| 摘要 |
PROBLEM TO BE SOLVED: To provide a crank shaft capable of reducing a weight while suppressing degradation of rigidity.SOLUTION: A shoulder portion of an arm of a crank shaft is provided with a recessed hole. When a direction connecting a center of a journal and a center of a pin is a vertical direction, and a direction orthogonal to the vertical direction is a lateral direction when viewed from the axial direction of the journal, the cross-sectional shape in the direction orthogonal to a depth direction of the hole is provided with a first bottom side in which a length in the lateral direction of the cross-sectional shape becomes longest, and a second bottom side disposed in an upper direction or a lower direction of the first bottom side through the center of gravity of the cross-sectional shape, and laterally connecting a pair of inflection points separating most from the first bottom side. A relationship of α/β≥1 is established when one of the first bottom side and the second bottom side is an upper side, the other is a lower side positioned at a lower direction of the upper side, a length of the upper side is α, and a length of the lower side is β.SELECTED DRAWING: Figure 3 |
