Note: Descriptions are shown in the official language in which they were submitted.
5~
BACXGROU'`~D OF TIIE INVE~rrIO~
This invention relates to gas turbine engines, and xelates
more particularly to an improved gas turbine engine and method
and control thexefor particularly useful as the power plant for
S 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 competitive in many
instances with more conventional internal com~ustion 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 vehicles such as on-the-road automobiles and heavy trucks.
The gas turbine offers signiicant advantayes of equivalent or
better operational e~ficiency, fuel savings, and less emissions
as well as being able to utiliz.e a variety of diferent fuels on
an economic basis. Further, the gas turbine engine in many
instances offers greater overall economy over the entire
operational lie of a vehicle.
The inherent operational characteristics of a gas turbine~
engine present, however, certain problcmx w~len utiliæed in a
ground vehicle. More specifically, A gas turbine encJinc gcnercllly
includes a gas genexator section which prov;ides a large presc;uriGed
air flow to a combustor wherein the air flow is mixed and ignited
with fuel to greatly increase the temperature oE th~ resulting gas
flow. Hot pres~urized cJas flow then drives one or more turbines to
produce useful rotary mechanical output power. Normally one o
these turbines is a portion cf the gas generator section for driving
- 2 - ~ ~
.. . . , .. . . ~ . . . . .... .. . . . ...
3579
the fan which provides the high volume pressurized air inlet
flow. Downstream power output turbines then generate -the useful
mechanical power output. Conventionally, the high speed, high
vol~Ime gas flow from the gas genera~or drives the ~urbines at
relatively high speeds. Other inherent characteristics of such
gas turbine engines relates to the thermodynamic and aerodynamic
processes carried out therewithin which dictate that operational
efficiency of -the engine increases substantially with increasing
maximum temperatur~ of the gas flow.
These operating characteristics of a gas turbine engine
present certain disadvantages in comparison to the normal
operation of reciprocatiny or rotary pist.on type internal
combustion engines for ground vehicles. More particularly, the
internal combustion engine inherently provides a substantial
amount of deceleration horsepower for the vehicle upon reduc.inc~'
fuel flow thereto through the drag imposed by the reciprocating
portio~ of the engine. In contrast, the high rotational inertia`
of the turbines of the gas turbine engine normally do not permit
such immediate, relatively high horsepower braking for a ground
vehicle simply upon reducing fuel flow to the combustor of the
gas turbine enyine. To overcome this disadvantacJe, a variety of
proposals have been offered in the past to increase the~ bra~inc3
characteristics of a gas turb:ine eng.ine when u~ilized Eor drivincr
a ground vehicle. Primarily, these concc~t~ relake to completely
extinguishincJ the combusti.on process within the combust.or to
produce ma~imum dynamic braki.ny. Ilowever, operational l..ife oE
gas turbine engine is su~stantially reduced by continllal thermal
cycling of the entire eny.ine as created upon extinyuishing the
combustion process. Furthe.r, such approaches adversely affect
emissions. Other concepts re].ating to improvinc3 the dynamic
hrakinc3 characteristics of a gas turbine engine revolve around
the utilization of a "fixed shaft" type of gas turbine engine
~3~79
wherein the gas generator section and the po~er drive section
are mechanically interconnected to drive the vehicle. While
such an arrangement improves the dynamic bra~ing, it greatly
- reduces the adaptability of t~e engine to perform various other
processes for driving a ground vehicle, and due to this limited
adaptability has met with limited success in use as the power
source for a high-production type of ground vehicle. An
example of such prior art structure is found in U. S. Patent
No. 3,237,40~. The no~nal method for dyn~nic 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 suEfered from the disadvantage of not
providing efficient, yet highly responsive acceleration in
lS comparison to internal combustion engines. Inherently, a free
tuxbine engine nonnally requires a substantially longer time in
developing the maximum torque required during acceleration of the
ground vehicle. Prior attemp-ts to solve this prohlem have
centered about methods such as operating the gas generator at
a constant, maximum speed, or other techniques which are equally
inefficient in utilization of fuel. Overall, prior ga~ turbine
engines for ground vehicles normally have suf~ered from a reduced
operational efficiency .in attemptlng to improve the accel~ration
or deceleration characterist.ics of the engine, and or resulted
in reduced efficiency by substantially varyincJ the turbine inlet
temperature of the gas turbine engine which i5 a primary fclctor
in the fuel conswnption of the engine. Further, prior art
attempts have generally been deficient in providing a relia~le
type of control system which is effective throughout all
57~
operational modes of a gas turbine engine when operating a
ground vehicle to produce safe, reliable, operatiny charac-
teristics. ~urther, such prior art gas turbine engines have
resulted in control arrangements which present a sl~stantial
change in required operator actions in comparison to dri~ing
an internal combustion powered vehicle.
Other problems related to prior art atternpts to
produce a gas turbine engine fox ground vehicle relate to
the safety and reliability of the control system in various
failure modes, safe and reliable types of controls, and in
the overall operational efficiency of the engine. A majority
of these problems may be considered as an outgrowth of attempts
t~ provide a gas turbin~ engine presenting operational char-
acteristics duplicative of the desirable, inherent actions of
an internal combustion engine.
Accordingly, it will be seen that it would be highly
desirable to provide a gas turbine engine and associated con-
trols which incorporate the desirable operational features of
both a gas turbine and internal cornbustion engine, but while
providing an economical end product of sufficiently rcliable
and sae design for hic~h volume production basis for grourld
vehicles.
Discussiolls of exemplary prior art structure relating
to the engine of the pre~ent invcntion may be found in U. S.
Patents No. 3,237,404 discusscd above; 3,660,976i 3,899,~77;
3,941,015 all of whioh appear to relate to ;chelne~s for trans-
mitting motive power from the gas generator to tlle er,c3ine out-
put shaft, and 3,688,605; 3,771,916 and 3,938,321 that relate
to other concepts for vehicular gas turbine engines. Examples
of concepts for variable nozzle engines may also be found in
U. S. Patents 3,686,860; 3,780,527 and 3,777,479. Prior art
fuel governor controls in the general class of that contcm-
plated by the present invention may be found in U.S. Patents
3,400,535; 3,50~,395; 3,568,439; 3,712,055; .~ ..........
--5--
;35~
3,777,480 and 3,913,316, none of which incorporate reset ~nd
override features as conternplated by the present invention;
and 3,521,446 which discloses a substanti~lly more complcx
fuel reset feature than that of the present invention. Exa~ples
of other fuel controls less pertinent to the present 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 inven-
tion while patents ~,976,683; 3,183,667 and 31820b323 relate to
the scheduling valve controls.
SUMM~Y OF TE~E INVENTION
An important object of the present invention is to provide
an improved gas turbine engine and method and more particularly
arrangements exhibiting desirable operakional features normall~
inherent to piston encJines.
Another important object is to provide provisions producing
improved fuel performance .in a variety of operations of a ground
vehicle driven by a gas turbine engine.
Another important object of the present invention is -to
provide improved acceleration, deceleration characteristics for a
gas turbine driven ground vehicle, and to provicle a more reliable,
longer life y~s ~urbi.ne engine for propuls.ion or power generating
purpose~.
In summary, the invention contemplatcc: a recuperated, ~ree
tuxbine typ~ engine w:i.t:h separatc ga~, generator and power turbine
sections. A ~uel gove.rnor cont.rol~ uel flow to the combustor to
se~ gas generator speecl in relation to thu throttle lever. Rc~t
soleno:ids can overr.ide and adju~t fuel flow in response to certain
opexat.ing parameters or conditions oE cnyine operation. For
instance, in response to low speecl on the output shaft of the
drive train clutch which is indicat;.ve of an impending desireA
encJine accelera-tion for increased torque output, a rese-t solenoid
357~
increases fuel flow ana the ga~ generator idle speed to sub-
stantially reduce time required in increasing engine tor~3ue
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 per-
formance. The scheduling valve is responsive to combustor
inlet gauge pressure an~ temperature, and also c~ntrols fuel
flow during deceleration in a manner maintaining combustion.
Variable turbine guide vanes are shifted first to maximize
power delivered to the gas generator during its acceleration,
and subsequently are shifted toward a position delivering
maximum power to the power turbine section. The variable
guide vane control includes a hydromechanical portion capable
of controlling power turbine section speed in relation to
throttle position, and has an electromechanical portion co-
operable therewith to place the guide vanes in a braking mode
for deceleration. Power feedback is incorporated to provide
yet greater brakiny characteristics. When such is selected,
.0 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 sectiorl a~sist~ in retardirlg the ~ngin~
output shaft.
More specifically the present invention contemplates
a gas turbine engine fuel control system comprising a housing
~aving an inlet ~:o~ receiving pressurized fuel flow and an
outlet for delivering Euel flow to the enyine; a fuel lever
pivotally mounted to said housing with first and second arms
extending oppositely Erom the pivo-t point, said first arm
movable toward and away from an opening carrying said fuel
flow to define a variable orifice for variably me-tering fuel
~ 7 -
~143S~9
flow to said outlet; means for continuously sensing a
preselec~ed parameter of engine operation and exerting a
firs-t force on said lever in relation to the value of said
sensed parameter; throttle means for continuously exerting
a variable second force on said lever opposing said first
force, and second force being indicative of a desired value
for said preselected parameter; means for selectively exerting
a third force on said lever opposing said second force upon
occurrence of one preselected condition of engine operation;
and means for selectively exerting a fourth force on said
lever upon occurrence of another preselected condition of
engine operation, said lever operable to mechanically sum said
first through fourth forces.
These and other objects and advantages of the
present invention are set forth in or will become apparent
from the following detailed description oE a preferred embodi-
ment when read in conjunction with the accompanying drawings.
- 7a -
~3~7'3
BRIEF DESCRIPTION OF T~IE DRA~INGS
In the drawin~s:
Fig. 1 is a left front perspective illustration of a gas
turbine engine and associated drive train embodying the
principles of the present invention;
Fig. 2 is a perspective illustration of the power feedback
drive train as incorporated in the engine with po~tions of the
engine shown in outline form;
Fig. 3 is a fragmentary, partially schematic, elevational
cross-section of the power feedback clutch and associated
hydraulic system, taken generally along lines 3-3 of Fig. 2;
Fig. ~ is a partiall~ schematic cross-sectional representa-
tion o the rotating yroup oE the engine with controls associated
the~ewith shown in schematic, block diayram form;
Fiy. 5 is a right front perspective view of a portion of
the housing, ducting passages and combustor of the engine with
portions broken away to reveal in~ernal details of construction;
Fiy. 6 is a partially schematic, plan cross-sectional view
o the fuel governor 60 with portions shown perspectively for
20 better clarity of operational interrelationships;
Fig. 6a is an enlarged partial elevational cross-sectiollal
view of the fuel pump taken yenerally along lines 6a-6a of FicJ. 6;
Figs. 6b, 6c, 6d are enlarged cross-section.ll views of a
portion of the ~uel yc)ve~nor control show:ing different
operational positions of solenoid 257;
Fig~ 7 is a ~chemat:ic, cross-sect:ional and parspective
functional representat~on of sched~ll:incJ valve 62;
Fiy. 8 is a plan cross-6ectional view through one port.ion
of the scheduliny valve~;
Fiy. 9 is a plan cross-sectional view of the scheduling
valve taken generally along lines 9-9 of Fig. 8;
Figs. 10 and 11 are enlarged views of portions of valve
282 showing the interrelationship of fuel metering passages as
would be viewed respectively along lines 10-10 and 11-11 of
Fig. 7;
~ _
~3~'3
Fi~. 12 is a schematic cross-sectional representation 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 views showing
various operational relationships between the variable yuide
vanes and the power turbine blades;
Fig. 17 is a schematic logic representation of a portion
of the electronic control module 68;
Fig. 18 is a graphical representation oE 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
1.5 F.ig. 20 is a graphical representation of the relationship
of fuel flow pennitted by the scheduling valve as a function of
combustor pressure along lines of constant com~ustor inlet
temperature.
