Patent Publication Number: US-10332822-B2

Title: Pedestal surface for MOSFET module

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/876,674, filed Oct. 6, 2015, now U.S. Pat. No. 10,074,592, issued Sep. 11, 2018, which claims priority to U.S. Provisional Patent Application Ser. No. 62/061,633, filed Oct. 8, 2014, both of which are hereby incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Vehicles, such as those employing an internal combustion engine and/or having a hybrid drive train that includes an electric machine, often employ what are commonly referred to as alternators. 
     Vehicle alternators are electric machines that selectively function as a generator or an electric motor. In conventional internal combustion engine drive vehicles, alternators are employed as an electric motor to provide torque to the engine when starting the engine. After the engine has been started, the alternator can function as a generator to generate current to recharge the vehicle battery. In hybrid vehicles, the alternator may be used as an electric motor to additionally provide torque for driving the vehicle. 
     The electrical circuitry employed with alternators can generate significant heat that must be dissipated. As modern vehicles place greater demands on alternators, the demands on the alternator circuitry also increases. Improvements which address the increased demands on electric machines such as those which are used as vehicle alternators are desirable. 
     SUMMARY 
     The present invention provides an electronic package for an electric machine wherein the electronic packages has power modules mounted on pedestal mounting surfaces that enhance the functionality of the electric machine. 
     The invention comprises, in one form thereof, an electronic package adapted for connection to a rear frame member of an electric machine. The electronic package includes a cooling tower having a metallic wall extending about a cooling tower central axis to define a radially outer wall surface. The radially outer wall surface is provided with a plurality of discrete, radially outwardly projecting pedestals at circumferentially distributed locations about the cooling tower central axis. Each pedestal defines the periphery of a planar mounting surface. The respective mounting surface of each pedestal is parallel with the cooling tower central axis wherein the radial distance between the cooling tower central axis and the radially outer wall surface is greater within the periphery of each pedestal mounting surface than outside the periphery of the respective pedestal mounting surface. A plurality of power modules are mounted to the pedestal mounting surfaces. Each of the power modules includes a planar metallic base defining a module mounting surface and an opposing base interior surface, the module mounting surface and the respective pedestal mounting surface in mutual surface-to-surface contact whereby the power module base and the cooling tower are in conductive thermal communication with each other. MOSFET power electronics devices of each power module are attached to and in conductive thermal communication with the base interior surface. Each of the power modules also includes a metallic cover plate is in spaced superposition relative to the base interior surface that is electrically isolated from the MOSFET power devices. A dielectric housing member defining a module housing wall surrounds the MOSFET power electronics devices and is disposed between the base and the cover plate and an electrical connection terminal communicating with the power electronics devices is disposed outside the periphery of the base module mounting surface of each power module. 
     In some embodiments of the electronic package, the cover plate is coextensive with an imaginary plane that is substantially parallel with the base interior surface of the respective power module. 
     In some embodiments of the electronic package, the module housing wall extends in a radial direction between the base and the cover plate of the respective power module. 
     In some embodiments of the electronic package, the cooling tower is at ground potential. 
     In some embodiments of the electronic package, the peripheries of the contacting module mounting surface and the pedestal mounting surface are of substantially identical shape and size. 
     In some embodiments of the electronic package, each power module comprises an electrically insulating layer intermediate the MOSFET power devices and base interior surface thereof with the MOSFET power devices attached to and in conductive thermal communication with the base interior surface through the intermediate electrically insulating layer. 
     In some embodiments of the electronic package, the module housing wall extends along the periphery of the base. 
     In some embodiments of the electronic package, a portion of the module housing member is disposed outside the periphery of the pedestal mounting surface and is in spaced superposition relative to the radially outer wall surface. A gutter is thereby defined between the superposed radially outer wall surface and the module housing member portion along which splash and splash-borne contaminants are guided away from the power module whereby separation distances are provided across which conductive traces of the contaminants are less likely to build up and result in current leakage from the module. 
     In some embodiments of the electronic package, the module housing member portion extends beyond the periphery of the pedestal mounting surface in a plane parallel with the base mounting surface. In such an embodiment, the pedestal may define a plurality of ledges extending between the respective power module and the radially outer wall surface that surrounds the pedestal. For example, the gutter may have a floor defined by a ledge. 
     In some embodiments of the electronic package, the entirety of each pedestal mounting surface is radially distanced from the radially outer wall surface outside the periphery of the pedestal mounting surface whereby radially projecting sides of the pedestal provide electrical clearance between the electrical connection terminals and the radially outer wall surface. 
     In some embodiments of the electronic package, the pedestals are equiangularly distributed about the radially outer wall surface. 
     In some embodiments of the electronic package, the pedestals are equidistance along the cooling tower central axis from an imaginary plane perpendicular to the cooling tower central axis. 
     In some embodiments of the electronic package, the metallic wall defines a radially inner wall surface, and the mass per unit area of the metallic wall in a radial direction between the radially inner wall surface and the radially outer wall surface is greater within the periphery of a pedestal mounting surface than outside of the periphery of the pedestal mounting surface whereby the thermal mass of the metallic wall is relatively greater in close proximity to the power modules. 
     In some embodiments of the electronic package, the metallic wall defines a radially inner wall surface and the thickness of the metallic wall between the radially inner wall surface and the radially outer wall surface is greater within the periphery of a pedestal mounting surface than outside the periphery of the pedestal mounting surface. 
     In some embodiments of the electronic package, each pedestal mounting surface is oriented tangentially relative to an imaginary circle concentric with and oriented perpendicularly relative to the cooling tower central axis. 
     In some embodiments of the electronic package, the radial distances from the cooling tower central axis to the radially outer wall surface are greatest at the pedestal locations whereby machining to flatten the pedestal mounting surfaces of a cooling tower&#39;s entire plurality of pedestals in one operation is facilitated. 
     In some embodiments of the electronic package, the radial distances from the cooling tower central axis to the radially outer wall surface are greatest along circumferentially opposite edges of the pedestal mounting surfaces. 
     Another embodiment takes the form of an electric machine that includes a stator defining the machine central axis, a rotor surrounded by and rotatable relative to the stator about the machine central axis, a rear frame member rotatably fixed relative to the stator and through which the machine central axis extends, and an electronic package as described herein wherein the machine central axis extends through the electronic package and the cooling tower is connected to the rear frame member. 
     In some embodiments of the electric machine, the machine central axis and the cooling tower central axis coincide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various objects, features and attendant advantages of the present invention will become fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings. Although the drawings represent embodiments of the disclosed apparatus, the drawings are not necessarily to scale or to the same scale and certain features may be exaggerated or omitted in order to better illustrate and explain the present disclosure. Moreover, in accompanying drawings that show sectional views, cross-hatching of various sectional elements may have been omitted for clarity. It is to be understood that this omission of cross-hatching is for the purpose of clarity in illustration only. 
