System and method for integrated use of starter on low pressure spool of turbine engine

Abstract

A propulsion system includes a gas turbine engine including a low speed spool and a high speed spool. The low speed spool includes a low pressure (LP) compressor coupled to the LP turbine via an LP shaft. The high speed spool includes a high pressure (HP) compressor coupled to the HP turbine via an HP shaft. A first starter motor is coupled to the HP shaft and configured to provide power to rotate the HP shaft to start the gas turbine engine. A second starter motor is coupled to the LP shaft and configured to provide torque to the LP shaft. The controller is configured to operate the second starter motor to provide torque to the LP shaft based on a basic LP shaft torque schedule.

Description

Technical Field

[0001] The present subject matter relates generally to turbine engines and, in particular, to the use of a starter on a low-pressure spool of a turbine engine. Background Art

[0002] A gas turbine system may include one or more engines for propulsion. Each engine may include a compressor, a combustor, and a turbine. The compressor compresses air from an air intake and then directs the compressed air to the combustor. In the combustor, the compressed air received from the compressor is mixed with fuel and combusted to produce combustion gases. The combustion gases are directed to the turbine. In the turbine, the combustion gases pass through the turbine blades, thereby driving the turbine blades and the shaft to which the turbine blades are attached to rotate. Typically, a starter coupled to the engine's high-pressure shaft is used to initiate the aircraft's starting operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] A full and enabling description of the disclosure, including the best mode thereof, for those skilled in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0004] Figure 1 is a cross-sectional side view of an embodiment of a propulsion system according to some embodiments;

[0005] Figure 2 is a graph of exemplary low pressure (LP) shaft speed relative to high pressure (HP) shaft speed when the controller does not operate the second starter motor to provide torque to the LP shaft, according to some embodiments;

[0006] Figure 3 is a graph illustrating an exemplary speed of the LP shaft relative to the speed of the HP shaft when the controller operates the second starter motor to provide torque to the LP shaft according to some embodiments;

[0007] Figure 4 is a graph illustrating an exemplary speed of the LP shaft relative to the speed of the HP shaft when the controller operates the second starter motor to provide torque to the LP shaft according to some embodiments;

[0008] Figure 5A is a graph illustrating an exemplary speed of the LP shaft relative to the speed of the HP shaft when the controller operates the second starter motor to provide torque to the LP shaft according to some embodiments;

[0009] Figure 5B According to some embodiments Figure 5A corresponding exemplary compressor pressure ratio / compressor flow graphs;

[0010] Figure 6Ais a graph illustrating an exemplary speed of the LP shaft relative to the speed of the HP shaft when the controller operates the second starter motor to provide torque to the LP shaft according to some embodiments;

[0011] Figure 6B Depicted are some embodiments of Figure 6A corresponding exemplary EGT / T5 / exhaust temperature plots;

[0012] Figure 7A is a graph illustrating an exemplary effect on HP shaft speed when torque is provided to the LP shaft according to some embodiments;

[0013] Figure 7B is a diagram showing a method according to some embodiments Figure 7A A graph of exemplary speeds of the LP shaft relative to the speed of the corresponding HP shaft;

[0014] Figure 8A is a graph illustrating an exemplary speed of the LP shaft 5055 relative to the speed of the HP shaft 4045 when the controller 212 operates the second starter motor 102 to provide torque to the LP shaft 5055 according to some embodiments;

[0015] Figure 8B Depicted are some embodiments of Figure 8A corresponding exemplary EGT / T5 / exhaust temperature plots;

[0016] Figure 9A A diagram depicting exemplary power requirements when supplied power demand is not limited, according to some embodiments;

[0017] Figure 9B Depicted are some embodiments of Figure 9A corresponding exemplary applied torque and shaft speed graphs;

[0018] Figure 10A A diagram depicting exemplary power demand when supplied power demand is limited according to some embodiments;

[0019] Figure 10B Depicted are some embodiments of Figure 10A corresponding exemplary applied torque and shaft speed graphs;

[0020] Figure 11 depicts a graph showing an exemplary speed of the LP shaft 5055 relative to the speed of the HP shaft 4045 during an electric taxi start scenario in accordance with some embodiments;

[0021] Figure 12 is a flow chart of a method for operating a propulsion system according to some embodiments; and

[0022] Figure 13 is a graph depicting an exemplary base LP shaft torque schedule, according to some embodiments. DETAILED DESCRIPTION

[0023] Reference will now be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the present disclosure, not limitation. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the present disclosure. For example, features shown or described as part of one embodiment can be used together with another embodiment to produce yet another embodiment. Therefore, the present disclosure is intended to encompass such modifications and variations as come within the scope of the appended claims and their equivalents.

[0024] As used herein, the terms "first," "second," and "third," etc., may be used interchangeably to distinguish one component from another and are not intended to indicate the position or importance of each component.

[0025] Unless otherwise specified herein, the terms "coupled," "fixed," "attached," and the like refer to both direct coupling, fixing, or attachment as well as indirect coupling, fixing, or attachment through one or more intermediate components or features.

[0026] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0027] As used herein throughout the specification and claims, approximate language can be applied to modify any quantitative expression that may allow variation without causing a change in the basic function associated therewith. Therefore, the value modified by one or more terms such as "approximately," "approximately," "almost," and "substantially" is not limited to the specified exact value. In some cases, approximate language can correspond to the precision of the instrument used to measure the value. For example, approximate language can refer to within a margin of 1%, 2%, 4%, 10%, 15%, or 20%. These approximate margins can be applied to a single value, defining any one or two endpoints of a numerical range, and / or the margin of the range between the endpoints. Here, as well as throughout the specification and claims, range limitations are combined and interchanged, and unless the context or language indicates otherwise, such ranges are identified and include all subranges contained therein. For example, all ranges disclosed herein include endpoints, and the endpoints can be combined independently of each other.

[0028] In some aspects, the systems and methods described herein are configured to increase air flow and / or pressure at the compressor inlet, which is conducive to compressor operability. In some embodiments, the improvement in compressor operability improves the start-up operability of the aircraft. In some aspects, the improved start-up operability can reduce and / or eliminate other subsystems (e.g., bleed air) required for starting. In some embodiments, the improvement in compressor operability improves the start-up time of the aircraft. In some aspects, the start-up time of the improved aircraft can improve the ground operation of the passenger aircraft.

[0029] In some embodiments, a propulsion system includes a gas turbine engine comprising a low-speed spool and a high-speed spool. The low-speed spool may include a low-pressure (LP) compressor coupled to an LP turbine via an LP shaft. The high-speed spool may include a high-pressure (HP) compressor coupled to an HP turbine via an HP shaft. In some embodiments, a first starter motor is coupled to the HP shaft and may provide power to rotate the HP shaft, thereby starting the gas turbine engine. In some embodiments, a second starter motor is coupled to the LP shaft and may provide torque to the LP shaft. In some embodiments, the propulsion system includes a controller. In some aspects, the controller operates the second starter motor to provide torque to the LP shaft based on a base LP shaft torque schedule.

[0030] In some embodiments, a method includes operating a propulsion system of an aircraft to start a gas turbine engine. In some aspects, the gas turbine engine includes a low-speed spool and a high-speed spool. The low-speed spool may include a low-pressure (LP) compressor coupled to an LP turbine via an LP shaft. The high-speed spool may include a high-pressure (HP) compressor coupled to an HP turbine via an HP shaft. In some embodiments, a first starter motor is coupled to the HP shaft, and a second starter motor is coupled to the LP shaft. In some embodiments, the method includes operating the second starter motor by a controller of the propulsion system to provide torque to the LP shaft based on a basic LP shaft torque schedule.

[0031] In some embodiments, a non-transitory, machine-accessible storage medium having computer instructions, wherein the computer instructions, when executed by a controller, cause the controller to operate a propulsion system of an aircraft to start a gas turbine engine. The gas turbine engine includes a low-speed spool and a high-speed spool. The low-speed spool may include a low-pressure (LP) compressor coupled to a low-pressure turbine via a low-pressure spool. The high-speed spool includes a high-pressure (HP) compressor coupled to an HP turbine via an HP spool, wherein a first starter motor is coupled to the HP spool and a second starter motor is coupled to the LP spool. In some embodiments, a non-transitory, machine-accessible storage medium having computer instructions, wherein the computer instructions, when executed by the controller, cause the controller to operate the second starter motor to provide torque to the LP spool based on a base LP spool torque schedule.

