Development of a Fast Response High Accuracy Virtual Air Flow Meter for Internal Combustion Engine Applications

Accurate control of the in-cylinder air/fuel ratio level is critical for both fuel saving and harmful emission reduction of an internal combustion engine. The fuel injection quantity is easy to control with today's electronically controlled fuel injection system, the difficulty is how to accurately determine the fresh charge mass trapped in-cylinder at the end of the gas exchange process, especially for transient operation mode of a vehicle when the throttle position, intake air pressure and engine speed are instantaneously changing. No physical airflow meter exists which has satisfactory response time and measurement accuracy. Described in this paper is a renovated air flow measurement technology combining fast response sensors with 1-dimensional pressure wave action simulation. Utilizing two dynamic pressure transducers(2P) to measure pressure fluctuation near the intake and exhaust ports and coupling the measured pressure signals into the numerical solver of a 1-dimensional gas exchange simulation software, together with the instant flow area at valve locations, the instantaneous gas mass flow rate through the engine intake and exhaust ports can be calculated. The fresh mass and un-swept burnt mass fraction trapped in the cylinder could also be traced along the entire gas exchange process. The response time and model accuracy of this synthetic virtual airflow meter technology is validated against GT-Power model and experiment tests, for both steady-state and transient operating modes.