Hybrid power system for different flight modes

Abstract

A first power source, a second power source, and a power controller are provided, wherein a vehicle including the first power source, the second power source, and the power controller is capable of flying in a transition mode between a hover mode and a forward flight mode. The power controller selects one or more of the first power source and the second power source to provide power to rotors included in the vehicle during the transition mode.

Description

[0001] Cross-references to other applications This application claims priority to U.S. Provisional Patent Application No. 62 / 912,872, filed October 9, 2019, entitled "Fixed-wing Aircraft with Tiltrotor," which is incorporated herein by reference for all purposes. Background Technology

[0002] New types of aircraft are being developed that can take off and land in dense urban areas, opening up new transportation routes and avoiding road congestion. For example, Kitty Hawk is developing a new electric vertical takeoff and landing (eVTOL) tiltrotor aircraft that can take off and land in a footprint of approximately 30 feet by 30 feet. Early prototypes have been built and tested, and further improvements in the vehicle's performance, such as increased range, are expected. Attached Figure Description

[0003] Various embodiments of the present invention are disclosed in the following detailed description and accompanying drawings.

[0004] Figure 1A This is a perspective view showing an embodiment of a forward-swept fixed-wing vehicle with tilt rotors.

[0005] Figure 1B This is a top view showing an embodiment of a forward-swept fixed-wing vehicle with tilt rotors.

[0006] Figure 2A This is a bottom view illustrating an embodiment of the boundary layer thickness, with the motor off.

[0007] Figure 2B This is a bottom view showing an embodiment of the boundary layer thickness, with the motor turned on.

[0008] Figure 3A The diagram shows an example of a tiltrotor configuration with corresponding lift vector, thrust vector, and drag.

[0009] Figure 3B The diagram illustrates an example of a fixed-wing configuration with a leading-edge mounted tiltrotor and corresponding lift vector, thrust vector, and drag.

[0010] Figure 3C The diagram illustrates an embodiment of a fixed-wing configuration having a trailing-edge mounted tiltrotor and corresponding lift vector, thrust vector, and drag.

[0011] Figure 4 This is a diagram illustrating an embodiment of the airflow generated when the tiltrotor mounted on the trailing edge of the main wing is closed.

[0012] Figure 5 This is a diagram illustrating embodiments of a forward-swept, tapered wing and a straight wing for comparison.

[0013] Figure 6A This is a diagram illustrating an embodiment of the takeoff tilt transition from a hovering position to a cruise position.

[0014] Figure 6B This is a diagram illustrating an embodiment of the landing tilt transition from a cruising position to a hovering position.

[0015] Figure 7 This is a diagram illustrating an embodiment of the velocity tilt diagram.

[0016] Figure 8 This is a diagram illustrating an embodiment of a vehicle having a hybrid power system comprising two battery subsystems.

[0017] Figure 9 The diagram illustrates an embodiment of a vehicle with a hybrid power system, which includes a battery subsystem and an internal combustion engine.

[0018] Figure 10 The diagram shows an embodiment of a vehicle having a dedicated cruise propeller and a dedicated tilt rotor for hovering and transition, as well as a hybrid power system including a battery subsystem and an internal combustion engine. Detailed Implementation

[0019] This invention can be embodied in a variety of ways, including as: a process; an apparatus; a system; a component of matter; a computer program product embodied on a computer-readable storage medium; and / or a processor, such as a processor configured to execute instructions stored in and / or provided by a memory coupled to the processor. In this specification, these embodiments or any other form of the invention may be referred to as technology. Generally, within the scope of this invention, the order of steps of the disclosed process may be varied. Unless otherwise stated, components described as configured to perform a task (such as a processor or memory) may be implemented as general components temporarily configured to perform the task at a given time or as specific components manufactured to perform that task. As used herein, the term "processor" refers to one or more means, circuits, and / or processing cores configured to process data (such as computer program instructions).

[0020] The following provides a detailed description of one or more embodiments of the present invention, together with accompanying drawings illustrating the principles of the invention. The invention is described in conjunction with such embodiments, but is not limited to any particular embodiment. The scope of the invention is limited only by the claims, and the invention covers many alternatives, variations, and equivalents. Numerous specific details are set forth in the following description to provide a thorough understanding of the invention. These details are provided for illustrative purposes, and the invention may be practiced according to the claims without requiring some or all of these specific details. For clarity, technical materials known in the art related to the invention have not been described in detail, so that the invention is not unnecessarily obscured.

[0021] This document describes various embodiments of an electric vertical takeoff and landing (eVTOL) tiltrotor aircraft with a hybrid power system. For context and background, it may be helpful to first describe an earlier version of the vehicle that uses a single type of cell and / or power system in all power systems (e.g., all cells have the same design with the same type of cells). Various embodiments of exemplary eVTOL tiltrotor aircraft with hybrid power systems, along with example applications and / or benefits, are then described. Of course, the hybrid power system described herein can be used in other vehicles.

[0022] Figure 1A This is a perspective view showing an embodiment of a forward-swept fixed-wing vehicle with tilt rotors. Figure 1B This is a top view illustrating an embodiment of a forward-swept fixed-wing vehicle with a tiltrotor. In the example shown, the main wings (100a and 100b) are fixed wings, which are attached to the fuselage (102a and 102b) in a fixed manner or position. In other words, the main wings are not rotatable tiltrotor wings. The main wings (100a and 100b) are also forward-swept (e.g., relative to the pitch axis). For example, in an aircraft embodiment with canards (as shown here), the forward-swept angle can be between approximately 14° and 16° θ. 掠 Alternatively, for aircraft embodiments without canards, the forward sweep angle can be as high as 35°.

