CONTROL-ORIENTED INVESTIGATION OF SWITCH-TYPE AIR/FUEL RATIO SENSORS

Abstract During the next years, the limiting values for NOx, HC, and CO concentrations in the exhaust gas of an SI engine will be further lowered by legislation. This makes improvements of the existing pollution control systems indispensable. In order to apply an effective control system, the dynamics of the Three Way Catalytic Converter (TWC) have to be analysed properly. Therefore, much attention has been paid to the modelling of the TWC in various investigations during recent years. However, less attention has been paid to the oxygen sensors and their behaviour upstream and downstream the TWC, especially during transients. This investigation focuses on the behaviour of the switch type air/fuel ratio sensor upstream and downstream the TWC both in steady-state and transient operating conditions. For this purpose a detailed model of the sensor has been derived, which fits the measurement data very well. The model has been inverted in order to calculate sets of gas concentrations which lead to a specific sensor voltage output. This allows a better interpretation of the measured air/fuel ratio transients in terms of TWC observation and thus an improvement of control oriented modelling of the TWC.