Patent Publication Number: US-2022239182-A1

Title: Capillary-cooled molded magnetic structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application is a continuation of U.S. patent application Ser. No. 16/783,085, filed Feb. 5, 2020, entitled “CAPILLARY-COOLED MOLDED MAGNETIC STRUCTURE”, which is a continuation of U.S. patent application Ser. No. 16/452,345, filed Jun. 25, 2019, entitled “CAPILLARY-COOLED MOLDED MAGNETIC STRUCTURE”, which is a continuation of U.S. patent application Ser. No. 16/380,624, filed Apr. 10, 2019, entitled “CAPILLARY-COOLED MOLDED MAGNETIC STRUCTURE”, which claims the benefit of U.S. Provisional Application No. 62/656,222, filed Apr. 11, 2018, entitled “CAPILLARY-COOLED MOLDED MAGNETIC STRUCTURE”, the entire contents of both of which are incorporated herein by reference. 
    
    
     DETAILED DESCRIPTION OF FIGURES 
       FIG. 1 a    shows a section of a capillary-cooled molded element  102  wherein coolant channels are established via one or more investment molds  104 . In turn, each investment mold  104  includes one or more inlet mold elements  106 , one or more outlet mold elements  108 , and one or more capillary mold elements  110 . Molded element  102  may be fabricated from a powder material which is compressed and heated to form a solid. In the case of magnetic components such as motor cores or transformer cores, a ferro-magnetic powder may be used. Various powder binders may be used to enhance desired properties such as thermal conductivity or modulus. 
       FIG. 1 b    shows a section of a capillary-cooled molded element  102  after investment mold(s)  104  have been removed. Channels formed by investment mold(s)  104  include inlet channel(s)  112 , outlet channel(s)  114 , and capillary channels  116 . Investment mold  104  can be removed by chemical or thermal means; forced air may be used to help remove dissolved or melted material. 
       FIG. 1 c    shows composite capillary element  103  comprising individual capillary-cooled molded elements  120  and  122  where cooling channels are provided by surface grooves on molded elements  120  and  122 . Channels are completed when an external surface, such as an enclosure, is brought in contact with the molded element. As shown, enclosure  124  surrounds molded element  122  such that grooves within molded element  122  become coolant flow channels. Likewise, molded element  122  surrounds molded element  120  such that grooves within molded element  120  become coolant flow channels. Specifically, inlet grooves  126  serve as inlet channels; outlet grooves  128  serve as outlet channels and capillary grooves  130  serve as capillary channels. 
     By maintaining large numbers of capillary channels, each having relatively small thickness dimensions, efficient heat transfer between the molded element and the coolant can be achieved. Furthermore, by using a relatively large number of inlet and outlet channels, capillary lengths can be kept relatively short—thus maintaining relatively low coolant head loss. 
       FIG. 2  shows an electric machine stator  140  comprising a molded ferromagnetic core  142  and a winding. In turn, the core includes a back iron portion  144  and a tooth portion. The winding includes active winding elements, end turn elements  154  and terminals  156 . Cooling channels are formed within the back iron via investment mold(s)  104 . Investment mold(s)  104  include inlet mold elements  106 , outlet mold elements  108 , and capillary mold elements  110 . Upon dissolution of mold(s)  104 , inlet, outlet and capillary channels are then present within back iron portion  144 . 
    
    
     In some embodiments, the winding is first wound as a planar element with the active winding elements compressed and bonded. The winding is then formed into a cylindrical shape and then may be coated with a thermally conductive insulating material. The winding is then over-molded with the core material and finally, the investment molds are removed (either chemically or thermally). With this construction approach, very high winding packing can be achieved, especially for the active winding elements. Additionally, excellent heat transfer can be achieved between the winding and the core due to the intimate contact between the core and the winding. 
       FIG. 3  shows cut-away views for a stator—rotor combination for an induction motor. Stator  140  is similar to that of  FIG. 2  except that end turn cooler elements  165  have been added at each end of rotor core  142 . End turn coolers  165  may be provided by simply extending molded core  142 , or they may be completely separate elements. In the former case, cooling channels may be provided within end turn coolers via added capillary elements  112  within investment mold  104 . In either case, end turn coolers  165  are in thermal contact with end turns  154  such that heat generated within end turns  154  is transferred to coolant flowing within end turn coolers  165 . Coolant may be fed in at inlet gap  161  and retrieved at outlet gap  163 . 
     Rotor  160  comprises molded rotor core  162 , rotor cage  164 , rotor manifolds  170 , and rotor shaft  180 . In turn, molded core  162  includes inlet, outlet and capillary channels which are formed by investment molds  104 . Rotor cage  164  includes active rotor bars  166  and end rings  168 . Rotor manifolds  170  include end ring capture elements  172  which extend into the end ring material to provide mechanical reinforcement (this feature may be advantageous in high speed applications). Rotor manifolds also include rotor manifold cavity  174  which enables coolant flow between rotor shaft  180  and inlet and outlet channels cast within rotor core  162 . Radial shaft holes  181  within shaft  180  enable coolant flow to or from shaft  180 . Rotor manifolds  170  may also include balance registers  178  which enable dynamic balancing by the addition of materials such as “balancing putty”. 
