Claims:We Claim:
1. A fuel injection pump (10) comprising:
a housing (12);
a fuel inlet (14) defined in said housing (12);
a pressure chamber (16) formed in a barrel, said pressure chamber in fluid communication with said fuel inlet (14);
a piston (20) disposed in said barrel (18) and adapted to pressurize fuel in said pressure chamber (16);
characterized in that:
said fuel inlet (14) comprises two cylindrical portions (23, 24) having a frusto-conical portion (26) there in between of said two cylindrical portions (23, 24).
2. The fuel injection pump (10) as claimed in claim 1, wherein a first said cylindrical portion (23) is larger than a second said cylindrical portion (24).

3. The fuel injection pump (10) as claimed in claim 1, wherein a residual fuel from said pressure chamber (16) flows into said second cylindrical portion (24) and then into said frusto-conical portion (26) of said fuel inlet (14).
4. The fuel injection pump (10) as claimed in claim 3, wherein a pressure of said residual fuel flowing into said frusto-conical portion (26) of said fuel inlet (14), is reduced due to a wider diameter of said frusto-conical portion (26).
5. The fuel injection pump (10) as claimed in claim 4, wherein said residual fuel exits into said first cylindrical portion (23) of said fuel inlet (14), from said frusto-conical portion (26) with a reduced pressure.
6. The fuel injection pump (10) as claimed in claim 1, further comprises a screw (28) positioned on said housing (12), in connection with said first cylindrical portion (23) of said fuel inlet (14).
7. The fuel injection pump (10) as claimed in claim 6, wherein said residual fuel with reduced pressure, encounters a surface of said screw (28) of said housing (12) while flowing back into a fuel tank via said fuel inlet (14).
, Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[0001] This invention relates to a fuel injection pump.

Background of the invention
[0002] A fuel injection pump is used to deliver pressurized fuel to an injector/ rail. The fuel injection pump comprises a housing with multiple flow passages within the housing. These passages serve to bring fuel into the fuel injection pump and to direct fuel out of the fuel injection pump. The flow passages are created by drilling through the housing of the fuel injection pump. Upon creation of the flow passages, the openings present at the housing of the fuel injection pump are sealed. Existing inlet port design of a barrel of the pump has a diverging taper and this makes the return fluid flow to diverge. The residual fuel flowing out of the pump will be at high pressure and the flow of the pressurized fuel causes the erosion of the housing. A baffle screw is placed in the front of the fluid stream to avoid the housing erosion. The cost of the baffle screw is high and an arrangement to avoid the usage of the baffle screw is required.

[0003] Prior art patent application US5248223 discloses a centrifugal fuel pump with a baffle disposed between a fuel inlet and an impeller of the pump. The baffle overlies the inlet opening and substantially prevents the impeller from producing a backflow of fuel through the inlet. The baffle also directs incoming fuel into a generally circumferential flow into the channel of the pump through which fuel is moved and its pressure increased by the rotating impeller. This improves the efficiency and maximum capacity of the pump.
Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[0005] FIG. 1 illustrates a fuel injection pump in accordance to one embodiment of the invention.

Detailed description of the embodiments
[0006] FIG. 1 illustrates a fuel injection pump 10 in accordance with one embodiment of the invention. The pump 10 comprises a housing 12 and a fuel inlet 14 defined in the housing 12. The pump 10 comprises a pressure chamber 16 formed in a barrel 18. The pressure chamber 16 is in fluid communication with the fuel inlet 14. The pump 10 comprises a piston 20 disposed in the barrel 18 and the piston 20 pressurizes the fuel in the pressure chamber 16. The fuel inlet 14 of the pump 10 comprises two cylindrical portions having a frusto-conical portion 26 there in between of the two cylindrical portions (23, 24).

[0007] Further the construction of the pump 10 and the components of the pump 10 is explained as follows. The fuel inlet 14 opens into the pressure chamber 16 of the pump 10. The fuel inlet 14 as disclosed above comprises a first cylindrical portion 23 and a second cylindrical portion 24. The first cylindrical portion 23 is larger than the second cylindrical portion 24. The first cylindrical portion 23 is in fluid connection with the housing 12 of the injection pump 10, whereas the second cylindrical portion 24 is in fluid communication with the pressure chamber 16. A frusto- conical portion 26, which is made between the first and second cylindrical portions (23,24), has a wider diameter at one end than at an apex of the conical portion 26, which is known to a person skilled in the art.

The fuel flows from the first cylindrical portion 23 into the frusto-conical portion 26 and then into the second cylindrical portion 24 before entering the pumping chamber 16. The piston 20 in the barrel 18 is operated with a cam (not shown) connected at one end of the piston. The cam moves the piston 20 in the barrel 18 from a bottom dead center point to a top dead center point. The fuel injection pump 10 further comprises an outlet 30 through which the pressurized fuel in the pressure chamber 16 is pumped into an injector. The fuel injection pump 10 further comprises a screw 28 positioned on the housing 12, in connection with the first cylindrical portion 23 of the fuel inlet 14. According to one embodiment, the screw 28 is made as a separated component and is assembled into the housing 12.

A method of working of above disclosed fuel injection pump 10 is explained as follows. The fuel from the fuel inlet 14 flows into the pressure chamber 16 of the pump 10 from a fuel tank. The cam operates the piston 20 present in the barrel 18 to pressurize the fuel in the pressure chamber 16. The piston 20 moves from the bottom dead center to the top dead center and due to the movement of the piston 20 in the barrel 18, the fuel is pressurized and is pumped into the fuel injector. For instance, if 5mm of fuel is pressurized in the pressure chamber 16, then a 3mm of fuel is pumped into the fuel injector via the outlet 30 .The remaining 2mm fuel remains in the pressure chamber 16. The remaining fuel present in the pressure chamber 16 is called residual fuel. The residual fuel present in the pressure chamber 16 will have a high-pressure value. The pressurized residual fuel will have a pressure of approximately 600bar.

When the residual fuel flows back into the tank via the fuel inlet 14, it encounters a portion of the housing 12 (with the screw 28). The residual fuel from the pressure chamber 16 flows into the second cylindrical portion 24 of the fuel inlet 14 and then into the frusto-conical portion 26. Due to the wider diameter of the frusto-conical portion 26, the pressure of the residual fuel is reduced. The residual fuel from the frusto-conical portion 26 exits into the first cylindrical portion 23. The pressure of the residual fuel while entering the first cylindrical portion 23 will be reduced due to the wider diameter of the frusto-conical portion 26. The pressure of the residual fuel will be reduced from 600 bar to approximately 450bar. The residual fuel with the reduced pressure flows towards the screw 28 of the housing 12 and from there back into the tank. The screw 28 of the housing 12 withstands the reduced pressure of the residual fuel while flowing back into the fuel tank.

With the above disclosed fuel injection pump, the pressure of the residual fuel is reduced with an additional cylindrical portion (first cylindrical portion 23) and a larger frusto-conical portion 26. The erosion of the housing 12 due to the flow of the high-pressure residual fuel is reduced. The usage of a baffle screw at the connection point of the fuel inlet 14 and the housing 12 is avoided, as the baffle screw is expensive when compared to the screw 28 that is disclosed in the invention.

[0008] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.