Patent Publication Number: US-2023156967-A1

Title: Circuit assembly

Description:
TECHNICAL FIELD 
     The present disclosure relates to a circuit assembly including a heat generating component. 
     BACKGROUND ART 
     In a known circuit assembly provided with a heat generating component, such as a relay or fuse that generates heat when energized, a heat dissipating structure for dissipating the heat of the heat generating component may be provided. For example, in the structure described in Patent Document 1, heat generated by a relay housed in a case is dissipated using an intermediate portion of a bus bar that connects a connection portion of the relay and a connection terminal of a battery disposed outside the case. Specifically, a structure is described in which the intermediate portion of the bus bar, which extends outside the case housing the relay, is brought into contact with a chassis or a housing that houses an entire power supply apparatus via an insulative heat dissipation sheet, whereby heat generated by the relay is conducted to the chassis or the housing and dissipated. 
     CITATION LIST 
     Patent Documents 
     
         
         Patent Document 1: JP 2014-79093A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the structure of Patent Document 1, the heat dissipating structure is provided in the intermediate portion of the bus bar that forms an energization portion connecting the relay and the battery. Thus, though heat dissipation of the relay via the bus bar is promoted, there is a problem in that, when a large current flows, heat generated at the connection portion of the relay cannot be quickly reduced. 
     In view of this, a circuit assembly with a novel structure that can quickly reduce heat generation at a connection portion of a heat generating component is provided. 
     Solution to Problem 
     A circuit assembly of the present disclosure includes a heat generating component that generates heat when energized; a energization member that connects to a connection portion of the heat generating component; a fastening member that fastens the energization member to the connection portion; and a heat capacity increasing component that thermally connects to a fastening site of the energization member and the connection portion and increases a heat capacity of the connection portion of the heat generating component. 
     Advantageous Effects of Invention 
     According to the present disclosure, heat generation at a connection portion of a heat generating component can be quickly reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrating a circuit assembly according to a first embodiment. 
         FIG.  2    is an exploded perspective view illustrating the circuit assembly illustrated in  FIG.  1    in a state with the lid member forming the case removed. 
         FIG.  3    is an exploded perspective view of the circuit assembly illustrated in  FIG.  1   . 
         FIG.  4    is a perspective view illustrating an energization member forming the circuit assembly illustrated in  FIG.  1   . 
         FIG.  5    is a cross-sectional view taken along V-V in  FIG.  2   . 
         FIG.  6    is a perspective view illustrating a circuit assembly according to a second embodiment and is an enlarged view of a main portion in a state with a lid member forming a case removed. 
         FIG.  7    is a cross-sectional view taken along VII-VII of  FIG.  6   . 
         FIG.  8    is a perspective view illustrating a circuit assembly according to a third embodiment and is an enlarged view of a main portion in a state with a lid member forming a case removed. 
         FIG.  9    is a cross-sectional view taken along IX-IX in  FIG.  8   . 
         FIG.  10    is a vertical cross-sectional view illustrating a circuit assembly according to a fourth embodiment and corresponds to  FIG.  9   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Description of Embodiments of Present Disclosure 
     Firstly, embodiments of the present disclosure will be listed and described. 
     A circuit assembly of the present disclosure is 
     (1) a circuit assembly including a heat generating component that generates heat when energized; a energization member that connects to a connection portion of the heat generating component; a fastening member that fastens the energization member to the connection portion; and a heat capacity increasing component that thermally connects to a fastening site of the energization member and the connection portion and increases a heat capacity of the connection portion of the heat generating component. 
     According to the circuit assembly of the present disclosure, the heat capacity increasing component that increases the heat capacity of the connection portion is provided at and thermally in contact with the fastening site of the connection portion corresponding to the heat generating site of the heat generating component and the energization member connected to the connection portion. Thus, heat at the connection portion transferred to the fastening site of the connection portion of the heat generating component and the energization member can be reduced by suppressing an increase in the temperature via the heat capacity increasing component thermally in contact with the fastening site. As a result, compared to a known structure in which an energization member is brought into contact with another member at a site separated from the connection portion of the heat generating component and heat is dissipated, heat generated at the connection portion of the heat generating component can be quickly reduce by the heat capacity increasing component. Note that the heat generating component includes a component that generates heat when energized, such as a relay, fuse, or the like. 
     The heat capacity increasing component may be any kind of component as long as the heat capacity of the connection portion of the heat generating component can be increased by thermally coming into contact with the heat capacity increasing component to the fastening site of the connection portion and the energization member. For example, a component made of metal with high thermal conductivity, such as iron, copper, aluminum, an alloy thereof, or the like or a synthetic resin may be used. Also, the shape of the heat capacity increasing component is not particularly limited and may be any shape as long as the shape allows for the heat capacity increasing component to be in thermal contact with the fastening site of the connection portion and the energization member. 
     Any known fastening member may be used as the fastening member as long as it can be used to fasten the energization member, and advantageous examples include a bolt, a rivet, and the like. 
     (2) Preferably, a heat conducting member and a case are further provided, wherein the energization member is thermally in contact with the case via the heat conducting member. The heat transferred to the energization member can be dissipated from the case via the heat conducting member. Thus, the heat of the heat generating component can be reduced. In the present aspect, preferably, a sheet-like heat conducting member is used. 
     (3) Preferably, the heat capacity increasing component is made of metal; and the heat capacity increasing component is fastened to the connection portion together with the energization member via the fastening member. Because the heat capacity increasing component is made of metal and fastened to the connection portion together with the energization member, the heat capacity of the connection portion can be easily and reliably increased. Note that the heat capacity increasing component may be formed integrally with the energization member or may be a separate component from the energization member. 
     (4) Preferably, the heat capacity increasing component is overlapped with a surface on an opposite side to a contact surface of the energization member with the connection portion. Because the heat capacity increasing component is overlapped with the surface on the opposite side to the contact surface of the energization member with the connection portion, when the connection portion is fastened with the fastening member, the heat capacity increasing component is avoided from being disposed between the energization member and the connection portion. Thus, the heat capacity of the connection portion can be increased without increasing the electrical conduction resistance. 
     (5) Preferably, the heat capacity increasing component is formed of an end portion of the energization member and is folded back and overlapped with a surface on an opposite side to a contact surface of the energization member with the connection portion. Because the heat capacity increasing component is formed of the end portion of the energization member, an increase in the number of parts can be suppressed. Also, because the heat capacity increasing component is folded back and overlapped with the surface on the opposite side to the contact surface of the energization member with the connection portion, when the connection portion is fastened with the fastening member, the heat capacity increasing component is avoided from being disposed between the energization member and the connection portion. Thus, the heat capacity of the connection portion can be increased without increasing the electrical conduction resistance. 
