| 摘要 |
PURPOSE:To permit the exhaust regulation and the fuel economization to be fulfilled by reducing or suspending the recirculation of exhaust in the region in which operation can be carried out with a lean air fuel ratio. CONSTITUTION:When an engine 12 which uses LPG as fuel is operated in the region where the revolution speed is over a certain value and the intake negative pressure is less than a certain value, a control valve 4 is kept in the closed valve state so that the lean air fuel ratio is obtained. At the same time, a direction selector valve 23 is operated to the atmosphere side, and an exhaust control valve 17 is closed to stop the recirculation of exhaust. The negative pressure introduced into a back pressure chamber 21 is lowered by positioning the direction selector valve 23 so as to communicate to both of the upstream side of a negative pressure passage 19 and the atmosphere side or switching the operation so as to communicate alternately to the upstream side and the atmosphere side, and the recirculation of exhaust is reduced by reducing the opening degree of the exhaust control valve 17. Therefore, the dilution of the mixed gas furthermore can be prevented, and the deterioration of the operation performance and the exhaust composition in this region can be prevented.
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