     In some embodiments, the combination of the cage and manifolds is cast or otherwise fabricated as a pre-formed element. This combination is then over-molded with core material followed by removal of investment mold  104  such that cooling channels within the rotor core are provided. Alternatively, rotor core  162  may first be molded as a separate element with the rotor cage subsequently added. 
     In some cases, a conventional lamination type rotor combined with a molded capillary-cooled stator may be advantageous. In other cases, the reverse may be called for—where the rotor uses a molded capillary-cooled core and the stator uses a conventional lamination structure. 
       FIG. 4  is a cut-away view showing molded stator core  142  and molded rotor core  162 . Stator core  142  includes closed winding slots  147  and molded rotor core  162  includes closed bar slots  169 . As shown, for both the stator and rotor cores, inlet channels  112  exit one face, and outlet channels  114  exit the opposite face. Inlet and outlet channels are connected via capillary channels  116  such that all coolant flow must flow through these capillary channels. 
     Since the stator winding is over-molded with the the core material, conventional tooth gaps are no longer needed. This may provide benefit in terms of reduced tooth tip and winding eddy losses. 
       FIG. 5  is a cut-away drawing for the combination of an induction machine stator  140  and rotor  160 . As shown, the stator consists of molded core  142  and winding  150 . The winding is pre-formed and the core is then molded over the winding. Active winding elements  152  may be compressed and bonded to form rigid elements of high packing density and thermal conductivity. End turn portions  154  of the winding may also be compacted. 
     Coolant channels are molded into the back-iron portion of the stator core  142 . These include axially directed inlet and outlet channels  112  and  114  which are alternately disposed. Capillary channels  116  interconnect adjacent inlet and outlet channels. The stator winding is terminated via terminals  156 . 
     Rotor  160  comprises a molded rotor core  162 , rotor cage  164 , and rotor manifolds  170 . In turn, rotor cage  164  comprises active rotor bars  166  and end rings  168 . Finally, rotor manifolds  170  comprise end ring capture elements  172 , manifold cavities  174 , and rotor manifold registers  178 . Inlet, outlet, and capillary channels may be included within molded core  162  for heat removal. Inlet channels receive coolant from an inlet manifold cavity  174 , while outlet channels deliver coolant to an outlet manifold cavity  174 . In turn, both of these manifold cavities are contiguous with respective radial shaft holes  181  ( FIG. 3 ). 
     End ring capture elements are peripheral manifold features which serve to reinforce end rings  168  such that high speed operation can be safely achieved. Manifold register  178  is a feature which allows the addition of balancing putty such that dynamic balancing can be easily achieved. 
       FIG. 6 a    shows a molded stator core section in the case where stator core  142  is formed separately such that a conventional winding can be added. Tooth gaps  182  are present such that winding conductors can be inserted into the winding slots. Cooling channels are similar to those described under  FIGS. 4 and 5 . 
       FIG. 6 b    shows the stator core section in the case where stator core  142  is molded over the winding. Tooth gaps are typically absent and are replaced with bridge elements  183 . With tooth slots bridged by core material, tooth tip losses are reduced thus providing both thermal and efficiency benefits. On the down-side, magnetic flux linkage between the stator and rotor may be reduced because of these tooth bridges—which, in turn, may reduce peak torque capability. Cooling channels are similar to those described in connection with  FIGS. 4 and 5 . 
       FIG. 7  shows a complete pre-formed winding  150  prior to over-mold of the core. Winding elements shown include active portions  152 , end turn portions  154 , and terminals  156 . It should be noted that stators for induction and brushless motors are typically quite similar. As such, stators described in this disclosure are applicable to either machine type. 
       FIG. 8  shows a complete pre-formed rotor cage  164  prior to over-mold of the core material. Cage elements include active rotor bars  166 , end rings  168  and rotor manifolds  170 . In some embodiments, the cage (combination of rotor bars and end rings) is assembled along with rotor manifolds  170 . With this construction approach, the rotor investment mold (not shown) may be incorporated within the cage during assembly. After the core material is over-molded, the investment mold is then removed—either by melting or by chemical dissolution. 
       FIG. 9  shows an exploded view of an axial gap stator  184  which consists of molded ferromagnetic core  142 , winding  150 , manifold housing  186 , inlet  190 , and outlet  192 . In turn, core  142  consists of a back iron portion  144  (located at the bottom) and tooth portions  146  (located at the top) which, in turn, contain winding slots  147 . Likewise, winding  150  comprises active winding elements  152  and end turn elements  154 . 
