FUEL-COOLED BRUSHLESS MACHINE SYSTEM FOR GAS TURBINE ENGINE

A brushless machine system and a method for operating same, the system comprising an electric machine assembly having a permanent magnet rotor and a stator with stator windings, a gas turbine engine fuel metering unit having a fuel pump for pumping liquid gas turbine engine fuel, and at least one passage extending between the electric machine assembly and the fuel metering unit, the cooling passage having a portion in contact with the stator such that liquid fuel passing therethrough cools the stator windings.

TECHNICAL FIELD

The present disclosure relates generally to brushless machines, and more particularly to fuel-cooling same.

BACKGROUND OF THE ART

In common type brushless machines, rotation is achieved by controlling the magnetic fields generated by the coils on the rotor while the magnetic field generated by the permanent stationary magnets remains fixed.

However, brushless machines have a higher initial cost than brushed machines. Some of the factors that affect the overall costs are assembly size, weight, duty cycle, and power output.

There is a need for improvement.

SUMMARY

In accordance with a broad aspect, there is provided a brushless machine system for a gas turbine engine. The system comprises an electric machine assembly having a permanent magnet rotor and a stator with stator windings, a gas turbine engine fuel metering unit having a fuel pump for pumping liquid gas turbine engine fuel, and at least one passage extending between the electric machine assembly and the fuel metering unit, the cooling passage having a portion in contact with the stator such that liquid fuel passing therethrough cools the stator windings.

In accordance with another broad aspect, there is provided a method for operating a brushless machine system for a gas turbine engine. The method comprises converting motive power into electrical power using an electric machine assembly having a permanent magnet rotor and a stator with stator windings, pumping liquid fuel through a gas turbine engine fuel metering unit having a fuel pump, and cooling the stator windings with the liquid fuel by flowing the liquid fuel through at least one passage extending between the machine assembly and the fuel metering unit, the at least one cooling passage having a portion in contact with the stator.

Features of the systems, devices, and methods described herein may be used in various combinations, in accordance with the embodiments described herein.

DETAILED DESCRIPTION

There is described herein a fuel-cooled brushless machine system. An electric machine assembly is combined with a fuel metering unit (FMU) and liquid fuel from the FMU is used to cool the stator windings of the electric machine. The savings provided by cooling the stator windings can be used for one or more of reducing the size of the machine, increasing the mechanical output duty cycle, increasing electrical generation capacity, improving system efficiency, and lowering the weight of the machine.

The fuel-cooled brushless machine system may be used in combination with any type of gas turbine engine, such as but not limited to a turbofan engine, a turboprop engine, a turboshaft engine, and the like. The engine may be used for various applications, such as aircraft, ships, trains, tanks, cars, buses, motorcycles, and the like. Any type of liquid fuel suitable for gas turbine engines may be used, namely aviation turbine fuel (ATF).

FIG. 1illustrates an example of a gas turbine engine10of a type preferably provided for use in subsonic flight. The engine10generally comprises in serial flow communication a fan12through which ambient air is propelled, a compressor section14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases. A reduction gearbox (RGB)20is used, in some instances, to couple the compressor-turbine assembly to the fan12. An accessory gearbox (AGB)22may be used to couple one or more accessories24to the engine10.

Referring now toFIG. 2, there is illustrated an example embodiment for a fuel-cooled brushless machine system200. The system200combines a fuel metering unit (FMU)214and an electric machine assembly201under a same housing202. The electric machine assembly201converts motive power into electrical power. At least one cooling passage302extends between the electric machine assembly201and the FMU214for flowing fuel therethrough. The fuel is used to cool the stator windings of the motor assembly201.

In some embodiments, the electric machine assembly201is a starter-generator. Alternatively, the electric machine assembly201may be any type of electrical generator or motor, such as an alternator, an inductor motor, or any other AC or DC brushless machine.

In some embodiments, the electric machine assembly201and FMU214are both powered by a drive shaft204that extends from the housing202. The system200may be coupled to an engine, such as gas turbine engine10, by connecting the shaft204to the RGB20or the AGB22of the engine10. The single shaft204allows a single gear set to be used to couple the system200to the engine10.

Although illustrated as cylindrical, the system200may be of various shapes, such as but not limited to elliptical, rectangular, and non-geometrical shapes. In some embodiments, the housing202covers less than the entire system200. For example, the surface203from which the shaft204extends may remain open. Other embodiments for the housing202may also apply.

FIG. 3is an example cross-section of the system200along lines A-A ofFIG. 2. In this example, the system200comprises a permanent magnet rotor206and a stator208. The stator208has one or more windings210a,210bthat are configured to conduct an output current induced in the windings210a,210bby rotation of the rotor206. The rotor206, stator208, and windings210a,210bare part of the motor assembly201. The shaft204extends through the motor assembly201. A bearing212allows the shaft to move inside the housing202.