         FIG. 1  is a side view of an alternator embodiment according to the prior art; 
         FIG. 2  shows a typical layout of a prior alternator&#39;s power and control electronics, disposed on the back face of the alternator&#39;s rear frame member; 
         FIG. 3  is an electrical schematic of a typical alternator&#39;s power electronics; 
         FIG. 4  is a side view of an alternator including an embodiment of an integrated electronics assembly or “electronic package” according to the present disclosure mounted on the back face of the alternator&#39;s rear frame member; 
         FIG. 5  is a rear perspective view of an electronic package according to the present disclosure showing paths of air flow and forced convection areas, and areas of natural convection; 
         FIG. 6  is another rear perspective view of the electronic package of  FIG. 5 ; 
         FIG. 7  is another rear perspective view of the electronic package of  FIG. 5 ; 
         FIG. 8  shows air-cooling of the integrated electronics utilizing the rearmost of dual internal fans in an electric machine embodiment according to the present disclosure; 
         FIG. 9  shows air-cooling of the integrated electronics utilizing an external front fan and/or peripheral airflow in an electric machine embodiment according to the present disclosure; 
         FIG. 10  shows liquid-cooling and air-cooling of the integrated electronics in an electric machine embodiment according to the present disclosure; 
         FIG. 11  is an axial rear view of the electronic package of  FIG. 5  with its cover removed; 
         FIG. 12  is a rear perspective view of the electronic package as shown in  FIG. 11 ; 
         FIG. 13  is another rear perspective view of the electronic package as shown in  FIG. 11 , showing the ingress of cooling air; 
         FIG. 14  is another rear perspective view of the electronic package as shown in  FIG. 11 , shown oriented as mounted to the rear frame member of an electric machine (not shown) in a normal installed position, showing splash drainage paths; 
         FIG. 15  is a front perspective view of the electronic package of  FIG. 14 , showing the axial end of the electronic package that interfaces with the rear frame member of the electric machine (not shown), showing splash drainage paths; 
         FIG. 16  is an axial rear view of the electronic package, similar to that of  FIG. 11 , showing radially inward conductive heat flow from the its power electronics modules to its main, cooling tower heat sink along a primary cooling path; 
         FIG. 17  is a rear perspective view of the electronic package, similar to that of  FIG. 13 , but with the control electronics assembly and B+ terminal omitted; 
         FIG. 18  is a rear perspective view of the cooling tower of the electronic package of  FIG. 5 ; 
         FIG. 19  is a rear perspective view of the interconnected MOSFET modules of the electronic package of  FIG. 5 , arranged relative to each other in their installed positions; 
         FIG. 20  is an axial rear view of the cooling tower of  FIG. 18 ; 
         FIG. 21  is another rear perspective view of the cooling tower of  FIG. 18 ; 
         FIG. 22  is a side view of the cooling tower of  FIG. 18 ; 
         FIG. 23  is a partial and partly sectioned view of a liquid-cooled embodiment of an electric machine according to the present disclosure, showing heat flow through the cooling tower towards the machine&#39;s rear frame member; 
         FIG. 24  is an axial rear view of the electronic package as shown in  FIG. 17 , showing bi-directional heat flow from the MOSFET modules, and indicating the positions of some power electronics devices within the modules; 
         FIG. 25  is a rear perspective view of the cooling tower of  FIG. 18 ; 
         FIG. 26  is a rear perspective view of electronic package of  FIG. 13 , with the covers of the power electronics module housings removed; 
         FIG. 27  is a rear perspective view of the interconnected MOSFET modules of  FIG. 19  without their covers; 
         FIG. 28  is a fragmented, partial rear perspective view of the interconnected MOSFET modules of  FIG. 27 , showing their power electronics devices and electrically insulative (T-Clad) base layers; 
         FIG. 29  is a cross-sectional view of a MOSFET module along line  29 - 29  of  FIG. 28 ; 
         FIG. 30  is a fragmented, rear perspective view showing an electric machine according to the present disclosure having an electronic package and a rear frame member of large diameter, with a phase lead wire exiting the frame member at a location radially outward of its connection point to its respective MOSFET module phase terminal; 
         FIG. 31  is a fragmented, rear perspective view showing an electric machine according to the present disclosure having, relative to the electric machine of  FIG. 30 , an identical electronic package and a rear frame member of relatively small diameter, with a phase lead wire exiting the frame member at a location radially inward of its connection point to its respective MOSFET module phase terminal; 
         FIG. 32  is a fragmented front perspective view of a portion of an electronic package embodiment according to the present disclosure, showing a recess or slot in the cooling tower between a circumferentially adjacent pair of MOSFET modules, through which a phase lead wire exiting a hole in a small diameter rear frame member (not shown) may be routed to its respective MOSFET module phase terminal; 
         FIG. 33  is a fragmented, rear perspective view showing an electric machine according to the present disclosure having an electronic package and a rear frame member whose back face is provided with a void by which the radial position at which the phase lead wire exits the frame member may be adapted to that of the MOSFET module phase terminal; 
         FIG. 34  is a view of the MOSFET module housing covers omitted from  FIG. 27 , arranged in their installed positions, showing the respective, integral bosses extending radially inward from the interior surfaces of the cover; 
         FIG. 35  is an axial view of a MOSFET module showing its respective power electronics devices, module housing cover, and the cover&#39;s integral bosses extending radially inward from the interior surface of the cover, with the module housing sidewalls omitted for clarity; 
         FIG. 36  is a rear perspective view of the electronic package as shown in  FIG. 17 , with portions of the MOSFET modules radially inward of their housing covers omitted, showing the bi-directional heat sinks of an electronic package according to the present disclosure, and paths of heat transfer from each MOSFET module into the main, cooling tower heat sink by conduction along a primary cooling path, and to ambient air via natural convection from the module housing covers along a parallel, secondary cooling path; 
         FIG. 37  is a rear perspective view of the main heat sink of the cooling tower, the control electronics assembly with circuits boards shown but lid or cover plate omitted, and the control electronics signal leads, of an electronic package embodiment according to the present disclosure; 
         FIG. 38  is a rear perspective view similar to that of  FIG. 37 , but with the control electronics assembly removed; 
         FIG. 39  is a rear perspective view similar to that of  FIG. 37 , but with the lid or cover plate of the control electronics assembly, and the circuit board portion located on the interior face thereof, omitted, showing the interior of the plastic cup or receptacle and control electronics circuit board portions mounted therein; 
         FIG. 40  is a rear perspective view similar to  FIG. 18 , showing only the main heat sink and the centrally located well thereof in which the plastic cup or receptacle of the control electronics assembly is normally contained; 
         FIG. 41  is a rear perspective view of the control electronics assembly and the signal leads of an electronic package embodiment according to the present disclosure; 
         FIG. 42  is a front perspective view of the signal leads and the lid or cover plate and of the control electronics assembly shown in  FIG. 41 , showing the control electronics circuit board portion disposed on the interior surface of the lid; 
         FIG. 43  is a rear perspective view of the control electronics assembly and signal leads shown in  FIG. 41 , with the lid or cover plate of the plastic cup removed, showing the circuit board portion normally disposed on the interior surface of the lid; 
         FIG. 44  is a rear perspective view of the control electronics assembly and signal leads as shown in  FIG. 43 , but with the circuit board portion normally disposed on the interior surface of the lid or cover plate omitted, showing the interior of the plastic cup and control electronics circuit board portions mounted therein; 
         FIG. 45  is a rear perspective view of a portion of a control electronics assembly embodiment as shown in  FIG. 39 ; 
         FIG. 46  is a side perspective view of the control electronics assembly portion of  FIG. 45 , with its circuit board portions omitted, showing only its plastic cup; 
         FIG. 47  is a rear perspective view of the plastic cup of  FIG. 45 , showing the cup interior; 
         FIG. 48  is another rear perspective view of the plastic cup of  FIG. 45 , showing the cup interior; 
         FIG. 49  is a front perspective view of the plastic cup of  FIG. 45 , showing the recess in which are normally disposed the electric machine shaft end and brush holder; 
         FIG. 50  is another front perspective view of the plastic cup of  FIG. 45 ; 
         FIG. 51  is a rear perspective view of the circuit board portions and signal leads shown in  FIG. 44 ; 
         FIG. 52  is a rear perspective view of an alternative embodiment of the circuit board portions and signal leads shown in  FIG. 51 , wherein the signal leads and the circuit board material on which control circuit portions are disposed, are integral with each other, and defined by a plastically deformed singular flexible circuit board material piece, also showing optional, additional circuit board portions in dashed lines; 
         FIG. 53  is a plan view of the singular flexible circuit board material piece of  FIG. 52  in its undeformed state, also showing the optional, additional circuit board portions in dashed lines; 
         FIG. 54  is a plan view of a nested plurality of undeformed flexible circuit board and signal lead material pieces arranged in a plane for shipping or assembly; 
         FIG. 55  is rear perspective view of the electronic package embodiment of  FIG. 7  with its cover omitted; 
         FIG. 56  is a rear perspective view of an alternative cooling tower embodiment provided with radially extending pedestals defining mounting surfaces for MOSFET modules; 
         FIG. 57  is a fragmented front perspective view of an electronic package including the cooling tower embodiment of  FIG. 56 ; 
         FIG. 58  is a sectional view along line  58 - 58  of  FIG. 11 , modified to include the cooling tower embodiment of  FIG. 56 , showing locations of gutters/ledges along cooling tower pedestal edges for splash drainage; 
         FIG. 59  is an enlarged view of rectangular outlined area  59  of  FIG. 58 , showing gutters/ledges along cooling tower pedestal edges for splash drainage; 
         FIG. 60  is a fragmentary, rear perspective view of a portion of the electronic package including the cooling tower embodiment of  FIG. 56 , showing gutters/ledges along cooling tower pedestal edges for splash drainage; 
         FIG. 61  is another fragmentary, rear perspective view of a portion of the electronic package of  FIG. 60 , showing gutters/ledges along cooling tower pedestal edges for splash drainage; 
         FIG. 62  is an enlarged, fragmented sectional view along line  62 - 62  of  FIG. 11 , modified to include the cooling tower embodiment of  FIG. 56 , showing the gutter/ledge along the rear edge of an example pedestal for splash drainage; and 
         FIG. 63  is an enlarged, fragmented front perspective view between circumferentially adjacent MOSFET modules of an electronic package embodiment of the present disclosure including the cooling tower embodiment of  FIG. 56 , showing gutters/ledges for splash drainage. 
