Abstract:
A fuel pump is provided having improved efficiency by lowering the wet circle index of the pump while maintaining robust axial clearances to meet the demands of an automotive application. One embodiment includes a fuel pump for pressurizing fuel for delivery to an engine of a motor vehicle. The fuel pump generally comprises a housing, a motor, a single sided impeller, a cover and a body. The provision of a single sided impeller greatly reduces the wet circle index and improves the pump efficiency. The cover, impeller, and body are structured to axially balance the impeller which is free floating on the shaft of the motor.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to automotive fuel pumps, and more particularly relates to a regenerative fuel pump having a rotary impeller. 
     BACKGROUND OF THE INVENTION 
     Regenerative fuel pumps have been widely used in automotive applications because of the low specific speed number (ratio of diameter and flow rate versus pressure), quiet operation, good handling of hot fuel, and durability. These regenerative fuel pumps generally include an impeller rotating on a shaft and positioned within an impeller chamber in the pump. The clearance between the opposing axial sides of the impeller and the corresponding walls of the impeller chamber must be closely regulated to permit the pump to handle fuel at relatively high pressures (i.e. greater than about 2 bar). The impellers are typically double sided impellers, meaning the impellers include vanes on each opposing side which have vanes positioned therein for pressurizing fuel on both sides of the impeller. In this manner, the impellers are relatively well balanced axially to maintain the necessary clearance for pumping high pressure fuel. 
     One drawback of these fuel pumps is that their wet circle index is relatively high, typically 1.7 or greater. The wet circle index is an index for the pump boundary layer and friction losses. The wet circle index can be defined as the wet circle length versus the flow channel cross-sectional area. That is, the wet circle length is the distance along the perimeter of the flow channel (i.e. circumference of a round flow channel), the follow channel being formed by both the impeller and the structures (e.g. body and cover structures) on opposing sides of the impeller. 
     Accordingly, there exist a need for a fuel pump with robust axial clearance requirements to permit pumping of high pressure fluid in an automotive environment, while at the same time having a lower wet circle index to reduce friction losses and improve the efficiency of the pump. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a fuel pump that improves the pump efficiency by lowering the wet circle index of the pump while maintaining robust axial clearances to meet the demands of an automotive application. One embodiment of the invention includes a fuel pump for pressurizing fuel for delivery to an engine of a motor vehicle. The fuel pump generally comprises a housing, a motor, a single sided impeller, a cover and a body. The provision of a single sided impeller greatly reduces the wet circle index and improves the pump efficiency. 
     According to more detailed aspects, the motor is situated in the housing and drives a shaft. The impeller is connected to the shaft for rotation as well as for axial translation relative to the shaft. That is, the impeller is free floating on the shaft. The cover includes a flow channel which is aligned with a flow channel formed in the impeller, rotation of the impeller and its vanes pressurizing the lower pressure fuel provided at an inlet end of the cover flow channel, which is forced to an outlet end of the cover flow channel. The impeller includes a flow passageway extending therethrough and in communication with the outlet end of the cover flow channel. The body defines an outlet passageway positioned to fluidically connect to the impeller flow passageway, thereby receiving higher pressure fuel for delivery to the engine. 
     The impeller is free floating on the shaft and is subjected to a cover-side force from fuel in the cover flow channel and the impeller flow channel, as well as a body-side force from fuel in the outlet passageway. The outlet passageway is at least partially exposed to the body side of the impeller, and the exposed area is sized to provide a body-side and force approximately equal to the cover-side and force. In this way, the impeller is balanced on the shaft to provide robust axial clearances for pumping higher pressure fuel. 
     According to still further details, the exposed area on the body-side of the impeller is less than the area of the cover-side of the impeller exposed to the cover flow channel, as the pressure on the body-side is generally greater than the average pressure on the cover-side of the impeller. Additionally, one or both of the body and the cover may define pressure balance channels in fluidic communication with either high or low pressure fuel, which can be adjusted to provide a balanced impeller. The pressure balance channels may take many forms and may be positioned at various radial and circumferential positions. 
