Rotor assembly for electric excited synchronous motor (EESM)

Abstract

To provide an electric excited synchronous motor having good cooling properties and a long service life.SOLUTION: A rotor assembly 2 for an electric excited synchronous motor (EESM) includes: a rotor shaft 3; a rotor core 4 with windings 5; and a first fluid guide element 7 and a second fluid guide element 8 arranged at ends of the rotor core, respectively. The rotor shaft includes an axial bore 14 and a plurality of radial bores 15. The rotor core includes: a plurality of inlet openings fluidically connected to the radial bores 15; and axial channels 28, 30 extending axially to a first outlet opening 29 and a second outlet opening 31 of the rotor core, respectively. The first and second fluid guide elements are fluidically connected to the respective outlet openings of the rotor core. A fluid structure receives cooling fluid from the rotor core, and guides the cooling fluid to escape openings arranged in a circumferential direction between two circumferentially adjacent winding ends 24 of the rotor.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a rotor assembly for a wound field synchronous motor (EESM) and an EESM equipped with such a rotor assembly.

[0002] In an EESM, the rotation of the shaft is synchronized to the frequency of the supply current. The rotation period is equal to an integer multiple of the alternating current (AC) period. A synchronous motor uses an electromagnet as the stator, which can generate a magnetic field that rotates in accordance with the amplitude of the current. The rotor is equipped with a permanent magnet or electromagnet, which allows the rotor to rotate at the same speed as the magnetic field of the stator in synchronization with it. As a result, the rotor provides a synchronized rotating magnetic field.

[0003] International Publication No. 2021 / 232835 discloses an electric motor including a rotor and a stator. The rotor includes a rotating shaft, a rotor core, and a plurality of rotor coils. The rotor core has a plurality of winding holes spaced apart around the rotating shaft. A gap is formed between two adjacent rotor coils, and a first axial hole is formed in the rotating shaft. The gap is configured to form a first heat dissipation passage communicating with the first axial hole, and a coolant flows into the rotating shaft through the first heat dissipation passage. In this way, the coolant is introduced from outside into the rotating shaft and, under the influence of centrifugal force, enters the first heat dissipation passage from the first axial hole, thereby dissipating heat from the rotor coils.

[0004] No. 1,101,1960 discloses a wound rotor motor having a vertically oriented shaft, with the stator and the lower coils of the rotor immersed in cooling oil, the shaft having passages through which cooling oil rises from a region below the rotor and is sprayed into a region above the rotor by centrifugal force generated by the rotation of the rotor.

[0005] Korean Patent No. 10-1967731 discloses a wound-type excitation motor including a support and cooling member for the coil. This motor includes a rotor with multiple cores protruding radially from the center, a field coil wound around each core, and multiple cooling and supporting members with a cooling structure that discharges heat generated inside the rotor to the outside. The inclusion of the cooling and supporting members firmly supports the coil wound around the rotor core, generating forced convection of air inside the rotor, which discharges heat generated inside the rotor to the outside and maximizing cooling performance.

[0006] WO 2018 / 095842, corresponding to FR 3059487, discloses a wound rotor having a shaft with alternating circumferential teeth and grooves, each tooth housing a longitudinal winding intended to form a rotor pole. Each winding defines a protruding coil head at each longitudinal end of the rotor. The rotor has at least one collar for mechanically retaining the rotor winding, the collar being located at the longitudinal end of the rotor and defining a central opening facing the coil head. The collar has at least one escape duct that allows the refrigerant flowing into the central opening to be supplied to the coil head.

[0007] Chinese Patent Application Publication No. 114567102 discloses a rotor cooling structure for an oil-cooled motor. The motor includes a rotor with a shaft, multiple rotor core assemblies, rotor end plates, and oil guide plates. The two axial ends of the rotor core are covered by rotor end plates. The rotor end plates have multiple first heat-dissipating oil passages that communicate radially outward on their end faces facing the rotor core. Multiple first oil spray openings are distributed annularly around the outer ring surface of the rotor end plates and communicate with the radially outer ends of the first heat-dissipating oil passages.