     
    
    
     Corresponding reference characters indicated corresponding parts throughout the several views. Although the drawings represent embodiments of the disclosed apparatus, the drawings are not necessarily to scale or to the same scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure. 
     DESCRIPTION 
     The invention is adaptable to various modifications and alternative forms, and the specific embodiments thereof shown by way of example in the drawings is herein described in detail. The exemplary embodiments of the present disclosure are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present disclosure. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     It shall be understood that the terms “radial” and “axial” are generally used herein to establish positions of individual components relative to the central axis of an electric machine or electronic package, rather than an absolute position in space. Further, regardless of the reference frame, in this disclosure terms such as “parallel” and “perpendicular” and the like are not used to connote exact mathematical orientations or geometries, unless explicitly stated, but are instead used as terms of approximation. Terms such as “forward,” “rearward,” “front,” and “rear” and the like are used in the context of the central axis extending between opposite front/forward and rear/rearward axial ends. Further, it should be understood that various structural terms used throughout this disclosure and claims should not receive a singular interpretation unless it is made explicit herein. 
     Although the disclosed embodiment relates to three-phase or six-phase (i.e., dual three-phase) synchronous machine topologies such as claw pole alternators and internal permanent magnet hybrid machines, the present disclosure could also be applied to other machine topologies such as switched reluctance or induction. Those having ordinary skill in the art will understand the above-mentioned six-phase (i.e., dual three-phase) machines are of the type having two, three-phase windings that are 30 degrees electrically apart for noise cancellation, as shown in  FIG. 3 . It is to be understood, however, that all aspects of the disclosure provided herein also relate and could be applied to pure six-phase machines as well as to five-phase machines or seven-phase machines, which are electric machine types well-known to those having ordinary skill in the relevant art. 
     The electric machine embodiments  130  exemplified herein have an intended power range of 1.5 to 17 kW, a voltage range of 12-60V, and stator outside diameters ranging between 120 and 200 mm. Referring to  FIG. 4 , the exemplary electronic package embodiments  132  disclosed herein are integrated electronic assemblies packaged as separable electric machine components adapted for being mounted to a rear frame member  134  of an electric machine  130 , at the axially rearmost portion of the machine, relative to the machine&#39;s normal orientation as typically installed. Typically, the rear frame of an electric machine radially and axially supports the rotor shaft  136  relative to the machine central axis  138  through a bearing. The rotor  140  may itself define the machine central axis  138 , as may the stator  142 . Integrated control and power electronics for electric machines are commonly located rearward of the stator and rotor, and mounted to the rear frame. A prior electric machine  100  including its integrated control and power electronics package  114  is shown in  FIG. 1 . 
     Cooling of the integrated electronics of prior electric machines typically relies at least in part on the means provided for cooling other components of the machine located internally of the machine housing, such as the stator windings or the rotor. Certain aspects of the invention(s) disclosed herein relate to the electronic package being mounted at the rear of an electric machine. 
     The rear frame may include a member  134  defining a generally planar back face  144  that extends perpendicularly relative to the central axis  138 . Liquid-cooled electric machines often provide a liquid coolant passage or water jacket portion  146  in the rear frame, located axially inside the back face  144 . Such a machine according to the present disclosure is shown in  FIG. 10 . 
     Referring to  FIG. 8 , the rear frame member  134  may house one of a pair of internal fans  148  rotatable with the rotor  140 . The rear fan  148  induces air flow in a forward direction from the rear of the machine  130 , axially inwardly towards the rotor  140 , through apertures  150  in the rear frame member  134 . Air drawn axially into the internal rear fan  148  is directed radially outwardly, usually past the stator windings which are cooled thereby, and expelled radially from the machine  130 . 
     Referring to  FIG. 9 , some electric machine embodiments  130  utilize an external fan (not shown), rotatable with the rotor  140  and located axially forward of the stator  142 , to draw air through openings in the machine housing. The external fan induces a forwardly directed air flow through apertures  150  in the rear frame member  134  and past the stator and the rotor. 
     Referring to  FIGS. 5 and 6 , the spatial arrangement of the components in an electronic package  132  according to the present disclosure maximizes the use of available package space. The exemplary embodiments provide power electronics devices  154  as power modules  154  or MOSFET modules  154  providing two parallel sets  156   a ,  156   b  of three-phase MOSFET rectifier/inverters  154 , as shown in  FIG. 3 . Prior electric machine  100  designs (see, e.g.,  FIGS. 1 and 2 ) representative of the current state of the art physically do not allow paralleling the power electronic devices. These prior machines utilize three MOSFET modules  116  arranged along with the control electronics  118  on the back face  112  of the rear frame  110 , generally as shown in  FIG. 2 . The lack of physical room available at this site precludes packaging paralleled MOSFET rectifiers/inverters there. Contradistinctively, electric machine embodiments  130  according to the present disclosure accommodate the packaging of six MOSFET modules  154 , provided as two parallel-connected sets  156   a ,  156   b  of three modules  154  as shown in  FIG. 3 . Relative to the power electronics  116  of current state of the art machines  100  of similar capacity, these two sets  156   a ,  156   b  of power modules  154  effectively reduce the current therethrough by approximately half, since they are in parallel. 
     In the example of a three-phase electric machine  130  that operates in a generating mode to produce 200 A of DC output current, a machine  100  designed according to the current state of the art would have 200 A flowing through each of its three MOSFET modules  116  for ⅓ of the time to rectify the stator output, whereas a machine  130  according to an embodiment of the present disclosure each MOSFET module  154  need only rectify 200 A/2 or 100 A. MOSFET loss is an ohmic type loss whereby the heat loss is proportional to current squared. Thus, compared to the prior state of the art electric machine  100 , an electric machine  130  according to the present disclosure, owing to its paralleled power electronics devices  154 , effectively cuts the power loss in each power electronics device  154  by ¼ th  (i.e., by ½ 2 ) and the overall heat loss in the power electronics in half (i.e., ¼×2=½), a result providing significant advantages vis-à-vis comparable prior electric machines  100 . 
     Referring to  FIGS. 1 and 2 , in a typical prior air-cooled electric machine  100 , the cooling air enters axially into the rear of the machine. However, the power and control electronics components  114  of these machines essentially consume the entire back face area of the machine&#39;s rear frame  110 , and does not permit sufficient axial air flow past the electronics for air cooling them. Heat from the power modules  116  must travel along the back face plane before reaching the cooling fins, which are located outside of the power modules. This travel distance adds thermal conduction resistance and raises the temperature of the power devices  116  accordingly. 
     Moreover, fins for cooling the power modules of these prior machines are not in an area of high velocity inlet air flow, and/or do not work in concert with the natural flow path of the incoming air, instead raising air flow resistance and thus lowering overall bulk cooling air flow rates. 
     According to another prior cooling approach, the power electronics  116  and control electronics  118  are spaced axially apart in the machine  100  and cooling air is drawn through radial inlets into the machine before turning and flowing axially within the machine. This type of layout, however, induces high pressure drops due to turning the cooling air flow, and thus reduces the bulk air flow rate. This layout also promotes recirculation of hot air exhausted from the rear of the machine  100  back into its radial cooling air inlets. This recirculation effectively raises the temperature of cooling air drawn into the machine  100 , thus raising component temperatures. These problems are overcome in an electric machine  130  according to the present disclosure. 
     Relative to the power module orientations in prior electric machines  100  (see, e.g.,  FIG. 2 ), the power modules  154  attached to the cooling tower  158  are turned on edge, which provides many design advantages. Referring to the exemplary embodiments of  FIGS. 4-7 and 11-25 , the electronic package  132  includes a metallic cooling tower  158  defined by an axially extending first wall  160  that extends between axially opposite first  162  and second  164  ends thereof and about the package central axis  168  such that, in an axial view ( FIG. 20 ), the cooling tower  158  is shaped like an extruded polygon with finned surfaces or ribs  170  extending inwardly of the cooling tower from the radially inner surface  172  of the first wall  160 . The cooling tower may, for example, be an aluminum casting or extrusion of which the first wall  160  and the ribs  170  are integrally formed members. In the exemplary embodiments, the package central axis  168  and the machine central axis  138  are coincident when the electronic package  132  is installed as a component of machine  130 . The axially opposite first wall ends  162 ,  164  respectively define the first and second axially opposite ends  162 ,  164  of the cooling tower  158 . An axially extending air passage  174  is defined by the radially inner surface  172  of the first wall  160 . 
