Abstract:
An impeller pump has a pump casing including a pump chamber and an inlet and an outlet thereon and an impeller therein, and including a heating device for heating the conveyed medium, which heating device forms an external wall of the pump chamber. The pump chamber extends annularly around the impeller and away from the pump chamber floor, wherein the outlet leads off on a region of the pump chamber which, viewed in the axial direction of the impeller pump, is pointing away from the pump chamber floor. The cross-sectional area of the pump chamber decreases in the axial direction of the longitudinal center axis of the impeller pump away from the pump chamber floor toward the outlet by virtue of an obliquely inwardly inclined external wall.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Application No. 10 2013 200 280.7, filed Jan. 10, 2013, the contents of which are hereby incorporated herein in its entirety by reference. 
     TECHNOLOGICAL FIELD 
     The invention relates to an impeller pump for the conveyance of a medium. 
     BACKGROUND 
     From EP 2150165 B1 it is known to configure an impeller pump of this kind in highly integrated design for use in a dishwasher. Here an annular pump chamber of circular cylindrical shape, which surrounds an inlet into the pump chamber and an impeller disposed in the pump chamber, is provided, wherein an external wall of the pump chamber is formed by a heating device. At that end of the pump chamber which is remote from the impeller, or on an upper rim or cover of the pump casing, there is provided an outlet from the pump chamber, from which the heated and conveyed medium is discharged. 
     BRIEF SUMMARY 
     The object of the invention is to provide an impeller pump stated in the introduction, with which problems of the prior art can be eliminated and it is possible, in particular, to improve the heating of a medium conveyed by the impeller pump. 
     This object is achieved by an impeller pump. Advantageous and preferred embodiments of the invention are the subject of the further claims and are described in greater detail below. The wording of the claims is expressly based on the content of the description. 
     It is provided that the impeller pump has a pump casing comprising a pump chamber, inlet and outlet. In the pump chamber, an impeller is provided behind the inlet and in front of the outlet within the conveyance path of the medium. In addition, a heating device for heating the conveyed medium, which forms at least a part of an external wall of the pump chamber, is provided. The impeller is here disposed on or above a pump chamber floor. Starting therefrom, the pump chamber extends annularly around the impeller and away from the pump chamber floor, advantageously along the axial direction or the longitudinal center axis. Viewed in this axial direction of the impeller pump, the outlet is disposed on a region of the pump chamber which is pointing away from the pump chamber floor. This means that the medium to be conveyed and heated passes through the inlet into the pump chamber, is moved or conveyed by the impeller into the pump chamber and along the heating device. The conveyed and heated medium then passes out to the outlet from the pump chamber and the whole of the impeller pump. 
     According to the invention it is provided that the cross-sectional area of the pump chamber decreases in the axial direction of the longitudinal center axis of the impeller pump away from the pump chamber floor toward the outlet or in the direction of the outlet. As a result of this decrease in the cross-sectional area of the pump chamber, the flow velocity of the conveyed medium is increased downstream or in the direction of the outlet. In this way, on the one hand, an overheating of the heating device can be avoided. In addition, the conveyed medium can be optimally heated. 
     In an advantageous embodiment of the invention, the cross-sectional area of the pump chamber can decrease monotonously in the axial direction or along the longitudinal center axis of the impeller pump away from the pump chamber floor toward the outlet. Particularly preferably, it can decrease in a strictly monotonous manner, i.e. it has a steadily diminishing cross section. The decrease can be achieved by virtue of an oblique wall of the pump chamber, namely the internal wall and/or the external wall. An angle of the sloping wall of the pump chamber to the longitudinal center axis of the impeller pump can here be small, advantageously ranging from 3° to 25°, particularly advantageously from 5° to 15°. 
     In one embodiment of the invention, at least the external wall of the pump chamber is slanted or inclined inward at an appropriate angle. If the external wall of the pump chamber is formed substantially or completely by the heating device, then the latter can be tubular in configuration. It can advantageously be configured such that it tapers conically away from the pump chamber floor, and can thus produce the decrease in cross section or cross-sectional area. Preferably, the heating device or the external wall of the pump chamber is rotationally symmetrical to the longitudinal center axis. In this way, a favorable shape for an advantageous flow is achieved. In addition, good producibility is thus obtained. 
     In a further embodiment of the invention, it can be provided that not only can an external wall run obliquely to the longitudinal center axis or not only does it produce the decrease in cross-sectional area of the pump chamber, but also a radially inner internal wall of the pump chamber can be slanted. It is here advantageously slanted outward for a still smaller cross-sectional area. An angle can here lie within an aforementioned range. 
     Preferably, the internal wall of the pump chamber runs straight, so that it thus runs parallel to the longitudinal center axis of the impeller pump. The cross section which it forms, or its radius, should be the same, this should also apply to its shape. 
