JPH035514Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

This invention relates to the improvement of the sprocket that is attached to the inner side of the two inner and outer sprockets that are attached to a bicycle crank with a sprocket support arm, so that a small diameter sprocket can be additionally attached to the inner side without changing the shape of the crank. Regarding what has been improved.

[Conventional technology]

As shown in FIG. 5 of the present application, the crank 1 with sprocket support arms has a plurality of sprocket support arms 5 extending radially in a boss portion 4 provided with a crankshaft insertion hole 3 at the base end of the crank arm 2. It is composed of integrally... The sprocket mounting portion 6 formed at the tip of each support arm 5 has a flat mounting surface on its outer and inner surfaces, and is provided with a pressed piece 6a through which a mounting hole 7 is passed. Positioning outer surfaces 8a..., 8b... in the form of cylindrical outer surfaces facing radially outward are located on both the inner and outer surfaces of the piece 6a at positions located slightly inward in the radial direction from the mounting hole 7. It is provided by bulging the appropriate part in a stepped manner. Each positioning outer surface 8a..., 8b...
It is part of a cylindrical surface concentric with the crankshaft insertion hole 3. In the example shown in this figure, five support arms 5 are provided at equal intervals, but there may be three support arms 5. On the other hand, inner and outer sprockets 9 are attached to sandwich the pressed piece 6a of the support arm 5,
10 has a ring shape as a whole, has sprocket teeth 11 formed on its outer periphery, and has five mounting holes 12 corresponding to the mounting holes 7 drilled in each of the support arms 5. Then,
A cylindrical positioning inner surface 13 that can come into contact with the positioning outer surface 8 is formed at a portion located radially inward of these through holes 12 . This positioning inner surface 13 may utilize the inner circumferential surface of the ring-shaped part of the sprocket, but in the illustrated example, a stay extending radially inward from the ring-shaped part is provided, and the through hole 12 is formed in this stay. At the same time, the positioning inner surface 13 is formed on the inner end surface of the stay. The length of the stay is longer on the outer sprocket, which has a larger number of teeth and a larger diameter ring-shaped portion. Each of the above sprockets 9 and 10 has a through hole 12
... are arranged inside and outside of the piece to be pressed so as to match the mounting hole 7 on the crank side, and by inserting and tightening the bolt 14 and nut 15 in the mounting hole 7 and the through hole 12, It can be installed by sandwiching the pieces. At that time, the above-mentioned positioning outer surface 8 is located on the support arm 5 side of the crank, and the sprockets 9, 1
0 is provided with a positioning inner surface 13 that can come into contact with the positioning outer surface 8, so when these positioning outer surfaces 8 and the positioning inner surface are brought into contact with each other, the center of each sprocket 9, 10 and the axis of the crankshaft are aligned. Easily brought into harmony with one's heart. As a result, the through holes 12 can be easily aligned with the mounting holes 7 by only slightly rotating the sprockets 9 and 10 in the circumferential direction, and the sprocket mounting workability is greatly improved.

[Problem that the invention attempts to solve]

As mentioned above, in a gear crank consisting of a conventional crank with a sprocket support arm and a sprocket attached to the sprocket, basically only two sprockets 9 and 10 can be attached, sandwiching the support arm 5 from the inside and outside. Ta. Furthermore, if the bolt 14 mentioned above is lengthened, it is possible to add a third sprocket to the inside of the inner sprocket 9, but in that case, the third sprocket passes through the mounting hole 7. Since the sprockets cannot be made smaller than a circle, the three sprockets installed in this way must have similar outer diameters with not much difference in the number of teeth. The third front sprocket that is usually required is a small diameter sprocket with a fairly small number of teeth.
In the conventional example, it was not possible to meet these requirements without changing the crank. This device is attached to a crank that has multiple attachment arms extending radially from the center.
In a bicycle sprocket formed so that a powerful driving torque is transmitted to the outer peripheral teeth through the mounting arm, there is no need to change the length of the support arm of the crank or the sprocket mounting portion at the tip of the support arm. The objective is to make it possible to add a third sprocket with a smaller diameter.

