Axial flux electric machine including a system for circulating a coolant through an air gap

Abstract

An electric motor includes a housing, a shaft, a rotor, a stator, and at least one coolant supply channel. The shaft is rotatably mounted within the housing and has a longitudinal axis. The rotor is fixed to the shaft for rotation therewith. The stator is spaced apart from the rotor along the longitudinal axis of the shaft to create at least one air gap between the stator and the rotor. The at least one coolant supply channel extends through at least one of the shaft and the stator and is configured to supply a coolant flow to the at least one air gap.

Description

Technical Field

[0001] The information provided in this section is for the purpose of generally presenting the background of the present disclosure. To the extent described in this section, the work of the presently named inventors and aspects of the description that may not have originally constituted prior art at the time of filing are neither explicitly nor implicitly admitted to be prior art to the present disclosure.

[0002] The present disclosure relates to an axial flux electric machine including a system for circulating a coolant through an air gap between a stator and a rotor. Background Art

[0003] The electric motor generally includes a housing, a shaft, a stator fixed to the housing, and a rotor fixed to the shaft. Each of the stator and the rotor has a ferromagnetic core. One of the stator and the rotor includes a coil winding, and the other of the stator and the rotor includes a permanent magnet. When current flows through the coil winding, the current generates a magnetic field that interacts with the magnetic field generated by the permanent magnet. This interaction generates a force that rotates the rotor and the shaft.

[0004] Two types of electric motors are radial flux motors and axial flux motors. In a radial flux motor, the stator and the rotor are spaced apart from each other in the radial direction of the shaft to create a radial gap between the stator and the rotor, and thus the magnetic flux of the radial flux motor extends radially. In an axial flux motor, the stator and the rotor are spaced apart from each other in the axial direction of the shaft to create an axial gap between the stator and the rotor, and thus the magnetic flux of the axial flux motor extends axially. Summary of the invention

[0005] An example of an electric motor according to the present disclosure includes a housing, a shaft, a rotor, a stator, and at least one coolant supply channel. The shaft is rotatably mounted in the housing and has a longitudinal axis. The rotor is fixed to the shaft so as to rotate therewith. The stator is spaced apart from the rotor along the longitudinal axis of the shaft to create at least one air gap between the stator and the rotor. At least one coolant supply channel extends through at least one of the shaft and the stator and is configured to supply a coolant flow to the at least one air gap.

[0006] In one example, the rotor includes permanent magnets that generate a magnetic flux extending along a longitudinal axis of the shaft.

[0007] In one example, the rotor includes a first portion and a second portion, the stator is disposed between the first portion and the second portion of the rotor in an axial direction parallel to a longitudinal axis of the shaft, and at least one air gap includes a first air gap disposed between the first portion of the rotor and the stator and a second air gap disposed between the second portion of the rotor and the stator.

[0008] In one example, at least one coolant supply passage extends through the shaft.

[0009] In one example, at least one coolant supply channel includes a main coolant channel and at least one branch coolant channel. The main coolant channel extends through the end of the shaft in the axial direction of the shaft. The at least one branch coolant channel extends from the main coolant channel through the outer radial surface of the shaft to the at least one air gap in the radial direction of the shaft.

[0010] In one example, the at least one branch coolant channel includes a pair of branch coolant channels disposed on opposite sides of the main coolant channel.

[0011] In one example, at least one coolant supply passage extends through the stator.

[0012] In one example, the housing defines an annular coolant jacket disposed radially outward from the stator, and the at least one coolant supply channel includes a main coolant channel and at least one branch coolant channel. The main coolant channel extends axially from one side of the housing through the housing to the annular coolant jacket. The at least one branch coolant channel extends radially inward from the annular coolant jacket through the housing and the stator, and extends axially through the stator to the at least one air gap.

[0013] In one example, the at least one branch coolant passage includes a pair of branch coolant passages disposed on opposite sides of the shaft.

[0014] In one example, the electric motor further includes at least one coolant return passage extending through the housing and configured to receive the coolant after the coolant flows through the at least one air gap.

[0015] In one example, the at least one coolant return passage is axially aligned with the at least one air gap and disposed radially outward of the at least one air gap.

[0016] In one example, the electric motor further comprises a sump and a pump. The sump is configured to collect coolant flowing through the at least one coolant return channel. The pump is operable to send coolant through the at least one coolant supply channel.

