Patent Description:
Through-flow gas turbine engines draw air into a central core of the engine near a forward portion of the engine, and exhaust combustion gases from an aft portion of the engine. Gases therefore flow through the core from the front to the rear of the engine.

In some conventional through-flow engines, air is drawn into the core and compressed with a compressor stage driven by a first turbine stage. A second turbine stage, separate from the first turbine stage and rotating a separate shaft, provides the rotational output of the engine.

<CIT> discloses a hybrid-electric drive system. <CIT> discloses a multi-spool gas turbine engine architecture. <CIT> discloses an integral offset oil tank for an inline accessory gearbox. <CIT> discloses an accessory gearbox for a gas turbine engine.

<CIT> discloses a turbomachine with alternatingly spaced turbine rotor blades.

According to the present invention, there is provided a through-flow gas turbine engine for an aircraft, as claimed in claim <NUM>.

In an embodiment of the above through-flow gas turbine engine, one of the spools comprises a low pressure compressor (LPC), the other of the electric motor and the electric generator disposed axially between the LPC and the RGB.

In an embodiment of either of the above, the electric motor and the electric generator are axially spaced apart from the AGB.

An embodiment of any of the above, additionally comprising an electrical power source configured to provide electrical power to the electric motor, the electric generator configured to provide electrical power to the electrical power source.

In an embodiment of any of the above, the core comprises an output shaft drivingly engaged to the rotatable load via the RGB, and the electric motor is drivingly engaged to the RGB, the electric motor and the output shaft operable to concurrently drive the rotatable load.

An embodiment of any of the above, additionally comprising an aft gear train, the electric motor or the electric generator drivingly engaged to the core via the aft gear train.

In an embodiment of any of the above, the electric generator is disposed axially between the outlet and the AGB and the electric motor is disposed axially between the inlet and the RGB, or the electric generator is disposed axially between the inlet and the RGB and the electric motor is disposed axially between the outlet and the AGB.

An embodiment of any of the above, additionally comprising a forward gear train, the electric motor drivingly engaged to the RGB via the forward gear train. In an embodiment of any of the above, the forward gear train is disposed axially between the electric motor and the RGB.

In an embodiment of any of the above, the forward gear train is operable to selectively drivingly engage the electric motor to the RGB.

According to another aspect of the present invention, there is provided a method of modifying a through-flow gas turbine engine for an aircraft, as claimed in claim <NUM>.

<FIG> illustrates a gas turbine engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication an air inlet <NUM>, a compressor section <NUM> for pressurizing the air from the air inlet <NUM>, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, a turbine section <NUM> for extracting energy from the combustion gases, an exhaust outlet <NUM> through which the combustion gases exit the gas turbine engine <NUM>. The gas turbine engine <NUM> has a longitudinal center axis <NUM>. The engine <NUM> in <FIG> is a turboprop engine <NUM> and includes a propeller <NUM> which provides thrust for flight and taxiing. The propeller <NUM> includes propeller blades 16B which rotate about the center axis <NUM> to provide thrust.

The gas turbine engine <NUM> (sometimes referred to herein simply as "engine <NUM>") has a central core <NUM> through which gases flow and which includes most of the turbomachinery of the engine <NUM>. The engine <NUM> is a "through-flow" engine <NUM> because gases flow through the core <NUM> from the air inlet <NUM> at a forward or front portion of the engine <NUM>, to the exhaust outlet <NUM> at an aft or rear portion of the engine <NUM>. This is in contrast to "reverse-flow" gas turbine engines in which gases flow through the core of the engine from an aft portion to a front portion. The direction of the flow of gases through the core <NUM> of the engine <NUM> is shown in <FIG> with arrows F. The direction of the flow of gases through the core <NUM> of the engine <NUM> can be better appreciated by considering that the gases flow through the core <NUM> opposite to a direction of travel D along which the engine <NUM> moves during flight. Stated differently, gases flow through the engine <NUM> from a front end of the core <NUM> towards a rear end of the core <NUM>.

It will thus be appreciated that the expressions "forward" and "aft" used herein may refer to the relative disposition of components of the engine <NUM>, in correspondence to the "forward" and "aft" directions of the engine <NUM> and aircraft including the engine <NUM> as defined with respect to the direction of travel D. In the embodiment shown, a component of the engine <NUM> that is "forward" or "upstream" of another component is arranged within the engine <NUM> such that it is located closer to the propeller <NUM>. Similarly, a component of the engine <NUM> that is "aft" or "downstream" of another component is arranged within the engine <NUM> such that it is further away from the propeller <NUM>.

Still referring to <FIG>, the core <NUM> of the engine <NUM> has multiple spools <NUM>. One or more of the spools <NUM> rotate about the center axis <NUM> to perform compression to pressurize the air received through the air inlet <NUM>, and to extract energy from the combustion gases before they exit the core <NUM> via the exhaust outlet <NUM> at an aft end of the core <NUM>. The core <NUM> may include other components as well, including, but not limited to, gearboxes, tower shafts, and bleed air outlets.

A first spool 20A includes at least one component to extract energy from the combustion gases that is part of the turbine section <NUM>. More particularly, the first spool 20A has a low pressure turbine <NUM> which extracts energy from the combustion gases. In <FIG>, the first spool 20A is free of a compressor component for pressurizing air from the air inlet <NUM>.

