Patent ID: 7874242

Claim:
A piston assembly in a fluid pressure cylinder, comprising: a piston rod; a piston mounted with respect to the piston rod and slidably inserted in a cylinder body of a double rod fluid pressure cylinder; the piston rod having a fixing groove formed around a circumference of a piston-fixing position thereof; the piston comprising: a circular-annular fixing ring mounted in the fixing groove of the piston rod; a piston body fixed to the fixing ring by a plurality of bolts and having a diameter larger than that of the fixing ring; the fixing ring comprising two semi-circular plated members; each of the semi-circular plated members having at least one threaded hole for bolt-fastening the piston body to the fixing ring; the semi-circular plated members are configured such that they are abutted against each other to thereby form the circular plated fixing ring having a first hole portion at a center thereof; the first hole portion of the fixing ring is tightly fitted in the fixing groove of the piston rod; the piston body having a second hole portion at a center thereof, which is fitted over the piston rod, a plurality of bolt holes corresponding to a threaded hole of the fixing ring, and a concave portion formed around the second hole portion on a side of one surface of the piston body; the fixing ring is fitted in an embedded state in a concave portion of the piston body; and the piston body is fixed to the fixing ring by the bolts which are threadedly inserted in the threaded hole and the bolt hole, wherein an outer circumferential surface of the fixing ring and/or an inner circumferential surface of the concave portion of the piston body is formed as a tapered surface which allows the outer circumferential surface of the fixing ring and the inner circumferential surface of the concave portion of piston body to be, as a whole or partially, pressedly contacted with each other when the fixing ring is fitted in the concave portion of the piston body, whereby the piston body is aligned with respect to the piston rod.