DETAILED nESCRIPTION OF THL: PREFER~cED EMBODIMENT
With reference to the fiyures, listed below are the
abbreviations uti:Lizecl in the following detailecl descript.ion
to denote var:ious parameters:
Np~ - Power Turbine 54 Speecl
Ngg o Ga~ Genercltc)r 52 Speecl
NgcJ* ~ Preselectecl G~s Gener~tor 52 Speecl
Nti = Tr~nsmissioll Input Sha:Et 36 Speecl
e - Predetermined Minirnum Speecl of
Transmission Input ShaEt 36
Wf = Fuel flow
B = Stator Vane 120, 122 Angle
B* = Predetermined S-tator Vane Angle
a = Throttle 184 Position
`'. 11~57g
a* = Preaetexmined Throttle Position
T2 - = Compressor Inlet Temperature
P2 - ~mbient Pressure
T3.5 Combustor Inlet Temperature
p3 5 = Combustor Pressure
p3 5* = Preselected Intermediate Value of
Combustor Pressure
T4 = Turbine Inlet Temperature
T6 = Turbine Exhaust Temperature
Engine 30
Referring now more parti.cularly to the drawings, an improved
gas turbine engine as contemplated by the present invention is
generally denoted by the numeral 30. As depicted in F.ig. 1 the
enyine is coupled to a subskantially standard drive train for a
vehicle, particularly a truck in the 450 to 600 horsepower class,
with a power output shaft 32 as the input to a drive train clutch
34- A transmission input shaft 36 extends between the clutch 34
and a "change speed" type of tran.smission 38. Transmission 38 is
of the manually shiftable gear type; however, it is to be under-
stood that various improvements of the present invention are
equally usable with other types of speed varying transmissions.
As is conventional the tran~miss:ion 3~ has A var.iety of differen~
positions including severll forward gears, reverse gec-ring, and a
neukral positioll. Xn the neut:ral po~.ition no power is transmitted
between the transm.~ssion .input s}la~t 36 arld the tr~rlsml~ision ou~put
shaf~ 40 which conventionally extends ko the final clrive ~2 and
drive wheels 44 of the vehicle. A manual shifting lever 46 provides
selection of the desired gear ratio, and a speed sensor 48 generates
a signal indicative of the speed oE transmission input shaft 36. As
schematically depicted in Fig. 1 and described in greater detail
hereinbelow, the speed sensor 4~ may be of any type compa-tible with
the control medium of the engine 30. Preferably, speed sensor 48
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,,, ,, , . . . . . , .. ,,, ~, ,, , . .. ,, . , . ", .. .. ... . .
~ 3~79
generates an electrical signal transmltted 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 generalor sec-
tion:52, a power turbirle 54 mounted on a shaft separate rom
that of the gas generator 52, and a recupera~or 56 that sca-
vanges waste heat from the exhaust flow from the engi~e fox
preheating the compressed fluid prior to the combustion process.
The engine further generally includes a source 58 of combus-
tible fuel, a fuel governor generally denoted by n-~eral 60
wh~ch also includes the fuel pump therein, a scheduliny valve
62 for controlling fuel flow normally during accelerat.ion or
deceleration of the engine through a fuel line 64 extending to
the gas generator section 52, and a control 66 for variably
positioning variable stator vanes included in the power tur-
bine section 54. An electronic control module 68 receives and
processes various input pararneter signals and produces output
control signals to the governor 60 and vane actuator control
66.
Conventi.onally, there is inc:luded an electrical 6to-
rage batt~ry 70 and associat~d starter motor 72 which .i.~ prc-
ferably s~l.ectively coupled to both the gas generator S2 and
a starter air pump 74. During ~;tartiny ~peration, ~.he motor
72 is energized to drive both an air starter purrlp 74 as well
as the main gas generator shaEt 76. As clearly illustrated i.n
Fig. 2, the preferred forrn 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. The two drive trains 78 and
80 are selectively interengageable through a relatively low
power, wet clutch generally denoted by the numeral 84. This
clutch is generally referred to as the power feedback clutch
and the structure thereof is described in detail below with
respect to Fig. 3, ........... ............................ ~
~1~35~9
while its ~unctional operation is described further below with
regard to the power feedback operation of the present invention.
Gas generator 52 generally includes an appropriately fi~tered
air inlet 86 through which ambient air is supplied to a pair of
series arranged centrifugal compressors 88 and 9o. Cross-over
ducting 92 carries the compressed air flow from the first
compressor 88 to the second compressor 90. The gas yenerator 52
further includes ducting 94 as depicted in Fig. 5 which surrounds
and collects the compressed air flow exhaust from the circular
periphery o the second stage compressor 90, and carries this
compressed air flow in a pair of feeder ducts 95 to recuperator
56 in non-mixing, heat exchange relationship with the recuperator.
While various ~orms o~ 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 "Metllod of
Manifold Construction for Formed Tube-Sheet Heat Exchanger",
dated July 15, 1975, issued to Fred W. Jacobsen et al. Though
not necessa:ry to the understanding of the present invention,
re~erence may be made to the above referenced pa-tent ~or a detailed
descri.ption of a recuperator and it~ operation. For purposes o~
the present inventi.on, it is su~ficienk to state that thc compressed
air flow from ducts 95 :is prellellt-ed in the recuperator by the waste
heat from khe exhaust 10w ~xom khe cny.in~. The prehc~ated,
compressed air 10w is then clucted thrc,ugh du~t 96 to a can-type
~S combustor 98. ~3 be,st scen in Fig. 5, he~clted flow Erorn khe
recuperator passes throuyh a pluralit~ o~ openincJs 97 into a
plenum portion o 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 ~rom openings 97-a
passes into the zone between the i,nner and outer liner to then
pass through the perforated inner liner 99 into the combustor zone.
One or more electrical ignition pluys 100 are suitably connected
to a source o~ high vol-tage electrical energy in a conventional
manner. The igni-ter plug i5 operable to ~aintain a continuous
- 12 ~
~3~79
combustion process within the interior of the combustor wherein
the fuel delivered from line 64 is mixed and burned with the
compressed air flow from duct 96.
The gas generator 52 further incluaes a gas genera-tor
turbine 102 of the radial inflow type. The compressed, heated
gas flow from combustor 98 is delivered across turbine inlet
choke nozæles 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 generator main shaft 76. This rotation of course
drives the two centrifugal compressors 88 and 90. Shaft 76 is
appropriately mounted by bearings 108 to the stationary housing
15 . 110 of the engine.
Power turbine section 54 generally includes a duct section
112 and appropriate vanes 114 therein for directing the flow o
gases from the gas generator power -turbine 102 -toward a pair o~
axial power turbines 116 and 1].8 mounted to the power turbine
main sha.ft 82. The power turbine section further includes sets
120 and 122 of variably pos.itionable guid~ v~lnes rcspectively
disposed ups~ream of a~soci.ated axial turbines 116, 1:l.8 and
th~ir associ.ated blaclec; ].17, 119. As d~picted irl Fi~J. 13, each
of the set~ o~ var:iable gulde vanes 120 and 122 are disposed .in
an annular array within the gas flow path and are both mounted
to a comrnon actuati.n~ mecharl.isr.l generally r~ferrcd to by the
numeral 124. The actuatincJ mechanism 124 comprises a pair of
ring years 126 and 128, one for each set of variable vanes, a
link 129 affixed to ring gear 126 and secured to rincJ gcar 128
via plate 129-a. Pivotally mourlted to the housing is a bell crank
130, and a t~isted link ].31 has opposite ends pivotally attached to
- 13 -
~1~357~
link 129 and one arm o~ ~ell cran~ 130. A linearl~ shiftable
input shaft 368 acts through a pivot link 132 and another arm
of the bell crank to cause rotation of cran}; 130 a~out its axis
133 and consequent simultaneous rotation of both ring years 126,
128. Rotation of input shaft 368 rotates each of the ring gears
126, 128 about an axis coincident with the rotational axis of
power driven shaft 82 to cause rotation of the two sets of guide
vanes in unison to various positions relative to the direction of
gas flow passing thereby. As shown in Figs. 14-16, guide vanes
120 are positioned in a central or "neutral" position of Fig. 14
causing substantially max.unum area ratio and minimum pressure
ratio across the downstream power turbine wheel blades 117 of
wheel 116 in order to minimize the amount of power transferred by
the gas flow into rotation of the turbine 116. The Fig. 14
position is graphically illustrated by the position arbitrarily
denoted O in Fig. 18. The guide vanes 120 are variably positioned
toward the Fic3. 15 position, noted as the +20 position in Fig. 18,
wherein high pressure ratio exists across blades 117 and maximum
power is transmitted frorn the gas flow to turbine 116 to rotate
the latter and transmit maximum power to shaft 82. Also, the
vanes are oppositely rotatable to the Fig. 16 position, noted as
the -95 position of Fiy. 18, wherein the gas flow is directed
by the variable vanes 120 to oppose and tcnd to retard the
rotation of wheel 116. While only vanes 120 and blades 117 are
illustrated in Figs. 14-16, it will be understood by those skilled
in the art that substantially identical operati.onal relation3hips
e~ist between vanes 122 and turbine blades 119 of -turbinc 118.
The gas ~l~w uporl ex.iting the last axial turbine 118 i5
collected in an exhaust duct 13~ wh:ich 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 gearinCJ. An air or water cooler 87
is also included to cool the lubricating fluid in engine 30 and
co~unicates with fluid reservoir 89 through hose 9~.
579
Fuel Governor 60
Referring now more particularly to Figs. 4, 6, 6A-6D, the
fuel governor 60 receives fuel from source 58 through an appropriate
filter 136 into an inlet port 138 of a fuel pump housing 140. It
will be apparent to those skilled in the art that the housing 140
is attached to and may be integrally formed with another portion .
of the main engine housing 110. The governor is operable to
schedule fuel flow output through either or both of the output
ducts 142, 144 for delivery to the scheduling valve 62. The
governor 60 is hydromechanical in nature but capable of being
; responsive to externally applied mecharical and electrical
siynals, and includes an appropriate drive connection schematically
illustrated by line 1~6, and associated speed reducing gearing 1~8
, as necessary to drive a gear 150 and drive shaft 152. Shaft 152
drives a fuel pumy in the form of a positive displac~ment rotary
gear pump 154 which receives fuel from inlet port 138 and displaces
it at a substantially higher pressure through an output conduit 156.
As clearly illustrated in Fig. 6A, the gear pump cornprises a pair
of intermeshing yeats 158 and 160, one of which is driven by drive
shaft 152 and the other of which is mounted to an idler shaft 162
journaled within housing 140. Supplied in parallel flow arrange-
ment from output conduit 156 are three passages, i.e. output duct
142, bypass bore 16~, and main flow metering passay~ 166. Contained
in bypass bore 164 is a bypass regulating valve poppet 168 slidable
within bore 16~ to variably meter excess flow frorn output condui~
156 to a return passage 170 connectcd back to the fuel inlet port
138. Pressure of fuel in bore 16~ urges poppet 168 downwardly
to increase bypass flow thrcugh passage 170, while a helical coil
compression spring means 172 acts against the pressure of fuel to
urge poppet 168 upwardly to reduce volume of flow from bore 164 to
passage 170. Through a pressure passage 182 the lower end of
bypass bore 16~ communicates with fuel supply conduit 64. Thus,
pressure of fluid in conduit 6~ is exerted upon the lower side of
bypass valve poppet 168 to assist spring 172 in opposing the
force created by the high pressure fluid in output conduit 156.
-- 15 -- .
3579
Passage 166 terminates in a metering no~,zle 174 secured by plate
176 to the housing, and having a reducecl diamete~ opening 17
communicating with a central cavity 180.
The fuel governor 60 further includes a manual throttle
input in the foxm 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 relative to housiny 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 engacJeable 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
through rollers 198. During its vertical or longitudinal shiftincJ,
spring s~op 200 is guided by a yuide shaft 202 which has an upper
guide roll pin 204 slidably extending through a central bore oE
spring stop 200. Guide rod 202 is threadably received and secured
such as by lock nut 206 to housiny 1~0.
The governor 60 fu.rther includes a mechanical speed ~ensor
which includes a flyweic~ht carr:icr 208 rigidly secur~d to rotate
with shaft 152. RotatincJ w.;.th carrier 208 are a plurality of
regularly sp~c~d flyweicJIIts 210 mountcd for pivotal movemen~ upon
pins 212 securin~ the wel.ghts 210 to carr:ier 208. Dependent upon
the speed of shcl~t :l52, the centri~ugcll f.orce cau.C,;es rotation o~
weiyhts 210 about pins 212 to cause the i.nner ends thcreof to
shiEt downwardly as viewed in E`ig. 6 and drive the inner rotating
race 214 oE 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 se~ment 220. At its lower end segment
220 carries a spriny stop shoulder 222, and a speeder spriny 224
operably extends between the s-top 222 of segmerlt 220 and the spring
- 16 -
35~9
stop 200 associated with the throttle input mechanism. Through
a prelo~d of ~pring 224 acting on segment 220 the flyweights
are normally urged upward to the zero or low speed position
illustrated in Fig. 6. Increasing speed of shaft 152 causes
downward shifting of segment 220. Thus it will be apparent that
throttle lever 184 ac-ts essentially 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
indicative of the difference between selected speed (position of
input throttle 184) and actual gas generator speed as sensed
through flyweights 210. Fig. 19 illustrates the action of spring
22~ in requesting different levels of yas generator speed Ngg, as
lS the throttle is moved through different positions, a.
