Abstract:
An electric machine for converting electrical energy to mechanical energy is disclosed. The electric machine includes a stator having an outer layer, a first intermediate layer, a second intermediate layer, and an inner layer. The electric machine further includes a rotor axially aligned and positioned within the stator. The rotor has at least one permanent magnet, and at least one busbar. The busbar is attached to the first intermediate layer. The busbar includes at least one bare power die in electrical communication therewith.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present invention claims priority to U.S. Provisional Serial No. 60/387,773, filed on Jun. 10, 2002, entitled “Machine Integrated Power”. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates to electric machines having integrated electronics.  
         BACKGROUND  
         [0003]    Conventionally, electric machines have their power electronics outside the housing of the electric machine. There are at least two reasons for separating the power electronics from the electric machine. First, the volume taken up by the power electronics is such that it is difficult to package the electric machine in the intended application. Second, the environment inside an electric machine housing is significantly harsher than the conventional environment for power electronics.  
           [0004]    One significant problem that must be addressed in power electronics apparatus is heat generation. Conventionally, a heat spreader is coupled to the power electronics to enhance heat dissipation. Metals (such as copper) are good for heat spreading, as they quickly conduct the heat away from the power die. Ceramics are not as good since their thermal conductivity is not nearly as good. Thus, metals are able to carry heat away from the die much more effectively than a ceramic substrate.  
           [0005]    Power dies, which are central to power electronics, create a great deal of heat and must have some form of cooling technology in place to dissipate heat. Power dies are typically packaged in a large insulating (typically ceramic) substrate. One of the reasons the ceramic substrate is used is to prevent stressing the die. More specifically, the coefficient of thermal expansion (CTE) of the ceramic substrate is more closely matched to the power die than to a metal substrate. This insulating or ceramic substrate is typically soldered to a metal heat spreader. The metal heat spreader is then mounted to a heatsink in the power electronics. The ceramic packaging, metal baseplate, heatsink and solder add to thermal resistance. A system that has a very low thermal resistance will be able to cool more efficiently.  
           [0006]    The cost and size of an electric machine can be reduced if the power electronics can be made so compact to be housed within the electric machine. Unfortunately, conventional inverters and the required cooling apparatus are too bulky to be placed inside an electric machine. Thus, a new and improved method and system for packaging power electronics is needed.  
         SUMMARY  
         [0007]    In one embodiment, the present invention provides a three phase inductance motor with power electronics inside the same housing as the electric machine. The power electronics can be arranged around the circumference of the three phase inductance motor (circumference mount).  
           [0008]    In an alternative embodiment the power electronics can arranged at the end of the motor (pancake mount).  
           [0009]    In the circumference mount embodiment, the capacitors utilized will be belt capacitors used for DC link capacitance.  
           [0010]    Alternatively in the circumference mount embodiment, conventional capacitors can be used for DC link capacitance.  
           [0011]    In the pancake mount embodiment, pancake capacitors will be utilized for the DC link capacitance.  
           [0012]    Alternatively in the pancake mount embodiment, conventional capacitors can be used for DC link capacitance.  
           [0013]    In one embodiment, the connectors of the DC link can be integrated with the busbar.  
           [0014]    In an alternative embodiment, the connectors of the DC link can utilize the housing of the three phase inductance motor as their housing.  
           [0015]    In one embodiment, bare power dies are connected using wirebonds.  
           [0016]    In an alternative embodiment, bare power dies will be connected to a busbar or a circuit board using area bonds.  
           [0017]    In an alternative embodiment, bare power dies are treated as bFlip Chip devices, and a thermally conductive underfill material is used to conduct heat from the top of the die to a thermally conductive medium over the die, as well as to the cold plate under the die.  
           [0018]    In an embodiment of the present invention, the bare power dies will be attached to a heat spreader by the use of a liquid metal die attach.  
           [0019]    In a preferred embodiment, a vapor liquid heat spreader is used beneath the bare power dies and busbar to cool the power electronics.  
