Patent ID: 8205437

Claim:
An exhaust system for an internal combustion engine, the system comprising: (a) a monolith substrate coated with a catalyst, the monolith substrate comprising a plurality of substantially parallel channels, each channel having a length extending from an upstream end to a downstream end; and (b) a first sensor disposed in a hole defined by an external wall of the monolith substrate, and (c) a reference sensor as a second sensor; wherein the monolith substrate comprises a portion of the plurality of channels wherein the catalyst composition in at least a part of the length of channels extending from the upstream end has an increased activity for a reaction for which the catalyst composition is intended relative to the catalyst composition in a remainder of the monolith substrate, the arrangement being such that the sensor is contacted with exhaust gas that has first contacted the catalyst composition having the increased activity; and wherein the reference sensor is disposed in a hole defined in part by an external wall of the monolith substrate and wherein the hole is located at a similar length of the plurality of channels as the first sensor, the arrangement being such that the reference sensor is contacted with exhaust gas that has not first contacted the catalyst composition having an increased activity.