[0008] EESMs are becoming increasingly popular, particularly for medium- to high-power applications, replacing permanent magnet synchronous motors (PMSMs) and, in turn, avoiding the use of heavy rare earth (HRE) magnets. However, the performance of EESMs is limited by the rotor and stator winding temperatures. Typical EESMs equipped with indirect cooling systems, such as housing water jackets, or even direct air-cooling systems, have limited heat rejection capabilities. To meet increasingly stringent performance demands, more advanced and effective direct cooling systems are needed.

[0009] The object of the present invention is to provide a rotor assembly, in particular for a wound field synchronous motor (EESM), with an efficient cooling structure. It is also an object to provide an EESM with such a rotor assembly, which in turn has good cooling properties and a long service life.

[0010] According to the present invention, there is provided a rotor assembly for a wound-field synchronous motor (EESM), the rotor assembly comprising: a rotor shaft; a rotor core connected to the rotor shaft and including a plurality of circumferentially distributed pole sections, around which windings are housed, the windings having a first winding end projecting axially beyond a first end face of the rotor core and, on the opposite side, a second winding end projecting axially beyond a second end face of the rotor core; a first fluid guide element arranged on the first end face of the rotor core; and a second fluid guide element arranged on the second end face of the rotor core, the rotor shaft comprising an axial bore and a plurality of radial bores extending from the axial bore and arranged in an axial central region of the rotor shaft, the rotor core comprising a plurality of inlet openings fluidically connected to the radial bores of the rotor shaft. a first fluid guide element fluidly connected to the first outlet opening of the rotor core and configured to receive the cooling fluid from the first opening of the rotor core and guide the cooling fluid to a first escape opening circumferentially arranged between two circumferentially adjacent first winding ends; and a second fluid guide element fluidly connected to the second outlet opening of the rotor core and configured to receive the cooling fluid from the second opening of the rotor core and guide the cooling fluid to a second escape opening circumferentially arranged between two circumferentially adjacent second winding ends.

[0011] The proposed rotor assembly provides a direct oil cooling system that uses centrifugal force from the rotor's rotation to drive cooling fluid through the rotor and onto the end windings. Therefore, extremely low pressure can be used to pump the cooling fluid into the hollow shaft. Within the shaft chamber, the cooling fluid is dispersed by centrifugation, creating a flow along the inner wall of the shaft, and then exits the shaft through a series of ducts or radial holes connecting the shaft chamber to passages extending across the rotor core. As the cooling fluid exits the rotor passages, they are fluidly connected to the rotor core, particularly to fluid guide elements that contact the end faces of the rotor core. The fluid guide elements guide and discharge the cooling fluid outward toward the rotor end windings. The cooling fluid may be any fluid suitable for cooling and / or lubricating an electric machine, such as oil.

[0012] To supply the cooling fluid into the rotor shaft, a supply element may be provided, in particular extending into an axial bore of the rotor shaft. The supply element may be configured, for example, in the form of a stationary lance that can be connected to a housing or a support part connected to the housing. In comparison with a rotary lance, the oil flow inside a stationary lance is not affected by the rotational speed of the electric machine. Since there are no centrifugal forces inside a stationary lance, the oil flow towards the shaft can be well controlled.

[0013] The plurality of radial holes may be arranged in a central region of the rotor shaft. More specifically, at least some of the plurality of radial holes of the rotor shaft may be arranged in a plane axially located in a central portion of the rotor core, for example, in the central third of the rotor core. Providing the radial holes in the central region has the advantage that a cooling fluid can flow from the central region to the first and second sides of the rotor core, thereby already absorbing heat from the rotor core.

[0014] The rotor core may optionally be composed of multiple laminations. The central group of rotor laminations may have radial holes. Rotor laminations axially arranged adjacent to the central group may have the same design. Axial passages extend through all laminations to the axial ends of the rotor core, thus allowing cooling fluid to exit the rotor core. The number of radial holes and axial passages in the rotor core may correspond to the number of pole sections and the number of respective windings of the rotor assembly. The axial passages may be arranged, for example, circumferentially in the region of the pole sections and the region of each winding. However, different numbers of passages and windings are also possible. The axial passages may be arranged radially between the inner peripheral surface of the rotor core and the radially inner ends of the pole sections that house the windings. In other words, the passages may be arranged radially inside the pole sections of the rotor core, particularly so as to overlap circumferentially with respect to the pole sections. The pole sections extend radially outward from the ring sections and may also be called salient poles or web sections.

