Patent Publication Number: US-8109731-B2

Title: Radial fan impeller

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/658,906 filed on Jan. 30, 2007 which is the National Stage of International Application No. PCT/EP2005/008250 filed Jul. 29, 2005. This application claims the benefit and priority of DE 20 2004 012 015.1, filed Jul. 31, 2004. The entire disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     This invention relates to a radial fan impeller, in particular for using in gas fans with a steep fan characteristic curve. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     EP 0 410 271 B1 describes a radial fan for conveying a gaseous medium in a device with high flow resistance, in particular a burner in a gas boiler. These types of burner have a relatively high flow resistance of in the region of 200 pascals or over. The medium to be conveyed can be air or a combustible gas/air mixture. The fan and the fan impeller of the same must therefore be designed to have a steep pressure/volume flow characteristic curve. This means that pressure changes should only be associated with small changes to the volume flow. For this, the known fan has a fan impeller, the diameter of which is more than ten times its flow discharge width. This is a closed wheel, covered on both sides, with a substantially flat lower portion having a central hub (first covering disc), a plurality of blades bent rearwards, and each being in the shape of a segment of a circle, and a circular, flat, plate-shaped cover (second covering disc) with a central, circular inlet opening. 
     Documents DE 41 41 359 A1, CH 301 116 and DE 102 04 037 A1 respectively describe similar fan impellers which are also closed, according to the first two documents shortened intermediary blades being provided. 
     These types of closed radial fan impeller, covered on both sides, are relatively difficult and expensive to produce. 
     A further radial fan is known from WO 02/45862 A2 which, however, has a fan impeller with a large axial length and flow discharge width in comparison with the diameter such that this fan is not suited, or is less well suited to the preferred application as a gas burner fan. This known fan impeller has blades which are all of the same length and is designed to be axially open on the hub side. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The object which forms the basis of this invention is to provide a radial fan impeller which, with particular suitability for a gas burner fan with a steep characteristic curve, can be produced easily and cost-effectively. 
     According to the invention this is achieved respectively by the combination of features of claims  1  and  11 . Preferred features of embodiments are the object of the dependent claims. 
     By designing the diameter to be at least ten times the flow discharge width of the blades, the desired steep characteristic curve is obtained. According to the invention, however, on their side facing away from the covering disc, the blades have free side edges which lie on a theoretical, level surface or any curved surface. By means of this embodiment of the fan impeller which, according to the invention, is open on this side, this can be produced very quickly and cost-effectively as a one-piece moulded part made of synthetic using a spraying method, in which a relatively simple spraying tool without or with just a few slides can be used because, due to the structure of the impeller, undercuts in the direction of demoulding can be avoided so that simple, axial demoulding of the moulded part is possible. 
     The radial fan impeller according to the invention is provided for use in a fan housing which has a wall adapted to the free blade side edges or to the theoretical surface shape defined by these such that between this wall and the fan impeller blades, only a narrow axial gap is formed. 
     The shortened intermediary blades respectively provided according to the invention between two blades have the advantage that, on the one hand, overall a relatively large number of blades and intermediary blades can be provided, and this is advantageous with regard to the flow movement in the flow channels formed between the blades with respect to air movement, flow displacement and the formation of swirl. On the other hand, however, the problem is avoided whereby with a correspondingly large number of long blades passing through to the inlet region, the intake or inflow region is partially blocked, and this would have a negative effect upon the delivery volume. In contrast to this, according to the invention, the radially inner inflow region in the region of the shorter intermediary blades is kept open. 
     With an alternative embodiment which can be protected independently, an annular covering disc is provided which has a wide R D  which, measured from the edge of the intake opening, is smaller than the distance edge—intake opening to discharge opening—circumferential edge. 
     It is advantageous here to provide the width with proportions such that, measured from the intake opening, it is substantially half the length of a blade. This particular embodiment also makes it possible to produce the fan impeller as a one-piece moulded part, an embodiment being considered to be particularly favourable with which the support disc is annular in form and has an annular width which substantially has the measurement outer edge of covering disc to discharge opening—circumferential edge ( 2 - 3 ′). 
