During execution of a first purification process of fluctuating a hydrocarbon concentration in exhaust gas flowing into a first catalyst with an amplitude within a prescribed range at a time interval within a prescribed range, when a switch request to a second purification process of purifying NOx in a second catalyst by adding urea water into the exhaust gas is generated, the switch to the second purification process is prohibited on the condition that a current NOx purification rate (a first purification rate R1) is higher than a purification rate (a second purification rate R2) on the assumption that the second purification process is executed, and an HC poisoning recovery stand-by process of reducing an additive amount of hydrocarbon per once in the first purification process is executed so as to reduce a slip amount of hydrocarbon into the downstream of the first catalyst.

The disclosure relates to internal combustion engines in general, and teaches various methods and apparatus for operating engines with an exhaust-gas turbocharger. Some embodiments include a method for operating an internal combustion engine having a fresh-gas tract for the supply of fresh gas to a cylinder, and an exhaust tract for the discharge of exhaust gas. They may include determining a value of a first operating condition of a catalytic converter arranged in the exhaust tract; determining a value of a second operating condition of the catalytic converter; calculating, as a function of the determined value, a first value for a maximum admissible scavenged-over quantity of fresh gas into the exhaust tract during scavenging operation; and setting the maximum admissible scavenged-over quantity to a second value lower than the first value if the value of the second operating condition reaches a predefined value.

An aftertreatment system comprises a selective catalytic reduction (SCR) unit, a reductant injector configured to insert reductant into the aftertreatment system, a first NO.sub.x sensor configured to measure an amount of NO.sub.x gases at a location upstream of the reductant injector, and a second NO.sub.x sensor configured to measure an amount of NO.sub.x gases at a location downstream of the SCR unit. A controller is programmed to estimate an amount of reductant deposits formed in the aftertreatment system based on at least the amount of NO.sub.x gases measured at the location upstream of the reductant injector, the amount of NO.sub.x gases measured at the location downstream of the SCR unit, and an amount of reductant that has been inserted into the aftertreatment system. The controller adjusts an amount of reductant to be inserted into the aftertreatment system based on the estimated amount of reductant deposits formed in the aftertreatment system.

In an exhaust gas purification system having an oxidation catalyst and an exhaust gas purifying unit formed so as to include a filter and a selective reduction-type NOx catalyst, at least one of supply of the fuel component and supply of ammonia or an ammonia precursor in an amount that is increased when a prescribed condition under which a part of a fuel component supplied to exhaust gas passes through to a downstream side of the oxidation catalyst is satisfied as compared to a non-passing time supply amount that is a supply amount of ammonia or the ammonia precursor to be supplied when the prescribed condition is not satisfied is controlled such that ammonia for NOx selective reduction by the increased ammonia or ammonia precursor reaches the exhaust gas purifying unit before the passed fuel component. Accordingly, an effect of a fuel component supplied to exhaust gas on a NOx purification performance of the selective reduction-type NOx catalyst is minimized in the exhaust gas purification system of the internal combustion engine which includes the filter and the selective reduction-type NOx catalyst.

A diagnostic device for an exhaust gas purification system that has a diesel oxidation catalyst (DOC), a diesel particulate filter, and an exhaust pipe injection device. The device includes a sensor for detecting a temperature of the DOC, a first calculation unit for converting an integration time of the detected temperature between regeneration intervals into a thermal history time with respect to a predetermined set temperature, and calculating a degree of degradation of the DOC based on this thermal history time, a second calculation unit for calculating a quantity of heat generated in the DOC based on the detected temperature during a forced regeneration execution period, and calculating another degree of degradation of the DOC based on the quantity of heat generated; and a diagnosis unit for diagnosing a degradation state of the DOC based on the degrees of degradation entered from the first and second calculation units.

In an exhaust gas purification system having an oxidation catalyst and an exhaust gas purifying unit formed so as to include a filter and a selective reduction-type NOx catalyst, at least one of supply of the fuel component and supply of ammonia or an ammonia precursor in an amount that is increased when a prescribed condition under which a part of a fuel component supplied to exhaust gas passes through to a downstream side of the oxidation catalyst is satisfied as compared to a non-passing time supply amount that is a supply amount of ammonia or the ammonia precursor to be supplied when the prescribed condition is not satisfied is controlled such that ammonia for NOx selective reduction by the increased ammonia or ammonia precursor reaches the exhaust gas purifying unit before the passed fuel component. Accordingly, an effect of a fuel component supplied to exhaust gas on a NOx purification performance of the selective reduction-type NOx catalyst is minimized in the exhaust gas purification system of the internal combustion engine which includes the filter and the selective reduction-type NOx catalyst.

Techniques for calibrating a catalyst model for a chemical reaction by a catalyst (e.g., a vehicle three-way catalytic converter) including optimizing an A-value for the chemical reaction by running the catalyst model and adjusting the A-value until results of the catalyst model are within a first threshold of the test data and setting the A-value to the optimized A-value, optimizing an E-value for the chemical reaction by running the catalyst model and adjusting the E-value until the catalyst model results are minimized relative to the test data within a second threshold of the test data, determining a new A-value based on the optimized E-value and setting the A-value to the new A-value and the E-value to the optimized E-value, and determining a reoptimized A-value by running the catalyst model and adjusting the A-value until the catalyst model results are within a third threshold of the test data.

In an internal combustion engine, a hydrocarbon feed valve (15), NO.sub.x storage catalyst (13), particulate filter (14), and electric resistance type sensor (29) are arranged in an engine exhaust passage in this order from an upstream side. The electric resistance type sensor (29) generates an output value corresponding to the amounts of deposition of particulate matter and hydrocarbons which are contained in the exhaust gas and deposited at the sensor part thereof. From the change of the output value of the electric resistance type sensor (29), it is judged if the hydrocarbons have slipped through the NO.sub.x storage catalyst (13) and if the particulate matter has slipped through the particulate filter (14).

The disclosure relates to internal combustion engines in general, and teaches various methods and apparatus for operating engines with an exhaust-gas turbocharger. Some embodiments include a method for operating an internal combustion engine having a fresh-gas tract for the supply of fresh gas to a cylinder, and an exhaust tract for the discharge of exhaust gas. They may include determining a value of a first operating condition of a catalytic converter arranged in the exhaust tract; determining a value of a second operating condition of the catalytic converter; calculating, as a function of the determined value, a first value for a maximum admissible scavenged-over quantity of fresh gas into the exhaust tract during scavenging operation; and setting the maximum admissible scavenged-over quantity to a second value lower than the first value if the value of the second operating condition reaches a predefined value.