| 摘要 |
<p>PURPOSE: To provide an apparatus and method for monitoring catalytic converter efficiency in treating exhaust gas from an internal combustion engine of a motor vehicle. CONSTITUTION: In a dual closed loop fuel control system having exhaust gas oxygen sensors 128 and 130 located upstream and down stream of a catalytic converter 124, the number of times that the downstream sensor switches from rich to lean and/or visa versa is compared to the number of times that the upstream sensor switches during normal system operation over a test period. An efficiency value of the catalytic converter 124 is determined by calculating a ratio of switching frequencies. Impact of 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 124. A failure signal can be generated when the efficiency value indicates catalytic converter efficiency below the minimum acceptable level.</p> |