     Inlet  190  introduces coolant flow into a first outer manifold cavity  194  from where it flows to radially directed inlet channels  112  and then on to azimuthal capillary channels  116 . Coolant is then received by outlet channels  114  and directed to inner manifold cavity  199  where it then flows to a second set of inlet channels  112 , then on to a second set of capillary channels  116  and finally is received by a second set of outlet channels  114  from where is then passed on to a second outer manifold cavity  196  and finally to outlet  192 . Partitions  191  isolate outer manifold cavities  194  and  196  such that all flow is forced to take the path described above. 
     In some embodiments, winding  150  is pre-formed and core  142  is molded over the winding. Alternatively, a core, which includes slot gaps, may be pre-formed such that the winding can be inserted in winding slots using conventional means. 
       FIG. 10  is a half section of an axial gap stator  184  which consists of molded ferromagnetic core  142  and winding  150 . In turn, core  142  consists of a back iron portion  144  and a tooth portion  146 . The back iron portion includes internal cooling channels consisting of inlet channels  112 , outlet channels  114  and interconnecting capillary channels  116 . 
     Core  142  is held in place by manifold housing  186 . Inlet and outlet flow is directed and constrained by cavities formed by manifold housing  186  and flow director  188 . Upper cavity  195  receives coolant flow from inlet  190  and distributes coolant flow to radial inlet channels  112 . Likewise lower cavity  196  receives coolant flow from outlet channels  114  and delivers this flow to outlet  192 . 
     The upper left detail shows a section of core  142  where inlet channels  112 , outlet channels  114  and capillary channels  116  are seen; arrows represent coolant flow. 
     Winding end turns  154  may be in thermal contact with manifold housing  186  such that a portion of the heat generated within the end turn is transferred to the manifold housing. 
       FIG. 11  is an exploded view of a magnetic core  142  which can be used for inductors or transformers. As with the previously described items, the core is molded from a ferromagnetic material which is molded over investment mold  104  such that inlet channels  112 , outlet channels  114  and capillary channels  116  are formed. In turn, investment mold(s)  104  include inlet mold elements  106 , outlet mold elements  108  and capillary mold elements  110 . Heat produced within an associated winding is transferred primarily to the core. The winding may be pressure potted with a thermally conductive resin to enhance thermal conductivity within the winding and between the mating surfaces of the winding and the core. 
       FIG. 12  is a sectional view of the capillary-cooled magnetic core  142  shown in  FIG. 11 . Inlet channel  112 , outlet channel  114  and capillary channels  116  are visible at the plane of the section. Housing manifold  186  serves to distribute flow received by inlet  190  to inlet channels  112 . Needed fluid sealing is provided by O-ring  200 . 
       FIG. 13 a    shows investment mold  104  as used in connection with the center prong for core elements shown in  FIGS. 11 and 12 . Each mold element  104  includes inlet mold element  106 , outlet mold element  108 , and multiple capillary mold elements  110 . 
       FIG. 13 b    likewise shows investment mold  104  as used in connection with the axial gap stator core elements shown in  FIGS. 9 and 10 . Each mold element includes inlet mold elements  106 , outlet mold elements  108 , and multiple capillary mold elements  110 . 
       FIG. 13 c    shows investment mold  104  used in connection with a tooth-cooled radial gap electric machine stator. The mold consists of multiple inlet mold elements  106 , outlet mold element  108 , radial capillary mold elements  204 , and axial capillary elements  110 . The resulting mold inlet and outlet mold channels are interconnected by a series combination of radial and axial capillary channels which are formed respectively by radial capillary mold elements  204  and axial capillary mold elements  110 . 
     The resulting coolant channels provided by investment mold  104  provide high contact surface area combined with short flow length. Tooth tips are efficiently cooled as associated heat flow lengths are quite short. This in turn provides for a low thermal impedance combined with low head loss. 
       FIG. 13 d    shows investment mold  104  used in connection with a tooth-cooled axial gap electric machine stator. The mold consists of multiple inlet mold elements  106  and outlet mold element  108 . The resulting mold inlet and outlet mold channels are interconnected by a series combination of axial capillary channels  211  and radial capillary channels  213  which are formed respectively by axial capillary mold elements  207  and radial capillary mold elements  209 . 
     The resulting coolant channels provided by investment mold  104  provide high contact surface area combined with short flow length. Tooth tips are efficiently cooled as associated heat flow lengths are quite short. This in turn provides for a low thermal impedance combined with low head loss. 
