Patent Description:
Fuel economy has always been a concern in aircraft engine design, and even more so in an era where reduction of carbon emissions has become a priority. Incorporating a hybrid heat/electric functionality to aircraft engines is a way to further optimize carbon fuel usage, but poses a number of challenges. For instance, in some embodiments, it can be desired to connect an electric machine directly to a low pressure/power shaft of a heat engine core, motivating the positioning of the electric machine in the exhaust/tail cone area of the aircraft engine. The exhaust/tail cone area is an area where temperatures can rise significantly during operation of the aircraft engine, and the electric machine generates temperature of its own during operation. Higher temperatures impose design constraints on the choice of materials, often leading to higher costs, and can also affect performance and durability of components. There thus remained room for improvement.

<CIT> discloses a cooling system in hybrid electric propulsion gas turbine engine.

In a further aspect of the present invention, there is provided a cooling system for an engine as claimed in claim <NUM>.

In another aspect of the present invention, there is provided a gas turbine engine as claimed in claim <NUM>.

In an embodiment, according to either of the above, the coolant fluid is a dielectric material.

In an embodiment, according to any of the above, the gas turbine engine further comprises a bypass duct annularly extending around the passage, the passage extending rearwardly from a fan and around an engine core, the engine core having an exhaust section and at least one rotary shaft disposed along the rotation axis, the electric machine being disposed in the exhaust section and being coupled to the rotary shaft.

In an embodiment, according to any of the above, the gas turbine engine further comprises at least first and second struts radially extending between the engine core and the bypass duct, the first and second conduits running along a respective one of the first and second struts.

In an embodiment, according to any of the above, the gas turbine engine further comprises a power cable electrically coupling the electric machine to an electric device external to the engine core, the power cable running along at least one of the first and second struts and being in thermal communication with a corresponding one of the first and second conduits.

In an embodiment, according to any of the above, the power cable runs along the second conduit and is in thermal communication therewith.

In an embodiment, according to any of the above, the surface cooler and the surface heater extend circumferentially relative to the rotation axis.

In an embodiment, according to any of the above, the surface cooler defines coolant paths laterally opposite to one another relative the first and second conduits, extending from the upper region of the condenser to the lower region of the condenser and extending at least partially circumferentially on respective sides of the surface.

In an embodiment, according to any of the above, the coolant circuit has a pumping device in fluid communication therewith, the pumping device being configured for pumping the coolant fluid in the coolant circuit.

In another aspect of the present invention, there is provided a method of cooling an electric machine as claimed in claim <NUM>.

<FIG> illustrates a turbofan engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases around the engine axis <NUM>, a turbine section <NUM> for extracting energy from the combustion gases, and an exhaust section <NUM> where the hot combustion gases are expelled.

It is noted that the terms "radial", "annular" and "circumferential" used throughout the description and appended claims are defined with respect to the engine axis <NUM>. It is further noted that the terms "upper" and "lower" used throughout the description and appended claims are defined with respect to gravity when the aircraft is in typical cruising conditions.

In this example, the turbofan engine <NUM> has an engine core <NUM> including a two spool arrangement provided by first and second shafts <NUM> and <NUM> that rotate about the engine axis <NUM>. The first shaft <NUM> corresponds to a low pressure spool <NUM>, and the second shaft <NUM> corresponds to a high pressure spool <NUM>. The first shaft <NUM> is coupled to a low pressure compressor section and a low pressure turbine section. The second shaft <NUM> is coupled to a high pressure compressor section and a high pressure turbine section. The shafts <NUM> and <NUM> are supported within a housing <NUM> of the engine core <NUM> for rotation and typically include multiple portions secured to one another, as is known in the art.

As shown, the turbofan engine <NUM> generally has a bypass duct <NUM> forming a bypass passage extending annularly around the engine axis <NUM>. The bypass passage extends rearwardly from the fan <NUM> and around the engine core <NUM> towards the exhaust section <NUM>. The fan <NUM> has multiple blades <NUM> and is typically coupled to the first shaft <NUM>.

