Patent Description:
According to one embodiment, an electric propulsion unit comprises at least one electric power system, such as a set of fuel cells for example, an electric motor powered by the electric power system, a propeller driven in rotation by the electric motor as well as a nacelle housing the at least electric power system and the electric motor.

During operation, the power supply system generates heat which must be removed. For this purpose, the electric propulsion unit includes a cooling system which includes two cooling circuits positioned for example on both sides of the nacelle.

Each cooling circuit comprises, depending on the direction of the air flow, an air inlet, an intake duct, a heat exchanger, an exhaust duct and an air outlet.

The intake and exhaust ducts are substantially aligned and channel an air flow oriented in a flow direction substantially parallel to the axis of rotation of the propeller, this air flow passing through the heat exchanger oriented substantially perpendicular to the flow direction.

According to a configuration, the air inlet is positioned on the side face of the nacelle and the air outlet at the rear of the nacelle. As the air inlet is positioned on the side face of the nacelle, the cooling circuit includes a fan positioned in the intake or exhaust duct to control the air mass flow in the cooling circuit.

The air inlet, the air outlet, the intake duct and the exhaust duct are sized according to the most important cooling needs of the electrical power system, in particular at the time of take-off when the thrust provided by the electric motor is the most important. As a result, the air inlet, the air outlet, the intake duct and the exhaust duct are oversized for other phases of flight.

Since the aerodynamic performance of the electric propulsion unit is closely linked to the dimensions of the air inlets, this aerodynamic performance is not optimal for most phases of flight. <CIT> discloses an electric propulsion unit of an aircraft comprising : at least an electric power system, at least an electric motor comprising an output shaft and powered by the electric power system, a propeller driven in rotation by the electric motor, a cooling system for the electric power system comprising a main cooling circuit which comprises :a main air inlet, at least one intake duct, at least one main heat exchanger, at least an exhaust duct, a main air outlet, a nacelle housing the electric power system and the electric motor and comprising: a central fairing, a front fairing which extends from the central fairing to a front end and a rear fairing which extends from the central fairing to a rear end, wherein the front fairing comprises a protrude positioned in a lower part of the front fairing, said protrude having a front face located in a transverse plane perpendicular to the output shaft, wherein the main air inlet is positioned on the front face, wherein the main cooling circuit is sized for the cooling needs of the electric power system during the cruise flight.

The present invention aims to remedy all or some of the drawbacks of the prior art. To this end, the subject of the invention is an electric propulsion unit of an aircraft according to claim <NUM>.

Positioning the main air inlet behind the propeller allows air flow to be generated in the main cooling circuit without the need for a fan. Additionally, this positioning does not significantly impact the aerodynamics of the electric propulsion unit.

According to another feature, the front face is located in the same transverse plane that the front end of the front fairing.

According to another feature, the main air inlet occupies the entire front face.

According to another feature, the main air outlet is positioned on the rear fairing and configured to eject an air flow generating an additional thrust.

According to another feature, the main air outlet comprises at least one main flap which is adjustable in order to adjust an air mass flow in the main cooling circuit.

According to another feature, the main heat exchanger comprises an inlet face connected to the intake duct and an outlet face substantially parallel to the inlet face and connected to the exhaust duct, and the inlet and outlet faces of the main heat exchanger are inclined with respect to a transverse plane perpendicular to the output shaft.

According to another feature, the central fairing comprises two side faces and the secondary air inlet is positioned on one of the side faces of the central fairing, said secondary air inlet being preferably of flush type.

According to another feature, the secondary air inlet comprises a secondary flap movable between a closed position in which the secondary flap completely closes the secondary air inlet and an at least partially open position in which the secondary flap at least partially clears the secondary air inlet.

According to another feature, the secondary cooling circuit comprises a fan to regulate an air mass flow in the secondary cooling circuit.

According to another feature, the secondary air outlet is positioned at a lower part of the rear fairing, between the main air outlet and the rear end of the rear fairing and configured to eject an air flow generating an additional thrust.

Also a subject of the invention is an aircraft comprising at least one electric propulsion unit according to one of the above features.

Other features and advantages will emerge from the description of the invention that will follow, said description being given by way of example only, with reference to the appended drawings, in which :.

According to an embodiment visible in <FIG>, an aircraft <NUM> comprises at least one wing <NUM> and several electric propulsion units <NUM> fixed under the wing <NUM>. The invention is not limited to this embodiment for the positioning of the electric propulsion units <NUM>.

As illustrated in <FIG>, each electric propulsion unit <NUM> comprises at least one electric power system <NUM> such as a set of fuel cells for example, at least one electric motor <NUM> powered by the electric power system <NUM>, a propeller <NUM> driven in rotation by the electric motor <NUM> as well as a nacelle <NUM> housing the electric power system <NUM> and the electric motor <NUM>.

The electric motor <NUM> includes an output shaft A18 supporting the propeller <NUM>. The propeller <NUM> comprises several blades P20.

