CA1136433A - Gas turbine engine - Google Patents

Abstract

ABSTRACT

A method of operating a control system for a gas turbine engine which includes provisions for adjusting fuel flow in relation to gas generator speed, and for adjusting guide vane position in relation to power turbine speed.

Description

113~433 BACKGROUND OF THE INVENTION
This invention relates to gas turbine engines, and relates more particularly to an improved gas turbine engine and method and control therefor particularly useful as the power plant for a ground vehicle.
Recent advances in gas turbine engine technology have improved their overall efficiency and economy to such an extent that this type of power plant has become compe-titive in many instances with more conventional internal combustion type power plants such as Otto or Diesel cycle engines. For instance, gas turbine technology has made significant inroads as the power plant for aircraft engines.
Similarly, attempts have been made to develop a gas turbine engine which would be competitive with the more conventional internal combustion engines in high-production ground vehi-cles such as on-the-road automobiles and heavy trucks. The gas turbine offers significant advantages of equivalent or better operational efficiency, fuel savings, and less emis-sions as well as being able to utilize a variety of different fuels on an economic basis. Further, the gas turbine engine in many instances ofers greater overall economy over the entire operational life of a vehicle.
The inherent operational characteristics of a gas turbine engine present, however, certain problems when uti-lized in a ground vehicle. More ~pecifically, a gas turbine engine generally includes a gas generator section which provides a large pressurized air flow to a combustor wherein the air flow is mixed and ignited with fuel to greatly in-crease the temperature of the resulting gas flow. Hot pressurized gas flow then drives one or more turbines to produce useful rotary mechanical output power. Normally one of these turbines is a portion of the gas generator section for driving the fan which provides the high volume 113i433 pressurized air inlet flow. Downstream power output turbines then generate the useful mechanical power output. Conven-tionally, the high speed, high volume gas flow from the gas generator drives the turbines at relatively high speeds.
Other inherent characteristics of such gas turbine engines relates to the thermodynamic and aerodynamic processes car-ried out therewithin which dictate that operational effici-ency of the engine increases substantially with increasing maximum temperature of the gas flow.
These operating characteristics of a gas turbine engine present certain disadvantages in aomparison to the normal operation ofreciprocating or rotàry piston type in-ternal combustion engines for ground vehicles. More parti-cularly, the internal combustion engine inherently provides a substantial amount of deceleration horsepower for the vehicle upon reducing fuel 10w thereto through the drag imposed by the reciprocating portion o the engine. In contrast, the high rotational inertia of the turbines of the gas turbine engine normally do not permit suah immediate, relatively high horsepower braking for a ground vehicle simply upon reducing fuel flow to the combustor of the gas turbine engine. To overcome this disadvantage, a variety of proposals have been offered in the past to increase the braking characteristics o a gas turbine engine when utili~ed or driving a ground vehicle. Primarily, these conaepts rclate to completely extinguishing the combustion process within the combustor to produce maximum dynamic braking.
However, operational lie o a gas turbine engine i9 sub-stantially reduced by continual thermal cycling of the entire engine as created upon extinguishing the combustion process.
Further, such approaches adversely afect emissions. Other concepts relating to improving the dynamic braking characte-ristics of a gas turbine engine revolve around the utilization of a "fixed shaft" type of gas turbine engine wherein the gas generator section and the power drive sec-tion are mechanically interconnected to drive the vehicle.
While such an arrangement improves the dynamic braking, it greatly reduces the adaptability of the engine to perform various other processes for driving a ground vehicle, and due to this limited adaptability has met with limited suc~
ces in use as the power source for a high-production type of ground vehicle. An e~ample of 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 course not readily applicable to ground vehicles.
Prior arrangements for gas turbine engines for ground vehicles also have suffered from the disadvantage of not providing efficient, yet highly responsive accelera-tion in comparison to internal combustion engines. Inherent-ly, a free turbine engine normally requires a substantially longer time in developing the maximum torque required during acceleration of the ground vehicle. Prior attempts to solve this problem have centered about methods such as operating the gas generator at a constant, maximum speed, or other techniques which are equally inefficient in utili~ation of fuel. Overall, prior gas turbine engines for ground vehi-cles normally have suffered from a reduced operational efficiency in attempting to improve the acceleration or de-celeration 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 factor in the fuel consumption of the engine.
Further, prior art attempts have generally been deficient in providing a reliable type of control system which is effective thoughout all operational modes of a gas turbine 1~3S433 engine when operating a ground vehicle to produce safe, reliable, operating characteristics. Further, such prior art gas turbine engines have resulted in control arrange-ments which present a substantial change in required operator actions in comparison to driving an internal combustion powered vehicle.
Other problems related to prior art attempts to produce a gas turbine engine for ground vehicle relate to the safety and reliability of the control system in vari-ous failure modes, safe and reliable types of control~,and in the overall operational efficiency of the engine.
A majority of these problems may be considered as an out-growth of attempts to provide a gas turbine engine presen-ting operational characteristics duplicative of the desi-rable, 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 asso-ciated controls which incorporate the desirable operational features of both a gas turbine~and internal combustion ~ 20 engine, but while providing an eaonomical end product of $ufficiently reliable and safe design for high volume pro-duction basis for ground vehicles.
Discussions of exemplary prior art structure relating to the engine of the pre~ent invention may be found in U. S. Patents No. 3,237,404 disaussed above;
3,660,976; 3,899,877; 3,941,015 all of whiah appear to relate to schemes for transmitting motive power from the :: : :
gas generator to the engine output shaft, and 3,688,605;
3,771,916 and 3,938,321 that relate to other concepts for vehicular gas turbine engines. Examples of concepts for variable nozzle engines may also be found in U. S. Patents 3,686,860; 3,780,527 and 3,777,4~9. Prior art fuel governor controls in the general class of that contemplated , ' ' : :

113~433 by the present invention may be found in U. S. Patents 3,400,535; 3,508,395; 3,568,439; 3,712,055; 3,777,480 and 3,913,316, none of which incorporate reset and override features 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.
Examples of other fueI controls less pertinent to the pre-sent invention may be found in Patents 3,851,464 and 3,888,078. Patent 3,733,815 relates to the automatic idle reset feature of the present invention while patents

2,976,683; 3,183,667 and 3,820,323 relate to the schedu-ling valve controls.
SUMMARY OF THE INVENTION
An important object of the present invention is to provide an improved gas turbine engine and method and more particularly arrangements exhibiting desirable opera-tional features normally inherent to piston engines.
Another important object is to provide provisions producing improved fuel performance in a variety of opera-tions of a ground vehicle driven by a gas turbine engine.
Another important object of the present inventionis to provide improved acceleration, deceleration charac-teristics for a gas turbine driven ground vehicle, and to provide a more reliable, longer life gas turbine engine for propul~ion or power generating purposes.
In summary, the invention contemplates a recupe-rated, ree turbine type engine~with separate gas generator and power turbine sections. A fuel governor controls fuel flow to the combustor to set gas generator speed in relation to the throttle lever. Reset solenoids can override and adjust fuel flow in response to certain operating parameters or conditions of engine operation. For instance, in res-ponse to low speed on the output shaft of the drive train _5_ . ~ :

,. , . . ~; .................................. , : -:. . . . .

113~433 clutch which is indicative of an Lmpending desired engine acceleration for increased torque output, a reset solenoid increases fuel flow and the gas generator idle speed to substantially reduce time required in increasing engine torque output. A scheduling valve is effective to control fuel flow during engine acceleration to prevent excessive recuperator inlet temperature and maintain turbine inlet temperature at a substantially constant, high level for maximum engine performance. The scheduling valve is res-ponsive to combustor inlet gauge pressure and temperature,and also controls fuel flow during deceleration in a manner maintaining combustion. Variable turbine guide vanes are shifted first to maximize power delivered to the gas gene-rator during its acceleration, and subsequently~are shifted toward a position delivering maximum power to the power turbine section. The variable guide vane control includes a hydromechanical portion capable of controlling power tur-bine 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 deoeleration.
Power feedback is incorporated to provide yet greater braking characteristics. When such is selected, the gas generator speed is automatically adjusted to approach power turbine speed, then through a relatively low power rated clutch the gas generator and power turbine sections are mechanically interconnected such that the rotational inertia of the gas generator section assists in retarding the en-gine output shaft.
More specifically the present invention contem-plates a free turbine type gas turbine engine comprising a a gas generator section having a drive shaft and an air inlet; means for delivering fueI flow to said gas generator section to maintain a combustion process therein and produce a motive output flow therefrom; a power turbine section driven by said output gas flow from said gas generator section and having a power output drive shaft; means for sensing the speeds of said gas generator and power output drive shafts; means for adjusting the incidence of said motive gas flow onto said power turbine section to alter the power transmitted to said drive shaft of the power turbine section; and control means for controlling fuel flow to said gas generator section in relation to the sen-sed speed of said gas generator section, and for control-ling said adjusting means in relation to the sensed speed of said power turbine shaft, said control means including a manual input fuel lever coupled with said adjusting means for selecting a desired power turbine shaft speed, said control means operable to control said adjusting means to alter power transmitted to the power turbine section to tend to maintain power turbine shaft speed at a level indicative of the position of said fuel lever. ~7 These and other objects and advantages of the present invention are set forth in or will become apparent from the following detailed description of a preferred embodiment when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
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 perSpeGtiVe illustration of the power ~ ~
30 feedback drive train as incorporated in the engine with por- -tions of the engine shown in outline form;
Fig. 3 is a fragmentary, partially schematic, ele-vational cross-section of the power feedback clutch and 113~i433 . .

associated hydraulic system, taken generally along lines

3-3 of Fig. 2:
Fig. 4 is a partially schematic cross-sectional representation of the rotating group of the engine with controls associated therewith shown in schematic, block diagram form;
Fig. 5 is a right front perspective view of a portion of the housing, ducting passagesand combustor of the engine with portions broken away 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 better clarity of operational inter-relationships;
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 of a portion of the fuel governor control showing different operational positions of solenoid 257;
Fig. 7 is a schematic, cross-sectional and pers-pective functional representation of scheduling valve 62;
Fig. 8 is~a plan aross-sectional view through one portion ofthe saheduling valve7 Fig. 9 is a plan aross-8ectional view of the sche-duling valve taken generally along lines 9-9 of Fig. 8;
Figs. 10 and 11 are enlarged views of portions of valve 282 showing the interrelationship of fuel metering passages as would be viewed respectively along lines 10-10 and 11-11 of Fig. 7;

Fig. 12 is a schematic cross-sectional represen-tation of guide vane control 66;
Fig. 13 is an exploded perspective illustration , .. . .

of the guide vanes and actuator linkage;
Figs. 14, 15 and 16 are circumferential viewsshowing various operational relationships between the variable guide vanes and the power turbine blades; - ' Fig. 17 is a schematic logic rèpresentation of a portion of the eIectronic control module 68;
Fig. 18 is a graphical representation of the area ratio across the power turbines as a function of guide vane angle; ;
Fig. 19 is a graphical representation of the desired gas generator section and power turbine section speeds selected in relation to throttle position; and Fig. 20 is a graphical representation of the relationship of fuel flow permitted by the scheduling valve ~ -as a function of combustor pressure along lines of constant combustor inlet temperature.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT
With reference to the figures, listed below are 20 the abbreviations utilized in the following detailed des- -cription to denote various parameters:
pt = Power Turbine 54 Speed ~-Ngg = Gas Generator 52 Speed Ngg* - Preselected Gas Generator 52 Speed Nti = Transmi-sion Input Shaft 36 Speed ~ ~ -e = Predetermined Minimum Speed of Transmission Input Shaft 36 Wf - Fuel flow B - Stator Vane 120, 122 Angle B* = Predetermined Stator Vane Angle a = Throttle 184 Position ~ -a* = Predetermined Throttle Position T2 = Compressor Inlet Temperature _g_ - : :

` 113S433 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 Exhaust Temperature En~ine 30 Referring 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 depic-ted in Fig. 1 the engine is coupled to a substantially stan-dard drive train for a vehicle, particularly a truck in the 450 to 600 horsepower class, with a power output shaft 32 as the input to a drive train clutch 34. A transmission input shaft 36 extends between the clutch 34 and a "change speed"
type of transmission 38. Transmis~ion 38 is o the manually shiftable gear type; however, it is to be understood that various 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 different posltions including several forward gears, reverse gearing, and a neutral position. In the neutral position no power is transmitted between the transmio8ion input shaft 36 and the transmission output~shaft 40 which conventionally extends to the final drive 42 and drive wheels 44 of the vehicle. A
manual shifting lever 46 provides selection of the desired gear ratiol and a speed sensor 48 generates a signal indi-cative of the speed of transmission input shaft 36~ As schematically depicted in Fig. 1 and described in greater detail hereinbelow, the speed sensor 48 may be of any type compatible with the control medium of the engine 30. Pre-ferabLy, speed sensor 48 generates an eIectrical signal . ~ .

