Split drainage system and method for an electric machine module

Abstract

Electric machine module (10), which comprises: a module housing (12) comprising an inner wall (40) and at least one end cap (16, 18), the module housing (12) at least partially defining a machine cavity (22); an electric machine (20) at least partially enclosed within the machine cavity (22), the electric machine (20) comprising a stator (26) and stator winding ends (28); and at least two drain holes (44) placed substantially circumferentially apart from one another and extending through a lower portion of the module housing (12), the at least two drain holes (44) providing gravity-fed fluid paths out of the machine cavity (22), the module housing (12) comprising a coolant jacket (36) and a plurality of coolant openings (38), the plurality of coolant openings (38) extending through the inner wall (40) to provide fluid communication between at least the coolant jacket (36) and the machine cavity (22).

Description

RELATED APPLICATIONS

[0001] This international application claims priority to U.S. patent application 12 / 904,848, filed October 14, 2010, the contents of which are incorporated herein by reference in their entirety. BACKGROUND

[0002] Conventional methods for cooling an electric machine involve circulating a coolant around the exterior of the electric machine within a cooling jacket. The coolant removes heat from the electric machine. In some machine designs, the degree of heat removal is increased by spraying coolant from the cooling jacket directly onto the stator winding ends. Gravity can cause the sprayed coolant to drain to the bottom of the electric machine's housing, and a drain hole is often located near the bottom of the housing to remove the coolant. Typically, the drain is located at the geometric lower center of the housing.

[0003] When properly dimensioned for gravity-fed drainage, the typical drain location does not allow the spent coolant to accumulate substantially at the bottom of the housing. Therefore, lower portions of the stator winding ends can overheat. Furthermore, when the electric machine is tilted, excessive amounts of coolant can accumulate within the housing around the electric machine. The accumulated coolant can flood an air gap between the electric machine stator and the electric machine rotor, causing adverse effects such as relatively large rotational losses and / or thermal failure of the electric machine.

[0004] Cooled electric machine modules with module housings are known from the publications DE 10 2008 001 622 A1 and US 7 157 818 B2. The fluid used for cooling can be discharged from the module housings after the cooling process through openings provided for this purpose.

[0005] The object of the invention is to provide an improved or alternative electric machine module. Furthermore, the object of the invention is to propose methods for cooling such an electric machine module and a method for draining coolant from such an electric machine module. SUMMARY

[0006] Some embodiments of the invention provide an electric machine module comprising a module housing, an inner wall, and at least one end cap. The module housing may at least partially define a machine cavity, and an electric machine may be at least partially enclosed within the machine cavity. The electric machine may include a stator and stator end windings. The electric machine module may also include at least two drain holes positioned substantially circumferentially apart from each other and extending through a lower portion of the module housing. The at least two drain holes may provide gravity-fed fluid paths out of the machine cavity.

[0007] Some embodiments of the invention provide an electric machine module comprising a module housing having an inner wall and at least one end cap. The module housing may at least partially define a machine cavity, and an electric machine may be at least partially enclosed within the machine cavity. The electric machine may include a stator and stator end windings. The electric machine module may also include a first drain hole extending through a lower portion of the module housing at a first angle from a vertical axis of the module housing in a positive direction, and a second drain hole extending through the lower portion of the module housing at the first angle from the vertical axis in a negative direction.At least one of the first drain hole and the second drain hole can provide a fluid path out of the machine cavity when the module housing is in a substantially upright position, when the module housing is rotated by a second angle from the substantially upright position in a first direction, and when the module housing is rotated by the second angle from the substantially upright position in a second direction opposite to the first direction.

