Patent Description:
<CIT> discloses an aircraft/gas turbine engine where electrical power is generated by the low speed spool, which is used to rotate the high speed spool during a windmill restart of the engine.

<CIT> discloses another prior art hybrid electric propulsion system.

According to one embodiment, a hybrid electric propulsion system according to claim <NUM> is provided.

The controller may be a full authority digital engine control (FADEC) that has full authority over the power source and the electric motor.

A technical effect of the apparatus, systems and methods is achieved by providing electric power to the high speed spool of the hybrid electric propulsion system in order to expand an in-flight windmill re-start envelope to include airspeeds and altitudes that would be excluded from an in-flight windmill re-start envelope that does not rely upon augmented rotational power to the high speed spool, wherein the controller has full authority of the power source and the electric motor.

The power source may be at least one of the following: a battery; a super capacitor; and an ultra capacitor.

The motor may be connected to an engine accessory gearbox that is operably coupled to the high speed spool.

The motor may be configured to only augment rotational power of the high speed spool during the detected in-flight windmill re-start condition of the gas turbine engine.

According to a further aspect, there is provided a method for stabilizing a compressor section of a gas turbine engine during an in-flight re-start of the gas turbine engine, comprising: providing power assist to a high speed spool of the gas turbine engine via an electric motor operably coupled to the high speed spool during the in-flight re-start of the gas turbine engine; determining, based at least in part on an altitude and airspeed associated with the hybrid electric propulsion system, that an opposite engine power assist is prohibited; detecting an in-flight windmill re-start condition of the gas turbine engine, wherein the in-flight windmill re-start condition of the gas turbine engine is based at least in part on the determination that opposite engine power assist is prohibited; wherein power is caused to be supplied from a power source to the electric motor by a controller; wherein the controller and the electric motor provide compressor stability to a high pressure compressor of the high speed spool during the in-flight re-start such that high pressure compressor bleed valves are not required for the in-flight re-start.

The in-flight re-start of the gas turbine engine may be autonomous.

The controller may have full authority of the power source and the electric motor.

The controller may be a full authority digital engine control (FADEC).

In some embodiments, stator vanes <NUM> in the low pressure compressor <NUM> and stator vanes <NUM> in the high pressure compressor <NUM> may be adjustable during operation of the gas turbine engine <NUM> to support various operating conditions. In other embodiments, the stator vanes <NUM>, <NUM> may be held in a fixed position.

The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

"Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R)/(<NUM> °R)]<NUM>, wherein °K= °R*<NUM>/<NUM>.

While the example of <FIG> illustrates one example of the gas turbine engine <NUM>, it will be understood that any number of spools, inclusion or omission of the gear system <NUM>, and/or other elements and subsystems are contemplated. Further, rotor systems described herein can be used in a variety of applications and need not be limited to gas turbine engines for aircraft applications. For example, rotor systems can be included in power generation systems, which may be ground-based as a fixed position or mobile system, and other such applications.

<FIG> illustrates a hybrid electric propulsion system <NUM> (also referred to as hybrid gas turbine engine <NUM>) including a gas turbine engine <NUM> operably coupled to an electrical power system <NUM> as part of a hybrid electric aircraft. One or more mechanical power transmissions <NUM> (e.g., 150A, 150B) can be operably coupled between the gas turbine engine <NUM> and the electrical power system <NUM>. The gas turbine engine <NUM> can be an embodiment of the gas turbine engine <NUM> of <FIG> and includes one or more spools, such as low speed spool <NUM> and high speed spool <NUM>, each with at least one compressor section and at least one turbine section operably coupled to a shaft (e.g., low pressure compressor <NUM> and low pressure turbine <NUM> coupled to inner shaft <NUM> and high pressure compressor <NUM> and high pressure turbine <NUM> coupled to outer shaft <NUM> as depicted in <FIG>). The electrical power system <NUM> can include a first electric motor 212A configured to augment rotational power of the low speed spool <NUM> and a second electric motor 212B configured to augment rotational power of the high speed spool <NUM>. Although two electric motors 212A, 212B are depicted in <FIG>, it will be understood that there may be only a single electric motor (e.g., only electric motor 212B for rotation of the high speed spool as discussed below) or additional electric motors (not depicted). The electrical power system <NUM> can also include a first electric generator 213A configured to convert rotational power of the low speed spool <NUM> to electric power and a second electric generator 213B configured to convert rotational power of the high speed spool <NUM> to electric power. Although two electric generators 213A, 213B are depicted in <FIG>, it will be understood that there may be only a single electric generator (e.g., only electric generator 213A) or additional electric generators (not depicted). In some embodiments, one or more of the electric motors 212A, 212B can be configured as a motor or a generator depending upon an operational mode or system configuration, and thus one or more of the electric generators 213A, 213B may be omitted.