~` 113~433 transmitted by conductor 50 to the electronic control module of the engine.
Referring to Figs. 1-4, engine 30 is of the free turbine, recuperated type incorporating a gas generator section 52, a power turbine 54 mounted on a shaft separate from that of the gas generator 52, and a recuperator 56that scavanges 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 combustible 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 du- ~;
ring 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 turbine section 54. An electronic control module 68 recéives and processes various input para-::.
meter signals and produces output control signals to the governor 60 and vane actuator control 66. ;~
Conventionally, there is included an electriaal -storage battery 70 and assoaiated starter motor 72 which is ~ :
preerably selectively coupled to both the gas generator 52 and a starter air pump 74. During starting operation, the motor 72 is energized to drive bath an air starter pump 74 as well as the main gas generator shaft 76. As clearly illustrated in Fig. 2, the preferred form of 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. me two drive trains 78 and 80 are selectively interengagable through a relatively low power, wet clutch generally denoted by the numeral 84. This clutch is generally referred to as the power feedback clutch and the structure thereof is described ' ~136433 in detail below with respect to Fig. 3, while its functional operation is described further below with regard to the power feedback operation of the present invention.
Gas generator 52 generally includes an appropri-ately filtered air inlet 86 through which ambient air is supplied to a pair of series arranged centrifugal compres-sors 88 and 90. Cross-over ducting 92 carries the compres-sed air flow from the first compressor 88 to the second compressor 90. The gas generator 52 further includes duc-10 ting 94 as depicted in Fig. 5 which surrounds and collectsthe compressed air flow exhaust from the circular periphery of the second stage compressor 90, and carries this compres-sed air flow in a pair of feeder ducts 95 to recuperator 56 in non-mixing, heat exchange relationship with the recupera-tor. While various ~orms of recuperator structure may be utilized in conjunction with the present invention, an exemplary form is as described in U.S. Patent No. 3,894,581 entitled "Method of Manifold Construction for Formed Tube-Sheet Heat Exchanger", dated July 15, 1975, issued to Fred 20 W. Jacobsen et al. Though not necessary to the understan-ding of the present invention, reference may be made to the above referenced patent for a detailed description of a recuperator and its operation. For purposes of the present Lnvention, it is sufficient to state that the cQmpressed air flow from duct~ 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 through duct 96 to a can-type combu8tor 98. A8 best seen in Fig. 5, ; heated flow from the recuperator passes through a plurality 30 of openings 97 into a plenum portion of duct 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 passes into .

113~i433 the ~one between the inner and outer liner to then pass through the perforated inner liner 99 into the combustor zone. One or more electrical ignition plugs 100 are suitably connected to a source of high voltage electrical energy in a conventional manner. The igni~er plug is operable to maintain a continuous combustion process with-in the interior of the combustor wherein the fuel delivered from the line 64 is mixed and burned with the compressed air flow from duct 96.
The gas generator 52 further includes a gas gene-rator turbine 102 of the radial inflow type. The compressed, -heated gas flow from combustor 98 is delivered across turbine inlet choke nozzles 104 disposed in a circular array about ;;
the annularly shaped inlet 106 to the gas generator turbine section. During engine operation, nozzles 104 maintain pressure in combustor 98 at a level higher than ambient.
Flow of this heated, compressed gas across turbine 102 causes high speed rotation of the turbine and the gas gene-rator main shaft 76. This rotation of course drives the two centrifugal compressors 88 and 93. Shaft 76 iu appro-priately mounted by bearings 108 to the stationary housing 110 of the engine.
Power turbine section 54 generally inaludes a duct section 112 and appropriate vanes 114 therein for directing the flow of gases from the gas generator power turbine 102 toward a pair of axial power turbines 116 and 118 mounted to the power turbine main shaft 82. The power turbine sec-tion further includes sets 120 and 122 of variably position-able guide vanes respectively disposed upstream of associated axial turbines 116, lI8 and their associated blades 117, 119.
As depicted in Fig. 13, each of the sets of variable guide vanes 120 and 122 are disposed in an annular array ~ithin the gas flow path and are both mounted to a common actuating :113~433 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 twisted link 131 has opposite ends pivo-tally attached to link 129 and one arm of bell crank 130.
A linearly shiftable input shaft 368 acts through a pivot link 132 and another arm of the bell crank to cause rota-tion 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 of power driven shaft 82 to cause rotation of the two sets of guide vanes in unison to various positions relative to the direc-tion of gas flow passing thereby. As shown in Figs. 14-16, guide vanes 120 are positioned in a central or "neutral"
position of Fig. 14 causing substantially maximum area ratio - and minimum pressure ratio across the downstream power tur-bine wheel blades 117 of wheel 116 in order to minimize the amount of power transferred by the gas flow into rota-tion of~the turbine 116. The Fig~ 14 position is graphically illustrated by the position arbitrarily denoted 0 in Fig.
18. The guide vanes }20 are variably positioned toward the Fig. 15 position, noted as the +20 position in Fig~. 18, wherein high pressu~ ratio exists across blades 117 and maximum power is transmitted from the gas flow to turbine 116 to rotate the latter and transmit maximum power to shaft 82. Also, the vanes are oppositely rotatable to the Fig.
30 16 position, noted as the -95 position of Fig. 18, wherein ;
the gas flow is directed by the variable vanes 120 to oppose and tend to retard the rotation of wheel 116. While only ;~
vanes 120 and blades 117 are illustrated in Figs. 14-16, it . ~ ~

113~i433 will be understood by those skilled in the art that substan-tially identical operational relationships exist between vanes 122 and turbine blades 119 of turbine 118.
The gas flow upon e~iting 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. An ~ ~-air or water cooler 87 is al80 included to cool the lubri-cating fluid in engine 30 and communicates with fluid r~servoir 89 through hose 91.
Fuel Governor 60 -Referring now more particularly to Figs. 4, 6, 6A-D, the fuel~ governor 60 receives fuel from source 58 through an appropriate filter 136 into an inlet port 138 of a fuel pump housing 140. It will be apparent to those skilled in the art that the housing 140 is attached to and may be in-tegrally formed with another portion of the main engine hou-sing 110. The governor is operable to schedule fueI flow :~ ~ 20 output through either or both of the output ducts 142, 144 for delivery to the scheduling valve 62. The governor 60 is hydromechanical in nature but capable of being responsive to externally applied mechanical and electrical uignals, and includes an appFopriate drive connection schematiaally illustrated by line 146, and associated speed reducing gearing 148 as necessary to drive a gear 150 and drive shaft :
152. Shaft 152 drives a fuel pump in the form of a positive displacement rotary gear pump 154 which receives fuel from inlet port 138 and displaces it at a ~ubstantially higher pressure through an output conduit 156. As clearly illustra-ted in Fig. 6A, the gear pump comprises a pair of inter-meshing gears 158 and 160, one of which is driven by drive shaft 152 and the other of whiah is mounted to an idler shaft ~ : .

-` ~13~i433 162 journalled within housin~ 140. Supplied in parallel flow arrangement from output conduit 156 are three passages, i.e. output duct 142, bypass bore 164, and main flow mete-ring passage 166. Contained in bypass bore 164 is a bypass regulating valve poppet 168 slidable within bore 164 to variably meter excess flow from 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 downward- .
ly to increase bypass flow through passage 170, while a helical coil compression spring means 172 acts against the pressure of fuel to urge poppet 168 upwardly to reduce volume of flow fxom bore 164 to passage 170. Through a pressure passage 182 the lower end of bypass bore 164 com-municates with fuel supply conduit 64. Thus, pressure of fluid in conduit 64 is exerted upon the lower side of by-pass valve poppet 168 to assist spring 172 in opposing the force created by the high pressure fluid in output conduit 156. Passage 166 terminates in a metering noæzle 174 secu-- red by plate 176 to the housing, and having a reduced : 20 diameter opening 178 communicating with a central cavity 180. ;~
The fuel governor 60 further includes a manual -: throttle input in the form of a throttle lever 184 shiftable . ~ .
between opposed adjustable stops 186, 188 adjustably secured ~ :
to housing 140. Through an appropriate bearing 190 a shaft 192 extending within internal cavity 180 is rotatable rela-tive to housing 140. Integrally carried by shaft 192 in an open-sided camming section 194 into which are pressed fit a pair of stub shafts 196 that respectively carry rollers 198. Rollers 198 are engageable with the lower shoulder of ~ :
a spring stop 200 such that rotation of the throttle lever 184 and shaft 192 causes consequent rotation of stub shafts 196 which are non-aligned with the main rotational axis of shaft 192, and thus vertical shifting of spring stop 200 - ' ~ '' ' ' `

113~4~3 through roller~ 198. During its vertical or longitudinal shi:Eting, spring stop 2no 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 speed sensor which includes a flyweight carrier 208 rigidly secured to rotate with shaft 152. Rotating with carrier 208 ~.
are a plurality of regularly spaced flyweights 210 mounted for pivotal movement upon pins 212 securing the weights 210 to carrier 208. Dependent upon the speed of shaft 152, the centrifugal force causes rotation of weights 210 about pins 212 to cause the inner ends thereof to shift downwardly as viewed in Fig. 6 and drive the inner rotating race 214 of a roller bearing assembly also downwardly. Through ball bearings 216 this downward force is transmitted to the non-rotating outer race 218 of the bearing assembly to cause downward shifting of non-rotating segment 220. At its lower end segment 220 carries a spring stop shoulder 222, and a speeder spring 224 operably extends between the stop 222 of segment 220 and the spring stop 200 associated with the throttle input.mechanism. Through a pr.eload of spring 224 acting on seg-ment 220 the flyweights are nor~ly urged upward to the æero or low speed position illu~trated in Fig. 6. Increasing speed of shaft 152 causes downward shifting of segment 220.
Thus it will be apparent that throttle lever 184 acts essen-tially to select gas generator speed as reflected by the speed of shaft 152, since the 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 152.

