficient in providing a reliable type of control system which i5 effective throuyhout all ", .. .. ..... . ....
3~
operational modes of a gas turbine engine w})en operating a ground vehicle to produce safe, reliable, operatin~ charac-teristics. Further, SUC~I prior art gas turbine engines have resulted in control arrangements which present a substantial change in required operator actions in comparison to driving an internal combustion powered vehicle.
Other problems related to prior art attempts to produce a gas turbine engine for yround vehicle relate to the safety and reliability of the control system in various failure modes, safe and reliable types of controls, and in the overall operational efficiency of the engine. A majorit.y of these problems may be considered as an outgrowth of attempts to provide a gas turbine engine presentiny operational char-acteristics duplicative of the desirable, inherent actions of an internal combustion engine.
Accordingly, it will be seen that it would be highly desirable..to provide a gas turhine engine and associated con-trols which incorporate the desirable operational features of both a gas turbine and internal combustion erlgine, but while providing an economical end product o~ suf~ici~ntly reliable and safe clesign for hi.~Jh vo:lurne production bas.is for ground vehicles.
Discussions of exelnplary prior art stru~ture relatirly to the enyine of the present inverlt:ic)n may be found in U. S.
Patents No. 3,7.37,404 d:i.scussed above; 3,660,976; 3,899,877;
3,941,015 all of which appear to relatc to schellles for trans-mitting motive power from the gas generator to the engine out-put shaft, and 3/688,605; 3,771,916 and 3,938,321 that relate to other concepts for vehicular gas turbine engines. Examples of concepts for variable noz~le engines may also be fo~lnd in U. S. Patents 3,686,860; 3,780,527 and 3,777,479. Prior art fuel governor controls in the general class of that contem-plated by the present invention may be found in U.S. Patents 3,400,535; 3,508,395; 3,568,~39; 3,712,055; .............
35~(~
3,777,~80 and 3,913,316, none of which incorporate reset and override features as contemplated by the presen-t invention and 3,5~1,446 t~hich discloses a substantially more cumplex ~ fuel reset feature than that of the present invention. Examples '5 of other fuel controls less pertinent to the present invention I may be found in Patents 3,851,464 and 3,888,078. Patent 3,733,815 relates to the automatic idle reset feature of the present inven-tion while patents 2,976,683; 3,183,667 and 3,820~323 relate to the scheduling valve controls.
~10 SU~qARY OF THE INVENTION
An important object of the present invention is to provide an improved gas turbine engine and method and more particularly arrangements exhibiting desirable operational features normally ! inherent to piston engines.
Another important ob~ect is to provide provisions producing improved fuel performance in a variety of operations of a ground i vehicle driven by a gas turbine engine.
¦ Another important object of the present invention i5 to ¦ provide improved acceleration, deceleration characteristics for a ~20 gas turbine driven ground vehicle, and to provide a more reliable, longer lie gas turbine engine for propulsion or power generating purposes.
In summar~, the invention contempla~es a recupera~ed, ~ree ¦ turbine type engine wi~h sepa:ra~e gas gcnerator and power turbine sections. ~ uel governor contxols fuel flow to the combustor to set gas generator speed in relation to the throttle lever. Reset solenoids can override and adjust fuel flow in response to certain operating parameters or conditions of engine operation. For instance, in response to low speed on the output shaft of the drive train clutch which is indicative of an impendin~ desired engine accelera-tion for increased torque output, a reset solenoid . . . . .. . . .... . , , , " ~ ~,,,, " .... ..... .... ... .... ...
8(~
increases fuel flow ana the gas generator idle speed to sub-stantially reduce time required in increasing engine torque output. A scheauling valve is effective to control fuel flow during engine acceleration to prevent excessive recuperator inlet temperature and maintain turbine inlet temperature at a substantially constant, high level for maximum engine per-formance. The scheduling valve is responsive to combustor inlet gauge pressure and ternperature, and also controls fuel flow duriny deceleration in a manner maintaining combustion.
Variable turbine guide vanes are shifted first to maximize power delivered to the gas generator during its acceleration, and subsequently are shifted toward a position delivering maximum power to the power turbine section. The variable guide vane control includes a hydrornechanical portion capable of controlling power turbine section speed in relation to throttle position, and has an electromechanical portion co-operable therewith to place the guide vanes in a braking mode for deceleration. Power feedback is incorporated to provide yet greater brakin~ characteristics. When such is selected, the gas generator speed is automatically adjusted to approach power turbine speed, then through a relatively low power rated clutch the gas gellerator and power turbine sections are mechanically interconnected such that th~ rotation~l inertia of the gas generator ~ection assis~s in retardirly the cngirle output shaft.
More speciEically the present invention contemplates a free turbine type gas turbine engine for driving a ground vehicle having a final drlve including a shiEtable transmission for delivering power to ground engageable wheels, and a clutch having input and output shafts, said clutch output shaft delivering power to said final drive, said englne comprising a gas generator section having an air inlet, a compressor for compressing air -Erorn said inlet, and a turbine for driving said compressor through a drive shafti means for delivering ~ 7 -1~3S80 fuel to said ~as generator section to maintain a comhustionprocess therein and produce a motive gas flow therefrom; a power turbine section havin~ a power output shaft ratatable freely of said gas generator shaft and operably connected to said clutch input shaft, said gas generator turbine and said power turbine section being driven by and disposed in series relative to said motive gas flow; a throttle shiftable away from an idle position to a substantially maximum power position;
a sensor for sensing the speed of said gas generator shaft;
fuel control means for controlling fuel flow to said gas generator section and responsive to said gas generator shaft speed sensor and said throttle, said fuel control means further including first means for maintaining the s~eed of said gas generator shaft at a first preselected minimum idle speed when said throttle is at said idle position; a clutch output shaft speed sensor; selectively energizable means operable when energized to adjust fuel flow to maintain the speed of said gas generator shaft at a second preselected idle speed substantially higher than said first idle speed when said throttle is at idle position, and said energizable means operably coupled with said clutch output shaft speed sensor to be energized and de-energ:Lzed whenever said speed of the clutch output shaft is rcspectively below and above a pre~determined value; and means or adjusting the incidence of said motive gas flow onto said power turbirle section to alter the po:rtion of power tran~:mitted from ~aid CJclS
flow to said gas generator turbine and to said power turbine section, sa:id adjusting means responsive to movement of said throttle to said maximum powex posi-tion to adjust said incidence of gas flow to transmit a preselected maximum portion of power to said gas generator turbine during engine acceleration.
These and other objects and advantages of the present invention are set forth in or will become apparent from the following detailed description of a preferred embodiment when read in conjunction with the accompanying drawings.
- 7a -~3~80 BRIEF DE:SCRIPTION OF T~IE DR~ GS
In the drawinys:
Fig. 1 is a left front perspective illustration of a gas turbine engine and associated drive train embodying the principles of the present invention;
Fig, 2 is a perspective illustration of the power feedback drive train as incorporated in the engine with portions of the engine shown in outline form;
Fig. 3 is a fragmentary, partially schematic, elevational cross-section of the power feedback clutch and associated hydraulic system, taken generally along lines 3-3 of Fig. 2;
Fig. 4 is a partially schematic cross-sectional representa-tion of the rotating group oE the engine with controls associated therewith shown in schematic, block diagram form;
Fig. 5 is a right front perspective view of a portion of the housing, ducting passages and combustor of the engine with portions broken away to reveal internal details o~ construction;
Fig. 6 is a partially schematic, plan cross-sectional view of the fuel governor 60 with portions shown perspectively for better clarity o~ operational in-terrelati.onships;
Fig. 6a is an enlarged partial elevational cro~s-sectiollal view of the fuel pump taken genexal.ly along lines 6~-6a o~ Fig. 6;
Fiy~. 6b, 6c, 6d a.re enlclrcJecl cross-sect.ional ViCW5 of a portion o the fuel governor control show.ing different operational position~ of solenoid 257;
Fig. 7 i5 a schematic, cros~-sectional and persE~ective funct:ional representation of ~.chedulincJ valve 62;
Fig. 8 is a plan cross-sectional view through one portion o~ the scheduling valve;
Fig. 9 is a plan cross-sectional view of the scheduling valve taken generally along lines 9-9 of Fig. 8;
Figs. 10 and 11 are enlarged views of portions of valve 282 showing the interrelationship of fuel metering passages as would be viewed respectivel~ along l.ines 10-10 and 11-11 of Fig. 7;
... . . .. . . ... ... . ....
;
~ 35~0 Fig. 12 is a schematic cross-sectional representation of guide vane control 66;
Fig. 13 is an exploded perspective illustration of the guide vanes and actu~tor linkage;
` 5 Figs. 14, 15 and 16 are circumferential views showing various operational relationships between the variable guide vanes and the power turbine blades;
Fig. 17 is a schematic logic representation of a portion of the electronic control module 68;
Fig. 18 is a graphical representation of the area ratio across the power turbines as a function of guide vane angle;
~ Fig. 19 is a graphical representation of the desired gas ; generator section and power turbine section speeds selected in relatio~ to throttle position; and Fig. 20 is a graphical representation of the relationship of fuel flow permitted b~ the scheduling valve as a function o~
combustor pressure along lines of constant combustor inlet temperature.
DETAILED DESCRIPTLON OP T~IE PREFERRED EM~ODIMENT
With reference to the figures, listed below are the abbreviations utilized in the following detailed description to den~te various pararneters:
Npt Power Turbine 54 Speed Ng~ = Gas Gen~rator 52 Speed ~5 Ng~* - Preselected Gas Gcnerator 52 Speed Nti = Transrnission Input Shaft 36 Spee~d e - Predete.rmined Minirnum Spe~ed o~
Translllission Irlput Sha~t 36 Wf = Fuel flow B = Stator Vane 120, 122 ~ngle B* = Predetermined St~tor Vane Angle a = Throttle 18~ Position _ g _ 8~
a* - Predetermined 'rhrottle Position T2 Compressor Inlet Temperature P2 = ~mbient Pressure T3 5 Combustor Inlet Temperature P3 5 = Combustor Pressure P3 5* = Preselected Intermediate Value of Combustor Pressure T4 = Turbine Inlet Temperature ~6 - Turbine Exhaust Temperature Engine 30 Referring now more particularly to the drawinys, an improved gas turbine engine as contemplated by the present invention is generally denoted by the numeral 30. As depicted in Fig. 1 the engine is coupled to a substantially standard drive train for a vehicle, particularly a truck in the 450 to 600 horsepower class, with a power output shaft 32 as the input to a drive train clutch 34. A transmission input sha~t 36 extends between the clutch 34 and a "chanye speed" type oE transmission 38. Transmission 38 is of the manually shiftabl.e gear typei however, it is to be under-stood that various improvements of the present invention are equally usable with other types oE speed varyiny trclnsmission~.
As .is conventional the tran.smission 38 has a variety of d.ifferent positions including several forward gears, reverse gear:ing, and a neutral position. ~n the neutral posit.ion no power is transmitted ~5 between the trarlsm:Lssion input shat 36 and the ~ransmiscion Outp-lt shaft ~0 which convent.ionally extends to the final dri.ve ~ and clrive wheels 4~ o the vehicle. ~ manual shiEting lever 46 provicles selection of the desired year ratio, and a speed sensor 43 genexates a signal indicative of the speed o transmission input shaft 36. As schematically depicted in Fig. 1 and described in greater detail hereinbelow, the speed sensor 4~ may be of any type compatible wi-th the control medium of the engine 30~ Preferably, speed sensor 48 ., , . .. . . .. . . , ,, ~ . . . ..
~c~3580 generates an electrical signal transmitted by conductor 50 to the electronic control module of the engine.
Referring to Figs. 1-4, engine 30 is of the free turbine, recuperated type incorporating a gas generator sec-tion:.52, a power turbine 54 mounted on a shaft separate from that of the gas generator 52, and a recuperator 56 that sca-vanges waste heat from the exhaust flow from the engine for preheating ~he compressed fluid prior to the combustion process.
The engine further generally includes a source 58 of combus-tible fuel, a fuel governor generally denoted by n~eral 60 which also includes the fuel pwnp therein, a scheduling valve 62 for controlling fuel flow normally during acceleration or deceleration of the engine through a fuel line 64 extending to the gas generator section 52, and a control 66 for variably positioning variable stator vanes included in the power tur-bine section 54. An electronic control module 68 receives and processes various input parameter cignals and produces output control signals to the governor 60 and vane actuator control 66.
Conventionally, there is included an electrical ~to-rage battery 70 and associated starter motor 72 which is pre-ferably selectively coupled to both the gas generator 52 and a ~tarter air pump 74. During ~tarting operation, the motor 72 is cnergized to drive both an ai.r starter pùmp 74 as well as the main gas generator ~haft 76. As clearly illustrated in Fic3. 2, the preferrecl foxm of the invent:ion also illclude~ a drive train 78 associclttd with gas genercltor ~haft 76, and another drive train 80.as60ciated with and dr.iven by a main shaft 82 of the power turbine 54. The two drive trains 78 and 80 are selectively interengageable through a relatively low power, wet clutch generally denoted by the numeral 84. This clutch is generally referred to as the power feedback clutch and the structure thereof is described in detail below with respect to Fig. 3, ....... ;; .......... ..... ~
r o while its functional operation is described further belo~ with rec3ard to the power feedback operation of the present inven-tion.
