Method of controlling a mechanical compression ratio, a closing timing of an intake valve and air stream
A spark ignition type internal combustion engine comprises a variable compression ratio mechanism able to change a mechanical compression ratio, a variable valve timing mechanism able to control a closing timing of an intake valve, and an air flow control valve controlling an air flow in a cylinder and able to control the amount of intake air fed into a combustion chamber. The mechanical compression ratio is made maximum so as to obtain the maximum expansion ratio at the time of engine low load operation and the actual compression ratio at the time of engine low load operation is made an actual compression ratio substantially the same as that at the time of engine medium and high load operation. When the engine load is in an extremely low load region, the air flow control valve is used to control an amount of intake air fed into the combustion chamber. Due to this, a high heat efficiency can be realized even in a region where the amount of intake air is difficult to control by changing the closing timing of the intake valve.
1. A spark ignition type internal combustion engine comprising a variable compression ratio mechanism able to change a mechanical compression ratio, a variable valve timing mechanism able to control a closing timing of an intake valve, and an air flow control valve controlling an air flow in a cylinder, wherein the mechanical compression ratio is made maximum so as to obtain the maximum expansion ratio at the time of engine low load operation and the actual compression ratio at the time of engine low load operation is made an actual compression ratio substantially the same as that at the time of engine medium and high load operation, and wherein said air flow control valve is used to control an air flow in a cylinder and an amount of intake air fed into the combustion chamber when the engine load is in an extremely low load region.
2. A spark ignition type internal combustion engine as set forth in claim 1 , wherein said closing timing of the intake valve is shifted as the engine load becomes lower in a direction away from intake bottom dead center until a limit closing timing enabling control of the amount of intake air fed into the combustion chamber.
3. A spark ignition type internal combustion engine as set forth in claim 2 , wherein said extremely low load region is a region of a load lower than the engine load when said closing timing of the intake valve reaches said limit closing timing.
4. A spark ignition type internal combustion engine as set forth in claim 3 , wherein at said extremely low load region, the closing timing of the intake valve is held at said limit closing timing.
5. A spark ignition type internal combustion engine as set forth in claim 2 , wherein in a region of a load higher than the engine load when the closing timing of the intake valve reaches said limit closing timing, the amount of intake air fed into the combustion chamber is controlled by changing the closing timing of the intake valve without depending on said air flow control valve and a throttle valve arranged in an engine intake passage.
6. A spark ignition type internal combustion engine as set forth in claim 5 , wherein in a region of a load higher than the engine load when the closing timing of the intake valve reaches said limit closing timing, the throttle valve is held in the fully opened state.
7. A spark ignition type internal combustion engine as set forth in claim 5 , wherein in a region of a load higher than the engine load when the closing timing of the intake valve reaches said limit closing timing, the air flow control valve is held in the fully opened state.
8. A spark ignition type internal combustion engine as set forth in claim 1 , wherein in said extremely low load region, a throttle valve arranged in an engine intake passage is substantially fully opened.
9. A spark ignition type internal combustion engine as set forth in claim 1 , wherein in said extremely low load region, said air flow control valve and a throttle valve arranged in an engine intake passage are used to control the amount of intake air.
10. A spark ignition type internal combustion engine as set forth in claim 9 , wherein at said extremely low load region, said air flow control valve is made smaller in opening degree as the engine load becomes lower, in the region of a load lower than the engine load when said air flow control valve becomes fully closed, a throttle valve arranged in an engine intake passage is used to control the amount of intake air fed into the combustion chamber.
11. A spark ignition type internal combustion engine as set forth in claim 1 , wherein said maximum expansion ratio is 20 or more.
12. A spark ignition type internal combustion engine as set forth in claim 1 , wherein at the time of engine low speed, regardless of the engine load, said actual compression ratio is made substantially 9 to 11.
13. A spark ignition type internal combustion engine as set forth in claim 12 , wherein the higher the engine speed, the higher the actual compression ratio.
14. A spark ignition type internal combustion engine as set forth in claim 1 , wherein said mechanical compression ratio is increased as the engine load becomes lower until a limit mechanical compression ratio.
15. A spark ignition type internal combustion engine as set forth in claim 14 , wherein in a region of a load lower than the engine load when said mechanical compression ratio reaches said limit mechanical compression ratio, the mechanical compression ratio is held at said limit mechanical compression ratio.