Cooling separator for wound rotor

Abstract

The invention relates to a cooling separator for a wound rotor. An electric machine includes a wound excitation rotor. The wound excitation rotor includes: a shaft defining a longitudinal axis; a plurality of laminations mounted to an outer surface of the shaft and including rotor teeth defining axial channels extending along a longitudinal axis; the plurality of excitation windings are arranged in the axial channel; and an excitation separator disposed in the axial channel to fix the plurality of excitation windings in the axial channel. The excitation divider includes a post at an axial end of the excitation divider, the post having a passage therethrough to allow fluid to flow out of the axial passage and into a side passage at one end of the rotor.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the prior filing date of U.S. Provisional Application Serial No. 63 / 588,869, filed on October 9, 2023, the entire disclosure of which is incorporated herein by reference. Background Art

[0003] Exemplary embodiments relate to the field of electric machines, and more particularly to a cooling system for an electric machine having a wound field rotor.

[0004] During operation, electric motors generate heat. Often, the rotating components of the electric motor may support a fan member that directs air flow through the internal motor components. Air flow may be helpful in smaller systems, such as alternators, and systems mounted in open areas, such as generators. In high output systems, particularly those mounted in enclosed areas, such as a motor vehicle engine compartment, air flow is not always sufficient.

[0005] An electric motor used as a prime mover in a motor vehicle typically includes a liquid coolant system. The electric motor includes a stator and a rotor. The liquid cooling system may include an inlet for receiving a coolant and an outlet for directing the coolant to a heat exchange system. The coolant may flow in a jacket arranged radially outside of the stator of the electric motor. Additional coolant may be directed onto the rotor, or between the rotor and a shaft supporting the rotor.

[0006] Cooling the outer surfaces of the rotor laminations and the interface between the rotor laminations and the shaft is beneficial. However, the rest of the rotor also generates heat, which reduces overall operating efficiency. Therefore, the industry is willing to accept cooling systems that interact with the internal rotor surfaces and the rotor winding surfaces to improve operating efficiency. Summary of the invention

[0007] According to a non-limiting example, a wound field rotor includes: a shaft defining a longitudinal axis; a plurality of laminations mounted to an outer surface of the shaft and including rotor teeth, the rotor teeth defining an axial channel along the longitudinal axis; a plurality of field windings disposed in the axial channel; and a field separator disposed in the axial channel to secure the plurality of field windings in the axial channel. The field separator includes a post at an axial end of the field separator having a channel therethrough to allow fluid to flow out of the axial channel and into a side channel located at one end of the rotor.

[0008] According to a non-limiting example, the electric machine includes a stator and a rotor rotatable within the stator. The rotor includes: a shaft defining a longitudinal axis; a plurality of laminations mounted to an outer surface of the shaft and including rotor teeth, the rotor teeth defining an axial channel extending along the longitudinal axis; a plurality of field windings disposed in the axial channel; and a field separator disposed in the axial channel to secure the plurality of field windings in the axial channel. The field separator includes a post at an axial end of the field separator, the post having a channel therethrough to allow fluid to flow out of the axial channel and into a side channel located at one end of the rotor.

[0009] According to a non-limiting example, a method of operating an electric machine includes flowing a coolant through a rotor of the electric machine. The rotor includes: a shaft defining a longitudinal axis; a plurality of laminations mounted to an outer surface of the shaft and including rotor teeth, the rotor teeth defining an axial channel extending along the longitudinal axis; a plurality of field windings disposed in the axial channel; and a field separator disposed in the axial channel to secure the plurality of field windings in the axial channel. The field separator includes a post at an axial end of the field separator, the post having a channel therethrough to allow coolant to flow out of the axial channel and into a side channel located at one end of the rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following description should not be considered limiting in any way. Referring to the drawings, similar elements are similarly numbered:

[0011] Figure 1 shows a cross-sectional side view of an electric machine including a wound field rotor with a cooling system according to a non-limiting example;

[0012] Figure 2 Shown is a view taken along line 2-2 Figure 1 A cross-sectional axial end view of a wound field rotor;

