Patent ID: 6560960
Filing Date: 2003-05-13
Classification: F01N,F02D,Y02T

Abstract:
Fuel control apparatus for an engine equipped with a catalyst which performs a three-way purification function at least when an air/fuel state of exhaust gas is in a state corresponding to a substantially stoichiometric air/fuel ratio, said fuel control apparatus comprising:a combustion state control means which operates the engine in either a stratified combustion state or a homogeneous combustion state based upon an operating condition of the engine, said stratified combustion state being executed when the engine is in a predetermined region of low rotational speed and low load side and said homogeneous combustion state being executed when the engine is in another predetermined region of high rotational speed and high load side; an in-cylinder air/fuel control means which controls an in-cylinder air/fuel ratio that is an average air fuel ratio prior to an ignition in an in-cylinder combustion chamber to be lean of the stoichiometric air/fuel ratio when the engine is in said stratified combustion state, said in-cylinder air/fuel control means also controlling an in-cylinder air/fuel ratio that is an average air fuel ratio prior to an ignition in an in-cylinder combustion chamber to be the substantially stoichiometric air/fuel ratio or slightly richer; a fuel cut control means which performs a fuel cut control of compulsorily stopping a fuel supply to the combustion chamber under a predetermined condition during a decelerating operation of the engine; a fuel cut control terminate means which resumes said fuel supply when said fuel cut control is executed and when an accelerator pedal is stepped on, or when the engine rotational speed becomes equal to a predetermined recovery rotational speed; a low catalyst temperature determining means for determining whether the catalyst is in a predetermined low temperature state where its exhaust purification performance is deteriorated; and an exhaust air/fuel ratio control means for controlling the exhaust air/fuel state to be within a range between a substantially stoichiometric air/fuel ratio and an air/fuel ratio of 12 regardless of the operating condition of the engine when said low catalyst temperature determining means determines that the catalyst is in said predetermined low temperature state and when said fuel cut control by said fuel cut control means is terminated by said fuel cut control terminate means; wherein the engine is further equipped with a fuel injector for injecting fuel directly into the in-cylinder combustion chamber and a throttle valve for controlling an intake air amount of the engine, said exhaust air/fuel ratio control means causing the fuel injector to additionally inject fuel during a cylinder expansion stroke or a cylinder exhaust stroke so that the exhaust air/fuel ratio is in a state corresponding to a state within a range between substantially stoichiometric air/fuel ratio and 12 of an air/fuel ratio, said fuel control apparatus further comprising: a throttle opening control means for closing the throttle valve when said fuel cut control is performed by said fuel cut control means and when the engine rotational speed is higher than a specific rotational speed which is higher than said predetermined recovery speed and causing the throttle valve to operate to open even if said fuel cut control is performed when the engine rotational speed decreases to said set rotational speed if the catalyst is determined to be in the low temperature state by said low catalyst temperature determining means.