Rotor having plurality of cooling nozzles and electric machine including rotor

Abstract

The invention relates to a motor which comprises a stator and a rotor. The stator includes: a stator core defining a stator bore; and a plurality of windings having end turns extending from the stator core. This includes a central region configured to be disposed in the stator bore, and first and second end regions extending from the central region and aligned with the end turns of the plurality of windings. The rotor defines a cooling hole in fluid communication with a low pressure cooling fluid source and includes a plurality of cooling nozzles in fluid communication with the cooling hole and disposed in the first and second end regions. The plurality of cooling nozzles extend radially outward such that each cooling nozzle is configured to pull the cooling fluid through the cooling hole in response to centrifugal force caused by rotation of the rotor within the stator hole and to eject the cooling fluid toward the end turn. The invention also relates to a rotor.

Description

Technical Field

[0001] The present disclosure relates generally to electric machines, and more particularly to rotors for electric machines and cooling such rotors through surrounding components of the rotor using cooling nozzles. Background Art

[0002] High-speed motors are widely used in various applications, including automotive applications. These motors are designed to operate at speeds exceeding 50,000 revolutions per minute (RPM). Accordingly, high-speed motors are known to generate a large amount of heat during operation, which can degrade performance and reliability.

[0003] Conventional cooling arrangements for cooling components of an electric machine are not suitable for high speed electric machines due to geometric design limitations, the risk of introducing rotational imbalance, and the risk of cavitation of the cooling fluid as it flows through the machine. Therefore, there is a need for an improved arrangement for cooling the rotor and surrounding components in a high speed electric machine. Summary of the invention

[0004] A general aspect of the present disclosure relates to an electric machine. The electric machine includes a stator and a rotor. The stator includes a stator core having a first end and a second end opposite to the first end. The stator core defines a stator hole extending between the first end and the second end and a rotation axis concentric with the stator hole. The stator also includes a plurality of windings operably attached to the stator core and having end turns extending beyond the first end and the second end of the stator core. The rotor is configured to rotate about the rotation axis in response to the plurality of windings being energized. The rotor includes a middle region disposed in the stator hole. The rotor also includes a first end region extending from the middle region and beyond the stator hole so that the first end region is aligned with the end turns extending beyond the first end of the stator core. The rotor further includes a second end region extending from the middle region and beyond the stator hole so that the second end region is aligned with the end turns extending beyond the second end of the stator core. The first end region, the middle region, and the second end region together define a cooling hole extending along the rotation axis between a fluid inlet defined by the first end region and a terminal defined by the second end region. The fluid inlet of the cooling hole is in fluid communication with a low-pressure cooling fluid source, and the fluid inlet is configured to receive cooling fluid from the low-pressure cooling fluid source. The rotor further includes a plurality of first cooling nozzles disposed in the first end region of the rotor, in fluid communication with the cooling hole, and extending radially outward. Each first cooling nozzle is configured to pull cooling fluid through the cooling hole in response to the centrifugal force caused by the rotation of the rotor around the rotation axis, and to spray cooling fluid toward the end turns extending beyond the first end of the stator core. The rotor additionally includes a plurality of second cooling nozzles disposed in the second end region of the rotor, in fluid communication with the cooling hole, and extending radially outward. Each second cooling nozzle is configured to pull cooling fluid through the cooling hole in response to the centrifugal force caused by the rotation of the rotor around the rotation axis, and to spray cooling fluid toward the end turns extending beyond the second end of the stator core.

