Abstract:
A power converter ( 100 ) comprises a cooler ( 20 ) having a cooling flow path ( 21 ) in which a refrigerant flows, a base plate ( 31 ) to which switching elements ( 32 ) are attached, a control circuit board ( 33 ) on which power-generating elements ( 34 ) are attached, and securing pins ( 40 ) that secure the base plate ( 31 ) onto the lower cooler wall ( 22 ) of the cooler ( 20 ) and support the control circuit board ( 33 ) so as to be spaced apart from the base plate ( 31 ). Upper end parts ( 41 ) of the securing pins ( 40 ) pass through the base plate ( 31 ) and the cooler lower wall ( 22 ), reaching inside the cooling flow path ( 21 ). First pass-through parts ( 42 ) of the securing pins for the lower cooler wall ( 22 ) are fitted by pressure into the lower cooler wall ( 22 ). Support column parts ( 46 ) of the securing pins ( 40 ) extend in a direction opposite the lower cooler wall ( 22 ), and the control circuit board ( 33 ) is secured to lower flanges ( 47 ) thereof. Thus, power converter can be reduced in size with a simple constitution.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the structure of a power converter. 
       BACKGROUND ART 
       [0002]    Many electric drive vehicles, such as hybrid electric vehicles and electric cars, are propelled by motors when DC/DC converters boost DC power output by a low-voltage batteries, of about 200 V, and an inverter converts the thus-obtained high-voltage DC power into three-phase electric power, which is in turn used to drive the motors. The types of DC/DC converters frequently employed are ones that accumulate, in reactors, DC power supplied by low-voltage batteries, and employ switching elements, such as IGBTs, to switch accumulated electric power to raise voltages. Since the switching elements generate much heat, there has been proposed an example method according to which a base plate, to which switching elements are fixed, is mounted on a radiator, for which radiator fins are provided, so that heat generated by the switching elements is dissipated to cool the switching elements (see, for example, Patent Document 1). 
         [0003]    In addition to switching elements that generate much heat, the DC/DC converter also requires power-generating elements, such as a coil, a transformer, and a capacitor, and a control element that controls the operation of the switching elements. 
         [0004]    Since the use of switching elements is accompanied by the generation of much heat, generally, the switching elements are arranged on a cooler through which cooling water flows, and a control circuit board, on which a control element and power generating elements are mounted, is arranged above the cooler, at a distance from and parallel to a base plate, by means of a plurality of support columns that are provided on the cooler in order to reduce the size of the DC/DC converter (see, for example, Patent Document 2). In this arrangement, since the base plate and the control circuit board are arranged as two layers, above the cooler, the installation space can be reduced. Furthermore, with this arrangement, heat generated by the control circuit board can be transferred to the cooler via the plurality of support columns, and therefore, the switching elements and the individual power generating elements mounted on the control circuit board can be cooled. Moreover, according to Patent Document 1, previously described, the control circuit board is fixed to bosses, provided for the base plate, so as to arrange the switching elements and the control circuit board as two layers, and as a result, a saving in space is obtained. 
       Citation List 
     Patent Documents 
       [0005]    Patent Document 1: Japanese Patent Laid-Open No. 2002-076257 
         [0006]    Patent Document 2: Japanese Patent Laid-Open No. 2007-266527 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    According the structure of prior art described in Patent Document 2, wherein the support columns attached to the cooling plate are employed to support the control circuit board, the support columns are provided on the cooler on the periphery of the base plate on which the switching elements are mounted, and therefore, there is a problem in that the size of the DC/DC converter is increased. Further, for the power module structure described in the prior art of Patent Document 1, since the control circuit board is fixed onto the bosses provided for the base plate, space on the base plate for arranging the switching elements is limited, and when large switching elements or many switching elements are to be arranged on the base plate, a problem has been encountered in that the size of the base plate, or of the entire DC/DC converter, would be increased. 
         [0008]    When the size and the capacity of the switching elements become greater, an increased amount of current flows through the power-generating elements and the control element mounted on the control circuit board, and the generation of heat is increased. In order to dissipate heat generated by the control circuit board for the prior art described in Patent Document 1 or Patent Document 2, more bosses or support columns must be provided, and a path for heat dissipation from the control circuit substrate to the cooler must be expanded. For such heat dissipation, bosses and support columns must be arranged not only on the periphery of the base plate, but also in the center of the base plate, for example. Therefore, the area of the base plate required for arranging the bosses or the support columns is increased, while the space provided for arranging the switching elements is reduced, and as a result, there is a problem in that the base plate becomes larger, and the DC/DC converter is increased in size. 
