Bicycle rear sprocket assembly

A bicycle rear sprocket assembly comprises a sprocket support and a first sprocket. The sprocket support includes a hub engagement part configured to engage with a bicycle hub assembly. The sprocket support includes a plurality of sprocket attachment members extending radially outwardly from the hub engagement part with respect to a rotational center axis of the bicycle rear sprocket assembly. The first sprocket is attached to the plurality of sprocket attachment members. The first sprocket includes a first sprocket body and a plurality of first sprocket teeth which extends radially outwardly from the first sprocket body with respect to the rotational center axis and a total number of which is equal to or larger than thirty-four. The first sprocket has a plurality of shifting facilitation areas. A total number of the plurality of shifting facilitation areas is a divisor of a total number of the plurality of sprocket attachment members.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a bicycle rear sprocket assembly.

Discussion of the Background

Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One bicycle component that has been extensively redesigned is a bicycle rear sprocket assembly.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, a bicycle rear sprocket assembly comprises a sprocket support and a first sprocket. The sprocket support includes a hub engagement part configured to engage with a bicycle hub assembly. The sprocket support includes a plurality of sprocket attachment members extending radially outwardly from the hub engagement part with respect to a rotational center axis of the bicycle rear sprocket assembly. The first sprocket is attached to the plurality of sprocket attachment members. The first sprocket includes a first sprocket body and a plurality of first sprocket teeth which extend radially outwardly from the first sprocket body with respect to the rotational center axis and a total number of which is equal to or larger than thirty-four. The first sprocket has a plurality of shifting facilitation areas. A total number of the plurality of shifting facilitation areas is a divisor of a total number of the plurality of sprocket attachment members.

With the bicycle rear sprocket assembly according to the first aspect, it is possible to save weight of the bicycle rear sprocket assembly without reducing rigidity of the sprocket support.

In accordance with a second aspect of the present invention, a bicycle rear sprocket assembly comprises a sprocket support and a first sprocket. The sprocket support includes a hub engagement part configured to engage with a bicycle hub assembly. The sprocket support includes a plurality of sprocket attachment members extending radially outwardly from the hub engagement part with respect to a rotational center axis of the bicycle rear sprocket assembly. A total number of the plurality of sprocket attachment members is equal to or larger than six. The first sprocket is attached to the plurality of sprocket attachment members. The first sprocket includes a first sprocket body and a plurality of first sprocket teeth extending radially outwardly from the first sprocket body with respect to the rotational center axis. The first sprocket has more than two shifting facilitation areas. A total number of the shifting facilitation areas is a divisor of a total number of the plurality of sprocket attachment members.

With the bicycle rear sprocket assembly according to the second aspect, it is possible to save weight of the bicycle rear sprocket assembly without reducing rigidity of the sprocket support.

In accordance with a third aspect of the present invention, the bicycle rear sprocket assembly according to the first aspect is configured so that a total number of the plurality of sprocket attachment members is equal to or larger than six.

With the bicycle rear sprocket assembly according to the third aspect, it is possible to enhance rigidity of the sprocket support.

In accordance with a fourth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to third aspects is configured so that a total number of the plurality of sprocket attachment members is equal to six. The first sprocket has three or six shifting facilitation areas.

With the bicycle rear sprocket assembly according to the fourth aspect, it is possible to perform shifting flexibly.

In accordance with a fifth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to fourth aspects is configured so that the shifting facilitation areas include at least one of at least one upshifting facilitation area and at least one downshifting facilitation area.

With the bicycle rear sprocket assembly according to the fifth aspect, it is possible to perform at least one of upshifting and downshifting smoothly.

In accordance with a sixth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to fifth aspects is configured so that the first sprocket is attached to the plurality of sprocket attachment members via adhesive.

With the bicycle rear sprocket assembly according to the sixth aspect, it is possible to save weight of the bicycle rear sprocket assembly with maintaining or improving coupling strength between the first sprocket and the plurality of sprocket attachment members.

In accordance with a seventh aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to sixth aspects is configured so that the sprocket support includes a plurality of support arms extending radially outwardly from the hub engagement part. The first sprocket is attached to the plurality of support arms.

With the bicycle rear sprocket assembly according to the seventh aspect, it is possible to maintain or improve rigidity of the sprocket support with simple structure.

In accordance with an eighth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to seventh aspects is configured so that at least one of the plurality of sprocket attachment members includes a first radial support surface and a first axial support surface. The first radial support surface faces radially outwardly. The first axial support surface faces in an axial direction. The first sprocket is attached to the first radial support surface and the first axial support surface.

With the bicycle rear sprocket assembly according to the eighth aspect, it is possible to increase an area of a surface coupling the first sprocket to the sprocket attachment members.

In accordance with a ninth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to eighth aspects is configured so that the sprocket support is made of resin.

With the bicycle rear sprocket assembly according to the ninth aspect, it is possible to save weight of the sprocket support.

In accordance with a tenth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to eighth aspects is configured so that the first sprocket is made of a metallic material.

With the bicycle rear sprocket assembly according to the tenth aspect, it is possible to improve strength of the first sprocket.

In accordance with an eleventh aspect of the present invention, the bicycle rear sprocket assembly according to the tenth aspect is configured so that the first sprocket is made of aluminum.

