CLIAMS:We Claim

1 A fuel pump comprising:
a plunger with a vertical groove extending from head of said plunger and in communication with a helix in said plunger and operable to block a spill port at start of fuel injection and unblock said spill port at end of said fuel injection;
characterized in that
a circular groove provided along circumference, of said head, of said plunger, wherein said circular groove adapted to advance fuel injection timing at full load engine operating conditions; and
a step groove provided at said head, of said plunger, adjacent to said vertical groove, wherein said step groove is adapted to retard fuel injection timing during part-load and no-load engine operating conditions.

2 The fuel pump as claimed in claim 1, wherein said plunger is rotated using a control rack.

3 The fuel pump as claimed in claim 2, wherein said control rack rotates said plunger, at full load engine operating conditions, such that said circular groove is enabled to advance fuel injection timing.

4 The fuel pump as claimed in claim 2, wherein said control rack rotates said plunger, at said part-load and no-load engine operating conditions, such that said step groove is enabled to retard fuel injection timing.

5 The fuel pump as claimed in claim 1, wherein depth of said step groove is larger than the depth of said circular groove.
,TagSPECI:Field of the invention
[001] This invention relates to a fuel pump.

Background of the invention
[002] In high pressure fuel pumps, use of a circular groove that is generally located at head of a plunger is used to advance and retard fuel injection timing. At full load, higher engine rpm is desired. To obtain such higher engine rpm, combustion of the fuel in the engine may be advanced. For obtaining such advanced combustion, advance of fuel injection timing is required. At higher engine rpm, start of fuel injection occurs when top edge of the circular groove reaches inlet port of the barrel, thereby advance fuel injection timing is obtained. However, at lower engine rpm, start of fuel injection occurs until lower edge of the circular groove reaches inlet port of the barrel. Additional time is required for the lower edge to reach the inlet port, thereby the fuel injection timing is considered to be retarded. Retardation of fuel injection timing enables reduced Nox emissions. Hence circular grooves are used for either advancing or retarding the fuel injection timing based on engine speed.

[003] At part-load and no-load engine operating condition, lower engine rpm is desired. At lower engine rpm, combustion, of the fuel, in the engine may be retarded, thereby fuel injection timing may also be retarded. A low load retard (LLR) groove may be used for retarding the fuel injection timing at part-load and no-load engine operating conditions. Hence, the LLR groove is generally used for retarding the fuel injection timing based on load of the engine.

[004] Presence of a circular groove in the plunger enables control of fuel injection timing based on engine speed and presence of the LLR groove enables control of fuel injection timing based on load of the engine. However, there is still a need for a technique to control fuel injection timing based on both speed and load for obtaining increased specific fuel consumption and reduction of Nox emissions.

Brief description of the accompanying drawings
[005] Figure 1 illustrates a plunger in a fuel pump, in accordance with one embodiment.

Detailed description
[006] Figure 1 illustrates a plunger 100 in a fuel pump, in accordance with one embodiment.

[007] The plunger 100 includes a vertical groove 115 extending downwards from head of the plunger. The vertical groove is also in communication with a helix 120 that is included in the plunger 100. The vertical groove 115 in combination with a helix 120 is used to block a spill port at start of fuel injection and to unblock the spill port at end of said fuel injection.

[008] The plunger 100 is characterized by a circular groove 105 along circumference, of the head, of the plunger. The circular groove 105 is adapted to advance fuel injection timing at high speed engine operating conditions.

[009] The plunger 100 is also characterized by a step groove 110 on the head of the plunger 100 adjacent to the vertical groove 115. The step groove 110 is adapted to retard fuel injection timing during part-load and no-load engine operating conditions.

[0010] Conventionally, the plunger 100 is housed within a barrel of the fuel pump and is driven by a CAM. The fuel is compressed within the barrel by movement of the plunger 100 in vertical direction from the bottom dead centre (BDC) towards top dead centre (TDC). Movement of the plunger 100 from the BDC towards the TDC causes closure of an input port of the barrel. Distance travelled by the plunger 100 from the BDC upto the closure of the input port is called as pre-stroke. Delivery of the fuel begins upon such closure of the input port. The delivery of the fuel into a high pressure line is called as effective stroke.

