Abstract:
A first board, on which electric wires are wired, includes a first part having a first thickness and a second part continued from the first part and having a second thickness smaller than the first thickness. A second board, on which bus bars are arranged, is disposed on the second part of the first board. The second board has a third thickness which is determined such that an additional thickness of the second thickness and the third thickness is not greater than the first thickness.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a circuit board assembling structure which is applied to an electric junction box or the like, and adapted to assemble a wiring circuit board on which electric wires are arranged and a bus bar circuit board on which bus bars are arranged thereby to constitute a circuit board assembly.  
           [0002]    [0002]FIG. 3 shows one example of a conventional circuit board assembling structure for an electric junction box, which is disclosed in Japanese Patent Publication No. 9-140028A (cf., page 3 and FIG. 2).  
           [0003]    This electric junction box  51  includes a plurality of bus bar circuit boards  52  to be stacked one on another, and a wiring circuit board  53  disposed below the bus bar circuit boards  52 . The bus bar circuit boards  52  and the wiring circuit board  53  constitute a circuit board assembly, and upper and lower covers  54  and  55  made of synthetic resin contain the circuit board assembly.  
           [0004]    Each of the bus bar circuit boards  52  includes a plurality of bus bars  56  made of conductive sheet metal in desired shapes, and an insulative substrate  57  on which the bus bars  56  are arranged. The bus bars  56  are provided with tab terminals  58  which are continuously extended from their end portions or intermediate portions. The terminals  58  are received in connector housings  59  of the upper cover  54  thereby to constitute a connector, or connected to fuses and relays in the upper cover by way of relay terminals  60  of a female type.  
           [0005]    The wiring circuit board  53  includes a plurality of electric wires  61 , and a case  62  made of insulative resin on which the electric wires  61  in desired shapes are arranged. Each of the electric wires  61  is press-fitted to one contact portion  63   a  of a terminal  63  at a desired position inside the case. The other contact portion  63   b  of the terminal  63  is passed through a hole  64  of the case  62  to be connected to a terminal of the bus bar  56 , or passed through the lower cover  55  to be received in connector housings below the lower cover  55 .  
           [0006]    The bus bars  56  are mainly suitable for a large current circuit such as a power source circuit, and the electric wires  61  are mainly suitable for a small or middle current circuit such as a signal circuit. The bus bars  56  and the electric wires  61  are connected to each other so that an electric power can be supplied to the connector of the lower cover  55 . Exterior wire harnesses (not shown) continued to the power source and an auxiliary equipment are connected to the connectors of the upper and lower covers  54 ,  55 .  
           [0007]    However, in the above described configuration, since the bus bar circuit boards  52  and the wiring circuit board  53  are stacked in a direction of their thickness, the more specifications of the circuits becomes complicated, the more the circuit board assembly become upsized in a vertical direction, so that the electric junction box  51  accordingly become large-sized. Further, since the bus bar circuit boards  52  has to be assembled to the wiring circuit board  53  after the wiring board  53  is assembled to the lower cover  55 , a lot of working steps are required in assembling the circuit board assembly, that is, the electric junction box  51 .  
         SUMMARY OF THE INVENTION  
         [0008]    It is therefore an object of the invention to provide a circuit board assembling structure in which a circuit board assembly can prevented from being upsized in a stacking direction thereby to obtain a compact electric junction box.  
           [0009]    It is also an object of the invention to provide a circuit board assembling structure which is easily assembled with less working steps.  
           [0010]    In order to achieve the above objects, according to the invention, there is provided a circuit board assembly, comprising:  
           [0011]    a first board on which electric wires are wired, the first board including a first part having a first thickness and a second part continued from the first part and having a second thickness smaller than the first thickness; and  
           [0012]    a second board on which bus bars are arranged, the second board disposed on the second part of the first board.  
           [0013]    In such a configuration, the circuit board assembly can be downsized in the thickness direction thereof by the size corresponding to the difference between the first thickness and the second thickness. The weight of the assembly can be also reduced. The first board and the second board are integrated in advance to constitute the circuit board assembly, and the assembly is then accommodated in a cover of an electric junction box. Accordingly, the electric junction box can be easily manufactured with less operation steps.  
           [0014]    Preferably, the second part is defined by forming stepped portions in both main faces of the first board; and the second board is disposed on each of the stepped portion.  
