TURBOSHAFT ENGINE COMPRISING A CONTROLLED
MECHANICAL COUPLING DEVICE, HELICOPTER EQUIPPED
WITH SUCH A TURBOSHAFT ENGINE, AND METHOD FOR
OPTIMISINGTHE ZERO-POWER SUPER-IDLE SPEED OF SUCH A
HELICOPTER
1. Technical field of the invention
The invention relates to a turboshaft engine that is intended for equipping
I 0 a multi-engine helicopter, in particular twin engine helicopter. The invention also
relates to a method for optimising the zero-power super-idling mode of a multiengine
helicopter, in particular twin-engine helicopter, ofthis kind.
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2. Technological background
A helicopter is generally provided with at least two turboshaft engines
which operate at speeds that depend on the flight conditions of the helicopter.
Throughout the following text, a helicopter is said to be in a cruise flight situation
when it is progressing in normal conditions, in a mode known by the abbreviation
20 AEO (All Engines Operative), during all the flight phases apmi from transitional
phases of take-off, ascent, landing or hovering flight. Throughout the following
text, a helicopter is said to be in a critical flight situation when it is necessary for
it to have available the total installed power, i.e. during the transitional phases of
take-ofT, ascent, landing and the mode in which one of the turboshaft engines is
25 malfunctioning, referred to by the abbreviation OEI (One Engine Inoperative).
It is known that, when the helicopter is in a cruise flight situation, the
turboshaft engines operate at low power levels, below their maximum continuous
power (hereinafter MCP). In some arrangements, the power provided by the
30 turboshaft engines during a cruise flight can be less than 50 % of the maximum
take-offpower (hereinafter MTO). These low power levels result in a specific
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consumption (hereinafter SC), which is defined as the relationship between the
hourly fuel consumption by the combustion chamber of the turbo shaft engine and
the power provided by said turboshaft engine, of approximately 30 % greater than
the SC of the MTO, and thus in an overconsumption of fi.Jel during cruise flight.
Finally, during holding phases on the ground, pilots generally prefer to put
the various turboshaft engines into idling mode so as to be certain of being able to
restart them. The turboshaft engines thus continue to consume h1el, despite not
providing any power.
At the same time, the turboshaft engines are also oversized so as to be able
to ensure flight over the entire flight range specified by the aircraft manufacturer,
and in particular flight at high altitudes and during hot weather. These flight
points, which are very restrictive, in particular when the helicopter has a mass that
15 is close to its maximum take-off mass, are only encountered in specific use cases
of some helicopters. As a result, although dimensioned so as to be able to provide
such powers, some turboshaft engines will never fly in such conditions.
These oversized turboshaft engines are disadvantageous in terms of mass
20 and fuel consumption. In order to reduce this consumption, in all the cases of
flight described above (cruise flight, OEI mode, taxiing, hovering flight, or
holding on the ground), it is possible to put one of the turboshaft engines into
standby mode. The active engine or engines then operate at higher power levels in
order to provide all the necessary power, and therefore at more favourable SC
25 levels.
As is known, a turboshaft engine of a helicopter comprises a gas generator
and a free turbine which is powered by the gas generator in order to provide
power. The gas generator is conventionally made up of air compressors which
30 supply a chamber for combusting the fi1el in the compressed air, which
compressors deliver hot gases to turbines for partially expanding gas, which
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turbines rotate the compressors by means of drive shafts. The gases then drive the
free power transmission turbine. The free turbine transmits power to the rotor of
the helicopter by means of a gearbox.
In FRII51717 and FRI359766, the applicants proposed methods for
optimising the specific consumption of the turboshaft engines of a helicopter by
the possibility of putting at least one turboshaft engine into a stable flight mode,
referred to as continuous flight mode, and at least one turboshaft engine into a
particular standby mode that it can leave in an emergency or in a normal manner,
I 0 according to need. A transition out of standby mode is referred to as 'normal'
when a change in the flight situation requires the turboshaft engine in standby to
be activated, for example when the helicopter is going to transition from a cmise
flight situation to a landing phase. A normal transition out of standby mode of this
kind occurs over a period of between I 0 seconds and I minute. A transition out of
15 standby mode is referred to as 'emergency' when there is a failure or a power
deficit in the active engine, or when the flight conditions suddenly become
difficult. An emergency transition out of standby mode of this kind occurs over a
period of less than I 0 seconds.
