阅读说明：本技术 多发动机系统和方法 (Multi-engine system and method ) 是由 K.摩根 S.马 P.博谢纳-马特尔 E.迪罗谢 于 2019-08-08 设计创作，主要内容包括：本发明涉及多发动机系统和方法。一种操作多发动机直升机的方法包括使用全权限数字发动机控制(FADEC),从而控制该多发动机直升机的第一发动机以主动模式操作,以满足多发动机直升机的功率或旋翼速度需求,以通过该多发动机直升机来执行巡航航段,并且控制该多发动机直升机的第二发动机以待机模式操作。控制该第二发动机的燃料流率,以将第一发动机和第二发动机之间的燃料流率差维持在70%和100%之间。(The invention relates to a multi-engine system and method. A method of operating a multi-engine helicopter includes using a Full Authority Digital Engine Control (FADEC) to control a first engine of the multi-engine helicopter to operate in an active mode to meet power or rotor speed requirements of the multi-engine helicopter to execute a cruise flight with the multi-engine helicopter and to control a second engine of the multi-engine helicopter to operate in a standby mode. The fuel flow rate of the second engine is controlled to maintain a fuel flow difference between the first engine and the second engine between 70% and 100%.)

1. A method of operating a multi-engine helicopter, comprising:

using full authority digital control (FADEC) to control a first engine of the multi-engine helicopter to operate in an active mode, the active mode including meeting power or rotor speed requirements of the multi-engine helicopter to perform a cruise flight with the multi-engine helicopter; and

using the full authority digital control to control a second engine of the multi-engine helicopter to operate in a standby mode during the cruise flight, including controlling a fuel flow rate of the second engine operating in the standby mode to maintain a fuel flow rate difference between the first engine and the second engine between 70% and 100%.

2. The method of claim 1, wherein said controlling said second engine is performed to maintain said fuel flow rate differential in a range of 70% to 90%.

3. The method of claim 2, wherein the controlling the second engine is performed to maintain the fuel flow rate difference in a range of 80% to 90%.

4. A method as set forth in claim 3 wherein said controlling said second engine is performed by using a fuel flow rate through said second engine as a control input variable to said second engine and said controlling said first engine is performed by using said power or rotor speed demand as a control input variable to said first engine.

5. The method of claim 4, wherein the controlling the first engine to operate in the active mode comprises controlling the first engine to drive a rotor of the multi-engine helicopter via a gearbox of the multi-engine helicopter, and controlling the second engine comprises decoupling the second engine from the gearbox.

6. The method of claim 4, wherein the controlling the first engine to operate in the active mode includes controlling the first engine to drive a rotor of the multi-engine helicopter via a gearbox of the multi-engine helicopter and controlling the fuel flow rate difference to drive the gearbox with the second engine at a power in a range of 0% to 1% of a rated full power of the second engine.

7. The method of claim 1, wherein the controlling the first engine and/or the second engine further comprises adjusting a first set of variable guide vanes upstream of a low pressure compressor section between an 80 degree position and a-25 degree position independent of a position of a second set of variable guide vanes upstream of a high pressure compressor section.

8. The method of claim 7, comprising performing at least one of: a) controlling a low pressure compressor section of the second engine to maintain a pressure ratio associated with the low pressure compressor section of the second engine between 0.9 and 1.4; and b) controlling the fuel flow through the second engine in a range of about 20% to about 10% of the cruise fuel flow through the first engine.

9. A multi-engine system comprising:

a first turboshaft engine and a second turboshaft engine driving a common gearbox configured to drive a load, at least the second turboshaft engine comprising:

at least two tube shafts independently rotatable with respect to each other, a low pressure tube shaft of the at least two tube shafts including a low pressure shaft interconnecting the low pressure compressor section to the low pressure turbine section, and a high pressure tube shaft of the at least two tube shafts including a high pressure shaft interconnecting the high pressure compressor section to the high pressure turbine section;

a first set of variable guide vanes disposed upstream of the low pressure compressor section; and

a second set of variable guide vanes disposed upstream of the high pressure compressor section,

the first set of variable guide vanes is separate from the second set of variable guide vanes, and

the low pressure compressor section includes a mixed flow rotor.

10. The multiple engine system of claim 7, wherein the first set of variable guide vanes is operable between an 80 degree position and a-25 degree position and the second set of variable guide vanes is operable between an 80 degree position and a-25 degree position.

11. The multiple engine system of claim 10, wherein the first set of variable guide vanes is operable between the 80 degree position and the-25 degree position associated with the first set of variable guide vanes, while the second set of variable guide vanes is maintained in a given position.

