Patent ID: 6915766

Claim:
A compression ratio controlling apparatus for a spark-ignited internal combustion engine, comprising: a variable compression ratio mechanism that is enabled to operatively vary a compression ratio of the engine; a detecting section that detects an engine speed and an engine load; and a compression ratio controlling section that controls the variable compression ratio mechanism on the basis of the detected engine speed and engine load in such a manner that the compression ratio is varied toward a target high compression ratio when the engine load falls in a predetermined low load region and toward a target low compression ratio when the engine load falls in a predetermined high load region, the compression ratio controlling section providing a predetermined delay for a variation in the compression ratio toward one of the target high and low compression ratios at a time at which a transient state of the change in the engine load occurs in accordance with at least one of an engine driving history immediately before the transient state thereof occurs and a wall temperature of a combustion chamber of the engine immediately before the transient state thereof occurs.