Abstract:
In order to provide a modular arrangement, an inverter for an electric traction motor used to drive an automotive vehicle is positioned in proximity with the traction motor. The inverter is located within a compartment adjacent to one end of the electric traction motor and is cooled in a closed system by spraying a liquid coolant directly onto the inverter. The liquid coolant absorbs heat from the inverter and is cooled by a heat exchange arrangement comprising a reservoir with pipes carrying a second coolant from the radiator of the automotive vehicle. In a preferred embodiment, the coolant is collected from the inverter in an annular reservoir that is integral with the compartment containing the inverter. In accordance with one embodiment of the cooling arrangement, heat from the inverter vaporizes the liquid coolant by absorbing heat from the inverter during a phase change from a liquid to a vapor. The vaporized coolant is condensed by a circulating second coolant in pipes connected to the vehicle&#39;s radiator through a condenser that is preferably coaxial with the motor and the annular reservoir, which annular reservoir in the second embodiment collects overspray liquid coolant. In order to avoid degrading the inverter, the coolant is a dielectric fluid.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is directed to cooling arrangements for integrated electric motor-inverters. More particularly, the present invention is related to cooling arrangements for integrated electric motor-inverters wherein the motor is a traction motor used to drive electric vehicles such as, but not limited to, gas-electric hybrid vehicles and fuel cell powered electric vehicles.  
       BACKGROUND OF THE INVENTION  
       [0002]     Vehicles which utilize electric traction motors to drive wheels of a vehicle, whether the electric motor is in a gas-electric hybrid vehicle or a fuel cell powered vehicle typically use a three-phase AC motor coupled with an inverter that converts direct current from a power source to alternating current. The inverter circuitry generally comprises IGBTs (insulated gate bipolar transistors) mounted on a DBC (direct bonded copper) substrate. The DBC has integrated bus bars, and with a circuit card and signal connector provides a power electronics package.  
         [0003]     As automotive vehicles start, change cruising speeds, accelerate and brake, power demands of electric traction motors driving the vehicles fluctuate over a wide range. Fluctuations in power demand cause temperature changes in the inverters connected to the traction motors. Since the inverters comprise IGBTs mounted on the DBCs with integrated bus bars, the inverters are comprised of different materials with various coefficients of expansion. Accordingly, heat fluctuations can degrade inverters as the integrated components thereof expand at different rates tending to shift slightly with respect to one another as the components respond to temperature variations. Accordingly, it is necessary to control temperature to keep expansions and contractions of the components within optimal levels. Currently, this is accomplished by circulating fluids through heat sinks associated with the DBC or by flowing air over the power electronics to absorb and carry away heat. While these approaches currently appear satisfactory, there remains a need to more precisely control the temperature of power electronics over the life of vehicles utilizing traction electric motors in order to sustain reliability of, as well as power consumption by, the vehicles.  
         [0004]     There is a continuing effort in configuring automotive vehicles to optimize the use of space within automotive vehicles while facilitating ease of assembly and maintenance. In accomplishing optimal use of space, attempts are made to organize related components into modules, however packaging inverters with motors present a problem because inverters have different cooling requirements.  
       SUMMARY OF THE INVENTION  
       [0005]     In view of the aforementioned considerations, a cooling arrangement for cooling components of an inverter circuit has the components packaged proximate an electric traction motor for driving at least one traction wheel of an automotive vehicle. The arrangement comprises a housing disposed proximate the electric traction motor, wherein the housing has a compartment with a space containing the components. The compartment has an inlet opening and an outlet opening for cooling fluid communicating with the space containing the components. The cooling fluid is a dielectric cooling fluid which is dispensed in liquid phase into the space and onto the components of the inverter circuit by a pump provided for cycling the dielectric coolant from a reservoir that collects the dielectric coolant from the components. The reservoir uses a second coolant in a liquid-fluid heat exchanger to transfer heat from the dielectric fluid before the dielectric fluid is again cycled over the components.  
