Control apparatus for internal combustion engine

1. A control apparatus for an internal combustion engine, comprising:

a fuel-injection-quantity calculation means for calculating a fuel injection quantity;

wherein the fuel injection quantity is corrected with a purge-air-concentration learnt value calculated by subjecting a purge air concentration to purge-air-concentration filtering, and

wherein fuel in the corrected fuel injection quantity is injected from an injector;

the control apparatus further comprising means for changing a filtering effect in the purge-air-concentration filtering, in a direction of enhancing exhaust gas purification, between when the purge air concentration is thick and when the purge air concentration is thin.

2. A control apparatus for an internal combustion engine as defined in claim 1 , wherein the filtering effect when the purge air concentration is thin is greater than the filtering effect when the purge air concentration is thick.

3. A control apparatus for an internal combustion engine as defined in claim 1 , wherein the filtering effect when an integrated value of purge air quantities is large is greater than the filtering effect when the integrated value is small.

4. A control apparatus for an internal combustion engine, comprising:

running-state detection means for detecting a running state of the internal combustion engine,

purge-air-quantity control means for controlling a quantity in which vaporized fuel from a fuel tank is introduced into a suction system of the internal combustion engine, on the basis of the detection output of the running-state detection means,

purge-air-quantity calculation means for calculating a purge air quantity which is introduced into the suction system of the internal combustion engine by the purge-air-quantity control means,

purge-air-integrated-quantity calculation means for integrating the purge air quantities calculated by the purge-air-quantity calculation means, to calculate a purge-air integrated quantity,

an air/fuel ratio sensor which detects an air/fuel ratio of a mixture fed into the internal combustion engine,

air/fuel-ratio control means for controlling an air/fuel-ratio feedback correction coefficient which makes a correction on the basis of a detection output of the air/fuel ratio sensor so that the air/fuel ratio of the mixture to be fed into the internal combustion engine becomes a target value,

purge-air-concentration calculation means for calculating a purge air concentration from the running state detected by the running-state detection means, the purge air quantity, and the air/fuel-ratio feedback correction coefficient, and

purge-air-concentration-learnt-value calculation means for subjecting the purge air concentration to purge-air-concentration filtering, to calculate a purge-air-concentration learnt value,

wherein the air/fuel ratio is corrected on the basis of the purge-air-concentration learnt value calculated by the purge-air-concentration-learnt-value calculation means;

the control apparatus further comprising means for setting a filter constant for use in the purge-air-concentration filtering, the filter constant set at a high purge air concentration when the purge-air integrated quantity is smaller than a predetermined value, and the filter constant set at a low purge air concentrations when the purge-air integrated quantity is not smaller than the predetermined value.

5. A control apparatus for an internal combustion engine as defined in claim 4 , further comprising purge-air-concentration-learning-completion decision means for deciding completion of the purge-air-concentration calculation on the basis of the air/fuel-ratio feedback correction coefficient,

wherein the filter constant for use in the purge-air-concentration filtering is set at a constant before the purge-air-concentration calculation completion, and thereafter,

wherein, when the purge-air integrated quantity is smaller than the predetermined value, the filter constant is set at the filter constant at the high purge air concentration, and

wherein, when the purge-air integrated quantity is not smaller than the predetermined value, the filter constant is set at the filter constant at the low purge air concentration.

6. A control apparatus for an internal combustion engine, comprising:

purge-air-quantity control means for controlling a quantity in which vaporized fuel from a fuel tank is introduced into a suction system of the internal combustion engine;

purge-air-quantity calculation means for calculating a purge air quantity which is introduced into the suction system of the internal combustion engine by the purge-air-quantity control means;

purge-air-integrated-quantity calculation means for integrating the purge air quantities calculated by the purge-air-quantity calculation means to calculate a purge-air integrated quantity;

purge-air-concentration calculation means for calculating a purge air concentration;

purge-air-concentration-learnt-value calculation means for subjecting the purge air concentration to purge-air-concentration filtering to calculate a purge-air-concentration learnt value; and

means for setting a filter constant for use in the purge-air-concentration filtering, the filter constant set at a high purge air concentration when the purge-air integrated quantity is smaller than a predetermined value, and the filter constant set at a low purge air concentration when the purge-air integrated quantity is not smaller than the predetermined value.