Individual Cylinder Fuel Control with a Switching Oxygen Sensor

In this paper we discuss in detail an algorithm that addresses cylinder-to-cylinder imbalance issues. Maintaining even equivalence-ratio (φ) control across all the cylinders of an engine is confounded by imbalances which include fuel-injector flow variations, fresh-air intake maldistribution and uneven distribution of Exhaust Gas Re-circulation (EGR). Moreover, in markets that are growing increasingly cost conscious, with ever tightening emissions regulations, correcting for such mismatches must not only be done, but done at little or no additional cost. To address this challenge, we developed an Individual Cylinder Fuel Control (ICFC) algorithm that estimates each cylinder’s individual φ and then compensates to correct for any imbalance using only existing production hardware. Prior work in this area exists1,2, yet all disclosed production-intent work was performed using wide-range oxygen sensors, representing cost increases. In our productionbound algorithm, modeling and control of the cylinders’ dynamic φ was performed using a single switching oxygen sensor. Our ICFC algorithm was developed on a 1996 Pontiac Grand Am with a production LD9 2.4L fourcylinder DOHC engine. It met internally defined performance requirements and LEV emissions. Other important contributions in this work include an analysis of exhaust gas transport and mixing phenomenon, and an analysis of digitally acquiring and post processing oxygen sensor data. RATIONALE FOR THE ALGORITHM’S DEVELOPMENT Both automotive manufacturers and their suppliers are under increasing pressure to reduce costs while meeting ever-tightening emission standards. This objective is impeded by cylinder-to-cylinder imbalances in air, fuel and diluent. Figure 1 shows typical contributions to maldistribution. ICFC provides an algorithmic solution rather than a hardware solution, and is a tool to help achieve both emissions and cost-reduction objectives. Figure 1. Maldistribution Contributions Presently, most automotive applications control the average φ of all the cylinders3, 6. With imbalances present, this method forces some of cylinders to run rich, and others to run lean. Many applications provide static calibration gains for each cylinder to correct for maldistribution, but provide only an average correction across a fleet of engines. They do not take into account differences from component to component or from engine to engine. Our ICFC algorithm was designed to reduce engine and component costs while maintaining or reducing engine emissions and emission variability, using only existing production hardware. It was implemented using a modelbased approach4 with a focus on reducing manual and iterative calibration processes5 associated with fuel and emissions control. ICFC is a real-time online adaptive controller than learns each cylinder’s maldistribution and stores the corrective terms into the Powertrain Control Module’s (PCM) memory. It accomplishes this task by analyzing each cylinder’s exhaust using a single oxygen sensor, and compensating for imbalances by individually modifying fuel-injector commands. Our ICFC, using a switching oxygen sensor, has shown the following benefits: 1. Cost Benefits • No requirement for additional hardware beyond that typical to current US and European production.