[0023] In this example, the main wings (100a and 100b) have six rotors (104a and 104b) attached to the trailing edge of the main wings. Rotors or propellers in this configuration are sometimes referred to as propulsion propellers (e.g., because at least when in their forward flight position, the propellers are behind the wing and "push" the vehicle forward). The forward flight mode is sometimes referred to herein as the cruise mode. For clarity, these rotors on the main wings are sometimes referred to as main wing rotors (e.g., to distinguish them from rotors attached to the canards). Of course, the number of rotors shown here is merely exemplary and not intended to be limiting.

[0024] In addition to the six main wing rotors, there are two rotors (106a and 106b) attached to the canards (108a and 108b). These rotors are sometimes referred to as canard rotors. The canards are thinner than the main wings, so unlike the main wing rotors, the canard rotors are attached to the far end of the canard, rather than the trailing edge.

[0025] All rotors in this example are tiltrotors, meaning they are capable of tilting or otherwise rotating between two positions. In the accompanying figures shown here, the rotors are in a cruise (e.g., forward-facing, backward-facing, etc.) position. In this position, the rotors rotate about (e.g., substantially) a longitudinal axis of rotation, causing them to provide (substantially) rearward thrust. When the rotors are in this position, the lift that keeps the tiltrotor vehicle airborne comes from the airflow above the main wings (100a and 100b) and canards (108a and 108b). In this particular example, the tiltrotor range of rotation has a minimum angular position of approximately 0°–5° and a maximum angular position of approximately 90°–95°. This range is specific to the design and / or implementation.

[0026] The rotors can also tilt downwards to a hovering (e.g., vertical takeoff and landing, downward orientation, etc.) position (not shown). In this second position, the rotors rotate about (e.g., substantially) a vertical axis of rotation, such that they provide (substantially) downward thrust. In this configuration, the lift that keeps the tilt-rotor vehicle in the air comes from the downward airflow from the rotors.

[0027] Generally, when tiltrotors are oriented to output thrust substantially downwards, they allow an aircraft to perform vertical takeoff and landing (VTOL). This mode or configuration (e.g., in terms of the aircraft's overall flight behavior and / or specifically in terms of the tiltrotor's position) is sometimes referred to as hovering. The ability to perform VTOL allows an aircraft to take off and land in areas without airports and / or runways. Once airborne, the tiltrotors (if desired) change position to output thrust (substantially) rearwards instead of downwards. This allows the aircraft to fly in a manner more efficient for forward flight; this mode or configuration is sometimes referred to as cruise.

[0028] Canards are useful because they can stall first (e.g., before the main wing), generating a large pitching moment and not losing much lift during stall, whereas a main wing stall results in a significant loss of lift with each change in pitching moment (e.g., causing the entire aircraft to descend or crash). Therefore, stalling with canards can be more benign than without them. Canard stall behavior combined with forward-swept wings is particularly beneficial because a main wing stall can generate an unfavorable pitching moment if it occurs at the wing root and a large and dangerous rollover moment if it occurs at the wingtip. Furthermore, canards can generate lift at low airspeeds and increase CL (Clear Coil). 最大(i.e., maximum lift coefficient), and provides struts to hold or otherwise attach the canard motor.

[0029] In some embodiments, the pylons (110a and 110b) for attaching the rotor to the canard and / or main wing include hinges and / or rotation mechanisms that allow the tilt rotor to rotate between the two positions shown. Any suitable hinge mechanism can be used. For example, for ultralight aircraft, there are very stringent weight requirements, and therefore a lightweight solution may be desired. Alternatively, a fixed tilt solution can also be used to meet very stringent weight requirements.

[0030] In some embodiments, the aircraft is designed such that the main wings (100a and 100b) and canards (108a and 108b) provide sufficient lift to perform a gliding landing if needed during an emergency. For example, some ultralight standards or specifications require safe landing in the event of one or more rotor failures, and the ability to perform a gliding landing would meet that requirement. One advantage of using a fixed wing for the main wing (e.g., compared to a tiltrotor) is that there is no risk of the wing getting stuck in an incorrect position (e.g., a hovering position) where a gliding landing is impossible because the wing position is unsuitable for a gliding landing.

[0031] Another advantage of a fixed wing with a trailing-edge mounted tiltrotor is the reduction (or absence) of stall behavior during the transition from hover to cruise (or vice versa). With a tiltrotor, the angle of attack changes during the transition, increasing the risk of stall. A fixed wing with a trailing-edge mounted tiltrotor does not change the wing's angle of attack (e.g., even if the rotor is switched off / on or the tiltrotor is displaced). Additionally, this configuration increases dynamic pressure and circulation above the main wing, significantly improving behavior during the transition (e.g., from hover to cruise or vice versa). In other words, a fixed wing utilizing a trailing-edge mounted tiltrotor can perform the transition more quickly and / or more efficiently than a tiltrotor (as an example).

[0032] Another advantage associated with fixed-wing vehicles with tiltrotors (e.g., compared to tiltrotors) is the use of a smaller mass fraction for (multiple) tilt actuators. That is, multiple actuators for multiple tiltrotors (still) comprise a smaller mass fraction than a single heavy-duty actuator for a tiltrotor. Tiltrotors also have fewer points of failure because there are multiple actuators compared to a single (and heavy-duty) actuator for a tiltrotor. Another advantage is that fixed-wing designs allow for smoother and / or faster transitions (e.g., between cruise mode or position and hover mode or position) compared to tiltrotor designs.

