Patent Publication Number: US-9425009-B2

Title: Electronic control device including interrupt wire

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 13/362,497 filed on Jan. 31, 2012, which is based on and claim priority to Japanese Patent Application No. 2011-22924 filed on Feb. 4, 2011, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an electronic control device including an interrupt wire for overcurrent protection. 
     BACKGROUND 
     Conventionally, an electronic control device includes a fuse in case of a fault in the electronic control device. In an electronic control device in which small components are densely arranged, because a short-circuit current generated at a short-circuit fault in the small components does not reach a high current, it takes a long time to interrupt by the fuse. Especially when a large fuse is used for protecting a plurality of electronic control devices so as to reduce the number of fuses and a cost, it takes a longer time. Thus, temperatures of the components may be increased at an interruption and a voltage drop in a power supply wire and the like may be caused for a long time. In contrast, in a common wire, such as a power supply wire (e.g., a battery path and a ground path), that supplies electric power required for operating many circuits and many components mounted in accordance with advancement and diversification of electronic control, a relatively high current flows. Thus, an interrupting current of a large fuse disposed in a common wire path is further increased, and the electronic control device does not secure a sufficient interrupt performance at a short-circuit fault in each circuit or each component. The above-described issue becomes noticeable, for example, in an electronic control device for a vehicle used at a higher temperature and including many mounted devices. 
     JP-A-2007-311467 discloses a printed circuit board control device in which an interrupt wire is disposed in a power supply wire in each substrate. If an overcurrent flows, the interrupt wire melts and the power sully wire is interrupted in each substrate or each device. 
     On a substrate in which components are densely mounted, a component-mounted wire, such as a land, on which an electronic component is mounted, and a common wire shared by a plurality of electronic components including the electronic component are disposed adjacent to each other. Thus, when an interrupt wire is disposed in a wire coupling the component-mounted wire and the common wire, neat generated by an overcurrent at the interrupt wire is transmitted to the component-mounted wire and the common wire. Thus, a temperature rise of the interrupt wire may vary and an interrupt performance of the interrupt wire may be decreased. As examples of the decrease in the interrupt performance, a melting time and an interrupting current of the interrupt wire may vary or may increase. 
     SUMMARY 
     In view of the foregoing problems, it is an object of the present invention to provide an electronic control device, which can restrict a decrease in an interrupt performance by an interrupt wire. 
     An electronic control device according to an aspect of the present invention includes a substrate, a plurality of component-mounted wires, a plurality of electronic components, a common wire, an interrupt wire, a connection wire and a solder. The component-mounted wires are disposed on the substrate. The electronic components are mounted on the respective component-mounted wires. The common wire is disposed on the substrate and is coupled with each of the electronic components. The interrupt wire is coupled between one of the component-mounted wires and the common wire. The interrupt wire is configured to melt in accordance with heat generated by an overcurrent so as to interrupt a coupling between the one of the component-mounted wires and the common wire via the interrupt wire. The interrupt wire is coupled with a connection object, which is one of the common wire and the one of the component-mounted wires, via the connection wire. The solder is disposed between each of the electronic components and a corresponding one of the component-mounted wires. The solder has a lower melting point than the interrupt wire. The connection wire has a first end portion adjacent to the interrupt wire and a second end portion adjacent to the connection object. A cross-sectional area of the first end portion of the interrupt wire is smaller than a cross-sectional area of the second end portion of the interrupt wire. 
