Seat

A seat comprising:

• a back portion frame;
• a cushion material including a lower layer portion stretched on the back portion frame at a portion corresponding to a region between a lower side of shoulder blades and a lumbar vertebrae region of a seated person, and a surface layer portion layered on the lower layer portion and stretched on the back portion frame;
• and
• a tension adjusting mechanism that connects at least one connection position of the lower layer portion that is located further upward than beneath the shoulder blades and a connection position further downward than the lumbar vertebrae region to the back portion frame;
• wherein:
• the tension adjusting mechanism generates tensile force which pulls the lower layer portion rearward at a time of sitting;
• the surface layer portion includes portions between a central portion in a left-right direction which support the seated person and both end portions in the left-right direction, and which elongate in a left-right direction more easily than the central portion and the both end portions;
• and
• the portions between the central portion in the left-right direction and both end portions in the left-right direction include elastic members which elongate more easily than the central portion and the both end portions.

A seat comprising:

• a seat frame that includes a fixed frame and a movable frame provided at a rear portion of the fixed frame, the movable frame being able to move in a front-rear direction;
• a cushion material that includes a cloth spring material with a front end portion that is anchored at the fixed frame and a rear end portion that is anchored at the movable frame, and a surface layer portion layered on the cloth spring material and stretched on the fixed frame;
• an urging member provided between the fixed frame and the movable frame, the urging member urging the movable frame rearward and adding tension to the cloth spring material at a time when a person sits in the seat;
• and
• a tension adjusting mechanism that connects connection positions of the cloth spring material to portions of the fixed frame that are rearward and downward with respect to the connection positions;
• the connection positions are provided on the cloth spring material at locations outward and rearward with respect to locations where ischial tuberosities of a person are located when the person is seated in the seat;
• wherein:
• the tension adjusting mechanism generates tensile force at the time when the person sits in the seat;
• the surface layer portion includes portions between a central portion in a left-right direction which support the seated person and both end portions in the left-right direction, and which elongate in a left-right direction more easily than the central portion and the both end portions;
• and
• the portions between the central portion in the left-right direction and both end portions in the left-right direction include elastic members which elongate more easily than the central portion and the both end portions.

A seat comprising:

• a frame;
• and
• a sheet of a cloth spring material;
• wherein:
• a front end portion of the sheet is attached along its length to a front portion of the frame;
• a rear end portion of the sheet is attached along its length to a rear portion of the frame;
• the front portion of the frame is provided so that the front portion of the frame and the front end portion of the sheet remain fixed in location when the seat is in use;
• the rear portion of the frame comprises a connecting portion and a torsion bar, the connecting portion being rotatable about the torsion bar;
• the rear end portion of the sheet is attached to the connecting portion so that the rear end portion of the sheet and the connecting portion rotate about the torsion bar against a torsional load of the torsion bar when the seat is in use;
• and
• rotation of the connecting portion about the torsion bar causes the location of the rear end portion of the sheet to change both in an up-down direction and a front-rear direction in accordance with a pushing force applied to the sheet so that a planar orientation of the sheet changes.