Patent Publication Number: US-8113790-B2

Title: Pump assembly

Description:
This application claims priority to United Kingdom Patent Application No. 0420410.3 filed Sep. 14, 2005, the entire disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a pump assembly, particularly, but not exclusively, to a water pump and brushless DC motor assembly for use in an automotive vehicle. 
     DESCRIPTION OF THE PRIOR ART 
     When designing a pump assembly for use in an automotive vehicle, for example for pumping coolant such as water around an internal combustion engine, there are various factors to be taken into consideration. Space in the engine compartment of an automotive vehicle is limited, and therefore it is desirable to provide a pump assembly which is as compact as possible. Moreover, as an electric motor generates heat when in use, where the pump is driven by an electric motor, it is desirable to provide some means of cooling the motor. It is known to cool the motor using pumped fluid, but in this case, it is preferable that steps are taken to ensure that the pumped fluid cannot cause corrosion of the motor. Finally, it is desirable to minimise the cost of manufacturing the pump assembly by producing a pump assembly that has a reduced number of component parts which are quick and easy to assemble. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention we provide a pump assembly including a pumping element mounted for rotation within a pump chamber, movement of the pumping element in the chamber causing pumping of fluid within the pump chamber, and a motor, the motor including a stator and a rotor which is connected to the pumping element such that activation of the motor causes movement of the pumping element and hence pumping of fluid within the pump chamber, there being a sealing assembly which permits fluid in the pumping chamber to flow around the rotor but which substantially prevents fluid from the pumping chamber from contacting the stator, the sealing assembly including a partition part which lies between the stator and the pumping chamber and a sealing part which lies between the stator and the rotor, wherein the sealing part is made from a polymeric material over-moulded onto the partition part. 
     By virtue of over-moulding the sealing part onto the partition part, a one piece sealing assembly may be manufactured relatively simply and inexpensively, a substantially fluid tight seal may readily be provided between the sealing part and the partition part, and the sealing part and partition part may be made from different materials. Making the sealing part from a polymeric material particularly advantageous as such a material has minimal effect on the magnetic fields between the motor rotor and stator, and thus is not significantly detrimental to the performance of the motor. 
     Preferably the partition plate is metallic. Thus, an electronic motor controller may be mounted on the partition part, and the partition part may act as a sink for heat generated by the motor controller. The partition part may, for example be made from cast aluminium. 
     The rotor may extend through an aperture provided in the partition part to the pumping element, and the partition part may further include a generally tubular attachment portion which extends from around the aperture axially of the rotor, the sealing part being over-moulded onto the attachment portion. 
     In this case, a free end of the attachment portion may be provided with a plurality of axially extending castellations. During the over-moulding process, the polymer from which the sealing part is moulded is forced around the castellations, and thus the castellations assist in preventing radial movement of the sealing part relative to the attachment portion and improving the seal between these two parts. 
     The attachment portion may additionally or alternatively be provided with at least one circumferential groove. During the over-moulding process, the polymer from which the sealing part is moulded is forced into the groove, and thus the groove assists in preventing axial movement of the sealing part relative to the attachment portion and improving the seal between these two parts. 
     The rotor may be mounted on a shaft for rotation about the shaft, and the sealing part may also be over-moulded around the shaft. 
     Thus, three separate components of the pump assembly may be combined into a single piece, and thus, manufacture and assembly of the pump assembly simplified further. 
     The shaft may be provided with a circumferential groove. Thus, during the over-moulding process, the polymer from which the sealing part is moulded is forced into the groove, and thus the groove assists in preventing axial movement of the sealing part relative to the shaft and improving the seal between these two parts. 
     The sealing part may be made from PPS. 
