Patent ID: 8429902

Claim:
A secondary air supply system for an internal combustion engine, comprising: a secondary air supply pipe that supplies secondary air to an upstream side of an exhaust purifying catalyst installed in an exhaust system of the internal combustion engine; a water temperature sensor that detects water temperature of an engine coolant that flows in the engine; an intake air temperature sensor, that detects temperature of intake air; an electronic control unit, including program logic, configured to perform: estimating an exhaust gas temperature before supply of the secondary air, based on at least one of a temperature of the engine coolant, an engine speed a load of the engine; estimating a temperature of the secondary air, based on at least one of an intake air temperature and the temperature of an engine coolant; estimating an exhaust gas temperature after supply of the secondary air, based on the estimated exhaust gas temperature before supply of the secondary air and the estimated secondary air temperature; and controlling starting or inhibiting supply of the secondary air, depending on the estimation of the exhaust gas temperature after supply of the secondary air.