CA1145959A - Gas turbine engine - Google Patents

Abstract

ABSTRACT

A gas turbine engine and method and control therefor particularly useful as the power plant for a ground vehicle.

Description

~ 5~59 BACKGROU~D OF T~l~ INVENTION
i . This invention 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 yround vehicle.
Recent advances in gas turbine engine technology have ~ improved their overall efficienc~ and economy to such an extent ! that this t~pe o~ power plant has become competitive in many Z instances with rnore conventional internal combustion type power 0 plants such as Otto or ~iesel cycle en~ines. For instance, gas ~ turbine technology has made significant inroaas as the power planl:
¦ for aircraft engines. Similarly, attempts have been made to ¦ develop a gas turbine engine which would ~e competitive with the more conventional internal combustion engines in high-production S ground vehicles such as on-the-road automobiles and heavy trucks.
The gas turbine of~ers significan-t advantages of equivalent or ; be~ter operational efficiency, fuel savings, and less emissions as well as being able to utilize a variety of differen-t ~uels on an economic basis. Further, the gas turbine engine in many ~O instances offers gxeater overall economy over the entire operational life of a vehicle.
The inherent operational characteristics o F a gas turbine engine present, however, certain problems when uti:Lized in a ground vehicle. More specifically, a gas t~rbine engine generaily ~5 includes a gas generator section which provides a large pressurized air flow to a com~ustor wherein the air flow is mixed and ignlted with fuel to greatly increase the temperature of the resulting gas flow. Hot pressurized gas flow then drives one or more turbines to produce useful ro-tary mechanical output power. Normally one of 0 tnese turbines is a portion of the gas senerator section for drivin~

, .

s~s~ ~
tile fan which provides the high volum~ pressurized air inlet ; flo~ ownstream power output kurbines then ~enerate the useul mechanical power output. Conventionally, the high speed, high volume ~as ~low from the gas generator drives the turbines at relatively high speeds. Other inherent characteristics of such gas turbine engines xelates to the thermodynamic and aerodynamic processes carried out therewithin which dictate that operational efficiency of the engine increases substantially with increasing maximum temperature Gf the gas flow.
: ` .
~Lo These operating characteristics of a gas turbine engine present certain disadvantages in comparison to the norma~
operation of reciprocating or rotary piston type internal combustion engines ~or ground vehicles. More particularl~, the ` : ~
~ ~ internal combustion engine inherently provides a substantial ... .
~lS amount o~ deceleration horsepower for the vehicle upon reducing' :,`~ .
fuel '~low thereto through the drag imposed ~y the recip~ocatin~
portio~ of the enyine. In contrast, the high rotational inertia ~.~ .: ...... . . ; . , of the turbines of the gas turbine engine normally do not permit such immediate, relatively high horsepower braking ~or a ground ~0 ~ vehicle simply upon reducing fuel flow to the combustor of the . . .
gas turbine engine. To overcome this disadvantage, a variety of proposals have heen ofered in the past to increase the braking , l :
characteristics oE a gas turbine engine when utilized for dri~ing a ground vehiole. ~Primarily, these concepts relate to completely ~5~ ~ extinguishing the combustion process ~ithin the combustor to produce~maximum dynamic~braking. However, operational life of a . : :
gas turbine englne is substantially reduced by continual thermal cycling of the entire engine as created upon extinguishing the combustlon process. ~Further, such approaches adversely affect .0~ emissions. Other concep~s relatin~g to improving the dynamic : , : : - , braking characteristics of a gas turbine engine revolve around the utilization of a "~ixe~ shaft" type oE gas turbine engine .,~ , :
:, ~ , '~.~- : : - .

. ~ , :~ , . . . .

~5~

wherein the gas ~enerator section and the power drive section are mechanically interconne~ted to drive the vehicle. While such an arrange~ent improves the dynamic braking, it greatly ~ reduces the adaptability of t~e engine to perform various other is 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 high-production type of ground vehicle. An I example o~ such prior art structure is found in U. S. Patent No. 3,237,404. The normal method for dynamic braking in gas turbine powered aircraft, thrust reversal, is of cour~e not ~¦ readily applicable to ground vehicles.
~ Prior arrangements for gas turbine engines for ground ~`~
`~¦ vehicles also have suffered from the disadvantage of not ~j providing efficient, yet highly responsive acceleration in ~;~15 comparison to internal combustion engines. Inherently, a free turbine engine ncrmally requires a substantially longer time in developing the maximum torque xequired during acceleration of the ground vehicle. Prior attempts to solve this problem have centered about methods such as operating the gas generator at ~20~ a constant, maximum speed, or other techniques which are e~ually inefficient~in utilization of fuel. Overall, prior gas turbine engines for ground vehicles normally have suffered from a reduced operational efficiency in attempting to improve the acceleration `~ ~ or deceleration characteristics of the engine, and or resulted in reduced efficiency by substantially varying the turbine inlet temperature of the gas turbine engine which is a primary actor in the fuel consumption of the engine. Further, priox axt . attempts have generally been deficien~ in providing~a relLable type of control system which is effective throughou~ all , , .

~ 4 : .~ ' ' ' . , ' ' , , .. ..
. ~ ~

5~S5~
: operational modes of a gas turbine enyine when operating a ground vehi.cle to produce safe, reliable, opelating charac-teristics. Further, such prior art gas -turbine engines have resul-ted in control arrangements which pre~ent 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 ground vehicle relate to the safety and re].iability of the control system in various failure modes, safe and reliable types of controls, and in the o~erall operational efficiency of the engine. A majority of these problems may be considered as an outgrowth of attempts to provide a gas turbine engine presenting 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 turbine engine and associated con-. ....... . . ; .
trols which incorporate the desirable operational features ofboth a gas turbine and lnternal combustion engine, but while providin~ an economical end product of sufficiently reliable and safe design or high volume production basis for ground vehicles.
Discussions of exemplary prior art structure relating to the engine of the present invention may be found in U. S.
Patents No. 3,237,404 discussed above.; 3,660,976; 3,899,877;
3,~41,015 all of which appear to relate to schemes for trans-. mitting motive power from the gas generator to the eng.~ne out~
put shaft, and 3,688,605; 3,77I,916 and 3,938,321 that relate to other concepts for vehicular gas turbine engines. Examples of concepts for variabl.e nozzle engines may also be found in . S. Patents 3,686,860; 3,780,5~7 and 3,777,479~ Prior artfuel governor controls in the general class of that con~em-plated by the present invention ma~ be found in U.S. Patents 3,400,535; 3,508,3gS; 3,568,439; 3,712,055; .

~5~S5~
.
3,777,480 and 3,913,316, none of which incorp~rate reset and override f~atures as contemplated by the present invention;
and 3,521,446 which discloses a substantially more complex fuel reset feature than that of the present invention. Exampl~s of other fuel controls less pertinent to the present inve~tion may be found in Patents 3,851,464 and 3,388,078. 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 SUMMARY OF THE INVENTION
.. .. ..
An important object o~ 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.
'15 Another important object is to provide provisions producing impxoved fuel performance in a variety of operations of a ground vehicle driven by a gas turbine engine.
Another important object of the present invention is to provide improved acceleration, deceleration characteristics for a ~20 gas turbine driven ground vehicle, and to provide a more reliable, longer life gas turbine engine for propulsion or power genexati~g purposes.
In s~unmary, the invention contemplates a recuperated, free turbine type engine with separate gas ~enerator and power turbine ~25 sec-~ions. ~ fuel governor controls fuel flow to the combustor to se-t gas generator speed in relation to the throttle lever. Reset solenoids can override and adjust fuel flow in response to certain operating parameters or conditlons of en~ine operation. For ~-instance, in response to low speed on the ou-tput shaft of the drive train clutch which is indicative of an impending desired ; enyine acceleration for increased torque output, a rese~ solenoid '' ' .:
.
., . .... ....... ~.. ..... ..... ~... ...... . ................ .. .

L 4L ~i~3 59 increases fuel flow and the gas ~enerator idle speed to sub~
stanti~lly reduc~ time ~quired in inc~easing engine tor~ue output. A scheduling valve i~ effective to control fuel flow during engine acceleration to prevent excessive recuperator inlet temperature and maintain turbine inlet t~nperature at a substantially constant, high level for maximum engine per-formance. The scheduling valve is responsive to combustor inlet gauge pressure and temperature, and also controls fuel flow ~uring deceleration in a manner m~intaining combustion.
Variable tur~ine guide vanes are shifted first to maxLmize power delivered to the gas generator during its acceleration, and subsequently are shifted toward a position deliveriny maximum power to the power turbine section. The variable guide vane control includes a hydromechanical portion capahle 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 braking characteristics. ~en such is selected, the gas generator speed is automatically adjusted to approach power turbine speed, then th~ough a relatively low power rated clutch -the ga~ generator and power turbine sections are mechanically interconnected such that ~he rotational inertia of the gas generator ~ection assists in retarding the engine ~ output shaft~
--~ More specifically the present inventian contemplates in a free turbine type gas turbine engine having a power turbine section driven by a motive qas flow developed by a gas generator section of the engine variabl~h positionable guide vanes dlsposed in said gas flow for altering the incid-ence thereof upon said power turbine section; a source of pressurized fluid; a housing having a fluid exhaust por-t, an inlet port communicating with said source, an internal cylinder, ,~ 7 and an internal bore communicating with said inlet and outlet ports; a piston movable in said cylinder and dividing the latter into opposed fluid chambers communicating with ,said bore at spaced locations therealong; linkage operably inter-connecti.ng said piston and said quide vanes whereby said guide vanes are positioned in relation to the position of said piston; a four-way valve movable within said bore to control : communica-tion of said opposed chambers with said inlet and outlet ports; a first feedback spring means extending between said piston and said four-way valve to urge the latte~r in a first direction in relation to the position of said piston;
a first stop movably mounted in said housing; second input spring means extending between said first stop and said four-way valve to urge the latter .in a second opposite direction in relation to the position of said first stop; and input means for adjusting the position of said first stop.
These and other objec~s and advantages o-f the present invention are sat forth in or will become apparent from the following de-tailed description of a preferred embodiment when read in conjunction with the accompany drawings.

- 7a - .

. ~ : ....... . ... . . .. . . ... .... . .... . .... ..... ,. , .. ~.. ........ . . .

~S~g BRIEF DESCRIPTION OF THE DR~WINGS
, In the drawings:
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 ragmentar~, par-tially schematic, elevational ~10 cross-section of the power feedback clutch and associated hydraulic system, taken generally along lines 3-3 of Fig. 2;
Fig. 4 is a partiall~ schematic cxoss-sectional representa-tion of the rotating group of the engine with controls associate~
therewith shown in schematic, block diagram~form;
Fig. 5 is a right fron-~ perspective view of a portion of the housing, ducting passages and combustor o the engine with portions broken awa~ to reveal internal details of construction;
Fig. 6 is a partially schematic, plan cross-sectional view of the fuel governor 60 with portions shown perspectively for ;~20 better clarit~ of operational interrelationships;
Fig. 6a is an enlarged partial elevational cross-sectional ; view of the fuel pump taken generally along lines 6a-6a of Fig. 6;
Figs. 6b, 6c~ 6d are enlarged cross-sectional views o~ a ~ portion of the fuel governor control showing different '25~ operational positlons of solenoid 257;
Fig~ 7 is a schematic, cross~sectional and perspective functional representation of scheduling valve 62;
Fig. 8 is a plan cross-sectional view through one portion o the scheduling valve;
-30 Fig. 9 is a plan cross-sectional view of the scheduling valve takèn generally along iines 9-9 of Fig. 8;
Figs. 10 and 11 are enlarged vie~s of portions of valve 282 showing the interrelationship of fuel metering passag~s as would be viewed respectively along lines 10-10 and 11-1~ of 3~ Fig. 7;

.. ... . ..