[0005] Another general aspect of the present disclosure includes a rotor for an electric machine, wherein the rotor is configured to rotate about an axis of rotation. The rotor includes a middle region extending between a first end and a second end, a first end region extending from the first end of the middle region, and a second end region extending from the second end of the middle region. The first end region, the middle region, and the second end region together define a cooling hole extending along the axis of rotation between a fluid inlet defined by the first end region and a terminal defined by the second end region. The fluid inlet of the cooling hole is configured to be arranged in fluid communication with a low-pressure cooling fluid source to receive cooling fluid from the low-pressure cooling fluid source. The rotor also includes a plurality of first cooling nozzles disposed in the first end region, in fluid communication with the cooling hole, and extending radially outward. Each first cooling nozzle has a first diameter (D1) and is configured to pull cooling fluid through the cooling hole in response to centrifugal force caused by the rotation of the rotor about the axis of rotation, and radially spray cooling fluid at a first flow rate. The rotor further includes a plurality of second cooling nozzles disposed in the second end region, in fluid communication with the cooling hole, and extending radially outward. Each second cooling nozzle has a second diameter (D2) greater than D1 and is configured to pull cooling fluid through the cooling holes in response to centrifugal forces caused by rotation of the rotor about the rotation axis and radially eject cooling fluid at a second flow rate equal to the first flow rate.

[0006] The present disclosure provides an improved arrangement for effectively cooling the rotor and surrounding components (such as the end turns of a plurality of windings) of an electric machine. In addition, the plurality of first cooling nozzles and the plurality of second cooling nozzles of the rotor provide the following advantages: the need for a high pressure cooling fluid source to push the cooling fluid through the cooling holes is eliminated, the possibility of cooling fluid cavitation during high speed operation of the electric machine is reduced, and the possibility of causing rotational imbalance in the rotor is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Advantages of the present disclosure will be readily appreciated as the same become better understood by referring to the following detailed description when considered in conjunction with the accompanying drawings.

[0008] Figure 1 is a cross-sectional view of an electric machine including a stator and a rotor, the rotor including a plurality of first cooling nozzles and a plurality of second cooling nozzles.

[0009] Figure 2 is a perspective cross-sectional view of a rotor including a plurality of first cooling nozzles and a plurality of second cooling nozzles.

[0010] Figure 3A is a partial cross-sectional view of a first end region of a rotor including a plurality of first cooling nozzles.

[0011] Figure 3Bis a partial cross-sectional view of a second end region of the rotor including a plurality of second cooling nozzles.

[0012] FIG. 4A to FIG. 4C is a partial cross-sectional view of a rotor showing various configurations of the transition between cooling holes and corresponding cooling nozzles.

[0013] Figure 5A is a perspective view of a rotor, wherein each of the first plurality of cooling nozzles and the second plurality of cooling nozzles each includes six cooling nozzles equally spaced about a rotation axis.

[0014] Figure 5B is a perspective view of a rotor, wherein each of the plurality of first cooling nozzles and the plurality of second cooling nozzles includes two opposing cooling nozzles.

[0015] Figure 6 is a cross-sectional view of an electric machine including a stator and a rotor, the rotor including a plurality of third cooling nozzles.

[0016] Figure 7 is a cross-sectional view of an electric machine including a stator and a rotor including a coupling area defining a fluid outlet.

[0017] Fig. 8A is a cross-sectional view of a rotor including a coupling area defining a fluid outlet.

[0018] Figure 8B is a cross-sectional view of another configuration of a rotor including a coupling region defining a fluid outlet and a stepped portion disposed adjacent the fluid outlet. DETAILED DESCRIPTION

[0019] Referring to the drawings, wherein like reference numerals are used to identify similar or identical parts throughout the various views, Figure 1 A rotor 20 and an electric machine 22 including the rotor are shown according to the present disclosure. The electric machine is typically high speed (e.g., over 50,000 RPM) and can be one of a variety of motor types, such as an AC induction motor or a DC brushless motor. It should also be understood that the electric machine 22 can be configured to operate as a generator. Of course, it should be further understood that in some applications (such as electric vehicles), the electric machine 22 can be configured to operate both as a motor (to propel the vehicle) and as a generator (to regeneratively brake the vehicle).

