Please refer to FIGS. 1 and 2, a conventional one-way clutch includes a first collar 1, a second collar 2, a circular holding frame 3, a plurality of rollers 4 and a plurality of elastic elements 5 at a number corresponding to the rollers 4. The first collar 1 and the second collar 2 are concentric and rotate relatively to each other. The first collar 1 may be held inside the second collar 2, and has a plurality of cavities 6 at a number corresponding to the rollers 4. The circular holding frame 3 is located between the first collar 1 and second collar 2 and fixedly located on the first collar 1, and also has a plurality of slots 7 at a number corresponding to the rollers 4 and exposing the cavities 6. Each cavity 6 has an inclined bottom surface 8 with a lower portion spaced from the second collar 2 at a distance greater than the diameter of the roller 4, and a higher portion spaced from the second collar 2 at a distance smaller than the diameter of the roller 4.
One roller 4 is held in the slot 7 and also the cavity 6. The elastic elements 5 press the side walls of the slots 7 to push the rollers 4 to contact with the higher portions of the inclined bottom surfaces 8.
By means of the aforesaid construction, the second collar 2 can be rotated against the first collar 1 towards the higher portions of the inclined bottom surfaces 8. As the rollers 4 are in contact with the higher portions of the inclined bottom surfaces 8, they also are in contact with the second collar 2 and first collar 1 at the same time. Hence the rollers 4 can serve as transmission medium to allow the second collar 2 to drive the first collar 1 rotating.
When the rotational speed of the first collar 1 is greater than that of the second collar 2, it drives the rollers 4 to contact with the lower portions of the inclined bottom surfaces 8 (as shown in FIG. 2), and then the rollers 4 can be separated from the second collar 2, so that torsional force cannot be transmitted between the second collar 2 and first collar 1.
FIG. 3 illustrates another conventional one-way clutch structure which has a first collar 1A located outside a second collar 2A, namely the first collar 1A and second collar 2A can be switched at different positions. This provides another equivalent structure as mentioned above and also can provide same transmission effect.
The conventional transmission structure requires the elastic elements 5 be positioned transversely, hence a greater amount of space is occupied that limits the number of the rollers 4 that can be deployed. In other words, when the second collar 2 rotates, the number of the rollers 4 serving as the transmission medium is limited, and the torsional force transmitted to the first collar 1 also is limited, hence such a structure is not adaptable to the condition that a greater torsional force is required for transmission.
Moreover, during assembly of the conventional structure the elastic elements 5 must be compressed, and incidental dropping of the elastic elements 5 could happen. Assembly is more difficult and requires more skillful workers equipped with special tools. All this makes production cost higher.