Patent Description:
Aircraft engines, such as gas turbine engines, may have two spools, namely a low-pressure spool and a high-pressure spool, which are independently rotatable from one another. Accessories, such as generators for example, are typically driven by the high-pressure spool. In some operating conditions, the power extracted by the accessory driven by the high-pressure spool may be limited. Hence, improvements are sought.

<CIT> discloses prior art systems and methods for transferring mechanical power in a turbine engine.

<CIT> discloses a prior art turbofan engine with spool power extraction via multiple generators.

<CIT> discloses a prior art gas turbine engine with a power transmission device for transmitting power from first and second turbine shafts to a power output shaft for driving auxiliary units.

<CIT> discloses a prior art superposition gearbox for engine performance.

According to a first aspect of the present invention, there is provided an aircraft power plant as set forth in claim <NUM>.

The aircraft power plant as defined above and described elsewhere herein may also include one or more of the following features.

In some embodiments, the coupling system includes: a first coupling device having a first engaged configuration and a first disengaged configuration, the first input engaged to the output via the first coupling device in the first engaged configuration and disengaged from the output in the first disengaged configuration, and a second coupling device having a second engaged configuration and a second disengaged configuration, the second input engaged to the output via the second coupling device in the second engaged configuration and disengaged from the output in the second disengaged configuration.

In some embodiments, one or both of the first coupling device and the second coupling device has at least one intermediary configuration in which an input of the one or both of the first coupling device and the second coupling device rotates at a different speed than an output of the one or both of the first coupling device and the second coupling device.

In some embodiments, the one or both of the first coupling device and the second coupling device is a viscous coupling device having two members rotatable one relative to the other, the two members spaced apart from one another by a gap filled with a fluid.

In some embodiments, an actuator is engaged to one of the two members, the actuator operable to move the one of the two members toward and away from the other of the two members to vary a dimension of the gap.

In some embodiments, the transmission includes: a first load path from the first input to the output via the first coupling device, the first load path including a first gear engaged to a first coupling input of the first coupling device, and a second gear engaging the output and engaged by a first coupling output of the first coupling device, and a second load path from the second input to the output via the second coupling device, the second load path including a third gear engaged to a second coupling input of the second coupling device, and the second gear engaging the output and engaged by a second coupling output of the second coupling device.

In some embodiments, the first coupling input is defined by a fourth gear meshed with the first gear, the first coupling output defined by a fifth gear meshed with the second gear, the fourth gear engaged to the fifth gear via a fluid received within a first gap defined between the fourth gear and the fifth gear, the second coupling input is defined by a sixth gear meshed with the third gear, the second coupling output defined by a seventh gear meshed with the second gear, the sixth gear engaged to the seventh gear via a fluid received within a second gap defined between the sixth gear and the seventh gear.

In some embodiments, the coupling system interconnects the output with the first input when an altitude of the aircraft power plant is below an altitude threshold.

In some embodiments, the coupling system interconnects the output with the second input when an altitude of the aircraft power plant is above an altitude threshold.

In some embodiments, a controller has a processing unit operatively connected to a computer-readable medium having instructions stored thereon executable by the processing unit for: receiving a signal from at least one sensor, the signal indicative of an operating condition of the aircraft power plant; based on the received signal, determining a configuration of the transmission, the configuration being one of: a first configuration in which the transmission drivingly engages the first input to the output while the second input is disengaged from the output, a second configuration in which the transmission drivingly engages the second input to the output while the first input is disengaged from the output, and a hybrid configuration in which both of the first input and the second input are drivingly engaged to the output through the transmission; and operating the transmission in the determined configuration.

In some embodiments, the signal is indicative of an altitude of the aircraft power plant, the determining of the configuration includes determining that the altitude is below an altitude threshold and the operating of the transmission includes operating the transmission in the first configuration.

In some embodiments, the signal is indicative of an altitude of the aircraft power plant, the determining of the configuration includes determining that the altitude is above an altitude threshold and the operating of the transmission includes operating the transmission in the second configuration.

In some embodiments, the determining of the configuration includes: determining that the configuration corresponds to the hybrid configuration; determining a power split between the high-pressure shaft and the low-pressure shaft as a function of the operating condition of the aircraft power plant; and driving the electrical machine per the determined power split.

