This invention relates to a cooling apparatus equipped with a heat sink for dissipating heat emitted from a heat source, and more particularly to a heat sink-equipped cooling apparatus suitable for use for cooling an electronic component such as a CPU or the like.
Heat generated or emitted from an electronic component such as a CPU or the like used in a computer is progressively increased with an increase in performance of the electronic component. Japanese Utility Model Publication No. 15982/1991 discloses a cooling apparatus which is so constructed that a cooling fan is arranged above a heat sink having a plurality of radiation fins radially arranged on a front surface of a base plate thereof, to thereby permit air discharged from the cooling fan to be fed to a central region of the base plate and then outwardly exhausted through the radiation fins. Another conventional cooling apparatus is disclosed in U.S. Pat. No. 5,629,834 (corresponding to Japanese Patent No. 2,765,801 and Japanese Patent Application Laid-Open Publication No. 111302/1985) and U.S. Pat. No. 5,782,292 (corresponding to Japanese Patent Application Laid-Open Publication No. 102566/1997), which includes a heat sink having a plurality of radiation fins arranged in directions of flowing of air radially discharged from an impeller of a fan. In the cooling apparatus disclosed, the radiation fins are arranged so as to surround a part of the impeller of the fan. A further conventional cooling apparatus is disclosed in U.S. Pat. No. 5,785,116 (corresponding to Japanese Patent Application Laid-Open Publication No. 219478/1998), which includes a heat sink having a plurality of radiation fins arranged on a base plate thereof so as to surround an impeller of a fan. The radiation fins are arranged in a manner to be inclined with respect to a central line extending through a center of the fan. In the cooling apparatus thus constructed, the heat sink including the plural radiation fins is formed by subjecting a cylindrical material to cutting which is carried out in a direction inclined with respect to a central line of the cylindrical material. Also, in the cooling apparatus, predetermined accurate relationship must be established between an angle of the radiation fins and an angle of the blades of the fan in order to permit the cooling apparatus to exhibit satisfactory cooling performance. Further, a motor of the fan is mounted on the heat sink.
The first and second conventional cooling apparatuses described above each are not suitable for use for cooling an electronic component increased in heat generation. The third conventional cooling apparatus described above is suitable for cooling an electronic component increased in heat generation as compared with the first and second cooling apparatuses. However, in the third cooling apparatus, the heat sink is increased in manufacturing cost and it is required to increase machining accuracy. Also, the third apparatus, as described above, is so constructed that the radiation fins are arranged so as to surround the impeller of the fan. Such arrangement causes a size of the cooling apparatus in a radial direction thereof to be significantly increased. Further, mounting of the motor of the fan on the heart sink in the third apparatus causes transmission of heat from the heat sink to the motor, leading to a deterioration in durability of the motor.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a heat sink-equipped cooling apparatus which is capable of exhibiting increased cooling performance and durability and reducing a size thereof in a radial direction thereof.
It is another object of the present invention to provide a heat sink-equipped cooling apparatus which is capable of being reduced in manufacturing cost thereof.
It is a further object of the present invention to provide a heat sink-equipped cooling apparatus which is capable of exhibiting increased cooling performance.
It is still another object of the present invention to provide a heat sink-equipped cooling apparatus which is capable of permitting the number of radiation fins arranged to be increased to a degree sufficient to enhance cooling performance of the cooling apparatus.
In accordance with the present invention, a heat sink-equipped cooling apparatus is provided. The cooling apparatus includes a heat sink for dissipating heat generated from a heat source. The heat sink includes a base plate increased in thermal conductivity and including a front surface and a rear surface with which the heat source is contacted, a virtual central line defined so as to extend in a direction perpendicular to the front surface of the base plate, a plurality of virtual vertical planes defined so as to extend in both a radial direction from the central line and a vertical direction perpendicular to the front surface of the base plate and be spaced from each other at equal intervals in a circumferential direction of a virtual circle defined about the central line, and a radiation fin unit mounted on the front surface of the base plate in a manner to be heat-transferable and including a plurality of radiation fins arranged so as to surround the central line while aligning the central line with a center in arrangement of the radiation fins. The cooling apparatus also includes a cooling fan including an impeller which includes a plurality of blades and is rotated by a motor and mounted on the heat sink so that the impeller is positioned above the radiation fin unit.
