Bicycle sprocket arrangement

Abstract

Bicycle sprocket assembly (12) comprising: a first sprocket (14) comprising: a first sprocket body (22) having a rotational center axis (A1); a shift facilitation region (SF) for facilitating a shifting operation in which a bicycle chain (C) is shifted between the first sprocket (14) and a second sprocket (16) adjacent to the first sprocket (14); and a plurality of first sprocket teeth (24), each having a maximum axial upper width (W12) and a maximum axial lower width (W13), the plurality of first sprocket teeth (24) comprising: a plurality of first teeth (26) adapted to engage an outer link space (C11) provided between an opposing pair of outer link plates (C1) of the bicycle chain (C), the plurality of first teeth (26) comprising: a switch relief tooth (48) extending radially outwardly from the first sprocket body (22), the switch relief tooth (48) being provided in the switch relief region (SF), the maximum axial upper width (W52) of the switch relief tooth (48) being smaller than the maximum axial lower width (W53) of the switch relief tooth (48); and a first drive tooth (50) extending radially outward from the first sprocket body (22), the first drive tooth (50) being provided outside the switch relief region (SF), the maximum axial upper width (W52) of the switch relief tooth (48) being smaller than the maximum axial upper width (W12) of the first drive tooth (50); and a plurality of second teeth (28) configured to engage an inner link space (C21) provided between an opposing pair of inner link plates (C2) of the bicycle chain (C), the plurality of second teeth (28) including a second drive tooth (52) extending radially outward from the first sprocket body (22), the plurality of second teeth (28) provided outside the shift facilitation area (SF) having the maximum axial width (W21) smaller than the maximum axial lower width (W13) of the first drive tooth (50).

Description

REFERENCE TO OTHER APPLICATIONS

[0001] This application claims priority to U.S. patent application 15 / 649,610, filed July 13, 2017. The entire disclosure of U.S. patent application 15 / 649,610 is hereby incorporated by reference BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0002] The present invention relates to a bicycle sprocket assembly. DISCUSSION OF THE BACKGROUND

[0003] Cycling is becoming an increasingly popular form of recreation as well as a means of transportation. Furthermore, cycling 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 undergone extensive redesign is the chainwheel assembly. Bicycle chainwheel assemblies are known, for example, from DE 10 2014 007 274 A1, DE 10 2015 000 474 A1, or DE 10 2015 011 214 A1. SUMMARY OF THE INVENTION

[0004] According to a first aspect of the present invention, a bicycle sprocket assembly comprises a first sprocket. The first sprocket includes a first sprocket body, a shift facilitation portion, and a plurality of first sprocket teeth. The first sprocket body has a rotational center axis. The shift facilitation portion serves to facilitate a shifting operation in which a bicycle chain is shifted between the first sprocket and a second sprocket adjacent to the first sprocket. The plurality of first sprocket teeth each have a maximum axial upper width and a maximum axial lower width. The plurality of first sprocket teeth include a plurality of first teeth and a plurality of second teeth. The plurality of first teeth are configured to engage an outer link space provided between an opposing pair of outer link plates of the bicycle chain.The plurality of first teeth includes a shift relief tooth and a first drive tooth. The shift relief tooth extends radially outward from the first sprocket body. The shift relief tooth is provided in the shift relief region. The maximum axial upper width of the shift relief tooth is less than the maximum axial lower width of the shift relief tooth. The first drive tooth extends radially outward from the first sprocket body. The first drive tooth is provided outside the shift relief region. The maximum axial upper width of the shift relief tooth is less than the maximum axial upper width of the first drive tooth. The plurality of second teeth are configured to engage an inner link space provided between an opposing pair of inner link plates of the bicycle chain.The plurality of second teeth includes a second drive tooth extending radially outward from the first sprocket body. The second drive tooth is located outside the shift relief area. The plurality of second teeth has a maximum axial width that is smaller than the maximum axial bottom width of the first drive tooth.

[0005] In the bicycle sprocket assembly according to the first aspect, it is possible to improve the chain holding performance by facilitating the shifting operation because the maximum axial upper width of the shift facilitating tooth is smaller than the maximum axial upper width of the first drive tooth.

[0006] According to a second aspect of the present invention, the bicycle sprocket assembly according to the first aspect is configured such that the shift facilitation tooth has a first radial height extending radially outward from the first sprocket body to a radially outermost edge of the shift facilitation tooth. The first drive tooth has a second radial height extending radially outward from the first sprocket body to a radially outermost edge of the first drive tooth. The first radial height is less than the second radial height.

[0007] In the bicycle sprocket assembly according to the second aspect, the first radial height smooths the insertion of the shift facilitation tooth into the outer link space of the bicycle chain.

[0008] According to a third aspect of the present invention, the bicycle sprocket assembly according to the first or second aspect is configured such that the shift facilitation tooth has a first radial height extending radially outward from the first sprocket body to a radially outermost edge of the shift facilitation tooth. The second drive tooth has a third radial height extending radially outward from the first sprocket body to a radially outermost edge of the second drive tooth. The first radial height is less than the third radial height.

[0009] In the bicycle sprocket assembly according to the third aspect, the first radial height smooths the insertion of the shift facilitation tooth into the outer link space of the bicycle chain.

[0010] According to a fourth aspect of the present invention, the bicycle sprocket assembly according to any one of the first to third aspects is configured such that the first sprocket has a first shift facilitation protrusion to facilitate the shifting operation. The shift facilitation tooth is provided on an upstream side of the first shift facilitation protrusion in a first circumferential direction in which the bicycle sprocket assembly is rotated about the rotational center axis during pedaling.

[0011] In the bicycle sprocket assembly according to the fourth aspect, the first shift facilitation protrusion allows the shift facilitation tooth to first engage the bicycle chain during the shifting operation.

[0012] According to a fifth aspect of the present invention, the bicycle sprocket assembly according to the fourth aspect is configured such that the shift facilitation tooth is spaced from the first shift facilitation projection by a first distance corresponding to two chain pitches of the bicycle chain.

[0013] In the bicycle sprocket assembly according to the fifth aspect, the first clearance effectively allows the shift facilitating tooth to first engage the bicycle chain in the shifting operation.

[0014] According to a sixth aspect of the present invention, the bicycle sprocket assembly according to the fourth or fifth aspect is configured such that the shifting facilitation tooth is configured to first engage an outer link space of the bicycle chain during a first shifting operation in which the bicycle chain is shifted from the second sprocket to the first sprocket. The first sprocket has a first pitch diameter that is larger than a second pitch diameter of the second sprocket.

[0015] In the bicycle sprocket arrangement according to the sixth aspect, the shift facilitation tooth facilitates the first shifting operation.

[0016] According to a seventh aspect of the present invention, the bicycle sprocket assembly according to any one of the first to sixth aspects is configured such that the plurality of second teeth includes a derailment tooth configured to first derail the bicycle chain from the first sprocket in a second shifting operation in which the bicycle chain is shifted from the first sprocket to the second sprocket. The first sprocket has a first pitch diameter larger than a second pitch diameter of the second sprocket. The shift facilitation tooth is provided on a downstream side of the derailment tooth in a first circumferential direction in which the bicycle sprocket assembly is rotated about the rotational center axis during pedaling.

[0017] In the bicycle sprocket assembly according to the seventh aspect, the shift facilitating tooth smooths the derailment of the bicycle chain from the first sprocket at the derailment tooth in the second shifting operation.

[0018] According to an eighth aspect of the present invention, the bicycle sprocket assembly according to the seventh aspect is configured such that the shift facilitation tooth is adjacent to the derailment tooth in the first circumferential direction without any other tooth being present between the shift facilitation tooth and the derailment tooth.

[0019] In the bicycle sprocket assembly according to the eighth aspect, the shift facilitating tooth further smooths the derailment of the bicycle chain from the first sprocket at the derailment tooth in the second shifting operation.

[0020] According to a ninth aspect of the present invention, the bicycle sprocket assembly according to any one of the first to eighth aspects is configured such that each of the plurality of first sprocket teeth includes a lower portion and an upper portion extending radially outward from the lower portion. The lower portion has the maximum axial lower width of each of the plurality of first sprocket teeth. The upper portion has the maximum axial upper width of each of the plurality of first sprocket teeth. The first sprocket has a reference circle with respect to a rotational center axis of the bicycle sprocket assembly. The lower portion is provided radially inward of the reference circle. The upper portion is provided radially outward of the reference circle.

[0021] In the bicycle sprocket assembly according to the ninth aspect, it is possible to improve the chain holding performance by facilitating the shifting operation.

[0022] According to a tenth aspect of the present invention, the bicycle sprocket assembly according to the ninth aspect is configured such that the first sprocket has a first pitch circle, a first outer circle, and a first inner circle. A first outer distance is defined radially outward from the first pitch circle to the first outer circle. The first outer distance is equal to or less than 3 mm. A first inner distance is defined radially inward from the first pitch circle to the first inner circle. The first inner distance is equal to or less than 4 mm. The reference circle is provided between the first outer circle and the first inner circle.

[0023] In the bicycle sprocket assembly according to the tenth aspect, it is possible to arrange the upper portion and the lower portion of the shift facilitating tooth at a preferable position.

[0024] According to an eleventh aspect of the present invention, the bicycle sprocket assembly according to the ninth or tenth aspect is configured such that each of the plurality of first teeth has a first protrusion provided on one of a first axial side and a second axial side of the lower portion. The first axial side is a rear side of the second axial side in an axial direction parallel to the rotational center axis.

[0025] In the bicycle sprocket assembly according to the eleventh aspect, the first protrusion further improves the chain holding performance.

[0026] According to a twelfth aspect of the present invention, the bicycle sprocket assembly according to the eleventh aspect is configured such that each of the plurality of first teeth has a second protrusion provided on a different one of the first axial side and the second axial side of the lower portion.

[0027] In the bicycle sprocket assembly according to the twelfth aspect, the first protrusion and the second protrusion further improve the chain holding performance.

[0028] According to a thirteenth aspect of the present invention, the bicycle sprocket assembly according to any one of the ninth to twelfth aspects is configured such that the lower portion of the plurality of first teeth includes a first chain engagement surface, a first lower drive surface, and a first chamfer provided between the first chain engagement surface and the first lower engagement surface. The first chain engagement surface faces the axial direction. The first lower engagement surface faces the first circumferential direction in which the bicycle sprocket assembly is rotated about the rotational center axis during pedaling.

[0029] In the bicycle sprocket assembly according to the thirteenth aspect, the first chamfer reduces the interference between the first tooth and the bicycle chain, thereby reducing the noise caused by the interference between the first tooth and the bicycle chain.

[0030] According to a fourteenth aspect of the present invention, the bicycle sprocket assembly according to any one of the ninth to twelfth aspects is configured such that the lower portion of the plurality of first teeth includes a first chain engagement surface, a first lower non-drive surface, and a second chamfer provided between the first chain engagement surface and the first lower non-drive surface. The first chain engagement surface faces the axial direction. The first lower non-drive surface faces a second circumferential direction opposite to a first circumferential direction in which the bicycle sprocket assembly is rotated about the rotational center axis during pedaling.

[0031] In the bicycle sprocket assembly according to the fourteenth aspect, the first chamfer and the second chamfer improve the chain holding performance and reduce noise.

[0032] According to a fifteenth aspect of the present invention, the bicycle sprocket assembly according to any one of the first to fourteenth aspects is configured such that the maximum axial lower width of the shift facilitation tooth is substantially equal to the maximum axial lower width of the first drive tooth.

[0033] In the bicycle sprocket assembly according to the fifteenth aspect, it is possible to improve the chain holding performance in the shift relief area as well as outside the shift relief area.

[0034] According to a sixteenth aspect of the present invention, the bicycle sprocket assembly according to any one of the first to fifteenth aspects is configured such that the first sprocket has a second shift facilitation protrusion to facilitate the shifting operation. The shift facilitation tooth is provided on a downstream side of the second shift facilitation protrusion in a first circumferential direction in which the bicycle sprocket assembly is rotated about the rotational center axis during pedaling.

[0035] In the bicycle sprocket assembly according to the sixteenth aspect, the second shift facilitating protrusion smooths the derailment of the bicycle chain from the first sprocket in the shifting operation.

[0036] According to a seventeenth aspect of the present invention, the bicycle sprocket assembly according to any one of the first to sixteenth aspects is configured such that the shift facilitation tooth is spaced from the second shift facilitation projection by a second distance corresponding to two chain pitches of the bicycle chain.

[0037] In the bicycle sprocket assembly according to the seventeenth aspect, the second clearance in the shifting operation effectively facilitates the derailment of the bicycle chain from the first sprocket.

[0038] According to an eighteenth aspect of the present invention, the bicycle sprocket assembly according to any one of the first to seventeenth aspects is configured such that the maximum axial upper width of the shift facilitation tooth is smaller than the maximum upper width of the second drive tooth.