[0017] Another example of an electric motor according to the present disclosure includes a housing, a shaft, a rotor, a stator, and at least one coolant supply channel. The shaft is rotatably mounted in the housing and has a longitudinal axis. The rotor is fixed to the shaft so as to rotate therewith. The rotor includes a first portion and a second portion. The stator is disposed between the first portion and the second portion of the rotor and is spaced apart from the rotor along the longitudinal axis of the shaft to create a first air gap between the stator and the first portion of the rotor, and a second air gap between the stator and the second portion of the rotor. At least one coolant supply channel extends through at least one of the shaft and the stator and is configured to supply a coolant flow to the first air gap and the second air gap.

[0018] In one example, a first portion of the rotor includes a first permanent magnet and a second portion of the rotor includes a second permanent magnet. The first permanent magnet and the second permanent magnet generate a magnetic flux extending along a longitudinal axis of the shaft.

[0019] In one example, at least one coolant supply passage extends through the shaft.

[0020] In one example, at least one coolant supply channel includes a main coolant channel and at least one pair of branch coolant channels disposed on opposite sides of the main coolant channel. The main coolant channel extends axially through the end of the shaft. The at least one pair of branch coolant channels radially extend from the main coolant channel through the outer radial surface of the shaft to the first air gap and the second air gap.

[0021] In one example, at least one pair of branch coolant channels includes a first pair of branch coolant channels and a second pair of branch coolant channels. The first pair of branch coolant channels radially extend from the main coolant channel through the outer radial surface of the shaft to the first air gap. The second pair of branch coolant channels radially extend from the main coolant channel through the outer radial surface of the shaft to the second air gap.

[0022] In one example, at least one coolant supply passage extends through the stator.

[0023] In one example, the housing defines an annular coolant jacket disposed radially outward from the stator, and at least one coolant supply channel includes a main coolant channel and at least one pair of branch coolant channels. The main coolant channel extends axially from one side of the housing through the housing to the annular coolant jacket. The at least one pair of branch coolant channels extends radially inward from the annular coolant jacket through the housing and the stator, and extends axially through the stator in a direction opposite to the first air gap and the second air gap.

[0024] In one example, the at least one pair of branch coolant channels includes a first pair of branch coolant channels and a second pair of branch coolant channels disposed on opposite sides of the shaft.

[0025] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings.The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present disclosure will be more fully understood based on the detailed description and accompanying drawings, in which:

[0027] Figure 1 is a cross-sectional view of an example of an electric motor according to the principles of the present disclosure; and

[0028] Figure 2 is a cross-sectional view of another example of an electric motor according to the principles of the present disclosure.

[0029] Among the drawings, reference numerals may be repeated to identify similar and / or identical elements. DETAILED DESCRIPTION

[0030] Axial flux machines have compact packaging at high power or high torque density. However, cooling axial flux machines is a challenge due to the compact packaging of axial flux machines. If the axial flux machine is not properly cooled, the axial flux machine may reach high temperatures. At high temperatures, the performance of the magnets in the axial flux machine may be significantly degraded or even permanently demagnetized.

[0031] To solve this problem, an axial flux motor according to the present disclosure includes a system for supplying coolant to the air gap between the stator and the rotor. The coolant in turn flows through the air gap to cool both the permanent magnets and the coil windings. Supplying the coolant flow through the air gap between the stator and the rotor in a radial flux motor produces a high drag torque. However, coolant can be supplied to the air gap between the stator and the rotor in an axial flux motor without producing a high drag torque.

[0032] Reference now Figure 1 , the electric motor 10 includes a housing 12, a shaft 14, a rotor 16, a stator 18, one or more coolant supply passages 20, and one or more coolant return passages 22. The housing 12 surrounds the rotor 16, the stator 18, and at least a portion of the shaft 14. The housing 12 may completely enclose the rotor 16 and the stator 18, except where the shaft 14 and the coolant return passages 22 extend through the housing 12. The coolant return passages 22 may be defined by the housing 12 and / or by a conduit inserted into the housing 12.

[0033] The housing 12 includes a body 24 and a pair of bearings 26. The body 24 may be formed (e.g., cast, molded) of metal or plastic. The body 24 includes a side wall 28, a first end cap 30, and a second end cap 32. The side wall 28 may have a cylindrical shape, and each of the first end cap 30 and the second end cap 32 may have a disc shape. The side wall 28, the first end cap 30, and the second end cap 32 may be integrally formed as a single body, or may be formed separately and connected together.

