Patent Application
20210143693
Electric traction motors and motor generator units, which are commonly referred to in the art as rotary electric machines, are used to perform work in a wide variety of electromechanical systems. Such machines include a rotating member, i.e., a rotor, that is spaced a short distance apart from a stationary member or stator. In a typical stator construction, multiple stator teeth are attached at one end to a cylindrical stator core to project radially toward the rotor. Adjacent stator teeth are separated from each other by a respective stator slot, with distal ends of the adjacent stator teeth spaced apart from each other by a tooth gap. Each stator slot is filled with conductive wires or solid bar segments to form a set of stator windings. In a polyphase rotary electric machine, an alternating current (“AC”) input voltage is applied to the stator windings to energize the stator. Interaction between the respective magnetic fields of the rotor and stator ultimately generates forces in the rotor-stator airgap. Rotation of the rotor results, with such rotation thereafter directed to a load.
A rotary electric machine may generate substantial amounts of heat. This is particularly true when the electric machine operates at high speeds and output torque levels. While the above-noted stator windings are well-insulated to ensure electrical isolation of the individual phase windings, heat is nevertheless generated during sustained high-power operations. Heat resulting from copper and iron losses within the stator can eventually degrade the insulation. As a result, thermal management systems are used in the construction of the stator to regulate the stator temperature. For instance, the stator's end windings, which may be exposed at distal ends of the stator, are often sprayed with coolant, or the stator housing may be wrapped in a cooling jacket.
The present disclosure relates to the enhanced convection-based cooling of a stator within a rotary electric machine. In particular, each of the above-described stator slots is fully enclosed at both of its radial ends to construct an in-slot coolant passage. An application-suitable coolant, such as but not limited to automatic transmission fluid, is circulated to a coolant manifold disposed at axial ends of the stator. The coolant manifold directs the coolant axially into the in-slot coolant passages, with the admitted coolant thereafter flowing axially through the stator. By enclosing the stator slots in this manner, a uniform/360° flow of coolant is established around the bar conductors forming the stator windings. Electromagnetic efficiency of the electric machine is thereby optimized with minimal degradation of torque performance by removing heat from the stator directly from its source, i.e., the energized stator windings.
In an exemplary embodiment, the rotary electric machine includes a rotor assembly, a stator, stator windings, and the above-noted coolant manifold. The rotor assembly includes a rotor and a rotor shaft that are connected together and configured to rotate about an axis of rotation. The stator, which is spaced apart from the rotor by a stator-rotor airgap, has a set of stator teeth collectively defining stator slots. Distal radial ends of adjacent pairs of the stator teeth are joined together or integrally formed such that the stator slots are fully enclosed, i.e., not contiguous with the airgap. The stator windings as contemplated herein are constructed from bar-type or “hairpin” conductors that extend axially through the stator within the stator slots.
The coolant manifold in this particular embodiment is in fluid communication with a coolant supply, constructed of non-magnetic material, and configured to seal against an axial end surface of the stator. Sealing in this manner encloses a portion of the stator windings, i.e., exposed turns of the stator windings, as will be appreciated by those of ordinary skill in the art. The coolant manifold receives coolant from the coolant supply, directs the received coolant into the closed stator slots through the axial end surface of the stator, and thereby cools the stator via forced convection.
A cross-sectional shape of the stator windings may be a non-rectangular polygon in some embodiments and a rectangular shape in others.
An outer perimeter surface of at least one of the stator windings may optionally define a concave channel configured to conduct more of the coolant along the outer perimeter surface.
The coolant manifold may include opposing axial walls joined by a radial wall, such that a manifold channel is defined by the coolant manifold and the axial end surface of the stator. The axial walls abut and seal against the end surface of the stator to thereby encapsulate the stator windings within the manifold channel. One of the axial walls may include a ramped surface, with the stator windings being skewed in a radially outward direction via the ramped surface.
A biasing member may be used to apply a continuous compressive force to the coolant manifold. For instance, the biasing member may be a fastener, beam, or other structure configured to react against a stationary member to thereby apply the continuous compressive force.
Spacing between adjacent stator windings within each of the enclosed stator slots may be unevenly distributed such that more coolant is directed to the stator windings located in proximity to an outer diameter surface of the stator relative to distribution to the stator windings located in proximity to an inner diameter surface of the stator.
The rotor shaft in some applications may be connected to a driven load, e.g., aboard a motor vehicle having a coolant pump. The coolant is circulated via the coolant pump in such an embodiment.
An electric propulsion system is also disclosed herein. An embodiment of the electric propulsion system includes a supply of coolant, a high-voltage battery pack, a direct current-to-direct current (“DC-DC”) converter connected to the high-voltage battery pack, a traction power inverter module (“TPIM”) connected to the DC-DC converter and configured to output an alternating current (“AC”) voltage, and the above-noted rotary electric machine. The electric machine in this embodiment is a polyphase rotary electric machine connected to the TPIM and energized via the AC voltage.
A method is also disclosed for cooling a stator of a rotary electric machine. The method may include providing the above-noted stator, which is spaced apart from the rotor by a stator-rotor airgap and has stator teeth collectively defining stator slots. Distal radial ends of adjacent pairs of the stator teeth are joined together or integrally formed such that the stator slots are not contiguous with the airgaps. Stator windings are constructed from hairpin or bar-type conductors and extend axially through the stator within the stator slots.
The method includes sealing an annular coolant manifold against an axial end surface of the stator to thereby enclose therein a portion of the stator windings. The method also includes circulating coolant from a coolant supply into the enclosed stator slots through the axial end surface of the stator via the annular coolant manifold to thereby cool the stator via forced convection.
The above summary is not intended to represent every possible embodiment or every aspect of the present disclosure. Rather, the foregoing summary is intended to exemplify some of the novel aspects and features disclosed herein. The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of representative embodiments and modes for carrying out the present disclosure when taken in connection with the accompanying drawings and the appended claims.
The present disclosure is susceptible to modifications and alternative forms, with representative embodiments shown by way of example in the drawings and described in detail below. Inventive aspects of this disclosure are not limited to the disclosed embodiments. Rather, the present disclosure is intended to cover modifications, equivalents, combinations, and alternatives falling within the scope of the disclosure as defined by the appended claims.
Referring to the drawings, wherein like reference numbers refer to the same or like components in the several Figures, an electric propulsion system 10 is depicted schematically in
An application-suitable coolant 21, e.g., automatic transmission fluid (“ATF”) or a diluted ethylene glycol mixture, may be stored in a sump 22 and circulated using a coolant pump (“P”) 20, with the resulting flow of coolant 21 indicated by arrow F. The coolant 21 is conducted into the coolant manifold 60A, which in turn seals against the stator 16. The coolant manifold 60A directs the coolant 21 into the stator 16, upon which the coolant 21 flows axially through the stator 16 via an enclosed slot structure as described in detail below with reference to
Within the exemplary electric propulsion system 10 depicted in
The electric propulsion system 10 includes an alternating current (“AC”) voltage bus 13. The AC voltage bus 13 may be selectively energized via a traction power inverter module (“TPIM”) 28 using a high-voltage battery pack (“BHV”) 24, for instance a multi-cell lithium ion, lithium sulfur, nickel metal hydride, or other high-energy voltage supply. The AC voltage bus 13 conducts an AC voltage (“VAC”) to or from phase windings of the electric machine 12 to generate output torque (arrow TM). The output torque (arrow TM) from the energized electric machine 12, when operating in a drive or motoring mode, is then imparted to a connected rotor shaft 50 and directed to a coupled load (“L”) 52, such as by not necessarily limited to road wheels of a motor vehicle, a propeller shaft, or a drive belt.
The electric propulsion system 10 shown schematically in
Referring to
The stator 16 is cylindrical in shape to circumscribe the likewise cylindrical rotor 40 of the rotor assembly 14 in the depicted exemplary embodiment, and is separated from the rotor 40 by the above-noted airgap G. In such a configuration, the stator 16 and rotor 40 may be constructed from a respective stack-up of thin lamination layers of electrical steel or another ferrous material, e.g., 2-5 mm thick, as will be appreciated by those of ordinary skill in the art.
The stator 16 also has radially-projecting stator teeth 32. Each stator tooth 32 extends radially inward from a cylindrical stator housing 30, with the stator housing having an outer diameter surface 160. The stator teeth 32 thus extend inward from the stator housing 30 toward an outer diameter surface 140 of the rotor 40. Adjacent stator teeth 32 of are separated from each other by a corresponding stator slot 33, i.e., each stator slot 33 is defined and flanked by an adjacent pair of the stator teeth 32. Stator windings 35 are then positioned within the stator slots 33.
In the depicted embodiments, the stator windings 35 are configured as bar segments constructed of copper or another electrically conductive material. Bar-type conductors, which are commonly referred to as “hairpin” conductors, are thus more substantial and rigid than the cylindrical copper wires typically wrapped or wound around the stator teeth 32. As noted above, a rotating stator magnetic field is generated when the stator windings 35 are sequentially energized by an AC output voltage, e.g., from the TPIM 28 depicted in
As will be appreciated by those of ordinary skill in the art, stator teeth of a typical stator would extend radially inward toward a rotor, such that each stator tooth forms a cantilever with a distal end. Adjacent stator teeth are separated from each other a short distance by an opening or tooth gap, with the tooth gaps being contiguous with the stator-rotor air gap G. In other words, the stator slots of a typical rotary electric machine are open to the stator-rotor airgap G. In contrast, each of the stator teeth 32 of the present disclosure, as shown in
To construct a stator 16 having such a configuration, the stator teeth 32 are joined together or integrally formed during manufacturing of the stator 16. For instance, the thin lamination layers noted above may be individually punched with a tool (not shown) having the desired shape of the stator slots 33 of
Referring briefly to
For instance, one or more corners 37 of the stator windings 135 of
Referring to
In order to convectively cool the stator 16 in accordance with the present disclosure, the coolant manifold 60A shown schematically in profile in
For example, end surfaces 74E of the axial walls 74 abut and seal against the end surface 70 of the stator 16 to thereby encapsulate the stator windings 35 within the manifold channel 76 as shown. To ensure proper sealing, a biasing member 65, e.g., a bolt or a beam, may react against a stationary member 80 to apply a continuous compressive force (arrow FC) to the coolant manifold 60A. Additionally, the end surfaces 74E define holes or slots 79 that allow the stator windings 35 to pass through into the stator slots 33 (see
Also shown in
As noted above, coolant 21 in the form of ATF is often sprayed and/or spilled directly onto exposed phase leads of the stator 16. The coolant 21 thereafter settles via gravity and is recirculated to the sump 22 of
Proper spacing of the stator windings 35 within the manifold channel 76 of
Referring again to
As will be appreciated, the above disclosure lends itself to a method for cooling the stator 16. For instance, the method may include providing the stator 16 of
The method may include sealing the coolant manifold 60A against an axial end surface 70 of the stator 16, as shown in
Sealing the coolant manifold 60A against the axial end surface 70 of the stator 16 may include encapsulating a portion of the stator windings 35 within the manifold channel 76, which as shown in
Enclosing the stator slots 33 to form the in-slot cooling passages 33C as set forth above therefore provides a variety of benefits beyond efficient cooling of the stator 16. Some benefits are primarily mechanical or structural in nature. For instance, a stator tooth of a typical electric machine forms a cantilever. Since cantilevers by definition are supported at just one end, the free end of such a stator tooth is prone to vibration and noise. Enclosing the stator slots 33 in accordance with the present disclosure eliminates such cantilevers and thereby adds structural rigidity to the stator 16. Slot noise due to torque ripple and the resulting undesirable NVH effects are reduced. Likewise, the disclosed construction of the stator 16 reduces torque ripple due to the minimization of the slotting effect within the stator-rotor airgap G, including possible reduction of windage or drag losses in the stator-rotor airgap G. These and other possible benefits will be readily appreciated by those of ordinary skill in the art in view of the forgoing disclosure.
While some of the best modes and other embodiments have been described in detail, various alternative designs and embodiments exist for practicing the present teachings defined in the appended claims. Those skilled in the art will recognize that modifications may be made to the disclosed embodiments without departing from the scope of the present disclosure. Moreover, the present concepts expressly include combinations and sub-combinations of the described elements and features. The detailed description and the drawings are supportive and descriptive of the present teachings, with the scope of the present teachings defined solely by the claims.