[0020] The electric machine 22 includes a stator 24. The stator 24 includes a stator core 26 having a first end 28 and a second end 30 opposite the first end 28. The stator core 26 may include a plurality of laminations of metal sheets; however, other configurations are contemplated. The stator core 26 defines a stator bore 32 extending between the first end 28 and the second end 30 and a rotation axis 34 concentric with the stator bore 32. The stator 24 also includes a plurality of windings 36 operably attached to the stator core 26 and having end turns 40, 42 extending beyond the first end 28 and the second end 30 of the stator core 26. The configuration of the plurality of windings 36 (e.g., the material, the cross-sectional shape of each winding, and the manner and mode in which the plurality of windings 36 are operably attached to the stator core 26) is not particularly limited. For example, the plurality of windings 36 may be configured as concentrated windings, distributed windings, lapped windings, wave windings, etc. In general, the plurality of windings 36 are configured to be energized to cause the rotor 20 to rotate about the axis of rotation 34. The stator 24 may also include a housing 44 surrounding the stator core 26. The housing 44 may define a cooling circuit 46 configured to receive and circulate a cooling fluid to cool the outer periphery of the stator core 26. The stator 24 may further include end caps 48, 50 disposed at each end of the stator 24 to close the stator 24.

[0021] Reference Figure 1 and Figure 2 , the rotor 20 includes a mid-region 52 extending between a first end 54 and a second end 56. Figure 1 As shown, the middle region 52 of the rotor 20 is disposed in the stator bore 32 such that the rotor 20 is configured to rotate about the rotation axis 34 in response to the plurality of windings 36 being energized. The middle region 52 of the rotor 20 may include a plurality of magnets 58. The plurality of magnets 58 may be configured to electromagnetically interact with the plurality of windings 36 in response to the plurality of windings 36 being energized to cause the rotor 20 to rotate about the rotation axis 34. The middle region 52 of the rotor 20 may also include a compression sleeve 60 surrounding the plurality of magnets 58. In one example, the compression sleeve 60 is constructed of a metal structure or a composite composition; however, other configurations are contemplated.

[0022] The rotor 20 also includes a first end region 62 extending from the first end 54 of the middle region 52. Figure 1 As shown, the first end region 62 extends beyond the stator bore 32 such that the first end region 62 is aligned with the end turns 40 extending beyond the first end 28 of the stator core 26. The rotor 20 further includes a second end region 64 extending from the second end 56 of the middle region 52. Figure 1As shown, the second end region 64 extends beyond the stator bore 32 such that the second end region 64 is aligned with the end turns 42 extending beyond the second end 30 of the stator core 26. The first end region 62 and the second end region 64 can have a tapered profile (i.e., the diameters of the first end region 62 and the second end region 64 can decrease as the first end region 62 and the second end region 64 extend away from the middle region 52). The second end region 64 can further include a coupling region 66 that extends through the end cap 50 and is configured to couple with an external component (such as a vehicle's powertrain) to transmit torque generated by the motor 22 to the external component. Likewise, in the case where the motor 22 is configured to operate as a generator, the coupling region 66 can be configured to receive torque and transmit torque from the external component to the rotor 20.

[0023] like Figure 1 and Figure 2 As shown, the first end region 62, the middle region 52, and the second end region 64 collectively define a cooling hole 68. The cooling hole 68 extends along the rotational axis 34 between a fluid inlet 70 defined by the first end region 62 and a terminal end 72 defined by the second end region 64. The cooling hole 68 can be defined by a cooling hole diameter (D CB ) is limited. Figure 1 As shown, the fluid inlet 70 is in fluid communication with a low-pressure cooling fluid source 74, and the fluid inlet is configured to receive cooling fluid from the low-pressure cooling fluid source 74. The cooling fluid can be any fluid suitable for achieving heat transfer from components of the electric machine 22. For example, the cooling fluid can include a liquid-based coolant, such as oil, water glycol, water propylene glycol, refrigerant, etc. The electric machine 22 can include a cooling fluid channel 76 defined by the end cover 48. The cooling fluid channel 76 can be arranged to be in fluid communication with the low-pressure cooling fluid source 74 and the fluid inlet 70 of the cooling hole 68 to guide the cooling fluid from the low-pressure cooling fluid source 74 to the cooling hole 68.

