Patent Publication Number: US-2015062811-A1

Title: Electric power conversion device for vehicle and railway vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-179843, filed Aug. 30, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an electric power conversion device for a vehicle, and a railway vehicle. 
     BACKGROUND 
     With respect to a railway vehicle, in general, as a device for performing a control of a main motor for driving (operating to move and control) the railway vehicle or the like, an electric power conversion device for a vehicle is mounted on an underfloor of a vehicle body, for example. 
     Conventionally, an electric power conversion device for a vehicle includes a control box which is mounted on an underfloor of a vehicle body and defines a sealed space in the inside thereof, a power unit part accommodated in the inside of the control box (a unit which performs power conversion by making use of a switching operation of a semiconductor element), and a heat removing part which is mounted on the control box in a state where the heat removing part is opened to the outside of the control box and radiates, convects (with adjacent air) and conducts heat generated from the power unit part into adjacent materials, including ambient air. A packing is interposed between the power unit part and the heat removing part thus maintaining the sealed state in the inside of the control box. 
     However, the electric power conversion device for a vehicle of the related art has a structure which uses such a packing and hence, the structure as a whole is liable to become complicated. Further, the heat removing part largely projects outwardly compared to the control box and hence, it is necessary to pay attention to an outfitting space which is set in advance, i.e., a space for placement of the power conversion device which is predefined or dictated as a design constraint of the device and the railway vehicle. In view of the above, there has been known a method where a semiconductor element which is liable to generate a large amount of heat is directly mounted on a control box by way of a heat receiving plate so that heat may be efficiently removed therefrom by making use of a heat conducting, convecting and radiating area of the control box thus performing cooling of the semiconductor element. 
     However, even when the heat receiving plate is directly mounted on the control box, it is difficult to bring both parts into close contact with each other due to unevenness, deflection or the like of surfaces of these parts and hence, a gap is liable to be formed between both parts. Since heat resistance is increased due to such a gap, heat generated from a semiconductor element may not be efficiently transferred to the control box through the heat receiving plate. Accordingly, it is difficult to perform cooling of the semiconductor element by sufficiently making use of a heat removing area of the control box. 
     Further, there may be a case where the heat removing part which includes fins or the like is integrally formed on the heat receiving plate. In this case, the heat receiving plate on which the semiconductor element is mounted is directly mounted on the control box together with the heat removing part. Accordingly, when the semiconductor element is removed from the control box for maintenance or the like, for example, it is necessary to remove not only the heat receiving plate but also the heat removing part simultaneously and hence, there is a room for enhancement in the ease of mounting or removing the semiconductor element. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a railway vehicle according to a first embodiment. 
         FIG. 2  is a constitutional view of an electric power conversion device for a vehicle shown in  FIG. 1 , and is also a perspective view of the electric power conversion device for a vehicle as viewed from a left side of the railway vehicle. 
         FIG. 3  is a perspective view showing a cooling air chamber and an area around the cooling air chamber shown in  FIG. 2  in an enlarged manner. 
         FIG. 4  is an exploded perspective view showing a state where a power unit shown in  FIG. 3  is mounted on partition plates. 
         FIG. 5  is a cross-sectional view taken along a line A-A in  FIG. 3 . 
         FIG. 6  is a cross-sectional view taken along a line B-B in  FIG. 3 . 
         FIG. 7  is a view showing a modification of the first embodiment, and is also an exploded perspective view showing a state before a power unit is mounted on partition plates. 
         FIG. 8  is a perspective view of an electric power conversion device for a vehicle of a second embodiment as viewed from a left side of a railway vehicle. 
         FIG. 9  is a cross-sectional view taken along a line C-C in  FIG. 8 . 
         FIG. 10  is a perspective view of an electric power conversion device for a vehicle of a third embodiment as viewed from a left side of a railway vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment, there is provided an electric power conversion device for a vehicle which may enhance cooling performance by efficiently transferring heat generated from a heat generation part to a heat radiation part and, at the same time, may enhance the ease of mounting or removing the heat generation part. 
     In general, according to one embodiment, an electric power conversion device for a vehicle includes: a box body partitioned into a cooling air chamber and amounting chamber; a heat generation part which is arranged in the inside of the mounting chamber and includes a semiconductor element which performs power conversion; and a heat removing part mounted on a partition between the cooling air chamber and mounting chamber, and configured to transfer heat generated from the heat generation part, wherein the heat generation part is attachably and detachably mounted on the heat removing part in a state where the heat generation part is arranged on a side opposite to the heat removing part with the partition sandwiched therebetween, and a heat transfer sheet is provided between the heat generation part and the heat removing part. 