As depicted, a nozzle <NUM> is disposed in the exhaust section <NUM> downstream from the low pressure turbine section <NUM>, and a tail cone <NUM> is arranged within the nozzle <NUM>. In this example, an electric machine <NUM> is disposed in the exhaust section <NUM> and coupled to a rotary shaft. The electric machine <NUM> may be directly or indirectly coupled to the rotary shaft. In some embodiments, a clutch can be used in the coupling. In this specific example, the electric machine <NUM> is arranged within the tail cone <NUM> and driven by the first shaft <NUM>. The electric machine <NUM> can provide a hybrid heat/electric functionality to the turbofan engine <NUM>. In a first mode of operation, the electric machine <NUM> can be driven by the first shaft <NUM> to generate electrical power for use by other components of the turbofan engine <NUM> or aircraft. In a second mode of operating, the electric machine <NUM> can draw external electrical power from the remainder of the turbofan engine <NUM> or aircraft to drive the first shaft <NUM> to further propulsion. As the exhaust section <NUM> is an area where temperatures can rise significantly during operation of the turbofan engine <NUM>, and the electric machine <NUM> typically generates heat of its own during operation in either mode of operation, it is desirable to cool the electric machine <NUM> from the combustion gases exiting the nozzle <NUM>.

As shown, the turbofan engine <NUM> is provided with a cooling system <NUM> having a coolant circuit <NUM> extracting heat from the electric machine <NUM> and releasing the extracted heat in the bypass passage. More specifically, and now referring to <FIG>, the coolant system <NUM> has a coolant circuit <NUM> having an evaporator <NUM> circumferentially disposed around at least part of the electric machine <NUM> and in thermal communication with the electric machine <NUM>. The coolant circuit <NUM> also has a condenser <NUM> which has a surface cooler <NUM> circumferentially disposed around at least part of the bypass passage or duct <NUM> and in thermal communication with the bypass duct <NUM>. As illustrated, a first conduit <NUM> fluidly connecting an upper region 104a of the evaporator to an upper region 106a of the condenser <NUM> is provided. A second conduit <NUM> is also provided to fluidly connect a lower region 106b of the condenser <NUM> to a lower region 104b of the evaporator <NUM>. Upon heating of the electric machine <NUM>, or more specifically heating of oil <NUM> contained in the electric machine <NUM> or from the hot combustion gases flowing annularly around the engine core, a coolant fluid <NUM> in the coolant circuit <NUM> can conveniently extract heat from the electric machine <NUM> and release the extracted heat in the bypass duct <NUM>. More specifically, the coolant fluid <NUM> circulating in the evaporator <NUM>, against the electric machine <NUM>, extracts heat from the electric machine <NUM> which contributes to evaporating the coolant fluid <NUM>. The evaporated coolant fluid <NUM> then circulates radially outwardly and upwardly to the upper region 106a of the condenser <NUM> via the first conduit <NUM>. The evaporated coolant fluid <NUM> circulates circumferentially along the surface cooler <NUM> and releases the extracted heat which results in condensing of the evaporated coolant fluid <NUM>. The condensed coolant fluid <NUM> then circulates radially inwardly and upwardly from the lower region <NUM> of the condenser <NUM> towards the electric machine <NUM> via the second conduit <NUM> where the cooling cycle described immediately above is repeated. Such a phase-change coolant cycle can be performed repetitively and simultaneously thereby cooling the electric machine <NUM> during use.

