Abstract:
A power control unit that controls a rotary electric machine that drives a vehicle, and that is mounted onto a motor case in which the rotary electric machine is housed, includes a fixed base that is made of resin; a cooler that is arranged on the fixed base and that includes a power module; and a control substrate that is arranged on the cooler. The fixed base inhibits conduction of heat from the motor case to the power control unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a power control unit that controls a rotary electric machine that drives a vehicle, and that is mounted onto a motor case in which the rotary electric machine is housed. 
         [0003]    2. Description of Related Art 
         [0004]    Electric vehicles in which the vehicle is driven by driving force from a rotary electric machine such as a motor-generator, hybrid vehicles in which the vehicle is driven by a combination of a rotary electric machine and an engine that is an internal combustion engine, and fuel cell vehicles in which the vehicle is driven by electric power generated by a fuel cell, and the like are known. These kinds of vehicles are equipped with a PCU (power control unit) that receives a supply of electric power from a battery, and has a step up converter and an inverter and the like that control the electric power to a motor-generator (hereinafter, also referred to as “motor”). 
         [0005]    Typically, in order to operate the motor efficiently, high voltage must be supplied. For example, a hybrid vehicle provided with a step up converter that steps up battery voltage of approximately 200 volts to approximately 600 volts is known. The step up converter includes a switching element and a reactor that is connected to the switching element. The reactor includes a core that uses magnetic material, such as an iron core, and a coil that is provided with the core. Also, the step up converter stores and releases electric power to and from the reactor by controlling the switching element on and off, thus enabling the voltage that is supplied from the battery to be stepped up and supplied to the inverter. At this time, in the reactor, the core generates heat from electromagnetic energy conversion, and the coil generates heat from the Joule heat of flowing current. If the heat is not suitably released, the temperature of the reactor will rise and the voltage conversion efficiency of the step up converter will decrease, so heat must be suitably released from the reactor. Thus, regarding heat release from a reactor, there is technology for releasing heat by cooling fins on the reactor, and technology for releasing heat using coolant, and the like. 
         [0006]    Japanese Patent Application Publication No. 2008-72813 (JP-A-2008-72813) describes a drive apparatus of a hybrid vehicle that is provided with a step up converter of which a reactor is a constituent element. With the drive apparatus described in JP-A-2008-72813, in order to promote heat release from the reactor when the inverter and the motor are arranged together in a single case, lubricating oil that has been drawn up by the rotation of a motor-generator is made to flow into a housing chamber in which the reactor is housed, and the reactor is cooled by the lubricating oil stored in the housing chamber. 
         [0007]      FIG. 5  is a view of a drive apparatus  100  according to related art, and shows a cross section of a motor-generator MG 2  and a reactor L 1  on the front side, and a differential gear, a power element substrate  109 , a capacitor C 2 , and a cooler  108  having cooling vents  106  and  107  behind the motor-generator MG 2  and the reactor L 1 . Lubricating oil is drawn up as shown by arrows F 1  and F 2 , by the rotation of the motor-generator MG 2 , and lubricating oil that has passed through an open portion  340  in the housing chamber flows into a reactor housing chamber  300 . The lubricating oil that flows in cools the reactor L 1  and is discharged from an oil drain hole  320  to an open portion  102  as shown by arrow F 3 . This kind of structure makes it possible to ensure the cooling ability of the reactor L 1 . 
         [0008]    As described above, with technology for cooling the reactor L 1  using lubricating oil when motor-generators MG 1  and MG 2 , a step up converter for driving these motors, and an inverter are all housed together, the temperature of the lubricating oil is regulated by coolant that cools a motor case and an engine case, so during normal operation, the coolant temperature and the oil temperature are substantially the same temperature (for example, approximately 85° C. to approximately 90° C.). On the other hand, in a heavy-load operating state, the heat rapidly generated by the engine and the motor-generators causes the oil temperature to become higher than the coolant temperature, so not only is the ability to cool the reactor a concern, but the transfer of heat to the step up converter and the inverter that are arranged near the reactor is also a concern. 
         [0009]    The step up converter and the inverter and the like have power element substrates, and the temperature of these power element substrates is regulated by the temperature of the coolant in the cooler  108 . Normally temperature regulation is performed by a large radiator and fan, but if heat exceeding the capacity of the cooler  108  is transferred to the cooler  108  in a heavy load state, the running performance of the vehicle may decrease due to output limiting control that accompanies a rise in the temperature of the power elements. 