12. The multi-engine system of claim 11, comprising: a medium pressure spool of the at least two spools, the medium pressure spool comprising a medium pressure shaft interconnecting a medium pressure compressor section to a medium pressure turbine section; and a third set of variable guide vanes disposed at an inlet of the intermediate pressure compressor section, the third set of variable guide vanes controlling an operating state of the intermediate pressure pipe shaft.

13. A turboshaft engine for a multi-engine system configured to drive a common load, the turboshaft comprising:

at least two tube shafts independently rotatable with respect to each other, a low pressure tube shaft of the at least two tube shafts including a low pressure shaft interconnecting the low pressure compressor section to the low pressure turbine section, and a high pressure tube shaft of the at least two tube shafts including a high pressure shaft interconnecting the high pressure compressor section to the high pressure turbine section; the low pressure compressor section is defined by a single mixed flow rotor; and

a plurality of sets of variable guide vanes including a set of variable guide vanes disposed at an inlet of each of the at least two tube shafts, a first set of the plurality of sets being mechanically separated from a second set of the plurality of sets.

14. The turboshaft engine of claim 13, wherein the first set of variable guide vanes is operable between an 80 degree position and a-25 degree position associated with the first set of variable guide vanes.

15. The turboshaft engine of claim 14, wherein the second set of variable guide vanes is operable between an 80 degree position and a-25 degree position associated with the second set of variable guide vanes.

16. The turboshaft engine of claim 15, wherein the first set of variable guide vanes is operable between the 80 degree position and the-25 degree position associated with the first set of variable guide vanes, while the second set of variable guide vanes is maintained in a given position.

17. The turboshaft engine of claim 16, wherein the high pressure turbine section includes only a single turbine stage.

18. The turboshaft engine of claim 17, comprising an intermediate pressure spool of the at least two spools, the intermediate pressure spool comprising an intermediate pressure shaft interconnecting the intermediate pressure compressor section to the intermediate pressure turbine section.

19. The turboshaft engine of claim 18, wherein the first set of variable guide vanes is disposed upstream of the low-pressure compressor section.

20. The turboshaft engine of claim 19, wherein the second set of variable guide vanes is disposed upstream of the high pressure compressor section.

Technical Field

The present application relates to a multi-engine system for an aircraft and a method of controlling such a system.

Background

Helicopters are usually equipped with at least two turboshaft engines. In such prior art helicopters, the engines of the helicopter may be connected to the main rotor through a common reduction gearbox, and each of the engines may be dimensioned such that the power of each engine is greater than the power required for cruising. Operating a single engine at relatively high conditions (region) while operating another engine at lower conditions during cruise conditions, rather than operating both engines at a moderate level, may allow for overall better fuel efficiency. The lower operating condition is sometimes referred to as a "standby" mode. While such prior art operating conditions may be suitable for operating such prior art helicopters, improvements are desired. For example, it is desirable to reduce the time required for the engine to power up from a standby mode. As another example, it would also be desirable to improve the prior art active-standby operating methods in order to increase fuel efficiency.

Disclosure of Invention

In one aspect, a multi-engine system is provided, comprising: a first turboshaft engine and a second turboshaft engine driving a common reduction gearbox configured to drive a common load, the second turboshaft engine configured to operate in a standby mode, at least the second turboshaft engine comprising: at least two tube shafts independently rotatable with respect to each other, a low pressure tube shaft of the at least two tube shafts including a low pressure shaft interconnecting the low pressure compressor section to the low pressure turbine section, and a high pressure tube shaft of the at least two tube shafts including a high pressure shaft interconnecting the high pressure compressor section to the high pressure turbine section; a first set of variable guide vanes disposed at an inlet of the low pressure compressor section, the first set of variable guide vanes controlling an operating state of the low pressure spool; and a second set of variable guide vanes disposed at an inlet of the high pressure compressor section, the second set of variable guide vanes controlling an operating state of the high pressure spool.

In another aspect, there is provided a turboshaft engine for a multi-engine system, the turboshaft engine configured to drive a common load, the turboshaft comprising: at least two tube shafts independently rotatable with respect to each other, a low pressure tube shaft of the at least two tube shafts including a low pressure shaft interconnecting the low pressure compressor section to the low pressure turbine section, and a high pressure tube shaft of the at least two tube shafts including a high pressure shaft interconnecting the high pressure compressor section to the high pressure turbine section; a set of variable guide vanes disposed at an inlet of each of the at least two tube shafts, the set of variable guide vanes configured to control an operating state of a respective one of the at least two tube shafts; and an output shaft drivingly engaged to the low pressure shaft and configured to drivingly engage a common output shaft that drives the common load and is drivingly engaged by another turboshaft engine.