     On the radially outer surface  176  of the cooling tower structure  158 , the power modules  154  are mounted on the flat polygon surfaces, which define mounting pads  178  for the power modules  154 . The mounting pads  178  are evenly distributed circumferentially around the radially outer surface  176  of the cooling tower  158 . For example, the mounting pads may be generally equiangularly distributed about radially outer surface  176 . The cooling tower  158  defines a main heat sink  180  for the power modules  154 , which are in conductive thermal communication with the mounting pads  178 . The cooling tower ribs  170  extend inwardly directly away from these power module mounting surfaces  178 . In the depicted embodiment, radially inward of the first wall  160  is a second wall  182 . The first wall  160 , the second wall  182  (included the depicted embodiment), and the ribs  170  are integrally formed members of the metallic cooling tower  158 . The second wall  182  extends axially between opposite first and second axial ends  162 ,  164  of the cooling tower  158 , and about the package central axis  168 . In an axial view, the second wall  182  defines another hollowed polygon whose radially inner surface  184  defines a space, or well  186 , that serves as the location for the control electronics  188 . In the depicted embodiment, the well  186  is bottomless within the cooling tower  158 , and has an axially projecting profile that may, for example, be polygonal though it is to be understood that in other embodiments, the well  186  structure can be of different shape or depth, or be omitted altogether. 
     The cooling tower  158  has a generous cross sectional area in planes perpendicular to the central axis  168  along the length of the electronic package  132 . Where used with an air-cooled machine  130 , axial air flow along the air passage  174  extending through the cooling tower  158  is uniform and near the radial center of the machine  130 , which works well with the natural air flow pattern in machines of dual internal fan construction; optimal performance in such machines results from the cooling air entering the rear fan  148  axially through the inside diameter of the fan blades. Furthermore, the heat sink  180  has fins or ribs  170  traversing the air passage  174 , between which cooling air flows. The ribs  170  extend radially inwardly from the angular locations of the power module  154  mounting locations, and also extend axially between the air passage inlet  190  and outlet  192 , which are defined at the respective, axially opposite first  162  and second  164  ends of the cooling tower  158 . The ribs  170  provide a large surface area from which heat is convectively transferred to the cooling air, which yields superior air cooling performance. The fins or ribs  170  of the heat sink  180  extend radially inwardly toward the central axis  168  of the cooling tower  158  from the mounting pad location of each respective power module  154 . The ribs  170  of the cooling tower  158  are positioned directly in the high velocity air flow of cooling air entering the rear of the electronic package  132 , and are arranged in concert with the natural flow path of air entering the air passage  174  through its inlet  190  near the first axial end  162  of the cooling tower  158 . 
     A cooling tower  158  according to the present disclosure provides maximized spatial dispersion of the individual MOSFETs both angularly about the central axis  168  and in the axial direction. Maximizing spatial dispersion between the power electronics devices  154  tends to minimize their thermal conduction interaction and resulting device temperature. 
     The cooling tower  158  provides a large degree of dispersion of the individual power modules  154 , which serves to minimize their thermal interaction and reduce their temperatures. This dispersion is a function of the cooling tower geometry, which in the exemplary embodiments circumferentially distributes six power modules  154  equally about the radially outer surface  176  of a cooling tower first wall  160  that extends between the axially opposite ends  162 ,  164  of the cooling tower and about the central axis of the electronic package. Ideally, heat loss sources, such as multiple MOSFET modules  154 , are spread as far apart from each other as possible to minimize their conductive thermal interaction. In an electronic package  132  having a cooling tower  158  as disclosed herein, the individual MOSFETs are substantially equally spaced over a 360 degree arc about the central axis  168  of the machine  130 . Further, the positive  194  and negative  196  MOSFETs within each power module  154  are widely separated in the machine&#39;s axial direction. 
     The depicted cooling tower embodiment provides a hollowed space or well  186  for control electronics packaging appropriately in the radial center of the main heat sink  180 . This central location maximizes distances between the control electronics circuitry  188  and each power module  154 . It also locates control electronics circuitry  188  in an optimal area for cooling, this area being furthest from the power module heat sources. Positioning the control electronics  188  at this location also maximizes available space utilization by locating the control electronics, which require relatively less cooling than do the power modules  154 , directly behind the rear bearing of the electric machine  130 . In some air-cooled machine embodiments, this area is in an air flow dead space, i.e., portion of an air passage through which no air flow would otherwise occur. In other words, air would not flow through this space but for the presence of the electronic control circuitry  188 . 
     Thermal benefits also result from locating the control electronics  188  near the radial center of the electronic package  132  and axially rearward the power electronic device positions. Cooling air enters the cooling tower  158  in an axial direction from the rear axial end  162  of the electronic package, and is drawn forward through the air passage  174 , towards the rear frame of the machine  130 . Positioning the electronic control circuitry  188  at this location, the coldest possible air is available for cooling its components, which typically are lower temperature rated. Moreover, since the control electronics  188  produce relatively little heat relative to the power electronics or the machine&#39;s stator  142  and rotor  140 , the control electronics do not increase the temperature of the cooling air in a meaningful way that is harmful to the downstream components. 
     Further, having the control electronics  188  in the center of the electronic package  132  maximizes the physical distance to its typically lower temperature rated components from the heat-producing MOSFETs, which are higher temperature rated. Since the waste heat from the MOSFETs is removed by the finned surface areas of the cooling tower  158 , the heat sink surfaces around the control electronics  188  will be cooler than those near the MOSFETs, which is beneficial for the control electronics. 
     Centrally locating the control electronics  188  also minimizes the electrical signal transmission distance between the control electronics and power electronics  152 , which beneficially minimizes electrical noise issues and cabling costs. 
     The radially outer surface  178  of the second wall  182  of the depicted embodiment is connected to the radially inner surface  184  of the second wall through the ribs  170 , some of which define radial spokes extending inwardly from angular locations between circumferentially adjacent power module mounting sites. The first  160  and second  182  walls and the ribs  170  are integrally formed as an aluminum casting or extrusion, and are therefore in conductive thermal communication with each other. The axial air passage  174  is defined between the first and second walls, which is traversed by the ribs. The axial cross-sectional shape of the air passage  174  is generally annular between the opposite axial ends  162 ,  164  of the cooling tower  158 . 
     The depicted cooling tower and power module layout works well with typical alternator construction. It allows the ambient cooling air to flow axially into the machine  130  near the central axis  138  with a very generous and angularly uniform inlet area, but at the same time provides a large surface area for mounting and conductive cooling of the MOSFET modules  134 . 
     The cooling tower  158  beneficially facilitates a very uniform flow of cooling air into the rear of the electronic package  132 . The typical electronics layout of prior air-cooled electric machines  100  is geometrically asymmetrical in an angular sense and has areas from which cooling air flow is completely blocked, as is apparent in the example of  FIG. 2 . Non-uniformity of the cooling air flow stream resulting from such air flow blockage can create hot spots on the stator  104  of the electric machine  100 , which in turn lowers the temperature capability and/or performance of the machine. In comparison, the greater uniformity of the electronics layout in the electronic package  132  provides a relatively uniform air inlet area to the cooling tower  158 , and a cooling air flow therethrough that is much more uniform, minimizing the possible occurrence of hot spots on the stator  142 . 
     The mounting direction of the power modules  154  being perpendicular to the orientation of the rear frame member  134  greatly minimizes the area the modules axially project onto the back face  144  of the machine  130 . Orienting the generally flat power modules  154  such that they are edge-wise to the back face  144  when mounted, or substantially parallel to the central axis  168 , better allows packaging of a MOSFET module number and size required for a desired electric machine design, and much greater design flexibility, vis-à-vis the electronics layouts of prior electric machines. 
     By virtue of cooling tower ribs or fins  170  being in the cooling stream of incoming air flow and radially extending inwardly from locations directly inward of the power module mounting locations  178 , minimal thermal conduction resistance exists between the power devices  154  and the cooling tower fins  170 . 
     A cooling tower structure  158  according to the present disclosure allows cooling air to enter axially into the electronic package  132  with minimal restriction and a high degree of angular uniformity. 
     In electric machine embodiments  130  of dual internal fan construction, cooling air must enter the rear centrifugal fan  148  at its inner blade diameter for the fan to function properly, and a cooling tower structure  158  according to the present disclosure lends itself naturally to this type of flow. External fan machines  130 , typical of current heavy duty alternators, also work well with this cooling tower structure, as the air can flow through the air passage  174  and into the rear of the machine  130  with little flow restriction. 
