Motor heat exchanger

Abstract

The present disclosure relates to a heat exchanger for an electric machine. The electric machine includes: a stator having a stator core and stator slots extending along a longitudinal axis of the stator; and a rotor assembly having a rotor configured to rotate about the longitudinal axis. The electric machine includes a coolant system having a stator cooling path that provides a first coolant fluid in direct contact with the stator to flow around the stator core and through the stator slots. The coolant system also includes a coolant circuit that provides a second coolant fluid to at least one rotatable component of the electric machine, such as at least one bearing. The coolant circuit and the stator cooling path are fluidly isolated from each other and arranged such that heat is exchanged between the first coolant fluid and the second coolant fluid at the stator.

Description

Technical Field

[0001] The present invention relates to a heat exchanger for an electric machine. In particular, the present invention relates to a heat exchanger comprised in an electric machine for an aircraft engine. Background Art

[0002] Electric machines, such as generators, have both an operating temperature range within which they can operate and an optimal temperature range within which they operate most efficiently. In use, generators generate heat due to inefficiencies in generating electricity. Generators are typically cooled by a circulating fluid to ensure that a) they remain within the operating temperature range, and b) they preferably remain within their optimal temperature range.

[0003] Aircraft propulsion systems typically include an engine that can be connected to a generator. In such a system, the generator can be driven by the turbine of the engine to generate the electricity required to power the electrical consumption of the aircraft.

[0004] Generally speaking, aircraft engine generators are cooled using an oil-filled system with circulating oil driven by a mechanical pump. In order to reduce the number of system components, some modern aircraft engines use a single oil system to cool multiple parts of the aircraft engine, such as the gearbox and the generator, both of which are cooled from a single cooling circuit using a shared fluid flow. However, failure of such a single oil system will cause multiple parts of the aircraft engine to overheat, which may cause the engine to fail as a whole. Further, a failure in one engine area (such as the generator) may cause a cascading effect in another system due to contaminants distributed by the shared fluid flow.

[0005] To improve redundancy, in some aircraft engines, the generator may have its own self-contained coolant system, along with its own coolant path, mechanical pump, gearbox, and connection to the drive shaft. However, in a confined space environment, it is often challenging to have multiple redundant coolant systems. The reason this is challenging is that in aircraft applications, the generator is usually at its highest load during the idling period of the aircraft before takeoff. At this time, all aircraft systems will be operating, and the entertainment and kitchen systems of the aircraft may be starting. During idling, the aircraft's engine will rotate at its lowest speed (because no thrust is required), so the drive to the coolant pump will be at its lowest speed. Additionally, in the case where the generator is running at the lowest speed, the current will be the highest, and therefore the heat generated due to the resistance in them will also be higher. In order to cope with these requirements, the prior art coolant system has been designed to provide sufficient fluid flow at idling speed to cope with the maximum generator output. Therefore, a coolant system with high cooling capacity is required to prevent the generator from overheating at idling speed with high demand.

[0006] UK Patent No. 2570656 describes a coolant system for an electrical generator having a turbine driven by fluid in a propulsion system fluid circuit. The turbine drives a pump which drives the coolant fluid around a separate cooling circuit.

[0007] There is a need for improvements in generator cooling systems. Summary of the invention

[0008] According to one aspect of the present invention, there is provided an electric machine, the electric machine comprising any one or all of the following features:

[0009] a stator comprising a stator core and a plurality of stator slots extending along a longitudinal axis of the stator;

[0010] a rotor assembly comprising a rotor configured to rotate about the longitudinal axis; and

[0011] A coolant system, the coolant system comprising:

[0012] a stator cooling path configured to provide a first coolant fluid flowing around the stator core and through the stator slots; and

[0013] a coolant circuit configured to provide a second coolant fluid to at least one rotatable component of the electric machine;

[0014] Therein, the coolant circuit and the stator cooling path are fluidly isolated from each other and are arranged such that heat is exchanged between the first coolant fluid and the second coolant fluid at the stator.

[0015] The at least one rotatable component of the electric machine may include cooled components of the rotor (such as rotor bearings), the rotor itself, and components associated with the rotor (such as splines and gear teeth). The term "rotatable component" refers to a component configured to rotate during operation of the machine, and is used herein to distinguish a coolant circuit from a stator cooling path that is alternatively configured to cool stationary components (i.e., the stator core and stator slots), or any other component fixed to the housing and / or stator that is not configured to rotate in operation.