Gas generator 5~ generally inclucles an appropriately filtered air inlet 86 throuyh which ambient air is supplied to a pair of 5 - series arranged centrifugal compressors 88 and 90. Cross-over ducting 92 carries the compressed air flow from the ~irst compressor 88 to the second compressor 90. The gas generator 52 further includes ducting 94 as depicted in Fig. 5 which surrounds and collects the compressed air flow exhaust from the circular periphery of the second stage compressor 90, and carries this compressed air flow in a pair of feeder ducts 95 to recuperator 56 in non-mixing, heat exchange relationship with the recuperatox.
While various forms of recuperator structure may be utilized in conjunction with the present invention, an exemplary form is as described in U. S. Patent No. 3,894,581 entitled "~ethod of Manifold Construction for ~'ormed r~ube-Sheet ~leat Exchanger", dated July 15, 1975, issued to Fred W. Jacobsen et al. Though not necessary to the understanding of the present invention, reference may be made to the above reEerenccd patent fc)r a detailed description o~ a recuperator and its operation. For purposes of the present invent~on, it i5 suE~icient to state that the compres~e~cl air 10w from ducts 95 is preheated ~n the recupc-~ra~or by the waste heat from the exhaust flow from tlle enqirle. The preheatecl, compressed air Elow is then ducl:ocl throllgh duc-t 96 to a can-type combustor 98. ~s best seen in FicJ. 5, hea-ted 10w from the recuperator passes throucJh a plu~allty oE openincJs 97 into a plenum portion of duct 96, then throucJh openinys 97-a in a portion of the housing structure supportiny combustor 98. Combustor 98 has a perforated inner liner 99, and airflow from openinc3s 97-a passes into the zone between the inner and outer liner to then pass through the perfora-ted inner liner 99 into the combustor zone.
One or more electrical iynition pluys 100 are suitably connected to a source of high voltac~e electrical enercJy in a conven-tional manner. The igniter pluy is operable to maintain a continuous 3~8~) combustion process within the interior of the combustor ~herein ' the fuel delivered from line 64 i5 mixed and burned with the compressed air flow from duct 96.
The gas generator 52 further includes a gas generator turbine 102 of the radial inflow type. The compressed, heated ', gas flow from combustor 98 is delivered across turbine inlet choke nozzles 104 disposed in a circular array about the annularly shaped inlet 106 to the gas generator turbine section. During engine operation, nozzles 104 maintain pressure in combustor 98 ~10 at a level higher than ambient. Flo~ of this heated, compressed gas across turbine 102 causes hiyh speed rotation oE the turbine and the gas generator main shaft 76. This rotation of course drives the two centrifugal compressors 88 and 90. Shaft 76 is appropriately mounted by bearings 108 to the stationary housing 110 of the engine.
, Power turbine section 54 generally includes a duct sec-tion 112 and appropriate vanes 114 therein for directing the flow o~
gases from the gas generator power turbine 102 toward a pair o~
axial power turbines 116 and 1].8 mounted to the power turbine main shaft 82. The power turbine section further includcs se-ts 120 and 122 of variably positionah:Le guide v~mes resp~ctively disp~sed upstre~m of associ.at~(l ax:ial turbi.nes 116, 118 and their associ.ated blades 117, 119. As depicted in Fig. 13, ea~h I of the sets of variable CJUide V<:lrleS 120 ~nd 122 arc d:isposed in an annular array within the gas fJ.ow path and are both rnounted to a conunon actuatincJ mecharlism generally referred to by the numeral 124. The actuatinc~ mechanism 12~ comprises a pair of ring gears 126 and 12~, one for eac}l set oE variable vanes, a link 129 affixed to rincJ gear 126 and secured to ring gear 128 via plate 129-a. Pivotally mounted to the housing is a bell cran~
130, and a twisted link 131 has opposite ends pivotally attached to 3S~
link 129 and one arm of bell cran~ 130. A linearly ~hiftable input shaft 368 acts through a pivot link 132 and another arm of the bell crank to cause rotation of crank 130 about its axis 133 and consequent simultaneous rotation of both ring gears 126, 128. Rotation of input shaft 368 rotates each of the ring gears 126, 128 about an axis coincident with the rotational axis of power driven shaft 82 to cause rotation of the two sets of guide vanes in unison to various positions relative to the direction of gas flow passing thereby. As shown in Figs. 14-16, guide vanes 120 are positioned in a central or "neutral" position of Fig. 14 causing substantially maximum area ratio and minimum pressure ratio across the downstream power turbine wheel blades 117 of wheel 116 in order to minimize the amount of power transferred by the gas flow into rotation of the tuxbine 116. The Fig. 14 position is graphically illustrated by the position arbitrarily denoted O in Fig. 18. The guide vanes 120 are variably positioned toward the Fig. 15 position, noted as the ~20 position in Fig. 18, wherein high pressure ratio exists across blades 117 and maximum power is transmitted from the gas flow to turbine 116 to rotate the latter and transmit maximum power to shaft 82. Also, the vanes are oppositely rotatable to the Fig. 16 position, noted as the -9S~ position of Yig. 18, wherein the gas flow is directed by the variable vanes 120 to opposc and tend to retard the rotati.on of wheel 116. While only varles 120 and blades 117 are illustrated in ~`igs. 14-16, it will be unders-toocl b~ those slcilled in the art that subs~an-tially identical operatiorlal relationships exist between vanes 122 and turbine blades 119 of turbine 118.
The gas flow upon exitiny the last axial turbine 118 is collected in an exhaust duct 134 which leads to the recuperator 56. The power turbine output shaft 82 is a part of or operably connected with the power output shaft 32 of the engine through appropriate speed xeduction gearing. ~n air or water cooler 87 is also included to cool the lubricating fluid in engine 30 and communicates with fluid reservoir 89 throuc3h hose 9~.
. , " t, Fuel Governor 60 ~ ~ ~ 35 ~
_ __ Referring now more particularly to Figs. ~, 6, 6A-6D, the fuel governor 60 receives fuel from source 58 through an appropriate filter 136 into an inlet port 138 of a fuel pump housing 140. It will be apparent to those skilled in the art that the housing 140 is attached to and may be integrally formed with another portion o the main engine housing 110. The governor is operable to schedule fuel flow output through either or both of the output ducts 142, 144 for delivery to the scheduling valve 62. The governor 60 is hydromechanical in nature but capable of being responsive to externally applied mecha~ical and electrical signals, and includes an appropriate drive connection schematically illustrated by line 146, and associated speed reducing gearing 148 as necessary to drive a year 150 and drive shaft 152. Shaft 152 drives a fuel pump in the form of a positive displacement rotary gear pump 154 which receives fuel from inlet port 138 and displaces it at a substantially higher pressure through an output conduit 156.
As clearly illustrated in Fiy. 6~, the year pump comprises a pair of intermeshing geats 158 and 160, one of ~hich is driven by drive shaft 152 and the other of which is moun-ted to an idlcr shaft 162 journaled within housing 140~ Suppli.ed in par~llel flow arrange-ment from output conduit 156 are three pas6~ges, i.e. output duct 1~2, bypass bore 16~, and main flow metcr.iny passaye 16G. Conkc~ined in bypass bore 16~ is a bypass reyul~ting valve poppet 168 slidable within bore 164 to variably metex excess flow Erom output conduit 156 to a return passage 170 connected back to the fuel lnlct port 138. Pressllr~ of fuel in bore 16~ urges poppet 168 downwardly to incr~ase bypass flow thrcugh passage 170, while a helical coil compress.ion spring means 1.72 acts against the pressure of fuel to urge poppet 168 upwardly to reduce volume of flow from bore 164 to , passage 170. Through a pressure passage 132 the lower end of ; bypass bore 164 communicates with fuel supply conduit 6~. Thus, pressure of fluid in conduit 6~ is exerted upon the lo~er side of bypass valve poppet 168 ~o assist spring 172 in opposing the force cre~ted by the hiy~l pressure fluid in output corlduit 156.
~3S8~
Passage 166 terminates in a meterinc3 nozzle 174 secured by plate 176 to the housing, and having a reduced diamet~r opening 178 communicating with a central cavity 180.
The fuel governor 60 further includes a manual throttle input in the form of a thro-ttle lever 184 shiftable bet~een opposed adjustable stops 186, 188 adjustably secured to housing 140. Through an appropriate bearing 190 a shaft 192 extending within internal cavity 180 is rotatable relative to housing 140.
Integrally carried by shaft 192 in an open-sided camming section 194 into which are pressed fit a pair of stub shafts 196 that respectively carry rollers 198. Rollers 198 are engayeable with the lower shoulder of a spr.ing stop 200 such that rotation of the throttle lever 184 and shaft 192 causes consequent rotation of stub shafts 196 which are non-aligned with the main rotational lS axis of shaft 192, and thus vertical shifting of spring stop 200 through rollers 198. During its vertical or longitudinal shiftiny, spring stop 200 is guided by a guide shaft 202 whi.ch has an upper guide roll pin 204 slidably extendi.ng through a central bore of spring stop 200. Guide rod 202 is threadably received and secured such as by lock nut 206 to housing 1~0.
The governor 60 further includcs a mechanical speed sensor which includes a flyweight carr.ic.r 208 rig:idly sc!cured to rotate~
with shaft 152. Rotatinc3 with carri.er 20~ ar~ a pll1rali.ty of regularly sp~cecl flywei.cJhts 210 mounted for pivotal mover~ent upon pins 212 securing ~he weicJ~Its 21.0 tC) Ctlrrler 208. De~ndent: UpOIl the spced of shaft 152, the centrifllcJal force causeC; rotat;on of weights 210 about pins 2:L2 ~o Cau';e the .inner ends thercoE to shift downwardly as viewed in E'ig. 6 and drive the inner rotating race 214 of a rcller bearing assembly also downwaLdly. Through ball bearings 216 this down~Jard force is transmitted to -the non-rotating outer race 218 of the bearing assembly to cause downward shif-ting of non-ro-tating segment 220. At its lo~er end sec3ment 220 carries a spring stop shoulcler 222, and a speeder spring 22fi operably extends between the stop 222 of segment 220 and the spring ~3~80 stop 200 associated with the throttle input mechanis~. Through a preload of spring 224 acting on segment 220 the flyweights are normally urged upward to the zero or low speed position illustrated in Fig~ 6. Increasing speed of shaft 152 causes downward shifting of segment 220. Thus it will be apparent that throttle lever 184 acts essen-tially to select gas generator speed as reflected by the speecl of shaft 152, since the compression of spring 224 is set by rotation of throttle lever 184 and then opposed by the centrifugal force sreated by the rotation of shaft L0 152. The vertical position of segment 220 therefore becomes indicative of the clifference between selected speed ~position of input throttle 184~ and actual yas yenerator speed as sensed through flyweights 210. Fiy. 19 illustrates the action of spring 22~ in requestiny different levels of gas generator speed Nggt as the throttle is moved through different positions, a.
Governor 60 further includes a main fuel throttle lever 226 pivotally mounted by pin 228 to housing 140. One arm 230 of lever 226 terminates in a sphcrically shaped end 230 with.in a receiving groove 232 on segment 220 of the speed error si.gnal mechanism.
An opposite arm 234 of lever 226 is movable toward and away from meteriny orifice 178 in response to sh:Lftiny of segment 220 to thereby variably meter fuel flow from passage 166 into internal cavity 180. It will be apparen~. that the rec~ll.ating valve poppet 168 is variably positiorled in response~ to the precisure differ~ntial ~5 between passacJe 168 and conduit 64 downstrearn oE the meteriny ; orifice 178 to var.iably metcr bypass fluid flow throucJh passac3e~
170 in order to maintain a substantia].ly constant pressure differential across the fluid meteriny orifice created between metering openincJ 178 and the arm 234 of fuel lever 226. Thus the 3~0 rate of fuel flow delivered from passage 166 to cavity 180 and output duct 144 is a function only substantially of the position of arm 234 relative to metering opening 178 whenever the latter is th~ fuel flow controlling parame~er. As appropriat~, a damping orifice 236 may be incorporated in pressure sensing line 182 to stabilize the movement of bypass valve poppet 168.
A uni-directional proportional solenoid 239 has an outer housing 238 integral with plate 176 or otherwise affixed in stationary relationship to housing 140. Disposed witnin the housing 238 is a coil 240. and a centrally arranged armature 242.
Rigidly securea to form a portion of armature 2~2 is a central plunger shaft 244 which has an upper end engaycable with lever arm 234. Linear gradient springs 246, 248 operably extend between stops on housing 238 to engage associated shoulders on the plunger shaft 244 to normally urge the latter to its de-energized position illustrated. Energization of the solenoid through appropriate electrical lead lines 250 causes upward shifting of the armature 242 and plunger shaft 244 so that the latter engages ana exerts an upward force on lever arm 234 opposing and subtracting from the force exerted by speeder spring 22~ upon lever 226.
