Abstract:
For protecting a sensitive electric device, a motor vehicle is constructed to have an electric device protecting structure near a dash panel to which a cowl box is connected. A watertight case installs therein the sensitive electric device and is installed in the cowl box. A passage structure is provided to establish an air flow communication between an interior of the watertight case and an interior of a passenger room.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to an electric device protecting structure for use in a motor vehicle, and more particularly to a watertight casing structure for protecting an electric device. More specifically, the present invention is concerned with an electric device protecting structure by which a sensitive electric device installed therein is protected from being affected by abnormal temperature, abnormal humidity and dusts. 
     2. Description of the Prior Art 
     In a motor vehicle, various electric devices are mounted, some of which are arranged in an engine room. However, since the engine room has therein an engine serving as a heat generator and is exposed to the outside through its opened bottom, the environment in the engine room is not suitable for such electric devices. Thus, in case of very sensitive electric devices which are for example an engine control module (ECM) or the like, it is usual to provide in the engine room so-called electric device protecting structures which house therein the electric devices. 
     FIG. 4 shows one known example of such electric device protecting structures, which is disclosed in Japanese Patent First Provisional Publication 9-207691. In the protecting structure of this example, there is employed a measure for protecting the electric device from heat generated from the engine. That is, a double wall casing structure  4  is provided at a certain position of the engine room, which comprises an inner case  1  and an outer case  2  between which an air flow passage  3  is defined. The air flow passage  3  is connected through a pipe or the like to an outside air intake opening exposed to the outside of the vehicle. An engine control module  5  which is sensitive to heat is installed in the inner case  1 . When the vehicle runs, outside air is forced to flow in the air flow passage  3  while cooling the engine control module  5  in the inner case  1 . 
     FIG. 5 shows another known example of the electric device protecting structures, which is disclosed in Japanese Patent First Provisional Publication 8-99590. That is, in this example, a heat sensitive electric control device  7  is installed in a cowl box  6  that is provided at an upper part of the engine room. Due to its isolated structure, the interior of the cowl box  6  is less affected by heat in the engine room and thus the interior is a suitable place for protecting the electric control device  7  from heat of the engine room. However, since the interior of the cowl box  6  is substantially exposed to the outside through openings and thus easily collects rainwater and the like, the electric control device  7  is constructed to have a sealed structure. 
     However, due to their inherent constructions, the above-mentioned two known examples have failed to provide users with satisfaction because of the following reasons. In the first example of FIG. 4, due to provision of the double wall structure, the protecting structure is bulky in size and thus largely occupies the limited space of the engine room. In the second example of FIG. 5, the sealed structure tends to lose its sealing ability quickly. That is, when energized, the electric control device  7  generates heat and thus heats the air in the sealed structure, and when deenergized, the electric control device  7  stops generating heat and thus cools the air in the sealed structure. The ON/OFF operation of the electric control device  7  thus induces expansion and contraction of air in the sealed structure causing higher pressure and lower pressure in the sealed structure. This phenomenon however applies the sealed structure with repeated stress. Thus, when the sealed structure is left in such severe condition, the sealing ability of the sealed structure becomes poor quickly. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an electric device protecting structure which is free of the above-mentioned drawbacks. 
     According to a first aspect of the present invention, there is provided an electric device protecting structure for use in a motor vehicle. The vehicle has an engine room and a passenger room which are separated by a dash panel and a cowl box which is supported by the dash panel while projecting into the passenger room. The electric device protecting structure comprises a watertight case substantially installed in the cowl box, the watertight case having a sensitive electric device hermetically installed therein; and a passage structure which establishes an air flow communication between an interior of the watertight case and an interior of the passenger room. 