[0032] Referring now to the drawings, wherein like numerals represent like elements throughout, certain embodiments will be described. Figure 1 Generally speaking, the embodiments of the engine 100 variously depicted and described herein include a computing system 210 configured to include one or more controllers and / or configured to perform the steps of the methods or other operations provided herein. For example, Figure 1 One embodiment of suitable components that may be included within computing system 210 is shown. Figure 1 As shown, computing system 210 may include a controller 212 (which may include one or more processors) and associated memory 214 configured to perform various computer-implemented functions (eg, execute the methods, steps, calculations, etc. disclosed herein).

[0033] As shown, the computing system 210 may include control logic 216 stored in a memory 214. The control logic 216 may include instructions that, when executed by the one or more controllers 212, cause the one or more controllers 212 to perform operations, such as the methods or operations described herein. Figure 1 As shown, computing system 210 may also include a communication interface module 230. In several embodiments, communication interface module 230 may include associated electronic circuitry for sending and receiving data. Thus, communication interface module 230 of computing system 210 may be used to send and / or receive data to and from engine 100 and any other suitable components of engine 100, including any number of motors, actuators, fuel lines, linkages, bucket or blade pitch change mechanisms, sensors, or other actuatable structures, such as one or more of such components depicted and described herein.

[0034] It should be understood that the communication interface module 230 can be any combination of suitable wired and / or wireless communication interfaces and can thus be communicatively coupled to one or more components of the engine 10 via wired and / or wireless connections. Thus, the computing system 210 can obtain, determine, store, generate, transmit, or perform any one or more steps described herein regarding the operation of the engine 100 or equipment to which the engine 100 is attached (e.g., an aircraft or other vehicle). In some embodiments, the computing system 210 can include a full authority digital engine control (FADEC) system. In some embodiments, the controller 212 includes an electronic engine controller for the FADEC system.

[0035] Furthermore, it should be understood that although Figure 1A single unducted rotor engine is depicted, but the description, functionality, and / or methods described herein are generally applicable to gas turbine engines. For example, the gas turbine engine may include a jet turbine engine, a turboprop engine, a turbofan engine, a turboshaft engine, or any other suitable engine, including a piston or reciprocating engine.

[0036] In addition, some embodiments of the gas turbine engine described below may include one or more electric motors. The electric motor may generally include a stator and a rotor, the rotor being rotatable relative to the stator. In addition, the electric motor may be configured to convert mechanical power into electrical power, or to convert electrical power into mechanical power. For example, the electric motor may be configured as an asynchronous or induction motor, which is operable to generate or utilize alternating current (AC) electrical power. Alternatively, the electric motor may be configured as a synchronous motor, which is operable to generate or utilize AC electrical power or direct current (DC) electrical power. In this manner, it will be understood that the stator, the rotor, or both may generally include one or more of a plurality of coils or windings, one or more permanent magnets, one or more electromagnets, etc., arranged in any suitable number of phases.

[0037] Figure 1 A front cross-sectional view of an exemplary embodiment of a single unducted rotary engine 100 is shown. Figure 1 As shown, the engine 100 takes the form of an open rotor propulsion system and has a rotor assembly 20 including an array of airfoil blades 21 about a longitudinal axis 11 of the engine 100. The blades 21 are arranged in a generally equidistant relationship about the longitudinal axis 11, and each blade 21 has a root 223 and a tip 246 and a span defined therebetween.

[0038] Furthermore, engine 100 includes a gas turbine engine having a core (or high-pressure system) 40 and a low-pressure system 50. Core engine 40 generally includes a high-pressure compressor 4042, a high-pressure turbine 4044, and a high-pressure spool 4045 extending therebetween and connecting the high-pressure compressor 4042 and the high-pressure turbine 4044. The high-pressure compressor 4042, the high-pressure turbine 4044, and the high-pressure spool 4045 may collectively define and be referred to as the engine's high-pressure spool / high-speed spool 4046. Furthermore, a combustion section 4048 is located between the high-pressure compressor 4042 and the high-pressure turbine 4044. The combustion section 4048 may include one or more configurations for receiving a mixture of fuel and air and providing a flow of combustion gases through the high-pressure turbine for driving the high-pressure spool 4046.

[0039] In some embodiments, the first starter motor 101 is coupled to the HP shaft 4045 to provide power to rotate the HP shaft 4045, thereby starting the gas turbine engine. In some embodiments, the first starter motor 101 may include an electric starter (e.g., an electric motor), a hydraulic starter, a pneumatic starter, and / or a fuel / air turbine starter (auxiliary power unit, APU), to name a few. In some embodiments, the first starter motor 101 may be coupled to the HP shaft 4045 via a gearbox (not shown).

[0040] The low-pressure system 50 similarly includes a low-pressure turbine 5050, a low-pressure compressor 5052, and a low-pressure shaft 5055 extending between and connecting the low-pressure compressor 5052 and the low-pressure turbine 5050. The low-pressure compressor 5052, the low-pressure turbine 5050, and the low-pressure shaft 5055 may collectively define and be referred to as a low-pressure spool / low-speed spool 5054 of the engine 100.

[0041] In various embodiments, the core engine 40 may include a tertiary flow path 1063, such as a flow that bypasses the core flow path downstream of one or more compressors. The tertiary flow path 1063 may generally define a concentric or non-concentric flow path relative to the flow path 1062 downstream of one or more compressor or fan stages. The tertiary flow path 1063 is configured to selectively remove a portion of the flow from the core flow path 1062, such as via one or more variable guide vanes, nozzles, or other actuable flow control structures. The tertiary flow path 1063 may bypass the combustion section 4048. In certain embodiments, the tertiary flow path 1063 also bypasses all or part of the flow path at the turbine section.

[0042] It should be understood that, unless otherwise specified, the terms "low" and "high" or their respective comparatives (e.g., lower, higher, where applicable), when used with a compressor, turbine, shaft or spool component, each refer to a relative pressure and / or speed within the engine. For example, a "low turbine" or "low-pressure turbine" or "low-speed turbine" defines a component that is configured to operate at a speed lower than a "high turbine" or "high-pressure turbine" or "high-speed turbine" at the engine (e.g., the maximum allowable speed that produces the corresponding air pressure). Alternatively, unless otherwise specified, the above terms may be understood in their superlative form. For example, a "low turbine" or "low-pressure turbine" or "low-speed turbine" may refer to the turbine with the lowest maximum speed that produces the corresponding air pressure within the turbine section. A "low compressor" or "low-pressure compressor" or "low-speed compressor" may refer to the compressor with the lowest maximum speed that produces the corresponding air pressure within the compressor section. A "high turbine" or "high-pressure turbine" or "high-speed turbine" may refer to the turbine with the highest maximum speed that produces the corresponding air pressure within the turbine section. A "high compressor" or "high-pressure compressor" or "high-speed compressor" may refer to the compressor with the highest maximum speed that produces a corresponding air pressure within the compressor section. Similarly, a low-speed spool or a low-pressure spool refers to a lower maximum speed or air pressure than a high-speed spool or a high-pressure spool. It should also be understood that in the above aspects, the terms "low" or "high" may additionally or alternatively be understood as a minimum allowable speed or air pressure, or a minimum or maximum allowable speed or air pressure relative to normal, desired, steady-state, etc., operation of the engine.

[0043] Although the engine 100 is depicted with the low-pressure compressor 5052 positioned forward of the high-pressure compressor 4042 (i.e., near the front end 98), in some embodiments, the compressors 4042, 5052 may be arranged in a staggered arrangement, i.e., the rotating airfoils in the low-pressure compressor 5052 are arranged alternately along the gas flow path with the rotating airfoils in the high-pressure compressor 4042. Additionally, or alternatively, although the engine 100 is depicted with the high-pressure turbine 4044 positioned forward of the low-pressure turbine 5050, in some embodiments, the turbines 4044, 5050 may be arranged in a staggered arrangement.

