Integrated Electric Propulsion Unit

Abstract

To provide an electric propulsion unit for aircraft.SOLUTION: An electric propulsion unit comprises a housing 112, an AC motor 30, a beta rod 58, a propeller 32, a governor 64, an inverter 50, and a controller MC. The AC motor includes a plurality of bearings 38 supported inside the housing, a hollow motor shaft, a stator 25, and a rotor. The beta rod is axially translatable inside the hollow motor shaft. The propeller is mechanically coupled to the hollow motor shaft. The propeller includes propeller blades 36 having an adjustable pitch angle. The governor is configured so as to adjust the pitch angle of the propeller blades. The inverter is connected so as to receive DC power and convert it to AC power. The controller is configured so as to control operation of the inverter and to control the pitch angle of the propeller blades.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates generally to electric propulsion units for aircraft. Some aircraft (hereinafter "electric aircraft") have an electrically powered propulsion system. In such aircraft, an electric motor converts electrical power into mechanical power for use in the propulsion system. For example, the electric motor may rotate one or more propellers of the aircraft to provide thrust. Electric aircraft come in a variety of forms. For example, an electric aircraft may be an airplane, a rotorcraft, a helicopter, a quadcopter, an unmanned aerial vehicle, or any other suitable type of aircraft. [Background technology]

[0002] A typical electric propulsion approach consists of assembling individual components that are federated to create an electric propulsion system. In this specification, the term "federated" is used to refer to components in an assembly, meaning that these components are designed independently of each other. The motor and inverter are federated components, each requiring a dedicated mechanical structure, dedicated cooling circuitry, and complex electrical and control interfaces. The inverter must be located in close proximity to the motor within the nacelle environment. Mechanical installation of the inverter and motor is challenging due to the small volume of the nacelle and installation constraints regarding the placement and routing of cooling channels, heat exchangers / exhaust ducts, electrical wires, and control lines.

[0003] Conventional approaches typically separate the inverter, motor, and transmission elements, creating large electrical and cooling interfaces between them. Most electric propulsion components—electric motor, power electronics, transmission, and battery—are packaged similarly to traditional turbine propulsion systems. Integrating the individual electric drivetrain elements is complex, costly, and time-consuming. Electric propulsion systems are complex systems, and their integration into the nacelle and aircraft fuselage presents significant challenges. Developing optimal integration techniques for mechanically integrating components within the nacelle would reduce weight and cost. Summary of the Invention

[0004] The subject matter disclosed in detail below relates to an integrated electric propulsion unit that reduces weight and cost compared to aircraft propulsion systems comprised of federated components. The system includes a simplified cooling system with one circuit for all components (motor, inverter, thrust bearing, governor, etc.) housed inside the nacelle. The system design simplifies the integration of electrical components, streamlines the number of electrical connections, simplifies EMI (electromagnetic interference) filters, simplifies electrical harnesses, and reduces the number of distribution panels. The propulsion control system is also integrated, reducing the number of controllers and simplifying control harness design.

[0005] In the context of the liquid transport system described below, the term "channel" refers to a hollow body containing a conduit that guides the flow of fluid from one opening at one end of the conduit to another opening at the other end. An opening through which a fluid enters a conduit is referred to herein as an "inlet," and an opening through which a fluid exits a conduit is referred to herein as an "outlet." Examples of channels disclosed herein include pipes, tubes, cold plates, cooling jackets, and internal passages in solid bodies. Additionally, in the context of the motor controller described below, the term "channel" refers to an inverter consisting of a set of power switches controlled by an inverter controller. For example, a motor controller having three inverters supplying phase AC power to the same motor is described as having three channels. Various embodiments of integrated electric propulsion units for aircraft are described below, one or more of which may be characterized by one or more of the following aspects.

[0006] One aspect of the subject matter disclosed in detail below is an electric propulsion unit including a housing, an AC motor disposed within the housing, the AC motor including a plurality of bearings supported within the housing, a hollow motor shaft rotatably coupled to the housing by the plurality of bearings, a stator supported by the housing, and a rotor attached to the hollow motor shaft, a beta rod axially translatable within the hollow motor shaft, a propeller mechanically coupled to the hollow motor shaft, the propeller including propeller blades having an adjustable pitch angle dependent on the axial position of the beta rod, a governor configured to adjust the pitch angle of the propeller blades by actuating axial translation of the beta rod, an inverter disposed within the housing and connected to receive and convert DC power to AC power, and a controller disposed within the housing, the controller configured to perform operations including controlling operation of the inverter and controlling the pitch angle of the propeller blades.

[0007] Another aspect of the subject matter disclosed in detail below is an electric propulsion unit including a housing, an AC motor disposed within the housing, the AC motor including a plurality of bearings supported within the housing, a motor shaft rotatably coupled to the housing by the plurality of bearings, a stator supported by the housing, and a rotor attached to the motor shaft, an inverter disposed within the housing and connected to receive and convert DC power into AC power, a controller disposed within the housing and configured to control operation of the inverter, and a cooling circuit configured to guide the flow of a circulating fluid. The cooling circuit includes an oil reservoir attached to the housing, a cooling pump attached to the housing, geared to the motor shaft, and in fluid communication with the oil reservoir, and a cooling channel disposed within the housing and connected to guide the circulating fluid from the cooling pump along a flow path to the oil reservoir. The cooling circuit typically also includes a heat exchanger.

[0008] A further aspect of the subject matter disclosed in detail below is an electric propulsion system including a first battery configured to generate DC power, a first DC power input line connected to the first battery, and an electric propulsion unit connected to the first DC power input line, the electric propulsion unit including a housing, an AC motor disposed within the housing, the AC motor including a plurality of bearings supported within the housing, a motor shaft rotatably coupled to the housing by the plurality of bearings, a stator supported by the housing, and a rotor attached to the motor shaft, a propeller mechanically coupled to the motor shaft, a first EMI filter disposed within the housing and connected to receive DC power from the first battery via the first DC power input line, a first DC bus bar disposed within the housing and connected to the first EMI filter, a first plurality of inverters disposed within the housing, each inverter connected to the first DC bus bar, and a controller disposed within the housing and configured to control operation of the first plurality of inverters.

[0009] A further aspect of the subject matter disclosed in detail below is an electric propulsion unit including a housing; an AC motor disposed within the housing, the AC motor including a plurality of bearings supported within the housing, a motor shaft having an axis of rotation rotatably coupled to the housing by the plurality of bearings, a stator supported by the housing, and a rotor attached to the motor shaft; a main drive gear having teeth attached to a forward end of the motor shaft, a hollow propeller shaft having an axis of rotation offset from the axis of rotation of the motor shaft, a propeller including propeller blades with an adjustable pitch angle; a beta rod axially translatable within the hollow propeller shaft; and a governor configured to adjust the pitch angle of the propeller blades by actuating axial translation of the beta rod; a propeller shaft drive gear attached to the hollow propeller shaft, the propeller shaft having teeth that mesh with the teeth of the main drive gear; a plurality of power modules disposed radially outward of the stator; and a controller disposed within the housing. The controller is configured to perform operations including controlling operation of the plurality of power modules and controlling the pitch angle of the propeller blades.

[0010] A further aspect of the subject matter disclosed in detail below is an electric propulsion unit including a housing, first and second pluralities of bearings supported within the housing, a main drive train shaft supported by the first and second pluralities of bearings supported within the housing, first and second hollow motor shafts surrounding corresponding portions of the main drive train shaft, first and second pairs of mechanical coupling devices selectively coupling the first and second hollow motor shafts to the main drive train shaft, first and second rotors attached to the first and second hollow motor shafts, respectively, first and second stators supported within the housing and positioned radially outward of the first and second rotors, respectively, a propeller mechanically coupled to the main drive train shaft, and a controller disposed within the housing and configured to selectively activate one of the pair of mechanical coupling devices to decouple one of the hollow motor shafts from the main drive train shaft.

[0011] Other aspects of the integrated electric propulsion unit for an aircraft are described below. [Brief explanation of the drawings]

[0012] The features, functions, and advantages described in the above sections may be achieved individually in various embodiments and may also be combined in further embodiments. To illustrate the above and other aspects, various embodiments are described below with reference to the drawings.