     In this way, the fuel pump of the present invention allows the impeller to maintain an axial clearance between the cover and the impeller that is less than or equal to 50 micron by sizing the area of the cover-side surface of the impeller that is exposed to fluid in relation to the area of the body-side surface of the impeller that is exposed to fuel. Likewise, the impeller maintains an axial clearance between the cover that is sufficient to pressurize fuel to at least 2 bar. Notably, the fuel pump does not require a bearing or other structural component to maintain the necessary clearance between the cover and the impeller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a cross-sectional view of a fuel pump constructed in accordance with the teachings of the present invention; 
         FIG. 2  is an exploded view, in perspective, of the cover, impeller and body forming a portion of the fuel pump depicted in  FIG. 1 ; 
         FIG. 3  is an exploded view, in perspective, similar to  FIG. 2  but showing the opposing sides of the cover, impeller and body; 
         FIG. 4  is an enlarged perspective view of the cover depicted in  FIGS. 1–3 ; 
         FIG. 5  is cross-sectional view of the cover, impeller, and body depicted in  FIGS. 1–3 ; 
         FIG. 6  is cross-sectional view of the cover, impeller, and body depicted in  FIGS. 1–3 ; 
         FIG. 7  is an enlarged perspective view similar to  FIG. 4  but showing an alternate embodiment of the cover; 
         FIG. 8  is an enlarged perspective view similar to  FIG. 4  but showing an alternate embodiment of the impeller depicted in  FIGS. 1–4 ; 
         FIG. 9  is an enlarged perspective view of an alternate embodiment of the body depicted in  FIGS. 1–3 ; and 
         FIG. 10  is an enlarged perspective view of an alternate embodiment of the body depicted in  FIGS. 1–3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the figures,  FIG. 1  depicts a cross-sectional view of a fuel pump  20  constructed in accordance with the teachings of the present invention. Notably, the fuel pump  20  includes a single sided impeller  50  which greatly reduces the wet circle index from about 1.8 to about 1.1, thereby reducing friction losses and increasing the hydraulic efficiency of the pump  20  typically about 20%–35%. Furthermore, the single sided impeller  50  is free floating while maintaining an axial clearance that is sufficient to handle fuels at higher pressure, typically about 2 bar or greater. 
     As shown in  FIG. 1 , the pump  20  generally includes a housing  22  which encloses a motor  24  therein. The motor  24  is operatively connected to a shaft  26  which defines a central axis  28  of the pump  20 . A cover  30  closes off the open end of the housing  22 , and includes an inlet  34  for receiving lower pressure fuel. A body  70  is positioned inside the housing  22  and inside the cover  30 . The impeller  50  is fitted between the cover  30  and body  70 . The impeller  50  is fitted on the shaft  26  for rotation, as well as axial translation relative to the shaft. That is, the impeller  50  is free floating on the shaft  26  as previously mentioned. 
     Turning now to  FIG. 2 , an exploded view of the cover  30 , impeller  50  and body  70  is shown in perspective. It can be seen that the impeller  50  includes a cover-side surface  52  which defines an impeller flow channel  58  therein. The impeller flow channel  58  extends circumferentially around the impeller  50  and is located adjacent the outer peripheral surface  51  of the impeller  50 . The impeller flow channel  58  includes a plurality of vanes  60  which are used to pressurize the fuel, as is known in the art. An impeller flow passageway  62  extends through the impeller from the cover-side surface  52  to the body-side surface  53  ( FIG. 3 ). The flow passageway  62  is defined by a plurality of circumferentially spaced apertures  64  aligned in an annular configuration as shown. The apertures  64  are separated by a plurality of spokes  66  having a circular cross-section to facilitate fluid flow. It will also be recognized by those skilled in the art that the spokes  66  can have other cross-sectional shapes different than circular, such as oval, elliptical, flat, curved or vane-shaped, which can vary along the length of the spoke  66 . Non-circular or vane-shaped spokes  66  will supplement the pumping action of the pump  20 . It can also be seen that the impeller  50  includes an aperture  54  which includes a flat  56  for receiving the shaft which rotatably drives the impeller  50 . 
