Technical context
The invention lies in the field of free-turbine
turbine engines for an aircraft having a plurality of
5 turbine engines. The aircraft may in particular be a
helicopter. It should be recalled that a turbine engine
with a free turbine includes a power turbine or "free''
turbine that, in a helicopter, drives the rotors of the
helicopter via an overrunning clutch (freewheel) and a
10 main gearbox (MGB) .
The engine also has a gas generator comprising in
particular a compressor, a combustion chamber, and a high
pressure (HP) turbine.
A speed-reducing accessory gearbox serves to connect
15 the shaft of the gas generator to an electrical machine
constituted by a stator and a rotor that is capable of
operating equally well as a motor (starter) or as a
generator.
In motor mode, the electrical machine is powered by
20 a source of electricity and it develops driving torque so
as to drive rotation of the gas generator of the engine,
in particular for the purpose of starting it, thus
providing assistance on starting.
In generator mode, the electrical machine is driven
25 in rotation by the gas generator so as to take mechanical
power from the gas generator, which power is then
converted into electrical power.
For an aircraft having two turbine engines in a
cruising flight situation, proposals are made in Document
30 US 2013/219905 to put one of the two engines into a
standby mode. Because of the freewheel, the free turbine
and the main gearbox are desynchronized. In parallel,
the other engine (or the other engines) is/are operated
at a power rating that is increased, thereby making it
35 possible to maintain normal flight conditions. The
overall fuel consumption of the system is decreased,
5
2
since the specific consumption of the turbine engine
maintained in operation is then smaller.
Several variants of such a standby mode have been
proposed.
In a first variant, the gas generator of the
desynchronized gas turbine may be regulated on a slow
idle power rating by continuing to deliver fuel thereto.
That can be done with or without additionally using the
electrical machine and the accessory gearbox to supply
10 the gas generator with prolonged assistance driving
torque (assistance for rotation at constant speed) .
In a second variant, it is proposed, in contrast, to
extinguish the combustion chamber of the turbine engine
completely, while using the rotary machine to maintain
15 the gas generator in rotation at a speed suitable for
facilitating re-ignition at the end of the stage of
cruising flight. That likewise constitutes prolonged
assistance (assistance for rotation at constant speed)
Those modes of operation are potentially maintained
20 throughout the duration of cruising flight.
In terms of the performance required of the rotary
machine driving the gas generator, normal restarting of
the desynchronized engine is then analogous to the usual
function of starting on the ground. Such normal
25 restarting generally lasts for a few tens of seconds
between beginning starting and the moment at which the
engine has reached a speed that is sufficient to generate
useful power on the free turbine. By way of example,
such starting is undertaken in order to proceed with a
30 maneuver, such as landing, that is anticipated with a
certain amount of time in advance and that, for its
execution, requires both engines to be operating
simultaneously.
Such restarting requires the rotation of the gas
35 generator of the engine to be accelerated. Such
acceleration is obtained by increasing the fuel flow
rate.
3
Nevertheless, it is sometimes necessary to be in a
position to reactivate the desynchronized engine rapidly,
in particular in an emergency situation, e.g. in the
event of a failure of another engine, if the total number
5 of engines is three or more, or of the other engine if
there are only two engines. In order to satisfy safety
requirements, the maximum time authorized between the
request for emergency starting and the moment at which
the engine as restarted in this way is capable of
10 delivering useful power is typically less than
10 seconds.
In particular, this need for it to be possible for
the engine that has been shut down to be restarted
quickly is the reason why the gas generator is maintained
15 rotating at a speed that facilitates re-ignition in the
modes of operation in which the combustion chamber is
extinguished.
Regardless of whether the gas generator is in an
idling situation or has its combustion chamber
20 extinguished, it is preferable, in particular for
emergency restarting, to apply high power to the gas
generator shaft because of the large amount of inertia of
the rotating assemblies and because of the opposing
25
torque from
needs to be
the compressor of the engine. This power
delivered over a duration that is short, 'Of
the order of a few seconds. It is estimated that, during
this short lapse of time, the power developed by the
emergency starting system needs to be approximately five
to ten times greater than the power needed for normal
30 starting.