In some embodiments, the determining of the power split includes determining the power split from a look-up table stored in the computer-readable medium.

According to a further aspect of the present invention, there is provided a method of driving an electrical machine with an aircraft power plant as set forth in claim <NUM>.

The method as defined above and described elsewhere herein may also include one or more of the following steps and/or features.

In some embodiments, the determining that the portion of the torque requirement of the electrical machine to be provided by the one of the high-pressure spool and the low-pressure spool includes: determining that an entirety of the torque requirement is to be provided to the electrical machine by the one of the high-pressure spool and the low-pressure spool; and drivingly engaging the electrical machine to the one of the high-pressure spool and the low-pressure spool while the other of the high-pressure spool and the low-pressure spool is disengaged from the electrical machine.

In some embodiments, the determining that the portion of the torque requirement of the electrical machine to be provided by the one of the high-pressure spool and the low-pressure spool includes: determining that the torque requirement is to be provided to the electrical machine by both of the high-pressure spool and the low-pressure spool; and drivingly engaging both of the high-pressure spool and the low-pressure spool to the electrical machine.

In some embodiments, the drivingly engaging of both of the high-pressure spool and the low-pressure spool to the electrical machine includes: drivingly engaging the high-pressure spool to the electrical machine via a first coupling device; and drivingly engaging the low-pressure spool to the electrical machine via a second coupling device, wherein one or both of the first coupling device and the second coupling device has at least one intermediary configuration in which an input of the one or both of the first coupling device and the second coupling device rotates at a different speed than an output of the one or both of the first coupling device and the second coupling device.

In some embodiments, the signal is indicative of an altitude of the aircraft power plant, the determining of the portion of a torque requirement of the electrical machine to be provided by one of the high-pressure spool and the low-pressure spool as a function of the operating condition of the aircraft power plant includes: determining that the altitude is below an altitude threshold; and determining that no torque is to be provided by the low-pressure spool.

In some embodiments, the signal is indicative of an altitude of the aircraft power plant, the determining of the portion of a torque requirement of the electrical machine to be provided by one of the high-pressure spool and the low-pressure spool as a function of the operating condition of the aircraft power plant includes: determining that the altitude is above an altitude threshold; and determining that no torque is to be provided by the high-pressure spool.

In at least some of the figures that follow, some elements appear more than once (e.g. there may be two, three, etc. of a given part in a given embodiment). Accordingly, only a first instance of each given element may be labeled, to maintain clarity of the figures.

Referring to <FIG>, an aircraft power plant is shown at <NUM>. The aircraft power plant <NUM> is referred to herein below simply as "power plant <NUM>" for the sake of conciseness. The power plant <NUM> includes a gas turbine engine <NUM>. The gas turbine engine <NUM> is shown in <FIG> as being a turboprop gas turbine engine drivingly engaged to a propeller <NUM> via a reduction gearbox <NUM>. It will be appreciated that the principles of the present disclosure may apply to any engine having two spools as will be explained below. These engines may include, for instance, turbofan and turboshaft.

The gas turbine engine <NUM> includes an inlet <NUM> at a rear of the gas turbine engine <NUM> relative to a direction of travel T of the power plant <NUM>. The gas turbine engine <NUM> includes an exhaust <NUM> at a front of the power plant <NUM> relative to the direction of travel T. The gas turbine engine <NUM> is therefore a reverse-flow engine in that air flows from the inlet <NUM> to the exhaust <NUM> in an annular gas path <NUM> from the rear to the front in the same direction as the direction of travel T.

The gas turbine engine <NUM> includes a low-pressure (LP) spool <NUM> and a high-pressure (HP) spool <NUM>. The term "spool" is herein intended to broadly refer to drivingly connected turbine and compressor rotors and is, thus, not limited to a compressor and turbine assembly on a single shaft. It also includes a rotary assembly with multiple shafts geared together. The LP spool <NUM> includes a LP compressor 24A, a LP or power turbine 24B, and a LP shaft 24C drivingly engaging the LP turbine 24B to the LP compressor 24A. The HP spool <NUM> includes a HP compressor 25A, a HP turbine 25B, and a HP shaft 25C drivingly engaging the HP turbine 25B to the HP compressor 25A. The gas turbine engine <NUM> includes a combustor <NUM> between the HP turbine 25B and the HP compressor 25A. In the embodiment shown, the HP shaft 25C is hollow and the LP shaft 24C extends within the HP shaft 25C. Other configurations are contemplated.

