Abstract:
A cooling apparatus integrally formed within a casing for an electronic device. A mounting board has heat generating members and the cooling apparatus mounted thereto. In an embodiment, a cooling fan having a flat motor is integrally formed with the mounting board by directly fixing a stator coil and a bearing of a motor on the mounting board. The reduced thickness of this structure permits the circuit element to be arranged on the bottom side of the mounting board, permitting increased surface area for the mounting of components of the electronic device. In another embodiment, the mounting board is made of multiple layers, and the field coils form a flat stator on the multiple layers of the mounting board. A bearing is integrally formed in the multiple layers of the mounting board. The rotor is spaced over the mounting board and opposes the flat stator which is integral with the mounting board to reduce the thickness of the motor and permit use of the mounting bottom of the mounting board for components of the electronic device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cooling apparatus for an electronic device having a thin machine body such as a mobile computer, a digital video camera and the like. 
     2. Description of the Prior Art 
     Conventionally, the thin electronic device of this kind is structured such that a mounting board  3  mounting a heat-generating circuit part  2  such as a semiconductor, a CPU and the like is arranged within a casing  1  as shown in FIG. 5, and a heat generated by the circuit part  2  is discharged out of the device via a heat transmission member  4  made of an aluminum plate or the like. 
     Here, in a heat discharge amount to an outer portion due to a heat transmission, the following relation (1) is established. 
     
       
         Qout∝Σ(Tsi−Ta)×Si  (1) 
       
     
     Qout: heat discharge amount 
     Tsi: temperature of a fine portion at i number when separating a surface of the casing into fine portions 
     Si: area of the fine portion at i number mentioned above 
     Ta: temperature of the open air 
     Accordingly, the temperature of the casing increases as a calorific power of the heat generating part to be cooled increases, and an area of a portion having a high temperature becomes widened in accordance therewith. 
     In accordance with the structure mentioned above, since the electronic device such as a mobile computer or a digital video camera is used by being held by a hand, an increase of the temperature of the surface of the casing gives an uncomfortable feeling to a user and may cause problems with of the device in some cases. 
     In this view, there has been developed an electronic device in which a fan is provided within the electronic device so as to forcibly discharge the heat generated within the casing to an outer portion. 
     FIG. 6 shows an embodiment of the electronic device provided with a cooling fan. The electronic device is structured such as to arrange a plurality of mounting boards  3  mounting heat-generating circuit parts  2  such as semiconductors and the like within the casing  1 . The electronic device is further structured such as to shorten a length of the mounting board  3  in a side of an inner bottom within the casing  1  so as to form a space with respect to a side surface of the casing  1 , to arrange a flat type cooling fan  5  having a frame serving as a heat sink in the space so that a minimum size thereof corresponds to a direction of thickness of the device, to transmit a heat generated in the circuit parts  2  to the cooling fan  5  via a heat transmission member  4  made of an aluminum or the like, and to forcibly discharge the heat out of the device body by an operation of the cooling fan  5 . 
     In a thin note type personal computer, the structure mentioned above is frequently employed, and it is desired to design a thin type electronic device so as to secure a sufficient reliability, to restrict a height of the cooling fan  5  to about 7.5 mm and to set a thickness of the device within 20 mm. 
     However, the electronic device shown in FIG. 6 has the following problems. 
     That is, in the case of the electronic device such as the mobile type personal computer having a significantly thin thickness, it is desired to further reduce the height of the cooling fan and reduce the occupied space in a direction of the thickness, so that it is hard that the device using the normal motor, for example, an outer rotor type motor satisfies the desire. 
     Further, when the mounting portion is constituted by two sheets of mounting boards having a size of 50 mm×100 mm, the parts mounting area is expressed by the following formula. 
     
       
         50 mm×100 mm×2 (surfaces)×2 (sheets)=20000 mm 2   
       
     
     When one of the mounting boards  3  is notched for arranging the cooling fan  5 , a non-mounting area is expressed by the following formula since the size of the cooling fan  5  is 40 mm×40 mm. 
      40 mm×40 mm×2 (surfaces)=3200 mm 2   
     Accordingly, the parts mounting area is reduced by 16%. 
     This causes a great limitation for designing an electronic device having a compact size, a high performance and a high function. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a cooling apparatus for an electronic device provided with a cooling fan having a compact size, a high performance and a high function, which can structure the cooling fan so as to reduce an occupied space in a direction of a thickness, to be easily assembled and reduce a parts mounting area as less as possible, thereby securing a thinness of the electronic device. 
     In order to achieve the object of the present invention, in accordance with the present invention, there is provided a cooling apparatus for an electronic device comprising a mounting board mounting electronic parts including heat generating parts such as semiconductors and arranged within a casing of a thin type electronic device such as a mobile personal computer and a digital video camera, and a cooling fan installed therein, wherein a flat cooling fan is constituted by a motor comprising a flat stator and a flat rotor opposing to a surface of the flat stator, a vane provided in the flat rotor of the motor and a frame, the cooling fan is arranged within the casing so that a height direction thereof corresponds to a direction of a thickness of the casing, and the heat generating parts on the mounting board and a frame of the cooling fan are thermally connected by a heat transmission member. 
     As mentioned above, since the structure is made such that the height of the cooling fan can be reduced to a significantly low level, the cooling fan can be easily assembled within the thin type casing and arranged on a partial surface of the mounting board, so that the electronic device with the cooling fan having a compact size, a high performance and a high function can be achieved without greatly reducing the area of mounting the parts on the mounting board and the heat generated by the heat generating parts within the electronic device can be sufficiently radiated so as to cool the heat generating parts. Accordingly, in the electronic device provided with the cooling apparatus such as the mobile type personal computer, the digital video camera and the like, the thin structure can be realized without reducing the cooling effect and without reducing the area for mounting the parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a main portion of an electronic device provided with a cooling fan in accordance with a first embodiment of the present invention; 
     FIG. 2A is a cross sectional view of a main portion of an electronic device provided with a cooling fan in accordance with a second embodiment of the present invention; 
     FIG. 2B shows a detail of FIG. 2A; 
     FIG. 3 is a pattern diagram of a field coil in the cooling apparatus of the electronic device in accordance with the second embodiment of the present invention; 
     FIG. 4 is a connection pattern diagram of a field coil in the cooling apparatus of the electronic device in accordance with the second embodiment of the present invention; 
     FIG. 5 is a cross sectional view of an electronic device provided with a cooling fan in accordance with a conventional embodiment; and 
     FIG. 6 is a cross sectional view of an electronic device provided with a cooling fan in accordance with another conventional embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     An embodiment in accordance with the present invention will be described below with reference to the accompanying drawings. 
     FIG. 1 is a cross sectional view of a main portion of an electronic device provided with a cooling fan in accordance with a first embodiment of the present invention. 
     In FIG. 1, reference numeral  1  denotes a thin type casing for an electronic device in which circuit parts such as semiconductors, resistances, condensers and the like, functional parts such as switches, connectors and the like, and electronic apparatuses such as a floppy apparatus, a hard disc apparatus and the like are arranged, and the casing  1  is made of a metal or a resin material. Reference numeral  3  denotes a mounting board arranged within the casing  1  so as to form multiple steps, and reference numeral  3   a  denotes a mounting board disposed at a lowermost portion in a direction of a thickness of the casing  1  among the mounting boards  3 . Heat generating circuit parts  2  such as the semiconductors and the like are mounted on the mounting board  3   a , and a flat cooling fan  6  is bonded and fixed to a portion near an end portion of the mounting board  3   a.    
     The cooling fan  6  is constituted by a motor portion comprising a flat stator  8  formed by molding a field coil  7 , a rotational axis  10  rotatably held on a center portion of the flat stator  8  by a bearing  9 , a flat rotor  12  formed by molding a permanent magnet  11  and opposing to the flat stator  8 , vanes  13  mounted to the flat rotor  12  so as to constitute a fan portion and a frame  14  made of a heat transmission material such as an aluminum and the like, surrounding the motor and an outer side of the fan portion, having an air suction port at an upper opening and provided with at least one air discharge port in a side wall, thereby being formed in a flat shape. The frame  14  is bonded and fixed to the mounting board  3   a  by an adhesive. Alternatively, the frame  14  is arranged and fixed to the mounting board  3   a  by forming a projection on a bottom surface of the frame  14  and a hole at a position corresponding to the projection of the mounting board  3   a  so as to press the projection of the frame  14  into the hole. 
     The heat generating circuit parts  2  and the frame  14  are connected to each other via a heat transmission member  4  made of a material having a good heat transmission such as an aluminum and the like. The heat transmission member  4  is not limited to a metal, and a carbon material such as a graphite and the like and a resin material may be used as far as they have a good heat transmission. The circuit parts  2  and the heat transmission member  4  are bonded and fixed to each other by an adhesive. Further, a heat transmission resin such as a grease, a silicone oil and the like are applied to a portion between the circuit parts  2  and the heat transmission member  4 , and an adhesion between the circuit parts  2  and the heat transmission member  4  is increased, so that the heat transmission member  4  may be held between the circuit parts  2  by a clip or the like, or the heat transmission member  4  and the circuit parts  2  may be overlapped and fixed to the mounting board  3   a  by a pin or the like. On the contrary, the heat transmission member  4  and the frame  14  are fixed to each other by an adhesion by an adhesive, a screwing, a welding or the like. Further, the heat transmission member  4  corresponds to a member formed by extending a part of the frame  14 , and may be integrally formed with the frame  14  or may be a frame cover. Further, in accordance with this embodiment, the heat transmission member  4  is formed in a flat plate shape, however, fins  4   a  may be provided on the heat transmission member  4 . 
     In the structure mentioned above, a heat generated by the circuit parts  2  mounted on the mounting board  3   a  is transmitted to the frame  14  of the cooling fan  6  via the heat transmission member  4 . Then, the vane  13  is rotated by operating the cooling fan  6 , so that an air is sucked from an opening in an upper side of the frame  14 , a heat of the frame  14  is exchanged with a wind generated by the sucked air, and a hot wind absorbing the heat is discharged out of the casing  1  through a discharge port for an air in the frame  14 . The circuit parts  2  on the .mounting board  3   a  are cooled by this operation, so that the temperature of the casing  1  in the electronic device is prevented from being increased. 
     In this case, the cooling fan  6  is structured such that a height in a direction of the thickness of the casing  1  is significantly reduced by the flat stator  8  and the flat rotor  12  so as to be applied to the thin electronic device, thereby being constituted as a flat type cooling fan. Accordingly, an occupied space within the casing  1  can be reduced so as to be easily assembled, and even when the mounting board  3  is mounted so as to form multiple steps, the cooling fan can be mounted on one of the mounting boards  3   a.    
     Further, since the mounting board  3   a  to which the cooling fan  6  is mounted can mount the circuit parts on a surface in the side where the cooling fan  6  is not mounted, the parts mounting area is not greatly reduced. That is, as shown in FIG. 1, in the case that the conventional flat-shaped cooling fan is mounted, both surfaces of a parts mounting area (B) can be used, however, on the contrary, in accordance with the first embodiment, one surface of a parts mounting area (A) is added. Accordingly, since the number of the mounting parts is increased, the electronic device can be made one having a high performance and a high function and provided with a cooling fan. Further, since a lot of parts can be mounted in the same space, the electronic device can be made compact. 
     Here, in accordance with the first embodiment, it is structured such that the cooling fan  6  is arranged on the mounting board  3 , however, it may be structured such that the cooling fan  6  is directly arranged inside the casing  1 , and in this case, it is possible to further widen the parts mounting area of the mounting board  3 . 
     Second Embodiment 
     FIG. 2A is a cross sectional view of a main portion in a cooling apparatus for an electronic device in accordance with a second embodiment of the present invention. FIG. 2B shows details of FIG.  2 A. 
     The cooling apparatus for the electronic device in accordance with the second embodiment is characterized in that the flat stator of the motor portion in the cooling fan is constituted by utilizing the mounting board  3 . 
     That is, reference numeral  3  denotes a mounting board, and at least a board on which a cooling fan  20  is provided among the mounting boards  3  is constituted by a multiple layered mounting board  16  obtained by integrally overlapping a plurality of printed circuit boards  15 , and a field coil  17  is formed at a predetermined position of each of the printed circuit boards  15  by printing and etching. Then, each of the field coils  17  is connected by a through hole  18  so as to constitute a flat stator  19 . Reference numeral  9  in the drawing denotes a bearing, which is pressed into the multiple layered mounting board  16  and fixed thereto. Reference numeral  10  denotes a rotational axis, reference numeral  11  denotes a permanent magnet, reference numeral  13  denotes a vane and reference numeral  14  denotes a frame. Since these elements are combined in the same manner as that of the first embodiment mentioned above so as to constitute the cooling fan  20 , an explanation thereof will be omitted. 
     FIG. 3 is a pattern diagram of a field coil in the cooling apparatus for the electronic device in accordance with the second embodiment of the present invention, and FIG. 4 is a connection pattern diagram of the field coil in the cooling apparatus for the electronic device in accordance with the second embodiment of the present invention. The multiple layered mounting board  16  is constituted by an N-layered printed circuit board  15 , and numbers from (1) to (N) are respectively applied to the printed circuit board  15  from a side of the flat rotor  12 , successively. FIG. 3 shows the patterns of the field coils  17  of the number from (1) to (N−1) of the printed circuit board  15  by an optional printed circuit board  15  in the number of (N−1). Coil patterns  30 ,  31 ,  32  and  33  are spiral patterns each having a fine pitch, and the coil patterns  30 ,  31 ,  32  and  33  have the same pitch interval and the same number of turn. In this embodiment, it is set that the coil pitch is 0.2 mm and the number of turns is 40. Reference numerals  18  and  34  denote a through hole provided at both end portions in a start and end portions of the coil pattern  30 , reference numerals  35  and  36  denote a through hole provided at both end portions in a start and end portions of the coil pattern  31 , reference numerals  37  and  38  denote a through hole provided at both end portions in a start and end portions of the coil pattern  32 , and reference numerals  39  and  40  denote a through hole provided at both end portions in a start and end portions of the coil pattern  33 . The same coil pattern is formed on the printed circuit board  15  in the number (1) of the printed circuit board  15  to the number (N−1) of the printed circuit board. 
     However, a hole component for detecting a magnetic pole of the flat rotor  12  is provided beside each of the coil patterns  30 ,  31 ,  32  and  33  in the number (1) of the printed circuit board  15  (not shown). Control means (not shown) flows electricity to the stator  19  in accordance with an information of the magnetic pole of the flat rotor  12  detected by the hole component, thereby rotating the cooling fan. 
     Connection patterns  49 ,  50 ,  51  and  52  are formed on the printed circuit board in the number (N) of the printed circuit board  15 , and a connection terminal  48  connected to the through hole  40  of the coil pattern  33  and a connection terminal  44  connected to the through hole  36  of the coil pattern  31  are formed in the connection pattern  49 . A connection terminal  47  connected to the through hole  39  of the coil pattern  33  and a connection terminal  43  connected to the through hole  35  of the coil pattern  31  are formed in the connection pattern  50 . A connection terminal  41  connected to the through hole  18  of the coil pattern  30  and a connection terminal  45  connected to the through hole  37  of the coil pattern  32  are formed in the connection pattern  51 . A connection terminal  42  connected to the through hole  34  of the coil pattern  30  and a connection terminal  46  connected to the through hole  38  of the coil pattern  32  are formed in the connection pattern  52 . The other end sides of the connection patterns  49 ,  50 ,  51  and  52  are connected to the control means. 
     N sheets of printed circuit boards  15  are layered so as to form a multi-layered mounting board  16 . At this time, the through hole  18  formed in (N−1) layers and the connection terminal  41  are electrically connected to each other. In the same manner, the through hole  34  formed in (N−1) layers and the connection terminal  42 , the through hole  35  formed in (N−1) layers and the connection terminal  43 , the through hole  36  formed in (N−1) layers and the connection terminal  44 , the through hole  37  formed in (N−1) layers and the connection terminal  45 , the through hole  38  formed in (N−1) layers and the connection terminal  46 , the through hole  39  formed in (N−1) layers and the connection terminal  47  and the through hole  40  formed in (N−1) layers and the connection terminal  48  are electrically connected to each other, respectively. 
     The control means flows electricity to the connection patterns  49 ,  50 ,  51  and  52  in accordance with a drive principle of a two-phase motor so as to rotate the cooling fan  20 . 
     In the case of this embodiment, a drive system is based on the two-phase motor, however, even in the case of a three-phase or more, it is possible to form the coil pattern on the basis of the same thought so as to drive, thereby obtaining the same effect, so that the drive system is not limited to the two-phase one. 
     Further, since the heat transmission structure from the circuit parts  2  to the frame  14  via the heat transmission member  4  is made in the same manner as that of the first embodiment mentioned above, an explanation thereof will be omitted. 
     In accordance with the structure mentioned above, since the flat stator  19  of the motor portion in the cooling fan  20  is constituted by utilizing the multi-layered mounting board  16 , the cooling fan  20  is made compact and the height thereof is made lower at a degree of the thickness of the mounting board, so that the occupied space for the cooling fan within the thin type casing is made significantly small, thereby obtaining the thin type electronic device provided with the cooling fan having a high performance and a high function.