Claims:We Claim:
1. A fuel pumping system (10) for an engine, said system (10) comprising:
- a housing (12) comprising at least one movable plunger (14) in a barrel (16) to pressurize fuel;
- a control rod (18) positioned in contact with said at least one movable plunger (14) in said barrel (16);
- a cap (20) to close an exposed end of said control rod (18) on said housing (12);
characterized in that:
- said control rod (18) comprising at least one cut-section (22) and a cavity (24) with a threaded inner surface; and
- a limiting screw (26) fitted into said cavity (24),
a rotation of said limiting screw (26) inside said cavity (24) of said control rod (18) linearly moves said control rod (18) to regulate a flow of fuel from said fuel pumping system (10).

2. The fuel pumping system (10) as claimed in claim 1, wherein said limiting screw (26) comprises a head portion (28), an intermediate portion (30) and a tail portion (32), said intermediate portion (30) comprises at least one cut-section (34) corresponding to said at least one cut-section (22) of said control rod (18).

3. The fuel pumping system (10) as claimed in claim 1, wherein said tail portion (32) comprises a threaded surface corresponding to said inner threaded surface of said control rod (18).

4. The fuel pumping system (10) as claimed in claim 1, wherein a position of said control rod (18) in said housing (12) is varied by rotation of said limiting screw (26), based on an amount of fuel to be injected during a start of said engine.

5. The fuel pumping system (10) as claimed in claim 1, wherein a position of said control rod (18) in said housing (12) is controlled by an actuating means (36).

6. The fuel pumping system (10) as claimed in claim 1, wherein a space is formed between said head portion (28) of said limiting screw (26) and said cap (20), when said at least one cut-section (34) of said intermediate portion (30) is locked into at least one cut-section (22) of said control rod (18).

7. A limiting screw (26) in a fuel pumping system (10), said limiting screw (26) comprising :
- a head portion (28);
- an intermediate portion (30) comprising at least one cut-section (34); and
- a tail portion (32) comprising a threaded surface,
said head portion (28) has a wider area than said intermediate portion (30) and said tail portion (32).

8. The limiting screw (26) as claimed in claim 1, wherein said head portion (28) comprises a cut-section (40) to accommodate a fitting tool during assembly of said limiting screw (26).

9. The limiting screw (26) as claimed in claim 1, wherein said intermediate portion (30) has wider area than said tail portion (32).
, 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 pumping system for an engine. More precisely, the invention is related to a limiting screw for the fuel pumping system.

Background of the invention
[0002] In conventional pumps with governing units, the control rod is designed to travel up to the max delivery position during starting of the engine. However, the start quantity, if too high, needs to be reduced by limiting the travel of the control rod to a suitable position. The control rod travel limitation at starting condition is achieved by adding a spring washer and a combination of shims of 0.3 mm, 0.5 mm and 1 mm. The number of shims define the limitation of the control rod and thereby reducing the start quantity to the required value.

[0003] A Prior art document US3620199 discloses a centrifugal governor for setting the fuel quantity control member of a fuel injection pump, there is provided an abutment for limiting the displacement of the member. The abutment is adjustable both linearly along the member and angularly to vary the orientation of a curved abutment edge cooperating with a follower nose connected to the fuel quantity control member.

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 pumping system for an engine, in accordance with an embodiment of the invention; and
[0006] Fig.2 illustrates a limiting screw for a fuel pumping system, in accordance with an embodiment of the invention.

Detailed description of the embodiments
[0007] Fig.1 illustrates a fuel pumping system 10 for an engine, in accordance with one embodiment of the invention. The system 10 comprises a housing 12 comprising at least one movable plunger 14 in a respective barrel 16 to pressurize fuel, and a control rod 18 positioned in contact with the at least one movable plunger 14. The system 10 further comprises a cap 20 fitted in proximity to the control rod 18 on the housing 12. The cap 20 closes the exposed end of the control rod 18. The system is characterized by, the control rod 18 comprises at least one cut-section 22 and a cavity 24 with a threaded inner surface. The system 10 further comprises a limiting screw 26 fitted into the cavity 24. A rotation of the limiting screw 26 inside the cavity 24 of the control rod 18 restricts the maximum travel of the control rod 18 linearly to regulate a flow of fuel from the fuel pumping system 10.