Still referring to <FIG>, the engine <NUM> includes a second spool <NUM> with at least one component to compress the air that is part of the compressor section <NUM>, and at least one component to extract energy from the combustion gases that is part of the turbine section <NUM>. The second spool <NUM> is also disposed along the center axis <NUM> and includes a high pressure turbine <NUM> drivingly engaged (e.g. directly connected) to a high pressure compressor <NUM> by a high pressure shaft <NUM>. The low pressure turbine <NUM> (sometimes referred to herein simply as "LPT <NUM>") in <FIG> is separated mechanically from a low pressure compressor <NUM> (sometimes referred to herein simply as "LPC (<NUM>) <NUM>"). The LPC <NUM> is part of the second spool <NUM> and is drivingly engaged to the high pressure turbine <NUM> and to the high pressure compressor <NUM> by the high pressure shaft <NUM>. Both the LPT <NUM> and the LPC <NUM> are disposed along the center axis <NUM>. In the depicted embodiment, both the LPT <NUM> and the LPC <NUM> are axial rotatable components having an axis of rotation that is coaxial with the center axis <NUM>. They can each include one or more stages of rotors and stators, depending upon the desired engine thermodynamic cycle, for example. Similarly to the LPT <NUM> and the LPC <NUM>, the high pressure turbine <NUM> (sometimes referred to herein simply as "HPT <NUM>") and the high pressure compressor <NUM> (sometimes referred to herein simply as "HPC <NUM>") can include axial rotary components. They can also each include one or more stages of rotors and stators, depending upon the desired engine thermodynamic cycle, for example. In the depicted embodiment, the HPC <NUM> includes a centrifugal compressor 42A or impeller which is driven by the HPT <NUM>. During operation of the engine <NUM>, the HPT <NUM> drives the HPC <NUM>.

The HPT <NUM> is forward of the LPT <NUM>, and adjacent to the combustor <NUM>. The HPC <NUM> is forward of the combustor <NUM>, and aft of the LPC <NUM>. The HPT <NUM> is aft of the HPC <NUM>. The HPC <NUM> is disposed axially between the LPC <NUM> and the HPT <NUM>, and the HPT <NUM> is disposed axially between the HPC <NUM> and the LPT <NUM>. The HPT <NUM> and the LPT <NUM> are in fluid communication, such that the combustion gases from the combustor <NUM> flow through the HPT <NUM> and then through the LPT <NUM>. From this arrangement of the HPT <NUM> and the HPC <NUM>, it can be appreciated that during operation of the engine <NUM>, the LPC <NUM> feeds pressurized air to the HPC <NUM>. Therefore, the pressurized air flow produced by the LPC <NUM> is provided to the HPC <NUM>. In <FIG>, the HPC <NUM> is mechanically coupled to the LPC <NUM> such that HPT <NUM> performs all of the compression work.

The LPT <NUM> is aft of the LPC <NUM>. The LPT <NUM> is forward of the exhaust outlet <NUM>. The LPC <NUM> is aft of the air inlet <NUM> and in fluid communication therewith. The LPC <NUM> is closer to, or at, a forward end of the core <NUM>. The LPC <NUM> is disposed between the air inlet <NUM> and the LPT <NUM> along a direction parallel to the center axis <NUM>. This arrangement of the LPT <NUM> and the LPC <NUM> provides for a through-flow engine <NUM> that has one or more low pressure compressors located at a front of the engine <NUM> which are driven by one or more rearwardly-positioned turbines. Still referring to <FIG>, the core <NUM> and the first spool <NUM> includes an output drive shaft <NUM>. The drive shaft <NUM>, sometimes also referred to herein as the "power turbine" or "PT" shaft <NUM>, extends forwardly from the LPT <NUM> and is drivingly engaged thereto. In <FIG>, the drive shaft <NUM> is coaxial with the center axis <NUM> and with the high pressure shaft <NUM>. The drive shaft <NUM> is concentric with the high pressure shaft <NUM> and is disposed within the high pressure shaft <NUM> along some of the length of the drive shaft <NUM>.

In light of the preceding, it can be appreciated that the LPT <NUM> is the "low pressure" turbine section when compared to the HPT <NUM>, which is sometimes referred to as the "gas generator". The LPT <NUM> is sometimes referred to as a "power turbine". The turbine rotors of the HPT <NUM> spin at a higher rotational speed than the turbine rotors of the LPT <NUM> given the closer proximity of the HPT <NUM> to the outlet of the combustor <NUM>. The engine <NUM> shown in <FIG> is thus a "two-spool" engine <NUM>.

The HPT <NUM> and the HPC <NUM> can have any suitable mechanical arrangement to achieve the above-described functionality. For example, and as shown in <FIG>, the second spool <NUM> includes the high pressure shaft <NUM> extending between the HPC <NUM> and the HPT <NUM>. The high pressure shaft <NUM> is coaxial with, and drivingly engaged to, the LPC <NUM> such that the high pressure shaft <NUM> drives the LPC <NUM>.

A rotatable load, which in the embodiment shown includes the propeller <NUM>, is mountable to the engine <NUM>, and when mounted, is drivingly engaged (e.g. directly or indirectly connected) to the LPT <NUM>, and is located forward of the LPT <NUM>. In such a configuration, during operation of the engine <NUM>, the LPT <NUM> drives the rotatable load such that a rotational drive produced by the LPT <NUM> is transferred to the rotatable load. The rotatable load can therefore be any suitable component, or any combination of suitable components, that is capable of receiving the rotational drive from the LPT <NUM>. The rotatable load may be part of the engine <NUM>, or a component separate from the engine <NUM> and mechanically linked thereto such as a helicopter rotor.

