A fuel pump

Abstract: A fuel pump for supplying diesel fuel to an engine includes a pump housing 12, a motor 14 mounted within the housing 12, a shaft 18 extending from the motor 14, an impeller 26 slidably attached to the shaft 18 which has a prime number of vanes 40 spaced unevenly about its circumference, a chamber body 22, and a chamber cover 24 with a bleed orifice 52. The chamber body 22 and cover 24 form a chamber for the impeller 26 and are held together by the housing 12. The chamber body 22 and cover 24 have pump channels 70,72 of constant depth and are made of phenolic with fibreglass fill. The impeller is made of phenolic with fibreglass fill and granular fill.

Description: The present invention relates to fuel pumps, and, more particularly, to an in-tank fuel pump for pumping highly viscous fuels. Historically, diesel-fuelled vehicles have used mechanical lift pumps located near the engine for supplying the engine with diesel fuel. By contrast, conventional gasoline engines have used regenerative turbine pumps located in the fuel tank for supplying spark-ignition engines with gasoline. While regenerative turbine pumps have many advantages for spark-ignition engines, they have not been widely used with diesel engines. This is because regenerative turbine pumps have traditionally been suited for providing high-flow, high-pressure fuel, whereas diesel engines require high-flow, low-pressure fuel. Furthermore, diesel fuel is more viscous than conventional gasoline, especially when cold, and is thus less inclined to flow smoothly. Diesel fuel also tends to cavitate or foam when hot, and sharp pressure rises, such as those which take place in regenerative turbine pumps, tend to aggravate this problem. It is known from US Patent 5,310,308 to provide fuel pump comprising a pump housing, a motor mounted within said housing a shaft extending from said motor and having an end rotatable against a shaft stop, an impeller slidably attached to said shaft for rotation therewith, a chamber body mounted within an end of said housing, said chamber body having a bore through which the shaft extends, a chamber body pump channel and a chamber outlet and a chamber cover engaging said chamber body and being held by said housing, the chamber cover defining a chamber cover pump channel and an inlet, the impeller being rotatable within the chamber body pump and chamber cover pump channels. European Patent Application EP-A-0563 957 and German Offenlegungshrift DE-A-3811990 also disclose rotary pumps having rotary members of a similar type. Several designers of diesel fuel systems have recently been attempting to replace mechanical lift pumps with non-regenerative in-tank electric DC fuel pumps, in order to improve fuel handling and extend pump life. These low pressure turbine paddle pumps generally have large cells between individual impeller blades to improve the flow of viscous fuels and minimise pressure to conserve power. It is known from GB-A-2,220,706 to provide a regenerative water pump which can provide a low pressure but high flow rate. The pump has a pump casing having a fluid chamber provided with an inlet and an outlet, an impeller mounted for rotation in the chamber and having a number of radially extending blades which may be straight or curved and may be of a uniform or non-uniform pitch. To provide a constant delivery pressure over a wide range of flows a pressure relief valve is provided. It is an object of the invention to provided a low pressure but high flow pump to supply diesel fuel to a diesel engine while minimising noise and maximising efficiency. According to the invention there is provided a fuel pump comprising a pump housing, a motor mounted within said housing, a shaft extending from said motor and having an end rotatable against a shaft stop, an impeller slidably attached to said shaft for rotation therewith, a chamber body mounted within an end of said housing, said chamber body having a bore through which the shaft extends, a chamber body pump channel and a chamber outlet, and a chamber cover engaging said chamber body and being held by said housing, the chamber cover defining a chamber cover pump channel and an inlet, the impeller being rotatable within the chamber body pump and chamber cover pump channels, the pump chamber channels forming a single working chamber in which the impeller rotates, and the impeller having a central core from which a prime number of vanes extends radially outwardly to define therebetween vane wells used to transport fuel from the inlet to the working chamber and to the outlet from the working chamber, each of the vane wells extending across the entire width of the impeller so as to be in communication with both of the chamber channels wherein the fuel pump is a diesel fuel pump having vanes that are substantially rectangular in profile and are spaced unevenly about a circumference of the core, the chamber cover has a bleed orifice therein and an interlocking lip and key notch for engaging with the chamber body so as to align the two parts in a correct working relationship and at least one pressure relief aperture is formed in the central core to equalize the pressure on each side of the central core. Preferably, the chamber body and said chamber cover may be comprised of phenolic with ten to thirty percent fibreglass