Abstract:
The description relates to a heatable pump housing part comprising a heat distribution sheet fixed on the housing part and a tubular heating element fixed on the heat distribution sheet. According to the invention the tubular heating element is positioned in a groove or a step on the housing part that is covered by the heat distribution sheet.

Description:
[0001]    This invention refers to a heatable part of a pump housing on which a heat distribution sheet is fixed on which a tubular heating element is arranged. Such a pump housing part is known from DE 199 03 951 A1. Heatable pump housing parts are, for example, required for washing machines or dishwashers. 
         [0002]    The pump housing known from DE 199 03 951 A1 has an aluminium heat distribution sheet fixed on a flat or conical cover surface. The heat distribution sheet distributes the heat generated from a tubular heating element, which is soldered onto the plate, quickly over a large area and transmits it to the stainless steel housing part situated below it. 
         [0003]    Furthermore, EP 1 507 914 B1 discloses another pump housing part. A tubular heating element is arranged in a suitably shaped groove of the housing part. To facilitate a good heat coupling between the tubular heating element and the housing part, joints and any free spaces between the tubular heating element and the walls and bottom of the groove are filled with a heat-conducting filler material. As examples for such filler material, bonding agents or solders are mentioned. 
         [0004]    The arrangement of a tubular heating element in a groove of a heatable pump housing part is also known from EP 1 201 933 B1, which discloses a cylinder- or ring-shaped stainless steel housing part that connects the cap and the bottom of a pump housing, and is positioned in a groove of a lateral surface area. 
         [0005]    A constant goal in the development of heatable pump housing parts for washing machines or dishwashers has always been to achieve with as little costs as possible a heat coupling as ideal and reliable as possible between the tubular heating element and the pump housing. The better the heat coupling, the faster is the rate, with which the heat generated by the tubular heating element is transmitted to the pump housing and from there to the fluid flowing through the pump housing. Moreover, with a better heat coupling one can reduce the operating temperature of the tubular heating element further. Lower operating temperatures of the tubular heating element help reduce the free spaces between this element and other components in the washing machine or dishwasher and particularly allow the use of more economical plastics in the vicinity of the tubular heating element, since these have to withstand less high temperatures. 
         [0006]    The reliability of the coupling is at least as important as a good heat coupling of the tubular heating element. If the heat coupling deteriorates during the operation, the heat generated by the tubular heating element cannot be dissipated properly; as a result, the tubular heating element gets overheated. 
         [0007]    An object of the present invention is to show a way, in which the heat coupling between the tubular heating element and the pump housing can be improved in a reliable manner at minimum costs. 
       SUMMARY OF THE INVENTION 
       [0008]    A pump housing part according to this invention has a groove or step, which is covered by the heat distribution sheet. When the tubular heating element is fixed in this groove or step, its area of contact with the heat distribution sheet increases, which subsequently improves the dissipation of heat. 
         [0009]    It is generally known that the process of soldering a tubular heating element to a heat distribution sheet and the heat distribution sheet to a steel body causes relative movements between the tubular heating element and the heat distribution sheet as well as between the heat distribution sheet and the steel body due to the heating in a soldering furnace; these movements are unproblematic only in case of soldered joints on plane surfaces. Nonetheless it is possible to avoid reliably that the heat distribution sheet rises up from the underlying housing part or the tubular heating element rises up from the heat distribution sheet in critical areas like at the edge of a step or the bottom of a groove during the soldering process for manufacturing a pump housing part according to the present invention. For example, this can be avoided by inductive soldering. Another way of ensuring a large contact area and a proper fastening of the tubular heating element in the step or groove in a reliable manner is to cut out securing straps from the heat distribution sheet and bend them upwards. Such securing straps will encompass the tubular heating element and give additional hold. 
         [0010]    To establish a large-surface contact between the tubular heating element and the heat distribution sheet in a reliable manner, the tubular heating element of a housing part according to this invention preferably has a more or less angular cross-section. For example, the tubular heating element can have an approximately rectangular, trapezoidal or triangular cross-section. In that case, it is preferred if the lower side of the tubular heating element, i.e. the side facing the pump housing, encases an angle less than 90°, particularly 60° to 80°, with an adjacent side. Thus, an enlarged contact area can be created easily and reliably between the tubular heating element and the heat distribution sheet. As another option, a rounded tubular heating element can be fixed in an groove having a round bottom, e.g. in a groove with a semi-circular cross-section. 
         [0011]    Preferably, the heat distribution sheet extends on both the sides of the groove or step, so that the heat generated by the tubular heating element is spread quickly over a maximum possible area of the housing part. 
