Two-stroke engine with supercharger

A two-stroke engine with a supercharger, the two-stroke engine including:

• an engine body that has a cylinder constituting a combustion chamber, a piston inserted in and fitted to said cylinder, and an intake valve and an exhaust valve arranged on top of the cylinder and respectively opening/closing an intake port and an exhaust port;
• and a supercharger that is provided in an intake passage connected to the intake port of said engine body, the two-stroke engine with the supercharger further comprising:
• an intake variable valve mechanism capable of varying at least closing timing of the intake valve;
• an exhaust variable valve mechanism capable of varying at least opening timing of the exhaust valve;
• engine speed detection means that detects an engine speed as a speed of the engine body;
• and
• control means that controls actuation of the engine body including the intake variable valve mechanism and the exhaust variable valve mechanism,
• wherein an open period of each of the intake valve and the exhaust valve is set to satisfy particular conditions that are that the open period includes compression bottom dead center, that the opening timing of the intake valve is later than the opening timing of the exhaust valve, and that the closing timing of the intake valve is substantially the same as closing timing of the exhaust valve or later than the closing timing of the exhaust valve,
• wherein the control means is configured to conduct compression self-ignition combustion, in which fuel is compressed to ignite by itself in the combustion chamber, when an operation state of the engine body is in a low-load side operation range where a load is smaller than a specified load and to conduct spark ignition combustion of the fuel in the combustion chamber when the operation state of the engine body is in a high-load side operation range, in which the load is equal to or larger than the specified load,
• wherein the supercharger is configured to be actuated when the operation state of the engine body is in the low-load side operation range or the high-load side operation range, and
• wherein the control means is further configured to actuate the intake variable valve mechanism and the exhaust variable valve mechanism in order to retard at least the closing timing of the intake valve and at least the opening timing of the exhaust valve from those in a case where the operation state of the engine body is in the low-load side operation range at the same engine speed as the engine speed detected by the engine speed detection means while the particular conditions are satisfied, when the operation state of the engine body is in the high-load side operation range.