Abstract: A NOx occluding member that occludes NOx when the air-fuel ratio is on the fuel-lean side is disposed in an engine exhaust passage. An NOx ammonia sensor is disposed in the engine exhaust passage downstream of the NOx occluding member. A surplus amount of a reducing agent that is not used to release NOx is determined from a change in the ammonia concentration detected by the NOx ammonia sensor when the air-fuel ratio is changed to the fuel-rich side so as to release the NOx from the NOx occluding member.

Abstract: In a fuel injection control apparatus of an internal combustion engine for controlling a fuel supply quantities by making use of a fuel behavior model obtained by modeling the dynamic behavior of fuel flowing from injector 27 into combustion chamber 14 of cylinder 10 of engine 1, the fuel behavior model is configured to estimate the dynamic fuel behavior such as attachment onto and detachment from a wall surface, e.g., using separate quantities, a wall surface adhesion quantity Fwv(k) of a low boiling point component and a wall surface adhesion quantity Fwp(k) of a high boiling point component at each time k, and to control an injected fuel quantity Fi(k) so that a fuel quantity Fc(k) of fuel flowing into the cylinder becomes a target value.

Abstract: An air-fuel ratio control apparatus of an internal combustion engine according to the present invention is provided with oxygen storage amount estimating means, downstream exhaust air-fuel ratio detecting means, maximum oxygen storage amount estimating means, and air-fuel ratio target setting means. The oxygen storage amount estimating means estimates an oxygen storage amount of an exhaust purifying catalyst, based on a history of an oxygen adsorption/desorption amount of the exhaust purifying catalyst located on an exhaust path. The downstream exhaust air-fuel ratio detecting means is located downstream of the exhaust purifying catalyst and detects an exhaust air-fuel ratio downstream of the exhaust purifying catalyst. The maximum oxygen storage amount estimating means estimates a maximum oxygen storage amount, based on an oxygen storage amount estimate when the exhaust air-fuel ratio detected is a predetermined air-fuel ratio.

Abstract: A direct-injection internal combustion engine can smoothly switch and transition between a first operation mode and a second operation mode according to an operating condition of the engine. An engine control amount in the first operation mode is calculated differently from an engine control amount in the second operation mode. However, even if the engine control amount requires correction only in the second operation mode, calculation of a correction amount is made during the first operation mode as well. During a transition from the first operation mode to the second operation mode, the correction amount calculated during the first operation mode is taken into account in calculating an engine control amount. As the correction amount is already available at the time of transition, a suitable engine control amount can be immediately obtained.

Abstract: In an exhaust gas purification device for an internal combustion engine, a NOX occluding and reducing catalyst is disposed in the exhaust gas passage of an engine. The NOX occluding and reducing catalyst absorbs NOX in the exhaust gas when the air-fuel ratio of the exhaust gas is at a lean air-fuel ratio and releases and reduces NOX when the air-fuel ratio of the exhaust gas is at a rich air-fuel ratio. The air-fuel ratio of the exhaust gas flowing out from the catalyst is detected by an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst. When the air-fuel ratio of the exhaust gas flowing into the catalyst is changed from a rich air-fuel ratio to a lean air-fuel ratio, the air-fuel ratio of the exhaust gas flowing out from the catalyst stays at a stoichiometric air-fuel ratio before it changes to a lean air-fuel ratio.

Abstract: In an exhaust gas purification device for an internal combustion engine, a NO.sub.X occluding and reducing catalyst is disposed in the exhaust gas passage of an engine. The NO.sub.X occluding and reducing catalyst absorbs NO.sub.X in the exhaust gas when the air-fuel ratio of the exhaust gas is at a lean air-fuel ratio and releases and reduces NO.sub.X when the air-fuel ratio of the exhaust gas is at a rich air-fuel ratio. The air-fuel ratio of the exhaust gas flowing out from the catalyst is detected by an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst. When the air-fuel ratio of the exhaust gas flowing into the catalyst is changed from a rich air-fuel ratio to a lean air-fuel ratio, the air-fuel ratio of the exhaust gas flowing out from the catalyst stays at a stoichiometric air-fuel ratio before it changes to a lean air-fuel ratio.

Abstract: In an exhaust gas purification device for an internal combustion engine, a three-way catalyst and a NO.sub.X occluding and reducing catalyst (a NORC) are disposed in the exhaust gas passage of an engine in this order from the upstream side. A first air-fuel ratio sensor is disposed in the exhaust gas passage between the three-way catalyst and the NORC, and a second air-fuel ratio sensor is disposed in the exhaust gas passage downstream of the NORC. An engine electronic control unit (ECU) changes the operating air-fuel ratio of the engine from a lean air-fuel ratio to a rich air-fuel ratio and a rich air-fuel ratio to a lean air-fuel ratio in order to evaluate the abilities of the three-way catalyst and the NORC. The ECU evaluates the catalytic abilities based on the output of the first air-fuel ratio sensor when the engine air-fuel ratio is changed. Further, the ECU evaluates the catalytic ability and the NO.sub.