HYDRAULIC DEVICE FOR THE EMERGENCY START-liP OF A TURBOSHAFT ENGINE,
PROPULSION SYSTEM OF A MULTI-ENGINE HELICOPTER EQUIPPED WITH SUCH A
DEVICE AND A CORRESPONDING HELICOPTER
1. Technical field of the invention
The invention relates to an autonomous hydraulic device for the emergency start-up of a
turboshaft engine. The invention also relates to an architecture of a propulsion system of a
multi-engine helicopter- in particular a twin-engine or three-engine helicopter- which is
equipped with at least one such device for emergency start-up. The invention also relates to
a helicopter comprising a propulsion system having such an architecture.
2. Technical background
A twin-engine or three-engine helicopter has, in a known manner, a propulsion system
comprising two or three turboshaft engines, each turboshaft engine comprising a gas
generator and a free turbine which is set into rotation by the gas generator and is rigidly
connected to an output shaft. The output shaft of each free turbine is suitable for putting into
motion a power transmission gearbox, which itself drives the rotor of the helicopter which is
equipped with blades having a variable pitch.
It is known that the turboshaft engines of the helicopter operate in regimes which are
dependent on the flight conditions of the helicopter. Throughout the following text, a
helicopter is said to be in a cruising flight situation when it is progressing in normal
conditions, during all the phases of the flight, apart from transient 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 the total installed power available, i.e. in the
transient phases of take-off, ascent, landing and in a regime in which one of the turboshaft
engines is malfunctioning, referred to by the abbreviation OEI (one engine inoperative).
It is known that when the helicopter is in the cruising flight situation, the turboshaft engines
operate at low power levels, which are less than the maximum continuous power thereof.
These low power levels lead to a specific consumption (hereafter referred to as Cs) which is
defined as the ratio between the hourly consumption of fuel by the combustion chamber of
the turbos haft engine and the mechanical power supplied by this turboshaft engine, which is
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greater than approximately 30 % of the Cs of the maximum take-off power, and thus an
overconsumption of fuel in cruising flight.
Furthermore, the turbos haft engines of a helicopter are designed to be oversized so that
they can keep the helicopter in flight in the event of a failure of one of the engines. This flight
situation corresponds to the OEI regime described above. This flight situation occurs
following the loss of an engine and translates into the fact that each engine in operation
supplies a power well above the rated power thereof in order to allow the helicopter to cope
with a perilous situation and then be able to continue the flight.
Secondly, the turboshaft engines are also oversized in order to be able to ensure flight over
the entire flight envelope specified by the aircraft manufacturer and in particular flight at high
altitudes and in hot weather. These flight points, which are very contradictory, in particular
when the helicopter has a mass which is close to the maximum take-off mass thereof, are
only encountered in specific cases of use.
These oversized turboshaft engines are disadvantageous in terms of mass and fuel
consumption. In order to reduce this consumption in cruising flight, it is envisaged to stop
one of the turboshaft engines in flight and to place said engine in a regime, referred to as
standby. The active engine(s) thus operates at higher power levels to supply all the
necessary power, and thus at more favourable Cs levels.
In FR1151717 and FR1359766, the applicants have proposed methods of optimising the
specific consumption of the turboshaft engines of a helicopter by means of the possibility of
placing at least one turboshaft engine in a stabilised power regime, referred to as a
continuous regime, and at least one turboshaft engine in a specific standby regime, from
which it can exit in an urgent or normal manner as required. An exit from the standby regime
is referred to as normal when a change in flight situation necessitates the activation of the
standby turboshaft engine, for example when the helicopter is going to pass from a cruising
flight situation to a landing phase. A normal exit of this type from standby is carried out over
a period of 10 s to 1 min. An exit from the standby regime is referred to as urgent when a
failure or a deficit of power of the active engine intervenes or the flight conditions suddenly
become difficult. An urgent exit of this type from standby is carried out over a period of less
than 10 s.
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The exit from a standby regime of a turboshaft engine and the passage from an economical
flight phase to a conventional flight phase is obtained for example by means of a pack for the
restart of the turboshaft engine which is associated with a device for storing energy such as
an electrochemical store of the Li-ion battery type or an electrostatic storage of the
overcapacity type, which makes it possible to supply to the turboshaft engine the energy
required for restarting and quickly reaching a rated operating regime.