         [0009]    One objective of the present invention is to provide a compact power converter having a simple structure. 
       Means for Solving the Problem 
       [0010]    A power converter according to the present invention includes a cooler having a cooling flow path, through which a refrigerant flows, a base plate, on which switching elements are mounted; a control circuit board, on which power-generating elements are mounted, and securing pins, which securely fix the base plate to a cooling flow path wall of the cooler, and also support the control circuit board a distance from the base plate, is characterized in that: one end of each of the securing pins passes through the base plate and the cooling flow path wall, and reaches inside the cooling flow path, and a part of the securing pin that passes through the cooling flow path wall is fastened to the cooling flow path wall; and the other end of each of the securing pins is extended to a side opposite to the cooling flow path wall, and the control circuit board is fixed to a distal end of the securing pin. 
         [0011]    For the power converter of this invention, it is suitable that the power converter be mounted on a transaxle, and it is appropriate that the part of each of the securing pins that passes through the cooling flow path wall be fitted by pressing into the cooling flow path wall; and it is furthermore appropriate that the part of each of the securing pins that passes through the cooling flow path wall be screwed in and secured to the cooling flow path wall, and it is suitable that the power converter be a DC/DC converter. 
         [0012]    For the power converter of the present invention, it is also appropriate that the base plate and the control circuit board of the power converter be arranged between the transaxle and the cooler. Furthermore, it is appropriate that the control circuit board be fixed to the distal ends of the securing pins by means of bolts that pass through the control circuit board. 
       Advantageous Effects of Invention 
       [0013]    The present invention provides effects such that the power converter can be reduced in size by means of a simple structure. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is an explanatory diagram illustrating the general structure of a power converter according to one embodiment of the present invention; 
           [0015]      FIG. 2  is an explanatory diagram illustrating a partial cross section of the power converter according to the embodiment of the present invention; 
           [0016]      FIG. 3  is a plan view of the switching element mounting available area of the base plate of the power converter according to the embodiment of the present invention; and 
           [0017]      FIG. 4  is an explanatory diagram illustrating the state, for a power converter according to another embodiment of the present invention, wherein a securing pin is fitted to the wall of a cooling flow path wall. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    The embodiments of the present invention will now be described by reference to the drawings. As shown in  FIG. 1 , a power converter  100  of one embodiment of the present invention is an integrated unit provided by stacking three cases; i.e., a lower case  10 , a center case  60 , and an upper case  70 , and fastening these cases with bolts  15  and  61 . A lower flange  12  of the lower case  10  is secured to the top of a transaxle  80  with bolts  13 . 
         [0019]    A cooler  20  is provided for the upper portion of the lower case  10 . The cooler  20  includes: a cooling flow path  21 , which is enclosed by a lower cooler wall  22 , an upper cooler wall  23 , and side walls  11  of the lower case  10 ; a refrigerant inlet port  24   a,  through which a refrigerant is to be introduced into the cooling flow path  21 ; and a refrigerant outlet port  24   b,  through which the refrigerant is discharged from the cooling flow path  21 . The lower cooler wall  22  is a cooling flow path wall. A base plate  31  on whose surface switching elements  32  are mounted is fixed to the lower face of the lower cooler wall  22  by means of securing pins  40 . The upper distal ends of the securing pins  40  are extended to the inside of the cooling flow path  21 . A control circuit board  33  where power-generating elements  34 , such as a coil and a capacitor, are mounted is fixed to the lower faces of the securing pins  40 . One part of the switching elements  32  and the control circuit board  33  constitute a DC/DC converter  30 . Between the control circuit board  33  and the transaxle  80 , an under cover  16  is attached by bolts  17  in order to block heat generated by the transaxle  80 , and to prevent entry of a foreign substance into the lower case  10 . Further, as shown in  FIG. 2(   a ), the control circuit board  33  is fixed to the lower faces of the securing pins  40  by means of bolts  35  that penetrate the control circuit board  33 . 
         [0020]    As shown in  FIG. 2(   a ), the securing pins  40  each include an upper end part  41  that projects into the interior of the cooling flow path  21 ; a first pass-through part  42  that passes through the lower cooler wall  22 ; a second pass-through part  43  that passes through the base plate  31 ; an upper flange  44  that has a larger diameter than the first and second pass-through parts  42  and  43 ; a support column part  46  that has a smaller diameter than the upper flange  44 , and extends downward from the upper flange  44 ; and a lower flange  47  that is provided at the lower end of the support column part  46  and has a larger diameter than the support column part  46 . 
