Claims:We Claim:
1. A fuel injection system (10) in a vehicle, said fuel injection system (10) comprising :
- a metering unit (12);
- a fuel tank (14);
characterized in that:
- an auxiliary valve (16) positioned upstream to said metering unit (12);
- a control unit (18) adapted to open said auxiliary valve (16) and to re-direct fuel back to said fuel tank (14) upon detection of failure in said metering unit (12).

2. The fuel injection system (10) as claimed in claim 1, wherein said auxiliary valve (16) is positioned between said metering unit (12) and an over flow valve (22).

3. The fuel injection system (10) as claimed in claim 1, wherein said auxiliary valve (16) is electrically actuated by said control unit (18).

4. The fuel injection system (10) as claimed in claim 1, wherein said failure in said metering unit (12) is any one chosen from a group comprising a failure in a rail pressure sensor, an open load failure, and a short-circuit in said metering unit (12).

5. The fuel injection system (10) as claimed in claim 1, wherein said control unit (18) is adapted to activate a limp home mode in said vehicle based on said detected failure in said metering unit (12).

6. The fuel injection system (10) as claimed in claim 1, wherein an inlet pressure at said metering unit (12) is reduced due to opening of said auxiliary valve (16) by said control unit (18).

7. The fuel injection system (10) as claimed in claim 1, wherein a flow out from said metering unit (12) is reduced due to said reduced inlet pressure, in a manner to maintain, a required pressure in a common rail (20) of said fuel injection system (10).
, Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[0001] This invention relates to a fuel injection system in a vehicle.

Background of the invention
[0002] Limp home functionality is incorporated in common rail system, to drive the vehicle with limited functionality by reducing the injection quantity during failure of metering unit. Since supply to metering unit is cut off, there will not be any control of rail pressure possible, the pressure in the rail will increase until the opening pressure of the pressure-limiting valve is reached. Once the pressure limiting valve opens, fuel will be relieved through the valve back to tank and pressure less than system pressure will be maintained. The pressure-limiting valve will open as far as the hydraulic force from the pump is greater than the spring force of the pressure-limiting valve. In instances where the hydraulic force is less than the spring force, the pressure-limiting valve will not open and pressure in the rail will increase much beyond the allowed threshold limit leading to damage of components.

[0003] A Prior art document US4887491 discloses a solenoid-actuated valve arrangement in a four-speed automatic transmission having a structure in combination with the manual valve in the hydraulic circuit that will enable a limp-home mode or limited transmission operation, which will permit the vehicle to operate in park, neutral, second or reverse gear as desired in that absence of electrical power to the solenoid-actuated valves.

Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0005] Fig.1 illustrates a fuel injection system in a vehicle in accordance with one embodiment of the invention.

Detailed description of the embodiments
[0006] Fig.1 illustrates a fuel injection system 10 in a vehicle according to one embodiment of the vehicle. The fuel injection system 10 comprises a fuel tank 14 and a metering unit 12. The fuel injection system 10 further comprises an auxiliary valve 16 positioned upstream to the metering unit 12 and a control unit 18 adapted to open the auxiliary valve 16 and to re-direct fuel back to the fuel tank 14 upon detection of failure in the metering unit 12.

[0007] Further the construction of the fuel injection system 10 and the components of the fuel injection system 10 is explained as follows. The fuel injection system 10 comprises an over flow valve 22 positioned upstream to the metering unit 12. The fuel tank 14 comprises a fuel pump 24 adapted to pump the fuel into the common rail 20 via the metering unit 12. The excess fuel that is flowing into the common rail 20 is returned to the fuel tank 14 by opening of the over flow valve 22. The over flow valve 22 is opened based on the pressure developed due to the flow of the fuel from the fuel tank 14. For instance, if the pressure of the fuel flowing from the fuel tank 14 and the fuel pump is more than 4 bar, then the over flow valve 22 is opened to re-direct an amount of fuel back to the tank 14, such that, a desired amount of pressure is maintained at the metering unit 12 followed by the common rail 20. The auxiliary valve 16 as disclosed in the invention is positioned between the over flow valve 22 and the metering unit 12 as shown in the figure 1.

[0008] The auxiliary valve 16 is positioned in series with the metering unit 12. The auxiliary valve 16 is electrically actuated by the control unit 18 that operates the metering unit 12. The auxiliary valve 16 is in closed position when the metering unit 12 is in normal operating mode. The control unit 18 adapted to open the auxiliary valve 16 , upon detecting a failure in the metering unit 12. The failure in the metering unit 12 is any one chosen from a group of failures comprising a short circuit to ground in the metering unit 12, an open load failure, a failure in a rail pressure sensor and the like. Upon detection of at least one failure as disclosed above, the control unit 18 opens the auxiliary valve 16 to reduce the pressure at the metering unit 12 and at the common rail 20. According to one embodiment of the invention, the control unit 18 is chosen from a group of control units like a microprocessor, a microcontroller, an integrated digital chip or the like.

[0009] A method of working of the fuel injection system 10 with the auxiliary valve 16 is explained as below. When the vehicle is in normal working mode, the fuel from the fuel tank 14 is pumped by the fuel pump 24 to the common rail 20 via the metering unit 12. The metering unit 12 maintains the required pressure needed at the common rail 20 for injection of the fuel into a cylinder of an engine during a combustion process. The over flow valve 22 present in the fuel injection system 10 is opened mechanically, when the pressure of the fuel from the fuel tank 14 is more than a predefined pressure, and an amount of fuel is pumped back to the tank 14 via the over flow valve 22, to reduce the pressure at the metering unit 12. However, during a failure (as disclosed above) in the metering unit 12, the pressure of the fuel at the common rail 20 increases, as there is no control of the flow of the fuel at the metering unit 12. Due to the excessive pressure at the common rail 20, the components of the common rail 20 are prone to get damaged. In order to avoid damage of the components, the control unit 18 activates a limp home mode in the vehicle, when a failure in the metering unit 12 is detected. The control unit 18 opens the auxiliary valve 16 positioned upstream to the metering unit 12, upon detection of at least one failure in the metering unit 12. When the control unit 18 opens the auxiliary valve 16, the fuel from the fuel tank 14 is re-directed back to the tank 14 via the auxiliary valve 16, thus a very less amount of pressure is maintained at the metering unit 12. The opening of the auxiliary valve 16 relieves the pressure at the metering unit 12. With the reduction in an inlet pressure of metering unit 12, a flow out at an outlet side of the metering unit 12 reduces. Due to reduce in the pressure at an outlet side of the metering unit, a pressure less than a system pressure is maintained in the common rail 20. A sufficient pressure is maintained in the common rail 20, which is required to move the vehicle to a safe place.

[0010] With the above disclosed fuel injection system 10 comprising an auxiliary valve 16, the pressure at the common rail 20 and the metering unit 12 is maintained within a predefined range. The usage of a pressure-limiting valve is avoided, as the opening of the auxiliary valve 16 reduces the pressure at the inlet side of the metering unit 12.

[0011] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.