Abstract:
Performance of an electric motor can be improved if coolant is provided to the coils of the stator. An electric motor is disclosed that has a shaft onto which the rotor is secured. The motor has a stator that is mounted on bearings that are mounted on the shaft. The stator has a plurality of coils. A coolant guide is provided that fills voids between the groups of windings. The coolant guide has a plurality of fingers with the fingers arranged between adjacent pairs of coils. The coolant guide has internal passages to accept pressurized coolant and outlet holes to spray coolant onto the coils. In other embodiments, the fingers guide coolant to reach all coils under the force of gravity.

Description:
FIELD 
     The present disclosure relates generally to an apparatus for providing coolant onto stator coils of an electric machine and to a method for manufacturing such apparatus. 
     BACKGROUND 
     The performance of an electric machine or electric motor can be increased if the components of the motor are prevented from overheating. It is known to provide a liquid to coils of the stator to remove energy. Some motors are flooded with a liquid coolant. However, with high-speed motors, the coolant increases the friction of the motor. It is desirable to provide the liquid coolant predominantly to the coils and to prevent coolant from contacting the rotor. Even if only the coils of the stator were flooded and the coolant kept off the rotor, to effectively cool the coils, it is more effective if flow to the coils is properly directed so that each coil receives sufficient coolant so that there are no hot spots. 
     SUMMARY 
     To promote more even cooling of the coils, a number of embodiments in which the coolant is distributed to the coils while avoiding coolant from contacting the rotor are disclosed. 
     To solve at least one problem in the prior art, an electric motor is disclosed. The electric motor has a housing, a shaft, and two bearings mounted between the shaft and the housing. A rotor is secured to the shaft between the bearings. The motor further includes a stator that is mounted in the housing and slid over the rotor. The stator has a plurality of coils. A coolant guide is provided that has a plurality of fingers arranged between adjacent pairs of the coils. 
     In some embodiments, the coolant guide has: a coolant inlet to receive pressurized coolant and coolant passages within the coolant guide which are in fluidic communication with the coolant inlet. Coolant passages extend into the fingers. Each finger of the coolant guide has a plurality of outlet holes arranged along at least a portion of the length of the fingers and the outlet holes are fluidly coupled to the coolant passages. 
     In other embodiments, the coolant guide has a first annular end cap, a second annular end cap, and a tubular shield having a first end and a second end with the first end coupled to the first annular end cap and the second end coupled to the second annular end cap. The coolant guide also has a coolant inlet at a position located higher than a first of the plurality of coils, a first coil. 
     In some embodiments, a surface of the tubular shield adjacent to the rotor has a plurality of axial grooves. 
     The stator further includes a back iron surrounding the plurality of coils and the back iron substantially abuts the first and second annular end caps. A drain opening is defined in one of the annular end caps. 
     In other embodiments, the coolant inlet is defined in the first annular end cap. At least a portion of the coolant supplied to the coolant inlet contacts a first of the plurality of coils, the first coil. Fingers adjacent to the first coil are a first and a second of the plurality of fingers, the first and second fingers. The first and second fingers are coupled to the first annular end cap. There is a first gap between the first finger and the second annular end cap. There is a second gap between the first finger and the second annular end cap. A first portion of coolant that is supplied to the first coil moves along the first finger toward the first gap and contacts a second of the plurality of coils, the second coil. A second portion of coolant that is supplied to the first coil moves along the second finger toward the second gap onto a third of the plurality of coils, the third coil. 
     In embodiments with more coils, the fingers adjacent the second coil are the first finger and a third of the plurality of fingers, the third finger. The fingers adjacent the third coil are the second finger and a fourth of the plurality of fingers, the fourth finger. The third and fourth fingers are coupled to the second annular end cap. There is a third gap between the third finger and the first annular end cap. There is a fourth gap between the fourth finger and the first annular end cap. At least a portion of the coolant that leaves the second coil contacts the third finger. A portion of coolant that is supplied to the second coil moves along the third finger toward the third gap and contacts a fourth of the plurality of coils, the fourth coil. A portion of coolant that is supplied to the third coil moves along the fourth finger toward the fourth gap and contacts a fifth of the plurality of coils, the fifth coil. 