In use, air enters the gas turbine engine <NUM> via the inlet <NUM> and flows into the annular gas path <NUM> through the LP compressor 24A and through the HP compressor 25A located downstream of the LP compressor 24A relative to a direction of the flow into the annular gas path <NUM>. The air, now compressed, is mixed with fuel into the combustor <NUM> and is ignited thereby generating combustion gases. The combustion gases flow out of the combustor <NUM> into the HP turbine 25B, which extracts energy from the combustion gases to drive the HP compressor 25A via the HP shaft 25C. The combustion gases then flow through the LP or power turbine 24B located downstream of the HP turbine 25B relative to the direction of the flow through the annular gas path <NUM>. The LP turbine 24B extracts power from the combustion gases to drive the LP compressor 24A via the LP shaft 24C. The LP turbine 24B further drivingly engages the propeller <NUM> via the reduction gearbox <NUM>. The reduction gearbox <NUM> drives the propeller <NUM> via an output shaft <NUM>.

In the embodiment shown, the gas turbine engine <NUM> includes variable inlet guide vanes (VIGV) <NUM> located upstream of the LP compressor 24A relative to the flow in the annular gas path <NUM>. The VIGV <NUM> includes airfoils <NUM> that are each pivotable about respective spanwise axes to orient the incoming flow from the inlet <NUM> toward the LP compressor 24A. In the present embodiment, the airfoils <NUM> extend in a direction being substantially axial relative to a central axis of the gas turbine engine <NUM>. In some embodiments, the airfoils <NUM> may extend in a direction having a radial component relative to the central axis of the gas turbine engine <NUM>. The VIGV <NUM> is operatively connected to a controller <NUM> of the aircraft power plant <NUM>; the controller <NUM> operable to vary angles of attack defined between the incoming flow and the airfoils <NUM>.

Still referring to <FIG>, the aircraft power plant <NUM> is used to drive an accessory such as an electrical machine <NUM>. Typically, the electrical machine <NUM> is driven solely by the HP spool <NUM>. The electrical machine <NUM> may be used in an electric motor configuration to drive the HP spool <NUM> for starting the gas turbine engine <NUM>. The electrical machine <NUM> may be used in a generator configuration to generate electrical power to be used by an aircraft equipped with the aircraft power plant <NUM>.

It was observed that, when the electrical machine <NUM> is being used in the generator configuration, the power extracted by the electrical machine <NUM> driven by the HP spool <NUM> may be limited for operability reasons. For instance, higher loads on the HP compressor 25A may reduce its surge margin, which may be undesirable. Typically, when this situation occurs, a second generator driven by the LP spool <NUM> is being used. However, this adds complexity and weight to the power plant <NUM>, which may be undesirable.

In the embodiment shown, the aircraft power plant <NUM> includes a transmission <NUM>, which may also be referred to as a differential, used to transmit a rotational input from both of the HP shaft 25C and the LP shaft 24C to the electrical machine <NUM>. Hence, if power extraction requirement for certain engine operating conditions makes the HP compressor 25A surge margin fall below the operability threshold, the transmission <NUM> is used to transmit power from the LP spool <NUM> to the electrical machine <NUM> used in the generator mode. Hence, the use of a second generator may be avoided.

In the embodiment shown, series of intermediary shafts <NUM> are used to connect the transmission <NUM> to the HP shaft 25C. It will be understood that any suitable connection may be used to drivingly engage the transmission <NUM> to the HP shaft <NUM>. The intermediary shafts <NUM> may be drivingly engaged to one another using bevel gears, universal joints, or any other suitable means. One of the intermediary shafts <NUM> is located radially outside the annular gas path <NUM> relative to an axis of rotation of the HP and LP shafts 25C, 24C. Although said intermediary shafts <NUM> are shown as being connected at a rear of the HP shaft 25C, they may alternatively be connected at a front thereof. In the present case, the transmission <NUM> is driven by the LP shaft 24C directly. However, it will be understood that intermediary shaft may be used to connect the LP shaft 24C to the transmission <NUM>.

