Claims:We claim:

1. A pump (100) for fuel injection systems, said pump (100) comprising :
- a pump bore (102) forming a pump chamber (110) at one end,
- a plunger (104) moving inside said pump bore (102),
- a top helix (116) cut out at the top portion of the plunger (104) on the circumferential surface
- a balancer groove (200) on the surface of the plunger (104)
- an inlet port (108) to draw fuel into the pump chamber (110)
- a delivery valve to deliver pressurized fuel from pump chamber (110)
- a spill port (112) to return excess fuel to a fuel tank;
said pump characterized by
- a ground grove (118) on the circumference of the plunger (104).

2. The fuel injection pump (100) according to claim 1 wherein said ground groove (200) is along the complete circumference of the plunger (104)
3. The fuel injection pump according to claim 1 wherein said ground groove (200) is along the partial circumference of the plunger (104)
4. The fuel injection pump according to claim 1 wherein said ground groove (200) is along the circumference of the plunger (104) in a perpendicular axis compared to the direction of motion of the plunger (104)
5. The fuel injection pump according to claim 1 wherein said ground groove (200) is along the circumference of the plunger 104 in a slanted axis compared to the direction of motion of the plunger (104)
6. A fuel injection system 400, said fuel injection system comprising a pump 100, an electronic injector 406 and an ECU (304);
said pump comprising
- a pump bore 102 forming a pump chamber (110) at one end,
- a plunger104 moving inside said pump bore (102),
- a top helix (116) cut out at the top portion of the plunger (104) on the circumferential surface
- a balancer groove (200) on the surface of the plunger (104)
- an inlet port (108) to draw fuel into the pump chamber (110)
- a delivery valve to deliver pressurized fuel from pump chamber (110)
- a spill port (112) to return excess fuel to a fuel tank
- a ground grove (118) around the circumference of the plunger (104)
7. A fuel injection system 400 according to claim 1 wherein the electronic injector (406) is controlled by said ECU (408)
, Description:Field of the invention:
[0001] This invention relates to the field of fuel injection pump in general. The invention is related to a pump with helix for control of fuel delivery to an injector.

Background of the invention:
[0002] Fuel pumps with a helix for control of fuel delivery are known in prior arts. The helix on the outer surface or the sleeve of the plunger are commonly known. This helix will decide the duration of the pressurizing of the fuel in the pump chamber. In mechanical pups, the piston rotates based on the load of the engine. The rotation of the plunger results in varied timings for the opening and/or closing of the spill port of the pump, thereby varying the duration of the pressurization of the fuel in the pump chamber.
[0003] The US patent US4824341 discloses a helix controlled fuel pump. The invention discloses a pump having a recess in the pump cylinder connecting the pump working space and the fuel bore hole by a peripheral groove for generating a pre-injection and a post injection.

Brief description of the accompanying drawings:
[0004] An embodiment of the disclosure is described with reference to the following accompanying drawing,
[0005] Fig. 1 illustrates a fuel pump with a ground groove on the plunger
[0006] Fig. 2. Illustrates magnified view of the plunger
[0007] Fig. 3 illustrates pressure curves for high speed and low speed of the engine
[0008] Fig. 4 illustrates a fuel injection system using the fuel pump

