Abstract: An under-floor catalyst (33) includes a GPF (41) capable of trapping fine exhaust particles in exhaust gas, and a downstream-side catalyst (42) positioned on the downstream side of GPF (41). GPF (41) can be supplied with secondary air. When an internal combustion engine (10) is stopped during travel, the secondary air is supplied to GPF (41) in which the fine exhaust particles are accumulated. At this time, the temperature of GPF (41) is equal to or higher than a predetermined temperature. Thus, a deterioration in the exhaust gas purification performance of under-floor catalyst (33) at the time of the start of internal combustion engine (10) can be suppressed.

Abstract: An internal combustion engine (1) has an electric heating catalyst (5) in an exhaust passage (2). When it is detected that a door has been opened, the electric heating catalyst (5) is preheated. If power of an engine controller (8) is lost during the preheating, information on an estimated temperature, which is stored in the engine controller (8), is lost. The engine controller (8) forbids energization of the electric heating catalyst (5) until a cooling period necessary for temperature of the electric heating catalyst (5) to fall elapses after recovery of the power of the engine controller (8). After the cooling period elapses, the preheating is started again.

Abstract: An internal combustion engine (1) has anelectric heating catalyst (5) in an exhaust passage (2) . When it is detected that a door has been opened, the electric heating catalyst (5) is preheated. If power of an engine controller (8) is lost during the preheating, information on an estimated temperature, which is stored in the engine controller (8), is lost. The engine controller (8) forbids energization of the electric heating catalyst (5) until a cooling period necessary for temperature of the electric heating catalyst (5) to fall elapses after recovery of the power of the engine controller (8) . After the cooling period elapses, the preheating is started again.

Abstract: An under-floor catalyst (33) includes a GPF (41) capable of trapping fine exhaust particles in exhaust gas, and a downstream-side catalyst (42) positioned on the downstream side of GPF (41). GPF (41) can be supplied with secondary air. When an internal combustion engine (10) is stopped during travel, the secondary air is supplied to GPF (41) in which the fine exhaust particles are accumulated. At this time, the temperature of GPF (41) is equal to or higher than a predetermined temperature. Thus, a deterioration in the exhaust gas purification performance of under-floor catalyst (33) at the time of the start of internal combustion engine (10) can be suppressed.

Abstract: Removal of poisoning substance (sulfur oxidant) is controlled based upon estimating an amount of the poisoning substance deposited in an exhaust gas purification catalyst disposed in an exhaust pipe for an internal combustion engine, a lower limit is set corresponding to a possible removal amount of the poisoning substance varying with a state of a catalyst, and the removal control of the poisoning substance is ended when the estimated amount is less than the lower limit. The estimated amount can be accurately calculated, thereby ending the removal control at a proper timing. Fuel economy and exhaust gas purification performance improves.

Abstract: In an internal combustion engine (1,100), a first exhaust passage (10A) having an oxygen storing catalyst (11A) is connected to cylinders of a first group (1A), and a second exhaust passage (10B) having an oxygen storing catalyst (11B) is connected to cylinders of a second group (1B). These exhaust passages are joined as a collective exhaust passage (10C). Normally, the air-fuel ratio of the first group (1A) is feedback controlled based on the oxygen concentration of the first exhaust passage (10A), and the air-fuel ratio of the second group (1B) is feedback controlled based on the oxygen concentration of the second exhaust passage (10B). When deterioration of the catalysts is diagnosed, the phases of the air-fuel ratio are made to coincide with each other between the groups by performing feedback correction of the air-fuel ratio of all groups based on the oxygen concentration of the first exhaust passage (10A).

Abstract: Removal of poisoning substance (sulfur oxidant) is controlled based upon estimating an amount of the poisoning substance deposited in an exhaust gas purification catalyst disposed in an exhaust pipe for an internal combustion engine, a lower limit is set corresponding to a possible removal amount of the poisoning substance varying with a state of a catalyst, and the removal control of the poisoning substance is ended when the estimated amount is less than the lower limit.

Abstract: In an internal combustion engine (1,100), a first exhaust passage (10A) having an oxygen storing catalyst (11A) is connected to cylinders of a first group (1A), and a second exhaust passage (10B) having an oxygen storing catalyst (11B) is connected to cylinders of a second group (1B). These exhaust passages are joined as a collective exhaust passage (10C). Normally, the air-fuel ratio of the first group (1A) is feedback controlled based on the oxygen concentration of the first exhaust passage (10A), and the air-fuel ratio of the second group (1B) is feedback controlled based on the oxygen concentration of the second exhaust passage (10B). When deterioration of the catalysts is diagnosed, the phases of the air-fuel ratio are made to coincide with each other between the groups by performing feedback correction of the air-fuel ratio of all groups based on the oxygen concentration of the first exhaust passage (10A).