Claims:We Claim:
1. A fuel injector (10) for controlling a flow of fuel to an engine, said fuel injector (10) comprising:
a housing (12);
an injector needle (14) positioned within a nozzle body (15), said injector needle (14) adapted to be lifted to facilitate injecting fuel out of said fuel injector (10); characterized in that
a drive unit (16) comprising a motor unit (18) and a motor shaft (20) coupled to said motor unit (18) that is positioned above said injector needle (14) and within said fuel injector (10), said motor unit (18) adapted to rotate said motor shaft (20) to facilitate delivering a metered quantity of fuel out of said drive unit (16).

2. The fuel injector (10) for controlling the flow of fuel to the engine in accordance with Claim 1 wherein said motor shaft (20) comprises at least a first fuel passage (22) and a second fuel passage (24) that is in flow communication with the at least first fuel passage (22).

3. The fuel injector (10) for controlling the flow of fuel to the engine in accordance with Claim 2 wherein said housing (12) comprises a third fuel passage (26) and a fourth fuel passage (28), said third fuel passage (26) adapted to supply pressurized fuel to said motor shaft (20), and said fourth fuel passage (28) adapted to supply pressurized fuel to said injector needle (14) of said fuel injector (10).

4. The fuel injector (10) for controlling the flow of fuel to the engine in accordance with Claim 3 wherein said third fuel passage (26) is in flow communication with said first fuel passage (22), said first fuel passage (22) adapted to receive fuel flow from said third fuel passage (26).

5. The fuel injector (10) for controlling the flow of fuel to the engine in accordance with Claim 3 wherein the at least the first fuel passage (22) connects from said third fuel passage (26) to said second fuel passage (24), said second fuel passage (24) adapted to deliver fuel out of said drive unit (16).

6. The fuel injector (10) for controlling the flow of fuel to the engine in accordance with Claim 3 wherein said motor unit (18) is adapted to rotate said motor shaft (20) to facilitate aligning said at least the first fuel passage (22) with said third fuel passage (26) to deliver fuel from said second fuel passage (24) to a spring chamber (32) via a fifth fuel passage (30).

7. The fuel injector (10) for controlling the flow of fuel to the engine in accordance with Claim 3 wherein said at least the first fuel passage (22) is in flow communication with said third fuel passage (26) to facilitate receiving fuel from said third fuel passage (26).

8. The fuel injector (10) in accordance with claim 3 wherein said drive unit (16) rotates the drive shaft (20) and aligns the first fuel passage (22) with said third fuel passage (26) and thus allowing fuel to flow to the spring chamber (32) and hence pressurizing the spring chamber (32) and closing the nozzle needle (14) due to fuel pressure acting on the nozzle needle (14), thereby avoiding the fuel flowing out of the fuel injector (10)

9. The fuel injector (10) in accordance with claim 3 wherein said drive unit (16) rotates the drive shaft (20) and aligns the first fuel passage (22) with the leak off bore (11) and thus allowing fuel to flow out of the spring chamber (32) and allowing the nozzle needle (14) to lift thereby allowing the fuel to flow out of the fuel injector (10)
, Description:Field of the invention
[0001] This invention relates to a fuel injector and more specifically to a fuel injector for controlling a flow of fuel to an engine.

Background of the invention
[0002] U.S. Patent Publication Number 2004/0025843 A1 describes a fuel injection system for internal combustion engines. A fuel injector with needle movement control using a drive unit (eg. stepper motor) is proposed to control the quantity of fuel injection accurately and also the injection timing. In addition, pilot and post injection capabilities are possible with the proposed concept. By controlling the rate of needle movement, rate of fuel injection can also be controlled and hence achieving the damped / boot injection characteristics.

