THERMAL MANAGEMENT SYSTEM AND METHOD FOR IN-SLOT COOLING OF ELECTRIC MOTORS

The thermal management system for in-slot cooling of electric motors includes separating structures, either in the form of a scaffolding structure or a monolithic winding structure which is placed in between the adjacent winding turns to physically separate the winding turns to define coolant fluid passages for circulation of a coolant fluid in direct contact with the lateral surfaces of the winding turns. The scaffolding and monolithic winding structures are made from an electrically insulating material and are filled with a dielectric fluid that serves both the coolant and the electrical insulator between the winding turns. An end-winding organizer may be positioned at two end regions of each stator tooth to provide a curved surface for the winding turns to be held in tension throughout the 180° winding end turns and is formed with grooves to define the passage for the coolant flow to ensure that the flowing coolant reaches the surface of the innermost winding turns.

FIELD

The present disclosure addresses electric motors, and more particularly, relates to systems, devices, and methods for cooling electric motors. The present disclosure further addresses a thermal management technique for in-slot cooling of electric motors by means of uniquely shaped separating (spacing) structures placed between the winding turns of the electric motor stator for physical separation of the winding turns to form therebetween continuous passages for a coolant circulation in direct contact with each winding turn, thus maximizing the contact area between the coolant and the windings to enhance the cooling of the electric motors.

Further, in particular, the present disclosure addresses a thermal management system for cooling electric motors which utilizes spacing structures which may be fabricated in various shapes from an electrically insulating material and which are disposed between adjacent winding turns, preferably, in contact with both surfaces of each winding turn, to form a continuous channel therebetween filled with a dielectric fluid that serves as both a coolant and an electrical insulator between adjacent winding turns. Such arrangement provides a fluid flow path through each stator slot with a maximum fluid contact area with the winding turns and minimal heat conduction path through low conductivity insulation layers.

The present disclosure also addresses a thermal management system for in-slot cooling of electric motors utilizing spacing structures having a scaffolding configuration which are placed between winding turns to provide structural integrity for the stator windings and to maintain a physical separation between the adjacent winding turns.

Furthermore, the present disclosure addresses a thermal management system for in-slot cooling of electric motors where a physical separation between the winding turns is achieved by a monolithic (one-piece) winding turns separating structure which supports a continuous coolant fluid passage between adjacent winding turns. Such a monolithic separating structure enables an easy manipulation for placement and retainment of the windings during the stator assembly.

In addition, the present disclosure addresses a thermal management system for in-slot cooling of electric motors where a separating structure is placed between adjacent winding turns which can provide high voltage stand-off with minimum partial discharge by using a dielectric fluid as a coolant to increase the dielectric stand-off capability between winding turns so that the insulation layer thickness around the winding strands can be reduced.

The present disclosure also addresses a thermal management system for in-slot cooling of electric motors, which includes an end winding organizer assembly configured with a mechanical guiding of jump turns from one layer to an adjacent layer of the windings, shaped with an array of grooves serving as a scaffolding structure to direct the coolant fluid to circulate along the inside surfaces of the winding turns that are in a direct contact with the end winding organizers mounted at the two ends (also referred to herein as end winding regions) of each stator tooth, and which provides an entrance portal and an exit portal, with the entrance portal for the coolant fluid to enter into an end winding region of a stator winding to flow down the length of the slot to the exit portal to exit at the opposite end of the stator winding.

BACKGROUND

Electric motors have assumed a major role in sustainable development. Compared to a traditional combustion engine, an electric motor has a significantly higher efficiency, as well as diminished emissions and acoustic noise. The reduced fuel consumption and potentially lower operational cost of electric motors have drawn attention from both academics and industry.

In numerous applications, for example, concerning electrified aerial and terrestrial vehicles, the weight and volume of the motors are of great importance. The need for dense packaging renders thermal management to be one of the major challenges in such applications. The thermal management system that cools motors must be able to maintain the temperatures of all components below their respective limits for safe and reliable operation under all conditions. In addition, the thermal management system itself should be effective, reliable, and light-weight with minimal waste heat resulting in a low input power requirement (i.e., the high coefficient of performance).

A traditional electric motor includes a stator and a rotor. The stator typically is built with three sets of windings to form a three-phase winding configuration. The rotor typically has either permanent magnets, electromagnets, short-circuited rotor bar conductors, or some other means of interacting with the stator-induced magnetic field to produce torque.

In high-speed, high-power motors, the stator windings, being subjected to high voltage and high current amplitudes, generate a substantial amount of heat, and require strong electrical insulation. However, in general, strong electrical insulation results in strong thermal insulation that prevents heat removal from the stator windings. In addition, as the motor torque increases during the motor operation, the heat loss in the stator winding increases faster than the torque. Conventional cooling techniques are not sufficient to overcome the heat associated problems in electric motors, and cooling requirements become a major barrier to further increasing the machine's torque production capabilities.

The current cooling technologies treat either the whole stator or all the winding turns around one stator tooth as a monolithic structure, applying cooling only along its outer surface. Such an approach cannot provide sufficient cooling for high-power motors, owing to substantial electrical insulation with low thermal conductivity being present in the heat removal path. As a result, the windings become extremely hot at high current levels due to the elevated thermal resistance from the interior of the winding coil to its outer surface that is in contact with the coolant.

In addition, the cooling performance of the conventional technologies is limited due to the high thermal resistance of the wire insulation around each wire strand that is needed to prevent partial discharge and eventual short-circuiting between adjacent turns.

