Abstract:
A box-shaped housing of an in-vehicle electronic control unit that controls an occupant crash protection system is installed to an installation surface of a vehicle and includes an opening end that defines an opening in an imaginary plane, a ceiling wall, and a peripheral wall. The housing receives a planar control circuit board of the control unit through the opening end toward the ceiling wall and securely holds the circuit board at the peripheral wall such that a plane of the circuit board is parallel to the imaginary plane. The peripheral wall includes an opening side wall section located adjacent to the opening end, and a ceiling side wall section having a thickness larger than a thickness of the opening side wall section.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and incorporates herein by reference Japanese Patent Application No. 2009-9854 filed on Jan. 20, 2009. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a housing for an in-vehicle electronic control unit, which is a box-shaped housing for an electronic control unit that is used for an occupant crash protection such as an air bag for protecting an occupant when a vehicle collides, and more particularly to a housing for an in-vehicle electronic control unit that protects a control circuit board disposed in a housing when a vehicle collides. 
         [0004]    2. Description of Related Art 
         [0005]    Conventionally, as a housing for an in-vehicle electronic control unit such as the above-described type, there is a housing for an electronic device described in JP-A-2008-41718 (corresponding to EP1,887,842A1). As shown in  FIG. 10 , a housing  100  is a housing of an electronic control unit (ECU) of a vehicle, and includes a base  30  and a case  20  that accommodate a circuit board  10 , on which an electronic component  12  is mounted. The housing  100  is attached to an attachment body (not shown) such as a vehicle. The base  30  is formed by pressing aluminum, and includes a holding part  31 , an attachment portion  33 , and a joining part  36 . The circuit board  10  is fixed onto the holding part  31 . The attachment portion  33  is screwed to the attachment body and has a through hole  34  through which a screw passes. The joining part  36  connects the holding part  31  and the attachment portion  33 . At least one of the attachment portion  33  and the joining part  36  serves as a stress absorption part for absorbing stress produced by the attachment body. 
         [0006]    Accordingly, by at least one of the attachment portion  33  and the joining part  36  functioning as the stress absorption part for absorbing stress produced by the attachment body, transmission of the stress produced by the attachment body to the circuit board  10  is limited. 
         [0007]    However, in the above-described publication JP-A-2008-41718, if the electronic device housing  100  is damaged after the housing  100  cracks due to deformation of the vehicle when the vehicle collides, for example, the circuit board  10  is also damaged or, the case  20  cracks and rain water or radiator liquid, for example, enters through this crack. As a result, the circuit board  10  is submerged, so that the electronic component  12  mounted on the circuit board  10  is damaged. 
         [0008]    For instance, stored data at the time of the collision is retrieved from a storage device of the ECU so as to analyze the collision. Nevertheless, when the circuit board  10  is damaged as above, the analysis of the collision by retrieving the stored data at the time of the collision from the storage device mounted on the circuit board  10  cannot be carried out. Furthermore, if the electronic device housing  100  is damaged, a power source line is short-circuited so as to catch fire, so that a vehicle fire may be caused. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention addresses at least one of the above disadvantages. 
