Patent Publication Number: US-7217084-B2

Title: Automotive fuel pump with pressure balanced impeller

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 10/842,685, filed May 10, 2004, now U.S Pat. No. 7,008,174, entitled “Fuel Pump Having Single Sided Impeller” which is incorporated herein in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to automotive fuel pumps, and, more specifically, to regenerative fuel pumps having a rotary impeller. 
     Regenerative fuel pumps are widely used in automotive applications. They generally include an impeller rotating on a shaft and positioned within a pumping chamber in the pump. The clearance between the opposing axial sides of the impeller and the corresponding walls of the pumping chamber must be closely regulated to permit the pump to handle fuel at relatively high pressures (i.e. greater than about 2 bar). It has not been possible to maintain a precisely centered position within the pumping chamber when the impeller is fixedly mounted at a particular axial position on the shaft. This is because wearing of the shaft support structure causes the shaft to shift axially over time. Therefore, the impeller is slidably mounted on the shaft to allow axial translation. 
     The impellers typically comprise double-sided impellers, meaning the impellers include vanes on each opposing side for pressurizing fuel on both sides of the impeller. Due to the pressurization taking place on both sides, the impellers are relatively well balanced axially to maintain the necessary clearance from each side of the pumping chamber. 
     One drawback of fuel pumps with double-sided impellers is that their wet circle index is relatively high, typically 1.7 or greater. The wet circle index characterizes the pump boundary layer frictional losses and can be defined as the wet circle length versus the flow channel cross-sectional area. The wet circle length is the distance along the perimeter of the flow channel (e.g., circumference of a round flow channel) formed by the impeller and the opposing structures (e.g., body and cover structures) of the pumping chamber. 
     A single-sided impeller (i.e., an impeller having vanes and an impeller flow channel on only one side) can achieve a decreased wet circle index relative to a double-sided impeller since the length of the flow channel can be cut in half. If the flow channel cross-sectional area is kept the same, then the frictional losses are also cut in half. A drawback of using single-sided impellers has been that they were not balanced because the fuel pressure acting on the vaned side of the impeller displaced it off center in the pumping chamber. 
     Parent application U.S. Ser. No. 10/842,685 teaches a single-sided impeller having specially added areas that are exposed to fuel on one side or the other of the impeller, the added areas being sized to provide a body-side force approximately equal to a cover-side force. Consequently, the impeller is balance on the shaft and maintains robust axial clearances (i.e., is centered in the pumping chamber) so that the pump operates at high efficiency. The added areas are created by forming additional channels in the internal surfaces of cover and body member defining the pumping chamber in a manner that deploys the necessary forces to balance the impeller. 
     The pressure provided by an additional channel is determined by the pressure at the point where the channel emerges from a flow channel or passageway. This particular pressure can then be applied against corresponding surfaces of the impeller to obtain an approximate balance. Since the pressure to be balanced along the flow channel varies, however, it can be difficult to obtain a precise balance. The shape, size, and position of the additional channels in the internal surface of the pumping chamber can be empirically determined by trial and error using computer simulations or actual testing. Such a process is time consuming and results in high development costs. Furthermore, different vehicle applications specify unique and different fuel pressures or other pump parameters and it is not possible to easily modify an existing design layout that provides balance in one vehicle application into a similar layout for a different vehicle application. Thus, it would be desirable to provide for improved pressure balancing performance for a single-sided impeller that can be developed in a shorter time and at lower cost. 
     SUMMARY OF THE INVENTION 
     The present invention employs pressure balancing features on the non-vaned side of the impeller to provide localized application of fluid forces so that the impeller is more precisely balanced while using a simple and straightforward development process. 
