Hybrid propulsion systems for aircraft

Abstract

To provide a hybrid propulsion system for aircraft that is small, lightweight, and features a simple cooling system. [Solution] A hybrid propulsion system for aircraft comprising: an engine that outputs rotational force; a motor that outputs rotational force; a reduction gear that outputs rotational force obtained by reducing the rotational force of the engine and the motor; a propeller that rotates by the rotational force of the reduction gear; an inverter that supplies power to the motor; a heat sink that dissipates heat generated by the inverter; and an air pipe that sends outside air to the engine, wherein the inverter is provided outside the air pipe and the heat sink is provided inside the air pipe.

Description

[Technical Field]

[0001] The present invention relates to a hybrid propulsion device for aircraft that uses both an engine and a motor. [Background Art]

[0002] Generally, an aircraft includes a fuselage, wings, and a propulsion device. The propulsion device is an apparatus for generating thrust for the aircraft, and is mounted in a nacelle suspended from the wings or the like. Different types of power sources are used for propulsion devices depending on the size and application of the aircraft. For small passenger aircraft carrying about dozens of people, turboprop engines are often used as the power source.

[0003] To maintain high engine efficiency of a turboprop engine, it is necessary to maintain a high rotational speed of the turbine output shaft. On the other hand, in order to suppress blade breakage and noise of the propeller, it is necessary to limit the rotational speed of the propeller shaft so that the blade tip does not exceed the speed of sound. Therefore, in most propulsion devices using turboprop engines, a reducer is arranged between the turbine output shaft and the propeller shaft to rotate both the turbine output shaft and the propeller shaft at optimal rotational speeds.

[0004] In recent years, hybrid propulsion devices have been developed that improve engine efficiency by combining a turboprop engine and an auxiliary motor, and achieve reductions in fuel consumption and CO₂ emissions. Since an inverter is essential for driving the auxiliary motor, installation of an inverter is also essential for a hybrid propulsion device. Since an operating temperature that guarantees performance and reliability is set for inverters and motors, it is necessary to continuously and appropriately cool the heat generated by the inverter and the motor during operation of the hybrid propulsion device for aircraft.

[0005] Here, the cooling system described in Patent Document 1 is known as a cooling system for motors and inverters included in aircraft propulsion systems. For example, the abstract of the same document states in the problem section, "To efficiently cool the rotor's electrical elements by utilizing the airflow generated by the rotor," and in the solution section, "The aircraft 100 has a fuselage 12, a front wing 14 and a rear wing 16 extending laterally from the fuselage and generating lift during cruising, a boom 18 extending in the longitudinal direction supported at a distance from the fuselage by these, at least one VTOL rotor 20 having one or more blades 23 supported on the boom and generating vertical thrust during takeoff and landing, and two radiators 61L, 61H housed within the boom between an inlet 70a and an outlet 70b provided on the boom, and a cooling system 60 that uses the radiator located on the inlet side and the radiator located on the outlet side of the two radiators to cool the elements of the at least one VTOL rotor that have a low management temperature and elements that have a high management temperature, such as a motor 21 and an inverter 22." In other words, this document discloses a cooling system configuration in which the motor and inverter in a non-hybrid propulsion system are cooled using a radiator. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-92951 [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, the cooling system described in Patent Document 1 cools the motor and inverter in the propulsion system using a radiator, but the document does not disclose anything regarding the application of this cooling system to a hybrid propulsion system that uses both an engine and a motor.

[0008] When hybrid propulsion systems are installed in aircraft, the cooling system must be miniaturized because the system must be placed in the limited space within the nacelle. Furthermore, since the weight of the system significantly affects the aircraft's range, lightweight cooling systems are also strongly required. In addition, in order to maintain a high level of aircraft safety, the system must be maintained at short intervals, but if the structure of the cooling system is complex, maintenance work becomes difficult, so a simple structure is strongly required for the cooling system.