Fig. 12 is ~ schematic cross-s~c-tional representation of guide vane con-trol 66;
Fig. 13 is an exploded perspective illustration o the guide vanes and actuator linkage;
Figs. 14, 15 and 16 are circum~erential 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 ccntrol module 68;
~: 10 Fig, 18 is a graphical representation of the area ratio across the power turbinas 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 relation to throttle position, and Fig. 20 is a graphical representation o~ the relationsh.~p : of fuel flow permitted by the scheduling valve as a function of . .
combustor pressure along lines of constant combustor inlet temperature.
, DETAILED DE_CRIPTION OF TXE PREFERRED EMBODIMENT
.
~20 With reference to the figures, listed below are the abbreviations utilized in the followincJ detailed description to denote various parameters:
pt - Power Turbine 54 Speed ~: Ngg - Gas Genexator 52 Speed Ngg* = Preselected Gas:Generator 52 5peed .
Nti = Transmission Input Shaft 36 Speed .
~:: e = Predetermined Minimum Speed of ~: Transmission Input Shaft 36 -. Wf . - Fuel flow ~`30 B = Stator ~ane 120, 122 ~ngle .
B = Predetermined St:ator Vane A~gle a . = Throttle 184 Position ' :
_ 9 _ .

.

s~ ~

a* = Predetermined Throttle Position T2 = Compressor Inle~ Temperature P2 = Ambient Pressure : T3 5 ~ Combustor Inlet Temperature P3 5 = Combustor Pressure P3 5* - Preselected Intermediate Value of Combustor Pressure T4 = Turbine Inlet Temperature -~ T6 ~ Turbine ~xhaust Temperature ~10 Engine 30 Referrin~ now more particularly to the drawings, an improved gas turbine engine as contemplated by the present invention is generally denoted by the numeral 30. As depicted in Fig } the engine is coupled to a substantially standard drive train fox a vehicle, particularl~ a truck in the 450 to 600 horsepower class, , . . .
with a power output sha~t 32 as the input ~o a drive train clutch 34. A t.ransmission input shaft 36 extends between the clutch 34 , ., , . , - .
: and a "change speed" type of transmission 38. Transmission 3a is of the manually shiftable gear type; however, it is to be under-.. .
~0 stood that vari.ous improvements of the present invention are , ~ , `- equally usable with other types of speed varying transmissions.
As is conventional the transmission 38 has a variety of differe~t positions including several forward gears, reverse gearing, and a . neutral position.. In the neutral posi~ion no power is transmitted ~25 between the transmission input shaft 36 and the transmission outpu.t shaft 40 which conventionally extends ~o the final drive 42 an~ ;

drive wheels 44 of the vehicle. ~ manual shifting lever 46 provides seletion of the desired gear ratio~ and a speed sensor 48 genera:tes a signal indicatlve of the speed of transmission input shat 3~. As ~30 schemati~ally depicted in Fig. 1 and described in grea-ter detail hereinbelow, ~he speed sensor 4~ may be o~ any type compatible with the control medium of the engine 30 Prefe.rab.ly, speed.sensor 48 ' ' , - 10 ~

~5~9 ~enerates an electri.ccll signal transmitted by conductor 50 to the electronic control rn~dule of the engine.
: Referring to Figs. 1~4, enyine 30 is of the free turbine, recuperated type incorporating a gas ge~erator se~-tion 52, a power turbine 54 mounted on a shaft separate ~rom that of the gas generator 52, and a recuperator 56 that sca-vanges waste heat from the exhaust flow from the engine for preheating the 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 numeral 60 which also includes the fuel pump 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 signals and produces output control signals to the go~ernor 60 and vane actuator control 66.
~: 20 Conventionally, there is included an electrical sto~
rage battery 70 and associated starter motor 7~ which i.s pre--ferably selectively coupled.to both the gas generator 52 and a startex air pump 74. During starting operation, the motor :~ 72 is energized to ariYe both an air starter pump 74 as well.
: as the main gas ge~eratox shaft 76. ~s clearly illustrated in Fig. 2, the preferred form o~ the invention also includes a ~ :
drive train 78 associated with gas generator shaft 76, and ~ :
. . another drive train 80 associated with and driven by a main .~ .
shaft 82 of the power turbine 54. The two drive trains 78 and . 30 80 are selectively interengageable through a relatively low power, wet clutch generally denoted by the numeral 84. This .~ clutch is generally referred to as t.he power feedback clutch and the structure thereof is descxibed in detail below with respect to Fig. 3, .... ~.~.......... ..........................

9~

w~lile its ~unctional operation is described further below, wit~
re~ard to the power feedback operation of the pre~ent inven-tion.
Gas generator 52 generally includes an appropriately filtered air inlet 86 throuyh which ambient air is supplied to a pair of series arranged centrifugal compressors 88 and 90. Cross-over ducting 92 carries the compressed air flow from the ~ixst compressor 88 to the second compressor 90. The gas generator 52 further includes ducting 94 as depicted in Fig. 5 which surrounds and collec~s the compressed air flow exhaust from the circular periphery of the second s-tage compressor 90, and carries this compressed air flow in a pair of feeder ducts 95 to recuperator 56 in non mixin~, heat exchange relationship with the recuperator.
While various ~orms of recuperator structure may be utilized i~
conjunction with the present invention, an exemplary form is as described in U. S. Patent No. 3,894,58~ entitled "Method of Manifold Construction for Formed Tube-Sheet Heat Exchanger", dated July 15, 1975, issued to Fred W. ~acohsen et al. Thou~h not necessary to the understanding of the present invention, reference may be made to the above referenced patent for a dekailed description of a recuperator and its operation. For purposes of the present inven-tion, it is suf1~ient to state that the compressed air flow from ducts 95 is preheated in the recuperator by the waste heat from the exhaust flow from the engine. The preheated, - compressed air flow is then ducted thrc,ugh duct 96 to a can-type combustor 98. As best seen in Fig. 5, heated flow from the recuperator passes thxough a plurality of openings 97 into a plenum portion of duc~ 96, then through openings 97~a in a portion of the housing structure supporting combustor 98. Combustor 98 has a perforated inner liner 99, and airflow from openings 97~a ,30 passes into the zone between the inner and outer liner to then pass through the perforated inner liner 99 into the combustor æone.
One or more electrical ignition plugs 100 are suitably connec~ed to a source of hiyh voltage elec~rical energy in a conventional manner. The igniter plug is operahle to maintain a continuous .

combustion process within the interior of the combustor wherein ~he Euel deliver~d from line 64 is mixed and burned Wit]l 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 10w 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 genera-tor turbine section. During engine operation, nozzles 104 maintain pressure in combustor 98 at a level higher than ambient... Flow of this heated, compressed gas across turbine 102 causes high speed rotation of the turbine and the ~as generator main sha~t 76. This rotation of course drives the two centrifugal compressors 88 and 90. Sha:Et 76 is . appropriately mounted by bearings 108 to the stationary hous.ing 110 of the engine.
Power turbine section 54 generally includes a duct section 112 and appropriate vanes 114 therein for directing the flow of gases from the gas genera-tor power turbine 102 toward a pair of axial power tuxbines 116 and 118 mounted to the power turbine ~20 main shat 82. The.power turbine section further includes se~.s 120 and 122 of variably positionable guide vanes respectively ~;~
disposed upstream of associated axial turbines 116, 118 and ~:
their associated blades 117, 119. As depicted in Fig. 13, each ~: o.the sets of varlable guide vanes 120 and 122 are disposed in ~25: an annular array within the gas flow path and are both mounted to a common ac-tuating mechanism generally referred to by the -numeral 124. The actuating mechanism 124 comprises a pair of ring gears 126 and 128, one for each set of variable vanes, a . . .
link 129 affixed to ring gear 126 and secured to ring gear 128 via plate 129-a. Pivotally mounted to the housing is a bell crank 130, and a twistecl link 131 has opposi~e ends pivotally attached to ~ ' . ' ' .

n~ 129 and one arm of bell cran~ 130. A linearly .shiftable 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 simul-taneous 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 o~
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 shGwn in Figs. 14-16, guide vanes ~10 120 are positioned in a central or "neutral" position o~ Yig. 14 causing substantially maximum area ratio and minimum pressure ratio across the downstream power turblne wheel blades 117 o wheel 116 in order to minimize the amount of power transferred by the gas flow into ro-tation of the turbine 116. Tlle Fig. 14 ~15 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 transmittecl from the gas flow to turbine 116 to rotate ~20 the latter and transmit maximum power to shaft 82. Also, the vanes are oppositely ro-tatable to the Fig. 16 position, noted as the -95 position of Fiy. 18, wherein the gas ~low is directed by the ~ariable vanes 120 to oppose and tend to retard the rotation of wheel 116. While only vanes 120 and blades 117 are illustrated in FigsO 14-16, it will be understood by those skilled in ~he art that substantially identical operational relationships exist between vanes 122 and turbine blades 119 of turbine 118.
The gas flow upon exiting 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 reduction gearing. .~n air or water cooler 87 is also included to cool th~ lubricating fluid in engine 30 and communicates with fluid reser~oir 89 throuyh hose 91.

. . .

i 1 Governor 60 _ . , .
Referring riow mor~ particularly to Fi~s. 4, 6, 6A-6D, the fuel governor 60 receives fuel from source 58 throush an a?propriate filter 136 into an inlet port 138 of a fuel pump housing 140. It wilL be apparent to those skilled in the art that khe housing 140 is attached to and may be integrally formed with another portion of 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 governox 60 is hydromechanical in nature but capable of being xesponsive to externally applied mechanical and electrical signals, and includes an appropriate drive connection schematically illustrated by line 1~6, and associated speed reducing gearing 148 as necessary to drive a gear 150 and drive shaft 152. Shaft 152 ~l5 drives a fuel pump in the form of a positive displacement rotary :: gear pump 154 which receives uel from inlet port 138 and displaces it at a substantially higher pressure through an output conduit 156.
As clearly illustrated in Fig. 6A, the gear pump comprises a pai.r Oe intermeshing geats 158 and 160, one of which is driven by drive ~0 shaft 152 and the other of which is mounted to an idler shaf~ 162 journaled w.ithin housing 140. Supplied in parallel flow arrang~-~ent from out.put conduit 156 are three passages, i.e. output duct ~` 142, bypass bore 164, and main flow metering passage 166. Contalned in bypass bore 164 is a bypass regulating valve poppet 168 slidable ~S~ : within bore 164 to variably meter excess flow rom output conduit 156 to a return passage 170 connected back to the fuel inlet port 138~ Pressure of fuel in bore 164 urges poppet 168 downwardly ~: to increase bypass flow thrcugh passage 170, while a helical coil compression spring means 172 acts against the pressure of fuel to ; J' ' urge poppet 168 upwardly to reduce volume of flow from bore 164 to :~ passage 1~0. Through a pressure passage 182 the lower end of bypass bore 16~ com~Qunicates with fuel. supply conduit 64. Thus, p~essure of fluid in conduit 64 is exerted upon the lower side of bypass valve poppet 16~ to assist spring 172 in opposin~ the force created by the hiyh pressure fluid in output conduit 156.

.- lS - .
, , ~ .. ~, .. .... . .