[0015] According to one embodiment, the first and second guide elements may have the same design. Therefore, features described for one guide element (first element) may also apply to the other guide element (second element). The fluid guide element may include an annular passage fluidly connected to an outlet opening of the rotor core and a plurality of fluid pockets fluidly connected to the annular passage and arranged on the inner circumferential surface of the guide element. The escape openings are fluidly connected to each of the fluid pockets. The annular passage of the fluid guide element may be arranged to radially overlap the side openings of the rotor core passage. Thus, the cooling fluid leaving the axial passages collects in the annular passage of the fluid guide element, and a ring-shaped pool of cooling fluid is formed by the annular passage. The ring-shaped pools are fluidly connected to the fluid pockets and each form an axial reservoir that centrifugally collects the cooling fluid before it is discharged to the outside by overflow.

[0016] The escape openings of the fluid guide elements may have an axial extension of at least 0.25 times, in particular at least 0.5 times, in particular at least 0.75 times the axial length of the end windings protruding beyond the end face of the rotor core. The openings thus have a slot-like design, which, in conjunction with the reservoir design, contributes to an axially wide oil cascade toward the rotor winding ends. Therefore, particularly effective cooling of the end windings is achieved.

[0017] In one embodiment, the fluid guide element may include a first ring portion and a plurality of winding support portions protruding radially from the first ring portion. The winding support portions may include head portions forming enlarged ends, thereby preventing the end windings from slipping off the support portions. The end windings surround the winding support portions, i.e., surround and / or engage with each winding support portion. The winding support portions may be shaped to correspond to the pole portions of the rotor core in cross section, i.e., form lateral extensions of the pole portions. Each winding, which may also be referred to as a coil, extends in a closed loop around an associated pole portion of the rotor core, the first winding support portion of the first fluid guide element, and, at the opposite end, the second winding support portion of the second fluid guide element. In embodiments with winding support portions, the fluid guide element serves two functions: cooling and supporting the end windings. Therefore, the fluid guide element may also be referred to as a cooling element and / or a support element.

[0018] The fluid guide elements may be made of a non-conductive material, in particular a material different from the material of the rotor core. For example, a plastic material may be used for the fluid guide elements. As mentioned above, some or all of the above-described configurations may be applied to the first guide element and / or the second guide element.

[0019] In one embodiment, a first end ring may be provided on a first side of the rotor core, and a second end ring may be provided on a second, opposite side. The first end ring and / or the second end ring may be made of, for example, but not limited to, a metallic material, particularly aluminum or an aluminum alloy. The end rings may be mechanically connected to the rotor core, more particularly to the rotor laminations. In one implementation, the first end ring and the second end ring may be axially fastened to each other by a plurality of fastening or clamping elements. The clamping elements may each be disposed circumferentially between two windings. The first end ring and / or the second end ring may include a flange portion for supporting the clamping elements and a jacket portion that substantially surrounds the end windings. Thus, the end rings have an L-shape when viewed in semi-longitudinal cross section. Furthermore, the end rings may include a plurality of land portions extending axially along the radially inner circumference of the jacket portion. The clamping element may extend axially through land portions which may each be disposed between two circumferentially adjacent end windings.

[0020] In a preferred embodiment, the end rings may be configured to collect cooling fluid arriving from the rotor end windings and effectively redirect the fluid toward the stator end windings through holes at several specific locations through the outer portion of the ring. The holes or openings allow cooling fluid flowing from the fluid guide elements to the end windings to be temporarily trapped within the end ring, from which the cooling fluid may escape radially outward through the openings and be centrifugally thrown against the stator before returning to the cooling system. The openings in the end rings may be circumferentially offset relative to the escape openings of each fluid guide element.

[0021] The rotor core has a plurality of longitudinally extending recesses or slots for accommodating windings, each recess being formed between two circumferentially adjacent pole pieces. A wedge element may be disposed in each longitudinal recess between two circumferentially adjacent windings. The wedge is fixed within the longitudinal recess and can prevent the rotor winding from being disengaged from the winding slot due to centrifugal force.

