Abstract:
In a centrifugal pump for pumping a fluid with central axial suctioning and radial discharging of the fluid to be pumped out of the impeller, the impeller includes an upper cover plate and a lower cover plate and multiple interposed blades therebetween. In the radial inner region, the blades extend essentially parallel to the rotation axis of the impeller in the axial direction of the pump and thus are upright, wherein said blades in the course radially outwards thereof are increasingly inclined or extend oblique.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Application No. 10 2012 209 832.1, filed Jun. 12, 2012, the contents of which are hereby incorporated herein in its entirety by reference. 
       TECHNOLOGICAL FIELD 
       [0002]    The invention relates to a pump, in particular for home appliances such as dish washers or washing machines. In this case, the pump is configured as so-called centrifugal pump. The invention also relates to a method for producing an impeller for such a pump. 
       BACKGROUND 
       [0003]    Such a pump is known from U.S. Pat. No. 8,245,718 B2. The centrifugal pump described therein comprises an impeller having an upper cover plate and a lower cover plate, between which multiple blades are located. 
       BRIEF SUMMARY 
       [0004]    The object underlying the present invention is to provide an aforementioned pump as well as a method for producing an impeller for such a pump by means of which problems from the prior art can be prevented and by means of which in particular an efficient pumping of fluid is possible as well as advantageously an easily producible, reliably operating impeller can be provided. 
         [0005]    Said object is achieved by means of a pump as well as by a method for producing an impeller. Advantageous as well as preferred embodiments of the invention are the subject-matter of the further claims and will be explained in more detail in the following. Some of the features named in the following are only described for the pump or for the impeller or only for the method. However, independently thereof, they shall be applicable to both the impeller and the pump as well as to the method. The wording of the claims is incorporated into the content of the description by explicit reference. 
         [0006]    With respect to such a pump, it is provided, in particular for home appliances such as dish washers or washing machines, that said pump comprises an impeller for pumping a fluid, wherein the pump is configured together with the impeller as a centrifugal pump with central axial suctioning and a radial or tangential discharging of the fluid to be pumped out of the impeller. The impeller comprises an upper cover plate and a lower cover plate, wherein multiple blades are located or arranged between the cover plates. Thus, the impeller is configured as so-called closed impeller. 
         [0007]    According to the invention, in the radial inner region the blades extend more upright or steeper in the axial direction of the pump or of the impeller parallel to the rotation axis of the impeller than in the further course of said blades outwards or towards the radial outer region, respectively. Thus, advantageously, in the radial inner region the blades are less steep inclined relative to the central longitudinal axis than in the radial outer region. Particularly advantageous, said blades extend approximately upright in the radial inner region. 
         [0008]    In the further course of said blades outwards or to the radial outer region, respectively, the blades are increasingly inclined or extend oblique or increasingly oblique, respectively. Thus, their inclination advantageously changes from slight or no inclination in the radial inner region up to the maximum inclination in the radial outer end region. 
         [0009]    As a result, on the one hand an advantageous pumping effect or flow guidance for the fluid can be achieved. Furthermore, especially in case the entire impeller is configured in one piece and the blades extend from the lower cover plate up to the upper cover plate, which will be described later in more detail, an improved producibility is achieved, in particular by means of synthetic material injection molding. 
         [0010]    In a further embodiment of the invention, it is provided that the inclination of the blades is configured such that the blades are inclined or extend in an oblique manner towards the upper cover plate in the rotation direction of the impeller. In tests, the aforementioned improved values in terms of flow guidance or better hydraulic characteristic values, respectively, were found, for example as compared to the impellers known from the aforementioned U.S. Pat. No. 8,245,718 B2 having upright extending blades. 
         [0011]    In a further embodiment of the invention, the change of the inclination can increase monotonously from radial inwards to radial outwards. That means that said inclination is at least not declining. Advantageously, here said inclination is steadily or strictly monotonously increasing, i.e. the inclination increases continuously. It may increase in a uniform manner, but that is not a must. If the inclination increases in an approximately uniform manner, on the one hand the shape can easily be produced and on the other hand the flow guidance can again be improved. 
         [0012]    It can be provided that in the radial inner region only a very short region of the blade extends upright or the blade immediately starts inclining towards the upper cover plate in the rotation direction of the impeller. 
         [0013]    A maximum inclination angle of the blades in the radial outer region can be smaller than 75° relative to the rotation axis. Advantageously, said angle is between 45° and 70°. For example, in this case said angle can be approximately 70° at the lower cover plate and approximately 50° at the upper cover plate. 
         [0014]    In a further embodiment of the invention, the blade can deviate from a straight extension as viewed in cross section. That means that it can be slightly curved in its course from the lower cover plate to the upper cover plate, advantageously again in the rotation direction. The curvature or deflection can be a few percent of the extension length between the lower cover plate and the upper cover plate, for example 1% to 10% or even up to 20%. Approximately 10% is preferred. 
