Electric machine with rotor cooling based on forced convection

Abstract

A rotating electric machine for use with a coolant includes a stator and a rotor assembly. The rotor assembly includes a rotor, a rotor shaft, and a first end ring and a second end ring. The rotor has an inner diameter surface and an outer diameter surface and a set of embedded rotor magnets near the outer diameter surface. The shaft is connected to the rotor and defines a main coolant channel along the axis of rotation. The radial shaft coolant channel is in fluid communication with the main coolant channel. The end ring is located at the opposite distal end of the rotor. The shaft coolant channel guides the coolant into the rotor and / or the end ring so that the coolant flows axially through the rotor cavity of the rotor and cools the rotor magnets via forced convection.

Description

Background Art

[0001] Electric traction motors and motor-generator units are commonly referred to as rotary electric machines. Such machines have a rotor and a stator separated from each other by a short distance by an air gap. A plurality of stator teeth project radially from a cylindrical stator core toward the rotor, with adjacent stator teeth separated from each other by respective stator slots. Each stator slot is filled with a conductor or solid bar segment that together form a set of stator windings. In a multi-phase rotary electric machine, an alternating current ("AC") input voltage is applied to the stator windings to energize the stator, thereby generating a rotating stator magnetic field.

[0002] The rotor of an interior permanent magnet ("IPM") type motor includes an array of embedded permanent magnets. Unlike the electromagnets created by the sequential excitation of the stator windings described above, the rotor magnets establish a rotor magnetic field that does not vary over time. The stator and rotor magnetic fields interact to create and maintain a force within the stator-rotor air gap that ultimately imparts rotation to the rotor and the connected rotor shaft.

[0003] The torque performance of a rotating electrical machine is affected by the operating temperature. Therefore, thermal management systems are often used to regulate the motor temperature in real time. The torque performance of an IPM traction motor is particularly highly dependent on the temperature of the rotor magnets embedded in the rotor steel lamination layers. For example, the problem of iron loss occurs in high power operating modes, and this iron loss ultimately increases with the rotor temperature and contributes to the rotor temperature. In certain applications, material-based approaches (e.g., using specialized high temperature resistant rotor magnets) for mitigating some of the problems typically associated with elevated rotor temperatures may be suboptimal due to increased cost and / or complexity. Therefore, more effective alternative methods for reducing the rotor / rotor magnet temperature within a rotating electrical machine are needed. Summary of the invention

[0004] The present disclosure relates to a forced convection based method and related structure for cooling a rotor of a rotating electrical machine. The scheme described herein can be used in a rotor assembly having a set of internal permanent rotor magnets that can be embedded within the lamination layers of a cylindrical rotor. The rotor can be constructed of steel or another ferrous material suitable for the application and enclosed between annular end rings such that the end rings are disposed at opposite distal ends of the rotor.

[0005] The disclosed method circulates a coolant suitable for the application, such as automatic transmission fluid ("ATF"), through a network of interconnected cooling channels and cavities of a rotor assembly. The coolant is ultimately directed axially through the rotor. Desired levels of convective cooling may occur in the various disclosed embodiments, either through direct / wet cooling of the individual rotor magnets or by passing the coolant through rotor cavities. Such cavities are defined in predetermined areas of the rotor having low magnetic flux density relative to other areas of the rotor. Otherwise, such low magnetic flux density areas would be largely unable to make an effective contribution to the overall torque performance of the motor. The present method allows the use of underutilized low magnetic flux density areas to provide greater advantages in cooling the rotor magnets and surrounding rotor with minimal degradation of the torque performance of the motor.

[0006] In an exemplary embodiment, a rotating electric machine includes a cylindrical stator and a rotor assembly, the rotor being separated from the stator by an air gap. The rotor assembly includes a cylindrical rotor having an axis of rotation and an inner diameter surface and an outer diameter surface. As described above, the rotor defines a plurality of cavities. Permanent rotor magnets are embedded within the rotor near the outer diameter surface.

[0007] The rotor assembly also includes a rotor shaft connected to the rotor. The rotor shaft defines an elongated main coolant channel along the axis of rotation. The main coolant channel configured to receive coolant also defines a plurality of radial axis coolant channels. Each radial axis coolant channel of the rotor shaft is in fluid communication with the main coolant channel and each cavity of the rotor.

[0008] The rotor assembly also includes a first end ring and a second end ring, respectively, located at opposite distal ends of the rotor. The end rings define corresponding annular pockets in fluid communication with the main coolant passage and the cavity of the rotor. The rotor shaft, the rotor, and the end rings are configured together to direct coolant radially and axially through the rotor via the main coolant passage, the radial shaft coolant passage, the cavity, and the annular pockets, thereby cooling the rotor magnets via forced convection.

[0009] In some embodiments, the cavity of the rotor extends from the inner diameter surface of the rotor toward the embedded rotor magnet, and the cavity is located in a low magnetic flux density area. In some embodiments, the rotor magnet can be disposed in a corresponding one of the cavities, in which case the cavity is referred to herein as a "magnet cavity" for increased clarity. Alternatively, the cavity can be located between the rotor shaft and the rotor magnet, in which case the cavity is referred to as a "rotor cavity" to distinguish it from the above-mentioned magnet cavity.