         [0010]    In particular, when the step up converter and the inverter that form the power control unit are arranged together with the motor in a single case as described above, the temperature of the power control unit will rise from heat conduction from the case, heat conduction from an aluminum die-cast cover that covers the power control unit, and the convective heat of the air inside the cover. 
       SUMMARY OF THE INVENTION 
       [0011]    The invention provides a power control unit that is mounted in such a way that cooling ability of the power control unit is ensured, even when a step up converter and an inverter that form the power control unit are housed together with a motor in a single case. 
         [0012]    One aspect of the invention relates to a power control unit that controls a rotary electric machine that drives a vehicle, and that is mounted onto a motor case in which the rotary electric machine is housed. This power control unit includes a fixed base that is made of resin; a cooler that is arranged on the fixed base and that includes a power module; and a control substrate that is arranged on the cooler. The fixed base inhibits conduction of heat from the motor case to the power control unit. This kind of structure enables the conduction of heat from the motor case to be inhibited, so a decrease in output that accompanies a rise in temperature of the power module can be prevented. 
         [0013]    In the power control unit described above, the fixed base may cover a bottom surface of the power control unit, and the power control unit may be connected to the rotary electric machine inside of the motor case via the fixed base. 
         [0014]    In the power control unit described above, the fixed base may include a terminal block, that includes a bus bar that connects the rotary electric machine to the power control unit. With this kind of structure, a heat release effect can be expected from the bus bar. 
         [0015]    In the power control unit having the structure described above, thin plate made of metal that inhibits the conduction of heat between the cooler and the fixed base, and fixing means for fixing the cooler, the thin plate, and the fixed base together, may be provided with the fixed base. The thin plate may form a space that is surrounded by the cooler and the thin plate, and the thin plate may be cooled by the cooler. According to this kind of structure, the space between the cooler and the thin plate can be used effectively, and the space between the fixed base and the thin plate can also be used as an insulating chamber, so convection heating from heated air can be prevented. 
         [0016]    In the power control unit having the structure described above, an electronic device may be arranged in the space that is surrounded by the cooler and the . thin plate. This kind of structure makes it possible to effectively cool the electronic device with the cooler. 
         [0017]    In the power control unit having the structure described above, the thin plate may form a space that is surrounded by the fixed base and the thin plate. 
         [0018]    The power control unit having the structure described above may also include a cover that is formed by a thin plate made of metal and that covers the power control unit. The cover may be attached to a base of the motor case, such that the fixed base is surrounded by the cover or the motor case, and the conduction of heat from the motor case to the power control unit is inhibited by the cover. 
         [0019]    In the power control unit having the structure described above, the base of the motor cover may surround a periphery of the fixed base. 
         [0020]    The invention makes it possible to provide a power control unit that is mounted in such as way that the temperature of the power control unit is able to be prevented from rising, and thus the cooling ability of the power control unit is able to be ensured, even when the step up converter and the inverter that form the power control unit are housed together with the motor in a single case, by inhibiting heat conduction from the case, heat conduction from the cover that covers the power control unit, and convection heat of the air inside the cover. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
           [0022]      FIG. 1  is a structural diagram of a drive apparatus with a power control unit according to the invention; 
           [0023]      FIG. 2  is a schematic diagram of the drive apparatus with the power control unit according to the invention; 
           [0024]      FIG. 3  is a view showing housing chambers of the drive apparatus with the power control unit according to the invention; 
           [0025]      FIG. 4  is a temperature graph diagram showing an overview of the temperature in each of the housing chambers shown in  FIG. 3 ; and 
           [0026]      FIG. 5  is a schematic diagram showing a drive apparatus according to related art. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0027]    Hereinafter, example embodiments of the invention will be described with reference to the accompanying drawings. 
         [0028]      FIG. 1  is a view of a drive apparatus  10  with a power control unit (PCU), and  FIG. 2  is a front view and a plan view of the drive apparatus  10  shown in  FIG. 1 . The upper portion of  FIG. 2  is a plan view of the drive apparatus  10 , and the lower portion of  FIG. 2  is a front view of a cross section taken along line G-G. First, the overall structure of the drive apparatus  10  will be briefly described with reference to  FIG. 2 . 
