Abstract:
A rotor can for a wet running electric motor includes an inner layer ( 2 ) made from a thermoplastic material which is at least partly surrounded by a supporting layer ( 4 ) in form of a thermoplastic tape layer attached to the outside of the inner layer ( 2 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Section 371 of International Application No. PCT/EP2010/005323, filed Aug. 31, 2010, which was published in the English language on Mar. 10, 2011, under International Publication No. WO 2011/026597 A and the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention refers generally to a rotor can for a wet running electric motor, and, in particular, for a pump unit, for example a circulator pump for a heating or air conditioning system. 
     Wet running motors comprise a rotor can between the stator and the rotor of the motor. Up to now these rotor cans are commonly manufactured from stainless steel. However, it is also known to make such a rotor can from plastic material. Since inside the rotor can there is a fluid under pressure the rotor can must be resistant against this inner pressure, in particular keep its predefined shape also under high inner pressure and high temperature. 
     Therefore, for use with high pressure and temperature it is known to reinforce the plastic material of the rotor can by fibers. The known rotor cans are made from a thermosetting plastic which has to be cured by heating. This results in a time consuming manufacturing process. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an objective of a preferred embodiment of the present invention to provide an improved rotor can for a wet running electric motor made from a plastic material which allows an easy, less time consuming manufacturing process and has a high stability and thin walls. 
     The above objective is achieved by a rotor can having an inner layer made from a thermoplastic material which is at least partly surrounded by a supporting layer in form of a thermoplastic tape layer attached to the outside of the inner layer, and a pump unit having the above features. Improved preferred embodiments are disclosed in the following description and the drawings. 
     The rotor can for a wet running electric motor according to a preferred embodiment of the present invention comprises an inner layer made from a thermoplastic material. This inner layer may be produced by injection molding. This inner layer is at least partly surrounded by a supporting layer. The supporting layer is attached to the outside of the inner layer and is made from a thermoplastic tape attached to the outside of the inner layer. The thermoplastic tape preferably has a high tensile strength in its longitudinal direction, for example, in circumferential direction when wound around the inner layer. Thus, the thermoplastic tape layer reinforces the inner layer against deformation due to the inner pressure acting on the inside of the inner layer and/or high temperature acting on the plastic material. Preferably, the thermoplastic tape layer is at least attached to the cylindrical section of the rotor can which inside the motor is arranged between the stator and the rotor. The closed top end section of the rotor can may be free of a thermoplastic tape layer. Instead, the inner layer may have a greater thickness in this section of the rotor can. 
     The thermoplastic tape layer preferably is attached to the inner layer in a heating process. Preferably, the inner layer and the supporting layer are heated when the supporting layer is attached to the outside of the rotor can, for example, wound around the rotor can. Furthermore, it is preferred to press the supporting layer onto the inner layer, so that the attachment is accomplished by a combination of melting and pressure for consolidation of the plastic material. The heating process can be initiated by electric induced warming up of the tape. If the tape is enforced by electric conducting fabrics for example carbon fibers these can be used as electrical resistances for warming up the tape. 
     Instead of directly winding the tape layer around the rotor can, it is also possible to wind the tape layer around a core, for example, a metal core to produce the supporting layer independently from the inner layer. The supporting layer manufactured in this way can be inserted into an injection mold for molding the inner layer and then the inner layer is molded directly inside the premanufactured supporting layer by an injection molding process. 
     Preferably, the inner layer is made from a fiber reinforced thermoplastic material. There may be aramid, carbon or glass fibers or the like in the material of the inner layer. 
     Further, it is preferred that the supporting layer is a fiber reinforced thermoplastic tape layer. The tape layer may be reinforced by glass, carbon or aramid fibers or the like. Preferably, these are continuous fibers arranged in the longitudinal direction of the tape layer, so that when wound around the inner layer the reinforcement fibers extend substantially in circumferential direction of the rotor can. This is a direction in which the tape has to absorb the highest tensile stress in the rotor can when a pressure is applied to the inside of the rotor can. 
     According to a preferred embodiment at least one end section of the rotor can is not surrounded by the supporting layer. This may in particular be the closed end section of the rotor can. This end section normally is not arranged between a rotor and stator, but axially outside the gap between rotor and stator. Therefore, the section may have a greater wall thickness so that a reinforcement by the supporting layer is not required. 
