Abstract:
An electric motor ( 4 ) is described, comprising a stator ( 10 ) of the type having polar expansions of the wound type, a rotor chamber ( 2 ) defined by a sealed case ( 9 ), closed by a sealing ring ( 1 ), a permanent magnet rotor ( 3 ), housed inside said rotor chamber ( 2 ) and a shaft ( 8 ) fixed to said rotor ( 3 ). The motor comprises a valve for letting fluid flow out from said rotor chamber. 
     Furthermore, an electric motor pump ( 5 ) is described, in particular for a dish washing machine or a clothes washing machine, comprising a rotor wheel ( 14 ) rotated by above said electric motor.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electric motor comprising a stator having polar expansions of the wound type, a rotor chamber defined by a sealed case closed by a sealing ring, a permanent magnet rotor housed inside said rotor chamber and a shaft rigidly connected to said rotor. 
         [0002]    The invention further refers to an electric motor pump, in particular for a dish washing machine or a washing machine or similar household appliance, said electric motor pump comprising a rotor wheel and an electric motor for rotating said wheel, said electric motor being of above said type. 
       KNOWN ART 
       [0003]    An electric motor pump is known, in particular for a washing machine or a dish washing machine, comprising an electric motor of above said kind. 
         [0004]    Said electric motor pump, during operation, runs through hot cycles, wherein high temperatures are reached, as well as cold cycles, in which lower temperatures are achieved, which near the external ambient temperature. 
         [0005]    The shaft is able to move axially, in a limited way, on its own axis. In this way, the permanent magnets tend to position themselves in a magnetic equilibrium state, of maximum efficiency, in order to allow maximum hydraulic efficiency of the electric motor pump. 
         [0006]    The sealing ring is normally formed as a hollow body with radial symmetry and with an end lip surrounding the shaft, which is optionally in sliding contact with the same, so that to prevent water leakage (in any case, friction should be low, in order to not excessively hinder shaft rotation). The end lip has a conical shape directed towards the outside, in other words, it converges towards the outside, and this too is provided in order to achieve at least a partial sealing. 
         [0007]    The sealing ring is often housed in a sealing ring holding disc, formed of plastic material. 
         [0008]    The sealing ring is designed in order to define a labyrinth, which allows a small water leakage, but inhibits dirt from passing through, since it is blocked by the interstices formed inside the labyrinth. 
         [0009]    Therefore, the rotor chamber fills with water: such an electric motor type is in fact normally called an “immersed rotor motor”. 
         [0010]    As already described, during hot cycles, high temperatures are achieved. In particular, inside the rotor chamber, these temperatures are so high as to cause water to evaporate: vapor exerts a pressure on the sealing ring, which is directed outwardly, in particular on the end lip, which opens in order to allow vapor venting. 
         [0011]    When, in particular during successive cold cycles; the temperature inside the rotor chamber drops, the rotor chamber is depressurized with respect to the outside: the sealing ring is subject to a force directed inwardly. The sealing ring does not allow air to pass, due to its conical shape directed towards the outside of end lip. Therefore, the end lip closes around the shaft, causing undesirable high friction forces. 
         [0012]    Moreover, the end lip and depressurization cause the shaft to be pushed inwardly, so that permanent magnets are displaced from their magnetic equilibrium of maximum efficiency, towards lower efficiency locations, thereby reducing the electric motor efficiency, and overall hydraulic efficiency of the electric motor pump. 
         [0013]    The technical problem to be solved by the present invention is to develop a motor having structural and functional features which remove above said drawbacks. 
       SUMMARY OF THE INVENTION 
       [0014]    The idea of the solution on which the present invention is based is to avoid pressure differences occurring between the inside of the rotor chamber and the outside. 
         [0015]    Based on this solution concept, the technical problem is solved by an electric motor according to claim  1 . 
         [0016]    This electric motor comprises a valve which allows fluid to flow from said rotor chamber. 
         [0017]    Preferably, said valve is unidirectional (check valve), in particular of the flap valve type. 
