PURPOSE: To make a compression ratio variable so as to improve output by controlling a sleeve valve, for opening/closing intake ports provided at the periphery of the lower part of a cylinder sleeve, in such a way as to reduce the opening area of the intake port at the specified low engine speed and load time in two-cycle operation.
CONSTITUTION: Plural intake ports 12 are bored at the peripheral wall, corresponding to the vicinity of the upper part of a piston head 21 positioned at the bottom dead center of a piston 2, of a cylinder sleeve 11 provided at the inner wall of a cylinder 1. These intake ports 12 are opened/closed by the rotation of a sleeve valve fitted at the cylinder sleeve 11. An intake and an exhaust valves 5, 6 driven by solenoid valve actuators 51, 61 are provided at the upper part of a cylinder 1. The sleeve valve 3 is controlled in such a way as to be rotated at the time of engine speed being below the set engine speed lower than the cycle change over judging engine speed and engine load being less than the set load higher than the cycle change-over judging load in two-cycle operation so as to move the operating timing of the intake ports 12 to the bottom dead center side.
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