[0013] [Figure 1] FIG. 1 illustrates a schematic of an electric propulsion unit with federated mechanical, cooling, and electrical / control components. [Figure 2] FIG. 1 illustrates an overview of an electric propulsion unit with integrated mechanical, cooling, and electrical / control functions, according to one embodiment. [Figure 3] FIG. 1 illustrates the integration of the mechanical components of an electric propulsion unit in a single package that connects directly to the primary structure of the aircraft. [Figure 4]FIG. 1 illustrates the integration of an electric propulsion unit's cooling, lubrication, and governor oil components into a single fluid system. [Figure 5] FIG. 1 illustrates integrated air cooling of the motor and inverter in an electric propulsion unit. [Figure 6] FIG. 1 illustrates the integration of electrical and control components in an electric propulsion unit. [Figures 7A-7D] FIG. 1 illustrates an exemplary implementation of a motor / inverter cooling integration and governor / pump approach. [Figure 8A] FIG. 1 illustrates a schematic diagram of an integrated multiple channel electric propulsion unit according to another embodiment. [Figure 8B] FIG. 8B illustrates an integrated multi-phase fault-tolerant motor design for the electric propulsion unit shown in FIG. 8A. [Figure 9A] FIG. 10 is a partial cross-sectional view of a dual motor electric propulsion unit with an integrated driveline according to another embodiment. [Figure 9B] FIG. 9B is an end view of the concentric shaft arrangement of the dual motor electric propulsion unit shown in FIG. 9A. [Figure 9C] FIG. 9B illustrates the drivetrain integration of the dual motor electric propulsion unit shown in FIG. 9A. DETAILED DESCRIPTION OF THE INVENTION

[0014] In the following description, reference is made to the drawings in which like elements in different drawings are designated with the same reference numerals.

[0015] Exemplary embodiments of an integrated electric propulsion unit for an aircraft are described in detail below, although not all features of an actual implementation may be described herein. Those skilled in the art will recognize that the development of any such embodiment involves many implementation-specific decisions to achieve the developer's specific objectives, such as compliance with system-related and business-related constraints, and such decisions will vary from implementation to implementation. Moreover, such a development effort may be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0016] For illustrative purposes, a system for allocating load power drawn from multiple batteries to power the propulsion of an electric aircraft is described below, although the techniques presented herein are not limited to use in aircraft and may also be applied to propulsion of other types of electric vehicles, such as automobiles, industrial trucks, and trains.

[0017] FIG. 1 illustrates components of a typical electric propulsion unit 100 (hereinafter, "federated EPU 100") having federated mechanical, cooling, and electrical / control components. The federated EPU 100 is comprised, in part, of a multi-channel motor controller (MC) that converts DC power to AC power. Each channel of the motor controller includes an inverter 50 controlled by a respective inverter controller 5. Each inverter 50 is preceded by a respective EMI filter 24 (and possibly other front-end circuitry). The federated EPU 100 further includes an AC motor 30 that receives AC power from the inverter 50 via multiple or multiple sets of AC power lines 6. The federated EPU 100 also includes a propeller 32 that is driven to rotate by the AC motor 30. The propeller 32 includes a propeller shaft 34 mechanically coupled to the output shaft of the AC motor 30 and multiple propeller blades 36. The propeller shaft 34 is coupled to a thrust bearing 38 to form a thrust bearing / propeller shaft assembly 70. The federation EPU 100 further includes a governor 42 (also known as a propeller governor) configured to maintain a constant rotational speed of the propeller 32 by varying the pitch angle (hereinafter "pitch") of the propeller blades 36. The hydraulic governor accomplishes this by controlling the flow of engine oil to a hydraulic mechanism within the propeller 32 using a hydraulic valve. A controller built into the governor is configured to control the flow of engine oil through the hydraulic valve (not shown in FIG. 1). When a decrease in blade pitch is required, the hydraulic valve opens and pump 40c (coupled with third manifold 54c and oil reservoir 46c) increases oil pressure, promoting a fast, positive response from the propeller 32. In a well-known manner, the hydraulic valve, depending on its position, allows oil to flow to the propeller (increase pitch), allows oil to flow back from the propeller (decrease pitch), or assumes a neutral position (constant pitch) where no oil flows.

[0018] In the example shown in FIG. 1 , inverters 50 form three motor controller channels for supplying AC current to each set of star-connected windings 26 (hereinafter, "motor stars 26") in the stator 25 of the AC motor 30. Each inverter 50 includes a set of power switches, which are cooled by a coolant supplied through respective cooling pipes 9 connected to a manifold 54a. The power switches of each inverter 50 are electrically connected to each set of star windings in the AC motor 30. The inverters 50 further include sensors (not shown in FIG. 1 ) that measure the voltage and current of the AC power signal output by the inverter 50, and the sensor data is fed back to the respective inverter controllers 5. The operation of the inverters is controlled by the inverter controllers 5. More specifically, the switching states of each set of power switches (e.g., MOSFETs) are controlled by the respective inverter controllers 5, which send gate drive signals to the gates of the semiconductor power switches. In this way, the inverters 50 can operate with different phases to convert DC power into multi-phase AC power for the AC motor 30. 1, the AC motor 30 is a 3×3 phase AC motor. The controller 5 controls the operation (switching) of each inverter 50.

[0019] In the system shown in FIG. 1 , the HVDC power source is battery 18. For example, battery 18 may include multiple battery modules arranged in parallel or series across positive and negative bus bars to form a battery pack. Each battery module is a series / parallel arrangement of individual cells (not shown in FIG. 1 ). Each battery module may be monitored by an associated module monitoring unit (not shown in FIG. 1 ). The HVDC power source also includes a battery management system 22 configured to manage the operation of battery 18. Each module monitoring unit associated with battery 18 communicates sensor data representing virtual cell voltages and individual cell temperatures to battery management system 22. Battery management system 22 also receives data from current sensors (not shown in FIG. 1 ). The system further includes a DC voltage conversion subsystem (not shown in FIG. 1 ) configured to receive high-voltage DC power from battery 18 via battery contactors and convert the high-voltage DC power to low-voltage DC power for use by other (non-propulsion) components within the system or the broader vehicle platform. The system shown in FIG. 1 further includes a distribution board 20. The distribution panel 20 includes an HVDC bus 4 connected to DC power input lines 8 via respective bus contactors 16. The DC power input lines 8 transmit HVDC power from the DC voltage conversion subsystem to each channel of the inverter 50. For example, the battery 18, the DC voltage conversion subsystem, and the distribution panel 20 may be installed in the fuselage 102 (or possibly in the wing), and the DC power input lines 8 may be routed to the wing 104. Separately routing each individual power and control line to the inverter is difficult due to space and bend radius constraints. Additionally, additional distribution panels are required to split the battery output into multiple channels to accommodate multiple inverter inputs or to accommodate additional power sources, such as additional batteries, generators, or fuel cells.

[0020] The federated EPU 100 further includes a thermal management system 108 configured to cool the inverter 50 and to cool and lubricate the motor 30 and thrust bearing / propeller shaft assembly 70. The thermal management system 108 includes a heat exchanger 56 that is supplied with cooling air 62 (indicated by a left-pointing arrow in FIG. 1 ) as the aircraft propels forward. The heat exchanger 56 is configured to use the cooling air 62 to remove heat from the coolant that returns from the inverter 50, the motor 30, and the thrust bearing / propeller shaft assembly 70 through separate cooling circuits. In the example shown in FIG. 1 , the cooling circuits include dedicated federated pumps 40a-40d and oil tanks 46a-46c.

[0021] More specifically, the cooling circuit for the inverters 50 includes a pump 40a and an oil reservoir 46a in fluid communication (via cooling pipes or channels) with a heat exchanger 56 and a first manifold 54a. From the first manifold 54a, the coolant circulates through respective cold plates inside each inverter 50 (the plates are thermally coupled to cool the power switches within each inverter) and then returns to the first manifold 54a. The pump 40a is driven by a motor 44a, which receives AC power from the inverter 45a.

[0022] The cooling / lubrication circuit for the motor 30 includes a pump 40b and an oil reservoir 46b in fluid communication with a heat exchanger 56 and a second manifold 54b (via cooling / lubrication pipes or channels). Coolant / lubrication oil circulates from the second manifold 54b through the stator 25, through the thrust bearing / propeller shaft assembly 70, and then back to the second manifold 54b through cooling pipes or channels. The pump 40b is driven by a motor 44b, which receives AC power from an inverter 45b.