[0039] In the bicycle sprocket assembly according to the eighteenth aspect, it is possible to improve the chain holding performance while effectively facilitating the shifting operation.

[0040] According to a nineteenth aspect of the present invention, the bicycle sprocket assembly according to any one of the first to eighteenth aspects is configured such that each of the plurality of first teeth has a drive surface and a non-drive surface. The shift facilitation tooth has a first circumferential length defined between the drive surface and the non-drive surface in a circumferential direction of the rotational center axis. The first drive tooth has a second circumferential length defined between the drive surface and the non-drive surface in the circumferential direction. The first circumferential length is smaller than the second circumferential length.

[0041] In the bicycle sprocket assembly according to the nineteenth aspect, it is possible to improve the chain holding performance while effectively facilitating the shifting operation.

[0042] According to a twentieth aspect of the present invention, the bicycle sprocket assembly according to the nineteenth aspect is configured such that the drive surface of the plurality of first teeth is arranged at a constant pitch in the circumferential direction.

[0043] In the bicycle sprocket assembly according to the twentieth aspect, it is possible to effectively distribute a rotational force applied to the plurality of first sprocket teeth.

[0044] According to a twenty-first aspect of the present invention, a bicycle sprocket assembly comprises a first sprocket and a second sprocket. The first sprocket includes a first sprocket body, a shift facilitation portion, and a plurality of first sprocket teeth. The first sprocket body has a rotational center axis. The shift facilitation portion serves to facilitate a shifting operation in which a bicycle chain is shifted between the first sprocket and a second sprocket adjacent to the first sprocket. The plurality of first sprocket teeth are made of a first material having a first wear resistance. The plurality of first sprocket teeth include a plurality of first teeth and a plurality of second teeth. The plurality of first teeth are configured to engage an outer link space provided between an opposing pair of outer link plates of the bicycle chain.The plurality of second teeth are configured to engage an inner link space provided between an opposing pair of inner link plates of the bicycle chain. The second sprocket includes a second sprocket body and a plurality of second sprocket teeth. The second sprocket body has a rotational center axis. The plurality of second sprocket teeth are made of a second material having a second wear resistance. A total number of the plurality of second sprocket teeth is smaller than a total number of the plurality of first sprocket teeth. The first wear resistance is greater than the second wear resistance.

[0045] In the bicycle sprocket assembly according to the twenty-first aspect, the first material reduces wear on the first sprocket, thereby reducing deterioration in shifting performance caused by wear on the first sprocket. Furthermore, the second material can reduce the weight of the second sprocket.

[0046] According to a twenty-second aspect of the present invention, a bicycle sprocket assembly comprises a first sprocket and a second sprocket. The first sprocket has a first pitch circle diameter. The first sprocket includes a first sprocket body, a shift facilitation region, and a plurality of first sprocket teeth. The first sprocket body has a rotational center axis. The shift facilitation region serves to facilitate a shifting operation in which a bicycle chain is shifted between the first sprocket and a second sprocket adjacent to the first sprocket. The plurality of first sprocket teeth includes a plurality of first teeth and a plurality of second teeth. The plurality of first teeth has a first maximum axial width. The plurality of second teeth has a second maximum axial width that is smaller than the first maximum axial width.The second sprocket has a second pitch circle diameter that is smaller than the first pitch circle diameter. The second sprocket includes a second sprocket body and a plurality of second sprocket teeth. The second sprocket body includes the rotational center axis. The plurality of second sprocket teeth includes a plurality of third teeth and a plurality of fourth teeth. The plurality of third teeth has a third maximum axial width. At least one tooth of the plurality of third teeth includes a radially outermost edge, a chain engagement surface, and an inclined surface. The chain engagement surface faces an axial direction parallel to the rotational center axis. The inclined surface extends from the chain engagement surface toward the radially outermost edge. The inclined surface is inclined relative to the chain engagement surface at an inclination angle equal to or greater than 40 degrees.The plurality of fourth teeth have a fourth maximum axial width that is smaller than the third maximum axial width.

[0047] In the bicycle sprocket assembly according to the twenty-second aspect, the inclined surface restricts at least one tooth of the plurality of third teeth from being inadvertently inserted into an inner link space defined between an opposing pair of outer link plates when a shifting operation from a second sprocket to a first sprocket is inadvertently completed with a failure. Thus, it is possible to maintain a correct chain phase for the second sprocket even after the shifting operation fails. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] A more complete understanding of the invention and many of the attendant advantages thereof will be readily obtained as the same become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. Fig. 1 is a side elevational view of a bicycle sprocket assembly according to a first embodiment. Fig. 2 is another side elevation view of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 3 is a perspective view of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 4 is a side elevational view of a first sprocket of the bicycle sprocket assembly shown in Fig. 1 is shown. Fig. 5 is a cross-sectional view of the first sprocket along the line VV of Fig. 4. Fig. 6 is a cross-sectional view of the first sprocket along the line VI-VI of Fig. 4. Fig. 7 is a side elevational view of a first tooth of the first sprocket shown in Fig. 1 illustrated bicycle sprocket arrangement. Fig. 8 is a side elevational view of a second tooth of the first sprocket shown in Fig. 1 illustrated bicycle sprocket arrangement. Fig. 9 is a partial perspective view of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 10 is another side elevational view of the first tooth of the first sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 11 is a partial perspective view of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 12 is another side elevational view of the second tooth of the first sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 13 is a cross-sectional view of the first sprocket along the line XIII-XIII of Fig. 22. Fig. 14 is a side elevational view of a second sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 15 is a cross-sectional view of the first sprocket along the line XV-XV of Fig. 14. Fig. 16 is a cross-sectional view of the first sprocket along the line XVI-XVI of Fig. 14. Fig. 17 is a partial side elevation view of the Fig. 1 illustrated bicycle sprocket arrangement with a bicycle chain (first gear shift). Fig. 18 is a partial side elevation view of the Fig. 1 shown bicycle sprocket arrangement with the bicycle chain (second gear shift). Fig. 19 is a cross-sectional view of the first sprocket along the line XIX-XIX of Fig. 22. Fig. 20 is a side elevational view of a switch relief tooth of the first sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 21 is another side elevational view of a switch relief tooth of the first sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 22 is a partial side elevation view of the Fig. 1 illustrated bicycle sprocket arrangement with the bicycle chain. Fig. 23 is a cross-sectional view of the first sprocket along the line XXIII-XXIII of Fig. 22. Fig. 24 is a side elevational view of a derailment tooth of the first sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 25 is another side elevational view of the derailing tooth of the first sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 26 is a cross-sectional view of the first sprocket along the line XXVI-XXVI of Fig. 22. Fig. 27 is a side elevational view of an additional tooth of the first sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 28 is another side elevational view of the additional tooth of the first sprocket of the Fig. 1 illustrated bicycle sprocket arrangement. Fig. 29 is a partial side elevation view of the Fig. 1 illustrated bicycle sprocket arrangement with the bicycle chain. Fig. 30 is a cross-sectional view of the first sprocket taken along the line XXX-XXX of Fig. 29. Fig. 31 is a cross-sectional view of the first sprocket taken along line XXXI-XXXI of Fig. 17. Fig. 32 is a cross-sectional view of the first sprocket along the line XXXII-XXXII of Fig. 17. Fig. 33 is a cross-sectional view of the first sprocket taken along the line XXXIII-XXXIII of Fig. 17. Fig. 34 is a partial perspective view of the bicycle sprocket assembly and a link plate of the bicycle chain (first shifting operation). Fig. 35 is a partial plan view of the bicycle sprocket assembly and the link plate of the bicycle chain (first shifting operation). Fig. 36 is a partial plan view of the bicycle sprocket assembly and the link plates of the bicycle chain. Fig. 37 is a partial perspective view of the bicycle sprocket assembly and the link plates of the bicycle chain. Fig. 38 is a partial perspective view of the bicycle sprocket assembly and the link plate of the bicycle chain (second shifting operation). Fig. 39 is a partial plan view of the bicycle sprocket assembly and the link plate of the bicycle chain (second shifting operation). Fig. 40 is a cross-sectional view of the first sprocket along the line XXXX-XXXX of Fig. 18. Fig. 41 is a partial perspective view of a bicycle sprocket assembly according to a second embodiment. Fig. 42 is a partial perspective view of the Fig. 41 illustrated bicycle sprocket assembly with a cross section. Fig. 43 is a partial perspective view of the bicycle sprocket assembly according to a modification of the second embodiment with a cross section. DESCRIPTION OF THE EMBODIMENTS

[0049] The embodiment(s) will now be described with reference to the accompanying drawings, in which like reference numerals designate corresponding or identical elements in the various drawings. First embodiment

[0050] With initial reference to Fig. 1, a bicycle crank assembly 10 includes a bicycle sprocket assembly 12 according to a first embodiment. The bicycle crank assembly 10 includes a crankshaft CA1 and crank arms CA2 and CA3. The crank arms CA2 and CA3 and the sprocket attachment member CA4 are attached to the crank axle CA1. The bicycle sprocket assembly 12 is attached to the crank arm CA2 for rotation about a rotational center axis A1 integrally with the crank axle CA1 and the crank arms CA2 and CA3. However, the bicycle sprocket assembly 12 may be attached to the crank axle CA1.

[0051] The bicycle sprocket assembly 12 is engageable with a bicycle chain C to transmit a pedaling force F1 between the bicycle chain C and the bicycle sprocket assembly 12. The bicycle sprocket assembly 12 is rotated in a first circumferential direction D11 about the rotational center axis A1 during pedaling. The first circumferential direction D11 extends along a circumferential direction D1 of the bicycle sprocket assembly 12. A second circumferential direction D12 extends along the circumferential direction D1 and is opposite to the first circumferential direction D11. In this embodiment, the bicycle sprocket assembly 12 is a front sprocket assembly. However, structures of the bicycle sprocket assembly 12 can also be applied to a rear sprocket assembly.

[0052] In the present application, the following directional terms "front," "rear," "forward," "backward," "left," "right," "across," "upward," and "downward," and other similar directional designations refer to those directions determined based on a user (e.g., a rider) sitting on a saddle (not shown) of a bicycle facing a handlebar (not shown). Accordingly, these terms, as used to describe the bicycle sprocket assembly 12, should be interpreted relative to the bicycle equipped with the bicycle sprocket assembly 12 as used in an upright riding position on a horizontal surface.

[0053] As in Fig. 2, the bicycle sprocket assembly 12 includes a first sprocket 14 and a second sprocket 16. The first sprocket 14 has a first pitch circle PC1. The second sprocket 16 has a second pitch circle PC2. The first pitch circle PC1 is defined by the centers C31 of pins C3 ( Fig. 18) of the bicycle chain C, which mesh with the first sprocket 14. The second pitch circle PC2 is defined by the centers C31 of the pins C3 ( Fig. 18) of the bicycle chain C, which engage with the second sprocket 16. The first sprocket 14 has a first pitch circle diameter PCD1. The second sprocket 16 has a second pitch circle diameter PCD2. The first pitch circle diameter PCD1 is a diameter of the first pitch circle PC1. The second pitch circle diameter PCD2 is a diameter of the second pitch circle PC2. The first pitch circle diameter PCD1 is larger than the second pitch circle diameter PCD2 of the second sprocket 16. In other words, the second pitch circle diameter PCD2 is smaller than the first pitch circle diameter PCD1. Thus, the first sprocket 14 can also be referred to as a larger sprocket 14, and the second sprocket 16 can also be referred to as a smaller sprocket 16.

[0054] The bicycle sprocket assembly 12 includes a mounting member 18. The mounting member 18 is coupled to the first sprocket 14 and the second sprocket 16. The mounting member 18 includes a mounting body 18A with an internal spline 18A1. The internal spline 18A1 is configured to mesh with an external spline of the crank arm CA2. Thus, the first sprocket 14, the second sprocket 16, and the mounting member 18 rotate together with the crank axle CA1 and the crank arms CA2 and CA3 about the rotational center axis A1.

[0055] As in Fig. As seen in Figure 3, the mounting member 18 includes connecting arms 18B extending radially outward from the mounting body 18A. The first sprocket 14 includes crank mounting portions 19. The second sprocket 16 includes additional crank mounting portions 20. The crank mounting portions 19 are each secured to the connecting arms 18B by fasteners such as bolts (not shown). The additional crank mounting portions 20 are secured to the connecting arms 18B by fasteners such as bolts (not shown).

[0056] The second sprocket 16 is adjacent to the first sprocket 14 in an axial direction D2 without another sprocket between the first sprocket 14 and the second sprocket 16. The axial direction D2 is parallel to the rotational center axis A1. A first axial direction D21 is defined along the axial direction D2. A second axial direction D22 is defined along the axial direction D2 and is opposite to the first axial direction D21. In this embodiment, the bicycle sprocket assembly 12 includes only the first sprocket 14 and the second sprocket 16. However, a total number of sprockets of the bicycle sprocket assembly 12 is not limited to this embodiment.

