Abstract:
The invention relates to a centrifugal pump ( 10 ) for liquids, comprising a pump spiral housing ( 12 ) and a pump wheel ( 28 ), which is driven by an integrated electromotor ( 14, 20, 34, 36 ), whereby the rotational axis thereof ( 29 ) is arranged in a coaxial in relation to the rotational axis ( 37 ) of the pump wheel ( 28 ). The pump spiral housing ( 12 ) is sealed by a sealing ring ( 72 ) and is connected to the motor housing by means of a bayonet catch ( 74, 78 ) and covers the front side thereof. According to the invention, the motor housing ( 14 ) is pot-shaped and is made of plastic and the base thereof ( 13 ) which is oriented towards the pump spiral housing ( 12 ) forms a common housing wall in relation to the pump spiral housing ( 12 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a centrifugal pump. 
         [0002]    DE 102 04 459 A1 discloses a pump for liquids, in particular a water pump. It is embodied as a centrifugal pump, a pump spiral housing enclosing a pump impeller, which is driven by an electric motor. The latter is arranged coaxially with the pump impeller and has a housing, which is open towards the pump spiral housing. The pump spiral housing is divided in a transverse plane to the axis of rotation of the pump impeller, one half of the pressure spiral being arranged in each part and an outer part enclosing the inner part with a cylindrical fit. A groove to accommodate a sealing ring, which in the assembly process is pushed into a cylindrical seat on the motor casing, is formed between an outwardly protruding shoulder on the free end of the inner part and the end face of the outer part. The sealing ring here bears both on the seating face of the motor casing and on the faces of the inner and outer part of the pump spiral housing forming the groove so that, once assembled, both the motor casing and the pump spiral housing are externally sealed. The connection joining the motor casing and the pump spiral housing together is in the manner of a bayonet catch. For this purpose, the outer part of the pump spiral housing, in proximity to the sealing ring, has radially oriented projections, which are spaced around the circumference and which in the assembly process, are inserted axially between corresponding undercuts and come to lie behind undercuts on the motor casing. Turning the pump spiral housing through a predefined angle relative to the motor casing brings the projections behind the undercuts, exerting an axial force on the sealing ring and causing the sealing ring to bear tightly against the adjoining components. A twist lock prevents the connection accidentally coming undone. No additional fasteners are needed for connecting the motor casing to the pump spiral housing and only one single sealing ring is required. This facilitates assembly and dismantling of the pump and minimizes production and repair costs. 
       SUMMARY OF THE INVENTION 
       [0003]    According to the invention the motor casing is of canister-shaped design and is made from plastics, its base facing the pump spiral housing forming a common housing wall with the pump spiral housing. This results in a compact construction with hermetic sealing between the current-carrying areas of the electric motor, that is to say the stator, a printed circuit board and an electronics cover, and the liquid-ducting parts of the pump section. At the same time this reduces the number of parts and facilitates the connection of the motor casing to the spiral housing in the manner of a bayonet catch. With the connection according to the invention, the rotation of the parts relative to one another produces no axial displacement of the parts. The axial marrying up of the parts is accomplished prior to the rotational movement, thereby avoiding tolerance problems. 
         [0004]    According to one development of the invention, the base of the motor casing has a protuberance, facing the open end and concentric with the axis of rotation, and having an approximately cylindrical dividing wall and an internal base. In its central area this base has a thickening, in which a bearing axis pointing towards the pump spiral housing is injection molded. A rotor of the electric motor, which usually comprises permanent magnets, is integrally formed with the pump impeller and is rotatably supported on the bearing axis by an injection molded bearing. The rotor and the pump impeller are advantageously secured axially on the bearing axis between the thickening and a mushroom-type stop. The latter is pushed onto the free end of the bearing axis and engages with a twist lock in a recess on the bearing axis. With its external contour the mushroom-type stop projects into an inlet connection on the spiral housing, its contour being designed so that favorable flow conditions are created in the transition from the inlet connection to the pump impeller. Here too, no additional fasteners are needed. 
         [0005]    According to one development of the invention a coil shell of the stator of the electric motor is inserted in the annular space between the dividing wall and the outer wall of the motor casing, the coil shell sealing said annular space with one end wall. The coil shell is likewise connected to the motor casing in the manner of a bayonet catch, projections on the circumference of its end wall engaging behind undercuts on the motor casing which are oriented radially inwards. The coil shell here suitably provides external support for the walls of the motor casing subjected to the delivery pressure and by way of its projections transmits the forces to the undercuts on the motor casing, so that the walls of the motor casing in this area can be kept very thin. It also prevents any elongation of the dividing wall. Elongation would result in a shift in the position of the electronics, which are accommodated in that part of the motor casing which towards the free end adjoins the coil shell. The forces transmitted to the coil shell by the inner walls of the motor casing act as tensile forces in the shell and are transmitted to the stable outer wall by the shortest route. In addition, this affords the same advantages in the connection between the coil shell and the motor casing as accrue from the connection between the pump spiral housing and the motor casing. Incorrect assembly is suitably prevented by at least one coding in the area of the undercuts on the motor casing. 