[0044] exist Figure 1, the core engine 40 is generally enclosed in a fairing 1056 defining a maximum diameter DM. The bucket assembly 30 extends from the fairing 1056 and is positioned rearward of the rotor assembly 20. In various embodiments, the maximum diameter is defined as the outwardly facing flowpath surface in the radial direction R that is in fluid communication with the fluid flow exiting the rotor assembly 20. In certain embodiments, the maximum diameter of the fairing 1056 substantially corresponds to the location or position of the roots 335 of the buckets 31 of the bucket assembly 30 extending from the fairing 1056. The rotor assembly 20 also includes a hub 1052 extending forward of the plurality of blades 21. In certain embodiments, the engine 100 defines a length L from a forward end 1042 of the hub 1052 to a rearward end 1043 of the fairing 1056.

[0045] Furthermore, it should be understood that the engine 100 also includes a cowling 1056 that surrounds the turbomachinery and at least partially defines an inlet 1058, an exhaust 1060, and a turbomachinery flowpath 1062 extending therebetween. For the illustrated embodiment, the inlet 1058 is an annular or axisymmetric 360-degree inlet 1058 located between the rotor assembly 20 and the bucket assembly 30 and provides a path for incoming atmospheric air to enter the turbomachinery flowpath 1062 (as well as the compressor, combustion section, and turbine) radially inward of the bucket assembly 30. This location may be advantageous for a variety of reasons, including managing icing performance and protecting the inlet 1058 from various objects and materials that may be encountered during operation.

[0046] As shown, the rotor assembly 20 is driven by the turbomachinery, and more specifically, by the low pressure spool 5054. More specifically, Figure 1 The engine 100 in the illustrated embodiment includes a power gearbox 1064, and the rotor assembly 20 is driven by the turbomachinery's low-pressure spool 5054 across the power gearbox 1064. In this manner, the rotating blades 21 of the rotor assembly 20 can rotate about the axis 11 and generate thrust to propel the engine 100 in a forward direction FW, thereby propelling an aircraft associated therewith.

[0047] The power gearbox 1064 can include a gear set for reducing the rotational speed of the low-pressure spool 5054 relative to the low-pressure turbine 5050 so that the rotor assembly 20 can rotate at a lower rotational speed than the low-pressure spool 5054. In certain embodiments, the power gearbox 1064 includes a gear ratio of at least 4:1. Although in various embodiments, a 4:1 gear ratio can generally allow the low-pressure turbine 5050 to rotate at approximately four times the rotational speed of the rotor assembly 20, it should be understood that other structures provided herein, such as blade pitch change mechanisms and / or motors, can allow the ductless rotor assembly 20 to operate substantially decoupled from the rotational speed of the low-pressure turbine 5050. In addition, when using a cross-counter-rotating or bladeless turbine, the gear ratio can be reduced without significantly losing the output power of the rotor assembly 20.

[0048] In some embodiments, the second starter motor 102 is coupled to the LP shaft 5055 to provide torque to the LP shaft 5055. In such embodiments, a power gearbox 1064 can be coupled to the second starter motor 102 and include a gear set to initiate and / or increase the rotation of the LP shaft 5055. In some embodiments, the second starter motor 102 can include an electric starter (e.g., an electric motor), a hydraulic starter, a pneumatic starter, and / or a fuel / air turbine starter (auxiliary power unit, APU), to name a few. In some embodiments, the two starter motors 101, 102 can correspond to a single starter motor that is configured to provide torque to either the LP shaft 5055 or the HP shaft 4045, or both, respectively.

[0049] During operation, computing system 210 and / or controller 212 associated with the engine may monitor operating and environmental conditions of the engine and / or the aircraft in which the engine is installed based on received data (e.g., engine sensor data, aircraft data, environmental data, etc.). In some embodiments, computing system 210 and / or controller 212 may determine whether one or more target values, thresholds, or parameters (e.g., target speed, target power, and / or target setpoint, to name a few) are met (matched or equal to) and / or exceeded (greater than) based on the received data. It should be understood that the description and / or functionality associated with controller 212 and / or methods performed thereby as described herein may be attributed to computing system 210.

[0050] Figure 2 2 is a graph 200 of the speed 204 of the LP shaft 5055 relative to the speed 202 of the HP shaft 4045 when the controller 212 is not operating the second starter motor 102 to provide torque to the LP shaft 5055, according to some embodiments. Figure 2As shown, at the intersection of the axes, when no torque is provided to the LP shaft 5055, the LP shaft 5055 rotates and / or accelerates solely based on the aerodynamic cycle driven by the rotation and / or acceleration of the HP shaft 4045. In these embodiments, the low pressure system 50 "follows for the ride" the high pressure system (core 40).

[0051] Figure 3 is a graph 300 illustrating an exemplary speed of the LP shaft 5055 relative to the speed of the HP shaft 4045 when the controller 212 operates the second starter motor 102 to provide torque to the LP shaft 5055 based on the base LP shaft torque schedule 310, according to some embodiments. Figure 3 In the example, at 308, the controller 212 causes the first starter motor 101 to provide power to rotate the HP shaft 4045, thereby starting the engine 100, and causes the second starter motor 102 to provide torque to the LP shaft 5055. In response, at 306a, the torque provided to the LP shaft 5055 increases, causing the rotational speed of the LP shaft 5055 to also begin to increase at 304a. The rotational speed of the HP shaft 4045 also increases in response to the operation of the controller 212 on the first starter motor 101. At 306b, the controller 212 causes the second starter motor 102 to provide constant torque to the LP shaft 5055 and / or maintain the currently applied torque. At 304b, the combination of the aerodynamic coupling of the air pressure caused by the rotational speed of the HP shaft 4045 and the torque applied to the LP shaft 5055 by the second starter motor 102 causes the speed of the LP shaft 5055 to reach a constant speed. At 306c, the second starter motor 102 begins to reduce and eventually stops the torque applied to the LP shaft 5055. At 304c, the idle speed of the LP shaft 5055 has been reached. In some embodiments, the idle speed of the LP shaft 5055 is less than or equal to the constant speed of the LP shaft 5055 at 304b. In some embodiments, at 302a, the second starter motor 102 has already begun to reduce the torque applied to the LP shaft 5055 before the idle speed of the HP shaft 4045 is reached at 302b. For example, the second starter motor 102 may begin to reduce the torque applied to the LP shaft 5055 before reaching the ground idle speed of the HP shaft 4045.

[0052] In some embodiments, although Figure 2 The starting time of the engine in (i.e. the time to reach the idle speed of the HP shaft 4045) is Figure 3 The starting time of the engine in is the same, but since torque is provided to the LP shaft 5055 during the engine starting, Figure 3The operability margin of the engine in the engine is greater. One benefit that arises from this is that other subsystems that may be needed to start the engine are reduced (less airflow required) and / or eliminated (e.g., less bleed air requirements to start the engine). Another benefit is that it covers more variable effects. For example, with a free-spinning LP shaft 5055 (i.e., the rotation of the LP shaft 5055 is due to aerodynamic coupling with the HP shaft 4045), there may be a variety of influences that may affect the start time of the aircraft and / or engine, including oil temperature, viscous drag terms, external environmental conditions and / or engine degradation (turbine, fan, etc.). In some embodiments, for example, direct speed control is provided to the LP shaft 5055 using electrical power, which regulates all of these effects by maintaining a fixed speed profile.

[0053] In some embodiments, there may be engine-to-engine variations in hardware, such as the tolerance stackup of all hardware components combined with the tolerance stackup of all electrical components. For example, while a "nominal" engine may be fine, a "minimum" engine (where all hardware stacks are at their maximum worst-case limits) may not be. In such an example, the bleed air system can be added so that it can be covered by the existing motor-generator subsystem on the LP system 50.

[0054] One of the benefits of providing torque to the LP shaft 5055 based on one or more basic LP shaft torque schedules described herein during starting of the engine (e.g., on the ground and / or in flight, to name a few), is that it allows the first starter motor 101 to be smaller in size relative to a standard or average size for an engine that does not implement or use the LP shaft torque schedules described herein; this reduces weight (e.g., engine weight, gearbox weight, to name a few) and / or reduces the envelope, thereby at least reducing specific fuel consumption (SFC), and / or making under-fairing integration easier, to name a few.