[0016] In order to integrate the motor into the aircraft engine in an independent and modular manner, the stator, rotor and corresponding bearings are preferably enclosed in the same package. The motor can be embedded in the tail cone at the rear of the low-pressure turbine of the aircraft engine. For structural and aerodynamic purposes, a turbine rear frame (TRF) can be set around the tail cone. In addition, the stator, rotor and lubricating oil are preferably cooled, which is usually achieved by linking to a cooling circuit of a heat exchanger located in the core compartment of the engine. The heat exchanger typically uses air or fuel as a coolant and provides a cooled fluid to the motor through a supply line and a return line extending through the support of the TRF.

[0017] The inventors have recognized that it is preferred that the oil used to cool the stator is independent of the oil used to lubricate and cool components associated with the rotor, such as bearings. Therefore, by providing a coolant system in which a coolant circuit for cooling at least one rotatable component of the rotor assembly is fluidly isolated from a stator cooling path for cooling the stator core and stator slots, the system can accommodate different requirements for each of the cooling circuits. For example, the system allows customization of the type of coolant used in the circuit, the coolant pressure, and the flow rate of the coolant. In addition, by providing the cooling circuits in a fluidly isolated manner, any metal debris in one cooling circuit will not enter another cooling circuit. It should be understood that the coolant can be any suitable fluid, such as a liquid or a gas, and is not limited to oil.

[0018] The present invention provides for exchanging heat between a first coolant fluid and a second coolant fluid at a stator. Therefore, a heat exchanger is provided at the stator. Therefore, heat is exchanged between the first coolant fluid and the second coolant fluid at the same area where heat is exchanged between the first coolant fluid and the stator. The TRF has a limited number of radial struts that can provide air, oil and electrical connections to the core of the low-pressure turbine. Therefore, by integrating the heat exchanger at the stator of the motor, the system avoids the need for additional supply lines and return lines for a separate cooling circuit that would require routing through the TRF. This reduces the resistance in the flow path in the TRF, because adding additional lines would require an increase in the thickness of one or more struts of the TRF, or would require adding new struts to the TRF. By avoiding the need for additional supply lines and return lines for coolant, the modularity of the motor is increased and its connection to the engine cooling system is simplified.

[0019] The present invention also provides a stator cooling path providing a first coolant fluid flowing around the stator core and through the stator slots. This is in contrast to existing coolant systems, which may employ a separate outer jacket to cool the stator core, and in which the stator teeth defining the stator slots may be cooled solely by conduction through the stator core. By providing the first coolant fluid around the stator core and also through the stator slots, the first coolant fluid may contact a larger surface area of ​​the stator, thereby improving the efficiency of cooling, while exchanging heat with the second coolant fluid in the same area (i.e., at the stator).

[0020] The stator cooling path may be configured to provide the first coolant fluid in direct contact with the stator. This has the advantage of increasing the efficiency of the stator cooling by the first coolant fluid.

[0021] The stator may be included in the housing. The stator cooling path may be configured to provide a first coolant fluid between the stator and the housing. Therefore, the stator cooling path may include a portion defined in an area between the stator and the housing. The stator may be concentrically received in the housing, and the stator cooling path may include a portion disposed in an annular area between the stator and the housing. The stator cooling path may include a channel. The channel may be configured to provide a first coolant fluid between the stator and the housing. The channel may be at least partially defined by at least one recess in the housing. The channel may be at least partially defined by the stator. The channel may be at least partially defined by a radially outer surface of the stator core. This has the advantage of providing a first coolant fluid in direct contact with the stator while providing a cooling channel via the housing of the stator to reduce the number of required components.

[0022] The channel may be helical relative to the longitudinal axis. That is, the stator cooling path may have a portion in the shape of a helix around the stator. This has the advantage of delivering the first coolant fluid around the circumference of the stator and axially along the radially outer surface of the stator.

[0023] The channel of the stator cooling path may be a first channel, and the coolant circuit may include a second channel. The second channel may be at least partially disposed within or adjacent to the first channel. The second channel may be configured to provide a second coolant between the housing and the stator. The second channel may be disposed in an annular region defined between the stator and the housing. The second channel may have a shape corresponding to the first channel. The second channel may be spiral. The first channel and the second channel may be in the form of a spiral having the same pitch. The second channel may include a spiral conduit received by the first channel.