With the bicycle rear sprocket assembly according to the eleventh aspect, it is possible to improve strength of the first sprocket with saving weight of the first sprocket

In accordance with a twelfth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to eleventh aspects further comprises a second sprocket, a third sprocket, and a fourth sprocket. The second sprocket includes a second sprocket body and a plurality of second sprocket teeth extending radially outwardly from the second sprocket body with respect to the rotational center axis. The third sprocket includes a third sprocket body and a plurality of third sprocket teeth extending radially outwardly from the third sprocket body with respect to the rotational center axis. The fourth sprocket includes a fourth sprocket body and a plurality of fourth sprocket teeth extending radially outwardly from the fourth sprocket body with respect to the rotational center axis.

With the bicycle rear sprocket assembly according to the twelfth aspect, it is possible to mount at least four sprockets to the bicycle rear sprocket assembly.

In accordance with a thirteenth aspect of the present invention, the bicycle rear sprocket assembly according to the twelfth aspect is configured so that the second sprocket, the third sprocket, and the fourth sprocket are attached to the plurality of sprocket attachment members.

With the bicycle rear sprocket assembly according to the thirteenth aspect, it is possible to effectively mount at least four sprockets to the sprocket support.

In accordance with a fourteenth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to thirteenth aspects is configured so that the first sprocket has a first pitch-circle diameter. The first pitch-circle diameter is the largest pitch-circle diameter in the bicycle rear sprocket assembly.

With the bicycle rear sprocket assembly according to the fourteenth aspect, it is possible to save weight of the bicycle rear sprocket assembly including the largest sprocket without reducing rigidity of the sprocket support.

In accordance with a fifteenth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to fourteenth aspects is configured so that the hub engagement part includes at least one spline configured to engage with the bicycle hub assembly.

With the bicycle rear sprocket assembly according to the fifteenth aspect, it is possible to mount the bicycle rear sprocket assembly to the bicycle hub assembly having a spline.

In accordance with a sixteenth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to fifteenth aspects is configured so that the first sprocket has an axial outward surface and an axial inward surface which is a reverse surface of the axial outward surface along the rotational center axis of the bicycle rear sprocket assembly. The first axial recesses are provided on the axial outward surface in the shifting facilitation areas. At least one second axial recess is provided on the axial inward surface in the at least one upshifting facilitation area.

With the bicycle rear sprocket assembly according to the sixteenth aspect, it is possible to further perform upshifting and downshifting smoothly.

In accordance with a seventeenth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to sixteenth aspects is configured so that at least one of the plurality of shifting facilitation areas is overlapped with one of the plurality of sprocket attachment members.

With the bicycle rear sprocket assembly according to the seventeenth aspect, it is possible to maintain or improve rigidity of the sprocket support for shifting.

In accordance with an eighteen aspect of the present invention, the bicycle rear sprocket assembly according to the seventeenth aspect is configured so that each of the plurality of shifting facilitation areas is overlapped with each of the plurality of sprocket attachment members.

With the bicycle rear sprocket assembly according to the eighteenth aspect, it is possible to maintain or improve rigidity of the sprocket support for shifting.

In accordance with a nineteenth aspect of the present invention, the bicycle rear sprocket assembly according to any one of the first to eighteenth aspects is configured so that at least one of the plurality of shifting facilitation areas is positioned between adjacent two of the plurality of sprocket attachment members.

With the bicycle rear sprocket assembly according to the nineteenth aspect, it is possible to perform shifting flexibly.

In accordance with a twentieth aspect of the present invention, the bicycle rear sprocket assembly according to the nineteenth aspect is configured so that each of the plurality of shifting facilitation areas is positioned between adjacent two of the plurality of sprocket attachment members.

With the bicycle rear sprocket assembly according to the twentieth aspect, it is possible to substantially equalize forces applied to respective sprocket attachment members. Accordingly, it is possible to maintain or improve rigidity of the sprocket support for shifting.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

Referring initially toFIG. 1, in accordance with a first embodiment, a bicycle rear sprocket assembly10comprises a sprocket support12and a first sprocket SP1. In this embodiment, the bicycle rear sprocket assembly10further comprises a second sprocket SP2, a third sprocket SP3, and a fourth sprocket SP4. The bicycle rear sprocket assembly10can further comprise fifth to twelfth sprockets SP5to SP12. However, at least one of the second to twelfth sprockets SP2to SP12can be omitted in the bicycle rear sprocket assembly10or more bicycle sprockets can be added to the bicycle rear sprocket assembly10. The plurality of sprockets SP1to SP12has a rotational center axis A1. The plurality of sprockets SP1to SP12is arranged in an axial direction D1parallel to the rotational center axis A1. In the illustrated embodiment, the first sprocket SP1corresponds to a low gear of the bicycle rear sprocket assembly10. However, the first sprocket SP1can correspond to another gear in the bicycle rear sprocket assembly10. For example, the first sprocket SP1can correspond to either the second sprocket SP2or the third sprocket SP3. Each of the plurality of the sprockets SP1to SP12is not limited to the illustrated embodiment.

The bicycle rear sprocket assembly10is configured to engage with a bicycle chain C. The bicycle rear sprocket assembly10is configured to be rotated about the rotational center axis A1in a driving rotational direction D21during pedaling. The driving rotational direction D21is defined along a circumferential direction D2of the bicycle rear sprocket assembly10.

In the present application, the following directional terms “front”, “rear”, “forward”, “rearward”, “left”, “right”, “transverse”, “upward” and “downward” as well as any other similar directional terms refer to those directions which are determined on the basis of a user (e.g., a rider) who sits on a saddle (not shown) of a bicycle with facing a handlebar (not shown). Accordingly, these terms, as utilized to describe the bicycle rear sprocket assembly10, should be interpreted relative to the bicycle equipped with the bicycle rear sprocket assembly10as used in an upright riding position on a horizontal surface.