     In the tapered region of the heating device or wall of the pump chamber, an output per unit of area of the heating means can remain the same, so that, in this region, less heating output is generated in total on account of the reduced area. Alternatively, the output per unit of area can increase, advantageously by 5% to 25%, or even 50%. It can here be provided, for example, that in the axial direction of the pump an output per unit of height remains roughly the same for the heating device. In this way, an increased output per unit of area likewise exists close to the outlet from the pump chamber, and thus the conveyed medium is heated even more on account of the here cumulative effect of the increased flow velocity. 
     In an advantageous embodiment of the invention, the heating device can extend from the pump chamber floor to just before the axial height of the outlet. It here advantageously overtops the impeller, at least in the axial direction toward the outlet, advantageously by a multiple of the height of the impeller. In the axial direction away from the outlet, the heating device can likewise overtop the impeller somewhat, though in this case, advantageously, only slightly. In particular, heating means or a heating element of the heating device should in this direction overtop the impeller only slightly, since the conveyance of medium into this region is less. 
     The heating device or heating means or a heating element of the heating device should run around at least the major part of the pump chamber. Advantageously, this is at least 70%, particularly advantageously it runs fully around. A heating device should here be understood as both a support and heating means disposed thereon, or one or more heating elements. Heating means on the heating device is provided all over or distributed over an area, for example in strips or in fields. To this end, one or more heating elements which to the person skilled in the art are known, however, from the prior art and which advantageously are thin-film or thick-film heating elements, can be provided. 
     The heating means should be provided on that side of the heating device which lies outside the pump chamber. In this way, corrosion problems and insulation problems are avoided or are less and an electrical connection becomes easier. 
     In yet another embodiment of the invention, the inlet can reach into the pump chamber to just before the impeller. It can end at less than 50% of the height of the pump chamber in the axial direction, for example at about 20% or 30% to 40%. The inlet thus lies very close to the impeller. The pump chamber has essentially only, on the one hand, the region in which the impeller runs or which the impeller requires, and, on the other hand, the region which extends annularly around the impeller and adjoins the latter within the conveyance path of the medium. 
     These and further features emerge, other than from the claims, also from the description and the drawings, wherein the individual features can be realized respectively in isolation or in plurality in the form of subcombinations in an embodiment of the invention and in other fields, and can constitute advantageous and inherently patentable embodiments for which protection is here claimed. The division of the application into individual sections, as well as subheadings, does not limit the statements made under these in terms of their generality. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Illustrative embodiments of the invention are represented schematically in the drawings and are explained in greater detail below. In the drawings: 
         FIG. 1  shows a lateral sectional view through an inventive pump comprising a pump chamber tapered by a conical shape of an external wall, 
         FIG. 2  shows a variation of the pump from  FIG. 1 , comprising a pump chamber tapered by a conical shape of internal wall and external wall, and 
         FIG. 3  shows a top view of the pump from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 , an inventive impeller pump is represented in sectioned side view. The pump  11  has a pump casing  12 , comprising a pump chamber  13 . An inlet  15  leads into the center of the pump chamber  13  and an outlet  16  leads out at the upper rim. It can be seen that the inlet  15  is axially aligned with the longitudinal center axis  17  (shown in dashed representation), while the outlet  16 , as is also shown by the top view from  FIG. 3 , runs at right angles thereto or tangentially to the circumferential pump chamber  13 . The pump chamber  13  is limited in the downward direction substantially by an external wall  19  and an internal wall  20 , as well as by a pump chamber floor  21 . It can also be seen that the height of the pump chamber  13  in the axial direction has roughly four to six times the width of the pump chamber  13  close to the pump chamber floor  21 , namely in the radial direction. 
     Just above the pump chamber floor  21  rotates an impeller  23 , which reaches to close to the inlet  15  and is driven by a pump motor (not represented) via a motor shaft  24 . The rotational direction of the impeller  23  is in  FIG. 3  counterclockwise and in  FIG. 1  on the left of the impeller  23  out of the plane of the drawing and on the right into the plane of the drawing, as is represented by appropriate symbols. In this respect, the structure of the pump  11  substantially corresponds to the prior art stated in the introduction, in the form of EP 2150165. Liquid which is to be conveyed and heated, in particular water in a dishwasher, washing machine or the like, is introduced to the inlet  15  along the longitudinal center axis  17  and is discharged by the rotating impeller  23  in the radial direction, namely just above the pump chamber floor  21 . The liquid has a circulating direction corresponding to the rotational direction of the impeller  23 . At the same time, it rises further and further upward in the pump chamber  13 , mainly along the external wall  19 , until it finally after several revolutions, advantageously three to ten revolutions, is fed out to the outlet  16 . In the pump chamber, it is hereupon warmed. This is respectively illustrated by the three arrows, wherein the arrow in the pump chamber  13  shows only the upward motional component and not the predominant motional component in the circulating direction in the pump chamber. 
