Patent Publication Number: US-2015077956-A1

Title: Vehicular electronic control unit with drainage structure

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2013-193394 filed on Sep. 18, 2013, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an electronic control unit for a vehicle, more specifically, relates to a drainage structure of the electronic control unit. 
     BACKGROUND 
     The number of electronic control units mounted in vehicles has been increased with progression of electronic control of the vehicles. In general, the electronic control unit is encased in a case, and a circuit board to which electronic components are integrated is accommodated in the case. When a water droplet adheres to the circuit board, a short-circuit may occur in a circuit. 
     Therefore, the electronic control unit requires a drip-proof structure. A conventional drip-proof structure will be described in regard to an airbag electronic control unit (ECU) as an example of the electronic control unit. 
     The airbag ECU determines whether a vehicle has collided with an object based on a detection result of an external acceleration sensor and a detection result of an internal acceleration sensor disposed in the airbag ECU to control activation of airbags. 
     For example, the airbag ECU may be arranged, under a floor, at a foot area of front passenger&#39;s seat and a substantially middle position with respect to a vehicle lateral direction, so as to determine not only a frontal collision but also a side collision. In a passenger&#39;s compartment, a cup holder for holding a drink cup may be provided above an area where the airbag ECU is arranged. 
     In such a case, if a drink spills from the drink cup of the cup holder, it may flow through a gap of the vehicle floor or the like and reach the case of the airbag ECU. If the airbag ECU is tilted relative to a horizontal direction while the vehicle is travelling on a slope, the water droplet may enter the inside of the case through a gap of the case or a connector. If the water droplet adheres to the circuit board, a short-circuit is likely to occur in the circuit. Accordingly, the airbag ECU requires a drip-proof structure for restricting the entry of water droplet from the outside of the case. 
     For example, an electronic control unit disclosed in JP2008-130359A is provided with a visor or a projection above a gap of the case or the connector for restricting the entry of the water droplet. As another example, it is proposed to attach a sheet to an upper surface of the case to cover the connector from the top. By such structures, the entry of the water droplet can be reduced. 
     However, even if the visor or the sheet is employed, it is not always true that the entry of the droplet is surely restricted. 
     SUMMARY 
     It is an object of the present disclosure to provide an electronic control unit with a drainage structure capable of draining a water droplet from a case, even if the water droplet enters the case. 
     According to an aspect of the present disclosure, an electronic control unit for a vehicle includes a circuit board, a connector and a case. The circuit board has an electronic component disposed thereon. The connector is integrated to a surface of the circuit board to electrically connect the circuit board and an external device. The case accommodates the circuit board and the connector therein in a state where an end surface of the connector exposes from the case. The circuit board is disposed in the case such that the surface to which the connector is integrated faces down, and a clearance between the circuit board and the connector is located at a position lower than the circuit board. 
     In this structure, since the circuit board is disposed in the case such that the surface to which the connector is integrated faces down, the surface of the circuit board is located at a level equal to or higher than an upper surface of the connector. In this case, since the lower surface of the circuit board is located at the level equal to or higher than the upper surface of the connector, even if a liquid entering the case from a clearance between the case and the connector flows along the upper surface of the connector, the liquid can be discharged to the outside of the case and the circuit board can be protected from such a liquid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated with like reference numbers and in which: 
         FIG. 1  is a schematic cross-sectional view of a vehicle ECU according to a first embodiment of the present disclosure; 
         FIG. 2  is a perspective view of a case of the vehicle ECU according to the first embodiment; 
         FIG. 3  is a schematic side view of the vehicle ECU, when viewed from a side of a front wall, according to the first embodiment; 
         FIG. 4  is a top view of a connector of the vehicle ECU for illustrating a recessed portion and a drainage groove according to the first embodiment; 
         FIG. 5  is a cross-sectional view of the connector integrated to a circuit board, taken along a line V-V in  FIG. 4 , according to the first embodiment; 
         FIG. 6  is a cross-sectional view of a vehicle ECU for illustrating a spreading pocket, a water-proof wall, and a water-proof pad provided on an upper wall of a case, according to a second embodiment of the present disclosure; 
         FIG. 7  is an enlarged cross-sectional view of a drainage structure of the vehicle ECU shown in  FIG. 6 ; 
         FIG. 8  is a top view of a connector of a vehicle ECU for illustrating a projected part according to a third embodiment of the present disclosure; and 
         FIG. 9  is a schematic cross-sectional view of the vehicle ECU according to the third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. 
