Patent Publication Number: US-11031761-B2

Title: Resin structure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2019-044087 filed on Mar. 11, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a resin structure. 
     Description of Related Art 
     A resin structure including a plurality of resin bodies assembled to each other such as a relay box (an electric connection box) mounted on a vehicle is widely known in the related art.
     [Patent Literature 1] JP-A-2017-022824   

     In the resin structure described above, a gap may occur in alignment portions between the resin bodies assembled to each other due to relative movement (backlash) between the resin bodies. Accordingly, in a case of high pressure cleaning of blowing water to such a resin structure from outside (hereinafter, simply referred to as “high pressure cleaning”), water is likely to enter the resin structure through the gap. When water entering the resin structure has a large flow velocity, the water may splash on inner surfaces of a bottom wall and a side wall of the resin structure and contact an electronic component such as a relay provided on an upper side in the resin structure. It is desirable to prevent such splashing of water. 
     SUMMARY 
     One or more embodiments provide a resin structure capable of preventing splashing of water entering the resin structure via a gap between resin bodies assembled to each other. 
     In an aspect (1), one or more embodiments provide a resin structure including a first resin body having an annular first side wall portion, a second resin body having a second side wall portion, and a third resin body having a bottom wall portion and an annular third side wall portion connected to the bottom wall portion. The second resin body is assembled to the first resin body, such that an upper edge of the second side wall portion and at least a portion of an annular lower edge of the first side wall portion in a circumferential direction are aligned. The third resin body is assembled to the second resin body, such that an annular upper edge of the third side wall portion and at least a lower edge of the second side wall portion are aligned. The third resin body includes a prevention mechanism that prevents flow of water entering an internal space defined by the bottom wall portion and the third side wall portion via a gap between the annular lower edge of the first side wall portion and the upper edge of the second side wall portion or a gap between the lower edge of the second side wall portion and the annular upper edge of the third side wall portion. 
     In an aspect (2), the prevention mechanism may be a rib protruding upward from an inner surface of the bottom wall portion in the internal space. 
     In an aspect (3), the second resin body may include a plate-shaped protrusion protruding from an inner surface of the second side wall portion toward inside of the resin structure and located above the rib. 
     In an aspect (4), the second resin body may be assembled to the first resin body such that the upper edge of the second side wall portion and a portion of the annular lower edge of the first side wall portion in the circumferential direction are aligned. The third resin body may be assembled to the first resin body and the second resin body such that the annular upper edge of the third side wall portion and an annular lower edge including a part other than the portion of the annular lower edge of the first side wall portion in the circumferential direction and the lower edge of the second side wall portion are aligned. 
     According to the aspect (1), a resin structure has a structure in which the second side wall portion is interposed between the first side wall portion and the third side wall portion. Accordingly, relative movement (backlash) is likely to occur between the first side wall portion and the second side wall portion and between the second side wall portion and the third side wall portion. Therefore, gaps due to the relative movement (backlash) are likely to occur in the alignment portion between the first side wall portion and the second side wall portion or the alignment portion between the second side wall portion and the third side wall portion. When high pressure cleaning is performed to the resin structure, water is likely to enter the internal space defined by the bottom wall portion and the third side wall portion of the third resin body via such gaps. When water entering the inner space has a large flow velocity, the water may splash on inner surfaces of the bottom wall portion and the third side wall portion and contact components or the like provided on an upper side in the resin structure. 
     According to the aspect (1), the prevention mechanism is provided in the third resin body in order to cope with this problem. Accordingly, the flow of water entering the internal space can be prevented by the prevention mechanism. Therefore, the entering water can be prevented from splashing on the inner surfaces of the bottom wall portion and the third side wall portion and the waterproof property for the components provided on the upper side in the resin structure can be enhanced. 
     In the aspect (1), another aspect in addition to the aspect (4) may also be included, in which the second resin body is assembled to the first resin body such that the annular upper edge of the annular second side wall portion and the annular lower edge of the first side wall portion are aligned, and the third resin body is assembled to the second resin body such that the annular upper edge of the third side wall portion and the annular lower edge of the annular second side wall portion are aligned. 
     According to the aspect (2), water entering the inner surface of the bottom wall portion in the internal space collides with the rib so that the water flow can be prevented. As a result, the flow of water entering the inner surface of the bottom wall in the internal space can be effectively prevented with a simple configuration. 
     According to the aspect (3), splashing water above the rib due to the collision with the rib collides with the protrusion of the second resin body so that the water can be prevented from moving upward further from the protrusion. As a result, the waterproof property for the components or the like located above the protrusion of the second resin body can be enhanced. 