The vertical position of segment 220 therefore becomes indi-cative of the difference between selected speed (position of 13L3~433 input throttle 184) and actual gas generator speed as sensedthrough flyweights 210. Fig. 19 illustrates the action of spring 224 in requesting different levels of gas generator speed Ngg, as the throttle is moved through different posi-tions, a.
Governor 60 further includes a main fuel throttle lever 226 pivotally mounted by pin 228 to housing 140. One arm 230 of lever 226 terminates in a spherically shaped end 230 within a receiving groove 232 on segment 220 of the speed error signal mechanism. An opposite arm 234 of lever 226 is movable toward and away from metering orifice 178 in response to shifting of segment 220 to thereby variably meter fuel flow from passage 166 into internal cavity 180.
It will be apparent that the regulating valve poppet 168 is variably positioned in response to the pressure differential between passage 168 and conduit 64 downstream of the mete-ring orifice 178 to variably meter bypass fluid flow through passage 170 in order to maintain a substantially constant pressure differenti~al across the fluid metering orifice cre-ated between metering opening 178 and the arm 234 of fuel -lever 226. Thus the rate of fuel flow delivered from pas-sage 166 to cavity 180 and output duct 144 is a function only substantially of the position of`arm 234 relative to metering opening 178 whenever the latter is the fuel flow controlling parameter. As appropriate, a damping orifice 236 may be incorporated in pressure sensing line 182 to stabilize the movement of bypass valve poppet 168.
A uni-directional proportional solenoid 239 has an outer housing 238 integral with plate 176 or otherwise affixed in stationary relationship to housing 140. Disposed within the housing 238 is a coil 240, and a centrally arran-ged armature 242. Rigidly seaured to form a portion of arma-ture 242 is a central plunger shaft 244 which has an upper 113~i433 end engageable with lever arm 234. Linear gradient springs246, 248 operably extend between stops on housing 238 to engage associated shoulders on the` plunger shaft 244 to normally urge the latter to its de-energized position illu-strated. 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 enga-ges and exerts an upward force on lever-arm 234 opposing and subtracting from the force~exerted by speeder spring 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" arrangement for arm 234 is utilized. In this arrangement a floating flat poppet-type face 252 is carried within arm 234 in alignment with metering opening 178. This floating face is normally spring loaded toward the metering orifice, and the upper end of plunger shaft 244 is engageable therewith. The purpose of floating face 252 is to compensate for manufacturing tolerances and to assure that a relatively flat surface is directly aligned with metering opening 178 and lying perpendicular to the fluid flow therefrom to assure proper metering of fuel thereacross.
The spring 254 loads floating faae 252 toward opening 178.
Pivoting of arm 234 against spring 254 to lncrease fuel flow is permitted until face 252 contaats the upper end of 245 of plunger 244. This stroking of arm 234 is quite limited but sufficient to create flow saturation of the annular orifice defined between opening 178 and face 252.
Disposed on the opposite side of lever arm 234 from solenoid 239 is a housing 256 of another directional, one-way solenoid 257 shown in Figs. 6B-6D. Solenoid 257 in-cludes a coil 258, armature 260, and plunger shaft 262 secu-red for movement therewith. Through appropriate stops, 113~i433 centering springs 264, 266 normally urge the plunger shaft 262 to the de-energized position illustrated. Upon energi-zation of the coil 258 through appropriate leader lines 268, the armature 260 and plunger shaft 262 are shifted down-wardly 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 sole-noid 257 is rigidly secured such as by bolts 272 to secure-10 ment plate 176. Similar to floating face 252l in the pre-ferred form the plunger 262 does not directly engage the lever arm 234, but rather acts through a floating-type pin 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 assure that plunger 262 can properly engage and exert a force on lever arm 234 regardless of variations of manufac-turing tolerances, and/or the position of lever 226 relative :-to its pivotal shaft 228.
:. ,-.
~ Both solenoids are urged to their de-energized ~ : :
~: , 20: position by linear gradient springs, and unlike on-off, : ::
digital-type solenoids, variation in current and/or voltage ~ input to their coils will cause an analog incremental posi-: tioning of the plunger 244 of solenoid 239, and will move plunger 262 to either it~ Fig. 6-C or 6-D position.
The plunger 262 of so.lenoid 257 can be shifted away from its de-energized Fig. 6-B state, to two different energized states shown in Figs. 6-C and 6-D. One electrical input signal of preselected, intermediate power causes the armature 262 to shift to the Fig. 6-C position, moving 30 plunger 262 until the face of its adjustable stop nut 263 contacts the spring stop 267. This travel of plunger piston 262 depresses plunger 272 and compresses spring 274 to shift arm 234 away from opening 178 and increase fuel flow until ~, ' .

113~33 gas generator speed increases to a level corresponding to the signal force generated by solenoid 257. Thus the plun-ger 272, spring 274 configuration assists in permitting a less-than-maximum power signal to produce a force of pre-selected magnitude on arm 234.
Another electrical input signal of greater power causes the armature to shift to the end of its stroke with face 261 thereof contact the adjacent stop face 259 of the housing 256 as shown in Fig. 6-D. This travel causes piston plunger 262 to compress centering spring 266 and cause its lower end to come into direct contact with arm 234 and urge the latter to permit maximum flow through the orifice pre-sented between opening 178 and piston 252. As described in greater detail belQw, energization of solenoid 257 to its Fig.
6-D position is essentially a false throttle signal dupli-cating the speed desired from the gas generator when the throttle is depressed to its maximum fuel flow, maximum power position.
Saheduling Valve 62 Referring now more particularly to Figs. 7-11, scheduling valve 62 generally includes a housing 276 which may be integral with both housings 140 and theistationary engine housing 110. Preferably housing 276 is dispo8ed in close proximity to both the fuel governor 60 and the com-bustor 98. Housing 276 includes an internal bore 278 into which open the two fuel ducts 142, 144 as well as the fuel line 64 and a low pressure return conduit 280 which returns fuel back to the source. Mounted for longitudinal sliding and rotation within` bore 278 is a metering valve 282 having "windowed" irregularly shaped openings 284, 286 that open into the hollowed interior cavity 288 of valve 282. Fuel line 144 continuously communicates with interior cavity 288.
Valve 282 further includes an opening 290 in continuous 113~33 communication with fuel line 64. Deceleration window 286 is in general alignment with fuel duct 142, and acceleration window generally aligns with opening 290. The particular configuration of each of the windows 284, 286 is clearly illustrated in Figs. 10 and 11.
Metering valve 282 is urged in one longitudinal direction by a biasing spring 292 which reacts against the housing 276 through a spring stop 294 acting on an alignment point 296 of a sealed block 298 mounted to housing 276 such as by snap ring 300. The preferred construction as illu~
strated in Fig. 9; however, the alignment point arrangment permitting rotation of valve 282 relative to housing 276 at -the end of spring 292 may alternately be accomplished via a ball 302 configuration as shown schematically in Fig. 7. At ~
the opposite end of valve 282 is a spherical ball 304 per- - ;
mitting rotation of valve 282 relative to a piston 306 car- ;~
ried in bore 278. Attached to housing 276 is a temperature sensitive element 312, 308, for example a thermally respon-sive cylinder, whose longitudinal length varies with respect ~20 to the temperature imposed thereon by the gas or other fluid in the temperature sensing chamber 310 within cylinder 312.
The housing 276 is mounted relative to the engine such that a portion thereof, particularly aylinder 312 and the asso-ciated ahamber 310 are in communiaation With and maintained at the same temperature, T3 5, as the compressed air flow being delivered into the combustor. Thermally insulative material 311 is incorporated as necessary to avoid over-heating of valve 62. For example the rightward end of Fig.
9 and the perforated cylindrical wall 312 may be disposed at the air inlet to the combustor and/or at the duct 96 carrying air from the recuperator 56 to combustor 98. In any case the scheduling valve is so arranged the cylinder ~ -312 expands and contracts longitudinally with ~respeat to ~13~i433 increase and decrease of combustor inlet temperature. Valve 288 is operably engaged by the thermally responsive element 312 through a relatively non-thermally responsive ceramic rod 308. Accordingly, valve 288 is shifted longitudinally relative to input port 142 and opening 290 in relation to the sensed combustor inlet temperature. Thus the metering fuel flow accomplished by window 284 is varied in relation to the sensed combustor inlet temperature as this window moves longitudinally relative to opening 290.
Housing 276 further includes another transverse bore 314 which crosses and intersects generally with the longitudinal bore 276. Mounted for longitudinal reciproca-tion 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 housing, an intermediate section 322 and a closing plug 324 threadably or otherwise secured to housing 276. The inner ends of the seals 320 are ~-~ secured on the movable piston, rod configuration ~16. The seal 320 in conjunotion with the end closing plug 324 define an interior pressure sensing chamber 326 to which one end of the piston 316 is exposed. Through a sensing line 32~ the combu~tor pressure P3 5 such as aombustor inlet pressure i~
transmitted into ahamber 326 to act upon one end of piston 316. At the opposite end of bore 314, a helical coil bia-sing spring means 330, grounded to housing 276 through a stationary stop 332, acts to urge the piston, rod configura-tion 316 in opposition to the pressure in chamber 326. ~he opposite end 334 of the piston configuration 316 is vented to atmospheric pressure through an appropriate port 336. A
seal schematically shown at 335, which may be of a structure like seals 3I8, 320 and section 348, is also included at this opposite end 334. Thus gauge pressure in the combustor, 113~i433 i.e. the difference between ambient pressure and the absolute pressure main~ained in combustor 98, acts upon piston 316 to shift the latter within bore 314.
An arm 338 is threadably secured within a trans-ver~e bore in metering valve 282 at one end, and at its other end the rod 338 has a spherical ball 340 mounted thereon which is received in a groove 342 in rGd, piston 316. It will there-fore be apparent that shifting of piston, rod 316 within bore 314 is translated into rotation of metering valve 282 about its major longitudinal axis. Accordingly, the respective openings between windows 284, 286 and the input ports 142 and opening 290 are also varied in relation to the magnitude of gauge pressure in compressor 98 by virtue of this rotational translation of metering valve 282. Groove 342 permits axial translation of arm 338 along with valve 282. While the rod, .
piston configuration 316 may be of varied arrangements, the preferred form as illustrated in Fig. 8 incorporates a threa-ded end section 344 which acts through appropriate spaces 346 to compress and secure the inner ends of sea~ 318, 320 to rod 316 through an intermediate section 348.
Thus, the scheduling valve acts as a mechanical analog computer in multiplying the parameters o aombustor ?
pressure, P3 5 and combustor inlet temperature, T3 5, such ~hat the positioning of valve 282 and the windows 284, 286 is a function of the product quantity of combustor pressure multiplied by combustor inlet temperature.
Conventionally, as shown in Fig. 4 the controls for engine 30 further includes a normally open, solenoid operated fuel sequencing solenoid valve 350 as well as a manually or electrical solenoid operated shut-off valve 352.
These valves are disposed downstream of scheduling valve 62 and in the preferred form may be included within and/or ad-jacent to the housing 276 of scheduling valve 62.

- - .

