Patent Publication Number: US-6210102-B1

Title: Regenerative fuel pump having force-balanced impeller

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     This invention relates generally to pumps, and in particular to a regenerative fuel pump having a vaned impeller. Such a pump is useful as an electric-motor-operated fuel pump for an automotive vehicle to pump liquid fuel from a fuel tank through a fuel handling system to an engine that powers the vehicle. 
     2) Background Information 
     In an automotive vehicle that is powered by an internal combustion engine, fuel may be pumped through a fuel handling system of the engine by an in-tank, electric-motor-operated fuel pump. 
     Examples of fuel pumps are shown in various patents, including U.S. Pat. Nos. 3,851,998; 5,310,308; 5,409,357; 5,415,521; 5,551,875; and 5,601,398. Commonly owned U.S. Pat. Nos. 5,310,308; 5,409,357; and 5,551,835 disclose pumps of the general type to which the present invention relates, and such pumps provide certain benefits and advantages over certain other types of pumps. 
     For developing pressures suitable for a vehicle fuel system, the impeller of a regenerative pump may have very close running tolerances to the walls of the pump parts that axially confront opposite faces of the impeller internally of the pump. Hence, dimensional stability of materials is an important design consideration, and certain materials have been found particularly suitable for the impeller and for the parts of the pump (a pump cover and a pump body, for example) that confront it. PPS and phenolic are examples of suitable impeller materials; those two materials, as well as aluminum, are suitable for the pump cover and pump body. 
     A representative pump is a wet pump that comprises an inlet in the pump cover and an outlet in the pump body. The inlet and the outlet are open to an annular pumping chamber that runs around the perimeter of the pump. The impeller comprises vanes that rotate within the pumping chamber to move fluid from the inlet to the outlet. When the pump is disposed within a fuel tank with its axis generally vertical and the cover facing a bottom wall of the tank, the inlet is open to liquid fuel in the tank. When the pump is operated by an associated electric motor, some pressure difference is developed across those portions of the impeller faces which are disposed radially inward of the annular pumping chamber and which have close running fits to confronting wall surfaces of the pump cover and the pump body, thus creating a force imbalance that acts on the impeller in a downward direction. The force of gravity is additive to that downward force imbalance. Force imbalance may act on an impeller in ways that increase running friction. Such friction may decrease pump efficiency and accelerate wear that leads to even further loss of pumping efficiency. 
     Various solutions have been proposed to minimize, and ideally eliminate, force imbalance acting on the impeller. Examples are found in U.S. Pat. Nos. 3,768,920; 4,586,877; 4,854,830; 4,872,806; 5,137,418; and 5,607,283. 
     SUMMARY OF THE INVENTION 
     Through continuing development, it has been discovered the inclusion of certain features in an impeller can provide a better solution to the force imbalance problem described above. 
     Because those features are incorporated in the impeller, they can be inherently created when an impeller that embodies them is fabricated by known impeller fabrication methods. Hence, the solution provided by the present invention is significantly cost-effective. 
     Briefly, the invention relates to the inclusion of what the inventors have called “lifting tail grooves” in association with force-balance through-holes that extend between opposite impeller faces. The lifting tail grooves are provided in the face of the impeller that is toward the pump inlet, sometimes herein called the down-face for convenience because it faces down when the pump is mounted inside a fuel tank in the manner mentioned above. Each lifting tail groove comprises a shaped cavity that adjoins a respective force-balance through-hole, and runs a short distance circumferentially in a sense that is opposite the sense in which the impeller is rotating. Hence each groove “tails away” from the respective through-hole. 
     Importantly, each lifting tail groove comprises a fluid reaction surface that is non-parallel to the plane of the impeller down-face. It is believed that as the impeller rotates, fluid lamina between the impeller down-face and the confronting wall surface of the pump cover tends to rotate in the same sense as the impeller, but at a slower velocity because of its inherent viscosity. Hence, it is believed that the fluid lamina tends to rotate counter-clockwise relative to the impeller. 
     After the fluid lamina has passed across a force-balance through-hole and begins to encounter the respective lifting tail groove, it acts on the fluid reaction surface of the lifting tail groove in a manner that has been found to create a useful upward component of force that is opposite the pressure-induced force imbalance acting on the impeller. This effect significantly improves force-balancing of the impeller. 
     A representative impeller may have a number of identical force-balance through-holes distributed in a uniform pattern with respect to the impeller axis. Identical lifting tail grooves are associated with the force-balance through-holes. 