[0057] Each of the first sprocket 14 and the second sprocket 16 is engageable with the bicycle chain C to transmit the pedaling force F1 between the bicycle sprocket assembly 12 and the bicycle chain C. The bicycle chain C is shifted between the first sprocket 14 and the second sprocket 16 by a derailleur (not shown).

[0058] As in Fig. 4, the first sprocket 14 includes a first sprocket body 22 and a plurality of first sprocket teeth 24. The first sprocket body 22 has the rotational center axis A1. The plurality of first sprocket teeth 24 extend radially outward from the first sprocket body 22. The plurality of first sprocket teeth 24 include a plurality of first teeth 26 and a plurality of second teeth 28. The plurality of first sprocket teeth 24 and the plurality of second teeth 28 extend radially outward from the first sprocket body 22. The first teeth 26 and the second teeth 28 are arranged alternately in the circumferential direction D1.

[0059] The first sprocket 14 includes a plurality of first tooth bottoms 25 provided between the plurality of first sprocket teeth 24. The plurality of first tooth bottoms 25 define a first root circle RC1. The first root circle RC1 coincides with an outer circumference of the first sprocket body 22.

[0060] As in Fig. As shown in Fig. 5, the plurality of first teeth 26 are configured to engage an outer link space C11 provided between an opposing pair of outer link plates C1 of the bicycle chain C. The first tooth 26 extends radially outward from the first sprocket body 22 to be received only in the outer link space C11.

[0061] The plurality of first teeth 26 have a first maximum axial width W11 defined in the axial direction D2. The first tooth 26 includes a first chain engagement surface 26A and a first additional chain engagement surface 26B. The first chain engagement surface 26A faces the axial direction D2. The first additional chain engagement surface 26B faces the axial direction D2 and is provided on a rear side of the first chain engagement surface 26A. The first maximum axial width W11 is defined between the first chain engagement surface 26A and the first additional chain engagement surface 26B in the axial direction D2. The first maximum axial width W11 may also be referred to as maximum axial width W11.

[0062] The first tooth 26 has a first center plane CP1 defined to bisect the first maximum axial width W11 in the axial direction D2. The first center plane CP1 is perpendicular to the rotational center axis A1. The first tooth 26 has a symmetrical shape with respect to the first center plane CP1. However, the first tooth 26 may have an asymmetrical shape with respect to the first center plane CP1.

[0063] The first tooth 26 includes a first inclined surface 26E, a first additional inclined surface 26F, and a radially outermost edge 26T. The first tooth 26 has a first radial length 26L defined radially from the root circle RC1 to the radially outermost edge 26T. The first inclined surface 26E extends from the radially outermost edge 26T toward the first chain engagement surface 26A. The first additional inclined surface 26F extends from the radially outermost edge 26T toward the first additional chain engagement surface 26B. The first inclined surface 26E is inclined relative to the first chain engagement surface 26A by a first inclination angle AG11. The first additional inclined surface 26F is inclined relative to the first additional chain engagement surface 26B by a first additional inclination angle AG12. The first inclination angle AG11 is essentially equal to the first additional inclination angle AG12.However, the first inclination angle AG11 may be different from the first additional inclination angle AG12.

[0064] An imaginary plane IP26A is defined along the first chain engagement surface 26A. An imaginary plane IP26B is defined along the first additional chain engagement surface 26B. An imaginary plane IP26E is defined along the first inclined surface 26E. An imaginary plane IP26F is defined along the first additional inclined surface 26F. A radial distance 26K1 is defined radially from the root circle RC1 to an intersection point P26A of the imaginary planes IP26A and IP26E. A radial distance 26K2 is defined radially from the root circle RC1 to an intersection point P26B of the imaginary planes IP26B and IP26F. The radial distance 26K2 is equal to the radial distance 26K1. However, the radial distance 26K2 can deviate from the radial distance 26K1.

[0065] As in Fig. As can be seen in Fig. 6, the plurality of second teeth 28 are configured to engage an inner link space C21 provided between an opposed pair of inner link plates C2 of the bicycle chain C. The second tooth 28 extends radially outward from the first sprocket body 22 to be received only in the inner link space C21 of the bicycle chain C during riding.

[0066] The plurality of second teeth 28 have a second maximum axial width W21 defined in the axial direction D2. The second tooth 28 includes a second chain engagement surface 28A and a second additional chain engagement surface 28B. The second chain engagement surface 28A faces the axial direction D2. The second additional chain engagement surface 28B faces the axial direction D2 and is provided on a rear side of the second chain engagement surface 28A. The second maximum axial width W21 is defined between the second chain engagement surface 28A and the second additional chain engagement surface 28B in the axial direction D2. The second maximum axial width W21 may also be referred to as maximum axial width W21.

[0067] The second tooth 28 has a second center plane CP2 defined to bisect the second maximum axial width W21 in the axial direction D2. The second center plane CP2 is perpendicular to the rotational center axis A1. In this embodiment, the second center plane CP2 coincides with the first center plane CP1. However, the second center plane CP2 may be offset from the first center plane CP1 in the axial direction D2. The second tooth 28 has a symmetrical shape with respect to the second center plane CP2. However, the second tooth 28 may have an asymmetrical shape with respect to the second center plane CP2.

[0068] As in Fig. As can be seen in Figure 6, the first maximum axial width W11 is greater than the second maximum axial width W21. In other words, the second maximum axial width W21 is smaller than the first maximum axial width W11. The first maximum axial width W11 is smaller than an axial width of the outer link space C11 and is greater than an axial width of the inner link space C21. The second maximum axial width W21 is smaller than the axial width of the inner link space C21. However, the first maximum axial width W11 may be equal to or smaller than the second maximum axial width W21.

[0069] The second tooth 28 includes a second inclined surface 28E, a second additional inclined surface 28F, and a radially outermost edge 28T. The second tooth 28 has a second radial length 28L defined radially from the root circle RC1 to the radially outermost edge 28T. The second inclined surface 28E extends from the radially outermost edge 28T toward the second chain engagement surface 28A. The second additional inclined surface 28F extends from the radially outermost edge 28T toward the second additional chain engagement surface 28B. The second inclined surface 28E is inclined relative to the second chain engagement surface 28A by a second inclination angle AG21. The second additional inclined surface 28F is inclined relative to the second additional chain engagement surface 28B by a second additional inclination angle AG22. The second inclination angle AG21 is essentially equal to the second additional inclination angle AG22.However, the second inclination angle AG21 may differ from the second additional inclination angle AG22.

[0070] In this embodiment, the first inclination angle AG11 is greater than the second inclination angle AG21 and the second additional inclination angle AG22. The first additional inclination angle AG12 is greater than the second inclination angle AG21 and the second additional inclination angle AG22. However, the first inclination angle AG11 can be equal to or smaller than the second inclination angle AG21 or the second additional inclination angle AG22. The first additional inclination angle AG12 can be equal to or smaller than the second inclination angle AG21 or the second additional inclination angle AG22.

[0071] An imaginary plane IP28A is defined along the second chain engagement surface 28A. An imaginary plane IP28B is defined along the second additional chain engagement surface 28B. An imaginary plane IP28E is defined along the second inclined surface 28E. An imaginary plane IP28F is defined along the second additional inclined surface 28F. A radial distance 28K1 is defined radially from the base circle RC1 to an intersection point P28A of the imaginary planes IP28A and IP28E. A radial distance 28K2 is defined radially from the root circle RC1 to an intersection point P28B of the imaginary planes IP28B and IP28F. The radial distance 28K2 is equal to the radial distance 28K1. However, the radial distance 28K2 can deviate from the radial distance 28K1.

[0072] As in Fig. 5 and Fig. As seen in Figure 6, the plurality of first sprocket teeth 24 each have a maximum axial upper width and a maximum axial lower width. Each of the plurality of first sprocket teeth 24 includes a lower portion and an upper portion extending radially outward from the lower portion. The upper portion has the maximum axial upper width of each of the plurality of first sprocket teeth 24. The lower portion has the maximum axial lower width of each of the plurality of first sprocket teeth 24.

[0073] As in Fig. As can be seen in Figure 5, the first tooth 26 has a maximum axial upper width W12 and a maximum axial lower width W13. The maximum axial upper width W12 is defined in the axial direction D2. The maximum axial lower width W13 is defined in the axial direction D2. The first tooth 26 includes an upper portion 26C and a lower portion 26D. The upper portion 26C extends radially outward from the lower portion 26D. The upper portion 26C has the maximum axial upper width W12. The lower portion 26D has the maximum axial lower width W13.

[0074] In this embodiment, the maximum axial upper width W12 is equal to the maximum axial lower width W13. The maximum axial upper width W12 and the maximum axial lower width W13 are equal to the first maximum axial width W11. However, at least one of the first maximum axial width W11, the maximum axial upper width W12, and the maximum axial lower width W13 may be different from another of the first maximum axial width W11, the maximum axial upper width W12, and the maximum axial lower width W13.

[0075] As in Fig. As shown in Figure 7, the first sprocket 14 has a reference circle RC21 with respect to the rotational center axis A1 of the bicycle sprocket assembly 12. The upper portion 26C is provided radially outside the reference circle RC21. The lower portion 26D is provided radially inside the reference circle RC21. The upper portion 26C is provided between the reference circle RC21 and the radially outermost edge 26T of the first tooth 26. The lower portion 26D is provided between the reference circle RC21 and the first root circle RC1.

[0076] The first sprocket 14 has a first outer circle RC22 and a first inner circle RC23. A first outer distance DS11 is defined radially outward from the first pitch circle PC1 to the first outer circle RC22. The first outward distance DS11 is equal to or less than 3 mm. A first inward distance DS12 is defined radially inward from the first pitch circle PC1 to the first inner circle RC23. The first inward distance DS12 is equal to or less than 4 mm. The reference circle RC21 is provided between the first outer circle RC22 and the first inner circle RC23. The reference circle RC21 is preferably provided on the first pitch circle PC1 or provided radially inward from the first pitch circle PC1. In this embodiment, the reference circle RC21 is provided between the first pitch circle PC1 and the first inner circle RC23.The reference circle RC21 is provided radially inside the first pitch circle PC1 by 1.8 mm. However, the reference circle RC21 can be provided in a radial area between the first outer circle RC22 and the first inner circle RC23.

[0077] As in Fig. 6, the second tooth 28 has a maximum axial upper width W22 and a maximum axial lower width W23. The maximum axial upper width W22 is defined in the axial direction D2. The maximum axial lower width W23 is defined in the axial direction D2. The second tooth 28 includes an upper portion 28C and a lower portion 28D. The upper portion 28C extends radially outward from the lower portion 28D. The upper portion 28C has the maximum axial upper width W22. The lower portion 28D has the maximum axial lower width W23. The second maximum axial width W21 of the second tooth 28 is smaller than the maximum axial lower width W13 of the first tooth 26.

[0078] In this embodiment, the maximum axial upper width W22 is equal to the maximum axial lower width W23. The maximum axial upper width W22 and the maximum axial lower width W23 are equal to the second maximum axial width W21. However, at least one of the second maximum axial width W21, the maximum axial upper width W22, and the maximum axial lower width W23 may be different from another of the second maximum axial width W21, the maximum axial upper width W22, and the maximum axial lower width W23.

[0079] As in Fig. As can be seen in Figure 8, the upper portion 28C is provided radially outside the reference circle RC21. The lower portion 28D is provided radially inside the reference circle RC21. The upper portion 28C is provided between the reference circle RC21 and the radially outermost edge 28T of the second tooth 28. The lower portion 28D is provided between the reference circle RC21 and the first root circle RC1.

[0080] As in Fig. 5, each of the plurality of first teeth 26 includes a first protrusion 26P1 provided on one of a first axial side 26S1 and a second axial side 26S2 of the lower portion 26D. Each of the plurality of first teeth 26 includes a second protrusion 26P2 provided on another of the first axial side 26S1 and the second axial side 26S2 of the lower portion 26D. The first axial side 26S1 is a rear side of the second axial side 26S2 in the axial direction D2 parallel to the rotational center axis A1. In this embodiment, the first protrusion 26P1 is provided on the first axial side 26S1 of the lower portion 26D. The second protrusion 26P2 is provided on the second axial side 26S2. However, at least one of the first protrusion 26P1 and the second protrusion 26P2 may be omitted from the first tooth 26.

[0081] In this embodiment, the first protrusion 26P1 is provided on the first axial side 26S1 of the upper portion 26C. The second protrusion 26P2 is provided on the second axial side 26S2 of the upper portion 26C. However, the first protrusion 26P1 may be provided on the first axial side 26S1 of only one of the upper part 26C and the lower part 26D. The second protrusion 26P2 may be provided on the second axial side 26S2 of only one of the upper portion 26C and the lower portion 26D.