Nowadays, the use of hollow conductors with a coolant fluid flowing through the winding's interior cavity is considered to be one of the best-known alternatives to the in-slot cooling technique. However, this approach is subject to at least two significant disadvantages: (a) the hollow conductors are used in the form of solid copper tubes that are vulnerable to high AC losses at high excitation frequencies that can significantly raise the losses in the stator windings far above their values at low frequencies, resulting in a drop of machine efficiency by several percentage points, and (b) the pressure drop needed to force sufficient coolant circulation through the full length of the hollow stator coil (winding) tends to be very high and requires large pumps with high losses in the cooling system to support the hollow conductor cooling technique.

It therefore would be highly desirable to provide effective cooling for electric motors which would be free of the shortcomings of the conventional cooling techniques, and which would be capable of a significant reduction of the stator winding temperature rise through the provision of an enhanced contact between a coolant and a high percentage of the heat-dissipating surfaces associated with each stator winding.

SUMMARY

It is therefore an object of the present disclosure to provide a technique for effective cooling of electric motors by the provision of a coolant circulation in direct contact with a high percentage of the heat-dissipating surfaces associated with the stator windings to reduce their thermal stress.

It is another object of the present disclosure to ensure an effective cooling of electric motors through provisioning of numerous interior fluid pathways inside the stator windings for a coolant fluid circulation between heat-dissipating surfaces achieved by installation of separating (spacing) structures for physically separating adjacent winding turns and providing continuous (unblocked) passages therebetween for the coolant fluid in contact with individual winding turns in a stator of an electric motor.

It is an additional object of the present disclosure to provide a thermal management system for in-slot cooling of electric motors which utilizes a system of separating (spacing) structures, for example, in the configuration of a scaffolding structure, or a monolithic (one-piece) spacer, fabricated from an electrically insulating material and having a volume filled with a dielectric fluid that serves both as a coolant and the electrical insulator when circulating between adjacent winding turns. Such arrangement reduces the required thickness of the insulating material around each winding wire strand which is beneficial for reducing the strand's thermal resistance, resulting in improved effectiveness of the cooling technique.

It is still an object of the present disclosure to provide a highly efficient thermal management system for in-slot cooling of electric motors which is applicable to various types of stator windings, for example, the windings formed with Litz wire, to reduce the AC losses to a negligible level, and where the pressure drop needed to force sufficient coolant circulation through the full length of the stator windings is low and does not require large pumps to support the cooling technique.

In one aspect, the subject matter constitutes a thermal management system for cooling electric motors, comprising elongated spacing structures disposed between winding turns of a stator winding and separating one winding turn from another to define coolant fluid passages between them. The coolant fluid passages extend continuously along substantially an entire lateral surface of each of the winding turns.

A dielectric coolant fluid circulates along coolant fluid passages between winding turns in contiguous contact with the lateral surface of the winding turns.

The elongated spacing structure may have a scaffolding configuration formed with longitudinal first bars and a plurality of second bars extending in an angular relationship with longitudinal first bars and connected thereto. The second bars may cross the longitudinal first bars at 90 degrees.

The longitudinal first bars are arranged in a first plane, and the plurality of second bars are arranged in a second plane which is different than the first plane. The first and second bars define an array of openings which provide a continuous path for a flow of the dielectric coolant fluid between the winding turns in contiguous contact with the lateral surface of each winding turn.

Alternatively, the elongated spacing structure is configured with a base frame and a plurality of first and second tabs extending in spaced apart relationship with one another and in opposite direction from the base frame. The first tabs are disposed in an alternating relationship with the second tabs in an integral coupling with the base frame.

The first tabs define a first tier, while the second tabs define a second tier. The stator winding is arranged in at least a first layer and at least a second layer with the first layer being positioned in the first tier, and the second layer positioned in the second tier. Each of the first and second layers accommodate at least two winding turns. The two winding turns in each of the first and second layers are separated by respective first and second tabs.

The elongated spacing structures are fabricated from an electrically insulating material. Preferably, the elongated spacing structures having a scaffolding configuration are disposed at both surfaces of each of the winding turns of the stator winding.

The spacing structure may also be sandwiched between a surface of the stator tooth and the winding turns, thereby forming a dielectric coolant passage therebetween.

The subject system further includes a pair of end-winding organizer members, each attached to a respective one of two opposite ends of the stator teeth where the end windings are located. The end-winding organizer members are configured with a supporting bottom member, an upper member, and a vertical column member extending between and connecting the supporting bottom member and the upper member. Each of the supporting bottom member, upper member and vertical column has a curved front portion and a respective flat rear wall in contact with the stator tooth end surface.

The rear walls of the supporting bottom member, upper member and vertical column member are aligned to one another for connection with the respective end of the stator tooth. Each of the curved front portions of the supporting bottom member and the upper member is formed with a respective coolant portal.

In addition, the curved front portion of the vertical column is formed with a plurality of grooves extending in the plane of the tooth axial direction. The grooves formed on the curved front portion of the vertical column extend in fluid communication with the coolant portals formed at the curved front portions of the supporting bottom member and the upper member, respectively.

One of two end-winding organizer members associated with each stator tooth is configured with a sloped jump turn holder assisting in the winding shift from the lower layer to the upper layer which is needed once in each stator tooth winding.

