CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    This invention relates to electric fuel pumps for use in automotive vehicles; and more particularly, to an improved construction for mounting an impeller to a drive shaft by which an electric motor driving the pump causes the impeller assembly of the pump to rotate, the improved construction reducing shaft wear and improving service life of the pump. 
         [0004]    A high-pressure electric fuel pump such as is commonly used in fuel injected automobile engines includes a housing in which is encased an electric motor and an impeller assembly driven by the motor. The impeller assembly is mounted on a drive shaft driven by the motor, with the suction created drawing low-pressure fuel into the pump from a fuel tank or reservoir of a fuel module. The impeller is designed to increase the fuel pressure from approximately atmospheric pressure on the input side of the pump to pressures ranging to 50 psi and higher on the outlet side of the pump, depending upon the particular application. 
         [0005]    Heretofore, the drive shaft has generally been a round shaft such as shown in  FIG. 1A , although other shaped shafts have been used. U.S. Pat. No. 4,209,284, for example, describes a drive shaft, referred to as a D-shaft (see prior art  FIG. 1B ), because a portion of the shaft is flattened so that the contour of the shaft, viewed axially, resembles the letter D. In U.S. Pat. Nos. 5,722,815 and 5,711,408 opposite portions of the shaft are flattened to create what is referred to as a “double-D” contour. There are also shaft constructions in which an intermediate or end portion of an otherwise circular shaft is shaped into an X pattern such as shown in U.S. Pat. No. 4,978,282, or a square shape with rounded corners such as shown in U.S. Pat. No. 4,639,202. These latter profiles are for mounting and locking the impeller assembly onto the shaft to improve pump efficiency by reducing the effects of wear between the impeller and motor shaft. 
         [0006]    While the various constructions shown in these patents may work for their intended purpose, there are improved impeller constructions by which the impeller assembly is mounted on the shaft and which are less susceptible to wear and further increase the efficiency of the fuel pump. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to a fuel pump supplying fuel to an internal combustion engine. The pump has an electric motor, a shaft driven by the motor, and a pump assembly including a pumping element mounted on the shaft. An improvement to the fuel pump includes the shaft being a multi-sided shaft with the pumping element having a central opening through which the shaft extends. This opening is a contoured opening having a plurality of sides each pf which is in contact with a side of the shaft to distribute the wear, which occurs between the shaft and the pumping element. This construction prolongs the operating life of the pump. 
         [0008]    Depending upon a particular application, the shaft has between 3-8 sides and this construction enables any wear between the shaft and pumping assembly element caused by vibrations and other forces acting on the pump to be better distributed so to reduce the wear. This improved construction not only increases the service life of the pump, but also the operating efficiency of the pump because there is less slippage between the shaft and the impeller mounted on the shaft, as the pump rotates at high speed. 
         [0009]    In one pump construction, a roller vane type pump has N vanes. For this pump, the pump shaft has a number of sides S determined by the equation S=N±1. 
         [0010]    Other objects and features will be in part apparent and in part pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]    The objects of the invention are achieved as set forth in the illustrative embodiments shown in the drawings, which form a part of the specification. 
           [0012]      FIGS. 1A and 1B  are simplified representations of prior art, shaft/pumping element constructions; 
           [0013]      FIGS. 2-7  are plan views of a pumping element/shaft construction in which the shaft has between 3-8 sides, and a central opening in the pumping element has a corresponding number of sides; 
           [0014]      FIG. 8  illustrates one embodiment of the invention with a roller vane pump; 
           [0015]      FIG. 9  illustrates a second embodiment of the invention with the roller vane pump; and, 
           [0016]      FIG. 10  is a plan view of a pump assembly element having a multi-sided insert for use with a corresponding multi-sided shaft. 
       
    
    
       [0017]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION OF INVENTION 
       [0018]    The following detailed description illustrates the invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what I presently believe is the best mode of carrying out the invention. 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. 
         [0019]    Referring to the drawings, an electric fuel pump for an automotive vehicle includes a motor (not shown) and a drive shaft  10  ( FIG. 1A ) or  10 ′ ( FIG. 1B ) rotatably driven by the motor when the pump is operating. A pumping assembly includes a pumping element  12  or  14 , which is attached to the shaft and rotates with the shaft. As shown in  FIGS. 1A and 1B , one type of pumping element  12  comprises an impeller, while another type of element  14  is for a roller vane pump in which rollers  16  are inserted in vanes  18  formed in the element. Operation of both types of pumps is well-known in the art, and is not described. 
         [0020]    As noted above, a persistent problem with existing pump constructions is wear between the pump shaft  10  or  10 ′ and the pumping element  12  or  14  which effectively reduces the useful life of the pump. A fuel pump improvement of the present invention is designed to reduce this wear and thereby increase the pump&#39;s useful life. As shown in  FIGS. 2-7 , the pump shaft is no longer round or D-shaped as shown in the prior art  FIGS. 1A and 1B , but is rather is a multi-sided shaft having between 3 and 8 sides in accordance with the invention. 
         [0021]    In  FIG. 2 , a motor shaft  103  is shown to be a three-sided shaft of a uniform geometric shape when viewed in cross-section. A pumping assembly element  20  has a central opening  22  which is generally triangular in shape with each side  22   a - 22   c  of the opening having an inwardly curving center section contacting one side of shaft  103 . This results in the element  20  having three points of contact with the motor shaft to effectively reduce the wear between the shaft and element  20 . The respective corners of the opening  22  are rounded so that the they have a generally lobular shape. 
