Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2001-10-25
2002-07-16
Joyce, Harold (Department: 3749)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C055S471000, C055S473000, C454S184000
Reexamination Certificate
active
06421238
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dustproof structure for a communication device which has both an air cooling function and a dustproof function using an air filter, and in particular, to a dustproof structure employing an economical air filter arrangement having a high efficiency.
This application is based on Patent Application No. Hei 10-374602 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
When a generally-known communication device having a shelf which contains a plurality of printed circuit boards is operated, electronic components, electronic circuits, a power supply, and the like generate heat, and relevant thermal stress degrades the reliability of the device. Therefore, it is necessary to cool the heated portions and discharge heat to the outside. Two kinds of cooling methods are known: natural air cooling and forced air cooling. In a modern communication device having a high thermal density, the forced air cooling using a fan is commonly used.
There are two types of forced air cooling using a fan. One is the draw-in method in which the fan is arranged at the exhaust side so that the air inside the chassis is drawn in and then expelled (or vented or exhausted) outside, and the other is the forcing method in which the fan is arranged at the suction side so that the outside air is forcibly introduced into the chassis.
If dust comes into the communication device, it may lead an undesirable effect such as contact failure, insulation failure, promotion of corrosion, degradation of the cooling effect, or the like. Therefore, if the communication device is used in a dusty area, a dustproof structure is necessary. For example, an air filter for filtering cooled air may be provided at the suction side. Japanese Unexamined Patent Application, First Publication, No. Sho 60-183623, discloses an example of the draw-in cooling method and a dustproof structure using an air filter.
Below, the above two forced air cooling methods will be compared in consideration of the dustproof effect. In the draw-in method, an air filter is provided at the air inlet, thereby preventing dust from flowing from the inlet into the chassis; however, air that does not pass through the air filter will flow through a gap or the like into the chassis together with dust. In the forcing method, an air filter is provided at the air inlet and all the air forced into the chassis passes through the air filter; thus, if the performance of the air filter is excellent, the reduction of dust introduced into the chassis can be maximized. Therefore, the forcing method is much more effective than the suction method in consideration of the dustproof effect.
Next, the air filter will be examined. Dust particles included in an air flow collide with and adhere to an air filter, and thereby the dust is removed. A fibrous material, nonwoven fabric, porous plastics, wire gauze, sintered metal, or the like can be used for manufacturing the air filter. The dust collecting efficiency and pressure loss are practical indices indicating the performance of the air filter. Generally, the higher the dust collecting efficiency, the greater the pressure loss is. An air filter having a higher dust collecting efficiency is effective for reducing the introduced dust. However, in this case, the pressure loss is also increased, which imposes a great burden on the air blowing system of the device.
Below, the air flow generated by the fan will be examined. In most cases, the wind blown from the fan does not have a uniform velocity distribution. For example, in the vicinity of the rotational shaft of the axial fan, an area having an extremely small wind velocity is present. Also in the axial fan, the spread of the ventilated area in the radial direction with respect to the rotational shaft is not very large, and the closer the area is to the fan, the more significant this tendency is. That is, in the vicinity of the fan, the spread of the ventilated area is hardly observed, and thus the cross-sectional area of the air flow is approximately equal to the projected area of the fan.
Accordingly, as for the forced air cooling method in consideration of the dustproof effect, the forcing method is much more effective. However, in the forcing method, the air filter is provided immediately below the fan, that is, positioned close to the fan. Such an arrangement makes the air flow concentrate at a part of the air filter.
In order to improve the dust collecting efficiency, it is important to effectively use the whole face or area of the air filter, and also to reduce the pressure loss as much as possible. A high-performance air filter having a high dust-collecting efficiency and relatively small pressure loss may be used; however, such a high-performance air filter is expensive and thus has a low economical efficiency.
Accordingly, a developed air-filter structure is required, whose whole area can be effectively used, and which has a higher dust collecting efficiency and a lower pressure loss at low cost.
FIGS. 7 and 8
show an example structure, in which cabinet
22
having printed circuit boards installed is cooled by using the forced air cooling method. A fan shelf
23
is provided below the cabinet
22
, and fan unit
25
is mounted in the fan shelf. One or more fans
24
are provided in the fan unit
25
. Each fan
24
is the axial type, and the blowing direction is the wind direction. That is, the outside air is forcibly introduced into the cabinet
22
by using the fans
24
in the forced air cooling method.
The cabinet
22
is not always used in a single structure, but a plurality of cabinets
22
may be stacked one on the other. In such an arrangement, the exhaust heat from a cabinet positioned at the windward side must be prevented from being drawn in by the cabinet directly above said cabinet, that is, the exhaust heat from the windward shelf should not be introduced into a cabinet positioned at the leeward side. To satisfy this requirement, air inlet
26
is provided at the suction (or draw-in) side, and air outlet
27
is provided at the exhaust side. The air inlet
26
and air outlet
27
have a structure in which the wind direction is changed using partition plate
28
. The outside air is introduced from the front side of the device into the air inlet
26
, while the air heated by a heated printed circuit board is expelled from the air outlet
27
to the back side of the device, so that the air in front of the device is drawn in and then expelled. According to this structure, even if a plurality of cabinets
22
are stacked, each cabinet is not affected by another shelf.
The air filter
29
whose object is dustproofing has a plate shape, in which both the dust collecting efficiency and pressure loss are uniform. The air filter
29
is inserted between the windward side of the fan unit
25
and air inlet
26
, or in the inlet
26
, so as to prevent dust from entering the cabinet
22
and fan unit
25
. Generally, an air filter has the characteristic that the higher the speed of the wind passing through the filter, the greater the pressure loss is. Therefore, according to the basic “continuation” principle (i.e., conservation of mass) in hydrodynamics, the portion having a wider cross-sectional area of the air-flow passage has a lower wind velocity, and can be effectively used.
In the air inlet
26
having the structure (see
FIG. 8
) in which the wind direction can be selected using partition plate
28
, the air filter may be mounted at the entrance of the inlet
26
(i.e., at the most windward side) in the vertical direction, or at the exit side of the air inlet
26
, that is, directly below the fan unit
25
in the horizontal direction. In consideration of the above-described characteristics of the air filter, it is generally preferable and efficient to arrange the air filter
29
in the horizontal direction, as shown in
FIGS. 7 and 8
.
In addition, the air filter
29
can be detached or removed from the front side or face
LandOfFree
Dustproof structure of communication device, using air... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dustproof structure of communication device, using air..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dustproof structure of communication device, using air... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2864532