     The exemplary cooling tower geometry is also compatible with liquid-cooled applications. In such applications, the back face  144  of the electric machine  130  is liquid cooled and the cooling tower  158  is mounted directly on this liquid cooled surface. The cross sectional area of the cooling tower&#39;s integrally connected, thermally conductive members  170  allows the heat to flow conductively through the cooling tower  158  from the MOSFETs to the back face  144  surface, from which is can be convectively removed by the liquid coolant circulating through a water jacket  146  defined by the frame&#39;s back face member  144 . In other words, the relative large cross sectional areas of the cooling tower wall  160  defining the outer wall surface  176 , and ribs  170 , provide a low conductive thermal resistance for transferring waste heat from the MOSFETs to the back face surface. In addition, natural convection additionally occurs from the rib surfaces of the heat sink, which further serves to remove the waste heat. Thus the cooling tower  158  is compatible with both air and liquid cooled electric machines  130 . 
     Beneficially, the electronic package  132  is adapted for attachment to the rear frame member  134  of an electric machine  130  via the cooling tower  158 , which is the main heat sink for the power modules  154 . The base plates  200  of the power modules  154  and the module mounting locations  178  on the cooling tower  158  are directly in surface-to-surface contact, whereby they are in conductive communication electrically and thermally. Because the module base plates  200  and the cooling tower  158  are electrically at ground potential, the cooling tower can be attached directly to the rear frame of the machine. 
     This is characteristic of the electronic package  132  is important for liquid-cooled applications, wherein the generous cross section of the heat sink  180  in planes perpendicular to the central axis  138  of the machine  130  facilitates the heat, transferred from the power devices  154  to the cooling tower  158  through their contacting mounting surfaces along a primary cooling path  202 , to be further conducted along the primary cooling path  202  to the back face  144  of the electric machine  130 . The back face  144  is formed on a rear frame member  134  and defines the rearwardly facing surface of the machine housing. In liquid cooling electric machines  130 , the back face frame member  134  typically defines a liquid coolant passage  146 . Heat is transferred convectively from the back face frame member  134  to the liquid coolant flowing through the water jacket  146 . Heat conducted from the cooling tower  158  to the back face  144  is removed by convection to the cooling liquid that is circulated across the back face member  134  of the frame. 
     Yet another machine topology that can utilize electronics packaging according to the present disclosure is an air-cooled electric machine  130  that has axially directed air flow substantially along the inside surface of the machine&#39;s outer frame diameter. In an embodiment of such a machine according to the present disclosure, both the liquid-cooled and air-cooled modes of cooling are employed. First, some of the heat from the MOSFETs is removed from the extensive surfaces of the cooling tower heat sink ribs  170  through convection to an axial flow of cooling air, as in an embodiment of a machine having dual internal fans. However, since the air must bend internally of the machine, at a point downstream of the cooling tower  158  and rear frame member  134  interconnection location, a pressure drop is introduced to the cooling air that lessens its flow and therefore its cooling capabilities. However, just as with liquid-cooled applications, the generous area of the heat sink  180  in axial cross sections all along the central axis  168 , allows the remaining portion of the heat transferred to the cooling tower heat sink  180  from the MOSFETs along the primary cooling path  202  to be conducted further along the path through the cooling tower  158 , and into the rear frame member  134  of the electric machine  130 , which can have additional surface finning to promote convective heat transfer to the cooling air, and/or openings to allow establishment of a parallel air flow path, so that sufficient cooling air enters into the machine for cooling of the machine&#39;s stator and rotor. 
     A cooling tower  158  according to the present disclosure offers a high amount of surface area for a given package size at the center of the structure that works in harmony with the natural cooling air flow stream direction in air-cooled machines. 
     The geometrical design and layout of a cooling tower according to the present disclosure provides an electronic package  132  compatible with air-cooled and/or liquid-cooled machines  130 . 
     The cooling tower  158  provides a very rigid and stiff support structure for the electronics to be mounted on. The cooling tower&#39;s stiffness is beneficial for engine-mounted electric machine applications, where vibration is a significant concern. The rear frame members  110  of prior electric machines  100  are typically subjected to various modes of bending and distortion when in use on an engine due to engine vibration. Axial oscillation of the rotor assembly mass, and forces on the shaft induced by dynamic belt loading on the drive pulley, exert gyrating forces on the rear bearing, thereby inducing dynamic forces on the machine&#39;s rear frame member  110 , which supports the rear bearing. In prior electric machines  100 , these bending modes create movement of the electronic components  114  relative to each other and can cause component fatigue failures, especially of connecting straps and the like. 
     In an electronic package  132  according to the present disclosure, all of the electronics are mechanically tied directly to the cooling tower structure  158  and are not subject to the bending modes of the rear frame member  134 . The integrally finned structure of the cooling tower  158 , though primarily for cooling purposes, also intentionally serves to provide mechanical stiffness to the cooling tower structure. The axial length of the cooling tower, its 360 degree profile about its central axis  168 , and its integral ribs  170  combine to provide an electronic package  132  according to the present disclosure relatively superior structural stiffness. Consequently, movement of the electronic components mounted to the cooling tower relative to each other is minimized, and the comparative vibration robustness of an electronic package as disclosed herein is greatly improved relative to the integrated electronics assemblies used in prior electric machines. Moreover, the rear frame member  134  of an electric machine  130  is advantageously stiffened by the attachment of the cooling tower  158  thereto. The stiffening of the rear frame member  134  minimizes its bending and distortion, which can in turn minimize other fatigue-related failures in the machine, such as throughbolt failure due to bending fatigue. 
     The highly rigid structure of the cooling tower  158  results from its having a profile extending 360 degrees about the central axis, and interlacing fins  170  that act as stiffening beams. 
     The cooling tower  158  is structurally rigid and minimizes vibration concerns since all power MOSFETs are mounted directly to it. Moreover, the rear frame member  134  of the electric machine  130  is also desirably stiffened by the electronic package  132  being mounted to the frame member  134  through the rigid cooling tower  158 . 
     The control electronics  188  are tucked into the body of the main cooling tower heat sink  180 , which minimizes the axial space required by the overall electronic package  132 . The central mounting location of the control electronics assembly minimizes air flow blockage, minimizes exposure of the control circuitry to heat losses from the power electronics, exposes the control electronics to the coolest cooling air entering the electric machine  130 , and minimizes the electrical signal transmission distance between the control electronics  188  and the power electronics  152 , which minimizes electrical noise problems and cabling costs. 
     In an exemplary embodiment of the electronic package  132  the MOSFETs  194 ,  196  and the MOSFET driver  204  contained in each power module  154  are in conductive thermal communication with the cooling tower heat sink  180 , about which the modules are circumferentially distributed. Conductive heat transfer to this main heat sink is the primary cooling path  202  for each MOSFET module  154 . Beneficially, the positive (or high side)  194  and negative (or low side)  196  power devices (MOSFETs) of each power module  154  beneficially share a common module heat sink. This desirable feature results from both the positive and negative MOSFETs  194 ,  196  being identical N-channel devices with the same polarity and, in the exemplary embodiment depicted, providing a thin layer  206  of thermally conductive electrical insulation that extends over the entire interior surface  208  of the metallic module base  200 , as shown in  FIG. 25 . The thin electrical insulation layer  200  has low thermal resistance, and may be an existing, commercially available material such as, for example, Thermal Clad™, commonly referred to as “T-Clad”, a product of Henkel Corporation (www.henkel.com) and formerly from The Bergquist Company of Chanhassen, Minn., USA. 
     In one embodiment, the insulation layer  206  is printed on a surface  208  of the module&#39;s heat-sunk metallic base  200 . Atop this insulation layer  206  is printed a copper trace or strip (not shown). Referring to  FIG. 26 , a much thicker strap  210  of copper suitable for the current levels conducted through the power modules  154  is soldered to the printed copper strip, and the positive MOSFETs  194  are attached directly to the copper strap  210 . Within each module  154  the drains of the positive MOSFETs are connected to the copper strap  210 . 