     (6) Preferably, the energization member includes a holding portion that holds the end portion of the energization member forming the heat capacity increasing component and the surface on the opposite side of the contact surface of the energization member with the connection portion in an overlapped state. With the holding portion, the gap between the energization member and the heat capacity increasing component (folded-back end portion of the energization member) can be kept small, and the energization member and the heat capacity increasing component can be stably brought into contact with one another across a wide contact area. Accordingly, the heat capacity of the connection portion can be more reliably increased. 
     (7) Preferably, a coefficient of linear thermal expansion of the heat capacity increasing component ranges from ⅓ to 3 times a coefficient of linear thermal expansion of the fastening member. Because the heat capacity increasing component has a coefficient of linear thermal expansion similar to that of the fastening member, looseness of the fastening member caused by heat generation is unlikely to occur. 
     (8) Preferably, the heat capacity increasing component and the fastening member are a same material. Because the coefficient of linear thermal expansion of the heat capacity increasing component and the fastening member is equal, looseness of the fastening member caused by heat generation can be more reliably suppressed. 
     (9) Preferably, the heat capacity increasing component is formed of a cap for installing on the fastening member. Even with a cap for installing on the fastening member, the heat capacity of the connection portion can be increased, and heat generation at a connection portion of a heat generating component can be quickly reduced. 
     (10) Preferably, the cap is made of metal. By using the cap made of a metal with high thermal conductivity, an increase in the temperature at the connection portion can be suppressed. 
     (11) Preferably, a heat conducting member is provided between the cap and the fastening member. Using the heat conducting member, heat can be stably transferred from the fastening member to the cap. In the present aspect, preferably, a grease-like heat conducting member is used, for example. 
     (12) Preferably, the cap is made of synthetic resin. For example, by using a synthetic resin that is softer than metal as the material for the cap, the cap can be installed on the fastening member substantially without gaps. Thus, heat can be stably transferred from the fastening member to the cap, and the heat capacity of the connection portion can be more reliably increased. 
     Details of Embodiments of Present Disclosure 
     Specific examples of the circuit assembly according to the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples and is defined by the scope of the claims, and all modifications that are equivalent to or within the scope of the claims are included. 
     First Embodiment 
     The first embodiment of the present disclosure will be described below with reference to  FIGS.  1  to  5   . A circuit assembly  10  of the first embodiment is installed in a vehicle (not illustrated), such as an electric vehicle or a hybrid vehicle, for example, and supplies and controls electric power from a power supply (not illustrated) such as a battery to a load (not illustrated) such as a motor. While the circuit assembly  10  can be oriented in any direction, in the following description, the X direction is defined as the forward direction, the Y direction is defined as the right direction, and the Z direction is defined as the upward direction. Also, for members including a plurality of members, a reference sign or number may only be given to one or more of the members of the plurality and not given to other members. 
     Circuit Assembly  10   
     The circuit assembly  10  includes a relay  12 , which is an example of a heat generating component that generates heat when energized; an energization bus bar  16 , which is an example of an energization portion connecting to a connection portion  14  of the relay  12 ; and a bolt  18 , which is an example of a fastening member that fastens the energization bus bar  16  to the connection portion  14  of the relay  12 . Also, the circuit assembly  10  includes a heat capacity increasing component  20  that is thermally in contact with a fastening site A (a region surrounded by a two-dot dash line in the diagrams) of the energization bus bar  16  and the connection portion  14 . The circuit assembly  10  further includes a case  22 . The relay  12 , the energization bus bar  16 , the bolt  18 , and the heat capacity increasing component  20  are all housed in the case  22 . The case  22  also houses a fuse  24  that generates heat when energized and a current sensor  26 . 
     Case  22   
     The case  22  has an overall box-like shape and is made of a synthetic resin, for example. In the first embodiment, the case  22  is substantially rectangular, extending in the left-and-right direction in a plan view. The case  22  is divisible in the up-and-down direction and includes a base member  28  located on the lower side and a lid member  30  located on the upper side. The base member  28  has a box-like shape opening upward. The lid member  30  has a box-like shape opening downward. Also, the case  22  is formed by the upper opening portion of the base member  28  being covered by the lid member  30  and the base member  28  and the lid member  30  being fixed together. The method of fixing together the base member  28  and the lid member  30  is not limited, and various known fixing methods, such as adhesion, welding, press-fitting, protrusion-recess fitting, and the like can be used. Note that the case  22  may be made of metal, and the surface of the case  22  may be provided with an insulating cover to ensure it has insulating properties. 
     The base member  28  includes a bottom wall  32  with a substantially rectangular shape extending in the left-and-right direction and a peripheral wall  34  that projects upward from the outer peripheral edge portion of the bottom wall  32 . In the first embodiment, a first housing recess portion  36  with a rectangular shape opening upward is formed in the upper surface of the bottom wall  32 . In other words, a level difference  38  is formed on the upper surface of the bottom wall  32 , and the portion surrounded by the level difference  38  corresponds to the first housing recess portion  36 . In particular, in the first embodiment, at the upper surface of the bottom wall  32 , four first housing recess portions  36  are formed with a predetermined size and at a predetermined separation distance in the left-and-right direction. 
     As illustrated in  FIG.  5   , a second housing recess portion  40  with a rectangular shape opening downward is formed at a position corresponding to the first housing recess portion  36  in the lower surface of the bottom wall  32 . In other words, a level difference  42  is formed on the lower surface of the bottom wall  32 , and the portion surrounded by the level difference  42  corresponds to the second housing recess portion  40 . Four second housing recess portions  40  are provided with a size and positions corresponding to the first housing recess portions  36 . Thus, in the first embodiment, at the positions where the first and second housing recess portions  36  and  40  are formed, the bottom wall  32  is thinner compared to other portions. 
     The lid member  30  includes an upper bottom wall  44  with a substantially rectangular shape extending in the left-and-right direction and a peripheral wall  46  that projects downward from the outer peripheral edge portion of the upper bottom wall  44 . In the first embodiment, opening portions  48   a  and  48   b  with a rectangular shape are formed in the left and right end portions of the upper bottom wall  44  extending through in the up-and-down direction. Also, a plurality of bolt insertion holes  50  are formed in the outer peripheral portion of the lid member  30  extending through in the up-and-down direction. 
     Relay  12 , Fuse  24 , and Current Sensor  26   
     The relay  12  includes a relay body  52  with a hollow rectangular parallelepiped-like shape. A pair of connection portions  14  and  14  (a first connection portion  14   a  and a second connection portion  14   b ) are provided on the front surface of the relay body  52  separated from one another in the left-and-right direction. An insulating plate  54  projecting frontward is provided between the first connection portion  14   a  and the second connection portion  14   b.    
