FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& The Patent Rules, 2003
COMPLETE SPECIFICATION
1. TITLE OF THE INVENTION:
PROPULSION UNIT WITH SELECTIVE COUPLING MEANS
2. APPLICANT:
Name: SAFRAN HELICOPTER ENGINES
Nationality: France
Address: 64510 Bordes, France.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in
which it is to be performed:
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DESCRIPTION
TECHNICAL DOMAIN
The invention relates to a propulsion unit such as a turboprop that is
made so as to limit its fuel consumption, particularly during taxiing steps of the aircraft on
which the propulsion unit is installed.
STATE OF PRIOR ART
The step during which an aircraft is moving or is waiting in an airport
before or after takeoff is calling the taxiing step.
This step usually takes 10 to 20 minutes, depending on the size of the
airport.
A conventional turboprop comprises mainly a turbomachine that
generates driving power and an external propeller driven by the turbomachine that
provides the driving force for displacement of the aircraft.
During the taxiing step, the turbomachine is permanently running, both
when the aircraft is moving and during waiting steps for example while waiting for
takeoff.
Thus, a large quantity of fuel is consumed during this taxiing step,
although energy needs from the turbomachine are limited.
For example, for an aircraft with about 70 seats, the consumed quantity
of fuel can exceed 50 kilograms for a taxiing step lasting more than 10 minutes. The
turbomachine consumes fuel and produces exhaust gases during this operation on the
ground. Since the aircraft speed is very low, the plume of exhaust gases is hardly diluted
by the surrounding air. The exhaust gases are then distributed around the entire airport
platform, to the detriment of airport personnel and passengers.
The turbomachine regime is defined more by its operating parameters
than by the power required during taxiing/stopped steps. The result is intensive use of
the throttle and the brakes. This type of control is unpleasant for the pilot and
uncomfortable for the passengers.
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PRESENTATION OF THE INVENTION
The invention discloses a propulsion unit, particularly for an aircraft,
comprising a turbomachine, a propeller that can be selectively coupled to said
turbomachine, a rotary electrical machine that can drive at least the turbomachine, and
means of selective coupling of the rotary electrical machine to the propeller and/or the
turbomachine, that can couple the propeller only to the rotary electrical machine during a
defined operation step of the propulsion unit, in which the turbomachine consists of a
free turbine turboprop, comprising a gas generator and a free turbine driven in rotation
by the gas flow generated by the gas generator, characterised in that the selective
coupling means are capable of coupling or not coupling the rotary electrical machine to
the gas generator and/or the free turbine.
Direct coupling of the rotary electrical machine to the propeller only
makes it possible to use electrical energy only, and only when the aircraft has to be
displaced. Therefore there is no consumption when the aircraft is stopped and also there
is no exhaust gas produced since the turbomachine can be stopped.
Preferably, the selective coupling means comprise a coupling device that
is permanently coupled to the rotary electrical machine and a clutch system for selective
coupling of the coupling device to the propeller depending on the operating phase of the
propulsion unit.
Preferably, the coupling means comprise a second clutch system, for
selective coupling of the coupling device to the gas generator.
Preferably, the coupling device supports a shaft that can be coupled to
the free turbine though a dog clutch.
Preferably, the rotary electrical machine consists in an alternator-starter
that can generate driving energy to drive the propeller and/or the turbomachine and that
can generate electricity from the driving energy produced by the turbomachine.
Preferably, the rotary electrical machine is connected to an electrical
energy accumulator and the rotary electrical machine is capable of drawing electricity
from or supplying electricity to said energy accumulator.
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The invention also discloses a method of controlling coupling means of a
propulsion unit according to the invention that is installed on an aircraft, characterised in
that it consists of controlling the coupling means so that the coupling device is only
coupled to the propeller during a taxiing step of the aircraft on a runway and so that the
coupling device is coupled to the propeller and the turbomachine at least when the
turbomachine operates in a steady state.
Preferably, during a step in which the turbomachine is started after said
taxiing step, the method comprises
- a first phase in which the coupling device is coupled to the propeller
and the gas generator simultaneously, and in which the coupling device is uncoupled
from the free turbine;
- a second phase in which the coupling device is coupled to the gas
generator only, and in which the coupling device is uncoupled from the propeller and the
free turbine, and;
- a third phase in which the coupling device is coupled to the
propeller and the free turbine simultaneously, and in which the coupling device is
uncoupled from the gas generator.
Preferably, during a step in which the turbomachine is started, the
method comprises
- a phase in which the coupling device is coupled to the gas
generator, and in which the coupling device is uncoupled from the propeller and the free
turbine;
- a phase in which the coupling device is coupled to the propeller and
the free turbine simultaneously, and in which the coupling device is uncoupled from the
gas generator.