Governor 60 further includes a main fuel throttle lever 226
pivotally mounted by pin 228 to housing 140. One arm 230 of lever
226 terminates in a 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 i~ movable toward and away from
meteriny orifice 178 in response to shifting of segrnent 220 to
thereby variably meter fue.l flow from passagc 166 into internal
cavity 180. It will be apparent that the rec3ulatinc3 valve poppet
168 is variably positioned .in response to the precisuxe differ~ntial
between passage 168 and conduit 64 downstrcam of the meter.in~
orifice 178 to variably meter b~pass fluld flow throuc3h passage
170 in order to maintain a substantially const~nt pressure
differential across the fluid metering oriEice cre~ted between
metering opening 178 and the arm 23~ of fuel lever 226. Thus the
xate of fuel flow delivered from passage 166 to cavity 180 and
output duct 144 is a function only substantially of the position
of arm 234 relative to meterincJ opening 178 whenever the latter is
57~
the fuel flow controlling parameter. As appropriate, ~ dam2ing
orifice 236 may be incorporated in pressure sensing line 1~2 to
stabilize the movement of bypass valve poppet 168.
A uni-directional proportional solenoid 239 has an outer
housing 238 inte~ral with plate 176 or other~lise affix~d in
stationary xelationship to housing 140. Disposed within the
housing 238 is a coi- 240, and a centrally arranged armature 2~2.
Rigidly secured to form a portion of armature 2A2 is a central
plunger shaft 244 which has an upper end engageable with lever arm
234. Linear gradient springs 246, 248 operably extend between
stops on housing 238 to engage associated shoulders on the plunger
shaft 244 to normally urge the latter to its de-energized position
illustrated. Energization of the solenoid through appropriate
electrical lead lines 250 causes upward shifting of the armature
242 and plunger shaft 244 so that the latter engages and exerts
an upward force on lever arm 234 opposinq and subtracting from
the fo.rce exerted by speeder spring 224 upon lever 226.
While the plunger shaft 244 could, if desired directly engacJe
the lever arm 234; in the preferred form a "flo.dting face"
arrangement for arm 234 is utilixed. In this arrangement a
floating flat poppet-type face 252 is carriccl within arm 234 in
alignment with metering opening 178. Thi~ float.ing face is normal.ly
spxing loaded toward the metering orifice, and the upper ~ncl of
plunger shaft 2~4 .is eng~geable thexewith. The purposc o floati.ncJ
face 252 is to compensate for manuEacturing tolerallces and to
assure that a relatively flat surface .i5 directly aligned with
metering opening 178 and l~ing perpendicular to the Eluid fl.ow
therefrom to assure proper metering of fuel thercacross. The
spring 25~ loads floating face 252 toward opening 178. Pivoting
of arm 234 against spring 254 to increase fuel flow is permitted
until face 252 contacts the upper end of 245 of plunger 244. This
stroking of arm 234 is quite limited bu-t sufficient to create flow
- 18 -
~1~357~
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-~ay solenoid 257
shown in ~igs. 6B-6D. Solénoid 257 includes a coil 258, armature
260, and plunger shaft 262 secured for movement therewith. Through
appropriate stops, centering springs 264, 266 normally urge the
plungex shaft 262 to the de-ènergized position illustrated. Upon
energization of thè coil 258 through appropriate leader lines 268,
the armature 260 and plunger shaft 262 are shifted downwardly
such th~t the plunger shaft: engages the lever arm 234 in a manner
exerting a force thereon tending to add to the force created b~
speeder spring 224 and rotating lever 226 to shift arrn 234 away
from opening 178. Housing 256 of solenoid 257 is rigidly secured
such as by bolts 272 to securement plate 176. Similar to floatincJ
face 252, in the preferred form the plunger 262 does not directly
engage the lever arm 234, but rather acts through a floatlng-type
pin 272 to e.xert 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 regardlesc. of var.iation6 in manufacturin~ tolerances,
and/or the position of lever 226 relative to its pivotal shaft 228.
Both solenoi.ds are urged to their de-energ.ized pc~ition by
linear gradi.ent sprinc3s, and unlike on-o~f, d:igital-type solenoids,
vaxiatiorl in current and/or voltage input to their coils will
cause an analog increment:al pOsition.i.nCJ o:E the plunger 2~4 of
~olenoid 239, and will move plunger 262 to either its Fig. 6-~ or
6-D position.
The plunger 262 of solenoid 257 can be shiftecl away from its
de-energi~ed Fig. 6-B state, to two different enercJized states
shown in Figs. 6-C and 6-D. One electrical input signal of
preselected,intermediate power causes the armature 262 to shift to
- 19 -
~143~79
the Fig. 6-C position moving plunger 262 until the face of i-ts
-adjustable stop nut 263 contacts the spring stop 267. This travel
of plunger piston 262 depresses plunger 272 ancl compresses spring
274 to shift arm 234 ~way from opening 178 and increase fuel flow
s until gas generator speed incre~.ses to a level corresponding to
the signal force generated by solenoid 257. Thus the plunger 272
spring 274 configuration assists in pe~nitting a less-than-maximum
power signal to produce a force of preselected magnitude on arm
234.
Another electrical input signal of greater power causes
the armature to shift to the end 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 encl to come
into direct contact with arm 234 and urge the latter to permit
maximum flow through the orifice presented between opening 178
and piston 252. As described in greater detail below energization
of solenoid 257 to its Fig. 6 D position is essentially a false
throttle signal duplicating the speed desired from the gas
generator when the throttle is depressed to its maximum fuel flow
maximum power position.
Schedulinc~ Valve 62
R~ferring now more particulclrly to Figs. 7~ cheduling
valve 62 generally includec; a housincJ 276 which m~y be intec3ral
wi.kh both housinys 1~0 and thc ~tationary engirle housing 110.
Preferabl~ housinc~ 276 ix disposed in close proximity to both the
fuel governor 60 and the combustor 98. ~lousing 276 includes an
internal bore 278 into which open the two fuel ducts 142 144 as
well as the fuel line 6~ 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
- 20 -
liL 1 ~3579
"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 cornmunication
with fuel line 64. Deceleration window 286 is in general
- alignment with fuel duct 142, and acceleration window gener~lly
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 illustrated in Fig. 9; however, the
alignment point arrangement permitting rotation of valve 282
relative to housing 276 at the end o~ spxing 292 may alternately
be accomplished via a ball 302 configuration as shown schematically
in Fi.g. 7. At the opposite end of valve 282 is a spherical ball
304 permitting rotation of valve 282 relative to a piston ~06
carried in bore 278. Attached to housing 276 is a temperature
sensitive element 312, 308, for example a thermally responsive
cylinder, whose longitudinal length varies with respect to the
temperature imposed thereon by the cJa~ or other fluid in the
temperature sensincJ chamher 310 within cylinder 312. Thc housinc3
276 is mounted relative to the cn~3ine 6uch that a portion thcrcof,
particularly cyl.inder 312 and Lhe a~90ciated chamber 310 ar~ in
communication w.ith and rnaintained at the same temperature, T3.5,
as the compre~sed air Elow b~incJ delivered into the combustor.
Thermally insulative material 311 is incorporated as necessary to
avoid overheating 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 cornbustor 98. In any case the scheduling
21 -
3~7~
valve is so arranged that cylinder 312 expands and contracts
longitudinall~ with respect to increase and decrease of combustor
inlet temperature. Valve 288 is operably engaged by the thermally
responsive element 312 through a relatively non-thermally respon-
sive ceramic rod 308. Accordingly, valve 288 is shifted loncJitudi-
' nally relative to input port 142 and opening 290 in relation to
the sensed combustor inlet temperature. Thus the metering fuel
flow accomplised by window 284 is varied in relation to the
sensed combustor inlet temperature as this window moves longitudi-
nally re].ative to opening 290.
I ~Iousing 276 further includes another transverse bore 314
j which crosses and intersects generally with the longitudinal bore
~ 276. Mounted for lonyitudinal reciprocation within this transverse
! bore 314 is a rod and piston configuration 316 which includes a
¦15 pair of diaphrac3m-type seals 318, 320 having outer ends rigidly
secured to houxing 276 by being compressed between the housing,
an intermediate sect.ion 322 and a closing plug 32~ -threadably
or otherwise secured to housinc~ 276. The inner ends of the sec~ls
1 320 are secured on the movable piston, rod conficJur~tion 316. The
seal 320 in conjunction with the cnd closing plug 32~ define an
interior pressur~ sensin~ charnber 326 to wh:ich one end oE the
piston 316 is expo.cd. Throuqh a sensinc3 ]..i.ne 328 tho cornbu.c;tor
pressuxe P3 5 such a5 COnlbU5tO.r i.nlet pre~i5ur~ iS trarlsmitted into
chamber 326 to act upon one encl of p:i.storl 316. At the opposite
end of bore 31~, a helical coil b:iLIs:;ncJ sprin~ meanF; 330, ~roundcd
to housing 276 throuyh a stationary stop 332, acts to urye the
piston, rod conficJuration 316 in opposition to the pressure in
char~ex 326. The opposite end 334 of the piston configurcltion 316
is vented to atmospheric pressure through an appropriate port 336.
A seal schematically showIl at 335, which may be of a structure like
seals 318, 320 and section 348, is also included at this opposite
end 334. Thus ~auge pressure in the combustor, i.e. the difference
S'~9
bett~een ambient pressure and the absolute pressure maintained in
combustor 98, acts upon piston 316 to shift the latter within
bore 314.
~n arm 338 is threadably secured wi-thin a transverse 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 rod, piston 316. It will therefore be apparent
that shifting of piston, rod 316 within bore 314 is translated
into rotat.ion of metering valve 282 about its major longitudinal
axis. Accordingly, the respecti.ve 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 meteriny valve 282.
Groove 3~2 permits axial translation of arm 338 along with valve
282. While the rod, piston configuration 316 ma~ be of varied
arrangements, the preferred form as illustrated in Fiy. 8
incorporates a threaded end section 3~ which acts through
appropriate spaces 346 to compress and secure the inner ends of
seals 318, 320 to rod 316 throuyh an intermed:iate section 343.
Thus, the schedulincJ valve acts as a mechanical analog
computer in multiplyiny the parametcrs of combustor pre.ssure, P3 5
and combustor inlet temperature, T3 5, ~uch tha-t the positioning of
valve 232 and the windowc; 2~, 2~6 is a Eunction oE the product
quantity of combusto:r pressure multi.plied by combuskor inlet
2~ temperature.
Conventionally, as shown in Fiy. q the controls for enyine
30 further includes a normally open, solenoid operated fuel
sequenciny solenoid valve 350 as well as a manually or electrical
solenoid operated shut-off valve 352. These valves are disposed
downstream of schecluling va].ve 62 and in the preEerred form may be
included within and/or adjacent to the housing 276 ~of scheduling
valve 62.
- 23 -
~3~79
The configuration of each of the windows 284, 286
as illustratea in Figs ~ and 9 are determined to ~olve a
qualitative empirical formula of the following fo~n:
Wf (Kl 2 3.5) 3.5 3 3 5
where: Kl, K2 and K3 are constants determined by
the operational characteristics of a particular gas turbine
engine and are reflected by the configuration of wind~w 284
and associated opening 290.