     A railway vehicle of the embodiment includes: the electric power conversion device for a vehicle; and a vehicle body where the box body is mounted on an underfloor. 
     Hereinafter, embodiments according to the invention are explained in conjunction with drawings. 
     First Embodiment 
     Constitution of Railway Vehicle 
     As shown in  FIG. 1 , a railway vehicle  1  of this embodiment includes a vehicle body  2  and an electric power conversion device  3  mounted on an underfloor of the vehicle body  2 . 
     The electric power conversion device  3  is a device which converts a DC power supplied from an overhead line  4  through a pantograph  5 , or a DC power supplied from a power supply source not shown in the drawing into an AC power, and supplies the AC power to main electric motors  8  which are mounted on a chassis  7  where left and right wheels  6  are pivotally supported and respective electrical equipment (air conditioner and the like) not shown in the drawing in the railway vehicle  1 , for example. The wheels  6  travel on rails arranged on a ground not shown in the drawing. 
     In this embodiment, the direction which connects a front side and a rear side of the vehicle body  2  is referred to as “longitudinal direction L1”, the vehicle width direction of the vehicle body  2  is referred to as “lateral direction L2”, and the height direction of the vehicle body  2  is referred to as “vertical direction L3”. 
     [Constitution of Electric Power Conversion Device for Vehicle] 
     As shown in  FIG. 2 , the electric power conversion device  3  includes: a box body (control box)  10  mounted on the underfloor of the vehicle body  2 , a power unit  20  accommodated in the inside of the box body  10 ; a filter capacitor  21 ; and a gate amplifier  22 . 
     (Box Body) 
     The box body  10  includes a ceiling wall portion  11  which faces an underfloor of the vehicle body  2 , a bottom wall portion  12  which faces a railway (rails not shown in the drawing), and four side wall portions  13 A,  13 B directed in the longitudinal direction L1, and  13 C,  13 D directed in the lateral direction L2. The box body  10  made of metal having a rectangular parallelepiped shape is formed by these respective wall portions (the ceiling wall portion  11 , the bottom wall portion  12 , and the side wall portions  13 A to  13 D). 
     The box body  10  is mounted on the underfloor of the vehicle body  2  in a suspended manner by way of a plurality of mounting members  14  mounted on the ceiling wall portion  11 . To be more specific, when the railway vehicle  1  is viewed from a front side, the box body  10  is mounted on the underfloor of the vehicle body  2  at a position close to one (left or right) side of the vehicle body  2  such that the box body  10  falls within an outfitting limit (predefined design constraint for size) not shown in the drawing. In this example, the one side is assumed to be the left. 
     The mounting members  14  are formed such that the mounting members  14  project outward in the lateral direction L2 from four corners of the ceiling wall portion  11 . A mounting position of the box body  10 , the number of mounting members  14  and the like are not limited to the above-mentioned case, and the mounting position of the box body  10 , the number of mounting members  14  and the like may be changed when necessary. 
     The box body  10  is partitioned into a cooling air chamber  16  and a mounting chamber  17  by four partition plates  15 A to  15 D which extend in the vertical direction L3. 
     The partition plates  15 A,  15 B are directed in the longitudinal direction L1, and face the side wall portions  13 A,  13 B of the box body  10  in an opposed manner with a space defined therebetween respectively. The partition plate  15 C is in contact with the side wall portion  13 C of the box body  10 . The partition plate  15 D is directed to a vehicle left side L, and faces the side wall portion  13 D of the box body  10  in an opposed manner with a space therebetween. 
     An inner space surrounded by these four partition plates  15 A to  15 D forms the cooling air chamber  16 . Accordingly, in the example shown in the drawing, the cooling air chamber  16  is arranged at the center portion of the box body  10  in the longitudinal direction L1 and at the position close to the center of the vehicle body  2  in the vehicle width direction. The cooling air chamber  16  is configured such that the cooling air chamber  16  pierces through the box body  10  in the vertical direction L3. The position of the cooling air chamber  16  is not limited to the above-mentioned position. 
     The cooling air chamber  16  is configured such that the cooling air chamber  16  pierces through the box body  10  in the vertical direction L3 and hence, the cooling air chamber  16  opens to the ceiling wall portion  11  and the bottom wall portion  12  respectively. Out of the portions where the cooling air chamber  16  has openings, the portion which of the chamber open to the bottom wall portion  12  forms an air chamber opening  16 A, and the portion of the chamber open to the ceiling wall portion  11  forms an air chamber opening  16 B. A heat radiation part  20 B of the power unit  20  is accommodated within the cooling air chamber  16 . 
