New Lambda - Lambda Air-Fuel Ratio Feedback Control 2007-01-1340
Previously air-fuel ratio control using a λ O2 sensor had two problems which resulted from the binary output characteristics: (1) Insufficient convergence performance after A/F disturbance, resulting in worsening of emissions in transient states, and (2) A narrow A/F control range, resulting in worsening of emissions due to mean A/F shift in the front A/F. However, we have executed a paradigm shift to mean A/F control focused on the O2 storage ability of the catalyst and on the conversion characteristics, and carried out the following improvements. (1) Using a catalyst O2 storage model, we analyzed the interaction among front A/F feedback, O2 storage behavior, the rear. O2 signal, and emissions. Based on the results of this analysis, we designed an optimal O2 storage capacity (OSC) using a new catalyst with improved O2 storage ability, and verified that the first problem was resolved. (2) Previously, it was difficult to design front λ O2 control due to its strong non-linearity. However we have derived a new linear model of the triangular A/F wave, enacted control improvements in order to expand the mean A/F control range, improved the robustness in response to front mean A/F shift due to variation in the front O2 sensor and the A/F imbalance between cylinders, and improved catalyst control performance. These technologies will allow us, without adding to the cost of a conventional system, to achieve the 75% low emission (☆☆☆☆) standard in the Japan new long-term regulation, considered to be at the strictest level worldwide, with the new driving mode that is scheduled to be introduced in 2011.