Cooling channels in a high-density motor

A stator includes a stator hub and a plurality of stator teeth extending from the stator hub that define a stator slot having a stator slot base. At least one winding is disposed in the stator slot and the stator also includes a back iron. The winding surrounds the back iron and is held apart from the stator slot base so that a fluid channel is defined between an inner winding portion of the at least one winding so fluid can be passed between the stator slot base and the inner winding portion to cool the inner winding portion.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to electrical machines. More specifically, the subject matter disclosed herein relates to passages for delivering a cooling fluid through a stator of a high-density electric motor

A typical liquid cooled electric machines/motors includes a rotor having a core and one or more rotor windings (conductors) extending therethrough. In some machines, permanent magnet machines, the rotor windings are replaced with a plurality of permanent magnets. The rotor is surrounded by a stator and an air gap exists between the rotor and stator.

Similarly, the stator includes a stator core having one or more stator windings extending therethrough. High power density electric machines (either generator or motor) produce intense resistive heating of both the stator and rotor windings and eddy current and magnetic hysteresis heating of the rotor and stator cores.

Typical methods of stator cooling include utilizing an end-turn spray and thermal conduction through the back iron to a cooled housing or fluid media.

For example, traditional motor thermal management is often in the form of external fins or liquid cooling jackets. Such systems typically direct cooling liquid through one or more channels in the back iron (housing) radially outboard of the stator core. These cooling methods, however, provide cooling only on the radial and axial periphery of the stator core. Therefore, a hot spot in the stator windings can occur at the axial centerline of the stator core.

BRIEF DESCRIPTION OF THE INVENTION

Disclosed is stator that includes a stator hub. The stator also includes a plurality of stator teeth extending from the stator hub that define a stator slot having a stator slot base, at least one winding disposed in the stator slot, and a back iron. The winding surrounds the back iron and is held apart from the stator slot base so that a fluid channel is defined between an inner winding portion of the at least one winding so fluid can be passed between the stator slot base and the inner winding portion to cool the inner winding portion.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the winding is encased in a potting material.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the winding is formed of Litz wire.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the at least one winding includes a plurality of windings with each winding including an outer winding portion connected to an inner winding portion by end turns and the stator further includes: one or more winding separators formed of insulating material and disposed between adjacent ones of outer winding portions.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the one or more winding separators include cooling passages formed therein.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the one or more winding separators include fins formed in the cooling passages thereof

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the stator further comprising insulators disposed between adjacent inner winding portions.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the insulators include fins that extend into the coolant channel.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the at least one winding includes 3, 5 or 3n windings where n is a whole number.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the stator slot includes walls and one or more fins extending from the tooth or the base into the coolant channel.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the stator can be in combination with an inlet header and outlet header that collectively provide fluid through the coolant channel.

Also disclosed is a method of cooling a stator of any prior embodiment or that is otherwise disclosed herein. The method can include providing fluid into the coolant channel from inlet header; and removing fluid from the coolant channel via an outlet header.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the at least one winding includes a plurality of windings with each winding including an outer winding portion connected to an inner winding portion by end turns and the stator further includes: one or more winding separators formed of insulating material and disposed between adjacent ones of outer winding portions.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the one or more winding separators include cooling passages formed therein, the method further comprising: providing fluid into the cooling passages in the winding separators and removing the fluid from the cooling passages in the winding separators by separator cooling inlet and outlet headers.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the separator cooling inlet and outlet headers are integrated with the inlet and outlet headers.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the at least one winding includes a plurality of windings with each winding including an outer winding portion connected to an inner winding portion by end turns and the stator further includes: one or more winding separators formed of insulating material and disposed between adjacent ones of outer winding portions; wherein the one or more winding separators include cooling passages formed therein; wherein the one or more winding separators includes a first winding separator and a second winding separator connected to one another by a manifold so that fluid entering the first winding separator is directed through the first winding separator in a first direction, through the manifold and into and through the second winding separator in a second direction.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the first and second directions are opposite of another.

