Method of dynamically estimating the fresh air flow rate supplied to an engine with high-pressure and low-pressure EGR circuits

A method for estimating a flow rate of cool air entering an engine, turbocharged by a turbocharger, including an intake manifold of volume Vcoll, an exchanger, an air filter, an HP EGR circuit, an LP EGR circuit, an intake butterfly valve, an exhaust butterfly valve, a flow meter, a pressure sensor, a temperature sensor connected to an electronic control unit, and a duct of volume Vcool between the flow meter and the inlet of the intake manifold, the method comprising:

• measuring a temperature Tape after the exchanger by the temperature sensor, a pressure in the manifold P coll by the pressure sensor, and a flow rate of cool air Qflowmeter by the flow meter;
• computing, by the ECU, an engine flow rate Qmot based on the measurement of the temperature Tape after the exchanger and of the pressure Pcoll in the intake manifold;
• computing, by the ECU, a mass of gas between the flow meter and the inlet of the intake manifold based on the measurement of the temperature Tape after the exchanger and of the pressure P coll in the manifold;
• computing, by the ECU, a mass of gas in the manifold based on the measurement of the temperature Tape after the exchanger and of the pressure Pcoll in the manifold;
• measuring or estimating the HP EGR flow rate;
• computing, by the ECU, a gas flow rate in the manifold based on the engine flow rate and on the mass of gas in the manifold;
• estimating, by the ECU, a rate of LP EGR at the inlet of the manifold based on the mass of gas between the flow meter and the manifold inlet and on the flow rate of gas in the manifold;
• computing, by the ECU, a mass of air between the flow meter and the manifold inlet based on the LP EGR rate at the inlet of the manifold and on the flow rate of cool air Qflowmeter measured by the flow meter;
• estimating, by the ECU, an EGR rate {circumflex over (τ)}EGR—mot at the engine inlet based on the mass of air between the flow meter and the inlet of the manifold, on the mass in the manifold and on the flow rate of cool air Qflowmeter measured by the flow meter,
• estimating, by the ECU, a dynamic engine air flow rate based on the engine flow rate and on the EGR rate at the engine inlet by expression {circumflex over (Q)}air—mot=(1−{circumflex over (τ)}EGR—mot)Qmot.