Abstract: A method is described for controlling an engine with a NOx trap. The method may include adjusting timing of subsequent desulfation based upon a delay between initiating the desulfation process and a temperature increase in the NOx trap.

Abstract: In a method and a device for the diagnosis of the effectiveness of a catalytic converter in the exhaust gas line when using a very late afterinjection or secondary injection, in order to provide a sensitive and yet robust diagnostic method while saving costs for additional exhaust gas temperature sensors and with fuel consumption increased only to a minimum extent, the diagnostic method delivering reliable results with only little delay, and a corresponding device which can also easily be used in various concepts for internal combustion engines, an increased compressor output, caused in the course of the test injection, of an exhaust gas turbocharger used downstream of the catalytic converter produce a higher charge pressure or a marked increase in the air mass flow (mL) such that the effectiveness of the catalytic converter is determined from a change in the intake air quantity of the internal combustion engine.

Abstract: A sensor controller for a particulate matter detection sensor includes a signal output circuit connected to the particulate matter detection sensor such that a sensor detection value is changeable in a predetermined output range by the signal output circuit, a heater configured to heat an attachment portion so as to burn and remove particulate matter attached to the attachment portion, a learning portion for calculating a sensor standard value in a state where the resistance between a pair of opposed electrodes is reduced based on an obtained sensor detection value and for storing the sensor standard value as a learning value, and a correcting portion for correcting the sensor detection value based on the sensor standard value stored by the learning portion.

Abstract: A method and a device for purging an injector in a fuel injector system of use in regeneration of a particle filter. The aging of fuel is determined and compared with a fuel aging threshold value, and a purge request is activated if the threshold value is exceeded. On activating the purge request the satisfaction of the conditions of purge activation are verified and, if satisfied, the purge is activated. The purge is continued while the conditions are satisfied until the quantity of fuel purged reaches a quantity of fuel to be purged.

Abstract: A method for reducing a temperature of an engine component is disclosed. In one example, an air-fuel ratio provided to an engine is adjusted to reduce a temperature of an engine component. The approach may be useful for controlling temperature and emissions from a turbocharged engine.

Abstract: A method is described for diagnosing an exhaust gas sensor which is situated in the exhaust gas area of an internal combustion engine for the purpose of detecting at least one exhaust gas component, which is heated with the aid of a sensor heater and whose temperature is detected. A device for carrying out the method is also described.

Abstract: Systems and methods for controlling regeneration of a diesel particulate filter in a vehicle engine exhaust include detecting a distance of an object from the exhaust and controlling a regeneration event if the distance is less than a threshold value. The system and method may include a particulate filter disposed in the exhaust of the vehicle and a proximity sensor disposed adjacent an exhaust opening and positioned to detect presence of an object near the opening. A controller in communication with the proximity sensor is adapted for controlling regeneration of the particulate filter in response to the proximity sensor detecting the object near the opening.

Abstract: A system comprises a fuel system for delivering fuel to an engine for combustion and a reductant storage system for delivering reductant to the exhaust stream for an SCR catalyst for NOx reduction. The fuel system further comprises a water separator for separating water-based fluid from fuel in the fuel tank, and a separation reservoir to collect the separated water-based fluid. Based on readings of a water-in-fuel sensor positioned within the reservoir, a type of degradation (e.g., water build-up, high-water-content fuel, mis-filling of the reductant, etc.) may be determined and indicated.

Abstract: A method of detecting failure of a substrate in a particulate filter includes comparing an absolute value of a difference between a theoretical temperature difference and an actual temperature difference between an upstream end and a downstream end of the particulate filter to a temperature differential threshold, and comparing an absolute value of a difference between a theoretical pressure difference and an actual pressure difference between the upstream end and the downstream end of the particulate filter to a pressure differential threshold. Failure of the substrate is indicated by one or both of the temperature difference and the pressure difference being greater than the temperature differential threshold and the pressure differential threshold respectively.

Abstract: A method for operating a metering valve and a device for performing the method, providing for diagnosis of the metering valve which defines a flow rate of a reagent to be introduced into an exhaust gas area of an internal combustion engine. The diagnosis is performed on the basis of an analysis of a measure for the flow rate during a diagnosis time. According to a first embodiment, after a diagnosis start signal has occurred with the metering valve closed, the reagent is brought to a predefined diagnosis starting pressure via a pump; the metering valve is then set at a predefined flow rate and the pressure difference occurring during the diagnosis time is analyzed. According to another embodiment, the amount of reagent delivered by the metering valve during the diagnosis time into a graduated beaker is analyzed.