[0008] Further, the construction of the fuel pumping system 10 and the components of the system 10 and their working is explained in detail. The fuel pumping system 10 comprise a fuel pump 38 to pump the fuel from a fuel tank 44 into an engine (not shown) through respective fuel injector (not shown). The fuel pump 38 comprises plungers 14 corresponding to the number of cylinders of the engine. The control rod 18 extends from a governing unit 42 into the fuel pump 38 and is positioned in contact with all the plungers 14 of the fuel pump 38. The linear movement of the control rod 18 by a mechanical arrangement in the governing unit 42 is translated to rotation of the plunger 14 (by rack and pinion mechanism), thus the orientation of the plunger 14 is varied.

[0009] Each of the plunger 14 of the fuel pump 38 comprises a helix cut-section The assembly of plunger and barrel together is known as element. The fuel from the gallery in the housing enters the element by an inlet hole in the barrel, gets pressurized by the plunger during its lift and is pumped out to the engine. The fuel is metered during the lift of the plunger 14, by the helix. The plunger 14 is enclosed in the barrel 16. The barrel 16 comprises an inlet and an outlet, through which the fuel is made to pass in and out of the plunger 14. Further explanation of the construction and the working of the plunger 14 in the pump 38 is limited, as the concept is well known in the state of the art. The Control Rod Position, (CRP) determines the fuel pumped out of the fuel pump 38. Higher the CRP, higher the quantity pumped out of the fuel pump 38. The control rod 18 of the fuel pumping system 10 comprises at least one cut-section 22 made as shown in the figure 1.

[0010] Figure 2 illustrates a limiting screw 26 for a fuel pumping system 10 in accordance to one embodiment of the invention. The limiting screw 26 comprises a head portion 28, an intermediate portion 30 and a tail portion 32. The head portion 28 is wider in area than the intermediate portion 30 and the tail portion 32. The intermediate portion 30 is wider in area than the tail portion 32. The head portion 28 comprises a cut-section 40 to accommodate a fitting tool to fit/screw the limiting screw 26 into the cavity 24 of the control rod 18. The fitting tool can be any of the tools like spanner, screw driver that is used to rotate and screw the limiting screw 26 into the cavity 24 as known to a person skilled in the art. According to one embodiment of the invention, the intermediate portion 30 has a regular polygonal shape with even number of sides, wherein the polygonal shape is chosen from a group of shapes comprising a square shape, a hexagonal shape and the like.

[0011] According to one embodiment of the invention, the tail portion 32 is in a cylindrical shape. However, the shape of the tail portion 32 is not restricted to the cylindrical shape, but can also be a spherical, a conical shape or the like. The intermediate portion 30 comprises at least one cut-section 34 corresponding to at least one cut-section 22 of the control rod 18. The cut-section 34 of the limiting screw 26 locks intermittently into the corresponding cut-section 22 of the control rod 18, when the limiting screw 26 is progressively screwed into the control rod cavity 24. The tail portion 32 comprises a threaded surface corresponding to the inner threaded surface of the control rod 18. The dimensions of the inner threaded surface of the control rod 18 is similar to the dimensions of the threaded surface of the limiting screw 26.

[0012] Based on a requirement from a manufacturer of the engine, the positon of the limiting screw 26 inside the control rod 18 is varied, thus altering a positon of the control rod 18. The alteration in the position of the control rod 18 changes the position of plunger(s) 14 of the fuel pump 38 in the barrel 16, thus the amount of fuel pumped from the plunger 14 is varied. One end of the control rod 18 is connected to a spring of the governing unit 42, such that, the expansion or contraction of the spring in the governing unit 42 moves the control rod 18 linearly. The movement of the control rod 18 rotates the plunger 14 of the fuel pump 38, thus varying the amount of fuel pumped. The limiting screw 26 present on the other end of the control rod 18 is fitted into the cavity 24 of the control rod 18 using any one of the fitting tool as mentioned above. For a square cross section 34, for every quarter turn of the limiting screw 26, restriction of position of the control rod 18 by the cap 20 is varied which is heard/felt as a click. For instance, for every quarter turn of the limiting screw 26, a 0.25mm in restriction of the control rod 18 position is changed (considering thread pitch of 1mm).