[0034] Each of the first end cap 30 and the second end cap 32 defines a bore 34 that receives and supports one of the bearings 26. The bearing 26 is secured to the body 24 using, for example, fasteners and / or an interference fit. The bearing 26 supports the shaft 14 while allowing the shaft 14 to rotate relative to the housing 12. The interface between the bearing 26 and the housing 12 and the interface between the bearing 26 and the shaft 14 can be sealed to prevent fluid from flowing therethrough.

[0035] The shaft 14 is rotatably mounted within the housing 12 via the bearing 26. The shaft 14 has a longitudinal axis 36, a first axial end 38, a second axial end 40 opposite the first axial end 38, and an outer radial surface 42 extending around the circumference of the shaft 14. In the example shown, the first axial end 38 of the shaft 14 is disposed within the hole 34 in the first end cover 30 and does not protrude beyond the first end cover 30 (e.g., to the left of the first end cover 30), while the second axial end 40 of the shaft 14 is disposed outside the housing 12 and protrudes beyond the hole 34 in the second end cover 32 (e.g., to the right of the hole 34 in the second end cover 32).

[0036] The rotor 16 is fixed to the shaft 18 so as to rotate therewith. The rotor 16 includes a first portion 44 and a second portion 46. Each of the first portion 44 and the second portion 46 includes a ferromagnetic (e.g., iron) core 48 and a permanent magnet 50. The ferromagnetic core 48 has an annular disk shape with a central hole 52 that is sized to receive the shaft 14 and to create a line-to-line, sliding, or interference fit between the central hole 52 and the outer radial surface 42 of the shaft 14. The ferromagnetic core 48 is attached to the shaft 14 using, for example, a key, a spline, and / or an interference fit between the central hole 52 in the ferromagnetic core 48 and the shaft 14. The ferromagnetic core 48 has a first axial surface 54, a second axial surface 56 opposite the first axial surface 54, and a radial surface 58. The first axial surface 54 faces away from the stator 18, and the second axial surface 56 faces the stator 18.

[0037] The permanent magnet 50 has an annular disk shape with a central hole 60 that is sized to receive the shaft 14 and create a clearance fit between the central hole 60 and the outer radial surface 42 of the shaft 14. The permanent magnet 50 is attached to the second axial surface 56 of the rotor 16 using, for example, an adhesive and / or fasteners. The permanent magnet 50 generates a magnetic flux 62 that extends along the longitudinal axis 36 of the shaft 14. In this regard, the electric motor 10 is an axial flux motor.

[0038] The stator 18 has an annular disk shape with a central hole 64 that is sized to receive the shaft 14 and create a clearance fit between the central hole 64 and the shaft 14. The stator 18 is disposed between the first portion 44 and the second portion 46 of the rotor 16. The stator 18 is spaced apart from the first portion 44 of the rotor 16 along the longitudinal axis 36 of the shaft 14 to create a first air gap 66 between the stator 18 and the first portion 44 of the rotor 16. The stator 18 is spaced apart from the second portion 46 of the rotor 16 along the longitudinal axis 36 of the shaft 14 to create a second air gap 68 between the stator 18 and the second portion 46 of the rotor 16. The size of each of the first air gap 66 and the second air gap 68 may be 1 millimeter (mm). Each coolant return passage 22 is axially aligned with one of the first air gap 66 and the second air gap 68 and is disposed radially outside the air gap 66 or 68.

[0039] The stator 18 includes a ferromagnetic core and coil windings. The coil windings in the stator 18 generate a magnetic flux 70 extending along the longitudinal axis 36 of the shaft 14 and in a direction opposite to the magnetic flux 62 generated by the permanent magnets 50. The stator 18 has a first axial surface 72, a second axial surface 74 opposite the first axial surface 72, and a radial surface 76. The first axial surface 72 faces the first portion 44 of the rotor 16, and the second axial surface 74 faces the second portion 46 of the rotor 16. The stator 18 is fixed to the side wall 28 of the housing 12 using, for example, adhesives, fasteners, and / or an interference fit between the radial surface 76 of the stator 18 and the side wall 28 of the housing 12.