     A part of the inside of the box body  10  other than the cooling air chamber  16  forms the mounting chamber  17 . A heat generation part  20 A of the power unit  20  is accommodated within the mounting chamber  17 . The filter capacitor  21 , the gate amplifier  22  and other various electric power conversion equipment not shown in the drawing are also accommodated within the mounting chamber  17 . 
     In the side wall portion  13 D of the box body  10  which is located to the vehicle left side L of the vehicle body  2 , an opening portion  18  is formed, through which the heat generation part  20 A accommodated within the mounting chamber  17  is introduced into, or removed from, the mounting chamber  17 . Usually, the opening portion  18  is closed by a cover (not shown in the drawing). 
     (Power Unit) 
     As shown in  FIG. 2  to  FIG. 4 , the power unit  20  includes a heat generation part  20 A, a heat radiation part  20 B, and a heat transferring sheet  24 . The heat generation part  20 A is arranged in the inside of the mounting chamber  17  and includes a semiconductor element  23  for performing power conversion. The heat radiation part  20 B is attached to the partition plate  15 D inside the cooling air chamber  16  and radiates heat generated at the heat generation part  20 A. The heat transfer sheet  24  is provided between the heat generation part  20 A and the heat radiation part  20 B. 
     (Heat Removing Part) 
     The heat radiation part  20 B is explained in detail. 
     As shown in  FIG. 3  and  FIG. 4 , the heat radiation part  20 B includes a heat radiation plate  25  and a plurality of cooling fins  26  which are integrally formed on the heat radiation plate  25 . 
     The heat radiation plate  25  is made of a metal material having excellent thermal conductivity (aluminum or the like, for example), and is formed in a rectangular shape which is elongated more in the vertical direction L3 than in the longitudinal direction L1 as viewed in the side view. First threaded holes  28  are formed in the heat radiation plate  25  at around four corners of the heat radiation plate  25  respectively such that the first threaded holes  28  correspond to four first bolt through holes  27  formed in the partition plate  15 D. The heat radiation plate  25  is made to overlap with the partition plate  15 D from a side of a cooling air chamber  16 , and is fixed to the partition plate  15 D by first fixing screws (bolts)  29  which are threadedly engaged with the first threaded holes  28  through the first bolt through holes  27 . 
     Four second threaded holes  30  for affixing the heat generation part  20 A to the heat radiation plate  25  are formed in the heat radiation plate  25  at portions positioned more inside of (more toward the center of) the heat radiation plate  25  than four first threaded holes  28 . 
     The cooling fins  26  are plate-shaped fins which are made of a metal material having excellent thermal conductivity (aluminum or the like, for example), and are arranged along the vertical direction L3 (along the direction from the air chamber opening  16 A to the air chamber opening  16 B of the cooling air chamber  16 ). Each cooling fin  26  has a length which extends to the air chamber opening  16 B from the air chamber opening  16 A. These cooling fins  26  are arranged parallel to each other in the longitudinal direction L1 with a gap therebetween. 
     The plurality of cooling fins  26  may be integrally mounted on the heat radiation plate  25  by thermally conductive caulking, brazing or the like, or may be integrally mounted on the heat radiation plate  25  by other methods. 
     (Heat Generation Part) 
     The heat generation part  20 A is detachably mounted on the heat radiation part  20 B in a state where the heat generation part  20 A is arranged on a side opposite to the heat radiation part  20 B with the partition plate  15 D sandwiched therebetween. In the example shown in the drawing, the heat generation part  20 A is directly mounted on the heat radiation part  20 B through a mounting opening portion  31  formed in the partition plate  15 D while sandwiching the heat transfer sheet  24  between the heat generation part  20 A and the heat radiation part  20 B. 
     Detailed explanation will now be given. 
     As shown in  FIG. 3  to  FIG. 6 , the heat generation part  20 A is a unit which includes a heat receiving plate (power unit block)  35 , a plurality of the semiconductor elements  23 , a conductor  36 , two smoothing capacitors  37 , and a gate substrate  38 . The plurality of the semiconductor elements  23  are mounted on the heat receiving plate  35 . The conductor  36  is made to overlap with the plurality of semiconductor elements  23  for forming a predetermined power conversion circuit pattern when the conductor  36  is made conductive with terminal portions (not shown in the drawing) of the respective semiconductor elements  23 . The two smoothing capacitors  37  are made to overlap with the conductor  36 . The gate substrate  38  is made to further overlap with these smoothing capacitors  37 . 
     In the respective drawings other than  FIG. 5  and  FIG. 6 , the heat generation part  20 A is illustrated in a simplified manner. 
