US Patent 7685989 Two-cycle engine

A 2-cycle engine 1 is provided with an ignition device 8; an exhaust control valve 24; and a controller 40 for controlling the ignition device 8 and the exhaust control valve 24. The controller 40 controls spark ignition combustion by activating the ignition device 8 in a high load range, and controls self-ignition combustion of a mixture in the combustion chamber 10 by adjusting pressure in a cylinder chamber 3a with adjustment of the opening of the exhaust port 21 in a low load range. In a low load and low rotational speed range, moreover, there is formed a stratified mixture field, in which the air and the fuel are much distributed in the central portion 10c of the combustion chamber 10 and in which burned gas remaining in the combustion chamber 10 is much distributed in the outer side 10b of the central portion of the combustion chamber 10, so that the self-ignition combustion of the mixture may be performed by forming the stratified mixture field in the low load and low rotational speed range.