Abstract:
A centrifugal pump for household appliances comprising a cover ( 1 ) having:—a first face internal to the pump adapted to be in contact with an operating fluid, and a second face external to the pump, opposite to the first face and provided with an annular groove ( 16 ) forming a projection inwards of the pump,—a heating element ( 11 ) fixed in the annular groove ( 16 ),—a first support element ( 21 ) arranged on the second face and provided with a first constraint ( 31 ) adapted to be fixed to a first safety device ( 41 ), said first support element ( 21 ) being in thermal contact with said operating fluid, whereby the first safety device ( 41 ) is adapted to come in thermal contact with the operating fluid,—a second support element ( 22 ) arranged on the second face, distinct from the first support element ( 21 ) and provided with a second constraint ( 32 ) adapted to be fixed to a second safety device ( 42 ), said second support element ( 22 ) being in thermal contact with said heating element ( 11 ), whereby the second safety device ( 42 ) is adapted to come in thermal contact with the heating element ( 11 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a centrifugal pump for household appliances, in particular a cover of centrifugal pump. 
       BACKGROUND ART 
       [0002]    In many applications of household appliances, a heater is required to bring an operating fluid, typically, to the operating temperature required. 
         [0003]    Heaters of the above type are typically, although not exclusively, coupled with circulating pumps of the above household appliances. 
         [0004]    Such heaters typically include a heating element, normally consisting of a resistance thermometer, and a device for temperature control both in normal operating conditions and in any anomalous or failure conditions. In theory, in order to monitor the temperature of the heater under all operating conditions, a single thermostat would be sufficient. However, to meet some safety principles, such as the presence of a redundant secondary protection in case of failure of the main protection, the thermostat that acts as the main protection must be complemented with a second safety device, typically a thermal fuse. 
         [0005]    The thermal fuse is normally used for abnormal and failure condition monitoring and for this reason, it must not intervene in the normal operation of the heater and at the same time, in abnormal and failure conditions it must start promptly before dangerous situations can occur, at the expense of any parts nearby. Laboratory tests show that, in order meet these specifications, the operating temperature of the thermostat must be around 100° C. while that of the thermal fuse is generally around 200° C. In order to meet these requirements, the thermostat is placed on a surface mainly in contact with water and which therefore, under normal operating conditions, is at a temperature of about 85-90° C., while the thermal fuse is placed on a surface mainly in contact with the heating element and which therefore, under normal operating conditions, is at a temperature of about 140-160° C. 
         [0006]    If the thermostat and thermal fuse are placed on the same support, this must necessarily be set at a temperature of 85-90° C. to allow the thermostat to perform its function. This would have as a contraindication the slowness of intervention of the thermal fuse, or rather its uselessness, since experimental tests confirm that usually the material thermal fuses are made of, in worst failure conditions, i.e. without circulating water, melts after 10-12 seconds while the thermal fuse would need around 20-25 seconds to intervene. 
         [0007]    In order to overcome this drawback, it is known to provide a single support with two distinct zones subject to different temperatures, one reserved to the thermostat and the other to the thermal fuse. A technical solution of this type is for example described in U.S. Pat. No. 7,560,672. 
         [0008]    However, such a solution cannot yet be considered optimal. In fact, the presence of a single support implicitly provides for the presence of a thermal bridge between the two zones intended for the thermostat and the thermal fuse, respectively. 
       SUMMARY OF THE INVENTION 
       [0009]    An object of the present invention is to provide a centrifugal pump for household appliances capable to effectively control the temperature of the operating fluid, typically water, and at the same time manage any abnormal or failure situations in a reasonable time. 
         [0010]    This object is achieved by a centrifugal pump for household appliances which, according to claim  1 , comprises a cover having:
       a first face internal to the pump adapted to be in contact with an operating fluid, and a second face external to the pump, opposite to the first face and provided with an annular groove forming a projection inwards of the pump,   a heating element fixed in the annular groove,   a first support element arranged on the second face and provided with a first constraint adapted to be fixed to a first safety device, said first support element being in thermal contact with said operating fluid, whereby the first safety device is adapted to come in thermal contact with the operating fluid,   a second support element arranged on the second face, distinct from the first support element and provided with a second constraint adapted to be fixed to a second safety device, said second support element being in thermal contact with said heating element, whereby the second safety device is adapted to come in thermal contact with the heating element.       
