Method for controlling an operating condition of a vehicle engine
A residual ratio factor characterizing the amount of residual exhaust gas left in a selected cylinder at the end of a piston intake stroke is determined from tabular and surface models based on previously gathered dynamometer data from a test vehicle at various engine speeds. The residual ratio factor is then used to calculate the mole fractions of air and residual exhaust gas in the selected cylinder, which, in turn, are used to determine mass airflow at an engine intake port at the end of the intake stroke. The mass airflow can then be used to derive further models for determining an engine operating parameter, such as fuel/air ratio, required for achieving at preselected vehicle operating condition.
1. A method for controlling an operating condition of a vehicle engine comprising:
determining a residual ratio factor from dynamometer data generated by a test vehicle engine at various engine speeds;
calculating mole fractions of air and residual exhaust gas in a selected cylinder of the engine at completion of an intake stroke for the selected cylinder, the calculation being a function of engine speed and a residual ratio factor;
using the mole fractions of air and residual exhaust gas to determine mass air flow of the engine; and
using the determined mass air flow to estimate an operating parameter of the vehicle engine required to achieve a desired vehicle operating condition.
2. The method of claim 1 wherein the operating parameter comprises air/fuel ratio.
3. The method of claim 1 wherein the operating parameter comprises spark timing.
4. The method of claim 1 wherein the operating parameter comprises engine output torque.