[0010] The rotor cavity may optionally include a main branch and at least one secondary branch intersecting the main branch. This branch embodiment may facilitate the distribution of coolant in low magnetic flux density regions of the rotor.

[0011] The first end ring and / or the second end ring define drain holes in fluid communication with a cavity of the rotor (i.e., a magnet cavity or a rotor cavity, depending on the embodiment). The drain holes may be evenly spaced relative to each other and located proximate an inner diameter surface of the rotor, the drain holes being configured to deposit coolant onto the stator as the coolant exits the rotor.

[0012] In some configurations, the rotor magnets may be arranged in a generally V-shaped configuration when the rotor is viewed along the axis of rotation.

[0013] In various embodiments, the radial shaft coolant passage may be located at the axial midpoint of the rotor or adjacent to the first end ring and / or the second end ring.

[0014] The stator may surround the rotor such that the air gap is a radial air gap. In such an embodiment, the electric machine may be configured as a radial flux type traction motor.

[0015] An electric propulsion system is also disclosed herein. The electric propulsion system includes a direct current ("DC") voltage bus and a traction power inverter module ("TPIM"). The TPIM is connected to the DC voltage bus and configured to receive a DC input voltage from the DC voltage bus, and output an alternating current (AC) voltage. The electric propulsion system includes a multi-phase rotating electric machine that is used with a coolant and is excited via an AC voltage from the TPIM. In the exemplary embodiment, the electric machine is configured as described above.

[0016] A method for cooling a rotating electric machine using ATF or another suitable coolant is also disclosed herein. A rotating electric machine cooled via the disclosed method includes a rotor located between a first end ring and a second end ring, the rotor defining a plurality of cavities. The method according to an embodiment includes circulating a coolant via a pump through a primary coolant channel defined by a rotor shaft of the electric machine. The primary coolant channel extends along an axis of rotation of the rotor shaft, which in turn is connected to the rotor.

[0017] The method may include directing coolant from a primary coolant passage through a radial shaft coolant passage defined by a rotor shaft and into a corresponding one of the cavities of the rotor directly or through a first end ring or a second end ring. The coolant is then discharged from the rotor through a discharge hole defined by the first end ring and / or the second end ring.

[0018] Solution 1. A rotating electric machine for use with a coolant, the rotating electric machine comprising:

[0019] stator; and

[0020] A rotor assembly separated from the stator by an air gap and comprising:

[0021] a rotor having an axis of rotation, an inner diameter surface, and an outer diameter surface, wherein the rotor defines a plurality of cavities;

[0022] A rotor magnet embedded in the rotor near the outer diameter surface;

[0023] a rotor shaft connected to the rotor, the rotor shaft defining a main coolant passage along an axis of rotation configured to receive coolant, and a plurality of radial shaft coolant passages, each radial shaft coolant passage being in fluid communication with the main coolant passage and the cavity; and

[0024] a first end ring and a second end ring respectively located at opposite distal ends of the rotor, each of the first end ring and the second end ring defining an annular pocket therein in fluid communication with the primary coolant passage;

[0025] Therein, the rotor shaft, rotor and end rings are collectively configured to direct coolant through the rotor via main coolant passages, radial shaft coolant passages, cavities and annular pockets, thereby cooling the rotor magnets via forced convection.

[0026] Aspect 2. The rotating electric machine according to aspect 1, wherein the rotor includes a predetermined low magnetic flux density region, and wherein the cavity extends from an inner diameter surface of the rotor toward the rotor magnet within the predetermined low magnetic flux density region.

[0027] Solution 3. The rotating electrical machine according to Solution 2, wherein each cavity includes a main branch and at least one secondary branch intersecting the main branch.

[0028] Aspect 4. The rotating electric machine according to aspect 1, wherein the cavity is a magnet cavity located near the outer diameter surface, and wherein each respective one of the rotor magnets is disposed within a respective one of the magnet cavities.

[0029] Embodiment 5. The rotating electric machine according to embodiment 1, wherein the first end ring and / or the second end ring defines a set of drain holes in fluid communication with the cavity.

[0030] Aspect 6. The rotating electric machine according to aspect 5, wherein the discharge holes are evenly spaced relative to each other and are located near the inner diameter surface of the rotor.

[0031] Aspect 7. The rotating electric machine according to aspect 6, wherein the discharge hole is configured to deposit the coolant onto the stator when the coolant exits the rotor through the discharge hole.

[0032] Aspect 8. The rotating electrical machine according to aspect 1, wherein the rotor magnets are arranged in a substantially V-shaped configuration when the rotor is viewed along the rotation axis.

[0033] Aspect 9. The rotating electrical machine according to aspect 1, wherein the shaft coolant passage is located at an axial midpoint of the rotor.

[0034] Aspect 10. A rotating electrical machine according to aspect 1, wherein the stator surrounds the rotor, the air gap is a radial air gap, and the electrical machine is configured as a radial flux type traction motor.

