Bicycle multiple chainwheel

Details Bicycle multiple chainwheel Bicycle multiple chainwheel

1990-07-02

1992-07-28

Dang, Hoang C.

Endless belt power transmission systems or components

Positive drive pulley or guide roll

And additional coaxial surface for engaging same belt in...

74457, 745942, 474164, F16H 5530

Patent

active

051336952

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a bicycle multiple chainwheel having at least two diametrically different sprockets. More specifically, the invention relates to a multiple chainwheel which is designed to provide smooth chain shifting from a larger sprocket to a smaller sprocket.


BACKGROUND ART

Many of currently available bicycles not only have a multiple freewheel to constitute a rear gear mounted on a rear wheel hub, but also incorporate a multiple chainwheel to constitute a front gear (front gear being usually called "chainwheel") mounted on a pedal crank, thereby increasing the number of selectable speeds. When, for example, a freewheel having five sprockets is combined with a chainwheel having three sprockets, it is possible to select fifteen speeds.
In a multiple chainwheel, a diametrically largest sprocket is located at the right as viewed in the bicycle running direction, and progessively smaller sprockets are arranged toward the left. A maximum speed is obtainable when the chain is in engagement with the largest sprocket.
With such a chainwheel, a speed change is performed by causing a front deraileur to laterally press a portion of the chain entering to the chainwheel in rotation, with the result that the chain is shifted from a smaller sprocket to a larger sprocket or vice versa. Obviously, the speed change performance of the chainwheel is determined by the smoothness and promptness in disengaging the chain from a presently engaging sprocket for engagement with a target sprocket.
However, a problem called "chain locking phenomenon " arises in shifting the chain from a larger sprocket to a smaller sprocket. This phenomenon is now described with reference to FIGS. 9 through 13.
FIGS. 9, 10, 11 and 13 are views, as seen from the left side of the bicycle, showing the successive stages of shifting a chain C from a larger sprocket 1 to smaller sprocket 2 of a chainwheel CW to illustrate the problem. FIG. 12 is a view as seen in the direction of an arrow XII in FIG. 11.
In FIGS. 9, 10, 11 and 13, the larger sprocket 1 is located farther from the viewer. The chain C comprises pairs of inner link plated Pa1, Pa2, and pairs of outer link plates Pb1, Pb2 which are alternate with the pairs of inner link plates and connected thereto by means of roller pins R. The chain C is engageable with each sprocket in a manner such that each tooth of the sprocket is inserted between a corresponding pair of inner link plates Pa1, Pa2 or outer link plates Pb1, Pb2 with the roller pins R received between the sprocket teeth.
In shifting the chain C in engagement with the larger sprocket 1 to the smaller sprocket 2, a portion of the chain C moving into engagement with the larger sprocket 1 is pressed toward the smaller sprocket 2 by an unillustrated front deraileur, thereby causing the chain C to disengage from the larger sprocket 1. The chain C is subjected to a tension applied by a tension spring incorporated in an unillustrated rear deraileur. Therefore, the chain C having disengaged from a tooth ta of the larger sprocket 1 starts shifting to the smaller sprocket 2 in a manner such that the chain C extends tangentially to the smaller sprocket from the roller pin RO (disengagement starting roller pin) immediately following the pair of link plates which have disengaged from the larger sprocket tooth ta, as shown in FIG. 10.
Now, a tangential line 1 for the smaller sprocket 2 is drawn from a teeth interval center 01 of the larger sprocket 1 located at the disengagement starting roller pin RO to a teeth interval center 02 of the smaller sprocket 2. When the length of the tangential line 1 is larger than an integral multiple (n) of the chain pitch (p) by a fragmentary amount x (i.e., the distance between the teeth interval centers 01 and 02 being np +x), the chain locking phenomenon occurs upon application, to the chainwheel CW, of a large rotational force.
Normally, at the time of chain shifting, the chainwheel rotates for a while with laterally displaced roller pins R (following the disengagement starting

REFERENCES:
patent: 4181033 (1980-01-01), Nagano
patent: 4259880 (1981-04-01), Ueno
patent: 4348200 (1982-09-01), Terada
patent: 4519791 (1985-05-01), Nagano
patent: 4521207 (1985-06-01), Huoted
patent: 4522611 (1985-06-01), Hiatt
patent: 4773893 (1988-09-01), Su et al.
patent: 4813916 (1989-03-01), Valin
patent: 4889521 (1989-12-01), Nagano

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