[0024] The stator cooling path may include a plurality of longitudinal recesses defined in the housing.The coolant circuit may be configured to be received by the plurality of longitudinal recesses defined in the housing.

[0025] The present invention also provides an aircraft engine assembly, the aircraft engine assembly comprising the above-described electric machine. The electric machine can be driven by the output of an engine of the aircraft engine assembly. The stator cooling path can be configured to guide a first coolant fluid from the electric machine to the engine compartment to cool the first coolant fluid. The present invention also provides an aircraft, the aircraft comprising the above-described aircraft engine assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Further features and advantages of the invention will become apparent from the following description of embodiments of the invention presented by way of example only and with reference to the accompanying drawings, in which:

[0027] Figure 1 is a schematic diagram showing a coolant system of an electric machine according to an embodiment;

[0028] Figure 2 is a cross-sectional view of a motor according to an embodiment;

[0029] Figure 3 is a perspective view of a stator of a motor according to an embodiment;

[0030] Figure 4A is a cross-sectional view showing a stator according to an embodiment;

[0031] Figure 4B is a perspective view of a portion of a coolant circuit according to an embodiment;

[0032] Figure 5 is an exploded view of a portion of a coolant circuit and a stator housing according to an embodiment;

[0033] Figure 6 is a schematic diagram of an aircraft according to an embodiment. DETAILED DESCRIPTION

[0034] An electric machine is disclosed in the context of an aircraft engine assembly. The electric machine disclosed herein includes a stator having a longitudinal axis. The stator may be formed by a plurality of stator laminations stacked together along the longitudinal axis. The stator has a stator core and a plurality of stator teeth extending radially from the stator core to define a plurality of slots. Such stator slots are configured to receive conductors for carrying current. The conductors may be in the form of stator windings or solid bar conductors. The electric machine also includes a rotor configured to rotate around the longitudinal axis of the stator. The rotor may include a plurality of permanent magnets or non-permanent magnetizable elements (such as windings) that generate a changing magnetic field when the rotor rotates around the axis, thereby generating a current in the stator conductor. Thus, the electric machine may be operated as a generator. It will be understood that the electric machine may also be operated as a motor. The rotor may be formed in a rotor assembly that is journaled by one or more bearings for rotation relative to the stator.

[0035] The stator is cooled by a first coolant fluid that flows around the stator core and passes through the stator slots. The stator cooling path can be supplied with a coolant circuit from outside the motor, such as a coolant from the main engine compartment. After the first coolant has flowed around the stator, the first coolant fluid returns to the external heat exchanger to be cooled and recirculated. The rotor, bearings and other associated elements (such as splines or gear teeth) are cooled and lubricated by the second coolant fluid. The second coolant fluid circulates around the motor through a coolant circuit included in the motor. The first coolant fluid and the second coolant fluid can be oil. Instead of cooling the second coolant fluid via an external heat exchanger, the motor disclosed herein is arranged so that heat is exchanged between the first coolant fluid and the second coolant fluid in the motor. This allows the second coolant fluid to be cooled by the first coolant fluid. To achieve this, the second coolant fluid circulating in the coolant circuit is brought into close contact with the first coolant fluid in the stator cooling path. For example, the coolant circuit can have a pipeline that travels in the stator cooling path so that the first coolant fluid is configured to at least partially surround the second coolant fluid. Once the second coolant fluid has been cooled by the first coolant fluid, the coolant circuit is configured to circulate the second coolant fluid toward the rotatable components of the rotor and / or bearings and then back to the sump.

[0036] Figure 11 is a circuit diagram including an electric machine 4 according to an embodiment of the present invention. The electric machine 4 includes a stator 100 and a rotor assembly 130. The stator 100 and the rotor assembly 130 may be contained in a housing 110. In the illustrated arrangement, the rotor assembly 130 includes a rotor 131 configured to rotate about a longitudinal axis of the stator 100. The rotor assembly 130 may be journaled for rotation relative to the housing 110 by one or more bearings 132, 133. In the illustrated arrangement, the rotor assembly 130 is supported by a first bearing 132 at a first axial end of the rotor assembly 130 and by a second bearing 133 at an opposite second axial end of the rotor assembly 130.

