Hybrid drive and fuel vaporizer for UAV and other mobile environments

[0001] This application is the national stage entry of International Application No. PCT/US2021/044366, filed Aug. 3, 2021, which claims the benefit of U.S. Provisional Application No. 63/060,367, filed Aug. 3, 2020, the disclosure of each of which is incorporated by reference herein in its entirety.

[0002] The present application relates to the field of hybrid, electro-mechanical drivetrains where battery supplied power is insufficient to provide a long endurance and, therefore, must be supplemented by energy derived from fuel in the course of combustion. An example of such drivetrains is the Aerial Vehicle, manned or unmanned, wherein the power-to-weight ratio and the specific energy are dominating factors. Furthermore, the present application also relates to the field of assistive devices to enable multi-fuel engines to start and operate efficiently.

[0003] Electrical motors are gaining in popularity for many mobile drives, such as unmanned aerial vehicles (“UAVs”), electric aircrafts, etc., but large and heavy batteries limit the specific energy and specific power. Hybrid drives that combine electric motors with a combustion engine are a potential solution. Novel hybrid drive configurations that enable high specific power and specific energy, as well as battery recharging during takeoff and landing, remote engine restarting, and quiet (electric motor only) operation during cruise are described herein.

[0004] In one embodiment, the invention provides a hybrid drive. The hybrid drive of this embodiment includes a load shaft; a motor/generator coupled to the load shaft; an internal combustion engine; an electromagnetic clutch, configured to disengageably couple the internal combustion engine to the load shaft, and located between the motor/generator and the internal combustion engine; and a power supply, coupled to the motor/generator and to the clutch.

[0005] The invention also provides a hybrid drive of another embodiment, wherein the embodiment includes a load shaft; a second electric motor, coupled to the load shaft; an over-running one-way clutch, coupled to the load shaft; a motor/generator, disengageably coupled to the load shaft through the over-running one-way clutch; an internal combustion engine, coupled to the load shaft and the second electric motor, so that the load shaft is driven by a source selected from the group consisting of the second electric motor, the internal combustion engine in combination with the motor/generator, and the internal combustion engine in combination with the motor/generator and the second electric motor; and a power supply, coupled to the second electric motor and the motor/generator.

[0006] In a related embodiment, the hybrid drive of these embodiments is configured so that the internal combustion engine both drives the load shaft and causes the motor/generator to recharge the power supply. Alternatively or in addition, the hybrid drive is configured so that the internal combustion engine is started by energy from the power supply delivered to the motor/generator. The power supply can include an electronic control unit configured to switch the motor/generator's mode of operation to a mode of operation selected from the group consisting of motor operation, generator operation, and combinations thereof. The hybrid drive may include at least one other electrically powered component, such as an additional electric motor. The power supply may be configured to deliver power to the at least one other electrically powered component.

[0007] In some embodiments, the motor/generator may be configured to start the engine. The motor/generator may be configured to start the engine prior to flight. The motor/generator may be configured to restart the engine during flight.

[0008] In another embodiment, there is provided an improved fuel vaporizer, of the type coupled for use with an internal combustion engine, and including a body, fuel and air inlets, an air/fuel outlet, and a heater that vaporizes the fuel, wherein the improvement is characterized in that the air inlet is disposed in a direction tangential to fuel flow so as to cause formation of an air vortex that quickly and thoroughly mixes with fuel from the fuel inlet. Optionally, the heater is operated by an arrangement selected from the group consisting of electrical means, exhaust gas, and combinations thereof. In a related embodiment, there is provided a hybrid drive, in accordance with any of the previously described embodiments, wherein the internal combustion engine is equipped with the improved fuel vaporizer of embodiments described in this paragraph.

[0009] In another embodiment, the invention provides an aircraft having a hybrid drive according to any one of the previously described embodiments, and wherein the aircraft further includes a thruster coupled to the load shaft.

[0010] In another embodiment, the invention provides a method of achieving a quiet mode of operation and during operation of an UAV using the hybrid drive of any of the previously described embodiments. In this embodiment, the method includes, in the following order:

• • [0011] turning off the internal combustion engine when the quiet mode of operation is required and driving the load shaft solely with the motor/generator; and
  • [0012] restarting the internal combustion engine when the quiet mode of operation is no longer required, using the motor/generator to restart the internal combustion engine.