Abstract: Detecting ash in a diesel particulate filter includes receiving data indicative of signal attenuation for ash-responsive and ash-insensitive RF signals transmitted through a diesel particulate filter containing trapped soot and ash. A difference between the RF signals, such as a difference in signal attenuation, may be leveraged to detect a relative ash loading state or a change in relative ash loading state of the diesel particulate filter, and responsively indicate that filter cleaning is needed.

Abstract: A method, a device and a computer program product for the diagnosis of an oxidation catalyst for the oxidation of NO into NO2 in a motor vehicle is provided. An exhaust gas aftertreatment system includes at least the aforementioned oxidation catalyst and a particulate filter and/or an NOx-reducing catalyst arranged downstream of the oxidation catalyst, and a predetermined quantity of a reducing agent is supplied to the exhaust system upstream of the oxidation catalyst, and the NOx content or NO2 content is measured downstream of the oxidation catalyst.

Abstract: An exhaust treatment system is provided. Method of increasing activation of NOx reduction catalyst using two or more reductant is discussed. The exhaust treatment system includes an exhaust source, a reductant source, a nitrogen oxide (NOx) reduction catalyst, a sensor, and a controller. The reductant source includes a first reductant and second reductant, and is disposed to inject a reductant stream into an exhaust stream from the exhaust source. The NOx catalyst is disposed to receive both the exhaust stream and reductant stream. The sensor is disposed to sense a system parameter related to carbon loading of the catalyst and produce a signal corresponding to the system parameter. The controller is disposed to receive the signal and to control dosing of the reductant stream based at least in part on the signal.

Abstract: A system and method for engine control and diagnostics are described. In one example, a catalyst is modeled as a non-linear integrator. The method may improve engine air-fuel diagnostics.

Abstract: A method for heating solid ammonia (NH3) in a main unit (12) to deliver gaseous ammonia into the exhaust gas (EG) downstream of an engine (16) includes the steps of diverting at least a portion of the exhaust gas from the exhaust gas passageway (14), fluidly communicating the exhaust gas on a delivery line (28) from the exhaust gas passageway to the main unit, heating the solid ammonia with the exhaust gas, and fluidly communicating the exhaust gas on a return line (30) from the main unit to the exhaust gas passageway.

Abstract: A method of controlling the regeneration of a particulate filter includes defining a regeneration trigger limit for at least one operating parameter of the vehicle, modifying the regeneration trigger limit based upon a sensed ambient operating condition and a sensed vehicle operating condition to define a modified regeneration trigger limit, and regenerating the particulate filter when the modified regeneration trigger limit for the operating parameter is reached.

Abstract: Provided is an exhaust purification device for an internal combustion engine, wherein the operation of an internal combustion engine can be prevented from being maintained when a particulate filter is melted. An exhaust purification device (1) for an internal combustion engine (2) is comprised of a particulate filter (10); a downstream-side temperature sensor (20a) which detects a downstream-side exhaust temperature (T1); a filter temperature sensor (20b) which detects a filter temperature (T10); an exhaust differential pressure detection device (21) which calculates an exhaust differential pressure (P(n)) between an upstream-side exhaust pressure (p1) and a downstream-side exhaust pressure (p2) at predetermined time intervals; a notification device (40); and an ECU (30) which controls the internal combustion engine (2).

Abstract: A regeneration control system for a vehicle includes a regeneration control module and a regeneration interrupt module. The regeneration control module selectively provides fuel to an oxidation catalyst for a regeneration event of a particulate filter that occurs during a predetermined melting period for frozen dosing agent. The regeneration interrupt module selectively interrupts the regeneration event and disables the provision of fuel to the oxidation catalyst before the regeneration event is complete when a temperature of a dosing agent injector that is located between the oxidation catalyst and the particulate filter is greater than a predetermined temperature.

Abstract: A diesel engine includes: a PM filter provided in its exhaust passage; a fuel injection valve for performing post fuel injection in a cylinder of an engine body in addition to primary fuel injection, in order to supply fuel to the PM filter, to maintain its purification performance; an oil level sensor for detecting a degree of dilution of engine oil; and a first indicator lamp that is turned on to indicate that the engine oil needs to be changed when the degree of dilution of engine oil detected by the oil level sensor is equal to or greater than an allowable level. The vehicle diesel engine overrides the prohibition of the post fuel injection until a distance traveled by the vehicle after the indicator lamp is turned on reaches a predetermined distance.