[0037] The motor 4 includes a coolant system. The coolant system includes a stator cooling path 111 and a coolant loop 140. The stator 100 is cooled by a first coolant fluid (not shown) provided through the stator cooling path 111. The first coolant fluid may circulate through an external coolant loop 200, which may be outside the motor 4. The external coolant loop 200 may include a tank 201 for storing the first coolant fluid, as well as a filter 204 and a pressure sensor 203. The first coolant fluid may be pumped around the external coolant loop 200 by a pump 202. Downstream of the stator cooling path 111, the external coolant loop 200 may include an external heat exchanger 206 and a bypass valve 205.

[0038] The external coolant loop 200 may be part of the core compartment of the engine. The first coolant fluid may be delivered toward the stator cooling path 111 of the electric machine 4 by a supply line (not shown) running through a support of the turbine rear frame (not shown) and may be returned to the heat exchanger 206 via a return line passing through a support of the turbine rear frame.

[0039] The coolant circuit 140 is configured to provide a second coolant fluid to at least one bearing 132, 133 and / or at least one rotatable component of the rotor assembly. Such rotatable components may include any component of the rotor assembly, such as a disconnect mechanism 134, an input shaft bearing 135, and other cooled components (such as gear meshes and bearings 136) that may need to be lubricated and / or cooled by the coolant circuit 140. The coolant circuit 140 of the motor 4 may include a sump 141 for storing the second coolant fluid, a pump 142 for pumping the second coolant fluid around the coolant circuit 140, a pressure sensor 143 for measuring the pressure of the second coolant fluid, a filter 144 for filtering the second coolant fluid, and a pressure relief valve 145.

[0040] The coolant circuit 140 and the stator cooling path 111 are fluidically isolated from each other. That is, the coolant system is arranged so that the first coolant fluid and the second coolant fluid do not contact each other. In order to cool the second coolant fluid flowing around the coolant circuit 140, a heat exchanger 120 is provided in the motor 4. The coolant circuit 140 can be configured so that the second coolant fluid is cooled by the heat exchanger 120, then flows toward the cooled components (such as bearings 132, 133) to cool and lubricate these cooled components, and then returns to the storage tank 141 for recirculation. Thus, heat is exchanged between the first coolant fluid and the second coolant fluid. The heat exchanger 120 can be arranged at the stator 100. That is, the heat exchanger 120 can be arranged adjacent to and / or around the stator 100. In this way, heat is exchanged between the first coolant fluid and the second coolant fluid at the stator 100. Thus, the first coolant fluid in the stator cooling path 111 may be configured to cool the second coolant fluid in the coolant circuit 140 at the stator 100 .

[0041] Figure 2 1 is a cross-sectional view of an electric machine 4 according to an embodiment of the present invention. In the arrangement shown, the rotor assembly 130 includes a shaft 137, which may be a low pressure (LP) shaft, connected to the rotor 131. The LP shaft 137 is rotatably received in the electric machine 4 by a first bearing 132 and a second bearing 133. The rotor 131 is mechanically connected to the LP shaft 137 and is configured to rotate therewith.

[0042] The shaft 137 can be configured to distribute the coolant in the coolant circuit to the cooled components of the electric machine 4. In the illustrated arrangement, the shaft 137 includes an axial bore 138. The axial bore 138 is configured to transfer the coolant from one axial end of the shaft to the other axial end of the shaft 137. The shaft 137 can also include one or more passages 139. The passages 139 can be fluidly connected to the bores 138 and can be configured to distribute the coolant radially from the axial bores 138. In this manner, the shaft 137 is configured to transfer the second coolant fluid along the shaft via the axial bores 138 while providing the coolant fluid to the cooled components of the electric machine 4 via the passages 139.