[0035] Solution 11. An electric propulsion system comprising:

[0036] a direct current ("DC") voltage bus;

[0037] a traction power inverter module ("TPIM") coupled to the DC voltage bus and configured to receive a DC input voltage from the DC voltage bus and to output an alternating current ("AC") voltage;

[0038] A multi-phase rotating electric machine, used with a coolant and excited via an AC voltage from a TPIM, comprising:

[0039] stator; and

[0040] A rotor assembly, the rotor assembly being separated from the stator by an air gap, the rotor assembly comprising:

[0041] a cylindrical rotor having an axis of rotation, an inner diameter surface, and an outer diameter surface, the rotor defining a plurality of cavities;

[0042] A rotor magnet embedded in the rotor near the outer diameter surface;

[0043] a rotor shaft connected to the rotor, wherein the rotor shaft defines a main coolant passage along the axis of rotation configured to receive coolant and further defines a radial shaft coolant passage in fluid communication with the main coolant passage and a respective one of the cavities; and

[0044] a first end ring and a second end ring respectively located at opposite distal ends of the rotor, each of the first end ring and the second end ring defining an annular pocket in fluid communication with the cavity; and

[0045] A load coupled to and driven by the rotor shaft, wherein the rotor shaft, the rotor, and the first and second end rings are collectively configured to direct a coolant through the rotor to cool the rotor and / or rotor magnets via forced convection.

[0046] Option 12. An electric propulsion system according to Option 11, wherein the load includes wheels.

[0047] Embodiment 13. An electric propulsion system according to embodiment 11, wherein the cavity is a magnet cavity, and each of the rotor magnets is disposed in a corresponding one of the magnet cavities.

[0048] Option 14. An electric propulsion system according to Option 11, wherein the rotor includes a predetermined low magnetic flux density region, and wherein the cavity extends from an inner diameter surface of the rotor toward the rotor magnets within the predetermined low magnetic flux density region.

[0049] Embodiment 15. The electric propulsion system of embodiment 11, wherein the first end ring and / or the second end ring defines a drain hole in fluid communication with the cavity.

[0050] Embodiment 16. An electric propulsion system according to embodiment 15, wherein the discharge holes are evenly spaced relative to each other and are located near the inner diameter surface of the rotor, and the discharge holes are configured to deposit coolant onto the stator when the coolant exits the rotor.

[0051] Embodiment 17. A method for cooling a rotating electric machine using a coolant, the rotating electric machine having a rotor positioned between a first end ring and a second end ring, wherein the rotor defines a plurality of cavities, the method comprising:

[0052] circulating a coolant via a pump through a primary coolant passage defined by a rotor shaft of the electric machine, wherein the primary coolant passage extends along an axis of rotation of the rotor shaft, and wherein the rotor shaft is connected to the rotor;

[0053] directing coolant from the main coolant passage through radial shaft coolant passages defined by the rotor shaft and into a respective one of the cavities either directly or through a first end ring or a second end ring; and

[0054] The coolant is discharged from the rotor through a discharge hole defined by the first end ring and / or the second end ring.

[0055] Embodiment 18. The method according to embodiment 17, wherein the rotor includes a predetermined low magnetic flux density region, and wherein the cavity extends from an inner diameter surface of the rotor toward the rotor magnets within the predetermined low magnetic flux density region.

[0056] Option 19. A rotating electric machine according to Option 17, wherein the cavity is a magnet cavity, and each respective one of the rotor magnets is disposed within a respective one of the magnet cavities, and wherein directing the coolant from the main coolant channel through the radial shaft coolant channel of the rotor shaft and into the respective one of the cavities includes placing the coolant in direct wetted contact with the rotor magnets.

[0057] Option 20. A method according to Option 17, wherein the first end ring and / or the second end ring defines a discharge hole connected to the cavity fluid of the rotor, the discharge holes are evenly spaced relative to each other and are located near the inner diameter surface of the rotor, and discharging the coolant from the rotor includes depositing the coolant on the stator of the motor when the coolant leaves the rotor.

[0058] The above summary of the invention is not intended to represent every possible embodiment or every aspect of the present disclosure. On the contrary, the foregoing summary of the invention is intended to illustrate some novel aspects and features disclosed herein. When considered in conjunction with the drawings and the appended claims, the above-mentioned features and advantages of the present disclosure and other features and advantages will be apparent from the following detailed description of representative embodiments and modes for implementing the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is a schematic diagram of a mobile platform having a rotating electric machine whose rotor is internally cooled via forced convection using a defined cavity as described herein.

[0060] Figure 2 yes Figure 1 A schematic diagram of a representative cross-sectional area of ​​an electric machine is shown, illustrating regions of different magnetic flux density and cooling channels for cooling the rotor.

[0061] Figure 3 Can be used as Figure 1 and 2 Schematic cross-sectional view of an exemplary rotor of a portion of an electric machine.

[0062] Figure 4 yes Figure 1 A schematic diagram of a representative portion of an electric machine is shown, illustrating an alternative embodiment of the cooling passages for the rotor.

[0063] Figure 5 and 6 yes Figure 1 A cross-sectional side view of a possible embodiment of forced convection based cooling of rotor magnets within an electric machine is shown.

