Apparatus and method of on-board catalytic converter efficiency monitoring
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United States of America Patent
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Mar 1, 1994
Grant Date -
N/A
app pub date -
Nov 25, 1992
filing date -
Nov 25, 1992
priority date (Note) -
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Abstract
Apparatus and method are disclosed for monitoring catalytic converter efficiency in treating exhaust gas, for example from an internal combustion engine of a motor vehicle. In a dual closed loop fuel control system having switch-type exhaust gas oxygen (EGO) sensors located upstream and downstream of the catalytic converter, the number of times the downstream EGO sensor switches from rich to lean and/or visa versa is compared to the number of times the upstream EGO sensor switches during normal system operation over the course of a test period. A catalytic converter efficiency value is determined by calculating the ratio of the switching frequencies. The impact of the speed and load dependence of the downstream EGO sensor switching frequency can be reduced by a normalizing effect of the frequency ratio calculation. The efficiency value is compared to a stored value predetermined to correspond to a minimum acceptable efficiency of the catalytic converter. A failure signal can be generated when the efficiency value indicates catalytic converter efficiency below the minimum acceptable level.
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