CLIAMS:1. A method for determining a position of a pressure limiter valve (52), said method comprising:
receiving a rail pressure signal by the engine control unit (12) from a rail pressure sensor (14);
receiving an engine speed signal by the engine control unit (12) from the engine speed sensor; characterized in that
determining if the rail pressure signal is an error signal by the engine control unit (12);
determining if the engine speed signal is greater than a threshold engine speed signal by the engine control unit (12) during engine idling if the rail pressure signal is an error signal; and
determining that the pressure limiter valve (52) is in a closed position if the engine speed signal is greater than the threshold engine speed signal during engine idling.

2. The method in accordance with Claim 1, comprising operating the pressure limiter valve (52) to open by the engine control unit (12) if the engine speed signal is greater than the threshold engine speed signal.

3. The method in accordance with Claim 4 wherein the engine speed signal being greater than the threshold engine speed signal occurs as a consequence of advancing of fuel injection within the engine.

4. The method in accordance with claim 1, wherein said method of determining that the pressure limiter valve is in a closed position is initiated at an engine operating point.

5. The method as claimed in claim 4, wherein said engine operating point is an engine idling point.
,TagSPECI:The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention:
[001] This invention relates to identifying a pressure limiter valve position by determining a speed level of an engine.

Background of the invention:
[002] Traditionally, when a rail pressure sensor of a common rail fails, the rail pressure sensor transmits an error signal to an engine control unit. On receiving the error signal, the engine control unit determines that a pressure limiter valve that is coupled to the common rail is open. In reality however, the pressure limiter valve remains closed until a threshold value of pressure is attained in the common rail. Due to the pressure limiting valve remaining closed, high engine speed fluctuations are observed due to high pressure that is built up in the common rail.

[003] U.S. Patent Number 6,964,262 describes an accumulator fuel injection system comprising a PC sensor for detecting a common rail pressure. A pressure limiter is provided for keeping the common rail pressure below a high limit pressure by opening the valve of the pressure limiter when the high limit pressure is attained to provide function of limp home. An engine control unit controls a rate of fuel to be injected from an injector such that the common rail pressure reaches the high limit pressure when an abnormality has occurred in a fuel supply pump, thereby facilitating opening the pressure limiter.

Brief description of the accompanying drawings
[004] An exemplifying embodiment of the invention is explained in principle below with reference to the drawings. The drawings are:

[005] Figure 1 shows a schematic view of an engine fuel injection system.

Detailed description of the invention:
[006] As shown in Figure 1, a schematic of an engine fuel injection system 10 is described. In addition, a method for determining a position of a pressure limiter valve 52 is described. The method comprises coupling a rail pressure sensor 14 to an engine control unit 12, coupling an engine speed sensor to the engine control unit 12, receiving an electronic signal by the engine control unit 12 from the rail pressure sensor 14, and determining if the received electronic signal is an error signal by the engine control unit 12. The method further comprises receiving an engine speed signal by the engine control unit 12 from the engine speed sensor, determining if the engine speed signal is greater than a threshold engine speed signal by the engine control unit 12, and determining that the pressure limiter valve 52 is in a closed position if the engine speed signal is greater than the threshold engine speed signal

[007] As shown in Figure 1, the engine fuel injection system 10 comprises a fuel tank 20. The fuel tank 20 is used to store and supply fuel to a high-pressure pump 25. The high-pressure pump 25 pressurizes fuel and delivers it for injection into an internal combustion engine. A common rail 30 is coupled to the high-pressure pump 25. More specifically, the common rail 30 is coupled to the high pressure pump 25 through a fuel supply path 34 that is used to deliver fuel to the common rail 30. The common rail 30 is coupled to at least one fuel injector 41 and delivers fuel through the fuel injector 41. The pressure limiter valve 52 is coupled to the common rail 30. The pressure limiter valve 52 is configured to open and release excess fuel from the common rail 30 when the pressure in the common rail 30 increases above a threshold pressure operating limit. The rail pressure sensor 14 is coupled to the common rail 30 and is configured to measure a pressure of fuel in the common rail 30.

[008] In an embodiment, the pressure limiter valve 52 is a mechanically actuated spring loaded valve that is configured to automatically open and release excess fuel from the common rail 30 when the pressure in the common rail 30 increases above the threshold pressure operating limit. The threshold pressure operating limit is fixed within the common rail 30 while fabricating the common rail 30 for a specific application.

[009] The engine fuel injection system 10 comprises the engine control unit 12. In the embodiment, the engine control unit 12 is coupled to the rail pressure sensor 14. The engine control unit 12 determines a pressure of fuel in the common rail 30 by means of the rail pressure sensor 14. The engine control unit 12 is coupled to the pressure limiter valve 52. In the embodiment, the engine control unit 12 opens the pressure limiter valve 52 to discharge excessive pressure that is built in the common rail 30 when the pressure in the common rail 30 increases above the threshold pressure operating limit.

[0010] The engine control unit 12 is coupled to the engine speed senor (not shown). The engine speed sensor is further coupled to the engine and determines the speed of the engine. The engine speed sensor transmits an electronic signal to the engine control unit 12, wherein the electronic signal is indicative of a level of engine speed that is sensed by the engine speed sensor.

[0011] The engine control unit 12 stores a reference value of engine speed that is expected from the engine. This reference value of speed level that is expected from the engine is stored within the engine control unit 12 in the form of a two dimensional map for various engine operating conditions including but not limited to an engine speed. In the embodiment, the engine speed level is sensed by the engine speed sensor during engine idling conditions. This level of engine speed that is sensed by the engine speed sensor during engine idling is compared with the reference value of speed level that is expected from the engine during engine idling from the two dimensional map.

[0012] The operation of the engine fuel injection system 10 is now described with an example. When the engine control unit 12 determines an error signal from the rail pressure sensor 14 indicating that the rail pressure sensor 14 is not functional, the engine control unit 12 will be unable to control a pressure of fuel in the common rail 30. Therein, the high pressure pump 25 supplies the common rail 30 with a constant amount of pressurized fuel. During engine idling conditions, as the volume of fuel flowing out of the common rail 30 decreases, the pressure in the common rail 30 begins to build up. The engine control unit 12 determines the engine speed that is sensed by the engine speed sensor during an engine idling point. This level of engine speed is compared with the reference value of speed that is expected from the engine during an engine idling point. If the level of engine speed is greater than the reference value of speed that is expected from the engine during the engine idling point, the engine control unit 12 determines that the pressure limiter valve 52 is in a closed position. The level of engine speed being greater than the reference value of speed occurs as a consequence of advancing of fuel injection within the engine. The engine control unit 12 therein controls the pressure limiter valve 52 to open, thereby ejecting fuel and decreasing the built up pressure in the common rail 30. The fuel in the common rail 30 is thereby circulated to the fuel tank 20 through a return fuel supply path 58.

[0013] The above described engine fuel injection system 10 is cost effective and highly reliable. The engine fuel injection system 10 facilitates determining if the common rail 30 is holding excess pressure beyond its normal operating pressure. Moreover, controlling the pressure limiter valve 52 to open using the engine control unit 12 facilitates discharging excess fuel within the common rail 30 through the return fuel supply path 58 thereby preventing damage to an engine cylinder / piston crown. In addition, the modular nature of each sub-system of the engine fuel injection system 10 facilitates easy disassembly and replacement of individual system components as required.

[0014] It must be understood that the embodiments explained in the above detailed description is only illustrative and does not limit the scope of this invention. The scope of this invention is limited only by the scope of the claims. Many modification and changes in the embodiments aforementioned are envisaged and are within the scope of this invention.