[0033] In some embodiments, the rotor is a variable-pitch propeller, which has different blade pitches when the rotor is in a hovering position and a cruise position. For example, different blade pitches (ranges) can achieve more efficient operation or flight when in a cruise position and a hover position. When the rotor is in a cruise position, adjusting the blade pitch to a "cruise pitch" (e.g., approximately 26°) achieves a lower frontal area (e.g., lower drag) that is beneficial for cruise. When the rotor is in a hover position, adjusting the blade pitch to a "hover pitch" (e.g., approximately 6°) achieves a higher disk area that is beneficial for hovering. In other words, a blade pitch may be very suitable for cruise mode but not for hover mode, and vice versa. The use of a variable-pitch propeller achieves better (e.g., overall) efficiency, resulting in less power consumption and / or increased flight range.

[0034] The following diagram illustrates the relationship with Figure 1A and 1B The exemplary aircraft shown here are associated with various benefits.

[0035] Figure 2A This is a bottom view illustrating an embodiment of the boundary layer thickness, with the motors off. In this example, laminar extension lines 200a, 202a, and 204a show laminar extension at different regions of the main wing. In this example, it is assumed that the aircraft is cruising (e.g., flying in a substantially forward direction). Figure 1A and 1B As shown in the figure, in this embodiment, the main wing rotor (206) is attached to the trailing edge of the main wing (208). The following figure shows the boundary layer thickness when the rotor is in operation.

[0036] Figure 2B This is a bottom view illustrating an embodiment of boundary layer thickness, with the motor turned on. In this example, the motor is on, and the rotor has an outlet airflow velocity of 30 m / s. With the motor on, a low-pressure region is formed towards the rear of the wing, which increases laminar extension on the main wing. See, for example, the corresponding... Figure 2A The laminar extension lines 200a, 202a, and 204a in the diagram are laminar extension lines 200b, 202b, and 204b. A comparison of these two groups shows that the laminar extension increases at the first two locations (i.e., at 200a / 200b and 202a / 202b). The last location (i.e., 204a / 204b) has only a slightly longer laminar extension due to interference from the canard rotor (210).

[0037] The drag from the main wing rotor (more precisely, the drag from the pylons used to attach the main wing rotor to the main wing) is hidden in the wake of the airflow from the main wing. See, for example, Figure 2AThis more clearly shows the pylon (220) connected or otherwise attached to most of the rear of the laminar extension (222). In the embodiment shown here, the pylon is also able to retain some of the boundary layer thickness away from the main wing, meaning the pylon has lower drag per unit surface area. This improves drag compared to some other alternative designs or configurations. This is described in more detail in the following figures.

[0038] Figure 3A This diagram illustrates an example of a tiltrotor configuration with corresponding lift vector, thrust vector, and drag. In this example, a fixed rotor (300) is attached to the tiltrotor (302) at a fixed position or angle. This is an alternative arrangement in the aforementioned aircraft(s) embodiments. The tiltrotor (302) rotates to direct the airflow generated by the fixed rotor (300) backward or downward. As shown here, for this configuration, drag (304) exists at the trailing edge of the tiltrotor, which is undesirable.

[0039] The lift (306) and thrust (308) of this configuration are also shown here, with the tiltrotor shown in the middle of the transition (e.g., between the cruise and hover positions). As shown here, the lift (306) and thrust (308) are substantially orthogonal to each other, which is inefficient. In other words, the tiltrotor is inefficient during its transition.

[0040] Figure 3B This diagram illustrates an example of a fixed-wing configuration with a tiltrotor mounted on its leading edge and corresponding lift vector, thrust vector, and drag. In this example, the tiltrotor (320) is attached to the leading edge of the fixed wing (322). This is another alternative arrangement configuration of the aforementioned aircraft(s). The corresponding drag (324) and thrust (326) of this arrangement are also shown. This configuration does not generate useful lift, and therefore the lift vector is not shown here.

[0041] Figure 3C The diagram illustrates an embodiment of a fixed-wing configuration with a trailing-edge mounted tiltrotor and corresponding lift, thrust, and drag vectors. In this example, the tiltrotor (340) is attached to the trailing edge of the fixed wing (342). In this configuration, the drag generated by the trailing-edge mounted tiltrotor (e.g., primarily due to its pylons, not shown) is concealed in the wake of the airflow from the main wing. Therefore, there is no drag (at least not due to the tiltrotor (340)).

[0042] The position of the trailing-edge mounted tiltrotor (340) relative to the fixed wing (342) also draws air (344) over the fixed wing, after which the air is redirected or bent through the rotor and downwards. This flow redirection over the wing generates a relatively large induced lift (346), as shown here. The thrust vector (348) generated by the rotor is also shown here. It should be noted that the induced lift (346) and thrust (348) are essentially in the same direction (i.e., both are essentially upwards), which is a more efficient arrangement, including during the transition. In other words, compared to other rotor and wing arrangements, a fixed wing using a trailing-edge mounted tiltrotor produces less drag and improved efficiency during the transition (e.g., because the lift and thrust vectors now point in essentially the same direction). Note, for example, separately Figure 3A and Figure 3B Resistance levels 304 and 324, and Figure 3A The orthogonal positions of lift 306 and thrust 308 in the figure.