[0064] The present disclosure is susceptible to modification and alternative forms, and representative embodiments are shown by way of example in the accompanying drawings and described in detail below. The inventive aspects of the present disclosure are not limited to the disclosed embodiments. On the contrary, the present disclosure is intended to cover modifications, equivalents, combinations and alternatives that fall within the scope of the present disclosure defined by the appended claims. DETAILED DESCRIPTION

[0065] Referring to the drawings, wherein like reference numerals designate the same or similar parts throughout the several views, Figure 1 An electric propulsion system 10 is schematically shown in FIG. The electric propulsion system 10 includes a rotating electric machine 12 having a rotor assembly 14 and a stator 16, which are also labeled “R” and “S”, respectively, for added clarity. The rotor assembly 14 is positioned adjacent to the stator 16 and is separated from the stator 16 by an air gap G, as shown in FIG. Figure 2In a non-limiting exemplary embodiment, the rotor assembly 14 is concentrically disposed within the stator 16, i.e., the stator 16 surrounds the rotor assembly 14 such that Figure 2 The air gap G is a radial air gap, and the motor 12 is implemented as a radial flux type motor. However, other embodiments may be implemented in which the relative positions of the rotor assembly 14 and the stator 16 are reversed, that is, the rotor assembly 14 may surround the stator 16. For consistency of description, the rotor assembly 14 will be described below as being radially located within the stator 16. Figure 1 embodiments without limiting the structure to this configuration.

[0066] The rotor assembly 14 of the present disclosure has a set of embedded permanent magnets, referred to herein as rotor magnets 55, and is Figure 3-6 Shown in. Figure 1 The electric machine 10 is thus implemented as an interior permanent magnet ("IPM") type electric machine. When used in a motor vehicle, powertrain, lift, or other beneficial application, the electric machine 10 may be an electric traction motor. The rotor magnets 55 may be composed of, for example, ferrite, neodymium iron boron, samarium cobalt, alnico, etc., or another material suitable for the application. In this IPM embodiment of the electric machine 10, the rotor magnets 55 are embedded within the individual steel lamination layers of the rotor 40 (see Figure 2 ).

[0067] As stated in this article, Figure 2 The rotor magnet 55 of the rotor 40 and the surrounding or nearby area such as Figure 1 Cooling is schematically shown via forced convection using a coolant 21 suitable for the application, such as automatic transmission fluid (“ATF”). The coolant 21 may be stored in a sump 22 and circulated through the rotor assembly 14 via a coolant pump (“P”) 20, as described below with reference to Figure 2-6 As described.

[0068] Continue to refer Figure 1 The electric propulsion system 10 may include an alternating current (“AC”) voltage bus 13. The AC voltage bus 13 may use a high voltage battery pack (“B HV ”) 24 is selectively excited via a traction power inverter module (“TPIM”) 28, such as lithium-ion, lithium-sulfur, nickel metal hydride or other high energy voltage source. The AC voltage bus 13 conducts the AC bus voltage (“VAC”) to and from the motor 10. When operating in a drive or motoring mode, the motor output torque (arrow T M ) is applied to the connected rotor shaft 50 and directed to a coupled load ("L") 52, depending on the application, such as one or more wheels of a motor vehicle (not shown), a propeller shaft, a drive belt, or other driven load.

[0069] The electric propulsion system 10 may also include a direct current to direct current (“DC-DC”) converter 26 configured to reduce or increase the relatively high DC bus voltage (“VDC”) as needed. The DC-DC converter 26 is connected between the battery pack 24 and the TPIM 28 via the positive (+) and negative (-) rails of the corresponding DC voltage bus 15. In some configurations, the auxiliary battery pack (“B AUX Auxiliary battery pack 124 may be connected to DC-DC converter 26 and may be implemented as lead-acid batteries or constructed of another chemistry suitable for the application and configured to store or supply a 12-15V auxiliary voltage (“V AUX ”) to a battery for one or more connected auxiliary devices (not shown).

[0070] refer to Figure 2 , the present solution contemplates the use of forced convection-based cooling of the rotor 40 through a cavity defined by the rotor 40 of the electric machine 12. Such a cavity may be implemented as a magnet cavity 42 or a rotor cavity 44 and 144, as described below. The stator 16 is cylindrical to surround the equally cylindrical rotor 40 of the rotor assembly 14 in the exemplary embodiment shown, and the stator 16 is separated from the rotor 40 by the above-mentioned air gap G. In this configuration, both the stator 16 and the rotor 40 may be constructed from a stack of thin lamination layers of electrical steel or another ferrous material, for example, each layer having a thickness of about 2-5 mm, as will be understood by a person of ordinary skill in the art. The stator 16 has radially projecting stator teeth 32, each of which extends inwardly from a cylindrical stator housing or core 30, and the stator core 30 has an outer diameter surface 160. That is, the stator teeth 32 extend from the stator core 30 toward the outer diameter surface 140 of the rotor 40. As will be understood by one of ordinary skill in the art, adjacent stator teeth 32 of the stator 16 are separated from one another by corresponding stator slots 33 .

[0071] When construct Figure 2 In the illustrated electric machine 12, the stator slots 33 are substantially filled with electrical conductors, typically copper wires or copper strips / "hairpins". Such conductors together form the stator windings 35 (see Figure 4 ). When the stator winding 35 is composed of Figure 1 The AC output voltage of the TPIM 28 is sequentially energized to generate a rotating stator magnetic field. The stator magnetic poles formed by the resulting rotating stator magnetic field are connected to the stator magnetic poles formed by the various rotor magnets 55 (see Figure 3-6 ) provide for the rotor poles to interact so that Figure 1 and 3 -6 The rotor shaft 50 rotates so that Figure 1 The load 52 provides power.