     In one aspect of the invention, a fuel pump is provided for pressurizing fuel to be delivered to an engine of the motor vehicle. The fuel pump comprises a housing and an electric motor mounted in the housing and having a shaft defining an axial direction. A cover is attached to the housing having an internal cover surface defining a cover flow channel extending circumferentially around the internal cover surface. The cover includes an inlet for coupling lower pressure fuel to the cover flow channel at an inlet end, the cover flow channel further including an outlet end providing higher pressure fuel. A body member is coupled to the cover and has an internal body surface. The body member and the cover cooperatively define a pumping chamber between the internal body surface and the internal cover surface. The internal body surface defines an outlet passageway to receive the higher pressure fuel for delivery to the engine. An impeller is mounted to the shaft for rotation therewith and for axial translation along the shaft within the pumping chamber, the impeller having a body-side surface and a cover-side surface. The cover-side surface defines an impeller flow channel extending circumferentially around the impeller juxtaposed with at least a major portion of the cover flow channel. The impeller includes a plurality of vanes positioned at least partially within the impeller flow channel. The body-side surface has a plurality of discontinuous undercut regions each coaxially aligned with at least a portion of the impeller flow channel. The impeller has a plurality of apertures wherein each aperture connects the impeller flow channel with a respective undercut region, whereby pressure forces against the impeller from the fuel are substantially balanced in the axial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional, perspective view of one end of a fuel pump containing the pumping chamber. 
         FIG. 2  is an exploded view of the cover, impeller, and body member of  FIG. 1 . 
         FIG. 3  is an exploded view of the cover, impeller, and body member of  FIG. 2  showing the opposite faces. 
         FIG. 4  is a plan view showing a cover flow channel in an internal cover surface. 
         FIG. 5  is a plan view showing an outlet passageway in an internal body surface. 
         FIG. 6  is a perspective view of a cover-facing side of the impeller of  FIG. 1 . 
         FIG. 7  is a perspective view of a body-facing side of the impeller of  FIG. 1 . 
         FIG. 8  is a perspective, cross-sectional view showing a portion of the cover-side of the impeller in greater detail. 
         FIG. 9  is a perspective view showing undercut regions of the body-side of the impeller in greater detail. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a fuel pump  10  comprises a housing  11  containing a cover  12  and a body member  13 . The enclosed space between cover  12  and body member  13  provides a pumping chamber wherein an impeller  14  is mounted for rotation with a motor shaft  15 . Shaft  15  is connected to a motor armature  16  and is retained at one end by a thrust bearing  17 . Impeller  14  is keyed upon shaft  15  in order to rotate therewith while allowing impeller  14  to translate along an axial direction  18  so that it can stay centered in the pumping chamber. Thus, when thrust bearing  17  wears during the lifetime of the fuel pump causing shaft  15  to shift in axial direction  18 , impeller  14  will not become bound against a side of the pumping chamber as it would if it were locked in a fixed axial position on shaft  15 . 
     Impeller  14  of the present invention is a single sided impeller to reduce the wet circle index from about 1.8 to about 1.1, thereby reducing friction losses and increasing the hydraulic efficiency of the pump by about 25%–35%. Furthermore, impeller  14  is axially free floating while maintaining an axial clearance that is sufficient to handle fuels at higher pressure, typically about 2 bar or greater. 
     Referring to  FIG. 2 , cover  12  includes a fuel inlet  20  for receiving lower pressure fuel from a fuel tank. Body member  13  includes an internal body surface  21  axially facing towards impeller  14 . Body member  13  defines an outlet  22  which cooperates with a recess  23  to guide higher pressure fuel toward outlet  22 . Body member  13  also defines a central aperture  24  and a bearing  25  through which shaft  15  extends for connection with impeller  14 . Body member  13  includes a peripheral rim  26  to further define the pumping chamber along with internal body surface  21 . 
       FIG. 2  shows a cover-side surface  30  of impeller  14  which defines an impeller flow channel  31 . Impeller flow channel  31  extends circumferentially around impeller  14  and is proximal to an outer peripheral surface  32  of impeller  14 . Mounted within impeller flow channel  31  are a plurality of vanes  33  which are used to pressurize the fuel, as known in the art. An impeller flow passageway  34  extends through impeller  14  from the cover-side surface  30  to a body-side surface  35  ( FIG. 3 ). Flow passageway  34  is defined by a plurality of circumferentially spaced apertures  36  separated by a plurality of spokes  37  each having a circular cross-section to facilitate fluid flow. It will be recognized by those skilled in the art that spokes  37  can have other cross-sectional shapes such as oval, flat, curved, or vane-shaped which can vary along the length of each spoke  37 . Non-circular or vane-shape spokes  37  could supplement the pumping action of pump  10 . Impeller  14  also includes a central aperture  40  including a flat  41  for receiving shaft  15 . 