A pump supplies the dielectric coolant fluid that enters the portals of an end-winding organizer member at one of the two ends of each stator tooth where it is directed to enter the stator slots along the two sides of the tooth, causing it to flow along the entire length of both slots through coolant fluid passages before exiting through the portals of the end-winding organizer member at the opposite end of the stator tooth.

In another aspect, the subject matter constitutes a method for thermal management of electric motors. The method comprises the steps of:

disposing elongated spacing structures between the winding turns to separate one winding turn from another and define coolant fluid passages which extend continuously along substantially an entire lateral surface of each of the winding turns, and

circulating a dielectric coolant fluid along the coolant fluid passages between winding turns in contiguous contact with the entire lateral surface of the winding turns.

The method assumes the steps of:

forming the elongated spacing structures in a scaffolding configuration or as a monolithic structure having a base frame and a plurality of first and second tabs extending in a spaced apart relationship with one another and in opposite direction from the base frame, where the winding turns are arranged in a first layer and a second layer, and where the winding turns in each of the layers are separated by respective first and second tabs.

The subject method further continues by sandwiching the elongated spacing structure between a surface of the stator tooth and the winding turn to define the coolant fluid passage therebetween.

These and other objects of the present disclosure will become apparent in view of the Patent drawings and the following description of the preferred embodiment(s).

DETAILED DESCRIPTION

Referring toFIGS. 1A-1B, an electric motor10(PM machine) is shown to include a rotor12and a stator14. The motor structure depicted in FIGS.1A-1B is just an exemplary structure chosen from numerous configurations of electric motors to which the principles of the subject disclosure are applicable, and other alternative configurations of the stator and rotor, as well as their interrelationships and mutual dispositions, are contemplated in the present system and method.

The rotor12is a moving part of the electric motor10which turns the shaft16to deliver the mechanical power. The stator14is the stationary part of the rotary system which provides a magnetic field that drives the rotating armature. The stator14in the exemplary embodiment of the electric motor10shown inFIGS. 1A-1Bis depicted as having twelve segmented stator teeth20and ten poles installed with the subject thermal management system25.

The example electric motor10(PM machine) depicted inFIG. 1Aincludes twelve stator windings18. Each stator winding18is a so-called “concentrated” winding which is wound around a single stator tooth20. Although twelve stator teeth20are shown in association with the stator14inFIG. 1A, it is to be understood that an alternative number of stator teeth may be provided depending on the design and application of the electric motor in question. The stator teeth20are spaced apart angularly one from another to form stator slots22therebetween.

The subject thermal management system25is installed in the electric motor10to attain a highly effective cooling of the stator windings18. The thermal management system25is configured to form numerous interior fluid pathways inside each stator winding18to enable direct contact of the coolant fluid32with the highest possible percentage of the heat-dissipating surfaces of each stator winding18, thereby significantly reducing its temperature, thus overcoming the deficiencies of conventional cooling techniques which treat either the whole stator or all the winding turns around a stator tooth as a monolithic structure and apply cooling only along the outer surface of the stator windings or the outer surface of the entire stator.

The subject thermal management system25includes a system of separating (spacing) structures24having different configurations. The separating structures24may be fabricated, for example, in the form of the scaffolding structure26presented inFIGS. 3A-3D, in the format of the monolithic (one-piece) winding structure28shown inFIGS. 4A-4B, or any other configuration capable of physical separation of the winding turns30from one another to define continuous channels therebetween for circulation of a coolant fluid32. The scaffolding and monolithic winding structures can be fabricated by a 3D printing process using improved materials with higher thermal conductivity but very low electrical conductivity.

In the subject in-slot scaffolding cooling, a stator slot22is flooded with a dielectric coolant32. The scaffolding structure is added between the winding turns to create a flow path by creating a thin, lattice-like structure to physically separate each of the winding turns30, considering the fact that stator windings18are tightly packed, as shown inFIG. 2. Since the wires are heavily insulated, or, in the case of the Litz wire, insulated by a layer of insulation around each individual wire strand, the heat conduction across multiple winding turns would be limited. The scaffoldings are placed on one or both sides of each wire turn, so that each individual turn contacts the coolant fluid directly on up to one or both of its lateral sides, thereby minimizing the length of the heat conduction path while maximizing the cooling surface area.

The scaffolding structures26may be installed between the winding turns30, as well as between respective winding turns30and a surface of the stator teeth20, either in the form of a continuous scaffolding structure extended throughout the stator winding18, or as a series of separate pieces extended throughout the stator winding18, with the separate pieces linked to one another or not.

As shown inFIGS. 1A-1B, 2, 4B, 5A, 9, 10, and 11, each stator tooth20has a corresponding stator winding18wound around the stator tooth20. Each winding18forms a number of winding turns30and a number of winding layers40,42. Although the number of winding tuns30and the number of the winding layers40,42may differ as required by a specific design, as an exemplary embodiment,FIGS. 1B, 2, 4B, 5A, 9, 10 and 11, depict the stator winding18wound around the stator tooth20using two layers,40,42, with the upper winding layer42formed, for example, with four winding turns30, and the bottom layer40formed, for example, with three winding turns30. It is to be understood that a different number of layers and a different number of winding turns in each layer may be formed around each stator tooth20in the stator14.