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modes:
The applicants have proposed in pm1icular the following two standby
- a standby mode referred to as normal super-idling, in which the
combustion chamber is ignited and the shaft of the gas generator
rotates at a speed of between 20 and 60 % of the nominal speed,
- a standby mode referred to as assisted super-idling, in which the
combustion chamber is ignited and the shaft of the gas generator
rotates, with mechanical assistance, at a speed of between 20 and 60
% of the nominal speed.
A disadvantage of the normal super-idling mode is the operating
temperatures, which become increasingly high as attempts are made to reach ever
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lower idling. However, this has the advantage of minimising the fuel consumption
in this mode.
The assisted super-idling mode makes it possible to remedy this problem
5 of operating temperature while further reducing the fuel consumption. However,
this requires the use of an electrical, pneumatic or hydraulic drive machine and of
a corresponding coupling.
In addition, the tcclmical problem now arises of achieving a super-idling
10 mode which is no longer mechanically assisted and is less limited by the
temperatures of the turboshaft engine. The technical problem addressed is
therefore that of providing a turboshaft engine that makes it possible to provide an
improved super-idling mode of this kind.
15 3. Aims of the invention
The invention aims to provide a turboshaft engine that can have a superidling
mode, in which the combustion chamber is ignited and the shaft of the gas
generator rotates at a speed of between 20 and 60 % of the nominal speed, and
20 that is less affected by the operating temperatures of the turbo shaft engine and is
not mechanically assisted by an external drive device.
25
The invention therefore aims to provide a turboshaft engine that can have a
new super-idling mode.
The invention also aims to provide a twin-engine helicopter comprising at
least one turboshaft engine according to the invention.
The invention also aims to provide a method for optimising the zero-power
30 super-idling mode of a twin-engine helicopter according to the invention
comprising at least one turboshaft engine according to the invention.
5
4. Disclosure of the invention
In order to achieve this, the invention relates to a turboshaft engine
5 comprising a gas generator that is capable of being rotated, and a free turbine that
is rotated by the gases of said gas generator.
A turboshaft engine according to the invention is characterised in that it
comprises a device for controlled mechanical coupling of said gas generator and
10 said free turbine, which device is capable of connecting said gas generator and
said free turbine mechanically and on demand as soon as the rotational speed of
said gas generator reaches a predetermined tln·eshold speed.
A turboshaft engine according to the invention thus makes }t possible to
15 connect the gas generator and the free turbine mechanically and on demand. The
command for connecting the gas generator and the free turbine depends on the
rotational speed of the gas generator. A turboshaft engine according to the
invention thus makes it possible to mechanically assist the rotation of the gas
generator in a manner that does not need to call on an external drive machine. The
20 power is obtained directly from the free turbine of the turboshaft engine and
transmitted by means of the coupling device.
Advantageously and according to the invention, the controlled mechanical
coupling device is capable of connecting said gas generator and said free turbine
25 mechanically and on demand as soon as the rotational speed of said gas generator
is less than said predetermined tlueshold speed, and of separating said gas
generator and said free turbine on demand as soon as said rotational speed of said
gas generator is greater than said predetermined threshold speed.
30 Thus, according to this aspect of the invention, the controlled coupling
device makes it possible to force the free turbine to drive the gas generator when
6
the gas generator is rotating at a speed that is less than a predetermined threshold
speed. In other words, a turboshaft engine according to the invention that is
equipped with a device for controlled mechanical coupling of the gas generator
and the free turbine makes it possible to switch the turboshaft engine, on demand,
5 from a configuration (or mode) referred to as free-turbine, in which the gas
generator and the free turbine are mechanically independent, to a configuration (or
mode) referred to as connected-turbine, in which the gas generator and the free
turbine are mechanically c01mected.