By proper formulation of the window 2a4 and opening
290, the solution to this equation as accomplished by schedu-
ling valve 62 holds a constant ma~imum turbine inlet tempera-
ture T4 during all or at least a portion of gas generator
acceleration. Accordingly, when window Z84 is the controlling
parameter for fuel flow, scheduling valve 62 empirically by
mechanical analogr controls fuel flow to maintain a substanti-
ally constant turbine inlet temperature, T4. Window 284 i5
the primary operating parameter during acceleration of the
enyine as described in greater detail below. In contrast,
window 286 is the controlling parameter during enyine decelera-
tion. While acceleration window 284 is contourcd to Jnaintain
a substantially constant maximwn yas generator turbine inlet
temperature to provide maximwn acceleration pcr~ormance within
tlle tem~erature limitations of the enyine, the deceleration
window 286 is contollred to limit and control fuel fluw to pre-
vent loss o~ combustion while af~ordin~3 suhstantial decc-lera-
tion of the engine. ~n extensive di~cussion of operation of
a similar type of tur~ine inlet temperature computing valve,
but which utilizes absolute rather than gauge col~ustor pres-
sure, may be found in United States Patent Application No.
30 689,339 of Rheinhold Werner, filed May 24, 1976, now V. S.
Patent No. 4,057,960.
-24-
~1~3S79
Vane Ac-tuator 66
Details of the vane actuator control 66 are illustrated in
Figs. 12 and 13. The vane control is hydromechanical in nature
and generally includes a housing 354 having a pair of hydraulic
pressure fluid supply ports 356, 358 respectively receiving
pressuri~ed fluid from a high pressure pump source 360 and lower
pressure pump source 362 each of which are driven through the
auxiliary power system of the engine. It is understood that the
pumps 360, 362 may provide various other functions within -the
engines also such as lubrication.
Housing 354 has an internal, fluid receiving cylinder 364
in which is reciprocally mounted a piston 366 dividing the
cylinder into opposed fluid pressure chambers. Rod or shaft 368
carried with piston 366 extends exteriorly of housing 354 and
is operably connected with the bell crank 130 of Fig. 13 so that,
as described previously, linear reciprocation of rod 368 causes
rotation of bell crank 130, ring gears 126, 128 and the sets of
variable guide vanes 120, 122.
High pressure hydraulic fluid from inlet port 356 is
delivered into a bore 370 within housing 354 located adjacent
cylinder 364. Also intersecting at sp~ced location~ along bore
370 are a high pressure fluid exhaust duct 372, and a pair of
fluid work conduits 37~, 376 re~pectively communicatiny with the
cylindex 364 on opposed sides of pi~ton 366. Mounted for
reciprocation within bore 370 i5 ~ dir~ctional fluid control valve
element 380 which is nominally yositionable in the open center
po ition illustrated wherein high pressure hydraulic fluid from
duct 356 communicates only with the eYhaust port 372. A series
of centering springs 382, 383, 384, 385 normally urge valve 380 to
the position shown. Valve 380 i5 of the-four-way type
and is shiftable one direc-tion to direct high pressure fluid from
- 25 -
~3~i79
port 356 to conduit 374 and the uppe~ side of piston 366, while
through conduit 376 the lower side of the cylinder carryin~ piston
366 is vented to a low pr~ssure return 386 via bore 370, and
communicating conduit 388. Valve 380 is shiftable in an opposite
direction to direct pressure fluid from inlet 356 to conduit 376
and the lower side of piston 366, while conduit 374 communicates
with return 386 throuyh a chamber 378 and return line 379. It
will be noted that piston 366 cooperates with housing 354, such
as with a circular wall protrusion 390 thereof to prevent fluid
communication between chamber 378 and c~linder 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 383-38S provides a high gain response
requiring large movement of piston 366 (e.g. 14 times) to
counteract as initial movement of valve 380 and return the valve
to its center position. Thus it will be apparent that piston
366 acts in servo-type following movément to the movement of an
"input piston" in the form of valve 380.
In bore 370 is a stepped d.iameter piston mech~nisln 392
shiftable in response to the rnagnitud~ of fluid pressure from
a conduit 39~ acting upon a shoul,der 393 of p:iston 392. ~iston
392 presents an adju.stable stop Eo.r vary:inc3 the compressive forcc
of spr.iny 383. Pressure ac-t:iny on shouldor 393 is opposed by a
spriny 385. Slidably extending through the cerltc:r o~ element 392
is a rod 395 which acts as a vari~bly positionabl~ ~:top upon the
spring 384 extending between the upper end of rod 395 ar-d valve
380. Rod 395 is longituclin~lly shiftable in response to rotation
of a fulcrum type lever 396 pivotally mounted to housiny 354 at
pivot 398.
- 26 -
~3~7~3
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 18~ of the engine ~cts to
depress a variably positionable spring stop 404 to increase the
force exerted by compression spring 406 in urging valve 402
downwarclly. Opposing spring 406 is a gradient compression,
helical coil spring 408 Valve 402 is variably positionable to
me~er hydraulic flow from port 358 to conduit 410. It wil:L 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. Conduit 410 leads to the larger face o~ a stepped
piston 416 reciproc~lly mount-ed within another bore 418 in
housing 354. One end on bore 418 is in restricted fluid
co~nunication with return 387 through an orifice 419. 'rhe
smaller diarneter section of stepped piston 416 receives pressuri~ed
1uid from conduit 420. Through an appropriate exhaust conduik
424 the intermediate section of the stepped piston, as well as
the upper end of valve 402 are exhausted to low pressure return
3~6 through the conduit 388.
Conduit ~20 provides a hydraulic sicJnal indicative. of the
speed of the power tu~hine shaft 82. In this collnect:ion, the
vane actuator inc:ludes a non-posi.tive clisp~ cernent type hydrLIul.ic
purnp, such as a ccnt.r:ifuc3cll purnp ~2? moullted to and rotated by
power turbine shaEt 82. Being a non~posit.ive d:ic;pLcrcernent type
pulnp, the pump 422 de:L:ivers pres~;ur:ized hydrclul.ic ~I.ow thrc~ugh
concluit 420 such that the pressure mainta:irled on the smaLler
diarneter oE st~pped piston 416 is a square funct.ion of the sp~ed
of power turbine shaft 82. Sirni:Larly, -the act.ion of throttling
valve 402 dev~lops a pressure on the large diameter of piston
416 in relation to ~ desired or selected speed reflected by the
position of the thxottle 184.
- 27 -
5~9
The valve 402 and piston ~]6 act as input signal means
and as a comparator to vary the compressive force of spring
384 as a function of the difference or error bet~een actual
power turbine speed and the power turbine speed requested by
throttle position. The requested ~pt is graphicall~ illustrated
in Fig. 19.
The vane actuator control 65 further includes a linear,
proportional solenoid ac-tuator 426 operably connected 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 therewlth a hydraul:ic
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 proportionàlly shiftable do~nwardl~
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 39~ increases proportionately
to the magnitude of the electronic signal, such pressure heing
essentially zero .in the absence of an energizati.on signal to
solenoid 426. It wi].l be noted that minimum pressure in conduit
39~ allows spr.ing.s 383 and 385 to exert maxirnum upward force on
valve 380, and that increasillg pressure in conduit 39~ 6hifts
piston 392 downwardly to reduce the forcc exerted hy sprincJs
333 r 385 upon valve 380, thus c1evelopilly arl over.ride force in the
form of reduced force from spring 383.
In the absence of an elec-tri.cal signal to solenold ~26
minimum pressure ifi exerted on shoulder 393 causing the guide
~anes to be controlled by power turbine speed. Thus, the guide
vane~ during start-up are at their Fig. 14 position and at other
conditions of engine operation are normally urged to maximum
power, Fig. 15 position.
- 28 -
579
As shown in Pig. 18, vane actuator 66 is operable to vary
guide vane angle, B, from O to +20 to alter t~e positive
incidence of gas flow upon the pOwer turbine blades and thus
alter power transmitted fro~,l the gas ~low to xotate 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 signals indicative of power
turbine speed (Npt) through a chopper 436 secured to power turbine
shaft 82 and an appropriate magnetic monopole 438 which transmitsan electronic signal indicative of power turbine speed through
lead line 440. Similarly, gas generator speed, Nggl is sensed
through a chopper 44Z, monopole 444 and lead lines 446. Trans-
ducers 448, 450, and 452 respectively generatc electrical input
signals indicative of the respective temperature sensed thereby,
i.e. compressor inlct temperature T2, turbine inlet temperature
T4, and turbine exhaust temperatuxe T6. As illustrated these
temperature signals are transmitted through l.inecs 454, ~56 and
458. The electronic control module also receivec; from an
ambient pressure sensor ~60 and assoc;.ated llne ~62 an electrical .
signal indicativc- o~ ambient pressure P2. The electronic control
module further receivcs from an appropria-te sens.incJ device an
electrical signal through lines 464 indicative of throttle 184
pcsition, "a." ~lso, a switch 466 is manually settable by the
vehicle operator when power feedback braking (described more in
greater detail below) is desired. A transducer 544 generates a
signal to an inverter 546 whenever the variable guide vanes are
- 29 -
~3~79
moved past a predetermined positîon B*.
¦ The electronic control module includes several output signals
! to energize and/or de-energize the various logic solenoids and
' relays including solenoid 518 through line 519, solenoid 257
.5 through line 268, fuel sequencing solenoid 350 through associatedline 351, fuel trim solenoid 239 through line 250, and the vane
~ solenoid 426 through line 427. The electronic control module
¦ includes function generators 514, 550 and 552. Box $14 is denotedas a "flat rating and torque limiting" func-tion 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
¦ 15 speed Ngg from line 446. The module further includes comparators
497, 534, 540, 554, 556 as well as the logical elements 498, 500
and 538. The logical elements are of the "lowest wins" type, i.e.
' they pass the algebraically lowest input signal.
The logic element 498 selects rom the signals 536 and 542
which have been generated in comparators 534 and 540 inclicating
the amount of over or undertemperature for T~ and 'r6. An
additional input Erom 456 is provided to lo~ic elernent 498 so as
to provide an indic~ltion of excessive T~ figures in the case o a
failed T4 sensor signal. The loqic element 500 receives inputs from
497 and 498. Comparatox 497 compares the electronic ~peed re~quest
with the actual yas generator speed ~46 to detcrmine if the engine
has been requested to accelerate or is in steady stcl~e. The
output of loyic element 500 is fed to inverter 546, generating
an appropriate signal in solenoid driver 558 which then moves
trim solenoid 426 a distance proportional to the magnitude of
signal 427.
~_ 30 -
~ ~35~3
The logic element 538 receives its inputs from comparators
554 and 556, logic element 49~ and a differentiator 548. As
noted, logical element 498 indica~es the lower of the two
temperature errors T~ and T6. The output of comparator 556 is
the error between the operator requested power turbine sp~ed Npt
and the actual power turbine speed Npt. The output of comparator
554 is indicative o~ the difference between the maxim~n 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 driver 560
with an output on line 250 which is passed on to the governor
reset decrease solenoid 239 in the fuel control 60.
As depicted in Fig. 17, the electronic control module
includes a comparator 468 and s~nthesizers or function generators
4~0, 472 and 474. Function generator 470 produces an output
signal in line 478 indicative of whether the difference between
power turbine speed and gas generator speed is less than a
preselected maximum such as five percent. Function generator
472 produces a siynal in line ~80 showing whether or not power
turb.ine speed i5 greater than gas generator speed, while function
generator 47~ gerlerates a signal in lines ~2 showing whether or
not gas generator speed is c3reclter tharl ~5 percent of its ma~.irnum
speed. The control log:;c further inc:Ludes functiorl yenerator ~6
and 488 which respectively gen~rate siynals in associated l:ine
490 and 492 showing whether or not translnissiorl :input speed i.s
above a preselected m.in.imum "e" and whether thxottle position is
below a preselected throttle posit.ion a*. Throttle position "a"
is obtained from a suitable pos;.tion sensor such as a variable
resistance potentiometer. Thus, output signal 464 is indi.cative
of throttle position "a."
- 30~ -
~1~35~
The electronic control module further includes the logical
gates 502, 504, 506, 508 and 562. Logical AND gate 502 receives
inputs from line 478 and ~ND gate 50O to produce an output signal
to solenoid driver 516 to activate power feedback clutch 84.
Logical AND gate 506 receive~ 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~O gas
generator speed signal and also enables solenoid driver 56~ through
OR gate 562 to produce the "a" signal in line 268 which is the
result of a constant 50% si.gnal plus the output of element 566.
Signal 26B then activates the governor reset increase solenoid
257 in the fuel control 60. Logical AND gate 508 receives its
inputs from lines 490 and 492. Its output signal generates a
:15 20% gas generator signal through function generator 568 which,
added to the constant 50% signal by su~ner 570 results in a
fast idle signal (7.0% gas genercltor speed) to the governor reset
increase solenoid 257. The output of AND gate 508 also generates
the enable signal to solenoid driver 564.