While the plunger shaft 244 could, i desired directly en~age the lever arm 234; in the p.reEerred form a "floatinc3 face"
arranyement for arm 234 is utilized. In tl~:is arranycment a floating flat poppe-t-type ace 252 is carried within arm 234 in alignment with meterinc3 operl:;ng 178. This 1Oat:inc3 ace is normal.l~
spring loaded towarcl the rneter:incJ or.i~.ice, alld the uppe.~r end o~
plunger shat 2~ :is engageable therewit~ l'he purpose o:f :~loat:incJ
face 25Z is to compensa-te or mc~nuEactur:ing tolc.rances and to assure that a relative:Ly flat surfacc is directly ~ligned with meteriny openiny 178 and ly.ing perpcndicul(lr to thc fluid Elow therefrom to assure propC!r metering of fuel thercacross. Th~
spring 25~ loads floati.ng face 252 toward open:ing 178. Pivoting of arm 234 against spring 254 to ;ncrease fuel flow i5 permitted until face 252 contac~s the upper end of 2~5 of plunger 244. This stroking of arm 234 is quite limited but sufficient to create flow saturation of the annular orifice defined between opening 178 and face 252.
Disposed on the opposit~ side of lever arm 234 from solenoid 239 is a housing 256 of another directional, one-way solenoid 257 shown in Figs 6B-6D. Solenoid 257 includes a coil 258, armature 260, and plunger shaft 262 secured for movement therewith. Through appropriate stops, centering sprinqs 264, 266 normally urge the plungex shaft 262 to the de-eneryized position illustrated. Upon energization of the coil 258 through appropriate leader lines 268, the armature 260 and plunyer shaft 262 are shifted downwardly such that the plunger shat engages the lever arm 234 in a manner exerting a Eorce thereon tending to add to the force created by speeder spring 224 and rotatîllg lever 226 to shift arrn 234 away from opening 178. Housing 256 of solenoid 257 is rigidly secured such as by bolts 272 to securement plate 176. Similar to floating ;Eace 252, in the preferred form the plunyer 262 does not directly engage the lever arm 234, but rather acts through a floating~type pin 272 to exert a force on arm 23~. The pin 272 is pre-loaded by a spring 27~ to give a floating action thereto in order to assure that plunger 262 can properly engage and e~ert a force on lever arm 234 reyardlcss of variA~ions in manufactnrlncJ tolerances, and/or the position of lever 226 rel~ti.ve to its pivotal shat 228.
Both solenoids ~xe urged to thelr de-energ:izecl pos:il:ion by linear gradient sprincJ;, and unlike on-oEf, digital-type solenoicl~, ;'5 variation in current and/or voltac3c ;nput to -~helr coil3 will cause an analog incremental positioniny oE the pluncJer 24~ of solenoid 239, arld will m~ve plunger 262 to either its ~ig. 6-C or 6-D position.
The plunger 262 oE solenoid 257 can be shifted away from its de-energized F:ig. 6-B state, to two different energi~ed states shown in Figs. 6-C and 6-D. One elec-trical input signal of preselected,intermediate power causes the armature 262 to shift to 35~
the Fig. 6-C position, moving p].unger 262 until the face of its adjustable stop nut 263 cc~ntacts the spring stop 267. This travel of plunger piston 262 depresses plunger 272 and compresses spring 274 to shift arrn 234 away from opening 178 and increase fuel flow S until gas generator speed increases to a level correspondiny to the signal force generated hy solenoid 257. Thus the plunger 272, spring 274 configuration assists in pe~nitting a less-than-rnaximum power signal to produce a force of preselected magnitude on arm 23~.
Another electrical input signal of greater power causes the armature to shift to the end of its stroke with face 261 thereof contact the adjacent stop ace 259 of the housing 256 as shown in Fig. 6-D. This travel causes piston plunger 262 to cornpress centering spring 266 and cause its lower end to come into direct contact with a~n 234 and urge the latter to permit maxim~n flow through the orifice presented between opening 178 and piston 252. As described in greater detail below, enerCJizcltion of solenoid 257 to its Fig. 6-D position is essentially a false throttle signal duplicating the speed desired from the gas c~enerator when the throt-tle i.s depressed -~o itC maximum fue]. flow, maximum power pos.ition.
SchedulincJ Valve 62 __~__ __ Referr$ng now more parkicu.laL^ly ~o liicJ~; 7 11, sched~:l.in~J
vcllve 62 ~enerall~ .includes a hous:incJ 276 wh.ich Inay be in~egral with both housincJs 1~0 and the ~tationc-ry ~ncJ:ine housin~J 110.
Preferably hou~inc~ 276 is disposed in close proximi~:y to both the.
fuel governor 60 and the combustor 98. ~lousincJ 276 includes an internal bore 278 into which open the two fuel ducts 142, 14~ as well as the fuel line 64 and a low pre.ssure return conduit 280 which returns fuel back to the source. Mounted for longituclinal sliding and ro~ation within bore 278 is a rnctering valve 282 havinc~
`; il4;~580 "windowed" irregularly shaped openings 284, 286 that open into the hollowed interior cavity 288 of valve 282. Fuel line 144 continuously communicates with interior cavity 288. Valve 282 further inclucdes an opening 290 in continuous communication with fuel line 64. Deceleration window 286 is in ~eneral alignment with fuel duct 142, and acceleration window generally aligns with opening 290. The particular con~iguration of each of the windows 284, 286 is clearly illustrated in Figs. 10 and 11.
Metering valve 282 is urged in one longitudinal direction by a biasing spring 292 which reacts against the housing 276 through a spring stop 294 acting on an alignment point 296 of a sealed block 29~ mounted to housing 276 such as by snap ring 300.
The preferred constructlon as illustrated in Fig. 9; however, the alignment point arrangement permitting rotation of valve 282 relative to housing 276 at the end of spring 292 may alternately be accomplished via a ball 302 configuration as shown schematically in Fig. 7. At the opposite end of valve 282 is a spherical ball 304 permitting rotation of valve 282 relative to a piston 306 carried in bore 278. Attached to housing 276 is a temperature sen~itive element 312, 308, for example a thermally responsive cylinder, whose longitudinal length varies with respect to the temperature imposed ther~on by the gas or other flu:id in the temperature sen~ing chamber 310 within cylinder 312. The housincJ
276 is mounted relative to ~he engine such that a portion thereof, particularly cylinder 312 and ~he associated charnber 310 are in cor~nunication with ancl maintained at the same temperature, T3 5, as the compre~sed air ~low being delivered into the combustor.
Thermally insulative material 311 is incorporatecl as necessary to avoid overheating of valve 62. For example the rightward end of Fig. 9 and the perfora-ted cylindrical wall 312 may be disposed at the air inlet to the combus-tor and/or at the duct 96 carrying air from the recuperator 56 to combustor 98. In any case the scheduling . . . ........
~35~0 valve is so arranged that cylinder 312 expands and contracts longitudinally with respect to increase and decrease of combustor inlet temperature. Valve 288 is operably engaged by the thermally responsive element 312 through a relatively non-thermally respon-sive ceramic rod 308. Accordingly, valve 288 is shifted longitudi-nally relative to input port 142 and opening 250 in relation to the sensed combustor inlet temperature. Thus the metering fuel flow accomplised by window 284 is varied in relation to the sensed combustor inlet temperature as this window moves longitudi--nally relative to opening 290.
Housing 276 further includes another transverse bore 314 which crosses and intersects generally with the longitudinal bore 276. Mounted for longitudinal reciprocation within this transverse bore 314 is a rod and piston configuration 316 which includes a pair of diaphragm-type seal5 318, 3Z0 having outer ends rigidly secured to housing 276 by being compressed between the housing, an intermediate section 322 and a closing plug 324 threadably or otherwise secured to housing 276. Th~ inner ends of the seals 320 are secured on the movable piston, rod confiyuration 316. The seal 320 in conjunction with the end closing pluy 324 define an interiox pressur~ sensin~ chambex 326 to which one end o~ the piston 316 is exposed. Thrc)ucJII a sensing line 328 the combustor pressure ~3 5 such as combuc;~or inlet pressuxc- .i.s transmitted .into chamber 326 to act UpOII one end o~ pi~torl 316. ~t the oppos.ite end o~ bore 31~, a heli.cal coil b.ias:in~J s~rirl(J mearl/; 330, ~rounded to hous:i.ng 276 through a sL:ationary stop 332, aCtsJ to urge the piston, rod con~icJuration 316 in opposition to thc pressure in chamber 326. The opposlte end 334 of the piston configuration 3~6 is ven-ted to atmospheric pressure thrcugh an appropriate port 336.
A seal schematically shown at 335, which may be of a structure like seals 318, 320 and secti.on 3~8, is also included at this opposite end 33~. Thus gauge pressure in the combustor, i.e. the difference 5~3~
between ambient pressure ancl the absolute pressure maintained in combustor 98, acts upon piston 316 to shift the latter within bore 314.
An arm 338 is threadably secured within a transv~rse bore in metering valve 282 at one end, and at its other end the rod 333 has a spherical ball 340 mounted thereon which is received in a groove 342 in rod, piston 316. It will therefore be apparent that shifting of piston, rod 316 within bore 314 is translated into rotation of metering valve 282 about its major longitudinal axis. Accordingly, the respective openings between windows 284, 286 and the input ports 142 and opening 290 are also varied in relation to the magnitude of yauge pressure in compressor 98 by virtue of this rotational translation of metering valve 282.
G~oove 342 permits ax.ial translation of arrn 338 along with valve 282. While the rod, piston configuration 316 may be of varied arrangements, the preferred form as illustrated in Fiy. 8 incorporates a threaded end section 3~4 which acts through appropriate spaces 3~6 to compress and secure the inner ends of seals 313, 320 to rod 316 throuyh an intermediate section 348.
Thus, the scheduling valve acts as a mechanical analog corr,puter in multiplying the parameters of combustor pressure, P3 5 and combustor .in:Let ternperaturc, T3 5, 3uch th.lt th~ pos.itioning o valve 282 and the windows 28~, 286 is a function of the product c~uantity of combustor pressure multiplied by coltlbusl:or il-llet temperature~
Conventionall~v, as shown in FicJ. q the controls for enc~ir-e 30 further includes a normally open, solenoid operated fuel sequencing solenoid valve 350 as well as a manually or electrical solenoid operated shut-off valve 352. These valves are disposed downstream of schedul.ing valve 62 and in the preferred form may be includecl within and/or adjacent to the housing 276 of schedulincJ
valve 62.
The configuration of each of the windc~ws 2~ 286 as illustrated in ~igs. 8 and 9 are determined to solve a qualitative empirical formula of the follo~ing form:
Wf ( 1 2 3.5) 3.5 3 3.5 where: Kl, K2 ana K3 are constants determined by the operational characteristics of a particular gas turbine engine and are reflected by the configuration of window 284 and associated opening 290.
By proper for~nulation of the window 284 and opening 29Q, the solution to this equation as accomplished by schedu-ling valve 62 holds a constant maximum turbine inlet tempera-ture T4 during all or at least a portion of gas generator acceleration. Accordingly, when window 284 is the controlling parameter for fuel flow, scheduliny valve 62 ernpirically by mechanical analog, controls fllel flow to maintain a substanti-ally constant turbine inlet temperature, T4. Window 284 is the primary operating parameter during acceleration of the engine as described in greater detail below. In contrast, window 2B6 is the controlling parameter during enyine decel.era-tion. While acceleration window 284 .is contourecl to rnaintai.n a substantially constant maximum ga~ cJenerator turbine inlet t~nperature to provide maximum accel.eration performance w.it}lin the temperature limitations of the engi.ne, the ~ecelc~rat:ion window 286 is contoure~l to limit and control fuel flow to pre-vent 105~ of combustion while affordinc3 substallt~ l clec~lera-tion of the engine. ~n extensive cliscllssion of opeIation of a similar type of turbine inlet temperature colnputing valve, but which utilizes absolute rather than ga~e combustor pres-sure, may be found in United States ~atent Application No.
30 689,339 of Rheinhold Werner, filed May 24, 1976, now ~. S.
Patent No. 4,0~7,960.
Vane Actuator 66 ` Details of the vane actuator control 66 are illustrated in Figs. 12 and 13. The vane control is hydromechanical in nature and generally includes a housing 354 having a pair of hydraulic .5 pressure fluid supply ports 356, 358 respectively receiving pressurized fluid from a high pressure pump source ,60 and lower pressure pump source 362 each of which are driven through the auxiliary power system of the engine. It is understood that the pumps 360, 362 may provide vari.ous other functions within the engines also such as lubrication.
Housing 354 has an internal, fluid receiving cylinder 364 in which is reciprocally mounted a piston 366 dividing the cylinder into opposed fluid pressure chambers. Rod or shaft 368 carried with piston 366 extends exteriorly of hbusing 354 and ~15 is operably connected with the bell crank 130 of Fig. 13 so that, as described previously, linear reciprocation of rod 368 causes rotation of bell crank 130, ring gears 126, 128 and the sets of variable guide vanes 120, 122.