As seen inFIG. 1, the plurality of sprockets SP1to SP12each includes a sprocket body and a plurality of sprocket teeth. More specifically, the first sprocket SP1includes a first sprocket body B1and a plurality of first sprocket teeth T1. The second sprocket SP2includes a second sprocket body B2and a plurality of second sprocket teeth T2. The third sprocket SP3includes a third sprocket body B3and a plurality of third sprocket teeth T3. The fourth sprocket SP4includes a fourth sprocket body B4and a plurality of fourth sprocket teeth T4.

The plurality of first sprocket teeth T1extend radially outwardly from the first sprocket body B1with respect to the rotational center axis A1. The plurality of second sprocket teeth T2extend radially outwardly from the second sprocket body B2with respect to the rotational center axis A1. The plurality of third sprocket teeth T3extend radially outwardly from the third sprocket body B3with respect to the rotational center axis A1. The plurality of fourth sprocket teeth T4extend radially outwardly from the fourth sprocket body B4with respect to the rotational center axis A1.

As seen inFIG. 2, the sprocket support12is a separate member from the plurality of sprockets SP1to SP12. The sprocket support12includes a hub engagement part14configured to engage with a bicycle hub assembly HB. As seen inFIGS. 2 to 4, the hub engagement part14includes at least one spline14aconfigured to engage with the bicycle hub assembly HB. However, the hub engagement part14can engage with the bicycle hub assembly HB via a different structure from the at least one spline14a. The sprocket support12includes a plurality of sprocket attachment members16extending radially outwardly from the hub engagement part14with respect to the rotational center axis A1of the bicycle rear sprocket assembly10. The first sprocket SP1is attached to the plurality of sprocket attachment members16. In the illustrated embodiment, the second sprocket SP2, the third sprocket SP3, and the fourth sprocket SP4are attached to the plurality of sprocket attachment members16. However, at least one of the second sprocket SP2, the third sprocket SP3, and the fourth sprocket SP4can be directly attached to the bicycle hub assembly HB. The fifth to eighth sprockets SP5to SP8can be attached to the plurality of sprocket attachment members16. The ninth to twelfth sprockets SP9to SP12can be directly or indirectly attached to the bicycle hub assembly HB. In the illustrated embodiment, the ninth sprocket S9is directly attached to the bicycle hub assembly HB. The tenth to twelfth sprockets SP10to SP12are attached to the bicycle hub assembly HB via an end cap11.

The first sprocket SP1is made of a metallic material. Preferably, the first sprocket SP1is made of aluminum. Similarly, the second sprocket SP2, the third sprocket SP3, and the fourth sprocket SP4are made of a metallic material. The second sprocket SP2, the third sprocket SP3, and the fourth sprocket SP4are made of aluminum. The fifth to twelfth sprockets SP5to SP12can be made of a metallic material. The fifth to twelfth sprockets SP5to SP12can be made of aluminum. However, materials of the first to twelfth sprockets SP1to SP12are not limited to this embodiment. Each of the first to twelfth sprockets SP1to SP12can be made of at least one of iron, titanium, and stainless steel. Each of the first to twelfth sprockets SP1to SP12can include a non-metallic material.

The sprocket support12is made of resin. However, the sprocket support12can be made of fiber-reinforced-plastic and carbon-fiber-reinforced-plastic. Further, the sprocket support12can be made of a metallic material such as iron, aluminum, titanium, and stainless steel. In a case where the sprocket support12is made of a material different from a material that the first to eighth sprockets SP1to SP8are made of, it is possible to expand the design flexibility of the bicycle rear sprocket assembly10. Further, in a case where the sprocket support12is made of a non-metallic material such as resin, it is possible to save the weight of the sprocket support12.

As seen inFIGS. 1 and 2, the sprocket bodies (e.g. B1, B2, B3, and B4) of the plurality of sprockets SP1to SP8are attached to the sprocket attachment members16of the sprocket support12without using a separate metallic fastening member such as a rivet and a bolt. Specifically, the first sprocket SP1is attached to the plurality of the sprocket attachment members16via adhesive. More specifically, the first sprocket body B1of the first sprocket SP1is attached to the plurality of the sprocket attachment members via adhesive. The second to fourth sprockets SP2to SP4are attached to the plurality of the sprocket attachment members16via adhesive. More specifically, the second to fourth sprocket bodies B2to B4of the second to fourth sprockets SP2to SP4are attached to the plurality of the sprocket attachment members via adhesive. The fifth to eighth sprockets SP5to SP8can be attached to the plurality of the sprocket attachment members16via adhesive. However, at least one of the sprockets SP1to SP8can be attached to the sprocket attachment members16in a different way such as diffusion bonding. The at least one of the sprockets SP1to SP8can be attached to the sprocket attachment members16via at least one metallic fastener.

As seen inFIGS. 3 and 4, a total number of the plurality of sprocket attachment members16is equal to or larger than six. More specifically, the total number of the plurality of sprocket attachment members16is equal to six. However, a total number of the sprocket attachment members16is not limited in this embodiment. As seen inFIGS. 3 and 4, the sprocket support12includes the plurality of support arms18extending radially outwardly from the hub engagement part14. However, the sprocket support12can have a shape like a dome, and the sprocket support12may not include the plurality of support arms18. The first sprocket SP1is attached to the plurality of support arms18. The second sprocket SP2, the third sprocket SP3, and the fourth sprocket SP4are attached to the plurality of support arms18. The fifth to eighth sprockets SP5to SP8can be attached to the plurality of support arms18. However, the first to eighth sprockets SP1to SP8can be attached to a different part of the sprocket support12from the plurality of support arms18.