10 The predetermined threshold speed is advantageously selected such that it
IS not possible for the gas generator and the free turbine to be mechanically
connected when the turboshaft engine is in super-idling mode, i.e. when the free
turbine is no longer producing any torque and is rotating freely at a speed that is
less than that at the inlet of the gearbox of the aircraft to which said turbine is
15 connected. By forcing the free turbine to rotate more slowly than its steady-state
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speed at zero torque, this will thus provide an engine torque that will allow the gas
generator to drive the compressor, thus corresponding to a c01mected-turbine
configuration.
A turboshaft engine according to the invention can thus be put into a
super-idling mode, during which the free turbine drives the gas generator, making
it possible to reduce the temperatures of the hot parts of the turboshaft engine and
to reduce the fuel consumption.
Advantageously and according to the invention, the threshold speed
depends on a nominal speed of said gas generator.
According to this aspect of the invention, the tlll'eshold speed is directly
dependent on the nominal speed of the gas generator.
Advantageously and according to this variant, the threshold speed is
7
selected within the range of [20 %.Nl, 60 %.Nl], where NJ is said nominal speed
of said gas generator.
In other words, a turboshaft engine according to this variant switches from
5 a free-turbine mode to a cmmected-turbine mode as soon as the rotational speed of
the gas generator drops below a threshold value that corresponds to an idling
mode (defined here as between 20 % and 60 % of the nominal speed of the gas
generator).
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Advantageously and according to the invention, said controlled
mechanical coupling device comprises:
means for reading information that is representative of said
rotational speed of said gas generator,
means for reversible mechanical coupling between a shaft that is
mechanically connected to said gas generator and a shaft that ts
mechanically connected to said free turbine,
means for controlling said coupling means on the basis of said
information that is representative of said rotational speed of said
gas generator, and on the basis of said threshold speed.
Advantageously and in a variant, the coupling device finther comprises
means for authorising said coupling means by way of a conm1and fi·om an engine
computer that has previously requested the engine be put into standby mode.
According to this aspect of the invention, reading means make it possible
to acquire information that is representative of the rotational speed of the gas
generator. Control means make it possible to interpret this information and to
compare it with the threshold speed. If the rotational speed is found to be lower
than the threshold speed, and if the engine computer has actually previously
30 requested the engine be put into standby mode, a command is sent to coupling
means which ensure mechanical coupling between the gas generator and the free
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turbine, thus switching the turboshaft engine to a connected-turbine mode. This
mechanical coupling is achieved by means of intermediate shafts that are
mechanically connected to the gas generator and to the free turbine, respectively.
Throughout the text, the term "shaft" denotes a means that is capable of
being rotated and of transmitting a torque. It can therefore be a longitudinally
extending shaft, but also simply a pinion gear.
These coupling means can be of any kind. According to an advantageous
I 0 variant, these coupling means arc selected from the group comprising at least one
friction clutch, a pawl, and a pawl provided with a synchronizer.
A pawl provided with a synchwnizer makes it possible to synchronise the
respective speeds of the shafts before clutching, making it possible to manage the
15 speed differential better than when there is no synchronizer.
Advantageously, these coupling means are designed to allow temporary
sliding, during a preliminary coupling phase, between the shaft that is
mechanically connected to said gas generator and the shaft that is mechanically
20 connected to said free turbine.
Advantageously, a turboshaft engine according to the invention further
comprises a device for spontaneously mechanically coupling said gas generator
and said free turbine, which device is capable of mechanically and spontaneously
25 connecting said gas generator and said free turbine as soon as the ratio of the
wtational speed of said gas generator to the rotational speed of said free turbine
reaches a predetermined threshold valne. This threshold value for the ratio of the
wtational speed of said gas generator to the rotational speed of said free turbine is
in particular less than that which is obtained when the controlled coupling device
30 is activated, such that, when the free turbine is rotating at its nominal speed while
coupled to the rotor, the gas generator rotates no more than I 0 to 20 % faster than
9
its rotational speed during idling flight.
