A pull cord device adapted to control raising and lowering of a base rail relative to a header rail of a window covering in an upright direction, said pull cord device comprising:
- a housing which is adapted to be disposed on one of the base rail and the header rail, and which has a restricting groove disposed therein;
- a spring motor which is disposed in said housing, and which has a coil spring that has a biasing force and that is wound about a winding axis;
- a cord spool which is disposed in said housing to rotate about a rotating axis that is parallel to the winding axis, which has a spool hub surrounding the rotating axis and a toothed gear wheel that is disposed radially and outwardly of said spool hub relative to the rotating axis, and which is configured to be biased by the biasing force of said coil spring to rotate;
- a pull cord having a leading cord end which is coupled with said spool hub so as to permit said pull cord to be wound thereon, a tailing cord end which is opposite to said leading cord end, and which is adapted to be connected to the other one of the base rail and the header rail, and a cord body which is interposed between said leading cord end and said tailing cord end, and which includes proximate and distal cord segments relative to said leading cord end, said proximate cord segment being disposed such that when said leading cord end is being reeled on or off of said spool hub, said proximate cord segment moves along a running path in a longitudinal direction that is transverse to the upright direction;
- a locking wheel mounted in and rotatable relative to said housing about a wheel axis parallel to the winding axis, and including
- a rim surrounding the wheel axis,
- a surrounding major wall extending from said rim in radial directions and towards the wheel axis, and
- a toothed segment which is disposed on said rim, and which is turnable between a locked position where said toothed segment engages said toothed gear wheel, and an unlocked position where said toothed segment disengage from said toothed gear wheel, the locked position being disposed behind the unlocked position in terms of a rotating direction of said locking wheel;
- a cord-release controlling member including a cord retaining region which engages said proximate cord segment with a holding friction force such that, when said toothed segment is in the unlocked position, said cord retaining region is movable with said proximate cord segment along the running path by virtue of counteraction of the holding friction force against the biasing force, and such that, when a pulling force is exerted on said distal cord segment to pull said proximate cord segment against the biasing force in the unlocked position, said proximate cord segment is movable relative to said cord retaining region once said cord-release controlling member is prevented from moving away from said locking wheel;
- a guideway disposed in said surrounding major wall, and including
- a first route which extends angularly about the wheel axis from an initial region to an interval region such that said first route corresponds to movement of said toothed segment between the locked and unlocked positions, and
- a looped route starting from and ending at said interval region, and defining a pause region, and first and second turning regions which are disposed upstream and downstream of said pause region respectively, and which are spaced apart from said pause region in the longitudinal direction such that said first and second turning regions respectively correspond to first and second biased movements of said proximate cord segment with said cord retaining region which are caused by the biasing force when said toothed segment is in the unlocked position, and such that said pause region corresponds to a pulled movement of said proximate cord segment relative to said cord retaining region against the biasing force when said toothed segment is in the unlocked position;
- a guided member which has a key end that is disposed to be guided along said guideway such that said key end cooperates with the wheel axis to define first, second, third, and fourth radii, respectively, in said first route, said first turning region, said pause region, and said second turning region, and such that said first radius is longer than said second radius, and said third radius is longer than said fourth radius but shorter than said second radius, said guided member further having a restricted end which is opposite to said key end and which is inserted into and which is slidable along said restricting groove;
- and
- a linkage which is disposed to couple said cord-release controlling member with said surrounding major wall such that when said cord-release controlling member is moved along the running path towards said locking wheel, said locking wheel is turned from the locked position to the unlocked position, and such that when said toothed segment is in the unlocked position, said cord retaining region remains unmoved in each of said first turning, pause and second turning regions.