[0011] End of the effective stroke defines end of fuel injection. The end of fuel injection is achieved when the helix 120 unblocks the spill port in the barrel. Unblocking of the spill port, by the helix 120, causes drop in pressure of the fuel. Further, the low pressure fuel flows from the vertical groove 115 along the helix 120 and thereby to the spill port.

[0012] The end of fuel injection is controlled by a control rack 125. The control rack 125 enables rotation of the plunger 100 such that the helix 120 unblocks the spill port. Rotation of the plunger 100, by the control rack 125, is achieved using a rack and pinion mechanism.

[0013] Time instant at which the closure of the input port occurs is referred to as fuel injection timing. The fuel injection timing can be advanced or retarded based on the engine operating conditions. The circular groove 105 and the step groove 110 provided in the plunger 100 are used for obtaining such advanced or retarded fuel injection timing.

[0014] As shown in Figure 1, the circular groove 105, of specific depth and width provided along circumference of the head of the plunger 100, enables advance of the fuel injection timing at full load engine operating conditions. The circular groove 105 defines a circular surface of smaller diameter with respect to the diameter of the plunger. The depth of the circular groove 105 is referred to as the extent to which the circular groove 105 extends from head of the plunger 100. The width of the plunger is based on the diameter of the circular surface. At full load engine operating conditions, high engine speed is required. During such high engine speed, the fuel injection timing is required to be advanced to obtain advanced combustion. Working principle of the circular groove 105 to achieve advanced fuel injection timing at high speed engine operating conditions is explained as below.

[0015] At high speed engine operating conditions, speed of the plunger moving towards the TDC is also high. Due to high speed of the plunger, leakage of fuel through the circular groove 105 is negligible because the fuel acts as a solid layer around the circular groove 105 and also due to high speed of the plunger 100 the time available for the leakage is small. Due to such effect, the input port is considered to be closed when the top edge, of the circular groove 105, reaches the input port before the bottom edge, of the circular groove 105, could reach the input port. Closure of the input port results in delivery of the fuel into the high pressure line. Hence, the circular groove 105 is considered to advance the fuel injection timing at high speed engine operating conditions.

[0016] Advancing the fuel injection ensures increased specific fuel consumption because combustion in the engine is advanced and such advanced combustion results in increased power.

[0017] During part-load and no-load engine operating conditions, the engine speed is lower. During lower engine speed, the fuel injection timing is required to be retarded. The step groove 110 is used for obtaining such retardation of the fuel injection timing. The step groove 110 of a specific depth and width is provided at the head of the plunger on the circular surface and is adjacent to the vertical groove. The depth of the step groove 110 is referred to as an extent to which the step groove 110 extends from the head of the plunger 110. Width of the step groove 110 is referred to as an extent to which the step groove 110 is made on the circular surface.

[0018] Retardation of the fuel injection timing using a step groove 110 is achieved when a control rack 125 rotates the plunger such that step groove 110 closes the input port during the part-load and no-load engine operating conditions. Working principle of the step groove 110 to achieve retarded fuel injection timing at part-load and no-load engine operating conditions is explained in detail as below.

[0019] At part-load and no-load engine operating conditions, the control rack 125 rotates the plunger appropriately such that the step groove 110 ensures closure of the input port. As the plunger moves towards the TDC, the input port is considered to be closed only when bottom edge of the step groove 110 reaches the input port as the top edge of a specific width is cut, thereby causing a delay in the fuel injection timing. Such delay is also referred to as retarded fuel injection timing with respect to the fuel injection timing during full load engine operating condition. The delay depends on depth and width of the step groove 110. Increased depth and width of the step groove results in increased delay of the fuel injection timing. Therefore, the depth and width of the step groove 110 may be designed based on the required delay of the fuel injection timing.

[0020] At part-load and no-load engine operating conditions, Nox emissions are higher. Therefore by retarding the fuel injection timing combustion of the fuel is retarded. Hence Nox formation is delayed. Also retardation of the fuel injection timing during the part-load and no-load engine operating conditions ensures the fuel, in the engine, is given sufficient time to burn completely thereby reducing Nox emissions.

[0021] Existence of the circular groove 105 and the step groove 110 on a single plunger enables advancement or retardation of the fuel injection timing based on engine speed and engine load. Such advancement or retardation based on engine operating conditions ensures reduced Nox emission, shortened ignition lag, improved cold startability and increased SFC.

[0022] It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to depth and width of the circular groove and the step groove are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.