[0055] Furthermore, a smaller size of the HP starter motor 101 is advantageous. For example, packaging of under-cowl components and / or reduction in gearbox (GB) size may result in an overall reduction in engine weight, thereby improving the specific fuel consumption (SFC) of the engine 100.

[0056] Figure 4 4 is a graph 400 illustrating an exemplary speed of the LP shaft 5055 relative to the speed of the HP shaft 4045 when the controller 212 operates the second starter motor 102 to provide torque to the LP shaft 5055 based on the base LP shaft torque schedule 410, according to some embodiments. Figure 45055 (e.g., during engine start). At a subsequent time and at 404, the controller 212 causes torque to be applied to the HP shaft 4045. For example, based on one or more predetermined or stored system-level requirements and / or scenarios (e.g., a default schedule or a generally accepted default schedule for aircraft engines), torque is applied to the HP shaft 4045 before, approximately simultaneously with, or after the LP shaft 5055 is applied. In some embodiments, near the time at which the idle speed of the HP shaft 4045 is reached at 406, the controller 212 causes the second starter motor 102 to begin reducing the torque applied to the LP shaft 5055 at 408. In some embodiments, the controller 212 begins reducing the torque applied to the LP shaft 5055 before the HP shaft 4045 reaches its idle speed. Figure 2 and Figure 3 One of the benefits of a faster start-up time (i.e., the time to reach idle speed of the HP shaft 4045) is improved ground handling of the passenger aircraft. Another benefit is improved aircraft utilization of the passenger aircraft.

[0057] Figure 5A is a graph 500A illustrating an exemplary speed of the LP shaft 5055 relative to the speed of the HP shaft 4045 when the controller 212 operates the second starter motor 102 to provide torque to the LP shaft 5055 based on a base LP shaft torque schedule, according to some embodiments. Figure 5B is with Figure 5A Corresponding exemplary compressor pressure ratio / compressor flow graph 500B. Figure 5A In the example of FIG. 1 , at 508, the controller 212 causes the first starter motor 101 to provide power to rotate the HP shaft 4045, thereby starting the engine 100. In response, the LP shaft 5055 may begin to rotate and / or accelerate based on an air power cycle driven by the rotation and / or acceleration of the HP shaft 4045. At 502, after applying torque to the first starter motor 101, the controller 212 causes torque to be applied to the LP shaft 5055. For example, torque may be applied to the LP shaft 5055 after torque is applied to the HP shaft 4045. In some embodiments, torque may be applied to the LP shaft 5055 10 seconds, 100 seconds, or any time between 10-100 seconds after torque is applied to the HP shaft 4045 based on engine operation, and / or when the engine reaches a known compressor operability shortfall (e.g., a pinched region 504 in compressor operability and / or any of the pinched regions described herein).

[0058] In some embodiments, the torque applied to the second starter motor 102 can be based on the LF shaft torque target clamping region 506. In some embodiments, the LF shaft torque target clamping region 506 is a threshold range from a known insufficient compressor operability on the compressor stall line 512 (e.g., the clamping region 504 in the compressor operability). The insufficient compressor operability may correspond to a specific time or time window when the engine is prone to stalling or has a high probability of stalling. In some embodiments, the basic LP shaft torque schedule can be a function of speed (e.g., LP shaft 5055 speed and / or HP shaft 4045 speed, to name a few), torque of the first starter motor 101 and / or the second starter motor 102, airflow (e.g., generated by the rotation of the LP shaft 5055 and / or HP shaft 4045, to name a few), and / or any specific set point (e.g., the clamping region 504 in the compressor operability) that can define the location of the point at which additional LP torque assistance is required.

[0059] exist Figure 5B , in the case where no torque is applied to the second starter motor 102, the compressor pressure ratio / compressor flow line of the engine is shown at "before situation" 510. As shown, "before situation" 510 intersects with insufficient compressor operability (e.g., clamping area 504 in compressor operability), indicating the possibility of engine stall during the starting operation of the engine. In some embodiments, applying torque to the second starter motor 102 based on the LF shaft torque target clamping area 506 reduces the compressor operability line, as shown in "after situation" 514. In some embodiments, reducing the compressor operability line to "after situation" 514 increases the stall margin or compressor operability margin. In some embodiments, the LF shaft torque target clamping area 506 can be based on the desired maximum design space 516.

[0060] In some embodiments, the base LP shaft torque schedule includes a schedule that specifies when to increase (ramp up), maintain (level off), and decrease (ramp down) the torque applied to the LP shaft 5055 to increase compressor operability margin (e.g., during ground starts, in-flight starts, to name a few). Illustrative, non-limiting examples of base LP shaft torque schedules are as follows: Figure 3 (e.g., applied low-pressure shaft torque 310), Figure 4 (applied low pressure shaft torque 410), Figure 5A (applied low pressure shaft torque 518), Figure 6A (applied low pressure shaft torque 618), Figure 7B (applied low pressure shaft torque 710), Figure 8A(e.g., applied low pressure shaft torque 820, which may include a "base" LP shaft torque schedule 802 and / or an adaptive LP shaft torque 804) and Figure 11 (LP starter torque 1108). For example, the basic LP shaft torque schedule may include the LF shaft torque target clamping region 506. In some embodiments, as Figure 5A As shown, torque is applied to the second starter motor 102 based on the LF shaft torque target clamping region 506, providing additional torque or speed to the LP shaft 5055, resulting in an increase in flow and / or pressure at the compressor inlet (e.g., inlet 1058), which increases the stall margin or compressor operability margin in this region. In some embodiments, the controller 212 can obtain a desired starting trajectory from a pilot and / or preprogrammed selection and determine an optimal LP torque starting curve based on one or more basic LP shaft torque schedules described herein.

[0061] In some embodiments, a combination of ramping up, leveling off, and ramping down of the basic LP shaft torque schedule can reduce the electrical power required to provide torque from the second starter motor 102 to the LP shaft 5055. Thus, the application of torque to the second starter motor 102 can be specifically designed to target a specific time or time window in the engine's compressor operability line that may need to be updated. For example, the controller 212 can target or specifically apply torque to the second starter motor 102 only in an unhealthy region of the engine's compressor operability line (e.g., a clamped region 504 in the compressor operability). For example, the unhealthy region of the engine's compressor operability line can be based on known data specific to the engine. For example, the controller 212 can receive sensor data from one or more sensors of the aircraft. In response to processing the received sensor data, the controller 212 can determine that the engine is in and / or is about to enter an unhealthy region of the compressor operability line. In some embodiments, in response to determining that the engine is in and / or is about to enter an unhealthy region of the compressor operability line, the controller 212 may execute an LP shaft torque schedule, such as the applied low-pressure shaft torque 518 and / or one or more of the basic LP shaft torque schedules described herein, and cause the second starter motor 102 to receive a signal prompting the second starter motor 102 to apply torque to the LP shaft 5055. In some embodiments, the second starter motor 102 may be driven by compressed air or electricity. In some embodiments, the controller 212 may determine which of the basic LP shaft torque schedules to execute based on the specific gas turbine engine. For example, the basic LP shaft torque schedule may be associated with one or more gas turbine engines.

[0062] Figure 6Ais an exemplary graph 600A illustrating the speed of the LP shaft 5055 relative to the speed of the HP shaft 4045 when the controller 212 operates the second starter motor 102 to provide torque to the LP shaft 5055 based on a base LP shaft torque schedule, according to some embodiments. Figure 6B Depicted are some embodiments of Figure 6A Corresponding exemplary EGT / T5 / exhaust temperature graph 600B. In some embodiments, in response to the controller 212 receiving data corresponding to an indication that a ratio of exhaust gas temperature (EGT) to an EGT target setpoint is greater than a threshold, the controller 212 can operate the second starter motor 102 to provide additional torque to the LP shaft 5055 based on a high EGT-to-LP shaft torque schedule (e.g., applied LP shaft torque 618). For example, the high EGT-to-LP shaft torque schedule can include a schedule for when to increase, maintain, and decrease the additional torque applied to the LP shaft 5055 to increase the EGT temperature margin.

