Abstract:
An Electronic Control Unit which houses electronic circuit for controlling various devices of vehicles in a sealing case is characterized in that the case has a ventilation hole to communicate an interior and an exterior of the case, the ventilation hole comprises a filter for preventing from entering contaminants from the outside, and a sectional area of the ventilation hole is gradually enlarged toward the interior of the case.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an Electronic Control Unit (hereinafter referred to as the “ECU”), and more particularly to an improved ECU which is installed in an engine room et al. 
   BACKGROUND OF THE INVENTION 
   Generally, the ECU for controlling the driving of various devices such as an electric motor is mounted not only in the interior, but also in the exterior of a car. This ECU is constructed by a case (hereinafter referred to as the “ECU-case”) for housing an electronic circuit (hereinafter referred to as the “ECU-circuit”) constituted by electronic parts such as CPU. The ECU-case consists of an ECU-case body, ECU-case lid covering over the ECU-case body. Harnesses for transmitting various input or output signals, cables leading to power source, and grounded wires are connected to the ECU-circuit. 
   The ECU has a ventilation hole (a vent) in the ECU-case to regulate the pressure within the ECU-case so as to avoid an adverse effect by thermal expansion or contraction of the air within the ECU-case. For example, an opening for penetrating harness leading to the ECU-circuit is provided in the ECU-case. A waterproof grommet is mounted in the opening of the ECU-case to enhance the sealability of the ECU-case. 
   The ECU is provided not only inside the cabin of a car, but also outside the cabin thereof, for example, in various places such as engine room, trunk room, and the like. In case that the ECU is provided, for example, in an engine room, enter of water, dust, and the like into the ECU case may cause of a short circuit of the ECU-circuit. Thus, the ECU-case is subjected to be sealed by filling of the sealing materials such as adhesives in the mated surfaces between the ECU-case body and the ECU-case lid. 
   However, the filling of sealing materials and waterproof grommet is very difficult for the perfect sealing of the ECU-case because of the following reasons. 
   Where self-heating of various electronical parts occur within the ECU-case or temperature of the air within an engine room fluctuate (that is, air temperature increase or decrease), the change in temperature of the air within the ECU-case or the difference in pressure of the air within the ECU-case occur in the air between the interior and the exterior of the ECU-case. 
   Because of the difference in pressure of the air between the interior and exterior of the ECU-case, the contaminants such as water, dust, et al would be often sucked into the ECU-case through the clearance between the waterproof grommet and the harness or through the clearance between the coating of harness and the wire. The difference in pressure of the air between the interior and the exterior of the ECU-case causes the incompleteness of the sealing materials for filling up the clearance such as the mated surface between the ECU-case body and the ECU-case lid. 
   Therefore, various improvements for preventing contaminants such as water, dust, and the like from entering into the ECU-case would be done and disclosed in the conventional patent literatures. 
   As shown in  FIG. 1 , Japanese Patent Laid-Open Publication No. 23636/1998 discloses an ECU constructed by double-hull structure, which the ECU-case body  101  is divided into an inner case  102  and an outer case  103  surrounding the inner case  102 . The ECU-case lid  104  is mounted on the ECU-case body  101 . The clearance of the mated surfaces between the ECU-case body  101  and the ECU-case lid  104  is sealed by packing and the like. The ECU-circuit is housed in the inner case  102  to be connected by a harness  105 . The harness  105  connects the ECU-circuit provided in the inner case  102  through waterproof grommets  106  to the outside device. The waterproof grommets  106  are mounted in the inner case  102  and the outer case  103 . 
   Thus, the waterproof grommet  106  is able to prevent contaminants such as water, dust, and the like from entering into the ECU-circuit in the inner case  102  because the contaminants pass through the waterproof grommet  106  to enter into the ECU-circuit within the ECU-case  102  twice. 
   However, Japanese Patent Laid-Open Publication No. 23636/1998 has a drawback on the ground that the ECU becomes large in size, difficult in assemblage, and costs too much in manufacturing, because of the double-hull structure of the ECU comprising the inner case  102  and the outer case  103 . 