     In yet other embodiments, a first end of the fingers is coupled to the first annular end cap and a second end of the fingers is coupled to the second annular end cap and the fingers have a plurality of holes defined along a portion of the length of the fingers. At least a portion of coolant supplied to the coolant inlet contacts a first of the plurality of coils. Fingers adjacent to the first coil are a first and a second of the plurality of fingers, the first and second fingers. A first portion of coolant that passes through holes in the first finger to drip onto a second of the plurality of coils, the second coil. A second portion of coolant passes through holes in the second finger to drip onto a third of the plurality of coils, the third coil. 
     In other embodiments, a first portion of the plurality of fingers extend outwardly from the first annular end cap and a second portion of the plurality of fingers extend outwardly from the second annular end. A first of the first portion of the plurality of fingers and a first of the second portion of the plurality of fingers extend between a first and a second of the plurality of coils with a gap between ends of the first of the first portion of the plurality of fingers and the first of the second portion of the plurality of fingers. 
     Also disclosed is an electronically controlled turbocharger that has a shaft having a turbine wheel affixed onto a first end of the shaft and a compressor wheel affixed onto a second end of the shaft; a rotor secured to the shaft and located between the turbine wheel and the compressor wheel; bearings mounted on the shaft, a first bearing located on the shaft between the turbine and the rotor; and a second bearing located on the shaft between the compressor wheel and the turbine wheel; a housing mounted onto the bearings; a stator supported in the housing; and a coolant guide having a plurality of fingers. The stator has a central opening. The stator is disposed over the rotor. The stator has a plurality of coils. The fingers of the coolant guide are arranged between adjacent coils. 
     The stator also includes a back iron. The coolant guide further includes a first annular end cap abutting a first end of the back iron and a second annular end cap abutting a second end of the back iron. 
     In some embodiments, the coolant guide has a coolant inlet to receive pressurized coolant and the coolant inlet is fluidly coupled to the coolant passages. The coolant passages extend into the fingers with an inlet to the coolant passage within the finger located at a first end of each finger. The fingers of the coolant guide have a plurality of outlet holes arranged along a portion of the length of the fingers. The outlet holes are fluidly coupled to the coolant passages. 
     In embodiments without a tubular shield, the stator further includes: a substantially-cylindrical back iron, a plurality of teeth extending from an inner surface of the back iron, and a bobbin slid over each tooth onto which the coils are wrapped. The bobbin has an inner plate, an outer plate, and a middle section extending between the bottom and top plates. Each of the inner plate, the outer plate, and the middle section define an opening along an axis of the bobbin to permit installation of the bobbins onto the teeth. Coils are wound around the middle sections of the bobbins. The outer plates abut the inner surface of the back iron. A material is placed between adjacent inner plates to substantially prevent flow of coolant through adjacent inner plates. 
     In some embodiments, a coolant inlet is defined in the first annular end cap. At least a portion of the coolant supplied to the coolant inlet drops onto a first of the plurality of coils, the first coil. Fingers adjacent to the first coil are a first and a second of the plurality of fingers, the first and second fingers. The first and second fingers are coupled to the first annular end cap. There is a first gap between the first finger and the second annular end cap and a second gap between the second finger and the second annular end cap. A first portion of coolant that is supplied to the first coil moves along the first finger toward the first gap and contacts a second of the plurality of coils, the second coil. A second portion of coolant that is supplied to the first coil moves along the second finger toward the second gap and contacts a third of the plurality of coils, the third coil. 
     The fingers adjacent the second coil are the first finger and a third of the plurality of fingers, the third finger. The fingers adjacent the third coil are the second finger and a fourth of the plurality of fingers, the fourth finger. The third and fourth fingers are coupled to the second annular end cap. There is a third gap between the third finger and the first annular end cap and a fourth gap between the fourth finger and the first annular end cap. 
