Multiple sprocket for a bicycle

Abstract

A multiple sprocket with differently sized sprockets for receiving a chain and for transmitting a peripheral force introduced by the chain to a hub of a rear wheel of a bicycle, with the option of changing the chain from one sprocket to another by means of a switching device, the sprocket and its teeth having switching aids that both facilitate gear changes and contribute to maintaining the engagement of the chain in the teeth of the sprocket, characterized by that the sprocket (6) for guiding the chain (2) in the area of ​​its root circle (7) has a sprocket width (11) which is insignificantly smaller than the distance between the inner plates (5) determined by the roller (3) of the chain (2), the resulting slight play of the chain (2) on the tooth (9) relating to a guide area (18) of a tooth gap base (19), and the axial guidance of the chain (2) on the sprocket (6) results essentially from the projection (8) of the inner plates (5) relative to the roller (3) in the guide area (18) on the root circle (7) of the sprocket (6).

Description

[0001] The invention relates to a multiple sprocket with differently sized sprockets for receiving a chain and for transmitting a circumferential force introduced by the chain to a hub of a rear wheel of a bicycle, with the possibility of changing the chain from one sprocket to another by means of a switching device, wherein the sprocket and its teeth have switching aids which both facilitate the gear change and contribute to maintaining the engagement of the chain in the teeth of the sprocket.

[0002] Gear changes on multiple sprockets can now be performed easily and safely with the help of a rear derailleur, provided the rider observes certain rules. For example, it's advisable not to pedal backward without pedaling at certain positions on the sprockets, or to shift multiple gears at once with high torque. Furthermore, sufficiently high pedal speeds are required when shifting.

[0003] To enable controlled shifting to smaller sprockets, the chain must be guided on the sprocket until a predetermined position is reached. In this position, the rollers run into the gaps between the teeth of the smaller sprocket when the bike moves down, preventing the chain from riding on its teeth. This results in a virtually jerk-free shifting process that can even be performed under load. The problem with controlled shifting to the next smaller sprocket is preventing the chain from immediately dropping and bypassing the designated positions. Even if the chain moves down at the designated positions, there is no guarantee that the chain will ride on the teeth with its plate links due to lateral offset, even if the rollers are in the correct position in relation to the gaps between the teeth.

[0004] In order to achieve the switching speed without over-shifting travel at the switch and at the same time a smooth transition of the chain, a number of improvements were proposed, such as in GB 475 021 A of November 11, 1937, where switching channels were incorporated into the toothing on the ring gear in both directions of rotation in order to create a low-noise transition for the chain at one point on the circumference.

[0005] According to European patent EP 0 642 972 B1, a number of modifications are made to the teeth of the sprocket and to the sprocket itself in order to facilitate shifting of the chain to both the smaller and the larger sprocket, particularly under load, with at least one position for changing the chain for both shifting directions.

[0006] DE 203 17 269 U1 shows a front sprocket that prevents the chain from slipping.

[0007] While these suggestions make it easier for technically minded riders to shift gears with fewer errors, an internal series of tests still predicts a 30% error rate. Shifting errors can, however, cause a chain to break under load and also subject the rider's muscles to a strong jolt, which can lead to cramps while riding.

[0008] The solutions proposed in this invention focus on specific sprocket geometries and can thus be specifically adapted to the respective size of the sprocket in question. Several changes in the geometry, which have the same effect, lead to optimal chain guidance against the deflection forces that occur during shifting: • The width of the sprocket in the area of ​​the root circle is increased considerably, so that the axial guidance of the chain on the sprocket is essentially achieved by a projection of the partial diameter of the inner plates compared to the diameter of the roller in the guide area at the root circle of the sprocket. • A shallow guide bevel runs along the tooth from a guide area on the root circle to the area of ​​the uppermost contact point of the roller on one of the flanks of the tooth, whereby the width of the tooth is reduced towards the top so that the inner plates do not become stuck due to the large sprocket width. When the roller engages in each tooth gap base, the chain is aligned with the sprocket and centers itself after being rejected either by the guide bevel or by a first rejection chamfer when shifting. Outer plates are not involved in guiding the chain. It has proven useful for the guide bevel to have an angle of 10° to 20° to the flat surface of the sprocket. For smaller sprockets, the angle is preferably in the range of 5° to 15°. • Towards the tip of the tooth, the guide bevel is followed by the much more steeply inclined first deflection bevel, which on the one hand deflects the chain again and throws it back to its starting position even if strong shifting forces deflect the chain so far despite the guide bevel described above that it threatens to descend uncontrollably towards the smaller sprocket. On the other hand, the first deflection bevel also acts as a lead-in bevel when the chain descends in a controlled manner from the larger to the smaller sprocket and is deflected too far by the chain arc created in the process. This directs the chain back again and prevents it from riding up. The second deflection bevel also serves to prevent the chain that is in engagement with a sprocket from engaging at the tip of the tooth, but rather deflects it in order to maintain the original engagement of the chain. • The first deflection bevel is followed by a second deflection bevel, which together forms a ridge as the uppermost elevation of the tooth. The second deflection bevel is shorter and steeper than the flat surface of the tooth, and is therefore spaced approximately one-third of the sprocket width from the ridge to the flat surface of the respective sprocket facing the smaller sprocket. A key feature is that the first deflection bevel and the second deflection bevel, required for shifting the chain to larger sprockets, have no vertical transition area. This results in optimal use of the available sprocket width and also improved shifting quality during uncontrolled shifting operations across multiple sprockets. • The proposed gear rim geometry is particularly suitable for the production of turned blanks for milled gear rim hollow bodies.

