Claims:CLAIMS
We claim:
1. A fuel injection system (100) for a vehicle, said fuel injection system (100) comprising:
- an injector (120) to inject fuel for combustion in an engine (101)
- an intake path (112) to guide air for combustion in said engine (101)
- an exhaust path (108) connected to said engine (101) to guide the burnt gases
said fuel injection system (100) characterized by
- an accumulator (102) having an inlet 104 and an outlet (106);
- a first valve (110) disposed in said exhaust path (108)
- a second valve (114) disposed between said accumulator and said intake path (112);
said inlet (104) of said accumulator (102) connectable to said exhaust path (108) through said first valve (110) and said outlet 106 of accumulator (102) connectable to intake path (112) through said second valve (114).
2. The fuel injection system (100) according to claim 1 wherein said first and second valves (110) and (114) are electronically controlled valves
3. The fuel injection system according to claim 1 wherein said first valve (110) has one inlet through which it receives exhaust gases
4. The fuel injection system according to claim 1 wherein said first valve (110) has two outlets; one outlet connectable to inlet of accumulator and other outlet connectable to further exhaust path (116)
5. A fuel injection system according to claim 1 wherein said first valve (110) closes inlet (104) of said accumulator (102) during normal mode of said engine (101)
6. A fuel injection system according to claim 1 wherein said first valve (110) connects said exhaust path (108) to said inlet (104) of said accumulator (102) after a predefined time T1 after detection of overrun condition of said engine (101)
7. A fuel injection system according to claim 6 wherein said overrun condition occurs when there is no demand for torque
8. A fuel injection system according to claim 1 wherein said first valve (110) connects exhaust path (108) to further exhaust path (116) after a predefined time T2 after detection of overrun condition of said engine
9. A fuel injection system according to claim 1 wherein said second valve (114) opens for a predefined time T3, when engine (101) is changing from overrun mode to normal mode

10. An electronic control unit (118) comprising:
- an input to receive a signal (122) indicative of an overrun condition of a vehicle
- A first output line connected to a first valve (110) said first valve (110) being placed in an exhaust path (108) of said engine (101)
- a second output line connected to a second valve (114) placed in an intake path (112) of said engine
said electronic control unit (118) adapted to control said first valve (110) and aid second valve (114) in a normal mode during normal mode of said engine; said electronic control unit (118) further adapted to control first valve (110) and second valve 114 in an overrun mode during overrun mode of said engine (101)

11. A method to store unburnt fuel-air mixture in an accumulator (102) during overrun condition of an engine (101) said method comprising steps of:
- detecting overrun condition of said engine (101)
- stopping the fuel injection by de-activating the injector (120)
- after a predetermined time T1, operating a first valve (110) to connect exhaust path 108 to inlet 104 of said accumulator (102)
- after a predetermined time T2, operating said first valve (110) to connect exhaust path (108) to further exhaust path (116)
- detecting engine (101) coming out of overrun mode
- Starting injections by activating the injector 120
- Opening a second valve (114) to release gases from said accumulator (102) into an intake path (112)
- after a predetermined time T3, closing said second valve (114)

, Description:Field of the invention:
[0001] This invention relates to the field of fuel injection systems.
Background of the invention:
[0002] Storing of fuel vapors in a canister is known in prior arts. At regular intervals these fuel vapors are released into intake path of fuel injection system.
[0003] The US patent US7305975 B2 discloses one such purging control of fuel vapors. Disclosed in the prior art is a system and a method for purging a vapor storage canister having adsorbed fuel vapor by drawing air through the storage canister. The engine controller uses the estimated amount of fuel vapor and air brought into the engine from the evaporative vapor storage canister for better control of engine air and fuel during purging.

Brief description of the accompanying drawings:
[0004] An embodiment of the disclosure is described with reference to the following accompanying drawing,
[0005] Fig. 1 illustrates a fuel injection system with an accumulator

Detailed description of the embodiments:
[0006] FIG. 1 illustrates a fuel injection system 100. The fuel injection system 100 may be referred as system in the rest of the document. The system provides a solution for storing unburnt fuel air mixture in an accumulator 102. The system 100 comprises the accumulator 102 having an inlet 104 and an outlet 106; the inlet 104 connected to an exhaust path 108 of a vehicle through a first valve 110; the outlet 106 connected to an intake path 112 of the vehicle through a second valve 114. The first valve 110 has one inlet (shall be referred as I1) and two outlets (shall be referred as O1 and O2) whereas the second valve has one inlet (shall be referred as I2) and one outlet (shall be referred as O2-2). The first valve 110 receives the exhaust gases through the inlet I1 and guides the same either to the accumulator 102 or to the further exhaust path 116 depending upon the engine operating mode. The second valve 114 is a simple open or close type valve. The second valve 114 is opened depending upon the engine operating modes.
[0007] The system has an injector 120 disposed in the intake path 112. There may be more than one intake path and in each intake path an injector is disposed.
[0008] The engine 101 has different modes of operations like normal mode and overrun mode. The normal mode is the one where fuel injections happen and engine 101 generates torque. These fuel injections may be in the intake path 112 of the engine 101. The fuel injected gets mixed with the air drawn from the intake path 112 and the air fuel mixture burns in the cylinders of the engine 101. The exhaust gases flow through exhaust path 108 and 116.
[0009] In the overrun mode, there is no demand from the driver for the torque. In other words the driver has removed the foot from the accelerator. In such a scenario the injections are stopped and the vehicle may be running because of its momentum. This may happen during downhill travel of the vehicle. During overrun mode, the engine 101 will not generate the torque, but the engine 101 itself will be driven by the vehicle. The overrun mode is also referred as overrun condition.
[0010] During normal mode of the engine 101, in the first valve, I1 is connected to O1 so that the exhaust gases flow through the exhaust path into atmosphere as shown by the arrow ‘A’. The second valve 114 normally remains closed.
[0011] In the overrun mode, in the first valve, I1 is connected to O2 so that the exhaust gases flow through the inlet 104 of the accumulator 102 and into the accumulator 102 for storing, as shown by the arrow ‘B’.
[0012] The second valve 114 normally remains closed. This valve is opened by the ECU 118 only for a short duration when the engine 101 changes mode from overrun to normal. After a predefined short interval of time, the outlet O2-2 is closed by closing the valve 114
[0013] When the ECU 118 detects that there is no torque demand, overrun condition occurs. In this situation ECU 118 cuts off the fuel injections for further cycles of engine operation by de-activating the injector 120. The ECU 118 will also cut off the spark ignitions as the case may be. Even though the fuel injection is stopped on detection of overrun condition, there will be some fuel air mixture already existing in the intake path 112 in the current driving cycle since it is manifold injection. In the absence of the present invention, this air fuel mixture will enter into the cylinder and comes out without burning, through the exhaust path 108 and 116 into the atmosphere as shown by ‘A’. This will cause pollution.
[0014] To prevent the unburnt air fuel mixture coming out of the exhaust path into the atmosphere, the invention proposes an accumulator 102 to store the air-fuel mixture on the detection of the overrun condition.
[0015] The method of storing the air-fuel mixture in the accumulator is explained below:
[0016] When there is no torque demand, the ECU 118 detects it as an overrun condition of the engine 101. The ECU 118 stops the fuel injections into the intake path 112. This is done by de-activating the injector by stopping power supply to the injector. After a predefined time T1, the ECU 118 connects the exhaust path 108 to the accumulator 102 as shown with ‘B’ and blocks the exhaust gases flowing into further exhaust path 116. This is done by connecting the inlet I1 in the first valve to outlet O2 which connects to the accumulator 102 to guide the exhaust gases to the accumulator 102. The unburnt air-fuel mixture enters into the accumulator 102. The unburnt air-fuel mixture gets stored into the accumulator 102.
[0017] After a pre-defined time T2 after detecting the overrun condition, the ECU 118 operates the first valve in such a way that the inlet of accumulator is closed and the exhaust gases pass through the further exhaust path 116 into atmosphere. This is to avoid any pressure increase in the accumulator 102 above a safe operating limit. The time durations T1 and T2 are calibrated during testing of the engine and the values for T1 and T2 are stored in the ECU 118.
[0018] When the ECU 118 detects that there is torque demand, then the injections are started again. This is done by activating the injector by providing power to the injector as required. The fuel is injected into the intake path 112. At the same time the second valve 114 is opened so that the gases stored in the accumulator 102 flow into intake path 112 mixing with air coming in from atmosphere. The first valve 110 is operated in such a way that the exhaust gases will not enter into accumulator but exit to atmosphere as shown by arrow ‘A’. This is achieved by connecting the inlet I1 to O1 leaving the exhaust gases into the atmosphere. After a predefined time T3 the second valve 114 is closed and remains closed.
[0019] The accumulator 102 will have a mechanical valve as backup to control the pressure inside. This mechanical valve is not shown in the figure. As the accumulator 102 size is limited, the accumulator 102 can store the air-fuel mixture only up to a predefined pressure limit. Once the pressure in the accumulator 102 reaches this predefined pressure limit, the mechanical valve opens automatically and releases the contents of accumulator into the intake path 112. Once the pressure in the accumulator 102 drops below the predefined limit, the mechanical valve closes automatically. This mechanical valve is a one way, spring actuated valve.
[0020] When the pressure in the accumulator 102 reaches the predefined limit, the spring expands and the mechanical valve opens. When the pressure in the accumulator 102 falls below the predefined limit, the spring contracts and the mechanical valve closes.
[0021] The ECU 118 controls the first and second valves (110 and 114) based on whether the engine is operating in normal mode or going to enter into overrun mode. For this purpose ECU 18 receives various sensor signals like signals from accelerator pedal, engine speed, vehicle speed etc. These signals are collectively shown as 122. The ECU 118 has input interfaces to receive these signals. The input interfaces may be input ports which are configured to receive these signals 122. The ECU 118 also has output interfaces which are connected to various actuators like first valve, second valve, injector etc. The output interfaces may be output ports which are configured to send signals to these actuators. The ECU 118 operates the first and second valves using an internal logic stored in it. As the input interfaces and output interfaces of the ECU 118 are commonly understood, they are not shown in fig.