Mixer and valve assembly

A vehicle exhaust system comprising:

• a first exhaust component configured to receive engine exhaust gases;
• a second exhaust component downstream of the first exhaust component;
• a mixer positioned between the first and second exhaust components, the mixer including
• an outer housing that defines an internal cavity to receive the engine exhaust gases from the first component, the outer housing including at least one injection opening,
• an upstream baffle positioned at an inlet end of the mixer housing, the upstream baffle comprising a plate having an open area that comprises a fixed geometric configuration through which exhaust gas enters the internal cavity, and
• a valve that is movable from a closed position toward an open position to provide a variable geometric configuration that changes the open area to reduce back pressure, and wherein the valve moves toward the open position in response to an exhaust gas flow rate exceeding a predetermined limit;
• and
• a doser configured to introduce fluid through the injection opening and into the internal cavity to mix with the engine exhaust gases to provide a mixture that is directed to the second exhaust component.

A method for reducing back pressure in a mixer for an exhaust system comprising the steps of:

• providing a mixer housing defining an internal cavity that receives engine exhaust gases;
• positioning an upstream baffle at an inlet end of the mixer housing, the upstream baffle comprising a plate having an open area that comprises a fixed geometric configuration through which exhaust gas enters the internal cavity;
• and
• moving a valve from a closed position toward an open position when an exhaust gas flow rate exceeds a predetermined limit to provide a variable geometric configuration that changes the open area to reduce back pressure.