     As noted above, the exemplary electronic package  132  utilized two parallel-connected sets  156   a ,  156   b  of three MOSFET power modules  154 . Amongst the three, circumferentially adjacent modules  154  of the first set  156   a , which are respectively in communication with an associated conductor  212   a  of the stator&#39;s first winding set  214   a , the copper straps  210  are interconnected to form a daisy-chained first power bus  216   a . Likewise, amongst the three, circumferentially adjacent modules  154  of the second set  156   b , which are respectively in communication with an associated conductor  212   b  of the stator&#39;s second winding set  214   b , which is shifted 30° relative to the first winding set  214   a , the copper straps  210  are interconnected to form a daisy-chained second power bus  216   b . The first and second power buses  216   a ,  216   b  are interconnected at the machine&#39;s B+ terminal  218 , which is a component of the electronic package  132 . 
     Similarly, another, parallel copper trace or strip (not shown) is printed atop the insulation layer  206 . Referring again to  FIG. 26 , a much thicker copper member  220  suitable for the current levels conducted through the power modules  154  is soldered to this printed copper strip, and the negative MOSFETs  196  are attached directly to the copper member  220 . Within each module  154 , the drains of the negative MOSFETs  196  and the sources of the positive MOSFETs  194  are electrically connected to the copper member  220 . The copper member  220  of each power module  154  extends from its module housing  222  to define the respective module&#39;s phase connection terminal  224 , to which the respective stator winding  212   b  associated with that power module  154  is connected via a phase lead wire. 
     The source of each negative MOSFET  196  is electrically connected to its module&#39;s metallic base  200 , and is grounded through the base and the respective mounting pad  178  of the cooling tower  158  to which the module base is attached. The MOSFET driver  204  of each power module  154  is mounted directly to the electrically insulative layer  206 , and is in communication with the control circuitry  188  via a respective signal lead  226 . 
     As mentioned above, its ability to share a common main heat sink  180  at ground potential for the positive  194  and negative  196  MOSFETS of its plurality of power modules  154 , rather than requiring separate positive and negative heat sinks at different potential levels as is typically done for the power electronics devices  116  of prior electric machines  100 , provides the inventive electronic package  132  substantially greater design flexibility, vis-a-vis prior integrated electronic packages  132 , to accommodate convection for air cooling, and/or conduction for liquid cooling via the back face  144  of an electric machine&#39;s rear frame. 
     Typically, the power electronics side of the phase connection to stator winding phase conductor  212   a ,  212   b  is in a fixed, rigid position. A typically-sized automotive alternator has a generally circular frame outside diameter of 140 mm. With reference to  FIG. 2 , the power module phase terminal connectors  120  in a prior electric machine  100  are radially located such that it can accommodate a narrow range of machine sizes, such as 129 to 144 mm stator outside diameter. 
     A slot or recess (hereinafter “void”)  228  provides clearance for packaging the respective phase lead wire  230  defined by a phase conductor  212   a ,  212   b  of the stator winding that extends between the stator  142  and the associated power module phase terminal connector  224 . Providing these voids  228  in the rear frame back face  144  and/or the electronic package&#39;s cooling tower  158  allows identical electronic package embodiments  132  to accommodate relatively larger variations in the radial position of the stator phase conductors  212   a ,  212   b . Thus, a single electronic package  132  size may be utilized in electric machines  130  of various stator sizes, including sizes so small as to radially position the location  232  of stator phase conductor egress from the back face  144  inside the perimeter of the cooling tower axial end  164  attached to the back face  144 , though the module phase terminal connector  224  locations are outside of that perimeter. 
     Prior electric machines  100 , which have electronic package layouts in which MOSFET modules  116  are mounted to back face  112 , with the module base mounting surfaces disposed in a plane perpendicular to the central axis  108 , as shown in  FIG. 2 , cannot feasibly provide such voids near the module phase lead connector terminals  120 , because the voids would be at the modules  116  themselves. It is desirable to accommodate a broader range of machine sizes, however. For instance, the design requirement desired for an embodiment of an electronic package  132  according to the present disclosure calls for accommodating a range of stator machine diameters ranging from 120 mm up to 190 mm. 
     However, the MOSFET modules  154  being mounted to the cooling tower  158  at circumferentially distributed locations about the central axis  138 , and in planes parallel with the central axis, provides a recess  228  between circumferentially adjacent power modules  154 . The cooling tower ribs or fins  170  in this area can be removed without a large detrimental thermal issue since the location lies in a naturally occurring adiabatic plane. 
     Via axial location of the MOSFET module  154  afforded by the cooling tower  158 , there is some axial space  234  between the phase lead connection  224  and the back frame  144  of the electric machine  130 . This yields valuable length between the stator end turns and the phase connection at the phase terminals  224  of the MOSFET module  154  for the stator conductor  230  to be routed and radially transition between the two locations relative to the machine shaft&#39;s axis of rotation  138 . 
     An electric machine embodiment  130  according to the present disclosure provides a slot opening or recess  228  in either or both of the cooling tower heat sink  180  and the rear frame  134 ,  144  of the electric machine  130 , in the area between circumferentially adjacent power modules  154 . 
     Certain exemplary electric machine embodiments  130  are provided with a plurality recesses or slots (“voids”)  228  circumferentially distributed along the corner  236  formed between the cooling tower&#39;s forward axial end  164 , which interfaces and is attachable to the machine&#39;s rear frame member  134 ,  144 , and radially outer surface  176 . Each void  228  is elongate in a radial direction and defines a recess opening axially forward, in the axial end surface  164  of the cooling tower  158 , and radially outward at locations between circumferentially adjacent power modules  154 , which are attached to mounting locations  178  on the cooling tower&#39;s radially outer surface  176 . Each void  228  extends radially inwardly from the radially outer wall surface  176  to radial positions along the length of the void  228  that coincide with the phase conductor pass through locations  232  for machines  130  of various small sizes. 
     Referring to  FIG. 30 , some electric machine embodiments  130  including such an electronic package  132  are of sufficiently large diametric size that their stator winding phase conductors  230  extend through the rear frame member  134  at locations  232  radially proximate or outward of the module phase terminal connectors  224 . In such machines the phase conductors  230  are directed radially inward from their respective apertures  228  to be connected to the associated module phase terminal  224 . 
     Referring to  FIG. 31 , other electric machine embodiments  130  include an identical electronic package  132  and are of relatively smaller diametric size. The phase conductors  230  extend through the rear frame member  134  at locations radially inward of the module phase terminal connectors  224 , and perhaps at radial positions inside the void  228 . In such machines the phase conductors  230  are directed radially outward from their respective apertures  232 , along the void  228 . The void  228  is sized for routing the phase conductor  230  to the power module phase terminal  224 , with clearance to the cooling tower  158  and the back face  144  to facilitate connection to the associated module phase terminal  224 . In such machines, wherein the forward axial end  164  of the cooling tower superposes the phase lead wire egress location  232 , the winding phase conductor (or phase lead wire)  230  can be routed radially along the void  228  with sufficient clearance to avoid wire damage and provide proper seating of the cooling tower  158  to the rear frame member  134 . 
     In other embodiments, the electronic package  132  may or may not include voids  228 , but the back face  144  is provided with an aperture  228  elongated in the radial direction through which the phase conductor  230  can exit the back face at positions  232  affording sufficient clearance to the cooling tower forward axial end  164 . 
     With ample space  234  for a simple phase lead terminal structure  224  having a wrap-around strap coming from the MOSFET module  154 , phase lead wires  230  of varying cross section can be accommodated. The connection is completed by soldering or welding the connection. 
     A one-piece molded plastic guide (not shown) provides the necessary electrical isolation between the stator winding phase conductor/phase lead wire  230 , and the frame  134 ,  144  and the metallic cooling tower  158 . This guide/insulator is simply trapped between the cooling tower and rear frame during assembly to hold the insulator(s) in position. 
     The exterior surface  238  of each power module cover plate  240  faces radially outward and is unobstructedly exposed to ambient air surrounding the electronic package  132 . This facilitates convective transfer of heat generated by the power electronics devices  154  to the air surrounding the electronic package through the cover plate  240 . The cover plate exterior surface  238  is configured, e.g., with fins  242 , to enhance convective heat transfer therefrom to the ambient air. An electronic package embodiment  132  according to the present disclosure is thus provided with bi-directional cooling of each power module  154  in opposite radial directions. 
     The MOSFET modules  154  are mounted to the cooling tower structure  158  such that bi-directional cooling of the power electronics can be maximized. Heat loss from each power module  154  initially follows a primary cooling path  202  radially inward through the module base  200  and into the main heat sink  180  defined by the cooling tower  158  at the module mounting location, from which the respective cooling fins  170  extend radially inwardly. Heat loss from each power module  154  also initially follows a respective secondary cooling path  244  radially outward through its cast aluminum cover plate  240 , and to the ambient air through the cover plate&#39;s finned exterior surface  238 . The bi-directional cooling paths  202 ,  244  from the power electronics devices  194 ,  196 ,  204  of each module  154  minimize the thermal resistance to heat flow from the power electronics devices housed therein. Heat loss from the plurality of power modules  154  collectively also follows radially inward and radially outward primary  202  and secondary  244  cooling paths, relative to the electronic package  132 . The primary and secondary cooling paths are parallel paths, rather than sequential paths. 