     If this annular width is substantially half the length of a blade, another movement can be provided to the air flow in the discharge region so that the shearing friction between the rear housing wall and the flow is limited to a reduced range. 
     It can be favourable here for the two disc rings, i.e. that of the covering disc and that of the supporting disc, to either overlap in the projection in the direction of the rotation axis depending upon the requirements, form a gap between them, or complement one another by adjoining to form a circular surface. An advantageous flow course can be achieved if the hub element is of a height which, measured from the level of the rear support disc, substantially corresponds to half the depth of the impeller. A cone is favourably formed on the hub element facing the flow side, the covering disc ( 2 - 9 ) and the cone of the hub substantially have a parallel course in the cross-section A-A. In this way, a favourable flow course is achieved in the inlet region of the impeller. 
     With one advantageous embodiment provision can be made such that on the outer circumference of the cone a region is formed, the flow surface of which runs substantially parallel to the rotation plane. By means of this design, before leaving the cone region, the flow is given another change in direction gradient which reduces a steep incidence of the flow in the open region of the impeller. 
     This effect can advantageously be further increased in that the flow surface of the outer circumferential region is disposed in one plane which, in relation to the flow channel, lies further inwards than the surface of the outer support disc defining the flow channel, i.e. the support disc can be designed to be thinner than the thickness of the outer circumferential region of the cone. 
     An advantageous embodiment can be designed such that the blades are axially wider in the intake region than in the outflow region. 
     It can also be favourable for at least one intermediary blade respectively to be disposed between the blades substantially in the region of the width of the support disc. 
     It is particularly favourable for two intermediary blades to be disposed respectively in pairs. It is particularly favourable here for the intermediary blades to have a radial extension which substantially corresponds to the distance between the outer circumference of the covering disc and the outer circumference of the rear-side support disc. 
     It is particularly advantageous for the intermediary blades to be held exclusively on the rear-side support disc. This embodiment simplifies to a particularly large extent the design of the radial fan impeller as a one-piece cast part. 
     In summary, the combination of features of claims  1  and  10  according to the invention leads to the following essential advantages of the radial fan impeller: 
     in particular in co-operation with a suitably adapted fan housing appropriate for producing high pressure or for producing a steep characteristic curve, with which a change to the counter pressure in the unit brings about no or only a slight change to the volume flow.
         short axial overall length   one-part production using a synthetic spraying method with simple demouldability and in a simple and cost-effective moulding tool   can thus be produced cost-effectively.       

     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       By means of preferred examples of embodiments illustrated in the drawings, the invention will be described in greater detail. The drawings show as follows: 
         FIG. 1  is a perspective view of a first embodiment of a radial fan according to the invention onto the side of the covering disc, 
         FIG. 2  is a perspective view of the fan impeller according to  FIG. 1  onto the other, open side of the blades, 
         FIG. 3  is a top view onto the side of the covering disc, 
         FIG. 4  is a cross-section in plane A-A according to  FIG. 3 , 
         FIG. 5  is a second embodiment of the radial fan impeller according to the invention in an axial section similar to  FIG. 4 , 
         FIG. 6  is an illustration similar to  FIG. 5  in an advantageous further development, 
         FIG. 7  is a top view of a further embodiment with a reduced covering and support disc, and 
         FIG. 8  is a view of a section along line A_A in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. In the different figures of the drawings, the same parts are always provided with the same reference numbers. 
     A radial fan impeller  1  according to the invention consists of a plurality of radial blades  2  distributed around the periphery, which viewed in the radial direction extend from an inner inlet region  4  to an outer discharge region  6 . According to  FIGS. 1 and 3 , the blades  2  have radially inner end edges  8  which lie on a theoretical surface enclosing the inlet region  4 , which is approximately cylindrical, but in particular conical, and which tapers viewed in the axial inflow direction (see arrow E in  FIG. 1  and  FIGS. 4 to 6 ) into the inlet region  4 . Furthermore, the blades  2  have outer end edges  10 . Between the blades  2  radial flow channels  12  are respectively formed with the substantially radial outflow direction A. 
     Furthermore, the blades  2  extend axially, i.e. viewed in the direction of a rotation axis  14 , between an inlet side  16  and an axially opposite hub side  18  (see with regard to this the sectional views in  FIGS. 4 to 6 ). 