[0043] Figure 2The solid arrows in the figure represent the flow direction of the second coolant fluid circulating in the coolant circuit 140. Starting from the reservoir 141, the coolant circuit 140 is configured to transfer the second coolant fluid toward the heat exchanger 120 at the stator 100 through the action of the pump 142. Downstream of the heat exchanger 120, the second coolant fluid can be transferred to other cooled components of the motor 4 via one or more conduits in the motor 4. In the illustrated arrangement, the coolant system 140 is configured to transfer the second coolant fluid through the housing 110 to the rotor assembly 130. At this time, the second coolant fluid can be provided to the hole 138 of the LP shaft 137 so as to supply the second coolant fluid to the bearings 132, 133 and other cooled components via the passage 139. The coolant circuit 140 of the motor 4 may also include one or more return passages 146, which are configured to guide the second coolant fluid back to the reservoir 141.

[0044] Figure 2 The dashed arrows in the figure represent the flow of the first coolant fluid in the external coolant circuit 200. In the illustrated arrangement, the housing 110 includes a supply channel 112 in fluid communication with the external coolant circuit 200. The supply channel 112 may be configured as a passage for transferring the first coolant fluid from a first surface of the housing 110 to a second surface of the housing 110. In the illustrated arrangement, the supply channel 112 is formed by radially extending holes in fluid communication with the stator cooling path 111. In this manner, the housing 110 is configured to transfer the first coolant fluid from the external coolant circuit 200 to the stator cooling path 111. Downstream of the stator cooling path 111 may be an outlet 113 configured to transfer the first coolant fluid away from the motor 4.

[0045] Figure 3A portion of an electric machine 4 is shown, specifically a stator 100 in a housing 110. The stator 100 includes a stator core 101 and a plurality of stator slots 102, which may be defined by a plurality of stator teeth 105 extending radially from the stator core 101. The housing 110 may form a jacket around the stator 100 to provide space for a coolant fluid to flow around the stator core 101. In addition, the electric machine 4 may include a stator sealing sleeve 104. In the illustrated arrangement, the stator sealing sleeve 104 is disposed about a longitudinal axis 106 of the stator 100 and may be formed as a cylindrical sleeve disposed radially inside the stator slots 102. In this manner, the stator core 101, the stator teeth 102, and the stator sleeve 104 may provide a series of longitudinally extending channels through which a coolant may flow to cool the stator slots 102 and the conductors therein. The stator sealing sleeve 104 may include glass fibers. The stator cooling path 111 is configured to provide a first coolant fluid that flows around the stator 100, in particular, floods the stator 100. Thus, the stator cooling path 111 may include the stator slots 102 and a space disposed around the stator core 101. In other words, the stator cooling path 111 represents a route around the stator 100 that may be taken by the first coolant fluid in order to cool the stator core 101 and the stator slots 102.

[0046] Figure 4A Further details of the housing 110 and the stator 100 according to an embodiment of the present invention are shown. At least a portion of the stator cooling path 111 can be configured to provide a first coolant between the stator 100 and the housing 110. In the illustrated arrangement, the stator core 101 has a cylindrical radial outer surface. The stator cooling path 111 can be at least partially disposed around the radial outer surface.

[0047] The stator cooling path 111 may include at least one channel arranged around the longitudinal axis 106 of the stator 100. The channel may be configured to provide a first coolant fluid between the stator 100 and the housing 110. In the illustrated arrangement, the channel is at least partially defined by one or more recesses in the housing 110 and at least partially defined by the stator 100, in particular by the stator core 101. The channel may include a portion defined by one or more surfaces of the housing 110 and one or more surfaces of the stator 100. The channel may have a rectangular cross section. In the illustrated arrangement, one side of the rectangular cross section is defined by the stator 100, more particularly by the stator core 101. In this way, the stator cooling path 111 may be arranged to provide a first coolant fluid in direct contact with the stator 100. The remaining three sides of the rectangular cross section may be defined by recesses in the housing 110. In the illustrated arrangement, the channel is in the form of a spiral arranged around the longitudinal axis 106. In this manner, the stator cooling path 111 may be configured to surround one or more surfaces of the stator 100 and provide the first coolant along the one or more surfaces.

[0048] refer to Figure 4A and Figure 4B , the coolant circuit 140 may include a conduit 121, which may be in the form of a spiral tube or pipe. The conduit 121 represents a portion of the coolant circuit 140 that is configured to circulate the second coolant fluid through the heat exchanger 120. In the illustrated arrangement, the conduit 121 is received within the stator cooling path 111. In particular, the conduit 121 is received by a spiral passage that partially defines the stator cooling path 111 around the stator 100. Thus, the stator cooling path 111 and the conduit 121 may together form the heat exchanger 120.

