Patent Publication Number: US-2021164495-A1

Title: Fan and intake grid for a fan

Description:
This application is a national stage entry under 35 U.S.C. 371 of PCT Patent Application No. PCT/DE2019/200013, filed Feb. 15, 2019, which claims priority to German Patent Application No. 10 2018 205 300.6, filed Apr. 9, 2018, the entire contents of each of which is incorporated herein by reference. 
    
    
     This disclosure relates to a fan (axial fan, radial fan or diagonal fan) having an impeller and a guide device in the flow path upstream from the impeller, upstream from the inlet area of an inlet nozzle, wherein the guide device is configured as an intake grid having flat webs, and wherein the webs form a plurality of flow channels resembling grid cells. In addition, this disclosure relates to an example guide device, configured in the sense of an intake grid having flat webs. 
     A generic fan having a guide device on the intake side is known from WO 03/05439.5 A1, for example. The guide device provided there serves primarily to smooth out the flow, and to reduce the noise. The known guide device produces a pre-swirl in the direction of rotation of the impeller. It is important here that acoustic improvements are generally associated with a reduction in air performance and efficiency. The guide device provided there is also very expensive to manufacture. 
     So-called guide wheels that are used to increase efficiency and/or air performance are also known from practice. However, these guide wheels result in acoustic disadvantages and have a complex design as well as being complicated to install in the respective fan products. They are usually installed upstream from fan impellers in a cylindrical installation space with approximately the same diameter as the fan impeller, and therefore they do not have a significantly larger flow-through area. Therefore, the air flow rates in the area of these guide wheels are relatively high, and give rise to undesirable acoustic effects. 
     This disclosure addresses the following technical problem. 
     Fans often generate more noise in response to perturbed incoming flow. In many fan applications, for example, in controlled residential ventilation (CRY), perturbed inflow conditions necessarily arise from the usual demands for a compact design. The resulting noise, Which often has major tonal components, is usually low-frequency noise. Noise abatement measures for this low-frequency noise are desirable in ventilation equipment, for example. 
     It is also already known that the noise associated with perturbed incoming flow can be reduced significantly by using so-called flow rectifiers. However, such flow rectifiers cause a substantial pressure drop that is not insignificant, and they also require a large installation space. Therefore, the object of this disclosure is to design and improve upon such a fan, so that the noise associated with a perturbed flow is reduced. The fan should be compact and should cause only an extremely minor pressure drop. Furthermore, an inlet guide device, which may be an intake grid and/or a guide baffle is to be provided, such that it meets the requirements defined above and can be manufactured by injection molding of plastics with economical tooling. It should have dimensional stability and should advantageously be able to take over the function of a touchproof grid on the intake side. 
     The object defined above is achieved with respect to an fan by alternative combinations of features according to the features of the independent claims  1 ,  2  and  3 . With respect to the intake grid, the object defined above is achieved by the features of claim  12 , which is based on the claims relating to the fan. 
     In the context of a first variant according to claim  1 , the webs extend mainly between two branches or between one branch each into a border area. An example embodiment includes three webs for each branch. With these features, flow channels resembling grid cells may be provided, these flow cells being suitable for reducing noise when there is perturbed flow. 
     Independent claim  2  achieves the object defined above by the fact that the flow channels have a honeycomb cross section. This design also yields a great stability. 
     The other independent claim  3  relates to another alternative, according to which the intake grid has a cage-type contour, wherein this embodiment is based on the outer and/or inner enveloping surface(s) of the intake grid. 
     The same thing is also true of the embodiment of the intake grid itself, which is defined in the other independent claim  12  with reference back to the claims relating to the fan. 
     The independent claims are based on the fundamental idea of providing an intake grid or inflow grid upstream from the inlet nozzle of a fan, in order to reduce the noise generated during perturbed flow in operation of the fan. The intake grid is defined by flat webs, such that the webs are arranged in relation to one another, so as to form flow channels resembling grid cells. Due to the skillful combination of webs forming branches and node points, it is possible to achieve advantageous geometric shapes, for example, so that the flow channels have a honeycomb cross section. The term “honeycomb” is to be understood in the broadest sense, so that it also includes polygons, such as grid cells having a rectangular, pentagonal or hexagonal structure or a cross section with even more corners. 
     According to the aforementioned flow channels resembling grid cells, it is also advantageous that the intake grid has a cage-type contour, such that the contour may refer to either the outer or inner enveloping surface of the intake grid. 