     Furthermore, according to the invention the blades  2  are only connected on their inlet side  16  by means of their radial extension as far as the discharge region  6  to a covering disc  20  which has a central inflow opening  22  opening out into the inlet region  4 . On the opposite hub side  18 , however, the blades are only connected by their radially inner end regions to a central hub  24  so that the flow channels  12  on this side are designed to be open in the axial direction. The blades  2  therefore have free side edges  26  on this side. 
     As is furthermore evident from  FIGS. 4 to 6 , the blades  2  and the covering disc  20  define an outer fan impeller diameter D which is at least ten times an axially measured flow discharge width B of the blades provided in the discharge region  6 . Preferably, the axially measured inner flow inlet width C of the blades  2  in the inlet region  4  is greater here than the outer flow discharge width in the outlet region  6  (see e.g.  FIG. 4 ). 
     In a further embodiment according to the invention, radially shorter intermediary blades  28  are connected to the covering disc  20  in regions respectively disposed between adjacent blades  2  (see in particular  FIGS. 1 and 2 ). These intermediary blades  28  extend from the outer circumference of the covering disc  20  over just one portion of the radial extension of the covering disc  20 , and end a radial distance away from the hub  24 . This can best be seen in  FIG. 2 . In the example of an embodiment shown, just one intermediary blade  28  is provided between two adjacent blades  2 , but two or more intermediary blades  28  can, however, also be provided which can then be designed with the same or a different radial length. 
     By means of the embodiment according to the invention described, the radial fan impeller  1  can advantageously be produced as a one-piece moulded part made of synthetic, and preferably of a synthetic with anti-static properties such that during operation static charges are avoided or dissipated by a housing (not shown). This contributes to a high level of safety during use, particularly with regard to the preferred application for conveying combustible gas/air mixtures with which ignitions caused by spark formation are avoided. 
     As is evident from  FIG. 2 , with this example of an embodiment provision is made such that the blades  2  and the intermediary blades  28 , considered in the radial direction, are designed to bend backwards in the direction of rotation  30 . The blades are arranged here such that their inlet angle is between approximately 30° and 45°, and their outlet angle is between approximately 45° and 90°. In order to illustrate this angle, reference is made to EP 0 410 271. Alternatively, however, an embodiment with blades  2  and intermediary blades  28  which are bent forwards or end radially in the discharge region  6  are also possible. 
     The hub  24  consists of an outer disc section  32  and a central mounting section  34  to be connected to a shaft (not shown), in particular in the form of a short pipe appendage. The disc section  32  is connected here on its radially outer periphery to the inner end regions of the blades facing towards the inlet region  4 . With the first embodiment according to  FIGS. 1 to 4 , provision is advantageously made such that the disc section  32  of the hub  24 , starting from its outer peripheral region connected to the blades  2 , projects for example in a convex or shell-like form into the inlet region  4  and towards the inflow opening  22  of the covering disc  20  such that the hub  24 —see in particular  FIG. 4  with regard to this—forms an accommodation space  36  for certain (not shown) fan function elements such as mounting elements, engine or rotor parts and/or similar on its side facing away from the inflow opening  22 . This advantageous embodiment leads to a short axial overall length of the whole fan. 
     As is also evident from  FIG. 2 , (at least) the intermediary blades  28  are connected to the covering disc  20  by means of a respective transition reinforcement  38  formed in the blade base region. Despite the connection-free design spaced apart from the hub  24 , this guarantees sufficient stability of the intermediary blades  28 . 
     In a further embodiment of the invention illustrated by  FIG. 6 , in their radially outer region which lies axially opposite the covering disc  20 , the blades  2  and the intermediary blades  28  are connected by means of a circumferential annular element  40  formed as one piece in order to provide mechanical reinforcement. 
     Finally, it should be mentioned that in the region of the inflow opening  22 , the covering disc  20  has an edge  42  in the form of a nozzle in the direction of flow. 
     In  FIGS. 7 and 8 , a further embodiment is shown for fulfilling the object according to the invention. Unlike the reference numbers of the preceding examples of embodiments, with the example of an embodiment described now, the reference numbers are provided with a number 2 and a hyphen. 