[0024] Continue to refer to Figure 1 and Figure 2, the rotor 20 also includes a plurality of first cooling nozzles 78 disposed in the first end region 62 of the rotor 20. Each first cooling nozzle 78 is in fluid communication with the cooling hole 68 and extends radially outward. Accordingly, each first cooling nozzle 78 is configured to pull the cooling fluid through the cooling hole 68 in response to the centrifugal force caused by the rotation of the rotor 20 around the rotation axis 34, and to eject the cooling fluid radially outward (i.e., toward the end turns 40 extending beyond the first end 28 of the stator core 26). Additionally, the rotor 20 further includes a plurality of second cooling nozzles 80 disposed in the second end region 64 of the rotor 20. Each second cooling nozzle 80 is in fluid communication with the cooling hole 68, and each second cooling nozzle extends radially outward. Accordingly, each second cooling nozzle 80 is configured to pull the cooling fluid through the cooling hole 68 in response to the centrifugal force caused by the rotation of the rotor 20 around the rotation axis 34, and to eject the cooling fluid radially outward (i.e., toward the end turns 42 extending beyond the second end 30 of the stator core 26). The flow of cooling fluid from the low pressure cooling fluid source 74, through the cooling holes 68 and out of the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 is Figure 1 The overall is indicated by an arrow.

[0025] In other words, when the electric machine 22 is operated at a high speed, each first cooling nozzle 78 is configured to pull cooling fluid through the cooling holes 68 in response to the centrifugal force caused by the rotation of the rotor 20 about the rotation axis 34, and to eject the cooling fluid radially outward toward the end turns 40 and into the first cooling fluid gallery 82 defined by the space between the first end region 62 and the end turns 40, thereby cooling the end turns 40. Similarly, when the electric machine 22 is operated at a high speed, each second cooling nozzle 80 is configured to pull cooling fluid through the cooling holes 68 in response to the centrifugal force caused by the rotation of the rotor 20 about the rotation axis 34, and to eject the cooling fluid radially outward toward the end turns 42 and into the second cooling fluid gallery 84 defined by the space between the second end region 64 and the end turns 42, thereby cooling the end turns 42. Advantageously, the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 described herein eliminate the need for a high pressure cooling fluid source for pushing cooling fluid through the cooling holes 68 when the electric machine 22 is operated at a high speed. Alternatively, in response to centrifugal forces caused by rotation of the rotor 20 about the rotation axis 34 , the first plurality of cooling nozzles 78 and the second plurality of cooling nozzles 80 draw cooling fluid through the cooling holes 68 by being in fluid communication with the cooling holes 68 and extending radially away from the cooling holes 68 , thereby ejecting (i.e., throwing) cooling fluid toward the end turns 40 , 42 .

[0026] It should also be understood that when the electric machine 22 is operated at a relatively low speed, the centrifugal force caused by the rotation of the rotor 20 about the rotation axis 34 may not be sufficient to cause the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 to pull the cooling fluid through the cooling holes 68 and eject the cooling fluid radially outward. Accordingly, when the electric machine 22 is operated at a relatively low speed, the low-pressure cooling fluid source 74 can be configured to provide cooling fluid to the fluid inlet 70 of the cooling holes 68 at a medium pressure (e.g., between about 2 bar and about 5 bar) to push the cooling fluid through the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 to cool the end turns 40, 42.

[0027] In order to reduce the possibility of cooling fluid cavitation during high-speed operation of the electric machine 22, the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 are configured to spray the cooling fluid at equal flow rates. In other words, the plurality of first cooling nozzles 78 are configured to spray the cooling fluid at a first flow rate in response to the centrifugal force caused by the rotation of the rotor 20 around the rotation axis 34, and the plurality of second cooling nozzles 80 are configured to spray the cooling fluid at a second flow rate equal to the first flow rate in response to the centrifugal force caused by the rotation of the rotor around the rotation axis.

