TRANSMISSION ASSEMBLY FOR AN AIRCRAFT AND A HELICOPTERt
FIELD OF THE INVENTION
The present description relates to a transmission
5 assembly for an aircraft and also to a helicopter
including such an assembly.
Such a transmission assembly may be used to control
independently the speed of rotation of an engine and the
speed of rotation of a torque receiver in order to
10 optimize the speed of each of them. This is useful in
particular in the field of aviation, and more
particularly in the field of helicopters.
STATE OF THE PRIOR ART
15 In a conventional helicopter, it is usual to connect
the gas turbine(s) of the aircraft to equipment that
takes off mechanical power such as the main gearbox
(MGB), the alternator, or indeed the load compressor.
Under such circumstances, the speed of the gas turbine is
20 imposed by the equipment to which it is connected: this
is problematic since the imposed speed does not
necessarily correspond to an energy optimum for the
entire system (the gas turbine or the receiver).
In particular, with an auxiliary power unit (APU),
25 some of the equipment connected to the APU operates at
speeds that vary depending on loading: this leads to the
APU running at an imposed speed that varies, which leads
to running it in irregular manner, and is therefore
harmful for its fuel consumption.
30 Helicopter propulsion is itself likewise concerned
by this problem. Specifically, the turbine engines drive
the main rotor of the helicopter via the main gearbox
(MGB) : the speed of rotation of the main rotor thus
imposes a speed of rotation on the turbine engines (as
35 scaled by the reduction ratio of the MGB). However,
t Translation of the title as established ex officio.
5
2
under certain conditions of flight, it is found that this
imposed speed does not correspond to the optimum speed
for the turbine engines, and that is unfavourable for
fuel consumption.
In order to solve that problem, a first solution
consists in controlling the speed of rotation of the main
rotor so as to approach the turbine speed that is the
most suitable. Nevertheless, that solution is limited,
since it is not possible to vary that speed beyond a
10 narrow range without affecting flight safety.
There therefore exists a real need for a
transmission assembly and a helicopter that enable the
engine speed to be optimized independently of the speed
of the torque receiver and that are exempt, at least in
15 part, from the drawbacks inherent to the above-mentioned
known configurations.
SUMMARY OF THE INVENTION
The present description provides an aircraft
20 transmission assembly comprising a first inlet shaft
configured to receive torque from a first engine, an
outlet shaft configured to transmit torque to a torque
receiver, a first transmis9ion member having at least two
degrees of freedom and comprising first, second, and
25 third movable portions, a controllable first reversible
electrical regulator machine, and a first reversible
electrical balancing machine, wherein the inlet shaft is
coupled to the first movable portion, the outlet shaft is
coupled to the second movable portion, the first
30 electrical regulator machine is coupled to the third
movable portion, and the first electrical balancing
machine is coupled in series with the inlet shaft or the
outlet shaft.
In the present description, the term "transmission
35 member having at least two degrees of freedom" is used to
mean a transmission member that associates at least three
movable portions presenting travel speeds that are
3
associated by a single mathematical relationship. For
example, in a transmission member having two degrees of
freedom, it is necessary to set the speeds of two of the
movable portions in order to determine the speed of the
5 third.
Thus, by means of such a configuration including a
transmission member having two degrees of freedom, it is
possible to control the speed of the regulator machine
positively or negatively so as to enable either the
10 torque receiver to operate at variable speed for constant
engine speed, or else the engine to operate at variable
speed for constant torque receiver speed. It is thus
possible to obtain savings in terms of fuel consumption
or gains in terms of performance.
15 Specifically, knowing the nominal speed of rotation
of the torque receiver and knowing the speed of rotation
desired for the engine, the mathematical relationship of
the transmission member makes it possible to calculate
the speed at which th€ electrical regulator machine needs
20 to be controlled.
The regulator machine may particular be controlled
as a function of flight conditions in order to follow
variations in the nominal speed for the torque receiver
or variations in the optimum speed for the engine,
25 thereby enabling significant savings to be obtairred in
fuel consumption and/or significant gains to be obtained
in performance for all stages of flight.
When the electrical regulator machine is operating
as a torque receiver, it converts the mechanical power it
30 takes off into electrical power that can be used by the
on-board equipment and/or by the electrical balancing
machine. The electrical balancing machine then operates
as a motor consuming electrical power in order to restore
mechanical power to the torque receiver, which mechanical
35 power is equivalent to the power taken off by the
electrical control machine.
