Claims:We Claim:
1. A fuel injection system (100)comprising at least:
a common rail high pressure pump (102);
a mechanical injector (104); and
an electronic control unit (106) adapted to control said common rail pump in order to deliver the required quantity of fuel to said mechanical injector 104.
2. The fuel injection system of claim 1, wherein a metering unit (108) is integrated with said common rail pump.

3. A method for controlling flow of fuel in a fuel injection system, said method comprising:

Receiving (200), by a common rail pump, the quantity of fuel to be delivered into said common rail high pressure pump 102 in dependence of fuel required to be delivered into an engine cylinder, from a control unit;

Actuating (202), a metering unit of said common rail high pressure pump 102 to deliver said quantity of fuel into said common rail high pressure pump 102; and

Delivering (204), said quantity of fuel to a mechanical injector, by said common rail pump for injection into said engine cylinder.
, Description:Field of the invention
[0001] This invention relates to the field of fuel injection system.

Background of the invention
[0002] Fuel injection system using a standalone mechanical injector offer a limited variation to different environmental conditions. Due to this, it is difficult to meet the ever changing and increasingly demanding emission requirements of the future with pure mechanical systems alone. This is because in the absence of any feedback from a mechanical injector, a mechanical fuel pump will pressurize fuel irrespective of the demand. However, a mechanical injector offers cost effective solution, for example, in single cylinder diesel engines. In emerging economies, the use of a mechanical injector cannot be done away with. Hence there is a need to control the quantity of fuel that is delivered to a mechanical injector.

Brief description of the accompanying drawing
[0003] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0004] FIG. 1 illustrates a fuel injection system; and
[0005] FIG. 2 illustrates a method for controlling flow of fuel in a fuel injection system.

Detailed description of the embodiments
[0006] FIG. 1 illustrates a fuel injection system 100. The fuel injection system 100 comprises at least a common rail high pressure pump 102, a mechanical injector 104 and an electronic control unit (106) adapted to control said common rail pump in order to deliver the required quantity of fuel to said mechanical injector 104.
[0007] The fuel injection system 100 disclosed herein is used to inject fuel from a mechanical injector 104 into an engine cylinder. In order to achieve injection of fuel from a mechanical injector 104 a common rail pump is employed. The fuel injection system 100 comprises at least a common rail high pressure pump 102. A metering unit 108 is integrated with the common rail high pressure pump 102. The function of the metering unit 108 is to ensure that the amount of fuel entering the common rail high pressure pump 102 is equal to the amount required by the mechanical injector 104. Since a mechanical injector 104 does not provide any real time feedback about the injection quantity, a control unit 106, will, based upon the speed and load on the engine, estimate the amount of fuel that needs to be delivered to the mechanical injector 104. The control unit 106 then actuates a metering unit 108, the fuel that is flowing from the fuel tank, will flow through the metering unit 108 and entering the pressurizing chamber of the common rail high pressure pump.
[0008] FIG. 2 illustrates a method for controlling flow of fuel in a fuel injection system 100. The method comprises receiving (200), by a common rail pump, the quantity of fuel to be delivered into the common rail high pressure pump 102 in dependence of fuel required to be delivered into an engine cylinder, from a control unit 106. Actuating (202), a metering unit 108 of the common rail high pressure pump 102 to deliver the quantity of fuel into the common rail high pressure pump 102 and delivering (204), the quantity of fuel to a mechanical injector 104, by the common rail pump for injection into the engine cylinder.
[0009] The working of the fuel injection system 100 is explained herewith. Fuel from a fuel tank (not shown) is delivered to the common rail pump. The common rail pump comprises a barrel and a plunger. The plunger is driven by the pump cam that is connected to the engine cam shaft. The rotational orientation of the pump cam is synchronized with the engine firing point. This phase relationship is stored in the engine control unit 106 (ECU) to be used for controlling injection timing. The pump cam moves the plunger in the delivery direction and the plunger spring ensures the plunger returns to the starting position by the end of each cycle.
[0010] The common rail pump also comprises the metering unit 108, the metering unit 108 will receive fuel from a fuel tank. The fuel will be delivered to the metering unit 108 from the tank (101) either by gravity feed, mechanical or electrical pre-feed pump. Excess fuel from the metering unit (108) will be delivered back to the tank. The fuel will be drawn into the plunger room through suction valve. The fuel quantity is electronically controlled by the metering unit (108) as per instructions from the ECU (106). The ECU generates actuating signals based on various inputs from sensors and actuators, for example, speed, temperature and accelerator pedal sensor. The fuel will be pressurized within the plunger room during compression stroke of the plunger and delivered through the delivery valve to the mechanical injector (104). After reaching a threshold pressure the injector will open and inject the fuel to the combustion chamber of the engine. The threshold pressure of the injector is mainly defined by force of the spring of the mechanical injector 104.
[0011] To avoid unwanted secondary injection after closing of the injector needle, the delivery valve should be designed as a constant pressure valve or a constant relief valve. The proposed fuel injection system 100, enables a common rail pump to deliver fuel to a mechanical injector 104. By using the above mentioned combination, it is possible to bring about a control to the mechanical injector 104.
[0012] In the proposed fuel injection system 100, it is possible to control the following. Injection quantity: controlled by actuation time of the metering unit 108. Start of injection: controlled only quantity dependent by actuation time of metering unit 108, small injection quantity will cause retarded start of injection, full injection quantity will cause advanced start of injection. Injection pressure: controlled by cam design, speed and actuation time of metering unit 108. Load and speed based pressure dependency feasible.
[0013] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention in terms of type of injector used. 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.