Patent Abstract:
In order to ensure waterproofing between a resin enclosure case and a heat sink, a canopy structure is provided in a portion, in which water is likely to penetrate, so as to prevent the water from entering the portion, thereby directing the water flow to the outside of the enclosure. This makes it easy to install and remove an electronic unit, so that an electronic component integrally formed with the heat sink can be easily replaced.

Full Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese patent application serial no. 2007-221425, filed on Aug. 28, 2007, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to electronic equipment, and more particularly to electronic equipment installed outdoors. 
     Outdoor equipment enclosures for North America must successfully complete the standards of North America. Particularly, it is necessary to pass the following three tests relating to waterproofing, which are described in “Generic Requirements for Electronic Equipment Cabinets”, Telcordia Technologies, March 2000, GR-487-CORE issue 2, Section 3.28. Incidentally, Wind Driven Rain test is the most severe of the three tests. 
     1. Wind Driven Rain test 
     After water spraying on the front surface, right surface, and left surface of an enclosure for 30 minutes each with a rainfall intensity of 150 mm/hr and a wind speed of 31 m/sec, the amount of water penetrating into the enclosure shall not exceed 1 cm^3 (cm 3 ) (1 gram of water) per 0.028 m^3 (m 3 ) (1 ft^3 (ft 3 )). 
     2. Rain Intrusion Test 
     Water droplets accumulated in the surface grooves and the door frame shall not enter the enclosure immediately after heavy rain. After water spraying on the front surface and the two side surfaces for 15 minutes each, the amount of water penetrating into the enclosure shall not exceed 1 cm^3 (cm 3 ) (1 gram of water) per 0.028 m^3 (m 3 ) (1 ft^3 (ft 3 )). 
     3. Lawn Sprinklers Test 
     After simulation of sprinkler water spraying at a downward angle of 45 degrees on the front surface and the two side surfaces for 15 minutes or 45 minutes in total, the amount of water penetrating into the enclosure shall not exceed 1 cm^3 (cm 3 ) (1 gram of water) per 0.028 m^3 (m 3 ) (1 ft^3 (ft 3 )). 
     Meanwhile, IPX4 defined in international standard IEC/EN60529 (JIS C0920) also specifies as criteria that water splashing against the enclosure shall have no harmful effect. In other words, the provisions of “Generic Requirements for Electronic Equipment Cabinets”, Telcordia Technologies, March 2000, GR-487-CORE issue 2, Section 3.28 are unique in that they require the prevention of water penetration, in addition to the protection against harmful effect of water splash. 
     In addition to the waterproof standard described above, the outdoor equipment enclosure for North America should meet the requirement that an electronic component housed therein can easily be replaced. In other words, the enclosure should have a structure capable of replacing an internal unit including an electronic component within the enclosure, instead of replacing the whole equipment, for the maintenance and replacement of the equipment. This is also the specification that allows the installation of the enclosure first and then the installation of the internal unit afterwards. 
     Further, from the point of view of the cost and weight, the material of the enclosure is preferably resin. However, it is difficult for a resin seal enclosure to fully achieve radiation performance. Hence, it is necessary to ensure the radiation performance by providing an opening in the resin enclosure through which a radiation fin of a heat sink thermally connected to the electronic component, is partially exposed to the outside of the resin enclosure. Here, the heat fin may be splashed with water, but the water penetration into portions other than the radiation fin is not allowed. 
     In general, the electronic component and the heat sink are connected via a thermally conductive sheet. For this reason, it is difficult to remove only a board in which the electronic component is mounted for maintenance and replacement, so that the electronic component is removed and replaced together with the heat sink. 
     In JP-A No. Hei 10-173371, there is described an enclosure structure of electronic equipment that facilitates heat conduction from the inside to the outside of the enclosure. The enclosure structure is designed to improve the efficiency of radiation from the inside to the outside of the enclosure, by providing a heat sink for radiating heat from the inside out, in which a radiation surface of the heat sink is exposed out to the bottom of the enclosure. However, this structure uses a packing (O-ring) for waterproofing. The use of the packing requires precise control of the amount of crush of the packing, thereby requiring a lot of screws for tightening the packing. Further, it is also necessary to manage a tightening torque. Consequently, it is difficult to easily install and remove the internal unit. 