[0028] To achieve this equal flow rate, the geometric parameters of each of the first cooling nozzle 78 and the second cooling nozzle 80 (particularly the ratio of length (L) to diameter (D)) are defined to generate a desired amount of suction force (i.e., the force that pulls the cooling fluid through the cooling holes 68) in response to the centrifugal force caused by the rotation of the rotor 20 about the rotation axis 34. In other words, the geometric parameters of each of the first cooling nozzle 78 and the second cooling nozzle 80 must be defined so that the suction force generated by each of the first cooling nozzle 78 and the second cooling nozzle 80 in response to the centrifugal force caused by the rotation of the rotor 20 about the rotation axis 34 is balanced so that the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 do not starve each other of cooling fluid flow from the cooling holes 68. Accordingly, in some configurations, the plurality of first cooling nozzles 78 are configured to reach a choked state (i.e., maximum flow rate) before the plurality of second cooling nozzles 80 in response to the centrifugal force caused by the rotation of the rotor 20 about the rotation axis 34.

[0029] Reference Figure 3A and Figure 3B, each first cooling nozzle 78 has a first diameter (D1), and each second cooling nozzle 80 has a second diameter (D2). Additionally, each first cooling nozzle 78 has a first length (L1), and each second cooling nozzle 80 has a second length (L2). In order to produce the desired suction force described above, D2 is greater than D1. For example, the ratio of (D2 / D1) can be between about 1.05 and about 1.10. Accordingly, when L1 and L2 are equal, (L1 / D1) is less than (L2 / D2). As a result, the suction force caused by the plurality of second cooling nozzles 80 is higher than the suction force caused by the plurality of first cooling nozzles 78, which compensates for the increased distance of the plurality of second cooling nozzles 80 from the fluid inlet 70. Another geometric parameter that may affect the flow rate of the cooling fluid through the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 is the cooling hole diameter (D CB ) to the first diameter (D1) of the first cooling nozzle 78 and / or the second diameter (D2) of the second cooling nozzle 80. In some configurations, (D CB / D1) is greater than 3.3, more typically greater than 3.8, and (D CB / D2) is greater than 2.8, more typically greater than 3.3. For example, the first diameter (D1) can be greater than the cooling hole diameter (D CB ), more typically between 20% and 26%, and most typically between 22% and 24%. In addition, the second diameter (D2) may be between 15% and 30% of the cooling hole diameter (D CB ), more typically between 24% and 32%, and most typically between 26% and 30%.

[0030] Reference FIG. 3A to FIG. 3B , each first cooling nozzle 78 may extend between a first nozzle inlet 86A in fluid communication with the cooling hole 68 and a first nozzle outlet 86B disposed on a first radial surface 88 of the first end region 62. Similarly, each second cooling nozzle 80 may extend between a second nozzle inlet 90A in fluid communication with the cooling hole 68 and a second nozzle outlet 90B disposed on a second radial surface 92 of the second end region 64.

[0031] Yet another geometric parameter that may affect the flow of cooling fluid through the first cooling nozzle 78 and the second cooling nozzle 80 is the geometry of the connection between the cooling nozzle 78, 80 and the cooling hole 68 (ie, the first nozzle inlet 86A and / or the second nozzle inlet 90A). FIG. 4A to FIG. 4C As shown, the first nozzle inlet 86A and / or the second nozzle inlet 90A may include a transition portion 94 between the cooling hole 68 and the corresponding cooling nozzle 78, 80. Each transition portion 94 may have a rounded profile (eg, Figure 4Aas shown) and chamfered profiles (as Figure 4B Accordingly, the transition portion 94 between the cooling hole 68 and the first nozzle inlet 86A and / or the second nozzle inlet 90A can be configured to modify and improve the flow characteristics from the cooling hole 68 to the corresponding cooling nozzle 78, 80. In one example, the transition portion 94 is formed by extrusion honing. In other examples, such as Figure 4C As shown, the transition portion 94 may be defined by a liner insert 96 disposed in each of the respective cooling nozzles 78 , 80 .