It is noted that as some portion of the coolant fluid <NUM> is evaporated in the evaporator <NUM>, some other portion of the coolant fluid <NUM> is condensed in the condenser <NUM> thereby provide a continuous and self-circulating cooling operation to the cooling circuit <NUM>. In some embodiments, the coolant fluid <NUM> circulating in the coolant circuit <NUM> allows a set temperature to be maintained without pumps and minimum maintenance. The coolant fluid <NUM> sealingly enclosed within the coolant circuit <NUM> self-circulates in a flow direction which is illustrated by the arrows A of <FIG> as soon as the heat generated by the electric machine <NUM> is sufficient to evaporate, or equivalently boil, the coolant fluid <NUM> into an evaporated fluid or vapor portion. Further, also required for self-circulation in the flow direction is the heat release potential of the condenser <NUM> which is preferably sufficient to condense all of the evaporated fluid into a condensed cooling fluid or liquid portion. In this way, the cooling fluid passively boils, flows and condenses repetitively in a number of cycles to transfer heat from a high temperature region, proximate the electric machine <NUM>, to a lower temperature region, proximate the bypass duct <NUM>. Doing so, the coolant fluid <NUM> undergoes a large volume change when it transforms from liquid to vapour phase, and subsequently back from vapour to liquid. The coolant system <NUM> takes advantage of the two-phase heat transfer available from the coolant fluid <NUM> in the coolant circuit <NUM>, which coolant fluid <NUM> is preferably water in this embodiment, however any other suitable working fluid may be used. Water can be preferred in some embodiments as it has convenient boiling and condensation points, and has relatively high thermal conductivity relative to air and other conveniently available liquids. Water is also inexpensive and present no environmental hazards. In some embodiments, purified water can be preferred as purified water exhibits a high thermal conductivity and good cooling properties, has a low electrical conductivity when free of ions and is non-flammable, a property of significant importance especially as the cooling system is operated proximate hot combustion gases. Any other dielectric liquid can also be used in some other embodiments. Examples of such dielectric liquids can include, but are not limited to, purified water, mineral oil, silicone oil, Fluorinert™ FC-<NUM>, and the like. While these dielectric liquids can insulate the electric machine during operation, such dielectric liquids may also in some instances prevent or rapidly quench electric discharges that may occur proximate the electric machine.

In some embodiments, the coolant circuit <NUM> has a pump <NUM> in fluid communication with the coolant circuit <NUM> for pumping the coolant fluid <NUM> around the coolant circuit <NUM>, thereby forcing the circulation. As emphasized with dashed lines, the pump <NUM> is optional as it can be omitted in some embodiments.

The surface cooler <NUM> may be annular such as illustrated. However, the surface cooler can be semi-annular as well, as long as it somehow partially or wholly surrounds the electric machine <NUM> along its circumference. When the surface cooler <NUM> is annular, the surface cooler <NUM> defines coolant paths <NUM> which are laterally opposite to one another relative the first and second conduits <NUM> and <NUM>. The coolant paths <NUM> extend from the upper region 106a of the condenser <NUM> to the lower region 106b of the condenser <NUM> and extend circumferentially on respective sides of the bypass duct <NUM>. In some embodiments, the surface cooler <NUM> is supported on an outer bypass duct wall or on an inner bypass duct wall. An example of such a surface cooler is described in Applicant's <CIT>. A fluid fill/gauge can be located for easy access on the surface cooler <NUM> in some embodiments.

Still referring to <FIG>, the evaporator <NUM> has a surface heater <NUM> circumferentially disposed around at least part of the electric machine <NUM> and in thermal communication with the electric machine <NUM>. The surface heater <NUM> may be annular such as illustrated. However, the surface heater <NUM> can be semi-annular as well, as long as it somehow partially or wholly surrounds the electric machine <NUM> along its circumference. As shown, the surface heater <NUM> defines heating paths <NUM> which are laterally opposite to one another relative the first and second conduits <NUM> and <NUM>. The heating paths <NUM> extend from the lower region 104b of the evaporator <NUM> to the upper region 104a of the evaporator <NUM> and extend circumferentially on respective sides of the electric machine <NUM>. As depicted in this specific embodiment, the surface cooler <NUM> and the surface heater <NUM> have an axis coinciding with one another, and also coinciding with the engine axis <NUM>. However, in some other embodiments, the axes of the surface cooler <NUM> and surface heater <NUM> may not coincide with one another. The surface cooler and the surface heater can extend circumferentially relative the engine axis <NUM>.

