Control unit of internal combustion engine

1. A control unit of an internal combustion engine comprising:

one or more processing devices receiving instructions to perform:

an exhaust gas recirculation (EGR) control step sending an EGR command signal so as to bring an EGR gas supply amount by an EGR apparatus to a target EGR gas supply amount to control an opening degree of an EGR valve;

a supercharger control step sending a supercharging command signal so as to bring a supercharging amount of a supercharger provided with a variable flow mechanism to a target supercharging amount to control an opening degree of the variable flow mechanism;

an in-cylinder oxygen excess ratio calculation step calculating an in-cylinder oxygen excess ratio based on an operating state of the internal combustion engine;

a transient state determination step determining whether the internal combustion engine is in a transient state based on the in-cylinder oxygen excess ratio in the cylinder calculated by the in-cylinder oxygen excess ratio calculation step; and

a switching step switching the EGR command signal and the supercharging command signal so that the opening degree of the EGR valve and the opening degree of the variable flow mechanism become smaller than in a normal state when the internal combustion engine is determined to be in the transient state by the transient state determination step;

wherein the transient state determination step comprises:

a first determination step determining whether the in-cylinder oxygen excess ratio calculated by the in-cylinder oxygen excess ratio calculation step is not greater than a first threshold value; and

a second determination step determining whether an in-cylinder oxygen excess ratio difference between the in-cylinder oxygen excess ratio calculated by the in-cylinder oxygen excess ratio calculation step and an optimum value of the in-cylinder oxygen excess ratio which is preliminarily set on the basis of the operating state of the internal combustion engine is not less than a second threshold value, and;

wherein the transient state determining step determines the internal combustion engine to be in the transient state when the first determination step determines that the in-cylinder oxygen excess ratio is not greater than the first threshold value and the second determination step determines that the in-cylinder oxygen excess ratio difference is not less than the second threshold value, such that the switching step switches the EGR command signal and the supercharging command signal to reduce the opening degree of the EGR valve and the opening degree of the variable flow mechanism than in the normal state to reduce emission amount of nitrogen oxides (NOx) and smoke (PM).

2. The control unit of an internal combustion engine according to claim 1 , wherein the switching step is configured to switch the EGR command signal and the supercharging command signal so as to bring the opening degree of the EGR valve to a lower limit which is preliminarily set and the opening degree of the variable flow mechanism to a lower limit which is preliminarily set.

3. The control unit of an internal combustion engine according to claim 2 , wherein the lower limit of the opening degree of the EGR valve is preliminarily set depending upon the operating state of the internal combustion engine.

4. The control unit of an internal combustion engine according to claim 1 , wherein the transient state determination step comprises a third determination step determining whether a supercharging pressure difference between a supercharging pressure of the supercharger and an optimum value of the supercharging pressure which is preliminarily set on the basis of the operating state of the internal combustion engine is not less than a third threshold value, and determining the internal combustion engine to be in the transient state when the third determination step further determines that the supercharging pressure difference is not less than the third threshold value.

5. The control unit of an internal combustion engine according to claim 1 , wherein the switching step cancels a switching control of the EGR command signal and the supercharging command signal when the internal combustion engine is determined not to be in the transient state by the transient state determination step.

6. The control unit of an internal combustion engine according to claim 5 , wherein the transient state determination step comprises:

a fourth determination step determining whether the in-cylinder oxygen excess ratio calculated by the in-cylinder oxygen excess ratio calculation step is greater than a fourth threshold value; and

a fifth determination step determining whether an in-cylinder oxygen excess ratio difference between the in-cylinder oxygen excess ratio calculated by the in-cylinder oxygen excess ratio calculation step and an optimum value of the in-cylinder oxygen excess ratio which is preliminarily set on the basis of the operating state of the internal combustion engine is less than a fifth threshold value, and

the transient state determination step determines the internal combustion engine not to be in the transient state when the fourth determination step determines that the in-cylinder oxygen excess ratio is greater than the fourth threshold value or the fifth determination step determines that the in-cylinder oxygen excess ratio difference is less than the fifth threshold value.

7. The control unit of an internal combustion engine according to claim 5 , wherein upon canceling the switching control, the switching step resets the EGR command signal so as to bring the opening degree of the EGR valve to a prescribed opening degree which is larger than the opening degree at the time of the switching control.

8. The control unit of an internal combustion engine according to claim 1 , wherein the one or more processors further executes:

a supercharging command signal limiting step limiting the supercharging command signal so as to bring the opening degree of the variable flow mechanism to an opening degree in a steady state of the internal combustion engine.