           [0020]    In another embodiment of the present invention, cooling is accomplished with air cooling.  
           [0021]    In yet another embodiment, cooling is accomplished with liquid cooling.  
           [0022]    In yet another embodiment, busbars upon which the bare power dies are mounted will contain liquid cooling features.  
           [0023]    In a preferred embodiment, an etched tri-metal circuit board is bonded to the bare power die to carry current.  
           [0024]    In another embodiment, etched tri-metal is used for the control circuits.  
           [0025]    In yet another embodiment, etched tri-metal circuit board is used for both the busbar and for the control electronics.  
           [0026]    These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0027]    [0027]FIG. 1 is a schematic of the machine integrated power with circumference mounted power electronics, in accordance with the present invention;  
         [0028]    [0028]FIG. 2 is a schematic of an up close view of circumference mounted power electronics, in accordance with the present invention;  
         [0029]    [0029]FIG. 3 is a schematic of the machine integrated power with pancake mounted power electronics, in accordance with the present invention;  
         [0030]    [0030]FIG. 4 is a schematic of a power die interconnect using liquid metal die attach, in accordance with the present invention;  
         [0031]    [0031]FIG. 5 a  is a schematic diagram of a power die interconnect using liquid metal die attach and flip chip technology, in accordance with the present invention;  
         [0032]    [0032]FIG. 5 b  is a schematic diagram of another embodiment of a power die interconnect using liquid metal die attach and flip chip technology, in accordance with the present invention;  
         [0033]    [0033]FIG. 5 c  is a schematic diagram of yet another embodiment of a power die interconnect using liquid metal die attach and flip chip technology, in accordance with the present invention;  
         [0034]    [0034]FIG. 6 is a schematic diagram of a liquid cooled busbar with an attached power die, in accordance with the present invention;  
         [0035]    [0035]FIG. 7 a  is a schematic diagram of a vapor liquid heat spreader, in accordance with the present invention;  
         [0036]    [0036]FIG. 7 b  is a schematic diagram of another embodiment of a vapor liquid heat spreader, in accordance with the present invention;  
         [0037]    [0037]FIG. 7 c  is a schematic diagram of yet another embodiment of a vapor liquid heat spreader, in accordance with the present invention; and  
         [0038]    [0038]FIG. 8 is a schematic diagram of an integrated electrical etched tri metal busbar connector, in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0039]    Referring now to FIG. 1, an electric machine  10  is illustrated in a circumference mount configuration. Preferably, electric machine  10  is a three phase inductance motor. Electric machine  10  includes a stator  12  and a rotor  14 . Stator  12  has at least four layers. The four layers are comprised of an outer layer  24 , a first intermediate layer  26 , a second intermediate layer  28  and an inner layer  30 . The layers are coupled to each other using mechanical fasteners or by similar means. Outer layer  24  is preferably a belt capacitor. The belt capacitor serves to electrically isolate electric machine  10  from the surrounding environment. The first intermediate layer  26  is a cold plate. The cold plate is used to cool the power electronics. Second intermediate layer  28  is a thermally insulating layer. The thermally insulating layer  28  provides a barrier against heat transmission. Inner layer  30  is a structural layer that supports the previously mentioned layers. A plurality of busbar retainers  22  are fixed to an exterior surface  29  of inner layer  30 . Busbar rings  20  are on the inside of inner layer  30 . Busbar rings  20  are held in place by busbar retainers  22 . Rotor  14  is attached to a shaft (not pictured). The shaft is mounted to a pole wheel (not pictured). Attached to rotor  14  are permanent magnets  16 . When stator  12  is energized, rotor  14  will rotate when the permanent magnets  16  couple with the flux emanating from stator  12 .  
