Abstract:
An impeller assembly includes a molded impeller and an insert within the impeller. The insert includes an unthreaded sleeve and a shoulder adjacent the sleeve for locating the impeller and the insert during manufacturing and installation. Methods of manufacturing and installing are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to molded impellers, and more particularly to a molded impeller having a locating insert therein. 
     Prior art pump impeller assemblies include an over-molded knurled insert for retaining and locating the impeller on a driveshaft. The insert includes internal threads that mate with external threads on the driveshaft and serve to locate the impeller relative to the driveshaft. It is important that the insert be properly positioned on the shaft because it locates the impeller, and such positioning, if incorrect, may reduce seal life, increase vibration and cause fluid leakage. However, prior art inserts, and the threads therein, do not satisfactorily locate the impeller on the driveshaft. This may be due in part to the difficulty of exactly controlling the location of thread surfaces. Moreover, the threads may not satisfactorily locate the impeller during molding of the impeller. The latter problem can cause eccentricity or “wobble” of the impeller during operation, necessitating a secondary machining operation or other measure to prevent contact of the impeller inlet with the pump housing. Such added manufacturing operations add to the cost of the impeller. In some cases a secondary seal ring must be added between the impeller and the housing, which again adds cost. Accordingly, an improved insert for the impeller is needed. 
     SUMMARY OF THE INVENTION 
     In one aspect, an impeller assembly comprises a molded impeller and an insert within the impeller. The insert includes an unthreaded sleeve and a shoulder adjacent the sleeve for locating the impeller and the insert. 
     In another aspect, a method of forming an impeller assembly in a mold comprises placing an insert over a positioning pin of the mold, the pin engaging a shoulder and a sleeve of the insert. Other steps include injecting a material into the mold for forming an impeller of the assembly and removing the positioning pin from the insert. 
     In still another aspect, the insert is mounted within the impeller for transmitting force to the impeller. The insert includes an outer surface and a plurality of protrusions extending outward from the outer surface and engaging portions of the impeller. The protrusions are sized and shaped to inhibit withdrawal of the insert from the impeller and for transmitting only radial force to the impeller so that substantially no axial force is transmitted to the impeller by the insert. 
     Various refinements exist of the features noted in relation to the above-mentioned aspects of the present invention. Further features may also be incorporated in the above-mentioned aspects of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present invention may be incorporated into any of the above-described aspects of the present invention, alone or in any combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective of an impeller assembly of one embodiment. 
         FIG. 2  is a section view of the assembly. 
         FIG. 3  is an exploded view of the assembly of  FIG. 1  from a rear perspective. 
         FIG. 4  is a perspective of an insert of the assembly. 
         FIG. 5  is a section view of the insert. 
         FIG. 6  is a front perspective of a pump housing that includes an impeller assembly of one embodiment. 
         FIG. 7  is a section view of the pump housing. 
         FIG. 8  is a section view of a mold of one embodiment. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1-3 , an impeller assembly of one embodiment is generally designated  11  and generally comprises an impeller  13 , a cap  15  and an insert  17 . The impeller  13  includes blades  21 , a hub  23  and a tube  25  extending from the hub. The cap  15  includes an inlet  27 . It should be understood that this configuration of the impeller is merely an example of each, and many other configurations are contemplated within the scope of this invention. 
     Referring to FIGS.  2  and  4 - 5 , the insert  17  of this embodiment is disposed in the tube  25  of the impeller  13 . A nose  31  of the insert extends into the hub  23  of the impeller. The insert  17  includes a blind bore  35 , i.e., the bore does not extend completely through the insert. An axis of the bore  35  defines a central axis CA of the insert and thus the impeller assembly  11 . The walls of the bore  35  include a threaded, inward portion  37  and an unthreaded, outward portion or sleeve  39 . A locating shoulder  41  extends between the two portions for locating the impeller  13  as described below. In this embodiment, the locating shoulder  41  forms a reference plane P. The shoulder includes a non-planar surface  42  and a planar contact surface  43  for contacting a tip of a positioning pin when the pin is received in the blind bore, the contact surface being spaced radially from the unthreaded interior surface by the non-planar surface and lying in the plane extending lateral to the bore axis. 
     The insert  17  of this embodiment is cylindrical in shape, an outer surface of the sleeve including a plurality of ribs  33  (or protrusions) extending therefrom. Broadly, the ribs engage portions of the impeller. The ribs  33  are sized and shaped to inhibit withdrawal of the insert from the impeller  13  and for transmitting only radial force to the impeller so that substantially no axial force is transmitted to the impeller by the insert. Each rib  33  of one embodiment includes an axially symmetric surface, e.g. surfaces  33   a  of  FIG. 4 , engaging the impeller to prevent an axial force from being transmitted to the impeller. The ribs  33  of this embodiment extend circumferentially on the outer surface, the ribs being symmetric and having no or substantially no surfaces angled relative to an axis of the insert so as to prevent an axial force being transmitted to the impeller. The ribs  33  may also be spaced apart axially (as shown) to further inhibit withdrawal of the insert. 
