Control system and control method of gasoline direct injection engine

1. A control system of a gasoline direct injection engine, comprising:

a low-pressure pump disposed at a fuel tank;

a high-pressure pump fluid-connected to the low-pressure pump and including:

a pressure chamber having an inlet and an outlet;

a plunger reciprocated in the pressure chamber by a fuel pump cam;

a high-pressure pump input valve disposed to selectively close the inlet of the pressure chamber and stop fuel flowing inside the high-pressure pump from the low-pressure pump; and

a high-pressure pump output valve disposed to selectively open the outlet of the pressure chamber and supply the fuel in the pressure chamber to injectors from the high-pressure pump in accordance with a reciprocation of the plunger;

an actuator connected to and operating the high-pressure pump input valve to selectively open the inlet of the pressure chamber;

a high-pressure pump pressure sensor measuring an internal pressure of the high-pressure pump;

a low-pressure pump pressure sensor measuring an internal pressure of the low-pressure pump;

an ignition key sensor;

a crankshaft rotation sensor; and

a control unit receiving signals from the high-pressure pump pressure sensor, the low-pressure pump pressure sensor, the ignition key sensor, and the crankshaft rotation sensor, and controlling the injectors and the actuator,

wherein the control unit is configured to:

determine whether a key for starting the engine is turned off,

determine a stroke of the high-pressure pump when the key for starting the engine is turned off,

control the actuator to operate the high-pressure pump inlet valve that selectively blocks a fluid flow between the low-pressure pump and the high-pressure pump so as to open the inlet of the pressure chamber when the determined stroke of the high-pressure pump is an expansion stroke and a difference in internal pressures of the high-pressure pump and the low-pressure pump is a predetermined pressure or less,

determine whether an RPM of the engine is less than or equal to a predetermined RPM to finish control process of the control unit,

determine a time point of closing the high-pressure pump input valve when the determined stroke of the high-pressure pump is a compression stroke,

wherein the time point of closing the high-pressure pump input valve is maintained at a current time point of closing the high-pressure pump input valve, when the internal pressure of the high-pressure pump is a predetermined critical pressure or less, and

wherein the time point of closing the high-pressure pump input valve is delayed by a predetermined time from the current time point of closing the high-pressure pump input valve when the internal pressure of the high-pressure pump is not the predetermined critical pressure or less, and

close the high-pressure pump input valve, if the high-pressure pump input valve is opened,

wherein the determining of the stroke of the high-pressure pump is performed by measuring the internal pressure of the high-pressure pump.

2. The system of claim 1 , wherein the actuator is a solenoid.

3. The system of claim 1 , wherein a first elastic member is mounted on the high-pressure pump inlet valve to elastically bias the high-pressure pump inlet valve toward the inlet of the pressure chamber.

4. The system of claim 1 , wherein a second elastic member is mounted on the high-pressure pump outlet valve to elastically bias the high-pressure pump outlet valve toward the outlet of the pressure chamber.

5. The system of claim 1 , wherein when the RPM of the engine is equal to the predetermined RPM, the RPM of the engine is 0.