[0008] Some embodiments of the invention provide a method for cooling an electric machine module. The method may include providing a module housing including an inner wall, at least one end cap, a coolant jacket, and a vertical axis. The module housing may at least partially define a machine cavity and may at least partially enclose an electric machine within the machine cavity. The electric machine may include a stator including stator end windings and defining a rotor, and a radial air gap defined between the stator and the rotor.The method may also include providing a plurality of coolant openings extending through the inner wall and in fluid communication with at least the engine cavity and the coolant jacket, introducing a coolant into the coolant jacket, and circulating the coolant from the coolant jacket through the plurality of coolant openings and into the engine cavity.The method may further comprise placing a first drain hole extending through a lower portion of the module housing at a first angle from a vertical axis of the module housing in a positive direction, placing a second drain hole extending through the lower portion of the module housing at the first angle from the vertical axis in a negative direction, and accumulating the coolant between the first drain hole and the second drain hole at a level of accumulated coolant that contacts the stator winding ends and remains below the radial air gap. DESCRIPTION OF THE CHARACTERS Fig. 1 is a front cross-sectional view of an electric machine module according to an embodiment of the invention. Fig. 2 is a perspective view of a module housing of an electric machine module according to another embodiment of the invention. Fig. 3 is a partial cross-sectional side view of an electric machine module according to an embodiment of the invention. Fig. 4 is another partial cross-sectional side view of an electric machine module according to an embodiment of the invention. Fig. Figure 5 is a partial cross-sectional side view of a conventional electric machine module. DETAILED DESCRIPTION

[0009] Before any embodiments of the invention are described in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of components set forth in the following description or illustrated in the following drawings. Other embodiments of the invention are possible, and it may be embodied or carried out in various ways. Likewise, it is to be understood that the phraseology and terminology used herein is for the purpose of description and is not to be considered limiting. The use of "including," "comprising," or "having," and variations thereof, is intended to encompass the items listed thereafter and their equivalents, as well as additional items.Unless otherwise specified or limited, the terms "attached," "connected," "supported," "coupled," and their variations are used generically and include both direct and indirect attachments, connections, supports, and couplings. Furthermore, "connected" and "coupled" are not limited to physical or mechanical connections or couplings.

[0010] The following discussion is presented to enable one skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the general principles herein may be applied to other embodiments and applications without departing from the embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to the illustrated embodiments, but are to be accorded the broadest scope consistent with the principles and features disclosed herein. The following detailed description should be read with reference to the figures, in which similar elements in different figures have similar reference numerals.The figures, which are not necessarily to scale, illustrate selected embodiments and are not intended to limit the scope of embodiments of the invention. Those skilled in the art will recognize that the examples provided herein have many useful alternatives and are within the scope of embodiments of the invention.

[0011] Fig. 1 shows an electric machine module 10 according to one embodiment of the invention. The electric machine module 10 may include a module housing 12 that includes a sleeve member 14, a first end cap 16, and a second end cap 18. In one embodiment, the module housing 12 may be constructed of cast aluminum. An electric machine 20 may be housed within a machine cavity 22 defined at least partially by the sleeve member 14 and the end caps 16, 18. For example, the sleeve member 14 and the end caps 16, 18 may be coupled together via fasteners (not shown) or another suitable coupling to enclose at least a portion of the electric machine 20 within the machine cavity 22. In some embodiments, the end caps 16, 18 may be identical components. In other embodiments, the end caps 16, 18 may include various individual features.Also, in some embodiments, the housing 12 may comprise a substantially enclosed, substantially cylindrical container 15 (as shown in FIG. Fig. 2) and a single end cap (not shown).

[0012] The electric machine 20 may include a rotor 24, a stator 26, stator winding ends 28, and bearings 30, and may be arranged around a main output shaft 31. As shown in Fig. 1, the stator 26 may substantially circumscribe the rotor 24, and a radial air gap 32 may be defined between the rotor 24 and the stator 26. In some embodiments, the electric machine 20 may also include a rotor hub 34 or have a "hubless" construction (not shown). The electric machine 20 may be, without limitation, an electric motor, such as a hybrid electric motor, an electric generator, or a vehicle alternator. In one embodiment, the electric machine 20 may be a high-voltage hairpin (HVH) electric motor for use in a hybrid vehicle.

[0013] Components of the electric machine 20, such as, but not limited to, the rotor 24, the stator 26, and the stator end windings 28, may generate heat during operation of the electric machine 20. These components may be cooled to improve the performance of the electric machine 20 and extend its service life.

