Closed-loop Individual Cylinder Air-Fuel Ratio Control via UEGO Signal Spectral Analysis

The paper presents the development and real time application of an original closed-loop individual cylinder AFR control system, based on a spectral analysis of the lambda sensor signal measured at the confluence of the various exhaust runners. The observation that any type of AFR disparity between the various cylinders is reflected in a specific harmonic content of the AFR signal spectrum, represents the starting point of the project. The proposed approach has been designed in order to be compatible with onboard application. The AFR individual cylinder closed-loop controller has been tested in real time, by implementing it in a virtual Electronic Control Unit, using rapid control prototyping techniques. The results observed on a 4 cylinder Spark Ignition 1.2 liter engine are encouraging, since in the investigated engine operating conditions the controller is able to guarantee AFR inequality below 0.01 lambda. The paper shows how the proposed controller can be applied to other engine configurations (6, 8, or 12 cylinder engines), if a lambda sensor is available per each engine bank.