     An intake grid of the type mentioned above fulfills the requirement of radial intake flow in the area near the nozzle plate. These flow channels have an advantageous effect of minimizing pressure losses. The cage-type outer contour is also advantageous for easy mold release in the context of injection molding technology used with plastic parts. Furthermore, compact grids having the respective properties can also be manufactured in this way. 
     The cage-type outer contour is advantageous if it is continuous and curved. The grid webs should be configured to be as thin as possible, for example, with a web thickness in the range of 0.25 mm to 1 mm. In the flow-through direction, they should be at least 5 mm deep (hence the term “flat web” used in the claims). 
     It is additionally advantageous that the grid webs form an unstructured grid, in which honeycomb grid cells are combined with one another. As already explained above, the grid cells may be polygonal and may be combined with one another. This makes it possible to achieve minimal obstruction by the grid webs, for example, when a certain maximum grid width is necessary because of the required noise reduction or taking into account touchproof aspects, resulting in a little loss of pressure and efficiency. 
     The intake grid also advantageously extends over the entire area up to the imaginary extension of the axis of the fan, i.e., it does not have a relatively large opening in the inner area or has none at all. Such a center opening is not necessary thanks to the teaching of this disclosure. In fact, it should be avoided entirely if the intake grid also fulfils a touchproof function. In addition, it has been found that a center opening would not be consistent with the goals of noise abatement and stability of the grid. 
     In any case, the design of the intake grid is advantageous, not only with respect to the flow channels that resemble grid cells, but also with respect to the continuous curved outer contour. Unstructured grids can be produced by using rectangular, pentagonal or hexagonal honeycomb elements, thereby making it possible to produce variable grid widths over the entire intake grid as needed. 
     The intake grid is intended for use in an axial fan, a radial fan or a diagonal fan and is configured according to the preceding description. 
    
    
     
       There are now various possibilities for advantageously designing and improving upon the teaching of this disclosure. Reference should be made first to the claims that refer back to claim  1  and, second, to the following discussion of embodiments of an intake and with reference to the drawings. Example embodiments and improvements on the teaching are also described in conjunction with the discussion of specific examples with reference to the drawings. The drawings show: 
         FIG. 1  a perspective view of one embodiment of an intake grid, as seen from the intake side, 
         FIG. 1 a    a perspective view of a schematic detail of a cell constructed of webs according to  FIG. 1 , identifying the example dimensions of the webs and cells, 
         FIG. 2  a perspective view of the intake grid from  FIG. 1 , as seen from the outflow side, 
         FIG. 3  an axial top view of the intake grid from  FIGS. 1 and 2 , as seen from the inflow side, 
         FIG. 4  an axial top view of the intake grid from  FIGS. 1 to 3 , as seen from the outflow side, 
         FIG. 5  a side view and a sectional view of the intake grid according to  FIGS. 1 to 4  in a plane through the axis, identifying the example dimensions of the intake grid, 
         FIG. 6  a perspective view of another embodiment of an intake grid, as seen from the inflow side, 
         FIG. 7  an axial top view of the intake grid from  FIG. 6 , as seen from the outflow side, 
         FIG. 8  a perspective view of another embodiment of an intake grid, as seen from the inflow side, 
         FIG. 9  a perspective view of the intake grid from  FIG. 8 , as seen from the outflow side, 
         FIG. 10  an axial top view of the intake grid from  FIGS. 8 and 9 , as seen from the inflow side, 
         FIG. 11  a side view and a sectional view of the intake grid according to  FIGS. 8 to 10  in a plane through the axis, identifying the example dimensions of the intake grid, 
         FIG. 12  a side view and a sectional view of an intake grid having curved webs, in a plane through the axis, 
         FIG. 13  a perspective view of another embodiment of an intake grid having a central closed injection area, as seen from the inflow side, 
         FIG. 14  an axial top view of the intake grid from  FIG. 13 , as seen from the inflow side, 
         FIG. 15  a side view of the intake grid according to  FIGS. 13 and 14 , 
         FIG. 16  a side view and a sectional view of the intake grid according to  FIGS. 13 to 15 , in a plane through the axis, 
         FIG. 17  a perspective schematic diagram of a fan having a motor, an impeller, an inlet nozzle, a nozzle plate and the intake grid according to  FIGS. 13 to 16 , as seen from the inflow side, and a sectional view in a plane through the axis. 
     
    
    
       FIG. 1  shows one embodiment of an intake grid  1  in a perspective view from the front, i.e., as seen from the inflow side. As in the diagram in  FIG. 17 , the intake grid  1  is advantageously mounted upstream from the inlet nozzle  2  of a fan, so that its axis corresponds approximately to the axis of rotation of the fan. During operation of the fan, air flows first through the intake grid  1  into the inflow nozzle  2  before undergoing a total increase in pressure in flowing through an impeller of fan, which is driven by a motor  4 . The intake grid  1  smooths out the incoming air flow, thereby reducing the noise generated in the impeller. 
