A signal processing algorithm for compensating for back flow effect in intake air mass measurement in internal combustion engines

We developed a method to compensate for back flow occurring during intake air mass measurement in internal combustion engines using frequency characteristics of the signal from an air flow sensor (AFS). The parameters of the AFS signal, which has close correlation with back flow ratio, were explored. The parameters were searched in terms of simulation, mathematical analysis and experiments. The simulation results showed that the normalized intensities f₂/f₁ and f₃/f₁ have close correlation with back flow ratio, where f₁ is the intensity of the base frequency of the intake air pulsation, f₂ is the intensity of twice of the frequency, and f₃ is the intensity of three times of the frequency. These two correlations were robust to the specification of the induction system, engine revolution speed, and load. The back flow ratio could be estimated using normalized frequency intensity f₂/f₁ and f₃/f₁ within an accuracy of 5%. The correlations between f₂/f₁, f₃/f₁ and the back flow ratio were validated by mathematical analysis. The correlations were also evaluated by experiments using a four cycle engine. The experimental results showed that the back flow ratio was estimated using f₂/f₁, f₃/f₁ within an accuracy of 5%.