As seen inFIGS. 3 and 4, at least one arm of the plurality of support arms18includes a first wall19a, a second wall19b, and one of the plurality of the sprocket attachment members16. In this embodiment, each of the plurality of support arms18includes the first wall19a, the second wall19b, and the one of the plurality of the sprocket attachment members16. The first wall19ais spaced apart from the second wall19bin the circumferential direction D2with respect to the rotational center axis A1. As seen inFIG. 2, each of the first wall19aand the second wall19bextends from the one of the plurality of the sprocket attachment members16in the axial direction D1with respect to the rotational center axis A1. More specifically, each of the first wall19aand the second wall19bis connected to one of the plurality of sprocket attachment members16and extends radially inwardly from the one of the plurality of sprocket attachment members16. Each of the first wall19aand the second wall19bextends from the one of the plurality of sprocket attachment members16toward a bicycle center plane BCP in the axial direction D1. Accordingly, the support arms18can improve the strength of the sprocket attachment members16.

As seen inFIG. 3, the plurality of support arms18are spaced apart from each other at circumferential intervals CL1in the circumferential direction D2with respect to the rotational center axis A1. In the illustrated embodiment, the plurality of support arms18respectively have maximum circumferential lengths CL2defined in the circumferential direction D2. Each of the maximum circumferential lengths CL2is shorter than or equal to the circumferential intervals CL1.

As seen inFIGS. 2 and 5, at least one of the plurality of sprocket attachment members16includes a first radial support surface16aand a first axial support surface16b. In the illustrated embodiment, each of the plurality of sprocket attachment members16includes the first radial support surface16aand the first axial support surface16b. The first radial support surface16afaces radially outwardly. More specifically, the first radial support surface16afaces radially outwardly with respect to the rotational center axis A1. Further, the first axial support surface16bfaces in the axial direction D1. More specifically, the first axial support surface16bfaces axially outwardly with respect to the bicycle center plane BCP. However, the at least one of the plurality of sprocket attachment members16can include a support surface facing in a different direction from a radial outward direction and the axial direction D1in place of the first radial support surface16aand the first axial support surface16b. The first radial support surface16aand the first axial support surface16bcan make it easier to radially and axially position the plurality of sprockets SP1to SP8relative to the sprocket attachment members16.

As seen inFIG. 2, the first sprocket SP1is attached to the first radial support surface16aand the first axial support surface16b. The second sprocket SP2, the third sprocket SP3, and the fourth sprocket SP4are attached to the first radial support surface16aand the first axial support surface16b. The fifth to eighth sprockets SP5to SP8can be attached to the first radial support surface16aand the first axial support surface16b. However, the first to eighth sprockets SP1to SP8can be attached to a support surface of the at least one of the plurality of sprocket attachment members16which faces in the different direction from the radial outward direction and the axial direction D1. In the following explanation, the first radial support surface16aand the first axial support surface16bto which the first sprocket SP1is attached can be referred to as a first radial support surface161aand a first axial support surface161b. Similarly, the first radial support surface16aand the first axial support surface16bto which the second sprocket SP2, the third sprocket SP3, the fourth sprocket SP4, the fifth sprocket SP5, the sixth sprocket SP6, the seventh sprocket SP7, and the eighth sprocket SP8are attached can be referred to as a first radial support surface162a,163a,164a,165a,166a,167a, and168aand a first axial support surface162b,163b,164b,165b,166b,167b, and168b, respectively.

As seen inFIG. 5, each of the first radial support surfaces161aand162ahas first restricting parts20. Each of the first restricting parts20includes a projection protruding radially outwardly with respect to the rotational center axis A1. As seen inFIG. 6, the first sprocket SP1has second restricting parts22. Each of the second restricting parts22includes a notch hollowed radially outwardly with respect to the rotational center axis A1to engage with each of the first restricting parts20. Further, as seen inFIG. 7, the first sprocket SP1has axial recesses24. Each of the axial recesses24is recessed from an axial inward surface IS1of the first sprocket SP1in the axial direction D1. The first axial support surface161bis fitted in the axial recesses24. Similarly, as seen inFIGS. 8 and 9, the second sprocket SP2has the second restricting parts22and the axial recesses24. The first restricting parts20of the first radial support surfaces161aand162aare configured to respectively engage with the second restricting parts22of the sprockets SP1and SP2to restrict the sprockets SP1and SP2from rotating relative to the sprocket support12about the rotational center axis A1. Accordingly, the driving force that the first sprocket SP1and the second sprocket SP2receive from the bicycle chain C can be transmitted to the sprocket support12.

Further, as seen inFIG. 5, each of the first radial support surfaces163a,164a,165a,166a,167a, and168ahas third restricting parts26. Each of the third restricting parts26includes a notch hollowed radially inwardly with respect to the rotational center axis A1. As seen inFIGS. 10 and 11, the third sprocket SP3has fourth restricting parts28. Each of the fourth restricting parts28includes a projection protruding radially inwardly with respect to the rotational center axis A1to engage with each of the third restricting parts26. Similarly, as seen inFIGS. 12 and 13, the fourth sprocket SP4has the fourth restricting parts28. Each of the fifth to eighth sprockets SP5to SP8has the fourth restricting parts28. The fifth to eighth sprockets SP5to SP8will not be illustrated in detail here for the sake of brevity, because each of the fifth to eighth sprockets SP5to SP8has substantially the same feature as the third or fourth sprocket SP3or SP4. The third restricting parts26of the first radial support surfaces163a,164a,165a,166a,167a, and168aare configured to respectively engage with the fourth restricting parts28of the sprockets SP3to SP8to restrict the sprockets SP3to SP8from rotating relative to the sprocket support12about the rotational center axis A1. Accordingly, the driving force that the third to eighth sprockets SP3to SP8receive from the bicycle chain C can be transmitted to the sprocket support12.