         [0015]    In yet another advantageous embodiment of the invention, the blades are curved in their longitudinal extension from radially inwards to radially outwards, particularly advantageous curved opposed to the rotation direction. A curvature can preferably be configured continuously. As a rough indication for the curvature, said curvature can be curved between 5% and 30% of the extension length between the radial innermost and the radially outermost location beyond the junction line between said two locations, advantageously 15% to 20%. 
         [0016]    It is considered to be preferred if all blades of the impeller are configured identically. Although that does not provide particular advantages for the production method, it does for the hydraulic properties as well as for the true-running of the impeller. Particularly advantageous, the impeller also comprises exclusively the aforementioned blades. 
         [0017]    Preferably, an impeller comprises three to eight blades. Particularly preferred, there are four to six blades. Here, with their extension direction, the blades do not point towards the rotation axis of the impeller, but past said axis. Furthermore, the blades also do not cover the radial inner region of the impeller or are only arranged outside of said region, respectively. Thus, for example, the innermost 10% to 40% of the radius may be free of blades. 
         [0018]    In a further advantageous embodiment of the invention, a centrally projecting protrusion is arranged on the lower cover plate of the impeller. Said protrusion may extend beyond the blades in the direction towards the upper cover plate. Here, the blades should extend almost up to the protrusion, i.e. have only a small radial distance to said protrusion at least in the region of the lower cover plate. 
         [0019]    It is considered to be advantageous when the blades and the cover plates of the impeller, in particular also the aforementioned protrusion, are produced integrally or in one piece. For that purpose, in particular a synthetic material injection molding method is suitable. In such a synthetic material injection molding method, it is possible that exclusively linear pushers are driven into regions between the later blades of the impeller along a plane perpendicular relative to the rotation axis of the impeller. The radial inner region of the impeller including the area of the upper face of the upper cover plate is produced by means of at least one further linear pusher which is approached along the direction of the rotation axis of the impeller. Thus, it is possible that for producing the impeller by synthetic material injection molding, only linear pushers are to be used and that otherwise usually required curved pushers can be dispensed with. That significantly simplifies the production method and reduces production time and cost. In order to be able to produce the blades by means of the aforementioned linear pushers perpendicularly relative to the rotation axis of the impeller, it is considered to be advantageous if the lower cover plate and the upper cover plate extend parallel or at the same distance to one another not only in the radial outer region or from inwards to outwards at least not approaching to one another, but particularly advantageous are plane as well. Advantageously, the entire lower cover plate is plane towards the inner space of the impeller. That is particularly advantageous also true for the bottom face of the upper cover plate. Since the aforementioned linear pushers should be driven in and driven out perpendicularly relative to the rotation axis of the impeller in a direction that runs past the rotation axis of the impeller, the aforementioned equal distances of the cover plates to one another are required at least on the sides thereof that face towards one another. 
         [0020]    It can be provided that for each blade one linear pusher is used, wherein advantageously a linear pusher forms or constitutes the front side of a blade and the back side of an adjacent blade etc., at least partly, for example at least the outer half blade. The push direction of said pusher can traverse the corresponding blade and preferably still encounter at least a part of the next subsequent blade viewed in the rotation direction. The oblique position of the blades in relation to the rotation axis of the impeller, which orientation becomes increasingly more oblique from inwards to outwards, does not at all present an obstacle to the use of the linear pushers. 
         [0021]    In an advantageous further embodiment of the invention, the linear pushers for all blades are driven in and driven out from radially outwards essentially in the same plane. Said plane should be parallel to the lower cover plate, in particular also to the upper cover plate, or better parallel to the inner faces of the cover plates, respectively. 
         [0022]    Said and further features arise besides from the claims also from the description and the drawings, wherein individual features can be realized in each case on their own or in sub-combinations thereof in an embodiment of the invention and in other fields and can represent advantageous as well as protectable embodiments per se, for which protection is hereby claimed. The division of the application into individual sections as well as cross-headings does not limit the general validity of the statements made therein. 
         [0023]    BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0024]    Exemplary embodiments of the invention are schematically illustrated in the drawings and will be explained in more detail in the following. The drawings show in: 
         [0025]      FIG. 1  an oblique view of an impeller of a pump according to the invention including a linear pusher used for production, 
         [0026]      FIG. 2  a sectional view through the impeller of  FIG. 1 , 
         [0027]      FIG. 3  a plane view of the impeller of  FIG. 1  with disassembled cover plate, 
         [0028]      FIG. 4  a side view of the arrangement of  FIG. 1 , and 
         [0029]      FIG. 5  a pump according to the invention with an impeller described herein. 
     
    
     DETAILED DESCRIPTION 
       [0030]    In  FIG. 5 , a pump  10  is shown very schematically, which pump is configured as a radial impeller pump. In the pump chamber, said pump comprises an impeller  11  which draws a fluid through a central suction structure and which discharges said fluid in radial direction into the pump chamber. From there, the fluid can exit through an outlet after a few circulations within the pump chamber. That is known from the prior art. The impeller  11  is specifically configured for said pump, as can be seen from the  FIGS. 1 to 4 . 
