Abstract:
A pump having a pump chamber and an impeller which rotates therein has an inlet leading into the pump chamber and an outlet leading out of the pump chamber, the pump having a pump motor having a rotor. The rotor and the impeller are connected to each other, the impeller being supported in an axial direction towards the inlet and an axial support being provided therefor against an axial bearing. In this instance, the axial bearing is located on a rotation axis of the rotor and includes a centrally supported concave bearing shell in which a convex-curved bearing projection of the impeller is in abutment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Application No. 10 2012 216 196.1 filed Sep. 12, 2012, the contents of which are hereby incorporated herein in its entirety by reference. 
       TECHNOLOGICAL FIELD 
       [0002]    The invention relates to a pump, preferably a pump having a pump chamber and an impeller which rotates therein, an inlet leading into the pump chamber and an outlet leading out of the pump chamber. 
       BACKGROUND 
       [0003]    A corresponding pump is known from EP 1052410 B1. An axial support for the impeller against the pump housing is achieved in this instance by means of two sliding rings in the form of a friction-type bearing which are arranged between an end face of the impeller and a shoulder in the pump housing at the inlet. In addition to an axial support for the impeller or a structural unit comprising the impeller and rotor of the pump motor, a seal is thereby provided between the intake side at the impeller inlet and pressure side at the impeller outlet in order to prevent a backflow through the gap between the pump housing and impeller back to the inlet. This is because such a backflow would substantially reduce the degree of efficiency of the pump. 
       BRIEF SUMMARY 
       [0004]    An object of the invention is to provide a pump of the type mentioned in the introduction, by means of which disadvantages of the prior art can be avoided and in particular a practical axial support of the impeller is possible with simple production. 
         [0005]    This object is achieved with a pump. Advantageous and preferred embodiments of the invention are set out in the additional claims and are explained in greater detail below. The wording of the claims is included in the content of the description by express reference. 
         [0006]    There is provision for the pump to have a pump chamber and a rotor or impeller which rotates therein. An inlet leads into the pump chamber in a pump housing and an outlet leads out again. In order to drive the impeller, the pump has a pump motor having a rotor, the rotor and the impeller being connected to each other. The pump motor is advantageously constructed without brushes. The impeller, which is generally pulled towards the inlet during operation, is supported in this axial direction towards the inlet or away from the rotor, for which very reason an axial support is provided against an axial bearing. 
         [0007]    According to the invention, the axial bearing is located on a rotation axis or rotary axis of the rotor, that is to say, centrally. This means that the rotation axis of the rotor and consequently also of the impeller extends through a bearing face of the axial bearing. This rotation axis of the rotor must not be mistaken for the motor shaft, even if the rotation axis naturally also extends centrally through the motor shaft. 
         [0008]    An advantage of this central construction and arrangement of the axial bearing is that a necessary bearing face can thus be kept relatively small. The relative speed with which the bearing faces on the axial bearing move against each other is also relatively low. It is thereby possible, on the one hand, to reduce the structural size, or the quantity of material for the axial bearing can be reduced, which is generally material which is specific, difficult to process and/or expensive. At the same time, the pressure forces occurring with such a pump, owing to the fact that the impeller is pulled towards the inlet, are not too large. In this regard, these forces can also be absorbed with an axial support of relatively small extent. Furthermore, a very low-friction support can also thereby be achieved in comparison with the previously mentioned support using sliding rings, which again has an advantageous effect on the energy consumption and degree of efficiency of the pump. 
         [0009]    Another advantage is that the arrangement of the impeller in the pump housing is thus possible in a far more precise manner, at the same time with simpler production of the pump. Owing to the support with the axial bearing in the region in which it is significant for the impeller, it may be very precise. This is explained in greater detail below. 
         [0010]    In an advantageous embodiment of the invention, the rotor and impeller are constructed as a structural unit. In this instance, they may not only be assembled together in some manner, but advantageously also be non-releasable or be produced in one piece. The construction of the rotor and impeller as a structural unit is advantageously carried out even before the pump is assembled. For example, the rotor and impeller may be produced as a structural unit in one piece from plastics material in a plastics injection-moulding operation, in a particularly advantageous manner in two or three steps. 
         [0011]    Furthermore, the structural unit comprising the rotor and impeller may advantageously be constructed in such a manner that the impeller is placed so to speak directly on the rotor, or at least no pump chamber wall is located therebetween. In particular, there is intended to be no pump chamber base therebetween so that construction and also assembly can be carried out very easily. Advantageously, the impeller has for this purpose a larger diameter than the rotor so that the structural unit can be mounted in the direction directed into the motor. 
