Foldable Bicycle Frame

The present invention relates to a foldable bicycle frame capable of being assembled instantaneously for use and folded easily and simply to facilitate storing when the bicycle is not used.

In conventional foldable bicycles, the folding and assembling are generally difficult and require specific tools and troublesome operations for rotating levers many times and so forth, resulting in it being impractical. In addition, it takes a considerable time to fold the bicycle when the bicycle is not used.

Accordingly, an object of the invention is to provide a foldable bicycle frame having a rigid construction and capable of being easily and promptly folded or assembled.

The invention will be described hereinunder in more detail with reference to the accompanying drawings.

FIG. 1 is a side elevational view of a bicycle according to one embodiment of the invention;

FIG. 2 shows a portion of the embodiment of FIG. 1 during folding;

FIG. 3 shows the embodiment shown in FIG. 1 after folding;

FIG. 4 is a partial view of the embodiment of FIG. 1, showing the upper seat stay being disengaged from the gripping portions of the locking plate by the gripping action of a hand;

FIG. 5 is a bottom view of a seat stay and the locking plate;

FIG. 6 is a an end view of the locking plate; and

FIG. 7 is a bottom view of the locking plate.

A hanger bracket 3 having a hanger portion 2 is provided on the mid portion of a lower frame 1. A front frame 9 formed integrally with a head pipe 8 is rotatably supported by a shaft 4 attached to the front end of the frame 1. Forks 10 provided at the rear end of the lower frame 1 support a rear wheel axle 11. A shaft attached to the hanger bracket 3 rotatably supports a seat tube 15. A front supply stay 18 is rotatably supported between a shaft 16 attached to the seat tube 15 and a shaft 17 attached to the front frame 9. A seat stay is divided into an upper seat stay 20 and a lower seat stay 25 so as to be able to be pivoted at its mid portion. Each of the upper and lower seat stays is constituted by a pair of members. The outer end of the upper seat stay 20 is pivotally secured to a portion of the seat tube 15 near the upper end of the latter, while the lower seat stay 25 is pivotally secured to the forks 10 provided at the rear end of the lower frame 1. The inner ends of the upper seat stay 20 and the lower seat stay 25 are connected to each other by means of a locking plate 24. More specifically, the inner end of the lower seat stay 25 is fixed to the locking plate 24, while the inner end of the upper seat stay 20 is rotatably and slidably secured by means of a connecting shaft 23 inserted through the locking plate 24. A compression spring 26 acts on the connecting shaft 23 so as to urge the two members of the upper seat stay 20 apart. The connecting ends of the upper seat stay 20 are fittingly supported by gripping portions 27 provided at both sides of the locking plate 24. The locking plate 24 is provided with a stop member or stopper 28 which prevents excessive sliding movement of the members of the upper seat stay 20 when the members are pressed toward each other in overcoming the force of the compression spring 26.

The folding and assembling of the foldable bicycle frame are effected in the following manner. Both members of the upper seat stay 20 fitting in the gripping portions 27 of the locking plate 24 by the action of the compression spring 26 and opposing each other are gripped by one hand as shown in FIG. 4, so that both members of the upper seat stay are slid inwardly, overcoming the force of the compression spring 26, into contact with the stopper 28 of the locking plate 24. The connecting ends of the upper seat stay then come out from the gripping portions 27 of the locking plate 24, so that the upper seat stay 20 is then able to rotate around the connecting shaft 23.

The outer end of the upper seat stay 20 is pivotally secured to the portion of the seat tube 15 near the upper end of the latter, while the lower end of the seat tube 15 is pivotally secured to the hanger bracket 3. The lower seat stay 25 is also pivotally secured to the forks 10 of the lower frame 1. Thus, the lower frame 1, front stay 18, upper seat stay 20 and the lower seat stay 25, in combination, constitute a quadrilateral link. As the upper seat stay 20 is rotated in the direction of arrow A in FIG. 2, the lower seat stay 25 and the seat tube 15 are rotated in the directions of arrows B and C, respectively, so that the frame is folded in such a manner that the seat tube 15 is inclined rearwardly until it comes into contact with the rear wheel axle 22.

To the contrary, when the frame is assembled from the folded state, the upper seat stay 20, the lower seat stay 25 and the seat tube 15 are rotated in a direction opposite to the arrows in FIG. 2, until the upper and lower seat stays 20 and 25 form a substantially straight line. Since the connecting ends of the member of the upper seat stay 20 are spread apart by the force of the compression spring 26, the connecting ends engage the gripping portions 27 of the locking plate 24, thus completing the assembling.

As has been described, according to the invention, all of the constituents of the frame are formed of metallic materials having a high mechanical strength and, hence, a high reliability, and can be folded and assembled easily and instantaneously without requiring any specific tools.

Namely, the folding and assembling can be made by a simple and single action of lifting and depression of the upper seat stay 20.

In addition, any excessive bending at the juncture between the upper seat stay 20 and the seat tube 15 is effectively prevented by the action of the stopper 28 to ensure a stable folding and assembling operation.