Among other solutions, US 2013/219905 suggests using
electrical energy, in particular from a supercapacitor,
to supply a burst of assistance for accelerating the
rotation of the gas generator. In general manner, since
35 a large amount of power is needed, it is advantageous to
have an electrical energy storage member that is capable
of delivering a large amount of power during a short
4
lapse of time. The electrical power may be applied via a
starter rotary machine.
Proposals are also made in Document US 2013/086919
to make use of two supercapacitors, each charged by a
5 respective electricity generator driven by the gas
generator of a respective one of the engines, and each
serving to provide a burst of power for starting another
engine that is in a shutdown state.
In Document US 2010/058731, a burst of acceleration
10 assistance is delivered to the gas generator of a
turboshaft engine, in particular by delivering mechanical
power to the gas generator via an electrical machine that
is driven in rotation by the free turbine.
Document US 2013/219905 also describes a turbine
15 engine assistance device.
Thus, solutions have been proposed to supply the
high power needed for emergency restarting of a turbine
engine.
However, in this context, given the stakes in terms
20 of safety, it can be understood that emergency starting
systems must be capable of guaranteeing a high level of
availability. Specifically, in the event of power being
lost from the turbine engine that is the only engine
providing the helicopter with propulsion, any inability
25 in an emergency to restart the turbine engine that was
initially in standby mode can lead to a total loss of
driving power.
Such a requirement for a high level of availability
can also apply to the function of normal restarting of an
30 engine on standby.
Specifically, when the second engine is operating in
nominal manner, inability to restart the turbine engine
that was initially in standby mode normally on returning
to a twin-engined flight condition, in particular when
35 preparing to land, can make it necessary to make use of
one engine inoperative (OEI) contingency power ratings on
the engine that is in operation.
5
This situation should be avoided since it increases
the workload on the crew and since the use of OEI
contingency ratings is very damaging for an engine.
5 Definition of the invention and associated advantages
To solve these problems, there is proposed an
assistance device for an aircraft free-turbine turbine
engine, the device comprising first power supply means
for electrically powering a first winding of a starter
10 rotary machine in order to drive the gas generator of the
engine, the device being characterized in that it further
comprises monitor means for monitoring the first power
supply means and the first winding, and second power
supply means, said monitor means causing the second power
15 supply means to supply electrical power to a second
winding of the rotary machine in order to drive said gas
generator in the event of the monitor means observing
insufficient power in the first power supply means or in
the first winding.
20 As mentioned above, it is specified that the first
assistance is assistance to rotary motion by mechanically
driving the gas generator by means of the rotor of the
starter rotary machine, and the second assistance is also
rotary motion assistance by mechanically driving the gas
25 generator by the rotor of a starter rotary machine, which
may be the previously-mentioned starter rotary machine or
another starter rotary machine.
By means of these characteristics, if the circuit
having the first winding and its power supply suffers a
30 failure (or more generally provides insufficient power),
thereby losing all or part of the ability of the first
winding to assist the gas generator, it is then possible
to mitigate the difficulty by using the second winding
and its power supply circuit.
35 The starter rotary machine(s) may be an alternating
current (AC) machine or a direct current (DC) machine.
6
The windings may be rotor windings or stator windings,
depending on the structure of the rotary machine used.
The second winding may be powered using elements
that are also used for powering the first winding, but
5 the power supply circuit could alternatively be entirely
distinct and segregated, which is advantageous. This
point is developed below.
In order to detect that the first assistance is not
sufficient, monitor means are used that monitor one or
10 more elements of the power train electrically powering
the starter rotary machine, the supervisor system of the
turbine engine, and/or the engine itself.
In an advantageous embodiment, the assistance device
comprises the starter rotary machine and also another
15 starter rotary machine for providing assistance in
accelerating the gas generator of a second turbine engine
of the aircraft, the second winding being electrically
connected in parallel with said other rotary machine to a
common electrical power supply path.