In the illustrated embodiment, the sprocket bodies B1to B4of the plurality of sprockets SP1to SP4can be respectively attached to the first radial support surface16aand the first axial support surface16bvia adhesive. Similarly, the sprocket bodies of the plurality of sprockets SP5to SP8can be respectively attached to the first radial support surface16aand the first axial support surface16bvia adhesive. However, the sprocket bodies (e.g. B1to B4) of the plurality of sprockets SP1to SP8can be attached to the first radial support surface16avia at least one metallic fastening member.

As seen inFIG. 2, the bicycle rear sprocket assembly10includes a plurality of spacers30,32,34,36,38,40, and42. The plurality of spacers30,32,34,36,38,40, and42are respectively provided between adjacent two of the plurality of sprockets SP1to SP8in the axial direction D1. In the illustrated embodiment, the plurality of spacers30,32,34,36,38,40, and42are respectively provided on the first radial support surface16a. The plurality of spacers30,32,34,36,38,40, and42allow the plurality of sprockets SP1to SP8to be easily positioned in the axial direction D1.

As seen inFIG. 2, in the illustrated embodiment, the plurality of spacers30,32,34,36,38,40, and42are respectively attached to the adjacent two of the sprocket bodies of the plurality of sprockets SP1to SP8. For example, the spacers30are attached to the sprocket bodies B1and B2. The spacers32are attached to the sprocket bodies B2and B3. The spacers34are attached to the sprocket bodies B3and B4. The plurality of spacers30,32,34,36,38,40, and42are respectively attached to the adjacent two of the sprocket bodies of the plurality of sprockets SP1to SP8via adhesive. Specifically, the spacers30are attached to the sprocket bodies B1and B2via adhesive. The spacers32are attached to the sprocket bodies B2and B3via adhesive. The spacers34are attached to the sprocket bodies B3and B4via adhesive. However, the plurality of spacers30,32,34,36,38,40, and42can be respectively attached to the adjacent two of the sprocket bodies of the plurality of sprockets SP1to SP8via diffusion bonding or at least one metallic fastening member.

As seen inFIGS. 6 and 7, the first sprocket SP1has a first pitch diameter L1. As seen inFIGS. 1 and 2, the first pitch diameter L1is the largest pitch-circle diameter in the bicycle rear sprocket assembly10. However, the first pitch diameter L1can correspond to another diameter, i.e. the first pitch diameter L1can be a smaller diameter than the largest pitch-circle diameter in the bicycle rear sprocket assembly10. A total number of the plurality of first sprocket teeth T1is equal to or larger than thirty-four. In the illustrated embodiment, the total number of the plurality of first sprocket teeth T1is equal to fifty-one. However, the total number of the plurality of first sprocket teeth T1is not limited to the illustrated embodiment.

As seen inFIG. 2, the first sprocket SP1has an axial outward surface OS1and an axial inward surface IS1which is a reverse surface of the axial outward surface OS1along the rotational center axis A1of the bicycle rear sprocket assembly10.FIG. 6shows the axial outward surface OS1of the first sprocket SP1.FIG. 7shows the axial inward surface IS1of the first sprocket SP1.

As seen inFIGS. 6 and 7, the first sprocket SP1has a plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13. That is, the first sprocket SP1has more than two shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13. A total number of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13is a divisor of the total number of the plurality of sprocket attachment members16. Since the total number of the plurality of sprocket attachment members16is equal to six, the total number of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13can be equal to two, three, or six. More preferably, the first sprocket SP1has three or six shifting facilitation areas. In the illustrated embodiment, the first sprocket SP1has six shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13. However, the number of shifting facilitation areas is not limited to the illustrated embodiment.

The plurality of the shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13include at least one of at least one upshifting facilitation area UFA11, UFA12, and UFA13and at least one downshifting facilitation area DFA11, DFA12, and DFA13. Specifically, the plurality of the shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13include at least one upshifting facilitation area UFA11, UFA12, and UFA13and at least one downshifting facilitation area DFA11, DFA12, and DFA13. The first sprocket SP1can have the plurality of shifting facilitation areas (the sum of the at least one upshifting facilitation area UFA11, UFA12, and UFA13and the at least one downshifting facilitation area DFA11, DFA12, and DFA13) which is not a divisor of the total number of the plurality of sprocket attachment members16. In such case, it is preferable that the first sprocket SP1can have a plurality of upshifting facilitation areas UFA11, UFA12, and UFA13which is a divisor of the total number of the plurality of sprocket attachment members16, and/or it is preferable that the first sprocket SP1can have a plurality of downshifting facilitation areas DFA11, DFA12, and DFA13which is a divisor of the total number of the plurality of sprocket attachment members16.