     The radial fan impeller  2 - 1  shown in  FIG. 7  has an annular covering disc  2 - 9  which surrounds the intake region  2 - 7  in an annular shape. Normally, a circular intake opening  2 - 10  is formed on the covering disc  2 - 9  which is surrounded by a circumferential opening lip  2 - 10 ′. Furthermore, the radial fan impeller  2 - 1  has a hub element  2 - 2  and a peripheral edge  2 - 3 . On its side facing towards the intake opening  2 - 10 , the hub element  2 - 2  has a cone  2 - 2 ′. The fan impeller  2 - 1  is provided with blades  2 - 6  extending substantially radially from the hub element  2 - 2  to the peripheral edge  2 - 3 . An intake region  2 - 7  and an outflow region  2 - 8  are defined by the blades. 
     The annular covering disc  2 - 9  has a width R D  which, measured from the edge of the intake opening ( 2 - 10 ), is half of the distance edge—discharge opening—circumferential edge  2 - 3 . 
     The width R D  therefore substantially corresponds to half of the blade length measured along the upper edge of the blade  2 - 6 . 
     The base of this type of blade is integrally connected at its radially inner point to the hub element. The support disc  2 - 11  extending on the rear side  2 - 5  is annular in form, and on its annulus has a width of R T , which, measured from the edge of the intake opening  2 - 10 , is substantially half of the edge discharge opening  2 - 10 —circumferential edge  2 - 3  measurement. This substantially corresponds to a half blade length measured along the rear side edge of the blade extension between the peripheral edge  2 - 3  and the base of the blade  2 - 6  on the cone  2 - 2 ′ of the hub  2 - 2 . 
     With such dimensions, as can be seen in  FIG. 7 , in the projection of the fan impeller onto the plane of the support disc towards the rotation axis, the outer circumference of the covering disc  2 - 9  and the inner circumference of the support disc  2 - 11  are congruent. Alternative embodiments can be provided, however, such that both disc rings  2 - 9 ;  2 - 11  overlap or form a gap between them dependent upon the requirement in the projection towards the rotation axis  2 - 12 . 
     The hub element  2 - 2  has a height which, measured from the plane of the rear support disc  2 - 11  substantially corresponds to half of the impeller height. In the example of an embodiment shown, the height of the hub corresponds to half of the height of the blades projecting into the intake opening  2 - 10 . 
     The surface F K  of the cone  2 - 2 ′ of the hub  2 - 2  extends substantially parallel to the inner surface F D  of the covering disc  2 - 9 . In the region of the base  2 - 14  of the cone, i.e. at its outer circumference, a region  2 - 21  is formed, the surface of which extends substantially parallel to the rotation plane of the fan impeller. The surface of the cone facing towards the flow and the rotation-parallel region are rounded here. Between the blades  2 - 6  extending from the edge of the intake opening  2 - 10  to the peripheral edge  2 - 3  of the fan impeller  2 - 1 , intermediary blades  2 - 16  are disposed substantially in the region of the width of the rear-side support disc  2 - 11 . The number of intermediary blades  2 - 16  can vary depending upon the application. Preferably, with the example of an embodiment shown, two intermediary blades  2 - 16  are disposed in pairs between two blades  2 - 6 . The radial extension of the intermediary blades  2 - 16  is of proportions such that it substantially corresponds to the distance  2 - 17  between the outer circumference  2 - 18  of the covering disc  2 - 9  and the outer circumference  2 - 19  of the rear-side support disc  2 - 11 . With the example of an embodiment shown, the intermediary blades  2 - 16  are only held on the rear-side support disc  2 - 11 , i.e. the front edge of the intermediary blades with this embodiment are free. Depending upon the arrangement of the covering and the support disc described above, the intermediary blades can however also be moulded onto the covering disc. The form of the course of the intermediary blades corresponds substantially to the corresponding form of the section of the blades  2 - 6  at a corresponding point. 
     As with the first example of an embodiment, the previous embodiment can also advantageously be produced as a one-piece moulded part made of synthetic. 
     The invention is not restricted to the examples of embodiments shown and described, but also includes all embodiments acting in the same way in the sense of the invention. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.