     According to a second aspect of the invention we provide a method of making a pump assembly including a pumping element mounted for rotation within a pump chamber, movement of the pumping element in the chamber causing pumping of fluid within the pump chamber, and a motor, the motor including a stator and a rotor which is connected to the pumping element such that activation of the motor causes movement of the pumping element and hence pumping of fluid within the pump chamber, there being a sealing assembly which permits fluid in the pumping chamber to flow around the rotor but which substantially prevents fluid from the pumping chamber from contacting the stator, the sealing assembly including a partition part which lies between the stator and the pumping chamber and a sealing part which lies between the stator and the rotor, wherein the method includes the step of overmoulding the sealing part onto the partition part. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention will now be described, by way of example only, with reference to the accompanying figures, of which: 
         FIG. 1  is an illustrative cross-sectional view through a pump assembly according to the invention, 
         FIG. 2  is an illustrative cross-sectional view through the sealing assembly, i.e. partition plate, sealing part and static shaft of the pump assembly of  FIG. 1 , 
         FIG. 3  is an illustrative perspective view of the sealing assembly of  FIG. 2 , 
         FIG. 4  is an illustrative perspective view of the partition plate of the pump assembly of  FIG. 1  from below, 
         FIG. 5  is an illustrative perspective view of the partition plate of the pump assembly of  FIG. 1  from above, 
         FIG. 6  is an illustrative perspective view of the volute of the pump assembly of  FIG. 1  from below, 
         FIG. 7  is an illustrative longitudinal cross-sectional view through the pumping element and rotor of the pump assembly of  FIG. 1 , 
         FIG. 8  is an illustrative perspective view of the pumping element and rotor of  FIG. 7 , 
         FIG. 9  is an illustrative perspective view of the shaft of the pump assembly of  FIG. 1 , 
         FIG. 10  is an illustrative perspective view of the pump assembly of  FIG. 1  viewed from below, and 
         FIG. 11  is an illustrative perspective view of the pump assembly of  FIG. 1  viewed from above. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     Referring now to the figures, there is shown a pump assembly  10  including a motor  12  and a pumping element  14 , in this example a pump impeller, which is mounted for rotation in a pump chamber  16 , rotation of the impeller causing pumping of fluid in the pump chamber  16 . The impeller  14  is of conventional configuration, and is provided with a top cap  14   a  which includes a nose portion which has an axially extending wall which encloses a generally cylindrical space. The pump assembly  10  also includes a pump housing  18  which has two parts, namely a volute  20  which encloses the impeller  14  and a motor housing  22  which encloses the motor  12 . A generally circular partition plate  24  is provided to separate the volume enclosed by the volute  20  from the volume enclosed by the motor housing  22 , the pump chamber thus being enclosed by the partition plate  24  and the volute  20 . The volute  20  is of conventional configuration and includes an inlet  20   a  which extends along the axis of rotation of the impeller  14 , and an outlet  20   b  which extends generally radially of the impeller  14 . Both the inlet  20   a  and outlet  20   b  have a generally circular cross-section, and to reduce energy losses in fluid passing from the pump chamber  16  into the outlet  20   b  as a result of the transition from an open chamber into a cylindrical tube, a recess  58  is provided in the surface of the partition plate  24  adjacent the outlet  20   b  into which a corresponding formation  58 ′ of the pump volute  20 , which extends the generally circular cross-section of the outlet  20   b  into the volute, fits in use. 
     The motor  12  includes a rotor  26  and stator  28 , both of which are mounted in the motor housing  22 . The rotor  26  is connected to and coaxial with the impeller  14  such that activation of the motor  12  causes rotation of the impeller  14  in the pump chamber  16 , and hence pumping of fluid in the pump chamber  16 . 
     The rotor  26  includes a magnet assembly  32  and generally cylindrical connecting portion  30  which connects the magnet assembly  32  and the impeller  14  and which extends through an aperture in the partition plate  24  to the impeller  14 . The magnet assembly  32  includes a plurality of magnets  32   a  which are arranged around the rotor  26  orientated axially with respect to the rotor  26 , and a cylindrical iron yoke  32   b  around an exterior surface of which the magnets  32   a  arranged. 