[0032] Reference Figure 5A and Figure 5B It is also contemplated that the number and arrangement of the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 may vary. Figure 5A In some configurations, the plurality of first cooling nozzles 78 include six first cooling nozzles 78A, 78B, 78C, 78D, 78E, 78F that are equally spaced about the rotation axis 34 and extend radially outward from the cooling hole 68, and the plurality of second cooling nozzles 80 include six second cooling nozzles 80A, 80B, 80C, 80D, 80E, 80F that are equally spaced about the rotation axis 34 and extend radially outward from the cooling hole 68. Figure 5B In other configurations, the plurality of first cooling nozzles 78 include two opposing first cooling nozzles 78A, 78B extending radially outward from the cooling hole 68, and the plurality of second cooling nozzles 80 include two opposing second cooling nozzles 80A, 80B extending radially outward from the cooling hole 68. Advantageously, Figure 5A and Figure 5B The plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 shown in the drawings are arranged in a manner that does not disrupt the rotational balance of the rotor 20. It is contemplated that the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 may have a different number of cooling nozzles than the examples given above, and the number of the plurality of first cooling nozzles 78 may not be equal to the number of the plurality of second cooling nozzles 80. It is worth noting that singular numbers of cooling fluid nozzles are not suitable because they would cause an imbalance of the rotor 20 about the rotational axis 34. The plurality of nozzles must be evenly distributed about the rotational axis 34 to produce a net zero effect on the rotational imbalance.

[0033] Reference Figure 6 In some examples, the motor 22 includes one or more bearings 98 for supporting the rotor 20 for rotation about the rotation axis 34. For example, Figure 6 As shown, the motor 22 includes a first bearing 98A supporting the first end region 62 of the rotor 20 and a second bearing 98B supporting the second end region 64 of the rotor. Figure 6As shown, the rotor 20 may further include a plurality of third cooling nozzles 100 in fluid communication with the cooling holes 68 and extending radially outward. The plurality of third cooling nozzles 100 may be configured to pull cooling fluid through the cooling holes 68 and spray the cooling fluid toward the one or more bearings 98 in response to the centrifugal force caused by the rotation of the rotor 20 about the rotation axis 34. Of course, the geometric parameters of the third cooling nozzles 100 may be defined as described above in the context of the first cooling nozzles 78 and the second cooling nozzles 80, so that the suction force generated by the plurality of third cooling nozzles 100 in response to the centrifugal force caused by the rotation of the rotor 20 about the rotation axis 34 does not starve the plurality of first cooling nozzles 78 and the plurality of second cooling nozzles 80 of cooling fluid flow from the cooling holes 68.

[0034] Reference Figure 7 and FIG. 8A to FIG. 8B In some configurations, the coupling region 66 defines a fluid outlet 102 that is in fluid communication with the cooling holes 68. Accordingly, the fluid outlet 102 can supply cooling fluid from the cooling holes 68 to an external component that is coupled to the coupling region 66 of the rotor. Figure 8B , the cooling hole 68 may define a stepped portion 104 disposed adjacent to the fluid outlet 102 (eg, between the plurality of second cooling nozzles 80 and the fluid outlet 102). In some examples, the stepped position 104 defines a stepped portion diameter (D SP ), the stepped portion diameter is the cooling hole diameter (D CB ) is 60% or less.

[0035] Several embodiments have been described in the foregoing description. However, the embodiments described herein are not intended to be exhaustive or to limit the invention to any particular form. The terms used are intended to have the nature of descriptive rather than restrictive words. In view of the above teachings, many modifications and variations are possible, and the invention may be implemented in ways other than those specifically described.

[0036] Various additional changes and modifications beyond those already mentioned herein may be made to the above-described embodiments. This disclosure is proposed for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments or limiting the scope of the claims to the specific elements shown or described in conjunction with these embodiments. For example, but not limited to, any individual element of the described embodiments may be replaced by an alternative element that provides substantially similar functions or otherwise provides sufficient operation. This includes, for example, currently known alternative elements (such as those currently known to those skilled in the art) and alternative elements that may be developed in the future (such as those elements that those skilled in the art may recognize as alternatives when developing). Any reference to a claim element in the singular (for example, using the article "one", "an", "the" or "said") should not be interpreted as limiting the element to the singular. It should also be understood that the term "include, includes, including" has the same meaning as the term "comprise, comprises, comprising".