         [0018]    In a preferred embodiment, said unidirectional valve is formed by a through bore provided on the sealing ring and by a opposing wall, which is able to close said bore. 
         [0019]    Preferably, said sealing ring is deformable between a first position, in which said bore is closed by a sealing ring holding disc, and a second position, in which said bore is separated from said sealing ring holding disc, so as to communicate said rotor chamber with the outside. 
         [0020]    At last, the present invention is solved by an electric motor pump according to claim  11 . 
         [0021]    The features and advantages of the solution according to the invention will become evident from the following description of an exemplary embodiment of same, which is provided only for illustrative and non limiting purposes, with reference to attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    In the drawings: 
           [0023]      FIG. 1  shows a sectional axial view of an electric motor pump endowed with an electric motor according to the invention; 
           [0024]      FIG. 2  shows a perspective sectional, axially exploded view of the electric motor pump of  FIG. 1 , during its hot cycle. 
           [0025]      FIG. 3  shows a partial enlarged view of  FIG. 2 , of the electric motor pump operating during its hot cycle; 
           [0026]      FIG. 4  shows a view analogous to  FIG. 3 , during its transient phase following transition from hot to cold cycle; 
           [0027]      FIG. 5  shows a plane view of a detail of electric motor pump in  FIG. 1 ; 
           [0028]      FIG. 6  shows a sectional view according to line A-A of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    An electric motor pump, for example for a clothes washing machine, according to the invention, is generally referenced by  5 . Said electric motor pump  5  comprises a rotor wheel  14  housed inside a rotor wheel chamber, which is not shown, since it is of the conventional type. Said rotor wheel  14  is connected to a suction conduit, for drawing liquids from external ducts, and to a pressure conduit, for pushing said liquid towards further external conduits. 
         [0030]    According to its use, the electric motor pump  5  runs through hot cycles alternating with cold cycles. 
         [0031]    Said rotor wheel  14  is rotated around an axis XX by an electric motor  4  inside the electric motor pump  5 , by means of a shaft  8 . 
         [0032]    The electric motor  4  is of the synchronous type, with permanent magnets, in the present case of the single-phase type (it may be for example of the two-phase type). 
         [0033]    This electric motor  4  comprises a stator  10  with a pair of polar expansions  10 A, which are wound around by conventional coils, said polar expansions  10 A being such as to generate a magnetic field in the air gap, as usual in electric motors. 
         [0034]    The electric motor  4  also comprises a rotor chamber  2 , which is defined in a sealed case  9 . 
         [0035]    Moreover, the electric motor  4  comprises a rotor  3  of the type comprising permanent magnets  13 , and which is housed inside said rotor chamber  2  and which is separated from the walls of said rotor chamber. 
         [0036]    Rotor  3  and shaft  8  are per se able to move freely, although in a limited way, along rotation axis XX, between a maximum efficiency position, in which permanent magnets  13  are positioned in their magnetic equilibrium position, and positions deviating from said maximum efficiency position. The attraction force exerted by said permanent magnets is such as to normally position the rotor  3  and shaft  8  in maximum efficiency positions. 
         [0037]    Shaft  8 , connected to stator  3 , is rotatably inserted into the stator structure by means of interposed bushings/bearings  7 ,  11 . The shaft  8 , in order to rotate the rotor wheel  14 , extends out of said rotor chamber  2 . 
         [0038]    A sealing ring  1  is disposed in order to close said rotor chamber  2 ; said sealing ring  1  is formed by a generally axially symmetrical body of plastic material, provided with a central bore along rotation axis XX, for being passed through by shaft  8 . 
         [0039]    According to the invention, the sealing ring  1  comprises an eccentric through bore  6 . 
         [0040]    Moreover, the sealing ring  1  is shape coupled to an external sealing ring holding disc  12 . 
         [0041]    In particular, the sealing ring  1  comprises an end portion defining an end lip  20 , which is of generally conical shape directed outwardly (the conical shape may also comprise a frusto-conical shape). The inside of end lip  20  is originally provided for a light sliding contact with the electric motor pump shaft, so as to provide a certain sealing, even if due to friction with said shaft, in the course of time, said end lip progressively wears out. 