     SUMMARY OF THE INVENTION 
     The present invention provides electronic equipment installed outdoors to house an electronic component and other parts, in which the electronic equipment meets the waterproof standard of North America and allows easy replacement of the electronic component housed therein. 
     The above can be achieved by electronic equipment including: an electronic component installed in an enclosure with a cover and a case having an opening; and an internal unit including a radiation fin and a heat sink for radiating heat generated by the electronic component, the radiation fin being inserted into the opening. The heat sink has a draining portion extending in a direction perpendicular to an extending direction of the radiation fin, in the bottom of the radiation fin. 
     Further, it can be achieved by electronic equipment including: an electronic component installed in an enclosure with a cover and a case having an opening; and an internal unit including a radiation fin and a heat sink for radiating heat generated by the electronic component, the radiation fin being inserted into the opening. The heat sink has a draining portion extending in a direction perpendicular to an extending direction of the radiation fin, in the bottom of the heat sink. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will now be described in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing a state in which an enclosure is mounted to an outdoor wall surface; 
         FIG. 2  is a perspective view showing a state in which a cover of the enclosure of electronic equipment is opened; 
         FIG. 3  is a front view of a case; 
         FIG. 4  is a cross-sectional view of an assembly of the electronic equipment; 
         FIG. 5  is a cross-sectional view of the electronic equipment; 
         FIG. 6  is a cross-sectional view of a key portion of the electronic equipment; 
         FIG. 7  is an assembly view of a key portion of the electronic equipment; 
         FIG. 8  is a cross-sectional view showing in detail a canopy structure of a heat sink; 
         FIG. 9  is a cross-sectional view showing in detail a portion for waterproofing of the case; 
         FIG. 10  is another cross-sectional view in the vicinity of the canopy structure; and 
         FIG. 11  is another cross-sectional view of a key portion of the electronic equipment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments will be described based on examples, with reference to the accompanying drawings. Like or corresponding parts are denoted by the same reference numerals and the description will not be repeated. Here,  FIG. 1  is a perspective view showing a state in which an enclosure is mounted to an outdoor wall surface.  FIG. 2  is a perspective view showing a state in which a cover of the enclosure of electronic equipment is opened.  FIG. 3  is a front view of a case.  FIG. 4  is a cross-sectional view of an assembly of the electronic equipment.  FIG. 5  is a cross-sectional view of the electronic equipment.  FIG. 6  is a cross-sectional view of a key portion of the electronic equipment.  FIG. 7  is an assembly view of a key portion of the electronic equipment.  FIG. 8  is a cross-sectional view showing in detail a canopy structure of a heat sink.  FIG. 9  is a cross-sectional view showing in detail a portion for waterproofing of the case.  FIG. 10  is another cross-sectional view in the vicinity of the canopy structure. 
     In  FIG. 1 , an outdoor enclosure  1  includes a heat sink cover  10 , a case  20 , and a cover  30 , and is fixed to a wall  70 . The heat sink cover  10 , the case  20 , and the cover  30  are all made of resin. The heat sink cover  10  has a lower air vent  110  and an upper air vent  120  for cooling streams. It is designed so that an internal unit can be installed later in a state in which the outdoor enclosure  1  is fixed to the wall  70 . 
     Incidentally, the lower air vent is not seen in  FIG. 1  due to perspective viewing, but it is explicitly shown in  FIG. 10  which will be described later. 
       FIG. 2  shows electronic equipment  1000  with the cover  30  open. The electronic equipment  1000  is in a state in which an internal unit  50  is connected to the outdoor enclosure  1 . Incidentally, in  FIG. 2 , the cover  30  and the case  20  are connected by hinges  40 , but it is also possible that the cover  30  may be removable and fixed to the case  20  by screws. Further, the cover  30  and the case  20  are resin sealed, so that it is possible to easily realize a water seal structure. 
     Incidentally, in order to simplify the illustration, there is shown that the height of the internal unit  50  is low relative to the depth of the case  20 . 