     In the above electronic control device, when heat generated at the interrupt wire is transmitted to the connection object via the connection wire, the heat is gradually diffused in the connection wire and is not absorbed excessively to the connection object. Therefore, even when the connection object is mounted on one of the component-mounted wire with the solder having a lower melting point than the interrupt wire, the solder is less likely to be melted by the heat from the interrupt wire. Accordingly, a temperature rise in the interrupt wire can be restricted and a decrease in an interrupt performance of the interrupt wire can be restricted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional objects and advantages of the present invention will be more readily apparent from the following detailed description when taken together with the accompanying drawings. In the drawings: 
         FIG. 1  is a block diagram showing a vehicle control system including a traction control device according to a first embodiment of the present disclosure; 
         FIG. 2  is a diagram showing a part of the traction control device according to the first embodiment; 
         FIG. 3  is a cross-sectional view of the traction control device taken along line III-III in  FIG. 2 ; 
         FIG. 4  is an enlarged view of a portion around an interrupt wire of the traction control device shown in  FIG. 2 ; 
         FIG. 5A  and  FIG. 5B  are diagrams showing two examples of a part of a traction control device according to a first modification of the first embodiment; 
         FIG. 6  is a diagram showing a part of a traction control device according to a second modification of the first embodiment; 
         FIG. 7  is a diagram showing a part of a traction control device according to a third modification of the first embodiment; 
         FIG. 8  is a diagram showing a part of a traction control device according to a second embodiment of the present disclosure; 
         FIG. 9  is an enlarged view of a portion around an interrupt wire of the traction control device shown in  FIG. 8 ; 
         FIG. 10A  and  FIG. 10B  are diagrams showing two examples of a part of a traction control device according to a modification of the second embodiment; 
         FIG. 11  is a diagram showing a part of a traction control device according to a third embodiment of the present disclosure; 
         FIG. 12  is a diagram showing a part of a traction control device according to a fourth embodiment of the present disclosure; 
         FIG. 13  is an enlarged view of a portion around an interrupt wire of the traction control device shown in  FIG. 12 ; 
         FIG. 14  is a diagram showing a device including a test interrupt wire and a test opening portion; 
         FIG. 15  is a graph showing a relationship between an interrupting current and a melting time of the test interrupt wire in each case where the test opening portion is defined and where the test opening portion is not defined; 
         FIG. 16  is a diagram showing a part of a traction control device according to a modification of the fourth embodiment; and 
         FIG. 17  is a diagram showing a configuration of a traction control device according to a fifth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     An electronic control device according to a first embodiment of the resent disclosure will be described with reference to drawings. The electronic control device according to the present embodiment can be suitably used as a traction control device  20  included in a vehicle control system  11 . As shown in  FIG. 1 , the vehicle control system  11  includes a plurality of electronic control devices  12  that include the traction control device  20 , an engine electronic control unit (ECU), a brake ECU, a steering ECU, a body ECU, a navigation device, and the like. 
     The traction control device  20  restricts an acceleration slip of a driving wheel. In a vehicle control such as a running control, the traction control device  20  is less important than other electronic control devices. 
     The electronic control devices  12  including the traction control device  20  are electrically coupled with a battery  13  via one of fuses  14   a ,  14   b  used for overcurrent protection. The battery  13  is a direct-current power source. Because each of the fuses  14   a ,  14   b  is disposed on a power supply path for supplying electric power to many electronic control devices, each of the fuses  14   a ,  14   b  may be a large fuse for 15 A or 20 A. When one of the electronic control devices  12  coupled with the fuse  14   a  has abnormality and an overcurrent greater than a predetermined current value is generated, the fuse  14   a  blows out by the overcurrent, and a power supply via the fuse  14   a  is interrupted. Thus, an adverse influence to the other electronic control devices  12  can be restricted. In an example shown in  FIG. 1 , each of the electronic control devices  12  is electrically coupled with the battery  13  via one of the fuses  14   a ,  14   b . However, all the electronic control devices  12  may also be electrically coupled with the battery  13  via a single fuse, or each of the electronic control devices  12  may also be electrically coupled with the battery  13  via one of more than two fuses. 
     The traction control device  20  according to the present embodiment will be described with reference to  FIG. 2  to  FIG. 4 . 
     The traction control device  20  includes the circuit substrate  21  housed in a casing (not shown). On the circuit substrate  21 , a plurality of electronic components  22  for restricting an acceleration slip is densely-mounted on the circuit substrate  21 . The circuit substrate  21  is electrically coupled with an external device and other electronic control devices  12  via, for example, a connector, and restricts an acceleration slip of the driving wheel based on a predetermined signal. 
     Each of the electronic components  22  on the circuit substrate  21  is electrically coupled with a power supply wire  23 . The power supply wire  23  is coupled with the battery  13  by the power supply path via the fuse  14   a  and supplies electric power from the battery  13  to each of the electronic components  22 . Thus, the power supply wire  23  is an example of a common wire shared by the electronic components  22 . 
     As shown in  FIG. 2  and  FIG. 3 , one of the electronic components  22  on the circuit substrate  21  is a ceramic capacitor  24 . The ceramic capacitor  24  may be formed by stacking a high-permittivity ceramic made of barium titanate and an internal electrode in layers for improving temperature characteristics and frequency characteristics, and thereby having a large capacity with a small size. 
     The ceramic capacitor  24  has outside electrodes  24   a  on either ends thereof. The outside electrodes  24   a  are mounted on respective lands  26  via solders  25 . Between one of the lands  26  and the power supply wire  23 , an interrupt wire  30  is coupled. The interrupt wire  30  melts by heat generated by an overcurrent and interrupts the electric coupling between the land  26  and the power supply wire  23  via the interrupt wire  30 . Thus, the interrupt wire  30  can achieve an overcurrent protection depending on the circuit substrate  21 . 
     The interrupt wire  30  has a wire width sufficiently smaller than a wire width of the power supply wire  23 . The wire width means a dimension in a direction that is perpendicular to a direction of electric current on a surface of the circuit substrate  21 . For example, the interrupt wire  30  has a wire width within a range from 0.2 mm to 0.3 mm, and the power supply wire  23  has a wire width of 2 mm. The lands  26  can work as component-mounted wires. 
