To prevent a system failure from occurring by preventing the inside of a secondary air supply system from being abnormally heated when the valve opening of the poppet valve of a secondary air control valve fails.

The final gear of a power transmission device for driving the poppet valve is composed of a first and a second rotating bodies 11, 12 which are separated from each other. The motor side first rotating body 11 is formed of a resin material lower in melting point than the material (metal material) of the valve side second rotating body 12. When the valve opening of the poppet valve fails due to the failure of an electric motor or the power transmission device, the heat of hot exhaust gases flowing into an air flow passage in a housing to the fitted projection 64 of the fitted tube part 62 of the first rotating body 11 to thermally deform (melting loss) and disconnect the fitted tube part 62 of the motor side first rotating body 11 from the fitted tube part 72 of the valve side second rotating body 12. Consequently, the poppet valve is closed by the spring force of a torsion spring.

COPYRIGHT: (C)2008,JPO&INPIT