Narrow—wide teeth chainring

Abstract

A sprocket for engagement with a drive chain has a plurality of teeth extending radially from a periphery of the sprocket, including a first and a second group of teeth; the teeth of the first group and the second group are alternately arranged so that each tooth of the first group is followed by a tooth of the second group, and vice versa; each tooth of the first group having a first maximum width, each tooth of the second group having a second maximum width which is larger than the first maximum width; each tooth of the second group has a protrusion on at least one lateral face of the tooth; the outer lateral face of the protrusion extends over a first portion of the lateral face of each tooth of the second group, the length being 50% of the length of the respective tooth or less.

Claims

1. A sprocket for engagement with a drive chain, comprising: a plurality of teeth extending radially from a periphery of the sprocket; each tooth of the plurality of teeth extending over a given circumferential length of the sprocket; each tooth of the plurality of teeth having a front flank contacting a roller of the drive chain in regular drive operation and a rear flank; the plurality of teeth including a first group of teeth and a second group of teeth, wherein the teeth of the first group and the second group are alternately arranged so that each tooth of the first group of teeth is followed by a tooth of the second group of teeth, and vice versa; each tooth of the first group of teeth having a first maximum width; each tooth of the plurality of teeth of the second group of teeth having a second maximum width which is larger than the first maximum width, wherein each tooth of the plurality of teeth of the second group of teeth has a protrusion on at least one lateral face of the tooth; wherein an outer lateral face of the protrusion extends over a first portion of the at least one lateral face of each tooth of the plurality of teeth of the second group of teeth, wherein the length of the first portion is 50% of the length of the respective tooth of the plurality of teeth or less and wherein the protrusion is located adjacent to the front flank of each tooth of the plurality of teeth of the second group of teeth, wherein a width of the respective tooth adjacent to the rear flank is equal to the width of each tooth of the first group of teeth.

2. The sprocket of claim 1 comprising two lateral faces, wherein each tooth of the plurality of teeth of the second group of teeth has a protrusion on each of the two lateral faces of each tooth of the plurality of teeth.

3. The sprocket of claim 1, wherein each tooth of the second group of teeth comprises front edges and the front edges are chamfered.

4. The sprocket of claim 1, wherein each tooth of the plurality of teeth comprises rear edges and the rear edges of each tooth are chamfered.

5. The sprocket of claim 3, wherein the extension of the chamfer of each of the front edges of each tooth of the plurality of teeth of the second group of teeth in the circumferential direction is between 1.5 and 2 times the extension of the chamfer of each of the rear edges of the same tooth.

6. The sprocket of claim 1, wherein each protrusion is chamfered or rounded towards the tooth tip.

7. The sprocket of claim 1, wherein each protrusion extends from the tip of the respective tooth to the bottom of the space between two adjacent teeth of the sprocket.

8. The sprocket of claim 4, wherein the extension of the chamfer of each of the front edges of each tooth of the plurality of teeth of the second group of teeth in the circumferential direction is between 1.5 and 2 times the extension of the chamfer of each of the rear edges of the same tooth.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The features and advantages of the invention will be more fully understood from the following description of one or more embodiments, in conjunction with the accompanying drawings, in which:

(2) FIG. 1 shows a schematic view of a drive chain of a bicycle;

(3) FIGS. 2 to 4 show a top section of a sprocket, wherein FIGS. 3 and 4 show identical side views of the sprocket and FIG. 2 depicts the sections of the teeth of the sprocket of FIG. 3 cut along line B-B which follows the lines connecting the axes of rollers of a chain engaging the sprocket; and

(4) FIG. 5 shows a sectional view of the chain of FIG. 1 with the engaged teeth of the sprocket of FIGS. 2 to 4.

(5) FIG. 6 shows a sectional view of the chain of FIG. 1 with the engaged teeth of a first alternative embodiment of a sprocket.

(6) FIG. 7 shows a sectional view of the chain of FIG. 1 with the engaged teeth of a second alternative embodiment of a sprocket.

DESCRIPTION OF EMBODIMENTS

(7) FIG. 1 shows a top view of a stretched roller chain as conventionally used for driving a bicycle or an e-bike. The drive chain is composed of a succession of outer chain links 1 followed by inner chain links 2. Each outer chain link 1 is composed of two outer link plates 3 and 4. The inner faces of the outer link plates 3 and 4 contact the outer faces of inner link plates 5 and 6, which form the inner chain link 2. The inner faces of the inner link plates 5 and 6 contact a roller 7 at each end of the inner chain links 5 and 6. A pin 8 extends through holes in the end sections of the outer link plates 3, 4, and inner link plates 5, 6, as well as through the roller 7. The ends of the pins 8 are deformed in order to securely fix the link plates 3-6 to the rollers 7. It can be seen in FIG. 1 that the drive chain has a succession of link spaces with a great width D.sub.1 between the outer link plates 3, 4, and link spaces with a smaller width D.sub.2 between the inner link plates 5, 6.