     The opposite sides of cover  12 , body member  13 , and impeller  14  are shown in exploded view in  FIG. 3 . Cover  12  includes an internal cover surface  45  facing axially toward impeller  14  and defining a cover flow channel  46  extending circumferentially around cover  12 . Cover-flow channel  46  is radially aligned with impeller flow channel  31  and vanes  33  for pressurizing fluid therein. Cover-flow channel  46  extends around cover  12  about 330°, thereby leaving a strip area  47  between the ends of cover-flow channel  46 . Cover-flow channel  46  has an inlet end  50  receiving lower pressure fuel from inlet  20  and an outlet end  51  that provides higher pressure fuel to the impeller flow passageway  34 . Internal cover surface  45  also defines a recess  48  which is sized to receive shaft  15  and thrust button  17 . 
     As can be recognized in  FIG. 3 , impeller  14  has a body side surface  35  which does not include any vanes or flow channels (i.e., impeller  14  is single sided). Body-side surface  35  includes a plurality of undercut regions and apertures as will be described below. 
       FIG. 4  shows an enlarged plan view of internal cover surface  45 . It can be seen that outlet end  51  curves radially inward to guide high pressure fuel toward the impeller flow passageway so that the pressurized fuel can cross the impeller into outlet  22  of body member  13 . Additionally, cover flow channel  46  includes a vapor vent hole  53  which is utilized to vent fuel vapor bubbles out of pump  10 . 
       FIG. 5  shows internal body surface  21  in its entirety. In this preferred embodiment, it is smooth other than recess  23  and outlet  22  which are radially aligned with impeller flow passageway  34  allowing high pressure fuel to exit the pumping chamber to pass through the remainder of pump  10  and out to the vehicle engine. 
     The cover-side surface of impeller  14  is shown in greater detail in  FIG. 6 . Circumferential impeller flow channel  31  is divided by a plurality of vanes  33  which may have any appropriate profile for accelerating fuel in the flow channel as is known in the art. Between each respective pair of vanes, a respective aperture locally couples the impeller flow channel  31  to the body side surface. Thus, the body-side surface is exposed to a source of pressure which is substantially equal to the pressure acting upon the cover-side surface at multiple points around the circumference of impeller  14 . 
       FIG. 7  shows the body-side surface  35  including a plurality of discontinuous undercut regions  56  communicating with each respective aperture  55 . Undercut regions  56  do not connect with one another because any fuel flow between regions would reduce pumping efficiency (by providing a short circuit path across a corresponding vane). Instead, rib portions  57  of body-side surface  35  are left intact between respective undercut regions  56 . 
     Fuel entering each undercut region via the respective aperture applies a pressure against the impeller over the corresponding area of the undercut regions, whereby the total pressure acting on the impeller may be balanced. Discontinuous undercut regions  56  may typically be substantially overlapping with corresponding portions of the impeller flow channel between each respective pair of vanes. Preferably, at least a portion of each undercut region  56  is coaxially aligned with the impeller flow channel. As shown in  FIG. 8 , undercut regions  56  may be exactly overlapping axially with impeller flow channel  31 . More or less area of the undercut regions may be desirable depending upon other characteristics of a particular impeller and pump in order to provide greater or lesser magnitudes of force against the impeller. Regions  56  may also be radially offset from impeller flow channel  31  if desired. Although the vanes, apertures, and undercut regions are shown with a one-to-one correspondence, a smaller number of undercut regions or apertures can be used while achieving the same beneficial results. Since the balancing forces are obtained locally from within the impeller flow channel along its circumference, the balancing forces vary in response to the way pressure against the impeller flow channel varies. Consequently, a well balanced impeller can be obtained over all pump operating conditions in a simple and straightforward manner without requiring complicated structures or a long and costly development process. 
     As shown in  FIG. 9 , ribs  57  are coplanar with surface  35  to avoid fuel leakage between apertures  55 . Therefore, successive apertures  55  are sufficiently isolated to maintain the necessary output pressure of the pump.