 
         [0015]    The centrifugal pump of the present invention, in particular the cover thereof, allows physically separating the two support elements intended for the thermostat and the thermal fuse, respectively. Advantageously, the shape and size of each support element can be defined and optimized irrespective of the shape and size of the other support element. Also the distance between the two support elements can be optimally defined without affecting other construction parameters, such as the size of the support elements themselves. 
         [0016]    Preferably, the first support element comprises a first tab and the second support element comprises a second tab. The first tab and the second tab are in thermal contact with the operating fluid and with the heating element. Moreover, preferably according to this aspect, the first support element includes a first plate spaced apart from the heating element and connected to the first tab. 
         [0017]    Preferably, said second support element includes a second plate spaced apart from said heating element and connected to said second tab. 
         [0018]    The first plate and the second plate can have the same extension in height from the heating element, and in particular they can be coplanar, or they can have a different extension in height, for example the first support element can have an extension in height greater than the second support element. 
         [0019]    Preferably, the heating element includes at least a first portion at a first temperature and a second portion at a second temperature, higher than the first temperature. Preferably, the first support element includes a third tab which is in thermal contact with the first portion and the second tab of the second support element is in thermal contact with the second portion. 
         [0020]    Advantageously, the fact that the first support element includes a tab for connection with the portion at a lower temperature of the heating element allows managing even special abnormal conditions, such as the excessive formation of scale. 
         [0021]    Preferably, the heating element is of electro-resistive type and extended between a first and a second pin adapted to be coupled to respective terminals of an electric potential source, and the at least one first portion is adjacent to the first pin. 
         [0022]    Preferably, another first portion adjacent to the second pin is provided. 
         [0023]    Preferably, the first safety device is a thermostat. 
         [0024]    Preferably, the second safety device is a thermal fuse. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0025]    Further features and advantages of the invention will appear more clearly from the detailed description of preferred, but not exclusive, embodiments of a heater for household appliances according to the present invention, shown by way of a non-limiting example with the aid of the accompanying drawings, in which: 
           [0026]      FIG. 1  is an axonometric view of a cover for centrifugal pump according to the present invention; 
           [0027]      FIG. 2  is a first sectional view of the cover in  FIG. 1 ; 
           [0028]      FIG. 3  is a second sectional view of the cover in  FIG. 1  coupled to two safety devices; 
           [0029]      FIGS. 4 and 5  are two axonometric bottom views of two components of the cover in  FIG. 1 , respectively; 
           [0030]      FIGS. 6 and 7  are two axonometric top views of the two components in  FIGS. 4 and 5 , respectively. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    With reference to the accompanying figures, a cover for centrifugal pump, in particular for household appliances, is indicated as a whole with reference numeral  1 . Cover  1  is particularly, although not exclusively, usable for a circulating pump, not shown in the accompanying figures, of a dishwasher. However, more generally, the centrifugal pump of the present invention can also be used in a plurality of similar applications for household appliances, in particular where it is necessary to heat in a controlled manner an operating fluid and at the same time manage, through monitoring of temperature, specific abnormal or failure situations. 
         [0032]    Cover  1  comprises a base  10  capable of being in contact with an operating fluid, typically water. In particular, a first face of the cover is susceptible of being in contact with the operating fluid, and a second face of the cover, opposite to the first face, is in thermal contact with the fluid. The cover is made of metal material, preferably stainless steel. 
         [0033]    Base  10  is circular in shape with a raised edge  15 , extending distally from the face of base  10  in contact with the fluid, and a central hole  17  which can be coupled with the suction conduit, not shown, of the circulating pump. Along the raised edge  15  there is a plurality of mating items  18 , which extend from the face in contact with the fluid of the base  10 , to constrain the base  10  to the outer housing of the circulating pump. The coupling elements  18  are, for example, of the snap type or other type per se known and conventional and therefore not described in further detail. 