     The rotor  26  is supported on a static shaft  34  which extends axially along and generally centrally of the rotor  26 . A first end  34   a  of the shaft  34  has a larger diameter than the remainder of the shaft  34 , and the end portion is retained in an aperture provided in a stiffener plate  23  which is mounted the motor housing  22 , whilst a second end  34   b  of the shaft  34  extends into the connecting portion  30  of the rotor  26 . The stiffener plate  23  is made from steel, and assists to prevent deformation of the housing  18  under the forces exerted by the pumped fluid on the rotor  26 . The shaft  34  is received in an aperture in the stiffener plate  23  in an interference fit, and the stiffener plate  23  is also engaged with the motor housing  22  in an interference fit. 
     The rotor  26  is provided with a bearing  36  which is mounted on an interior surface of the iron yoke  32   b  and which engages with the smaller diameter portion of the shaft  34  to support the rotor  26  whilst permitting rotation of the rotor  26  about the shaft  34 . As the first end  34   a  has a larger diameter than the remainder of the shaft  34 , and the bearing  36  is engaged with the smaller diameter portion of the shaft  34 , the larger diameter portion  34   a  supports the bearing and ensures that the bearing  36  cannot move axially downwardly relative to the shaft  34 . A collar part  38  is mounted around the second end  34   b  of the shaft  34  and engages with the shaft  34  in an interference fit and with the bearing  36  to further restrict axial movement of the rotor  26  with respect to the shaft  34 . Mounting the rotor  26  on a static shaft  34  on a single bearing  36  ensures that frictional losses between the rotor  26  and the shaft  34  are minimised and that the rotor  26  has relatively low inertia. 
     The stator  28  is of conventional construction and includes a plurality of cores made from a magnetizable material around with are wound coils of an electrically conductive wire. 
     There is a gap between the connecting portion  30  of the rotor and the partition plate  24  so that a portion of the high pressure fluid within the pump chamber  16  is driven into the motor housing  22  around the rotor  26  and thus assists in cooling the motor  12  and bearing  36  and lubricating the bearing  36 . 
     In this example, the diameter of the aperture in the partition plate  24  through which the connecting portion  30  of the rotor  26  extends is significantly larger than the outer diameter of the connecting portion  30 . The connecting portion  30  is, however, provided with a radially outwardly extending fin formation  42  which is of substantially the same thickness as the connecting portion  30  and which locally increases the diameter of the connecting portion  30  within the aperture in the partition plate  24  to substantially the same diameter as the nose portion of the impeller top cap  14   a . Configuring the fin formation  42  such that the diameter of the fin formation  42  is approximately equal to the outer diameter of the nose portion of the impeller top cap  14   a,  ensures that the axial forces exerted by the high pressure fluid in the pump chamber  16  are balanced, and therefore there is no net axial thrust exerted on the impeller  14 . 
     High pressure fluid within the pump chamber  16  will flow both towards the inlet  20   a  through the gap between the volute  20  and the impeller nose portion and into the motor housing  22 . 
     A generally circular ridge formation  24   b  extends from the partition plate  24  around the impeller  14 . Flow of fluid from the pump chamber  16  into the motor housing  22  is thus dictated by the spacing of the impeller  14  from the ridge  24   b  and the partition plate  24  and the spacing of the fin formation  42  from the partition plate  24 , which are typically of the order of 0.5 mm. 
     Two grooves  34   c  are provided in the radially outwardly extending surface of the shaft  34  between the larger diameter first end  34   a  and the adjacent smaller diameter portion of the shaft  34 , on which the bearing  36  is supported. The two grooves  34   c  extend radially outwardly of the shaft  34 , and rotation of the bearing  36  around the shaft  34  causes fluid in the rotor chamber  41  to be drawn along the grooves  34   c  radially inwardly of the shaft  34 , between the shaft  34  and the bearing  36  to cool and lubricate the bearing, over the second end  34   b  of the shaft  34  and back into the pump chamber  16  via a central aperture in the impeller  14 . 
     A sealing part  40 , which, in this example, comprises a tube wall enclosing a generally cylindrical space hereinafter referred to as the rotor chamber  41 , is mounted around the rotor  26 , between the rotor  26  and the stator  28  to prevent fluid from the pump chamber  16  from coming into contact with the stator  28 . The sealing part  40  is provided at a first end with a radially inwardly extending closure formation  40   a  which engages with the shaft  34  between the bearing  36  and the first end  34   a  of the shaft  34 . An opposite end  40   b  of the sealing part  40  engages with a generally tubular attachment portion  24   c  of the partition plate  24 . The attachment portion  24   c  extends from the edge of the aperture in the partition plate  24  towards the magnet assembly  32  enclosing a generally cylindrical space. 
