Process for model-assisted determination of the fresh-air mass flowing into the cylinders of an internal combustion engine with external exhaust-gas recycling

In a process for determining a quantity of fresh-air mass flowing into a cylinder of an internal combustion engine, the internal combustion engine having an inlet pipe, a throttle valve, a first sensor device for detecting a degree of opening of the throttle valve, an exhaust-gas recycling device with an exhaust-gas recycling valve, a second sensor device for detecting a degree of opening of the exhaust-gas recycling valve, a load sensor producing a load signal, and an electronic control device calculating a basic injection time on a basis of the load signal and a speed of the internal combustion engine, the improvement which comprises:

• reproducing conditions in the inlet pipe using an inlet pipe flow model, and using the degree of opening of the throttle valve, the degree of opening of the exhaust-gas recycling valve, an ambient pressure, an exhaust-gas temperature, a temperature in the inlet pipe and parameters representing a valve setting as input variables of the inlet pipe flow model;
• forming a model variable for an air mass flow at the throttle valve and for a residual-gas mass flow at the exhaust-gas recycling valve;
• forming a model variable for an air mass flow into the cylinder as a function of an inlet pipe pressure;
• forming a model variable for a residual-gas mass flow into the cylinder as a function of a residual-gas partial pressure;
• calculating the inlet pipe pressure as a decisive variable for determining an actual load of the internal combustion engine from the model variables of air mass flow at the throttle valve, the residual-gas mass flow at the exhaust-gas recycling valve and the air mass flow into the cylinder;
• calculating the residual-gas partial pressure in the inlet pipe from the model variables of the residual-gas mass flow at the exhaust-gas recycling valve and the residual-gas mass flow into the cylinder;
• determining a fresh-gas partial pressure from the inlet pipe pressure and the residual gas partial pressure;
• and
• deriving a total air mass flowing into the cylinder by integrating a relationship between the fresh-gas partial pressure and a fresh-air mass flow into the cylinder.