     In each of the embodiments, a drainage structure of a vehicle electronic control unit (vehicle ECU) will be described using an airbag ECU for controlling activation of airbags as an example. 
     In the drawings, an arrow indicating an up and down direction corresponds to a direction when the vehicle ECU is mounted in a vehicle. In the following description, the width direction of a connector  4 , a spreading pocket  26 , a front wall  21 , or the like corresponds to a right and left direction in  FIG. 3 , and an up and down direction in  FIG. 4 . 
     First Embodiment 
     A drainage structure of a vehicle ECU  1  according to the first embodiment will be described with reference to  FIGS. 1 to 5 . As shown in  FIG. 1 , the vehicle ECU  1  has a case  2 , a circuit board  3 , and a connector  4 . 
     As shown in  FIG. 2 , the case  2  is a housing or an accommodation member made of a resin or a metal. The case  2  has a substantially rectangular parallelepiped-shape with an opening at a bottom. The case  2  has a front wall  21 , a right side wall  22 , a left side wall  23 , a rear wall  24 , and an upper wall  25 , which are integrally formed. 
     The front wall  21  is formed with a front opening portion  210 . The front opening portion  210  provides an opening for exposing at least a part of the connector  4 . The opening of the front opening portion  210  penetrates through the front wall  21  in a thickness direction of the front wall  21 , and is in communication with a space provided by the front wall  21 , the right side wall  22 , the left side wall  23  and the rear wall  24 . The front opening portion  210  is located at a substantially middle of the front wall  21  with respect to a width direction of the front wall  21 . The front wall  21  has a front projection  211  on a perimeter of the front opening portion  210 . The front projection  211  perpendicularly projects from the front wall  21 . The front projection  211  will be also referred to as the opening wall. 
     As shown in  FIGS. 2 and 3 , the right side wall  22  and the left side wall  23  have fixing portions  220 ,  230 . The fixing portion  220  projects from a middle portion of a bottom surface  22   a  of the right side wall  22  toward outside of the case  2 . The fixing portion  230  projects from a middle portion of a bottom surface  23   a  of the left side wall  23  toward outside of the case  2 . The fixing portions  220 ,  230  project in directions opposite to each other. The fixing portions  220 ,  230  are integrally formed with the right side wall  22  and the left side wall  23 . The fixing portions  220 ,  230  are formed with through holes for allowing fixing members (not shown), such as bolts, to pass through. The case  2  is fixed to a predetermined attachment surface P of a vehicle by fixing the fixing members through the fixing portions  220 ,  230 . 
     Bottom surfaces  220   a,    230   a  of the fixing portions  220 ,  230  are located lower than the bottom surfaces  22   a,    23   a  of the right and left side walls  22 ,  23 . Therefore, when the case  2  is fixed to the attachment surface P of the vehicle, the bottom surfaces  220   a,    230   a  of the fixing portions  220 ,  230  are in contact with the attachment surface P, and a clearance is formed between the bottom surfaces  22   a,    23   a  of the right and left side walls  22 ,  23  and the attachment surface P. In other words, a space is formed between the bottom of the case body and the attachment surface P of the vehicle. As such, the case  2  is fixed in a state of being spaced from the attachment surface P as being supported at the fixing portions  220 ,  230 . 
     As shown in  FIG. 1 , the circuit board  3  and the connector  4  are disposed in the case  2 . The circuit board  3  is provided with electronic components such as an acceleration sensor for detecting a collision and a microcomputer. The connector  4  is integrated to the circuit board  3 . The connector  4  electrically connects external devices (not shown) to the circuit board  3 . 
     As shown in  FIG. 3 , a front part of the connector  4  opposite to the circuit board  3  has a shape to be capable of being located in the front opening portion  210 . An end surface of the front part of the connector  4  slightly projects and exposes from the front projection  211 , as shown in  FIG. 1 . 
     As shown in  FIG. 1 , the upper wall  25  has a spreading pocket  26  and a water-proof wall  27  on an inner surface  25   a.  The water-proof wall  27  is located adjacent to the front wall  21 . The spreading pocket  26  is provided by a space defined by the front wall  21 , the water-proof wall  27 , and the inner surface  25   a  of the upper wall  25 . 