A turboshaft engine according to another embodiment comprises a device
for spontaneous mechanical coupling in addition to a device for controlled
5 mechanical coupling when the gas generator reaches a tlu·eshold speed. Unlike for
the controlled mechanical coupling device, the mechanical connection between
the gas generator and the free turbine by means of the spontaneous mechanical
coupling device does not depend on the rotational speed of the gas generator but
on the ratio of the rotational speed of the gas generator to the rotational speed of
I 0 the fi·ee turbine.
A turboshaft engine according to this variant of the invention thus makes it
possible to force the free turbine to drive the gas generator when predetermined
conditions are reached. In other words, a turboshaft engine according to the
IS invention that is provided with a device for spontaneously mechanically coupling
the gas generator and the fi·ee turbine makes it possible to automatically and
spontaneously switch the turboshaft engine from the configuration referred to as
free-turbine to the configuration referred to as cotmected-turbine, without an
external assistance and/or control device. This switching from a free mode to a
20 cmmected mode thus depends not only on the rotational speed of the gas
generator, but also on the ratio of the rotational speed of the gas generator to the
rotational speed of the free turbine.
Advantageously and according to this variant, said spontaneous
25 mechanical coupling device is capable of mechanically and spontaneously
cmmecting said gas generator and said free turbine as soon as the ratio of the
speeds is less than said predetermined threshold value, and of spontaneously
separating said gas generator and said fi·ee turbine as soon as said ratio is greater
than said predetermined tlueshold value.
30
Advantageously, connected-turbine operation close to idling improves the
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transient performance, in pmiicular in the event of a drop in the revolutions of the
rotor during rapid pitching. This is because the gas generator then rotates at a
speed that is greater than the speed required at zero power in free-turbine mode.
The engine thus very rapidly produces a consequent power on the free turbine that
5 corresponds to the value that the free-turbine turboshaft engine would have at this
speed, plus the additional power resulting from rapidly reaching the acceleration
limit, even before the gas turbine has stmied to accelerate.
Advantageously and according to this variant, said spontaneous
I 0 mechanical coupling device comprises at least one free wheel which connects a
first shaft which, together with said gas generator, has a reduction ratio Kl, and a
second shaft which, together with the free turbine, has a reduction ratio K2, said
fi'ee wheel being arranged such that said li'ee turbine spontaneously drives said
gas generator, by means of said shafts and said free wheel, as soon as said ratio of
15 the speeds is less than the ratio K2/K 1.
Advantageously, a turboshaft engine according to this variant comprises a
stmier-generator that is rigidly connected to an intermediate shaft, and said
spontaneous mechanical coupling device comprises two free wheels which
20 connect said intermediate shaft to said first shaft which, together with said gas
generator, has a reduction ratio Kl, and to said second shaft, respectively, which
second shaft, together with the free turbine, has a reduction ratio K2, said wheels
being arranged such that said free turbine spontaneously drives said gas generator
by means of said shafts and said free wheels as soon as the ratio of the speeds is
25 less than the ratio K2/Kl. Moreover, said stmier-generator rigidly cormected to
the intermediate shaft is thus driven by the free turbine when said starter-generator
is functioning as a generator, and said starter-generator drives the gas generator
when said starter-generator is functioning as a starter.
30 The invention also relates to a twin-engine helicopter, characterised in that
it comprises at least one turboshaft engine according to the invention.
I I
The invention also relates to a method for optimising the zero-power
super-idling mode of a twin-engine helicopter comprising at least one turboshaft
engine comprising a gas generator that is capable of being rotated and a free
5 turbine that is rotated by the gases of said gas generator, characterised in that it
comprises a step of controlled mechanical coupling of said gas generator and said
free turbine as soon as the rotational speed of said gas generator reaches a
predetermined threshold speed.