[0013] For different positions of the limiting screw 26 inside the control rod 18, the restriction for the maximum CRP is changed. If the space formed between the control rod 18 and the head portion 28 of the limiting screw 26 is minimum, then position of the control rod 18 is such that a maximum amount of fuel is pumped out from the fuel pump 38. The limiting screw 26 can be progressively screwed-in in steps of quarter turns (for a square cross-section 34) such that the position of the control rod 18 is changed such that the fuel pumped out from the fuel pump 38 is progressively reduced with every quarter turn of the limiting screw 26. In one position of the limiting screw 26 inside the control rod 18, a space is formed between the cut-section 22 of the control rod 18 and the cut-section 34 of the limiting screw 26 (intermediate portion 30), such that, a limited amount of fuel is pumped into the plunger 14 of the fuel pump 38. In another position of the limiting screw 26 inside the control rod 18, a space is formed between the head portion 28 of the limiting screw 26 and the cap 20 , such that, a maximum amount of fuel is made to flow into the plunger 14 of the fuel pump 38. In this position, the cut-section 34 of the limiting screw 26 is locked into the cut-section 22 of the control rod 18. The spring (not shown) connected to the control rod 18, moves the control rod 18 towards the cap 20 for the maximum possible amount of fuel to be pumped out from the fuel pump 38 during the start of the engine. The maximum possible amount of fuel pumped out by the fuel pump 38 is determined by the position of the control rod 18 during the start of the engine.

[0014] For instance, the above arrangement (cap 20 and the assembly of the control rod 18 with the limiting screw 26 in contact with each other) is useful in cold regions, where a large amount of fuel is required to start the engine. However, as mentioned earlier, for every quarter turn of the limiting screw 26 in the control rod 18, the position of the control rod 18 is varied, thus varying the position of the plunger 14 and the amount of fuel pumped out of the fuel pump 38. Depending on the requirement from the manufacturer, the position of the limiting screw 26 is set into the control rod 18, such that , the required amount of fuel is pumped out during the start of the engine, the limiting screw 26 is fitted into the control rod 18. The fitting of the limiting screw 26 into the control rod 18 is done during the calibration process.

[0015] According to one embodiment of the invention, the position of the limiting screw 26 inside the control rod 18 is varied dynamically using an actuating means (not shown). The actuating means is positioned in the housing 12 of the fuel pump 38 or in proximity to the limiting screw 26 in the place of the cap 20 on the housing 12. The actuating means varies the position of the limiting screw 26 (by rotating the limiting screw 26 into the cavity 24 of the control rod 18) based on the amount of fuel required during the start of the engine.

[0016] According to one embodiment of the invention, a control unit (not shown) electronically controls the limiting screw 26 dynamically. Based on the atmospheric temperature received either from an external source like (cloud server) via a communication means or by detecting the surrounding temperature using a sensing element, the amount of fuel during the start of the vehicle is determined. Based on a current position of the limiting screw 26 and the control rod 18, the control unit alters the position of the limiting screw 26 inside the control rod 18, thus varying the position of the control rod 18 and the plunger 14 that is in contact with the control rod 18. By this, the required amount of fuel is varied flowing from the fuel pump 38.

[0017] With the above limiting screw 26 of the fuel pumping system 10, the fuel flow setting for the starting of the engine is controlled effectively. The usage of multiple shims (shims are like thin metal washers) between the control rod 18 and the cap 20 as in the conventional pump is eliminated. In the case of shims, repeated assembly and disassembly of shims for the fuel flow setting by trial and error to achieve the required fuel flow, which is tedious and time consuming. The position of limiting screw 26 into the control rod 18 is set based on the requirement of the amount of fuel to be pumped during the starting of the engine. The limiting screw 26 is set into the control rod 18 with much ease and with less human intervention. The number of turns/clicks is predefined in the calibration instruction such that the required amount of fuel for starting the engine can be set.

[0018] 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.