     In other words, the spreading pocket  26  is disposed adjacent to the front wall  21 . The spreading pocket  26  is a recess that extends over the entire width of the inner surface  25   a  of the upper wall  25 . For example, the width of the inner surface  25   a  is measured in a direction perpendicular to a paper surface of  FIG. 1 . 
     A front clearance is provided between the front projection  211  and the connector  4 . Therefore, there is a fear that a liquid, such as a water droplet enters inside of the case through the front clearance. In the spreading pocket  26 , the water droplet entering the case  2  from the front clearance and blocked by the water-proof wall  27  is spread. 
     A surface of the water-proof wall  27  provides an end surface of the spreading pocket  26 . The water-proof wall  27  projects perpendicularly downwardly from the inner surface  25   a.  The spreading pocket  26  and the water-proof wall  27  are located above an upper surface  4   a  of the connector  4  when the circuit board  3  and the connector  4  are disposed in the case  2 . A clearance provided between a bottom end surface of the water-proof wall  27  and the upper surface  4   a  of the connector  4  is smaller than a clearance provided between the front wall  21  (e.g., the front projection  211 ) and the upper surface  4   a  of the connector  4 . 
     The circuit board  3  and the connector  4  are disposed in the case  2  in such a manner that the connector  4  is located under the circuit board  3 , in a vehicle up and down direction, that is, in a vertical direction. In other words, the circuit board  3  is disposed above the upper surface  4   a  of the connector  4 , within the case  2 . Therefore, even if the water droplet reaches the circuit board  3  through the clearance between the water-proof wall  27  and the upper surface  4   a  of the connector  4 , the water droplet flows to a position lower than the circuit board  3 . 
     As shown in  FIG. 4 , the connector  4  has a recessed portion  41  and a drainage groove  42  on the upper surface  4   a.  The recessed portion  41  is formed to extend over the entire width of the upper surface  4   a,  that is, in a direction parallel to the front wall  21 . The drainage groove  42  is formed to extend from the recessed portion  41  to an end surface  4   b  from which terminals  45  projects. The end surface  4   b  will be also referred to as a terminal-side end surface  4   b.  The terminal-side end surface  4   b  is opposite to the end surface that exposes from the front opening portion  210 . 
     A first end of the drainage groove  42  is continuous from the recessed portion  41 . The first end of the drainage groove  42  is formed to project from a part of the recessed portion  41 . A second end of the drainage groove  42  is located on the terminal-side end surface  4   b.  A bottom surface of the recessed portion  41  has inclination with respect to a width direction (e.g., the right and left direction in  FIG. 4 ) of the recessed portion  41  such that the bottom surface of the recessed portion  41  is tilted downwardly toward the drainage groove  42 . 
     As shown in  FIG. 5 , a part of the drainage groove  42  formed on the upper surface  4   a  is tilted downwardly toward the terminal-side end surface  4   b . A part of the drainage groove  42  located on the terminal-side end surface  4   b  is a groove extending over the entire height of the terminal-side end surface  4   b . At a lower end of the drainage groove  42 , the bottom surface of the drainage groove  42  is gradually inclined toward the terminal-side end surface  4   b.  The part of the drainage groove  42  located on the terminal-side end surface  4   b  extends downwardly toward the attachment surface P of the vehicle, which is not illustrated in  FIG. 5 . In other words, the downward corresponds to a lower side in  FIG. 5 , which is adjacent to the vehicle attachment surface P. 
     The drainage groove  42  is formed at a position apart from positions where the terminals  45  project. In the present embodiment, the terminals  45  of the connector  4  are separated into a first terminal group  451  and a second terminal group  452 . The number of the terminals  45  of the first terminal group  451  is greater than the number of the terminals  45  of the second terminal group  452 . The drainage groove  42  is formed in a space between the first terminal group  451  and the second terminal group  452 . 
     The connector  4  is joined to the circuit board  3  by a general joining method. For example, the connector  4  may be connected to the circuit board  3  by soldering. Further, the connector  4  may be connected to the circuit board  3  further using fixing members, such as screws, so as to strengthen the connection to the circuit board  3 . 
     In such a case, even when the connector  4  is connected to the lower surface of the circuit board  3 , durability of the connector  4  with respect to a direction of gravity improves. In this case, the lower surface of the circuit board  3  corresponds to a main surface to which electronic components are mainly mounted. When the circuit board  3  is fixed to the case  2  so that the main surface faces down, the circuit board  3  can be easily located at a position higher than the connector  4  within the case  2 . 