         [0006]     In a further aspect of the cooling arrangement, the reservoir is proximate the compartment containing the components, and with the pump, is an integral part of part of the housing.  
         [0007]     In a further aspect of the cooling arrangement, the compartment is disposed at one end of the electric traction motor and extends laterally with respect thereto, while the reservoir is disposed in the housing, which housing extends around the traction motor and coaxially with respect to the traction motor.  
         [0008]     In a further aspect of the cooling arrangement, the cooling arrangement further includes a control for monitoring the cooling requirements of the components, the control being connected to the pump to power the pump in accordance with the cooling requirements.  
         [0009]     In a further aspect of the cooling arrangement, the cooling arrangement is in combination with a cooling system for a fuel cell stack or a gas-powered traction engine, the cooling system having the second coolant circulating through a radiator.  
         [0010]     In a further aspect of the cooling arrangement, the components comprise an insulated gate bipolar transistor arrangement.  
         [0011]     In a further aspect of the cooling arrangement, the dielectric coolant is a mixture of polypropylene glycol methyl ether and hexamethyldisiloxane.  
         [0012]     In still a further aspect of the cooling arrangement, the dielectric coolant has a phase change point selected to absorb a substantial quantity of heat at the boiling temperature of the coolant before the coolant evaporates.  
         [0013]     In still a further aspect of the cooling arrangement, a condenser converts vaporized coolant to liquid coolant before recycling the coolant onto the components.  
         [0014]     In still a further aspect of the cooling arrangement, the condenser is coaxial with the reservoir and the electric motor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein:  
         [0016]      FIG. 1  is a schematic view of an automotive vehicle having a gas-electric hybrid drive;  
         [0017]      FIG. 2  is a schematic view of an automotive vehicle that uses fuel cell power to drive an electric traction motor;  
         [0018]      FIG. 3  is a schematic view of a first embodiment of a cooling system for cooling inverter components coupled to the electric traction motors of  FIG. 1  or  2 ;  
         [0019]      FIG. 4  is an elevation of a spray cooled, integrated motor-inverter, configured to employ the cooling arrangement of  FIG. 3 ;  
         [0020]      FIG. 5  is a perspective view, partially in section, of a spray cooled, integrated motor-inverter configured similar to that of  FIG. 4 ;  
         [0021]      FIG. 6  is a perspective view, partially in section, of the spray cooled integrated-motor inverter of  FIG. 5 , but shown from the opposite sides;  
         [0022]      FIG. 7  is a schematic diagram of a spray cooled coolant loop utilized with the vehicles of  FIGS. 1 and 2 , but configured in accordance with a second embodiment of the invention;  
         [0023]      FIG. 8  is a cross section of a spray cooled integrated motor-inverter configured in accordance with the second embodiment of the present invention shown in  FIG. 7 , and  
         [0024]      FIG. 9  is a perspective view, partially in elevation, of an integrated spray cooled motor-inverter configured similar to  FIG. 8 .  
     
    
     DETAILED DESCRIPTION  
       [0025]     Referring now to  FIG. 1 , there is shown an example of a gas-electric drive  10  for powering a vehicle  12  utilizing an internal combustion engine  14  and an electric traction motor  16  to drive, through a transmission  20 , wheels  18  of the vehicle. A power splitter  22  determines whether the internal combustion engine  14  or the electric motor  16  drives the transmission  20 , or whether the transmission  20  or internal combustion engine drives an electric generator  24 . In another embodiment, the generator  24  is mounted next to the electric traction motor  16  and cooled with the same arrangement as the traction motor. The electric generator  24  charges a battery  26  and/or provides current to an inverter  28  that delivers current to the electric traction motor  16 . In accordance with the present invention, the electric traction motor  16  and inverter  28  are configured as a modular unit  30 . This provides an opportunity for a reduction in the space consumed by the electric traction motor  16  and inverter  28 . Since the inverter  28  generates heat, the inverter requires a cooling arrangement  32 . In accordance with one aspect of the present invention, the cooling arrangement  32  has a sealed cooling circuit which is coupled thermally to a radiator  34  which cools the internal combustion engine  14 . The cooling arrangement  32  may be remote from the module  30 , as shown in  FIG. 1 , or integral therewith as shown in  FIG. 2 .  