[0023] Cooling / lubrication pipes must run from two separate cooling circuits to each inverter and motor star. The large number of cooling pipes and the wiring of two different types of circuits adds complexity and integration challenges. Furthermore, dedicated pumps and oil reservoirs for each circuit make integration within the nacelle more complex and difficult. The thrust bearing / propeller shaft assembly 70 and governor 53 are federated components that require their own dedicated mechanical structures and cooling / lubrication circuits. The thrust bearing 38 mechanically decouples the motor 30 from the propeller 32. The thrust bearing 38 requires a motor cooling system and a lubrication system that can be paralleled with an additional dedicated scavenging pump 40d. The governor 42 is typically used to control propeller pitch with a hydraulic actuator / beta rod system. This system requires a high-pressure oil system, achieved by an additional pump 40c and oil reservoir 46c.

[0024] As shown in FIG. 1, the system further includes an engine control unit 10 (hereinafter, "ECU 10"), which is installed inside the engine nacelle. The ECU 10 communicates with an inverter controller 5 in an inverter 50. The inverter controller 5 is communicatively connected to the ECU 10 to receive control signals from the ECU 10 and send feedback signals to the ECU 10, and the ECU serves to monitor and adjust all of the inverter controllers 5. The ECU 10 is also communicatively connected to an electric propulsion controller 12 (hereinafter, "EPC 12"), which controls the overall operation of the aircraft's electric propulsion motor drive system shown in FIG. 1.

[0025] The EPC 12 receives commands from the flight control computer 14, which receives pilot thrust and pitch inputs from thrust control levers 21 and pitch control levers 23 located on the flight deck. The EPC 12 also receives signals corresponding to propeller rotational speed from speed and position sensors (not shown in FIG. 1). Additionally, the EPC 12 receives signals representing measured current from current sensors (not shown in FIG. 1). The EPC 12 sends instructions to the engine control unit 10 to control inverter operation based on information from the sensors and pilot inputs. The EPC 12 also interfaces with the battery management system 22. The EPC 12 is configured to send digital torque command signals 51 to the engine control unit 10 and analog pitch command signals 52 (e.g., feathering commands) to the governor 42. The EPC 12 is also configured to control the state of the battery contactors 48 and the bus contactor 16 of the distribution board 20.

[0026] According to the configuration shown in Figure 1, the system is controlled by the EPC 12, which receives input from the pilot via thrust control levers 21 and pitch control levers 23. Optimal propulsion system operation requires that the propeller speed remain constant regardless of thrust and pitch commands. The EPC 12 receives center data indicative of the propeller speed from the speed sensor, compares this measured speed with a reference speed signal, and generates and sends torque commands to the ECU 10.

[0027] A typical motor controller for an EPU uses multiple inverters, requiring separate DC power lines to connect to a distribution board 20 inside the fuselage 102 and route through the wings 104 into the nacelle. An AC power line 6 must be routed from each inverter 50 to each motor star 26 within the nacelle. All DC and AC power lines are prone to electromagnetic interference (EMI) and require EMI filters 24 and / or shielding. The distribution board is relatively complex and includes dedicated power channels for each inverter with its own contactor, fuse devices, and protective coordination functions. Because multiple inverters are powered from the same HVDC bus 4, electrical integration is challenging, and strict power quality and interaction requirements must be established to suppress crosstalk and circulating currents between the inverters. The additional filters and countermeasures add weight to the system. Furthermore, the AC motors 30 and inverters 50 each have their own housings, significantly increasing weight and cost. Furthermore, the control functions must communicate with the multiple inverters. A local ECU 10 is required in the nacelle to multiplex information from the EPC 12 or flight control computer 14 to the inverter controller 5.

[0028] Mechanically installing all of the above-mentioned federated components within the nacelle requires the construction of a web mechanical structure (hereinafter, "space frame 60") that interconnects all of the components and interfaces the completed assembly with the aircraft's primary structure 106 (see FIG. 1). The space frame 60 and the individual component structures must be designed to achieve the appropriate resonant modes and damping depending on the propeller and airframe characteristics. The design process is therefore challenging, requiring individual component design, system modeling, and iteration until convergence. Additionally, the federated component integration approach entails significant weight penalties due to the multiple housings and additional web structures.

[0029] FIG. 2 illustrates an integrated EPU 110 with integrated mechanical, cooling, and electrical / control functions, according to one embodiment. As used herein, the term “integrated” refers to components of an assembly, meaning that the components are designed in conjunction to optimize a given set of parameters. The concept presented here involves combining the motor 30, inverter 50 with its respective hardware logic inverter controller 7 (hereinafter “hardware manager 7”), thrust bearing / transmission / propeller shaft assembly 72 (hereinafter “TB / T / PS 72”), and governor 64 into a single package to form the integrated EPU 110. The goal is to integrate all powertrain components into a single entity, optimizing weight, cost, volume integration, installation, and maintenance, rather than “crowbar” (cram) the system into an existing architecture. The integrated EPU 110 is constructed as a monoblock, integrated package assembly that groups all of the electric propulsion system’s functions. Such an integrated EPU package can be dropped into the nacelle to perform the aircraft's engine functions. This plug-and-play approach, combined with the integrated system, allows for installation of only one unit; the only assembly required is for the integrated EPU 110 to be connected to the battery 18 and thermal management system 108. While Figure 2 shows an example of an electric propeller drive, this concept can also be applied to electric and hybrid turbofan engines. The proposed integrated system eliminates interface components, connector systems, separate cooling circuits, and sealing. The integrated system allows for a smaller, lighter package, improving efficiency and cost. The system also enables important tradeoffs, such as integrating motor design (losses, volume) and transmission design (specific speed), cost tradeoffs (motor, transmission), and system weight reduction.

[0030] According to one embodiment, the integrated EPU 110 includes a motor / inverter integrated power electronics device 76 integrated within an EPU housing 112. The EPU housing 112 is divided into an inverter power electronics device housing 114 and a motor housing 116. The EPC 12 is housed in the inverter power electronics device housing 114. A single DC power input line 8 supplies DC power to all inverters 50 via a common EMI filter 24 and a common low-inductance DC busbar 15 (hereinafter referred to as the "common DC busbar 15") with alternating conductor / insulator layers. Each conductor layer of the laminated common DC busbar 15 is connected to the EMI filter 24 and each inverter among the multiple inverters 50. The integrated EPU 110 further includes a TB / T / PS assembly 72 integrated with an EPU housing drive end plate 80. The governor 64 is integrated with the EPU housing rear end plate (not visible in FIG. 2).

[0031] According to the embodiment shown in Figure 2, the governor 64 is connected to an integrated beta rod 58 that can translate axially to change the pitch of the propeller blades 36. Additionally, a geared multi-element cooling / lubrication pump 66 and an oil cooling reservoir 68 are integrated at the bottom of the EPU housing 112. The pumping element of the geared multi-element cooling / lubrication pump 66 (described below with reference to Figure 4) is gear driven directly from the main motor shaft (not shown in Figure 2). The EPU housing 112 serves as the primary component directly connected to the aircraft primary structure 106.

[0032] The high level of integration achievable by packaging all of the individual cooperating modules into one system to form the integrated EPU 110 allows for optimal weight, cost, and package size. Due to the concentration of functions in one housing, installing the EPU in the nacelle is much simpler than a federated design. The presented highly integrated mechatronic module provides nacelle integration and optimal solution with minimal interface via cables and fluid pipes.

[0033] The integrated EPU 110 presented herein provides state-of-the-art transmission technology, electric motors, and power electronics in a single package. This integrated EPU approach achieves significant optimizations in nacelle installation and aircraft component simplification compared to federated approaches: (a) Significant weight and cost savings compared to individually packaged component designs by consolidating and optimizing the EPU packaging and integrating it with the space frame 60 to form an integrated mechanical attachment point 74; (b) Significant cost savings and ease of installation and maintenance compared to state-of-the-art piecemeal approaches by installing the complete EPU directly inside the nacelle; and (c) a simplified thermal interface due to the use of a single cooling line 82 from the integrated EPU 110 to the heat exchanger 56 (external to the integrated EPU 110) with no other cooling / oil line connections inside the nacelle. (d) The electrical wiring system is simplified by not including any external AC wires between the motor 30 and the inverter 50, but rather by using a single DC power input line 8 to supply DC power to the inverter 50 via a common DC bus bar 15 inside the EPU housing 112. (e) The aircraft distribution panel is simplified / eliminated due to the lack of individual power distribution units for each inverter 50. (f) The control interface is simplified by housing the EPC 12 within the inverter power electronics well 114, providing a simple communication interface with the flight control computer 14 (shown by a pair of double-headed arrows in FIG. 2). (g) The mechanical interface is simplified by providing integrated mechanical attachment points 74 for load transfer from the integrated EPU 110 to the aircraft primary structure 106. (h) An integrated air-cooling system can be incorporated between the rotor and the inverter system surrounding the rotor (not shown in FIG. 2, but see FIGS. 7A-7D below). (i) The functions of the ECU are performed by the EPC installed inside the nacelle, which also has the advantage of reducing weight and costs compared to the federated system shown in Figure 1.