[0009] Therefore, the object of the present invention is to provide a hybrid propulsion system for aircraft that is small, lightweight, and has a simple cooling system. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a hybrid propulsion system for aircraft comprising: an engine that outputs rotational force; a motor that outputs rotational force; a reduction gear that outputs rotational force obtained by reducing the rotational force of the engine and the motor; a propeller that rotates by the rotational force of the reduction gear; an inverter that supplies power to the motor; a heat sink that dissipates heat generated by the inverter; and an air pipe that sends outside air to the engine, wherein the inverter is provided outside the air pipe and the heat sink is provided inside the air pipe. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a hybrid propulsion system for aircraft that is small, lightweight, and has a simple cooling system. Other problems, configurations, and effects will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0012] [Figure 1] A schematic top view of an aircraft equipped with the propulsion system of Example 1. [Figure 2] Schematic diagram of the external appearance of the propulsion system of Example 1. [Figure 3]A schematic diagram showing the mechanical, electrical, and thermal connections of each element of the propulsion system in Example 1. [Figure 4] A schematic diagram showing the propulsion system as shown in Figure 2, with the nacelle omitted from the illustration. [Figure 5] A schematic diagram showing the cooling system of the propulsion device in Example 1. [Figure 6] A schematic diagram showing the mechanical, electrical, and thermal connections of each element of the propulsion system in Example 2. [Figure 7] A schematic diagram showing the cooling system of the propulsion device in Example 2. [Figure 8] A schematic diagram showing the mechanical, electrical, and thermal connections of each element of the propulsion system in Example 3. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments of the hybrid propulsion system for aircraft according to the present invention (hereinafter simply referred to as the "propulsion system") will be described with reference to the drawings. In the following, identical or corresponding components will be denoted by the same or similar reference numerals, and repeated descriptions of these components may be omitted. [Examples]

[0014] Figure 1 is a schematic top view of an aircraft equipped with the propulsion system 1 of Embodiment 1. This aircraft is a small passenger aircraft that flies by utilizing the thrust generated by rotating the propeller of the propulsion system 1, which is suspended below the wing.

[0015] Figure 2 is a schematic diagram of the external appearance of the propulsion device 1 of this embodiment. As shown here, the propulsion device 1 has a nacelle 11 that forms the outer shell and a propeller 12 attached to the propulsion direction side (hereinafter this direction will be defined as the "forward side"), and the lower front part of the nacelle 11 has an air intake 11a for taking in outside air.

[0016] Figure 3 is a schematic diagram showing mechanical, electrical, and thermal connections of respective elements of the propulsion device 1 according to the present embodiment. As shown herein, the propulsion device 1 of the present embodiment is a hybrid propulsion device in which a propeller 12, an engine 13, a speed reducer 14, a motor 15, an inverter 16, a radiator 17, and a battery 18 are connected as illustrated. Details of each element will be sequentially described below.

[0017] A propeller shaft 12a of the propeller 12, an engine output shaft 13a of the engine 13, and a motor output shaft 15a of the motor 15 are each mechanically connected via the speed reducer 14 such as a gear box. Accordingly, the rotational force output by the engine 13 and the rotational force output by the motor 15 are appropriately decelerated by the speed reducer 14 and then transmitted to the propeller 12. The engine 13 is a turboprop engine or the like that outputs a main rotational force, and the motor 15 is an electric motor that outputs an auxiliary rotational force in a limited period such as when the engine is started.

[0018] The inverter 16 is a power converter that converts DC power supplied from the battery 18 into three-phase AC power and supplies the three-phase AC power to the motor 15. Since the inverter 16 operates normally at a temperature equal to or lower than a predetermined temperature, it is necessary to always maintain the inverter 16 at the predetermined temperature or lower by efficiently dissipating heat generated from semiconductor elements constituting the power conversion circuit.

[0019] Therefore, in the present embodiment, the radiator 17 is thermally connected to a casing of the inverter 16, so that heat of the inverter 16 can be efficiently dissipated. The radiator 17 in the present embodiment is a metal plate-shaped fin 17a. The fin 17a may be formed integrally with the casing of the inverter 16, or may be closely attached to the casing of the inverter 16 via a heat transfer member. Furthermore, the fin 17a is not limited to a metal plate-shaped fin, and may be other types of fins such as pin fins formed by arranging columnar members, corrugated fins, and porous metal fins.

[0020] Figure 4 is a schematic diagram showing the propulsion system 1 from Figure 2 with the nacelle 11 omitted from the illustration. As shown here, in addition to the elements described above, the propulsion system 1 includes an air pipe 19 for supplying outside air taken in from the air intake 11a to the engine 13. Furthermore, an inverter 16 is positioned on the outer wall surface of the air pipe 19 (the front upper surface in the example of Figure 4) so ​​that the heat sink 17 can be placed inside the air pipe 19. In this figure, the motor 15 is positioned on the front of the housing of the reduction gear 14, but the motor 15 may be positioned in a location other than that shown in the illustration depending on the design specifications such as the output capacity, rotational speed, and cooling method of the motor 15.