     According to the aspect (4), the second side wall portion is interposed between the first side wall portion and the third side wall portion only in a portion of the resin structure in the circumferential direction and the first side wall portion and the third side wall portion are directly assembled in a portion other than the portion of the resin structure in the circumferential direction. Therefore, water may enter the internal space from outside only in this portion in the circumferential direction via a gap in the alignment portion between the first side wall portion and the second side wall portion or the alignment portion between the second side wall portion and the third side wall portion. Also in this structure, according to the present invention, the flow of water entering the internal space via the gap can be prevented by the prevention mechanism and the entering water can be prevented from splashing to the inner surface of the third side wall portion from the inner surface of the bottom wall portion. 
     According to one or more embodiments, it is possible to provide a resin structure capable of preventing splashing of water entering the resin structure via a gap between resin bodies assembled to each other. 
     The present invention is briefly described above. Details of the present invention will be clarified by reading a mode for carrying out the present invention described below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a resin structure according to an embodiment. 
         FIG. 2  is a perspective view of the resin structure in which only a first upper cover and a second upper cover are disassembled. 
         FIG. 3  is an enlarged perspective view of a front end portion of a frame. 
         FIG. 4  is a perspective view of an under cover. 
         FIG. 5  is a plan view of the under cover. 
         FIG. 6  is a perspective view of a lower cover. 
         FIG. 7  is an enlarged plan view of a front end portion of the lower cover. 
         FIG. 8  is a perspective view showing a state in which the frame, the under cover, and the lower cover are assembled to each other. 
         FIG. 9  shows a positional relationship between a rib of the lower cover and a protrusion of the under cover. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiment 
     Hereinafter, a resin structure  1  according to an embodiment of the present invention shown in  FIG. 1  will be described with reference to the drawings. The resin structure  1  is typically a relay box (an electric connection box) that is mounted on a vehicle and accommodates electronic components such as a relay. Hereinafter, “from-rear direction”, “width direction”, “up-lower direction”, “front”, “rear”, “upper”, and “lower” are defined as is shown in  FIG. 1  for convenience of description. The “front-rear direction”, the “width direction”, and the “upper-lower direction” are orthogonal to one another. When the resin structure  1  is mounted on the vehicle, the “font-rear direction”, the “width direction”, and the “upper-lower direction” correspond to the front-rear direction, the width direction, and the upper-lower direction of the vehicle, respectively. 
     As shown in  FIGS. 1 and 2 , the resin structure  1  includes a frame  2 , a first front cover  3  and a second front cover  4  assembled above a front end portion of the frame  2 , a first upper cover  5  assembled above the frame  2  to block an upper opening of a rear region of the frame  2 , a second upper cover  6  assembled above the frame  2  and the first front cover  3  to block an upper opening of a front region of the frame  2  and the first front cover  3 , an under cover  7  assembled below the front end portion of the frame  2 , a lower cover  8  assembled below the frame  2  and under cover  7  to block lower openings of the frame  2  and the under cover  7 , and a side cover  9  assembled to an outer surface (a side surface) of the frame  2  on its one side in the width direction. All the eight components constituting the resin structure  1  are resin molded bodies. 
     As shown in  FIG. 2 , electronic components (and other components) R such as a relay are accommodated inside the frame  2  and the first front cover  3  (and the second front cover  4 ). The present invention relates to structures of the frame  2 , the under cover  7 , and the lower cover  8  of the resin structure  1 . Accordingly, only the structures of the frame  2 , the under cover  7 , and the lower cover  8  will be described in detail below. 
     The frame  2  will be described first. As shown in  FIGS. 1 to 3 , the frame  2  includes an annular side wall portion  11  constituting most of the appearance of a side surface of the resin structure  1 . The side wall portion  11  is integrally provided with a locking portion  12  on outer surfaces of a plurality of positions (three positions in the present embodiment) on a front end portion of a lower end portion of the side wall portion  11 . The locking portion  12  has a through hole extending in the upper-lower direction. The locking portion  12  has a function of assembling the under cover  7  to the frame  2 . 
     The side wall portion  11  is integrally provided with a locking portion  13  on outer surfaces of a plurality of positions (eight positions in the present embodiment) on the lower end portion of the side wall portion  11  in the circumferential direction. The locking portion  13  has a through hole extending in the upper-lower direction. The locking portion  13  has a function of assembling the lower cover  8  to the frame  2 . 