Abstract: A main feedback control based on an output of an upstream sensor, and a sub-feedback control based on an output of a downstream sensor are executed. A specified fuel disturbance is inputted and an output of the downstream sensor is measured to derive a characteristic value. Based on the characteristic value, it is determined whether a purifying capacity of the exhaust gas purifying system including the catalyst, the upstream sensor, and the downstream sensor is deteriorated.

Abstract: The invention intends to provide a technology which makes it possible to diagnose with higher accuracy whether or not abnormality occurs in a filter regeneration system causing excessive execution frequency of a regeneration process. The filter regeneration system initiates execution of the regeneration process, incase an estimated particulate matter (PM) accumulation amount at the filter reaches a pre-determined regeneration requiring accumulation amount; or in case the pressure upstream of the filter or the differential pressure across the filter reaches a pre-determined regeneration requiring value, the value being larger than the pressure or the differential pressure corresponding to the regeneration requiring accumulation amount. Then, the diagnosis is carried out based on a ratio of an estimated PM accumulation amount at the initiation of the execution of the regeneration process to the regeneration requiring accumulation amount.

Abstract: A method for controlling an urea-SCR system may include a first step for calculating a target urea injection amount, a second step that uses urea injection pressure and urea injection time to calculate a real urea injection amount, a third step that calculates a difference value between the target urea injection amount and the real urea injection amount, and monitors the difference value at a predetermined time interval, a fourth step that accumulates difference values for a determined time when the difference value exceeds a predetermined level, and transfers an alarm signal to a driver when the average value thereof exceeds a predetermined level, and/or a fifth step that starts to accumulate a number of engine starts and driving distance after transferring the alarm signal, and when the number of engine starts is larger than a predetermined value or the driving distance is longer than a predetermined value, if the difference value does not become lower than a predetermined level, executes urea recharging me

Abstract: An object of the invention is to realize a method of determining an abnormality in a particulate filter (5) capable of trapping and oxidizing particulate matter contained in exhaust gas in which even a minor abnormality in which small quantity of particulate matter can pass through the particulate filter (5) can be determined with a high degree of accuracy. To achieve this object, the abnormality determination method according to the invention, the transition of the inflowing exhaust gas temperature in and the outflowing exhaust gas temperature out of the particulate filter (5) during deceleration operating, and the degree of decrease in the outflowing exhaust gas temperature relative to the inflowing exhaust gas temperature is computed based on the transition. If the degree of decrease exceeds a threshold value, it is determined that the particulate filter (5) is abnormal.

Abstract: A target air-fuel ratio of exhaust gas is changed back and forth between rich and lean in short periods, and it is determined that the catalyst is degraded when the air-fuel ratio of exhaust gas is lean by the time a predetermined period of time has passed from the time the target air-fuel ratio started to be changed.

Abstract: The task for the present invention is to reduce more of an oxide that is stored in a NOx storage reduction catalyst, even in a case where a clogging has occurred in a reducing agent adding valve that is provided in an exhaust passage of an internal combustion engine. The present invention is provided with rich spike control performing means that, when an oxide that is stored in the NOx storage reduction catalyst is reduced, performs a rich spike control and that, when lowering the air-fuel ratio in the exhaust gas, performs addition of a reducing agent by the reducing agent adding valve multiple times, which is performed when a crank angle of the internal combustion engine is in a specified range. When the clogging has occurred in the reducing agent adding valve, the number of times the air-fuel ratio in the exhaust gas is lowered while the rich spike control is being performed by the rich spike control performing means is increased.

Abstract: A control apparatus for an internal combustion engine has an oxygen storage volume computing unit for computing an oxygen storage volume of a catalyst by using a real air/fuel ratio detected by an air/fuel ratio sensor installed on the upstream side of a catalyst, a center air/fuel ratio representing a stoichiometric air/fuel ratio and an estimated air flow volume or detecting a flow rate of air flowing into the catalyst. A center air/fuel ratio correcting unit for correcting a center air/fuel ratio based on output of a rear air/fuel ratio sensor provided on the downstream side of the catalyst, and an oxygen storage volume computed by an oxygen storage volume computing unit, and the oxygen storage volume computing unit computes an oxygen storage volume by using a center air/fuel ratio corrected by the center air/fuel ratio correcting unit.