[0014] In some embodiments, as in Fig. 1, the module housing 12 may include a coolant jacket 36. The coolant jacket 36 may substantially enclose or at least partially surround the stator 26 and may contain a coolant, such as oil (e.g., engine oil, transmission oil, etc.) or a similar liquid cooling fluid. The coolant jacket 36 may be in fluid communication with a fluid source (not shown) containing the coolant. The coolant may be pressurized as it enters the coolant jacket 36 such that it is circulated through the coolant jacket 36. Heat energy generated by the electric machine 20 may be transferred to the coolant as it circulates through the coolant jacket 36 to thereby cool the electric machine 20. In some embodiments, the coolant may be introduced into the coolant jacket 36 via a coolant inlet (not shown).In one embodiment, the coolant inlet may be placed near a generally lower portion of the module housing 12.

[0015] In some embodiments, the coolant jacket 36 may be formed within the sleeve member 14 or the reservoir 15 of the module housing 12, where a radially innermost wall 40 of the sleeve member 14 or the reservoir 15 may substantially separate the coolant jacket 36 from the machine cavity 22. In other embodiments, the module housing 12 may include an inner sleeve member (not shown), and the coolant jacket 36 may be defined between the inner sleeve member and the sleeve member 14 or reservoir 15 (i.e., such that the inner sleeve member forms the inner wall 40 substantially separating the coolant jacket 36 and the machine cavity 22). In such embodiments, for example, the inner sleeve member may be a stainless steel ring into which the stator 26 is press-fitted.

[0016] The coolant circulating through the coolant jacket 36 may be sprayed or dispersed into the machine cavity 22 from a plurality of coolant openings 38 extending through the inner wall 40 of the module housing 12, as shown in Fig. 1. The plurality of coolant openings 38 may be in fluid communication with at least the machine cavity 22 and the coolant jacket 36. The plurality of coolant openings 38 may be located axially along the module housing 12 substantially adjacent to the stator end windings 28 (e.g., located near both axial ends of the module housing 12). As a result, the coolant from the coolant jacket 36 may be distributed through the plurality of coolant openings 38 at least partially onto and / or around the stator end windings 28. The distributed coolant may absorb thermal energy from the stator end windings 28, which may result in cooling the electric machine 20. In one embodiment, the plurality of coolant openings 38 may be located circumferentially around a generally upper portion of the module housing 12.In another embodiment, the plurality of coolant openings 38 may be located substantially entirely around a perimeter of the module housing 12. In other embodiments, the plurality of coolant openings 38 may be positioned to distribute coolant throughout the machine cavity 22 by other methods, such as through coolant channels (not shown) in the end caps 16, 18.

[0017] The distributed coolant may flow due to gravity toward a lower portion of the machine cavity 22. As the distributed coolant flows downward, it may continue to remove heat energy from the electric machine components, such as, but not limited to, the stator 26, the rotor 24, the rotor hub 34, and the bearings 30. At least a portion of the distributed coolant may then accumulate near the lower portion of the machine cavity 22. After accumulating near the lower portion of the machine cavity 22, the coolant may still be substantially cooler than the electric machine components with which it is in contact, such as the stator 26 and the stator end windings 28, and thus may continue to remove heat energy from the stator 26 and / or the stator end windings 28.

[0018] In some embodiments, the module housing 12 may include a split drainage system 42 to remove the accumulated coolant from the engine cavity 22. As shown in Fig. 3, the split drainage system 42 may include drain holes 44 extending through the housing 12 (i.e., through the sleeve member 14, the reservoir 15, the inner sleeve member, and / or the end caps 16, 18 in some embodiments). The drain holes 44 may provide gravity-fed fluid paths from the machine cavity 22. In one embodiment, at least two drain holes 44 may be located at or near each of the two ends of the module housing 12 (i.e., at least two drain holes 44 may be located near a first axial end and at least two additional drain holes 44 may be located at a second axial end opposite the first axial end). The at least two drain holes 44 at each axial end may be circumferentially spaced from each other along the lower portion of the module housing 12, as shown in Fig. 2. For example, as shown in the Fig. 3 and Fig. 4, the two drain holes 44 may be offset by an angle Θ in a positive direction and a negative direction from a vertical axis 48 of the housing 12 (i.e., a first drain hole 44 is offset from the vertical axis 48 by the positive angle Θ, and a second drain hole 44 is offset from the vertical axis 48 by the negative angle Θ). The angle Θ may be greater than zero degrees, and in one embodiment, the angle Θ may be approximately 35 degrees or less. Further, in some embodiments (not shown), the first drain hole 44 may be offset from the vertical axis 48 by a first angle, and the second drain hole 44 may be offset from the vertical axis in the negative direction by a second angle that is different from the first angle.