     As shown in  FIG. 3 , the side wall portion  11  is provided with a rectangular concave portion  14  on an outer surface of one position on the lower end portion of the side wall portion  11 . The concave portion  14  is recessed and opened in the thickness direction of the side wall portion  11 . The concave portion  14  has a function of fitting and locking a distal end portion of an extension piece  35  of the lower cover  8  described below. 
     Next, the under cover  7  will be described. As shown in  FIGS. 4 and 5 , the under cover  7  includes a side wall portion  21 . An upper edge of the side wall portion  21  has a shape corresponding to a front end portion (a portion in the circumferential direction) of an annular lower edge of the side wall portion  11  of the frame  2 . The side wall portion  21  is integrally provided with a flat plate-shaped protrusion  22  protruding in the horizontal direction from an inner surface of the side wall portion  21  toward the inside of the resin structure  1 . 
     The side wall portion  21  is integrally provided with a locking piece  23  extending upward on outer surfaces of a plurality of positions (three positions in the present embodiment) on an upper end portion of the side wall portion  21  in the circumferential direction. The locking piece  23  has a function of assembling the under cover  7  to the frame  2 . 
     The side wall portion  21  is integrally provided with a locking portion  24  on an outer surface of one position on a lower end portion of the side wall portion  21 . The locking portion  24  has a through hole extending in the upper-lower direction. The locking portion  24  has a function of assembling the lower cover  8  to the under cover  7 . 
     The side wall portion  21  is integrally provided with a holding portion  25  on an outer surface of another position on the lower end portion of the side wall portion  21 . The holding portion  25  has a through hole  26  extending in the upper-lower direction. The holding portion  25  has a function of holding the extension piece  35  of the lower cover  8 . The holding portion  25  is provided with a locking claw  27  that locks a locking step portion  36  provided on the extension piece  35  of the lower cover  8  described below. 
     The under cover  7  has a semi-cylindrical groove  28  opened downward at a lower end portion thereof. The groove  28  has a function of constituting an upper part of an inner wall defining an insertion hole H (see  FIGS. 1 and 8 ) through which electric wires (not shown) led out from the inside of the resin structure  1  are inserted. 
     Next, the lower cover  8  will be described. As shown in  FIGS. 6 and 7 , the lower cover  8  integrally includes an annular side wall portion  31  constituting most of the appearance of a lower side surface of the resin structure  1 , and a bottom wall portion  32  constituting most of the appearance of a bottom surface of the resin structure  1 . The bottom wall portion  32  blocks an annular lower opening of the side wall portion  31 . 
     An annular upper edge of the side wall portion  31  has a shape corresponding to an annular lower edge constituted by (i) a part other than the front end portion (the portion in the circumferential direction), to which the under cover  7  is assembled, of the annular lower edge of the side wall portion  11  of the frame  2  and (ii) a lower edge of the under cover  7 . 
     The bottom wall portion  32  has a shape inclined upward from front to rear. Accordingly, an inner surface of the bottom wall portion  32  also has a shape inclined upward from front to rear. 
     The side wall portion  31  is integrally provided with a locking piece  33  extending upward on outer surfaces of a plurality of positions (eight positions in the present embodiment) on an upper end portion of the side wall portion  31  in the circumferential direction. The locking piece  33  has a function of assembling the lower cover  8  to the frame  2 . 
     The side wall portion  31  is integrally provided with a locking piece  34  extending upward on an outer surface of one position on a front end portion of the upper end portion of the side wall portion  31 . The locking piece  34  has a function of assembling the lower cover  1  to the under cover  7 . 
     The side wall portion  31  is integrally provided with the extension piece  35  extending upward on an outer surface of another position on the front end portion of the upper end portion of the side wall portion  31 . As will be described below, the extension piece  35  has a function of holding the under cover  7  in cooperation with the concave portion  14  of the frame  2 . The extension piece  35  includes the locking step portion  36  on an outer surface thereof. The extension height of the extension piece  35  is larger than the protruding height of the locking pieces  33 ,  34 . 
     The lower cover  8  has a semi-cylindrical groove  37  opened upward at an upper end portion of a front end portion thereof. The groove  37  has a function of constituting a lower part of the inner wall defining the insertion hole (see  FIGS. 1 and 8 ) through which electric wires (not shown) led out from the inside of the resin structure  1  are inserted. 
