Pull cord device and window covering including the same

1. 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 container to be disposed on one of the base rail and the header rail;

a spring driving unit disposed in said container and including a cord spool and a spring motor that biases said cord spool to rotate in a cord-winding direction;

a pull cord having one end coupled to said cord spool, extending out of said container, and further having an opposite end to be coupled to the other one of the base rail and the header rail;

a braking unit disposed in said container and operatively associated with said cord spool and said pull cord for retaining releasably the base rail at a desired height relative to the header rail; and

a one-way damper unit including:

a housing mounted to said container;

a unidirectional clutch disposed in said housing, forming a gap with said housing, and having:

a casing having an inner casing surface formed with a groove that extends at an angle with respect to an axis and that has a deep groove portion and a shallow groove portion angularly spaced apart from said deep groove portion, said shallow groove portion having a depth with respect to the axis that is shallower than that of said deep groove portion;

a main shaft having an insert segment extending into said casing along the axis, and a connecting segment extending from said insert segment outwardly of said casing; and

a clutching member disposed in said casing and including: a fixing frame formed with a mounting slot; a clutching body disposed in said mounting slot, contacting said insert segment of said main shaft, and extending into said groove, said clutching body having a cross-sectional dimension shorter than a smallest distance between an outer surface of said insert segment and a groove bottom of said deep groove portion, and longer than a largest distance between said outer surface of said insert segment and a groove bottom of said shallow groove portion; and a spring member disposed between said fixing frame and said clutching body for biasing said clutching body toward said shallow groove portion;

a damping liquid that fills said gap between said housing and said unidirectional clutch; and

a driven wheel coupled to said connecting segment of said main shaft and driven rotatably by said spring driving unit.

2. The pull cord device as claimed in claim 1 , wherein said fixing frame includes a pair of fixing rings, and a connecting member interconnecting said fixing rings and extending parallel to the axis, said mounting slot being defined by said fixing rings and said connecting member, said spring member being a spring plate disposed between said connecting member and said clutching body.

3. The pull cord device as claimed in claim 1 , wherein said casing has an open end through which said connecting segment of said main shaft extends, and said unidirectional clutch further includes an annular plug that is disposed at said open end of said casing and that is sleeved on said connecting segment of said main shaft.

4. The pull cord device as claimed in claim 3 , wherein said housing has an open end through which said connecting segment of said main shaft extends, and said one-way damper unit further includes a sealing lid disposed at said open end of said housing and forming a fluid-tight seal with said annular plug.

5. The pull cord device as claimed in claim 3 , wherein said casing includes an outer casing part and an inner casing part disposed in and coupled co-rotatably to said outer casing part, said outer casing part including an end wall and an outer surrounding wall extending from a periphery of said end wall parallel to the axis and cooperating with said end wall to confine a receiving space, said receiving space having a first section proximate to said end wall and configured to receive said inner casing part, and a second section wider than said first section and configured to receive said annular plug.

6. The pull cord device as claimed in claim 5 , wherein said outer surrounding wall has an inner wall surface formed with a shoulder at a junction of said first and second sections of said receiving space, said annular plug abutting against said shoulder.

7. The pull cord device as claimed in claim 5 , wherein said inner casing part includes an annular end flange that defines a shaft hole through which said connecting segment of said main shaft extends, and an inner surrounding wall that extends from an outer periphery of said end flange parallel to the axis, said unidirectional clutch further including a coupling unit for coupling said inner surrounding wall co-rotatably to said outer surrounding wall.

8. The pull cord device as claimed in claim 7 , wherein said coupling unit includes a key that extends parallel to the axis and that is formed on one of said inner surrounding wall and said outer surrounding wall, and a keyway that extends parallel to the axis, that is formed in the other one of said inner surrounding wall and said outer surrounding wall, and that engages said key.

9. A window covering comprising:

a header rail;

a base rail movable relative to said header rail in an upright direction;

a plurality of slats disposed between said header rail and said base rail;

a container disposed on one of said base rail and said header rail;

a spring driving unit disposed in said container and including a cord spool and a spring motor that biases said cord spool to rotate in a cord-winding direction;

a pull cord having one end coupled to said cord spool, extending out of said container, and further having an opposite end coupled to the other one of said base rail and said header rail;

a braking unit disposed in said container and operatively associated with said cord spool and said pull cord for retaining releasably said base rail at a desired height relative to said header rail; and

a one-way damper unit including:

a housing mounted to said container;

a unidirectional clutch disposed in said housing, forming a gap with said housing, and having:

a casing having an inner casing surface formed with a groove that extends at an angle with respect to an axis and that has a deep groove portion and a shallow groove portion angularly spaced apart from said deep groove portion, said shallow groove portion having a depth with respect to the axis that is shallower than that of said deep groove portion;

a main shaft having an insert segment extending into said casing along the axis, and a connecting segment extending from said insert segment outwardly of said casing; and

a clutching member disposed in said casing and including: a fixing frame formed with a mounting slot; a clutching body disposed in said mounting slot, contacting said insert segment of said main shaft, and extending into said groove, said clutching body having a cross-sectional dimension shorter than a smallest distance between an outer surface of said insert segment and a groove bottom of said deep groove portion, and longer than a largest distance between said outer surface of said insert segment and a groove bottom of said shallow groove portion; and a spring member disposed between said fixing frame and said clutching body for biasing said clutching body toward said shallow groove portion;

a damping liquid that fills said gap between said housing and said unidirectional clutch; and

a driven wheel coupled to said connecting segment of said main shaft and driven rotatably by said spring driving unit.