Turbocharged engine and method of operating same

Claim 1

An engine system comprising: an internal-combustion engine having an air intake and an exhaust-gas output; an exhaust-gas turbine connected to said exhaust-gas output and drivable by the pressure therein at a speed generally proportional to the exhaust-gas pressure; a supercharger driven by said turbine and connected to said air intake of said engine to feed air to said engine at a pressure generally proportional to the turbine speed; a valve connected across said turbine and openable to shunt engine exhaust gases around said turbine and thereby reduce said turbine speed and therewith the pressure at which said supercharger feeds air to said engine, said valve having a valve seat having an inner edge defining a predetermined flow cross-sectional area, said seat being formed with a tapered region, and a valve body having an end face engageable over said seat, of an area substantially greater than said flow cross-sectional area, and having an outer edge lying outside said inner edge of said seat and closely adjacent said tapered region when said valve is closed, said body being movable in a closing direction toward said seat and in an opening direction away from said seat, said outer edge forming with said tapered region an increasingly large flow cross section as said end face pulls away from said seat on displacement of said body in said opening direction, whereby the overall flow cross-section of said valve is uniformly increased as said valve opens; and means responsive to engine speed, connected to said valve, and including a spring urging said valve body in said closing direction, said means being for opening said valve above a predetermined engine speed and for generally proportionally decreasing said exhaust-gas pressure with increasing engine speed above said predetermined engine speed.