4
Conversely, when the electrical regulator machine
operates as a motor, it consumes electrical power,
thereby injecting additional mechanical power into the
system. The electrical balancing machine then operates
5 as a torque receiver converting into electrical power
mechanical power that is equivalent to the additional
power injected by the electrical regulator machine.
Thus, it is possible to control the speed of the
engine while providing effective transmission of
10 mechanical power from the engine to the torque receiver
and without giving rise to an undesired reduction or
increase in power. Nevertheless, the electrical machines
may also be controlled so as to obtain a nonzero power
budget for the purpose of delivering additional
15 electrical power to on-board equipment or, on the
contrary, for the purpose of supplying additional
mechanical power to the torque receiver during certain
stages of flight.
In certain embodiments, the assembly further
20 comprises an energy storage device configured to exchange
electrical energy both with the first electrical
regulator
balancing
machine and also with the first electrical
machine. It is thus possible to store any
surplus energy generated when there is a nonzero power
25 balance between the electrical regulator machine and the
electrical balancing machine. The storage device may be
connected to the on-board electricity network.
In certain embodiments, the assembly further
comprises a freewheel coupled in series between the first
30 electrical regulator machine and the first transmission
member. This is particularly useful in the event of the
electrical regulator machine failing while the engine
speed is faster than the speed of the equipment in order
to ensure a reduction ratio between the engine and the
35 equipment.
5
In certain embodiments, the first transmission
member is an epicyclic gear train having a sun gear,
planet gears connected to a planet carrier, and a ring.
The present description also provides a helicopter
5 having a first engine, including at least a first turbine
engine, a-rotor, and a transmission assembly according to
any of the above embodiments, the transmission assembly
being configured to transmit torque coming from the first
engine to the rotor. Such a configuration makes it
10 possible to decouple the speed of the turbine engine from
the speed of the rotor.
In certain embodiments, the helicopter also has a
main gearbox (MGB) . Such an MGB includes an epicyclic
gear train providing a speed step-down ratio between the
15 turbine engine and the rotor. In certain embodiments,
the MGB may be used as the first transmission member.
In certain embodiments, the planet carrier of the
first transmission member, which is distinct from the MGB
and constitutes the first movable portion of the
20 transmission member, is coupled to the first engine, the
ring of the first transmission member, constituting its
second movable portion, is coupled to an inlet of the
main gearbox, and the sun gear of the first transmission
member, constituting its third movable portion, is
25 coupled to the first electrical regulator machine. In
this configuration, the transmission member provides a
reduction of speed between the turbine engine and the
inlet of the MGB: this speed reduction can be adjusted by
controlling the speed of the electrical regulator
30 machine, thereby enabling the turbine engine to be
controlled to operate at its optimum speed.
In certain embodiments, the helicopter further
comprises a second engine, including at least one turbine
engine, a second transmission member analogous to the
35 first transmission member, a second reversible electrical
regulator machine, and a second reversible electrical
balancing machine.
6
In certain embodiments, the helicopter comprises a
common energy storage device configured to exchange
electrical energy with the first and second electrical
regulator machines and with the first and second
5 electrical balancing machines. In such helicopters
having a plurality of turbine engines, this configuration
makes it possible to share the energy storage device,
thereby reducing costs and also reducing on-board volume
and weight.
10 In certain embodiments, the first and second
electrical balancing machines form a single common
electrical balancing machine that is coupled to the third
movable portions of the first and second transmission
members. This sharing reduces costs and also reduces on-
15 board volume and weight.
In certain embodiments, the first and second
electrical balancing machines form a single common
electrical balancing machine coupled in series between
the outlet from the main gearbox and the rotor. This
20 sharing reduces costs and also reduces on-board volume
and weight.
Naturally, these various kinds of sharing can be
envisaged in analogous manner for any number of engines.
In certain embodiments, the helicopter comprises a
25 main gearbox (MGB) including an epicyclic gear train
constituting the first transmission member. This takes
advantage of the epicyclic gear train that is
conventionally present in an MGB, thus making it possible
to avoid having an additional specific gearbox member.
