Abstract:
A fan for cooling a circuit board ( 26 ) has a fan wheel ( 10; 10 ′) that is adapted for rotation about a rotation axis ( 11 ) and in a predetermined rotation direction ( 14 ), and an outer wall ( 18 ) that is rigidly joined to an inner wall ( 16 ). Defined between the two walls ( 16, 18 ) are curved air-directing conduits ( 39 ) that extend from an axial air entrance opening ( 40 ) to a radial air exit opening ( 42 ). The axial air entrance opening ( 40 ) is at a lesser distance from the rotation axis than the radial air exit opening ( 42 ), and the air-directing conduits ( 39 ) are separated from one another by air-directing blades ( 30, 32, 34, 36, 38 ) that each extend, oppositely to the predetermined rotation direction ( 14 ), from a point between two adjacent air entrance openings ( 40 ) to a point between two adjacent air exit openings ( 42 ).

Description:
CROSS-REFERENCE 
     This application is a section 371 of PCT/EP2005/10624, filed 1 Oct. 2005 and published 20 Apr. 2006 as WO 2006-40031-A, and claims priority from DE 20 2004015 896.5 and DE 20 2005 015 357.5, the entire contents of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a fan having a fan wheel, which latter can also be referred to as an air-directing wheel. 
     BACKGROUND 
     In particular for cooling electronic components that are arranged on circuit boards, a powerful stream of air proceeding approximately parallel to the plane of the circuit board is needed. So-called circuit board fans, such as those shown e.g. by EP 0 666 424 A1, AMRHEIN et al., are used for this. A fan of this kind draws in air by means of its fan wheel in an axial direction, and blows it in a radial direction onto adjacent electronic components in order to cool them. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to make available a novel fan. 
     According to the invention, this object is achieved by a fan in which curved fan blades define a plurality of helical conduits between respective axial entrance openings and respective radial exit openings. Because the air-directing blades extend, oppositely to the predetermined rotation direction, from the entrance openings to the exit openings, the air pressure in the fan wheel can build up over a longer distance, which is favorable to air output. A configuration of this kind moreover enables, when necessary, a very compact and low design. 
     Another manner of achieving the stated object is to define a plurality of helical air-directing conduits which each extend over more than one-fifth the entire angular extent of the fan wheel. A fan of this kind is particularly suitable for cooling electrical components on circuit boards. 
    
    
     