[0040] The coolant supply passage 20 delivers coolant to the first air gap 66 and the second air gap 68. The coolant supply passage 20 may be defined by the shaft 18 and / or by a pipe inserted into the shaft 18. The coolant supply passage 20 includes a main coolant passage 78, a first pair of branch coolant passages (or orifices) 80, and a second pair of branch coolant passages (or orifices) 82. The main coolant passage 78 extends in an axial direction 84 or axially along the longitudinal axis 36 of the shaft 14. In addition, the main coolant passage 78 extends through the second axial end 40 of the shaft 14, but the main coolant passage 78 does not extend through the first axial end 38 of the shaft 14. In this regard, the main coolant passage 78 may be considered a blind hole in the shaft 14.

[0041] The branch coolant passage 80 extends radially outwardly (e.g., in radial direction 86) from the main coolant passage 78 through the outer radial surface 42 of the shaft 18 in opposite directions to the first air gap 66. The branch coolant passage 82 extends radially outwardly in opposite directions from the main coolant passage 78 through the outer radial surface 42 of the shaft 18 to the second air gap 68. In the example shown, the branch coolant passages 80, 82 do not extend completely in the radial direction 86. However, the direction in which the branch coolant passages 80, 82 extend is within a small angle (e.g., 15 degrees) of the radial direction 86.

[0042] During operation of the electric motor 10, the pump 88 sends coolant (e.g., oil) from the sump 90 to the main coolant passage 78 through the coolant supply line 92. The pump 88 and the sump 90 may be considered part of the electric motor 10 and / or part of the cooling system of the electric motor 10. The coolant flows axially from the coolant supply line 92 through the second axial end 40 of the shaft 18 and into the main coolant passage 78 of the shaft 14. The coolant flows radially outward from the main coolant passage 78 through the branch coolant passages 80, 82 to and through the first air gap 66 and the second air gap 68, respectively. The rotation of the rotor 16 and the shaft 18 may exert centrifugal force on the coolant flowing out of the branch coolant passages 80, 82, which may cause the coolant to flow through the first air gap 66 and the second air gap 68. Additionally or alternatively, the pump 88 may pressurize the coolant flowing through the coolant supply line 92, and the pressurization may cause the coolant to flow through the first air gap 66 and the second air gap 68.

[0043] On the side of the motor 10 farthest from the reservoir 90 (e.g., Figure 1 ), after the coolant flows through the first air gap 66 and the second air gap 68, the coolant flows in the axial direction 84. More specifically, the coolant flows axially between the radial surface 58 of the rotor 16 and the inner radial surface 94 of the housing 12, and flows toward the first end cover 30 and the second end cover 32 of the housing 12. The coolant then flows radially (e.g., in a downward direction) toward the portion of the sidewall 28 closest to the reservoir 90 due to, for example, gravity. Once the coolant has reached the portion of the sidewall 28 closest to the reservoir 90, the coolant flows axially to the coolant return passage 22.

[0044] On the side of the motor 10 closest to the reservoir 90 (e.g., Figure 1 ), the coolant flows directly to the coolant return channel 22 after passing through the first air gap 66 and the second air gap 68. The coolant flowing through the coolant return channel 22 is collected by the sump 90. Therefore, the coolant can circulate again through the first air gap 66 and the second air gap 68 of the motor 10 in the above-mentioned manner.

[0045] Reference now Figure 2, the electric motor 100 is the same as the electric motor 10, except that the electric motor 100 includes a coolant supply passage 102 in place of the coolant supply passage 20, and the electric motor 100 includes a coolant jacket 104. In addition, the coolant return passage 22 is moved closer to the first end cover 30 and the second end cover 32 to accommodate the coolant jacket 104. In the example shown, one coolant return passage 22 is aligned with the gap between the first end cover 30 of the housing 12 and the first portion 44 of the rotor 16, and the other coolant return passage 22 is aligned with the gap between the second portion 46 of the rotor 16 and the second end cover 32 of the housing 12. The coolant jacket 104 is defined by the side wall 28 of the housing 12 and has an annular or toroidal shape that extends around the entire circumference of the side wall 28.

[0046] The coolant supply passage 102 includes a main coolant passage 106, a first pair of branch coolant passages 108, and a second pair of branch coolant passages 110. The main coolant passage 106 extends from the coolant supply line 92 to the coolant jacket 104 in the axial direction 84. The main coolant passage 106 may be defined by the housing 12 and / or by a pipe inserted into the housing 12.