         [0026]     Referring now to  FIG. 2 , a fuel cell drive system  10 ′ utilizes a fuel cell  40  to power an electric traction motor  16  which drives the wheels  18  through a transmission  20 ′. The fuel cell  40  is connected either directly or through a battery pack  26 ′ to inverter  28 ′ for the motor  16 . As with the gas-electric hybrid of  FIG. 1 , the inverter  28 ′ is integral with the motor  16  to provide a power module  30 ′. Moreover, as with the gas-electric hybrid of  FIG. 1 , the inverter  28 ′ has a cooling arrangement  32 ′ that is coupled thermally to a radiator  34 ′ used to cool the fuel cell  40 . The motor  16  and inverter  28 ′ are associated in a module  30 ′, which module  30 ′ includes the cooling arrangement  32 ′ integral therewith. Alternatively, the cooling arrangement  32 ′ can be remote from the module  30 ′, as is shown by the cooling arrangement  32  of  FIG. 1 .  
         [0027]     Referring now to  FIG. 3 , a first embodiment of the cooling system  32  or  32 ′ shown in  FIGS. 1 and 2 , respectively, is usable with either the gas-electric hybrid drive  10  or the fuel cell drive  10 ′. The gas-electric hybrid drive  10  and the fuel cell drive  10 ′ are merely exemplarily of various configurations for such drives. For example, the gas-electric hybrid drive  10  can be configured as a parallel arrangement, a series arrangement or any other effective arrangement, as can the fuel cell drive  10 ′. The gas-electric hybrid drive  10  may use a gasoline engine, a diesel engine, a turbine engine or any other engine configuration.  
         [0028]     The inverter  28  is positioned within a compartment  50  which is disposed adjacent to the electric motor  16 . The inverter  28  includes insulated gate bipolar transistors (IGBTs)  52  which are bonded with a direct bonded copper (DBC) substrate  54  that is integrated with an AC/DC bus to form an inverter circuit. The IGBT  52  is cooled by a coolant dispenser  60  which has spray nozzles  62  that dispense coolant  64  in liquid form directly on the IGBTs  52  and the associated DBC  54  and bus. While the illustrated embodiment sprays the coolant  64  as liquid droplets, in other embodiments the coolant is dispensed in stream form or flooded over the inverter  28 . In still another embodiment, the inverter  28  is immersed in the liquid coolant  64 , but preferably the liquid coolant  64  is sprayed as a mist or in discreet droplets onto the inverter  28 .  
         [0029]     By using the coolant dispenser  60 , coolant liquid  64  is applied directly to the source of heat of the IGBT  52 , which allows the power density (power per unit volume) of the motor inverter  28  to be increased. To be cooled by the liquid coolant  64 , heat generated by the IGBT  52  need not travel through multiple layers of materials, a few of which have low thermal conductivity. Rather, a direct thermal path provided by spray cooling reduces the temperature of the IGBT  52 . With lower temperature for the IGBT  52 , increased power is available through the inverter  28  to the traction motor  16 . Alternatively, with improved cooling a smaller inverter  28  may be provided to produce the same power level for the traction motor  16 .  
         [0030]     The spray cooling provided by the spray nozzles  62  is also usable on other components associated with the inverter  28 , such as capacitors, transformers, integrated circuits and bus bars that are temperature sensitive. The spray cooling provides cooling to wire bonds between the elements of the IGBT  52  and prevents wire bonds from overheating, consequently helping to minimize failure. Accordingly, along with the resulting reduction of component temperatures, improved reliability is provided.  
