Various embodiments of the teachings herein include methods for determining the sulfur content in an exhaust tract of a motor vehicle. The method may include: determining a change in the nitrogen oxide abatement efficiency of a coated particulate filter arranged in the exhaust tract and/or a determined ammonia storage capacity change of a coated particulate filter arranged in the exhaust tract; comparing the determined change to a threshold value; identifying an excessive sulfur content if the comparison shows that the determined change exceeds the threshold value; and undertaking one or more corrective actions in response to identifying an excessive sulfur content.

Various embodiments include a method for regenerating a coated particulate filter arranged in an exhaust-gas duct of a motor vehicle. The method may include: detecting a need for particulate filter regeneration; determining a first diagnosis value before initiating particulate filter regeneration; after determining the first diagnosis value, carrying out particulate filter regeneration; determining a second diagnosis value after particulate filter regeneration; determining a difference between the first determined diagnosis value and the second determined diagnosis value; comparing the determined difference with a threshold value; and identifying a particulate filter defect if the determined difference exceeds the threshold value.

In a method and device for controlling and/or monitoring the function of a secondary air supply in an emission control system of an internal combustion engine, the emission control system includes at least two catalytic converters situated in succession in an exhaust duct, it being possible for the second catalytic converter to be implemented as a combination of catalytic converter and particulate filter. For a secondary air diagnosis and for secondary air control, a two-point lambda probe is situated, with respect to a direction of flow of exhaust gas, downstream of the first catalytic converter. Measures are applied for compensating tolerance and aging effects of the two-point lambda probe. This results in particular in cost advantages in emission control systems for fulfilling stricter emission requirements. In particular, this makes it possible to operate the particulate filter in optimized fashion.

A method and control device for correcting an output signal of an exhaust gas sensor in an exhaust gas conduit of an internal combustion engine, a secondary air delivery system for delivering air into the exhaust gas conduit being associated with the exhaust gas conduit upstream from the exhaust gas sensor in the flow direction of the exhaust gas. During a measurement of the output signal of the exhaust gas sensor, air is delivered to the exhaust gas conduit via the secondary air delivery system during a correction phase by way of which a correction of the output signal of the exhaust gas sensor is derived. In this operating mode, a defined oxygen content exists in the gas mixture surrounding said sensor, so that the output signal can be compared with reference values.

In a method and a device for monitoring the operability of an emission control system of an internal combustion engine, at least two catalytic converters are situated in succession in an exhaust duct. For tracking control, breakthrough detection for diagnosing the first catalytic converter, and for a second balancing for the storage capacity of oxygen or rich gas of the second catalytic converter, a two-point lambda probe be used and, for the latter, tolerance and aging effects are compensated. This results in particular in cost advantages in emission control systems for fulfilling stricter emission and diagnostic requirements.

A catalyst for purification of exhaust gas including a substrate, and a catalyst coat layer which is formed on a surface of the substrate and contains catalyst particles, wherein the catalyst coat layer has an average thickness ranging 25 to 150 μm, a void fraction, as determined by scanning electron microscope observation of a cross-section of the catalyst coat layer, ranging 1.5 to 8.0% by volume, 60 to 90% by volume of all voids in the catalyst coat layer are high-aspect ratio pores which have equivalent circle diameters ranging 2 to 50 μm in a cross-sectional image of a cross-section of the catalyst coat layer perpendicular to a flow direction of exhaust gas in the substrate, and which ratios of 5 or higher, the high-aspect ratio pores have an average aspect ratio ranging 10 to 50, and a noble metal is supported on the entire catalyst coat layer.

An electronic control unit (ECU) of an internal combustion engine, which includes an air-fuel ratio sensor arranged at a downstream side of an exhaust purification catalyst, is configured to judge if a state of the air-fuel ratio sensor is normal or abnormal based on the first characteristic of change of air-fuel ratio and, if a judgment cannot be made based on the first characteristic, the ECU is configured to judge if the state of the air-fuel ratio sensor is normal or abnormal based on a second characteristic of change of air-fuel ratio. As a result, it is possible to suppress the effects of the change of state of the exhaust purification catalyst while accurately diagnosing the abnormality of deterioration of response of a downstream side air-fuel ratio sensor.

A selective catalytic reduction system control system (10) and method of its use include an ammonia (“NH.sub.3”) slip sensor (13) located within an interior space (27) of an exhaust stack (15) of a selective catalytic reactor (31), toward an inlet end (25) of the stack (15); a housing (17) located within the interior space of the exhaust stack; the housing including face panels 19; a nitrogen oxides (“NOx”) sensor (11) contained within an interior space (29) defined by the face panels of the housing, at least two of the face panels (19.sub.I, 19.sub.O) containing an oxidation catalyst; and a dosing controller (59) in communication with the NH.sub.3 and NOx sensors, the dosing controller including a microprocessor with dosing logic embedded thereon. The housing with oxidation catalyst acts as a linear box, isolating the NOx sensor from NH.sub.3 slip, linearizing the NOx sensor signal.

A selective catalytic reduction (SCR) catalyst is disposed in an exhaust gas system of an internal combustion engine. A reductant injector is coupled to the exhaust gas stream at a position upstream of the SCR catalyst, and first and second NO.sub.x sensors provide NOx measurements upstream of and downstream of the SCR catalyst, respectively. A system and method is disclosed for operating the system to determine a NOx amount and/or a NH3 slip amount downstream of the SCR catalyst by decoupling NOx-NH3 measurements from the output of the second NOx sensor to provide control of the reductant injection amount.

Systems and methods for controlling a gasoline urea selective catalytic reductant catalyst are described. In one example, an observer is provided that corrects an estimate of an amount of NH.sub.3 that is stored in a SCR. The amount of NH.sub.3 that is stored in the SCR is a basis for generating additional NH.sub.3 or ceasing generation of NH.sub.3.