[0082] As in Fig. As can be seen in Figure 7, the plurality of first teeth 26 include a drive surface 26DS1 and a non-drive surface 26DS2. The drive surface 26DS1 faces the first circumferential direction D11, in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. The non-drive surface 26DS2 faces the second circumferential direction D12, which is opposite to the first circumferential direction D11. As shown in Fig. 4, the drive surface 26DS1 of the plurality of first teeth 26 is arranged in the circumferential direction D1 with a constant pitch.

[0083] As in Fig. 7 and Fig. 9, the lower portion 26D of the plurality of first teeth 26 includes the first chain engagement surface 26A, a first lower engagement surface 26G, and a first chamfer 26R1. The first chamfer 26R1 is provided between the first chain engagement surface 26A and the first lower engagement surface 26G. The first lower engagement surface 26G faces the first circumferential direction D11 in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. The drive surface 26DS1 includes the first lower engagement surface 26G. The upper portion 26C and the lower portion 26D include the first chain engagement surface 26A. However, the first chain engagement surface 26A may be provided only for the lower portion 26D. The upper portion 26C and the lower portion 26D include the first chamfer 26R1.

[0084] The lower portion 26D of the plurality of first teeth 26 includes a first lower non-drive surface 26K and a second chamfer 26R2. The second chamfer 26R2 is provided between the first chain engagement surface 26A and the first lower non-drive surface 26K. The first lower non-drive surface 26K faces the second circumferential direction D12, which is opposite to the first circumferential direction D11 in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. The non-drive surface 26DS2 includes the first lower non-drive surface 26K. The upper portion 26C and the lower portion 26D include the second chamfer 26R2.

[0085] As in Fig. 10 and Fig. As shown in Figure 11, the lower portion 26D of the plurality of first teeth 26 includes a third chamfer 26R3. The third chamfer 26R3 is provided between the first additional chain engagement surface 26B and the first lower engagement surface 26G. The upper portion 26C and the lower portion 26D include the third chamfer 26R3.

[0086] The lower portion 26D of the plurality of first teeth 26 includes a fourth land 26R4. The fourth land 26R4 is provided between the first additional chain engagement surface 26B and the first lower non-drive surface 26K. The upper portion 26C and the lower portion 26D include the fourth land 26R4.

[0087] As in Fig. As can be seen in Figure 8, each of the plurality of second teeth 28 includes a drive surface 28DS1 and a non-drive surface 28DS2. The drive surface 28DS1 faces the first circumferential direction D11, in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. The non-drive surface 28DS2 faces the second circumferential direction D12, which is opposite to the first circumferential direction D11. As shown in Fig. 4, the drive surface 28DS1 of the plurality of second teeth 28 is arranged in the circumferential direction D1 with a constant pitch.

[0088] As in Fig. 8 and Fig. 9, the upper portion 28C of the plurality of second teeth 28 includes the second chain engagement surface 28A, a second upper drive surface 28G, and a first chamfer 28R1. The first chamfer 28R1 is provided between the second chain engagement surface 28A and the second upper drive surface 28G. The second upper drive surface 28G faces the first circumferential direction D11. The drive surface 28DS1 includes the second upper drive surface 28G. The upper portion 28C and the lower portion 28D include the second chain engagement surface 28A. However, the second chain engagement surface 28D may be provided only for the lower portion 28D.

[0089] The upper portion 28C of the plurality of second teeth 28 includes a second upper non-drive surface 28K and a second chamfer 28R2. The second chamfer 28R2 is provided between the second chain engagement surface 28A and the second upper non-drive surface 28K. The second upper non-drive surface 28K faces the second circumferential direction D12. The non-drive surface 28DS2 includes the second upper non-drive surface 28K.

[0090] As in Fig. 11 and Fig. As can be seen in Figure 12, the upper portion 28C of the second teeth 28 includes a third land 28R3. The third land 28R3 is provided between the second additional chain engagement surface 28B and the second upper drive surface 28G.

[0091] The upper portion 28C of the second teeth 28 has a fourth land 28R4. The fourth land 28R4 is provided between the second additional chain engagement surface 28B and the second upper non-drive surface 28K.

[0092] The structures of the first tooth 26 and the second tooth 28 are not limited to this embodiment. At least one of the first tooth 26 and the second tooth 28 may have other shapes, such as a twisted shape or a curved shape.

[0093] As in Fig. As seen in Figure 13, the first sprocket 14 includes a first side surface 14A and a second side surface 14B. The first side surface 14A is provided on the first sprocket body 22. The second side surface 14B is provided on the first sprocket body 22. The second side surface 14B is provided on a rear side of the first side surface 14A in the axial direction D2. The first side surface 14A faces the first axial direction D21. The second side surface 14B faces the second axial direction D22. The first side surface 14A faces the second sprocket 16 in the axial direction D2.

[0094] As in Fig. 14, the second sprocket 16 includes a second sprocket body 32 and a plurality of second sprocket teeth 34. The second sprocket body 32 has the rotational center axis A1. The plurality of second sprocket teeth 34 extend radially outward from the second sprocket body 32. The plurality of second sprocket teeth 34 include a plurality of third teeth 36 and a plurality of fourth teeth 38. The plurality of third teeth 36 and the plurality of fourth teeth 38 extend radially outward from the second sprocket body 32. The third teeth 36 and the fourth teeth 38 are arranged alternately in the circumferential direction D1.

[0095] As in Fig. 4 and Fig. As seen in Figure 14, a total number (28 in this embodiment) of the plurality of second sprocket teeth 34 is less than a total number (40 in this embodiment) of the plurality of first sprocket teeth 24. However, the total number of the plurality of first sprocket teeth 24 is not limited to this embodiment. The total number of the plurality of second sprocket teeth 34 is not limited to this embodiment. For example, the total number of the plurality of second sprocket teeth may be 26. The total number of the plurality of first sprocket teeth may be 38. The plurality of first sprocket teeth 24 are made of a first material having a first wear resistance. The plurality of second sprocket teeth 34 are made of a second material having a second wear resistance. The first wear resistance is greater than the second wear resistance. However, the first wear resistance may be equal to or less than the second wear resistance.Examples of the first material include iron, stainless steel, and a metallic material with a plated layer. The plated layer may, for example, comprise a nickel-chromium plating plated on a base material made of an aluminum alloy. Examples of the second material include iron, stainless steel, aluminum, and titanium.

[0096] As in Fig. As shown in Fig. 15, the plurality of third teeth 36 are configured to engage the outer link space C11 provided between the opposing pair of outer link plates C1 of the bicycle chain C. The third teeth 36 extend radially outward from the first sprocket body 22 to be received only in the outer link space C11.

[0097] The plurality of third teeth 36 have a third maximum axial width W31 defined in the axial direction D2. The third tooth 36 includes a third chain engagement surface 36A and a third additional chain engagement surface 36B. The third chain engagement surface 36A may also be referred to as a chain engagement surface 36A. The third additional chain engagement surface 36B may also be referred to as a chain engagement surface 36B. The third chain engagement surface (the chain engagement surface) 36A faces the axial direction D2. The third additional chain engagement surface 36B (the chain engagement surface) faces the axial direction D2 and is provided on a rear side of the third chain engagement surface 36A. The third maximum axial width W31 is defined between the third chain engagement surface 36A and the third additional chain engagement surface 36B in the axial direction D2.

[0098] The third tooth 36 has a third center plane CP3 defined to halve the third maximum axial width W31 in the axial direction D2. The third center plane CP3 is perpendicular to the rotational center axis A1.

[0099] At least one tooth of the plurality of third teeth 36 includes a radially outermost edge 36T and an inclined surface 36E and an inclined surface 36F. The third tooth 36 has a third radial length 36L defined radially from the root circle RC1 to the radially outermost edge 36T. The inclined surface 36E extends from the chain engagement surface 36A toward the radially outermost edge 36T. The inclined surface 36F extends from the chain engagement surface 36B toward the radially outermost edge 36T. The inclined surface 36E is inclined relative to the chain engagement surface 36A by an inclination angle AG31 that is equal to or greater than 40 degrees. The inclined surface 36F is inclined relative to the chain engagement surface 36B by an inclination angle AG32 that is equal to or greater than 40 degrees. In this embodiment, the inclination angle AG31 is equal to the inclination angle AG32. The inclination angle AG31 is 45 degrees. The inclination angle AG32 is 45 degrees.However, the inclination angles AG31 and AG32 are not limited to this embodiment and the above ranges. The inclination angle AG31 may be different from the inclination angle AG32. The inclination angle AG31 may be 90 degrees. The inclination angle AG32 may be 90 degrees. Preferably, the inclination angles AG31 and AG32 are in a range of less than or equal to 90 degrees and greater than or equal to 40 degrees.

[0100] Each of the inclination angles AG31 and AG32 is greater than the first inclination angle AG11 ( Fig. 5) and the first additional inclination angle AG12 ( Fig. 5). However, at least one of the inclination angles AG31 and AG32 may be equal to or smaller than the first inclination angle AG11 ( Fig. 5) or the first additional inclination angle AG12 ( Fig. 5).

[0101] An imaginary plane IP36A is defined along the chain engagement surface 36A. An imaginary plane IP36B is defined along the chain engagement surface 36B. An imaginary plane IP36E is defined along the inclined surface 36E. An imaginary plane IP36F is defined along the inclined surface 36F. A radial distance 36K1 is defined radially from the root circle RC1 to an intersection point P36A of the imaginary planes IP36A and IP36E. A radial distance 36K2 is defined radially from the root circle RC1 to an intersection point P36B of the imaginary planes IP36B and IP36F. The radial distance 36K2 is equal to the radial distance 36K1. However, the radial distance 36K2 can differ from the radial distance 36K1.

[0102] Each of the radial distances 36K1 and 36K2 is greater than the radial distances 26K1 and 26K2 ( Fig. 5). Each of the radial distances 36K1 and 36K2 is greater than the radial distances 28K1 and 28K2 ( Fig. 6). However, at least one of the radial distances 36K1 and 36K2 may be equal to or less than at least one of the radial distances 26K1 and 26K2 ( Fig. 5). At least one of the radial distances 36K1 and 36K2 may be equal to or smaller than at least one of the radial distances 28K1 and 28K2 ( Fig. 6).

[0103] The third radial length 36L is greater than the first radial length 26L ( Fig. 5). However, the third radial length 36L may be equal to or less than the first radial length 36L ( Fig. 5).

[0104] As in Fig. As seen in Fig. 16, the plurality of fourth teeth 38 are configured to engage the inner link space C21 provided between the opposing pair of inner link plates C2 of the bicycle chain C. The fourth tooth 38 extends radially outward from the second sprocket body 32 to be received only in the inner link space C21.

[0105] The plurality of fourth teeth 38 have a fourth maximum axial width W41 defined in the axial direction D2. The fourth tooth 38 includes a fourth chain engagement surface 38A and a fourth additional chain engagement surface 38B. The fourth chain engagement surface 38A faces the axial direction D2. The fourth additional chain engagement surface 38B faces the axial direction D2 and is provided on a rear side of the fourth chain engagement surface 38A. The fourth maximum axial width W41 is defined between the fourth chain engagement surface 38A and the fourth additional chain engagement surface 38B in the axial direction D2.

[0106] The fourth tooth 38 has a fourth center plane CP4 defined to halve the fourth maximum axial width W41 in the axial direction D2. The fourth center plane CP4 is perpendicular to the rotational center axis A1. In this embodiment, the fourth center plane CP4 coincides with the third center plane CP3. However, the fourth center plane CP4 may be offset from the third center plane CP3 in the axial direction D2.

[0107] As in Fig. As can be seen in Figure 16, the third maximum axial width W31 is greater than the fourth maximum axial width W41. In other words, the fourth maximum axial width W41 is smaller than the third maximum axial width W31. The third maximum axial width W31 is smaller than an axial width of the outer link space C11 and is greater than an axial width of the inner link space C21. The fourth maximum axial width W41 is smaller than the axial width of the inner link space C21. However, the third maximum axial width W31 may be equal to or smaller than the fourth maximum axial width W41.

[0108] At least one tooth of the plurality of third teeth 38 includes a radially outermost edge 38T and an inclined surface 38E and an inclined surface 38F. The fourth tooth 38 has a fourth radial length 38L defined radially from the root circle RC1 to the radially outermost edge 38T. The inclined surface 38E extends from the chain engagement surface 38A toward the radially outermost edge 38T. The inclined surface 38F extends from the chain engagement surface 38B toward the radially outermost edge 38T. The inclined surface 38E is inclined relative to the chain engagement surface 38A by an inclination angle AG41. The inclined surface 38F is inclined relative to the chain engagement surface 38B by an inclination angle AG42. In this embodiment, the inclination angle AG41 is equal to the inclination angle AG42. However, the inclination angle AG41 may differ from the inclination angle AG42.

[0109] The inclination angle AG31 ( Fig. 15) is greater than the inclination angles AG41 and AG42. The inclination angle AG42 is greater than the first inclination angle AG11 and the first additional inclination angle AG12. At least one of the inclination angles AG31 and AG32 ( Fig. 15) may, however, be equal to or less than at least one of the inclination angles AG41 and AG42.

