Butterfly valve for turbocharger systems

A series sequential turbocharger system being coupled to an engine, the turbocharger system comprising:

• a low pressure turbocharger having a low pressure compressor and a low pressure turbine, the low pressure compressor being rotatably coupled to the low pressure turbine, and the low pressure compressor being in fluid communication with an intake manifold of the engine, and the low pressure turbine being in fluid communication with an exhaust manifold of the engine;
• a high pressure turbocharger having a high pressure compressor and a high pressure turbine, the high pressure compressor being rotatably coupled to the high pressure turbine, the high pressure compressor being in fluid communication with the intake manifold of the engine, and the high pressure turbine being in fluid communication with the exhaust manifold of the engine;
• a butterfly valve for controlling a gas stream in the turbocharger system, the butterfly valve having:
• a housing with a valve passageway through which the gas stream passes from a first end of the valve to a second end of the valve, the valve passageway including:
• a shaft axis;
• bores on opposite sides of the passageway, the bores being aligned along the shaft axis with one another;
• lap seating surfaces on opposite sides of the passageway facing opposite ends of the valve, the shaft axis being between the lap seating surfaces;
• a butterfly valve element in the valve passageway between the bores, the butterfly valve element having counter bores;
• two bushings, each bushing being received in a different one of the bores and extending from the bore inwardly into a different one of the counter bores of the butterfly valve element;
• a shaft extending along the shaft axis and in each of the bushings so as to journal the shaft relative to the housing;
• and
• wherein there is a first slip fit creating a first rotary joint between the bushings and the counter bores and a second slip fit creating a second rotary joint between the shaft and the bushings, and one of the slip fits is closer than the other to insure the butterfly valve element seats flatly against the seating surfaces.