         [0012]    In an embodiment of the invention, the axial bearing is located in a continuation of the inlet, in the region thereof or inside the inlet. It is thereby possible, using the axial bearing according to the invention, for the basic structure of the impeller not to have to be changed to an excessive degree. 
         [0013]    Furthermore, in a particularly advantageous manner the inlet is one of the components of the pump housing which are closest to the impeller in the region of the axis of rotation or rotary axis of the rotor. Consequently, the arrangement of the axial bearing is relatively simple in this instance. Finally, the axial bearing which is arranged in the inlet region also disrupts the influx of the conveyed fluid into the pump only to a small extent since such impeller pumps are generally pressure pumps and not suction pumps. In this instance, the arrangement of the axial bearing on the rotation axis of the rotor centrally in the inlet is also advantageous, which inlet also advantageously extends coaxially relative to this rotation axis, whereby no excessively large flow resistance is also formed. 
         [0014]    In another advantageous embodiment of the invention, the axial bearing may be located, when viewed radially, inside the impeller or at the axial height thereof, in particular in the upper end region thereof. The structure of the impeller can thus simply be substantially conventional. 
         [0015]    In a preferred embodiment of the invention, the axial bearing is located substantially freely in the inlet or is arranged therein. It is supported at the inlet by means of a plurality of supports, in particular in the manner of struts, which extend in a particularly preferred manner in a radial direction and which may be constructed so as to be planar in cross section in such a manner that they form the smallest possible flow resistance in an axial direction. A plurality of supports may be provided for the axial bearing and may be distributed in a uniform manner around the axial bearing or in a peripheral direction. For example, there may be from two to four supports for sufficiently stable retention of the axial bearing. 
         [0016]    The impeller may have a tubular upper portion, which is directed in the direction towards the inlet. The inlet, in particular a previously mentioned extended inlet, may have or form a collar which engages over the tubular upper portion of the impeller and which is also substantially in the form of a short pipe. This collar may in particular form a tapered portion of the inlet. The tubular upper portion and the collar overlap each other in an axial direction, which serves to prevent excessively great previously mentioned backflow of water from the pressure side to the intake side. In this instance, in a particularly advantageous manner, the collar may extend a little into the tubular upper portion of the impeller. The supports for the axial bearing provided at the inlet extend at the end of this collar or as far as possible in the direction towards the impeller and may consequently be arranged inside the tubular upper portion of the impeller. Consequently, the axial bearing extends practically as far as possible in the direction towards the impeller. 
         [0017]    Advantageously, the axial bearing has a friction-type bearing or plain bearing, which the impeller or the structural unit which is formed therewith abuts. The friction-type bearing may have a bearing face. In a particularly advantageous manner, a bearing projection is arranged on a projection or a protuberance inside the impeller, this bearing projection being able to cooperate with the friction-type bearing of the axial bearing. The friction-type bearing and bearing projection may be constructed in this instance in such a manner that they have a curvature and an indentation which are placed one against the other or on each other and rotate one inside the other. The shape of the curvature and indentation advantageously allows the structural unit or the impeller to be centred on the rotation axis of the rotor and also consequently of the entire pump. This means that the other support of the structural unit or also of the rotor of the pump motor has to be constructed in a less complex manner, in particular also requires no further radial bearing since the centering thereof at the side of the structural unit remote from the impeller must be present only at that location and does not have to extend over the entire length of the structural unit. The curvature and indentation are advantageously constructed in such a manner that the indentation has a larger radius or is less extensively curved than the curvature which is located therein. The previously mentioned self-centering is thus advantageously carried out. 
         [0018]    It is possible to construct the friction-type bearing on the axial bearing so as to be curved in a concave manner away from the impeller and the bearing projection on the impeller with a convex curvature away therefrom. Consequently, quasi a tip or a curvature of the bearing projection of the impeller engages in the recess or indentation of the axial bearing at the inlet of the pump housing. A substantially uniform or rounded curvature is preferred. For the portion which is curved in a convex manner in each case, that is to say, quasi the tip on the axial bearing, a very fine tip could in fact also be provided. Then, however, a substantially point-like bearing would be produced and is again liable to wear and further places very high demands on production. 
         [0019]    It is possible to construct a portion of the axial bearing from plastics material. The other portion may also comprise plastics material, alternatively metal or graphite or ceramic material. At least one inwardly curved friction-type bearing in the form of a recess should be produced from plastics material. In this instance, for such bearings, generally preferred plastics materials can be used, for example, polyamide, Teflon-reinforced plastics materials, POM or generally fibre-reinforced plastics materials. Metal materials which may be used include a sintered bronze or brass, in particular also as a result of the corrosion resistance thereof when the pump is used in a dishwasher. 
