| 摘要 |
PURPOSE:To improve the exhaust gas purifying characteristic while to improve the operationability and fuel economy by separating the normal engine operating region into theoretical air-fuel ratio operating region of relatively low speed and lean air-fuel ratio operating region of relatively high speed. CONSTITUTION:In an engine employing LPG as fuel, the control valve 15 in the incremental fuel path 14 is controlled to obtain mixture gas of theoretical air-fuel ratio on the basis of the output from 02 sensor when a control unit 16 will decide on the basis of the outputs from a pressure sensor 19 and a rotary speed sensor 20 that it is under theoretical air-fuel ratio operating region I where the intake negative pressure is higher than predetermined level or the rotary speed is lower than predetermined level upon finish of idling to open a throttle valve 17. Upon decision that it has transisted to lean air-fuel ratio operating region II where the intake negative pressure is lower than prede termined level or the rotary speed is higher than predetermined level, the control valve 15 is closed to feed only basic quantity of LPG weighed through a jet 3 to a mixer 5 thus to feed the mixture gas of lean air-fuel ratio to engine 11.
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