[0013] Figure 3 Shows Figure 2 A plan view of a rotor lamination of a wound field rotor;

[0014] Figure 4 Shows Figure 2 A plan view of another rotor lamination of a wound-field rotor;

[0015] Figure 5 Shows Figure 2 A plan view of another rotor lamination of a wound-field rotor;

[0016] Figure 6 Shows Figure 2 A plan view of another rotor lamination of a wound-field excitation rotor;

[0017] Figure 7shows a plan view of a winding end turn insulator according to a non-limiting example;

[0018] Figure 8 is a perspective view of a wound field rotor in an exemplary embodiment;

[0019] Fig. 9 yes Figure 8 A perspective view of a rotor with a balancing ring for fixing the rotor;

[0020] Fig.10 is a perspective view of an excitation separator in an exemplary embodiment;

[0021] Fig.11 shows a longitudinal cross-section of the rotor taken through the excitation separator;

[0022] Fig.12 a perspective view showing a cross section of the rotor, illustrating a flow circuit of a coolant fluid through the rotor;

[0023] Fig.13 an expanded view showing a cross-section of a first column in a first embodiment; and

[0024] Fig.14 An enlarged view of a cross section of a first column in a second embodiment is shown. DETAILED DESCRIPTION

[0025] With reference to the accompanying drawings, a detailed description of one or more embodiments of the disclosed apparatus and method is given herein by way of example and not limitation.

[0026] According to a non-limiting example, in Figure 1 An electric machine is generally indicated at 10. The electric machine 10 includes a housing 12 having an outer surface 14 and an inner surface 16. A stator 20 is fixedly connected to the inner surface 16. The stator 20 includes a stator winding 22 having a first end turn 24 and a second end turn 26. A wound field rotor 30 is rotatably mounted in the housing 12 radially inwardly of the stator 20. The wound field rotor 30 is supported on a shaft 32 in the housing 12.

[0027] In a non-limiting example, the shaft 32 is supported at a first end (not separately labeled) by a first bearing 34 and at a second end (also not separately labeled) by a second bearing 36. The shaft 32 includes an outer surface 39 and an inner surface 41 defining a coolant flow path 43. Coolant (such as oil) from a coolant supply system 46 passes through the coolant flow path 43, passes internally through the wound field rotor 30, and then enters the housing 12 and then enters the coolant exhaust system 48. The coolant may flow through a plurality of channels, one of which is indicated at 50 ( Figure 2 ), the channel extending through the shaft 32.

[0028] In a non-limiting example, the wound field rotor 30 includes a plurality of laminations 54 having a discontinuous outer annular surface 58 and an inner annular surface 56 defining a plurality of rotor teeth 60. A plurality of field windings 64 are wound around each of the plurality of rotor teeth 60. A plurality of channels are defined between adjacent windings of the plurality of field windings 64, one of which is indicated at 66. As will be described in detail herein, the plurality of laminations 54 define an internal cooling circuit 68 disposed between the inner annular surface 56 and the discontinuous outer annular surface 58. As will be more fully apparent herein, the cooling circuit 68 includes a first circuit portion (not separately labeled) that feeds each channel 66, thereby cooling the inner surface of the field windings 64, and a second circuit portion (also not separately labeled) that extends axially through the laminations 54 to cool the wound field rotor 30 from the inside, as well as to spray coolant onto the first stator end turns 24 and the second stator end turns 26.

[0029] Will refer to Figure 3-Figure 6 , and continue to refer to Figure 1 and Figure 2 1 to describe the different lamination sections of the laminations 54. The rotor laminations 54 include a first or center lamination section 72 ( Figure 3 ), which has a first inner surface portion 74, a first outer surface portion 76, and a first plurality of rotor tooth elements 78 connected by a first web portion 80. A first channel portion 82 extends from the first inner surface portion 74 into the first web portion 80. The first channel portion 82 is aligned with the channel 50 and defines a coolant inlet. At this point, it should be understood that the first channel portion is provided at each channel 50.

