Control device for internal combustion engine

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

a catalyst provided in an exhaust system of the internal combustion engine, for cleaning an exhaust gas;

a first air/fuel ratio sensor provided to an upstream side of the catalyst, for detecting an air/fuel ratio of the exhaust gas on the upstream side of the catalyst;

a second air/fuel ratio sensor provided to a downstream side of the catalyst, for detecting an air/fuel ratio of the exhaust gas on the downstream side of the catalyst;

a first air/fuel ratio feedback control means for controlling the air/fuel ratio of the exhaust gas on the upstream side of the catalyst based on an output value of the first air/fuel ratio sensor and a controlling constant group containing a plurality of controlling constants;

a second air/fuel ratio feedback control means for calculating a target average air/fuel ratio corresponding to a target value of an average air/fuel ratio of the exhaust gas on the upstream side of the catalyst based on an output value of the second air/fuel ratio sensor and a predetermined output target value; and

a conversion means for calculating at least two controlling constants of the controlling constant group by using the target average air/fuel ratio as a common index.

2. A control device for an internal combustion engine according to claim 1 , wherein the controlling constant is any one of a delay time, a skip amount, an integral constant, and a reference voltage.

3. A control device for an internal combustion engine according to claim 1 , wherein controlling constant is set for each operating condition.

4. A control device for an internal combustion engine according to claim 1 , wherein a forced variation is applied to the target average air/fuel ratio with a predetermined amplitude in a predetermined cycle.

5. A control device for an internal combustion engine according to claim 4 , wherein the forced variation is applied upon failure diagnosis.

6. A control device for an internal combustion engine according to claim 4 , wherein a value changed from a normal value is used as a gain in the second air/fuel ratio feedback means for a period in which the forced variation is applied.

7. A control device for an internal combustion engine according to claim 1 , wherein the second air/fuel ratio feedback control means performs a proportional calculation and uses a value changed from a normal value as a gain of the proportional calculation in the second air/fuel ratio feedback control means over a transient operation period of the internal combustion engine.

8. A control device for an internal combustion engine according to claim 1 , wherein the second air/fuel ratio feedback control means uses values changed from normal values as upper and lower limit values of the target average air/fuel ratio over a transient operation period of the internal combustion engine.

9. A control device for an internal combustion engine according to claim 1 , wherein the second air/fuel ratio feedback control means performs a proportional calculation and uses a value changed from a normal value as a gain of the proportional calculation in the second air/fuel ratio feedback control means over a predetermined period after a transient operation of the internal combustion engine.

10. A control device for an internal combustion engine according to claim 1 , wherein the second air/fuel ratio feedback control means uses values changed from normal values as upper and lower limit values of the target average air/fuel ratio over a predetermined period after a transient operation of the internal combustion engine.

11. A control device for an internal combustion engine according to claim 1 , wherein the second air/fuel ratio feedback control means performs an integral calculation and stops updating the integral calculation by the second air/fuel ratio feedback control means over a transient operation period of the internal combustion engine and a predetermined period after the transient operation.

12. A control device for an internal combustion engine according to claim 9 , wherein the predetermined period after the transient operation is a period after termination of the transient operation of the internal combustion engine until an integrated air quantity reaches a predetermined value.

13. A control device for an internal combustion engine according to claim 1 , wherein the output of the first air/fuel ratio feedback control means is corrected based on the target average air/fuel ratio.

14. A control device for an internal combustion engine according claim 1 , wherein the second air/fuel ratio feedback control means detects a control cycle of the first air/fuel ratio feedback control means to correct the controlling constant based on the target average air/fuel ratio.

15. A control device for an internal combustion engine, comprising:

a catalyst provided in an exhaust system of the internal combustion engine, which cleans an exhaust gas;

a first air/fuel ratio sensor which is located on an upstream side of the catalyst and detects an air/fuel ratio of the exhaust gas on the upstream side of the catalyst;

a second air/fuel ratio sensor which is located on a downstream side of the catalyst and detects an air/fuel ratio of the exhaust gas on the downstream side of the catalyst;

a first air/fuel ratio feedback control unit which controls the air/fuel ratio of the exhaust gas on the upstream side of the catalyst based on an output value of the first air/fuel ratio sensor and a controlling constant group containing a plurality of controlling constants;

a second air/fuel ratio feedback control unit which calculates a target average air/fuel ratio corresponding to a target value of an average air/fuel ratio of the exhaust gas on the upstream side of the catalyst based on an output value of the second air/fuel ratio sensor and a predetermined output target value; and

a conversion unit which calculates at least two controlling constants of the controlling constant group using the target average air/fuel ratio as a common index,

wherein the controlling constant is any one of a delay time, a skip amount, an integral constant, and a reference voltage.