[0022] The object is further achieved by a wound-field synchronous motor (EESM) comprising: a housing; a stator arranged in the housing and including a stator core and a winding; and a rotor rotatably supported in the housing about a rotation axis, the rotor being configured according to any one of the above embodiments. In this way, an EESM is provided having very good cooling characteristics and therefore a long service life. [Brief explanation of the drawings]

[0023] Preferred embodiments will now be described with reference to the drawings. [Figure 1A] 1 shows a rotor assembly for an electric machine in longitudinal section; [Figure 1B] 1B shows the rotor assembly of FIG. 1A in a first cross-sectional view taken along section line 1B-1B. [Figure 1C] 1C shows the rotor assembly of FIG. 1A in a second cross-sectional view taken along section line 1C-1C. [Figure 2] FIG. 1B shows a three-dimensional exploded view of the rotor assembly of FIG. 1A. [Figure 3A] FIG. 1B illustrates, in a partially cut-away view, the rotor assembly of FIG. 1A with a flow of cooling fluid entrained. [Figure 3B] FIG. 1B shows the rotor assembly of FIG. 1A in an improved embodiment. [Figure 4] FIG. 1B shows details of the rotor assembly of FIG. 1A in a perspective view with one end portion of the assembly partially cut away. [Figure 5A]1B shows a detail of the rotor assembly of FIG. 1A in a perspective view of the side of the fluid guide element facing the rotor core. [Figure 5B] 1B is a partially cutaway view showing a detail of a fluid-guiding element of the rotor assembly of FIG. 1A. [Figure 5C] 5B shows a cross-sectional view of a portion of the fluid guide element of FIG. 5A. FIG. [Figure 5D] FIG. 5D shows an axial view of the fluid guiding element of FIG. 5C with the flow of cooling fluid drawn in. [Figure 6] 1A-1D are partial cutaway perspective views showing first to fourth details of passages F of the rotor assembly of FIG. 1A, respectively. [Figure 7A] 1A to 6D show an electric motor according to the present invention in longitudinal section, the electric motor including the rotor assembly shown in FIGS. [Figure 7B] FIG. 7B shows a perspective view, partially cut away, of the electric motor assembly of FIG. 7A.

[0024] 1A to 6D, which will be described together below, show a rotor assembly 2 according to the invention for an electric machine 2, in particular for a wound field synchronous motor (EESM).

[0025] The rotor assembly 2 comprises components including a rotor shaft 3, a rotor core 4 connected to the rotor shaft 3, windings 5 ​​housed in pole sections 6 of the rotor core 4, and fluid guide elements 7, 8 at each axial end of the rotor core 4. A first end ring 9 may be provided at a first axial end 10 of the rotor core, and a second end ring 12 may be provided at an opposite second axial end 13 of the rotor core. The rotor shaft 3 is provided with axial holes 14 and a group of radial holes 15.

[0026] A supply element (not shown) may be provided which, in the installed state of the rotor assembly, may extend axially in the axial bore 14 of the rotor shaft 3. The supply element may, for example, be configured in the form of a stationary lance which may be connected to the housing or to a support part of the housing. In comparison with a rotary lance, the oil flow inside a stationary lance is not affected by the rotational speed of the electric machine. The absence of centrifugal forces inside a stationary lance makes it possible to better control the oil flow towards or into the shaft.

[0027] In the axial region of the radial holes 15, the rotor shaft 3 may optionally have an annular recess 16 on its inner circumferential surface. Therefore, the cooling fluid flowing along the inner wall of the axial holes 14 due to centrifugal force can easily reach the openings of the radial holes 15, which are radially recessed compared to the radius of the end portion of the shaft inner wall. The group of radial holes 15 is preferably, but not exclusively, arranged in one plane P, as shown in FIGS. 1A and 1B . The radial holes 15 are particularly arranged in the central region of the rotor shaft 3. More specifically, at least some of the radial holes 15 are arranged in the middle section of the rotor core 4, particularly in the middle third of the rotor core, for example, in a plane P axially located exactly in the middle of the rotor core.