[0030] Figure 48 and 9. The second lamination portion 86 is shown in FIG. The second lamination portion 86 is positioned adjacent each side of the first lamination portion 72. The second lamination portion 86 includes a second inner surface portion 88 and a second outer surface portion 90 defining a plurality of rotor tooth elements 92. The rotor tooth elements 92 are connected by a second web portion 94. A second channel portion 96 is defined in the second web portion 94. The second channel portion 96 includes a first end 98 extending generally radially along the second web portion 94 and a second end 100 connected to the first end 98 and extending circumferentially along the second web portion 94. The first end 98 is registered with the first channel portion 82.

[0031] Figure 5 1 shows a third lamination portion 105 according to a non-limiting example. The third lamination portion 105 includes a third inner surface portion 106 and a third outer surface portion 108 defining a third plurality of tooth elements 110. The tooth elements 110 are connected by a third web portion 112. A third channel portion 114 is defined in the third web portion 112 at each of the plurality of tooth elements 110. In addition, the third web portion 112 includes a radial outer surface 115 extending between adjacent tooth elements 110. A scalloped area 116 is formed in the radial outer surface 115 to expose the outer edge 101 of the second channel portion 96. In this way, the fluid entering the first channel portion 82 can flow into the second channel portion 96, and the first part of the fluid can enter each channel 66 from the outer edge 101 via the scalloped area 116, and the second part of the fluid can pass through the inner end 102 and enter the third channel portion 114. Therefore, the second channel portion 96 divides the cooling circuit 68 into a first circuit portion and a second circuit portion.

[0032] Figure 6 , a fourth lamination stack portion 119 according to a non-limiting example is shown. The fourth lamination stack portion 119 is positioned against the third lamination stack portion 104 and includes a fourth inner surface portion 122 and a fourth outer surface portion 124 defining a plurality of tooth elements 126. The tooth elements 126 are connected by a fourth web portion 128. The fourth lamination stack portion 119 includes a fourth channel portion 130, which is positioned on the fourth web portion 128 at each tooth element 126. The fourth channel portion extends radially along the fourth web portion 128 and is fluidly connected to the third channel portion 114 forming a second circuit portion of the cooling circuit 68, which extends axially from each third lamination stack portion 104 along the lamination stack 54.

[0033] In a non-limiting example, the end turn insulator 136 ( Figure 1) is mounted to the fourth lamination portion 119 at each axial end (not separately labeled) of the laminations 54. The end turn insulator 136 includes a central web 138 having an inner surface segment 140, the inner surface segment 140 including a plurality of recesses 142. The recesses 142 may be arranged to receive fasteners (not shown) that connect the laminations 54. The end turn insulator 136 also includes an outer surface segment 144 from which a plurality of tooth supports 146 extend, the tooth supports 146 providing structural support for the rotor teeth 60. Each of the plurality of tooth supports 146 includes a first surface 148, which may be an axially outward facing surface, and a second surface 150, which may be an axially inward facing surface.

[0034] In a non-limiting example, the second surface 150 includes a channel 154 that directs coolant from the fourth channel portion 130 radially outward to the first end turn 24 and the second end turn 26. In a non-limiting example, the first surface 148 includes a first angled surface 158 and a second angled surface 160 that help guide and support one of the plurality of field windings 64 extending around each of the plurality of rotor teeth 60. Thus, the end turn insulator 136 not only supports the plurality of laminations 54, but also provides guidance and insulation for each field winding 64, and also forms part of the cooling circuit 68. In addition, the end turn insulator 136 can be used to establish a desired rotational balance for the wound field rotor 30.