[0043] The following figure illustrates an embodiment of flow redirection in more detail.

[0044] Figure 4 This diagram illustrates an embodiment of the airflow generated when the tiltrotor mounted on the trailing edge of the main wing is closed. In this example, a tiltrotor aircraft (400) is shown, but for comparative purposes, the main wing rotor is closed. With the rotor closed, the airflow inflow (402) and airflow outflow (404) move in essentially the same direction. That is, the airflow does not turn (e.g., downwards) as it passes the rotor.

[0045] Aside from the rotor being open, tiltrotor 420 shows the same vehicle as tiltrotor 400. In this example, the airflow inflow (422) and airflow outflow (424) have significantly different directions, and there is a noticeable directional change or bend in the airflow as it passes through the rotor of the exemplary tiltrotor shown. As described above, this generates significant lift, which is desirable because less power is consumed and / or the tiltrotor's range is increased.

[0046] In this example, the main rotor (426) is in the hovering position. As shown here, these rotors are slightly pitched or otherwise tilted (e.g., the top of the main rotor is slightly forward-pointing and the bottom is slightly rearward-pointing). In this figure, the tilt is shown as θ. 俯仰(428), and in some embodiments, this is a rotational range or movement of approximately 90° (e.g., ~3° upward from the horizontal when in the cruise position (e.g., for minimum drag) and ~93° downward from the horizontal when in the hover position, resulting in a rotational range of ~96°). While such skewing or pitching of the rotor is not absolutely necessary for flow steering, in some embodiments, the main rotor is skewing or otherwise pitched to increase or otherwise optimize the amount of flow steering. In some embodiments, the canard rotor is similarly pitched. It should be noted that the tiltrotor 420 is shown in a nose-up position, and therefore the vertical axis (e.g., relative to the tiltrotor) is not perpendicular to the ground and / or reference frame.

[0047] In some embodiments, when the rotor is in the hovering position, the rotor (e.g., the main wing rotor and / or canard rotor) is tilted slightly outward away from the fuselage or otherwise angled. In some embodiments, this tilt (e.g., outward) is approximately 10° to obtain greater yaw authority.

[0048] In some embodiments, the main wing is not only swept forward but also tapered (e.g., the wing tapers outward toward the wingtip). Various wing and / or tail embodiments are illustrated in the following figures.

[0049] Figure 5 This is a diagram illustrating embodiments of a forward-swept, tapered wing and a straight wing for comparison. In the example shown, wing 500 is a straight wing without tapering (e.g., the wing has the same width from center to wingtip). An exemplary rotor (502) is shown at the trailing edge of the straight wing (500).

[0050] The thrust center (504), indicated by the dotted line, is determined by the rotor's position or arrangement and extends through the center of the main rotor (502). For simplicity, the canard rotor is omitted in this example. The lift center is based on the wing shape. For a rectangular wing such as wing 500, the lift center (506), indicated by the solid line, extends along the wing center. The calculation of the aerodynamic center is more complex (e.g., the aerodynamic center depends on the wing's cross-section, etc.), and the aerodynamic center 508, indicated by the dashed line, is exemplary and / or typical for this type of wing.

[0051] As shown here, the arrangement of the straight wing (500) and its corresponding main rotor (502) creates a thrust center (504) that is relatively far from both the lift center (506) and the aerodynamic center. This separation is undesirable. More specifically, when the main rotor (502) is in a hovering position, if the thrust center (504) is far from the lift center (506), the transition (e.g., in the context of the aircraft moving as a whole, such as switching from essentially upward flight to essentially forward flight, or vice versa) will generate very large moments and may overturn the vehicle or impair acceleration or stability and / or require a large and / or suboptimal propulsion system. During cruise, if the thrust center (504) is far from the lift center (506), it is less important (e.g., because the thrust moment is smaller and more easily balanced by the aerodynamic moment), but it is still undesirable.

[0052] In contrast, the trailing-edge arrangement of a forward-swept and tapered wing (520) and its corresponding rotor (522) produces thrust centers (524), lift centers (526), ​​and aerodynamic centers (528) that are closer to each other. For example, the forward sweep of the wing causes the rotor to move forward to varying degrees. This causes the thrust center to move forward (e.g., toward the leading edge and toward other centers). The tapering of the wing prevents the aerodynamic and lift centers from shifting forward too much (and more importantly, away from the thrust center) due to the forward sweep. For example, for a forward-swept wing without tapering (not shown), the thrust center would move forward by approximately the same amount as the aerodynamic and lift centers, and would result in a greater separation between the three centers than shown here in wing 520.

[0053] Some other benefits of forward-swept, tapered wings include better pilot visibility and a better fuselage-to-wing junction (e.g., allowing the main wing spars to pass behind the pilot's seat without passing through the pilot). Furthermore, the tapering reduces wing moment and brings the engine's thrust center closer to the wing-to-fuselage junction, resulting in less moment from the wing to the fuselage when the direction of flight is referenced. This leads to a shorter tail boom (e.g., reducing aircraft weight) and improved pitch stability.

[0054] The following figure illustrates an exemplary tilt transition of the rotor between the cruise position and the hover position.

[0055] Figure 6AThis diagram illustrates an embodiment of the takeoff tilt transition from a hovering position to a cruise position. In some embodiments, the exemplary tiltrotor aircraft performs this transition shortly after takeoff (e.g., substantially vertically). It should be noted that this tilt transition is optional, and the aircraft can fly entirely with the rotor in the hovering position (although not optimally). This can be done, for example, if a tilt maneuver is risky and it is preferable to perform the maneuver at a higher altitude.