     The motor  12  is a brushless D.C. motor, and operation of the motor  12  is controlled by an electronic control unit (ECU)  44 . Power is supplied to the ECU  44  via electrical connectors  45  which are mounted on the exterior of the motor housing  22 , and in this example, an electrical filter  29  for filtering the electrical current to the ECU  44  is mounted in the motor housing  22  adjacent the stator  28 . As the stator  28  is of a smaller diameter than the diameter of the partition plate  24 , the motor housing  22  includes a larger diameter portion which is mounted around the partition plate  24 , and a smaller diameter portion which encloses the stator  28  and electrical filter  29 . The electrical connectors  45  may thus be mounted on the portion of the motor housing  22  which extends generally parallel to the partition plate  24  between the larger diameter portion and the smaller diameter portion, in order to maintain a compact pump assembly  10  configuration. 
     The ECU  44  is mounted on the partition plate  24  on the motor housing  22  side of the plate  24  around the aperture through which the rotor  26  extends. Thus, the electronic components that comprise the ECU  44  are arranged in a generally annular array around the rotor  26 . The partition plate  24  is made from cast aluminium, and acts as a heat sink for heat generated by the ECU  44 , and is cooled by fluid within the pump chamber  16 . Moreover, mounting the ECU  44  within the pump housing  18  on the partition plate  24  may assist in reducing the overall volume of the pump assembly  10 . 
     In this embodiment of the invention, the volute  20  is asymmetric, and the inlet  20   a  does not extend centrally of the volute  20 . As the inlet  20   a  extends coaxially with the impeller  14  and hence also the motor rotor  26 , it will be appreciated that the impeller  14  and rotor  26  also do not extend centrally of the pump housing  18 . Similarly, the aperture through the partition plate  24  is not located centrally of the partition plate  24 , and there is a larger area  24   a  of partition plate  24  on one side of the aperture. 
     By virtue of this asymmetrical arrangement, the main heat generating electronic components of the ECU  44  may be concentrated on the larger area  24   a  of the partition plate  24 . The outlet  20   b  from the volute  20  is located above this larger area  24   a  of the partition plate  24 , and thus the area of the partition plate  24  supporting these heat generating electronic components of the ECU  44  is cooled by high pressure fluid at the pump outlet. This arrangement may further assist in cooling the ECU  44 . 
     Cooling of the ECU  44  may be further improved by providing features on the surface of the partition plate  24  adjacent the outlet  20   b  which induce turbulence in fluid passing to the outlet  20   b . Such features could be a plurality of ridges. 
     The method of manufacturing the pump assembly  10  will now be described. 
     In this example, the rotor  26  and impeller  14  are integrally constructed as a one-piece rotor assembly by injection moulding of a polymer around the magnet assembly  32  and bearing  36 . The bearing  36  is mounted in a mould cavity, one end of the bearing  36  engaged with a tool such that the bearing  36  is supported within the mould cavity. 
     The magnets  32   a  are mounted around the iron yoke  32   b  and glued in place. The iron yoke  32   b  includes a radially outwardly extending shoulder formation  32   d  on its exterior surface, and when the magnets  32   a  are located in the desired position relative to the iron yoke  32   b , the magnets  32   a  engage with the shoulder formation  32   d , and thus further movement of the magnets  32   a  relative to the iron yoke  32   b  is restricted and the likelihood of the magnets  32   a  slipping relative to the iron yoke  32   b  during the moulding process is reduced. 