         [0031]     Because spray cooling provides increased cooling capacity, spray cooling improves resistance of the inverter  28  to transient power fluctuations. Transient power fluctuations exist on the input to the power inverter  28  due to sudden increases in power demanded by the vehicle  12  for short periods of time. The fluctuations can be caused by increased resistance to the output of the motor  16  which in turn cause temperature increases in the IGBT  52 . By having direct application of the cooling media  64  to the IGBT  52 , temperature change is reduced in both time duration and temperature increase.  
         [0032]     In order that the coolant  64  not electrically interact with or degrade the components of the inverter  28 , the coolant is a dielectric coolant. A suggested coolant is a mixture of methylsiloxane and an organic compound such as polypropylene glycol methyl ether, wherein the coolant has minimal instability and reactivity. An example of such a liquid is OS-120 available from Dow Corning Corporation, which is a mixture of hexmethyldisiloxane and propylene glycol methyl ether, the hexmethyidisiloxane having a percentage by weight greater than 60% and the propyleneglycol methyl ether having a percentage by weight in a range of 10% to 30%. Other dielectric coolants which have minimal instability and reactivity with the electrical components of the inverter may be used as alternatives to OS-120.  
         [0033]     Referring again to  FIG. 3 , the coolant  64  is sprayed as a liquid and is collected in a sump portion  70  of the compartment  50  and through a spray return  72  to a reservoir  74  which is connected through a filter  75  to a pump  76 . The pump  76  is connected to the dispenser  60  that supplies recycled liquid coolant to the spray nozzles  62  for continued cooling of the inverter  28 . While the coolant  64  is circulating through the reservoir  74 , it is cooled by a second liquid coolant  77 , such as a water ethylene glycol solution, which flows through tubes  78  in the reservoir  74 . The second liquid coolant  77  is supplied by the radiator  34 , which cools the internal combustion engine  14  of  FIG. 1  or is supplied by the radiator  34 ′, which cools the fuel cell stack  40  of  FIG. 2 . The pump  76  is preferably a variable speed pump which is controlled by the output of the IGBTs  52 . As the output of the IGBTs  52  increases, the speed of the pump  76  increases which increases the amount of liquid coolant  64  sprayed through spray nozzles  62 . Alternatively, the temperature of the IGBT  52  may be monitored with a thermocouple arrangement with the speed of the pump  76  being increased as the temperature of the IGBT increases to spray more liquid coolant and thereby decrease the temperature of the IGBT.  
         [0034]     Referring now to  FIG. 4 , there is shown a preferred arrangement for the spray cooled coolant loop  30  or  30 ′, wherein the spray cooled coolant loop of  FIG. 3  is integral with the compartment  50  containing the inverter  28  supported on a base  79 . In  FIG. 4 , the reservoir  74  and cooling coils  78  are disposed in a reservoir portion  74  that surrounds the motor  16  and extends coaxially with respect to the motor. The reservoir  74  is substantially annular in shape and includes the cooling channels or cooling channel  78  connected by an inlet  80  and an outlet  82  to a vehicle radiator such as one of the vehicle radiators  34  or  34 ′ of FIGS.  1  and  2 , respectively. The reservoir  74  is filled by heated liquid coolant  64  flowing from the inverter  28  through an opening, such as the opening  83  in the support  79  for the inverter, and is connected by a return  84  to a sump  86  that is connected to the coolant pump  76  through the filter  75 . The coolant pump  76  is connected by line  87  to the dispenser  60  and spray nozzles  62 . The spray nozzles  62  preferably dispense the coolant  64  in liquid phase as droplets or a mist onto the inverter  28 . Heat is then transferred from the inverter  28  to the liquid coolant  64 . The liquid coolant  64  then drains into and cools in the reservoir  74 , where heat is removed therefrom by the second coolant  77  circulating through the channels or channel  78  over or past which the heated liquid coolant  64  flows. Preferably, the pipe channels are next to an inner wall  88  of the reservoir  74  so that the second cooling fluid  77  rejects heat from the stator  89  of the motor  16 . The pump  76  recycles the liquid coolant  64  in accordance with the power demands of the inverter  28 .  