       FIG. 14  shows a radial gap electric machine stator where surface grooves are molded into the core element to provide cooling channels for coolant. Specifically, electric machine stator  140  comprises a molded ferromagnetic core  142  and winding  150 . In turn, molded ferromagnetic core  142  includes a back iron portion  144  and a core tooth portion  146 . The outer surface of molded core  142  includes inlet grooves  126 , outlet grooves  128 , and capillary grooves  130 ; capillary grooves  130  provide flow channels between adjacent inlet and outlet grooves. Enclosure  124  fits tightly over core  142  such that inlet, outlet and capillary grooves become enclosed channels. 
     Winding  150  consists of active winding elements  152  and end turn elements  154 . Active winding elements  152  fit between adjacent core teeth. The winding is shown as an “open delta”—wherein no neutral splice is used; alternative winding arrangements are possible. Winding conductors terminate with terminal pins  156 . Manifolds used to direct inlet flow into inlet channels and to collect coolant from outlet channels are not shown. 
       FIG. 15  is a cut-away view of an axial gap machine stator where surface grooves are molded into the core element to provide cooling channels. Specifically, electric machine stator  140  comprises a molded ferromagnetic core  142  and winding  150 . In turn, molded ferromagnetic core  142  includes a back iron portion  144  and a core tooth portion  146 . The outer surface of molded core  142  includes inlet grooves  126 , outlet grooves  128 , and capillary grooves  130 ; capillary grooves  130  provide flow channels between adjacent inlet and outlet grooves. Both the inlet and outlet grooves are blocked at the I.D. The core and winding are held in place by manifold housing  186 . Annular flow director  188  in combination with manifold housing  186  serves to create two cavities within manifold—upper manifold cavity  194  and lower manifold cavity  196 . Flow director  188  is shaped such that flow received from inlet  190  is directed to inlet channels  112  formed by inlet grooves  126 . Likewise, flow director  188  also serves to direct flow received from outlet channels  114  formed by grooves  128  to outlet  192 . 
     In some embodiments, the number of capillary channels is large compared with the number of inlet or outlet channels such that the wall area associated with the capillary channels is large compared with that of the inlet or outer channels. Likewise, the thickness of the capillary channels is relatively small compared with either the inlet or outlet channels. Since heat transfer is proportionate to heat flow area divided by heat flow distance, it follows that the majority of heat transfer is due to the capillary channels. In, some such embodiments the majority of head loss is due to laminar viscous effects caused by coolant flow through the capillary channels. Since head loss is proportionate to the length of the capillary channels, it is desirable to maintain short capillary lengths. This in turn means that the number of inlet and outlet channels should be as large as practically possible. 
       FIG. 16  shows a radial gap electric machine stator  140  which corresponds to mold elements shown in  FIG. 13 c   . The stator is composed of molded ferromagnetic core  142  and winding  150 . In turn, molded ferromagnetic core  142  is composed of back iron portion  144  and tooth portion  146 . Likewise, winding  150  is composed of active winding elements  152  and end turn elements  154 . 
     Inlet channels  112  transport coolant from a manifold (not shown) to multiple feeder channels  204 , located within stator teeth (not shown) which then radially direct coolant to capillary channels  116  which are oriented axially within tooth tips—from where coolant then flows to a second set of feeder channels  206  and on to outlet channels  114 —where it is then collected by a manifold (not shown). Heat transfer between the core and coolant is primarily due to feeders  204  and capillary channels  116 . 
       FIG. 17  is an exploded cut-away view of an axial gap electric machine stator  140  fabricated using mold elements shown in  FIG. 13 d   . The stator is composed of molded ferromagnetic core  142  and winding  150 . In turn, molded ferromagnetic core  142  is composed of back iron portion  144  and tooth portion  146 . Likewise, winding  150  is composed of active winding elements  152  and end turn elements  154 . 
     Inlet channels  112  transport coolant from a first manifold (not shown) to multiple feeder channels  206 , located within stator teeth (not shown) which then axially direct coolant to capillary channels  116  which are radially oriented within tooth tips. Coolant then collected by a second set of feeder channels  204  and passed on to outlet channels  114 —where it is then collected by a second manifold (not shown). Heat transfer between the core and coolant is primarily due to feeders  204  and capillary channels  116 . 
     In some embodiments the capillary channels  116  have a cross section that is rectangular or oblong with a smaller dimension selected to be sufficiently small to provide good heat transfer without excessive head loss. For example, each of the capillary channels  116  may have a smaller dimension between 0.010 inches and 0.050 inches (e.g., a smaller dimension of 0.025 inches) and the the capillary channels  116  may be spaced apart by between 0.050 inches and 0.200 inches (e.g., by 0.100 inches). Each inlet channel  112  may have a cross sectional shape and size that allows fluid to flow to a plurality of capillary channels  116  without excessive head loss, e.g., each channel may be approximately square, or round, with a cross sectional dimension (e.g., diameter, or square side length) of between 0.100 inches and 0.200 inches (e.g., a cross sectional dimension of 0.125 inches). The outlet channels  114  may have similar shapes and sizes.