As seen inFIGS. 6, 14, 15, and 17, first axial recesses44are provided on the axial outward surface OS1in the shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13. More specifically, as seen inFIGS. 6, 14, and 15, at least one first outer axial recess44ais provided on the axial outward surface OS1in the upshifting facilitation areas UFA11, UFA12, and UFA13. As seen inFIGS. 6 and 17, at least one second outer axial recess44bis provided on the axial outward surface OS1in the downshifting facilitation areas DFA11, DFA12, and DFA13. As seen inFIGS. 7, 15, and 16, at least one second axial recess46is provided on the axial inward surface IS1in the at least one upshifting facilitation area UFA11, UFA12, and UFA13.

The at least one first outer axial recess44aand the at least one second axial recess46avoid excessive interference with the bicycle chain C during upshifting operation to facilitate upshifting from the first sprocket SP1to the second sprocket SP2. The at least one second outer axial recess44bguides the bicycle chain C toward the first sprocket SP1from the second sprocket SP2to facilitate engagement of the bicycle chain C with one of the plurality of first sprocket teeth T1. Accordingly, each of the at least one upshifting facilitation area UFA11, UFA12, and UFA13is defined by the at least one first outer axial recess44aand the at least one second axial recess46. Each of the at least one downshifting facilitation area DFA11, DFA12, and DFA13is defined by the at least one second outer axial recess44b. However, other structure than the at least one first outer axial recess44aand the at least one second axial recess46(e.g. protrusion) can be provided in the at least one upshifting facilitation area UFA11, UFA12, and UFA13. Other structure than the at least one second outer axial recess44b(e.g. protrusion) can be provided in the at least one downshifting facilitation area DFA11, DFA12, and DFA13. In such case, at least one of the first axial recesses44can be omitted in the shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13. At least one second axial recess46can be omitted in the at least one upshifting facilitation area UFA11, UFA12, and UFA13.

As seen inFIGS. 6 and 7, at least one of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13is overlapped with one of the plurality of the sprocket attachment members16. In other words, the at least one of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13is overlapped with one of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the first sprocket SP1. In another aspect, one of the plurality of the sprocket attachment members16is provided between the at least one of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13and the rotational center axis A1of the first sprocket SP1. More specifically, each of the plurality of downshifting facilitation areas DFA11, DFA12, and DFA13is overlapped with one of the plurality of the sprocket attachment members16. In other words, each of the plurality of downshifting facilitation areas DFA11, DFA12, and DFA13is overlapped with one of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the first sprocket SP1. In another aspect, one of the plurality of the sprocket attachment members16is provided between each of the plurality of downshifting facilitation areas DFA11, DFA12, and DFA13and the rotational center axis A1of the first sprocket SP1.

As seen inFIGS. 8 and 9, the second sprocket SP2has a second pitch diameter L2. As seen inFIGS. 1 and 2, the second pitch diameter L2is the second largest pitch-circle diameter in the bicycle rear sprocket assembly10. A total number of the plurality of second sprocket teeth T2is equal to or larger than thirty-four. In the illustrated embodiment, the total number of the plurality of second sprocket teeth T2is equal to forty-five. However, the total number of the plurality of second sprocket teeth T2is not limited to the illustrated embodiment.

As seen inFIG. 2, the second sprocket SP2has an axial outward surface OS2and an axial inward surface IS2which is a reverse surface of the axial outward surface OS2along the rotational center axis A1of the bicycle rear sprocket assembly10.FIG. 8shows the axial outward surface OS2of the second sprocket SP2.FIG. 9shows the axial inward surface IS2of the second sprocket SP2.

As seen inFIGS. 8 and 9, the second sprocket SP2has a plurality of shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23. In the illustrated embodiment, a total number of the plurality of shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23is equal to six. However, some of the plurality of shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23can be omitted. In such case, the total number of the plurality of shifting facilitation areas is a divisor of the total number of the plurality of sprocket attachment members16. The plurality of the shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23include at least one of at least one upshifting facilitation area UFA21, DFA22, and DFA23and at least one downshifting facilitation area DFA21, DFA22, and DFA23. Specifically, the plurality of the shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23include at least one upshifting facilitation area UFA21, DFA22, and DFA23and at least one downshifting facilitation area DFA21, DFA22, and DFA23. The upshifting facilitation areas UFA21, DFA22, and DFA23have substantially the same structure as the upshifting facilitation areas UFA11, UFA12, and UFA13of the first sprocket SP1, but their positions with respect to the plurality of the sprocket attachment members16are different from those of the upshifting facilitation areas UFA11, UFA12, and UFA13of the first sprocket SP1. The downshifting facilitation areas DFA21, DFA22, and DFA23have substantially the same structure as the downshifting facilitation areas DFA11, DFA12, and DFA13of the first sprocket SP1, but their positions with respect to the plurality of the sprocket attachment members16are different from those of the downshifting facilitation areas DFA11, DFA12, and DFA13of the first sprocket SP1. Thus, elements in shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23having substantially the same function as those in shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13, respectively will be numbered the same here, and will not be described and/or illustrated again in detail here for the sake of brevity.

As seen inFIGS. 8 and 9, at least one of the plurality of shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23is overlapped with one of the plurality of the sprocket attachment members16. In other words, the at least one of the plurality of shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23is overlapped with one of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the second sprocket SP2. In another aspect, one of the plurality of the sprocket attachment members16is provided between the at least one of the plurality of shifting facilitation areas UFA21, DFA22, DFA23, DFA21, DFA22, and DFA23and the rotational center axis A1of the second sprocket SP2. More specifically, each of the plurality of downshifting facilitation areas DFA21, DFA22, and DFA23is overlapped with one of the plurality of the sprocket attachment members16. In other words, each of the plurality of downshifting facilitation areas DFA21, DFA22, and DFA23is overlapped with one of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the second sprocket SP2. In another aspect, one of the plurality of the sprocket attachment members16is provided between each of the plurality of downshifting facilitation areas DFA21, DFA22, and DFA23and the rotational center axis A1of the second sprocket SP2.