         [0029]    The drive apparatus  10  in  FIG. 2  includes a transaxle  30  that has motor-generators MG 1  and MG 2  that are connected to an engine via a power distributing apparatus, a fixed base  22  that is made of resin and is arranged covering an open portion of a transaxle case  31 , a thin plate  23  made of steel sheet that is arranged on the fixed base  22 , a cooler  27  arranged on the thin plate  23 , smoothing capacitors  28  arranged above the cooler  27 , a control substrate  29  arranged above the smoothing capacitors  28 , and a cover  43  made of steel sheet that covers all of these. The cooler  27  has a resin portion on an upper surface, an aluminum portion on a lower surface, and a heat conductive base  12  that conducts heat well, has fins on the inside, and is attached to the resin portion on the upper surface. A DC/DC converter  25  and a filter capacitor  24  are arranged on the lower surface of the cooler  27 , and power elements  13  are arranged via the heat conductive base  12  on the upper surface of the cooler  27 . Also, an external connector  42  is provided on the upper surface of the control substrate  29 . The cover  43  is attached by bolts to a flange portion of the transaxle case  31 , and rubber rings  52  are provided in gaps between cooling lines  17  of the cooler  27  and the cover  43 . Further, a reactor  38  is arranged on the lower surface of the fixed base  22 . This reactor  38  is cooled by lubricating oil sprayed up by the rotation of rotors  34  and  35  of the motor-generators MG 1  and MG 2  housed inside the transaxle case  31 . 
         [0030]    The fixed base  22  in  FIG. 2  has a terminal block  21 . A bus bar  44  that extends from stator coil terminals  32   a  and  33   a  of the motor-generators MG 1  and MG 2  is connected, with branches, to the plurality of power elements  13  fixed to the cooler  27 , via the terminal block  21 . Therefore, some of the heat released from the power elements  13  is released into the PCU case via the bus bar  44 . Also, the fixed base  22  is connected via a surface seal  51  to the transaxle case  31 , so the transaxle  30  is sealed by the fixed base  22 . With this kind of structure, the PCU  20  according to this example embodiment reduces the number of parts by being connected by the bus bar  44  that is connected via the terminal block  21 , instead of a wire harness that connects the motor-generators MG 1  and MG 2  together. Moreover, having the fixed base  22  that separates the PCU  20  from the transaxle  30  be made of resin that is less heat conductive than the aluminum transaxle case  31  makes it possible to inhibit heat from being conducted from the transaxle  30  to the PCU  20 . Next, the drive apparatus  10  in  FIG. 1  that shows a cross section taken along line H-H in the upper drawing in  FIG. 2  will be described. 
         [0031]      FIG. 1  is a sectional front view of the drive apparatus  10  taken along line H-H. The mounting structure of the power control unit (PCU) according to the invention will be described in detail with reference to  FIG. 1 . Portions that have already been described will be omitted in order to avoid redundant descriptions. The drive apparatus  10  in  FIG. 1  includes a transaxle chamber formed by covering the transaxle case  31  that has an open portion by the fixed base  22 , and a PCU chamber that is divided by the fixed base  22  and the cover  43 . In the transaxle chamber are arranged the stators  32  and  33  that form the motor-generators MG 1  and MG 2 , the rotors  34  and  35  that are arranged inside the stators and rotate about shafts  36  and  37 , and the reactor  38  that is arranged on the lower surface of the fixed base  22 . 
         [0032]    Also, the PCU chamber is formed by the thin plate  23  that is made of steel sheet and arranged on the fixed base  22 , the cooler  27  that is arranged on the thin plate  23 , the smoothing capacitors  28  and the control substrate  29  that are arranged above of the cooler  27 , and the cover  43  that is made of steel sheet and is attached to the transaxle case  31  so as to cover from the fixed base  22  to the control substrate  29 . The thin plate  23  and the cooler  27  form an insulating chamber by being fastened to the fixed base  22  by bolts  26 , such that the conduction of heat from the transaxle  30  is inhibited. Furthermore, the cover  43  that is made of steel sheet and is attached to the transaxle case  31  is thinner and has lower heat conductivity than the aluminum wall surface, and thus inhibits the conduction of heat from the transaxle  30 . Next, cooling means will be described. 
         [0033]    The drive apparatus  10  in  FIG. 1  has two cooling means. The first cooling means is the cooler  27  that cools the power elements  13 , the DC/DC converter  25 , the filter capacitor  24 , the smoothing capacitors  28 , and the control substrate  29 . The second cooling means is lubricating oil that cools the reactor  38  by being sprayed by the rotation of the rotors  34  and  35  about the shafts  36  and  37  of the motor-generators MG 1  and MG 2 . In a typical vehicle, an oil cooler is not provided, so lubricating oil is cooled by heat being released from the oil pan and by coolant that cools the engine. Therefore, in a heavy-load operating state, the temperature of the lubricating oil may become higher than the temperature of the coolant. 