     In some embodiments, a first end of the fingers is coupled to the first annular end cap and a second end of the fingers is coupled to the second annular end cap and the fingers have a plurality of holes defined along a portion of the length of the fingers. At least a portion of coolant supplied to the coolant inlet drops onto a first of the plurality of coils. Fingers adjacent to the first coil are a first and a second of the plurality of fingers, the first and second fingers. A first portion of coolant that passes through holes in the first finger drips onto a second of the plurality of coils, the second coil. A second portion of coolant that passes through holes in the second finger drips onto a third of the plurality of coils, the third coil. 
     In some embodiments, the coolant guide also has a tubular shield with a first end of the tubular shield coupled to the first annular end cap and a second end of the tubular shield coupled to the second annular end cap. 
     Also disclosed is a method to assemble an electric motor in which fingers of a coolant guide are slid between adjacent coils of a stator of the electric motor. The coolant guide includes an annular cap to which a least a portion of the fingers are coupled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional representation of an electronically-controlled turbocharger (ECT) that includes a high-speed electric motor; 
         FIG. 2  is an exploded view of a stator and an embodiment of an coolant guide; 
         FIG. 3  is a view of the stator and coolant guide of  FIG. 2  as assembled; 
         FIG. 4  is a cross-sectional illustration of the stator and coolant guide of  FIG. 2 ; 
         FIG. 5  shows a detail of a portion of the back iron, a tooth coupled to the back iron, and a bobbin; 
         FIG. 6  is an exploded view of a stator and an embodiment of an coolant guide; 
         FIG. 7  is an illustration of the stator and coolant guide of  FIG. 6  as cut in half and flattened; 
         FIG. 8  is a cross-sectional illustration of the stator and coolant guide of  FIG. 6 ; 
         FIG. 9  is an exploded view of a stator and an embodiment of a coolant guide; 
         FIG. 10  is a cross-sectional illustration of the stator and coolant guide of  FIG. 9 ; 
         FIG. 11  is a cross-sectional illustration of a stator and coolant guide using an adhesive or potting material between adjacent bobbins; 
         FIG. 12  is an exploded vies of a stator and an embodiment of a coolant guide; and 
         FIG. 13  is a flowchart showing processes that may be undertaken to assemble an electric machine having a coolant shield. 
     
    
    
     DETAILED DESCRIPTION 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
     In the present disclosure, an electric motor is described. However, the electric motor may be alternatively called an electric machine. An electric machine can be operated as an electric motor in which electric energy is supplied to cause the electric machine to rotate or can be operated as a generator in which electric energy is extracted from the rotating electric machine. 
     The present disclosure can be applied to any electric machine. It is particularly helpful for high-speed motors. One such application is an electronically-controlled turbocharger (ECT) in which rotational speeds can be as high as 350,000 rpm in some applications. An ECT  40  is shown in cross section of an ECT  40  in  FIG. 1 . The ECT includes a compressor section  50 , an electric machine section  52 , and a turbine section  54 . Coupled to a common shaft  60  are: a compressor wheel  62  fixed axially by nut  64 , a rotor  66  of the electric machine, and a turbine wheel  68  (welded). Alternatively, turbine wheel  68  may be threaded onto shaft  60 . 
     The embodiment in  FIG. 1  includes four housing sections that are coupled together: a compressor housing section  70 , two electric machine housing sections  72  and  73 , and a turbine housing section  74 . (In embodiments without a turbomachine, i.e., just a high-speed electric machine, the housing for the motor may include fewer sections.) Rotating shaft  60  is supported in the housings by bearings  76  and  78 . A thrust bearing  58  is provided between the compressor and the housing. An electrical connector  56 , which couples with high power electronics (not shown), exits ECT  40 . 
     In the embodiment in  FIG. 1 , lubricant is used as the coolant for the electric motor. Thus, the lubrication system and the cooling system are integrated. Or, the two systems may be separated, which allows different fluids to be used in the systems. 