         [0042]    A bushing/bearing  7  is shape coupled to said sealing ring  1 , in order to define a labyrinth  22 , for decelerating and/or reducing the liquid inflow inside the rotor chamber  2 , and which is able to inhibit dirt from entering the inside of the rotor chamber  2 . 
         [0043]    The sealing ring holding disc  12 , which is coaxial with shaft  8 , comprises an annular protrusion  23 , which is coaxial with axis XX, which defines a wall  31  opposed to said bore  6 . Advantageously, a valve  30 , of the flap type, is formed by the bore  6  of sealing ring  1  and by opposed wall  31  of sealing ring holding disc  12 . The sealing ring is able to deform between a first position ( FIGS. 1 and 3 ), in which said bore  6  is closed by said sealing ring holding disc  12 , and a second position ( FIG. 4 ), in which said bore  6  is separated from said sealing ring holding disc  12 , so as to fluidly communicate said rotor chamber  2  with the outside. 
         [0044]    Due to the sequence of alternating hot and cold cycles, programmed for the washing machine, the rotor chamber  2  is subject to a variable pressure, varying between a pressure higher than the external ambient pressure, which is normally reached during hot cycles, by which water inside the rotor chamber  2  evaporates and vapor pushes outwardly, and a pressure lower than the external ambient pressure, which is normally reached by a quick temperature drop due to a cold cycle immediately following a hot cycle. 
         [0045]    When the rotor chamber  2  is at a pressure higher than the ambient pressure, the valve  30  is closed, as shown in  FIGS. 1 and 3 . In this situation, vapor exits the rotor chamber  2  passing through interstices formed by labyrinth  22 , or between the bushing/bearing  7  and shaft  8 , venting through the end lip  20 , which therefore opens. It is to be noted that vapor pushes the bushing/bearing  7  against the sealing ring  1 , and the sealing ring  1  against the sealing ring holding disc  12 . Bore  6  of ring  1  is closed by the sealing ring holding disc  12 . 
         [0046]    When the rotor chamber is at a pressure lower than external ambient pressure, valve  30  opens. In fact, the external ambient pressure, since it is higher than the pressure inside the rotor chamber  2 , pushes inwardly: the rotor  3  temporarily shifts inwardly, so that wall  31  of sealing ring holding disc  12  is temporarily separated from sealing ring  1 , and bore  6  is opened. 
         [0047]    Since, as can be seen, valve  30  is connected to labyrinth  22 , it can fluidly communicate the rotor chamber  2  to the outside, so that air may pass into rotor chamber in order to achieve pressure equilibrium between the inside of rotor chamber  2  and the outside. 
         [0048]    In fact, between the sealing ring  1  and sealing ring holding disc  12 , a passage a is formed (shown in an exaggerated scale in  FIG. 4 , in order to be easily visible), which therefore permits a fluid passage b to be formed. Due to passage b, air passes through labyrinth  22  and reaches rotor chamber  2 . Therefore, depression inside rotor chamber  2  ceases to exist and sealing ring  1  may return to said initial position ( FIGS. 1 and 3 ). 
         [0049]    It is to be noted that the presence of valve  30  does not imply dirt entering said rotor chamber, since labyrinth  22  defined by contact ring and bushing/bearing is provided. 
         [0050]    Permanent magnets  13  may therefore remain in a magnetic equilibrium position, thus of maximum efficiency, without reducing overall hydraulic efficiency of electric motor pump. 
         [0051]    The greatest advantage of electric motor according to the present invention is its continuity regarding efficiency, since efficiency during hot cycles is same as during cold cycles, without efficiency drops due to movements of permanent magnets and friction between sealing ring lips and shaft. 
         [0052]    A further advantage of the present invention is its simple construction, which is a very important aspect for a mass produced item. 
         [0053]    Moreover, such an electric motor is more reliable and allows long maintenance-free life.