US Patent 7401592 Hybrid exhaust valve assembly

An exhaust valve assembly includes a flapper valve fixed to a valve shaft where the flapper valve is movable between a closed position, an intermediate position, and an open position. A resilient member biases the flapper valve toward the closed position. An electric actuator actively moves the flapper valve at least from the closed position to the intermediate position. A coupling mechanism couples the valve shaft to an electric actuator shaft and allows the flapper valve to move to the open position in response to exhaust flow sufficient to overcome a biasing force of the resilient member without requiring input from the electric actuator.