     The bottom wall portion  32  is provided with a plurality of ribs  38  in an internal space defined by the side wall portion  31  and the bottom wall portion  32  at a front end portion of the bottom wall portion  32 . The plurality of ribs  38  protrude upward from the inner surface of the bottom wall portion  32 . In particular, in the present embodiment as is shown in  FIG. 7 , a plurality of ribs  38  extending in the width direction from the side wall portion  31  on one side in the width direction to the other side in the width direction are arranged side by side in the front-rear direction. A plurality of ribs  38  extending in the width direction from the side wall portion  31  on the other side in the width direction to the one side in the width direction are also arranged side by side in the front-rear direction. The function of the ribs  38  will be described below. 
     The bottom wall portion  32  has a water drain hole  39  in a position of the front end portion of the bottom wall portion  32  that does not interfere with the ribs  38 . The water drain hole  39  penetrates in the upper-lower direction. The structures of the frame  2 , the under cover  7 , and the lower cover  8  are described above. 
     Next, procedures for assembling the frame  2 , the under cover  7 , and the lower cover  8  will be described. When assembling the frame  2 , the under cover  7 , and the lower cover  8 , the under cover  7  is first assembled to the frame  2 . To assemble the under cover  7  to the frame  2 , a plurality of locking pieces  23  (see  FIG. 4 ) of the under cover  7  are inserted and locked to through holes of a plurality of locking portions  12  of the frame  2  from below. Accordingly, as shown in  FIG. 8 , the under cover  7  is assembled to the frame  2  such that the upper edge of the side wall portion  21  of the under cover  7  and the front end portion (the portion in the circumferential direction) of the annular lower edge of the annular side wall portion  11  of the frame  2  are aligned. 
     Next, the lower cover  8  is assembled to the frame  2  and the under cover  7 . To assemble the lower cover  8  to the frame  2  and the under cover  7 , the extension piece  35  (see  FIG. 6 ) of the lower cover  8  is first inserted into the through hole  26  (see  FIG. 4 ) of the holding portion  25  of the under cover  7  from below. Next, with the state in which the extension piece  35  is inserted into the through hole  26  (that is, the extension piece  35  is held by the holding portion  25 ) maintained, one locking piece  34  of the lower cover  8  is inserted and locked to a through bole of one locking portion  24  of the under cover  7 , a plurality of locking pieces  33  of the lower cover  8  are respectively inserted and locked to through holes of a plurality of locking portions  13  of the frame  2 , and the locking step portion  36  of the extension piece  35  is locked to the locking claw  27  of the holding portion  25 . In this way, the lower cover  8  can be assembled to the frame  2  and the under cover  7  with the state in which the extension piece  35  is held by the holding portion  25  maintained. Accordingly, this operation can be easily performed. 
     Accordingly, as shown in  FIG. 8 , the lower cover  8  is assembled to the frame  2  and the under cover  7  such that the annular upper edge of the annular side wall portion  31  of the lower cover  8  and the annular lower edge constituted by (i) the part other than the front end portion (the portion in the circumferential direction), to which the under cover  7  is assembled, of the annular lower edge of the side wall portion  11  of the frame  2  and (ii) the lower edge of the side wall portion  21  of the under cover  7  are aligned. Accordingly, the assembly of the frame  2 , the under cover  7 , and the lower cover  8  is completed. 
     When the assembly of the frame  2 , the under cover  7 , and the lower cover  8  is completed (an assembly completed state), as shown in  FIG. 8 , the insertion hole H into which electric wires (not shown) are inserted is defined by the groove  28  of the under cover  7  and the groove  37  of the lower cover  8 . 
     In the assembly completed state, as shown in  FIG. 9 , the protrusion  22  of the under cover  7  is located above a plurality of ribs  38  of the lower cover  8 . A function of the arrangement relationship between the ribs  38  and the protrusion  22  will be described below. 
     The resin structure  1  has a structure in which the under cover  7  is interposed between the frame  2  and the lower cover  8 . Accordingly, relative movement (backlash) is likely to occur between the frame  2  and the under cover  7  and between the under cover  7  and the lower cover  8 . Therefore, gaps due to the relative movement (backlash) may occur in an alignment portion C 1  (see  FIG. 8 ) between the side wall portion  11  and the side wall portion  21  or an alignment portion C 2  (see  FIG. 8 ) between the side wall portion  21  and the side wall portion  31 . When high pressure cleaning is performed to the resin structure  1  from a front side, water is likely to enter the internal space defined by the bottom wall portion  32  and the side wall portion  31  of the lower cover  8  via such gaps. When water entering the inner space has a large flow velocity, the water may splash on inner surfaces of the bottom wall portion  32  and the side wall portion  31  (see white arrows in  FIGS. 6 and 7 ) and contact the electronic components R (see  FIG. 2 ) provided on an upper side in the resin structure  1 . 
