Abstract: An internal combustion engine is provided in which a prescribed amount of fuel is injected over a predetermined period until an air-fuel ratio sensor is activated when fuel cut control of the internal combustion engine is stopped to resume normal engine operation. If an EGR gas is inducted immediately before the fuel cut control is started, the prescribed amount is reduced.

Abstract: The invention relates to a dosing module (10) for injecting a reduction agent, in particular a urea-water solution, into an exhaust pipe of an internal combustion engine, in particular of a self-igniting internal combustion engine, to reduce nitrogen oxides in the exhaust stream, wherein the dosing module has a main cooling element (12) through which a cooling liquid flows, in particular for cooling an injection valve (64) for the reduction agent. According to the invention, an additional cooling element (14), through which the cooling liquid likewise flows, in particular for cooling in the region of an electrical plug connection (22) and of an electromagnet (80) for actuating the injection valve (64), is placed on the basis cooling element (12), wherein a guide insert (30) for the cooling liquid is arranged in the main cooling element (12).

Abstract: A secondary air supply system includes an electric air pump that supplies secondary air to a location upstream of an exhaust gas purification catalyst arranged in an exhaust passage; a control valve that opens/closes a secondary air supply passage; a pressure detector that detects a pressure between the pump and the control valve; and a control unit that detects a first pressure in a first operating state where the control valve is closed, and detects a second pressure in a second operating state where the control valve is open, using the pressure detector. The control unit corrects at least one of the first and second pressures based on a first driving voltage for the pump in the first operating state and a second driving voltage in the second operating state, and estimates a secondary air flow rate based on the first and second pressures after correction.

Abstract: An internal combustion engine includes fuel injection valves and an ECU. In the internal combustion unit, predetermined injection is performed when the bed temperature of a catalyst is lower that a predetermined temperature. In the predetermined injection, fuel is injected from a first fuel injection valve, from among the fuel injection valves, within the valve opening period of an intake valve, and fuel is injected from a second fuel injection valve, from among the fuel injection valves, within the valve opening period of an exhaust valve. In the internal combustion engine, a first injection amount is specifically injected from the first fuel injection valve in the predetermined injection.

Abstract: Various methods and system are described for determining ambient humidity via an exhaust gas sensor disposed in an exhaust system of an engine. In one example, a reference voltage of the sensor is modulated between a first and second voltage during non-fueling conditions of the engine. The ambient humidity is determined based on an average change in pumping current while the voltage is modulated.

Abstract: In an exhaust gas treatment method for an internal combustion engine, a DPF abnormal combustion causing operation is determined to have occurred when the internal combustion engine shifts from a high rotation or high load operation region ? to a low rotation, low load operation region ? within a set time T1. When it is determined that a DPF abnormal combustion causing operation has occurred, abnormal combustion of PM collected in the DPF is suppressed by fully opening an intake throttle valve (44) in order to increase an exhaust gas flow so that heat is removed by sensible heat of the exhaust gas, thereby cooling a DPF device (52), and continuing a late post-injection in order to reduce an oxygen concentration of the DPF.

Abstract: A system for a vehicle includes a steady-state (SS) temperature module and a mass temperature module. The SS temperature module generates a SS temperature of a downstream-most catalyst of an exhaust system at a predetermined location between upstream and downstream faces of the downstream-most catalyst. The predetermined location is a predetermined distance upstream from the downstream face. The mass temperature module generates an instantaneous temperature of the downstream-most catalyst at the predetermined location as a function of the SS temperature.

Abstract: A method unloads hydrocarbon emissions deposited by an exhaust gas on an after-treatment device that is employed in an exhaust system for an internal combustion engine. The method includes determining whether the engine has been operating at a preset idle speed for a predetermined amount of time. The method also includes increasing the preset idle speed by a predetermined value if the engine has been operating at a preset idle speed for a predetermined amount of time. The increasing of the engine idle speed increases a flow rate of the exhaust gas to the after-treatment device and unloads the deposited hydrocarbon emissions. A system for unloading hydrocarbon emissions deposited on an after-treatment device and a vehicle employing such a system are also disclosed.