30 In certain embodiments, the sun gear of the first
transmission member, constituting its first movable
portion, is coupled to the first engine, the planet
carrier of the first transmission member, constituting
its second movable portion, is coupled to the rotor, and
35 the ring of the first transmission member, constituting
its third movable portion, is coupled to the first
electrical regulator machine. In this configuration, the
7
transmission member reduces speed between the turbine
engine and the rotor: this speed reduction is adjustable
by controlling the speed of the electrical regulator
machine, thereby enabling the turbine engine to be
5 controlled to operate at its optimum speed.
10
In certain embodiments, the first electrical
balancing machine is coupled in series between the first
movable portion of the transmission member and said inlet
of the main gearbox.
In certain embodiments, the first electrical
balancing machine is coupled in series between the first
engine and the first movable portion of the transmission
member.
In certain embodiments, the first electrical
15 balancing machine is coupled in series between the outlet
from the main gearbox and the rotor.
In certain embodiments, the first engine further
comprises a second turbine engine and an intermediate
transmission box having a first inlet coupled to the
20 first turbine engine, a second inlet coupled to the
second turbine engine, and an outlet coupled to the first
movable portion of the first transmission member.
The above-described characteristics and advantages,
and others, appear on reading the following detailed
25 description of embodiments of the proposed transmission
assembly and helicopter. The detailed description refers
to the accompanying drawings.
30
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are diagrammatic and seek
above all to illustrate the principles of the invention.
In the drawings, from one figure to another,
elements (or portions of element) that are identical are
identified by the same reference signs. Also, elements
35 (or portions of element) belonging to embodiments that
are different, but that have functions that are
5
8
analogous, are identified in the figures by numerical
references incremented by 100, 200, etc.
Figure 1 is a block diagram of a first embodiment of
a transmission assembly.
Figure 2 shows the configuration of the transmission
member in the first embodiment.
Figure 3 is a graph showing different speeds for the
first embodiment as a function of the selected piloting.
Figure 4 is a block diagram of a second embodiment
10 of a transmission assembly.
Figure 5 is a block diagram of a third embodiment of
a transmission assembly.
Figure 6 is a block diagram of a fourth embodiment
of a transmission assembly.
15 Figure 7 is a block diagram of a fifth embodiment of
a transmission assembly.
Figure 8 shows the configuration of the transmission
member in a sixth embodiment.
Figure 9 is a graph showing different speeds for the
20 sixth embodiment as a function of the selected piloting.
Figure 10 shows a variant of the Figure 1
embodiment.
DETAILED DESCRIPTION OF EMBODIMENT(S)
25 In order to make invention more concrete,
30
embodiments of the helicopter transmission assembly are
described in detail below with reference to the
accompanying drawings. It should be recalled that the
invention is not limited to these embodiments.
Figures 1, 2, 3 show a first embodiment of a
helicopter having a rotor 90 driven in rotation by a gas
turbine 10 via a main gearbox (MGB) 60. On a helicopter,
the MGB 60 is a mechanical assembly for transmitting
power, with a reduction in speed, from the engine(s) 10
35 to the rotor 90; the MGB may also provide an angle
transmission between the drive shaft and the rotor shaft,
9
and may also serve to drive various accessories such as
pumps or alternators.
The speed of rotation Nr of the rotor 90 is imposed
by flight requirements: this speed Nr thus also imposes
5 the speed of rotation Nt of the turbine engine 10 via the
transmission assembly as a function of its stepdown
ratio, with the MGB 60 contributing in particular to
provide this ratio.
In this first embodiment, the transmission assembly
10 comprises an epicyclic gear train 20 having a sun gear
21, planet gears 22 mounted on a planet carrier 22a, and
a ring 23.
The planet carrier 22a is coupled to the drive shaft
lOa of the gas turbine 10. The ring 23 is coupled to the
15 inlet shaft 60a of the MGB 60. The sun gear 21 is
coupled via a shaft 30a to a controllable reversible
electrical machine 30 of the speed-change drive unit type
referred to as the electrical regulator machine.
A second reversible electrical machine 40, referred
20 to as a balancing machine, is provided on the shaft 60a
between the epicyclic gear train 20 and the MGB 60.
25
An energy storage device 50 is provided so as to be
capable of exchanging electyical energy with the speedchange
drive unit 30 and with the balancing machine 40.
There follows an explanation of the operation of
this first embodiment of the transmission assembly, given
with reference to Figure 3, which shows the speeds of
rotation: N3 of the speed-change drive unit 30, Nt of the
gas turbine 10, and Ne of the inlet shaft 60a of the MGB
30 60.