[0019] The drain holes 44 may be fluidly connected to an external cooling device (e.g., a heat exchanger, a radiator) so that the coolant drained from the module housing 12 can be cooled and returned to the coolant jacket 36 (e.g., through the coolant inlet). In some embodiments, a drain pan (not shown) may collect the coolant from the drain holes 44, and a connecting hose or the like may be connected to a drain outlet of the drain pan to direct the coolant to the external cooling device and / or a pump.

[0020] As in Fig. 4, the distributed coolant may flow downward along the stator end windings 28, removing heat from the end windings 28, until gravity causes it to drip (or drain) from the stator end windings 28 to the bottom of the machine cavity 22. Conventional electric machine modules, as shown in Fig. 5, include a drain at the geometric lower center of the machine housing. As shown in Fig. As shown in Figure 5, there may be an area 46 between the coolant drain point and a coolant pool 47 near the single drain where the stator end windings 28 are not directly cooled by the coolant. In some applications, inadequate cooling of this area 46 (e.g., due to minimal contact with the coolant) may cause the stator end windings 28 to overheat. As shown in Figures Fig. 3 and Fig. 4, the split drainage system 42 may allow additional coolant to accumulate within the machine cavity 22 (e.g., at least between the first drain hole 44 and the second drain hole 44). As a result, additional cooling may be achieved by using the split drainage system 42 compared to a single, central drain, since a larger coolant accumulation 47 may allow more coolant to come into contact with the stator winding ends 28. Furthermore, as shown in Fig. 4, the split drainage system 42 and the resulting larger coolant pool 47 reduce the area 46 in which the stator winding ends 28 are not in direct contact with the coolant, thereby minimizing the risk of overheating of the stator winding ends 28.

[0021] By being angularly and axially offset, the drain holes 44 can enable substantially normal function of the split drainage system 42 when the electric machine 20 is tilted back and forth or to one side or the other. In some embodiments, the drain holes 44 can be located axially inward closer to the stator 26 (e.g., than the axial ends of the module housing 12) to minimize the effects of side-to-side tilting of the electric machine 20 on coolant drainage.

[0022] In some embodiments, the angular displacement of the drain holes 44 (i.e., the magnitude of the angle Θ) may be selected based on a size of the machine cavity 22, a desired amount of coolant accumulation, and other factors, such as the applications for which the electric machine 20 is to be used and how much tilting would be expected in such applications. For example, the drain holes 44 may be circumferentially spaced from the vertical axis 48 to allow for a coolant accumulation 47 that is deep enough to provide optimal cooling of at least some of the stator end windings 28, but shallow enough not to flood the radial air gap 32 during expected tilting (i.e., such that a depth or level of coolant accumulation remains below the radial air gap 32).

[0023] In another example, the drainage holes 44 may be relocated to allow a coolant pool 47 deep enough to provide optimal cooling of at least some of the stator end windings 28, to allow substantially constant drainage during the expected tilt, and to maintain the coolant pool level below the air gap 32 over a range of tilt angles of the electric machine module 10, as shown in Fig.4. In some embodiments, the expected tilt may range from a substantially upright position of the electric machine module 10 (i.e., zero degrees of rotation) to a second angle or degree from the substantially upright position in both a forward direction and an aft direction. Because the two drain holes 44 are circumferentially spaced from each other and substantially offset from the vertical axis 48, at least the first drain hole 44 may provide a fluid path for draining the coolant (i.e., for exiting the coolant from the machine cavity 22) when the electric machine module 10 is tilted or rotated in the forward direction to the second angle from the substantially upright position such that the coolant accumulation level remains below the air gap 32.Similarly, at least the second drain hole 44 may provide a fluid path for the coolant to drain when the electric machine module 10 is tilted or rotated rearwardly to the second angle from the substantially upright position, such that the coolant accumulation level remains below the air gap 32. When the electric machine module 10 is placed in the substantially upright position, at least one of the first drain hole 44 and the second drain hole 44 may provide fluid paths for the coolant to drain.