     Also a plurality of leg portions  56  projecting outward in the left-and-right direction are provided on the relay body  52 . Bolt insertion holes are formed in the leg portions  56  extending through in the up-and-down direction. 
     The fuse  24  includes a fuse body  60  with a substantially rectangular parallelepiped-like shape. Connection portions  62  and  62  that are made of metal and project to both sides in the left-and-right direction are provided on the fuse body  60 . Bolt insertion holes are formed in the connection portions  62  and  62  extending through in the up-and-down direction. 
     The current sensor  26  includes a sensor body  66  with a substantially rectangular parallelepiped-like shape. Connection portions  68  and  68  that are made of metal and project to both sides in the left-and-right direction are provided on the sensor body  66 . Bolt insertion holes are formed in the connection portions  68  and  68  extending through in the up-and-down direction. 
     Energization Bus Bar  16   
     The energization bus bar  16  is formed by bending a metal plate material in a predetermined shape via a pressing process or the like. The material of the energization bus bar  16  is not limited, however copper, copper alloy, aluminum, aluminum alloy, or the like are preferably used. Note that the coefficient of linear thermal expansion of copper is approximately 16 to 17 (×10 −6 /K). Also, the coefficient of linear thermal expansion of aluminum is approximately 23 to 24 (×10 −6 /K). In the first embodiment, as also illustrated in  FIG.  4   , the pair of energization bus bars  16  and  16  (first energization bus bar  16   a  and second energization bus bar  16   b ) are provided separated from one another in the left-and-right direction. 
     The first energization bus bar  16   a  extends overall in the left-and-right direction. The first energization bus bar  16   a  includes, at the right end portion, a bolt fastening portion  72  with a rectangular shape extending in the up-and-down direction (YZ plane). A heat transfer portion  74  is a rectangular shape extending in the horizontal direction (XY plane) extends from the back of the lower end of the bolt fastening portion  72 . Also, the first energization bus bar  16   a  includes, at the left end portion, an external connection portion  76  with a rectangular shape extending in the horizontal direction (XY plane). Also, the heat transfer portion  74  and the external connection portion  76  are connected by a portion bent like a crank in the intermediate portion in the left-and-right direction. 
     Furthermore, the upper end portion of the bolt fastening portion  72  of the first energization bus bar  16   a  is folded forward and overlaps the lower end portion of the bolt fastening portion  72 . Note that the upper end portion of the bolt fastening portion  72  prior to being folded back is indicated by a two-dot dash line in  FIG.  4   . The folded back and overlapped portion corresponds to the heat capacity increasing component  20 . In other words, in the first embodiment, the heat capacity increasing component  20  is made of metal and uses the same material as the energization bus bar  16  (first and second energization bus bars  16   a  and  16   b ). The first energization bus bar  16   a  is formed with double thickness at the position where the heat capacity increasing component  20  is formed. Also, the back surface of the bolt fastening portion  72  corresponds to a contact surface  78  that comes into contact with the first connection portion  14   a  of the relay  12 . Thus, the upper end portion (heat capacity increasing component  20 ) of the bolt fastening portion  72  corresponding to the end portion of the first energization bus bar  16   a  is overlapped with a front surface  79  corresponding to the surface of the bolt fastening portion  72  on the opposite side to the contact surface  78 . 
     Also, the first energization bus bar  16   a  is provided with a holding portion  80  that holds the heat capacity increasing component  20  and the front surface  79  of the bolt fastening portion  72  in an overlapped state. The shape of the holding portion  80  is not limited, however in the first embodiment, the holding portion  80  is a metal member formed integrally with the first energization bus bar  16   a . Specifically, a pair of band-like holding portions  80  and  80  are provided on the left and right sides of the bolt fastening portion  72 . Also, by bending and crimping the holding portions  80  and  80  with the heat capacity increasing component  20  (upper end portion of the bolt fastening portion  72 ) overlapped with the front surface  79  of the bolt fastening portion  72 , the overlapped state of the heat capacity increasing component  20  (upper end portion of the bolt fastening portion  72 ) can be held. 
     Also, a bolt insertion hole  82  is formed in the bolt fastening portion  72  extending through in the front-and-back direction. In the first embodiment, the bolt insertion hole  82  is formed in the portion where the heat capacity increasing component  20  is provided (the portion where the upper end portion of the bolt fastening portion  72  is folded back and overlapped). Thus, the bolt insertion hole  82  is formed in the portion where the first energization bus bar  16   a  has double thickness extending through in the front-and-back direction. Note that the bolt insertion hole  82  may be formed by forming a through hole in both the upper end portion and the lower end portion of the bolt fastening portion  72  prior to folding back the upper end portion of the bolt fastening portion  72 , folding back the upper end portion of the bolt fastening portion  72 , and connecting the through holes. Alternatively, the bolt insertion hole  82  may be formed at the portion of double thickness after the upper end portion of the bolt fastening portion  72  is folded back and overlapped. By inserting the bolt  18  into the bolt insertion hole  82  and fastening it to the first connection portion  14   a , the first energization bus bar  16   a  provided with the heat capacity increasing component  20  is affixed. In other words, by fastening the bolt  18 , not only is the first energization bus bar with single thickness fixed to the first connection portion  14   a , but the heat capacity increasing component  20  also with single thickness is also fixed. 
     Also, in the first embodiment, the bolt insertion hole  82  has an elliptical shape elongated in the up-and-down direction. Thus, when the relay  12  and the first energization bus bar  16   a  are fastened together as described below, the position in the up-and-down direction of the first energization bus bar  16   a  relative to the relay  12  can be adjusted. As a result, as described below, the heat transfer portion  74  can be more reliably thermally brought into contact with the case  22  (or a heat conduction sheet  114  described below). Also, a bolt insertion hole  84  is formed in the external connection portion  76  extending through in the thickness direction (up-and-down direction). 
     The second energization bus bar  16   b  has a substantially symmetrical shape in the left-and-right direction to the first energization bus bar  16   a . That is, the bolt fastening portion  72  is provided at the front of the left end portion of the second energization bus bar  16   b . The heat transfer portion  74  extends backward from the lower end portion of the bolt fastening portion  72 . Also, a fuse connection portion  86  with a rectangular shape extending in the horizontal direction (XY plane) is provided on the right end portion of the second energization bus bar  16   b . The heat transfer portion  74  and the fuse connection portion  86  are connected by a portion bent like a crank in the intermediate portion in the left-and-right direction. Also, a bolt insertion hole  88  is formed in the fuse connection portion  86  extending through in the thickness direction (up-and-down direction). 