     Pressurized lubricant, which is engine oil in one embodiment, is provided to ECT  40  through inlet  80 . Lubricant from inlet  80  fills manifold  82 . Manifold  82  is fluidly coupled to oil passages  84  and  86  with passage  84  providing lubricant to bearing  76  and passage  86  providing lubricant to bearing  78 . A plug  85  is provided at the outside end of passage  84  to seal off the drilling to form passage  84 .  FIG. 1  shows one embodiment of an ECT, a non-limiting application that uses a high-speed electric motor. 
     In  FIG. 2 , a stator and cooling guide assembly  100  is shown in an exploded view. A stator  102  has coils  106 , conductors  104 , and a back iron  108 . A tubular shield  110  slides into a central opening in stator  102 . Shield  110  is provided to prevent coolant from accessing the rotor (not shown). A first end cap  112  has an opening  114  to provide an exit point for conductors  104  of stator  102  when assembled. An annular end cap  112  couples to tubular shield  110  via a tubular portion  116  of end cap  112  that protrudes from the central opening of end cap  112 . End cap  112  has a hole  118  for draining coolant. Tubular shield  110  is also coupled to another annular end cap  120  at a tubular portion  124 . End cap  120  has an inlet opening  122  that can be used to provide coolant to stator  102 . End cap  120  also has multiple finger supports  126  on the side of end cap  120  that faces stator  102 . 
     Stator  102  has six coils  106 , not all of which can be separately identified in  FIG. 2 . There are spaces between adjacent coils. Fingers  130  are inserted into finger supports  126  and then inserted in the spaces between adjacent coils. An edge  132  of fingers  130  sits against the outer surface of tubular shield  110 . An end  134  of fingers  130  that is opposite the end inserted into finger supports  126  of end cap  112 . In other embodiments, end  134  is pressed against end cap  112  when assembled and end  134  is glued to end cap  132 . Fingers  130  have a plurality of holes  136 . Coolant is provided at an upper side of stator  102 . Coolant drips through holes  136  to provide coolant to coils that are below the top coil. The number, size, and location of holes  136  can be adjusted depending on the location of the finger within the stator to distribute coolant as desired. Depending on the features of the coolant guide and input flow rate, the coils may be substantially flooded with coolant or coolant provided to the coils may quickly pass through to the cavity of the next lower coil. In either case, the coolant is directed in a manner in which all coils are provided coolant. In systems in which the stator is flooded, but without guiding, the coils are less uniformly cooled because there is no established path to ensure that all coils have coolant flow. 
     The term, drip, herein is not intended to be limited to individual drips, but instead also refers to streams of coolant. 
     The components shown in  FIG. 2 , other than those associated with the stator, are collectively called a coolant guide. That is annular end caps  112  and  120 , tubular shield  110 , fingers  130 , and possibly other elements, depending on the embodiment, make up a coolant guide. 
     An assembled version of stator  102  and the coolant guide of  FIG. 2  is shown in  FIG. 3 . A cross section through the stator and coolant guide of  FIG. 2  is illustrated in  FIG. 4 . The cross section is through holes  136  in fingers  130 . Back iron  108  has teeth extending inwardly (not visible in  FIG. 4 ) over which bobbins  200  are installed. Coils  202  are wrapped around bobbins  200 . The cross section in  FIG. 4  does not pass through a coolant inlet or outlet so those are not visible. Coolant  210  is provided to the stator and can be seen pooling in lower areas in each of the spaces between fingers  130 . Also, a few drips  212  are shown in the illustration. 
     A portion of back iron  108  and of bobbin  200  is shown in cross section in  FIG. 5 . Bobbin  200  has an outer plate  204 , a middle section  206 , and an inner plate  208 . Along a central axis  218  of bobbin  200  is an opening  216  so that bobbin  200  can be slid over a tooth  220  that extends from back iron  108  (inwardly in relation to the back iron). Such an embodiment simplifies production as coils can be wound around the bobbins prior to sliding the bobbins over the teeth connected to the back iron. In alternative embodiments, the coils are wound directly onto the teeth, which is difficult within the interior of the stator. 
     An alternative embodiment of a coolant guide is illustrated in  FIG. 6 . An annular end cap  162  is coupled to a tubular shield  190  at edge  166 . An opening  164  accommodates conductors  104 . A drain hole  163  is provided in end cap  162 . Drain hole  163  can be located higher or lower and can be bigger or smaller depending on how much flooding is desired. A second end cap  170  has an opening  172  to serve as a coolant inlet. A lip  174  couples to tubular shield  190 . End cap  162  has two fingers  180  extending from the inside surface of end cap  162 . Fingers  180  extending from end cap  162  are substantially diametrically opposed. The coolant guide also has an annular end cap  170  with four fingers  180  extending from the inner surface. Two fingers near the top form an angle of about 60 degrees and the two fingers near the bottom also form an angle of 60 degrees. Fingers  180  coupled to end cap  162  do not extend all the way to end cap  170  (when assembled). Similarly, fingers  180  coupled to end cap  170  do not extend all the way to end cap  162 . By doing so, coolant is directed through a labyrinth-like structure within the coolant guide. In an alternative embodiment, fingers  180  also have holes (like the embodiment in  FIG. 2 ) so that the coolant drips through fingers  180  and moves through the labyrinth-like path. Tubular shield  190  has a plurality of axial grooves  192  that provide an egress route for coolant that finds its way to the rotor (rotor not shown in  FIG. 3 ; but when the motor is completely assembled the rotor is inside tubular shield  190 ). It has been found that at some operating conditions coolant finds its way to the rotor. Grooves  192  provide an exit path for the coolant. Tubular shield  110  without grooves  192  or tubular shield  190  with grooves  192  may be used in any embodiment depending on the application. 
     In  FIG. 7 , an illustration of a portion of the stator and a portion of the coolant guide of  FIG. 6  is shown as cut in half through a central axis of the stator and opened up so that the back iron is flat. The tubular shield is removed in this illustration. From this view, a half of an inner plate  208   a  of bobbin  200   a  (not shown) about which an upper coil is wound, a half of an inner plate  208   d  of bobbin  200   d  (not shown) about which an upper coil is wound, and two middle inner plates  208   b ,  208   c  of bobbins  200   b ,  200   c  (not shown) are visible. As there is an opening defined in the bobbins (element  216  in  FIG. 5 ), ends of teeth  220   a ,  220   b ,  220   c , and  220   d  are also visible. 
     Fingers  180   a  and  180   c  are coupled to end cap  170 . Finger  180   b  is coupled to end cap  162 . End cap  170  has a coolant inlet  172  defined at an upper edge. Coolant is provided to the top coil, which is associated with top plate  208   a . Coolant builds up in the voids and travels from right to left with respect to the illustration to exit at the left hand side of finger  180   a  where there is a gap  222   a . Drips of coolant  232  collect at that bottom of the region associated with top plate  208   b . Coolant  230  travels from left to right to gap  222   b  where it drips in the region associated with top plate  208   c . Coolant then travels from right to left to gap  222   c . Coolant  230  exits at drain  168 . 
     A cross section of the coolant guide and stator of  FIG. 6  is shown in  FIG. 8 . Flow out of the page is shown by plusses  240  and flow into the page is shown by Xes  242 . Flow surrounding the upper coil is moving out of the page. Coolant flows in the regions association with the adjacent coils  200   b  and  200   c . In this way, the coolant flows through a labyrinth so that coolant flows by each of the coils. 
     Another embodiment of a coolant guide and stator are shown in  FIGS. 9 and 10 . In  FIG. 9 , an assembly  248  of the stator and the coolant guide is shown exploded. Annular end caps  250  and  251  on each have six fingers  252  protruding from each end cap  250  and  251  toward stator  102 . The assembled stator and coolant guide is shown in cross section in  FIG. 10 . Fingers  252  from the two end caps  250  and  251  do not meet in the middle, but instead leave a gap  254  for coolant to trickle downward to lower coils. In  FIG. 10 , a cross-sectional view showing gap  254  between fingers  252  is shown. 