     One end of the interrupt wire  30  is coupled with the power supply wire  23  via a connection wire  40 , and the other end of the interrupt wire  30  is coupled with the land  26  via a connection wire  50 . The connection wires  40  and  50  are made of conductive material, such as copper, in a manner similar to the interrupt wire  30  and the power supply wire  23 . The connection wires  40  and  50  have a greater conductor volume than the interrupt wire  30 . The connection wire  40  coupled with the power supply wire  23  can work as a first connection wire, and the connection wire  50  coupled with the land  26  can work as a second connection wire. 
     As shown in  FIG. 4 , a wire width of the connection wire  40  increases toward the power supply wire  23  in a stepwise manner so that a cross-sectional area S 1   a  at an end of the connection wire  40  adjacent to the interrupt wire  30  is smaller than a cross-sectional area S 1   b  at the other end of the connection wire  40  adjacent to the power supply wire  23 . Similarly, a wire width of the connection wire  50  increases toward the land  26  in a stepwise manner so that a cross-sectional area S 2   a  at an end of the connection wire  50  adjacent to the interrupt wire  30  is smaller than a cross-sectional area S 2   b  at the other end of the connection wire  50  adjacent to the land  26 . 
     As shown in  FIG. 3 , the interrupt wire  30  has a wire thickness thinner than wire thicknesses of the connection wires  40  and  50 . In  FIG. 3 , thicknesses of wires, such as an interrupt wire  30 , are shown in a magnified way. The wire thickness means a dimension in a direction that is perpendicular to the circuit substrate  21 . On an inside of the interrupt wire  30 , a heat transmission restriction member  27  is disposed. The heat transmission restriction member  27  is made of, for example, resist material, so that the heat restriction member  27  restricts transmission of heat toward an inside of the circuit substrate  21 . The interrupt wire  30  is easily shaped to have the thinner thickness than the connection wires  40  and  50  by disposing the heat transmission restriction member  27  on the inside of the interrupt wire  30  during shape formation of the interrupt wire  30 . Further, the cross-sectional areas S 1   a  and S 2   a  become smaller by disposing the heat transmission restriction member  27 . 
     In the traction control device  20  having the above-described configuration, for example, when a short-circuit fault occurs in the ceramic capacitor  24  and an overcurrent flows in the interrupt wire  30 , the interrupt wire  30  generates heat in accordance with the overcurrent. When the generated heat becomes greater than a predetermined temperature, the interrupt wire  30  melts, and the electric coupling via the interrupt wire  30  is interrupted. Accordingly, the other electronic components  22  coupled with the power supply wire  23  can be protected against the overcurrent. The current at interruption is not high enough to blow the fuse  14   a . Thus, the damage of the traction control device  20  does not influence to the other electronic control devices  12  supplied with power via the fuse  14   a . A time from generation of the overcurrent to the melting of the interrupt wire  30  is a few milliseconds, and a melting time of each of the fuses  14   a ,  14   b  is generally about 0.02 seconds. Thus, the overcurrent protection can be appropriately achieved even to an electronic control device or an electronic component that is required to improve a processing speed. 
     In particular, heat generated at the interrupt wire  30  by an overcurrent is transmitted to the power supply wire  23  via the connection wire  40 . When the interrupt wire  30  having a small wire width is directly coupled with the power supply wire  23  having a large wire width, the heat is easily transmitted to the power supply wire  23 . Thus, the temperature of the interrupt wire  30  decreases and the temperature decrease has a variation. Similarly, when the interrupt wire  30  is directly coupled with the land  26 , the temperature of the interrupt wire  30  decreases and the temperature decrease has a variation. Further, since the heat transmitted from the interrupt wire  30  is concentrated at a connecting portion between the interrupt wire  30  and the land  26 , the solder  25  adjacent to the interrupt wire  30  melts and a melt conductor generated by the melting of the interrupt wire  30  may scatter around the connecting portion between the interrupt wire  30  and the land  26 . 
     In the traction control device  20  according the present embodiment, the heat generated at the interrupt wire  30  is transmitted to the power supply wire  23  via the connection wire  40 , which has the smaller cross-sectional area S 1   a  adjacent to the interrupt wire  30  compared with the cross-sectional area S 1   b  adjacent to the power supply wire  23 . Additionally, the heat generated at the interrupt wire  30  is transmitted to the land  26  via the connection wire  50 , which has the smaller cross-sectional area S 2   a  adjacent to the interrupt wire  30  compared with the cross-sectional area S 2   b  adjacent to the land  26 . 