[0024] Also, in some embodiments, the angular displacement of the drain holes 44 may be based on the operating temperature ranges of the electric machine 20. For example, in one embodiment, the split drain system 42 may function across substantially all operating temperature ranges of the electric machine 20, despite the influence that temperature may have on the viscosity and flow rate of the coolant.

[0025] Furthermore, in some embodiments, the diameter of each drain hole 44 may be selected based on a size of the machine cavity 22, a flow rate of coolant into the machine cavity 22, and / or other factors. In some embodiments, the diameter of each drain hole 44 may be between approximately 10 millimeters and approximately 30 millimeters.

[0026] Those skilled in the art will appreciate that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that many other embodiments, examples, uses, modifications, and variations from the embodiments, examples, and uses are intended to be encompassed by the claims appended hereto. Various features and advantages of the invention are set forth in the following claims.

Claims

[1] Electric machine module (10), which comprises: a module housing (12) comprising an inner wall (40) and at least one end cap (16, 18), the module housing (12) at least partially defining a machine cavity (22); an electric machine (20) at least partially enclosed within the machine cavity (22), the electric machine (20) comprising a stator (26) and stator winding ends (28); and at least two drain holes (44) placed substantially circumferentially apart from one another and extending through a lower portion of the module housing (12), the at least two drain holes (44) providing gravity-fed fluid paths out of the machine cavity (22), the module housing (12) comprising a coolant jacket (36) and a plurality of coolant openings (38), the plurality of coolant openings (38) extending through the inner wall (40) to provide fluid communication between at least the coolant jacket (36) and the machine cavity (22). [2] The electric machine module (10) of claim 1, wherein at least some of the plurality of coolant openings (38) are located axially along the module housing (12) substantially adjacent to the stator winding ends (28). [3] The electric machine module (10) of claim 1, wherein the at least two drain holes (44) comprise a first group of two drain holes (44) located near a first axial side of the module housing (12) and a second group of two drain holes (44) located near a second axial side of the module housing (12), the second axial side being opposite the first axial side. [4] The electric machine module (10) of claim 1, wherein the at least two drain holes (44) are fluidly coupled to an external cooling device. [5] Electric machine module (10), which comprises: a module housing (12) comprising an inner wall (40) and at least one end cap (16, 18), the module housing (12) at least partially defining a machine cavity (22), the module housing (12) comprising a vertical axis (48); an electric machine (20) at least partially enclosed within the machine cavity (22), the electric machine (20) comprising a stator (26) and stator winding heads; a first drain hole extending through a lower portion of the module housing (12) and positioned at a first angle from the vertical axis (48) in a counterclockwise direction; and a second drain hole extending through the lower part of the module housing (12) and placed at the first angle from the vertical axis (48) in a clockwise direction, wherein at least one of the first drain hole and the second drain hole provides a gravity-fed fluid path out of the machine cavity (22) when the module housing (12) is in a substantially upright position, when the module housing (12) is rotated a second angle from the substantially upright position in a first direction, and when the module housing (12) is rotated the second angle from the substantially upright position in a second direction opposite the first direction. [6] The electric machine module (10) of claim 5, wherein a first drain hole of the at least two drain holes (44) provides a gravity-fed fluid path to drain coolant from the machine cavity (22) when the module housing (12) is rotated in a first direction, and a second drain hole of the at least two drain holes (44) provides a gravity-fed fluid path to drain coolant from the machine cavity (22) when the module housing (12) is rotated in a second direction opposite the first direction. [7] Electric machine module (10) according to claim 5, wherein the electric machine (20) is a hybrid electric machine (20). [8] The electric machine module (10) of claim 5, wherein the module housing (12) includes a coolant jacket (36) and a plurality of coolant openings (38) extending through the inner wall (40), the plurality of coolant openings (38) being in fluid communication with at least the coolant jacket (36) and the machine cavity (22), and at least some of the plurality