Patent Application
20060165515
The present invention relates generally to automotive fuel pumps, and more particularly relates to a regenerative fuel pump having a single sided rotary impeller.
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.
Another problem with these types of fuel pumps is that as the fuel is pressurized, back pressure builds up within the pumping chamber causing backflow leakage which reduces the efficiency of the pump.
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 while providing a more gradual pressure increase of the fuel to lessen back pressure within the fuel pump.
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 impeller has opposed axially facing surfaces including a body-side surface and a cover-side surface. The cover-side surface defines first and second impeller flow channels that extend circumferentially around the impeller. The impeller further includes a plurality of vanes, each of the first and second impeller flow channels having a portion of the vanes positioned at least partially therein. The second impeller flow channel is positioned radially inward of the first impeller flow channel, and the impeller defines a flow passageway extending therethrough.
The cover includes a cover surface defining a cover flow channel extending circumferentially around the cover. The cover flow channel receives fuel from an inlet formed in the cover. A first portion of the cover flow channel is at least partially aligned with the first impeller flow channel and a second portion of the cover flow channel is at least partially aligned with the second impeller flow channel. The cover flow channel includes an outlet end that extends radially inwardly for fluid communication with the flow passageway of the impeller.
Rotation of the impeller and its vanes pressurizes the lower pressure fuel provided at the inlet of the cover flow channel, which is then forced to the 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.
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:
Referring to
Notably, the fuel pump 14 includes an impeller 34. In one embodiment, the impeller 34 of the fuel pump is a single-sided impeller, 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 fuel pump 14 typically about 20%-35%. Furthermore, the single sided impeller 34 is free floating while maintaining an axial clearance that is sufficient to handle fuels at higher pressure, typically about 2 bar or greater.
The present invention could also be practiced with a dual-sided impeller such as the one described in U.S. Pat. No. 6,688,844, which issued on Feb. 10, 2004, is assigned to the assignee of the present application, and is hereby incorporated by reference into the present application.
The fuel pump 14 generally includes a housing 36 which encloses a motor 38 therein. The motor 38 is operatively connected to a shaft 40 which defines a central axis 42 of the pump 14. A cover 44 closes off the open end of the housing 36, and defines the inlet 24 for receiving lower pressure fuel. A body 46 is positioned inside the housing 36 and adjacent the cover 44. The impeller 34 is fitted between the cover 44 and the body 46. The impeller 34 is fitted on the shaft 40 for rotation, as well as axial translation relative to the shaft 40. That is, the impeller 34 is free floating on the shaft 40 as previously mentioned.
Turning now to
As previously discussed, the present invention can be practiced with a single-sided impeller 34 or a dual-sided impeller. With a single sided impeller 34 the first and second flow channels 50, 52 are formed within the cover-side surface 48 but do not extend through the impeller 34. With a dual-sided impeller (not shown), the first and second impeller flow channels 50, 52 extend through the impeller to the body-side surface, as described in U.S. Pat. No. 6,688,844.
Each of the first and second impeller flow channels 50, 52 includes a plurality of vanes 56 which are used to pressurize the fuel, as is known in the art. As shown, the radial widths of the first and second impeller flow channels 50, 52 are substantially equal, however, it should be understood that the invention could be practiced wherein the radial width of the first and second impeller flow channels 50, 52 are not substantially equal.
An impeller flow passageway 58 extends through the impeller 34 from the cover-side surface 48 to a body-side surface 60, opposite the cover-side surface 48. The impeller flow passageway 58 is only necessary with a single-sided impeller 34. With a dual-sided impeller, the fuel flow is through the impeller flow channels 50, 52. The impeller flow passageway 58 is defined by a plurality of circumferentially spaced apertures 62 aligned in an annular configuration as shown. The apertures 62 are separated by a plurality of spokes 64 having a circular cross-section to facilitate fluid flow. It will also be recognized by those skilled in the art that the spokes 64 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 64. Non-circular or vane-shaped spokes 64 will supplement the pumping action of the fuel pump 14. It can also be seen that the impeller 34 includes an aperture 66 which includes a flat 68 for receiving the shaft 40 which rotatably drives the impeller 34.
