The present invention relates in general to an internal combustion engine equipped with a variable valve timing (VVT) control mechanism capable of control ling the opening and closing timings of the intake and exhaust valves, and more particularly to an intake air quantity calculating apparatus for use in an internal combustion engine with such a VVT control mechanism, for calculating an intake air quantity for control of a fuel injection quantity, etc. by correcting an intake air quantity detected by an airflow meter by using an airflow error correcting term. The present invention further relates to a method of calculating an intake air quantity in such an internal combustion engine.
In control of a fuel injection quantity, etc. on the basis of an intake air quantity detected by an airflow meter, since an airflow meter, particularly a hot-wire airflow meter produces an error in detection of air flow under an influence of an intake air pulsation, it has heretofore been practiced to determine, as a parameter of engine load for knowing the magnitude of pulsation, the quantity of air passing through a throttle valve from a throttle valve opening degree and engine speed (xcex1xe2x88x92N) and determine an airflow error correction term or coefficient KTRM from the quantity of air passing through the throttle valve and the engine speed to correct the intake air quantity by using the airflow error correction term KTRM. It has further been practiced to modify the correction term KTRN in accordance with an EGR rate as disclosed in Japanese patent provisional publication No. 11-62674.
However, in the engine equipped with a WVT control mechanism capable of variably controlling the opening and closing timings of the intake and exhaust valves (for example, in an engine adapted to control the intake air quantity on the basis of the closing timing of the intake valve), the load of the engine (i.e., the throttle valve opening degree and the engine speed) and the intake pipe pressure does not correspond to each other, so that the load of the engine and the magnitude of pulsation does not correspond to each other, thus causing a problem that adequate or accurate correction of the intake air quantity cannot be attained.
It is accordingly an object of the present invention to provide an intake air quantity calculating apparatus for an internal combustion engine equipped with a VVT control mechanism which can attain an improved accuracy in calculation of the intake air quantity through accurate correction of an air flow meter-detected intake air quantity in accordance with the magnitude of pulsation.
It is a further object of the present invention to provide a method of calculating an intake air quantity of an internal combustion engine with a variable valve timing control mechanism, through correction of an intake air quantity detected by an air flow meter, can attain an improved accuracy in calculation.
To accomplish the above objects, the present invention provides an intake air quantity calculating apparatus for an internal combustion engine with a variable valve timing control mechanism. The apparatus comprises an air flow meter for detecting an intake air quantity of the engine, and a calculator for calculating a corrected intake air quantity through correction of the intake air quantity detected by the air flow meter. The calculator includes a pulsation rate determining section for determining an intake air pulsation rate on the basis of an intake pipe pressure and an engine speed of the engine, an air flow error correction term determining section for determining an air flow error correction term for correction of an error of the intake air quantity detected by the air flow meter, on the basis of the intake air pulsation rate, and a correcting section for correcting the intake air quantity detected by the air flow meter by using the air flow error correction term.
Further, the present invention provides a method of calculating an intake air quantity of an internal combustion engine with a variable valve timing control mechanism, through correction of an intake air quantity detected by an air flow meter. The method comprises determining an intake air pulsation rate on the basis of an intake pipe pressure and an engine speed of the engine, determining an air flow error correction term for correction of an error of the intake air quantity detected by the air flow meter, on the basis of the intake air pulsation rate, and correcting the intake air quantity detected by the air flow meter by using the air flow error correction term.