BRIEF DESCRIPTION OF THE DRAWINGS
Other characteristics and advantages of the invention will become clear
after reading the detailed description given below which will be understood more easily
with reference to the appended figures among which figures 1 to 6 are diagrammatic
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representations of a propulsion unit according to the invention, showing different
operating steps of the propulsion unit.
DETAILED PRESENTATION OF PREFERRED EMBODIMENTS
The figures show a propulsion unit 10, for example for an aircraft, that
comprises a turbomachine 12 generating driving energy for the propulsion unit 10, a
propeller 14 that will be driven by the turbomachine for propulsion of the aircraft, and a
rotary electrical machine that is connected to an electrical energy accumulator such as a
battery.
The rotary electrical machine 16 is an alternator-starter type of
reversible electrical machine. It is capable of generating driving power from electricity
stored in the battery that can be transmitted to the turbomachine 12 when it is operating
in starter mode.
The rotary electrical machine 16 is also capable of receiving at least part
of the driving energy generated by the turbomachine 12 when it is in alternator mode, to
generate electricity that will be redistributed to the entire aircraft and to the battery.
The turbomachine 12 is preferably a free turbine turboprop that
comprises a gas generator composed of one or several compressors and one or several
turbines with one or several stages and that comprises a free turbine that drives a drive
shaft 18 of the propeller 14.
A reduction gear (not shown) is placed between the shaft 18 of the
turbine and the propeller 14 to reduce the rotation speed of the propeller 14.
The propulsion unit 10 also comprises coupling means 20 for selectively
coupling the turbomachine 12, the propeller 14 and the rotary electrical machine 16 to
each other.
The coupling means 20 comprise a coupling device 22 mounted free to
rotate about a principal axis A that is permanently coupled to the rotary electrical
machine 16 through a set of gears 24.
The coupling device 22 includes a shaft 26 that will or will not be
coupled to the shaft 18 of the free turbine though a dog clutch 28.
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The dog clutch 28 can be in two different states, namely an engaged
coupling state of the shaft 26 of the coupling device 22 to the shaft 18 of the free turbine,
and a disengaged state in which it does not couple the two shafts 26, 18 together. The
state of the dog clutch can be modified depending on the operating phase of the
propulsion unit, as will be described later.
The coupling means 20 comprise a first clutch system 30 connecting the
coupling device 22 with a propeller 14 supporting shaft 32. The first clutch system 30 is
capable of occupying one state among the engaged, disengaged and slipping states, for
rotational coupling or uncoupling of the coupling device 22 to the propeller 14 supporting
shaft 32.
The first clutch system 30 comprises a first planar ring 34 fixed in
rotation with the coupling device 22 and a second planar ring 36 facing it fixed in rotation
to the propeller 14 supporting shaft 32. The two planar rings 34, 36 of the first clutch
system 30 will or will not come into contact with each other, depending on whether the
first clutch system is in one of its states defined above.
The coupling means 20 comprise a second clutch system 40 connecting
the coupling device 22 to a gas generator shaft 42. The second clutch system 40 is capable
of occupying one state among the engaged, disengaged and slipping states, for rotational
coupling or uncoupling of the coupling device 22 to the gas generator shaft 42.
The second clutch system 40 comprises a first planar ring 44 fixed to the
coupling device 22 in rotation and a second planar ring 46 fixed in rotation to the gas
generator shaft 42.
The two planar rings 44, 46 of the second clutch system 40 will or will
not come into contact with each other, depending on whether the second clutch system
is in one of its states defined above.
The coupling means 20 also comprise control and drive means for the
dog clutch 28 and clutch systems 30, 40 to provoke or not provoke coupling of the
turbomachine 12, the propeller 14 and the rotary electrical machine 16 to each other.
The propulsion unit is designed so that in one configuration of the
coupling means 20, the rotary electrical machine 16 is coupled to the propeller 14 only. In
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this configuration of the coupling means 20, the rotary electrical machine 16 and the
propeller 14 are not coupled to the gas generator nor with the free turbine of the
turbomachine 12.
This configuration of the coupling means 20 is preferably used when the
aircraft is operating in a taxiing step, so that there is no need to use the power of the
turbomachine 12, and the turbomachine 12 can even be kept in the stopped state.
This makes it possible to drive the propeller 14 without consuming fuel
nor producing exhaust gas. The electrical energy used to rotate the propeller 14 is only
used when it is necessary, therefore there is no excessive consumption of electricity.
The following description will describe several operating steps of the
propulsion unit 10 comprising the coupling means 20 that have just been described.
Taxiing step
Figure 2 shows the configuration of the propulsion unit 10 when the
aircraft is operating in a taxiing step.