Referring now to <FIG>, the transmission <NUM> is described in more detail. The transmission <NUM> has a first input 60A drivingly engaged by the HP shaft 25C, herein via the intermediary shafts <NUM>. The transmission <NUM> has a second input 60B drivingly engaged by the LP shaft 24C. The transmission <NUM> has an output 60C drivingly engaging the electrical machine <NUM>. The transmission <NUM> is operable in a plurality of configurations to select which of the LP and HP spools <NUM>, <NUM>, or a combination thereof, drives the electrical machine <NUM> as a function of operating conditions of the power plant <NUM>. The transmission <NUM> includes a coupling system, which will be described below. The coupling system is used to selectively interconnect the output 60C with one of: the first input 60A, with the second input 60B disconnected from the output 60C; the second input 60B, with the first input 60A disconnected from the output 60C; and both of the first input 60A and the second input 60B.

The transmission <NUM> has a first configuration in which the transmission <NUM> drivingly engages the first input 60A to the output 60C while the second input 60B is disengaged from the output 60C. In the first configuration, solely the HP shaft 25C drives the electrical machine <NUM> and the LP shaft 24C is disengaged from the electrical machine <NUM>. Hence, no power is extracted from the LP shaft 24C in the first configuration of the transmission <NUM>. In some operating conditions, the gas turbine engine <NUM> may benefit from having higher loads extracted from the HP spool <NUM>. For instance, at low altitude take-off during a hot day, higher loads on the HP spool <NUM> may reduce its rotational speed, which may avoid the HP spool <NUM> from reaching its speed limit. Hence, during these operating conditions, the LP spool <NUM> may be disengaged from the electrical machine <NUM> to maximize the load on the HP spool <NUM>. During starting of the gas turbine engine <NUM>, the electrical machine <NUM> is operated as an electrical motor and is coupled solely to the HP shaft 25C to accelerate the HP spool <NUM>. Hence, during engine start-up, the LP spool <NUM> may be disengaged from the electrical machine <NUM>.

The transmission <NUM> has a second configuration in which the transmission <NUM> drivingly engages the second input 60B to the output 60C while the first input 60A is disengaged from the output 60C. In the second configuration, solely the LP shaft 24C drives the electrical machine <NUM> and the HP shaft 25C is disengaged from the electrical machine <NUM>. Hence, no power is extracted from the HP shaft 25C in the second configuration of the transmission <NUM>. In certain operating conditions, the LP shaft 24C of the gas turbine engine <NUM> may have a fixed rotating speed that may benefit from having higher loads on the LP compressor 24C connected thereto. For instance, at high altitude during cruise, higher loading on the LP compressor 24C may result in the opening of the VIGV <NUM>, which may allow more air mass flow in the gas turbine engine <NUM>. This may result in the gas turbine engine <NUM> having higher output power capability. In such operating condition, the HP spool <NUM> may be decoupled from the electrical machine <NUM>, leaving the entire load to the LP spool <NUM> to maximize engine available power and spare the surge margin of the HP compressor 25A. In these operating conditions, the LP compressor 24A may be less sensitive surge-margin-wise than the HP compressor 25A to accessory power extraction. That is, more power can be extracted from the LP spool <NUM> before the surge margin of the LP compressor 24A is affected as much as the surge margin of the HP compressor 25A would be for the same power extraction by the electrical machine <NUM>.

The transmission <NUM> may have a hybrid configuration in which both of the first input 60A and the second input 60B are drivingly engaged to the output 60C through the transmission <NUM>. In this hybrid configuration, both of the LP and HP spools <NUM>, <NUM> provide power to the electrical machine <NUM>. The hybrid configuration may be used to smoothly switch between the first and second configurations. This may allow the gas turbine engine <NUM> to run optimally from performance and operability standpoints. During engine operation, the controller <NUM> may receive data about engine inlet total pressure and total temperature and, from the received data, may determine an optimal split between the power extracted from the LP and HP spools <NUM>, <NUM> to drive the electrical machine <NUM>. When the total pressure and total temperature are above respective thresholds, more power may be extracted from the HP spool <NUM> than from the LP spool <NUM>. When the total pressure and total temperature are below respective thresholds, more power may be extracted from the LP spool <NUM> than from the HP spool <NUM>.

The electrical machine <NUM> may have a torque requirement for proper operation at a given operating condition. For instance, the torque requirement of the electrical machine <NUM> may be dictated by a power output required from the electrical machine <NUM> when operated as a generator. The transmission <NUM> may allow one or both of the HP and LP spools <NUM>, <NUM> to fulfill the torque requirement of the electrical machine <NUM>.

The transmission <NUM> may further be able to provide adequate speed ratios to cater to the difference between the rotational speeds of the HP and LP spools <NUM>, <NUM> and the desired rotating speed of the electrical machine <NUM>. Gears of varying diameters may be used for that purpose as will be described below.

Still referring to <FIG>, the coupling system of the transmission <NUM> includes a first coupling device <NUM> and a second coupling device <NUM>. The first coupling device <NUM> is used to transmit a rotational input from the HP shaft 25C to the electrical machine <NUM>. The first coupling device <NUM> has a first engaged configuration and a first disengaged configuration. The first input 60A of the transmission <NUM> is engaged to the output 60C of the transmission <NUM> via the first coupling device <NUM> in the first engaged configuration and disengaged from the output 60C in the first disengaged configuration. Similarly, the second coupling device <NUM> having a second engaged configuration and a second disengaged configuration. The second input 60B of the transmission <NUM> is engaged to the output 60C of the transmission <NUM> via the second coupling device <NUM> in the second engaged configuration and disengaged from the output 60C in the second disengaged configuration.

The first coupling device <NUM> has a first coupling input 61A drivingly engaged by the first input 60A of the transmission <NUM>, and has a first coupling output 61B drivingly engaging the output 60C of the transmission <NUM>. Similarly, the second coupling device <NUM> has a second coupling input 62A drivingly engaged by the second input 60B of the transmission <NUM>, and has a second coupling output 62B drivingly engaging the output 60C of the transmission <NUM>. The first coupling input 61A is engaged to the first coupling output 61B in the first engaged configuration and disengaged from the first coupling output 61B in the first disengaged configuration. The second coupling input 62A is engaged to the second coupling output 62B in the second engaged configuration and disengaged from the second coupling output 62B in the second disengaged configuration.

The first and second coupling devices <NUM>, <NUM> may be a clutches, a visco-couplers, and so on. The first and second coupling devices <NUM>, <NUM> may allow slippage between their respective first and second coupling inputs 61A, 62A and first and second coupling outputs 61B, 62B. That is, in the first and second disengaged configurations, the first coupling input 61A and the second coupling input 62A may rotate while no torque is transferred to the first coupling output 61B and the second coupling output 62B. In the first and second engaged configurations, the first coupling input 61A may rotate at the same speed as the first coupling output 61B and the second coupling input 62A may rotate at the same speed as the second coupling output 62B. In the embodiment shown, the first and second coupling devices <NUM>, <NUM> have an intermediary configuration in which the first coupling input 61A rotates at a different speed than the first coupling output 61A and in which the second coupling input 62A rotates at a different speed than the second coupling output 62B. In some embodiments, only one of the first and second coupling devices <NUM>, <NUM> may have this intermediate configuration. Any suitable coupling devices that may allow slippage as described herein may be used without departing from the scope of the present disclosure. This intermediary configuration, allowing slippage between the respective inputs and outputs, may allow the driving of the electrical machine <NUM> with both of the HP and LP spools <NUM>, <NUM> while avoiding the HP spool from being engaged to the LP spool, which would make the gas turbine engine <NUM> a single-spool engine, which may be undesirable in some operating conditions. However, in some other configurations, performance benefits may be achieved.

In the intermediate configuration of the first coupling device <NUM>, a torque is transferred from the first coupling input 61A to the first coupling output 61B, but the transferred torque may be less than a torque received at the first coupling input 61A from the HP shaft 25C. Similarly, in the intermediate configuration of the second coupling device <NUM>, a torque is transferred from the second coupling input 62A to the second coupling output 62B, but the transferred torque may be less than a torque received at the second coupling input 62A from the LP shaft 24C. Hence, the first and second coupling devices <NUM>, <NUM> may be used to modulate the torque received from the HP and LP shafts 25C, 24C such that the torque transmitted via the first and second coupling devices <NUM>, <NUM> corresponds to the torque requirement of the electrical machine <NUM> while extracting the most optimal power from the HP and LP shafts 25C, 24C to avoid surge margin or excessive rotating speeds issues as discussed above.