When it is desired to servocontrol Nt on a speed
equal to Ne as changed by the ratio of the epicyclic gear
train 20, the speed-change drive unit 30 is controlled on
zero speed: this configuration balances the speeds and is
35 represented by the line A.
When it is desired to servocontrol Nt on a speed
faster than the equilibrium speed, the speed of the
10
speed-change drive unit 30 is controlled towards a
positive value: this configuration is represented by the
line B.
unit 30
In this configuration, the speed-change drive
takes off mechanical energy: this energy is
5 converted into electricity, transmitted to the storage
device 50, and transferred by the storage device to the
balancing machine 40, which then re-converts it into
mechanical energy and restores it to the inlet shaft 60a
of the MGB 60 in order to satisfy its power need.
10 Conversely, when it is desired to servocontrol Nt on
a speed slower than the equilibrium speed, the speed of
the speed change drive unit 30 is controlled towards a
negative value: this configuration is represented by the
line C. In this configuration, the speed-change drive
15 unit 30 injects mechanical energy into the system: in
order to balance powers, an equivalent quantity of energy
is taken from the inlet shaft 60a of the MGB 60 by the
balancing machine 40, is converted into electricity, and
is transferred to the speed-change drive unit 30 by the
20 storage device 50.
In a variant shown in Figure 10, a freewheel 70 may
be provided on the shaft 30a between the electrical
regulator machine 30 and the epicyclic gear train 20.
Figures 4 to 7 show other variants of this first
25 embodiment when the helicopter has two gas turbines
driving the same rotor.
In the second embodiment shown in Figure 4, the
helicopter has two power lines, each driven by a
respective gas turbine 110, 110', which power lines are
30 combined within the MGB 160 in order to drive the rotor
190.
Each power line has a respective epicyclic gear
train 120, 120' and a respective speed-change drive unit
130, 130' that are connected in a manner analogous to the
35 first embodiment.
Nevertheless, in this second embodiment, the
transmission assembly has first and second reversible
11
electrical balancing machines 140, 140' provided on
respective drive shafts 110a, 110a', i.e. between their
respective gas turbines 110, 110' and epicyclic gear
trains 120, 120'.
5 Also, the transmission assembly has a single energy
storage device 150 capable of exchanging electrical
energy with the first speed-change drive unit 130, the
second speed-change drive unit 130', the first electrical
balancing machine 140, and the second electrical
10 balancing machine 140'.
The third embodiment, shown in Figure 5, is
analogous to the second embodiment except that it has a
single reversible electrical balancing machine 240
provided on the rotor shaft 290a, i.e. on the outlet
15 shaft of the MGB 260.
The fourth embodiment, shown in Figure 6, is
analogous to the second embodiment except that instead of
the first and second speed-change drive units, it has a
single speed-change drive unit 330 common to the first
20 and second power lines. More precisely, the sun gears 21
of both epicyclic gear trains 320, 320' are coupled with
the common speed-change drive unit 330 via a single shaft
330a.
Furthermore, the first and second reversible
25 electrical balancing machines 340, 340' are provided on
their respective inlet shafts 360a, 360a' of the MGB,
i.e. between their respective epicyclic gear trains 320,
320' and the MGB 360.
In the fifth embodiment, shown in Figure 7, the
30 transmission assembly includes an intermediate
transmission box 480 that has a first inlet coupled to
the first gas turbine 410 and a second inlet coupled to
the second gas turbine 410'. The intermediate
transmission box 480 combines these two inlets and
35 outputs the combined power from the two gas turbines 410,
410' via a combined drive shaft 410a.
12
The configuration that is then to be found at the
outlet from the intermediate box 480 is analogous to the
.configuration of the first embodiment.
Figures 8 and 9 show a sixth embodiment of a
5 helicopter having a rotor 580 driven in rotation by a gas
turbine 510 via a main gearbox (MGB) 560. In this sixth
embodiment, the epicyclic gear train of the MGB enables
the invention to be performed without introducing an
additional epicyclic gear train.
10 The sun wheel 561 of the MGB 560 is coupled to the
drive shaft 510a of the gas turbine 510. The planet
carrier 562a is coupled to the rotor shaft 590a of the
rotor 590. While the ring 563 is coupled via the shaft
530a to the speed-change drive unit 530. An electrical
15 reversible balancing machine 540 is provided on the rotor
shaft 590a between the MGB 560 and the rotor 590.