Abstract: In accordance with the embodiments of the present invention, an engine is disclosed. The engine includes at least one donor cylinder and at least one non-donor cylinder coupled to an intake manifold feeding intake air and an exhaust manifold. The exhaust manifold is configured to carry an engine exhaust emission from the donor cylinder and the non-donor cylinder. The engine also includes an exhaust gas recirculation manifold extending from the donor cylinder to the intake manifold for recirculating a donor cylinder exhaust emission from the donor cylinder to the donor, and non-donor cylinders via the intake manifold. The engine further includes an after-treatment system and a sensor configured to sense a temperature of the engine exhaust emission and a device configured to receive a sensing signal from the sensor and to control a parameter of the engine and a component of the engine in response to the sensing signal.

Abstract: A system and method for determining a rate of ammonia deposition and controlling an engine is described. In one example, an amount of ammonia deposited in an engine exhaust is determined and the deposited ammonia is purged after the amount of ammonia deposited reaches a threshold level. The method may decrease ammonia use and ammonia emissions from a vehicle.

Abstract: A system includes a main engine operating on gaseous fuel from a tank. An auxiliary engine operates using gaseous fuel vented from the tank. A first exhaust passage receives a first stream of exhaust gas from the main engine. A second exhaust passage receives exhaust gas from the auxiliary engine, which passes through an ammonia-producing catalyst. A third exhaust passage is fluidly connected to the first and second exhaust passages and routes exhaust gas through a NOx reducing catalyst. The system operates such that a mass flow of ammonia generated by the ammonia-producing catalyst substantially matches a total mass flow of NOx gas in the third exhaust passage that is treated within the ammonia-producing catalyst.

Abstract: A method for controlling emissions in an engine system including an internal combustion engine and a catalytic converter with oxygen storage capacity. The method includes determining a real time oxygen storage level of the three-way catalytic converter based on a real time exhaust gas flow rate and a real time measured upstream oxygen quantity with respect to the catalytic converter. Further, maintaining an optimal oxygen storage level of the three-way catalytic converter for different types of fuel used in the internal combustion engine.

Abstract: An exhaust gas purification device arranged in an exhaust system of an engine, and includes a renewing device for burning and removing a particulate matter within the exhaust gas purification device. The renewing device is operable in the case that a clogged state of the exhaust gas purification device is equal to or more than a prescribed level, wherein the exhaust gas purification system includes renewal admittance input means which allows an actuation of the renewing device, and rotating speed holding input means for holding a rotating speed of the engine to a predetermined rotating speed, and in the case that a turn-on operation of the rotating speed holding input means is carried out in a state in which an allowing operation of the renewal admittance input means is carried out, the rotating speed holding motion of the engine is executed in preference to an actuation of the renewing device.

Abstract: A method of controlling an internal combustion engine that includes an exhaust line fitted with a particulate filter, the method including: a) acquiring a charge parameter relating to a fill level of the particulate filter, b) comparing the charge parameter with at least one determined threshold, and c) bringing the internal combustion engine to a set operating point determined as a function of various criteria of differing levels of importance. Prior to c) and with one of the criteria being the mass flow rate of particles entering the particulate filter, a constraint level coefficient is determined as a function of the result of the comparing b) and applied to the particulate mass flow rate to weight importance of this criterion in determining the engine operating point.

Abstract: In an engine system with a reformer being installed in an exhaust pipe to reform a fuel, a control valve for controlling a flow rate of exhaust gas is provided downstream from an installed position of the reformer in the exhaust pipe. In the engine system with the reformer, since a part of the exhaust gas can be trapped in a space between the reformer and an engine chamber by closing the control valve during an exhaust stroke, the reforming efficiency of the reformer can be heightened.

Abstract: In a method and apparatus for operating an internal combustion engine, a lambda control is carried out, in which a trim regulation is provided, which operates with a P regulator component and an I regulator component. To prevent overshooting when the trim regulation is carried out, operation takes place in a first mode with compulsory adjustment and in a following second mode with increased regulator amplification factors.

Abstract: An internal combustion engine is coupled to an electric power generator. An exhaust manifold for the engine includes an exhaust gas conduit. A housing includes a catalyst in fluid communication with the conduit to receive exhaust produced by the engine. The catalyst is operable to reduce one or more constituents of the exhaust.