10 Advantageously, a method according to the invention fh1ther comprises a
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step of spontaneously mechanically coupling said gas generator and the free
turbine as soon as the ratio of the rotational speed of said gas generator to the
rotational speed of said free turbine reaches a predetennined threshold value.
The invention also relates to a turboshaft engine, to a helicopter, and to a
method for optimising the zero-power super-idling mode, characterised in
combination by all or some of the features mentioned above or in the following.
5. List of dmwings
Other aims, features and advantages of the invention will emerge from
reading the following description, which is given purely by way of non-limiting
example and relates to the accompanying drawings, in which:
- Fig. I is a schematic view of a turboshaft engine according to a first
embodiment of the invention,
- Fig. 2 is a schematic view of a turboshaft engine according to a
second embodiment of the invention,
- Fig. 3 is a schematic view of a turboshaft engine according to a third
embodiment of the invention.
6. Detailed description of an embodiment of the invention
fl 12
As shown in the drawings, a turboshaft engine according to the invention
comprises a gas generator 5 and a fi·ee turbine 6 that is powered by the gas
generator 5. As is known, a gas generator 5 comprises at least one air compressor
5 7 that supplies a chamber 8 for combusting fhel in the compressed air and which
supplies hot gases to at least one turbine 9 for partially expanding gas, which
turbine rotates the compressor 7 by means of a drive shaft I 0. The gases also
drive the free power transmission turbine 6. Tllis free turbine 6 comprises a power
transmission shaft II that is cotmected to a power transmission gearbox (not
10 shown in the drawings) by means of a free wheel 12. This free wheell2makes it
possible to prevent mechanical locking of the turboshaft engine from causing
mechanical locking of the power transmission gearbox and, by extension, of the
rotor of the helicopter on which said turbo shaft engine is mounted.
15 A turboshaft engine according to the invention fmther comprises a device
40 for controlled mechanical coupling of the gas generator 5 and the free turbine
6, which device is capable of connecting the gas generator 5 and the fi·ee turbine 6
mechanically and on demand as soon as the rotational speed NGG of the gas
generator is less than a predetermined threshold speed. Throughout the text, the
20 rotational speed N GG of the gas generator denotes the rotational speed of the
25
drive shaft I 0 of the gas generator. In the same way, the rotational speed NTL of
the free turbine denotes the rotational speed of the drive shaft II of the free
turbine.
This threshold speed is fixed at 30 %.NI for example, where Nl is the
nominal rotational speed of the gas generator. In other words, the controlled
mechanical coupling device 40 is capable of ensuring coupling between the gas
generator and the free turbine when the turboshaft engine is in an idling mode. As
soon as the rotational speed NGG of the gas generator is greater than the threshold
30 speed, the gas generator and the free turbine are mechanically independent of one
another.
13
According to the embodiment in the drawings, the control device 40
comprises a shaft 42 that is mechanically connected to the gas generator 5 and a
shaft 43 that is mechanically cmmected to the free turbine. The control device 40
5 fmiher comprises means for reading information that is representative of said
rotational speed NGG of the gas generator 5. These reading means comprise, for
example, a speed sensor that is mounted on the shaft of the gas generator 5, and
therefore the information provided is a direct measurement of the speed of the gas
generator 5. The control device fmiher comprises means 41 for reversibly
I 0 coupling the two shafts 42, 43 and means for controlling these coupling means 41.
According to an embodiment, the coupling means 41 comprise a friction
clutch, such as a centrifugal clutch, a cone clutch, a single-disc clutch or a
multiple-disc clutch. Coupling means of this kind have the advantage of allowing
15 sliding between the shafts in a first coupling phase. According to an embodiment,
the means for controlling this fiiction clutch are actuator-like hydraulic or
electrical control means. Moreover, the control means comprise a module that is
capable of receiving the measurement of the speed of the gas generator and of
comparing said measurement with the threshold speed. A module of the kind is,
20 for example, a software element, a sub-unit of a software program, or a hardware
element, or a combination of a hardware element and a software subprogram.
