Method and system for air-fuel ratio control

Abstract

Methods and systems are provided for learning fuel injector error for cylinder groups during a deceleration fuel shut-off (DFSO), where all cylinders of an engine are deactivated, sequentially firing each cylinder of a cylinder group, each cylinder fueled via consecutive first and second fuel pulses of differing fuel pulse width from an injector. Based on a lambda deviation between the first and second pulses, a fuel error for the injector and an air-fuel ratio imbalance for each cylinder is learned. Alternatively or additionally, a difference in crankshaft acceleration between the first and second pulses relative to the expected deviation may be used to learn torque error, and adjust fuel injector error and air-ratio imbalance for each cylinder.

Description

technical field [0001] The present description generally relates to methods and systems for controlling a vehicle engine to monitor air-fuel ratio imbalances during deceleration fuel cutoff (DFSO) conditions. Background technique [0002] Engine parameters such as air-fuel ratio (AFR) can be controlled to ensure improved engine performance, efficient use of exhaust catalysts and reduced exhaust emissions. In particular, engine emissions may be degraded if engine exhaust is not as rich or lean as expected due to variations in the engine air-fuel ratio between cylinders of the engine. Additionally, there may be a torque imbalance between the engine cylinders, which can lead to NVH issues. [0003] One way to determine changes in air-fuel ratio between engine cylinders is to sense engine exhaust via an oxygen sensor. Additionally or alternatively, crankshaft acceleration may be estimated at desired AFR. Fuel and / or charge air parameters may then be adjusted based on the chan...

AI Technical Summary

Problems solved by technology

Also, when fuel pulses are scheduled through the injector, the purge of fuel vapors and use of positive crankcase ventilation (PCV) can further corrupt the oxygen sensor output, requiring complex calculations to compensate for ingested hydrocarbons

If AFR monitoring is scheduled with extraction or PCV disabled, there may be limited opportunities for AFR monitoring

On the other hand, if extraction is disabled to accomplish AFR monitoring, the fuel vapor canister may not be cleaned effectively, causing emissions issues

Images