As seen inFIGS. 10 and 11, the third sprocket SP3has a third pitch diameter L3. As seen inFIGS. 1 and 2, the third pitch diameter L3is the third largest pitch-circle diameter in the bicycle rear sprocket assembly10. A total number of the plurality of third sprocket teeth T3is equal to or larger than thirty-four. In the illustrated embodiment, the total number of the plurality of third sprocket teeth T3is equal to thirty-nine. However, the total number of the plurality of third sprocket teeth T3is not limited to the illustrated embodiment.

As seen inFIG. 2, the third sprocket SP3has an axial outward surface OS3and an axial inward surface IS3which is a reverse surface of the axial outward surface OS3along the rotational center axis A1of the bicycle rear sprocket assembly10.FIG. 10shows the axial outward surface OS3of the third sprocket SP3.FIG. 11shows the axial inward surface IS3of the third sprocket SP3.

As seen inFIGS. 10 and 11, the third sprocket SP3has a plurality of shifting facilitation areas UFA31, UFA32, UFA33, DFA31, DFA32, and DFA33. In the illustrated embodiment, a total number of the plurality of shifting facilitation areas UFA31, UFA32, UFA33, DFA31, DFA32, and DFA33is equal to six. However, some of the plurality of shifting facilitation areas UFA31, UFA32, UFA33, DFA31, DFA32, and DFA33can be omitted. In such case, preferably, the total number of the plurality of shifting facilitation areas is a divisor of a total number of the plurality of sprocket attachment members16. The plurality of the shifting facilitation areas UFA31, UFA32, UFA33, DFA31, DFA32, and DFA33include at least one of at least one upshifting facilitation area UFA31, UFA32, and UFA33and at least one downshifting facilitation area DFA31, DFA32, and DFA33. Specifically, the plurality of the shifting facilitation areas UFA31, UFA32, UFA33, DFA31, DFA32, and DFA33include at least one upshifting facilitation area UFA31, UFA32, and UFA33and at least one downshifting facilitation area DFA31, DFA32, and DFA33. The third sprocket SP3can have the plurality of shifting facilitation areas (the sum of the at least one upshifting facilitation area UFA31, UFA32, and UFA33and the at least one downshifting facilitation area DFA31, DFA32, and DFA33) which is not a divisor of the total number of the plurality of sprocket attachment members16. In such case, it is preferable that the third sprocket SP3can have a plurality of upshifting facilitation areas UFA31, UFA32, and UFA33which is a divisor of the total number of the plurality of sprocket attachment members16, and/or it is preferable that the third sprocket SP3can have a plurality of downshifting facilitation areas DFA31, DFA32, and DFA33which is a divisor of the total number of the plurality of sprocket attachment members16. The upshifting facilitation areas UFA31, DFA32, and DFA33have substantially the same structure as the upshifting facilitation areas UFA11, UFA12, and UFA13of the first sprocket SP1, but their positions with respect to the plurality of the sprocket attachment members16are different from those of the upshifting facilitation areas UFA11, UFA12, and UFA13of the first sprocket SP1. The downshifting facilitation areas DFA31, DFA32, and DFA33have substantially the same structure as the downshifting facilitation areas DFA11, DFA12, and DFA13of the first sprocket SP1, but their positions with respect to the plurality of the sprocket attachment members16are different from those of the downshifting facilitation areas DFA11, DFA12, and DFA13of the first sprocket SP1. Thus, elements in shifting facilitation areas UFA31, DFA32, DFA33, DFA31, DFA32, and DFA33having substantially the same function as those in shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13, respectively will be numbered the same here, and will not be described and/or illustrated again in detail here for the sake of brevity.

As seen inFIGS. 10 and 11, at least one of the plurality of shifting facilitation areas UFA31, DFA32, DFA33, DFA31, DFA32, and DFA33is overlapped with one of the plurality of the sprocket attachment members16. In other words, the at least one of the plurality of shifting facilitation areas UFA31, DFA32, DFA33, DFA31, DFA32, and DFA33is overlapped with one of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the third sprocket SP3. Further, as seen inFIGS. 10 and 11, the at least one of the plurality of shifting facilitation areas UFA31, DFA32, DFA33, DFA31, DFA32, and DFA33is overlapped with one of the plurality of the sprocket attachment members16as seen along the rotational center axis A1. More specifically, each of the plurality of shifting facilitation areas UFA31, DFA32, DFA33, DFA31, DFA32, and DFA33is overlapped with each of the plurality of the sprocket attachment members16. In other words, each of the plurality of shifting facilitation areas UFA31, DFA32, DFA33, DFA31, DFA32, and DFA33is overlapped with each of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the third sprocket SP3. Further, as seen inFIGS. 10 and 11, each of the plurality of shifting facilitation areas UFA31, DFA32, DFA33, DFA31, DFA32, and DFA33is overlapped with each of the plurality of the sprocket attachment members16as seen along the rotational center axis A1.

As seen inFIGS. 12 and 13, the fourth sprocket SP4has a fourth pitch diameter L4. As seen inFIGS. 1 and 2, the fourth pitch diameter L4is the fourth largest pitch-circle diameter in the bicycle rear sprocket assembly10. In the illustrated embodiment, the total number of the plurality of fourth sprocket teeth T4is equal to thirty-three. However, the total number of the plurality of fourth sprocket teeth T4is not limited to the illustrated embodiment.