[0063] In some embodiments, the base LP shaft torque schedule (e.g., a high EGT specific shaft torque schedule) can be a function of speed (e.g., LP shaft 5055 speed and / or HP shaft 4045 speed, to name a few), torque of the first starter motor 101 and / or the second starter motor 102, airflow (e.g., generated by rotation of the LP shaft 5055 and / or HP shaft 4045, to name a few), and / or any particular set point (e.g., clamping region 604 in EGT / T5) that can define the location of the point at which additional LP torque assist is required.

[0064] To illustrate, in Figure 6AIn the embodiment of the present invention, at 608, the controller 212 causes the first starter motor 101 to provide power to rotate the HP shaft 4045, thereby starting the engine 100. In response, the LP shaft 5055 may begin to rotate and / or accelerate based on an aerodynamic cycle driven by the rotation and / or acceleration of the HP shaft 4045. After applying torque to the first starter motor 101, the controller 212 causes the torque to be applied to the LP shaft 5055. For example, at 602, after applying torque to the HP shaft 4045, torque may be applied to the LP shaft 5055. In some embodiments, torque may be applied to the LP shaft 5055 20 seconds, 100 seconds, or any time between 20 and 100 seconds after applying torque to the HP shaft 4045. In some embodiments, the LP starter motor 102 provides additional torque in and around a pinch point area surrounding a starter notch. The starter notch may correspond to a point where the HP starter motor 101 stops providing torque but the engine is not yet idling. For example, this is during starting when engine heat tends to be high (e.g., the progression region between starter cut and idle). In some embodiments, the pinch region may include one or more of the pinch regions described herein. In some embodiments, engines of different designs may have different thermal pinch points. Thus, the LP shaft torque schedule may be based on observations and / or data collected from a running engine.

[0065] In some embodiments, the torque applied by the second starter motor 102 to the LP shaft 5055 can be based on the LF shaft torque target clamping region 606. In some embodiments, the LF shaft torque target clamping region 606 is a threshold range from a known insufficient compressor operability on the EGT / T5 limit line 612 (e.g., the clamping region 604 in EGT / T5). Insufficient compressor operability may correspond to a specific time or time window when the engine is prone to stalling or has a high probability of stalling.

[0066] exist Figure 6BIn FIG, the engine's EGT / T5 / exhaust temperature graph is shown at "before case" 610, where the second starter motor 102 is not applying torque to the LP shaft 5055. As shown, "before case" 610 intersects with insufficient compressor operability (e.g., clamping region 604 in EGT / T5), indicating the possibility of engine stall during the engine's starting operation. In some embodiments, the second starter motor 102 applies torque to the LP shaft 5055 based on the LF shaft torque target clamping region 606, causing the compressor operability line to drop, as shown in "after case" 614. In some embodiments, dropping the compressor operability line to "after case" 614 increases the stall margin or compressor operability margin. In some embodiments, the LF shaft torque target clamping region 606 can be based on a desired maximum design space EGT target setpoint (e.g., target design maximum EGT / T5 616).

[0067] In some embodiments, the base LP shaft torque schedule includes a schedule for when to increase (ramp up), maintain (plateau), and decrease (ramp down) the torque applied to the LP shaft 5055 to increase the compressor operability margin. Figure 6A In some embodiments, the basic LP shaft torque schedule may include a LF shaft torque target clamping region 606. Figure 6A As shown, the second starter motor 102 applies torque to the LP shaft 5055 based on the LF shaft torque target clamping region 606, providing additional torque or speed to the LP shaft 5055, resulting in increased flow and / or pressure at the compressor inlet (e.g., inlet 1058), which increases the stall margin or compressor operability margin in this region. In some embodiments, a combination of ramp-up, plateauing, and ramp-down of the basic LP shaft torque schedule can reduce the electrical power required by the second starter motor 102 to provide torque to the LP shaft 5055. Thus, the torque applied by the second starter motor 102 to the LP shaft 5055 can be specifically designed to target specific times or time windows within the engine's compressor operability line when an update may be required. For example, the controller 212 can target or specifically apply torque to the LP shaft 5055 via the second starter motor 102 only during unhealthy regions of the engine's compressor operability line (e.g., clamping region 504 within the compressor operability line). For example, the unhealthy region of the engine's compressor operability line can be based on known data specific to the engine.

[0068] Figure 7A is an exemplary graph 700A illustrating exemplary effects on the speed of the HP shaft 4045 when torque is provided to the LP shaft 5055, according to some embodiments. Figure 7B is a diagram showing a method according to some embodiments Figure 7A700B shows an exemplary graph of the speed of the LP shaft 5055 relative to the corresponding speed of the HP shaft 4045. In some embodiments, there may be an ideal relationship between the HP airflow and the fan airflow. In an illustrative, non-limiting example, the controller 212 may use the core speed and the fan speed as proxies for the HP airflow and the fan airflow, respectively. For example, for a given core speed, the controller 212 may determine a desired fan speed. In such an example, the controller 212 may set the torque to match the fan speed to the desired fan speed (which is a function of the current core speed).

[0069] To illustrate, in Figure 7A In the embodiment of the present invention, at 702, the controller 212 causes the first starter motor 101 to provide power to rotate the HP shaft 4045, thereby starting the engine 100, without providing torque to the LP shaft 5055. In some embodiments, at 708, the controller 212 causes the first starter motor 101 to provide torque to the HP shaft 4045 and causes the second starter motor 102 to provide torque to the LP shaft 5055. In some embodiments, the basic LP shaft torque schedule may include the following: Figure 7B 710 is shown. In some embodiments, the base LP shaft torque schedule includes a schedule for when to increase, maintain, and / or decrease the torque applied to the LP shaft 5055 so as to match the speed of the LP shaft 5055 to a target speed of the LP shaft 5055 within a threshold (e.g., the applied LP shaft torque 710). In some embodiments, application of the base LP shaft torque schedule can allow the speed of the HP shaft 4045 to be matched to within a threshold of the fan speed target 706, as shown. Figure 7A In some embodiments, application of the base LP shaft torque schedule may allow the speed 714 of the LP shaft 5055 to be matched within a threshold of the LP shaft speed target 712, as shown in FIG. Figure 7B shown.

[0070] In some embodiments, the base LP shaft torque schedule (e.g., the applied LP shaft torque 710 schedule) can be a function of the airflow generated by the rotation of the HP shaft 4045. For example, the controller 212 can determine a desired speed for the LP shaft 5055. Based on the determined desired speed for the LP shaft 5055, the controller 212 can determine the applied LP shaft torque 710 schedule to achieve the fan speed target 706.

[0071] Figure 8A is an exemplary graph 800A illustrating the speed of the LP shaft 5055 relative to the speed of the HP shaft 4045 when the controller 212 operates the second starter motor 102 to provide torque to the LP shaft 5055 based on a base LP shaft torque schedule, according to some embodiments. Figure 8BAccording to some embodiments Figure 8A Corresponding exemplary EGT / T5 / exhaust temperature map 800B. In some embodiments, controller 212 can adaptively modify base LP shaft torque schedule 802 to correspond to adaptive LP shaft torque 804 in response to an indication that the ratio of exhaust gas temperature (EGT) to the EGT target is greater than a threshold. In some embodiments, controller 212 can apply base LP shaft torque schedule 802 when the first starter motor 101 may not be operating as expected by controller 212. In such embodiments, controller 212 can cause the second starter motor 102 to apply a wider range of torque and / or additional torque up to a predetermined maximum limit.

[0072] For example, the applied torque may be allowed to vary from the nominal torque schedule (e.g., the base LP shaft torque schedule) to protect constraints up to a predetermined amount to protect mechanical constraints on the HP and LP starter motors 101, 102 (e.g., either the HP starter motor 101 or the LP starter motor 102 may be an electric motor). For example, the maximum torque of the motor generator may be 100 horsepower (HP), the aircraft supplies electrical power to fully supply 100 HP of torque, and the base LP shaft torque schedule applies 50 HP of torque. In this example, because the motor cannot supply more than 100 HP of torque, the controller 212 may not allow more than 100 HP of torque (50 base + 50 adaptive) when executing the adaptation cycle (e.g., generating adaptive LP shaft torque 804).