High pressure hydraulic fluid from inlet port 356 is delivered into a hore 370 within housing 354 located adjacent cylinder 36~. Also intersec~.inc3 at spaced locat.ions along bore 370 are a hicJh pressure flu.id exhaust duct 372, and a pa.ir of fluid work conduit~ 37~, 376 re-3pcctively conunurl.icatlng w.ith the cylinder 36~ on opposecl ~,.ide-; of pistorl 36G~ ~tounted for reciproc~tion with:in bore 370 i~ a directiorlal fl.uid -ontro]. valve element 380 which is norninally positionable .in the op~n center position illustrated whercin high pressure hydraulic fluid from duct 356 communicates only with the exhaust port 372. A series of center.ing springs 382, 383, 38~, 385 normally urge valve 380 to . the position shown. Valve 3~0 is of the.four-way type and is shiftable one direction to dlrect high pressure fluid from ~3~8~
port 356 to conduit 374 and the upper side of pis-ton 366, ~hile through conduit 376 the lower side of the cylinder carrying piston 366 is vented to a low pressure return 386 via bore 370, and communicating conduit 388. Valve 380 is shiftable in an opposite direction to direct pressure fluid from inlet 356 to conduit 376 and the lower side of piston 366, whlle conduit 374 communicates with return 386 throuyh a chamber 378 and return line 379. It will be noted that piston 366 cooperates ~7ith housing 354, such as with a circular wall protrusion 390 thereof to prevent fluid communication between chamber 378 and cylinder 364.
Spring 382 acts to sense the position of piston 366 and the guide vane angle, and as a feedback device in acting upon valve 380. The relative compression rates of spring 382 in comparison to the springs 383-385 provides a h;gh gain response requiring large movement of piston 366 (e.g. 14 times) to counteract as initial movement of valve 380 and return the valve to its center position. Thus,it will be apparent that piston ,, 366 acts in servo-type followiny movement to the movement of an "input piston" in the form of valve 380.
In bore 310 i.s a stepped diameter piston mechanisrn 392 shiftable in response to the magnitude o fluid pressure from a conduit 394 acting upon a shoulder 393 of piston 392. Piston 392 presents ian adjustable stop Eor varying the compress.ive force of spring 333. Pxessure acting on shoulder 393 is opposed by a spring 385. Slidably extendin~ throucJh thc center o:E elem~nt 392 is a rod 395 which ac~s as a var.iably positionab~ s~op upon the spring 384 extendiny between the upper end O:e rod 395 and valve 380. Rod 395 is longitud.inally shiftable in response to rotation of a fulcrum type lever 396 pivotally mounted to housing 354 at pivot 398.
~3~80 Vane actuator control 66 further includes ~nother bore 400 in which is mounted a control pressure throt-tling valve 402.
An input from the throttle lever 184 of the engine acts to depress a variably positionable spring stop 404 to increase the force exerted by compression spring 406 in urging valve 40 downwardly. Opposing spring 406 is a gradient compression, helical coil spring 408. Valve 402 is variably positionable to meter hydraulic flow from port 358 to conduit 410. It will be noted that conduit 410 also communicates with the lower end of throttling valve 402 via a condui.t 412 having a damping orifice 414 therein. Conduit 410 leads to the laryer face of a stepped piston 416 reciprocally mounted within another bore 418 in housing 354. One end on bore 418 is in restricted fluid communication with return 387 through an orifice 419. The :1.5 smaller diameter section of stepped piston 416 receives pressurized ; fluid frorn conduit 420. Through an appropriate exhaust conduit 424 the intermediate section of the stepped piston, as well as the upper end of valve ~02 are exhausted to low pressurc return ; 386 through the conduit 388.
Conduit 420 provides a hydraulic signal indica-tive of the speed of the power turbine shaft 82. In this connection, the vane actuator includes a non-positive displacement type hydrauli.c pump, such as a centr:ifugal pump ~22 mountcd to and rot~ted by power.turbine shaft: 82. ~eing a non-positive displaccment type ~5 pump, the pump 422 delivers pressur.ized hyclraulic flow through conduit 420 5uch that. the pressure maintain~d on the smaller di~neter of stepped p.iston 416 is a square funct:ioll of the speed of power turhine shaft 82. Similarly, the action of throttling valve ~02 develops a pressure Oll the large diameter of piston ~16 in relation to a desired or selected speed reflected by the position of the throttle 18~.
~3~81~) The valve 402 and piston 416 act as input signal means and as a comparator to vary the compressive force of spring 384 as a function of the difference or error bet~een actual power turhine speed and the power turbine speed requested by throttle position. The requested Npt is graphically illustrated in Fig. l9.
The vane actuator control 66 further includes a linear, proportional solenoid actuator 426 operably connected by electrical connector lines ~27 to electronic ~ontrol module 68.
Actuator 426 includes a housing 428 enclosing a coil 430, and a centrally arranged armature which carries therewith a hydraulic directional control valve 432. Valve 432 is normally urged upwardly by spring 434 to the position communicating condu.it 394 with return 386. Valve 432 is proportionally shiftable downwardly lS in response to the magnitude of the energization signal to proportionally increase communication between conduits 372 ancl 394 while decreasing communication between conduit 394 and drain.
As a result, pressure in conduit 39~ increases proportionately to the magnitude of the electronic siynal, such pressure b~ing essentiall.y zero in the absence of an energization signal to soleno.id 426. It will be noted that mi.nimum pressure i.n condu:it 394 allows springs 3~3 and 385 to exert maximum upwclrd oxce on valve 380, and t~lat increasincJ pressurc in condui.t 39~ shifts piston 392 downwardly to reducc thc fc)rce. exc~rted by spr.inc3.s 383, 385 upon valve 380, thus developinc3 arl ovcrride force in the form of reducecl force from s~xiny 333.
In the absence of an clectrical signal to solerloid ~26 minimum pressure is exertea on shoulder 393 causincJ the yuide vanes to be controlled by power turbine speed. Thus, the yuide vanes during start-up are at thei.r Fig. 14 position and at other conditions of engine operation are normally urged to maximum power, Fiy. 15 position.
~. , '' ~: . . . ..
As shown in Fig. 18, vane aCtUatGr 66 is operab'.e to vary guide vane angle, B, from 0 to -~20 to alter the positive - incidencc of gas flow upon the power turbine blades and thus alter power transmi-tted frorn the gas ~low to rotate the power turbine wheels in a direction transmitting motive power to the vehicle. The vane actuator 66 is also operable to shift the guide vanes to a negative incidence position and modulate the guide vane position within zone "d" of Fig. 1~. In these negative ineidence positions, gas flow is directed to oppose and thus tend to deeelerate the rotation of the power turbine wheels.
Electronic Control 68 A portion of the control logic o~ the eleetronie eontrol module 68 is illustrated in Fig. 17. The electronic cont.rol module receives input electrical signals indicative of power turbine speed (Np~) through a chopper 436 secured to power turbine sha~t 82 and an appropriate magnetic monopole 438 which transmits an electron.ie signal indicative of power turbine speed through lead line 440. S.imilarly, gas gen~rator speed, NgcJ, is sensed through a chcpper 442, monopole 444 and lead lines 446. Trans-ducers 448, 450, and 452 respectively generate electrical input signals .i.ndieative o~ the reC;pect.i.ve temperaturc sensed thereby, i.e. comp.ressor i.nlet te~npe.rat~lre T2, turbine .inlct tcmpe:rature T4, and turbine exhaust tornpcrature ~6 ~s i.l:Lustratcd these temperature s.icJnals are trclnsmitted throllgll lines 454, 45~ and 458. The eleetxon.ie control module also r~ceives from an ambient pressure sensor ~60 and assoe:i.ated l.ine ~62 an elcctrical sic3nal indieative of c~lbient pressure P2. The electronic control rnodule further receive-s from an appropriate sensin~J device an eleetrical signal throucJh lines 464 indicative of throttle 184 . 30 position, "a." Also, a switch 466 is manually settable by thevehicle operator when power feedback brakinc3 (described more in ; greater detail below) is desired. A transducer 544 generates a signal to an invcrter 546 wherlever the variable guide vanes are .
.
, S8~
moved past a predetermined position B*.
The electronic control module includes sever21 output signals to energize and/or de-energize the various logic solenoids and relays including solenoid 518 through line 519, solenoid 257 S through line 268, fuel sequenciny solenoid 350 through associated line 351, fuel trim solenoid 239 through line 250, and the vane solenoid 426 through line 427. The electronic control module includes function generators 514, 550 and 552. Box 51~ is denoted as a "flat rating and torque limiting" ~unction and generates c~
signal indicative of maximum allowable gas generator speed as a function of c~mbient conditions T2 and P2 and power turbine speed Npt. Element 550 transforms the throttle position signal "a" into an electronic gas generator speed request signal, and function generator 552 produces a signal as a function of gas generator lS speed Ngg from line 4~6. The module further includes comparators 497, 534, 540, 554, 556 as well as the logical elernents 498, 500 and 538. The logical e].ements are of the "lowest wins" type, i.e.
they pass the algebraically lowest input signal.
The log.ic element ~9~ selects from the signcllc, 536 ancl 542 which have been gc-3nerated in cormparators 534 and 540 indicatir--~
the amount oE over or undert~empexclt:u.re for T~ and T6. An additional .input f.rom ~56 is provicled to loyic element ~98 so ac;
to p.rovide an indicat:i.orl o.~ exo~-3ssi.ve~ T~ f:igurc3s in the case o~ a ~ailed T~ sensor sign-ll. 'rhe lo~ic elemerl~. 500 xecei.ves inputs Erom 4g7 and ~98. Comp~lrator 497 cornp.;r~3~ ~he elc-3ctxon:i.c speed reque~,t with the actual. gas generator s~eed ~ t:o determi.ne if tlle ellgine.
has been reques~ed to accclerate or is i.n steady state. The output o;E logic element 500 is fed to inverter 546, gcnerating an appropriate signal in solenoid driver 55~ which then moves trim solenoid 426 a distance proportional to the magnitude c~f signal 427.
~ 30 -3~
The logic element 538 recei~res its inpu-ts from ~omparators 554 and 556, logic elemen~ 49~ and a differentia-tor 5~8. As noted, lo~ical element ~98 indicates the lower of -the two . temperature errors T~ and T6 The output of comparator 556 is the error between the operator requested power ~urbine speed Npt and the actual power turbine speed Npt. The output of comparator 554 is indicative of the difference be~ween the maximum allowable gas generator speed determined by function generator 514 and the actual gas generator speed 446. The logic elemen~ 538 selects the algebraically lowest signal and outputs it to solenoid driver 560 with an output on line 250 which is passed on to the governor reset decrease solenoid 239 in the fuel control 60.
As depicted in Fig~ 17, the electronic control module includes a comparator 468 and s~nthesizers or function generators
4~0, 472 and 474. Function generator 470 produces an output signal in line 478 indicative of whether the difference between power turbine speed and gas generator speed is less than a preselected maximum such as five percent. Function generator 472 produces a signal in line 480 showing whether or not power turbine speed is greater than gas generator speed, while function generator 474 generates a signal in lines 482 showing whether or not gas generator speed is greater than 45 percent of its maximum speed. The control logic further inclu~es function generator 486 and 48~ which respective:Ly generate signals in associated line 2S 490 and 49~ showing whether or not transmission input speed is above a preselected minimum "e" and whether throttle position is below a preselected throttle position a*. Throk-tle position "a"
is obtained from a suitable position sensor such as a variable resistance pokenti.ometer. Thus, outpu-t signal 464 is indicative 3~ of throttle position "a."
~- 30a -1~35~
i The electronic control module further includes the logical gates 502, 504, .'j06, 508 and 562. Logical AND gate ~02 receives inputs from line 478 and AND gate 50Z to produce an output sign~l to solenoid driver 516 to activate power feedback clutch 84.
j 5 Logical AND gate 506 receives its inputs from line 482, switch 466 and line 492 and produc~s an input signal to ~ gates 502 , and 504. Logical AND gate 504 receives an input from line 480 and the inverted input from line 478. Its output generates a 50~ gas generator speed signal and also enables solenoid driver 56~ through OR gate 562 to produce the "a" signal in line 268 which is the result of a constant 50% signal plus the output of elemen-t 566.
Signal 268 then activates the governor reset increase solenoid 257 in the fuel control 60. Logical AND gate 508 receives its inputs from lines 490 and 492. Its output signal generates a 20% gas generator signal through function generator 568 which, added to the constant 50~ signal by su~er 570 results in a fast idle signal (7.0% gas generator speed) to the governor reset increase solenoid 257. The output of AND gate 508 also generates the enable signal to solenoid drive~ 564.
~ .
.
., ' .
- 30b -~351~
Power Feedback Clutch 84 _ _ _ While various forms of clutches could be utilize~
for power feedback clu-tch 84, the preferred ~orm shown in Fig.