         [0040]    With reference to FIG. 2, power electronics  23  (including bare power dies  36 ) that are shown integrated into electric machine  10 . Motor phase busbars  32  extend from busbar rings  20 . Bare power dies  36  are mounted to a liquid cooled busbar  34 . Extending from bare power dies  36  are wire bonds  38 . At either end of belt capacitor  24  is a low side link  40  and a high side link  42 . Here, bare power dies  36  create heat. To prevent bare power dies  36  from failing because of heat, liquid cooled busbar  34  is used to cool bare power dies  36 . Wire bonds  38  connect bare power dies  36  to electric machine  10 . Low side link  40  and high side link  42  connect to the power electronics to a supply current.  
         [0041]    In alternative embodiment, as shown in FIG. 3, electric machine  10  is a pancake mount configuration  44 . For a pancake mount, power electronics  23  (i.e. bare power dies  36 ) are mounted at an end of electric machine  10  as opposed to the circumference mount (as shown is FIG. 1) where the power electronics are mounted around the circumference of electric machine  10 . Substantially, all other aspects of the pancake mount configuration  44  are similar to the circumference mount.  
         [0042]    Attached to motor housing  46  are at least two layers: lower layer  48  and upper layer  50 . Lower layer  48  is a pancake capacitor. Upper layer  50  is a pancake cold plate. The pancake cold plate is used to cool power electronics  23  while the pancake capacitor is used to provide electrical noise insulation from electric machine  10 . Projecting out from upper layer  50  is positive DC link connector  54  and negative DC link connector  56 . Mounted to upper layer  50  is a high side busbar  62 . Liquid cooled busbar  62  is used to cool bare power dies  36 . Connecting bare power dies  36  to busbars  62  are wire bonds  38 . Low side busbars  64  extend radially outward from the center of pancake mount  44 . Pancake mount  44  operates substantially the same way as the circumference mount. Thus, when the stator housing (not shown) is energized, the rotor (not shown) will rotate when the permanent magnets (not shown) couple with the flux emanating from stator housing.  
         [0043]    [0043]FIG. 4 illustrates an attachment method for mounting a bare power die  36  to a liquid cooled busbar  62 . A liquid metal die attach  66  is deposited between liquid cooled busbar  34 , which for a pancake mount is high side and low side busbar  62  and  64 , and bare power die  36 . A sealant  72  serves to bond bare power die  36  to liquid cooled busbar  34  and contain liquid metal die attach  66  between liquid cooled busbar  34  and bare power die  36 . In operation, liquid metal die attach  66  absorbs heat from bare power die  36 . As liquid metal die attach  66  heats up, the CTE of liquid metal die attach  66  closely resembles that of bare power die  36 , so stress induced damage to bare power die  36  is eliminated. In turn, liquid metal die attach  66  conducts heat to the liquid cooled busbar  34 . The construction and operation of liquid cooled busbar  34  will be described hereinafter.  
         [0044]    [0044]FIG. 5 a  illustrates alternative attachment methods for bare power dies  36 . Similar to the attachment method illustrated in FIG. 4, liquid metal die attach  66  is deposited between bare power die  36  and liquid cooled busbar  34 . Liquid metal die attach  66  is held in place by sealant  72 . However, in contrast to previously described embodiments, bare power die  36  is connected to the power electronics via the use of electrical interconnect liquid metal die attach  74  from the top of bare power die  36 . Similar to liquid metal die attach  66 , electrical interconnect liquid metal die attach  74  has sealant  76  that holds the liquid metal die attach used for electrical interconnect in place. The electrical interconnect liquid metal die attach  74  bands bare power die  36  to interconnect substrate  77 . The interconnect substrate  77  transfers thermal energy from bare power die  36  to a top side heat sink  80 . Further, a thermal adhesive  78  is disposed between interconnect substrate  77  and heat sink  80  to facilitate heat transfer. Above the thermal adhesive is a top side heat sink  80 . The role of the thermal adhesive  78  and the top side heatsink  80  is to provide additional cooling to the bare power die  36 .  