The configuration of each of the windows 284, 286 as illustrated in Figs. 8 and ~ are determined to solve a qualitative empirical formula of the following form:
Wf = (Kl - K2 T3 5) P3 5 + K3T3 5 where: Kl, K2 and K3 are constants determined by the operational characteristics of a particular gas turbine engine and are reflëcted by the configuration of window 284 and associated opening 290.
By proper formulation of the window 284 and opening 290, the solution to this equation as accomplished by ~che-duling valve 62 holds a constant maximum turbine inlet tem- ~
perature T4 during all or at least a portion of gas generator ~.
acoeIeration. Accordingly, when window 284 i6 the control-ling parameter for fuel flow, scheduling valve 62 empirically by mechanical analog, controls fuel flow to maintain a sub-stantially constant turbine inlet temperature, T4. Window 284 is the primary operating parameter during acceleration of the engine as described in greater detail below. In con-~ trast, window 286 is the:controlling:parameter during engine i`~ 20 deceleration. While acceleration~window 284 is contoured to maintain a substantially~aonstant~maximum gas generator tur-bine inlet temperature~to:provide maximum accleration per-: formance within the temperature limitations of the engine, the deceleration window 28~ iS aontoured to limit.and con-;~ trol fuel flow to prevent 1088 of aombu~tion while affording ~ubstantial deceleration of the engine. An extensive discus-sion of operation of a similar type of turbine inlet tempera-ture computing valve, but which utilizes absolute rather than gauge combustor pressure, may be found in United States 30 Patent Application No. 689,339 of Rheinhold Werner, filed May 24, 1976, now U. S. Patent No. 4,057,960.

Vane Actuator 66 -Details of the vane actuator control 66 are .... ' ' ' ' ' , ' ' ' .. . . .

1~36i433 illustrated in Figs. 12 and 13. The vane control is hydro-mechanical in nature and generally includes a housing 354 having a pair of hydraulic pressure fluid supply ports 356, 358 respectively receiving pressurized fluid from a high pressure pump s~urce 360 and lower pressure pump souree 362 eaeh of which are driven through the auxiliary power system of the engine. It is understood that the pumps 360, 362 may provide various other funetions within the engines also sueh as lubrication.
Housing 354 has an internal, fluid reeeiving cy-linder 364 in which is reciprocally mounted a piston 366 dividing the eylinder into opposed fluid pressure chambers.
Rod or shaft 368 earried with piston 366 extends exteriorly of housing 354 and is operably conneeted with the bell crank 130 of Fig. 13 so that, as described previously, linear reci-procation of rod 368 causes rotation of bell erank 130, ring gears 126, 128 and the sets of variable guide vanes 120, 122.
High pressure hydraulie fluid from inlet port 356 is delivered into a bore 370 within housing 354 loeated adja-cent eylinder 364. Also interseating at spaced locationsalong bore 370 are a high pressure fluid exhaust duet 372, and a pair of fluid work eonduits 374, 376 respeetively com-munieating with the cylinder 364 on opposed sides of piston 366. Mounted for reeiproaation within bore 370 is a diree-tional fluid eontrol valve element 380 whieh is nomlnally positionable in the open eentre position illustrated wherein high pressure hydraulie fluid from duet 356 eommunieates only with the exhaust port 372. A series of eentering springs 382, 383, 384, 385 normally urge valve 380 to the position shown. Valve 380 is the four-way type and is shiftable one direetion to direet high pressure fluid from port 356 to eon-duit 374 and the upper side of piston 366, while through eon-duit 376 the lower side of the aylinder carrying piston 366 ., ~
., . , . ~ , :

3t~433 is vented to a low pressure return 386 via bore 370, andcommunicating conduit 388. ValVe 380 is shiftable in an opposite direction to direct pressure fluid from inlet 356 to conduit 376 and the lower side of piston 366, while con-duit 374 communicates with return 386 through a chamber 378 and return line 379. It will be noted that piston 366 co-operates with housing 354, such as with a circular wall protrusion 390 thereof to prevent fluid communic~tion 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 centre position. Thus it will be apparent that piston 366 acts in servo-type follo-wing movement to the movement of an "input piston" in the form of valve 380.
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 com-pre~sive orce of spring 383. Pressure acting on shoulder 393 i8 opposed by a spring 385, SlLdably extending through the centre of element 392 is a rod 395 which acts as a variably positionable stop upon the spring 384 extending between the upper end of rod 395 and valve 380. Rod 395 is longitudinally shiftable in response to rotation of a fulcrum type lever 396 pivotally mountèa to housing 354 at pivot 398.
Vane actuator control 66 further includes another bore 400 in which is mounted a control pressure throttling valve 402. An input from the throttle lever 184 of the .

.

1~3Çi433 .

engine acts to depress a variably positionable spring stop 404 to increase the force exerted by compression spring 406 in urging valve 402 downwardly. Opposing spring 406 is a gradient compression, helical coil spring 408. Valve 402 is variably positionable to meter hydraulic flow from port 358 to conduit 410. It will be noted that conduit 410 also communicates with the lower end of throttling valve 402 via a conduit 412 having a damping orifice 414 therein. Con-duit 410 leads to the larger face of a stepped piston 416 rPciprocally mounted within another bore 418 in housing 354. One end on bore 418 is in restricted fluid communica-tion with return 387 through an orifice 419. The smaller diameter section of stepped piston 416 receives pressurized fluid from conduit 420. Through an appropriate exhaust con-duit 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. ~-Conduit 420 provides a hydraulic signal indicative ~:
of the speed of the power turbine shaft 82. In this connec-tion, the vane actuator includes a non-positive dîsplacement type hydraulic pump, such as a centrifugal pump 422 mounted ~: to and rotated by power turbine shaft 82. Being a non-positive displacement type pump, the pump 422 delivers pres-surized hydraulic flow through conduit 420 such that the pressure maintained on the smaller diameter of stepped pis-ton 416 is a square function of the speed of power turbine shaft 82. Similarly, the action of throttling valve 402 develops a pressure on the large diameter of piston 416 in relation to a desired or selected speed reflected by the 30 position of the throttle 184. -The valve 402 and piston 416 act as input signal means and as a comparator to vary the compressive force of spring 384 as a function of the difference or error between 3~ 33 actual power turbine speed and the power turbine speedrequested by throttle position. The requested Npt is gra-phically illustrated in Fig. l9.
The vane actuator control 66 further includes a linear, proportional solenoid actuator 426 operably con-nected by electrical connector lines 427 to electronic control module 68. Actuator 426 includes a housing 428 enclosing a coil 430, and a centrally arranged armature which carries therewith a hydraulic directional control valve 432. Valve 432 is normally urged upwardly by spring 434 to the position communicating conduit 394 with return 386. Valve 432 is proportionally shiftable downwardly in response to the magnitude of the energization signal to proportionally 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 essentially zero in the absence of an energization signal to solenoid 426. I* will be noted that ~0 minimum pressure in conduit 394 allows springs 383 and 385 ; to exert maximum upward force on valve 380, and that in-creasing pressure in conduit 394 shifts piston 392 down-wardly to reduce the force exerted by springs 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 minimum pressure is exerted on shoulder 393 causing the guide vanes to be controlled by power turbine speed. Thus, the guide vanes during start-up are at their Fi~. 14 posi-tion and at other conditions of engine operation are normallyurged to maximum power, Fig. 15 position.
As shown in Fig. 18, vane actuator 66 is operable to vary guide vane angle, B, from 0 to ~20 to alter the ~L3~33 positive incidence of gas flow upon the power turbine bladesand thus alter power transmitted from the gas flow 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 directed to oppose and thus tend to decelerate the rotation of the power turbine wheels.
Electronic Control 68 A portion of the control logic of the electronic control module 68 is illustrated in Fig. 17~ The electronic control module receives input electrical signalsindicative of power turbine speed (Npt) through a chopper 436 secured to power turbine shaft 82 and an appropriate magnetic mono-pole 438 which transmits an electronic signal indicative of power turbine speed through lead line 440. Similarly, gas generator speed, Ngg, is sensed through a chopper 442, mono-pole 444 and lead lines 446. Transducers 448, 450 and 452 respectively generate electrical input signals indicative ~ ~ .
of the respective temperature sensed thereby, i.e. compres-, sor lnlet temperature T2, turbine inlet temperature T4, and turbine exhaust temperature T6. As illustrated these tem-perature signals are transmitted through lines 454, 456 and 458. The electronic control module also receives from an ambient pressure sensor 460 and associated line 462 an elec- ; -trical signal indicative of ambient pressure P2. The elec-tronic control module further receives from an appropriate sensing device an electrical signal through lines 464 indi-cative of throttle 184 position, "a". Alao, a switch 466 is manually settable by the vehicle operator when power feed-back braking (described more in greater detail below) is desired. A transducer 544 generates a signal to an inverter .