         [0020]    A friction-type bearing of the axial bearing on the pump housing or at the inlet is advantageously injected on or injected in. Consequently, it can be secured thereto in the same operating step of the production of the pump housing. 
         [0021]    A bearing projection of the impeller adjoining the friction-type bearing of the axial bearing is advantageously also injected thereon or therein. The advantages of simple and precise production are also achieved in this instance. Alternatively, it could also be a separate component which can be inserted from above and which, as a result of the abutment pressure on the axial bearing during operation of the pump, cannot in any case fall out of the impeller. 
         [0022]    Advantageously, the structural unit rotates on a fixed motor shaft which extends coaxially with the rotation axis of the rotor. This motor shaft may be secured to the end facing away from the impeller, in particular on a motor housing at the end of the pump facing away from the inlet. Preferably, it is a round motor shaft, which rotates in a bearing socket which is arranged, in particular injected, in the rotor. The length of the motor shaft may be freely selected within wide limits. It may be almost as long as the entire structural unit comprising the rotor and impeller. However, since at the other end the axial bearing ensures the support and in particular also the centering of the structural unit, the motor shaft does not need to be particularly long and may protrude only a few centimetres or only by a small amount into the rotor. Substantially, this short motor shaft must then ensure radial securing or centering of the rotor or the structural unit. The centering at the other end of the structural unit is formed by the axial bearing at the inlet, which is generally sufficient. 
         [0023]    This and other features will be appreciated not only from the claims but also the description and the drawings, the individual features being able to be implemented individually or together in the form of sub-combinations in an embodiment of the invention and in other fields and being able to constitute advantageous embodiments which are patentable per se and for which protection is claimed in this instance. The sub-division of the application into individual sections and intermediate headings do not limit the statements made therebelow in terms of their general validity. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0024]    Embodiments of the invention are schematically illustrated in the drawings and are explained in greater detail below. In the drawings: 
           [0025]      FIG. 1  is a lateral cross section through a pump according to the invention having a structural unit comprising the impeller and rotor on a fixed motor shaft, which can be supported against an axial bearing in the pump inlet, 
           [0026]      FIG. 2  is an enlarged view of the axial bearing from  FIG. 1  in the not-yet-supported state before the pump motor is started up, 
           [0027]      FIG. 3  is a plan view of the pump from  FIG. 1 , when viewed in the direction directed into the inlet on the axial bearing, 
           [0028]      FIG. 4  shows a modification of an axial bearing similar to  FIG. 2  with transposed curvatures, and 
           [0029]      FIG. 5  is another modification of an axial bearing according to  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  is a lateral cross section of a pump  11  according to the invention. It has a pump portion  12  having a pump chamber  13  in a pump housing  14 . The pump  11  is in this instance obviously constructed as an impeller pump and can advantageously be used in a water-guiding household appliance, in particular a dishwasher or a washing machine. 
         [0031]    A central inlet  16  extends into the pump chamber  13  along a longitudinal centre axis which is illustrated with dot-dash lines. The inlet  16  has an inlet pipe  17 , which opens in a radially inner collar  18 . Furthermore, an outlet  19  is provided on the pump housing  14 , see in this regard also the plan view from  FIG. 3 . 
         [0032]    On the other hand, the pump  11  has a motor portion  20  having a stator  21  and a rotor  22 , which has a rotor plate assembly  23  and magnets  23 ′. Therefore, this is a brushless wet rotor as is known and conventional for such application fields. 
         [0033]    In the rotor  22  is a bearing socket  25  which runs on a motor shaft  26  which is securely inserted in the motor portion  20 . The region of the rotor  22  surrounding the rotor plate assembly  23  and the magnets  23 ′ is adjoined by an impeller  30  or is constructed integrally therewith, in particular by means of previously mentioned plastics injection-moulding. The impeller  30  has a base plate  31  and a cover plate  32  with bent impeller blades  33  which are arranged therebetween. Such impellers are known to the person skilled in the art, see in this regard, for example, U.S. Ser. No. 13/910,185 from the same Applicant with a filing date of Jun. 5, 2013. Furthermore, the impeller  30  has a tubular upper portion  34 , which adjoins the cover plate  32 . In the central region, a central projection  35  protrudes above the base plate  31 . The motor shaft  26  may extend as far as this central projection  35  but does not have to be so long and may extend, for example, only as far as the lower end of the bearing socket  25 . At the end of the central projection  35  there is provided or arranged a bearing projection  37  which is slightly curved in a convex manner or in the direction towards the inlet  16 . This can be seen from the powerful enlargement in  FIG. 2  explained below. 