- 30b --
3S7~
Power Feedback Clutch 84
While various forms of clutches could be utilized
for power feedback clutch 84, the preferred form shown in Fiq.
3 comprises a "wet" type hydraulically actuated clutch which
incluaes a shaft 520 from the gear train ~8 associatea with
gas generator shaft 76, and a shaft 522 interconnected with
the gear train 80 associated with the power turbine output
shaft 82. The clutch operates in a continual bath of lubri-
cating cooling fluid. The ges generator shaft 520 drives a
plurality of discs 524, which are interposed in discs 526 con-
nected to the output shaft 522. The clutch actuator is in a
form of a solenoided operated directional hydraulic control
valve 518 which, in t:he energized position illustrated, ports
pressurized fluid such as from source 362 into a fluid pres-
sure chamber 528 to urye piston 530 against the urgings of a
xeturn spring 532 to force the plates 524, 526 into inter-
engagement such that the power from ~haft 522 may be fed back
to s~as generator shaft 520 to assist in braking. When the
solenoid actuator 518 is de-energized, the chamber 528 i6 ex-
20 hausted to a low pres;ure drain to permit the spring 532 to
shift piston 530 away from the position shown and disengaye
the plates 524, 526.
OPE ~AT-.tON
Starting
-
In a conv~antiorlal maTIner start mot:or 72 is electri-
cally energized to initiate rotation of ga~; clenerator drive
shaft 76 and the input shaft 152 of fuel governor 60~ The
control module 68 energizes the normally open fuel sequence
solenoid 350, and solenoid 352 is also in an open position to
30 clear fuel line 64 for delivery to the combustor. As neces-
sary, an assist pneumatic pump 74 delivers pressurized air
into cornbustor 98 along with the action of ignition plugs 100.
Motor 72 is utilized to drive the various components described
--~1--
~ .t~
until the gas generator ~ection reaches its self-sustaini~g
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 1~8 to
permit 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 flow
through line 64 to the col~ustor.
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 to maintain
a low idle value of approximately 50~ of maximum gas generator
rated speed. Accordingly, the mechanical flyw~iyht governor
operates in opposition to speeder spring 224 to adjust ~uel
lever 226 and maintain fue~l flow t:hrough orifice 178 to hold
gas genercltor speed at a nomirlal 50% of maximum. This 50% low
idl~ speed is eff~ctive whenever ~:>roportional solcnoid 257 i~
in the de-energi.zed state i.llustrated in Fiy. f,.
The electronic control module 68 normally maintai.Jls
solenoid 257 in the de-energized state to ~elect 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 occurs whenever the clutch 34 is engaged with transmis-
sion 38~in its neutral position~ or whenever the vehicle ismoving regardless of whether or not the clutch 34 is engaged or
disengaged. Accordingly, during idlin~ when not anticipating ac-
celeration o~ the engine, the comparator 486 of ~he electronic
_3~_
~ ~3~79
col~trol module 68 not~s that the speed of shaft 36 is ab~ve
a pre-determined minimum, "e", such that no signal is trans-
m:itied from comparator 486 to AND gate 508. Solenoid 257
remains de-energized, and the gas generator speed is ~ontrol~
led by the governor to approximately 50% its maximum speed,
Hi~h Idle
Maximum power is normally required to be developed
from an en~ine driving a ground vehicle upon initiating acce-
leration of the vehicle from a stationary or su~stantially
stationary start. As a natural consequence of normal engine
operator action upon starting from a stationary start, trans-
mission input shaft 36 comes to a zero or very low rotational
speed as clutch 34 is disengaged while gear shift lever,46 is
articulated to shift the transmission into gear, Once the
speed of shaEt 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%, ~o that ~u~ner 570 provide~ a 70% con~and
signal to solenoid driver 564 that has been abled through the
output of AND gate 508 and OR yate S6'~. Accordingly, solenoid
257 is energized by an appropriate current signal throu~h line
268 to shift to its Fig. 6C posikion. In this position the
solenoid 257 has been sufficiently energizecl to drive shaft
262 and,plunger 272 downwardly as viewed in Fig. 6C and exert
a force on fuel lever 226 tending to rotate the latter away
froïn and increase the size of orifice 178. The additional force
exerted by solenoid 257 is sufficient to incrcase fuel flow
through orifice 178 to increase gas generator speed to a pre-
determinedhigher level such as 70% of maximum gas generator
:~-33-
~3~i7~
speed. The flyweight governor operates to hold -the yas gene-
rator speed constant at this level.
In this manner, the idle speed of the ~as generator
section is reset to a higher value in anticipation of a re-
quired accelexation such that more power will be instantly
available for accelerating the vehicle. At the same time,
when acceleration is not anticipated; ........................
-33a-
1~35~3
as determined by whether or not transmissio~ input shaft 36 is
rotatinc~ or station~ry, the electronic control module 6~ 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 ~uel
consumption of the engine is maintained at a substantially lowex
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 governor 60 this
generates a gas generator section speed error signal in that the
depression of lever 184 rotates shaft 192 to increase compression
of speeder spring 224 beyond tha-t force being generated by the
mechanical flyweight speed sensor. Fuel lever 226 rotates in a
20 direction substantially clearing the openiny 178 to increase fue]
flow to the combustor.
At the same time, depression of throttle lever 184 generates
a power turbine section speed error s.ic3nal to vane ackuator control
66. More particularly, depre~s.ion of throttle 18~ compresses sprin~
406 to shi~t valvc ~02 downwardly and .increase the pressurc main-
ta.ined in cha~lber 41~ substantially beyond that beincJ g~nerated
by the hydraulic speed signal generator of pressure developed by
pump 422 and exerted on the other side of the step piston ~16.
Accordingly, lever 396 is rotated generally cloc~wise about its
pivot 3~8 in Fiy. 12, allowing downward retraction, if necessary,
; of plunger 395 and reduction of compression on spring 384.
-- 3~ -
3579
Summer 497 of the electronic control m~dl~le deter-
mines a large disparity between accelerator position and gas
generator speed to develop an elec-tronic signal to element
500 overriding other signals thereto and reducing the siynal
in line 42~ to zerO to de-erlergize the solenoid 426 of guiae
vane control 65. The spring bias urges plunger 430 and valve
432 to the posi~ion shown in Fig. 12 to minimize hydr~ulic
pressure developed in conduit 394 and exerted on piston shoul-
der 393. As discussecl above in the vane control 66 descrip-
10 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 rninimizing power transfer to the power tur-
bine vanes. ~ore particularly, the guide vanes 120 are disposed
in their Fig. 14 position to reduce the pressure drop or pres-
sure ratio across turbine blade~ ll7 to a minim~n value, this
position correspondirlg to the 0 position of Fig. 18.
Since the nozzles 104 maintain the combustor 98 in a
choked cond.ition, this reduction in pressure ratio acrc~ss the
turbine blades 117 creates a ~;ubstarlti.al increasc i.n pressllre
ratio across the radial inflow turbi.ne 102 of the cJas, genera-
tor section. Accordin(31y posi.ti.oning of the gui.de vanes in
their Fig. 1~ position by allow.iny the springs 382-385 to
position valve 3S0 and piston 366 in its "neutral" poSitiQn~
alters the power spli.t between the gas generator turbine 102
and the power turbines 116, 118 such that a preselçcted maxi-
mum portion of power from the motive gas flow is transmitted
to the gas generator turbine 102. As a result, ~aximum acce-
leration of the gas generator section from either its low or
high idle setting towarcl-its maximum speed ... .... .......
-35-
~35~
is achieved. As noted previously, the requirement fo~ impending
acceleration has been sensed, and the engine is normally already
at its high idle setting so that gas generator speed promptly nears
its maximum value.
As gas generator speed increases, the combustor pressure P3 5
accordingly increases. This causes rotation of the metering valve
282 of the fuel schedule control 62 to increase the amount of overlap
between acceleration schedule window 284 and opening 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 recuperator 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 windo~ 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.s, at the sensed gauge pressure P3 5 ~o produce a
desired combustor exhaust or gas generator turbine inlet temperature
T4.
This increase ln fuel 10w created by the rotation of valve
282 and as compensatcd by axial translation of the v~lve provides
an "effective" fuel Plow ~hat increases power de~ve10ped and
transmitted from the gas 10w to ga5 gerlerat:or turbine 102. ~r)lls
then causes another increase in c3as generator speed, and colnbustor
pressure P3 S 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 relatively
constant, high value. In this manner the gas generator section is
accelerated most rapidly and at maximum efficiency since the turbine
inlet temperature T4 is maintained at a high, constant value.
- 36 -
43~
While the accelera-tion window 284 and openi~ 2~0 may be
relatively arran~ed and configured to maintain a constant T~
throughout acceleration, a preferred form contemplates maintaining
a substantially constant T4 once the power turbine has initia-ted
; rotation, while limiting turbine outlet or recuperat~r inlet
temperature during a first part of the acceleration operation. In
this manner excessive T6 is avoided when the power turbine section
is at or near stall. More specifically, it will be noted that upon
starting acceleration of the vehicle, the free power turbine secti.on
54 and its shaft 82 are st.a-tionary 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 flowing through the power turbine section,
and the recuperator inlet temperature T6 starts approaching the
temperature of gas flow exiting the gas generator radial tuxbine 102.
If combustor exhaust or gas generator turbine inlet temperature T4
is maintained at its maximum constant value at this time, it is
possible that T6 may become excessively high in instances of high
inertial load which lengthens the time of this substantial "stall"
condition on the power turbine sec tion. Of course, as the pow~r
turbine sect.ion overcomcs the inertia and reaches higher speeds,
temperatu.re drop ac.ross the power turbines increaseC; to ho:Ld down
recuperator inlet tempcrature T6.
For such free turbine type ~ngines, rc:lative].y compl.icated
: and cxpense controls, electronic and/or mechan:lcal, are normal.:Ly
expected in order to avoicl exces~:ive T6 while p.rovid.ing responsive
acceleration under the cond:itions in questioIl. ~n i.mportan-t discovery
of the present invention, as ~mbodied in schedul.ing 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 acceleration.
At the same time this improved arrangement has eliminated the need
for compensation for substantial variations in ambi.ent pressure and
- 37 -
3579
thus the need to compensate for the variations in altitude
that would be expected to be enc~untered by a ground vehic1.e.
In this connection it woul.d be expected that absolute combustor
pressure P3 5 must be the pararneter in solving the eq~ation
described previously such that the scheduling valve could
reliably compute the turbine inlet temperature T4 created by
a particular combination of combustor pressure, P3 5, and in-
let temperature, T3 ~.
However, a discovery of the present invention is
10 that by proper selection of the constants Kl, K2 as embodied
in the si.æe and configuration of openinys 284, 290, and by
utilization of coJ~bustor gauye pressure rather than combustor
absolute pressure~ mechanically simple and economical struc-
ture with minimum control complexity can accomplish the desired
control of both T6 and T4 durin~ acceleration. Window ~84 and
opening 290 are relatively arranyed such that when valve 282
rotates to a minimum 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
20 valve 282 is still capable of translating axially. This gi~es
rise to the thi.rd term, K3T3 5, in the equcltion set forth
above and dictates an initial condîtion of fuel flow when
window 284 becomes the controlling uel flow parameter upon
~tarting acceleration.
The constants Kl, K2 are chose~n, thei.r ~ct:ual ValllCs
beiny determined by the aerodynalnic and thcrmodyn.~nic charac-
teristics of the engine, such .that ~t a prese].eeted value,
P3 5*, intermediate the maximum and minimum values thereof,
the acceleration window controls fuel flow to maintain a con-
30 stant T4. At combustor pressures below this preselected value,
the acceleration window provides fuel flow allowing T4 to re-
duce ~elow the preselected maximum desired level therefor. It
has been found that an inherent function of using gauge com-
bustor pressure rather than absolute . ~ t
-38-
57~
pressure, in combination with these chosen values of ~ K2 and a
preselected minimum f~lel flow at minimum P3 5 ~sdetermined by K3 ,
is that fuel flow is controlled by the acceleration window to
prevent recuperator inlet temperature T6 from exceeding a preselec-ted
value. This approach still utilizes the simple geometry of window
284 and 290, both rectangles, that mechanically compute the product
j of T3 5 multiplied by P3 5. Accordingly, at pressureslower than P3 5*
which are characteristic of the conditions under which the turbine
I section "stalling" occurs, the utilization of gauge combustor
pressure prevents potentially damaging excessive T6 . The design
point for window 284 is, of course, the condition of maximum vehicle
inertia experienced on turbine shaft 82, lesser values of such
inertia naturally permittincJ more rapid turbine shaft speed increase
and less time in the "stalling" condition above described.