113~33 546 whenever the variable guide vanes are moved past a pre-determined position B*.
The electronic control module includes several output signals to energize and/or de-energize the various logic soleno~sand relays including solenoid 518 through line 519, solenoid 257 through line 268, fuel sequencing 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 gene-rators 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 conditions T2 and P2 and power turbine speed Npt. Element 550 transforms the throttle position signal "a" into an electronic gas generator speed request signal, and function generator 552 produces a signal as a function of gas generator speed Ngg from line 446. The module further includes~c:omparators~497,~ 534,~540, 554, 556 as well as the logical elements 498, 500 and 538. The logical ele-ments are of the "lowest wins" type, i.e. they pass the alge-braically lowest input signal.
The logic element 498 selects from the slgnals 536 and 542 which have been generated in comparators 534 and 540 indicating the amount o~ over or undertemperature for T4 and T6. An additional input from 456 is provided to lo~ic ele-ment 498 so as to provide an indication of excessive T4 figures in the aase of a failed T4 sensor signal. The logic element 500 receives inputs from 497 and 498. Comparator 497 compares the electronic speed request with the actual gas generator speed 446 to determine if the engine has been requested to acoelerate or is in steady state. The output of logic element 500 is fed to inverter 546, generating an appropriate signal in solenoid driver 558 which then moves ~3~433 trim solenoid 426 a distance proportional to the magnitude of signal 427.
The logic element 538 receives its inputs from comparators 554 and 556, logic element 498 and a differen-tiator 548. As noted, logical element 498 indicates the lower of the two temperature errors T4 and T6. The output of comparator 556 is the error between the operator reques-ted power turbine speed Npt and the actual power turbine speed Npt. The output of comparator 554 is indicative of the difference between the maximum allowable gas generator speed determined by function generator 514 and the actual gas generator speed 446. The logic element 538 selects the algebraically lowest signal and outputs it to solenoid dri-ver 560 with an output on line 250 which is passed on to the governor reset decrease solenoid 239 in the fuel control 60.
As depicted in Fig. 17, the electronia controllmo-dule includes a comparator 468 and synthesizers or function generators 470, 472 and 474. Function generator 470 produces an output signal in line 478 indicative of whether the dif-ference between power turbine speed and gas generator speedis less than a preselected maximum such as five percent.
Function generator 472 produces a signal in line 480 showing whether or not power turbine speed is greater than gas gene-rator speed, while ~unction generator 474 generates a signal in lines 482 showing whether or not gas generator speed is greater than 45 percent of its maximum speed. The control logic further includes function generator 486 and 488 which respectively generate signals in associated line 490 and 492 showing whether or not transmission input speed is above a preselected minimum "e" and whether throttle position is below a preselected throttle position a*. Throttle position "a" is obtained from a suitable position sensor such as a variable resistance potentiometer. Thus, output signal 464 1~3~i433 is indicative of throttle position "a".
The electronic control module further includesthe logical gates 502, 504, 506, 508 and 562. Logical AND
gate 502 receives inputs from line 478 and AND gate 506 to produce an output signal to solenoid driver 516 to activate power feedback clutch 84. Logical AND gate 506 receives its inputs from line 482, switch 466 and line 492 and produces an input signal to AND gates 502 and 504. Logical AND gate 504 receives an input from line 480 and the inverted input from line 478. Its output generates a 50~ gas generator speed signal and also enables solenoid driver 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 ele-ment 566. Signal 268 then activates the governor reset in-crease solenoid 257 in the fuel control 60. Logical AND
gate 508 receives its inputs from lines 490 and 492. Its output signal generates a 20% gas generator signal through function generator 568~which, added to the constant 50% sig-nal by summer 570 results in a fast idle signal (70~ gas 20 generator speed) to the governor reset increase solenoid 257. `
The output of AND gate 508 also generates the enable signal to solenoid driver 564.
Power Feedback Clutch 84 While various forms clutahes could be utilized for power feedback clutch 84, the preferred form shown in Fig. 3 comprises a "wet" type hydraulically actuated clutch which includes a shaft 520 from the gear train 78 associated with gas generator shaft 76, and a shaft 522 interconnected with the gear train B0 associated with the power turbine output shaft 82. The clutch operates in a continual bath of lubri-cating cooling fluid. The gas generator shaft 520 drives a plurality of discs 524, which are interposed in discs 526 connected to the output shaft 522. The clutch actuator is 113~33 in a formofasolenoided operated directional hydraulic controlvalve 518 which, in the energized position illustrated, ports pressurized fluid such as from source 362 into a fluid pres-sure chamber 528 to urge piston 530 against the urgings of a return spring 532 to force the plates 524, 526 into inter-engagement such that the power from shaft 522 may be fed ~ack to gas generator shaft 520 to assist in braking. When the solenoid actuator 518 is de-energized, the chamber 528 is exhausted to a low pressure drain to permit the spring 532 to shift piston 530 away from the position shown and dis-engage the plates 524, 526.
OPERATION
Starting -In a conventional manner start motor 72 is elec-trically energized to initiate rotation of gas generator ~ ~
drive shaft 76 and the input shaft 152 of fuel governor 60. ~ ;
The control module 68 energizes the normally open fuel se-quence solenoid 350, and solenoid 352 is also in an open position to clear fuel line 64 for delivery to the combustor.
As necessary, an assist pneumatic pump 74 delivers pressuri-zed air into combustor 98 along with the action of ignition plugs 100. Motor 72 is utilized to drive the various compo-nents described until the gas generator section reaches its self-sustaining speed, normally in the range of approximately 40~ of maximum rated gas generator speed.
During initial rotation and starting of the engine, the low speed of rotation of fuel governor drive shaft 152 cannot overcome the bias of speeder spring 224, and thus fuel lever 226 is disposed away from and clearing orifice 178 to permlt fuel flow from line 166 to output line 144.

Also during this initial starting, the combustor temperature ~T3 5) and combustor pressure (P3 5) are both relatively low such that scheduling valve 62 also permits significant fuel -~ . ,: ~ , - 113~i433 flow through line 64 to the combustor.
Low Idle As gas generator shaft 76 speed climbs beyond the self-sustaining speed, start motor 72 is shut off and the combustion process permits self-sustaining operation of the gas generator. Speeder spring 224 is normally set t~ main- ~-tain a low idle value of approximately 50% of maximum gas generator rated speed. Accordingly, the mechanical fly-weight governor operates in opposition to speeder spring 10224 to adjust fuel lever 226 and maintain fueI flow through orifice 178 to hold gas generator speed at a nominal 50% of maximum. This 50% low idle speed is effective whenever pro-portional solenoid 257 is in the de-energized state illu-strated in Fig. 6.
The electronic control module 68 normally maintains solenoid 257 in the de-energized state to select the low idle gas generator speed whenever the transmission input shaft speed of shaft 36, as sensed by speed sensor 48, is rotating.
Such normally ocours whenever the clutch 34 is engaged with transmission 38 in its neutral position, or whenever the vehicle is moving regardless of whether or not the clutch 34 is engaged or disengaged. Accordingly, during idling when not anticipating aoceleration of the engine, the aomparator 486 of the electronia aontrol module 68 notes that the speed of ~haft 36 i9 above a predetermined minimum, "e", suah that ~;no signal is transmitted from comparator 486 to AND gate 508.
Solenoid 257 remains de-energized, and the gas generator speed is controlled by the governor to approximately 50%
its maximum speed.
High Idle Maximum power is normally required to be developed from an engine driving a ground vehiole upon initiating acce~
leration of the vehicle from a stationary or substantially . ~ . , , -~

~36~3~

stationary start. As a n~tural 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 shaft 36 drops below a predetermined 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 energize comparator 488 and also send a positive signal to AND gate 508. The output of AND gate 508 energizes function generator 568 to add 20% to the constant idle command of 50~, so 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.
Accordingly, solenoid 257 is energized by an appropriate current signal through line 268 to shift to its Fig. 6C po-sition. In this position the solenoid 257 has been suffi-ciently energized to drive shaft 262 and plunger 272 down-wardly as viewed in Fig. 6C and exert a force on fuel lever 226 tending to rotate the latter away from and increase the size of orifice 178. The additional force exerted by sole-noid 257 is sufficient to increase fuel flow through orifice 178 to increase gas generator speed to a predetexmined hi~her level, such as 70% of maxlmum gas generator speed. ~he fly-weight governor operates to hold the gas generator speed constant at this level.
In this manner, the idle speed of the gas genera-tor section is reset to a higher value in anticipation of a required acceleration such that more power will be instant-ly available for accelerating the vehicle. At the same time, when acceleration is not anticipated, as determined by whether or not transmission input shaft 36 is rotating or '' ~

.

113~433 stationary, the electronic control module 68 is operable to de-energize solenoid 257 and reduce gas generator speed to a lower idle value just above that necessary to maintain a self-sustaining operation of the gas generator section. In this manner power necessary for acceleration is available when needed; however during other idling operations the fuel flow and thus fuel consumption of the engine is main-tained at a substantially lower value. This is accomplished by producing a signal, minimum speed of shaft 36, which is anticipatory of a later signal (rotation of accelerator lever 184) requesting significant increase in power transmitted to drive the vehicle.
Acceleration . _ :
Acceleration of the gas turbine engine is manually selected by depressing the accelerator 184. To fuel gover-nor 60 this generates a gas generator section speed error signal in that the depression of lever 184 rotates shaft 192 to increase compresslon of speeder spring 224 beyond that force being generated by the mechanical flyweight speed sen-sor. Fuel lever 226 rotates in a direction substantiallyclearing 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 406 to shift valve 402 down-wardly and increase the pressure maintained in chamber 418 substantially beyond that being generated by the hydraulic speed signal generator of pressure developed by pump 422 .: :
and exerted on the other side of the step piston 416. Ac-cordingly, lever 396 is rotated generally clockwise about its pivot 398 in Fig. 12, allowing downward retraction, if necessary, of plunger 395 and reduction of compression on ~ -, ' ' ~ .,.. ,.: :.

113~i433 spring 384.
Summer 497 of the electronic control module deter-mines a large disparity between accelerator position and gas generator speed to develop an electronic signal to element 500 overriding other signals thereto and reducing the signal in line 427 to zero to de-energize the solenoid 426 of guide vane control 66. The spring bias urges plunger 430 and valve 432 to the position shown in Fig. 12 to minimize hydraulic pressure developed in conduit 394 and exerted on piston shoul-der 393. As discussed above in the vane control 66 descrip-tion, springs 382-385 position valve 380 to cause following movement of piston 366 to its nominal or "neutral" position.
In this position vane piston 366 and rod 368, the guide vanes 120 are disposed in their Fig. 14 position wherein the gas flow from the combustor is directed onto the power turbine vanes in a manner minimizing power transfer to the power tur-bine vanes. More particularly, the guide vanes 120 are dis-posed in their Fig. 14 position to reduce the pressure drop or pressure ratio across turbine blades 117 to a minimum value, this position corresponding to the 0 position of Fig.
18.
Since the nozzles 104 maintain the combustor 98 in a chokedcondition, this reduction in pressure ratio across the turbine blades 117 areates a substantial increase in pressure ratio across the radial inflow turbine 102 of the gas generator section. Accordingly positioning o~ the guide vanes in their Fig. 14 position by allowing the springs 382-385 to position valve 380 and piston 366 in its "neutral"
position, alters the power split between the gas generator turbine 102 and the power turbines 116, 118 such that a pre-selected maximum portion of power from the motive gas flow is transmitted to the gas generator turbine 102. As a result, maximum acceleration of the gas generator section from either 113~i433 its low or high idle setting toward its maximum speed is achieved. As noted previously, the requirement for impen-ding acceleration has been sensed, and the engine is nor-mally 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 sche-dule window 284 and opening 298 in the fuel scheduling valve.
Increase in this opening causes a consequent increase in fuel flow to combustor 98 and an ultimate resulting increase in the inlet temperature T3 5 through the actions of recupera-tor 56.
To the operation of engine 30, increase in T3 5 is in practical effect the same as a further fuel flow increase.
Accordingly, in solving the above described equation the win-dow 284 shifts to reduce fuel flow with increasing T3 5 to produce an "effective" fuel flow, i.e. one combining the effects of actual fuel flow and inlet temperature T3 5, at the sensed gauge pressure P3 5 to produce a desired combustor ~-exhaust or gas generator turbine inlet temperature T4.
This increase in fuel flow created by the rotation of valve 282 and as compensated by axial translatiQn of the valve provides an "effective" fuel flow that increases power developed and transmitted from the gas flow to gas genera-tor turbine 102. This then causes another increase in gas generator speed, and combustor pressure 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 while maintaining combustor outlet temperature T4 at a -3g-.