         [0034]    In  FIG. 2 , it can be seen that, although an axial bearing  39  according to the invention is illustrated, it is illustrated for reasons of clarity in a state in which no abutment has yet been achieved. There is thus still a small spacing which, for example, may correspond to an idle state of the pump  11 . Opposite the bearing projection  37 , the axial bearing  39  has a bearing shell  40  which is arranged, for example, pressed or injected, in a bearing retention member  41 . Under some circumstances, it may also be the same component. The bearing retention member  41  is in turn retained by means of three struts  42  whose radial arrangement can be seen from  FIG. 3 , on the pump housing  14  or on the inlet pipe  17  and collar  18 . The axial bearing  39  or bearing retention member  41  and struts  42  may also advantageously be constructed integrally with the inlet. 
         [0035]    If the pump  11  is started, it draws the impeller  30  in the direction towards the inlet  14 , that is to say, downwards in  FIG. 1 . The bearing projection  37  thereby moves into abutment with the bearing shell  40  of the axial bearing  30 . The respective curvature ensures that a centering of the structural unit comprising the impeller  30  and rotor  22  is carried out relative to the dot-dash longitudinal centre axis or rotation axis of the rotor. To this end, the bearing projection  37  which is curved outwards is provided with a smaller radius or a more highly curved surface than the inwardly curved recess of the bearing shell  40 . The difference may, for example, be set out geometrically in such a manner that, if circular faces or substantially circular faces are involved, the radius of the bearing shell  40  is from 1.5 times to 4 times as large as that of the bearing projection  37 . The bearing projection  37  may comprise in this instance the same plastics material as the other impeller  30 . Alternatively, it may comprise a separate applied material. The same applies to the bearing shell  40 ; in this regard, reference is made to the examples of respective material selections described in the introduction. 
         [0036]      FIG. 4  shows a modification of an axial bearing  139 . In principle, the principle of the arrangement of the axial bearing  139  on the rotation axis of the rotor is the same, and three struts  142  are also provided in this instance. However, the bearing retention member  141  is not inwardly curved in this instance as in  FIG. 2 , but instead is curved outwards or forms the outwardly curved portion of the axial bearing  139 . 
         [0037]    Adjacent thereto, the bearing projection  137  of the impeller  130  has a recess shell  138  as a quasi-bearing shell. As indicated, this may comprise a different material from that of the bearing projection  137  and may be injected or secured. In a similar manner to that in  FIG. 2 , in  FIG. 4  the curvatures are constructed to differing degrees for a good relationship comprising a mutually abutting face and centering effect. 
         [0038]      FIG. 5  illustrates another modification, which resembles that of  FIG. 2 . The axial bearing  239  has in this instance a bearing shell  240  which is retained by three struts  242 . The bearing shell  240  is carried by a bearing retention member  241  and advantageously comprises hard material or metal, in particular brass. There is provided on the bearing projection  237  of the impeller  230  a bearing tip  244  which also advantageously comprises metal and is secured or injected. 
         [0039]    Whilst the bearing shell  240  is substantially curved in a similar manner to that in the previous embodiments, the bearing tip  244  is constructed in a much more acute manner. It may either be constructed directly as a tip which is as fine as possible, or alternatively also have a flattened portion of approximately 1 mm diameter at the front or a corresponding rounded portion. In particular in connection with the slightly more powerfully inwardly curved bearing shell  240 , very good centering is also thereby achieved. If the respective materials are sufficiently wear-resistant, a very low-friction bearing can also thereby be achieved, which again has an advantageous effect on the energy consumption and degree of efficiency of the pump. 
         [0040]    Another great advantage of the construction of the pump  11  having an axial bearing  39  is that the axial position of the impeller  30  in the pump chamber  13  can be determined in a precise manner. In particular, a gap between the impeller  30  or covering plate  32  and tubular upper portion  34  towards the pump housing  14 , in particular in the region of the inlet pipe  17  or collar  18 , may be minimized without running the risk of direct abutment occurring. 
         [0041]    A typical loss flow from the pressure side to the intake side for impeller pumps can thereby be reduced. The degree of efficiency or the energy efficiency of the pump  11  is thereby increased. This very precisely fitting bearing is in addition to the axial support further promoted by the centering by means of the specific configuration of the axial bearing  39 . 
         [0042]    Owing to the construction of the impeller  30 , together with the rotor  22  and its portion of the axial bearing, very light and precise assembly can also be achieved.