Adjustable resistance tail plug

1. An adjustable resistance tail plug for a roller blind device, the roller blind device including an aluminum tube, a blind body that is scrolled by the aluminum tube, and a mounting bracket that is disposed at one side of the aluminum tube, said adjustable resistance tail plug comprising a fixed seat, an adjusting wheel, a sleeve, a screw rod unit, an outer casing, a friction wheel and a clutch spring, said fixed seat being adapted to be disposed on said mounting bracket, and having a first circumferential surface that surrounds an axis, and a second circumferential surface that surrounds said axis, said second circumferential surface being located at one side of said first circumferential surface opposite to said mounting bracket, a section of said fixed seat that has said second circumferential surface having an outer diameter smaller than another section of said fixed seat that has said first circumferential surface, said adjusting wheel being rotatably sleeved on said first circumferential surface, said sleeve being rotatably sleeved on said adjusting wheel, said screw rod unit being connected to said fixed seat and extending along said axis, said outer casing including a casing body that is adapted to be disposed on the aluminum tube and that is connected to said screw rod unit, and an inner cavity that formed in said casing body, said inner cavity being for receiving said sleeve, a portion of said adjusting wheel and a portion of said fixed seat, said friction wheel being located within said inner cavity, engaging threadably said screw rod unit, and being driven by said sleeve to move relative to said casing body along said axis, so as to adjust a friction force between said casing body and said friction wheel, said clutch spring being sleeved on said second circumferential surface, and being partially located between said sleeve and said adjusting wheel, said clutch spring being switchable between a contracted state and an expanded state, when in the contracted state, said clutch spring being tightened to abut against said second circumferential surface so that said sleeve is prevented from rotating relative to said fixed seat by said clutch spring, when in said expanded state, said clutch spring releasing said second circumferential surface, and said adjusting wheel being rotatable with said sleeve through said clutch spring about said axis.

2. The adjustable resistance tail plug as claimed in claim 1 , wherein said adjusting wheel includes a rotary section surrounding said first circumferential surface, a sleeve connecting section connected to said rotary section, and a toggling section extending from said sleeve connecting section away from said rotary section along said axis, said sleeve connecting section surrounding said first circumferential surface and being surrounded by said sleeve, said toggling section extending about said axis, and defining a notch that corresponds in position to said second circumferential surface, said clutch spring including a winding section that helically surrounds said second circumferential surface, and two protrusions that are respectively connected to two opposite sides of said winding section and that extend into said notch, said clutch spring being tightened to abut against said second circumferential surface when said protrusions are far away from each other in said notch.

3. The adjustable resistance tail plug as claimed in claim 2 , wherein said sleeve includes a sleeve section sleeved on said sleeve connecting section, and an engaging section connected to one side of said sleeve section opposite to said rotary section, said sleeve section having a first annular wall that corresponds in position to said sleeve connecting section, a second annular wall that corresponds in position to said toggling section, and a boss that extends from said second annular wall toward said notch and into a space between said protrusions of said clutch spring, said engaging section being inserted into said friction wheel.

4. The adjustable resistance tail plug as claimed in claim 2 , wherein said casing body has a large diameter portion that is adjacent to said rotary section and that has an inner diameter larger than an outer diameter of said friction wheel, and a taper portion that is located at one side of said large diameter portion opposite to said rotary section, said taper portion having an inner diameter decreasing from one side thereof adjacent to said large diameter portion toward another side thereof distal from said large diameter portion, the another side of said taper portion of said casing body that is distal from said large diameter portion having an inner diameter smaller than the outer diameter of said friction wheel.

5. The adjustable resistance tail plug as claimed in claim 2 , wherein said casing body has a large diameter portion adjacent to said rotary section and having an inner diameter larger than the outer diameter of said friction wheel, a taper portion located at one side of said large diameter portion opposite to said rotary section, a middle diameter portion located between said large diameter portion and said taper portion and having an inner diameter smaller than that of said large diameter portion, and a small diameter portion located at one side of said taper portion opposite of said middle diameter portion and having an inner diameter smaller than that of said middle diameter portion and smaller than the outer diameter of said friction wheel, said taper portion tapering from said middle diameter portion to said small diameter portion.

6. The adjustable resistance tail plug as claimed in claim 1 , wherein said friction wheel includes a wheel body threadably engaging said screw rod unit, and at least one friction member disposed on an outer periphery of said wheel body.

7. The adjustable resistance tail plug as claimed in claim 1 , wherein said fixed seat includes a fixed seat body extending in the direction of said axis, and a fixed hole formed in said fixed seat body, said fixed seat body having said first circumferential surface and said second circumferential surface.

8. The adjustable resistance tail plug as claimed in claim 7 , wherein said fixed hole is a non-circular hole, said fixed seat further including a fixed member that extends into said fixed hole and that is connected to said mounting bracket.

9. The adjustable resistance tail plug as claimed in claim 7 , the mounting bracket having a mounting frame, wherein said fixed hole is a non-circular hole, and permits the mounting frame to be inserted therein.

10. The adjustable resistance tail plug as claimed in claim 1 , wherein said screw rod unit includes a threaded member that permits said friction wheel to threadably engage therewith, and a fastener screwed in said threaded member, said fastener being inserted into and positioned in said casing body.

11. The adjustable resistance tail plug as claimed in claim 1 , wherein said screw rod unit includes a threaded member extending through said casing body, a fastener screwed to said threaded member, and a compression spring surrounding said threaded member and located between and abutting against said friction wheel and said casing body along said axis, said threaded member permits said friction wheel to threadably engage therewith, said threaded member extending into said fixed seat so as to be connected to said fixed seat, said threaded member having a threaded section, and a non-threaded section connected to one side of said threaded section and one side of said casing body along said axis.