Supercharger for an engine

An engine system with turbocharger comprising:

• an exhaust manifold having plural independent exhaust passages, each of the exhaust passages being connected to an exhaust port of a corresponding engine cylinder;
• a collective part formed by gathering said independent exhaust passages in said exhaust manifold or on a downstream side of said exhaust manifold;
• an exhaust turbocharger connected to a downstream side of said collective part;
• a variable exhaust valve for changing each passage cross-sectional area of said independent exhaust passages at an upstream side of said collective part;
• an exhaust valve timing changing mechanism;
• and
• a controller for controlling said variable exhaust valve;
• wherein said controller is configured to perform independent exhaust throttle control for reducing a passage cross-sectional area of at least one of said independent exhaust passages below a maximum area with said variable exhaust valve at least in a predetermined low engine speed range in a supercharging operation range of said engine;
• wherein said predetermined low engine speed range is a range where an engine speed is lower than a predetermined engine speed at which a waste gate valve of said exhaust turbocharger begins to open;
• wherein said controller is further configured to decrease said passage cross-sectional area as the engine speed becomes lower during said independent exhaust throttle control;
• and
• wherein said controller is further configured to retard an exhaust valve opening timing via said exhaust valve timing changing mechanism such that an exhaust valve opening timing at which said independent exhaust throttle control is performed, is later than an exhaust valve opening timing at which said independent exhaust throttle control is not performed, delay of the exhaust valve opening timing being limited to immediately before the exhaust bottom dead center.