         [0035]      FIGS. 5 and 6  show the module  30  or  30 ′ of  FIG. 4  as it might appear in an installed embodiment where it is seen that the compartment  50  has a base  90  therein which supports the coolant dispenser  60  having the spray nozzles  62  that dispense liquid coolant  64 . Also supported on the base  90  is the inverter  28  that is comprised of the DBC substrate  54  with the insulated gate bipolar transistors (IGBTs)  52  thereon and is integrated with the AC/DC bus to form one phase of the inverter circuit. In  FIGS. 5 and 6  these elements are at different angular positions with respect to the compartment  50  then in  FIG. 4  in order to illustrate an alternative arrangement. Also mounted on the base  90  is a circuit card  92  that is connected to a signal connector  94  for controlling the input and output current of the inverter  28 . The inverter  28  is connected to a DC power source such as the batteries  26  or  26 ′, or the generator  24 , of  FIG. 1  or  2  by a pair of direct current terminals  95  and  96 . The annular reservoir portion  74  of the module  30 , which includes the channels  78  for the second coolant  77 , extends from a mounting ring  97  to which a cover  98  is bolted by bolts  100  that are received in relieved portions  102  of the cover and threaded into lugs  104  on the mounting ring  97 . The inlet  80  and outlet  82  supplying the second coolant  77  to the channels  78  is connected through the outer wall of the reservoir portion  74  to the channels.  
         [0036]     Openings, such as openings  83 , in the mounting ring  96  allow coolant  64  that is pooled on the base  90  to flow into the annular reservoir  74  where it is cooled by the gas engine or fuel cell coolant  77  which has passed through the radiator  34  or  34 ′. The coolant pump  76  returns the liquid coolant  64  filtered by the filter  75  to the nozzles  62  via the inlet line  87 . The filter  75  and the pump  76  are disposed within a housing portion  107  that also includes the sump  86 . By having the cover  98  mounted with bolts  100  to the mounting ring  96  to form the compartment  50 , the circuit card  92  and inverter  28  are accessible for maintenance if required. The compartment  50  and the reservoir  74  cooperate to define a housing  108  in which the compartment extends laterally from the axis  110  of the motor  16 , and in which the reservoir is an annular space that is coaxial with the motor.  
         [0037]     Referring now to  FIGS. 7-9  where a second embodiment of the invention is shown, in  FIGS. 7-9  similar reference numerals identify similar structure shown in  FIGS. 3-6 . The cooling arrangement described in the second embodiment of the invention takes advantage of the latent heat of vaporization of coolant  64 . When coolant  64  is sprayed onto components that are hotter than the vapor temperature of the coolant, the coolant changes state or phase from a liquid to a vapor  64 ′. The vapor  64 ′ carries the waste heat away from the inverter  28  as the vapor disperses into the chamber  50 ′. In the embodiment of  FIGS. 7-9 , the coolant loop  30  or  30 ′ includes a condenser  200  which is separate from the reservoir  74 ′, as well as a separate line  206  for conveying vaporized coolant  64 ′ from the compartment  50 ′ to the condenser  200 . As with the first embodiment of  FIG. 3 , a second coolant  77  from the vehicle radiator  34  or  34 ′ is circulated through the coolant pipes  78 ′ to change the phase of the coolant  64 ′ from a vapor back to a liquid. The liquid  64  from the condenser mixes with the liquid in the reservoir  74 ′ and is filtered by a filter  75  prior to being pumped by the pump  76  back to the fluid dispenser  60 , where the coolant  64  is sprayed in liquid form onto the power inverter  28 .  
