Intake air amount estimation apparatus and method for internal combustion engine

An intake air amount estimation method for an internal combustion engine, comprising the steps of:

• setting a first relational expression between an intake pipe pressure and an amount of intake gas flowing into cylinders in the case of a first valve timing of the internal combustion engine wherein a valve timing can be changed in at least two stages between the first valve timing and a second valve timing and wherein an exhaust gas recirculation passage provided with a control valve is connected to an intake pipe downstream of a throttle valve;
• setting a second relational expression between the intake pipe pressure and the intake gas amount in the case of the second valve timing;
• calculating, in the case of the first valve timing, an amount of recirculated exhaust gas flowing past the control valve which is based on an intake pipe pressure at the time when the control valve is at a specific opening degree, as an amount of intake exhaust gas flowing into the cylinders during steady operation of the engine;
• calculating, on the basis of the intake exhaust gas amount and by means of the first relational expression, an amount of intake air that is drawn via the throttle valve at the time when the control valve is at the specific opening degree in the case of the first valve timing;
• and
• calculating, on the basis of the intake exhaust gas amount and by means of the second relational expression, an intake air amount at the time when the control valve is at the specific opening degree in the case of the second valve timing, on the assumption that the intake exhaust gas amount for the specific opening degree based on the intake pipe pressure remains unchanged irrespective of a valve timing.

An intake air amount estimation apparatus for an internal combustion engine, comprising:

• a relational expression setter that sets, on the assumption that an amount of recirculated exhaust gas flowing past a control valve which is based on an intake pipe pressure is equal to an amount of intake exhaust gas flowing into cylinders during steady operation of the internal combustion engine wherein a valve timing is variable and wherein an exhaust gas recirculation passage provided with the control valve is connected to an intake pipe downstream of a throttle valve, a relational expression between an intake pipe pressure Pm and an amount KL of intake air drawn via the throttle valve during steady operation of the engine as KL=e(Pm−g)+r, using coefficients “e” and “r” that are determined in advance in accordance with an engine speed, the valve timing, and an opening degree of the control valve and a coefficient “g” that is determined in advance in accordance with the engine speed alone or its combination with the valve timing and/or the opening degree of the control valve;
• a first calculator that calculates, as an amount of intake exhaust gas flowing into the cylinders during steady operation of the engine, an amount of recirculated exhaust gas flowing past the control valve which is based on an intake pipe pressure at the time when the control valve is at a specific opening degree;
• and
• a second calculator that calculates, on the basis of the intake exhaust gas amount and by means of the relational expression, the intake air amount at the time when the control valve is at the specific opening degree.

An intake air amount estimation method for an internal combustion engine, comprising the steps of:

• setting, on the assumption that an amount of recirculated exhaust gas flowing past a control valve as an amount based on an intake pipe pressure is equal to an amount of intake exhaust gas flowing into cylinders during steady operation of the internal combustion engine wherein a valve timing is variable and wherein an exhaust gas recirculation passage provided with the control valve is connected to an intake pipe downstream of a throttle valve, a relational expression between an intake pipe pressure Pm and an amount KL of intake air drawn via the throttle valve during steady operation of the engine as KL=e(Pm−g)+r, using coefficients “e” and “r” that are determined in advance in accordance with an engine speed, the valve timing, and an opening degree of the control valve and a coefficient “g” that is determined in advance in accordance with the engine speed alone or its combination with the valve timing and/or the opening degree of the control valve;
• calculating, as an amount of intake exhaust gas flowing into the cylinders during steady operation of the engine, an amount of recirculated exhaust gas flowing past the control valve which is based on an intake pipe pressure at the time when the control valve is at a specific opening degree;
• and
• calculating, on the basis of the intake exhaust gas amount and by means of the relational expression, the intake air amount at the time when the control valve is at the specific opening degree.