[0028] The rotor core 4 is rigidly connected to the rotor shaft 3. The axial connection may be provided by the rotor core 4 being axially supported at one end against a flange portion 17 of the rotor shaft 3 and axially fastened at the opposite end to the rotor shaft 3 by a threaded sleeve 18. The non-rotatable connection may be provided by a force-locking engagement, such as a transition fit, between the rotor shaft 3 and the rotor core 4 and / or a form-locking engagement, such as a spline connection. The rotor core 4 includes a plurality of axially extending recesses 41 in a radially outer section of the rotor core, and the pole portions 6, 6' are each formed between two circumferentially adjacent recesses 41. The recesses 41 may also be referred to as slots.

[0029] Each pole section 6, 6' supports a winding 5, 5' that surrounds the respective pole in a closed loop, as seen particularly in Figure 2. Therefore, the pole section can also be referred to as a winding support or salient pole. In cross section, as shown in Figures 1B and 1C, the winding support may have a T-shape with a radial portion 22 and a head portion 23 that extends circumferentially relative to the radial portion 22. The T-shape contributes to secure positioning of the windings 5, 5' even at high rotational speeds and prevents the windings from slipping off the winding support due to centrifugal force. Each winding 5, 5', also referred to as a coil, includes a first winding end 24 that extends axially beyond the first end face 25 of the rotor core 4 and a second winding end 26 that protrudes axially beyond the opposite second end face 27 of the rotor core 4. The winding ends 24, 25 form a U-shaped return section of the winding. The windings 5, 5' supported by the rotor core 4 generate a constant magnetic field. Therefore, in an operating state, the rotor core 4 rotates about the rotation axis A, driving the rotor shaft 3 and the drive system rotatably connected to the rotor shaft 3.

[0030] At its radially inner circumferential surface 20, rotor core 4 includes a plurality of inlet openings 19 fluidly connected to radial bores 15 of rotor shaft 3. To this end, inlet openings 19 of rotor core 4 are preferably aligned with radial outlet openings of rotor shaft 3. Inlet openings 19 may extend radially to axial passages connected to inlet openings 19. More specifically, first axial passages 28 extend axially from inlet openings 19 to first outlet openings 29 in a first end face 25 of rotor core 4, and second axial passages 30 extend axially to second outlet openings 31 in a second end face 27 of rotor core 4.

[0031] The rotor core 4 may be constructed from multiple laminations. As seen in FIGS. 1A and 1B, the central set of rotor laminations includes an inlet opening 19. Rotor laminations axially adjacent to the central lamination preferably have the same configuration as each other, as shown in FIG. 1C. The laminations define axially extending passages 28, 30. The axial passages 28, 30 extend through all of the laminations to the axial ends 25, 27 of the rotor core 4. From the midsection of the rotor core 4, a portion of the cooling fluid flows in a first axial direction to the first side 10, and a portion of the cooling fluid flows in an opposite second axial direction 13 to the second side, thereby absorbing heat from the rotor core 4.

[0032] 1B and 1C, the number of radial holes 19 and the number of axial passages 28, 30 in the rotor core 4 correspond to the number of windings 5, 5' in the rotor assembly 2. In this embodiment, the axial passages 28, 30 are circumferentially disposed in the region of the pole sections 6, 6' and in the region of each winding 5, 5'. Furthermore, the axial passages 28, 30 are radially disposed between the inner peripheral surface 20 of the rotor core and the radially inner ends 21 and / or shoulders of the pole sections 6, 6' that house the windings 5, 5'. However, it should be understood that the number and configuration of the radial and axial passages may differ from the example shown.

[0033] The first and second fluid guide elements 7, 8 are arranged in particular to axially contact the end faces 25, 27 of the rotor core. The fluid guide elements 7, 8 are preferably connected to the rotor core 4 via first and second end rings 9, 12 that clamp the rotor core 4. In this embodiment, the first and second fluid guide elements 7, 8 have the same design, so that the features described for one element also apply to the other. The first fluid guide element 7 is fluidly connected to the first outlet opening 29 of the rotor core 4 and includes a fluid structure 32 configured to receive and guide the cooling fluid to a first escape opening 33 circumferentially arranged between two circumferentially adjacent end windings 5, 5′.