     Furthermore, the upper end portion of the bolt fastening portion  72  of the second energization bus bar  16   b  is folded forward, forming the heat capacity increasing component  20 . Also, the state of the heat capacity increasing component  20  (upper end portion of the bolt fastening portion  72 ) being folded and overlapped with the front surface  79  is held by the holding portions  80  and  80 . Also, in a state in which the heat capacity increasing component  20  is provided, the bolt insertion hole  82  is formed in the bolt fastening portion  72  extending through in the thickness direction (front-and-back direction). By inserting the bolt  18  into the bolt insertion hole  82  and fastening it to the second connection portion  14   b , the second energization bus bar  16   b  provided with the heat capacity increasing component  20  is affixed. In other words, by fastening the bolt  18 , the heat capacity increasing component  20  together with the second energization bus bar  16   b  is fixed to the second connection portion  14   b.    
     Third Energization Bus Bar  90  and Fourth Energization Bus Bar  92   
     As illustrated in  FIGS.  2  and  3   , a third energization bus bar  90  is connected to the fuse  24  and the current sensor  26 . Also, at the current sensor  26 , a fourth energization bus bar  92  is connected on the opposite side to the side where the third energization bus bar  90  is connected. The third and fourth energization bus bars  90  and  92  are also formed by bending a metal plate material in a predetermined shape via a pressing process or the like as with the first and second energization bus bars  16   a  and  16   b.    
     The third energization bus bar  90  includes, on the left and right end portions, a fuse connection portion  94  and a sensor connection portion  96  with a rectangular shape extending in the horizontal direction. That is, on the left side of the third energization bus bar  90 , the fuse connection portion  94  is provided, and on the right side, the sensor connection portion  96  is provided. A bolt insertion hole is formed in both the fuse connection portion  94  and the sensor connection portion  96  extending through in the thickness direction (up-and-down direction). 
     In the first embodiment, the third energization bus bar  90  includes a substantially trough-shaped portion extending in the front-and-back direction and opening upward. The fuse connection portion  94  and the sensor connection portion  96  extends outward in the left-and-right direction from the left and right end portions of the upper opening portion of the substantially trough-shaped portion. Also, the bottom wall of the substantially trough-shaped portion corresponds to a heat transfer portion  102  thermally in contact with the case  22  (base member  28 ) when the circuit assembly  10  is assembled. 
     The fourth energization bus bar  92  has a structure similar to that of the third energization bus bar  90 . In other words, the fourth energization bus bar  92  includes a substantially trough-shaped portion extending in the front-and-back direction and opening upward. A sensor connection portion  104  extends to the left from the left end portion of the upper opening portion of the substantially trough-shaped portion, and an external connection portion  106  extends to the right from the right end portion. A bolt insertion hole is formed in the sensor connection portion  104  extending through in the thickness direction (up-and-down direction). Also, a bolt insertion hole  110  is formed in the external connection portion  106  extending through in the thickness direction (up-and-down direction). Also, the bottom wall of the substantially trough-shaped portion corresponds to a heat transfer portion  112  thermally in contact with the case  22  (base member  28 ) when the circuit assembly  10  is assembled. 
     Bolt  18   
     The relay  12  and the first and second energization bus bars  16   a  and  16   b  are fixed together via the bolts  18  and  18 . Specifically, the first and second connection portions  14   a  and  14   b  and the bolt insertion holes  82  and  82  of the bolt fastening portions  72  and  72  are aligned in position, and the bolts  18  and  18  are inserted and fastened. A known material, such as iron or stainless steel, may be used as the material of the bolt  18 . In the first embodiment, the bolt  18  is made of iron. Note that the coefficient of linear thermal expansion of iron is approximately 11 to 12 (×10 −6 /K). 
     Heat Conduction Sheets  114  and  116   
     When the circuit assembly  10  is assembled, the heat transfer portions  74 ,  74 ,  102 , and  112  of the first to fourth energization bus bars  16   a ,  16   b ,  90 , and  92  are thermally in contact with the case  22  (base member  28 ). In the first embodiment, the heat conduction sheets  114 , i.e., heat conducting members, are housed in the first housing recess portions  36  of the base member  28 . Also, the heat transfer portions  74 ,  74 ,  102 , and  112  are thermally in contact with the base member  28  via the heat conduction sheets  114 . 
     Also, in the first embodiment, heat conduction sheets  116  are housed in the second housing recess portions  40  of the base member  28 . When the circuit assembly  10  is installed in a vehicle, the base member  28  is thermally in contact with a heat dissipating body  118 , such as a vehicle body panel or housing, via the heat conduction sheets  116 . 
     The heat conduction sheets  114  and  116  have a sheet-like shape flat in the up-and-down direction are made of a synthetic resin with a larger thermal conductivity than air. Specifically, a silicone-based resin, a non-silicone-based acrylic resin, a ceramic-based resin, or the like can be used. A more specific example is heat-conductive silicone rubber. The heat conduction sheets  114  and  116  have flexibility and elasticity and can elastically deform, changing in the thickness dimension, in response to a force applied in the up-and-down direction. Note that in the first embodiment, the heat conduction sheets  114  and  116  are used as heat conducting members provided on the upper and lower surfaces of the base member  28 . However, the heat conducting members are in no way limited to this configuration. The heat conducting members may have a discretionary shape, and a heat dissipating gap filler or heat conducting grease made of a silicone-based resin may be used, for example. 
     In particular, in the first embodiment, because the heat conduction sheets  114  are housed in the first housing recess portions  36  with the level difference  38 , the heat conduction sheets  114  are positioned relative to the base member  28 . Also, because the heat conduction sheets  116  are housed in the second housing recess portions  40  with the level difference  42 , the heat conduction sheets  116  are positioned relative to the base member  28 . Furthermore, the heat conduction sheets  114  are preferably sandwiched between the heat transfer portions  74 ,  74 ,  102 , and  112  and the base member  28  in a compressed state in the up-and-down direction. By compressing the heat conduction sheets  114 , the heat transfer portions  74 ,  74 ,  102 , and  112  and the base member  28  can be brought into contact with a high degree of adhesion. Accordingly, the heat conduction sheets  114  can efficiently transfer heat from the heat transfer portions  74 ,  74 ,  102 , and  112  to the base member  28 . In a similar manner, the heat conduction sheets  116  are preferably sandwiched between the base member  28  and the heat dissipating body  118  in a compressed state in the up-and-down direction. By compressing the heat conduction sheets  116 , the base member  28  and the heat dissipating body  118  can be brought into contact with a high degree of adhesion. Accordingly, the heat conduction sheets  116  can efficiently transfer heat from the base member  28  to the heat dissipating body  118 . 
