Claims:We Claim:
1. A method to operate a common rail fuel injection system to reduce fuel injection into cylinders of an engine, the method comprising the steps:
- operating at least one injector of said engine in reduced energizing mode
- operating at least one other injector of said engine in normal mode
2. A method according to claim 1 wherein one injector is operated in normal mode in one cycle of injection
3. A method according to claim 1 wherein remaining injectors are operated in reduced energizing mode in said one cycle of injection
4. A method according to claim 1 wherein reduced energizing mode is the one where said injector is energized and is de-energized before fuel starts exiting from the nozzle holes of said injector
5. A method according to claim 1 wherein normal mode is one where injector is energized to inject required quantity of fuel into said cylinder of an engine.
6. A method according to claim 1 wherein malfunction indication is activated when at least one injector is operated in reduced energizing mode.
7. A method according to claim 1 wherein engine is operated in limp home mode when at least one injector is operated in reduced energizing mode.
8. A method according to claim 1 wherein at least one injector is operated in reduced energizing mode when faster reduction of engine speed is required.
9. An engine control unit adapted :
- determine rail pressure
- operating at least one injector in reduced energizing mode and operating at least one other injector in normal mode if rail pressure is above a threshold
, 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
[001] This invention relates to the field of common rail fuel injection system an internal combustion engine. The invention relates in specific to operating common rail fuel injection system to reduce the pressure in the common rail.

Background of the invention

[002] Typically whenever there is any malfunction in a pump or a metering valve in a common rail fuel injection system, the pressure in the common rail may exceed a pre-defined threshold. For this purpose a pressure relief valve which is provided in the common rail, opens. This is detected by an Engine Control Unit (ECU) and the engine is operated in limp home mode where engine has only limited speed and can travel only a limited distance.

[003] The prior art EP 0 896 144 A2 discloses a fuel injection control apparatus for an accumulator type engine efficiently reduces fuel pressure in an accumulator pipe if the fuel pressure exceeds a target pressure, thereby ensuring stable combustion.

Brief description of the accompanying drawing

[004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[005] Fig. 1 illustrates a common rail fuel injection system
Fig. 2 illustrates a sectional view of a common rail injector
Fig. 3 illustrates graph of pressure in common rail
Fig. 4 illustrates flow chart of method according to one embodiment of the
invention.

Detailed description of the embodiments

[006] FIG. 1 illustrates a typical common rail fuel injection system 100. The common rail fuel injection system 100 is just referred as system in this document. The system 100 comprises a fuel tank 102, a low pressure fuel pump 103, a fuel filter 104, a metering unit, a high pressure fuel pump 106, a common rail 108, a high pressure fuel path 110, an ECU 112 and a set of injectors 114. Only the important components of the system 100 are shown.

[007] The low pressure fuel pump may be an electric feed pump which may be located inside the fuel tank 102. The feed pump 103 can be a mechanical feed pump which is part of high pressure pump along with Metering Unit. The low pressure pump draws the fuel from the tank 100. The fuel then passes through a fuel filter 104 which removes any solid particles from the fuel. The fuel passes through the metering unit. The metering unit, which is associated with the high-pressure pump includes a regulating valve which is actuated electromagnetically. The metering unit is disposed in the high-pressure pump 106, and the outlet of the regulating valve discharges into the low-pressure region of the high-pressure pump 106.

[008] The metering unit may form part of the high pressure pump 106 and may be integrated in the housing of the high pressure pump106. In another embodiment the metering unit may be external to the high pressure pump106. The metering unit regulates the flow rate of the fuel supplied from the feed pump to regulate the fuel pressure as required to supply fuel to the engine which is not shown. The metering unit supplies fuel at regulated pressure to the inlet of the high pressure pump 106. The metering unit may be controlled by an ECU 112 depending upon the operating conditions of the engine. This is achieved by controlling a solenoid provided in the fuel metering unit, by the ECU 114.

[009] The fuel is pressurized by the pump 106 and delivered to the common rail 108 which stores the fuel. To the common rail 108 are connected the injectors which inject fuel into the cylinders of the engine.

[010] Shown in fig 2 is a sectional view of a common rail injector 114. The common rail injector 114 is also referred just as an injector in this document. The injector 114 is electronically controlled by the ECU 112. The injector comprises an inlet 200, a ball valve 202 with a spring 204, a leakage path, a return path 206 fluidly connecting to ball valve 202, a nozzle 208 and a solenoid 210 controlled by the ECU 112.

[011] The common rail 108 supplies fuel to the injector 114 through the inlet 200. The fuel passes into the chamber which is normally blocked by the ball valve 202. The fuel also enters into the passage 212 leading to the nozzle 208 of the injector 114, filling the gap between the housing and the nozzle 208. When the solenoid 210 in the injector 112 is not energized, the ball valve 202 remains closed and the nozzle 208 is in a position where the nozzle holes are closed. This causes an equilibrium of pressure caused by the fuel entering into the injector 114 closing the holes in the nozzle. Because of this the fuel is not injected. When the injections need to occur, the ECU 112 energizes the solenoid 210, the armature moves towards the coil of the solenoid 210 thereby opening the ball valve 202. As the ball valve 202 opens, the fuel starts flowing through it into the return path 206 and then towards the tank 102. This causes reduced force on the nozzle and the nozzle 208 moves in the direction of the ball valve 202. This is called lifting of the nozzle. When the nozzle 208 lifts, the nozzle holes are uncovered and the fuel is sprayed through the holes in to the engine cylinder. Once the required quantity of fuel is sprayed into the cylinder for one cycle, the ECU 112 de-energizes the solenoid. The de-energizing of the solenoid causes the armature to move back to the original position closing the ball valve 202 because of the spring 204. This leads to the movement of nozzle 208 to close the nozzle holes. If there are multiple cylinders, the ECU 112 repeats the steps of energizing and de-energizing the injectors one after another. This will lead to engine generating power continuously as long as the engine is running. The injector 114 also has a leakage path through which the excess fuel keeps returning to the tank 102. The pressure sensor included as part of the system continuously monitors the rail pressure and provides the pressure information to the ECU 112. For the safe operation of the system 100, the rail pressure has a pre-defined threshold within which the system should operate in normal mode. Normal mode is the mode where the injectors are working as explained above and engine is generating specified power depending upon the operating conditions of the engine.

[012] If the metering unit starts malfunctioning, the common rail 108 receives more fuel than what is required to maintain pressure below pre-defined threshold. In such scenario, the pressure exceeds the threshold and may lead to unsafe operation of the system 100 and the engine.

In such a scenario the rail pressure needs to be brought back below the threshold.

The invention proposes a method to bring down the rail pressure below the threshold.

[013] In the proposed method, when the pressure in the rail exceeds the threshold, the ECU 112 energizes the injector 114 for a short duration which is lesser than the lag time of the injector 114. The lag time of the injector is the duration defined as the time between the energizing of the injector 114 and the actual lift of the nozzle 208. This is typically about 100 to 250 micro seconds. If the injector 114 is energized for a period for less than the lag time and de-energized within that duration, the nozzle 208 will not lift and the injections do not occur. But the ball valve 202 opens for a short duration and the fuel starts flowing through the return path 206 into the return lines 113. This is referred as reduced energizing mode in this document. In one cycle one injector is operated in reduced energizing mode whereas other injectors are operated in normal mode. Normal mode is the one where injector 114 is opened for required amount of time to inject required quantity of fuel so that engine keeps running. The required quantity of fuel is calculated by the ECU 114 based on engine operating conditions like engine speed, engine load, temperature, pressure etc. The reduced energizing mode is the one where injectors are energized for less than lag duration and hence injections do not occur.

[014] Assume the engine has four cylinders and there is one injector in each cylinder. In one cycle the first injector 114 is operated in normal mode and rest of the injectors are operated in reduced energizing mode. In second cycle the second injector is operated in normal mode and rest of the injectors are operated in reduced energizing mode. By repetitively operating the injectors in this way, the engine will be running at lower injections and also the pressure in the common rail 108 is brought down at faster rate.

[015] Shown in fig. 3 is a graph showing rail pressure Vs time. Normally the rail pressure will be operating below the threshold represented as A. The typical operating pressure is shown as in the line section B. The line section B represents the rail pressure as required based on the engine operating conditions. At point C, the metering unit has failed and the rail pressure continuously increases. At point D, the pressure crosses the threshold and is detected by the ECU 112. The ECU 112 starts to operate the injectors in reduced energizing mode and the pressure starts dropping as shown in E.

[016] Once the metering unit failure is detected, the limp home mode is activated by the ECU 112 for the engine if required.

[017] Shown in fig. 4 is a flowchart representing the method proposed by the invention. In step S1 the ECU reads rail pressure. In step S2, the checks whether the rail pressure is above the threshold. If the rail pressure is above the threshold, then proceeds to step S3 else step 6. In step 3 at least one injector is operated in reduced energizing mode. In step 4 at least one other injector is operated in normal mode. In step 5 the malfunction indication is activated. The malfunction indication may be a lamp or an audio signal. Then it goes back to step 1. In step 6 injectors are operated in normal mode and if required limp home mode is activated.

[018] One use case of the proposed invention is when the metering unit fails and the pressure in the common rail 108 exceeds the threshold. The injectors 114 are operated in reduced energizing mode as explained and the rail pressure is brought back within the threshold. Once the failure of metering unit is detected, the engine can be operated in limp home mode. The limp home mode is the one where only a limited quantity of fuel is supplied to the engine so that the vehicle can be taken to a garage. In the limp home mode, the speed of the vehicle is kept below a threshold and the distance for which the vehicle can travel is limited. During the limp home mode a warning lamp is activated to inform the user that the engine is not working in normal mode and the vehicle needs to be taken to the garage.

[019] One more use case of operating injectors in reduced energizing mode is when it is required to reduce the speed of the engine at faster rate. For example, when the user is accelerating at high speed and suddenly removes the foot from the accelerator pedal. In this case the injectors are operated as explained above, so that in each injection cycle, only one injector injects fuel and the rest of the injectors do not inject any fuel. This is repeated till speed of the vehicle is brought down to required level.

[020] The invention also proposes an ECU adapted to determine rail pressure; energize at least one injector and de-energize the injector before fuel starts exiting from the nozzle holes of the injector, if rail pressure is above a threshold or if engine speed is to be reduced at a faster rate. The ECU achieves this by reading rail pressure, comparing it with threshold, operating the injectors 114 in reduced energizing mode as long as the rail pressure is above a threshold, providing indication to the user that the metering unit has a malfunction when the rail pressure crosses a threshold. The ECU achieves this by a set of instructions and also input and output interfaces to read the rail pressure and to control the injectors.

[021] The invention proposes a simple method to reduce the pressure in the common rail by making use of the lag time of the injectors. The method can be also used to reduce speed of the engine at a faster rate if required.

[022] The method to operate the common rail fuel injection system comprises the steps: operating at least one injector in reduced energizing mode, operating at least one other injector in normal mode

[023] The invention makes use of known components in the fuel injection system to operate the common rail. The injector energizing and de-energizing action is used effectively to reduce the rail pressure whenever the rail pressure crosses the threshold.
Here the pressure is brought down without affecting the operation of the engine while moving.