       BRIEF FIGURE DESCRIPTION 
       Further details and advantageous refinements of the invention are evident from the exemplifying embodiments, in no way to be understood as a limitation of the invention, that are described below and depicted in the drawings. 
         FIG. 1  is a side view of a preferred embodiment of a fan wheel for a fan according to the present invention, at enlarged scale; 
         FIG. 2  is a section looking along line II-II of  FIG. 1 ; 
         FIG. 3  is a section looking along line III-III of  FIG. 1 ; 
         FIG. 4  is a perspective depiction showing a section through the fan wheel of  FIGS. 1 to 3 , sectioned along a section line that coincides with section line III-III of  FIG. 1 ; 
         FIG. 5  is a sectioned depiction showing the fan wheel of  FIGS. 1 to 4  as part of a fan in the installed state between two plate-shaped components, and enlarged to a scale of approximately 6:1; 
         FIG. 6  is a depiction analogous to  FIG. 5  showing a variant of the fan wheel, which in this case has a greater axial length and extends with its intake openings through an opening of a circuit board, in order to draw in cool air from the space above said circuit board; and 
         FIG. 7  is a depiction analogous to  FIG. 4 , in which inner air-directing wall  16  is equipped with orifices  80 ′ through which a portion of the delivered air can flow downward and can there cool components as well as the motor of the fan wheel. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a side view of fan wheel  10  of a circuit board fan as depicted in  FIGS. 5 and 6 . Fan wheel  10  rotates during operation in the direction of an arrow  14  in a predetermined rotation direction, about a rotation axis  11 .  FIG. 6  shows a somewhat differently dimensioned fan wheel that is labeled  10 ′ but corresponds to fan wheel  10  of  FIGS. 1 to 5  in terms of its construction and drive system. An electronically commutated external-rotor motor  12 , which is depicted in section in  FIGS. 5 and 6 , preferably serves to drive fan wheel  10 . 
     As the section according to  FIG. 2  shows, fan wheel  10  has an inner air-directing wall  16  that is implemented in concave fashion when viewed from above, and an external air-directing wall  18  that is likewise implemented in concave fashion when viewed from above, the curvatures of air-directing walls  16 ,  18  being designed so as to yield an air passage  20 . During operation, i.e. upon rotation of fan wheel  10 , air is drawn into this air passage  20  in the direction of arrows  22 , i.e. approximately axially, and this air is blown out again in a radial plane (arrow  24 ), for example onto electronic components  28  on a circuit board  26 , as depicted in  FIG. 5 . This is therefore a special design of a diagonal fan wheel that deviates greatly from the known designs. Air inlet  40  (dimensional arrow X 1 ) is preferably larger than air outlet  42  (dimensional arrow X 2 ) in order substantially to improve the pressure buildup in fan wheel  10 , and thereby the cooling effect. 
     The two air-directing walls  16 ,  18  are joined to one another inside air passage  20  by five air-directing blades  30 ,  32 ,  34 ,  36 ,  38 . In  FIG. 3 , air-directing blade  30  is depicted in partly cutaway fashion in order to show the entire profile of air-directing blade  38 . 
     The profile of the air-directing blades may be inferred particularly well from  FIGS. 3 and 4 , which show a horizontal section through fan wheel  10  (along line III-III of  FIG. 1 ). 
     For example, in  FIG. 4  air-directing blade  30  begins at approximately the 7:30 position (with reference to a clock face), extends in the upper part of  FIG. 4  oppositely to rotation direction  14  approximately as far as the 5:00 position, and from there extends further, according to the lower part of  FIG. 4  and as shown in  FIG. 3 , to approximately the 2:00 position. 
     An air-directing blade thus extends, in this example, over approximately 160 to 180° from the inlet to the outlet. As a result, in this example five air-directing conduits  39  are formed, which each begin at an annular-sector-shaped inlet  40  on the upper end face of fan wheel  10  and extend over approximately 180° to an associated outlet  42  on the periphery of said fan wheel  10 . This outlet itself has an extension of approximately 120° since the air-directing blades form an oblique delimitation of outlet  42 , and has approximately the shape of a parallelogram. In  FIG. 1 , for example, outlet  42  visible there is delimited by the two air-directing blades  36 ,  38  and by the two air-directing surfaces  16 ,  18 . 
     The number of air-directing blades depends on the air flow demand and on the allowable noise emission. If the rotation speed must be low for noise-related reasons, this influences the number of blades required. This number can be optimized by experiment. 
     The sectioned depiction of  FIG. 2  shows, on the inner side of air-directing surface  16 , a part  52  of rotor  50 . Part  52  is preferably implemented integrally with fan wheel  10  and has in cross section approximately the shape of a shell. Located at its center is an opening  54  for a rotor shaft  56  (cf.  FIGS. 5 and 6 ). A bearing tube  58 , into which a sintered bearing  60  is pressed, is provided for journaling of shaft  56 . Stator  62  of the motor is pressed onto the outer side of bearing tube  58 . 
     A closure plug  64  is pressed onto the lower end of bearing tube  58 , and said plug has resilient prongs  66  that, upon assembly, latch into an annular groove  68  at the lower end of shaft  56  and prevent the latter from being pulled out. 
     A magnetic yoke  70  is mounted in rotor part  52  as shown in  FIGS. 5 and 6 , and a rotor magnet  72  that coacts with stator  62  is mounted on said yoke. 
     For assembly, according to  FIGS. 5 and 6 , firstly stator  62  is installed on circuit board  26  by the fact that the lower end of bearing tube  58  is pressed into an aperture  74  of circuit board  26  as far as a stop  76 ′. 
     An air guidance part  76 , which is equipped with support feet  78  and latching feet  80  and is mounted on circuit board  26  in the manner depicted by being latched in, is then mounted around stator  62 . Part  76  directly adjoins outlet openings  42  of fan wheel  10 . Its distance from circuit board  26  increases in the direction away from stator  62 . This part  76  improves cooling and prevents unnecessary eddying of the air at the points where it emerges from fan wheel  10 . 
     Also contributing to improved cooling is the fact that for all air conduits the air inlet opening, symbolized by arrow X 1 , is larger than the air outlet opening, symbolized by arrow X 2 . A greater pressure buildup thereby occurs, which substantially improves the cooling effect. 
     Circuit board  26 , on which stator  62  and part  76  are installed, can be transported in this form. At the destination location, fan wheel  10  is mounted by introducing shaft  56  into bearing  60 , and by latching resilient prongs  66  in place there. In order to prevent frictional losses, these prongs preferably have no sliding contact with annular groove  86 . Assembly of fan wheel at a later time is advisable because shaft  56  has, in practice, a diameter corresponding approximately to that of a knitting needle, so that it could easily bend upon impact. Assembly at the service location of the unit prevents damage during transport. 
     The construction of motor  12  is the same in the context of  FIG. 6  as in  FIG. 5 , except that fan wheel  10 ′ extends farther upward; this can be advantageous in terms of flow engineering. The air conduits in fan wheel  10 ′ have, in principle, the same helical shape that was described in detail with reference to  FIGS. 1 to 5 . Part  76  is likewise identical to part  76  that was described in the context of  FIG. 5 . In  FIG. 6  as well, inlet opening X 1  is larger than outlet opening X 2 , in order to achieve good pressure buildup and good cooling. 
     From what is depicted in  FIGS. 5 and 6 , it is apparent to one skilled in the art that motor  12 , as well as components (not depicted) arranged on circuit board  76  beneath fan wheel  10 , are poorly cooled because very little air exchange takes place there. 
     For this reason, in the variant according to  FIG. 7 , several orifices  80 ′ are provided in inner wall  16  of fan wheel  10 , which preferably are distributed symmetrically in order to prevent imbalances in fan wheel  10 . Orifices  80 ′ are each preferably located, as depicted, approximately adjacent to the point at which a vane  30 ,  32 ,  34 ,  36 ,  38  transitions into the lower (in  FIG. 7 ) part of inner wall  16 , so that cooling air is transported through these orifices  80 ′ into the region located between circuit board  76  and inner wall  16  of fan wheel  10 . This air, on the one hand, cools motor  12 , and, on the other hand, cools electronic components (not depicted) that are arranged there on circuit board  76 . The area available on circuit board  76  for population with components is thereby enlarged. 
     Numerous variants and modifications are of course possible within the scope of the present invention.