Claims:We Claim:
1. A fuel pump (10), comprising:
a barrel (20); and
a plunger (30) arranged for reciprocating inside the barrel (20), the plunger (30) comprising a first helical groove (305) for a main fuel injection and a second helical groove (310) for a post fuel injection;
characterized in that:
the first helical groove (305) and the second helical groove (310) being disposed on diametrically opposite sides of the plunger (30).

2. The fuel pump (10) as claimed in claim 1, further comprising a first stop groove (320) and a second stop groove (325) disposed on the plunger (30), the first stop groove (320) being connected to the first helical groove (305) and the second stop groove (325) being connected to the second helical groove (310), the first stop groove (320) and the second stop groove (325) orientated axially and opening into a plunger chamber (330).

3. The fuel pump (10) as claimed in claim 1, wherein a first distance (340) between the first helical groove (305) and an end of the plunger (30) is lesser than a second distance (350) between the second helical groove (310) and the end of the plunger (30), the end of the plunger (30) proximal to a plunger chamber (330).

4. The fuel pump (10) as claimed in claim 1, wherein a pitch of the first helical groove (305) and a pitch of the second helical groove (310) are same.

5. The fuel pump (10) as claimed in claim 1, wherein a pitch of the first helical groove (305) and a pitch of the second helical groove (310) are different.

6. The fuel pump (10) as claimed in claim 1, wherein a helix width of the first helical groove (305) and a helix width of the second helical groove (310) are same.

7. The fuel pump (10) as claimed in claim 1, wherein a helix width of the first helical groove (305) and a helix width of the second helical groove (310) are different.

8. The fuel pump (10) as claimed in claim 1, further comprising a third groove (355) disposed on the plunger (30), the third groove (355) connected to the second helical groove (310) and disposed proximal to an intersection of the second helical groove (310) and the second stop groove (325).

9. The fuel pump (10) as claimed in claim 1, a diameter of a first port (370) disposed in the barrel (20) and arranged for pressure release from a plunger chamber (330) through the first helical groove (305) is lesser than a diameter of a second port (375) disposed in the barrel (20) and arranged for pressure release from the plunger chamber (330) through the second helical groove (310). , Description:FIELD OF THE INVENTION
[0001] The invention relates to a fuel pump for main injection and post injection.

BACKGROUND OF THE INVENTION
[0002] A fuel pump or a fuel injection pump in diesel engines is used to supply fuel to the cylinders of engines at high pressures. The fuel pump primarily has a barrel and a plunger reciprocating inside the barrel for pressurizing the fuel to be delivered to the engine cylinder. The plunger is actuated by a cam, the cam being driven by the engine. As the plunger moves inside the barrel and towards the top dead center, the fuel is pressurized and once the pressure inside the plunger chamber exceeds the threshold pressure to open the nozzle, the fuel is injected. US4881506 discloses a fuel injection pump with a barrel and a plunger adapted to reciprocate inside the barrel. The plunger on the outer surface has a first groove and a second groove for facilitating a main fuel injection and an auxiliary fuel injection.

BRIEF DESCRIPTION OF DRAWINGS
[0003] Embodiments of this disclosure are explained in principle below with reference to the drawings. The drawings are:
[0004] FIGURE 1 illustrates a plan view of a fuel pump comprising a plunger in a barrel;
[0005] FIGURE 2a illustrates a cross-sectional elevation of the barrel and the plunger in a first position;
[0006] FIGURE 2b illustrates a developed view of an outer surface of the plunger in the first position;
[0007] FIGURE 3a illustrates a cross-sectional view of the barrel and the plunger in a second position;
[0008] FIGURE 3b illustrates a developed view of the outer surface of the plunger in the second;
[0009] FIGURE 4a illustrates a cross-sectional view of the barrel and the plunger in a third position;
[00010] FIGURE 4b illustrates a developed view of the outer surface of the plunger in the third position;
[00011] FIGURE 5a illustrates a cross-sectional view of the barrel and the plunger in a fourth position; and
[00012] FIGURE 5b illustrates a developed view of the outer surface of the plunger in the fourth position.