     Since the pump casing  12  according to  FIG. 3  is substantially, except for the outlet  16 , of rotationally symmetrical configuration, it is evident that the cross section of the pump chamber  13 , which along the circulating direction at an axial height is always the same, tapers from the pump chamber floor  21  or from the impeller  23  and toward the outlet  16 . In particular, the width of the pump chamber  13  right at the top beneath the apex or just in front of the outlet  16  amounts to only about 40% of the width at the height of the impeller  23 . This is therefore a significant reduction in the cross-sectional area of the pump chamber. Here it can also be seen that the internal wall  20  stands at right angles to the plane of the pump chamber floor  21 , and the angle β between its course and the perpendicular to the pump chamber floor  21  or to the longitudinal center axis  17  measures 0°. The internal wall  20  also runs straight. 
     The external wall  19  likewise runs straight, but stands at an angle α of about 10° to the perpendicular to the pump chamber floor  21 . Thus the external wall  19  is tilted inward or slanted by α=10°. 
     It can further be seen that the internal wall  20  is configured in one piece with the inlet  15 , as well as with the upper region of the pump casing  12 , configured virtually as a cover, from which also the outlet  16  leads off in one piece. This part is advantageously made of plastic. The largest region of the external wall  19  (also referred to herein as outer wall  19 ) is configured as a heating device  26 , as is fundamentally known also from the external wall of EP 2150165. There, however, the heating device is of circularly cylindrical and straight configuration, i.e. of constant cross-sectional area, which is specifically not the case here. The heating device  26  represented on the left in  FIG. 1  has a support as part of the external wall  19 , which support advantageously consists of metal or a special steel. On its outer side, as is known, once again, from the prior art, it is at least partially provided with an insulation, to which, once again, heating elements are applied. In the case of the heating device  26  represented on the left, these are heating elements  28   a  to  28   e , which are configured, for example, as broadly circumferential resistance strips, advantageously in a thick-film heating element. They can be electrically connected to one another in parallel. It can be seen that the width of the heating elements  28  decreases away from the pump chamber floor  21  toward the outlet  16 , and thus the heat generation in the upward direction increases due to the cumulative effect of heating elements  28   a  to  28   e.    
     On the right in  FIG. 1 , a heating device  26 ′ comprising a planar heating element  28 ′ is represented. This is meant primarily to illustrate that here, unlike on the left side, the output per unit of area in the direction away from the pump chamber floor  21  remains the same for the heating device  26 ′. 
     The principal technical effect of the decrease in cross-sectional area or the tapering of the pump chamber  13  from bottom to top consists in the fact that here the flow velocity is increased. This promotes a heat removal from the heating device  26 . Specifically in connection with the heating device  26  (represented on the left) with upwardly increasing output per unit of area of the heating means, this is of advantage. In this way, a better heating of the conveyed medium or of the conveyed liquid can be achieved without local overheating of the heating device  26 . 
     It can be seen that the external wall  19  is formed above the heating device  26  by the plastics part of the pump casing  12 . A sealed connection between these two parts is easily realizable for the person skilled in the art, for example by means of rubber seals. Although the heating device  26  could also be extended still higher, there are then, however, design problems on account of the outlet  16 . In similar form, a seal can also be made between the lower region of the heating device  26  or  26 ′ and the pump chamber floor  21 . 
     In the variation of the invention as a pump  111  according to  FIG. 2  (shown in simplified representation), a pump casing  112  comprising a pump chamber  113  is once again provided, as well as an inlet  115 , an outlet  116  and a longitudinal center axis  117  (shown in dashed representation). An external wall  119  is once again slanted relative to the longitudinal center axis  117  or to a pump chamber floor  121 . However, it can here clearly be seen that the angle α′ is smaller than in  FIG. 1  and advantageously is only 5°. Here too, however, an internal wall  120  of the pump casing  112  is obliquely inclined, namely obliquely outward. An angle β′ here likewise measures 5° in accordance with the angle α′, though this is not absolutely necessary. Likewise, as a result, a pump chamber  113  of, in the direction away from the pump chamber floor  121 , reduced cross-sectional area, i.e. an upwardly tapered pump chamber  113 , is thereby obtained. 
     With respect to the heating device  126 , as a large part of the external wall  119  of the pump chamber  113 , a planar heating element  128  is shown in purely general representation. For this heating element  128 , the same design options as in  FIG. 1 , or even yet further options, can apply. 
     The top view of the pump  11  according to  FIG. 1 , which is represented in  FIG. 3 , is meant essentially to illustrate to what extent the pump  11  or the pump casing  12  without the outlet  16  is of rotationally symmetrical, i.e. circular configuration. This applies above all to the external wall  19  and the internal wall  20 . This rotational symmetry is not essential, however, though it is simple and advantageous for the manufacture of the pump, in particular as regards the manufacture of the heating device  26  as a fundamental component of the external wall  19 .