         [0031]    In the oblique view according to  FIG. 1 , the impeller  11  comprises an upper cover plate  13  and a lower cover plate  20 . The upper cover plate  13  comprises a central suction opening  14 . Concentrically thereto, the lower cover plate  20  comprises an axle seat  21  by means of which the impeller  11  is plugged onto an axle of the pump motor. The axle seat  21  configured as rounded-off elevation also deflects the drawn in fluid radially outwards. As can be seen from  FIG. 1 , the upper face of the upper cover plate  13  is flat except for a slightly thicker edge of the suction opening  14 , as can also be seen in particular from  FIG. 4 . The same is true also for the bottom face of the lower cover plate  20 , but in both cases this is not obligatory. 
         [0032]    Likewise, however, a bottom face  16  of the upper cover plate  13  is flat or planar, in particular plane-parallel to the upper face. Except for a central region with the axle seat  21 , this is also true for an upper face  23  of the lower cover plate  20 . In particular the bottom face  16  and the upper face  23  are again plane-parallel to one another except for the region of the axle seat  21 . 
         [0033]    The impeller  11  comprises five blades  27 , the shape or course of which can especially be seen from  FIGS. 2 and 3 . The blades  27  are in each case configured or shaped identically. An outer edge  28   a  of the blades  27  corresponds to an outer edge  18  of the upper cover plate  13  and an outer edge  24  of the lower cover plate  20 . The outer edge  28   a  of the blades  27  extends significantly inclined or oblique, see in particular  FIGS. 1 and 4 . Here, the initial angle towards the lower cover plate  20  is approximately 20°, in the upper region towards the upper cover plate  13  the angle is greater, namely approximately 40°. 
         [0034]    In the longitudinal course of the blades  27  radially inwards, the inclination decreases more and more, down towards an inner edge  28   b,  where said blades extend almost perpendicular relative to the cover plates  13  and  20  and parallel to the central longitudinal axis of the pump or to the rotation axis of the impeller  11 . The inner edge  28   b  of the blades  27  is located approximately at the point where the slowly increasing axle seat  21  starts. 
         [0035]    Furthermore, the blades  27  are arranged at an equal distance to one another or are distributed equally, respectively. The side view according to  FIG. 4  shows that the inclination steadily increases at the outer edge  28   a  of the blades  27 , i.e. strictly monotonously. It can be seen from the plane view according to  FIG. 3  that a curvature of the blades  27  also increases from outwards to inwards, although only slightly. 
         [0036]    Per se, such an impeller  11  could be designed from multiple parts during the production in any manner, with blades changing in terms of their inclination in the longitudinal course thereof, since a production by means of synthetic material injection molding is very variable, for example. In particular when a separate upper cover plate is applied to the blades, for example by adhesive bonding, the upper cover plate and the lower cover plate could also be configured in a curved manner, as known from other impellers of similar pumps, see for example U.S. Pat. No. 8,245,718 B2. 
         [0037]    However, in order to allow a one-piece configuration and production and to avoid elaborate, expensive and susceptible curved pushers, at least the bottom face  16  of the upper cover plate  13  and the upper face  23  of the lower cover plate  20  have to be plane-parallel to one another or expand from inwards to outwards in a continuous manner, namely in each case in the radial direction. Thus, they cannot be curved as known from the aforementioned prior art. 
         [0038]    In the case of an impeller  11  configured that way, a linear pusher  30  can be used for production as shown in the figures, or five such linear pushers are used, respectively. The push direction S is illustrated. A mold side  31  facing rightwards in the  FIGS. 3 and 4  is configured exactly the way as to correspond to the side of the blades  27  facing the lower cover plate  20  and in the rotation direction of  FIG. 3 . A blade region  33  on the mold side  31  corresponds exactly to said side of the blade  27 . Adjacent thereto, there is an inner region  34  which towards the axle seat  21  so to say defines in each case the inner edges  28   b  of the blades  27 . The axle seat  21  per se is produced by means of another pusher, which in  FIG. 3  is driven into the drawing plane. 
         [0039]    Another blade region  33 ′ on the linear pusher  30  forms, on the blade  27  adjacent in the circumferential direction, the side of the blade  27  facing in the counter-rotation direction, i.e. the side facing the afore described blade. 
         [0040]    By means of the impeller  11  having the blades differently inclined in the longitudinal course thereof, very good pumping characteristics of the impeller can be achieved. A desired and very advantageous one-piece production is achieved by means of the plane-parallel cover plates or the plane-parallel faces of the cover plates facing to one another, and by means of the illustrated and described linear pushers. Even though the molding tool for the impeller is somewhat more elaborate, the production method per se by means of synthetic material injection molding can be controlled in a good manner and results in good properties of the impeller. It is still much more easy to realize than with curved pushers.