| 摘要 |
PROBLEM TO BE SOLVED: To delicately and accurately determine a change in the valve timing more than a conventional determination, in an engine 1 mounted with VVT 13 capable of varying the operation timing of intake to exhaust valves 11 and 12. SOLUTION: This diagnostic system has an ion current detecting circuit 33 detecting an ion current generated in a combustion chamber 6 of the engine 1. In decelerating operation of the engine 1, an intake passage 15 is throttled by a throttle valve 18, and an ion current value is detected when filling efficiency of intake air to a cylinder 2 becomes relatively low. An evaluation value (an ion parameter Ip) expressing a combustion state is determined from the detected ion current value, and an internal EGR quantity is estimated on the basis of the ignition timing, the filling efficiency ce and an engine speed ne in addition to this ion parameter Ip. A VVT phase, that is, the valve timing is estimated from the estimated internal EGR quantity, to thereby diagnose failure of a VVT control system. COPYRIGHT: (C)2008,JPO&INPIT
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