~~ssage 166 terminates in a meterincJ nozzle 174 secured by plate 176 to the housin~, and h~ving a reduced di~eter opening 178 communicating with a central cavity 180.
The fuel governor 60 further includes a manual throttle input in the Eorm of a throttle lever 1~4 shif-table between opposed adjustable stops 186, 188 adjustably secured to housing 140. Through an appropriate bearing 190 a shaft 192 extenc~iny 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 it a pair of stub shafts 196 that respectively carry rollers 198. Rollers 198 are engageab1e with the lower shoulder of a spring stop 200 such that rotation of the I

throttle lever 18~ and shaft 192 causes consequent ro-tation of stub shaf-ts 196 which are non~aligned with the main rotational axis of shaft 192, and thus vertical shifting of spring stop 200 through rollers 198. During its vertical or longituclinal shifting, spring stop 200 is guided by a guide shaft 202 which has an upper guide roll pin 204 slidably extending through a central bore of spring stop 200. Guide rod 202 is threadably received and secured such as by lock nut 206 to housing 140.
.; .
The governor 60 further includes a mechanical speecl sensor which includes a flyweight carrier 208 rigidly secured to rotate with shaf-t 152. Rotating with carrier 208 are a plurality of regularly spaced f1~weights 210 mounted for pi:votal movement upon pins 212 securing the weights 210 to carrier 208. Dependent upon ` the speed o~ sha~t 152, the centrifugal force causes ro~ation of `~ weights 210 abou~ pins 212 to cause the inner ends thereof to shift downwardly as viewed in Fig. 6 and drive the inner rota~ing race 214 of a roller bearing assembly also downwardly. Through ball bearings 216 this clownward force is transmitted to the non-rotating outer race 218 of the bearing assembly to cause downward shif~ing of non-rotatiny segmen~ 220. At its lower end segment 220 carries a spring stop shoulder 22~, ancl a speeder spring 224 operably extends between ~he stop 222 of segment 220 and the spring .. . ..

op 200 associated with the throttle input mechanlsm. Th~ough a preload of sprins 224 ~ctiny on se~ment 220 the ~lyweights are normally urgea upward to the zero or low speed position illustrated in ~ig. 6. Increasing speed of shaft 152 causes downward shifting of segment 220. Thus it will be apparent that s:: throttle lever 184 acts essen-tially to select gas generator speed as reflected by the speed of shaft 152, since ~he compression of spring 224 is set by rotation of throttle lever 184 and then opposed by the centrifugal force created by the rotation of shaft lS2. The vertical position of segment 220 therefore becomes indicative of the difference between selected speed (position of ,, ~
input throttle 184~ and actual gas generator speed as sensed ;
through fl~weiyhts 210. Fig. 19 iIlustxates the aation of spring '~: 22~ in requesting different levels of gas generator speed Ng~, as ~:15 the throttle is moved through different positions, ~.
~:~ Governox 60 further includes a main fuel throttle lever 226 pivotally mounted by pin 228 to housing 140. One arm 230 o lever .
~.................................. . :,, .. ~ .
226 ter~inates in a spherically shaped end 230 wi-thin a receiving groove 232 on segment 220 of the speed error signal mechanism.
An opposite arm 234 of lever 226 is movable toward and awa~ from ;~ .
metering orifice 178 in response to`shifting of segment 220 to hereby variably meter fuel flow`from passage 166 i}ltO internal cavity 180. It will be apparent that the regulating valve poppet . 168 is variabl~ posi~ioned in response to the pressure differential ~25 ~etween passage 168 and conduit 64 aownstream of the me~ering ~ ` orifice 178 to variabl~ meter bypass fluid:flow through passage '!.~ '~ 170 in order to maintain a substantially cons~ant pressure . ~ differential across the fluid metering orifice created between ; metering opening 178 and the arm~234 of fuel lever 226. rrhus the ~30:~ rate of fuel flow delivered from passage 166 to cavity 180 and output duct 144 is a function onl~ substantially of the pGsition of arm 23~ relative to me~ering opening 178 whenever the latter is ' ~. ~ , ' :
~f, ~'~ ' ' , , ~ ` .
S ,~ , , ~ 17 -.. . .

,',"~ ' .
.,. ~ . . . .. . ~ .. .... .. . .. ... ....... .. .......

5~
,e fuel ~low controllin~ par~meter. As appropriat~, a d~mpiny orifice 236 may be incorporated in pressure sensing line 182 -to stabili~e the movement of bypass valve poppet 168~
A uni-directional propor-tional solenoid 239 has an outer housing 238 integ~al with plate 176 or otherwise affixed in stationary relationship to housin~ 140. Disposed within the housing 238 is a coil 2~0, and a centrally arranged armature 242.
Rigidly secured to form a por-tion of armature 242 is a central plunger shaft 244 which has an upper end engageable 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 nonnally 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 and exerts an upward force on lever arm 234 opposing ana subtracting from the force exerted by speeder spriny 224 upon lever 226.
While the plunger shaft 244 could, if desired directly engage the lever arm 234, in the preferred form a "floating face"
~20 arrangement for arm 23~ is utilized. In this arrangement a floating flat poppet-type face 252 is carried within arm 234 in alignment with metering openîng 178. This floating face is normally spring loaded toward the metering orifice, and the upper end of plunger shat 244 is engageable therewith. The purpose of floating face 252 is to compensate for manufacturing tolerances and to assure that a relatlvely fla-t surface is directly aligned with metering opening 178 and lying perpendicular to the ~luid flow therefrom to assure proper metering of uel thereacross. The spring 254 loads floating face 252 toward opening 178. Pi~oting of arm 234 against spring 254 to increase fuel Elow i5 pexmitted until face 252 contacts the upper end of 245 of plunger 244. This stroking of arm 234 is quite limited but sufficien-t to create flow .
. .. ..

s~s9 'turatiOn of the annular orifice defined ~etween opening 178 and face 252.-Disposed on the opposite side o~ lever arm 234 from solenoid 239 is a housing 256 of another directional, one-way solcnoid 257 '-~5 - 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 springs 264, 266 normally urge the plunger shaft 262 to the de-energized position illustrated. Upon -;, energization of the coil 258 through appropriate leader lines 268, ~10 the armature 260 and plunger shaft,262 are shifted downwardly such that the plunger shaft engages the lever arm 234 in a manner exerting a force thereon tending to add to the force created by speeder spring 224 and rotating lever 226 to shift arm 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 face 252, in the preferred form the plunger 262 does not directly .
~' engage the lever arm 234, but rather acts through a'floating-typepin 272 to exert a force on arm 234. The pin 272 is pre-loaded by a spring 274 to give a floating action thereto in order to ~20 assure that plunger 262 can properly engage and exert a force on '~ lever arm 234 regardless of varia-tions in manufacturing tolerances, .~ and/or the posit,ion o lever 226 relative to its pivotal shaft 228.
Both solenoids are urged to their de-energized position by '~ linear gradient springs, and unlike on-off, digital-t~pe solenoids, ~5 variation in curren~ and/or voltage inpu~ ~o their coils will cause an analog incremental positloning of the plunger 244 of ~ . :
solenoid 239, and will m~ve plunger 262 to either its Fig. 6-C,or ~: 6-D position.
: - The plunger 262 of solenoid 257 can be shifted away from its .0: ,de-energized Fig. 6-B state, ~o two different energized states , shown in Figs. 6-C and 6-D. One elec-txical input signal of preselecLed~lntermedlate power causes the armature 262 to shift to .. .

~e Fig. 6-C position, moving plun~er 262 until the face o its adjustable stop nut 263 contacts the sprin~ stop 267. This travel of plun~er piston 262 depresses plunger 272 and compresses spring 274 to shift arm 234 away from openiny 178 and increase fuel flow until gas generator speed incre~ses to a level corresponding to the signal force generated by solenoid 257. Thus the plunger 272, spring 274 configuration assists in permitting a less-than~maximum power signal to produce a force of preselected magnitude on arm 234.
Another electrical input signal of greater power causes the armature to shift to the end o its stroke with face 261 thereo contact the adjacent stop face 259 of the housing 256 as shown in ~ig. 6-D. This travel causes piston plunger 262 to compress centering spring 266 and cause its lower end to come ~15 in~o direct contact with arm 234 and urge the latter to permit maximum flow through the orifice presented between opening 178 and piston 252. As described in greater detail below, energization of solenoid 257 to its Fig. 6-D position is essentially a fzlse throttle signal duplicating the speed desired from the gas generator when the throttle is depressed to its maximum fuel flow, maximum power position.
he.duling Valve 62 ;; ReEerring now more particularly to Figs. 7-11, scheduling valve 62 genexally includes a housing 276 which may be integral with both housinss 140 and the stationary engine housing 110 Pre~erabl~ housing 276 is disposed in close proximity to both the fuel governor 60 and the combustor 98. Housing 276 includes an internal bore 278 into whlch open the two fuel ducts 142, 144 as well as the fuel line 64 and a low pressure return conduit 2ao which returns fuel back to the source. Mounted for longitudinal slidiny and rotation wlthin bore ~78 is a metering ~alve 282 having : .
:~ ' , ' windowed" irregularly shaped openings 284, 286 that open into the hollowed interior cavi.ty 288 of valve 282. Fuel line 144 continuously communicates with interior cavity 288. Valve 282 further includes an opening 290 in continuous communication ~:5 with fuel line 64. Deceleration window 286 is in general alignmen-t with fuel duct 142, and acceleration window genera].ly aligns with opening 290. The particular con~iguration of each of the windo~s 284, 286 is clearly illustrated in Figs. 10 and 11.
Metering valve 282 is urged in one longitudinal direc-tion by a biasing spxing 292 which reacts against the housing 27~
through a spring stop 294 acting on an alignment point 296 of a sealed block 298 mounted to housing 276 such as by snap ring 300.
The preferred construction as illustrated in Fig. 9; however, the alignment point arrangement permitting rotation of valve 282 relative to h~using 276 at the end of spring 292 may alternately be accomplished via a ball 302 configura-tion 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 ~20 sensitive element 312, 308, for example a thermally responsive cylinder, whose longitudinal length varies with respect to the .~ tempera-ture imposed thereon by the gas or other fluid in the tempera-ture sensing chamber 310 within cylinder 312. The housing ~: 276 is mounted relative to the engine such that a portion thereof, ~5 particularly cylinder 312 and the associated chamber 310 are in communication with and maintained at the same temperature, T3.5, as the compressed air 1Ow being delivered into the combustox~
Thermally insulative material 311 is incorporated as necessary to : avoid overheating of ~alve 62. For example the rightward end of Fig. 9 and.the perforated cylindrical walI 312 may be disposed at the air inl.et ~o the combustor and/or at the duct 96 carrying air from the recupera~or 56 to combustor 98. In any case the scheduling - 21 - . . .

vdlve is so ~rLanged tha~ cylinder 312 expands and con~racts longitudinally with respect to increase and decreas~ of combustor inlet temperature. Valve 288 is operably engaged by the the~nall~
responsive element 312 through a relatively non-chermally respo~-sive ceramic rod 308. Accordingly, valve 288 is shifted lonyitudi-nally relative to input port 142 and opening 290 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.
; }Iousing 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 seals 318, 320 having outer ends rigidly secured to housing 276 by being compressed between the housiny, an intermediate sectIon 322 and a closin~ plug 324 threadably ~ OL~ otherwise secured to housing 276. The inner ends of the seals : 3Z0 are secured on the movable piston, rod configuration 316. The ~20 seal 320 in conjunction with the end closing plug 32~ define a~
interior pressure sensing ch~mber 326 to which one end of the piston 316 is exposed. Through a sensing line 328 the combustor pressure P3 5 such as combustor inlet pressure is transmitted i~to chamber 326 to act upon one end of piston 316. .At ths opposite end of bore 314, a helical coi.l biasing spring means 330, grounded :~ to housing 276 ~hrough a stationary s~op 332, acts to urge the :
pis~on, rod configuration 316 in opposition to the pressure in chamber 326. The opposite end 334 of the piston configuration 316 is vented to atmospheric pressure thrcugh an appropriate port 336.
A seal schematically shown at 335, which may be o-f a structure like seals 318, 320 and section 348, is also included at this opposite : end 334. Thus gauge pressure in the combustor, i.e. the difference - 22 - .
.".

55~
~ ~een ambient pressure and the absolute pressure maintained in combustor 98, acts upon pi.ston 316 to shift the latt~r withi.n bore 314.
~n arm 338 is threadably secured within ~ transverse boxe in metering valve 282 at one end, and at its other end the rod 338 has a spherical ball 340 mounted ~hereon 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 rotati3n of metering valve 282 about its major longitudinal o axis. Accordingly, the respective openings between windows 2$4, . 286 and the input ports 142 and opening 290 are also varied in relation to the magnitude of gauge pressure in compressor 98 by virtue of this rokational translation of me~ering valve 282.
Groove 342 permits axial translation o~ arm 338 along with val~e .5 282. While the rod, piston conflguration 316 may be of varied ` arrangements, the preerred form as illustrated in Fig. 8 incorporates a threaded end section 344 which acts through . . .
appropriate spaces 346 to compress and secure the inner ends of seals 318, 320 to rod 31.6 through an intermediate section 348.
0 Thus, the scheduling valve acts as a mechanical analog computer in multiplying the parameters o combustor pressure, P3 5 :~ and combustor inlet temperature, T3 5, such khat the positioning o~
valve 282 and -the.windows 284, ~86 is a function o~ the product quantit~ or combustor pressure multiplied by combustor inlet temperature. : ; ~ ;
Conventional1y, as shown in~Fig. 4.the con~rols for engine 30 fuxther 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 .o downstream of scheduIing valve 62 and in the preferred ~orm may be .
included within and/or adjacent to the housing 276 of scheduling valve 62.