     Thus, when heat generated at the interrupt wire  30  by an overcurrent is transmitted to the power supply wire  23  via the connection wire  40  and is transmitted to the land  26  via the connection wire  50 , because heat required for melting the interrupt wire  30  is held by the connection wires  40  and  50 , the heat is not absorbed excessively to the power supply wire  23  and the land  26  compared with a case where heat is transmitted directly to the power supply wire  23  and the land  26 . Accordingly, a variation in a temperature rise of the interrupt wire  30  can be restricted, and a variation in the melting time can be restricted even when the melting time is short as described above. Thus, a decrease in an interrupt performance of the interrupt wire  30  can be restricted. In particular, the heat generated at the interrupt wire  30  by the overcurrent is gradually diffused in the connection wire  50  and is widely transmitted to the land  26 . Thus, a local temperature rise in the land  26  can be restricted. Therefore, even when the ceramic capacitor  24  is mounted on the land  26  with the solder  25  having a lower melting point than a melting point of the interrupt wire  30 , the solder  25  is less likely to be melted by the heat from the interrupt wire  30 . In contrast, during a steady state of the traction control device  20 , the interrupt wire  30  generates heat due to the current flowing through the interrupt wire  30 . In the steady state, an overcurrent is not generated. Because the heat generated at the interrupt wire  30  can be diffused via the connection wires  40  and  50  during the steady state, a temperature rise in the interrupt wire  30  can be restricted and a long-term reliability of the traction control device  20  can be increased. 
     Because the heat transmission restriction member  27  having the wire thickness thinner than wire thicknesses of the connection wires  40  and  50  is disposed on the inside of the interrupt wire  30 , the cross-sectional areas S 1   a  and S 2   a  of the interrupt wire  30  are easily decreased compared with a case where the heat transmission restriction member  27  is not disposed. Specifically, transmission of the heat generated by the interrupt wire  30  can be restricted by the heat transmission restriction member  27 . Thus, the variation in the temperature rise of the interrupt wire  30  can be restricted. Additionally, because the wire thickness of the interrupt wire  30  becomes smaller, the melt conductor generated by the melting of the interrupt wire  30  has a smaller volume and adverse effect caused by a flow of the melt conductor to other electronic components  22  can be restricted. 
     Additionally, because the connection wires  40  and  50  have the greater conductor volumes than the interrupt wire  30 , the connection wires  40  and  50  can store heat from the interrupt wire  30 . 
     The power supply wire  23  is coupled with the battery  13 , which supplies power not only to the traction control device  20  but also to other electronic control devices  12 , by the power supply path, and the fuse  14   a  for protecting the traction control device  20  and other electronic control devices  12  is disposed on the power supply path. Even when a short-circuit fault occurs in the traction control device  20  including the interrupt wire  30 , the interrupt wire  30  melts. Thus, influence of the short-circuit fault on the power supply to other electronic control devices  12  can be restricted. 
     A traction control device  20  according to a first modification of the first embodiment will be described with reference to  FIG. 5A  and  FIG. 5B . As shown in  FIG. 5A , in the traction control device  20 , connection wires  40  and  50  may be partially arc-shaped. Specifically, the connection wire  40  is partially arc-shaped (R-shape) so that an area of a cross section, which is perpendicular to a direction from the interrupt wire  30  to the power supply wire  23 , gradually increases toward the power supply wire  23 . Similarly, the connection wire  50  is partially arc-shaped (R-shape) so that an area of a cross section, which is perpendicular to a direction from the interrupt wire  30  to the land  26 , gradually increases toward the land  26 . 
     The connection wires  40  and  50  having above-described shape can restrict a temperature decrease in the interrupt wire  30 . Additionally, because a heat transmission path, which is extended in an arc manner, is secured by the connection wires  40  and  50 , a local temperature rise in the interrupt wire  30  can be restricted. 
     As shown in  FIG. 5A , side ends of the connection wire  40  are smoothly connected with respective side ends of the interrupt wire  30  and the wire width of the connection wire  40  gradually increases toward the power supply wire  23 . Similarly, side ends of the connection wire  50  are smoothly connected with respective side ends of the interrupt wire  30  and the wire width of the connection wire  50  gradually increases toward the land  26 . Thus, when the interrupt wire  30  and the connection wires  40  and  50  are formed using etching liquid, the etching liquid can uniformly flow at connecting portions of the interrupt wire  30  and the connection wires  40  and  50 . Accordingly, the etching liquid is less likely to stay at the connecting portions and a variation in the wire width of the interrupt wire  30  can be restricted. Thus, a decrease in the interrupt performance by the interrupt wire  30  can be restricted. 
     As shown in  FIG. 5B , in the traction control device  20  according to the first modification of the first embodiment, the connection wires  40  and  50  may also be partially taper-shaped. Specifically, the connection wire  40  is partially taper-shaped so that the area of the cross section gradually increases toward the power supply wire  23 . Similarly, the connection wire  50  is partially taper-shaped so that the area of the cross section gradually increases toward the land  26 . The connection wires  40  and  50  having a tapered-shape provide similar effects with the connection wires  40  and  60  having an arc-shape. 