         [0034]      FIG. 3  is a view showing the amount of heat (also referred to as “heat quantity) (H 1  to H 5 ) and housing chambers (chamber A to chamber D and engine compartment E) of the drive apparatus with the power control unit.  FIG. 4  is a temperature graph diagram showing an overview of the temperature in each of the housing chambers shown in  FIG. 3 . In particular, the conduction of heat when the temperature of the lubricating oil is higher than the temperature of the coolant in a heavy-load operating state will be described in detail. The amount of heat=specific heat×density×volume×temperature difference. The specific heat (J/(kg×K)) is the amount of heat necessary to increase the temperature of an object with a unit mass (1 kg) by a unit temperature (1 K). Heat conduction includes heat conductivity (W/(m×K)=J/(s×m×K)), that is a value indicative of the amount of heat that it takes to transfer 1 K one meter downstream in one second, and a heat transfer coefficient (W/(m2×K)=J/(s×m 2 ×K)), that is a value indicative of the amount of heat that it takes to transfer I K from an area 1 m 2  in one second. Heat conduction will hereinafter be described using one or both of these values or the like, but for the sake of convenience in the description, the amount of heat is used, and the devices of the power control unit in  FIG. 3  are omitted. 
         [0035]    In a heavy-load operating state, the temperature on the transaxle  30  side in  FIG. 3  becomes higher than the temperature of the coolant on the PCU  20  side. More specifically, the spray of lubricating oil in chamber A inside of the transaxle case in  FIG. 3  causes a first heat quantity H 1  to be applied to the fixed base  22 . For example, the fixed base  22  is made of thermosetting resin (such as phenolic resin with a specific heat of 1.57 to 1.76 j/g×K) having a bus bar inside by insert molding. Therefore, compared with the aluminum partition wall, the specific heat is greater (the specific heat of aluminum is 0.9 j/g×K) and the heat conductivity is smaller. Accordingly, in the temperature graph in  FIG. 4 , when the first heat quantity H 1  passes through the fixed base  22 , it becomes a second heat quantity H 3 . Also, even though a third heat quantity H 2  that has passed through the partition wall of chamber A in  FIG. 3  reaches the cover  43  that covers the PCU  20 , it is cooled by the air current in chamber D, so the temperature of the cover  43  becomes a temperature that is sufficiently lower than the temperature of the transaxle case, as shown on the right side of  FIG. 4 . 
         [0036]    The end portion of the thin plate  23  in  FIG. 3  is fastened to the end portion of the cooler  27 , and thus conducts heat from the thin plate  23  to the cooler  27 , such that the second heat quantity H 3  that has passed through chamber B formed by the fixed base  22  and the thin plate  23  in  FIG. 4  becomes low. Furthermore, a fourth heat quantity H 4  that passes through chamber C formed by the thin plate  23  and a cooler base  11  in  FIG. 3  is near the cooler  27 , so although there is heat conduction by convective heat, it is a temperature that is very near the coolant temperature. Similarly, a fifth heat quantity H 5  that passes through chamber D formed by the cover  43  and the heat conductive base  12  in  FIG. 3  also becomes heat conducted by convective heat, but it is near the cooler  27 , so it becomes a temperature that is very close to the coolant temperature, and as a result, the heat of the power elements is able to be released. 
         [0037]    As described above, using the power control unit (PCU) according to the invention enables heat transfer to be prevented in chamber B that is formed by the fixed base  22  and the thin plate  23 , and the engine compartment E that is formed by the transaxle case  31  and the cover  43 , and moreover, as well as enables convective heat to be prevented in chambers C and D that are formed one on either side of the cooler  27 , in a structure in which a step up converter and an inverter that form a power control unit are arranged together with a motor in a single case. This kind of function makes it possible to prevent the temperature of the power control unit from rising, and thus ensure the cooling ability of the power control unit. Also, the thin plate  23  also functions as a cover for the DC/DC converter  25  and the filter capacitor  24 , and is thus effective for preventing foreign matter from getting in. 
         [0038]    In this example embodiment, the fixed base  22  is made of phenolic resin, but the invention is not limited to this. That is, the fixed base  22  may be made of any material as long as insert molding is possible and the material has heat resistant and oil resistant properties. 
         [0039]    While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiments are shown in various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the invention.