The shaft204is also connected to the FMU214. In some embodiments, the FMU214pumps, meters, and filters fuel received from a fuel tank and supplies the gas turbine engine10with fuel for combustion. Control of the FMU214may be hydromechanical, hydromechanical/electronic, or Full Authority Digital Engine Control (FADEC). The FMU214is composed of at least a fuel pump311for pumping fuel. In some embodiments, the FMU214is also composed of one or more other components, such as filters, sensors, valves, controllers and the like. For example, the FMU214may comprise a mechanical speed governor, a solenoid, a fuel bypass valve, a servo pressure regulator, an enrichment solenoid, a servo metering valve assembly, a fuel shutoff valve, a metering head sensor, and a pressurizing valve. The FMU214may dynamically alter the position of various valves to either increase or decrease the flow of fuel to the engine10as a function of demand. In some embodiments, one or more of the filters, sensors, pressure valves, controllers, etc., are external to the FMU214and to the system200.

The fuel pump311is powered by the shaft204. The fuel pump311is configured to receive fuel at a first pressure, i.e. low pressure, and increase the pressure to a second pressure, i.e. high pressure. Low pressure fuel is received from a fuel tank, external to the system200, and provided to the fuel pump311in the FMU214. High pressure fuel is then pumped out of the FMU214and provided to an engine, such as gas turbine engine10. Fuel is received, from the fuel tank or an intermediary component, at a fuel inlet308, and output from the system200at a fuel outlet310.

One or more cooling passages302,304are provided to cool the windings210a,210bof the stator208. The cooling passages302,304have at least a portion that is in contact with the stator208. For example, the passages302,304may correspond to tubing that runs at least in part over the stator208such that the cold fuel absorbs some of the heat generated by the windings210a,210b. In another embodiment, the passages302,204are channels or grooves that run at least in part through the stator208. It will be understood that the passages302,304may be embodied through various configurations, several of which are illustrated herein. The arrows in the passages302,304indicate the direction of fuel flow.

In the example ofFIG. 3, a first cooling passage302runs from the FMU214to a first fuel outlet310. Fuel flows from the FMU214through the first cooling passage302, contacts the stator208to cool the windings210aand exits the system200through the fuel outlet310. A second cooling passage304runs from the FMU214to a second fuel outlet312. Fuel flows from the FMU214through the second cooling passage304, contacts a different portion of the stator208to cool the windings210band exits the system200through the second fuel outlet312. In this example, fuel is initially received at fuel inlet308and flown into the FMU214through a passage306. The fuel pump311increases the fuel pressure from low to high before flowing the fuel through the first and second cooling passages302,204. The windings210a,210bare thus cooled with high pressure fuel.

FIG. 4illustrates another example embodiment for the system200. Fuel is received at fuel inlets308,314and flown directly in the cooling passages302,304respectively, where it contacts the stator208and cools the windings210a,210b, respectively. The fuel is then directed towards the FMU214, where the fuel pressure gets increased by the fuel pump311before the fuel is flown out of the FMU214through passage316towards fuel outlet310. The fuel that cools the windings210a,210bis thus low pressure fuel. While the embodiments ofFIGS. 3 and 4illustrate two cooling passages302,304, more than two cooling passages may be provided.

In some embodiments, each winding210a,210bis provided with a cooling passage302,304for cooling. Alternatively, a cooling passage302is provided to cool more than one winding210a,210b, as illustrated in the embodiment ofFIG. 5. In this example, cooling passage302is provided between the FMU214and the stator208. Fuel is initially received at fuel inlet308and flown through passage306towards the FMU214. Fuel is flown from the FMU214into the cooling passage302towards the stator208to cool the windings210a,210bbefore returning to the FMU214. The fuel pump311increases the fuel pressure and high pressure fuel is flown towards fuel outlet310via passage316. In the embodiment ofFIG. 5, the fuel used to cool the windings210a,210bmay be low pressure fuel or high pressure fuel. It will be understood that a cooling passage302may be used to cool more than two windings210a,210b.

FIG. 6illustrates yet another embodiment for the system200. Fuel is received via fuel inlet308and flown through cooling passage302at low pressure. Cooling passage302is used to cool both windings210a,210b. Cooling passage302redirects the fuel towards the FMU214after coming into contact with the stator208. The fuel pump311increases the fuel pressure and high pressure fuel is delivered to the fuel outlet310via passage316.

