Adaptive exhaust valve with purpose-designed spring

An internal combustion engine system comprising

• an internal combustion engine configured to produce exhaust gases as a product of a combustion reaction,
• an exhaust discharge pipe coupled to the internal combustion engine and defining a passageway that is configured to direct the exhaust gases from the internal combustion engine to atmosphere, and
• an adaptive valve assembly coupled to the exhaust discharge pipe and configured to receive the exhaust gases prior to the exhaust gases reaching the atmosphere, the adaptive valve assembly comprising
• a valve flapper arranged in the passageway and configured to pivot about a flapper pivot axis from a normally-closed position to an opened position and
• a flapper mount assembly configured to couple the valve flapper to the pipe for movement about the flapper pivot axis from the normally-closed position to the opened position, the flapper mount assembly including a bushing system having a thrust bushing and a barrel bushing opposite the thrust bushing relative to the valve flapper, a valve shaft coupled to the valve flapper and supported axially and radially by the thrust bushing and radially by the barrel bushing to allow rotation of the valve flapper about the flapper pivot axis, and a resilient member configured (i) to apply a torsional force about the flapper pivot axis on the valve shaft to bias the valve flapper toward the normally-closed position and (ii) to apply a force on the valve shaft to bias the valve shaft generally along the flapper pivot axis into engagement with the thrust bushing and laterally about a lateral axis at the thrust bushing into engagement with a downstream side of the barrel bushing so that shaft-to-bearing chatter is reduced.