| 摘要 |
PURPOSE:To lighten weight, heighten rigidity in the shaft direction and the radial direction and uniform coefficient of contraction at the time of molding by forming hollow parts with large diametrical hollow parts and small diametrical hollow parts among the large diametrical parts and arranging each of the hollow parts symmetrically on the section of a piston in the radial direction. CONSTITUTION:A resin piston 4 is formed into a dome shape with bottom walls partitioning and forming a hydraulic pressure chamber among the bottom walls of a cylinder hole, and a plural number of hollow parts in the shaft direction are formed on the side of a friction pad. These hollow parts are made of seven pieces of large diametrical hollow parts 4b with circular sections and six pieces of small diametrical hollow parts 4c with circular sections, and one of the seven large diametrical hollow parts 4b is arranged on the shaft center of the resin piston 4 and the other six are arranged in equal distance with equal intervals outside of the shaft center and the six small diametrical hollow parts 4c are arranged with equal intervals between the large diametrical hollow parts 4b outside so that each of these hollow parts 4b, 4c is to be symmetrical against the section in the radial direction of the resin piston 4. |
