ABNORMALITY DIAGNOSIS DEVICE FOR VARIABLE COMPRESSION RATIO MECHANISM

PROBLEM TO BE SOLVED: To diagnose abnormality of a variable compression ratio mechanism with good accuracy, in an abnormality diagnosis device for diagnosing abnormality of the variable compression ratio mechanism which can switch a mechanical compression ratio of an internal combustion engine at least into two stages.SOLUTION: In a state where an internal combustion engine is operated in a high expansion ratio, while an intake pressure is kept constant, compression ratio switching processing is executed for controlling a variable compression ratio mechanism and an adjusting device in order to switch a mechanical compression ratio. In the case where an intake amount difference Δmc which is a difference of the intake air amount before and after the execution of the compression ratio switching processing is equal to or greater than an intake amount difference threshold value Δmcthre, the variable compression ratio mechanism is diagnosed to be normal, and in the case where the intake amount difference Δmc is below the intake amount difference threshold value Δmcthre, the variable compression ratio mechanism is diagnosed as abnormal.SELECTED DRAWING: Figure 6 【課題】本発明は、内燃機関の機械圧縮比を、少なくとも２段階に切り換え可能な可変圧縮比機構の異常を診断するための異常診断装置において、可変圧縮比機構の異常を精度良く診断することを課題とする。【解決手段】本発明は、内燃機関を高膨張比運転させた状態で、吸気圧力を一定に保ちつつ、機械圧縮比を切り換えるべく、可変圧縮比機構及び調整装置を制御するための圧縮比切換処理を実行し、その圧縮比切換処理の実行前後における吸入空気量の差である吸気量差Δｍｃが吸気量差閾値Δｍｃｔｈｒｅ以上であれば、可変圧縮比機構が正常であると診断し、且つ前記吸気量差Δｍｃが前記吸気量差閾値Δｍｃｔｈｒｅ未満であれば、可変圧縮比機構が異常であると診断する。【選択図】図６