Patent ID: 7627417

Claim:
A variable compression ratio internal combustion engine comprising: a compression ratio changing mechanism that can change the compression ratio of the internal combustion engine: a supercharger driven by exhaust gas from said internal combustion engine for supercharging intake air to said internal combustion engine; and basic compression ratio derivation section for deriving a basic compression ratio with which a specific heat efficiency can be achieved with knocking in said internal combustion engine being suppressed, in accordance with a running condition of said internal combustion engine, wherein while said internal combustion engine is running, the compression ratio of the internal combustion engine is set to said basic compression ratio by said compression ratio changing mechanism, and when said internal combustion engine enters a specific acceleration state, the compression ratio of the internal combustion engine is changed by said compression ratio changing mechanism to a specific compression ratio suitable for acceleration that is lower than said basic compression ratio, wherein said compression ratio suitable for acceleration is determined in the range in which an engine torque associated with acceleration to be larger than or equal to said basic engine torque, said engine torque associated with acceleration results when an increase in the engine torque due to an increase in the exhaust gas pressure of said internal combustion engine caused by the changing of the compression ratio from said basic compression ratio to said compression ratio suitable for acceleration and a decrease in the engine torque due to a decrease in heat efficiency of said internal combustion engine caused by the changing of the compression ratio from said basic compression ratio to said compression ratio suitable for acceleration are added to a basic engine torque that is defined as the engine torque in the state in which the compression ratio is said basic compression ratio.