Spark Ignition Type Internal Combustion Engine

Abstract

A spark ignition type internal combustion engine comprises a variable compression ratio mechanism able to change a mechanical compression ratio, an actual compression action start timing changing mechanism able to change a start timing of an actual compression action, and an exhaust valve. At the time of engine low load operation, the mechanical compression ratio is maximized to obtain a maximum expansion ratio, and the actual compression ratio is set so that no knocking occurs. The maximum expansion ratio is 20 or more. The closing timing of the exhaust valve at the time of engine low load operation is made substantially intake top dead center. Due to this, even if operating the internal combustion engine in a state of a large expansion ratio, the temperature of the exhaust purification catalyst can be maintained at a relatively high temperature.

1 . A spark ignition type internal combustion engine comprising a variable compression ratio mechanism able to change a mechanical compression ratio, an intake variable valve timing mechanism able to change the closing timing of the intake valve, and an exhaust valve,
 wherein at the time of engine low load operation, the variable compression ratio mechanism controls the mechanical compression ratio so as to be maximized to obtain a maximum expansion ratio and the intake variable valve timing mechanism controls the closing timing of the intake valve so that the actual compression ratio is set so that no knocking occurs,   wherein said maximum expansion ratio is 20 or more, and   wherein the closing timing of the exhaust valve at the time of engine low load operation is made substantially intake top dead center.   
   
   
       2 . A spark ignition type internal combustion engine comprising a variable compression ratio mechanism able to change a mechanical compression ratio, an intake variable valve timing mechanism able to change the closing timing of the intake valve, and an exhaust variable valve timing mechanism able to change the closing timing of the exhaust valve,
 wherein at the time of engine low load operation, the variable compression ratio mechanism controls the mechanical compression ratio so as to be maximized to obtain a maximum expansion ratio and the intake variable valve timing mechanism controls the closing timing of the intake valve so that the actual compression ratio is set so that no knocking occurs,   wherein said maximum expansion ratio is 20 or more, and   wherein a settable region of the closing timing of the exhaust valve at the time of engine low load operation is limited more to an intake top dead center side than that at the time of engine high load operation.   
   
   
       3 . A spark ignition type internal combustion engine as set forth in  claim 2 , wherein at the time of engine low load operation, the closing timing of the exhaust valve is made substantially intake top dead center. 
   
   
       4 . A spark ignition type internal combustion engine as set forth in  claim 2 , wherein the closing timing of the exhaust valve and the opening timing of the intake valve are controlled so that at the time of engine low load operation a period where the opening of the intake valve and the opening of the exhaust valve overlap is made minimum. 
   
   
       5 . A spark ignition type internal combustion engine as set forth in  claim 2 , wherein the closing timing of the exhaust valve and the opening timing of the intake valve are controlled so that at the time of engine low load operation the period where the opening of the intake valve and the opening of the exhaust valve overlap becomes zero. 
   
   
       6 . A spark ignition type internal combustion engine as set forth in  claim 1 , wherein at the time of engine low load operation, the opening timing of the intake valve is made substantially intake top dead center. 
   
   
       7 . A spark ignition type internal combustion engine as set forth in  claim 1 , wherein the actual compression ratio at the time of engine low load operation is made substantially the same actual compression ratio as at the time of engine medium and high load operation. 
   
   
       8 . A spark ignition type internal combustion engine as set forth in  claim 7 , wherein, at the time of engine low speed, regardless of the engine load, said actual compression ratio falls within a range of 9 to 11. 
   
   
       9 . A spark ignition type internal combustion engine as set forth in  claim 8 , wherein the higher the engine speed, the higher the actual compression ratio. 
   
   
       10 . (canceled) 
   
   
       11 . A spark ignition type internal combustion engine as set forth in  claim 1 , wherein the amount of intake air fed into the combustion chamber is controlled by changing the closing timing of the intake valve. 
   
   
       12 . A spark ignition type internal combustion engine as set forth in  claim 11 , wherein the closing timing of the intake valve is shifted as the engine load becomes lower to 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. 
   
   
       13 . A spark ignition type internal combustion engine as set forth in  claim 12 , 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 without regard to a throttle valve arranged in an engine intake passage by changing the closing timing of the intake valve. 
   
   
       14 . A spark ignition type internal combustion engine as set forth in  claim 13 , 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 at the fully opened state. 
   
   
       15 . A spark ignition type internal combustion engine as set forth in  claim 12 , wherein in a region of a load lower than the engine load when the closing timing of the intake valve reaches said limit closing timing, a throttle valve arranged in an engine intake passage is used to control the amount of intake air fed into the combustion chamber. 
   
   
       16 . A spark ignition type internal combustion engine as set forth in  claim 12 , wherein in a region of a load lower than the engine load when the closing timing of the intake valve reaches said limit closing timing, the lower the load, the larger the air-fuel ratio is made. 
   
   
       17 . A spark ignition type internal combustion engine as set forth in  claim 12 , wherein in a region of a load lower than the engine load when the closing timing of the intake valve reaches said limit closing timing, the closing timing of the intake valve is held at said limit closing timing. 
   
   
       18 . 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 to the limit mechanical compression ratio. 
   
   
       19 . A spark ignition type internal combustion engine as set forth in  claim 18 , 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.