   As shown in  FIG. 2 , Japanese Patent Laid-Open Publication No. 289171/1999 discloses an ECU-case  111  manufactured by the plastics-injection mold and an earth (ground) bus-bar  112  embedded into the ECU-case  111  at the time of being injection-molded. The earth (ground) bus-bar  112  is constructed to form a pair of conductive contacts  112   a ,  112   b  for projecting inwards or outwards from the ECU-case  111 , respectively. As a path between the conductive contacts  112   a ,  112   b  is formed to be electrically conductive in the earth (ground) bus-bar  112 , the both conductive contacts  112   a ,  112   b  are in an electrical conduction each other. Therefore, as the earth (ground) bus-bar  112  is integrally embedded into the ECU-case  111 , the clearance for harness connecting between the interior and the exterior of the ECU-case  111  does not exist and the sealing of the clearance therebetween is not required. 
   An ECU-circuit housed in the ECU-case  111  is connected through a grounded wire to an inner portion of the earth (ground) bus-bar  112   a  projecting inside the ECU-case  111 , and an outer portion of the earth (ground) bus-bar  112   b  projecting outside the ECU-case  111  is connected through a grounded wire to an external earth (ground). Thus, a path between the ECU-circuit and the external earth (ground) has a good electrical conduction through the earth (ground) bus-bar  112 . Therefore, to apply the earth (ground) bus-bar&#39;s method instead of the other harness-connection method, waterproof grommets are not required so as to prevent contaminants such as water, dust, and the like from entering into the ECU-case  111 . 
   However, a plurality of conductive contacts, which are mutually insulated, like an earth (ground) bus-bar are required to apply this method to every harness. Thus, it has a drawback on the ground that the ECU-case becomes large. It has also a drawback on the ground that there is few freedom as for the layout of the ECU-circuit and the installation of the harness, as a position for mounting the conductive contacts projecting inside or ouside the ECU-case must be restricted by a extremely severe requirement. Further, it has a drawback on the ground that the difference in pressure between the interior and the exterior of the ECU-case causes to be the entry of water through the clearance between harness&#39; coating and wire, and to be the breaks of sealing for the clearance of the ECU-case. 
   As shown in  FIG. 3 , Japanese Patent Laid-Open Publication No. 134939/2002 discloses the ECU-case  120  in which the clearance between an ECU-case body  121  and an ECU-case cover  122  is constructed to be sealed by filling of adhesives  123 . The ECU-case  120  has a cylindrical boss  124  to form a ventilation hole  125  therein. A filter unit is mounted on top of the cylindrical boss  124  to cover the ventilation hole  125 . 
   This filter unit is constructed by a rubber-made inner pipe  126 , a fiber-made filter film  127 , and a plastic barrier cap  128 . The cylindrical boss  124  and the inner pipe  126  are lapped one over the other and a path  129  is formed between the inner pipe  126  and the barrier cap  128 . Numeral  130  shows a connector. 
   In the above ECU-case  120 , ventilation air can mutually communicate through a passage for communicating the interior and the exterior of the ECU-case  120 , which leads from the ventilation hole  125  through fiber-made filter film  127  to the path  129 . Thus, even if the changes in temperature occur in the air within the ECU-case  120 , the contaminants such as water, dust, and the like would not be sucked into the ECU-case  120 , as there is no differenece in pressure between the interior and the exterior of the ECU-case  120 . That is, the filter unit can prevent the contaminants from entering into the ECU-case  120 . 
   However, the filter unit is complicated in structure and the device is large in size, thus the ECU case  120  has a drawback for higher manufacturing costs. 
   Japanese Patent Laid-Open Publication No. 353675/2002 discloses the same ventilation system as the ECU disclosed in Japanese Patent Laid-Open Publication No. 134939/2002, but they are different from the position for mounting the ECU. 
