Mechanical stretching device for movable seat unit and seat unit

A mechanical stretching device for a movable seat unit, comprising:

• a seat assembly, comprising a base assembly, a lateral plate attached to a seat of the seat unit, and a central driven member coupled between the base assembly and the lateral plate;
• a backrest assembly, pivotally connected to a rear part of the lateral plate, comprising a backrest connecting member configured to be attached to a backrest of the seat unit and a backrest link assembly pivotally connected to the backrest connecting member, the backrest link assembly comprising a first backrest link hinged to the central driven member and a second backrest link hinged to the lateral plate, wherein the first backrest link is hinged to the second backrest link;
• a leg stretching device, pivotally connected to a front part of the lateral plate, comprising a plurality of links pivotally connected with each other and a first footrest member configured to be attached to a footrest,
• wherein the mechanical stretching device allows the seat unit to be switched between a sitting position, a TV position, and/or a lying position;
• the first footrest member is folded below a seat when in the sitting position;
• the first footrest member is stretched forward when in the TV position;
• and the backrest is relined backward, a highest point of the footrest is higher than a highest point of the backrest, and the first footrest member is stretched forward and upward, when in the lying position.