In the example of <FIG>, the mechanical power transmission 150A includes a gearbox operably coupled between the inner shaft <NUM> and a combination of the first electric motor 212A and first electric generator 213A. The mechanical power transmission 150B can include a gearbox operably coupled between the outer shaft <NUM> and a combination of the second electric motor 212B and second electric generator 213B. In embodiments where the electric motors 212A, 212B are configurable between a motor and generator mode of operation, the mechanical power transmission 150A, 150B can include a clutch or other interfacing element(s).

The electrical power system <NUM> can also include motor drive electronics 214A, 214B operable to condition current to the electric motors 212A, 212B (e.g., DC-to-AC converters). The electrical power system <NUM> can also include rectifier electronics 215A, 215B operable to condition current from the electric generators 213A, 213B (e.g., AC-to-DC converters). The motor drive electronics 214A, 214B and rectifier electronics 215A, 215B can interface with an energy storage management system <NUM> that further interfaces with an energy storage system <NUM>. The energy storage management system <NUM> can be a bi-directional DC-DC converter that regulates voltages between energy storage system <NUM> and electronics 214A, 214B, 215A, 215B. The energy storage system <NUM> can include one or more energy storage devices, such as a battery, a super capacitor, an ultra capacitor, and the like. The energy storage management system <NUM> can facilitate various power transfers within the hybrid electric propulsion system <NUM>. For example, power from the first electric generator 213A can be transferred <NUM> to the second electric motor 212B as a low speed spool <NUM> to high speed spool <NUM> power transfer. Other examples of power transfers may include a power transfer from the second electric generator 213B to the first electric motor 212A as a high speed spool <NUM> to low speed spool <NUM> power transfer.

A power conditioning unit <NUM> and/or other components can be powered by the energy storage system <NUM>. The power conditioning unit <NUM> can distribute electric power to support actuation and other functions of the gas turbine engine <NUM>. For example, the power conditioning unit <NUM> can power an integrated fuel control unit <NUM> to control fuel flow to the gas turbine engine <NUM>. The power conditioning unit <NUM> can power a plurality of actuators <NUM>, such as one or more of a low pressure compressor bleed valve actuator <NUM>, a low pressure compressor vane actuator <NUM>, a high pressure compressor vane actuator <NUM>, an active clearance control actuator <NUM>, and other such effectors. In some embodiments, the low pressure compressor vane actuator <NUM> and/or the high pressure compressor vane actuator <NUM> can be omitted where active control of stator vanes <NUM>, <NUM> of <FIG> is not needed. Collectively, any effectors that can change a state of the gas turbine engine <NUM> and/or the electrical power system <NUM> may be referred to as hybrid electric system control effectors <NUM>. Examples of the hybrid electric system control effectors <NUM> can include the electric motors 212A, 212B, electric generators 213A, 213B, integrated fuel control unit <NUM>, actuators <NUM> and/or other elements (not depicted).

In one non-limiting embodiment and through electrical boost provided to the high speed spool <NUM> and/or the low speed spool <NUM> variable vane actuators of the high speed spool <NUM> and/or the low speed spool <NUM> may be reduced and/or eliminated as the need for variable vanes may be reduced or eliminated.

<FIG> is a schematic diagram of control signal paths <NUM> of the hybrid electric propulsion system <NUM> of <FIG> and is described with continued reference to <FIG> and <FIG>. A controller <NUM> can interface with the motor drive electronics 214A, 214B, rectifier electronics 215A, 215B, energy storage management system <NUM>, integrated fuel control unit <NUM>, actuators <NUM>, and/or other components (not depicted) of the hybrid electric propulsion system <NUM>. In embodiments, the controller <NUM> can control and monitor for fault conditions of the gas turbine engine <NUM> and/or the electrical power system <NUM>. For example, the controller <NUM> can be integrally formed or otherwise in communication with a full authority digital engine control (FADEC) of the gas turbine engine <NUM>. In embodiments, the controller <NUM> can include a processing system <NUM>, a memory system <NUM>, and an input/output interface <NUM>. The controller <NUM> can also include various operational controls, such as a power transfer control <NUM> that controls the hybrid electric system control effectors <NUM> as further described herein.