     The radially inwardly facing interior surface  246  of each module cover plate  240 , which is exposed to the MOSFETs  194 ,  196  and the MOSFET driver  204  within the module  154 , is provided with integrally cast bosses  248  that extend radially inwardly toward the MOSFETs and the MOSFET driver. Relative to each power module  154 , the cast aluminum module cover  240  and its integral bosses  248  define a heat sink for heat loss from the power electronics devices, and the secondary cooling path. From an electrical standpoint, the cast aluminum cover  240  cannot touch these electronic components or their wire bonds, and so the boss  248  surfaces are spaced therefrom. Disposing the boss surfaces as close as possible to the MOSFETs  194 ,  196  and the MOSFET driver  204  while maintaining gaps therebetween, however, enhances the overall cooling of the power modules  154 . Heat transfer to the boss surfaces could potentially be enhanced by further minimizing the gap between the bosses  248  and the MOSFETs  194 ,  196  and/or the MOSFET driver  204 . Such a modification could entail lengthening the boss  248  and slightly plastically deforming the natural arc or bend in the wire bonds to the MOSFETs and the MOSFET driver through use of a simple axial press and an appropriate shaped tool. Minimize the gaps between these devices and the heat sink would reduce the conduction temperature drop along the secondary cooling path, and therefore further reduce the device temperature. 
     Although the MOSFET driver  204  produces very minimal heat in comparison to the MOSFETs  194 ,  196 , it is important to maintain the driver temperature as low as possible. Each MOSFET has a targeted operating temperature in the 150° C. range. Because the MOSFET driver is packaged with the MOSFETs in the power module housing  222 , without special provisions made for cooling the driver  204 , it would also be subject to an environment in the 150° C. range since it is surrounded by surfaces generally at this higher temperature. 
     Ambient cooling air surrounding the electric machine  130  is typically in the 125° C. range. Bi-directional cooling for the MOSFET driver  204  in the power module enables cooling the MOSFET driver to temperatures lower than the MOSFET temperatures. By positioning the integrally-formed boss  248  extending from the interior surface  246  of the cast aluminum module cover plate  240  into close, spaced proximity to the MOSFET driver, heat from the space immediately about the driver, including heat loss from the driver itself, is transferred to the boss  248  surface and conducted along the secondary cooling path  244  to the exterior cover plate surface  238 , from which it is convectively lost to the ambient air. The MOSFET driver can thus be cooled to a temperature lower than the bulk temperature around the driver  204  and close to the ambient air temperature, thereby improving the driver&#39;s reliability. 
     A secondary benefit of providing the cast aluminum cover plate  240  with the integral bosses  248  is that the bosses serve to increase thermal capacity. Bi-directional transient cooling is provided by the increased thermal capacity provided by the cast aluminum bosses. In use, a power module  154  is not only subject to continuous electrical operation but, by the nature of the product and its usage, also experiences peak use conditions. Under such conditions high transient electrical loading occurs, during which the devices  194 ,  196 ,  204  are typically at their greatest temperatures. The high transient electrical loading therefore translates into high transient thermal loading, which can undermine the reliability of the power electronics devices. The mass of the main heat sink  180  portion in the vicinity of the power module mounting locations  178  significantly helps absorb the transient thermal energy, but the mass of the cast aluminum cover plate bosses  248 , whose surfaces are positioned in close proximity to the power electronics devices  194 ,  196 ,  204  and form parts of the secondary cooling path  244 , also helps absorb the transient thermal energy and keep the devices relatively cooler during machine operation under peak use conditions. From a thermal capacitance perspective, a thermal capacitor is thus effectively provided radially inwardly and radially outwardly of the power electronics components of each MOSFET module, and serve to absorb the thermal transients. 
     The bi-directional cooling facilitated by the cast aluminum module cover plate  240  also helps achieve a common electronic package design embodiment to be used for both air-cooled and liquid-cooled applications. Such embodiments are necessarily sub-optimized thermally relative to each cooling medium individually to allow the physical layout and design of the electronic package  132  to remain common. However, removal of some of the waste heat from the power MOSFETs  194 ,  196  via the secondary cooling path  244  lessens the requirement for heat transfer therefrom via the primary cooling path  202 . The removal of a portion of the generated heat through the module cover plate  240  via the secondary cooling path  244  helps minimize compromises that sub-optimize cooling performance relative to each medium individually, and facilitates providing a common electronic package  132  design that meets the thermal requirements of both cooling media. 
     Bi-directional cooling of the power electronics devices beneficially allows identical embodiments of an electronic package  132  according to the present disclosure, to be used in both air-cooled and liquid-cooled electric machines  130 . Bi-directional cooling of each power module  154  is provided by the power module being mounted in thermally conductive contact to the main heat sink  180 . The main heat sink in turn transfers heat received from the power electronics devices to an air or liquid cooling medium. Bi-directional cooling of each power module  154  is also provided by the finned, cast aluminum module cover plate  240 , which transfers heat received through bosses  248  from the power electronics devices, convectively to ambient air. 
     In other words, MOSFET cooling along the primary cooling path  244  is initially by conduction through the power module mounting surface  178  of the main heat sink  180 , and subsequently by convection from the main heat sink  180 , or an electric machine rear frame member  134 ,  144  to which the cooling tower  158  is attached, to an air or liquid cooling medium. MOSFET cooling along the secondary cooling path  244  is initially by conduction through the module cover plate  240  heat sink, and subsequently by convection to ambient air from the fins  242  formed on the outside surface  238  of module cover plate  240 . 
     As discussed above, placement of the electronic control circuitry  188  at a radially central location in the cooling tower air passage  174  in air-cooled electric machine embodiments  130 , particularly in electric machine embodiments exhibiting an air flow dead zone, minimizes the negative impact on air flow due to blockage. Minimizing the axially projected area of the radially centrally positioned control electronics  188  in air-cooled electric machine embodiments can, however, provide improvements to the air flow through the cooling tower  158 , particularly in machine embodiments  130  not characterized by an air flow dead space. 
     To this end, certain embodiments of an electronic package according to the present disclosure include electronic control circuitry  188  having circuit board material portions  250  turned on edge relative to their typical orientation in prior electric machines  100 , so as to extend in directions substantially parallel with the cooling tower central axis  168 . In other words, the control circuitry portions  252  of such embodiments are oriented substantially perpendicularly relative to a generally planar back face  144  of the rear frame. This orientation allows the electronic control circuitry  188  to be contained within a minimal axially projected area, near the radial center of the cooling tower  158 . 
     In the depicted embodiment, electronic control circuit portions  252  so oriented are disposed within a plastic cup or receptacle  254  defined by a floor  256  and enclosing side walls  258  that extend along the radially inner surfaces  184  of the second cooling tower wall  182  that defines the well  186 . In this embodiment, the axially forward surface  260  of the receptacle floor  256  is substantially flush with the second axial end  164  of the cooling tower  158 , which is adapted for attachment to a rear frame member  134 ,  144  of an electric machine  130 . The receptacle floor  256  of this embodiment is recessed to receive the rear axial end of the rotor shaft and a brush holder. The side walls  258  of the receptacle define an opening  262  over which a metallic lid or cover plate  264  containing the regulator terminal  266 , is mounted to enclose the receptacle&#39;s interior space. The control circuitry  188 , receptacle  254  and cover plate  264  define a control electronics assembly  268 . The control electronics assembly is mounted within and protected by surrounding second wall  182  of the cooling tower  158 . The receptacle  254  may be made of glass-filled nylon, and thermally isolates the control electronics  188  from heat generated by and lost by the MOSFETs, by greatly increasing the conductive thermal resistance therebetween. The lid  264 , however, is metallic and exposed to the oncoming cooling air to provide heat sinking for control electronics components (such as the field output device) which do produce a small amount of heat, generally in the 5-10 watt range. Placing control circuit portions  252  including these types of control electronics components on the axially forwardly facing interior surface  270  of the receptacle lid  264  thermally isolates those components from the rest of the control electronics circuitry. 