[0110] An imaginary plane IP38A is defined along the chain engagement surface 38A. An imaginary plane IP38B is defined along the chain engagement surface 38B. An imaginary plane IP38E is defined along the inclined surface 38E. An imaginary plane IP38F is defined along the inclined surface 38F. A radial distance 38K1 is defined radially from the root circle RC1 to an intersection point P38A of the imaginary planes IP38A and IP38E. A radial distance 38K2 is defined radially from the root circle RC1 to an intersection point P38B of the imaginary planes IP38B and IP38F. The radial distance 38K2 is equal to the radial distance 38K1. However, the radial distance 38K2 can differ from the radial distance 38K1.

[0111] Each of the radial distances 36K1 and 36K2 ( Fig. 15) is greater than the radial distances 38K1 and 38K2. However, at least one of the radial distances 36K1 and 36K2 may be equal to or less than at least one of the radial distances 38K1 and 38K2.

[0112] The third radial length 36L ( Fig. 15) is greater than the fourth radial length 38L. The third radial length 36L ( Fig. 15) may, however, be equal to or less than the fourth radial length 38L.

[0113] In this embodiment, the structure of the third tooth 36 is substantially the same as that of the first tooth 26. The structure of the fourth tooth 38 is substantially the same as that of the second tooth 28. Thus, they will not be described in detail here for the sake of brevity.

[0114] The structures of the third tooth 36 and the fourth tooth 38 are not limited to this embodiment. The third tooth 36 may have a structure different from that of the first tooth 26. The fourth tooth 38 may have a structure different from that of the second tooth 28. At least one of the third tooth 36 and the fourth tooth 38 may have a different shape, such as a twisted shape or a bent shape.

[0115] As in Fig. As seen in Figure 17, the first sprocket 14 includes a first shift facilitation protrusion 42 to facilitate the shifting operation. The first shift facilitation protrusion 42 is configured to facilitate a first shifting operation in which the bicycle chain C is shifted from the second sprocket 16 to the first sprocket 14. The first shift facilitation protrusion 42 is provided on the first side surface 14A to lift the outer link plate C1A in the first shifting operation. In this embodiment, the first shift facilitation protrusion 42 is attached to the first sprocket body 22 with a fastening structure, such as a rivet.

[0116] The first sprocket 14 includes a first additional shift facilitation protrusion 44 configured to facilitate the first shifting operation. The first additional shift facilitation protrusion 44 is provided on the first side surface 14A to move the inner link plate C2A toward the first sprocket 14 during the first shifting operation. In this embodiment, the first additional shift facilitation protrusion 44 is attached to the first sprocket body 22 with a fastening structure, such as a rivet.

[0117] As in Fig. As seen in Fig. 18, the first sprocket 14 includes a second shift facilitating protrusion 46 to facilitate the shifting operation. The second shift facilitating protrusion 46 is provided on the first side surface 14A to facilitate a second shifting operation in which the bicycle chain C is shifted from the first sprocket 14 to the second sprocket 16. The second shift facilitating protrusion 46 is configured to engage with the outer link plate C1B to adjust a chain phase of the bicycle chain C for the second sprocket 16 while the bicycle chain C is shifted from the first sprocket 14 toward the second sprocket 16. In this embodiment, the second shift facilitating protrusion 46 is fixed to the first sprocket body 22 with a fixing structure such as a rivet.

[0118] As in Fig. 4, the first sprocket 14 includes a pair of first switch facilitation protrusions 42. The first sprocket 14 includes a pair of first additional switch facilitation protrusions 44. The first sprocket 14 includes a pair of second switch facilitation protrusions 46. However, the total number of the first switch facilitation protrusions 42 is not limited to this embodiment. A total number of the first additional switch facilitation protrusions 44 is not limited to this embodiment. A total number of the second switch facilitation protrusions 46 is not limited to this embodiment. At least one of the first switch facilitation protrusion 42, the first additional switch facilitation protrusion 44, and the second switch facilitation protrusion 46 may be omitted from the first sprocket 14.

[0119] The first sprocket 14 includes a shift facilitation area SF for facilitating a shifting operation in which the bicycle chain C is shifted between the first sprocket 14 and the second sprocket 16 adjacent to the first sprocket 14. In this embodiment, the first sprocket 14 includes a pair of shift facilitation areas SF. However, a total number of shift facilitation areas SF is not limited to this embodiment.

[0120] The first switch facilitation protrusion 42, the first additional switch facilitation protrusion 44, and the second switch facilitation protrusion 46 are provided in the switch facilitation region SF. The switch facilitation region SF is defined from the first tooth 26X of the plurality of first teeth 26 to the first tooth 26Y of the plurality of first teeth 26. The first tooth 26X is closest to the first switch facilitation protrusion 42 among the plurality of first sprocket teeth 24. The first tooth 26Y is closest to the second switch facilitation protrusion 46 among the plurality of first sprocket teeth 24. The switch facilitation region SF has an angular range of less than 180 degrees. The switch facilitation region SF has an angular range of preferably less than 60 degrees.

[0121] As in Fig. As seen in Figure 17, the plurality of first teeth 26 include a switch relief tooth 48. The switch relief tooth 48 extends radially outward from the first sprocket body 22. The switch relief tooth 48 is provided in the switch relief region SF.

[0122] The shift facilitation tooth 48 is configured to first engage with the outer link space C11 of the bicycle chain C in the first shifting operation in which the bicycle chain C is shifted from the second sprocket 16 to the first sprocket 14. The shift facilitation tooth 48 is provided on an upstream side of the first shift facilitation projection 42 in the first circumferential direction D11 in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. As shown in Fig. As shown in Figure 17, the shift relief tooth 48 is spaced from the first shift relief projection 42 by a first distance DT1, which corresponds to two chain pitches PT of the bicycle chain C. The chain pitch PT is defined between the centers C31 of adjacent two pins C3 of the bicycle chain C. Examples of the chain pitch PT include 12.7 mm and 13 mm. The first pitch circle PC1 can be varied according to the chain pitch.

[0123] The shift relief tooth 48 is provided on a downstream side of the second shift relief protrusion 46 in the first circumferential direction D11, in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. The shift relief tooth 48 is spaced from the second shift relief protrusion 46 by a second distance DT2, which corresponds to two chain pitches PT of the bicycle chain C.

[0124] As in Fig. As seen in Fig. 19, the shift facilitation tooth 48 is configured to engage the outer link space C11 provided between the opposed pair of outer link plates C1 of the bicycle chain C. The shift facilitation tooth 48 extends radially outward from the first sprocket body 22 to be received only in the outer link space C11.

[0125] The switch facilitation tooth 48 has a maximum axial width W51 defined in the axial direction D2. The switch facilitation tooth 48 includes a chain engagement surface 48A and an additional chain engagement surface 48B. The chain engagement surface 48A faces the axial direction D2. The additional chain engagement surface 48B faces the axial direction D2 and is provided on a rear side of the chain engagement surface 48A. The maximum axial width W51 is defined between the chain engagement surface 48A and the additional chain engagement surface 48B in the axial direction D2.

[0126] The shift relief tooth 48 includes an inclined surface 48E, an inclined surface 48F, and a radially outermost edge 48T. The inclined surface 48E extends from the radially outermost edge 48T toward the chain engagement surface 48A. The inclined surface 48F extends from the radially outermost edge 48T toward the additional chain engagement surface 48B. The inclined surface 48E is inclined relative to the chain engagement surface 48A by an inclination angle AG51. The inclined surface 48F is inclined relative to the additional chain engagement surface 48B by an additional inclination angle AG52. The inclination angle AG51 is substantially equal to the additional inclination angle AG52. However, the inclination angle AG51 may differ from the additional inclination angle AG52.

[0127] The switch relief tooth 48 has a maximum axial upper width W52 and a maximum axial lower width W53. The maximum axial upper width W52 is defined in the axial direction D2. The maximum axial lower width W53 is defined in the axial direction D2. The switch relief tooth 48 includes an upper portion 48C and a lower portion 48D. The upper portion 48C extends radially outward from the lower portion 48D. The upper portion 48C has the maximum axial upper width W52. The lower portion 48D has the maximum axial lower width W53. The maximum axial upper width W52 is defined on the reference circle RC11.

[0128] In this embodiment, the maximum axial upper width W52 differs from the maximum axial lower width W53. The maximum axial upper width W52 of the switch facilitation tooth 48 is smaller than the maximum axial lower width W53 of the switch facilitation tooth 48. However, the maximum axial upper width W52 may be equal to or greater than the maximum axial lower width W53. At least one of the maximum axial width W51, the maximum axial upper width W52, and the maximum axial lower width W53 may differ from another of the maximum axial width W51, the maximum axial upper width W52, and the maximum axial lower width W53.

[0129] A ratio of the maximum axial upper width W52 to the maximum axial lower width W53 is in the range of 10% to 90%. The ratio of the maximum axial upper width W52 to the maximum axial lower width W53 is preferably in the range of 20% to 80%. More preferably, the ratio of the maximum axial upper width W52 to the maximum axial lower width W53 is in the range of 30% to 70%. In this embodiment, the ratio of the maximum axial upper width W52 to the maximum axial lower width W53 is 65%. However, the ratio of the maximum axial upper width W52 to the maximum axial lower width W53 is not limited to this embodiment and the above ranges.

[0130] The switch relief tooth 48 has an additional axial width W54. The additional axial width W54 is defined in the axial direction D2. The additional axial width W54 is defined on the first pitch circle PC1. The additional axial width W54 is smaller than the maximum axial upper width W52. A ratio of the additional axial width W54 to the maximum axial lower width W53 is in the range of 10% to 90%. The ratio of the additional axial width W54 to the maximum axial lower width W53 is preferably in the range of 20% to 50%. In this embodiment, the ratio of the additional axial width W54 to the maximum axial lower width W53 is 34%. However, the ratio of the additional axial width W54 to the maximum axial lower width W53 is not limited to this embodiment and the above ranges.

[0131] The switch facilitation tooth 48 has a symmetrical shape with respect to the first center plane CP1. However, the switch facilitation tooth 48 may have an asymmetrical shape with respect to the first center plane CP1.

[0132] As in Fig. As shown in Figure 20, the upper portion 48C is located radially outside the reference circle RC21. The lower portion 48D is located radially inside the reference circle RC21. The upper portion 48C is located between the reference circle RC21 and the radially outermost edge 48T of the switch relief tooth 48. The lower portion 48D is located between the reference circle RC21 and the first root circle RC1.

[0133] As in Fig. As seen in Figure 19, the switch facilitating tooth 48 includes a first protrusion 48P1 provided on one of a first axial side 48S1 and a second axial side 48S2 of the lower portion 48D. The switch facilitating tooth 48 includes a second protrusion 48P2 provided on another of the first axial side 48S1 and the second axial side 48S2 of the lower portion 48D. The first axial side 48S1 is the rear side of the second axial side 48S2 in the axial direction D2 parallel to the rotational center axis A1. In this embodiment, the first protrusion 48P1 is provided on the first axial side 48S1 of the lower portion 48D. The second protrusion 48P2 is provided on the second axial side 48S2. However, at least one of the first protrusion 48P1 and the second protrusion 48P2 may be omitted from the switch facilitating tooth 48.

[0134] In this embodiment, the first protrusion 48P1 is provided only on the first axial side 48S1 of the lower portion 48D. The second protrusion 48P2 is provided only on the second axial side 48S2 of the lower portion 48D. However, the first protrusion 48P1 may be provided on the first axial side 48S1 of the upper portion 48C and the lower portion 48D. The second protrusion 48P2 may be provided on the second axial side 48S2 of the upper portion 48C and the lower portion 48D.

[0135] As in Fig. As can be seen in Figure 20, the switch relief tooth 48 includes a driving surface 48DS1 and a driving surface 48DS2. The driving surface 48DS1 faces the first circumferential direction D11. The non-driving surface 48DS2 faces the second circumferential direction D12.

[0136] As in Fig. 9 and Fig. As shown in Figure 20, the lower portion 48D of the shift facilitation tooth 48 includes the chain engagement surface 48A, a first lower engagement surface 48G, and a first chamfer 48R1. The first chamfer 48R1 is provided between the chain engagement surface 48A and the first lower engagement surface 48G. The first lower engagement surface 48G faces the first circumferential direction D11. The drive surface 48DS1 includes the first lower engagement surface 48G.

[0137] The lower portion 48D of the shift facilitation tooth 48 includes a first lower non-drive surface 48K and a second land 48R2. The second land 48R2 is provided between the chain engagement surface 48A and the first lower non-drive surface 48K. The first lower non-drive surface 48K faces the second circumferential direction D12, which is opposite to the first circumferential direction D11. The non-drive surface 48DS2 includes the first lower non-drive surface 48K.