[0009] State-of-the-art cassette hubs consist of a multitude of sprockets, all lined up on a carrier of a rear wheel hub and connected to it in a rotationally fixed manner. However, multi-chain sprockets of the proposed type consist of only two parts: a largest sprocket and the hollow sprocket body, which are connected to each other and to the carrier in a rotationally fixed manner. To produce a blank for the hollow sprocket body, it is turned from solid material with all internal and external contours and sprockets. The hollow sprockets are milled at the tooth gaps and below the sprockets to create a cassette hub optimized in terms of weight and strength. Further weight reduction can be achieved by reducing the sprocket width below the root circle, which can be achieved with annular recesses.Very thin wall thicknesses can be achieved, which ensure sufficient strength for the hollow body of the gear rim if milling operations below the gear rims are to be avoided.

[0010] All in all, according to this invention, the following four interconnected elements constitute the improvement of the proposed gear ring shapes compared to the prior art: • the guide bevel • the first rejection phase • the second deflection phase and • the low axial play of the chain on the sprockets in the area of ​​their root circles.

[0011] The invention aims to create a multi-chain sprocket whose sprockets have a geometric shape that optimally guides the chain against the deflection forces that occur during shifting. Shifting errors are to be avoided even if the chain does not ascend or descend in the intended positions. Furthermore, an optimum balance between weight and strength is to be achieved.

[0012] The solution to the problem is described in the characterizing parts of the main claim and the two subordinate claims. Further details can be found in the respective subclaims.

[0013] Several sketches illustrate a multi-gear sprocket for a hub on the rear wheel of a bicycle. They show: Fig. 1 a chain with a roller and inner plates on a sprocket in engagement with a tooth, the flat surface of which facing the larger sprocket has a guide bevel, followed by a first deflection chamfer and a second deflection chamfer in partial section; Fig. 2 a multiple sprocket, consisting of a hollow sprocket body and a largest sprocket on a carrier of a hub in partial section; Fig. 3 a section of the hollow body of the toothed rim with the design of a tooth tip and with recesses in partial section; Fig. 4 a representation of an annular guide area of ​​the inner plates on the gear rim along its root circle as a sketch.

[0014] According to the Fig. 1 shows a partial section of a sprocket 6 of a sprocket hollow body 1, with which a chain 2 having a roller 3, an outer plate 4 and an inner plate 5 cooperates. Furthermore, it can be seen that the roller 3 rests against the root circle 7 of the sprocket 6 and the two inner plates 5 enclose a tooth 9 with a sprocket width 11 with a slight play, wherein the inner plates 5 form a projection 8 relative to the root circle 7, since they have a larger partial diameter than the roller 3. A tooth 9 has a guide bevel 12 pointing towards the larger sprocket 6, which extends from the root circle 7 to a tooth tip 10 and forms an angle 13, as can be seen from the Fig. 3. The angle 13 is preferably designed with a size of 10° to 20°. The contour of the tooth tip 10 is further formed by a first deflection chamfer 14 and by a second deflection chamfer 15, the first deflection chamfer 14 and the second deflection chamfer 15 forming a roof shape with a ridge 16 as the highest elevation. The less inclined first deflection chamfer 14 and the guide bevel 12 together take up approximately two-thirds of the entire gear rim width 11 in the projection along the flat surfaces, while the second more inclined second deflection chamfer 15, located opposite the ridge 16, only takes up approximately one-third of the gear rim width 11.

[0015] The Fig. 2 shows a multiple sprocket consisting of a largest sprocket 20 and the sprocket hollow body 1. The largest sprocket 20 and the sprocket hollow body 1 are connected to each other and to a driver 21 in a rotationally fixed manner, wherein the driver 21 transmits the introduced torque to a hub 22 of the bicycle.

