Method and apparatus for controlling an engine

A control device of an engine capable of combustion in a lean air-fuel ratio, comprising:

• an HC adsorbing catalyst having an HC adsorbing function for adsorbing HC in an exhaust gas pipe of the engine at a low temperature and for emitting the adsorbed HC at a high temperature, and a three-way purifying function on the same carrier;
• an NOx adsorbing (occluding) catalyst having an NOx adsorbing (occluding) function for adsorbing or occluding NOx in oxidizing atmosphere and for emitting NOx in reducing atmosphere, and a three-way purifying function on the same carrier;
• and
• means for directly or indirectly detecting a temperature of the HC adsorbing catalyst and a temperature of the NOx adsorbing (occluding) catalyst;
• and
• means for controlling said engine such that driving state of said engine is controlled in accordance with the temperature of the HC adsorbing catalyst and the temperature of the NOx adsorbing (occluding) catalyst.

A control device of an engine capable of combustion in a lean air-fuel ratio, comprising:

• an NOx adsorbing catalyst disposed in an exhaust system of said engine and having an NOx adsorbing function for adsorbing NOx in oxidizing atmosphere and for emitting NOx in reducing atmosphere and a three-way purifying function on the same carrier;
• an HC adsorbing catalyst disposed after said NOx adsorbing catalyst having an HC adsorbing function for adsorbing HC in an exhaust gas pipe of the engine at a low temperature and for emitting the adsorbed HC at a high temperature and a three-way purifying function on the same carries;
• and
• means for directly or indirectly detecting a temperature at an outlet of the NOx adsorbing catalyst;
• and
• means for controlling a engine control parameter in accordance with the detected temperature at the outlet of said NOx adsorbing catalyst,
• wherein said engine control parameter includes an air-fuel ratio of a mixture into said engine,
• when a temperature at an outlet of the NOx adsorbing catalyst is equal to/lower than a predetermined value, said controlling means controls said engine to be operated in a stoichiometric air-fuel ratio or a rich air-fuel ratio;
• and
• when a temperature of the outlet of said NOx adsorbing catalyst is equal to/higher than the predetermined value, said controlling means controls said engine to be operated in a lean air-fuel ratio.

A control device controlling an engine having an NOx adsorbing catalyst disposed in an exhaust system of said engine and having an NOx adsorbing function for adsorbing NOx in oxidizing atmosphere and for emitting NOx in reducing atmosphere and a three-way purifying function on the same carrier, and an HC adsorbing catalyst disposed after said NOx adsorbing catalyst having an HC adsorbing function for adsorbing HC in an exhaust gas pipe of the engine at a low temperature and for emitting the adsorbed HC at a high temperature and a three-way purifying function on the same carrier, said device comprising:

• means for directly or indirectly detecting a temperature at an outlet of the NOx adsorbing catalyst;
• and
• means for controlling a engine control parameter in accordance with the detected temperature at the outlet of said NOx adsorbing catalyst,
• wherein said engine control parameter includes an air-fuel ratio of a mixture into said engine,
• when a temperature at an outlet of the NOx adsorbing catalyst is equal to/lower than a predetermined value, said controlling means controls said engine to be operated in a stoichiometric air-fuel ratio or a rich air-fuel ratio;
• and
• when temperature of the outlet of said NOx adsorbing catalyst is equal to/higher than the predetermined value, said controlling means controls said engine to be operated in a lean air-fuel ratio.