According to another embodiment, the coupling means 41 comprise a pawl
that is optionally equipped with a synchronizer for better managing the speed
25 differential, making it possible to directly couple the shafts 42 and 43.
Fig. 2 and 3 show two embodiments in which the turboshaft engine fhrther
comprises a device 20 for spontaneously mechanically coupling the gas generator
5 and the free turbine 6. This spontaneous mechanical coupling device 20 is
30 capable of mechanically and spontaneously connecting the gas generator 5 and the
free turbine 6 as soon as the ratio of the rotational speed of the shaft I 0 of the gas
5
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generator 5 to the rotational speed of the shaft II of the free turbine 6 is less than
a predetermined tlucshold value, and of spontaneously separating the gas
generator 5 and the free turbine 6 as soon as the ratio is above this predetermined
threshold value.
According to a first embodiment, and as shown in Fig. 3, this spontaneous
mechanical coupling device 20 comprises a shaft 22 that is mechanically
connected to the shaft 10 of the gas generator 5. Said shafts 22 and 10 have a
reduction ratio between them of Kl.
The spontaneous mechanical coupling device 20 further comprises a shaft
23 that is mechanically connected to the shaft 11 of the free turbine 6. Said shafts
23 and 11 have a reduction ratio between them ofK2.
15 The spontaneous mechanical coupling device 20 further comprises a free
20
wheel 21 that is arranged between the shafts 22 and 23.
Therefore, the rotational speed of the shaft 22 is equal to Kl.NGG, where
NGG is the rotational speed of the shaft 10 of the gas generator 5.
The rotational speed of the shaft 23 is equal to K2.NTL, where NTL is the
rotational speed of the shaft 11 of the free turbine 6.
The free wheel 21 is oriented such that the shaft 23 can drive the shaft 22
25 by means of said free wheel 21.
If the rotational speed of the shaft 23 is less than the rotational speed of the
shaft 22, the two shafts are independent. Otherwise, the two shafts are connected.
In other words, the shafts are independent if the following equation is
30 complied with: K2.NTL < Kl.NGG. The shafts are thus independent if the ratio
NGG/NTL > K2/Kl.
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If the speed ratio is less than or equal to K2/K 1, an engine torque is thus
transmitted fi·om the free turbine 6 to the gas generator 5.
In other words, the spontaneous mechanical coupling device 20 described
in cormection with Fig. 3 makes it possible to mechanically and spontaneously
cormect the gas generator 5 and the free turbine 6 when the ratio NGG/NTL is less
than or equal to K2/K 1, which ratio thus acts as a predetermined threshold value.
The device also makes it possible to spontaneously separate the gas generator 5
10 and the fi·ee turbine 6 as soon as the ratio NGG/NTL exceeds K2/Kl.
If the rotational speed NGG of the gas generator 5 is less than the
threshold speed, the controlled mechanical coupling device 40 ensures that the gas
generator 5 and the free turbine 6 are mechanically coupled by means of the
15 coupling means 41. When this coupling has taken effect, the ratio NGG/NTL
becomes significantly greater than K2/Kl. The spontaneous mechanical coupling
device 20 is therefore not active and the free wheel 21 slides. The two control
devices 20, 40 are therefore entirely compatible with one another.
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According to a second embodiment, and as shown in Fig. 2, the turboshaft
engine fmiher comprises a starter-generator 30. In this case, the coupling device
comprises, in addition to the shafts 22 and 23 described in cotmection with Fig. 2,
an intermediate shaft 25 that is rigidly connected to the starter-generator 30.
The coupling device 20 further comprises a first free wheel 26 that
connects the intermediate shaft 25 to the shaft 23. Said device fi.trther comprises a
second free wheel 24 that cormects the intermediate shaft 25 to the shaft 22.