         [0022]    In  FIG. 3 , a motor shaft  104  is shown to be a four-sided shaft of a generally square geometric shape when viewed in cross-section. A pumping assembly element  30  has a central opening  32  which is also generally square in shape, with rounded corners. Each side  32   a - 32   d  of the opening has an inwardly curving center section contacting one side of shaft  103 . Element  30  has four points of contact with motor shaft  104 ; again, to reduce the wear between the shaft and pumping assembly element. 
         [0023]      FIG. 4  illustrates a motor shaft  105  which is a five-sided shaft having a generally pentagonal shape when viewed in cross-section. A pumping assembly element  40  has a central opening  42 , also generally pentagonal in shape, with rounded corners. Each side  42   a - 42   e  of the opening has an inwardly curving center section contacting one side of shaft  104 . Pumping assembly element  40  has five points of contact with shaft  105  so to reduce wear between the shaft and the element. 
         [0024]      FIG. 5  shows a six-sided generally hexagonally shaped motor shaft  106  on which is installed a pumping assembly element  50 . Element  50  has a central, hexagonally shaped opening  52 , with rounded corners. Each side  52   a - 52   f  of the opening has an inwardly curving center section contacting one side of shaft  106 . The six points of contact between shaft  106  and pumping assembly element  50  again helps reduce wear between the shaft and the element. 
         [0025]    In  FIG. 6 , a motor shaft  107  is shown to be a seven-sided shaft of a uniform geometric shape when viewed in cross-section. A pumping assembly element  60  has a central opening  62  of a generally seven-sided shape, with rounded corners. Each side  62   a - 62   g  of the opening has an inwardly curving center section contacting one side of shaft  107 . This results in element  60  having seven points of contact with shaft  107  to reduce the wear between the shaft and element  60 . 
         [0026]    In  FIG. 7 , a motor shaft  108  is shown to be an eight-sided shaft of a generally octagonal shape as viewed in cross-section. A pumping assembly element  70  has an octagonal central opening  72  with rounded corners, and with each side  72   a - 72   h  of the opening having an inwardly curving center section contacting one side of shaft  108 . Element  80  therefore has eight points of contact with motor shaft  108  to reduce the wear between the shaft and pumping assembly element. 
         [0027]    Those skilled in the art will appreciate that the motor shaft can have more than eight sides without departing from the scope of the invention. Further, as shown in the drawings, the pumping assembly element attached to the motor shaft has a central opening which is complementary with the shaft. That is, it has the same number of sides as the shaft, and is oriented to the shaft so there is only a point contact between each side of the shaft and the adjoining side of the pumping assembly element defining the opening. Affecting point contact between the shaft and pumping assembly element helps distribute wear between the two. Also, the more sides the shaft has (and correspondingly, the more sides to the opening in the pumping assembly element), the greater the distribution of any wear. The result is a longer service life for the fuel pump and savings in replacement costs. 
         [0028]    Turning now to  FIG. 8 , a pumping assembly element  80  is for use in a roller vane fuel pump the operation of which is known in the art, and is not described. The vane pump includes five rollers  82  which are received in pockets  84  formed in element  80  and spaced equidistantly thereabout. In this application, the fuel pump employs the four-sided shaft  104  previously described. Element  80  has a central opening  86  with respective inwardly curving sides  86   a - 86   d.    
         [0029]      FIG. 9  also illustrates a pumping element  90  for a roller vane pump having five rollers  92  which are received in pockets  94  formed in element  90  and equidistantly spaced thereabout. Now, the fuel pump employs the six-sided shaft  106  previously described. Element  90  has a central opening  96  with respective inwardly curving sides  96   a - 86   f.    
         [0030]    For the particular pump application shown in  FIGS. 8 and 9 , it has been found that for a roller vane pump having N number of vanes or rollers, that a pump shaft and corresponding pumping assembly element having one more, or one fewer, sides S than the number of vanes provides a significant improvement in wear over conventional roller vane pump constructions. As a consequence, in designing roller vane pumps, the type of shaft and pumping assembly element which should be used in the fuel pump is determined by the formula S=N±1. 
         [0031]    Finally, and as shown in  FIG. 10 , a pumping assembly element  100  has a central opening  122  in which is received a collar or insert  124  for attaching element  100  to a multi-sided shaft made in accordance with the present invention. In  FIG. 10 , the shaft is a four-sided shaft  104 ; although one of the other shafts previously described could be used. Collar  124  insert has a central, four sided opening  132  (with sides  132   a - 132   d ) which is complementary with the shaft  104 . Again, if a different shaft were used, an insert with a complementary opening would be used with element  100 . An advantage to this embodiment of the invention is that element  100  can be used with any of the multi-sided shafts  103 - 108  simply by using a different insert with that shaft. This could reduce the costs of the pump since only one pumping assembly element is required. 
         [0032]    In view of the above, it will be seen that the several objects and advantages of the present invention have been achieved and other advantageous results have been obtained.
A fuel pump ( 10) supplying fuel to an internal combustion engine includes an electric motor ( 14), a shaft ( 16) driven by the motor, and a pump assembly ( 18) including a pumping element ( 20) mounted on the shaft. A fuel pump improvement includes the shaft being a multi-sided shaft with the pumping element having a central opening ( 22) through which the shaft extends. This opening is a contoured opening having a plurality of sides ( 24 a - 24 c) each of which is in contact with a side ( 22 a - 22 c) of the shaft to distribute wear which occurs between the shaft and the pumping element. This construction prolongs the operating life of the pump. In a roller vane type pump having N vanes, the motor shaft has a number of sides S determined by the formula S=N+-1, and N>3.