[0021] Figure 5 is a schematic diagram showing the cooling system of the propulsion device 1 in this embodiment, and is a transparent view of the side of the air pipe 19. As shown here, in addition to the air intake 11a described above, the air pipe 19 is equipped with an engine connection port 19a opening on the upper rear side and a radiator insertion port 19b opening on the upper front side. Therefore, the low-temperature outside air taken in by the propulsion device 1 from the air intake 11a cools the radiator 17 (and the inverter 16 thermally connected to the radiator 17) inserted into the radiator insertion port 19b, and then flows out from the engine connection port 19a and is supplied to the engine 13. In Figure 5, a radiator 17 (fin 17a) of a size that occupies only a part of the flow path cross-section of the air pipe 19 is shown as an example, but depending on the air flow velocity, the pressure loss of the radiator 17, the required heat dissipation performance, etc., the radiator 17 may be structured to occupy the entire flow path cross-section of the air pipe 19, or it may be structured to occupy only a narrower area.

[0022] Thus, in the propulsion system 1 of this embodiment, the heat sink 17 is air-cooled using high-speed, low-temperature outside air flowing through the air pipe 19 connecting the air intake 11a and the engine 13. As a result, it is a small, lightweight, and simple cooling system that can efficiently dissipate the heat generated in the inverter 16.

[0023] Therefore, this embodiment allows for a simpler configuration compared to the case where liquid refrigerant is used to cool the inverter 16, as it eliminates the need for refrigerant piping and pumps. This makes assembly, disassembly, and other maintenance easier, resulting in good maintainability. Furthermore, even in the case of an air-cooled system, it is possible to use a smaller heat sink 17 compared to other configurations as a means of effectively utilizing the airflow in the air piping 19 for heat dissipation. As a result, this embodiment allows for hybridization of the aircraft's propulsion system without increasing its size, thereby reducing energy consumption and CO2 emissions. [Examples]

[0024] Next, the propulsion device 1A of Example 2 will be described with reference to Figures 6 and 7. Note that common points with Example 1 will not be explained again.

[0025] Figure 6 is a schematic diagram showing the mechanical, electrical, and thermal connections of each element of the propulsion device 1A in this embodiment. Figure 7 is a schematic diagram showing the cooling system of the propulsion device 1A in this embodiment.

[0026] As shown in both figures, the propulsion system 1A of this embodiment utilizes a heat exchanger 17b and refrigerant piping 17c as the radiator 17. The heat exchanger 17b consists of a heat absorption section provided within the housing of the inverter 16 and a heat exhaust section located within the air piping 19. The refrigerant piping 17c is an annular flow path that penetrates both the heat absorption section and the heat exhaust section of the heat exchanger 17b. In addition to the heat exchanger 17b and refrigerant piping 17c, the radiator 17 of this embodiment also includes a pump (not shown) for circulating the liquid refrigerant in the refrigerant piping 17c. Here, considering that the aircraft operates at high altitudes, an antifreeze such as oil with a low freezing point or an aqueous solution of ethylene glycol is used as the liquid refrigerant to prevent freezing in low-temperature environments.

[0027] When the cooling system pump is driven, the liquid refrigerant circulating in the refrigerant piping 17c absorbs heat from the inverter 16 as it passes through the heat absorption section of the heat exchanger 17b, becoming hot, and then dissipates the heat to the outside air in the air piping 19 as it passes through the heat dissipation section, becoming cold. In this configuration, unlike Embodiment 1 where the inverter 16 and fins 17a were integrated, it is not necessary to install the inverter 16 on the outer wall surface of the air piping 19, thus increasing the degree of freedom in the installation position of the inverter 16 compared to Embodiment 1. Although Figure 7 illustrates a configuration in which the inverter 16 is installed on the underside of the housing of the reduction gear 14, away from the outer wall surface of the air piping 19, the installation position of the inverter 16 is not limited to this example.