As mentioned above, during this taxiing step, the coupling means 20
couple only the rotary electrical machine 16 to the propeller 14.
In this configuration of the coupling means 20, the dog clutch 28 is in a
disengaged state in which it does not couple the shaft 26 of the coupling device 22 to the
free turbine shaft 18. Therefore the rotary electrical machine 16 is not coupled to the free
turbine of the turbomachine 12.
The first clutch system 30 is in the engaged position, in other words the
two planar rings 34, 36 are in contact with each other and the second clutch system 40 is
in the disengaged position, in other words the two planar rings 44, 46 are not in contact
with each other.
Also, in this configuration of the coupling means 20, the rotary electrical
machine 16 operates in starter mode, in other words it produces driving energy and this
driving energy is transmitted to the propeller only through the coupling device 22 and the
first clutch system 30.
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Figures 3 to 5 show other states of the propulsion unit 10 and its
coupling means 20, representing the different operating phases of the coupling means 20
during a step to start the turbomachine that is implemented after the taxiing step.
Starting the turbomachine 12 consists mainly of rotating the gas
generator until it reaches an operating speed of the turbomachine. Starting from this
operating speed, the free turbine generates driving energy that can be transmitted to the
propeller.
Coupling of the propeller and the electrical machine to the gas generator
In a first phase of the start up step that takes place immediately after
the taxiing phase, the gas generator is coupled to the rotary electrical machine 16 and to
the propeller 14.
In the previous taxiing step, the propeller 14 is rotating at high speed.
Coupling of the gas generator to the propeller 14 makes it possible to use the kinetic
energy stored by the propeller 14 to participate in driving the gas generator.
To achieve this, as shown on figure 3, the second clutch system 40
changes state to its engaged state, in other words the two planar rings 44, 46 are brought
into contact to each other. The gas generator is then coupled to the coupling device 22.
The dog clutch 28 and the first clutch system 30 are held in the same
state as before, in other words the dog clutch 28 is in a disengaged state and the first
clutch system 30 is in the engaged position.
The rotary electrical machine 16 operates in driving energy production
mode, and this energy and the kinetic energy of the propeller 14 are transmitted to the
gas generator to start the turbomachine 12.
Coupling of the electrical machine to the gas generator
After a certain time, the kinetic energy of the propeller 14 is no longer
sufficient to participate in driving the gas generator to start the turbomachine 12. The
propeller 14 can also produce a resisting torque that would uselessly consume a certain
quantity of energy generated by the rotary electrical machine 16.
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This configuration can also be used at the beginning of starting the
turbomachine 12. When the taxiing phase described above does not occur, the propeller
14 is not moving and therefore cannot participate in driving the gas generator.
Consequently, as can be seen on figure 4, in this phase of the starting
step, the propeller 14 is uncoupled from the rotary electrical machine and the gas
generator.
To achieve this, the first clutch system 30 changes state to its
disengaged state, in other words the two planar rings 34, 36 are no longer in contact with
each other.
Consequently, in this phase, the rotary electrical machine is coupled
only to the gas generator, all the energy produced by the rotary electrical machine 16 is
used to start the turbomachine, therefore there is no loss of energy caused by the
resisting torque of the propeller 14.
Coupling of the free turbine to the coupling device
Finally, in a third phase of the start-up step, shown in figure 5, the
turbomachine 12 is started, and the free turbine is capable of producing driving energy.
In this phase, the rotary electrical machine 16 is coupled to the propeller
14 and to the free turbine and is uncoupled from the gas generator.
To achieve this, the first clutch system 30 changes state to its engaged
state, in other words the two planar rings 34, 36 are in contact with each other and the
propeller 14 is then coupled to the rotary electrical machine 16 through the coupling
device 22.
The dog clutch 28 also changes to its engaged state coupling the free
turbine shaft 18 to the shaft 26 of the coupling device 22, to couple the rotary electrical
machine 16 to the free turbine.
The second clutch system 40 is kept in the engaged position.
The energy produced by the free turbine drives the propeller 14 and the
rotary electrical machine 16, that then functions in electricity generation mode. Thus, the
propulsion unit 10 can both start the aircraft movement and generate electricity that is
redistributed to the entire aircraft, including to the battery.
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Operation under steady state
Figure 6 shows the state of the propulsion unit 10 when the
turbomachine 12 is in operation.
This state of the propulsion unit 10 corresponds to the aircraft takeoff,
flight, and landing phases.
In this state of the propulsion unit 10, the coupling means 20 couple the
rotary electrical machine 16 to the free turbine shaft 18 of the free turbine and to the
propeller. On the other hand, in this state, the coupling means 20 do not couple the
rotary electrical machine 16 to the gas generator.