[0013] In a related similar embodiment, utilizing an UAV having the previously described hybrid drive including a second electric motor, the invention provides a method of achieving a quiet mode of operation, and the method includes, in the following order:

• • [0014] turning off the internal combustion engine when the quiet mode of operation is required and driving the load shaft solely with the second motor; and
  • [0015] restarting the internal combustion engine when the quiet mode of operation is no longer required, using the motor/generator to restart the internal combustion engine.

[0016] In another embodiment, there is provided a method of achieving dash speed operation of a UAV using the first above-described hybrid drive embodiment, in which the method includes driving the load shaft with both the motor/generator and the internal combustion engine.

[0017] In another embodiment, there is provided a method of achieving dash speed operation of a UAV using the second above-described hybrid drive embodiment, in which the method includes driving the load shaft with a combination of the motor/generator, the second electric motor, and the internal combustion engine.

[0025] Definitions. As used in this description and the accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires:

[0026] An “electric motor/generator” or “motor/generator” is an electric machine that can work as an electric motor, i.e. to drive a shaft, when powered by a power supply, and which can work as an electrical generator, when powered by an engine (the generated electricity can be used to recharge the power supply).

[0027] “Power supply” means a rechargeable source of electricity, for example, batteries, supercapacitors, or other devices capable of accepting, storing, and releasing electrical energy.

[0028] “UAV” means unmanned aerial vehicle.

[0029] “VTOL” means vertical take-off and landing.

[0030] “Dash speed” means a speed that is unsustainable during normal operations but that is necessary for mission requirements, for example, high-speed cruise, which is normally not economical.

[0031] A “set” includes at least one member.

[0032] Electric motors powered by batteries have gained popularity because they are compact, durable, and quiet. Unfortunately, battery capacity is not sufficient in many cases, and using larger batteries is not feasible because it reduces the specific energy of the system. FIG. 1 shows a hybrid drive, which was used to fly an UAV. The hybrid drive of FIG. 1, which includes an engine and a motor/generator, is augmented by a fuel vaporizer in accordance with an embodiment of the present invention. Not only does such a drive increase the system endurance, it also enables the motor/generator to be used as a generator to recharge the batteries depleted during takeoff, and to be used to start the engine before flight and/or restart the engine during flight. Such a configuration is especially valuable for vehicles that operate using VTOL.

[0033] A block-diagram of the hybrid drive of FIG. 1 is shown in FIG. 2. During takeoff, or during high-load demand on the load shaft (i.e. high-speed dashing), the load shaft power is generated by the engine as well as the motor/generator, which is energized by a power supply. When the clutch is engaged, the engine is coupled to the motor/generator, and maximum power is provided to drive the load shaft. Maximum power can be provided only for a relatively short period of time and is dependent upon the capacity of the power supply. For fixed wing aircrafts under typical cruising conditions, only about 20-30% of maximum power is required and the motor/generator may be switched to operate as a generator to recharge the depleted power supply. Switching of the motor/generator's operation from motor operation to generator operation (and vice versa) is controlled by an electronic control unit (“ECU”), which is part of the power supply. When the motor/generator is in generator mode, it is driven by the engine to generate electrical power that recharges the power supply. During flight, there may be a need for a “quiet” mode of operation. During such a quiet mode of operation, the engine is shut down, the clutch is disengaged from the motor/generator, and the flight continues, wherein the motor/generator, operating as a motor, is entirely electrically powered by the power supply. After a quiet mode of operation is completed, the engine may be restarted using the motor/generator, often at high altitude and very low temperatures. Solid lines indicate power consumption from the power supply by the motor/generator and EM clutch. Dashed lines indicate power production by the motor/generator. In some embodiments, a thruster may be coupled to the load shaft.