Hereinafter in the description, a longitudinal direction D1 is a direction parallel to the output shaft A18. A transverse plane is a plane perpendicular to the longitudinal direction D1. A vertical median plane P1 is a plane passing through the output shaft A18, vertical when the aircraft is on the ground. The terms "front" and "rear" refer to the direction of the air flow around the electric propulsion unit <NUM> in flight, the latter flowing from front to rear.

The electric propulsion unit <NUM> may include at least one auxiliary equipment <NUM>, such as a tank for example.

The nacelle <NUM> comprises a primary structure <NUM> supporting the electric power system <NUM> and the electric motor <NUM> as well as a secondary structure comprising a fairing <NUM>, supported by the primary structure <NUM>, enveloping the primary structure <NUM>, the electric power system <NUM> and the electric motor <NUM> contributing to the aerodynamic performance of the aircraft <NUM>. The fairing <NUM> comprises a central fairing <NUM> with a substantially constant cross section in the longitudinal direction D1, an approximately conical front fairing <NUM> which extends from the central fairing <NUM> to a front end <NUM> and an approximately conical rear fairing <NUM> which extends from the central fairing <NUM> to a rear end <NUM>. According to one embodiment, the electric motor <NUM> is positioned in the front fairing <NUM> and the electric power system <NUM> in the central fairing <NUM>.

According to a configuration, the central fairing <NUM> comprises two side faces <NUM>, <NUM> which are substantially plane and parallel to the vertical median plane P1. The front end <NUM> of the front fairing <NUM> comprises a hole crossed by the output shaft A18.

The electric propulsion unit <NUM> includes a cooling system to remove the heat produced by the electric power system <NUM>.

Said cooling system comprises a main cooling circuit <NUM> which comprises, from front to rear, a main air inlet <NUM>, at least one intake duct <NUM>, at least one main heat exchanger <NUM>, at least an exhaust duct <NUM> and a main air outlet <NUM>.

Said main cooling circuit <NUM> is substantially symmetrical with respect to the vertical median plane P1.

The front fairing <NUM> comprises a protrude <NUM> positioned in the lower part of the front fairing <NUM>, said protrude <NUM> having a front face <NUM> located approximately in the same transverse plane as the front end <NUM> of the front fairing <NUM>. Thus, the front face <NUM> is located just behind the blades P20 of the propeller <NUM>.

According to a feature of the invention, the main air inlet <NUM> is positioned on the front face <NUM>, at least a part of the intake duct <NUM> being housed in said protrude <NUM>.

Positioning the main air inlet <NUM> just behind the propeller <NUM> allows air flow to be generated in the main cooling circuit <NUM> without the need for a fan. Additionally, this positioning does not significantly impact the aerodynamics of the electric propulsion unit <NUM>.

According to a configuration, the main air inlet <NUM> occupies the entire front face <NUM>.

The main air outlet <NUM> is positioned just behind the central fairing <NUM>, in the lower part of the rear fairing <NUM>. The main air outlet <NUM> being positioning in the rear fairing <NUM>, it is configured to eject an air flow substantially parallel to the longitudinal direction D1 generating additional thrust.

According to an embodiment, the main air outlet <NUM> comprises at least a main flap <NUM> configured to at least partially close the main air outlet <NUM>. According to a configuration, the main flap <NUM> is movable between a closed position in which it completely closes the main air outlet <NUM> and a fully open position in which it completely clears the main air outlet <NUM>. The main flap <NUM> can occupy different intermediate positions between the closed and fully open positions. The position of the main flap <NUM> is adjustable in order to adjust an air mass flow in the main cooling circuit <NUM>. For this purpose, the cooling system comprises a control for controlling the position of the main flap <NUM>.

According to an embodiment, the main heat exchanger <NUM> comprises an inlet face <NUM> and an outlet face <NUM>, substantially parallel to the inlet face <NUM>. The intake duct <NUM> connects the main air inlet <NUM> and the inlet face <NUM> of the main heat exchanger <NUM>. The exhaust duct <NUM> connects the outlet face <NUM> of the main heat exchanger <NUM> and the main air outlet <NUM>.

According to a configuration, the inlet and outlet faces <NUM>, <NUM> of the main heat exchanger <NUM> are not parallel to a transverse plane but inclined. According to an embodiment, the inlet and outlet faces <NUM>, <NUM> of the main heat exchanger <NUM> form an angle greater than <NUM>° with a transverse plane. This configuration makes it possible to increase the section of the main heat exchanger <NUM> and therefore the exchange surface by limiting the increase in the cross section of the central fairing <NUM>.

According to a feature of the invention, the main cooling circuit is sized for the cooling needs of the electric power system during the cruise flight. Consequently, it is undersized for the most important needs, especially during take-off. Thus, the sections of the main air inlet <NUM> and the main air outlet <NUM> are smaller than those of a cooling circuit of the prior art, what tends to reduce the impact on the aerodynamics of the aircraft.

According to claim <NUM>, the cooling system comprises at least a secondary cooling circuit <NUM> which comprises, from front to rear, a secondary air inlet <NUM>, at least one intake duct <NUM>, at least one secondary heat exchanger <NUM>, at least an exhaust duct <NUM> and a secondary air outlet <NUM>.