[0035] In a non-limiting example, the wound field rotor 30 further includes a plurality of field separators. Figure 1 and Figure 2 One of the excitation separators is shown at 163. The excitation separator 163 extends between adjacent rotor teeth of the plurality of rotor teeth 60 and bridges each channel 66. The excitation separator 163 includes a generally v-shaped cross-section and is made of a compliant or non-compliant material. Each excitation separator 163 includes a first leg 167 that engages with one of the plurality of rotor teeth 60 and a second leg 169 that engages with an adjacent one of the plurality of rotor teeth 60. In a non-limiting example, the excitation separator 163 can flex when the wound-field rotor 30 generates torque. In this way, the excitation separator 163 can keep the coolant in each channel 66, but also allow some leakage, that is, the coolant is thrown onto the stator 20 to provide additional cooling.

[0036] Figure 8800 is a perspective view of a wound field rotor 30 in an exemplary embodiment. The wound field rotor 30 includes a shaft 32 extending along the longitudinal axis of the electric machine or motor. The shaft 32 includes a coolant flow path 43 along the longitudinal axis. The laminations (i.e., the first lamination portion 72, the second lamination portion 86, the third lamination portion 105, and the fourth lamination portion 119) surround the outer surface of the shaft 32, thereby producing the rotor teeth 60. The first bearing 34 and the second bearing 36 fix the shaft 32 to the housing 12. The excitation winding 64 is wound around the rotor teeth 60 to form a coil loop, one side of the coil loop passes through the axial channel on one side of the rotor tooth, and the other side of the coil loop passes through the adjacent axial channel. Therefore, each axial channel includes loops from two adjacent excitation windings 64. The excitation separator 163 fills the gap between adjacent teeth at the outer surface of the lamination, and easily extends inward to separate adjacent excitation windings from each other, and maintains the structure of the excitation winding during the rotation of the wound field rotor 30.

[0037] Fig. 9 yes Figure 8 900 is a perspective view of a rotor with balancing rings for securing the rotor. A first balancing ring 902 is placed on the rotor teeth 60 at a first end of the rotor. A second balancing ring 904 is placed on the rotor teeth 60 at a second end of the rotor. The first balancing ring 902 includes escape holes 906, which are located on either side of the excitation separator 163 when the first balancing ring 902 is assembled on the rotor teeth 60. The escape holes 906 pass through the first balancing ring 902 from the inside of the rotor to the outside of the rotor. Similarly, the second balancing ring 904 includes escape holes 908, which are located on either side of the excitation separator 163 when the second balancing ring 904 is assembled on the rotor teeth 60. The escape holes 908 pass through the second balancing ring 904 from the inside of the rotor to the outside of the rotor. The escape holes can be oriented in a radial direction.

[0038] Fig.10 1000 is a perspective view of an excitation separator 163 in an exemplary embodiment. The excitation separator 163 includes an axially extending track 1002 supported at a first end by a first post 1004 and at a second end by a second post 1006. The track 1002 includes an arch 1008 that elevates a lower surface 1010 of the track above a bottom surface 1012 of the first post 1004 and a bottom surface 1014 of the second post 1006. The track 1002 includes a radially outward track surface 1016. The first post 1004 includes a first outer post surface 1018 on its radially outer side, and the second post 1006 includes a second outer post surface 1020 on its radially outer side.

[0039] The first post 1004 includes a body having an axial inner surface 1022, a first circumferentially facing surface 1024, and a second circumferentially facing surface 1026 opposite the first circumferentially facing surface 1024. A passage passes through the first post 1004 from the axial inner surface 1022 to at least one of the first circumferentially facing surface 1024 and the second circumferentially facing surface 1026. In one embodiment, the passage includes at least one axially extending passage (represented by opening 1028) penetrating into the body of the first post 1004 from the axial inner surface 1022 and at least one circumferentially extending passage (represented by opening 1030) passing through the body of the first post 1004 from the first circumferentially facing surface 1024 to the second circumferentially facing surface 1026. The at least one axially extending passage intersects with the at least one circumferentially extending passage within the body of the first post 1004. In one embodiment, the at least one axially extending passage includes a single axially extending passage, and the at least one circumferentially extending passage includes three circumferentially extending passages, each of which intersects with the single axially extending passage. The three circumferentially extending channels may have the same size or the same radius. However, in alternative embodiments, the circumferentially extending channels may have different sizes or different radii.