In the embodiment shown, a reduction gearbox <NUM> (sometimes referred to herein simply as "RGB <NUM>") is drivingly engaged to the core <NUM> to be driven by one or more components thereof. In <FIG>, the RGB <NUM> is disposed axially between the core <NUM> and the propeller <NUM>. In <FIG>, the RGB <NUM> is disposed axially between the LPC <NUM> and the propeller <NUM>. In an alternate embodiment, the RGB <NUM> may be part of the core <NUM>. In <FIG>, the RGB <NUM> is mechanically coupled to a front end of the drive shaft <NUM>, which extends between the RGB <NUM> and the LPT <NUM>. The output drive shaft <NUM> of the core <NUM> is thus drivingly connected to the propeller <NUM> via the RGB <NUM>. The RGB <NUM> processes and outputs the rotational drive transferred thereto from the LPT <NUM> via the drive shaft <NUM> through known gear reduction techniques. The RGB <NUM> allows for the propeller <NUM> to be driven at its optimal rotational speed, which may be different from the rotational speed of the LPT <NUM>.

The propeller <NUM> is mechanically coupled to the output of the RGB <NUM> via a propeller shaft <NUM>. The output of the RGB <NUM> is a gear, shaft, spline, or other rotating mechanical component. The propeller shaft <NUM> allows the rotational drive outputted by the RGB <NUM> during operation of the engine <NUM> to be transferred to the propeller <NUM> to provide propulsion during flight.

Still referring to <FIG>, the engine <NUM> also includes an accessory gearbox <NUM>. The accessory gearbox <NUM> (sometimes referred to herein simply as "AGB <NUM>") receives a rotational output and in turn drives accessories (e.g. fuel pump, starter-generator, oil pump, scavenge pump, etc.) that contribute to the functionality of the engine <NUM>. The AGB <NUM> can be designed with side-facing accessories, top-facing accessories, or rear-facing accessories depending on the installation needs. The AGB <NUM> is aft of the core <NUM>. The AGB <NUM> is aft of the exhaust outlet <NUM>. The AGB <NUM> is aft of the LPT <NUM>. During operation of the engine <NUM>, the drive shaft <NUM> or another shaft coupled to the drive shaft <NUM>, transmits a rotational drive of the LPT <NUM> to the AGB <NUM> which in turn drives the accessories of the AGB <NUM>. In an alternate possible configuration of the engine <NUM>, an example of which is shown below, the engine <NUM> is free of an AGB <NUM>. The AGB <NUM> can be arranged relative to the core <NUM> of the engine <NUM> differently than as shown in <FIG>. For example, the AGB <NUM> may be mounted on the side of the engine <NUM>, and forward of the exhaust outlet <NUM>. The circumferential angular position of the AGB <NUM> may be selected to suit specific installation needs. Other positions and arrangements for the AGB <NUM> are thus possible.

Still referring to <FIG>, the engine <NUM> has an electric motor <NUM>. The electric motor <NUM> is drivingly engaged to the propeller <NUM> or to some component thereof to providing a rotational output to the propeller <NUM> to rotate the propeller blades 16B and generate thrust during any suitable aircraft flight condition. The electric motor <NUM> is provided with an electrical input such as electrical power and generates a mechanical, rotational output to drive the propeller <NUM>. In <FIG>, the electric motor <NUM> is provided only with an electrical input and is not also provided with a mechanical input. The output of the electric motor <NUM> is coupled, directly or indirectly, only to the propeller <NUM> or components that drive the propeller <NUM>, and is free of mechanical connection to another component of the engine <NUM>. For example, in <FIG>, the output of the electric motor <NUM> is coupled to the RGB <NUM>, which is itself coupled to the propeller shaft <NUM> of the propeller <NUM>.

The electric motor <NUM> may have any suitable structure or component to achieve the functionality ascribed to it herein. The electric motor <NUM> may be selected to be sufficiently powerful to drive the propeller <NUM> either without using fuel in the engine <NUM>, or in conjunction with a reduced amount of fuel being used in the core <NUM> during at least one mode of operation of the engine <NUM>. Electricity for driving electric motor <NUM> may be supplied by an electric power source <NUM> under the control of a suitable controller <NUM> such as an EEC (Electronic Engine Controller) or FADEC (Full Authority Digital Engine Control). The electric power source <NUM> may, for example, include one or more batteries 62A, an auxiliary power unit (APU) and/or an electric generator from another engine of the same aircraft onto which the engine <NUM> is mounted. The controller <NUM> may be configured to control the operation of the electric motor <NUM> by providing suitable control signals to the electric motor <NUM> and/or providing suitable conditioning of the electric power supplied to the electric motor <NUM> by the electric power source <NUM>. The controller <NUM> may actuate the amount of electric power supplied to the electric motor <NUM> in response to control signals it receives, such as for example, commands sent via a control interface (e.g., panel) from a pilot of an aircraft to which engine <NUM> is mounted. The controller <NUM> and the electric power source <NUM> may be configured to supply enough electric power to the electric motor <NUM> in order to produce some or all of the torque required to rotate the propeller <NUM> during at least one mode of operation of the aircraft.