of coolant openings (38) being located axially along the module housing (12) substantially adjacent the stator winding ends (28). [9] The electric machine module (10) of claim 5, wherein the first drain hole and the second drain hole are located near a first axial end of the module housing (12), further comprising a third drain hole extending through the module housing (12) and located near a second axial end of the module housing (12) opposite the first drain hole, and a fourth drain hole extending through the module housing (12) and located near the second axial end of the module housing (12) opposite the second drain hole. [10] The electric machine module (10) of claim 5, wherein the first drain hole and the second drain hole are fluidly connected to an external cooling device. [11] The electric machine module (10) of claim 5, wherein the first angle is greater than zero degrees. [12] The electric machine module (10) of claim 5, wherein the first drain hole and the second drain hole are placed substantially circumferentially away from the vertical axis (48) along a lower portion of the module housing (12) to allow the accumulation of a coolant within the machine cavity (22) at least between the first drain hole and the second drain hole, wherein at least one of the first drain hole and the second drain hole provides the gravity-fed fluid path for exiting the coolant from the machine cavity (22). [13] The electric machine module (10) of claim 12, wherein the electric machine (20) comprises a rotor (24) substantially defined by the stator (26) and a radial air gap (32) defined between the rotor (24) and the stator (26), wherein the allowable accumulation of coolant within the machine cavity (22) is at a level below the radial air gap (32) when the module housing (12) is in a substantially upright position, when the module housing (12) is rotated by the second angle from the substantially upright position in the first direction, and when the module housing (12) is rotated by the second angle from the substantially upright position in the second direction. [14] The electric machine module (10) of claim 12, wherein the level of allowable accumulation of coolant within the machine cavity (22) substantially reaches the stator winding ends (28) located between the first drain hole and the second drain hole. [15] A method for cooling an electric machine module (10), the method comprising: Providing a module housing (12) comprising an inner wall (40), at least one end cap (16, 18), a coolant jacket (36) and a vertical axis (48), wherein the module housing (12) at least partially defines a machine cavity (22) and at least partially encloses an electric machine (20) within the machine cavity (22), wherein the electric machine (20) comprises a stator (26) comprising stator winding heads (28) and defining a rotor (24), and a radial air gap (32) defined between the stator (26) and the rotor (24); Providing a plurality of coolant openings (38) extending through the inner wall (40), the plurality of coolant openings (38) being in fluid communication with at least the machine cavity (22) and the coolant jacket (36); Introducing a coolant into the coolant jacket (36); Circulating the coolant from the coolant jacket (36) through the plurality of coolant openings (38) and into the machine cavity (22); Placing a first drain hole extending through a lower portion of the module housing (12) at a first angle from the vertical axis (48) in a positive direction; Placing a second drain hole extending through the lower part of the module housing (12) at the first angle from the vertical axis (48) in a negative direction; and Accumulating the coolant between the first drain hole and the second drain hole at a level of accumulated coolant that contacts the stator winding ends (28) and remains below the radial air gap (32). [16] A method for draining coolant from an electric machine module (10) according to any one of claims 1 to 14, wherein the first drain hole and the second drain hole are placed at the first angle in the positive direction and the first angle in the negative direction, respectively, to maintain the level of accumulated coolant below the radial air gap (32) when the module housing (12) is in a substantially upright position, when the module housing (12) is rotated by a second angle from the substantially upright position in a first direction, and when the module housing (12) is rotated by the second angle from the substantially upright position in a second direction opposite to the first direction. [17] The method of draining coolant according to claim 16, wherein the first angle is greater than zero degrees and the second angle is greater than zero degrees. [18] A method of draining coolant according to claim 16, and further comprising draining the coolant from the engine cavity (22) through at least one of the first drain hole and the second drain hole.

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