fill in which case, the chamber body and said chamber cover may be comprised of phenolic with approximately twenty percent fibreglass fill. Alternatively, the impeller may be comprised of phenolic with ten to thirty percent fibreglass fill and twenty to forty percent granular fill. Preferably, said impeller may be comprised of phenolic with approximately twenty percent fibreglass fill and approximately thirty percent granular fill. Said vanes may be curved in the direction of rotation. In which case, the vanes may be curved to define a vane curve angle of five to twenty degrees between a perpendicular to an outer edge of said vane and a perpendicular to the central core of said impeller. Preferably, said vane curve angle is ten degrees. The chamber body pump channel and the chamber cover pump channel may be of uniform depth. Said unevenly spaced vanes may define a constant swept volume per a quarter of a circumference of said impeller for a particular quartering thereof. The present invention provides a new and improved fuel pump for supplying fuel to a diesel engine. More specifically, the present invention provides improved pumping efficiency by reducing sharp changes in pressure. A primary advantage of this invention is that it reduces cavitation. An additional advantage is that it maintains close tolerances without excessive machining of parts. A further advantage is that it reduces fuel pump noise. The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a fuel pump according to the present invention; Figure 2 is an impeller for a preferred embodiment of a fuel pump according to the present invention; Figure 3 is a cross-section of the impeller shown in Fig.2, Figure 4 is a close-up of an impeller vane for a preferred embodiment of a fuel pump according to the present invention, Figure 5 is a cross-section through pumping chamber having a chamber body and chamber cover for a preferred embodiment of a fuel pump according to the present invention, Figure 6 is an interior view of the chamber cover chamber shown in Figure 5, and Figure 7 is an interior view of the chamber body chamber shown in Figure 5. Referring now to Figure 1, a fuel pump 10 includes a housing 12 for containing a motor 14, preferably a DC electric motor, within a motor space 16. Motor 14 has a shaft 18 extending therefrom in a direction from pump outlet 30 to pump inlet 28. Shaft 18 extends through pump chamber 20. Pump chamber 20 includes a chamber body 22 and a chamber cover 24 with an impeller 26 therebetween. Shaft 18 is preferably keyed to receive impeller 26 and rests against a shaft stop 32 in chamber cover 24. Shaft 18 is rotated by motor 14 and in turn rotates impeller 26 within pump chamber 20. Fuel is received through pump inlet 28 by rotation of impeller 26 and supplied to an engine via a fuel line (not shown) attached to pump outlet 30. Referring now to Figure 2, an impeller 26 for a preferred embodiment of a fuel pump 10 for pumping highly viscous fuels includes a central core 34 having a plurality of vanes 40 on its periphery. A parting line 42, or vane divider, runs between vanes 40 along the edge of central core 34, which is detailed in Figure 3. Vanes 40 have vane wells 62 therebetween for scooping volumes of fuel received through pump inlet 28 and are curved, as detailed further in Figure 4. Continuing with Figure 2, impeller 26 has a keyed centre hole 36 for receiving shaft 18, upon which it free rides. Impeller 26 also has preferably at least one pressure relief hole 38 for permitting a relatively small flow of fuel through the impeller 26 during operation to equalize pressure, which prevents free-riding impeller 26 from tending to ride more towards chamber cover 24. Impeller 26 preferably has a prime number of unevenly spaced vanes 40 to minimise noise by, among other features, reducing the number of harmonic sound waves that can potentially be generated. Note that while a preferred embodiment includes unevenly spaced vanes 40, vane spacing is preferably selected such that the swept volume of each quarter, or ninety angular degrees, of impeller 26 is approximately equal for a particular quartering of impeller 26. This helps keep impeller 26 balanced and operating smoothly with minimal wobble. Continuing with Figure 2, impeller 26 is preferably made of phenolic, a thermoset-type plastic, with approximately twenty percent fibreglass fill and thirty percent granular fill, such as, for example, glass or graphite. Note that while the preferable fibreglass fill is twenty percent, it may range from ten to thirty percent. Also note that while the preferable granular fill is thirty percent it may range from twenty to forty percent. Also note that the combined fibreglass and granular fill percentage should be in the range of forty to sixty percent. For the fundamental impeller material, phenolic is preferred because it is relatively stable and easily moulded to provide close tolerances, and also because it can be cast at higher temperatures. Phenolic has good wear characteristics and can take added fills with ease and success. Fills, such as, for example, fibreglass, glass, and graphite, are preferred to improve fuel pump stability and wear. Referring now to Figure 3, a cross-section of an impeller 26 for a preferred embodiment of the present invention is shown. Central core 34 preferably