[0034] To improve the power to weight ratio of the drivetrain, an alternative hybrid drive embodiment of the present invention, shown in FIG. 3, may be used. Compared to the configuration shown in FIG. 2, the electromagnetic clutch (which is typically bulky, heavy and requires power to operate) is replaced with a combination of a second electric motor and an over-running one-way clutch. Solid lines indicate power consumption from the power supply by the motor/generator and/or motor and dashed lines indicate power production by the motor/generator. Here, the engine's shaft is rigidly coupled to the motor/generator and the engine's shaft is coupled to the load shaft via an over-running one-way clutch. The load shaft is rigidly coupled to a second electric motor (referred to as “motor” in FIG. 3). Depending upon the load shaft power requirements during the takeoff, cruise, or landing, the power to the load shaft may be delivered in one of the three ways, as detailed below.

[0035] In a first embodiment, power to the load shaft may be delivered by the engine along with the motor/generator and the second electric motor, which allows for the production of the full power necessary for takeoff and/or dash speed operation. Takeoff may be horizontal or vertical.

[0036] In a second embodiment, power to the load shaft may be delivered by the engine along with the motor/generator, i.e., without the second electric motor (the second electric motor's windings are not activated).

[0037] In a third embodiment, power to the load shaft may be delivered only by the second electric motor. Here, the engine is shut down and the windings of the motor/generator are deactivated. Powering the load shaft in this way may be useful when a quiet mode of operation of the vehicle is required.

[0038] In various embodiments, including but not limited to the first and second embodiments detailed above, the system may also deliver electrical power to the power supply, thereby recharging it, by putting the motor/generator in generator mode. When the motor/generator is in generator mode, it is driven by the engine to generate electrical power that recharges the power supply. The motor/generator's operation may be switched from motor operation to generator operation (and vice versa) by an ECU, which is part of the power supply. The power supply may also be used to deliver power to other electrically powered components, such as additional electric motors that may be needed for VTOL operation or to satisfy payload needs.

[0039] In various embodiments, the hybrid drive trains disclosed herein may be used not only in air vehicles, but also in terrain vehicles as well as in boats. In some embodiments, a thruster may be coupled to the load shaft.

[0040] In various embodiments, including but not limited to the first, second, and third embodiments detailed above, the motor/generator, being coupled to the power supply, is configured to start the engine in preparation for flight (prior to flight) and/or restart the engine during flight.

[0041] To enable an internal combustion engine to start or restart, when at a cold temperature (for example, below zero degrees Celsius), especially for a drive system that operates on heavy fuels in a spark ignition mode, the engine may be equipped with a fuel processor that converts liquid fuel into a gaseous fuel in accordance with embodiments of the present invention.

[0042] For example, to enable multi-fuel capabilities, an engine may be fed with an air/fuel mixture that, when liquid fuels are used, is obtained by evaporating the fuel in a fuel processor, e.g., a fuel vaporizer. Exemplary fuel vaporizer configurations are shown in FIGS. 5 and 6. Fuel vaporizers can improve the startability of an engine with spark ignition (“SI”) running on heavy fuels such as kerosene, Jet A, JP8, or diesel fuel. Heavy fuels generally will not vaporize in an engine that is cold (for example, below zero degrees Celsius) at the low compression ratios of a typical SI engine. Higher compression ratios are not possible in SI configurations due to detonation and knock once the engine starts, because heavy fuel remains liquid and an acceptable mixture of air and fuel is not available at the spark plug/ignition source. (Although we provided zero degrees Celsius as a reference temperature indicating a “cold” engine, the actual temperature at which an SI-based engine is considered “cold,” so as to constitute a candidate for use of a fuel vaporizer, depends on a wide range of factors, including, but not limited to, size of the engine, thermal mass of the engine, outside temperature, as well as the engine's geometry, RPM, and compression ratio.) The use of controlled and rapid evaporation of the fuel, in combination with an air stream, improves the quality of the air/fuel mixture at the spark plug, enabling faster starting, more reliable starting, and lower emissions during cold conditions. Furthermore, the vaporizer can be used not only for starting of the engine, but at all times of engine operation.

[0043] In vaporizers described in the prior art, such as the vaporizer shown in FIGS. 4A and 4B, engines required minutes, rather than seconds, to start, a duration which is unacceptably long for many applications. In some embodiments of the present invention, fuel vaporizers operating at 12 v/24 v DC power, have been tested and shown to start an engine (26 cc/chamber spark ignited Jet Fuel LPI engine, cold-soaked for 24 hours at −25° C.) within seconds.