[0072] The number, type, location and / or relative orientation of the rotor magnets 55 ultimately affects the magnitude and distribution of the magnetic flux in the ferrous material of the electric machine 12. The rotor magnets 55 may be arranged in a generally V-shaped configuration as shown (i.e., when the rotor 40 is viewed along its rotational axis AA), such as Figure 3 4, where the ends of the rotor magnets 55 adjacent to the outer diameter surface 140 of the rotor 40 are spaced further apart from each other than the opposite ends of the rotor magnets 55 located adjacent to the inner diameter surface 240. Since the rotor 40 is annular or ring-shaped, the inner diameter surface 240 is presented opposite the outer diameter surface 140, adjacent to the rotor shaft 50, as shown. Figure 3 shown.

[0073] The present cooling method based on forced convection includes initially identifying regions of different magnetic flux density within the electric machine 12. Some regions will be relatively weak and therefore underutilized in the torque generation process, i.e., low magnetic flux density regions LL. Medium and high magnetic flux density regions are similarly labeled MM and HH, respectively. Because different configurations and intended end uses of the electric machine 12 will have unique magnetic flux density distributions, the terms "high," "medium," and "low" are used herein only in a relative sense.

[0074] Once the low flux density regions LL have been pre-identified offline, such as via modeling or testing of the rotor 40 with its embedded rotor magnets 55, embodiments of the present teachings define a plurality of rotor cavities 44 and 144 in the rotor 40. For clarity of illustration, Figure 2 4 and 144. Such rotor cavities 44 are mainly arranged in the low magnetic flux density area LL of the rotor 40. As shown in the figure, a given set of rotor cavities 44 is laterally connected via rotor cavities 144 to improve the flow of coolant 21 (see Figure 1 ). The rotor cavity 44 extends in a generally radial direction, ie, from the rotor shaft 50 (see Figure 3 ) outwardly and toward magnet cavity 42 and rotor magnet 55 located therein, but not reaching magnet cavity 42 and rotor magnet 55 located therein. Although rotor cavity 44 may also extend partially into medium flux density region MM, because such region is arbitrarily defined in relative terms for a given motor 12, rotor cavity 44 is ideally limited to the low flux density region LL to the extent possible to minimize degradation in torque performance.

[0075] In another embodiment, Figure 1The coolant 21 circulates through the magnet cavities 42 in direct / wetted contact with and cooling the rotor magnets 55. In the assembled IPM configuration of the electric machine 12, each respective one of the rotor magnets 55 is positioned within a respective magnet cavity 42. In such an embodiment, the rotor magnets 55 are directly wetted by the coolant 21 and thereby cooled by the coolant 21 as the coolant 21 flows axially through the rotor 40. Both embodiments will now be described in more detail with reference to the remaining drawings.

[0076] refer to Figure 3 , Figure 1 The rotor assembly 14 schematically shown in FIG. 1 includes a rotor 40, a rotor shaft 50, and rotor magnets 55. The rotor shaft 50, which may be journaled or splined to the rotor 40 to rotate therewith about the axis of rotation AA of the rotor assembly 14, defines a primary coolant passage 46. The primary coolant passage 46 extends along the axis of rotation AA and is thus coaxial with the axis of rotation AA. Thus, the supply of coolant 21 to the rotor 40 is initially made through the primary coolant passage 46, from which the coolant 21 is supplied radially outwardly through the radial shaft coolant passages 48 defined by the rotor shaft 50, for example, in a non-limiting embodiment, through eight evenly spaced radial shaft coolant passages 48.

[0077] Depending on the configuration, Figure 1 The coolant 21 may enter the rotor cavity 44 to indirectly cool a particular set of rotor magnets 55, i.e., by reducing the temperature of the rotor 40 in the area near the rotor magnets 55. Alternatively, the coolant 21 may enter the magnet cavity 42 directly. For simplicity and clarity of illustration, Figure 3 4 shows a single set of rotor cavities 44 extending toward and between adjacent sets of rotor magnets 44. However, in actual construction of the rotor assembly 14, multiple sets of similar rotor cavities 44 will be evenly spaced around the circumference of the rotor shaft 50 and extend to Figure 2 The low magnetic flux density region LL of the rotor 40 is shown. In this way, the coolant 21 is guided toward each magnet cavity 42.

[0078] Figure 4 The exemplary embodiment of FIG. 4 shows a possible configuration of the rotor 40, wherein the rotor cavity 44 is configured with a multi-branch / T shape. For reference, a portion of the stator 16 is also shown, which shows the stator windings 35 filling the stator slots 33 near the rotor magnets 55. The rotor magnets 55 are disposed near the outer diameter surface 140 of the rotor 40, close to the stator windings 35, to help ensure a strong mutual field interaction between the magnetic fields of the rotor 40 and the stator 16.