Abstract: Provided is an exhaust gas processing device for a diesel engine which can carry out sufficient regeneration processing of a DPF. A DPF regeneration control section continues normal regeneration processing by a DPF regeneration control section when an accelerated regeneration starting operation section does not perform accelerated regeneration starting operation after notification of accelerated regeneration requiring information is started. The DPF regeneration control section prohibits the normal regeneration processing, and an accelerated regeneration re-requirement notification section starts notification of accelerated regeneration re-requiring information, when a PM accumulation amount estimate becomes equal to or higher than an accelerated regeneration re-requirement determination value J4.

Abstract: Some implementations of a system for controlling an internal combustion engine (e.g., a natural gas fired internal combustion engine or another type of engine) can include an air-fuel ratio controller that is configured to monitor sensor feedback from an exhaust path and to thereafter automatically adjust the air-fuel mixture. The system can be employed in particular methods to control emissions from the engine, for example, by reducing pollutants emitted as components of the exhaust from the engine.

Abstract: In an internal combustion engine, inside an engine exhaust passage, a hydrocarbon feed valve (15) and an exhaust purification catalyst (13) are arranged. A first hydrocarbon feed method which injections hydrocarbons from the hydrocarbon feed valve (15) by predetermined feed intervals (?T) so that the air-fuel ratio of the exhaust gas falls to the demanded minimum air-fuel ratio (X) to thereby remove the NOx contained in the exhaust gas and a second hydrocarbon feed method which lowers the feed amount of hydrocarbons from the hydrocarbon feed valve (15) and feeds fuel to the combustion chambers (2) during a second half of the expansion stroke or the exhaust stroke are selectively used.

Abstract: Embodiments for regenerating a particle filter are provided. In one example, a method includes operating a spark-ignition internal combustion engine having a particle filter for collecting and burning soot particles in exhaust gas comprises in order to initiate regeneration of the particle filter. The method may include, in response to a regeneration condition, increasing exhaust temperature by retarding spark timing and once regeneration is reached, operating the engine with lean combustion to regenerate the particle filter, where a degree of leanness is based on each of a state of the filter and an upstream three-way catalyst.

Abstract: A method and a device for operating a hybrid vehicle, which ascertain the torque necessary for starting the non-operating internal combustion engine, and this torque is reserved by an additional drive unit. The torque necessary for starting the non-operating internal combustion engine is minimized by appropriately adjusting parameters of the internal combustion engine system.

Abstract: Fuel in a fuel tank is supplied by a low-pressure pump to intake passage injectors mounted on an intake manifold via a low-pressure fuel supply pipe and a low-pressure fuel distribution pipe. A high-pressure pump is provided on the low-pressure fuel supply pipe. The pressure of the fuel is boosted by the high-pressure pump, and then is supplied to in-cylinder injectors via a high-pressure fuel distribution pipe. In an intake passage injection (MPI) mode, excitation of a solenoid is stopped and operation of an electromagnetic spill valve is stopped so as reduce vibration and noise caused by the seating of the electromagnetic spill valve in a valve seat.

Abstract: A method of controlling an internal combustion engine and exhaust system having an SCR, and engine and exhaust system including an SCR, described herein, monitors, in real time, NOx conversion efficiency of an exhaust flow output by the internal combustion engine through the SCR. A determination is made as to whether the monitored NOx conversion efficiency exceeds a predetermined target conversion efficiency, such as a target based on a predetermined allowable amount of NOx emission. While the monitored NOx conversion efficiency exceeds the predetermined amount, the NOx concentration level in the exhaust flow is increased by an amount based on the difference in the monitored conversion efficiency and the predetermined target conversion efficiency.

Abstract: An exhaust gas treatment device for preventing a large quantity of unburned HC components from being released to the outside until a diesel oxidation catalyst reaches an activation temperature after early post-injection. By reducing a throttle opening of a variable throttle mechanism (77) provided in an oil passage (72), or increasing a set value of an oil pressure level detected in an oil pressure sensor (78) provided on the downstream side of the variable throttle mechanism, power of an oil circulation pump (74) is increased before a start point t1 of the early post-injection. With this arrangement, by increasing a load of a diesel engine to increase a temperature rise gradient of exhaust gas at the stage of increasing the temperature of the diesel oxidation catalyst, the unburned HC component released until the diesel oxidation catalyst reaches the activation temperature is reduced.