DETAILED DESCRIPTION
[00013] FIGURE 1 illustrates a plan view of a fuel pump 10 comprising a barrel 20 and a plunger 30, the plunger 30 arranged for reciprocating inside the barrel 20. The plunger 30 comprises a first helical groove 305 for a main fuel injection and a second helical groove 310 for a post fuel injection. The first helical groove 305 and the second helical groove 310 are disposed on diametrically opposite sides of the plunger 30. Helical grooves are grooves that are helical and are understood by a person of ordinary skill in the art. In the arrangement illustrated in FIGURE 1, disposing on diametrically opposite sides of the plunger 30 refers to the first helical groove 305 and the second helical groove 310 initiating on diametrically opposite sides of the plunger 30 and proceeding helically around an outer surface 315 of the plunger 30.
[00014] FIGURE 2a illustrates a cross-sectional elevation of the barrel 20 and the plunger 30 in a first position. As illustrated in FIGURE 1 and FIGURE 2a, a first stop groove 320 and a second stop groove 325 are disposed on the plunger 30. The first stop groove 320 is connected to the first helical groove 305 and the second stop groove 325 is connected to the second helical groove 310. The first stop groove 320 and the second stop groove 325 are orientated axially and opens into a plunger chamber 330. Orientated axially refers to the first stop groove 320 and the second stop groove 325 parallel to or collinear to an axis 335 of the plunger 30. The first stop groove 320 and the second stop groove 325 are disposed on an outer surface 315 of the plunger 30. The stop grooves 320 and 325 and the plunger chamber 330 in the context of fuel pumps are understood by a person of ordinary skill in the art.
[00015] FIGURE 2b illustrates a developed view of an outer surface 315 of the plunger 30 in a first position. It is evident from FIGURE 2b that a first distance 340 between the first helical groove 305 and an end 345 of the plunger 30 is lesser than a second distance 350 between the second helical groove 310 and the end 345 of the plunger 30, the end 345 of the plunger 30 proximal to the plunger chamber 330. In other words, the end 345 of the plunger 30 is an end that is proximal to the plunger chamber 330 and in contact with the fuel in the plunger chamber 330. The reference point for measurement of both the first distance 340 and the second distance 350 is a point of start or initiation of the first helical groove 305 and the second helical groove 310 respectively. The reference point for measurement can be any other equivalent point along the first helical groove 305 and the second helical groove 310 as well.
[00016] A pitch of the first helical groove 305 and a pitch of the second helical groove 310 can be same. Alternately, the pitch of the first helical groove 305 and the pitch of the second helical groove 310 can be different. In others words, the pitch of the first helical groove 305 and the pitch of the second helical groove 310 can be equal or unequal. The pitch of the helical groove is understood by a person of ordinary skill in the art. As described earlier with respect to FIGURE 2b, the pitch of the first helical groove 305 is lesser than the pitch of the second helical groove 310. An example of the pitch of the first helical groove 305 can be 30.3° with respect to the end 345 of the plunger 30 and the pitch of the second helical groove 310 can be 37° with respect to the end 345 of the plunger 30.
[00017] A helix width of the first helical groove 305 and a helix width of the second helical groove 310 can be same. Alternately, the helix width of the first helical groove 305 and the helix width of the second helical groove 310 can be different. The helix width is a width of the helical groove as is understood by the person of ordinary skill in the art. An example of the helix width for both the first helical groove 305 and the second helical groove 310 can be 3mm.
[00018] The direction of the first helical groove 305 and the second helical groove 310 is such that the helix in the first helical groove 305 and the second helical groove 310 spiral away from the end 345 of the plunger 30.
[00019] As illustrated in FIGURE 2a and FIGURE 2b the fuel pump further comprises a third groove 355 disposed on the plunger 30, the third groove 355 being connected to the second helical groove 310 and disposed proximal to an intersection of the second helical groove 310 and the second stop groove 325. Moreover, the second helical groove 310 comprises two adjacent sides, a bounded side 360 and an unbounded side 365. As the name depicts, the bounded side 360 is bound by the second helical groove 310 and the second stop groove 325. The unbounded side 365 only has the second helical groove 310 adjacent the same. The third groove 355 is disposed on the bounded side 360. The shape of the third groove 355 is triangular and is connected to the second helical groove 310 in such a way that one side of the third groove 355 is parallel to a surface on the end 345 of the plunger 30.
[00020] As illustrated in FIGURE 2a and FIGURE 2b, the barrel 20 in the fuel pump 10 comprises two ports, a first port 370 or a leak port and a second port 375 or an inlet port. The leak port and the inlet port in this context are understood by the person of ordinary skill in the art.
[00021] A diameter of the first port 370 disposed in the barrel 20 and arranged for pressure release from the plunger chamber 330 through the first helical groove 305 is lesser than a diameter of the second port 375 disposed in the barrel 20 and arranged for pressure release from the plunger chamber 330 through the second helical groove 310. This will be further described hereinafter. As an example, the diameter of the first port 370 can be 0.5mm and the diameter of the second port 375 can be 3mm.
[00022] The working principle of the fuel pump 10 is described below. The description below is in the context of a constant load, so that there is no rotation of the plunger about the axis 335. As described earlier, FIGURE 2a and FIGURE 2b illustrate views of the barrel 20 and plunger 30 in the first position. In the first position, the first port 370 and the second port 375 are fully open and fuel flows into the plunger chamber 330 through the second port 375.
