The present invention relates to a control device of an internal combustion engine which is provided with a valve moving apparatus having a hydraulic valve characteristic changing mechanism for changing valve operation characteristic such as lift of a suction valve or an exhaust valve and a hydraulic valve phase variable mechanism for altering phase of the suction valve or the exhaust valve. According to the control device, when the valve operation characteristic is changed, a map storing control amounts for controlling combustion condition of the engine such as amount of injected fuel is changed at a timing reflecting property of a working oil such as viscosity of the working oil supplied to the valve characteristic changing mechanism.
An internal combustion engine provided with a valve moving apparatus having a hydraulic valve characteristic changing mechanism for changing valve operation characteristic by driving a suction valve and an exhaust valve with a cam for low speed of small lift and small valve opening time on a low rotational speed of the engine and with a cam for high speed of large lift and large valve opening time on a high rotational speed of the engine has been known (Japanese Patent Publication No. 2619696).
The above valve characteristic changing mechanism has connecting pins provided on respective rocker arms of the suction valve and the exhaust valve, and an oil pressure changing valve. The connecting pins are moved by pressure of oil which is changed over by the oil pressure changing valve, to connect or disconnect the rocker arms, so that the rocker arms, therefore the suction valve and the exhaust valve, are driven by the cam for low speed or the cam for high speed.
When the valve operation characteristic is changed, a map of fuel injection amount and a map of ignition time are changed into maps for low speed or maps for high speed corresponding to the valve operation characteristic, to carry out fuel injection amount control and ignition time control. In that case, a delay time required for changing actions of the valve characteristic changing mechanism of all cylinders to be completed by the oil pressure changed by the oil pressure changing valve is previously set in a timer, and change of the maps is carried out after the delay time elapses for the fuel injection amount control and the ignition time control adapted to the valve operation characteristic.
However, in the above-mentioned prior art, as the delay time to be set in the timer, a fixed value decided from a viewpoint of prevention of engine stall and prevention of deterioration of drive ability is adopted, so that the delay time does not correspond to change of property of the working oil of the valve characteristic changing mechanism. Therefore, sometimes, notwithstanding that actually valve characteristic changing mechanisms of all cylinders have been already changed into high speed side (or low speed side), maps for fuel injection amount ad ignition time remain in maps for low speed (or for high speed), because the oil property (oil viscosity susceptible to temperature, for example) is altered influenced by operational condition of the engine to alter operation response of the valve characteristic changing mechanism. And, in a short period when a suction air amount, a fuel injection amount and an ignition time are not adapted to each other due to a time lag between a valve operation characteristic changing time point and a map changing time point, air-fuel ratio or ignition time deviates from an optimum value to produce undesirable results regarding engine performance other than the prevention of engine stall and the prevention of deterioration of drive ability, especially regarding exhaust emission.
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