[0079] In the schematic diagram of the inner layer of the rotor 40 and the stator 16 Figure 4, with cross-hatching omitted for clarity, the rotor cavities 44 are shown as providing a branched / generally T-shaped flow distribution pattern. In the illustrated embodiment, each rotor cavity 44 includes a main branch 64 extending radially outward from the rotor shaft 50 and in fluid communication with the main coolant passage 46. Coolant flow (arrow F) flows from the main coolant passage 46 through the radial shaft coolant passages 48 (see FIG. 4 ) within the rotor shaft 50. Figure 3 ), and enters the corresponding main branch 64 of each rotor coolant channel 44. Instead of using Figure 3 The plurality of linear rotor chambers 44 shown in the simplified embodiment of Figure 4 The branch embodiment of FIG. 4 intersects the rotor cavity 44 with a secondary branch 62 , which terminates at a branch end 65 .

[0080] Such branch ends 65 may be parallel to the main branch 64 or slightly angled as shown to provide a desired distribution of the coolant 21 . Figure 4 The branch configuration may use additional secondary branches 62 to further distribute the coolant 21 through the low flux density area LL (see Figure 2 ), and may be distributed over short distances to Figure 2 The medium flux density region MM (“LL-MM”) shown is therefore Figure 4 The embodiments are non-limiting and exemplary of the present teachings. That is, within the scope of the present disclosure, the rotor cavity 44 may have other shapes, sizes, and contours as needed to provide the desired distribution of the coolant 21 within the rotor 40.

[0081] refer to Figure 5 and 6 , for simplicity of explanation, both omit the stator 16 of the motor 12, and the rotor assembly 14 includes a first end ring 70A and a second end ring 70B, which enclose the rotor 40 between them. In other words, the end rings 70A and 70B are disposed at opposite distal ends of the rotor 40 so that the rotor magnets 55 extend axially between the end rings 70A and 70B. The rotor shaft 50 surrounded by the rotor 40 and the end rings 70A and 70B is rotatably supported by bearing assemblies 80A and 80B at its distal end. The size, shape, and configuration of the bearing assemblies 80A and 80B are merely representative and have nothing to do with the convection cooling function of the disclosed rotor assembly 14, and are therefore shown only as a reference.

[0082] Figure 1The delivery of the coolant 21 to the rotor assembly 14 via forced convection relies on the presence of a suitable cooling manifold. Within the scope of the present disclosure, such a manifold includes the rotor shaft 50 and the end rings 70A and 70B. That is, in some configurations, the coolant 21 can circulate through the rotor shaft 50, enter one of the end rings 70A or 70B, pass through the rotor cavity 44 or the magnet cavity 42, and flow out through the other end ring 70B or 70A. Alternatively, the coolant 21 can circulate through the rotor shaft 50, enter the rotor cavity 44 or the magnet cavity 42, and flow out of the end rings 70A and / or 70B. Both options are shown in Figures 5 and 6.

[0083] More specifically, the coolant flow (arrow F) of the coolant 21 is axially delivered into the rotor 40 via the main coolant passage 46 defined by the rotor shaft 50. Figure 5 In an exemplary embodiment of the present invention, coolant flow (arrow F) may enter the main coolant passage 46 along the rotation axis AA, for example, from Figure 5 The coolant 21 then enters the radial shaft coolant passage 48 located near the end ring 70B (from Figure 5 40 ), and then enters the annular / circular recess 72 defined by the second end ring 70B near the outer diameter surface 140 of the rotor 40. An alternative embodiment is also shown in which the coolant passage 48A is located at the axial midpoint of the rotor 40, the coolant passage 48A extending between and terminating at the main coolant passage 46 and the magnet cavity 42. Such a location can facilitate more evenly distributed cooling of the rotor 40, for example by minimizing the distance that the coolant 21 must travel in the axial direction through the rotor 40.

[0084] To ensure that the coolant 21 is collected and evenly distributed to the magnet cavity 42, the recess 72 is formed by Figure 5 The end rings 70A and 70B are defined in close proximity to the rotor magnets 55, i.e., at the distal end of the rotor 40. In the illustrated embodiment, once the coolant 21 substantially fills the recess 72 of the end ring 70B, for example, the coolant 21 enters the magnet cavity 42 (see Figure 3 ), thereafter flowing axially through the rotor 40 through each fluidly connected magnet cavity 42. The coolant 21 eventually enters the pocket 72 of the end ring 70A before exiting the rotor assembly 14.

[0085] Although the rotor magnets 55 will occupy most of the available space within the magnet cavity 42 in a fully constructed embodiment of the rotor assembly 14, some space will remain around the periphery of the rotor magnets 55. Figure 3 The remaining space best shown at the end of the rotor magnet 55 shown allows the coolant 21 to flow freely through the connected magnet cavity 42, i.e., at Figure 5 The coolant 21 thus flows axially through the rotor 40 , making wetted contact with the rotor magnets 55 , which absorb heat therefrom via forced convection.

[0086] To facilitate coolant 21 exiting the rotor 40 and subsequent distribution, the first end ring 70A, remotely positioned relative to the second end ring 70B, may be perforated to define a set of drain holes 90. Each drain hole 90 is sized, shaped, and spaced to allow coolant 21 to freely exit the rotating rotor 40. In some embodiments, the second end ring 70B may be similarly perforated. Figure 5 and 6 The discharge holes 90 are configured to evenly distribute the coolant 21 as it leaves the distal end of the rotor 40, such as by spraying or pouring the discharged coolant 21 onto the adjacent stator windings 35 (see Figure 4 ) and / or other suitable exposed portions of the stator 16 / motor 12. For optimal distribution of the exiting coolant 21, the discharge holes 90 should be located as close as possible to the inner diameter surface 240 of the rotor 40 due to the expected effect of centrifugal forces acting on the coolant 21. The coolant 21 can then return to the Figure 1 The storage tank 22 is shown.