     Assembly Process of Circuit Assembly  10   
     Next, a detailed example of the assembly process of the circuit assembly  10  will be described. Note that the assembly process of the circuit assembly  10  is not limited to that described below. 
     First, the lid member  30 , the relay  12 , the fuse  24 , the current sensor  26 , the first to fourth energization bus bars  16   a ,  16   b ,  90 , and  92 , and the bolts  18  are prepared. Then, the relay  12  is placed against the upper bottom wall  44  of the lid member  30  inverted upside down and the bolts are inserted in the leg portions  56  and fastened in the not-illustrated bolt fixing portions provided in the lid member  30 . This fixes the lid member  30  and the relay  12  together. Then, the first and second energization bus bars  16   a  and  16   b  are placed above the relay  12 , and the first and second connection portions  14   a  and  14   b  of the relay  12  and the bolt insertion holes  82  and  82  of the first and second energization bus bars  16   a  and  16   b  are aligned in position. Then, the bolts  18  and  18  are inserted in the first and second connection portions  14   a  and  14   b  and the bolt insertion holes  82  and  82  to fasten them together. In this manner, the relay  12  and the first and second energization bus bars  16   a  and  16   b  are fixed together. 
     Next, the third energization bus bar  90  and the fourth energization bus bar  92  are placed against the upper bottom wall  44  of the lid member  30 , and the fuse  24  and the current sensor  26  are also placed from above. In this manner, the fuse connection portion  86  of the second energization bus bar  16   b  and the connection portion  62  on the left side of the fuse  24  are aligned and overlapped. Also, the connection portion  62  on the right side of the fuse  24  and the fuse connection portion  94  of the third energization bus bar  90  are aligned and overlapped. The sensor connection portion  96  of the third energization bus bar  90  and the connection portion  68  on the left side of the current sensor  26  are aligned and overlapped. Also, the connection portion  68  on the right side of the current sensor  26  and the sensor connection portion  104  of the fourth energization bus bar  92  are aligned and overlapped. Then, the bolts are inserted in the overlapped connection portions  62  and  68 , the fuse connection portions  86  and  94 , and the sensor connection portions  96  and  104  and fastened to not-illustrated bolt fixing portions provided on the lid member  30 . In this manner, in addition to the relay  12  and the first and second energization bus bars  16   a  and  16   b , the fuse  24 , the current sensor  26 , the third energization bus bar  90 , and the fourth energization bus bar  92  are fixed to the lid member  30 . 
     The base member  28  and the heat conduction sheets  114  and  116  are also prepared. Then, the heat conduction sheets  114  are housed in the first housing recess portions  36  of the base member  28  and fixed via adhesive or the like. The heat conduction sheets  116  are also housed in the second housing recess portions  40  and fixed via adhesive or the like. Then, the upper opening portion of the lid member  30  to which the relay  12 , the fuse  24 , the current sensor  26 , and the first to fourth energization bus bars  16   a ,  16   b ,  90 , and  92  are fixed is covered with the base member  28  to which the heat conduction sheets  114  and  116  are fixed, and the lid member  30  and the base member  28  are fixed together to form the case  22 . Then, by inverting it, the circuit assembly  10  is completed. 
     Note that the order of fixing the relay  12 , the fuse  24 , the current sensor  26 , and the first to fourth energization bus bars  16   a ,  16   b ,  90 , and  92  to the lid member  30  is not limited to that described in the process described above. Also, the heat conduction sheets  114  provided between the first to fourth energization bus bars  16   a ,  16   b ,  90 , and  92  (heat transfer portions  74 ,  74 ,  102 , and  112 ) and the base member  28  may be fixed to the lower surface of the heat transfer portions  74 ,  74 ,  102 , and  112  and not fixed to the base member  28 . In a similar manner, the heat conduction sheets  116  provided on the lower surface of the base member  28  may be fixed to the heat dissipating body  118  and not fixed to the base member  28 . 
     In the circuit assembly  10  assembled in this manner, the external connection portions  76  and  106  of the first energization bus bar  16   a  and the fourth energization bus bar  92  are exposed to the outside via the opening portions  48   a  and  48   b  of the lid member  30 . Then, in a state where terminal portions provided on terminals of not-illustrated external electrical wires and the bolt insertion holes  84  and  110  of the external connection portions  76  and  106  are aligned in position and not-illustrated bolts are inserted and fastened, the external electrical wire and the first energization bus bar  16   a  and the fourth energization bus bar  92  are electrically connected. Also, by overlapping the circuit assembly  10  and the heat dissipating body  118  and inserting and fastening not-illustrated bolts in the bolt insertion holes  50  provided in the outer peripheral portion of the case  22  (lid member  30 ), the circuit assembly  10  is fixed to the heat dissipating body  118 . In this manner, in the first embodiment, the heat conduction sheets  116  are compressed between the circuit assembly  10  and the heat dissipating body  118  in the up-and-down direction. 
     The circuit assembly  10  of the first embodiment is provided with the heat capacity increasing components  20  and  20  that are thermally in contact with the fastening sites A of the first and second connection portions  14   a  and  14   b  of the relay  12  at the first and second energization bus bars  16   a  and  16   b . Specifically, by folding back and overlapping the upper end portion of the bolt fastening portions  72  and  72  of the first and second energization bus bars  16   a  and  16   b , the heat capacity increasing component  20  is formed. Accordingly, at the fastening sites A of the first and second energization bus bars  16   a  and  16   b  and the first and second connection portions  14   a  and  14   b  of the relay  12 , the first and second energization bus bars  16   a  and  16   b  have double thickness. Thus, compared to a case in which the first and second energization bus bars have simply single thickness, the heat capacity of the first and second energization bus bars  16   a  and  16   b  can be increased. In this manner, an increase in the temperature of the first and second energization bus bars  16   a  and  16   b  and thus the first and second connection portions  14   a  and  14   b  that connect to the first and second energization bus bars  16   a  and  16   b  can be suppressed, and the problem of heat generation when a large current temporarily flows can be solved. 
     Also, in the first embodiment, the heat transfer portions  74 ,  74 ,  102 , and  112  of the first to fourth energization bus bars  16   a ,  16   b ,  90 , and  92  are each thermally in contact with the case  22  (base member  28 ). Thus, the heat generated at the relay  12 , the fuse  24 , and the current sensor  26  when energized can be dissipated via the case  22 . Accordingly, the problem of heat generated by the relay  12 , the fuse  24 , and the current sensor  26  can be solved. In particular, in the first embodiment, the heat conduction sheets  114  are provided between the heat transfer portions  74 ,  74 ,  102 , and  112  and the base member  28 . Thus, a stable transfer of heat from the heat transfer portions  74 ,  74 ,  102 , and  112  to the base member  28  can be achieved. Furthermore, the heat conduction sheets  116  are provided on the lower surface of the base member  28 . Thus, the base member  28  and the heat dissipating body  118  are thermally in contact with each other via the heat conduction sheets  116 . Accordingly, the heat generated at the relay  12 , the fuse  24 , and the current sensor  26  is dissipated also from the heat dissipating body  118 , allowing the heat dissipation effect to be improved. 