3 comprises a "wet" type hydraulically actuatea clutch which includes a shaft 520 from the gear train 7~ associated with gas generator shaft 76, and a shaft 522 interconnected with the gear train 80 associated with the power turbine output shaft 82. The clutch operates in a continual bath of lubri-cating cooling fluid. The gas generator shaft 520 arives a plurality of discs 524, which are interposed in discs 526 con-nected to the output shaft 522. The clutch actuator is in a form of a solenoided operated directional hydraulic control valve 518 which, in the energized position illustrated, ports pressurized fluid such as from source 362 into a fluid pres-sure chamber 528 to urge piston 530 against the urgings of a return spriny 532 to force the plates S24, 526 into inter-en~agement such that the power from shaft 5Z2 may be ~ed back to gas generator shaft 520 to assist in braking When the solenoid actuator 518 is de-energiæed, the chamber 528 is ex-hausted to a low pressure drain t-o permit the spring 532 to shift piston 530 away from the position shown and dis~ngage the plates 524, 526.
OPERATION
Startiny In a convention-ll manner st,lrt Ino~or 72 i6 ~lectri-cally energized to initiate ro~ation of gas generator drive shaft 76 and the input shaft 152 of fuel ~overllor 60. The : control module 68 energizes the normally open fuel sequence solenoid 350, and solenoid 352 is also in an open position to clear fuel line 64 for delivery to the co~ustor. As neces-sary, an assist pneumatic pump 74 delivers pressuri~ed air into combustor 98 along with the action of ignition plugs 100.
Motor 72 is utilized to drive the various co~nponents aescribed .
~L~43~8~
until the gas generator section reaches its self-sustaining speed, normally in ~he range of approxi~ately 40~ of ma~imum rated gas generator speed.
During initial rotation and starting of the engine, the low speed of rotation of fuel governor drive shaft 152 cannot overcome the bias of speeder spring 224, and thus fuel lever Z26 is disposed away from and clearing orifice 178 to permit fuel flow from line 166 to output line 144. Also during $his initial starting, the combusior temperature (T3 5) and combustor pressure (P3 5) are both relatively low such that scheduling valve 62 also permits siynificant fuel flow through line 64 to the combustor.
ow Idle_ As y~s generator shaft 76 speed climbs beyond the self-sustaining speed, start motor 7Z is shut off and the combustion process permits self-sustaining operation of the gas generator. Speeder spring 224 is normally set to maintain a low idle value of approx.unately 50% of maximum gas generator rated speed. Accordingly, the mechanical flyweight governor operates in opposition to speecler spring 22~ to adjust fuel lever 226 and maintain fuel flow through orifice 178 tu hold gas generator speed at a nominal 50~ of mlxim~rl. Thi~ 50~ low idle speed is e~fective whcnever ~roportional sol.crloid 257 i~;
in the de--energixed state .illustrated in Fig. 6.
The electronic control modul~ ~,8 r-lormally mai.nta:ins solenoid 257 in the de-enerc3iæed state to select the low idle gas generator speed whenever the transmission input sha~t speed of shaft 36, as sensed by speed sensor. 48, is rotating. Such normally occurs whenever the clutch 34 is engaged with transmis-sion 38 ! in its neutral position, or whenever the vehicle ismoving regardless of whether or not the clutch 34 is engaged or disengaged. Accordingly, during idling when not anticipating ac-celeration of the engine, the comparator 486 of the electronic ' , .
358~
control module 68 notes that the speed of sh~ft 36 is above a pre-determined minimum, "e", such that no signal is trans-mitted from comparator 486 to AND gate 508. Solenoid 257 remains de-energized, and the gas generator speed is control-led by the governor to approximately 50% its maximum speed.
~h Idle Maximum power is norma]ly required to be developed from an engine driving a ground vehicle upon initiating acce-leration of the vehicle from a stationary or substantially stationary start. As a natural consequence of normal engine operator action upon startiny frorn a stationary start, trans-mission input shaft 36 coJnes to a zero or very low rotational spee~ as clutch 34 i5 disengaged while gear shift lever 46 is articulated to shift the transmission i.nto gear. Once the speed of shaft 36 drops below a pxedetermined speed, "e", comparator 486 of the electronic control module c3cnerates an output signal to AND gate 508. Since accelerator lever 18~
is still at its idle position, t:he sensor assoc;.ated wi.th line 464 generates a signal to energize comparator 488 and also send a positi~e siynal to AND gate 508. The out:p~t of AND ga~e 508 energizes function cJenerakor 568 to add 20% to the constant idle command of 50%, so that 3ulmner 570 provides a /0'~ cor~nand si~nal to solerloid driver 564 that has been abled t~lrouyh the output oE AN~ gate 508 and OR gate 567.. Accordi~ 31y, solenoi.d 257 is energized by an appropr.iat:e c~lrrent si~n~ throu~Jh l.ine 268 to shift to its Yi.y. 6C pos:ition. In tll;.s pOsitioll the ; solenoid 257 has been sufficierltly eneryized to drive shaft 262 and plunger 272 downwardly as viewed in Fiy. 6C and exert a force on fuel lever 226 tending to rotate the latter away from and increase the si~e of orifice 178. The additional force exerted by solenoid 257 is sufficient to increase f-lel flow through orifice 178 to increase yas generator speed to a pre-determinedhigher leve~ such as 70% of maximum gas generator ~-33-1~358~ -speed. The flyweiyht governor operates to hold the gas gene-xator speed constant at thi.s level.
In this manner, the idle speed of the gas generator section is xeset to a higher val~le in anticipation of a re-quired acceleration such that more po~-er will be instantly available for accelerating the vehicle. At the same time, when acceleration is not anticipated, ..... ~
-33a- t as detexmined by whet}-er or not transmission input shaft 36 is rotating or st~tionary, the electronic control module 68 i~
operable to de-ener~ize solenoid 257 and reduce gas generator speed to a lower idle value just above that necessary to maintain a self-sustaining operation of the gas generator section. In this manner power necessary for acceleration is available when needed;
however during other idling operations the fuel f 10W and ~hus fuel consumption of the engine is maintained at a substantially lower value. This is acccmplished by producing a signal, minimum speed lG of shaft 36, which is anticipatory of a later signal ~rotation of accelerator lever 184~ requesting significant increase in power transmitted to drive the vehicle.
Acceleration Acceleration of the gas turbine engine is manually selected by depressing the accelerator 184. To fuel yovernox 60 this generates a gas generator section speed error signal in that the depression of lever 184 ro-ta-tes shaft 192 to increase compression of speeder spring 224 beyond that Eorce being generated by the mechanical flyweight speed sensor. Fuel lever 226 rotates in a direction substantially cleariny the opening 178 to increase fuel flow to the combustor.
At the same time, depression of throttle lever 184 qenerates a power turbine section speed error signal to vane actuator control 66. More particularly, depre.ssion oE throttlc 18i compresses sprincJ
406 to shift valve ~02 downwardly and increase the pressure rnain-tained in ch~mber ~18 substantially beyond that being generated by the hydraulic speed sicJrlal cJenercltor o~ pressure developed by pump 422 and exerted on the other side of the step piston 416.
Accordingly, Iever 396 is rotated generally cloc~wise about its ; 30 pivot 398 in Fig. 12, allowing down~ard retraction, i~ necessary, ~ of plunger 395 and reduction of compression on spring 384.
,..
~., 1~435BO
Summer 497 of the electronic contr~l rn~du~e aeter-mines a larye disparity hetween accele~ator position and yas generator speed to de~elop an electronic signal to element 500 overriding other signals thereto and reducing the signal in line 427 to zero to de-energize the solenoid 426 of guide vane control 66. The spring bias urges plunger 430 and valve 432 to the position shown in Fig. 12 to minimize hydraulic pressure developed in conduit 394 and exerted on piston shoul-~er 393, As discussed above in the vane control 66 descrip-10 tion, springs 382-385 position valve 380 t~ cause following movement of piston 366 to its nominal or "neutral" position.
In this position vane piston 366 and rod 368, the guide vanes 120 are disposed in their Fig. 14 position wherein the gas flow from the combustor is directed onto the power turbine vanes in a manner minimizing power transfer to the power tur-bine vanes. More particularly, the guide vanes 120 are disposed in their Fig. 14 position to redu~e the pre6sure drop or pres-sure ratio across turbine blades 117 to a minimum value, this position correspondirlg to the 0~ position of Fig. 18.
Since the no7,zles 104 maintain the colr~ustor 9R in a choked condition, this reduction in pressure ratio across the turbine blades 117 creates a su~stantial increclse in pressure ratio across the radial irlflow turbin~ 102 of the ga~ gener~-tor section. Accordingly po~it:iorliny of the g~lide vane~s in ; their ~'ig. 14 position by alJowirly the sE)riny.s 382-385 to position valve 380 and piston 366 in its "neutral" position, alters the power split between the yas generator turbine 102 and the power turbines 116, 118 such that a preselected maxi-mum portion of power from the motive gas flow is transmitted to the gas generator turbine 102. As a result, maximum acce-leration of the gas generator section from either its low or high idle setting toward its maximum speed ... .............
~35~3~
is achieved. As notecl previously, the requirement ~o- impending acceleration has been scnsed, and the engine is norMally already at its high idle setting so that gas generator speed promptly nears its maximum value.
As gas generator speed increases, the co~.bustor pressure P3 5 accordingly increases. This causes rotation of the metering valve 282 of the fuel schedule control 62 to increase the amount of overlap between acceleration schedule window 284 and opening 298 in the fuel scheduling valve. Increase in this opening causes a consequent increase in fuel flow to combus-tor 98 and an ultimate resulting increase in the inlet tempera-ture T3 5 through thc actions of recuperator 56.
To the operation of engine 30, increase in T3 5 is in practical effect the same as a further fuel flow increase. Accordinyly, in solving the above described equation the window 2~ shifts to reduce fuel flow with increasing T3 5 to produce an "effec-tive" fuel flow, i.e. one combining the effects of actual fuel flow and inlet temperature T3 5, at the sensed gaucJe pressure P3 5 to produce a ~ desired combustor exhaust or gas yeTlerator turbine inlet temperature ; 20 T4. .
This increase in fuel flow created by the rotation oE valve 282 and as compensated ~y axial trallslat.ion of the valve provides an "effective" fuel tlow that increases powcr developed arld transmitted from thc CJc15 flow to cJas cJerlcratc)r turbine 102. This then causes anoth~r increaC;e in CJaS gerlerclt:or Spee(l, and com~ustor ., .
pressure P3 5 acJain increclse~. Schedll1irl~3 valve thuc; acts in regenerative ~a~;hion to ~urther accelerclte thc ~JclS yen~rator section.
As noted previously, the schedulirlcJ valve is so contoured to satisfy the equation discussed previously and allow continued increase in P3 5 while maintaining comhustor outlet temperature T~ at a relatively constant, high value. In this manner the gas generator section is acceleratecl most rapidly and at maximu~ eLficiency since the turbine inlet teMperature T~ is main~airled at a high, constant value.
- 3~ -While the acceleration window 284 and openi~ 29C may be relatively arranged and configured to maintain a constant T4 throug}lout acceleration, a ~referred form contemplates maintaining a substantially constant T4 once the power turbine has initiated , rotation, ~hile limiting turbine outlet or recuperator inlet temperature during a first part of the acceleration operation. In this manner excessive T6 is avoided when the power turbine section is at or near stall. More specifically, it will be noted that upon starting acceleration of the vehicle, the free power turbine section 54 and its shaft 82 are stationary or rotating at a very low speed due to the inertia of the vehicle. Thus there is l.ittle temperature drop in the gas flow while flowing through the power turbine section, and the recuperator inlet temperature T6 starts approaching the temperature of gas flow exiting the gas generator radial turbine 102.
jl5 If combustor exhaust or gas generator turbine inlet temperature T4 ¦ is maintained at its maximum constant value at this time, it is possible that T6 may become exces6ively high in instances of high inertial load which lengthen~ the time of this substantial "stall"
condi.tion on the power turbine sect.ion. Of course, as the power turbine section overcomes the inertia and reaches higher speeds r temperature drop across the power turbines increase~ to hold down recuperator inlet temperature T6.
i For such free turbine typc engincs, relat.ively complica-ted and expense con~rols, electronic and/or mechani.cal, are normally .
expected in order ~o avold excessiva T6 while providing responsiv~
acceleration under the condit.ions .in c~uestion. An important discov~ry of the present invention, as ~mbodied in sch~duling valve 62, is in providing an extremely simple, economical, mechanical structure capable of limiting T6 during the critical turbine section stall period but yet still promo-ting very responsive engille acceleration.
At the same time this improved arrangemen-t has eliminated the need for compensati.on for substantial variations in ambien-t pressure and ~3~8(~1 thus the need to compensate for the variations in altitude that would be expected to be encollntered by a ground vellic.le.
In this connection it would be expected that abs~lute combusto~
pressure P3 5 must be the parameter in solving the equ~tion described previously such that the scheduling valve could reliably compute the turbine inlet temperature T4 created by a particular combinati~n of cornbustor pressure, P3 5, and in-let temperature, T3 5.
However, a discovery of the present invention is that by proper selection of the constants Kl, K2 as embodied in the size and configuration of openinys 284, 290, and by utilization of cornbustor gauye pressure rather than combustor absolute pressure, mechanically simple and economical struc ture with minimuro control complexity can accomplish the desired control of both T6 and T4 during acceleration. Window ~84 and opening 290 are relatively arranged such that when valve 282 rotates to a minimuTn P3 5, a slight overlap remains between the window and opening. Thus, a mini.mum fuel flow, Wf, .is maintained at this condition which is a function of T3 5 since valve 282 is still capable of translatiny ax:icl].ly. ThiF. c3ivcs rise to the third term, K3T3 5, in the~ equatiorl set Lorth above and dictates an ini.t.i~l condition of fllel. f.l.ow wherl window 2~4 becomes the control.linq uel flow par..llnet.er upon starting accelerati.on.