Abstract: A system includes an engine configured to operate in a first operating state and a second operating state, a particulate filter configured to receive exhaust gas from the engine and filter particulate matter from the exhaust gas, and an oxidation catalyst configured to generate heat to increase a temperature of the exhaust gas during a regeneration process. A sensor is configured to measure an actual temperature of the exhaust gas during the regeneration process. A controller is configured to define a fuel conversion factor based, at least in part, on the actual temperature and an expected temperature of the exhaust gas. The controller is further configured to analyze the fuel conversion factor over time relative to at least one of the first and second operating states of the engine and diagnose a fault in the regeneration process based, at least in part, on the fuel conversion factor.

Abstract: Embodiments for reducing ammonia slip are provided. In one example, a method for reduction of ammonia emissions from an engine exhaust gas aftertreatment device with an SCR catalyst comprises determining a concentration of NOx and/or ammonia in the exhaust gas aftertreatment device, comparing a determined value of NOx and/or ammonia concentration with a nominal value for NOx and ammonia, respectively, and if an actual or shortly forecasted ammonia concentration is above the respective nominal value, triggering engine conditions with higher exhaust NOx concentration. In this way, ammonia slip may be reduced without degrading fuel economy.

Abstract: A method to control valves in a cylinder operating in a multi-stroke cylinder mode. Valves are controlled to improve engine emissions as operating conditions vary.

Abstract: An exhaust gas treatment system for an internal combustion engine is provided, including an exhaust gas conduit, a flow-through container of absorbent particles, an electrically heated catalyst (“EHC”) device, a selective catalytic reduction (“SCR”) device, and a control module. The exhaust gas conduit is in fluid communication with, and is configured to receive an exhaust gas from the internal combustion engine. The exhaust gas contains oxides of nitrogen (“NOx”) and water. The flow-through container of absorbent particles is in fluid communication with the exhaust gas conduit and configured to receive the exhaust gas. The flow-through container substantially adsorbs the water from the exhaust gas below a threshold temperature. The EHC device is in fluid communication with the exhaust gas conduit and is configured to receive the exhaust gas. The EHC device is located downstream of the flow through container, and is selectively activated to produce heat.

Abstract: A system includes an internal combustion ignition engine with an exhaust gas flow, a particulate filter in the exhaust gas flow, a NOx reduction catalyst in the exhaust gas flow downstream of the particulate filter, a first oxygen sensor coupled to the exhaust gas flow downstream of the NOx reduction catalyst, and a second oxygen sensor coupled to the exhaust gas flow between the particulate filter and the NOx reduction catalyst. A controller includes an exhaust conditions module that interprets a first oxygen signal from the first oxygen sensor and a second oxygen signal from the second oxygen sensor and a combustion control module that commands a high engine-out air-fuel ratio when the first oxygen signal indicates a low oxygen content and commands a low engine-out air-fuel ratio when the first oxygen signal indicates a high oxygen content.

Abstract: Provided is a control apparatus for an internal combustion engine that can favorably achieve compatibility between suppressing deterioration of a catalyst and suppressing progression of rich poisoning thereof when the internal combustion engine has a configuration that performs valve stopping control during a fuel-cut operation. Variable valve operating apparatuses are provided having valve stop mechanisms that can respectively change an operating state of an intake valve and an exhaust valve between a valve operating state and a closed-valve stopped state. When an integrated fuel injection amount is equal to or greater than a predetermined value ? when executing a fuel-cut operation, it is determined that rich poisoning of an upstream catalyst is in a progressed state. In that case, valve stopping control of the intake and exhaust valves is prohibited to thereby supply oxygen to the upstream catalyst.

Abstract: A method for exhaust gas recirculation (EGR), in particular in internal combustion engines, in particular for reducing NOx emission, by actuating an EGR valve (2) and/or a throttle flap (3), characterized in that during a predetermined period of time after determining an NOx value of the values for actuating the EGR valve (2) and/or the throttle flap (3) a mathematical model is employed, in which the currently determined NOx values, the period of time elapsed since completing the NOx measurement and the parameters relevant for the NOx reduction of the internal combustion engine (1) are included.

Abstract: A control system for an internal combustion engine is provided, and includes an exhaust gas conduit, an oxidization catalyst (“OC”) device, a temperature sensor, an intake mass air flow sensor, an engine air intake mechanism, and a control module. The exhaust gas conduit is in fluid communication with, and is configured to receive an exhaust gas. The OC device is in fluid communication with the exhaust gas conduit. The OC device has an OC light-off temperature. The OC device is selectively activated to the light-off temperature to induce oxidization of the exhaust gas. The temperature sensor is situated in the exhaust stream upstream of the OC device. The temperature sensor monitors an exhaust gas temperature. The intake mass air flow sensor measures an air mass entering the internal combustion engine. The engine air intake mechanism is selectively activated to modulate the air mass entering the internal combustion engine.