As seen inFIG. 2, the fourth sprocket SP4has an axial outward surface OS4and an axial inward surface IS4which is a reverse surface of the axial outward surface OS4along the rotational center axis A1of the bicycle rear sprocket assembly10.FIG. 12shows the axial outward surface OS4of the fourth sprocket SP4.FIG. 13shows the axial inward surface IS4of the fourth sprocket SP4.

As seen inFIGS. 12 and 13, the fourth sprocket SP4has a plurality of shifting facilitation areas UFA41, UFA42, UFA43, DFA41, and DFA42. The plurality of the shifting facilitation areas UFA41, UFA42, UFA43, DFA41, and DFA42include at least one of at least one upshifting facilitation area UFA41, UFA42, and UFA43and at least one downshifting facilitation area DFA41and DFA42. Specifically, the plurality of the shifting facilitation areas UFA41, UFA42, UFA43, DFA41, and DFA42include at least one upshifting facilitation area UFA41, UFA42, and UFA43and at least one downshifting facilitation area DFA41and DFA42. The fourth sprocket SP4has the plurality of shifting facilitation areas (the sum of the at least one upshifting facilitation area UFA41, UFA42, and UFA43and the at least one downshifting facilitation area DFA41and DFA42which is not a divisor of the total number (six) of the plurality of sprocket attachment members16. However, the fourth sprocket SP4has a plurality of upshifting facilitation areas UFA41, UFA42, and UFA43which is a divisor of the total number (six) of the plurality of sprocket attachment members16, and the fourth sprocket SP4has a plurality of downshifting facilitation areas DFA41and DFA42which is a divisor of the total number (six) of the plurality of sprocket attachment members16. The upshifting facilitation areas UFA41, UFA42, and UFA43have substantially the same structure as the upshifting facilitation areas UFA11, UFA12, and UFA13of the first sprocket SP1, but their positions with respect to the plurality of the sprocket attachment members16are different from those of the upshifting facilitation areas UFA11, UFA12, and UFA13of the first sprocket SP1. The downshifting facilitation areas DFA41and DFA42have substantially the same structure as the downshifting facilitation areas DFA11, DFA12, and DFA13of the first sprocket SP1, but a total number of them and their positions with respect to the plurality of the sprocket attachment members16are different from those of the downshifting facilitation areas DFA11, DFA12, and DFA13of the first sprocket SP1. Thus, elements in shifting facilitation areas UFA41, UFA42, and UFA43having substantially the same function as those in shifting facilitation areas UFA11, UFA12, and UFA13, respectively will be numbered the same here, and will not be described and/or illustrated again in detail here for the sake of brevity. Elements in shifting facilitation areas DFA41and DFA42having substantially the same function as those in shifting facilitation areas DFA11, DFA12, and DFA13will be numbered the same here, and will not be described and/or illustrated again in detail here for the sake of brevity.

As seen inFIGS. 12 and 13, at least one of the plurality of shifting facilitation areas UFA41, UFA42, UFA43, DFA41, and DFA42is overlapped with one of the plurality of the sprocket attachment members16. In other words, the at least one of the plurality of shifting facilitation areas UFA41, UFA42, UFA43, DFA41, and DFA42is overlapped with one of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the fourth sprocket SP4. Further, as seen inFIGS. 12 and 13, the at least one of the plurality of shifting facilitation areas UFA41, UFA42, UFA43, DFA41, and DFA42is overlapped with one of the plurality of the sprocket attachment members16as seen along the rotational center axis A1. More specifically, each of the plurality of shifting facilitation areas UFA41, UFA42, UFA43, and DFA42is overlapped with each of the plurality of the sprocket attachment members16. In other words, each of the plurality of shifting facilitation areas UFA41, UFA42, UFA43, and DFA42is overlapped with each of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the fourth sprocket SP4. Further, as seen inFIGS. 12 and 13, each of the plurality of shifting facilitation areas UFA41, UFA42, UFA43, and DFA42is overlapped with each of the plurality of the sprocket attachment members16as seen along the rotational center axis A1. However, at least one of the plurality of the shifting facilitation areas DFA41is positioned between adjacent two of the plurality of sprocket attachment members16. In other words, at least one of the plurality of the shifting facilitation areas DFA41is positioned between adjacent two of the plurality of sprocket attachment members16in the circumferential direction D2.

Modifications

In the above embodiments, one of the upshifting facilitation areas and the downshifting facilitation areas can be omitted in each of the sprockets SP1to SP8. In addition, the number of shifting facilitation areas in each of the sprockets SP1to SP8is not limited to the above embodiment.

In each of the sprockets SP1to SP3, at least one of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, DFA13, UFA21, UFA22, UFA23, DFA21, DFA22, DFA23, UFA31, UFA32, UFA33, DFA31, DFA32, and DFA33is positioned between adjacent two of the plurality of the sprocket attachment members16. For example, as seen inFIG. 18, the first sprocket SP1can have a shape in which at least one of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13is positioned between adjacent two of the plurality of the sprocket attachment members16. In other words, at least one of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13is positioned between adjacent two of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the first sprocket SP1. More specifically, each of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13is positioned between adjacent two of the plurality of the sprocket attachment members16. In other words, each of the plurality of shifting facilitation areas UFA11, UFA12, UFA13, DFA11, DFA12, and DFA13is positioned between adjacent two of the plurality of the sprocket attachment members16as seen from the rotational center axis A1of the first sprocket SP1.