Onboard detection of oxygen sensor switch rate for determining air/fuel ratio control system failure

DETAILED DESCRIPTION OF THE INVENTION Referring to the figure, a block diagram of an is exhaust gas oxygen sensor failure detection method starts by sampling an exhaust gas oxygen sensor output signal level at a block 12.
Logic flow from block 12 goes to a decision block 14 wherein it is asked if the exhaust gas oxygen output level has changed.
If the level has changed, logic flow goes to a block 16 wherein a simple average of the transport delay time between EGO sensor switches is determined.
Advantageously, the transport delay time for various engine operating speed/load conditions is stored in a table in an engine control system associated with control of the engine.
These transport delay times are then selected in accordance with the speed and load operating conditions of the engine and used as inputs for calculating the new rolling average.
Transport delay is the time between the injection of an air/fuel ratio charge into a cylinder and the time that the effect of that air/fuel ratio charge reaches the exhaust gas oxygen sensor downstream of the combustion cylinder.
Logic flow from block 16 goes to a block 18 wherein there is calculated a new value of the rolling average of the transport delay time.
Logic flow from block 18 goes to a block 20 wherein there is calculated the current exhaust gas oxygen switching time.
Logic flow from block 20 goes to a block 21 wherein there is calculated the rolling average of the exhaust gas oxygen sensor switching time.
Logic flow then goes to a decision block 22 wherein the exhaust gas oxygen sensor rolling average switching time is compared to the transport delay rolling average.
If the exhaust gas oxygen rolling average is large compared to the transport delay rolling average, indicating slow sensor switching, logic flow goes to a block 24 wherein a lazy exhaust gas oxygen sensor switching rate error is indicated.
Logic flow then goes to a block 26 wherein the lazy exhaust gas oxygen sensor code is stored for future indication.
Logic flow from block 26 goes to a block 28 indicating continuation of logic flow