Abstract: Provided is an exhaust purification system for an internal combustion engine.

Abstract: A device and a method are provided for diagnosing a technical apparatus which is particularly developed as an internal combustion engine. When specified states of the technical apparatus are present, the means of diagnosis are activated, and when at least one of the specified technical states is no longer present, the means of diagnosis are deactivated. Upon the deactivation, information is stored that identifies which technical state is no longer present.

Abstract: Termination of regeneration of a particulate filter may be based on a variable percent threshold of stored particulate, where the percent threshold of stored particulate depends on a current soot burn rate. In one example approach, a method for controlling regeneration of a diesel particulate filter comprises: terminating regeneration based on a particulate burning rate; wherein the particulate burning rate is based on operating conditions of the diesel particulate filter; the operating conditions including an amount of stored particulate in the diesel particulate filter and a temperature of the diesel particulate filter.

Abstract: A system for a vehicle includes a change determination module, a sulfur determination module, and a final equivalence ratio (EQR) module. The change determination module estimates a change in an amount of sulfur within a catalyst of an exhaust system of the vehicle. The sulfur determination module estimates the amount of sulfur within the catalyst based on the change. The final EQR module selectively adjusts fueling of an engine based on the amount of sulfur.

Abstract: A technique which accurately detects the deterioration of an exhaust gas purification catalyst which is applied to an internal combustion engine capable of using gas fuel and liquid fuel. Where only the gas fuel is used which is difficult to cause the oxygen occluded in the exhaust gas purification catalyst to be released therefrom even if the air fuel ratio of exhaust gas discharged from the internal combustion engine is changed to a rich side, a catalyst deterioration determination part determines whether the exhaust gas purification catalyst has deteriorated, based on either one of a change in an output of an oxygen concentration detection part only at a lean side, and changes in the output of the oxygen concentration detection part at the rich side and at the lean side.

Abstract: An exhaust system for an internal combustion engine is provided. The system comprises an exhaust tract which is connectable to an outlet side of the internal combustion engine, at least one catalytic converter arranged in the exhaust tract downstream of the engine, a particle filter downstream of the at least one catalytic converter, and a secondary-air inlet port provided in the exhaust tract upstream of the particle filter for introducing compressed secondary air into the exhaust tract via at least one flutter valve. In this way, additional oxygen may be supplied to the particulate filter to perform filter regeneration.

Abstract: A method for operating an internal combustion engine is proposed, in whose exhaust gas zone a particle filter is disposed, which is cyclically loaded with particles and thermally regenerated, as well as an apparatus for the implementation of the method, which prevents thermal overload of the particle filter after turning off the internal combustion engine. A test is made when the internal combustion engine is turned off to determine whether an exothermal reaction takes place. Provided that an exothermal reaction takes place in the particle filter, a butterfly valve is closed, which prevents exhaust gas flow through the particle filter and, if the circumstances arise, a resulting oxygenation ingress in the particle filter.

Abstract: In systems in which there is insufficient pressure difference between the intake and the exhaust to drive the EGR, an EGR pump is provided. In a dual-engine system, disclosed herein, the EGR system, i.e., the EGR cooler and EGR pump, is shared to obviate the need for two of each. Shutoff valves may be provided between the EGR system and a secondary of the two engines to isolate the secondary engine when it is not operating. When the engines are OPOC engines, exhaust aftertreatment devices, such as diesel oxidation catalysts and/or diesel particulate filters, may be placed upstream of where the EGR gases tee off from the engine's exhaust to thereby maintain a high pressure ratio across an exhaust turbine located downstream in the engine's exhaust.

Abstract: A system may include a hydrocarbon (HC) absorber positioned in an exhaust flow path and an electrically heated catalyst (EHC) positioned in the exhaust flow path downstream of the HC absorber.