     This means, in this preferred embodiment the end section of the inner layer has a greater thickness, for example, wall thickness than the middle section of the rotor can which is arranged in the gap between rotor and stator of the motor. 
     In a further preferred embodiment the rotor can comprises a bearing for a rotor shaft which bearing is molded in by the thermoplastic material of the inner layer. For example, the bearing may be inserted into the injection mold prior to the molding process, so that the thermoplastic material of the inner layer during injection molding flows around this bearing and the bearing is molded into the inner layer. This allows an easier and secure connection of the bearing inside the rotor can. For holding the bearing, the inner layer of the rotor can may have a greater thickness around the bearing to absorb the forces acting on the rotor can in the region surrounding the bearing. 
     Instead directly molding in the bearing, a bearing housing for a bearing of a rotor shaft may be molded in by the thermoplastic material of the inner layer. This means, a bearing housing is formed in the inner layer during the injection molding process of the inner layer. Alternatively, a premanufactured bearing housing, in particular a bearing housing from, for example, metal, may be inserted into the injection mold prior to molding the inner layer so that bearing housing is molded in by the thermoplastic material during the injection molding process. Later, when assembling the pump the bearing may be set into this bearing housing. Thus, the bearing housing forms a defined support for the bearing. 
     Preferably, the bearing housing is made from the same thermoplastic material as the inner layer. This ensures a secure junction between the bearing housing and the inner layer of the rotor can. Preferably, the bearing housing is molded in by the thermoplastic material of the rotor can during an injection molding process. Thus, the bearing housing and the material of the rotor can are melted together during the injection molding process. 
     As described before preferably the inner layer is an injection molded part. However, the inner layer may also be formed in another suitable manner. For example, the inner layer may be produced from a thermoplastic tube. 
     According to a further preferred embodiment the thermoplastic tape layer is prestressed so that a radially inwardly directed force is supplied to the inner layer. This may be achieved by stretching the tape before winding it around the inner layer. 
     Further, it is preferred that the tape layer is attached to the inner layer substantially without overlap. This means that there is no overlap between two consecutive laid ribbons or windings of the tape. However, the last winding of the tape may have an overlap, since it is preferred that the last winding around the inner layer extends in a plane perpendicular to the longitudinal axis of the rotor can. 
     According to a special preferred embodiment of the present invention two tape layers may be attached to the inner layer. These two layers may be arranged superposed on the outside of the inner layer. The two tape layers may be wound in opposite directions around the inner layer. By such winding an improved reinforcement of the inner layer can be achieved. 
     In a preferred embodiment the rotor can has an end flange surrounding an open end of the rotor can. Preferably, this end flange is integrally formed with the inner layer, for example by an injection molding process. The end flange is used for fixing and sealing the rotor can, for example, on a pump housing. 
     According to a further preferred embodiment the matrix of the tape is the same as the matrix of the inner layer, for example, the basic materials of the inner layer and the supporting layer are the same, so that a physical and/or chemical bonding can be achieved between the tape and the inner layer. This is a great advantage compared to the thermosetting materials used in the prior art rotor cans. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  is a rotor can according to a first preferred embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the rotor can according to  FIG. 1 ; 
         FIG. 3  is a rotor can according to a second preferred embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of the rotor can shown in  FIG. 3 ; 
         FIG. 5  schematically shows how a supporting layer is applied to an inner layer according to a first preferred method of the present invention; 
         FIG. 6   a  and  FIG. 6   b  schematically show how a tape layer is applied to the inner layer according to a second preferred method of the present invention; 
         FIG. 7   a - FIG. 7   d  show a method of applying the supporting layer to the inner layer according to a third preferred embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of a bearing housing with a bearing inserted; 
         FIG. 9  is a bottom view of a bearing housing with a bearing inserted; and 
         FIG. 10  a top view on a side of the bearing housing to be joined with the rotor can. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “bottom” and “top” designate directions in the drawings to which reference is made. The word “inwardly” refers to a direction away from the geometric center of the device, and designated parts thereof, in accordance with the present invention. Unless specifically set forth herein, the terms “a,” “an” and “the” are not limited to one element, but instead should be read as meaning “at least one.” The terminology includes the words noted above, derivatives thereof and words of similar import. 