         [0010]    According to the present invention, there is provided a box-shaped housing of an in-vehicle electronic control unit that controls an occupant crash protection system, which protects an occupant of a vehicle in a case of collision of the vehicle. The box-shaped housing is adapted to be installed to an installation surface of the vehicle and includes an opening end, a ceiling wall, and a peripheral wall. The opening end defines an opening in an imaginary plane and is adapted to be placed adjacent to the installation surface of the vehicle. The ceiling wall is opposed to the opening end in a predetermined direction, which is generally perpendicular to the imaginary plane. The peripheral wall extends from the opening end to the ceiling wall in the predetermined direction. The box-shaped housing is adapted to receive a planar control circuit board of the in-vehicle electronic control unit through the opening end toward the ceiling wall in the predetermined direction and is adapted to securely hold the planar control circuit board at the peripheral wall such that a plane of the planar control circuit board is generally parallel to the imaginary plane. The peripheral wall includes an opening side wall section and a ceiling side wall section. The opening side wall section is located adjacent to the opening end. The ceiling side wall section has a wall thickness larger than a wall thickness of the opening side wall section and is located on a ceiling wall side of the opening side wall section, which is opposite from the opening end in the predetermined direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which: 
           [0012]      FIG. 1A  is a perspective view illustrating an electronic control unit in accordance with an embodiment of the invention; 
           [0013]      FIG. 1B  is a perspective view illustrating an housing case of the electronic control unit in accordance with the embodiment; 
           [0014]      FIG. 1C  is a perspective view illustrating a control circuit board of the electronic control unit in accordance with the embodiment; 
           [0015]      FIG. 1D  is a perspective view illustrating a housing cover of the electronic control unit in accordance with the embodiment; 
           [0016]      FIG. 2  is a block diagram illustrating an ECU circuit in accordance with the embodiment; 
           [0017]      FIG. 3A  is a perspective view illustrating the housing case which is a housing for an in-vehicle electronic control unit in accordance with the embodiment, with an opening of the case directed upward; 
           [0018]      FIG. 3B  is a cross-sectional view illustrating the housing case taken along a line IIIB-IIIB in  FIG. 3A ; 
           [0019]      FIG. 4  is a partially perspective view illustrating a crack on the housing case in accordance with the embodiment; 
           [0020]      FIG. 5  is a diagram illustrating how molds are drawn from the housing case in accordance with the embodiment, when thick walls of side walls of the case project inward of the case; 
           [0021]      FIG. 6  is a diagram illustrating a structure of the housing case of the embodiment with a board attachment portion of the case projected toward the opening of the case; 
           [0022]      FIG. 7A  is a diagram illustrating a structure of the housing case of the embodiment in which a corner part between the side walls of the case is bent; 
           [0023]      FIG. 7B  is an enlarged view illustrating an area surrounded by a square  91  in  FIG. 7A ; 
           [0024]      FIG. 8  is a diagram illustrating a structure of the housing case in accordance with the embodiment in which a side wall of the case around a vehicle attachment portion of the case is made even thinner than a thin wall of the case; 
           [0025]      FIG. 9  is a diagram illustrating how molds are drawn from a housing case in accordance with a comparative example when thick walls of side walls of the case project outward of the case; 
           [0026]      FIG. 10  is a perspective view illustrating a configuration of a previously proposed housing for an in-vehicle electronic control unit; and 
           [0027]      FIG. 11  is a partially perspective view illustrating a crack on a previously proposed housing case. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    An embodiment of the invention will be described below with reference to the accompanying drawings. The same numerals are used to indicate components that correspond to each other in the drawings of the embodiment, and description of the corresponding component is omitted on a timely basis to avoid repetition. 
         [0029]    An electronic control unit (ECU)  50  illustrated in  FIGS. 1A to 1D  includes a housing case  51 , a control circuit board  52 , and a housing cover  53 . The housing case  51  has a shape of a box that opens on its lower side. The control circuit board  52  is inserted into the housing case  51  through an opening of the case  51  and fixed thereto. The housing cover  53  is fixed to the opening of the housing case  51  to cover this opening. 
         [0030]    An ECU circuit  52   a  illustrated in  FIG. 2  and configured on the control circuit board  52  includes an acceleration sensor  55 , a storage device  56 , a microcomputer  57 , and external interfaces (IF)  58   a  to  58   n . The acceleration sensor  55  detects acceleration of a vehicle, and the storage device  56  stores data. The acceleration sensor  55  and the storage device  56  are connected to the microcomputer  57 . An air bag (not shown) or an external acceleration sensor (not shown), for example, is connected to the external interfaces (IF)  58   a  to  58   n . If the microcomputer  57  determines that the vehicle has collided in accordance with acceleration detected by the acceleration sensor that is connected to the external IFs  58   a  to  58   n , or by the acceleration sensor  55 , the microcomputer  57  carries out control, for example, to open the air bag. Furthermore, the microcomputer  57  conducts control to store data such as information on the vehicle collision in the storage device  56 . 
         [0031]    The housing case  51  is a component that features the present embodiment, and formed as illustrated in  FIGS. 3A and 3B . 
