| 摘要 |
PROBLEM TO BE SOLVED: To prevent breakage of a connection part of a hub with each vane. SOLUTION: A peripheral edge 3 of a hub 2 is formed in rotational symmetry of approx. an triangle whose projecting ends 2A are rounded in such a constitution that arc-shaped edge portions 4 having a small curvature and arc-shaped edge portions 5 having a large curvature are provided alternately in continuity, and in the part of the edge portion 4 between the projecting ends 2A a vane 1 is installed in eccentricity toward the side of hub rotation, and ribs 7A and 7B for reinforcement are installed ranging from the center of the hub 2 provided with a mounting hole 6 to the arc-shaped edge portion 4 where the vane 1 is attached. In this installation of ribs 7A and 7B, the one 7a is located in eccentricity toward the forefront end 1A of the mounting part on hub 2 of the vane 1 positioned on the side of hub rotation while the other 7B is located in eccentricity toward the tail end 1B of the mounting part on hub 2 of the vane 1 positioned on the side opposite the forefront 1A, in such an arrangement that the dimension L1 between the mounting part forefront 1A of the vane 1 and the mounting end of the rib 7A is smaller than the dimension L2 between the mounting part tail 1B of the vane 1 and the mounting end of the rib 7B.
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