Claims

1. A motor, comprising: A stator, the stator comprising: a stator core having a first end and a second end opposite the first end, the stator core defining a stator bore extending between the first end and the second end and an axis of rotation concentric with the stator bore; and a plurality of windings operably attached to the stator core and having end turns extending beyond first and second ends of the stator core; and a rotor configured to rotate about the rotation axis in response to the plurality of windings being energized, the rotor comprising: a middle region, the middle region being disposed in the stator hole; a first end region extending from the mid-region and beyond the stator bore such that the first end region is aligned with end turns extending beyond a first end of the stator core; a second end region extending from the middle region and beyond the stator bore such that the second end region is aligned with end turns extending beyond a second end of the stator core, wherein the first end region, the middle region, and the second end region collectively define a cooling hole extending along the rotational axis between a fluid inlet defined by the first end region and a terminal end defined by the second end region, the fluid inlet being in fluid communication with a source of low-pressure cooling fluid and configured to receive cooling fluid from the source of low-pressure cooling fluid; a plurality of first cooling nozzles disposed in a first end region of the rotor in fluid communication with the cooling holes and extending radially outward, each first cooling nozzle being configured to draw cooling fluid through the cooling holes in response to centrifugal forces caused by rotation of the rotor about the rotational axis and to spray cooling fluid toward end turns extending beyond the first end of the stator core; and a plurality of second cooling nozzles disposed in a second end region of the rotor, in fluid communication with the cooling holes and extending radially outward, each second cooling nozzle being configured to draw cooling fluid through the cooling holes in response to centrifugal forces caused by rotation of the rotor about the rotation axis and to spray cooling fluid toward end turns extending beyond the second end of the stator core.

2. The motor according to claim 1, wherein: Each of the first cooling nozzles has a first diameter (D1), each of the second cooling nozzles has a second diameter (D2), and D2 is greater than D1.

3. The motor according to claim 2, wherein: Each of the first cooling nozzles has a first length (L1), each of the second cooling nozzles has a second length (L2), and (L1 / D1) is less than (L2 / D2).

4. The motor according to claim 2, in, The cooling hole is composed of the cooling hole diameter (D CB ) is limited, and Among them, (D CB / D1) is greater than 3.3, and (D CB / D2) is greater than 2.

8.

5. The motor according to claim 2, in, The plurality of first cooling nozzles are configured to spray cooling fluid at a first flow rate in response to a centrifugal force caused by rotation of the rotor about the rotation axis, and The plurality of second cooling nozzles are configured to spray cooling fluid at a second flow rate equal to the first flow rate in response to a centrifugal force caused by rotation of the rotor about the rotation axis.

6. The motor according to claim 5, wherein: The first plurality of cooling nozzles are configured to reach a choked state before the second plurality of cooling nozzles in response to centrifugal forces caused by rotation of the rotor about the rotation axis.

7. The motor according to claim 1, in, Each first cooling nozzle extends between a first nozzle inlet in fluid communication with the cooling hole and a first nozzle outlet disposed on a first radial surface of the first end region, wherein each second cooling nozzle extends between a second nozzle inlet in fluid communication with the cooling hole and a second nozzle outlet arranged on a second radial surface of the second end region, and Wherein, each of the first nozzle inlet and the second nozzle inlet includes a transition portion between the cooling hole and the corresponding cooling nozzle, wherein each transition portion has one of a chamfered profile and a rounded profile.

8. The motor according to claim 1, wherein: The low pressure cooling fluid source is configured to provide cooling fluid to the fluid inlet at a pressure between about 2 bar and about 5 bar.