has a circular central trough 44 on both sides with a raised portion 46 surrounding keyed centre hole 36. Pressure relief holes 38 are preferably cylindrical in shape and provide a channel between sides of impeller 26 for permitting pressure to equalize. Vanes 40 are generally rectangular in profile, with adjacent vanes connected by parting line 42 which extends around the periphery of central core 34. Parting line 42 preferably represents the outermost circumferential extension of central core 34 such that a line perpendicular to impeller surface 48 and running through parting line 42 profile preferably intersects central core edge profile 50 at an angle of approximately six degrees. Angled edge profile 50 is useful for increasing centrifugal force and gaining mini-regenerative turbine pumping characteristics, which may be desirable for specific applications. Referring now to Figure 4, a profile of an individual vane 40 for a preferred embodiment of the present invention reveals vane curvature. Vanes 40 may be straight or curved at an angle . In a preferred embodiment,  is between five and twenty degrees, with ten degrees being preferable. Note that angle  is defined as the angle made by the intersection of a perpendicular to vane outer edge 54 with a perpendicular 56 to central core 34. Curved vanes 40 are preferable because they provide greater pump efficiency. Vanes 40 are generally of greater thickness than those used in, for example, regenerative turbine gasoline fuel pumps, because vanes 40 must move diesel fuel, which is of greater viscosity. For example, in a preferred embodiment with an impeller 26 of 29.63 mm diameter and 5.3 mm height, vanes 40 are nineteen in number and of 1.5 mm thickness. Referring to Figure 5, pump chamber 20 for a preferred embodiment of a fuel pump according to the present invention includes chamber body 22 and chamber cover 24. Chamber body 22 includes a bearing hole 58 through which shaft 18 extends. Impeller 26 (not shown) rotates on shaft 18 within central hollow 66 created by the interlocking of chamber body 22 with chamber cover 24. Chamber cover 24 has an interlocking lip 68 for mating at close tolerances with chamber body 22 to provide a relatively tight seal that need not be machined. Chamber cover 24 includes shaft stop 32 for guiding the rotation of shaft 18 to provide stability. Note that pump channels 70, 72 of chamber body 22 and chamber cover 24 are preferably of constant depth and no ramping is provided, in order to minimise unnecessary increases in fuel pressure. Continuing with Figure 5, chamber body 22 and chamber cover 24 are preferably made of phenolic with twenty percent fibreglass fill to reduce warping during part cooling. Note that while the preferable fibreglass fill is twenty percent, it may range from ten to thirty percent. Also, note that unlike impeller 26, chamber body 22 and cover 24 do not contain granular fill. This is because chamber body 22 is used as a bearing for shaft 18. Chamber cover 24 and chamber body 22 are preferably keyed 74 for proper alignment of pump inlet 28 and chamber outlet 60. Once chamber cover 24 and chamber body 22 have been fitted over impeller 26 and interlocked to create pump chamber 20, pump chamber 20 is placed inside housing 18 against housing stop 64 and held; in place by crimping the housing 18 against pump chamber 20, as shown in Figure 1. Referring now to Figure 6, the interior of chamber cover 24 for a preferred embodiment of the present invention is shown to demonstrate the preferable geometry of the chamber cover pump channel 72. Note that cover pump channel 72 is of constant depth, with no narrowing or incline of the walls throughout and no ramping. These could be utilised, but a preferred embodiment omits them because they are typically used to build pressure and pressure is not desired in the instant situation. Similarly, note that pump inlet 28 preferably has a shortened entrance with no ramping. This is because fuel pump 10 operates on the paddle wheel principle, in which impeller 26 (not shown) scoops liquid fuel from pump inlet 28 and provides it to chamber outlet 60. Vapour bleed orifice 52 is preferably positioned between 170 and 180 angular degrees from pump inlet 28. Vapour bleed orifice 52 is for bleeding fuel vapour out of pump chamber 20 before vapour reaches chamber outlet 60, which is essential for proper operation. Note that because pump cover 24 is preferably made of phenolic with 20% fibreglass fill it has less boundary layer friction when fluid flows over it and serves as a bearing for shaft 18. Chamber cover 24 has a key notch 74 for proper orientation with chamber body 22. Turning finally to Figure 7, the interior of chamber body 22 for a preferred embodiment of the present invention is shown to demonstrate the preferable geometry of the chamber body pump channel 70. Note that chamber body pump channel 70 is of constant depth, with no narrowing or incline of the walls throughout and no ramping. These could be utilised, but a preferred embodiment omits them because they are typically used to build pressure and pressure is not desired in the instant situation. Similarly, note that chamber outlet 60 preferably has a short egress, which may be angled by, for example, forty-five degrees, in order to improve pump efficiency by reducing fuel turbulence.