[0056] The tiltrotor aircraft 600 illustrates an exemplary aircraft after it has performed a vertical takeoff. In this state shown here, the main rotor and canard rotor are in a hovering position (e.g., rotating about a substantially vertical axis of rotation, causing the rotor to generate substantially downward thrust).

[0057] The tiltrotor then transitions from a completely upward direction of movement to a direction of movement with at least some forward motion, with the rotor remaining in the hover position until the tiltrotor reaches a desired altitude (602) from which the transition began. In other words, the vehicle transitions first and then changes the rotor tilt. In one example, the altitude at which the tiltrotor begins the rotor tilt change from the hover position to the cruise position is high enough to allow for recovery time in case of problems during the transition. Switching the rotor between the hover and cruise positions is a high-risk time, where the likelihood of problems (e.g., rotor failure, rotor jamming, etc.) is higher. While tiltrotor aircraft may have systems and / or technologies for recovery (e.g., compensating for rotor failure by increasing the thrust of the remaining rotors, deploying parachutes, etc.), these systems and / or technologies require time (i.e., sufficient altitude) to function.

[0058] From position 602, the tiltrotor flies substantially forward and moves the tilt rotors from the hovering position (e.g., where thrust is output substantially downward) to the cruise position. Once in the cruise position 604, the rotors rotate about a substantially longitudinal axis, causing them to output rearward thrust.

[0059] Figure 6B This diagram illustrates an embodiment of the tilt-rotor transition from a cruise position to a hovering position during landing. For example, an exemplary tiltrotor aircraft may perform this transition before vertical landing. As with previous transitions, this transition is optional. For example, if desired, the exemplary tiltrotor aircraft may keep the tilt rotor in a cruise position and perform a gliding landing instead of a vertical landing.

[0060] The tiltrotor aircraft 610 is shown with its rotor in the cruise position. While flying in a substantially forward direction, the tiltrotor moves from the cruise position shown at 610 to the hover position shown at 612. With the tiltrotor in the hover position (612), the tiltrotor descends with some forward movement to position 614 (at least in this example), thus maintaining (lower) power usage and preserving a better option in the event of motor or other component failure (e.g., the tiltrotor could increase rotor power and exit the landing process or path) until it finally lands on the ground.

[0061] Figure 7 This is a diagram illustrating an embodiment of a velocity tilt diagram. In the diagram shown, the x-axis represents the forward velocity of the aircraft, and the y-axis represents the tilt (e.g., the position or angle of the tilt wing or tilt rotor), ranging from (e.g., minimum) cruise position (700) to (e.g., maximum) hover position (702).

[0062] The first operational envelope (704), shown with solid line boundaries and filled with a grid pattern, is associated with the tiltrotor aircraft. See, for example, [link to relevant documentation]. Figure 4 The tiltrotor aircraft 400 and Figure 3A The tiltrotor 302 and fixed rotor 300 are shown in the diagram. A second operational envelope (706), shown with a dashed boundary and gray fill, is associated with (e.g., similar) an aircraft having a forward-swept, fixed wing with a trailing-edge mounted tiltrotor. See, for example, the embodiment described above.

[0063] In the diagram shown here, the tiltrotor operating envelope (706) is a superset of the tiltrotor operating envelope (704), indicating that the former's aircraft configuration is safer and / or more airworthy than the latter, and is also capable of flying faster and slower at similar tilt positions. For a fixed wing, the wing is already (and / or always) pointing in the (forward) direction of travel. When the tiltrotor is at or near (e.g., maximum) hover position (702), the vehicle can fly almost all the way to the stall speed (e.g., V2) without having to tilt the motors up to the cruise position. It should be noted, for example, that the tiltrotor operating envelope (706) can remain at (e.g., maximum) hover position (702) until V2. This greatly increases the number of operating states of the tiltrotor operating envelope (706) compared to the tiltrotor operating envelope (704). For example, note all the gray areas above the tiltrotor operating envelope (704).

[0064] Another effect that can contribute to an extended operating envelope in tiltrotor configurations at or near hover includes flow steering (e.g., see...). Figure 4The flow deflection above the main wing causes some additional lift. In some embodiments, when in normal hovering (e.g., at the minimum tilt position 700), this flow deflection and the lift it generates are amplified or optimized by tilting the main wing rotor from directly downward to a slightly rearward angle.

[0065] In contrast, when the tiltrotor is tilted upward in (e.g., at its maximum) hover position (702), it presents a larger frontal area. Therefore, the tiltrotor cannot fly forward at any suitable speed until it is in or near full (e.g., minimum) cruise position (700) or almost there.

[0066] Return to Figure 1A and 1B Early prototypes of the tiltrotor vehicle used battery systems with a single type of cell to simplify the design. For example, lithium-ion cells tend to be either high discharge rate (i.e., capable of outputting high current levels) or high energy, but not both (e.g., because energy capacity typically decreases as discharge rate capacity increases). For instance, batteries and / or cells with an energy density less than or equal to 190 Wh / kg are generally capable of supporting high current consumption and are accordingly considered or classified as high discharge rate, while those with an energy density greater than or equal to 235 Wh / kg are considered or classified as high energy. The cell used in the early prototypes was a compromise between the two, allowing for the use of a single type of cell, which reduced design complexity. Since the rest of the vehicle differs significantly from existing vehicles, it was desirable to maintain design simplicity as much as possible in the early prototypes.

