Claims:We Claim:
1. A fuel injection system (100), said fuel injection system (100) comprising at least a low pressure circuit comprising a fuel tank (102), a fuel filter (103) and a high pressure pump (104), characterized in that:
an auxiliary tank (106) located downstream to said fuel filter (103) and upstream to said high pressure pump (104);
said auxiliary tank (106) opening into a first flow path (107) and a second flow path (109), said first flow path (107) comprising a first control valve (108) and second flow path (109) comprising a second control valve (110), the operating pressure of first control valve 108 is not equal to the operating pressure of said second control valve 110.

2. The fuel injection system 100 of claim 1, wherein said first flow path (107) is in flow communication with the inlet of the high pressure pump (104).

3. The fuel injection system 100 of claim 1, wherein said second flow path (109) is in flow communication with said fuel tank (102).
, 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 the field of fuel injection system.

Background of the invention
[0002]A high pressure fuel injection pump supplies fuel to the engine for combustion via a common rail and injector. The pressure at which the high pressure fuel injection pump receives fuel is an important parameter for ensuring complete and proper filling of fuel within the high pressure fuel injection pump. For example, if a high pressure fuel injection pump is calibrated to receive fuel at a pressure between 1-5 bar, there exists a situation where the fuel pressure may drop or exceed this limit. Lower delivery pressure causes failure in the components of fuel injection pump due to cavitation as well as engine stalling due to insufficient fuel delivery from the fuel Injection pump. Whereas, higher fuel inlet pressure to fuel injection pump may cause failure in the sealing rings.

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 method of controlling flow of fuel in a fuel injection system.

Detailed description of the embodiments
[0005] FIG. 1 illustrates a fuel injection system 100. The fuel injection system 100 comprises a low pressure circuit comprising a fuel tank 102, a fuel filter and a high pressure pump 104. An auxiliary tank 106 is located downstream to the fuel tank 102 and upstream to the high pressure pump 104. The auxiliary tank 106 opens into a first flow path 107 and a second flow path 109, the first flow path 107 comprises a first control valve 108and the second flow path 109 comprises a second control valve 110, the operating pressure of first control valve 108is not equal to the operating pressure of the second control valve 110. The first flow path 107 is in flow communication with the inlet of the high pressure pump 104. The second flow path 109 is in flow communication with the fuel tank 102.

[0006]The working of the fuel injection system 100 will be explained in further detail. The fuel injection system 100 disclosed herein is used for injecting fuel into the engine cylinder. The fuel injection system 100 comprises a low pressure circuit comprising a fuel tank 102 to store fuel, fuel from the fuel tank 102 flows through the fuel filter and then enters the high pressure pump 104. An auxiliary tank 106 is located downstream to the fuel tank 102 and upstream to the high pressure pump 104. The auxiliary tank 106 opens into a first flow path 107 and a second flow path 109, the first flow path 107 comprises a first control valve 108 and the second flow path 109 comprises a second control valve 110, the operating pressure of first control valve 108 is not equal to the operating pressure of the second control valve 110. The first flow path 107 is in flow communication with the inlet of the high pressure pump 104. The second flow path 109 is in flow communication with the fuel tank 102.

[0007]The fuel-injection system supplies fuel to the diesel engine. The high pressure pump 104 generates the necessary fuel pressure for injection and delivers the fuel at the required rate. For the high pressure pump 104 to generate sufficient pressure, injection quantity at desired injection rate, sufficient amount of fuel should be available inside the gallery of the high pressure pump, the gallery of the high pressure pump is the location where the fuel is pressurized. If the gallery of the high pressure pump is not supplied with sufficient fuel from the fuel tank, the high pressure pump will not be able to deliver the desired amount of fuel at desired rate. If the gallery is not filled completely with the fuel, during working of the high pressure pump, negative pressure and/ or vacuum is generated which will create cavitation, thus causing failure of the parts of the high pressure pump 104. Also in this condition, due to non-availability of sufficient fuel inside the gallery, the high pressure pump will not be able to supply desired amount of fuel, which will affect the drive ability of end application as well as load taking capability of the engine.

[0008] The low pressure circuit disclosed herein, is the fuel circuit, that connects from fuel tank 102 to the inlet of the high pressure pump 104, through series of components in between, like, for example the fuel filter 103. A feed pump (not shown) delivers the fuel from the fuel tank 102 to the high pressure pump continuously. It is necessary because there is possibility of formation of vapor bubbles and subsequently cavitation in the high pressure pump 104 due to suction of the rapidly moving plunger (not show) of the high pressure pump 104. This would lead to uncontrolled variations in the rate of delivery of fuel to the cylinders, causing rough running and possibly even mechanical damage to the engine.

[0009]In case of electrical feed pump, as soon as the ignition is switched on, feed pump starts delivering fuel from fuel tank 102 to the high pressure pump 104. If the engine is not cranked, then the fuel that is getting delivered to high pressure pump 102 will flow back to the fuel tank 102 through overflow valve and return line. In case of mechanical feed pump, when the ignition is switched on and cranked, starter motor rotates the crankshaft that is coupled with gear mechanisms, that drives cam shaft, in turn driving mechanical feed pump. Therefore, when mechanical feed pump is driven during cranking phase, it draws the fuel from fuel tank and delivers the fuel to FIP through series of components as mentioned above. The delivery pressure is decided based on the specification of FIP inlet pressure.

[0010]When the high pressure pump 104 works as explained above, the delivery pressure either drops due to the components based on the design, or else delivery pressure will be higher than the maximum limit. Both of these situations creates adverse effect on the components of the fuel injection system. Lower delivery pressure causes component failure due to cavitation as well as engine stalling due to insufficient fuel delivery from the high pressure pump. Whereas, higher fuel inlet pressure to high pressure pump 104 will cause. Therefore, both lower pressure & higher pressure (beyond specified pressure) is not desirable.

[0011]As described in fig. 1, fuel inlet pressure retainer comprises an auxiliary tank 106. When this component is included in the low pressure circuit, initially the auxiliary tank 106 is empty. When priming is done, the auxiliary tank 106 starts filling with fuel. The auxiliary tank 106 is filled unless and until valve opening pressure of first control valve 108 is reached. Once the valve opening pressure is reached, the delivery begins from reservoir to inlet of the high pressure pump. With this, it can be ensured that the fuel delivery is greater than minimum inlet pressure as per specification. The operating pressure of the first control valve 108 can be set at little higher pressure than the inlet pressure of the high pressure pump. The second control valve 110 is provided to ensure that the inlet pressure of the high pressure pump does not exceed maximum specified pressure of fuel at inlet. During working, if the maximum pressure limit is exceeded (which will be opening pressure of the second control valve 110), the second control valve 110 opens releasing the pressure and draining back the fuel to fuel tank through return line.

[0012]Draining bolt (not shown) may be provided proximal to the first control valve 108. This is to ensure proper filling in of fuel inside auxiliary fuel tank 102 by bleeding the air bubbles when fuel is refilled after the fuel tank is empty. Once the fuel tank is empty and the fuel is filled in the tank, bleeding screw (not shown) present in the high pressure pump is loosened. During priming, fuel is drawn from the fuel tank 102 and gets supplied to the auxiliary fuel tank 106. Priming to be continuously done, unless and until the fuel droplets along with air bubbles are observed at the bleeding screw outlet. Once all the air bubbles get eliminated and continuous flow of fuel is observed, priming is to be stopped and bleeding screw is to be tightened. When above said operation is done, it is ensured that the auxiliary fuel tank 106 is filled with fuel and the pressure inside the reservoir has reached the valve opening pressure of first control valve 108 (Fig. 1). The first control valve 108 opening pressure should be greater than the minimum fuel inlet pressure specification.

[0013]When this is ensured, it can be seen that, the delivery pressure from the auxiliary fuel tank 106 is always more than the minimum pressure requirement. The valve opening pressure (the first control valve 108 and the second control valve 110) can be adjusted by varying the spring stiffness, based on the requirement. Therefore, when the engine is cranked, feed pump starts delivering the fuel and the fuel already present inside the auxiliary fuel tank 102 is pushed further towards high pressure pump.

[0014]During this operation, there is also possibility of the inlet pressure of the high pressure pump to exceed maximum inlet pressure as specified. In this condition the second control valve 110 opening pressure (Fig. 2) needs to be set slightly less than maximum inlet pressure of the high pressure pump 104. Hence, when the pressure beyond first control valve 108 is same as or greater than second control valve 109 opening pressure, the second control valve opens to release the pressure and drains back excess fuel to the fuel tank through return line. As the second control valve 109 opening pressure will be set slightly less than maximum specification of fuel inlet pressure, it can be ensured that the fuel inlet pressure of the high pressure pump does not exceed the maximum specified limit.

[0015]By using the above mentioned the problem of lack of pressure during first filling of high pressure pump 104 can be avoided.

[0016] ‘Adapted’ or ‘arranged’, in the context of the instant disclosure, refers to the technical capability or the technical capacity of a component, in relation to which the term ‘adapted’ or ‘arranged’ is used, to carry out or executed a specified action or actions, upon the requirement of the specified action or actions to be carried out or executed. Moreover, the usage of the term ‘adapted’ or ‘arranged’ here, is in reference with the normal technical capability or technical capacity of the component, imparted by the design or the structure or the composition of the component, and not in reference with any special or extraneous capability or capacity, beyond the scope of the normal technical capability or technical capacity. Therefore there is a need to address this problem.

[0017]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 the type of high pressure pump 104 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.