In this case too, the energy produced by the free turbine drives the
propeller 14 and the rotary electrical machine 16, that functions in electricity generation
mode.
To achieve this, in the same way as for the state shown in figure 5, the
first clutch system 30 is in its engaged state, in other words the two planar rings 34, 36
are in contact with each other and the propeller 14 is coupled to the rotary electrical
machine 16.
The dog clutch 28 is in its engaged state coupling the free turbine shaft
18 to the shaft 26 of the coupling device 22, to couple the rotary electrical machine 16 to
the free turbine.
On the other hand, the second clutch system 40 is in the engaged
position, in other words the two planar rings 44, 46 are not in contact with each other,
therefore the rotary electrical machine 16 is not coupled to the gas generator.
In the above description of the propulsion unit 10, the propeller 14 and
its associated shaft 32, the shaft 18 of the free turbine, the coupling device 22, the dog
clutch 28 and the gas generator shaft 42 are all coaxial with the principal axis A. It will be
understood that the invention is not limited to this embodiment and that the principal
axis of one or several of these components may be offset from or inclined relative to the
principal axis A. The propulsion unit will then comprise appropriate redirectingmeans.
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WE CLAIM:
1. Propulsion unit (10), particularly for an aircraft, comprising:
- a turbomachine (12);
- a propeller (14) that can be selectively coupled to said turbomachine
(12);
- a rotary electrical machine (16) that can drive at least the
turbomachine (12), and
- means (20) of selective coupling of the rotary electric machine (16) to
the propeller (14) and/or the turbomachine (12), that can couple the propeller (14) only
to the rotary electrical machine (16) during a defined operation step of the propulsion
unit (10),
in which the turbomachine (12) consists of a free turbine turboprop,
comprising a gas generator and a free turbine driven in rotation by the gas flow
generated by the gas generator,
characterised in that the selective coupling means (20) are capable of
coupling or not coupling the rotary electrical machine (16) to the gas generator and/or
the free turbine.
2. Propulsion unit (10) according to the previous claim, characterised in
that the selective coupling means (20) comprise a coupling device (22) that is
permanently coupled to the rotary electrical machine (16) and a clutch system (30) for
selective coupling of the coupling device (22) to the propeller (14) depending on the
operating phase of the propulsion unit (10).
3. Propulsion unit (10) according to either claim 1 or 2, characterised in
that the coupling means (20) comprise a second clutch system (40), for selective coupling
of the coupling device (22) to the gas generator.
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4. Propulsion unit (10) according to any one of claims 1 to 3,
characterised in that the coupling device (22) supports a shaft (26) that can be coupled to
the free turbine through a dog clutch (28).
5. Propulsion unit (10) according to any one of the previous claims,
characterised in that the rotary electrical machine (16) comprises an alternator-starter
that can generate driving energy to drive the propeller (14) and/or the turbomachine (12)
and that can generate electricity from the driving energy produced by the turbomachine
(12).
6. Propulsion unit (10) according to the previous claim, characterised in
that the rotary electrical machine (16) is connected to an electrical energy accumulator
and the rotary electrical machine (16) is capable of drawing electricity from or supplying
electricity to said energy accumulator.
7. Method of control over coupling means (20) of a propulsion unit (10)
according to any one of the previous claims, in combination with claim 2, installed on an
aircraft, characterised in that it consists of controlling the coupling means so that the
coupling device (22) is coupled to the propeller (14) only during a taxiing step of the
aircraft on a runway and so that the coupling device (22) is coupled to the propeller (14)
and the turbomachine (12) at least during an operating step of the turbomachine (12) in
steady state.
8. Method of control according to the previous claim, characterised in
that during a start step of the turbomachine (12) following said taxiing step, it comprises :
- a first phase in which the coupling device (22) is coupled to the
propeller (14) and the gas generator simultaneously, and in which the coupling device
(22) is uncoupled from the free turbine;
- a second phase in which the coupling device (22) is coupled to the
gas generator only, and in which the coupling device (22) is uncoupled from the propeller
(14) and the free turbine, and
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- a third phase in which the coupling device (22) is coupled to the
propeller (14), and the free turbine simultaneously
9. Method of control over coupling means (20) of a propulsion unit (10)
according to any one of claims 1 to 7, in combination with claim 2, installed on an aircraft,
characterised in that during a step in which the turbomachine (12) is started, it comprises:
- a phase in which the coupling device (22) is coupled to the gas
generator only, and in which the coupling device (22) is uncoupled from the propeller (14)
and the free turbine, and
- a phase in which the coupling device (22) is coupled to the propeller
(14) and the free turbine simultaneously, and in which the coupling device is uncoupled
from the gas generator.
Dated this 20th day of May, 2017.
(CHETAN CHADHA)
PATENT AGENT
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