| 摘要 |
PROBLEM TO BE SOLVED: To accurately determine fuel properties. SOLUTION: Before an air-fuel ratio sensor installed in an exhaust pipe is activated during the early warming up control of a catalyst, wet quantity decrease control is performed to reduce the wet quantity sticking to the internal wall or the like of an intake port by controlling the opening timing of an intake valve to the delay side from a normal valve opening position. Then, when the air-fuel ratio is activated, the opening timing of the intake valve is gradually returned to the normal valve opening position to complete the wet quantity decrease control and to change over to a state of easily producing the wet. Consequently, the heavier the fuel property is, the more the wet quantity is increased, and the air-fuel ratio of exhaust gas changes in a lean direction. As a result, the difference of the fuel properties (the heavy property of fuel) can be detected as the change of the air-fuel ratio of the exhaust gas, and the fuel properties can be accurately determined on the basis of the output of the air-fuel sensor or a control parameter changing in conjunction with the output.
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