[0138] As in Fig. 11 and Fig. As seen in Figure 21, the lower portion 48D of the switch relief tooth 48 includes a third chamfer 48R3. The third chamfer 48R3 is provided between the additional chain engagement surface 48B and the first lower engagement surface 48G. The upper portion 48C and the lower portion 48D include the third chamfer 48R3. The chain engagement surface 48A is provided only in the lower portion 48D.

[0139] The lower portion 48D of the shift facilitation tooth 48 has a fourth land 48R4. The fourth land 48R4 is provided between the additional chain engagement surface 48B and the first lower non-drive surface 48K. The upper portion 48C and the lower portion 48D include the fourth land 48R4. The additional chain engagement surface 48B is provided only in the lower portion 48D.

[0140] As in Fig. As seen in Figure 17, the plurality of first teeth 26 includes a first drive tooth 50. The first drive tooth 50 extends radially outward from the first sprocket body 22. The first drive tooth 50 is provided outside the shift relief area SF.

[0141] As in Fig. 5, the first drive tooth 50 has the first maximum axial width W11, the first chain engagement surface 26A, the first additional chain engagement surface 26B, the first inclined surface 26E, the first additional inclined surface 26F and the radially outermost edge 26T, the first inclination angle AG11, the first additional inclination angle AG12, the maximum axial upper width W12, and the maximum axial lower width W13. Therefore, the first drive tooth 50 will not be described in detail here for the sake of brevity. As shown in Fig. 6, the maximum axial width W21 of the plurality of second teeth 28 is smaller than the maximum axial lower width W13 of the first drive tooth 50. In other words, the maximum axial lower width W13 of the first drive tooth 50 is greater than the maximum axial width W21 of the second tooth 28.

[0142] As in Fig. 19, the maximum axial upper width W52 of the switch facilitation tooth 48 is smaller than the maximum axial upper width W12 of the first drive tooth 50. The maximum axial lower width W53 of the switch facilitation tooth 48 is substantially equal to the maximum axial lower width W13 of the first drive tooth 50. The maximum axial width W51 and the maximum axial lower width W53 are substantially equal to the first maximum axial width W11, the maximum axial upper width W12, and the maximum axial lower width W13. The maximum axial upper width W52 is substantially equal to the maximum axial width W21, the maximum axial upper width W22, and the maximum axial lower width W23. However, the dimensional relationship between the widths W11, W12, W13, W51, W52, and W53 is not limited to this embodiment. The dimensional relationship between the widths W21, W22, W23 and W52 is not limited to this embodiment.

[0143] As in Fig. As shown in Figure 17, the plurality of second teeth 28 includes a second drive tooth 52 extending radially outward from the first sprocket body 22. The second drive tooth 52 is provided outside the shift relief area SF.

[0144] As in Fig. 6, the second drive tooth 52 has the maximum axial width W21, the second chain engagement surface 28A, the second additional chain engagement surface 28B, the second inclined surface 28E, the second additional inclined surface 28F, the radially outermost edge 28T, the second inclination angle AG21, the second additional inclination angle AG22, the maximum axial upper width W22, and the maximum axial lower width W23. Thus, the second drive tooth 52 is substantially identical to the second tooth 28 and will not be described in detail here for brevity.

[0145] As in Fig. 19, the maximum axial upper width W52 of the switch facilitation tooth 48 is less than the maximum upper width W22 of the second drive tooth 52. However, the maximum axial upper width W52 of the switch facilitation tooth 48 may be equal to or greater than the maximum upper width W22 of the second drive tooth 52.

[0146] As in Fig. As seen in Figure 18, the plurality of second teeth 28 includes a derailer tooth 54 configured to first derail the bicycle chain C from the first sprocket 14 in a second shifting operation in which the bicycle chain C is shifted from the first sprocket 14 to the second sprocket 16. The shift facilitation tooth 48 may also be referred to as a first shift facilitation tooth 48. The derailer tooth 54 may also be referred to as a second shift facilitation tooth 54.

[0147] The shift facilitation tooth 48 is provided on a downstream side of the derailment tooth 54 in the first circumferential direction D11, in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. The shift facilitation tooth 48 is adjacent to the derailment tooth 54 in the first circumferential direction without any other tooth between the shift facilitation tooth 48 and the derailment tooth 54 D11.

[0148] As in Fig. As can be seen in Fig. 23, the derailing tooth 54 is configured to engage the inner link space C21 between the opposed pair of inner link plates C2 of the bicycle chain C. The derailing tooth 54 extends radially outward from the first sprocket body 22 to be received only in the inner link space C21.

[0149] The derailment tooth 54 has the maximum axial width W21 defined in the axial direction D2. The derailment tooth 54 has a chain engagement surface 54A and an additional chain engagement surface 54B. The chain engagement surface 54A faces the axial direction D2. The additional chain engagement surface 54B faces the axial direction D2 and is provided on a rear side of the chain engagement surface 54A. The maximum axial width W21 is defined between the chain engagement surface 54A and the additional chain engagement surface 54B in the axial direction D2.

[0150] The derailment tooth 54 has an inclined surface 54E, an additional inclined surface 54F, and a radially outermost edge 54T. The inclined surface 54E extends from the radially outermost edge 54T toward the chain engagement surface 54A. The additional inclined surface 54F extends from the radially outermost edge 54T toward the additional chain engagement surface 54B. The inclined surface 54E is inclined relative to the chain engagement surface 54A by a second inclination angle AG61. The additional inclined surface 54F is inclined relative to the additional chain engagement surface 54B by a second additional inclination angle AG62. The second inclination angle AG61 is substantially equal to the second additional inclination angle AG62. However, the second inclination angle AG61 may differ from the second additional inclination angle AG62.

[0151] As in Fig. As can be seen in Figure 23, the derailing tooth 54 has a maximum axial upper width W22 and a maximum axial lower width W23. The derailing tooth 54 includes an upper portion 54C and a lower portion 54D. The upper portion 54C extends radially outward from the lower portion 54D. The upper portion 54C has the maximum axial upper width W22. The lower portion 54D has the maximum axial lower width W23. The maximum axial width W21 of the derailing tooth 54 is less than the maximum axial lower width W13 of the first tooth 26.

[0152] As in Fig. As can be seen in Figure 24, the upper portion 54C is provided radially outside the reference circle RC21. The lower portion 54D is provided radially inside the reference circle RC21. The upper portion 54C is provided between the reference circle RC21 and the radially outermost edge 54T of the derailment tooth 54. The lower portion 54D is provided between the reference circle RC21 and the first root circle RC1.

[0153] The derailment tooth 54 has a drive surface 54DS1 and a non-drive surface 54DS2. The drive surface 54DS1 faces the first circumferential direction D11, in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. The non-drive surface 54DS2 faces the second circumferential direction D12, which is opposite to the first circumferential direction D11.

[0154] As in Fig. 9 and Fig. As seen in Figure 24, the lower portion 54D of the derailing tooth 54 includes the chain engagement surface 54A, a second lower engagement surface 54G, and a first recess 54R1. The first recess 54R1 is provided between the chain engagement surface 54A and the second lower engagement surface 54G. The upper portion 54C and the lower portion 54D include the chain engagement surface 54A. The upper portion 54C and the lower portion 54D include the first recess 54R1.

[0155] The lower portion 54D of the derailer tooth 54 has a second lower non-drive surface 54K and a second recess 54R2. The second recess 54R2 is provided between the chain engagement surface 54A and the second lower non-drive surface 54K. The non-drive surface 54DS2 includes the second lower non-drive surface 54K. The upper portion 54C and the lower portion 54D include the second recess 54R2.

[0156] As in the Fig. 11 and Fig. As shown in Figure 25, the lower portion 54D of the anti-derailment tooth 54 includes a third recess 54R3. The third recess 54R3 is provided between the additional chain engagement surface 54B and the second lower engagement surface 54G. The upper portion 54C and the lower portion 54D encompass the additional chain engagement surface 54B. The upper portion 54C and the lower portion 54D encompass the third recess 54R3.

[0157] The lower portion 54D of the anti-derailment tooth 54 has a fourth recess 54R4. The fourth recess 54R4 is provided between the additional chain engagement surface 54B and the second lower non-drive surface 54K. The upper portion 54C and the lower portion 54D encompass the fourth recess 54R4.

[0158] As in Fig. As seen in Figure 17, the plurality of second teeth 28 includes an additional switch relief tooth 56. The additional switch relief tooth 56 is closest to the first additional switch relief protrusion 44 among the plurality of first sprocket teeth 24. The additional switch relief tooth 56 may also be referred to as a third switch relief tooth 56.

[0159] The switch facilitation tooth 48 is provided on an upstream side of the additional switch facilitation tooth 56 in the first circumferential direction D11. The switch facilitation tooth 48 is adjacent to the additional switch facilitation tooth 56 in the first circumferential direction D11 without another tooth between the switch facilitation tooth 48 and the additional switch facilitation tooth 56. The switch facilitation tooth 48 is provided between the derailment tooth 54 and the additional switch facilitation tooth 56 in the circumferential direction D1.

[0160] As in Fig. 26, the additional shift relief tooth 56 is configured to engage the inner intermediate link space C21 between the opposed pair of inner link plates C2 of the bicycle chain C. The additional shift relief tooth 56 extends radially outward from the first sprocket body 22 to be received only in the inner link space C21.

[0161] The additional switch facilitation tooth 56 has the maximum axial width W21 defined in the axial direction D2. The additional switch facilitation tooth 56 includes a chain engagement surface 56A and an additional chain engagement surface 56B. The chain engagement surface 56A faces the axial direction D2. The additional chain engagement surface 56B faces the axial direction D2 and is provided on a rear side of the chain engagement surface 56A. The maximum axial width W21 is defined between the chain engagement surface 56A and the additional chain engagement surface 56B in the axial direction D2.

[0162] The additional shift relief tooth 56 includes an inclined surface 56E, an additional inclined surface 56F, and a radially outermost edge 56T. The inclined surface 56E extends from the radially outermost edge 56T toward the chain engagement surface 56A. The additional inclined surface 56F extends from the radially outermost edge 56T to the additional chain engagement surface 56B. The inclined surface 56E is inclined relative to the chain engagement surface 56A by a second inclination angle AG71. The additional inclined surface 56F is inclined relative to the additional chain engagement surface 56B by a second additional inclination angle AG72. The second inclination angle AG71 is substantially equal to the second additional inclination angle AG72. However, the second inclination angle AG71 may differ from the second additional inclination angle AG72.

[0163] As in Fig. 26, the additional switch relief tooth 56 has a maximum axial upper width W22 and a maximum axial lower width W23. The additional switch relief tooth 56 includes an upper portion 56C and a lower portion 56D. The upper portion 56C extends radially outward from the lower portion 56D. The upper portion 56C has the maximum axial upper width W22. The lower portion 56D has the maximum axial lower width W23. The maximum axial width W21 of the additional switch relief tooth 56 is less than the maximum axial lower width W13 of the first tooth 26.

[0164] As in Fig. As can be seen in Figure 27, the upper portion 56C is provided radially outside the reference circle RC21. The lower portion 56D is provided radially inside the reference circle RC21. The upper portion 56C is provided between the reference circle RC21 and the radially outermost edge 56T of the additional switch relief tooth 56. The lower portion 56D is provided between the reference circle RC21 and the first root circle RC1.

[0165] The additional shifting relief tooth 56 includes a drive surface 56DS1 and a non-drive surface 56DS2. The drive surface 56DS1 faces the first circumferential direction D11, in which the bicycle sprocket assembly 12 is rotated about the rotational center axis A1 during pedaling. The non-drive surface 56DS2 faces the second circumferential direction D12, which is opposite to the first circumferential direction D11.

[0166] As in Fig. 9 and Fig. As seen in Figure 27, the lower portion 56D of the additional shift facilitation tooth 56 includes the chain engagement surface 56A, a second lower engagement surface 56G, and a first recess 56R1. The first recess 56R1 is provided between the chain engagement surface 56A and the second lower engagement surface 56G. The upper portion 56C and the lower portion 56D include the chain engagement surface 56A. The upper portion 56C and the lower portion 56D include the first recess 56R1.

[0167] The lower portion 56D of the additional shift facilitation tooth 56 includes a second lower non-drive surface 56K and a second recess 56R2. The second recess 56R2 is provided between the chain engagement surface 56A and the second lower non-drive surface 56K. The non-drive surface 56DS2 includes the second lower non-drive surface 56K. The upper portion 56C and the lower portion 56D include the second recess 56R2.

[0168] As in Fig. 11 and Fig. As seen in Figure 28, the lower portion 56D of the additional shift relief tooth 56 includes a third recess 56R3. The third recess 56R3 is provided between the additional chain engagement surface 56B and the second lower engagement surface 56G. The upper portion 56C and the lower portion 56D include the additional chain engagement surface 56B. The upper portion 56C and the lower portion 56D include the third recess 56R3.