[0047] Each branch coolant passage 108 includes a first portion 112 and a second portion 114. The first portion 112 of each branch coolant passage 108 extends radially inward from the coolant jacket 104 to the second portion 114 of the branch coolant passage 108. The second portion 114 of each branch coolant passage 108 extends axially (e.g., leftward) from the first portion 112 of the branch coolant passage 108 to the first air gap 66 between the stator 18 and the first portion 44 of the rotor 16.

[0048] Each branch coolant channel 110 includes a first portion 116 and a second portion 118. The first portion 116 of each branch coolant channel 110 extends radially inward from the coolant jacket 104 to the second portion 118 of the branch coolant channel 110. The second portion 118 of each branch coolant channel 110 extends axially (e.g., leftward) from the first portion 116 of the branch coolant channel 110 to the second air gap 68 between the stator 18 and the second portion 46 of the rotor 16.

[0049] During operation of the electric motor 100, the pump 88 sends coolant (e.g., oil) from the sump 90 through the coolant supply line 92 to the main coolant passage 106. The coolant flows axially from the coolant supply line 92 through the main coolant passage 106 to the coolant jacket 104. The coolant flows radially inward from the coolant jacket 104 through the first portion 112 of the branch coolant passage 108 to the second portion 114 of the branch coolant passage 108, and through the second portion 114 to the first air gap 66. Similarly, the coolant flows radially inward through the first portion 116 of the branch coolant passage 110 to the second portion 118 of the branch coolant passage 110, and through the second portion 118 to the second air gap 68. The rotation of the rotor 16 and the shaft 18 may exert centrifugal force on the coolant flowing out of the branch coolant passages 108, 110, which may cause the coolant to flow through the first air gap 66 and the second air gap 68. Additionally or alternatively, the pump 88 may pressurize the coolant flowing through the coolant supply line 92 , and this pressurization may cause the coolant to flow through the first air gap 66 and the second air gap 68 .

[0050] On the side of the motor 100 farthest from the reservoir 90 (e.g., the upper half of the motor 100 as shown in FIG. 02 ), after the coolant flows through the first air gap 66 and the second air gap 68, the coolant flows in the axial direction 84. More specifically, the coolant flows axially between the radial surface 58 of the rotor 16 and the inner radial surface 94 of the housing 12, and flows toward the first end cover 30 and the second end cover 32 of the housing 12. The coolant then flows radially (e.g., in a downward direction) toward the portion of the side wall 28 closest to the reservoir 90 due to, for example, gravity. Once the coolant has reached the portion of the side wall 28 closest to the reservoir 90, the coolant flows axially to the coolant return passage 22.

[0051] On the side of the motor 100 closest to the reservoir 90 (e.g., Figure 2 ), the coolant flows directly to the coolant return channel 22 after passing through the first air gap 66 and the second air gap 68. The coolant flowing through the coolant return channel 22 is collected by the sump 90. Therefore, the coolant can circulate again through the first air gap 66 and the second air gap 68 of the motor 100 in the above-mentioned manner.

[0052] exist Figure 1 and Figure 2In the example shown in , the rotor 16 is in two parts (i.e., the first part 44 and the second part 46), and the stator 18 is an integral part disposed between the two parts of the rotor 16. In other examples, each of the rotor 16 and the stator 18 can be an integral part. In other examples, the stator 18 can be in two parts, and the rotor 16 can be an integral part disposed between the two parts of the stator 18. In these other examples, Figure 1 The motor 10 of FIG. 1 is unchanged except for the above-mentioned changes in the rotor 16 and the stator 18. Figure 2 In the electric motor 100, the branch coolant passages 108, 110 also extend through both stators 18 because the stators 18 are connected to the housing 12 via the interface between the radial surface 76 of the stator 18 and the side wall 28 of the housing 12. After the coolant flows through the first air gap 66 and the second air gap 68, it flows back to the coolant return passage 22 along the inner radial surface 94 of the housing 12 due to gravity.