[0040] Similarly, the second post 1006 includes a body having an axial inner surface 1032, a first circumferential facing surface 1034, and a second circumferential facing surface 1036 opposite the first circumferential facing surface 1034. A passage extends through the second post 1006 from the axial inner surface 1032 to at least one of the first circumferential facing surface 1034 and the second circumferential facing surface 1036. In one embodiment, the passage includes at least one axially extending passage ( Fig.11 1040) and at least one circumferentially extending passage (represented by opening 1040) through the body of the second post 1006 from the first circumferentially facing surface 1034 to the second circumferentially facing surface 1036. The at least one axially extending passage intersects the at least one circumferentially extending passage within the body of the second post 1006. In one embodiment, the at least one axially extending passage comprises a single axially extending passage, and the at least one circumferentially extending passage comprises three circumferentially extending passages, each of which intersects the single axially extending passage.

[0041] The excitation separator 163 can be made of a material suitable for the design specifications. Exemplary materials include, for example, aluminum, steel, plastic, etc. Steel and aluminum can be selected to improve thermal conductivity, while plastic can be selected to improve insulation. In other embodiments, the excitation separator 163 can be made of a metal material coated with an insulating material.

[0042] In an alternative embodiment, the field separator 163 may have ribs that extend radially inward (into the arch 1008) to hold the field wires in place. Additionally, the coils may be varnished. Varnishing the coils helps hold the field separator 163 on the shaft 32. The varnish may also act as a seal between the field separator 163 and the laminations, preventing oil from escaping into the air gap.

[0043] Fig.11 A longitudinal cross-sectional view 1100 of the rotor taken through the excitation separator 163 is shown. The track 1002 is placed between adjacent excitation windings 64. The first post 1004 is supported at a first end between the fourth lamination portion 119 (at the bottom surface 1012) and the first balance ring 902 (at the first outer cylindrical surface 1018). The first balance ring 902 includes an end cap 1102 and a lip 1104. The lip 1104 extends axially on the first outer cylindrical surface 1018 to secure the excitation separator 163 at the first end. A first portion 1110 of the first post 1004 is supported by the fourth lamination portion 119. A second portion 1112 of the first post 1004 is not supported by the fourth lamination portion 119, but rather depends on a first side channel 1142 at the first end of the rotor. The first side channel 1142 extends circumferentially around the rotor axis at the end of the rotor.

[0044] Similarly, the second post 1006 is supported at a first end between the fourth lamination portion 119 (at the bottom surface 1014) and the second balance ring 904 (at the second outer cylindrical surface 1020). The second balance ring 904 includes an end cap 1106 and a lip 1108. The lip 1108 extends axially on the second outer cylindrical surface 1020 of the second post 1006 to secure the excitation separator 163 at the second end. The first portion 1114 of the second post 1006 is supported by the fourth lamination portion 119. The second portion 1116 of the second post 1006 is not supported by the fourth lamination portion 119, but is suspended on the second side channel 1144 at the second end of the rotor. The second side channel 1144 extends circumferentially around the rotor axis at the end of the rotor. Fig.11 Also shown is an axially extending channel 1146 for the second column 1106.

[0045] Fig.12 A perspective view 1200 of a cross section of a rotor is shown, illustrating a flow circuit of a coolant fluid through the rotor. The flow circuit includes a plurality of paths 1202A-1202H through which coolant flows sequentially from one path to the next. A first path 1202A allows coolant to flow through a hollow hole in the shaft. A second path 1202B allows coolant to flow out of the hollow hole to the outer surface of the shaft. A third path 1202C allows coolant to pass radially outward through the laminations, such as Figure 3-Figure 5 1002D). The coolant is pushed outward by the centrifugal force of the rotating rotor and thus fills the arches 1008 in the field separator until it can be discharged into the openings of the axially extending channels in the first column 1004 and the second column 1006 at both axial ends of the coils. The axially extending channels are close to the laminations (e.g., the fourth lamination section 119).