     Also, in the first embodiment, the heat capacity increasing components  20  and  20  are formed by the upper end portions of the bolt fastening portions  72  and  72  of the first and second energization bus bars  16   a  and  16   b , and the bolt insertion holes  82  and  82  are formed on the portions where the heat capacity increasing components  20  and  20  are provided. Accordingly, by fastening the bolts  18  and  18 , the heat capacity increasing components  20  and  20  are fixed together with the first and second energization bus bars  16   a  and  16   b . In other words, in the first embodiment, the first and second energization bus bars  16   a  and  16   b  and the heat capacity increasing components  20  and  20  are integrally formed. This allows an increase in the number of parts to be avoided. Also, compared to a case in which the heat capacity increasing component is a separate member from the first and second energization bus bars  16   a  and  16   b , the ease of assembly can be improved. 
     In particular, in the first embodiment, the upper end portions of the bolt fastening portions  72  and  72  are folded outward (forward) and overlapped. Accordingly, compared to a case in which the upper end portions of the bolt fastening portions are folded inward, the electrical path from the first and second connection portions  14   a  and  14   b  to the external connection portion  76  and the fuse connection portion  86  can be shortened. This allows an increase to the electrical conduction resistance when energized to be avoided. Also, the thermal path from the first and second connection portions  14   a  and  14   b  to the heat transfer portions  74  and  74  can be shortened. Accordingly, the heat generated at the first and second connection portions  14   a  and  14   b  is quickly dissipated via the heat transfer portions  74  and  74 . 
     Also, the first and second energization bus bars  16   a  and  16   b  are provided with the holding portions  80  and  80  that hold the heat capacity increasing components  20  and  20  (upper end portions of the bolt fastening portions  72  and  72 ) in an overlapped state. Thus, no gap is formed between heat capacity increasing components  20  and  20  and the bolt fastening portions  72  and  72 , i.e., between the upper end portions and the lower end portions of the bolt fastening portions  72  and  72  overlapping one another, and the heat capacity at the position where the heat capacity increasing components  20  and  20  are provided can be stably increased. 
     Note that the coefficient of linear thermal expansion of the heat capacity increasing component  20  (first and second energization bus bars  16   a  and  16   b ) is preferably set within a range of from ⅓ to 3 times the coefficient of linear thermal expansion of the bolts  18  and  18 . The coefficient of linear thermal expansion of the heat capacity increasing component  20  (first and second energization bus bars  16   a  and  16   b ) is more preferably set within a range of from ½ to 2 times the coefficient of linear thermal expansion of the bolts  18  and  18 . The coefficient of linear thermal expansion of the heat capacity increasing component  20  (first and second energization bus bars  16   a  and  16   b ) is even more preferably set within a range of from ⅔ to 3/2 times the coefficient of linear thermal expansion of the bolts  18  and  18 . The coefficient of linear thermal expansion of the heat capacity increasing component  20  (first and second energization bus bars  16   a  and  16   b ) is most preferably set to be equal to the coefficient of linear thermal expansion of the bolts  18  and  18 . By setting the coefficient of linear thermal expansion of the heat capacity increasing component  20  (first and second energization bus bars  16   a  and  16   b ) to from ⅓ to 3 times, i.e., relatively close to, the coefficient of linear thermal expansion of the bolts  18  and  18 , looseness of the bolts  18  and  18  when heat is generated at the relay  12  can be suppressed. Note that, for example, in a case in which the first and second energization bus bars  16   a  and  16   b  are made of copper and the bolts  18  and  18  are made of iron, the coefficient of linear thermal expansion of the heat capacity increasing components  20  and  20  is approximately 1.4 times the coefficient of linear thermal expansion of the bolts  18  and  18 . 
     In particular, because the coefficient of linear thermal expansion of the heat capacity increasing component  20  (first and second energization bus bars  16   a  and  16   b ) and the bolts  18  and  18  are equal, i.e., the heat capacity increasing component  20  (first and second energization bus bars  16   a  and  16   b ) and the bolts  18  and  18  are made of the same material, looseness of the bolts  18  and  18  when heat is generated at the relay  12  can be further suppressed. 
     Second Embodiment 
     The second embodiment of the present disclosure will be described below with reference to  FIGS.  6  and  7   . A circuit assembly  120  of the second embodiment has basically a similar configuration to the circuit assembly  10  of the first embodiment but is different in that heat capacity increasing components  122  and  122  are separate members from first and second energization bus bars  124   a  and  124   b , which are energization members. Hereinafter, the members and portions that are essentially the same as those in the embodiment described above are given the same reference sign as in the embodiment described above and a detailed description thereof will be omitted. Note that  FIGS.  6  and  7    are diagrams illustrating the circuit assembly  120  in a state with the lid member  30  that forms the case  22  removed. 
     The heat capacity increasing component  122  according to the second embodiment has a rectangular block shape. A through hole  126  is formed in a substantially central portion of the heat capacity increasing component  122  extending through in the front-and-back direction. The material of the heat capacity increasing component  122  is not limited and can be any material that is capable of increasing the heat capacity of the first and second energization bus bars  124   a  and  124   b  and thus the first and second connection portions  14   a  and  14   b  when assembled. A metal with a high thermal conductivity is preferably used. Iron, copper, aluminum, an alloy thereof, or the like is more preferably used as the material of the heat capacity increasing component  122 . In the second embodiment, the heat capacity increasing component  122  is made of metal. Note that the heat capacity increasing component  122  is preferably made of a metal with a lighter specific gravity than copper and iron. This is because a metal with a light specific gravity can reduce the effects of vibration in the bolt  18 . 