According to a configuration, the secondary air inlet <NUM> is positioned on one of the side faces <NUM>, <NUM> of the central fairing <NUM>. The secondary air inlet <NUM> is flush with the outside surface of the nacelle to limit its impact on the aerodynamics of the aircraft.

The secondary air outlet <NUM> is positioned in the lower part of the rear fairing <NUM> between the main air outlet <NUM> and the rear end <NUM> of the rear fairing <NUM>. The secondary air outlet <NUM> being positioned in the rear fairing <NUM>, it is configured to eject an air flow substantially parallel to the longitudinal direction D1, generating additional thrust.

According to an embodiment, the secondary cooling circuit <NUM> comprises a fan <NUM>, positioned in the exhaust duct <NUM>, to regulate an air mass flow in the secondary cooling circuit <NUM> according to the cooling needs of the electric power system <NUM>.

According to a configuration, the secondary air inlet <NUM> comprises a secondary flap <NUM> movable between a closed position, visible in the upper part of <FIG>, in which it completely closes the secondary air inlet <NUM> and an at least partially open position, visible in the lower part of <FIG>, in which it at least partially clears the secondary air inlet <NUM>. The secondary flap <NUM> can occupy different intermediate positions between the closed and partially open positions. The position of the secondary flap <NUM> is adjustable in order to adjust an air mass flow in the secondary cooling circuit <NUM>. When the secondary flap <NUM> is in the closed position, it greatly reduces the impact of the secondary air inlet <NUM> on the aerodynamics of the aircraft.

The cooling system comprises a control for controlling the position of the secondary flap <NUM> which can be the same as that of the main flap <NUM>.

According to a configuration, the secondary air outlet <NUM> comprises a movable flap <NUM> to close it when the secondary cooling circuit <NUM> is not used in order to limit the impact of said secondary air outlet <NUM> on the aerodynamics of the aircraft.

The secondary cooling circuit <NUM> is sized to increase the cooling capacity of the main cooling circuit <NUM> and meet the most important cooling needs of the power supply system <NUM> during certain phases of flight such as take-offs.

According to a configuration, the cooling system comprises only one secondary cooling circuit <NUM>. According to another configuration visible in <FIG>, <FIG> and <FIG>, the cooling system comprises two secondary cooling circuits <NUM>, <NUM>', arranged on either side of the vertical median plane P1, approximately symmetrical with respect to this vertical median plane P1. According to an operating principle, the main and secondary cooling circuits <NUM>, <NUM> operate simultaneously during the take-off and climb flight phases when the cooling needs are the greatest.

The secondary cooling circuit <NUM> is deactivated, the secondary flaps <NUM> being in the closed position during the cruising and descent flight phases. Only the main cooling circuit <NUM>, sized for these phases of flight, operates.

At low speed, when the aircraft is on the ground and the propeller <NUM> is not rotating, at least one secondary cooling circuit <NUM> can be activated by its fan <NUM> if cooling is required.

The invention makes it possible to optimize the cooling capacity according to the cooling needs, what contributes to reduce the drag during certain phases of flight such as the cruising phase.

Claim 1:
Electric propulsion unit of an aircraft comprising :
- at least an electric power system (<NUM>),
- at least an electric motor (<NUM>) comprising an output shaft (A18) and powered by the electric power system (<NUM>),
- a propeller (<NUM>) driven in rotation by the electric motor (<NUM>),
- a cooling system for the electric power system (<NUM>) comprising a main cooling circuit (<NUM>) which comprises :
o a main air inlet (<NUM>),
o at least one intake duct (<NUM>),
o at least one main heat exchanger (<NUM>),
o at least an exhaust duct (<NUM>),
o a main air outlet (<NUM>),
- a nacelle (<NUM>) housing the electric power system (<NUM>) and the electric motor (<NUM>) and comprising:
o a central fairing (<NUM>),
o a front fairing (<NUM>) which extends from the central fairing (<NUM>) to a front end (<NUM>) and
o a rear fairing (<NUM>) which extends from the central fairing (<NUM>) to a rear end (<NUM>),
wherein the front fairing (<NUM>) comprises a protrude (<NUM>) positioned in a lower part of the front fairing (<NUM>), said protrude (<NUM>) having a front face (<NUM>) located in a transverse plane perpendicular to the output shaft (A18), wherein the main air inlet (<NUM>) is positioned on the front face (<NUM>), wherein the main cooling circuit (<NUM>) is sized for the cooling needs of the electric power system (<NUM>) during the cruise flight and wherein the cooling system comprises at least one secondary cooling circuit (<NUM>) which comprises a secondary air inlet (<NUM>), at least one intake duct (<NUM>), at least one secondary heat exchanger (<NUM>), at least an exhaust duct (<NUM>), a secondary air outlet (<NUM>), said at least one secondary cooling circuit (<NUM>) being sized to increase the cooling capacity of the main cooling circuit (<NUM>).