~3~433 relatively constant, high value. In this manner the gasgenerator section is accelerated most rapidly and at maxi-mum efficiency since the turbine inlet temperature T4 is maintained at a high, constant value.
While the acceleration window 284 and opening 290 may be relatively arranged and configured to maintain a constant T4 throughout acceleration, a preferred form con-templates maintaining a substantially constant T4 once the power turbine has initiated rotation, while limiting turbine outlet or recuperator inlet temperature during a first part of the acceleration operation. In this manner e~cessiYe T6 is avoided when the power turbine section is at or near stall. More specifically, it will be noted that upon star-ting acceleration of the vehicle, the free power turbine section 54 and its shaft 82 are stationary or rotating at a very low speed due to the inertia of the vehicle. Thus there is little temperature drop in the gas flow while flo- -wing through the power turbine section, and the recuperator inlet temperature T6 starts approaching the temperature of gas flow exiting the gas generator radial turbine 102. If combustor exhaust or gas generator turbine inlet temperature T4 is maintained at its maximum constant value at this time, it i~ possible that T6 may beaome exaessively high in in-stanaes of high inertial load whlah lengthens t~e time of this substantial "stall" aondition on the power turbine sea-tion. Of course, as the power turbine section overcomes the inertia and reaches higher 8peeds, 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, electronic and/or mechani-cal, are normally expected in order to avoid excessive T6 while providing responsive acceIeration under the conditions ` 1~3f~433 in question. An important discovery of the present inven-tion, as embodied in scheduling valve 62, is in providing an extremely simple, economical, mechanical structure capable of Limiting T6 during the critical turbine section stall period but yet still promoting very responsive engine acce-leration. At the same time this improved arrangement has eliminated the need for compensation for substantial vari-ations in ambient pressure and thus the need to compensate for the variations in altitude that would be expected to be 10 encountered by a ground vehic:le. In this connection it would be expected that absolute combustor pressure P3 5 must be the parameter in solving the equation described previous-ly such that the scheduling valve could reliably compute the turbine inlet temperature T4 created by a particular combina-tion of combustor pressure, P3 5, and inlet temperature, T3 5.
However, a discovery of the present invention is that by proper selection of the constants Kl, K2 as embodied in the size and configuration of openings 284, 290, and by utilization of combustor gauge pressure rather than combus-20 tor absolute pressure, mechanically simple and economicalstructure with minimum control complexity can accomplish the desired control of both T6 and T4 during acaeleration. Win-dow 284 and opening 290 are relatively arran~ed suah that when valve 282 rotates to a minlmum P3 5, a slight overlap remains between the window and opening. Thus, a minimum fuel flow, Wf, is maintained at this condition which is a function of T3 5 since valve 282 is still capable of trans-lating axially. This gives rise to the third term, K3T3 5, in the equation set forth above and dictates an initial 30 condition of fuel flow when window 284 becomes the control-ling fuel flow parameter upon starting acceleration.
The constants Kl, K2 are chosen, their actual values being determined by the aerodynamic and thermodynamic cha-racteristics of the engine, such that at a preselected value, ` 1~3~i~33 P3 5*, intermediate the maximum and minimum values thereof, the acceleration window controls fuel flow to maintain a constant T4. At combustor pressures below this preselected value, the acceleration window provides fuel flow allowing T4 to reduce below the preselected maximum desired level therefor. It has been found that an inherent function of using gauge combustor pressure rather than absolute pressure, in combination with these chosen values of Kl, K2 and a pre-selected minimum fuel flow at minimum P3 5 as determined by K3, is that fuel flow is controlled by the acceleratioD
window to prevent reauperator inlet temperature T6 from ex- ~
ceeding a preselected value. This approach still utilizes ~ -the simple geometry of window 284 and 290, both rectangles, that mechanically compute the product of T3 5 multiplied by P3 5. Accordingly, at pressures lower than P3 5* which are characteristics of the conditions~under which the turbine s-section "stalling" occurs, the utilization of gauge combus-tor pressure prevents potentially damaging excessive T6. The design point for window 284 is, of course, the condition of ~ ~ 20 maximum vehicle inertia experienaed on turbine shaft 82, lesser values of such inertia naturall~ permitting more :: : :
rapid turbine shaft speed inarease and less time in the "stalling" aondition above described.
From inspeation of the equation solved by valve -~
282 it will be apparent;that fuel flow Wf is a linear or straight line function of P3 5 as shown in Fig. 20, with a slope determined by R1 and K2, an intercept specified by K3, ;~ and passing through the point producing the preselqcted turbine inlet temperature T4 at the selected intermediate value P3 5*. Of course, a family of such straight line curves of Wf V8 . 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 " ~i35433 value at pressures at and above the preselected intermediate P3 5*, in the preferred form compound curvature of the win-dow 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 the theoretically desired precisely constant T4, resulting in practical effect in maintaining a substantially constant T4 at a desired maximum value once combustor gauge pressure exceeds the pre~
selected level P3 5*. Accordingly, the present invention inherently limits recuperator temperature T6 to solve the problem of recuperator overheating when starting to acce-lerate a high inertial load, yet still maintains a maximum T4 for high engine efficiency throughout the remainder of acceleration once the inertia is substantially overcome and .~:
for the majority of time during acceleration. At the same - :~
time, and contrary to what might normally be expected, it has been found that the need for altitude compensation is obviated since there exists a minimum fuel flow at minimum combustor pressure, which minimum fuel flow varies linearly with combustor inlet temperature T3 5. Thus the present invention provides a simple mechanical solution to the inter-dependent and complex problems of limiting two different temperatures T4, T6 for different purposes, i.e. avoiding recuperator overheating while affording high engine opera- :
ting efficiency and thus highly responsive acceleration.
As the gas generator continues to accelerate, the flyweight governor 208 of the fuel governor 60 begins exer-ting greater downward force to counteract the bias of speederspring 224. Accordingly, the fuel lever 226 begins rotating in a generally counter-clockwise direction in Fig 6 to begin metering fuel flow through opening 178. Once the opening -113~i~33 178 becomes smaller than that afforded by metering window 284 in scheduling valve 62, the operation of the scheduling valve is overridden and the fuel governor 60 begins control-ling fuel flow to the combustor in a manner trimming gas generator speed to match the speed selected by the rotation of 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 summer 497 10 such that once gas generator speed Ngg approaches that selec-ted by the position of the accelerator pedal as sensed electronically through line 464, the override signal gene-rated by summer 497 is cut off. In response, element 500 is allowed to generate a signal energizing the proportional solenoid 426 of the guide vane control 66. Valve 432 asso-ciated with solenoid 426 is shifted to increase pressure exerted upon piston shoulder 393 to permit the piston 366 and the guide vanes to shift from the Fig. 14 disposition thereof towards the Fig. 15 position. This shifting of the 20 guide vanes from the Fig. 14 to the Fig. 15 position again alters the work split between the gas generator turbine 102 t and the power output turbines 116, 118 such that greater power ls developed aaross the output turbines and transmitted to output shaft 82 while a lesser portion is transmitted to turbine 102.
Thus it will be apparent that acceleration of the engine and vehicle ocaurs by first altering the work split so that maximum power is developed across the gas generator turbine 102, then increasing fuel flow along a preseleated 30 schedule to regeneratively further increase power developed across the gas generator while maintaining turbine combus-tor exhaust temperature T4 at a substantially constant, pre-selected maximum. Once substantial acceleration of the gas ~13~33 generator section has been accomplished, the guides vanes are then rotated to alter the power or work split so as to develop a greater pressure ratio across and transmit more power to the power turbines 116, 118 and the power output shaft 82.
Cruise During normal cruise operation (i.e. travelling 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 generator turbine 102 and the power output turbines 116, 118 so as to maintain a substantially constant combustor exhaust temperature T4. This is accomp-lished by the electronic control module which includes a summer 534 developing an output signal in line S36 to the logic box 498 indicative of the difference between the ac-tual and desired turbine inlet temperature T4. More parti-cularly, solenoid 426, as discussed previously, is maintained normally energized to generate maximum pressure upon the pis-ton shoulder 393 of the guide vane actuator. For instance, assuming that T4 is above the preselected desired value ~: -; thereof, a signal is generated to line 536 and element 498 to reduce the magnitude of the electric signal through line 427 to solenoid 426. Accordingly, the spring bias 434 of -the solenoid begins urging valve 432 in a direation reduaing fluid com~unication between conduits 372 and 394 while cor-respondingly increasing communication between conduit 394 and exhaust conduit 386. The reduction in pressure exerted upon piston 393 accordingly allows spring 385 to increase the spring bias of spring 383 to cause upward travel of valve 380 and corresponding downward trav~l o~piston366 t~ drive the vanesbackwardsfrom theirFig. 13disposition (+20 position of Fig. 18) toward a wider open position increasing the area ratio and reducing the pressure ratio across the vanes of the 113~;433 turbines 116, 118. Accordingly, in response to T4 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 gene-rator turbine 102 causes an increase in gas generator speed. Such increase in gas generator speed is then sen-sed by the flyweight governor 208 of the fuel governor 60 to cause counter-clockwise rotation of fuel lever 226 and reduce fuel flow through opening 178. The reduction in fuel to the combustor 98 accordingly reduces the combustor exhaust or turbine inlet temperature T4 toward the preselec-ted value thereof. Thus, the guide vane control operates to adjust the guide vanes as necessary and causes a consequent adjustment in fuel flow by the fuel governor 60 due to change in gas generator speed Ng~ so as to maintain the combustor exhaust temperature T4 at the preselected, maximum value.
It will be apparent also from the foregoing that reduction in turbine inlet temperature T4 below the preselected desi-red value thereof causes a corresponding movement of the guide vanes 120, 122 to increase the pressure ratio across :the power turbines 116, 118. Accordingly this causes a re-duction in pressure ratio across gas generator turbine 102 to reduce gas generator speed. In response the fuel governor ~shifts fuel lever 226 in a alocXwise rotation as viewed in Fig. 6 to increase fuel flow to the combustor and thus in-crease turbine inlet temperature T4 back to the desired value.
It will be apparent that the change in guide vane position also directly alters the combustor exhaust temperature T4 due to the difference in air flow therefrom: however, the major alteration of combustor exhaust temperature is effec-ted by altering the fuel flow thereto as described above.

During the cruise operation therefore, it should now be apparent that fuel governor 60 acts to adjust fuel ~3~3~i433 flow in such a manner as to maintain a gas generator speedin relation to the position of the accelerator lever 184.
Clearly, the fuel governor 60 operates in conjunction with or independently of the vane control 66, dependent only up-on the gas generator speed N~g.
While the electronic control module operates the -~
guide vane control solenoid 426 to trim turbine inlet tempe-rature T4 during cruise, the hydromechanical portion of the guide vane control 66 acts in a more direct feedback loop to trim the speed of power 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 pres-sure developed in line 410. A graphical representation of the action of valve 402 and piston 416 in compressing spring 384 and requesting different desired power turbine speeds Npt 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 rotation of accelerator lever 184, pressure at the lower diameter of piston 416 becomes substantially greater than that on the larger face thereof to rotate lever 396 80 as to increase compression of the biasing spring 384 aating on valve 380.
The resulting upward movement of valve 380 causeY a corres- ~`
ponding downward movement of piston 366 and accordingly shifts the guide vanes toward the Fig. 14 position, i.e.
opens the guide vanes to increase the area ratio and reduce the pressure ratio aaross 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 aaceIerator lever 184. It will be apparent that whenever the speed of the power turbine shaft .