[0034] In federated systems, the motor, inverter, and transmission are built independently and separately. The federated system is assembled by bolting components together or connecting them with plugs, cables, harnesses, and pipes. The assembly is then tested and calibrated. The integrated system presented here, on the other hand, allows for design optimization by leveraging various synergies between different subassemblies and utilizing the innovative design freedoms afforded by the integrated package. For example, the integrated package allows for optimization of the motor size by adjusting the gear ratio. The thrust bearing / propeller shaft assembly can also be optimized as an integrated system. The interoperability of different assemblies allows for optimization of cooling. For example, the water-cooled jacket inside the motor can be eliminated, instead relying on transmission oil for cooling, allowing for a compact design with a combined housing.

[0035] As previously mentioned, a typical state-of-the-art electric propulsion approach houses a large number of individual components, such as inverters, motors, governors, thrust bearings / propeller shafts, and controllers, as well as their supporting components (e.g., cooling pumps, cooling oil tanks, etc.), in a nacelle enclosure. Typically, all of these components are interconnected to a secondary, web-like structure (e.g., the space frame 60 in FIG. 1 ). The space frame 60 is connected to the primary aircraft structure 106. The multiple individual components that must be installed make integration within the nacelle extremely challenging in terms of weight and volume, resulting in a complex approach. System interconnections, such as electrical wiring, cooling pipes, and control harnesses, are difficult to construct within the nacelle and prone to failure. The federated nacelle mechanical / packaging design is suboptimal because each component has its own nonstructural housing, and the space frame 60 is required to provide the main load path to the primary aircraft structure 106. The large number of housings contributes to the overall cost and weight disadvantages of the federated approach. The space frame 60 must provide multiple mounting points and support for the various components (inverter, controller, motor, etc.), which requires complex design and reinforcement.

[0036] FIG. 3 illustrates the integration of mechanical components of an integrated EPU 110 into a single package that couples directly to the primary aircraft structure 106, according to one embodiment. This mechanical integration allows the EPU housing 112 to serve as the direct structural path to the primary aircraft structure 106, thereby reducing overall weight compared to state-of-the-art federated approaches. By combining all of the individual component housings into a single, integrated package, further optimization is performed to reduce the overall weight of the mechanical structure. The EPU housing 112 can be optimally designed to vibrate at natural frequencies outside of undesirable areas that may interact with system stimuli (propeller, airframe). EPU integration by combining all of the individual housings allows for optimal frequency design of the system by using all available materials in one central location to create a rigid, sturdy monoblock package.

[0037] The integrated EPU 110 shown in FIG. 3 includes a TB / T / PS assembly 72 integrated directly into the motor drive side of the EPU housing 112. This integration within the EPU housing 112 eliminates the need for a dedicated housing for the thrust bearing / propeller shaft functions and associated support structures. Integration within the EPU housing 112 also facilitates lubrication through integration with the internal oil system (described below). The TB / T / PS assembly 72 includes a ground ring (not shown in FIG. 3) for shaft grounding and bearing current protection. Optionally, the TB / T / PS assembly 72 can include a reduction gear / transmission and clutch function between the motor 30 and the propeller 32. The motor shaft can be used directly as the transmission shaft, simplifying the interface with the transmission system. More specifically, the system is designed without a quill shaft or propeller shaft, which would isolate the motor from thrust, bending moments, and axial misalignment, and therefore directly couples the motor shaft to the propeller. Additionally, the thrust bearing 38 can be the motor drive side bearing, thereby eliminating the additional bearing required in a typical federated approach. The integration of the TB / T / PS assembly 72 reduces the number of bearings and interfaces at the system level, resulting in weight and cost improvements compared to state-of-the-art federated approaches.

[0038] Additionally, the motor star 26 of the motor 30 and the inverter 50 of the motor controller (MC) are co-located within the EPU housing 112, allowing for shared mechanical structures and cooling channels and facilitating electrical connection between the motor windings and the inverter phase legs. The inverter power electronics compartment 114 shown in FIG. 2 is separated from the motor 30 by a bulkhead that does not impede the electrical interconnection between the inverter 50 and the motor star 26. In an alternative embodiment (described below with reference to FIGS. 7A and 7B ), the motor controller may surround the stator 25 (360°), using the stator core or housing as a support structure, and use the stator cooling channels or jacket to cool the inverter 50's semiconductor power switches. Co-locating the inverter 50 and motor 30 also eliminates the need for heavy additional housings and thick connecting AC wires. This co-location also allows for integrated cooling systems between the inverter 50, motor star 26, and stator 25 cores. The motor 30 has multiple motor stars 26 distributed at equal angular intervals around the stator core, with the inverter modules similarly distributed to facilitate integration of the winding electrical connections and cooling.

[0039] The embodiment shown in FIG. 3 further includes incorporating governor functionality into the integrated EPU package. The governor 64 includes a hydraulic actuator (not shown) coupled to a mechanical system including an integrated beta rod 58 that controls the pitch of the propeller blades. The governor 64 is mounted to the aft side of the EPU housing 112. The governor 64 is actuated by oil 88 supplied directly from the EPU integrated oil system (not shown in FIG. 3). The integrated beta rod 58 is located within a hollow motor shaft 78 that traverses from the governor well through the inverter power electronics well 114 and the motor well 116. The integrated beta rod 58 is supported within the hollow motor shaft 78 by inserts 86a and 86b, which keep the integrated beta rod 58 centered within the hollow motor shaft 78 to prevent excessive vibration. The inserts 86a and 86b are fixed within the hollow motor shaft and rotate with it. However, inserts 86a and 86b are configured to support beta rod 58 so that beta rod 58 can slide axially (e.g., by bearings) within openings in the inserts. Fluid pressure in integrated beta rod 58 is controlled by the state of hydraulic valves in governor 64. This pressure within beta rod 58 causes piston movement and changes in pitch of propeller blades 36 in a known manner.

[0040] The integrated EPU concept presented herein simplifies the oil circuits for lubrication and cooling by allowing them to be shared among various components such as the motor windings, motor bearings, inverter, thrust bearings, and governor. All of the oil circulation system is internal to the EPU housing 112, with only the heat exchanger 56 located external to the EPU housing 112 but inside the nacelle. The gear-type multi-element pump 66 and oil cooling reservoir 68 are integrated with the EPU housing 112 and the oil distribution circuits, manifolds (plenums), and channels to the various elements.

[0041] Modern federated systems typically use multiple pumps and reservoirs for motor and inverter cooling, thrust bearing lubrication, and governor oil pressure, resulting in systems that may include as many as four separate fluid systems. The large number of fluid systems negatively impacts system weight and cost due to the duplication of many components. A typical federated system also requires numerous interconnected pipes and tubing to distribute multiple fluids at different pressures to propulsion unit components. Installing dedicated pumps and reservoirs for each circuit in the nacelle negatively impacts weight, volume, and cost. Additionally, some components, such as motors, have internal bearings lubricated with grease, which negatively impacts reliability and maintenance due to the complexity of having multiple circuits for cooling, lubrication, and scavenging for each component.

[0042] Figure 4 illustrates an integrated single fluid system for providing cooling, lubrication, and governor oil within the integrated EPU 110. By creating a highly integrated mechatronic packaging approach, cooling synergies between different propulsion elements that share cooling can be achieved with appropriate hydraulic interfaces at the system level. The integrated EPU concept allows all cooling or lubrication subsystems to be integrated into a single fluid system. The integrated EPU 110 has an integrated oil reservoir 68 that receives oil return from all of the various components requiring cooling, lubrication, or oil pressure. The integrated EPU 110 also incorporates an integrated gear-type multi-element pump directly coupled to the motor main shaft. Driving this pump from the motor shaft eliminates the need for a drive motor and inverter, which would otherwise be required with a federated pump. The integrated pump contains various elements to provide sufficient flow and pressure to the various components. In Figure 4, the oil flow channels are represented by arrows.

