The field of the invention relates to air/fuel control systems. In one particular aspect of the invention, the field relates to monitoring emissions of an internal combustion engine while controlled under an air/fuel control system.
U.S. Pat. No. 5,259,189 discloses an engine air/fuel control system responsive to a feedback variable derived from an exhaust gas oxygen sensor positioned upstream of a catalytic converter. The catalytic converter is monitored by a hydrogen and/or carbon monoxide sensor positioned downstream of the converter. An indication of converter failure is provided when the sensor output exceeds a specified threshold value.
The inventors herein have recognized numerous problems and disadvantages with the above approach. For example, use of a hydrogen and/or carbon monoxide sensor appears to have the limitation of detecting converter degradation only when rich excursions in the engine air/fuel ratio occur and not when lean excursions occur. The inventors herein recognize that detection of lean excursions requires a nitrogen oxide sensor. Another problem of the above approach appears to be that transient operation under high engine load conditions may result in an erroneous indication of converter failure.
USPTO Backgrounds
USPTO Backgrounds