To avoid stress concentration on a female screw portion 41 of a lower link 4, which does not serve as a through-hole.
The lower link 4 as part of a double link type piston crank mechanism is divided into a lower link upper 31 and a lower link lower 32 along a division plane 24 passing through the center of a crank pin bearing portion 21 for assembling efficiency on a crank pin. One bolt 33 for fastening both of them is threaded to the female screw portion 41 of the lower link upper 31, but the female screw portion 41 does not serve as the through-hole. To avoid the possibility of stress concentration, an opening portion 42 passing through the lower link upper 31 is formed corresponding to the front end of the bolt 33, where the front end of the bolt 33 protrudes. The opening portion 42 expands larger to the opposite side to the crank pin bearing portion 21 than along the center line of the bolt 33. Thus, the flow of stress due to great load F2 from a pin boss portion 22 for an upper pin is separated from a thread of the female screw portion 41 to avoid the stress concentration.
USHIJIMA KENJI
MOGI KATSUYA
IMAZU MASATSUGU
Hiromichi Kobayashi
Tomioka Kiyoshi
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