Abstract: A cogeneration system includes a fuel evaporator; an internal combustion engine which outputs mechanical energy by combusting fuel evaporated by the fuel evaporator; an electric energy generator that converts the mechanical energy to an electric energy; a cold energy recovery portion which recovers cold energy generated when the fuel evaporator evaporates the fuel; an exhaust heat recovery portion which recovers heat exhausted from the engine; and a gas cleaner that cleans nitrogen oxides contained in gas exhausted from the engine. When the fuel is supplied to the gas cleaner, the fuel reduces the nitrogen oxides by reacting with the nitrogen oxides.

Abstract: A system for regenerating a particulate filter mounted on an exhaust pipe of a gasoline engine including a plurality of cylinders and an ignition device for igniting fuel and air in the cylinder, a three-way catalyst device mounted on the exhaust pipe connected to the gasoline engine, and to oxidize or reduce exhaust gas, the particulate filter mounted on the exhaust pipe downstream of the three-way catalyst device to trap particulate matter and regenerate the particulate matter using heat of the exhaust gas, a differential pressure sensor mounted upstream and downstream of the particulate filter and to measure a pressure difference of the particulate filter, and a control portion to receive the measured pressure difference and control parameters to determine an amount of non-ignited fuel which is not ignited and flows to the three-way catalyst device among the fuel flowing into the plurality of cylinders.

Abstract: A method to operate a vehicle equipped an internal combustion engine and a transmission coupled to drive wheels. The vehicle is equipped with a parking brake and has an electronic control unit with memory and the engine in fluid communication with an exhaust aftertreatment system. The method includes the steps of determining whether the engine is operating in idle mode for a predetermined period of time; determining whether NOx emissions exceed a predetermined level after the predetermined period of time; and limiting the engine speed not to exceed a predetermined engine speed until an operator engages the parking brake and engages an engine ignition switch.

Abstract: A cold start NO2 generation system includes a catalyst control module that identifies a portion of a three-way catalyst that corresponds to a nitrogen dioxide zone. A diagnostic module determines a temperature in the nitrogen dioxide zone, and a fuel control module adjusts an air/fuel ratio based on the temperature in the nitrogen dioxide zone. A cold start NO2 generation method includes identifying a portion of a three-way catalyst that corresponds to a nitrogen dioxide zone. The method further includes determining a temperature in the nitrogen dioxide zone and adjusting an air/fuel ratio based on the temperature in the nitrogen dioxide zone.

Abstract: In an internal combustion engine including an NSR catalyst and an SCR, to provide an exhaust purifying system that can limit aggravation of emissions by allowing the SCR to recover effectively from degraded performance caused by poisoning. An exhaust purifying system for an internal combustion engine capable of a lean burn operation includes an NSR catalyst disposed in an exhaust passage of the internal combustion engine; an SCR disposed downstream of the NSR catalyst; means for detecting sulfur poisoning of the SCR; and means for increasing a bed temperature of the SCR when the poisoning detecting means detects sulfur poisoning of the SCR. The temperature increasing means includes bank control, stoichiometric control, and rich spike control, any one of which is selected for performance according to an operating condition of the internal combustion engine.

Abstract: In one example, a method of operating an engine in a vehicle is described. The method comprises delivering a first substance to a cylinder of the engine from a first injector; delivering a second substance to the cylinder of the engine from a second injector, where the second substance has a greater heat of vaporization than the first substance; and increasing injection of the second substance responsive to an exhaust over-temperature condition.

Abstract: An exhaust emission control device includes a first detection unit for detecting a NOx adsorption amount and an oxygen storage amount of a three-way catalyst and a NOx purification catalyst during rich spike, a second detection unit for detecting the oxygen storage amount of the three-way catalyst and the NOx purification catalyst until the output of a second air-fuel sensor becomes lean after the rich spike, and a deterioration determination unit for determining deterioration of the NOx purification catalyst based on a detected value of the first detection unit and that of the second detection unit.

Abstract: Inside of an engine exhaust passage, a hydrocarbon feed valve (15) and an exhaust purification catalyst (13) are arranged. At the time of engine operation, a first NOx purification method which maintains the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst (13) lean while injecting hydrocarbons from the hydrocarbon feed valve (15) at predetermined feed intervals to thereby remove the NOx which is contained in exhaust gas and a second NOx purification method which switches the air-fuel ratio of the exhaust gas flowing to the exhaust purification catalyst (13) from lean to rich by intervals longer than the above predetermined feed intervals to thereby remove the NOx are selectively used in accordance with the sulfur poisoning of the exhaust purification catalyst (13).