Each winding turn30has at least one, but preferably, both lateral winding turn surface(s), installed with a separating structure (also referred to herein as a spacing structure, or a separating member)24configured either in the form of the scaffolding structure26or the monolithic winding structure28, or any other form applicable herein. The spacing structures24form physical separation between the adjacent winding turns30in each winding layer40and42and define gaps between the adjacent winding turns30. Each gap constitutes a continuous coolant fluid passage for the coolant fluid circulation between the adjacent winding turns30. Preferably, the separating structures24also are disposed between the winding turns and the tooth body to physically separate them from one another and define the coolant fluid passages between the innermost winding turns and the tooth body.

Thus, the separating structures24, in the form of the scaffolding structures26and/or the monolithic winding structures28, physically separate adjacent winding turns30as well as the winding turns from the tooth body to form corresponding gaps (also referred to therein as coolant fluid passages) therebetween. Each gap (coolant fluid passage)44formed between the adjacent winding turns30, as well as the gap (coolant fluid passage)46formed between the winding turn closest to the stator tooth and the stator tooth body (surface), is maintained by the separating structures24which can be configured either as the scaffolding structures26(shown inFIGS. 2, 3A-3D, 5A, 9, 10), or as the monolithic winding structure28(shown inFIGS. 4A-4B and 11), or any other configuration which corresponds to the principles of the subject thermal management system and method.

For example, the scaffolding structures26(in any configuration shown inFIGS. 3A-3D) have been developed with the purpose of, when installed inside the stator winding, maintaining the respective coolant fluid passages44(between the adjacent winding turns30), as well as the coolant fluid passages46(between the stator tooth20surface and the winding turns30), which define the uninterrupted (continuous) fluid passages for directing a flow of a coolant fluid32around and in contact with each individual winding turn30in the stator windings18, and thus provide the fluid flow paths in the stator slots22formed between the stator teeth20. Such arrangement provides an enhanced direct contact area for the coolant fluid32with the winding turns30with the coolant fluid32capable of reaching all sides of the winding turns. The subject structure also minimizes the heat conduction path through the low conductivity insulation layers and maintains a physical separation between adjacent winding turns30and the separation between the winding turns30and the tooth body that enhances the winding structural integrity and the galvanic isolation between these elements. Since the dielectric fluid32is used as a coolant, the dielectric standoff capability is increased between the winding turns30so that the insulation layer thickness around the winding strands can be reduced, which is beneficial for the operation of the electric motor installed with the subject thermal management system25.

Different types of windings and insulation are contemplated for being used in the present structure. Such windings may, for example, include Litz wire which is a particular type of a multistrand wire or cable used in electronics to carry alternating current (AC) at radio frequencies. The Litz wire is designed to reduce the skin effect and proximity effect losses in conductors used at frequencies up to about 1 MHz. It consists of numerous thin wire strands, individually insulated, and twisted or woven together, following one of several carefully prescribed patterns often involving several levels (groups of twisted wires which are twisted together). The result of this winding pattern is to equalize the proportion of the overall length over which each strand is at the outside of the conductor. This approach has the effect of distributing the current equally among the wire strands and reducing the electrical resistance of the Litz wire at high electrical frequencies.

In one example of different varieties of windings and insulations used with the present thermal management system, the coolant fluid32may partially flow into the interior of the Litz wire turns, reaching all sides of the Litz wire bundles, or even individual wire strands inside the bundles, thus greatly enhancing the cooling effectiveness of the subject thermal management system.

Shown inFIGS. 1A-1B, 2, 5A, 10, and 11is a pump50which is operated to supply the dielectric coolant fluid32into the stator slots22. The system may use a single or multiple dielectric coolant fluids, which, as an example, may be chosen from the coolants presented in Table 1, or other coolant fluids having a suitable viscosity and dielectric properties.

The dielectric coolant fluid32circulates within the stator slots22through the gaps44and46formed inside the stator windings18by the separating structure24(either in the configuration of the scaffolding structures26, or winding structure28, or any other configuration capable of providing a stable physical separation between the winding turns and defining the uninterrupted fluid passages for the coolant fluid circulation) installed within the stator windings18. The separating structures24, in the form of the scaffolding structures26and/or monolithic winding structures28, provide structural integrity to the stator windings18and maintain physical separation between the winding turns30and the stator tooth surface, for the dielectric coolant fluid32to circulate through all coolant fluid passages44and46along all stator slots22in the stator14. As presented inFIG. 1A, the coolant fluid32aenters into the stator slot22directed by the pump50, circulates through the coolant fluid passages44,46defined within the stator windings18, passes along and through the stator slots22between the stator teeth20, and exits (coolant32b) the electric motor through the same slot. The coolant fluid32bexiting from the electric motor may be further cooled and returned into the thermal management system25for further circulation within the stator windings18as long as needed for the operation of the electric motor10.

Shown inFIG. 2is a coolant flow52through the scaffolding structures26installed in each stator winding18. Each scaffolding structure26includes longitudinal (horizontal) bars36and crossing bars38. The crossing bars36extend in a crossing relationship with the longitudinal bars35at various angles, including a right angle as shown inFIGS. 3A-3B, and with different positional patterns, as shown inFIGS. 3A-3D, or any other configuration of the scaffolding structure26which can provide an arrangement devoid of a blockage in the passage for the coolant flow52. The variety of candidate scaffolding structures shown inFIGS. 3A-3Bare examples only and not intended to represent an exhaustive set of scaffolding geometries.

The longitudinal bars36and crossing bars38are positioned in two different planes, so that the coolant fluid filling the volume of the scaffolding structure26, may flow freely without interruptions through and along the scaffolding structures26between the winding turns30and between the winding turns and the stator tooth surface.

