Abstract:
A fan structure, suitable for rack-mounting adjacent to heat-generating electrical equipment, features an improved noise-damping outflow baffle containing a plurality of non-return flaps, serving to prevent reverse flow of air when fan activity is interrupted. In a preferred embodiment, four generally sickle-shaped flaps are used, each connected, along a straight edge thereof, by a pair of elastomeric hinge connections to a surrounding frame. The hinge connections urge the flaps closed whenever they are not forced by airflow into an open orientation. The axes of rotation of the flaps are chosen to keep them from jamming against one another. Since the flaps act as vanes, tending to straighten out an originally helical flow of air induced by the fan, they minimize the pressure drop which has therefore been associated with outflow baffles. The use or elastomers at critical points in the structure reduce noise and clatter.

Description:
CROSS-REFERENCE 
       [0001]    This application claims priority from German Utility Model application DE 20 2006 013 982.6, filed 5 Sep. 2006, the entire content of which is nereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention related to a fan such as an axial or diagonal fan. 
       BACKGROUND 
       [0003]    To cool electronic devices, frequently several fans are operated in parallel in a plug-in unit or the like, for example in a so-called “rack” for servers or in the switch cabinet of a grund station for cell phones. The use of the plurality of fans serves to provide a degree of redundancy, i.e. of one of the fans fails, then the remaining fan or fans assure(s) a continued sufficient supply of cooling air. 
         [0004]    If one of the fans in a plug-in unit fails, while the other fans continue to run, then a reverse flow of air would circulate through the stopped fan, which makes it necessary to take steps minimize this reverse flow. To this end, check valve flaps, also called non-return or anti-blowback flaps, are used, which automatically close when the air flows in the wrong direction. An example of this is disclosed in U.S. Pat. No. 6,174,232, STOLL+/IBM, which also describes the problem that the check valves used represent an additional flow resistance, and thus reduce the performance of the fan. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore an object of the present invention to provide a new fan structure which overcomes, or at least minimizes, such disadvantages. 
         [0006]    According to the invention, this object is achieved by using an outflow baffle which is configured to at least partially straighten out the originally helical flow of existing air, thereby converting this helical motion into static pressure. By using this outflow baffle or guide element, one version of which is known in principle from U.S. Pat. No. 6,017,191, HARMSEN, a part of the pressure loss that is caused by the at least one non-return or check valve flap is compensated for, by the fact that the outflow baffle generates an additional static pressure. In addition, the outflow baffle reduces the helical motion of the air flowing out of the outflow baffle. This helical motion might cause the flap(s) to clatter or flutter; the outflow baffle reduces this effect, so that a plug-in fan unit with improved fans of this kind operates more quietly, because the flow strikes the flaps with a reduced amount of helical motion, which also improves efficiency. 
     
     
       BRIEF FIGURE DESCRIPTION 
         [0007]    Other details and advantageous modifications of the invention can be understood from the exemplary embodiments, which are described below and shown in the drawings. These examples are not intended to limit the invention in any way. 
           [0008]      FIG. 1  is a perspective top view of an outflow baffle, viewed from its air inlet side, with the flaps closed; 
           [0009]      FIG. 2  shows the outflow baffle of  FIG. 1 , viewed from its air outlet side, likewise with the flaps closed; 
           [0010]      FIG. 3  is an enlarged view of one of the four check valve flaps; 
           [0011]      FIG. 4  is a depiction of the outflow baffle analogous to the one in  FIG. 2 , but with the flaps open; 
           [0012]      FIG. 5  shows the outflow baffle of  FIG. 4 , viewed form its air inlet side, with the flaps open; 
           [0013]      FIG. 6  is an enlarged view analogous to that of  FIG. 4 , but with the flaps open; 
           [0014]      FIG. 7  is a perspective view analogous to the ones in  FIGS. 4 through 6 , with the four flaps in the open position; 
           [0015]      FIG. 8  shows a device fan (axial or diagonal fan) whose outlet side has an outflow baffle according to  FIGS. 1 through 7  mounted on it, with closed flaps; 
           [0016]      FIG. 9  is a view analogous to the one in  FIG. 8 , but with the flaps open; 
           [0017]      FIG. 10  is a top view analogous to  FIG. 8 , of the combination of a device fan and an outflow baffle, with the flaps closed; 
           [0018]      FIG. 11  is a section through a hinge element of a closed non-return flap, viewed along the line XI-XI of  FIG. 10 ; 
           [0019]      FIG. 12  is a section, viewed along the line XII-XII of  FIG. 10 ; 
           [0020]      FIG. 13  is a section, viewed along the line XIII-XIII of  FIG. 10 ; 
           [0021]      FIG. 14  is a section, viewed along the line XIV-XIV of  FIG. 10 ; 
           [0022]      FIG. 15  is a top view analogous to  FIG. 9 , of the combination of a device fan and an outflow baffle, with the flaps open; 
           [0023]      FIG. 16  is a section through a hinge element of an open flap, viewed along the line XVI-XVI of  FIG. 15 ; 
           [0024]      FIG. 17  is a section, viewed along the line XVII-XVII of  FIG. 15 ; and 
           [0025]      FIG. 18  is a section, viewed along the line XVIII-XVIII of  FIG. 15 . 