- 23 -. -5~
The configuration of each of the wind~1s ~4, Z~
as illustrated in Fiys. 8 and 9 are determined to solve a qualitative ~pirical formula of the following form:
W~ (Kl - K2 T3 5) P3 ~ K T
where~ 2 and ~3 are constants determined by :~ the o~erational characteristics of a particular gas turbine engine and are reflected by the configuration of window 284 and associated opening 290.
By proper formulation of th~ window 284 and opening 290, the solutlon to this equation as accomplished by schedu-ling val~e 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, scheduling valve 62 empiricall~ by mechanical analog, controls fuel flow to maintain a substanti-ally constant turbine inlet temperature, T4. Window 284 is the primaxy operating parameter during acceleration of the engine as described in greater detail below. In contrast, window 286 is the controlling parameter during engine decelera-tion~ While acceleration window 284 is contoured to maintain a substantially constant maximum gas generator turbine inlet temperature to provide maximum acceleration performance within the temperature limitations of the engine, the deceleration window 286 is contoured to limit and control f~uel flow to pre-vent loss of combustion while affording substantial decelera-tion of the engine. An extensive discussion of operation of a similar type of turbine inlet temperature computing ~al~e, but which utilizes absolute rather than gauge combustor pres-~: sure, may be found in United States Patent Application No.
689,339 of Rheinhold Werner, filed May 24, 1976, now ~. S.
Patent No~ 4 rO57~960.

.

ne ~ctuator 66 Details of the v~ne actuator contro]. 66 are illus-trated in Figs. 12 and 13. The vane control is hydromechanical in nature and generally includes a housi~-lg 354 having a pair of hydraulic pressure fluid supply ports 356, 358 respectively receiving pressurized fluid from a high pressure pump source 360 and lower pressure pump source 362 each of which are driven through the auxiliary power sys-tem of the engine. It is unders~ood that the pumps 360, 362 may provide various other functions within *he 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 in-to opposed fluid pressure chambers. Rod or shaf~ 368 carried with piston 366 extends exteriorly of housing 354 and ~;l5 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, lZ8 and the sets of variable guide vanes 120, 122;
High pressure hydraulic fluid from inlet por-t 356 is 0 delivered into a bore 370 wlthin housing 354 located adjacent cylinder 364. ~lso intersecting at spaced locations along ~ore 370 are a high pressure ~luid exhaust duct 372, and a pair of flu.id work conduits 374, 376 respectively communicating with the cylinder 364 on opposed sides of piston 366. Mounted for ~:25 reciprocation within~bore 370 is a di.rectional fluid control valve element 380 which i5 nominally positionable in the open center position illustrated wherein high pressure hydraulic fluid from duct 356 communicates only with the exhaust port 372. A series of centering springs 382, 383, 384, 385 normaLly urge valve 380 to O . the position shown. Valve 380 is of the-four~way type and is shi~table one direction to direct high pressure fluid from s~

poxt 3~6 ~o conduit 374 and.the upper side o~ piston 366, while 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 ~56 to conduit 376 and the lower side of piston 366, while conduit 374 communicates with return 386 through a chamber 378 and return line 379. It - will be noted that piston 366 cooperates with housing 354, such as with a circular wall protrusion 390 thereof to prevent fluid 10~ 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 high 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 following movement to the movement of an ~ .
`. "input piston" in the ~orm of valve 380.
, . . .
~0 In bore 370 is a stepped diameter piston mechanism 392 : shiftable in response to the magnitude of fluid pressure from a conduit 394 acting upon a shoulder 393 of piston 392. Piston 392 presents an adjustable stop for varying the compressive force .: : of spring 383. Pressure acting on shoulder 393 is opposed by a .~5 sp7ing 385. Slidably extending through the center o element 392 is a rod 395 which acts as a variably positionable stop upon the spring 384 extending between the upper end o~ rod 395 and valve 380. Rod 39S is longitudinally shiftable in response to rotation of a fulcrum t~pe lever 395 pivo~.ally mounted to housing 354 at pivot 39~.

-.

~ 26 -.

s~ss~
vane ac~uator cont~ol 66 ~urther includes another bore 400 in which is mounted a control pressure thro~tlin~ valve 402 An input from the throttle lever 184 ~f the engine acts to depress a variably positionable spring stop 404 to increase the force exerted by compression sprincJ 406 in urging valve ~02 downwardly. Opposin~ spring 406 is a gradient cornpression, helical coil spriny 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 ~ith the lower end of o throttling valve 4Q2 via a conduit 412 having a damping orifice ~14 therein. Conduit 410 leads to the larger face o~ a stepped piston 416 reciprocally mounted within another bore 418 in housing 354. One end on bore 418 is in restxicted fluid - communication with return 387 through.an ori~ice 419. The .5 . smaller diameter section of stepped piston 416 receives pressurizedfluid from conduit 420. Through an appropriate exhaust conduit 424 the intermediate section of the stepped piston, as well as the upper end of valve 402 are exhausted to low pressure return ~ 386 through the conduit 388. ~ .
~:0 Conduit 420 provides a hydraulic siyna1 indicative of the speed of the power turbine shaf~ 82. In this.connection, the vane actuator includes a non-positive displacement type hydraulic pump, such as a centrifugal pump 422 mounted to and rotated hy power turb.ine shaft 82. Being a non-positive displacement type 5 ~ pump, the pump 42Z delivers pressurized hydxaulic flow through conduit 420 such that the pressure maintained on the smaller diameter of stepped piston 416 is a square ~unction of the speed of power turbLne shaft 82. Similarly, the action of throttling valve 402 develops a pressure on the large diameter of piston 0 416 in relation to a desixed or selected speed reflected by the : position of the throttle 184.

.

..'..........

.`` f~ 5~
The valve 402 and pi.ston 416 act as inpu-~ signal means and as a comparator to vary the compressive force of spring 384 as a function of the difference or error between actual power turbine 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 operabl~ connected by electrical connector lines 427 to electronic control module 68.
Actuator 426 includes a housing 428 enclosing a coil 430, ana a centrally arranged armature which carries therewith a hydraulic directional control valve ~32. Valve 432 is normally urged upwardly b~ spring 434 to the position communicating conduit 394 . with return 386. Valve 432 is propoxtionally shiftable downwardly in response to the magnitude of the energization signal to propoxtionally increase communication between conduits 372 and -394.while decreasing communication between conduit 394 and drain.
- As a result, pressure in conduit 394 increases proportionately to the magnitude of the electronic signal; such pressure being -~0 essentially zero in the absence of an enexgization signal to ~- solenoid 426. It will be'noted that minimum pressure in conduit ~: 394 allows springs 383 and 385 to exert maximum upward force on valve 380, and, that increasi.ng pressure in conduit 394 shifts, piston 392 downwardly to reduce the force exerted by springs ~25 383, 385 upon valve. 380, thus developing an override force in the form of reduced force from spring 383.
'In the absence of an electrical signal to solenoid 426 minimu~ pressure is exerted on shoulder 393 causing the guide vanes to be controlled by power turbine speed. Thus, the gulde ~'30 vanes during start-up are at their Fig. 14 position and at other :
: conditions ~f engine operation are normally urged to maximum power, Fig. lS position.

, , .. ... .. ... . .....

a55~
As shown in Fi~. 18, vane actuator 66 is operable to vary yuide vane angle, B, from O -to -~20 to alter the positive incidence of gas flow upon the po~er turbine blades and thus alter pow~r transmitted from the gas ~lo~ 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. 18. In these negative incidence positions, gas flow is dixected to oppose and thus tend to decelerate the rotation of the power turbine wheels.
Electronic Control 68 A portion o~ the control logic of the electronic control module 68 is illustrated in Fiy. 17. The electronic con~rol module receives input electrical signals indicative of power tur~ine speed (Npt~ throuyh a chopper 436 secured to power turbine shaft 82 and an appropriate magnetic monopole 438 which transmits an electronic signal indicative of power turbine speed through lead line 440. Similarly, gas generator speed, Nggr i5 sensed through a chopper 442, monopole 444 and lead lines 446. Trans-ducers 448, 450, and 452 respectivel~ generate electrical input signals indicative of the respective temperature sensed thereby, i.e. compressor inlet temperature T2, turbine inlet temperature T4, and turbine exhaust temperature T6. As illustrated these temperature signals are transmi~ted through lines 454, 456 and ~25 458. The electronic control module also re`ceives from an ambient pressure sensor 460 and associated line 462 an electrical signal indicative of ambient pressure P2. The electronic control module further receîves from an appropriate sensing device an electrical signal through lines 464 indicative of throttle 184 ~30 position, "a." Also, a switch 466 is manually sèttable by the ~ehicle operator when power feedback braking ~described more in greater detail below) is desired. A transducer 544 generates a siynal to an inverter 5~6 whenever the variable guide vanes are .

..~v~d past a predeterm;ned position B*.
Tne electronic control module includes several outpuk signals to energize and/or de-energize the various logic solenoids and rela~s including solenoid 518 through llne 519~ solenoid 257 `, through line 268, fuel sequenc;ng 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 514 is denoted as a "flat rating and torque limiting" function and generates a signal indicative of maximum allowable gas generator speed as a function of ambient cond.itions T2 and P2 and power turbine speed Npt. Element 550 transfor~s the throttle position signal "a" into an electronic gas generator speed request signal, and function generator 552 produces a signal as a ~unction of gas genexator ~15 speed Ngg rom line 446. The module u~ther includes comparators 497, 534, 540~ 554, 556 as well as the logical elements 498, 500 and 538. The logical elements are of the "lowest wins" typ~, i.e.
they pass the algebraically lowest input s.ignal.
The logic element 498 selects from the signals 536 and 542 which have been generated in comparators 534 and 540 indicating the amount of over or undertemperature for T~ and T6. An additional input from 456 is provided to logic element 498 so as to provicle an indication of excessive T4 figures in the case of a failed T4 sensor signal. The logic element 5~0 receives inputs from ~25 497 and 498. Comparator 497 compaxes the electronic speed request with the actual gas generator speed 446 to determine if the engine has been requested to accelerate or is in steady state. The output of logic elemenk 500 is fed to inverter 546, generating an appropriate signal in solenoid driver 558 which then moves trim solenoid 426 a distance proportional to the magnitude of signal ~27.
' ' ~ 30 -.. .. .

The logic elemen-t 538 receives its inputs frorn eompa~to~s 5S4 and 556, logic element ~9~ and a differentiator 548. ~s noted, logical element ~98 indicates the lower of the two temperature errors T~ and T6. The outpu-t vf compaxator 556 ~s the error between the operator requested powe~ turbine speed Np.t and the actual power turbine speed Npt. The output of comparator 554 is indicative of the difference between the maxim-~ allowable gas generator speea dete.rmined by .~unction generator 514 and the actual gas generator speed 446. The logic element 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.
~s depicted in Fig. 17, the electronic control module includes a comparator 46S and synthesizers or function generators 470, 472 and 474~ Function generator 470 produces an output signal in line ~78 indicative of ~hether the difference between power turbine speed and gas generator speed is less th.an a preselected maximum such as five percent. Function generator 472 produces.a signal in line 480 showing whether or not power ~;20 turbine speed is greater than gas generator speed, while function - generator 474 generates a si~nal 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 488 which respectively generate signals in associated iine ;2~5 490 and 492 showing whether or not transmission input speed i~
above a preselected minimum l'e" and whether throttle position is below a presele~ted throttle position a*. Throttle position "a"
is obtained from a suitable position sensor such as a variable : resist~nce potentiometer. Thus, output signal 464 is indicative ~3- of throttle position 'a."

~ . ' .

.
. ~- 30a -- ~ .

The electronic control module further includes the logical gat~s 502, 504., S06, 508 and 562. Logical AND gate 502 receives inputs from line 478 ancl AND ga-te 506 to produce an output signal -to solen~id driver 516 to activate power f~edback clu-tch 84.
Logical AND gate 506 receives its inputs from line 482, switch 466 and line 492 and produces an inpu-t signal to AND gates 502 and 504. Logical AND gate 504 receives an inpu~ from line 480 and ~he inverted input from line 478. Its output genera~es a 50~ gas generator speed signal and also enables solenoid driver 564 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 element 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 outpu-t signal generates a 20o gas generator signal through unction generator 568 which, added to the constant 50% signal by summer 570 results in a ..
- fast idle signal (Z0~O gas generator speed) to the governor reset increase solenoid 257. The output o~ A~?D gate 508 also genera-tes the enable signal to solenoid driver 564.

, .

' .
- -30b - .

