| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent backflow of an exhaust gas to an intake passage due to stop of an engine in a state that an intake valve and an exhaust valve are opened in an overlapped state, with a simple structure.SOLUTION: A throttle valve 22 is kept in a state of being slightly opened even when an operation is stopped, as a reference state, to prevent malfunction and the like due to freezing of water droplets. When the operation is stopped and wind blows to an exhaust passage 26 in a state that an intake valve 11 and an exhaust valve 12 are opened, an oxygen concentration detection sensor 27 disposed in a catalyst case 25 detects decrease or disorder of oxygen concentration, and the throttle valve 22 is fully closed on the basis of the detection signal. As there is no escape of fresh air accumulated in the intake passage 20, backflow of an exhaust gas to an intake port 9 and the intake passage 20 is prevented. Thus next starting can be performed without problems. The throttle valve 22 is returned to the reference state after a lapse of a prescribed time.</p> |