[0087] Figure 6 Shown according to Figure 3 and 4 An alternative method for providing cooling of the rotor 40 based on forced convection is provided in accordance with an embodiment of the present invention. In this embodiment, the recess 72 is disposed relative to the Figure 5 The position of the recess 72 in the rotor 40 is moved radially inward toward the rotor shaft 50 so that the recess 72 is adjacent the rotor cavity 44. Coolant flow (arrow F) is directed into the coolant passage 48A along the rotational axis AA, into the rotor cavity 44, and is directed axially outward in both axial directions through the rotor 40, i.e., toward the first end ring 70A and the second end ring 70B. The coolant 21 exits the rotor 40 through the above-mentioned discharge holes 90, which are ideally located as close to the inner diameter surface 240 of the rotor 40 as possible within the packaging constraints of the particular application.

[0088] therefore, Figure 5 and 6 The embodiments of the present invention provide an alternative method of using forced convection to cool the rotor magnets 55. Thus, the increase in the convection area of ​​the rotor 40 results in a lower temperature of the rotor 40 and its embedded rotor magnets 55. For example, in Figure 5In the exemplary embodiment of , the rotor magnets 55 are cooled by the flow of coolant 21 axially along the primary coolant passages 46, radially into the end rings 70B and pockets 72, and then axially around the rotor magnets 55 via the interconnected magnet cavities 42. Thus, heat is transferred directly from the rotor magnets 55 to the circulating coolant 21 before the heated coolant 21 is ultimately exhausted through the exhaust holes 90.

[0089] Similarly, Figure 6 The embodiment allows the coolant 21 to directly enter the low magnetic flux density area LL in the rotor 40 through the rotor cavity 44. Figure 2 Thus, heat from the rotor magnets 55 and the laminations of the rotor 50 is transferred to the coolant 21, and the heated coolant 21 is then discharged from the rotor 40, as shown in FIG. Figure 5 Therefore, Figure 2-6 The various embodiments may be used as improvements to the general state of the art for rotor cooling in rotating electric machines, such as the electric machine 12 described herein.

[0090] In view of the foregoing disclosure, it is easy to imagine using Figure 1 The method of cooling the motor 12 with a coolant 21 may include, for example, circulating the coolant 21 through the pump 20 Figure 5 and 6 The method may further include directing the coolant 21 from the main coolant passage 46 through the radial shaft coolant passage 48 or 48A of the rotor shaft 50 and directly into a corresponding one of the rotor cavities 42 or 44 or through the first end ring 70A or the second end ring 70B into a corresponding one of the rotor cavities 42 or 44. In addition, the method may include discharging the coolant 21 from the rotor 40 through a set of discharge holes 90 defined by the first end ring 70A and / or the second end ring 70B.

[0091] Although some best modes and other embodiments have been described in detail, there are various optional designs and embodiments for practicing the present teachings defined in the appended claims. Those skilled in the art will recognize that the disclosed embodiments may be modified without departing from the scope of the present disclosure. Moreover, the present concept explicitly includes combinations and sub-combinations of the described elements and features. The detailed description and drawings support and describe the present teachings, and the scope of the present teachings is limited only by the claims.

Claims

1. A rotating electrical machine for use with a coolant, the rotating electrical machine comprising: stator; and A rotor assembly separated from the stator by an air gap and comprising: a rotor having an axis of rotation, an inner diameter surface, and an outer diameter surface, wherein the rotor defines a plurality of cavities; A rotor magnet embedded in the rotor near the outer diameter surface; a rotor shaft connected to the rotor, the rotor shaft defining a main coolant passage along an axis of rotation configured to receive coolant, and a plurality of radial shaft coolant passages, each radial shaft coolant passage being in fluid communication with the main coolant passage and the cavity; and a first end ring and a second end ring respectively located at opposite distal ends of the rotor, each of the first end ring and the second end ring defining an annular pocket therein in fluid communication with the primary coolant passage; wherein the rotor shaft, rotor and end rings are collectively configured to direct coolant through the rotor via main coolant passages, radial shaft coolant passages, cavities and annular pockets to cool the rotor magnets via forced convection, The rotor includes a low magnetic flux density region, a medium magnetic flux density region and a high magnetic flux density region, wherein the medium magnetic flux density region has a higher magnetic flux density than the low magnetic flux density region, and the high magnetic flux density region has a higher magnetic flux density than the low magnetic flux density region and the medium magnetic flux density region, and the cavity of the rotor is separated from the high magnetic flux density region.

2. The rotating electrical machine according to claim 1, wherein: The cavity extends from an inner diameter surface of the rotor toward the rotor magnets in a region of low magnetic flux density.

3. The rotating electrical machine according to claim 2, wherein: Each cavity includes a main branch and at least one secondary branch intersecting the main branch.