Such a pack for the emergency restart of the turboshaft engine in standby has the
disadvantage of substantially increasing the total weight of the turbos haft engine. The benefit
in terms of fuel consumption which is obtained by placing the turboshaft engine in standby is
thus partly lost by the excess weight brought about by the restart device and the associated
energy storage device, in particular when each turboshaft engine is equipped with an
emergency restart device of this type.
Furthermore, these electrical engineering components can be dependent on the electrical
architecture of the helicopter on which they are mounted.
The inventors have thus sought to reconcile problems which are incompatible a priori,
namely the possibility of placing the helicopter in the economical flight phase, i.e. of placing
at least one turboshaft engine in standby without generating too great an excess weight of
the assembly of the propulsion system, but whilst also allowing an emergency exit from the
standby regime.
In other words, the inventors have sought to propose a new device for the emergency restart
of a turbos haft engine and a new architecture of the propulsion system of a twin-engine or
three-engine helicopter.
3. Aims of the invention
The invention aims to provide a device for the quick start-up of a turboshaft engine which
overcomes the disadvantages of the previous solutions.
The invention also aims to provide a propulsion system of a multi-engine helicopter.
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The invention also aims to provide a propulsion system of a multi-engine helicopter which
allows the turboshaft engine to be placed in standby and allows the quick restart thereof.
The invention also aims to provide, in at least one embodiment of the invention, a propulsion
system which has a mass and a volume which are not prohibitive to being carried in a
helicopter.
The invention also aims to provide, in at least one embodiment of the invention, a propulsion
system which has a lower cost than the architectures from the prior art which have the same
performance.
The invention also aims to provide a method for the quick start-up of a turbos haft engine.
4. Summary of the invention
For this purpose, the invention relates to a device for the emergency start-up of a turboshaft
engine of a helicopter, characterised in that it comprises:
- a hydraulic motor which is mechanically connected to said turboshaft engine and is
suitable for setting into rotation said engine to facilitate the start-up thereof,
- a hydropneumatic store which is connected to said hydraulic motor by means of a
hydraulic circuit for supplying pressurised liquid to said hydraulic motor,
- a hydraulic valve which has controlled quick opening, is arranged on the hydraulic
circuit between said store and said hydraulic motor, and is suitable for being placed
on command at least in an open position in which the liquid can supply said hydraulic
motor, thus facilitating a start-up of said turboshaft engine, or in a closed position in
which said hydraulic motor is no longer supplied with pressurised liquid,
- a reservoir for recovering liquid which is connected to said hydraulic motor by means
of a purge valve.
A device for the start-up of a turboshaft engine according to the invention thus provides a
hydraulic device - which is preferably completely independent of the hydraulic network of the
helicopter on which such a turboshaft engine is intended to be mounted - to ensure the startup
of the turboshaft engine.
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A turboshaft engine comprises, in a known manner, a gas generator and a free turbine which
is powered by the gas generator and connected to a power transmission gearbox.
Preferably, a device for start-up according to the invention provides that the gas generator of
the turboshaft engine is set into rotation by the hydraulic motor which is suitable for
transforming the hydraulic power of the pressurised liquid with which the engine is supplied
into mechanical power for driving the gas generator.
Liquid is supplied to the hydraulic motor by means of the cooperation of a hydropneumatic
store and a valve which has controlled quick opening.
A start-up device of this type is thus independent of the power supply network of the
helicopter and does not require bulky storage batteries. The proposed solution thus makes it
possible to ensure a quick start-up of a turboshaft engine, in particular a turboshaft engine
which is placed in a standby regime, without causing problems in terms of bulk, mass and
cost.
Furthermore, a device according to the invention is simple to use and can be tested on a rig
before the integration thereof in a helicopter.
The assembly formed by the recovery reservoir and the purge valve allows the liquid to be
expelled from the hydraulic circuit once the pressure of the liquid in this circuit exceeds a
predetermined threshold, and allows this expelled liquid to be recovered in the recovery
reservoir. The purge valve defines the predetermined threshold above which the liquid is
expelled from the hydraulic circuit.
Advantageously and according to the invention, the hydropneumatic store is selected from
the group comprising a bladder-type store, a membrane-type store and a piston-type store.
