Top-down bottom-up window covering

A top-down bottom-up window covering, comprising:

• a headrail;
• a middle rail, which is movably provided below the headrail;
• a bottom rail, which is movably provided below the middle rail;
• a covering structure provided between the middle rail and the bottom rail;
• a first rotating shaft, which is provided at the headrail and is adapted to receive or release a first cord, wherein an end of the first cord is fixed at the middle rail;
• a second rotating shaft, which is provided at the headrail and is adapted to receive or release a second cord, wherein an end of the second cord is fixed at the bottom rail;
• a lifting control structure provided at the headrail and adapted to control the first rotating shaft or the second rotating shaft to rotate;
• a pre-stress unit, which is provided at the headrail and is concurrently movable along with the first rotating shaft;
• and
• a one-way clutch, which is located between the first rotating shaft and the lifting control structure;
• wherein, when the middle rail is pulled upward by the first cord, the one-way clutch is in an engaged state for keeping a link between the first rotating shaft and the lifting control structure;
• when the middle rail is not pushed and not pulled upward by the first cord, and the bottom rail is lifted, the one-way clutch is in the engaged state for keeping the link between the first rotating shaft and the lifting control structure;
• when the middle rail is pushed upward, the one-way clutch is in a disengaged state for breaking the link between the first rotating shaft and the lifting control structure, and a driving force provided by the pre-stress unit drives the first rotating shaft to receive the first cord.