         [0021]    As shown in  FIG. 2(   b ), the first pass-through part  42  of the securing pin  40 , defined by a chain line A and a chain line B, passes through a hole  22   a  that is formed in the lower cooler wall  22 . The outer diameter of the first pass-through part  42  is greater than the inner diameter of the hole  22   a  so as to provide a press fit, and the first pass-through part  42  of the securing pin  40  is fitted by pressing into the hole  22   a.  Further, the second pass-through part  43  of the securing pin  40 , defined by the chain line B and a chain line C, passes through a hole  31   a  formed in the base plate  31 . The outer diameter of the second pass-through part  43  is greater than that of the first pass-through part  42 , and a step is formed between the first pass-through part  42  and the second pass-through part  43 . Furthermore, as well as for the first pass-through part  42 , the outer diameter of the second pass-through part  43  is larger than the inner diameter of the hole  31   a  to provide a press fit, and similarly to the first pass-through part  42 , the second pass-through part  43  of the securing pin  40  is fitted by pressing into the hole  31   a.  The upper flange  44  of the securing pin  40  is provided so that the outer diameter thereof is larger than the inner diameters of the second pass-through part  43  and the hole  31   a,  and the upper face closely contacts the lower face of the base plate  31 . Moreover, an annular groove  36  is formed in the face of the base plate  31  around the hole  31   a  on the lower cooler wall  22  side, and an O-ring  36   a  is fitted in the groove  36 . Similarly, an annular groove  48  is formed in the face of the upper flange  44  of the securing pin  40  on the base plate side, and an O-ring  48   a  is fitted in the groove  48 . When the securing pin  40  is pushed into the base plate  31  and the lower cooling wall  22  and the first pass-through part  42  is securely fitted in the lower cooler wall  22 , the base plate  31  is sandwiched between the lower cooler wall  22  and the upper flange  44  of the securing pin  40  and is fixed to the lower face of the lower cooler wall  22 . At this time, the O-rings  36   a  and  48   a  are squeezed, respectively, between the wall face of the groove  36  and the lower cooler wall  22  and between the wall face of the groove  48  and the base plate  31 , so that leakage of the refrigerant from the holes  22   a  and  31   a  can be avoided. 
         [0022]    When the operation of the power converter  100  with the above described arrangement is begun, heat generated by the switching elements  32  is transferred from the switching elements  32  to the base plate  31  and the lower cooler wall  22 , and is discharged outside the power converter  100  by the refrigerant that flows along the cooling flow path  21  of the cooler  20 . Further, heat generated by the power-generating elements  34  mounted on the control circuit board  33  is transferred from the power-generating elements, via the control circuit board  33  and the lower faces of the lower flanges  47  of the securing pins  40 , and is passed along the support column parts  46  and reaches the upper end parts  41 . Since the upper end parts  41  are projected into the interior of the cooling flow path  21 , heat that has reached the upper end parts  41  is discharged outside the power converter  100  by the refrigerant. Therefore, in the present embodiment, the control circuit board  33  and the power-generating elements  34  can be cooled more effectively than in the conventional case. Further, since the control circuit board  33  and the power-generating elements  34  can be effectively cooled in this manner, as shown in  FIG. 2 , the control circuit board  33  of the DC/DC converter  30  can be arranged on the transaxle  80  side to reduce the size of the power converter  100 . 
         [0023]    Furthermore, since the securing pins  40  of the power converter  100  of this embodiment include a function for fixing the base plate  31  to the lower cooler wall  22  and a function for supporting the control circuit board  33  apart from the base plate  31 , there is no requirement for separate arrangement of bolts used to fix the base plate  31  to the lower cooler wall  22  and support columns to support the control circuit board  33 . 
         [0024]    Therefore, a large area as hatched in  FIG. 3  can be prepared as a switching element mounting available area  37 , and the power converter  100  can be reduced in size. The switching element mounting available area  37  is an area excluding switching element mounting disabled areas, indicated by chain lines, around the upper flanges  44  of the securing pins  40 . Further, in a case wherein the power converter  100  is directly fixed to the transaxle  80 , the number of support columns must be increased in order to prevent resonance of the control circuit board  33 ; however, according to the present embodiment, since the securing pins  40  include a function for fixing the base plate  31  to the lower cooler wall  22  and a function for supporting the control circuit board  33  a distance from the base plate  31 , and since also the upper end parts  41  are projected into the interior of the cooling flow path  21 , the size of the switching element mounting available area  37  is reduced only slightly, even when the number of securing pins  40  is increased, and further, cooling of the control circuit board  33  and the power-generating elements  34  can be more effectively performed by increasing the number of securing pins  40 . 
