Method and system for determining cylinder air charge for variable displacement internal combustion engine

A method for predicting cylinder air charge for a variable displacement internal combustion engine operating in a transition from a first number of activated cylinders to a second number of activated cylinders, comprising the steps of:

• determining the effective flow area of the air intake passage of the engine and generating a signal corresponding to said area;
• measuring the instantaneous mass airflow into the engine and generating a signal corresponding to the airflow;
• determining the speed of the engine and generating a signal corresponding to said speed;
• and
• calculating the mass of air admitted to each engine cylinder during its intake stroke, based upon the values of the flow area, speed, and mass airflow signals.

A system for predicting cylinder air charge for a throttled, variable displacement, reciprocating internal combustion engine operating in a steady state condition, comprising:

• an engine speed sensor for determining the speed of the engine and for generating a signal corresponding to said speed;
• an airflow sensor for determining the instantaneous mass airflow into the engine and for generating a signal corresponding to said airflow;
• and
• a controller for receiving said speed and said mass airflow signals and for iteratively calculating the mass of air admitted to each engine cylinder during its intake stroke, based upon the values of said signals, with said controller first determining an instantaneous mass value by integrating the value of said airflow signal over a period based upon the number of cylinders in operation, and with said controller modififying the instantaneous mass value and a previously calculated mass value as functions of a time constant selected at least in part upon the number of cylinders in operation, with said controller continuing the iterations by substituting each newly calculated value for air charge for the previously calculated value.