[0073] In another example, the maximum torque of the motor generator may be 100 HP, the aircraft supplies electrical power to fully supply 80 HP of torque, and the base LP shaft torque schedule applies 50 HP of torque. In this example, because the aircraft cannot supply sufficient electrical power to enable the motor to produce more than 80 HP of torque, the controller 212 may not allow more than 80 HP of torque (50 base + 30 adaptive) when executing the adaptation cycle.

[0074] In an illustrative, non-limiting example, Figure 8AIn the example, at 808, the controller 212 may cause the first starter motor 101 to provide power to rotate the HP shaft 4045, thereby starting the engine 100. In response, the LP shaft 5055 may begin to rotate and / or accelerate based on the aerodynamic cycle driven by the rotation and / or acceleration of the HP shaft 4045. After the first starter motor 101 applies torque to the HP shaft 4045, the controller 212 may cause the second starter motor 102 to apply torque to the LP shaft 5055. For example, at 806, after applying torque to the HP shaft 4045, torque may be applied to the LP shaft 5055. In some embodiments, torque may be applied to the LP shaft 5055 at any time between 0 and 60 seconds after the torque is applied to the HP shaft 4045. In some embodiments, torque may be applied to the LP shaft 5055 at any time starting from 0 until the engine reaches idle speed.

[0075] In some embodiments, the torque applied by the second starter motor 102 to the LP shaft 5055 may be based on a pinched region in EGT / T5 808. In some embodiments, the pinched region in EGT / T5 808 may include a specific value or threshold range from a known insufficient compressor operability.

[0076] exist Figure 8B In the base case 814, the controller 212 operates the second starter motor 102 to provide torque to the LP shaft 5055 based on the base LP shaft torque schedule 802. In some embodiments, after applying the base LP shaft torque schedule 802, the controller 212 may then apply one or more adders, multipliers, and / or offsets to the base LP shaft torque schedule 802. For example, the resulting LP shaft torque schedule that may be applied corresponds to the adaptive LP shaft torque 804. For example, one or more adders, multipliers, and / or offsets may be applied after applying the base LP shaft torque schedule 802. In some embodiments, torque may be applied to the LP shaft 5055 at any time between 0 and 60 seconds after torque is applied to the HP shaft 4045. In some embodiments, torque may be applied to the LP shaft 5055 at any time starting from 0 until the engine reaches idle speed.

[0077] In some embodiments, adaptive LP shaft torque 804 may include applying predefined adders, multipliers, and / or biases when controller 212 detects one or more abnormal scenarios. For example, if controller 212 detects a shortfall in the HP starter and engine 100 is likely to be running hotter relative to average operating temperatures during an EGT / T5 hot pinch, controller 212 may bias base LP shaft torque schedule 802 to provide more assistance. In some embodiments, base case 814 may operate closer to EGT / T5 limit line 810. In some embodiments, for adaptive case 816, controller 212 may maintain the same compressor operability margin as for nominal starting case 818. For example, nominal starting case 818 indicates that HP starter motor 101 is operating as expected and outputting the required torque / air pressure to HP compressor 4042, and / or EGT temperature is normal (e.g., between 660 degrees Celsius and 1000 degrees Celsius). In some embodiments, the nominal start conditions may correspond to the start conditions expected by controller 212 (default conditions or a default value or range of values, or customary in a particular engine for an aircraft, to name a few). In some embodiments, there are many factors that may cause an engine to not operate as expected. For example, maintenance issues, engine degradation, low starter air pressure / power supply, environmental effects (temperature, altitude, etc.), how long the engine has been shut down, and the thermal state of the engine before shutting down and restarting, to name a few.

[0078] In some embodiments, the controller 212 may not allow the second starter motor 102 to exceed its capacity. For example, the controller 212 may select "maximum" between the final "bias" schedule and the capacity of the second starter motor 102. For example, the capacity may be limited to a predetermined maximum torque (in Newton meters) or a predetermined maximum power (in kilowatts). In some embodiments, the controller 212 may not allow the second starter motor 102 to request more electrical power than can be supplied. In some embodiments, the controller 212 may calculate the use of a "fail-safe" or "default" schedule rather than simply applying adders, multipliers, and / or biases.

[0079] Figure 9A Depicted is an exemplary power demand graph 900A when the supplied power demand is not limited, according to some embodiments. Figure 9B Depicted are some embodiments of Figure 9A 900B is a graph of corresponding exemplary applied torque and shaft speed. In some embodiments, Figure 9AIn the example shown in FIG. 1 , if the supplied power demand 902 is not limited, the first starter motor 101 and the second starter motor 102 may request up to their corresponding rated power (e.g., HP starter power 904, LP starter power 906). Figure 9B The corresponding applied torques (e.g., HP starter torque 908, LP starter torque 910) and their resulting corresponding shaft speeds (e.g., HP shaft speed 912, LP shaft speed 914) of the first starter motor 101 and the second starter motor 102 are shown, respectively. However, in most engine environments (e.g., during ground starting, in-flight starting, to name a few), the priority between the first starter motor 101 and the second starter motor 102 can be determined by the controller 212, as shown in FIG. Figures 10A-10B shown.

[0080] Figure 10A Depicted is an exemplary power demand graph 1000A when supplied power demand is limited, according to some embodiments. Figure 10B Depicted are some embodiments of Figure 10A 1000B shows an exemplary graph of corresponding applied torque and shaft speed. In some embodiments, the controller 212 can detect that the total power required to provide the respective torques to each of the HP shaft and the LP shaft is greater than the total power supplied by the first starter motor and the second starter motor. In response, the controller 212 can prioritize the first starter motor 101 in power distribution until the speed or power of the HP shaft 4045 matches the target speed or power of the HP shaft 4045 within a threshold. In an illustrative, non-limiting example, Figure 10A , if the supplied power demand 1002 is limited, the first starter motor 101 can request up to its rated power 1004. The power demand of the first starter motor 101 can take precedence over the power demand of the second starter motor 102. For example, at 1006, the power requested by the second starter motor 102 can be limited based on the supplied power demand 1002. In such an embodiment, once the supplied power is high enough, the second starter motor 102 can request the required LP starter power 1008. In some embodiments, once all the power requested by the first starter motor 101 is supplied, the second starter motor 102 can request any remaining power.

[0081] In an illustrative, non-limiting example, Figure 10BThe corresponding applied torques (e.g., HP starter torque 1010, LP starter torque 1012) of the first starter motor 101 and the second starter motor 102 and their resulting corresponding shaft speeds (e.g., HP shaft speed 1014, LP shaft speed 1016) are shown, respectively. At 1018, at the point in time when the power requested by the second starter motor 102 is limited, the corresponding applied torque provided by the second starter motor 102 to the LP shaft 5055 is reduced. In some embodiments, the controller 212 can calculate the desired torque insertion or addition between the HP shaft 4045 and the LP shaft 5055 based on one or more embedded models of the HP and LP systems to account for starting time, operability, engine heat (i.e., peak temperature) and / or vibration, to name a few.

[0082] In some embodiments, the controller 212 can use one or more embedded models to determine the additional torque to be applied to at least one or both of the HP shaft 4045 or the LP shaft 5055 based on one or more of engine start time, operability margin, engine heat, and / or vibration. For example, the one or more embedded models can consider the HP torque required to start the core shaft (e.g., HP shaft 4045) and the LP torque required for assistance. In some embodiments, the one or more embedded models and / or one or more base LP shaft torque schedules described herein can be stored in the memory 214.

[0083] In some embodiments, the embedded model may refer to a physics-based model, typically a high-fidelity model, that runs within the FADEC controller and simulates all parts of the engine, including pressures, temperatures, etc. at each station along the engine. In some embodiments, this embedded model can function like a "digital twin," where a tracking filter updates the model to match the given engine on or associated with the controller 212. This model can then be used to infer the relationship between the HP and LP starter motors 101, 102 and expected speeds, temperatures, etc., and can be used to optimize the scheduled torque application.

