An improved NO.sub.x sensor with an NH.sub.3 oxidation catalyst. A sensor module may include a support component, a NO.sub.x sensing material positioned on the support component, and an NH.sub.3 oxidation catalyst. The NH.sub.3 oxidation catalyst may be layered on top of the NO.sub.x sensing material or the NH.sub.3 oxidation catalyst may be positioned upstream of the NO.sub.x sensing material such that the NH.sub.3 oxidation catalyst selectively converts NH.sub.3 to N.sub.2 while permitting NO.sub.x through to the NO.sub.x sensing material.

When the air fuel ratio dither control is carried out, an air fuel ratio of a mixture in each of one or more lean cylinders and one or more rich cylinders is controlled in a feedback manner based on an average value of a detected value of an air fuel ratio sensor, so that an average value of an air fuel ratio of exhaust gas flowing into the three-way catalyst becomes a predetermined target exhaust gas air fuel ratio. At this time, the air fuel ratio dither control is carried out, by setting at least a cylinder with the highest gas impingement intensity in a cylinder group of an internal combustion engine as the one or more lean cylinders.

An exhaust system includes a diesel oxidation catalyst (DOC) device mounted to an exhaust pipe for exhausting an exhaust gas of an engine and purifying hydrocarbon (HC) and carbon monoxide (CO) among the exhaust gas, an urea injector positioned at a rear of the diesel oxidation catalyst device for injecting an urea aqueous solution to an inside of the exhaust pipe, a mixer positioned at the rear of the urea injector, a diesel particulate matter filter (DPF) positioned at the rear of the mixer and coated with a catalyst devoid of a noble metal or a hydrolysis catalyst that does not oxidize ammonia and hydrolyzes the injected urea to reduce a particulate material of the exhaust gas, and a selective catalytic reduction (SCR) device positioned at the rear of the diesel particulate matter filter.

Methods and systems are provided for a soot sensor. In one example, a method diverting exhaust gas from a main exhaust passage to a second exhaust passage comprising a soot sensor with a rotatable component configurable to capture soot.

An internal combustion engine has an exhaust gas aftertreatment system comprising in the given order in the flow direction of the exhaust gas: a device for metering ammonia and/or a compound that can be decomposed to form ammonia into the exhaust gas to be cleaned, as a reducing agent; one or more SCR catalysts, which form a first SCR unit; one or more SCR and/or ammonia oxidation and/or ammonia slip catalysts, which form a second SCR unit; and a NO.sub.x sensor in the exhaust gas tail pipe. An amount, to be metered into the exhaust gas, of ammonia and/or of the decomposable compound is set using the nitrogen oxide concentration in the exhaust gas tail pipe that is determined by the NO.sub.x sensor, and the occurrence or non-occurrence of an ammonia excess in the region of the NO.sub.x sensor can be determined from the sensor signal of the NO.sub.x sensor by evaluating said sensor signal.

A method is disclosed for cleaning a component of an exhaust aftertreatment system located downstream of a combustion engine in an exhaust flow path delimited by an outer wall. The exhaust aftertreatment system includes a first device releasably mounted in the outer wall upstream of the component and a second device releasably mounted in the outer wall downstream of the component, each of the devices being a sensor or an injector. The method includes sealing the exhaust flow path upstream of the first device and downstream of the second device, removing at least the first and second devices, thereby providing at least two openings in the outer wall, so that a cleaning flow path is provided, and introducing cleaning fluid into at least one of the openings, so that the cleaning fluid flows across the component via the cleaning flow path.

A signal processing apparatus for a gas sensor is applied to a gas sensor that is disposed on an exhaust passage of an engine to detect a concentration of a specific component in exhaust gas flowing through the exhaust passage. The signal processing apparatus includes a filtering means that attenuates exhaust pulsation noise included in a detection signal of the gas sensor, and a filter characteristic setting means that variably sets filter characteristics of the filtering means based on engine speed.

A particulate matter sensor unit is configured to sense particulate matter included in exhaust gas of a vehicle. The particulate matter sensor unit includes: a sensing unit sensing the particulate matter in the exhaust gas; a holding unit including a plurality of holders covering an exterior of the sensing unit, a front outer surface of each holder being formed by a tapered inclination outer surface; a shell having a hollow portion therein so that the holding unit is inserted and fitted into the shell, an inclination inner surface being formed in the hollow portion to correspond to the inclination outer surface; a cap unit installed in front of the shell to cover a sensing body of the sensing unit and guiding a flow of the exhaust gas to go through the sensing body; and a cover fixed to a rear end of the shell to support the holding unit.

An exhaust sensor module assembly has a sensor module and a shield. The shield is shaped to receive the module. The shield has a first mounting leg and a first flange extending from a first end of a base plate, and a second mounting leg and a second flange extending from a second end of the base plate. The shield is rotationally symmetric about an axis extending through and normal to the base plate.

An exhaust gas purification device having such a structure that exhaust gas can uniformly flow into without depending on a shape of an exhaust gas inlet pipe. A gas purification body which purifies the exhaust gas, a purification casing which accommodates the gas purification body, an exhaust gas inlet pipe which communicates with an exhaust gas inflow port of the purification casing, and an exhaust gas outlet pipe which communicates with an exhaust gas outflow port of the purification casing. The exhaust gas inlet pipe is attached to the purification casing in such a manner as to cover the exhaust gas inflow port and extend in a longitudinal direction of the purification casing. An introduction passage of the exhaust gas is formed by an outside surface of the purification casing and an inside surface of a pipe wall of the exhaust gas inlet pipe. A portion extending along the purification casing in the pipe wall is inclined so as to come close to the outside surface of the purification casing in proportion to heading for an exhaust gas outlet side from an exhaust gas inlet side.