20 This makes it possible to share the energy sources
and the power supply means and thus to reduce the weight
of the elements needed. In particular, the energy source
in question may be the source for priority use when
restarting the second engine, and which is thus used in
25 an emergency for restarting the first engine, should ,its
starter circuit using the first winding fail. The source
may be an energy storage element, suitable for use in
particular for emergency restarting.
The assistance device may include a power converter
30 and is preferably configured so that a power converter
transmits electrical energy to the second winding of the
starter rotary machine, or exclusively to the other
starter rotary machine. This configuration may be
implemented using a pair of contactors included in the
35 assistance device and not capable of both being in the
closed position simultaneously, so as to ensure
7
electrical energy is transmitted exclusively to the
second winding or to the other starter rotary machine.
In an embodiment, said starter rotary machine
included in the assistance device is a fault-tolerant AC
5 rotary machine being a double winding or double star
machine, the second winding being its second winding.
In known manner, such AC rotary machines of
synchronous or asynchronous type are characterized by two
independent sets of three-phase windings on the stator
10 that are wound on a common magnetic circuit, each winding
being powered by its own DC/AC power converter. Although
covering numerous architecture variants, the design of
such machines relies on the general principle that
consists in guaranteeing a high level of electrical
15 isolation and physical,
between each of the two
thermal, and magnetic segregation
windings. This separation makes
it possible to ensure that an electrical failure, such as
for example a short circuit or an open circuit, occurring
in the first winding or its DC/AC power supply converter,
20 has no functional impact on the second winding and thus
on the ability of the starter to deliver assistance
torque to the gas generator. By sharing the stator
magnetic circuit and the mechanical elements such as the
rotor, the bearings, and the structure (casing), a rotary
25 machine of this type is substantially more compact and
lighter in weight than a set of two completely
independent machines giving equivalent overall
performance, while also providing a high level of
tolerance to internal electrical faults or to faults in
30 the power supply converter.
35
The use of a double winding machine also makes it
possible to install only one rotary machine, thereby
simplifying assembly on the accessory gearbox of the
turbine engine.
In an embodiment, the first winding is of dimensions
enabling it to provide acceleration assistance with
~----
8
performance that is better than the performance provided
by the second winding.
Thus, the starter rotary machine may be of
dimensions enabling emergency starting (rapid starting)
5 of the turbine engine with electrical power being
supplied to said first winding only, while still
retaining reasonable dimensions overall, and still
providing redundancy in the ability to start in a nonurgent
situation (normal starting).
10 In an embodiment, the second winding is of
dimensions enabling acceleration assistance to be
provided with performance similar to that provided by the
first winding.
This provides complete redundancy in ability to
15 restart, and providing the windings and the magnetic
circuit are of appropriate dimensions, this includes the
ability to perform an emergency restart.
In an embodiment, the assistance device has two
power converters, each serving to transmit electrical
20 power in controlled manner to said first and second
windings respectively.
This makes it possible to obtain a fine transition
between two assistances in the event of detecting a
failure in the first circuit. This also enables
25 acceleration assistance to be controlled while using ·two
windings, which is useful in particular in an emergency
situation since it is then possible to benefit for this
acceleration simultaneously from the power developed by
each of the windings.
30 In an embodiment, the assistance device has a first
electrical energy source for powering one of the first
winding and the second winding, and the assistance device
also is configured so that the other one of the second
winding and the first winding can be powered by a second
35 energy source that is distinct from the first energy
source, thereby providing greater safety in the event of
9
a failure of one of the energy sources or of its
electrical connections.
In an embodiment, the device further comprises
another starter rotary machine for delivering
5 acceleration assistance to the gas generator of a second
turbine engine of the aircraft, said other rotary machine
having a winding referred to as a ''third'' winding, the
assistance device further including an electrical energy
source configured as a function of need to power the
10 first or the other winding.
15
Thus, on a twin-engined aircraft, acceleration
assistance is obtained for each of the engines, while not
increasing the sources of energy since the energy source
for the first engine is also used for the second engine.