[0043] As shown in FIG. 4, the elements of the integrated gear-type multi-element pump include a high-flow, low-pressure cooling / lubrication pump 66a (hereinafter, "cooling / lubrication pump 66a," designated "Pc" in FIG. 4) that sequentially supplies cooling oil to the inverter 50 and then the motor 30, while simultaneously supplying oil for lubrication to the thrust bearing 38. More specifically, the cooling / lubrication pump 66a draws oil from an integrated oil reservoir 68 and then pumps the oil through the heat exchanger 56 to the internal manifold 54d. This pressurized oil then flows in parallel through the inverter / motor cooling channel 11 and the bearing lubrication channel 90. After cooling the motor 30, the oil returns to the integrated oil reservoir 68 through the internal manifold 54e and return channel 91.

[0044] The integrated gear multi-element pump elements further include a scavenging pump 66b (labeled "Sc" in FIG. 4) that supplies pressure to the bearing scavenging channel 92 to recover oil from the thrust bearing 38 and other motor bearings. The recovered oil returns from the thrust bearing 38 through the bearing scavenging channel 92 and the scavenging pump 66b to the integrated oil reservoir 68.

[0045] The integrated gear-type multi-element pump elements further include a low-flow, high-pressure governor pump 66c (hereinafter "governor pump 66c," designated "Pg" in FIG. 4) that increases oil pressure to the governor 64 to actuate blade pitch angle adjustments. Pressurized oil flows from the governor pump 66c through a governor pressurized oil channel 94 to the governor 64. Oil in the governor 64 is returned to the integrated oil reservoir 68 through an oil return channel 96.

[0046] In this way, oil distribution to multiple components (motor, inverter, bearings, governor) is done within the EPU integrated package, without external oil lines or piping. The only hydraulic / oil connection required is to the external heat exchanger 56 in the nacelle. This EPU integrated thermal / oil management system allows a single pump and reservoir system to supply cooling or lubricating oil at the appropriate flow rate and pressure to all oil-cooled or oil-lubricated components. Where possible, relay tubing and internal passages are used to eliminate piping and fittings, which add weight and cost and can be a source of leaks.

[0047] Additionally, individually designed (federated) components may have different fluid, temperature, and pressure requirements. Integrating the design of all components allows for compatibility. A typical federated approach does not accommodate shared internal cooling between the inverter and motor windings because this requires complex and cumbersome piping between these elements. While it is possible to connect the entire inverter block (three inverters) in series with the entire motor block (three motor stars) with some external oil distribution, this can result in suboptimal thermal performance (high inverter-to-motor winding delta temperature) and hydraulic performance (large pressure drop). Co-locating the motor and inverter elements allows for shared cooling between each inverter and its associated motor star in a series cooling configuration. The main cooling oil loop is split into three independent parallel paths to cool each inverter / motor star combination. The inverter 50 and motor star 26 can directly share the same cooling jacket, or the inverter cold plate can be connected in series with the motor star cooling path. According to this proposed configuration, the channels of each inverter and motor are connected in series, and three independent cooling circuits (loops) are connected in parallel, thereby reducing the overall pressure drop and achieving an optimal cooling method.

[0048] To activate the governor pitch control, an additional low-flow pump element is used to boost pressure from the main low-pressure / high-flow circuit to generate the high pressure (low flow) required by the governor. The use of a boost element in series with the main circuit allows for an optimally small element configuration for the governor circuit. To scavenge the bearings, an additional small scavenging element is used to scavenge only the bearing elements, rather than scavenging the entire flow from the motor as in the federated approach.

[0049] Furthermore, the approach presented here uses one cooling system for all propulsion elements by allowing cooling to be shared between the transmission, governor, inverter, and motor, thereby significantly simplifying the cooling system compared to state-of-the-art approaches, and by integrating the gear pump and oil tank, it provides an optimized approach in terms of weight and volume.

[0050] In a typical EPU, the motor rotor can be cooled by various methods depending on the detailed motor design. However, for high-power motors, one preferred design is to not spray oil into the gap between the stator and rotor, as oil can cause significant hydraulic and mechanical losses. One simple design can cool the rotor using a combination of convection and conduction cooling. More advanced designs use airflow ingested from the rotor wheel to cool the rotor magnets.

[0051] Inverter power electronics currently use liquid cooling systems to remove heat generated by semiconductor power switches, filters, and circuit boards. The semiconductor power switches are mounted in direct contact with a cold plate through which a cooling liquid flows. Cooling the electronic control boards and capacitors can be difficult due to a lack of space on the cold plate and the lack of a separate cooling medium to transfer heat away from these components.

[0052] In a typical federated design, rotor air cooling cannot be achieved within the inverter design. The inverter cold plate footprint must accommodate all components, including semiconductor power switches and DC link capacitors, allowing these components to directly contact the cold plate. The control and driver boards are typically not in contact with the cold plate and are exposed to high operating temperatures due to insufficient cooling. Adding an external fan or building heat transfer to external structures through housing fins increases weight and cost, which can significantly impact the inverter design.

[0053] Figure 5 illustrates the integrated air cooling of the motor 30 and inverter 50 in the integrated EPU 110. The left-pointing arrows indicate the cooling air flow through the integrated EPU 110. The integrated EPU 110 is designed to redirect the motor rotor air cooling to the inverter power electronics compartment 114 to cool components not in direct contact with the cold plate. The motor's rotor wheel is designed with an impeller function to draw cooling air 62a from the center of the rotor. The motor's front panel has a grill with air inlets that allow air to flow through the rotor's inner ring. The rotor wheel has fins on the back of the rotor magnets to allow air to flow near the magnets at the appropriate speed and flow rate. The cooling air 62a drawn into the rotor wheel is used to remove heat from the magnets and reduce their operating temperature.

[0054] As cooling air 62b exits the motor, a portion of it can be directed directly into the inverter power electronics housing 114 to cool components such as driver and control boards, as well as filter components such as capacitors and inductors. This forced-air cooling provides efficient, lightweight cooling for all electronic components not in contact with the cold plate. Alternatively, this air can be directed over cooling fins integrated into the inverter power electronics housing 114 to enhance the convection cooling achieved through this interface. Cooling air 62c exiting the inverter 50 cools the common EMI filter 24, and cooling air 62d exiting the inverter 50 cools the EPC 12.

[0055] By providing forced air cooling to the power electronics, the inverter can be designed compactly with liquid cooling for the semiconductor power modules and air cooling for the DC link capacitors and control / driver board components. Air can be blown directly onto these components or onto a fin structure (cold plate or housing) that is in thermal contact with these components. The proposed compact design also reduces the footprint of the inverter cold plate. Thus, the integrated EPU 110 presented herein achieves significant design optimization by allowing the inverter and motor to share the liquid and air cooling system.

[0056] Additionally, integrating all inverters 50 into a single package provides multiple electrical synergies, optimizing the power electronics design and motor windings. Figure 6 illustrates the integration of electrical and control components in an integrated EPU 110 according to one embodiment. This EPU inverter integration allows the EPU's single DC terminal and DC power input 8 to be placed on a single harness between the integrated EPU 2 and the battery 18. Using a single DC dual (positive / negative) harness simplifies aircraft wiring between the battery 18 and the EPU 2 compared to using three DC dual harnesses. Additionally, the number of redundant connectors on the EPU and battery is reduced. Therefore, this integrated approach simplifies DC power distribution and routing by using a single input and a common DC bus bar 15 within the EPU housing 112. Typically, aircraft wiring requires shielding for safety and EMI reasons. Using a single wiring harness makes shielding significantly easier than using multiple wiring harnesses. Simplifying the harness and eliminating redundant connectors allows for simpler integration within the aircraft, thereby reducing weight, volume, and cost. This integrated approach also allows for power to be fed directly from the battery 18 to a common bus bar within the EPU housing 112 without the need for a dedicated inverter power distribution.

[0057] Furthermore, co-locating the inverter and motor eliminates the need for thick AC connection wires. In a typical federated approach, for each inverter 50, three single-phase conductors must be routed between the inverter and each motor star 26 of the motor. For high-power propulsion motors, it is common to have multiple motor stars per inverter to achieve the required power rating. This results in the need for many thick wires (9-18) to interconnect the inverter 50 and motor star 26. These wires are complex, costly, and have a significant impact on weight and volume. The integrated EPU 110 shown in Figure 5 eliminates all AC wiring, and the connection between the motor star windings and the inverter phase legs is made directly by a small busbar 57 within the integrated package.