     The body  70  generally includes a body surface  72  facing axially towards the impeller  50 . The body  70  defines an outlet  74  through which pressurized fuel flows for ultimate delivery to the engine. The body  70  also defines a central aperture  76  and a bearing  75  through which the shaft  26  extends for connection to the impeller  50 . The body  70  includes a peripheral rim  78  which defines an impeller chamber  80  therein. That is, the peripheral rim  78  and the body surface  72  define an impeller chamber  80  that is sized to receive the impeller  50 , as best seen in  FIG. 1 . Finally, the body  70  defines an outlet passageway  82  which is fluidically connected to the outlet  74 . The outlet passageway  82  is at least partially defined by a recess  84  formed in the body surface  72 . It can be seen that the recess  84  extends radially inwardly from the outlet  74  and has a figure-eight or hour-glass shape. 
     The opposing sides of the cover  30 , impeller  50  and body  70  are shown in the exploded view of  FIG. 3 . The cover  30  includes a cover surface  32  facing axially towards the impeller  50 . The cover surface  32  defines a recess  36  which is sized to receive the shaft  26  and a thrust button as shown in  FIG. 1 . The cover surface  32  also defines a cover flow channel  38  which extends circumferentially around the cover  30 . The cover flow channel  38  is radially aligned with the impeller flow channel  58  and its vanes  60  ( FIG. 2 ) for pressurizing fuel therein. The cover flow channel  38  extends around the cover  30  about 330°, thereby leaving a strip area  44  between the ends of the cover flow channel  38 . 
     It will also be recognized from  FIG. 3  that the impeller  50  includes a body-side surface  52  which does not include any vanes or flow channels, the impeller  50  thus being single sided. 
     An enlarged view of the cover  30  is shown in  FIG. 4 . In particular, the cover flow channel  38  can be seen, which includes an inlet end  40  and an outlet end  42 . Additionally, the cover flow channel  38  includes a vapor vent hole  46  which is utilized to vent unwanted fuel vapors in the pump  20 . The outlet end  42  of the cover flow channel  38  turns and extends radially inwardly, which will be discussed in further detail below. 
     The flow pathway(s) through the cover  30 , impeller  50  and body  70  will now be described with reference to the cross-sectional views of  FIGS. 5 and 6 . When assembled together as shown, the cover  30  and body  70  sandwich the impeller  50  therebetween, the impeller  50  being positioned within the impeller chamber  80  defined by the peripheral rim  78  of the body  70 . Working from left to right in  FIG. 5 , the cover  30  generally includes an inlet  34  through which lower pressure fuel is received for pumping to the engine. The inlet  34  extends axially and communicates with the inlet end  40  of the cover flow channel  38 . The cover flow channel  38  is radially aligned with the impeller flow channel  58  formed in the impeller  50 . Fuel thus flows into the cover flow channel  38  and impeller flow channel  58 , which is pressurized by the vanes  60  and the rotation of the impeller  50  relative to the stationary cover  30  and body  70 . 
     Turning to  FIG. 6 , the fuel is pressurized as it flows from the inlet end  40  to the outlet end  42  of the cover flow channel  38 . As shown in the figure, the outlet end  42  of the cover flow channel  38  turns and extends radially inwardly to a position aligned with the flow passageway  62  of the impeller  50 . The outlet passageway  82  defined by the body  70  is fluidically connected to the flow passageway  62  of the impeller  50 . In this way, higher pressure fuel is allowed to flow through the impeller  50 , through the outlet passageway  82  and into the outlet  74  defined in the body  70 . 
     Accordingly, by way of the present invention, a more efficient pump  20  is provided by the provision of a single sided impeller  50 . The cover flow channel  38  and impeller flow channel  58  are sized to provide a pump  20  which is capable of pumping the same volume of fluid as a comparable pump having a double sided impeller, while at the same time employing a single sided impeller that reduces the wet circle index, and hence losses to friction. 
     However, a predetermined clearance must be maintained between the impeller  50  and the cover  30  and body  70 . In particular, the application of the pump  20  to a motor vehicle requires that the fuel is pressurized to a relatively high level, namely about 2 bar or above. Thus, an axial clearance of about 50 micron (or 0.05 mm) or less must be maintained between the impeller  50  and the cover  30  and body  70 . That is, the cover-side surface  52  of the impeller  50  must be maintained within 50 micron (axially) of the cover surface  32  of the cover  30  to be capable of pressurizing fuel to 2 bar or greater. 