Referring now toFIGS. 4A-4B, an alternative embodiment of the separating structure24may be configured as a monolithic winding structure28, which constitutes an integral configuration formed with a horizontal frame54which is positioned between and defines the layers40and42of the winding turns.

The winding structure28is a one-piece winding structure utilized to provide the physical separation and continuous coolant fluid path. The winding structure28enables an easy manipulation, placement, and retainment of the windings during assembly. Although shown in FIGS.4A-4B with four winding turns30in the upper tier (layer42) and three winding turns30in the lower tier (layer40), it is to be understood that any other number of the winding turns in each layer is contemplated in the subject system.

The horizontal frame54in the monolithic winding structure28may be formed with parallel beams54aextending longitudinally along the frame54and forming supporting elements for vertical members integrally connected with the parallel beams54aof the horizontal frame54. Although the horizontal frame54is shown with three parallel beams54ait is to be understood that any number of the parallel beams54ais contemplated for the design of the monolithic winding structure28, depending on the number of the winding turns desired in the winding18.

The vertical members are represented by upper vertical members56aand lower vertical members56bwhich extend from the horizontal frame54in opposite directions and in an alternative fashion.

When the monolithic winding structure28is installed with the stator winding18, as shown inFIG. 4B, the winding turns30in one tier of the monolithic winding structure28, for example, in the upper layer42, extend above the horizontal frame54with the vertical member56aseparating one from another. Similarly, the winding turns30in another tier of the monolithic winding structure28, for example, in the lower layer40, extend below the horizontal frame54. The winding turns30in the lower layer40are separated one from another by the bottom vertical members56b,as shown inFIGS. 4A-4B. The monolithic winding structure28thus provides physical separation between each winding turn30in each winding layer40and42, and forms coolant fluid passages44therebetween and the coolant fluid passages46between the winding turns and the stator tooth body (surface) through which the dielectric coolant fluid32circulates, as shown by the coolant flow60inFIG. 4B.

When the stator slots22are flooded with the dielectric coolant fluid32, being directed in by the pump50, the dielectric coolant fluid32circulates through the gaps44and46formed between the adjacent winding turns30and between the winding turns and the tooth body surface, respectively. The circulation of the dielectric coolant fluid32in contiguous contact with each winding turn30along its entire length, as well as between the stator tooth surface and the winding turns, provides highly efficient cooling.

To further improve the effectiveness of the subject technique, the material used for the scaffolding structure26and winding structure28, may be selected to have a high thermal conductivity to enhance its ability to conduct heat away from the stator windings18. This approach effectively reduces the thermal resistance encountered by heat flowing from the winding turns to the coolant by making it easier for the heat to flow from the winding turns into the scaffolding material which then can serve the same role as the heat fins in conventional fluid convection cooling systems.

The scaffolding and the winding structures26and28may be fabricated by a 3D printer using the improved materials with a high thermal conductivity.

As an example, the materials presented in Table2are considered suitable for fabrication of the scaffolding structures and monolithic winding structures.

To implement the scaffolding structure in the end-winding of the stator, the winding turns need to be organized and carefully positioned. An end-winding organizer has been designed for this purpose. It is especially beneficial for Litz wire. However, the end-winding organizer is applicable in other types of wire used in winding turns as well.

Referring toFIGS. 5A-5B, an end-winding organizer assembly62is provided in the subject system (which includes two end-winding organizer members64a,64b) to enhance the fabrication process for high-quality winding configurations. The end-winding organizer assembly62provides a convenient curved surface against which the winding turns can be held in tension during their 180-degree mechanical bends in the end winding regions66a,66bat both ends of each stator tooth20before re-entering the adjacent slot.

One of the two end-winding organizer members64a,64bassociated with each stator tooth20can include sloped mechanical guides92serving as a jump turn holder for the jump turn94, which is the winding turn that connects two adjacent layers40and42of the winding turns (as shown inFIGS. 5A-5B). Only one of the two end-winding organizer members64a,64bassociated with each stator tooth20requires mechanical guides92because the stator winding needs to shift from the lower layer40to the upper layer42only once in each stator winding18. The second end-winding organizer member associated with the stator tooth20does not need the mechanical guides92(jump turn holder), but only needs the grooves90that extend in the plane of the tooth axial direction. The system of grooves90are formed on the surface of the end-winding organizer member64a,64bwhich are intended to serve the same function as the inter-turn scaffolding to ensure that the flowing coolant reaches the surface of the innermost turns that contact the end-winding organizer surface. Each end-winding organizer member64a,64balso provides two portals78a,84aand78b,84b,respectively, for the coolant fluid32aflowing into and fluid32bflowing out of the winding structure at the two ends of the stator slot22to ensure that the coolant reaches all the winding turns in both their in-slot region100and end-winding regions66a,66b,respectively.

As shown inFIGS. 5A-5B, one of two end-winding organizer members, for example, the end-winding organizer64ahas the slot84ain its upper surface and the slot78ain its lower surface to allow the coolant fluid32ato have an easy path to enter both layers42and40, respectively, of the stator winding18at the end region area66a.These two slots84a,78aserve as the entry portals for the end-winding organizer member64aat one end66aof the stator tooth20. The slot84b(shown inFIG. 5A) and the slot78b(best shown inFIGS. 10-11) are formed in another end-winding organizer member64bpositioned at the opposite end region66bof the stator tooth20to serve as the exit portals for the coolant fluid32bto exit the respective stator slot22.

