Patent ID: 7059120

Claim:
A device for controlling an internal combustion engine having an exhaust passage, the device comprising: an upstream-side catalyst arranged in the exhaust passage, having oxygen storing capability; a downstream-side catalyst arranged in the exhaust passage downstream of the upstream-side catalyst, having oxygen storing capability; an air-fuel ratio sensor arranged in the exhaust passage between the upstream-side catalyst and the downstream-side catalyst for detecting an air-fuel ratio; and stored oxygen amount control means for calculating an amount of stored oxygen of the downstream-side catalyst based on a control state of the engine and an output of the air-fuel ratio sensor, and controlling the amount of stored oxygen of the downstream-side catalyst based on the calculated amount of stored oxygen of the downstream-side catalyst, wherein said stored oxygen amount control means comprises secondary air supplying means for supplying secondary air into the exhaust passage between the upstream-side catalyst and the downstream-side catalyst, and wherein the secondary air is supplied to the downstream-side catalyst when the calculated amount of stored oxygen of the downstream-side catalyst is less than an allowable lower limit.