The electric motor <NUM> may comprise one or more rotors and one or more respective stators. In some embodiments, the plurality of rotor/stator pairs may be angularly or circumferentially distributed about a shaft axis of rotation. One or more of rotors may have a respective rotor axis of rotation that is radially offset from a center axis of the electric motor <NUM>. In some embodiments, each rotor axis may be radially offset from the center axis at a substantially uniform offset distance. Each rotor may be drivingly engaged (e.g., coupled via a shaft) to a respective drive gear for transferring motive power from the rotors to the propeller <NUM>. The electric motor <NUM> may be drivingly engaged to transmit and/or receive motive power to/from the propeller <NUM> in any suitable manner. In some embodiments, the electric motor <NUM> may be drivingly engaged to the propeller <NUM> via the drive gears drivingly engaged to a common gear, which is in turn drivingly engaged with the RGB <NUM> via suitable meshed gearing. The structure and principle of operation of possible configurations for the electric motor <NUM> are described in <CIT> and in <CIT>, both of which are assigned to Pratt & Whitney Canada Corp. The electric motor <NUM> may be "built-in" into the engine <NUM>, such that the electric motor <NUM> has all of its components assembled together to provide a single output to the propeller <NUM>. For example, and as shown in <FIG>, the electric motor <NUM> and its components may be housed in an annular electric motor housing <NUM> which is attached to any suitable fixed structure, such as bearings or a portion of the engine casing. The electric motor <NUM> may therefore be relatively easily inserted and mounted within the engine <NUM>. Accordingly, the electric motor <NUM> and its physical integration within the engine <NUM> may, in some embodiments, allow for modifying an existing through-flow, multiple-spool engine <NUM> to be provided with the electric motor <NUM>.

Referring to <FIG>, the engine <NUM> has an electric generator <NUM>. During operation, the electric generator <NUM> converts the mechanical output of the core <NUM> into electrical power that is supplied to the electric motor <NUM>. In <FIG>, the electric generator <NUM> is mechanically driven by the core <NUM>. The electric generator <NUM> is configured to provide electrical power to the electric motor <NUM>. In <FIG>, the electric generator <NUM> is a separate component from the electric motor <NUM>. One possible configuration of this separateness may include the electric generator <NUM> and the electric motor <NUM> being enclosed in separate containers with wiring extending between them to supply electrical power to the electric motor <NUM>. Another configuration of this separateness is shown in <FIG>, where the electric motor <NUM> and the electric generator <NUM> are physically separate features that are axially spaced apart from each other along the center axis <NUM>. In <FIG>, the electric generator <NUM> during operation supplies electrical power only to the electric motor <NUM>.

The electric generator <NUM> may be "built-in" into the engine <NUM>, such that the electric generator <NUM> has all of its components assembled together to provide a single, portable structure. For example, and as shown in <FIG>, the electric generator <NUM> and its components may be housed in an annular electric generator housing <NUM> which is attached to the bearings supporting the drive shaft <NUM> or the AGB <NUM>. The electric generator <NUM> may therefore be relatively easily inserted and mounted within the engine <NUM>. Accordingly, the electric generator <NUM> and its physical integration within the engine <NUM> may, in some embodiments, allow for modifying an existing through-flow, multiple-spool engine <NUM> to be provided with the electric generator <NUM>.

Referring to <FIG>, the output drive shaft <NUM> has a drive shaft section 24A which is a segment of the output drive shaft <NUM> or a separate shaft coupled thereto to be rotated by the output drive shaft <NUM>. The drive shaft section 24A transmits the rotational output of the LPT <NUM>. The drive shaft section 24A, which is itself driven by the drive shaft <NUM> of the LPT <NUM>, is drivingly engaged with the electric generator <NUM> to provide the motive power thereto. The "power turbine" shaft <NUM> in <FIG> thus provides some or all of the mechanical input to the electric generator <NUM>. In an alternate embodiment, the electric generator <NUM> is driven by another component, such as the HPT <NUM>, to be used as an electrical power source for the electric motor <NUM>.

In <FIG>, the electric power source <NUM> is configured to provide electrical power to the electric motor <NUM>, and the electrical generator <NUM> is configured to provide electrical power to the electric power source <NUM>. The electric motor <NUM> is thus supplied with electrical power from another electric power source <NUM>, such as the batteries 62A, and the electric generator <NUM> is connected to the batteries 62A. Thus, in <FIG>, the electric generator <NUM> supplies electrical power to the electric motor <NUM> indirectly via the one or more batteries 62A. Wiring from the controller <NUM> to the electric motor <NUM>, to the batteries 62A, and to the electric generator <NUM> coordinates the draw or supply of electrical power. The wiring may be routed outside the structure of the engine <NUM>. The electric generator <NUM> may be located elsewhere in the engine <NUM> in alternate configurations. In an alternate embodiment, the electric generator <NUM> provides electrical power directly to the electric motor <NUM>, such as via wiring <NUM>, and to the batteries 62A simultaneously. The electric generator <NUM> and the batteries 62A may thus be used to power the electric motor <NUM> together, or individually. The electric generator <NUM> may thus charge the batteries 62A and power the electric motor <NUM> at the same time, and the electric generator <NUM> may temporarily cease supplying the electric motor <NUM> with electrical power when the electric motor <NUM> is supplied with electrical power by the batteries 62A. The controller <NUM> may provide full digital envelope protection, to optimize "hybrid" operation of the engine <NUM> through all phases of flight. The controller <NUM> may be configured to control the operation of the electric motor <NUM> by optimizing the hybrid engine functionality either via the batteries 62A or directly from the electric generator <NUM>.