In the same way as for the embodiment of Fig. 3, the rotational speed of
30 the shaft 22 is equal to K l.NGG, and the rotational speed of the shaft 23 is equal
toK2.NTL.
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The wheels 26, 24 are oriented such that the intermediate shaft 25 that is
rigidly connected to the stmier-generator 30 is capable of driving the shaft 22, and
the shaft 23 is capable of driving the intermediate shaft 25 that is rigidly
5 connected to the stmier-generator 30.
10
The two free wheels 26, 24 drive simultaneously if the ratio NGG/NTL is
equal to K2/KI.
If the ratio NGG/NTL is less than or equal to K2/KI, the shafts 10, 11 are
thus mechanically connected and an engine torque is transmitted from the free
turbine 6 to the gas generator 5.
If the ratio NGG/NTL IS greater than K2/Kl, the shafts are thus
15 mechanically independent.
20
The starter-generator 30 is either driven by the free turbine (when
fimctioning as a generator) or drives the gas generator (when fimctioning as a
starter).
In other words, the mechanical spontaneous coupling device 20 described
111 connection with Fig. 2 also makes it possible to mechanically and
spontaneously connect the gas generator 5 and the free turbine 6 when the ratio
NGG/NTL is less than or equal to K2/KI. The device also makes it possible to
25 spontaneously separate the gas generator 5 and the free turbine 6 as soon as the
ratio NGG/NTL exceeds K2/KI. Fmihermore, the generator and/or stmier
function is possible in this embodiment.
If the rotational speed NGG of the gas generator 5 is less than the
30 threshold speed, the controlled mechanical coupling device 40 ensures that the gas
generator 5 and the free turbine 6 are mechanically coupled by means of the
il 17
coupling means 41. When this coupling has taken effect, the ratio NGG/NTL
becomes significantly greater than K2/Kl. The spontaneous mechanical coupling
device 20 is therefore not active and at least one of the two free wheels 21, 26
slides. The two control devices 20, 40 are therefore entirely compatible with one
5 another.
10
The invention also relates to a method for optimising the zero-power
super-idling mode of a twin-engine helicopter comprising at least one turboshaft
engine according to one of the embodiments described.
A method of this kind therefore comprises a step of mechanically coupling
the gas generator 5 and the free turbine 6 as soon as the rotational speed NGG of
the gas generator 5 is less than a predetermined threshold speed.
15 A method according to the invention is advantageously implemented by a
turboshaft engine according to one of the embodiments described. A turboshaft
engine according to one of the embodiments described advantageously
implements a method according to the invention.

CLAIMS
1. Turboshaft engine comprising a gas generator (5) that is capable of being
rotated, and a free turbine ( 6) that is rotated by the gases of said gas generator,
5 characterised in that it comprises a device ( 40) for controlled mechanical coupling
of said gas generator (5) and said free turbine (6), which device is capable of
connecting said gas generator (5) and said free turbine (6) mechanically and on
demand as soon as the rotational speed of said gas generator ( 5) reaches a
predetermined threshold speed.
10
2.. Turboshaft engme according to claim 1, characterised in that said
controlled mechanical coupling device ( 40) is capable of connecting said gas
generator (5) and said fi·ee turbine (6) mechanically and on demand as soon as
said rotational speed (NGG) of said gas generator (5) is less than said
15 predetermined threshold speed, and of separating said gas generator (5) and said
free turbine (6) on demand as soon as said rotational speed (NGG) of said gas
generator (5) is greater than said predetermined threshold speed.
3. Turbo shaft engine according to either claim 1 or claim 2, characterised in
20 that said threshold speed depends on a nominal speed of said gas generator (5).
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4. Turboshaft engine according to claim 3, characterised in that said
tlu·eshold speed is selected within the range of [20 %.N1, 60 %.N1], where N1 is
said nominal speed of said gas generator.