     A traction control device  20  according to a second modification of the first embodiment will be described with reference to  FIG. 6 . In the traction control device  20 , a plurality of interrupt wires  30  may be disposed respectively to a plurality of electronic components  22 . In each of the interrupt wires  30 , at least a connection wire  40  or  50  is disposed between an end of the interrupt wire  30  and the power supply wire  23  or a component-mounted wire, such as the land  26 . As shown in  FIG. 6 , an interrupt wire  30  is electrically coupled with a land  26   a  of an electronic component  24   d  via a connection wire  40  and is coupled with the power supply wire  23  via a connection wire  50 . Another interrupt wire  30  is electrically coupled with the power supply wire  23  via a connection wire  40 . 
     A traction control device  20  according to a third modification of the first embodiment will be described with reference to  FIG. 7 . In the traction control device  20 , at least one interrupt wire  30  may be coupled between an array-type ceramic capacitor  24   f  having a plurality of outside electrodes and the power supply wire  23 . The ceramic capacitor  24   f  is formed by arraying four multilayer capacitors in a package. As shown in  FIG. 7 , the ceramic capacitor  24   f  has four outside electrodes which are respectively mounted on lands  26   c  to  26   f . Four interrupt wires  30  are disposed between respective lands  26   c  to  26   f  and the power supply wire  23 . Each of the interrupt wires  30  is coupled with the power supply wire  23  via the connection wire  40 , and is coupled with a corresponding land of the lands  26   c  to  26   f  via the connection wire  50 . 
     As described above, in a case where a plurality of interrupt wires  30  is disposed on the circuit substrate  21 , the variation in the temperature rise in each of the interrupt wires  30  can be restricted by disposing the connection wires  40  and  50  in each interrupt wire  30 . Thus, the decrease in the interrupt performance by the interrupt wires  30  can be restricted. 
     A traction control device  20  according to a fourth modification first embodiment will be described. In the traction control device  20 , the interrupt wire  30  may be made of material, such as aluminum, having a lower thermal conductivity than the connection wires  40  and  50 . Accordingly, heat generated at the interrupt wire  30  by an overcurrent is less likely to be transmitted to the connection wires  40  and  50 , and thereby the variation in the temperature rise of the interrupt wire  30  can be restricted. Further, the decrease in the interrupt performance by the interrupt wire  30  can be restricted. 
     Second Embodiment 
     A traction control device  20   a  according to a second embodiment of the present disclosure will be described with reference to  FIG. 8  and  FIG. 9 . 
     The traction control device  20   a  according to the present embodiment includes connection wires  40   a  and  50   a  instead of the connection wires  40  and  50  described in the forgoing embodiment. 
     As shown in  FIG. 8  and  FIG. 9 , the connection wire  40   a  includes a heat storage portion  41  adjacent to the interrupt wire and a narrow-down portion  42  adjacent to the power supply wire  23 . The narrow-down portion  42  is designed so that a total cross-sectional area S 3   a  of a connecting portion of the connection wire  40   a  with the power supply wire  23  is smaller than a cross-sectional area of a middle portion of the connection wire  40   a , that is, a cross-sectional area S 3   b  of the heat storage portion  41 . 
     Similarly, the connection wire  50   a  includes a heat storage portion  51  adjacent to the interrupt wire  30  and a narrow-down portion  52  adjacent to the land  26 . The narrow-down portion  52  is designed so that a total cross-sectional area S 4   a  of a connecting portion of the connection wire  50   a  with the land  26  is smaller than a cross-sectional area of a middle portion of the connection wire  50   a , that is, a cross-sectional area S 4   b  of the heat storage portion  51 . 
     Thus, heat transmitted to the connection wire  40   a  from the interrupt wire  30  is less likely to be transmitted to the power supply wire  23  via the narrow-down portion  42 , and the heat storage portion  41  stores heat. Because the heat storage portion  41  stores heat from the interrupt wire  30 , when the interrupt wire  30  melts, a temperature of the heat storage portion  41  is relatively high. Thus, the variation in the temperature rise of the interrupt wire  30  can be restricted, and a decrease in the interrupt performance by the interrupt wire  30  can be restricted with certainty. Additionally, by disposing the connection wire  50   a  in a similar manner with the connection wire  40   a , the variation in the temperature rise of the interrupt wire  30  can be restricted, and a decrease in the interrupt performance by the interrupt wire  30  can be restricted with certainty. 
     By setting the interrupt wire  30  and the connection wires  40   a  and  50   a  to have a predetermined depth and to be made of a predetermined material, an interrupt condition is fixed so as to restrict the variation, and a set of the interrupt wire  30  and the connection wires  40   a  and  50   a  can be widely used. In addition, because heat storage amounts of the connection wires  40   a  and  50   a  can be respectively controlled with volumes of the heat storage portions  41  and  51 , the melting time of the interrupt wire  30  can be easily controlled. 