S~S~
Power-Feed~ack (lutch 84 While various forms of clu-tches could be utilized for power feedbac]c clutch 84, the preferred ~orm shown in Fig.
3 compr~ses a '`wet" type hydraulically actuated clutch which includes a shaft 520 from ~he gear train 78 associated with gas generator shaft 76, and a shaft 522 intelconnected with the gear train ~0 associated with the power turbine output shaft 82. The clutch operates in a con~inual bath of lubri-cating cooling fluid. The gas generator shaft 520 drives a - lQ plurality o~ discs 5~4, 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 ~luid such as from source 362 into a fluid pres-: sure chamber 52~ to urge piston 53~ against the urgings of a return sprin~ 532 to force the plates S24, 526 into intex-engagement such that the power from shaft 522 may be ~ed bac~
~ to gas generator shaf~ 520 to assist in brakin~ When the - solenoid actuator 518 is de-energized, the chamber 528 is ex-hausted to a low pressure drain to permit the spring 532 to shift piston 530 away from the position shown and disengaye the plates 524, 526.
OPERATION
Startin~
; In a conventional manner start motor 72 i~ electri-cally en~rgi~ed to initiate rotation of gas generato~ drive shaft 76 and ~le input shaft 152 o~ fuel governor 60~ The control module 68 ener~i~es the normally open f~lel sequence solenoid 350, and solenoid 352 i5 also in an open position tv clear fuel line 64 for deli~ery to ~he combustor. As neces-sa~y, an assist pneumatic pump 74 delivers pressurized air into combustor 98 along with the action of ignition plugs 100~
Motor 72 is utilized to drive ~e ~arious components described 9~
until the gas generator section reaches its sel~-sustaining speed, normally in the range of approx;mately 40~ of maximum .. rated gas generator speed.
During initial ~otation and s-tartiny o~ the enyine, the low speed o~ rotation of fuel governor drive shaft 152 cannot overcome the bias of speeder spring 224, and thus fuel lever 226 is disposed away from and clearing orifice 17~ to permit fuel ~low from line 166 to output line 144. ~lso during this initial starting, the combustor temperature (T3 5) and comhustor pressure (P3 5) are both relatively low such that scheduling valve 62 also pe.rmits significant fuel flow through line 64 to the combustor~
Low Idle As gas generator shaft 76 speed climbs beyond the ` self-sustaining speed, start motox 72 is shut off and the combustion process permits self-sustaining operation of the gas generator. Speeder s~riny 224 is normally set to maintain a low idle value of approximately 50% of maximum gas generator rated speed. Accordingly, the mechanical flyweight governor operates in opposition to speeder sprin~ 224 to adjust fuel lever 226 and maintain fuel flow through orifice 178 to hold gas generator speed at a nominal 50% of maximum. This 50% low idle speed is efective whenever proportional solenoid 257 is ::
in the de~energized state illustrated ln Fig. 6.
The electronic control module 68 normally main~ains solenoid 257 in the de-energized state to select the low idle gas generator speed whenever the transmission input shaft speed of sha~t 36, as sensed by speed sensor 48, is rotating. Such normally occurs whenever the clutch 34 is engaged with trans~is-sion 3~ in its neutral p~sition, or whenever the vehicle ismoving regardless of whether or not the clutch 34 is engaged or disengaged. Accord:ingly, during idling when not anticipating ac-celeration of the engine, the co~parator 486 of the electronic 5~ :

control module 6~ notes that the speea o~ shaft 36 is above a pre-determined minim~, "e", such th~t no sigllal is trans-mitted from comparator 486 to ~ND gate 508. Solenoid 2S7 re~ains ae-energized, and the gas generator speed is control-led by the governor to approxim~tely 50% its maximum speed.
Idle Maximwn power is normally 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. ~s a natural consequence of normal engine operator action upon starting from a stationary start, trans-mission input shaft 36 comes to a zero or very low rotational speed as clutch 34 is disengaged while gear shift lever 46 is articulated to shift the transmission into gear. Once the speed of sha~t 36 drops below a predetermlned speed, "e", comparator 486 of the electronic control module generates an output signal to AND gate 508. Since accelerator lever 184 is still at its idle position, the sensor associated with line ; 464 generates a signal to energi~e comparator 48~ and also send a positive signal to AND gate 508. 'rhe output of ~ND gate 508 energizes functioll generator 568 to add 20% to the constant idle command of 50~, 80 that summer 570 provides a 70% command signal to solenoid driver 564 that has been abled through the output of AND gate 508 and OR gate 562. Accoraingly, solenoid 257 is energi~ed by an appropriate current signal through line 26~ to shift to its Fig. 6C~position. In this position the solenoid 257 has been sufficiently energized to drive shaft 262 and plunger 272 downwardly as viewed in Fig. 6C and exert a force on fuel lever 226 tending to rotate ~he ~atter away from and increase the size of orifice 178. The additional force exerted by solenoid 257 is sufficient to increase fuel flow through orifice 178 to increase gas generator speed to a pre-determinedhigher level such as 70~ of maximum gas generator ;, 33 speed. The flywei~ht governor operates to hold the gas gene-rator speed constant at this level.
In this manner, the idle speed of the gas generator section is reset to a higher value in anticipa-tion of a re-quired acceleration such that ~ore power will be instantly available for accelerating the vehicle. At the same time, when acceleration is not anticipated, ........................

``' ' ' ' .

-~3~

5~

determilled by ~Ihe-ther ~r not transmission input shaft 36 is rotating or stationary, the electronic control module 68 is operable -to de-ener~iz~ solenoid 257 and reduce gas generator speed to a lower iclle value just above that necessar~ to maintain a self-sustaining operation of the gas generator section. In this manner power necessary for acceleration is available when needed;
ho~ever during other idling operations the fuel flow and thus fuel consumption of the engine lS maintained at a substantially lower value. This is accomplished by producing a signal, minimum speed of shaft 36, which is anticipatory o~ a later signal ~rotation of accelerator lever 184~ requestin~ significant increase in power transmitted to drive the vehicle.
Acceleration Accelexation of the gas turbine engine is manually selected !5 ~ by depressing the accelerator 184. To fuel governor 60 this generates a gas generatox section speed error siynal in tha~ the depxession of lever 184 ro-tates shaft 192 to increase compression of speeder spring 224 beyond that force being generated by the mechanical flyweight speed sensor. Fuel lever 226 rotates in a .0 direction substantially clearing the opening 178 to increase fuel flow to the combustor.
At the same time, depression of throttle lever 184 generates a power turbine section speed error signal to vane actuator control ;~ 66. More particularly, depression of throttle 184 compresses spring ~S 406 to shift valve 402 downwardly and increase the pressure main-tained in chamber 418 substantially beyond that being generated ,~ by the hydraulic speed signal generator of pressure developed by pump 422 a~id exerted on the other side o~ the step piston 416.
Accordingly, lever 396 is rotated generally clockwise about its ;0 pivot 398 in Fig. 12, allowing downward retraction, if necessary, of plunger 395 and reduction o~ compression on spring 384.
:, - 3~ -S-lmmer 497 of the electronic control module deter-mines a large disparity bet~een accelerator position and ~as generatox speed to deYel~p an electronic signal t:o 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 spriny bias urges plunger 430 and valve 432 to the position shown in Fig~ 12 to minimize hydraulic pre~sure developed in conduit 394 and exerted on piston shoul-der 393. As discussed above in the ~ane control 66 descrip-tion, springs 382-385 position valve 380 to cause ~ollowing 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 minimizlng power transfer to the power tur-bine vanes. More paxticularly, the guide vanes 120 are disposed in their Fig.~14 position to reduce the pressure d~op or pres-sure ratio across turbine blades 117 to a minimwn value, this position corresponding to the 0 position of Fi~. 18.
Since the no~zles 104 maintain the combustor 98 in a `
choked condition, this reduction in pressure ratio across the turbine blades 117 creates a substantial increase ln pressure ratio across the radial inflow turbine 102 of the gas genera-tor section. Accordingly positioning of the guide vanes in their ~i~. 14 position b~ allowing the sprin~s 382-385 to position valve 380 and piston 366 in its "neutral" position, alters the power split between the gas generator turhine 102 and the power turbines 116, 118 such that a preselected max.i- :~
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 .......... ~
.

l~S~59 achieved. As noted previously, the requirement ~o- impending i acceleration has heen sensed, 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 combustor 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 29~ in the fuel scheduling valve. Increase in this opening causes a L0 consequent increase in fuel flow to combustor 98 and an ultimate ; resulting increase in the inlet temperature ~3 5 through the actions o~ recuperator 56.
To the operation of engine 30, increase in T3 5 is in practical effect the same as a further fuel flow increase. Accordingl~, in L5 solving the above described equation the window 284 shifts to !~ reduce fuel flow with increasing T3 5 to produce an "effectivel' fuel ~I flow, i.e. one combining the effect~ of actual fuel flo~.~ and inlet temperature T3 5, at the sensed gauge pressure P3 5 to produce a desired combustor exhaust or gas generator turbine inlet temperature This increase in fuel flow created by the rotation of valve 282 and as compensated by axial translation of the valve provides an "effective" fuel flow that increases power developed and transmitted from the gas flow to gas generator turbine 102~ This then causes another increase ln gas generator speed, and combustor pr~ssuxe P3 5 again increases. Scheduling valve thus acts in regenerative fashion to further accelerate the gas generator section.
, ~ .
As noted previously, the scheduling valve is so contoured to satisfy the equation discussed previously and allow continued increase in P3 5 ~lO while maintaining combustor outlet temperature T~ at a relatively constant, high value. In this manner the gas generator section is accelerated most rapidly and at maximum efficiency since the turbine inlet temperature T~ is maintained at a high, constant value.

: ' . ' , 5~S~3 I While the acceleration window 284 and openi~ 2gO may be :, relatively arran~ed and configured to maintain a constant T4 throughout acceleration, a preferred form-contemplates maintaining a substa~tially constant T~ once the power turbine has initiated rotation, while limiting turbine outlet or recuperator inle-t temperature during a first part of the acceleration operation. In this manner.excessive T6 is avoided when the pow~r turbine section i is at or near stall. ~ore specifically, it will be noted that upon I starting acceleration of the vehicle, the free power turbine section ~.
.lO 54 and its sha~t 82 are stationary or rotating at a very low speed due to the inertia of the vehicle. Thus there is little temperature ' drop in the gas flow while ~lowing through the power turbine section, `¦ and the recuperator inlet temperature T6 sta~ts approaching ~he ! temperature of gas flow e~iting the gas generator radial turbine 102.
~15 If combustor exhaust or gas generator turbine inlet temperature ' is maintained at its maximum constant value at this time r it is possible that T6 may become excessively high in instances of hi~h ~' inertial load which lengthens the.time'of this substantial "stall"
-' . condition on the power turbine section, Of course, as the power , turbine section overcomes the inertia and reaches higher speeds, .. temperature drop across the power turbines increases to hold down ' recuperator inlet temperature T6.
: For such free turbine type engines, relatively complicated . .
and expense controls, electron.ic and/or mechanicall are normally . - :
'`;25~ expected in order to avoid excessive T6 while providing responsive :~. accelerati.on under the conditions in question. An important discovery of the present invention, as embodied in scheduling valve 62, is in : providing an extremel'y simple, economical, mechanical structure f capable of limitin~ T6 during the-critical turbine section stall ~30 period but yet still promoting very responsive engine accelerati.on, ,~
At the samfe time this improved arranyement has eliminated the need : . for compensation for substantial variaf~ions in ambieni_ pressure and _ 37 _ .

thus the need to compensate for the variations in altitude that would be expected to be en~ountered by a grollnd vehicle.
In this connection it would be expected that absolute combustor press~lre P3 5 must be the parameter in solving the equation described previously such that the scheduling valve could reliably compute the turbine inlet temperature T4 created by a particular combination of combustor 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 conEiguration of openings 284, 290, and hy utilization of combustor gauge pressure rather than combustor absolute pressure, mechanically slmple and economical struc-ture with minimum control complexity can accomplish the desired ~. control of both T6 and T4 during acceleration. ~indow 284 and opening 290 are relatively arranged such that when valve 282 rotates to a minimum P3 5, a slight overlap remains between i, : the window and opening. Thus, a minimum fuel flow, Wf, is maintained at this condition which is a function of ~3 5 since valve 282 is still capable of translatiny axially. This gives rise to the third term, K3T3 5, in the equation set forth . .
above and dictates an initial condition of fuel flow when window 284 becomes the controlling fuel flow parameter upon ; ~ starting acceleration.
The constants Kl, K2 are chosen, their actual values being determined by the aerodynamic and thenmodynamic charac-terlstics of the engine, such.that at a preselected value, ~ P3 5~, intermediate the maxLmum and minimum values thereof J
`- the acceleration window controls fuel flow to maintain a con-stant T4. At combustor pressures below this preselected value, the acceleration window provides fuel flow allowing T4 to re-duce below the preselected maximum deslred level therefor.. It . has been found that an inherent function of using yauge com-bustor pressure rather than absolute ................ .........
-:~a-~5~59 L.cessure, in combination with these chosen values of Kl, K2 and a preselected minimum fuel flow at minimum P3 5 ~ determined ~y K3 , ' is that fuel flow is controlled by the acceleration window to prevent recuperator inlet temperature T6 from exceecling a preselectecl 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 pressur~ lower 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.
;,15 From inspection of the equation solved by valve 282 it will be ! apparent that uel flow Wf is a linear or straight line function o~
' P3 5 asshown in Fig. 20, with a slope determined by Kl and K2, an `. intercept specified by K3, and passing through the point producing :~ the preselected turbine inlet temperature T4 at the selected intermediate value P3 5*. Of course, a family of such straight line curves of Wf vs. P3 5 results for different values of T3 5 While, : if desired, curve fitting of window 284 and opening 290 could be utilized to maintain T4 at precisely the same valua at pressures at and abov~ the preselected intermediate P3 5*, in the preferred ~ . , .
form comp.ound curvature of the wlndow and opening is not utilized.