Specifically, the end-winding organizer assembly62includes two end-winding organizer members64aand64bpositioned at two end winding regions66a,66b,respectively, at both ends of the stator tooth20, to facilitate the winding turn pattern and to mechanically guide jump turns from one layer40to another layer42in the winding18.

Each end-winding organizer member64a,64bincludes a bottom supporting structure68, an upper structure70and a vertical column70which extends between the bottom supporting structure68and the upper structure70and supports both the upper structure70and the bottom structure68in the horizontal and axial orientation.

The bottom supporting structure68defines the base of the end winding organizer member64a,64b.The bottom supporting structure68has a rear wall74and a curved front portion76which extends from the rear wall74and supports the lower layer40of the stator winding18, as well as prevents it from moving upward or downward(radially) in response to electromagnetic forces that the end winding may experience. The front portion76of the bottom supporting structure68has an opening78aor78bformed therein that serves as an entry or exit portal for the coolant fluid, depending on which end66aor66bof the stator tooth the end-winding organizer member (64aor64b) is mounted.

The upper structure70has a rear wall80, a curved front portion82which has a slot84aor84bformed therein that also serves as either an entry or exit portal for the coolant fluid depending on which end66aor66bof the stator tooth20the end-winding organizer member (64aor64b) is mounted. The upper structure70serves to support the upper layer42of the winding18in the presence of electromagnetic forces that the end winding may experience.

The vertical column72has a rear wall86and a curved front portion88which is configured with a system of grooves90. The system of grooves90support the function of the end winding organizer structures64a,64bto serve as a scaffolding structure that allows the coolant fluid to flow through the grooves90and along the inside surfaces of the winding turns30that are in direct contact with the end winding organizer members64a,64bin the end winding regions66a,66b,respectively, of the stator tooth20.

The mechanical guides92(jump turn holder) are formed between the upper layer42and the lower layer40on one of the end-winding organizer members64aor64bassociated with each stator tooth20. The mechanical guides92facilitate the transition of the jump turn94wire from one layer (for example,40) to another layer (for example,42) during the winding of the wires, as shown inFIGS. 5A-5B.

The rear walls74,80, and86of the bottom supporting structure68, upper structure70, and the vertical column72, respectively, are aligned one with another and are shaped to match the cross-sectional outline of the stator tooth at the ends66a,66bof the stator tooth20so that the innermost stator tooth winding turns on both winding layers together with their separators will maintain close contact with each stator tooth surface and organizer surface as they emerge from the tooth slot into the end winding regions66a,66bon both sides of the stator tooth20.

The end winding organizer assembly62enhances the effectiveness of the cooling of the stator as it provides slots78a,78band84a,84bwhich are formed to be in fluid connection with the system of the coolant fluid passages inside the stator windings and with the grooves90, and thus serve as the portals for the coolant fluid32ato enter into the end winding region66aof the winding at one end (for example, through the slots74a,84a) before flowing down the length of the stator slot and subsequently exiting (32b) the winding through the slots78b,84bmounted at the opposite end66bof the stator tooth20, as schematically presented inFIGS. 5A-5B.

A CFD (Computational Fluid Dynamic) simulation of the scaffolding-based in-slot cooling using the subject thermal management system for the Litz wire based stator wiring has been carried out and delivered promising results. Assuming 21 W/cm3heat loss in the Litz wire with 8.7 mm×2.3 mm cross section, seven winding turns around each stator tooth, and eighteen stator teeth in total, the stator can be easily cooled below the 180° C. maximum temperature limit with 55° C. Polyalphaolefin (PAO) coolant fluid.

The calculated relationship between the flow rate, pressure drop, and maximum hot-spot temperature of the scaffolding structure anywhere inside the stator slot or end windings is shown inFIG. 6. The total volume flow rates presented are for an electric motor that includes 18 stator teeth and 18 stator slots, with each stator slot equipped with the subject in-slot cooling technology. The predicted pressure drop along the length of the stator slots as a function of the total coolant flow in the stator is appealingly low. The maximum winding temperature drops rapidly to conservatively low levels as the flow rate is increased to moderate levels.

All four of the scaffolding structures geometries shown inFIGS. 3A-3Dare calculated to achieve similarly attractive predicted thermal performance shown by the pressure drop and maximum temperature values inFIG. 7for the same operating conditions as inFIG. 6.

For the example stator winding coil with seven winding turns arranged in two layers as shown inFIGS. 1B, 2, 4B, 5A, 9, 10, and 11, the predicted thermal performance of the monolithic winding structure as reflected in the predicted maximum hot-spot temperature and the calculated pressure drop along the length of its seven turns is comparable to that of the scaffoldings, as shown in FIG.8.

A prototype of the subject thermal management system shown inFIG. 9has been built and tested. The scaffolding structures, end-winding organizer members, and one stator tooth for the prototype have been 3D printed, and the Litz wire was used to carry high current to generate the expected heat load in the machine.

Referring toFIG. 10, which represents an exemplary process for assembling the subject system using the scaffolding structure26, the method begins with Step1wherein the stator teeth20and two end-winding organizer members64a,64bare provided.

Subsequently, in Step2, the stator tooth and end-winding organizer assembly104is formed by assembling each stator tooth20with two end organizers members64a,64b.The two end-winding organizer members64a,64bare attached to the end winding regions66a,66b,respectively, of the stator tooth20to form the combined stator tooth and end-winding organizer assembly104.