   The filter unit in the Japanese Patent Laid-Open Publication No. 353675/2002 is mounted in the vicinity of electronic parts formed of exothermic element such as power transistor. Thus, it has a specific effect that the difference in temperature and pressure of the air between the interior and the exterior of the ECU-case would make it smaller, and the contaminants such as water, dust, and the like are effectively prevented from entering into the ECU-case. 
   However, the filter unit is complicated in structure and costs too much in manufacturing as well as Japanese Patent Laid-Open Publication No. 134939/2002. Therefore, although the ECU discloses the protective art against the invasion of contaminants such as water, dust, and the like therein, the ECU has some drawbacks. 
   SUMMARY OF THE INVENTION 
   As above described, the ventilation structure of the conventional ECU has a drawback that it is complicated in structure, large in size, and costs too much. That is, the conventional ECU-case is subjected to be constructed by a double-hull structure, to have an earth (ground) bus-bar embedded into a plastics-molded ECU-case, and to have a complicated filter-unit structure, and the like. 
   The present invention has been achieved under these circumstances, and an object of the present invention is to provide an ECU which can prevent clogging of a ventilation hole and a filter to improve ventilation efficiency, and which is simple in structure and lower in cost. 
   The object of the present invention is attained by providing an ECU which has a ventilation section so as to reduce the difference in temperature and pressure between the interior and the exterior of the ECU-case, and the ventilation section is simple in structure and low-cost. That is, 
   the above object is attained by an ECU which houses electronic circuit for controlling various devices of vehicles in a sealing case characterized in that the case has a ventilation hole to communicate an interior and an exterior of the ECU-case, the ventilation hole comprises a filter for preventing from entering contaminants from the outside, and a sectional area of the ventilation hole is gradually enlarged toward the interior of the ECU-case. 
   In addition, the above object is effectively attained by that the ventilation hole is of a tapered shape such that a cross section of the hole is gradually enlarged toward the interior of the ECU-case. 
   Further, the above object is effectively attained by that the ventilation hole comprises a barrier room provided in the exterior of the ECU-case, the barrier room having a small hole for communicating the interior and the exterior of the ECU-case with each other. 
   Furthermore, the above object is effectively attained by that the small hole of the barrier room comprises at least one small hole or slit for communicating between the interior and the exterior of the ECU-case with each other. 
   Still Furthermore, the above object is effectively attained by that the small hole of the barrier room is provided with a barrier net having at least one small hole or slit for communicating between the interior and the exterior of the ECU-case with each other. 
   Still Furthermore, the above object is more effectively attained by that the ECU comprises a ventilation hole which communicates the interior and the exterior of the ECU-case with each other, so as to reduce the pressure difference between the interior and the exterior of the ECU-case resulting from an increase of temperature or pressure within the ECU-case due to a self-heating element. 
   In addition, the above object is attained by an electric power steering system using the above ECU. 
   According to the ECU of the present invention, the ventilation hole which communicates the interior and the exterior of the ECU-case with each other is provided in the ECU-case, the filter is arranged in the ventilation hole formed in the ventilation section, and the sectional area of the ventilation hole is gradually enlarged toward the interior of the ECU-case, with an inlet of the ventilation hole narrowed. As a result, according to the present invention, a ventilation mechanism of the ECU can be realized by a simple structure. In addition, even if the ECU is disposed in an environment in which water relatively frequently splashes on the ECU such as in an engine room, and the temperature or the pressure within the ECU-case rises due to a self-heating element within the ECU, then it is possible to reduce the pressure difference between the interior and the exterior of the ECU-case, and prevent the contaminants such as water, dust, and the like from entering into the ECU-case. 
   Further, since the inlet of the ventilation hole is narrowed, it is possible to prevent contaminants such as water or dust from being directly hit against the filter from the outside. Even if such contaminants as water, salt water, or muddy water enter into the ventilation hole, an impact speed at which the contaminants is hit against the filter can be decreased and the filter can be prevented from being damaged, by gradually enlarging the sectional area of the ventilation hole toward the interior of the ECU-case. Besides, it is possible to prevent clogging of the filter caused by adhesion of the water, salt water, muddy water, or the like onto the filter, and prevent deterioration of filter function. Consequently, it is made difficult to damage the filter, thus improving durability of the filter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view which depicts case body and case lid of the case body consisting the conventional ECU case. 