[0169] The lower portion 56D of the additional shift facilitation tooth 56 has a fourth recess 56R4. The fourth recess 56R4 is provided between the additional chain engagement surface 56B and the second lower non-drive surface 56K. The upper portion 56C and the lower portion 56D encompass the fourth recess 56R4.

[0170] The additional switch facilitating tooth 56 has substantially the same structure as that of the derailment tooth 54. However, the structure of the additional switch facilitating tooth 56 may differ from that of the derailment tooth 54.

[0171] As in Fig. 20, the switch relief tooth 48 has a first radial height H1 extending radially outward from the first sprocket body 22 to the radially outermost edge 48T of the switch relief tooth 48. The first radial height H1 extends radially outward from the first root circle RC1 to the radially outermost edge 48T.

[0172] As in Fig. 7, the first drive tooth 50 has a second radial height H2 that extends radially outward from the first sprocket body 22 to the radially outermost edge 26T of the first drive tooth 50. The second radial height H2 extends radially outward from the first root circle RC1 to the radially outermost edge 26T. As shown in Fig. 7 and Fig. As can be seen in Figure 20, the first radial height H1 is smaller than the second radial height H2. However, the first radial height H1 can be equal to or greater than the second radial height H2.

[0173] As in Fig. 8, the second drive tooth 52 has a third radial height H3 that extends radially from the first sprocket body 22 to the radially outermost edge 28T of the second drive tooth 52. The third radial height H3 extends radially outward from the first root circle RC1 to the radially outermost edge 28T. As shown in Fig. 8 and Fig. 20, the first radial height H1 is smaller than the third radial height H3. Further, the third radial height H3 is smaller than the second radial height. Since the third radial height H3 is smaller than the second radial height, it is possible to reduce a possibility of inadvertent disengagement of the bicycle chain C (chain falling off) from the second drive tooth 52 in a second shifting operation in which the bicycle chain C is shifted from the first sprocket 14 to the second sprocket 16. However, the first radial height H1 may be equal to or greater than the third radial height H3.

[0174] As in Fig. 24, the derailing tooth 54 has a fourth radial height H4 extending radially outward from the first sprocket body 22 to a radially outermost edge 54T of the derailing tooth 54. The fourth radial height H4 extends radially outward from the first root circle RC1 to the outermost edge 54T. As shown in Fig. 20 and Fig. As can be seen in Figure 24, the first radial height H1 is smaller than the fourth radial height H4. However, the first radial height H1 can be equal to or greater than the fourth radial height H4.

[0175] As in Fig. 27, the additional switch relief tooth 56 has a fifth radial height H5 extending radially outward from the first sprocket body 22 to a radially outermost edge 56T of the additional switch relief tooth 56. The fifth radial height H5 extends from the first radially outward root circle RC1 to the radially outermost edge 56T. As shown in Fig. 20 and Fig. As can be seen in Figure 27, the first radial height H1 is smaller than the fifth radial height H5. However, the first radial height H1 can be equal to or greater than the fifth radial height H5.

[0176] As in Fig. As can be seen in Figure 20, the switch relief tooth 48 has a first circumferential length CL1 defined between the drive surface 48DS1 and the non-drive surface 48DS2 in the circumferential direction D1 of the rotational center axis A1. The first circumferential length CL1 extends, as viewed in the axial direction D2, from an intersection point P11 of the reference circle RC21 with the drive surface 48DS1 to an intersection point P12 of the reference circle RC11 with the non-drive surface 48DS2 in the circumferential direction D1.

[0177] As in Fig. As can be seen in Figure 7, the first drive tooth 50 has a second circumferential length CL2 defined between the drive surface 26DS1 and the non-drive surface 26DS2 in the circumferential direction D1. The second circumferential length CL2 extends, when viewed in the axial direction D2, from an intersection point P21 of the reference circle RC21 with the drive surface 26DS1 to an intersection point P22 of the reference circle RC11 with the non-drive surface 26DS2 in the circumferential direction D1. As shown in Fig. 7 and Fig. As can be seen in Figure 20, the first circumference length CL1 is smaller than the second circumference length CL2.

[0178] As in Fig. As can be seen in Figure 8, the second drive tooth 52 has a third circumferential length CL3 defined between the drive surface 28DS1 and the non-drive surface 28DS2 in the circumferential direction D1. The third circumferential length CL3 extends, when viewed in the axial direction D2, from an intersection point P51 of the reference circle RC21 with the drive surface 28DS1 to an intersection point P52 of the reference circle RC11 with the non-drive surface 28DS2 in the circumferential direction D1. As shown in Fig. 8 and Fig. 20, the first circumference length CL1 is smaller than the third circumference length CL3. As shown in Fig. 7 and Fig. As can be seen in Figure 8, the third circumferential length CL3 is smaller than the second circumferential length CL2. However, the third circumferential length CL3 can be equal to or greater than the second circumferential length CL2.

[0179] As in Fig. As can be seen in Figure 24, the derailment tooth 54 has a fourth circumferential length CL4 defined between the drive surface 54DS1 and the non-drive surface 54DS2 in the circumferential direction D1. The fourth circumferential length CL4 extends, when viewed in the axial direction D2, from an intersection point P41 of the reference circle RC21 with the drive surface 54DS1 to an intersection point P42 of the reference circle RC11 with the non-drive surface 54DS2 in the circumferential direction D1. As shown in Fig. 8 and Fig. As can be seen in Figure 24, the fourth circumference length CL4 is smaller than the third circumference length CL3.

[0180] As in Fig. As can be seen in Figure 27, the additional switch relief tooth 56 has a fifth circumferential length CL5 defined between the drive surface 56DS1 and the non-drive surface 56DS2 in the circumferential direction D1. The fifth circumferential length CL5 extends, when viewed in the axial direction D2, from an intersection point P51 of the reference circle RC21 with the drive surface 56DS1 to an intersection point P52 of the reference circle RC11 with the non-drive surface 56DS2 in the circumferential direction D1. As shown in Fig. 8 and Fig. 27, the fifth circumference length CL5 is smaller than the third circumference length CL3. As shown in Fig. 24 and Fig. As can be seen in Figure 27, the fifth circumference length CL5 is smaller than the fourth circumference length CL4.

[0181] As in Fig. 29, the first sprocket 14 includes a guide portion 60. The guide portion 60 is provided on a downstream side of the second shift facilitation protrusion 46 to reduce interference between the second shift facilitation protrusion 46 and the bicycle chain C in the first shifting operation. In other words, the guide portion 60 is configured to guide the bicycle chain C toward the second sprocket 16 to prevent the bicycle chain from inadvertently engaging the second shift facilitation protrusion 46 in the first shifting operation. The guide portion 60 is provided between the first additional shift facilitation protrusion 44 and the second shift facilitation protrusion 46 in the circumferential direction D1. The guide portion 60 is provided between the first switch facilitation protrusion 42 and the second switch facilitation protrusion 46 in the circumferential direction D1.The guide portion 60 has a longitudinal portion extending in the circumferential direction D1 from the first additional switch facilitating projection 44 to the second switch facilitating projection 46. As shown in . Fig. 30, the guide portion 60 extends from the first sprocket body 22 toward the second sprocket 16 in the axial direction D2. A first axial distance DT21 is defined between the first center plane CP1 and an axial end surface 60A of the guide portion 60 in the axial direction D2. A second axial distance DT22 is defined between the first center plane CP1 and an axial end surface 46A of the second switch facilitating projection 46 in the axial direction D2. The first axial distance DT21 is greater than the second axial distance DT22. However, the first axial distance DT21 may be equal to or less than the second axial distance DT22. The guide portion 60 may be omitted from the first sprocket 14.

[0182] The first shifting operation is described below with reference to the Fig. 17 and 31 to 35 are described in detail.

[0183] As in Fig. 17 and Fig. As can be seen in Fig. 31, the outer link plate C1A of the bicycle chain C is lifted by the first shift facilitating projection 42 in the first shifting operation when the bicycle chain C is moved toward the first sprocket 14 by the front derailleur in a state in which the bicycle chain C is engaged with the second sprocket 16. As shown in Fig. 32, the inner link plate C2A of the bicycle chain C is engaged with the first additional shift facilitating projection 44 and is moved in the first shifting operation by the first additional shift facilitating projection 44 toward the first sprocket 14. As shown in Fig. 17 and Fig. 33, the outer link plates C1C of the bicycle chain C are received by the shift facilitating tooth 48 in the first shifting operation.

[0184] As in Fig. 33, the upper portion 48C of the shift facilitation tooth 48 is easily inserted into the outer link space C11C of the bicycle chain C because the upper portion 48C has the maximum axial upper width W52 smaller than the maximum axial lower width W53 of the bottom portion 48D. As shown in Fig. As can be seen from Figs. 33 to 35, the outer link plate C1C1 of the bicycle chain C is guided by the inclined surface 48F when the upper portion 48C is inserted into the outer link space C11C. This facilitates the first shifting operation in which the bicycle chain C is shifted from the second sprocket 16 to the first sprocket 14.

[0185] As in Fig. 30, the guide portion 60 reduces the interference between the second shift facilitating protrusion 46 and the bicycle chain C in the first shifting operation, thereby smoothing the first shifting operation even when the first sprocket 14 includes the second shift facilitating protrusion 46.

[0186] As in Fig. 22 and Fig. 26, the additional shift facilitating tooth 56 engages the inner link space C21 of the bicycle chain C in place of the first additional shift facilitating projection 44 in a first chain engagement state in which the first sprocket 14 is engaged with the bicycle chain C to transmit the pedaling force F1 after the first shifting operation.

[0187] As in the Fig. 19 and Fig. 22, in the first chain engagement state in which the first sprocket 14 is engaged with the bicycle chain C after the first shifting operation to transmit the pedaling force F1, the shift facilitating tooth 48 engages the outer connection space C11 of the bicycle chain C. As shown in Fig. 36 and Fig. As shown in Fig. 37, the lower portion 48D of the switch facilitating tooth 48 holds the outer link plates C1 and the inner link plates C2. For example, the first chamfer 48R1 of the lower portion 48D is in contact with the inner link plate C2E, and the third chamfer 48R3 of the lower portion 48D is in contact with the inner link plate C2F. Thus, the outer link plates C1 and the inner link plates C2 are held in the first chain engagement state by the switch facilitating tooth 48.

[0188] The second switching operation is described below with reference to the Fig. 18, Fig. 33, Fig. 38 and Fig. 39 described in detail.

[0189] As in Fig. 18, the bicycle chain C is first derailed from the first sprocket 14 at the derailing tooth 54 when the bicycle chain C is moved by the front derailleur toward the second sprocket 16 in a state where the bicycle chain C is engaged with the first sprocket 14. As shown in Fig. 33, Fig. 38 and Fig. 39, the upper portion 48C of the shift facilitation tooth 48 allows the outer link plates C1D of the bicycle chain C to move relative to the shift facilitation tooth 48 toward the second sprocket 16 until the outer link plate C1D1 comes into contact with the inclined surface 48F, since the upper portion 48C has the maximum axial upper width W52 smaller than the maximum axial lower width W53 of the lower portion 48D. This makes it easier for the derailment tooth 54 to first engage the inner link plates C2B ( Fig. 18) to derail.

[0190] As in the Fig. 18 and Fig. As shown in Fig. 40, the outer link plate C1B is engaged with the second shift facilitating protrusion 46 to adjust the chain phase of the bicycle chain C for the second sprocket 16 such that the outer link plates C1 of the bicycle chain C engage with the third teeth 36 in the second shifting operation. This facilitates the second shifting operation in which the bicycle chain C is shifted from the first sprocket 14 to the second sprocket 16. Second embodiment

[0191] A bicycle sprocket assembly 212 according to a second embodiment will be described below with reference to Fig. 41 to 43. The bicycle sprocket assembly 212 has the same structure and / or configuration as the bicycle sprocket assembly 212, with the exception of the second shift facilitating protrusion 46 and the guide portion 60. Thus, elements having substantially the same function as those in the first embodiment are numbered alike and will not be described and / or illustrated in detail again for brevity.

[0192] As in Fig. As seen in Figure 41, in the bicycle sprocket assembly 212, the first sprocket 14 includes a second shift facilitation protrusion 246 to facilitate the shifting operation. In this embodiment, the second shift facilitation protrusion 246 extends in the circumferential direction D1. The second switch facilitation protrusion 246 is provided by being integrally formed with the second switch facilitation protrusion 46 and the guide portion 60. Thus, the second switch facilitation protrusion 246 has substantially the same function as the second switch facilitation protrusion 46 and the guide portion 60.

[0193] As in Fig. 42, which shows a cross-sectional view of the switch relief projection 246, the second switch relief projection 246 is provided integrally with the first sprocket body 22. As shown in Fig.However, as shown in Fig. 43, which shows a cross-sectional view of the switch relief projection 246, the second switch relief projection 246 may be a separate member from the first sprocket body 22. In this modification, the second switch relief projection 246 includes a projection body 246A and coupling parts 246B. The coupling parts 246B couple the projection body 246A to the first sprocket body 22. The coupling parts 246B have a structure such as rivets.