     One general aspect of the present invention relates to a pump comprising: a pump housing comprising an internal pumping chamber and a fluid inlet to, and a fluid outlet from, the pumping chamber spaced arcuately apart about an axis; and a pumping element that is disposed within the housing for rotation about the axis and that has a body comprising a vaned periphery operable with respect to the pumping chamber to pump fluid from the inlet to the outlet when the pumping element is rotated, the pumping element body further having mutually parallel opposite faces circumferentially bounded by its vaned periphery. The pump housing comprises wall surfaces confronting the opposite faces of the pumping element body with close running clearance, the inlet being proximate one wall surface and the outlet being proximate the other wall surface. The pumping element body comprises a pattern of through-holes extending between its faces with the one face that confronts the wall surface to which the inlet is proximate further comprising in association with each through-hole, a groove that adjoins and tails circumferentially away from the respective through-hole in a sense opposite the sense in which the pumping element rotates to pump fluid from the inlet to the outlet and that inclines from the through-hole to end by merging with the one face of the pumping element body at a location spaced circumferentially from the respective through-hole. 
     Another general aspect relates to a pump comprising: a pump housing comprising an internal pumping chamber and a fluid inlet to, and a fluid outlet from, the pumping chamber spaced arcuately apart about an axis; and a pumping element that is disposed within the housing for rotation about the axis and that has a body comprising a vaned periphery operable with respect to the pumping chamber to pump fluid from the inlet to the outlet when the pumping element is rotated, the pumping element body further having mutually parallel opposite faces circumferentially bounded by its vaned periphery. The pump housing comprises wall surfaces confronting the opposite faces of the pumping element body with close running clearance, the inlet being proximate one wall surface and the outlet being proximate the other wall surface. The pumping element body comprises a pattern of through-holes that have wall surfaces extending parallel to the pump axis between its faces with the one face that confronts the wall surface to which the inlet is proximate further comprising in association with each through-hole, a groove that adjoins and tails circumferentially away from the respective through-hole along an arc that is concentric with the pump axis in a sense opposite the sense in which the pumping element rotates to pump fluid from the inlet to the outlet, and that merges with the one face of the pumping element body at a location spaced circumferentially from the respective through-hole. 
     Other general and more specific aspects will been set forth in the ensuing description and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings that will now be briefly described are incorporated herein to illustrate a preferred embodiment of the invention and a best mode presently contemplated for carrying out the invention. 
     FIG. 1 is a longitudinal cross section view of a fuel pump embodying principles of the invention, as taken in the direction of arrows  1 — 1  in FIG.  2 . 
     FIG. 2 is an end view taken in the direction of arrows  2 — 2  in FIG.  1 . 
     FIG. 3 is a full plan view of one face of an impeller of the pump of FIGS. 1 and 2, as taken in the direction of arrows  3 — 3  in FIG.  1  and enlarged. 
     FIG. 4 is a full plan view of an opposite face of the impeller, as taken in the direction of arrows  4 — 4  in FIG.  1  and enlarged. 
     FIG. 5 is a fragmentary cross section view taken in the direction of arrows  5 — 5  in FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show an automotive vehicle fuel pump  10  embodying principles of the present invention and having an imaginary longitudinal axis  12 . Pump  10  comprises a housing that includes a pump cover  14  and a pump body  16  cooperatively arranged to close off one axial end of a cylindrical sleeve  18  and to cooperatively define an internal space for a pumping element, specifically an impeller  20 , that can rotate about axis  12 . The opposite axial end of sleeve  18  is closed by a part  22  that contains an exit tube  24  via which fuel exits pump  10 . Part  22  is spaced from pump body  16  to provide an internal space for an electric motor  26  that rotates impeller  20  when pump  10  runs. Motor  26  comprises an armature including a shaft  28  journaled for rotation about axis  12  and having a keyed connection at one end for imparting rotational motion to impeller  20 . The internal space cooperatively defined by pump cover  14  and pump body  16  for impeller  20  includes an annular pumping chamber  30 . 
     Pump  10  is intended to be at least partially submerged in a fuel tank of an automotive vehicle for running wet. A passage that extends through pump cover  14  provides an inlet  32  to pumping chamber  30 . A passage that extends through pump body  16  provides an outlet  34  from pumping chamber  30 . Fuel that leaves outlet  34  passes through motor  26  and exits pump  10  via tube  24  from whence the fuel is pumped to an engine through an engine fuel handling system (not shown). 