[0046] Path 1202E shows the flow of coolant in the first column 1004. It passes through the first axially extending channel into at least one circumferentially extending channel. Path 1202F allows the coolant to leave the circumferentially extending channel. The circumferentially extending hole discharges the fluid onto the end turns 24 of the excitation winding. The fluid can then fill the first side channel 1142 formed by the first balance ring 902 along path 1202G. Path 1202G also allows the fluid to flow radially outward, especially during rotation of the rotor. Path 1202H allows the fluid to flow out of the rotor through the escape hole 906 in the lip 1104 of the first balance ring 902. The escaping fluid is thus sprayed onto the stator. A similar flow circuit can be used for fluid flowing to the second column 1006 and into the second side channel 1144 through the axially extending channel 1146 in the second column. The fluid leaves the rotor from the second side channel 114 via the escape hole 908 in the second balance ring 904 to be sprayed onto the stator.

[0047] Fig.13 An enlarged view 1300 of a cross section of the first column 1004 in the first embodiment is shown. The enlarged view 1300 shows an axially extending channel 1302 extending from an opening 1028 at an axial inner surface 1022 of the first column 1004. The opening 1028 has a selected size or a selected radius. The radius of the opening 1028 of the axially extending hole can be selected to reduce fluid turbulence. The axially extending channel 1302 extends from the opening 1028 to the outer end of the first column 1004. The axially extending channel 1302 has a reduced flow cross section in a narrow section 1304 close to the opening 1208. The axially extending channel 1302 extends to an outlet hole 1306 at an axial outer surface 1308 of the first column. If desired, the outlet hole 1306 can be sealed or closed. In one embodiment, the outlet hole 1306 is sealed by applying epoxy to the excitation separator at the outlet hole 1306. In another embodiment, the opening can be sealed by positioning the first balance ring 902 as close to the outlet hole 1306 as possible. The second column 1006 may be similarly designed.

[0048] Fig.14An enlarged view 1400 of a cross section of a first column in a second embodiment is shown. Enlarged view 1400 shows an axially extending passage 1402 extending from an opening 1028 at an axially inner surface 1022 of the first column 1004. The size of the opening 1028 in the second embodiment is smaller than that of the first embodiment. The axially extending passage 1402 extends from the opening 1028 to the outer end of the first column 1004. The flow cross section of the axially extending passage 1402 increases in the expansion section 1404 adjacent to the opening 1208. The axially extending passage 1402 extends to an outlet hole 1406 at an axially outer surface 1408 of the first column. If desired, the outlet hole 1406 may be provided using the outlet hole 1406 described above with reference to FIG. Fig.13 The second column 1006 can be similarly designed.

[0049] The terms used herein are intended only to describe specific embodiments and are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" used herein also include the plural forms. It will also be understood that the terms "include" and / or "comprise" when used in this specification specify the presence of stated features, wholes, steps, operations, elements, and / or parts, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, parts, and / or combinations thereof.

[0050] Although the present invention has been described with reference to one or more exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and elements thereof may be replaced with equivalents without departing from the scope of the present invention. In addition, many modifications may be made to adapt specific situations or materials to the teachings of the present invention without departing from the basic scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed as the best mode for carrying out the present invention, but the present invention will include all embodiments falling within the scope of the claims.

Claims

1. A wound-rotor excitation rotor, comprising: an axis defining a longitudinal axis; a plurality of laminations mounted to an outer surface of the shaft, the laminations including rotor teeth defining axial passages extending along the longitudinal axis; a plurality of excitation windings disposed in the axial channel; as well as An excitation separator is arranged in the axial channel to fix the multiple excitation windings in the axial channel, and the excitation separator includes a column located at an axial end of the excitation separator, and the column has a channel passing therethrough to allow fluid to flow out of the axial channel and into a side channel at one end of the rotor.

2. The wound field rotor of claim 1, wherein the channel comprises an axially extending channel and at least one circumferentially extending channel, wherein the axially extending channel intersects the at least one circumferentially extending channel in the body of the post.