     The intake grid  1  consists of a plurality of webs  5 , which define grid cells  6 . Air flows through the grid cells  6  during operation of the fan, i.e., the cells form flow channels. The speed of the incoming air flow is lower in an area upstream from an inlet nozzle  2  than in the interior of an inlet nozzle  2 , because the flow-through area for the air mass flow rate conveyed by the fan is 110 greater in an area upstream from an inlet nozzle  2  than in the inlet nozzle  2 . The intake grid  1  is used in such an area of low flow rates, i.e., the flow-through rate with the intake grid  1  is lower than the flow-through rate in the inlet nozzle  2 . This minimizes flow losses and the noise generated at the intake grid  1 . 
     However, since the inflow in an area upstream from an inlet nozzle  2  is not smooth, i.e., is not primarily parallel to the axis, it is also a great advantage not to design the contour of the intake grid  1  to be completely smooth. The contour may also be described by the outer enveloping surface  7  and/or the inner enveloping surface  8  ( FIG. 2 ) of the intake grid  1 . These enveloping surfaces  7 ,  8  are defined by the totality of the end faces  7   a  and  8   a  of the webs  5  on the inlet and/or outlet ends (see  FIG. 1 a   ), respectively, supplemented by imaginary continuous completion of surfaces or curved and continuous completion of surfaces in the area of flow channels  6 . 
       FIG. 1 a    shows a detailed, enlarged diagram of an area of the intake grid  1  from  FIG. 1 . The webs  5  have a significant depth t ( 9 ), as seen in the direction of through-flow, advantageously approximately 6-20 mm. For this reason, the webs  5  are also referred to as “flat” webs. A grid cell  6  includes a cell width w ( 12 ), for example, defined by the radius of the largest inner sphere of the cell  6 . A small grid width w ( 12 ) is advantageous in order to achieve good acoustic values, for example, a value w ( 12 ) of no more than two to three times the web depth t ( 12 ) for most of the cells  6  of an intake grid  1 . The intake grid  1  in the embodiment according to  FIG. 1  is also a touchproof device, which must conform to requirements according to standards and regulations with regard to the cell width w ( 12 ) as a function of the shape of the cell and the distance of the cell  6  from a rotating part of the fan. Therefore, the cell width w ( 12 ) also has an upper size limit. 
     For the loss of pressure and efficiency to be low, it is advantageous for the obstruction of the flow-through area by the grid webs  5  to be as low as possible. This can be achieved by having thin webs (web thickness d ( 10 ) that are advantageously mostly ≤2 mm [≤1 mm]) and/or by minimizing the total web length (sum of all web lengths l ( 11 ) of an intake grid ( 1 ). The web lengths  1  are determined on the basis of the neutral fibers  13 , advantageously on the outer or inner enveloping surface  7  and/or  8 ). An “unstructured” grid design with honeycomb cells  6  as in the embodiment may be very advantageous for the required total web length under the conditions described for the maximum grid width w ( 12 ). 
       FIG. 2  shows a perspective view of the intake grid  1  according to  FIG. 1 , as seen from the outflow side. The intake grid  1  has mounting areas  18  on the outer area, which serve to attach the intake grid  1  to the inlet nozzle  2  or the nozzle plate  32  ( FIG. 17 ). Various options may be considered for the design of the mounting areas  18 . Possible fastenings include screws, rivets, snap-fit hooks, bayonet closures, adhesive bonding, interlocking, hook-and-loop fastenings or others. In this embodiment, a screw hole is provided in each of four mounting areas  18 . 
     The cage-type contour of the inner enveloping surface  8  of the intake grid  1  can be seen well in the view according to  FIG. 2 . This contour continues for a short distance on the outer circumference, advantageously more than 10 mm or more than 8% of the outside diameter D ( 20 ) ( FIG. 5 ), approximately parallel to the imaginary center axis, approximately on a cylinder surface (cylinder surface-type area  34 ). This cylinder surface-type area  34  contains the cells  19  of the outer row, two neighboring cells of which are separated from one another by a web  35  of the outer row. The cells  19  of the outer row have a very elongated shape. In order to ensure that they are touchproof and to achieve the acoustic improvements, the cell widths w (inner sphere radii, determined in the cells  19  of the outer row essentially by the distance between two neighboring webs  35  of the outer row) of these cells tend to be lower in comparison with the inner sphere radii of the other cells  6 . In an area near the axis, the contour runs flat or planar, approximately orthogonal to the axis (flat area  33 ). In this embodiment, the transition from the flat area  33  to the cylinder surface-type area  34  takes place over a short transitional area  24 , which has a curvature. In this embodiment, the outer enveloping surface  7  and the inner enveloping surface  8  are approximately parallel. The areas  33 ,  34 ,  24  can be classified on the basis of the outer and/or inner enveloping surface(s)  7  and/or  8 , respectively. 