The body 46 generally includes a body surface 70 facing axially towards the impeller 34. The body 46 defines an outlet 72 through which pressurized fuel flows for ultimate delivery to the engine. The body 46 also defines a central aperture 74 and a bearing surface 76 through which the shaft 40 extends for connection to the impeller 34. The body 46 includes a peripheral rim 78 which defines an impeller chamber 80 therein. That is, the peripheral rim 78 and the body surface 70 define an impeller chamber 80 that is sized to receive the impeller 34, as best seen in
The opposing sides of the cover 44, impeller 34 and body 46 are shown in the exploded view of
A first portion 92 of the cover flow channel 90 extends around the cover 44 about 330° before turning radially inward such that a second portion 94 of the cover flow channel 90 continues to extend around the cover 44 radially inward of the first portion 92 of the cover flow channel 90. The second portion 94 of the cover flow channel 90 terminates at an outlet end 96 of the cover flow channel 90. In this way, the total length of the cover flow channel 90 extends more than 360 degrees around the cover 44.
The first portion 92 of the cover flow channel 90 is radially aligned with the first impeller flow channel 50 and its vanes 56 for pressurizing fuel therein and the second portion 94 of the cover flow channel 90 is radially aligned with the second impeller flow channel 52 and its vanes 56 for pressurizing fuel therein.
It will also be recognized from
An enlarged view of the cover 44 is shown in
When assembled together as shown in
As shown in
Accordingly, by way of the present invention, a more efficient fuel pump 14 is provided by the provision of a cover flow channel 90 that extend more than 360 degrees around the cover 44. This long cover flow channel 90 allows more gradual pressure increase of the fuel therein, thereby lowering the amount of backpressure and corresponding backpressure leakage.
However, a predetermined clearance must be maintained between the impeller 34 and the cover 44 and body 46. In particular, the application of the fuel pump 14 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 34 and the cover 44 and body 46. That is, the cover-side surface 48 of the impeller 34 must be maintained within 50 micron (axially) of the cover surface 86 of the cover 44 to be capable of pressurizing fuel to 2 bar or greater.
Unfortunately, the impeller 34 cannot be fixed on the shaft 40. In the harsh environment of a motor vehicle, the fuel pump 14 will be subjected to continuous and repeated operation which causes wear on the thrust button supporting the shaft 40. Thus, over the life of the fuel pump 14, the shaft 40 may shift its position, making it impossible to maintain the ideal clearance between the impeller 34 and the cover 44. Thus, the automotive environment of the fuel pump 14 requires the impeller 34 to be free floating on the shaft 40.
Therefore, the fuel pump 14 according to the teachings of present invention regulates the area of the impeller 34, and in particular the area of the body-side surface 60, that is exposed to the higher pressure fuel in the outlet passageway 82. In particular, the area of the impeller 34 which is exposed to fuel on its body side 60 is closely sized relative to the area of the cover-side 48 of the impeller 34 which is exposed to fluid. It will be recognized that the area of the impeller 34 which is exposed to fluid on its cover-side surface 48 is defined by the axially facing area of the cover flow channel 90. It will also be recognized that the pressure of fluid in the cover flow channel 90 varies from the inlet 24 to the outlet end 96. Thus, the pressure of the fluid in the cover flow channel 90 must be averaged, and for purposes here can be generalized as approximately one half of the change in pressure from the inlet 24 to the outlet end 96.
For example, if lower pressure fluid is provided at the inlet 24 at about 0 bar, and is pressurized by the fuel pump 14 to a pressure of about 4 bar at the outlet end 96, the average pressure in the cover flow channel 90 can be estimated to be 2 bar. In this example, the higher pressure fuel in the outlet passageway 82 of the body 46 is thus also about 4 bar. Accordingly, the area of the impeller 34 (and in particular the body side surface 60) which is exposed to the outlet passageway 82 is controlled in relation to the exposed area corresponding to the cover flow passageway 90, thereby providing a generally balanced force on opposing sides of the impeller 34. Stated another way, the impeller 34 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 34, encompass the fact that the actual pressure within the cover flow channel 90 may vary depending upon particular conditions (e.g. pulsations or other pressure variations) which in turn causes the opposing axial forces on the impeller 34 to vary, which in turn causes the impeller 34 to float on the shaft 40, and is known in the art. In this way, the impeller 34 is allowed to translate axially along the shaft 40 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.
The foregoing description of the embodiments described herein 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. 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.
