Patent ID: 7284369

Claim:
A secondary air supply system of an internal combustion engine comprising: an exhaust gas purifying apparatus provided in an exhaust passage of the internal combustion engine; a secondary air supplying apparatus for supplying secondary air via a secondary air passage to an upstream side of the exhaust gas purifying apparatus; an opening/closing valve provided in the secondary air passage, for opening and closing the secondary air passage; a pressure sensor provided between the secondary air supply apparatus and the opening/closing valve in the secondary air passage, for detecting pressure within the secondary air passage; flow rate calculating means for calculating a secondary airflow rate based upon both secondary air supply pressure, which is detected by the pressure sensor under a predetermined secondary air supply condition that the secondary air supply apparatus is operated and the opening/closing valve is opened, and reference pressure which is detected by the pressure sensor under different condition from the predetermined secondary air supply condition; and learning means for storing the reference pressure detected under the different condition from the secondary air supply condition into a backup-purpose memory as a reference pressure learn value; wherein the flow rate calculating means calculates the secondary airflow rate by employing the reference pressure learn value stored in the backup-purpose memory, wherein when the learning means stores the reference pressure into the backup-purpose memory as the reference pressure learn value, the learning means converts the reference pressure into pressure under such a condition that both a power supply voltage of the secondary air supply apparatus and atmospheric pressure are set to predetermined defined values so as to calculate the reference pressure learn value; and wherein the flow rate calculating means corrects the reference pressure learn value based upon both a power supply voltage and atmospheric pressure acquired time to time, calculates the secondary airflow rate, or converts the secondary air supply pressure into pressure under such a condition that both the power supply voltage of the secondary air supply apparatus and atmospheric pressure are set to the predetermined defined values, and calculates the secondary airflow rate.