Honda Motor Co., Ltd.

Hiroyuki Tsukagoshi

Kensuke Mori

Masako Takahashi

Koichiro Matsushita

Reina Kurosu

A cooling structure of an internal combustion engine includes a thermostat provided to switch circulation between a radiator passage and a bypass passage in an engine body, to thereby enable acceleration of early warming up via the bypass passage without impairing the external appearance or increasing the size of the internal combustion engine. The cooling structure also includes an in-cylinder-block fluid passage partitioned up and down in an axial direction of a cylinder axis into an in-cylinder-block upper fluid passage and an in-cylinder-block lower fluid passage by a partition wall. The bypass passage is partially composed of the in-cylinder-bock lower fluid passage.

Cooling structure for internal combustion engine

An internal combustion engine includes: an engine main body demarcating a breather chamber that is partitioned from a crank chamber, disposed above the crank chamber, and has an inlet opening opened toward the crank chamber; a multistage transmission housed in the crank chamber and having speed change gear trains that are respectively supported by a pair of transmission shafts and mesh with each other; and a breather passage disposed above the transmission shafts and extending in an up-down direction from the crank chamber to the inlet opening of the breather chamber, the inlet opening being disposed above a half in a height direction of the breather chamber. Accordingly, the internal combustion engine can suppress the entry of splashed oil into the breather chamber more than ever before.

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Wako, Japan

Hiroyuki Tsukagoshi