Snap-action valve for exhaust system

1. A muffler for an internal combustion engine exhaust system, the muffler comprising:

a housing having an outer shell and input and output headers enclosing opposite ends of the shell;

a partition inside the housing dividing a housing interior into first and second chambers, each having sound absorbing material positioned therein, the partition having at least one aperture therethrough providing for fluid communication between the first and second chambers;

a through pipe extending through the input and output headers and the partition and having a first plurality of perforations enabling fluid communication between the through pipe and the first chamber, and a second plurality of perforations enabling fluid communication between the through pipe and the second chamber; and

a valve assembly having a valve flap positioned inside the through pipe between the first and second pluralities of through pipe perforations for rotation about an axle pivotally coupled to the pipe between a fully closed position wherein a first peripheral portion of the valve flap is in contact with an inner surface of the through pipe and a fully open position wherein a plane of the valve flap is substantially parallel to a longitudinal axis of the through pipe and a second peripheral portion of the valve flap is in contact with an inner surface of the through pipe.

2. The muffler of claim 1 wherein the valve flap in the fully closed position intersects the longitudinal axis of the through pipe at an acute angle.

3. The muffler of claim 1 further comprising:

a bias element forcing the valve flap toward the fully closed position, the bias element mounted exteriorly of the through pipe between the through pipe and the axle.

4. The muffler of claim 3 wherein exhaust pressure in the through pipe forces the valve flap to the fully open position whenever the exhaust pressure is high enough to overcome bias element force.