       FIG. 2  is a perspective exploded view of the conventional ECU. 
       FIG. 3  is a cross-sectional view which depicts schematic structure of the conventional ECU. 
       FIG. 4  depicts an attachment state of the ECU in the electric power steering system according to the first embodiment of the present invention. 
       FIG. 5  is an external perspective view which depicts enlarged ECU. 
       FIG. 6  is a cross-sectional view of the ventilation section taken along a line X—X of the  FIG. 5 . 
       FIG. 7  is a cross-sectional view of the ventilation section corresponding to  FIG. 6  which depicts the second embodiment of the present invention. 
       FIG. 8   a  is a cross-sectional view of the ventilation section corresponding to  FIG. 6  which depicts the second embodiment of the present invention,  FIG. 8   b  is a plan view of the barrier net, and  FIG. 8   c  to  FIG. 8   j  is a plan view of the barrier net corresponding to  FIG. 8   b , respectively. 
       FIG. 9   a  is a cross-sectional view of the ventilation section corresponding to  FIG. 6  which shows the fourth embodiment of the present invention,  FIG. 9   b  is a side view of the barrier room,  FIG. 9   c  is a partially cut cross-sectional view which depicts a modification of the barrier room, and  FIG. 9   d  is a side view which depicts a modification of the barrier room shown in  FIG. 9   c.    
       FIG. 10  depicts a state in which the ECU of the electric power steering system according to the present invention is attached to the gearbox. 
   

   DESCRIPTION OF REFERENCE SYMBOLS 
     2  ECU 
     3  ECU-case 
     5  ventilation section 
     6  ventilation hole 
     7  filter 
     8  barrier room 
     8   a  small hole 
     10  barrier net 
     11  barrier room 
     11   a  protrusion 
     12  slit 
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described hereinafter with reference to the drawings. 
   (First Embodiment) 
     FIG. 4  is a perspective view which depicts a front structure of an automobile. In an engine room A, an ECU  2  is attached to a partition  1  of the engine room A from a cabin. As enlarged and shown in  FIG. 5  in detail, this ECU  2  is constituted so that connectors  4 ,  4  are provided on a bottom of ECU-case  3   a  of an ECU-case  3  which stores electronic components such as a power transistor serving as a heating element and a microcomputer, and so that the connectors  4 ,  4  are connected with various sensors such as a torque sensor through a harness. 
   A ventilation section (breathing section)  5  which communicates an interior and an exterior of the ECU-case  3  with each other is provided on the bottom of ECU-case  3 . The ventilation section  5  reduces a pressure difference between the interior and the exterior of the ECU-case  3  resulting from a rapid increase of temperature or pressure of the air within the ECU-case  3 . As shown in  FIG. 6 , this ventilation section  5  is formed integrally with the ECU-case  3 , and formed into a cylinder extending inwards from the bottom of ECU-case  3   a  and opened on both ends, and has a cylindrical boss  5   a  protruding outwards. 
   A tapered ventilation hole  6  is formed in the ventilation section  5  so that a sectional area of the ventilation hole  6  is enlarged from the bottom of ECU-case  3   a  toward the interior of the ECU-case  3 . A filter  7  consisting of a fiber material is attached to the interior of the ventilation hole  6  so as to prevent entry of water and dust. This filter  7 , which is formed by a material that transmits only the air, e.g., a commercially and easily available material such as Gore Tex®, prevents water from entering into the ECU-case  3 . 
   The ventilation hole  6  is formed so that an inlet of the ventilation hole  6  is narrowed by the cylindrical boss  5   a  protruding outwards from the ECU-case  3 , and so that the sectional area is enlarged toward the interior of the ECU-case  3 . 