         [0006]    In a further development the coil shell, in the area of the annular space in the motor casing, is wound from its end wall to the base of the motor casing with varnished copper wire, the wire ends of which are laid to support points for insulation displacement connectors. A coil formed from the varnished copper wire is arranged in a radially open annular space in the coil shell, via the opening in which a stator ring is pressed onto the coil shell as far as the end wall. The stator ring is in contact with yoke parts, which are injection molded in the coil shell. Advantageously resting on the support points is a printed circuit board, which is held by insulation displacement connectors and the tracks of which are bonded by press-in contacts of the insulation displacement connections. This affords a secure mounting of the bearing plate, which requires no great assembly outlay, since during assembly the bonding ensues automatically from the method of fastening. It is furthermore advisable, in a pocket in the end wall of the coil shell, on the side facing the rotor, to provide a Hall sensor, the pins of which are laid to a support point and are electrically bonded to the insulation displacement connections by pressing the insulation displacement connections into the assigned support point. These connections have press-in contacts, which hold a printed circuit board and accordingly bond the tracks thereof. Connector pins for a connector are prefitted to the printed circuit board. 
         [0007]    The motor casing is suitably sealed at the end face by an electronics cover. This has an injection molded seal, through which the connector pins are fed during the assembly process. The electronics cover is likewise assembled without any additional fasteners. For this purpose the electronics cover, on its circumference, has pliable hooked catches, which latch in the recesses in the outer wall of the motor housing during the assembly process. In order to facilitate assembly, pins are molded onto the electronics cover, which engage in pre-centering sleeves in order to center the electronics cover in relation to the coil shell and the printed circuit board. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Further advantages are set forth in the following description of the drawing. Exemplary embodiments of the invention are represented in the drawing. The drawing, the description and the claims contain numerous features in combination. The person skilled in the art will also give appropriate consideration to individual features and will be capable of bringing these together in further suitable combinations. 
           [0009]    In the drawing: 
           [0010]      FIG. 1  shows a longitudinal section through a centrifugal pump according to the invention, 
           [0011]      FIG. 2  shows a perspective longitudinal section through a motor casing, 
           [0012]      FIG. 3  shows a perspective view of a coil shell, 
           [0013]      FIG. 4  shows an enlarged detail from  FIG. 3 , 
           [0014]      FIG. 5  shows a longitudinal section through a coil shell, 
           [0015]      FIG. 6  shows a perspective partial view of a motor casing with a fitted coil shell, 
           [0016]      FIG. 7  shows a perspective view of a centrifugal pump with a cutaway motor casing and coil shell and 
           [0017]      FIG. 8  shows a perspective view of a centrifugal pump with a fitted printed circuit board. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The main integral parts of a centrifugal pump  10  according to the invention are a pump spiral housing  12  with an inlet connection  102  and an outlet connection  104 , a pump impeller  28  and an electric motor with a motor casing  14 , a stator  34  and a coil shell  40  together with a printed circuit board  94  and an electronics cover  20 . The motor casing  14  is made of plastics and is of canister-shaped design. It comprises a base  13 , which is open to the pump spiral housing  12  and which forms a common housing wall with the integrally formed pump spiral housing  12 . Outwardly adjoining the base  13  is an outer wall  15 , whilst in the central area the base  13  has a slight depression, which is formed by an inner base  17  and a dividing wall  19 . At its center the inner base  17  has a thickening  18 , in which a bearing axis  22  is injection molded. The motor casing  14  is therefore hermetically sealed off from the pump spiral housing  12 . By means of an injection molded bearing  30 , a rotor  36  is supported on the bearing axis  22  so that it can rotate about an axis of rotation  29 . Molded onto the rotor  36  at the end face is the pump impeller  28 , which projects axially into the pump spiral housing  12  and through which the flow passes radially from the inlet connection  102  to the outlet connection  104 . The axis of rotation of the pump impeller  28  is denoted by  37 . The rotor  36  and the pump impeller  28  are axially secured on the bearing axis  22  between the thickening  18  and a mushroom-type stop  24 , on which the bearing  30  rises axially. The mushroom-type stop  24  is pushed over the free end of the bearing axis  22  and latched in a recess  32 , the mushroom-type stop  24  having a twist lock not represented in further detail. The external contour of the mushroom-type stop  24  facing the inlet connection  102  is designed to produce a favorable incident flow against the pump impeller  28 . 