     Because the connecting portion of the connection wire  40   a  with the power supply wire  23  is formed as the two narrow-down portions  42 , when the heat from the interrupt wire  30  is transmitted to the power supply wire  23  via the two narrow-down portions  42 , the heat is transmitted to the power supply wire  23  while being diffused in the narrow-down portions  42 . Thus, a local temperature rise in the power supply wire  23  can be restricted. Additionally, by disposing the connection wire  50   a  in a similar manner with the connection wire  40   a , a local temperature rise in the land  26  can be restricted. 
     The number of the narrow-down portions  42  of the connection wire  40   a  may also be one or more than two depending on the interrupt condition. Similarly, the number of the narrow-down portions  52  of the connection wire  50   a  may also be one or more than two depending on the interrupt condition. 
     A traction control device  20   a  according to a modification of the second embodiment will be described with reference to  FIG. 10A  and  FIG. 10B . As shown in  FIG. 10A , the heat storage portion  41  of the connection wire  40   a  and the heat storage portion  51  of the connection wire  50   a  may be partially arc-shaped. Specifically, the heat storage portion  41  of the connection wire  40   a  is partially arc-shaped (R-shape) so that an area of a cross section, which is perpendicular to the direction from the interrupt wire  30  to the power supply wire  23 , gradually increases toward the power supply wire  23 . Similarly, the heat storage portion  51  of the connection wire  50   a  is partially arc-shaped (R-shape) so that an area of a cross section, which is perpendicular to the direction from the interrupt wire  30  to the land  26 , gradually increases toward the land  26 . 
     As shown in  FIG. 10B , the heat storage portion  41  of the connection wire  40   a  and the heat storage portion  51  of the connection wire  50   a  may also be partially taper-shaped. Specifically, the heat storage portion  41  of the connection wire  40   a  is partially taper-shaped so that the area of the cross section gradually increases toward the power supply wire  23 . Similarly, the heat storage portion  51  of the connection wire  50   a  is partially taper-shaped so that the area of the cross section gradually increases toward the land  26 . 
     Connection wires  40   a  and  50   a  having above-described shape can restrict a temperature decrease in the interrupt wire  30 . Additionally, because a heat transmission path, which is extended in an arc manner, is secured by the connection wires  40  and  50 , a local temperature rise in the interrupt wire  30  can be restricted. In particular, because the heat transmitted from the interrupt wire  30  can be transmitted uniformly in the heat storage portions  41  and  51 , the heat can be uniformly stored in the heat storage portions  41  and  51 . 
     The above-described configurations of the connection wires  40   a  and  50   a  may be applied to other embodiments and modifications. 
     Third Embodiment 
     A traction control device  20   b  according to a third embodiment of the present disclosure will be described with reference to  FIG. 11 . 
     The traction control device  20   b  according to the present embodiment includes an interrupt wire  30   a  instead of the interrupt wire  30  described in the forgoing embodiments. In order to achieve a densely mounting, the power supply wire  23  is disposed between the lands  26  on which the outside electrodes  24   a  of the ceramic capacitor  24  are mounted. 
     As shown in  FIG. 11 , the interrupt wire  30   a  includes a first wire section  31  and a second wire section  32  that is shorter than the first wire section  31 . The first wire section  31  and the second wire section  32  are coupled to each other at a predetermined angle. The predetermined angle is determined so that the first wire section  31  is coupled with the power supply wire  23  and the second wire section  32  is coupled with the land  26 . For example, the predetermined angle is 90 degrees. 
     By bending the interrupt wire  30   a  at the predetermined angle, a wire length of the interrupt wire  30   a  can be increased compared with a case where the interrupt wire  30   a  has a straight shape while coupling the power supply wire  23  and the land  26 . Accordingly, a required wire length of the interrupt wire  30   a  can be secured in a limited mounting area. Thus, the decrease in the interrupt performance by the interrupt wire  30   a  can be restricted and a size of the traction control device  20   b  can be decreased. 
     In the traction control device  20   b  according to the present embodiment, the first wire section  31  is coupled with the power supply wire  23 , and the second wire section  32  is coupled with the land  26 . Alternatively, the first wire section  31  may be coupled with the land  26 , and the second wire section  32  may be coupled with the power supply wire  23 . Further, a position of the predetermined angle at which the first wire section  31  and the second wire section  32  are coupled to each other may be set according to positions of the power supply wire  23  and the land  26 . In  FIG. 11 , the interrupt wire  30   a  is coupled with the power supply wire  23  via the connection wire  40 . The interrupt wire  30   a  may be coupled with the land  26  via the connection wire  50 . The first wire section  31  may have a arrow portion at a middle portion of an entire length of the interrupt wire  30   a  including the first wire section  31  and the second wire section  32 . The narrow portion has a wire width narrower than the other portion of the first wire section  31 . Accordingly, when the interrupt wire  30   a  melts, the interrupt wire  30   a  is likely to melt at the narrow portion. Thus, a variation in a melted portion can be restricted. In order to restrict a heat concentration at a connecting portion of the first wire section  31  and the second wire section  32 , the connecting portion may be formed in such a manner that the connecting portion has similar wire widths with the first wire section  31  and the second wire section  32  at adjacent two side ends. The above-described configuration of the interrupt wire  30   a  may be applied to other embodiments and modifications. 