[0034] More specifically, the fluid guide elements 7, 8 include a ring portion 34 and a plurality of winding support portions 35 projecting radially from the ring portion. As can be seen particularly in FIGS. 5A-5C , the ring portion 34 includes, at its axial end portion in contact with the adjacent end faces 25, 27 of the rotor core 4, an annular passage 48 and a plurality of fluid pockets 49 fluidly connected to the annular passage and disposed on the inner circumferential surface 50 of the fluid guide elements 7, 8. The annular passage 48 is configured to receive cooling fluid from adjacent outlet openings 29 of the rotor core. To this end, the annular passages 48 of the fluid guide elements 7, 8 are preferably positioned so as to radially overlap the side openings 29 of the rotor core passages. Thus, the cooling fluid leaving the axial passages 28, 30 collects in the annular passages 48 of each fluid guide element 7, 8, forming a ring-shaped pool of cooling fluid. The ring-shaped pools are fluidly connected to the fluid pockets 49 and form axial reservoirs that centrifugally collect the cooling fluid before it is discharged by overflow through the radial holes 51 extending through the ring portions 34 of the fluid guide elements 7, 8. The radial holes 51 fluidly connect the radially inner fluid pockets 49 to the radially outer escape openings 33. The radial holes 51 and / or the escape openings 33 have an axial extension of at least 0.5 times, more particularly at least 0.75 times, the axial length of the end windings 24, 26 that protrude beyond the end faces of the rotor core. This slot-like design, in conjunction with the reservoir design, contributes to an axially wide oil cascade of the cooling fluid toward the rotor winding ends 24, 26, as shown in FIG. 5D.

[0035] The winding support portion 35 includes a head portion 36 that forms an enlarged end, preventing the end windings 24, 26 from slipping off the support portion 35 due to centrifugal force. The end windings 24, 26 surround the winding support portion 35, 38 in a U-shape when viewed radially. The winding support portion 35, 38 preferably corresponds to the pole portion 6, 6' of the rotor core 4 in cross section, i.e., forms a lateral extension of the pole portion 6, 6' at the axial end of the rotor core. The windings 5, 5' each extend in a closed loop around the associated pole portion 6, 6' of the rotor core, the first winding support portion 35 of the first fluid guide element 7, and the second winding support portion 38 of the second fluid guide element 8 at the opposite end. The fluid guide elements contribute to good cooling and support of the end windings 24, 26. The fluid guiding elements 7, 8 may be made from a non-conductive material, in particular a plastic material.

[0036] A first end ring 9 is provided on a first side 10 of the rotor core, and a second end ring 12 is provided on an opposite second side 13. The end rings 9, 12 may be made of a metallic material, in particular aluminum or an aluminum alloy. The end rings 9, 12 are mechanically connected to the rotor core 4 and are axially clamped toward each other by a number of clamping elements 40 distributed around the entire circumference. As can be seen in particular in Figures 1B and 1C, the clamping elements 40 are circumferentially arranged in the region between two adjacent windings 5, 5'.

[0037] The first end ring 9 and the second end ring 12 preferably have the same design, so that features described for one ring may also apply to the other ring. The end rings 9, 12 may include a flange portion 42 on which a clamping element 40 is axially supported and a jacket portion 43 that substantially surrounds each end winding 24, 26. As seen particularly in FIG. 2 , the end rings 9, 12 each include a plurality of ribs 44 with land portions extending axially along the radially inner periphery of the jacket portion 43. The land portions are axially supported against wedge elements 45 disposed within slots 41 in the rotor core 6. The clamping elements 40 extend axially through the ribs 44 of the opposing end rings 9, 12 and through the wedge elements 45 disposed axially between the end rings 9, 12. The groove wedges provide circumferential support for the windings 5, 5′, helping to hold the windings in place even under high centrifugal forces.

[0038] The L-shape of the end rings 9, 12, which have flange and jacket portions, contributes to the temporary collection of cooling fluid that escapes from the end windings 24, 26. The end rings 9, 12 may include a plurality of holes 46 distributed across the circumference. The holes 46 may be located at the edge 11 between the flange and jacket portions. In the circumferential direction, the holes may be located between the openings 47 for the fastening members 40. The holes 46 allow the cooling fluid coming from the end windings 24, 26 of the rotor assembly 2 to be guided towards the end windings of the stator of the electric machine.