[0067] For subsequent versions and / or prototypes of the vehicle, increasing the vehicle's range is a desired performance improvement. Hybrid power systems (e.g., including two or more different power systems used at different times or in different modes during flight) are more complex than battery systems with a single type of cell (e.g., because vehicles with hybrid power systems need to safely turn various power systems on and off during flight, and other design considerations), but the increased range makes the trade-off worthwhile.

[0068] The following figures illustrate various embodiments of the hybrid power system that can be used in the tiltrotor vehicle described above. First, an embodiment of a hybrid power system with two types of batteries is described. Then, an embodiment of a hybrid power system with both a battery and an internal combustion engine is described. It should be noted that the hybrid power system described herein can be applied to other types of vehicles, not just the exemplary tiltrotor vehicle described herein.

[0069] Figure 8This diagram illustrates an embodiment of a vehicle with a hybrid power system comprising two battery subsystems. In the example shown, the tiltrotor vehicle includes one high-discharge-rate battery (800) and five high-energy batteries (802). In this example, the high-discharge-rate battery (800) has an energy density of ~180 Wh / kg and accounts for ~15% of the total battery weight, while the high-energy batteries (802) have an energy density of ~270 Wh / kg. The high-energy batteries are more limited in their discharge rate but are suitable for the power requirements of cruise flight.

[0070] For example, consider Figure 6A The flight sequence shown. For hovering ( Figure 6A 600 in the middle) and transition state ( Figure 6A The 602 in the middle requires a relatively high discharge rate because greater thrust from the rotor is needed during these flight modes (e.g., because there is little or no lift on the wings, so all or most of the lift comes from the rotor). In contrast, during cruise ( Figure 6A The power required for 604 (in this context) is much lower, approximately 30% of the power needed during hovering. Therefore, during vertical takeoff (i.e., Figure 6A (Hover mode 600) and when the vehicle transitions from hover mode to forward flight ( Figure 6A In the case of 602), the high-discharge-rate battery (800) is used to supply power to the tilt rotor. During forward flight or cruise ( Figure 6A In 604), a high-energy battery (802) is used to supply power.

[0071] The advantage of the exemplary hybrid power system shown here is that it increases (e.g., cruise) range compared to earlier non-hybrid power systems initially used for early prototypes (e.g., with a single type of battery cell). For example, the initial battery system used a single type of cell with an energy density of ~200 Wh / kg, a compromise. This resulted in the need for more cells to achieve the overall current levels required for the energy-consuming hovering and transition phases of flight. The end result of this compromise was a lower (e.g., cruise) range than offered by the exemplary hybrid power system. For example, the exemplary hybrid power system shown here can produce a cruise battery capacity and cruise range increase of ~15% over earlier non-hybrid power systems.

[0072] As illustrated in this example, in some embodiments, the first power source (e.g., in a hybrid power system) comprises a high-discharge-rate battery with an energy density less than or equal to 190 Wh / kg, and the second power source (e.g., in a hybrid power system) comprises a high-energy battery with an energy density greater than or equal to 235 Wh / kg. In some embodiments, during a transition mode, the power controller is configured to select the high-discharge-rate battery to power the rotor in the vehicle and to select the high-energy battery to power the rotor. In some embodiments, the weight of the high-discharge-rate battery is less than or equal to 20% of the total battery weight.

[0073] One consideration when using a hybrid power system is determining when to switch the power supply to the tiltrotor's power subsystem. In one example, after vertical takeoff, current sensors monitor the bus current, and as the aircraft enters cruise mode, the power source switches from a high-discharge (800) battery to a high-energy (802) battery as current consumption from the motors decreases and stabilizes. That is, the test for switching during a takeoff sequence can be based on the flight mode or state the vehicle is in (e.g., the flight computer or controller may have flight state variables with values ​​of HOVER_ST, TRANS_ST, or FF_ST) and whether the average current consumption (e.g., within a travel time window) is less than or equal to a certain threshold.

[0074] In some cases, the thresholds or states that trigger changes in the power subsystems that power the tiltrotor are different for takeoff sequences (e.g., hover, transition, and forward flight sequences) and landing sequences (e.g., forward flight, transition, and hover sequences). For example, a current sensor, as described above, can be used to determine when to switch from high discharge to high energy during takeoff. However, during landing, especially in the final approach phase, even as the rotor tilts to hover mode, current consumption remains low as the aircraft descends. As the vehicle approaches the ground, power consumption increases suddenly, requiring a power source switch very close to the ground, with no margin for error in the event of a switching drive failure. In this situation, it might be desirable to switch the power source at the start of the transition phase (e.g., when the flight state variable transitions from FF_ST to TRANS_ST), regardless of current consumption, rather than waiting until the power demand increases as the aircraft approaches the ground.

[0075] A key consideration in aircraft hybrid power systems is the safe switching between different power sources. In one example, for safety, switching is achieved using more than one electronically activated mechanical or semiconductor-based switch, sized such that the system will continue to function even if any one switch fails. Furthermore, for safety, the switches can be configured to fail in the open-circuit position of one power source but remain closed for the other, thus preventing situations where both battery packs are simultaneously connected to the bus or neither is connected.

[0076] In some embodiments, the hybrid power system includes a battery and an internal combustion engine. Various examples of this are illustrated in the following figures. As will be described in more detail below, in some embodiments, there are one or more cruise-dedicated (i.e., fixed) propellers used for forward flight mode (and possibly to some extent during transition modes), but not for hovering mode.