     In the same manner as the heat radiation plate  25 , the heat receiving plate  35  is a generally flat plate which is made of a metal material having excellent thermal conductivity (aluminum or the like, for example), and is formed in a rectangular shape which elongated more in the vertical direction L3 than in the longitudinal direction L1 as viewed in a side view. Second through bolt holes  40  are formed in the heat receiving plate  35  at the four corners of the heat receiving plate  35  respectively such that the second bolt through holes  40  correspond to the four second threaded holes  30  formed in the heat receiving plate  35 . 
     The heat receiving plate  35  is made to overlap with the heat radiation plate  25  from a side of a mounting chamber  17  with the heat transfer sheet  24  sandwiched between the heat receiving plate  35  and the heat radiation plate  25  through the mounting opening portion  31  formed in the partition plate  15 D, and is directly fixed to the heat radiation plate  25  by second fixing screws (bolts)  41  threadedly engaged with the second threaded holes  30  through the second bolt through holes  40 . 
     The semiconductor elements  23  contained in the heat generation part  20 A perform power conversion by switching on and off in response to turn-on/turn-off signals from the gate amplifier  22 . 
     In the example shown in the drawing, four semiconductor elements  23  are mounted on the heat receiving plate  35  in total such that the two semiconductor elements  23  are arranged in a spaced-apart manner in the longitudinal direction L1 and the two semiconductor elements  23  are also arranged in a spaced-apart manner in the vertical direction L3. The number of the semiconductor elements  23  is not limited to the number adopted in the above-mentioned case. Components other than the semiconductor elements  23  are not limited to those adopted in the above-mentioned case, and other parts may be incorporated when necessary. 
     The heat generation part  20 A of the power unit  20 , since the semiconductor elements  23  generate heat attributed to a power loss at the time of power conversion by the above-mentioned switching, has a tendency that a temperature of the heat generation part  20 A becomes higher than temperatures of the gate amplifier  22  and the filter capacitor  21  which are accommodated in the inside of the mounting chamber  17 . Accordingly, the radiation of heat generated from the heat generation part  20 A of the power unit  20  is more predominant than the radiation of heat generated from the gate amplifier  22  or the filter capacitor  21 . 
     A pair of frame plates  42  are mounted on the heat receiving plate  35  at portions thereof positioned to the sides of the semiconductor elements  23  in the longitudinal direction L1. The pair of frame plates  42  are formed in a trapezoidal shape as viewed in a side view, and each is formed on the heat receiving plate  35  in an extended manner with the semiconductor elements  23  located therebetween. A handle  42   a  is mounted on a top portion of each of the pair of frame plates  42 . Due to such a constitution, the heat generation part  20 A may be mounted easily or removed easily from the heat radiation plate  25 , or may be easily carried by using the handles  42   a.    
     The mounting opening portion  31  formed in the partition plate  15 D has a rectangular shape as viewed in a side view, and a size of the mounting opening portion  31  is sized to be larger than an size of the heat receiving plate  35  and is sized to be smaller than the size of the heat radiation plate  25 . Accordingly, the heat generation part  20 A may be directly fixed to the heat radiation part  20 B by way of the heat receiving plate  35  while preventing the inside of the mounting chamber and the inside of the cooling air chamber  16  from communicating with each other through the mounting opening portion  31 . 
     An opening periphery of the mounting opening portion  31  is sealed by a sealing material  43  over the whole circumference of the mounting opening portion  31 . Accordingly, a gap formed between the opening periphery of the mounting opening portion  31  and the heat radiation plate  25  is securely sealed so that communication between the inside of the mounting chamber  17  and the inside of the cooling air chamber  16  through the mounting opening portion  31  is prevented more effectively. In  FIG. 4 , the illustration of the sealing material  43  is omitted. 
     (Heat Transfer Sheet) 
     As shown in  FIG. 4 , the heat transfer sheet  24  is a sheet which has high thermal conductivity due to mixing of a heat conductive material (not shown in the drawing) such as metal fillers therein, and also has excellent flexibility and an excellent adhesiveness. The heat conductive material is arranged in the thickness direction in the heat transfer sheet  24 , so that the thermal conductivity of the heat transfer sheet  24  in the thickness direction thereof is higher than the thermal conductivity of the heat transfer sheet  24  in the planar direction thereof, i.e., a higher thermal conductivity between the heat receiving plate  35  and the heat radiation plate  25 , than between the center and perimeter edges thereof. 