     The coolant guide embodiments in  FIGS. 2, 6, and 9  all show a tubular shield. In  FIG. 11 , there is no tubular shield. Instead an adhesive, potting, or other sealant  260  is forced into the region between adjacent inner plates  216  of bobbins  200  and ends of fingers  270 . In the embodiment shown in  FIG. 11 , a groove  262  remains. Groove  262  may be helpful in providing an axial egress route for coolant that inadvertently accesses the rotor area. 
     The embodiments described above use gravity feed within the stator to distribute the coolant to the coils. Alternatively, the coolant guide may have internal passages that are pressurized by having internal passages within at least one of the end caps fluidly coupled to the pressurized coolant. One embodiment of such a coolant guide and stator  102  is shown in an exploded view in  FIG. 12 . Annular end caps  300  have fingers  302  that extend from end caps  300  into voids between coils in stator  102 . Annular end cap  300  has a ring portion  306  which has an internal volume (not visible). Coolant passages (not visible) which are fluidly coupled to the internal volume within ring portion  306  are provided within fingers  302 . The coolant passages are in fluidic communication with the internal volume in annular portion  306 . Fingers  302  have one or more holes  304  along their length. Coolant within fingers  302  is pressurized and sprays onto coils  106  from holes  304 . In one embodiment, annular end caps  306  are identical and each are provided pressurized coolant to be sprayed onto the coils. In another embodiment, one of the annular end caps has fingers that extend substantially through the entire gap between adjacent fingers. The other annular end cap has no fingers. In such an embodiment, pressurized coolant is only provided to the annular end cap with fingers. In yet another embodiment, each annular end cap has three fingers with coolant provided to one of the end caps and flow going back and forth between the end caps in a labyrinthine manner, e.g., from a cavity in the first end cap through a first finger with some of the flow spraying on a first coil with most of the flow going to a passage in the second end cap that feeds a second finger. Note that the pressurized embodiment discussed immediately above does not include elements  308 . 
     In yet another embodiment consistent with  FIG. 12 , coolant is provided to a coolant guide  300  by gravity feed on at least one of the fingers  302 . Coolant collects on the cupped portion of fingers  302 . An opening  308  allows oil to flow through finger  302  through fingers  302  through holes  304 . There may be two passages through finger  302 , each at openings  308  and outlets at two or more holes  304 , on different surfaces of finger  302 . In this embodiment, coolant is provided to coils  106  via gravity feed. 
     Elements of the coolant guides may be coupled via bolts, adhesive, friction welding, or any suitable coupler. The embodiments discussed above have six coils. However, this is a non-limiting example. Electric machines with other numbers of coils are within the scope of the present disclosure. 
     A process by which the coolant guide is assembled to the stator is shown in  FIG. 13 . The stator is built up in block  550 . As the present disclosure is directed toward the coolant guide included in the stator assembly, details in assembling the stator are not included here. In block  552 , fingers are affixed onto a first annular end cap. In block  554 , fingers, if any, are affixed to a second annular cap. In some embodiments, the fingers and the end cap are integrally formed. The fingers of the first annular end cap are slid inside the stator in block  556 . The tubular shield is slid into the stator in block  558 . In embodiments without a tubular shield, the potting or adhesive is instead applied to the gaps between adjacent bobbins instead. In block  560 , the first annular end cap is coupled to a first end of a tubular shield. In block  562 , fingers of the second annular end cap are slid into voids between adjacent coils. In embodiments with no fingers on the second end cap, the second annular end cap is simply placed onto the stator. The second annular end cap is affixed to a second end of the tubular shield in  564 . In embodiments where the fingers are attached at both ends is shown in block  566 . In block  570  the rotor is built up and then affixed to the shaft in block  572 . The stator is slid over the rotor in block  580 . 
     While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.