[0039] The path F of the cooling fluid from entering the rotor shaft 3 to exiting the end rings 9, 12 is shown in more detail in Figures 6A-6D.

[0040] 7A and 7B show an electric machine 52 according to the present invention, which includes the rotor assembly shown in FIGS. 1A to 6D. The electric machine 52 is configured in the form of a wound-field synchronous motor (EESM). The electric machine 52 includes a housing 53, a stator 54 connected to the housing 53, and the rotor assembly 2 according to the present invention described above. The rotor assembly 2 is arranged coaxially with the stator 54 and is supported by bearings 55, 55' on the housing 53 so as to be rotatable about the rotation axis. The stator 54 includes a stator core 56 and windings 57. The windings are connected to an AC power source and are capable of generating a rotating magnetic field.

[0041] It can be seen that the holes 46 in the end rings 9, 12 are positioned radially inward of and axially overlap the end windings 58, 58' of the stator winding 57. In this way, cooling fluid flowing from the end windings 24, 26 to the end rings 9, 12 of the rotor assembly 2 can flow radially outward through the holes 46 to cool the end windings 58, 58' of the stator 54. This contributes to an overall more efficient electric machine. [Explanation of symbols]

[0042] 2 Rotor Assembly 3 Rotor shaft 4 rotor core 5 windings 6 pole part 7 First fluid guide element 8 Second fluid guide element 9 First End Ring 10 first axial end 11 Edge 12 Second End Ring 13 Second axis end 14 Axial hole 15 Radial hole 16 Annular recess 17 Flange part 18 Threaded Sleeve 19 Entrance opening 20 Circumferential surface 21 Radial inner end 22 Radial section 23 Head part 24 First winding end 25 First end face 26 Second winding end 27 Second end face 28 first axial passage 29 First Exit Aperture 30 second axial passage 31 Second exit opening 32 Fluid structure 33 Escape opening 34 First ring part 35 first winding support portion 36 First head part 37 Second ring part 38 Second winding support part 39 Second head part 40 Fastening member 41 Winding groove 42 Flange part 43 Jacket part 44 Ribs 45 Wedge element 46 Exit opening 47 Aperture 48 Circular Passage 49 Fluid Pocket 50 Inner surface 51 holes 52 Electrical Machinery 53 Housing 54 Stator 55,55' bearing 56 stator core 57 Windings 58,58' Winding end A axis F flow P plane

Claims

1. A rotor assembly (2) for a wound field synchronous motor (EESM), comprising: a rotor shaft (3); a rotor core (4) connected to the rotor shaft (3) and including a plurality of circumferentially distributed pole portions (6, 6'), around which windings (5, 5') are housed, respectively, and the windings (5, 5') have a first winding end (24) that protrudes axially beyond a first end face (25) of the rotor core (4) and an opposite second winding end (26) that protrudes axially beyond a second end face (27) of the rotor core (4); a first fluid guide element (7) arranged at a first end of the rotor core (4); a second fluid guide element (8) arranged at a second end of the rotor core (4); Equipped with The rotor shaft (3) comprises an axial bore (14) and a plurality of radial bores (15) extending from the axial bore (14) and arranged in an axial central region of the rotor shaft (3), the rotor core (4) comprises a plurality of inlet openings (19) fluidly connected to the radial holes (15) of the rotor shaft (3), and axial passages (28, 30) extending axially from the inlet openings (19) to a first outlet opening (29) in the first end face (25) of the rotor core (4) and a second outlet opening (31) in the second end face (27) of the rotor core (4); the first fluid guide element (7) is fluidly connected to the first outlet opening (29) of the rotor core (4) and comprises a fluid structure (32) configured to receive cooling fluid from the first outlet opening (29) of the rotor core (4) and guide the cooling fluid to a first escape opening (33) circumferentially arranged between two circumferentially adjacent first winding ends (24); the second fluid guide element (8) is fluidly connected to the second outlet opening (31) of the rotor core (4) and comprises a fluid structure configured to receive the cooling fluid from the second outlet opening (31) of the rotor core (4) and guide the cooling fluid to a second escape opening circumferentially arranged between two circumferentially adjacent second winding ends (26). Rotor assembly.

2. A rotor assembly according to claim 1, characterized in that a supply element is provided for directing a cooling fluid into the axial bore (14) of the rotor shaft (3).