[0053] The foregoing description is merely illustrative in nature and is in no way intended to limit the present disclosure, its application or use. The broad teachings of the present disclosure can be implemented in various forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure should not be so limited, because other modifications will become apparent after studying the drawings, the specification and the appended claims. It should be understood that one or more steps within the method can be performed in a different order (or simultaneously) without changing the principles of the present disclosure. In addition, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the present disclosure can be implemented in the features of any of the other embodiments and / or combined with the features of any of the other embodiments, even if the combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and the permutation of one or more embodiments with each other remains within the scope of the present disclosure.

[0054] When an element or layer is referred to as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it may be directly on, directly engaged, connected, or coupled to the other element or layer, or there may be intervening elements or layers. Conversely, when an element or layer is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, there may be no intervening elements or layers. Other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0055] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR, and should not be construed to mean "at least one of A, at least one of B, and at least one of C."

[0056] Although the terms first, second, third, etc. can be used to describe various elements, components, regions, layers and / or sections in this article, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or section from another region, layer or section. Unless the context clearly indicates, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in this article. Therefore, without departing from the teaching of the exemplary embodiment, the first element, component, region, layer or section discussed below can be referred to as the second element, component, region, layer or section.

[0057] For ease of description, spatially relative terms such as "inside", "outside", "under", "below", "lower", "above", "upper", etc. may be used herein to describe the relationship of one element or feature to another element or feature shown in the figures. Spatially relative terms may be intended to include different orientations of the device in use or operation in addition to the orientation shown in the figures. For example, if the device in the figure is turned over, the elements described as being "below" or "below" other elements or features will be oriented to be "above" other elements or features. Therefore, the example term "below" may include both the orientations of "above" and "below". The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein are interpreted accordingly.

Claims

1. An electric motor, comprising: case; a shaft rotatably mounted within the housing and having a longitudinal axis; a rotor fixed to the shaft for rotation therewith, the rotor comprising a first portion and a second portion, and each of the first portion and the second portion comprising a ferromagnetic core and a permanent magnet, the ferromagnetic core being in the shape of an annular disk with a central hole and attached to the shaft, the permanent magnet being in the shape of an annular disk with a central hole and having a clearance fit with the shaft at the central hole, the permanent magnet being attached to the ferromagnetic core; a stator including a ferromagnetic core and coil windings generating a magnetic flux extending along the longitudinal axis of the shaft and in a direction opposite to the magnetic flux generated by the permanent magnets of the rotor, the stator being spaced apart from the rotor along the longitudinal axis of the shaft to generate at least one air gap between the stator and the rotor; as well as at least one coolant supply channel extending through at least one of the shaft and the stator and configured to supply a coolant flow to the at least one air gap, wherein the at least one coolant supply passage extends through the stator, the housing defining an annular coolant jacket disposed radially outwardly of the stator; as well as The at least one coolant supply passage includes a main coolant passage extending axially from one side of the housing through the housing to the annular coolant jacket, and at least one branch coolant passage extending radially inwardly from the annular coolant jacket through the housing and the stator and axially through the stator to the at least one air gap, and Each of the at least one branch coolant channel includes a first portion and a second portion, the first portion of the branch coolant channel extending radially inward from the coolant jacket to the second portion of the branch coolant channel, and the second portion of each branch coolant channel extending axially from the first portion of the branch coolant channel to the at least one air gap between the stator and the rotor.

2. The electric motor according to claim 1, wherein: The rotor includes permanent magnets that generate a magnetic flux extending along a longitudinal axis of the shaft.

3. The electric motor according to claim 1, wherein: The stator is disposed between the first and second portions of the rotor in an axial direction parallel to the longitudinal axis of the shaft; and The at least one air gap includes a first air gap disposed between a first portion of the rotor and the stator and a second air gap disposed between a second portion of the rotor and the stator. 4 . The electric motor according to claim 1 , wherein the at least one branch coolant passage comprises a pair of branch coolant passages disposed on opposite sides of the shaft. 5 . The electric motor of claim 1 , further comprising at least one coolant return passage extending through the housing and configured to receive coolant after the coolant flows through the at least one air gap. 6 . The electric motor of claim 5 , wherein the at least one coolant return passage is axially aligned with the at least one air gap and disposed radially outward of the at least one air gap.

7. The electric motor of claim 5, further comprising a sump and a pump. 8 . The electric motor of claim 7 , the sump being configured to collect coolant flowing through the at least one coolant return passage.

9. The electric motor of claim 7, the pump being operable to send coolant through the at least one coolant supply passage.

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