     The iron yoke  32   b  is then placed around the bearing  36 . The bearing  36  is also provided with a radially outwardly extending shoulder formation  36   a  on its exterior surface, and the iron yoke  32   b  is provided with a corresponding shoulder formation  32   c  on its interior surface. The shoulder formations  36   a ,  32   c  are located such that they engage when the iron yoke  32   b  is in the desired position relative to the bearing  36 , the shoulder formations  36   a ,  32   c  thus restricting further movement of the iron yoke  32   b  relative to the bearing  36 , and hence reducing the possibility of the iron yoke  32   b  slipping relative to the bearing  36  during the moulding process. 
     The magnets  32   a  are then placed around the iron yoke  32   b.    
     By virtue of the provision of the shoulder formations  36   a ,  32   c ,  32   d  there is no need to provide separate tools to support the magnets  32   a  and iron yoke  32   b  in the mould cavity during the moulding process, and hence manufacture of the rotor  26  is simplified. 
     Fabricating a one piece rotor  26  and impeller  14  by over moulding material ensures that, providing the bearing  36  is correctly located on the appropriate tool during the moulding process, there will be concentricity of the impeller  14 , rotor  26  and bearing  36 , and that the magnets  32   a  and iron yoke  32   b  are completely sealed from contact with fluid in the rotor chamber  41 , and therefore corrosion of the magnets  32   a  and iron yoke  32   b  is substantially prevented. This also simplifies construction of the rotor  26  as no fasteners are required to retain the magnets  32   a , iron yoke  32   b  and bearing  36  on the rotor  26 . 
     To enhance the sealing of the magnets  32   a  and iron yoke  32   b , at each end of the iron yoke  32   b  there is a step in the interior surface of the iron yoke  32   b  which extends around the entire circumference of the interior surface, such that end portions of the interior surface of the iron yoke  32   b  are spaced from the bearing  36 . Thus, during moulding of the polymeric portion of the rotor  26 , molten polymer is forced into and fills these spaces, and further assists in sealing the magnets  32   a  and iron yoke  32   b  from fluid in the rotor chamber  41 . 
     The partition plate  24  is made by pressure die-casting an appropriate aluminium alloy. As the partition plate  24  is in contact with fluid within the pump chamber  16 , if the pump is used to pump a fluid which is corrosive to aluminium, for example if the pump is used in fuel cell applications, then it is necessary to apply a corrosion resistant coating to the surfaces in contact with pumped fluid. Such a corrosion resistant coating may be applied by electroless nickel plating for example. Rather than applying a corrosion resistant coating, it is, of course, possible to make the partition plate  24  from a corrosion resistant material such as stainless steel, but a stainless steel partition plate  24  would not only increase the cost and weight of the pump assembly, but would also not provide such an effective heat sink as an aluminium partition plate  24 . The partition plate  24  may alternatively be made from a polymeric material. 
     The static shaft in this example is machined from stainless steel bar, but may be made from any other appropriate material, such as a ceramic, or polymer. 
     Whilst the sealing part  40  could be integral with the partition plate  24 , in order to provide an effective heat sink, the partition plate  24  is preferably metallic. The sealing part  40  is preferably made from a polymer, however, as such a material would have minimal effect on the magnetic fields between the rotor  26  and the stator  28 . Moreover, it is desirable to minimise the gap between the rotor  26  and stator  28 , and thus the sealing part  40  should be as thin as possible. In contrast, a thicker partition plate  24  is required to provide structural integrity and to act as an effective heat sink, and moulding a component with such variation in section thickness can be problematic. Thus, in this example, the sealing part  40  is not integrally formed with the partition plate  24 , but is, instead, made by injection moulding a polymeric material around the partition plate  24  and the shaft  34  to form a one piece sealing can assembly. The partition plate  24  and shaft  34  are located in mould tools which hold the parts in position in the mould cavity during the injection moulding process, and the sealing part  40  is then overmoulded around the attachment portion  24   c  of the partition plate  24  and the shaft  34 . In this example, the sealing part  40  is made from 0.5 mm thick PPS. The sealing part  40  may, however, be made from any other appropriate polymer, e.g. PPA. 
     Overmoulding the sealing part  40  ensures that a substantially fluid tight seal is provided between the sealing part  40  and the partition plate  24  and shaft  34 , and thus leakage of fluid from the rotor chamber  41  into the remainder of the motor housing  22  is substantially prevented. 