     The case  20  will be described with reference to  FIG. 3 . In  FIG. 3 , the maximum profile of the case  20  is substantially square with 303×296 mm sides. The case  20  has frame-side hinge portions  41  on the left side surface, and an opening  210  of 186×214 mm in a central portion thereof. There are eight screw holes  203  provided around the opening  210  of the case  20  to fix the internal unit  50 . 
     The components of the electronic equipment will be described with reference to  FIG. 4 . Incidentally,  FIG. 4  is a cross-sectional view taken along line A-A of  FIG. 3 . In  FIG. 4 , the electronic equipment is configured such that the heat sink cover  10  is attached to the case  20 , in which the internal unit  50  is installed, and then covered with the cover  30 . 
     The cover  30  has door-side hinge portions  42  which are engaged with the frame-side hinge portions  41  of  FIG. 3 , and thus the hinges  40  are formed. The internal unit  50  includes a heat sink  530 , a radiation fin  540 , a thermally conductive sheet  550 , an electronic component  560 , a board  520 , a sealed case  510 , and sealed case fixing screws  580 . The electronic component  560  is mounted to the board  520 , in which heat is transmitted to the heat sink  530  through the thermally conductive sheet  550  and is radiated to the air outside of the enclosure from the radiation fin  540 . The internal unit  50  is fixed to the case  20  by the eight internal unit fixing screws  570 . Upon assembly, the radiation fin  540  and a part of the heat sink  530  are inserted into the opening  210  (186 mm in height). In other words, the internal unit  50  can easily be replaced by simply removing the eight internal unit fixing screws  570 . 
     The cross sectional structure after assembly as the electronic equipment will be described with reference to  FIG. 5 .  FIG. 5  is also a cross-sectional view taken along line A-A of  FIG. 3 . In  FIG. 5 , the air entering from the lower air vent  110  of the heat sink cover  10  flows upward while depriving the heat of the radiation fin  540 . Then, the air flows out from the upper air vent  120 . As shown in  FIG. 3 , the case  20  has the opening  210  through which the radiation fin  540  is exposed to the outside of the case  20 . The size of the opening  210  is determined depending on the size of the radiation fin  540  to be exposed. The size of the radiation fin  540  is determined by the results of a thermal simulation and a temperature test. In the waterproof test, almost all the water can be prevented by the heat sink cover  10 . However, the remaining water flowing along the heat sink  530  or the radiation fin  540  inside the heat sink cover  10  is prevented from entering the enclosure  1  by a draining portion which will be described with reference to FIG.  6  and the subsequent figures. 
     Incidentally, the upper air vent  120  and the lower air vent  110  are not shown in the cross section of the case  10  in  FIGS. 4 and 5 . This is because the center cross section is taken as A-A cross section. Obviously the upper air vent  120  and lower air vent  110  both having many holes are expressed when other cross sections are taken. 
     The detail in the vicinity of the canopy portion will be described with reference to  FIGS. 6 and 7 , which are enlarged views of B portion of  FIG. 5 . 
     In  FIG. 6 , if assuming that a canopy  531  is not provided, water droplets flowing from the upper portion along the heat sink  530  just flows into the enclosure from a gap  60  between the case  20  and the heat sink  530 . For this reason, the canopy is provided in the heat sink  530  so that the water droplets flowing from the upper portion along the canopy  531  and falls down from the tip of the canopy  531 . Due to the canopy  531 , the water droplets are prevented from entering a gap  60  between the case  20  and the heat sink  530 . As a result, it is possible to prevent the water penetration into the enclosure  1 . Preferably the canopy  531  is long enough to cover the gap  60  between the case  20  and the heat sink  530 . However, as shown in  FIG. 7 , it could make it difficult to install the internal unit  50  to the case  20  due to interference between the case  20  and the canopy  531 . For this reason, a length b of the canopy  531  is preferably determined so as not to exceed the size of the opening  210  of the case  20 . In the embodiment, a distance a between the opening  210  of the case  20  and the lower canopy  531  is defined as 1.94 mm. 