Referring to <FIG>, the starter-generator of, or in, the AGB <NUM> is a separate component from the electric motor <NUM> and from the electric generator <NUM> described above. The electric motor <NUM> and the electric generator <NUM> are axially spaced apart from the AGB <NUM>. The electric motor <NUM> and the electric generator <NUM> are separate from the AGB <NUM> and positioned outside of the casing of the AGB <NUM>. The starter-generator of the AGB <NUM> is spaced apart from the electric motor <NUM> and from the electric generator <NUM>, and is housed in a separate enclosure. The starter-generator of the AGB <NUM> may be configured as, or include, an electric starter/generator drivingly engaged to a drive shaft of the core <NUM>, to start rotation of the rotatable components of the core <NUM>, such as the compressor section <NUM>. In certain engine operating conditions, the drive shaft <NUM> of the core <NUM> may provide rotational drive to the starter-generator of the AGB <NUM> to generate electrical power for various functions unrelated to the operation of the engine <NUM>. This functionality of the starter-generator of the AGB <NUM> is thus separate from that of the electric motor <NUM> which is used to provide rotational drive only to the propeller <NUM>. Furthermore, although the electric generator <NUM> may also be driven by the core <NUM>, the electrical power thus generated by the electric generator <NUM> is supplied only to the electric motor <NUM> directly or via the batteries 62A. Similarly, although the electric generator <NUM> may be housed partially or completely within the AGB <NUM>, the electrical power generated by the electric generator <NUM> is supplied only to the electric motor <NUM> directly or via the batteries 62A.

Referring to <FIG>, one of the electric motor <NUM> and the electric generator <NUM> is disposed axially between the RGB <NUM> and the air inlet <NUM>, and the other of the electric motor <NUM> and the electric generator <NUM> is disposed axially between the exhaust outlet <NUM> and the AGB <NUM>. One of the electric motor <NUM> and the electric generator <NUM> is axially downstream of the exhaust outlet <NUM> and axially upstream of the AGB <NUM>, and the other of the electric motor <NUM> and the electric generator <NUM> is axially downstream of the RGB <NUM> and axially upstream of the air inlet <NUM>. The expression "disposed axially" refers to the axial extent of the electric motor <NUM> and the electric generator <NUM> fitting within axially-extending spaces (i.e. spaces defined with a distance vector along the center axis <NUM>) between the air inlet <NUM> and RGB <NUM> and between the exhaust outlet <NUM> and the AGB <NUM>. In <FIG>, the entire axial extent of the electric motor <NUM> and of the electric generator <NUM> fits within these axially-extending spaces, such that there is no axial overlap between these electric features (electric motor <NUM> and electric generator <NUM>) and the components they are axially positioned between. The engine <NUM> is thus a through-flow, multi-spool gas turbine engine <NUM> that incorporates an electric motor <NUM> and an electric generator <NUM>. This "hybrid" architecture allows the engine <NUM> to generator rotational output from the combustion of fuel in the combustor <NUM> and from the use of electric power supplied by the electric generator <NUM> to the electric motor <NUM>.

Different configurations of this hybrid architecture of the engine <NUM> are possible, and some are described in greater detail below.

Referring to <FIG>, the electric feature (the electric motor <NUM> or the electric generator <NUM>) disposed axially between the RGB <NUM> and the air inlet <NUM> is also disposed axially between the RGB <NUM> and the LPC <NUM>. The electric feature (the electric motor <NUM> or the electric generator <NUM>) is axially downstream of the RGB <NUM> and axially upstream of the LPC <NUM>. In the configuration shown in <FIG>, the LPC <NUM> is the most forward or most upstream compressor component of the compressor section <NUM>. Referring to <FIG>, the air inlet <NUM> has an upstream opening 11A through which air enters the air inlet <NUM>. The upstream opening 11A is forward of the LPC <NUM> and aft of the electric feature (the electric motor <NUM> or the electric generator <NUM>). The upstream opening 11A is axially between the LPC <NUM> and the electric feature (the electric motor <NUM> or the electric generator <NUM>).

Referring to <FIG>, the electric motor <NUM> is disposed axially between the RGB <NUM> and the LPC <NUM> and the air inlet <NUM>. Positioning the electric motor <NUM> between the RGB <NUM> and the LPC <NUM> places the electric motor <NUM> in a colder part of the engine <NUM>, which may contribute to improving the working life of the electric motor <NUM>. Positioning the electric motor <NUM> between the RGB <NUM> and the LPC <NUM> may facilitate servicing or repair of the electric motor <NUM> because the only components that may need to be removed to access the electric motor <NUM> are the propeller <NUM> and the RGB <NUM>. Positioning the electric motor <NUM> between the RGB <NUM> and the LPC <NUM> may allow the electric motor <NUM> to be provided as a stand-alone or self-sufficient module which is free of any structural attachment to the casing of the engine <NUM>. The electric generator <NUM> in <FIG> is disposed axially between the exhaust outlet <NUM> and the AGB <NUM>. The electric generator <NUM> in <FIG> is driven by the LPT <NUM>. This positioning of the electric generator <NUM> thus brings it physically closer to the LPT <NUM>, thereby facilitating the mechanical connection between the two components via the drive shaft section 24A of the drive shaft <NUM>. The engine <NUM> shown in <FIG> is thus a through-flow, multi-spool engine with an electric motor <NUM> built into the engine <NUM> and disposed in between the RGB <NUM> and the LPC <NUM>, and an electric generator <NUM> built into the engine <NUM> and disposed between the exhaust outlet <NUM> and the AGB <NUM>.

