Sensor Selection for Observer Feedback in Turbocharged Spark Ignited Engines

Precise air/fuel control is necessary for low emissions in turbocharged (TC) SI-engines. Observers are often proposed for accurate cylinder air charge estimation in air/fuel controllers. First it is shown using a structural method that the system is locally structurally observable using observer-feedback from any measured state. A systematic method to select observer feedback signals is important as the number of possible sensor combinations reach 680 when 3 sensors are used which could be placed at 17 different locations. Here a systematic method based on observability index is proposed that is able to point out one combination of measured signals as good candidates to observe the states needed for CAC estimation. Finally the results are valid for all TC SI-engines with the same structure but the method is generally applicable.