     Fourth Embodiment 
     A traction control device  20   c  according to a fourth embodiment of the present disclosure will be described with reference to  FIG. 12  and  FIG. 13 . 
     In the traction control device  20   c  according to the present embodiment, a solder resist layer  28 , which functions as a protective layer to protect the surface of the circuit substrate  21 , defines an opening portion  28   a  so that at least a portion of the interrupt wire  30  is exposed outside. In  FIG. 12 , the solder resist layer  28  is not shown for convenience of drawing. 
     As shown in  FIG. 12  and  FIG. 13 , the solder resist layer  28  defines the opening portion  28   a  so that the middle portion of the entire length of the interrupt wire  30 , which is most likely to generate heat, is exposed outside. Reasons of providing the opening portion  28   a  will be described with reference to  FIG. 14  and  FIG. 15 . 
     In a device shown in  FIG. 14 , a part of a test interrupt wire  101  is exposed outside through a test opening portion  102  defined by a solder resist layer. The test interrupt wire  101  is supplied with a predetermined current, and an interrupting current I with which the test interrupt wire  101  melts and a melting time t when the test interrupt wire  101  melts are measured. Furthermore, an interrupting current I and a melting time t of a test interrupt wire  101  in a case where a solder resist layer does not define a test opening portion  102  are also measured. The test interrupt wire  101  has an entire length L 1  of 2.55 mm and has a width W 1  of 0.25 mm. The test opening portion  102  has an opening length L 2  of 0.6 mm in a direction parallel to a length direction of the test interrupt wire  101  and has an opening width W 2  of 0.25 mm in a width direction of the test interrupt wire  101 . In  FIG. 14 , the opening width W 2  is drawn as being longer than the with W 1  for convenience of drawing. 
     In  FIG. 14 , a bold solid line S 1  shows a relationship between the interrupting current I and the melting time t of the test interrupt wire  101 , a part of which is exposed through the test opening portion  102 , and a range between bold dashed lines centered on the bold solid line S 1  shows a variation range of the melting time t with respect to the interrupting current I. A thin solid line  82  shows a relationship between the interrupting current I and the melting time t of the test interrupt wire  101  in a case where a test opening portion  102  is not defined, and a range between thin dashed lines centered on the thin solid line  82  shows a variation range of the melting time t with respect to the interrupting current I. 
     As shown in  FIG. 14 , at the same interrupting current, the melting time t decreases and the variation range decreases when the test opening portion  102  is defined by the solder resist layer. In contrast, in the case where the test opening portion  102  is not defined by the solder resist layer, the melting time t of the test interrupt wire  101  increases in each overcurrent range and the variation range increases compared with the case where the test opening portion  102  is defined. This is because a melt conductor generated by melting of the test interrupt wire  101  flows from the test opening portion  102  and the melt conductor is less likely to stay at a position of the test interrupt wire  101  before melting. 
     Thus, when at least a part of the interrupt wire  30  is exposed through the opening portion  28   a , the melting time t decreases, the overcurrent protection action can be achieved early, and a temperature rise in a protected component can be restricted. Furthermore, a time for which a voltage of the power supply wire  23  decreases due to interruption by the interrupt wire  30  can be reduced. In addition, because the variation of the melting time t decreases, a capacity of a stabilizing capacitor that is designed in view of the melting time of the interrupt wire  30  in each device or each circuit can be reduced, and a cost and a size can be reduced. Furthermore, because the melting time t decreases also in a rated region of current, a circuit can be designed more freely. 
     Thus, when the interrupt wire  30  melts in accordance with heat generated by the overcurrent, a melt conductor generated by melting of the interrupt wire  30  flows from the opening portion  28   a . Accordingly, the melt conductor is less likely to stay at a position of the interrupt wire  30  before melting, variations in the melt position and the melting time due to stay of the melt conductor can be restricted, and a decrease in an interrupt performance by the interrupt wire  30  can be restricted. 
     In the traction control device  20   c  according to the present embodiment, the opening portion  26   a  is defined so that the middle portion of the interrupt wire  30  which is most likely to melt is exposed outside. Alternatively, the opening portion  28   a  may be defined so that another portion of the interrupt wire  30  or the whole interrupt wire  30  is exposed outside. The above-described configuration of the opening portion  28   a , through which at least a portion of the interrupt wire  30  is exposed, may be applied to other embodiments and modifications. 