[0058] Furthermore, the AC wires in a typical federated approach are a significant source of EMI disturbances and overvoltage stress on the motor windings. The AC wires are typically required to be fairly short to limit overvoltage stress on the motor windings and well shielded to reduce EMI disturbances on peripheral devices. The integrated approach presented herein solves both of these challenges in a simple manner, since connections are made as short as possible to limit overvoltage stress on the windings and the EPU housing 112 provides EMI shielding. Furthermore, such integration allows for a higher inverter switching frequency because AC parasitic capacitance is nearly zero and does not limit inverter switching. Increasing the switching frequency reduces motor rotor losses and optimizes the motor magnetic design.

[0059] The integrated package presented herein also enables optimized filtering using interleaved lumped filtering of EMI (see common EMI filter 24 in FIG. 6 ). All inverters 50 are connected to a common DC busbar 15 and share one common DC link capacitor (not shown in FIG. 6 ). Using a lumped DC link capacitor shared by three inverters reduces the size of the DC link capacitor required relative to the total number of inverters compared to the total size of three DC link capacitors for three separate inverters. All inverters 50 are directly connected to the common DC link capacitor using the common DC busbar 15. In one presented embodiment, the common DC busbar 15 is a low-inductance laminated busbar with alternating conductor and insulator layers, and the switching pattern of the inverters 50 is such that the AC power signals are interleaved in phase. This approach suppresses disturbances generated by the three interleaved inverters, thereby reducing the capacitance of the DC link capacitor compared to a federated approach. In a typical federated approach, the input filter of each inverter includes a differential inductor to suppress potential circulating currents between the inverters. The integrated approach presented herein eliminates the separate input filter inductors at each inverter, thereby reducing weight / volume and improving efficiency. In contrast, a typical federated approach cannot achieve this optimization because the inverters 50 are independent of each other and cannot interleave their switching patterns. Additionally, federated inverters require DC input filter inductances to suppress recirculating currents because their switching patterns are random relative to each other.

[0060] The inverter DC input is the primary interface with the rest of the electrical system. The longest supply path in the system is the DC power input line 8 from the battery 18 to the inverter 50. Controlling EMI emanating from this interface is important. In a federated approach, each inverter requires a dedicated filter sized for that single inverter's switching pattern. The integrated approach presented herein incorporates a common EMI filter 24 in a common-mode / differential-mode configuration for the group of inverters 50. The common EMI filter 24 is sized as a function of the interleaved inverter switching patterns, thereby reducing the weight and volume of the integrated EPU 110.

[0061] In the integrated approach presented herein, all inverters 50 are powered by a single DC power input line 8 via a common DC bus bar 15. In the event of an inverter failure, an active short circuit (ASC) scheme (closing the power switch of the failed inverter) is used to isolate the other inverters (i.e., other motor controller channels) even if one inverter fails. In the integrated approach presented herein, an ASC is used per motor star to accommodate inverter failures; that is, there is no need to open contactors or blow fuses for each inverter. The integrated approach allows for a fault-tolerant design with minimal power distribution.

[0062] According to one embodiment, the embedded EPC 12 is a controller configured with software modules that enable the following functions: (a) motor speed loop, (b) pitch control loop, (c) motor current loop, (d) interleaving of power signals output by the inverter 50, and (e) mode control.

[0063] In summary, the integrated approach presented here combines a common DC link capacitor, one DC terminal, simplified DC power distribution, simplified wiring, and integrated speed / position sensor control to provide electrical synergy.

[0064] 7A-7D illustrate an exemplary implementation of the motor / inverter cooling integration and governor / pump approach.

[0065] FIG. 7A shows an integrated EPU 110 in which a motor shaft 33 is rotatably mounted within an EPU housing 112 (only a portion of which is shown in FIG. 7A ). The motor shaft 33 is supported by motor shaft bearings 35. A rotor core 39 of a rotor 28 is mounted on the hollow motor shaft 33 with multiple permanent magnets 37 disposed on its outer periphery. The rotor 28 is surrounded by a stator 25, which includes a stator core 27 and stator windings 29. The stator 25 is surrounded by a cooling jacket 41, which has channels through which coolant 19 flows (from right to left, as indicated by the leftward arrow in FIG. 7A ). The cooling jacket 41 is attached to the back iron of the stator 25. (The back iron is a housing radially outward from the stator core.) Attached to the outer surface of the cooling jacket 41 are multiple power modules 31, each including its own inverter and inverter controller. The cooling jacket 41 is configured such that the coolant 19 flowing through the channels of the cooling jacket 41 cools both the stator 25 and the power module 31 .

[0066] Continuing with reference to FIG. 7A, the EPU 110 further includes a main drive gear 49 attached to the forward end of the motor shaft 33. Teeth of the main drive gear 49 mesh with teeth of a pump drive gear 47 and a propeller shaft drive gear 55, both of which are offset from the central axis of the motor shaft 33. A pump 98 pumps coolant through the cooling jacket 41 and has an input shaft attached to and rotatably driven by the pump drive gear 47. The propeller shaft drive gear 55 is attached to a hollow propeller shaft 34 offset from the motor shaft 33. The propeller shaft 34 is supported by a thrust bearing 38. As part of the transmission subassembly, a gear set is adapted to reduce the rotational speed of the propeller shaft 34 relative to the rotational speed of the motor shaft 33. A governor 64 is located aft of the offset propeller shaft drive gear 55 and controls the axial displacement of a beta rod 58 inside the hollow propeller shaft 34 to vary the pitch of the propeller blades (not shown in FIG. 7A).

[0067] FIG. 7B illustrates an alternative embodiment of the EPU 110, in which the stator 25 is cooled using a combination of jacket / back-iron cooling and a flooded stator. More specifically, the outlet of the cooling jacket 41 is in fluid communication with the stator internal cooling channels 3 having outlets 3a. With a flooded stator, the stator windings 29 are immersed in the cooling liquid for direct, efficient cooling. The stator 25 includes a stator housing 43 (also known as a back-iron) that defines the stator internal cooling channels 3, allowing the cooling liquid to circulate directly through the winding slots formed in the stator core 27. Similar to the configuration shown in FIG. 7A, the power modules 31 are mounted directly to the cooling jacket 41. 7B uses a planetary gearbox 53 to allow the hollow motor shaft 78 to spin faster than the propeller shaft 34, with the governor 64 mounted to the rear of the EPU housing 112 and the beta rod 58 extending the length of the EPU 110. Additionally, the pump 98 is coupled to the planetary gears of the planetary gearbox 53.

[0068] The motor configuration shown in Figure 7C is similar to that shown in Figure 7B, except that the pump 98 is geared to the hollow motor shaft 78 using a gear set on the rear side of the motor 30. The motor transmission elements are configured as a direct drive without a speed reducer. Optionally, a mechanical linkage 59 may be incorporated.

[0069] FIG. 7D shows another embodiment of the EPU 110, in which the stator 25 is cooled using flooded stator cooling. Similar to the embodiment shown in FIG. 7B, the internal stator cooling channels 3 are formed in part by the stator housing 43. Each internal stator cooling channel 3 has an inlet 3b and an outlet 3a. With a flooded stator, the stator windings 29 are immersed in the cooling fluid, providing direct and efficient cooling of the motor. The power modules 31 are located adjacent to the motor end-winding wells at the rear of the motor. In each power module 31, a cooling fluid (e.g., oil) flows through its respective cold plate 1 to cool the inverter components (e.g., power switches, capacitors, etc.). The oil first flows through the cold plate 1 and then enters slots (not shown in FIG. 7D) in the stator core 27. Thus, the motor stars associated with one inverter are arranged to receive the cooling fluid in series. Thus, each inverter-motor star pair is arranged in parallel with one another, allowing the cooling flow to be split.

[0070] In all configurations shown in Figures 7A-7D, the thrust bearing 38 is cooled in parallel with the main cooling channels and scavenged by an additional integrated pump element (not shown in Figures 7A-7D). Governor oil pressure is supplied from the main flow using an integrated boost pump element. An oil reservoir is integrated into the EPU package, although not shown in Figures 7A-7D for simplicity. The governor location is shown as aft of the motor, but could be located forward for different types of governors, such as counterweight types.

[0071] To improve the availability of the electric propulsion system, state-of-the-art configurations use two separate, overlapping electric propulsion channels (A / B) to drive the propellers 32. The main drawback is that many components are duplicated, such as the housing, mechanical structures, cooling systems (pumps, oil tanks, etc.), bearings, shafts, and controllers. Furthermore, coordinating the two different channels can be challenging, as can integrating components such as the governor 64. The duplicated components also add weight and bulk to the dual electric propulsion system.

