FIELD OF INVENTION:

The invention relates to a hydraulic control mechanism for a fuel injector.

BACKGROUND OF THE INVENTION:

An injection pump to pressurize fuel in fuel injection systems is known. US patent 6336443 discloses one such injection pump. The patent discloses an injection pump in which the supply onset can be set freely for two different operating modes of the engine. The supply onset is attained in the cylinder by use of a second control bore, which cooperates with a plunge cut in the cylinder and with a piston stop groove that extends longitudinally along the pump piston from the upper control edge. The piston in the injector is rotated to control the amount of fuel injected. The piston is rotated using a mechanical control rod.

ADVANTAGES OF THE INVENTION:

By using hydraulic control mechanism to control the alignment of the piston in the high pressure pump, the high pressure pump is controlled independent of engine speed and driver demand. The engine speed and driver demand influence the high pressure pump to some extent, but these are not the only factors influencing the high pressure pump.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1: Shows the schematic of the injector according to the invention.

DESCRIPTION OF THE INVENTION:

Shown in fig. 1 is the control mechanism 100 to control the amount of fuel provided by the high pressure pump 200 to an injector which is not shown. The high pressure pump 200 is referred as pump in rest of this document. The control mechanism comprises a plunger 101 movably placed in a bore 102, the bore 102 having a first side 103 and a second side 104, a fuel supply path 106 supplying fuel to the first side 103 of the bore, the second side 104 of the bore 102 connected to the fuel supply path 106 via a valve 108.

The other side of the fuel supply path 106 is connected to a fuel feed pump which is not shown in the fig. The fuel feed pump supplies the fuel through the fuel supply path 106. The bore 102 has a stopper 110 which determines one end position of the plunger 101. The bore 102 receives the fuel in its first side 103 through the fuel supply path 106 which creates a pressure PI in the first side 103. The fuel coming through the fuel supply path 106 also passes through the valve 108 and fills the second side 104 of the bore 102.

A second fuel supply path 112 connects the outlet of the valve 108 to a high pressure pump 200. The high pressure pump 200 is referred as pump in the rest of the document. An overflow valve 118 connected to the 112 regulates the pressure of the fuel supplied to the pump 200. The pressure at the inlet of the pump 200 is same as the pressure in the second side 104 of the bore and this pressure is maintained at a constant level by the over flow valve 118. If the pressure at the inlet of the pump 200 exceeds a threshold, the overflow valve 118 opens and the excess fuel flows back to the reservoir which is not shown. In an alternative design, a fixed throttle may create back pressure on the second side 104 depending upon flow rate.

The pressure in the second side 104 of the bore is referred as P2. Depending upon the amount of the opening of the valve 108, the pressure PI on the first side 103 varies. Depending upon the pressure difference between PI and P2 the plunger 101 moves within the bore 102. When the valve 108 is completely open, the pressure PI and P2 are equal. When the differential pressure between PI and P2 is zero, the plunger 101 moves to left as the forces acting on the surface of plunger on the second side 104 are higher compared to the forces acting on the surface of plunger on the first side 103 because of the difference in the surface areas of first side and second side. The valve 108 is never completely closed; there is a maximum limit to which the valve 108 is closed. When the valve 108 is closed to the maximum limit, the pressure difference between P1 and P2 is maximum. At any given point, the current position of the plunger 101 is directly dependant on the balance of forces acting on the surfaces of first side and second side of the plunger.

The far end of the plunger 101 is mechanically coupled to a control rod 300 shown in fig 4. The plunger 101 moves the control rod 300. The linear motion of the control rod 300 is converted into rotary motion of the piston 203 of the pump 200 shown in fig 2.

The outlet 112 is connected to the pump 200. The outlet 112 supplies fuel to the pump 200. The pump 200 pressurizes the fuel to high pressure and delivers to the engine which is not shown. The pump has a return path to return excess fuel to the reservoir.

A controller 110 controls the amount of opening of the valve 108 in dependence upon the speed signal 114 and a signal 116 from an accelerator pedal.

A return flow path 120 is provided to protect the pump 200 from excess pressurization. When the pressure in the pump chamber exceeds a predefined pressure, the over flow valve 118 opens and the excess fuel returns to the reservoir.

Shown in fig. 2 is the pump 200. The pump 200 comprises a housing 202, the piston 203 moving in a bore 204. An inlet 206 supplies fuel to the pump 200 and the pump 200 delivers the pressurized fuel through an outlet 208. The fuel is pressurized in the pump chamber 210. A Spill port 212 carries the excess fuel back to the reservoir which is not shown. The piston 203 is moved in the pumping direction by a cam 209. The piston 203 is retracted by a spring 213.

Shown in fig. 3 is a cut section of the pump. The same reference numbers are used to indicate the same parts as in fig. 2. The piston 200 has a spill passage 214 and a helical groove 216. The spill passage 214 opens to the pump chamber 210. When the spill passage 214, the helical groove 216 and the spill port 212 are aligned communicatively, the fuel flows from the pump chamber 210 to the spill port 212. Here the term aligned communicatively indicates that the elements referred are fluidly connected and allow the fuel to pass through them.