     The heat transfer sheet  24  is formed in a rectangular shape and has substantially the same size as the heat receiving plate  35  as viewed in a side view. The heat transfer sheet  24  is brought into contact with the whole surface of the heat receiving plate  35 . The heat transfer sheet  24  has a two-layered structure which is formed of a sheet body  24   a  and a non-adhesive layer (a layer made of aluminum, for example)  24   b . The non-adhesive layer  24   b  is arranged against the side or generally planar face of the heat generation part  20 A. The sheet body  24   a  has a slight adhesiveness so that the sheet body  24   a  may be temporarily fixed to the heat radiation plate  25  by adhesion. 
     In the example shown in the drawing, four corners of the heat transfer sheet  24  are notched in a circular arc shape (i.e., has arc shaped cutouts at the corners) so that contact (electrical conduction) between the non-adhesive layer  24   b  and the second fixing screws  41  is prevented. 
     (Filter Capacitor and Gate Amplifier) 
     As shown in  FIG. 2  and  FIG. 3 , the filter capacitor  21  and the gate amplifier  22  are accommodated in the inside of the mounting chamber  17  in a state where the filter capacitor  21  and the gate amplifier  22  are directly mounted on the partition plates  15 A,  15 B respectively by fastening means such as screws (not shown in the drawing), and are arranged parallel to each other in the longitudinal direction L1 with the cooling air chamber  16  sandwiched therebetween. The filter capacitor  21  and the gate amplifier  22  are electrically connected with the semiconductor elements  23  of the power unit  20 . 
     Mounting positions of the filter capacitor  21  and the gate amplifier  22  are not limited to the above-mentioned positions, and may be changed suitably provided that the mounting positions are within the mounting chamber  17 . Various equipment necessary for performing power conversion may be arranged in the inside of the mounting chamber  17  in addition to the above-mentioned heat generation part  20 A, the filter capacitor  21  and the gate amplifier  22  of the power unit  20 . 
     [Manner of Operation and Advantageous Effects] 
     Next, the manner of operation of the electric power conversion device  3  having the above-mentioned constitution is explained. 
     When a DC power is supplied to the electric power conversion device  3  from the overhead line  4  or a power supply source not shown in the drawing, to prevent an inrush current to the power unit  20 , the DC power is initially charged into the filter capacitor  21  shown in  FIG. 2  and, thereafter, is supplied to the semiconductor elements  23  of the power unit  20 . When the DC power is supplied to the semiconductor elements  23 , the semiconductor elements  23  performs switching in response to the turn-on/turn-off signals from the gate amplifier  22  thus performs the power conversion from a DC power into an AC power. Accordingly, power necessary for moving of the railway vehicle  1  is ensured. 
     Heat generated from the semiconductor elements  23  at the time of performing the power conversion may be sequentially transferred to the heat radiation part  20 B arranged in the inside of the cooling air chamber  16 , in the order of the heat receiving plate  35 , the heat transfer sheet  24 , the heat radiation plate  25  and the cooling fins  26 , and the heat radiation part  20 B radiates, by radiative, convective and conductive heat transfer of the heat into the adjacent air environment in the cooling air chamber  16 . Due to such radiation of heat into the air in the cooling chamber, outside air in the cooling air chamber  16  is warmed so that a natural convection which flows toward the air chamber opening  16 B from the air chamber opening  16 A is induced in the cooling air chamber  16 . 
     Accordingly, heat transferred from the heat generation part  20 A may be transferred to outside air which constantly flows into the inside of the cooling air chamber  16  through the air chamber opening  16 A, and the heat generation part  20 A may be cooled due to a heat exchange performed by the radiation, convection and conduction of heat into this air stream. In such transfer of heat, the heat radiation part  20 B includes the plurality of cooling fins  26  and hence, the heat exchange between heat and outside air which flows in the cooling air chamber  16  may be smoothly performed. Accordingly, heat transfer performance is enhanced and hence, the heat generation part  20 A may be rapidly cooled. 
     Particularly, the heat transfer sheet  24  is provided between the heat generation part  20 A and the heat radiation part  20 B and hence, heat generated from the semiconductor elements  23  of the heat generation part  20 A may be efficiently transferred to the heat radiation part  20 B with little thermal resistance. Further, the heat transfer sheet  24  is sandwiched between the heat receiving plate  35  and the heat radiation plate and hence, any extremely small surface unevenness, deflection portions or the like of the heat receiving plate  35  and the heat radiation plate  25  may be absorbed by making use of flexibility (elasticity) of the heat transfer sheet  24 . Accordingly, the heat transfer sheet  24  is brought into close, intimate, contact with the heat receiving plate  35  and the heat radiation plate  25  without forming a gap therebetween. Due to such a constitution, heat may be transferred to the heat radiation part  20 B from the heat generation part  20 A with extremely high efficiency. Accordingly, excellent cooling performance may be exhibited and hence, it is possible to prevent the temperature elevation in the heat generation part  20 A and the temperature elevation in the mounting chamber  17 . 