     Unfortunately, the impeller  50  cannot be fixed on the shaft  26 . In the harsh environment of a motor vehicle, the fuel pump  20  will be subjected to continuous and repeated operation which causes wear on the thrust button supporting the shaft  26 . Thus, over the life of the pump  20 , the shaft  26  may shift its position, making it impossible to maintain the ideal clearance between the impeller  50  and the cover  30 . Thus, the automotive environment of the pump requires the impeller  50  to be free floating on the shaft  26 . 
     Therefore, the pump  20  according to the teachings of present invention regulates the area of the impeller  50 , and in particular the area of the body-side surface  53 , that is exposed to the higher pressure fuel in the outlet passageway  82 . This is best seen in the cross-sectional view of  FIG. 6 . In particular, the area of the impeller  50  which is exposed to fuel on its body side  53  is closely sized relative to the area of the cover-side  52  of the impeller  50  which is exposed to fluid. It will be recognized that the area of the impeller  50  which is exposed to fluid on its cover-side surface  52  is defined by the axially facing area of the cover flow channel  38 . It will also be recognized that the pressure of fluid in the cover flow channel  38  varies from the inlet end  40  to the outlet end  42 . Thus, the pressure of the fluid in the cover flow channel  38  must be averaged, and for purposes here can be generalized as approximately one half of the change in pressure from the inlet end  40  to the outlet end  42 . 
     For example, if lower pressure fluid is provided at the inlet end  40  at about 0 bar, and is pressurized by the pump  20  to a pressure of about 4 bar at the outlet end  42 , the average pressure in the cover flow channel  38  can be estimated to be 2 bar. In this example, the higher pressure fuel in the outlet passageway  82  of the body  70  is thus also about 4 bar. Accordingly, the area of the impeller  50  (and in particular the body side surface  53 ) which is exposed to the outlet passageway  82  is controlled in relation to the exposed area corresponding to the cover flow passageway  38 , thereby providing a generally balanced force on opposing sides of the impeller  50 . Stated another way, the impeller  50  is subject to a cover-side force and a body-side force, which are designed to be approximately equal. 
     As used herein, the terms about, approximately, generally and the like, when used in relation to the forces and pressures on the impeller  50 , encompass the fact that the actual pressure within the cover flow channel  38  may vary depending upon particular conditions (e.g. pulsations or other pressure variations) which in turn causes the opposing axial forces on the impeller  50  to vary, which in turn causes the impeller  50  to float on the shaft  26 , and is known in the art. In our example, the exposed area of the body-side surface  53  of the impeller  50  is approximately one half of the exposed area on the cover-side surface  52  of the impeller  50 . In this way, the impeller  50  is allowed to translate axially along the shaft  26  to accommodate pressure variations, while at the same time maintaining an appropriate axial clearance of about 50 micron or less to ensure the ability of the pump to pressurize fuel to high pressure, namely about 2 bar or greater. 
     It will be recognized by those skilled in the art that additional structures may be employed in the cover  30 , impeller  50  and/or body  70  in order to facilitate the balancing of the impeller  50  along the shaft  26 . Several of numerous embodiments for the cover  30  and body  70  have been depicted in  FIGS. 7–10 . In particular,  FIG. 7  depicts the cover  30  having a pressure balance channel  48  formed in the cover surface  32 . The pressure balance channel  48  is positioned radially inside the cover flow channel  38 . The pressure balance channel  48  includes a narrowed portion  49  linking the pressure balance channel  48  to the outlet end  42  of the cover flow channel  38 . In this manner, higher pressure fuel proximate the outlet end  42  is permitted to flow through the relatively narrow linking portion  49  to the pressure balance channel  48 . The pressure balance channel  48  thus contains fluid which provides a portion of the cover-side force on the impeller  50 , determined by the axially facing area of the pressure balance channel  48 . 
     It will also be noted that the pressure balance channel  48  is circumferentially aligned with the inlet end  40  of the cover flow channel  38 . This construction is employed so that the cover-side force on the impeller  50  is balanced over the entire cover-side area of the impeller  50  (i.e. balancing higher and lower forces). Thus, the pressure balance channel  48  (filled with higher pressure fluid) is aligned with the portion of the cover flow channel  38  having lower pressure fuel (i.e. the inlet end  40 ). The pressure balance channel  48  extends about 180° or less around the cover  30 , but could extend more. It will also be seen that the narrow linking portion  49  of the pressure balance channel  48  is positioned in circumferential alignment with the strip portion  44  of the cover  30 . 