In an embodiment, the starter rotary machine
included in the assistance device is also a generator
actuated by the engine when it is active, the second
winding being the winding of a second rotary machine
included in the assistance device, which second machine
20 is a starter only.
The generator may be used to recharge an energy
storage element included in the assistance device or
external thereto.
The energy storage element may be usable to supply
25 the electrical power for assisting acceleration of the
gas generator. As mentioned in the introduction, this is
useful, in particular during a stage of flight of the
aircraft in which a second engine delivers power to the
rotary wing of the aircraft in order to enable it to fly,
30 and in an emergency whenever it is appropriate to restart
(reactivate) the first engine.
By having two distinct rotary machines, with only
one serving to generate electricity, it is possible to
dimension the two windings and the yokes of the rotary
35 machines better, while installing energy storage for
emergency restarting of an engine in flight and while
ensuring physical and functional segregation, which
5
10
enhances the availability of the normal or emergency
engine starting function, between the two rotary machines
and their power supply converters, in embodiments in
which they are connected to such converters.
In an embodiment, the second winding is the winding
of a second rotary machine included in the assistance
device, the second rotary machine being a DC machine, and
the first rotary machine also included in the assistance
device, being an AC machine.
10 This makes it possible to provide torque/speed
control for the first rotary machine operating with AC
that is used on a priority basis and to have an emergency
rotary machine that is powered directly from the on-board
DC network of the aircraft, which machine is presently
15 the starter device in the majority of helicopters of
small or medium power that are provided with turbine
engines and with an electrical starter.
In an embodiment, the first winding is powered by an
electricity storage member and the second winding is
20 powered by the on-board network of the aircraft. An
aircraft is thus provided, e.g. a twin-engined
helicopter, having an assistance device of the invention,
the second winding being powered by the on-board network
of the aircraft.
25 This makes it possible to have stored power for
emergency restarting or starting while still being
capable of mitigating a failure of the electrical storage
member but without duplicating it, which can be
considered as penalizing in terms of size and weight.
30 In an embodiment, the means for powering the second
35
winding include a contactor that is closed if the monitor
means observe a difficulty or inability in acceleration
of said gas generator, e.g. for starting said engine
using the first winding.
A contactor is an electromechanical device that is
simple and presents a low risk of failure.
11
There is also provided a method of assisting an
aircraft free-turbine turbine engine, the method
comprising a step of electrically powering a first
winding of a starter rotary machine by first electrical
5 power supply means in order to drive the gas generator of
the engine, the method being characterized in that it
further comprises a step of monitoring the first power
supply means and the first winding and a step of
electrically powering a second winding of the rotary
10 machine by second electrical power supply means in order
to drive said gas generator if it is observed during the
monitoring step that there is insufficient power in the
first power supply means or in the first winding.
15 List of figures
20
Figure 1 shows the context of embodiments of the
invention.
Figure 2 shows a first embodiment of the invention.
Figure 3 shows a second embodiment of the invention.
Figure 4 shows another embodiment of the invention.
Detailed description of embodiments
With reference to Figure 1, the general electrical
architecture of an embodiment of the proposed system is
25 as follows. It is given in the context of a helicopter
having two turbine engines.
The main gearbox MGB is driven by the turbine
engines GTl and GT2. In this example they are free
turbine turboshaft engines. Each has a gas generator and
30 a power turbine (free turbine) driving the main gearbox
(MGB) via a freewheel.
Electricity is generated on board the aircraft by at
least two alternators ALTl and ALT2 driven by the MGB.
Although this architecture, which is usually reserved for
35 heavy helicopters, is not crucial for using the present
invention, and does not constitute an essential
characteristic, it is technically preferable to the
12
conventional solution on heavy aircraft that consists in
driving the electricity generators from the gas
generators of the turboshaft engines. Specifically,
since a fuel saving in cruising flight is obtained by
5 putting one of the engines on standby, as mentioned in
the introduction, where standby is a mode of operation
that is incompatible with taking any power from the gas
generator, it appears pertinent, in particular in terms
of safety, to decouple functionally the generation of
10 electricity on board the aircraft from the mode of
operation of its engines.
