| 摘要 |
A four-stroke cycle internal combustion engine in which an oil reservoir for storing lubricating oil is arranged below a crank chamber housing a crankshaft, and oil mist formed in the oil reservoir is supplied to the interior of the crank chamber and to a valve chamber through an oil mist passage for providing fluid communication between the oil reservoir and the valve chamber. The oil mist passage include pre-separation oil mist passage section formed in the crankshaft, and having one end in fluid communication with the oil reservoir and the other end opened on the radial outer-periphery of the crankshaft; a cylindrical centrifugal-separation chamber surrounding the outer-periphery of the crankshaft on which the other end is opened; and a post-separation oil mist passage section extending from the centrifugal-separation chamber in the opposite direction of the rotational direction of the crankshaft and in fluid communication with the valve chamber. The oil mist passage further includes an oil return passage providing fluid communication between the centrifugal-separation chamber and the oil reservoir. The oil return passage extends from the centrifugal-separation chamber in the same direction as the rotational direction of the crankshaft. Oil mist of adequate concentration thereby being supplied into each of the crank chamber and the valve chamber.
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