       FIG. 3  shows the intake grid  1  according to  FIGS. 1 and 2  in an axial top view from the front (as seen from the inflow side). Such an intake grid  1  is advantageously manufactured by injection molding of plastics. It is additionally advantageous to also select the line of sight from  FIG. 3  as the direction of mold release for an injection mold to minimize the complexity of the mold. Then one mold part is moving toward the observer in relation to the intake grid  1 , this part advantageously being the nozzle side of the mold, and another mold part is moving away from the observer. To simplify manufacturing, the injection mold advantageously has no other slide valves. 
     The mounting areas  18  are configured together with the grid webs  5 , so that they can be released from an injection mold in a sliding direction parallel to the axis (corresponding to the line of sight in this diagram) without any undercuts. It can be seen that some of the grid webs  5  do not run parallel to the center axis (=line of sight), but instead their orientation is optimized to the intake conditions. The webs may advantageously also have a curvature to guide the flow optimally. For example, a web  29  that is an axially aligned web is marked, i.e., it runs parallel to the axis (line of sight and sliding direction), which facilitates mold release. Axially aligned webs  29  are advantageously provided with a mold release angle. However, there are also webs  30 ,  30   a  that are not aligned axially, because all the webs  5  are optimized to the directions of flow. The two radially outermost rows of grid webs  5 , running approximately circumferentially, are situated in the transitional area  24  of the enveloping surfaces  7  or  8  and are coordinated so as to result in only a few undercut areas or none at all, i.e., they conceal one another only slightly or not at all, as seen in the axial direction. In the embodiment shown here, for example, there is a small undercut area  17  in the combination of the web  5   a  of the radially outermost row of webs  5  and of the web  5   b  of the second row of webs  5 , because these two webs have a slight overlap area in the line of sight. When a suitable, relatively elastic material is chosen, minor undercuts can be produced, while nevertheless allowing unmolding of parts in the axial direction using a simple open-and-close mold. This makes it possible to easily and economically produce a contour that is highly optimized fluidically. In addition, there is a minor undercut area in the branching area branching area  15  between the two webs  30  and  30   a  that are not aligned axially, because the x-components of their surface normal vectors have different plus or minus signs. This minor undercut can also be removed easily from a simple open-and-close mold if a suitable material is chosen. 
     In this embodiment, the cells in the area near the axis are smaller than those in an area remote from the axis. The cell size, i.e., cell width w ( 12 , see  FIG. 2 ), is optimized with regard to the requirements about compliance with contact protection regulations and acoustic improvements and/or flow smoothing measures. The distribution of cells is optimized by using an algorithm. There are a wide variety of cell contours (looking at one of the enveloping surfaces  7  or  8 ), for example, regular and irregular rectangles, pentagons and hexagons. Each cell (looking at an enveloping surface  7  or  8 ) describes approximately an area of points that are closest to an imaginary central point (on the enveloping surface) in comparison with the imaginary central points of all other cells. Consequently, the structure of grid  1  of this example includes exactly three webs  5  in most branching areas  15 , and four webs  5  converge in far fewer branching areas. Furthermore, there are no relatively small cells at the border with a flow-through area of less than 50% with respect to the flow-through area of one of the neighboring cells that are formed by an effect of “cutting through outer cells at the border.” 
     According to  FIG. 4 , the intake grid  1  from  FIGS. 1 to 3  is shown in an axial top view from the rear (as seen from the outflow side). The webs  35  of the outer row that are aligned in the axial direction have one free end  14 . Therefore, they can be unmolded by a mold slide valve moving in the direction of the outflow side (toward the observer) when opening. The fact that the ends  14  of the outer webs  35  are not connected is a disadvantage with respect to strength and dimensional stability, but this can be compensated by a high-quality material or by thick walls d ( 10 ). 