     According to a second aspect of the present invention, there is provided an electric device protecting structure for use in a motor vehicle. The motor vehicle has an engine room and a passenger room which are separated by a dash panel and a cowl box which is supported by the dash panel while projecting into the passenger room. The electric device protecting structure comprises a watertight case held by the dash panel, the watertight case including a major part installed in the cowl box and a base part projected into the engine room, the major part having therein a sensitive electric device installed therein; an opening formed in the base part for passing therethrough a wire harness of the electric device to the engine room; a sleeve having one end connected to the opening and extending obliquely downward; and a passage structure which establishes an air flow communication between an interior of the watertight case and an interior of the passenger room. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an electric device protecting structure which is a first embodiment of the present invention; 
     FIG. 2 is a perspective view of the electric device protecting structure of the first embodiment, which is viewed from the engine room; 
     FIG. 3 is a sectional view of an electric device protecting structure which is a second embodiment of the present invention; 
     FIG. 4 is a sectional view of a known electric device protecting structure; and 
     FIG. 5 is a partially broken view of a vehicle body, showing another known electric device protecting structure. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to FIGS. 1 and 2, there is shown an electric device protecting structure  100  which is a first embodiment of the present invention. The structure  100  is arranged in association with a dash panel and a cowl box of a motor vehicle. 
     In FIGS. 1 and 2, particularly FIG. 1, denoted by numeral  11  is a dash panel by which an engine room  12  and a passenger room  13  are separated from each other. The dash panel  11  is provided at its upper portion with a cowl box  14  which is projected into the passenger room  13  while extending transversely. Denoted by numeral  15  is a top panel which covers the cowl box  14 . The cowl top panel  15  is formed with a plurality of slots  16  through which outside air is led into the cowl box  14 . Although not shown in the drawing, the cowl box  14  is formed with an air outlet port through which the outside air is led to an outside air inlet port of an air conditioning device. 
     Projected into the cowl box  14  through an opening  11 A formed in the dash panel  11  is an electric device unit  17  such as engine control module or the like, which is held by the dash panel  11  and the cowl box  14 . The electric device unit  17  generally comprises an electric device  20  and a watertight case  18  which tightly houses therein the electric device  20 . A lower wall of the watertight case  18  is equipped with a heat insulating sheet  34  for putting thereon the electric device  20 . Preferably, the heat insulating sheet  34  is made of ethylene propylene dien monomer (EPDM) in view of its satisfied heat resistance, thermal conductivity and hygroscopicity. 
     The watertight case  18  comprises an upper shell  18 A and a lower shell  18 B which are coupled together with a watertight packing  19  hermetically interposed therebetween. A wire harness  21  of the electric device  20  extends to the engine room  12  through a harness pull-out opening  22  formed in the case  18  and a sleeve  23  connected to the harness pull-out opening  22 . As shown, the sleeve  23  has a leading end directed obliquely downward, so that entering of water into the interior of the watertight case  18  through the sleeve  23  is avoided. 
     As is seen from FIGS. 1 and 2, the electric device unit  17  is held in the opening  11 A having a major part  17 A thereof placed in the cowl box  14  and a base part  17 B thereof projected into the engine room  12 . The major part  17 A of the unit  17  is secured to the cowl box  14  through a bracket  24 A and bolts and the base part  17 B of the unit  17  is secured to the dash panel  11  through brackets  24 B and bolts  26 . As is seen from FIG. 1, the harness pull-out opening  22  is formed in the base part  17 B of the electric device unit  17 . 
     As is seen from FIG. 1, the base part  17 B of the unit  17  has a wall thicker than that of the major part  17 A. Due to provision of such thicker wall of the base part  17 A, sound transmission from the engine room  12  to the interior of the unit  17  is minimized. 
     As is seen from FIGS. 1 and 2, the base part  17 B of the unit  17  is formed at its lower wall with a hose connecting opening  25  to which an upper part  27 A of a bellows type hose  27  is connected. A lower part  27 B of the hose  27  is hermetically connected to an opening  28  formed in the dash panel  11 . For this hermetical connection, an annular groove  29  formed around the lower part  27 B snugly receives a peripheral edge of the opening  28 , as shown. 
     The lower part  27 B of the hose  27  is integrally formed with a sleeve portion  31  through which another wire harness  30  passes for being led into the passenger room  13 . The interior  27 C of the hose  27  and the interior  31 A of the sleeve portion  31  are partitioned by a partition wall  31 B. That is, the interior  27 C of the hose  27  and the interior  31 A of the sleeve portion  31  are isolated from each other. 
     As is seen from FIG. 1, a sound insulating layer  32  is bonded to the dash panel  11  from the passenger room  13 . The insulating layer  32  is formed with an opening  32 C in which the lower end  27 B of the hose  27  is received. The insulating layer  32  comprises a first layer  32 A of air permeable insulating material such as cotton or the like and a second layer  32 B of insulation sheet such as rubber sheet or the like. The opening  32 C of the insulating layer  32  is covered with a sound insulating pad  33  made of foamed polyurethane or the like. 