The positions of the electric motor <NUM> and the electric generator <NUM> may be reversed. <FIG> shows another possible architecture of the engine <NUM> in which the positions of the electric features (the electric motor <NUM> or the electric generator <NUM>) are interchanged. In this architecture of the engine <NUM>, the electric generator is designated with the reference number <NUM>', and is disposed axially between the air inlet <NUM> and the RGB <NUM>. In this architecture of the engine <NUM>, the electric motor is designated with the reference number <NUM>', and is disposed axially between the exhaust outlet <NUM> and the AGB <NUM>. In this architecture of the engine <NUM>, the output drive shaft <NUM>, which is itself driven by the LPT <NUM>, is drivingly engaged with the electric generator <NUM>' to provide the motive power thereto. In this architecture of the engine <NUM>, the electric motor <NUM>' provides its rotational output to the drive shaft <NUM> or to the drive shaft section 24A. The engine <NUM> may thus be a through-flow, multi-spool engine with an electric generator <NUM>' built into the engine <NUM> and disposed in between the RGB <NUM> and the LPC <NUM>, and an electric motor <NUM>' built into the engine <NUM> and disposed between the exhaust outlet <NUM> and the AGB <NUM>.

In <FIG>, the electric motor <NUM> and the electric generator <NUM> are coaxial with the spools <NUM> and with the center axis <NUM>. In an alternate embodiment, the electric motor <NUM> and/or the electric generator <NUM> may have components, such as rotor or internal gears, which rotate about an axis that is transverse to the center axis <NUM>, such that the electric motor <NUM> and/or the electric generator <NUM> is not coaxial with the spools <NUM> or the center axis <NUM>. The electric motor <NUM> is mounted at a location within the engine <NUM> that is spaced a distance measured in a radial direction from the center axis <NUM>, from the drive shaft <NUM> of the LPT <NUM>, and from the propeller shaft <NUM>. In <FIG>, a component of the electric motor <NUM>, such as its rotor and the axis about which the rotor rotates, is spaced a distance measured in a radial direction from the center axis <NUM>, from the drive shaft <NUM> of the LPT <NUM>, and from the propeller shaft <NUM>. The electric motor <NUM> is therefore radially offset from the propeller <NUM> or the drive shaft <NUM>. One or more components of the electric generator <NUM> may also be radially offset from the propeller <NUM> or the drive shaft <NUM> in the same manner as the electric motor <NUM>.

Referring to <FIG>, the electric motor <NUM> is indirectly mounted to the propeller shaft <NUM>. The engine <NUM> includes a forward gear train <NUM> drivingly engaged to both the output of the electric motor <NUM> and the RGB <NUM>, so as to drivingly engage the electric motor <NUM> to the RGB <NUM>. The electric motor <NUM> is thus indirectly coupled to the propeller attachment via the forward gear train <NUM>. The forward gear train <NUM> has any suitable arrangement of gearing and ratios to allow an output from the electric motor <NUM> to be supplied to the RGB <NUM>. In <FIG>, the electric motor <NUM> has a motor output shaft <NUM> which meshes with, and drives, an input gear 66A of the forward gear train <NUM>. An output gear 66B of the forward gear train <NUM> engages and drives a gear 35A of the RGB <NUM>, to transfer the rotational drive from the motor output shaft <NUM> to the RGB <NUM> and ultimately to the propeller <NUM>. In <FIG>, the forward gear train <NUM> modifies the speed and torque of the output of the electric motor <NUM> as desired, to supply the modified output directly to the RGB <NUM>. The forward gear train <NUM> is disposed axially between the electric motor <NUM> and the RGB <NUM>. The forward gear train <NUM> is disposed axially between the electric motor <NUM> and the propeller <NUM>. The forward gear train <NUM> is enclosed or housed outside of the electric motor housing <NUM>. In <FIG>, the forward gear train <NUM> is a separate component from the electric motor <NUM>, and is separate from the internal gearing of the electric motor <NUM>. In embodiments, one of which is described in greater detail below, the electric motor <NUM> is coupled directly to the desired component of the propeller <NUM>, and there is no forward gear train <NUM> provided between the electric motor <NUM> and the propeller <NUM>.

In <FIG>, the forward gear train <NUM> is operable to selectively drivingly engage the electric motor <NUM> to the RGB <NUM>. The forward gear train <NUM> allows the electric motor <NUM> to engage the RGB <NUM> to transfer a rotational drive thereto, and also allows the electric motor <NUM> to disengage from the RGB <NUM> such that the output of the electric motor <NUM> is not supplied to the propeller <NUM>. This selective engagement may be achieved using any suitable mechanism, such as a clutch. This selective engagement of the electric motor <NUM> via the forward gear train <NUM> may allow for the electric motor <NUM> to provide the sole rotational drive to the propeller <NUM> via the RGB <NUM>, to provide rotational drive concurrently with the drive shaft <NUM> of the core <NUM>, or to provide no rotational drive to the RGB <NUM> (or to the propeller <NUM>) at all such that the RGB <NUM> is driven entirely by the output of the core <NUM>. This selective engagement of the electric motor <NUM> may be used, for example, to allow only the electric motor <NUM> to provide rotational drive to the propeller <NUM> via the RGB <NUM> during a cruise, taxi, or descent flight condition. This selective engagement of the electric motor <NUM> may be used, for example, to allow both the electric motor <NUM> and the core <NUM> to provide rotational drive to the propeller <NUM> via the RGB <NUM> during a take-off flight condition, such that the electric motor <NUM> and the output shaft of the core <NUM> (i.e. the drive shaft <NUM> of the LPT <NUM>) are operable to concurrently drive the propeller <NUM> via the RGB <NUM>. The engine <NUM> may therefore have a dual connection to the RGB <NUM>, and thus to the propeller <NUM> - one output connection from the electric motor <NUM> and the second output connection from the core <NUM> and its LPT <NUM>.