The processing system <NUM> can include any type or combination of central processing unit (CPU), including one or more of: a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. The memory system <NUM> can store data and instructions that are executed by the processing system <NUM>. In embodiments, the memory system <NUM> may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms in a non-transitory form. The input/output interface <NUM> is configured to collect sensor data from the one or more system sensors and interface with various components and subsystems, such as components of the motor drive electronics 214A, 214B, rectifier electronics 215A, 215B, energy storage management system <NUM>, integrated fuel control unit <NUM>, actuators <NUM>, and/or other components (not depicted) of the hybrid electric propulsion system <NUM>. The controller <NUM> provides a means for controlling the hybrid electric system control effectors <NUM> based on a power transfer control <NUM> that is dynamically updated during operation of the hybrid electric propulsion system <NUM>. The means for controlling the hybrid electric system control effectors <NUM> can be otherwise subdivided, distributed, or combined with other control elements.

The power transfer control <NUM> can apply control laws and access/update models to determine how to control and transfer power to and from the hybrid electric system control effectors <NUM>. For example, sensed and/or derived parameters related to speed, flow rate, pressure ratios, temperature, thrust, and the like can be used to establish operational schedules and transition limits to maintain efficient operation of the gas turbine engine <NUM>.

Referring now to <FIG>, a hybrid electric propulsion system <NUM> (also referred to as hybrid gas turbine engine <NUM>) including a gas turbine engine <NUM> operably coupled to an electrical power system <NUM> as part of a hybrid electric aircraft in accordance with one non-limiting embodiment of the present disclosure is illustrated, In this embodiment, the engine <NUM> has a power source <NUM> such as a battery, a super capacitor, an ultra capacitor or an equivalent thereof, which supplies power to a motor <NUM>, which is connected to an engine accessory gearbox <NUM> that is operably coupled to the high speed spool <NUM> such that the motor <NUM>, when operated will provide power assist to the high speed spool <NUM> via the accessory gearbox <NUM>. In other words, the accessory gearbox will have at least one component (e.g., a gear train or other equivalent device) operably coupled to the high speed spool <NUM> and the motor <NUM> such that operation of the motor <NUM> will rotate the component which in turn will rotate the high speed spool <NUM>. The power assist to the high speed spool <NUM> via the motor <NUM> will add enough stability to the high pressure compressor in order to allow re-starting without external power assist which may be provided by an auxiliary power unit (APU) or from an opposite engine (e.g., cross-bleed start).

In one non-limiting embodiment, motor <NUM> may be motor 212B of the embodiment illustrated in <FIG>, which is configured to provide power assist to the high speed spool <NUM>. Alternatively, motor <NUM> may be part of a different configuration or system configured to only provide power assist to the high speed spool <NUM> in order to expand an in-flight re-start envelope.

In an alternative embodiment, motor <NUM> may be operatively coupled to the low speed spool <NUM> via accessory gearbox <NUM> in order to provide additional thrust to the engine <NUM>.

The system may be referred to a power assist system <NUM> that limits or avoids pilot or aircraft control intervention during an in-flight engine start process or re-start, in a "windmill" envelope where external power source such as APU or opposite engine power assist is not available or prohibited. In this "windmill" envelope the engine re-start may be autonomous (e.g., without pilot or aircraft control intervention) and the full authority digital engine control (FADEC) controls the power source and the engine.

In one embodiment, the engine re-start is autonomous (e.g., without pilot or aircraft control intervention) and the full authority digital engine control (FADEC) controls the power source and the engine. As such and in one embodiment, the power source <NUM> and the motor <NUM> of the power assist system <NUM> is under the full authority of the FADEC.

In one embodiment and as mentioned above, the controller <NUM> can control and monitor for fault conditions of the gas turbine engine <NUM> and/or the electrical power system <NUM>. For example, the controller <NUM> can include a processing system <NUM>, a memory system <NUM>, and an input/output interface <NUM>.