4. The rotating electrical machine according to claim 1, wherein: The cavities are magnet cavities located proximate the outer diameter surface, and wherein each respective one of the rotor magnets is disposed within a respective one of the magnet cavities.

5. The rotating electrical machine according to claim 1, wherein: The first end ring and / or the second end ring define a set of drainage holes in fluid communication with the cavity.

6. The rotating electrical machine according to claim 5, wherein: The discharge holes are evenly spaced relative to one another and are located proximate the inner diameter surface of the rotor.

7. The rotating electrical machine according to claim 6, wherein: The drain holes are configured to deposit coolant onto the stator as the coolant exits the rotor through the drain holes.

8. The rotating electrical machine according to claim 1, wherein: The rotor magnets are arranged in a generally V-shaped configuration when the rotor is viewed along the axis of rotation.

9. The rotating electrical machine according to claim 1, wherein: The shaft coolant passage is located at the axial midpoint of the rotor.

10. The rotating electrical machine according to claim 1, wherein: The stator surrounds the rotor, the air gap is a radial air gap, and the electric machine is configured as a radial flux type traction motor.

11. An electric propulsion system comprising: DC voltage bus; a traction power inverter module connected to the DC voltage bus and configured to receive a DC input voltage from the DC voltage bus and output an AC voltage; A multi-phase rotating electric machine, used with a coolant and excited via an AC voltage from a traction power inverter module, comprising: stator; and A rotor assembly, the rotor assembly being separated from the stator by an air gap, the rotor assembly comprising: a cylindrical rotor having an axis of rotation, an inner diameter surface, and an outer diameter surface, the rotor defining a plurality of cavities; A rotor magnet embedded in the rotor near the outer diameter surface; a rotor shaft connected to the rotor, wherein the rotor shaft defines a main coolant passage along the axis of rotation configured to receive coolant and further defines a radial shaft coolant passage in fluid communication with the main coolant passage and a respective one of the cavities; and a first end ring and a second end ring respectively located at opposite distal ends of the rotor, each of the first end ring and the second end ring defining an annular pocket in fluid communication with the cavity; and a load coupled to and driven by the rotor shaft, wherein the rotor shaft, the rotor, and the first and second end rings are collectively configured to direct a coolant through the rotor to cool the rotor and / or the rotor magnets via forced convection, The rotor includes a low magnetic flux density region, a medium magnetic flux density region and a high magnetic flux density region, wherein the medium magnetic flux density region has a higher magnetic flux density than the low magnetic flux density region, and the high magnetic flux density region has a higher magnetic flux density than the low magnetic flux density region and the medium magnetic flux density region, and the cavity of the rotor is separated from the high magnetic flux density region.

12. The electric propulsion system according to claim 11, wherein: The load includes wheels.

13. The electric propulsion system of claim 11, wherein: The cavities are magnet cavities, and each of the rotor magnets is disposed within a respective one of the magnet cavities.

14. The electric propulsion system of claim 11, wherein: The cavity extends from an inner diameter surface of the rotor toward the rotor magnets in a region of low magnetic flux density.

15. The electric propulsion system of claim 11, wherein: The first end ring and / or the second end ring defines a drain hole in fluid communication with the cavity.

16. The electric propulsion system of claim 15, wherein: The drain holes are evenly spaced relative to one another and are located proximate an inner diameter surface of the rotor, the drain holes being configured to deposit coolant onto the stator as the coolant exits the rotor.

17. A method for cooling a rotating electrical machine using a coolant, the rotating electrical machine having a rotor between a first end ring and a second end ring, wherein: The rotor defines a plurality of cavities, and the method comprises: circulating a coolant via a pump through a primary coolant passage defined by a rotor shaft of the electric machine, wherein the primary coolant passage extends along an axis of rotation of the rotor shaft, and wherein the rotor shaft is connected to the rotor; directing coolant from the main coolant passage through radial shaft coolant passages defined by the rotor shaft and into a respective one of the cavities either directly or through a first end ring or a second end ring; and discharging coolant from the rotor through a discharge hole defined by the first end ring and / or the second end ring, The rotor includes a low magnetic flux density region, a medium magnetic flux density region and a high magnetic flux density region, wherein the medium magnetic flux density region has a higher magnetic flux density than the low magnetic flux density region, and the high magnetic flux density region has a higher magnetic flux density than the low magnetic flux density region and the medium magnetic flux density region, and the cavity of the rotor is separated from the high magnetic flux density region.

18. The method according to claim 17, wherein: The cavity extends from an inner diameter surface of the rotor toward the rotor magnets in a region of low magnetic flux density.

19. The method according to claim 17, wherein: The cavities are magnet cavities, and each respective one of the rotor magnets is disposed within a respective one of the magnet cavities, and wherein directing coolant from the main coolant passage through the radial shaft coolant passage of the rotor shaft and into the respective one of the cavities includes placing the coolant in direct wetted contact with the rotor magnets.

20. The method according to claim 17, wherein: The first end ring and / or the second end ring define discharge holes in fluid communication with the cavity of the rotor, the discharge holes being evenly spaced relative to each other and located near the inner diameter surface of the rotor, and discharging coolant from the rotor includes depositing the coolant on the stator of the electric machine when the coolant leaves the rotor.

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