9. The electric machine of claim 1, further comprising one or more bearings supporting the rotor for rotation about the rotation axis, in, The rotor further includes a plurality of third cooling nozzles in fluid communication with the cooling holes and extending radially outward, each third cooling nozzle being configured to draw cooling fluid through the cooling holes in response to centrifugal forces caused by rotation of the rotor about the rotation axis and to spray cooling fluid toward the one or more bearings.

10. The electric machine according to claim 1, wherein: The second end region further includes a coupling region configured to couple with an external component; and The coupling region defines a fluid outlet in fluid communication with the cooling hole, the fluid outlet being configured to supply cooling fluid from the cooling hole to the external component.

11. A rotor for an electric machine and configured to rotate about a rotation axis, the rotor comprising: a middle region having a first end and a second end opposite the first end; a first end region extending from a first end of the middle region; a second end region extending from a second end of the middle region, wherein the first end region, the middle region, and the second end region collectively define a cooling hole extending along the rotational axis between a fluid inlet defined by the first end region and a terminal end defined by the second end region, the fluid inlet being configured to be arranged in fluid communication with a low-pressure cooling fluid source to receive cooling fluid from the low-pressure cooling fluid source; a plurality of first cooling nozzles disposed in the first end region, in fluid communication with the cooling hole and extending radially outward, each first cooling nozzle having a first diameter (D1) and configured to draw cooling fluid through the cooling hole in response to centrifugal force caused by rotation of the rotor about the rotational axis and to eject cooling fluid radially outward at a first flow rate; and a plurality of second cooling nozzles disposed in the second end region, in fluid communication with the cooling hole and extending radially outward, each second cooling nozzle having a second diameter (D2) greater than D1 and configured to pull cooling fluid through the cooling hole in response to centrifugal force caused by rotation of the rotor about the rotation axis and radially eject cooling fluid at a second flow rate equal to the first flow rate.

12. The rotor according to claim 11, wherein: The first plurality of cooling nozzles are configured to reach a choked state before the second plurality of cooling nozzles in response to centrifugal forces caused by rotation of the rotor about the rotation axis.

13. The rotor according to claim 11, wherein: Each of the first cooling nozzles has a first length (L1), each of the second cooling nozzles has a second length (L2), and (L1 / D1) is less than (L2 / D2).

14. The rotor according to claim 11, in, The cooling hole has a cooling hole diameter (D CB ),and Among them, (D CB / D1) is greater than 3.3, and (D CB / D2) is greater than 2.

8.

15. The electric machine according to claim 11, in, Each first cooling nozzle extends between a first nozzle inlet in fluid communication with the cooling hole and a first nozzle outlet disposed on a first radial surface of the first end region, wherein each second cooling nozzle extends between a second nozzle inlet in fluid communication with the cooling hole and a second nozzle outlet arranged on a second radial surface of the second end region, and Wherein, each of the first nozzle inlet and the second nozzle inlet includes a transition portion between the cooling hole and the corresponding cooling nozzle, wherein each transition portion has one of a chamfered profile and a rounded profile.

16. The rotor according to claim 15, wherein: The transition portion is formed by extrusion honing.

17. The rotor according to claim 15, wherein: The transition section is defined by a liner insert which is arranged in the respective cooling nozzle.

18. The rotor according to claim 11, in, The plurality of first cooling nozzles include two opposing first cooling nozzles extending radially outward from the cooling hole, and The plurality of second cooling nozzles include two opposite second cooling nozzles extending radially outward from the cooling hole.

19. The rotor according to claim 11, in, The plurality of first cooling nozzles include six first cooling nozzles equally spaced about the rotation axis and extending radially outward from the cooling hole, and The plurality of second cooling nozzles include six second cooling nozzles that are equally spaced about the rotation axis and extend radially outward from the cooling hole.

20. The rotor of claim 11, wherein: The second end region further includes a coupling region configured to couple with an external component; and The coupling region defines a fluid outlet in fluid communication with the cooling hole, the fluid outlet being configured to supply cooling fluid from the cooling hole to the external component.

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