DETAILED DESCRIPTION OF THE INVENTION

As motors have become more compact alternative methods of cooling the stator may be beneficial. Herein disclosed is a stator core that can be used to improve cooling. In that core there is provided a flow channel that cools at least one half of a particular winding. Each turn can be separated from an adjacent winding by a separator as well. The separator can be formed of ceramic. In one embodiment, the flow channel is provided with a flow of coolant. If the ceramic separators are present, those separators can also be provided with a flow of coolant but that is not required.

In one embodiment, the flow channel is defined due having the winding being wrapped around a back iron portion of the stator. In each particular stator slot, the windings are wound such that they form multiple (three) bunches (or loops) separated by an insulating layer. Each bunch has a one turn of the coil and is wrapped from in inner to outer diameter of the stator (or vice-versa). The coolant flows through the flow channel directly cooling one half of the winding per slot. The heat generated by the winding section on the OD side gets effective conducted to the ID section of the winding due to very high thermal conductivity. The heat then gets directly dissipated into the coolant. The flow channel may be connected to an inlet and an outlet header to facilitate a flow through design in one embodiment.

FIG.1shows a schematic illustration of a cross section of an electric motor100that may incorporate embodiments of the present disclosure are shown. While shown as having rotor magnets external to or outside of the stator, the orientation could be reversed. Further, the teachings herein could be applied to a context where the magnets are u-shaped and surround both inner and outer portions of the stator.

In more detail,FIGS.1and2which, respectively, illustrates a cross-sectional view of the electric motor100and a perspective view of a simplified stator core104. The electric motor100includes a stator102configured to surround but not rotate with a rotor shaft142.

The stator102include a stator core104and one or more stator windings110supported or otherwise carried by the core104. The windings can be formed as individual potted Litz wire windings in one embodiment. The stator core104includes ring hub106and a plurality of teeth108that extend outwardly from the ring hub106. The adjacent teeth108form a stator slot112into which one or more stator windings may be disposed. That is, each slot can have a single stator winding110disposed therein or it can include two or more windings as shown in further examples below.

The motor100also includes a rotor140. The rotor shown inFIG.1includes a rotor shaft142that rotates about a rotation axis144. The rotor140also includes a magnet carrying structure146connected to the shaft142. The structure146carries one or more permanent magnets148.

As shown, the stator102(and the windings110carried by the stator102) is located radially inboard of the rotor magnets148relative to the rotation axis144, with a radial air gap150located between the rotor140and the stator104. As illustrated, the rotor140is mounted on a shaft110by the structure146. When in a “motor” mode where current is applied into the windings110that current will interact with the magnets148and cause the magnets/structure to rotate so as cause rotation of the rotor shaft142about axis144so that the shaft142can provide motive force to a load. Alternatively, in a “generator” mode, the shaft142can be driven such that interaction of the magnets cause a current to flow in the windings110to drive an electrical load.

The stator core104can be formed from a plurality of axially stacked laminations, which are stacked along the rotation axis144. In some embodiments, the laminations116are formed from a steel material, but one skilled in the art will readily appreciate that other materials may be utilized. In an alternative embodiment, the stator104can be formed as individual stator sections as is known in the art.

The stator windings110, as shown, include core segments110aextending through the stator core104and end turn segments110bextending from each axial stator end of the stator core104. As discussed above, when the stator windings110are energized via an electrical current therethrough, the resulting field drives rotation of the rotor140about the rotation axis144.

Electric motors, as shown inFIGS.1-2, may require cooling due to high density configurations, various operational parameters, or for other reasons. For example, high-power-density aviation-class electric motors and drives may require advanced cooling technologies to ensure proper operation of the motors/drives. These machines are generally thermally limited at high power ratings and their performance can be improved by mitigating thermal limitations. To maintain desired temperatures, a thermal management system (TMS) is integrated into the system, which provides cooling to components of the system. Onboard an aircraft, power requirements, and thus thermal management system (TMS) loads, are substantially higher during takeoff. Sizing of the TMS for takeoff conditions (i.e., maximum loads) results in a TMS having a high weight to accommodate such loads. This results in greater weight and lower power density during cruise conditions which do not generate such loads, and thus does not require a high cooling capacity TMS. Balancing weight constraints and thermal load capacities is important for such aviation applications.