[0072] In contrast, an integrated EPU allows for optimal dual-electric propulsion configurations. A dual-channel integrated EPU package can reorganize two separate electric propulsion channels. FIG. 8A illustrates an integrated EPU 110 with multiple integrated channels, according to one embodiment. Motor controller channel A includes three inverters 50a that receive DC power from battery 18a via a series connection of battery contactor 48a, DC power input line 8a, EMI filter 24a, and low-inductance busbar 15a. Battery 18a is managed by battery management system 22a. Similarly, motor controller channel B includes three inverters 50b that receive DC power from battery 18b via a series connection of battery contactor 48b, DC power input line 8b, EMI filter 24b, and low-inductance busbar 15b. Battery 18b is managed by battery management system 22b.

[0073] The integrated EPU 110 shown in FIG. 8A allows for mutual cooling systems between the two channels, using the same pump and sump circuits. Mechanical structures and housings can be integrated into a single package, minimizing weight and volume. As with the single-channel package, electrical interconnection between the motor 30 and inverter 50 is direct via a compact bus bar 57, eliminating the need for large AC wires. The EPU housing 112 is directly connected to the aircraft primary structure 106 via integrated mechanical attachment points 74 for propeller load and torque response. The governor 64 and transmission (not shown in FIG. 8A) are integrated into the rear and front of the package, respectively. Two separate power electronics wells are formed for motor controller channel A and motor controller channel B.

[0074] FIG. 8B illustrates an integrated multi-phase fault-tolerant motor design for the electric propulsion unit shown in FIG. 8A. Motor channel A and motor channel B can be realized with an integrated multi-phase fault-tolerant motor design. The motor design magnetically and electrically decouples the motor stars (more specifically, decouples motor star 26a of motor channel A from motor star 26b of motor channel B). Special winding techniques (e.g., concentrated windings), winding arrangement (stator position), motor pitch, and slot design minimize the magnetic and electrical coupling between the motor stars of motor channel A and motor channel B. Furthermore, the stator layout thermally decouples motor star 26a of motor channel A from motor star 26b of motor channel A. The integrated motor of this example has three motor stars 26a of motor channel A and three motor stars 26b of motor channel B. According to the proposed design, a common stator core 27 is implemented for motor channel A and motor channel B. Furthermore, rotor elements (shaft, magnet, bearings, etc.) are shared between motor channel A and motor channel B.

[0075] If the motor star of motor channel A (or B) fails, that motor star A (or B) is shorted in an active short circuit (ASC) fashion by closing the power switch in the inverter of the associated motor controller channel A (or B). The stator slots and windings are sized to provide an impedance of approximately 1 PU to limit the short circuit current to its maximum rated current. In this condition, during ASC, the losses in the failed motor star are equal to the nominal losses. At nominal speed, the motor star connected to the shorted power switch generates minimal drag torque, allowing the intact motor star to continue driving the propeller.

[0076] In the event of a distribution failure of motor channel A (or B), all inverters of the associated motor channel A are commanded to close the power switches (3 or 6 switches) of one or both rows, effectively short-circuiting all motor stars of the failed motor channel. In this case, motor channel A does not provide energy to the short circuit in the inverter. At nominal speed, all motor stars of the shorted motor channel A (or B) generate a minimal drag torque, allowing motor channel B (or A) to continue driving the propeller.

[0077] The integrated multiphase fault-tolerant motor design described above allows for two independent motor functions without duplicating significant components such as the stator magnetic core, rotor magnet, shaft, bearings, housing, support structure, etc. The presented approach optimizes weight and cost. Dual motor functions can be achieved without the use of mechanical clutches or disconnectors.

[0078] To reduce control complexity, one EPC can be used for both motor controller channels A / B to command different inverters and coordinate control between both motor channels A / B. The EPC is integrated into the power electronics housing in a manner similar to the single package configuration shown in Figure 6.

[0079] FIG. 9A illustrates a schematic diagram of a dual-motor EPU 110′ with an integrated drivetrain according to another embodiment. The dual-motor EPU 110′ includes a first motor 30a disposed in the front section of the EPU housing 112 and a second motor 30b disposed in the rear section of the EPU housing 112. The first motor 30a includes a hollow motor shaft 78a, a rotor core 39a attached to and surrounding the hollow motor shaft 78a, and a stator core 27a surrounding the rotor core 39a. The second motor 30b includes a hollow motor shaft 78b, a rotor core 39b attached to and surrounding the hollow motor shaft 78b, and a stator core 27b surrounding the rotor core 39b. The two motors are arranged axially side-by-side. This exemplary approach integrates the power electronics of each motor and actively shares cooling between the power module 31 and the stator cores 27a, 27b.

[0080] The hollow motor shafts 78a and 78b are selectively coupled to and surround a corresponding portion of the hollow main drive shaft 17. The beta rod 58 is axially translatable within the hollow main drive shaft 17. The hollow motor shafts 78a and 78b are coupled to the hollow main drive shaft 17 using respective sets of mechanical coupling devices 13, one of which is partially shown in FIG. 9B. Mechanical coupling devices 13 include, for example, override clutches, synchro-self-shifting (SSS) clutches, and sprag clutch types. The triangle in FIG. 9B represents the spline interface between the mechanical coupling devices 13 and the hollow main drive shaft 17. Each motor 30a and 30b includes a respective set of motor shaft bearings 35 mounted to the EPU housing 112 to independently support the rotors 28a and 28b. Thus, when both hollow motor shafts 78a and 78b are coupled to hollow main drive shaft 17, both motors 30a and 30b drive the rotation of hollow main drive shaft 17.

[0081] Alternatively, if hollow motor shaft 78a is decoupled from hollow main drive shaft 17 while hollow motor shaft 78b remains coupled, only motor 30b drives the rotation of hollow main drive shaft 17. On the other hand, if hollow motor shaft 78b is decoupled from hollow main drive shaft 17 while hollow motor shaft 78a remains coupled, only motor 30a drives the rotation of hollow main drive shaft 17. Thus, if one of the motors fails, its mechanical coupling device 13 decouples the rotor of the failed motor. The rotor of the failed motor is stopped, and its corresponding stator winding is de-energized. The healthy motor can continue to operate and rotate without any influence from the failed motor. This mechanical decoupling allows one motor to be independently disengaged in the event of a failure or abnormal operation. One significant difference from the approach shown in FIG. 8A is that the rotor of the failed motor is stopped, preventing back-EMF generation. This feature eliminates the need to continue to apply short-circuit current to the failed motor or electronics. When a fault is detected in one of the motors, its associated inverter is commanded to enter ASC mode, and the rotor automatically responds by slowing down and mechanically disengaging. During ASC, torque increases as the motor speed decreases. Once the rotor reaches zero speed, the ASC state is maintained as long as the rotor is at zero speed. The healthy motor continues to rotate and drive the propeller independently of the failed motor. The motor and inverter only need to maintain a short circuit (for a few seconds) while the failed motor's rotor is decelerating. This configuration allows for the weight and size of the motor's magnetic and electrical components, as well as the size of the power switches, to be reduced.

[0082] Thus, the main trade-off is the use of a mechanical disconnect device instead of a high-impedance motor design. However, a hybrid approach can combine both approaches. If one motor star of motor 30a fails, the failed motor star is placed in ASC mode. The remaining two motor stars of motor 30a continue to operate and drive. Motor 30b also continues to operate normally. If more than one motor star fails or the distribution is shorted on motor 30a, motor 30a is disengaged (all motor stars are placed in ASC mode) and motor 30b continues to operate normally. This hybrid approach also provides redundant motor disconnection for safety purposes.

[0083] The mechanical coupling devices 13 (which may be selectively activated to perform the decoupling function) may be tightly integrated with the motor shaft bearings 35 (shown in FIG. 9C), thereby minimizing the weight and size impact of adding a decoupling device to each motor. More specifically, the inner walls of the bearings and the outer walls of the clutch may be the same component, thereby reducing part count and complexity and providing fewer failure modes. In the event of a fault, such as an overspeed or mechanical failure, such as a bearing failure or rotor bottom-down, the mechanical coupling devices 13 may be used to simultaneously decouple both motors 30a and 30b from the main driveline shaft 17.

[0084] The approach presented herein is easily scalable, as multiple motor inverter modules can be stacked with mechanical coupling to the main drivetrain shaft 17. The example presented with two motors can easily be expanded to three or more motors. Individual motors can be designed with minimal impedance or with impedances on the order of 1 PU, depending on the safety and isolation methods selected. Alternatively, if mechanical decoupling is not required, multiple motors can be stacked with direct coupling (without a mechanical coupling device), each with impedances on the order of 1 PU.