As shown in <FIG>, the transmission <NUM> includes a first driving gear 63A drivingly engaged by the HP shaft 25C and a second driving gear 63B drivingly engaged by the LP shaft 24C. The first driving gear 63A is meshed with a first idler gear 63C that defines the first coupling input 61A of the first coupling device <NUM>. The second driving gear 63B is meshed with a second idler gear 63D that defines the second coupling input 62A of the second coupling device <NUM>. The first coupling output 61B is defined by a third idler gear 63E and the second coupling output 62B is defined by a fourth idler gear 63F.

The first idler gear 63C is drivingly engageable to the third idler gear 63E via a film 61C of a fluid located within a gap between the first idler gear 63C and the third idler gear 63E. Similarly, the second idler gear 63D is drivingly engageable to the fourth idler gear 63F via a film 62C of a fluid located within a gap between the second idler gear 63D and the fourth idler gear 63F. The films 61C, 62C may include a viscous fluid, such as oil. Distances between the first idler gear 63C and the third idler gear 63E and between the second idler gear 63D and the fourth idler gear 63F may be varied with first and second actuators 61D, 62D, which are herein engaged respectively to the third and fourth idler gears 63E, 63F although other configurations are contemplated. It will be appreciated that the film may be suitably contained between members secured to the gears for rotation with the gears. These members may include, for instance, discs, plates, and so on. A housing may be provided around the gears to contain the fluid within the gaps.

The actuators 61D, 62D may be operatively connected to the controller <NUM> to vary the distances between the gears. The torque is transferred via shearing stress of the viscous fluid located within the gaps between the gears. The smaller the distance, the greater the torque transferred via the first and second coupling devices <NUM>, <NUM> up to a point where both gears of each pairs of the idler gears rotate at the same speed. When the distances are increased, the torque transferred decreases up to a point where no torque is transferred.

Both of the third and fourth idler gears 63E, 63F are meshed with a driven gear <NUM> that is drivingly engaged to the electrical machine <NUM> via an output shaft <NUM> of the transmission <NUM>. Hence, the power extracted from the HP and LP shafts 25C, 24C may converge to the same driven gear <NUM> to drive the electrical machine <NUM>. In the present embodiment, all of the gears are depicted as bevel gears. It will be appreciated that other configurations are contemplated without departing from the scope of the present disclosure. The diameters of the gears is selected to provide required speed ratios between the HP and LP shafts 25C, 24C and the output shaft <NUM> of the transmission <NUM>.

The transmission <NUM> therefore includes a first load path and a second load path. The first load path extends from the first input 60A to the output 60C via the first coupling device <NUM>. The first load path includes the first driving gear 63A engaged to the first coupling input 61A of the first coupling device <NUM> and the driven gear <NUM> engaging the output 60C of the transmission <NUM> and engaged by the first coupling output 61B of the first coupling device <NUM>.

The second load path extends from the second input 60B of the transmission <NUM> to the output 60C via the second coupling device <NUM>. The second load path includes the second driving gear 63B engaged to the second coupling input 62A of the second coupling device <NUM>, and the driven gear <NUM> engaging the output 60C and engaged by the second coupling output 62B of the second coupling device <NUM>.

Referring now to <FIG>, another embodiment of an aircraft power plant is shown at <NUM>. For the sake of conciseness, only elements that differ from the aircraft power plant <NUM> described above are described below.

The aircraft power plant <NUM> has a transmission <NUM> that includes first and second clutches <NUM>, <NUM> each operable in an engaged configuration and a disengaged configuration. The transmission <NUM> may be operatively connected to the controller <NUM> to control operation of the first and second clutches <NUM>, <NUM>. The first and second clutches <NUM>, <NUM> may be dog clutches, viscous clutches, and so on. The first clutch <NUM> has an input drivingly engaged to the HP shaft 25C and an output drivingly engaging a first gear 163A. The second clutch <NUM> has an input drivingly engaged to the LP shaft 24C and an output drivingly engaging a second gear 163B. The first and second gears 163A, 163B are meshed with a third gear 163C, which is drivingly engaged to the electrical machine <NUM> via an output shaft <NUM> of the transmission <NUM>. In use one or both of the first and second clutches <NUM>, <NUM> may be in its engaged configuration to provide a rotational input to the electrical machine <NUM>. The transmission <NUM> may be limited to having only one of the two spools <NUM>, <NUM> engaged to the electrical machine <NUM> at a time.