[0077] Figure 9 This diagram illustrates an embodiment of a vehicle with a hybrid power system comprising a battery subsystem and an internal combustion engine. In the example shown, during cruise mode, the internal combustion engine (e.g., an engine including a fuel tank (900) and a gearbox (902)) drives a generator (904) via an engine-generator shaft (906), wherein power electronics (908) control the generation of electrical power through the internal combustion engine for an electric tilt rotor. During hover mode, the electrical power supplied by the internal combustion engine is supplemented by the battery (910).

[0078] In some embodiments, the generator (904) is used to charge the battery (910) during the cruise phase (e.g., slowly). For example, since the battery is only used during hover mode (e.g., for takeoff and landing), the battery can be charged during cruise mode because it does not discharge during this period. This can increase the vehicle's available hover time during landing (which could be attractive if the landing zone is occupied and the vehicle needs to hover when the landing zone is cleared) and / or allow for the use of smaller capacity (and therefore lighter) batteries.

[0079] For comparison, it is assumed that the early prototype of the vehicle was equipped with a 100kg battery pack (e.g., a non-hybrid battery system with a single type of cell). For the exemplary hybrid system shown here, it is assumed... Figure 8The high-discharge-rate battery is used in the battery (910). If so, the battery section (910) in this hybrid example would weigh approximately 16 kg. The hybrid power internal combustion engine section (e.g., including the fuel tank (900) and the engine (902) with a gearbox) along with its fluid and support systems would occupy approximately 38 kg. The generator (904) and power electronics (908) would occupy approximately 16 kg. This leaves approximately 30 kg for fuel, which increases cruising range by 50% compared to the non-hybrid battery configuration in comparison. Despite the increased complexity, safety challenges (e.g., due to flammable liquids), noise, and vibration issues, the increased range may make this trade-off worthwhile for applications with longer ranges. Additionally, compared to Figure 8 Unlike the hybrid example shown, in this embodiment, one of the power subsystems (the internal combustion engine) is always on. This may be attractive for safety reasons, as there is no possibility that the first power subsystem is off and the second power subsystem cannot be turned on.

[0080] As illustrated in this example, in some embodiments, the first power source (e.g., in a hybrid system) includes an internal combustion engine, and the second power source includes (e.g., a high-discharge-rate) battery; during a transition mode, the power controller is configured to select the internal combustion engine to provide power to the rotor and deselect the battery so that the battery does not provide power to the rotor; during a hover mode, the power controller is configured to select both the internal combustion engine and the battery to provide power to the rotor. In some embodiments, when the battery is deselected and does not provide power to the rotor, the internal combustion engine is used to charge the battery at least for a certain period of time.

[0081] Figure 10 A diagram illustrating an embodiment of a vehicle is provided, which includes a dedicated cruise propeller and a dedicated tilt rotor for hovering and transitions, as well as a hybrid power system comprising a battery subsystem and an internal combustion engine. In the example shown, the battery subsystem (1000) drives the (electric) tilt rotor during hovering and transitions (shown here as a downward tilt position for hovering). In some embodiments, the battery subsystem (1000) includes various types of cells (e.g., high-energy batteries and high-discharge-rate batteries), which are switched on and off during the various flight modes described above (e.g., see...). Figure 8 ).

[0082] The hybrid power system further includes an internal combustion engine that drives a cruise-dedicated propeller (1002). In this example, the cruise-dedicated propeller is mounted to the nose of the aircraft, but such a propeller can be located in multiple places (e.g., a pusher propeller on the tail cone). During cruise (i.e., forward flight) mode, the engine (1004) turns a gearbox (1006), which in turn turns the cruise-dedicated propeller (1002) via a propeller shaft (1008). Fuel is stored in a fuel tank (1010).

[0083] For comparison, it is assumed that an early prototype of the vehicle was equipped with a 100kg battery pack (e.g., a non-hybrid battery system with a single type of cell). In this comparison, it is assumed that the battery section (1000) in this example uses high-discharge-rate batteries, and that the battery section in this hybrid example weighs approximately 16kg. The internal combustion engine, along with its fluid and support systems, as well as the gearbox and additional propeller (1002), accounts for approximately 45kg. This leaves approximately 39kg for fuel, which increases the cruising range by almost 100% compared to the configuration in the comparison. In some long-range applications, the increased range provided makes any trade-offs in terms of complexity, safety concerns (e.g., related to flammable liquids on board), noise, and vibration worthwhile.

[0084] As illustrated in this example, in some embodiments, the first power source (e.g., in a hybrid power system) includes an internal combustion engine, and the second power source includes a battery. The vehicle includes a tilt rotor, and the vehicle also includes a cruise-dedicated rotor. The power controller is configured to: select the internal combustion engine to provide power to the cruise-dedicated rotor during forward flight mode, and deselect the internal combustion engine during hover and transition modes, so that the internal combustion engine does not provide power to the cruise-dedicated rotor.

[0085] In this example, the tilt propeller is used for hovering and transitions and is shut off during the cruise portion of flight. In some embodiments, the tilt propeller is foldable to reduce drag, allowing the propeller blades to be folded (e.g., backwards) during cruise mode to reduce drag during cruise.

