| 摘要 |
PROBLEM TO BE SOLVED: To increase durability, by increasing rigidity of a hydraulic servo piston to reduce stress on a window hole portion. SOLUTION: The hydraulic servo piston comprises a pressure receiving head portion 1 and a cylindrical portion 2, and has a thick-wall portion 11 formed at a circumferential portion 1a corresponding to a window hole 3 that is the nearest to the pressure receiving head portion and having thickness larger than that of other circumferential portion 1b. Forming of the thick-wall portion 11 increases rigidity of the pressure receiving head portion 1, reduces stress on the window hole 3, and increases durability of the hydraulic servo piston.
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