Claims: A fuel pump comprising: a pump housing (12); a motor (14) mounted within said housing (12); a shaft (18) extending from said motor (14)and having an end rotatable against a shaft stop (32); an impeller (26) slidably attached to said shaft (18) for rotation therewith; a chamber body (22) mounted within an end of said housing (12), said chamber body (22) having a bore (58) through which the shaft (18) extends, a chamber body pump channel (70), and a chamber outlet (60); and a chamber cover (24) engaging said chamber body (22) and being held by said housing (12), the chamber cover (24) defining a chamber cover pump channel (72) and an inlet (28); the impeller (26) being rotatable within the chamber body pump and chamber cover pump channels (70 and 72), the pump chamber channels (70, 72) forming a single working chamber in which the impeller (26) rotates, and the impeller (26) having central core (34) from which a prime number of vanes (40) extends radially outwardly to define therebetween vane wells (62) used to transport fuel from the inlet (28) to the working chamber and to the outlet (60) from the working chamber, each of the vane wells (62) extending across the entire width of the impeller (26) so as to be in communication with both of the chamber channels (70,72), characterised in that the fuel pump is a diesel fuel pump having vanes (40) that are substantially rectangular in profile and are spaced unevenly about a circumference of the core (34), that the chamber cover (24) has a bleed orifice (52) therein and an interlocking lip (68) and key notch for engaging with the chamber body (22) so as to align the two parts in a correct working relationship and that at least one pressure relief aperture (38) is formed in the central core (34) to equalize the pressure on each side of the central core (34). A fuel pump as claimed in Claim 1, wherein said chamber body and said chamber cover are comprised of phenolic with ten to thirty percent fibreglass fill. A fuel pump as claimed in Claim 1 or in Claim 2 wherein said chamber body and said chamber cover are comprised of phenolic with approximately twenty percent fibreglass fill. A fuel pump as claimed in any of Claims 1 to 3 wherein said impeller is comprised of phenolic with ten to thirty percent fibreglass fill and twenty to forty percent granular fill. A fuel pump as claimed in Claim 4, wherein said impeller is comprised of phenolic with approximately twenty percent fibreglass fill and approximately thirty percent granular fill. A fuel pump as claimed in any preceding claim wherein said vanes are curved in the direction of rotation. A fuel pump as claimed in Claim 6, wherein said vanes are curved to define a vane curve angle of five to twenty degrees between a perpendicular to an outer edge of said vane and a perpendicular to the central core of said impeller. A fuel pump as claimed in Claim 6 or 7, wherein said vane curve angle is ten degrees. A fuel pump as claimed in any preceding claim wherein the chamber body pump channel and the chamber cover pump channel are of uniform depth. A fuel pump as claimed in any preceding claim wherein said unevenly spaced vanes define a constant swept volume per a quarter of a circumference of said impeller for a particular quartering thereof.

Inventors: GASTON ROBERT DUANE, YU DEQUAN, GASTON, ROBERT DUANE, YU, DEQUAN
Applicants: FORD MOTOR CO, FORD MOTOR COMPANY
Application year: 1996
Main classification: F04D5
IPC codes: F04D29, F04D5