         [0045]    In yet another embodiment of the present invention, an alternative attachment method for attaching bare dies  36  to liquid cooled busbar  34  is provided and illustrated in FIG. 5 b . In the present attachment method, bare power die  36  is secured to busbar  34  using liquid metal die attach  66 , which forms a mechanical as well as an electrical connection to busbar  34 . Epoxy  67  acts as an underfill and contains liquid die attach  66  within a predefined area. For example, liquid die attach  66  may electrically interconnect bare power die&#39;s gate and source to busbar  34 . Further, a conductive metallic tab  69  is provided over and soldered to a top surface of bare die  36  for providing electrical connection to busbar  34 . For example, metal tab  69  may connect a drain of bare power die  36  to busbar  34 . An adhesive layer  71  is provided over metal tab  69  for adhering a heat sink  73  to metal tab  69 . Thus, heat is transferred to the substrate and heat sink using both sides of die  36 . Epoxy or underfilment  67  is provided to accommodate for mismatch in thermal coefficients of expansion.  
         [0046]    Referring now to FIG. 5 c , an alternate method for attaching power die  36  to busbar  34  is illustrated, in accordance with the present invention. Bare power die  36  is electrically interconnected to busbar  34  using liquid metal die attach  66  within a predefined area and an adhesive sealant  72 . Adhesive sealant  72  contains liquid metal die attach  66  as well as provides adhesion of bare power die  36  to busbar  34 . Further, a metal tab connection  69  electrically interconnects a drain of bare power die  36  to busbar  34 . Further, a heat sink  73  is adhered or attached to metal tab connection  69  with liquid metal die attach  66 . Additionally, heat sink  73  has a bottom surface  75  that includes an electrically insulating but thermally conducting material. Bottom surface  75  may be flame or blast sprayed with a ceramic or may be anodized aluminum.  
         [0047]    [0047]FIG. 6 is cross-sectional view of bare power die  36  and liquid cooled busbar  34  or pancake mount busbar  62 , as shown in FIG. 2 and FIG. 3, respectively. As shown, bare power die  36  is bonded to electrically conductive busbar  84  via liquid metal die attach  66  and sealant  72 . Coupled to and extending from bare power die  36  is wire bond  38 . Further, electrically conductive busbar  84  is coupled to an electrically insulative material  86 . In turn, electrically insulative material  86  is coupled to a thermally conductive material  88 . Defined within thermally conductive material  88  is cooling channel  90 .  
         [0048]    In operation, liquid metal die attach  66  transfers heat from the bare power die  36  to electrically conductive busbar  84 . Electrically conductive busbar  84  is electrically insulated from thermally conductive material  88  by insulative material  86 . To cool bare power die  36 , cooling channel  90  is filled with a liquid that absorbs heat from thermally conductive material  88 .  
         [0049]    An alternative form of cooling busbar  84  is a vapor liquid heat spreader (VLHS)  90 , as shown in FIG. 7 a . Liquid  92  is heated by the power electronics. As the liquid heats up, it becomes vapor (as indicated by arrow  94 ). Vapor  94  rises to the top of VLHS  90  where it is cooled by fins  96 . Vapor  94  then cools and becomes liquid  92 . Conductive porous material  98  channels liquid  92  back down to the bottom of VLHS  90  and then the process repeats itself. Arrows  91  indicate where heat is absorbed by VLHS  90  and arrows  93  indicate where heat is expelled from VLHS  90 .  
         [0050]    Referring now to FIG. 7 b , an alternate embodiment of a vapor liquid heat spreader  95  is illustrated, in accordance with the present invention. Vapor liquid heat spreader  95  includes a cold plate  97  having a plurality of fins or condenser plates  99 . Further, cold plate  97  includes sides  101  which define, along with cold plate  97 , a cavity  103 . Within cavity  103  is a dielectric liquid  105 . Further, evaporators  107  and  109  are provided for vaporizing dielectric liquid  105 . Pressure build-up at the evaporator forces the vapor of the dielectric liquid to radiate outward as indicated by arrows A and B. The vapor of the dielectric liquid condenses over a wide area spreading its latent heat. The cold plate is cooled by free or forced convection of air or liquid. Condensate is returned to evaporator  107  or  109  by capillary action or gravity.  