Such a store comprises for example an enclosure made of metal or composite materials, a
pressure sensor which makes it possible to ensure the availability of the store, a safety
valve, a gas reservoir of the nitrogen, helium or argon type, and a reservoir of oil which is
used as a liquid for supplying the hydraulic circuit.
Advantageously and according to the invention, the hydraulic motor comprises a props haft
which is mechanically connected to a shaft, referred to as a gearbox shaft, of an accessory
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gearbox of said turboshaft engine by meshing means comprising at least one free wheel
which is supported by said propshaft
An accessory gearbox of a turboshaft engine makes it possible to drive the auxiliary systems
which are required for the operation of the gas generator of the turboshaft engine and of
equipment of the helicopter, such as the air-conditioning devices. According to this variant,
the hydraulic motor is directly integrated in this accessory gearbox, and this makes it
possible firstly to facilitate the installation and interconnection thereof with the gas generator
of the turbos haft engine, and secondly, to supply, if necessary, some of the power required
to drive the auxiliary systems and/or power the equipment of the helicopter.
The presence of the free wheel makes it possible to avoid the hydraulic motor from being
spontaneously driven by the accessory gearbox when the gas generator supplies
mechanical power.
Advantageously and according to this variant, said meshing means further comprise:
a first meshing stage comprising said propshaft supporting a main pinion which is
mounted on said free wheel and a pinion, which is referred to as a pumping pinion,
a second meshing stage comprising said gearbox shaft supporting a main pinion
which is meshed with said main pinion from said first meshing stage, and a pinion,
which is referred to as a pumping pinion,
- an intermediate meshing stage comprising an intermediate shaft supporting a
connection pinion, which is movable between an engaged position in which it is
meshed together with said pumping pinions from the first and second meshing
stages, and a disengaged position, in which it does not interfere with said pumping
pinions.
A device according to this variant allows reversible operation of the device. In particular, it
not only makes it possible to ensure a start-up of the turboshaft engine by the hydraulic
motor, but also to reload the hydropneumatic store using the hydraulic motor as a hydraulic
pump. For this purpose, an intermediate stage comprises a connection pinion which is
suitable for being displaced from a position in which it is not coupled either to the propshaft
or to the gearbox shaft (the hydraulic motor thus operates as a motor and supplies
mechanical power to drive the shaft of the accessory gearbox) to a position in which it is
coupled together with the propshaft and the gearbox shaft (the hydraulic motor thus acts as
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a hydraulic pump, and the shaft of the accessory gearbox sets into rotation the propshaft by
means of the intermediate shaft. This intermediate shaft, which is arranged between the
gearbox shaft and the propshaft, reverses the direction of rotation of the propshaft with
respect to the first position, thus imparting a hydraulic pump function on the hydraulic motor).
When the hydraulic motor is used as a hydraulic pump to ensure the reloading of the
hydropneumatic store, it is useful to provide a device for controlling the purge valve to
prevent the non-return operation thereof.
The invention also relates to a propulsion system of a multi-engine helicopter comprising
turboshaft engines which are connected to a power transmission gearbox, characterised in
that it comprises:
at least one turboshaft engine among said turboshaft engines, referred to as a hybrid
turboshaft engine, which is capable of operating in at least one standby regime
during a stabilised flight of the helicopter, the other turboshaft engines operating only
during this stabilised flight,
- at least one device for the emergency restart of a hybrid turboshaft engine according
to the invention which is suitable for being able to take this hybrid turboshaft engine
out of said standby regime and reach a regime, referred to as the rated regime, in
which it supplies mechanical power to said power transmission gearbox.
A device for the start-up of a turboshaft engine according to the invention is intended in
particular to be integrated in a propulsion system of a multi-engine helicopter comprisfng at
least one turboshaft engine which is capable of being placed in standby. The hydraulic startup
device makes it possible to ensure the emergency restart of the turbos haft engine in
standby when required.
A hybrid turboshaft engine is a turbos haft engine which is designed to be able to be placed,
on command and voluntarily, in at least one predetermined standby regime, which it can exit
in a normal or quick manner (also referred to as an urgent manner). A turboshaft engine can
only be in standby during a stabilised flight of the helicopter, i.e. when there is no failure of a
turbos haft engine of the helicopter, during a cruising flight situation, when said helicopter is
progressing in normal conditions. The exit from the standby regime consists in passing the
turboshaft engine into the acceleration mode of the gas generator by means of a drive which
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is compatible with the exit mode imposed by the conditions (normal exit from standby or
quick exit from standby (also referred to as emergency exit).
Advantageously, a propulsion system according to a variant of the invention comprises two
hybrid turboshaft engines and two emergency restart devices according to the invention,
each hybrid turboshaft engine being associated with a restart device.
According to this variant, the system has a separate hydraulic supply for each hydraulic
motor for restarting each hybrid turboshaft engine.
Advantageously, a system according to another variant of the invention comprises two
hybrid turboshaft engines and a single restart device according to the invention which
comprises two hydraulic motors which are connected to each hybrid turboshaft engine,
respectively, said hydraulic valve being a latching valve which is controlled to orient the fluid
towards said hydraulic motor of the hybrid turboshaft engine to be restarted.
According to this variant, the latching valve is controlled to orient the liquid of the hydraulic
circuit towards the hybrid turboshaft engine which has to be restarted.
The invention also relates to a helicopter comprising a propulsion system according to the
invention.
The invention also relates to a method for the emergency start-up of a turboshaft engine of a
helicopter, characterised in that it comprises:
a step of controlling the opening of a hydraulic valve which is arranged on a hydraulic
circuit between a hydropneumatic store and a hydraulic motor which is mechanically
connected to said turboshaft engine,
- a step of guiding the liquid which is taken off towards said hydraulic motor,
- a step of transforming, by means of said hydraulic motor, the hydraulic power of the
pressurised liquid into mechanical power to bring about the start-up of the turboshaft
engine.
The invention also relates to a device for the start-up of a turboshaft engine, a propulsion
system of a multi-engine helicopter, a helicopter which is equipped with a propulsion system,
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and a method for the start-up of a turboshaft engine, characterised in combination by all or
some of the features mentioned above or below.
5. List of the drawings
Other aims, features and advantages of the invention will become apparent upon reading the
following description which is provided purely on a non-limiting basis and relates to the
accompanying drawings, in which:
- Fig. 1 is a schematic view of a device for the start-up of a turboshaft engine
according to one embodiment of the invention,
- Fig. 2 is a schematic view of an architecture of a propulsion system of a helicopter
according to one embodiment of the invention,
- Fig. 3 is a schematic view of an architecture of a propulsion system of a helicopter
according to another embodiment of the invention,
- Fig. 4 is a schematic view of meshing means of a start-up device according to one
embodiment of the invention in a position in which the device operates in the motor
mode,
- Fig. 5 is a schematic view of meshing means of a start-up device according to one
embodiment of the invention in a position in which the device operates in the pump
mode.
6. Detailed description of an embodiment of the invention
In the drawings, the scales and the proportions are not respected for the sake of illustration
and clarity.
Fig. 1 is a schematic view of a device for the start-up of a turboshaft engine 6 according to
one embodiment of the invention.
Such a device comprises a hydraulic motor 7 which is mechanically connected to the
turboshaft engine 6 by means of a free wheel 8. This hydraulic motor 7 can be a motor
having axial or radial pistons. The function thereof is to transform the hydraulic power that it
receives into mechanical power, thus making it possible to bring about the start-up of the
turboshaft engine.
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This hydraulic motor 7 is preferably mounted on the turboshaft engine 6 by means of an
accessory gearbox, which is not shown in Fig. 1.
The device further comprises a hydropneumatic store 9 which is connected to the hydraulic
motor 7 by means of a hydraulic circuit 10 for supplying pressurised liquid to this hydraulic
motor 7. This hydropneumatic store 9 is, according to the embodiment in Fig. 1, a monobloc
piston-type store 16. The piston 16 defines a compartment 17 for gas having a variable
volume and a compartment 18 for oil having a variable volume. The gas compartment 17 is
for example filled with nitrogen, helium or argon. This gas from the gas compartment 17
exerts a pressure on the piston 16 which can be moved towards an increase in the volume
of the gas compartment 17 and a reduction in the volume of the oil compartment 18. The oil
is thus pushed towards the hydraulic circuit 10.
The supply of the hydraulic motor 7 is dependent on a h~draulic valve 11 which has
controlled quick opening and is arranged on the hydraulic circuit 10 between the store 9 and
the hydraulic motor 7.