         [0012]    Preferably, the tubular heating element is arranged in a groove of the housing part that is covered by the heat distribution sheet. This offers the advantage that an even larger area of contact can be created between the tubular heating element and the heat distribution sheet, as compared to the arrangement of the tubular heating element in a step, because a groove with a trapezoidal or rectangular cross-section is formed by two steps; and this enables the heat distribution sheet to touch the tubular heating element on three side faces. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Further details and advantages of the invention are explained with the help of embodiments with reference to the drawings attached herewith. In the figures: 
           [0014]      FIG. 1  shows an embodiment of a pump housing part of this invention; 
           [0015]      FIG. 2  shows a sectional view of  FIG. 1 ; 
           [0016]      FIG. 3  shows a sectional view of another embodiment; 
           [0017]      FIG. 4  shows a sectional view of another embodiment; and 
           [0018]      FIG. 5  shows a sectional view of another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The pump housing part  1  shown in  FIGS. 1 and 2  is a cap. The housing part  1  has a base body made of stainless steel  2  forming a connecting tube  3 . The pump housing part  1  can be heated with a U- or C-shaped tubular heating element  4 , which is soldered onto a heat distribution sheet  5  that spreads over a cover surface of the housing part and is soldered with it. 
         [0020]    As shown in the sectional view of  FIG. 2 , the heat distribution sheet  5  covers a U- or C-shaped groove in the housing part. The groove can have an angular cross-section, particularly rectangular or trapezoidal, or a U-shaped cross-section. The tubular heating element  4  is arranged in this groove, such that it touches both the side walls of the groove. On both the sides, the heat distribution sheet  5  projects by more than 0.5 cm beyond the side walls of the groove. An advantage of this is that a larger area of contact is created between the tubular heating element  4  and the heat distribution sheet  5 . It is preferred that the heat distribution sheet primarily covers substantially the whole upper side of the housing part, especially at least 70% of this area. A part of the upper side, i.e. the part between the ends of the tubular heating element  4 , may remain uncovered since no heat is generated in this area. 
         [0021]    The heat distribution sheet  5  has securing straps  6 . The plate encompasses the tubular heating element  4  with the help of these straps. The securing straps  6  are cut out from the heat distribution sheet  5  and bent upwards. 
         [0022]      FIG. 3  shows another embodiment of a heatable pump housing part, which mainly differs from the embodiment shown in  FIG. 2  only in that the groove does not have a uniform depth and hence, the tubular heating element  4  is tilted against the cover surface plane. This has the advantage that the heat exchanger surface is the largest where the tubular heating element  4  is heated the most. Generally, the tubular heating element is hotter in the centre areas than at the ends. 
         [0023]      FIG. 4  shows another embodiment, which mainly differs from the aforementioned embodiment only in that the tubular heating element  4 , is fixed in a step. This also increases the area of contact between the tubular heating element  4  and the heat distribution sheet  5 , since the tubular heating element  4  is in contact with two surfaces of the heat distribution sheet  5  that run transverse to one another. 
         [0024]    In the embodiments displayed, the tubular heating element  4  has an approximately trapezoidal cross-section and its footprint faces the heat distribution sheet  5 . As seen in the embodiment displayed in  FIG. 5 , such a tubular heating element  4  can also be arranged in a reverse orientation in the groove, i.e. with its footprint facing away from the bottom of the groove. In the latter case, the walls of the groove or the two steps, which form the groove, are arranged aslant to one another. 
         [0025]    The tubular heating element  4  carries a support plate  7 , as shown in  FIGS. 1 and 5 , for fixing a safety switch. The support plate  7  is preferably made of aluminium or of a good heat-conducting aluminium alloy and enables a heat coupling between the tubular heating element  4  and a thermostatic protective switch or a thermostat, with which the tubular heating element  4  can be cut off when heated beyond a rated operating temperature. Safety switches, which feature a switching operation through the snapping of a bimetallic element, are particularly suitable. 
         [0026]    The heat distribution sheet  5  has a thickness of 1 mm to 1.5 mm. In the embodiment displayed, the thickness of this plate is 1.2 mm. The heat distribution sheet  5  is inductively soldered with the base body  2  and the tubular heating element  4 . 
       REFERENCE NUMBERS 
       [0000]    
       
           1  Pump housing 
           2  Base body 
           3  Connecting piece 
           4  Tubular heating element 
           5  Heat distribution sheet 
           6  Securing straps 
           7  Support plate