Patent ID: 7793495

Claim:
An exhaust system for a motor vehicle engine comprising: an exhaust pipe; a vent flap forming a portion of the exhaust pipe when closed, the vent flap being pivotally attached along one edge to the exhaust pipe to open inwardly into the exhaust pipe to constrict and accelerate exhaust gas flow to draw outside air into the exhaust pipe through an opening the exhaust pipe left by movement of the vent flap; the position of the vent flap being responsive to exhaust gas temperature to open in response to the exhaust gas temperature reaching a preselected critical temperature; the vent flap including a permanent magnet; an anchor magnet positioned to repel the permanent magnet of the vent flap to urge the vent flap into a closed position; and a layer of material of high magnetic susceptibility between the anchor magnet and the permanent magnet of the vent flap with a curie point selected to match the preselected critical temperature.