     Pumping chamber  30  has a typical circumferential extent of more than 270°, but less than 360°, with inlet  32  at one end of the pumping chamber and outlet  34  at the opposite end. Hence, outlet  34  is shown out of position in FIG.  1 . Impeller  20  comprises a circular body  36  having a series of circumferentially spaced apart vanes  38  around its outer periphery. As impeller  20  is rotated by motor  26 , its vaned periphery rotates through pumping chamber  30  to create a pressure differential between inlet  32  and outlet  34  that draws fluid through inlet  32 , moves the fluid through pumping chamber  30 , and forces the fluid out through outlet  34 . 
     The portion of impeller body  36  that is surrounded by vanes  38  comprises flat, mutually parallel, opposite faces  40 ,  42  that are perpendicular to axis  12 . Face  40  is a down-face that is confronted by a wall surface of pump cover  14 , and face  42  is an up-face that is confronted by a wall surface of pump body  16 . Those wall surfaces of cover  14  and pump body  16  confront the opposite faces  40 ,  42  of the pumping element body with close running clearance. 
     In accordance with the inventive principles, FIGS. 35 show “lifting tail grooves”  44  associated with force-balance through-holes  46  that extend between opposite impeller faces  40 ,  42 . A representative impeller, like the one shown, may have a number of identical force-balance through-holes  46  distributed in a uniform pattern with respect to axis  12 . Impeller  20  has two circular rows of identical circular through-holes  46 , one concentric within the other relative to axis  12 , each row containing six through-holes  46  centered at  60 ° intervals about axis  12 . 
     The through-holes of one row are circumferentially offset 30° from those of the other row. The through-holes are straight, with their axes being parallel to axis  12 . 
     Identical lifting tail grooves  44  are associated with through-holes  46 . Lifting tail grooves  44  are provided in down-face  40  of impeller  20 , but not in up-face  42 . Each lifting tail groove  44  is a shaped cavity that adjoins a respective force-balance through-hole  46 , and runs a short distance circumferentially in a sense that is opposite the sense in which the impeller rotates to pump fluid from inlet  32  to outlet  34 . Each groove may be considered to have an imaginary axis that extends generally circumferentially from the center of the respective through-hole  46 . That axis may be substantially straight, as shown in the drawing, or slightly curved, such as following a circular arc that is concentric with axis  12 . Hence in any case, each groove  44  may be said to “tail away” from the respective through-hole  46 . 
     As viewed in plan, each lifting tail groove  44  has a radial dimension, i.e. width, that is substantially equal to the diameter of the respective through-hole  46  from which it tails away, and ends in a generally semi-circular edge  50  as it merges with down-face  40 . Importantly, each lifting tail groove  44  comprises a fluid reaction surface  48  that is nonparallel to the plane of down-face  40 . As marked on FIG. 5, reaction surface  48  is disposed at a small acute angle A (slightly exaggerated in FIG. 5 for purposes of illustration) with respect to the plane of down-face  40 . Examples of angles that are believed most suitable range from about 1° to about 3°. While excessive inclination that may impair effectiveness of reaction surface  48  should be avoided, angles as large as 7° to 10° may be effective in certain pump designs. 
     Where lifting tail groove  44  adjoins through-hole  46 , the depth of surface  48  may range up to about 1.0 mm, but about 0.2 mm to about 0.4 mm is a preferred range based on development of an impeller as shown in the drawings. Surface  48  inclines upward toward the plane of down-face  40  along its circumferential extent from through-hole  46 , finally merging with the flat planar surface of the down-face along a generally semi-circular edge  50  that ends some 30° clockwise from the corresponding through-hole. Surface  48  may be flat, substantially flat, or slightly concave. 
     It is believed that as the impeller rotates, fluid lamina between the impeller down-face and the confronting wall surface of the pump cover tends to rotate in the same sense as the impeller, but at a slower velocity because of its inherent viscosity. Hence, it is believed that the fluid lamina tends to rotate counter-clockwise relative to the impeller. 
     After the fluid lamina has passed across a force-balance through-hole and begins to encounter the respective lifting tail groove, it acts on the fluid reaction surface of the lifting tail groove in a manner that has been found to create a useful upward component of force that is opposite the pressure-induced force imbalance acting on the impeller. This effect significantly improves force-balancing of the impeller. To the extent that there is a component of force acting circumferentially on surface  48 , it is believed to act in the same way as circumferential force caused by fluid viscosity as the impeller rotates. 
     While a presently preferred embodiment has been illustrated and described, it is to be appreciated that the invention may be practiced in various forms within the scope of the following claims.