The input/output interface <NUM> is configured to collect sensor data from the one or more system sensors and interface with various components and subsystems, such as components of the motor drive electronics 214A, 214B, rectifier electronics 215A, 215B, energy storage management system <NUM>, integrated fuel control unit <NUM>, actuators <NUM>, and/or other components (not depicted) of the hybrid electric propulsion system <NUM>. Thus, the controller <NUM> provides a means for controlling the hybrid electric system control effectors <NUM> based on a power transfer control <NUM> that is dynamically updated during operation of the hybrid electric propulsion system <NUM>. The means for controlling the hybrid electric system control effectors <NUM> can be otherwise subdivided, distributed, or combined with other control elements.

The power transfer control <NUM> can apply control laws and access/update models to determine how to control and transfer power to and from the hybrid electric system control effectors <NUM>. For example, sensed and/or derived parameters related to speed, flow rate, pressure ratios, temperature, thrust, and the like can be used to establish operational schedules and transition limits to maintain efficient operation of the gas turbine engine <NUM>. As such, the controller <NUM> is capable of determining an in-flight windmill re-start condition of the engine <NUM> by sensing the aforementioned parameters related to speed, flow rate, pressure ratios, temperature, thrust, fuel flow and the like. Once, the controller determines that the engine <NUM> is in an in-flight windmill re-start condition or "windmill" envelope the controller <NUM> causes power to be supplied from a power source <NUM> to the electric motor <NUM> in order to augment rotational power of the high speed spool <NUM> or the low speed spool <NUM> during the detected in-flight windmill re-start condition.

This "windmill" envelope is illustrated by the cross-hatched region in <FIG>, which shows the envelope where autonomous re-start is preferred or required. This region being referred to as an autonomous windmill envelope or re-start envelope <NUM>, which is identified by arrow <NUM>. <FIG> being a plot of altitude vs. airspeed for an in-flight re-start envelope. The unshaded area <NUM> may be referred to a region (altitude vs. airspeed) where auxiliary power unit (APU) or opposite engine power assist is available or allowed.

By employing a power source <NUM> such as a battery, a super capacitor, an ultra capacitor or an equivalent thereof and motor <NUM>, and controller <NUM>, additional power is added to the high spool <NUM> of the engine <NUM> to provide an in-flight re-start in the autonomous windmill envelope. As such, the autonomous windmill re-start envelope is expanded in the directions of arrows <NUM> and <NUM>. This expanded boundary is illustrated by the grey areas <NUM> and <NUM> illustrated with the dotted line boundary in <FIG>. The grey regions <NUM> and <NUM> with the dotted line boundary, shows that the re-start envelope <NUM> is expanded by internal battery and/or capacitor power assist.

As such, the following non-limiting benefits are derived from various embodiments of the present disclosure: improved re-start reliability for required windmill envelope; improved rotor lock avoidance within required envelope; allows envelope expansion to the same re-start time; and allows envelope expansion to the same operability constraints, such as compressor stability and burner light-ability.

In one embodiment and to maintain operational stability of the compressor section <NUM> of the engine <NUM> during in-flight engine re-start, the controller <NUM> or (FADEC) of the gas turbine engine <NUM> will be configured to add enough power to the high speed spool <NUM> via motor <NUM> to provide compressor stability to the high pressure compressor <NUM> such that high pressure compressor bleed valves or are no longer needed.

Claim 1:
A hybrid electric propulsion system (<NUM>) comprising:
a gas turbine engine (<NUM>; <NUM>) comprising a low speed spool (<NUM>) and a high speed spool (<NUM>), the low speed spool comprising a low pressure compressor (<NUM>) and a low pressure turbine (<NUM>), and the high speed spool comprising a high pressure compressor (<NUM>) and a high pressure turbine (<NUM>);
an electric motor (212A, 212B; <NUM>) configured to augment rotational power of the high speed spool (<NUM>) or the low speed spool (<NUM>); and
a controller (<NUM>) operable to:
determine, based at least in part on an altitude and airspeed associated with the hybrid electric propulsion system, that an opposite engine power assist is prohibited;
detect an in-flight windmill re-start condition of the gas turbine engine, wherein the in-flight windmill re-start condition of the gas turbine engine is based at least in part on the determination that opposite engine power assist is prohibited; and
cause power to be supplied from a power source (<NUM>) to the electric motor (212A, 212B; <NUM>) in order to augment rotational power of the high speed (<NUM>) or the low speed spool (<NUM>) during the detected in-flight windmill re-start condition;
wherein the controller (<NUM>) and the electric motor (212A, 212B; <NUM>) provide compressor stability to the high pressure compressor (<NUM>) during the detected in-flight windmill re-start condition such that high pressure compressor bleed valves are not required.