Brief description of the accompanying drawings
[0003] Figure 1 illustrates a schematic diagram of a drive unit integrated with a fuel injector for controlling a flow of fuel to an engine.
[0004] Figure 2 illustrates a schematic diagram of a drive unit, motor unit (example stepper motor), and a motor shaft that is coupled to the motor unit.
[0005] Figure 3 illustrates a working principle of control of fuel injection characteristics (quantity, timing, pilot, damped/boot, main and post injection).

Detailed description of the invention
[0006] A fuel injector 10 for controlling a flow of fuel to an engine is described. The fuel injector 10 comprises a housing 12 and an injector needle 14 positioned within the nozzle body 15, the injector needle 14 adapted to be lifted to facilitate injecting fuel out of the fuel injector 10. A drive unit 16 comprising a motor unit 18 and a motor shaft 20 is coupled to the motor unit 18 that is positioned above the injector needle 14 and within the fuel injector 10, the motor unit 18 adapted to rotate the motor shaft 20 to facilitate delivering a metered quantity of fuel out of the drive unit 16.

[0007] Figure 1 illustrates a schematic diagram of the drive unit 16 integrated with the fuel injector 10 for controlling a flow of fuel to the engine. The fuel injector 10 comprises the drive unit 16 that may be inserted within the fuel injector 10. A fuel pump (not shown) is in flow communication with the fuel injector 10 and supplies pressurized fuel to the fuel injector 10. The fuel injector 10 comprises an injector needle 14 that is positioned within a bore of a nozzle body 15 and controls a flow of fuel out of the fuel injector 10. A spring chamber 32 is defined above the injector needle 14 and houses a spring member 33 therein.
[0008] The drive unit 16 of the fuel injector 10 comprises a motor unit 18 and a motor shaft 20 that is coupled to the motor unit 18. The motor shaft 20 comprises at least a first fuel passage 22 and a second fuel passage 24 that is orthogonal to and in flow communication with the at least first fuel passage 22. The second fuel passage 24 is in flow communication with a fifth fuel passage 30 that is in flow communication with the spring chamber 32 and supplies fuel to the spring chamber 32. The first fuel passage 22 that is in flow communication with the second fuel passage 24 delivers fuel to the second fuel passage 24 that then flows to the fifth fuel passage 30 that is in flow communication with the spring chamber 32 and supplies fuel to the spring chamber 32. When the motor unit 18 rotates the motor shaft 20, the first fuel passage 22 rotates and changes position which in turn helps to control the injection characteristics as will be described in more detail below.
[0009] The fuel injector 10 comprises a third fuel passage 26 and a fourth fuel passage 28 that each originate from a fuel inlet port 23 of the fuel injector 10. The third fuel passage 26 is adapted to deliver fuel to the first fuel passage 22. The fourth fuel passageway 28 that originates from the fuel inlet port 23 is adapted to deliver pressurized fuel to the injector nozzle body 15 of the fuel injector 10.
[0010] The first fuel passage 22 provided in the motor shaft 20 can be aligned with leak off bore 11 in the housing 12 of the fuel injector 10. When the first fuel passage 22 is aligned with the leak off bore 11, then the fuel in the spring chamber 32 is in flow communication with the leak off bore 11 in the housing 12 of fuel injector 10 through the fuel passage 24 and the first fuel passage 22.
[0011] Figure 2 illustrates a schematic diagram of a motor unit 18 and a motor shaft 20 that is coupled to the motor unit 18. The motor shaft 20 includes the first fuel passage 22 that is defined on the motor shaft 20. The drive shaft rotates and aligns the first fuel passage 22 partially or fully with the third fuel passage 26 to facilitate receiving fuel from the third fuel passage 26.
[0012] Figure 3 illustrates the schematic diagram of working of the fuel injector 10. The motor unit 18 (example – stepper motor) is controlled by an electronic control unit (17) to decide timing of when to rotate and the extent of rotation of the motor shaft 20 depending on the engine speed and load conditions to inject the accurate quantity of fuel at a desired time. When the drive unit receives the signal from the electronic control unit (17), the motor shaft 20 which is coupled to the motor unit 18 rotates accurately to the desired value based on the input signal from the electronic control unit (17). The first fuel passage 22 that is defined on the motor shaft 20 rotates and aligns either with the fuel passage 26 or with the leak off bore 11.
[0013] High pressure fuel from the fuel pump (not shown) enters the fuel passage 23. When the first fuel passage 22 is aligned with the third fuel passage 26, fuel from the fuel passage 23 enters the third fuel passage 26 and then to the first fuel passage 22 and finally into the spring chamber 32 via the fuel passage 24 fuel passage 30 respectively. This pressurized fuel in the spring chamber 32 applies pressure on the nozzle needle 14, and this creates a downward force on the nozzle needle 14.
[0014] The high pressure fuel from the fuel pump (not shown) also flows towards the nozzle 15 through the fuel passage 28 and applies the pressure on the nozzle needle 14. This creates an upward force on the nozzle needle 14. Since the area of the nozzle needle 14 at nozzle body 15 is less due to the closed nozzle needle 14 and fuel pressure does not act below the nozzle needle 14 seat edge 19, the upward force acting on the nozzle needle 14 is less. The downward force which is acting on the nozzle needle 14 on the spring chamber 32 side is higher since the area of nozzle needle 14 is higher, and in addition to this the spring force due to the spring 33 also acts together. Since in this condition, the down force acting on the nozzle needle 14 is higher compared to the upward force, the nozzle needle 14 is in a closed condition and no fuel injection occurs out of the fuel injector 10.
[0015] When the first fuel passage 22 is aligned with the leak off 11, the fuel in the spring chamber 32 escapes into the leak off 11 via the fuel passages 30, 24, and 22 respectively. Therefore, the fuel pressure in the spring chamber 32 is relieved. At the nozzle body 15 of the nozzle needle 14, still the same high pressure is acting due to the fuel in the fourth fuel passage 28. Due to this fuel, the upward force acting on the nozzle needle 14 is much higher compared to the downward force which is now only the spring force due to the spring 33. Hence, the nozzle needle 14 lifts, and fuel gets injected out of the injector 10 through spray holes provided (not shown) in the nozzle needle 14.
[0016] When the desired quantity of fuel is injected out of the fuel injector 10, the electronic control unit (17) sends the signal to the drive unit 16. The motor unit 18 in the drive unit 16 rotates the motor shaft 20. The first fuel passage 22 provided in the motor shaft 20 rotates. Leak off bore 11 no more aligns with the first fuel passage 22 and hence fuel flowing out of the fuel injector 10 through the leak off bore 11 from spring chamber 32 through the fuel passages 30, 24, 22 ceases. The motor shaft 20 is rotated until the first fuel passage 22 aligns with the third fuel passage 26. When the third fuel passage 26 is aligned with the first fuel passage 22, high pressure fuel enters the spring chamber 32 through the fuel passages 26, 22, 30 and starts filling the spring chamber 32. Pressure of the fuel in the spring chamber 32 builds and downward force on the nozzle needle 14 increases and the nozzle needle 14 closes, and hence the fuel getting injected out of the fuel injector 10 ceases.
[0017] Partial alignment (as shown in the figure 3) of the first fuel passage 22 with the leak off bore 11 helps to control the quantity and rate of fuel injection. Pilot, post and damped / boot injection characteristics can be realized through partial alignment of the first fuel passage 22 and the leak off bore 11. Full alignment of the first fuel passage 22 and the leak off bore 11 results in main injection. The duration of alignment of the first fuel passage 22 and the leak off bore 11 controls the quantity and duration of fuel injection. Time at which the first fuel passage 22 and the leak off bore 11 are aligned controls the fuel injection timing.
[0018] 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 leverage and dimensions of various components are envisaged and form a part of this invention. The scope of the invention is only limited by the scope of the claims.