     The intake grid  1  in this embodiment includes four identical segments. This is an advantage in construction of the part and the mold required for production, because the number of differently shaped grid cells  6  is thereby reduced by a factor of 4 (factor=number of segments). Due to this segmentation, the flow pattern is independent of the alignment x (quadrant) of the intake grid  1  in assembly. A different number of segments is also possible. The segments may differ in minor ways, for example, with regard to mounting measures, if the number of mounting measures does not correspond to the number of segments, or in an inner area near the axis, where segmentation may be more difficult under some circumstances. In a case of large outside diameters, segmentation can be used advantageously, so that the intake grid  1  can be assembled from a plurality of injection-molded segments, for example, by clipping, snapping, screwing, gluing, fastening to the nozzle plate or the like. With this multi-part approach, it is also conceivable to produce a different separate central part in addition to the actual identical segments, although this different part then requires a separate injection mold. However, the central part may have a simple design, for example, being planar, i.e., flat. 
     In the embodiment shown here, there is a central branching point  16  of four (=number of segments in the embodiment) webs  5  at the center, on the axis. 
       FIG. 5  shows the intake grid  1  according to  FIGS. 1 to 4  in a side view and in a sectional view of a plane through the axis. The shape of the cage-type contour of the enveloping surfaces  7  on the inflow side and/or enveloping surfaces  8  on the outflow side can be seen well here. The outer enveloping surface  7  has an outside diameter D ( 20 ), which is also referred to as the diameter D ( 20 ) of the intake grid  1 , but the diameter of the mounting areas  18  is not taken into account here. The outer enveloping surface  7  and the inner enveloping surface  8  run approximately parallel to one another in this embodiment. The distance of the enveloping surfaces  7  and  8  from one another is advantageously 6 mm to 18 mm or approximately 3%-10% of the diameter D ( 20 ) of the intake grid  1 . The contour runs for a distance approximately axially parallel (cylinder surface-type part  34 ) in the upper and lower areas near the mounting level. The transition to the flat area.  33  is continuous and curved in a transitional area  24 , at the right in the diagram (inflow side). The transitional area  24  is short in the radial direction, amounting to less than 12.5% of the outside diameter D ( 20 ). The flat area  33  has a diameter DE ( 21 ), which is advantageously relatively large and amounts to at least 75°/h of the value of the outside diameter D ( 20 ). The intake grid  1  has an axial design height H ( 22 ), and the cylinder surface-type area on the outer enveloping surface  7  has an axial extent of HZ ( 23 ). HZ ( 23 ) is advantageously greater than 6% of the diameter D ( 20 ). 
     The cage-type contour of the intake grid  1  and/or its enveloping surfaces  7 ,  8  is/are well adjusted with regard to flow conditions. Air flowing in from the nozzle plate  32  in the radial direction is to be expected in the cylinder cage-type area  34 ; this can be achieved in short distances approximately across the enveloping surfaces  7 ,  8  and thus with minor flow losses due to the cylinder surface-type shape of the grid  1  in this area. An axial inflow is more to be expected in the flat, i.e., planar area  33 , then also passing through the grid  1  for a short distance across the enveloping surfaces  7 ,  8 . Due to the transitional area  24 , which has a compact design and a small extent, a small design height H ( 22 ) can be achieved, which is advantageous for a small space requirement of the intake grid  1 . The axial design height H ( 22 ) is advantageously no greater than 25% of D ( 20 ). 
     In addition, the targeted alignment of the webs can be seen well, not always running exactly perpendicular to the enveloping surface, but instead being configured to be deviating significantly from the exact inflow direction in some cases. In this embodiment, the webs  5  are not curved in the flow-through direction. However, this is quite conceivable with other embodiments. With the radially outer webs  35 , the outer ends  14  are open, i.e., they are not connected to one another (except in the mounting areas  18 ). 
       FIG. 6  shows another embodiment of an intake grid  1 , as seen in a perspective view from the front (from the inflow side). Unlike the embodiment according to  FIGS. 1-5 , the outer ends  14  of the webs  35  of the outer row are connected by an outer connecting ring  25 . This increases the dimensional stability of the outer webs  35 , which may be advantageous with regard to compliance with requirements for touchproof protection, for example, when using softer or more elastic materials. The outer connecting ring  25  may also be advantageous for the filling performance of an injection mold. The connecting ring  25  is connected to the webs  35  by means of an attachment  27 . This attachment is configured as an extension area of the outer webs  35  in the form of a curvature with a large radius of curvature &gt;3 mm. The mounting areas  18  are integrated into the connecting ring  25 . 