       
    
    
     DETAILED DESCRIPTION  
       [0026]    It should be noted that the hinges of the flaps in the preferred exemplary embodiment are preferably implemented as elastic bands or strips, and that these bands are shown in a sectional view only in  FIGS. 11 ,  12 ,  16 , and  17 , whereas in  FIGS. 13 ,  14 , and  18 , these elastic strips are omitted for the sake of clarity. 
         [0027]      FIG. 1  shows an outflow baffle  30  of the type that may be used in the invention. Naturally, such outflow baffles can be configured in an extremely wide variety of forms, i.e. the example shown does in fact represent the best embodiment currently available, but can be varied in a multitude of ways. Such an outflow baffle is often referred to as a set of outlet guide vanes. 
         [0028]    An outflow baffle of this kind functions as follows: 
         [0029]    Due to the rotation of the fan impeller, the air that comes out of an axial or diagonal fan flows in a helical motion, i.e. it moves approximately in corkscrew fashion. This helical motion does not have any useful function, but producing it requires energy. The outflow baffle transforms this helical motion into a static pressure that is useful in a fan, because it pushes the air through the electronic circuit or other device to be cooled. 
         [0030]    The outflow baffle  30  has an outer frame  32  that is approximately square in the embodiment shown, but which could also be round, for example. In its four corners, this frame  32  has four mounting openings  34  of the usual kind known from device fans. 
         [0031]    The openings  34  are used for the purpose of mounting the fan. A total of eight air-guiding elements  33  through  40 , spaced apart from one another at similar angular intervals, extend radially inward from the frame  32  to an approximately rectangular inner holding element  43 . The air-guiding elements  33  through  40  have approximately the same profile as the blades of the associated fan, i.e. usually an airfoil profile, and they are so shaped that they counteract the helical motion of the air, flowing out of the associated fan  44  depicted by way of example in  FIGS. 8 and 9 . 
         [0032]    In these two figures, the reference numeral  46  indicates the direction of the air flow and the reference numeral  48  indicates the rotation direction of the fan. This permits those skilled in the art to infer the type of helical motion of the air flowing out of the device fan  44 . 
         [0033]    The air-guiding elements  33  through  40  are preferably integrally joined to both the frame  32  and the inner holding element  43  so that the elements  33  through  40  support the holding element  43 . It has a bottom  50  and is approximately the same size as the hub  52  ( FIG. 15 ) of the fan impeller  54  of the associated fan  44 . This hub  52  usually supports the drive motor (not shown) for the fan impeller  54 . 
         [0034]    In  FIG. 15 , the five blades  58  of the fan impeller  54  are shown, by way of example. The drawing shows a fan  44  with five blades  58 , the leading edges  60  of which are sickle-shaped. Preferably at their radially outer edges, the blades  58  have widened regions  62 , which reduce the fan noise. 
         [0035]    The rotation direction  48  is also indicated in  FIG. 15 , i.e. the fan impeller  54  here rotates clockwise and in the direction toward the concave sides  62 ′ of the radial holding elements  33  through  40 . Between themselves, these radial holding elements define flow openings for the air supplied by the fan  44 , for example the flow opening between the holding elements  37  and  38  in  FIG. 1 . When one fan in a battery of fans malfunctions, these flow openings must be closed by closing elements. To this end, according to  FIG. 2 , four non-return or check valve flaps  72 ,  74 ,  76 ,  78  are arrayed symmetrically around the inner holding element  43  and, in the exemplary embodiment, these four valve flaps are identically formed. To achieve a good damping action, they are preferably made of fiberglass-reinforced polypropylene. As  FIG. 2  shows, in their closed position, the valve flaps  72 ,  74 ,  76 ,  78  are recessed into the surface of the outflow baffle  30  so that, during transport, they are protected by the protruding outer rim  32  of the outflow baffle  30 . 