         [0051]    Referring now to FIG. 7 c , a schematic diagram illustrates the attachment of bare power die  36  to cold plate  97 . Bare power die  36  would in one embodiment be attached to a busbar  34  by methods previously described. In operation, power die  36 , as well as other electronic components  111  attached to busbar  34 , will create heat which will be dissipated by dielectric liquid  105 . Evaporators  113  are submerged in dielectric liquid  105 . A plurality of cooling fins  115  are disposed along cold plate  97  to dissipate heat generated by bare power dies  36  and electronic components  111 . As the vapor of dielectric  105  rises and spreads, latent heat is transferred to cooling fins  115 .  
         [0052]    The vapor liquid heat spreaders of the present invention have many advantages over prior art heat spreaders. For example, the vapor liquid heat spreaders eliminate bulky and heavy metallic slabs, in traditional heat spreaders. Further, the thermal stack is simplified resulting in a reduced cost. Additionally, an insulating element is provided in the thermal stack to prevent electrical transmission. Thus, the resulting heat spreader has enhanced thermal performance.  
         [0053]    [0053]FIG. 8 shows the use of etched tri-metal (ETM) technology to construct a busbar  100 . Generally, ETM circuit board  106  has three layers: an upper layer  102 , a middle layer  104  and a lower layer  106 . In an embodiment of the present invention, upper layer  102  and lower layer  106  are made of copper and middle layer  104  is made of aluminum. U.S. Pat. No. 3,801,388 to Akiyama et al., U.S. Pat. No. 4,404,059 to Livshits et al., U.S. Pat. No. 5,738,797 to Belke, Jr. et al. and U.S. Pat. No. 6,381,837 to Baker et al, all of which are incorporated herein by reference, disclose various methods for constructing ETM circuit boards. Bare power dies  36  are area bonded to busbars  100 . Busbars  100  are cooled by specially etched forced or free convection cooling constructions, integrated with traditional control electronics, connected to external electrical systems by etched connector features, etched to construct electronic circuitry and populated with electronic content.  
         [0054]    Advantages and benefits of the present invention include elimination of separate components through integration, which includes elimination of the interconnection system between the inverter and motor. Normally, this would consist of a large connector on both the inverter and the motor and a large shielded cable in-between. The elimination of these components significantly decreases the volume, cost and weight of the electric machine. Elimination of the inverter housing, which is the heaviest part of the inverter, includes a combination of busbar and connector contacts, a combination of the connector housing with module housing, and a combination of motor phase busbars with power electronic busbars.  
         [0055]    Shrinking the volume of required components involves maximization of the use of packaging space through utilization of pancake capacitors and shrinking the volume requirement of the DC link capacitance by the cooling approaches described above. This is accomplished by placing the pancake capacitor just inside the electronics coldpate.  
         [0056]    In conventional inverters, the busbars are large because they serve to connect electronic components that are bulky and are spread out in space. By the elimination of power switch packaging and utilizing a capacitor package which is optimized for the inverter package, all of the connection points are brought close together which allows for significant reduction in the busbar size, weight, and cost. The volume taken up by the power switches is greatly reduced as the bare power dies are introduced directly into the inverter package. Ordinarily, a standard transistor package must be utilized, and the inverter package mechanicals need to be designed around it. In the present invention, the switches are bare power dies, and the dies are placed in a configuration to minimize the size requirement for the overall inverter.  
         [0057]    Improvement of the electrical and thermal properties of the inverter through integration is achieved, since the bare power dies can be mounted closer to the DC link busbar. The electromagnetic compatibility (EMC) of the inventor-motor combination of the present invention is much improved, since the power dies are in close proximity to the motor phase windings, where the power is produced or consumed, and then the assembly is enclosed in a single, thick metallic housing. The inductance from the bare power die to DC link is greatly reduced, since there is a direct metal attachment (liquid metal die attach) between the die and the copper DC link busbar.  
         [0058]    As any person skilled in the art of electric machines having integrated electronics will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.