         [0032]    As shown in  FIGS. 3A and 3B , board attachment portions  71   a ,  71   b ,  71   c ,  71   d  having generally cylindrical shapes are provided for two inner surfaces of the housing case  51  opposed to each other. The two attachment portions  71   a ,  71   b  are provided for one of the two inner surfaces, and the two attachment portions  71   c ,  71   d  are provided for the other one of the two inner surfaces. Two vehicle attachment portions  72   a ,  72   b  are formed on an edge of one of both the opposing side walls, for which the board attachment portions  71   a  to  71   d  are provided. The vehicle attachment portions  72   a ,  72   b  project from the one of the opposing side walls outward of the housing case  51  in a direction perpendicular to the edge. A vehicle attachment portion  72   c  is formed on an edge of the other one of the opposing side walls. The vehicle attachment portions  72   a  to  72   c  are formed for screwing the housing case  51  horizontally to a vehicle body therethrough, and the board attachment portions  71   a  to  71   d  are formed for screwing the control circuit board  52  horizontally to the housing case  51  therethrough. 
         [0033]    The housing case  51  is characterized in that side walls (peripheral wall  51   e ) of the housing case  51  are divided into an opening side (i.e., opening end  51   f -side) and a case ceiling side (i.e., covering side; ceiling wall  51   d -side) of the housing case  51  with a horizontal line H 1  as a boundary therebetween, and that a wall thickness of a side wall  51   b  on the case ceiling side is made larger than a wall thickness of a side wall  51   a  on the opening side. The horizontal line H 1  indicates an attachment position of the control circuit board  52  to the housing case  51  through the board attachment portions  71   a  to  71   d . Therefore, the side wall  51   a  is also referred to as a thin wall portion  51   a , and the side wall  51   b  is also referred to as a thick wall portion  51   b . The horizontal line H 1  is also referred to as a boundary line H 1 . Accordingly; the peripheral wall  51   e  of the housing case  51  includes the thin wall portion  51   a  and the thick wall portion  51   b . In addition, in  FIG. 3A , the opening end  51   f  of the housing case  51  defines an opening in an imaginary plane, which is generally parallel to an installation surface  200  of the vehicle body (see  FIG. 6 ). 
         [0034]    By forming the housing case  51  in the above-described manner, when deformation of the vehicle in the case of the vehicle collision is transmitted to the ECU  50  so that a crack develops in the housing case  51 , as illustrated in  FIG. 4 , for instance, a crack develops on the thin wall portion  51   a  of the housing case  51  which is attached to the vehicle at the vehicle attachment portions  72   a  to  72   c . Although this crack runs over the thin wall portion  51   a , it is highly possible that the crack does not spread to the thick wall portion  51   b  because the thick wall portion  51   b  has a larger wall thickness. Accordingly, the crack runs on the thin wall portion  51   a , and thereby only the thin wall portion  51   a  is damaged as indicated by a dashed arrow Y 1 . Additionally, the vehicle attachment portions  72   a  to  72   c  are easily damaged, since they project from the side walls of the housing case  51  outward of the housing case  51 . 
         [0035]    This phenomenon is compared with a housing case of a conventional ECU illustrated in  FIG. 11 , provided that a side wall  83  of the conventional housing case, on which a board attachment portion  81  and a vehicle attachment portion  82  are formed, has a uniform wall thickness. When a vehicle collides, deformation of the vehicle caused by the vehicle collision is transmitted to the ECU, so that a crack appears on the side wall  83  of the housing case as indicated by a dashed arrow Y 2 . Because the side wall  83  has a uniform wall thickness, this crack spreads on the side wall  83  to reach a case ceiling (covering) of the housing case, for instance. In other words, it is highly possible that the crack arrives at the side wall on a control circuit board-side, and as a result, the control circuit board is damaged. 
         [0036]    Therefore, in the case of the construction of the housing case  51  of the present embodiment, the control circuit board  52  is mounted on the thick wall portion  51   b  side, and it is unlikely that the crack caused by the vehicle collision reaches the thick wall portion  51   b . Consequently, the thick wall portion  51   b  is not damaged, so that the control circuit board  52  is protected. As a result, the housing case  51  of the present embodiment may be used for instance, for retrieving stored data at the time of the collision from the storage device  56  of the ECU  50  to conduct analysis of the collision. 