[0086] In some embodiments, the cruise-specific rotor includes a cruise-specific propulsion rotor located behind the tail of the vehicle (e.g., so that the wake generated by the cruise-specific rotor does not interfere with the airflow above the canards or main wings). In some embodiments, the second power source includes a high-discharge-rate battery with an energy density less than or equal to 190 Wh / kg and a high-energy battery with an energy density greater than or equal to 235 Wh / kg (i.e., the battery subsystem itself is a hybrid system, such as...). Figure 8 (Example shown).

[0087] As mentioned above, hybrid power systems can be useful in increasing range. In some embodiments, the battery provides the additional thrust needed during hovering and / or transition modes, but the internal combustion engine and generator provide the lower power required for cruise flight. For a given vehicle weight, this will significantly increase range because the energy density of liquid fuels is much higher than that of batteries.

[0088] In another embodiment, the hybrid power system uses two electric (i.e., battery) systems, one utilizing high-power output cells for hovering and / or transition modes, and the other using high-energy-density cells (e.g., which typically have lower current output capabilities) to provide cruise power, thereby extending the range compared to a single electric system (i.e., a battery with a single composition type).

[0089] Although the foregoing embodiments have been described in detail for clarity of understanding, the invention is not limited to the details provided. Many alternative ways of carrying out the invention exist. The disclosed embodiments are illustrative and not restrictive.

Claims

1. A hybrid power system, comprising: Including the primary power source of the internal combustion engine; Including a second power source for the battery; as well as Power controller, wherein: The hybrid power system is included in a vertical takeoff and landing (VTOL) vehicle that flies in a transition mode, the transition mode occurring: (1) after a hovering mode and before a forward flight mode during vertical takeoff, or (2) after a forward flight mode and before a hovering mode during vertical landing; and The power controller selects one or more of the first power source and the second power source to provide power to the vertical takeoff and landing vehicle including the rotor, including by: Receive the current consumption associated with the vertical take-off and landing vehicle; Receive one or more flight status variables associated with the flight computer, the flight status variables indicating whether the vertical takeoff and landing vehicle is in hover mode, forward flight mode or transition mode; During vertical descent, the power controller performs a power source switch, causing the second power source to supply power to the rotor. This includes, during vertical landing, in a transition mode occurring after the forward flight mode and before the hovering mode, supplementing the power supplied to the rotor via the first power source, independent of the current consumption and in response to one or more flight state variables associated with the flight computer; and During vertical takeoff, the power controller selects one or more of the first and second power sources to provide power to the rotor, at least in part based on the current consumption.

2. The hybrid power system according to claim 1, wherein, The vertical takeoff and landing vehicle also includes multiple propulsion tiltrotors.

3. The hybrid power system according to claim 1, wherein, The internal combustion engine charges the battery at least for a certain period of time during the forward flight mode.

4. The hybrid power system according to claim 1, wherein, The vertical takeoff and landing vehicle also includes multiple propulsion tiltrotors and cruise-specific propellers.

5. The hybrid power system according to claim 1, wherein, The vertical takeoff and landing vehicle also includes multiple propulsion tiltrotors and cruise-specific propellers, wherein the multiple propulsion tiltrotors are used only for hovering and transition.

6. The hybrid power system of claim 1, wherein in response to a change in flight state variables from those associated with the forward flight mode to those associated with the transition mode, the power controller determines to allow the second power source to provide power to the rotor.

7. A method for managing a hybrid power system, comprising: Provides a primary power source including an internal combustion engine, as included in a hybrid system; Provide a second power source, including batteries, as included in hybrid systems; and Provide a power controller, included in a hybrid system, wherein: The hybrid power system is included in a vertical takeoff and landing (VTOL) vehicle that flies in a transition mode, the transition mode occurring: (1) after a hovering mode and before a forward flight mode during vertical takeoff, or (2) after a forward flight mode and before a hovering mode during vertical landing; and The power controller selects one or more of the first power source and the second power source to provide power to the rotor included in the vertical takeoff and landing vehicle, including by: Receive the current consumption associated with the vertical take-off and landing vehicle; Receive one or more flight status variables associated with the flight computer, the flight status variables indicating whether the vertical takeoff and landing vehicle is in hover mode, forward flight mode or transition mode; During vertical descent, the power controller performs a power source switch, causing the second power source to supply power to the rotor. This includes, during vertical landing, in a transition mode occurring after the forward flight mode and before the hovering mode, supplementing the power supplied to the rotor via the first power source, independent of the current consumption and in response to one or more flight state variables associated with the flight computer; and During vertical takeoff, the power controller selects one or more of the first and second power sources to provide power to the rotor, at least in part based on the current consumption.

8. The method for managing a hybrid power system according to claim 7, wherein, The vertical takeoff and landing vehicle also includes multiple propulsion tiltrotors.

9. The method for managing a hybrid power system according to claim 7, wherein, The internal combustion engine charges the battery at least for a certain period of time during the forward flight mode.

10. The method for managing a hybrid power system according to claim 7, wherein, The vertical takeoff and landing vehicle also includes multiple propulsion tiltrotors and cruise-specific propellers.

11. The method for managing a hybrid power system according to claim 7, wherein, The vertical takeoff and landing vehicle also includes multiple propulsion tilt rotors and a cruise-specific propeller, wherein the multiple propulsion tilt rotors are used only for hovering and transition.

12. The method for managing a hybrid power system according to claim 7, wherein, In response to a change in flight state variables from those associated with the forward flight mode to those associated with the transition mode, the power controller determines to allow the second power source to provide power to the rotor.

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