   According to the above structure, it prevents contaminants such as water or dust (the contaminants include muddy water or salt water splashing cleaning water from the ground while a car is washed.) from entering into the ECU-case  3 . The contaminants enter from the outside through a passage formed within the cylindrical boss  5   a  and the ventilation section  5 , and the filter  7  into the ECU-case  3 . Then, it prevents from entry of contaminants by enlarging a sectional area toward the interior of the ventilation section  5  so as to decrease progressive speed of the contaminants. Then, the contaminants enter at lower speed through the filter  7  into the ECU-case  3 . It is thereby possible to prevent the contaminants being directly hit against the filter  7  from the outside. 
   In addition, by narrowing the inlet of the ventilation hole  6 , it is possible to prevent high-pressure water from being directly hit against the filter  7  from the outside, to lessen an impact force, and to prevent filter  7  from being damaged by the impact of the high-pressure water, salt water, muddy water, or the like. 
   Besides, it is possible to prevent deterioration of a filter function due to adhesion of the water, salt water, muddy water or the like onto the filter  7 , and prevent clogging of the filter  7 . That is, the ventilation hole  6  is formed into a tapered shape, the sectional area of which is enlarged toward the interior of the ECU-case  3 . 
   Therefore, an inflow speed, at which the contaminants hit against the filter  7  flows in from the ventilation hole  6 , can be decreased, and an impact force of the contaminants against the filter  7  is reduced. Thus, this can makes it difficult to damage the filter  7  and improves the durability of the filter  7 . As a result, even if the temperature or pressure within the ECU-case  3  is raised by a self-heating element stored in the ECU  2 , the pressure difference between the interior and the exterior of the ECU-case  3  can be reduced or relieved. This is because the ventilation hole  6  communicates with the outside. 
   (Second Embodiment) 
     FIG. 7  depicts a second embodiment of the present invention. A ventilation section  5  is equal in structure to that according to the first embodiment. The ventilation section  5  comprises a tapered ventilation hole  6  so that a sectional area of the hole  6  is gradually enlarged toward an interior of an ECU-case  3 , and a filter  7  is attached to the interior of the ventilation hole  6  so as to prevent entry of water, dust, or the like. 
   According to this second embodiment, a barrier room  8  is provided on the ECU-case  3  so as to cover an inlet of the ventilation hole  6 , and a small hole  8   a  is formed in a part of the barrier room  8 . As a result, even if water, dust, or the like enter into the ECU-case  3  from the outside, the contaminants stay within the barrier room  8 . Therefore, it is possible to prevent the contaminants from directly entering into the ventilation hole  6 , and decrease an entry speed of the contaminants. Hence, the second embodiment can exhibit the advantages indicating in the first embodiment more effectively. 
   (Third Embodiment) 
     FIG. 8   a  depicts a third embodiment of the present invention. A ventilation section  5  is equal in structure to that according to the second embodiment. The ventilation section  5  comprises a tapered ventilation hole  6  so that a sectional area of the ventilation hole  6  is enlarged toward an interior of an ECU-case  3 . In addition, a filter  7  is attached to the interior of the ventilation hole  6 , a barrier room  8  is provided on the exterior of the ventilation hole  6  so as to cover an inlet of the ventilation hole  6 , and a small hole  8   a  is formed in a part of the barrier room  8 . 
   According to the third embodiment, a circular small hole is formed at the exterior of the ventilation hole  6 , and a barrier net  10  composed of an annular member  10   a  fitted and inserted into the small hole and a shield rod  10   b  radially extending from a center of the small hole is arranged on the exterior of the ventilation hole  6 . It is thereby possible to prevent the contaminants such as relatively large mud or dust from entering into the ECU-case  3  when water, dust or the like is to enter into the ECU-case  3  from the outside. Hence, the third embodiment can far more effectively exhibit the advantages indicating in the first and the second embodiments. 
   In addition, the barrier net  10  may be in a variety of shapes, e.g. shapes shown in  FIG. 8   c  to  FIG. 8   j . In short, any shape to be easily manufacured may be used as the barrier net  10 , only if the hole or the slit formed in the barrier net  10  provides ventilation function. 