     The case  2  may have a connector support portion (not shown) that projects from at least one lower end portion of the front projection  211  toward the other lower end portion of the front projection  211 . In such a case, since the connector  4  is supported by the connector support portion from its bottom, the durability of the connector with respect to the direction of gravity further improves. 
     Next, a drainage path in the vehicle ECU  1  configured as above will be described. 
     For example, there is a case where a droplet of the drink from a drink container disposed in the cup holder will drop on the upper wall  25  of the case  2 . It is assumed that this droplet moves toward the connector  4  due to the traveling of the vehicle and enters the case through the clearance between the front projection  211  and the connector  4 . 
     The droplet entered is blocked by the water-proof wall  27 , and is spread in the spreading pocket  26 . A part of the droplet spread flows in the width direction of the spreading pocket  26 . The spreading pocket  26  is the recess formed to extend in the entire width of the inner surface  25   a  of the upper wall  25 , which has substantially the same width as the front wall  21 . On the other hand, the connector  4  has the width that can be received in the front opening portion  210  that is formed at the part of the width of the front wall  21 . 
     For this reason, when the droplet flows in the width direction of the spreading pocket  26 , the droplet flows down along right and left side surfaces of the connector  4  and drops on the attachment surface P of the vehicle to be discharged to the outside of the case  2 . 
     The droplet does not flow to the side ends of the spreading pocket  26  in the width direction. Even if the droplet passes through the clearance between the water-proof wall  27  and the upper surface  4   a  of the connector  4 , the droplet flows in the recessed portion  41 . In the recessed portion  41 , the droplet flows toward the drainage groove  42  due to the inclination of the bottom surface of the recessed portion  41 . The droplet further flows down along the drainage groove  42 , and drops on the attachment surface P to be discharged to the outside of the case  2 . 
     In the present embodiment, the spreading pocket  26  is formed to extend over the entire width of the inner surface  25   a  of the upper wall  25 . The connector  4  is not present under both of the side ends of the spreading pocket  26 . For this reason, the droplet entering the case  2  can drop from the side ends of the spreading pocket  26  with respect to the width direction. The droplet dropped can be discharged from the case  2  through the clearance provided between the case  2  and the attachment surface P of the vehicle. 
     Further, the droplet spreads in the width direction of the connector  4  within the spreading pocket  26 . Therefore, a force of the droplet to enter the clearance provided between the water-proof wall  27  and the upper surface  4   a  of the connector  4  can be reduced, and hence the entry of the droplet to the circuit board  3  can be suppressed. 
     The circuit board  3  is located at a position higher than the upper surface  4   a  of the connector  4 . With this configuration, the droplet entering from the clearance provided between the water-proof wall  27  and the connector  4  flows on the upper surface  4   a  of the connector  4 , which is located lower than the circuit board  3 , due to the force of gravity. Since the upper surface  4   a  of the connector  4  has the recessed portion  41 , and the bottom surface of the recessed portion  41  is sloped down toward the drainage groove  42 , the droplet is easily introduced to the drainage groove  42 . 
     Further, the bottom surface of the part of the drainage groove  42  formed on the upper surface  4   a  is sloped down toward the terminal-side end surface  4   b.  The droplet is easily introduced toward the lower end of the terminal-side end surface  4   b,  and hence is easily dropped on the attachment surface P of the vehicle. As such, the droplet can be discharged to the outside of the case  2  without reaching the circuit board  3 . 
     Accordingly, an occurrence of a short-circuit due to adhesion of the droplet to the circuit board  3  can be reduced. 
     The case  2  is directly fixed to the attachment surface P of the vehicle through the fixing portions  220 ,  230 . As such, the attachment surface P serves to cover the bottom opening of the case  2 . Accordingly, a cover member to cover the bottom opening of the case  2  is not necessary. 
     (Modification 1) 
     In the structure described above, the drainage groove  42  is exemplary located in the space between the first terminal group  451  and the second terminal group  452 . However, the arrangement of the drainage groove  42  is not limited to the above-described example. 
     As another example, the space between the first terminal group  451  and the second terminal group  452  may be eliminated. Instead, an area where the terminals  45  are not arranged may be formed at a position corresponding to one end of the terminal-side end surface  4   b  with respect to the width direction, and the drainage groove  42  may be formed in this area to be in communication with the recessed portion  41 . Namely, the drainage groove  42  may be formed at an end of the connector  4  with respect to the width direction. 
     (Modification 2) 
     In the structure described above, the bottom surface of the recessed portion  41  is exemplarily sloped down toward the drainage groove  42  with respect to the width direction. The bottom surface of the recessed portion  41  may be further sloped down toward the drainage groove  42  from the ends of the recessed portion  41  with respect to the longitudinal direction of the recessed portion  41 . In this case, the droplet can be further effectively introduced to the drainage groove  42 . 
     Second Embodiment 
     Next, a drainage structure in a vehicle ECU  10  according to a second embodiment of the present disclosure will be described with reference to  FIGS. 6 and 7 . 
     Similar to the vehicle ECU  1  of the first embodiment, the vehicle ECU  10  includes a case  20 , the circuit board  3 , and a connector  40 . 
     Hereinafter, the parts same as or equivalent to those of the first embodiment are designated with the same reference numbers, and descriptions thereof will not be repeated. 
     The case  20  has substantially the similar structure to the case  2  of the first embodiment. The case  20  has the front wall  21 , the right side wall  22 , the left side wall  23 , the rear wall  24  and the upper wall  25 , which are integrally formed. 
     The circuit board  3  and the connector  40  that is connected to the circuit board  3  are disposed in the case  20 . The connector  40  has an upper surface  40   a.  In the present embodiment, the upper surface  40   a  is a plain surface without having the recessed portion  41  and the drainage groove  42  as the first embodiment. 
     As shown in  FIG. 6 , the upper wall  25  has the spreading pocket  26  and a water-proof wall  270  on the inner surface  25   a.  The length of the water-proof wall  270  is shorter than that of the water-proof wall  27  of the first embodiment with respect to the vehicle up and down direction. A water-proof pad  28  is provided at the lower end of the water-proof wall  270 . 
     The water-proof pad  28  is a member made of silicon. The water-proof pad  28  is fixed at the lower end surface of the water-proof wall  270  over the entire width of the water-proof wall  270 . A length of the water-proof pad  28  in the vehicle up and down direction is set to a length equal to or greater than the clearance between the lower end surface of the water-proof wall  270  and the upper surface  40   a  of the connector  40 . For example, the water-proof pad  28  has a reversed U shape in a cross-section defined in the up and down direction. The water-proof pad  28  has a double-blocking structure for the droplet entering the case  2 . For example, the water-proof pad  28  has double nail portions. 
     In particular, as shown in  FIG. 7 , the water-proof pad  28  has two pad ends, such as a first pad end  28   a  and a second pad end  28   b,  opposite to the base portion fixed to the lower end surface of the water-proof wall  270 . Each of the pad ends  28   a,    28   b  is narrowed toward its tip end. In other words, each of the pad ends  28   a,    28   b  is tapered off toward its tip end. 
     The two pad ends  28   a,    28   b  are expanded to separate from each other as a function of distance from the lower end surface of the water-proof wall  270 , so that the first pad end  28   a  extends more to the front wall  21  and the second pad end  28   b  extends more to the circuit board  3 . The second pad end  28   b  adjacent to the circuit board  3  extends nearer to the clearance between the circuit board  3  and the connector  40 , to close the clearance between the circuit board  3  and the connector  40 . 
     Next, a drainage path of the vehicle ECU  10  configured as above will be described. 
     The droplet entering the case  20  from the clearance between the front projection  211  and the connector  40  is blocked by the first pad end  28   a  of the water-proof pad  28 , and is spread within the spreading pocket  26 . A part of the droplet spread flows toward the side ends of the pad end  28   a  with respect to the width direction, and drops along the right and left side surfaces of the connector  40 . The droplet then drops on the attachment surface P of the vehicle, and flows out from the case  20 . 
     Even if the droplet enters further inside of the case  20  through the clearance between the first pad end  28   a  and the upper surface  40   a  of the connector  40 , the droplet is blocked by the second pad end  28   b  and flows toward the side ends of the second pad end  28   b  with respect to the width direction. The droplet further flows down along the right and left side surfaces of the connector  40 , and drops on the attachment surface P of the vehicle to be discharged to the outside of the case  20 . 
     In the present embodiment, the droplet entering the case  20  from the clearance between the front projection  211  and the connector  40  flows along the upper surface  40   a  of the connector  40 . In this case, the first pad end  28   a  of the water-proof pad  28  is in contact with the upper surface  40   a  of the connector  40 , and a clearance between the upper surface  40   a  of the connector  40  and the first pad end  28   a  hardly exists. Therefore, the first pad end  28   a  restricts the droplet from entering further inside of the case  2  toward the circuit board  3 . 
     The droplet flowing to the first pad end  28   a  spreads in the width direction of the connector  4  within the spreading pocket  26 , and flows toward the ends of the pad end  28   a  with respect to the width direction to be discharged to the outside of the case  20 . As such, the force of the droplet to enter the clearance between the upper surface  40   a  of the connector  40  and the first pad end  28   a  is reduced. 
     Even if the droplet enters further inside through the clearance between the upper surface  40   a  of the connector  40  and the first pad end  28   a,  since the second pad end  28   b  extends to the clearance between the circuit board  3  and the connector  40  to block the clearance, the entry of the droplet toward the circuit board  3  can be restricted. 
     The droplet entering the water-proof pad  28 , that is, the droplet entering the space between the pad end  28   a  and the pad end  28   b  flows toward the side ends of the second pad end  28   b  with respect to the width direction, and hence is discharged to the outside of the case  20 . 
     Further, the circuit board  3  is located at a position higher than the upper surface  40   a  of the connector  40 . Therefore, even if the droplet enters the clearance between the second pad end  28   b  and the upper surface  4   a  of the connector  40  toward the circuit board  3 , it is less likely that the droplet will adhere to the circuit board  3 . Accordingly, an occurrence of a short-circuit due to the droplet adhering to a wiring of the circuit board  3  can be reduced. 
     (Modification 3) 
     In the structure described above, the water-proof pad  28  exemplarily has the double block and discharging structure in which the entry of the droplet is restricted by the two pad ends  28   a,    28   b  and the droplet is discharged to the outside of the case  20 . Alternatively, the water-proof pad  28  may have only one pad end. Also in the case where the water-proof pad  28  has one pad end, it is preferable that the pad end extends from the lower end surface of the water-proof wall  270  toward the front wall  21  or the circuit board  3 , instead of extending straight from the lower end surface of the water-proof wall  270 . 
     (Modification 4) 
     In the structure described above, the water-proof pad  28  is exemplarily disposed at the lower end surface of the water-proof wall  270  projecting from the inner surface  25   a  of the upper wall  25  of the case  20 . Alternatively, the water-proof pad  28  may be provided directly on the inner surface  25   a.    
     In such a case, the length of the water-proof pad  28  in the vehicle up and down direction is equal to or greater than the distance between the inner surface  25   a  and the upper surface  40   a  of the connector  40 . In this case, the base end of the water-proof pad  28  is in contact with the inner surface  25   a  of the upper wall  25 , and the pad ends  28   a,    28   b  are in contact with the upper surface  40   a  of the connector  40 . Also in this case, the droplet entering the case  2  from the clearance between the front projection  211  and the connector  4  can be blocked. 
     Third Embodiment 
     A drainage structure of a vehicle ECU  100  according to a third embodiment of the present disclosure will be described with reference to  FIGS. 8 and 9 . 
     Similar to the vehicle ECU  1  of the first embodiment, the vehicle ECU  100  has a case  200 , the circuit board  3 , and a connector  400 . 
     Hereinafter, parts same as or equivalent to those of the first embodiment or the second embodiment will be designated with the same reference numbers, and descriptions thereof will not be repeated. 
     The case  200  has substantially the similar structure to the case  2  of the first embodiment. The case  200  has the front wall  21 , the right side wall  22 , the left side wall  23 , the rear wall  24  and an upper wall  250 , which are integrally formed. The inner surface  250   a  of the upper wall  250  is not provided with the water-proof wall  27 ,  270 . 
     Similar to the first embodiment, the circuit board  3  and the connector  400  connected to the circuit board  3  are disposed in the case  200 . 
     As shown in  FIG. 8 , the connector  400  has a projected wall  43  on the upper surface  400   a.  The projected wall  43  projects from the upper surface  400   a,  and extends substantially over the entire width of the upper surface  400   a  in the width direction of the connector  400 . 
     In the present embodiment, the projected wall  43  includes a first projected-wall portion  43   a  and a second projected-wall portion  43   b.  The first projected-wall portion  43   a  is adjacent to the front wall  21 , and the second projected-wall portion  43   b  is adjacent to the circuit board  3 . 