This hydraulic valve 11 is controlled by a control device 12, which is preferably the control
computer of the turboshaft engine 6, which further makes it possible to define the operating
regime of the turboshaft engine.
When the valve 11 is controlled in opening, the oil from the oil compartment 18 of the store 9
is ejected towards the hydraulic motor 7 so that said motor transforms the hydraulic power of
the oil which is received into mechanical power at the output.
The start-up device also comprises a reservoir 14 for recovering liquid which is connected to
the hydraulic motor 7 by means of a purge valve 15. This valve is set in such a way that the
oil is ejected from the circuit 10 once the pressure exceeds a predetermined threshold.
The start-up device from Fig. 1 is advantageously provided in an architecture of a propulsion
system of a twin-engine helicopter as shown in Fig. 2.
According to the embodiment in Fig. 2, the propulsion system comprises two turboshaft
engines 6, 16 which are connected to a power transmission gearbox 22, which in turn drives
a rotor of the helicopter (not shown in the drawings). Each turboshaft engine is a hybrid
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turbos haft engine, which can be placed in at least one standby regime during a stabilised
flight of the helicopter, from which it can exit again in an emergency by means of a start-up
device according to the invention. A turboshaft engine comprises, in a known manner, a gas
generator, a combustion chamber and a free turbine.
The standby regime is for example one of the following operating regimes:
- a standby regime, referred to as a conventional idling regime, in which the
combustion chamber is ignited, and the shaft of the gas generator rotates at a speed
of between 60 and 80 % of the rated speed,
- a standby regime, referred to as a conventional super-idling regime, 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 rated speed,
- a standby regime, referred to as an assisted super idling regime, 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 rated speed,
- a standby regime, referred to as a banking regime, in which the combustion chamber
is extinguished, and the shaft of the gas generator rotates, with mechanical
assistance, at a speed of between 5 and 20 % of the rated speed,
a standby regime, referred to as a shutdown regime, in which the combustion
chamber is extinguished, and the shaft of the gas generator is at a complete stop.
The start-up device comprises, in addition to the elements described in connection with Fig.
1, a hydraulic motor 17 which is connected to the turboshaft engine 16 by means of a' free
wheel18. Furthermore, the hydraulic circuit 10 extends from the hydropneumatic.store 9 as
far as the hydraulic motor 17 and the hydraulic motor 7.
The controlled valve 11 is, according to this embodiment, a three-way valve which is suitable
for allowing, on command, either the supply of the hydraulic motor 17 which is connected to
the turboshaft engine 16, or the supply of the hydraulic motor 7 of the turboshaft engine 6.
The command is dependent on the turbos haft engine in standby which has to exit the
standby regime thereof in an emergency.
The operating principle of the start-up device of this architecture is, for each turboshaft
engine 6, 16, identical to that described in connection with Fig. 1.
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Fig. 3 is a propulsion system according to another embodiment of the invention. According to
this embodiment, a separate start-up device is provided for each turboshaft engine. In other
words, a hydropneumatic store 29, 39 is associated with each hydraulic motor 7, 17, and a
valve 21, 31 is associated with each store 29, 39 to ensure the supply of the motors and the
restart of the corresponding turboshaft engine. The valves 21, 31 are controlled by the
control unit 12. Only the reservoir 14 for recovering oil is common to the two start-up
devices. According to another variant which is not shown in the drawings, all the elements
are separate, including the recovery reservoir 14.
The propulsion system further comprises, for each engine 6, 16, a separate purge valve 15,
15' which is associated with this engine. Each purge valve 15, 15' has a dual function.
Firstly, when the associated engine is inactive, it makes it possible to keep the oil inside said
engine. The purge valve thus makes it possible to avoid the engine starting empty.
Secondly, when one of the two engines starts, the oil from the return line of the engine in
operation must be prevented from supplying the other engine (which would otherwise also
start rotating). The purge valve thus makes it possible in this situation to act as a non-return
device for isolating the other engine.
Furthermore, according to the embodiment from Fig. 3, the hydropneumatic stores 29, 39
are bladder-type stores. Each store 29, 39 comprises a bladder 28, 38 containing a gas, of
the nitrogen, argon or helium type, which is arranged within the enclosure of the store· which
is filled with oil. Such a bladder plays the role of the gas compartment 17 of the store 9 from
Fig. 1. In another embodiment, the hydropneumatic stores are membrane-type or piston-type
stores.