     A traction control device  20   c  according to a modification of the fourth embodiment will be described with reference to  FIG. 16 . As shown in  FIG. 16 , a pair of adherent wires  60  may be disposed adjacent to the interrupt wire  30 . The adherent wire  60  can work as an adherent member or an adsorption member to which the melt conductor generated by melting of the interrupt wire  30  adheres. The adherent wire  60  may be made of the same material as the power supply wire  23 . When the melt conductor of the high temperature is generated by melting of the interrupt wire  30 , the melt conductor flow on the surface of the circuit substrate  21  and adheres to the adherent wires  60  adjacent to the interrupt wire  30 . 
     Accordingly, the melt conductor is held by the adherent wires  60  and loses flowability by releasing heat and being hardened. Thus, a decrease in the interrupt performance by the interrupt wire  30  can be restricted, and influence of the flow of the melt conductor on other electronic components can be restricted. The adherent wires  60  may be disposed with respect to the interrupt wire  30 , a part of which is exposed outside through the opening portion  28   a , the adherent wires  60  may also be disposed with respect to the interrupt wire  30  whose surface is entirely covered with the solder resist layer  28 , and the adherent wires  60  may also be disposed with respect to the interrupt wire  30  not covered with the solder resist layer  28 . 
     Fifth Embodiment 
     An electronic control device  110  according to a fifth embodiment of the present disclosure will be described with reference to  FIG. 17 . The electronic control device  110  includes a substrate  120  and circuit blocks  130 ,  140 ,  150  disposed on the substrate  120 . The circuit block  130  performs a similar function to the traction control device  20  according to the first embodiment. The circuit blocks  140 ,  150  perform different functions from the circuit block  130 . The different functions are more important than the function of the circuit block  130 . For example, the circuit block  140  performs a function corresponding to the engine ECU, and the circuit block  150  performs a function corresponding to the brake ECU. 
     The circuit blocks  130 ,  140 ,  150  are electrically coupled with the power supply wire  23 , which supplies electric power from the battery  13 , via branch wires  131 ,  141 ,  151 , respectively. The above-described interrupt wire  30  is disposed on the branch wire  131  coupled with the circuit block  130  so as to function as overcurrent protection for the circuit block  130 . On the power supply wire  23 , an interrupt wire  122  that functions as overcurrent protection for the substrate  120  is disposed. In other words, the interrupt wire  122 , which protects the substrate  120  including all the circuit blocks  130 - 150 , and the interrupt wire  30 , which protects the circuit block  130 , are disposed on the substrate  120 . 
     Accordingly, even, when overcurrent is caused by a short-circuit fault in the circuit block  130  and the interrupt wire  30  melts due to the overcurrent, the circuit blocks  140 ,  150  are still electrically coupled with the power supply wire  23  via the branch wires  141 ,  151 . Thus, only the circuit block  130  coupled with the melt interrupt wire  30  stops and the circuit blocks  140 ,  150  keep operating. In particular, since the function of the circuit block  130  is less important than the functions of the circuit blocks  140 ,  150 , influence of the stop of the less important circuit block  130  on the functions of the more important circuit blocks  140 ,  150  can be restricted. When an overcurrent is caused by a short-circuit fault in the circuit blocks  140 ,  150  without the interrupt wire  30 , the overcurrent flows to the power supply wire  23 , the interrupt wire  122  melts, and the circuit blocks  130 ,  140 ,  150  are deactivated. Thus, the overcurrent is less likely to flow to other circuit block. 
     Especially in a case where a wire width of the interrupt wire  30  is smaller than a wire width of the interrupt wire  122  so that a current value at interruption by the interrupt wire  30  is smaller than a current value at interruption by the interrupt wire  122 , when an overcurrent is caused by a short-circuit fault in the circuit block  130 , the interrupt wire  30  melts earlier than the interrupt wire  122  with certainty. Thus, the influence on other circuit blocks  140 ,  150  can be restricted with certainty. The above-described configuration including two interrupt wires on one substrate may be applied to other embodiments and modifications. 
     Other Embodiments 
     The present invention is not limited to the above-describe embodiments and the above-described modifications may include various changes and modifications. For example, the connection wire  40  coupled at one end of the interrupt wire  30  may be electrically coupled with the common wire, which is shared by the electronic components  22  to be protected against overcurrent, instead of the power supply wire  23 . 
     The connection wire  50  coupled at the other end of the interrupt wire  30  may be electrically coupled with a component-mounted wire on which an electronic component is disposed, such as an internal layer fully covered with a protective layer made of, for example, solder resist. 
     At least one of the connection wires  40  and  50 , and the interrupt wire  30  may be provided for each substrate for overcurrent protection of the electronic control devices  12  including the engine ECU the brake ECU, the steering ECU, the body ECU, and the navigation ECU. 
     The above-described other embodiments may also be applied to the connection wires other than the connection wires  40  and  50 , and the interrupt wires other than the interrupt wire  30 .