     The heat transfer sheet  24  is sandwiched between the heat receiving plate  35  and the heat radiation plate  25  and is brought into close contact with both plates and hence, the heat receiving plate  35  may be mounted on the heat radiation plate  25  with a small play in an extremely stable manner. Accordingly, the heat generation part  20 A may be fixed to the heat receiving plate  35  in a sufficiently stable manner by making use of the four second fixing screws  41  arranged at four corners of the heat receiving plate  35  respectively. 
     In this embodiment, the heat receiving plate  35  is directly mounted on the heat radiation plate  25  with the heat transfer sheet  24  sandwiched therebetween, and the thermal conductivity of the heat transfer sheet  24  in the thickness direction is configured to be larger than the thermal conductivity of the heat transfer sheet  24  in the planar direction. Due to such a constitution, heat generated from the heat generation part  20 A may be transferred to the heat radiation part  20 B more efficiently and hence, the high cooling performance may be expected. 
     The heat generation part  20 A and the heat radiation part  20 B are arranged in the inside of the mounting chamber  17  and the cooling air chamber  16  which are partitioned by the partition plate  15 D respectively. Accordingly, a hermetically sealed state may be formed in the inside of the mounting chamber  17  with a structure which uses no packings. Accordingly, the whole constitution of the electric power conversion device  3  may be simplified due to the structure which uses no packings while enhancing the waterproof property of the arrangement. 
     The heat generation part  20 A is detachably mounted on the heat radiation part  20 B which is mounted on the partition plate  15 D by making use of the second fixing screws  41 . Accordingly, only the heat generation part  20 A need be mounted or removed while leaving the heat radiation part  20 B as is, and the heat generation part  20 A may be introduced into or removed from the box body  10  through the opening portion  18 . Accordingly, it is possible to enhance the ease of mounting or removing the heat generation part  20 A so that, for example, a maintenance operation of the heat generation part  20 A or the like may be smoothly performed. 
     Further, the power unit  20  adopts the structure where the heat generation part  20 A and the heat radiation part  20 B are separable from each other and hence, the heat generation part  20 A and the heat radiation part  20 B may be designed individually whereby the constitution of the power unit  20  may be simplified and miniaturized. 
     Since the heat transfer sheet  24  includes the non-adhesive layer  24   b , in removing the heat generation part  20 A, the heat transfer sheet  24  and the heat receiving plate  35  may be easily separated from each other. Accordingly, the operability of mounting or removing the heat generation part  20 A may be further enhanced. Further, for example, peeling off or breaking or the like of the heat transfer sheet  24  is scarcely generated when the heat generation part  20 A is mounted or removed and hence, the heat transfer sheet  24  may be used without being replaced more than necessary. 
     As has been explained above, according to this embodiment, heat generated from the heat generation part  20 A of the power unit  20  may be efficiently transferred to the heat radiation part  20 B and hence, excellent cooling performance may be realized. Accordingly, the temperature elevation in the heat generation part  20 A and the temperature elevation in the mounting chamber  17  may be effectively prevented and, at the same time, the operability of mounting or removing the heat generation part  20 A may be also enhanced. 
     Since the railway vehicle  1  includes the electric power conversion device  3  having the constitution as described above, power supply can be stabilized and accordingly the railway vehicle  1  can realize excellent traveling performance. 
     Modification of First Embodiment 
     In the first embodiment described above, the heat generation part  20 A is directly mounted on the heat radiation part  20 B through the mounting opening portion  31  formed in the partition plate  15 D in a state where the heat transfer sheet  24  is sandwiched between the heat generation part  20 A and the heat radiation part  20 B. However, the mounting of the heat generation part  20 A is not limited to such a mode. For example, as shown in  FIG. 7 , the heat generation part  20 A may be mounted to the heat radiation part  20 B, but with the partition plate  15 D sandwiched therebetween, i.e., without forming the mounting opening portion  31  in the partition plate  15 D. 
     In this case, the heat transfer sheet  24  is not arranged on the heat radiation plate  25  but it is arranged on a side of a heat generation part  20 A of the partition plate  15 D such that the heat transfer sheet  24  is sandwiched between the heat receiving plate  35  of the heat generation part  20 A and the partition plate  15 D. Third bolt through holes  50  are formed in the partition plate  15 D at positions corresponding to the second threaded holes  30  formed in the heat radiation plate  25 . 