[0028] The propulsion system 1A of this embodiment has a configuration that places greater emphasis on the cooling performance of the inverter 16. In the air-cooling system of Embodiment 1, it can be difficult to sufficiently reduce the thermal resistance from the heat-generating part inside the inverter 16 to the heat sink 17. Therefore, as in this embodiment, by circulating a liquid coolant inside the inverter 16 and performing heat exchange with the liquid coolant in close proximity to the heat-generating part, higher heat dissipation performance can be obtained. [Examples]

[0029] Next, with reference to Figure 8, the propulsion device 1B of Example 3 will be described. Note that common points with Example 2 will not be explained again.

[0030] Figure 8 is a schematic diagram showing the mechanical, electrical, and thermal connections of each element of the propulsion device 1B in this embodiment. As is obvious from comparing Figure 6 and Figure 8, the propulsion device 1B in this embodiment differs from Embodiment 2 in that the refrigerant piping 17c also passes inside the motor 15. The heat absorption section of the heat exchanger 17b has a first heat absorption section that is thermally connected to the inverter 16 and a second heat absorption section that is thermally connected to the motor 15, and the refrigerant piping 17c is an annular flow path that penetrates the first heat absorption section, the second heat absorption section, and the heat exhaust section of the heat exchanger 17b. In other words, this embodiment can efficiently cool both the motor 15 and the inverter 16.

[0031] The propulsion system of this embodiment achieves a simpler structure by sharing the cooling systems for the motor 15 and the inverter 16. Although the cooling system for the motor 15 is not mentioned in Embodiments 1 and 2, a commonly used liquid cooling system requires a separate refrigerant system that circulates a different refrigerant from the inverter cooling system. In the case of air cooling, it is difficult to directly cool the motor housing using the airflow in the air piping due to the mounting position. By using a common cooling system for the inverter 16 and the motor 15, as in this embodiment, a compact and lightweight propulsion system for a hybrid aircraft can be provided.

[0032] While the embodiments of the cooling system for the hybrid propulsion system according to this disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments, and any design changes, etc., that do not depart from the gist of this disclosure are also included in this disclosure. [Explanation of Symbols]

[0033] 1, 1A, 1B...propulsion device, 11… Nasser, 11a... Air intake, 12... Propeller, 12a... Propeller shaft, 13…Engine, 13a... Engine output shaft, 14...Reducer, 15…motor, 15a...motor output shaft, 15b... Three-phase AC cable, 16... Inverter, 17...Radiator, 17a... Finn, 17b...heat exchanger, 17c... Refrigerant piping, 18... Battery, 19...Air piping, 19a...Engine connection port, 19b... Heat sink insertion port

Claims

1. An engine that outputs rotational force, A motor that outputs rotational force, A reduction gear that outputs a rotational force obtained by reducing the rotational force of the engine and the motor, A propeller that rotates due to the rotational force of the aforementioned reduction gear, An inverter that supplies power to the motor, A heat sink for dissipating heat generated in the inverter, It includes an air pipe that supplies outside air to the engine, The inverter is provided outside the air piping, A hybrid propulsion system for an aircraft, characterized in that the heat sink is provided inside the air piping.

2. A propulsion system for an aircraft according to claim 1, The heat sink is a metal fin that is formed integrally with the inverter housing or directly fixed to the inverter housing. The inverter is provided on the outer wall surface of the air piping, A hybrid propulsion system for an aircraft, characterized in that the fins are inserted into the air piping from the heat sink inlet of the air piping.

3. A propulsion system for an aircraft according to claim 1, The heat exchanger comprises a heat exchanger having a heat absorption section and a heat dissipation section, a refrigerant pipe which is an annular flow path that penetrates both the heat absorption section and the heat dissipation section, and a pump that circulates the liquid refrigerant in the refrigerant pipe. The heat-absorbing section is thermally connected to the inverter, A hybrid propulsion system for an aircraft, characterized in that the heat dissipation section is provided inside the air piping.

4. A propulsion system for an aircraft according to claim 1, The heat exchanger comprises a heat exchanger having a first heat absorption section, a second heat absorption section, and a heat dissipation section; a refrigerant pipe which is an annular flow path that penetrates the three sections: the first heat absorption section, the second heat absorption section, and the heat dissipation section; and a pump that flows the liquid refrigerant in the refrigerant pipe. The first heat absorption section is thermally connected to the inverter, The second heat-absorbing section is thermally connected to the motor, A hybrid propulsion system for an aircraft, characterized in that the heat dissipation section is provided inside the air piping.

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