         [0025]    At the time of maintenance for the power converter  100  of the present embodiment, the bolts  13  used to fix the lower case  10  to the transaxle  80  are removed so as to separate the entire power converter  100  from the transaxle  80 , and thereafter, the bolts  17  are removed from the lower face to separate the under cover  16 , and the bolts  35  used to fix the control circuit board  33  are removed, so that replacement of the control circuit board  33  of the DC/DC converter  30  can be easily performed. Specifically, it is not required that the center case  60  and the upper case  70 , where the control circuit board, etc., of the inverter, are stored, be disassembled in the named order, beginning from the top; the entire power converter  100  need simply be removed from the transaxle  80 , and be turned over, so that the control circuit board  33  of the DC/DC converter  30  can be easily exchanged. Further, since the center case  60  and the upper case  70 , where the control circuit board, etc., of the inverter are stored, need not be disassembled, entry of foreign substances into these cases during the performance of maintenance can be prevented. 
         [0026]    In the above described embodiment, the first and second pass-through parts  42  and  43  of the securing pins  40  are fitted, by pressure, into the holes  22   a  in the lower cooler wall  22  and the holes  31   a  in the base plate  31 , respectively; however, the first pass-through parts  42  may be fitted into the holes  22   a  by pressure, while the second pass-through parts  43  may be inserted into the holes  31   a  with a gap relative to the holes  31   a.    
         [0027]    Another embodiment of the present invention will now be described by reference to  FIG. 4 . The reference numerals provided for the embodiment described by reference to  FIGS. 1 to 3  are also employed to denote corresponding portions, and no further explanation for them will be given. The embodiment shown in  FIG. 4  employs a structure wherein the first pass-through parts  42  of the embodiment, described by reference to  FIG. 2(   b ), are employed as threaded parts  51 , the holes  22   a  of the lower cooler wall  22  are employed as screw holes  22   b , and the diameter of holes  31   a  of a base plate  31  is slightly larger than the diameter of second pass-through parts  43  in order to obtain a small gap between the holes  31   a  and the second pass-through parts  43 . Furthermore, as shown in  FIG. 4 , in this embodiment, the diameter of the upper end parts  41  of securing pins  40  are set smaller than the root diameter of the threaded parts  51 . 
         [0028]    In the present embodiment, the threaded parts  51  of the securing pins  40  are fitted by pressure into the screw holes  22   b  of the lower cooler wall  22 , the base plate  31  is fixed by being sandwiched between the lower cooler wall  22  and upper flanges  44  of the securing pins  40 , and the O-rings  36   a  and  48   a  are squeezed, so that the leakage of a refrigerant through the screw holes  22   b  can be prevented. 
         [0029]    The present embodiment provides the same effects as those obtained in the embodiment previously described by reference to  FIGS. 1 to 3 . Moreover, in the present embodiment, not only can replacement of a control circuit board  33  be easily performed, but also the base plate  31  can be removed by disengaging the securing pins  40 , and therefore, in a case wherein switching elements  32  have malfunctioned, the exchange of the switching elements  32  can be easily performed without disassembling the center case  60  and the upper case  70  wherein an inverter, etc., are stored. 
       REFERENCE SIGNS LIST 
       [0030]      10 : lower case 
         [0031]      11 : side wall 
         [0032]      12 : lower flange 
         [0033]      13 ,  15 ,  17 ,  35 ,  61 : bolt 
         [0034]      16 : under cover 
         [0035]      20 : cooler 
         [0036]      21 : cooling flow path 
         [0037]      22 : lower cooler wall 
         [0038]      22   a,    31   a : hole 
         [0039]      22   b : screw hole 
         [0040]      23 : upper cooler wall 
         [0041]      24   a : refrigerant inlet port 
         [0042]      24   b : refrigerant outlet port 
         [0043]      30 : DC/DC converter 
         [0044]      31 : base plate 
         [0045]      32 : switching element 
         [0046]      33 : control circuit board 
         [0047]      34 : power-generating element 
         [0048]      36 ,  48 : groove 
         [0049]      36   a,    48   a : O-ring 
         [0050]      37 : switching element mounting available area 
         [0051]      40 : securing pin 
         [0052]      41 : upper end part 
         [0053]      42 : first pass-through part 
         [0054]      43 : second pass-through part 
         [0055]      44 : upper flange 
         [0056]      46 : support column part 
         [0057]      47 : lower flange 
         [0058]      51 : threaded portion 
         [0059]      60 : center case 
         [0060]      70 : upper case 
         [0061]      80 : transaxle 
         [0062]      100 : power converter