     The heat capacity increasing components  122  of the second embodiment are fixed to the relay  12  together with the first and second energization bus bars  124   a  and  124   b  via the bolts  18 . In other words, the first and second connection portions  14   a  and  14   b  of the relay  12 , the bolt insertion holes  82  of the first and second energization bus bars  124   a  and  124   b , and the through holes  126  of the heat capacity increasing components  122  are aligned in position with one another. Then, by inserting and fastening the bolts  18 , the heat capacity increasing components  122  and  122  are fixed to the relay  12  together with the first and second energization bus bars  124   a  and  124   b . Accordingly, the heat capacity increasing components  122  and  122  are thermally in contact with the fastening sites A of the first and second energization bus bars  124   a  and  124   b  and the first and second connection portions  14   a  and  14   b . In particular, in the second embodiment also, the heat capacity increasing component  122  is overlapped with the front surface  79 , which is the surface on the opposite side to the contact surface  78  with the first and second connection portions  14   a  and  14   b  at the bolt fastening portion  72  of the first and second energization bus bars  124   a  and  124   b . Note that in the first embodiment, the upper end portion of the bolt fastening portion  72  is folded back, and the fastening site of the bolt  18  at the first and second energization bus bars  16   a  and  16   b  have double thickness. However, the fastening site of the bolt  18  on the first and second energization bus bars  124   a  and  124   b  of the second embodiment have single thickness. 
     In the circuit assembly  120  of the second embodiment also, because the heat capacity increasing component  122  is provided, the heat capacity at the fastening site A of the first and second connection portions  14   a  and  14   b  of the relay  12  and the first and second energization bus bars  124   a  and  124   b  is increased. Thus, heat generation at the relay  12  can be suppressed. Thus, a similar effect to that of the first embodiment is achieved. 
     In particular, in the circuit assembly  120  of the second embodiment, the heat capacity increasing component  122  is a separate member from the first and second energization bus bars  124   a  and  124   b . Thus, for the material of the heat capacity increasing component  122 , a material that tends to increase the heat capacity more than the first and second energization bus bars  124   a  and  124   b  can be used. Alternatively, for the material of the heat capacity increasing component  122 , the same material (for example, iron) as the bolt  18  may be used, allowing looseness of the bolt  18  when heat is generated at the relay  12  to be reduced. The shape of the heat capacity increasing component  122  is not limited to a rectangular block shape, and a simple flat plate shape like a bus bar, a shape that tends to increase the heat capacity, or a shape capable of suppressing looseness of the bolt  18  when heat is generated may be used. 
     Also, in the second embodiment also, the heat capacity increasing component  122  is provided overlapping the front surface  79  of the bolt fastening portion  72  of the first and second energization bus bars  124   a  and  124   b . Thus, the electrical path from the first and second connection portions  14   a  and  14   b  to the external connection portion  76  and the fuse connection portion  86  and the thermal path to the heat transfer portions  74  and  74  can be shortened, an increase in the electrical conduction resistance can be prevented, and heat can be quickly transferred. 
     Third Embodiment 
     The third embodiment of the present disclosure will be described below with reference to  FIGS.  8  and  9   . A circuit assembly  130  of the third embodiment has basically a similar configuration to the circuit assembly  120  of the second embodiment but is different in that, instead of the heat capacity increasing component  122 , caps  132  and  132  made of metal are installed on the bolts  18  as heat capacity increasing components. Note that in the third embodiment, the first and second energization bus bars  124   a  and  124   b  with a similar structure to that of the second embodiment are used. Also,  FIGS.  8  and  9    are diagrams illustrating the circuit assembly  130  in a state with the lid member  30  that forms the case  22  removed. 
     That is, in the third embodiment, the heat capacity increasing component is formed by the cap  132  installed on the head portion of the bolt  18 . Thus, a housing recess portion  136  that houses the head portion of the bolt  18  is formed in the cap  132 . Accordingly, the cap  132  is thermally in contact with the fastening site A of the first and second energization bus bars  124   a  and  124   b  and the first and second connection portions  14   a  and  14   b  via the bolt  18 . In the third embodiment, the cap  132  is made of a metal with a high thermal conductivity. The cap  132  is preferably made of iron, copper, aluminum, an alloy thereof, or the like, for example. That is, the heat capacity increasing component is not limited to a configuration in which it is fixed to a heat generating member (relay  12 ) together with an energization member (first and second energization bus bar) via a fastening member (bolt  18 ). 
     The caps  132  are installed on the head portions of the bolts  18  after the first and second energization bus bars  124   a  and  124   b  are fixed to the first and second connection portions  14   a  and  14   b  of the relay  12  via the bolts  18 . Alternatively, the first and second energization bus bars  124   a  and  124   b  may be fixed to the first and second connection portions  14   a  and  14   b  of the relay  12  via the bolts  18  after the caps  132  are installed on the head portions of the bolts  18 . A portion of the cap  132  on the outer peripheral side of the housing recess portion  136  may be in contact with the front surface  79  of the bolt fastening portion  72  of the first and second energization bus bars  124   a  and  124   b  or may not be in contact. 
     Note that preferably, a heat conducting grease  138 , which is a heat conducting member, is provided between the inner surface of the housing recess portion  136  of the cap  132  and the head portion of the bolt  18 . In this manner, even in a case in which a manufacturing error or the like causes a gap to be formed between the cap  132  and the bolt  18 , heat can be stably transferred from the bolt  18  to the cap  132 . 
     In the circuit assembly  130  of the third embodiment, the caps  132  that increase the heat capacity of the first and second connection portions  14   a  and  14   b  are provided on the bolts  18  that fix together the relay  12  and the first and second energization bus bars  124   a  and  124   b . As a result, an increase in the temperature of the bolts  18  and thus the first and second connection portions  14   a  and  14   b  when heat is generated at the relay  12  can be suppressed by the caps  132 . 
     In particular, in the third embodiment, because the caps  132  are made of metal, the heat capacity can be easily increased. Also, because the caps  132  are separate members from the first and second energization bus bars  124   a  and  124   b  and the bolts  18 , for the material of the caps  132 , a material that tends to increase the heat capacity more than the first and second energization bus bars  124   a  and  124   b  and the bolts  18  can be used. Note that by making the cap  132  and the bolt  18  have a similar coefficient of linear thermal expansion or by the cap  132  and the bolt  18  being the same material, a gap can be made unlikely to form between the cap  132  and the bolt  18  when heat is generated at the relay  12 . Note that the cap  132  is preferably made of a metal with a lighter specific gravity than copper and iron. This is because a metal with a light specific gravity can reduce the effects of vibration in the bolt  18 . 
     Fourth Embodiment 
     The fourth embodiment of the present disclosure will be described below with reference to  FIG.  10   . A circuit assembly  140  of the fourth embodiment has basically a similar configuration to the circuit assembly  10  of the first embodiment but is different in that a cap  142  made of synthetic resin is installed on the bolt  18  as a heat capacity increasing component. In other words, the cap  142  is thermally in contact with the fastening site A of the first and second energization bus bars  16   a  and  16   b  and the first and second connection portions  14   a  and  14   b  via the bolt  18 . Note that  FIG.  10    is a diagram illustrating the circuit assembly  140  in a state with the lid member  30  that forms the case  22  removed. 