     Turning to  FIG. 8 , the cover  30  is again shown, but has an alternate version of the pressure balance channel  148 . The pressure balance channel  148  still includes a narrowed linking portion  149  proximate the strip area  44 . The linking portion  149  connects the pressure balance channel  148  to the higher pressure fuel found at the outlet end  42  of the cover flow channel  38 . In this embodiment, the pressure balance channel  148  is bifurcated by a wall  147  into an outer portion  148   a  and an inner portion  148   b . The wall  147  is radially aligned with the impeller flow passageway  62  to prevent flow thereto. The inner portion  148   b  extends radially inwardly to a point adjacent the recess  36 , while the outer portion  148   a  is positioned adjacent the cover flow channel  38 . As in the embodiment depicted in  FIG. 7 , the pressure balance channel  148  is circumferentially aligned with the inlet end  40  and spaced radially inwardly therefrom, and also spans about 180° circumferentially. It will also be recognized by those skilled in the art that either of the embodiments depicted in  FIGS. 7 and 8  could include pressure balance channels  48 ,  148  circumferentially aligned with the outlet end  42  of the cover flow channel  38 , and including a linking portion  49 ,  149  which fluidically connects the pressure balance channel  48 ,  148  to the inlet end  40  of the cover flow channel  38  which contains lower pressure fuel. 
       FIG. 9  depicts a perspective view of the body  70  which has been shown to include a pressure balance channel  86  defined in the body surface  72 . The pressure balance channel  86  extends circumferentially around the body  70 . The pressure balance channel  86  extends 360° or less around the body  70 . The pressure balance channel  86  is radially aligned with at least a portion of the outlet  74  and outlet passageway  82 , although it will be recognized that the pressure balance channel  86  can be positioned anywhere on the body surface  72 , and can take any shape, so long as the axial area of the pressure balance channel  86  is sized to properly create balanced forces on the impeller  50 . Thus, the embodiment depicted in  FIG. 9  provides a pressure balance channel  86  in the body  70  which receives higher pressure fluid from the outlet passageway  82  to form a portion of the body-side force on the impeller  50 . 
     With reference to  FIG. 10 , another embodiment of the body  70  has been depicted including a first pressure balance channel  186  and second pressure balance channel  188 . The pressure balance channels  186 ,  188  are kidney-shaped and generally span about 180° or less around the body  70 . The first pressure balance channel  186  is fluidically connected to the outlet passageway  82  and outlet  74 , thereby receiving higher pressure fuel. The second balance channel  188  is fluidically connected to lower pressure fuel found proximate the inlet  34  of the cover  30  by way of a passageway  189  formed in the peripheral rim  78  of the cover  70 . Generally, the pressure balance channel  186  having higher pressure fuel is circumferentially aligned with the higher pressure portion of the cover flow channel  38  (i.e. the outlet end  42 ), while the pressure balance channel  188  having lower pressure fluid is circumferentially aligned with the portion of the cover flow channel  38  having lower pressure fuel (i.e. adjacent inlet end  40 ). In this manner, the stronger cover-side forces on the impeller  50  are balanced against the stronger body-side forces on the impeller, and the same for the lower cover-side and body-side forces on the impeller (i.e. due to lower pressure fluid). 
     Accordingly, those skilled in the art with recognize that the present invention, as described by the numerous embodiments constructed in accordance with the teachings herein, provides a fuel pump which reduces the wet circle index and increases the efficiency of the pump. A single sided impeller which is free floating on the shaft assists in increasing the efficiency. At the same time, the impeller is balanced along the drive shaft and maintains an axial clearance between the cover and body that is less than about 50 micron, thereby allowing the fuel pump to be applied and the harsh environment of a motor vehicle and to pump fuel at pressures of 2 bar or greater as is required by the conditions of operation. 
     The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. For example, all of the flow channels and pressure balance channels formed in any of the cover  30 , impeller  50  or body  70  can be of any cross-sectional shape such as square, rectangular, semicircular, semioval, semielliptical, etc. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.