Method to optimize engine operation using active fuel management

A method for operating an internal combustion engine, the method comprising:

• providing a vehicle having an internal combustion gasoline engine including multiple cylinders and wherein the engine is capable of running on at least one of a plurality firing fractions;
• providing a vacuum offset (Offsetvac) to adjust airflow capacity for each of the plurality of firing fractions providing a vacuum offset (Offsetvac) to adjust airflow capacity for each of the firing fractions by:
• increasing Offsetvac if an intake manifold vacuum (Vac) is less than a first predetermined threshold for a period of time (T);
• decreasing Offsetvac if an intake manifold vacuum (Vac) is greater than a first predetermined threshold for a period of time (T) and an engine load is high;
• and
• maintaining a current Offsetvac.;
• determining a torque capacity of each of the plurality firing fractions and a plurality of available firing fractions that provides at least enough torque capacity to accommodate a current torque requested (Treq) by:
• determining the net torque capacity (Tnet) of the engine;
• determining the maximum brake torque (TFF) for each firing fraction;
• and
• determining a minimum firing fraction that produces at least enough brake torque TFF to accommodate a current torque request Treq;
• determining a plurality of viable firing fractions of the plurality of available firing fractions;
• and
• determining and implementing an optimal firing fraction of the viable firing fractions if the optimal firing fraction provides enough fuel economy benefit over a current firing fraction.

A method for operating an internal combustion engine, the method comprising:

• providing a vehicle having an internal combustion gasoline engine including multiple cylinders and wherein the engine is capable of running on at least one of a plurality firing fractions;
• providing a vacuum offset (Offsetvac) to adjust airflow capacity for each of the plurality of firing fractions providing a vacuum offset (Offsetvac) to adjust airflow capacity for each of the firing fractions by:
• increasing Offsetvac if an intake manifold vacuum (Vac) is less than a first predetermined threshold for a period of time (T);
• decreasing Offsetvac if an intake manifold vacuum (Vac) is greater than a first predetermined threshold for a period of time (T) and an engine load is high;
• and
• maintaining a current Offsetvac.;
• determining a torque capacity of each of the plurality firing fractions and a plurality of available firing fractions that provides at least enough torque capacity to accommodate a current torque requested (Treq) by:
• determining the net torque capacity (Tnet) of the engine;
• determining the maximum brake torque (TFF) for each firing fraction by the equation:
• TFF=Tnet*FF+Tfriction
• wherein Tfriction is a constant torque loss due to friction losses of the engine;
• and
• determining a minimum firing fraction that produces at least enough brake torque TFF to accommodate a current torque request Treq;
• determining a plurality of viable firing fractions of the plurality of available firing fractions;
• and
• determining and implementing an optimal firing fraction of the viable firing fractions if the optimal firing fraction provides enough fuel economy benefit over a current firing fraction.