Abstract: An oxygen sensor for a motor vehicle having an electrode within an outer shell measures oxygen in exhaust gas exiting the vehicle and generates a signal based on the oxygen measurement. A communication device, powered by a battery or capacitor, wirelessly transmits the measured amount of oxygen from the electrode to a powertrain control module. The flow of exhaust gas through the exhaust system spins blades to spin a generator in a rotational power generation device to generate electrical current to be stored and used by the battery or capacitor. The rotational power generation device may be located in the exhaust pipe, such as through an exhaust pipe wall, and either be connected to the oxygen sensor shell or separate and connected only with electrical wires between the generator and the battery or capacitor.

Abstract: When a concentration measured by a sensor is lower than a predetermined threshold, it is judged that a liquid is any different type of aqueous solution, and also, it is judged whether or not the different type discrimination is adequate. When the discrimination is adequate, the number of different type discriminating times is counted up based on a predetermined counted value, and when the number thereof is equal to or larger than a determination threshold, the different type discrimination is determined. At this time, at least one of the predetermined counted value and the determination threshold is dynamically set based on a liquid level of a reducing agent tank, so that the counting and/or the different type discriminating determination is performed considering convection which is changed according to a level change to thereby discriminate with high precision whether or not the liquid is the different type of aqueous solution.

Abstract: In a method for determining the conversion performance of an oxygen storage-capable catalytic converter of an internal combustion engine, it is proposed that the catalytic converter be supplied with a stoichiometric exhaust gas composition, a known emission change is briefly undertaken and at the same time the signals of a lambda probe located downstream from the catalytic converter are detected so that based on the emission change and signals of the lambda probe a differentiated conclusion about the conversion performance of the catalytic converter for the pollutants hydrocarbon HC and nitrogen oxides NOx is delivered. According to the invention a simple and cost-effective method for differentiation of the pollutants hydrocarbon HC and nitrogen oxides NOx and thus for carrying out an improved diagnosis method is made available.

Abstract: A vehicle includes an internal combustion engine 1 and a rotating electric machine 5 as drive power sources and drives a wheel using a driving force of the internal combustion engine 1 and/or the rotating electric machine 5. A diagnostic control unit 700 diagnoses the vehicle while controlling the same. The diagnostic control unit 700 shifts an operating point of the internal combustion engine 1 to a plurality of diagnostic operating points to diagnose a catalyst or an oxygen sensor. Meantime, the diagnostic control unit 700 compensates for an excess or a deficiency in the driving force of the internal combustion engine 1 accompanied by the shift of the operating point by letting the rotating electric machine 5 perform a power running or regeneration operation.

Abstract: An object of the present invention is to prevent, in connection with an exhaust gas purification apparatus regeneration system of an internal combustion engine, the possible travel distance of a vehicle after warning by a warning apparatus for warning excessive smallness of the fuel quantity is started from being unduly shortened even if regeneration control is executed while the warning is given by a warning apparatus. The system according to the invention has a warning apparatus that gives warning when the remaining fuel quantity is equal to or smaller than a first specified fuel quantity. When it is predicted that the regeneration control in which fuel is supplied to the exhaust gas purification apparatus will be executed when the remaining fuel quantity is equal to or smaller than the first specified remaining quantity, warning by the warning apparatus is started before the remaining fuel quantity becomes equal to the first specified remaining quantity (S104, S105).

Abstract: Methods for updating the PF soot load of an engine are provided herein. In one example, a soot storage estimate is based on processing operations that occur at different timings. The method can improve soot estimation during some conditions.

Abstract: The present invention has an object to provide an exhaust gas purifying apparatus for an internal combustion engine capable of obtaining accurate temperature information relating to a catalyst placed in an exhaust passage of the internal combustion engine. The degree of influence emthc of a catalyst inlet gas temperature and catalyst rear end temperature ethuf[end] is calculated (Step 102). An estimated value ethco of an outlet gas temperature is calculated by weighted averaging the inlet gas temperature and the catalyst rear end temperature ethuf[end] considering the degree of influence emthc (Step 104). A temperature correction coefficient ekthuf[x] for each region of the catalyst is calculated as a function f(emthc) of the degree of influence emthc (Step 108).