3~433 82 is below that selected by accelerator lever 184, the com-pression of spring 384 is reduced to tend to increase the pressure ratio across the power turbine vanes 117, 119 to tend to increase power turbine speed Npt.
The portion of vane control 66 for trimming power turbine speed in relation to accelerator position is prefe-rably primarily digital in action since as shown in Fig. 19, a small change in throttle lever position increases the re-quested Npt from 25% to 100%. The actions of valve 402, lQ piston 416 and plunger 395 are such that when the accelera- t tor is at a position greater than a*, this portion of the control continually requests approximately 105% power tur-bine 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 causes the control to request only approximately 25% of màximum N
: pt ; Thus, in normal cruise the guide vanes control 20 ` operates in conjunction with the fuel governor to maintain a substantially constant turbine exhaust temperature T4; -~ fuæl governor 60 operates to trim gas generator speed Ngg to : a value selected by the accelerator lever 184; and the hydromechanical portion of guide Yane 66 operates to trim power turbine output speed Npt to a level in relation to the position of accelerator pedal 184. It will further be : apparent that during the cruise mode of operation, the ori-fice created at opening 178 of the fuel governor is substan-tially smaller than the openings to fuel flow provided in 30 the scheduling valve 62 so that the scheduling valve 62 nor-mally does not enter into the control of the engine in this -phase.
Safetv Ove~ride .'' ': ~ , , 1~3~433 During the cruise or other operating modes of the engine discussed herein, several safety overrides are con-tinually operable. For instance solenoid 239 of the fuel governor 60 operates to essentially reduce or counteract the effect of speeder spring 224 and cause a consequent reduction in fuel flow from orifice 178 by exerting a force on fuel lever 226 tending to rotate the latter in a counter-clockwise direction in Fig. 6. As illustrated in Fig. 17, the electronic control module includesa logic element 538 which is responsive to power turbine speed Npt, gas genera-tor speed Ngg, turbine inlet temperature T4, and turbine ex-haus~ or recuperator inlet temperature T6. Thus if turbine inlet temperature T4 exceeds the preselected maximum, a pro-portional electrical signal is transmitted to lines 250 to energize solenoid 239 and reduce fuel flow to the engine.
Similarly, excessive turbine exhaust temperature T6 results in proportionately energizing the solenoid 239 to reduce fuel flow to the combustor and thus ultimately reduce turbine exhaust temperature T6. Also, logic element 438 is respon- -~
sive to power turbine speed soas~;to~prQportionately energize solenoid 239 whenever power turbine~speed exceeds a preselec-ted maximum. Similarly, the electronic control module operates to energize solenoid 239 whenever gas generator speed exceeds a preseleated maximum established by ~unation generator 514 as a function of P2, T2 and Npt. Normally the preselected maximum parameter values discussed with regard to these safety override operations, are slightly above the normal operating values of the parameters so that the sole-noid 239 is normally inoperable except in instances of one of these parameters substantially exceeding the desired value thereof. Thus, for instance, during a cruise mode of opera-tion or "coasting" when the vehicle is travelling downhill being driven to a certain extent by its own inertia, the .
.

" 1~3~33 solenoid 239 is operable in response to increase of power turbine out~ut shaft 82 beyond that desired to cut back on fuel flow to the combustor to tend to control the power turbine output speed.
While as discussed previously with regard to the t cruise operation of the vehicle, the guide vane control normally is responsive to combustor exhaust temperature T4 as reflected in the signal generator by element 435, the logic element 498 is also responsive to the turbine exhaust temperature T6 in comparison to a preselected maximum there-of 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 ele-ment 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 pres-sure 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 reduceæ fuel flow to the combustor so that turbine exhaust temperature ~6 i8 prevented from increasing beyond a pre-selected maximum limit.
As desired, the solenoid 239 may be energized in response to other override parameters. For instance, to protect the recuperator 56 from exaessive thermal stresses, the logic element 538 may incorporate a differentiator 548 associated with the signal from the turbine exhaust tempera-ture T6 so as to generate a signal indicative of rate of change of turbine exhaust temperature T6. Logic element 538 can thus generate a signal energizing solenoid 239 whenever the rate of change of turbine exhaust temperature T6 exceeds a preselected maximum. In this manner solenoid 239 can con-trol maximum rate of change of temperature in the recuperator ` 1136~433 and thus the thermal stress imposed thereon. Similarly, the logic element 538 may operate to limit maximum horse-power developed across the power turbine and/or gas gene-rator shafts.
Gear Shift Because turbine engine 30 is of the free turbine type with a power output shaft 82 not physically connected to the gas generator shaft 76, the power turbine shaft 82 would normally tend to greatly overspeed during a gear shif-ting operation wherein upon disengagement of the drive clutch34 to permit gear shifting in box 38, substantially all in-ertial retarding loads are removed from the power turbine drive shaft 82 and associated power shaft 32. Of course, during normal manual operation upon gear shifting, the accelerator lever 184 is released so that the fuel governor 60 immediately begins substantially reducing fuel flow to combustor 98. Yet because of the high rotational 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 contemplated by the present invention utilizes the guide vane aatuator control 66 to shift the guide vanes 120, 122 toward their 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 the 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 synchronous shifting of gear box 38 and consequent re-engagement of drive clutch 36 may be conveniently and speedily accemplished without damage to the engine or drive train.