Fig. 4 and 5 are schematic views of one embodiment of the mechanical connection between
the hydraulic motor 7 and an accessory gearbox 13 of the turboshaft engine 6.
This mechanical connection is formed by meshing means which comprise a first meshing
stage formed by a propshaft 40, which is the output shaft of the hydraulic motor 7, a main
pinion 41 which is supported by the propshaft 40 and mounted on the free wheel 8, and a
pumping pinion 42.
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The meshing means further comprise a second meshing stage formed by a gearbox shaft
60, a main pinion 61 which is supported by the gearbox shaft 60 and meshed with the main
pinion 41 from the first meshing stage, and a pumping pinion 62 which is supported by the
gearbox shaft 60.
The meshing means lastly comprise an intermediate meshing stage which is formed by an
intermediate shaft 50 supporting a connection pinion 52.
The connection pinion 52 is configured to have two positions, an engaged position which is
shown by Fig. 5, and a disengaged position which is shown by Fig. 4.
In the engaged position in Fig. 5, the pinion is set into rotation by the pumping pinion 62
which is supported by the shaft 60 of the accessory gearbox 13, and said pinion sets into
rotation the pumping pinion 42 which is supported by the propshaft 40. Thus, in this position,
the shaft 40 is set into rotation by the shaft 60 of the accessory gearbox. The hydraulic motor
7 thus operates in the hydraulic pump mode, and this makes it possible to re-inject the oil
towards the hydropneumatic store. The free wheel 8 permits the free rotation of the pinion
41.
In the disengaged position in Fig. 4, the pinion 52 is not mechanically connected to the
pumping pinions 42, 62. Also, in this position, the main pinion 41 which is supported by the
propshaft 40 drives the pinion 61 which is supported by the shaft 60 of the accessory
gearbox. This position is the position which allows the quick start-up of the turboshaft
engine.
The displacement of the pinion 52 from the disengaged position into the engaged position
can be ensured by a hydraulic, pneumatic or electric actuator, or by any equivalent means.
The principle of using a device for the start-up of a turboshaft engine within a twin-engine
architecture as shown in Fig. 2 is as follows:
- when the flight conditions are favourable, an order is emitted to place a turboshaft
engine in standby to save fuel (standby regime selected from the standby regimes
mentioned above).
- the computers of the turboshaft engines then determine which turboshaft engine can
be placed in standby and order the placement in standby thereof (in the following, the
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turboshaft engine 6 is considered to be placed in standby, and only the turbos haft
engine 16 supplies power to the power transmission gearbox 22),
- the turboshaft engine 6 is in the standby regime (this standby regime can be one of
the above-mentioned standby regimes, with an ignited or extinguished chamber, with
or without mechanical assistance),
- during the flight, the turboshaft engine 16 suddenly fails, or the pilot decides to carry
out an emergency restart of the turboshaft engine 6 for a specific emergency
manoeuvre,
- the combustion chamber of the turboshaft engine 6 is then quickly reignited (in the
case of a standby regime with an extinguished chamber),
- after a predetermined period of time, the control unit 12 orders the opening of the
latching valve 11 towards the turboshaft engine 6,
- the hydraulic motor 7 then passes quickly (in a period of time of less than a second)
from 0 rpm to the docking speed of the gas generator initially in the standby regime
whilst transforming the hydraulic power into mechanical power, making it possible to
drive the gas generator of the turboshaft engine 6 by means of the free wheel 8,
- the hydraulic motor 7 follows the drive of the turbos haft engine 6 for a short period of
time, for example of less than 10 seconds, during which time the turbos haft engine
has reached the emergency regime thereof,
- the emergency start-up of the turboshaft engine 6 is thus obtained.
The docking speed corresponds to the standby speed of the gas generator divided by the
ratio of reduction in speeds between the shaft of the gas generator and the input of the
accessory gearbox of the turboshaft engine on which the hydraulic starter is mounted.
A device according to the invention thus makes it possible to quickly restart a turboshaft
engine in standby which has recourse only to members which are inexpensive, are simple to
use and install, can be tested on rigs and make it possible to reload the hydropneumatic
store.
The invention is not limited to only the described embodiments. In particular, the propulsion
system can comprise three turboshaft engines for equipping a three-engine helicopter, and a
person skilled in the art can easily determine, based on the teachings of the present text,
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how to adapt the described embodiments to a multi-engine, in particular three-engine,
propulsion system.

Claims
1. Device for the emergency start-up of a turboshaft engine (6) for a helicopter,
characterised in that it cqmprises:
a hydraulic motor (7) which is mechanically connected to said turboshaft engine (6)
and is suitable for setting into rotation said engine to facilitate the start-up thereof,
a hydropneumatic store (9) which is connected to said hydraulic motor (7) by means
of a hydraulic circuit (10) for supplying pressurised liquid to said hydraulic motor (7),
a hydraulic valve (11) which has controlled quick opening, is arranged on the
hydraulic circuit (10) between said store (9) and said hydraulic motor (7), and is suitable for
being placed on command at least in an open position in which the liquid can supply said
hydraulic motor (7), thus facilitating a start-up of said turboshaft engine (6), or in a closed
position in which said hydraulic motor (7) is no longer supplied with pressurised liquid,
a reservoir (14) for recovering liquid which is connected to said hydraulic motor (7) by
means of a purge valve ( 15).
2. Device according to claim 1, characterised in that said hydropneumatic store (9) is
selected from the group comprising a bladder-type store, a membrane-type store and a
piston-type store.
3. Device according to either claim 1 or claim 2, characterised in that said hydraulic
motor (7) comprises a propshaft (40) which is suitable for being mechanically connected to a
shaft, referred to as a gearbox shaft (60), of an accessory gearbox (13) of said turbos haft
engine (6) by meshing means comprising at least one free wheel (8) which is supported by
said propshaft (40).
4. Device according to claim 3, characterised in that said meshing means further
comprise:
a first meshing stage comprising said propshaft (40) supporting a main pinion (41)
which is mounted on said free wheel (8) and a pinion, referred to as a pumping pinion (42),
. a second meshing stage comprising said gearbox shaft (60) supporting a main pinion
(61) which is meshed with said main pinion (41) from said first meshing stage, and a pinion,
referred to as a pumping pinion (62),
an intermediate meshing stage comprising an intermediate shaft (50) supporting a
connection pinion (52) which is movable between an engaged position in which it is engaged
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together with said pumping pinions (42, 62) from the first and second stages, and a
disengaged position in which it does not interfere with said pumping pinions (42, 62).
5. Propulsion system for a multi-engine helicopter comprising turbos haft engines (6, 16)
which are suitable for being connected to a power transmission gearbox (22),
characterised in that it comprises:
at least one turboshaft engine (6, 16) among said turboshaft engines, referred to as a
hybrid turboshaft engine, which is capable of operating in at least one standby regime during
a stabilised flight of the helicopter, the other turboshaft engines operating only during this
stabilised flight,
at least one device for the emergency restart of a hybrid turboshaft engine according
to any of claims 1 to 4 which is suitable for being able to take this hybrid turboshaft engine
out of said standby regime and reach a regime, referred to as the rated regime, in which it
supplies mechanical power to said power transmission gearbox.
6. System according to claim 5, characterised in that it comprises two hybrid turboshaft
engines (6, 16) and two emergency restart devices according to any of claims 1 to 5, each
hybrid turboshaft engine being associated with a restart device.
7. System according to claim 5, characterised in that it comprises two hybrid turboshaft
engines (6, 16) and a single restart device according to any of claims 1 to 5 which comprises
two hydraulic motors (7, 17) which are connected to each hybrid turboshaft engine (6, 16),
respectively, said hydraulic valve (11) being a three-way valve which is controlled to orient
the fluid towards said hydraulic motor of the hybrid turboshaft engine to be restarted.
8. Helicopter comprising a propulsion system according to any of claims 5 to 7.
9. Method for the emergency start-up of a turbos haft engine (6) of a helicopter,
characterised in that it comprises:
a step of controlling an opening of a hydraulic valve (11) which is arranged on a
hydraulic circuit (10) between a hydropneumatic store (9) and a hydraulic motor (7) which is
mechanically connected to said turboshaft engine (6),
a step of guiding the liquid which is taken off towards said hydraulic motor (7),
a step of transforming, by means of said hydraulic motor (7), the hydraulic power of
the pressurised liquid into mechanical power to bring about the start-up of the turboshaft
engine (6).