     Further, the heat receiving plate  35  is made to overlap with the partition plate  15 D from a side of a mounting chamber  17  in a state where the heat transfer sheet  24  is sandwiched between the partition plate  15 D and the heat generation part  20 A, and is fixed to the heat radiation part  20 B by the second fixing screws  41  threadedly engaged with the second threaded holes  30  through the second bolt through holes  40  and the third bolt through holes  50  with the partition plate  15 D sandwiched therebetween. 
     Even with the electric power conversion device  3  having the above-mentioned constitution, heat generated from the semiconductor elements  23  may be transferred to a side of the heat radiation part  20 B in the order of the heat receiving plate  35 , the heat transfer sheet  24 , the partition plate  15 D and the heat radiation plate  25  and hence, the electric power conversion device  3  according to this modification may acquire the manner of operation and advantageous effects substantially equal to those of the above-mentioned first embodiment. 
     Particularly, in this modification, heat transferred to the partition plate  15 D may be transferred not only to the heat radiation plate  25  but also to a greater extent to the remaining partition plates  15 A to  15 C so that heat may be radiated by making use of whole area of the partition plates  15 A to  15 D whereby a greater cooling capacity may be expected. 
     In the first embodiment, however, heat can be directly transferred to the heat radiation plate  25  from the heat receiving plate  35  by way of the heat transfer sheet  24 . Accordingly, the first embodiment is more preferable. 
     Second Embodiment 
     Next, an electric power conversion device for a vehicle of the second embodiment is explained. 
     The constitution which makes this embodiment different from the first embodiment is as follows. In the first embodiment, the cooling air chamber  16  is arranged such that the cooling air chamber  16  penetrates the box body  10  in the vertical direction L3 using the partition plate  15 D. In the second embodiment, the cooling air chamber  16  is arranged such that the cooling air chamber  16  penetrates the box body  10  in the longitudinal direction L1. 
     In the second embodiment, constitutional elements identical with the constitutional elements of the first embodiment are given same symbols, and the explanation of these elements is omitted. 
     [Constitution of Electric Power Conversion Device for Vehicle] 
     As shown in  FIG. 8  and  FIG. 9 , in an electric power conversion device  60  of this embodiment, a bottom wall portion  61  of the box body  10  constitutes a partition plate, and the cooling air chamber  16  and the mounting chamber  17  are vertically partitioned by the bottom wall portion  61 . Accordingly, the cooling air chamber  16  of this embodiment is of an external air chamber type (an open volume of air below the mounting chamber) where the cooling air chamber  16  is arranged below the mounting chamber  17 . 
     The air chamber opening  16 A faces one side of the vehicle body  2 , and the air chamber opening  16 B faces another side of the vehicle body  2 . Accordingly, the cooling air chamber  16  is formed such that the air chamber opening  16 B and the air chamber opening  16 A are arranged parallel to each other in the longitudinal direction L1. 
     The example shown by  FIG. 8  and  FIG. 9 , the cooling air chamber  16  is exposed. However, except for the air chamber opening  16 A and the air chamber opening  16 B, the cooling air chamber  16  can be covered by a cover material. 
     The power unit  20  differs from the power unit  20  of the first embodiment only with respect to the following constitution. That is, the power unit  20  of this embodiment is mounted on the bottom wall portion  61  while the power unit  20  of the first embodiment is mounted on the partition plate  15 D. Accordingly, the power unit  20  is explained simply. 
     As shown in  FIG. 9 , the heat radiation part  20 B of the power unit  20  is mounted on the bottom wall portion  61  from a side of a cooling air chamber  16  (lower side) by the first fixing screws  29 . The heat generation part  20 A of the power unit  20  is made to overlap with the heat radiation plate  25  from a side of a mounting chamber  17  (upper side) through the mounting opening portion  31  formed in the bottom wall portion  61  with the heat transfer sheet  24  sandwiched therebetween, and the heat generation part  20 A is directly fixed to the heat radiation plate  25  by the second fixing screws  41 . 
     The filter capacitor  21  and the gate amplifier  22  are placed in the mounting chamber  17  in a state where the filter capacitor  21  and the gate amplifier  22  are also directly mounted on the bottom wall portion  61  respectively by fastening means such as screws not shown in the drawing. The mounting of the filter capacitor  21  and the gate amplifier  22  are not limited to such a mode, and these parts may be mounted at any position provided that these parts are mounted within the mounting chamber  17 . 
     The opening portion  18  formed in the box body  10  is formed at a position where the heat generation part  20 A may be introduced into or removed from the box body  10  through the opening portion  18  while moving the heat generation part  20 A along the bottom wall portion  61 . A size of the opening portion  18  is set to a size which corresponds to a side surface of the heat generation part  20 A whose cross-sectional area is smaller than an upper surface of the heat generation part  20 A. Usually, the opening portion  18  is closed by a cover  62 . 