The constar-tC Kl, K2 are ChO';eTI, t:heir c~L:tUal value~
being determined by the aerodynalni.c and thermodynamic charac-teristics of the engine, such .that at a preselec~ed value, P3 5*, intermediate the maxim~o and minimum values thereof, the acceleration window controls fuel.flow to main-tain a con-stant T4. At combustor pressures below this preselected value,the acceleration window provides fuel flow allowing T~ to re-duce below the preselected maximUTn desired level therefor. It has been found that an inherent function of using gauge COT0-bustor pressure rather than absolute ... ...................... t -3~-~358~
pressure, in combination with these chosen values f Kl~ K2 and a preselected minimum fuel flow at minimum P3 5 ~ determined by K3 , is that fuel flow is controlled by the acceleration window to prevent recuperator inlet temperature T6 from exceediny a preselected value. This approach still utilizes the simple geometry of window 284 and 290, both rectangles, that mechanically compute the product of T3 5 multiplied by P3 5. Accordingly, at pressureslower than P3 5*
which are characteristic of the conditions under which the turbine section "stalling" occurs, the utilization of gauge combustor pressure prevents potentially damaging excessive T6 The design point for window 284 is, of course, the condition of maximum vehicle inertia experienced on turbine shaft 82, lesser values of such inertia naturally permitting more rapid turbine shaft speed increase and less time in the "stalling" condition above described.
From inspection of the equation solved by valve 282 it will be apparent that fuel flow Wf is a linear or straight line function of P3 5 asshown in Fig. 20, with a slope determined by Kl and K~, an intercept specified by K3, and passing through the point produc.ing the preselected turbine inlet temperaturc ~r~ at the selected intermediate value P3 5*. Of course, a family o~ such straigllt line curves o W~ vs. P3 S results for differellt va].ues o~ T3 5 Whi.lc, if desired, curve ~itting of window 2~4 and opening 290 could be utilized to maintain Ir~ at precisely the same value at pressurcs at and above the preselectecl interlllediate P3 5*, in the prcEerred form compound curvaturc of the window and opaning is not utilized.
Instead, the window and opellincJ are of rectangular conEiguration thùs permitting T4 to increase very slightly at combustor pressures ahove P3 5*. However, it has been found that such arrangement affords an excellent, practical approximation to the theoretically ' desired precisely constant T4 , resulting in practical effect in maintaining a substantially constant T4 at a desired maximum value once combustor gauge pressure exceeds the preselected level P3 5*.
. - 39 -L35~30 - ~ccordinqly, the ~resent invention inherentlv li.mits recup~r~tor temperature ~6 to solve the problem ~f re~uperat~r overheati.ng when starting to accelerate a high inertial load, yet still maintains a ma~imUm T4 for high engine efficiency throughout the remainder of acceleration once the inertia is substantially overcome and for the majority of time during acceleration. At the same time, and contrary to what might normally be expected, it has been found that the need for altitude compensation is obviated since there exists a minimum fuel flow at minimum combustor pressure, which minimum fuel flo~7 '10 varies linearly with combustor inlet temperature T3 5. Thus the present invention provides a simple mechanical solution to the interdependent and complex problems of limiting two different temperatures T4, T6 for different purposes, i.e. avoiding recupera-tor overheating while affording high eny.ine operating efficiency and thus highly responsive acceleration.
As the gas generator continues to accelerate, thé flyweight governor 208 of the fuel governor 60 begins exerting greater downward force to countexact the bias of speeder spring 224.
Accordingly, the fuel lever 226 begins ro-tating in a generally counter-clockwise direction in Fi.g. 6 to beqin metering fuel ~low through opening 178. Once the opening 178 become~ smaller than thnt afforded by me~erinq window 7~4 in ~chec1uldincJ valve 62, the operation of the ~chedulincJ valve is overr:idden and ~he fue.l governor 60 becJins controlling fuel flow to the combustor in a manner ~rimm:incJ gas y~nerator speed to match thc speed se].cct.ed by tlle rotation o~ the sha~t 192 assoc:iated wi.th the acceleration lcv~-3r 184 in the fuel governor 60.
Similarly, this increase .in gas generator speed is sensed in the electronic control module 63 by sun~er 497 such that once yas generator speed Ngg approAches tha~ selected by the position of the accelerator pedal as sensed el.ectronicall.y through line 464, the override signal generated by sun~er 497 is cut oEf. In response, element 500 is allowed to generate a signzl energizing the propor~ional solenoi.d 4~6 of -the guide vane control 66. Valve 432 ~ 40 -3 ~O
associated with solenoid 426 i5 shifted to increase pressure e~erted upon piston shoulder 393 to permit the piston 366 and the guide vanes to shift from the Fig. 14 disposi-tion thereof towards the Fig. 15 positi.on. This shifting cf the guide vanes from the Fig. 14 to the ~ig. 15 position again alters the work split between the gas generator turbine 102 and the power output turbines 116, 118 such that greater power is developed across the output turbines and transmitted to output shaft 82 while a lesser : portion is transmitted to turbine 102.
Thus it will be apparent that acceleration of the engine and vehicle occurs by first altering the work split 50 that maximum po~7er is developed across the gas generator turbine 102, then increasing fuel flow along a preselected schedule to regenera-tively further increase power developed across the gas generator while maintaining turbine combustor exhaust temperature T4 at a substartially constant, preselected maximum. Once substantial acceleration of the yas generator section has been accornplished, the guide vanes are then rotated to alter the power or work split so as to develop a greater pressure ratio across and transmit more power to the power tuxbines 116, 118 and the power output shaft 82.
Cruise During normal cruise operation (i.e~ travelin~ along at a relatively constant speed or power output lev~l) the cJuide vane control 66 acts primaril.y to alter the work spl.it between the gas generator turbine 102 and the power output turbines l.l~, 118 so a5 to maintain a substant.ial.l.y constant combustor exhauc.t temperature T4 . This is accompl.ished by the electronic control module whic:h includes a surNmer 534 developing an output siynal in line 536 to the logic box 498 indicative of the difference between the actual and desired turb.ine inlet temperature T~. ~lore particularly, solenoid 426, as discussed previously, is maintalned normally energized to gene-rate maximum pressure upon the piston shoulder 393 of the guide vane actuator. For instance, assuming that T~ is above the preselec-ted ~1~3~8~
desired value thereof, a signal is generated to line 536 and element 498 to reduce the macJnitude of the electric si~nal through line 427 to solenoid 426. Accordingly, the spri.ng bias 434 of the solenoid begins urging valve 432 in a direction reducing fluid communication between conduits 372 and 394 while correspondingly increasing communication between con~uit 394 and exhaust conduit 386. The reduction in pressure exerted upon piston 393 accordingly allows spring 385 to increase the spring bias of spring 383 to cause upward travel of valve 380 and corresponding downward travel of piston 366 to drive the vanes bac~wards from their Fig 13 disposition (-~20 position of Fig. 18) toward a wider open position increasing the area ratio and reducing .; the pressure ratio across the vanes of the turbines 116, 118.
Accordingly, in response to T~ over-temperature, the guide vanes are slightly opened up to reduce thc pressure r~tio across the turbines 116, 118. In response the increased pressure ratio across gas generator turbine 102 causes an increase in gas generator speed.
Such increase in gas cJenerator spced is then sensed by the flyweight i' governor 208 of the fuel governo:r 60 -to cause counter-clockwise rotation o~ fuel lever 226 and reduce fuel flow throucJh opening 178.
The reduction in fuel to the combustor 98 accordincJly r~duces the combustor exhaus~. or turbi.ne inle~ ~elllpecatu.re T~ toward t:he pre~
selected v~lue thereoE. T~lu~;, thc! ~Juide vane con ~rol operatcs to adjust the guide vanc~ as n~cessa.l-y and C~IUSC.'~ a COrlSe'C~Uent adjllSt-;~S ment irl fuel 1Ow by the fuel governo.r 60 due to chancJe in gas generator speed NcJg so as to mai.ntaln the com~ustox exhaust temperature T~ at the presel~c~ecl, maximu~l value~. It will be apparent also from the ~oregoing that reduction in turbine inlet tempera-ture T~ below t~le preselected desired value -thereof causes a corresponding movement o~ the guide vanes 120, 122 to incre~se the pressure ratio across the power turbines 116, 118. Accordingly this causes a reduction in pressure ratio across gas generator ~ ~2 - .
i8~
turbine 102 t,o reduce ~as generator speed. In rcsponse the fue].
c~overnor shifts fuel lever 226 in a clockwise rotation as viewed in Fig. 6 to incr~ase fuel flow to the combustor and thus increase turbine inlet tem~erature T4 back to the clesired value. It will be apparent that the change in guide vane position also directly alters the combustor exhaust temperature T4 due to the difference in air flow therefrom; however, the major alteration of combustor exhaust temperature is effected by altering the fuel flo~ thereto as described above.
During the cruise operation therefore, it should now be apparent that fuel governor 60 acts to adjust fuel flow in such a manner as to maintain a gas ~enerator speed in relation to the positlon of the accelerator lever 18~. Clearly, the fuel governor 60 operates in conjunction with or indepenclently of the vane control 66, dependent only upon the gas generator speed Ngg.
While the electronic control module operates the guide vane control solenoid 426 to tri.m turb.ine in.let temperature T~ during cruise, the hydxorrlechanical portion oE the c3uide vane control 66 acts in a more direct feedback loop to trirtl the spe~d of power turbine output shaft ~2. 2~ore part.i.cularly, thc actual powcr turbine speed as senscc'l by the pressurc! develope(l i!l li.rle ~20 :iS
conti.nuously comparec'l to the accel~r.lt:or ,1C!Ver pos.i.t;.c,n as reflec:ted by the pressure dcvel.opecl .in l:ille ~10. ~ cJraph.ical rcpxcsentclt.Lor of the action of valve ~02 and p.iston ~:l.6 i.n comprcs~i.ncJ sprincJ
384 and reclucs~:ing different desi.r~d powcr turb.ine 5})C`edS Npt in relat:iorl to the throttl.e posit.ic>rl, a, is showtl ;.n I':i~J. 19. Thus, in response to arl .incre.lse i.n specd of powex ~urbi.ne shclft: 82 beyond that selec-ted by the rotation of accelerato:r lever 18~, pressure at the lower dlameter of piston 416 becomes substant.ially grea-ter than that on the larger face thereof to'rotate lever 396 so as to increase compression of the biasing spring 3~34 actin~ on - ~3 -3581?
valv~ 380. The resulting up~ard movement of valve 380 causes a correspondinc~ downward movement of piston 366 and accordinyly shifts the guide vanes toward the Fig. 1~ position, i.e. opens the guide vanes to increase the area ratio and reduce the pressure ; ratio across the vanes 117, 119 of the two po~er turbine wheels.
This reduces the power transmitted from the gas flow to the power turbine wheel and thus causes a slight decrease in power turbine output shaft speed back to that selected by the accelerator lever 184. It will be apparent that whenever the speed of the power . '0 turbine shaft 82 is beloti that selected by accelerator lever 184, the compression of spring 384 is reduced to tend to increase the pressure ratio across the power turbine vanes 117, 11~ to tend to increase power turbine speed Npt.
; , The port.ion of vane control G6 for trimming power turbine ; 15 speed in relation to accelerator.pos.ition is preferably primarily digital in action since as shown in Fig. 19, a small change in throttle lever position increases the requested Npt from 25~ to 100%. The actlons of valve 402, piston ql6 and plunger 395 are such that when the accelerator is at a position greater than a*, this portion of the control continually requests approx;mately i 105% power turbine speecl Np.~. Through a small amount o~ rotation of the accelerator below a*, the contro]. provides a request of power turbine spe~d pro~.)ortional to the accelerator pos:itic)n~
Positioning o:E the accelerator to an ancJle below thi.C; small arc causes the control to reclues~ only app.rc)ximately 25't of maxirnum Npt ~
Thus, in normal cruise the guide vanes control operates in conjunction with the ~uel c3overnor to maintain a substantially constant turbine exhaust ~ernperature T4; fuel governor 60 operates ~0 to trim gas generator speed Nc3g to a value selec-ted by the accelerator - 4~ -~435BO
lever 18~; and the hydromechanical portion of guide v2ne 66 operates to trim power turbir-e outpt speed Npt to a level in relation to the posit.ion of accelerator pedal 184. It will further be apparent that during the cruise mode of opera-tion, the orifice created at opening 178 of the fuel governor is substantially smaller than the openings to fuel flow provided in the scheduling valve 62 so that the scheduling valve 62 normally does not enter into the control of the engine in this phase.
Safety Override During the cruise or other operating modes of the engine discussed herein, several safety overrides are continually operable.
