Model-based cylinder-by-cylinder air-fuel ratio control for SIengines using sliding observers

摘要

Exhaust stoichiometric air-fuel ratio is required for a 3-waycatalytic converter to reduce exhaust emissions from an SI engine. Onlywhen the combustion inside cylinders of an SI engine is kept close toits stoichiometric value can the catalytic converter then mostefficiently reduce the harmful CO, HC, and NOx in the exhaust mixture.By this method the air pollution from the engine exhaust can be reduced.The purpose of air-fuel ratio (AFR) control is to maintainstoichiometric combustion in an SI engine. Currently one way to controlAFR is by using the signal(s) from one or dual oxygen sensors installedon the exhaust pipes as a feedback signal to correct the fuel amountinjected into intake manifold runner. The AFR signals obtained by such amethod are mean values for the ratios in all cylinders. This makes acylinder-by-cylinder control difficult. This paper proposes a new methodfor a cylinder-by-cylinder AFR control. In this method nonlinear stateestimation is used to estimate the amounts of fuel and air beinginjested into each individual cylinder, and these air-fuel ratio signalsare transmitted back to the electronic control module to correct thefuel amount injected into each runner port. The fuel mass in a cylinderis estimated by a cylinder pressure and combustion heat releaseobserver, while the air mass into a cylinder is estimated by arunner-by-runner intake manifold pressure observer. This control methodnot only fulfils the AFR control cylinder by cylinder, but also mayeliminate the need for conventional costly oxygen sensors