In another aspect, a method of operating a multi-engine system drivingly coupled to a load is provided, the method comprising: operating a first turboshaft engine of the multi-engine system to drive the load while a second turboshaft engine of the multi-engine system is operating in a reduced power mode; increasing the output power level of the second turboshaft engine to drive the load by: a first set of variable guide vanes directing the air flow through the second turboshaft engine; compressing the gas stream by a low pressure compressor section; directing the airflow through a second set of variable guide vanes; and compressing the airflow by a high pressure compressor section, the low pressure compressor section and the high pressure compressor section rotating independently with respect to each other.

In another aspect, a method of operating a multi-engine helicopter is provided, comprising: using full authority digital control (FADEC) to control a first engine of the multi-engine helicopter to operate in an active mode, the active mode including meeting power or rotor speed requirements of the multi-engine helicopter to perform a cruise flight with the multi-engine helicopter; and using the FADEC to control a second engine of the multi-engine helicopter to maintain a fuel flow differential between the first engine and the second engine in a range of 70% to 100%, excluding 100%.

In some embodiments, the controlling the second engine is performed to maintain the fuel flow rate difference in a range of 70% to 90%.

In some embodiments, the controlling the second engine is performed to maintain the fuel flow rate difference in a range of 80% to 90%.

In some embodiments, said controlling said second engine is performed by using a fuel flow rate through said second engine as a control input variable to said second engine, and said controlling said first engine is performed by using said power or rotor speed demand as a control input variable to said first engine.

In some embodiments, the controlling the first engine to operate in the active mode includes controlling the first engine to drive a rotor of the multi-engine helicopter via a gearbox of the multi-engine helicopter, and controlling the second engine includes decoupling the second engine from the gearbox.

In some embodiments, the controlling the first engine to operate in the active mode includes controlling the first engine to drive a rotor of the multi-engine helicopter via a gearbox of the multi-engine helicopter and controlling the fuel flow rate difference to drive the gearbox with the second engine at a power in a range of 0% to 1% of a rated full power of the second engine.

In some embodiments, the method includes adjusting the first set of VGVs upstream of the low pressure compressor section of the first engine between an 80 degree position and a-25 degree position independent of the position of the second set of VGVs upstream of the high pressure compressor section of the first engine.

In some embodiments, the method comprises performing at least one of: a) controlling a low pressure compressor section of the second engine to maintain a pressure ratio associated with the low pressure compressor section of the second engine between 0.9 and 1.4; and b) controlling the fuel flow through the second engine in a range of about 20% to about 10% of the cruise fuel flow through the first engine.

In another aspect, a multi-engine system is provided, comprising: a first turboshaft engine and a second turboshaft engine driving a common gearbox configured to drive a load, at least the second turboshaft engine comprising: at least two tube shafts independently rotatable with respect to each other, a low pressure tube shaft of the at least two tube shafts including a low pressure shaft interconnecting the low pressure compressor section to the low pressure turbine section, and a high pressure tube shaft of the at least two tube shafts including a high pressure shaft interconnecting the high pressure compressor section to the high pressure turbine section; a first set of variable guide vanes disposed upstream of the low pressure compressor section; and a second set of variable guide vanes disposed upstream of the high pressure compressor section, the first set of variable guide vanes being separate from the second set of variable guide vanes, and the low pressure compressor section including a mixed flow rotor.

In some such embodiments, the first set of variable guide vanes is operable between an 80 degree position and a-25 degree position and the second set of variable guide vanes is operable between an 80 degree position and a-25 degree position.

In some such embodiments, the first set of variable guide vanes is operable between the 80 degree position and the-25 degree position associated with the first set of variable guide vanes, while the second set of variable guide vanes is maintained in a given position.

In some such embodiments, the multi-engine system comprises: a medium pressure spool of the at least two spools, the medium pressure spool comprising a medium pressure shaft interconnecting a medium pressure compressor section to a medium pressure turbine section; and a third set of variable guide vanes disposed at an inlet of the intermediate pressure compressor section, the third set of variable guide vanes controlling an operating state of the intermediate pressure pipe shaft.

In another aspect, there is provided a turboshaft engine for a multi-engine system, the turboshaft engine configured to drive a common load, the turboshaft comprising: at least two tube shafts independently rotatable with respect to each other, a low pressure tube shaft of the at least two tube shafts including a low pressure shaft interconnecting the low pressure compressor section to the low pressure turbine section, and a high pressure tube shaft of the at least two tube shafts including a high pressure shaft interconnecting the high pressure compressor section to the high pressure turbine section; the low pressure compressor section is defined by a single mixed flow rotor; and a plurality of sets of variable guide vanes including a set of variable guide vanes disposed at an inlet of each of the at least two tube shafts, a first set of the plurality of sets being mechanically separated from a second set of the plurality of sets.