For instance solenoid 239 of the fucl governor 60 operates to essentially reduce or counteract the effect of speeder spring 224 and cause a consequent reduction in fuel flow from orifice 178 by exertiny a force on fuel lever 226 tending to rotate the latter in a counter-clockwise direction in Fig. 6. As illustrated in Fig. 17, the electronic control module includes a logic element 538 which is responsive to power turbine speed Np,t, gas generator speèd Ngg/
turbine inlet temperature T~, and turbine exhaust or recuperator inlet temperature T6. Thus if turbine inlet ternperature T~ exceeds the preselected maximurn, a proportional electr,ical s].-Jnal i5 trans-mitted to lines 250 to enerc~ .e solenoi.d 239 and reduce fuel flow to thc encJine. Similar:Ly, exce.ssive turb.ine exhaust tcmperature T~
results in proportiona~:c~J,y enery:iæ:in~ tlle solenoid 239 to reduce fuel flow to the comblls~or and thus u].t:Lmately r~ducc turbine exhaust temperature T6. ~lso, locJic element ~38 .is responsiv~ to power turbine gpeed so as to proportionately enercJi~e solenoid 239 whenever power turbine speed exceeds a preselected maxlmum. Simi-larly, the electronic colltrol module operatcs to energize solenoid 239 whenevex gas generator speed exceeds a preselected maximum established by function generator 514 as a function of P2, T2 and Npt.
Normally the preselected maximum parameter values discussed with regard to these safety overri.de operations, are slightly above the - ~5 -~3S80 normal operatin~ values of the parameters so th~t the solenoid 239 is normall~ inoperable except in instances of one of these parameters substantially exceeding the desired value thereof.
Thus, for instance, during a cruise mode of operation or "coastiny"
when the vehicle is traveling do~mhill being deiven to a certain extent by its own inertia, the solenoid 239 is operable in response to increase of power turbine output shaft 82 beyond that desired to cut back on fuel flow to the combustor to tend to control the power turbine-output speed.
While as discussed previously with regard to the cruise operation of the vehicle, the yuide vane control normally is responsive to combustor exhaust tempera-ture T4 as reflected in the signal yenerator by element 435, the logic elemen-t ~98 is also responsive to the turbine exhaust temperature T6 in comparison to ]5 a preselected maximum thereof as determined by summer 540 which generates a signal through line 542 to elernent 498 whenever turbine exhaust temper~-ture T6 exceeds the preselected maximum.
Logic element 498 is responsive to signal from either line 542 or 536 to reduce the magnitude of the electronic signal supplied throuyh line 427 to solenoid ~26 and thus reducc the pressurc ratio across the turbine wheels 11.6, 118. As discuc;~ecl previously, this change in pressu-re ratio tends to increase cJas cJenerator speed and in response the ~uel yove~rnor 60 recl~lces f~lel Elow to the combustor so that turb.inc exhclust tcmE~ercltu:re T6 is ~revcnted Erom increasiny beyond a preselec~ed maxi.mllrn limi.t.
As desired, the solenoic1 239 may be encr~Jizcd :in response ~o other override parameters. For instancc, to protect the recuperator 56 from excessive thermcll stresses, the logic element 538 may inCorporate a differentiator 548 associated with the signal from the turbine exhaust temperature T6 so as to generate a signal indicative of rate of change o~ turbine exhaust temperature T6.
~43580 Logic element S38 can thus generate a signal energizing solenoid 239 whenever the rate of change of turbine exhaust temperature T6 exceeds a preselected maximum. In this manner solenoid 239 can control maximum rate of change of temperature in the recuperator and thus the thermal stress imposed thereon. Similarly, the logic element 538 may operate to limit maximum horsepower developed across the power turbine ana/or gas generator shafts.
Gear Shift Because turbine engine 30 is of the free turbine type with a power output shaft 82 not physically connected to the gas generator shaft 76, the power turbine shaft 82 would normally tend to greatly overspeed during a gear shifting operation wherein upon disengaye-ment of the drive clutch 34 to permit gear shifting in box 38, substantially all inertial retarding loads are removed from the lS power turbine drive shaft 82 and associated power shaft 32. Of course, during normal manual operation upon gear shifting, the accelerator lever 184 is releasecl so that the fuel governor 60 immediately begins substantially reducing fuel flow to combustor 98. Yet because o the high rotational inertia of the power turb.ine shaft 82 as well as the high volumetric gas flow thereacross from the combustor, the power turbine sha:Et would still ~end to over speed.
Accordin~ly, the control sy:teln as cont~mplated by the prc:sent invention uki.l.i.z.es the gu.ide vane actu~tor contro]. 6~) to shift the ~5 guide vanes 120, 122 ~oward th~:ir Fic3. 16 "re~erse" position such that the gas flow from the eng.ine impinges oppositely on the vancs 117, 119 of the power turbine wheels in a manner opposing rotation of these power turbine wheels. Thus the gas flow Erom the engine is used to decelerate, rather than power, the turbine shaft 82.
As a result, the power turbine shaft tends to reduce in speed to the point whcre s~ynchrorlous shifting of gear box 38 and consequent 3~80 re-enga~ement of drive clutch 36 may be conveniently and speedily accomplished without damage to the engine or drive train.
~lore particularly, the hydromechanical portion of guide vane control 66 is so arranged that upon release of accelerator lever ~5 184 such as durin~ gear shifting, a very large error signal is created by the high pressure from the power turbine speed sensor line 420 to rotate lever 396 counter-clockwise and substantially greatly increase the compression of spring 384. Sufficient compression of spring 38~ results to urye valve 380 upwardly and drive piston 366 down~ardly to its position illustrated in Fig. 12.
This pos.ition of piston 366 corresponds to positioning the guide vanes 120, 122 in their Fig~ 16 disposition. The gas flow from the combustor is then directed by the guide vane across the turbine wheel vanes 117, 119 in opposition to the rotation thereof to ,15 decelerate the power turbine shaEt 82~ Since the drive clutch 34 is disengaged during this gear shi~ting operation, the power turbine shaft 82 rather rapidly decelerates by virtue of the opposing gas flow created by the posi.tioning of guide vanes 120 in their Fig. 16 position. Yet more speci~ically, the arrangemerlt of springs ~06, 408 and the relative maynitude of pr~ssure developed .in conduit 410 ancl 420 causes the hydromechaniccll portion of varle actuator control 6 to operate in thc manncr above describecl to shift the guide vanes 120 to their necJat:ive or reverC;e disposition illustratecl in Fig. 16 and moclulate cJuick~ v~lne pO';i.t-i.OI- within ~one "d" of Fic3. 18 in relati.on to the mac3nituclc oE Npt exccs~, whencver the accelerator lever 1~4 is movecl to less than a pre-;electecl accelerator lever position a*. As the speecl of power turbine shaft 82 reduces, the piston 416 begins shlftincJ in an opposite direction to reduce compression of sprinc3 384 once turbine speed reduces to a preselec-ted value. The action of piston 416 is in the preferred form capable of modulatiny the degree of compression of spring 384 in relation to the maynitude of the Npt error. The yreater the speed _ ~8 -~35~30 error, the more the guide vanes are rotated to a "harder"
braking position. Thus, the positionof the guide vanes are maintained in a reverse brakin~ mode and are modulated through zone "d" near the maximum braking position -95 of Fig. 18 in ; relation to the power turbine speed error. Once gear shifting is completed, of course, the control system operates through the acceleration operation discussed previously to again increase power turbine speed.
Deceleration L0 A first mode of deceleration of the gas turbine engine is accomplished by reduction in fuel flow along the deceleration schedule afforded by deceleration window 2~6 of scheduling valve 62. More particularly, the release of accelerator lever 184 causes the fuel governor 60 to severely restrict fuel flow !.5 throucJh opening 17~. As a consequence the minimum fuel flow to the gas turbine engine i5 provlded throucfh deceleration fuel line 142 and the associated deceleration window 2~6 o~ the scheduling valve. As noted previously dcceleration window 2~ is particularly configured to the gas turbine engine 50 as to continually reduce ~0 fuel flow along a schedule which rnaintclin.C~ combustion in the combustor 98, i.e., substantially along the operat.illg l:i.ne of the ga~ turb.it~e engine to ma.in~clin combuGtion but below the "rcciuired to run Ji.ne." ~s notcd previously, evcn w.ithou~ rol,a~:ion of acceler tor lever 1~, the solclloicl 23~ Ccltl be enercJ.ized i.n '5 partic~l.ar instanc~s to genc.rat:c ~ fa.l.c;e accelerator lever sigrlal to fue~ lev~r 226 to accompl:ish decelera~ion by sevcxcly rcstrict.ing fuel f.low, This deceleration by limiting fuel flow is accomplished by reduci.,lg the accelerator lever to a position at or just above ;0 a pre~,~].ected accelerator position, a*. This accelerator position is normally just slig~ltly above the minimum accelerator position, :~43~
an~ scn~rall~ c~rresp~ds ~ the positi~n ~f the accelerator lever during the "coasting" condition wherein the engine i~
somewhat driven by the inertia of the vehicle such as when coasting downhill. Since this deceleration by restricting fuel flow is acting ~nly through govern~r 60, it will be apparent that the guide vane control is unaffectred thereby and continues operating in the modes and conditions aiscussed previously. This is particularly true since the accelerator has been brought down to, but not below the preselected acce-lerator position a* to which the hydromechanical portion ofvane actuator 66 is responsive.
Upon further rotating accelerator lever 184 below the position a* and towards it minimurn position, a second mode of deceleration or brakiny of the vehicle occurs. In this mode, the movement of the accelerator lever below the position a* causes the hydromechanical portion of guide vane actuator 66 to generate a substantially large error signal with regard to power turbine speed so as to rotate the guide vanes 120 to their Fig. 16 reverse or `'braking" position. More particular-ly, as discussed above with regard to the gear shift operationof the vehicle, this large error signal of the power turbine speed in comparison to the accelerator levcr position causes siynificant counter-clockwise rotation of lever 396 and conse-quent compression of sprin~ 384. This drives t~re piston 366 and the guicle vanes toward the Fi~. 16 position thereof. As a result, the gas flow from the gas turbine engine opposes rotation of the turbine wheels 116, 118 and produces s~stan-tial tendency for deceleration of output shaft 82~ It has been found that for a gas turbine engine in the 450 to 600 horsepower class, that this reversing of the guide vanes in combination with minimurn fuel flow to the combustor as permit-ted by deceleration window 286 provides on the order of 200 or more horsepower braking onto the turbine output shaft 82.
~ 3~8~
It will be noted that during t},is second mode o~
deceleration, as well as duriny the gear shift operation dis-cu~sed previously, that since the guide vanes are now in a reversed disposition, the logic accomplished by the electronic control module 68 in controlling solenoid 426 to prevent over temperature of T4 or T6 is now opposite to that required.
Accordingly, the electronic control logic further includes a transducer 544 which senses whenever the guide vanes pass over centre as noted by the predetermined angle B* of Fig. 18, and are in a negative incidence disposition. This signal generated by transducer 544 energizes a reversin~3 device such as an in-verter 546 which reve~ses the signal to the solenoid 426. More particularly, if during this deceleration operation with the guide vanes in the negative incidence position of Fig. 16, there occurs an excess cor~ustor exha-lst temperature T~ or ex-cess turbine exhaust temperature T6, the siynal generated by ele~lent 500 to reduce the magnitude of the current signal is reversed by element 546. Accordingly occurrence high T4 or high T6 while element 546 is encrgiz~d generates an electrical signal of increasing strent3th to solenoid 42G. ~n response, the solenoid 426 drives valve 432 in a direc~ion intreasirlg pressure in conduit 394 and upon shoulder 393; Thi~ reduces the magnitude of t:he bi.asing ~.pr:;ng 3~3 and causts v-llvt;~ 3~0 to move downwardly. In a followirlg mo~em~nt th~ piston 366 moves upwardly to reduce the compre~sion of sprint3 38~ 'hus the guide vanes 120 are reversely tri~ned away from the ma~imurn braking position shown in Fig. 16 back towards the neutral position of Fig. 14. This movement of course reduces the mag-nitude of power transmitted from the gas flow in opposing rota-tion of the guide vanes 117 to cause a consequent reduction infuel flow as discussed previously. T~le reduced fuel flow then reduces the magnitude of the over temperat-lre parameter T4 or T6. Such ~ction to control T4 or T6 will .....................
3~130 substan~ially only occur when fuel flow beiny delivered to the combustr i5 more than permi-tted by the deceleration schedule 286.
Thus such action is more likely to occur during the "coasting"
operation than during hard braking during the second mode of deceleration. Such is natural with operation of the engine, i however, since during hard deceleration, fuel flow to the combustor is at a minim~n and combustor exhaust temperature is relatively low. However, during unusual conditions, and even with the guide vanes in a negative incidence position, the electronic control module is still operable to return the guide vanes toward their neutral position to tend to reduce any over temperature conditions.
ower Feedback ~raking A third mode of deceleration of the vehicle can be manually selected by the operator. Such will normally occur when, after initiation of the first two modes of deceleration described above, the vehicle still is being driven by its own inexti.a at too high a speed, i.e. power turbine shaft 32 speed Npt is still too high.