Herein, channels in various parts of the stator assembly are disclosed as well as a header that delivers coolant into those channels. In one embodiment, the channel is formed between the core and windings on an inner diameter of the windings. In another, the channels are formed in separators (discussed below) that are disposed between the outer diameters of the windings. Of course, embodiments may also cover situations where channels are formed in both the separators and between the stator and the windings.

FIG.3shows a perspective view of a stator/rotor combination. The combination shown inFIG.3is applicable to all embodiments and can be arranged proximate headers to provide coolant into and out of it.

For brevity, the combination shown inFIG.3will be referred to motor300. The motor1000includes a stator302. The stator is formed of a stator core304and one or more stator windings310supported or otherwise carried by the core304. As illustrated, the core304is formed of separate stator segments304athat, when combined formed ring hub306. The hub306includes a plurality of teeth308that extend outwardly from the ring hub306.

The motor300includes a plurality of windings310. The windings310can include “inner” windings310aand “outer” windings310bthat are joined by end turns310caround a stator back iron320in one embodiment. Of course, other configurations can be possible. In one embodiment, the windings can be formed as individual potted Litz wire windings. The windings310can be formed as individual windings that form a loop as shown inFIG.4in one embodiment. The potting material is by reference number333and the multiple strands inFIG.3indicate that windings310contain wires that can be Litz wires.

FIG.4shows a side view of a winding310arranged such that surrounds the back iron320. The end turn310cgoes around the back iron. The wires that form the winding310can be arranged so that they form discreet loop shaped units and a segmented back iron can be provide to thread into the inner portion321of the loops. Or course, distributed windings could also be utilized with the teachings herein.

Referring again toFIG.3, the motor300also includes a rotor340. While not shown, it is understood that the rotor shown inFIG.3includes a rotor shaft that rotates about a rotation axis. The rotor340carries one or more permanent magnets344. The motor300works as described above.

As configured, the stator core304includes the ring hub306and a plurality of teeth308that extend outwardly from the ring hub306. The adjacent teeth308form a stator slot112into which one or more stator windings may be disposed. That is, each slot can have a single stator winding310disposed therein or it can include two or more windings as shown inFIG.3and further examples below.

The windings310can be arranged such that a cooling channel350is formed between an ID of the windings and a base112aof the slot112that where the windings reside. In one embodiment, the cooling channel350is provided a cooling flow from one or more headers as illustrated inFIG.5. It shall be understood that the back iron320can help to maintain the windings310a desired distance from the base112ato establish the channel350.

FIG.5illustrates a simple cross section through one segment304aof the motor300to illustrate how fluid can be passed though the channel350. As illustrated a coolant delivery system that includes an inlet header502and an outlet header504is arranged relative to the segment304aso that it can provide fluid into the channel350and remove it from the channel. The fluid passes, in this example, in the direction indicated by arrow A. Such a configuration can result in flow continuity and reduced pressure drop.

As illustrated inFIG.3, each outer winding310bis separated from each other by phase separators325(separators for short herein). These separators can be any separator as described herein. An insulator330is disposed between each of the inner windings310a.

The phase separators325can be formed of electric insulators such as polymers (nomex, kapton etc) or ceramics such as Al2O3 or AlN. Alternatively, the separators can be formed of highly thermal conductors such as copper/aluminum (not conducting electricity by offering high thermal conductivity to extract heat). The configuration of the insulators separators and windings is better viewed inFIG.6.

FIG.6shows an end view of one segment304awithout illustrating the end turns310cin detail for clarity. As illustrated, the segment includes teeth308that define a stator slot112. The slot112is partially filled with three windings that include three ID windings310a(1),310a(2),310a(3) and three outer windings310b(1),310b(2),310b(3). As shown as being discrete inFIG.6, it shall be understood that each inner winding310acan be electrically joined to a corresponding outer winding310band this correspondence is indicated by the numbers in parenthesis following the winding number.

While shown as being a three-phase motor in the examples, it should be noted that any multi-phase (3-phases, 5 phases and 3*n phases) can be implemented according to the teachings herein. For example, in the case of a 5-phase motor, there would be five ID windings310a(1)-310a(5) and five outer windings310b(1)-310b(5).

The inner and outer windings310a/310bare on opposite sides of the back iron320. The back iron320or other elements are arranged such that the inner windings310aare separated from the base112aof the slot112to define the channel350

The coolant flows through the flow channel350directly cools one half of the winding (e.g., inner windings310a) in the slot112. The heat generated by the outer winding portion310bgets effective conducted to the inner windings310awinding due to very high thermal conductivity as the inner windings are cooled by the passing coolant liquid. Of course, after the coolant passes through, it can be cooled at an external location and recirculated back into the stator.

As shown, each outer winding310bis separated from its adjacent neighbor by a separator325. Optionally, each separator325can include a flow channel as indicated by the dot therein. Thus, based onFIG.6the skilled artisan will realize at least 2 configurations: 1) a configuration where the separators325include a flow channel and the flow channel350is present and 2) a configuration where the separators325do not include a flow channel and flow channel350is present. Further, the skilled artisan will realize that the flow channels can be connected to any of the headers disclosed above so that coolant can be provided to them. Additional headers can be provided for the separators or the separators325can be attached to the same header that delivers fluid to the channel320.

Further, inFIG.6, optional insulators330can be provided between adjacent inner windings310aand between the inner windings310aand the teeth308. As shown inFIG.6, those insulators are level or flush with the inner diameter of the ID windings310a. In one embodiment, as shown inFIG.7, the insulators can include fins or pins720that extend into the stator slot350. These fins/pins720can enhance heat transfer capacity of the insulators330as there is more contact with the coolant in the flow channel350. As also shown inFIG.7, an inner wall730of the tooth308or the base112of the cooling channel can include fins740to increase heat transfer as well. It should be noted that the fins720/740are both optional so configurations without any fins, with both fins720/740or with only one of fins720/740are contemplated.

In the prior examples illustrated above it was assumed that the flow through the flow channels has been uni-directional in a manner the same or similar or to that shown inFIG.5. To that end, the headers502/504could provide for fluid through the separators325. Alternatively, the separators could have their own inlet and outlet headers802,804for uni-directional flow as shown inFIG.8. In particular,FIG.8illustrates a simple cross section through one segment304aof the motor300to illustrate how fluid can be passed though the separators325. InFIG.8, the coolant channel through the separator325is identified by reference numeral880. As illustrated a coolant delivery system that includes an inlet header802and an outlet header804is arranged relative to the segment304aso that it can provide fluid into the separator coolant channel880and remove it from the channel. The fluid passes, in this example, in the direction indicated by arrow B. Such a configuration can result in flow continuity and reduced pressure drop.

Optionally, in this or any other embodiment, the separator coolant channel880can have optional fins/pins882therein to increase heat transfer. Further, in one embodiment, the separators could be shaped as shown inFIG.9. In such a case, fluid with make a complete “loop” through the separator allowing for the outlet header804to be eliminated, integrated into inlet heater802or placed on the same side as the inlet header802.

As shown inFIG.9, two separators325a,325bare serially connected by a connector or manifold920. In such a case, the coolant flows in one separator325ain a first direction (e.g., direction C), through the manifold920and out the second separator325bin a second direction D). In one embodiment and as illustrated, the first and second directions C/D are opposite of another.

Of course, the combination of the two separators325a,325band the manifold920could be one element and could be formed in manner disclosed herein including additive manufacturing. In one embodiment, the winding separators325and manifold920are made up of ceramic and are cast with a through hole passing through the entire length of them.