     In the circuit assembly  140  of the fourth embodiment, the cap  142  that increases the heat capacity of the first and second connection portions  14   a  and  14   b  is provided on the bolt  18  that fixes together the relay  12  and the first and second energization bus bars  16   a  and  16   b . Thus, an effect of suppressing an increase in the temperature from the cap  142  is added to that of the heat capacity increasing component  20  of the first embodiment. In particular, in the fourth embodiment, because synthetic resin which is relatively softer than metal is used for the cap  142 , the head portion of the bolt  18  and the cap  142  can be brought into close contact substantially without gaps, allowing for the contact area between the cap  142  and the head portion of the bolt  18  to be substantially ensured. In this manner, heat can be stably transferred from the bolt  18  to the cap  142 . Furthermore, because the cap  142  made of synthetic resin is used, electrical insulating properties at the head portion of the bolt  18  is ensured. 
     Other Embodiments 
     The technology described in the present specification is not limited to the embodiments described above with reference to the drawings, and, for example, the following embodiments are also included in the technical scope of the technology described in the present specification. 
     (1) In the embodiments, the heat capacity increasing components  20  and  122  and the caps  132  and  142  are provided at the fastening site A of the first and second connection portions  14   a  and  14   b  of the relay  12 , which is the heat generating component, and the first and second energization bus bars  16   a ,  124   a ,  16   b , and  124   b . However, no such limitation is intended. The heat capacity increasing component may be provided at a fastening site of the connection portion of the fuse or current sensor that generates heat when energized and the energization member (for example, the second to fourth energization bus bars in the embodiments). In other words, the heat generating component according to the present disclosure may be a fuse or a current sensor instead of or in addition to the relay. Note that the number of heat generating components provided is not necessarily a plurality and it is sufficient that one or more are provided. 
     (2) In the third embodiment, the cap  132  is used as the heat capacity increasing component instead of the heat capacity increasing component  20  of the first embodiment. However, the cap  132  may be used in addition to the heat capacity increasing components  20  and  122  of the first and second embodiments. 
     (3) The heat capacity increasing components  20  and  122  and the caps  132  and  142  of the embodiments, in a configuration other than that of the fourth embodiment, may be used in a combination of two or more. In other words, the heat capacity increasing component of the first and second embodiments combined may be used at the fastening site of the first and second connection portions of the relay and the first and second energization bus bars, for example. Alternatively, the heat capacity increasing component of the first and second embodiment may be used at the fastening site of the first and second connection portions of the relay and the first and second energization bus bars together with the heat capacity increasing component of the third and fourth embodiment at the fastening site of the connection portion of a fuse or current sensor and the energization member. 
     (4) In the embodiments, the heat capacity increasing components  20  and  122  and the caps  132  and  142  as heat capacity increasing components are provided at the fastening sites A of the first and second connection portions  14   a  and  14   b  of the relay  12  and the first and second energization bus bars  16   a ,  124   a ,  16   b , and  124   b . However, no such limitation is intended. It is sufficient that the heat capacity increasing component is provided at at least one fastening site of the connection portion and the energization member. Note that this also applies to a case in which the heat capacity increasing component is provided at the fastening site of the connection portion of a fuse or a current sensor and the energization member. 
     (5) A heat dissipation mechanism (for example, the heat transfer portions  74 ,  102 , and  112 , heat conduction sheets  114  and  116 , and the like) for dissipating heat from the component (for example, the relay  12 , the fuse  24 , and the current sensor  26  in the embodiments) that generates heat when energized is not necessary. Even in a case in which the heat dissipation mechanism is provided, the structure is not limited to that described in the embodiments, and a known heat dissipation mechanism may be used. For example, a through hole may be provided in the case (the bottom wall of the base member, for example), and the heat transfer portion may be thermally in contact with the heat dissipating body directly or via the heat conducting member (the heat conduction sheet, for example). 
     (6) In the embodiments, the relay  12 , the fuse  24 , the current sensor  26 , and the first to fourth energization bus bars  16   a ,  124   a ,  16   b ,  124   b ,  90 , and  92  are all fixed to the lid member  30 , but one or more may be fixed to the base member. 
     (7) In the embodiments, the bolt  18  is used as an example of the fastening member. However, the fastening member is not limited to the bolt, and a known fastening member such as a rivet capable of fastening together the energization member and the connection portion can be used. 
     (8) The heat capacity increasing component according to the present disclosure is not limited to the shape and material described in the embodiments, and the shape and material are not limited as long as that by providing the heat capacity increasing component, the heat capacity increases more than in the case of a single energization member. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               10  Circuit assembly (first embodiment) 
               12  Relay (heat generating component) 
               14  Connection portion 
               14   a  First connection portion 
               14   b  Second connection portion 
               16  Energization bus bar (energization member) 
               16   a  First energization bus bar 
               16   b  Second energization bus bar 
               18  Bolt (fastening member) 
               20  Heat capacity increasing component 
               22  Case 
               24  Fuse 
               26  Current sensor 
               28  Base member 
               30  Lid member 
               32  Bottom wall 
               34  Peripheral wall 
               36  First housing recess portion 
               38  Level difference 
               40  Second housing recess portion 
               42  Level difference 
               44  Upper bottom wall 
               46  Peripheral wall 
               48   a ,  48   b  Opening portion 
               50  Bolt insertion hole 
               52  Relay body 
               54  Insulating plate 
               56  Leg portion 
               60  Fuse body 
               62  Connection portion 
               66  Sensor body 
               68  Connection portion 
               72  Bolt fastening portion 
               74  Heat transfer portion 
               76  External connection portion 
               78  Contact surface 
               79  Front surface (surface on opposite side to contact surface) 
               80  Holding portion 
               82 ,  84  Bolt insertion hole 
               86  Fuse connection portion 
               88  Bolt insertion hole 
               90  Third energization bus bar 
               92  Fourth energization bus bar 
               94  Fuse connection portion 
               96  Sensor connection portion 
               102  Heat transfer portion 
               104  Sensor connection portion 
               106  External connection portion 
               110  Bolt insertion hole 
               112  Heat transfer portion 
               114  Heat conduction sheet (heat conducting member) 
               116  Heat conduction sheet 
               118  Heat dissipating body 
               120  Circuit assembly (second embodiment) 
               122  Heat capacity increasing component 
               124   a  First energization bus bar (energization member) 
               124   b  Second energization bus bar (energization member) 
               126  Through hole 
               130  Circuit assembly (third embodiment) 
               132  Cap (heat capacity increasing component) 
               136  Housing recess portion 
               138  Heat conducting grease (heat conducting member) 
               140  Circuit assembly (fourth embodiment) 
               142  Cap (heat capacity increasing component) 
             A Fastening site