The stroke of the piston 203 is not variable. Also the fuel supplied through the inlet 206 is of constant pressure. Hence the fuel entering into the pump chamber 210 for a given pumping cycle is of constant volume, the pumping cycle comprising a suction stroke and a pumping stroke. The amount of fuel delivered by the pump 200 is regulated by the effective stroke of the piston 203. The effective stroke of the piston is the length of the movement of the piston 203 before the spill passage 214 gets connected to the spill port 212.

One method to regulate the amount of fuel delivered through the outlet 208 is by varying the effective stroke of the piston 203, which is achieved by rotating the piston 203. By rotating the piston 203, the spill passage 206 is connected to the spill port 212 through the helical grove 216 either early or late in the pumping stroke of the piston 203. The moment the spill passage 214 is connected to the spill port 212, a part of the fuel starts flowing from the pump chamber 210 through the spill port 212, thereby reducing the pressure in the pumping chamber 210.

If the spill passage 214 is connected to the spill port 212 early in the pumping stroke of the piston 203, the pressure in the pumping chamber 210 drops early in the pumping stroke, thereby delivering lesser fuel through the outlet 208.

If the spill passage 214 is connected to the spill port 212 late in the pumping stroke of the piston 203, high pressurization of the fuel occurs for more time in the pumping chamber 210 thereby delivering more fuel through the outlet 208.

So by connecting the spill passage 214 to the spill port 212 either early or late in the pumping stroke, the amount of the fuel delivered through the outlet 208 is controlled.

The effective stroke of the pump is determined by the orientation of the piston 203 in radial direction. At one extreme position of the piston 203 in radial direction, the spill passage 214 is continuously in connection with the spill port 212 for the entire duration of the pumping stroke of the piston 203. Under this position, the fuel is not delivered through the outlet 208 because the fuel continuously escapes through the spill port 212 and pressurization of the fuel is not possible in the pump chamber 210. This position is used for no load condition of the engine.

At the other extreme position of the piston 203 in the radial direction, the spill passage 214 is connected to the spill port 212 very late in the pumping stroke so that the fuel is pressurized for the maximum duration of the pumping stroke thereby delivering maximum fuel through the outlet 208. This position is used for the full load condition of the engine.

Any other position of the piston 203 between the no load condition and the full load condition is used to deliver different amount of fuel.

The working of the pump is well known and not explained in this document.

The amount of fuel injected by the pump 200 is determined by the length of the effective stroke of the piston 203. The length of the effective stroke of the piston is controlled by rotating the piston 203 in appropriate direction.

The rotation of the piston is achieved by using the control mechanism shown in fig. 1. The control mechanism explained with respect to fig. 1, creates a differential pressure on the sides of the plunger. Because of the differential pressure experienced by the sides of the plunger, the plunger moves in a direction in which the pressure is relatively lesser.

Shown in fig. 4 is the mechanical connection between the piston 203 of the pump and a control rod 300. The plunger 101 is mechanically coupled to the control rod 300 which in turn is coupled to the piston 203 of the pump 200. The linear motion of the plunger 101 is converted into rotary motion of the piston 203. The rotary motion of the piston 203 changes the alignment of the spill passage 214, helical groove 216 and the spill port 212 thereby changing the amount of fuel injected through the pump 200.

The amount of opening of the valve 108 is controlled by a controller 110. The controller 110 receives the engine/vehicle speed, the accelerator pedal position and computes the amount of fuel to be injected.

The amount of opening of the valve 108 is computed in dependence of the amount of fuel to be injected.

The fuel which is to be pumped itself is used to control the movement of the plunger which finally controls the amount of fuel injected into the engine. The ECU controls movement of the plunger accurately in dependence of the amount of fuel to be injected.

WE CLAIM:

1. A control mechanism for a fuel pump for an engine, the said control mechanism
comprising.

a plunger (101); the plunger (101) movably placed in a bore (102); the bore (102) having a first side (103) and a second side (104); the first side (103) connected to a fuel supply path (106); the second side (104) connected to the fuel supply path (106) via a valve (108); the second side (104) also connected to an outlet (112); the outlet 112 connected to a pressure regulating element which is either a overflow valve (118) or a throttle; the amount of opening of the valve (108) determining the position of the plunger (101) within the bore (102).

2. A control mechanism according to claim 1 wherein the plunger (101) is mechanically coupled to a control rod (300)

3. A control mechanism according to claim 1 wherein the linear motion of the control rod 300 rotates a piston (203) of a pump (200)

4. A control mechanism according to claim 1 wherein the outlet (112) is connected to the pump (200)

5. A control mechanism according to claim 1 wherein the pressure difference between first side (103) and second side (104) causes the plunger (101) to move linearly in the bore (102).

6. A control mechanism according to claim 1 wherein the velocity of the movement of the plunger (101) is proportional to the pressure difference between the first side (103) and the second side (104)

7. A control mechanism according to claim 1 wherein the pressure difference between the first side (103) and the second side (104) is dependant upon the amount of opening of the valve (108)

8. A controller (110) to control the amount of opening of a valve (108) in dependence of a speed signal (114) and a signal from accelerator pedal (116).