~15 From inspec-tion of the equati.on solved by valve 282 it will be
¦ apparent that Euel flow Wf is a linear or straight line function of
¦ P3 5 asshown in Fi.g. 20, with a slope determined by Kl and K2, an
t intercept specified by K3, and pasSincJ through the po.int produclng
~ the preselected turbine inlet temperature T4 at the selected
120 intermediate value P3 5*. Of course, a fam.ily o such straight line
I curves o~ W~ vs. P3 5 results ~or d:iferent values of T3 5 While,
j if desired, curve itting o~ w.indow 2~4 and opening 290 could be
utilixed ~o maintain T~ at prec.isely ~he same value at pressures
at and above thc preselected interrllecli.ate P3 5*, in the preferred
Eorm eompound curva~ure of the window and openi.ncJ is not utilized.
Instead, the winclow and opel-ing are of rectancJular conigurati.on
thus permi-tting T~ to increase very slightly at cornbustor pressures
above P3 5*. However, it has been found that such arrangement
affords an excellent, praetical approximation to the theoretieal.ly
desired precisely constant T4 , resulting in practical effect in
maintaining a substantially constant T4 at a desired maximum value
once combustor gauge pressure exceeds the preselected level P3 5*.
- 39 -
~3~79
~ccordincJl~, the presen-t invention inherently limits recuperator
temperature T6 to solve the probl~n of recuperator overheati.ng
when starting to accelerate a high inertial load, yet still maintains
a maximum T~ for high engine efficiency throughout the remainder of
acceleration oncc the inertia is substantially overcome ancl for the
majority of time during acceleration. ~t the same time, and contrary
to what might normally be e.xpected, it has been found that the need
for altitude compensation is obviated since there exists a minimum
fuel flow at minimum co~bustor pressure, which minirnum fuel flow
varies linearly with combustor inlet temperature T3 5. Thus the
present invention provides a simple mecha~ical solution to the
interdependent and complex problems of limitiny two different
temperatures T4, T6 for different purposes, i.e. avoidinq recuperakor
overheating while affording high engine operating eficiency and thus
highly responsive accelerati.on.
: As the yas yenerator cont:inues to accelerate, the fl.yweight
governor 208 of the fuel governor 60 begins exerting greater
downward force to counte:ract the bias of speeder sprinq 224.
Accordingly, the fuel lever 226 begins rotating in a generally
counter~clockwise direction in ~ig. 6 to begin meter:ing fuel flow
through opening 178. O11Ce the opening 178 becomes smaller than that
afforded by meter:iny window 2~ in schedulding valve 62, the operation
of the scheduling valve i~ overr.idden and the fuel governor 60 begins
controlliny ~uel flow ko the combustor in a manner ~ri.mmirlcJ gas
~enerator speel to match the speed selected by the .rotatiorl oE th~
sha~t 192 as~oci.at.ecl witl1 thc-~ acce].exation lever 18~ :in the fuel
governor 60.
Similarly, this increase in gas generator speed is sensed
in the electronic control module 68 by summer 497 such that once
:; 30 gas generator speed Ngg approaches that selected by the position of
; the accelerator pedal as sensed electronical.ly through line 46~, the
?. override signal generated by surnmer 497 is cut oEf. In response,
~; elernent 500 is allowed to generate a signal energizing the
proportional solenoid 426 of the guide vane control 66. Valve 432
. .
- 40 -
~1~3579
~sscciated with solenoid 426 is shifted to increase pressure
exerted upon piston shoulder 393 to permit the piston 366 and
the suide vanes to shift from the Fig. 14 disposition thereof
towards the Fig. 15 position. This shifting of the guide vanes
from the Fig. 14 to the Fig. 15 position again alters the wor~
split between the gas generator turbine 102 and the power output
turbines 116, 118 such that g~eater power is developed across the
output turbines and transmitted to output shaft 82 while a lesser
portion is transmitted to turbine 102~
Thus it will be apparent that acceleration of the engine
and vehicle occurs by first altering the work split so that
maximum power is developed acxoss the gas generator turbine 102,
then increasing fuel 10w alony a preselected schedule to regenera-
tively further increase power developed across the gas generator
while main:taining turbine combustor exhaust temperature T4 at a
substar;tially constant, preselected maximum. Once substantial
acceleration of the gas generator section has been accomplished,
the guide vanes are then rotated to alter the power or work split
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
~ uring normal cruise operation (i.e. traveliny along at a
relatively constant speed or power output level) the ~uide vane
control 66 acts primarily to al~er the work split bekween the gas
generator turbine 102 and the power output turb:ines 11~, 118 so as
to maintain a substantially constan~ combustor exhaust temperature
T4 . This is accomplished by the electronlc control module which
includes a summer 534 developiny an output signal in llne 536 to
the logic box 4~8 indicative of the difference between the actual
and desired turbine inlet temperature T4. ~lore particularly, solenoid
426, as discussed previously, is maintained normally energized to gene-
rate maximum pressure upon the piston shoulder 393 of the guide vaneactuator. For instance, assuming that ~4 is above the preselected
.
,357~
desired value thereof, a signal is generated to line 536 and
element 498 to reduce the mac~nitude of the electric signal
through line 427 to solenoid 426. Accordingly, the spring bias
43-l of the solenoid be~ins urging val~e 432 in a direction
reducing fluid communication between conduits 372 and 394 while
correspondingly increasing communication between conduit 394 and
exhaust conduit 386. The reduction in pressure exerted upon
piston 393 accordingly allows spring 385 to increase the spriny
bias of spring 383 to cause upward travel of valve 380 and
corresponding downward travel of piston 366 to drive the vanes
backwards from their Fig. 13 disposi-tion (-~20 position of Fig. 18)
toward a wider open position increasing the area ratio and reducing
the pressure ratio across the vanes of the turbines 116, 118.
Accordingly, in response to T4 over-temperature, the guide vanes
~5 are slightly opened up to reduce the pressure ratio across the
turbines 116, 118. In response the increased pressure ratio across
gas generator turbine 102 causes an increase in gas generator speed.
Such increase in gas generator speed is then sensed by the flywe.i~ht
governor 208 of the fuel governor 60 to cause counter-clockwise
rotation of fuel lever 226 and reduce fuel flow through opening 178.
The reduc-tion in fuel to the combustor 98 accordingl.y reduces the
combustor exhaust or turbine inlet tempcrature T4 toward the pre-
selected value thereoE. ~hus, ~he guidc vane con~:rol operates to
adjust the ~uide vaneC; as necessary and causes a conseq-lent adjust-
~5 ment in fuel flow by the fuel governor 60 clue to charlcJc in ya5
generator speed ~gg so as to rnaintain the com~ustor exhauc;t
temperature T4 at the precelected, maximurn value. It will be
apparent also frorn the forec3Oing that reduction in turbine inlet
~ ternperature T~ below the preselected desired value thereof causes a
t'~ o corresponding movement of the guide vanes 120, 122 to increase the
pressure ratio across the power turbines 116, 118. Accordingly
'~!~,
this causes a reduction in pressure ra-tio across gas generator
,
- ~2 -
~ ~35~
turbine 102 to reduce gas generator spee~. In respons~ t:he fue~.
governor shits fuel lever 226 in a clockwise rotation as vie~ed
in Fig. 6 to increase fuel flow to the combusto~ and tllus increase
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 effected by altering the fuel flow thereto as described
above.
0 During the cruise operation therefore, it should now be
apparent that fuel governor 60 acts to adjust fuel flow in such
a manner as to maintain a gas yenerator speed in relation to the
position of the accelerator lever 18~. Clearly, the fuel governor
60 operates i.n conjunction w~th or independently of the vane
control 66, dependent only upon the gas generator speed Ngg~
While the electronic control rnodu].e operates the guide vane
controJ. solenoid 426 to trim turbine inlet temperature T~ durincJ
cruise, the hydromechanical por-tion of the guicle vane control 66
acts in a more direct feedback loop to trim the speed of power
!0 turbine output shaft 82. More particularly, the actual powex
turbine speed as sensed by the pressure developed .in line ~20 is
continuously compared to the acceleratc)r leve:r position as re1ected
by the pressure developed in li.ne ~10. ~ gr,lphical reurc-;en~.at:lon
of the action of valve ~02 and piston ~16 in compressincJ qpring
384 and recluestinc3 different desirecl powc~r turbine speeds Npt in
relation to the throttle position, a, is shown in Fi~ . Thus,
in response to an i.ncrease in speed of power turbi.ne shclft 82
beyond that selected by the rotation of accelerator lever 184,
pressure at the lower d.iameter of piston ~16 becomes substantially
greater than that on the larger face thereof to rota-te lever 396
so as to increase compression of the biasing spring 384 ac-ting on
, .
. - ~3 -
5~7~
valve 380. The resultinc~ up~7ard movement of valve 380 causes a
correspondinc~S downt~ard movement of piston 366 and accordingly
shifts the guide vanes toward the Fig. 14 position, i.e. opens ~he
guide vanes to increase the area ratio and reduce the pressure
ratio across the vanes 117, 119 of the two po~er turbine wheels.
This reduces the power transmitted from the gas flow to the power
turbine wheel and thus causes a slight decrease in power turbine
output shaft speed back to that selected by the accelerator lever
184. It will be apparent that whenever the speed of the power
turbine sha~t 82 is belo~i that selected by accelerator lever 184,
Z the compression of spring 384 is reduced to tend to increase the
pressure ratio across the power turbine vanes 117, 119 to tend to
s, increase power turbine speed Npt.
I The portion of vane control 66 for trimming power turbine
sl]5 speed in relation to accelerator position is preferably primaril~
digital in action since as shown in Fig. 19, a small change in
throttle lever position increases the requested Npt from 25~ to
100%. The actions of valve 402, piston 416 and plunger 395 are
I such that when the accelerator is at a position greater than a*,
this portion of the control continually requests approximately
j 105~ power turbine speed Npt. Through a small amount of rotation
of the accelerator below a*, the control provides a request of
power turbine speed proportional to the ~ccelerator position.
Positioninc3 of the accelerator to an anglc below this small arc
?5 causes the con~rol to request only approxlmately 25~ of maY.imum
P
Thus, in normal cruise thc-~ gui.de vanes control operc-.tes in
conjuncticn with the fue]. governor to maintain a substarltially
constant turbine exhaust ternperature T4; fuel governor 60 operates
to trim gas generator speed N~c~ to a value selected by the accelerator
- 4~ -
35~
lever 18~; and the hydromechanical portion of guide ~iane 66
operates to trim power turhine outpt speed Npt to a ].evel i.n
relation to the position of accelerator pedal 184. It will
further be apparent that durin~ the cruise mode of operation, the
orifice created at opening 178 of the fuel governor is substantially
smaller than the openings to fuel flow provided in the scheduling
valve 62 so that the scheduling valve 62 normally does not enter
into the control of the engine in this phase.
Safety Override
During the cruise or other operating modes of the engine
discussed herein, several safety overrides are continually opera~le.
For instance solenoid 239 of the uel governor 60 operates to
essentially reduce or counteract the effect of speeder spring 22~
and cause a consequent reduction in fuel flow from orifice 178 by
exerting a force on fuel lever 22F, tend.ing to rotate the latter in
a counter-clockwise direction in Fig. 6. As illustrated in Fig. 17,
the electronic control module includes a logic element 538 which is
, responsive to power turbine speed Npt, gas qenerator speed N~g/
turbine inlet temperature T4, and ~urbine exhaust or recuperator
inlet temperature T6. Thus if turbine lnle~ tempera-ture T~ exceeds
the preselected maxim~n, a proportional electrical .s.ignal is trans-
mitted to lines 250 to energize solenold 239 and reduce fuel flow
', to the engine. Similarly, excessive turbine exhaust temperature T6
results in proportionately energizinc3 'the solenoid 239 to reduce
fuel flow to the combustor and thus ultimately reduce turbine
exhaust temperature T6. Also, logic element ~38 is responsive to
'; power turbine speed so as to proportionately energize solenoid 239
whenever power turbine speed exceeds a preselected maximum. Simi-
larly, the electronic control module opera-tes to energiæe solenoid
239 whenever gas generator speed exceeds a preselected maximum
; established by function generator 514 as a function of P2, T2 and Npt.