         [0034]    Base  10  further comprises a circular groove  16 , basically rectangular in section, adjacent to the raised edge  15 . In other words, groove  16  is defined by the raised edge  15  and by a circular inner area  45  which, seen in plan from the top, substantially is a circular crown and which is arranged around the central hole  17 . Preferably, the height of the inner zone  45 , measured from the bottom of groove  16 , is less than the height of the raised edge  15 . The thickness of cover  1  is thin enough so that the features of a face thereof that are raised are recesses of the other opposite face, and vice versa. For example, a relief zone of the face adapted to be in contact with the fluid, corresponds to groove  16 , and a recess of the face adapted to be in contact with the fluid, corresponds to the inner zone  45 . Cover  1  further comprises a heating element  11  accommodated and fixed, for example by welding and preferably by brazing, in the circular groove  16 . The heating element  11  is of electro-resistive type, tubular in shape and extended between a first end pin  12  and a second end pin  13  susceptible of being coupled with the respective terminals of an electric potential source, not shown, so as to allow the flow of current and the consequent generation of heat which allows heating the operating fluid in contact with cover  1 . Pins  12  and  13  are raised in relation to the circular groove  16  and circular in shape, while the portion of heating element  11  between pins  12  and  13  is rectangular in shape so as to adapt to the shape of the section of the circular groove  16 . The end portions  11   a  of the heating element  11  accommodated within the circular groove  16  and adjacent to pins  12 ,  13  are the part with the lowest temperature of the heating element  11 , while the intermediate central portion  11   b  between pins  12 ,  13  is the part with the highest temperature of the heating element  11 . 
         [0035]    Cover  1  further comprises a first support element  21  provided with a first constraint  31 , or fastening portion, consisting of a threaded hole, for a first safety device  41 , adapted to control the temperature of the operating fluid under normal operating conditions and consisting of a thermostat. Thermostat  41  is fixed to the first support element  21  by means of a screw  43  screwed into the threaded hole  31 . The first support element  21  is in thermal contact with the operating fluid to act as a thermal bridge between the operating fluid and thermostat  41 . This allows the thermostat to control the temperature generated by the heating element  11 , through the control of its power supply, so that the operating fluid is maintained at the normal operating temperature, typically in the range between 85° C. and 90° C. 
         [0036]    Heater  1  further comprises a second support element  22  provided with a second constraint  32 , or fastening portion, consisting of a threaded hole, for a second safety device  42 , adapted to cut out the power supply of the heating element upon reaching predetermined abnormal or failure conditions which cause a sudden rise in temperature, for example the interruption of the operating fluid flow, i.e. in case of dry running. The second safety device  42  typically consists of a thermal fuse fixed to the second support element  22  by means of a screw  44  screwed into the threaded hole  32 . The second support element  22  is in thermal contact with the heating element  11  to act as a thermal bridge between the heating element  11  and the second safety device  42 . This allows the thermal fuse to intervene quickly if the temperature on the surface of the heating element  11  reaches temperatures considered not compatible with a normal operation of the heater, i.e. temperatures typically higher than 140° C. 
         [0037]    The first and the second support elements  21 ,  22 , which are two separate pieces, are mutually arranged in such a way that the first support element  21  is closer to one of the end portions  11   a , which is colder, in relation to the second support element  22  and that this is instead closer to the central portion  11   b , which is warmer. This allows the second support element  22  to be prompter, compared to the first support element  21 , in feeling the temperature variations of the heating element. 
         [0038]    The first and the second support elements  21 ,  22  comprise a respective plate-shaped element  53 ,  54 , or plate, having a distal face  21   a ,  22   a  from the heating element  11 , in contact with the thermostat  41  and the thermal fuse  42 , respectively, and a proximal face  21   b,    22   b  facing the heating element  11  and spaced therefrom. The distal  21   a ,  22   a  and proximal  21   b,    22   b  faces are oriented substantially parallel to the heating element  11 , in particular to the face thereof facing towards them. 
         [0039]    The first and the second support elements  21 ,  22  comprise a first tab  23  and a second tab  24 , respectively, parallel to the plate-shaped elements  53 ,  54  of the first and second support elements  21 ,  22 , respectively, and respectively connected to them through a lateral connection  27 ,  28 , substantially orthogonal to the first and to the second tab  23 ,  24  and proximal to the central hole  17 . The first and the second tab  23 ,  24  have an initial portion  48 ,  49  which has the same circumferential extension as the connecting portion  27 ,  28 . The first tab  23  continues, from the initial portion  48  thereof, in radial direction and distal from the central hole  17  with a first flap  23 ′ and a second flap  50  which are circumferentially reciprocally spaced apart, forming a gap. The first flap  23 ′ is in contact with the inner zone  45 , and thus in thermal contact with the fluid and with the heating element  11 ; the second flap  50 , which is smaller in size compared to the first flap  23 ′, extends in a radial direction and distal from the central hole  17 , being in contact with the inner zone  45  but not in contact with the heating element  11 . The second tab  24  of the second support element  22  continues, from the initial portion  49  thereof, with a flap  24 ′ which extends in radial direction and distal from the central hole  17 , which is in contact with the inner zone  45  and with the heating element  11 . The circumferential extension of flap  24 ′ is less than the circumferential extension of the initial portion  49 . The contact with the inner zone  45  of the first and of the second tab  23 ,  24  provides a better heat distribution, providing a better thermal contact for the thermostat and the thermal fuse, respectively. 