     Further, the length b of the canopy  531  may be any value as long as the water droplets can be cut. However, the present inventors consider that preferably the length b is about the same as a height c, because the canopy  531  could be destroyed when it is too long. Also, in order to prevent the destruction of the canopy  531 , a wall thickness d should have a certain thickness. In addition, it is necessary to provide a space  532  to prevent the water droplets from entering the gap  60  between the case  20  and the heat sink  530  along the canopy  531 . At this time, when the space  532  is small, the water droplets may enter the gap  60  along the canopy  531  during a storm, so that the space  532  should have a certain area. Further, preferably an angle dimension e of the canopy  531  is determined so that the water droplets fall in a direction separating from the gap  60 . In the embodiment, the length b is defined as 9.84 mm, the height c as 7.67 mm, the wall thickness d as 3 mm, and the angle e as 10.16 degrees, respectively. The waterproof test was performed under Wind Driven Rain with a sample of the above dimensions, and confirmed that the sample was acceptable. 
     Incidentally, the draining portion described with reference to  FIGS. 6 and 7  is not provided in an upper portion of  FIG. 5 . This is because even if the water droplets enter the gap  60  in the upper portion of  FIG. 5 , the water does not flow in a direction against the force of gravity unless a capillary tube is formed therein. 
     The detailed structure of the heat sink and the case will be described with reference to  FIGS. 8 and 9 . In  FIG. 8 , the heat sink  530  includes a first groove  533  and a second groove  534  in the vicinity of the canopy  531 . The first and second grooves  533 ,  534  are continuously present around the outer periphery of the heat sink  530 . A hole  535  is a screw hole used for screw fixing the internal unit  50  to the case  20 . 
     While in  FIG. 9 , the case  20  includes a first rib  201  and a second rib  202 . The first and second ribs  201 ,  202  are continuously present around the opening  210  of the case  20 . A screw hole  203  is a lower hole used for screw fixing the internal unit  50  to the case  20 . 
     The first rib  201  is fitted into the first groove  533  upon assembly. Similarly, the second rib  202  is fitted into the second groove  534 . Even if the water droplets may not be completely prevented by the canopy  531  and may enter from the gap  60  between the case  20  and the heat sink  530 , a first fitting portion between the first groove  533  and the first rib  201  prevents the water from penetrating into the enclosure  1  (water sealing). The first fitting portion has a small space in which the water droplets are held by the surface tension, so that the water is prevented from penetrating into the enclosure. In the embodiment, an f dimension (f 1 ) of the space is defined as  1  mm. The water penetration is also prevented in the fitting portion between the second groove  534  and the second rib  202 . Thus, the case has a double water-proof structure. Incidentally, an f dimension (f 2 ) of the second fitting portion is defined as f 2 &lt;f 1  to realize higher water sealing performance. 
     In  FIG. 10 , almost all the water droplets flow from the upper portion along the heat sink  530 . However, it is possible that water droplets are blown into the case from the lower air vent  110  of the heat sink cover  10  during a storm at an intensity equivalent to the Wind Driven Rain test. In order to prevent this, there is provided a rib  204  in the bottom of the gap  60  between the case  20  and the heat sink  530 . The waterproof performance is improved as a height g of the rib is higher. However, when the rib is too high, the air flow to the radiation fin  540  is blocked and the radiation performance is degraded. For this reason, the height g is determined within the range in which the radiation is not blocked. In the embodiment, the value of g is defined as 5 mm. Here, the value of g is determined so that the tip of the rib  204  is located on a line connecting the canopy  531  and the left-end hole on the heat sink  530  side of many holes forming the lower air vent  110 . 
     Next, a variation of the draining portion will be described with reference to  FIG. 11 . Here,  FIG. 11  is a cross-sectional view of a key portion of the electronic equipment. In  FIG. 11 , although a canopy portion  531 A does not extend outwardly, the water is cut in a position sufficiently distant from the enclosure  1  by the grooves  533  and  534 . As a result, the water is prevented from entering the enclosure  1 . 
     Incidentally, the draining portion may include other variations than the above described structures of the canopy portions  531  and  531 A, as long as the water is cut in the direction of the force of gravity. 
     According to the present invention, it is possible to provide electronic equipment installed outdoors to house an electronic component and other parts, in which the electronic equipment meets the waterproof standard of North America and allows easy replacement of the electronic component housed therein.

Technology Classification (CPC): 7