This invention relates to the field of operating an electric feed pump in a fuel injection system.
Background of the invention
[0002] In a fuel injection system, an electrical feed pump (EFP) has to supply fuel from a reservoir/ fuel tank to the inlet of common rail fuel injection system. For the feed pump control (FPC) the EFP must be able to supply varying flow rate based on engine demand at different pressures. The pulse width modulation (PWM) signal (duty cycle) in terms of voltage supply to control the EFP flow rate is supplied by the engine control unit (ECU). During overrun condition, fuel from the EFP flows to the high pressure fuel injection pump, and returns to the fuel tank through a zero-delivery throttle (ZDT). The ZDT is a flow path connecting the high pressure fuel injection pump and the fuel tank.
[0003] Prior art patent application US3 822677 discloses a fuel pump control circuit to provide optimum fuel delivery at constant operating pressure to the fuel injector valve means of an electronically controlled fuel supply system, By energizing the pump in response to the engine operating parameters which determine the engine fuel requirement, a minimum of fuel in excess of the fuel requirement is recirculated from the area of the engine back to the fuel reservoir. In order to suitably energize the fuel pump, the pump is provided with a maximum voltage during the time period of the injection pulse with the energizing voltage decreasing thereafter so that a minimum of fuel is circulated through the fuel supply system during the no injection phase. This provides a variable level of average fuel pump energization.

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 method of operating an electric feed pump in a fuel injection system.
Detailed description of the embodiments
[0006] FIG. 1 illustrates a method of operating an electric feed pump in a fuel injection system. The fuel comprising atleast a fuel injection pump located downstream to the electric feed pump, and an injector. A shut-off condition of the injector is detected (100) by a control unit. The load on the engine is also detected (102) by the control unit. The control unit verifies (104) if the shut-off condition corresponds to an engine overrun condition. The electric feed pump is operated (106) at a voltage, such that pressure of fuel through the electric feed pump is less than opening pressure fuel injection pump.
[0007] The working of the electric feed pump in the fuel injection system will be explained in further detail. The electric feed pump is used to supply fuel from the tank to the inlet of the fuel injection pump. A voltage is supplied to the electric feed pump in order to pump fuel out of the fuel injection pump. The magnitude of voltage is such that the pressure of the fuel that flows to the inlet of the fuel injection pump must be sufficient enough to open an inlet valve of the fuel injection pump. When an engine is under overrun condition, fuel is not required to be delivered to the injector in the fuel injection system. In such a condition, in order to save energy, and to prevent further pressurization of the fuel reaching the fuel injection pump, the electronic control unit, operates the electric feed pump in a manner such that pressure of fuel through said electric feed pump is less than opening pressure fuel injection pump. This results is in

the inability of fuel to flow from the electric feed pump into the fuel injection. Since the fuel does not reach the fuel injection pump, the need for a return line during from the fuel injection is not required. Hence during engine overrun condition, the need for the electric feed pump to supply fuel to the fuel injection pump is not required. This results in the elimination of zero-delivery throttle. After completion of the engine overrun condition, when the load on the engine increases, there is need for fuel to be pressurized by the high pressure pump. Hence the voltage that is supplied to the electric feed pump will be such that that pressure of fuel through said electric feed pump is greater than opening pressure of fuel injection pump when said load on said engine corresponds to engine operating condition. The engine operating condition here refers to the condition where there is a demand for power from the user of a vehicle by operating the throttle, this demand increases the load on the engine. Hence to meet the demand from the engine, the electric feed pump starts supplying fuel for injection.
[0008] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. 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.

CLAIMS
We Claim:
1. A method for operating an electric feed pump in a fuel injection system, said
fuel injection system comprising atleast a fuel injection pump located
downstream to said electric feed pump, and an injector, said method
comprising:
detecting (100), by a control unit, shut-off condition of said injector;
detecting (102) by said control unit a load on said engine; verifying (104), by said control unit, if said shut-off condition corresponds to an engine overrun condition based on said load; operating (106) said electric feed pump at a voltage, such that pressure of fuel through said electric feed pump is less than opening pressure of fuel injection pump during said engine overrun condition.
2. The method of claim 1, said method comprising operating said electric feed
pump at a voltage, such that pressure of fuel through said electric feed pump
is greater than opening pressure of fuel injection pump when said load on
said engine corresponds to engine operating condition.