~, . - .
- . : , 1~3~433 More particularly, the hydromechanical portion of guide vane control 66 is so arranged that upon release of accelerator lever 184 such as during gear shifting, a very large error signal is created by the high pressure from the po~er turbine speed sensor line 420 to rotate lever 396 counter-clockwise and substantially greatly increase the compression of spring 384. Sufficient compression of spring 384 results to urge valve 380 upwardly and drive piston 366 downwardly to its position illustrated in Fig. 12. This position of piston 366 correspon~ 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 rota-tion thereof to decelerate the power turbine shaft 82. Since the drive clutch 34 is disengaged during this gear shifting operation, the power turbine shaft 82 rather rapidly decele-rates by virtue of the opposing gas flow created by the posi-tioning of guide vanes 120 in their Fig. 16 position. Yet 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 their negative or reverse disposition illustrated in Fig. 16 and modulate guide vane position 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 of power turbine shat 82 reduces, the piston 416 begins shifting in an opposite direotion to reduce compres-sion of spring 384 once turbine speed reduces to a preselec-ted value. The action of piston 416 is in the preferred form capable of modulating the degree of compression of spring 384 in relation to the magnitude of the Npt error.

```` 113~433 The greater the speed error, the more the guide vanes are rotated to a "harder" braking position. Thus, the position of the guide vanes are maintained in a reverse braking mode and are modulated through zone "d" near the maximum braking position -95 of Fig. 18 in relation to the power turbine speed error. Once`gear shifting is completed, of course, the control system operates through the acceleration opera-tion discussed previously to again increase power turbine speed.
Deceleration A first mode of deceleration of the gas turbine engine is accomplished by reduction in fuel flow along the deceleration schedule afforded by deceleration window 286 of scheduling valve 62. More particularly, the release ~f acce-lerator lever 184 causes the fuel governor 60 to severely restrict fuel flow through opening 178. As a consequence the minimum fuel flow to the gas turbine engine is provided through deceleration fuel line 142 and the associated decele- .7 ration window 286 of the scheduling valve. As noted previ-ously deceleration window 286 is particularly configured to the gas turbine engine 50 as to continually reduce fuel flow along a schedule which maintains combustion in the combustor 98, i.e., substantially along the operating line of the ga~
turbine engine to maintain combustion but below the "required to run line". As noted previously, even without rotation of accelerator lever 184, the solenoid 239 can be energized in particular instances to generate a false accelerator lever signal to fuel lever 226 to accomplish decleration by severe-ly restricting fuel flow.
This deceleration by limiting fuel flow is accom-plished by reducing the accelerator lever to a position at or just above a preselected accelerator position, a*. This acceIerator position is normally ~ust slightly above the ,;., ,:,~

1~36433 minimum accelerator position, and generally corresponds to the position of the accelerator lever during the "coasting"
condition wherein the engine is somewhat driven by the in-ertia of the vehicle such as when coasting downhill. Since this deceleration by restricting fuel flow is acting only through governor 60, it will be apparent that the guide vane control is unaffected thereby and continues operating in the modes and conditions discussed previously. This is parti-cularly true since the accelerator has been broughtdown to, but not below the preselected accelerator position a* to which the hydromechanical portion of vane actuator 66 is respansive.
Upon further rotating accelerator lever 184 below the position a* and towards its 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 o guide vane actuator 66 to generate a substantially large error signal with regard to power turbine speed so as to rotate the guide vanes 120 to their Fig. 16 reverse or "braking" position.
More particularly, as discussed above with regard to the gear shift operation of the vehicle, this large error signal of the power turbine speed in aomparison to the acaelerator lever position causes significant aounter-clockwise rotation of lever 396 and conseque~ compression of spring 384. This drives the piston 366 and the guide vanes toward the Fig. 16 position thereof. As a result, the gas flow from the gas turbine engine opposes rotation of the turbine wheels 116, -118 and produces substantialtendency for deceleration of out-put shaft 82. It has been found that for a gas turbine en-gine in the 450 to 600 horsepower class, that this reversing of the guide vanes in combination with minimum fuel flow to the combustor as permitted by deceleration window 2~6 provides , ` 1~3~33 on the order of 200 or more horsepower braking onto the tur-bine output shaft 82.
It will be noted that during this second mode of deceleration, as well as during the gear shift operation di~cussed previously, that since the guide vanes are now in a reversed disposition, the logic accomplished by the elec-tronic control module 68 in controlling solenoid 426 to pre-vent over temperature of T4 or T6 is now opposite to that required. Accordingly, the electronic control logic further includes a transducer 544 which senses whenever the guide vanes pass over centre as noted by the predetermined angle B*
of Fig. 18, and are in a negative incidence disposition.
$his signal generated by transducer 544 energizes a reversing device such as an inverter 546 which reverses the signal to the solenoid 426. More particularly, if during this dece-leration operation with the guide vanes in the negative in-cidence position of Fig. 16, there occurs an excess combustor exhaust temperature T4 or excess turbine exhaust temperature `
T6, the signal generated by element 500 to reduce the magni- -~
tude of the current signal is reversed by element 546. Accor-dingly occurrence 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 4 32 in a direction increasing pressure in con-duit 394 and upon shoulder 393. This reduces the magnitude of the biasing spring 383 and causes valve 380 to move down-wardly. In a following movement the piston 366 moves upwardly to reduce the ¢ompression of spring '`~82. ~Thus the~guide~vanes 120 are reversely trimmed away from the maximum braking position shown in Fig. 16 back towards the neutral position of Fig. 14. This movement of course reduces the magnitude of power transmitted from the gas flow in opposing rotation of the guide vanes 117 to cause a consequent reduction in ~13~433 fuel flow as discussed previously. The reduced flow flow then reduces the magnitude of the over temperature parameter T4 or T6. Such action to control T4 or T6 will substanti-ally only occur when fuel flow being delivered to the com-bustor is more than permitted by the deceleration schedule 286. Thus such action is more likely to occur during the "coasting" operation than during hard braking during the second mode of deceleration. Such is natural with operation of the engine, however, since during hard deceleration, fuel flow to the combustor is at a minimum and combustor exhaust temperature is relatively low. However, during unusual con-ditions, and even with the guide vanes in a negative inci-dence position, the electronic control module is still operable to return the guide vanes toward their neutral posi-tion to tend to reduce any over temperature conditions.
Power Feedback Brak n~
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 dealeration 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 ~peed Npt may be in a range o approximate~y 90% of its maximum speed while the gas generator 8peed Ngg has been braught down to at or near its low idle speed of approximately 50% maximum ga~ generator speed.
This third mode of deceleration, termed pawer feed-back braking, i8 manually selected by closing power feedback switah 466. In response the electronic control module 68 generates signals which ultimately result in mechanical inter-connection of the gas generator shaft with the power turbine shaft such that the inertia of the gas generator shaft is imposed upon the drive train of the vehicle to produce "`` 1~3~33 additional braking effects thereon. More particularly, upon closing switch 466, AND gate 506 generates a signal to AND
gate 5~4 since the accelerator level is below a preselected point a* causing function generator 488 to generate a sig-nal to AND gate 506, and since the gas generator is opera-ting at a speed above 45% of itsrated value as determined by element 474. Element 472 develops a signal through line 480 to AND gate 504 since power turbine speed is greater than gas generator speed in this operational mode. Element 470 also notes that the effective relative speeds of the gas ganerator shaft and power turbine shaft are outside a pre- ~
selected limit, such as the plus or minus 5% noted at compa- i ~-rator 470. Accordingly~element 470 does not generate a sig- ~
nal to AND gates 502, 504. More specifically the element ~ -470 is not necessarily comparing the actual relative speeds of the gas generator power turbine shafts. Rather, the ;
element is so arranged that it only generates a signal to AND gates 502, 504 whenever the relative speeds of the shafts 520, 522 in the power feedback clutch 84~are within~the pre-selected predetermined limits of one another. Thus the com-; parator 468 wilI compensate, as required, for differences in the actual speeds of the gas generator and power turbine shaft, as well as the gear ratios of the two respective drive trains 78 and 80 a~aociated with the two shafts 502, 522 of the feedback clutch 84.
Because of the difference between Npt and Ngg, nosignal from element 470 is transmitted to either hND gate 502 or 504. As noted schematically by the circle associated with the input from element 470 to AND gate 504, that input is inverted and AND gate 504 is now effective to generate an output signal since no signal is coming from element 470, and since signals are being received from AND gate 506 and ele-ment 472. The output signal from AND gate 504 accomplishes 113~433 two functions. First, a signal of 50% Ngg magnitude is generated in function generator 566 and added to the con-stant 50% bias of signal of summer 570. The resulting sig-nal is equivalent to a 100% Ngg speed command. Secondly, the output from AND gate 504 passes through OR gate 562 to produce a signal to solenoid 257. This signal is of suffi-cient magnitude to shift solenoid 257 to its Fig. 6D position clearing opening 178 for substantial fuel flow to the combus-tor. It will be apparent that full energization of solenoid 257 to its Fig. 6D position is essentially a false accelera-tor lever signal to the fuel lever 226 causing lever 226 to rotate to a position normally caused by depressing accelera-ting lever 184 to its maximum flow position. Secondly, the signal from summer 570 is also an input to element 497 such that an artificial full throttle signal is generated which overrides the energization signal which is maintaining the guide vanes in their Fig. 16 braking position during the second mode of deceleration discussed previously. The ener-gization of the guide vane solenoid 426 causes increase of pressure in conduit 394 allowing the springs382-385 to shift the piston 366 and the associated guide vanes toward their Fig. 14 "neutral" position.
Accordingly, it will be sqen that the signal from AND gate 504 produaes an acceleration ~ignal to the engine, placing the guide vanes 120, 122 in their neutral position such that maximum pressure ratio is developed across the gas generator turbine 102, and at the same time fuel flow to the combustor 98 has been greatly increased. In response, the gas generator section begins increasing in speed rapidly to-ward a value such that the speed of shaft 522 of the feed-back clutch approaches the speed of its other shaft 520.
Once the power turbine and gas generator shaft speeds are appropriateIy matched such that the two shafts 1~3~33 520, 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 immediate-ly stops the output signal from AND gate 504 to de-energize 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 such .: , .
that the guide vane 120, 122 are again shited back to their Flg~ 16 braking disposition in accord with the operation dis-cussed above with respect with the second mode of delecera-tion.
The logic element AND gate 502 now develops a posi-tive output signal to operate to driver 516 and energize 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 elec-tronic control module, in addition to the other functions described previously, also assures that since the two shafts 520, 522 are in near synchronous speed, relatively small torque miss-match across the plates 524, 526 of the clutch is experienced. Acaordingly, the size of clutah 84 oan be relatively small. Thus it will be seen that the eleatronic control module 68 operates automatically first to increa~e gas generator speed to essentially match power turbine speed, and then to automatically return the guide vanes to their - Fig. 16 braking disposition at the same time as clutch 84 is engaged.
This interconnection of the gas turbine engine drive train with the gas generator shaft 76 causes the rota-tional inertia of gas generator 76 to assist in decelerating the vehicle. It has been found that for a 450 to 600 ~3~433 horsepower class engine described, this power feedback bra-king mode adds in the neighbourhood of 200 to 250 horsepower braking in addition to the 200 horsepower braking effects produced by the positioning of guide vane 120, 122 in their Fig. 16 position. Because the fuel governor is again seve-rely restricting flow through orifice 178, the fuel flow is controlled by deceleration window 286 permitting the gas generator section to decelerate while maintaining the com-bustion process in combustor 98. Thus reduction of fuel flow provides the deceleration effect of the rotational in-ertia of the gas generator upon the drive train of the vehicle . -It will be apparent from the foregoing that the ~
present invention provides substantial braking for decelera- -tion purposes while still utilizing the optimum operating characteristics of a free turbine type of agas turbine engine with the gas generator section mechanically interconnected with the power turbine section only in a specific instance of a manually selected "severe" third mode type of decelera-;20 tion operation. Throughout all deceleration modes and en-gine operation, a continuous combustion process is maintained in the combustor. Thus substantial deceleration oacurs with-out extinguishing the combustion process therein.
This power feedback brakin~ operation aan be de-activiated in several ways: manually by opening switch 466 to stop the output signal from AND gate 506; providing a NOT signal to turn off driver 516 and solenoid 518 to disen-gage clutch 84. Furthermore, if the manual switch is not opened and the engine continues to decelerate, element 474 also operates to deaativate the power feedback operation whenever gas generator speed Ngg reduces to a value below 45% of its maximum rate of speed. Also, depression of the acceIerator to a value of above a* also deactivates the power 3S~33 feedback operation by stopping an output signal from AND
gate 506.
From the foregoing it will now be apparent that ~ -the present invention provides an improved cycle of opera-tion for a gas turbine engine peculiarly adapted for opera-ting 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 greater adaptability and variability of engine opera-tion is provided. At the same time the engine can operate throughout its entire operating cycle while maintaining a continuous combustion process within the combustor 98. This avoids various problems of operation and service life asso-ciated with repeated start and stop of the combustion process.
The novel cycle contemplates a utilization of a combustor 98 having choked nozzles 102 to provide a variable pressure with-in the combustor as the speed of the gas generator section varies. Gas generator section speed is normally trimmed to a preselected value relative to the position of the accelera-tor lever 184, while the guide vanes 120, 122 operate to trim the turbine inlet temperature T4 to a preselected substan-tially constant value to maintain high engine operational efficiency. Further, the guide vane control operat~s indi-rectly to alter the fuel flow through fuel governor 60 by altering the speed of the gas generator section such that the various controls are operable in an integral manner with-out counteracting one another. At 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 inven-tion provides the gas turbine engine peculiarly adapted for driving a ground vehicle in that responsive acceleration simi-lar to that produced by an internal combustion engine is provided by both the automatic high idle operation as well as by the manner of acceleration of the gas turbine engine.
Such is accomplished by first altering the work split to develop maximum power to the gas generator 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 producing maximum acceleration without over heating the en-gine. Yet the scheduling valve also limits T6 during theinitial portion of acceleration when turbine "stalling" con-ditions are prevalent. Acceleration is then completed once substantial acceleration of the gas generator séction is accomplished, by re-altering the power split to develop greater power across the power turbine wheels 116, 118.
It is further noted that the present invention provides an improved method and apparatus for decelerating the vehicle in a three stage type of operation by first re-ducing fuel flow, then by placing the guide vanes in the braking mode, and then by manually selecting the power feed-back operation.
The primary operating elements of the fuel governor 60, scheduling valve 62, and guide vane control 66 are hydro-mechanical in nature. This, in conjunation with the opera-tion of solenoid 426 of the guide vane contral which i9 nor-mally energized, provides an engine and control system peculiarly adapted to provide safe engine operation in the event of various failure modes. More particularly, in the event of complete loss of electrical power to the electronic control module 68, the mechanical portion of fuel governor 60 continues to adjust fuel flow in relation to that selec-ted by accelerator lever 184. Scheduling valve 62 is in no way affected by such electrical failure and is capable of 113~433 controlling acceleration and/or deceleration to both preventover 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 electrical failure and capable of adjusting the guide 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 pres-sure upon face 393 of the control piston ~92. However, the speed control afforded by lever 396 is still maintained and the guide vanes can be appropriately positioned to maintain functional engine operation during this failure of the elec-trical system. Thus, while certain desirable features of the engine control will be lost in the event of eleatrical failure, the engine can still function properly with appro-priate acceleration and deceleration so that the vehicle may still be operated ln a safe manner even though at a possible -~
loss of opertional efficiency and loss of the ability to provide power feedback braking.
From the foregoing it will be apparent that the pre-~;~ sent invention provides an improved method of automatically setting and resetting the idle of the gas generator section 80 that the engine is highly re-ponsive in developing an in-crea~e in output power suah as when contemplating aaceleration of the vehicle. Further the pre~ent invention provides an improved method of controlling fuel flow hydromechanically in relation to gas generator speed, as well as overriding normal speed control operation of the fuel governor to in-crease or decrease fuel flow in response to occurrence of various conditions which energize 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 L3~;433 is maintained throughout, while also controlling fuel flowduring deceleration to avoid extinguishing the combustion process within a combustor. The invention further contem-plates an improved method of controlling guide vane position in such an engine both by hydromechanical operation to con-trol speed of a rotor such as turbine wheels 116, 118, and by electrical override operation dependent upon the amount of energization of the proportional solenoid 426.
The foregoing has described a preferred embodiment of the invention in sufficient detail that those skilled in the art may make and use it. However, this detailed descrip-tion should be considered exemplary in nature and not as limiting to the scope and spirit of the present invention as set forth in the appended claims.
Having described the invention with sufficient clarity that those skilled in the art may make and use it, what is claimed as new and desired to be sècured by Letters ~ -Patent is:

Claims (7)

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

1. A method for accelerating a gas turbine engine from a minimum idle speed, said engine including a gas generator section having a combustor receiving a flow of fuel and an inlet air flow, said gas generator section operable to develop a gas flow for separately driving said gas generator and a power output turbine section, said gas turbine engine operable to drive a ground vehicle having a final drive including a shiftable transmission, and a clutch with input and output shafts respectively connectable to said power turbine section and said final drive, said method comprising the steps of:
generating a first signal to request acceleration of said engine;
sensing clutch output shaft speed;
automatically generating a second signal antici-patory of said first signal whenever said clutch output shaft speed is less than a preselected value;
increasing the speed of said gas generator section to a second idle speed substantially higher than said mini-mum idle speed in response to said second signal whereby the speed of said generator section is at said second idle speed prior to generation of said first signal;
sensing the temperature of inlet air flow to the combustor and the pressure maintained in the combustor;
metering fuel flow to the combustor along a pre-selected empirical schedule as a function of said sensed temperature and sensed pressure in response to said first signal to maintain the temperature of gas flow exhausting from said combustor at a substantially constant level during at least a portion of acceleration of the engine; and altering the incidence of gas flow onto said power turbine section in response to said first signal to transmit a preselected maximum portion of power from said gas flow to said gas generator section.

2. A method as set forth in Claim 1, wherein said sensed temperature and sensed pressure are sensed mechanically.

3. A method as set forth in Claim 1, wherein said metering step includes controlling fuel flow during engine acceleration and deceleration along different preselected empirical acceleration and deceleration schedules.

4. A method as set forth in Claim 1, wherein said sensed pressure is gauge pressure in the combustor.

5. A method as set forth in Claim 1, wherein said altering step includes adjusting variable guide vanes asso-ciated with said turbine section.

6. A method as set forth in Claim 1, wherein said first signal is indicative of a desired gas generator sec-tion speed.

7. A method as set forth in Claim 6, including the steps of sensing actual gas generator section speed, and further metering fuel flow as a function of said sensed gas generator section speed to bring the latter to said desired gas generator speed.