Normally the preselected max,imum parameter values discussed with
regard to these safety override operations, are slightly above the
- ~5 -
79
normal operating values of the parameters so that the solenoid
239 is normally inoperable except in inst~nces of one of these
parameters substantially exceeding the desired value thereof.
Thus, for instance, during a cruise mode of operation or "coasting"
when the vehicle is traveling do~mhill being dei~en to a certain
extent by its own inertia, the solenoid 239 is operable in
response to increase of power turbine output shaft 82 beyond that
desired to cut back on fuel flow to the combustor to tend to
control the po~ler turbine-output speed,
While as discussed previously with regard to the 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 thereof as determined by summer 540 which
generates a signal through line 542 to element 498 whenever
turbine exhaust temperature T6 exceeds the preselected maximum.
Logic element 498 is responsive to signal from either line 542 or
536 to reduce the magnitude of the electronic signal supplied
throuyh line 427 to solenoid 426 and thus reduce the pressure
ratio across the turbine wheels 116, 118. ~s discussed previously,
this change in pressure ratio tendr; to increase gas genercltor speed
and in response the Euel governor 60 redtlces uel flow to the
combustor so that turbine exhaust temperature T6 is pxcvented from
increasing beyond a preselected maximum limi~.
As desired, the solenoid 23~ may be ener~izcd in response to
other override parameters, For instance, to protect the recupexator
56 from excessive thermal stresses, thc logic element 538 may
incorporate a differentiator 548 associatcd with thc signal from
the turbine exhaust temperature T6 so as to generate a signal
indicative of rate of change of turbine e~haust temperature T6.
- ~6 -
,3579
Loc3ic element 538 can thus cJenerate a signal energ;~inc~ solenoid
239 whenever the rate of change of turbine exhaust temperature T6
e~cceeds a preselected maximum. In this manner solenoid 239 can
control maximum rate of change of temperature in the recuperator
ancd thus the thermal stress imposed thereon. Similarly, ti-e logic
element 538 may operate to limit maximum horsepower developed across
the power turbine and/or gas yenerator shafts.
Gear Shift
Because turbine engine 30 is of the free turbine type with a
power output shaft 82 not physically connecked to the gas yenerator
shaft 76, the power turbine shaft 82 would normally tend to greatly
; overspeed during a gear shifting operation wherein upon disengage-
ment of the drive clutch 34 to permit gear shifting in box 38,
substantially all i.nertial retard.ing loads are removed from the
power turbine drive shaft 82 and associated power shaft 32. of
course, during normal rnanual operation upon gear shiftiny, the
accelerator levex 184 is released so that the fuel governor 60
; immed:iately begins substantially reducing fuel flow to combustor
98. Yet becau~e of the hic3h rotati.onal inertia of the power turbine
shaft ~2 as wel]. as thc- hi~h volumetric gas flow thereacross from
the combustor, the power turbine shclft would stlll terld to over
speed.
Accordingly, the control ~y;tem as contelnplclt~d by the present
in~en-tion ut.i]..iz.es th~ yu:idc! vane actuator control 66 to shift the
gui~ vanes 120, 122 toward their F:icJ. 16 "reveLc:e" position such
that the gas 10w from tl~e eng.ine impin~e; oppos.itely 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 tur~ine 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
. - ~7 -
~ ~3S~9
re-engagement of drive clutch 36 may be conveniently ~nd speedil~
accomplished without damage to the engine or drive train.
~ore particularly the hydromechanical nortion of guide -~ane
control 66 is so arranged that upon release of accelerator lever
S 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 corresponds to position.ing the guide
vanes 120 122 in their Fig. 16 disposition. The gas flow from
the combustor is then directed by the guidc vane across the t~lrbine
wheel vanes 117 119 in opposition to the rotation thereof to
dec~lerate the power turbine shaft 82. Since the drive clutch 34
is disengaged during this year shifting operation the power turbine
shaft 82 rather rapid-ly decelerates by virtue of the opposing gas
flow created by the positioning of guide vanes 120 in their Fig. 16
position. Yet more specifically the arrangement of springs 406
~08 and the relative magnLtude of pressure developed in condui.t ~10
and 420 cau~es the hydromechanical portion of vane actuator control
66 to operate in the manrler ~bove describecl to shift the guide
vanes 120 to their nec3ative or rcverse disE)osition ill-lstrated
in Fig. 16 and modulatc yuide vane position withirl ~one d o
Fig. 18 in relation to the m~(3ni-tude o~ Npt excess whenever the
accelerator lever 18~ i~ movcd to less than a preselected accelerator
lever position a*. ~s the speed oE power turbine shaft 82 reduces
the piston 416 beyins shift.ing in an opposite direction to reduce
compression of spriny 38~ 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. The greater the speed
_ 48 -
~357~
error, the more the guide vanes are rotated to a "harcler"
braking position. Thus, the positionof the guide vanes are
maintained in a reverse braking mode and are modulated through
zone "d" near the maximum braking position -9S of Fig. 1~ in
relation to the power turbine speed error. Once gear shifting
is completed, of course, the control system operates through the
acceleration operation discussed previously to again increase
power turbine speed.
Deceleration
A first mode of deceleration of the gas turbine engine is
aecomplished by reduction in fuel flow along the deeeleration
sehedule afEorded by deceleration window 286 of scheduling
valve 62. More particularly, the release of accelerator lever
184 causes the fuel governor 60 to severely restrict fuel flow
through opening 17~. As a consequence the minimum fuel flow to
the gas turbine engine is provided throuc~h deceleration fuel line
142 and the associated deceleration window ~6 of the scheduling
valve. As noted previously deceleration window 286 is particularly
eonfigured to the gas tuxbine engine so as to continually reduce
fuel,flow along a,sche~ule which maintains combustion in the
eombustor 98, i.e., substantially alonc~ the oper~ting line of the
gas turbin~ encJine to maintain eombustion but below the "re~uired
to run line." A., noted previously, even without rotation of
accelerator l~v~r 18~, the solcIIoicl 239 ean be enercJized in
partieular instanees to cJener~te a false accelerator lever signal
to fuel lever 226 to aecomplish deceleration by severely r~strictincJ
fuel flow.
This deceleration by limitincJ fuel flow is accomplished by
reducin~ the accelerator lever to a position at or just above
a preselec-ted aecelerator position, a*. This accelerator position
is normally just slicjhtly above the minimum accelerator p~sition,
_ ~9 _
~3579
a~l g^nerally cc-respor.ds to the position of the accelerator
lever during the "coasting" condition wherein the engine i5
somewhat driven by the inertia of the vehicle such as when
coasting downhill. Since this deceleration by restricting
fuel flow is acting onl~ through governor 60, it will be
apparent that the guide vane control is unaffectred thereby
and continues operating in the modes and conditions discussed
previ~usly. This is particularly true since the accelerator
has been brought down to, but not below the preselected acce-
lerator position a* to which the hydromechanical portion ofvane actuator 66 is responsive.
~ pon further rotatiny accelerator lever 184 below
the position a* and towards it minimum position, a second mode
; of decelerativn or braking of the vehicle occurs. In this
mode, the movement of the accelerator lever below the position
a* causes the hydromechanical portion of guide vane actuator
66 to generate a suhstantially large error signal with regard
to power turbine speed so as to rotate the guide vanes 120 to
their Fig. 16 reverse or "brakiny" position. More particular-
ly, as discussed above with regard to the gear shift operation
of the vehicle, this large error signal of the power turbine
speed in compariæon to the accelerator lever position causes
significant counter-clockwise rotation of lever 3~6 and conse-
quent compression of spring 38~. Thi~ drives the piston 366
and the guide vanes toward the Fig~ 16 position thereof. ~s
a result, the cyas flow from the gas turb;ne enyine oppose~
rotation of the turbine wheels 116, 118 and produces substan-
tial tendency for deceleration of output shaft 82. It has
been found that for a gas turbine engine in the 450 to 600
horsepower class, that this reversiny of the guide vanes in
combination with minimum fuel flow to the combustor as permit-
ted by deceleration window 286 provides on the order of 200 or
more horsepower braking onto the turbine output shaft B2.
-50-
It will be noted that during this second mode of
deceleration, as well as during the gear shift operation dis-
cussed previously that since the guide vanes are now in a
reversed disposition; the ]ogic accomplished by the electronic
control module 68 in controlling solenoid 426 to prevent over
ternperature of T4 or T6 is n~w opposite to that r~quired.
Accordingly, the electronic control logic further includes a
transducer 544 which senses whenever the guide vanes pâSS o~ver
centre as noted by the predetennined angle B* of Fig. 18, and
are in a negative incidence disposition. This signal generlted
by transducer 544 energizes a reversing device such as an in-
; verter 546 which reverses the signal to the solenoid 426. More
pa~ticularly, if ~luriny this deceleration operation with the
guide vanes in the negative incidence position of Fig. 16,
there occurs an excess combustor exhaust temperature T4 or ex-
cess turbine exhaust temperature T6, the signal generated by
element 500 to reduce the magnitude of the current ~ignal is
reversed by element 546. Accordingly occurrence high T4 or
high T6 while element 5~6 is eneryized generates an electrical
signal of increasing strength to solenoid 426. Ln response,
the solenoid 4~6 drives valve 432 in a direction increasing
pressure in conduit 394 and upon shoulder 393; rrhis reduces
the magrlitude of the biasinc3 sprirly 383 and causcs valvç 3~0
to move downwarclly. ~n a followin~J movement the pi~ton 366
moves upwardly to reduce the c:ompression of spring 3~2. Thus
the yuide vanes 120 are rever;ely t:rilMned away ~rolu the maximum
braking position shown in Fig. 16 back towards the neutral
position of Fig. 14. This movement of course reduces the ma~-
nitude of power transrnitted from the gas flow in opposing rota-
tion of the guide vanes 117 to cause a consequent reduction infuel flow as discussed previously. The reduced fuel flow then
reduces the magnitude of the over temperature parameter T~ or
T6. Such action to control T4 or T6 will ........ ~
35'7~
substantially only occur when ~uel flow being delivered to the
combustor is more than permitted by the deceleration schedule ~86.
Thus such action is more likely to occur during the "coasting"
operation than during hard br~king during the second mode o~
deceleration. Such is natural with operation of the engine,
ho~.ever, since durlng hard deceleration, fuel flow to the
combustor is at a minimum and combustor exhaust temperature is
relatively low. However, during unusual conditions, and even with
the guide vanes in a negative incidence position, the electronic
control module is still operable to return the guide vanes toward
their neutral position to tend to reduce any over temperature
conditions.
Power Feedback B a ~
A third mode of deceleration of the vehicle can be manually
selected by the operator. Such will norrnally occur when, after
initiation of the first two modes of decelera-tion 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 hiyh.
Thus power turbine ~haEt speed Npt may be in a ranye of approxi-
mately 90~ of its maximum speed while the gas generator speed N~g
has been brought down to at or neclr its low idle speed of approxi-
mately S0~ maximum gas generator spced.
This third mode of deceler-ltiorl, ternled ~owe~ feedhack
braking, i5 manual.ly selccted by closing power feedback swi.tch ~G6.