         [0038]     In the embodiment of  FIGS. 7-9 , the pump  76 ′ is preferably a variable output pump which is controlled by a controller  210  that is activated by an output current signal from the IGBTs  52  that increases the rate of pumping as the output power of the IGBTs increases. By providing variable spray cooling, temperature control under all operating conditions is achieved. This increases component reliability by minimizing temperature changes so that the inverter  28  operates under substantially isothermal conditions. By consistently controlling the amount of dielectric coolant  64  sprayed through the atomizer nozzles  62  so as to create a liquid mist, at maximum power dissipation conditions, constant flow of the liquid mist exhibits a phase change converting to a vapor  64 ′ when sprayed on the inverter  28 . When the phase change occurs, the power dispensing IGBTs  52  remain at substantially constant temperature regardless of increasing power dissipation. By varying the flow of the liquid coolant  64  relative to actual component power dissipation, the phase change region of the fluid comprising the liquid coolant  64  is utilized so that the coolant accommodates all operating conditions.  
         [0039]     An example of a coolant utilized in the embodiment of  FIGS. 7-9  is the aforementioned OS-120 available from Dow Corning Corporation of Midland, Mich.; OS-120 being a mixture of methylsiloxane and an organic compound. OS-120 has a boiling point of about 98° C. and is a dielectric material that does not degrade when used to cool the interconnected electrical components. The dielectric liquid coolant  64  continues to absorb heat at 98° C. without changing phase to its vapor form  64 ′ until the heat capacity of the coolant reaches its boiling point, at which time the liquid coolant vaporizes carrying away heat generated by the IGBTs  52  and by other components of the power electronics package.  
         [0040]     Referring now to  FIG. 8 , the spray cooling arrangement of  FIG. 7  is preferably utilized in the form of a module  30  or  30 ′ as exemplified by  FIG. 8 . Vapor  64 ′ is pulled by negative pressure of the pump  76 ′ through openings  83 ′ in base  79 ′ and into the condenser  200 , which is formed as an annular channel  201  having the pipes  78 ′ located therein or adjacent thereto. The vaporized coolant  64 ′ is condensed to the liquid coolant  64  on condenser  200  prior to passing into passageway  206 . Any remaining vapor  64 ′ mixes with the liquid coolant  64  in the reservoir  74 ′ and all of the cooled and condensed coolant is sucked through the passageway  206  and into the sump  86  by the pump  76 ′. The liquefied and cooled coolant  64  then is recycled by the pump  76 ′ from the sump  86  and sprayed in as a liquid mist  64  through the nozzles  62 .  
         [0041]     Referring now to  FIG. 9 , a perspective view illustrates a configuration of the modular unit  30  or  30 ′ shown in  FIG. 8 , which modular unit is configured similarly to the first modular unit shown in  FIGS. 5 and 6 . A structural difference between the embodiment of  FIG. 9  and that of  FIGS. 5 and 6 , is that in  FIG. 9  the condenser  200  is included and includes an annular channel  201  which is coaxial with both the cooling reservoir  74 ′ and electric motor  16  to provide a compact, modular motor-inverter having the spacial and convenience aspects of the modular unit illustrated in  FIGS. 5 and 6 . Preferably, in  FIG. 9  the condenser  200  is disposed between the reservoir  74 ′ which collects oversprayed liquid  64  and the annular channel  201  in which the vaporized coolant  64 ′ is condensed. In other configurations the condenser may be disposed outboard of the annular channel  201  or may be positioned next to the inner wall  88  proximate the stator  89  of the motor  16 . In still another arrangement separate channels  78  and  78 ′ cool the liquid  64  and condense the vapor  64 ′ within the module  30  or  30 ′. As with  FIGS. 5 and 6  with respect to FIG.  4 , the angular location of the inverter  28  with respect to the nozzles  62  in  FIG. 9  differs from the location in  FIG. 8 , in order to illustrate an alternative arrangement.  
         [0042]     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.