3. 3. A rotor assembly according to claim 1 or 2, characterized in that at least some of the radial holes (15) of the rotor shaft (3) are arranged in a plane (P) that lies axially within a central portion of the rotor core (4).

4. 4. A rotor assembly according to claim 1, wherein the number of radial holes (15) and the number of axial passages (28, 30) of the rotor core (4) correspond to the number of pole sections (6, 6').

5. A rotor assembly according to any one of claims 1 to 4, characterized in that the axial passages (28, 30) are arranged radially inside the pole sections (6, 6') that house the windings (5, 5').

6. the first fluid guide element (7) comprises a first annular passage (48) fluidly connected to the first outlet opening (29) of the rotor core (4) and a plurality of first fluid pockets (49) on its inner circumferential surface (50) fluidly connected to the first annular passage (48), the first escape openings (33) being fluidly connected to the first fluid pockets (49), respectively; and / or The second fluid guide element (8) includes a second annular passage fluidly connected to the second outlet opening of the rotor core (4), and a plurality of second fluid pockets fluidly connected to the second annular passage on an inner circumferential surface thereof, and the second escape openings are fluidly connected to the second fluid pockets, respectively. A rotor assembly according to any one of claims 1 to 5, characterized in that it comprises:

7. the first escape opening (33) of the first fluid guide element (7) has an axial extension of at least 0.25 times the axial length of the first winding end (24) protruding beyond the first end face (25) of the rotor core (4); and / or The second escape opening of the second fluid guide element has an axial extension of at least 0.25 times the axial length of the second winding end (26) protruding beyond the second end face (27) of the rotor core (4). The rotor assembly of claim 6 .

8. the first fluid guide element (7) comprises a first ring portion (34) and a plurality of first winding support portions (35) radially projecting from the first ring portion (34), the enlarged ends of the first winding support portions (35) forming a first head portion (36), the first winding end portion (24) surrounding the first winding support portions (35), and / or The second fluid guide element (8) includes a second ring portion (37) and a plurality of second winding support portions (38) projecting radially from the second ring portion (37), the enlarged ends of the second winding support portions (38) forming second head portions (39), and the second winding end portions (26) surrounding the second winding support portions (38). A rotor assembly according to any one of claims 1 to 7, characterized in that it comprises:

9. 9. A rotor assembly according to claim 1, wherein at least one of the first and second fluid guide elements is made from a non-conductive material different from the material of the rotor core.

10. a first end ring (9) is provided on a first side of the rotor core (4) and a second end ring (12) is provided on an opposite second side, and the first end ring (9) and the second end ring (12) are axially fastened to each other by a plurality of fastening elements (40) each extending between two circumferentially adjacent windings (5, 5'); At least one of the first end ring (9) and the second end ring (12) comprises a flange portion (42) for supporting the clamping element (40) and a jacket portion (43) surrounding the end windings (5, 5'), and the end ring comprises a plurality of outlet openings (46). A rotor assembly according to any one of claims 1 to 9, characterized in that it comprises:

11. 11. A rotor assembly according to claim 1, wherein the outlet openings (46) of the end rings (9, 12) are arranged circumferentially offset with respect to the escape openings (33) of each of the fluid guide elements (7, 8).

12. 12. A rotor assembly according to claim 1, wherein the end ring (9, 12) includes a plurality of ribs (44) extending axially between two circumferentially adjacent end windings (5, 5').

13. Rotor assembly according to any one of claims 10 to 12, characterized in that the end rings (9) are made from a non-ferromagnetic material, in particular aluminium.

14. 14. A rotor assembly according to claim 1, wherein a winding slot (41) is formed between each two circumferentially adjacent pole portions (6, 6') in the rotor core (4), and a wedge element (45) is arranged between each two circumferentially adjacent windings (5, 5').

15. A wound field synchronous motor (EESM), a housing (53); a stator (54) disposed within the housing (53) and including a stator core (56) and a winding (57); a rotor assembly (2) rotatably supported within the housing (53) about a rotation axis (A); In a wound field synchronous motor (EESM), The rotor assembly (2) is configured in accordance with any one of claims 1 to 14. A wound field synchronous motor (EESM) characterized by:

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