         [0036]      FIG. 3  is a very enlarged depiction of the flap  78 . By means of an elastic strip  80  at its radially inner corner  82 , this flap is attached to the inner holding element  43  at the latter&#39;s bottom left corner  84  in  FIG. 3 . The elastic band  80  is comprised of an elastomeric plastic, preferably a thermoplastic elastomer (TPE), whose hardness is adjusted as needed. This strip  80  made of TPE is injection-molded onto the corner  82  of the valve flap  78  and onto the corner  84  of the inner holding element  43 , i.e. it is attached to the valve flap  78  and the holding element  43  by being melted onto them. The injection procedure occurs while the valve flap  78  is in its closed position, as shown in  FIG. 3 . Therefore, when the valve flaps  72 ,  74 ,  76 ,  78  are open, as shown in  FIG. 4 , the TPE bands exert a restoring force on them, which attempts to pivot them into their respective closed positions, whenever air pressure slackens. 
         [0037]    As shown in  FIG. 3 , flap  78  has a straight inner edge  88  whose upper end  90  in  FIG. 3  likewise has a TPE band  92  injection-molded onto it; the right end of this band  92  in  FIG. 3  is injection-molded onto a projection  94  that protrudes inward from the frame  32  and the left end of this band  92  in  FIG. 3  is injection-molded onto the right, upper end  90  of the valve flap  78 . As a result, the flap  78  in  FIG. 3  can be pivoted from the left, for example by pressure of air driven from the fan, toward the right into an approximately perpendicular position, as shown in  FIG. 4 . Because of their identical form and identical attachments, the same applies to the other flaps  72 ,  74 , and  76 . 
         [0038]    Adjoining the straight edge  88  and situated at a right angle to it, the flap  78  has a short, straight section  98  at the top, adjoined by a circular arc-shaped section  100 , which is complementary to the opposing rim  102  of the outflow baffle  30 . At its bottom end in 
         [0039]      FIG. 3 , the section  100  transitions into a straight edge  104 , which extends parallel to the edge  88 , and the edge  104  extends down to a recess  106  at the bottom left corner of the valve flap  78 . In  FIG. 3 , a straight lower edge  108  extends horizontally from this recess  106  to the corner  82 . The valve flap  78  thus has approximately the outline of a rectangle whose upper left corner has been cut off. 
         [0040]    As shown in the drawing, the recess  106  contains a projection or stop  94 ′ of the frame  32 ; the drawing also shows that an elastic band  92 ′ for the valve flap  76  is injection-molded onto this projection or step  94 ′. 
         [0041]      FIG. 11  is a section, viewed along the line XI-XI of  FIG. 10 , through the elastic hinge band  92  made of TEP. At one end, this band is attached to a post  94  made of plastic, e.g. fiberglass-reinforced polypropylene, and is attached to this post by being melted onto it. At the other end, the hinge band is attached to the valve flap  78  (likewise comprised of polypropylene) that is provided with a cavity  110  for this purpose, which cavity is filled with the TPE of the band  92 . As shown in the drawing, the band  92  also extends over the top of the post  94 , in order to achieve a particularly durable attachment. 
         [0042]      FIG. 12  is a section, viewed along the line XII-XII of  FIG. 10 . At the left is the valve flap  78 , which has a cavity  112  to which the left end of the elastic hinge band  80  is attached by being melted into it. At the right, is the inner holding element  43 , which is provided with a cavity  114  at the top, to which the right end of the hinge band  80  is attached, likewise by being melted onto it. 
         [0043]      FIG. 13  is a section, viewed along the line XIII-XIII of  FIG. 10 . The elastic hinge band is not shown here; only the corresponding cavity  116  at the top of the inner holding element  43  and a cavity  118  of the valve flap  74  are shown. Arranged as shown in  FIG. 13 , the parts are inserted into an injection mold (not shown) in which the hinge band is injection-molded out of TPE; this band has an appearance that is mirror-symmetrical to the band  80  shown in  FIG. 12  and is therefore not shown here. 