     The axial force caused by prior art inserts is undesirable because they may contribute to withdrawal of the insert  17  from the impeller  13 , especially where a relatively large force is transmitted through the insert. In one example, the drive shaft forces the insert and impeller to go from 0 to 3600 RPM in 150 milliseconds. Such force causes a “cycling force” on the drive mechanism. In the prior art where the outer surface includes angled knurling on the outer surface, the angled knurling may cause an axial, rather than a purely radial force. In this embodiment, the ribs or protrusions are said to be “square” with the impeller so that all or substantially all the driving torque is torsional or radial and there is no or an insignificant amount of axial force that may damage the assembly. 
     In one embodiment of a suitable method for making the assembly, the insert  17  is placed over a positioning pin  45  of a portion  46  of an injection mold  47  prior to injection molding. The positioning pin  45  engages the sleeve  39  and the shoulder  41  and the pin contacts the planar contact surface  43 . The positioning pin  45  is sized to fit snugly in the sleeve  39  so that the sleeve and shoulder  41  are precisely located and temporarily fixed relative to the positioning pin. The positioning pin  45  is likewise precisely located relative to the other portions of the mold  47 . The material that will form the impeller  13  is injected into the die and around the insert  17 . 
     After the material solidifies, the formed impeller  13  is fixed to the insert  17 . Because the insert  17  cannot move relative to the pin, and because the impeller  13  becomes fixed to the insert during molding, the potential for “float” during molding is eliminated. 
     Thereafter, the impeller assembly may be installed inside a pump housing, such as the housing  51  shown in  FIGS. 6 and 7 . In this embodiment, a stationary seal  53  and a rotary seal  55  are placed around the tube  25  for sealing between the impeller  13  and the housing  51 . The seals are designed to prevent fluid flow to the motor, e.g., through an opening  57  in the housing. Many other seal configurations are contemplated within the scope of the invention. The housing shown has two sections, though many other configurations are contemplated. The assembly is also mated with a shaft, e.g., drive shaft DS shown in  FIG. 7 , by placing the insert over the shaft and mating the internal threads of the insert with the external threads on the shaft. 
     The insert  17  of this embodiment is also advantageous for at least some of the following reasons. The sleeve  39  of the insert  17  accurately locates the insert during molding (e.g., injection molding). The arrangement reduces the tolerance build-up or “stack”. The pin of the mold is precisely located against the sleeve  39  of the insert  17 . In particular, the shoulder  41  forms the reference plane P off of which the other features of the assembly  11  are formed. Because the pin of the mold is shaped like the driveshaft, the impeller assembly  11  fits precisely on the shaft. The sleeve  39  also serves as an inspection feature for incoming part inspection. For example, the reference plane P can be used to check the location of other features during inspection. Moreover, the sleeve  39  eliminates the need to thread the insert  17  onto and off of the pin prior to and after the molding process. The sleeve  39  only needs to be slipped over the pin, which makes production quicker and cheaper. 
     The alignment of the impeller-shaft assembly  11  is controlled by the fit of the sleeve  39  of the insert  17  with respect to the shaft extension. In particular, the internal diameter of the sleeve  39  controls concentricity and thus controls eccentricity or “wobble”, especially at the outer edges of the impeller, and the shoulder  41  controls perpendicularity. Accordingly, the size and shape of the sleeve  39  is tightly controlled, e.g., the diameter is controlled to within about 0.001 inches or even about 0.0006 inches. 
     By tightly controlling alignment, the insert  17  eliminates the need to machine the impeller, in particular the inlet  27  and more generally the outer diameter of the impeller. Such machining has been done in the past to prevent contact of the inlet with the housing at gap G. The insert  17  also allows the gap G to be minimized because there is no eccentricity, i.e., the impeller axis will be substantially coaxial with that of the insert and the driveshaft. Therefore, the insert  17  also may eliminate the need to add a seal between the impeller and the housing, e.g., where the gap G was too large around prior art impeller assemblies. The insert  17  also extends the life of the seals  53 ,  55 . By controlling concentricity and thus “wobble” of the impeller, the seals are not worn as quickly. Note that in the prior art where the impeller would move radially relative to the housing, the seals were stressed on each rotation. In this embodiment, the insert, impeller and housing are all co-axial, the insert and impeller rotating concentrically without wobble. In this way, there is reduced or no radial movement of the impeller within the housing so that rotation of the impeller does not stress or wear any seals (e.g., seals  53 ,  55 ) between the impeller and the housing. 
     The insert  17  and impeller  13  may be formed of a variety of materials. In one embodiment, the impeller  13  is made of a molded plastic, and the insert  17  is made of a metal, e.g., brass, powder metal or steel. The metal may be chosen based on the material of the driveshaft DS, for example. 
     When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. For example, the impeller is suitably formed over the insert by over-molding, but other methods of forming the impeller are contemplated. The insert may have many other configurations within the scope of the invention. For example, the nose of the insert need not extend into the hub, its shape may be other than cylindrical, and the bore could be open at both ends. These are merely some examples of possible changes to the constructions described above. Also, the various constructions need not necessarily have all the various advantages listed herein.