In the heat sink, the radiation fins each include a lower edge positioned on a side of the base plate, an upper edge positioned opposite to the lower edge, an inner edge connecting the lower edge and the upper edge and positioned on the side of the center line, and an outer edge connecting the lower edge and the upper edge and positioned opposite to the inner edge, and a radiation surface positioned between the lower edge and the upper edge. The radiation fins each are fixedly mounted directly or indirectly on the front surface of the base plate so as to be positioned on an intersection line between the virtual vertical plane corresponding to each of the lower edges and the front surface of the base plate. Also, the radiation fins each are arranged while being inclined in an identical direction with respect to the virtual vertical plane (or toward one side in the circumferential direction of the virtual circle) so that an inclination angle xcex8 of predetermined degrees between the radiation surface of the radiation fin and the virtual vertical plane may be defined. The radiation fin unit and cooling fan are arranged in positional relationship to each other which permits each of the blades of the cooling fan and the upper edge of each of the radiation fins to be opposite to each other. The cooling fan is arranged so as to permit cooling air to be fed to the radiation fins of the radiation fin unit. For this purpose, the cooling fan may be operated so as to blow air against the radiation fins. Alternatively, it may be operated so as to suck air from a side of the radiation fins.
When the impeller of the cooling fan and the heat sink are arranged in proximity to each other, air fed from the fan is substantially kept from being fed to a portion of the heat sink which is not opposite to the blades of the fan or a portion of the heat sink which is opposite to a cup member on which the blades of the impeller are fixed. Also, an air stream generated due to rotation of the impeller is not permitted to flow in an axial direction of the motor but is caused to flow in a direction of rotation of the impeller. Thus, arrangement of the radiation fins in a mere radial manner causes the radiation fins to act as flow resistance, to thereby fail to permit an increase in cooling performance of the cooling apparatus. This is also true of a structure which is constructed so as to forcibly flow air in a radial direction using an axial fan adapted to feed air in an axial direction, to thereby flow the air around radiation fins positioned outside an impeller, leading to cooling of the radiation fins. On the contrary, the structure of the present invention that air fed in the axial direction of the motor from the cooling fan is blown against the radiation fins from above the radiation fin unit enhances cooling performance of the cooling unit. Although this is not clearly supported by any specific theory, it would be considered that arrangement of the radiation fins employed in the present invention reduces flow resistance to air discharged from the cooling fan and produces a rapid air stream along the radiation surface of each of the radiation fins, to thereby increase the cooling performance. Thus, the cooling apparatus of the present invention exhibits cooling performance at substantially the same or higher level as an expensive cooling apparatus conventionally used without being increased in dimensions in a radial direction thereof and ensuring satisfactory durability of the motor.
Especially in the present invention, inner edges of two adjacent radiation fins of a plurality of radiation fins are connected with each other in a manner to be heat-transferable or in a manner that a thermal conductive passage is formed between the inner edges. When this configuration is adopted, a continuous, cylindrical and thermally conductive passage is formed in the center of a radiation fin unit. Normally it is difficult to cool the central portion of the radiation fin unit. With this formation, heat-radiation from each radiation fin is highly promoted also from the center of the radiation fin unit through this heat-transferable passage, thus resulting in more efficiently cooling the central part of the heat sink. Compared with the case in which inner edges of the radiation fins constituting a radiation fin unit are not connected with each other in a manner to be heat-transferable, it is possible to further enhance the radiation efficiency of a cooling apparatus as a whole when inner edges of the radiation fins are thermally connected with each other.
Furthermore, when the configuration according to the present invention is adopted, the generation of the noise is reduced compared with the conventional cooling apparatuses which have the same capacitance as the present fin unit, irrespective of the direction in which the impeller of the cooling fan is rotated.
Configuration for connecting inner edges of a plurality of the radiation fins in a manner to be heat-transferable can be in any suitable manner. For example, inner edges may be connected with each other by adhesive made of metal material or synthetic resin which are increased in thermal conductivity. Also each of inner edges of radiation fins may be connected to the outer surface of a metal cylinder (a cylinder of inverted frust-conical shape) positioned in the center of a radiation fin unit. From a view point of manufacturing, it is easier to use adhesives than a cylinder.
Ideally, plural virtual vertical planes are defined so as to be spaced from each other at equal intervals in the circumferential direction of a virtual circle. This ensures substantially uniform cooling of each of the radiation fins and base plate, to thereby further enhance cooling efficiency of the cooling apparatus.
The radiation fin unit may be formed by subjecting a single metal plate increased in thermal conductivity to bending. This reduces a manufacturing cost of the cooling apparatus and facilitates simplified manufacturing thereof.
A plurality of radiation fins need not be completely flat plates. The radiation fins can be curved along intersection lines between the virtual vertical planes and the front surface of the base plate. When curved radiation fins are used, the gap between inner edges of radiation fins become larger, and it becomes difficult to connect the inner edges of the radiation fins. In this case also, with the above-mentioned metal cylinder it is possible to easily connect the inner edges of the radiation fins with each other.
To further enhance cooling efficiency it is preferable to provide radiation fins with extended portions which are, around the central line, positioned outside of the blades of the fan so as to surround the blades aligning the center of the arrangement of the extended portions of the radiation fins with the center line. With this arrangement the area of radiation surface can be enlarged and radiation efficiency is increased. Also radiation efficiency may be heightened by providing uneven surface to the radiation fins thereby increasing the the area of radiation surface.
In the present invention, the radiation fin unit may be constructed so as to attain both simplified manufacturing of the cooling apparatus and mass production thereof. More specifically, a single fin mounting metal plate to be joined to the front surface of the base plate is provided. The radiation fins each are formed of a flat metal plate. Also, the radiation fins each are fixed at the lower edge thereof on the fin mounting metal plate. The radiation fins may be mounted on the fin mounting metal plate in any suitable manner.
The present invention may be constructed so as to further promote mass production of the cooling apparatus. For this purpose, the fin mounting metal plate is formed with a plurality of slits in a manner to radially extend from the central line and be spaced from each other at predetermined intervals in the circumferential direction. The radiation fins each are integrally formed at the lower edge thereof with a fit projection which is fitted in each of the slits. Also, the radiation fins each are joined to the fin mounting metal plate while keeping the fit projection fitted in each of the slits. This facilitates not only positioning of the radiation fins on the fin mounting metal plate, but joining of the radiation fins to the fin mounting metal plate while keeping the radiation fins inclined.
In manufacturing the radiation fin unit as described above, joint means for joining each radiation fin to the fin mounting metal plate can be also used for connecting inner edges of radiation fins, thereby facilitating a simplified manufacturing. In this case fit projections of the radiation fins may be projected from the rear side of the fin mounting metal plate. This will permit the radiation fins to be contacted directly with the base plate, when a radiation fin unit is joined to the front surface of the base plate, thereby heightening the radiation efficiency.
Alternatively, the base plate may be formed with a plurality of slits in a manner to radially extend from the central line and be spaced from each other at predetermined intervals in the circumferential direction. This reduces the number of parts required although it somewhat increases a manufacturing cost of the apparatus. Alternatively, the radiation fins each equipped with the fixing flange may be directly fixed on the front surface of the base plate.
The radiation fins may be formed into the same configuration. This leads to a reduction in manufacturing cost of the radiation fins and therefore the cooling apparatus. In order to cut out a number of radiation fins from a single large-sized metal plate by punching with increased yields, the radiation fins each preferably have a main portion formed into a substantially rectangular shape. Thus, the radiation fin unit is permitted to be provided at a central portion thereof with a space of a frust-conical configuration while having a center positioned on a central line of the radiation fin unit and being gradually reduced in diameter toward the base plate.
The inclination angle xcex8 of the radiation fins is basically varied depending on the number of radiation fins. An increase in number of radiation fins leads to a reduction in inclination angle, whereas a decrease in the number leads to an increase in inclination angle. However, the inclination angle xcex8 is preferably less than 45 degrees. The inclination angle of 45 degrees or more leads to a reduction in number of the radiation fins, to thereby cause a deterioration in cooling performance of the radiation fins. More preferably, the inclination angle xcex8 is less than 45 degrees and more than 15 degrees, because it permits to increase the number of radiation fins to a degree sufficient to ensure satisfactory cooling performance of the radiation fin unit.
The cooling fan is preferably constituted by a so-called axial fan. The blades of the cooling fan are preferably inclined in a direction identical with a direction in which the radiation fins are inclined. In this instance, the cooling fan may-be operated to rotate the impeller in the direction in which the radiation fins are inclined. This enhances cooling performance of the cooling fan compared with the opposite case.