     For this reason, the resin structure  1  is provided with the plurality of ribs  38  on an inner surface of the lower cover  8 . Accordingly, water entering the inner surface of the bottom wall portion  32  in the internal space from the front side collides with the plurality of ribs  38  so that the water flow can be prevented. Therefore, the entering water can be prevented from splashing on the inner surfaces of the bottom wall portion  32  and the side wall portion  31  and the waterproof property for the electronic components R provided on the upper side in the resin structure  1  can be enhanced. 
     In addition, splashing water above the ribs  38  due to the collision with the ribs  38  collides with the protrusion  22  of the under cover  7  located above the ribs  38  so that the water can be prevented from moving upward further from the protrusion  22 . As a result, the waterproof property for the electronic components R located above the protrusion  22  of the under cover  7  can be enhanced. The function of the arrangement relationship between the ribs  38  and the protrusion  22  is described above. 
     In the assembly completed state, the distal end portion of the extension piece  35  of the lower cover  8  held by the holding portion  25  of the under cover  7  is locked to the concave portion  14  of the frame  2  by being fitted into the concave portion  14 . In other words, the under cover  7  is held (fixed) at an intermediate portion of the extension piece  35  whose base end portion and distal end portion are fixed by the frame  2  and the lower cover  8 , respectively. Therefore, relative movement (backlash) is less likely to occur between the frame  2  and the under cover  7  and between the under cover  7  and the lower cover  8 , and gaps due to the relative movement (backlash) is less likely to occur in the alignment portion C 1  between the side wall portion  11  of the frame  2  and the side wall portion  21  of the under cover  7  and the alignment portion C 2  between the side wall portion  21  of the under cover  7  and the side wall portion  31  of the lower cover  8 . This makes it less likely for water to enter the resin structure  1  through these gaps. 
     &lt;Functions and Effects&gt; 
     According to the resin structure  1  in the embodiment of the present invention, relative movement (backlash) is likely to occur between the frame  2  and the under cover  7  and between the under cover  7  and the lower cover  8  due to the structure in which the under cover  7  is interposed between the frame  2  and the lower cover  8 . Therefore, gaps due to the relative movement (backlash) may occur in the alignment portion C 1  between the side wall portion  11  and the side wall portion  21  or the alignment portion C 2  between the side wall portion  21  and the side wall portion  31 . When high pressure cleaning is performed to the resin structure  1  from the front side, water is likely to enter the internal space defined by the bottom wall portion  32  and the side wall portion  31  of the lower cover  8  via such gaps. When water entering the inner space has a large flow velocity, the water may splash on the inner surfaces of the bottom wall portion  32  and the side wall portion  31  (see white arrows in  FIGS. 6 and 7 ) and contact the electronic components R provided on the upper side in the resin structure  1 . 
     For this reason, the resin structure  1  is provided with the plurality of ribs  38  on the inner surface of the lower cover  8 . Accordingly, water entering the inner surface of the bottom wall portion  32  in the internal space from the front side collides with the plurality of ribs  38  so that the water flow can be prevented. Therefore, the entering water can be prevented from splashing on the inner surfaces of the bottom wall portion  32  and the side wall portion  31  and the waterproof property for the electronic components R provided on the upper side in the resin structure  1  can be enhanced. 
     In addition, splashing water above the ribs  38  due to the collision with the ribs  38  collides with the protrusion  22  of the under cover  7  located above the ribs  38  so that the water can be prevented from moving upward further from the protrusion  22 . As a result, the waterproof property for the electronic components R located above the protrusion  22  of the under cover  7  can be enhanced. 
     Other Embodiments 
     The present invention is not limited to the above embodiment and various modifications can be adopted within the scope of the present invention. For example, the present invention may be appropriately modified, improved or the like. In addition, materials, shapes, dimensions, numbers, arrangement locations and the like of elements in the above embodiment are optional and not limited as long as the object of the present invention can be achieved. 