Referring now to <FIG>, the turbofan engine may have at least first and second struts <NUM> and <NUM> radially extending between the engine core <NUM> and the bypass duct <NUM>. Preferably, the first and second conduits <NUM> and <NUM> run along a respective one of the first and second struts <NUM> and <NUM>. In embodiments where the first and second struts <NUM> and <NUM> are hollow, the first and second conduits <NUM> and <NUM> may be disposed within a corresponding one of the first and second struts <NUM> and <NUM>. In this way, the first and second conduits <NUM> and <NUM> may be relatively aerodynamically hidden from the flow of hot combustion gases, which may not be as much detrimental to the efficiency of the turbofan engine. It is intended that a power cable <NUM> electrically coupling the electric machine <NUM> may be provided. Power may be generated by the electric machine <NUM> in the first mode of operation whereas power may be brought to the electric machine <NUM> in the second mode of operation. In either mode of operation, the power cable <NUM> may generate heat by itself. In such embodiments, it may be desirable to dispose the power cable <NUM> alongside the second conduit <NUM>, the one carrying the condensed, cold coolant liquid, within or alongside the second strut <NUM>. In such embodiments, the condensed coolant fluid <NUM> can extract heat from the power cable <NUM> as the condensed coolant fluid <NUM> circulates radially inwardly and upwardly from the lower region 106b of the surface cooler <NUM> to the electric machine <NUM>. In an alternate embodiment, the power cable <NUM> can extend within the corresponding one of the first and second conduits <NUM> and <NUM>.

<FIG> shows a method of cooling an electric machine of a turbofan engine.

As shown, as per step <NUM>, a coolant fluid circulates against the electric machine and extracts heat from the electric machine. The extracting includes evaporating the coolant fluid.

A step <NUM>, the evaporated coolant fluid circulates radially outwardly and upwardly to an upper region of the surface cooler.

At step <NUM>, the evaporated coolant fluid circulates circumferentially along the surface cooler and releases the extracted heat thereto. The releasing includes condensing the evaporated coolant fluid.

At step <NUM>, the condensed coolant fluid circulates radially inwardly and upwardly from a lower region of the surface cooler to the electric machine.

In some embodiments, the steps of circulating includes actively driving the circulating using at least a pump. The pump can be in fluid communication with the condenser, the evaporator, the first and second conduits, or a combination thereof, depending on the embodiment. The pump can be powered by the electric machine in some embodiments. However, in some other embodiments, the pump can be powered using a power source external to the electric machine. The pump can be omitted in at least some embodiments. As discussed above, the coolant fluid can be an dielectric material electrically insulating the electric machine during use.

Claim 1:
A cooling system (<NUM>) for an engine (<NUM>) having an air mover (<NUM>) configured for generating a flow of air around a rotation axis (<NUM>), a surface (<NUM>) extending around the rotation axis delimiting a passage (<NUM>) for the flow of air downstream of the air mover (<NUM>), and an electric machine (<NUM>) disposed within the surface (<NUM>) and coupled to the air mover (<NUM>), the cooling system (<NUM>) comprising:
a coolant circuit (<NUM>) having a condenser (<NUM>) having a surface cooler (<NUM>) circumferentially disposed around at least part of the surface (<NUM>) and in thermal communication therewith; and
a coolant fluid (<NUM>) in the coolant circuit (<NUM>),
characterised in that:
the coolant circuit (<NUM>) further comprises:
an evaporator (<NUM>) circumferentially disposed around at least part of the electric machine (<NUM>) and in thermal communication therewith;
a first conduit (<NUM>) fluidly connecting an upper region (104a) of the evaporator(<NUM>) to an upper region (106a) of the condenser (<NUM>); and
a second conduit (<NUM>) fluidly connecting a lower region (106b) of the condenser (<NUM>) to a lower region (104b) of the evaporator (<NUM>); and
the evaporator (<NUM>) has a surface heater (<NUM>) disposed at least partially around the electric machine (<NUM>) and in thermal communication therewith, and the surface heater (<NUM>) defines heating paths (<NUM>) opposite to one another, extending from the lower region (104b) of the evaporator (<NUM>) to an upper region (104a) of the evaporator (<NUM>) and circumferentially disposed around at least part of corresponding sides of the electric machine (<NUM>).