   (Fourth Embodiment) 
     FIG. 9   a  depicts a fourth embodiment of the present invention. A ventilation section  5  is equal in structure to that according to the third embodiment. The ventilation section  5  comprises a tapered ventilation hole  6  so that a sectional area of the hole  6  is enlarged toward the interior of an ECU-case  3 , and a filter  7  is attached on top of the ventilation hole  6 . 
   As shown in  FIG. 9   b , a barrier room  11  is provided on an exterior of the ECU-case  3  so as to cover an inlet of the ventilation hole  6 , and the barrier room  11  has a plurality of slits  12  formed along a peripheral side surface. It is thereby possible to prevent the contaminants such as relatively large mud or dust from entering into the ECU-case  3 , when water, dust and the like is to enter into the ECU-case  3  from the outside. Hence, the fourth embodiment can far more effectively exhibit the advantages indicated in the first, the second, and the third embodiments. 
   In the barrier room  11 , the contaminants such as the water or mud may possibly be deposited at a position Z shown in  FIG. 9   a . Therefore, as shown in  FIG. 9   c , protrusion  11   a  in a lowest portion of the barrier room  11  (lower side in  FIG. 9   a ) may be eliminated, whereby the deposition of the contaminants can be prevented. According to this modification, the same advantage as that of the fourth embodiment can be obtained. The opening area of the barrier room  11  becomes large, when the slits  12  are provided as shown in  FIG. 9   b . While, where the opening area of the slits  12  is smaller as shown in  FIG. 9   d , it is possible to more effectively prevent the contaminants from entering through the slits  12  into the ventilation hole  6 . According to this modification, the same advantage as that of the fourth embodiment can be obtained. 
     FIG. 10  depicts a gearbox  22  which stores a deceleration unit which decelerates a rotative speed from an electric motor  20 , and which transmits the decelerated rotation to a steering shaft  21 , and depicts a state in which an ECU  23  is attached to the gearbox. As can be seen, even if an attachment position of the ECU  23  is restricted, the same function and advantage as those of the respective embodiment can be attained only by constituting a ventilation hole which communicates an interior and an the exterior of the ECU  23  with each other as described in the respective embodiment. 
   Therefore, according to the ECU of this invention, a ventilation hole  6  for communicating an interior and an exterior of the ECU-case  3  is provided in the ECU-case  3 . The sectional area of the ventilation hole  6  is gradually enlarged toward the interior of the ECU-case  3 . Hence, according to the present invention, a ventilation system of the ECU  2  can be constructed in a simple structure. Even if the ECU  2  is provided in a place like an engine room to be under the condition subjected to water and the like, and the temperature and the pressure within the ECU-case  3  increase owing to self-heating element, it prevents water from sucking into the ECU-case  3  by relieving the pressure difference between the interior and the exterior of the ECU-case  3 . 
   It prevents from impact of contaminants such as water, salt water, muddy water, dust, et al against the filter  7  from the outside. Even if the contaminants enter into the ventilation hole  6 , as the speed and force of impact against the filter  7  reduces, it prevents from failures of the filter  7  by enlarging the sectional area of the ventilation hole  6  toward the interior of the ECU-case  3 . Further, it prevents form clogging of the filter  7  caused by the adhesion of the contaminants against the filter  7 . Thus, the filter  7  becomes sturdy and trouble-free so that the durability of filter improves remarkably. 
   Further, the ventilation hole  6  may be of a tapered shape, funnel (cone) shape, or pyramid shape as being gradually enlarged in sectional area toward the interior of the ECU-case  3  from the outside. Further, an outside opening for ventilating the ECU-case  3  is provided not at a cylindrical boss, but at a barrier room  11 , thus to prevent from entering into the ECU-case effectively. At least one small hole or at least one narrow slit are provided in the barrier room  11  to communicate to the outside. A barrier net  10  is provided between the barrier room  11  and the ventilation hole  6 , it prevents from entering water, dust, and the like effectively. 
   From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the claims.