Abstract: A piston manufacturing device includes a first forming device (42) configured to form an annular groove (61) in a piston (11), and a second forming device (52) configured to press an edge (15) of an opening (14) of the piston (11) toward other end side in an axial direction of the piston (11) and to form a thick section (65) extruded from an inner circumferential surface (12b) arranged between the edge (15) and the groove (61) toward an axial center side of the piston (11), wherein a recessed section (53) is formed at a portion of the second forming device (52) that is arranged to abut the edge (15) so that an inner circumferential side of the edge (15) is plastically deformed toward the other end side in an axial direction of the piston (11).

Abstract: A master cylinder comprises a cylinder body in a cylindrical form having one end closed and including a discharge passage and a supply passage for a brake fluid, the supply passage being communicated with a reservoir. A piston is slidably disposed in the cylinder body, so as to form a pressure chamber for supplying a fluid pressure to the discharge passage. A piston seal is provided in a circumferential groove formed in the cylinder body, which has an inner circumferential surface thereof in slidable contact with the piston and is capable of sealingly disconnecting the supply passage and the pressure chamber. The cylinder body includes a communication groove which opens into the circumferential groove and extends from the circumferential groove toward the closed end of the cylinder body to thereby connect the circumferential groove and the discharge passage. The communication groove is formed outwardly beyond a bottom surface of the circumferential groove relative to a radial direction of the cylinder body.

Abstract: A master cylinder comprises a cylinder body in a cylindrical form having one end closed and including a discharge passage and a supply passage for a brake fluid, the supply passage being communicated with a reservoir. A piston is slidably disposed in the cylinder body, so as to form a pressure chamber for supplying a fluid pressure to the discharge passage. A piston seal is provided in a circumferential groove formed in the cylinder body, which has an inner circumferential surface thereof in slidable contact with the piston and is capable of sealingly disconnecting the supply passage and the pressure chamber. The cylinder body includes a communication groove which opens into the circumferential groove and extends from the circumferential groove toward the closed end of the cylinder body to thereby connect the circumferential groove and the discharge passage. The communication groove is formed outwardly beyond a bottom surface of the circumferential groove relative to a radial direction of the cylinder body.