           [0015]    In such a configuration, since two of the second boards are provided for the single first board, the assembly can be adapted to various circuit configurations. Especially in a case where circuits to be connected are arranged in both sides facing the main faces, such adaptation can be performed efficiently. In a case where the stepped portions are formed symmetrically with regard to the thickness direction of the first board, the assembly can be obtained with good balance.  
           [0016]    Here, it is preferable that the second board disposed on one of the stepped portion is fixed on another board on which electric wires are wired.  
           [0017]    In such a configuration, at the same time when the two boards for wiring electric wires are stacked, the second board on one wiring board is disposed on one of the stepped portions of the other wiring board. Since the other second board is disposed in advance in the other stepped portion of the other wiring board, the two of the second boards can be arranged at the same time when both the wiring boards are stacked. Therefore, a work for electrical connection between the first board and the second board by press-fitting or welding can be simplified. After the connection has been finished, both the wiring boards are stacked.  
           [0018]    Preferably, the second board has a third thickness which is determined such that an additional thickness of the second thickness and the third thickness is not greater than the first thickness.  
           [0019]    In such a configuration, not only the circuit board assembly can be made compact in the direction of thickness, but other components such as other circuit boards, covers, electronic control units can be disposed on a same plane without a clearance or with a slight clearance, across the first board and the second board. Moreover, since the circuit board assembly has no protuberance both on the main faces, the circuit board assembly can be smoothly mounted into the cover of the electric junction box, thus enhancing assembling workability.  
           [0020]    Preferably, the second board is formed with grooves for receiving the bus bars.  
           [0021]    In such a configuration, the bus bars can be positioned and arranged easily and accurately, and at the same time, the thickness of the second board including the bus bars can be reduced. Moreover, since the bus bars are insulated from one another by the grooves, additional insulating means is not necessary.  
           [0022]    Preferably, the electric wires and the bus bars are electrically connected.  
           [0023]    In such a configuration, the first board and the second board are connected to each other, and the circuit board assembly which is integral in both electrical and structural aspects can be formed. For example, by employing press-fitting terminals as terminals of the bus bars, connection between the electric wires and the terminals, that is, interconnection between the boards becomes easy and efficient. Large electric current such as a power source flows by way of the bus bars, and small or middle electric current such as a signal flows by way of the electric wires.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0025]    [0025]FIG. 1 is an exploded upper perspective view showing a circuit board assembling structure according to one embodiment of the invention;  
         [0026]    [0026]FIG. 2 is an exploded lower perspective view showing the circuit board assembling structure; and  
         [0027]    [0027]FIG. 3 is an exploded perspective view showing a conventional circuit board assembling structure. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    One embodiment of the invention will be described below in detail referring to the accompanying drawings.  
         [0029]    As shown in FIGS. 1 and 2, a circuit board assembling structure according to the invention includes a plurality of (two sheets in this embodiment) wiring circuit boards  1 ,  2 , two sheets of bus bar circuit boards  5 ,  6  disposed in stepped parts  3 ,  4  which are respectively formed on an upper face and a lower face of the lower wiring circuit board  1 , and a plurality of (two sheets) bus bar circuit boards  8  which are stacked on the upper wiring circuit board  2  by way of a base board  7 . This circuit board assembling structure is particularly characterized in that the two sheets of the bus bar circuit boards  5 ,  6  are disposed within a range of thickness of the lower wiring circuit board  1 .  
         [0030]    The lower wiring circuit board  1  has the stepped parts  3 ,  4  on both upper and lower faces in a forward half area, as shown in FIG. 2 (as seen from the bottom), thereby to form a thinned part  9  at the middle in a direction of thickness of the wiring circuit board  1 . The bus bar circuit boards  5 ,  6  are disposed on both upper and lower faces of the thinned part  9  (FIG. 1).  
         [0031]    A thickness of the bus bar circuit boards  5 ,  6  which have the same thickness is equal to or smaller than a depth of the step, and the total thickness of the thin-walled part  9  and the bus bar circuit boards  5 ,  6  is equal to or smaller than a thickness of other part  10  (see FIG. 2) in a rear half of the wiring circuit board  1 . Accordingly, respective outer faces of the bus bar circuit board  5 ,  6  are not protruded from the upper and lower faces of the wiring circuit board  1  (see FIG. 1).  
