Method for producing piston assembly and hydraulic fluid device

A fluid pressure device comprising:

• a body having a slide hole inside the body;
• a piston unit movable in an axial direction inside the slide hole;
• and
• a piston rod protruding from the piston unit in the axial direction;
• wherein:
• the piston unit includes a packing and a piston body comprising a plurality of members, the piston body being provided with a packing mounting groove in which the packing is mounted;
• the piston body includes, as the plurality of members, a first piston member and a second piston member stacked in the axial direction;
• a combination of at least two members of the plurality of members defines the packing mounting groove;
• and
• one or both of the first piston member and the second piston member are provided with a hollow portion having a depth in the axial direction, wherein:
• the hollow portion has a through-hole passing through only one of the first piston member and the second piston member in the axial direction;
• one member of the first piston member and the second piston member that is provided with the through-hole includes a protruding portion protruding toward another member of the first piston member and the second piston member that is not provided with the through-hole;
• and
• the protruding portion has, on an outer circumferential part thereof, a recess portion recessed inward and which constitutes part of the through-hole.

A fluid pressure device comprising:

• a body having a slide hole inside the body;
• a piston unit movable in an axial direction inside the slide hole;
• and
• a piston rod protruding from the piston unit in the axial direction;
• wherein:
• the piston unit includes a packing and a piston body comprising a plurality of members, the piston body being provided with a packing mounting groove in which the packing is mounted;
• the piston body includes, as the plurality of members, a first piston member and a second piston member stacked in the axial direction;
• a combination of at least two members of the plurality of members defines the packing mounting Groove;
• and
• one or both of the first piston member and the second piston member are provided with a hollow portion having a depth in the axial direction, wherein:
• the hollow portion includes a first hollow portion defined in the first piston member and a second hollow lightening portion defined in the second piston member;
• one of the first hollow portion and the second hollow portion is a through-hole passing through the corresponding piston member in the axial direction;
• and
• another of the first hollow portion and the second hollow portion is a bottomed groove having a depth in the axial direction.

A method for producing a piston assembly provided with a piston unit including a packing mounted in a packing mounting groove and a piston rod protruding from the piston unit, comprising the steps of:

• stacking a plurality of members including a first piston member and a second piston member by relatively moving the packing and the plurality of members in an axial direction in sequence, relative to the piston rod;
• and
• securing the first piston member and the second piston member to the piston rod;
• wherein:
• the plurality of members constitute a piston body provided with the packing mounting groove;
• a combination of at least two members of the plurality of members defines the packing mounting groove;
• and
• one or both of the first piston member and the second piston member are provided with a hollow portion having a depth in the axial direction, wherein
• the hollow portion has a plurality of bottomed grooves disposed at intervals in a circumferential direction of the piston body;
• and
• each of the bottomed grooves has an arc shape extending in the circumferential direction of the piston body.