Abstract: Methods and systems for reducing overstress of a DPF are provided herein. One example of such a method is based on a radial temperature gradient near the exit face of the diesel particulate filter. In this way, it becomes possible to more closely correlate radial stresses to actual risk of DPF fracture.

Abstract: A method includes raising a temperature of an SCR catalyst for a predetermined time period while dosing urea. The method further includes maintaining the temperature of the SCR catalyst without dosing urea for a second predetermined time period. The method further includes filtering out at least low frequency data from a first NOx sensor upstream of the SCR catalyst and from a second NOx sensor downstream of the SCR catalyst, and comparing the filtered data from the first NOx sensor and the second NOx sensor without dosing urea over a third predetermined time period. The method further includes providing a NOx sensor condition index for at least one of the first NOx sensor and the second NOx sensor in response to the comparing.

Abstract: A quantity of unburned fuel is provided through a combustion chamber of an engine and an exhaust conduit to a catalytic converter. The catalyst in the converter is determined to be non-operational if a post-catalyst temperature sensor does not indicate a sufficient temperature increase between readings before and after provision of the unburned fuel to the combustion chamber. The unburned fuel may be provided by withholding spark ignition to create a misfire in the combustion chamber or, particularly in a direct injection engine, by injecting the fuel during the exhaust stroke.

Abstract: A regeneration control system for a vehicle comprises a regeneration control module and a disabling module. The regeneration control module selectively initiates a regeneration of a particulate matter filter of the vehicle. The disabling module selectively disables the regeneration control module based on a location of the vehicle provided by a global positioning system (GPS).

Abstract: An exhaust purification device has a NOx catalyst that occludes NOx contained in exhaust gas at a lean air fuel ratio and that purifies (reduces) and discharges the occluded NOx at a rich air fuel ratio. The device performs full purge for discharging substantially an entirety of the occluded NOx at once based on establishment of an execution condition of the full purge to recover exhaust purification performance of the NOx catalyst. The device has a program for performing partial purge for discharging only part of the occluded NOx before the execution of the full purge. The device consecutively and repeatedly performs the partial purge except for the period in which the full purge is performed.

Abstract: A throttle operation is performed after an internal combustion engine is started. Then, temperature of a catalyst is obtained based on a signal output from a temperature sensor fitted to the catalyst. It is then determined whether the temperature obtained is equal to or higher than the activation temperature. If it is determined that the temperature of the catalyst has not reached the activation temperature, the throttle operation continues. On the other hand, if it is determined that the temperature of the catalyst is equal to or higher than the activation temperature, the non-throttle operation is performed instead of the throttle operation.

Abstract: A temperature-sensitive type urea sensor 74 is adopted for use in an engine exhaust gas purifying apparatus. The magnitude of convection of urea aqueous solution generated in a storage tank 41 is determined based on temperature information detected by the urea sensor 74. For detection of abnormality, a detected concentration Dn is adopted when the percentage GRDt of temperature change of urea aqueous solution is small, so that convection is small and it is determined not to affect accurate detection of an abnormality.

Abstract: In a control device for an internal combustion engine provided with a NOX catalytic converter in an exhaust passage thereof, the progress of sulfur purging is computed from the consumption of reducing agent contained in the exhaust gas in the NOX catalytic converter. This computation may be based on the air fuel ratio of exhaust gas upstream of the NOX catalytic converter and the estimated consumption of the reducing agent contained in the exhaust gas or on the difference between the air fuel ratios of exhaust gas upstream and downstream of the NOX catalytic converter. In either case, the accuracy can be improved by taking into account the space velocity of the exhaust gas.

Abstract: In order to suppress deposition of constituent of a reducing agent (dissolved matter) in an exhaust passage of an engine enhancing an elimination rate of NOx even when temperature of an exhaust emission from the engine is low, an exhaust emission purifying apparatus is provided with an electro-generative-heat carrier provided on an upstream side of an injection nozzle that supplies the reducing agent into the exhaust emission on upstream side of a reduction catalyst in an exhaust pipe, the exhaust emission being heated to a temperature equal to or higher than a melting point of the dissolved matter whereby deposition of the dissolved matter on an inner wall surface of the exhaust pipe is suppressed to effectively use the supplied reducing agent for catalytic reduction reaction, even when the exhaust emission temperature is lower than the melting point of the dissolved matter of the reducing agent.