5. Turboshaft engine according to any of claims I to 4, characterised in that
said controlled mechanical coupling device ( 40) comprises:
means for reading information that is representative of said
rotational speed (NGG) of said gas generator,
means ( 41) for reversible mechanical coupling between a shaft ( 42)
that is mechanically connected to said gas generator and a shaft
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(43) that is mechanically connected to said free turbine (6),
means for controlling said coupling means ( 41) on the basis of said
information that is representative of said rotational speed of said
gas generator, and on the basis of said threshold speed.
6. Turboshaft engine according to claim 5, characterised in that said coupling
means ( 41) are selected from the group comprising at least one friction clutch, a
pawl, and a pawl provided with a synclnonizer.
10 7. Turboshaft engine according to either claim 4 or claim 5, characterised in
15
that said coupling means ( 41) are designed to allow temporary sliding, during a
preliminary coupling phase, between the shaft ( 42) that is mechanically connected
to said gas generator (5) and the shaft (43) that is mechanically cmmected to said
free turbine ( 6).
8. Turboshaft engine according to any of claims I to 7, characterised in that it
further comprises a device (20) for spontaneously mechanically coupling said gas
generator (5) and said free turbine (6), which device is capable of mechanically
and spontaneously connecting said gas generator (5) and said free turbine (6) as
20 soon as the ratio of the rotational speed (NGG) of said gas generator (5) to the
rotational speed (NTL) of said fi·ee turbilie (6) reaches a predetermined tlu·eshold
value.
9. Turboshaft engme according to claim 8, characterised in that said
25 spontaneous mechanical coupling device (20) is capable of mechanically and
spontaneously connecting said gas generator (5) and said free turbine (6) as soon
as the ratio of the speeds is less than said predetermined threshold value, and of
spontaneously separating said gas generator (5) and said free turbine (6) as soon
as said ratio (NGG/NTL) is greater than said predetermined tlneshold value.
30
10. Turboshaft engine according to either claim 8 or claim 9, characterised in
~I 20
that said spontaneous mechanical coupling device (20) comprises at least one free
wheel (21) which connects a first shaft (22) which, together with said gas
generator, has a reduction ratio Kl, and a second shaft (23) which, together with
the free turbine (6), has a reduction ratio K2, said free wheel (21) being arranged
5 such that said free turbine (6) spontaneously drives said gas generator (5), by
means of said shafts and said free wheel (21 ), as sooi1 as said ratio (NGG/NTL) of
the speeds is less than the ratio K2/Kl.
II. Turboshaft engine according to claim I 0, characterised in that it comprises
I 0 a starter-generator (30) that is rigidly connected to an intermediate shaft (25), and
in that said spontaneous mechanical coupling device (20) comprises two free
wheels (24, 26) which connect said intermediate shaft (25) to said first shaft (22),
which, together with said gas generator (5), has a reduction ratio Kl, and to said
second shaft (23), respectively, which second shaft, together with the free turbine
15 (6), has a reduction ratio K2, said wheels (24, 26) being arranged such that said
free turbine (6) spontaneously drives said gas generator (5) by means of said
shafts and said free wheels when said ratio (NGG/NTL) of the speeds is less than
the ratio K2/Kl.
20 12. Twin-engine helicopter, characterised in that it compnses at least one
turboshaft engine according to any of claims I to II.
13. Method for optimising the zero-power super-idling mode of a twin-engine
helicopter comprising at least one turboshaft engine comprising a gas generator
25 (5) ~hat is capable of being rotated and a free turbine (6) that is rotated by the
gases of said gas generator (5), characterised in that it comprises a step of
controlled mechanical coupling of said gas generator (5) and said free turbine (6)
as soon as the rotational speed of said gas generator reaches a predetermined
threshold speed.
30
14. Optimisation method according to claim 13, characterised in that it fhrther
5
21
comprises a step of spontaneously mechanically coupling said gas generator and
the free turbine as soon as the ratio of the rotational speed (NGG) of said gas
generator (5) to the rotational speed (NTL) of said free turbine (6) reaches a
predetermined tln·eshold value.