Individual cylinder air-fuel ratio control for engines with unevenly spaced firing order

The most recent European regulations for two- and three-wheelers (Euro 5) are imposing an enhanced combustion control in motorcycle engines to respect tighter emission limits, and Air-Fuel Ratio (AFR) closed-loop control has become a key function of the engine management system also for this type of applications. In a multi-cylinder engine, typically only one oxygen sensor is installed on each bank, so that the mean AFR of two or more cylinders rather than the single cylinder one is actually controlled. The installation of one sensor per cylinder is normally avoided due to cost, layout and reliability issues. In the last years, several studies were presented to demonstrate the feasibility of an individual AFR controller based on a single sensor. These solutions are based on the mathematical modelling of the engine air path dynamics, or on the frequency analysis of the lambda probe signal. This work presents a novel approach that has been developed specifically for engines with big-bang (or unevenly spaced) firing order, which is typically adopted in motorcycle applications with either V (all of them) or in-line cylinder configuration. This approach is much simpler if compared to previously published solutions, because it doesn’t require a mathematical model of the air path dynamics, it doesn’t need high computational resources, and it is reliable and robust up to high engine speeds, which are often reached in motorcycle engines. The control algorithm was developed, designed and tested in a simulation environment, by means of a 1-D model of a twin-cylinder motorcycle engine, and then real-time implemented and experimentally validated on the vehicle.