Referring to <FIG>, the engine <NUM> also has an aft gear train <NUM> drivingly engaged to the drive shaft section 24A so as to receive a rotatable input from the drive shaft section 24A, and drivingly engaged to an input shaft <NUM> of the electric generator <NUM>. The electric generator <NUM> is thus indirectly coupled to the LPT <NUM> via the aft gear train <NUM> to receive motive input directly from the aft gear train <NUM>. The aft gear train <NUM> has any suitable arrangement of gearing and ratios to allow an output from the LPT <NUM> to be supplied to the electric generator <NUM>. Referring to <FIG>, the aft gear train <NUM> is drivingly engaged to an input of the AGB <NUM>. In <FIG>, the aft gear train <NUM> is disposed axially between the electric generator <NUM> and the AGB <NUM>. In <FIG>, the aft gear train <NUM> is disposed axially between the LPT <NUM> and the electric generator <NUM>. In <FIG>, the aft gear train <NUM> is disposed axially between the exhaust outlet <NUM> and the electric generator <NUM>. In the architecture of the engine <NUM> where the electric motor <NUM>' is disposed axially between the exhaust outlet <NUM> and the AGB <NUM>, the aft gear train <NUM> is drivingly engaged to the drive shaft section 24A and to the electric motor <NUM>', to transmit the rotatable output of the electric motor <NUM>' to the drive shaft section 24A. Features shown in <FIG> which are not provided with reference numbers and which are similar to the features shown in other figures bear the same reference numbers as the features shown in other figures, and the description of these features herein applies mutatis mutandis to the features shown in <FIG>.

<FIG> shows a configuration of the engine <NUM> where the electric motor <NUM> is mounted directly to the rotatable load, i.e. the propeller <NUM>, whereby the configuration shown in <FIG> is not covered by the claims. Features shown in <FIG> which are not provided with reference numbers and which are similar to the features shown in other figures bear the same reference numbers as the features shown in other figures, and the description of these features herein applies mutatis mutandis to the features shown in <FIG>. In <FIG>, the electric motor <NUM> is coupled directly to the propeller shaft <NUM> of the propeller <NUM>, and there is no forward gear train <NUM> or RGB <NUM> provided between the electric motor <NUM> and the propeller <NUM>. The electric motor <NUM> is thus drivingly engaged only to the propeller <NUM>. This direct configuration may take different forms. In <FIG>, the motor output shaft <NUM> of the electric motor <NUM> is drivingly engaged to the propeller shaft <NUM> to provide the rotational output of the electric motor <NUM> to the propeller <NUM>. The motor output shaft <NUM> is supported by bearings 68A at an aft end of the motor output shaft <NUM>, and is supported via the propeller shaft <NUM> via its bearings 35AB. In <FIG>, the propeller shaft <NUM> and the motor output shaft <NUM> are integral with one another. In <FIG>, the propeller shaft <NUM> and the motor output shaft <NUM> are one integral shaft with a diameter that varies over its axial length. This direct configuration of the electric motor <NUM> and the propeller <NUM> may allow for the rotational output speed of the electric motor <NUM> to be selected to exactly match the desired rotational speed of the propeller <NUM> at a specific flight condition, such as cruise or take-off. Therefore, the electric motor <NUM> may be designed or selected so that its output speed is the same or similar to the rotating speed of the propeller <NUM>. This is in contrast to the output speed of the drive shaft <NUM> of the LPT <NUM> or "power turbine" which is typically used to drive the propeller <NUM>, but which often rotates at a much higher speed than the propeller <NUM> and thus requires speed reduction via the RGB <NUM>. In <FIG>, the engine <NUM> is a through-flow, multi-spool engine with an electric motor <NUM> having a direct shaft connection with the propeller <NUM>. In <FIG>, the output of the LPT <NUM> is not be used to drive the propeller <NUM>.

<FIG> shows a configuration of the engine <NUM> where the electric motor <NUM> drives the rotatable load, i.e. the propeller <NUM>, via the forward gear train <NUM> and the RGB <NUM>, whereby the configuration shown in <FIG> is not covered by the claims.

Features shown in <FIG> which are not provided with reference numbers and which are similar to the features shown in other figures bear the same reference numbers as the features shown in other figures, and the description of these features herein applies mutatis mutandis to the features shown in <FIG>. In <FIG>, the electric motor <NUM> is coupled indirectly to the propeller shaft <NUM> of the propeller <NUM>, via the forward gear train <NUM> and the RGB <NUM> provided between the electric motor <NUM> and the propeller <NUM>. The motor output shaft <NUM> is supported by bearings 68A at an aft end of the motor output shaft <NUM>. In <FIG>, the output of the LPT <NUM> is not used to drive the propeller <NUM>. The motor output shaft <NUM> is not drivingly engaged to the core <NUM> of the engine <NUM>.

