US Patent 7331422 Vortex muffler

A muffler includes an inner passage residing in an outer shell, and a stationary fan residing in the inner passage. The fan creates a vortex in a flow through the inner passage thus improving the flow and reducing the exhaust sound level. The inner passage includes an inner passage shell and the fan comprises vanes extending inward from the inner passage shell and turned at approximately a 45 degree angle to a centerline of the inner passage. Pinch zones at the entrance and exit from the inner passage further reduce the exhaust sound level. The inner passage shell is preferably a perforated inner passage shell, and a sound deadening material resides between perforated inner passage shell and the outer shell.