         [0019]    The pump spiral housing  12  is connected to the motor casing  14  in the manner of a bayonet catch, by pushing radial projections  74  on the circumference of the motor casing  14  axially through between corresponding undercuts  78  on the pump spiral housing  12  and turning the pump spiral housing  12  through an angle of approximately  150  relative to the motor casing  14 , so that the projections  74  come to lie behind the undercuts  78 . Prior to the rotational movement an axial force is exerted on a sealing ring  72  in the form of an O-ring arranged between the spiral housing  12  and the base  13  of the motor casing  14 . In the limit position, a hooked catch  80  arranged in the peripheral direction on the circumference of the motor casing  14  engages with a stop  82  on the pump spiral housing  12 , so that the motor casing  14  is also circumferentially fixed in relation to the pump spiral housing  12 . 
         [0020]    A coil shell  40  of the stator  34  is inserted into the annular space between the outer wall  15  and the dividing wall  19  of the motor casing  14 . It is connected to the motor casing  14  in the manner of a bayonet catch by pushing projections  56  on the circumference of an end wall  41  of the coil shell  40  between corresponding undercuts  62  on the motor casing  14  and turning to the right through approximately 40° so that they come to lie behind the undercuts  62 , thereby fixing the stator  34  to the coil shell  40  in the motor casing  14 . At least one coding  64 , and advantageously three codings, ensure that only one fitting position is possible. In the area of its projection  56  the coil shell  40  has a hooked catch  58 , which serves as twist lock and engages in a recess  66  in the motor casing  14  when the coil shell  40  is in the limit position ( FIG. 6 ). In the assembly process, the hooked catch  58  is tensioned by the inside of the outer wall  15  of the motor casing  14  diverging conically outwards. 
         [0021]    In order to be able to design the dividing wall  19  and the base  17  of the motor casing  14 , which are exposed to the delivery pressure of the centrifugal pump  10 , as thin as possible, so as to reduce the distance between the rotor  36  and the stator  34 , the coil shell  40  supports this area and by way of its projections  56  transmits the forces to the undercuts  62  of the motor casing  14  as tensile forces by the shortest possible route. The coil shell  40  likewise prevents elongation of the dividing wall  19 , which would shift the position of the electronics, especially a printed circuit board  94 , in an axial direction. 
         [0022]    The coil shell  40 , in the area of the annular space between the dividing wall  19  and outer wall  15 , is wound between its end wall  41  and the base  13  of the motor casing  14  with a varnished copper wire  52 , the ends of which are laid to support points  42 ,  44 ,  46  on the side of the end wall  41  of the coil shell  40  facing the electronics cover  20 . The coil formed by the varnished copper wire  52  is accommodated in a radially open annular space in the coil shell  40 . The annular space is sealed by a stator ring  38 , which is pressed onto the coil shell  40  and bonds yoke parts  39 , which are injection molded into the coil shell  40  in the area of the coil. 
         [0023]    A Hall sensor  98 , which is inserted into a pocket  60  in the coil shell  40 , is provided on the coil shell  40 , its pre-bent pins  54  being laid to a support point  44 . The position of the Hall sensor  98  can be secured by a bonding point. The ends of the varnished copper wire  52  and the pins  54  are bonded by insulation displacement connections  48 , which are pressed into the associated support points  42 ,  44 . The insulation displacement connection  48 , which is assigned to the support point  46 , only has retaining functions, in order to fix the printed circuit board  94  to the support points. The insulation displacement connections  48  have press-in contacts  86  at their free ends. The printed circuit board  94  is now pressed onto these and its tracks are bonded. All necessary electrical connections to the electronics are thereby established. Connector pins  88  for the connector are pre-fitted to the printed circuit board  94  by soldering or pressing in. 
         [0024]    The electronics cover  20  with a pre-fitted O-ring  96  on its circumference is pushed into the open end of the motor casing  14 , the O-ring  96  being compressed by the inside of the outer wall  15  diverging conically outwards. The electronics cover  20  has hooked catches  92  spaced around its circumference, which are radially pliable and engage in recesses  16  in the motor casing  14  when the electronics cover  20  is in the limit position. To facilitate assembly, pins  90  which slide in pre-centering sleeves  50 , are molded onto the inside of the electronics cover  20 . These sleeves are molded onto the coil shell  40 . The electronics cover  20  has openings with an injection molded seal  26 , through which the connector pins  88  of the printed circuit board  94  are pushed. In order that the printed circuit board  94  is not thereby subjected to bending stresses, support points  100 , on which the printed circuit board  94  rests, are provided on the coil shell  40  in the area of the connector pins  88 . In the event of variations in length due to internal pressure or thermal expansion of the components, these can be transmitted to the plug-and-socket connection by displacement of the connector pins  88  through the molded-on seal  26 , without any great force being exerted on the electrical connections of the printed circuit board  20 .