Freewheel assembly switchable between fixed-gear and freewheel modes

1. A freewheel assembly for a bicycle, comprising:

(a) a sprocket; and

(b) a drive ring that is mountable on a freewheel hub;

wherein the sprocket and drive ring are in a freewheeling relationship, where the sprocket freely rotates counterclockwise relative to the drive ring, but is rotationally locked to the drive ring when rotating clockwise, and

a reversible non-frictional positive locking mechanism, which, when engaged, rotationally locks the sprocket to the drive ring so as to prevent freewheeling, thereby converting the assembly to fixed-gear operation.

2. The freewheel assembly of claim 1 , wherein the non-frictional positive locking mechanism comprises a pin or set screw movably affixed to the sprocket, said pin or set screw being movable into engagement with a cavity in the drive ring, so as to rotationally lock the drive ring to the sprocket.

3. A hub for a bicycle wheel, comprising a freewheel hub and the freewheel assembly according to claim 2 .

4. A bicycle wheel, comprising the hub according to claim 3 .

5. The freewheel assembly of claim 1 , wherein the non-frictional positive locking mechanism comprises one or more pins affixed to a rotating ring and set into spiral tracks in the sprocket, configured so that rotation of the ring moves the pins through the tracks and the spiral tracks imparts an axial movement to the pins, and wherein the axial movement brings the pins into recessed pin receiving cavities in the drive ring, resulting in a mechanical connection between the sprocket and the drive ring.

6. A hub for a bicycle wheel, comprising a freewheel hub and the freewheel assembly according to claim 5 .

7. A bicycle wheel, comprising the hub according to claim 6 .

8. A hub for a bicycle wheel, comprising a freewheel hub and the freewheel assembly according to claim 1 .

9. A bicycle wheel, comprising the hub according to claim 8 .