     Referring to the drawings in detail, wherein like numerals indicate like elements throughout the several views, a rotor can as shown in  FIGS. 1-4  preferably has an inner layer  2  made from a thermoplastic material. The inner layer  2  is preferably formed by injection molding. On a circumferential outside of the inner layer  2 , the inner layer  2  is surrounded by a supporting layer  4  in form of a tape layer. The tape layer is preferably manufactured by winding a thermoplastic tape around the inner layer  2 . The inner layer  2  and the tape of the supporting layer  4  may be fiber reinforced, for example, by glass, aramid or carbon fibers. The reinforcing fibers of the thermoplastic tape are extending continuously in longitudinal direction of the tape so that the fibers are circumferentially wound around the inner layer  2 . By this, the reinforcement fibers may absorb the tensile stress induced by the pressure acting onto the inside of the rotor can. 
     The inner layer  2  and the supporting layer  4  are preferably formed from the same thermoplastic material so that there can be achieved a chemical and/or physical bonding between inner layer  2  and supporting layer  4 . Preferably both, the inner layer  2  and the thermoplastic tape of the supporting layer  4  are heated when winding the supporting layer around the inner layer  2 . 
     In the preferred embodiment shown in  FIGS. 1 and 2 , the rotor can has an end flange  6  surrounding the open end  8  of the rotor can. The end flange  6  is used to align, seal and fix the rotor can to a pump housing. 
     The end opposite to the open end  8  is a closed end  10  of the rotor can. At the closed end  10  inside the rotor can a bearing  12  for a rotor shaft is arranged. The bearing  12  may be held in a bearing housing formed in the inside of the inner layer  2 . Further, the bearing  12  may be molded in by the material of the inner layer during injection molding. 
     Compared to the preferred embodiment shown in  FIGS. 1 and 2 , the closed end  10  of the preferred embodiment shown in  FIGS. 3 and 4  is flat, for example, extends substantially perpendicularly to the longitudinal axis of the rotor can. Further, the rotor can according to  FIGS. 1 and 2  has a light conical shape, whereas the rotor can according to the preferred embodiment shown in  FIGS. 3 and 4  has a basically cylindrical shape. In the preferred embodiment shown in  FIGS. 3 and 4 , the closed end  10  has an axially extending stop means  14  projecting in axial direction from the closed end  10 . The stop means is used to fix the rotor can with its closed end  10  inside a stator housing. 
     The supporting layer  4  may be applied to the inner layer  2  as shown in  FIG. 5 . In this preferred embodiment the inner layer  2  is manufactured in a first step by injection molding. In a second step the supporting layer in form of a thermoplastic, fiber reinforced tape is wound around the inner layer  2  starting from the open end  8 . The first ribbon or winding of the thermoplastic tape  16  is wound on a plane perpendicular to the longitudinal axis of the rotor can, for example, parallel to the end flange  6 . The following windings or ribbons are wound in a slight angle α in a screw like manner around the cylindrical portion of the inner layer  2 . This winding is carried out in a manner that the single windings of the thermoplastic tape do not overlap each other. Before and during the winding process the inner layer  2  and the tape  16  may be heated. Further, the first winding may be fixed by welding. 
     In  FIG. 5  the winding process is started from the open end  6 . However, it is also possible to start the winding at the closed end  10 . In case that two layers of thermoplastic tape are wound around the inner layer  2  it is also possible to start the winding of the first layer at the closed end  10  and to start the winding of the second layer from the open end  8 , or vice versa. Further, it could also be started and stopped in the middle of the rotor can seen in the longitudinal direction. 