     In this embodiment, the connecting ring  25  is in a plane representing the screw-on plane toward the nozzle  2  and/or the nozzle plate  32 . In other advantageous embodiments, the connecting ring  25  may run with an axial offset from the screw-on plane, away from the mounting areas  35 . This results in space between the nozzle  2  and the nozzle plate  32  and the connecting ring  25  in the mounted condition. The presence of such a space may be necessary for any screw heads that are present and may be used for screw connection of the nozzle  2  and the nozzle plate  32 , or for positioning pressure unmolding devices. If the connecting ring runs with an axial offset from the screw-on plane in some areas, then some or all of the webs  35  of the outer row may protrude beyond them to the nozzle  2  and/or to the nozzle plate  32 , or they may end at the connecting web  25 , as seen in the axial direction. Additional webs may also be mounted in the area between the connecting web and the screw-on plane. In other embodiments, it is also conceivable for the connecting ring  25  to be interrupted in some areas and thus individual outer ribs  35  with open outer ends  14  may also be present. These outer ribs  35  with open outer ends  14  may also be shortened, so that the outer ends  14  are situated at a distance from the screw-on plane. This may also serve to create space for screw heads, pressure unmolding devices or the like between the screw-on plane and the intake grid  1  in the mounted condition. 
       FIG. 7  shows the intake grid  1  according to  FIG. 6  in an axial top view from the rear (as seen from the outflow side). In this diagram, one can see that the connecting ring  25  is situated completely outside of all webs  5  radially, except for the axially aligned webs  35  of the outer row with their attachments  27  to the connecting ring  25 . This is advantageous for easy mold release of the grid  1  from a simple open-and-close injection mold.  FIG. 7  shows as an example four identical cells  26  of the grid  1  including four identical segments. Since the number of different cells is greatly reduced by such segmentation, this reduces the cost of construction of the grid  1  and the respective injection mold. 
       FIG. 8  shows an intake grid  1  in a perspective view as seen from the front (from the inflow side). The cells  6  and the webs  5  there are not arranged in a honeycomb nor is the arrangement unstructured. Instead there are webs  5  running radially and over the circumference. Four webs  5  running radially meet at a central branching point  16  in the central axial area. The number of webs  5  that meet in each branching area  15  is usually four. The intake grid  1  has a cage-type contour of the outer enveloping surface  7 . In this embodiment, there is no transitional area formed between the flat area  33  and the cylinder surface-type area  34 , but instead there is a “kink” separating or connecting these two areas. A design similar to that according to  FIG. 8  with a steady tangential transitional area  24 , resembling that of the embodiment according to  FIGS. 1-5 , is conceivable. The mounting areas  18  in the Intake grid  1  according to  FIG. 8  are attached between two neighboring webs  35  of the outer row of the grid  1 , as seen in the circumferential direction. 
     The webs  5   a  and  5   b , which are shown as examples, have a large undercut area  17  with respect to a direction of mold release parallel to the axis. Because of this large undercut area, mold release from a simple open-and-close injection mold, parallel to the axial direction, is not conceivable. It is conceivable to have mold release with slide valves that yield mold release radially outward in a star pattern, forming the part of the grid  1  that corresponds to the cylinder surface-type part  34 . 
       FIG. 9  shows the intake grid  1  according to  FIG. 8  in a perspective view from the rear (as seen from the outflow side). The cage-type contour of the inner enveloping surface  8  can be seen well here. 
       FIG. 10  shows the intake grid  1  according to  FIGS. 8 and 9  in an axial top view from the front (as seen from the inflow side). Four identical cells  26  of the four-part segmentation are shown as examples. 
       FIG. 11  shows the intake grid  1  according to  FIGS. 8 to 10  in a side view and in a sectional view of a plane through the axis. With this grid  1 , the diameter D ( 20 ) of the grid  1  corresponds to the diameter DE ( 21 ) of the flat, i.e., planar area  33 , because no transitional area is formed. The axial design height H ( 22 ) of the grid  1  is slightly larger than the axial height HZ ( 23 ) of the cylindrical part, because the mounting areas  18  protrude to the right axially beyond the grid (toward the screw-on plane). This means that in the mounted condition, there is a small distance between the nozzle  2  and/or the nozzle plate  32  and the grid  1  and/or the webs  35  of the outer row beyond the mounting areas. This distance offers space for the screw heads of screws connecting the nozzle  2  and the nozzle plate  32 , for example, or space for pressure unmolding devices in the radius of the inlet nozzle  2 . A similar design, wherein space is formed between at least a few outer grid webs  35  and/or also an outer connecting ring  25  and the nozzle  2  and/or the nozzle plate  32 , is also conceivable for embodiments having unstructured grids similar to those in  FIGS. 1 to 7 and 12 to 16 . Likewise, in embodiments having unstructured grids, it is also conceivable for no transitional areas to be formed between the cylinder surface-shaped area  34  and the flat, i.e., planar area  33  of the intake grid, but instead they abut against one another at a kink. 