[0194] The term "comprising" and its derivatives, as used herein, are intended as open-ended terms that specify the presence of the stated features, elements, components, groups, integers, and / or steps, but do not preclude the presence of other unstated features, elements, components, groups, integers, and / or steps. This concept applies to words of similar meaning, such as the terms "comprising," "including," and their derivatives.

[0195] The terms “member”, “region”, “section”, “part”, “element”, “body” and “structure” can, when used in the singular, have the dual meaning of a single part or of several parts.

[0196] The ordinal numbers such as "first" and "second," as mentioned in the present application, are merely identifiers and have no further meaning, such as a specific order or the like. Furthermore, for example, the term "first element" does not in itself imply the presence of a "second element," and the term "second element" does not in itself imply the presence of a "first element."

[0197] The term "pair of" as used herein may include the configuration in which the pair of elements have different shapes and structures from each other, as well as the configuration in which the pair of elements have the same shapes and structures.

[0198] The terms “a” (or “an”), “one or more” and “at least one” may be used interchangeably herein.

[0199] Finally, terms such as "substantially," "by," and "approximately," as used herein, mean a reasonable variation of the modified term such that the final result is not significantly altered. All numerical values ​​described in this application may be construed to include the terms "substantially," "by," and "approximately."

[0200] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

[1] Bicycle sprocket assembly (12) comprising: a first sprocket (14) comprising: a first sprocket body (22) having a rotational center axis (A1); a shift facilitation region (SF) for facilitating a shifting operation in which a bicycle chain (C) is shifted between the first sprocket (14) and a second sprocket (16) adjacent to the first sprocket (14); and a plurality of first sprocket teeth (24), each having a maximum axial upper width (W12) and a maximum axial lower width (W13), the plurality of first sprocket teeth (24) comprising: a plurality of first teeth (26) adapted to engage an outer link space (C11) provided between an opposing pair of outer link plates (C1) of the bicycle chain (C), the plurality of first teeth (26) comprising: a switch relief tooth (48) extending radially outwardly from the first sprocket body (22), the switch relief tooth (48) being provided in the switch relief region (SF), the maximum axial upper width (W52) of the switch relief tooth (48) being smaller than the maximum axial lower width (W53) of the switch relief tooth (48); and a first drive tooth (50) extending radially outward from the first sprocket body (22), the first drive tooth (50) being provided outside the switch relief region (SF), the maximum axial upper width (W52) of the switch relief tooth (48) being smaller than the maximum axial upper width (W12) of the first drive tooth (50); and a plurality of second teeth (28) configured to engage an inner link space (C21) provided between an opposing pair of inner link plates (C2) of the bicycle chain (C), the plurality of second teeth (28) including a second drive tooth (52) extending radially outward from the first sprocket body (22), the plurality of second teeth (28) provided outside the shift facilitation area (SF) having the maximum axial width (W21) smaller than the maximum axial lower width (W13) of the first drive tooth (50). [2] Bicycle sprocket assembly (12) according to claim 1, wherein the switch relief tooth (48) has a first radial height (H1) extending radially outward from the first sprocket body (22) to a radially outermost edge (48T) of the switch relief tooth (48), the first drive tooth (50) has a second radial height (H2) extending radially outward from the first sprocket body (22) to a radially outermost edge (26T) of the first drive tooth (50), and the first radial height (H1) is smaller than the second radial height (H2). [3] Bicycle sprocket assembly (12) according to claim 1 or 2, wherein the switch relief tooth (48) has a first radial height (H1) extending radially outward from the first sprocket body (22) to a radially outermost edge (48T) of the switch relief tooth (48), the second drive tooth (52) has a third radial height (H3) extending radially outward from the first sprocket body (22) to a radially outermost edge (28T) of the second drive tooth (52), and the first radial height (H1) is smaller than the third radial height (H3). [4] Bicycle sprocket assembly (12) according to one of claims 1 to 3, wherein the first sprocket (14) has a first switch facilitating projection (42) to facilitate the switching operation, and the shift facilitation tooth (48) is provided on an upstream side of the first shift facilitation projection (42) in a first circumferential direction (D11) in which the bicycle sprocket assembly (12) is rotated about the rotational center axis (A1) during pedaling, wherein the shift facilitation tooth (48) is preferably spaced from the first shift facilitation projection (42) by a first distance (DT1) corresponding to two chain pitches (PT) of the bicycle chain (C). [5] Bicycle sprocket assembly (12) according to claim 4, wherein the shift facilitating tooth (48) is configured to first engage with an outer link space (C11) of the bicycle chain (C) in a first shifting operation in which the bicycle chain (C) is shifted from the second sprocket (16) to the first sprocket (14), the first sprocket (14) having a first pitch circle diameter (PCD1) that is larger than a second pitch circle diameter (PCD2) of the second sprocket (16). [6] Bicycle sprocket assembly (12) according to one of claims 1 to 5, wherein the plurality of second teeth (28) have a derailment tooth (54) configured to derail the bicycle chain (C) first from the first sprocket (14) in a second shifting operation in which the bicycle chain (C) is shifted from the first sprocket (14) to the second sprocket (16), wherein the first sprocket (14) has a first pitch circle diameter (PCD1) that is greater than a second pitch circle diameter (PCD2) of the second sprocket (16), and the switch facilitation tooth (48) is provided on a downstream side of the derailment tooth (54) in a first circumferential direction (D11) in which the bicycle sprocket assembly (12) is rotated about the rotational center axis (A1) during pedaling, wherein the switch facilitation tooth (48) is preferably adjacent to the derailment tooth (54) in the first circumferential direction (D11) without another tooth being present between the switch facilitation tooth (48) and the derailment tooth (54). [7] Bicycle sprocket assembly (12) according to one of claims 1 to 6, wherein each of the plurality of first sprocket teeth (24) comprises a lower portion (26D) and an upper portion (26C) extending radially outward from the lower portion (26D), the lower portion (26D) having the maximum axial lower width (W13) of each of the plurality of first sprocket teeth (24), and the upper portion (26C) having the maximum axial upper width (W12) of each of the plurality of first sprocket teeth (24), the first sprocket (14) has a reference circle (RC21) with respect to a rotational center axis (A1) of the bicycle sprocket assembly (12), the lower section (26D) is provided radially inside the reference circle (RC21) and the upper section (26C) is provided radially outside the reference circle (RC21). [8] Bicycle sprocket assembly (12) according to claim 7, wherein the first sprocket (14) has a first pitch circle (PC1), a first outer circle (RC22) and a first inner circle (RC23), a first outer distance (DS11) is defined radially outward from the first pitch circle (PC1) to the first outer circle (RC22), the first outer distance (DS11) is equal to or less than 3 mm, a first inner distance (DS12) is defined radially inward from the first pitch circle (PC1) to the first inner circle (RC23), the first inner distance (DS12) is equal to or less than 4 mm, and the reference circle (RC21) is provided between the first outer circle (RC22) and the first inner circle (RC23). [9] The bicycle sprocket assembly (12) according to claim 7 or 8, wherein each of the plurality of first teeth (26) has a first protrusion (26P1) provided on one of a first axial side (26S1) and a second axial side (26S2) of the lower portion (26D), the first axial side (26S1) being a rear side of the second axial side (26S2) in an axial direction (D2) parallel to the rotational center axis (A1), preferably each of the plurality of first teeth (26) has a second protrusion (26P2) provided on another of the first axial side (26S1) and the second axial side (26S2) of the lower portion (26D). [10] The bicycle sprocket assembly (12) according to any one of claims 7 to 9, wherein the lower portion (26D) of the plurality of first teeth (26) has a first chain engagement surface (26A), a first lower drive surface (26G), and a first chamfer (26R1) provided between the first chain engagement surface (26A) and the first lower drive surface (26G), the first chain engagement surface (26A) facing an axial direction (D2), the first lower drive surface (26G) facing a first circumferential direction (D11) in which the bicycle sprocket assembly (12) is rotated about the rotational center axis (A1) during pedaling. [11] The bicycle sprocket assembly (12) according to any one of claims 7 to 10, wherein the lower portion (26D) of the plurality of first teeth (26) comprises a first chain engagement surface (26A), a first lower non-drive surface (26K), and a second chamfer provided between the first chain engagement surface (26A) and the first lower non-drive surface (26K), wherein the first chain engagement surface (26A) faces the axial direction (D2), the first lower non-drive surface (26K) faces a second circumferential direction (D12) opposite a first circumferential direction (D11) in which the bicycle sprocket assembly (12) is rotated about the rotational center axis (A1) during pedaling. [12] The bicycle sprocket assembly (12) of any one of claims 1 to 11, wherein the maximum axial lower width (W53) of the shift facilitation tooth (48) is substantially equal to the maximum axial lower width (W13) of the first drive tooth (50). [13] Bicycle sprocket assembly (12) according to one of claims 1 to 12, wherein the first sprocket (14) has a second switch facilitating projection (46) to facilitate the switching operation, and the shift facilitation tooth (48) is provided on a downstream side of the second shift facilitation projection (46) in a first circumferential direction (D11) in which the bicycle sprocket assembly (12) is rotated about the rotational center axis (A1) during pedaling, wherein the shift facilitation tooth (48) is preferably spaced from the second shift facilitation projection (46) by a second distance (DT2) corresponding to two chain pitches (PT) of the bicycle chain (C). [14] Bicycle sprocket assembly (12) according to one of claims 1 to 13, wherein the maximum axial upper width (W52) of the shift facilitation tooth (48) is smaller than the maximum upper width (W22) of the second drive tooth (52). [15] Bicycle sprocket assembly (12) according to one of claims 1 to 14, wherein each of the plurality of first teeth (26) comprises a drive surface (26DS1) and a non-drive surface (26DS2), the switch relief tooth (48) has a first circumferential length (CL1) defined between the drive surface (26DS1) and the non-drive surface (26DS2) in a circumferential direction (D1) of the rotational center axis (A1), the first drive tooth (50) has a second circumferential length (CL2) defined between the drive surface (26DS1) and the non-drive surface (26DS2) in the circumferential direction (D1), and the first circumferential length (CL1) is smaller than the second circumferential length (CL2), wherein the drive surface (26DS1) of the plurality of first teeth (26) is preferably arranged with a constant pitch in the circumferential direction (D1). [16] Bicycle sprocket assembly (12) comprising: a first sprocket (14) comprising: a first sprocket body (22) having a rotational center axis (A1); a shift facilitation area (SF) for facilitating a shifting operation in which a bicycle chain (C) is shifted between the first sprocket (14) and a second sprocket (16) adjacent to the first sprocket (14); and a plurality of first sprocket teeth (24) made of a first material having a first wear resistance, wherein the plurality of first sprocket teeth (24) include a plurality of first teeth (26) adapted to engage an outer link space (C11) provided between an opposing pair of outer link plates (C1) of the bicycle chain (C); and a plurality of second teeth (28) adapted to engage an inner link space (C21) provided between an opposing pair of inner link plates (C2) of the bicycle chain (C); and a second sprocket (16) comprising: a second sprocket body (32) having a rotational center axis (A1); and a plurality of second sprocket teeth (34) made of a second material having a second wear resistance, wherein a total number of the plurality of second sprocket teeth (34) is less than a total number of the plurality of first sprocket teeth (24), wherein the first wear resistance is greater than the second wear resistance. [17] Bicycle sprocket assembly (12) comprising: a first sprocket (14) having a first pitch circle diameter (PCD1), the first sprocket (14) comprising: a first sprocket body (22) having a rotational center axis (A1); a shift facilitation region (SF) for facilitating a shifting operation in which a bicycle chain (C) is shifted between the first sprocket (14) and a second sprocket (16) adjacent to the first sprocket (14); and a plurality of first sprocket teeth (24), comprising a plurality of first teeth (26) having a first maximum axial width (W11), and a plurality of second teeth (28) having a second maximum axial width (W21) which is smaller than the first maximum axial width (W11); and a second sprocket (16) having a second pitch circle diameter (PCD2) which is smaller than the first pitch circle diameter (PCD1), the second sprocket (16) comprising: a second sprocket body (32) with the rotational center axis (A1); and a plurality of second sprocket teeth (34), comprising a plurality of third teeth (36) having a third maximum axial width (W31), wherein at least one tooth of the plurality of third teeth (36) comprises a radially outermost edge (38T), a chain engagement surface (36A) oriented in an axial direction (D2) parallel to the rotational center axis (A1), and an inclined surface (36E, 36F) extending from the chain engagement surface (36A, 36B) toward the radially outermost edge (38T), the inclined surface (36E, 36F) being inclined relative to the chain engagement surface (36A, 36B) by an inclination angle (AG31, AG32) equal to or greater than 40 degrees, and a plurality of fourth teeth (38) having a fourth maximum axial width (W41) which is smaller than the third maximum axial width (W31).

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