| 摘要 |
PROBLEM TO BE SOLVED: To reduce a weight of a trunnion while ensuring the rigidity by making a cross section area of of a central part of each trunnion near each displacement shaft, smaller than that near both ends of each trunnion close to each shaft. SOLUTION: A trunnion 6a comprises a bent parts 32, 32 bent in the same direction at both ends of an intermediate part 33, and the shafts are concentrically and integrally formed with outer surfaces of these bent parts 32, 32. The sectional shape of an intermediate part 33 of the trunnion 6a on the surface expanded in the direction perpendicular to the central axial direction of the shafts 5, 5 is different from that of a central part and that near both ends. That is, the cross section of the central part of the trunnion 6a is smaller than that near both ends of the trunnion 6a. Accordingly, the section modulus of the central part to which only the comparatively small bending stress is added, can comparatively be reduced.
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