     In the above embodiment, the under cover  7  is interposed between the frame  2  and the lower cover  8  only in a portion of the resin structure  1  in the circumferential direction and the frame  2  and the lower cover  8  are directly assembled in a portion other than the portion of the resin structure  1  in the circumferential direction. In contrast, the under cover  7  may be interposed between the frame  2  and the lower cover  8  over the entire circumference of the resin structure  1  in the circumferential direction. In this case, the under cover  7  is assembled to the frame  2  such that the annular upper edge of the side wall portion  21  of the annular under cover  7  and the annular lower edge of the side wall portion  11  of the frame  2  are aliened, and the lower cover  8  is assembled to the under cover  7  such that the annular upper edge of the side wall portion  31  of the lower cover  8  and the annular lower edge of the annular side wall portion  21  are aliened. 
     The above embodiment adopts a plurality of ribs  38  as a “prevention mechanism” of the present invention. In contrast, one rib  38  may be employed as the “prevention mechanism” of the present invention. In addition, the “prevention mechanism” of the present invention may adopt any mechanism other than the “rib” as long as the mechanism has a function of preventing the flow of water entering the internal space defined by the bottom wall portion  32  and the side wall portion  31  of the lower cover  8 . 
     The above embodiment adopts the flat plate-shaped protrusion  22  protruding in the horizontal direction from the inner surface of the side wall portion  21  of the under cover  7  toward the inside of the resin structure  1  as a “protrusion” of the present invention. In contrast, the “protrusion” of the present invention may have any shape and posture as long as the protrusion is located above the rib  38  and protrudes from the inner surface of the side wall portion  21  toward the inside of the resin structure  1 . 
     In the above embodiment, the resin structure  1  is a relay box (an electric junction box) that accommodates a plurality of electronic components R, but the resin structure  1  may have functions other than the relay box (the electric junction box). 
     Here, features of the above embodiment of the resin structure  1  according to the present invention are briefly summarized and listed in the following [1] to [4].
     [1] A resin structure ( 1 ) comprising:   

     a first resin body ( 2 ) having an annular first side wall portion ( 11 ); 
     a second resin body ( 7 ) having a second side wall portion ( 21 ); and 
     a third resin body ( 8 ) having a bottom wall portion ( 32 ) and an annular third side wall portion ( 31 ) connected to the bottom wall portion ( 32 ), 
     wherein the second resin body ( 7 ) is assembled to the first resin body ( 2 ), such that an upper edge of the second side wall portion ( 21 ) and at least a portion of an annular lower edge of the first side wall portion ( 11 ) in a circumferential direction are aligned, 
     wherein the third resin body ( 8 ) is assembled to the second resin body ( 7 ), such that an annular upper edge of the third side wall portion ( 31 ) and at least a lower edge of the second side wall portion ( 21 ) are aligned, and 
     wherein the third resin body ( 8 ) includes a prevention mechanism ( 38 ) that prevents flow of water entering an internal space defined by the bottom wall portion ( 32 ) and the third side wall portion ( 31 ) via a gap between the annular lower edge of the first side wall portion ( 11 ) and the upper edge of the second side wall portion ( 21 ) or a gap between the lower edge of the second side wall portion ( 21 ) and the annular upper edge of the third side wall portion ( 31 ).
     [2] The resin structure ( 1 ) according to [1],   

     wherein the prevention mechanism is a rib ( 38 ) protruding upward from an inner surface of the bottom wall portion ( 32 ) in the internal space.
     [3] The resin structure ( 1 ) according to [2],   

     wherein the second resin body ( 7 ) includes a plate-shaped protrusion ( 22 ) protruding from an inner surface of the second side wall portion ( 21 ) toward inside of the resin structure ( 1 ) and located above the rib ( 38 ). 
     [4] The resin structure ( 1 ) according to any one of [1] to [3], 
     wherein the second resin body ( 7 ) is assembled to the first resin body ( 2 ) such that the upper edge of the second side wall portion ( 21 ) and a portion of the annular lower edge of the first side wall portion ( 11 ) in the circumferential direction are aligned, and 
     wherein the third resin body ( 8 ) is assembled to the first resin body ( 2 ) and the second resin body ( 7 ) such that the annular upper edge of the third side wall portion ( 31 ) and an annular lower edge including a part other than the portion of the annular lower edge of the first side wall portion ( 11 ) in the circumferential direction and the lower edge of the second side wall portion ( 21 ) are aligned. 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
     
         
         
           
               1  resin structure 
               2  frame (first resin body) 
               7  under cover (second resin body) 
               8  lower cover (third resin body) 
               11  side wall portion (first side wall portion) 
               21  side wall portion (second side wall portion) 
               22  protrusion 
               31  side wall portion (third side wall portion) 
               32  bottom wall portion 
               38  rib (prevention mechanism) 
             C 1  alignment portion 
             C 2  alignment portion