In the subsequent Step3, the winding wire is brought in contact with the scaffolding structure26to form a two-layered assembly.

In Step4, the two-layered assembly of the scaffolding structure26and the winding wire is wound around the stator tooth and end winding organizer assembly104with the scaffolding structure26in contact with the tooth surface and the winding turn30spaced from the stator tooth surface by the scaffolding structure26, to form a first winding turn30in the layer42. The first winding turn30is separated from the stator tooth surface by the gap46which defines the coolant fluid passage46between the winding turn and the stator tooth surface. The configuration of the winding/scaffolding structure formed and shown in Step4is for ease of understanding of the fabrication process.

However, it may be preferred to form the winding in accordance with a specific fabrication strategy underlying the initiation of the winding operation near the middle of the stator winding length, with one half of it being wound to form the upper layer, while the other half of the winding length used to form the lower layer. Otherwise, if trying to form the two layered winding in Step4, beginning with one end of the winding wire, the upper layer would be formed, and the wire would subsequently have to be squeezed between the upper and lower layers to return to the stator tooth surface on the lower layer to start winding at the lower layer. The wire being squeezed between the upper and lower layers disrupts the winding and is a serious problem because there is no space allocated for it in the stator slot area.

Thus, the first turn in the upper layer42that appears in Step4is positioned near the center of the Litz wire length that comprises both layers40,42of the stator winding. Starting from this first turn, approximately one half of the wire length is used to form the upper layer of the stator winding and approximately half the other half of the stator winding length is used to form the lower winding layer after transitioning from the upper layer42to the lower layer40using the jump turn mechanical guides92provided by one of the two end-winding organizer members64a,64b.

As shown in the subsequent Step5, the process is continued by applying a second turn of the upper layer42winding consisting of the scaffolding structure26and the winding wire in the same layer42(thus forming the coolant fluid passage44between the adjacent winding turns30). Step5also shows the application of the first turn of the lower layer40after the wire for the other half of the stator winding passes through the mechanical guides92in one of the end-winding organizer members64aor64b.The same two-layered assembly of the scaffolding structure26and the winding turn30shown in Step3is used during the formation of the lower layer40.

The process of Step5further continues for adding turns till a required number of turns is attained as, for example, presented in Step6, i.e., until all winding turns30with the intermediately positioned scaffolding structures26are wound around the assembly104.

Steps3-6show the operation of repeated winding of the scaffolding structures26with the winding turns30around the stator tooth and end-winding organizer assembly104. The resulting structure of the present thermal management system25is shown in Step7.

Although Steps6and7show the assembly104with two layers40and42of the windings turns30positioned intermittently with the scaffolding structures26, where the layer40has four winding turns30, while the layer42has three winding turns30intermittent with the scaffolding structure26between each of those winding turns30, it is to be understood that a different number of winding turns30in each layer, and a different number of layers is also contemplated in the subject thermal management system.

During the winding of the stator winding18around the stator tooth20, the scaffolding structure26between the winding turns30can be incorporated in the stator winding in several alternative forms: (a) as a plurality of individual scaffolding structures for each straight run of winding, or (b) as a plurality of individual scaffolding structures linked together, or (c) as a single continuous, flexible coil that is wound together with the stator winding.

Step7shows the jump turn94extending from the winding turn30on the lower level40to the upper layer42with the help of the mechanical guides92provided at the end winding organizer member64aas shown inFIGS. 5A-5B.

Subsequent to the coiling of the stator winding18with the intermittently positioned scaffolding structures26around the assembly104of each stator tooth20, the stator14is positioned in the required disposition with the rotor12, and the dielectric coolant fluid32is pumped by the pump50into the stator slot(s)22between the stator teeth20. The pump50, being actuated, directs the dielectric coolant fluid32ainto the stator slot(s)22, particularly through the portals (slots)78aand84aformed in the corresponding end-winding organizer member64aand provides the circulation of the dielectric coolant fluid32along the stator slots22through the coolant fluid passages44,46(formed between adjacent wiring turns30as well as between the wiring turns and the surface of the stator teeth20), and the grooves90(formed at the front surface of the vertical column72of the end-winding organizer members64a,64b). The coolant fluid32b,after circulation inside the stator windings18, exits from the system via the exit portal (slot)78b(best shown in Steps1and2ofFIG. 10) and the exit portal (slot)84bprovided for this purpose in the end-winding organizer member64bat the opposite end66bof the stator tooth20. The coolant fluid32bmay be further supplied to the pump50for further entrance into the system and re-circulation.

In an alternative process, shown inFIG. 11, the subject thermal management system utilizes the monolithic winding structure28detailed inFIGS. 4A-4B. This variation of the spacing structure is based on the use of a complex, one-piece winding structure28, rather than multiple scaffolding structures26, to provide the physical separation and to define continuous coolant fluid passages. This structure enables easier manipulation, placement, and retainment of the windings during assembly as shown inFIG. 11.

The process depicted inFIG. 11begins in Step1, where the monolithic winding structure28is installed with wires of the stator winding18. The wires are introduced in the upper tier and the lower tier of the monolithic winding structure28and are separated from one another by the vertical members56aand56b,respectively. Although one wire is shown in Step1ofFIG. 11for each tier, it is to be understood that for the exemplary embodiment of the subject process, four wires are installed in the upper tier and three wires are installed in the lower tier. Different number of wires than the exemplary number shown herein may be installed in the monolithic winding structure28, depending on the requirement to the design of the stator in the electric motor.