In response the electronic control module. 68 gellerates signals
whi~h ultimately reslllt in mechanical intercollnection o the c3as
generator sh~Et ~ith the power turhine shaft such that the inertia
of the gas generator shaft is imposed upon the drive train oE the
vehicle to produce additional braking ef~ects thereon. More
particularly, upon closing switch 466, AND gate 506 generates a
signal to AND gate 504 since the accelerator level is below a
- 52 -
~ ~3 :i7~
~-^se'cc'cd point a* ^ausing ~unc-~ic~n ~c~nerato~ A ~8 to ycnelat2
a signal to ~ND gate 506, and since the gas generator is opera~
ting at a speed above 45~ of its ra-ted value as deterrnined by
element 474. Element 472 develops a signal through line 480 to
AND gate 504 since power turbine speed is greater than gas
gen~rator speed in this operational mode. Eleme~t 470 also
notes that the effective relative speeds of the gas generator
shaft_and power turbine shaft are outside a preselected limit,
such as the plus or minus 5% noted at cornparator ~70. Accor-
dingly element 470 does not yenerate a signal to AND gates 502,
504. More specifically the element 470 is not necessarily com-
paring the actual relative speeds of the gas yene~ator power
turbine shafts. Rather, the element is so arranged that it
only yenerates a signal to ~ND gates 502, 504 whenever the
relative speeds of the shafts 520, 522 in the power feedback
clutch 84 are within the preselected predeterlnined limits of
one another. Thus the comparator 468 will compensate, as re-
quired, for differences in the actual speeds of the gas c3eIlera-
tor and power turbine shaft, as well as the gec-~r ratios of the
two respective drive trains 7~ and 80 associated with the two
shafts 502~52~ of the feedback clutch 8q~
Beause of the dif~rerlce between Npt ancl N~3cJ~ no
sic3nal frorn element 470 is ~raIlcmitted to either ~ND g~te~ 5t)2
or 504~ As noted schematically b.y the circle ac;c;ocic~ted with
the input from elcment 470 to ~N~ gat~ 504, that inpllt i5 :in-
verted and ~ND gate 50~ is now e~fective to generatc an OlltpUt
signal since rlo signal is comlng from el~ment ~70, and since
signals are being received from AND gate 506 and element 472.
The output signal from AN~ gate 504 accomplishes two unctions.
First, a signal of 50% Ngg magnitude is generated in function
generator 566 and added to the constant 50% bias signal of sum-
mer 570. The resulting signal is equivalent to a 100% ~gg
speed command. Secondly, the output frclm AND gate 504 passes
throucgh OR gate 562 to produce a signal to solenoid 257. This
siynal is of sufficient magnitude to shi~t
-53-
3~7~
solenoid 257 to its Fig. 6D position cleariny opening 178 for
substantial fuel flow to the combustor. It will be apparent that
full ener~ization of solenoid 257 to its Fig. 6D position is
essentially a false accelerator lever sign~l to the ~uel lever ~2G
causing lever 226 to rotate to a position normally caused by
depressing accelerating lever 1~4 to its maximum flow position.
Secondly, the signal from summer 570 is also an input to element
497 such that an artificial full throttle si~nal is generated
which overrides the energization signal which is maintaining
the guide vanes in their Fig. 16 braking position during the
I second mode of deceleration discussed previously. The energiza-
, tion o the guide vane solenoid 426 causes increase of pressure
j in conduit 394 allowing the springs 382-385 to shift the piston
~ 366 and the associated guide vanes toward their Fig. 14 "neutral"
¦15 position.
Accordingly, it will be seen that the sic~nal from AND gate
~ 504 produces an acceleration signal to the engine, placing the
l~ cJuide vanes 120, 122 in their neutral position such that maximum
pressure ratio is developed across the cJas yencrator tur~ine 102,
~20 and at the same ti.me ~uel fl.ow to the combustor 98 ha~ heen greatly
increased. In responC;e~ the gas ~enerator section bec~ins incr~asing
in speed rapidly toward a value such that the speed of shaft 522
of the feedback clutch approaches the~ spced of its other shait 520.
Once the power twrbine and gas ~enerator sha~-t speeds are
~25 ap~ropriately matched such that the two sha~-tc; 520, 522 oE the
feedback clutch are within the pre~electcd limits dctermined by
element 470 of the electronic control module, electronic control
module develops a positive signal to both AND cJates 502, 504.
This positive signal immediately stops the output signal from AND
gate 504 to de-energize the proportional solenoid 257 of the fuel
c~overnor and again reduce fuel Elow back toward a minimum value,
and at the same time stops the overri.de signal to element 500
.
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3579
such that the c~uide vane 120, 122 are again shifted back to their
Fi~. 16 bra~in~ disposition in accord with the operation discussed
above with respec-t with the second mode of deceleration.
The logic element AND gate 502 now develops a positive
output signal to operate to driver 516 and energize clutch
actuator solenoid valve 518. In response the clutch 34 beco~es
engaged to mechanically interloc~ the shafts 520 and 522 as ~ell
as the gas generator and power turbine shafts 76, 82. Incorporation
of the logic element 470 in the electronic control module, in
addition to the other functions described previously, also assures
that since the two shafts 520, 522 are in near synchronous speed,
relatively small torque miss-mateh across the plates 524, 526 of
I the elutch is experienced. Aecordingly, the size of clutch 8~ can
be relatively small. Thus it will ~e seen that the electronic
eontrol module 68 operates automatically first to increase gas
- generator speed to essentially mateh power turbine speed, and then
to automatically return the guide vanes to their Fig. 16 braking
disposition at the sc~ne time as cluteh 84 is enyayed.
This interconnection of the CJas turbine enyine drive train
.20 with the gas genera-tor ~haft 76 eauses the rotational iner-tia of
yas generator 76 to ass.ist i.n dec~leratincJ the vellic].e. It ha~
been found that ~or a 450 to 600 horsepower class cr-cJine described,
this power feedback braki.ng mode addc; in th~ nc1.c~llborhood oE 200
to 250 horsepower bxaki.ng .in additiorl to thc 200 hor.c;epower
braking effects produeed by the position~ g of gllide vane 120,
122 in their Fi.g~ 16 position. Because thc' fuc'l CJOVerrlOr iS
again severely restrictiJIcJ flow throucJh orifi.ec 178, the fuel
flow is eontrolled by deceleration window 286 permittincJ the yas
yenerator section to decelerate while maintaining the combustion
s~9
process in combustor 98. Thus reduction of fuel flow provides
the decelera-tion effect of the rotational inertia of the yas
generator upon the drive train of the vehicle.
It will be apparent from the foregoing that the present
invention provides substantial braking for deceleration purposes
while still utilizing the optimum operating characteristics of a
free turbine type of a gas turbine engine with the yas genera-tor
section mechanically interconnected with the power turbine section
' only in a specific instance of a manually selected "severe" thi~d
mode type oE deceleration operation. Throughout all deceleration
modes and engine operation, a continuous combustion process is
, maintained in the combustor. Thus substantial deceleration occurs
without exti.nyuishing the combustion process therein.
I This power feedback braking operation can be deactivated in
several ways: manually by openiny switch 466 to stop the output
signal from AND gate 506;providing a NOT siynal to turn o~f
driver 516 and solenoid 51~ to disenyage clutch 8~. Furthermore,
i the manual switch is not opened and the engine continues -to
decelerate, elem~nt 47~ also opera-tes to deactivat~ the power
feedback operation whene,ver gas generator speed NCJcJ reduces to a
value below 45% o~ its mE~ximum rate o~ speed. Also, deE)resslon
o~' the accelerator to a value o~ a}-~ove a* also declctivates the
power feedback operation by ~3~0pp:in~J an outE~ut s:ignal frorn AND
gate 506.
From the foregoing it wi;ll now he apparent that the present
invention provides an improved cycle of ope~ratiorl for a gas
turbine engine peculiarly adapted for operating a ground vehicle
in a safe, familiar manner while still retaining the inherent
beneEits of a gas turbine engine. More speciCically~ by utilization
of a free turbine type engine yreater adaptability and variability o~
engine operation is provided. ~t the same time the engine can operate
- 56 -
~357~
throuc3hoUt its entire operatinCJ cycle while maintainirly a
continuous combustion process within the combustor 98. Tllis
avoids various problems of operation and service life associated
with repeal:ed start and stop o~ the cc,mbustion prGcess. The novel
cycle contemplates a utilization of a combustor 98 having choked
nozzles 102 to provide a variable pressure within the combustor
as the speed of the gas generator section varies. Gas generator
section speed is normally trimmed to a preselected value relative
to the position of the accelerator lever 184, while the guide
vanes 120, 122 operate to trim the turbine inlet temperature T4
to a preselected substantially constant value to maintain hic3h
engine operational efficiency. Further, the guide vane control
operates indirectly to alter the fuel f]ow through fuel governor
60 by altering the speed of the gas generator section such that
L5 the various controls are operable in an integral manner without
counteracting one another. ~t the same time a trim of power
turbine shaft speed Npt is provided by the guide vane control 66.
Furthermore it will be seen that the present invention provides
the gas turbine engine peculiarly adapted for drivinc3 a ~round
vehicle in that responsive acceleration similar to that produced
by an internal combustion enginc is prov:ided by both the automatic
high idle operation as well as by the manner of accelerat:ion of
the gas turbine engine. Such is accolllplished by first: alter:in~
the work split to develop maximum power to the CJaS yCnercltOr
~5 section. The scheduling valve con~rol 62 therl acts in rec3enercltive
fash:ion to incre~C;e fuel ~low to the combustor in such a manner
that gas generator sE)eed is incre~ascd whlle mailltLIin.illcJ a substan-
tially congtant maximum turbine :inlet temperature T~ thereby produ~
cing maximum acceleration without overheating the engine. Yet the
scheduling valve also limits T~ durinc3 the initial por-tion of
acceleration when turbine "stalling" conditions are prevalent.
~ccelera-tion is therl completed once substantial acceleration of
- 57 -
s7g
t~e gas generator section i5 accomplished, by re-alteriny the
power split to d~velop greater power ~cross the po~er turbine
wheels 116, 118.
It is further noted that the present invention pro~Jides an
improved method and apparatus for decelerating the vehicle in a
three stage type of operation by first reducing fuel flow, then
by placing the guide vanes in the braking mode, and ~hen by
manually selecting the power feedback operation.
The primary operating elements of the fuel governor 60,
scheduling valve 62, and guide vane control 66 are hydromechanical
in nature. This, in conjunction with the operation of solenoid
~26 of the guide vane control which is normally ~nergized,
provides an engine and control system peculiarly adapted to
prov.ide 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 ~uel governor 60 continues to adjust fuel
flow in relation to that selected by accelerator lever 184.
Scheduling valve 62 is in no way affected by such electrical
failure and is capable of controlling acceleration and/or
deceleration to both prevent over heating oE the encJine durlng
acceleration as well clS to rna:intain combustion during deceleration.
The hydromechanical port:ion of the vane ~ctuator control will
still b~ operable in the evcnt of olectr,ical failure and c~pable
of adju~ting the cJuicle vanes c15 appropriate to maintain funct.ional
cngine op~r~tlon. Upon electrical failure thc ~olenoid ~26 of
the guide vane control becomes dc-energized causinc3 1055 of pressure
upon face 393 of the control piston 392. Ilowever, the speed control
afforded by lever 396 is still maintained and the quide vanes can
be appropriately positioned to maintain functional engine operation
during this failure of the electrical system. Thus, while certain
desirable features of the engine control will be lost in the event
of e].ectrical failure, the engine can still function properly with
- 58 -
3~9
; ' appropriate acceleration and deceleration so that the vehicle
m~y still be operated in a safe manner even though ~t a possible
loss of operational efficiency and loss of the ability to provide
power feedback braking.
From the foxegoing it will be apparent that the presellt
, invention provides an improved method of automatically setting
and resetting the idle of the gas generator section so that the
' engine is highly responsive in developing an increase in output
power such as when contemplatinc3 acceleration of the vehicle.
Further the present invention pxovides an improved method of
controlli.ng fuel flow hydromechanically in relation to gas
genera~ox speed, as well as overriding normal speed control
operation of the fuel governor to increase or decrease fuel flow
in response to occurrence of various conditions which energize
either of the solenoids 239, 257. Further the present invent:i,on
provi.des an improved method for controlling fuel flow to the
combustor durinc3 acceleration such that constant turbine inlet
temperature T4 is maintained throughout, while also controllinc3
fuel flow during deceleration to avoid extinguishiny the combust.ion
process within a combustor. The invention further contemplates
an improved ~nethod of con~rollincJ c3uide vane position in such an
engine both by hydxomechani.cal operation to corltrc)l ~peed of a
rotor such a5 tu.rbine wheels 11.6, 118, and by electrical. overricie
oper~tion depen~ent upon thc~ amount of enerc3ization o~ t:he~
proportional ~olenoi.d ~26.
The fo.recJoiny has clescribed a preferxed cmbod:iment of th~
invent,ion in sufficient detail that those skillecl in -the art may
make and use it. However, this detailed description should be
considered exemplary in nature and not as limitincJ to the scope
and spirit of the present invention as set forth in the appended
'~ claims.
- 59 -
" .
3S~3
E~avin~ described the invention with sufficient clarity tha~:
those skilled in the art may make and use it, what is claimed as
ne~ and desired to ~e secured by LetteFs Patent is:
- 60 - .