[00023] FIGURE 3a illustrates a cross-sectional view of the barrel 20 and the plunger 30 in a second position. FIGURE 3b illustrates a developed view of the outer surface 315 of the plunger 30 in the second position. In the second position, the cam activates the plunger 30 and the plunger 30 moves towards the top dead center, thereby compressing and pressurizing the fuel. The moving plunger closes both the first port 370 and the second port 375, thereby preventing any movement of fuel through the first port 370 and the second port 375. As the plunger 30 moves further towards the top dead center and reaches the pressure that opens the nozzle, the pressurized fuel is dispensed through the nozzle.
[00024] FIGURE 4a illustrates a cross-sectional view of the barrel 20 and the plunger 30 in a third position. FIGURE 4b illustrates a developed view of the outer surface 315 of the plunger 30 in the third position. With the plunger 30 moving towards the top dead center, it is evident from FIGUREs 4a and 4b that the first helical groove 305 is aligned with the first port 370, thereby creating a pressure release path for the plunger chamber 330. The pressurized fuel flows from the plunger chamber 330 through the first stop groove 320 and the first helical groove 305 into the first port 370. The pressure reduces in the pressure chamber 330 to less than what is required to open the nozzle and therefore the main injection stops. The plunger 30 continues to travel towards the top dead center, being still actuated by the cam.
[00025] FIGURE 5a illustrates a cross-sectional view of the barrel 20 and the plunger 30 in a fourth position. FIGURE 5b illustrates a developed view of the outer surface 315 of the plunger 30 in the fourth position. In this position, the plunger 30 has moved further towards the top dead center from the third position. In the process of moving from the third position to the fourth position, the fuel is compressed and pressurized in the plunger chamber 330. When the pressure of the fuel in the plunger chamber 330 crosses the threshold pressure for opening the nozzle, the nozzle opens and dispenses pressurized fuel into the cylinder in what is called post-injection. As the plunger 30 moves still further towards the top dead center, the fourth position as mentioned above is reached in which the second port 375 is aligned with the second helical groove 310, which creates a pressure release path for the plunger chamber 330. The pressurized fuel flows from the plunger chamber 330 through the second stop groove 325 and the second helical groove 310 into the second port 375. The pressure reduces in the pressure chamber 330 to less than what is required to open the nozzle and therefore the post-injection stops. The plunger 30 subsequently carries on with the next cycle.
[00026] The main injection and post injection is achieved in the same stroke of the plunger 30. An advantage of having the first helical groove 305 and the second helical groove 310 on diametrically opposite sides of the plunger 30 is improved ease in manufacturability.
[00027] The plunger 30 also can be rotated on the axis 335 of the plunger 30. The rotation of the plunger 30 for varying engine load conditions effecting varying quantity of fuel dispensed to the engine cylinder is understood by the person of ordinary skill in the art. As the plunger rotates, the angular orientation of both the first helical groove 305 and the second helical groove 310 change simultaneously, thereby changing the angular position at which the first helical groove 305 and the second helical groove 310 align with the first port 370 and the second port 375 respectively. For example, at low engine loads, the first helical groove 305 and the second helical groove 310 align with the first port 370 and the second port 375 adjacent the intersection of the helical grooves with their associated stop grooves. At medium loads, the first helical groove 305 and the second helical groove 310 align with the first port 370 and the second port 375 near a middle portion of the helical grooves.
[00028] A greater value of the pitch of the helical groove in the context of fuel pumps leads to a longer injection time and thereby more quantity of fuel injected into the cylinder, due to the fact that the plunger moves towards the top dead center for a longer time before pressure is released through the helical groove, in comparison with a helical groove of a smaller pitch. In the example shown in FIGURE 2b, in comparison to post injection from a second helical groove having the same pitch as the first helical groove, a greater pitch for the second helical groove 310 results in a relatively longer injection time and consequently a greater amount of fuel injected for the post injection.
[00029] A greater helix width of the helical groove in the context of fuel pumps leads to a faster pressure release from the plunger chamber, because a greater width allows more pressurized fuel to flow and to be released per unit time. A greater helix width of the helical groove also allows the associated port to be aligned with the helical groove for a longer time than a helical groove of a smaller or narrower helix width, leading to a longer pressure release time.
[00030] The third groove 355, also referred to as a start limiting groove is for limiting the post injection in lesser engine loads, which is described below. The structural arrangement of the third groove 355 is such that, the second port 375 encounters and aligns with the third groove 355 before the second helical groove 310, when the plunger is moving towards the top dead center. Therefore, even before the pressure in the plunger chamber 330 crosses the threshold pressure for nozzle opening and post injection, the pressure in the plunger chamber 330 is released as the second port 375 aligns with the third groove 355 and forms a pressure release path. As can be seen from FIGURE 2b, the third groove 355 is disposed proximal to the second stop groove 325 and distal from an end of the second helical groove 310, such that the second port 375 encounters the third groove 355 only during lower engine loads. Hence, for medium and higher engine loads, the third groove 355 is not involved in the pressure release.
[00031] The advantage of having the first port 370 being smaller than the second port 375 is that, a smaller port controls or restricts the pressure release, thereby not completely emptying the plunger chamber 330 of fuel. This helps retain some fuel for the post-injection.
[00032] It is to be understood that the foregoing description is intended to be purely illustrative of the principles of the disclosed techniques, rather than exhaustive thereof, and that changes and variations will be apparent to those skilled in the art, and that the present invention is not intended to be limited other than as expressly set forth in the following claims.