In the following Step2, the monolithic winding structure28filled with the wires (winding turns30) installed therein is wound around the stator tooth and end-winding organizer assembly104(fabricated in accordance with the Steps1-2of the process shown inFIG. 10). As opposed to the process using the scaffolding structure26, as shown inFIG. 10, the fabrication of the stator winding utilizing the monolithic winding structure28forms both layers40and42simultaneously.

The process continues till the final structure of the stator winding18is wound around the stator tooth and end-winding organizer assembly104as shown in Step3, with the coolant fluid passages44and46formed for the coolant fluid circulation inside the stator windings18. Similar to Step7ofFIG. 10, subsequent to the coiling of the stator winding18with the intermittently positioned vertical members56aand56b(also referred to herein as tabs) of the monolithic winding structure28around the assembly104of each stator tooth20, the stator is positioned in the required disposition with the rotor, and the dielectric coolant fluid32is pumped by the pump50into the stator slot(s)22between the stator teeth20. The pump50, being actuated, directs the dielectric coolant fluid32ainto the stator slot(s)22, particularly through the portals (slots)78aand84aon the corresponding end-winding organizer member64aand provides the circulation of the dielectric coolant fluid32along the stator slots22through the coolant fluid passages44,46(formed between adjacent wiring turns30and between the wiring turns and the surface of the stator tooth20), and the grooves90(formed at the front surface of the vertical column72of the end-winding organizer members64). The coolant fluid32, after circulation inside the stator windings18, may exit from the system (shown as fluid flow32b) via the exit portals (slots)78b,84bat the end-winding organizer member64bat the opposite end66bof the stator tooth20, and may be further supplied to the pump50for further entrance into the system and re-circulation.

The present thermal management system25is contemplated to be applied to two major classes of concentrated stator windings.FIGS. 12A-12Bare representative of these two classes of concentrated windings, whereFIG. 12Adepicts a “double-layer winding”120(the word “layer” here is being used in a different context from the winding layer discussed in the previous paragraphs) with a stator winding18A around each stator tooth20. As a result, each stator slot22A is shared by a coil-side from the stator windings18A around each of the two adjacent stator teeth20.FIGS. 1A-1B, 2, and 5Ashow a double-layer winding embodiment.

FIG. 12Bdepicts an alternative class of concentrated windings known as a “single-layer winding”122in which a stator winding18B is installed around every second stator tooth20in sequence around the circumference of the machine so that half of the stator teeth20have no concentrated stator windings around them. This configuration is distinguished by having stator slots22B that are completely filling by the winding turns of only one stator winding18B, not two.

Both of these two classes of concentrated windings18A and18B shown inFIGS. 12A-12Bare contemplated for being used with the subject thermal management system25with the stator winding18(18A or18B) wound around each or each second stator tooth20in the stator14.

As presented supra, a unique thermal management system has been developed for directing the flow of a cooling fluid around individual wire turns in stator windings. The subject thermal management system utilizes a scaffolding structure placed between winding turns, which provides: (1) a fluid flow path through stator slots from one end to the other; (2) maximum fluid contact area with the winding turns that may, in some cases, reach all four sides of the rectangular winding turns; (3) minimization of the heat conduction path through low conductivity insulation layers; (4) structural integrity to maintain a physical separation between the winding turns; and (5) high voltage standoff with minimal partial discharge by using a dielectric fluid as the coolant to increase the dielectric standoff capability between winding turns so that the insulation layer thickness around the winding strands can be reduced.

Depending on the type of windings and insulation used, for example, in the case of the Litz wire type of the winding, the coolant may partially flow into the interior of the Litz wire turns, reaching all sides of the Litz wire bundles or even individual wire strands inside the bundles, thus further enhancing the cooling effectiveness of the subject system.

An alternative to the scaffolding structure, a monolithic one-piece winding structure may be also utilized in the subject thermal management system, which is capable of fulfilling the functions of scaffoldings (physical spacing of the wire turns and defining the coolant fluid passages therebetween), but also beneficially enables an easy manipulation, placement, and positioning of the stator windings during assembly.

The present system includes an end-winding organizer that: (1) facilitates the winding turn pattern at the end winding region, including mechanical guiding of jump turns from one layer to an adjacent layer: (2) serves as a scaffolding structure that allows coolant to flow along the inside surfaces of the winding turns that are in direct contact with the end-winding organizer at the end winding regions; and 3) provides slots that serve as the portals for the coolant fluid to enter into the end winding region of the stator winding at one end before flowing down the length of the stator slot and subsequently exiting the stator winding through the end-winding organizer opening at the opposite end of the coil.

To improve the effectiveness of the subject technique, the material used for the scaffolding structure and the monolithic winding structure may be chosen to have a high thermal conductivity to enhance its ability to conduct heat away from the stator windings. This improvement effectively reduces the thermal resistance from the winding turns to the coolant by making it easier for the heat to flow from the winding turns into the scaffolding material which can serve the role of the heat fins.

Although aspects of the present disclosure have been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the present disclosure as defined in the appended claims. For example, functionally equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and in certain cases, particular locations of the elements may be reversed or interposed, all without departing from the spirit or scope of the present disclosure as defined in the appended claims.