Automotive fuel pump with pressure balanced impeller

A rotary fuel pump 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 within the pumping chamber. A generally disc-shaped impeller body has an impeller with a body-side surface and a cover-side surface. The cover-side surface defines an impeller flow channel extending circumferentially around the impeller. 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.

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.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring toFIG. 1, a fuel pump10comprises a housing11containing a cover12and a body member13. The enclosed space between cover12and body member13provides a pumping chamber wherein an impeller14is mounted for rotation with a motor shaft15. Shaft15is connected to a motor armature16and is retained at one end by a thrust bearing17. Impeller14is keyed upon shaft15in order to rotate therewith while allowing impeller14to translate along an axial direction18so that it can stay centered in the pumping chamber. Thus, when thrust bearing17wears during the lifetime of the fuel pump causing shaft15to shift in axial direction18, impeller14will not become bound against a side of the pumping chamber as it would if it were locked in a fixed axial position on shaft15.

Impeller14of 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, impeller14is axially free floating while maintaining an axial clearance that is sufficient to handle fuels at higher pressure, typically about 2 bar or greater.

Referring toFIG. 2, cover12includes a fuel inlet20for receiving lower pressure fuel from a fuel tank. Body member13includes an internal body surface21axially facing towards impeller14. Body member13defines an outlet22which cooperates with a recess23to guide higher pressure fuel toward outlet22. Body member13also defines a central aperture24and a bearing25through which shaft15extends for connection with impeller14. Body member13includes a peripheral rim26to further define the pumping chamber along with internal body surface21.

FIG. 2shows a cover-side surface30of impeller14which defines an impeller flow channel31. Impeller flow channel31extends circumferentially around impeller14and is proximal to an outer peripheral surface32of impeller14. Mounted within impeller flow channel31are a plurality of vanes33which are used to pressurize the fuel, as known in the art. An impeller flow passageway34extends through impeller14from the cover-side surface30to a body-side surface35(FIG. 3). Flow passageway34is defined by a plurality of circumferentially spaced apertures36separated by a plurality of spokes37each having a circular cross-section to facilitate fluid flow. It will be recognized by those skilled in the art that spokes37can have other cross-sectional shapes such as oval, flat, curved, or vane-shaped which can vary along the length of each spoke37. Non-circular or vane-shape spokes37could supplement the pumping action of pump10. Impeller14also includes a central aperture40including a flat41for receiving shaft15.

The opposite sides of cover12, body member13, and impeller14are shown in exploded view inFIG. 3. Cover12includes an internal cover surface45facing axially toward impeller14and defining a cover flow channel46extending circumferentially around cover12. Cover-flow channel46is radially aligned with impeller flow channel31and vanes33for pressurizing fluid therein. Cover-flow channel46extends around cover12about 330°, thereby leaving a strip area47between the ends of cover-flow channel46. Cover-flow channel46has an inlet end50receiving lower pressure fuel from inlet20and an outlet end51that provides higher pressure fuel to the impeller flow passageway34. Internal cover surface45also defines a recess48which is sized to receive shaft15and thrust button17.

As can be recognized inFIG. 3, impeller14has a body side surface35which does not include any vanes or flow channels (i.e., impeller14is single sided). Body-side surface35includes a plurality of undercut regions and apertures as will be described below.

FIG. 4shows an enlarged plan view of internal cover surface45. It can be seen that outlet end51curves radially inward to guide high pressure fuel toward the impeller flow passageway so that the pressurized fuel can cross the impeller into outlet22of body member13. Additionally, cover flow channel46includes a vapor vent hole53which is utilized to vent fuel vapor bubbles out of pump10.

FIG. 5shows internal body surface21in its entirety. In this preferred embodiment, it is smooth other than recess23and outlet22which are radially aligned with impeller flow passageway34allowing high pressure fuel to exit the pumping chamber to pass through the remainder of pump10and out to the vehicle engine.

The cover-side surface of impeller14is shown in greater detail inFIG. 6. Circumferential impeller flow channel31is divided by a plurality of vanes33which 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 channel31to 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 impeller14.

FIG. 7shows the body-side surface35including a plurality of discontinuous undercut regions56communicating with each respective aperture55. Undercut regions56do 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 portions57of body-side surface35are left intact between respective undercut regions56.

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 regions56may 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 region56is coaxially aligned with the impeller flow channel. As shown inFIG. 8, undercut regions56may be exactly overlapping axially with impeller flow channel31. 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. Regions56may also be radially offset from impeller flow channel31if 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 inFIG. 9, ribs57are coplanar with surface35to avoid fuel leakage between apertures55. Therefore, successive apertures55are sufficiently isolated to maintain the necessary output pressure of the pump.