| 摘要 |
PROBLEM TO BE SOLVED: To reduce the consumption of oil, inhibit the pump loss to improve the fuel consumption, prevent the suction of dust from the exterior to an oil seal part, and improve the reliability of a check valve even under the operation condition of a partial load, by controlling the internal pressure of a crank case at predetermined negative pressure value. SOLUTION: A first blowby gas exhaust port 26a communicated into a crank case 16 of an internal combustion engine and the throttle valve 30 downstream side of an intake pipe 28 are connected together by a ventilation path in which the gas flows, an opening-closing valve 46 for opening and closing the ventilation path is formed on the midway of the ventilation path, and the opening-closing valve 46 is closed when the negative pressure in the crank case 16 is higher than a predetermined value.
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