     To avoid the welding of the first winding layer on the inner layer  2  it is possible to use a metallic adapter  18  as shown in  FIG. 6   a  and  FIG. 6   b . As shown in  FIG. 6   a , the metallic adapter is set onto the closed end  10  of the inner layer  2  which has been formed before by injection molding. The metallic adapter  18  has an inner shape corresponding to the shape of the closed end  10  of the rotor can, so that the closed end  10  of the rotor can fits into the metallic adapter  18  so that the outer circumferential surface of the metallic adapter  18  is aligned with the outer circumferential surface of the cylindrical portion of the inner layer  2 . As shown in  FIG. 6   b , the winding of the tape  16  is started on the metallic adapter  18 . Thus, the first winding can be welded, for example, closed by welding on the metallic adapter  18  so that the inner layer  2  is not influenced by this welding process. Then, the thermoplastic tape  16  is wound around the inner layer  2  as described with reference to  FIG. 5 . After the winding the layer formed by the thermoplastic tape  16  is cut circumferentially near the closed end at the axial end of the metallic adapter  18 . Then, the metallic adapter  18  can be removed. 
     According to the preferred method shown in  FIGS. 5 and 6 , the supporting layer is attached to the inner layer  2  after injection molding of the inner layer  2 . However, it is also possible to first form the supporting layer by winding a thermoplastic tape  16  and then in a second step to form the inner layer by injection molding directly onto the inside of the supporting layer  4 . This is shown in  FIGS. 7   a  to  7   d.    
     In the first step the supporting layer  4  is formed on a metallic core  20  by winding the thermoplastic tape  16  around this core  20 . After the winding the core  20  is removed from the inside of the so formed supporting layer  4  as shown in  FIG. 7   a.    
     In the next step the supporting layer  4  formed by winding the tape  16  and a bearing  12  are inserted into a mold  22  for injection molding. The mold is formed by an outer part  22  and an inner part  24 . This supporting layer  4  is inserted into the outer part  22 . Then the inner part  24  of the mold is inserted into the supporting layer  4  so that a gap  26  is formed between part  22  and  24  of the mold. The bearing  12  is supported by the inner part  24  of the mold. This is shown in  FIG. 7   b.    
     In the next step as shown in  FIG. 7   c  through an opening  28  in the outer part of the mold  22  a thermoplastic material is injected into the gap  26 . The thermoplastic material flows inside the gap between the supporting layer  4  and the inner part  24  of the mold and forms the inner layer  2  inside the outer supporting layer  4  as shown in  FIG. 7   d.    
     As described above and shown in  FIG. 8  the bearing  12  may be held in a bearing housing  30 . The bearing housing  30  has a receptacle  32  into which the bearing  12  is inserted. The bearing housing  30  preferably is made from a plastic material, further preferred from the same plastic material as the inner layer of the rotor can. This ensures a secure connection between the bearing housing  32  and the inner layer  2  of the rotor can during an injection molding process. Both parts may be melted together. The bearing housing  30  may be premanufactured and inserted into the mold prior to the injection molding, so that the bearing housing  30  is molded in by the thermoplastic material of the inner layer during the injection molding process of the inner layer. The bearing  12  may be inserted into the receptacle prior to the injection molding process or after the injection molding process. 
     As shown in  FIG. 9  the bearing  12  may have an outer contour which is not cylindrical to prevent a rotation of the bearing relative to the bearing housing  30 . In the example shown in  FIG. 9 , there are three flat surfaces  34  provided on the circumference of the bearing  12 . The receptacle  32  has a cylindrical shape. Thus, between the flat surfaces  34  and the inner circumference of the receptacle  32  free spaces  36  are formed. These free spaces  36  are filled with plastic material during the injection molding process and a positive joint between the receptacle and the bearing is achieved. Thus, a bearing  12  cannot rotate inside the receptacle  32 . Further, the bearing  12  has through holes  38  for ventilation and lubrication which extend parallel to the rotational axis X of the rotor shaft from one end surface to the opposite other surface. The entering of injection material, for example, thermoplastic material during the injection molding process, is prevented by the core forming the inner shape of the rotor can during injection molding. 
     As shown in  FIG. 10  the end face of the bearing housing  30  opposite to the receptacle  32  is provided with radially extending ribs  40 . These ribs  40  stiffen the bearing housing  30  to prevent the bearing housing from collapsing. The bearing housing  30  includes holes or recesses communicating with the through holes  38  in the bearing to allow ventilation and lubrication through these through holes. In case that the bearing housing  30  should collapse during the injection molding process these recesses or holes may be closed. Therefore, it is important to prevent the bearing housing  30  or bearing holder from collapsing. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.