Engine power train control method and control apparatus for a vehicle

摘要

The present invention provides an engine power train control method and control apparatus for a vehicle having an engine and an automatic transmission capable of quickly changing an air-fuel ratio to meet the requirements of the exhaust gas without producing shocks and without reducing an engine torque. The invention has following components. An air-fuel ratio command value is varied stepwise for transition between an air-fuel ratio for lean-burn operation and a stoichiometric air-fuel ratio and, at the same time, an air amount fed to the engine is varied stepwise. In a fixed period following the completion of the stepwise variation of air-fuel ratio command value, a basic fuel amount fed to the engine is varied stepwise from a value determined according to the air amount and an engine speed to a value determined according to a position of an accelerator pedal of the vehicle and the engine speed. The invention provides that shocks do not occur and the operability is improved, because the engine torque remains substantially constant through the air-fuel ratio transition.