In the architecture of the engine <NUM> shown in <FIG>, the electric motor <NUM> and the electric generator <NUM> are disposed axially adjacent one another, whereby the configuration shown in <FIG> is not covered by the claims.

Features shown in <FIG> which are not provided with reference numbers and which are similar to the features shown in other figures bear the same reference numbers as the features shown in other figures, and the description of these features herein applies mutatis mutandis to the features shown in <FIG>. The axially-adjacent electric motor <NUM> and electric generator <NUM> may be disposed axially between the LPC <NUM> and the RGB <NUM>, or between the exhaust outlet <NUM> and the AGB <NUM>. The electric motor <NUM> and the electric generator <NUM> in <FIG> are separate from each other in the same manner as explained above. In one possible configuration, the electric motor <NUM> is disposed axially between the RGB <NUM> and the electric generator <NUM>, and the electric generator <NUM> is disposed axially between the air inlet <NUM> or LPC <NUM> and the electric motor <NUM>. In another possible configuration also shown in <FIG>, the electric motor <NUM>' and the electric generator <NUM>' are disposed axially between the exhaust outlet <NUM> and the AGB <NUM>. The electric motor <NUM>' is disposed axially between the exhaust outlet <NUM> and the electric generator <NUM>', and the electric generator <NUM>' is disposed axially between the AGB <NUM> and the electric motor <NUM>'. The electric motor <NUM>,<NUM>' and the electric generator <NUM>,<NUM>' are disposed in series or sequentially, and are axially adjacent, or next to, one another. The engine <NUM> disclosed herein may therefore be a through-flow, multi-spool engine <NUM> with a cooperating electric motor <NUM>,<NUM>' and electric generator <NUM>,<NUM>' disposed axially adjacent one another.

<FIG> shows a configuration of the engine <NUM> which has no AGB, whereby this configuration is not covered by the claims. Features shown in <FIG> which are not provided with reference numbers and which are similar to the features shown in other figures bear the same reference numbers as the features shown in other figures, and the description of these features herein applies mutatis mutandis to the features shown in <FIG>. One of the electric motor <NUM> and the electric generator <NUM> is disposed axially between the RGB <NUM> and the air inlet <NUM>, and the other of the electric motor <NUM> and the electric generator <NUM> is disposed axially aft of the exhaust outlet <NUM>. Any accessories of the engine <NUM> may be distributed to suitable locations in and around the engine <NUM>, and they may be driven by the core <NUM> or their own motive devices, such as individual electric motors. The configuration of the engine <NUM> shown in <FIG> therefore has no "mechanical" AGB - i.e. an AGB which receives a mechanical rotational input. In this configuration of the engine <NUM>, the electric generator <NUM> may be used as an engine starter, in addition to its functionality of providing electrical power to the electric motor <NUM>. The engine <NUM> shown in <FIG> is a through-flow, multi-spool engine <NUM> with an electric motor <NUM> or an electric generator <NUM> disposed aft of the exhaust outlet <NUM>, and is free of a mechanical AGB.

Referring to <FIG>, there is disclosed a method of modifying a through-flow gas turbine engine comprising multiple spools <NUM> drivingly engaged to the RGB <NUM>, to the AGB <NUM>, and to the rotatable load. The method includes mounting the electric motor <NUM> within the gas turbine engine <NUM> and drivingly engaging the electric motor <NUM> to the rotatable load. The method includes mounting the electric generator <NUM> within the gas turbine engine <NUM> to provide electrical power to the electric motor <NUM>. The method includes positioning one of the electric motor <NUM>,<NUM>' and the electric generator <NUM>,<NUM>' axially between the exhaust outlet <NUM> and the AGB <NUM>, and positioning the other of the electric motor <NUM>,<NUM>' and the electric generator <NUM>,<NUM>' axially between the air inlet <NUM> and the RGB <NUM>.

Claim 1:
A through-flow gas turbine engine (<NUM>) for an aircraft, comprising:
a core (<NUM>) comprising multiple spools (<NUM>) rotatable about a center axis (<NUM>) of the gas turbine engine (<NUM>), each spool (<NUM>) configured to extract energy from combustion gases, air and combustion gases configured to flow through the core (<NUM>) in an aft direction from an air inlet (<NUM>) at a forward end of the core (<NUM>) to an outlet (<NUM>) at an aft end of the core (<NUM>);
an accessory gearbox (AGB) (<NUM>) drivingly engaged to the core (<NUM>) and disposed aft of the outlet (<NUM>);
a reduction gearbox (RGB) (<NUM>) drivingly engaged to the core (<NUM>) and disposed forward of the inlet (<NUM>), the RGB (<NUM>) having an RGB output to provide rotational output to a rotatable load (<NUM>); and
an electric motor (<NUM>,<NUM>') drivingly engaged to the rotatable load (<NUM>), and an electric generator (<NUM>,<NUM>') configured to provide electrical power to the electric motor (<NUM>,<NUM>'), one of the electric motor (<NUM>,<NUM>') and the electric generator (<NUM>,<NUM>') disposed axially between the outlet (<NUM>) and the AGB (<NUM>) and the other of the electric motor (<NUM>,<NUM>') and the electric generator (<NUM>,<NUM>') disposed axially between the inlet (<NUM>) and the RGB (<NUM>).