     As shown in  FIG. 9 , the first projected-wall portion  43   a  and the second projected-wall portion  43   b  are arranged parallel to each other to define a groove  44  between them. The groove  44  will be hereinafter referred to the projected wall groove  44 . 
     A bottom surface of the projected wall groove  44  is located at a position slightly higher than the upper surface  400   a  of the connector  400 . Both ends of the bottom surface of the projected wall groove  44  are sloped down toward the right and left side surfaces of the connector  400 , as shown in  FIG. 8 . This slope begins from a position more to a middle of the first and second projected-wall portions  43   a,    43   b  than the ends of the first and second projected-wall portions  43   a,    43   b  with respect to the width direction. 
     Next, a drainage path in the vehicle ECU  100  configured as above will be described. 
     The droplet entering the case  200  from the clearance between the front projection  211  and the connector  400  is blocked by the first projected-wall portion  43   a  adjacent to the front wall  21 . The droplet is introduced to the ends of the first projected-wall portion  43   a  in the width direction, and flows down along the right and left side surfaces of the connector  400 . The droplet drops on the attachment surface P of the vehicle, and flows out from the case  200 . 
     The droplet flowing over the first projected-wall portion  43   a  is blocked by the second projected-wall portion  43   b  adjacent to the circuit board  3 , and flows in the projected wall groove  44  formed between the first projected-wall portion  43   a  and the second projected-wall portion  43   b.  The droplet flows toward the ends of the projected wall groove  44 . 
     Further, the droplet is introduced toward the right and left side surfaces of the connector  400  by the slopes at the ends of the bottom surface of the projected wall groove  44 . The droplet flows down along the right and left side surfaces of the connector  400 , and drops on the attachment surface P of the vehicle to be discharged to the outside of the case  200 . 
     In the present embodiment, the droplet entering the case  200  from the clearance between the front projection  211  and the connector  400  flows along the upper surface  400   a  of the connector  400 . The first and second projected-wall portions  43   a,    43   b  are formed on the upper surface  400   a  to extend substantially over the entire width of the connector  400 . Therefore, the droplet can be introduced toward the ends of the projected wall  43  in the width direction two times, i.e., by two steps by the first projected-wall portion  43   a  and the second projected-wall portion  43   b.  As such, the droplet can be positively discharged to the outside of the case  200 . 
     On the upper surface  400   a,  even if the droplet flows over the second projected-wall portion  43   b  toward the circuit board  3 , the circuit board  3  is located at a position higher than the upper surface  400   a  of the connector  400 . Also with this configuration, an occurrence of a short-circuit due to the droplet adhering to a wiring of the circuit board  3  can be reduced. 
     (Modification 5) 
     In the structure described above, the projected wall  43  exemplarily includes two projections (i.e., the first projected-wall portion  43   a  and the second projected-wall portion  43   b ) on the upper surface  400   a  of the connector  400 . As the drainage structure, the projected wall  43  may have only one projected-wall portion. 
     (Modification 6) 
     The projected wall  43  may have three or more projected-wall portions to further restrict the droplet from flowing toward the circuit board  3  and further positively discharge the droplet to the outside of the case  200 . 
     (Modification 7) 
     Side grooves may be formed on the right and left side surfaces of the connector  400  to extend from the projected wall groove  44  formed on the upper surface  400   a.  In this case, the droplet introduced to the ends of the projected wall groove  44  flows in the side grooves formed on the right and left side surfaces of the connector  400 . As such, the droplet is further properly flows down to the lower ends of the right and left side surfaces. Thus, it is less likely that the droplet flowing along the right and left side surfaces of the connector  400  will flow or move toward the terminal-side end surface of the connector  400 . 
     (Modification 8) 
     In each of the embodiments described above, the airbag ECU for controlling activation of the airbags is employed as the vehicle electronic control unit. However, the electronic control unit to which the present disclosure is employed is not limited to the airbag ECU. For example, the present disclosure may be employed to any electronic control unit, such as an engine electronic control unit for controlling an engine. 
     While only the selected exemplary embodiments and examples have been chosen to illustrate the present disclosure, it will, be apparent to those skilled in the art from this disclosure that various changes and modifications can be made therein without departing from the scope of the disclosure as defined in the appended claims. Furthermore, the foregoing description of the exemplary embodiments and examples according to the present disclosure is provided for illustration only, and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents.