CLIAMS:We Claim:
1. Fuel metering unit (101) for an electric feed pump (100), said electric feed pump in flow communication with a fuel tank (102), characterized in that, said fuel metering unit (101) comprising,
a valve (104) located at the inlet of said electric feed pump (100), and
an electrical interface (106) adapted to receive signal from an electronic control unit (ECU) to actuate said valve (104).

2. The electric feed pump 100 of claim 1, wherein said electric feed pump 100 is an in-tank electric feed pump 100.

3. The electric feed pump 100 of claim 1, wherein said electric feed pump 100 is an in-line electric feed pump 100.

4. The electric feed pump 100 of claim 1, wherein said valve 104 is one of a solenoid valve, and a hydraulic valve.

5. An electric feed pump 100,
said electric feed pump 100 in flow communication with a fuel tank 102,
characterized in that a fuel metering unit (101) integrated with said electric feed pump, said fuel metering unit 101 comprising,

a valve (104) located at the inlet of said electric feed pump (100), and
an electrical interface (106) adapted to receive signal from an electronic control unit (ECU) to actuate said valve (104).

,TagSPECI:Field of the invention
[0001] This invention relates to a fuel metering unit for an electric fuel feed pump in a fuel injection system.

Background of the invention
[0002] Metering of fuel in a common rail fuel injection system is required to ensure that the required quantity of fuel as desired by the high pressure pump is supplied by a fuel tank. Fuel injection system employing a mechanical supply pump, have a fuel control unit (FCU) also called as a metering unit to supply fuel to the high pressure pump. In newer generation of common rail fuel injection system, we have an electric feed pump that supplies fuel to the high pressure pump. The subject of interest here is about the latter kind of system, i.e common rail fuel injection system employing an electric feed pump. The electric feed pump generally operates at full capacity (rated voltage and pressure). The voltage and pressure to the EKP is generally at the maximum rated value for the low pressure circuit in the common rail fuel injection system. Hence, here is need to reduce the load on the electric feed pump because the electric feed pump need not operate at full capacity throughout the working of the high pressure pump.

[0003] Prior art patent application JP-11229999 discloses a solenoid valve for metering distributed along a first fuel path, to perform fuel connection from a low-pressure feed pump to a high-pressure pump. A hydraulic actuation type throttle valve is arranged along a second fuel path, by-passing the solenoid valve. The amount of opening of the throttle valve can be adjusted based on the downstream-side pressure of the solenoid valve.

Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[0005] FIG. 1 illustrates a fuel metering unit for an electric feed pump; and

[0006] FIG. 2 shows a graph showing the current consumed in an electric feed pump, with and without inlet metering and the rate of flow of fuel through the electric feed pump.

Detailed description of the embodiments
[0007] FIG. 1 illustrates a fuel metering unit 101 for an electric feed pump 100. The electric feed pump 100 in flow communication with a fuel tank 102. The fuel metering unit 101 is characterized in having a valve 104 located at the inlet of the electric feed pump 100, and an electrical interface 106 adapted to receive signal from an electronic control unit (ECU), to actuate the valve 104. The valve 104 may be located at the inlet of the electric feed pump 100. The electric feed pump 100 may be an in-tank electric feed pump 100, the electric feed pump 100 may also be an in-line electric feed pump 100. The function of the fuel metering unit 101 is to meter the quantity of fuel that is reaching the electric feed pump 100 in dependence of the fuel that needs to be delivered to the high pressure fuel injection pump 110. This is achieved by having an electrical interface 106 adapted to receive signal from an ECU to actuate the valve 104, the same will now be described in further detail.

[0008] For the purpose of better understanding, the fuel metering unit 101 for an electric feed pump 100 is described with respect to an in-tank electric feed pump 100. An electric feed pump 100 is in flow communication with the fuel present in the fuel tank 102. A valve 104 is located at the inlet of the electric feed pump 100. The valve 104 may also be integrated with the electric feed pump 100. The valve 104 may be a solenoid valve 104 or a hydraulic valve. The function of the valve 104 is to meter the quantity of fuel entering the electric feed pump 100 in dependence of signals received from the ECU and when the electric feed pump is actuated so as to create a suction effect at the outlet of the valve. An electrical interface 106 is adapted to receive signal from an electronic control unit (ECU), to actuate the valve 104. Depending upon the amount of fuel that needs to be made available at the inlet of the fuel injection pump 110, the ECU sends a signal to the electrical interface 106. A voltage of suitable magnitude is supplied to the electric feed pump 100. The solenoid valve 104 is actuated by the ECU in a manner such that the flow of fuel that is coming out of the electric feed pump 100 is equal to the quantity that is required at the inlet of the fuel injection pump 110. By having the solenoid valve 104 at the inlet to the electric feed pump 100, the overflow valve that is generally required in the low pressure circuit leading to the high pressure fuel injection pump 110 is no longer required. The fuel flows from the electric feed pump 100 via a fuel filter to reach the fuel injection pump 110. Since the amount of fuel flow out of the electric feed pump 100 is equal to that required at the inlet of fuel injection pump 110, a reduction in hydraulic energy in the low pressure circuit is achieved.

[0009] FIG. 2 shows a graph showing the current consumed in an electric feed pump, with and without inlet metering and the rate of flow of fuel through the electric feed pump. The x-axis of the graph represents the pressure of fuel in the low pressure circuit. The Y-axis of the graph represents the flow rate of fuel out of the electric feed pump. The Z-axis of the graph represents the current supplied to the electric feed pump with and without inlet metering. Curve C1 represents the rate of flow of fuel out of the electric feed pump without inlet metering, curve C2 represents the current supplied to electric feed pump with and without inlet metering. Curve C3 represents the rate of flow of fuel from the electric feed pump, modified to meet the engine requirement by having metering at inlet of the electric feed pump. Curve C4 represents rate of flow of fuel corresponding to the engine requirement. The following observations can be made from the graph. By having a valve at the inlet of the electric feed pump, it is now possible to match the flow of fuel (C3) according to engine requirement (C4). The valve 104 meters flow of fuel from the fuel tank 102 to an inlet of the electric feed pump 100 in dependence of signal received from the ECU when the electric feed pump is actuated. Since the amount of fuel reaching the inlet of the high pressure pump is metered by actuating the valve, only a specified quantity of fuel as required to the injected into the engine is now sent from the electric feed pump. Hence, the curve (C3) and curve (C4) now follow a linear pattern. At any point on curve (C4) say Q2, Q2 representing the flow of fuel at a given engine operating condition, the current supplied to the electric feed pump corresponding to Q2 is I2. Conversely, if we consider the curve (C1), at any point on curve (C1) say Q1, Q1 representing the flow of fuel at a given engine operating condition, the current supplied to the electric feed pump corresponding to Q1 is I1. A saving in electric energy supplied to the electric feed pump is achieved, the saving being approximately equal to the difference between I1 and I2. Also, a reduction in the rate of flow of fuel (approximately equal to the difference between Q1 and Q2) is now achieved. Hence, a saving in both electric and hydraulic energy can be achieved by having inlet metering for the electric feed pump.

[00010] 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 valve used and the configuration of the electric feed pump. 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.