Patent ID: 8036855

Claim:
A failure diagnosis apparatus for a homogeneous charge compression ignition engine having combustion modes switchable between compression-ignited combustion, which is performed together with internal EGR, and spark-ignited combustion, wherein the engine includes an intake variable valve mechanism for varying an operation state of an intake valve and an exhaust variable valve mechanism for varying an operation state of an exhaust valve, the intake variable valve mechanism includes an intake camshaft, an intake cam for spark-ignited combustion fixed to the intake camshaft, and an intake cam for compression-ignited combustion fixed to the intake camshaft, with the intake variable valve mechanism being switchable between a first intake operation state in which movement of the spark-ignited combustion intake cam is transmitted to the intake valve and a second intake operation state in which movement of the compression-ignited combustion intake cam is transmitted to the intake valve, the exhaust variable valve mechanism includes an exhaust camshaft, an exhaust cam for spark-ignited combustion fixed to the exhaust camshaft, and an exhaust cam for compression-ignited combustion fixed to the exhaust camshaft, with the exhaust variable valve mechanism being switchable between a first exhaust operation state in which movement of the spark-ignited combustion exhaust cam is transmitted to the exhaust valve and a second exhaust operation state in which movement of the compression-ignited combustion exhaust cam is transmitted to the exhaust valve, and the engine further includes an intake variable valve timing mechanism which advances or retards the intake camshaft and an exhaust variable valve timing mechanism which advances or retards the exhaust camshaft, the apparatus comprising: an intake amount detector which detects the intake amount of a mixture drawn into a combustion chamber of the engine; a determination unit which determines whether a failure has occurred in the intake variable valve mechanism and the exhaust variable valve mechanism from information on changes in the intake amount detected by the intake amount detector, wherein the determination unit determines whether a failure has occurred from information on switching from the spark-ignited combustion to the compression-ignited combustion, information on changes in the intake amount, and predetermined first reference change information, and the determination unit determines whether a failure has occurred from information on switching from the compression-ignited combustion to the spark-ignited combustion, information on changes in the intake amount, and predetermined second reference change information; and a control unit which executes backup combustion control when the determination unit determines that a failure has occurred.