Abstract: A sensor for an exhaust gas purifying apparatus includes an examining filter and a holding member. The examining filter is provided in a secondary exhaust line diverging from a primary exhaust line of an internal combustion engine. The holding member holds the examining filter on the secondary exhaust line. The holding member holds an approximately 10% to approximately 50% part by area of a peripheral portion of the examining filter so as to cover the part from a peripheral side of the examining filter.

Abstract: The individual cylinders of the internal combustion engine are divided into at least two cylinder banks wherein each is assigned a separate exhaust-gas channel. Secondary air is conveyed by a compressor. The flow of the secondary-air mass flow is set independently by an electrically controllable throughflow control. A value for the entire secondary-air mass flow is determined from the signal of a secondary-air mass sensor. The throughflow control is controlled into an open position, the value for the entire secondary-air mass flow is detected and subsequently the throughflow control is controlled into a closed position, the values for the secondary-air mass flows are detected before and after closure, and these values are compared with a plurality of different threshold values and, as a function of the result of the comparisons, a determination is made of the fault location with regard to the respective cylinder bank.

Abstract: The present invention provides a catalyst deterioration detection device that can avoid erroneous detection of catalyst deterioration by averting the influence of gas status changes at a catalyst outlet on the oxygen storage amount. Step 106 is performed to set a lean side target air-fuel ratio at afL1 and a rich side target air-fuel ratio at afR1 and calculate a maximum oxygen storage amount Cmax1. Next, step 108 is performed to set the lean side target air-fuel ratio at afL2 and the rich side target air-fuel ratio at afR2 and calculate a maximum oxygen storage amount Cmax2. Subsequently, step 110 is performed to set the lean side target air-fuel ratio at afL3 and the rich side target air-fuel ratio at afR3 and calculate a maximum oxygen storage amount Cmax3. If all the calculated maximum oxygen storage amounts Cmax1, Cmax2, Cmax3 are equal to or smaller than a reference value Cmaxth, step 116 is performed to detect catalyst deterioration.

Abstract: An engine exhaust passage has an SOx trapping catalyst (11), a particulate filter (13) holding an NOx storing/reducing catalyst, and an NOx storing/reducing catalyst (15) forming a post-treatment system and a fuel feed valve (17) for feeding fuel for post processing in the post-treatment system arranged inside it. When any catalyst has a degree of degradation exceeding a predetermined degree of degradation, the method of feeding the post-treatment fuel is reset so that the post-treatment fuel required for purification of the exhaust gas can be fed into the catalyst with the lowest degree of degradation to make the catalyst with the lowest degree of degradation handle the purification action of the exhaust gas.

Abstract: A method for regenerating an exhaust aftertreatment system, in particular a particulate filter of an internal combustion engine, situated in a vehicle, having regeneration cycles controlled by a control device. An optimized regeneration of the exhaust aftertreatment system is achieved by supplying information relating to the travel route to the control device and controlling the regeneration cycles, taking the information into consideration.

Abstract: A method of operating an engine having a diesel particulate filter in a vehicle is disclosed. In one example, the filter is regenerated in response to a temperature differential across each of a plurality of filter channels. The method can improve the timing of filter regeneration.

Abstract: In an apparatus for diagnosing an exhaust gas purifying device, a catalyst deterioration level detector 104 detects the deterioration level of a catalyst from a relationship between a catalyst-upstream air-fuel-ratio detector 101 and a catalyst-downstream air-fuel-ratio detector 102. A catalyst-deterioration-level correction section 111 corrects the catalyst deterioration level detected by the catalyst deterioration level detector 104 based on a falling response ratio representing the ratio between a falling response index of the catalyst-upstream air-fuel-ratio detector 101 and a falling response index of the catalyst-downstream air-fuel-ratio detector 102 or based on a rising response ratio representing the ratio between a rising response index of the catalyst-upstream air-fuel-ratio detector 101 and a rising response index of the catalyst-downstream air-fuel-ratio detector 102.

Abstract: In an exhaust emission purifying apparatus for reductively purifying NOx in the exhaust emission by using a liquid reducing agent or its precursor, to be referred to as “liquid reducing agent” herein, a dosing flow rate of the liquid reducing agent according to engine operating conditions is computed, and the dosing of the liquid reducing agent is controlled based on the computed dosing flow rate, and also, it is judged whether or not a supply system of the liquid reducing agent is failed, based on a ratio between an integrated amount obtained by sequentially integrating the dosing flow rate and a consumed amount of the liquid reducing agent.