[0044] Referring to FIGS. 5A and 5B, in an embodiment of the present invention, fuel (represented by arrows with dark fill) is fed into fuel inlet 502 of the fuel vaporizer from a metering device (not shown) and is heated by a suitable heat source, such as a glow plug (506 of FIGS. 5A and 5B) or an electrical spiral (606 of FIG. 6), in the annulus between the heating element and the casing until it evaporates. Air inlet 510 supplies fresh air (represented by arrow with no fill and solid outline) in a tangential direction, in relation to the direction of flow of fuel, in such a manner as to create a vortex of air. Such a configuration achieves rapid vaporization of fuel and superior air/fuel vapor mixing because the vortex carries fuel to the working chamber of an engine through air/vaporized fuel outlet 508. Furthermore, we have determined that the suction produced by a rotor or piston of an engine is sufficient to produce sufficient evaporation and mixing of fuel with air only when a vortex is formed downstream from the fuel inlet, thus eliminating the need to pressurize the air. Air flow is generated in part, or entirely, by air induction into the engine's working chamber. Fuel vaporizers described herein may complement a conventional fuel system and may be used to aid cold starting of an engine. In some embodiments, the fuel vaporizer may be operational only during a period before, during, or slightly after the starting of the engine. In some embodiments, an electronic control system may switch the fuel source from the fuel vaporizer to the main fuel system when the engine is fully started and operational. A set of thermocouples or other temperature sensing devices, located on or within the evaporator body 504 is used for feedback into the controller. A valve may optionally be installed at the fuel inlet, and another valve may optionally be installed at the air inlet. In other embodiments, a fuel vaporizer may be used as the sole source of the fuel/air mixture to an engine, rather than as an intermittent source.

[0045] Fuel vaporizer heating may be achieved in various ways. In some embodiments, the glow plug shown in FIG. 5 may be replaced with a heater wire that is wound into a helix and placed inside heat conductive body 504 that will be in contact with a fuel. Heating may be achieved electrically, similar to the glow plug configuration shown in FIG. 5. In other embodiments, electrical heating may be supplemented by flowing hot exhaust gases through the fuel vaporizer to reduce electrical energy consumption. In some embodiments, startup of a fuel vaporizer may be achieved by electrical means. In some embodiments, for example, when temperature of exhaust gasses is sufficient to evaporate fuel, heating of the fuel vaporizer may be achieved entirely through the use of exhaust gases.

[0046] In some embodiments, the tube within the fuel vaporizer that is in contact with the fuel may be coated with a catalytic substance to lower the energy requirements of the vaporizer.

[0047] FIG. 6, shows an alternative embodiment of a fuel vaporizer. Fuel (represented by the arrow with dark fill) entering fuel inlet 602 fills a portion of the heat insulating body 604, leaving the space for the fuel to evaporate and, optionally, to mix with incoming fresh air (represented by arrow with no fill and solid outline) from air inlet 610 prior to its exit from air/fuel outlet 608. In some embodiments it is desirable not only to evaporate the fuel but also to superheat the fuel, in which case it can be injected into the engine at higher pressures. In some embodiments, a fuel vaporizer heating element, such as spiral heating element 606, is heated electrically). Other embodiments use exhaust gas to heat the fuel (e.g., through heating of the entire fuel vaporizer or using additional heating pipes configured to circulate exhaust gases therethrough or using combinations thereof. Care must be taken to monitor carefully the temperature of heating element 606 and/or the air/fuel mixture so that the vaporized fuel does not coke within the fuel vaporizer and the air/fuel mixture formed in the vaporizer does not spontaneously combust In some embodiments, fuel vaporizers that do not require pressurized air may be used with spark ignition engines, Reactive Control Compression Ignition engines, and Homogeneous Charge Compression Ignition engines, for example. In some embodiments, fresh air may be pressurized to pressures above those in the engine's working chambers so that the fuel vaporizer may be used with compression ignition (“CI”) engines.

[0048] Combinations of the fuel vaporizer embodiments disclosed above may be used in a single device to achieve fuel vaporization and mixing.

[0049] The embodiments of the invention described above are intended to be merely exemplary; numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in any appended claims.