The transmissions <NUM>, <NUM> described herein may allow higher power extraction for a single generator and may void the possible addition of a second generator.

Referring now to <FIG>, a method of driving the electrical machine is shown at <NUM>. The method <NUM> includes receiving a signal from at least one sensor <NUM> (<FIG>), the signal indicative of an operating condition of the aircraft power plant at <NUM>. The method <NUM> includes determining a portion of a torque requirement of the electrical machine <NUM> to be provided by one of the high-pressure spool <NUM> and the low-pressure spool <NUM> as a function of the operating condition of the aircraft power plant at <NUM>. The method <NUM> then includes transmitting the portion of the torque requirement from the one of the high-pressure spool <NUM> and the low-pressure spool <NUM> to the electrical machine <NUM> and transmitting a remainder of the torque requirement from the other of the high-pressure spool <NUM> and the low-pressure spool <NUM> to the electrical machine <NUM>. In some embodiments, the remainder of the torque requirement may be zero such that all of the torque requirement is to be fulfilled by only one of the two spools <NUM>, <NUM>.

In the embodiment shown, the determining that the portion of the torque requirement of the electrical machine <NUM> to be provided by the one of the high-pressure spool <NUM> and the low-pressure spool <NUM> may include: determining that an entirety of the torque requirement is to be provided to the electrical machine <NUM> by the one of the high-pressure spool <NUM> and the low-pressure spool <NUM>; and drivingly engaging the electrical machine <NUM> to the one of the high-pressure spool <NUM> and the low-pressure spool <NUM> while the other of the high-pressure spool <NUM> and the low-pressure spool <NUM> is disengaged from the electrical machine <NUM>.

The determining that the portion of the torque requirement of the electrical machine to be provided by the one of the high-pressure spool <NUM> and the low-pressure spool <NUM> may include: determining that the torque requirement is to be provided to the electrical machine <NUM> by both of the high-pressure spool <NUM> and the low-pressure spool <NUM>; and drivingly engaging both of the high-pressure spool <NUM> and the low-pressure spool <NUM> to the electrical machine <NUM>. This may be done by drivingly engaging the high-pressure spool <NUM> to the electrical machine <NUM> via the first coupling device <NUM>; and drivingly engaging the low-pressure spool <NUM> to the electrical machine <NUM> via the second coupling device <NUM>. As explained above, one or both of the first coupling device <NUM> and the second coupling device <NUM> may have at least one intermediary configuration in which an input of the one or both of the first coupling device <NUM> and the second coupling device <NUM> rotates at a different speed than an output of the one or both of the first coupling device <NUM> and the second coupling device <NUM>.

The signal may be indicative of an altitude of the aircraft power plant <NUM>. In such a case, the method <NUM> may include: determining that the altitude is below an altitude threshold; and determining that no torque is to be provided by the low-pressure spool <NUM>. Or, the method <NUM> may include determining that the altitude is above an altitude threshold; and determining that no torque is to be provided by the high-pressure spool <NUM>.

The method <NUM> may include determining an optimal configuration corresponding to one of the first, second, and hybrid configurations of the transmission <NUM> based on the received signal; and operating the transmission <NUM> in the determined optimal configuration. In some cases, the signal may be indicative of an altitude of the aircraft power plant <NUM> and the determining of the optimal configuration includes determining that the altitude is below an altitude threshold and the operating of the transmission may include operating the transmission in the first configuration in which in which the transmission <NUM> drivingly engages the first input 60A to the output 60C while the second input 60B is disengaged from the output 60C and in which the LP shaft 24C is disengaged from the electrical machine <NUM>. In some cases, the determining of the optimal configuration may include determining that the altitude is above an altitude threshold and the operating of the transmission includes operating the transmission in the second configuration in which in which the transmission <NUM> drivingly engages the second input 60B to the output 60C while the first input 60A is disengaged from the output 60C and in which the HP shaft 25C is disengaged from the electrical machine <NUM>.