ALT1 and ALT2 power the electricity network of the
aircraft, with it being possible for other energy sources
available for powering this network to be constituted by
15 an on-board auxiliary power unit (APU), one or more
storage batteries, or indeed a ground power unit (when on
the ground) .
Each engine GT1 and GT2 has a respective rotary
machine GS1 and GS2 suitable for operating as a starter
20 and as a generator and mechanically connected to the gas
generator of the corresponding engine via an accessory
gearbox.
In order to optimize the compactness and the weight
of the device, it is preferable for GS1 and GS2 to
25 present a machine architecture that is compatible with
being driven at high speed by the gas generator, and thus
without a rotor winding, such as by way of example and in
non-exhaustive manner: a brushless synchronous machine
with permanent magnets; a variable reluctance machine; or
30 a brushless squirrel-cage asynchronous machine.
The two machines GS1 and GS2 are included in an
assistance device 100 operating independently of the
electricity network of the aircraft.
With reference to Figure 2, there is shown a first
35 embodiment of the assistance device 100. The electrical
machines GS1 and GS2 are double-winding electrical
machines, or AC rotary machines that are fault-tolerant.
5
13
These machines are constituted by a single magnetic
circuit or yoke and two distinct multiphase stator
windings or coils, referenced Sll and Sl2 for GSl and S21
and S22 for GS2.
By way of example, GSl and GS2 are machines of
synchronous or of asynchronous type.
The windings Sll and S12 are connected respectively
to reversible DC/AC power converters CV31 and CVS2. Each
of them constitutes an interface between the multiphase
10 AC circuit of the winding and a DC circuit constituted by
15
a DC bus connecting the converter to an electricity
storage member. The electricity storage members are
referenced respectively Sl and 32, and the DC buses
connecting them are referenced bus No. 1 and bus No. 2.
In this example the electricity storage members are
DC members, e.g. being supercapacitors, hybrid
capacitors, storage batteries, or flywheels incorporating
respective DC/AC converters.
The windings 312 and 321 are connected to the
20 opposite power converters, i.e. respectively to CVS2 and
CV31. The windings S12 and 322 are thus in branch or
parallel connections relative to each other at the outlet
from the converter CVS2, while the windings 311 and 321
are in branch connections relative to each other at the
25 outlet from the converter CVSl.
Contactors Kll, K21, K12, and K22 are present for
electrically isolating or connecting the respective
windings 311, S21, S12, and 322, and they operate or are
actuated in coordinated manner so that the converters
30 CVSl and CVS2 can each be used for controlling at most a
single rotary machine at any given instant. Thus,
closing the contactor Kll or K21 causes the contactor K21
or Kll to be opened, and closing the contactor K12 or K22
causes the contactor K22 or K12 to be opened.
35 Given that in any event it is only necessary to
start a single engine at a time, this set of contactors
and the associated control logic advantageously enables
14
the power converters to be shared between the two rotary
machines, thereby reducing the number of machines needed
from four to two, while conserving the level of
redundancy that is required to ensure that the normal and
5 emergency starting functions are available, thereby
securing a distinct improvement in terms of weight and
size.
A contactor KC serves to connect together the two DC
buses No. 1 and No. 2 electrically, or on the contrary to
10 isolate them from each other.
In this example, the rotary machines GS1 and GS2 are
both generators and starters. When operating as
generators, they are driven in rotation by the gas
generator of the corresponding engine, and they are
15 capable via one or the other of their stator windings of
transferring electrical energy to the storage elements S1
and/or S2, or to the sole storage element if only one
storage element is provided.
Once the electrical energy storage elements have
20 been charged, it is possible to undertake a stage of
single-engined flight. In the presently-described
scenario, the engine GT1 delivers driving power while the
engine GT2 is maintained in one of the standby modes
described in the introduction. In order to restart the
25 engine GT2, e.g. prior to landing, or in the event of
losing power from the engine GT1, it is proposed to begin
by electrically isolating the buses No. 1 and No. 2 from
each other using the contactor KC so as to ensure that a
failure does not propagate from one portion of the system
30 to another. Thereafter the contactor K21 is closed with
the contactor K11 being open, and the converter CVS1 is
inhibited, ready to operate but not actually powering the
winding 821.
Simultaneously, the contactor K22 is closed, K12
35 being open, and the converter CVS2 is operated as an
inverter to control the rotary machine GS2 operating in
motor mode and to regulate the torque it delivers in
15
application of a relationship optimized for normal or
emergency starting of the engine as a function of
circumstances. The gas generator of the engine GT2 is
thus actuated so as to enable the engine to be started.
5 If a failure or insufficient power occurs on the
power train S2-CVS2-K22-S22 and threatens the ability to
accelerate the gas generator of the engine GT2
sufficiently, this is identified by monitor means 120.
The monitor means 120 then cause the converter CVSl to be
10 put into action.
In a first variant, the converter CVS2 is
disconnected from the winding S22 by using the contactor
K22, or is put on standby, and the power converter CVSl
acts alone to power the winding S21 in application of a
15 torque control relationship identical to that being
implemented by the converter CVSl. Thus, the starting
sequence is continued. Although energy was initially
taken from the storage member S2, it is subsequently
taken from the storage member Sl.
20 In a second variant, and in the event of a partial
or progressive failure of the power train
S2-CVS2-K22-S22, a strategy of controlling the converters
sequentially is implemented, with torque being
transferred from one branch to the other in full or in
25 part, and in continuous manner.
It is thus possible for assistance by means of the
two windings to be mutually exclusive, or on the contrary
to be simultaneous.
It is specified that a failure or insufficient power
30 in the power train S2-CVS2-K22-S22 may be detected by the
monitor means 120 at each of the elements in the power
train S2-CVS2-K22-S22 (including on the DC bus), or at
the system for supervising the engine GTl, e.g. by
comparing the acceleration of the gas generator with a
35 predetermined chart.
The power train Sl-CVSl-Kll-Sll and the assistance
in accelerating the gas generator of the engine GTl are
16
monitored in the same manner by monitor means 110 that
perform a role symmetrical to the monitor means 120.
In a variant, each of the windings Sl1, S12, S21,
and S22 is of dimensions that are sufficient, in motor
5 operation, to enable it on its own to supply the
performance necessary for emergency starting of the
corresponding engine, and a fortiori for normal starting.
Thus, in the event of a failure or insufficient power in
one of the power trains, normal starting and emergency
10 starting can be carried out in full with the replacement
power train.
In another variant, only the windings Sll and S21
are of dimensions enabling them individually to supply
the performance needed for an emergency start.
15 Nevertheless, all four windings Sl1, S21, S12, and S22
are of dimensions suitable for enabling them to supply
the performance necessary for normal starting. Thus, in
the event of a failure or insufficient power on one of
the power trains involving Sl1 or S21, normal starting
20 can be carried out in full with a replacement power
train, while emergency starting is performed using
performance similar to that required for normal starting,
using one of the windings S12 or S22.
Finally, in another variant, the windings S11 and
25 S12 (respectively S22 and S21) are of dimensions enabling
them together, when powered simultaneously, to deliver
the torque and power performance required for emergency
starting the engine GTl (or respectively GT2). For such
emergency starting, both converters CVS1 and CVS2 are
30 activated simultaneously, one as a master and the other
as a slave, so as to power both windings in coordinated
manner. It is also proposed in this variant that the
windings S11 and S12 (respectively S22 and S21) should be
of dimensions suitable for enabling normal starting using
35 only one winding, thus making it possible in the event of
a failure or insufficient power in one of the power
17
trains involved to ensure that normal starting of the
engine can be carried out in full in any event.
With reference to Figure 3, there is described
another embodiment of an assistance device, given
5 reference 101. The double-winding machines are replaced
by sets of two single-winding rotary machines.
Thus, replacing GS1, there is an AC rotary machine
M1A having a single stator winding together with, on
another outlet of the assistance gearbox of the engine
10 GT1, another AC rotary machine M1B likewise having a
single stator winding. In this embodiment, the winding
S11 is the winding of the machine M1A and the winding S12
is the winding of the machine M1B. The windings are
multiphase windings.