[0084] In some embodiments, if another engine (not shown) is to be started, another controller (not shown) associated with the other engine may request additional power to shut down engine 100. For example, in response to starting a gas turbine engine (e.g., engine 100), controller 212 may detect that the other gas turbine engine has not yet started. In some embodiments, engine 100 may provide supplemental electrical power to assist in starting the other engine. For example, in response to detecting that the other gas turbine engine has not yet started, controller 212 may allocate at least a portion of the total power supplied to at least one of first starter motor 101 or second starter motor 102, or both, to start the other gas turbine engine.

[0085] Figure 11 An exemplary graph 1100 is depicted illustrating the speed of the LP shaft 5055 relative to the speed of the HP shaft 4045 during an electric taxi start scenario based on a base LP shaft torque schedule (e.g., LP starter torque 1108), according to some embodiments. In some embodiments, electric taxiing is a form of taxiing that an aircraft can perform using only aerodynamic coupling, which occurs when torque is provided only to the second starter motor 102 and not to the first starter motor 101. In these embodiments, the resulting aerodynamic coupling provides sufficient torque to the fan shaft or HP shaft 4045 to generate sufficient thrust to move the aircraft. For example, the base LP shaft torque schedule may include a first schedule for increasing, maintaining, and / or decreasing torque applied to the LP shaft 5055 to generate sufficient thrust to move the aircraft during an electric taxi on a runway, and a second schedule for when torque applied to the HP shaft 4045 by the first starter motor 101 is provided relative to the first schedule.

[0086] In an illustrative, non-limiting example, to further enhance ground operations (e.g., reduce ground time), one or more engines of the aircraft may be started during an electric ground taxi scenario. For example, the engine 100 may perform an enhanced start while the LP rotor of the LP compressor is in a taxi thrust setting, which enables the engine to be started while the aircraft is in motion (i.e., taxiing to a runway).

[0087] In an illustrative, non-limiting example, the HP shaft 4045 and / or the core engine 40 can be started during an electric ground taxi scenario. For example, the controller 212 can maintain a constant fan speed (e.g., the rotational speed of the rotor assembly 20) and allow the electric power provided by the second starter motor 102 to gradually decrease as the aerodynamic drive mechanical torque (e.g., LP aerodynamic torque 1110) provided during the starting operation process. For example, as the LF shaft 5055 gains aerodynamic torque as the HP shaft 4045 accelerates, the controller 212 can reduce the electric power demand on the second starter motor 102 while the aerodynamic assist gradually increases. For example, when the HP system reaches "idle," the second starter motor 102 can be turned off and / or can be at a lower adaptive power setting.

[0088] In an illustrative, non-limiting example, Figure 11, at 1104, the speed of the LP shaft 5055 follows the power requested by the second starter motor 102 at 1102. At 1114, as the first starter motor 101 provides torque to the HP shaft 4045, the speed 1112 of the HP shaft 4045 may begin to increase. At 1116, the aerodynamic coupling driven by the speed of the HP shaft 4045 is illustrated by the LP aerodynamic torque 1110. In some embodiments, at 1118 and / or near 1114 and / or 1116, the controller 212 may cause the second starter motor 102 to reduce and / or stop applying torque to the LF shaft 5055. In some embodiments, the application of the LP starter torque 1108 schedule may be based on the total LP torque 1106 schedule determined by the controller 212. In some embodiments, as the HP shaft 4045 begins to accelerate (due to the command start at 1114 ), the controller 212 can maintain the speed 1104 of the LP shaft 5055 at the requested speed 1102 of the LP shaft 5055 by exchanging the LP starter torque 1108 for the LP aerodynamic torque 1110 .

[0089] Figure 12 is a flow chart of a method 1200 for operating a propulsion system according to some embodiments. In some embodiments, the method 1200 is used to Figure 1 engine 100. Method 1200 may include operating a propulsion system of an aircraft to start a gas turbine engine at step 1202. In some embodiments, the gas turbine engine includes a low-speed spool and a high-speed spool. The low-speed spool may include a low-pressure (LP) compressor coupled to an LP turbine via an LP shaft. The high-speed spool may include a high-pressure (HP) compressor coupled to an HP turbine via an HP shaft. In some embodiments, a first starter motor is coupled to the HP shaft. In some embodiments, a second starter motor is coupled to the LP shaft. Alternatively or in addition, method 1200 may include operating a second starter motor by a controller of the propulsion system at step 1204 to provide torque to the LP shaft based on a basic LP shaft torque schedule. In some embodiments, the basic LP shaft torque schedule may include one or more basic LP shaft torque schedules described herein.

[0090] Figure 13 is a diagram of an exemplary basic LP shaft torque schedule according to some embodiments. In some embodiments, at step 1204, the basic LP shaft torque schedule for operating the second starter motor may be Figure 3 、 4, 5A-5B, 6A-6B, 7A-7B, 8A-8B, 9A-9B, 10B, and 11. For example, the controller 212 may determine which of the basic LP shaft torque schedules to use based on one or more of EGT / T5 / exhaust gas temperature, a ratio of EGT to an EGT target setpoint, a pinch region in EGT / T5, an EGT / T5 / exhaust gas temperature of the engine, a pinch region in compressor operability, and an EGT / T5 thermal pinch point.

[0091] There are several benefits to having the starter motor provide torque to the LP shaft according to the basic LP shaft torque schedule. For example, it reduces (reduced airflow required) and / or eliminates other subsystems that may be required to start the engine (e.g., less bleed air required to start the engine). Another benefit is that it covers more variable effects. For example, for a free-spinning LP shaft (i.e., the LP shaft's rotation is due to aerodynamic coupling with the HP shaft 4045), there may be a variety of effects that may affect the start time of the aircraft and / or engine, including oil temperature, viscous drag terms, external environmental conditions, and / or engine degradation (turbine, fan, etc.). Another benefit is that it allows the size of the starter motor coupled to the HP shaft to be smaller relative to a standard or average-sized engine that does not implement or use the basic LP shaft torque schedule described herein; this reduces weight (e.g., engine weight, gearbox weight, to name a few) and / or reduces the envelope, thereby at least reducing specific fuel consumption (SFC), and / or making under-fairing integration easier, to name a few. Another benefit is faster engine start times, thereby improving ground handling of the passenger aircraft. Another benefit is increased aircraft utilization of passenger aircraft.

[0092] Further aspects of the present disclosure are provided by the subject matter of the following clauses:

[0093] A propulsion system comprises: a gas turbine engine, the gas turbine engine including a low-speed spool and a high-speed spool, the low-speed spool including a low-pressure (LP) compressor coupled to an LP turbine via an LP shaft, and the high-speed spool including a high-pressure (HP) compressor coupled to an HP turbine via an HP shaft; a first starter motor coupled to the HP shaft and configured to provide power to rotate the HP shaft to start the gas turbine engine; a second starter motor coupled to the LP shaft and configured to provide torque to the LP shaft; and a controller configured to operate the second starter motor to provide the torque to the LP shaft based on a base LP shaft torque schedule.

[0094] A propulsion system as in any preceding clause, wherein the base LP shaft torque schedule includes a schedule for when to increase, maintain, and decrease the torque applied to the LP shaft to increase compressor operability margin.

[0095] The propulsion system of any preceding clause, wherein the base LP shaft torque schedule is associated with the gas turbine engine.

[0096] A propulsion system as described in any preceding clause, wherein, in response to the controller receiving data corresponding to an indication that a ratio of exhaust gas temperature (EGT) to an EGT target set point is greater than a threshold, the controller is further configured to operate the second starter motor to provide additional torque to the LP shaft based on a high EGT-to-LP shaft torque schedule, and wherein the high EGT-to-LP shaft torque schedule includes a schedule for when to increase, maintain, and decrease the additional torque applied to the LP shaft to increase the EGT temperature margin.

[0097] A propulsion system as described in any preceding clause, wherein the base LP shaft torque schedule includes a schedule for when to increase, maintain and decrease the torque applied to the LP shaft to match the speed of the LP shaft to the target speed of the LP shaft within a threshold.

[0098] The propulsion system of any preceding clause, wherein the controller is further configured to adaptively modify the base LP axle torque schedule in response to an indication that a ratio of exhaust gas temperature (EGT) to an EGT target is greater than a threshold.