~; Instead~ the window and opening are of rectangular configuration . ~
thus permitting T4 to increase very slightly at combustor pressures ;~ above P3 5*. However, it has been found that such arrangement . affords an excellent, practical approximation to ~he theoretically desired precisely constant T4 ,.resulting in practical effect in ~ .
maintaining a substantially constant T4 at a desired maximum valu~

~: once combustor gauge press~lre exceeds the preselected level P3 ~*.
;:~ ' ' , ! - ~ccordin~lY~ t~e presen-t invention inherently limlts recuperator emperature T6 to solve the problem of recuperator overheating when starting to accelerate a high iner-tial load, yet still maintains a maximum T4 for high engine efficiency throughout the remainder of i5 acceleration once the inertia is substantially overcome and for the majority of time duriny acceleration. At the same time, and contrary to what miyht 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 flow ~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 dif~erent purposes, i.e. avoiding recuperator overheating while affording high engine operating efficiency and thus highly responsive acceleration.
~ As the gas generator continues to accelerate, the flyweight t governor 208 of the fuel governor 60 begins exertiny greater downward force to counterac-t the bias o~ speeder spring 224.
Accordingly, the fuel lever 226 begins rotatiny in a generally counter-clockwise direction in Fig. 6 to begin me-tering fuel flow through opening 178. Once the opening 178 becomes smaller than that aforded by meterin~ window 284 in schedulding valve 62, the operation of the scheduling va]ve is overridden and the fuel governor 60 begins controlling fuel flow to the combustor in a manner trimming gas generator speed to match the speed selec-ted by the rotation o~ the shaft 192 associated with the acceleration lever 184 in the fuel governor 60.
Similarly, this increase in gas generator speed is sensed~
in the electronic control module 68 by su~mer 497 such that once ;

3G yas generator speed N~g approacnes that selected by the position of the accelerator pedal as sensed electronically throuyh line 464~ the override signal generated by summer 497 is cut off. In response, element 500 is allowed to yenerate a siynal eneryiæing the proportional solenoid 426 of the guide vane con-trol 66. Valve 432 .

, ~5~59 ~,soclated with solenoid 426 is ~hifted to increase ~ressure exerted upon piston shoulder 393 to permit the piston 366 and the guide vanes to shlft from the Fig. 14 disposition thereo~
towards the Fig. 15 posi-tion. This shifting of the guide v~nes from the Fi~ 14 to the Fig~ 15 position again alters the wor~
I split between the gas generator turbine 102 and the power output turbines 116, 118 such that ~reater power is developed across the output turbines and transmitted to output shaft 82 while a lesser ~l portion is transmitted to turbine 102.
~10 Thus it will be apparent tha~ acceleration of the englne and vehicle occurs by first altering the work split so that maYimum power 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 ~,15 while maintaining turbine combustor exhaust temperature T4 at a `1 substantially constant, preselected maximum. Once substantial acceleration of the gas generator section has been accomPlished, the guide vanes are then rotated to alter the power or work split t so as to develop a greater pressure ratio across and transmit more , po~er to the power turbines 116, 118 and the power output shaft ~2 Cruise During normal cruise operation (i.e. travellng along at a relatively constant speed or power output level) the guide vane control 66 acts primarily to alter the work split between the gas ~ - :
~5 generator turbine 102 and the power output turbines 116 r 118 50 as to maintain a substantially constant combustor exhaust temperature T4 ~ This is accomplished by the electronic control mudul~ which . I , .
includes a summer 534 developing an output signal in line 536 to the logic box 498 indicative of the dif~erence between the actual ~30 and desired turbine inlet temperature T~. More particularly, solenoid 426, as discussed previously, is maintained normally energi~ed to gene-rate maximum pressure upon the piston shoulder 393 of the guide vane actuator For instance, assumirlg tha~ T4 is above the preselec~ed ; , .

~-sired value thereof, a signal is generated to line 53~ and element 498 to reduce the magnitude of the electri~ signal throuqh line 427 to solenoid 426. Accordingly, the spring bias 434 of the solenoid begins urging valve 432 in a dir~ction reducing fluid communication between conduits 372 and 394 while correspondingly increasing com~unication between conduit 39~ 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 downwaxd travel of piston 366 to drive the vanes backwards from their Fig. 13 disposition (+20 position of ~ig. 18) toward a wider open position increasing the araa ratio and reducing the pressure ratio across the vanes o~ the turbines 116, 118.
Accordingly, in response to T~ over-temperature, the guide vanes are slightly opened up to reduce the pressure ratio 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 generator speed i5 then sensed by the flyweight governor 208 of the fuel governor 60 to cause counter-clockwise rotation o~ fuel lever 226 and reduce fuel flow through opening 178.
The reduction in fuel to the combustor 98 accordingly reduc~s the combustor exhaust or turbine inlet temperature T4 toward the pre-selected value thereof. Thus, the guide vane control operates to adjust the guide vanes as necessary and causes a consequent adjust-ment in fuel 10w by the fuel governor 60 due to change in gas generator speed Ngg so as to maintain the combustor exhaust temperature T4 at the preselected, maximum value. It will be apparent also from the foregoing that reductlon in turbine inle~
temperature T~ below the preselected desired value thereof causes a corresponding movement of the guide vanes 120, 122 to increase the pressure ratio across the power turbines 116, 118. ~ccordinyly this causes a reduction in pressure ratio across gas generator ~ .

5~5~

¦ turbine 102 to reduce gas generator speed. In response the fu~lgovernor shifts fuel lever 226 in a clockwise rotation as viewed in Fig. 6 to increase fuel ~low to the combustor and thus increase turbine inlet temperature T4 ~ac~ to the desired value. It will be apparent that the chan~e in gui~e vane position also directly alters I the combustor exhaus-t temperature T4 due to the difference in air i flow therefrom, however, the major alteration of combustor exhaust i temperature is effectea by altering the fuel flow thereto as described above.
`10 During the cruise operation therefore, it should now be I apparent that fuel governor 60 ~cts to adjust ~uel flow in such ! a manne~ as to maintain a gas generator speed in relation to ths ¦ position of the accelerator levex 184. Clearly, the fuel governor 1 60 operates in conjunctiGn with or independently of the vane ~il5 control 66, dependent only ùpon the gas generator speed Ngg.
While the electronic control module operates the guide vane ~` control solenoid 426 to ~rim turbine inlet temperature T4 during ¢ruise, the hydromechanical portion of the guide vane contxoi 66 acts in a more direct feedback ]oop to trim the speed o power `20 turbine output shaft 82. More particularly, the actual power turbine speed as sensed by the pressure developed in line 420 is continuously compared to the accelerator lever position as reflected by the pressure developed in- line 410. A graphical representation t of the action of valve 402 and piston 416 in compressing spring ~25 384 and requesting dlfferent desired power turbine speeds Np~ in relation to the throttle position~ a, is shown in Fig. 19. Thus, ` in response to an increase in speed of power turbine shaft 82 beyond that selected by the rotatlon of accelerator lever 184, pressure at -~he lower diameter of piston 416 becomes substantially - greater than that on the larger face thereof to ro-tate lever 396 so as to increase compression of the biasing spring 384 acting on .

55a ~dlve 380. The resultin~ up~lard movement of v~lve 380 causes a corresponding downward movement of pis-ton 366 and accordingly shits the ~uide vanes to~ard the Fig. 14 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 power 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.

turbine shaft 82 is belo~i that selected by accelerator lever 184, the compression o spring 384 is reduced to tend to increase the pressure xatio across the power turhine vanes 117, 119 to tend to increase power turbine speed Npt.
. The portion of vane control 66 or trimming power turbine speed in relation to accelerator position is preferably primarily digital in action since as show.n in Fig. 19, a small change in - throttle lever position increases the re~uested Npt from 25% to 100~. The actions of valve 402, piston 416 and plunger 395 are such that when the accelerator is at a position gxeater than a*, this portion o the control continually requests approximately 105% power turbine speed Npt. Through a small amount of rotation of the accelerator below a*, the control provides a request of power turbine speed proportional-to the accelerator position.
. Positioning of the accelerator to an angle below this small arc ;25 causes the control to request only approximately 25% o maximum Npt-Thus, in normal cruise the guide vanes control operates in conjunc~ion with the fuel governor to maintain a substantially constant turbine exhaust temperature T4; fuel governor 6D operates to trim gas generator speed Ngg to a value selected by the accelerator ''''~ , . ' ' .

595~ .
ever 18~; and the hydromechanical poxt.ion o~ yuide ~.7~ne 66 operates to trim power turbine outpt speed Npt to a level in relation to the position of accelerator pedal 184. It will further ~e apparent that during the cruise mode o~ operation, 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 . ~uring the cruise or other operating modes of the engine discussed herein, several safety overrides are continually operable~
For instance solenoid 239 of the fuel governor 60 operates to essentially reduce or counteract the e~fect of speeder spring 22~ :
and cause a consequent reduction in fuel flow from orifice 178 by exexting a force on fuPl.lever 226 tending to rotate the latter in a counter-clockwise direction in Fig. 6. As illustrated in Fig. 17, the electronic cnntrol module includes a logic element 538 which is responsive to power turbine speed Np.t, yas generator speed Ngg, turbine inlet temperature T~, an~ turbine exhaust or recuperator inlet temperature T6. Thus if tuxbine inlet tempexa~ure T~ exceeds .
the preselected maximum, a proportional electrical~signal is trans-mitted to lines 250 to energize solenoid 239 and reduce uel flow to the engine. Similarly, excessive turbine e~haust temperatuxe T6 .
results in proportiona~ely energizing~ the~solenoid 239 to reduce ~: 25 ` fuel flow to the combustor and thus~ultimately reduce turbine ~. ~
. ~ exhaust temperature.T6. Also, logic elemen~ 438 is responsive to . power turbine speed so as to proportionately energize solenoid 239 ` whenever power turbine speed exceeds a preselected maximum~ Simi-:; :: : .
larly, the electronic:control module operates to energize solenoid . ~
~` 30 239 whenever gas generator speed~:exceeds a preselected maximum . established by function generator;514~as a function of P2, T2 and Npt.

Normally the preselected maxlmum parameter.values discussed with ~ regard to these~s~fety override opera-tions, are slightly ~bo~e the :~ , . :
. - ~5 -.
.