(8) FIGS. 2 to 4 explain the structure of the new sprocket described herein. The sprocket is preferably a single chainring that may be fixed to a crank set of a bicycle. The arrows 9 and 10 in FIGS. 2 and 3 indicate the direction of rotation during regular drive operation of the sprocket 11 when driven by the crank in order to move the bicycle forward. The head of each of the arrows 9 and 10 indicates the forward direction of the teeth on the upper part of the sprocket 11 shown in FIGS. 3 and 4. The front flank of the teeth contacts the rollers 7 of the chain 15 during such drive operation and is located on the right side of each tooth shown in FIGS. 2, 3 and 4. FIG. 2 shows sectional views of the two different varieties of teeth of the sprocket 11 cut along the line B-B in FIG. 3. The line B-B is defined by straight lines connecting the axes of the two rollers of a chain link accommodated by the spaces between the teeth of the sprocket.

(9) The sprocket 11 has two different kinds of teeth 12, 16 which alternate. The first group of teeth are narrow teeth 12 that have a small width and a basically rectangular section in a plane perpendicular to this radial center line of each tooth 12. The tip of each narrow tooth 12 is chamfered or rounded so that the width of the narrow tooth 12 decreases in the direction towards the tip of the tooth 12. The narrow teeth 12 have a front flank on the right side contacting the roller in regular drive operation and a rear flank on the left side in the drawings. Both the front flank and the rear flank are provided with a chamfer 13, 14, in order to avoid physical contact with the inner chain links 5, 6 of the chain 15 and to provide a gap between the inner chain links 5,6 and the flanks for easy penetration of the teeth. A wide tooth 16 is arranged between each pair of narrow teeth 12. The wide tooth 16 has a protrusion 17, 18 on each lateral face 19, 20. The rear portions of the lateral faces 19, 20 of the wide teeth 16 are plane. The protrusion 17, 18, basically extends over the portion of the tooth adjacent the front flank 21 of the wide tooth 16. The protrusion 17,18 generally covers the front half of the lateral face 19, 20 of the wide tooth 16. As can be seen in FIG. 4, the protrusion ends a short distance of approximately 0.3 millimeters from the centerline of the wide tooth 16.

(10) In the direction towards the center of the sprocket 11, the protrusion 17,18 reaches a straight line tangent to the radius of the space between the protrusion 17, 18 and the adjacent narrow tooth 12. The angle between the bottom edge of the protrusion 17 visible on the right-hand side of FIG. 4 and the central edge of the protrusion 17 is approximately 105°.

(11) As can be seen in FIGS. 2 and 4, the wide tooth 16 has a chamfer 22 at the edges of each of the protrusions 17, 18, facing the roller 7 of the chain 15. Again, this chamfer 22 avoids physical contact between lateral parts of the chain 15 and the protrusions 17, 18. The chamfer 22 at each of the front edges of the wide tooth 16 extends over 1 mm in the circumferential direction of the sprocket 11 and over 0.75 mm in the lateral direction. The rear chamfer 14 on the edges of each wide tooth 16 corresponds to the rear chamfer 14 on the edges of each narrow tooth 12 and has a lateral and circumferential extension of 0.5 mm.

(12) FIG. 5 shows the engagement of the teeth 12 and 16 of the sprocket 11 in the link spaces of the chain 15. FIG. 5 is a sectional view of the chain 15 and the sprocket taken along straight lines extending between the axes of the rollers 7 or pins 8 of the chain 15. It can be seen that the wide teeth 12 have a somewhat T-shaped form. The wide part only extends over the front portion of the wide teeth 16. The rear portion of the wide teeth 16 has basically the same width as the narrow teeth 12. The extended width of the wide teeth 16 provides for good guidance of each tooth in the chain link spaces between the outer link plates 3, 4. At the same time, the wide tooth 16 does not occupy the entire link space. In case of a clogging of the link space, the tooth can more easily enter the link space compressing any dust or soil into the free spaces. Nevertheless, the front part of the wide tooth 16 has an increased stability and provides the necessary lateral guidance for securely engaging with the chain 15.

(13) FIGS. 6 and 7 show identical views of the chain 15 and the narrow teeth 12 and wide teeth 16′, 16″ of different embodiments of the sprocket. Identical parts are marked with the identical reference numbers as in FIGS. 1-5. In FIG. 6, each wide tooth 16′ has a protrusion adjacent the front flank on the left lateral surface and a protrusion adjacent the real flank on the right lateral surface. As a further alternative, the protrusions may adjacent to the rear flanks of the tooth on both lateral surfaces. FIG. 7 shows a further alternative of the shape of the wide teeth 16″ with lateral protrusions in the middle of the two lateral surfaces of each wide tooth 16″. In all embodiments, the longitudinal extension of the outer lateral face of the protrusion equals less than half of the longitudinal extension of the tooth itself reducing the sectional area of the wide teeth while maintaining good lateral guidance.

LIST OF REFERENCE NUMBERS

(14) 1 outer chain link 2 inner chain link 3 outer link plate 4 outer link plate 5 inner link plate 6 inner link plate 7 roller 8 pin 9 direction of rotation 10 direction of rotation 11 sprocket 12 narrow tooth 13 chamfer 14 chamfer 15 chain 16 wide tooth 16′ wide tooth 16″ wide tooth 17 protrusion 18 protrusion 19 lateral face 20 lateral face 21 front flank 22 chamfer D.sub.1 great width D.sub.2 smaller width