         [0044]      FIG. 14  is a section, viewed along the line XIV-XIV of  FIG. 10 . The elastic element is not shown here and only a cavity  120  of the inner holding member  43  is shown, in which this elastic element is anchored by means of an injection-molding process. 
         [0045]      FIG. 15  is a depiction analogous to  FIG. 10 , but the flaps  72 ,  74 ,  76 ,  78  are shown in their open positions that they assume when the fan  44  is operating; the elastic hinge strips  80 ,  92  etc. are then bent by approx. 90° and exert a corresponding restoring force on the check valve flaps  72 ,  74 ,  76 ,  78 . Only two of the total of eight hinge strips are shown. 
         [0046]      FIG. 16  is a section, taken along line XVI-XVI of FIG  15 . This corresponds to the sectional view in  FIG. 11 , with the flap closed. The reference numerals are the same as in  FIG. 11  and the reader is therefore referred to this earlier description. 
         [0047]      FIG. 17  is a section, taken along line XVII-XVII of  FIG. 15 . This section corresponds to the one in  FIG. 12 , with the difference that in  FIG. 12 , the valve flap  78  is closed and in  FIG. 17 , it is open. The reference numerals are the same in both figures.  FIG. 17  shows that, when open, the flap  72  adjacent to the valve flap  78  strikes with its bottom left corner  124  against the TPE material of the hinge band  80 , which prevents clattering. Because of the symmetry of the arrangement, this applies equally to all of the valve flaps of the outflow baffle  30 , which is why this outflow baffle can also be referred to as super-silent. 
         [0048]      FIG. 18  is a section, taken along line XVIII-XVIII of  FIG. 15 , i.e. with the flap  74  open. The hinge band  126  is indicated in phantom with dot-and-dash lines. 
         [0049]    It will be apparent that the present invention thus achieves a variety of advantageous effects. Since the outflow baffle  30  is combined to form a unit with the flaps  72 ,  74 ,  76 ,  78 , this structural unit can be combined as needed with any fan  44  of the same size, as shown by way of example in  FIGS. 8 and 9 , thus only increasing the price of the fan  44  by an insignificant amount. Alternatively, the outflow baffle  30  can also be made part of the fan  44 , if this is desirable due to the size of the production run. 
         [0050]    The outflow baffle generates an additional static pressure, which compensates for at least part of the pressure less incurred by the flaps  72 ,  74 ,  76 ,  78 . 
         [0051]    The flaps can easily be injection-molded onto the outflow baffle  30  by means of the connecting elements mode of TPE. Alternatively, the flaps might be entirely comprised of TPE, in which case they would not require any special connecting elements. 
         [0052]    A very reasonably priced design is achieved since the outflow baffle with its valve flaps can be ready-made in one injection-molding procedure. This avoids the need for the labor-intensive step of manually assembling individual parts, e.g. springs. 
         [0053]    An outflow baffle of this type functions regardless of its position, which, in practice, is a significant advantage. Since the hardness of the TPE material can be adjusted, this means that the stiffness of the connecting elements can also be adjusted. It is therefore possible to change the outflow baffle depending on the intended air output, i.e. with a low air output, connecting elements are used that have only a low rigidity, whereas for higher air outputs, correspondingly stiffer connecting elements can be used. 
         [0054]    An outflow baffle according to the invention, including its non-return flaps, requires only a small amount of space and generates only a small amount of noise, since it is possible to use plastic materials having a high level of internal damping. 
         [0055]    An outflow baffle of this kind can particularly easily be adapted to axial fans and diagonal fans. 
         [0056]    The outflow baffle upstream of the flaps acts on these flaps with an air flow having a reduced helical motion. As a result, the flaps have a lower tendency to vibrate/clatter, compared to prior art flap arrangements. 
         [0057]    The injection-molded flap stops prevent the flaps from touching or getting caught on one another, and thus from jamming. 
         [0058]    This also gives the customer the option of ordering the outflow baffles in the desired numbers and makes it very simple to keep a few spare outflow baffles on hand and to replace any malfunctioning or broken outflow baffles, as needed, with these spare parts, without having to replace the entire fan. 
         [0059]    Naturally, numerous variations and modifications are possible, within the scope of the present invention.