I .Jrmal operating values of the parameters so that the solenoid 239 is normally inoperable except in instances of one of these parameters substantially exceedincJ the desired value thereoE.
Thus, for instance, during a cruise mode of operation or "coastiny"
when the vehicle is traveling downhill being deiven to a certain extent by its own inertia, the solenoid 239 is operable in response to increase of power turbine output shaft a2 beyond that desired to cut back on fuel flow to the combustor to tend to control the power turbine-output speed.
While as discuss~Qd previously with regaxd to the cruise operation of the vehicle, the guide vane control normally is j responsive to combustor exhaust temperatur~ T4 as refleGted in the signal generator by element 435, the logic element ~98 is also ~ responsive to the turbine exhaust temperature T6 in comparison to ,15 a preselected maximum thereof as determined by summer 540 which ~ generates a signal through line 542 to element 498 whenever - turbine exhaust temperature T6 exceeds the preselected maximum.
Logic élement 498 is responsive to signal from either line 542 or 536 to reduce the magnitude of the electronic signal supplied through line 427 to solenoid 426 and thus reduce the pressure ratio across the turbine wheels 116, 118~ As discussed previously, this change in pressure ratio tends to increase gas generator speed and in response the fuel governor 60 reduces fuel flow to the combustor so that turbine exhaust temperature T6 is prevented from increasing beyond a preselected maximum limit.
As desired, the solenoid 239 may be energize~ in response to other override parameters. For instance/ to protect the recuperator 56 from excessive thermal stresses, the logic element 538 may incorporate a differen-~iator 548 associated with the signal from the turbine exhaust temperature T6 so as to generate a signal indicative of rate of change of turbine exhaust temperature T6.

.

11~595g ogic element 53$ can thus generate.a signal ener~izing solenoid

2.39 whenever the rate of change of turbine exhaust temperature T6 i exceeds a preselec-ted maximum. In this manner solenoid 239 can j control maximum rate of change of temperature in the recuperator and thus the thermal stress imposed thereon~ Simi.larly, the loyic element 538 may operate to limit maximum horsepower developed across the power turbine and/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 l overspeed during a gear shiting operation wherein upon disengage-¦ ment of the drive clutch 34 to permit gear shifting in box 33, substantially all inertiaI retarding loads are removed from the ~! 15 power turbine drive shaft 82 and associated power shaft 32. o~
¦ course, during normal manual operation upon gear shifting r the ~j accelerator lever 184 is released so that the fuel governor 60 ~ immediately begins substantially reducing fuel flow to combustor ;~' g8. Yet because of the high rotat.ional inertia of the power turbine shaft 82 as well as the high volumetric gas flow thereacross from .~ the combustor, the power turbine shaft would still tend to over ;~ speed.
Accordingly, the control system as con-templated by the present invention utilizes the guide vane actuator control 66 to shift the guide vanes 120, 122 toward theLr Fig. 16 "reverse" position such that the gas flow from the engine impinges oppositely on the vanes 117, 119 of the power turbine wheels in a manner opposing rotation of these power turbine wheels. Thus ~he gas flow from 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 where s~nchronous shifting of gear box 38 ana consequent -- ~7 -ii9~9 re-engagement of drive clutch 36 ma~ be conveniently and speedily accomplished without d~mage -to the engine or drive train.
More particularly, the hydromechanical portion o~ guide vane control 66 is so arranged that upon release of acceler~tor lever 184 such as during 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 o spring 384 results to urge valve 380 upwardl~ and drive piston 366 downwardly to its position illustrated in Fig. 12.
This position 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 ratation thereof ~o decelerate the power turbine shaft 82. Since the drive clutch 34 is disengaged during this gear shifting operaLion, the power turbine ; shat 82 rather rapidly decelerates by virtue of the opposing gas flow created by the positioning of guide vanes 120 in their Fig. 16 position. ~et more specifically, the arrangement of springs 406, 408 and the relative magnitude of pressure developed in conduit 410 and 420 causes the hydromechanical portion of vane actuator control 66 to operate in the manner above described to shift the guide vanes 120 to ~heir negative or reverse disposition illustrated ~ in Fig. 16 and modulate guide vane pasition within zone "d" of Fig; 18 in relation to the magnitude of Npt excess, whenever the accelerator lever 184 is moved to less than a preselected accelerator lever position a*. As the speed o~ power turbine shaft 82 reduces, the piston 416 begins shi~ting in an opposite direction to reduce ; compression of spring 384 once turbine speed reduces to a preselec-ted value.~ The action of piston 416 is in the pre~erred form capable of modula-ting the degree of compression of spring 384 in relation to the magnitude of the Npt error. The greater the speed , s~
errOr, the more the guide vanes are rotated -to a "harder"
braking position. Thus, the positionof the guide vanes are maintained in a reverse brakiny mode and are modulated through.
zone 'Id" 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 preiviously to again increase power turbine speed.
Deceleration ~I.0 A first mode of deceleration of the gas turbine engine is i accomplished by reduation ir. fuel flow along the deceleration schedule afforded by deceleration window 286 of scheduling valve 62. More particula.rly, the release o accelerator lever 184 causes the fuel governor 6Q to severely restrict fuel flow ~lS through opening 17~. As a consequence the minimum fuel flow to the gas turbine engine is provided throu~h deceleratlon fuel line ~, 142 and the associated deceleration window. 2~6 of the scheduling .
-~: valve. As noted previously decelera~ion window 286 is ~articularly : .con~igured to the sas turbine.engine so as to continually reduce !0 fuel flow along a ~chedule which maintains combustion in the combustor 98, i e., subs-tantially along the operating line of the gas turbine engine to maintain combustion but below the "re~uired to run line." ~s noted previously, even without rotation of accelerator lever 184, the solenoid 239 can be energized in : ~ .
!5 par~icular instances to generate a false accelerator lever signal to ~uel lever 226 to accomplish deceleration by severely restricting ~ fuel flow.
-~ This deceleration by limiting fuel flow is accomplished by reducing the accelerator lever to a position at or just above .
:~0 a preselected accelerator position, a*. This accelerator position ; is normally ~ust sligh~ly above the mLnimum accelerator position, . - ' , , .

.
_ ~9 _ S~5~
ner~lJ~ ~orr~s~nn~s to the posi~iDn of the ~e1er~or lever during the "coastiny" condition wherein the enyine is somewhat driven by the inertia of the vehicle such ~s when coasting aownhill. Since this deceleration by restricting fuel flow i~ actin~ only through governor 60, it will be apparent that the yuide vane control is unaffectred thereby and continues operating in the modes and conditions discussed previously. This i5 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 minimum position, a second mode of deceleration or braking 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 '1braking" position. More particula~-ly, as discussed above with regard to the year shift operationof the vehicle, this large error signal of the power turbine speed in comparison to the accelerator lever position eauses siyrli~icant counter-clockwise rotation of lever 396 and conse-quent compression of spring 384~ This drives the piston 366 and the guide vanes toward the FigO 16 position thereof. As a resultr the gas flow from the gas turbine engine opposes rotation of the turbine wheels 116, 118 and produces substan-tial tendency for deceleration of OUtpllt shaft 82 0 It has been found that for a gas turbine engine in the 450 to 600 - 30 horsepower class, that this reversing of the guide vanes in combination with minLmum fuel flow to ~he combustor as permit-ted by deceleration window 286 provides on the order of 200 or more horsepower braking onto the turbine output shaft 8~

"
~50 , : :

55~S~3 `~ ~t will be noted that duriny this second mode of decelera-tion, as well as during the gear shift operation dis-cussed previously, that since the guide vanes a~e now in a reversed dispo~sition, the logic accomplished by the electronic control module 68 in controllin~ solenoid 426 to prevent over temperature of T4 or T6 is now opposite to that required.
~ccordingly, the electronic control logic further includes a tr~nsducer 544 which senses whenever the guide vanes pass over centre as noted by the preaetermined angle B* of Fig. 1~, and are in a nega~ive inciaence disposition. This signal generated by transducer 544 energizes a reversing device such as an in-verter 546 which reverses ~he signal to the solenoid 426. ~ore part.icularly, if during this de~eleration operation with the guide vanes in the negative incidence position of Fig. 16, there occurs an excess combustor exhaust temperature T4 or ex-cess turbine exhaust temperature T6, the signal generated by element 500 to reduce the magnitude of the current signal is reversed by element 546~ Accoxdingly occurxence high T4 or high T6 while element 546 is energized generates an electrical signal of increasing strength to solenoid 426. In response, the solenoid 426 drives valve 432 in a direction increasing pressure in conduit 394 and upon shoulder 393. This reduces ~he magnitude of the biasing spring 383 and caùses val~e 3~0 to move downwardly. In a followins movement the piston 366 moves upwardly to reduce the compression of spring 38~. Thus the ~uide vanes 120 are reversely trimmed away from the maximum brakin~ position shown in Fig. 16 back towards the neutral position of Fig~ 14. This movement of course reauces the mag-nitude of power trans~itted from the gas flow in opposing r~-ta-tion of the guide vanes 117 to cause a consequent reduction infuel flow as discussed previously. The reduced fuel flow then reduces the magnitude of the over temperature parameter T4 or T~. Such action to control T4 or T6 will ............. O

SS~S~
-.bstantially only occur when f~lel flow being delivered to ~he combustr is more than permitted by the deceleration schedule 286.
Thus such action is more likely to occur during the "coastiny"
operation than during hard bra~ing during the second mode of deceleration. Such is natural with operation of the enyine, however, since during hard deceleration, fuel -Elow to the combustor is at a minimum and combustor exhaust temperature is relatively low. However, during unusual conditions, and even with the guide vanes in. a neyative incidence positlon, the electronic control module is still operable to return the guide vanes toward their neutral position to tend to reduce any over temperature conditions.
! Power Feeaback Braking . ~
` 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 inertia at too high a speed, i.e. power turbine shaft 82 speed Npt is still too high.
Thus power turbine shaft speed l~pt may be in a range of approxi mately 90% of its maximum speed while the gas generator.speed Nyy has been brought down to at or near its low idle speed of approxi-mately 50~ maximum gas generator speed.
This third mode of decelera~ion, t.ermed~power eedback ~ braking, is manually selected by closing power feedback s~ritch 466.
:25 In response the electronic control module 68 generates s-ignals which ul-timately result in mechanical interconnection of the gas ~ generator shaft with ~he power turbine shaft such that the inertia : of th~ gas generator sha~t is imposed upon the drive train of the vehicle to produce additional braking effects thereon. More particularly, upon closing switch 466, AND gate 506 generates a signal to A~D yate 504 since the accelerator level is below a _ 52 - . :

s~
~:>r~:s~l~cted ~oin~ a* c~lu~ y f~ l;ic~n ~e~ at~L ~Z i:c~ y~neLat~
a signal to AND gate 506, and since the gas generator is opera-ting at a speed above 45% of its rated value as determined by element 474. Element 47~ develops a signal thr~uyh line 480 to AND yate 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 the gas generator shaf~ 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 com-paring the actual relative speeds of the gas generator power turbine shafts. Rather, the element is so arranged thàt it only generates a signal to AND gates 502l 504 whenever the relative speeds of the shafts 520, 522 in the power ~eedback clutch 84 are within the preselected preaetermined limits of one another. Thus the comparator 468 will compensate, as re-quired, for differences in the actual speeds of the gas genera-tor and power turbine shaft, as well as the gear ratios of the ; 20 two respective drive trains 78 and 80 associated with the two shafts 502,5~2 of the feedback clutch 84.
Because of the difEerence between Npt and Ngg, nG
signal from element 470 is transmitted to either AND gate 502 or 504. As noted schematically by the circle associated with the input from element 470 to AND gate 504, that input is in~
verted and AND gate $04 is now effective to generate an output signal since no signal is coming from element 470, and sinc~
signals are being received from AND gate 506 and element 472.
The output signal from AND gate 504 accomplishes two functions.
First, a signal of 50-3 Ngg magnitude is generated in function generator 566 and added to the constant 50~ bias signal of sum-mer 570. The resulting signal is equivalent to a 100% N~g - speed command. Secondly, the output from AND gate 504 passes ~hrough OR ~ate 562 to produce a signal to solenoid 257. This signal is of sufficicnt magnitude to shift --^.- ---.-.~.-..

~5~5~
,olenoid 257 to its Fig. 6D position clearing openiny 178 fox substantial fuel flow to the ~ombuskor, It will b~ apparcn~ that full energization of solenoid 25~ to its Fig. 6~ -position ls essentially a false accelexator lever signal to the fuel lever 226 causing lever 226 to rotate to a position normally caused b~
depressing accelerating lever 1~4 to its maximum flow position.
Secondly, the sign-al from summer 570 is also an input to element 497 such that an artificial full throttle signal is generated which overrides the ener~ization signal which is maintaining the guide vanes in their Fig. 16 braking position during the second mode of deceleration discussed previously. The ener~iza-tion of the guide vane solenoid 426 causes increase of pressure in conduit 394 allowing the springs 382-385 to shift -the piston 366 and the associated guide vanes toward their Fig. 14 "neutral"
; 15 position.
Accordingly, it will be seen that the signal from AND gate . . .
504 produces an acceleration signal to the engine, placing the guide vanes 120, 122 in their neutral pOSitiOIl such that ma~imum ` pressure ratio is developed across the gas generator turbine 102, - 20 and at the same time fuel flow to the combustor 98 has been greatl~
increased. In response, the gas generator sec-tion begins increasing in speed rapidly toward a value such that the speed of shaft 522 of the feedback clutch approaches the speed o~ its other shaft 520 Once the power turbine and gas generator shaft speeds are appropria-tely matched such that the two shafts 520, 522 of the feedback clutch are within the preselected limits determined by element 470 of the electronic control module, electronic control module develops a positive signal to both AND gates 502, 504, -~
This positive signal immediately stops the output signal from AND
~30 gate 504 to de-ènergi~e the proportional solenoid 257 of the fuel .
governor and again reduce fuel flow back toward a minimum value, and at the same time stops the override signal to element 500 .
.

