Fuel injection device of direct injection engine

1. A fuel injection device of a direct injection engine, comprising:

an engine body;

a fuel injection valve for directly injecting fuel containing gasoline into a cylinder of the engine body; and

a controller for controlling the fuel injection by the fuel injection valve, the fuel injection valve including:

a nozzle hole for opening to face inside the cylinder;

a valve body for stroking to open and close the nozzle hole;

a first solenoid coil for stroking the valve body by a first stroke amount; and

a second solenoid coil for stroking the valve body by a second stroke amount,

wherein the controller operates the first solenoid coil and not the second solenoid coil to stroke the valve a first lift amount and thereby perform the fuel injection at least in an intake stroke period, when an operating state of the engine is within a range where an engine load is at least below a predetermined load within a low-engine-load range where compression-ignition combustion is performed, and

wherein the controller operates at least the second solenoid coil to stroke the valve body a second lift amount that is greater than the first lift amount and thereby perform the fuel injection with a fuel pressure of 40 MPa or above in a period between a late stage of compression stroke and an early stage of expansion stroke, only when the operating state of the engine is within a low-engine-speed range where an engine speed is below a predetermined speed within a high-engine-load range where the engine load is higher than the low-engine-load range.

2. The device of claim 1 , wherein spark-ignition combustion is performed within the high-engine-load range.

3. The device of claim 2 , wherein the valve body is a needle arranged in a fuel passage that is formed inside the fuel injection valve, the needle stroking to open and close the nozzle hole,

wherein the fuel injection valve further includes a first movable core arranged in the fuel passage and for being attracted to stroke the needle during the operation of the first solenoid coil, and a second movable core for being attracted to stroke the needle during the operation of the second solenoid coil, and

wherein the controller operates both the first and second solenoid coils at least within the low-engine-speed range of the high-engine-load range.

4. The device of claim 3 , wherein a geometric compression ratio of the cylinder is set to be 15:1 or above.

5. The device of claim 2 , wherein a geometric compression ratio of the cylinder is set to be 15:1 or above.

6. The device of claim 1 , wherein the valve body is a needle arranged in a fuel passage that is formed inside the fuel injection valve, the needle stroking to open and close the nozzle hole,

wherein the fuel injection valve further includes a first movable core arranged in the fuel passage and for being attracted to stroke the needle during the operation of the first solenoid coil, and a second movable core for being attracted to stroke the needle during the operation of the second solenoid coil, and

wherein the controller operates both the first and second solenoid coils at least within the low-engine-speed range of the high-engine-load range.

7. The device of claim 6 , wherein a geometric compression ratio of the cylinder is set to be 15:1 or above.

8. The device of claim 1 , wherein a geometric compression ratio of the cylinder is set to be 15:1 or above.

9. A method for operating a fuel injection device of a direct injection engine, the engine having an engine body, a fuel injection valve for directly injecting fuel containing gasoline into a cylinder of the engine body, and a controller operatively coupled to the fuel injection valve, the fuel injection valve including a nozzle hole for opening to face inside the cylinder, a valve body for stroking to open and close the nozzle hole, a first solenoid coil for stroking the valve body by a first stroke amount, and a second solenoid coil for stroking the valve body by a second stroke amount, the method comprising:

operating, via the controller, the first solenoid coil and not the second solenoid coil to stroke the valve a first lift amount and thereby perform the fuel injection at least in an intake stroke period, when an operating state of the engine is within a range where an engine load is at least below a predetermined load within a low-engine-load range where compression-ignition combustion is performed, and

operating, via the controller, at least the second solenoid coil to stroke the valve body a second lift amount that is greater than the first lift amount and thereby perform the fuel injection with a fuel pressure of 40 MPa or above in a period between a late stage of compression stroke and an early stage of expansion stroke, only when the operating state of the engine is within a low-engine-speed range where an engine speed is below a predetermined speed within a high-engine-load range where the engine load is higher than the low-engine-load range.

10. The method of claim 9 , further comprising:

performing, via the controller, spark-ignition combustion within the high-engine-load range.

11. The method of claim 10 , further comprising:

operating, via the controller, both the first and second solenoid coils at least within the low-engine-speed range of the high-engine-load range.

12. The method of claim 9 , further comprising:

operating, via the controller, both the first and second solenoid coils at least within the low-engine-speed range of the high-engine-load range.