     [Manner of Operation and Advantageous Effects] 
     The electric power conversion device for a vehicle  60  of this embodiment may acquire the following manner of operation and advantageous effects in addition to the manner of operation and advantageous effects substantially equal to the manner of operation and the advantageous effects of the first embodiment. 
     The cooling air chamber  16  is arranged along the longitudinal direction L1 and hence, air passing under the vehicle during vehicle movement may be taken into the inside of the cooling air chamber  16  during traveling of the railway vehicle  1 . Accordingly, outside air whose temperature is increased due to a heat exchange with cooling fins  26  may be rapidly discharged from the cooling air chamber  16  and, further, a large amount of outside air is taken into the inside of the cooling air chamber  16  and hence, it is possible to positively accelerate the heat transfer from the heat generation part  20 A. Due to such a constitution, cooling performance may be further enhanced. 
     To remove and replace the heat generation part  20 A, the heat generation part  20 A may be pulled out from the box body  10  through the opening portion  18  in the side of the box body  10  by moving the heat generation part  20 A such that the heat generation part  20 A slides on the bottom wall portion  61 , for example, and hence, it is unnecessary to raise the heat generation part  20 A. Due to such a constitution, for example, even when the heat generation part  20 A is large and heavy, the heat generation part  20 A may be easily removed so that a burden imposed on an operator may be reduced. Accordingly, the operability of mounting or removing the heat generation part  20 A may be further enhanced. 
     Further, the opening portion  18  is formed in the side wall portion  13 D which faces the vehicle left side L and hence, a mounting and removing operation of the heat generation part  20 A may be performed extremely easily. Further, the heat generation part  20 A may be pulled out in a state where a side of a side surface which has small cross-sectional area is set on a viewer&#39;s side and hence, a size (width) of the opening portion  18  may be set smaller compared to the opening portion  18  of the first embodiment. 
     Third Embodiment 
     Next, an electric power conversion device for a vehicle of the third embodiment according to the invention is explained. 
     The constitution which makes this embodiment different from the second embodiment is as follows. In the second embodiment, relative air movement between the cooling air chamber and the ambient surroundings caused by movement of the train vehicle air flow caused by movement causes air to pass through the inside of the cooling air chamber  16  (through the exposed fins of the heat exchanger extending below the box body  10 ). In the third embodiment, outside air is forcibly taken into the cooling air chamber  16  by making use of a fan. 
     In the third embodiment, constitutional elements identical with the constitutional elements of the second embodiment are given same symbols, and the explanation of these constitutional parts is omitted. 
     [Constitution of Electric Power Conversion Device for Vehicle] 
     As shown in  FIG. 10 , in an electric power conversion device  70  of this embodiment, the box body  10  includes an air chamber wall portion  71  which surrounds the periphery of the cooling fins  26 , and an inner space surrounded by the air chamber wall portion  71  and the bottom wall portion  61  constitutes the cooling air chamber  16 . Fans  72  which take outside air into the inside of the cooling air chamber  16  are arranged at portions of the air chamber wall portion  71  which are positioned at the air chamber opening  16 A. In the example shown in the drawing, the two fans  72  are arranged in a spaced-apart manner in the lateral direction L2. A discharge opening  73  for discharging the outside air from the cooling air chamber  16  therethrough is formed in a portion of the air chamber wall portion  71  which is positioned at the air chamber opening  16 B. 
     [Manner of Operation and Advantageous Effect] 
     According to the electric power conversion device  70  of this embodiment, a fixed amount of outside air may be forcibly taken into the inside of the cooling air chamber  16  by operating the fans  72  and hence, heat may be radiated in a stable manner while preventing the stagnation of outside air. Particularly, forced-air cooling is adopted and hence, cooling is not significantly influenced by the speed of the railway vehicle  1 , and cooling may be performed by taking outside air into the inside of the cooling air chamber  16  even when the railway vehicle  1  is in a stopped state. Accordingly, stable cooling performance may be ensured. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 
     For example, in the respective embodiments, the heat transfer sheet which exhibits higher thermal conductivity in the thickness direction than the planar direction and has the two-layered structure which includes a non-adhesive layer is adopted. However, the heat transfer sheet is not limited to the such a heat transfer sheet. The heat transfer sheet may not include the non-adhesive layer, or the direction of the thermal conductivity may not be the thickness direction. In any case, it is sufficient for the heat transfer sheet that the heat transfer sheet may transfer heat generated from a heat generation part to a heat radiation part.