         [0037]    The housing case  51  may be formed such that, as indicated by a numeral t 1  in  FIG. 4 , the thick wall portion  51   b  projects further inward of the housing case  51  than the thin wall portion  51   a . In other words, an outer surface of the side wall of the housing case  51  is made planar. 
         [0038]    When the above-described housing case  51  is molded, as shown in  FIG. 5 , a lower mold  85  may have flat side surfaces, and an upper mold  86  may be formed such that a side surface part of the upper mold  86  from a bottom face of the mold  86  up to a predetermined height, which is for forming the corresponding thick wall portion  51   b  of the housing case  51 , is recessed by a thickness difference t 1  shown in  FIG. 4 . By molding the housing case  51  using these lower and upper molds  85 ,  86 , since the side surfaces of the lower mold  85  are flat, and side surfaces of the upper mold  86  are recessed from their bottoms up to the predetermined position, the upper mold  86  is pulled out of the housing case  51  in an upward direction Y 4  and the lower mold  85  is pulled out of the case  51  in a downward direction Y 5 , so that it is easy to draw the molds. 
         [0039]    If an outer lateral surface  51   b - 1  of a housing case  51 - 1  is projected outward of the case  51 - 1  as shown in a comparative example of  FIG. 9 , a side surface of an upper mold  87  may be flat. However, a side surface of a lower mold  88  needs to be recessed inversely corresponding to the projection of the outer lateral surface  51   b - 1  from a bottom face of the mold  88  up to a predetermined height position. For this reason, the upper mold  87  is pulled out easily, but the lower mold  88  needs to be pulled in right and left directions as indicated respectively by arrows Y 9 , Y 8 , so that it is difficult to draw the molds. 
         [0040]    As illustrated in a partially cross-sectional view of the housing case  51  in  FIG. 6 , an end portion of the board attachment portion  71   a , which is formed on the boundary line H 1  generally between the thin wall portion  51   a  and the thick wall portion  51   b , may be projected toward the opening of the housing case  51  by an arbitrary length t 2  with the end portion away from the thin wall portion  51   a.    
         [0041]    By forming the housing case  51  in the above-described manner, the control circuit board  52 , which is fixed on the ends of these projected portions, is fixed, with the board  52  away from the side wall (thin wall portion  51   a ) of the housing case  51 , because of projected portions of the board attachment portions  71   a  to  71   d . Accordingly, when the thin wall portion  51   a  cracks by the vehicle collision, even if rain or radiator liquid, for example, enters into the housing case  51  from the crack along the wall portion  51   a , they do not reach the control circuit board  52 . Thus, the control circuit board  52  is protected. 
         [0042]    Furthermore, as illustrated in  FIG. 7B , a portion within a range of a square indicated by a numeral  91  in  FIG. 7A  may be formed into a curved shape R. More specifically, a crossing portion between a vertical line along a corner part of the housing case  51  where the side walls of the case  51  are in contact with each other, and a horizontal line which is the boundary line H 1  between the thin wall portion  51   a  and the thick wall portion  51   b , is referred to as the curved shape R. Accordingly, if a crack, which has appeared on the thin wall portion  51   a , develops to the corner part of the housing case  51  as indicated by an arrow Y 10  in  FIG. 7B , this crack is diverted at the portion of the curved shape R toward the opening of the housing case  51 ; i.e., toward the vehicle attachment portions  72   a  to  72   c , thereby to the outside of the housing case  51 . As a result, the crack does not reach the thick wall portion  51   b , so that the control circuit board  52  is protected. 
         [0043]    In addition, as shown in  FIG. 8 , a portion of the thin wall portion  51   a  around the vehicle attachment portion  72   a  that is attached to the edge of the opening of the thin wall portion  51   a , may be an even thinner wall portion  51   c . The above-described portion of the thin wall portion  51   a  is surrounded with a boundary line H 2 . In the case of this construction of the housing case  51 , the even thinner wall portion  51   c  is destroyed at the time of the vehicle collision, so that a crack or the like does not appear on the other part of the housing case  51 . Therefore, the generally entire housing case  51  is protected. 
         [0044]    Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.