15 The machine M1A is both a generator and a starter,
while the machine M1B is a starter only. M1B may
possibly be mechanically connected to the gas generator
of the engine via a freewheel, thus making it possible to
design the starter only for the maximum drive speed in
20 starter mode, i.e. in the range 50% to 60% of NG, instead
of for the maximum speed of the gas generator, i.e. 100%
of NG. Thus, during stages of flight during which the
engine is in operation, the electrical energy storage
element Sl is recharged via the machine M1A and the
25 converter CVS1, with the rotary machine M1B being left at
rest.
It is also specified that one of the two machines
M1A or M1B is of dimensions enabling it to supply the
required performance in the event of emergency starting,
30 while the other machine need only be of dimensions
enabling it to supply the performance required for normal
starting.
Similar elements are installed on the assistance
gearbox of the engine GT2, with the electrical machines
35 being referenced M2A and M2B.
Monitor means 111 and 121 monitor the acceleration
assistance of the gas generators of the engines, as in
18
Figure 2, so as to cause the power converters CVS1 and
CVS2 to be put into operation.
With reference to Figure 4, there is presented
another embodiment of an assistance device, given
5 reference 102. The machines M1B and M2B are replaced by
DC machines with brushes and commutators, and given
references D1 and D2. Their respective rotor windings
S12 and S21 are connected to the on-board DC network of
the helicopter, which is a network operating at 28 volts
10 DC (VDC) comprising in particular at least one storage
battery B. Contactors KB1 and KB2 (generally not
coordinated with each other) serve to isolate these
machines from the on-board network, or on the contrary to
connect them thereto.
15 A single electrical energy storage member S may also
serve in the variant shown to replace the storage members
S1 and S2 in the above-described embodiment. Contactors
KS1 and KS2 enable this member S to be connected either
to the converter CVS1 or to the converter CVS2. It is
20 nevertheless possible to use two storage members as shown
in Figures 2 and 3.
Monitor means 112 and 122 monitor the acceleration
assistance of the gas generators of the engines, as in
Figures 2 and 3, this time for the purpose of causing the
25 switches KB1 and KB2 to switch over.
In the event of a failure or insufficient power
preventing starting of an engine, e.g. the engine GT1, by
using the corresponding AC rotary machine, i.e. the
machine M1A for the engine GT1, the contactor KB1 is
30 closed and the DC motor D1 takes over, making it possible
to perform normal starting of the engine GT1, even though
the assistance torque is no longer specifically
controlled.
The DC machines D1 and D2 may be generators as well
35 as being starters. If they are not generators, they may
be connected to the accessory gearbox of the
corresponding engine via respective freewheels.
19
The invention is not limited to the embodiments
described, but extends to any variant within the ambit of
the scope of the claims.

CLAIMS
1. An assistance device (100; 101; 102) for an aircraft
free-turbine turbine engine (GTl), the device comprising
first power supply means (Kll, CVSl) for electrically
5 powering a first winding (Sll) of a starter rotary
machine (GSl, MlA) in order to drive the gas generator of
the engine (GTl), the device being characterized in that
it further comprises monitor means (110; 111; 112) for
monitoring the first power supply means and the first
10 winding, and second power supply means (Kl2, CVS2, KBl),
said monitor means causing the second power supply means
to supply electrical power to a second winding (Sl2) of
the rotary machine in order to drive said gas generator
in the event of the monitor means (110; lii; II2)
I5 observing insufficient power in the first power supply
means or in the first winding.
2. An assistance device according to claim I, comprising
the starter rotary machine (GSI, MIA) and also another
20 starter rotary machine (GS2; M2A) for providing
assistance in accelerating the gas generator of a second
turbine engine (GT2) of the aircraft, the second winding
(Sl2) being electrically connected in parallel with said
other rotary machine (GS2; M2A) to a common electrical
25 power supply path (CVS2).
3. An assistance device according to claim 2, including a
power converter (CVS2) and configured so that said power
converter (CVS2) transmits electrical energy to the
30 second winding (Sl2) of the starter rotary machine (GSI,
MIA), or exclusively to the other starter rotary machine
(GS2, M2A).
4. An assistance device according to claim 3, having a
35 pair of contactors (Kl2, K22) that cannot both be in the
closed position simultaneously, so as to ensure
electrical energy is transmitted exclusively to the
21
second winding (Sl2) or to the other starter rotary
machine (GS2, M2A).
5. An assistance device according to any one of claims 1
5 to 4, wherein the monitor means (110; 111; 112) monitor
one or more elements (Sl, CVSl, Kll, Sll) of the power
train electrically powering the starter rotary machine
(GSl; MlA) .
10 6. An assistance device according to any one of claims 1
to 5, wherein the monitor means (110; 111; 112) monitor
the supervisor system of the turbine engine (GTl).
7. An assistance device according to any one of claims 1
15 to 6, including said starter rotary machine (GSl), which
is a fault-tolerant AC rotary machine being a double
winding or double star machine, the second winding (S12)
being its second winding.
20 8. An assistance device according to claim 7, wherein the
second winding (Sl2) is of dimensions enabling
acceleration assistance to be provided with performance
similar to that provided by the first winding (Sll).
25 9. An assistance device according to claim 7, wherein the
second winding (Sl2) is of dimensions enabling
acceleration assistance to be provided with performance
greater than that of the second assistance.
30 10. An assistance device according to any one of claims 1
to 9, having two power converters (CVSl, CVS2), each
serving to transmit electrical power in controlled manner
to said first and second windings (Sll, S12)
35
respectively.
11. An assistance device according to any one of claims 1
to 10, having a first electrical energy source (Sl, S)
22
for powering a first one of the first winding and the
second winding (S11, S12), the assistance device also
being configured so that the other one of the second
winding and the first winding (S12, S11) can be powered
5 by a second energy source (S2; B) that is distinct from
the first energy source.
12. An assistance device according to any one of claims 1
to 11, further comprising another starter rotary machine
10 (M2A) for delivering acceleration assistance to the gas
generator of a second turbine engine (GT2) of the
aircraft, said other rotary machine (M2A) having a
winding (S22) referred to as a "other" winding, the
assistance device further including an electrical energy
15 source (S1, S2, KC; S, KS1, KS2) configured as a function
of need to power the first or the other winding (S11,
S22) .
13. An assistance device according to any one of claims 1
20 to 12, wherein the starter rotary machine (M1A) is
included in the assistance device and is also a generator
configured to be actuated by the turbine engine (GT1),
the second winding (S12) being the winding of a second
rotary machine (M1B; 01) included in the assistance
25 device and constituting a starter only.
14. An assistance device according to any one of claims 1
to 13, wherein the second winding (S12) is the winding of
a second rotary machine (01) included in the assistance
30 device, the second rotary machine being a DC machine, and
the first rotary machine (M1A), included in the
assistance device, being an AC machine.
15. An assistance device according to any one of claims 1
35 to 14, wherein the means for powering the second winding
comprise a contactor (KBl) that is closed if it is
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5
10
23
observed that it is not possible to accelerate said gas
generator using the first winding.
16. An aircraft including an assistance device according
to any one of claims 1 to 15, wherein the first winding
(Sll) is powered by an electricity storage member (S) and
the second winding is powered by the on-board network of
the aircraft.
17. A method of assisting an aircraft free-turbine
turbine engine (GTl), the method comprising a step of
electrically powering a first winding (Sll) of a starter
rotary machine (GSl, MlA) by first electrical power
supply means (Kll, CVSl) in order to drive the gas
15 generator of the engine (GTl), the method being
characterized in that it further comprises a step of
monitoring the first power supply means and the first
winding and a step of electrically powering a second
winding (Sl2) of the rotary machine by second electrical
20 power supply means (Kl2, CVS2, KBl) in order to drive
said gas generator if it is observed during the
monitoring step that there is insufficient power in the
first power supply means or .in the first winding.