초록 ▼

A direct injection spark ignition multi-cylinder internal combustion engine operative in a controlled auto-ignition combustion mode includes a direct fuel injection system, a spark ignition system and a controllable engine valve system. The air/fuel ratio in the exhaust gas feedstream and an intake

A direct injection spark ignition multi-cylinder internal combustion engine operative in a controlled auto-ignition combustion mode includes a direct fuel injection system, a spark ignition system and a controllable engine valve system. The air/fuel ratio in the exhaust gas feedstream and an intake mass air flow are measured and an actual air/fuel ratio is calculated based upon the intake mass air flow and engine fueling. Magnitude of a negative valve overlap period between an exhaust valve closing and an intake valve opening is adjusted based upon the measured mass air flow. Timing of pre-injection fueling is adjusted during the negative valve overlap period based upon the measured air/fuel ratio.

대표청구항 ▼

The invention claimed is: 1. Method for operating an internal combustion engine including a direct fuel injection system, a spark ignition system and a controllable engine valve system, comprising: operating the engine in a controlled auto-ignition mode; measuring an air/fuel ratio in an exhaust ga

The invention claimed is: 1. Method for operating an internal combustion engine including a direct fuel injection system, a spark ignition system and a controllable engine valve system, comprising: operating the engine in a controlled auto-ignition mode; measuring an air/fuel ratio in an exhaust gas feedstream; measuring an intake mass air flow; determining an actual air/fuel ratio based upon the measured intake mass air flow and an engine fueling; adjusting magnitude of a negative valve overlap period between an exhaust valve closing and an intake valve opening based upon the measured intake mass air flow; and controlling timing of pre-injection fueling during the negative valve overlap period based upon the measured air/fuel ratio. 2. The method of claim 1, comprising adjusting the magnitude of the negative valve overlap period and controlling the timing of pre-injection fueling during the negative valve overlap period based upon the measured air/fuel ratio and the measured mass air flow. 3. The method of claim 1, further comprising: determining a preferred engine operating point; determining a preferred intake mass air flow based upon the preferred engine operating point; and adjusting the magnitude of the negative valve overlap period between the exhaust valve closing and the intake valve opening based upon a difference between the preferred intake mass air flow and the measured intake mass air flow. 4. The method of claim 3, comprising decreasing the negative valve overlap period between the exhaust valve closing and the intake valve opening to increase the measured intake mass air flow. 5. The method of claim 3, comprising increasing the negative valve overlap period between the exhaust valve closing and the intake valve opening to decrease the measured intake mass air flow. 6. The method of claim 5, comprising simultaneously equally advancing the exhaust valve closing and retarding the intake valve opening to increase the magnitude of the negative valve overlap period. 7. The method of claim 5, comprising simultaneously equally retarding the exhaust valve closing and advancing the intake valve opening to decrease the magnitude of the negative valve overlap period. 8. The method of claim 1, wherein operating the engine in the controlled auto-ignition mode comprises controlling an engine intake air throttle to a substantially wide-open position and controlling timings of injections of the engine fueling comprising the pre-injection fueling and a main fueling. 9. The method of claim 8, comprising: calculating an actual air/fuel ratio for the engine fueling; determining an amount of fuel reforming; and controlling timing of the pre-injection fueling during the negative valve overlap period based upon the amount of fuel reforming and the actual engine air/fuel ratio. 10. The method of claim 9, comprising determining the amount of fuel reforming based upon a difference between the actual air/fuel ratio and the measured air/fuel ratio. 11. The method of claim 10, comprising advancing timing of the pre-injection fueling during the negative valve overlap period to increase the amount of fuel reforming. 12. The method of claim 10, comprising retarding timing of the pre-injection fueling during the negative valve overlap period to decrease the amount of fuel reforming. 13. Method for operating an internal combustion engine in a controlled auto-ignition combustion mode, comprising: determining a preferred engine operating point; determining a fueling rate, a preferred air/fuel ratio and a preferred mass air flow based upon the preferred engine operating point; measuring an air/fuel ratio of the exhaust gas feedstream; measuring mass air flow of engine intake air; determining an actual air/fuel ratio based upon the measured mass air flow and the fueling rate; controlling engine valve timing to achieve a preferred negative valve overlap period based upon the preferred air/fuel ratio; and controlling timing of a pre-injection fueling during the negative valve overlap period to achieve a preferred amount of fuel reforming. 14. The method of claim 13, comprising determining the amount of fuel reforming based upon a difference between the actual air/fuel ratio and the measured air/fuel ratio. 15. The method of claim 14, further comprising: determining the amount of fuel reforming based upon a difference between the actual air/fuel ratio and the measured air/fuel ratio; and increasing the difference between the actual air/fuel ratio and the measured air/fuel ratio by advancing timing of the pre-injection fueling to increase the amount of fuel reforming. 16. The method of claim 14, further comprising decreasing the difference between the actual air/fuel ratio and the measured air/fuel ratio by retarding timing of the pre-injection fueling to decrease the amount of fuel reforming. 17. Method for controlling fuel reforming in a direct injection spark ignition internal combustion engine operating in a controlled auto-ignition combustion mode, comprising: determining a preferred engine operating point based upon an operator torque request; determining a fueling rate, a preferred air/fuel ratio and a preferred mass air flow based upon the preferred engine operating point; measuring an air/fuel ratio of the exhaust gas feedstream; measuring mass air flow of engine intake air; determining an actual air/fuel ratio based upon the measured mass air flow and the fueling rate; and controlling timing of a pre-injection fueling during the negative valve overlap period based upon a difference between the actual air/fuel ratio and the measured air/fuel ratio. 18. The method of claim 17, further comprising controlling engine valve timing to achieve a preferred negative valve overlap period based upon the preferred air/fuel ratio. 19. The method of claim 17, further comprising advancing timing of the pre-injection fueling during the negative valve overlap period to increase the amount of fuel reforming. 20. The method of claim 19, further comprising retarding timing of the pre-injection fueling during the negative valve overlap period to decrease the amount of fuel reforming.