[0016] From the Fig. 3 further shows that the radially inward-facing, disc-shaped extension of the sprockets 6 has a recess 17 machined during turning, which is so deep that the remaining disc-shaped material makes up approximately half of the sprocket width 11 and provides just sufficient strength for machining and for transmitting the torques introduced by the chain 2. These recesses 17 achieve low wall thicknesses inside the sprocket hollow body 1, with the advantage that no further milling operations are required there to reduce weight. Since the blank of the sprocket hollow body 1 is produced from solid material primarily by turning operations, the inventive contour of the sprockets 6 is finished during this operation.This contour includes the guide bevel 12, the first deflection chamfer 14, the second deflection chamfer 15, the flat surface facing the smaller gear rim 6 and also the recesses 17. These recesses 17 have the advantage that milling operations can be carried out on the teeth 9 without sacrificing the filigree structure of the gear rim hollow body 1.

[0017] Finally, the Fig. 4 shows a partial area of ​​the gear rim 6 with three teeth 9, just as two rollers 3 with an inner link plate 5 fit into a tooth gap base 19, thereby creating a guide area 18 that forms around the tooth gap base 19 in the area of ​​the root circle 7 with a width that corresponds to the projection 8, namely the difference between the diameter of the roller 3 and the partial diameter of the inner link plate 5. In this guide area 18, the clearance between the gear rim width 11 and the distance between the inner links 5 determined by the roller 3 is at its smallest. List of reference symbols 1 gear ring hollow body 2 chain 3 rolls 4 outer flap 5 inner flap 6 sprocket 7 Foot circle 8 Overhang 9 tooth 10 tooth tip 11 Sprocket width 12 guide bevel 13 angles 14 first rejection phase 15 second rejection phase 16 First 17 Recess 18 Management area 19 Tooth gap base 20 largest sprocket 21 carriers 22 Hub

Claims

[1] Multiple sprocket with different sized sprockets for receiving a chain and for transmitting a circumferential force introduced by it to a hub of a rear wheel of a bicycle with the possibility of changing the chain from one sprocket to another by means of a switching device, wherein the sprocket and its teeth have switching aids which both facilitate the gear change and contribute to maintaining the engagement of the chain in the teeth of the sprocket, characterized by , that the sprocket (6) for guiding the chain (2) in the area of ​​its root circle (7) has a sprocket width (11) which is insignificantly smaller than the distance between the inner plates (5) determined by the roller (3) of the chain (2), the resulting slight play of the chain (2) on the tooth (9) relating to a guide area (18) of a tooth gap base (19), and the axial guidance of the chain (2) on the sprocket (6) results essentially from the projection (8) of the inner plates (5) relative to the roller (3) in the guide area (18) on the root circle (7) of the sprocket (6). [2] Multiple sprocket according to claim 1, characterized by that the teeth (9) have a flat guide bevel (12) on the side facing the larger sprocket (6), which runs in the direction from the tooth tip (10) to the root circle (7), where the sprocket (6) reaches its full sprocket width (11) and where the chain (2) forms a guide area (18) due to the projection (8) of the inner plates (5) relative to the roller (3). [3] Multiple sprocket according to claim 2, characterized by that the guide bevel (12) has an angle (13) to the flat surface of the gear ring (6) which lies within a range of 10° to 20°. [4] Multiple sprocket according to claim 2 or 3, characterized bythat the guide bevel (12) in the case of small gear rims (6) has an angle (13) to the flat surface of the gear rim (6) which lies within a range of 5° to 15°. [5] Multiple sprocket according to one of claims 2 to 4, characterized by that the guide bevel (12) is already applied to the blank of the gear ring hollow body (1) by a turning operation. [6] Multiple sprocket according to one of the preceding claims, characterized by that a tooth tip (10) has a first deflection bevel (14) following a guide bevel (12) in the direction from the tooth tip (10) to the root circle (7), which first deflection bevel forms a roof shape with a ridge (16) at the tooth tip (10) with a second deflection bevel (15) pointing towards the smaller tooth rim (6). [7] Multiple sprocket according to claim 6, characterized bythat the first deflection chamfer (14) and the second deflection chamfer (15) are already applied to the blank of the gear ring hollow body (1) by a turning operation. [8] Multiple sprocket according to claim 6 or 7, characterized by that the ridge (16) is at a distance of approximately one third of the width of the gear rim (11) from the plane surface of the gear rim (6) in question facing the smaller gear rim (6). [9] Multiple sprocket according to one of claims 6 to 8, characterized by that the second deflection bevel (15) has a greater inclination relative to the ridge (16) than the first deflection bevel (15). [10] Multiple sprocket according to one of claims 6 to 9, characterized by that annular recesses (17) are arranged on the flat surfaces of the toothed rings (6). [11] Multiple sprocket according to one of claims 6 to 10, characterized bythat the recesses (17) are already made on the blank of the gear ring hollow body (1) by a turning operation.

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