Patent ID: 8069652

Claim:
A control apparatus for an internal combustion engine having an oxygen storage volume computing means for computing an oxygen storage volume of a three-way catalyst based on an amount of air flowing into said three-way catalyst, an actual air/fuel ratio detected by a front air/fuel ratio sensor installed on an upstream side of said three-way catalyst and a center air/fuel ratio as a reference for increasing or decreasing of the oxygen storage volume of said three-way catalyst, the control apparatus comprising: diagnosis permit determining means for determining whether to issue a permit to execute diagnosis of the three-way catalyst based on a running condition; diagnosis-stages control means for controlling a diagnosis process based on an output of said oxygen storage volume computing means and output of a rear air/fuel ratio sensor installed on a downstream side of said three-way catalyst when the diagnosis permit determining means determines to permit to execute said diagnosis of the three-way catalyst; target air/fuel ratio change-over means for changing over a target air/fuel ratio based on output of said diagnosis-stages control means; oxygen storage capacity computing means for computing said oxygen storage capacity of said three-way catalyst while the actual air/fuel ratio is deviating from the center air/fuel ratio by said target air/fuel ratio change-over means; and catalyst deterioration determining means for determining deterioration of said three-way catalyst based on said oxygen storage capacity.