In some embodiments, two or more cooling passages302,304are connected together so that fuel will flow sequentially therethrough. An example is illustrated inFIG. 7. Fuel is initially received at fuel inlet308and flown towards the FMU214through passage306. Fuel pump311raises the pressure of the fuel and high pressure fuel is flown through cooling passage302to cool windings210a. Passage outlet313is connected to passage inlet315to allow fuel to flow from the first cooling passage302to the second cooling passage304. The fuel flowing through the second cooling passage304cools windings210band exits the system200via fuel outlet310. The direction of flow may also be reversed, as illustrated in the example ofFIG. 8. Fuel is received at fuel inlet308and flown through cooling passage304to cool windings210b. The fuel, which is at low pressure, is then sent to cooling passage302via passage outlet313and passage inlet315. The fuel flows through cooling passage302to cool windings210abefore being sent to the FMU214. The fuel pump311increases the fuel pressure and high pressure fuel is output at fuel outlet310via passage306. More than two cooling passages302,304may be connected via passage outlets313and passage inlets315to flow fuel sequentially therethrough.

It will be understood that many other configurations may be used for cooling passages302,304, as well as for passages306,316. One or more fuel inlet and outlet308,310may be positioned as desired to provide a flow of fuel that will cool the windings210a,210band pass through fuel pump311to increase fuel pressure for delivery to engine10. One or more passage inlets and outlets313,315may be used to direct the fuel from one cooling passage302to another304, and vice versa.

FIGS. 3 to 8illustrate the electric machine assembly201of system200as an outer rotor design. An example is illustrated inFIG. 9A, which is a cross-sectional view of the system200ofFIG. 2taken along lines B-B. The windings210a,210bare located in the core of the electric machine assembly201on the stator208. It should be understood that the electric machine assembly201may also be provided as an inner rotor design, as illustrated inFIG. 9B. The stator windings210a,210bsurround the rotor206and are affixed to the outer stator208. Although illustrated as round, the rotor206may also be of a different shape, such as the rectangular rotor206illustrated inFIG. 9C. In some embodiments, the rotor206is itself made of a material that is a permanent magnet. In other embodiments, one or more permanent magnet902a,902b,902c,902dis affixed to the rotor, as illustrated in the example ofFIG. 9D. It should be understood that various configurations may be used for the electric machine assembly201, with regards to at least the number of windings210a,210b, the position of the windings210a,210b, the arrangement of the windings210a,210b, the position and arrangement of the rotor206and stator208, the position and arrangement of one or more permanent magnet902a-902d, and any other design detail regarding the electric machine assembly201.

The system200as described herein is operated by inducing an output current in at least one winding210a,210bof the stator208by rotation of the permanent magnet rotor206. The fuel pump311of the FMU214may be powered with the shaft204that is mounted to the rotor206. Fuel is received at a first pressure at one or more fuel inlet308,314and output at a second pressure at one or more fuel outlet310,312. The windings210a,210bare cooled with the fuel by flowing the fuel in one or more cooling passage302,304having a portion in contact with the stator208. Fuel is directed to the FMU214to increase the pressure from the first pressure (low pressure) to the second pressure (high pressure) before being output at the outlets310,314.

In some embodiments, one or more of the fuel cooling passages302,304flows the fuel through the stator208. Alternatively, a tubing external to the stator208is used to contact the stator208with the fuel.

The direction of fuel flow between the FMU214and the electric machine assembly201through the one or more cooling passages302,304and the arrangement of the one or more fuel inlets308,314and fuel outlets310,312may vary. For example, fuel may be received at a fuel inlet308, flown through a cooling passage302in contact with the stator208to cool windings210a, and directed towards the FMU214. Fuel pressure is raised by the fuel pump311and then the fuel is flown through another cooling passage304in contact with the stator208to cool windings210b, after which the fuel is output via fuel outlet310. In this example, there is no need for passage306, and coil windings210aare cooled with low pressure fuel while coil windings210bare cooled with high pressure fuel. Other embodiments also apply, as described herein with reference toFIGS. 3 to 8.

The electric machine assembly201as described herein may be under-designed compared to the specifications needed for a particular application. In other words, the electric machine assembly201may be designed to over-heat when running at full capacity, and the fuel running through the one or more cooling passages is used to prevent the over-heating. Indeed, coil winding temperature increase is one of the main factors that govern assembly size, weight, duty cycle, and power output for a brushless motor. Under-designing may therefore result in gains in terms of weight and/or costs of the system200, and power density and efficiency can be maximized by using the cooling passages to cool the windings. Under-designing of the electric machine assembly201may refer to the number of windings used, the wire gauge, the overall size of the electric machine assembly201, and any other design characteristic that affects performance of the system200.

The common shaft204used by the electric machine assembly201and the FMU214provides savings in terms of gearings used to couple the system200to the engine10. A single set of gears may be used for the system200instead of the traditional two sets of gears, where one gear set couples a machine to an engine and another gear set couples an FMU to the engine. Additional savings of assembly time and engine installation time, wire harness complexity reduction, and gearbox size may also be obtained.