         [0032]    Both the upper and lower faces of the thinned part  9  are preferably reinforced with grid-shaped ribs (not shown) while reducing the weight thereof.  
         [0033]    Therefore, the upper wiring circuit board  2  is stacked on the lower wiring circuit board  1  without clearance, and components such as a lower cover, an electronic control unit, etc. (not shown) can be arranged below the lower wiring circuit board  1  without clearance, or with a slight clearance. Therefore, the space saving can be attained.  
         [0034]    As shown in FIG. 1, each of the wiring circuit boards  1 ,  2  in the respective layers includes a case  11  made of insulative resin, and a plurality of electric wires  12  which are arranged in desired shapes and connected at press-fitting portions  14  of terminals  13 . The case  11  is formed in a flat shape having at least a frame-shaped vertical peripheral wall  16  and a horizontal bottom wall  17 .  
         [0035]    The terminals  13  of the wiring circuit boards  1 ,  2 , to which the electric wires  12  are press-fitted, are fixed inside frame-shaped retaining walls  18  in the case  11 . Tab-shaped or pin-shaped contact portions  15 ,  19  of the terminals  13  project to an opposite side to the press-fitting portions  14 . For example, the tab electric contact portions  15  are contained in connector housings of a main cover (not shown) located on the upper wiring circuit board  2 , and the pin-shaped contact portions  19  are passed through the lower wiring circuit board  1  to be connected to the electronic control unit (not shown). A manner of arranging the electric wires  12  and positioning the terminals  13  on the wiring circuit boards  1 ,  2  in the upper and lower layers can be appropriately determined according to the specification of the circuits.  
         [0036]    As shown in FIG. 2, each of the upper and lower bus bar circuit boards  5 ,  6  includes an insulative substrate  20  made of synthetic resin, and bus bars  21  made of conductive metal in various shapes and arranged on the insulative substrate  20 . The insulative substrate  20  is formed with grooves  22  having a same depth as a thickness of the bus bars  21 . The bus bars  21  are positioned and received in the grooves  22 , and insulated from one another by partitions (represented also by numeral  20 ) between the grooves  22 . The bus bars  21  have clamping terminals  24  for connecting fuses, press-fitting terminals  25  for connecting the electric wires, and tab terminals  26  adapted to be contained in the connector housings, relay mounting parts and so on of the cover (not shown).  
         [0037]    The clamping terminals  24  are horizontally projected from front edges of the wiring circuit boards  1 ,  2 , and received in a fuse block  27  as shown in FIG. 1. As shown in FIG. 2, the clamping terminals  24  are vertically bent along the front end face of the wiring circuit board  1  from the bus bar circuit board  5  in the lower layer, and horizontally projected in a forward direction. The clamping terminals  24 , which are projected from the bus bar circuit board  6  in the upper layer, are aligned on a same plane as a lower face of the insulative substrate  20 , that is, aligned with the clamping terminals  24  of the bus bar circuit board  5  in the lower layer.  
         [0038]    The press-fitting terminals  25  of the bus bars  21  are extended toward the electric wires  12  of the wiring circuit boards  1 ,  2 , as shown in FIG. 2, and press-fitted to the electric wires  12  provide inside the retaining walls  18  of the cases  11 . Press-fitting of the electric wires  12  is conducted after the lower bus bar circuit board  5  has been mounted on a bottom face of the lower wiring circuit board  1  (an upper side in FIG. 2), as shown in FIG. 2.  
         [0039]    The upper bus bar circuit board  6  is mounted on a bottom face of the upper wiring circuit board  2 . Pressure fitting of the electric wires  12  is conducted in this state. After the electric wires  12  in the respective layers are press-fitted, the wiring circuit boards  1 ,  2  in both the layers are stacked (assembled) on each other, while the upper bus bar circuit board  6  is received in the stepped part  4  at an upper side of the lower wiring circuit board  1 . The bus bar circuit boards  5 ,  6  are respectively fixed to the wiring circuit boards  1 ,  2 , by press fitting the electric wires  12  to the press-fitting terminals  25 .  