     The construction of the control electronics assembly&#39;s cup  254  and lid  264  provides protection for the control electronics  188  by shielding them from external splash and contaminants. It also reduces overall cost by providing a protective housing for the electronics that does not require additional packaging or overmolding of the circuit board for protection. In addition, the surrounding wall  182  of the cooling tower well  186  provides means for mounting and protecting the control electronics assembly  268 . As noted above, the well structure  186  can be of different shape or depth or be omitted altogether. Likewise, configuration of the control electronics assembly  268  may likewise be other than as shown. 
     While certain embodiments of the electronic package  132  include electronic control circuitry  188  utilizing only rigid circuit board material  250 , certain other embodiments of the electronic package  132  include electronic control circuitry  188  utilizing flexible circuit board material  272 . Such material is commercially available from, for example, Minco Products, Inc. of Minneapolis, Minn., USA (www.minco.com). This material can yield the same type of properties and design flexibility, including multiple layers, as conventional, rigid circuit board material. However, the flexible circuit board material  272  can be bent, twisted, folded or otherwise deformed, and still perform substantially like rigid circuit board material. 
     According to a first embodiment of this design, component hardboards including control circuit portions  252  to be carried by the flexible circuit board material  272  are laminated to the flexible circuit board material. The flexible circuit board material  272  is produced with electrically conductive traces or wires  274  through which conductors of control circuit portions  252  included on separate component hardboards  250  may be electrically interconnected. In corners between adjacent rigid component hardboards  250 , the flexible circuit board material  272  (and its interconnecting conductive traces  274 ) is deformed to facilitate hardboard positioning in different planes, thus allowing the rigid component circuit boards  250  to be interconnected without the use of any pin type connectors and/or cabling. 
     In some alternative embodiments, the control circuitry layout is broken up into multiple control circuit portions  252 , which are then printed/assembled on flexible circuit board material  272  to be provided as a singular piece  276  of flexible circuit board material  272  in the control circuitry  188 . The electrically conductive traces  274  of multiple flexible circuit board layouts are printed on a sheet of flexible circuit board material substrate, the individual flexible circuit board material pieces  276  are then cut from the sheet. Similar versions of flexible circuit board material  272  may be produced that vary in length and conductor configuration to accommodate optional control circuit portions, as indicated by the dashed outlines in  FIGS. 52  and  53 . Referring to  FIG. 54 , the flexible control circuit material  272  nests nicely in an undeformed state, which facilitates high material utilization of storage and shipping containers. 
     Some embodiments take further advantage of the properties of flexible circuit board material  272  and the in these embodiments the control circuitry  188  includes integrally formed signal leads  278  between the control circuitry  188  and the MOSFET gate driver  204 . The signal leads  278  include conductors  274  printed on the same, singular piece of flexible circuit board material  272  used for the control circuitry. In other words, the signal leads  278  of flexible circuit board material  272  extend to the various MOSFET gate drivers  204  and are simply bent into position along the wall of the molded plastic MOSFET module housing  222  material. Connector bodies  282  can be added directly to the flexible circuit board material  272  at the terminal ends of the signal leads  278  and their respective conductors  274 . These connectors are then plugged into the MOSFET driver connector terminals  284  of respective MOSFET modules  154  to complete the circuit. Thus, a separate wiring harness containing signal leads for communicating the gate driver signals from the control circuit assembly  188  to the six MOSFET modules  154 , and the separate, associated wiring connections between that wiring harness and the control circuitry, are eliminated. 
     A pedestal  286  of aluminum material is provided on the cooling tower first wall  160  where the MOSFET modules are mounted. Pedestal  286  can be machined by the side edges of an axially moveable cutting tool, thereby providing a simpler approach to forming a flat mounting surface and minimizing the thermal drop between the MOSFET modules  154  and the heat sink  180 . The entire axial extent of the pedestal mounting surface can thus be cut at once by clamping the cooling tower  158  in an upright position at a milling station thereby allowing easy access to the pedestal mounting surfaces. In addition, at one fixed milling station, a tool path can be set up to machine all pedestal mounting surfaces at once. 
     Another benefit relating to this seemingly subtle, but rather important design feature concerns the thermal aspects of the design. The electronic package  132  disclosed herein will be used in electric machine  130  applications with very demanding transient loading on the power electronics, such as providing the starting torque for an engine. 
     With these short transient conditions, the high current and resulting temperature increase can be best endured by providing sufficient thermal mass located as close as possible to the MOSFET to absorb the transient spike in heat generated during this period of time. The pedestal  286  of additional aluminum mass is provided to the cooling tower at the mounting surface exactly where it is needed without adding mass throughout the entire peripheral surface of the cooling tower which would result in little benefit at additional cost. This also has a secondary benefit to increase the cross sectional area radially inward of the MOSFETs where is it most needed for conductive heat spreading. Again, increasing the cross-sectional area of the heat sink further away from the MOSFETs is comparatively less effective and would increase cost while providing limited benefit. Through use of a separate pedestal for each respective MOSFET module, the thermal conduction benefit is maximized while minimizing the additional material cost. 
     Another subtle but significant benefit of the disclosed pedestal structure is the electrical clearance it provides between ground and the B+ and phase lead conductors  216   a ,  216   b ,  230 . By having each MOSFET module  154  mounted on a respective pedestal mounting surface  288  at an increased radial distance from the radial outer surface of the first wall  160 , and then overhanging the plastic rear shroud  290  of the electronic package around the module  154  and over the edge of its pedestal, the electrical clearance between the conductors  216   a ,  216   b ,  230  and the grounded cooling tower heat sink  180  is increased directly by the radial height of the pedestal  286 . 
     Yet another benefit provided by the novel pedestal structure relates to improved contamination and splash protection. Were the MOSFET modules  154  mounted with base  200  flush against the exposed, radially innermost, portion of the power module mounting surface of the radially outwardly oriented cooling tower heat sink surface, any encountered splash could run down the face of the heat sink, e.g., radial outer surface  176 , and road contaminants in the splash could then directly span or bridge the radial distance from grounded portions of the module  154  or heat sink  186  to locations where the conductors  216   a ,  216   b ,  224  exit the module, or result in contaminants being deposited along the edge of the MOSFET module base heat sink-to-cover interface. This could undesirably lead to road contaminants entering into the MOSFET module(s) or result in current leakage from the module(s) or the conductors. By having each power module  154  mounted to the mounting surface of a radially outwardly projecting pedestal  286 , with the module housing  222  having an overhung portion  296 , a natural gutter  298  is formed that channels road splash away from this area. Electrical clearances between the module conductors  216   a ,  216   b ,  226  and the radially outer surface  176  is increased, which minimizes the possibility of these detrimental occurrences. A portion  296  of the plastic MOSFET module housing  222  extends beyond the perimeter of the pedestal  286  of the cooling tower heat sink  188  to create a ledge  300  which forms a natural gutter  298  that guides splash and provides drainage away from the area. The ledge  300  also lengthens the path between the module&#39;s copper terminals  216   a ,  216   b ,  224  and ground (i.e., the heat sink  180 ), and defines a geometry that is much harder for a conductive trace (e.g., from contaminates such as road salts) to build up. Such a conductive trace can often lead to current leakage problems. 
     The entirety of each pedestal  286  projects radially outwardly of the remainder of the tower structure  180 , with its respective radially outwardly facing, planar MOSFET module mounting surface  288  being substantially parallel with the shaft axis. Thus, the tower is provided with a plurality of discrete, circumferentially distributed pedestals about the central axis. The pedestals  286  are evenly distributed (e.g., generally equiangularly) about radially outer surface of the cooling tower, and the module mounting surfaces are oriented tangentially relative to an imaginary circle concentric with, and oriented perpendicularly relative to the longitudinal direction of, the axis. 
     The pedestal surface  288  for MOSFET module attachment provides additional mass and cross sectional area for absorbing a thermal transient, thereby minimizing thermal conduction spreading resistance from the heat source, and does so in a manner that minimizes the amount of material added, and facilitates the ease and speed of machining the pedestal surfaces to which the MOSFET modules are mounted. 
     The pedestal mounting surface  288  for each MOSFET module provides increased separation, and electrical clearance, between the conductors exiting the modules and the exposed surfaces of the cooling tower heat sink  180 , which is at ground potential. 
     The pedestals  286  provide splash and contaminant protection for the MOSFET modules by creating gutters  298  to guide splash and direct splash-borne contaminants away from the modules  154 , and provide separation distances across which conductive traces of the contaminants are less likely to build up, which reduces the likelihood of current leakage from the modules. 
     While exemplary embodiments have been disclosed hereinabove, the invention is not necessarily limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the present disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this present disclosure pertains and which fall within the limits of the appended claims.