       FIG. 12  shows another embodiment of an intake grid  1  in a side view and in a sectional view of a plane through the axis. The webs  5  in this embodiment are partially curved, as seen in the sectional view. Therefore, an even better configuration of the grid  1  and/or the webs  5  to the incoming flow can be achieved. Furthermore, advantages can be achieved in mold release with fixed surface angles of the webs  5  on the inflow side (outer enveloping surface  7 ) that are more favorable for flow. In addition, a targeted, low-loss deflection of the inflow can be achieved as needed with the help of curved webs  5 . Any curvatures (direction, amount) are conceivable. Curved webs  5  may also be axially aligned webs at the same time. In this way, webs  35  of the outer row, for example, may also be curved and aligned axially. 
       FIG. 13  shows another embodiment of an intake grid  1  in a perspective view from the front (from the inflow side). The grid  1  has an unstructured arrangement, so that three webs  5  meet at the branching areas  15  in most cases. An outer connecting ring  25  by means of which the webs  35  of the outer row are connected to one another is formed. The attachments  27  of the outer webs  35  to the connecting ring  27  are configured as rounded forms with relatively large radii of curvature in extension of the webs themselves. The attachments  27  advantageously extend over a large portion of the radial extent of the connecting ring  25  (over more than half of this area) as seen in the radial direction. Four mounting areas  18  are integrated into the shape of the connecting ring  25 . The outer webs  35   b , which are situated approximately centrally in the mounting areas  18 , as seen in the circumferential direction, have a reduced outside diameter in order to gain access to the screw connection of the intake grid to the mounting areas  18 . These outer webs  35   h , which have a reduced outside diameter, are advantageously extended inward, to achieve the required stability and the required cross section for the injection molding process (see also the web  35   b  of the outer row in the area of a mounting area  18  in  FIG. 16 ). 
     In the embodiment according to  FIG. 13 , a closed central injection area  28  is provided. In injection molding of plastics, the molten plastic is injected centrally in this injection area  28  and is then distributed into the webs  5  via this disk-shaped area. In this embodiment, the innermost webs  5  have an inner end  31 , where they are attached to the central injection area  28 . 
       FIG. 14  shows the intake grid  1  according to  FIG. 13  in an axial top view from the front (as seen from the inflow side). This embodiment is configured without any undercuts at all with respect to mold release in the axial direction. This greatly facilitates the production of molds and ensures a reliable injection molding process with short cycle times. As an example, this shows two webs  5   a  and  5   b , whose positions are coordinated so that they do not overlap, as seen in this axial top view. To achieve this, it is important to have a close coordination of the shape of the enveloping surfaces  7  and  8 , the choice of web depths t ( 9 ), and the position and alignment of webs, taking into account compliance with regulations requiring touchproof measures. 
     To prevent undercut areas close to the branching areas  15 , when using axially aligned webs  29 , it is important to prevent two webs  30  that are not aligned axially from meeting at a branching area  15 , such that vectors normal to the wall and aligned toward the same cell  6  have x components (axially parallel components) with different plus and minus signs. Consequently, in this embodiment with a branching area  15 , two webs  30  that are not aligned axially often meet at one axially aligned web  29 , or three axially aligned webs  29 . Other combinations occur less often. Axially aligned webs  29  are advantageously configured with mold release angles, to facilitate mold release from an injection mold. In an injection mold, both sides of an axially aligned web are formed by the same mold part. Strictly speaking, the property of being “axially aligned” applies to a central surface between the two sides of an axially aligned web  29 . 
     To design a grid that is completely free of undercuts, limitations with regard to acoustics and efficiency must be accepted under some circumstances. Depending on the circumstances, it may also be advisable to accept minor undercuts, which can nevertheless allow unmolding with a simple mold (forced unmolding, rotational movement of mold parts, mapping of component contour areas on ejectors or the like). 
     In this embodiment, all the webs  5  are configured as axially aligned webs  29  in a radially inner area, approximately beyond a certain limit radius. Consequently, the mold may be configured so that no mold parting line runs obliquely through the cells in the case of the corresponding inner cells  6  with only or mainly axially aligned webs  29 , but instead the complete contour of the cells can be introduced into a mold part. This further facilitates production of molds. This can be implemented well without any major loss of efficiency or acoustics because of the axial inflow in the inner area near the axis. 