In some such embodiments, the first set of variable guide vanes is operable between an 80 degree position and a-25 degree position associated with the first set of variable guide vanes.

In some such embodiments, the second set of variable guide vanes is operable between an 80 degree position and a-25 degree position associated with the second set of variable guide vanes.

In some such embodiments, the first set of variable guide vanes is operable between the 80 degree position and the-25 degree position associated with the first set of variable guide vanes, while the second set of variable guide vanes is maintained in a given position.

In some such embodiments, the high pressure turbine section includes only a single turbine stage.

In some such embodiments, the turboshaft engine includes an intermediate pressure spool of the at least two spools, the intermediate pressure spool including an intermediate pressure shaft interconnecting the intermediate pressure compressor section to the intermediate pressure turbine section.

In some such embodiments, the first set of variable guide vanes is disposed upstream of the low pressure compressor section.

In some such embodiments, the second set of variable guide vanes is disposed upstream of the high pressure compressor section.

Drawings

Referring now to the drawings wherein:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is a schematic illustration of an exemplary multi-engine system showing an axial cross-sectional view of two exemplary turboshaft engines;

FIG. 3A is a schematic view of one of the two turboshaft engines of FIG. 2;

FIG. 3B is a schematic illustration of one of the two turboshaft engines of FIG. 2 according to another exemplary representation; and

FIG. 4 is a diagram illustrating a method of operating a multi-engine helicopter.

Detailed Description

FIG. 1 illustrates one example of a gas turbine engine 10. In this example, the gas turbine 10 is a turboshaft engine 10, which generally includes the following components in series-flow communication, namely: a Low Pressure (LP) compressor section 12 and a High Pressure (HP) compressor section 14 for pressurized air; a combustor 16 in which compressed air is mixed with fuel and ignited to generate an annular flow of hot combustion gases; a high pressure turbine section 18 for extracting energy from the combustion gases and driving the high pressure compressor section 14; and a lower pressure turbine section 20 for further extracting energy from the combustion gases and driving the low pressure compressor section 12. Turboshaft engine 10 may include a transmission 38 driven by low-pressure shaft 32 and driving a rotatable output shaft 40. The transmission 38 may vary the ratio between the rotational speeds of the low pressure shaft 32 and the output shaft 40.

The low pressure compressor section 12 may rotate independently of the high pressure compressor section 14. The low pressure compressor section 12 may include one or more compression stages and the high pressure compressor section 14 may include one or more compression stages. In the embodiment shown in fig. 1, low pressure COMPRESSOR section 12 comprises a single COMPRESSOR stage 12A, which COMPRESSOR stage 12A comprises a single MIXED FLOW Rotor (MFR), as described in commonly owned U.S. patent 6,488,469B 1 entitled "MIXED FLOW AND center FLOW COMPRESSOR FOR GAS TURBINE ENGINE" AND which is expressly incorporated herein by reference in its entirety. The MFR of the' 469 patent is one example of an MFR that can be used to practice the present techniques, as noted in this document. It is contemplated that other MFRs may be used as well.

Turboshaft engine 10 has a plurality, i.e. two or more, tube shafts which can perform compression to pressurize the air received through air inlet 22 and which extract energy from the combustion gases before they exit via exhaust outlet 24. In the illustrated embodiment, turboshaft engine 10 includes a low-pressure spool 26 and a high-pressure spool 28 mounted for rotation about an engine axis 30. The low and high pressure spool shafts 26, 28 are independently rotatable relative to each other about an axis 30. The term "spool" is intended herein to broadly refer to the drivingly connected turbine and compressor rotors.

The low pressure spool shaft 26 may include a low pressure shaft 32 interconnecting the low pressure turbine section 20 with the low pressure compressor section 12 to drive the rotors of the low pressure compressor section 12. In other words, the low pressure compressor section 12 may include at least one low pressure compressor rotor directly drivingly engaged to the low pressure shaft 32, and the low pressure turbine section 20 may include at least one low pressure turbine rotor directly drivingly engaged to the low pressure shaft 32 to rotate the low pressure compressor section 12 at the same speed as the low pressure turbine section 20. In other embodiments, the low pressure compressor section 12 may be connected via, for example, a gear train to run faster or slower than the low pressure turbine section 20. The high pressure spool shaft 28 includes a high pressure shaft 34 that interconnects the high pressure turbine section 18 with the high pressure compressor section 14 to drive the rotor of the high pressure compressor section 14. In other words, the high pressure compressor section 14 may include at least one high pressure compressor rotor directly drivingly engaged to the high pressure shaft 34, and the high pressure turbine section 18 may include at least one high pressure turbine rotor directly drivingly engaged to the high pressure shaft 34 such that the high pressure compressor section 14 rotates at the same speed as the high pressure turbine section 18. In some embodiments, the high pressure shaft 34 may be hollow and the low pressure shaft 32 extends therethrough. The two shafts 32, 34 are free to rotate independently of each other.

The turboshaft engine 10 includes a set of Variable Guide Vanes (VGV) 36 at the inlet or otherwise upstream of each compressor section 12, 14. In other words, the first set of variable guide vanes 36 may be disposed upstream of the low pressure compressor section 12, and the second set of variable guide vanes 36 may be disposed upstream of the high pressure compressor section 14. Each of these variable guide vane arrays 36 may be independently controlled. Each set of variable guide vanes 36 may direct air to the first stage of a respective compressor section 12, 14. In operation, the set of variable guide vanes 36 may efficiently and quickly regulate the airflow and power of the turboshaft engine 10.

In some embodiments, the set of variable guide vanes 36 upstream of the low pressure compressor section 12 is mechanically decoupled from the set of variable guide vanes 36 upstream of the high pressure compressor section 14 (i.e., there is no mechanical coupling with the variable guide vanes 36 upstream of the high pressure compressor section 14). In some such embodiments, both sets of blades 36 may be operatively connected to, for example, a full authority digital controller (FADEC) or other suitable controller to thereby operate independently of one another. In other words, in some embodiments, the vane 36 and/or the engines 10A, 10B may be controlled using a full authority digital control (FADEC), such as a conventional FADEC, to perform the various control steps and methods as described in this document. For the purposes of this document, the term "independently" means that one set of blades 36 can be operated without causing any change to the state of the other set of blades 36.

In one aspect, this may allow the spool 26, 28 to operate in the following manner, namely: there is no pneumatic coupling between the spool shafts 26, 28. Thus, each of the tube shafts 26, 28 may operate at different speeds and at any speed over a wide range of speeds. On the other hand, independent operation of the blades 36 may allow the two spool shafts 26, 28 to operate at constant speed throughout all operating ranges, including from standby to cruise power (or more). In some embodiments, this may allow the two tube shafts 26, 28 to operate at a speed very close to or the same as the speed of the tube shafts 26, 28 operating at maximum power. In some embodiments, this may also allow one of the quill 26, 28 to operate at high speed while the other operates at a lower speed.

Such a control strategy may allow power recovery of engine 10 to be relatively less affected by the inertia of the quill 26, 28 and, therefore, more rapid due to the fast acting VGV/vane system 36 and/or fuel control. In some embodiments and applications, this may allow for greatly accelerating the power response recovery of engine 10. As an example, the authors of the present technology have found that the use of blades 36 as described above in conjunction with a low pressure compressor section 12 having one or more MFRs and/or a high pressure compressor section 14 having one or more MFRs may provide relatively more air and/or flow control authority and range through the core of the engine 10, 10A, 10B and/or a significantly faster power response recovery of the engine 10, 10A, 10B when compared to at least some prior art engines of similar size and output operated using prior art control methods, such as when operated using the control methods as described herein.

As an example, it has been found that the engine architecture described herein may allow each set of blades 36 to be configured to be adjustable, and may be adjusted to a range of up to about 80 degrees and about (negative) -25 degrees, as shown, for example, in FIG. 1 with respect to one of the sets of blades 36. In a more specific embodiment, the VGV 36 used in conjunction with the MFR may range from 78.5 degrees to-25 degrees, more specifically from 75 degrees to-20 degrees, and still more specifically from 70 degrees to-20 degrees. The other set of blades 36 may be configured to be adjustable and may be adjustable within a similar range of positions. In at least some embodiments and applications, such a function may be performed while avoiding compressor instability, whereas in at least some prior art engines, the vanes may only be controlled, for example, between about 0 and 30 degrees. Thus, the MFR of the engine 10, 10A, 10B as described herein can operate substantially stably even with extreme VGV "off" (e.g., up to 80 degrees). This facilitates the ability of an engine having such MFR and VGV operated in combination as described herein to operate at a very low power setting associated with a "standby" mode as defined herein, wherein the compressor of the engine operating in the standby mode is operated at very low conditions (low flow and/or low pressure ratio).

As one non-limiting example, operating such an embodiment may require a control method that may include: the low pressure compressor section 12 is operated in a low power (or no power) mode (also known as an "idle cruise condition" (ICR) or "sub-idle" cruise condition range) at a constant speed within a pressure ratio range of 0.9 to 1.4, while the vanes 36 upstream thereof are adjusted according to a suitable arrangement. For example, one such arrangement may include the following: a high closing angle (e.g., 50 to 80 degrees) to cater for lower pressure ratio conditions operating at a pressure ratio of 0.9 to 1.4. As another non-limiting example, some such embodiments may require the following control strategies: the low pressure compressor section 12 is operated in a standby mode (also known as the ICR range) at a constant speed over a range of pressure ratios from 1.0 to 1.7, while the vanes 36 upstream thereof are adjusted according to a suitable arrangement. For example, one such arrangement may include the following: a high closing angle (e.g., 50 to 80 degrees) to cater for a lower pressure ratio condition of 1.0 to 1.7. In some such embodiments, the position of the vane 36 may be mapped linearly over a range of pressures.

In some embodiments, such improved airflow control authority and/or control may allow engine 10 to operate in a continuously reduced power mode at a fuel flow rate in a range of about 30% down to about 12% of a reference fuel flow rate through engine 10. The reference fuel flow may be, for example, a takeoff fuel flow or a cruise fuel flow. In some embodiments, such airflow control authority and/or control may allow engine 10 to be operated in a continuously reduced power (or substantially no power) mode at a fuel flow rate in a range of about 20% down to about 10% of a cruising (or take-off) fuel flow rate through engine 10. In yet another aspect, such improved airflow control authority and/or control may allow for a reduction in the size of discharge valves associated with compressor sections 12, 14. In yet another aspect, such improved airflow control authority and/or control may allow for maintaining high compressor 12 speeds, as the pressure ratio and mass flow can be significantly reduced at a given speed by the upstream VGV 36 and compressor stage 12, while allowing for a rapid increase in engine power and speeding up the core compressor out of standby mode when needed, without the assistance of a power source from outside the (engine). In yet another aspect, such improved airflow control authority and/or control may allow the high pressure compressor section 14, such as the 2 nd stage high pressure compressor section 14, to operate at approximately 17-25% of its pressure ratio at a design point and at a corrected speed of 40-60% of its design point through the setting/adjustment of a single upstream VGV stage 36. In some embodiments, all of this may be provided while requiring less than 15-20% of the compressor process discharge flow through the associated process discharge valve. Such valves may be conventional and therefore will not be described in detail herein.

FIG. 2 illustrates a schematic diagram of an exemplary multi-engine system 42 that may be used as a power plant. The multiple engine system 42 may include one or more turboshaft engines 10A, 10B. The multi-engine system 42 may manage operation of the engines 10A, 10B to reduce overall fuel consumption, particularly during cruise operating conditions. This management of operation may be referred to as a "fuel savings mode" in which one of the two engines is operated in a "standby mode" while the other engine is operated at normal cruise power. The multi-engine system 42 may be used as a twin-pack (twin-pack) for an aircraft such as a helicopter. In addition to aerospace applications, the multi-engine system 42 may also be used in marine and/or industrial applications.

Multi-engine system 42 may include a first turboshaft engine 10A and a second turboshaft engine 10B. First turboshaft engine 10A and second turboshaft engine 10B may be configured to drive a common load 44. In some embodiments, the common load 44 may comprise a rotor of a rotary wing aircraft. For example, the common load 44 may be a main rotor of a helicopter. Depending on the type of common load 44 and its operating speed, each of the turboshaft engines 10A, 10B may be drivingly coupled to the common load 44 via a gearbox 46, which gearbox 46 may be of a variable speed (e.g., reduced speed) type. For example, the gearbox 46 may have a plurality of drive shafts 48 to receive mechanical energy from the respective output shafts 40A, 40B of the respective turboshaft engines 10A, 10B. The gearbox 46 may be configured to direct at least some of the combined mechanical energy from the plurality of turboshaft engines 10A, 10B to a common output shaft 50 to drive the common load 44 at a suitable operating (e.g., rotational) speed. It should be appreciated that multi-engine system 42 may be configured to drive other accessories of an associated aircraft, for example. Gearbox 46 may be configured to allow common load 44 to be driven by either first turboshaft engine 10A or second turboshaft engine 10B, or by a combination of both first turboshaft engine 10A and second turboshaft engine 10B together.

In operation, multi-engine system 42 may operate turboshaft engines 10A, 10B in a fuel saving mode. That is, the first turboshaft engine 10A may be in an active mode, and the second turboshaft engine 10B may be in a standby mode. For example, first turboshaft engine 10A may be operated in an active mode at full power to supply the power or rotor speed requirements of common load 44. Second turboshaft engine 10B may be operated in an idle or low power state to minimize fuel consumption. In some embodiments, first turboshaft engine 10A may be operated using a standby-mode control strategy as described above with respect to engine 10. The standby or idle state may indicate that the engine is operating in a lower power state and/or in a minimum fuel flow state. In principle, one high power engine may be operated more efficiently than two lower power engines to provide the same power output, thereby potentially reducing overall fuel consumption when operating the engines in the fuel economy mode as compared to conventional twin engines where each engine is operated in a reduced power state.

In use, the first turboshaft engine 10A can be operated according to an active mode, while the second turboshaft engine 10B can be operated according to a standby mode. During operation, the second turboshaft engine 10B may be required to provide more power with respect to the low-power state of the standby mode. For example, this may only occur in an emergency "single engine off" (OEI) condition of the helicopter powering multi-engine system 42, where power recovery from lower power to high power may take some time. In general, the response time for power recovery from standby mode to active mode may be reduced by reducing the inertial mass of each tube shaft of turboshaft engine 10. In other words, the response time may be reduced by reducing the inertial mass of the low-pressure spool 26 and the inertial mass of the high-pressure spool 28. For example, the inertial mass of each tube shaft 26, 28 of the turboshaft engine 10 is lower than the inertial mass of the individual compressor tube shaft of the baseline turboshaft engine, as compared to the baseline turboshaft engine having a single compressor tube shaft and delivering the same power as the turboshaft engine 10. The lower inertial mass may make turboshaft engine 10 more reactive to power or rotor speed requirements. In other words, the turboshaft engine 10 may have a faster acceleration from standby mode to full power relative to the baseline turboshaft engine. In some embodiments, the multi-engine system 42 may include a baseline turboshaft in place of the first turboshaft engine 10A.

Multi-engine system 42 may include a transmission 52 driven by output shaft 40B and driving rotatable drive shaft 48. The transmission 52 may be controlled to vary the ratio between the rotational speeds of the output shaft 40B and the propeller shaft 48.

With reference to fig. 3A, a schematic view of a second turboshaft engine 10B is shown. Turboshaft engine 10B includes a first set of variable guide vanes 36A disposed at the inlet of low-pressure compressor section 12. That is, the first set of variable guide vanes 36A is located upstream of the low pressure compressor section 12 with respect to the direction of airflow through the turboshaft engine 10B. The first set of variable guide vanes 36A may be configured to control the operating state of the low spool shaft 26. The low pressure compressor section 12 may include one or more compression stages driven by one or more turbine stages of the low pressure turbine section 20. For example, in the embodiment shown in fig. 3A, the low pressure compressor section 12 includes a single compressor stage 12A of Mixed Flow Rotor (MFR) and the low pressure turbine section 20 includes two power turbine stages 20A. In another example, the low pressure compressor section 12 may include two compressor stages. The two compressor stages may include two axial compressors, or as another example, a single axial or centrifugal stage. The low pressure turbine section 20 may include three turbine stages. The output shaft 40B may be directly coupled to the low pressure shaft 32.

The turboshaft engine 10B includes a second set of variable guide vanes 36B disposed at the inlet of the high pressure compressor section 14. That is, the second set of variable guide vanes 36B is located upstream of the high pressure compressor section 14 with respect to the direction of airflow through the turboshaft engine 10B. The second set of variable guide vanes 36B may be configured to control the operating state of the high pressure spool shaft 28. The high pressure compressor section 14 may include one or more compression stages or a single centrifugal stage driven by one or more turbine stages of the high pressure turbine section 18. For example, in the embodiment shown in fig. 3A, the high-pressure compressor section 14 includes two compressor stages 14A, which include a Mixed Flow Rotor (MFR) and a centrifugal impeller, and the high-pressure turbine section 18 includes a single power turbine stage 18A. The two compressor stages 14A may include two centrifugal impellers. In another example, the high pressure compressor section 14 may include three compressor stages. The three compressor stages may include two axial compressors and a centrifugal impeller. The high pressure turbine section 18 may include two turbine stages.

Referring to FIG. 3B, a schematic diagram of a second turboshaft engine 10B is shown according to another exemplary representation. Turboshaft engine 10B may have three or more power spool shafts. In the embodiment shown in fig. 3B, the turboshaft engine comprises an intermediate pressure pipe shaft 27. The intermediate pressure spool shaft 27 includes an intermediate pressure shaft 33 that interconnects the intermediate pressure turbine section 19 with the intermediate pressure compressor section 13 to drive the rotor of the intermediate pressure compressor section 13. In other words, the intermediate pressure compressor section 13 may include at least one intermediate pressure compressor rotor directly drivingly engaged to the intermediate pressure shaft 33, and the intermediate pressure turbine section 19 may include at least one intermediate pressure turbine rotor directly drivingly engaged to the intermediate pressure shaft 33, such that the intermediate pressure compressor section 13 rotates at the same speed as the intermediate pressure turbine section 19. In other embodiments of engine 10B, there may be no compressor on the low spool shaft 26.

In view of the above-described technology, and referring now to FIG. 4, the present technology provides a method 60 of operating a multi-engine helicopter (H). For example, the method 60 may be used to operate an engine system 42 such as described above with respect to FIG. 2 during a cruise segment.

In some embodiments, method 60 may include controlling one or more of engines 10A, 10B to operate in an active mode to meet power or rotor speed requirements of a multi-engine helicopter (H) to implement a cruise flight with the multi-engine helicopter (H), using, for example, full authority digital control (FADEC). The method 60 may also include controlling one or more of the other engines 10A, 10B of the multi-engine helicopter (H) to operate in a standby mode, wherein the fuel flow rate in the standby engine is controlled such that the difference in fuel flow rate between the active and standby engines is maintained between 70% and 100%, i.e. in the range of 70% to 100% (excluding 100%, considering that this would mean that the standby engine is completely off, which is undesirable). Thus, it should be understood that a range of 70-100% as expressed herein may include the lower end of the range (i.e., 70%) but need exclude 100% with respect to the fuel flow difference between the two engines. In some embodiments of method 60, the fuel flow difference between the active and standby engines may be controlled to be in the range of 70% and 90%. In some embodiments of method 60, the fuel flow rate difference may be controlled to be in the range of 80% and 90%.

In at least some instances, maintaining the fuel flow difference within such a range may be achieved by an engine architecture having a combination of MFRs 12, 14 and independently regulated VGV banks 36, as described above, and may provide fuel economy improvements over at least some prior art multiple engine operating conditions. Such operation may be referred to as asymmetrically operating the engines 10A, 10B. In some embodiments, in such asymmetric operation, a standby engine of engines 10A, 10B may be controlled by using a fuel flow rate through the standby engine of engines 10A, 10B as a control input variable to the standby engine of engines 10A, 10B. In some such embodiments, an active one of engines 10A, 10B (e.g., that meets the power or rotor speed requirements of one or more rotors of helicopter 42) may be controlled by using the power or rotor speed requirements of the helicopter as control input variables to the active one of engines 10A, 10B.

In some such embodiments, controlling the active engine may include controlling the active engine to drive a rotor 44/load 44 of the multi-engine helicopter (H) via a gearbox 46 of the multi-engine helicopter (H), and controlling the standby engine may include decoupling the standby engine from the gearbox 46. For this purpose, for example, a conventional helicopter gearbox can be used, which decouples a given engine when the engine decelerates below a given power and/or rotational speed. In some such embodiments, controlling the active engine may include controlling the active engine to drive the rotor/load 44 via the gearbox 46 and controlling the fuel flow difference to drive the gearbox 46 with the standby engine at a power in the range of 0% to 1% of the rated full power of the standby engine.

In some such embodiments, the method 60 may include adjusting the first set of VGVs 36 upstream of the low pressure compressor section 12 of the active engine between an 80 degree position and a-25 degree position (or, more particularly, between 75 degrees and-20 degrees positions) independent of the position of the second set of VGVs 36 upstream of the high pressure compressor section 14 of the active engine. In some such embodiments, the method 60 may include performing at least one of: a) controlling the low pressure compressor section 12 to maintain a pressure ratio associated with the low pressure compressor section 12 between 0.9 and 1.4; and b) controlling the fuel flow through the standby engine to be in the range of about 20% to about 10% of the cruise fuel flow (or take-off fuel flow) through the active engine.

The above description is intended to be exemplary only, and those skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the compressor rotor may comprise an axial compressor or a centrifugal impeller. The multi-engine system may have more than two turboshaft engines, in which case one or more of these turboshaft engines may be operated in a standby mode. As another example, although method 60 is described with respect to a helicopter (H), it is contemplated that method 60 may also be applied to other types of multi-engine aircraft. Still other modifications that fall within the scope of the invention will be apparent to those skilled in the art upon review of this disclosure.