         [0040]    In particular, the first tab  23  allows the first support element  21  to be in contact with the heating element so as to feel the temperature thereof and allow the thermostat, and more generally the control system to which the thermostat is connected, to manage, together with the water temperature in normal operation, also other potentially harmful conditions but not such as to require the intervention of the fuse mounted on the second support element  22 , for example the presence of air bubbles in the operating fluid which may bring the measured temperature to values above 100° C., but still lower than the triggering temperature of the thermal fuse. 
         [0041]    Preferably, the first support element  21  further comprises a third tab  25 , which is part of the plate-shaped element  50 , in contact with the raised edge  15  of base  10  and raised thereon. 
         [0042]    Moreover, preferably, the first support element  21  has a total size greater than the second support element. This helps to allow the first support element  21  to be mainly sensitive to temperature variations of the operating fluid and the second support element  22  to be mainly sensitive to temperature variations of the heating element  11 . Preferably, the two support elements  21 ,  22  have the same extension in height, i.e. in distal direction in relation to the heating element  11 . Even more preferably, the two plate-shaped elements  53 ,  54  are coplanar. Alternatively, the extension in height of the first support element  21  is greater than that of the second support element  22 . Moreover, preferably, the distal face from the bottom of groove  16  of the inner zone  45  is coplanar with the distal face from the bottom of groove  16  of the resistive element  11 . 
         [0043]    Moreover, the first support element  21  comprises a fourth tab  26 , smaller in size compared to the first and third tab  23 ,  25 , connecting the plate-shaped element  50  of the first support element  21  with the end portion  11   a , at a lower temperature, of the heating element  11 . The fourth tab  26  allows the first support element  21  to be sensitive to temperature variations of less warm portion of the heating element. This allows the thermostat  41  to react promptly, before the intervention of the thermal fuse  42 , to manage rises in temperature of the heating element  11 , for example due to the formation of scale, which makes heat discharge more difficult. 
         [0044]    The second support element  22  further comprises two lateral teeth  51 ,  52 , which extend from the two opposite lateral edges, in circumferential direction, of the plate-shaped element  54 , up to coming into contact with the heating element  11 , to which they are welded. 
         [0045]    The invention therefore achieves the above object while obtaining a plurality of further advantages. In particular, the particular shape of the support elements  21 ,  22  and the presence of additional tabs on the first support element allows managing a plurality of abnormal situations, such as the presence of air bubbles or scale, by means of the thermostat, and thus without the intervention of the fuse, which would necessarily require a replacement with a new fuse and thus a maintenance intervention. 
         [0046]    Preferably, the heating element  11  is sized so as to be radially spaced from the raised edge  15 , in particular from the inner lateral surface of the latter, i.e. that facing the central hole  17 , leaving a portion of groove  16  exposed. In this case, a portion of the heating element  22  is brazed to the bottom of groove  16 , and the inner lateral surface of the heating element  11  is brazed to the lateral surface of the inner zone  45 , surrounding it. 
         [0047]    Preferably, in this case, a stiffening element  46  is provided, adapted to provide greater mechanical resistance to the heating element  11 , substantially flat, having a face fixed, for example by welding, to the distal face from the bottom of groove  16  of the heating element  11 , covering a portion of the latter. The stiffening element  46  is preferably arranged between the end portion  11   a , opposite to that which is in contact with the first support element  21 , and the second support element  22 . Preferably, the stiffening element  46  is provided with a flap  47  which extends in the radial direction towards the inner zone  45  and is in contact with the latter, so as to provide a better heat distribution. 
         [0048]    According to a variant, the tabs of the first and second support element, which are in contact with the heating element, have a further portion which extends approximately perpendicularly, so as to be arranged between the inner zone  45  and the heating element. Thanks to this portion, which is in contact with the heating element, further heat exchange surface is provided.