     To enhance the sealing between the sealing part  40  and the shaft  34 , the shaft  34  is provided with two circumferential grooves. During injection moulding of the sealing part  40 , molten polymer flows into and fills these grooves, and thus, the grooves not only ensure that there is mechanical locking of the shaft  34  relative to the sealing part  40 , but that there is a substantially fluid tight seal between these two parts. Whilst in this example the sealing part  40  is overmoulded around the shaft  34 , the shaft may, instead be integral with the sealing part  40 . 
     To enhance the sealing between the sealing part  40  and the partition plate  24 , the attachment portion  24   c  is provided with axially extending castellations  24   d  at the free end thereof, and an exterior surface of the attachment  24   c  is provided with two circumferential grooves  24   e . During overmoulding of the sealing part  40 , molten polymer flows into and fills the grooves  24   e  and the spaces of the castellations  24   d , and when the polymer sets, this provides mechanical locking of the sealing part  40  relative to the partition plate  24 , and may assist in improving the seal between the partition plate  24  and the sealing part  40 . The use of both axial castellations  24   d  and radial grooves  24   e  ensures that differential thermal expansion of the polymeric sealing part  40  and metallic partition plate  40  can be accommodated and a good seal provided over a wide range of temperatures and pressures. 
     The volute  20  is made from injection moulded PPS, and the motor housing  22  is made by deep drawing steel sheet to a thickness of 1.2 mm. Provision of a metallic motor housing  22  ensures that heat from the stator  28  may be lost through the motor housing  22 . 
     The pump assembly  10  is then assembled by first mounting the ECU  44  on the partition plate  24 . The cast partition plate  24  is provided with mounting features for attachment of the ECU  44 . Such features may, for example be axially extending pins which pass through appropriate apertures in the ECU  44  and which are then deformed to retain the ECU  44  on the partition plate  24 . The use of integral mounting features simplifies assembly of the pump assembly  10  as separate fasteners are not required. 
     The stator  28  is then located around the sealing part  40 . The exterior surface of the sealing part  40  is provided with a plurality of axially extending locating ridges  46 , which are spaced so as to fit into gaps between adjacent cores of the stator  28 , and a plurality of axially extending abutment ridges  48  which are located adjacent the partition plate  24  and which engage with the stator  28  to ensure that the stator is correctly aligned, radially and axially, with respect to the sealing part  40 . The locating ridges  46  and abutment ridges  48  not only ensure that the stator  28  is correctly aligned, but also provide the sealing part  40  with structural stability without increasing the gap between the rotor  26  and the stator  28 . 
     Whilst in this example, the location ridges  46  and abutment ridges  48  are regularly spaced around the sealing part  40 , this need not be the case, and the ridges  46 ,  48  may be unevenly spaced on one or more of the ridges  46 ,  48  may be different to the others to ensure that the stator  28  can only be fitted in one particular orientation around the sealing part  40 . 
     Once the stator  28  is in place, electrical connections between the stator  28  and the ECU  44  are completed, and the electrical filter  29  installed adjacent the stator  28 . The motor housing  22  is then placed around the stator  28 , the electrical connections between the ECU  44  and the external electrical connectors  25  are completed and the motor housing  22  bonded to the stator  28  using thermal adhesive. The motor housing  22  extends around partition plate  24 , and a sealing element, in this example an O-ring, is located between the partition plate  24  and the motor housing  22  to substantially prevent ingress of dirt or moisture into the motor housing  22 . 
     The rotor  26  and impeller  14  assembly is then inserted into the rotor chamber  41  and the collar part  38  placed around the static shaft  34  to prevent axial movement of the rotor  26  relative to the shaft. 
     Finally, an O-ring  50  is located in a groove around the outer circumference of the partition plate  24  and the volute  20  is mounted around the partition plate  24  such that the O-ring  50  provides a substantially fluid tight seal between the partition plate  24  and the volute  20 . Attachment formations on the volute  20  are engaged with corresponding attachment formations on the motor housing  22  to retain the volute  20  on the pump assembly  10 . 
     When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.