         [0040]    As shown in FIG. 2, positions and shapes of boundaries  28  between the bus bar circuit boards  5 ,  6  and the wiring circuit boards  1 ,  2  are appropriately set, according to pressure fitting positions of the electric wires  12  to the bus bars  21 , layouts of the bus bars  21  and so on. The lower wiring circuit board  1  has short support posts  29  which serve to support the electronic control unit (not shown) and to fix the unit thereon with screws. The bus bar circuit boards  5 ,  6  have holes  30  allowing the support posts  29  to pass through. The holes  30  and the support posts  29  serve also as members for positioning the bus bar circuit boards  5 ,  6  with respect to the wiring circuit boards  1 ,  2 .  
         [0041]    In this embodiment, a plurality of (two sheets) of the bus bar circuit boards  8  are also provided on the upper face of the upper wiring circuit board  2  by way of the base plate  7 , as shown in FIG. 1. Electronic components (not shown), for example, are disposed in an inner space of the base plate  7 , and connected to the electric wires  12  and so on. It is also possible to provide the bus bar circuit boards  8  directly on the upper face of the upper wiring circuit board  2 , while omitting the base plate  7  and the electronic components.  
         [0042]    Each of the bus bar circuit boards  8  has clamping terminals  31 . continued from bus bars  32  as well as the bus bar circuit boards  5 ,  6 . The clamping terminals  31  are thus arranged in two upper and lower rows. In correspondence with the clamping terminals  24  arranged in a row, a bus bar  34  having clamping terminals  33  laterally arranged in a row is disposed in advance in the fuse block  27  (FIG. 1). The clamping terminals  24 ,  31 ,  33  in four rows are composed of the bus bars  21 ,  32 ,  34 . Fuses  36  are contained in chambers  35  arrayed in two upper and lower rows in the fuse block  27 , and a pair of upper and lower tab terminals  37  of the fuses  36  are clamped for connection by the clamping terminals  24 ,  31 ,  33  in the respective rows.  
         [0043]    The fuse block  27  is joined to a circuit board assembly  37  which includes the wiring circuit boards  1 ,  2  and the bus bar circuit boards  5 ,  6 ,  8 , in a direction of an arrow shown in FIG. 1. At the same time, a side terminal  38  of the bus bar  34  in the fuse block  27  comes into contact with a side terminal  39  of the bus bar  32  of the bus bar circuit board  8 . Both the terminals  38 ,  39  are connected by welding or by other means.  
         [0044]    A sub assembly  40  which is composed of the circuit board assembly  37  and the fuse block  27  is covered for protection with the main cover and the lower cover (not shown), and the electronic control unit (not shown) is mounted outside the lower cover, thereby to constitute the electric junction box. The bus bars  21  of the bus bar circuit board  5 ,  6  are connected to the fuses  36  by way of the clamping terminals  24 , to the relays and the connectors of the exterior wire harnesses by way of the tab terminals  26 , and to the connectors of the exterior wire harnesses and the electronic control unit (not shown) by way of the press-fitting terminals  25 , the electric wires  12  and the terminals  15 ,  19 .  
         [0045]    Incidentally, it is possible to omit the upper wiring circuit board  2  and the bus bar circuit board  8  mounted thereon, and to connect the fuses  36  laterally arranged in a single row by the lower wiring circuit board  1  and two sheets of the bus bar circuit boards  5 ,  6 . The stepped portion formed on the wiring circuit board  1  may be single so that a single bus bar circuit board is attached.  
         [0046]    Moreover, positions, numbers, etc. of the tab terminals  26 , the clamping terminals  24 , and the press-fitting terminals  25  of the bus bar circuit boards  5 ,  6 , and positions, numbers, etc. of the terminals  13  of the wiring circuit boards  1 ,  2  can be appropriately determined according to the specifications of the circuits. Further, it is possible to form terminals to be connected to the electric wires  12  by soldering, welding or press-fitting and so on, in place of the press-fitting terminals  25  of the bus bars  21 .  
         [0047]    It is also possible to omit the electronic control unit in constituting the electric junction box. It is also possible to form terminals for connecting relays or terminals for connecting connectors, in place of the clamping terminals  24  for connecting the fuses. Further, directivity of the upper layer and the lower layer can be appropriately changed according to a manner of installing the electric junction box. Further, the circuit board assembling structure according to the invention can be applied as the circuit board assembly for various appliances, a control panel, etc., besides the electric junction box.