     It is thus to be noted that the interior of the electric device unit  17 , more specifically, the interior of the watertight case  18  is fluidly communicated with the interior of the passenger room  13  through the hose  27  and the air permeable first layer  32 A of the insulating layer  32 . 
     In the following, advantages of the electric device protecting structure  100  of the first embodiment will be described. 
     First, as is described hereinabove, the major part  17 A of the electric device unit  17  is installed in the cowl box  14 . Accordingly, it often occurs that the major part  17 A gets wet with rainwater or the like. However, the watertight case  18  of the unit  17  protects the electric device  20  from such water. That is, the sleeve  23  and the watertight packing  19  applied to the case  18  improve the waterproof of the case  18 . 
     Second, the interior of the watertight case  18  is fluidly communicated with the passenger room  13  through the hose  27 . Thus, even when electric device  20  is energized and deenergized, undesired repetition of higher and lower pressure does not occur in the watertight case  18 . That is, if, due to heat generation from the device  20 , the pressure in the case  18  is about to increase, the same is instantly led to the passenger room  13  through the hose  27 , and if, due to OFF condition of the device  20 , the pressure in the case  18  is about to decrease, the pressure of the passenger room  13  is instantly led into the case  18  through the hose  27 . Accordingly, the sealing ability of the watertight case  18  is kept for a long time. That is, the durability of watertight case  18  is increased. 
     Third, the interior of the watertight case  18  is communicated with only the passenger room  13  of which air is relatively clean as compared with the outside air. Accordingly, the electric device  20  in the case  18  is protected from contamination. This assures reliable operation of the electric device  20 . 
     Fourth, for mounting thereon the electric device  20 , the lower wall of the watertight case  18  is equipped with the heat insulating sheet  34 . Thus, the lower wall is protected from collecting dew drops thereby assuring reliable operation of the electric device  20 . 
     Fifth, the hose  27  is of a bellows type and thus can be easily flexed and bent. Thus, freedom of positioning of the watertight case  18  and the opening  28  of the dash panel  11  increases. That is, the electric device protecting structure  100  is equally applicable to both a vehicle having a steering wheel at a left side and a vehicle having the steering wheel at a right side. 
     Sixth, the base part  17 B of the electric device unit  17  has a thicker wall, and the sound insulating layer  32  and the sound insulating pad  33  are attached to the dash panel  11 . Thus, the passenger room  13  is sufficiently insulated from noises generated in the engine room  12 . 
     Referring to FIG. 3, there is shown an electric device protecting structure  200  which is a second embodiment of the present invention. 
     Since the structure  200  of the second embodiment is similar to the structure  100  of the above-mentioned first embodiment, only portions which are different from those of the first embodiment  100  will be described in detail in the following. 
     As shown in the drawing, in this second embodiment  200 , in place of the hose ( 27 ) used in the first embodiment  100 , a piping structure  50  is used for establishing the fluid communication between the interior of the watertight case  18  and the passenger room  13 . 
     The piping structure  50  comprises a pipe  35  integrally formed on a back wall of the watertight case  18 . A cylindrical rubber seal  38  is intimately put in the pipe  35  having an enlarged head thereof projected from the pipe  35 . A bottom wall  14 A of the cowl box  14  is formed, at a position facing the pipe  35 , with an opening  37 . In assembly, the pipe  35  abuts against a periphery of the opening  37  with the projected head of the seal  38  compressed therebetween. 
     In the second embodiment  200 , both the upper and lower walls of the watertight case  18  are equipped with heat insulating sheets  34  respectively. 
     Because of the similar structure to the first embodiment  100 , the electric device protecting structure  200  of the second embodiment can have the same advantages as those of the first embodiment  100  except the fifth advantage brought by the hose ( 27 ). In addition to such advantages, the structure  200  of the second embodiment can be made compact in size due to usage of the compact piping structure  50 . 
     The entire contents of Japanese Patent Application P10-293662 (filed Oct. 15, 1998) are incorporated herein by reference. 
     Although the invention has been described above with reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Various modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings.