Patent Publication Number: US-6210134-B1

Title: Cooling device and cooling-fan-motor thereof for electronic apparatuses

Description:
FIELD OF THE INVENTION 
     The present invention relates to cooling devices and the cooling-fan-motors thereof employed in electronic apparatuses having slim bodies. 
     BACKGROUND OF THE INVENTION 
     In the conventional slim electronic apparatus as shown in FIG. 8, printed wired assembly substrates  3  (hereinafter referred to as PWAs) are placed. On the PWAs, heat generating components  2  such as semiconductors and a CPU are mounted. The heat generated from components  2  travels through heat conductive member  6  such as an aluminum plate, and is discharged outside the apparatus. The discharged heat amount is calculated with the following expression. 
     
       
         Q out ∝ Σ(Tsi−Ta) ×Si 
       
     
     where: 
     Q out=discharged heat amount 
     Tsi=a temperature at an “i” th cell of the housing surface, which is finely divided into cells 
     Si=an area of the “i” th cell 
     Ta=outer temperature 
     Accordingly, the housing temperature rises and an area of high temperature increases as greater built-up heat amounts are produced by the components. 
     When this structure is employed in an electronic apparatus such as a mobile computer or a digital video camera, the interior built-up heat could potentially damage its internal electronic operating components. Further, since these apparatus are held by a user&#39;s hand during operation, the temperature rise on the housing surface makes the user uncomfortable. Therefore, it has been proposed to discharge the interior built-up heat forcibly outside the apparatus by providing a cooling fan in the apparatus. 
     In the prior art depicted in FIGS. 9A and 9B, components  2  that generate heat, such as semiconductors, are mounted on a PWA  3  that is installed in housing  1 . On one of inside faces of housing  1 , cooling fan  5  is provided. The height of fan  5  is substantially equal to that of a housing  1  and frame  4  of fan  5  functions as a heat sink. The heat produced by components  2  travels to fan  5  via heat conductive member  6  made of e.g. aluminum. Then fan  5  drives blades  7  to forcibly discharge the heat outside the apparatus. 
     FIG. 10 is a cross section of an essential part of another electronic apparatus with a conventional cooling fan. In FIG. 10, a plurality of PWAs accommodating heat generating components  2  such as semiconductors are installed in the housing  1 . PWA  3  installed at the lowest place in housing  1  is shortened at its end in order to provide a space between PWA  3  and a side of the housing. In this space, flat cooling fan  8  is disposed so that its shortest side extends in the height direction of the apparatus. The frame of fan  8  functions as a heat sink. The heat produced by components  2  travels to fan  8  via heat conductive member  6  made of e.g. aluminum. Then fan  8  forcibly discharges the heat outside the apparatus. The structure in FIG. 10 mentioned above is employed in a large number of slim notebook-type personal computers. In addition to ensuring reliability of the personal computers, it is desirable that the height of cooling fan  8  be as low as ca. 7.5 mm so that the total housing height of the apparatus should be less than 20 mm. 
     The structure in FIG. 9 is compared with that in FIG. 10 to find the following fact. The structure in FIG. 9 can be employed in the electronic apparatuses such as notebook type personal computer of which total height ranges from 25 to 40 mm. However, in the case of mobile computers requiring a further compact and slim body, the height of cooling fan  5 , i.e. 2 ×(a+b+c) becomes a possible obstacle to meeting requirements. 
     where “a”=radius of motor, “b”=blade height, “c”=frame thickness 
     The height of an electronic apparatus that requires an extra slim body is often restricted by the height of cooling fan  5 . In order to reduce the height of fan  5 , each dimension mentioned above, i.e. “a”, “b” and “c” should be reduced; however, the following inconveniences accompany this reduction: 
     Reduction of dimension “a”: decreasing the motor power and lowering the motor efficiency; 
     Reduction of dimension “b”: decreasing the air volume; and 
     Reduction of dimension “c”: degrading the strength of the frame; and weakening the heat sink function, 
     The height of cooling fan  5  is thus cannot readily lowered, which has been an obstacle to further downsizing of compact electronic apparatuses such as mobile personal computers. 
     The structure shown in FIG. 10 has been proposed to overcome the problem of the structure shown in FIG.  9 . However, in the case of compact electronic apparatuses such as a mobile personal computers this structure of FIG. 10 still has the following problem. Two sheets of double sided PWA accommodate the components. Assume that each PWA measures 50 mm×100mm Then the total components-mounting-area is thus 50 mm×100 mm×2 sides×2 sheets=20000 mm 2 . 
     In order to dispose a fan  8  that measures 40 mm×40 mm, one PWA 3 should be cut out, which reduces the components-mounting-area by 40 1mm×40 mm×2 sides=3200 mm 2 . As a result, the total components-mounting-area is reduced by 16%. 
     This area-reduction decreases the number of components which can be mounted, and has been an obstacle to realizing compact size electronic apparatus having high performance and versatile functions. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problems above and aims to provide a compact and high performance cooling-device for electronic apparatuses requiring a cooling fan and a fan motor whereby the apparatuses can be thin in size and for which a reduction of the component-mounting-area can be minimized. 
     An arrangement according to the present invention utilizes: 
     (a) PWAs including heat-generating electronic components such as semiconductors, and being disposed in a housing of a thin-type electronic apparatus, such as a mobile personal computer or a digital video camera, so that a given space is provided between the housing and the PWAs; 
     (b) a cooling fan motor having a small and tubular case made of heat-conductive materials such as copper, aluminum and the like, the cooling fan motor having a height smaller than the height of the housing, and being disposed in the given space provided in the housing; and 
     (c) an air discharge opening through which the heated air in the housing is discharged. 
     This structure described above allows the cooling fan motor to reduce its occupying space in the housing. The cooling fan thus can be placed to function efficiently. The build-up heat in the housing can be satisfactorily dissipated, which permits the interior components to be sufficiently cooled down. As a result, the structure according to the present invention can allows the electronic apparatuses such as mobile personal computers and digital video computers to be slimmed down without degrading cooling efficiency or decreasing the components-mounting-area. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section of an electronic apparatus having a cooling fan in accordance with a first exemplary embodiment of the present invention. 
     FIG. 2 is a perspective view depicting a slim housing of the electronic apparatus used in the first exemplary embodiment of the present invention. 
     FIG. 3 is an elevational cross section of a cooling fan motor to be disposed in the electronic apparatus used in the first exemplary embodiment of the present invention. 
     FIG. 4 is a cross section of the cooling fan to be disposed in the electronic apparatus used in the first exemplary embodiment of the present invention. 
     FIG. 5 is a cross section of a cooling fan in accordance with a second exemplary embodiment of the present invention. 
     FIG. 6 is a perspective view of blades in accordance with a third exemplary embodiment of the present invention. 
     FIG. 7 is a cross section of a cooling fan in accordance with a fourth exemplary embodiment of the present invention. 
     FIG. 8 is a cross section of an essential part of a conventional electronic apparatus. 
     FIG.  9 A and FIG. 9B are cross sections of an essential part of a conventional electronic apparatus having a cooling fan. 
     FIG. 10 is a cross section of an essential part of another conventional electronic apparatus having a cooling fan. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention are described below with reference to the accompanying drawings. 
     Exemplary Embodiment 1 
     FIG. 1 to FIG. 4 show structures of an electronic apparatus having a cooling fan and a cooling fan motor. When there are the same elements as used in the prior art, the same symbols are used. 
     In these drawings, a plurality of PWAs 3 and 3 a  are mounted in a slim housing  1  in a multistory manner. The PWAs accommodate electronic components. Among the PWAs mounted in the multistory manner, PWA 3 a  mounted as the lowest story (nearest to the housing bottom) accommodates heat generating components such as semiconductors. PWA  3   a  has a little shorter length than others. Small space  9  for accommodating a cooling fan is provided between a face plate of housing  1  and one edge of PWA  3   a . Cooling fan motor  10  is placed so that its height is less than the height of housing  1 . Air discharge openings are provided in housing  1  as shown in FIG.  2 . 
     As shown in FIG. 3, the cooling fan motor comprises: 
     (a) a tubular case  11 , having a small diameter and made of a heat-conductive material such as copper or aluminum, for functioning as a heat exchanger that transfers and dissipates heat; 
     (b) a motor section  14  provided on a first end of case  11 , and comprising stator  12  and rotor  13 ; and 
     (c) a rotary shaft  15  coupled to rotor  13  and rotatably supported by stator  12 . 
     Shaft  15  extends to a second end of case  11 , and is disposed at the center of both ends of case  11 . The second end of case  11  is open. Shaft  15  has a plurality of blades  16  intervals of a given distance. Fins  17  are placed at given locations between blade  16  and motor section  14  as well as between respective blades, and protrude into the case. Fins  17  are shaped into plates or poles and placed approximately at the same intervals as that of the blades  16 . On the side of case  11 , an air intake opening  18  is provided. Rotary shaft  15 , blades  16  and some part of rotor  13  can be molded in a monoblock with synthetic resin. 
     Motor section  14  can be placed outside an end  1  of case  11  instead of inside of the end. Air intake opening  18  can be placed at the end where motor section  14  is mounted. The shape of fins  17  can be a cylinder, a triangle pole, a pin or other shape which can dissipate heat. 
     Cooling fan motor  10  is placed in space  9  in such a manner that the height of motor  10  is lower than the height of the housing. To be more specific, a longitudinal direction of shaft  15  parallel with one side of PWA  3   a . Heat conductive member  6  made of an aluminum plate, copper plate or graphite is coupled to heat generating components  2  such as semiconductors. The side face of case  11  is wrapped with a curved end of heat conductive member  6  and both of the elements are thermally coupled. 
     The end part of heat conductive member  6  can be coupled to case  11  by adhesive, welding, or crimping. Member  6  and case  11  can be in a monoblock. Depending on the placement of mounted components and a relation between PWAs  3 , space  9  can be tilted with regard to an edge of the PWA  3   a  and not necessarily placed at the end of the housing  1 . 
     An operation of, the cooling fan is described hereinafter. The heat generated by components  2  on PWA  3   a  travels to case  11  of cooling fan motor  10  via heat conductive member  6 . Driving cooling fan motor  10  draws air through air intake opening  18  into housing  1 . The wind produced by blades  16  hit each fin  17  in case  11 . Heat is exchanged from case  11  and fins  17 , both having the conducted heat, and the wind produced by blades  16 . The heated air is discharged outside housing  1  through the air discharge opening. This operation cools down components  2  on PWA  3   a , and produces air-flow in housing  1  thereby preventing the housing temperature from rising. 
     A dimension of cooling fan motor  10  is described hereinafter. In FIG. 3, case  11  measures as follows: diameter φ=15 mm, length L2=20 mm, length of motor section  14 , L3=7 mm. The diameter φ is substantially equal to dimension  2   a  of conventional cooling fan motor  5  shown in FIG.  9 . The diameter φ is expressed as (2 a+ 1) mm inclusive of the thickness of the case per se. 
     Assume that conventional housing  1  shown in FIG. 9A has a height of e.g. ca. 25 mm and cooling fan  5  has a height of 25 mm. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Prior art shown in Fig. 9 
                   
                 Present invention 
               
               
                   
               
             
            
               
                 Height of cooling fan 5 
                   
                 Diameter φ of cooling fan motor 10 
               
               
                   
                   
                 inclusive case 11 per se 
               
               
                 2(a + b + c) 
                 &gt; 
                 2a + 1 
               
               
                 25 mm 
                 &gt; 
                 15 mm 
               
               
                   
               
            
           
         
       
     
     As such, cooling fan motor  10  of the present invention is lower than conventional cooling fan  5  by ca. 10 mm. Motor  10  can be therefore mounted in the electronic apparatuses having thinner housings. PWA  3  mounted at the upper store can avoid being shortened so that the components-mounting-area can avoid a substantial reduction. 
     Cooling fan motor  10  of the present invention reduces its occupying space substantially, thereby slimming and downsizing electronic apparatuses. 
     Assume that the dimensions of conventional cooling fan  5  and fan motor  10  of the present invention are as follows: 
     
       
         L1 of fan  5 =10 mm, L2 of motor  10 =20 mm. 
       
     
     Then both volumes are expressed as shown in Table 2. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Volume of fan motor 10 
               
               
                 Volume of conventional fan 5 
                   
                 inclusive case 11 
               
               
                   
               
             
            
               
                 {2(a + b + c)} 2  × L1 
                 &gt; 
                 π × }(2a + 1)/2} 2  × L2 
               
               
                 25 2  × 10 = 6250 mm 3   
                 &gt; 
                 π × 15 2 /4 × 20 = 3533 mm 3   
               
               
                   
               
            
           
         
       
     
     This comparison tells that fan motor  10  of the present invention only occupies 57% of the area occupied conventional fan  5 . As a result, fan motor  10  can be employed in the slimmer housing of downsized apparatuses. 
     According to the first exemplary embodiment, rotary shaft  15  of motor section  14  is extended from rotor  13 , and blades  16  are provided on shaft  15 , thereby reducing the diameter of motor  10 . A plurality of blades  16  can be provided on extended shaft  15 , thereby increasing air volume. As a result, the space occupied by motor  10  can be smaller than that by the prior art, and the heat produced by components  2  travels sufficiently to case  11  and fins  17  via heat conductive member  6 . Then the cooling fan dissipates the heat and cools down the house interior. The rotational part of the cooling fan is not exposed so that motor  10  can be incorporated in the housing with ease. 
     In this exemplary embodiment, heat conductive member  6  is handled as a discrete element; however, it may be formed by an extended part of tubular case  11  of motor  10 . Tubular case  11  may have a flat part on its side. 
     Exemplary Embodiment 2 
     A cooling fan motor  19  shown in FIG. 5 has advantages due in a fan case and structure therein. A case  20  is shaped in a rectangular tube of which plan cross section of the case shows a rectangle. Motor section  14 , blades  16  and fins  17  are provided in the case, which is the same arrangement as the first exemplary embodiment depicted in FIG.  3 . Further, a motor driving circuit  22  is disposed in a space  21  in a corner of case  20  in which motor section  14  is mounted. 
     This structure of cooling fan motor  19  increases an area for heat-exchange thanks to the shape of the rectangular tube case  20 , and the cooling efficiency is thus improved. Motor driving circuit  22  this needs not to be mounted outside of motor  19 , e.g. on the PWA, which spares the space supposed to be occupied by circuit  22  in the housing. As a result, electronic apparatuses can be further slimmed down. Rectangular tube case  20  can be fit in a corner of housing  1  so that case  20  can be fixed to housing  1  in a more stable manner. 
     Exemplary Embodiment 3 
     The blades of a cooling fan motor in accordance with the third exemplary embodiment depicted in FIG. 6 has an advantage due to its structure. Spirally shaped blades  24  are continuously formed on a rotary shaft  23  in the longitudinal direction. In this exemplary embodiment, shaft  23  formed by an extended portion of some part of the rotor and spiral blades  24  are molded into a monobody with synthetic resin. 
     This structure increases an active area of the blades substantially, and provides for an easy assembly because the blades are incorporated into the rotary shaft. The heat conducted to the case is dissipated efficiently by the wind produced by spiral blades  24 , whereby the case is cooled down sufficiently. 
     Exemplary Embodiment 4 
     A cooling fan motor  25  in the fourth exemplary embodiment shown in FIG. 7 has a case  26  that is shaped in a rectangular tube. A plan cross section of case  26  shows a rectangle. Fins  27  are provided on the corners of case  26  and protrude inward thereof. 
     A cooling fan having spiral blades  24  that are described in the third exemplary embodiment can be incorporated into case  26 . Spiral blades  24  can dissipate the heat effectively and cool down case  26  sufficiently with wind via fins  27 . Case  26  having fins  27  can be combined with blades  16  and fins  17  discussed in the first exemplary embodiment that is depicted in FIG.  3 . 
     As discussed above, the present invention can effectively dissipate the interior built-up heat produced by the heat-generating components and cool down the housing with the cooling fan motor. The cooling fan motor comprises a motor section and a fan, and is placed at the end of the small tubular case that occupies less space in the housing than a conventional case. The cooling fan motor can thus contribute to realizing smaller and slimmer electronic apparatuses such as mobile computers, digital video cameras and the like, which may produce great merit in industrial applications.