Detailed description of the embodiments:
[0009] FIG. 1 shows a cross section of a pump 100 used in a typical fuel injection system. The fuel pump is also referred as pump. The pump 100 comprises a barrel 102, a plunger 104, an inlet port 108, a spill port 112 and a delivery valve 114. The plunger 104 is driven by the pump cam which is not shown. The pump cam is driven by the engine which is not shown. The rotational orientation of the pump cam is synchronized with the engine firing point. This phase relationship is typically stored in an Engine Control Unit ECU which controls the engine operations. The phase relationship is used for controlling injection timing. The pump cam moves the plunger 104 in the delivery direction (pointed upwards in the figure) and the plunger spring not shown ensures the plunger 104 returns to the starting position by the end of each cycle. The straight line motion of the plunger 104 is not variable and is set for a given application. In fig. 1, the top dead centre TDC is upwards and the bottom dead centre BDC is downwards. The bore 102 has the inlet port 108 for drawing the fuel from the fuel tank into the pump chamber 110. The pump 100 has the spill port 112 through which the excess fuel returns to the tank. The pressurized fuel is delivered through the delivery valve 114 which could be a one way or a two-way valve.
[0010] It is also possible that the pump 100 does not have the spill port 112. In such cases, the pump 100 manages the excess fuel through the inlet port 108 itself.
[0011] When the plunger 104 moves towards the BDC, the fuel is sucked into the pump chamber 110 through the inlet port 108. When the plunger 104 moves towards the TDC, the fuel is pressurized in the pump chamber 110 and delivered through the delivery valve 114.
[0012] The plunger 104 has a top helix 116 cut on the circumferential surface. The plunger 104 also has a ground groove 118, the ground groove being around the circumference of the plunger 104. The plunger has a vertical grove which is shown in fig 2.
[0013] Fig 2 shows, the top helix 116, vertical groove 200 and the ground groove 118 in a magnified view. Also shown in the fig. 2 are the reference positions of the inlet port 108 and the spill port 112 during the operation of the pump 100.
[0014] Fig 3 shows the pressure curves for two speeds of the engine. The pressure curve PC1 is for the high speed operation of the engine and the pressure curve PC2 is for the low speed operation of the engine. The X axis represents the time ‘t’ with respect to rotation of the cam shaft of the engine and the Y axis represents the pressure at which the fuel is delivered.
[0015] The operation of the pump is explained below with the help of fig. 2 and fig. 3 together.
[0016] Figure 2 shows the position of inlet port 108 as the plunger moves up and down in reciprocating manner due to the drive cam. The point at which bottom edge of the helix 116 on the plunger 104 closes the inlet port 108 on its upward motion, marks the beginning of the pressure generation phase. This point is shown as A in figure 3 and is referred to as start of delivery. As the plunger 104 continues to move upwards towards TDC, the fuel pressure increases, the delivery valve 114 opens thereby delivering the pressurized fuel. The pressure of the fuel in the pump chamber 110 increases till the ground groove 118 comes in fluid communication with the spill port 112 or the inlet port 108. However at high engine speeds, the small depth of ground groove 118 will prevent it from being active and the inlet port 108 and the spill port 112 will continue to be closed by the plunger 104 through the full-stroke of the plunger 104 until the plunger reaches the TDC. In other words, at the high sped of the engine, there is not enough time where the ground groove fluidly communicates with the spill port 112 or the inlet port 108 during upward motion of the plunger 104. Under this scenario, the fuel will not flow into spill port 112 or the inlet port 108. This increases the fuel pressure to a maximum value shown as D when the plunger reaches TDC. Point D is when the pump reaches peak injection pressure for this operating point. After this point is the dwell period where the pressure is held at a peak pressure because of cam profile. Hence, the end of pressurization is dependent on the plunger stroke, thus, delivering required fuel to the fuel injection system and raising the injection pressure. On the return stroke, the delivery valve 114 closes because pressure inside the pump chamber 110 is lesser than the fuel pressure on the injector side. As the plunger travels downwards, the helix uncovers the inlet port again and fuel from the pump inlet begins to flow into the pump chamber 110. The fuel pressure in pump chamber 110 stabilizes at the pump inlet pressure. The plunger travel between the points at which the inlet port 108 is closed (point A) and TDC (point D) position of plunger is called the effective stroke of the pump 100. The position of the helix 116 along the circumference can be altered by rotating the regulative sleeve which is not shown in fig. This alters the effective stroke and the start of delivery (pt.’A’ in fig.3) and therefore the pressure developed by the pump 100 during a given cycle. The regulating sleeve is mechanically linked to the load linkage of the engine or the accelerator pedal of the engine.
[0017] At low pump speeds, the ground groove 118 becomes active due to the longer time during plunger stroke available for the flow to be established between pump chamber 110 and the spill port 112 or input port 108 through balancer groove 200. The speed at which the ground groove 118 becomes active can be changed by changing the depth and/or width of the ground groove 118 on the plunger circumference. Hence at low pump speed, injection pressure curve is as shown in PC2 in figure 3. Here, initially the pressure keeps increasing when the plunger 104 is moving towards TDC and the plunger closes the inlet port 108 and the spill port 112. This portion is shown as the curve between point A and B. As the plunger 104 keeps moving towards the TDC, the ground groove 118 comes in contact with the spill port 112 thereby establishing a fluid communication between the pump chamber 110 with the spill port 112 through the balancer groove 200. This results in part of the fuel returning to fuel tank through the spill port 112 thereby decreasing the pressure at the delivery valve 114. This portion is shown as the curve between point B and C. As the plunger 104 keeps moving towards the TDC, the ground groove closes the spill port and the pressure starts increasing again at the delivery valve 114 and reaches a peak pressure shown as D2 when the plunger 104 reaches TDC point. The pressure is held at this point because of the profile of cam. Once the cam rotates further, the plunger starts moving back towards the BDC.
[0018] Problem addressed by this solution is that without ground groove 118, at lower pump speed and same regulating sleeve position, injection pressure would have been higher, as shown at D due to the same start of pressurization and plunger stroke. By introducing ground groove 118, this rate of pressurization has been interrupted with points B & C, thus reducing the peak injection pressure to D2 at this operating point. This gives additional flexibility on pressure control based on engine speed to the otherwise inflexible conventional mechanical system. More flexibility on system pressure can also be provided by inclining the ground groove to a certain angle. This arrangement would give flexibility of change in injection pressure due to change in end of delivery by rotating regulating sleeve.
[0019] The ground groove may be fully along the circumference of the plunger or may cover only partially along the circumference. Also the groove may be slanting to the direction of the motion of the plunger.
[0020] Shown in fig. 4 is a fuel injection system 400 comprising a fuel tank 402, a fuel filter 404, a fuel pump 100, an electronic injector 406 and an engine control unit 408, apart from all the required sensors which are not shown. Here the pump 100 is the mechanical pump as illustrated in Fig. 1. The electronic injector 406 is an electronically controlled injector which may be a common rail injector controlled by the engine control unit 408. This system 400 is a hybrid fuel injection system where the pump 100 and the pump control logic are mechanical whereas the injector 406 and the injector controls are electronically operated. Here injector control refers to the ECU and the other sensors and actuators. The pump control logic refers to the mechanism to rotate the plunger of the pump 100. The rotation of the plunger 104 may be mechanically controlled by an accelerator pedal. Whenever the accelerator is pressed or depressed, the plunger rotates accordingly within the bore 102 and the position of the helix is varied circumferentially thereby varying the pressure of the fuel injection. The duration of the fuel injection is controlled by the engine control unit 408 by operating the solenoid in the fuel injector 406. It is also possible that the rotation of the plunger 104 is electronically controlled by the ECU depending upon the amount of accelerator pedal pressed.
[0021] By having the hybrid configuration, the fuel injection system 400 is a low cost system which meets requirements of varying the fuel injection pressure in dependence of the engine speed. By having a mechanical pump and an electronic injector, we are getting the advantage of simple low cost fuel injection system with pressure control for varying engine speed.