[0049] The arrangement of the heat exchanger 120 is not limited to a spiral duct 121 disposed in a spiral channel formed in the stator cooling path 111. In an alternative embodiment, the heat exchanger may include a first channel and a second channel at least partially surrounding the stator core 101 or running in parallel along the stator core. The first channel and / or the second channel may be spiral, or may extend at least partially along the longitudinal or axial direction of the stator. The first channel may be in fluid communication with the stator cooling path 111 to provide a first coolant fluid to the stator, and the second channel may be in fluid communication with the coolant circuit 140 to circulate a second coolant fluid through the heat exchanger 120.

[0050] Figure 5A further embodiment of a heat exchanger 120' is shown, which includes a stator cooling path 111' and a conduit 121'. In this arrangement, the stator cooling path 111' includes a plurality of longitudinally extending channels, which can be arranged as recesses in the housing 110'. Such channels can be fluidly connected to each other at their respective ends to form a path for the coolant fluid to flow around the stator core 101. The channel can be configured to receive a conduit 121' that can have a shape corresponding to the channel. In the arrangement shown, the conduit 121' is boustrophedonic. That is, the conduit 121' can have a shape that is configured so that the second coolant fluid can flow along the axis in a first longitudinal direction, then change direction and flow along the axis in an opposite second longitudinal direction, then change direction again and flow in the first longitudinal direction, and so on. Figure 5 As shown, this shape can be formed as an imaginary cylinder configured to be received within the housing 110 in the axial direction indicated by the arrow in the figure, particularly within the channel of the stator cooling path 111 ′, as shown by the dotted line representing the duct 121 ′ within the housing 110 ′.

[0051] Figure 6 is a schematic diagram showing an aircraft 1. The aircraft comprises an aircraft engine 2 connected to an external coolant circuit 200. The aircraft further comprises an electric machine 4 comprising a stator 100, a rotor assembly 130 and a coolant circuit 140 which may be driven by a pump 142. The electric machine 4 may be driven by the engine 2 via an input shaft 3. Heat may be exchanged between a second coolant fluid in the coolant circuit 140 and a first coolant fluid in the external coolant circuit 200 at the stator 100.

[0052] Various modifications may be made to all of the above-described embodiments, whether by way of addition, deletion, and / or substitution, to provide further embodiments, any and / or all of which are intended to be encompassed by the appended claims.

Claims

1. A motor, comprising: a stator comprising a stator core and a plurality of stator slots extending along a longitudinal axis of the stator; a rotor assembly including a rotor configured to rotate about the longitudinal axis; as well as A coolant system, the coolant system comprising: a stator cooling path configured to provide a first coolant fluid in direct contact with the stator and flowing around the stator core and through the stator slots; and a coolant circuit configured to provide a second coolant fluid to at least one rotatable component of the electric machine; Therein, the coolant circuit and the stator cooling path are fluidly isolated from each other and are arranged such that heat is exchanged between the first coolant fluid and the second coolant fluid at the stator.

2. The motor according to claim 1, wherein: The stator is included in a housing, and the stator cooling path is configured to provide the first coolant fluid between the stator and the housing.

3. The motor according to claim 2, wherein: The stator cooling path includes a channel configured to provide the first coolant fluid between the stator and the housing.

4. The motor according to claim 3, wherein: The passage is at least partially defined by at least one recess in the housing.

5. The motor according to claim 3 or claim 4, wherein: The channel is at least partially defined by the stator.

6. The electric machine according to any one of claims 3 to 5, wherein: The passage is helical relative to the longitudinal axis.

7. The electric machine according to any one of claims 3 to 6, wherein: The channel of the stator cooling path is a first channel, and the coolant circuit includes a second channel disposed at least partially within or adjacent to the first channel.

8. The electric machine according to claim 7, wherein: The second passage includes a spiral shaped conduit received by the first passage.

9. An electric machine according to any preceding claim, wherein: The coolant circuit is configured to provide the second coolant fluid between the housing and the stator.

10. An electric machine according to any preceding claim, wherein The stator cooling path includes a plurality of longitudinal recesses defined in the housing.

11. An aircraft engine assembly comprising an electric machine according to any preceding claim.

12. An aircraft comprising an aircraft engine assembly according to claim 11.

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