There follows an explanation of the operation of
this sixth embodiment of the transmission assembly, given
with reference to Figure 9, which shows the speeds of
20 rotation: N3 of the speed-change drive unit 530, Nt of
the gas turbine 510, and Nr of the rotor 590.
When it is desired to servocontrol Nt on a speed
equal to Nr, as changed by the reduction ratio of the MGB
560, the speed-change drive unit 530 is controlled on
25 zero speed: this configuration balances the speeds and is
represented by the line A.
When it is desired to servocontrol Nt on a speed
faster than the equilibrium speed, the speed of the
speed-change drive unit 530 is controlled towards a
30 negative value: this configuration is represented by the
line B. In this configuration, the speed-change drive
unit 530 takes off mechanical energy: this energy is
converted into electricity, transmitted to the storage
device, and transferred by the storage device to the
35 balancing machine 540, which then re-converts it into
mechanical energy and restores it to the rotor shaft 590a
in order to satisfy its power need.
13
Conversely, when it is desired to servocontrol Nt on
a speed slower than the equilibrium speed, the speed of
the speed-change drive unit is controlled towards a
positive value: this configuration is represented by the
5 line C. In this configuration, the speed-change drive
unit 530 injects mechanical energy into the system: in
order to balance powers, an equivalent quantity of energy
is taken from the rotor shaft 590a by the balancing
machine 540, is converted into electricity, and is
10 transferred to the speed-change drive uni.t 530 by the
storage device.
The embodiments or implementations described in the
present description are given by way of nonlimiting
illustration, it being easy in the light of this
15 description for a person skilled in the art to modify
these embodiments or implementations, or to envisage
others, while remaining within the ambit of the
invention. In particular, the present description
applies equally well to gas turbines having a free
20 turbine and to gas turbines having a linked turbine.
Furthermore, the various characteristics of these
implementations or embodiments may be used on their own
or combined with one anoth~r. When they are combined,
these characteristics may be combined as described above
25 or in other ways, the invention not being limited to the
specific combinations described in the present
description. In particular, unless specified to the
contrary, a characteristic described with reference to
any one implementation or embodiment may be applied in
30 analogous manner to any other implementation or
embodiment.

CLAIMS
1. A helicopter comprising a first engine including at
least a first turbine engine (10), a rotor (90), and a
transmission assembly, the transmission assembly being
5 configured to transmit torque coming from the first
engine (10) to the rotor (90);
wherein the transmission assembly comprises a first
inlet shaft (lOa) configured to receive torque from the
first engine (10);
10 an outlet shaft (60a) configured to transmit
torque to the rotor (90);
a first transmission member (20) with at least two
degrees of freedom comprising first, second, and third
movable portions;
15 · a controllable first reversible electrical
regulator machine (30); and
· a first reversible electrical balancing machine
( 4 0) ;
wherein the inlet shaft (lOa) is coupled to the
20 first movable portion (22a);
· the outlet shaft (60a) is coupled to the second
movable portion (23);
· the first electrical regulator machine (30) is
coupled to the third movable portion (21); and
25 · the fjrst electrical balancing machine (10) is
coupled in series with the inlet shaft or the outlet
shaft ( 60a) .
2. The helicopter according to claim 1, wherein the
30 transmission assembly further comprises an energy storage
device (50) configured to exchange electrical energy both
with the first electrical regulator machine (30) and also
with the first electrical balancing machine (40).
35 3. The helicopter according to claim 1 or claim 2,
wherein the transmission assembly further comprises a
freewheel (70) coupled in series between the first
15
electrical regulator machine (30) and the first
transmission member (20).
4. The helicopter according to any one of claims 1 to 3,
5 wherein the first transmission member (20) is an
epicyclic gear train having a sun gear (21), planet gears
(22) connected to a planet carrier (22a), and a ring
( 2 3) .
10 5. The helicopter according to claim 4, further
comprising a main gearbox (60);
15
wherein the planet carrier (22a) of the first
transmission member (20), constituting its first movable
portion, is coupled to the first engine (10);
· the ring (23) of the first transmission member
(20), constituting its second movable portion, is coupled
to an inlet (60a) of the main gearbox (60); and
· the sun gear (21) of the first transmission member
(21), constituting its third movable portion, is coupled
20 to the first electrical regulator machine (30).
6. The helicopter according to claim 5, further
comprising a second engine, including at least one
turbine engine (110'), a second transmission member
25 (120') analo