[0099] A propulsion system as described in any preceding clause, wherein the controller is further configured to: detect that the total power required to provide corresponding torque to each of the HP shaft and the LP shaft is greater than the total supplied power of the first starter motor and the second starter motor; and prioritize the first starter motor in power distribution until the speed or power of the HP shaft matches the target speed or power of the HP shaft within a threshold.

[0100] A propulsion system according to any preceding clause, wherein the controller is further configured to: in response to starting the gas turbine engine, detect that other gas turbine engines have not yet been started; and allocate at least a portion of the total supplied power of at least one or both of the first starter motor or the second starter motor to start the other gas turbine engine.

[0101] A propulsion system as described in any preceding clause, wherein the controller is further configured to: determine additional torque to apply to at least one or both of the HP shaft or the LP shaft based on one or more of engine start time, operability margin, engine heat and vibration using one or more embedded models.

[0102] A propulsion system as described in any preceding clause, wherein the base LP shaft torque schedule includes a first schedule for when to increase, maintain and decrease the torque applied to the LP shaft to generate sufficient thrust to move the aircraft during electric taxiing on a runway and a second schedule for when the torque applied to the HP shaft is provided by the first starter motor relative to the first schedule.

[0103] A method comprising: operating a propulsion system of an aircraft to start a gas turbine engine, the gas turbine engine including a low-speed spool and a high-speed spool, wherein the low-speed spool includes a low-pressure (LP) compressor coupled to an LP turbine via an LP shaft, and the high-speed spool includes a high-pressure (HP) compressor coupled to an HP turbine via an HP shaft, and wherein a first starter motor is coupled to the HP shaft and a second starter motor is coupled to the LP shaft; and operating the second starter motor, by a controller of the propulsion system, to provide torque to the LP shaft based on a base LP shaft torque schedule.

[0104] A method as in any preceding clause, wherein the base LP shaft torque schedule includes a schedule for when to increase, maintain, and decrease the torque applied to the LP shaft to increase compressor operability margin.

[0105] A method as in any preceding clause, wherein the base LP shaft torque schedule is associated with the gas turbine engine.

[0106] The method according to any preceding clause, further comprising: receiving by the controller data corresponding to an indication that a ratio of exhaust gas temperature (EGT) to an EGT target is greater than a threshold; and in response to receiving the data, operating by the controller the second starter motor to provide additional torque to the LP shaft based on a high EGT to LP shaft torque schedule, wherein the high EGT to LP shaft torque schedule includes a schedule for when to increase, maintain, and decrease the additional torque applied to the LP shaft to increase the EGT temperature margin.

[0107] A method as in any preceding clause, wherein the base LP shaft torque schedule comprises a schedule for when to increase, maintain, and decrease the torque applied to the LP shaft so as to match the speed of the LP shaft to a target speed of the LP shaft within a threshold.

[0108] The method of any preceding clause, further comprising adaptively modifying the base LP axle torque schedule in response to an indication that a ratio of exhaust gas temperature (EGT) to an EGT target is greater than a threshold.

[0109] The method according to any of the preceding clauses, further including detecting by the controller that the total power required to provide corresponding torque to each of the HP shaft and the LP shaft is greater than the total supplied power of the first starter motor and the second starter motor; and prioritizing by the controller the first starter motor in power distribution until the speed of the HP shaft matches the target speed of the HP shaft within a threshold.

[0110] The method according to any of the preceding clauses further includes, in response to starting the gas turbine engine, detecting by the controller that other gas turbine engines have not yet been started; and allocating by the controller at least a portion of the total supplied power of at least one or both of the first starter motor or the second starter motor to start the other gas turbine engine.

[0111] The method of any preceding clause, further comprising determining, by the controller, using one or more embedded models, additional torque to apply to at least one or both of the HP shaft or the LP shaft based on one or more of engine start time, operability margin, engine heat, and vibration.

[0112] A non-transitory, machine-accessible storage medium having computer instructions, and wherein the computer instructions are configured to, when executed by a controller, cause the controller to: operate a propulsion system of an aircraft to start a gas turbine engine, the gas turbine engine comprising a low-speed spool and a high-speed spool, wherein the low-speed spool comprises a low-pressure (LP) compressor coupled to a low-pressure turbine via a low-pressure shaft, and the high-speed spool comprises a high-pressure (HP) compressor coupled to an HP turbine via an HP shaft, and wherein a first starter motor is coupled to the HP shaft and a second starter motor is coupled to the LP shaft; and operate the second starter motor to provide torque to the LP shaft based on a base LP shaft torque schedule.

[0113] A controller for a propulsion system, the controller comprising: at least one processor configured to: operate a first starter motor to provide power to rotate a high pressure (HP) shaft to start a gas turbine engine; and operate a second starter motor to provide torque to a low pressure (LP) shaft based on a base LP shaft torque schedule, wherein the gas turbine engine includes a low-speed spool and a high-speed spool, the low-speed spool including an LP compressor coupled to an LP turbine via the LP shaft, and the high-speed spool including an HP compressor coupled to the HP turbine via the HP shaft.

[0114] This written description uses examples to disclose the present disclosure, including the best mode, and also to enable any person skilled in the art to practice the present disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the present disclosure is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

1. A propulsion system, characterized in that: include: a gas turbine engine comprising a low-speed spool comprising a low-pressure (LP) compressor coupled to an LP turbine via an LP shaft and a high-speed spool comprising a high-pressure (HP) compressor coupled to an HP turbine via an HP shaft; a first starter motor coupled to the HP shaft and configured to provide power to rotate the HP shaft to start the gas turbine engine; a second starter motor coupled to the LP shaft and configured to provide torque to the LP shaft; as well as A controller configured to: The second starter motor is operated to provide the torque to the LP shaft based on a base LP shaft torque schedule.

2. The propulsion system according to claim 1, characterized in that The basic LP shaft torque schedule includes a schedule for when to increase, maintain, and decrease the torque applied to the LP shaft to increase compressor operability margin.

3. The propulsion system according to claim 1, characterized in that Wherein the base LP shaft torque schedule is associated with the gas turbine engine.

4. The propulsion system according to claim 1, characterized in that in, In response to the controller receiving data corresponding to an indication that a ratio of exhaust gas temperature (EGT) to an EGT target set point is greater than a threshold, the controller is further configured to operate the second starter motor to provide additional torque to the LP shaft based on a high EGT to LP shaft torque schedule, and wherein the high EGT to LP shaft torque schedule includes a schedule for when to increase, maintain, and decrease the additional torque applied to the LP shaft to increase the EGT temperature margin.

5. The propulsion system according to claim 1, characterized in that The basic LP shaft torque schedule includes a schedule for when to increase, maintain, and decrease the torque applied to the LP shaft so as to match the speed of the LP shaft to a target speed of the LP shaft within a threshold.

6. The propulsion system according to claim 1, characterized in that Wherein the controller is further configured to adaptively modify the base LP axle torque schedule in response to an indication that a ratio of exhaust gas temperature (EGT) to an EGT target is greater than a threshold.

7. The propulsion system according to claim 1, characterized in that The controller is further configured to: detecting that a total power required to provide a corresponding torque to each of the HP shaft and the LP shaft is greater than a total supplied power of the first starter motor and the second starter motor; and The first starter motor is prioritized in power distribution until the speed or power of the HP shaft matches a target speed or power of the HP shaft within a threshold.

8. The propulsion system according to claim 7, characterized in that The controller is further configured to: In response to starting the gas turbine engine, detecting that other gas turbine engines have not been started; and At least a portion of the total supplied power of at least one of the first starter motor or the second starter motor, or both, is allocated to start the other gas turbine engine.

9. The propulsion system according to claim 1, characterized in that The controller is further configured to determine, using one or more embedded models, additional torque to apply to at least one or both of the HP shaft or the LP shaft based on one or more of engine start time, operability margin, engine heat, and vibration.

10. The propulsion system according to claim 1, wherein: wherein the base LP shaft torque schedule includes a first schedule for when to increase, maintain, and decrease the torque applied to the LP shaft to generate sufficient thrust to move the aircraft during electric taxiing on a runway, and a second schedule for when the torque applied to the HP shaft is provided by the first starter motor relative to the first schedule.

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