     The embodiment according to  FIG. 14  is constructed from twelve identical segments, wherein the 12-fold rotational symmetry through the only four mounting areas  18  is interrupted locally. The number of different cells  6  is definitely reduced by segmentation with a large number of segments. In this embodiment, the intake grid  1  has a total of 312 cells  6 , but due to the segmentation, there are only 26 cells  6  of different designs. Embodiments with eight segments are also advantageous. 
     In the embodiment with four mounting areas  18 , the number of segments is advantageously a multiple of 4. Segmentation can also be used to produce an intake grid  1 , in multiple parts, with larger outside diameters. 
       FIG. 15  shows the embodiment according to  FIGS. 13 and 14  in a side view. The attachment areas  27  of the outer webs  35  to the outer connecting ring  25  can be seen well. The attachment area  27 , which is embodied here as a curvature, may also be embodied in some other form, for example, as a chamfer. 
       FIG. 16  shows the embodiment according to  FIGS. 13 to 15  in a side view and in a sectional view of a plane through the axis. The webs  5   a  and  5   b  described as examples do not overlap, as seen in the axial direction. In addition, the connecting ring  25  does not conceal the web  5   a , as seen in the axial direction. All of this is advantageous for a simple design of the injection mold, because undercuts between the webs  5   a  and  5   b  and the connecting ring  25  are to be avoided with regard to mold release parallel to the axial direction. For better accessibility, the webs  35   b  of the outer row, which are in the area of the mounting areas  18 , are adapted to the screws with which the intake grid  1  is screwed onto an inlet nozzle  2  or onto a nozzle plate  32 , and their outside diameter is reduced. To have a web depth t there that is favorable for the strength and the injection molding process, these webs  35   b  also have at least a slight inward offset in the diameter. 
     The central injection area  28  can be seen well in the sectional view. In the injection molding process, the molten plastic injected centrally in this area can be distributed well to the webs  5  through the inner ends  31 . The inner ends  31  here advantageously have a curvature with the central injection area  28  and/or they are provided with a chamfer. 
       FIG. 17  shows as an example a fan with an intake grid  1 , a nozzle  2 , which is mounted on a nozzle plate  32 , and a fan impeller  3 , which is driven by a motor, as shown schematically. During operation, the air flows first through the intake grid  1  and into the inlet nozzle  2 , before undergoing a total increase in pressure when flowing through the rotating impeller  3  of the fan. Turbulence in the inflow causes more noise to be generated in the fan. An intake grid  1  smooths out the inflow and thereby reduces the noise. Depending on the embodiment, the intake grid  1  also takes on the function of a touchproof measure on the intake side. The pressure drop occurring as air flows through the grid  1  is minimized by the advantageous design. This embodiment shows a diagonal fan  3 . The intake grid  1  may be used equally well with a radial fan or an axial fan. 
     With regard to additional advantageous embodiments of the teaching, reference is made to the general part of the description and the accompanying claims in order to avoid repetition. 
     Finally, it should be pointed out explicitly that the examples of embodiments of the teaching as described above are presented merely to illustrate the claimed teaching, but the teaching is by no means limited to these embodiments. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               1  Intake grid 
               2  Inlet nozzle 
               3  Fan impeller 
               4  Motor 
               5 ,  5   a ,  5   b  Web 
               6  Grid cell, flow channel 
               7  Outer enveloping surface on the inflow side 
               7   a  Outer end face of the webs on the inflow side 
               8  Inner enveloping surface 
               8   a  Inner end face of the webs on the outflow side 
               9  Web depth t 
               10  Web thickness d 
               11  Web length l 
               12  Cell width w, inner sphere radius 
               13  Neutral fiber of a web 
               14  Outer end of a web, border area 
               15  Branching area of webs 
               16  Central branching point of webs 
               17  Undercut area 
               18  Mounting area 
               19  Cell of the outer row 
               20  Diameter D of the grid 
               21  Diameter DE of the flat, i.e., planar grid part 
               22  axial height H of the grid 
               23  Axial height HZ of the cylinder surface-type part 
               24  Transitional area of the enveloping surface 
               25  Outer connecting ring 
               26  Identical cells of a segmentation 
               27  Attachment of the connecting ring 
               28  Closed, central injection area 
               29  Axially aligned web 
               30 , 30   a  Web not axially aligned 
               31  Inner end of a web (border area) 
               32  Nozzle plate 
               33  Flat, i.e., planar area of the intake grid 
               34  Cylinder surface-type area of the intake grid 
               35  Web of the outer row 
               35   b  Web of the outer row in the area of a mounting area  18