| 摘要 |
PROBLEM TO BE SOLVED: To widely keep a gap between a piston 3 at the bottom dead center of the piston 3 and a counterweight 12 and enlarge the variable range of a compression ratio. SOLUTION: A variable compression ratio mechanism is constructed by a double link mechanism using an upper link 21, a lower link 22 and a control link 23. At a lower compression ratio, the bottom dead center of the piston 3 is lowered. An outer edge 13 of the counterweight 12 for the crank shaft 10 is in an approximately circular shape, and a radial distance rc of a central portion closest to a pin boss portion at the center of the piston 3 at the bottom dead center of the piston 3 is shorter than a radial distance rs of both side portions. Thus, a gap c can be kept widely between the piston 3 and the counterweight 12 and the variable range of the compression ratio is enlarged while the inertial moment of the counter weight 12 is sufficiently maintained.
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