| 摘要 |
PROBLEM TO BE SOLVED: To surely operate a control valve element even in a low and intermediate rotating region of an engine by setting operating pressure from the engine for drivingly controlling the control valve element to a combustion pressure. SOLUTION: In a low and intermediate rotating region of an engine, and in a region where combustion pressure led from the inside of a cylinder into a pressure chamber 12 is smaller than urging force of a spring 17, a valve element part 6a of a control valve element 6 is protruded upward slantly into an exhaust port 4, and thereby, an upper part of the exhaust port 4 is narrowed. When engine rotating speed is increased and combustion pressure is increased, the valve element part 6a of the control valve element 6 is retreated, and it is gradually immersed into a valve element housing part 5. Furthermore, as reciprocating cycle of a piston 2 is shortened, a timing for opening the exhaust port 4 is hastened. And then, when the engine speed attains a high rotation region and combustion pressure led into a pressure chamber 13 of a driving part 8 is larger than energizing force of the spring 17, the valve element part 6a of the control valve element 6 is retreated to an upper wall of the exhaust port 4. It is thus possible to obtain operating pressure having high pressure by setting operating pressure to combustion pressure of the engine.
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