[Means to solve the problem]

In order to solve the above problems, this invention takes the following technical measures. That is, the present invention provides a bicycle sprocket that is attached to a crank, the center of which is fixed to the shaft end of the crankshaft, and which has a plurality of sprocket support arms extending radially from the center. A plurality of mounting holes are provided on the circumference corresponding to the mounting holes, outer teeth are formed radially outward from these mounting holes, and radially inward from each of the mounting holes. a cylindrical inner positioning inner surface that is formed on one side and can come into contact with the cylindrical outer positioning surface of each of the sprocket support arms; a support part integrally formed to extend further radially inward from the positioning inner surface; , and a plurality of third sprocket mounting holes formed on the circumference at predetermined intervals.

[Action and effect]

As with the conventional sprocket, the sprocket of this invention includes a plurality of mounting holes and a cylindrical positioning inner surface facing radially inward, which is provided radially inward of each mounting hole. Therefore, by simply placing the inner positioning surface against the outer positioning surface provided on the sprocket mounting part of the crank support arm and rotating it slightly, you can easily match the above mounting hole with the crank side mounting hole.
The sprocket can be easily attached to the crank by inserting bolts into these through holes and attachment holes. Furthermore, in the present invention, a plurality of mounting holes for mounting the third sprocket are provided on the circumference at predetermined intervals in the support portion that extends integrally to a portion further radially inward from the positioning inner surface. Therefore, by setting the multiple mounting holes further radially inward than the mounting holes provided in the support arm of the crank, even the third sprocket, which has a considerably smaller diameter than the sprocket of this invention, can be installed. It can be installed without any problem. Moreover, since this third sprocket is attached to the sprocket attached to the crank, there is no need to make any changes to the crank. As described above, according to the bicycle sprocket of the present invention, the radial sprocket mounting arm integrally included in the crank prevents the sprocket from bending or deforming.
While maintaining the advantage of the sprocket support structure that uses a crank with a mounting arm, which allows powerful driving torque to be effectively transmitted to the outer teeth of the sprocket, this design does not require any changes to the crank side. This has the remarkable effect of making it possible to easily add a third sprocket with a smaller diameter.

[Explanation of Examples]

Hereinafter, embodiments of this invention will be described in detail with reference to FIGS. 1 to 4. In these figures, members or portions that are equivalent to those of the conventional example shown in FIG. 5 are given the same reference numerals. As shown in FIG. 1, a crank 1 with a sprocket support arm is attached to the shaft end of a crankshaft 19 of a screwless type that is rotatably inserted and supported in a hanger pipe 16 via two bearing parts 17 on the left and right. Furthermore, a piece to be pressed 6 is attached to the sprocket mounting portion 6 of the support arm 5 of the crank.
The inner sprocket 9 and the outer sprocket 10, which are arranged to sandwich the sprocket a, have through holes 12a,
12b and the mounting hole 7 drilled in the pinched piece 6a
It is attached by inserting the bolt 14 and nut 15 into the hole and tightening them together. Note that the nut 15 has a counterbore formed inside the through hole 12a so that the nut 15 is not exposed on the inner surface of the inner sprocket 9 and obstructs the running of the chain that is connected to the third sprocket 20, which will be described later. A special shape is used that has a flange that can be accommodated in the flange and a cylindrical body that extends from the flange, and that can be accommodated in the through hole 12a and the attachment hole 7. In both the inner sprocket 9 and the outer sprocket 10, positioning inner surfaces 13a and 13b are formed in the radially inward portions of the through holes 12a and 12b, and are cylindrical inner surfaces facing radially inward to facilitate installation. These positioning inner surfaces 13
a, 13b are in contact with and guided by cylindrical positioning outer surfaces 8a, 8b formed on the sprocket mounting portion 6 on the support arm side and facing radially outward, whereby the position in the direction perpendicular to the crankshaft is determined. As mentioned above, the bolts 14 and nuts 15 are used to connect the inner and outer sprockets 9 and 10 to the pressed piece 6.
The work of fixing by sandwiching a can be easily performed. Details of an example of the inner sprocket 9 featured in this invention are shown in FIGS. 2 and 3. As is clear from FIG. 2, in contrast to the conventional sprocket 9, in this inner sprocket 9, a support portion 21 is integrally extended inside the circle indicated by the imaginary line A, that is, the circle formed by the positioning inner surface 13a. ing. In this example, this support portion 21 includes a stay 22 including a mounting hole 12a for the crank.
is further extended radially inward as it is, and each of these stays 22 is connected by an annular reinforcing ring 23, and a mounting hole 24 is provided at the tip of the stay 22 for mounting the third sprocket 20.
is opened concentrically with the through hole 12a. The pitch circle of this mounting hole 24 is the pitch circle diameter of the mounting hole 26 of the commercially available small diameter sprocket 20 to be mounted (for example, in the case of a 28T sprocket).
74mm). In this example, as shown in FIG. 1, the crank-side positioning outer surface 8a is formed with an arcuate protrusion on the back surface of the support arm 5, and the radially outer surface of this protrusion is used as the positioning outer surface 8a.
Because the positioning inner surface 13a is used as It is formed using the inner wall of both sides. As a result, in this example, the stays 22 or the mounting holes 24 are
It is possible to arrange it on a radial line passing through a. As a result of the above, in the present invention, as shown in FIG. It can be conveniently installed using. In that case, there is a third sprocket on the inside of the inner sprocket 9.
A small-diameter sprocket 20 is placed so that the mounting hole 24 and the mounting through-hole 26 are aligned with each other with a spacer 27 in between, and the bolt 28 and nut 29 that are passed between the mounting hole 24 and the mounting through-hole 26 are tightened. Just wear it. Note that the bolts 28 and nuts 29 are attached to the inner and outer sprockets 9 and
Substantially the same bolts 14 and nuts 15 used to attach 10 are used. The second embodiment of the sprocket 9 of the present invention is shown in the fourth embodiment.
As shown in the figure. In this example, the third sprocket 20
A support stay 22 for supporting the mounting hole 12a is provided at a position offset in the circumferential direction with respect to a radial line passing through the attachment hole 12a. More specifically, an inner ring 23' having an inner circumferential circle forming a positioning inner surface 13a
A support stay 22 extends from a portion of the inner peripheral surface of the inner ring 23' that is displaced in the same direction as the mounting hole 12a, and a mounting hole 24 is provided at the end of the support stay 22. Even in this case, the effects of the present invention can be exerted in the same manner as in the first embodiment. Of course, the scope of the present invention is not limited to the embodiments described above, and in particular, the shape of the support portion 21 for attaching the third sprocket 20 can be modified in various ways.

[Brief explanation of drawings]

FIG. 1 is a partially sectional side view of a bicycle gear crank equipped with the sprocket of the present invention, and FIG. 2 is a rear view of the first embodiment of the sprocket of the present invention.
3 is a sectional view of the sprocket shown in FIG. 2, FIG. 4 is a back view of a second embodiment of the sprocket of the present invention, and FIG. 5 is an exploded perspective view of a conventional gear crank. 11...Tooth portion, 12...Mounting hole, 13...
Positioning inner surface, 21...Support part, 24...Mounting hole.

Claims (1)

[Scope of utility model registration request] A bicycle sprocket that is attached to a crank, the center of which is fixed to the shaft end of the crankshaft, and has a plurality of sprocket support arms extending radially from the center, the sprocket having a plurality of sprocket support arms that correspond to the mounting holes of each of the sprocket support arms. a plurality of mounting holes provided on the circumference; an outer peripheral tooth portion formed radially outward from the mounting holes; and a peripheral tooth portion formed radially inward from each of the mounting holes; A cylindrical inner positioning inner surface that can come into contact with the cylindrical outer positioning outer surface of each sprocket support arm, a support part integrally formed to extend radially inward from the positioning inner surface, and a predetermined interval between the sprocket support arms. A bicycle sprocket, comprising a plurality of mounting holes for mounting a third sprocket formed on the circumference.