~5~35~

.
;uch tha-t the guide vane 120, 122 are again shiftecl back to their . Fig . 16 brakin~ disposition in accord with the operation dlscussed above ~ith respect with the second mode of deceleration.
The logic element AND gate 502 now develops a positive output signal to operate to driver 516 and eneryize clutch actuator solenoid valve 518. In response the clutch 84 becomes 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 con~rol module, in addition to the other functions described previously, also assures that since the two shafts 52Q, 522 are in near synchronous speed, relatively small tor~ue miss-match across the plates 524, 526 of the clutch is experienced. ~ccordingly, the size o clutch 8~ can I be relatively s~all. Thus it will be seen that the electronic `~i15 control module 68 operates automatically first to increase gas i generator speed to essentially match power turbine speed, and ~hen 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 o gas generator 76 to assist in decelerating the vehicle. It has been found that for a 450 to 600 horsepower class engine described, this power feedback braking mode adds in the neighborhood of 200 to 25Q horsepower braking in addition to the 200 horsepower braking effects produced by the positioning of guide vane 120, 122 in their Fig. 16 position. ~ecause the fuel governor is again severely restricting flow through orifice 178/ the fuel flow is con~rolled by deceleration window 286 permitting the gas generator section to decelerate while maintaining the combustion ~, , - .

.

process in combtls-tor 98. Thus reduction of fuel flow provides the deceleration effect o the rotational inertia of the gas generator upon the drive train of the vehicle.
It will be apparent from the foregoing that the presen~
invention provides substantial braking for deceleration pu~poses while still utilizing the optimum operatiny characteristics of a free turbine type of a gas turbine engine with the gas generator section mechanically interconnec~ed with the power turbîne section only in a specific instance of a manually selected "severe" third mode type of deceleration operation. Throughout all deceleration modes and engine opera~ion, a continuous combustion process is maintained in the combustor. Thus substantial deceleration occurs without extinguishing the combus-tion process therein.
- This power feedback braking operation can be deactivated in several ways: manually by opening switch 466 to stop the output signa]. from AND gate 506;providing a NOT signal to turn of driver 516 and solenoid 518 to disengage clutch 84. Furthermore~
if the manual switch is not opened and the engine continue~ to decelerate, element 474 also operates to deactivate the power ~eedback operation whenever gas generator speed NgcJ reduces to a value below 45% of its maximum rate of speed. Also, depression of the accelerator to a value of above a* also deactivates the power eedback operation by stopping an output signal from AND
gate 506.
From the foregoing it ~ill now be apparent that the present invention provides an improved cycle o~ operation for a gas turbine engine peculiarly adapted for opexating a ground vehicle in a safe, familiar manner while still retaining the inherent benefits of a gas turbine engine. More specifically, by utilization of a free turbine type engine grea~er adaptability and variability of engine operation is provided. ~t the same time the engine can operate ;: ' ' .

roughout its entlre operatin~ cycle whlle maintainirlg a continuous combustion process wi-thin the combustor 98. This avoids various problems of operation and service life associated i with repeated start and stop of the cc,mbustion process~ The novel

3 cycle contemplates a utilization of a combustor 98 having choked ¦ nozzles 102 to provide a variable pressure within the combustor i 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 guide vanes 120, 122 opexate to trim the turbine inlet temperature T4 ¦ to a preselected substantiall~ constant value to maintain high engine operational efficiency. Further, the guide vane control operates indirectly to alter the ~uel flow through fuel governor 60 by altering the speed of the gas generator section such that the varlous controls are operable in an integral manner without ~ounteracting one another. A-t the same time a trim of power ~¦ turbine shaft speed Npt is provided by the guide vane control 66.
Furthermore it will be seen that the present invention provides , the gas turbine engine peculiarly adapted for driving a ground vehicle in tha-t responsive acceleration simllar to tha~ produced Il by an internal combustion engine is provided by both the automatic I high idle operation as well as by the manner of acceleration OL
¦ the gas turbine engine. Such is accomplished by ~irst altering j the work split to develop maximum power to the gas generator ~S section. The scheduling valve control 62 then acts in regenerative fashion to increase fuel flow to the combustor in such a manner that gas generator speed is increased while maintaining a substan-tially constant maximum turbine inlet temperature T4 thereby produ~
cing maximum acceleration without overheating the engineO Yet the scheduling valve also limits T6 during the initial portion of acceleratlon when turbine "stalling" conditions are prevalent.
~cceleration is then completed once substantial acceleratlon o~
;' , ' ' ' ' .

L5~
.
Ie ~as ~eneratOr section is accomplished, by re-altering the power split to ~evelop greater power across the pow2r turbine wheels 116, 118. ?
It is further noted tha-t the present invention provicles 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 v~nes in the braking 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 guide vane control which is normally energized, provides an engine and con-trol system peculiarly adapted to provide safe en~ine operation in the event of various failure modes. More particularly, in the event of complete loss of j electrical power to the electronic control module 68, the mechanical portion of fuel governor 60 continues to adjust fuel flow in relation to that selected by accelerator lever 184.
Scheduling valve 62 is in no way affected by such electrical ~20 failure and is capable of controlling acceleration and/or decelera~ion to both prevent over heating of the engine during acceleration as well as to maintain combustion during deceleration.
The hydromechanical portion of the vane actuator control will still be operable in the event of electr~ical failure and capable ~`5 of adjusting the ~uide vanes as appropriate to maintain functional engine operation. Upon electrical failure the solenoid 426 of the guide vane control becomes de-energized causing loss of pressure upon face 3g3 of the control piston 392~ However, the speed control afforded by lever 396 is still maintained and the guide vanes can ~0 be appropriately positioned to maintain functional en~ine operation during this failure of the electrical system. Thus, while certain desirable eatures of the engine control will be lost in the event oE electrical failure, the en~ine can still function properly with ' ~ .

35~
¦ ,propriate acceleration and deceleration so that the vehicle ~I may still be operated in a safe manner even though a-t a possible ! loss of operational efficiency and loss of the ability to provide ¦ power feedback braking.
i~ From the foregoing it will be apparent that the present ¦ invention provides an improved method of automatically setting and resetting the idle of the gas generator sec-tion so that the engine is highly responsive in developing an increase in output power such as when contemplating acceleration of the vehicle.
Further the present invention provides an improved method of controlling fuel flow hydromechanical.ly in relation to gas ~ generator speed, as well as overriding normal speed control ¦ opexation of the fuel governor to increase or decrease fuel flow ¦ in response to occurrence of various conditions which energize - 15 either of the solenoids 239, 257. Further the present invention provides an improved method for controlling fuel flow to the : combustor during acceleration such that constant turbine inlet temperature T4 is maintained throughout, while also controlliny fuel flow during deceleration to avoid extinguishing the combustion ~0 process within a combustor. The invention further contemplates ¦ an improved method of controlling guide vane position in such an ¦ engine both by hydromechanical operation to control speed of a ¦ rotor such as turbine wheels 116, 118, and by electrical override operation dependent upon the amount o energization of the .25 proportional solenoid 426.
The foregoing ha~ described a preferred embodimen~ of the . invention in suficient detail that those skilled in the art may make and use i~. However, this detailed description should be considered exemplary in nature and not as limitiny to the scope and spirit of the present invention as set forth in the appended claims.
.

S9 - ' ~5~159 Having described the invention with sufficient clarity that those skilled in the art may make a~d use it, what is claimed as new and desired to be secured by Letters Patent i::

.
.

.
.

; ' ' ~
~` , ' - ' :, ' ' ,'' ~; .' , ' ' . ' ' ' ' ', .
:~ ' , ' ' ' '' ~.

;
', ' .
.:

' .

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a free turbine type gas turbine engine having a power turbine section driven by a motive gas flow developed by a gas generator section of the engine:
variably positionable guide vanes disposed in said gas flow for altering the incidence thereof upon said power turbine section;
a source of pressurized fluid;
a housing having a fluid exhaust port, an inlet port communicating with said source, an internal cylinder, and an internal bore communicating with said inlet and outlet ports;
a piston movable in said cylinder and dividing the latter into opposed fluid chambers communicating with said bore at spaced locations therealong;
linkage operably interconnecting said piston and said guide vanes whereby said guide vanes are positioned in relation to the position of said piston;
a four-way valve movable within said bore to control communication of said opposed chambers with said inlet and outlet ports;
a first feedback spring means extending between said piston and said four-way valve to urge the latter in a first direction in relation to the position of said piston;
a first stop movably mounted in said housing;
second input spring means extending between said first stop and said four-way valve to urge the latter in a second opposite direction in relation to the position of said first stop; and input means for adjusting the position of said first stop.

2. A gas turbine engine as set forth in Claim 1, wherein said input means includes a second fluid operated piston disposed in a second bore in said housing and operably engaging said first stop, and manual signal means for exerting a first fluid force on said second piston urging the latter to move in a direction reducing the urgings of said input spring means on said four-way valve.

3. A gas turbine engine as set forth in Claim 2, wherein said manual signal means includes a manually positionable throttle, and a second valve for metering fluid flow to one side of said second piston to vary the fluid pressure exerted on said one side in relation to throttle position.

4. A gas turbine engine as set forth in Claim 3, wherein said input means further includes speed sensing means associated with said power turbine section for exerting a second fluid force on an opposite side of said second piston opposing said first fluid force, the magnitude of said second fluid force being indicative of the speed of said power turbine section.

5. A gas turbine engine as set forth in Claim 4, wherein said speed sensing means is operable to vary the fluid pressure exerted on said opposite side of the piston in relation to said speed of the power turbine section.

6. A control as set forth in Claim 5, further including an electronic control for sensing a parameter of engine operation other than said power turbine speed and for generating an electrical signal indicative of said parameter;
and transducer means responsive to said electrical signal and operably associated with said four-way valve for exerting a mechanical override force on said four-way valve in relation to said electrical signal, said override force capable of overriding said input spring means to move said four way valve in relation to said parameter.

7. A control as set forth in Claim 6, wherein said transducer means is arranged and configured whereby upon loss of electrical power to said electronic control, said four-way valve is moved by said feedback spring and input spring means.

8. A control as set forth in Claim 7, wherein said transducer means is arranged whereby the maxiumum value of said override force occurs when said electrical signal is at a minimum value.

9. A control as set forth in Claim 8, including a second adjustable stop; a third spring extending between said second stop and said four-way valve for exerting said override force on said four-way valve, said transducer means operable to move said second stop in a direction reducing the compression of said third spring and the magnitude of said override force as the strength of said electrical signal increases; and a fourth spring exerting a biasing force on said second stop urging the latter in an opposite direction increasing the compression of said third spring and the magnitude of said override force.

10. A control as set forth in Claim 9, wherein said second adjustable stop comprises a stepped piston in said first mentioned bore having a surface area exposed to another fluid chamber, said transducer means comprising a solenoid having a third valving member positioned in response to said electrical signal to control fluid communication of said source with said another chamber to alter pressure of fluid in said another chamber as a function of said electrical signal.

11. A control as set forth in Claim 10, wherein said transducer means includes a fifth spring urging said third valving member in opposition to said electrical signal and toward a position developing maximum fluid pressure in said another chamber.

12. A control as set forth in Claim 11, wherein said third valving member is operable to reduce fluid pressure in said another chamber as said electrical signal increases in strength.

13. A control as set forth in Claim 12, wherein said first stop includes a plunger operably engaged by said second piston, said plunger extending through a bore in said second stop to be movable independently thereof, said second and third springs being concentrically arranged and contacting the same end of said four-way valve.