Method and system for monitoring a catalytic converter

Details Method and system for monitoring a catalytic converter Method and system for monitoring a catalytic converter

1999-06-21

2001-03-06

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

Methods

C060S277000, C060S285000, C701S102000

Reexamination Certificate

active

06195986

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method and system for determining the efficiency of a catalytic converter based on signals generated by pre-catalyst and post-catalyst exhaust gas oxygen sensors.
BACKGROUND ART
Increasingly stringent federal regulations limit the permissible levels for emissions. As such, vehicle manufacturers have developed various methods to reduce emissions while improving vehicle performance and fuel economy. Catalytic converters, positioned in the engine exhaust path, are often used to reduce emission levels of regulated exhaust gases. The conversion efficiency of a catalytic converter may be monitored using a pre-catalyst O
2
sensor positioned upstream from the catalytic converter and a post-catalyst O
2
sensor positioned downstream from the catalytic converter.
One method known for indicating conversion efficiency of the catalyst is to calculate a ratio of downstream sensor transitions or switches to upstream sensor transitions or switches. An increasing switch ratio is generally indicative of a degrading catalyst. When the switch ratio exceeds a threshold value, a malfunction indicator light (MIL) is illuminated so the vehicle operator will seek service. This method of catalyst monitoring is disclosed in Orzel 5,357,751, assigned to the assignee of the present invention, and is referred to as the Switch Ratio (SR) method. Another method for indicating conversion efficiency of the catalyst is based on the ratio of the arc lengths of the downstream sensor signal to the arc lengths of the upstream sensor signals identified as an Index Ratio (IR) method in contrast to the SR method. This method is disclosed in U.S. patent application Ser. No. 08/785,406, filed Jan. 22, 1997, assigned to the assignee of the present invention, and incorporated herein by reference.
The test cycle for catalyst monitoring requires collection of data from each of the sensors while the engine is operating in each of a plurality of inducted airflow ranges or air mass (AM) cells. In each method a predetermined number of transitions or switches of the upstream sensor in each AM cell is required to complete the test cycle. These methods rely on AM cell calibration and assume that sensor signal transitions occurring in a defined AM cell are valid for ratio computation regardless of engine speed and load conditions. The determination of SR and IR based on data taken while the driver is operating the vehicle at a high load, low rpm or low load, high rpm condition results in increased SR and IR variability even though operation is within one of the plurality of inducted airflow ranges. The determination of catalyst conversion efficiency based solely on AM conditions may result in error, and may reduce the ability to discriminate between a good and a failed catalyst.
DISCLOSURE OF THE INVENTION
It is a general object of the present invention to reduce the variability between catalyst monitor tests that use the switch ratio or index ratio metric.
In carrying out the above object and other objects, features and advantages of the present invention, a method for monitoring emissions of an internal combustion engine is provided that further refines the engine operating conditions under which data is collected from the front and rear sensors. More specifically, data collected only at predefined inducted air mass and engine speed and load conditions is used in determining catalyst deterioration in order to avoid areas of engine speed and load instability that might impair test to test repeatability of the monitor output.
The above object and other objects, features, and advantages of the present invention will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.


REFERENCES:
patent: 5301501 (1994-04-01), Shimizu et al.
patent: 5357751 (1994-10-01), Orzel
patent: 5653102 (1998-03-01), Ozel et al.
patent: 5724809 (1998-03-01), Mitsutani
patent: 5875628 (1998-03-01), Mitsutani
patent: 5887421 (1999-03-01), Mitsutani

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