The signal indicative of the altitude may be provided by the sensor <NUM>, which may be a total temperature sensor, a temperature sensor, an altimeter, a total pressure sensor, and/or a pressure sensor. Other parameters may be used to determine which of the two spools is to drive the electrical machine <NUM>. An engine inlet temperature signal from a temperature sensor can be used in conjunction with the aforementioned pressure signal. A compressor discharge / combustor cavity pressure (P3) signal could also be used in conjunction with engine rotating speed sensor and other engine temperature and pressure sensors as an indication of compressor surge margin status and could drive a change in the spool driving the electrical machine <NUM>.

In some other cases, the determining of the optimal configuration includes: determining that the optimal configuration corresponds to the hybrid configuration. The method <NUM> may then include determining an optimal power split between the high-pressure shaft 25C and the low-pressure shaft 24C as a function of the operating condition of the aircraft power plant <NUM>; and driving the electrical machine <NUM> per the determined optimal power split. The determining of the optimal power split includes determining the optimal power split from a look-up table stored in a computer-readable medium of the controller <NUM>.

The power split may, for instance, require that torque requirement of the electrical machine <NUM> be divided in half between the two spools <NUM>, <NUM>. Hence, <NUM>% of the torque requirement may be provided by the HP spool <NUM> and <NUM>% of the torque requirement may be provided by the LP spool <NUM>. In some cases, a <NUM>/<NUM> split is desirable. The controller <NUM> may be able to compute the optimal power split.

It is understood that, in some cases, a total torque of the two spools <NUM>, <NUM> may be greater than the torque requirement of the electrical machine <NUM>. In this case, the first and second coupling devices <NUM>, <NUM> may suitably reduce the torque they receive from the respective spools <NUM>, <NUM> to ensure that the proper torque is provided to the electrical machine <NUM>. The controller <NUM> may control the first and second coupling devices <NUM>, <NUM> to adjust or modulate the torque that is transmitted from the spools <NUM>, <NUM> to the output 60C of the transmission <NUM>. This may include controlling a dimension of the gaps, and hence a thickness of the films 61C, 62C by powering the actuators 61D, 62D.

With reference to <FIG>, an example of a computing device <NUM> is illustrated. For simplicity only one computing device <NUM> is shown but the system may include more computing devices <NUM> operable to exchange data. The computing devices <NUM> may be the same or different types of devices. The controller <NUM> may be implemented with one or more computing devices <NUM>. Note that the controller <NUM> can be implemented as part of a full-authority digital engine controls (FADEC) or other similar device, including electronic engine control (EEC), engine control unit (ECU), electronic propeller control, propeller control unit, and the like. In some embodiments, the controller <NUM> is implemented as a Flight Data Acquisition Storage and Transmission system, such as a FAST™ system. The controller <NUM> may be implemented in part in the FAST™ system and in part in the EEC. Other embodiments may also apply.

The memory <NUM> may include a suitable combination of any type of computer memory that is located either internally or externally to device, for example random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

The methods and systems for driving an electrical machine described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device <NUM>. Alternatively, the methods and systems for driving an electrical machine may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems for driving an electrical machine may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods and systems for driving an electrical machine may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit <NUM> of the computing device <NUM>, to operate in a specific and predefined manner to perform the functions described herein, for example those described in the method <NUM>.

Claim 1:
An aircraft power plant (<NUM>) comprising:
a high-pressure spool (<NUM>) including a high-pressure compressor (25A), a high-pressure turbine (25B), and a high-pressure shaft (25C) drivingly engaging the high-pressure turbine (25B) to the high-pressure compressor (25A);
a low-pressure spool (<NUM>) including a low-pressure compressor (24A), a low-pressure turbine (24B), and a low-pressure shaft (24C) drivingly engaging the low-pressure turbine (24B) to the low-pressure compressor (24A);
an electrical machine (<NUM>) operable as a generator; and
a transmission (<NUM>) having a first input (60A) drivingly engaged by the high-pressure shaft (25C), a second input (60B) drivingly engaged by the low-pressure shaft (24C), and an output (60C) drivingly engaging the electrical machine (<NUM>), the transmission (<NUM>) having a coupling system selectively interconnecting the output (60C) with one of:
the first input (60A), with the second input (60B) disconnected from the output (60C);
the second input (60B), with the first input (60A) disconnected from the output (60C); and
both of the first input (60A) and the second input (60B).