The effect of intake system geometry on the sensitivity of hot film type air flow meter

The air fuel ratio of current gasoline engine is mostly controlled by various air flow meters. When CVVT (Continuous Variable Valve Timing) device is applied to gasoline engine for higher engine performance, MAP (Manifold Absolute Pressure) sensor can not be applied anymore due to intake valve motion. Therefore HFM (Hot film airflow meter) is used for measuring the intake air flow instead of MAP sensor. Usually HFM has a little sensitivity in flow direction, therefore reverse flow from engine to air cleaner can not be measured. Also, HFM maker request enough straight duct length nearly 10 times of a duct diameter making a fully developed flow. But, most vehicles have no enough space to install such an intake system in engine room. Thus the inserted duct was applied to confirm the stable fully developed flow in air duct. The various duct configurations in front of HFM effect on the sensitivity of HFM. The less sensitivity of flow direction and installment restrictions influence on the precision of hot film flow meter. Also, intake air flow oscillates because of intake process in four stroke gasoline engine, so oscillation of intake air flow also has an effect on the precision of HFM. This paper mainly focused on the analysis of the reverse flow and flow fluctuation in throttle upstream, and the geometry of intake systems which influence on air mass flow measurement of HFM.