[0085] The flowcharts and block diagrams of the various illustrated embodiments illustrate the structure, functionality, and operation of some possible implementations of the apparatus and methods in the example embodiments. In this regard, each block in the flowcharts or block diagrams may represent a module, segment, function, and / or part of an operation or step. For example, one or more of the blocks may be implemented by program code, hardware, or a combination of program code and hardware. If implemented in hardware, the hardware may be, for example, in the form of an integrated circuit that is manufactured or configured to perform one or more steps illustrated in the flowcharts or block diagrams.

[0086] The embodiments disclosed above employ one or more controllers. Such devices typically include processors or computers, such as central processing units, microprocessors, reduced instruction set computer processors, application specific integrated circuits, programmable logic circuits, field programmable gate arrays, digital signal processors, and / or other circuits or processing devices capable of performing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a non-transitory, tangible, computer-readable storage medium, such as, for example, a storage device and / or a memory device. Such instructions, when executed by a controller, cause the controller to perform at least a portion of the methods described herein.

[0087] The methods described herein may be encoded as executable instructions embodied in a non-transitory, tangible, computer-readable storage medium, such as a storage device and / or a memory device, that, when executed by a processing or computing system, cause the system device to perform at least a portion of the methods described herein.

[0088] While an integrated electric propulsion unit for an aircraft has been described with reference to various embodiments, those skilled in the art will recognize that various modifications may be made and equivalents may be substituted for components without departing from the scope of the teachings herein. Additionally, many modifications may be made to adapt the disclosure herein to a particular situation without departing from its scope. Accordingly, it is intended that the claims not be limited to the specific embodiments disclosed herein.

[0089] NOTE: The following notes describe various aspects of this disclosure.

[0090] A1. Housing and an AC motor disposed within the housing, the AC motor including a plurality of bearings supported within the housing, a motor shaft rotatably coupled to the housing by the plurality of bearings, a stator supported by the housing, and a rotor attached to the motor shaft; an inverter disposed within the housing and connected to receive and convert DC power into AC power; a controller disposed within the housing and configured to control operation of the inverter; a cooling circuit configured to guide the flow of a circulating fluid, the cooling circuit comprising: an oil reservoir attached to the housing; a cooling pump mounted on the housing, geared to the motor shaft, and in fluid communication with the oil reservoir; a cooling channel disposed within the housing and connected to guide the circulating fluid from the cooling pump along a flow path to the oil tank.

[0091] A2. The electric propulsion unit of Appendix A1, wherein the cooling channel includes a first channel portion passing through the inverter and a second channel portion passing through the stator and in fluid communication with the first channel portion.

[0092] A3. A thrust bearing / transmission / propeller shaft assembly including a thrust bearing, a transmission, and a propeller shaft; and The electric propulsion unit of Claim A1, further comprising a propeller attached to the propeller shaft and including propeller blades with adjustable pitch.

[0093] A4. The cooling circuit is a heat exchanger disposed external to the housing and in fluid communication with the cooling pump; a manifold disposed within the housing and in fluid communication with the heat exchanger; The electric propulsion unit of claim A3, further comprising: a bearing lubrication channel in fluid communication with the manifold and the thrust bearing.

[0094] A5. The cooling circuit is a bearing scavenging pump in fluid communication with the oil reservoir; The electric propulsion unit of Claim A4, further comprising: a bearing scavenging channel in fluid communication with the thrust bearing and the bearing scavenging pump.

[0095] A6. A governor configured to adjust the pitch angle of the propeller blades, wherein the cooling circuit a governor pump in fluid communication with the manifold; a governor pressurized oil channel in fluid communication with the governor pump and the governor; The electric propulsion unit of Claim A4, further including an oil return channel in fluid communication with the governor and the oil reservoir.

[0096] A7. Housing and an AC motor disposed within the housing, the AC motor including a plurality of bearings supported within the housing, a motor shaft having a rotation axis rotatably coupled to the housing by the plurality of bearings, a stator supported by the housing, and a rotor attached to the motor shaft; a main drive gear having teeth attached to a forward end of the motor shaft; a propeller including a hollow propeller shaft having a rotation axis offset from the rotation axis of the motor shaft and propeller blades with adjustable pitch angle; a beta rod capable of axial translation within the hollow propeller shaft; a governor configured to adjust the pitch angle of the propeller blades by actuating axial translation of the beta rod; a propeller shaft drive gear attached to the hollow propeller shaft and having teeth that mesh with the teeth of the main drive gear; a plurality of power modules arranged radially outward of the stator; a controller disposed within the housing, controlling the operation of the plurality of power modules; and and a controller configured to perform operations including controlling the pitch angle of the propeller blades.

[0097] A8. The electric propulsion unit of Appendix A7, further including a cooling jacket disposed between the stator and the power module.

[0098] A9. Housing and first and second pluralities of bearings supported within the housing; a main driveline shaft supported by the first and second plurality of bearings supported within the housing; first and second hollow motor shafts surrounding corresponding portions of the main drive train shaft; first and second pairs of mechanical coupling devices selectively connecting the first and second hollow motor shafts to the main drive train shaft, respectively; first and second rotors attached to the first and second hollow motor shafts, respectively; first and second stators supported within the housing and disposed radially outward of the first and second rotors, respectively; a propeller mechanically coupled to the main driveline shaft; a controller disposed within the housing and configured to selectively activate one of a pair of mechanical coupling devices to decouple one of the hollow motor shafts from the main drive train shaft.

Claims

1. Housing and an AC motor disposed within the housing, the AC motor including a plurality of bearings supported within the housing, a hollow motor shaft rotatably coupled to the housing by the plurality of bearings, a stator supported by the housing, and a rotor attached to the hollow motor shaft; a beta rod axially translatable within the hollow motor shaft; a propeller mechanically coupled to the hollow motor shaft, the propeller including propeller blades having an adjustable pitch angle dependent on the axial position of the beta rod; a governor configured to adjust the pitch angle of the propeller blades by actuating axial translation of the beta rod; an inverter disposed within the housing and connected to receive and convert DC power into AC power; a controller disposed within the housing, controlling the operation of the inverter; and and a controller configured to perform operations including controlling the pitch angle of the propeller blades.

2. 10. The electric propulsion unit of claim 1, further comprising one or more inserts secured within the hollow motor shaft and configured to support the beta rod so that the beta rod can slide axially.

3. 3. The electric propulsion unit of claim 1 or 2, further comprising a thrust bearing / transmission / propeller shaft assembly integrated with a drive end plate of the housing.

4. 4. The electric propulsion unit according to claim 1, wherein the governor is integrated with a rear end plate of the housing.

5. 5. The electric propulsion unit of claim 1, further comprising: a first cooling channel thermally coupled to the inverter; and a second cooling channel thermally coupled to the stator, the second cooling channel in fluid communication with the first cooling channel.

6. The electric propulsion unit of claim 5 , wherein the first cooling channel is a cold plate.

7. The electric propulsion unit of claim 5 or 6, wherein the stator includes a stator housing, and a portion of the second cooling channel is defined by the stator housing.

8. 8. The electric propulsion unit according to claim 1, wherein the stator includes a stator housing, the inverter is disposed radially outward from the stator housing, and the electric propulsion unit further includes a cooling jacket disposed between the inverter and the stator housing.

9. Housing and an AC motor disposed within the housing, the AC motor including a plurality of bearings supported within the housing, a motor shaft having a rotation axis rotatably coupled to the housing by the plurality of bearings, a stator supported by the housing, and a rotor attached to the motor shaft; a main drive gear having teeth attached to a forward end of the motor shaft; a propeller including a hollow propeller shaft having a rotation axis offset from the rotation axis of the motor shaft and propeller blades with adjustable pitch angle; a beta rod capable of axial translation within the hollow propeller shaft; a governor configured to adjust the pitch angle of the propeller blades by actuating axial translation of the beta rod; a propeller shaft drive gear attached to the hollow propeller shaft and having teeth that mesh with the teeth of the main drive gear; a plurality of power modules arranged radially outward of the stator; a controller disposed within the housing, controlling the operation of the plurality of power modules; and and controlling the pitch angle of the propeller blades. and a controller configured to:

10. The electric propulsion unit of claim 9 , further comprising a cooling jacket disposed between the stator and the power module.

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