3. The wound field rotor of claim 2, wherein the at least one circumferentially extending channel comprises three circumferentially extending channels.

4. The wound field rotor of claim 1 wherein the side channels extend circumferentially around a rotor axis of the rotor.

5. The wound field rotor of claim 4 further comprising a balancing ring securing the post to at least one of the plurality of laminations, the balancing ring having a lip extending axially on a radially outer surface of the post, the lip having an escape hole to allow fluid to flow out of the rotor from the side passage.

6. The wound field rotor of claim 2, wherein the axially extending channel comprises one of: (i) a narrow section adjacent to an opening of the axially extending channel; and (ii) an expanded section adjacent to an opening of the axially extending channel.

7. The wound field rotor of claim 1, wherein the posts further comprise a first post at a first axial end of the field separator and a second post at a second axial end of the field separator.

8. A motor, comprising: stator; A rotor capable of rotating within the stator, the rotor comprising: an axis defining a longitudinal axis; a plurality of laminations mounted to an outer surface of the shaft, the laminations including rotor teeth defining axial passages extending along the longitudinal axis; a plurality of field windings disposed in the axial passage; and An excitation separator is arranged in the axial channel to fix the multiple excitation windings in the axial channel, and the excitation separator includes a column located at an axial end of the excitation separator, and the column has a channel passing therethrough to allow fluid to flow out of the axial channel and into a side channel at one end of the rotor.

9. The electric machine of claim 8, wherein the channel comprises an axially extending channel and at least one circumferentially extending channel, wherein the axially extending channel and the at least one circumferentially extending channel intersect in the body of the post.

10. The electric machine of claim 9, wherein the at least one circumferentially extending channel comprises three circumferentially extending channels.

11. The electric machine of claim 8, wherein the side passages extend circumferentially around a rotor axis of the rotor.

12. The electric machine of claim 11 further comprising a balancing ring securing the post to at least one of the plurality of laminations, the balancing ring having a lip extending axially on a radially outer surface of the post, the lip having an escape hole to allow fluid to flow out of the rotor from the side passage.

13. The electric machine of claim 9, wherein the axially extending channel comprises one of: (i) a narrow section adjacent to an opening of the axially extending channel; and (ii) a divergent section adjacent to an opening of the axially extending channel.

14. The electric machine of claim 8, wherein the posts further include a first post at a first axial end of the field separator and a second post at a second axial end of the field separator.

15. A method of operating a motor, comprising: A coolant is passed through a rotor of the electric machine, the rotor comprising: a shaft, defining a longitudinal axis; a plurality of laminations mounted to an outer surface of the shaft, the laminations including rotor teeth defining axial passages extending along the longitudinal axis; a plurality of field windings disposed in the axial passage; and An excitation separator is arranged in the axial channel to fix the multiple excitation windings in the axial channel, and the excitation separator includes a column located at an axial end of the excitation separator, and the column has a channel passing therethrough to allow coolant to flow out of the axial channel and into a side channel at one end of the rotor.

16. A method according to claim 15, wherein the channel includes an axially extending channel and at least one circumferentially extending channel, wherein the axially extending channel intersects with the at least one circumferentially extending channel in the body of the column, and the method further includes allowing the fluid to flow from the axial channel into the column via the axially extending channel and then flow out of the column via the at least one circumferentially extending channel.

17. The method of claim 16, wherein the at least one circumferentially extending channel comprises three circumferentially extending channels.

18. The method of claim 15, wherein the side passage extends circumferentially around a rotor axis of the rotor.

19. The method of claim 18, wherein the rotor has a balancing ring securing the post to at least one of the plurality of laminations, the balancing ring having a lip extending axially on a radially outer surface of the post, the method further comprising flowing fluid through an escape hole in the lip to allow fluid to flow out of the rotor from the side passage.

20. The method of claim 16, wherein the axially extending passage comprises one of: (i) a narrow section adjacent to an opening of the axially extending passage; and (ii) a divergent section adjacent to an opening of the axially extending passage.

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