Thus power turbine shaft speed Npt may be in a range of approxi-mately 90~ of its max:imum speed while the gas generator speecl NCJcJ
has been brought down to at or nenr its low id:l.e speed o.E approx.i.-mately 50~ max.irnum gas ~enerator speecl.
This third mode oE deceleration, termcd power .~eed~clck braking, is manually selec~ed by clos.ing power feed~ack switch ~66.
In respon6e the electroni.c conl:rol module 68 genercltes signals whicb ult.imately result .in mechanica.l. interconnect:ic)n o~ the (Jns generator shaft with t~le power turbine shaft such that the inertia of the gas genera-tor shaft is imposed upon the drive train oE the vehicle to produce additional braki.ng effects thereon More particularly, upon closiny switch 466, AND gate 506 generates a . signal to AND gate 50~ since the accelerator level is below a , pre-c'ectr~d po~n' a* causin~ fllnc~ion gc~nr~rator A~R to gener~t-o a signal to AND gate 506, and since the gas yenerator is opera-ting at a speed above 45~ of its rated value as determined ~y element 474. El~ment 472 develops a signal through line 480 tc>
AND gate 504 since power turbine speed is greater than gas generator speed in this operational mode. Element 470 also notes that the effective relative speeds of t'ne gas generator shaft and power turbine shaft are outside a preselected limit, such as the plus or minus 5% noted at comparator 470. Accor-dingly element 470 does not generate a signal to AND gates 502, 504. More specifically the element 470 is not necessarily c~m-paring the actual relative speeds of the gas generator power _ turbine shafts. Rather, the element is so arranged that it only generates a signal to AND gates 502, 504 wnenever tne relative speeds of the shafts 520, 522 in the power feedback clutch 84 are within the preselected predetermined limits of one another. Thus the comparator 468 will compensate, as re-quired, for differences in''the actu'al speeds of the gas genera- '' tor and power turbine ~haft, as well as the gear ratios o~ the two respective drive trains 78 and 80 associat~d with the two shafts 502,522 of the feedback clutch 8~.
Because o~ the di~ferenc~ ~tween Npt and Ngg, no signal from elelnent 470 i5 translnitted to either ~NI~ y.lte 502 or 504~ As noted scheJnati~ally by the circle ~l.;sociatcd wi~h the input from element 47n to AND gatc 504, thc~t input i~ in~
verted and AND gate 504 is now efective to generate ~n output signal since no signal is coming from el~ment 470, and since signals are being received from AND ~ate 506 and element 472.
The output signal from AND gate 504 accoinp~Lishes two functions~
First, a signal of 50~ Ngg magnitude is generated in function generator 566 and aclded to the constant 50~ bias signal of sum-mer 570. The resulting signal is equi~alent to a 100~ Ngg ~peed command. Secondly, the output~frc~n AND yate 504 passes through OR gate 562 to produce a signal to solenoid 257. Thi6 signal is of sufEicient maynitl~de to shi~t --------------------53~
S8C~ -solenoid 2SI to its Fi~. 6D position clearing opening 178 for substantial fuel flow to the combustor. It will be apparent that full enerc;ization of solenoid 257 to its Fig. 6D position is essentially a false accelerator lever signal to the fuel lever 22G
causing lever 226 to rotate to a position normally caused by depressing accelerating lever 184 to its maximum flo~ position.
Secondly, the signal from summer 570 is also an input to element 497 such that an artificial full throttle signal is generated which ove~rrides the energization signal which is maintaining the guide vanes in their Fig. 16 braking position during the second mode of deceleration discussed previously. The enerc~iza-tion of the yuide vane solenoid 426 causes increase of pressure in conduit 394 allowing the springs 382-385 to shift the piston 366 ~nd the assoclated ~uide vanes toward their Fig. 14 "neutral"
position.
Accordingly, it will be seen that the signal from AND yate 504 produces an acce~leratiorl siynal to the engine, placing the guide vanes 120, 122 in their neutral position such that maximum pressure ratio is developed across the gas generator turbine 102, and at the same time fuel flow to the combustor 98 has been c3reatly increased. In response, t}-e ga6 generator section beg.ins increasing in sp~ed rap.idly toward a value such that the sp~ed of shaft 522 of the feedback clutch approac,hc-~.ci -the spt-~c!d of its other shaPt 520.
Once the power turbine and C3cl5 generaLor shaEt spe~ds are ~5 appropriately m~tched such that t.he two shafts 520, 522 of the feedback clutch are w.ithin the pre~st-~lected limits tl~tcrmint!cl by element ~70 of the electronic control modult-~, elect:ronic,~ control module develops a positive si.gnal to both AND gates 502, 504.
This positive signal immediately sto~s the output signal from AND
3n gate 504 to de-energize the~ proportional solenoid 257 of the fuel governor and aqain reduce fuel flow back toward a minimum value, and at the samc~ time s~ops the~ override sicJnal to elemen-t 500
5~
such that the guide vane 120, 122 are again shifted back. to their Fig. 16 braking disposition in accord with the operation discussed above with respect with the second mode of deceleration.
The logic element ~ND gate 502 now develops a positive output signal to operate to drlver 516 and eneryize clutch actuator solenoid valve 518. In response the clutch 84 heco~es engaged to mechanically interlock the shafts 520 and 522 as well as the gas generator and power turbine shafts 76, 82. Incorporation of the logic element 470 in the electronic control module, in addition to the other functions described previously, also assures that since the two shafts 520, 522 are in near synchronous speed, relatively small torc~ue miss-match across the plates 524, 526 o the clutch is experienced. Accordingly, the size of clutch 84 can be xelatively small. Thus it will be seen that the electronic control module 68 operates automatically first to increase gas generator speed to essentially match power turbine speed, and then to automatically return the~ guide vanes to their Fig. 16 braking disposition at the same time as clutch 84 is engaged.
This interconnection of the gas turbine engine drive train with the gas generator shaft 76 causes the rotational inertia oE
gas genexatox 76 to as~ist in decelerating the vehicle. It has been found that for a ~50 to 600 horsepower clac;s engine described, this power feedback braking mode aclds in the neighbortlood oE 200 to 250 horsepower braki.nc3 in addit:ion to the 200 horsepower br~king effects produced by thc positiorling of guide vane 120, 122 in their ~'ig. 16 position. Because the Euel governor i5 again se~erely restrict.ing flow through or:iEic~e 178, the fuel flow is controlled by decelercltion window 2~6 perm:itt.ing the gas gencrator section to decelerate while maintainlng the combustion ~3~8~
process in combustor 98. Thus reduction of fuel flow provides the deceleration efect of the rotational inertia of the gas generator upon the drive train of the vehicle.
It will be apparent from the foregoing that the present invention provides substantial braking for deceleration purposes while still utilizin~ the optirnum operating characteristics of a free turbine type of a gas turbine engine with the ~as generator section mechanically interconnected with the power turbine sec-tion only in a spec;fic instance of a manually selected "severe" third mode type of deceleratîon operation. Throuyhout all deceleration modes and engine operation, a continuous combustion process is maintained in the cornbustor. Thus substantial deceleration occurs without extinguishing the combustion process therein.
This power feedback braking operation can be deactivated in lS several ways- manually by opening switch 466 to stop the output signal from AND gate 506;providing a NOT signal to turn off driver 516 and solenoid 518 to disengage clutch 8~. Furtherrnore, if the manual switch is not opened and the engine continues to decelerate, element 474 also operates to deactivate the power feedback operation wherlcver gas generator speed Nc~cJ reduces to a value b~low ~5~ of its rtlaxilnum xate o speed. ~lso, depression of ~he accelerator to a value of ahove a* also deact:ivates the power fe~dback opera~ion ~y s~oppincJ an output si~Jnal from AND
gate 506.
From the foregoin(J it will now be apparent that the pre-;ent invention provides an improvecl cycle oE operation ~or a CJas turbine engine peculiarly adapted for operatinc3 a ground vehicle in a safe, familiar manner while still retainincJ the inherent benefits of a gas turbine engine. More speci ically, by utilization of a free turbine type engine greatcr adapta~ility and variability of engine operation is provided. ~t the same time the engine can operate 8~
throughout its entire operatincj cycle while maintaini"g a continuOus combustion process within the combustor 98. This avoids various problems of operation and service life associated with repeated start and stop of the cc,mbustion process. The nove]
cycle contemplates a utili~ation of a combustor 98 having cho~.ed nozzles 102 to provide a variable pressure ~ithin the combustor as the speed of the gas generator section varies. Gas generator section speed is normally trimmed to a preselected value relative to the position of the accelerator lever 184, while the gui.de vanes 120, 122 operate to trim the turbine inlet temperature T4 to a preselected substantially constant value to maintain high en~ine operational efficiency. Further, the guide vane control operates indirectly to alter the fuel flow through fuel governor 60 by altering the speed of the gas generator section such that the various contxols are operable i.n an integral manner without counteracting one another. At the s~ne time a trim of power turbine shaft syeed Npt is provided by the guide vane control 66.
Furthermore it will be seen that the preserlt invention provides the gas turbine en~ine peculiarly adapted for dr:iv.ing a ground vehicle in that xesponsive accele.rat.ion sim:i.lar to that produced by an internal combustion engine .i.s provided by both the Automat:i.c high idle operat:Lon as we].l. cls by the manner of accele.rcltion of the gas tuxbine engine. Suc:h i.~i accornpli.shed by fircit alter:in the work split to develop maximum power to the gas yencrator section. The schedulincJ valve conk:rol 62 then acts in re~enerat:ive fashion to increase fuel ~low to the cornbustor in such a manner that ga~ generator speed is increased while mainta:ining a substan-tially constant maximum turb:ine inlct temperature T9 thereby produ-cing maximum acceleration without overheating the engine~ Yet the scheduling valve also limits T6 during the ini-tial portion of acceleration when turbine "stalling" conditions are prevalent.
Accelerati.on is then completed once substantial acceleration of 3~8~
the c~as generator section is accomplished, by xe-altering the power split to develop c3reater power across the power turbine wheels 116, 118.
It is fur-ther noted that the present invention prov.ides an .~ improved method and apparatus for decelerating the vehicle in a three stage type of operation by first reducing fuel flow, then by placing the guide vanes in the bra~ing mode, and then by manually selecting the power feedback operation.
The primary operating elements of the fuel governor 60, scheduling valve 62, and guide vane control 66 are hydromechanical in nature. This, in conjunction with the operation of solenoid 426 of the yuide vane control which is normally energized, provides an encJine and control system peculiarly adapted to provide safe engine operation in the event of various failure modes. More parti.cularly, in the event of cornpletc loss of electrical power to the electronic control module 68, the mechanical portion of fuel governor 60 continues to adjust fuel.
flow in relation to tha-t selected by accelerator lever 184.
Scheduling valve 62 is in no way affected by such clectrical failure and is capable of controlling acceleration and/or deceleration to both prevent over ~lea~inCJ of the encJi.nc during ~ccelerat:ion as well as to ma:in~a:i.n combustion durin(J deccleration.
The hydrornechanica]. por~lon ~f the vane act-lcltor control w:L11 still be operable in the event of ~lectrical failure and capable :~5 of adjus-t:ing the cJuide VCllles as appropriate to ma;intalll func-t:ic~l~al enc~ine opera~.ion. Upon electrical failure the solenoid ~26 o.E
the guide vane control becomes de~energized causing loss of pressure upon face 393 of the control. piston 392. However, the speed control afforded by lever 396 is still maintained and the guidc vanes can be appropriately positioned to maintain functional engine operation during this failure of the electrical sys-tem. Thus, while certain desirable features of the engine control w;].l be lost in the event of electrical failure, the engine can stil] function properly with : - 5~ -1~43~80 appropriate aeceleration and deceleration so that the vehicle may still be operated in ~ safe manner even though at a possible loss of operational ef~iciency and loss of the ability to provide power feedback braking.
5~ From the foregoing i.t will be appa~en~ that the present invention provides an improved method of automatically setting and resetting the idle of the gas generator section so that the engine is highly responsive in developing an increase in output power such as when contemplating acceleration o the vehicle.
.10 Further the present invention provides an improved method of controlling fuel flow hydromechanically in relation to gas generator speed, as well as overriding normal speed control operation of the fuel governor to increase or decrease fuel flow in response to occurrence of various conditicns which energize either of the solenoids 239, 257. Further the present invention provides an improved method for controlling fuel flow to the .
combustor during accel,eration such that constant turbine inlet temperature T4 is maintained throughout, while also controlling fuel flow during deceleration to avoid extinguishing ~he combust,ion process within a combustor. The invention further contemplates an improved method of controllin~ guide vane position in such an enyine both by hydromechanical operation to control speed of a rotor such as turbine wheelq 116, 118, and by electrical override operatiotl dependent upon the amount o~ enerc3i~ation of the proportional solenoid 426.
The ~oregoing }IAS described a pre~erred embodiment of the invention in sufficient detail that those skilled in the art may make and use it. However, this detailed description should be considered exemplary in nature and not as limiti.ng to the scope and spirit of the present invention as set forth in the appended claims.
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~1~3~81D
Having described the invention with sufficient clarîty that those skilled in the art may make and use it, what is claimed as new and desired to be secured by Letters Patent is:
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